Steering Angle Sensor: Description and Operation

Cumulative steering angle sensor: BMW 1, 3, 5, 6-series

Installation location:
Vehicles equipped with 2ng generation Active steering have a cumulative steering angle sensor. The cumulative steering angle sensor is flange-mounted to the output end of the steering gear/box.






The illustration shows the BMW 3-Series






Note:
No cumulative steering angle sensor from X5. The 3rd generation Active Steering no longer has a cumulative steering angle sensor. Further model series to follow.

Construction:
The cumulative steering angle sensor consists of a magnetoresistive element and a permanent magnet. The permanent magnet is mounted on the end of the steering pinion.

The cumulative steering angle sensor is connected to the AL control unit and the DSC control unit by the F-CAN (chassis CAN = sub-bus of the PT-CAN). The angles measured by the cumulative steering angle sensor are signalized by the AL control unit. The DSC control unit uses calculated values delivered by the AL control unit through the F-CAN. Moreover, the DSC sensors and the steering angle sensor in the steering column switch cluster (SZL) are also connected to the F-CAN.






The illustration shows the F-CAN in the BMW 5-series from 09/2005






How the cumulative steering angle sensor works:
The cumulative steering angle sensor measures the angle of rotation of the steering pinion. The angle measured at the steering pinion is the cumulative steering angle (total steering angle consisting of:

- Steering angle, applied at the steering wheel.

- Steering angle, applied at the electronic servomotor at the planetary gearbox with override function

The cumulative steering angle sensor has a measuring range of 180°. The half turns are counted in the AL control unit and in the DSC control unit. The signal from the cumulative steering angle sensor is sent on the F-CAN (every 10 milliseconds). This signal is received by the AL control unit and the DSC control unit broadcasts the cumulative steering angle to the other bus nodes on the PT-CAN. The cumulative steering angle is the definitive signal for all the control units that need the steering angle sensor signal.

The steering angle sensor is discontinued from the E70.

The Active Steering control unit computes a "virtual" cumulative steering angle. This virtual sensor supplies the same information as the cumulative steering angle sensor. The virtual cumulative steering angle sensor describes the exact position of the steering rack. Cumulative steering angle 0° = exact middle of the steering rack.

The control unit Active Steering derives from the cumulative steering angle from the following signals:

- Steering angle sensor signal

- The motor-position sensor registers the position of the electric servo motor.

Note:
Commissioning if a signal is missing.
If the signal from the motor-position sensor is lost, the position of the steering rack is unknown and must be recalibrated. For this reason, Active steering must be commissioned as new.