Method of controlling hydraulic pressure for an automatic transmission gear system

In a method for feedback controlling a vehicular automatic transmission, in which hydraulic pressure is supplied to a frictional engaging element which engages a rotatable element of a planetary gear set in order to change the actual rotation rate of said rotatable element to converge with a predetermined reference value during a shift from one speed ratio to another, the improvement which comprises setting the hydraulic pressure during the initial stage of gear shifting by;

• reading, from a memory, data representing a first operating condition of the vehicle at a time immediately after the start of the feedback controlling during a preceding shift, and data representing a first hydraulic pressure supplied to said frictional engaging element at that time;
• determining a second hydraulic pressure to be supplied to said frictional engaging element immediately before the start of feedback control of a current shift, according to said first operating condition and said first hydraulic pressure;
• executing said feedback control;
• replacing, in said memory, said data representing said first operating condition and said first hydraulic pressure with data representing a second operating condition of said vehicle during the initial stage of said feedback control and a second hydraulic pressure supplied to said frictional engaging element at that time.