Integrated sensor system
The sensors that were previously accommodated separately in the DSC sensor are now installed in the ICM control unit.
The ICM control unit uses these sensors to calculate variables that provide key information on the vehicle's dynamic state:
- Longitudinal acceleration and pitch of the vehicle in the longitudinal direction
- Lateral acceleration and pitch of the vehicle in the lateral direction
- Yaw rate.
| Index | Explanation |
|---|---|
| 1 | Yaw rate sensor |
| 2 | Second redundant yaw rate sensor |
| 3 | Longitudinal and lateral acceleration sensor |
| 4 | Second redundant lateral acceleration sensor |
All sensors integrated into the ICM control unit are known as micromechanical sensors. By applying this principle, the dimensions of these sensors can be reduced to the extent that they can be accommodated in housings that are similar in size to microprocessor housings. The sensors are of course designed on the basis of prevailing stresses in the vehicle (thermal, mechanical). However, when servicing the vehicle, the ICM control unit must be handled with the same degree of care as the familiar DSC sensor.
The longitudinal and lateral acceleration sensors operate according to the capacitive principle. They consist of two electrodes, that mesh in a comb-like form. One of the electrodes has a unidirectional moving bearing which means that if a force acts on the sensor, the electrode is displaced. This changes the gap between the two electrodes and in turn changes the capacitance which is calculated back to the size of the force applied by means of evaluating circuits.
Instead of recording the acceleration directly, the sensors record it indirectly by measuring the force on the sensor element. The force applied may have several causes and the sensor cannot differentiate between these:
- Inclination of the vehicle or road (e. g. gradient accelerating force)
- Change in speed (drive or braking force)
- Cornering (centrifugal force).
| Index | Explanation |
|---|---|
| F1 | Motive force |
| F2 | Gradient accelerating force |
| Inclination of road |
In the graphic two longitudinal forces are shown acting on the vehicle: a motive force and a gradient accelerating force. These forces are produced due to the inclination of the road. As a result, a force acts on the vehicle and can be calculated as follows:
Fresulting = F1 - F2
Only the resulting force can be measured by the sensor. The measured force is processed in the control unit. The change in road speed is taken into account.
The actual acceleration of the vehicle and the gradient of the road are the only calculation results provided.
A similar calculating process is used for the lateral direction. The calculation results produced in this case are the lateral tilt and lateral acceleration of the vehicle.
The sensor that determines the yaw rate also employs the principle of force measurement, a principle also used by the acceleration sensors. The yaw rate sensor measures the force that acts on a sensor element oscillating across the direction of rotation.
The sensor signals are initially referenced to the sensor housing. However, in order to be useful to the dynamic driving systems, these variables must be referenced to the vehicle coordinate system. The ICM control unit performs the necessary conversion.
A synchronization process is carried out when the ICM control unit is started up during which corresponding correction values are determined and saved.
- the ICM control unit has been replaced or
- if requested by the test schedule in the diagnostic system due to a fault code memory entry.
The calibration must be performed with the vehicle standing on a level surface in the longitudinal and lateral direction. Terminal 15 must also be switched on.