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Active Front Steering (AFS) provides an electronically controlled superposition of an active angle to the steering wheel angle. This steering system developed by ZF Lenksysteme and BMW AG enables driver dependent as well as automatic steering interventions. The permanent mechanical connection between steering wheel and road wheels remains. Since the AFS system was recently introduced together with the new BMW 5 series, the most of the investigations of steering systems do not include the dynamic behavior of such mechatronic actuators. On the other hand, these kind of models are required to design control algorithms and model based monitoring functions that provide the desired accuracy and real-time algorithms that run on a series electronical control unit. This paper summarizes a validated mathematical model of the AFS actuator including 8 rigid bodies, 46 constraint relations and a synchronus motor.

Active Front Steering (AFS) is a newly developed technology for passenger cars that realises an electronically controlled superposition of an angle to the hand steering wheel angle that is prescribed by the driver. It enables functionalities such as (vehicle velocity) variable steering ratio, steering lead, as well as it provides an interface to support vehicle dynamics control systems. This paper focuses on application dependent safety functions and steering assistance functions. All functions described are model based, their accuracy is demonstrated.

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.