Steering Angle Sensor: Description and Operation

NOTE: Numbers in parentheses ( ) indicate a component or tool in the associated illustration.






DESIGN
Digital sensor with 9 light-emitting diodes (a) for photoelectric barrier measurement. The steering angle sensor consists of two microcomputers which form a unit with a signal measuring ring. 9 light-emitting diodes (a) are equi-spaced on the signal measuring ring. They are located in a photoelectric barrier channel which 8 apertures (b) of different lengths pass through. The photoelectric harriers are located in the upper section of the contact spiral (A45) and only form the complete functional unit of the optical steering angle sensor (N49) by assembling (clipping together) both components.

FUNCTION
In the center position of the steering the 8 apertures (b) assume a defined position relative to the 9 light-emitting diodes (a). This center position is recorded by the computer in the steering angle sensor. When the steering wheel is turned the position of the apertures changes relative to the light-emitting diodes (light/dark). A quite specific signal pattern for calculating the respective steering wheel position results due to the different length apertures and aperture spacings. Angle values are calculated with the aid of the signal patterns and converted into serial information for the control modules connected. The signals are recorded by light-emitting diodes and photoelectric barriers in 2.5° steps. The signal recording system is designed for a steering angle of ± 720° (4 steering wheel revolutions).

Voltage is supplied via terminal 30 so that the steering angle is also recorded after "ignition OFF*.

The steering angle sensor must be reinitialized after the voltage is interrupted (terminal 30). This is achieved by turning the steering wheel from stop to stop.