LEEVENSPARK

de-Dion Drive The de-Dion axle is often considered as the halfway stage between the normal axle and independent suspension. This layout provides many of the advantages of the independent suspension, but the system is not classed as independent, as the rear wheels are still linked by an axle tube. In the basic arrangement illustrated in Fig. 26.33, laminated springs are mounted on the frame by a 'fixed' pivot at the front and a swinging shackle at the rear. To support the wheel on a stub axle shaft, each spring is equipped with a hub mounting, which is rigid­ly connected to a tubular axle beam. The final-drive unit, which is bolted to a cross-member of the frame, transfers the drive to road wheels through two universally jointed shafts.  The main propeller shaft is fitted with a universal joint at each end to allow for flexing of the Fig. 26.33. de-Dion drive. frame. In this design, the torque reaction of the final-drive casing is absorbed by the frame, and the driving thrust is

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

Four-link (Semi-Hotchkiss) Drive When helical springs are used in conjunction with a live rear axle, these springs cannot take driving and braking thrust, torque reaction or give lateral support to the rear axle. Therefore additional arrangements must be incorporated to meet these requirements. It may appear that the helical spring provides a reduction in the unsprung weight, but in practice when the weight of the additional locating arms and rods fitted to support this arrangement is added, the unsprung weight difference becomes very small. However, this layout allows for an accurate positioning of the axle which is an advantage. The rear axles is positioned by upper and lower trailing suspension arms in the four-link drive system layout as illustrated in Fig. 26.29.  These arms transmit driving thrust and prevent rotation of the axle casing. A transverse stabilizer, called a Panhard rod, connects the rear axle to the vehicle body and thereby controls sideways movement of the axle.

Rear-wheel Drive Arrangements The statement "every action has an equal and opposite reaction", means that every component that produces or changes a torque also exerts an equal and opposite torque tending to turn the casing. To understand the torque reaction consider the Fig. 26.25A, which represents a tractor with its rear driving wheels locked in a ditch. In this situation torque reaction is likely to lift the front of the tractor rather than turn the rear wheels. When the above principle is applied to rear axles, some arrangement must be provided to prevent the axle casing turning in the opposite direction to the driving wheels. A torque (t) applied to the wheel, which may be considered as a lever (Fig. 26.25B), produces a tractive effort (Te) at the road surface, and an equal and opposite forward force at the axle shaft. This driving thrust must be transferred from the axle casing to the frame in order to propel the vehicle. The maximum tractive effort is limited by the a