Control system for changing servo timings of hydraulic pressure based on a torque input in automatic transmission

Claim 1

A control system for servo hydraulic pressure in an automatic transmission provided with planetary gear mechanisms disposed between an input shaft and an output shaft, each planetary gear mechanism having plural shifting elements which can be connected to establish different power flow paths in accordance with engagement and release of frictional engagement elements to achieve a chosen one of plural gear speed stages, said control system comprising: first frictional engagement means and first fluid pressure communication means for feeding servo pressure to said first frictional engagement means for engagement and for draining servo pressure from said first frictional engagement means for release; second frictional engagement means and second fluid pressure communication means for feeding servo pressure to said second frictional engagement means for engagement and for draining servo pressure from said second frictional engagement means for release; a shift valve for switching said feeding and draining of said servo pressure to and from each of said first and second frictional engagement means, thereby controlling switching of said first and second frictional engagement means between engaged and released states, and thereby shifting between first and second gear speeds; a first solenoid for switching said shift valve; a directional control valve, for controlling feeding or draining or said servo pressure to or from the first frictional engagement means, provided in a first servo pressure feed/drain line connecting said shift valve and said first frictional engagement means; a second solenoid for switching said directional control valve; detection means including an input torque detector for detecting input torque to the automatic transmission; and an electronic control unit for outputting control signals to the first and second solenoids in accordance with a determination of a power-on or power-off down-shift, based on the detected input torque, said electronic control unit changing timings of control signals output to the first and second solenoids in accordance with said determination, so timings of feeding and draining of the servo pressure to and from the first and second frictional engagement means are changed by predetermined relative amounts.