Abstract: A fluid coupling has a lockup mechanism, which is unlocked at an increased speed upon a large displacement of an accelerator pedal, and is provided with an activator for applying hydraulic pressure to the lockup mechanism to couple and uncouple the fluid coupling. The activator is controlled by a release controller so as to decrease graudally the hydraulic pressure at a predetermined rate. The fluid coupling is thus uncoupled with a gradual decrease of coupling force when an engine operates in a predetermined engine operating condition. The predetermined rate of pressure change is modified so as to advance uncoupling of the fluid coupling when an engine load is higher than a predetermined engine load, while the release controller controls the activator so as to decrease gradually the hydraulic pressure.

Abstract: The coupling force of a fluid coupling interposed between the combustion engine and the driving wheels is controlled when the automotive vehicle is decelerated. When the automotive vehicle is brought into a decelerated state, the supply of fuel to the combustion engine is suspended by cutting the fuel off. The control of cutting fuel off is delayed by a given period of time after the control over the coupling force of the fluid coupling has been started. The given delay time is so set as to correspond to the state in which the fluid coupling slips.

Abstract: A slip control system for a lock-up clutch of an automatic trnasmission includes a torque converter having an input member, connected to an engine output shaft so that engine output torque is transmitted, and an output member, driven by virtue of a rotation of the input member through a hydraulic fliud. A slip control device controls an engaging force of the lock-up clutch to carry out a slip control so that an amount of slippage in the lock-up clutch is controlled to a target value, corresponding to a target speed difference between the input and output members. An acceleration detecting device detects an accelerating condition of a vehicle, and an engine load detecting device detects an engine load. A slip control changing device suppresses a responsiveness in controlling the slippage in accordance with change in the engine load at the end of the accelerating condition of the vehicle.