Control strategy of a novel electric power steering system integrated with active front steering function

A novel electric power steering system (EPS) integrated with active front steering (AFS) is developed. It has functions of both AFS system and EPS system with two actuator units: the AFS actuator unit and the EPS actuator unit. The AFS actuator unit controls the displacement transfer behavior of the steering system, and improves the handling stability under adverse road conditions by varying the steering ratio directly related to the speed and road conditions. The EPS actuator unit controls the force transfer behavior of the steering system, and improves the steering portability and road feel of the vehicle. Based on a dynamic model, the mixed H₂/H_∞ control strategy of the EPS actuator and the active steering intervention control strategy of the AFS actuator are designed. The simulation indicates that the novel EPS system with the designed control strategies has obvious advantages in vehicle handling stability and the driver's road feel over the traditional EPS system, and extends the vehicle's steering performance.