An automatic transmission ratio shift control system and method for a
powertrain having an engine and multiple-ratio gearing controlled by
friction elements actuated by hydraulic pressure, an electronic
controller for establishing torque transitions among the friction
elements as the gear ratio changes, the engine speed being controlled by
an electronic throttle control. The strategy employs an electronic
throttle and closed loop engine speed control and uses fuel and air as an
energy source to increase engine speed during a power-off downshift. The
engine speed is boosted to a level close to the synchronous speed in
conjunction with release of the off-going friction element. The on-coming
friction element is then applied as the engine speed approaches a desired
speed. The engine speed increase is timed to lead an increase in torque
converter speed.