Control system for hydraulic transmission

摘要

A control system for a hydraulic transmission for a vehicle powered by an internal combustion engine has a low speed clutch and a high speed clutch, both actuated hydraulically. An oil draining line is connected to a low speed clutch when a control valve assembly is in its high speed position. The control valve assembly has an orifice and a drain oil control valve arranged in parallel. The valve is moved toward closed position when there is an increase in the throttle valve opening of the engine driving the hydraulic transmission. The drain oil control valve includes a valve having an intermediate throttling position between open and closed positions. The drain oil control valve is moved to its open position when oil pressure fed to the high speed clutch increases to a predetermined pressure, which pressure varies in response to the opening of the engine throttle valve.