Dynamic Drive
Dynamic Drive
Vertical dynamics management control unit
The following functions can be added to the vertical dynamics management control unit (VDM):
- Vertical dynamics management
- active roll stabilization (marketing designation: Dynamic Drive)
This document describes the Dynamic Drive system.
The CAS control unit controls activation of the VDM Vertical Dynamics Management control unit with Terminal 15N power; this VDM ECU is protected by a fuse (5 amp). At the same time, the VDM control unit is supplied with terminal 30. The VDM control unit is located in the right-hand side of the passenger compartment in the footwell area of the A-pillar.
Dynamic Drive prevents or reduces the vehicles tendency to roll while cornering at high speed or during high-speed evasive maneuvers. Vibration comfort is increased. The turn-in ability of the vehicle is optimized.
Brief component description
The following components are described for Dynamic Drive:
- Valve block
- Swivel motor
- Tandem pump
- Suction throttle valve
- Oil-level switch
Valve block, dynamic drive
The valve block for Dynamic Drive is installed behind the right front wheel well. The valve block is electrically connected to the VDM control unit. The stabilizers on the front and rear axles are split and connected in the centre to a swivel motor. The swivel motors are hydraulically activated via the valve block. This enables very rapid application of a defined torque onto the stabilizer in the desired direction.
The valve block is located in the right front wheel arch near the A-pillar.
The following components of the valve block are described:
Front and rear pressure-control valves
The pressure-control valves are located within the valve block. The pressure control valves are activated by the VDM control unit. In the process, the hydraulic pressure (differential pressure) is set for the stabilizers (up to 180 bar). When the vehicle is being driven straight ahead, the pressure control valves are applied with preliminary current (0.35 Ampere). The oil flow flows freely to the oil reservoir. On cornering, the pressure control valves are supplied with current. The hydraulic pressure in the swivel motors is regulated to the setpoint value. Due to factors inherent in the design, the hydraulic pressure on the swivel motor of the front axle is greater than or equal to the hydraulic pressure at the swivel motor of the rear axle.
Front and rear pressure sensors
The pressure sensors monitor the hydraulic pressure to the stabilizers on the front and rear suspensions. The sensor signals (tension) are routed to the VDM control unit. The pressure in the return line to the oil reservoir is not monitored (circulating flow approx. 2 bar).
NOTICE: Observe the service function.
The diagnosis system includes a service function that allows the system to "learn" pressure sensor deviations from their basepoint (c. 0.7 volts): Chassis and suspension - Dynamic Drive - Learn sensor system. Precondition: Engine off.
Directional control valve
The directional-control valve is governed by the VDM control unit. The direction valve sets the direction of the hydraulic fluid for right-hand and left-hand bends as well as of the return flow of oil. The 4-2 directional control valve "swaps" the pressure side towards the stabilizer. The direction valve is the component of the active roll stabilization where safety is most critical. This is why the direction valve is monitored by a separate sensor.
Shift position sensor
The position sensor monitors the position of the directional-control valve. The shift-position sensor works according to the Hall effect. There is a magnetic hollow cylinder at the direction valve into which the shift-position sensor protrudes. This enables the shift-position sensor to detect the following 2 positions: no activation, activation curve (0.7 Volt, intermediate range 3.0 Volt, 4.2 Volt). The sensor signals are routed to the VDM control unit.
Safety valve
The safety valve is controlled by the VDM control unit, and closes off the front suspension swivel motor when not under power (hydraulic blocking). The safety valve is de-energized under the following conditions: Open circuit in the voltage supply and system fault. The rear axle swivel motor is connected hydraulically and by the return line to the oil reservoir. This limits the system pressure and creates a circulating flow.
Structure and inner electrical connection
The shift-position sensor and the two pressure sensors are supplied with current by the VDM control unit (initial current 0.35 ampere, maximum 2.5 ampere). The pressure control valves are activated by the VDM control unit with a pulse-width-modulated signal (5% to 95%). The direction valve as well as the safety valve are either energized or de-energized (activated or not activated).
Setpoint values and signal path of pressure sensors
The signal for evaluation of hydraulic pressure depends on the pressure. The measuring range of approx. 0.5 - 4.5 Volts corresponds to a hydraulic pressure of 0 bar to 200 bar.
Observe the following setpoint values for the components on the valve block:
Size Value
Supply voltage for pressure 5 V
sensors and shift-position sensor
Pressure control valves, 0.35 A
preliminary current applied
Response time of direction valve approx. 30 ms
Maximum stabilization torque at approx. 800 Nm
the swivel motor (rear axle)
Delivery rate of tandem pump 5.2 to 9 l/min
with suction throttle valve 3.0 l/min
Temperature range -40 to 140 °C
Failure of the component
If one of the components on the valve block fails, the following behavior is to be expected:
- Fault memory entry in the control unit for vertical dynamics management (VDM)
- Check Control message in the instrument panel
Active anti-roll bars
The active anti-roll bars are vertically split in the middle. The active anti-roll bar consists of a swivel motor and, attached to it, the two halves of the anti-roll bar with press-fitted roller bearing mountings. The swivel motor shaft and housing are each attached to one half of the anti-roll bar. In the swivel motor, the opposing chambers are linked. This means the chambers each have the same pressure. Two chambers are supplied with high pressure via one connection. The two other chambers are connected to the return line to the expansion tank. Variation of the pressure varies the force generated by the motor. That force produces torque which rotates the shaft relative to the housing. As one half of the anti-roll bar is attached to the shaft and the other to the housing, the two halves of the anti-roll bar then twist in opposite directions to one another. The momentum that this creates counteracts / stabilizes the rolling motion. The maximum system pressure is 180 bar.
Tandem pump
Depending on the engine version and equipment specification, the fitted tandem pumps are flanged onto the engine. The tandem pump supplies the hydraulic circuits for both Dynamic Drive and the power steering. The pump consists of a radial piston for the Dynamic Drive System and a vane-pump section for the power steering. Dynamic Drive and the power steering share a common fluid cooler and fluid reservoir.
Suction throttle valve
The suction throttle valve is attached to the tandem pump.
When the vehicle is being driven straight ahead, the volumetric flow of the tandem pump is throttled on the intake side by the application of current. This lowers the pressure of the circulating flow. The tandem pump consumes less power. This lowers CO2 emissions.
Function of suction throttle valve
The oil flow flows before the tandem pump through the suction throttle valve. The control unit for vertical dynamics management activates the suction throttle valve when the vehicle is being driven straight ahead. Activation is carried out when the vehicle is being driven straight ahead as well as when the vehicle is stationary (engine running). This lowers the loss due to unnecessary pump output.
The tandem pump's deliverty rate remains proportional to the pump's rotation rate as long as this rate remains below the tandem's pump's governed maximum (corresponding to an engine speed of roughly 1000 rpm).
Structure and inner electrical connection
The suction throttle valve is connected by means of a 2-pin plug connection.
The suction throttle valve is a solenoid valve. The VDM control unit supplies the suction throttle valve with current (approx. 0.85 Ampere).
Characteristic curve and setpoint values for tandem pump
During idling, the pump speed is approx. 750 rpm. At this idle speed, the tandem pump delivers a volumetric flow of approx. 5 l/min at approximately 3 bar. This ensures adequate system dynamics even at idle speed. At a pump speed of 1250 rpm, the maximum volumetric flow is limited to 9 l/min.
Observe the following setpoint values for the suction throttle valve:
Size Value
Voltage range 8 to 16 V
Response time at 20 C and 13 V ≤ 40 ms
Power consumption at 25 C and approx. 1 A
13 V
Temperature range -40 °C to 140 °C
Oil reservoir and oil-level switch
The oil reservoir contains an oil filter and an oil-level switch with float. In contrast to the oil-level switch, the oil filter cannot be replaced separately. A dipstick designed to allow checks of the fluid level is attached to the screw-on cap.
The oil-level switch detects whether the required oil level in the oil reservoir is exceeded or undershot. The VDM control unit sends the signal on the bus system to the instrument panel. The instrument panel issues a Check Control message. Normal motion of the oil in the oil reservoir does not lead to a Check Control message.
There is a permanent magnet in the moving float; this triggers the reed contact in the oil-level switch firmly fitted in the reservoir. Here, the reed contact converts the float movement into an electrical signal. The Reed contact remains closed when the fluid level is above "minimum" (roughly 10 mm below the "minimum" graduation).
On the oil-level switch, short circuit or line disconnection cannot be detected. A line disconnection is interpreted as oil loss. A short circuit is not detected.
Structure and inner electrical connection
The reed contact has the effect of a switch. If the reed contact is activated, ground is switched through to the VDM control unit.
Characteristic curve for filter element as well as bypass valve and setpoint values
The oil reservoir contains a mechanical bypass valve that opens if the filter element is soiled. The bypass valve opens at approx. 3 bar excess pressure.
Observe the following setpoint values for the oil-level switch:
Size Value
Maximum power consumption 15 mA
Maximum contact resistance 500 mOhms
Temperature range -40 °C to 120 °C
Failure of the component
If the oil-level switch fails, the following behavior is to be expected:
- Fault entry in the VDM
- Output of a Check Control message in the instrument panel
- Failsafe function, also applies to power steering
General notes
On checking the oil level, the influence of the oil temperature must be taken into account (volume expansion).
There is a "MAX" mark on the oil dipstick. The mark indicates the maximum permitted oil level measured at room temperature (20 C). Due to thermal expansion, at oil temperatures of 50 to 70 °C the oil level is approx. 15 mm above the mark. With regard to the oil level, follow the repair instructions.
Vehicles without active roll stabilization can be recognized by the lack of oil-level switch.
Oil cooler
The oil cooler keeps the oil temperature below 120°C. The fluid temperature may rise to a maximum of 135 °C, but this should only be for brief periods.
Notes for Service department
WARNING: Rolling motion on commissioning
During commissioning, the vehicle performs very strong and rapid rolling motions. For this reason, no persons may be located directly at the vehicle, particularly in the proximity of moving vehicle components. There must be no objects underneath the vehicle or in the wheel arches. The commissioning procedure may only be carried out with the vehicle standing of a firm, flat surface with all four wheels on the ground. Under no circumstances may the commissioning be carried out when the vehicle is on the following surfaces:
- Vehicle hoists
- Wheel alignment units
- Shock absorber test units
- Brake test units
- Power output test units
Disregarding these instructions could put lives at risk.
General notes
After opening the system hydraulics (valve block, swivel motors, lines), run commissioning.
Once the Dynamic Drive control unit has been encoded/programmed it will be necessary to perform a startup routine.
Diagnosis instructions
Initial operation
The startup routine allows the system to "learn" the parameters and the "zero points" (home positions) of all sensors. Commissioning is divided into 5 phases and it takes around 25 seconds.
1. Check of direction valve
2. Low pressure test
3. Front axle high pressure test
4. Rear axle high pressure test
5. Check pressure control valve
NOTICE: Temperature on commissioning
The oil temperature is an important parameter for the commissioning. The commissioning procedure (by means of diagnosis command) must not be carried out at extreme temperatures (ambient and system temperatures).
Information on encoding and programming
After encoding or programming the control unit carry out the startup routine.
Information on Check Control messages
The following warnings and their causes can appear as Check Control messages in the CID:
Message: Ride comfort restricted.
The following warning message indicates that Dynamic Drive has been deactivated:
- Ride comfort restricted.
IMPORTANT NOTICE: The vehicle will exhibit more body roll during cornering than a vehicle without Dynamic Drive.
Precondition for continued driving to the next workshop:
- Reduce cornering speed.
- No significant oil loss.
Possible causes of the warning message:
- Defect on the front axle pressure sensor
- Defect in the pressure build-up (pump)
- Defect in at least one active stabilizer bar
- Fault in the Dynamic Drive
In order to be able to pinpoint the cause more exactly, read the fault memory and run through the displayed test plan. When the fault has been remedied, delete the fault memory.
Message: Steering fault. Stop the vehicle carefully
The following warning message alerts the driver to a loss of hydraulic fluid in the suspension-control and steering systems:
- Steering fault. Stop the vehicle carefully
In this case, it is not possible to continue driving to the next workshop.
Possible causes of the warning message:
In order to be able to pinpoint the cause more exactly, read the fault memory and run through the displayed test plan. When the fault has been remedied, delete the fault memory.
Message: Restricted cornering behavior.
The following warning message alerts the driver that's Dynamic Drive's suspension stabilization is operating at reduced efficiency, although continued driving remains possible:
- Restricted cornering behavior.
The driver should contact a service facility at the next opportunity.
Possible causes of the warning message:
- Defective CAN message (driving speed)
- Defective lateral acceleration sensor
- Fault in the rear-axle circuit
- Mistake during pre-drive check
In order to be able to pinpoint the cause more exactly, read the fault memory and run through the displayed test plan. When the fault has been remedied, delete the fault memory.
We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.