Downshift control device for automatic transmission

Abstract

A downshift control device for an automatic transmission is provided in which the transmission is shifted down by releasing an oil pressure from a first engaging element that has been engaged while applying an oil pressure to a second engaging element that has been released. This downshift control device determines whether a downshift command is generated to shift down the transmission while an accelerator pedal is being depressed, and detects a gear ratio that changes during the pedal-depressed downshift control. First control actuator controls the back pressure of a first accumulator provided in an oil path leading to the first engaging element, and second control actuator controls back pressure of a second accumulator provided in an oil path leading to the second engaging element. The present control device outputs to the first control actuator a command to increase the back pressure in a later period of shifting that starts when the detected gear ratio reaches a first predetermined gear ratio, and a command to reduce the back pressure in a terminal period of shifting that follows the later period of shifting. The control device also outputs to the second control actuator a command to reduce the back pressure until when the detected gear ratio reaches a second predetermined gear ratio that is larger than the first predetermined gear ratio and is obtained just before completion of shifting, and a command to increase the back pressure after a point of time when the detected gear ratio reaches the second predetermined gear ratio.