Double transition downshift control for an automatic transmission

Claim 1

In an automatic transmission including input and output shafts coupled through first and second interconnected gearsets, each gearset being adapted to provide multiple speed ratios, and various selectively engageable torque transmitting devices adapted to change speed ratios provided by said first and second gearsets to thereby establish multiple overall speed ratios between said input and output shafts, a downshift from a second speed ratio to a first speed ratio being carried out by releasing an off-going torque transmitting device to increase the speed ratio provided by said first gearset while applying an on-coming torque transmitting device to decrease the speed ratio provided by said second gearset, thereby achieving an increase in the overall speed ratio between said input and output shafts, a method of operation for coordinating such release and apply, comprising the steps of: initiating the apply of said on-coming torque transmitting device at a predefined rate to effect an initial decrease in said overall speed ratio; releasing said off-going torque transmitting device when a specified decrease in the overall speed ratio is detected to thereby achieve the increase in said overall speed ratio; detecting a condition of improper torque capacity of said on-coming torque transmitting device based on improper excursions of said overall speed ratio during such apply and release; and adjusting the rate of apply of said on-coming torque transmitting device in subsequent downshifting in response to such detection to thereby avoid said condition of improper capacity during such subsequent downshifts.