Device for transmitting torque between two rotatable, coaxial shaft members

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 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.