Control Algorithms for Superposition Steering Systems to Adapt and Improve Steering Characteristics

Active Front Steering (AFS) provides an electronically controlled superposition of an angle to the steering wheel angle. This additional degree of freedom enables a continuous and driving-situation dependent adaptation of the steering characteristics. Features like steering comfort, effort and steering dynamics are optimized and stabilizing steering interventions can be performed.

After the successful introduction of the AFS System together with the new BMW 5-series into the international market, ZF Lenksysteme focuses on a modular system concept with new and improved functionalities. Currently, the variable steering ratio (VSR) provides the most evident benefit for the driver. This function represents an adaptation of the static steering characteristics by adjusting the steering ratio between the steering wheel angle and an average road wheel angle to the driving situation as a function of the vehicle velocity. This paper describes new approaches that provide an improvement of the static and dynamic characteristics of the steering system