DSC Control Unit
DSC Control UnitThe DSC control unit regulates all DSC sub-functions.
E60 - Wheel speed sensor
Installation location
The 4 wheel speed sensors are each affixed to the respective wheel hub.
Construction
E60 - Wheel speed sensor
Installation location
The 4 wheel speed sensors are each affixed to the respective wheel hub.
Construction
The increment wheel assigned to the wheel speed sensor is integrated in the wheel bearing.
The housing of the wheel speed sensor contains 3 Hall sensors (elements) adjacent to each other.
The measuring procedure employing 3 Hall sensors allows the wheel speed sensor to recognise forwards and backwards travel.
How it works
The signal is converted entirely within the wheel speed sensor.
The signals from 2 of the Hall sensors (1 and 3) are used to generate a difference signal. The signal frequency and the air gap between the wheel speed sensor and increment wheel are derived from this difference signal. The time lag between the signal from the middle Hall sensor and the difference signal is used to identify forwards or backwards travel.
The additional information about the air gap and the direction of rotation is given by the pulse width of the current pulse.
When the vehicle is stationary a current pulse is generated approximately every 740 milliseconds contrasting with previous wheel speed sensors. This current pulse indicates the availability of the wheel speed sensor.
E60 - DSC sensor
Installation Location
The standard DSC sensor is underneath the driver's seat. For reasons of safety on vehicles with Active Front Steering a second DSC sensor is integrated along with the standard DSC sensor as a redundant sensor. The second DSC sensor is located underneath the front-passenger seat.
Construction
The DSC sensors are a combination of lateral acceleration sensor and yaw-rate sensor. The DSC sensor consists of:
- Housing cover
- Board with electronic evaluation unit for converting signals
- Sensor electronics:
The sensor electronics consists of 2 piezoelectric acceleration sensors. A spring-mounted weight is hung in the measuring cell of the acceleration sensor.
- Damper to prevent mechanical overstressing
- Housing with connector
Technically, the two DSC sensors are virtually identical. DSC sensor 2 has an extra terminating resistor. The two DSC sensors have different part numbers. In addition, the DSC sensors make use of a different identifier in the CAN bus. This excludes the possibility of confusing the DSC sensors.
How It Works
when the vehicle accelerates, the spring-mounted hanging weight is also accelerated. The force needed to achieve this is generated by mechanical tension in the piezoelectric material. This results in a shift in the electric charge. This charge shift is picked up by electrodes and processed as an electric signal. The yaw rate is derived from the difference between the two acceleration signals.
The second DSC sensor redundantly registers the signals for lateral acceleration and yaw rate. The fact that two DSC sensors are used means that plausibility can be monitored. The two DSC sensors are triggered (excited) by the DSC control unit every 10 milliseconds. Each time they are triggered, the two DSC sensors send their signals to the F-CAN.
E60 - Steering-angle sensor
Installation Location
The steering-angle sensor is integrated in the steering-column electronic circuitry. The steering-column electronic circuitry is part of the steering column switch cluster (SZL).
Construction
The steering-angle sensor is a potentiometer with 2 sliding contacts offset by 9O~. The use of 2 sliding contacts allows the direction of turn to be recognised.
How It Works
DSC needs the steering angle for its regulation function. The steering angles detected by the sliding contacts (2 voltage values) make up a complete turn of the steering wheel. Once the steering wheel has been turned through 36O~ the voltage values are repeated. The steering-angle sensor thus also counts the number of turns of the steering wheel.
The entire steering angle measured by the steering-angle sensor is made up of:
- Steering-angle sensor correction value
This correction value determines the straight-ahead position of the steering wheel. The correction
value is defined and stored when the steering-angle sensor is csljbrsted.
- Current messured steering sogle
- Number of turns of steering wheel
The steering angle including the number of turns of the steering wheel must be available when the ignition is switched ON. For this reason the steering column switch cluster (SZL) and with it the steering-angle sensor has permanent current via terminal 30. This allows steering movements to be registered even when terminal R is switched OFF.
Open circuits would cause the number of turns of the steering wheel stored in the steering-angle sensor to be lost To ensure that the steering-angle sensor remains functional even in the event of an open circuit the DSC control unit "learns" the steering angle via a plausibility check (initialisation). The DSC control unit computes the steering angle from the wheel speeds on the front axle. The plausibility check compares these signals with those from other sensors to recognise whether the vehicle is operating with an incorrectly calibrated steering-angle sensor.
If initialisation after setting oft up to a threshold speed of approx. 25 km/h is unsuccessful then:
- DSC is deactivated
- The DSC warning light comes on
- A fault entry is stored in the DSC control unit (not in the steering-angle sensor)
Note: steering-angle sensor failure
If the steering-angle sensor fails, ABS will remain active.