Lane Keeping Assist function - GF54.71-P-0005CE
MODEL 204.0/2 with CODE (476) Lane Keeping Assist as of model year 2012 /YoM 11 facelift
MODEL 204.3 with CODE (476) Lane Keeping Assist
MODEL 204.9 with CODE (476) Lane Keeping Assist as of model year 2013 /facelift 12
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 over the chassis CAN to the multifunction camera.
Lane Keeping Assist, general
The Lane Keeping Assist function 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 function takes the driver's behavior into consideration and decides the point at which a warning is to be issued.
As of 1.6.12 an option is available to the driver to configure the sensitivity of the Active Lane Keeping Assist in the instrument cluster's "Assistance" menu.
The following operating modes are available for selection:
- Standard (high sensitivity, warnings issued earlier and more frequently)
- Adaptive (low 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 Lane Keeping Assist principle
The Lane Keeping Assist function operates on a speed-dependent basis. The vehicle speed is calculated from the wheel speed signals of the rpm sensors.
The Electronic Stability Program control unit directly reads in the signals from the rpm sensors and sends them over the chassis CAN to the instrument cluster. The instrument cluster calculates the vehicle speed to be displayed and sends this over the chassis CAN to the multifunction camera.
The Lane Keeping Assist function includes 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 image 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 actions of the Lane Keeping Assist function are all derived from this. 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.
When in construction site areas, the Lane Keeping Assist function is unable to issue warnings because of possible multiple lane markings.
The current Lane Keeping Assist status, in particular, the warning readiness, is indicated continuously in the instrument cluster's multifunction display. 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
Deliberate driver activity is recorded as follows:
Turn signaling:
The steering column tube module control unit directly reads in the switch position of the combination switch and sends it over the chassis CAN to the multifunction camera.
Acceleration:
The accelerator pedal sensor registers any accelerator pedal actuation.
The CDI control unit or the ME-SFI [ME] control unit directly reads in the signals from the accelerator pedal sensor and sends them over the chassis CAN to the multifunction camera.
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. The Electronic Stability Program control unit evaluates the data for the vehicle motion (yawing moment) and sends the data and the status of the brake lights switch over the chassis CAN to the multifunction camera.
The yaw behavior of the vehicle is detected by the yaw rate sensor for lateral and longitudinal acceleration. This is designed as a separate component on vehicles with code (233) DISTRONIC PLUS, code (237) Active Blind Spot Assist or code (238) Active Lane Keeping Assist and model 204.077/277/377 and it communicates over the dynamics CAN with the Electronic Stability Program control unit. For vehicles, for which the above-mentioned limitation does not apply, the yaw rate sensor for lateral and longitudinal acceleration is integrated into the Electronic Stability Program control unit.
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 by the driver, crossing over the lane marking at an angle of ∠> 3° or a lateral acceleration of a > 4 m/s2
, then 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 function deems the driver to be "distracted". As soon as the vehicle drives over the lane marking, an active warning is output.
The 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 system warns earlier and possibly more often.
The following controls are monitored:
- Audio system controls:
- Radio or
- COMAND controller unit
- 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
- 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 are recorded as follows:
Control interventions on audio system:
Control interventions on the audio system control buttons are sent by the radio or the COMAND controller unit over the interior CAN, front SAM control unit and chassis CAN to the multifunction camera.
Control interventions on comfort functions:
Control interventions on the steering column adjustment switch, the cruise control lever and on the multifunction steering wheel button groups are read in by the steering column tube module control unit and sends them 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 control interventions on the driver-side power window and outside mirror adjustment switch group, are read in by the left door control unit over the left door LIN and they are then sent over the interior CAN, front SAM control unit and the chassis CAN to the multifunction camera.
Control interventions on the interior illumination (without code (414) Power glass tilting/sliding roof):
The status of the front dome lamp switch, the front left reading lamp switch and the front right reading lamp switch is directly read in by the front SAM control unit and they are then sent over the chassis CAN to the multifunction camera.
Control interventions on the interior illumination (with code (414) Power glass tilting/sliding roof):
The status of the front dome lamp switch, the front left reading lamp switch and the front right reading lamp switch is directly read in by the overhead control panel control unit and it is then sent over the interior CAN, front SAM control unit and the chassis CAN to the multifunction camera.
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 then sends a request over the chassis CAN to actuate the steering wheel vibration motor 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 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
For vehicles up to 31.5.12 a warning can be issued again after a suppression only after approx. t = 3 s and after turn signaling only after t = 10 s.
For vehicles as of 1.6.12 a warning can be issued again after a suppression in the "Standard" mode only after approx. t = 3 s, and in the "Adaptive" mode only after approx. t = 5 s, and after 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.
| Lane Keeping Assist electrical function schematic | PE54.71-P-2057-97FAA | ||
| Overview of system components for Lane Keeping Assist | GF54.00-P-9998CE |