Drive mechanism in part-time four-wheel drive vehicle

Claim 1

A drive mechanism comprising driving and driven members coaxially coupled with each other for relative rotation, friction clutch means operatively associated with said driving and driven members and operable between a first condition wherein said driving and driven members are drivingly connected and a second condition wherein relative rotation between said driving and driven members is permitted, said clutch means including friction members cooperating with said driving and driven members and arranged to be engaged when said clutch means is in the first condition, a fluid pump arranged between said driving and driven members to be driven by relative rotation therebetween, said fluid pump being located adjacent one side of said clucth means and axially movable in a direction to effect a frictional pressure engagement of said friction members when applied at one side thereof with a discharge pressure thereof, and a flow control valve disposed in a communication passage for fluid circulation between discharge and suction ports of said fluid pump to control an amount of fluid under pressure passing therethrough from the discharge port toward the suction port; wherein said flow control valve includes an axially displaceable valve element disposed in said communication passage and shiftable between a first position in which it is retained to fully open said communication passage and and second position in which it is retained to close said communication passage for interrupting the flow of fluid under pressure from the discharger port of said pump, and wherein a shift mechanism is adapted to shift said valve element to and from the second position.