The Use of Viscous Couplings to Alleviate Transmission Wind-Up in Military Vehicles When Driven On-Road

Many of the high-mobility wheeled vehicles used by the British Army employ permanent all-wheel drive transmission systems with just one transverse differential. Since all the wheels on each side of the vehicle rotate at the same angular velocity severe transmission wind-up can be developed on roads.

The possibility of using viscous couplings to alleviate this problem has been investigated by computer simulation backed up by practical trials on a 4 × 4 armoured reconnaissance vehicle. The results suggest that with a suitable choice of coupling characteristic this solution can dramatically reduce the wind-up torque during low-speed manoeuvres with no significant effect on off-road mobility or handling on roads. It can reduce the wind-up caused by non-uniform tyre wear but not to the extent anticipated. To safeguard handling stability under heavy braking there may be a need to bias the brake effort distribution to the front.