ZF Torque Sensor

This sensor measures the torque applied by the driver at the steering wheel. Based on this, the control unit calculates the steering assistance for the motor. The torque sensor sits on the steering pinion (5). A pole wheel (9) is fitted on the input shaft (2)

which is connected to the steering pinion by means of the torsion bar (1).

The measuring range covered by the sensor is between +/- 8 and +/- 10 Nm.

Configuration of the torque sensor on the steering pinion:

1 Torsion bar,

2 Input shaft,

3 Sensor module,

4 Clock spring,

5 Steering pinion,

6 Plug,

7 Index magnet (optional),

8 Index sensor (optional),

9 Pole wheel

Steering Torque

If the steering torques are higher, a mechanical angle limiter prevents overload of the torsion bar. When the driver applies a torque on the steering wheel, the torsion bar is rotated as is the magnet relative to the sensor. The sensor consists of magnetoresistive elements which change their resistance when the field direction changes. In the process, the voltage follows a sine and cosine curve when the magnet is rotated. The direct rotation angle of the torsion bar is then calculated by means of an inverse tangent function.

The high safety demands on electric steering systems require detection of all faults occurring on the sensor and creation of a safe condition of the steering system. The sensor data are transmitted to the electronic control unit via a very rugged digital interface. Optionally, the torque sensor can also accommodate an index magnet (7) and an index sensor (8). The index sensor delivers a signal to the ECU for each full steering wheel turn. In combination with the data from the rotor position sensor and the wheel speeds, the electronic control unit is able to calculate the steering angle with a resolution < 0.05 degrees