Every Boy’s
Mechanical
Library

AUTOMOBILES

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 enginry. 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

Every Boy’s Mechanical Library

AUTOMOBILES

BY
J. S. ZERBE, M.E.
Author of
Motors—Aeroplanes

ILLUSTRATED

NEW YORK
CUPPLES & LEON COMPANY

Copyright, 1915, by
CUPPLES & LEON COMPANY

CONTENTS

LIST OF ILLUSTRATIONS

INTRODUCTORY

The building and development of auto vehicles form one of the most remarkable pages in the history of manufactures. The subject nearest the boy is the motorcycle, which is a direct development of the bicycle. From this to the larger power vehicles is but another step, so that in setting forth the structures involved the aim should be to show how one form of device grew out of the preceding one, and how each structure following in the train, became desirable and necessary.

It would be impossible in a limited work of this kind to show the various modifications of all the elements which make up a complete structure.

When these vehicles were first brought out, the mechanism was exceedingly simple, being, in reality, nothing more than the hitching up of some form of motive power with running gears.

But now all that is changed. The old type steering mechanism was imperfect; the attachment of the wheels to the axles had to be modified; the wheels themselves entirely revolutionized; speed changing and reversing especially adapted for quick and positive work; and even the easy starting of the motor had to be provided for.

The entire equipment required a multiplicity of new devices, such as signaling apparatus, lighting systems, safety appliances, means to prevent skidding, wind shields, a reorganization of body and seating arrangement, and a reconstruction of the springs and their attachment to the chassis.

The electrical part has made as rapid strides, and in the development the sparking mechanism has approached perfection, and brought into existence a wonderful variety of systems, so that each cycle of improvements has made them more efficient, but simpler to construct, understand and use.

It is a rare thing to-day to see any of the power machines dragged home by horse power. Not many years ago this was a common sight. The size, shape, and materials used, have been understood by scientific analysis and study, so that breakage, under ordinary uses, is not at all a common thing.

It is the aim of this book to show in as simple a manner as possible how this wonderful transformation has been brought about, and to furnish one or more types of each element, properly constructed and arranged, so that the boy may understand how each part is built, and the particular reasons for the structures.

In no branch of manufactures can be found such a variety of technical designations as have grown out of this industry. By virtue of necessity, many of these names have been coined to suit the conditions. This knowledge is imparted in these pages, which contains a complete glossary of every term used in the art.

The Author.

AUTOMOBILES

CHAPTER I
AUTOMOBILE HISTORY AND DEVELOPMENT

It is generally believed that automobiles originated within the present century, this idea having gained currency because, until within the past twenty years, no practical machines were put on the market.

Development of the Industry.—The development of the industry has been a peculiar one, in some respects. As early as the year 1275, Roger Bacon speculated on the possibilities of using steam, or some other form of motive power on wagons, for propelling them.

This is remarkable, when it is understood that the steam engine, as constructed by Watt, was not invented until about 1780. Prior to Watt, steam engines were in operation, the valves of which were manually operated. Watt’s energies were directed to making the valves work automatically, and in economizing the use of steam.

The First Patent.—In 1619, two Englishmen, Ramsey and Wildgoose, secured a patent for “drawing carts without horses,” and even before that time inventors in Germany had made vehicles which were propelled by powerful springs. In the Netherlands devices were constructed to move wagons by means of the wind.

Newton’s Car.—In 1700 Sir Isaac Newton invented a steam car, in which he used Hero’s steam engine, and N. J. Cuguet, a Frenchman, invented a steam car which had some remarkable properties.

Watt’s Invention.—Later Watt invented, and was granted a patent, in 1784, for a steam vehicle, and twelve years thereafter, the first American patent was issued to W. Read, of Massachusetts, for a steam-driven automobile.

These were followed by Symington, about the same time, together with Trevithick, in 1802, Evans in 1805, and Griffith in 1821. While numerous others contributed to the art, the foregoing were the pioneers.

Evans has the distinction of being the first to build a combined boat and wagon; and Griffith was the originator of the body type which had cabins or apartments for the use of travelers.

Traction.—Steam engines were in a fairly perfected condition two hundred years ago, and it has been considered remarkable that for over one hundred and fifty years no practical road device was brought out.

The reason for this was not due to engine faults, but attributable to other things which were not understood at the time. One of these was the question of traction.

Push Legs.—It was believed in the early history of the art, that some other means should be adopted for applying the power, rather than to exert it on the wheels; but as late as 1824 Gordon secured a patent for an improved form of “push legs,” which stepped along and thus propelled the vehicle. This form of propulsion has been revived, in a measure, by the so-called “caterpillar tractors,” in which the wheels are provided with feet, which step along, and are thus specially adapted for heavy trucks on soft roads or on cross country travel.

Power.—One other difficulty was in the construction of the boiler. What is now understood as the water tube boiler was then unknown, hence they were made in such a manner that a large body of water had to be carried in the boiler, and this meant great weight to be transported.

Springs.—Prior to the attempted introduction of steam, vehicles had springs, and the great problem then appeared to find a type of vehicle which would permit the transfer of the power from the engine to the wheels, since the springs change the relative positions of the engine and axle.

Water Tube Boiler.—From 1820 to 1840 was the great period of boiler development. The water tube type provided a means whereby considerably less than one-half of the water was required in the boiler itself; and in 1832 a motor drawn vehicle, having springs arranged for carrying the entire load, was devised by Dr. Church, of Birmingham, England.

The First Differential.—Hills, in 1840, made the first differential. Before that time the power was applied to a single wheel, but in that year Dietz invented a form of rubber tire. This, and the differential, made wheels the tractors for all time.

But now a new era was ushered in. It was not a period of active work in the development of motor-driven wagons, but the possibilities of using other than steam-driven vehicles was felt.

The First Gas Motor Car.—In France, Lenoir was the first to devise a gas motor car. Compressed gas was used; and Ravel, in 1870, also produced a gas-driven machine. As early as 1862 Gardner used a gas motor fed with carbureted air instead of gas, but the weight of the engine was against all attempts in that direction.

Gasoline Car.—Markus, of Vienna, built a gasoline car in 1877, and this was followed by Levassor, the engineer of Panhard and Levassor, in France, who used Daimler’s invention in the development of their car. Gottlieb Daimler, the father of the automobile industry, produced the first practical gasoline motor, his invention being based on the four-cycle type of engine.

The invention of the gasoline, or the Internal Combustion Engine as it is called, was the first great advance. The weight of the fuel was so small, compared with the power produced, that it revolutionized the art.

And now began that series of developments which embraced every part of the vehicle from the wheels to the top. At first the improvements were slowly effected, and many of them were most unsatisfactory.

Flash Boiler System.—The flash system of using water in boilers, invented by Serpollet in France, for a long time kept even pace with gasoline cars, in economy, and in ease of management; but now that system has been entirely driven out, and gasoline taken its place. This, in time, must make way for a still cheaper fuel, and one more easily handled, either through the crude oil itself, or from some cheap derivative of it; or, possibly, a spirit distillation, in the form of alcohol, which will take the place of the high-priced article now so universally used.

The natural consequence of improvements has been to bring forth a multiplicity of devices, particularly in the direction of more readily assimulating and using the hydro-carbon fuels. The efforts of inventors will now be in the direction of eliminating many of them.

The Carbureter.—Heretofore the carbureter has been regarded as an essential element in every system. What a world, or, rather, worlds of troubles, hung about the carbureter. It was, and is, delicate, susceptible of the most minute adjustment, and in times past, before it had reached the present perfected form, was the bane of every motorist.

A fuel, ignitable at a very low temperature, or capable of ready volatilization, has been considered absolutely necessary to successful operation. Such is not the case now.

Improved Structure.—The delicate parts of the operative mechanism are being replaced by strong, non-breakable forms, all of which tend to make a more perfect machine, and this, in turn, insures a greater demand for vehicles.

The Order of Development.—In undertaking any work requiring mechanical skill, and in which the action of coöperative elements is necessary, the uses must be considered. In a vehicle, the first element is the weight to be carried; then the strength of the frame and wheels necessary to maintain the load.

Next should follow, in order, the power needed, and this entails a consideration of the speed element. These features are comparatively simple with a motorcycle; but they are more complex with the automobile type, particularly as to the structure of the frame and the gearing and wheels which are to be operated by the motor.

Speed vs. Power.—Thus, a motor exerting twenty horse power may run the vehicle at a maximum of twenty miles an hour, and carry a load of fifteen hundred pounds; or it may have a maximum speed of eight miles an hour, and carry three thousand pounds with equal safety. It will thus be seen that speed is just as important as power, in considering utility.

Lighter Vehicles.—The tendency of the day is toward lighter vehicles, brought about, in a large measure, by improved materials in every direction. It is no longer urged that heavy, ponderous machines are required to furnish stable and durable vehicles.

Nothing can stop or retard this great industry. It is attractive to men and fascinating to boys. To acquire a knowledge of its “mysteries,” should be a part of the education of every young man.

CHAPTER II
THE FRAME, AND ITS ACCESSORIES

Under this title should be included the frame, axles, springs, wheels, steering gear and brakes.

From the beginning it was recognized that the different strains and stresses set up by the passing of the wheels over uneven ground and by the motor and driving mechanism, must be taken care of before reaching the body of the automobile, which otherwise would soon go to pieces.

Fig. 1. Views of Plain Frame.

The Frame.—Therefore, not only springs had to be interposed between the body and the wheel axles, but also a substructure for the body, called the frame, which must be rigid enough to prevent any destructive strains from reaching the body.

In Fig. 1, A shows a top view of a frame made up of channel bars and B shows a side view to illustrate how the torsion or twist takes place. It will be understood that the frame thus made is not designed to lend itself to the entire inequalities of the road, as the springs are interposed for that purpose.

Experience in the construction and use of tubular frames, as first employed in bicycles, proved too expensive for assembling, when used in automobiles. The tubular form of construction was very soon displaced by frames consisting of metal parts bolted or riveted together. The main or side members are now usually made of channel steel which gives great rigidity and strength, compared with its weight.

Fig. 2. Quarter Elliptic.

How the Frame is Suspended.—The important feature is to mount this frame on the axle. The frame, carrying a body and all the load of the vehicle, has to permit three distinct movements.

First. That due to the inequalities of the road, which produces a torsional twist.

Second. A lateral swing, caused by traveling alongside a hill, or due to centrifugal force when making a turn rapidly.

Third. A fore and aft movement, as when traveling over undulating surfaces, or in suddenly stopping and starting.

Fig. 2^a. Half Elliptic.

For these reasons springs must be made to compensate for such motions, and to absorb the jar as much as possible.

Fig. 3. Three-quarter Elliptic.

The Springs.—Many forms of spring mountings have been devised, but the following illustrations show the types which set forth the principles involved. Outside of coiled springs which are used in some forms of delivery cars, the standard springs are leaf springs, built up from a number of steel leaves.

There are four distinct forms of springs used, as follows:

1. The quarter elliptic, used on Ford, and similar cars, as illustrated in Fig. 2.

2. The half elliptic, Fig. 2a, which is the most widely-used form. These springs are usually attached with their front end directly to the frame, and with the rear end by means of a shackle; the center is fastened by spring clips to the axle.

Fig. 4. Full Elliptic.

Where a distance rod is used, as on the rear axle, both ends are attached by shackles.

3. The three quarter elliptic, Fig. 3, always used as a suspension for the rear axle. This form gives more flexibility than a half elliptic, and is still stiffer so far as side motion is concerned, than the following type.

4. The full elliptic, Fig. 4, was formerly used much more than at the present time.

There are also in use springs comprising a combination of half elliptic, or three quarter elliptic, on each axle, in which the front end is shackled to the frame, and the rear ends connected by shackles to another half elliptic spring, the center of which is fastened to the frame.

Fig. 4^a. Cantilever Spring.

Fore and Aft Motion. Provision must be made, in all cases, for the fore and aft movement of the car body which takes place in stopping or starting, and, particularly when the wheels strike an obstruction.

Fig. 5. Fore and Aft Motion.

Flues. Fig. 5 shows a side view of a car, in which the dotted lines indicate the position of the body, relative to the normal, when the wheels strike an obstacle.

Lateral Motion. In like manner when the car swings around a corner, or is traveling along a hill-side, the springs must hold the body from swinging too far. Fig. 6 illustrates, by means of the dotted lines, the side movement. It is obvious, therefore, that the springs have a duty to perform in addition to that of merely giving flexibility to the body.

Fig. 6. Lateral Motion.

Cantilever Spring.—A special form of half elliptic springs, lately developed, and of increasing use, is the cantilever spring, where the axle is attached to one end, the center of the spring being pivoted to the frame, and the other end shackled to or sliding in the frame.

Shock Absorbers.—Shock absorbers are mechanical means placed between the frame and the axles for the purpose of dampening the sudden recoil of the springs after being compressed, when meeting a road obstacle. In the absence of such a device the recoil is likely to suddenly throw up the frame, body and passengers, or produce an unpleasant shock.

Originally, simple leather straps were used, reaching from the body to the axle, which only limited, but did not dampen or gradually absorb the shock. Now different forms of frictional resisting toggle-levers are used, which not only absorb the shocks, but also prevent the bumping of the axle against the frame, and eliminate breaking of springs.

The Axle.—Axles are of two kinds, generally designated as “live,” when they turn the wheels; and “dead” when they do not turn the wheels, but simply support the weight of the frame and of the body.

Dead axles are used with double chain drive, as, in that case, the sprocket wheels are attached directly to the sides of the wheels and the wheels turn on the studs, or ends of the dead axle.

Live Axles.—1. Plain live axles originally consisted of a shaft without differential gearing, having one wheel fast on it, the other turning. Modern construction shows two axle shafts in a housing, the weight of the car, and the tooth pressure of the differential being carried by the axle shafts.

2. Semi-floating axles have the weight of the car carried by the axle shafts, whereas the tooth pressure of the differential is supported by the housing, and only the turning effect or torsion is transmitted by the axle shafts.

Fig. 7. Floating Axle.

Fig. 8. Semi-floating Axle.

3. Full floating axles carry the full weight of the car, and the differential bevel gear teeth pressure with the housing, so that the axle shafts carry no load but only the torsional stress.

Both full and semi-floating constructions are applied to rear axles only. The front wheels are now universally applied to knuckles, which swing on vertical pivot pins at the ends of the dead axles.

Wheels.—Wheels are now in a transition state. The ultimate wheel has not yet appeared; but whatever its form or construction, certain things are essential.

Flexibility.—In the ordinary wagon or carriage wheel, there is but little, if any, flexibility; but in automobiles, where speed is a consideration, elasticity, either in the rim, or in some other part of the wheel, is necessary.

One of the reasons for this is, that on account of tire expense, motor wheels are smaller than carriage wheels. Making them smaller, however, produces certain disadvantages. One is that in going over the inequalities of the road, the axle on the small wheel has a greater vertical movement than on a large wheel, and the jar on striking an obstruction is more pronounced, also. These disadvantages, however, are more than counterbalanced by the elasticity of the invention.

Large vs. Small Wheels.—Fig. 9 shows a large wheel A, passing over a depression B. The large arc of the wheel does not permit the rim to go to the bottom. On the other hand, the small wheel C goes to the bottom of the depression, and the vertical distance which the axle of this wheel must travel, is three times as far as in the case of the wheel A.

In Fig. 10, where the large wheel strikes an obstruction D, the angle of its upward movement, as designated by the line E, is much less than the impact force of the small wheel, as shown by the greater slope or incline of the line F.

Fig. 9. Crossing Depression.

Fig. 10. Striking Obstruction.

Minimizing Shocks.—It is obvious, therefore, that if part of this shock can be taken up by the tire, the difference due to the smaller diameter of the wheel, will not be so apparent.

The thickness, or widths of the tires also minimizes the impact and distribute the jars while running, so that with these advantages a small wheel has been found to be more practical than a large one.

Resiliency.—Most wheels are now made with wooden spokes, secured by means of a pair of metal-flanged hub plates, bolted together so as to clamp the radiating spokes, but wire wheels are now coming more into favor, whereas cast or pressed solid steel wheels are used on some heavy trucks.

CHAPTER III
TIRES, TUBES, AND RIMS

Tires.—Three kinds of tires are now used, namely: Solid, cushion, and pneumatic. These forms all use rubber, or some compound with the qualities and characteristics of rubber, so as to afford a good tractive surface, as well as resiliency.

Fig. 11. Solid Tire.

The solid tires are used on heavy trucks, where weight and not speed must be provided for.

Cushion tires are sometimes employed on cars and trucks of medium weight.

Pneumatic tires, in which air is used, are universally used in automobiles for all other purposes.

Fig. 12. Single Tube.

The air is confined in two ways:

First, by what is known as the “single tube.” (Fig. 12.)

Second, by the “double,” or inner tube system. (Fig. 13.)

The single tube is well adapted for light vehicles, or where great speed or weight are not considered, and this type is now confined to bicycles. But it has certain disadvantages, namely: That of creeping, due to the impossibility of properly securing it to the rim of the wheel. Sand and grit are also liable to creep in between the tire and rim, and wear the material, thereby ruining it.

The outer casing, or shoe, is split on its inner side, and usually provided with an annular flange on each side of the split, which rests against the rim of the wheel, and is adapted to receive a rim which securely fastens the annular flange of the shoe, to the rim of the wheel.

Fig. 13. Double Tube.

Various ways are provided for holding the shoe to the rim of the wheel; but in the different types shown by the illustrations, Figs. 13 and 14, the shoe has a flange which is held within channels on the rim, or by some form of fastening device.

The inner tube is usually of thin elastic rubber, so made that when properly inflated it will fit the outer tube or casing. The outer part, which can be made of a different rubber compound, and is better adapted to stand wear, whereas, the inner tube, which is made of the best, and more costly material is protected.

Advantage of Double Tube.—The great advantage of the double tube is due to the positive means of fastening it to the rim of the wheel, so as to prevent creeping.

In the single tire construction the latter is liable to roll out of its bed where quick turns are made, but with the double tube this is not possible.

Fig. 14. Illustrating Tire-removing Tool.

Putting On and Taking Off Double Tubes.—To do this properly with clincher tires is quite an art. A pair of blunt, round-ended levers is best for the purpose.

The practice is to use cold chisels, screw drivers and like sharp or pointed tools. This is bad practice. A pair of levers, as shown in Fig. 14, can be made by any one, and you may be sure that their use will not be liable to jag a hole in the inner tube during the removal process.

When the inner tube is put into the outer casing, or tire, as it is called, powdered talcum should be liberally applied, to the tube and also placed within the casing. The tube is then put in and carefully distributed and straightened out before the clinchers are put on.

A little air blown into the tube will prevent it from being pinched under the flanges of the casing. The spare tubes should be inclosed in a receptacle of some kind which will exclude light, and protect them from heat. With the advent of the quick detachable rims of different forms these troubles have happily disappeared in the modern automobile.

Damages to Tires.—Many things must be provided for in the matter of tire keep. The thing most necessary to guard against is punctures, caused either by sharp stones, or nails. When a casing has a heavy protective tread the inner tube may not be effected, but it frequently happens that the outer casing is slitted for some distance, and the great pressure forces the thin wall of the inner tube into the slitted opening, and it is thus ruptured, not on account of its being punctured, but because the outer tire did not afford protection against the pressure.

Repairs to Tires.—It is not a difficult job to repair tires, and the apparatus for doing it is very simple. Rubber, in its natural state, is a white, thick, milky juice, which after several heating and refining processes becomes dark and sticky.

Vulcanizing.—When in this condition and properly mixed with sulphur, it may be vulcanized, which destroys the stickiness, and makes it firm and elastic. Vulcanizing is a kind of baking process, the maximum heat being about 275 degrees, but generally less. The time required is from 12 to 15 minutes, dependent on the thickness of the mass to be vulcanized.

Fig. 15. Vulcanizer.

When the torn or cut portion of the tube or tire is carefully cleaned, it is filled with the plastic rubber, and the heater is applied. The heater, one form of which is shown in Fig. 15, is merely a shell with a heater connection, and this being partly filled with water, generates steam, the temperature of the shell being, of course, dependent on the pressure of the steam developed.

To repair the inner tube, it should be first rubbed with sand paper, and liquid rubber cement applied. When this becomes tacky apply the patch and dry. It is then ready to be vulcanized.

Oil as an Enemy of Tires.—All literature on the subject of tires give warnings as to the insidious character of oil, which deteriorates the rubber. Most manufacturers now make an oil proof quality, but the cheaper grades are not to be depended on.

The action of oil shows itself in several ways, but principally because it dissolves the rubber.

Non-Skidding Tires.—Various means are provided in the shape of tire treads to prevent skidding, the most important being vacuum cups, the herring-bone formation, and various ribbed or ridged surfaces. Nevertheless, for smooth asphalt pavements, chains or similar substitutes are found most satisfactory.

Sudden application of the brakes, or the sliding of wheels on hillsides or the skidding of the car in making short turns at too great speeds, are the most destructive things for tires, however good they may be.

Tires For City Use.—A tire which may be of good service for country roads, might not be available for city work. The tendency of many drivers is to hug the curb too closely, and the result is a wear on the side, which is its weakest point. It is like the side of a shoe, the upper of which can be readily worn through, whereas the sole will stand hard usage.

In country use the great danger is in the winter months, where the wheels must pass over or along frozen ruts. There the same difficulties of side wear are liable to destroy the best material.

Side Slipping.—The same remarks apply to the weakness of tires due to side slipping. The fibers of the fabric are ruptured at the weak point and the least external abrasion assists in destroying it.

Fig. 16. Turning Action on Front Wheel.

Faulty Alinement.—Another cause of ruptured tires is attributable to improper alinement of wheels, due to the wheel being not exactly true, through a bent axle, or improper adjustment. This is more frequently the case with front than with rear wheels.

It will be readily understood that while the rear wheels have the traction applied to them, the front wheels, fixed as they are, to the short turning knuckles, are affected by a movement diagonally across the tire, at every turn which is made.

This is shown by reference to Fig. 16. The movement of the car is in the direction of the arrow A, consequently, when the wheels are turned, the momentum of its forward end is in the direction of the arrows B B.

When the turn is to the right, the strain is on the inside of one tire and on the outside of the other, and when the movement is to the left the conditions are reversed in the stress, and this explains why the tires of front wheels are so liable to yield, in all cases where turns are made at high speeds.

Broken Fabric.—The fabric of a tire may be ruptured without giving any indications on its outer side. When there is a strong impact force, like a transverse ridge, which will force in the tire, several things occur. First, the body of the tire is flattened out so that it has a bulging cheek on each side; and, second, a strain is produced on the longitudinal fibers.

Bruises.—The result of such a severe bruise is to cause a break, not transversely, or longitudinally, but usually, obliquely, for the following reason. The fabric has one set of its threads running across the tire, and the other set around the perimeter. This arrangement of the fabric usually prevents a straight break in either direction, and the weakest part of the fabric is across the diagonal direction.

Fig. 17. Illustrating the Strain on Fabric. Fig. 18.

Try the experiment with a handkerchief, as shown in Fig. 17 by stretching it in the direction of the threads; and then look at Fig. 18, in which case the tension is diagonally, or across the corners. This will be sufficient, probably, to suggest to your mind the reason for the break on diagonal lines.

The rubber material is not sufficient to prevent the stretch which the fabric permits, hence the break follows.

Under Inflation.—To permit a wheel to run flat causes a tire to stretch more on the tread than along the clinch line.

Stretched Tires.—A good illustration of this is shown in Fig. 19, where the tread is a succession of irregular wavy surfaces, whereas the sides remain round and full.

Many attribute this to poor or defective tires. The best tire in the market will show symptoms of this kind, if allowed to run when deflated. In such cases the flatness produces a continual pouching out of the sides, which follow the wheel around, and tend to produce a creeping of the fabric.

Fig. 19. Effect of Flat-Tire.

In time the rubber works away, or along on the fabric, until it becomes stretched at the tread, and all the pressure in the tire will not again restore it to the proper condition.

Blistered Tires.—A blister is a plain case of the rubber being separated from the fabric. At first the injury may be a small cut down to the fabric, which, after being neglected for a time, permits sand to enter, and a grinding takes place, each movement of the parts causing a further separation, and pressure expands the rubber, until, finally, it bulges out and gives an unsightly appearance, as well as starts the tire on its road to destruction.

Such defects can be cured, if taken in time, as many compounds are on the market for this purpose.

Rim Cutting.—This is caused by sand or sharp particles being forced in between the tire and edges of the rim, which causes a wearing out at the contact points. Insufficient air is another cause. The tires flatten and are then cut by the metal.

Frequently the tire is too small for the rim, and this is always bad for it. Heavy loads will cause cutting, because the tire will be flattened out, although inflated to the proper tension.

It is good practice to turn a tire, when one side wears more than the other. This wearing on one edge excessively, shows some defect in the wheel alinement, which needs correcting. Possibly the wheels may not be parallel. This is a frequent trouble with front wheels, on account of the bending of the arm which runs from the knuckle.

Inflation Pressures.—Manufacturers of tires furnish data with respect to the proper pressures for their products, and these vary somewhat, and it is wise to observe the pressures which they indicate for the different sizes.

Expansion of Heated Air.—There is another cause of tire expansion, not generally considered, which is due to the expansion of heated air. It is not infrequently the case that a tire will, in running, heat up fifty or sixty degrees, which means an expansion of one-eighth the volume of air within the tube. If, therefore, there is any weakness in the walls of the tire, a blowout follows.

As this heating is liable to take place to a greater extent in the summer than in winter, it is obvious that it is better to under inflate during that period, than to have an over pressure, particularly with old, or considerably worn, or injured tires.

CHAPTER IV
THE STEERING GEAR AND BRAKES

The Steering Column.—This is a very important mechanical element of the car. Its direct useful functions are to carry or hold the mechanism for steering the machine, and for the motor control, controlling the air supply for the fuel, as well as for regulating the sparking mechanism.

Motor Control.—Some machines are provided with a foot lever mechanism (accelerator) as well as the throttle lever on the steering wheel. This is advantageous, because in moving through crowded streets, where frequent and quick changes are necessary, the foot is the most convenient for controlling purposes.

Throttle Movement.—A downward pressure of the foot opens the throttle, and a spring returns it to its normal position. The foot throttle is also convenient when shifting the transmission gear, as both hands are otherwise engaged, one to operate the gear-shifting levers, and the other for steering.

The hand throttle on the steering wheel, however, is most convenient for long runs, when little change is required, and it can then be set so as to avoid the use of the foot lever.

The levers are so arranged that they do not entirely close the throttle, but, when fully thrown to a closed position, will still provide a sufficient opening to keep the engine running light.

Fig. 20. Steering Wheel.

Steering Wheel Type.—The drawing, Fig. 20, shows a type of steering wheel, which has a segment A. The long lever B is for throttling purposes, as above described, and the short lever C for operating the sparking device.

These levers are differently disposed and arranged on the wheel, or on the column supporting the wheel shaft, but the illustration is sufficient to show the principle of construction, and we are interested only in the types and not in the modifications which are available, and are constantly being made to meet certain conditions.

Fig. 21. Steering Gear.

Steering Gear.—Fig. 21 shows an approved form of construction for the gear, which converts the rotating motion to a direct line movement. In this the hollow supporting column A, is firmly fixed to a base B.

The shaft C which passes through the column, has a worm D at its lower end, and is journaled in a base E, which carries a cross shaft F, in which is mounted the worm wheel G. One end of the shaft F has an arm H for moving the arms of the wheel knuckles.

Within the tubular shaft C, is a tubular shaft I, for the throttle lever to operate, the lower end of which has an arm J, and within the shaft I, is a shaft K for the sparking lever, the lower end having an arm L.

In the best cars all these parts are made adjustable, so as to provide for wear. In examining or selecting a car, this is one of the points to note.

Fig. 22. Type of Front Axle.

Front Axle.—Fig. 22 shows a common form of front axle, with knuckles and cross connecting rod A, the latter providing means, by the nuts B C, for alineing the wheels.

The Brakes.—These are made in two types, one which is usually in the form of a contracting band, and the other which expands.

All cars are now equipped with two braking systems, one being the service, or running brake, and the other the emergency brake. These brakes are all of the drum type, and are either expanding, or contracting bands tightening against the drums.

Fig. 23. Contracting Brake.

Fig. 24. Expanding Brake.

Running Brake.—The running brake is operated by the foot pedal, whereas the emergency brake is generally connected up with the lever at the side of the seat.

The foot pedal is on some cars connected with the clutch in such a way that when pedal is pressed to set the brake, the clutch is released. This prevents an inexperienced or confused driver from applying the brake when he forgets to release the clutch.

Double-Acting Contracting Brake.—Fig. 23 shows the manner in which a double-acting contracting brake operates. As the band A, has a tension on each end, when the rod B, is drawn forwardly, it is immaterial which way the brake drum C travels.

In Fig. 24 the drum C has a pair of oppositely-disposed shoes D, which are held in such a position that they are not revoluble, and may be moved outwardly by the lever E and links F.

These figures, of course, show merely the simple forms of the two types, and do not go into the refinements of construction which make them so effective in service.

It is obvious, however, that the power exerted through either type of brake, depends on the leverage afforded by the relative lengths of the limbs of the bell-crank lever E, to each other.

Contracting Brake.—Fig. 25 shows a well-known type of contraction brake, in which the cylinder A, has thereon two brake bands B C, hinged together at their rear ends. At their front ends they are connected with a bell-crank lever D, the forward movement of the upper end of the lever being such as to cause the bands to pinch the drum A.

A contractile spring E draws back the lever when the foot releases the pedal, and the link F, between the bell-crank lever and the upper band C, has a turnbuckle arrangement to provide for taking up in case of wear.

The brake bands have means for automatically holding them clear of the wheels when not in use.

Fig. 25. Contract Mechanism.

Equalizers.—Sometimes the brake is placed on the propeller shaft; but when one of the brakes is placed on each wheel, an equalizing bar, or other means, must be used. One form of this is shown in Fig. 26, in which A is the bar, B the rod which goes to the brake lever, and C C, the rods that run back to the brakes on the wheels.

Naturally, the equalizer will not act with the same effect on both wheels, unless they are in the same condition. Frequently one of the brake cylinders will be dry and the other coated with grease, or accumulate moisture from some source. It is, therefore, a necessary part of inspection and care to keep them in serviceable condition.

Fig. 26. Equalizer Bar.

The Emergency Brake.—The emergency brake has a pawl which acts in the teeth of a segment alongside of the lever, so it may be held in any position to which the lever may be thrown. This lever has no provision whereby the clutch is disengaged when the brake is applied, for the reason that should it become necessary to stop a car going up hill, and when the emergency brake is required, the brakes would have to be released before the clutch could be thrown in, so that the car would be likely to start down hill before this could be done. On this account the emergency brake has no connection with the clutch.

Fig. 27. Rear axle. Service and Emergency Brake.

Combined Service and Emergency Brake.—Fig. 27 represents a standard type of service and emergency brake, each of the internal expanding type. As both are inclosed in a drum they are absolutely free from dirt and dust, and the construction shown eliminates rattling of the parts.

The wheel bearing is also represented by the annular ball-bearing type of construction, in which the balls are unusually large, and therefore, capable of taking great weight and high speed without undue wear.

CHAPTER V
THE DIFFERENTIAL

The Meaning of Differential.—This is a term used to designate the difference in the turning movement of two wheels on opposite ends of an axle. For various reasons they do not turn at the same rate of speed, particularly in turning corners, where the outer wheel must travel a greater distance than the inner wheel.

If both wheels are fixed to the shaft the latter would be submitted to a torque, or one of the wheels would slip, and thus be destructive of tires.

On the other hand, if one wheel should be loose, then, as power is applied to the shaft, the tractive action would be on one wheel only, and this would be bad practice, and frequently cause the wheel to slip, and thus unduly increase the wear of the tire.

The differential is made up of a system of gears, which are so arranged that one wheel may turn independently of the other, and at the same time the effective driving power is utilized by each.

Various forms of this mechanism have been developed. While the differential is an exceedingly simple piece of mechanism, it is not such an easy matter to describe its operation, so that the principle will be explained by a series of illustrations.

Equalizer Bar.—Examine Fig. 28. Let A be an equalizer bar, mounted on the end of a thrust bar B, by a pivot C, so the ends will swing back and forth freely. A horizontal bar D is hinged at each end of the equalizer, which bars project forwardly parallel with each other and these are provided with right-angled bends E E, simply for convenience in describing the operation.

Fig. 28. Equalizing Mechanism.

Fig. 29. Resistance in Equalization.

While differential gears are very simple structurally, it is not an easy matter to explain the principle on which a faster motion is transmitted to one wheel than another, and under conditions where the speed is constantly changing.

Fig. 30. Equalizer and Differential Movements.

For instance, in Fig. 30, a cord A, over a pulley B, has weights C, D, at its ends. If the pivot or fulcrum E, of the wheel, is stationary, as in sketch 1, and the wheel is turned, say a quarter of the way around, one weight will move down below the line X the same distance that the other weight moves above it, as shown in 2.

Thus far we have an equalizer, pure and simple. But a differential requires something more. It is necessary, under certain conditions, for the weight D to move a greater distance in the same time than C, or the reverse. Or, as sometimes happens, one of the weights, as for instance, in 3, remains fixed while the other moves.

In this case, with the pivot pin E fixed, such a thing would be impossible, hence, in order to make such a relative movement between the two weights, the pin must move, and this motion is shown in 3, where it moves down from the line F. That movement, or change of position of the pivot E, is what takes place in the small intermediate gears in a train of differential gearing.

Transmission Wheel.—In Fig. 32 is shown a section of the differential housing, 1, in which, for convenience, all refinements of construction are eliminated. This shows the divided axle shafts 5, 6. In Fig. 33 is shown a side view of the same housing. This may be connected with the motor shaft by means of bevel gears, or driven by a sprocket chain. In either case the housing 1 is the substitute for the thrust bar B, in Fig. 28, and the bevel pinions 2, which are mounted within the wheel 1, represent the equalizer bar of that figure.

Fig. 31. Differential in Housing.

The gears which make up the train are usually put into a suitable casing, as illustrated in Fig. 31, which gives a good example of the construction. The housing A is fixed to the side of a large bevel gear B, this gear being designed to receive power from the motor through a bevel pinion C. One part of the axle D passes through the gear B, and is fixed to a bevel gear E within the housing, and the other part of the axle F passes through the housing and is fixed to a bevel gear G, the same size as gear E.

Intermediate the two gears is a pair of bevel pinions H, H, and these latter are mounted on pivots I, I, projecting inwardly from the housing.

The fact that the pinions are attached to housing has the effect of complicating the matter, so that it may be well to show the relative arrangement of the gears without the housing.

Fig. 32. Section of Differential.

Fig. 33. Side View of Differential Wheel.

In Fig. 34 we have added to Fig. 33, two bevel gears 3, 4, which are mounted on the axles 5, 6, these representing the rear drive axles of the car.

Action of Transmission Gearing.—From the foregoing it will be seen that the axles abut each other, within the hub of the large gear 1, within which they are journaled. We might, therefore, call these pinions the counterparts of the bars E E.

Fig. 34. Top View of Differential Wheel.

As long as the resistance to the turning movements of the pinions 3, 4 is the same, the housing through pinions 2, 2, will simply carry the bevel gears 3, 4 around with it, without turning them, just the same as the equalizer bar B was moved forward without either end swinging back or forth; but the moment the wheel of the shaft 5, for instance, is compelled to travel at a higher rate of speed, or the wheel on shaft 6 meets with a greater resistance, the small equalizing gears 2 will turn, and the revoluble motion of the housing 1, while transmitting the power, and also carrying the gears, will act, in effect, the same as the push bar shown in the previous illustration.

Like the equalizing bar, the effect is to turn one wheel, say 3, with less, and the other wheel 4 with more than the normal power or speed.

Fig. 28 shows the principle on which all differential automobile gearing is based, that is, that both wheels receive half of the driving power even if one wheel should turn faster, as shown at Fig. 29, which is the case when turning a corner. This is what causes the power to drive both wheels at all times, whether going straight or on a turn.

Fig. 34^a. Differential Gears.

If, however, one wheel gets on slippery ground, then A, Fig. 29, will move forward, without pulling on the lower end. As the lever A has the same action as the pinion in a differential, shown in Fig. 34a, it will be seen that if the pinion center is moved in the direction of the arrow, and if the wheel W¹ slips, the pinion will simply roll on the bevel gear G² without driving it on the wheel W².

This is the disagreeable characteristic of a differential, that makes one wheel spin when it touches a slippery spot on the road, and stalls the car, because the other wheels cannot get any driving power.

CHAPTER VI
THE DRIVE

The term used to designate the transmission of power from the engine to the wheels, is called the drive.

In nearly all cars the engine shaft runs fore and aft, and consequently is at right angles to the axles. This, of course, necessitates some sort of gearing between the engine shaft and axle. This change is made in the bevel gear drive hereafter explained.

As the engine is mounted on the frame of the car, which rests on springs, and the axle is below the springs, it is obvious that the drive must be transmitted between two parts which have a relative up and down movement.

This necessitates several things, structurally, which should be considered.

First. A flexible joint must be interposed in the system, where a shaft is used to transmit the power.

Second. Torsion rods are necessary to prevent the housing or casing of the rear axle from turning, due to reaction of the driving bevel gear.

Third. A rod, or rods, are required to prevent a fore and aft movement of the rear axle. The rods run from the ends of the rear axle housing to some convenient point on the frame.

Illustrating Power Transmission.—For convenience, these mechanical elements are illustrated on a frame.

Fig. 35. Radius Rods.

Fig. 35 shows a frame which has its rear axle provided with a pair of radius rods A A. These have their rear ends attached, in any suitable manner, to the axle housing, near the springs and the forward ends are brought forward and pivoted to the cross beam B.

Torsion Rod.—These rods thus take care of any undue strain which takes place by the wheel striking obstructions.

C represents the torsion rod which has its rear end firmly secured to the housing D, and its forward end to the cross piece E. This prevents the housing from turning, and also serves to provide against any undue thrust of the driving bevel.

Some cars dispense with the torsion rod, by incasing the shaft in a torsion tube. Such a form of construction is shown in Fig. 36.

The torque tube A, as it is called, is rigidly secured to the housing B, of the rear axle, the forward end being pivoted to a cross piece C of the frame.

Fig. 36. Torque Tube.

The radius rods D D, have their forward ends attached to a sleeve E, located near the forward end of the torque tube A, and the rear ends are secured to the axle housing F at the spring seats.