Revolution speed ratio control system for a continuously variable transmission

A revolution speed ratio control system for a continuously variable transmission comprising a driving pulley provided on an input shaft;

• a driven pulley provided on an output shaft disposed in parallel with said input shaft;
• an endless belt wound on both said pulleys;
• each of said pulleys comprising a fixed member secured to said input or output shaft and having a conical surface, and a movable member which has a conical surface facing that of said fixed member and is provided so that said movable member is rotated together with said input or output shaft and can be slid on said shaft in the axial direction thereof;
• and said endless belt has both its oblique side surfaces frictionally engaged with said conical surfaces of said fixed and movable members;
• an electronic control circuit including a means for calculating the actual revolution speed ratio between said driving and driven pulleys of said transmission, a means for generating a first electric control signal corresponding to the difference between said actual revolution speed ratio and an aimed revolution speed ratio between said pulleys determined by information of the input torque of said input shaft and required torque for said output shaft, and a means for generating a second electric control signal determined by the sum of an electric signal corresponding to said actual revolution speed ratio and an electric signal corresponding to said difference;
• and a hydraulic control circuit including a pressure oil source, a first cylinder which is provided on said input shaft and supplied with working oil from said pressure oil source to push the movable member of said driving pulley toward the fixed member thereof, a second cylinder which is provided on said output shaft and supplied with working oil from said pressure oil source to push the movable member of said driven pulley toward the fixed member thereof, a first control valve which is disposed in an oil passage for connecting said pressure oil source and said first cylinder to each other and acts on the basis of said first electric control signal to control the flow rate of the working oil supplied to or drained from said first cylinder, and a second control valve which is disposed in an oil passage for connecting said pressure oil source and said second cylinder to each other and acts on the basis of said second electric control signal to control the pressure of the working oil supplied to said second cylinder.