Handling Enhancement Due to an Automotive Variable Ratio Electric Power Steering System Using Model Reference Robust Tracking Control

An automotive steering system that can vary the overall steering ratio as a function of the vehicle's forward speed has the potential to enhance the lateral handling qualities of the vehicle for different driving situations. A “quicker” steering ratio at low speeds can help provide greater ease in maneuvering the automobile. A “slower” steering ratio at higher speeds can alleviate the “dartiness” experienced by some vehicles with a fixed overall steering ratio. The concept of a vehicle's “sensitivity” to steering inputs from the driver is exploited to provide the basis for developing how the overall steering ratio is customized as a function of vehicle speed.

This paper compares the on-center handling performance of an automotive power steering system that is capable of varying the overall steering ratio versus vehicle speed against that of a traditional manual steering system with a fixed overall steering ratio. Dynamic simulation results demonstrate that the variable ratio steering system is capable of improving the on-center handling performance of the vehicle based on industry standard performance measurements.