Control system for an infinitely variable transmission

Claim 1

An improved control system for an infinitely variable transmission for transmitting the power of an internal combustion engine, the system comprising a drive pulley having a hydraulically shiftable disc and a hydraulic cylinder for shifting the disc, a driven pulley having a hydraulically shiftable disc and a hydraulic cylinder for operating the disc, a belt engaged with both pulleys, a first hydraulic circuit having a pump for supplying oil, a transmission ratio control valve having a spool for controlling the oil supplied to the cylinder of the drive pulley to change the transmission ratio, wherein the improvement comprises: the transmission ratio control valve being provided to shift the spool by pressure of oil; a second hydraulic circuit for supplying oil to the transmission ratio control valve so as to shift the spool; control valve means provided in the second hydraulic circuit for controlling the amount of control oil supplied to the transmission ratio control valve; sensing means for sensing operating conditions of the engine and the transmission and for producing operating condition signals dependent on the conditions; means for detecting deceleration rate and for producing a deceleration signal; a control unit responsive to the operating condition signals from the sensing means and deceleration signal for producing an output singal for operating the control valve, so that the shifting of the spool in a downshifting direction is increased.