Non-Lock-Up Operation

When there is no necessity for engagement of the lock-up clutch, the TCM sends signals of a small duty ratio to the lock-up duty solenoid. As the solenoid valve opens for only short periods, the quantity of ATF it drains is small, so that the lock-up duty pressure remains high enough to push the spool of the lock-up control valve to the position at which the ATF from the pressure regulator valve can flow through the lock-up release circuit into the space between the impeller cover and the lock-up clutch piston. The ATF then keeps the lock-up clutch away from the impeller cover, so that the engine power is transmitted hydraulically from impeller to turbine to the input shaft. The ATF flows out of the torque converter through the lock-up engagement circuit to the ATF cooler circuit.