Camera-Based Driver Support Systems

Camera-Based Driver Support Systems

Camera-based driver support systems (KAFAS)
Depending on the options fitted, various camera-based systems are available. Technically, the system is implemented with a joint camera and a joint control unit, the KAFAS control unit. The functions of the camera based driver support systems are:
- Lane departure warning
- High-Beam Assistant (not permitted in Japan)
- Road sign recognition Speed Limit Info)

NOTICE: Optional equipment 5AC, high-beam assistant.

If the customer exclusively orders the High-Beam Assistant (5AC), the system is implemented with its own camera and its own control unit in the inside mirror.
The lane departure warning and high-beam assistant are known systems. The road sign recognition is only possible with the Professional navigation system.







Brief component description
The following components for the camera-based driver support systems (KAFAS) are described:

Turn signal/high beam switch and operating facility for assist systems
The high-beam assistant is switched on and off at the turn signal/high beam switch. To do this, the light switch must be in automatic driving lights control or low-beam headlight position. The lane departure warning is switched on and off with the button in the assist system operating facility.







The operating facility for assist systems is connected via LIN bus to the footwell module (FRM). A bus signal from the FRM to the camera-based driver support systems control unit reports operation of the button. The ICM control unit only allows switch-on of the lane departure warning if the system is functioning trouble-free. Only then is there positive confirmation by means of a bus signal to the footwell module (FRM) to activate the function indicator light of the button. If there is a fault in the system, the function indicator light remains switched off despite keystroke. This allows the driver to see that the lane departure warning is not available.

Video camera
The video camera for the lane departure warning installed in the mirror base of the inside mirror monitors the near field of the vehicle. The video camera records the roadway up to approx. 40 meters in front of the vehicle and up to approx. 5 meters to the right and left at the sides of the vehicle. Image data are routed over a LVDS data line to the KAFAS control unit and evaluated. The control unit uses image processing to search in the imagery recorded by the video camera for possible existing lane and road markings.







KAFAS: Control unit for camera-based driver support systems
The KAFAS control unit is located in the driver's footwell next to the central gateway module. The light points, light colors and light intensities recorded by the video camera are evaluated by the KAFAS control unit. Evaluation by the KAFAS control unit results in an activation or deactivation request.The video camera is connected to the KAFAS control unit via a twelve-pin line.The KAFAS control unit is connected to the powertrain CAN.







Vibration actuator in the steering wheel
The vibration actuator is fitted in the spoke of the steering wheel. The vibration actuator has the task of causing the steering wheel to vibrate. The driver assistance systems 'lane departure warning' and 'lane change warning' use this vibration to warn the driver regarding dangerous situations.
The steering wheel module also housed inside the steering wheel activates the vibration actuator. The request for activation of the vibration actuator is sent by the Integrated Chassis Management (ICM) as follows: via FlexRay to the steering column switch cluster. The SZL forwards this request across the LIN bus to the steering wheel module.







System functions
The following system functions are described:
- Functional networking
- High-beam assistant
- Lane departure warning
- Road sign recognition
- System limits

Functional networking
A complex system network with distributed functions in other control units is necessary for implementation of the lane departure warning as well as the high-beam assistant. The following graphic shows the system network.







High-beam assistant
When solely a high-beam assistant (5AC) is installed, the system network looks like:







Lane departure warning
The prerequisites for a lane departure warning are an identified lane and a specific driving speed. These make the system fundamentally ready to give a warning. When crossing over a lane is imminent, the system warns the driver through a vibrating steering wheel. The system firstly uses one or two identified lanes to calculate the vehicle position relative to these lanes. The time remaining to cross over a lane is calculated with the aid of the steering angle and the driving speed. A warning is output in good time before crossing over the marking.
A warning is only output once when approaching a road marking. The warning lasts for a maximum of 2.5 seconds. No further warning is output if the vehicle remains on the lane marking. A renewed warning is only possible after steering back into the lane or a lane change.In the case of an intentional lane change by the driver:The operation of the turn indicator as an input signal means that no warning is output.

The warning is ended in the following conditions:
- Driver steers back into the lane
- Lane change is carried out
- Vehicle is on the line for longer than 2.5 seconds
- Turn indicator for lane change is operated
- Brake is operated (dependent of brake pressure).

The minimum speed for a warning is country-specific.
- Europe: 70 km/h
- United States: 40 mph
- Japan: 50 km/h

The displays for system and warning readiness are shown on the instrument cluster as well as the Head-Up Display.

High-beam assistant
The video camera monitors the area in front of the vehicle for light sources. Traffic driving in front or approaching is identified at a distance of approx. 400 meters. The detection range of the video cameras is approx. 1000 meters. The video camera field of view has a horizontal side angle of approx. 15° to the left and right. The video camera field of view has a vertical elevation angle of approx. 5° up and down. The video camera records points of light when it is in operation. Distinction can be drawn between different parameters such as light colour and light intensity.
The recorded light points, light colors and light intensities picked are evaluated by the KAFAS control unit. After evaluation the control unit gives a recommendation to switch on or off. The KAFAS or FLA control unit transmits the recommendation to the footwell module. The recommendation to switch on or off also incorporates the driving speed. At speeds below 38 km/h the high-beam assistant is switched off. At a speed higher than 50 km/h it is switched on depending on all other parameters. The high-beam headlight is not switched on when the vehicle is in an environment with sufficient lighting. The KAFAS control unit (or FLA) transmits a deactivation recommendation to the footwell module (FRM).

Road sign recognition

Marketing designation: Speed Limit Information
Road sign recognition displays current top speed limitations on the instrument cluster as well as the Head-Up Display. Road sign recognition therefore provides the driver with an aid to prevent excessive speeds.
Responsibility for the vehicle and driven speed lies exclusively with the driver. The display of top speed limitations is based upon the following evaluations:
- Data from navigation system
- Image data from the video camera

The KAFAS control unit uses data on top speed limitations if they are stored in the navigation data for the road currently being driven. In parallel to this, the video data from the video camera are also evaluated in the KAFAS control unit. The image data are read in by the KAFAS control unit and evaluated for speed limit and end of speed limit traffic signs. If the video camera identifies signed, local, temporary top speed limitations, these are displayed with priority over the navigation data. In the case of covered or non-identifiable signs for ending top speed limitations, the displays are cancelled in accordance with a specified time and route parameters.

System limits
The system function may be limited under certain road and ambient conditions, for example, snow covered roadway, fog, rain, oncoming light and dazzling due to the physical limits of the optical system.

Notes for Service department

General notes
In the event of replacement of the camera or windscreen, calibration of the lane departure warning is required, as in these cases the position of the camera could have changed. If the control unit is replaced, no calibration is required. In this case, the calibration data stored in the camera are transferred to the control unit and stored there.

Diagnosis instructions

NOTICE: Use the service functions.

The BMW diagnosis system provides the following service functions for the lane change warning:
- Calibration of lane departure warning


We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.