For the car of not extremely high price, the idea in designing the modern motor-vehicle engine is to produce a motor with high efficiency and power, with smaller fuel consumption, and lighter weight. To this end the small bore, long stroke, high-speed motor has been perfected, and is often fitted with aluminum pistons and a counterbalanced crank shaft.
The motor is engaged or disengaged from the driving system by a common mechanical device called a clutch, which is held in the engaged position by a spring, and may be disengaged by the operation of a foot pedal. The most common types of clutch are the cone and the multiple disk, either of the dry or oil type. A clutch is necessary in order that the motor may be started without the car moving, and that the gears may be shifted.
With but one possible exception, the selective type of gear system is used. The application of the power generated by the motor is controlled by the use of gears of various sizes, usually ranging from one which gives the motor a great power advantage, without high speed, called low, through an intermediate step, to direct drive, or high gear. A reverse gear is also provided. By disengaging the clutch and moving a hand lever any desired gear can be engaged by the opera tor, which counteracts the low speed range of efficient operation of this gaso line motor. The gears are inclosed in a housing, and should run in a heavy oil or a grease. Various types of friction
drive have been tried, but without excep tion were unsuccessful.
The power is often transmitted from the gears through a universal joint to a shaft which operates a gear in the differ ential at the rear axle. By means of the differential gearing in the rear axle, com pensation is made for different speeds with which the rear wheels must move when the car is not running in a straight line. By means of a shaft inside the rear axle, the power is transmitted to the rear or driving wheels.
Steering is accomplished by the front wheels, which are movable, and controlled by a gear and arm, operated by a steer ing wheel.
Usually the car has two sets of brakes, the service brake, which is usually an external contracting hand brake operat ing on a drum mounted on rear wheels, and the emergency brake, which is often an internal expanding shoe brake, also operating on the rear wheels, although brakes operating on the transmission are common.
The frame of the car is of wood or steel. Rolled or pressed steel channel bars seem to be held in highest favor, and the various types of springs, such as flat, full, three-quarter, and semi-ellip tic and platform are used to improve the riding qualities of the car. The artillery type of wooden wheels is held in highest favor, though wire and sheet or solid metal wheels are favored by some design ers and drivers.