A Stability Compensator Design Method to Preserve the Intended Steering Feel of Electric Power Steering Systems

Abstract: Speed-sensitive steering assistance is integral to the functionality of electric power steering (EPS) systems. While increasing assistance gain can enhance steering ease, it often compromises system stability, leading to steering oscillations that reduce driving comfort and pose significant safety risks. Consequently, ensuring stability remains a critical priority in EPS design. Despite this, existing research on stability compensators for speed-sensitive steering assistance has predominantly focused on achieving system stability, with limited attention to the effect of the compensator on steering feel. In this study, a novel approach to the design of stability compensators in EPS is presented, which aims to maintain system stability while mitigating the disturbance to steering feel. A dynamic model of the EPS system is first constructed, accounting for system inertia and viscous damping. Parameters for this model are identified through analysis of vehicle frequency sweep tests, and model accuracy is verified by comparing simulated frequency responses with experimental data. Using this validated model, sufficient conditions for system stability are derived, and the impact of the stability compensator on steering feel is analyzed. Subsequently, design objectives for the stability compensator are formulated, and optimization algorithms are employed to fine-tune compensator parameters. The stability of the system is then assessed across the primary vehicle speed range. Finally, comprehensive vehicle steering tests are conducted under various operational conditions. Experimental results demonstrate that the proposed stability compensator effectively stabilizes speed-sensitive steering assistance while preserving a favorable steering feel. The design methodology presented herein provides guidance for developing speed-sensitive steering assistance functions in practical vehicle applications. Keywords: Electric power steering (EPS) system, stability compensator, steering feel, optimization algorithm, vehicle test