Special System Functions: Initialization

Because of current statutory requirements, the dynamic steering system is designed in such a way that, despite the possibility for electro-mechanical adjustment, a permanent mechanical connection exists between the steering wheel and the steering pinion. Even when dynamic steering is off, it is possible to steer the wheels with the steering wheel (for example, when the vehicle is on a workshop hoist), Such a steering operation is executed without steering angle overlap by the dynamic steering system, that is, without implementing the variable characteristic curve. The next time the system starts, when the engine is started, the steering angle of the front wheels will no longer match the steering angle defined by the variable characteristic curve at the corresponding steering wheel angle. The task of the initialization routine now is to determine this deviation from the nominal value and to implement the necessary steering angle overlap in order to restore the correct steering angle at the front wheels. This process is indicated in the center display of the instrument cluster by flashing of the warning lamp and by the text "Initialization" when the engine starts. If the vehicle is set in motion during this initialization routine, the display remains active until the initialization procedure is complete. In this case, the initialization procedure takes place "in the background" and is virtually unnoticed by the driver. The initialization is implemented with the signals generated by the motor position sensor and the steering angle sensor. The steering angle sensor indicates to the control module the momentary position of the steering wheel. The motor position sensor signals the position of the hollow shaft, and therefore, the eccentricity of the bearing. The control module calculates the difference between the nominal and actual motor positions and makes the necessary correction by activating the motor. If this difference is greater than a steering wheel angle of 8°, the correction is made when the vehicle is stationary. If the vehicle is driven away immediately, the correction is aborted and substituted by a correction during the steering input. If minor deviations occur, a correction is generally made during the next driver steering input.