Design of a Torque Control Strategy for Enhanced Comfort in Heavy Trucks

Sammanfattning: Heavy trucks vehicles by design often suffer from issues causing driver discomfort. That discomfort is here considered caused by oscillations in the driveline, which are affecting the driver. The driveline oscillations – sometimes referred to as shunt and shuffle - exist because of the sheer amount of power in a heavy truck engine, combined with a driveline where the components are relatively weak. If this engine power is simply output to the driveline without control, the driveline will twist and bend, causing oscillations. The purpose of this work is to investigate how engine torque can be controlled when large torque changes are requested. The specific situation of interest is when the driver fully depresses and releases the accelerator pedal, referred to as a tip-in and tip-out. The goal is to device a strategy that in this situation prevents any driveline oscillations and thus improves the driving comfort. What is presented is an investigation of some different strategies for applying torque and what seems achievable, using optimal control. This investigation then leads to a suggested alternative to today's strategy of applying torque. The suggested strategy is implemented in the ECU and tried in different vehicles. This first attempt at an implementation proves itself by reaching the target (maximum) torque in the same time as the conventional strategy, indicating no reduced performance. In several cases, large improvements can even be seen. Even while reaching the target level faster, the strategy manages to reduce the oscillations in the driveline. The goal of this work can therefore be considered achieved. While the suggested strategy works well in many cases, much work is still required to get it fully functional. New problems have been posed, regarding the subjective notion of how a driver actually wants a tip-in to feel. This might then lead the following research in completely different directions. Seen from a bigger perspective, the main result of this thesis is the fact that only with little effort in simple ways, great gains can be achieved.