Measuring principle of the steering-angle sensor
The steering-angle sensor is fixed onto the steering shaft, where the hub gear wheel of the sensor transmits the rotary movement of the shaft to two measuring gear wheels. In each measuring gear wheel a magnet is mounted, whose field changes its direction in accordance with the rotational movement. Below each magnet, a GMR sensor element is located to detect the angle position of the magnet above. The analog values of the GMR elements are converted into digital information directly on the circuit, which is then sent to the microprocessor via serial interface.
The measuring gears have different numbers of teeth and therefore change their turning position at different speeds. By means of mathematic functions, it is possible to determine the absolute steering-wheel angle from the position of the measuring gears. In addition, this function enables error correction and a plausibility test of individual signals. This measuring principle enables the measurement of the complete angle range of several steering-wheel turns without the use of a rotation counter.