Adaptive clutch control of a closed-throttle downshift

A clutch control method for downshifting a vehicle automatic transmission to a target speed ratio, the transmission having an input shaft coupled to receive closed-throttle output torque from an internal combustion engine during a period of vehicle deceleration, and an off-going clutch that is released when the input shaft is below an idle speed of the engine, allowing the closed-throttle output torque to raise the input speed to a synchronous speed of the target speed ratio, and an on-coming clutch that is engaged to complete the shift, the method comprising the steps of:

• carrying out a primary clutch control by:
• (1) filling the on-coming clutch for a fill period in preparation for engagement, (2) supplying a maintenance pressure to the on-coming clutch to maintain it in readiness for engagement, and (3) raising the pressure supplied to the on-coming clutch by an amount designed to maintain the input speed in coincidence with the synchronous speed once the input speed reaches the synchronous speed;
• during the primary clutch control:
• (1) computing a transmission shaft jerk, (2) comparing the computed jerk to a threshold, and (3) indicating an over-fill or an over-pressure condition if the computed jerk exceeds the threshold;
• carrying out a contingent clutch control in response to a detected inability of the primary clutch control to maintain the input speed in coincidence with the synchronous speed, by controlling the pressure supplied to the on-coming clutch to re-establish coincidence between the input speed and the synchronous speed;
• determining a measure of an effort required by the contingent clutch control to re-establish coincidence between the input speed and the synchronous speed;
• engaging the on-coming clutch to complete the shift;
• and
• upon completion of the shift, adaptively increasing one of the fill period and the maintenance pressure if the measure of the effort required by the contingent control exceeds a first threshold level, adaptively decreasing the fill period for a subsequent shift if the over-fill condition is indicated, and adaptively decreasing the maintenance pressure of a subsequent shift if the over-pressure condition is indicated.

A clutch control method for downshifting a vehicle automatic transmission to a target speed ratio, the transmission having an input shaft coupled to receive closed-throttle output torque from an internal combustion engine during a period of vehicle deceleration, and an off-going clutch that is released when the input shaft is below an idle speed of the engine, allowing the closed-throttle output torque to raise the input speed to a synchronous speed of the target speed ratio, and an on-coming clutch that is engaged to complete the shift, the method comprising the steps of:

• carrying out a primary clutch control by:
• (1) filling the on-coming clutch for a fill period in preparation for engagement, (2) supplying a maintenance pressure to the on-coming clutch to maintain it in readiness for engagement, and (3) when the input speed reaches the synchronous speed, raising the pressure supplied to the on-coming clutch by an amount designed to maintain the input speed in coincidence with the synchronous speed;
• carrying out a contingent clutch control in response to a detected inability of the primary clutch control to maintain the input speed in coincidence with the synchronous speed, by controlling the pressure supplied to the on-coming clutch to re-establish coincidence between the input speed and the synchronous speed;
• determining a measure of an effort required by the contingent clutch control to re-establish coincidence between the input speed and the synchronous speed;
• and
• upon completion of the shift, adaptively increasing one of the fill period and the maintenance pressure if the measure of the effort required by the contingent control exceeds a first threshold level.