Road Torque Modeling for Electric Power Steering Systems

Abstract

The rack force transmitted to a rack bar through a tie-rod is regarded as a major external force to the electric power steering (EPS) system. However, since road torque generated between the tire and the road surface is transmitted to the rack bar under the influence of road wheels and various linkages and bushings, it is difficult to equalize the rack force and road torque. This paper proposes a road torque modeling method and identifies the characteristics of EPS systems, including road torque. To estimate the road torque acting on the tire, an EPS system model including road wheels is proposed. The proposed EPS system model and the road torque model in the vehicle driving situations are validated with vehicle experiment results. The experimental results show that the proposed road torque model represents the characteristics of road torque in both stop and driving conditions, and the newly proposed EPS system model expresses the characteristics of the actual system better than the conventional EPS system model in the stop state.