Lock-up controlling apparatus for automatic transmission

Abstract

In response to a signal indicating the present throttle valve opening degree detected by a throttle valve sensor and a signal indicating the present vehicle speed detected by a vehicle speed sensor, a lock-up controller determines whether a lock-up clutch should be brought into the operatively connected state or it should be released from the operatively connected state, and on completion of the foregoing determination, the controller outputs a certain signal to a solenoid valve. In the case that the lock-up clutch has been released, this state is maintained. On the contrary, in the case that the lock-up clutch has been in the operatively connected state, the controller determines whether maintains this state or selects a lock-up clutch releasing pattern depending on the present throttle valve opening degree. Specifically, the controller selects a pattern in such a manner that the operative connecting force of the lock-up clutch is quickly reduced at the time of coasting of a vehicle, it is slowly reduced at the time of an intermediate throttle valve opening degree, and it is appreciably slowly reduced at the time of a large throttle valve opening degree. With such control, a driver does not unpleasantly feel a stifling shock at the time of coasting, and moreover, acceleration behavior of the vehicle is enhanced at the time of a large throttle valve opening degree.