Viscous Coupling (VCU)

Viscous Coupling (VCU)







The VCU comprises a short cylinder which contains an inner shaft with slotted discs attached to its outer surface, and a similar set of discs attached to the inner surface of the cylinder. Both sets of discs are arranged so that they interleave alternately and in close proximity to each other. The VCU is sealed, and filled with a type of silicone jelly which has the property of increasing its viscosity with rises in temperature and shear forces.

Variations in speed between the front and rear output shafts are transmitted through the VCU, with the speed differential occurring between the inner shaft and the cylinder. In normal road conditions where the speed variation between front and rear shafts is low, the difference in rotational speed between the VCU discs is also low. As a result, the shear forces acting on the silicon jelly are marginal and offer little resistance to the different rotational speeds of the output shafts.

In cases where large rotational speed differences occur between the front and rear output shafts, such as in rough terrain conditions, the speed variation between the discs is high with a subsequent increase in the shear forces acting on the viscous jelly. The resulting increase in viscosity generates sufficient shear resistance to force both sets of discs to rotate at similar speeds, reducing axle slippage and loss of traction.