Lane Keeping Assist, function - GF54.71-P-0005CA
MODEL 207 up to model year 2014 with CODE 476 (Lane keeping assist)
Function requirements, general
- Circuit 15 ON
- Function enabled in instrument cluster
- Vehicle speed v = 60 to 250 km/h
- Recognizable lane markings present on both sides (no construction site markings (yellow/white), no snow, not covered up, i.e. contrast too low)
- Radius of curve r >150 m
- Track width s = 2.5 up to 4.6 m
The electronic ignition lock control unit sends the status of circuit 15 to the multifunction camera via the chassis CAN.
Lane Keeping Assist, general
The Lane Keeping Assist detects any unintentional driving across lane markings and issues a haptic warning to the driver in certain circumstances through initiating vibrations on the steering wheel.
Crossing over lane markings is optically recorded and processed by the multifunction camera. The haptic warning is generated by the steering wheel vibration motor. The Lane Keeping Assist takes the driver's behavior into consideration and decides the point at which a warning is to be issued.
As of 1.6.12, the driver can select the sensitivity of the Lane Keeping Assist in the "Assistance" menu of the instrument cluster.
The following operating modes are available for selection:
- Standard (high sensitivity, warnings issued earlier and more frequently)
- Adaptive (lower sensitivity, warnings issued later and less often)
Under the following conditions any driving over lane markings is detected, but a warning is not issued:
- Driver activities through evaluation of steering-wheel movement, brake requests and the accelerator pedal position
- Sporty cornering (corner cutting)
- Turn signals
- Active control interventions by braking assistance systems
Illustration of the principle of Lane Keeping Assist
Lane Keeping Assist operation is speed-dependent. The vehicle speed is calculated from the wheel speed signals.
The wheel speeds are recorded by the following sensors:
- Left front axle RPM sensor
- Right front axle RPM sensor
- Left rear axle RPM sensor
- Right rear axle RPM sensor
The Electronic Stability Program control unit reads in the signals from the RPM sensors directly and sends them to the instrument cluster via the chassis CAN. The instrument cluster calculates the listed vehicle speed and sends this over the chassis CAN to the multifunction camera.
The Lane Keeping Assist consists of the following subfunctions:
- Function sequence for lane recognition
- Function sequence for recognition of driver activity
- Function sequence for recognition of control interventions
- Function sequence for issuing warning
Function sequence for lane recognition
The multifunction camera, which is mounted at the top center of the windshield, visually records the road space in front of the vehicle. For this purpose, the multifunction camera records pictures of the lane at a fixed scanning rate and makes these pictures available to the integrated control unit. The multifunction camera measures the lane based on the lane markings.
Schematic of lane recognition by multifunction camera
Based on the recorded picture sequences and the measurement values resulting from the lane markings, the multifunction camera calculates each lane. This calculation is based on a corresponding algorithm. On the basis of this data, the multifunction camera determines the relative position of the vehicle in the lane. The Active Lane Keeping Assist measures are all derived from this position. No lane information can be issued in cases where there are no lane markings or if they are not visible (e.g. owing to dirt or snow), where there is a low contrast between the road surface and the lane markings or where there is a high level of glare.
For multiple markings on the traffic lane, the inner marking is always taken as the reference point.
In construction site areas, the Lane Keeping Assist may be unable to issue warnings due to multiple markings. The current status of the Lane Keeping Assist, especially the warning readiness, is indicated continuously in the multifunction display of the instrument cluster. This status information is sent by the multifunction camera over the chassis CAN to the instrument cluster.
Possible displays:
- Function status
- Icon off: Lane Keeping Assist deactivated
- Icon yellow (1): Lane Keeping Assist activated but not ready to issue warnings (e.g. v < 60 km/h)
- Warning readiness
- Icon green (2): Lane Keeping Assist activated and ready to issue warnings
- Message for function errors in multifunction display
Function sequence for recognition of driver activity
The following situations suggest driver activity and result in suppression of any pending warning:
- Turn signals
- Accelerate
- Brakes
- Steering intervention
Turn signaling:
The steering column tube module control unit reads in the position of the combination switch directly and sends it to the multifunction camera via the chassis CAN.
Acceleration:
The accelerator pedal sensor registers any accelerator pedal actuation. The CDI control unit (with diesel engine) or the ME-SFI control unit (with gasoline engine) reads in the signals from the accelerator pedal sensor directly and sends them to the multifunction camera via the chassis CAN.
Brakes:
Operation of the brake pedal is detected by the brake lights switch. The Electronic Stability Program control unit directly reads in the status of the brake lights switch. In addition, the Electronic Stability Program control unit evaluates the data for the inherent motion of the vehicle (yawing moment) and sends this data as well as the status of the brake light switch to the multifunction camera via the chassis CAN. The yaw behavior of the vehicle is detected by the yaw rate sensor for lateral and longitudinal acceleration which communicates with the Electronic Stability Program control unit via the vehicle dynamics CAN.
Steering intervention:
Steering movements are recorded by the steering angle sensor. The steering column tube module control unit directly reads in the steering angle sensor signals and sends them over the chassis CAN to the multifunction camera.
If the multifunction camera detects active corner cutting, crossing over of the lane marking at an angle of ∠> 3° or a lateral acceleration of a > 4 m/s2
, a pending warning is also suppressed.
Function sequence for recognition of control interventions
All controls in the driver's immediate vicinity are monitored. If a control intervention is registered, the Lane Keeping Assist deems the driver to be "distracted". As soon as the vehicle drives over the lane marking, an active warning is output. Control interventions are evaluated by the multifunction camera. The warning threshold is adjusted to match the control actuating frequency, i.e. the Lane Keeping Assist warns earlier and possibly more often.
The following controls are monitored:
- Audio system controls:
- Radio (with code (510) Audio 20 with CD changer or with code (523) MB Audio 20 radio) or radio with auto pilot system (with code (511) Audio 50 APS incl. DVD changer or with code (525) MB Audio 50 APS radio) or COMAND controller unit (with code (512) COMAND APS incl. DVD changer or code (526) COMAND with single DVD drive (without navigation) or code (527) COMAND APS with single DVD drive (with navigation) or code (528) COMAND incl. DVD changer)
- Comfort function controls:
- Cruise control lever
- Driver-side power window and outside mirror adjustment switch group (only the outside mirror adjustment is monitored)
- Steering column adjustment switch (with code (275) Memory package (driver seat, steering column, mirror))
- Left multifunction steering wheel button group or right multifunction steering wheel button group
- Interior illumination controls:
- Front dome lamp switch
- Left front reading lamp switch
- Right front reading lamp switch
Control interventions on audio system:
Control interventions at the audio system control buttons are sent to the multifunction camera by the radio or the COMAND controller unit via the interior CAN, front SAM control unit and chassis CAN.
Control interventions on comfort functions:
Control interventions at the steering column adjuster switch, at the cruise control lever and at the multifunction steering wheel button groups are read in by the steering column tube module control unit, and they are sent over the chassis CAN to the multifunction camera.
The steering wheel electronics read in the control interventions on the multifunction steering wheel button groups directly and transmit them to the steering column tube module control unit over the steering LIN.
The left front door control unit reads in control interventions at the driver-side power window and outside mirror adjustment switch group via the left door LIN and sends them to the multifunction camera via the interior CAN, front SAM control unit and chassis CAN.
Interior illumination control interventions:
The front SAM control unit reads in the status of the front dome lamp switch and the front reading lamp switches in the overhead control panel electronics directly and sends these status signals to the multifunction camera via the chassis CAN.
Function sequence for issuing warning
The warning is issued haptically by the steering wheel vibration motor, which is integrated into the multifunction steering wheel. The multifunction camera sends the request to actuate the steering wheel vibration motor over the chassis CAN to the steering column tube module control unit. The steering column tube module control unit forwards the request over the steering LIN to the steering wheel electronics which actuate the steering wheel vibration motor. The steering wheel vibration motor is actuated for a duration of t = 1.5 s.
The intensity of the haptic warning is adapted to the vehicle speed, to cover for perceptible influences from the suspension at high speeds.
The warning is terminated when the triggering conditions are no longer given or when driver activity is detected (braking, accelerating, steering or turn signaling).
The warning is also terminated if, during a warning, a driver response is detected (e.g. steering back into the lane or turn signaling).
The following situations will result in suppression of a warning output, because it is assumed that the driver activity is intentional:
- Status changes of steering wheel, brake or accelerator pedal
- Recognized "corner cutting" (by means of lane recognition and the current vehicle position the multifunction camera recognizes a road with bends and concludes "corner cutting"). Warnings about corner cutting are not issued until a defined lateral acceleration is reached.
- Active flashing function (corresponding turn signaling)
- Active or passive safety functions active
On vehicles up to 31.5.12, a warning can only be output again approx. t = 3 s after warning suppression and t = 10 s after turn signaling. On vehicles as of 1.6.12, following suppression the next warning can be issued in "Standard" mode only after approx. t = 3 s, in "Adaptive" mode only after approx. t = 5 s and following turn signaling only after t = 10 s.
The corresponding information for suppression of the warning is received by the multifunction camera over the chassis CAN. If corner cutting is detected, the warning is delayed until a defined threshold (lateral acceleration depending on ground speed) is reached. Only then is the warning issued.
| Electrical function schematic for Lane Keeping Assist | PE54.71-P-2057-97EAA | ||
| Overview of system components for Lane Keeping Assist | GF54.71-P-9995CA |