Model Based Powertrain Control - Damping of Oscillations in a Heavy Duty Vehicle
Torsional resonances in the vehicle powertrain are undesired phenomena in automotive vehicles, since they cause longitudinal oscillations in the vehicle, which affect the driveability in a negative way and cause mechanical wear. It is the damping of these torsional resonances that has been the goal for this research work. The thesis has an experimental focus on powertrain control, modelling and verification.
A two-inertia model of a heavy duty vehicle powertrain has been implemented in Matlab/Simulink and has been verified experimentally. Different model based linear controllers have been developed and validated both through simulations and experiments in a heavy duty vehicle. The aim with the controllers is to damp out the oscillations that occur in the powertrain during a tip-in and a tip-out (when the accelerator pedal is pressed and released). The controllers use the engine as an actuator to work in anti-phase with the powertrain oscillations.
The focus has been to develop a control system that takes the engine limitations like e.g.~the smoke limiter into consideration. To keep the control signal below the maximum available engine torque, a reference governor has been introduced in the control system. Another requirement on the control system has been to keep good response of the vehicle during the control.
Simulations show that it is possible to achieve a damped powertrain with a control signal that works within the limits of the engine and that gives good response of the vehicle. Also the experimental results show that the control system has a damping effect on the powertrain and that it is possible to achieve this result without loosing any response. This gives an indication that the suggested control method might be a feasible approach to reduce powertrain oscillations in a vehicle. More work is however needed to commercialize this idea. For example, the impact of backlash and model variations must be investigated and taken care of in a final control system.