Simulation of Straight-Line Type Assist Characteristic of Electric Power-Assisted Steering

Electric Power-Assisted Steering (EPAS) is a new power steering technology that will define the future of vehicle steering. The assist of EPAS is the function of the steering wheel torque and vehicle velocity. The assist characteristic of EPAS is set by control software, which is one of the key issues of EPAS. The straight-line type assist characteristic has been used in some current EPAS products, but its influence on the steering maneuverability and road feel hasn't been explicitly studied in theory.

In this paper, the straight-line type assist characteristic is analyzed theoretically. Then a whole vehicle dynamic model used to study the straight-line type assist characteristic is built with ADAMS/Car and validated with DCF (Driver Control Files) mode of ADAMS/Car. Based on the whole vehicle dynamic model, the straight-line type assist characteristic's influence on the steering maneuverability and road feel is investigated. Based on the driver's request for the ideal relationship between steering wheel torque and vehicle velocity, the vehicle speed proportional coefficient of the assist characteristic can be determined by making steering wheel torque at different vehicle lateral acceleration agree with the request of the driver at a certain velocity. The target of this paper is analyzing the influence of the straight-line type assist characteristic on the steering maneuverability and road feel, and studying how to apply simulation method to determine the straight-line type assist characteristic of EPAS, which will direct and benefit the adjustment of the assist characteristic during the road test.