Slip control apparatus for motor vehicle lock-up clutch

An apparatus for controlling an amount of slip of a lock-up clutch disposed between a pump impeller and a turbine impeller in a fluid-filled power transmitting device of a motor vehicle, said apparatus including slip control means for controlling the amount of slip of said lock-up clutch while a running condition of the vehicle is in a predetermined slip control area, such that an actual slip speed of said lock-up clutch coincides with a target slip speed, said apparatus comprising:

• slip speed monitoring means for determining whether a speed difference between speeds of said pump and turbine impellers tends to be increasing, by determining whether a rate of increase of an opening of a throttle valve of an engine of the vehicle drops below a predetermined first threshold;
• enabling means for enabling said slip control means to initiate a slip control operation to control the amount of slip of said lock-up clutch, when said slip speed monitoring means determines that said rate of increase drops below said predetermined first threshold;
• and
• slip control terminating means for commanding said slip control means to terminate said slip control operation when said rate of increase of the opening of said throttle valve exceeds a predetermined threshold value which is substantially larger than said predetermined first threshold value.