Lock-Up Control

The torque converter clutch piston in the torque converter is locked to eliminate torque converter slip 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 lock-up piston.

Conditions for Lock-up Operation 

When vehicle is driven in 4th gear position, 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.

Fig 1: Conditions For Lock-Up Operation Chart

Courtesy of NISSAN MOTOR CO., U.S.A.

Torque Converter Clutch Solenoid Valve Control 

The torque converter clutch solenoid valve is controlled by the TCM. The plunger closes the drain circuit during the OFF period, and opens the circuit during the ON period. If the percentage of OFF-time increases in one cycle, the pilot pressure drain time is reduced and pilot pressure remains high.

Fig 2: Identifying Torque Converter Clutch Solenoid Control Valve

Courtesy of NISSAN MOTOR CO., U.S.A.

The torque converter clutch piston is designed to slip to adjust the ratio of ON-OFF, thereby reducing lock-up shock.

OFF-time INCREASING

Amount of drain DECREASING

Pilot pressure HIGH

Lock-up RELEASING

Fig 3: Positioning Torque Converter Clutch

Courtesy of NISSAN MOTOR CO., U.S.A.

Torque Converter Clutch Control Valve Operation 

Fig 4: Identifying Torque Converter Clutch Control Valve Operation

Courtesy of NISSAN MOTOR CO., U.S.A.