Matching strategy of electric power steering assistant characters based on the vehicle inherent road feel

Abstract

Matching the assistant characters of an electric power steering (EPS) system so that the vehicle achieves a high performance is one of the key technologies in EPS design. A study on the matching strategy of EPS assistant characters is conducive to obtaining a good ‘vehicle performance’ earlier in the design process. This paper describes a method for designing the assistant characters of an EPS system based on the vehicle’s inherent ‘road feel’ denoted here as the steering torque gradient at a 0 g or 0.1 g lateral acceleration under the condition that the steering system is not a power-assisted system. With the aim of obtaining the vehicle’s inherent road feel, the relations between the steering resistant torque and the vehicle’s travel states are analysed on the basis of a two-wheel vehicle model with a uniform normal tyre force distribution in steady state circle cornering. It is found that the vehicle’s inherent road feel decreases with increasing speed especially in the low-speed regions. The matching strategy of EPS assistant characters based on the vehicle’s inherent road feel is presented and illustrated by designing the assistant characters of a sample EPS system utilized in a passenger car. It is found that the EPS system designed by this strategy can supply a good steering feel to the driver.