Robust position control of a Steer-by-Wire rack actuator

Authors

C. Frohn, C. Kreis, B. Boßdorf-Zimmer - Volkswagen AG, R. Henze - TU Braunschweig

Summary

Steer-by-wire (SbW) systems have been the subject of research for several years. Nevertheless at the moment there are no globally available series vehicles without a mechanical back up system. This is partially due to the challenges for vehicle safety that arise by mechanically decoupling the steering wheel from the steering rack. Among those challenges is the requirement for the control loop of the steering rack to be proven permanently available. As a result a robust stable position controller needs to be developed.

Developing a robust stable position controller for a SbW rack actuator is especially challenging because of two aspects: first the controlled system is nonlinear and the nonlinear effects cannot be neglected. Second the plant itself is time varying in that regard that the operating point as well as the mechanical properties will change over time and will differ between the cars. In addition the controller cannot be too numerically complex as it has to be calculated by the steering rack control unit. Lastly the SbW system has to fulfill high performance requirements.
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