METHOD OF SHIFTING A TRANSMISSION

摘要

A method of controlling a multiple step downshift is disclosed. Two offgoing shift elements are released and two oncoming shift elements are engaged to complete the downshift. During a first phase of the downshift, one of the offgoing shift elements controls the rate of increase of input shaft speed. During a second phase of the downshift, one of the oncoming shift elements controls the rate of increase of the input shaft speed. The method computes target torque capacities such that output torque and input shaft acceleration are continuous during the transition between phases. Furthermore, the method computes target torque capacities such that both oncoming clutches reach zero relative speed simultaneously as the input shaft reaches the final speed ratio.

主权项

1. A method of operating a transmission having first, second, third, and fourth shift elements, the method comprising:
initiating a downshift from a first transmission speed ratio in which the first and second shift elements are engaged and the third and fourth shift elements are disengaged to a second transmission speed ratio in which the first and second shift elements are disengaged and the third and fourth shift elements are engaged; during a first phase of the downshift, controlling an input shaft speed by modulating a torque capacity of the first shift element; and during a subsequent second phase of the downshift, controlling the input shaft speed by modulating a torque capacity of the third shift element.