Lock-up control system for vehicle drivetrain with torque converter

Abstract

An engine-transmission drivetrain includes a torque converter situated between the engine output shaft and the transmission. The torque converter includes a lock-up clutch. A speed sensor, which measures the rotational speed of an output shaft of the transmission, generates a pulse signal. A transmission controller includes a deceleration dependent lock-up release command generator and a torque converter speed dependent lock-up release command generator. The pulse signal from the speed sensor is used as inputs to both of the lock-up release generators. In the deceleration dependent lock-up release command generator, the pulse signal is processed to derive information as to the magnitude of deceleration which the transmission output shaft is subject to. In the torque converter speed dependent lock-up release generator, the pulse signal is processed to derive information as to rotational speed of an output element of the torque converter. At deceleration with the magnitude of deceleration greater than or equal to a predetermined reference, the deceleration dependent lock-up release generator gains authority over the lock-up release control. At deceleration with the magnitude of deceleration less than the predetermined reference, the torque converter speed dependent lock-up release generator gains authority over the lock-up release control.