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Active front steering is starting to establish as steering technology for passenger cars that realizes a mechatronic superposition of an angle to the hand steering wheel angle that is prescribed by the driver. This contribution describes algorithms, used to ensure - along with others - the overall functional safety of the system (i.e. preventing hazardous behavior). A kinematic constraint, modelled as a dynamic system, is used to estimate the steering wheel angle. This estimated signal is compared with the measured signal. Using change detection algorithms typical failure patterns of the steering wheel sensor are detected quite easily. Sample results and measurements from a prototype vehicle are presented.

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.

This paper focuses on control strategies that are needed to stabilise a backing trailer and steer it into the desired direction. A model of the trailer and the car is used in order to calculate the desired steering wheel angle. An important constraint is that the driver should not be disturbed by the steering intervention. Measurements are done with a prototype car with an active front steering system. The results show that the drivers manage to fulfill the given driving task faster and with less steering wheel activity than without the assistant.

When developing new automotive systems a great deal of the development effort is devoted to ensure a sufficient functional safety of the system. A question that arises during early risk analyses of such a system is that of the controllability of possible system hazards. While this question is answered in early stages very often using worst-case risk graphs, the question comes back later in a much more precise way: in case of active steering systems component failures would produce a deviation between desired and actual road wheel position, the deviation can be measured in terms of amplitude and/or time. The central question is how much deviation can be controlled by the driver? Note, that there will always be a certain, even small, deviation between desired and actual road wheel position since the steering systems controller contains feedback control algorithms aiming at minimising the regulation error but not actually making it disappear totally.