Dynamic Stability Control
Dynamic Stability Control
NOTICE: Structure of this document.
The most important diagnosis instructions are described at the start of this document. These are followed by the functional description.
Diagnosis instructions
Remedy faults or delete fault memory and ensure indicator and warning lights go out
If there are problems deleting the fault memory after a repair or if the DSC indicator and warning lamp does not go out, use the following procedure:
1. Remedy fault with ignition off
2. Switch ignition ON, delete fault code memory
3. Switch ignition OFF, wait 5 - 10 seconds, switch ignition on again
4. Delete fault memory again
5. Switch ignition OFF, wait 5 - 10 seconds, switch ignition on again
6. Ignition OFF, DSC indicator and warning lamp goes out
IMPORTANT: In some cases, indicator and warning lights for certain faults only go out after a short test drive.
Sequence for replacement of DSC unit or DSC control unit
After replacing the DSC unit or DSC control unit The parameters for the Run Flat Indicator (RPA) as well as for the cruise control system must be coded using Progman.
Carry out the following repair operations:
1. Encoding DSC
2. Brake bleeding procedure for DSC unit
3. Brake line mix-up test:
4. Initialize Run Flat Indicator (see operating instructions)
Replacement of steering angle sensor
The steering angle sensor forms a unit with the steering column switch cluster. The steering angle sensor cannot be replaced on its own. The "steering angle sensor calibration" service function or the "activate/adjust Active Steering" service function on vehicles with Active Steering must be performed after the following repair operations:
- Replacement of steering column switch cluster (SZL)
- Adjusting procedure on the steering geometry
- Repair work on the steering and/or front suspension
Introduction
Dynamic Stability Control
The new BMW 7-Series is equipped with Dynamic Stability Control (DSC) as standard equipment. Dynamic Stability Control could only be implemented in coordination with the central vehicle dynamics control in the Integrated Chassis Management's (ICM) master control unit. The newly introduced function "Driving Dynamics Control" also influences the operation of DSC. Depending on the selected stage (COMFORT, NORMAL, SPORT, SPORT+), the threshold values and characteristics of the DSC interventions also have to be adapted. Alongside the co-ordination, there are other changes to Dynamic Stability Control that concern the installation position, display functions, as well as diagnosis and repair.
Brief component description
The following components for dynamic stability control are described:
DSC unit
The DSC unit consists of the DSC control unit and a hydraulic unit. The DSC control unit activates the hydraulic unit via valve coils.
The DSC unit contains a brake pressure sensor. This brake pressure sensor registers the braking pressure applied by the brake pedal and the brake booster. The brake pressure sensor has a measuring range from 0 to 250 bar. Its zero point is only synchronized during driving.
The new concept of the DSC unit enables more exact control. 2 x 3 pump elements with white box 6.5 mm work in the pump motor. This concept results in significantly improved pressure dynamics. It means that the brake pedal pulses to a lesser degree during ABS control. It also leads to higher control quality with Hill Descent Control (HDC).
The power distribution box at the junction box electronics (JBE) supplies the DSC unit with voltage. Once terminal 30 for the return-flow pump, once terminal 30 for the solenoid valves. The DSC control unit receives terminal 30F.
4 wheel speed sensors
The active wheel speed sensors are connected to the DSC control unit. The complete signal processing takes place in the active wheel speed sensors.
The active wheel speed sensors also detect the direction of travel.
The wheel speed is measured at a magnetic increment wheel. The magnetic increment wheel is divided into 96 increments per rotation of the wheel. Each increment change is detected by the active wheel speed sensor and converted into a defined signal protocol of a pulse-width modulated signal.
ICM: Control unit for Integrated Chassis Management
New: Sensors that used to be installed separately in the DSC sensor are now fitted in the ICM control unit. The ICM control unit uses these sensors to calculate variables that are important for the dynamic handling characteristics of the vehicle at that time:
- Longitudinal acceleration and vehicle inclination in longitudinal direction
- Lateral acceleration and vehicle inclination in transverse direction
- Yaw rate
Initially, the sensor signals are related to the sensor housing. However, the driving stability control needs these variables related to the co-ordinate system of the vehicle. The ICM control unit performs the necessary conversion. The correction values necessary for this are determined by an adjustment during commissioning of the ICM control unit.
An adjustment of the integrated sensors is necessary after replacement of the ICM control unit. The adjustment must take place while the vehicle is on a subsurface that is horizontal in longitudinal direction and transverse direction. Terminal 15 must be switched on.
Steering angle sensor
The steering angle sensor is installed in the steering column switch cluster (SZL). The steering angle sensor measures the steering wheel angle optically and without contact. The steering angle sensor is fitted on the printed circuit board with the evaluation electronics. The steering angle sensor consists of the following components: encoded disc and optical sensor.
The encoded disc is connected to the steering wheel via the coil spring cassette. When the steering wheel is moved, the encoded disc moves within the optical sensor. There are various line patterns for evaluation on the encoded disc.
The SZL is connected across the FlexRay via the central gateway module (ZGM) with the DSC control unit.
DTC button
The DTC button is located in the centre console operating facility. The DTC button is used to change the operating mode of the chassis control system. The DTC button can be used to select 3 switching states:
- DTC button not pressed after terminal change: DSC in operation (standard)
- Press DTC button briefly: DTC
- Press DTC button for longer period: DSC and ASC switched off, ABS and ABD-X still active
New is the display with selected DTC button. "TRACTION" can be seen in the revolution counter of the instrument panel. The symbol of the indicator light has changed as a result of legal regulations: Skidding vehicle with the labelling "OFF".
The DSC receives additional input signals from the following components:
Parking brake button
The parking brake button is located in the centre console behind the gear lever switch (GWS). With the engine running or vehicle moving: The parking brake has a hydraulic effect on the disc brakes of the front and rear axle via the DSC. With the engine off and vehicle at a standstill: The parking brake employs Bowden cables and the electromechanical actuator unit to operate the drum brakes on the rear axle. Driving off against the blocked brake pressure leads to another pressure increase and a Check Control message. Starting the engine leads to a switch from electromechanical to hydraulic parking brake engagement.
The DSC receives additional input signals from the following components:
Brake fluid level switch
A low brake fluid level is picked up (in the expansion tank via a reed contact) and notified to the DSC control unit. With a low brake fluid level, DSC is disabled. Otherwise, there is a danger that air will be drawn into the brake system.
The brake fluid level switch is activated in response to a low fluid level in the brake fluid reservoir. The DSC control unit sends the signal of the bus system to the instrument panel. The instrument panel issues a Check Control message. The usual motion of the brake fluid within the reservoir does not generally trigger a Check Control message.
There is a permanent magnet in the moving float; this triggers the reed contact in the brake fluid level switch firmly fitted in the fuel tank. Here, the reed contact converts the float movement into an electrical signal. The reed contact is closed while the brake fluid level is above the minimum mark.
Brake light switch
Together with the signal from the brake pressure sensor, braking operations are detected. Two Hall effect sensors as switches are installed in the brake light switch: the brake light switch and the brake light test switch (redundancy for safety reasons). The signals indicate whether the brake pedal has been pressed. The data interchange is digital.
The two redundant signals from the brake light switch are read in by the Car Access System (CAS). The CAS forwards the signals on the bus system, e.g. for the engine control system.
The signals from the brake light switch are hard-wired and branched off for the following systems:
- Dynamic Stability Control (DSC) for the brake intervention
- Footwell module (FRM) for reversing light
2 brake pad wear sensors
The brake pad wear sensors (front left and rear right in the inner brake pads) provide additional information on the thickness of the brake pad. This additional information (2 data points) is compared to the value calculated by the DSC.
A critical brake pad thickness is indicated in the instrument panel by a Next Service indicator (Condition Based Service CBS) as well as the red general brake warning light.
The following additional control units are involved in the dynamic stability control:
Instrument panel: Instrument panel
In the event of failure malfunction of the DSC, a Check Control symbol appears in the LC display. The Check Control symbols all have a certain meaning.
If there is a Check Control message, additional supplementary instructions can be displayed on the central information display (CID).
CAS: Car Access System
The CAS receives a processed speed signal from the DSC. The CAS recognizes from the signal whether the vehicle is stationary or moving.
JBE: Junction Box Electronics
The power distribution box at the JBE supplies the DSC unit with voltage. Terminal 30 for the return pump and the solenoid valves. Terminal 30 for the DSC control unit.
System functions
The following illustration shows the functional networking.
The following system functions are described for the DSC:
- DTC: Dynamic Stability Control
- Brake standby through application at an early stage of the brake pads when required
- Dry braking of the brake discs on wet roadways
- Fading Brake Support
- Drive-off assistant
- Cruise control with brake function
- electromechanical and hydraulic parking brake
- ABS: Antilock braking system
- EBV: Electronic brake force distribution
- CBC: Cornering Brake Control
- MSR: Engine drag torque control
- ASC: Automatic Stability Control
- DSC: Dynamic Stability Control
- DBC: Dynamic Brake Control
- Trailer Stability Control
Other known system functions for the DSC are:
The following additional functions that do not belong to driving dynamics control are integrated:
- RPA: Run Flat Indicator
- CBS: Condition Based Service
DTC: Dynamic Traction Control
DTC is a drive-optimized version of DSC for certain road conditions. The dynamic traction control (DTC) provides improved traction with partially reduced driving stability and is thus only recommended for exceptional situations. In the following exceptional situations, it can be useful to activate DTC briefly:
- When 'rocking out' or driving off in deep snow or on loose surfaces.
- When driving on snow-covered upward inclines, in slush as well as on uncleared roadways
- When driving with snow chains.
The function DTC corresponds to that of DSC with a slightly modified control strategy. DTC can be activated by shutting down DSC (DTC button). With brake intervention, DTC replicates the function of a conventional differential interlock. This effect of this is to increase the input torque on those wheels that are on a higher-friction surface. Advantage: Higher traction is available with DTC. Interventions to stabilize the vehicle (e.g. reduction in the engine output) are carried out slightly later than in the case of DSC. In certain situations, the driver must intervene correctively to stabilize the vehicle.
Brake standby through application at an early stage of the brake pads when required
Application of the brake pads at an early stage shortens the response time of the brakes. With rapid closure of the throttle (angle of the accelerator pedal), the brake pads are applied immediately. The DSC creates a low brake pressure without perceptibly decelerating the vehicle. This compensates for the clearance between the brake pad and brake disc. If there is no braking within half a second, the created early brake pressure is taken back. Applying the brake pads at an early stage is active at a driving speed greater than 70 kph.
Dry braking of the brake discs on wet roadways
Dry braking removes the moisture deposited on the brake disc when driving on wet roads or in the rain. Here, the brake pads are applied slightly. This function also shortens the brakes' response time. DSC employs a cyclical control process to reduce braking pressure in response to signals from the rain sensor and the position of the wash/wipe switch. This creates no measurable deceleration on the vehicle. The brake pads are cyclically applied. The brake discs are wiped regularly in the process. The frequency and duration of brake-pad applications varies according to:
- The intensity of the rain, e.g. speed of the wiper
- Driving speed greater than 70 km/h
Fading Brake Support
Fading means: the braking effect diminishes due to high brake disc temperature. As a reaction to detected fading, DSC increases the brake pressure beyond the brake pressure applied by the driver. At very high brake disc temperature, the fading compensation leads to the following being displayed:
- Brake warning lamp in yellow
- Check Control symbol in the LC display in the instrument cluster in yellow
The DSC detects fading as follows: The DSC compares the current vehicle deceleration with a set point value related to the current brake pressure. The DSC increases the brake pressure until the target deceleration is reached or until all the wheels are subject to ABS control. The operation is terminated when the brake pedal is no longer pressed or a speed threshold is undershot.
Drive-off assistant
When driving off on an incline, a change from the brake pedal to the accelerator pedal is required. Here, the drive-off assistant prevents the vehicle from rolling in the following situations:
- uphill in a forward gear
- uphill in reverse gear
Here, the brake pressure required to stop the vehicle is maintained. The gradient is picked up by the longitudinal acceleration sensor in the DSC control unit. The necessary braking torque or engine torque is calculated from the gradient. After detection of the wish to drive off, the brake pressure is reduced as soon as the applied engine torque is sufficient to move the vehicle in the desired direction of travel. If the parking brake is operated, the drive-off assistant is disabled. If there is no wish to drive off within approx. 2 seconds after releasing the brake pedal, the drive-off assistant is also disabled.
Cruise control with brake function
The functionality of the cruise control system with its braking function is integrated in DSC. The cruise control maintains the speed at the selected level, between 30 km/h and 250 km/h. In comparison with a conventional cruise control, it has the following additional functions:
- If the engine drag torque in coasting (overrun) mode is not sufficient to maintain the selected speed, the DSC additionally decelerates by means of controlled brake intervention.
- Depending on the current lateral acceleration, the speed in longitudinal direction is transverse acceleration during controlled cornering. At the end of the bend, the set speed is readjusted.
- The so-called "hand gas mode" enables the driver to use the steering-column lever to continuously accelerate or decelerate in 2 stages. This means that the desired speed is reached more quickly.
- During controlled downhill driving, the overrun fuel cutoff as well as shift down of the automatic transmission are adapted. The DSC uses a substitute temperature model to regulate the distribution of torque between the front and rear axle. The overrun fuel cutoff has a favorable effect on fuel consumption. Automatic shift down and distribution of torque relieve the load on the wheel brake during hill descents.
EMF: electromechanical and hydraulic parking brake
The EMF is an electromechanical parking brake. DSC generates hydraulic stopping power whenever the engine is running. EMF uses an actuator to provide mechanical retaining force when the engine is off.
ABS: Antilock braking system
The antilock braking system (ABS) prevents the wheels from blocking on braking. Advantage: short stopping distance, the direction of the vehicle remains stable and the vehicle can be steered. The brake pressure on all wheels is regulated in such a way that each wheel runs in an optimized slip range. Here, the slip is regulated in such a way that the highest possible braking and cornering forces can be transferred.
EBV: Electronic brake force distribution
The electronic braking force distribution (EBV) is an element of the ABS. EBV regulates the braking force distribution between the front and rear axles depending on the vehicle load. Advantage: Independently of the vehicle load, optimized stopping distances with simultaneous high driving stability are achieved. The brake pads wear more evenly. If the ABS fails, the EBV function remains as long as possible. The EBV function requires the signals from at least 1 wheel speed sensors per axle.
CBC: Cornering Brake Control
The Cornering Brake Control (CBC) is an extension of the ABS. CBC increases driving stability when braking in curves ( curve logic ). Advantage: optimization of the driving stability with partial braking on cornering. The shift in wheel loads on cornering (even with light braking) can reduce driving stability. If required, CBC creates a stabilizing counter-torque outside of the ABS control range during light braking.
MSR: Engine drag torque control
The engine drag torque control (MSR) prevents the blocking tendency of the drive gear on smooth roadways. On downshifting or in the case of an abrupt load reversal (especially on a roadway with a low coefficient of friction), there is a danger that the drive gears block due to the engine drag torque. Via the wheel speed sensors, MSR detects the blocking tendency even as it is about to happen. MSR briefly reduces the engine drag torque by accelerating slightly. Advantage: The drive wheels retain their lateral stability in overrun mode.
ASC: Automatic Stability Control
The Automatic Stability Control (ASC) uses brake and engine interventions to prevent the wheels from spinning on accelerating. Advantage: More traction and better driving stability. If the wheels on the driven axle have different levels of adhesion, the wheel with the tendency to slip is braked. If necessary, the engine performance is also reduced.
DSC: Dynamic Stability Control
The current driving condition of the vehicle is detected by the dynamic stability control (DSC) by evaluation of the sensor signal. This driving condition is compared with the set point values determined using a calculation model. In this way, the system recognizes unstable driving conditions. In the case of deviations that are above a control threshold stored in the DSC control unit, the vehicle is stabilized. The stabilization (within physical boundaries) is achieved by reducing the engine performance and individual braking of wheels. DSC intervention override the functions ABS and ASC. The DSC function can be deactivated using a button.
DBC: Dynamic Brake Control
The Dynamic Braking Control (DBC) provides support in emergency braking situations by automatically boosting the brake pressure. Advantage: Shortest possible stopping distances in emergency braking situations by achieving ABS control operation on all four wheels. In emergency braking situations, it is frequently the case that the brake pedal is not pressed strongly enough. ABS control range is then not activated. In the following situations, the return pump increases the brake pressure until ABS control range is activated:
- Rapid operation of the brake pedal with inadequate brake pedal force
- When the brake pedal is depressed slowly and the demand for deceleration is subsequently high, after one wheel reaches the ABS control threshold. Which wheel locks first will depend will depend upon the vehicle's load factor and the road surface's coefficient of friction. Example of a typical situation: The traffic situation slows, making light braking necessary at first, but then demands as short a stopping distance as possible.
Trailer Stability Control
The trailer stabilization control detects seesaw motion of a trailer around the vertical axis. The system works as of a speed of approx. 65 kph with the electrical connector for trailer occupied. The dynamic stability control (DSC) monitors the yawing motion of the vehicle with the help of the DSC sensors. If the limit value is exceeded on the swinging trailer, the engine output is reduced. The DSC also automatically brakes all 4 wheels. With disabled or defective DSC, the trailer stabilization control is also disabled.
RPA: Run Flat Indicator
The Run Flat Indicator (RPA) is not a function of the driving dynamics control. The RPA is integrated in the DSC control unit, as for this function the 4 wheel speed signals are required. By comparing the wheel speeds of all four wheels, the system detects differences in the tire rolling circumferences of the individual wheels. This enables a gradual tire pressure loss to be detected. The Run Flat Indicator can be initialized in the Central Information Display (CID).
CBS: Condition Based Service
CBS is not a function of the driving dynamics control. Condition Based Service means "demand-based service". Various service operations and components such as engine oil and brake pads are integrated in CBS. The remaining distances for the front and rear brake pads are calculated separately in the DSC control unit. When making the calculation, the condition of the brake pad wear sensors is taken into account (data point at 6 mm and 4 mm).
In a running production change, the 2-stage brake pad wear sensor was discontinued in the F0x and F1x, where it was replaced by a single-stage brake pad wear sensor.
Notes for Service department
General notes
IMPORTANT: Replace DSC control unit.
When replacing the DSC control unit, the repair instructions must be followed (special tools needed).
Diagnosis instructions
The following service functions are available in the diagnosis system:
- Venting procedure
- Brake line mix-up test:
- Steering angle sensor adjustment
- Adjustment / commissioning of active steering (must be carried out after adjustment of the steering angle sensor)
- Adjustment of ICM sensor system
Notes on encoding/programming
After replacement, the DSC control unit must be encoded.
Switch-on conditions
After every engine start, the DSC is operational.
We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.