Abstract: A torque transfer assembly for a motor vehicle comprises a ring gear subassembly and a differential subassembly rotatably supported in said ring gear subassembly, a friction clutch pack for coupling the ring gear subassembly to the differential subassembly, and a hydraulic clutch actuator for selectively frictionally loading the clutch pack. The hydraulic clutch actuator includes a variable pressure relief valve assembly to selectively control the friction clutch pack. The variable pressure relief valve assembly includes a valve closure member, a valve seat complementary to the valve closure member, and a electro-magnetic actuator for engaging the valve closure member and urging thereof against the valve seat with an axial force determined by a magnitude of an electric current supplied to the electro-magnetic actuator so as to selectively vary a release pressure of the pressure relief valve assembly based on the magnitude of the electric current.

Abstract: A differential assembly for a motor vehicle comprises a differential case rotatably supported in an axle housing, opposite output shafts drivingly connected to the differential case, a friction clutch pack for controlling the differential action, and a hydraulic clutch actuator for selectively fictionally loading the clutch pack. The hydraulic clutch actuator includes a variable pressure relief valve assembly to selectively control the friction clutch pack. The variable pressure relief valve assembly includes a valve closure member, a valve seat complementary to the valve closure member, and an electro-magnetic actuator for engaging the valve closure member and urging thereof against the valve seat with an axial force determined by a magnitude of an electric current supplied to the electro-magnetic actuator so as to selectively vary a release pressure of the pressure relief valve assembly based on the magnitude of the electric current.

Abstract: A hydraulically actuated friction coupling comprises a hollow case, an output shaft drivingly connected to the case, a friction clutch pack for selectively engaging and disengaging the case and the output shaft, and a hydraulic clutch actuator. The hydraulic actuator includes a hydraulic pump for generating a hydraulic pressure to frictionally load the clutch pack, and a piston assembly disposed within the case between the pump and the clutch pack. The piston assembly includes an annular pressure plate adjacent to the pump, an annular thrust plate axially spaced from the pressure plate and adjacent to the clutch pack, and a pair of concentric radially spaced resilient annular seal members bonded to the pressure and thrust plates so as to define an annular cavity within the piston assembly. The annular cavity in the piston assembly is in fluid communication with an output port of the hydraulic pump.