Abstract
GM developed an experimental "integrated" friction launch transmission based on a 6-speed RWD automatic transmission architecture. This experimental transmission uses an existing reaction clutch to idle and launch the vehicle, rather than a torque converter or standalone input or output clutch.
During vehicle launch, lockup shock can be minimized by increasing the gain of launch clutch torque with respect to slip speed ("slip gain") near lockup. However, high slip gain, combined with actuator / sensor delays and a lightly damped powertrain resonant mode, can easily cause instability.
Smooth, stable lockup control was achieved using pole-zero cancellation, in the form of a notch filter near the powertrain resonant frequency. This approach is robust to both variable gain and transport delay, and allowed a significant increase in control bandwidth. Vehicle data show that consistently smooth launches can be obtained with this control system. The compensation approach described here should also be applicable to other types of friction launch transmission.
Keywords:launch, transmission, shudder, control, clutch