Line pressure control system for automatic transmission

Claim 1

A hydraulic pressure control system for an automatic transmission comprising: a transmission gear mechanism having a plurality of gear stages and frictional elements for switching power transmitting paths in the transmission gear mechanism, hydraulic control means for controlling engagement and disengagement of the frictional elements to establish one of said gear stages, line pressure control means for controlling line pressure of said hydraulic control means, speed detecting means for detecting an actual speed of an input element of the transmission gear mechanism during a shift operation switching the gear stage of the transmission gear mechanism, electronic control means for detecting a shift operation, based on a signal from the speed detecting means, and determining an end to said shift operation from a difference between a target speed and said actual speed of said input element, calculating an actual shift operation time period based on the end to said shift operation, calculating a time difference between said actual shift operation time period and a target time period, and determining a compensation coefficient, based on said time difference, when said shift operation is a shift-up operation, and determining a speed change rate of the input element, based on the actual speed of the input element, when said shift operation is a shift-down operation, and compensation means for compensating the line pressure based on a signal from the electronic control means representing said compensation coefficient.