Electronic control system for automatic transmission

Abstract

An upshift gear ratio change is made in an automatic transmission by monitoring the driveline torque and operating a closed loop control system in response to that torque to in turn control the torque to obtain a desired shift. Shift quality is optimized, while torque transients are minimized, by initially closing the loop at the end of the static phase of the upshift when the driveline torque drops to its minimum turnaround point, the torque thereafter being controlled such that it increases from the turnaround point at a specified rate and in accordance with a predetermined first ramp command. As the increasing driveline torque then reaches a prescribed reset level, at an early stage in the dynamic phase, the closed loop control system is released and reset in order to control the torque in accordance with a second ramp command, the second ramp, that the torque is made to follow, thereby starting at a higher level than the first ramp. By initially closing the loop at the relatively low turnaround point undesired torque transients are precluded, and then by resetting the loop shortly thereafter, so that the torque ramp starts at a relatively high level, shift duration is maintained at a desired length and shift quality is enhanced. As a result, each time there is an upshift in the transmission there will be a smooth transition from the original engine speed to the new engine speed.