Continuously variable ratio transmission

摘要

A continuously variable ratio transmission of the rolling friction type has a hydraulic control circuit including an end loading device for the transmission located upstream of a double sided piston used to balance roller reaction torque, and a valve for controlling the force exerted by the double sided piston. The valve has two outlets each feeding one side of the piston and communicating with the transmission's sump by way of a device for equalizing the flow rates from the two outlets to the sump. A feedback arrangement provides that the force exerted on the spool of the control valve is always proportional to the force exerted by the piston. The piston travel is limited by hydraulic end stops, upstream of which is provided a pressure relief valve to eliminate damaging transient overloads being exerted by the end loading device. The circuit also includes a facility whereby normal electrical/electronic control of the control valve can be overridden in an emergency.