Suspension Control ( Automatic - Electronic ): Description and Operation
Vertical Dynamics Management
Vertical dynamics management (VDM)
The Vertical Dynamics Management system is optional equipment (SA223).
Vertical Dynamics Management (VDM) is a convenience-oriented suspension control system for individual wheel control of damping forces.
Vertical dynamics management offers the following advantages:
- greater on-road comfort
- enhanced agility of vehicle
- improved self-steering response and response to load reversals
- improved driving safety and shortening of the stopping distance
Brief component description
The following components are described for vertical dynamics management:
VDM: Vertical dynamics management
The VDM control unit is bolted to the right-hand spare wheel well under a plastic insert.
The VDM control unit is the central control unit for the Vertical Dynamics Management system. The VDM control unit is connected via the wiring harness and the shock absorber wiring harness to the EDC valves on the shock absorbers and to the vertical acceleration sensors. The shock absorber wiring harness can be replaced separately (shock absorber wiring harness comprises twin-core sheathed wiring).
EDC means: Electronic Damper Control
The EDC valves are activated by 4 output stages in the VDM control unit.
Vertical dynamics management increases on-road comfort. Greater on-road comfort is achieved when the vehicle body moves vertically as little as possible:
The VDM control unit is supplied via terminal 15N by the front power distribution box.The supply to terminal 30F (load) is connected to the rear power distribution box.
The vertical dynamics management is activated under the following conditions:
- Ignition on (terminal 15).
- Speed greater than approx. 3 km/h
Front and rear shock absorbers
The aim of this control is to offer high driving dynamics combined with the highest possible standards of convenience. This adapts the damper settings to suit the driving situation, achieving an optimum balance in response to the feedback from the roadway.
The EDC valves activate the shock absorbers (characteristics map for the damping). The maximum current for activation of the valve coil is 1.6 amperes. The EDC valves are activated by twisted-pair twin-core wiring (shock absorber wiring harness does not feature twisted pair wiring).
On each of the shock absorbers of the front axle, a vertical acceleration sensor is mounted.
The vertical acceleration sensor measures the acceleration of the wheel (±15 g).
The interface to the VDM control unit establishes a three-pin plug connection. The VDM control unit supplies the vertical acceleration sensor with 5 volts. The transition from main wiring harness to the wiring harness on the shock absorber is provided by a connector box in the wheel arch.
Drive dynamic control switch
The driving dynamic control switch and the gear selector switch are used to operate Dynamic Driving Control. The new Dynamic Driving Control has the following features:
1. All of the drive and driving stability control systems installed in the vehicle are activated. The central control unit for this is the Integrated Chassis Management (ICM).
2. A choice of 3 programs is available:
- NORMAL
- SPORT
- SPORT+ (not Vertical Dynamics Management)
Driving Dynamics Control influences vertical dynamics management as well as other systems.
The drive dynamic control switch is connected to the control unit for Integrated Chassis Management (ICM). The ICM control unit places the signals on the FlexRay.
The following other components deliver signals for Vertical Dynamics Management (VDM):
Height sensors
With the optional equipment of xenon light, there are 2 ride height sensors:
- Front left ride height sensor
- Rear left ride height sensor
The VDM control unit then uses these signals in addition to the plausibility check (not relevant to this function).
The height-level sensors are electrically connected to the Integrated Chassis Management (ICM). The ICM control unit implements the signal on the FlexRay.
The ride height sensors deliver dynamic information on the height of the vehicle body. From this, the Vertical Dynamics Management-system calculates the movements of the vehicle body and the individual acceleration levels achieved by the wheels.
ICM: Integrated chassis management
Integrated Chassis Management (ICM) assumes the following functions in vertical dynamics management:
- Central signal plausibility check for longitudinal and lateral acceleration, and yaw rate
- Central provision of driving speed, longitudinal inclination and lateral inclination
- Central co-ordination of the display of Check Control messages for the suspension control system
System function
The following system functions are described for vertical dynamics management:
- Functional networking
- Damping of the wheel accelerations as well as body movements
- Fail safe
Functional networking
A complex composite system with distributed functions in other control units is necessary for the implementation of vertical dynamics management.
Damping of the wheel movements as well as body movements
To dampen the wheel movements and body movements, the motion of the vehicle is monitored. Here, the following axes are included:
- Vehicle vertical axis
- Vehicle lateral axis
- Vehicle longitudinal axis
The following signals, e.g., are used for monitoring:
- Pitch rate, roll rate, vertical acceleration
- Wheel acceleration
- Driving speed
- Lateral and longitudinal acceleration
The signals are used to calculate the required level of damping force.
Vertical Dynamics Management damps body movements to enhance ride comfort. Vertical Dynamics Management damps wheel movements to enhance safety. The aim is to prevent the wheels from losing contact with the roadway. Depending on the situation, optimized vertical force must be assured.
The vertical dynamics management also takes account of lateral acceleration (e.g. transition from straight-ahead driving to entering a curve). If a rise in lateral acceleration is detected, the VDM control unit shuts down as the vehicle starts to negotiate a bend in the road. This means that the shock absorbers can be activated accordingly in advance. This means that the VDM contributes to reducing the rolling motion of the vehicle.
The vertical dynamics management also detects braking and acceleration. To achieve this, the DSC provides the brake pressure signal. High levels of brake pressure normally lead to a pitching motion of the vehicle. These VDM counteracts this pitching motion through targeted control inverventions.
Depending on the applicable customer request, the drive dynamic control switch can be used by the VDM control unit to adjust the damping force characteristics. A positive influence on control of driving safety is a feature of every program.
Fail safe
Depending on the type of fault that has occurred, the fail safe takes effect in 3 stages:
- Stage 1: substitute values
If for example the signal from the lateral acceleration sensor is not available, other parameters are used as substitute values for the identification of cornering. The driver does not receive a Check Control message: no fault entry (only a slight loss of comfort is perceptible). Any repair required is performed by fault entries from the transmitter control unit.
- Stage 2: constant power supply
The VDM control unit specifies a constant damping force for all 4 wheels (medium-hard damping). A faulty vertical acceleration sensor can, for example, be the causal factor here. A Check Control message is output to the driver. A fault is entered in the fault memory (forced activation of DSC).
- Stage 3: no power supply
If there is undervoltage on the load line (failure of fuse):
The VDM control unit no longer energizes the EDC valves. This causes the valve to move to a position that corresponds more to medium to harder damping. A Check Control message is output to the driver. A fault is entered in the fault memory (forced activation of DSC).
Check Control message
Notes for Service department
Diagnosis instructions
IMPORTANT: Perform start-up.
After a replacement of the VDM control unit, of a vertical acceleration sensor and of a shock absorber, a start-up must be performed.
Path: Service functions > chassis and suspension > Vertical Dynamics Management > start-up
Notes on encoding/programming
After replacement, the VDM control unit must be recoded.
We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.