FINAL DRIVE
From the change-speed mechanism the power is passed to the driving wheels by the final drive.
Fig. 37.—A, Propeller or driving-shaft drive; B, single-chain drive.
In the most usual construction the engine is so placed that the crank shaft is at right angles to the axle, and it is therefore necessary to change the direction in which the power acts, which is done by means of bevel gears. In ordinary spur gears the teeth are parallel to the shaft, and the two shafts that carry them are parallel, while in bevel gears the teeth are at an angle, and the shafts may be at right angles to each other. In Fig. 37 the diagram of the single-chain drive illustrates a car in which the engine is in the center of the frame, and as the crank shaft is parallel to the axle, the power may be directly applied. In the illustration of the propeller or driving-shaft drive the crank shaft is at right angles to the axle, and the power is turned by means of the bevel gears at the rear axle.
The single-chain drive can only be used for light cars, and is usually applied in connection with a change-speed mechanism of the planetary type.
Fig. 38.—Typical Universal Joint.
The propeller-shaft drive requires the use of universal joints, which are devices that permit one shaft to drive another, even though they are at an angle with each other. A typical universal joint is illustrated in Fig. 38. The ends of the shafts bear yokes, the ends of which are pivoted to a block of metal of + shape. When the two shafts are in line, the joint will force one to rotate with the other, and this will not be prevented if the two are out of line, for then the pivots will act, the + swinging on its pivots in the yokes.
