Control system for an infinitely variable transmission

Claim 1

In a system for controlling the transmission ratio of an infinitely variable transmission for transmitting power of an internal combustion engine, the transmission comprising a primary pulley having a hydraulically shiftable disc and a hydraulic cylinder for shifting the disc, a secondary pulley having a hydraulically shiftable disc and a hydraulic cylinder for operating the disc, and a belt engaged with both of the pulleys, the system comprising a first hydraulic circuit means having a pump for supplying pressurized oil, and a transmission ratio control valve having a spool responsive to speed of the engine for controlling the pressurized oil so as to move the disc of the primary pulley to change the transmission ratio, the improvement comprising: a second hydraulic circuit means for applying control oil to one end of the spool of the transmission ratio control valve so as to axially move the spool; an electronic control circuit means responsive to first pulses proportional to the speed of said engine for producing a first output signal dependent on the engine speed; the electronic control circuit means including range change means, the latter for causing the electronic control circuit means to produce a second output signal dependent on said engine speed; the second hydraulic circuit means including a modulator valve for producing constant pressure control oil; and the second hydraulic circuit means including an electromagnetic valve having a coil responsive to said first output signal and said second output signal, respectively, for draining a part of the constant pressure control oil so as to control the control oil applied to the end of the spool of the transmission ratio control valve, thereby controlling the transmission ratio.