Torque-tube Drive

Torque-tube Drive

This drive system is generally used in passenger cars and light commercial vehicles. Whereas the Hochkiss drive uses stiff springs to resist torque reaction and driving thrust, the torque tube drive permits the use of either 'softer' springs or another form of spring, like helical to perform their only intended duty so that a 'softer' ride is possible. Figure 26.30 illustrates a layout using laminated springs, which are connected to the frame by a swinging shackle at each end. A tubular member called torque-tube, encloses the propeller shaft and is bolted rigidly to the axle casing. The torque-tube is positioned at the front by a ball and socket joint, which is located at the rear of the gearbox or cross-member of the frame. Bracing rods are introduced between the axle casing and the torque tube to strengthen the arrangement. A small-diameter propeller shaft is installed inside the torque tube and splined to the final-drive pinion. A

universal joint is installed in the centre of the ball joint to allow for angular deflections of the drive.

Fig. 26.30. Torque tube drive.

 

In this design the torque reaction and driving thrust are taken up by the torque tube. Since the forward thrust from the ball is taken on the rear housing of the gearbox, arrangements must be incorporated to transfer this force through the gearbox mountings to the frame. When helical or torsion bar springs are used as alternatives to laminated springs, side movement of the axle must be controlled by providing some form of transverse stabilizer, such as a Panhard rod, between the frame and the axle. This system uses one universal joint and a slip joint. Since the torque tube is fitted rigidly to the rear-axle centre housing, this eliminates the use of a universal joint at the rear end of the propeller shaft.

A torque tube has been presented diagrammatically in Fig. 26.31, indicating all the forces acting on this drive. All the notations of section 26.3.1 hold good for this case also.

Fig. 26,31. Forces acting on torque tube drive

Fig. 26.32. Free body diagram of torque tube.

26.3.4.