Fig. 41.—Torsion Rod.
Fig. 42.—Double Side-Chain Drive.
In Fig. 42 is shown a car with double-chain drive, in which the bevel gears that change the direction in which the power is applied are contained within the gear case that incloses the change-speed mechanism. As will be seen from Fig. 34, the bevel gears connect the square shaft with the jack shaft, which is a shaft passing across the car, and bearing on its ends the sprockets by which the wheels are driven. This type of drive requires the use of a dead axle, which is stationary with the wheels running loose on its ends, like the axle and wheels of a coach. An axle of this type may have great strength with light weight, and is usually a manganese-bronze or steel forging. The sprockets on the rear wheels are bolted to the spokes, and should be, of course, exactly in line with the sprockets on the jack shaft in order that the chains may run true.
DIFFERENTIAL
When a car takes a corner, the outside wheels make a larger curve than the inside, and cover a longer distance. As the front wheels are loose on the axle, they accommodate themselves to this; but as both rear wheels are driven by the engine, it is necessary to apply a device that will permit them to rotate at different speeds without interfering with their driving the car. This is accomplished by means of a compensating and differential gear.
To understand the necessity for a differential, stand behind a wagon, with one hand on each tire; push, and if the vehicle is steered straight ahead, the hands will move ahead equally; but if the vehicle turns, the hand on the outside wheel will move ahead faster than the other. Now take a stick, and run it through the rear wheels so that it bears against the spokes; press it forward from its center, and if the vehicle moves straight ahead, the stick will go forward equally; but if the vehicle turns, the outside end of the stick will go ahead faster and farther than the other, although the pressure is being applied to its center.
Fig. 43.—Differentials.