| 摘要 |
An electronic pressure control valve (40) is connected to a lockup clutch (4) directly connected to input/output shafts (1a, 2a) of a torque converter (2). In order to change the speed, the lockup clutch (4) is disconnected when the filling of transmission clutches (21-24) to be engaged next has been finished, to prevent the nonavailability of torque. With respect to the lockup clutch (4) in which an inner pressure (Pt) of the torque converter is applied to a back pressure portion of a piston, the inner pressure of the torque converter (2) is applied to the side of a proportional solenoid (42) of the pressure control valve (40), to enable an initial pressure to decrease. During a speed changing operation, the lockup clutch (4) is not completely disconnected to maintain the low pressure, whereby a shock due to the lockup clutch shifting operation is lessened. In order to gradually increase the hydraulic pressure, a degree of opening of a throttle, the weight of the vehicle and a gear ratio are determined, and a rate of gradual increase is varied in accordance with these values. In order to drive the vehicle at a regular speed, the hydraulic pressure in the lockup clutch is controlled so that it is in the vicinity of the level of the engine output torque, to thereby widen the region of travelling with the lockup clutch used. |
