BMW 7 Owners & Service Manuals

BMW 7 Series: Components

Active Roll Stabilization (ARS)

Control Unit

The VDM control unit is located in the passenger compartment near the right-hand A-pillar. The VDM control unit receives its power supply via Terminal 15N and is protected by a 5A fuse. The VDM control unit is activated exclusively by the Car Access System (CAS) via a Terminal 15N lead as of status "Ignition ON".

Vertical Dynamics Systems
Fig. 115: Identifying VDM Control Unit Location

INDEX REFERENCE CHART

  1. VDM control unit

A vehicle authentication process takes place when the system is started. This compares the vehicle identification number from the CAS with the vehicle identification number which is encoded on the VDM control unit.

That is followed by a check of the VDM control unit's hardware and software. All outputs (valve solenoids and sensors) are subjected to a comprehensive check for short circuits and circuit breaks. If there is a fault, the system switches the actuators to a safe-driving mode.

The VDM control unit switches off if the voltage is too low/too high.

VDM control unit inputs

From the input signals, the VDM control unit calculates the control signals to the actuators. The input signals are also checked for plausibility and used for system monitoring.

The VDM control unit receives the following input signals:

  • FlexRay bus
  • Front-suspension circuit pressure (analog)
  • Rear-suspension circuit pressure (analog)
  • Switch position detector reading (analog)
  • Fluid level sensor signal (analog)

The most important control signal for the ARS function is the lateral acceleration measured by the ICM control unit, which is sent to the VDM via the FlexRay bus. Additional lateral dynamics information from the FlexRay bus which is also provided by the ICM comprises the road speed signal and the steering angle. From that, the stabilization requirement is calculated and the relevant active forces are applied. The road speed and steering angle information is also used to improve the reaction time of the system.

VDM control unit outputs

All outputs are compatible with diagnostics and protected against short-circuit. The outputs include controls for:

  • Pressure regulating valves for front and rear axle
  • Failsafe valve
  • Directional valve
  • Intake restrictor valve
  • 5 V power supply for the sensors:
    • Pressure sensors at the front and rear axle
    • Switch-position detector (SSE)

The valves are controlled by the supply of current regulated by pulse-width modulation (PWM). The current measurements of the individual coil currents are designed with redundancy. The valve currents are mutually checked for plausibility on a continuous basis.

Thanks to the current measurement, the pressure can be set more precisely and the switch valves can be monitored electronically. Fault symptoms of the output signals are:

  • Short circuit to Terminal 30 and Terminal 31
  • Open circuit and
  • Valve short circuits
  • Sensor power supply faults

A message is sent to the DME via the FlexRay bus from the central dynamic handling controller on the ICM.

The message contains information on how much power the tandem pump currently requires to supply the active anti-roll bars. In this way, output at the engine can be increased to satisfy the additional power requirement. A regular data signal (alive signal) is broadcast and read by other VDM control units to identify whether the system is still active. In addition, a function status signal is broadcast which communicates the status of the ARS function. The VDM control unit transmits an additional status message via the FlexRay to the instrument cluster in order to actively initiate display messages.

That status message is assigned a priority among all suspension/steering messages by the message co-ordinator on the ICM control unit and passed to the instrument cluster. All signal faults are recorded and permanently stored in the fault memory. If the alive signal fails, the ICM control unit automatically sends a message to the instrument cluster to activate the ARS warning lamp.

Vertical Dynamics Systems
Fig. 116: Identifying ARS Indicator Lamp (Red)

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