Control system for servo hydraulic pressure in vehicular automatic transmission

摘要

A control system is provided for servo hydraulic pressure in a vehicular automatic transmission having planetary gear mechanisms. Shifting elements of the mechanisms can be connected to establish a different power flow in accordance with engagement or release of frictional engagement devices under the control of servo hydraulic pressure to achieve plural speed stages. The system comprises a servo pressure feed line for feeding, even in a non-running range, servo hydraulic pressure to at least one particular device out of plural frictional engagement devices which are caused to simultaneously engage in a reverse range of the transmission, a directional control valve disposed in the line to control feed or drain of the servo hydraulic pressure to or from said particular device through the line, and a solenoid valve for controlling the control valve to prevent the feed of the servo hydraulic pressure at vehicle speeds above a predetermined value.