EPS control design method for steering mechanism characteristic compensation to reduce the efforts required for handling

Abstract

This paper proposes the steering characteristic compensation functions to adapt the driving situations by electric power steering (EPS). The desired compensatory handling characteristics are defined depending on the compensatory handling situations. Therefore, compensatory handling situations are divided into on center region, off center region and outside of off center region and discussed the influence of steering characteristic. In on center area, stick slip phenomenon is caused by combination of steering friction and high hand and arm system compliance with relaxed muscle condition. For this problem, torsion bar damping control is proposed and its effectiveness is demonstrated by simulation. In off center region, both steering feedback and low steering effort which are normally considered as trade-off are required. To solve this problem, structural damping which characteristic is Coulomb's friction increasing according to self-aligning torque is effective. Thus, structural damping compensation function is proposed by applying disturbance observer design technique and its feasibility is demonstrated by experiments. In outside of off center region, it is showed that the power assist characteristic function design contributes the driver recognition of tire grip condition by letting the driver estimate future torque based on linear tire characteristic.