Variably controlled torque coupling device for on-demand all-wheel drive drivetrains

A torque-coupling device for selectively, on-demand actuating of a secondary drive axle assembly of a all-wheel-drive motor vehicle, said torque coupling device comprising:

• a hollow housing;
• an input shaft and an output shaft both rotatably supported within said housing;
• a clutch casing drivingly coupled to one of said input shaft and said output shaft;
• a friction clutch assembly disposed within said clutch casing for selectively frictionally engaging and disengaging said input shaft and said output shaft, said clutch assembly comprising at least one first member coupled to rotate with said input shaft and at least one second member coupled to rotate with said output shaft, said members being frictionally engageable with one another;
• and
• hydraulic clutch actuator for selectively frictionally loading said friction clutch assembly, said actuator comprising:
• a hydraulic pump disposed within said clutch casing to generate a hydraulic pressure to frictionally load said friction clutch assembly;
• and
• a variable pressure relief valve assembly fluidly communicating with said hydraulic pump to selectively control said hydraulic pressure,
• wherein said variable pressure relief valve assembly including a valve closure member, a valve seat complementary to said valve closure member and an electro-magnetic actuator for engaging said valve closure member and urging thereof against said valve seat so as to selectively vary a release pressure of said pressure relief valve assembly based on a magnitude of an electric current supplied to said electro-magnetic actuator, said valve closure member is movable between a closed position when said valve closure member engages said valve seat and an open position when said valve closure member is axially spaced from said valve seat, and
• wherein said electro-magnetic actuator including a coil winding and an armature axially movable relative thereto in response to a magnetic flux generated by said coil winding when said electrical current is supplied thereto, said armature engages said valve closure member and urges said valve closure member against said valve seat with an axial force determined by said magnitude of said electric current for selectively setting up said release pressure of said valve closure member.