System for controlling the transmission ratio of an infinitely variable transmission

Claim 1

In a system for controlling the transmission ratio of an infinitely variable transmission for an engine mounted on a vehicle, the engine having a throttle valve and an electromagnetic clutch having a coil for transmitting the power of the engine to the transmission, said transmission comprising a primary pulley having a hydraulically shiftable disc and a hydraulic cylinder for operating the disc, a secondary pulley having a hydraulically shiftable disc and a hydraulic cylinder for operating the disc of the secondary pulley, and a belt engaged with both pulleys, the improvement comprising; a hydraulic circuit having a transmission ratio control valve having an end chamber and a spool moved by control oil supplied to the end chamber for selectively shifting the disc of the primary pulley in the downshift direction and upshift direction, respectively, first passages including a supply passage for supplying oil to the hydraulic cylinder of the primary pulley passing through the transmission ratio control valve and a first drain passage for draining the oil in the hydraulic cylinder of the primary pulley passing through the transmission ratio control valve, a control oil passage for supplying a part of drain oil in the first drain passage as the control oil to the end chamber, and a second drain passage for draining the oil in the end chamber; said hydraulic circuit including means comprising a regulator valve provided in the control oil passage for keeping the pressure of the control oil in the control oil passage constant; first means for detecting conditions of transient acceleration of the vehicle for producing a first signal; second means responsive to said first signal for producing a control signal representing variation rate of the transient; said hydraulic circuit including third means including a solenoid operated valve provided in the second drain passage and a solenoid responsive to the control signal for operating the solenoid operated valve to control the amount of oil in the end chamber for shifting said spool of said transmission ratio control valve in the downshift direction, and clutch control means responsive to the control signal for decreasing clutch current passing through the coil of the electromagnetic clutch so as to increase speed of the engine for a period.