BMW 7 Series: Sensors For DSC

Wheel speed sensors

The same type of wheel-speed sensor is used on the F01/F02 as on the E70/E71 (DF11i made by Robert Bosch GmbH).

They are four active wheel-speed sensors, all four of which are connected by dedicated two-core leads directly to the DSC control unit. The wheel-speed data is transmitted to the DSC control unit as a pulse-width-modulated signal.

The active wheel speed sensors enable detection of direction of rotation and clearance gap.

Detection of direction of rotation is required for the hill-start assistance and Automatic Hold functions, among others. The clearance-gap sensing function allows sensor positioning faults to be detected. If there is too much play in the wheel bearings, the wheel-speed signal can also become unreliable. That situation is also detectable by the clearance- gap sensing capability of the wheel-speed sensors.

It can therefore be guaranteed that the DSC control unit only operates on the basis of correctly detected wheel-speed signals.

Fig. 60: Identifying Wheel Speed Sensors Components

INDEX REFERENCE CHART

1. Sensor ring/ferromagnetic wheel bearing seal carrier
2. IC sensor with Hall sensor
3. Sensor housing

The DSC control unit broadcasts the wheel-DSC sensor in ICM speed sensor signals via the FlexRay network and directly wired links to the other systems on the vehicle.

The DSC sensor, which was previously a separate component, has been integrated in the ICM control unit on the F01/F02.

Fig. 61: Identifying Dynamic Handling Signals By ICM Control Unit

INDEX REFERENCE CHART

1. DSC sensor integrated in ICM control unit
2. ICM control unit

v - Road speed
ax - Linear acceleration
ay - Transverse acceleration
DSC - Dynamic Stability Control
AL - Active steering
HSR - Rear suspension slip angle control
VDM - Vertical Dynamics Management

Fig. 62: Identifying Yaw Rate Sensor, Second, Back-Up Yaw Rate Sensor And Linear And Lateral Acceleration Sensor

INDEX REFERENCE CHART

1. Yaw rate sensor
2. Second, back-up yaw rate sensor
3. Linear and lateral acceleration sensor
4. Second, back-up lateral acceleration sensor

With the aid of the signals from those integrated sensors and the wheel-speed signals provided by the DSC control unit, the ICM control unit calculates the following variables that are of significance for the vehicle's dynamic handling status:

• Road speed
• Linear acceleration and pitch
• Lateral acceleration and roll
• Yaw rate

Steering-angle sensor in SZL

With the aid of the steering-angle sensor, the SZL is able to provide the following signals via the FlexRay bus system:

• Steering angle
• Steering rate

Those variables are used as input signals by the dynamic handling systems to determine the driver's intention when cornering. On the F01/F02 it is important to note that the steering-angle sensor signals are first analyzed by the ICM control unit and then provided to control units of the other dynamic handling systems as the "effective steering-angle signal".

Detection of the steering angle and the steering rate is performed by an optical proximity sensor, the optical steering angle sensor.

Information such as the absolute steering angle or the steering wheel rotation is calculated. The optical steering-angle sensor detects steering angles from -640º to +640º.

If the SZL suffers a power loss, e. g. if the battery terminals are disconnected, the steering wheel rotation data is lost. The SZL is then initially unable to determine the absolute steering angle and can only identify the relative steering angle.

This temporary fault status can be remedied by turning the steering wheel from lock to lock. Alternatively, the SZL can detect the straight-ahead position from the wheel-speed signals from the front wheels when driving in a straight line.

In either case, the absolute steering angle is then known again.

Fig. 63: Schematic Diagram Of Optical Steering-Angle Sensor, F01/F02

INDEX REFERENCE CHART

1. Light-emitting diode
2. Fiber optics unit
3. Code disc
4. Steering column
5. Photo-transistors
6. Output: Conversion to electrical signals
7. PCB

NOTE: If at least one of the following conditions exists, the steering column switch cluster has to perform steering-angle sensor calibration:

• Wheel alignment carried out
• SZL replaced or re-programmed
• Diagnosis system test procedure specifies calibration.

NOTE: When calibrating the steering angle sensor, the instructions given by the diagnosis system must be followed precisely.

The vehicle must be standing on a level surface during calibration. The steering wheel must be aligned visually in the straight-ahead position.

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