Shift control device for automatic transmission

A shift control device for an automatic transmission capable of automatically shifting to a desired gear position by selectively engaging a plurality of friction elements via working-fluid pressure, and of switching to a drive-downshift forcible termination control when a time rate of change in transmission input speed is reduced to below a threshold value owing to a drop in transmission input torque during drive downshift from a higher gear position to a lower gear position with an accelerator pedal depressed, said shift control device comprising:

• (a) a drive-downshift control determining section that determines whether the transmission is in a drive downshift control;
• (b) an inertia phase control determining section that determines whether the transmission is in an inertia phase control according to which a transmission input speed is rising to an after-shifting synchronous speed;
• (c) an arithmetic-calculation section that calculates a time rate of change (ΔNt) in transmission input speed (Nt);
• (d) a first comparison section that compares the time rate of change (ΔNt) in transmission input speed to a first predetermined threshold value (ΔNtS);
• (e) an estimation section that estimates a value equivalent to the transmission input torque (Tt);
• (f) a second comparison section that compares the value equivalent to the transmission input torque (Tt) to a second predetermined threshold value (TtS);
• and
• (g) a drive-downshift forcible termination control section that executes the drive-downshift forcible termination control only when the time rate of change (ΔNt) in transmission input speed is reduced to below the first predetermined threshold value (ΔNtS) and the value equivalent to the transmission input torque (Tt) is reduced to below the second predetermined threshold value (TtS), to forcibly terminate the drive downshift.