A torque transfer mechanism (22) having a multi-plate friction clutch (80) connecting a pair of rotary members (32,42) and a electrohydraulic clutch actuator (52) for controlling engagement of the friction clutch (80). The clutch actuator includes a hydraulic pump (122), a hydraulically-actuated rotary operator (124), and a ball ramp mechanism (126). The hydraulic pump (122) draws low pressure fluid from a sump (200) and delivers high pressure fluid to a series of actuation chambers (162) defined between coaxially aligned first (132) and second (134) components of the rotary operator (124). The magnitude of the fluid pressure delivered to the actuation chamber (162) controls angular movement of the second component (134) relative to the first component (132) for energizing the ball ramp mechanism (126). The ball ramp mechanism (126) applies a clutch engagement force on the friction clutch assembly (80), thereby transferring drive torque from the first rotary member (32) to the second rotary member (42). A hydraulic control system adaptively regulates the fluid pressure delivered to the actuation chamber (162).