In the A4LD automatic transmission, when certain situations occur, the electronic control unit de-energizes the lock-up solenoid valve and releases the lock-up clutch. These situations include: the engine cooling water temperature is below 53℃ or above 116℃, the throttle valve is completely closed, the throttle valve is suddenly opened or closed, the accelerator pedal is pressed hard or the throttle valve is fully opened, and the intake manifold vacuum is low. When the engine speed is lower than the set value, and when the car is braking.

Specifically, when the engine cooling water temperature is lower than 53°C, the lock-up clutch will not be locked, so that the engine can be fully warmed up and can withstand the work load smoothly; when the cooling water temperature is higher than 116°C, the same will not happen. The purpose of locking is to reduce the load on the transmission system and help cool the engine. When the cooling water temperature is within the normal range, the electronic control unit will pay close attention to the electric signal sent by the throttle position sensor. Unlock the clutch during the throttle period to reduce engine emissions and improve fuel economy: If the signal indicates that the throttle valve is open or fully open, the electronic control unit will also notify the lock solenoid valve to de-energize for faster Accelerate the vehicle and utilize its unique torque-increasing effect in the torque converter. The purpose of disengaging the lock-up clutch even when the throttle valve is opened and closed suddenly and briefly is to prevent the lock-up clutch from repeatedly operating during this period. Correspondingly, in the electronic control unit, the memory program can ensure that after a slight change in the throttle position, the action of the lock-up clutch is delayed for a period of time.

The electronic control unit in the system also pays close attention to the engine speed signal provided by the ignition sensor and the intake manifold vacuum signal provided by the intake manifold absolute pressure sensor. When the engine speed drops below the determined function value at a low vacuum, the electronic control unit will notify the lock solenoid valve to de-energize, so as to ensure that the torque converter changes from fourth gear to third gear without locking the torque converter. Downshifting of gears, in order to obtain the best shifting smoothness and softness.

In addition, in any case, as long as the electric signal from the brake switch indicates that the driver is braking, the control unit of the electronic control system will also notify the lock solenoid valve to de-energize to prevent damage to the engine during sudden braking.

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