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

Claim 1

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, and a first hydraulic circuit having a pump for supplying oil regulated by the line pressure control valve to the first hydraulic cylinder via the transmission ratio control valve and to said second hydraulic cylinder, the improvement in the system comprising: a second hydraulic circuit for supplying control oil to 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 control oil supplied to the line pressure control valve; sensor means for sensing operating conditions and for producing first signals; first means responsive to at least one of the first signals for producing an engine torque representing engine torque in acceleration state and steady state respectivley; second means responsive to at least one of the first signals when the throttle valve is closed during driving of the vehicle for producing an acceleration/deceleration signal representing engine braking conditions; third means responsive to the engine torque signal for producing a second signal representing a cluch torque necessary to transmit said engine torque through the clutch; fourth means responsive to the second signal for producing a third signal representing a desired line pressure in the first hydraulic circuit providing a transmitting torque at the belt larger than the clutch torque; fifth means responsive to the third signal for operating said control valve means so as, via the line pressure control valve, to provide the desired line pressure in the first hydraulic circuit, the transmitting torque at the belt provided by said desired line pressure being larger than the clutch torque; sixth means responsive to the acceleration/deceleration signal in deceleration state for producing a first correcting signal dependent on weight of the vehicle, and, respectively, in acceleration state for producing a second correcting signal dependent on engine speed; and said third means being responsive to the first correcting signal and the second correcting signal respectively for correcting the second signal to provide a clutch torque and a transmitting torque so as to provide an engine braking effect.