Without going into detail, the foregoing gives the makeup of the car and the simple principles of its operation. To control the car requires various other parts. The first is the steering wheel and its mechanism. The wheel is mounted on a shaft running within a tube, and to the lower end of this shaft is a worm controlling a gear, and by levers and ball joints operating the steering knuckle on one of the front wheels, the other being operated simultaneously by the tie rod connection. On the steering wheel or steering column are mounted the spark-timing lever and the throttle lever. The spark lever regulates the time of the spark within the combustion chamber and the throttle the amount of mixture admitted to the combustion chamber.
At the feet of the driver are the pedal for engaging the clutch, that for applying the brake, and the accelerator pedal, which operates the throttle as well as the lever before mentioned. The throttle lever on the steering column is for the regular running adjustment, while the accelerator pedal is for temporary increase of the mixture in starting or in speeding up. There may also be a pedal for the self-starter, though the switch often is upon the dash. On the Ford and some other cars the gear shift is controlled by pedals, but usually the shift is made by a lever placed convenient to the right hand of the driver. With it is installed also the emergency brake lever, which is used for locking the car when standing and for alternating with the foot brake on long hills.
On the dashboard may be mounted the ignition and lighting switch, the speedometer, sight oil feed, and sundry other dials and switches, depending upon the fastidiousness of the owner. Where there is a self-starter there is a charge and discharge dial, the ammeter, which tells whether the generator is working, and how.
CHAPTER IV
WHAT MAKES THE ENGINE GO
As has been stated on a previous page, it takes three things to start an engine and three more to keep it going. The first three essentials are a proper mixture of gasoline and air, ignition at the right moment, and compression.
Gasoline will continue to burn after ignition, but, contrary to the common idea, it will not explode unless confined, and not even then unless it has vaporized and the vapor is mixed with air. It takes about two hundred cubic feet of air to a pint of gasoline vaporized to produce good combustion, though the air supply is usually much more than this to insure carrying off the unburned nitrogen from the air. For starting and speeding up, more gasoline is admitted to the vaporizing chamber as the rich mixture ignites more quickly, but for running, a leaner mixture produces better results.
But whatever the mixture which is burned, there would be little or no power produced if the mixture were not confined under pressure. It is, of course, a fact that a tank filled with gasoline vapor and air will explode with great force if ignited, though there be only the ordinary atmospheric pressure upon the tank. But it must be remembered that if the pressure were sixty or seventy pounds to the square inch the explosion would destroy everything in the vicinity. Taking advantage of this fact the designers of the gasoline engine provided for compressing the gas before ignition, to produce the greatest amount of power for driving the car. Valves are provided which admit the charge of mixture to the combustion chamber, closing tight after the charge is received. Then the piston rises, compressing the contents of the combustion chamber until a pressure of between forty and seventy-five pounds per square inch is reached. It is upon the principle of the muzzle-loading rifle or shotgun, or in blasting, where the charge is tamped down, or confined by wads, and the exploding powder is held until the pressure sends the bullet on its errand, or rends the rock.
Just as the piston reaches the highest point, and the compression is at the maximum, a spark is introduced into the combustion chamber. Under the pressure the gases burn much more rapidly and the explosive force is greater. The gas does not burn instantaneously, however. It takes a distinct interval of time for all the gas mixture to ignite; for this reason, when the engine is running under its own power, the spark comes just before the time of greatest pressure, and before the piston reaches top center, so that by the time the piston starts the downward stroke the highest efficiency of power will have been reached. For this reason the spark-timing control lever is advanced after the engine is started to give the best results. But the engine is always cranked with the spark fully retarded.
The carburetor, meanwhile, has been called upon to send into the combustion chamber through the intake manifold and intake valves a charge of gas mixture; the quantity is regulated by the throttle. For starting, a lever is manipulated which depresses the float in the fuel chamber of the carburetor, permitting an extra supply to be drawn into the mixing chamber, thus making the mixture richer and more readily fired. When the engine has started running, the throttle is closed to a point where the motor does not race. The correct running position is given by the manufacturer and experience will soon determine where the best results are obtained.
The ignition system must deliver to the combustion chamber at the right instant a spark of sufficient intensity to fire the charge. Whether the electric current is obtained from battery or magneto, it must be hot enough to do its work and there must be a timing device which will send the spark into each cylinder when it is needed. These come in several forms and are described in detail in the manufacturer’s instruction books, in connection with the ignition and wiring diagrams.