Patent ID: 7056261

Claim:
A hydraulic circuit for a continuously variable transmission comprising a continuously variable ratio unit (“variator”) which is controllable by means of at least one hydraulic actuator acting on a movable torque transmission element of the variator, the actuator having opposed first and second working chambers, the circuit comprising first and second flow lines both connected to respective actuator working chambers for feeding fluid thereto and therefrom and means for supplying fluid flow through both of the flow lines, variable control valve means being incorporated in both flow lines for generating an adjustable back pressure therein, a further valve having a variable opening and being connected between the two flow lines, upstream of the variable control valve means, whereby opening of the further valve enables flow of fluid from one flow line to the other in order to reduce pressure difference between the lines, and an electronic control unit (ECU) whereby the state of the further valve is determined in dependence on measured transmission and/or vehicle operating conditions, the ECU being arranged to detect a requirement for rapid ratio change and to open the further valve in response.