Part 3 - System Functions
Dynamic Stability Control
Brief Description Of Components
For Brief Description Of Components, please refer to Part 2 - Brief Description of Components
System Functions
The following new system functions for E70 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 roads
- Fading compensation
- Drive-off assistant
- Cruise control with braking function
- Electromechanical and hydraulic parking brake
Other known system functions for the DSC are:
- ABS: Anti-lock braking system
- EBV: Electronic charge-air pressure distribution
- CBC: Cornering brake control
- MSR: Engine drag-torque control
- ASC: Automatic Stability Control
- DSC: Dynamic Stability Control
- DBC: Dynamic Braking Control
- ADB-X: 4-wheel drive control
- HDC: Hill Descent Control
- Trailer stabilization control
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 an optimized version of DSC for certain road conditions on forward momentum. 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 free" or driving off in deep snow or on loose ground.
- When driving on snow-covered upward inclines, in slush as well as on uncleared roads
- 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). By means of brake intervention, DTC replicates the function of a conventional differential interlock. It increases the input torque to wheels on a road surface with a higher coefficient of friction.
Advantage: with DTC, greater traction is available. 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 roads
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 response time of the brakes. Depending on the signal of the rain sensor or the position of the wiper switch, the DSC creates low brake pressure in cycles. This does not lead to any perceptible braking on the vehicle. The brake pads are applied in cycles. The brake discs are wiped regularly in the process. How often and for how long the brake pads are applied depends on:
- The intensity of the rain, e.g. speed of the window wiper
- Driving speed greater than 70 kph
Fading compensation
Fading means: the braking action 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:
- General 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 target 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 switch 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 hold the vehicle is maintained. The road surface inclination is picked up by the longitudinal acceleration sensor in the DSC control module. The necessary braking torque or engine torque is calculated from the road surface inclination. 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 actuated, 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 braking function
The cruise control with braking function is functionally integrated in the DSC. The cruise control keeps the selected speed constant between 30 kph and 250 kph.
In comparison with the conventional cruise control, there are the following additional functions:
- If the engine drag torque on coasting 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 lateral acceleration during controlled cornering. At the end of the bend, the required speed is reset.
- 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 hill descent, the coasting cutout as well as shiftdown 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 coasting cutout has a favourable effect on fuel consumption. Automatic shiftdown and distribution of torque relieve the load on the wheel brake during hill descents.
EMF: electromechanical and hydraulic parking brake
The EMF is a parking brake.
With the engine running, the DSC applies the retaining force hydraulically.
With the engine off, the EMF applies the retaining force mechanically via the actuating unit.
ABS: Anti-lock braking system
The anti-lock braking system (ABS) prevents the wheels from blocking on braking. Advantage: short braking 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 charge-air pressure distribution
The electronic braking force distribution (EBV) is a component of the ABS. EBV regulates the braking force distribution between the front and rear axles depending on the load. Advantage: independently of the load, optimized braking distances with simultaneous high driving stability are achieved. The brake lining wear is better distributed. If the ABS fails, the EBV function remains as long as possible. The EBV function requires the signals from at least 2 wheel-speed sensors per axle.
CBC: Cornering brake control
The Cornering Brake Control (CBC) is an expansion of the ABS. CBC increases driving stability on 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 stabilising counter-torque outside of the ABS feedback control range during light braking.
MSR: Engine drag-torque control
The engine drag-torque control (MSR) prevents the blocking tendency of the drive wheels on smooth roadways. On downshifting or in the case of abrupt load changes (especially on a roadway with a low coefficient of friction), there is a danger that the drive wheels 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 cornering forces even in the coasting (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 output is also reduced.
DSC: Dynamic Stability Control
The current drive status of the vehicle is detected by the dynamic stability control (DSC) by evaluation of the sensor signal. This drive status is compared with the target values determined using a calculation model. This enable detection of unstable driving states even as they are about to happen. In the case of deviations that are above a control threshold saved in the DSC control module, the vehicle is stabilized. The stabilization (within physical boundaries) is achieved by reducing the engine output and individual braking of wheels. DSC intervention override the functions ABS and ASC. The DSC function can be deactivated using a button. The R56 has no dynamic traction control (DTC).
DBC: Dynamic Braking Control
The Dynamic Braking Control (DBC) provides support in emergency braking situations by automatically boosting the brake pressure. Advantage: the shortest possible braking distances in emergency braking situations by reaching the ABS feedback control range on all 4 wheels. In emergency braking situations, it is frequently the case that the brake pedal is not pressed strongly enough. This means that the ABS feedback control range is not reached. The return-flow pump brings the braking into the ABS feedback control range by increasing the brake pressure in the following situations:
- Rapid operation of the brake pedal with inadequate pedal force
- Slow operation of the brake pedal and subsequent high deceleration requirement if one wheel reaches the control threshold for ABS.
Which wheel blocks first depends on the load and road surface coefficient of friction.
Such situations are typical:
if the traffic situation means that initial braking is light but the traffic situation then requires a braking distance that is as short as possible.
4-wheel drive control
The dynamic stability control (DSC) specifies the target value for 4-wheel drive control with xDrive. The DSC control module calculates the locking moment for the multi-plate clutch in the transfer case & special transmission. The nominal value depends on the tendency of the vehicle to oversteer or understeer and the wheelslip. The nominal value is sent on the PT-CAN to the VTG control module. The VTG control module returns the actually set locking moment to the DSC control module. The DSC control module calculates the locking moment of the multi-plate clutch as follows:
- Pre-activation = driver's demand
- Driving dynamics control
- Detection of different tyre rolling circumferences
HDC: Hill Descent Control
Hill Descent Control (HDC) is an automatic cruise control for hill descents with 4-wheel-drive vehicles. The HDC can be switched on and off at the center console switch center. HDC automatically reduces the driving speed. The driving speed is reduced to slightly more than walking speed by means of brake intervention on all four wheels. This results in a stable hill descent on a steep and smooth / icy road surface. The HDC keeps this speed constant (the DSC functions all remain active). The accelerator pedal and brake pedal or the steering-column lever for cruise control can be used to vary the driving speed steplessly within specified values. Ex works, the lower freely programmable button on the multifunction steering wheel is set for the HDC.
Trailer stabilization 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 module, as for this function the 4 wheel-speed signals are required. The system uses the 4 wheel speeds to compare deviations in the rolling circumferences of the individual wheels. This means that a creeping loss of tyre inflation pressure is detected.
The Run Flat Indicator can be initialized as follows:
- On vehicle with Car Communication Computer (CCC): in the Central Information Display (CID) in the menu "Setup"
- On vehicles without Car Communication Computer (CCC): in the instrument cluster in the on-board computer functions
CBS: Condition Based Service
CBS is not a function of the driving dynamics control. Condition Based Service means "requirement-oriented service". Various maintenance items are integrated in the CBS, e.g. engine oil, spark plugs and brake pads. The remaining distances for the front and rear brake pads are calculated separately in the DSC control module. The state of the brake pad wear sensors is also used for the calculation (reference point at 6 mm and 4 mm).
Notes for Service department
General information
Important! Replacing the DSC control module.
On replacement of the DSC control module, the repair instructions must be observed (special tool necessary).
Diagnosis instructions
The following service functions are available in the BMW diagnosis system:
- Brake bleeding procedure
- Check for swapped brake lines
- Steering angle sensor calibration
- Calibration / commissioning of active steering (must be carried out after calibration of the steering-angle sensor)
- Calibration of DSC sensor
Notes on encoding / programming
After replacement, the DSC control module must be encoded.
Switch-on conditions
After every engine start, the DSC is operational.
No liability can be accepted for printing or other faults. Subject to changes of a technical nature