Automatic transmission control system having two accumulators for four clutches controlled by a single accumulator back pressure valve

A control system for controlling an automatic transmission of a vehicle, which includes a hydraulic control circuit for controlling coupling pressure supplied to a plurality of frictional coupling elements of the automatic transmission which are (1) selectively coupled and uncoupled so as to shift the automatic transmission into desired gears and (2) divided into a first group of frictional coupling elements having a coupling pressure controlled in accordance with a control pressure and a second group of frictional coupling elements having a coupling pressure independent from said control pressure, said hydraulic control circuit comprising:

• driving condition detecting means for detecting driving conditions of the vehicle;
• an oil pump for generating a hydraulic pressure;
• solenoid valve means for regulating said hydraulic pressure so as to provide said control pressure in accordance with vehicle driving conditions detected by said driving condition detecting means;
• regulating valve means, provided for each frictional coupling element in said first group, for regulating a coupling pressure supplied to each frictional coupling element in said first group in accordance with said control pressure;
• accumulating means for controlling a supply of said coupling pressure of specified frictional coupling elements of said second group of frictional coupling elements during shifting of said automatic transmission;
• and
• control valve means for controlling a back pressure supplied to said accumulating means in accordance with said control pressure.