BMW 7 Series: Signal Provision

Signals from integrated sensor system

The sensors that were previously accommodated separately in the DSC sensor are now installed in the ICM control unit. The following variables can be recorded with these sensors.

• Longitudinal acceleration and pitch of the road or vehicle in the longitudinal direction
• Lateral acceleration and pitch of road or vehicle in lateral direction
• Rotational speed around vertical axis (yaw rate)

The sensor signals are initially referenced to the sensor housing. However, 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 appropriate 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 be switched on.

Signals from External Sensors

The ICM control unit imports the following signals that are important for dynamic driving systems from external sources:

• Wheel speeds, four signals transmitted via FlexRay from DSC.
• Ride-level heights, four signals, wired directly to ICM control unit.
• Steering wheel angle, transmitted via FlexRay from steering column switch cluster.
• Position of actuators for Active Steering and rear axle slip angle control, transmitted via FlexRay.

The ICM calculates the actual speed at which the vehicle moves along the driving axis on the road based on the four wheel-speed signals. If dynamic driving systems intervene and affect the wheel speeds, this is taken into account in the calculation. The status of the ABS control (for example) is also imported in this instance.

The road speed thus determined for the first time in the F01/F02 is now used as the reference for practically all systems in the vehicle. This means that a multiple calculation no longer needs to be performed in many other control units.

The ICM control unit also derives the following information from the wheel-speed signals:

• Distance travelled
• Wheel tolerance check: The marginal differences in wheel speeds (e. g. due to differences in tire diameter) are identified and adjusted by the ICM.
• Snow chain detection: If snow chains are fitted, the driver can enter this information manually via the Central Information Display. The wheel speeds are also used by the HSR control unit to automatically determine whether snow chains are mounted on the rear wheels. The result of this identification is transmitted to the ICM control unit via the FlexRay.

Although, from a theoretical standpoint, it may be more appropriate to assign the ride-height sensors to the Vertical Dynamics Management, the four ride-height sensors are directly connected to the ICM control unit.

The ICM control unit imports the analog voltage signals of the ride-height sensors. These are converted into the actual ride-level heights in millimeters. To perform this conversion, the ICM control unit must be able to map the voltage signals it receives to reference values as otherwise it will not be able to determine the actual ridelevel heights. These reference values are determined by means of a synchronization procedure.

The harmonized ride-level heights are made available by the ICM control unit as bus signals. They are imported from:

• the Vertical Dynamics Management system for the Vertical Dynamics Control and Active Roll Stabilization and also from the
• footwell module for the headlight-range adjustment function.

The ride-level heights are not transmitted as bus signals for the purposes of electronic ride-height control (EHC). Instead, an additional direct line connection exists between the ride-height sensors of the rear axle and the EHC control unit.

The ICM control unit determines the resulting steering lock angle of the front wheels based on the steering wheel angle and location of the Active Steering actuator motor.

As the rear axle can also be steered, a reliable conclusion regarding the driving dynamics cannot be obtained purely on the basis of the steering angle of the front wheels. This is why the ICM control unit also takes the steering angle of the rear wheels into account. The effective steering angle (of the front and rear wheels) is then determined using both steering angles.

This is a purely theoretical computing value that indicates the steering lock of the vehicle's front wheels that would be required to achieve the same vehicle motion if the rear axle could not be steered. The easiest way for all systems in the vehicle to evaluate the data on the steering wheel movement is to use this effective steering angle.

Processing and distribution of signals

Fig. 19: ICM Signals Diagram

INDEX REFERENCE CHART

1. Ride-height sensors
2. Steering column switch cluster with steering angle sensor
3. Dynamic Stability Control
4. Wheel-speed sensors
5. Integrated Chassis Management
6. Footwell module
7. KAFAS control unit
8. Instrument cluster
9. Engine control system
10. Electronic transmission control unit
11. Dynamic Stability Control
12. AS control unit
13. HSR control unit
14. Driving dynamics functions in the ICM control unit
15. DSC sensor in the ICM control unit (longitudinal acceleration, lateral acceleration, yaw rate)
16. Redundant DSC sensor in the ICM control unit (lateral acceleration, yaw rate)
17. "Signal processing" function in the ICM control unit

The signals from the sensors are processed before being made available in the vehicle via the FlexRay bus system. Specific examples of this have already been referred to above. To formulate this in more general terms, the ICM control unit uses all available sensor signals and several computing models to improve the quality of the signals provided. This means that they contain fewer errors and therefore allow the signal "users" (e. g. the dynamic driving systems) to operate with a greater degree of precision.

A new aspect of the F01/F02 is that the signals are not available to just a few systems in the vehicle.

In the F01/F02, the signals provided by the ICM are not used exclusively by the dynamic driving systems. The drive control units, driver assistance systems, information systems and body electrical system share the signals, instead of recording or preparing these separately.

NOTE: This has a distinct advantage when it comes to the diagnosis of signal faults: Faults in all signals described here are stored centrally in the fault memory of the ICM control unit.

In previous vehicles, it was possible for one signal fault to produce a large number of branches in the test schedule trees. The ICM architecture in the F01/F02 means that the test schedule can quickly pinpoint the ICM control unit in the event of a signal fault. The test schedule then shows the effective repair measure in each case.

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