Part 2 - Brief Description of Components

Dynamic Stability Control

Brief Description Of Components
The following components for dynamic stability control are described:

DSC unit
The DSC unit consists of the DSC control module and a hydraulic unit. The DSC control module activates the hydraulic unit via valve coils.

Index:

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 calibrated while the vehicle is being driven.

The new concept of the DSC unit enables more exact control. 2 x 3 pump elements with 6.5 mm work in the pump motor. This concept results in significantly improved pressure dynamics. It means that the brake pedal pulses to lesser degree during ABS control. It also leads to higher control quality with Hill Descent Control (HDC).

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The 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 module receives terminal 30g.

4 wheel-speed sensors
The active wheel-speed sensors determine the circumferential wheel speed of the individual wheels. In addition, the wheel-speed sensors detect the direction of rotation (forwards or backwards). When a wheel is at a standstill, the wheel-speed sensor transmits an impulse every 0.75 seconds. The current impulse indicates the availability of the wheel-speed sensor.

The following advantages result from active wheel-speed sensors:
- rapid and reliable detection of the direction of travel
- improved activation of the transmission control
- improved activation of the navigation system

Index:

On the front and rear axles, there is a circle of magnets (increment wheel) around the wheel bearing. The north and south poles of the increment wheel alternate. A north pole with a south pole corresponds to 1 increment (comparable with tooth/gap of an increment gear). The wheel-speed sensor consists of 3 Hall sensors and an electronic evaluation unit.

The active wheel-speed sensors change their electrical resistance under the influence of a magnetic field. Each increment causes 2 impulses in the wheel-speed sensor (96 impulses / rotation of wheel). For data transfer to the control module, additional data is appended to the edge of the impulse. Functionally, this integrated data processing goes beyond pure engine speed detection. The following additional information is possible, e.g.:
- Direction of rotation of the wheel
- Air gap
- Vehicle at a standstill

DSC sensor
The DSC sensor measures:
- Rotation of the vehicle around the vertical axis (yaw rate)
- Lateral acceleration of the vehicle
- Longitudinal acceleration of the vehicle

Index:

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 module.

The DDE control module supplies the DSC sensor with voltage.

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 board with the electronic evaluation unit. The steering-angle sensor consists of the following components: code disk and optical sensor.

The code disk is connected to the steering wheel via the buffer spring cassette. When the steering wheel is moved, the code disk moves within the optical sensor. There are various line patterns for evaluation on the code disk.

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The SZL is connected via the chassis CAN (F-CAN) with the DSC control module.

DTC button and HDC button
The DTC button is used to change the operating mode of the chassis control system. The DTC button bears the lettering "DTC". The DTC button can be used to select 3 switching states:
- DTC button not pressed after terminal change: DSC in operation (default)
- Press DTC button briefly: DTC in operation (notification "DTC" appears in the instrument cluster above indicator lamp)
- Press DTC button for longer period: DSC and ASC switched off, ABS and ABD-X still active (indicator lamp in instrument cluster lights up continuously)

E70:
the DTC button is in the center console switching center (no control module). The center console switching center is connected to the integrated heater / automatic climate control (IHKA). The IHKA sends the signal on the K-CAN.

E60 and E61 as of 03/2007:
the DTC button is in the switch block to the left of the ashtray. The switch block is connected to the center console switch center (SZM). The SZM control module is installed in the carrier behind the glove compartment.

Index:

E70:
the HDC button is also in the center console switching center.

E60 and E61:
the hill descent control (HDC) can be assigned to the freely programmable buttons on the steering wheel. The HDC can also be activated via iDrive.

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 module. 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 module receives both signals. The engine control module sends the signal on the PT-CAN. The DSC control module uses both signals to detect whether the brake pedal has been pressed.

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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 internal brake pads) provide additional information on the thickness of the brake pad. This additional information (2 reference points) is used to calibrate the calculated value of the DSC.

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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 following additional control modules are involved in the dynamic stability control:

KOMBI: Instrument cluster
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 distributor at the junction box electronics supplies the DSC unit with voltage.
Terminal 30 for the return-flow pump as well as the solenoid valve.
Terminal 30g for the DSC control module.

Circuit:

The graphic shows the E70

Index:

System Functions

For desription of System Functions, please refer to Part 3 - System Functions.

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