Abstract: A hydraulic coupling assembly is provided for an auxiliary drive axle of an all wheel drive motor vehicle. The hydraulic coupling assembly comprises a rotatable casing, first and second output shafts axially outwardly extending from said casing, at least one hydraulically operated, selectively engageable friction clutch assembly for operatively coupling the casing to at least one of the output shafts, and at least one hydraulic clutch actuator. The hydraulic actuator includes a hydraulic pump located within the casing and adapted to generate a hydraulic pressure to frictionally load the friction clutch assembly, and a variable pressure relief valve assembly fluidly communicating with the hydraulic pump to selectively control the hydraulic pressure generated by the pump. The variable pressure relief valve assembly includes an electro-magnetic actuator selectively for varying a release pressure of the pressure relief valve assembly based on a magnitude of an electric current applied thereto.

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 hydraulic coupling assembly is provided for an auxiliary drive axle of an all wheel drive motor vehicle. The hydraulic coupling assembly comprises a rotatable casing, first and second output shafts axially outwardly extending from said casing, at least one hydraulically operated, selectively engageable friction clutch assembly for operatively coupling the casing to at least one of the output shafts, and at least one hydraulic clutch actuator. The hydraulic actuator includes a hydraulic pump located within the casing and adapted to generate a hydraulic pressure to frictionally load the friction clutch assembly, and a variable pressure relief valve assembly fluidly communicating with the hydraulic pump to selectively control the hydraulic pressure generated by the pump. The variable pressure relief valve assembly includes an electro-magnetic actuator selectively for varying a release pressure of the pressure relief valve assembly based on a magnitude of an electric current applied thereto.