The present invention is directed to a power transfer system for a
four-wheel drive vehicle equipped with a torque transfer coupling which
includes a clutch pack and a ball-screw actuator. The ball-screw actuator
functions to axially translates an apply plate to operatively engage the
clutch pack and vary the frictional engagement. This arrangement yields
numerous operational advantages over the prior art including, but not
limited to, establishing a direct drive between the motor output shaft and
the apply plate, concentric mounting of the actuator elements with the
motor output shaft, and a simplified mechanical arrangement that reduces
the number of frictional elements increasing operational efficiency and
decreasing motor requirements.
