Automatic gearbox - Jatco (Torque Converter): Description and operation (page 2 of 4)

Torque Converter Lock-Up Mechanism In a torque converter there is always a certain amount of slip between the impeller and turbine. This will contribute to a reduction in fuel economy especially during high speed cruising.

This is eliminated by the torque converter lock-up mechanism. The lock-up mechanism is attached to the turbine and controls a lock-up clutch which is integral with the torque converter.

The lock-up mechanism comprises a lock-up solenoid valve, a lock-up control valve and a lock-up clutch.

The lock-up control is provided by the EAT ECU which operates the lock-up solenoid valve. The EAT ECU controls lock-up clutch engagement and release according to the lock-up schedule programmed into the ECU and the vehicle speed and throttle angle.

The lock-up mechanism operates with the gearbox in 'D' (normal mode 4th and 5th gears) and in manual 4th and 5th gears. In an emergency condition when high fluid temperatures are reached, the EAT ECU can also operate the lockup mechanism in 2nd and 3rd gears to help reduce fluid temperatures.

In addition to the lock and unlock conditions, the lock-up control can also initiate smooth lock-up, coast lock-up and lock-up prohibition control.

Smooth lock-up minimises lock-up shock by smoothly and slowly engaging the lock-up clutch.

Coast lock-up control maintains the lock-up condition after the throttle pedal has been released in the lock-up range at certain high speed driving. This prevents the lock-up control switching between the locked and unlocked condition caused by repeated on-off use of the throttle pedal.

Lock-up prohibition control prevents clutch lock-up within the range if the fluid temperature is below 40°C (104°F). This promotes faster warm-up of the gearbox fluid. This strategy is also used by the EAT ECU to prevent lock-up in 1st gear, park, reverse and neutral ranges.