CONTROL CIRCUIT FOR A CONTINUOUSLY VARIABLE RATIO TRANSMISSION

摘要

A continuously variable ratio transmission (1) of the rolling friction type has a hydraulic control circuit. The circuit includes an electromagnetically actuated control valve (23) and is arranged such that the force exerted on the control valve is always proportional to the roller (5) reaction torque, even when the ratio is changing. The transmission ratios obtainable are limited by hydraulic end stops (18) located downstream of an end loading device (25) for the transmission so that roller torque and end load are related under the majority of circumstances. An ultra high pressure blow-off valve (39) is incorporated however, to avoid transient extremes of pressure causend by the end stops damaging the input or output discs (3, 4). Means (57) are also provided enabling electrical operation of the control valve (23) to be overridden in an emergency.