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modeling, control & safety of active steering systems

Active front steering 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. The driver controls the vehicles course via the hand steering wheel. Active front steering actuates an additional angleusing its electric motor. Both angles result in an pinion angle down at the steering rack. The resulting (average) road wheel angle can then be calculated via the pinion angle and a static nonlinearity that accounts for the relation between pinion angle and rack displacement as well as for the steering geometry. Having this basic framework at hand, one can start looking at functions that manipulate the motor angle in order to e.g. achieve a desired overall steering ratio that depends on vehicle speed and pinion angle. This desired motor angle will then be passed to the motor's feedback control algorithm. Details on the system setup, its functionality and components as well as connection to other chassis systems have been published in Some more details on the mathematical modelling an parameter estimation are given in A great deal of functionality that is housed in the electronic control unit is devoted to ensure the overall functional safety of the system. Some general information and overview on system safety are published in Developing such a safety related system properly asks for a safety related development process along with traceble risk assessment from vehicle to component level. This has been described in The technical safety concept demands diagnoses of a certain level for safety related components. E.g., beyond usual sensor diagnosis such as analogue signal monitoring, test patterns etc (all of them described in recognised safety standards), more advanced methods are needed in order to detect sensor failures of certain types or in certain situations. This can be handeled using change/fault detection algorithms described in
Last update: Mon May 7 20:57:36 2007 by Wolfgang Reinelt . Legal Disclaimer