Transient Condition (BOC Locked), Front Wheel Slip, Forward Direction
When the front wheels lose traction and begin to slip, the propeller shaft and rear axle pinion speed difference decreases to zero. At this point the input shaft (cam) becomes the driving member of the BOC (Fig 2 ), compressing the rollers against the outer race. This locks the input shaft with the outer race and transmits torque to the housing of the viscous coupler, that in turn transmits torque to the rear axle pinion. It should also be noted that when the device is locked, the inner shaft and the outer race are rotating at the same speed. The rollers are pinched at this point and will stay locked until a torque reversal (no front wheel slip) occurs. When locked, the viscous coupler slips during the torque transfer and the amount of torque transferred is dependent on the coupling characteristic and the amount of front wheel slip.