there is proposed a practical approach to a shift , in an automatic transmission , in which a release element is released and an apply element is engaged . the release element is released or vented at an appropriate timing after development of torque by the apply element but before initiation of inertia phase . specifically , the release element is released when transmission output torque reaches a value calculated out of gear ratio after shift , transmission input torque and transmission input acceleration . if desired , without relying on measurement of output torque , the release element may be released when transmission output acceleration , namely , vehicle acceleration , reaches a value which may be fixed or accelerator position dependent .