Active Front Steering (Part 1): Mathematical Modeling and Parameter Estimation

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.