ALL WHEEL DRIVE SYSTEM FOR A MOTOR VEHICLE

An all wheel drive system for a motor vehicle comprising a front differential, a pair of front halfshaft assemblies operatively connected to the front differential whereby the front differential supplies torque to the pair of front half shaft assemblies, each of the pair of front half shaft assemblies connected to a respective front wheel, a power takeoff unit operatively connected to the front differential, a constant velocity joint connected to the power takeoff unit whereby the front differential supplies torque to the constant velocity joint through the power takeoff unit, a first propshaft having a first end and a second end, the first end connected to the constant velocity joint, a plunging constant velocity joint connected to the second end of the first propshaft, a second propshaft having a first end and a second end, the first end connected to the plunging constant velocity joint, a universal joint having a first end and a second end, the first end of the universal joint connected to the second end of the second propshaft, a self contained speed sensing torque transfer device connected to the second end of the universal joint such that torque is selectively transferable when the self contained speed sensing torque transfer device is engaged, the self contained speed sensing torque transfer device including, a hub connected to a first set of friction plates, the hub also connected to the second end of the universal joint, a housing connected to a second set of friction plates whereby the first and second set of friction plates are disposed in a selectively interconnecting relationship; a piston located adjacent the first and second set of friction plates, a self contained shear pump for generating a pressure proportional to the speed difference between the hub and the housing, the pump comprising, a feed disc affixed to the hub, a fluid reservoir, a pump disc affixed to the housing and in fluid communication with the fluid reservoir, the pump disc having a circumferential pumping groove and at least one connecting hole forming a shear channel with the feed disc, the pump generating pressure on the piston at a set speed difference such that the piston transmits pressure to the first and second set of friction plates and torque is thereby transferable from the first set of friction plates to the second set of friction plate thereby transferring torque to the housing, a rear differential connected to the housing of the speed sensing torque transfer device, and a pair of rear halfshaft assemblies operatively connected to the rear differential for transferring torque to the rear halfshaft assemblies, each of the rear halfshaft assemblies connected to a respective rear wheel whereby under normal operating conditions the all wheel drive system provides substantially all torque to the front differential, and in a slip condition when either of the front wheels begins to slip the front differential rotates at a higher speed than the rear differential and the self contained speed sensing torque transfer device engages thereby providing torque to the rear differential until the slip condition is resolved whereupon substantially all torque is transferred back to the front wheels.