Steering Angle Sensor: Description and Operation

NOTE: The steering sensor consists of a torque sensor, an interface.








TORQUE SENSOR
The torque sensor converts steering torque input and its direction to voltage signals, in conjunction with the interface. A torsional force caused by steering operation is converted to an axial movement of a slider core. A variable differential transformer is installed around the slider core. Within the transformer are three coils, a primary coil on the inside, and two secondary coils, one for right turns and one for led turns. Alternating current is passed through the primary coil when the system is energized. The amount of mutual induction from the primary coil to the secondary coils changes depending on the position of the slider coil. The input shaft and the slider are one piece. Rotation of the shaft moves the slider in a circular direction. The pinion is turned via the torsion bar. The slider core is installed on the pinion shaft on grooves, and turns with the pinion shaft. When there is little resistance, the input shaft torsion bar, pinion shaft, and the slider core turn together to the same angle. The slider core does not move up/down. When there is resistance on the input shaft (hard to steer situation), and the slider pin is turned at an angle by the steering wheel, the torsion bar is twisted due to the resistance. Accordingly, the pinion shaft turns at a smaller angle. The difference in the turning angles changes the position of the slider pin in the groove, forcing the slider core upward or downward, depending on the direction of the direction of the turn.





INTERFACE CIRCUIT
The interface circuit is housed inside the steering gearbox near the pinion. It rectifies and amplifies the signals from the torque sensor, and transmits the steering signals to the EPS control unit.