This paper deals with the mathematical modelingand the nonlinear control of an electrohydraulic closed-center power-steering system. The system under consideration is characterized by its high energetic efficiency at a full electric power-steering functionality. Based on a nonlinear mathematical model of the system, a flatness-based controller for the servo actuator is designed. Afterwards, an interpretation of the overall steering control system as a mechanical impedance matching problem yields a controller with good performance and robust behavior. Finally, measurement results on a test stand and in a test car show the usefulness of the proposed control approach.
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