Method of controlling gear change in an automatic transmission

In an automatic transmission 16, clutch-to-clutch closed throttle downshifting is controlled by filling the on-coming clutch C1-C5 at a maximum pressure command for a set period while commanding the off-going clutch pressure to a low value and exhausting the off-going clutch C1-C5 before the end of the fill period. At the end of the fill period the on-coming pressure is set to an initial value and then ramped up until turbine speed Nt is pulled up due to off-going clutch slippage. Then a closed-loop profile control period starts wherein slip of the on-coming clutch C1-C5 is measured and controlled on the basis of a slip profile. When synchronization of the on-coming clutch is detected, maximum pressure is commanded. If the throttle is opened during the downshift, the algorithm reverts to a powered downshift algorithm if the off-going clutch still has pressure or to an open-loop ramp control of the on-coming clutch if the off-going clutch has been exhausted.