Model-based control of an automatic transmission power-on downshift

This invention relates to a shift control for an automatic transmission, and more particularly to a model-based clutch pressure control for carrying out a power-on downshift. An improved control for an automatic transmission power-on downshift, wherein a dynamic model of the transmission is used to schedule the on-coming and off-going clutch pressures based on the transmission input torque and a desired trajectory of the input shaft during the shift. The shift is initiated with the off-going clutch by using the dynamic model achieve consistent initiation of clutch slippage, and to conform the input speed to the desired trajectory. When the input speed nears a synchronization speed for the target speed ratio, the dynamic model is used to engage the on-coming clutch at a rate based on the input torque while maintaining the input speed in synchronism with the target speed ratio. As a result, the control responds appropriately to dynamic changes in input torque, the input speed more accurately tracks the desired trajectory, and the shifts are completed at or near synchronism. Additionally, scheduling the clutch pressures based on the dynamic model achieves more consistent shift feel and improved adaptability to different powertrain and vehicle-type configurations while reducing the number of calibrated parameters requiring adaptive correction.