Shift control system for automatic transmission inhibits shift on failure dete ction

摘要

A shift control system of an automatic transmission for setting a predetermined gear stage by applying first frictional engagement means and releasing second frictional engagement means, comprising: a pressure regulating mechanism for regulating an oil pressure to be fed to or drained from the first frictional engagement means; a failure detector for detecting a failure of an apparatus to participate in the regulation and control of the oil pressure which is to be fed to or drained from at least one of the first and second frictional engagement means; and a gear stage inhibitor for inhibiting the setting of the predetermined gear stage if the failure is detected by the failure detector. The system preferably detects apparatus failure and/or abnormal lockup clutch operation and inhibits change from 1st to 2nd ratio, enforcing change from 1st to 3rd instead. The system preferably also increases a reduction of engine torque during shift if failure detection occurs. A system preventing "tie-up" (simultaneous engagement of the clutches/brakes for two ratios at once) is also claimed.