Automatic transmission control system

摘要

An automatic transmissions control system varies times to start a shift to securing a good response in engagement pressure for an engagement-side frictional element as well as suppressing occurrence of hydraulic pressure vibrations at low temperatures. The control system has an engagement pressure at-low-temperature regulation section that selectively controls at least one of the first and second engagement-pressure regulator valves, when the oil temperature is detected to be lower than a predetermined oil temperature and the shift condition is determined to exist requiring a shift operation such that the first engagement-pressure regulator valve provides a maximum hydraulic pressure to engage the first frictional element to start a shift with the maximum hydraulic pressure being continuously provided until the shift ends, and/or the second engagement-pressure regulator valve provides a minimum hydraulic pressure to obtain complete disengagement of the second frictional element to start a downshift as the shift operation.