BMW 7 Series: Vertical Dynamics Control (VDC)

Control Unit

Fig. 124: Identifying VDM

INDEX REFERENCE CHART

1. VDM

The location of the VDM control unit is dependent on the country in which the vehicle is sold.

• On left-hand drive vehicles the control unit is fitted inside the passenger compartment near the right A-pillar (as illustrated)
• On right-hand drive vehicles the control unit is fitted inside the passenger compartment near the left A-pillar

There are two different versions of the VDM control unit according to the equipment options fitted on the vehicle.

• The basic version of the VDM control unit is used if the vehicle has only the standard VDC equipment
• The high-speed version of the VDM control unit is used if, as well as the standard VDC system, the vehicle also has ARS Active Roll Stabilization (Dynamic Drive). In that case, the output stages for controlling the ARS valve manifold are also integrated in the VDM control unit.

EDC Satellite Control Unit with Damper

The VDC dampers on the rear suspension are either steel-spring or air-spring versions depending on the optional equipment fitted.

Fig. 125: Identifying EDC Satellite Control Module And VDC Damper

INDEX REFERENCE CHART

1. VDC damper with steel spring
2. VDC damper with air spring
3. Front EDC satellite control module
4. Rear EDC satellite control module
5. EDC data-map valve for compression control
6. EDC data-map valve for extension control
7. EDC data-map valve for extension control
8. EDC data-map valve for compression control

Fig. 126: Identifying EDC Satellite Control Unit And Damper Tube

INDEX REFERENCE CHART

1. Damper tube
2. EDC satellite control unit
3. EDC data-map valve for extension and compression control

1. FE = Extension force
2. FC = Compression force
3. VE = Extension velocity
4. VC = Compression velocity
5. Extension and compression characteristic data map

Difference between a VDC (1) and a VDC (2) damper:

A VDC (1) damper with only one EDC data map valve uses combined extension/compression adjustment which has to be cycled extremely rapidly.

With this type of control, the damper adjustment is based on wheel frequency.

The wheel frequency is the frequency at which the wheel oscillates along the z-axis.

Fig. 127: VDC Damper Fluid Flow Diagram With EDC Data-Map Valves

INDEX REFERENCE CHART

1. Extension progression
2. Compression progression

1. Damper tube
2. EDC data-map valve for extension
3. EDC satellite control unit
4. EDC data-map valve for compression

A VDC (2) damper with two EDC data-map valves uses independent extension/compression adjustment which does not demand such a high cycling rate.

With this type of control, the damper adjustment can be based on body frequency.

The body frequency is the frequency at which the body oscillates along the z-axis.

Fig. 128: EDC Satellite Control Unit Fluid Flow Diagram During Extension

INDEX REFERENCE CHART

1. EDC data-map valve for compression
2. EDC data-map valve for extension
3. Force/direction of piston rod movement
4. Fluid medium
5. Data-map control

1. FE = Extension force
2. FC = Compression force
3. VE = Extension velocity
4. VC = Compression velocity
5. Extension data map
6. Compression data map

The two EDC data-map valves firstly enable independent extension control and, therefore, data-map compatible design, and secondly independent compression control and, therefore, data-map compatible design.

Fig. 129: EDC Satellite Control Unit Fluid Flow Diagram During Compression

Control strategy

The fundamental control principle is known as the "Skyhook system", the name of which reveals the primary control objective of holding the vehicle stationary in a vertical direction regardless of driving situation as if suspended from a "hook in the sky".

To achieve this highest of all comfort objectives, the movements of the entire body have to be evaluated. Thus an overall analysis is performed of the ride height data and z-axis acceleration rates.

Furthermore, VDC regulation takes into consideration steering inputs (e. g. transition from straight-ahead travel to cornering) based on the steering angle curve. If VDC detects a rapid increase in the steering angle, the controller infers that the vehicle is entering a bend and can preventively adjust the dampers on the outside of the bend to a harder setting in advance. Thus VDC assists the ARS system, if fitted, and contributes to reducing vehicle roll (roll tendency).

Moreover, VDC is able to detect the braking operations by the driver based on the brake pressure information supplied by DSC. A high brake pressure normally results in pitching of the vehicle body; VDC counteracts that effect by setting the front dampers to higher damping forces. This also results in an improvement in the front/rear brake force distribution, which in turn reduces the braking distance (by comparison with a vehicle without VDC).

On the E70/E71 with VDC (1), the "Sport" button for switching between comfort and sports setting only affected the VDC characteristics.

With the introduction of the handling setting switch, the VDC setting is incorporated in a number of modes which bring about a coordinated overall setting across all systems.

Ride-height Sensor

Fig. 130: Identifying Ride-Height Sensor Components

INDEX REFERENCE CHART

1. Electrical connector
2. Sensor housing
3. Lever

The angle of a pivoting lever is converted into a voltage signal by the ride height sensor. The greater the angle (relative to a defined starting or zero position), the greater is the output voltage. It is generated by a Hall-effect sensor element.

Designs

There are always four ride-height sensors fitted on all F01/F02 models.

The ride-height sensors fitted all operate according to the same principle but there are different designs (different part numbers). The reason for the differences are the available space and the starting position (zero position) of the individual ride-height sensors.

Depending on whether or not the vehicle is fitted with Electronic Height Control (EHC), double or single ride-height sensors are fitted on the rear suspension.

On the front suspension, single ride-height sensors are always used.

FRONT AND REAR SUSPENSION DESIGNS

RHS = Ride-height sensor

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