An electronic controller for a continuously variable transmission and a method of control of a continuously variable transmission

The invention concerns an electronic controller for a continuously variable transmission of the type having a variator (10) with a rotary variator input (17) coupled to a first variator race (14a) and a rotary variator output (29) coupled to a second variator race (16a). At least one roller (20) runs upon the said races to transfer drive from one to the other. The roller is movable to steplessly vary the variator ratio. The variator further comprises at least one hydraulic actuator (36), (38) which acts upon the roller and through which net torque acting on the variator races is referred via the roller to the variator's casing. A hydraulic arrangement is provided for applying to the actuator at least one hydraulic control pressure which determines force applied' by the actuator and thus determines the reaction torque. The variator is coupled between a rotary transmission input (17) and a rotary transmission output (714) such that the transmission ratio is a function of the variator ratio. The electronic controller is adapted to cany out the following steps in a loop: measure a speed ratio of the continuously variable transmission; compare the measured speed ratio with a target speed ratio; determine a transmission output torque request on the basis of the said comparison; convert the output torque request to a control pressure request, taking account of the speed ratio; differentiate the control pressure request with respect to lime to obtain a compensation value and apply the compensation value to the control pressure request; and output the resulting compensated control pressure request to the hydraulic valve arrangement.