Improving vehicle dynamics by active rear wheel steering systems

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Improving vehicle dynamics by active rear wheel steering systems

Kreutz, Marlene / Horn, Martin / Zhetner, Josef

In this article we have outlined two approaches to the control of an active rear wheel steering system. An essential prerequisite for a successful application of the model based concept is an accurate parameterisation of the single track model. This fact is among others due to the required specification of the reference yaw rate r_ref. In the present case, the proposed control strategy proved to be very efficient in the mu-split braking situation. A drawback of the concept, however, is that the adaption to different car types requires considerable effort. The second approach that is based on a mass-spring-damper structure overcomes the mentioned drawbacks. In addition, it permits intuitive controller tuning and thus provides portability to different vehicle types. In contrast to dynamical manoeuvres (e.g. lane changes) the handling of the vehicle in mu-split braking situations cannot be improved drastically. To achieve similar results as the model based control system, additional measures have to be taken. During mu-split braking situations, which can be detected from online measurements, the mass-spring-damper system has to be replaced by a standard proportional-integral controller. Considering the driving comfort, the 'straight line driving' behaviour of the vehicle plays a major role. Due to its integral part, the model based controller shows undesirable control activity, e.g. forced by bumpy roads. In contrast, the mass-spring-damper structure exhibits satisfactory 'straight line' performance. Using springs and dampers with nonlinear characteristics the straight line driving behaviour can even be improved.