Method for controlling continuously variable drive ratio transmissions

Abstract

A continuously variable drive ratio transmission for motor vehicles is interposed between a prime mover and a drive shaft. When a single foot pedal is depressed the prime mover is brought to the driving condition thereof so as to drive the vehicle. When the single foot pedal is released the drive ratio of the transmission is decreased and the prime mover is brought to the braking condition thereof in response to the releasing of the pedal so as to apply the dynamic brakes on the vehicle. The depression and release of the foot pedal, respectively, rotate first and second cams incorporating cam surfaces representing desired speeds of the prime mover for any pedal setting. Hydraulic pressure is used to detect the operational position of the pedal, to activate a changeover valve for selecting a first or second piston, respectively, controlled by the cams in accordance with the position of the pedal, for comparing the speed of the engine with the position of the selected piston, and for varying the drive ratio between the prime mover and the drive shaft until the difference between the speed of the engine and the desired speed represented by the cam surface is reduced to a null.