Method for controlling locking pressure of lockup clutch in torque converter

The invention provides a method for controlling the locking pressure of a lockup clutch in a torque converter. In the third stage, a just-transmitted point of the second stage serves as a base of theduty ratio of the closed-lock clutch, and a value of the duty ratio of the lockup clutch duty ratio is increased according to the first slope; whether the sliding speed of the lockup clutch is less than a predetermined threshold is judged, and if the sliding speed of the lockup clutch is less than the predetermined threshold, the predetermined time is delayed to enter the fourth stage; and otherwise, the fourth stage is directly entered. The first slope of the third stage is adaptive to the sliding speed of the lockup clutch and the input torque of an engine, so that the lockup clutch can smoothly transition before compression, the stable state is achieved, and the impact generated by the fixed slope pressing is reduced; and in addition, the just-transmitted point of the second stage serves as the base of the duty