Patent ID: 7204170

Claim:
A device for transmitting torque between two rotatable, coaxial shaft members, the device containing: a clutch between the two shaft members and engageable—to counteract rotational speed differential between the shaft members—by means of a hydraulic piston under the control of an electrically controlled throttle or pressure valve; a clutch pump for supplying hydraulic pressure to the hydraulic piston; wherein the hydraulic piston, the valve, and the clutch pump are connected in a hydraulic system also containing a feeder pump for maintaining a certain base pressure in the system; characterized by means in the hydraulic system for conditionally allowing flow from the feeder pump past the valve and to the hydraulic piston irrespective of the flow from the clutch pump; wherein the clutch pump is a differential pump driven by the rotational speed differential between the two shaft members; in which the hydraulic system in a closed portion comprises lines from the differential pump, through the electrically controlled throttle or pressure valve to the clutch, the portion including check-valves, and in which oil may be supplied by the feeder pump from a reservoir and may be removed to the reservoir via an overflow valve; and wherein the feeder pump and the differential pump are connected in series by means of a check-valve between the overflow valve and the feeder pump.