The R56 is equipped as series standard with an anti-lock braking system (ABS). As an optional extra, an anti-lock braking system with automatic stability control (ABS+T) is offered. The Dynamic Stability Control (DSC) is also an optional extra. System supplier for the DSC is TRW.
The DSC differs from ABS or ASC+T in that it has the following functions:
DSC is a driving dynamics system that maintains driving stability. DSC optimises:
The DSC also detects unstable driving states such as understeer or oversteer. DSC helps to maintain the vehicle on a safe course within the physical boundaries.
To do so, the DSC must be aware of the following dynamic driving parameters:
In addition, the driver request is detected from the steering angle and the brake pressure the driver applies to the pedal. Furthermore, wheel-speed sensors deliver information on the speed of the individual wheels. The available measured values are used to determine the actual status in which the vehicle is moving at the moment. The actual condition is compared with target values calculated in the DSC control unit. If the current actual values deviate from the target state, DSC becomes active and actively intervenes in the brake system or in the engine management system, as the case may be.
The following components for dynamic stability control are described:
The DSC unit consists of the DSC control unit and a hydraulic unit. With electronic activation from the DSC control unit, the hydraulic unit controls the DSC hydraulically.
Index |
Explanation |
Index |
Explanation |
|---|---|---|---|
1 |
Hydraulic unit |
2 |
DSC control unit |
3 |
Plug-in connection |
4 |
Pump motor |
The DSC unit contains a brake pressure sensor. This brake pressure sensor picks up the braking pressure applied via the brake pedal and the brake booster.
The brake pressure sensor has a measuring range of 0 to 250 bar. Its zero point is only synchronised while the vehicle is being driven. The DSC must detect that there is no deceleration.
The fuse carrier in the engine compartment supplies the DSC unit with voltage. Terminal 30 once for the return-flow pump, terminal 30 once for the solenoid valves.
The junction box electronics (JBE) supply the DSC control unit with terminal 30.
The wheel-speed sensors measures the individual wheel speeds. The wheel-speed sensors have no detection for the direction of rotation of the wheels.
Index |
Explanation |
Index |
Explanation |
|---|---|---|---|
1 |
Wheel-speed sensor, front axle |
2 |
Wheel-speed sensor, rear axle |
The sensor element and the electronic evaluation unit are fitted separately within the sensor housing. This arrangement ensures advantages with regard to temperature characteristics of the sensor. The wheel-speed sensor consists of the sensor itself and an electronic evaluation unit. The permanent magnet in the wheel-speed sensor creates a magnetic field. The field lines of the magnetic field run at a right angle to the sensor layer on the sensor element. The deflection of the field lines by the increment gear causes changes in resistance in the thin ferromagnetic layer of the sensor element.
The DSC sensor measures:
Index |
Explanation |
Index |
Explanation |
|---|---|---|---|
1 |
DSC sensor |
2 |
Plug-in connection |
The sensor element consists of 2 piezo-electric acceleration sensors. A mass is suspended on a spring in the measurement cell of the acceleration sensor.
With an accelerates motion, 2 masses suspended on springs are also accelerated. The force necessary for this creates a mechanical voltage in the piezoelectrical material. The shift in electrical charge this creates is picked up with electrodes made of metal and processed as an electrical signal. The yaw rate is derived from the difference between the two acceleration signals. The DSC sensor thus delivers a yaw rate and an acceleration signal.
The longitudinal acceleration sensor is required for the drive-off assistant.
The DSC sensor is connected via the chassis CAN (F-CAN) with the DSC control unit as well as the steering column switching centre.
The DSC sensor is supplied with voltage from the junction box.
The steering-angle sensor picks up the angle of rotation at the steering wheel.
The steering angles determined by the wiping contacts (2 voltage values) comprise a full steering-wheel turn. After 360° steering-wheel turn, the voltage values are repeated. This means that the steering-angle sensor also counts the steering-wheel turns. The total steering angle is thus formed from the currently measured steering angle and the number of steering-wheel turns.
Index |
Explanation |
Index |
Explanation |
|---|---|---|---|
1 |
Steering column switch cluster (SZL) |
2 |
Steering angle sensor |
The steering-angle sensor is connected via the chassis CAN (F-CAN) with the DSC control unit as well as the DSC sensor.
This button is used to switch off the chassis control system. In the, R56 there is no dynamic traction control (DTC) for the DSC.
Index |
Explanation |
Index |
Explanation |
|---|---|---|---|
1 |
DSC button or ASC button |
2 |
DSC (Dynamic Stability Control) |
3 |
Instrument cluster (KOMBI) |
4 |
Additional instrument (KOMBI2) |
5 |
Junction box electronics (JBE) |
6 |
Switch block, centre console |
The DTC button is in the switch block on the centre console.
The center console switch block is connected to the junction box electronics (JBE). The JBE is connected to the DSC via the PT-CAN (Powertrain CAN).
The DSC receives additional input signals from the following components:
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.
Together with the signal from the brake pressure sensor (only with DSC), braking operations are detected.
The brake-light switch contains 2 switches (2-stage). A signal is then made available to the DSC across a line. The engine control unit receives both signals. The engine control unit sends the signal on the PT-CAN. The signals indicate to the DSC control unit whether the brake pedal is pressed.
The Car Access System (CAS) supplies the brake-light switch with terminal R.
The brake pad wear sensors (front left and rear right in the internal brake pads) provide additional information on the thickness of the brake pad. This additional information (2 reference points) is used to synchronise the calculated value of the DSC.
Index |
Explanation |
Index |
Explanation |
|---|---|---|---|
1 |
Brake pad wear sensor (example, rear axle) |
2 |
Brake caliper |
3 |
Brake disc |
|
|
A critical brake lining thickness is indicated in the instrument cluster by a service requirement display (Condition Based Service CBS) as well as the general brake warning light in red.
The parking-brake switch is connected to the junction box electronics (JBE). The signal is then made available to the DSC on the PT-CAN. Skidding deliberately initiated by the driver is this detected by the DSC. There is no control operation. Reason: a handbrake turn should remain technically possible.
The following additional control units are involved in the dynamic stability control:
In the event of failure of the DSC (or ABS / ASC) a Check Control symbol appears in the LC display. The Check Control symbols all have a certain meaning.
Note: All Check Control messages can be called up using the service function!
The Check Control messages can be called
up using the service functions, grouped in various documents. Path in the BMW diagnosis system: Complete vehicle -> Service functions -> check Control messages.
On vehicles with Car Communication Computer (CCC): If there is a Check Control message, the relevant instructions can be displayed on the Central Information Display.
The CAS receives a processed speed signal from the DSC. The CAS recognises from the signal whether the vehicle is stationary or moving.
The following system functions are described for the chassis control systems (depending on fitted optional extras):
Index |
Explanation |
Index |
Explanation |
|---|---|---|---|
ABS |
Anti-lock braking system |
ASC+T |
Automatic stability plus traction control |
DSC |
Dynamic Stability Control |
EBV |
Electronic brake force distribution |
CBC |
Cornering brake control |
MSR |
Engine drag-torque control |
DBC |
Dynamic Braking Control |
AFA |
Drive-off assistant |
RPA |
Run Flat Indicator |
CBS |
Condition Based Service |
The following additional functions that do not belong to driving dynamics control are integrated:
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 optimised slip range. Here, the slip is regulated in such a way that the highest possible braking and cornering forces can be transferred.
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, optimised 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.
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.
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.
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.
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 stored in the DSC control unit, the vehicle is stabilised. The stabilisation (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).
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:
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:
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 unit. 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.
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. 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 initialised as follows:
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 unit. The state of the brake pad wear sensors is also used for the calculation (reference point at 6 mm and 4 mm).
Note! Do not disconnect the DSC control unit and hydraulic unit.
At the beginning of series production, the DSC unit must not be dismantled. Dismantling is planned for a later stage.
The following service function is available in the BMW diagnosis system:
After replacement, the DSC control unit must be coded.
After every engine start, the DSC is operational.
No liability can be accepted for printing or other errors. Subject to changes of a technical nature