Antilock Brakes / Traction Control Systems: Description and Operation
Dynamic Stability Control (DSC)
Dynamic stability control
The MINI is equipped as standard with an antilock braking system (ABS). An antilock braking system with automatic stability control (ABS+T) is offered as optional equipment. The Dynamic Stability Control (DSC) is also optional equipment. System supplier for the DSC is TRW.
NOTE: DSC standard equipment starting 03/2009.
Starting 03/2009, DSC is standard equipment.
The DSC differs from ABS or ASC+T in that it has the following functions:
- DSC control unit with integrated brake pressure sensor
- Steering angle sensor in the steering column switch cluster (SZL)
- DSC sensor
DSC is a driving dynamics system that maintains driving stability. DSC optimises:
- driving stability on driving off, accelerating and braking
- traction
The DSC also detects unstable driving conditions 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 handling characteristics parameters:
- the yaw rate as a measure for the rotational movement of the vehicle around the vertical axis
- the lateral acceleration as a measure of the coefficient of friction of the roadway
- the driving speed
In addition, the driver's choice 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 condition in which the vehicle is moving at the moment. The actual condition is compared with nominal values calculated in the DSC control unit. If the current actual values deviate from the desired state, DSC becomes active and actively intervenes in the brake system or in the engine control, as the case may be.
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. With electronic activation from the DSC control unit, the hydraulic unit controls the DSC hydraulically.
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 servo. 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 pump, terminal 30 once for the solenoid valves. The junction box electronics (JBE) supply the DSC control unit with terminal 30.
4 wheel speed sensors
The wheel speed sensors measures the individual wheel speeds. The wheel speed sensors have no detection for the direction of rotation of the wheels.
The sensor element and the evaluation electronics are housed 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 evaluation electronics. 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 wheel causes changes in resistance in the thin ferromagnetic layer of the sensor element.
DSC sensor
The DSC sensor measures:
- Rotation of the vehicle around the vertical axis (yaw rate)
- Lateral acceleration of the vehicle
- Longitudinal acceleration of vehicle
The sensor element consists of 2 piezoelectric acceleration sensors. A mass is suspended on a spring in the measuring 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 and suspension CAN (F CAN) with the DSC control unit as well as the steering column switch cluster.
The DSC sensor is supplied with voltage from the junction box.
Steering angle sensor
The steering angle sensor picks up the angle of rotation at the steering wheel. The steering angles determined by the sliding 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.
The steering angle sensor is connected via the chassis and suspension CAN (F-CAN) with the DSC control unit as well as the DSC sensor.
DSC button or ASC button
This button is used to switch off the suspension control system. In the, R56 there is no dynamic traction control (DTC) for the DSC.
The DTC button is in the switch block on the centre console.The centre console switch block is connected to the junction box electronics (JBE). The JBE is connected to the DSC via the PT CAN (drive train CAN).
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.
Brake light switch
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.
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 general brake warning light in red.
Parking brake switch
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:
INSTRUMENT PANEL: Instrument panel control unit
In the event of failure of the DSC (or ABS / ASC) a Check Control symbol appears in the liquid crystal 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.
CAS: Car access system
The CAS receives a processed speed signal from the DSC. The CAS recognises from the signal whether the vehicle is stationary or moving.
System functions
The following system functions are described for the suspension control systems (depending on fitted optional extras):
- 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 Braking Control
- AFA: Drive-off assistant
The following additional functions that do not belong to driving dynamics control are integrated:
- RPA: Run Flat Indicator
- CBS: Condition Based Service
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 optimised 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, optimised 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 2 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: optimisation 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 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 an abrupt load reversal (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 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 nominal values determined using a calculation model. In this way, the system recognises unstable driving conditions. 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 performance 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: 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
- 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 vehicle 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 stopping distance that is as short as possible.
AFA: 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 actuated, the driveoff 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.
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. The system uses the 4 wheel speeds to compare deviations in the tire rolling circumference of the individual wheels. This means that a creeping loss of tire inflation pressure is detected. The Run Flat Indicator can be initialised 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 panel in the on-board computer functions
CBS: Condition Based Service
CBS is not a function of the driving dynamics control. Condition Based Service means "demand-based service". Various service 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. When making the calculation, the condition of the brake pad wear sensors is taken into account (data point at 6 mm and 4 mm).
Notes for Service department
General notes
NOTE: Do not disconnect the DSC control unit and hydraulic unit.
At the series launch, the DSC unit must not be dismantled. Dismantling is planned for a later stage.
Diagnosis instructions
The following service function is available in the BMW diagnosis system:
- Steering angle sensor adjustment
- Adjustment of DSC sensor
- Adjustment, DSC unit
Notes on encoding/programming
After replacement, the DSC control unit must be encoded.
Switch-on conditions
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.