Shift control system for automatic transmission

A shift control system of an automatic transmission for setting a transmission torque capacity of each of first and second frictional engagement means to not less than a predetermined value at a transitional time of a shift which is executed by releasing said first frictional engagement means and applying said second frictional engagement means, comprising:

• tie-up detecting means for detecting a tie-up in which both said first frictional engagement means and said second frictional engagement means are given a predetermined or higher torque capacity to lower an output torque at said transitional shift time;
• means for learning and controlling the reduction of the apply pressure of said first frictional engagement means in accordance with the tie-up state detected by said tie-up detecting means;
• and
• means for inhibiting the setting of the gear stage, which is effected by applying said first frictional engagement means and releasing said second frictional engagement means, when the learning and control cannot be executed.

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 valve mechanism for lowering the oil pressure of said first frictional engagement means on the basis of the oil pressure of said second frictional engagement means;
• pressure regulating means for regulating the oil pressure to be fed to and drained from said first frictional engagement means;
• failure detecting means for detecting a failure of said pressure regulating means;
• and
• lowering means for lowering the oil pressure of said first frictional engagement means when the failure is detected.

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 a oil pressure to be fed to or drained from said first frictional engagement means;
• failure detecting means 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 said first and second frictional engagement means;
• and
• gear stage inhibiting means for inhibiting the setting of said predetermined gear stage when the failure is detected by said failure detection means,
• wherein said failure detecting means includes means for detecting the failure when a time period from an instant when a shift command is outputted to the instant when an inertial phase is started exceeds a predetermined value.