Subject: Automobile Engineering

Topic: Transmission Systems, Live Axle & Differential

Difficulty: Low

In all the drives employed for the rear axle the spring take the weight of the body. Many drives are used, out of which the two important ones are the Hotchkiss drive & the Targe-tube drive.

Hotchkiss Drive : This is the simplest & most widely used type of a rear axle drive. In this case, the spring besides taking weight of the body also take the torque reaction, driving thrust & the side thrust. Fig:11.1 shows such a drive. The propeller shaft is provided with two universal joints & also a sliding joint. The spring is fixed rigidly in the middle, to the rear axle. The front end of the spring is fixed rigidly on the frame, while the rear end is supported in a shackle. The driving thrust is transmitted to the frame by the front half of the springs.

Torque Tube Drive: In this type of drive, the spring takes only the side thrust besides supporting the body weight. The torque reaction, braking torque & the driving thrust are taken by another member which is called the torque tube. One end of torque is attached to the axle casing, while the other end which is spherical in shape fits in the cup fixed to the frame as shown fig:11.2. The torque tube encloses the propeller shaft. Since in this case, the torque tube takes the torque reaction the centre line of the bevel piston shaft will not shift it & function it will always pass through the centre of the bevel pinion shaft will not shift & further it will always pass through the centre of the spherical cup if the propeller shaft is connected to the gearbox shaft by means of a universal joint situated exactly at the center of the spherical cup. In such a situation, no universal joint is needed at the rear & of the propeller shaft. Also no sliding joint is provided because both the pinion shaft & propeller shaft in this case will move about the same centre i.e about the centre of the spherical cup.Clearly torque reaction & the driving thrust are taken by the torque tube.