A growing number of vehicles are equipped with systems that require steering-angle information. This sensor was developed to serve the market demand for cost effective and modular steering-angle sensors for present and future requirements.
sensor concepts for upper/premium or compact/small vehicles
by many driving safety and driver assistance systems
The steering-angle sensor is based on Giant Magnetoresistance technology (GMR element) and provides an absolute steering-angle value over the complete steering-angle range (multi-turn sensor). A unique feature of this steering-angle sensor is the output of the correct angle within the measurement range directly after ignition-on. Movement of the steering wheel or other measures for initialization of the sensor (True Power-on) is not required even after disconnection and re-establishment of the power supply.
No standby current is necessary. The steering angle and steering-angle velocity is made available via CAN interface. Sensor-internal plausibility tests and special self-diagnostic functions allow the use of this sensor in safety systems. The sensor concept also allows the integration of a second microprocessor for safety-related applications.
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.
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