Automotive vehicle lock-up clutch control apparatus wherein change of line pressure for lock-up clutch slip control valve is restricted during slip control mode

An apparatus for controlling the amount of slip of a lock-up clutch which is provided in a fluid-operated power transmitting device disposed between an engine and an automatic transmission of an automotive vehicle, for direct connection of the engine and the automatic transmission, said apparatus comprising:

• a pressure regulating valve for regulating a line pressure depending upon a load acting on said engine;
• a lock-up clutch slip control valve operable in a slip control mode, for receiving said line pressure regulated by said the pressure regulating valve, and regulating a hydraulic pressure applied to said lock-up clutch to control the amount of slip of the lock-up clutch;
• slip control mode detecting means for detecting an operation of said lock-up clutch slip control valve in said slip control mode;
• and
• line pressure change restricting means, responsive to said slip control mode detecting means, for restricting an operation of said pressure regulating valve to restrict a change of said line pressure with a change in said load of the engine, while said lock-up clutch slip control valve is operated in said slip control mode.