Lock-Up Operation

The Transmission Control Module (TCM) sends output signal to the lock-up duty solenoid. Since the lock-up duty solenoid operates in proportion to the duty ratio, the amount of ATF drained from there is increased, thus lock-up duty pressure being reduced.

As a result, the lock-up control valve moves downward, which connects the torque converter regulator valve and the lock-up control valve apply port to each other.

In this condition, the oil pressure from the torque converter valve flows through the lock-up control valve apply port to the torque converter and the torque converter clutch. This causes a pressure differential across the lock-up piston. The piston is then forced against the impeller cover and turned as an integral unit with the cover. Thus, power from the engine is directly transmitted to the transmission input shaft. That is, the transmission is directly coupled to the engine.

Smooth control 

The lock-up duty solenoid is controlled by the TCM and controls the operation of the lock-up control valve. Because the lock-up operating pressure is controlled by the lock-up control valve, the force applied to the lock-up clutch is controlled for smooth clutch operation.

When locking up, the clutch is set in the half-engaged state beforehand. After this, the lock-up operating pressure is gradually increased to achieve smooth locking up.