Patent ID: 7331899

Claim:
A method for controlling engagement and release of pressure actuated torque establishing friction elements during a coasting downshift of a multiple-ratio transmission in a hybrid electric vehicle powertrain having an engine, an electric motor and a battery, the motor being disposed in a power flow path between the engine and a power input element of the transmission as driving power is delivered to a transmission power output member, and an electronic controller responsive to powertrain operating variables for controlling actuating pressure for the friction elements by releasing actuating pressure for an off-going friction element in synchronism with increasing actuating pressure for an oncoming friction element during a coasting downshift event, the method comprising the steps of: commanding a torque level for the motor before a start of the coasting downshift, the torque level command being based on a desired negative regenerative braking torque; commanding an initial high pressure for a pressure actuator for the oncoming friction element to fill the actuator quickly; commanding a pressure for a pressure actuator for the off-going friction element to a level that is a function of transmission input torque; ramping down the pressure of the pressure actuator for the off-going friction element during a coasting downshift start mode prior to an inertia phase of the coasting downshift; controlling pressure of the actuator for the oncoming friction element using closed loop control during the inertia phase; and ramping up electric motor torque from a current negative regenerative torque level, the desired negative torque level being a calibrated level for each coasting downshift.