Lock-Up Control

A/T CONTROL SYSTEM


Lock-up Control

The torque converter clutch piston in the torque converter is locked to eliminate torque converter slip and to increase power transmission efficiency. The solenoid valve is controlled by an ON-OFF duty signal sent from the TCM. The signal is converted to an oil pressure signal which controls the torque converter clutch piston.

CONDITIONS FOR LOCK-UP OPERATION
When vehicle is driven in 3GR and 4GR positions, vehicle speed and throttle opening are detected. If the detected values fall within the lock-up zone memorized in the TCM, lock-up is performed.






TORQUE CONVERTER CLUTCH SOLENOID VALVE CONTROL

Lock-up Control System Diagram






Lock-up Released
In the lock-up released state, the torque converter clutch control valve is set into the unlocked state by draining the torque converter clutch piston applying pressure and the torque converter clutch piston release pressure is generated.
In this way, the torque converter clutch piston is not coupled.

Lock-up Applied
In the lock-up applied state, the torque converter clutch control valve is set into the locked state by generating the torque converter clutch piston applying pressure and the torque converter clutch piston release pressure is drained.
In this way, the torque converter clutch piston is pressed and coupled.

SMOOTH LOCK-UP CONTROL
When shifting from the lock-up released state to the lock-up applied state, the current output to the torque converter clutch solenoid is controlled with the TCM. In this way, when shifting to the lock-up applied state, the torque converter clutch is temporarily set to the half-clutched state to reduce the shock.

Half-clutched State
The current output from the TCM to the torque converter clutch solenoid is varied to steadily increase the torque converter clutch solenoid pressure.
In this way, the lock-up applying pressure gradually rises and while the torque converter clutch piston is put into half-clutched status, the torque converter clutch piston applying pressure is increased and the coupling is completed smoothly.