Abstract: A method is provided for use in a vehicle including an automatic transmission having at least one load carrying friction element, such as clutch, of optimizing the line pressure in the transmission by slipping the weakest friction element by a small amount. The method includes the steps of decreasing the line pressure from a predetermined base pressure to allow for incipient slip across the weakest friction element and then increasing the line pressure to obtain a temporary pressure at which the weakest friction element is no longer slipping. The method also includes the step of further increasing the line pressure from the temporary pressure to obtain an operating line pressure. Preferably, the operating line pressure provides the weakest friction element with additional capacity for transmitting torque without slip for normal driving conditions, i.e. sensed vehicle throttle positions within a predetermined hysteresis band.

Abstract: A scavenging system for a hydraulic circuit includes a sump passage connecting the sump to a reservoir, a solenoid-operated switching valve, a logic control circuit controlling operation of the switching valve and a passage connecting the reservoir to the inlet of a hydraulic pump that supplies the hydraulic circuit. A vacuum source, such as the intake manifold of an internal combustion engine or a vacuum pump, is connected through a ball check valve and vacuum regulator to a space in the reservoir above the fluid. Fluid level sensing switches sense the level of fliud within the reservoir and produce electronic signals used by the logic circuit to control the solenoid-operated switching valve. An oil filter cap allows the reservoir to be filled while maintaining vacuum within the reservoir. A heat exchanger located within the reservoir draws excess heat from the fluid by passing engine coolant through the exchanger.