Hydraulic control system for a V-belt transmission

摘要

An automatic transmission provided with a combination of a belt drive continuously-variable speed transmission mechanism and a hydraulic control circuit. The belt drive continuously-variable speed transmission mechanism has an input variable-pitch pulley assembly and an output variable-pitch pulley assembly. The hydraulic control circuit includes a regulator valve, a throttle pressure valve, a reduction ratio detecting valve, a reduction ratio control valve and a reduction ratio control mechanism. The reduction ratio control valve has an axially slidable spool and two pressure chambers formed in the valve body thereof at both axial ends of the spool respectively. The reduction ratio control mechanism includes conduits for conducting the working fluid of a throttle pressure to the pressure chambers of the reduction ratio control valve and two solenoid valves adapted to drain the corresponding pressure chambers, respectively, when actuated.