Driving Dynamics Systems - Overview - E65: Other BMW 7 series E65/E66 facelift

Objectives Of The Article

After Completing this article, you will be able to

1. List the Driving Dynamics Systems.
2. Demonstrate how to deactivate Dynamic Traction Control.
3. Explain how EDC-K influences hydraulic damper operation.
4. Identify the correct EDC-K solenoid valve resistance value.
5. Describe the Dynamic Drive influence on the stabilizer bars.
6. Name the Dynamic Drive components and locations.
7. Understand the Valve Block sub-components and functions.
8. Explain the Oscillating Motors hydraulic/mechanical operation.
9. Describe "Fail-safe" hydraulic flow.
10. Demonstrate Dynamic Drive Commissioning.

Purpose Of The Systems

The E65 chassis offers the driver optimum ride comfort, driving safety, good agility and excellent handling. The chassis also adapts to changes in road conditions: traffic, ice, snow etc. Vehicle speed and changes in the direction of travel generate forces that have an effect on the chassis which requires the driver to react correctly to maintain safe driving.

The following forces occur while driving

1. Vertical forces - uneven road surfaces, bumps and potholes
2. Lateral forces - centrifugal forces during cornering and crosswinds
3. Longitudinal forces - acceleration, deceleration and braking

The following vehicle structure movements occur as a result of these forces

Scheme 6

1. Around the transverse axis: pitch
2. Around the longitudinal axis: roll
3. Around the vertical axis: yaw

Active Driving Dynamics Systems are integrated in the E65 chassis which support the driver both actively and passively by suppressing the effects of these forces as much as possible. The Driving Dynamics Systems include

1. Dynamic Stability Control (DSC) with subsystems
2. Electronic Damping Control (EDC-K) continually adjustable system
3. Dynamic Drive active roll stabilizer bar (ARS)

The Driving Dynamics Systems monitor the driving conditions using sensors. The sensor signals are transmitted to the control modules that interpret and evaluate the driving conditions. The control modules send output signals to actuators that will counter these forces providing adaptation for the road and driving situations.

Systems Indications

The indicator/warning lamps, Check Control, On-board Computer messages and Control Displays as well as the respective activation are described in the iDrive display and controls.

Dynamic Stability Control (DSC)

The DSC controls the vehicle stability in all driving conditions, counteracting the driving dynamics forces by using brake intervention or engine load control depending on the situation. DSC consists of the following subsystems

1. ABS Anti-Lock Braking System
2. ASC Automatic Stability Control
3. MSR Engine Drag Torque Reduction
4. DBC Dynamic Brake Control
5. CBC Cornering Brake Control

The following are new in the E65

Scheme 7

1. FBS Fading Brake Support
2. FLR Driving Performance Control
3. DTC Dynamic Traction Control
4. Parking Brake (hydraulic service brakes)

Electronic Damping Control (EDC-K)

The continuous Electronic Damping Control (EDC-K) absorbs vertical forces while driving and dampens these forces to the chassis. The forces are measured by two vertical acceleration sensors on the front axle (left and right) and one at the rear axle (right). The front sensors are located in the wheel housings and the rear on the trunk tray underneath the trunk ventilation ports. The dampening characteristics are mapped in the control module to continuously regulate the EDC-K providing maximum comfort.

The EDC-K works with infinitely variable valves in the dampers to regulate the hydraulic fluid flow using electromagnetic control valves. EDCK provides the actual damping force required at any time.

The steering angle sensor is used along with the front wheel speed sensors to determine the lateral acceleration. The controller provides the opportunity to select from two basic settings: Comfort or Sports.

Scheme 8

Dynamic Drive

Dynamic Drive controls two active stabilizer bars based on the lateral acceleration. The active stabilizers are split with a hydraulic actuator in between them so that the left and right sides can be turned in opposing directions. These active stabilizers set the stabilizing torque using hydraulic actuators so that

Scheme 9

1. The rolling motion of the body is minimized or eliminated while cornering.
2. The extent to which the body rolls on straight, uneven road surfaces is reduced.
3. A high degree of agility and precision adjustment is achieved using the full speed range.
4. An optimum self steering characteristic is produced.

History

The history of wheel slip control systems used in BMWs is covered in the Chassis Dynamics course (ST056). DSC III was technically modified (deletion of the pre-charging unit), the functions were extended and renamed DSC 5.3. The DSC 5.3 was further developed into DSC 5.7 by adding these functions

1. Dynamic Brake Control (DBC)
2. Dynamic Brake Support (DBS)
3. Maximum Brake Support (MBS)

These functions have been used in Bosch systems since 1999. For the E65, DSC 5.7 is further developed and expanded to include the software functions to achieve improved system operation

1. FBS Fading Brake Support
2. FLR Driving Performance Control
3. Parking Brake (hydraulic service brakes)
4. DTC Dynamic Traction Control

In addition, the evaluation of the 2-stage brake lining wear sensors is integrated in the DSC control module. The DSC system is connected to the PT-CAN Bus.

Scheme 10

DSC

DSC calculates the current driving conditions and corrects detected driving instability through active brake interventions. For example, in the event of vehicle oversteer, DSC initiates brake intervention at the front wheel furthest from the curve to create a stabilizing, opposing torque.

In the event of vehicle understeer, active interventions at the wheels nearest to the curve provide a stabilizing counter torque. DSC stabilization is performed in all driving situations: normal running, acceleration and braking.

Scheme 11

The DSC control module is combined with the hydraulic unit and is located on the right front strut tower in the engine compartment. The DSC function can be deactivated by the Controller in the Control Display menu and the DSC light in the instrument cluster will illuminate to alert the driver. DSC can be reactivated by the Controller or automatically when the ignition is cycled.

Scheme 12

Anti-Lock Braking System (ABS)

The ABS system will operate under a full or fail-safe state

1. ABS full system: the control module achieves a stabilizing effect on the driver's requests through active brake pressure increase at the individual wheels. Information from the wheel speed sensors, the yaw rate and steering angle sensors determine the vehicle speed. At vehicle speeds <60 km/h an individual control operation matching each situation shortens the braking distance.
2. ABS fail-safe level: the ABS adopts the fail-safe level in the event of a sensor failure or a CAN Bus fault. In this case, the vehicle speed is determined by the wheel speed sensors. In addition, the "select low" control for rear axle stabilization will be applied and the active interventions during brake activation and MSR will be deactivated.

Automatic Stability Control (ASC)

ASC prevents the wheels from spinning during acceleration on all types of road surface. The ASC function is the same as models currently in use.

Dynamic Brake Control (DBC)

The DBC function is designed to provide the maximum braking force available during rapid (panic) braking situations and includes the following subfunctions.

Dynamic Brake Support (DBS): DBS assists the driver in panic braking situations. This function is triggered by a sufficiently fast actuation of the brake pedal.

The brake pressure generated by the driver is increased by the hydraulic pump to the extent that the front and rear axles go into ABS control mode. The driver can achieve a full deceleration with low pedal force.

Fading Brake Support (FBS): FBS is a new subfunction of DBC that compensates for the brake force loss from an increase in brake temperature. The diminishing braking effect due to hot brakes requires the driver to press the brake pedal more firmly.

This increase in pressure is assumed by an activation of the DSC hydraulic pump. The temperature measurement is a virtual value which is calculated by the DSC control module based on wheel speed, brake pressure, braking time (length) and ambient temperature.

Cornering Brake Control (CBC)

The CBC function is activated in the event of medium to high lateral acceleration. If a vehicle drives into a curve under braking and threatens to oversteer, an increase in stability is achieved through a partial release of the rear wheel brake nearest the curve.

During corner braking, CBC provides the best possible directional stability through optimum brake force distribution. The hydraulic pressure in the rear brake calipers is controlled individually to prevent the vehicle from oversteering.

CBC controls the vehicle prior to ABS or DSC intervention. CBC also operates even when DSC is deactivated and CBC is deactivated in the event of an ABS failure.

Driving Performance Control (FLR)

FLR is a new subfunction of DSC that protects the brakes against overloading (misuse). When a temperature of over 600°C is determined, the engine power is reduced (max. engine torque 330 N.m) by the ECM. This engine torque reduction is stored as a fault (driving performance control active).

Parking Brake (Hydraulic Section)

DSC controls the hydraulic function of the Parking Brake. The "Automatic Hold" and "Dynamic Braking" functions affects a hydraulic braking operation on the front and rear service brakes.

Scheme 13

Scheme 14

Sensors

The DSC 5.7 receives input signals from the following sensors

1. Wheel speed sensors (4 active wheel speed sensors with direction of rotation detection)
2. Steering angle sensor (located in the SLZ), made available over the PT-CAN Bus
3. Brake fluid level warning switch (level monitoring in brake fluid reservoir)
4. Brake light switch (BS)
5. Rotation rate sensor - yaw (satellite of DSC on PT-CAN Bus)
6. Transversal acceleration sensor (integrated in rotation rate sensor)

The Rotation rate (yaw) sensor is located under the carpet in front of the passenger's seat in the passenger compartment.

Scheme 15

Scheme 16

1. Pressure sensor (installed at the inlet of front brake circuit)

With EDC I in the 1987 E32, BMW AG was the first European manufacturer to introduce a fully automatic electronically adjustable damper system. EDC I provided manual selection during driving between hard, sport and soft damping. Since the market launch, this 2-stage system has been continuously enhanced and evolved into EDC III, it has set the standard for adjustable damper systems in the 5 and 7 Series.

EDC III evaluates the status of the road surface, vehicle load, driving speed and driver's request to automatically activate one of three damper programs: soft, medium or hard. The driver also has the option of selecting a comfort or sports program.

EDC-K is a further development of EDC III. The German abbreviation "K" stands for continuous damping force adjustment. The major change from EDC III is the damper valves and the activation control.

Scheme 17

EDC-K operates with a continuously adjustable valve in each damper. The damping force is adjusted for individual piston speed. The damping force adapts continuously to the low frequency movement of the vehicle body, resulting in a significant increase in driving comfort. The driver has the option to select a comfort or sports setting by using the Controller in the Control Display menu.

The EDC-K system is an option offered under the Adaptive Ride Package.

System Components

EDC-K Control Module: The control module is located in front of the glovebox and is powered by B+, operating within a voltage range of 9 to 16V. In the event of undervoltage, the EDCK system shuts down to prevent excessive battery draw.

The control module incorporates various control functions that determines the current applied to the damper valves.

Scheme 18

Vertical Acceleration Sensors: The three vertical acceleration sensors provide a varying voltage signal (0.2 - 4.5V) to the control module indicating the speed of body movement. The three sensors are identical and have a measuring range of +/- 2.5 g.

The front sensors (1) are mounted on the inside top of the wheel archs and the rear sensor (2) is mounted on the side of the rear wheel arch.

Scheme 19

Electronically Adjustable Dampers: The front and rear axles are equipped with twin tube gas pressurized dampers supplied by Mannesmann Sachs Boge. The fully variable dampers are map controlled and do not have fixed stages.

Each damper incorporates an adjustable proportioning control valve on the piston. The wiring harness for this valve is routed through the hollow piston rod. Damper oil flows through this valve during compression and rebound. The control valve generates a pressure drop between the lower and upper chambers depending on the oil flow volume.

The front and rear axles are separately activated to achieve an optimum response for vibrations in all driving conditions. The valves are deactivated in the event of a control module failure or when the ignition is switched "OFF". The dampers automatically rest in the hardest setting (without power). On vehicles equipped with Dynamic Drive, the spring struts have different valve configurations on the front and rear axles. The dampers are de-energized when the vehicle is stationary. They are energized initially from 5 km/h.

Scheme 20

Infinitely Variable Control Valve: Without power, the maximum hydraulic resistance is set by the screw (1), which pre-tensions the valve spring (6). This is the hardest damper setting, also known as the fail-safe (rest) setting.

The valve spring provides maximum tension on the armature (7), which presses down on the EDC-K Damper valve (3). This in turn presses down on the floating seat ring (5) which offers resistance to the oil flow by restricting the orifices (indicated by arrows).

When the solenoid coil (2) is energized by the EDC-K control module, the armature is magnetically pulled upwards against the valve spring tension. The armature will exert less pressure on the EDC-K Damper valve. The tension is decreased on the floating seat ring decreasing the orifice restriction. The oil flow will increase, resulting in softer damping.

When the solenoid coil receives maximum power, the effect will be the lightest tension on the floating seat ring. The orifices are unrestricted, providing the softest damping.

Damper Valve - Hydraulic Details

Compression Stage: The rod and attached piston is forced downwards in the damper cylinder. The oil in the cylinder provides lubrication and resistance to the piston movement (shown to the right).

The oil is forced through the primary valve which pushes the EDC-K Damper valve upwards. The floating seat ring rests at the bottom and the oil will flow through the orifices which control the rate (direction indicated by the arrow).

Scheme 21

Rebound Stage: The rod and attached piston is forced upwards in the damper cylinder. The oil in the cylinder provides resistance to the piston movement (shown to the left).

The oil will flow through the orifices forcing the floating seat ring up against the EDC-K Damper valve. The oil continues to flow through the primary valve to control the rate (direction indicated by the arrow).

The armature is controlled (electronically) by the EDC-K control module to regulate the EDC-K Damper valve and floating seat ring positions which varies the resistance to oil flow by restricting the orifices.

Scheme 22

Vertical Dynamics Control

Vertical Dynamics Control responds to vertical (up/down) body movements based on wheel/body acceleration and speed. A distinction is made between a low frequency body vibration (approx. 1 Hz) and a high frequency wheel vibration (approx. 10 to 15 Hz). Because the body speed cannot be measured, a characteristic value is calculated from the acceleration signals. This value is adapted based on the vehicle speed, frequency ranges and road surfaces.

The higher frequency vibrations of the axle are calculated as the wheel dynamics value based on the wheel speed signal inputs. The value is determined from the irregularities of the wheel rotation when driving over bumps. This control operation takes place separately for both axles.

Longitudinal Dynamics Control

The Longitudinal Dynamics Control responds to acceleration and braking body movements (forward/backward). The vehicle speed signals are monitored by the control module: two direct wheel speed inputs from the DSC control module and three digital inputs from the PT-CAN Bus. Two of the signals on the PT-CAN Bus correspond to the 2 wheel speed signals from DSC and the third signal is the averaged vehicle speed.

The EDC-K control module assesses the plausibility of these signals. A Longitudinal Dynamics value is calculated from the wheel speed signal, which represents the level of acceleration or deceleration. The dampers are adjusted (on both axles) to the harder setting to counter act the longitudinal movement.

Transversal Dynamics Control

The Transversal Dynamics Control responds to transversal movement (dive and squat - front to back roll). This value is calculated from the steering angle sensor and the vehicle speed signals. The onset of "yaw" movement is detected very early from the steering angle sensor signal. A harder damper setting to support the vehicle as it enters a curve is activated at an early stage. The front and rear axles are separately controlled.

Copy Control

The Copy Control function responds to the compression and rebound of the body (encountering bounces on one side of the vehicle) while driving straight ahead. Through comfortable damper tuning, EDC-K responds to one sided unevenness due to the road surface. This prevents a side to side rolling motion while driving straight ahead.

Once vehicle "copying" is detected, a harder damping combination is applied to the front and rear axles. Detection is based on the evaluation of the right and left vertical acceleration signals from the front axle.

Tolerance Adaptation

The damper force is diminished as part of the operating time function. Diminishing damper forces are compensated by current (amperage) reductions which are calculated by the tolerance control. This also individually compensates for mechanical damper wear on each axle.

Control Strategy

All of the dampers are controlled simultaneously until a single damper control in particular is required. For stability reasons, the smallest desired output current of the four damper controls (hardest damper setting) is set.

Plausibility Monitoring And Safety Concept

The EDC-K inputs and outputs are checked for plausibility. Depending on the type of fault, restricted operation of the damper control system will occur while a high degree of safety and comfort is maintained.

The control display informs the driver when an EDC-K system fault has occurred. There are two different shutdown options in the event of faults.

1. In partial operation, medium damping is set by a fixed current at the front and rear axle valves.
2. When the entire system is shut down, the de-energized valves instantly switch (spring loaded) and remain in the "hard damping" setting.

In the event of system faults, the chassis and suspension is set to a safe condition that is acceptable to the driver. The valves, sensors, electric circuits and EDC-K control module are fault monitored.

System Faults and Reactions

SYSTEM FAULTS AND REACTIONS

CAN Interface

The steering angle value is prepared and is transmitted by the SZL over the CAN Bus. Both of the front wheel speed signals (including the direct DSC wheel speed signal), the vehicle speed reference value and the mileage reading are provided by the DSC control module over the CAN Bus to the EDC-K control module.

Power Supply

Low current supply to the damper valves results in hard damping and a high current results in soft damping. The EDC-K control module determines the setpoints and outputs pulsewidth modulated (PWM) signals to the damper valves to regulate the current flow. Current flow limitation is ensured by an overcurrent detection and deactivation. All of the analog inputs are protected by diodes against positive and negative overvoltage. The following analog signals are processed by the EDC-K control module

1. Vehicle supply voltage
2. EDC-K switched output voltage
3. Damper valve voltage and current

Valve Activation/Output Stage Circuit

The solenoid valves have low resistance, approximately 2.2 ohms per valve at room temperature because high current is needed at a low voltage. The current is set in the 0 to 2 Amps range depending on the desired damping force. The setpoint value will not exceed 2 Amps to avoid valve damage. The solenoid valves are connected in series for each axle and are supplied with a ground (PWM for continuous adjustment) from the EDC-K control module.

Rear Axle EDC-K Valves Series Connection

Scheme 23

Notes On Service

When the steering angle sensor is removed, the steering wheel must be manually positioned to the straight ahead position and this position re-initialized in the SZL. The steering wheel straight ahead position is permanently monitored while driving.

EDC-K diagnosis detects electronic damper faults on the complete axle only. Mechanical testing of individual dampers can be carried out in the damper test. Mechanical wear causes the dampers to weaken over the service life, therefore a running time memory adapts the damper curves towards a harder setting (over time). Faulty dampers must be replaced together (in pairs) on a single axle. After a replacement, the running time memory for the front or rear axle must be reset with the DISplus.

A 10 Pin Adapter Cable is available to adapt the MFK cables to the EDC-K control module when using the DISplus (Test Plan).

Special Tool #90 88 6 372 050

Scheme 24

Stabilizer Bars On The Front And Rear Axles

Body roll is built up over the vehicle's longitudinal axis as a result of the centrifugal force at the center of gravity. This force causes the vehicle body to lean towards the outside wheels while cornering and quickly draws the vehicle closer to the limits of driving dynamics. The tilt angle of the body and the increased wheel load is counteracted by the use of stabilizer bars.

Scheme 25

When cornering, the wheel on the outside of the corner compresses the spring, and the inner wheel extends the spring which causes the stabilizer bar to turn (twist).

The forces on the mounting points of the stabilizer bar generate a torque that counteracts the body angle providing better load distribution on both wheels on the same axle.

The suspension is firmer with a solid stabilizer bar. The disadvantage is that when you are driving straight ahead during a one-sided compression (bounce), this transmits a "copying" effect through the suspension, which reduces comfort.

Scheme 26

Purpose Of The System

The Dynamic Drive - Active Roll Stabilizer Bar (ARS) is a revolutionary step for chassis technology. ARS goes a long way towards removing the conflict between handling/agility and comfort. ARS has two stabilizer bars that have a positive effect on the body roll and handling, allowing softer springs and dampers to increase comfort.

Active Stabilizer Bar on the Rear Axle

Scheme 27

Dynamic Drive controls two active stabilizer bars on the axles depending on the lateral acceleration.

Oscillating Motor

The two separate stabilizer bars on each axle are mounted in roller bearings and are connected by a hydraulic oscillating motor.

One half of the stabilizer bar is connected to the oscillating motor shaft and the other is connected to the oscillating motor housing.

Active stabilizer bars introduce fewer forces into the body as compared to solid stabilizer bars because the separate "halves" will not copy one sided suspension compressions (bounces).

Scheme 28

The active stabilizer bars set the stabilizing torque, resulting in

1. Minimizing or completely eliminating body roll while cornering
2. Reduction in the "copying effect" of the vehicle
3. A high degree of agility and precision throughout the entire speed range
4. Produces optimum self steering characteristics
5. Improved suspension comfort (when driving straight ahead) because the stabilizer bar halves are independent and do not stiffen the basic suspension during a one-sided compression.

The distribution of the active body torque between the front and rear axle depends on the road speed. The following describes the different body torque distribution.

Self Steering Affect

The self steering affect is influenced by the distribution of the stabilizing torque on the axles. The greater the stabilizing torque on an axle, the lower the lateral forces will be that are transmitted on this axle. Two situations are described below with a different distribution of stabilizing torque on the axles

Identical stabilizing torque on both axles: Handling is "NEUTRAL". The front wheels will apply about the same amount of lateral force to the road as the rear wheels (without drive torque). A vehicle that is tuned to neutral handling provides very agile handling and the steering reacts very quickly. The driver experiences precise handling.

Larger stabilizing torque on the front axle: Handling is "UNDERSTEERING". The front wheels cannot apply the same amount of lateral force to the road as the rear axle wheels. The vehicle tends to go straight requiring an increase in steering to make the vehicle turn.

Dynamic Drive sets the stabilizing torque on the front and rear axle to create a different handling characteristic for low and high speeds.

Road Speed Handling

Low Neutral

High Understeer

Passenger vehicles are designed for slight understeer depending on the speed range. Dynamic Drive is tuned to neutral in the lower speed range, requiring less steering to go around the same corner. This produces optimum handling and agility. In a higher speed range, Dynamic Drive is designed so that a larger active stabilizing torque will occur on the front axle as compared to the rear axle. This means that the vehicle with Dynamic Drive reduces over sensitive steering a higher speeds to enhance handling characteristics .

System Dynamics

When the vehicle changes lanes, corners or changes direction quickly (winding roads), Dynamic Drive reacts very quickly. The system dynamics reaction time is shown in the following steps

Process Signal detection by sensors, processing of sensor signals and valve control. Change of direction, switching over the torque direction, direction valve. 0 to 30 bar (0 to 350 N) 0 to 180 bar (0 to 2100 N)

Time approx. 10 ms approx. 30 ms approx. 120 ms approx. 400 ms

Scheme 29

Dynamic Drive (ARS) consists of the following components

Scheme 30

ARS Control Module: The control module is located on the right side "A" pillar in front of the glovebox and is powered by B+ through a 10 Amp fuse. The control module is activated by a CAN alarm lead from the CAS module when the ignition is switched "ON".

A vehicle authentication process takes place when the system is started. This compares the vehicle identification number from CAS with the vehicle identification number which is encoded in the ARS control module.

Scheme 31

After the ignition is switched "ON", the ARS hardware and software is self-checked. All of the outputs (magnetic valves) are checked for short circuits and breaks. When there is a fault, ARS switches the actuators to a safe driving condition. The control module will switch off in the event of undervoltage or overvoltage.

Scheme 32

Inputs: The ARS control module requires dynamic driving input signals to calculate the required activation. The following input signals are monitored and checked for plausibility

1. Lateral acceleration
2. PT-CAN Bus
3. Front axle ARS circuit pressure
4. Rear axle ARS circuit pressure
5. Selector position recognition sensor (SSE)
6. Fluid level sensor signal

The PT-CAN provides additional information about lateral dynamics

1. Vehicle speed signal (DSC)
2. Steering wheel turning angle (Steering Angle Sensor)
3. Yaw velocity - Transversal acceleration (Rational Rate Sensor)

These inputs allow the ARS control module to determine the stabilization requirement at the appropriate inertia moments. The reaction time is decreased by using the vehicle speed and steering angle inputs.

Outputs: All of the outputs are check by diagnostics and are short circuit protected. The outputs (and control) include the following

1. Pressure control valves for the front and rear axle ARS
2. Directional valve
3. Fail-safe valve
4. V sensor voltage supply

The valves are controlled by pulse width modulation current. The individual coil current requirements are constantly checked for plausibility. The current measurements allows the pressures to be precisely set and electrical monitoring of the hydraulic the shift valves.

The PT-CAN sends a message to the ECM indicating how much engine power is required to drive the tandem hydraulic pump to activate the ARS stabilizer bars.

An "alive" data signal is provided and monitored by other control modules to detect the system status. All signal faults are permanently stored. Output faults include short circuits (B+ and ground) and open circuits.

Sensor System

Lateral Acceleration Sensor: The lateral acceleration sensor is located under the carpet in front of the passenger's seat (1). While cornering, the vehicle's lateral acceleration is measured (range is +/-1.1 g).

Transversal acceleration (yaw velocity) is provided by the Rotation Rate Sensor (2) via the DSC control module.

Scheme 33

Front and Rear Axle Stabilizer Bar Pressure Sensors: The pressure sensors provide the ARS control module with the front (1 below left) and rear (2 below left) axle stabilizer bar hydraulic operating pressures. The sensors are mounted on the valve block assembly and the pressure values are initialized in the control module (during assembly line commissioning). The voltage value is proportional to the operating pressure (in bar shown below right).

Scheme 34

Scheme 35

Selector Position Recognition Sensor (SSE): The SSE is mounted on the valve block assembly (3 above left). This sensor allows the ARS control module to detect the specific position of the directional valve (4 above left). The 2 positions detected are

1. Left hand control (direction of torsional twist)
2. Right hand control (direction of torsional twist)

w: The fluid level sensor allows the ARS control module to detect the fluid supply level in the reservoir (power steering reservoir) for the tandem pump. The fluid level sensor indicates when the fluid drops below the minimum level and triggers a warning message.

Normal fluid movement (slosh) will not trigger the sensor. Short/open circuits are not detected by the fluid level sensor circuit and a circuit break is interpreted as a loss of fluid.

Scheme 36

Actuator System

Pressure Control Valves: There is a pressure control valve for both the front (1 below) and rear (2 below) axle hydraulic circuits. The valves adjust the front and rear axle stabilizer bar actuation pressures. When driving straight ahead, the pressure control valves are de-energized opening the valve diameters allowing the fluid to return to the reservoir (circulating).

When cornering, the valves are energized to readily increases the pressure in the oscillating motors to the setpoint value.

Depending on the lateral acceleration and the vehicle speed, the pressures for the front axle are regulated between 5 to 180 bar and 5 to 170 bar for the rear axle.

Scheme 37

Directional Valve: The directional valve (3 above right) is electrically actuated by the ARS control module to control the direction of the hydraulic pressure for right and left hand twists.

Fail-safe Valve: The fail-safe valve (4 above right) is electrically actuated by the ARS control module to open the front axle hydraulic circuit to the oscillating motor. The circuit is closed when the fail-safe valve is de-energized, decreasing the system pressure (circulating).

Check Valves: The check valves (internal in the valve block) allow the hydraulic fluid to be drawn from the reservoir preventing cavitation in the oscillating motor.

Valve Block: The valve block is an electrically controlled hydraulic distribution assembly and is located behind the right front wheel housing panel (at the base of the A-pillar).

Scheme 38

Valve Block Functions

1. Distribution of hydraulic fluid flow to the oscillating motors: The pressure at the front axle oscillating motor is greater than or equal to the pressure at the rear axle oscillating motor.
2. Measuring the actual pressure of the high pressure hydraulic fluid: There is a pressure sensor for both the front and rear axle oscillating motor hydraulic circuits on the valve block.
3. Fast and precise regulation via the pressure control valves: Introduced pressure changes as a result of uneven roads are passively regulated to reduce noise as much as possible.
4. Adjustment of the volume flow direction (left hand/right hand twist) via a directional valve: The directional valve position is detected by a selector position recognition sensor (SSE).
5. Switch to Fail-safe mode in the event of power supply failure or a fault is detected in the system: The front axle oscillating motor hydraulic circuit is closed off and hydraulic flow is diverted to the reservoir. The check valves will open to allow the hydraulic fluid to be drawn from the reservoir. The rear axle oscillating motor hydraulic circuit is also deactivated and hydraulic flow is diverted to the reservoir.
6. Limiting the system pressure in the event of a fault: The Fail-safe valve causes the circuit to close when de-energized, decreasing the system pressure (circulating).

Valve Block Sub-Components

VALVE BLOCK SUB-COMPONENTS

Active Stabilizer Bar (one assembly per axle): The active stabilizer bar consists an oscillating motor and two stabilizer bar halves with press fit roller bearings to mount the assembly to the axle carrier.

The oscillating motor and the oscillating motor housing joins the two halves of the stabilizer bar.

The rear axle Active Stabilizer Bar is shown on the right.

Scheme 39

The Active Stabilizer Bar assembly has three tasks

1. The oscillating motor decouples the two halves of the stabilizer bar.
2. The oscillating motor guides the torque into the two halves of the stabilizer bar.
3. In the event of system failure (Fail-safe mode), the front axle stabilizer bar creates sufficient damping from the oscillating motor hydraulic fluid (hydraulic locking) to work like a conventional stabilizer bar.

Exception: If the oscillating motor chambers do not contain any fluid as a result of a leak, the front axle stabilizer bar will not dampen and rely on the spring strut assemblies.

Oscillating Motors: The oscillating motors are split chamber hydraulically controlled rotary actuators. This motor contains a total of four chambers, opposing chambers are connected with one another and receive the same hydraulic pressure.

Two chambers are supplied with high pressure through an internal connection and the other two chambers are connected to the reservoir return line.

The pressure and drain (return) is switched between the two pairs for right or left hand torsional twists.

Scheme 40

The different pressures result in the high and low forces that apply torque. One half of the stabilizer bar is connected to the shaft and the other half is connected to the housing.

The two halves will turn in opposite directions. As a result, the shaft will turn in an opposite direction of the housing.

The stabilizer bar is mounted to the axle carrier. The torque generated while cornering will force the body upwards on the outside of the curve and pull it down on the inside of the curve.

Scheme 41

Scheme 42

The maximum torque influence on the front and rear axle occurs when there is a high degree of lateral acceleration (producing body roll). During this situation, the system pressure is 180 bar at the front axle and 170 bar at the rear axle. The front oscillating motor is smaller than the rear one and builds up a force of 600 N.m at 180 bar. The rear oscillating motor builds up a force of 800 N.m at 170 bar. The oscillating motors also act as torsional vibration dampers (hydraulic cushion).

During torsional twists, the fluid is displaced from two chambers returning through the lines and the valve block to the reservoir. The return path has a slight hydraulic resistance which creates damping. With fail-safe (hydraulic blocking), the oscillating motor will turn as a unit because of the closed circuit hydraulic locking occurring internally (like a conventional stabilizer bar).

Tandem Pump: The tandem pump mounted on the engine and is driven by the ribbed V-belt. The pump assembly consists of a radial piston pump for Dynamic Drive and a vane pump for the power steering.

When the engine is idling, the pump speed is approx. 750 RPM providing a minimum flow rate of 4.5 l/min at 0 - 5 bar and 3.3 l/min at 180 bar. This volume and pressure provides sufficient system dynamics when the engine is idling. At a pump speed of approx. 1165 RPM, the flow rate is limited to 7 l/min. Dynamic Drive and power steering share the fluid reservoir and fluid cooler.

Scheme 43

Fluid Reservoir: The fluid reservoir is identical on all E65 vehicles, whether equipped with Dynamic Drive or not. The fluid reservoir also supplies the power steering hydraulic circuit.

The reservoir contains a fluid filter (as on models in current use) and a fluid level sensor to detect when the fluid level drops below the minimum amount.

Scheme 44

Fluid Cooler: The cooler ensures a long term fluid temperature of < 120 °C and a short term fluid temperature of < 135 °C in all hydromechanical components under all operating conditions.

Scheme 45

Hydraulic Lines and Hoses: The hydraulic lines and hoses are designed for extremely high pressures. The hydraulic component connections and fittings are designed with different dimensions and lengths to avoid improper installation.

Hydraulic noises transmitted to the vehicle interior predominantly occurs through the assemblies and connections. The lines and hoses must be properly positioned through the mounting supports (noise insulation) and not touch the body surface. The supply hose in the engine compartment has excess loops (and length) to also reduce hydraulic noise.

Dynamic Drive System Pre-Drive Procedure

When the ignition is switched "ON", the ARS control module self test is first performed. The electrical valve functions are conducted to detect short/open circuits in the valve solenoid coils, connectors and harness. The sensors are checked for short/open circuits in the harness, connectors or the internal electronics.

Finally, the hydraulic safety functions are checked before the vehicle moves as part of the "Pre-drive Check".

A test pressure (<60 bar) is set between the pump and the fail-safe valve. This allows the ARS control module to check if the fail-safe valve is actually in the de-energized fail-safe position. When in this position, the system pressure is decreased (circulating).

When the fail-safe valve is energized (FS as shown to the right) by the ARS control module, the front axle hydraulic circuit is open providing pressure to the oscillating motor (SMV).

The front axle pressure control valve function is tested simultaneously. If pressure does not build up at the front axle stabilizer bar, the Predrive Check criteria will not be met.

Scheme 46

The Dynamic Drive function is deactivated when the vehicle is stationary (inertia is not present) and all the valves are de-energized. This also applies when the vehicle is at a standstill on an incline (one sided load). Even though the lateral acceleration sensor provides a signal, the vehicle speed signal is not present.

When the vehicle speed is >15 km/h, the ARS function is started.

Straight Ahead Driving

When the engine is running, the tandem pump supplies hydraulic fluid to the system at a pressure of 3 to 5 bar. The front and rear axle stabilizer bar pressure valves are de-energized (open) and pressure is not applied to the oscillating motors. The hydraulic fluid circulates directly back to the reservoir for as long as the vehicle is driven straight ahead.

Cornering

When cornering, the signals from the lateral acceleration sensor are conveyed to the ARS control module. The control module outputs a pulse width modulated signal (PWM) to the front and rear axle stabilizer bar pressure valves. The stronger the lateral acceleration, the greater the signal (current flow). The increasing valve current will progressively close the valves forming a higher pressure in the stabilizer bar oscillating motors.

The pressure sensors provide the ARS control module with the stabilizer bar oscillating motor pressures. To direct the buildup pressure according to the corner (left hand or right hand twist), the directional valve is actuated by the control module. The SSE sensor detects the directional valve selector position.

Restricted Function

The system reverts to fail-safe mode when a fault is detected. The control module stores the fault and indicates fail-safe mode in the instrument cluster. The fail-safe situation is shown to the right in the hydraulic overview diagram.

Scheme 47

In the event of system failure, the fail-safe valve (FS) is de-energized and sprung closed. The hydraulic fluid in the front stabilizer bar is sealed in, ensuring the stability and understeer effect of a conventional stabilizer bar.

The check valves (RVV1, RVV2) allow the hydraulic fluid to be drawn from the reservoir preventing cavitation in the oscillating motor when the vehicle is driven straight.

External Leakage

External leakage is detected by the front or rear pressure sensors and the ARS control module will deactivate Dynamic Drive (system failure).

Scheme 48

Restricted Control Comfort

Lateral acceleration is calculated from the vehicle speed and steering wheel angle (CAN signals). This signal is faster than the actual lateral acceleration and compensates for the hydromechanics time delay. If there is a fault with these two signals, the system reacts with delayed rolling compensation. This only happens with extremely fast steering, when cornering normally it is barely detectable.

If the lateral acceleration senor is faulty, the lateral acceleration is calculated solely from the can signals. The driver will not feel any restriction in function.

If there is a fault in the rear axle circuit and there is stabilizing on the front axle only, the driver feels that the vehicle is making larger rolling movements. Agility is reduced at road speeds <120 km/h.

The system also reacts this way if the Pre-drive Check brings up the "fail-safe valve stuck open" message.

In the event of an electrical fault on the rear axle pressure sensor, there may be roll angle compensation defects. To be on the safe side, slightly more stabilization torque is transferred to the front axle than in the normal operating mode (this can be felt by the driver).

Warning message Handling instructions

Cornering stability slightly restricted Chassis stability slightly restricted when cornering. Drive on, contact BMW Center as soon as possible

Restricted System Monitoring

Dynamic Drive receives the following sensor signals from the DSC and SZL via the PT CAN Bus

1. Lateral acceleration
2. Yaw velocity
3. Road speed
4. Steering wheel angle

These signals are used to check the lateral acceleration sensors.

Control comfort is restricted if the engine speed signal (DmE) fails.

In the event of a fault with the CAN signals and the yaw velocity, the system is missing two pieces of information. Since this information is used solely to check the other signals, the ARS function remains available with full control.

Although there is no restriction of the Dynamic Drive function, the driver will be shown the "chassis control comfort" display. The driver is instructed to drive to the workshop if possible.

Warning message Handling instructions

Cornering stability slightly restricted Chassis stability slightly restricted when cornering. Drive on, contact BMW Center as soon as possible.

A "dynamic" driver will notice the loss of the steering angle signal and the warning messages will be acknowledged. The warning message will disappear once it has been acknowledged. When the cause of the fault is corrected, the ARS control module will have full capacity.

Depending on how fast a fault is detected, there are two reset opportunities

1. When the ignition is off, all faults which have been corrected will be reset. You must wait until the sleep mode has been activated before switching the ignition back on.
2. Faults that occur sporadically and can generally be traced back to CAN bus communication malfunctions, are automatically reset when driving straight ahead or when stationary. In this case, the driver may not be aware of the re-activation when driving or when the car is stationary.

The faults are stored in memory with important additional information. The additional information includes the mileage when the fault occurred, details of whether the fault is present and the frequency of the fault occurrence.

Note. When there is a Dynamic Drive failure, the DSC can not be deactivated or if it is already deactivated it will not switch back on automatically.

Dynamic Drive Commissioning

The commissioning procedure must be carried out using the DISplus after the hydraulic system was opened or a component was replaced (in particular the lateral acceleration sensor). This procedure is found under Service Functions - Chassis - Dynamic Drive - Start Startup - Test Plan and follow the on screen instructions. The following criteria must be met for matching the lateral acceleration sensor and the two pressure sensor offset values

1. The vehicle must stand level on all four wheels (on the ground).
2. The vehicle must be unloaded.
3. The engine must be idling at operating temperature.
4. The doors must be closed and occupants are not allowed in the vehicle .

Note. Stay clear of the moving chassis parts during the commissioning. The ground and side to side clearance must not be limited or obstructed and the doors must be closed. The arms of the lift hoist must not be situated underneath the vehicle. Vehicle will not be able to be driven (transmission will remain in "Park" during this procedure).

The commissioning is performed in five steps that are automatically carried out during the procedure

COMMISSIONING PROCEDURE

Dynamic Drive Bleeding

After all work on the Dynamic Drive and the steering system in which hydraulic lines have been opened, the steering system must be bled and initial operation of the Dynamic Drive (commissioning) must be performed with the DISplus.

Procedure

1. Check fluid level in the powersteering reservoir; if necessary, top up to the "MAX" level while the engine is stopped.
2. Start the engine. Turn the steering wheel left and right to the full lock twice.
3. Check the fluid level with the engine stopped; if necessary, top up to the "MAX" level.
4. Start the engine, connect vehicle to the DISplus.
5. Start the Commissioning procedure which is found under Service Functions - Chassis - Dynamic Drive - Start Startup - Test Plan and follow the on screen instructions.

Note. Refer to the Repair Instructions for details on the Dynamic Drive bleeding procedure.