CHAPTER III

WHAT AN AUTOMOBILE IS

It matters not whether one call it an automobile, a tin lizzie, a gas wagon, or what not, it consists of a steel frame upon which are mounted wheels, an engine, appliances for connecting the engine to the driving wheels, a fuel supply tank, a system for producing ignition at the right moment, and appliances for regulating the speed of the engine and the direction of the car. A seat for the driver and sundry pedals and levers are needed to accomplish speed and steering control, and sundry other parts have their place, but the above covers in a general way the necessities of an automobile.

An automobile, as the name suggests, is a car which contains its own propelling force and to which it is not necessary to hitch a horse, or steam engine, or something else to make it go. This in spite of the fact that occasionally it _is_ necessary to hitch something else to an auto to make it go.

The assembly, generally speaking, consists of the chassis, corresponding to the running gear of a wagon; the engine, mounted on the chassis; and the body.

The chassis usually is made of angle iron riveted together in form convenient for supporting the other parts. This rests upon the springs which take up the road shocks in part, and the springs rest upon the axles.

The rear axles—there is a separate axle for each rear wheel—are fixed, that is, they keep the wheels from oscillating, and they are joined in the center by the differential, a device driving the axle shafts by which one wheel is permitted to revolve at a differing speed as compared with the other, in turning a corner. Since, in turning, the outer wheel must travel a much longer distance than the inside wheel, if no device were installed to take up this difference, the outer wheel would scrape over the ground on every curve, or the inner wheel would spin without forward motion. In either event it would be disastrous to tires.

To keep the differential housing from twisting, a torque rod or tube connects it to the frame; to keep the rear axles at right angles to the frame and to transmit the driving thrust to the load, radius rods connect the axles to the frame forward.

The forward axle, unlike in an ordinary wagon, is fastened to the chassis frame, through springs, and does not turn. On either end is a yoke from which is suspended a steering knuckle, the wheel turning on a tapered spindle forged with the knuckle. The two knuckles are fastened together by a tie rod, which has some form of a turn buckle by which the wheels may be made to run parallel, or practically so. As a matter of fact the wheels are not parallel. They foregather slightly, so that the lines, projected forward far enough, would meet and make a pointed effect, like the bow of a boat. Its effect is to bring a slight but constant pressure upon both wheels and makes them less likely to swerve through contact with road unevenness. Also the wheels undergather, so that the load is brought over the center of knuckle support, minimizing the strain.

This deviation of the wheels from true produces a very slight wear on the tires, but it is more than compensated for by the other advantages noted. The deviation is worked out scientifically and the owner need not trouble himself about it. His only concern is that the tie rod be not bent so that the foregather is increased, when there would be excess wear of tires.

The brake drums are attached to the rear wheels and have inside and outside bands with mechanism to tighten them against the drum providing the necessary friction. The levers which connect the bands to the brake pedal or emergency lever are termed the brake linkage.

The motor, or engine, rests upon the chassis frame forward, being fastened thereto by bolts. Forward of it is a radiator, if it is a water-cooled motor, to which it is connected by pipes; the cooling system may be either pump or thermo-syphon type. Some few motors are air-cooled. The principle of cooling is that the motor should be kept just cool enough to prevent the lubricating oil from burning off the cylinder walls.

Attached to the motor are the carburetor, in which air and gasoline are mixed properly for rapid combustion, wires to supply ignition to the mixture at the proper time, a device for giving lubrication, and exhaust pipes leading to the muffler, the latter designed to stifle the noise of rapid explosions, which otherwise would be deafening.

The ignition system may be either battery and coil, or high-tension magneto which has its own coil and distributor, or a combination of both these systems. Where there is a self-starter there is a storage battery, which supplies current to the starting motor, and from which the ignition current is drawn, and a generator to keep the battery charged, and the generator may be provided with a circuit breaker and distributor, or a separate magneto or coil may be used.

The lubricating device may either be a gravity or force-feed oiler system with pipes leading to the various bearings, or the chief lubrication may be by the splash system, where a reservoir of oil is kept under the crank case from which it is pumped to oil pans under the cranks, being splashed by projections which dip into the oil and throw it all over the inside mechanism.

Also attached to the carburetor is the pipe from the fuel supply tank. This supply may come by gravity or under pressure, and a late device which is furnished with many cars is a vacuum gravity system, the gasoline being drawn from the main tank, by a vacuum created in the intake manifold, into a small container attached under the hood, whence it flows by gravity to the carburetor, maintaining a uniform supply.

The motor consists of one or more cylinders, inside of each being a piston which fits tight, the escape of gas being further prevented by piston rings which seal the cylinder with the aid of the lubricating oil. The pistons are attached to a connecting rod by a wrist pin, the connecting rod being attached at the other end to the crank which rests in bearings. The action of the engine is that by drawing down the piston a vacuum is created in the upper part of the cylinder called the combustion chamber. At the right moment an inlet valve is opened and a charge of gas and air, called mixture, is sucked in. The valve closes and the piston rising compresses the charge. When the piston reaches its highest point a spark is introduced through spark plug or igniter. This fires the mixture, bringing a rapid expansion, and this drives the piston downward, producing force. This revolves the crank shaft, which turns the force into rotary motion. This operation repeated rapidly furnishes the motion which drives the car. The fly wheel carries the crank over the strokes which do not produce power.

There are four strokes to each motor cycle. The first, which takes in the mixture, is called the suction stroke; the next is the compression stroke, the third is the power stroke, and the last is the exhaust stroke when the burned gases are expelled from the combustion chamber. These four strokes take two complete revolutions of the crank shaft, so that the four _cycle_ is really two _circles_.

Power having been created and turned into motion, the next step is to connect it to the propelling or drive wheels. The first device for controlling the power is the clutch, which provides means of applying or cutting off the power or motion quickly without stopping the engine. This is done by friction in some form. The most common are the cone clutch, where male and female cones are engaged by pressure, the friction transmitting the power to the driving shaft; and the multiple disc clutch, where numerous thin discs of metal or metal and textile material are compressed together by a lever and transmit the power.

To provide for varying speeds and for reversing, also extra power to the rear wheels for hill climbing, sandy roads, etc., gears are necessary. In a general way this is a set of cog wheels of varying sizes, so arranged on parallel shafts that by engaging different size gears on the shafts a certain speed will be transmitted, other gear sets producing another speed or a reverse motion. The diagram in