The Hotchkiss drive is the simplest of the drive systems and is the most widely used. The arrangement of the parts can be seen in the picture.
The suspension spring are bolted rigidly to the rear axle casing. The front ends of the springs are pivoted on pins. These pins are carried in brackets bolted to the vehicle frame. The rear ends of the springs are connected to the frame by swinging links or shackles. This arrangement permits the deflection of the spring when the vehicle is accelerated or braked. The propeller shaft is provided with two universal joints one at each end and a sliding joint at one end. This arrangement permits the rear axle assembly to move up and down due to projections and depression on the road surface.
Engine power is always transmitted from the gear box to the final drive in the differential, through the propeller shaft. From the differential the driving torque is transmitted to the road wheels through the axle shafts. In this transmission system, the suspension springs act as torque and thrust members.
Torque tube drive
The torque tube drive, which is still fairly widely used is shown in picture. There is a tubular member called torque surrounds the propeller shaft and is bolted to the rear axle casing. The front end of this member is spherical in shape. The spherical end fits in a cup bolted to a cross member of the vehicle frame. The torque tube incorporates bearings which supports the propeller shaft. The propeller shaft itself is usually made of hollow steel tubing which construction gives it a light weight and torsional strength.
The suspension leaf springs are bolted to the spring seats that are provided on the axle casing. Each end of the springs are shackled to the frame. The tubular member will transmit the thrust from the axle to the frame and will also take the torque reaction. Often radius rods are used to assist the torque tube to take the twist and thrust of the vehicle drive.
With this construction, the centre line of the final drive bevel pinion shaft will always pass through the centre of the spherical cup. Now, if the propeller shaft is connected to the gear box shaft by a universal joint situated exactly at the centre of that cup, no other universal joint will be needed and no sliding joint will be necessary. This is because both pinion shaft and propeller shaft will move about the same centre, namely that of the spherical cup, when the axle moves up and down.
In this system, the spring seats are sometime pivoted to the axle casing by means of spherical pivots. This relieves the springs of twisting stresses when the axle assumes angular positions relatively to the frame.
In one design, however, two extra heavy radius rods are used in place of the torque tube to take the thrust. They are connected between the rear axle housing and the X section of the car frame. An open propeller shaft and two universal joints are used with this design.
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