Hydraulic control apparatus for belt-and-pulley type continuously variable transmission, incorporating means for optimizing belt tensioning pressure

A hydraulic control apparatus for controlling a hydraulically operated continuously variable transmission of a motor vehicle having an engine, said transmission including a first and a second shaft, a pair of variable-diameter pulleys provided on said first and second shafts, respectively, a transmission belt connecting the pair of pulleys, and a pair of hydraulic actuators for changing effective diameters of said pulleys for continuously variably changing a speed ratio of the transmission, one of said pair of hydraulic actuators receiving a belt tensioning pressure for controlling a tension of said transmission belt;

• said hydraulic control apparatus comprising;
• an engine-output detecting valve for generating an engine output fluid pressure indicative of a currently required output of said engine in response to a member which is displaced with said currently required output;
• a solenoid-operated valve including a solenoid coil receiving said engine output fluid pressure and regulating said engine output fluid pressure to a modified engine output fluid pressure at an output of the solenoid operated valve based on said engine output fluid pressure generated by said engine-output detecting valve by controlled energization of said solenoid coil, said modified engine output fluid pressure being obtained so that said belt tensioning pressure is controlled to an optimum level;
• and
• a pressure regulating valve for regulating said belt tensioning pressure based on at least said modified engine output fluid pressure.