Automatic transmission with hydraulic actuation system having pump control of accumulator pressure

摘要

An automatic transmission has a hydraulic actuation system comprising a spring accumulator 275 charged by an electrically driven pump 223 which is switched on and off so as to provide a predetermined accumulator pressure at commencement of a synchronizing stage of a gear change. The hydraulic system comprises a main control valve 120 that selectively connects a clutch actuator 22 and/or a gear engagement actuator 114, 115 to the accumulator or to a reservoir 278. A pressure transducer 282 monitors the pressure in the accumulator 275 and sends signals to a control unit 36 which uses these signals in a closed feedback loop to provide an accurate control of the pressure by switching the pump 223 on and off The pump 223 has an output which is connected to the accumulator 275 via a non-return valve 276 and delivers fluid to a side of piston 285 remote from spring 287, thereby compressing the spring 287 and pressurizing the fluid.