System for controlling the pressure of oil in a system for continuously variable transmission

In a control system for a continuously variable transmission for transmitting the power of an internal combustion engine having a throttle valve to driving wheels of a motor vehicle through a clutch, the transmission having a drive pulley including a hydraulically shiftable disc and a first hydraulic cylinder for shifting the disc, a driven pulley including a hydraulically shiftable disc and a second hydraulic cylinder for operating the disc of the driven pulley, and a belt engaged with both pulleys, the control system having a line pressure control valve having ports and a shiftable spool, a transmission ratio control valve having ports and a shiftable spool, a first hydraulic circuit having a pump for supplying oil regulated by the line pressure control valve via said line pressure control valve to the first hydraulic cylinder and to said second hydraulic cylinder, the improvement in the system comprising:

• a second hydraulic circuit for supplying the oil to adjacent an end of the line pressure control valve so as to shift the spool of the line pressure control valve;
• control valve means provided in the second hydraulic circuit for controlling the amount of the oil supplied to adjacent the end of the line pressure control valve;
• first means for detecting opening degree of said throttle valve of said engine and for producing a first signal dependent on said opening degree;
• second means responsive to the first signal for producing a second signal representing changing rate of throttle opening degree;
• third means responsive to the second signal exceeding a predetermined magnitude for detecting a potential rapid acceleration for producing a third signal;
• fourth means responsive to the third signal for controlling said control valve means to increase the line pressure for a predetermined time so as to prevent slipping of the belt at the rapid acceleration.