Partial Lock-up

As the speed of the vehicle reaches the programmed value, the torque converter clutch solenoid valve is turned ON by the PCM to release the LC pressure (LA) in the left cavity of the lock-up shift valve. The modulator pressure (6) is applied to the right side of the lock-up shift valve, then the lock-up shift valve is moved in the left side to switch the port leading the torque converter pressure to the right side of the torque converter. The torque converter pressure (91) is applied to the right side of the torque converter to engage the lock-up clutch. The PCM also controls A/T clutch pressure control solenoid valve C, and the LS C pressure (58) is applied to the lock-up control valve and the lock-up timing valve. When the LS C pressure (58) is lower, the torque converter pressure (91) from the lock-up timing valve is lower. The torque converter clutch is engaged partially. The LS C pressure (58) increases, and the lock-up timing valve is moved to the left side to uncover the port leading the torque converter pressure to high. The torque converter clutch is then engaged securely. Under this condition, the torque converter clutch is engaged by pressure from the right side of the torque converter; this condition is partial lock-up.