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, a hydraulic control mechanism for controlling engagement and disengagement of the frictional elements to establish one of said gear stages, line pressure control valve means, providing a line pressure control, for controlling line pressure of said hydraulic control mechanism, solenoid valve means for receiving a control signal and controlling a pilot pressure based on the control signal allowing the line pressure control valve means to control the line pressure, frequency control means for increasing a control signal frequency for the solenoid valve means from a first frequency during a non-shifting operation to a second frequency during a shift operation of the transmission independently of said line pressure control to increase responsiveness of said line pressure control valve means during said shift operation. speed detecting means for detecting a rotation speed of an input member of the transmission gear mechanism, and line pressure compensation means for compensating the line pressure, based on the rotation speed of said input member, said line pressure compensation means comprising shift time detecting means for detecting an actual shift operation time period based on a speed change rate of said input member, and target time setting means for setting a target shift operation time period for the shift operation, the line pressure compensation means compensating the line pressure in accordance with a time difference between the actual shift operation time period and the target shift operation time period.