Patent ID: 7281617

Claim:
A power transmission device comprising: a rotary input member adapted to receive drive torque from a source of drive torque; a rotary output member adapted to transmit drive torque to an output device; a torque transmission mechanism operable for transferring drive torque from said input member to said output member, said torque transmission mechanism including a friction clutch operably disposed between said input member and said output member and an electrohydraulic control system for controlling engagement of said friction clutch, said electrohydraulic control system including a clutch actuator, a fluid pump, a motor driving said fluid pump, and a controller, said clutch actuator including a rotary operator and a thrust mechanism, said rotary operator having first and second components with a plurality of actuation chambers and a plurality of return chambers, said first component being fixed for rotation with one of said input and output members and said second component adapted to rotate relative to said first component, and said thrust mechanism being operable for applying a clutch engagement force on said friction clutch in response to rotation of said second component relative to said first component, said controller being operable for controlling the fluid pressure supplied to at least one of said actuation chambers and said return chambers to thereby control rotation of said second component relative to said first component of said rotary operator; wherein said electrohydraulic control system is configured so that said actuation chambers are divided into at least two groups, wherein a first group is configured such that said actuation chamber or actuation chambers included therein contain a relatively high pressure fluid when said second component is rotated relative to said first component in an actuating direction regardless of a relative position of said first and second components and wherein a second group is configured such that said actuation chamber or actuation chambers included therein contain a relatively low pressure fluid when said second component is positioned relative to said first component within a predetermined actuating interval and contain said relatively high pressure fluid when said second component is rotated relative to said first component in said actuation direction by an amount that exceeds said predetermined actuating interval.