BMW 7 Series: Detecting The Controls

The multifunction steering wheel has additional buttons. The buttons increase in-car comfort and convenience by providing for comfort and convenience functions.

The steering column switch cluster reads in the signals from the steering-wheel buttons. The steering column switch cluster transmits these signals across the FlexRay. The associated ECU executes the request.

Steering wheel

The steering wheel is equipped with the following components:

• Fanfare-horn button
• Priming caps for the driver's airbag
• Driver's airbag
• Buttons for radio operation
• Buttons for telephone operation
• Cruise control system buttons
• Steering wheel electronics
• Steering wheel heating
• Vibration actuator.

The fanfare-horn button is connected directly to the steering column switch cluster. The junction box electronics requests the button status of the fanfare-horn button in cycles.

The steering column switch cluster evaluates the button status and sends this across the FlexRay to the junction box electronics.

The buttons for the radio, telephone and cruise control system are connected via the LIN bus. The applies to the steering wheel electronics. The central control unit for this equipment attached to the LIN bus is the steering column switch cluster.

The right-hand button block contains the master function for the left-hand button block and has an electronic evaluation unit. The electronic evaluation unit picks up the button status of the individual buttons. The electronic evaluation unit implements the button status on the LIN bus. The steering column switch cluster requests the button status in cycles and thus finds out whether a button was operated or not. The steering column switch cluster transmits the button status across the FlexRay. In this way, the information reaches the other control units in the vehicle network.

NOTE: The signal sent from the steering column switch cluster across the FlexRay must be implemented in the central gateway module on the K-CAN2, PT-CAN or MOST. This enables the footwell module, the junction box electronics etc. to execute the desired requests.

Resetting the Turn Indicator

The footwell module the information regarding the steering-wheel turn requires to reset the turn indicator lights.

The steering column switch cluster determines this steering-wheel turn and makes it available across the FlexRay. The central gateway module implements the signal on the K-CAN2, thus providing the footwell module with the information. Depending on the steering-wheel position, the footwell module decides whether the turn indicator has to be deactivated or not.

Steering-wheel-rotation information

The optical steering-angle sensor detects the neutral position within 360º of the optical steering-angle sensor.

With a steering wheel turn of more than 360º, the information regarding the steering-wheel turn is also included in the steering angle calculation.

Receiving and Transmitting Signals

The detected and calculated data from the steering column switch cluster are forwarded across the FlexRay to the corresponding control units.

The steering column switch cluster can be diagnosed via the central gateway module with the BMW diagnosis system. The diagnosis information can be called up via the FlexRay.

Vibration actuator

The KAFAS control unit, for example, requests activation of the vibration actuator via the PT-CAN. The central gateway module implements the signal on the FlexRay. This means the Integrated Chassis Management receives the request for activation. The Integrated Chassis Management co-ordinates activation of the vibration actuator.

NOTE: Coordination is necessary, as the lane departure warning and lane change warning can be fitted in the vehicle. Depending on the request from the two assistance systems, the Integrated Chassis Management forwards this to the vibration actuator.

The steering wheel electronics evaluate the request, activate the vibration actuator and monitor its function. In the event of a defect in the vibration actuator or steering wheel electronics, the steering column switch cluster indicates this via the FlexRay.

Priming caps for the driver's airbag

The priming caps of the driver's airbag are connected directly via the coil spring to the Crash Safety Module, ACSM. Triggering the airbag is the responsibility of the Crash Safety Module.

Redundant signal

The signals from the steering column stalk for turn-indicator/high-beam switch for turn indicator lights as well as headlight flasher are transferred across the FlexRay. To increase the availability, the steering column switch cluster is connected directly by a cable to the footwell module. The signals e.g. for the headlight flasher or turn indicator lights are transferred redundantly across this cable.

Optical Steering-angle Sensor

All systems that influence driving dynamics are required alongside other data for the steering angle and steering-angle speed as the basis for calculation.

The steering angle as well as steering-angle speed are picked up by a non-contact optical measuring system, the optical steering-angle sensor.

The data of the optical steering-angle sensor are processed by the electronics in the steering column switch cluster and sent across the FlexRay to the Integrated Chassis Management.

Information such as the absolute steering angle or the steering-wheel-turn is calculated. The optical steering angle sensor picks up a steering angle of -640º/+640º.

Fig. 130: Structural Principle Of Optical Steering-Angle Sensor F01/F02

COMPONENTS DESCRIPTION CHART

1. LED
2. Light-conducting element
3. Code disc
4. Steering column
5. Photo-transistors
6. Output: Conversion into electrical signals
7. Printed-circuit board

Detecting Steering Angle and Steering-Angle Speed

To pick up the steering angle, a code disc is illuminated from above by an LED and a light-conducting element.

Due to the pattern in the code disc, the light from above only reaches down to certain areas. There, the light encounters photo-transistors.

The pattern of the code disc corresponds to the digital code of the steering angle.

The photo-transistors convert the light signals into electrical signals. As the signals are not yet sufficiently unambiguous, they are processed by downstream electronics.

Thereafter, the signals are digitized and have the signal states 1 or 0.

The steering column switch cluster receives the current value of the steering angle, the digital code, and forwards this across the FlexRay.

A section of the code disc and the optical sensor are shown below.

COMPONENTS DESCRIPTION CHART

Relative steering angle (+- 640º)

The relative steering angle specifies the angle position of the steering wheel. The information regarding the relative steering angle is always retained, even if the power to the control unit is switched off. A renewed zeropoint adjustment is only necessary if the steering column switch cluster has been replaced. This also applies if the dynamic stability control system is replaced or repairs become necessary on the steering/steering column.

Absolute steering angle

The absolute steering angle is a calculation based on the relative steering angle and the information regarding steering-wheel turn. The absolute and relative steering angles are defined during the zero-point adjustment of the steering column switch cluster. The steering column switch cluster knows every position of the steering wheel across the entire range of steering rotation.

A precondition before every zero-point adjustment is the straight-ahead setting of the wheels and of the steering wheel.

Steering-angle speed

The steering-angle speed is the product of the change in the individual steering-angle data during steering wheel turn.

The steering column switch cluster calculates the value and forwards it across the FlexRay to the vehicle network.

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