Gearshift controlling system for vehicle automatic transmission

摘要

A gearshift controlling system for controlling a vehicle automatic transmission. In the system, a first alternative throttle opening degree is predetermined in case of failure of a throttle position sensor, and a second alternative throttle opening is similarly determined such that a gear ratio can be determined based on the detected vehicle speed and the second alternative engine load in a gear ratio decreasing or increasing direction. Either of the first alternative throttle opening degree or the second alternative throttle opening is selected and the gear ratio to be shifted to is determined in accordance with the predetermined gearshift schedule based on the detected vehicle speed and the selected alternative engine load, to output the gearshift command, thereby preventing unexpected gearshift to occur.