Control circuit for fluid coupling with lock-up clutch

Abstract

A control circuit of a fluid coupling with a lock-up clutch includes a fluid coupling having a power chamber into which a working fluid is introduced for performing a transfer action between input and output elements via the fluid, a clutch member which suitably connects and disconnects the input and output elements, a working chamber formed separately of the power chamber, and a piston member displaced by a pressure difference between the working and power chambers to selectively engage and disengage the clutch member. The control circuit also includes a fluid pressure source for supplying the working fluid to the power chamber, a lock-up clutch control unit for selectively supplying and discharging a fluid to and from the working chamber to control the engagement and disengagement of the clutch member, a control apparatus responsive to supply and discharge of the fluid to and from the working chamber by the lock-up clutch control unit for lowering pressure inside the power chamber to a hydraulic pressure in proportion to that from a throttle valve, and an oil line for supplying a lubricant pressure line via a port in the lock-up clutch control unit with some of such working fluid to be supplied to the working chamber.