Drive shafts (Vcu): Description and operation

VCU

The VCU automatically controls the transfer of drive to the rear wheels by limiting the speed differential between the front and rear propeller shafts . The unit is supported in two propeller shaft bearings attached to the floor cross member.

The VCU comprises a short cylinder which contains an input shaft supported in a roller bearing race at the front and a ball bearing race at the rear. Within the cylinder, slotted discs are alternately attached to the outer surface of the input shaft and the inner surface of the cylinder. An output shaft is welded onto the rear of the cylinder. A torsional damper is bolted to a flange on the output shaft. The input shaft is attached to the front propeller shaft and the output shaft is attached to the rear propeller shaft.

The cylinder is a sealed unit filled with a silicon jelly. The viscosity of the silicon jelly increases when subjected to shear. When there is a speed differential between the front and rear propeller shafts , adjacent slotted discs in the VCU rotate in relation to each other. The shearing action of the rotating slotted discs increases the viscosity and resistance to rotation of the silicon jelly.

Section through VCU

1. Cylinder
2. Slotted discs
3. Input shaft
4. Roller bearing
5. Ball bearing
6. Torsional damper flange
7. Output shaft