Patent ID: 6415213
Filing Date: 2002-07-02
Classification: F16H

Abstract:
A method of controlling on-coming and off-going pressures supplied to on-coming and off-going clutches in a vehicle automatic transmission to downshift the transmission from a current speed ratio to a target speed ratio, the transmission having an input shaft coupled to receive engine output torque, the method comprising the steps of:using an inverse dynamic model of the transmission to determine an off-going pressure sufficient to balance the engine output torque in the current speed ratio, and progressively reducing the off-going pressure to said determined pressure; once the off-going clutch begins to slip, using the inverse dynamic model of the transmission to estimate an off-going pressure for allowing the engine output torque to increase a speed of the input shaft toward a synchronous speed of the target speed ratio at a desired rate, and setting the off-going pressure in accordance with the estimated off-going pressure; determining an on-coming pressure for balancing the engine output torque in the target speed ratio, and engaging the on-coming clutch at the determined on-coming pressure when the input shaft speed nears said synchronous speed; controlling the on-coming and off-going pressures to maintain the input shaft speed at said synchronous speed; and raising the on-coming pressure and releasing the off-going pressure to complete the downshift after the input shaft speed has been maintained at said synchronous speed.