Abstract: In a circuit for controlling the engaged and disengaged state of a torque converter lockup clutch 54 supplied with pressurized fluid on alternate side of a clutch piston, a first valve 116 regulating magnitude of pressure in a lock circuit 104, 106, 124, which causes the lockup clutch to engage, and maintains a pressure differential between lock pressure and unlock pressure, which causes the lockup clutch to disengage. A shuttle valve 122, supplied with control pressure from a solenoid-operated valve 94 when the lockup clutch is engaged, prevents fluid at lock pressure venting from the lock circuit.

Abstract: A torque converter lockup clutch is pressurized from a source of regulated line pressure through a lockup clutch control valve, which directs pressure to either of two passages to apply and release the clutch. The control valve is supplied with control pressure from a solenoid-operated valve that produces high and low fluid pressure states corresponding to commands to engage and release the lockup clutch. A second control pressure, opposing the effect of the solenoid-operated control pressure, is applied to the control valve when the vehicle operator manually selects certain gear ratios, principally the lowest forward and reverse gear ratios. A line pressure regulator valve produces line pressure whose magnitude is proportional to the magnitude of a control pressure representing a commanded engine torque output.