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Model based driveline control

A cars powertrain consists of everything that is needed for its propulsion. The components in the driveline that transfer the power from the engine to the driven wheels are not absolutely stiff, hence they will wind up due to the torque and act as torsion springs. If you suddenly demand a bigger torque by stepping on the accelerator pedal, a so called tip in manoeuvre, and that torque is acquired from the engine as quickly as possible, the driveline will not be able to transfer that fast torque change due to its weakness and as a result it will start to oscillate. These oscillations will be transferred to the driven wheels and make the car to accelerate jerkily which will be experienced as uncomfortable by the passengers. Furthermore, there is a backlash in the driveline that will make the weakness in the driveline even more excited than it should have been if the backlash did not existed. To avoid too big problems with these oscillations there is a control system that controls the demanded torque. This control system is today an open loop control system, i.e. a filtering of the demanded torque. As the cars computer power is increasing steadily there is an interest of investigating if it is possible to get a higher performance control system by using a more advanced, closed loop, model based control system. In this thesis such a control system is developed. First a model of the system is constructed; this model is used to design an observer that estimates the non measurable states in the driveline. The results show that this observer estimates these states fine on the basis of the available signals. The observer is the base for the driveline control system and simulations show that this control system is a considerable improvement compared to the control system used today.

Magnus Nordenborg


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