Introduction / Status: Introduction

The steering angle sensor is integrated with the contact roller for the SRS-system and is installed on the steering wheel lever module. The function of the sensor is to sense the driver's steering wheel movements. The steering angle sensor consists of a steel disc with two hole-patterned grooves illuminated by several installed pairs of light-emitting diodes and phototransistors. The disc is mounted so that it follows the steering column's movements and then the phototransistors can sense the disc's movement. One pair of light-emitting diodes (IY, IX) reads an index groove with a unique groove pattern. The other pair (A, B) reads a groove with a repeated pattern around the disc (dark, light, dark, light, etc. The grooves' resolution is 1.5 degrees. Since the steering wheel can be turned several revolutions an additional two groups of light-emitting diodes must be used (R1, R2, R3, R4) to read off which steering wheel revolution one is at (normal <3). During the movement the SAS control module (Steering Angle Sensor) processes all information about the steering wheel's absolute position. In connection with start of the vehicle one has to turn the steering wheel a small angle, approx. 5 degrees in any direction to enable the control module to determine the steering wheel's position. This means that the wheel's angle and direction can be determined in relation to the driving direction. The information is used in the DSTC-system (together with other information about the vehicle's driving situation) to decide if the vehicle is driven stable and safe or is in a skid situation.