Motors
by James Slough Zerbe · English · Gutenberg #42369 · 297,293 chars · public domain (US)
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Title: Motors
Author: James Slough Zerbe
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Language: English
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Transcriber's Note
Italic text is denoted by _underscores_ and bold text by =equal signs=.
Whole numbers with fractional parts are denoted as 7-3/4.
_Every Boy's
Mechanical
Library_
[Illustration]
MOTORS
Every Boy's Mechanical Library
By J. S. ZERBE, M.E.
Price, per volume, 60 cents, Net. Postage extra.
AUTOMOBILES
This is a subject in which every boy is interested. While few mechanics
have the opportunity to actually build an automobile, it is the
knowledge which he must acquire about every particular device used, that
enables him to repair and put such machines in order. The aim of this
book is to make the boy acquainted with each element, so that he may
understand why it is made in that special way, and what the advantages
and disadvantages are of the different types. To that end each structure
is shown in detail as much as possible, and the parts separated so as to
give a clear insight of the different functions, all of which are
explained by original drawings specially prepared to aid the reader.
MOTORS
To the boy who wants to know the theory and the practical working of the
different kinds of motors, told in language which he can understand, and
illustrated with clear and explicit drawings, this volume will be
appreciated. It sets forth the groundwork on which power is based, and
includes steam generators, and engines, as well as wind and water
motors, and thoroughly describes the Internal Combustion Engine. It has
special chapters on Carbureters, Ignition, and Electrical systems used,
and particularly points out the parts and fittings required with all
devices needed in enginery. It explains the value of compounding,
condensing, pre-heating and expansion, together with the methods used to
calculate and transmit power. Numerous original illustrations.
AEROPLANES
This work is not intended to set forth the exploits of aviators nor to
give a history of the Art. It is a book of instructions intended to
point out the theories of flying, as given by the pioneers, the
practical application of power to the various flying structures; how
they are built; the different methods of controlling them; the
advantages and disadvantages of the types now in use; and suggestions as
to the directions in which improvements are required. It distinctly
points out wherein mechanical flight differs from bird flight, and what
are the relations of shape, form, size and weight. It treats of kites,
gliders and model aeroplanes, and has an interesting chapter on the
aeroplane and its uses in the great war. All the illustrations have been
specially prepared for the work.
CUPPLES & LEON CO., Publishers, NEW YORK
[Illustration]
_Every Boy's Mechanical Library_
MOTORS
BY
J. S. ZERBE, M.E.
_Author of Aeroplanes--Automobiles_
_ILLUSTRATED_
NEW YORK
CUPPLES & LEON COMPANY
Copyright, 1915, by
CUPPLES & LEON COMPANY
CONTENTS
PAGE
Introductory 1
The Subject. The Inquisitive Trait. The Reasons for Doing
Things. The Mystery of Mechanism. Curiosity which prompts
Investigation. The Sum of Knowledge.
Chapter I. Motors and Motive Power 5-21
The Water Fall. Water moves in One Direction only. What is
Energy. Stored or Potential Energy. Kinetic Energy.
Friction. Resistance. Inertia. The Law of Bodies. Internal
and External Resistance. Momentum. Energy Indestructible.
Wind Power. Rectilinear Motion. Oscillating Motion.
Movements in Nature. How Man Utilizes the Various Movements.
Kinds of Potential Energy. The Power in Heat. Energy in
Steam. Energy from the Sun. Power from Water. The Turbine.
Calculating Power of a Turbine. Horse Power. Foot Pounds.
Power and Time. Gravitation. Utilizing the pull of Gravity.
Taking Advantages of Forces. Pitting Forces Against each
Other. Centripetal and Centrifugal Forces. Power not Created.
Developing the Power of Motors. Experimenting.
Chapter II. The Steam Generator 22-31
Water as an absorbent of Heat. Classification of Boilers.
Mode of applying Heat. The Cylindrical Boiler. The Cornish
Boiler. The Water Tube Boiler. Various Boiler Types. Compound
Steam Boiler. Locomotive Steam Boiler. Vertical Steam Boiler.
Chapter III. Steam Engines 32-59
The Original Turbine Engine. The Reciprocating Engine.
Atmospheric Engine. The Piston. Importance of the Valve.
Expanding the Steam. Balanced Valve. Rotary Valve. Engine
Accessories. Efficiency of Engines. How Steam acts in a
Cylinder. Indicating the Engine. Mean Efficiency.
Calculating Horse Power. Condensation. Atmospheric Pressure.
The Condenser. Pre-heating. Superheaters. Compounding. Triple
and Quadruple Expansion Engines. The Steam Turbine. Pressure
and Velocity. Form of Blades. Compounding the Jet.
Chapter IV. Fuels and Combustion 60-67
Solid Fuels. Liquid Fuels. Combustion. Oxidation. The
Hydro-Carbon Gases. Oxygen and the Atmosphere. Internal
Combustion. Vaporizing Fuel. Explosion by Heat Compression.
How Compression Heats. Elasticity of Gases. Advantages of
Compression. The Necessity of Compression.
Chapter V. The Internal Combustion Engine 68-82
Fixed Gases. Gas Engines. Energy of Carbon and Hydrogen.
The Two-Cycle Type. Advantages of the Two-Cycle Engine. The
Four-Cycle Engine. The Four Cycles. Ignition Point. Advantages
of the Four-Cycle Type. The Loss in Power. Engine
Construction. Valve Grinding. The Crank Shaft. The Cams.
Chapter VI. Carbureters 83-101
Functions of a Carbureter. Rich Mixtures. Lean Mixtures.
Types of Carbureters. The Sprayer. The Surface Type.
Governing a Carbureter. Primary Air. Needle Valve. Secondary
Air. Requirements in a Carbureter. Size of a Carbureter. Rule
for Size of Carbureters. The Throttle. Flooding.
Adjustability. Surface Carbureters. Float Chamber.
Chapter VII. Ignition, Low Tension System 102-120
Electricity. Magnetism. The Armature. Characteristics of
Electricity. Make and Break System. Voltage. High and Low
Voltage. Low Tension method. Disadvantages of Make and Break.
Amperes. Resistance. Direct Current. Alternating Current.
Induction. Generating Electricity. Primary Battery. Making a
Dry Cell. Energy in a cell. Wiring Methods. Series Connection.
Multiple Connection. Series Multiple. Watts. Testing a Cell.
Testing with Instruments. Simple Battery Make and Brake
System. To Advance the Spark. The Magneto in the Circuit.
Magneto Spark Plug.
Chapter VIII. Ignition, High Tension 121-140
Magnetos. Alternating Current. Cutting Lines of Force.
Plurality of Loops. The Electro Magnet. The Dynamo Form. The
Magneto Form. Advantages of the Magneto. Induction Coil.
Changing the Current. Construction of a Coil. Primary Coil.
Secondary Coil. Contact Maker. High Tension with Battery and
Coil. Metallic Core for Induction Coil. The Condenser.
Operations of a Vibrator Coil. The Distributor. Circuiting
with Distributor.
Chapter IX. Mechanical Devices Utilized in Power 141-157
The Unit of Time. Horse Power. Proney Brake. Reversing
Mechanism. Double Eccentric Reversing Gear. Balanced Slide
Valve. Balanced Throttle Valve. Engine Governors. Injectors.
Feed Water Heaters.
Chapter X. Valves and Valve Fittings 158-171
Check Valve. Gate Valve. Globe Valve. The Corliss Valve.
Corliss Valve-operating Mechanism. Angle Valve. Rotary Valves.
Rotable Engine Valves. Throttle Valves. Blow-off Valves.
Pop-Safety Valves.
Chapter XI. Cams and Eccentrics 172-178
Simple Cams. Wiper Wheels. Cylindrical Cam Motion. Eccentrics.
Triangularly-formed Eccentrics.
Chapter XII. Gears and Gearing 179-190
Racks and Pinions. Mangle Rack. Controlling the Pinion. Dead
Center. Crank Motion Substitute. Mangle Wheels. Quick Return
Motion. Accelerated Motion. Quick-return Gearing. Scroll
Gearing.
Chapter XIII. Special Types of Engines 191-201
Temperatures. Artificial Heat. Zero. Liquids and Gases.
Refrigeration. Rotary Engines. Caloric Engines. Adhesion
Engines.
Chapter XIV. Enginery in the Development of the Human Race 202-207
Power in Transportation. Power vs. Education and the Arts.
Lack of Power in the Ancient World. The Early Days of the
Republic. Lack of Cohesiveness in Countries Without Power.
The Railroad as a Factor in Civilization. The Wonderful
Effects of Power. England as a User of Power. The Automobile.
High Character of Motor Study. The Unlimited Field of Power.
Chapter XV. The Energy of the Sun, and How Heat is Measured 208-216
Fuel Economy. Direct Conversion. The Measurement of Heat.
Caloric. Material Theory. Heat Transmitted in Three Ways.
Conduction. Convection. Radiation.
Glossary 217
LIST OF ILLUSTRATIONS
FIG. PAGE
1. Undershot Wheel 13
2. Overshot Wheel 14
3. Primitive Boiler 24
4. Return Tubular Boiler 25
5. Cornish, or Scotch Boiler 25
6. Water Tube Boiler. End view 27
7. Water Tube Boiler. Side view 29
8. The Original Engine 33
9. Horizontal Section of Tube 33
10. Steam-Atmospheric Engine 35
11. Simple Valve Motion. First position 38
12. Simple Valve Motion. Second position 38
13. Effective pressure in a Cylinder 42
14. Indicating pressure line 44
15. Indicating the Engine 45
16. Compound Engine 53
16a. Relative Piston Pressures 54
17. Changing Pressure into Velocity 55
18. Reaction against Air 56
19. Reaction against Surface 56
20. Turbine. Straight Blades 57
21. Curved Blades 58
22. Compound Turbine 58
23. Two-Cycle Engine. First position 71
24. Two-Cycle Engine. Second position 73
25. Two-Cycle Engine. Third position 73
26. Four-Cycle Engine. First position 75
27. Four-Cycle Engine. Second position 75
28. Four-Cycle Engine. Third position 76
29. Four-Cycle Engine. Fourth position 76
30. Valve Grinding 81
31. Carbureter 87
32. Carbureter 95
33. Surface Carbureter 98
34. Dry Cell 108
35. Series Connection 109
36. Multiple, or Parallel Connection 110
37. Series-Multiple Connection 111
38. Circuit Testing 113
39. Make and Break, with Battery 114
40. Make and Break, with Magneto 117
41. Magneto Spark Plug 119
42. Illustrating Alternating Current 122
43. Alternating Current. Second position 122
44. Alternating Current. Third position 123
45. Alternating Current. Fourth position 124
46. Making the Circuit 125
47. The Dynamo 126
48. The Magneto 126
49. Current by Induction 128
50. Induction Coil 129
51. Typical Induction Coil 130
52. Contact Maker 131
53. Typical Circuiting, Jump spark Ignition 132
54. Metallic Core, Induction Coil 133
55. Condenser 134
56. Vibrator Coil and Connections 135
57. The Distributer 137
58. Circuiting with Distributer 138
59. Illustrating the Unit of Time 142
60. The Proney Brake 143
61. Double Eccentric Reversing Gear 146
62. Reversing Gear, Neutral 146
63. Reversing Gear, Reversed 147
64. Single Eccentric Reversing Gear 147
65. Balanced Slide Valve 148
66. Valve Chest. Double Port Exhaust 149
67. Balanced Throttle-Valve 150
68. Watt's Governor 151
69. The Original Injector 152
70. Injector with movable Combining Tube 154
71. Feed Water Heater 156
72. Check Valve 158
73. Gate Valve 159
74. Globe Valve 160
75. Corliss Valve 162
76. Corliss Valve-operating Mechanism 163
77. Angle Valve 164
78. Rotary-Valve 165
79. Two-way Rotary 165
80. Rotary Type 166
81. Two-Way Rotary Type 166
82. Butterfly Throttle 167
83. Angle Throttle 167
84. Slide Throttle 168
85. Two-slide Throttle 168
86. Blow-off Valve 169
87. Safety Pop Valve 170
88. Heart Shaped 173
89. Elliptic 173
90. Double Elliptic 173
91. Single Wiper 174
92. Double Wiper 174
93. Tilting Cam 174
94. Cam Sector 175
95. Grooved Cam 175
96. Reciprocating Motion 175
97. Pivoted Follower for Cam 176
98. Eccentric 177
99. Eccentric Cam 177
100. Triangularly-formed Eccentric 178
101. Rack and Pinion 180
102. Rack Motion 180
103. Plain Mangle Rack 181
104. Mangle Rack Motion 181
105. Alternate Circular Motion 181
106. Controlling Pinion for Mangle Rack 182
107. Illustrating Crank-pin Movement 183
108. The Dead Center 184
109. Crank Motion Substitute 184
110. Mangle Wheel 185
111. Quick Return Motion 186
112. Accelerated Circular Motion 187
113. Quick Return Gearing 188
114. Scroll Gearing 189
115. Simple Rotary Engine 196
116. Double-feed Rotary Engine 198
117. Adhesion Motor 200
INTRODUCTORY
The motor is the great dominating factor in the world of industry. Every
wheel and spindle; every shaft and loom, and every piece of mechanism
which has motion, derives it from some sort of motor.
The term _motor_ has a wider significance than any other word. A steam
engine is a motor, and so, also, is a dynamo, a water wheel or a wind
mill.
It would be just as descriptive to call a wind mill a wind _motor_, or a
steam engine a steam _motor_, as to adhere to the old terms; and, on the
other hand, since it would be out of place to call a dynamo or a wind
mill an engine, the word _motor_ seems best adapted to express the
meaning of every type of mechanism which transforms energy into motion.
In considering the subject I shall proceed on the theory that the boy
knows nothing whatsoever of the subject, nor the terms used to designate
the various phases, subjects and elements. It must be elementary in its
character, and wholly devoid of technical terms or sentences.
While it is necessary to give information in a book of this character,
on the methods for figuring out power, it must be done without resorting
to the formulas usually employed in engineering works, as they are of
such a nature that the boy must have some knowledge of the higher
mathematics to follow out the calculations employed.
Indeed, every phase should be brought within the mental view of the boy,
and to do this may occasionally necessitate what might appear to be long
drawn out explanations, all of which, it is hoped, will be the means of
more clearly presenting the subject.
The opening chapters, which treat of the fundamentals, will be as nearly
complete as possible, and thus lay a foundation for the work we shall be
called upon to perform, when we treat of the structures of the different
parts and devices in the various types of motors.
The object is to explain power in its various phases, how derived, and
the manner in which advantage is taken of the elements, and substances
with which we are brought into contact. The reasons for each step are
plainly set forth with the view of teaching the boy what power means,
rather than to instruct him how to make some particular part of the
machinery.
_The Inquisitive Trait._--My experience has impressed me with the
universality of one trait in boys, namely, that of inquisitiveness. Put
a machine before a boy and allow him to dissect it, and his curiosity
will prompt him to question the motive for the particular construction
of each part of its make-up.
_The Reasons for Doing Things._--He is interested in knowing the reason
why. Every boy has the spirit of the true investigator,--that quality
which seeks to go behind or delve down deeply. This is a natural
instinct.
_The Mystery of Mechanism._--If this taste is gratified, and he thereby
learns the mystery of the machine, what a wonderful world is opened to
him! The value of the lesson will depend, in a large measure, on the
things which he has found out for himself. It is that which counts,
because he never forgets that which he has dug out and discovered.
_Curiosity Which Prompts Investigation._--I recall a farmer's boy whose
curiosity led him to investigate the binding mechanism of a reaper. It
was a marvel to him, as it has been to many others. He studied it day
after day, and finally, unaided mastered the art. That was something
which could not be taken away from him.
It was a pleasure to hear him explain its operation to a group of boys,
and men, too, in which he used the knot itself to explain how the
various fingers and levers coöperated to perform their functions. It was
an open book to him, but there was not one in the group of listeners who
could repeat the explanation.
_The Sum of Knowledge._--It is the self-taught boy who becomes the
expert. The great inventors did not depend on explanations. A book of
this character has a field of usefulness if it merely sets forth, as far
as possible, the sum of useful knowledge which has been gained by
others, so as to enable the boy to go forward from that point, and thus
gain immensely in time.
There is so much that has been developed in the past, with reference to
the properties of matter, or concerning the utility of movements, and
facts in the realm of weights, measures, and values of elements which he
must deal with, that, as he studies the mechanical problems, the book
becomes a sort of cyclopedia, more than a work designed to guide him in
the building of special engines or motors.
The Author.
MOTORS
CHAPTER I
MOTORS AND MOTIVE POWER
What makes the wheels turn round? This simple question is asked over and
over again. To reply means pages of answers and volumes of explanations.
The Water Fall.--Go with me to the little stream I have in mind, and
stand on the crest of the hill where we can see the water pouring down
over the falls, and watch it whirling away over the rocks below.
The world was very, very old, before man thought of using the water of
the falls, or the rushing stream below, to grind his corn or to render
him other service.
Water Moves in One Direction Only.--What the original man saw was a body
of water moving in one direction only. When he wanted to grind corn he
put it in the hollow of a rock, and then beat it with a stone, which he
raised by hand at each stroke. In doing so two motions were required in
opposite directions, and it took thousands of years for him to learn
that the water rushing along in one direction, could be made to move the
stone, or the pestle of his primitive grinding mill, in two directions.
It took him thousands of years more to learn another thing, namely, that
the water could be made to turn the stone round, or rotate it, and thus
cause one stone, when turning on another, to crush and grind the grain
between them.
Now, as we go along with the unfolding of the great question of
_motors_, we must learn something of the terms which are employed, to
designate the different things we shall deal with, and we ought to have
some understanding of the sources of power.
What Is Energy?--The running, as well as the falling water represent
energy. This is something which is in the thing, the element, or the
substance itself. It does not come from without. It is not imparted to
it by anything.
Stored or Potential Energy.--At the top of the falls, look at that
immense rock. It has been there for centuries. It, also, has energy.
There is stored within it a tremendous power. You smile! Yes, the power
has been there for ages, and now by a slight push it is sent crashing
down the precipice. The power developed by that fall was thousands of
times greater than the push which dislodged it.
But, you say, the push against the stone represented an external force,
and such being the case, why do you say that power is within the thing
itself? The answer is, that not one iota of the power required to push
the stone off its seat was added to the power of the stone when it fell.
Furthermore, the power required to dislodge the stone came from within
me, and not from any outside source.
Here we have two different forms of energy, but both represent a moving
force. The power derived from them is the same.
Kinetic Energy.--The energy of the falling water or stone is called
_Kinetic_ energy. In both cases the power developed came from within
themselves and not from any exterior source.
The difference between Potential and Kinetic Energy is therefore that
Potential Energy represents the capacity to do work, while Kinetic
Energy is the actual performance of work.
Friction.--In every form of energy there is always something to detract
from it or take away a portion of its full force, called _friction_.
When a shaft turns, it rubs against the bearings, and more or less power
is absorbed.
When a wheel travels over the ground friction is ever present. The
dislodging of the stone required ten pounds of energy, but a thousand
pounds was developed by the fall. The water rushing along its rocky bed
has friction all along its path.
Resistance.--This friction is a resistance to the movement of a body,
and is ever present. It is necessary to go back and examine the reason
for this. As long as the stone was poised at the top of the precipice it
had latent or potential energy, which might be termed _power at rest_.
When it fell it had power in motion. In both cases gravity acted upon
the stone, and in like manner on the water pouring over the falls.
Inertia.--Inertia or momentum is inherent in all things and represents
the resistance of any body or matter, to change its condition of rest or
standing still into motion, and is then called _Inertia of Rest_, or the
resistance it offers to increase or decrease its speed when moving, and
is then called _Inertia of Motion_.
Inertia or momentum is composed by the weight of the body and its speed
and is measured by multiplying its weight by its speed.
The law is, that when a body is at rest it will remain at rest
eternally, and when in motion it will continue in motion forever, unless
acted on by some external force or resistance. An object lying on the
ground has the frictional resistance of the earth to prevent its moving.
When the object is flying through space it meets the air and has also
the downward pull of gravity, which seek to bring it to rest.
These resisting forces are less in water, and still less in gases, and
there is, therefore, a state of mobility in them which is not found in
solids.
Internal and External Resistance.--All bodies are subject to internal,
as well as external resistance. The stone on the cliff resisted the
movement to push it over. Weight was the resisting internal force, but
when the stone was moving through the air, the friction with the air
created external resistance.
Energy Indestructible.--There is another thing which should be
understood, and that is the absolute indestructibility of energy. Matter
may be changed in form, or in the direction of its motion, by the change
of kinetic into potential energy, or vice versa, but the sum total of
the energy in the world is unalterable or constant.
The tremendous power developed by the stone when it plunged through
space and struck the rocks below, developed a heat at its impact. Thus
the moving force which was a motion in one direction was converted into
another form of energy, heat. The expansion of the material exposed to
the heat also represented energy.
When powder explodes and absolutely changes the form of the substance,
its volume of expansion, if it should be retained within a vessel, would
perform a certain amount of work, and the energy is thus transferred
from one form to another without ceasing.
Wind Power.--Primitive man also saw and felt the winds. He noted its
tremendous power, but he could not see how a force moving in one
direction only could be utilized by him.
Rectilinear Motion.--This movement of the wind in one direction, like
the water flowing along the bed of the river, is called _rectilinear_
motion. It required invention to convert rectilinear into circular
motion.
Oscillating Motion.--When he threshed his grain and winnowed it by
shaking it to and fro, to rid it of the chaff, the idea of using the
wind to produce an oscillating motion did not occur to him. After
circular motion was produced, the crank was formed and thus the
oscillating movement was brought about.
Movements in Nature.--All movements in nature are simple ones, of which
the following are illustrations:
1. _Rectilinear_, which, as stated, means in a straight line.
2. _Circular_, like the motion of the earth on its axis, once every
twenty-four hours.
3. _Oscillatory_, like a to and fro movement, the swaying branches of
trees, or the swinging of a pendulum.
How Man Utilizes the Various Movements.--What man has done is to utilize
the great natural forces in nature in such a way as to produce these
movements at will, in either direction, with greater or less speed, at
regular or irregular intervals, and at such amplitudes as are required
to perform the necessary work.
Kinds of Potential Energy.--Now, materials have within themselves
_potential_ energy of various kinds. Thus, powder, if ignited, will
burn, and in burning will expand, or explode, as we term it. This is
true also of oils and gases. The expansion pressure produced from such
substances depends on the speed at which they will burn, and in so
confining the burning substances that a great pressure is produced.
The Power in Heat.--The pressure of all such substances against the
confining medium depends on heat. Any gas which has 523 degrees of heat
imparted to it will expand double its volume. If one cubic inch of
water is converted into steam the latter will occupy one cubic foot of
space under atmospheric pressure,--that is, it will expand over 1700
times.
Energy in Steam.--If the steam thus generated is now subjected to 523
degrees of heat additional, it will occupy over 3400 cubic inches of
space. It will thus be seen why steam, gas, and gasoline engines are
called _heat engines_, or heat _motors_.
Energy From the Sun.--Many attempts have been made to utilize the heat
of the sun, to turn machinery, but the difficulty has been to secure
sufficient heat, on the one hand, and on the other to properly cool down
the heated gases, so that the various liquid and solid fuels are
required to make the heat transformations.
Power From Water.--In the use of water two forms are available, one
where the water is moving along or falling in a constant open stream;
and the other where the flowing water is confined and where its flow can
be regulated and controlled. The latter is more available for two
reasons:
First: Economy in the use of water.
Second: Ability to control the speed or movement of the motor.
With running or falling streams a large surface is required, and the
wheels turn slowly. Two well-recognized forms of wheels have been
employed, one called the undershot, or breast wheel, shown in Fig. 1,
and the other the overshot, illustrated in Fig. 2.
[Illustration: _Fig. 1. Undershot Wheel._]
In both types it is difficult to so arrange them as to shut off the
power or water pressure when required, or to regulate the speed.
The Turbine.--Wheels which depend on the controllable pressure of the
water are of the turbine type. The word is derived from the Latin word
_turbo_, meaning to whirl, like a top. This is a type of wheel mounted
on the lower end of a vertical or horizontal shaft, within, or at the
bottom, of a penstock. The perimeter of the wheel has blades, and the
whole is enclosed within a drum, so that water from the penstock will
rush through the tangentially-formed conduit into the drum, and strike
the blades of the wheel.
[Illustration: _Fig. 2. Overshot Wheel._]
A column of water one inch square and twenty-eight inches high weighs
one pound,--or, to express it in another way, the pressure at the
bottom of such a column is one pound, and it is a pound for each
additional 28 inches.
If there should be a head or height of water column of seven feet, the
pressure on each square inch of water at the bottom of the penstock
would be three pounds to the square inch. Assuming the opening or duct
leading to the wheel blades should be 12 × 12 inches, and also the
blades be 12 × 12 inches, the area would be equal to 144 square inches,
and this multiplied by three pounds would equal 432 pounds pressure
against the blades.
Calculating Power of a Turbine Wheel.--The power of such a wheel depends
principally on two things. First, the arrangement of the blades with
reference to the inflowing water; and, second, the discharge port, or
ability of the water to free itself from the wheel casing.
Let us assume that the diameter of the wheel at the center of the blades
is two feet, which would, roughly estimating, give a circumference of
six feet, or a travel of each particular blade that distance at each
turn of the wheel.
If the wheel turns one hundred times a minute, and this is multiplied by
the circumference of the wheel (six feet), the result is 600 feet. This,
again, multiplied by 432 pounds (which represents the pressure of the
water on the entire discharge opening), and we have a product of
259,200, which represents _foot pounds_.
This means the same work as if 259,200 pounds would have been lifted
through a space of one foot in one minute of time. To ascertain how much
power has been developed we must know how many foot pounds there are in
a horse power.
Horse Power.--It is determined in this way: any force which is capable
of raising 550 pounds one foot in one second of time, is developing one
horse power. A man might have sufficient strength to raise such a weight
once, twice, or a dozen times in succession, but if he should try to do
it sixty times a minute he would find it a trying, if not impossible
task.
Foot Pounds.--If he should be able to lift 550 pounds sixty times within
a minute, he would have lifted 33,000 pounds one foot in one minute of
time (550 × 60), and thus have developed one horse power.
As the water wheel, in our calculations above, raised 259,200 pounds in
that period of time, this figure divided by 33,000 shows that a little
more than 7-3/4 horse power was developed, assuming, of course, that we
have not taken into account any waste, or loss by friction, or
otherwise.
This method of determining one horse power should be carefully studied.
Always keep in mind the main factor, 33,000 pounds, and this multiplied
by one foot, the result will be 33,000 _foot pounds_,--that is, one
horse power.
It would be just the same, however, if it were possible to raise one
pound 550 times in one second, or one pound 33,000 times within a
minute.
Power and Time.--You are thus brought face to face with another thing
which is just as important, namely, that, in considering power, time, as
well as energy, must be considered. If a man, by superior strength,
could be able to raise 550 pounds once within a second, then skip a few
seconds, take another hold, and again raise it that distance, he would
not be developing one horse power for a minute, but only for one second
while he lifted the weight. For the whole minute he would only develop a
certain number of foot pounds, and less than 33,000 foot pounds.
If, within a minute, he succeeded in raising it one foot for six times,
this would be six times 550, equal to 3,300 foot pounds, or just
one-tenth of one horse power for one minute; so _time_ is just as
important as the amount lifted at each effort.
Gravitation.--Now, let us examine power from another standpoint. Every
attempt which man makes to produce motion is an effort to overcome some
resistance. In many cases this is "weight or gravity." While humanity
unceasingly antagonizes the force of gravity it is constantly utilizing
the laws of gravitation.
Utilizing the Pull of Gravity.--The boy laboriously drags his sled to
the top of the hill against gravity, and then depends on that force to
carry him down. We have learned to set up one force in nature against
the other. The running stream; the moving winds; the tides; the
expansive force of all materials under heat, are brought into play to
counteract the great prevailing agency which seeks to hold everything
down to mother earth.
Utilizing Forces.--The Bible says: Blessed is he who maketh two blades
of grass grow where one grew before. To do that means the utilization of
forces. Improved machinery is enabling man to make many blades grow
where one grew before. New methods to force the plow through the soil;
to dig it deeper; to fertilize it; and to harvest it; all require power.
Pitting Forces Against Each Other.--Man has discovered how to pit the
forces of nature against each other, and the laws which regulate them.
Centripetal and Centrifugal Forces.--Gravity, that action which seeks to
draw all matter toward the center of the earth, is termed _centripetal_
force. But as the earth rotates on its axis another force is exerted
which tends to throw substances outwardly, like dirt flying from the rim
of a wheel. This is called _centrifugal_ force.
Man utilizes this force in many ways, one of which is illustrated in the
engine governor, where the revolving balls raise the arms on which they
swing, and by that means the engine valve is regulated.
Power Not Created.--In taking up the study of this subject start with a
correct understanding of the source of all power. It is inherent in all
things. All we can do is to liberate it, or to put the various materials
in such condition, that they will exert their forces for our uses. (See
Page nine, "Energy Indestructible.")
A ton of coal, when burned, produces a certain amount of heat, which, if
allowed to escape, will not turn a wheel. But if confined, it expands
the air, or it may convert water into steam which will turn ponderous
machinery. Niagara Falls has sent its great volume into the chasm for
untold centuries, but it has never been utilized until within the last
twenty years. The energy has been there, nevertheless; and so it is with
every substance of which we have knowledge.
The successive steps, wherein the experimenter and the inventor have
greatly improved on the original inventions, will be detailed as we go
along through the different types of motors.
Developing the Power of Motors.--This development in the art is a most
fascinating study. It is like the explorer, forcing his way through a
primeval forest. He knows not what is beyond. Often, like the traveler,
he has met serious obstructions, and has had to deviate from his course,
only to learn that he took the wrong direction and had to retrace his
steps.
The study of motors and motive power is one which calls for the highest
engineering qualities. In this, as in every other of the mechanical
arts, theory, while it has an important function, occupies second place.
Experimenting.--The great improvements have been made by building and
testing; the advance has been step by step. Sometimes a most important
invention will loom up as a striking example to show how a valuable
feature lies hidden and undeveloped.
An illustration of this may be cited with respect to the valve of the
steam engine. For four hundred years there was no striking improvement
in the valve. The various types of sliding and rocking valves were
modified and refined until it was assumed that they typified perfection.
At one stroke the Corliss valve made such an immense improvement that
the marvel was as much in its simplicity as in its performance.
The reasons and the explanations will be set forth in the section which
analyzes valve motion. In this, as in other matters, it shall be our aim
to explain why the different improvements were regarded as epochs in the
production of motors.
CHAPTER II
THE STEAM GENERATOR
The most widely known and utilized source of power is the steam engine.
Before its discovery wind and water were the only available means,
except the muscular power of man, horses and other animals, which was
used with the crudest sort of contrivances.
In primitive days men did not value their time, so they laboriously
performed the work which machinery now does for us.
The steam engine, like everything else which man has devised, was a
growth, and, singular as it may seem, the boiler, that vital part of the
organism, was, really, the last to receive due consideration and
improvement.
As the boiler is depended upon to produce the steam pressure, and since
the pressure depends on the rapid and economical evaporation of water,
the importance of the subject will be understood in treating of the
steam engine.
Water as an Absorbent of Heat.--Water has the capacity to absorb a
greater amount of heat than any other substance. A pewter pot, which
melts at 500 degrees, will resist 2000 degrees of heat if it is filled
with water, since the latter absorbs the heat so rapidly that the
temperature of the metal is kept near the boiling point of water, which
is 212 degrees.
Notwithstanding the great heat-absorbing qualities of water, a large
portion of the heat of the fuel passes through the flues and escapes
from the stack. This fact has caused inventors to devise various forms
of boilers, the object being to present as large an area of water as
possible to the heat of the burning fuel. How that was accomplished we
shall try to make plain.
Classification of Boilers.--Numerous types of boilers have been devised,
the object being, in all cases to evaporate the largest amount of water
with the minimum quantity of fuel. All boilers may be put under two
general heads, namely, those which contain a large quantity of water,
and those which are intended to carry only a small charge.
In the first division the boilers are designed to carry a comparatively
small pressure, and in the latter high pressures are available.
Mode of Applying Heat.--The most important thing to fully understand is
the manner in which heat is applied to the boiler, and the different
types which have been adapted to meet this requirement.
The Cylindrical Boiler.--The most primitive type of boiler is a plain
cylindrical shell A, shown in Fig. 3, in which the furnace B is placed
below, so that the surface of the water in contact with the fire area is
exceedingly limited.
[Illustration: _Fig. 3. Primitive Boiler._]
In such a type of boiler it would be impossible for water to extract
more than quarter the heat of the fuel. Usually it was much less. The
next step was to make what is called a return tubular type in which the
heat of the burning gases is conveyed to the rear end of the boiler, and
then returned to the front end through tubes.
Fig. 4 shows this construction. The head of the shell holds the ends of
a plurality of tubes, and the products of combustion pass through the
conduit, below the boiler to the rear end, and are conducted upwardly to
the tubes. As all the tubes are surrounded by water, it will absorb a
large amount of the heat as the gases move through, and before passing
out of the stack.
[Illustration: _Fig. 4. Return Tubular Boiler._]
[Illustration: _Fig. 5. Cornish, or Scotch Boiler._]
The Cornish Boiler.--One of the most important inventions in the
generation of steam was the Cornish boiler, which for many years was the
recognized type for marine purposes. It had the advantage that a large
amount of water could be carried and be subjected to heat at all times.
Aside from that it sought to avoid the great loss due to radiation.
It will be seen from an examination of Fig. 5 that the shell is made
very large, and its length does not exceed its diametrical measurement.
Two, and sometimes three, fire tubes are placed within the shell, these
tubes being secured to the heads. Surrounding these fire tubes, are
numerous small tubes, through which the products of combustion pass
after leaving the rear ends of the fire tubes.
In these boilers the tubes are the combustion chambers, and are provided
with a grating for receiving the coal, and the rear ends of the tubes
are provided with bridge walls, to arrest, in a measure, the free exit
of the heated gases.
These boilers would be very efficient, if they could be made of
sufficient length to permit the water to absorb the heat of the fuel,
but it will be seen that it would be difficult to make them of very
great length. If made too small diametrically the diameter of the fire
boxes would be reduced to such an extent that there would not be
sufficient grate surface.
It is obvious, however, that this form of boiler adds greatly to the
area of the water surface contact, and in that particular is a great
improvement.
[Illustration: _Fig. 6. Water Tube Boiler: End View._]
The Water Tube Boiler.--In the early days of the development of boilers,
the universal practice was to have the products of combustion pass
through the flues or the tubes. But quick generation of steam, and high
pressures, necessitated a new type. This was accomplished by connecting
an upper, or steam drum, with a lower, or water drum, by a plurality of
small tubes, and causing the burning fuel to surround these tubes, so
that the water, in passing upwardly, would thus be subjected to the
action of the fuel.
This form of boiler had two distinct advantages. First, an immense
surface of water could be provided for; and, second, the water and steam
drums could be made very small, diametrically, and thus permit of very
high pressures.
In Fig. 6, which is designed to show a well known type of this
structure, A A, represent the water drums and B, the steam drum. The
water drums are separated from each other, so as to provide for the
grate bars C, and each water drum is connected with the steam drum by a
plurality of tubes D.
It will thus be seen that a fire box, or combustion chamber, is formed
between the two sets of tubes D, and to retain the heat, or confine it
as closely as possible to the tubes, a jacket E is placed around the
entire structure.
The ends of the water and steam drums are connected by means of tubes F,
shown in side view, Fig. 7, for the return or downward flow of the
water. The diagrams are made as simple as possible, to show the
principal features only. The structure illustrated has been modified in
many ways, principally in simplifying the construction, and in providing
means whereby the products of combustion may be brought into more
intimate contact with the water during its passage through the
structure.
[Illustration: _Fig. 7. Water Tube Boiler: Side View._]
As heretofore stated, this type of boiler is designed to carry only a
small quantity of water, so that it is necessary to have practically a
constant inflow of feed water, and to economize in this respect the
exhaust of the steam engine is used to initially heat up the water, and
thus, in a measure, start the water well on its way to the evaporation
point before it reaches the boiler.
Various Boiler Types.--The different uses have brought forth many kinds
of boilers, in order to adapt them for some particular need. It would
be needless to illustrate them, but to show the diversity of structures,
we may refer to some of them by their characteristics.
Compound Steam-Boiler.--This is a battery of boilers having their steam
and water spaces connected, and acting together to supply steam to a
heating apparatus or a steam engine. These are also made by combining
two or more boilers and using them as a feed water heater or a
superheater, for facilitating the production of steam, or to be used for
superheating steam.
The terms _feed water heater and super heater_ are explained in chapter
III.
Locomotive Steam-Boiler.--This is a tubular boiler which has a contained
furnace and ash pit, and in which the gases of combustion pass from the
furnace directly into the horizontal interior tubes, and after passing
through the tubes are conveyed directly into the smoke box at the
opposite ends of the tubes. The name is derived from the use of such
boilers on locomotive engines, but it is typical in its application to
all boilers having the construction described, and used for generating
steam.
Vertical Steam-Boiler.--This is a form of construction in which the
shell, or both the shell and the tubes, are vertical, and the tubes
themselves may be used to convey the products of combustion, or serve
as the means for conveying water through them, as in the well known
water tube type.
This form of boiler is frequently used to good advantage where it is
desired to utilize ground space, and where there is sufficient head
room. Properly constructed, it is economical as a steam generator.
From the foregoing it will be seen that the structural features of all
boilers are so arranged as to provide for the exposure of the largest
possible area of water to a heated surface so that the greatest amount
of heat from the fuel may be absorbed.
CHAPTER III
STEAM ENGINES
The first steam engine was an exceedingly simple affair. It had neither
eccentric, cylinder, crank, nor valves, and it did not depend upon the
pressure of the steam acting against a piston to drive it back and
forth, because it had no piston.
It is one of the remarkable things in the history and development of
mechanism, that in this day of perfected steam engines, the inventors of
our time should go back and utilize the principles employed in the first
recorded steam engine, namely, the turbine. Instead of pressure exerting
a force against a piston, as in the reciprocating engine, the steam
acted by impacting against a moving surface, and by obtaining more or
less reaction from air-resistance against a freely discharging steam jet
or jets.
The original engine, so far as we have any knowledge, had but one moving
part, namely, a vertical tubular stem, to which was attached a cross or
a horizontal tube.
The Original Engine.--Figure 8 is a side view of the original engine.
The vertical stem A is pivoted to a frame B, and has a bore C which
leads up to a cross tube D. The ends of the tube D are bent in opposite
directions, as shown in the horizontal section, Fig. 9.
[Illustration: _Fig. 8. The Original Engine._]
[Illustration: _Fig. 9. Horizontal Section of Tube._]
Steam enters the vertical stem by means of a pipe, and as it rushes up
and out through the lateral tubes D, it strikes the angles E at the
discharge ends, so that an impulse is given which drives the ends of the
tube in opposite directions. As the fluid emerges from the ends of the
tubes, it expands, and on contacting with the air, the latter, to a
certain extent, resists the expansion, and this reacts on the tube.
Thus, both forces, namely, impact and reaction, serve to give a turning
motion to the turbine.
The Reciprocating Engine.--The invention of this type of engine is
wrapped in mystery. It has been attributed to several. The English
maintain that it was the invention of the Marquis of Worcester, who
published an account of such an engine about 1650. The French claim is
that Papin discovered and applied the principle before the year 1680.
In fact, the first actual working steam engine was invented and
constructed by an Englishman, Captain Savery, who obtained a patent for
it in 1698. This engine was so constructed as to raise water by the
expansion and condensation of steam, and most engines of early times
were devoted solely to the task of raising water, or were employed in
mines.
Atmospheric Engines.--When we examine them it is difficult to see how we
can designate them as steam engines. The steam did not do the actual
work, but a vacuum was depended on for the energy developed by the
atmospheric pressure.
A diagram is given, Fig. 10, showing how engines of this character were
made and operated. A working beam A was mounted on a standard B, and one
end had a chain C on which was placed heavy weights D. Near this end was
also attached the upper end of a rod E, which extended down to a pump.
[Illustration: Fig. 10. Steam-Atmospheric Engine.]
The other end of the working beam had a chain F, which supported a
piston G working within a vertically-disposed cylinder H. This cylinder
was located directly above a boiler I, and a pipe J, with a valve
therein, was designed to supply steam to the lower end of the cylinder.
A water tank K was also mounted at a point above the cylinder, and this
was supplied with water from the pump through a pipe L. Another pipe M
from the tank conducted water from the tank to the bottom of the
cylinder.
The operation of the mechanism was as follows: The steam cock N, in the
short pipe J, was opened to admit steam to the cylinder, below the
piston. The stem of the steam cock also turned the cock in the water
pipe M, so that during the time the steam was admitted the water was
shut off.
When the steam was admitted so that it filled the space below the
piston, the cock N was turned to shut off the steam, and in shutting off
the steam, water was also admitted. The injection of water at once
condensed the steam within the cylinder so a partial vacuum was formed.
It will be remembered that as steam expanded 1700 times, the
condensation back into water made a very rarified area within the
cylinder, and the result was that the piston was drawn down, thus
raising both the weight D and also the pump rod E. This operation was
repeated over and over, so long as the cock N was turned.
The turning of the stem of this cock was performed manually,--that is,
it had to be done by hand, and boys were usually employed for doing
this. When, later on, some bright genius discovered that the valve
could be turned by the machinery itself, it was regarded as a most
wonderful advance.
The discovery of this useful function has been attributed to Watt. Of
this there is no conclusive proof. The great addition and improvements
made by Watt, and which so greatly simplified and perfected the engine,
were through the addition of a separate condenser and air pump, and on
these improvements his fame rests.
From the foregoing it will be seen that the weight D caused the piston
to travel upwardly, and not the force of the steam, and the suction
produced by the vacuum within the cylinder did the work of actuating the
pump piston, so that it drew up the water.
The Piston.--From this crude attempt to use steam came the next step, in
which the steam was actually used to move the piston back and forth and
thus actually do the work. In doing so the ponderous walking beam was
dispensed with, and while, for a long period the pistons were
vertically-placed, in time a single cylinder was used, and a crank
employed to convert the reciprocating into a circular motion.
Fig. 11 shows a simple diagram of a steam engine, so arranged that the
operation of the valves may be readily understood. The cylinder A has a
steam chest B, which contains therein a slide valve C to cover the ports
at the ends of the cylinder. This figure shows the crank turning to the
right, and the eccentric D on the engine shaft is so placed, that while
the crank E is turning past the dead center, from 1 to 2, the slide
valve C is moved to the position shown in Fig. 12, thereby covering port
F and opening port G.
[Illustration: _Fig. 11. Simple Valve Motion. First position._]
[Illustration: _Fig. 12. Simple Valve Motion. Second position._]
It will be seen that the slide valve is hollowed within, as at H, and
that the exhaust port I leads from this hollowed portion while the live
steam from the boiler enters through pipe J and fills the space K of
the chest.
In Fig. 11 live steam has been entering port F, thus driving the piston
to the right. At the same time the exhaust steam at the right side of
the piston is discharging through the port G and entering the hollow
space within the slide valve. In Fig. 12 the conditions are reversed,
and now live steam enters port G, and the exhaust passes out through
port F.
When the engine crank reaches the point 3, which is directly opposite 1,
the reverse action takes place with the slide valve, and it is again
moved to its original position, shown in Fig. 12.
Importance of the Valve.--Every improvement which has been made in the
engine has been directed to the valve. The importance of this should be
fully understood. As the eccentric is constantly turning it is a
difficult matter to so arrange the valve as to open or close it at the
correct time, absolutely, and many devices have been resorted to to
accomplish this.
Expanding the Steam.--As all improvements were in the direction of
economizing the use of steam, it was early appreciated that it would be
a waste to permit the steam to enter the cylinder during the entire
period that the engine traveled from end to end, so that the valve had
to be constructed in such a way that while it would cut off the
admission of steam at half or three-quarters stroke, the exhaust would
remain on until the entire stroke was completed.
Some engines do this with a fair degree of accuracy, but many of them
were too complicated for general use. In the form of slide valve shown
the pressure of the steam on the upper side, which is constant at all
times, produces a great wearing action on its seat. This necessitated
the designing of a type of valve which would have a firm bearing and be
steam tight without grinding.
Balanced Valve.--One of the inventions for this purpose is a valve so
balanced by the steam pressure that but little wear results. This has
been the subject of many patents. Another type also largely used in
engines is known as the _oscillating_ valve, which is cylindrical or
conical in its structure, and which revolves through less than a
complete revolution in opening and closing the ports.
Rotary Valve.--The rotary valve, which constantly turns, is employed
where low pressures are used, but it is not effectual with high
pressures. This is also cylindrical in its structure, and has one or
more ports through it, which coincide with the ports through the walls
of the engine, as it turns, and thus opens the port for admitting live
steam and closing the discharge port at the same time or at a later
period in its rotation.
Engine Accessories.--While the steam engine is merely a device for
utilizing the expansive force of steam, and thus push a cylinder back
and forth, its successful operation, from the standpoint of economy,
depends on a number of things, which are rarely ever heard of except by
users and engineers.
Many of these devices are understood only by those who have given the
matter thorough study and application. To the layman, or the ordinary
user, they are, apparently, worth but little consideration. They are the
things, however, which have more than doubled the value of the steam
engine as a motor.
Efficiency of Engines.--When it is understood that with all the
refinements referred to the actual efficiency of a steam engine is less
than 30 per cent. some idea may be gained of the value which the various
improvements have added to the motor.
Efficiency refers to the relative amount of power which is obtained from
the burning fuel. For instance, in burning petroleum about 14,000 heat
units are developed from each pound. If this is used to evaporate water,
and the steam therefrom drives an engine, less than 4200 heat units are
actually utilized, the remaining 9800 heat units being lost in the
transformation from the fuel to power.
[Illustration: _Fig. 13. Effective pressure in a Cylinder._]
The value of considering and providing for condensation, compression,
superheating, re-heating, compounding, and radiation, and to properly
arrange the clearance spaces, the steam jackets, the valve adjustments,
the sizes of the ports and passages, and the governor, all form parts of
the knowledge which must be gained and utilized.
How Steam Acts in a Cylinder.--Reference has been made to the practice
of cutting off steam before the piston has made a full stroke, and
permitting the expansive power of the steam to drive the piston the rest
of the way, needs some explanation.
As stated in a preceding chapter the work done is estimated in foot
pounds. For the purpose of more easily comprehending the manner in which
the steam acts, and the value obtained by expansion, let us take a
cylinder, such as is shown in Fig. 13, and assume that it has a stroke
of four feet. Let the cylinder have a diameter of a little less than one
foot, so that by using steam at fifty pounds pressure on every square
inch of surface, we shall have a pressure of about 5000 pounds on the
piston with live steam from the boiler.
In the diagram the piston moves forwardly to the right from 0 to 1,
which represents a distance of one foot, so that the full pressure of
the steam of the boiler, representing 5000 pounds, is exerted on the
piston. At 1 the steam is cut off, and the piston is now permitted to
continue the stroke through the remaining three feet by the action of
the steam within the cylinder, the expansive force alone being depended
on.
As the pressure of the steam within the cylinder is now much less and
decreases as the piston moves along, we have taken a theoretical
indication of the combined pressure at each six inch of the travel of
the piston. The result is that we have the following figures, namely,
4000, 2700, 1750, 1000, 450 and 100. The sum of these figures is 10,000
pounds.
The piston, in moving from 0 to 1, moved one foot, we will say, in one
second of time, hence the work done by the direct boiler pressure was
5000 _foot pounds_; and since the piston was moved three feet more by
the expansion of the steam only, after the steam pressure was shut off,
the work done in the three seconds required to move the piston, was an
additional 5000 foot pounds, making a total of 10,000 foot pounds for
four seconds, 150,000 foot pounds per minute, or about 45 horse power.
[Illustration: _Fig. 14. Indicating pressure Line._]
This movement of the piston to the right, represented only a half
revolution of the crank, and the same thing occurs when the piston moves
back, to complete the entire revolution.
Indicating the Engine.--We now come to the important part of engine
testing, namely, to ascertain how much power we have obtained from the
engine. To do this an indicator card must be furnished. A card to
indicate the pressure, as we have shown it in the foregoing diagram
would look like Fig. 14.
The essential thing, however, is to learn how to take a card from a
steam engine cylinder, and we shall attempt to make this plain, by a
diagram of the mechanism so simplified as to be readily understood.
[Illustration: _Fig. 15. Indicating the Engine._]
In Fig. 15 we have shown a cylinder A, having within a piston B, and a
steam inlet pipe C. Above the cylinder is a drum D, mounted on a
vertical axis, and so geared up with the engine shaft that it makes one
complete turn with each shaft revolution. A sheet of paper E, ruled with
cross lines, is fixed around the drum.
The cylinder A has a small vertical cylinder F connected therewith by a
pipe A, and in this cylinder is a piston H, the stem I of which extends
up alongside of the drum, and has a pointed or pencil J which presses
against the paper E.
Now, when the engine is set in motion the drum turns in unison with the
engine shaft, and the pressure of the steam in the cylinder A, as it
pushes piston B along, also pushes the piston H upwardly, so that the
pencil point J traces a line on the ruled paper.
It will be understood that a spring is arranged on the stem I in such a
manner that it will always force the piston H downwardly against the
pressure of the steam.
Mean Efficiency.--We must now use a term which expresses the thing that
is at the bottom of all calculations in determining how much power is
developed. You will note that the pressure on the piston during the
first foot of its movement was 10,000 pounds, but that from the point 1,
Fig. 13, to the end of the cylinder, the pressure constantly decreased,
so that the pressure was not a uniform one, but varied.
Suppose we divide the cylinder into six inch spaces, as shown in Fig.
13, then the pressure of the steam at the end of each six inches will be
the figures given at bottom of diagram, the sum total of which is
30,000, and the figures at the lower side show that there are eight
factors.
The figure 10,000 represents, of course, two six inch spaces in the
first foot of travel.
The result is, that, if we divide the sum total of the pressures at the
eight points by 8, we will get 3750, as the mean pressure of the steam
on the piston during the full stroke of the piston.
In referring to the foot pounds in a previous paragraph, it was assumed
that the piston moved along each foot in one second of time. That was
done to simplify the statement concerning the use of foot pounds, and
not to indicate the time that the piston actually travels.
Calculating Horse Power.--We now have the first and most important
factor in the problem,--that is, how much pressure is exerted against
the piston at every half revolution of the crank shaft. The next factor
to be determined is the distance that the piston travels in one minute
of time.
This must be calculated in feet. Let us assume that the engine turns the
crank shaft at a speed of 50 revolutions a minute. As the piston travels
8 feet at each revolution, the total distance traveled is 400 feet.
If, now, we have a constant pressure of 3750 pounds on the piston, and
it moves along at the rate of 400 feet per minute, it is obvious that
by multiplying these two together, we will get the figure which will
indicate how many pounds the steam has lifted in that time.
This figure is found to be 1,500,000, which means foot pounds, as we
have by this means measured pressure by feet, or pounds lifted at each
foot of the movement of the piston.
As heretofore stated, we must now use the value of a horse power, so
that we may measure the foot pounds by it. If we had a lot of wheat in
bulk, and we wanted to determine how much we had, a bushel measure would
be used. So with power. The measure, as we have explained, is 33,000,
and 1,500,000 foot pounds should give as a result a little over 45 horse
power.
Condensation.--We now come to the refinements in engine
construction,--that which adds so greatly to the economy of operation.
The first of these is condensation. The first reciprocating engine
depended on this to do the actual work. In this age it is depended upon
simply as an aid.
The first thing however that the engineer tries to do is to prevent
condensation. This is done by jacketing the outside of the cylinder with
some material which will prevent radiation of heat, or protect the steam
within from being turned back into water by the cool air striking the
outside of the cylinder.
Atmospheric Pressure.--On the other hand, there is a time when
condensation can be made available. The pressure of air on every square
inch of surface is 14-3/4 pounds. When a piston moves along and steam is
being exhausted from the cylinder, it must act against a pressure of
14-3/4 pounds on every square inch of its surface.
The problem now is to get rid of that back pressure, and the old type
engines give a hint how it may be done. Why not condense the steam
discharged from the engine cylinder? In doing so a vacuum is produced on
the exhaust side of the piston, at the same time a pressure is exerted
on its other side.
The Condenser.--Thus the condenser is brought into existence, as an aid.
By jacketing condensation is prevented; it is fought as an enemy. It is
also utilized as a friend. It is so with many of the forces of nature,
where man for years vainly fought some principle, only to find, later
on, that a friend is more valuable than a foe, and to utilize a material
agency in nature is more economical than to fight it.
Pre-heating.--The condenser does two things, both of which are of great
value to the economical operation of the engine. For the purpose of
rapidly converting the steam back into water as it issues from the
engine cylinder, water is used. The steam from the cylinder has a
temperature of 212 degrees and upwards, dependent on its pressure.
Water, ordinarily, has a temperature of 70 degrees, or less, so that
when the steam strikes a surface which is cooled down by the water, it
is converted back into liquid form, but at a temperature less than
boiling water. The water thus converted back from the steam gives up
part of its heat to the water which cools the condenser, and the water
from the condenser, as well as the water used to cool the condenser, are
thus made available to be fed into the boiler, and thus assist in again
converting it into a steam.
The economy thus lies in helping the coal, or other fuel, do its work,
or, to put it more specifically, it conserves the heat previously put
out by the coal, and thus saves by using part of the heat over again.
Superheaters.--Another refinement, and one which goes to the very
essence of a heat motor, is the method of superheating the steam. This
is a device located between the boiler and the engine, so that the
steam, in its transit from the boiler to the engine, will be heated up
to a high degree, and in the doing of which the pressure may be
doubled, or wonderfully increased.
This may be done in an economical manner in various ways, but the usual
practice is to take advantage of the exhaust gases of the boiler, in the
doing of which none of the heat is taken from the water in the boiler.
The products of combustion escaping from the stacks of boilers vary.
Sometimes the temperature will be 800 degrees and over, so that if pipes
are placed within the path of the heated gases, and the supply steam
from the boiler permitted to pass through them a large amount of heat is
imparted to the steam from a source which is of no further use to the
water being generated in the boiler.
Compounding.--When reference was made to the condensation of steam as it
issued from the boiler, no allusion was made to the pressure at which it
emerged. If the cylinder was well jacketed, so that the amount of
condensation in the cylinder was small, then the pressure would still be
considerable at the exhaust. Or, the steam might be cut off before the
piston had traveled very far at each stroke, in which case the exhaust
would be very weak.
In practice it has been found to be most economical to provide a high
boiler pressure, and also to superheat the steam, but where it is not
superheated, and a comparatively high boiler pressure is provided,
compounding is resorted to.
To compound steam means to use the exhaust to drive a piston. In such a
case two cylinders are placed side by side, one, called the high
pressure cylinder, being smaller than the low pressure cylinder, which
takes the exhaust from the high pressure.
The exhaust from the second, or low pressure cylinder may then be
supplied to a condenser, and in that case the mechanism would be termed
a compound condensing engine. If a condenser is not used, then it is
simply a compound engine.
Triple and Quadruple Expansion Engines.--Instead of using two cylinders,
three, or four, are employed, each succeeding cylinder being larger than
the last. As steam expands it loses its pressure, or, stated in another
way, whenever it loses pressure it increases in volume. For that reason
when steam enters the first cylinder at a pressure of say 250 pounds, it
may exhaust therefrom into the next cylinder at a pressure of 175
pounds, with a corresponding increase in volume.
To receive this increased volume, without causing a sensible back
pressure on the first cylinder, the second cylinder must be larger in
area than the first; in like manner when it issues from the exhaust of
the second cylinder at 125 pounds pressure, there is again an increase
in volume, and so on.
[Illustration: _Fig. 16. Compound Engine._]
Examine Fig. 16, which shows a pair of cylinders, A being the high, and
B the low pressure cylinders, the exhausts of the high pressure being
connected up with the inlets of the low pressure, as indicated by the
pipes, C D.
The diagram does not show the valve operations in detail, it being
sufficient to explain that when the valve E in the pipe C is closed, the
valve F, at the other end of the cylinders, in the pipe D, is closed.
The same principle is employed in the triple and quadruple expansion
engines, whereby the force of the steam at each exhaust is put to work
immediately in the next cylinder, until it reaches such a low pressure
that condensation is more effective than its pressure.
The diagram, as given, is merely theoretical, and it shows the following
factors:
First: The diameter of each piston.
Second: The area of each piston in square inches.
[Illustration: Fig. 16a. Relative Piston Pressures.]
Third: The steam pressure in each cylinder.
Fourth: The piston pressure of each cylinder.
It will be seen that an engine so arranged is able to get substantially
the same pressure in each of the second, third and fourth cylinders, as
in the first (see Fig. 16a), and by condensing the discharge from the
fourth cylinder a most economical use of steam is provided for. The
Steam Turbine.--We must now consider an entirely new use of steam as a
motive power. Heretofore we have been considering steam as a matter of
pressure only, in the development of power. It has been observed that
when the pressure of steam decreases at the same temperature it is
because it has a greater volume, or a greater volume results.
[Illustration: Fig. 17. Changing Pressure into Velocity]
When steam issues from the end of a pipe its velocity depends on its
pressure. The higher the pressure the greater its velocity. The elastic
character of steam is shown by its action when ejected from the end of a
pipe, by the gradually enlarging area of the discharging column.
In a reciprocating engine the power is derived from the pressure of the
steam; in a turbine the power results from the impact force of the steam
jet. Such being the case velocity in the movement of the steam is of
first importance.
Pressure and Velocity.--To show the effectiveness of velocity, as
compared with pressure, examine Fig. 17. A is a pipe discharging steam
at a pressure of 100 pounds. To hold the steam in the pipe would
require a pressure of 100 pounds against the disk B, when held at 1, the
first position.
Suppose, now, the disk is moved away from the end of the pipe to
position 2. The steam, in issuing forth, strikes the disk over a larger
area, and in escaping it expands, with the result that its velocity from
1 to 2 is greater than the movement of the steam within the pipe that
same distance.
[Illustration: _Fig. 18. Reaction against Air._]
[Illustration: _Fig. 19. Reaction against Surface._]
The disk is now moved successively to positions 3, 4, 5, and so on. If
we had a measuring device to determine the push against the disk at the
various positions, it would be found that there is a point at some
distance from the end of the pipe, at which the steam has the greatest
striking force, which might be called the focal point.
A blow pipe exhibits this same phase; the hottest point is not at the
end of the pipe, but at an area some distance away, called the focal
point of heat.
The first feature of value, therefore, is to understand that pressure
can be converted into velocity, and that to get a great impact force,
the steam must be made to strike the hardest and most effective blow.
When a jet of steam strikes a surface it is diverted or it glances in a
direction opposite the angle at which it strikes the object. In
directing a jet against the blades of a turbine it is impossible to make
it strike squarely against the surface.
[Illustration: Fig. 20. Turbine Straight Blades.]
Let us assume that a wheel A, Fig. 20, has a set of blades B, and a
steam jet is directed against it by the pipe C. It will be seen that
after the first impact the steam is forced across the blades, and no
further force is transferred to them.
Form of Blades.--The blades are therefore so curved, that the steam
after the first impact cannot freely pass along the blade, as it does on
a straight blade, but imparts on every element of the curved-back blade,
thereby giving up continually part of its speed to the blade.
This is clearly shown in Fig. 21, where the pipe D ejects the stream of
steam against the concaved blades E. Many modifications have been made
in the shapes of these blades, all designed to take advantage of this
action.
[Illustration: _Fig. 21. Curved Blades._]
[Illustration: _Fig. 22. Compound Turbine._]
Compounding the Jet.--We may extend the advantages gained by this form
of blades, and diverting the course of the jet, so that it will be
directed through a series of wheels, each of which will get the benefit
of the moving mass from the pipes.
Such a structure is shown in Fig. 22, in which three bladed wheels A, B,
C, are caused to rotate, a set of stationary blades D, E, being placed
between the three moving wheels, but the stationary blades are disposed
in reverse directions. When the steam from pipes F, F, impinges against
the blades of the first wheel A, it is directed by the stationary blade
D to the next wheel B, and from the stationary blade E to the blades of
the next wheel C, thus, in a manner somewhat similar to the compounding
effect of the steam engine, utilizes the pressure which is not used at
the first impulse.
CHAPTER IV
FUELS AND COMBUSTION
All fuels must be put into a gaseous state before they will burn. This
is true of coal as well as of hydro-carbon oils.
Neither coal nor petroleum will burn in its native state, without the
addition of oxygen. This is absolutely necessary to support combustion.
Burning is caused by the chemical union of oxygen with such substances
as will burn.
This burning process may be slow, and extend over a period of years, or
it may be instantaneous, in which latter case the expansion of the
heated gases is so great as to cause an explosion. When a sufficient
amount of oxygen has been mixed with a fuel to permit it to burn, a high
temperature is necessary to cause the immediate burning of the entire
mass.
If such a temperature is not present the course of combustion is not
arrested, but it will, on its own account, start to oxydize, and
eventually be reduced to the same condition that would take place if
exploded by means of a flame.
Solid Fuels.--The great fuels in nature are carbon and hydrogen, carbon
being the substance most widely known and depended upon. Hard coal, for
instance, is composed almost wholly of carbon; whereas soft coal has a
considerable quantity of hydrogen.
As coal was formed by wood, which, through long process of time became
carbonized, it contains considerable foreign matter which will not burn,
forming ash.
Liquid Fuels.--The volatile oils, however, have very little
non-combustible matter. Ordinary petroleum contains about 80 per cent,
of carbon, and from 12 to 15 per cent. of hydrogen, the residue being
foreign matter, all more or less susceptible of being consumed at high
temperatures.
Combustion.--The term _combustion_, in its general sense, means the act
of burning; but in a larger and more correct application it refers to
that change which takes place in matter when oxygen unites with it.
Oxygen is a wonderful element, and will unite with all known substances,
unlike all other elements in this respect. It may take years for it to
form a complete unity. Thus, wood, in time, will crumble, or rot, as it
is called. This is a slow process of combustion, brought about without
applying heat to it, the change taking place in a gradual way, because
oxygen unites with only a small portion of the wood.
Oxidation.--Iron will rust. This is another instance of combustion,
called oxidation. When oxygen unites with a substance it may produce an
acid, or an alkali, or a neutral compound. When wood is burned it
produces an ash, and this ash contains a large amount of potash, or lye,
which is an alkali, or a salt. So when other substances are burnt the
result may be an acid, like sulphur, or it may be unlike either acid or
the alkali.
The unity of oxygen with the food in the body is another instance of
oxidation, which produces and maintains the heat necessary for
existence.
Carbon or hydrogen, as a fuel, are inert without oxygen, so that in
considering the evolution of a force which is dependent on heat, we
should know something of its nature, thereby enabling us to utilize it
to the best advantage.
The Hydro-carbon Gases.--If petroleum, or gasoline, should be put into
the form of a gas, and as such be confined in a receiver, without adding
any oxygen, it would be impossible to ignite it.
The character of the material is such that it would instantaneously
extinguish any flame. Now, to make a burning mixture, at least three
parts of oxygen must be mixed with one of the hydro-carbon, before it is
combustible.
Oxygen and Atmosphere.--The atmosphere is not oxygen. Only one-fifth of
common air is oxygen, the residue being, principally, nitrogen, which is
not a fuel. To produce the proper aëration, therefore, at least fifteen
parts of air must be mixed with one part of hydro-carbon gas.
The term _hydro-carbon_ is applied to petroleum, and its products,
because the elements carbon and hydrogen make up the largest part of the
oil, whereas this is not the case with most of the other oils.
We are now dealing with a fuel such as is needed in _Internal Combustion
Engines_, and it is well to know some of the problems involved in the
use of the fuel, as this will give a better understanding of the
structure of the devices which handle and evolve the gases, and properly
burn them within the engine.
Vaporizing Fuel.--As the pure liquid will not burn in that state the
first essential is to put it into a gaseous form, or to generate a vapor
from it. The vapor thus made is not a gas, in the true sense of that
term, but it is composed of minute globules of finely-divided particles
of oil.
Nearly all liquids will vaporize if permitted to come into contact with
air. The greater the surface exposed to air the more rapidly will it
turn into a vapor.
By forcibly ejecting the liquid from a pipe or spraying device, and
mingling air with it, evaporation is facilitated, and at the same time
the proper admixture of air is provided to make a combustible substance
the moment sufficient heat is brought into contact with it.
This is what actually takes place in a gasoline engine, and all the
mechanism is built with this end in view.
It has been the universal practice to make an explosive mixture of this
character, and then ignite it by means of an electric spark, but it is
now known that such a fuel can be exploded by pressure, and this needs
some explanation.
Explosion by Compression.--The study of the compressibility of gases is
an interesting one. As we have previously stated, the atoms, comprising
the gases, are constantly moving among themselves with great rapidity,
so that they bombard the sides of the receiver in which they are
confined, and also contact with each other in their restless movements.
When compression takes place the speed of the movements of the atoms is
greatly accelerated, the friction of their movements is increased, and
heat is evolved. As the pressure becomes greater the heat increases
until it is of such intensity that the gas ignites, and an explosion
follows.
How Compression Heats.--The theory of the compressibility of gases may
be stated as follows: Let us assume that the temperature of the air is
70 degrees Fahrenheit, and we have a receiver which holds two cubic feet
of this air.
If the contained air is now compressed to a volume of one cubic foot,
the temperature of two cubic feet is compressed into one cubic foot, and
there is now 140 degrees of heat within the receiver.
If this cubic foot of air is again compressed to half its volume, the
temperature is correspondingly increased. While this it not absolutely
true in practice, owing to the immense loss caused by radiation, still,
it will enable the mind to grasp the significance of compression, when
the subject of heat is concerned.
Elasticity of Gases.--The great elasticity of gases, and the perfected
mechanical devices for compressing the same, afford means whereby ten or
twenty atmospheres can be forced into a receiver, and thereby produce
pressures of several hundred pounds, which would mean sufficiently high
temperatures to ignite oils having the higher flash point.
Advantages of Compression.--The compression system permits of the
introduction of a larger quantity of fuel than is usually drawn into the
cylinder, and thereby a greater and more efficient action is produced on
the piston of the engine on account of quicker combustion and therefore
higher gas pressures.
The compression, however, rarely if ever exceeds six atmospheres or
about 90 pounds per square inch.
_The Necessity of Compression._--There are two reasons why compression
is necessary before igniting it. First, because it is essential to put
sufficient gas in the cylinder to make the engine efficient.
To illustrate: Suppose we have a cylinder capable of drawing in 150
cubic inches of gas, and this is compressed down to 25 cubic inches, the
space then occupied by the gas would represent what is called the
clearance space at the head of the cylinder. To compress it to a greater
degree the clearance space might be made smaller, which could be done in
several ways, but whether the gas thus drawn in should be compressed to
30, or 25, or even 10 cubic inches, it is obvious that there would be
no more fuel in the cylinder in one case than in the other. As however
the mean effective pressure, which determines the efficiency of the
motor, increases with the compression pressure, the latter should be as
high as possible, but not so high that premature explosion takes place
owing to the heat created by compression.
Second: The more perfect the mixture of the vaporized product with the
air, the more vigorous will be the explosion. The downward movement of
the piston draws in the charge of air and sprayed jet of gasoline, and
the only time for mixing it is during the period that it travels from
the carbureter through the pipes and manifold to the cylinder.
Having in mind the statement formerly made that compression causes a
more rapid movement of the molecules of a gas, it is obvious that the
upward movement of the piston, in the act of compressing the gas has a
more positive action in causing an intimate mixture of the hydro-carbon
gases than took place when the gases were traveling through the pipes on
their way to the cylinder.
CHAPTER V
THE INTERNAL COMBUSTION ENGINE
It will be observed that in a steam engine the heat is developed outside
of the cylinders and the latter used solely for the purpose of taking
the steam and utilizing it, by causing its expansion to push a piston to
and fro.
We shall now consider that type of motor which creates the heat within
the cylinder itself and causes an expansion which is at once used and
discharged at the reciprocating motion of the piston.
The original method of utilizing what is called _Internal combustion_
Motors, was to employ a fixed gas. A _fixed_ gas is one which will
remain permanently in that condition, unlike a vapor made from gasoline.
The difference may be explained as follows:
Fixed Gases.--If the vapor of gasoline, or petroleum, is subjected to a
high heat, upwards of 1500 degrees, it is so changed chemically, that it
will not again return to a liquid state. This is called _fixing_ it. Gas
is made in that way from the vapor of coal, and fixed, producing what
is called illuminating gas.
Although the temperature of fixing it is fully three times greater than
is required to explode it, the fact that it is heated in closed retorts,
and oxygen is prevented from mixing with it, prevents it from burning,
or exploding.
Gas Engines.--Such a gas has been used for many years in engines which
were usually of the horizontal type, and were made exceedingly heavy and
cumbrous, and provided with enormous fly wheels. Gases thus made are not
as rich as those generated direct from the hydro-carbon fuels, because,
being usually made from coal they did not have a large percentage of
hydrogen.
Energy of Carbon and Hydrogen.--When a pound of carbon is burned, it
develops 14,500 heat units, and a pound of hydrogen over 52,000 heat
units. Assuming that 85 per cent. of a pound of petroleum is carbon, and
15 per cent. is hydrogen, the heat units of the carbon would be 12,225,
and the heat units of the 15 per cent. of hydrogen would be 12,800. The
combined value is, therefore, 25,025, which is almost double that of
coal gas.
This fact makes the gasoline engine so much more efficient, and for the
same horse power the cylinders can be made smaller, and the whole
structure much lighter in every way.
Gasoline motors are of two types, one in which an explosion takes place
at every revolution of the crank, called the _two-cycle_, and the other
the _four-cycle_, in which the explosion occurs at every other turn of
the crank.
The terms _two-cycle_ is derived from the movement of the piston, as
that moves downwardly during the period when the crank is making a half
turn, and returns in its upward stroke when the crank completes the
turn, or that two half turns of the crankshaft complete the cycle.
Four-cycle engines have two such complete movements at each impulse, or
require four half turns of the crankshaft to complete the cycle.
The Two-Cycle Type.--In order to clearly distinguish between this and
the four-cycle, it would be well to examine the diagram, Fig. 23. For a
clearer understanding the drawing is explained in detail.
The cylinder A, within which the piston works, has a removable cap B,
and at its lower end a removable crank case C. The case is designed to
entirely close the lower end of the cylinder so that it is air tight,
for reasons which will be explained.
The outer jacket, or casing D, at the upper end of the cylinder, is
designed to provide a space E, for the circulation of water, to cool
the cylinder during its working period. The crankshaft F passes through
the crank case, the latter having suitable bearings G for taking care of
the wear.
[Illustration: _Fig. 23. Two-cycle. First Position._]
The piston H is connected up with the rod I, the latter being hinged at
a point within the piston, as shown. The crank case has an inlet port,
provided with a valve which opens inwardly, so that when the piston
moves upwardly the valve will open and air will be drawn into the crank
case and space below the piston.
At one side is a vertical duct K, which extends from a point directly
above the crank case, to such a position that when the piston is at its
lowest point gas can be discharged into the space above the piston.
On the opposite side of the cylinder, and a little above the inlet port
of the duct K, is a discharge port M. The inlet port and the discharge
port, thus described, are both above the lower end of the piston when it
is at its highest point.
The spark plug is shown at N. On the upper end of the piston, and close
to the side wall through which the inlet port K is formed, is an
upwardly-projecting deflecting plate O, the uses of which will be
explained in the description of its operation.
Fig. 23 shows the piston at its highest point, and we will now assume
that ignition takes place, thus driving the piston downwardly until the
upper end of the piston has fully uncovered the discharge port M, as
shown in Fig. 24. This permits the exhaust to commence, and as the
piston proceeds down still further, so as to uncover the inlet port K,
the gas, which at the down stroke has been compressed in the space below
the piston, rushes in, and as it strikes the deflecting plate O, is
caused to flow upwardly, and thus helps to drive out the burnt gases
remaining at the upper end of the cylinder.
[Illustration: Two-cycle Engine.
Fig. 24. Second position. Fig. 25. Third position.]
This action is called scavenging the cylinder, and the efficiency of
this type of engine is largely due to the manner in which this is done.
It is obvious that more or less of the unburnt gases will remain, or
that some of the unburnt carbureted air will pass out at each discharge,
and thus, in either case, detract from the power of the subsequent
explosion.
As the piston now moves upwardly to complete the cycle, the piston
closes both of the ports, thus confining the gas which was previously
partly compressed, and as the piston proceeds the gas is still further
compressed until the piston again reaches the upward limit of its
motion.
Advantages of the Two-Cycle Engine.--This kind of engine has several
distinct advantages. It has less weight than the four-cycle; it gives
double the number of impulses for a given number of revolutions of the
crankshaft; and it dispenses with valves, springs, cam-shafts, stems and
push rods.
More or less danger, however, attends the operation of a two-cycle
engine, principally from the fact that an explosive mixture in a
partially compressed condition is forced into the space which the
instant before was occupied by a flame, and it is only because the
expansion of the burst gases at the previous charge has its temperature
decreased so far below the explosion point, that the fresh gas is not
ignited, although there have been occasions when explosions have taken
place during the upstroke.
The Four-Cycle Engine.--The most approved type is that which is known as
the _four-cycle_. This will also be fully diagrammed so as to enable us
to point out the distinctive difference.
[Illustration: Four-cycle Engine.
Fig. 26. First position. Fig. 27. Second position.]
Figs. 26 and 27 show sections of a typical four-cycle engine, in which
the inlet and the exhaust valves are mechanically operated. The cylinder
A is either cast with or separate from the crank case B, and has a
removable head C. The upper end of the cylinder has a water space formed
by the jacket D.
The inlet port E and the discharge port F are both at the upper end of
the cylinder. The crank shaft G passes horizontally through the crank
case, and it is not necessary, as in the case of the two-cycle-engine,
to have the case closed tight.
The piston H is attached to the connecting rod I, which is coupled to
the crank, as shown. The crank shaft has a small gear J, which meshes
with two gears of double size on opposite sides of the crank shaft, one
of the gears K, being designed to carry the cam L for actuating the stem
L´, which opens the valve M in the port that admits the carbureted air.
[Illustration: Four-cycle Engine.
Fig. 28. Third position. Fig. 29. Fourth position.]
The other large gear N is mounted on a shaft which carries a cam O that
engages the lower end of a push rod P, to open the valve Q in the
discharge port F. It should be observed that the stems L´, P, are made
in two parts, with interposing springs R, so the valves may be firmly
seated when the stems drop from the cams.
The spark plug S is located in the head, close to the inlet port. The
character of the igniting system is immaterial, as the object of the
present diagrams is to show the cycle and method of operating the engine
at each explosion, and to fully illustrate the manner in which it is
distinguished from the two-cycle type.
A fly wheel is necessary in this as in the other type, and in practice
the two gear wheels, K, N, are placed outside of the case B, and only
the small gear, and the cam shafts, on which the cams are mounted, are
within the case.
The operation is as follows: In Fig. 26 the piston is shown in a
position about to commence its downward movement, and we will assume
that the ignition has just taken place. Both valves M, Q, are closed, as
it will be noticed that the cams L, O, are not in contact with the lower
ends of the push rods.
The explosion drives the piston down to the position shown in Fig. 27,
when the cam O begins to raise the stem P, and thus opens the discharge
valve Q, permitting the burnt gases to escape as the piston travels
upwardly to the position shown in Fig. 28.
At this position the valve Q closes, and the cam L opens the inlet
valve M, so that as the piston descends the second revolution, the
carbureted air is drawn in until the crank has just turned at its lowest
limit of movement, as shown in Fig. 29.
The upward stroke of the piston now performs the work of compressing the
carbureted air in the cylinder, and it is ready for the ignition the
moment it again reaches the position shown in Fig. 26.
The Four Cycles.--The four distinct operations thus performed are as
follows: First, the explosion, and downward movement of the piston.
Second, the upward movement of the piston, and the discharge of the
burnt gases. Third, the down stroke of the piston, and the indrawing of
a fresh charge of carbureted air. Fourth, the upward movement of the
piston, and the compression of the charge of carbureted air.
The order of the engine performance may be designated as follows: 1.
Impulse. 2. Exhaust. 3. Admission. 4. Compression.
Ignition Point.--While the point of ignition, shown in the foregoing
diagrams, represents them as taking place after the crank has passed the
dead center, the firing, in practice, is so adjusted that the spark
flashes before the crank turns past the dead center.
The reason for this will be apparent on a little reflection. As the
crank turns very rapidly the spark should be _advanced_, as it is
called, because it takes an interval of time for the spark to take
effect and start the explosion. If the sparking did not take place until
the crank had actually passed the dead center, the full effect of the
compression and subsequent explosion pressure would not be had.
Advantage of the Four-Cycle Type.--The most marked advantage in the
four-cycle type is its efficiency. As it has one full stroke within
which to exhaust the burnt gases, the cylinder is in a proper condition
to receive a full value of the incoming charge, and there is no
liability of any of the unburnt gases escaping during the exhaust from
the previous explosion.
The next important advantage of this type is in the fact that it can be
operated at a higher speed than the two-cycle type, and this is a great
advantage, notwithstanding the less number of impulses in the four-cycle
type.
The Loss in Power.--The great disadvantage in all engines of this class
is the great loss resulting from their action. The explosion which takes
place raises the temperature to fully 2000 degrees of heat, and unless
some provision is made to keep the cylinder down to a much lower
temperature the engine would soon be useless.
High temperatures of this character absolutely prevent lubrication, a
thing which is necessary to insure proper working. For this reason a
water jacket is provided, although there are engines which are cooled by
the action of air.
In any event, the heat imparted to the cylinder is carried away and
cannot be used effectively, so that fully one-half of the power is
dissipated in this direction alone.
The next most serious loss is in the escape of heat through the burnt
gases, which amounts to seventeen per cent. If the expansive force of
the burnt gases at the time of ignition is 250 pounds per square inch,
and at the time of the discharge it is fifty pounds, only four-fifths of
its power is effectively used.
As, however, the discharge is against the air pressure of nearly fifteen
pounds per square inch, it is obvious that thirty-five pounds per inch
is driven away and lost.
The third loss is by conduction and radiation, which amounts to fifteen
per cent. or more, so that the total loss from all sources is about
eighty-four per cent., leaving not more than sixteen per cent. of the
value of the fuel which is converted into power.
Engine Construction.--In the construction of engines the utmost care
should be exercised in making the various parts. The particular
features which require special care are the valves, which should be
ground to fit tightly, the proper fitting of the piston rings, crank
shaft and connecting rod bearings as well as the accurate relining of
these bearings.
[Illustration: Fig. 30. Valve Grinding.]
Valve Grinding.--Fig. 30 shows a valve and valve seat. The valve has
usually a cross groove so that a screw driver in a drill stock may be
used to turn it and to exert the proper pressure. The finest emery
powder and a first class quality of oil should be used. The valve is
seated and after the oil and emery powder are applied the drill stock
is used to turn the valve.
After twenty or thirty turns, wipe off the parts and examine the contact
edges, to see whether the entire surfaces are bright, which will
indicate that the valve fits true on its seat. Never overgrind. This is
entirely unnecessary. It is better also to rock the crank of the drill
stock back and forth, instead of turning it in one direction only.
The Crank Shaft.--The crank shaft is the most difficult part of the
engine to build. It is usually made of a single forging of special steel
and the cranks and bearings are turned out of this, requiring the utmost
care. Formerly these were subject to breakage, but improved methods have
eliminated all danger in this direction.
The Cams.--Notwithstanding the ends of the push rods are provided with
rollers to make the contact with the cams, the latter will wear, and in
doing so they will open the valves too late. The slightest wear will
make considerable difference in the inlet valve, and it requires care
and attention for this reason, in properly designing the cams, so that
wear will be brought to a minimum.
CHAPTER VI
CARBURETERS
A carbureter is a device which receives and mixes gasoline and air in
proper proportions, and in which a vapor is formed for gasoline engines.
The product of the carbureter is a mixture of gasoline vapor and air,
not a gas. A gas, as explained, is of such a character that it remains
fixed and will not stratify or condense.
Functions of a Carbureter.--The function of a carbureter is to supply
air and gasoline by means of its adjustable features so as to make the
best mixture. The proportions of air and gasoline will vary, but
generally the average is fifteen parts of air to one of gasoline vapor.
If there is too much gasoline, proportionately, a waste of fuel results,
as a great amount of soot is formed under those conditions. If there is
an excess of air the mixture, when ignited, will not have such a high
temperature, hence the expansive force is less, and the result is a
decrease of power.
While it is possible to get a rapid evaporation from gasoline by
heating it, experience has shown that it is more economical to keep the
gasoline cool, or at ordinary temperatures, provided the carbureter is
properly constructed, because the vapor, if heated, when drawn into the
engine, will be unduly expanded, and less fuel in that case is drawn in
at each charge, and less power results.
Rich Mixtures.--There are conditions under which rich mixtures are
advantageous. This is a mixture in which there is a larger percentage of
gasoline than is necessary for instantaneous combustion. For ordinary
uses such a mixture would not be economical.
At low speeds, however, or when carrying heavy loads, it is desirable,
for the reasons that at a slow speed the combustion is slower.
Rich mixtures are objectionable at high speeds because, as the
combustion is slow, incomplete combustion within the power stroke
results, the temperature of the gas at the end of the stroke is very
high, and this will seriously affect the exhaust valves. Furthermore,
there is likelihood of the gas continuing to burn after it is discharged
from the cylinder.
Lean Mixtures.--Such a mixture is one which has a less amount of
gasoline than is necessary to make a perfectly explosive compound. For
high speeds a lean mixture is desirable, principally because it burns
more rapidly than a rich mixture.
Types of Carbureters.--There are two distinct types of carbureters, one
which sprays the gasoline into a conduit through which air is passing,
and the other in which a large surface of gasoline is placed in the path
of the moving air column, which was originally used, but has been
absolutely replaced by the jet carbureters on account of their better
control features.
It will be remembered that reference was made to the manner in which
vaporization takes place, this term being used to designate that
tendency of all liquids to change into a gaseous state. All carbureters
are designed with the object of mechanically presenting the largest
possible area of oil to the air, so that the latter will become
impregnated with the vapor.
The Sprayer.--The best known type depends on dividing up the gasoline
into fine globules, by ejecting it from a small pipe or jet. The spray
thus formed is caught by the air column produced by the suction of the
engine pistons, and during its passage through the throttle and the
manifold, is in condition where a fair mixture of air and vapor is
formed, which will readily ignite.
The Surface Type.--This form of carbureter provides a pool of gasoline
with a large surface, within the shell, so arranged that as the air is
drawn past the pool it must come into contact with the oil, and thus
take up the necessary quantity of evaporated gasoline for charging the
air.
The _surface_ type has not been used to a large extent, but the
_sprayer_ is universally used, and of this kind there are many examples
of construction, each having some particular merit.
Governing a Carbureter.--It is a curious thing that one carbureter will
work admirably with one engine, and be entirely useless in another. This
is due to several factors, both in the engine design and in the
carbureter itself. The quality of mixture that an engine will take
depends on its speed. The suction of the pistons depends on the speed of
the engine.
If, at ordinary speed the carbureter gives a proper mixture, the throats
and passages through the pipes and manifold, as well as the valve which
discharges the gasoline, may be in a prime condition to do good work;
but when the pistons work at double speed the inrush of air may not
carry with it the proper amount of fuel; or, under those conditions, the
air may receive too great an amount of gasoline, proportionally.
The latter is usually the case, hence provision must be made for such a
contingency, and we shall therefore take up the various features
essential in the construction of the carbureter, so as to show what
steps have been taken to meet the problems arising from varying speeds,
differences in the character of the fuel, regulating the inflow and
mixture of gasoline and air, and adjustments.
[Illustration: _Fig. 31. Carbureter._]
So many different types of carbureters have been devised, that it is
difficult to select one which typifies all the best elements of
construction.
In Fig. 31 we have shown a well known construction, and which will
illustrate the features of the sprayer type to good advantage. The body
of the device, represented by A, has a flange by means of which it is
secured to the pipe which carries the carbureted air to the engine. The
lower end of this tubular body is contracted, as shown at B, so as to
form what is called a venturi tube.
Exteriorly this contracted tube is threaded, as shown at C, so as to
receive thereon a threaded body D, the lower end of the body having an
enlarged disk-head E, integral therewith, and an upwardly-projecting
annular flange F is formed around this disk to receive and hold a
cylinder G, which constitutes the float and fuel chamber.
The upper end of this cylinder rests against a seat cast with the body
A, and packing rings are placed at the ends of the cylinder to prevent
the oil from leaking out. Within the tubular body D is a vertical tube
H, integral with the disk head E, and oil is supplied to this tube
through ducts I, which communicate with the chamber within the reservoir
G.
A drain cock is at the lower end of this tube, and an adjustable cap K
screws on the tubular stem of the drain tube, around which air is
admitted, the air passing upwardly through vertical ducts L, as shown,
and thus mixes with air at the contracted part of the venturi tube.
A ring-like float N is placed within the glass chamber, and this is
adapted to engage with the inner end of a lever N´, this lever being
pivoted at O, within a side extension P of the carbureter shell. The
inner end of this lever has a link hinged thereto, the lower end of
which serves as a needle valve to close the ejecting orifice of the tube
L.
The outer end of the lever N´ engages a shoulder on a
vertically-disposed needle valve Q, which has its point in the inlet
opening of the pipe R, through which gasoline is supplied to the glass
chamber. A spring T serves to keep the valve stem normally on its seat.
Directly opposite this chambered extension P is another extension U,
also cast with the shell, through which is a vertical stem V. This stem
carries a downwardly-opening valve W, that seats against a plug, and a
spring X below the valve, serves to keep it against its seat, unless
there should be an extraordinarily heavy pull or suction.
This is the auxiliary air inlet, and the lower spring is actuated only
when the engine is running at moderate speeds, but when running at high
speed and an additional quantity of air is required the upper spring Y
is compressed, and thus a much greater quantity of air is allowed to
pass in and mingle with the spray at the throttle valve Z.
The throttle valve is mounted in the discharge opening, and is
controlled by a lever on the outside of the carbureter.
The device operates as follows: Primary air enters the opening between
the cup K and the disk-head E, passing up into the space around the oil
tube H. As the spring T, around the needle valve Q, draws up the valve
from its seat, oil is permitted to flow in through the duct R and fill
the chamber, until the float engages with the inner end of the lever N,
and raises it, thus uncovering the ejecting end of the tube H, and at
the same time closing the inlet tube R.
The suction from the engine then draws air through the primary duct, as
stated, and also an additional quantity through the secondary source, by
way of the valve W, this valve being so regulated as to supply the
requisite quantity.
The auxiliary air source serves the purpose that means should be
provided to supply more than the ordinary amount of air, when running at
high speeds.
From the foregoing it will be observed that a carbureter must be so
constructed that it will perform a variety of work. These are: First,
Automatic means for filling the float chamber when the gasoline goes
below a certain level. Second, Cutting off the supply of gasoline.
Third, Providing a primary supply of gasoline for spraying purposes.
Fourth, Furnishing an auxiliary air supply. Fifth, Throttling means in
the discharge opening.
It is thus a most wonderful contrivance, and considering that all the
elements necessary to make it work satisfactorily are provided with
adjustable devices, it may be seen that to make it perform correctly
requires a perfect understanding of its various features.
Requirements in a Carbureter.--In view of the foregoing it might be well
to know how to select a carbureter that is ideal in its operation.
First. The adjustment of the auxiliary valve should be of such a
character that at the slowest speed the valve should not be lifted from
its seat.
Second. It must be so arranged that it is not difficult to change the
relative amount of air and gasoline.
Third. The floating chamber should be so arranged that the float will
act on the lever which lifts the valve of the injecting pipe, even
though the carbureter body should be tilted at an angle. This is
particularly important when the carbureter is used in automobiles.
Fourth. The valves should be in such position that they are readily
accessible for cleaning or for examination.
Fifth. The float should be so arranged that it is adjustable with
reference to the lever that it contacts with.
Sixth. A gauze strainer should be placed at the gasoline inlet, and it
is also advisable to have a similar strainer above the mixing chamber,
beyond the throttle.
Seventh. There should be no pockets at any point in the body to hold the
gasoline which might condense.
Eighth. The body of the carbureter should be so constructed that every
part is easily accessible, and draining means provided so that every
particle of gasoline can be withdrawn.
Ninth. Means for heating it, in case of cold weather.
Size of the Carbureter.--The proper size of a carbureter for an engine
has been the subject of considerable discussion and experimenting. If
its passages are too large, difficulty will be experienced in starting
the engine, because the pulling draft through the primary will not be
sufficient to make a spray that will unite with the air.
A carbureter too large will only waste fuel, even after the engine has
been cranked up so it will start.
If the carbureter is too small the engine will not develop its required
output of power. While it might work satisfactorily at low speeds it
would be entirely inefficient at high speeds.
Rule for Size of Carbureter.--In all cases the valve opening and
cylinder capacity in the engine should determine this. The size of the
opening of the carbureter outlet should be the same as that of the
engine valve, which is also the case where the carbureter supplies a
multi-cylinder, as there is only one valve open at the same time.
It was formerly the custom to use a carbureter for each cylinder but the
practice has been abandoned, because it is obvious that a single
carbureter will, owing to the continuous suction, supply a mixture of
more nearly uniform character than two or more, even though they should
supply the mixture to a common manifold.
The Throttle.--Much of the economy in running an engine depends on the
manipulation of the throttle. As an example, with a certain motor and
carbureter it will be found that for maximum speed the throttle should
be open about one-eighth of the way. The proper way, in starting the
engine, is to open the throttle fully half way, and to retard the
spark. As soon as the engine begins to run properly, the spark is
advanced and the throttle closed down to the required point.
The engine speed may always be maintained by the throttle under a
constant varying load, by adjusting the throttle valve. A rich mixture
may be obtained by throttling the primary air supply.
The throttle may also be a most effective means of economizing fuel when
the engine has a first class sparking device, as in that case the
throttle can be closed down to provide a very small opening.
Flooding.--One of the most prevalent troubles in carbureters is the
liability to flood. This is usually caused by foreign matter getting
under or in the float valve, so that it will not properly seat.
Sometimes the mere moving of the float will dislodge the particle.
Another cause of flooding is due, frequently, to an improperly-arranged
float, which, when the engine is inclined, will prevent improper seating
of the valve, and flooding follows.
The greatest care should be exercised in seeing that the gasoline supply
is free from all impurities when it is poured into the tank. To strain
it is the best precaution, and it pays to be particular in this respect.
It is surprising to see the smallest speck, either stop the flow
entirely, or produce an overflow, either of which will cause a world of
trouble.
Water is another element which has no place in a carbureter. An
indication of this is the irregular movement of the engine. The only
remedy is to stop and drain the carbureter. A few drops may cause all
the trouble.
[Illustration: _Fig. 32. Carbureter._]
Types of Carbureters.--In Fig. 32 we show another type of carbureter,
which is simple in construction, and has many desirable features. The
cylindrical body of the carbureter, A, has a downwardly-projecting
globular extension B, at one side of which is a flange C to secure it to
the pipe, and through this is the discharge opening D. This globular
extension serves as the mixing chamber.
Within the cylindrical shell is an upwardly-projecting circularly-formed
extension E, and the top or cap F of the cylindrical body A has a
downwardly-projecting cylindrical rim G which overlaps the lower
circular extension E, and it is so constructed that a very thin annular
slit H is thus formed between the two parts, through which fuel oil
flows from the float chamber I into the space around the central tube J
which passes down through the two circular extensions E, G.
This central tube J is designed for the auxiliary air supply. It extends
down to the globular base B, and has a valve K seated against its end.
The stem L of the valve is vertically-movable within an adjustable stem
M, and a helical spring N, capable of having its tension adjusted by the
stem M, bears upwardly against the valve so as to keep it normally
against the lower end of the tube J.
The auxiliary air, therefore, passes down centrally through the tube J,
while the primary air supply passes through openings O, surrounding the
tube J, downwardly past the slitted opening H, and thence to the
discharge port D.
Surrounding the tubular projections E, G, and within the float chamber
I, is the float P. This is designed to strike the bifurcated ends of a
lever Q, which is hinged near its outer end, as at R, and has its short
projecting end resting beneath the collar of a vertical needle valve S.
This needle valve is vertically placed within a chambered extension T at
the side of the shell A, and its lower end rests within the opening of
the inlet U which supplies the gasoline to the chamber I. The upper end
of the valve stem passes through a plug V, through which is a vent hole
W.
A spring X is used between the plug and the collar on the lower end of
the needle valve, so that the valve is kept on its seat thereby, unless
the gasoline in the chamber should fall so low as to cause the float to
rest on the inner end of the lever Q, when the needle valve would be
unseated thereby.
All the parts of this device seem to be accessible, and it is presented
as an example of construction that seems to meet pretty nearly all of
the ideal requirements of a device for furnishing a perfect admixture.
Surface Carbureter.--This type of carbureter also requires a float but
does not have secondary air inlet mechanism. It has one striking
advantage over the sprayer system, in the particular that the suction
of the engine is not depended upon to draw the gasoline from the float
chamber. It is much more sensitive to adjustment in the float level and
needle valve than the other type.
[Illustration: _Fig. 33. Surface Carbureter._]
The diagram, Fig. 33, shows a body A, somewhat bowl-shaped, with a
chambered extension, B, at one side, at the lower side of which is the
fuel inlet duct C. Directly above this duct the upper wall of the
extension has a plug D, the lower end of which carries therein the upper
end of a vertically-movable needle valve, E, the lower end of the valve
resting within the duct C.
A float F within the bowl-shaped body is secured at one side to a lever
G, which is hinged at a point near the needle valve E, and the short end
of this lever connects with this needle valve in such a manner that as
the float moves upwardly the valve is seated, and when the level of the
fuel oil falls below a certain point the needle is lifted from its seat,
and oil is permitted to flow into the float chamber.
The cap H of the float chamber has cast therewith a U-shaped tube, the
inlet end I being horizontally-disposed, while the discharge end J is
vertical. Directly above the lowest part of the bend in this tube, the
vertical dimension of the tube is contracted by a downwardly-projecting
wall K, so as to form a narrow throat L.
Below this contracted point, the U-shaped tube has integral therewith a
downwardly-projecting stem M, the lower end of which passes through an
opening in the float chamber, and is threaded, so as to receive a nut,
by means of which the cap H may be firmly fixed to the float chamber.
This stem M has a vertical duct N, which communicates with the float
chamber, and is provided with a drain plug O. Alongside of this duct is
a tube P which extends up into the U-shaped tube and is open at its
lower end so that the level of the gasoline within the bent tube cannot
extend above the end of this drain tube P.
An adjustable valve stem Q passes through one side of the bent tube, the
lower end being pointed and adapted to regulate the inflow of gasoline
through the duct N, and into the U-shaped tube.
A throttle valve R is placed in the discharge end of the U-shaped tube,
which is susceptible of regulation by means of a lever S. The diagram
shows the gasoline within the U-shaped tube, so that it is on a level
with the gasoline in the float chamber.
In operation a sufficient amount of gasoline is permitted to enter the
float chamber so that a pool is formed in the bottom of the U-shaped
tube. When suction takes place the air rushes through the tube, at I,
down beneath the wall K, and in doing so it sweeps past the surface of
the pool at that point, absorbing a greater or less amount of the vapor.
In order to adjust the device so that a smaller amount of the liquid
fuel will be exposed, the carbureter is adjusted so it will close the
needle valve before the level of the liquid is so high, and thereby a
less surface of oil is formed within the U-shaped tube.
It is obvious that this type of carbureter, owing to the absence of the
secondary air-supply mechanism, can be readily regulated and all
adjustments made while running, while for automobile uses the lever S,
which controls the throttle, can be connected up with a dash-board
control.
CHAPTER VII
IGNITION. LOW TENSION SYSTEM
Electricity, that subtle force, which manifests itself in so many ways,
is nevertheless beyond the power of man to see. The only way in which we
know of its presence is by the results produced by its movements,
because it can make itself known to our senses only by some form of
motion.
The authorities regard light, heat and electricity as merely different
forms of motion. The most that can be done with such a force is to learn
the laws governing it.
Magnetism.--This is a form of electricity. In fact, it is one of the
most universal manifestations, for without it electricity would be
useless. When the first permanent magnet was found at Magnesia, it was
not considered electricity. The sciences had not arrived at that point
where they were able to classify it as belonging to lightning and other
manifestations of that kind which we now know to be electricity.
The Armature.--But magnetism can no more be seen than electricity
flowing through a wire. If a piece of metal has magnetism it will
attract a piece of iron or steel placed in close proximity, and thus we
are permitted to see the action.
The lightning in the upper atmosphere burns the gases in its path. This
enables us to see, not the current, but its action,--the result produced
by its power.
The electric current has many peculiar manifestations, the causes of
some of them being known and utilized. In the use of this medium for
igniting the fuel gas, many of the phases of electrical phenomena are
brought into play, and it is necessary, therefore, to know something of
the fundamentals of the science to enable us to apply it.
Characteristics of Electricity.--When a current passes along a wire, it
does not describe a straight path, but it moves around the conductor in
the form of circles. The current is not confined wholly to the wire
itself, but it extends out a certain distance from it at all points.
Magnetic Field.--Every part of a wire which is carrying a current of
electricity has, surrounding it, a magnetic field, of the same
character, and to all intents and purposes, of the same nature as the
magnetic field at the ends of a magnet.
Elasticity.--This current has also something akin to elasticity. That
is, it surges to and fro, particularly when a current is interrupted in
the circuit. At the instant of breaking a current in an electric light
circuit there is a momentary flash which is much brighter than the
normal light, which is due to the regular flow of the current.
This is due to the surging movement, or the elastic tension, in the
current. Advantage is taken of this characteristic, in making a spark.
This spark is produced at the instant that the ends of the wires are
separated.
The Make and Break System.--No spark is caused by putting the two ends
together, or by making the connection, but only by breaking it, hence it
is termed the _make_ and _break_ method of ignition.
When the connection is broken the current tries to leap across the gap,
and in doing so develops such an intense heat that the spark follows. As
a result of the high temperature it is necessary to use such a material
where the gap is formed that it will not be burned. For this purpose
platinum, and other metals are now employed.
Voltage.--This plays an important part in ignition. Voltage is that
quality which gives pressure or intensity to a current. It is the
driving force, just as a head of water gives pressure to a stream of
water.
High and Low Voltage.--A high tension current,--that is, one having a
high voltage, will leap across a gap, whereas a low voltage must have an
easy path. When the ends of a wire in a circuit are separated, air acts
as a perfect insulator between them, and the slightest separation will
prevent a low current from jumping across.
This is not the case with a high tension current, where it will leap
across and produce the flash known as the _jump spark_.
Low Tension System.--Two distinct types of ignition have grown out of
the voltage referred to, in which the _make_ and _break_ system uses the
low tension, because of its simplicity in the electrical equipment.
Disadvantages of the Make and Break.--There is one serious drawback to
the extended use of this system, and that is the necessity of using a
moving part within the cylinder, to make and break the contact in the
conductor, as it is obvious that this part of the mechanism must be
placed within the compressed mixture in order to ignite it.
Amperes.--A current is also measured by amperes,--that is, the quantity
flowing. A large conductor will take a greater quantity of current than
a small one, just as in the case of water a large pipe will convey a
greater amount of the liquid.
Resistance.--All conductors offer resistance to the flow of a current,
and this is measured in _Ohms_. The best conductor is silver and the
next best is copper, this latter material being used universally, owing
to its comparative cheapness.
Iron is a relatively poor conductor. Resistance can be overcome to a
certain extent, however, if a large conductor is used, but it is more
economical to use a small conductor which has small resistance, like
copper, than a heavy conductor, as iron, even though pound for pound the
latter may be cheaper.
Direct Current.--There are two kinds of current, one which flows in one
direction only, called the _Direct_. It is produced in a dynamo which
has a pair of commutator brushes so arranged that as the armature turns
and its wires move through the magnetic fields of a magnet, and have
direction of the current alternate, these brushes will change the
alternations so the current will travel over the working conductors in
one direction only.
Primary and secondary batteries produce a direct current. These will be
described in their appropriate places.
Alternating Current.--This is a natural current. All dynamos originally
make this kind of current, but the commutator and brushes in the direct
current machine change the output method only. The movement of this
current is likened to a rapid to and fro motion, first flowing, for an
instant, to one pole, and then back again, from which the term
_alternating_ is derived.
While the sudden breaking in a circuit will produce a spark with either
the direct or the alternating currents, the direct is usually employed
for the make and break system, since batteries are used as the
electrical source.
On the other hand the jump spark method employs the alternating current,
because the high tension can be most effectively produced through the
use of _induction coils_, which will be explained in connection with the
jump spark method of ignition.
Generating Electricity.--There are two ways to produce a current for
operating an ignition system, one by a primary battery, and the other by
means of a magneto, a special type of dynamo, which will be fully
explained in its proper place.
Primary Battery.--As we are now concerned with the make and break
system, the battery type of generation, and method of wiring up the
same, should first be explained.
Thus, in Fig. 34, a primary battery is shown, in which the zinc cell A
has an upwardly-projecting wing B at one side, to which the conductor is
attached; and within, centrally, is a carbon bar C. An electrolyte,
which may be either acid or alkali, must be placed within the cell.
[Illustration: _Fig. 34. Dry Cell._]
Making a Dry Cell.--The zinc is the negative, and the carbon the
positive electrode. The best material for the electrolyte is crushed
coke, which is carbon, and dioxide of manganese is used for this
purpose, and the interstices are filled with a solution of sal-ammoniac.
The top of the cell is covered with asphaltum, so as to retain the
moistened material and the liquid within the cell, and thus constituted,
it is called a _dry cell_.
Energy in a Cell.--A battery is made up of a number of these cells. Each
cell has a certain electric energy, usually from one and a half to one
and three-quarter volts, and from twenty-five to forty amperes.
The amperage of a cell depends on its size, or rather by the area of the
electrodes; but the voltage is a constant one, and is not increased by
the change, formation, or size of the electrodes.
For this reason the cells are used in groups, forming, as stated, a
battery, and to get efficient results, various methods of connecting
them up are employed.
[Illustration: _Fig. 35. Series Connection._]
Wiring Methods.--As at least six cells are required to operate a coil,
the following diagrams will show that number to illustrate the different
types of connections.
Series Connection.--The six cells, Fig. 35, show the carbon electrodes
A, of one cell, connected by means of a wire B with the zinc electrode
wing C of the next cell, and so on, the cell at one end having a
terminal wire D connected with the zinc, and the cell at the other end a
wire E connected with the carbon electrode.
The current, therefore, flows directly through the six cells, and the
pressure between the terminal wires D, E, is equal to the combined
pressure of the six cells, namely, 1-1/2 × 6, which is equal to 9 volts.
The amperage, however, is that of one cell, which, in these diagrams,
will be assumed to be 25.
[Illustration: _Fig. 36. Multiple, or Parallel Connection._]
Parallel Connection.--Now examine Fig. 36. In this case the carbon
electrodes A are all connected up in series, that is, one following the
other in a direct line, by wires B, and the zinc electrodes C, are, in
like manner, connected up in series with each other by wires D. The
difference in potential at these terminals B, D, is the same as that of
a single cell, namely, one and a half volt.
The amperage, on the other hand, is that of the six cells combined, or
150. This method of connecting the cells is also called _parallel_,
since the two wires forming the connections are parallel with each
other, and remembering this it may be better to so term it.
Multiple Connections.--This is also designated as _series multiple_
since the two sets of cells each have the connections made like the
series method, Fig. 35. The particular difference being, that the zinc
terminals of the two sets of cells are connected up with one terminal
wire A, and the carbon terminals of the two sets are joined to a
terminal B.
[Illustration: _Fig. 37. Series-Multiple Connection._]
The result of this form of connection is to increase the voltage equal
to that of one cell multiplied by the number of cells in one set, and
the amperage is determined by that of one cell multiplied by the two
sets.
Each set of cells in this arrangement is called a battery, and we will
designate them as No. 1, and No. 2. Each battery, therefore, being
connected in series, has a voltage equal to 4-1/2 volts, and the
amperage 50, since there are two batteries.
Now the different arrangement of volts and amperes does not mean that
the current strength is changed in the batteries or in the cells. If
the pressure is increased the flow is lessened. If the current flow, or
the quantity sent over the wires is increased, the voltage is
comparatively less.
Watts.--This brings in another element that should be understood. If the
current is multiplied by the amperes a factor is obtained, called
_Watts_. Thus, as each cell has 1-1/2 volts and 25 amperes, their
product is 37-1/2 watts.
To show that the same energy is present in each form of connection let
us compare the watts derived from each:
Series connection: 9 volts × 25 amperes, equal 225 watts.
Parallel connection: 1-1/2 volts × 150 amperes, equal 225 watts.
Series Multiple connection: 4-1/2 volts × 50 amperes, equal 225 watts.
From the foregoing, it will be seen that the changes in the wiring did
not affect the output, but it enables the user of the current to effect
such changes that he may, for instance, in case a battery should be
weak, or have but little voltage, so change connections as to
temporarily increase it, although in doing so it is at the expense of
the amperage, which is correspondingly decreased.
It would be well to study the foregoing comparative analysis of the
three forms of connections, so far as the energy is concerned, because
there is an impression that increasing the voltage, is adding to the
power of a current. It does nothing but increase the pressure. There is
not one particle of increase in the energy by so doing.
[Illustration: _Fig. 38. Circuit Testing._]
_Testing a Cell._--The cells should be frequently tested, to show what
loss there is in the amperage. This is done by putting an ammeter in the
circuit. If a meter of this kind is not handy, a good plan is to take
off one of the wire connections, and snap the wire on the terminal, and
the character of the spark will show what energy there is in the cell.
Testing With Instruments.--The method of testing with voltmeter and
ammeter, is shown in Fig. 38. The voltmeter is placed in a short circuit
between the two terminal wires, whereas the ammeter is placed in circuit
with one of the wires. The reason for this is that the voltmeter
registers the pressure, the power, or the difference of potential
between the two sides of the cell, and the ammeter shows the quantity of
current flowing over the wire.
In practice batteries are not used continuously for igniting. They are
temporarily employed, principally for starting, because their continued
use would quickly deplete them.
[Illustration: _Fig. 39. Make and Break, with Battery._]
Simple Battery Make and Break System.--In order to show this method in
its simplest form, examine Fig. 39, which diagrams the various parts
belonging to the system.
We have illustrated it with two cylinders, portions of the heads being
shown by the outlines A, A. B, B represent terminals which project into
the cylinders, and are insulated from the engine heads. Through the
sides of the engine heads are rock shafts C, the ends within the
cylinder having fingers D which are adapted to engage with the inner
ends of terminals B, B.
On the ends of the rock shafts outside of the cylinders, they are
provided with levers E, E, one end of each being attached to a spring F,
so that the tension of the spring will normally keep the upper end of
the finger D in contact with the terminal B. The cut shows one finger
engaging with B, and the other not in contact.
The other end of the lever E rests beneath a collar or shoulder G on a
vertical rod H. The lower end of this rod engages with a cam I on a
shaft J, and when the cam rotates the rod drops off the elevated part of
the cam, and in doing so the shoulder G strikes the end of the lever E
and causes the finger to rapidly break away from the terminal B, where
the spark is produced.
To Advance the Spark.--For the purpose of advancing or retarding the
spark, this rod has, near its lower end, a horizontally-movable bar K,
which may be moved to and fro a limited distance by a lever L, this
lever being the substitute in this sketch of the lever on the steering
wheel of an automobile.
The spark is advanced or retarded by causing the lower end of the rod H
to be moved to the left or to the right, so that it will drop off of
the raised portion of the cam earlier or later.
The wiring up is a very simple matter. The battery M has one end
connected up with one terminal of a switch N, while the other terminal
of the switch has a wire connection with the terminal plugs B, B, in the
cylinder heads.
The other end of the battery is connected with the metal of the engine,
which may be indicated by the dotted line O which runs to the rock shaft
C, and thus forms a complete circuit.
The operation is as follows: When the key P of the switch is moved over
so that it contacts with the terminal N, the battery is thrown into the
circuit, and the current then passes to the plug B of the first
cylinder, as the finger D in that cylinder is in contact with that
terminal, and it passes along the finger D, and rock-shaft C, to the
metal of the engine, and passes thence to the battery, this course being
indicated by the dotted line O.
At the same time, while cylinder No. 2 is also connected up with the
battery, the shoulder of the rod H has drawn the finger D from its
contact with the plug B, hence the current cannot pass in that
direction.
As the cam I, of cylinder No. 1, turns in the direction of the arrow,
the rod drops down and suddenly makes a break in the terminal of this
cylinder, causing the ignition, to be followed by a like action in No.
2.
The Magneto in the Circuit.--To insure the life of the battery, so that
it may be in service only during that period at the starting, when the
magneto is not active, the latter is so placed in the circuit, that, at
the starting, when, for instance, the automobile is being cranked, it is
cut out by the switch on the dash board.
[Illustration: Fig. 40. Make and Break, with Magneto.]
In Fig. 40, a simple two-pole switch is used. With the magneto it is
necessary to have a three-point switch, R, and a plain coil S is placed
between the switch and battery.
One side of the magneto T is connected by wire U with one of the points
of the switch R, and the other side of the magneto is connected with
the metal of the engine, which is indicated by the dotted line V.
In all other respects the mechanism is the same. The starting operation
has been explained with reference to the preceding figure, and when the
engine has picked up, and is properly started, the switch bar is thrown
over so it contacts with the point connected up with the wire U leading
to the magneto.
This, of course, cuts out the battery, and the engine is now running on
the magneto alone. The object of the coil S is to oppose a rapid change
of the current at the moment of the interruption. The coil induces a
counter current the moment the break is made, and as the current
continues to flow for a very short period after the break a spark of
greater intensity is produced than if the circuit should be permitted to
go from the battery to the sparker directly, as in the previous
illustration.
The best spark is produced by quickly making the break between the
points B, D, so that particular attention has been given to mechanism
which will do this effectively.
Magneto Spark Plug.--One of the devices to obviate the difficulty of
providing moving mechanism outside of the engine cylinder, is shown in
Fig. 41. In this the coil A is connected with a terminal B at the head
of the device and the other is connected to the plug C which screws into
the cylinder head.
[Illustration: _Fig. 41. Magneto Spark Plug._]
Within the core is a pivotally-mounted lever D, the upper end E of which
is attracted by the tubular metallic core F, and the lower end having a
contact point G, which is adapted to engage with a stationary point H.
The pivot I, on which the lever D is mounted, provides a means whereby
the lever swings, and a spring J is so arranged that when the lower end
of the lever is disengaged from the contact, the spring will return it
to its normal position.
In its operation when a contact is formed by the timing device of the
magneto, so as to give a spark, the circuit passes to the terminal B,
coil A, and plug C, thus forming a complete circuit. This energizes the
core A, pulling the upper end of the lever, and at the same time causes
the lower end to disengage the two contacts G, H, which breaks the
circuit and produces a spark.
The breaking of the circuit deënergizes the core, and the spring again
draws the lever back to its normal position, ready for the next
completion of the circuit by the timing device.
Such an arrangement is as simple as the spark plug usually employed in
the use of the high tension system, although it is more expensive than
the plug.
CHAPTER VIII
IGNITION. HIGH TENSION
This system is used to the largest extent, so that we ought to have a
full explanation of the devices which are required to do the work. While
magnetos are used with the low tension system, for the reasons stated,
they are especially necessary with the _Jump Spark_ method.
Magnetos.--The most important element in this system is the magneto, so
we shall try and make the subject as explicit as possible. As stated, a
magneto is a special type of dynamo which will now be explained. For
this purpose it will be necessary to show the elementary operation of an
alternating current dynamo.
Alternating Current.--In Fig. 42 A is a bar of soft iron, around which
is a coil of wire B, the wire being insulated, so that it will not touch
the bar. There is no magnetism in this bar, and this simple form of
structure is shown, merely to represent what is called the _field_ of a
dynamo.
The object of the coil of wire is to make a magnet of the bar, for the
moment a current is sent over the wire, a magnet is formed, and the
magnetism leaves the bar the moment the current ceases to flow. If this
bar should be of hard steel it would retain the magnetism.
[Illustration: _Fig. 42. Illustrating Alternating Current._]
[Illustration: _Fig. 43. Alternating Current. Second position._]
Now, the primary difference between the magneto and the dynamo, is that
this field bar is a permanent magnet in the magneto, whereas the field
is only a temporary magnet in the dynamo. This should always be kept in
mind.
The end of a magnet, whether it is a temporary one, or permanent, has a
magnetic field of force at the ends as well as at all parts of it,
exterior to the surface of the bar. Such a field is indicated, and in
the dynamo, no such field exists unless a current is passing over the
wire B, which is called the _field winding_.
The U-shaped piece of metal C represents the armature. It is shown
hinged to the top of two posts, for clearness in understanding, and is
adapted to turn to the right, and in turning the loop passes the end of
the field bar B, and passes through the magnetic field which is
indicated by the dotted lines D.
[Illustration: _Fig. 44. Alternating Current. Third position._]
Now, if the loop is simply permitted to remain in the position shown in
Fig. 42, a current would flow through the loop, this transference of the
current being called induction, and this characteristic of the flow of
electricity will be explained and its utility explained.
Cutting Lines of Force.--The loop will now be turned to the right so
that it passes the magnetic field and goes beyond it in its revolution.
This motion of passing the armature through the magnetic field is called
_cutting_ the _lines of force_. While the loop was lying within the
magnetic field, and also when it was moving through the field, the
current set up in the loop flowed in the direction of the darts F, or to
the right, through the pivots D.
In Fig. 43 the loop is shown as having made a quarter turn, and it is
now vertical, or at right angles to its former position. The loop in
thus passing away loses its force, until it reaches the position shown
in Fig. 44, when there is a surging back of the current to the opposite
direction, as indicated by the arrows.
[Illustration: _Fig. 45. Alternating Current. Fourth position._]
When the loop reaches the lowest position, shown in Fig. 45, it again
begins to get the influence of the magnetic field, and a reversal back
to its former direction takes place, this surging movement back and
forth being due to the reversal of the polarity in the coil brought
about by the position in which it is placed relative to the magnetic
field.
It is now an easy matter to connect the ends of the loop with wire
conductors. This is shown in Fig. 46, where a small metal wheel G is
placed on each end of the spindle, and in having a strip of metal
bearing H on the wheel. These are not commutator brushes, but are merely
wiping brushes to take the current from the turning parts. Wires I
connect with these wiping bars, and through them the current is
transmitted to perform the work.
[Illustration: _Fig. 46. Making the Circuit._]
Plurality of Loops.--The dynamo may have a plurality of loops, which are
called _coils_, and there may be a single magnet or any number of
magnets. Instead of driving these coils past the face of the magnet, or
magnets, the latter may be driven past the coils. In fact with most of
the alternating current machines the fields are the rotating parts and
the armatures, or the coils, are fixed.
The voltage is increased if the coils have a large number of turns on
the armature, and also if the armature, or the turning part, is speeded
up. Voltage will also be higher if larger or more powerful magnets are
used in the magnetos.
The Electro-Magnet.--The permanent magnet, such as is used in the
magneto, is distinguished by the fact that it contains a permanent
charge of magnetism, but this is not an _electro-magnet_. This is a
magnet made of soft iron, so it will be readily demagnetized. While not
shown in the diagrams, an iron core may be placed within the loop or
coil, and this is done in all dynamos, because the iron core acts as a
carrier of the magnetism, concentrating it at the center, because it is
a much better conductor than air.
[Illustration: _Fig. 47. The Dynamo._]
[Illustration: _Fig. 48. The Magneto._]
The Dynamo Form.--Consult the diagram, Fig. 47. The iron heads A
represent the bar in the previous diagrams, and B the wire around the
bar. C is the armature, which in this case represents a number of loops,
or coils, and D is the commutator, which is used in the direct current
machine to correct the alternations referred to in the previous
diagrams, so as to send the current in one direction only, the
commutator brushes E being used to carry off the current for use.
The Magneto Form.--The metal loop F, in Fig. 48, being a permanent
magnet, the armature, G, formed of a plurality of loops, has no field
wires to connect with it, as in the case of the dynamo.
Advantage of the Magneto.--The magneto has a pronounced advantage over
the dynamo, as a source of power for ignition purposes, in the
particular that the strength of the magnetic field is constant. In a
dynamo this varies with the output, because when used on an automobile
where the speed is irregular, the voltage will vary. The voltage of the
magneto is a constant one, and is thus better adapted to meet the needs
of ignition.
Induction Coil.--The induction coil is a device which is designed to
produce a very high voltage from a low tension, so that a current from
it will leap across a gap and make a hot spark.
We stated in a previous section that a current leaps across from one
conductor to another, so that electricity can be transferred from a
wire to another not touching it, by means of induction.
Look at Fig. 49, which represents two wires side by side. The current is
flowing over one wire A, and by bringing wire B close to A, but not
touching it, a current will be induced to leap across the gap and the
wire B will be charged. If the ends of the wire B are brought together,
so as to form a circuit, and a current detector is placed in the circuit
it will be found that a current is actually flowing through it, but it
is now moving in a direction opposite to the current flowing through A.
[Illustration: _Fig. 49. Current by Induction._]
Changing the Current.--But we have still another thing to learn. If the
two wires are not of the same thickness it would not prevent the current
from leaping across, but another astonishing thing would result.
First, we shall use a wire B double the thickness of wire A. If now, we
had an instrument to test the voltage and the amperage, it would be
found that the voltage in B is less than that in A, and also that the
amperage is greater.
Second, if the conditions are reversed, and the wire A is thicker than
B, the latter will have an increase of voltage, but a lower ampere flow
than in A.
Now this latter condition is just what is necessary to give a high
tension. Voltage is necessary to make a current leap across a gap. By
this simple illustration we have made an induction coil which may be
used for making a high tension jump spark.
Construction of a Coil.--Two wires side by side do not have the
appearance of a coil, and even though such an arrangement might make a
high tension current, it would be difficult to apply. To put the device
in such a shape that it can be utilized, a spool is made, as shown in
Fig. 50.
[Illustration: Fig. 50. Induction Coil.]
This spool A has a number of layers of thick, insulated wire B first
wound around it, the layers being well insulated from each other, and
the opposite ends brought out at one end or at the opposite ends, as
shown at C, D. On this is a layer of finer wire, also insulated, this
wire E having its terminals also brought out at the ends of the spool,
and after the whole is thus wound, the outside of the coil is covered
with a moisture proof material.
The Primary Coil.--The winding of thick wire is called the _primary_
coil. The current from the battery or the electric generator is led to
this inner coil.
[Illustration: _Fig. 51. Typical Induction Coil._]
The Secondary Coil.--The fine wire wrapping represents the secondary
coil, which is raised to a high voltage, and this actuates the sparking
mechanism.
In the art it is customary to illustrate the various contrivances by
certain conventional forms. Fig. 51 shows the manner of designating an
induction coil in a diagram, in which the heavy zig-zag line indicates
the primary, and the lighter zig-zag lines the secondary coil.
[Illustration: _Fig. 52. Contact Maker._]
Contact Maker.--A simple little device used in the primary circuit of an
induction coil, is known as a _contact maker_. This, as shown in Fig.
52, is merely a case A, through which is a shaft B that carries within
the shell a cam C. A spring finger D has its free end normally bearing
against the cam, and when the nose on the cam moves out the spring
finger, the latter is moved outwardly so it contacts with a plug E in
the side wall of the case, although it is insulated therefrom. This
contact establishes a current through the plug, spring finger and case.
The diagram, Fig. 53, illustrates the principles of construction and
arrangement of a high tension jump spark ignition, in which the
electrical source is a battery actuating an induction coil.
High Tension With Battery and Coil.--The battery A has one side
connected up by wire B with one terminal of the primary C in the
induction coil, and the other side of the battery has a wire D leading
to the contact maker. A switch E is placed in the line of this wire.
[Illustration: _Fig. 53. Typical Circuiting, Jump Spark Ignition._]
The other terminal of the primary has a wire F leading to the insulated
contact plug G of the contact maker. This completes the generating
circuit. The cam H is on a shaft I, which travels one half the speed of
the engine shaft.
One side of the secondary coil J has a wire K leading to the spark plug,
while the other terminal of the secondary has a wire L which is grounded
on the engine M.
When the nose of the cam pushes over the spring finger and closes the
cam, the circuit through the finger flows through the primary coil and
excites the secondary. When the cam again immediately breaks the circuit
a high tension current is momentarily induced in the secondary, so that
the current leaps the gap in the spark plug and makes the spark.
[Illustration: _Fig. 54. Metallic Core, Induction Coil._]
Metallic Core for Induction Coil.--In the previous description of the
induction coil it was stated that the spool might be made of wood. These
coils are also provided with metal cores, which can be used to make what
is called a vibratory coil.
The Condenser.--A necessary addition to the circuiting provided by an
induction coil, is a _condenser_. This is used in the primary circuit to
absorb the self-induced current of the primary and thus cause it to
oppose the rapid fall of the primary current.
The condenser is constructed of a number of tinfoil sheets, of suitable
size, each sheet having a wing at one end, and these sheets are laid on
top of each other, with the wings of the alternate sheets at opposite
ends. Very thin sheets of waxed paper are placed between the tin foil
sheets so that they are thus insulated from each other.
The wings at the ends are used to make connections for the conducting
wires. The device is not designed to conduct electricity, but to act as
a sort of absorbent, if it might so be termed. The large surface affords
a means where more or less of the current moves from the conductor at
one end to the conductor at the other end, and as it is designed to
absorb a portion of the current in the line it is merely bridged across
from one side of the circuit to the other.
[Illustration: _Fig. 55. Condenser._]
The diagram, Fig. 55, represents the conventional form of illustrating
it in sketching electrical devices.
Operation of a Vibrator Coil.--The illustration, Fig. 56, shows the
manner in which a vibrator coil is constructed and operated. The coil
comprises a metal core A, the primary winding B being connected at one
terminal, by a wire C, with a post D, and the other terminal by a wire E
with one side of a battery F. A switch G is in the line of this
conductor.
[Illustration: _Fig. 56. Vibrator Coil and Connections._]
The post D holds the end of a vibrating spring H, which has a hammer H´
on its free end, which is adapted to contact with the end of the metal
core A, but is normally held out of contact, so that it rests against
the end of an adjusting screw I which passes through a post J.
The post J is connected up with the battery by a wire K, and a wire L
also runs from the wire K to the conductor C, through a condenser M.
The secondary coil N, has the outlet wires O, P, which run to the spark
plug Q on the engine.
The operation is as follows: When the switch G closes the circuit, the
battery thus thrown in the primary coil magnetizes the core A, and the
hammer H´ is attracted to the end of the core, thus breaking the circuit
at the contact screw I. The result is that the core is immediately
demagnetized, and the spring H draws the hammer back to be again
attracted by the core which is again magnetized, so that the hammer on
the vibrator arm H goes back and forth with great rapidity.
From the foregoing explanations it will be understood how the primary
induces a high tension current in the secondary, and in order that the
spark may occur at the right time, a _timer_ for closing and opening the
primary circuit must be provided. By this means an induced high tension
current is caused to flow at the time the spark is needed in the cycle
of the engine operation.
_The Distributer._--The distributer is a timing device which controls
both the primary and the secondary currents, and it also has reference
to the revolving switch on the shaft of a magneto whereby the current is
distributed to the various cylinders in regular order.
Fig. 57 shows a form of distributer which will illustrate the
construction. A is the shaft which is driven at one half the engine
speed. It is usually run by suitable gearing direct from the shaft of
the magneto.
[Illustration: _Fig. 57. The Distributer._]
Its outer end rests in a bearing plate B, of insulating material, which
plate serves as the disk to hold the contact plates, 1, 2, 3, 4, to
correspond with the four cylinders to which the current is to be
distributed.
Wires 5, 6, 7, and 8, run to the respective spark plugs C from these
contact plates. The projecting end of the shaft A carries thereon a
contact finger D, which is designed to contact with the respective
plates, and an insulating ring E is interposed between the shaft and
finger so as to prevent short circuiting of the high tension current.
On the side of the finger is a hub F, integral therewith, and a wiper
attached to a post bears against the hub so as to form continuous
contact. A wire leads from the post to one terminal of the secondary
coil.
[Illustration: _Fig. 58. Circuiting with Distributer._]
Circuiting With Distributer.--The diagram Fig. 58 shows the complete
connections of a system which comprises a magneto, induction coil,
condenser, and a distributer. The magneto A has on its armature shaft B
two revolving disks C, D, one of which must be insulated from the shaft,
and one end of the coil E of the armature is connected with one of these
disks, and the other end of the coil is attached to the other disk.
Alongside of these disks is another disk F which has projecting points G
to engage with and make temporary contact with a spring finger which
actuates the interrupter I, this being a contact breaker which breaks
the primary current at the time a spark is required.
One terminal of this interrupter is connected by a wire J with one end
of the primary winding K, of the induction coil, and the other end of
the primary has a wire L which runs to the disk C.
The other terminal of the interrupter has a wire M leading to a
condenser N, and from the other side of the condenser is a wire O
leading to the wire J before described. The wiper of the other disk D
has a wire connection with the wire M.
The distributer shaft P is so mounted that it may receive its motion
from the shaft of the magneto, and for this purpose the latter shaft has
a gear Q one half the diameter of the gear R on the distributer shaft.
The distributer S has been described with sufficient clearness in a
preceding diagram, to show how the wires T lead therefrom and connect up
with the spark plugs U. One terminal of the secondary coil V is
connected by a wire W with the wiper X which contacts with the hub of
the distributer finger X´, and the other terminal of the primary is
grounded at Y, which represents the metal of the engine.
CHAPTER IX
MECHANICAL DEVICES UTILIZED IN POWER
One of the most important things in enginery is the capacity to
determine the power developed. Although the method of ascertaining this
appears to be somewhat complicated, it is really simple, and will be
comprehended the more readily if it is constantly borne in mind that a
certain weight must be lifted a definite distance within a particular
time.
The Unit of Time.--The unit of time is either the second, or the minute,
usually the latter, because it would be exceedingly difficult to make
the calculations, or rather to note the periods as short as a second,
and a very simple piece of mechanism to ascertain this, is to mount a
horizontal shaft A, Fig. 59, in bearings B, B, and affix a crank C at
one end.
It will be assumed that the shaft is in anti-friction bearings so that
for the present we shall not take into account any loss by way of
friction.
A cord, with one end attached to the shaft and the other fixed to a
weight D, the latter weighing, say 550 pounds, is adapted to be wound
on the shaft as it is turned by the crank.
Knowing the length of the cord and the time required to wind it up, it
will be an easy matter to figure out the power exerted to lift the
weight, which means, the power developed in doing it.
[Illustration: _Fig. 59. Illustrating the Unit of Time._]
Suppose the cord is 100 feet long, and it requires one and a half
minutes to raise the weight the full limit of the cord. It is thus
raising 550 pounds 100 feet in 45 seconds.
One horse power means that we must raise 550 pounds one foot in one
second of time, hence we have developed only 1/45th of one horse power.
Instead of using the crank, this shaft may be attached to the engine
shaft so it will turn slowly. Then add sufficient weight so that the
engine will just lift it, and wind the cord on the shaft.
You can then note the time, for, say, one minute, and when the weight is
lifted, make the following calculation: Weight lifted one hundred feet
in one minute of time was 825 pounds. Multiply 100 by 825, which equals
82,500. This represents _foot pounds_.
[Illustration: Fig. 60. The Proney Brake.]
As there are 33,000 foot pounds in a horse power, 82,500 divided by this
figure will show that 2-1/2 horse power were developed.
The Proney Brake.--Such a device is difficult to handle, but it is
illustrated merely to show the simplicity of the calculation. As a
substitute for this mechanism, a device, called the _Proney brake_ has
been devised, which can be used without rewinding of a cord. This is
accomplished by frictional means to indicate the power, and by the use
of weights to determine the lift.
The following is a brief description of its construction: The engine
shaft A, Fig. 60, which is giving out its power, and which we want to
test, has thereon a pulley B, which turns in the direction of the
arrow. Resting on the upper side of the pulley is a block C, which is
attached to a horizontal lever D by means of bolts E, these bolts
passing through the block C and lever D, and having their lower ends
attached to the terminals of a short sprocket chain F.
Block segments G are placed between the chain and pulley B, and when the
bolts E are tightened the pulley is held by frictional contact between
the block C and the segments G.
The free end of the lever has a limited vertical movement between the
stops H, and a swinging receptacle I, on this end of the lever, is
designed to receive weights J.
The first thing to do is to get the dimensions of the pulley, its speed,
and length of the lever. By measurement, the diameter of the pulley is
six inches. To get the circumference multiply this by 3.1416. The
distance around, therefore, is a little over 18.84 inches. The speed of
the pulley being 225 times per minute, this figure, multiplied by 18.84,
gives the perimeter of the pulley 4239 inches.
As we must have the figures in feet, dividing 4239 by 12, we have 353.25
feet.
The length of the lever from the center of the pulley to the suspension
point of the receptacle, is 4 feet, and this divided by the radius of
the pulley (which is 6 inches), gives the leverage. One half of six
inches, is three inches, or 1/4 of one foot, and 4 divided by this
number, is 1' 4", or 1-1/3 feet, which is the _leverage_.
Now, let us suppose the weight J is 1200 pounds. This must be multiplied
by the leverage, 1-1/3 feet, which equals 1800, and this must be
multiplied by the feet of travel in the pulley, namely, 353.25, which is
equal to 635,850. This represents _foot pounds_.
Now, following out the rule, as there are 33,000 foot pounds in a horse
power, the foregoing figure, 635,850, divided by 33,000, equals 19 horse
power within a fraction.
Reversing Mechanism.--A thorough knowledge of the principles underlying
the various mechanical devices, and their construction, is a part of the
education belonging to motors. One of the important structures, although
it is very simple, when understood, requires some study to fully master.
This has reference to reversing mechanism, which is, in substance a
controllable valve motion, whereby the direction of the valve is
regulated at will.
All motions of this character throw the valve to a neutral point which
is intermediate the two extremes, and the approach to the neutral means
a gradual decrease in the travel of the valve until the reciprocating
motion ceases entirely at the neutral position.
[Illustration: _Fig. 61. Double Eccentric Reversing Gear._]
[Illustration: _Fig. 62. Reversing Gear, Neutral._]
Double Eccentric Reversing Gear.--A well known form of gear is shown in
Fig. 61, in which the engine shaft A has two eccentrics B, C, the upper
eccentric B being connected with the upper end of a slotted segment D by
means of a stem E, and the other eccentric C is connected with the lower
end of the segment by the stem F. The eccentrics B, C, are mounted on
the shaft so they project in opposite directions.
The slotted segment carries therewith the pin G of a valve rod H, and
the upper end of the segment has an eye I, to which eye is a rod J
operated by a lever.
[Illustration: _Fig. 63. Reversing Gear, Reversed._]
[Illustration: _Fig. 64. Single Eccentric Reversing Gear._]
By this arrangement the link may be raised or lowered, and as the valve
rod pin has no vertical movement, either the connecting link E or F may
be brought into direct line with the valve rod H.
Fig. 61 shows the first position, in which the valve rod H is in direct
line with the upper connecting rod E, actuated by the cam B.
Fig. 62 shows the neutral position. Here the pin G serves as a fulcrum
for the rocking movement of the segment; whereas in Fig. 63 the valve
rod H is in line with the lower connecting rod F, so that the valve is
pushed to and fro by the eccentric C.
[Illustration: _Fig. 65. Balanced Slide Valve._]
It is more desirable, in many cases, to use a single eccentric on the
engine shaft, which can be done by pivoting the segment L, Fig. 64, to a
stationary support M, and connecting one end of the segment by a link N
with the single eccentric O.
In this construction the valve rod P is shifted vertically by a rod Q,
operated from the reversing lever, thus providing a changeable motion
through one eccentric.
Balanced Slide Valves.--In the chapter pertaining to the steam engine,
a simple form of slide valve was shown, and it was stated therein that
the pressure of the steam bearing on the valve would quickly grind it
down. To prevent this various types of balanced valves have been made, a
sample of which is shown in Fig. 64.
The valve chest A has in its bottom two ports C, D, leading to the
opposite ends of the cylinder, and within is the sliding valve E, which
moves beneath an adjustable plate F connected with the top or cover G of
the valve chest.
[Illustration: _Fig. 66. Valve Chest. Double Port Exhaust._]
This is also modified, as shown in Fig. 66, in which case the slide
valve H bears against the cover I at two points, so that as there is
steam on the upper surface to a slightly greater area than on the lower
side, there is sufficient downward pressure to hold it firmly on its
seat, and at the same time not cause any undue grinding. This valve also
has double exhaust ports J, J.
Balanced Throttle Valve.--Fig. 67 will give a fair idea of the
construction of throttle valves, the illustration showing its connection
with a simple type of governor.
[Illustration: _Fig. 67. Balanced Throttle-Valve._]
Engine Governors.--Probably the oldest and best known governor for
regulating the inlet of steam to an engine, is what is known as the Watt
design. This is shown in Fig. 68.
The pedestal A which supports the mechanism, has an upwardly-projecting
stem B, to the upper end of which is a collar C, to which the
oppositely-projecting pendent arms D are hinged. These arms carry balls
E at their free ends.
[Illustration: Fig. 68. Watt's Governor.]
The lower part of the stem has thereon a sliding collar F, and links G,
with their lower ends hinged to the collar, have their upper ends
attached to the swinging arms D. The collar has an annular groove at its
lower end, to receive therein the forked end of one limb of a bell-crank
lever H, the other limb of this lever being connected up with the engine
throttle, by means of a link L.
Centrifugal motion serves to throw out the balls, as indicated by the
dotted lines J, and this action raises the bell-crank lever, and opens
the throttle valve.
Numerous types of governors have been constructed, some of which operate
by gravity, in connection with centrifugal action. Some are made with
the balls adapted to swing downwardly, and thrown back by the action of
springs. Others have the balls sliding on horizontally-disposed arms,
and thrown back by the action of springs; and gyroscopic governors are
also made which are very effective.
[Illustration: _Fig. 69. The Original Injector._]
Fly wheel governors are not uncommon, which are placed directly on the
engine shaft, or placed within the fly wheel itself, the latter being a
well known form for engines which move slowly.
Injectors.--The Injector is one of the anomalies in mechanism. It
actually forces water into a boiler by the action of the steam itself,
against its own pressure. It is through the agency of condensation that
it is enabled to do this.
The illustration, Fig. 69, which represents the original type of the
device, comprises a shell A, within which is a pair of conically formed
tubes, B, C, in line with each other, the small ends of the tubes being
pointed towards each other, and slightly separated. The large end of the
conical tube C, which points toward the pipe D, which leads to the water
space of the boiler, has therein a check valve E.
The steam inlet pipe F, has a contracted nozzle G, to eject steam into
the large end of the conical tube B, and surrounding the nozzle F is a
chamber which has a pipe H leading out at one side, through which cold
water is drawn into the injector.
Surrounding the conical pipes B, C, is a chamber I, which has a
discharge pipe J. The action of the device is very simple. When steam is
permitted to flow into the conical tube B, from the nozzle G, it passes
out through the drain port J, and this produces a partial vacuum to form
in the space surrounding the nozzle G.
As a result water is drawn up through the pipe H, and meeting with the
steam condenses the latter, thereby causing a still greater vacuum, and
this vacuum finally becomes so great that, with the inrushing steam,
and the rapid movement through the conical tubes, past their separated
ends, a full discharge through the drain J is prevented.
[Illustration: Fig. 70. Injector with Movable Combining Tube.]
As it now has no other place to go the check valve E is unseated, and
the cold water is forced into the boiler through the pipe D, and this
action will continue as long as condensation takes place at the nozzle
G.
Many improvements have been made on the original form, mostly in the
direction of adjusting the steam nozzle, and to provide the proper
proportion of flow between the steam and water, as this must be adjusted
to a nicety to be most effective.
An example of a movable tube which closes the outlet to the overflow,
is shown in Fig. 70. The steam inlet tube A is at one end of the shell,
and the outlet tube B to the boiler, at the other end, and intermediate
the two is a tube C, with its open flaring end adapted to receive the
steam from the tube A. This tube is longitudinally-movable, so that the
controlling lever D may move it to and fro.
A chamber E surrounds the nozzle A, and has a water inlet pipe F, while
the space G between the ends of the pipes B, C, has an outlet H, a
single check valve I being interposed. In operation the tube C may be
adjusted the proper distance from the end of the pipe B, and when the
current is once established through the injector, the pipe C may be
brought into contact with B, and thus entirely cut out the movement of
the water to the overflow.
Feed Water Heater.--An apparatus of this kind is designed to take the
exhaust steam from the engine and condense it, and from the condenser it
is again returned to the boiler. The water thus used over again goes
into the boiler at a temperature of over 180 degrees, and thus utilizes
the heat that would otherwise be required to raise the temperature of
the water from the natural heat, say 70, up to that point.
In Fig. 71 the illustration shows a typical heater, which comprises an
outer shell A, each end having a double head, the inner head B being
designed to receive the ends of a plurality of horizontally disposed
pipes, and the outer heads C, separated from the inner head so as to
provide chambers, one end having one, and the other head being provided
with two horizontal partitions D, so the water may be diverted back and
forth through the three sets of pipes within the shell.
[Illustration: _Fig. 71. Feed Water Heater._]
The three sets of pipes, E, F, and G, are so arranged that they carry
the water back and forth from one head to the other, and for this
purpose the water for cooling the steam enters the port H at one end,
passes through the upper set of pipes E to the other end, then back
through the same set of pipes on the other side of a partition, not
shown, and back and forth through the two lower sets of pipes F, G.
The steam enters at the port I at the top of the shell, and passes down,
as it is condensed, being discharged at the outlet J.
CHAPTER X
VALVES AND VALVE FITTINGS
In the use of steam, compressed gas, or any medium which must have a
controllable flow, valves are a necessary element; and the important
point is to know what is best adapted for the use which is required in
each case.
For this reason one of the best guides is to fully understand the
construction of each. The following illustrations and descriptions will
give a good idea of the various types in use.
[Illustration: _Fig. 72. Check Valve._]
Check Valve.--Fig. 72 shows a longitudinal section of a check valve,
which is designed to prevent the water from returning or backing up
from the pressure side. The cylindrical body A is threaded at each end,
and has an inclined partition B therein which has a circular aperture.
[Illustration: _Fig. 73. Gate Valve._]
The upper side of the shell has an opening, adapted to be closed by a
cap C, large enough to insert the valve D, which is hinged to the upper
side of the partition. Water or gas is forced in through the valve in
the direction of the arrow, and the hinged valve is always in position
to close the opening in the partition.
In case the valve should leak it may be readily ground by taking the
small plug E from the opening, and with a screw driver, turning the
valve, and thereby fit it snugly on its seat.
[Illustration: _Fig. 74. Globe Valve._]
Gate Valve.--The cylindrical shell A has its ends internally threaded,
and is provided, midway between its ends, with a partition wall B,
having a central aperture. The upper side of the shell has an opening to
receive the bonnet C, through which the valve stem D passes. This stem
carries at its lower end a gate E which rests against the partition B.
The stem D is threaded to screw into the threaded bore of the gate. A
packing gland F surrounds the stem D. It will thus be seen that the
turning of the stem D draws the gate up or down, and thus effects an
opening, which provides a direct passage for the water through the valve
body.
Globe Valve.--A globe valve has the advantage that the valve is forced
against its seat by the pressure of the wheel, differing from the gate
valve, that depends on the pressure of the fluid to keep it tight.
The valve body A has therein a Z-shaped partition B, the intermediate,
horizontally-disposed limb of the partition being directly below the
opening through the body, which is designed to receive the bonnet C.
The bonnet has a central vertical bore, the lower end of which is
threaded to receive the wheel spindle. The lower end of the spindle
carries the circular valve, which is seated in the opening of the
Z-shaped partition.
The Corliss Valve.--The valve itself is of the rotary type, as shown in
Fig. 75, in which the port A goes to the cylinder, and B is the passage
for the steam from the boiler. The cylindrical valve body C has within
the aperture B a gate D, one edge of which rests against the abutment
through which the port A is formed, and this gate has within it the bar
E which is connected with the crank outside of the casing.
The Corliss Valve-Operating Mechanism.--As the operation of the valves
in the Corliss type of engine is so radically different from the
ordinary reciprocation engine, a side view of the valve grouping and its
connecting mechanism are shown in Fig. 76.
[Illustration: _Fig. 75. Corliss Valve._]
The cylinder has an inlet valve A at each end, and an outlet valve B at
each end for the discharge of the steam. C is a valve rod from the
eccentric which operates the valves, and D a wrist plate, having an
oscillatory or rocking motion around its center E. The attachments F F,
of the steam rods, open the inlet ports A A, and G G, are the
attachments of exhaust rods which open and close the exhaust valves B B.
H H are catches which can be unhooked from the stems of the valves A by
the governor rods J J.
The vertical links K, K are connected at their lower ends with the
pistons of dash pots, and have their upper ends attached to the valve
spindles, and act to close the valves A A when the catches H are
released by the governor rods J by means of the weights of the pistons
in the dash pots.
[Illustration: _Fig. 76. Corliss Valve-operating Mechanism._]
The dash pots L L act in such a manner as to cushion the descent of the
links K and thus prevent undue shock. M is a wrist plate pin by which
the valve rod C can be released from the wrist plate.
The whole purpose of the mechanism is to provide a means for closing the
valves which are at the steam inlet ports, by a sudden action. The
exhaust valves, on the other hand, are not so tripped but are connected
directly with the wrist plate which drives all four of the valves.
The wrist plate or spider has a rocking motion, being driven by an
eccentric rod from the engine-shaft. The mechanism thus described gives
a variable admission as the load varies, but a constant release of the
exhaust and a constant compression to act as a cushion.
[Illustration: _Fig. 77. Angle Valve._]
It gives a high initial pressure in the cylinder, and a sharp cut off,
hence it is found to be very efficient.
Angle Valve.--One of the most useful is the angle valve, which is
designed to take the place of an angle bend or knee in the line of the
piping. The mechanism is the same as in the well known globe valve
construction, the bonnet A being on a line with one of the right-angled
limbs of the body.
The pressure of the fluid should always be on the lower side of the
valve C, coming from the direction of the arrow B, for the reason that
should the steam pressure be constant on the other side, it would be
difficult to repack the gland D without cutting off the steam from the
pipe line.
[Illustration: _Fig. 78. Rotary Valve._]
[Illustration: _Fig. 79. Two-way Rotary._]
Referring back to the illustration of the globe valve, it will be
noticed that the same thing, so far as it pertains to the direction of
the steam, applies in that construction, and a common mistake is to
permit the pressure of the steam to be exerted so that it is constantly
acting against the packing of the spindle.
Rotary Valves.--Two forms of rotary valves are shown, one as illustrated
in Fig. 78, where the rotating part, or plug, A has one straight-way
opening B, which coincides with two oppositely-projecting ports C, D.
The other form, Fig. 79, has an L-shaped opening E through the rotating
plug F, and the casing, in which the plug is mounted has three ports,
one, G, being the inlet, and the other two H, I, at right angles for the
discharge of the fluid.
[Illustration: Fig. 80. Rotary Type.]
[Illustration: _Fig. 81. Two-way Rotary Type._]
Rotable Engine Valves.--So many different forms of the rotable valve
have been made, that it is impossible to give more than a type of each.
For engine purposes the plugs are usually rotated in unison with the
engine shaft, and a single delivery valve of this kind is shown in Fig.
80.
This has three ports in the casing, namely the inlet port A, and two
outlet ports C, D. The plug has a curved cut out channel E, and this
extends around the plug a distance equal to nearly one-half of the
circumference, so that the steam will be diverted into, say, B, for a
period equal to one-quarter turn of the plug, and then into port C, for
the same length of time.
Fig. 81 shows a valve which has a double action. The plug G has two
oppositely-disposed curved channels, H, I, and the casing has a single
inlet port J, and two oppositely-disposed outlet ports K, L.
[Illustration: _Fig. 82. Butterfly Throttle._]
[Illustration: _Fig. 83. Angle Throttle._]
When the plug turns the port L serves to convey the live steam to the
engine, while the other port K at the same time acts as the exhaust, and
this condition is alternately reversed so that L acts as the discharge
port.
Throttle Valves.--The throttle valves here illustrated are those used in
connection with gasoline engines. The best known is the _Butterfly_
valve, shown in Fig. 82, and this is also used as a damper, for
regulating the draft in furnaces and stoves.
This type is made in two forms, one in which the two wings of the valve
are made to swing up or down in unison, and the other, as illustrated,
where the disk A is in one piece, and turns with the spindle B to which
it is fixed.
[Illustration: _Fig. 84. Slide Throttle._]
[Illustration: _Fig. 85. Two-slide Throttle._]
In Fig. 83 the wing C is curved, so that by swinging it around the
circle, the opening of the discharge pipe D is opened or closed.
Another design of throttle is represented in Fig. 84. One side of the
pipe A has a lateral extension B, which is double, so as to receive
therein a sliding plate C, which is easily controllable from the
outside.
Fig. 85 shows a form of double sliding plate, where the double lateral
extensions project out in opposite directions, as at D, D, and within
these extensions are sliding plates which are secured together in such a
way that as one is pushed in the other also moves in, and thus acts in
unison to close or to open the space between them. It is the most
perfect form of throttle valve, as it causes the gases to open directly
into the center of the outgoing pipe.
Blow-off Valves.--The illustration shows a type of valve which is used
on steamboats and very largely on farm boilers throughout the country.
The pipe A from the boiler has cast therewith, or otherwise attached, a
collar B, which has a standard C projecting upwardly at one side, to the
upper end of which is hinged a horizontal lever D, which has a weight at
its other end.
[Illustration: _Fig. 86. Blow-off Valve._]
The upper end of the pipe has a conically-ground seat, to receive a
conical valve E, the stem of which is hinged, as at F, to the level. The
weight may be adjusted to the pressure desired before blowing out and
the only feature in this type of valve is the character of the valve
seat, which is liable, through rust, and other causes, to leak.
Pop, or Safety Valve.--As it has been found more desirable and practical
to use a form of valve which is not liable to deterioration, and also to
so arrange it that it may be manually opened, the _Safety Pop_ valve was
devised.
[Illustration: _Fig. 87. Safety Pop Valve._]
This is shown in Fig. 87, in which the valve seat base A, which is
attached to the top of the boiler, has a cup-shaped outlet B, that is
screwed to it, and this carries a lever C, by means of which the valve
may be manually opened.
A vertical shell D is attached to the cup-shaped portion, and this has a
removable cap E. The valve F is seated within a socket in the base, and
has a disk head, to receive the lower end of a coiled spring G.
The spring is supported in position by a stem H which extends down from
the head, and an adjusting nut I serves to regulate the pressure desired
before the steam in the boiler can act.
CHAPTER XI
CAMS AND ECCENTRICS
More or less confusion arises from the terms _cams_ and _eccentrics_. A
cam is a wheel which may be either regular in shape, like a
_heart-wheel_, or irregular, like a _wiper-wheel_.
The object in all forms of cams is to change motion from a regular into
an irregular, or reversely, and the motion may be accelerated or
retarded at certain points, or inverted into an intermittent or
reciprocating movement, dependent on the shape of the cam.
A cam may be in the shape of a slotted or grooved plate, like the needle
bar of a sewing machine, where a crank pin works in the slot, and this
transmits an irregular vertical movement to the needle.
A cam may have its edge provided with teeth, which engage with the teeth
of the engaging wheel, and thus impart, not only an irregular motion but
also a turning movement, such forms being largely used to give a quickly
rising or falling motion.
What are called _wiper-wheels_ are designed to give an abrupt motion and
such types are used in trip hammers, and to operate stamp mills. In
harvesters, printing presses, sewing machines, and mechanism of that
type, the cam is used in a variety of forms, some of them very ingenious
and complicated.
[Illustration: _Fig. 88. Heart-shaped._]
[Illustration: _Fig. 89. Elliptic._]
[Illustration: Fig. 90. Double Elliptic.]
Cams are also used for cutting machines, or in tracing apparatus where
it would be impossible to use ordinary mechanism. All such forms are
special, requiring care and study to make their movements co-relate with
the other parts of the mechanism that they are connected up with.
Simple Cams.--Fig. 88 shows a form of the most simple character, used,
with some modifications, to a larger extent than any other. It is called
the _heart-shaped_ cam, and is the regular type.
Fig. 89 is an elliptical cam, which is also regular. What is meant by
_regular_ is a form that is the same in each half portion of its
rotation.
Fig. 90 is a double elliptic, which gives a regular movement double the
number of times of that produced by the preceding figure, and the
differences between the measurements across the major and minor axes may
vary, relatively, to any extent.
[Illustration: _Fig. 91. Single Wiper._]
[Illustration: _Fig. 92. Double Wiper._]
[Illustration: _Fig. 93. Tilting Cam._]
Wiper Wheels.--Wiper wheels are cams which give a quick motion to
mechanism, the most common form being the single wiper, as shown in Fig.
91.
The double wiper cam, Fig. 92, has, in some mechanism, a pronounced
difference between the lengths of the two fingers which form the wipers.
The form of cam shown in Fig. 93 is one much used in iron works for
setting in motion the tilt hammer. Only three fingers are shown, and by
enlarging the cam at least a dozen of these projecting points may be
employed.
Cam Sectors.--Fig. 94 shows a type of cam which is designed for rock
shafts. The object of this form of cam is to impart a gradually
increasing motion to a shaft. Assuming that A is the driving shaft, and
B the driven shaft, the cam C, with its short end D, in contact with the
long end E of the sector F, causes the shaft B to travel at a more
accelerated speed as the other edges G, H, approach each other.
[Illustration: _Fig. 94. Cam Sector._]
[Illustration: _Fig. 95. Grooved Cam._]
[Illustration: _Fig. 96. Reciprocating Motion._]
Cylinder Cam.--Fig. 95 shows one form of cylinder A with a groove B in
it, which serves as a means for moving a bar C back and forth. The bar
has a projecting pin D, which travels in the groove.
This form of movement may be modified in many ways, as for instance in
Fig. 96, where the drum E has a sinuous groove F to reciprocate a bar G
to and fro, the groove being either regular, so as to give a continuous
back and forth movement of the bar; or adapted to give an irregular
motion to the bar.
[Illustration: _Fig. 97. Pivoted Follower for Cam._]
Double Cam Motion.--Cams may also be so arranged that a single one will
produce motions in different directions successively, as illustrated in
Fig. 97. The horizontal bar A, hinged at B to the upper end of a link C,
has its free end resting on the cam D.
The arm A has also a right-angled arm E extending downwardly, and is
kept in contact with the cam by means of a spring F. Connecting rods G,
H, may be hinged to the arm E and bar A, respectively, so as to give
motion to them in opposite directions as the cam revolves.
Eccentrics.--An eccentric is one in which the cam or wheel itself is
circular in form, but is mounted on a shaft out of its true center. An
eccentric may be a cam, but a cam is not always eccentric in its shape.
The term is one in direct contrast with the word _eccentric_.
[Illustration: _Fig. 98. Eccentric._]
[Illustration: _Fig. 99. Eccentric Cam._]
Fig. 98 shows the wheel, or the cam, which is regular in outline, that
is circular in form, but is mounted on the shaft out of its true center.
In this case it is properly called an eccentric cam but in enginery
parlance it is known as the eccentric, as represented in Fig. 99.
Triangularly-Formed Eccentric.--Fig. 100 illustrates a form of cam which
has been used on engines. The yoke A being integral with the bar B,
gives a reciprocating motion to the latter, and the triangular form of
the cam C, which is mounted on the shaft D, makes a stop motion at each
half-revolution, then produces a quick motion, and a slight stop only,
at the half turn, and the return is then as sudden as the motion in the
other direction.
[Illustration: Fig. 100. Triangularly-formed Eccentric.]
CHAPTER XII
GEARS AND GEARING
For the purpose of showing how motion may be converted from a straight
line or from a circular movement into any other form or direction, and
how such change may be varied in speed, or made regular or irregular,
the following examples are given, which may be an aid in determining
other mechanical devices which can be specially arranged to do
particular work.
While cams and eccentrics may be relied on to a certain extent, there
are numerous places where the motion must be made positive and
continued. This can be done only by using gearing in some form, or such
devices as require teeth to transmit the motion from one element to the
other.
The following illustrations do not by any means show all the forms which
have been constructed and used in different machines, but they have been
selected as types merely, in order to give the suggestions for other
forms.
Racks and Pinions.--The rack and pinion is the most universal piece of
mechanism for changing motion. Fig. 101 illustrates it in its most
simple form. When constructed in the manner shown in this figure it is
necessary that the shaft which carries the pinion shall have a rocking
motion, or the rack itself must reciprocate in order to impart a rocking
motion to the shaft.
[Illustration: Fig. 101. Rack and Pinion.]
[Illustration: Fig. 102. Rack Motion.]
This is the case also in the device shown in Fig. 102, where two rack
bars are employed. A study of the cams and eccentrics will show that the
transference of motion is limited, the distances being generally very
small; so that the rack and pinions add considerably to the scope of the
movement.
The Mangle Rack.--The device called the _mangle rack_ is resorted to
where a back and forth, or a reciprocating movement is to be imparted
to an element by a continuous rotary motion.
[Illustration: Fig. 103. Plain Mangle Rack.]
[Illustration: Fig. 104. Mangle Rack Motion.]
[Illustration: Fig. 105. Alternate Circular Motion.]
The plain mangle racks are shown in Figs. 103 and 104, the former of
which has teeth on the inside of the opposite parallel limbs, and the
latter, Fig. 104, having teeth not only on the parallel sides, but also
around the circular parts at the ends.
This form of rack may be modified so that an alternate circular motion
will be produced during the movement of the rack in either direction.
Fig. 105 is such an instance. A pinion within such a rack will turn
first in one direction, and then in the next in the other direction, and
so on.
If the rack is drawn back and forth the motion imparted to the pinion
will be such as to give a continuous rocking motion to the pinion.
Controlling the Pinion.--Many devices have been resorted to for the
purpose of keeping the pinion in engagement with the teeth of the mangle
rack. One such method is shown in Fig. 106.
[Illustration: Fig. 106. Controlling Pinion for Mangle Rack.]
The rack A has at one side a plate B, within which is a groove C, to
receive the end of the shaft D, which carries the pinion E. As the
mangle rack moves to such a position that it reaches the end of the
teeth F on one limb, the groove C diverts the pinion over to the other
set of teeth G.
All these mangle forms are substitutes for cranks, with the advantage
that the mangle gives a uniform motion to a bar, whereas the to and fro
motion of the crank is not the same at all points of its travel.
Examine the diagram, Fig. 107, and note the movement of the pin A which
moves along the path B. The crank C in its turning movement around the
circle D, moves the pin A into the different positions 1, 2, 3, etc.,
which correspond with the positions on the circle D.
[Illustration: Fig. 107. Illustrating Crank-pin Movement.]
The Dead Centers.--There is also another advantage which the rack
possesses. Where reciprocating motion is converted into circular motion,
as in the case of the ordinary steam engine, there are two points in the
travel of a crank where the thrust of the piston is not effective, and
that is at what is called the _dead centers_.
In the diagram, Fig. 108, the ineffectiveness of the thrust is shown at
those points.
Let A represent the piston pushing in the direction of the arrow B
against the crank C. When in this position the thrust is the most
effective, and through the arc running from D to E, and from H to G,
the cylinder does fully four-fifths of the work of the engine.
[Illustration: _Fig. 108. The Dead Center._]
While the crank is turning from G to D, or from I to J, and from K to L,
no work is done which is of any value as power.
If, therefore, a mangle bar should be used instead of the crank it would
add greatly to the effectiveness of the steam used in the cylinder.
[Illustration: _Fig. 109. Crank Motion Substitute._]
Crank Motion Substitute.--In Fig. 109 the pinion A is mounted so that
its shaft is in a vertical slot B in a frame C. The mangle rack D, in
this case, has teeth on its outer edge, and is made in an elongated
form. The pinion shaft moves up and down the slot and thus guides the
pinion around the ends of the rack.
[Illustration: Fig. 110. Mangle Wheel.]
Mangle Wheels.--The form which is the most universal in its application
is what is called the _mangle wheel_. In Fig. 110 is shown a type
wherein the motion in both directions is uniform.
Mangle wheels take their names from the ironing machines called
_mangles_. In apparatus of this kind the movement back and forth is a
slow one, and the particular form of wheels was made in order to
facilitate the operation of such machines. In some mangles the work
between the rollers is uniform back and forth. In others the work is
done in one direction only, requiring a quick return.
In still other machines arrangements are made to provide for short
strokes, and for different speeds in the opposite directions, under
certain conditions, so that this requirement has called forth the
production of many forms of wheels, some of them very ingenious.
[Illustration: _Fig. 111. Quick Return Motion._]
The figure referred to has a wheel A, on one side of which is a
peculiarly-formed continuous slot B, somewhat heart-shaped in general
outline, one portion of the slot being concentric with the shaft C.
Within the convolutions of the groove is a set of teeth D, concentric
with the shaft C. The pinion E, which meshes with the teeth D, has the
end of its shaft F resting in the groove B, and it is also guided within
a vertical slotted bar G.
The pinion E, therefore, travels over the same teeth in both directions,
and gives a regular to and
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