BMW 7 Series: 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.

Fig. 40: Identifying Yaw Rate Sensor, Longitudinal And Lateral Acceleration Sensor And Second Redundant Yaw Rate Sensor

INDEX REFERENCE CHART

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.

NOTE: The ICM control unit must not be exposed to strong vibrations. The integrated sensor system will be destroyed if the housing is struck by hard objects, or if the control unit is dropped. The control unit must not be installed in the vehicle in this case.

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).

Fig. 41: Identifying Longitudinal Forces Acting On Vehicle

INDEX REFERENCE CHART

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:

F resulting = 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.

NOTE: Calibration of the sensors integrated into the ICM control unit is necessary in the following cases

• 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.

Connector

The control unit has a 54-pin plug via which the power supply, sensors, actuators and bus systems are connected.

As is the case with the controller housing, the plug does not have a watertight design. This is The control unit has a 54-pin plug via which not necessary as it is installed on the inside of the vehicle.

Fig. 42: Identifying ICM Control Unit Installation Location

Installation Location

The ICM control unit is installed in the center console behind the sensor for the crash safety module. This means that the position of the control unit and its integrated sensor system in the vehicle, near to its center of gravity, is ideal from the point of view of driving dynamics. The mounting points on the body are precisely determined and are measured when the vehicle is manufactured and must not be replaced with any other mounting points.

The housing of the control unit is connected to the metal body of the transmission tunnel with four screws and spacer sleeves made of aluminum. The control unit must be mounted on the vehicle body free of play as otherwise vibrations may be induced in the control unit housing which would severely impair the operation of the integrated sensor system. A secondary task of this mounting is to conduct heat away from the control unit to the body.

Fig. 43: Identifying ICM Control Unit Components

INDEX REFERENCE CHART

1. Upper section of housing
2. Mounting bolt
3. Connector
4. Spacer sleeve
5. Lower section of housing

For the mounting to be able to perform these tasks, the following points must be observed when mounting and replacing the ICM control unit:

NOTE: Only screws and spacer sleeves that are in perfect condition may be used.

To ensure sufficient heat dissipation and to avoid vibrations, the sides and top of the control unit housing must not come into contact with other vehicle components. Instead, the spaces provided around the control unit as part of the engineering design must always remain free of other components.

Fig. 44: Identifying ICM Control Unit Installation Situation

INDEX REFERENCE CHART

1. Wiring harness, e. g. for rear display
2. The compartment on the right next to the ICM control unit must remain unoccupied
3. ICM control unit
4. The compartment on the left next to the ICM control unit must remain unoccupied

The wiring harness that runs in the center console in particular must never be routed in, or even pushed into, the spaces on either side of the ICM control unit.

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