Method of shifting a transmission

摘要

A method of down-shifting a transmission avoids output shaft oscillations by briefly increasing the torque capacity of an off-going element at the end of the inertia phase. The torque capacity of the off-going element is then reduced to zero when the measured transmission speed ratio begins to decrease. The method is suitable for downshifts that involve multiple off-going elements and multiple on-coming elements such as a shift from tenth gear to sixth gear in a ten speed transmission.

主权项

1. A method of shifting a transmission comprising:
while operating at a first transmission speed ratio, commanding a sufficient torque capacity of a first offgoing element to prevent slip across the first offgoing element and commanding a zero torque capacity of a first oncoming element; during an inertia phase of a downshift from the first transmission speed ratio to a second transmission speed ratio, reducing the torque capacity of the first offgoing element such that slip occurs across the first offgoing element and a ratio of an input speed to an output speed increases; and in response to the ratio of the input speed to the output speed reaching the second transmission speed ratio, increasing the torque capacity of the first offgoing element to absorb excess energy that may excite driveline oscillations and increasing the torque capacity of the first oncoming element to establish the second transmission ratio.