Rotary shift control valving mechanism for a power transmission

摘要

An automatic transmission drive ratio control for operating a five speed automatic transmission is provided. The control is particularly adapted for use with a twin countershaft automatic transmission that requires only one torque transfer device for each drive ratio. A system of valves is employed to direct the flow of pressurized fluid necessary for the on-going actuation of each drive ratio and the simultaneous off-going actuation of the previously actuated drive ratio. The flow control for actuating and deactuating the torque control devices is directly effected by a two-position spool valve operating in concert with a rotary valve, pressurized hydraulic fluid used to position the spool valve and the rotary valve is primarily provided by three on/off solenoid shift control valves. A failure of the electrical supply to the solenoid valves will effect a shift to the third drive ratio when the transmission is operating in the first through fourth drive ratios, but will effect a shift to the fifth drive ratio should the electrical failure occur while operating in the fifth drive ratio.