Active Lane Keeping Assist, function - GF54.71-P-0004CE

MODEL 204.0/2 

with CODE (238) Active Lane Keeping Assist 

as of model year 2012 

/YoM 11 model refinement package 

MODEL 204.3 with CODE (238) Active Lane Keeping Assist 

Function requirements, general 

• Circuit 15 ON
• Function enabled via the instrument cluster
• Vehicle speed:
  • Warning at v = 60 to 270 km/h
  • Intervention by the brake system at v = 60 up to 200 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):
  • s = 2.5 to 4.6 m for warning
• s = 2.6 to 4.4 m and v = 60 to 200 km/h for intervention by the brake system (excepted here are track widths s > 3.9 m, which may be driven at a speed of v < 100 km/h)

The status of circuit 15 is sent by the electronic ignition lock control unit over the chassis CAN to the video and radar sensor system control unit.

Interventions by the brake system only ever take place when:

• an easily visible, uninterrupted line is crossed over
• trailer not detected on vehicle
• the Electronic Stability Program (ESP) is not shifted to passive (without model 204.077/277/375) or ESP is not shifted to the "SPORT HANDLING MODE" (model 204.077/277/375)
• run-flat tire is not active

Active Lane Keeping Assist, in general (Shown on model 221) 

The Active Lane Keeping Assist system detects when lane markings are unintentionally crossed over by means of the multifunction camera and warns the driver in certain situations by means of a warning system in the steering wheel when the lane is exited.

If the driver fails to react to the warning, specific interventions by the brake system are authorized from the video and radar sensor system control unit to return the vehicle to the road lane.

If the driver indicates to the system that he/she is "active" before the intervention by the brake system, the intervention by the brake system is suppressed or canceled.

If the video and radar sensor system control unit detects activity of the anti-lock braking system (ABS), acceleration skid control (ASR), Brake Assist System (BAS), PreSafe system or the Active Blind Spot Assist, which require an intervention by the brake system, a brake intervention by the Active Lane Keeping Assist is also suppressed or immediately canceled.

Interventions by the brake system only occur when a lane divider line is crossed over (lane barrier) at an angle of ∠ < 3° and only when the lane is restricted through two lane markings. By contrast, a warning is always issued when a broken line is crossed over.

The Active Lane Keeping Assist system operates on a speed-dependent basis and therefore it requires the speed to be calculated, and this is defined by the wheel speeds.

The wheel speeds are recorded by the following components:

• Left front axle speed sensor
• Right front axle speed sensor
• Left rear axle speed sensor
• Right rear axle speed sensor

The Electronic Stability Program control unit reads in the RPM sensor signals directly and sends them over the chassis CAN to the video and radar sensor system control unit, instrument cluster and the multifunction camera.

The RPM sensor signals are used by the listed control units for internal calculation of the vehicle speed.

The instrument cluster also sends the current vehicle speed over the chassis CAN to the multifunction camera.

The Active Lane Keeping Assist system is made up 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 active intervention by the brake system 

Function sequence for lane recognition 

The multifunction camera, which is mounted at the top center on the front window, visually monitors the road space in front of the vehicle.

To this end, the multifunction camera uses a fixed scan rate to document pictures of the lane and then sends them to the control unit integrated into the multifunction camera.

The picture data are also sent over a low voltage differential signaling line to the video and radar sensor system control unit. The multifunction camera then measures the lane based on the lane markings.

Schematic of lane recognition by multifunction camera 

The documented picture sequences and measurement values, which are generated from the lane marking pictures, lanes are calculated in the multifunction camera and in the video and radar sensor system control unit independent of each other and using corresponding algorithms.

The algorithm stored in the multifunction camera is also used to enable the warning function.

The algorithm in the video and radar sensor system control unit issues a brake function enable following positive verification with the multifunction camera algorithm.

The data are then used by the multifunction camera and the video and radar sensor system control unit to determine the relative position of the vehicle in the lane. The Active Lane Keeping Assist system measures are then all derived from this position.

No lane information can be issued where there are no lane markings or if they are covered up (e.g. by dirt or snow) or where there is a low contrast between the road surface and lane marking 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 area the system is unable to issue warnings because of possible multiple lane markings.

The instrument cluster continuously displays the current status, in particular the warning readiness.

Possible displays:

• System status
  • Icon off: Active Lane Keeping Assist deactivated
  • Icon yellow (1): Active Lane Keeping Assist activated, but not ready to issue warnings

  (e.g. v < 60 km/h)

• Warning readiness
  • Icon green (2): Active Lane Keeping Assist activated and ready to issue warnings
• Message for system errors in multifunction display (A1p13)

Function sequence for recognition of driver activity 

The following situations suggest driver activity and result in suppression of any pending warning or brake intervention:

• Turn signals
• Accelerate
• Brakes
• Steering intervention

The listed situations are recorded by the corresponding components and sent over chassis CAN to the video and radar sensor system control unit and the multifunction camera:

Turn signaling:

The signals from the combination switch are read in by the steering column tube module control unit and sent over the chassis CAN.

Acceleration:

Operation of the accelerator pedal is registered by the accelerator pedal sensor. The signals from the accelerator pedal sensor are read in directly by the CDI control unit or ME-SFI [ME] control unit and sent over the chassis CAN to the ESP control unit.

Brakes:

The status of the service brake is recorded by the brake lights switch, which is read in directly by the Electronic Stability Program control unit. In addition to this, the data of the yaw rate sensor for lateral and longitudinal acceleration are recorded, which sends its data over the vehicle dynamics CAN to the Electronic Stability Program control unit.

The Electronic Stability Program control unit sends the status of the service brake, including the vehicle deceleration data, over the chassis CAN.

Steering intervention:

The signal from the steering wheel angle sensor is sent by the steering column tube module control unit over chassis CAN.

If the multifunction camera and the video and radar sensor system control unit detect active corner cutting by the driver, crossing the lane marking at an angle of ∠ > 3° or lateral acceleration of a > 4 m/s ² any pending warning or intervention by the brake system is suppressed.

The lateral acceleration is evaluated by the video and radar sensor system control unit antiproportional to the vehicle speed.

Function sequence for recognition of control interventions 

All controls in the driver's immediate vicinity are monitored. If a control intervention is detected, the Active Lane Keeping Assist system regards the driver to be "distracted" and an active warning is issued as soon as the vehicle crosses over the lane marking. The control interventions are recorded by the multifunction camera. The warning threshold is adapted to match the control actuating frequency, i.e. the Active 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
• Controls on the interior illumination (with code (414) Power glass tilting/sliding roof):

• Front dome lamp switch
• Left front reading lamp switch
• Right front reading lamp switch

Control interventions on audio system:

The control interventions on the audio system control buttons are sent by the radio or the COMAND controller unit over the body CAN to the front SAM control unit.

Control interventions on comfort functions:

The control interventions on the steering column adjustment and the cruise control lever are read-in directly by the steering column tube module control unit.

The steering column tube module control unit also reads in the control interventions from the multifunction steering wheel button groups through the steering wheel electronics over the steering LIN.

This information is sent over the chassis CAN to the steering column tube module control unit.

The control interventions on the driver-side power window and outside mirror adjustment switch group are read in by the left front door control unit over the door LIN.

The left front door control unit sends this information over the interior CAN to the front SAM control unit. The front SAM control unit sends this information to the chassis CAN.

Control interventions on the interior illumination (with code (414) Power glass tilting/sliding roof):

Control interventions on the interior illumination are read in by the overhead control panel control unit, which sends the information on the control interventions over the chassis CAN.

Control interventions on the interior illumination (without code (414) Power glass tilting/sliding roof):

Control interventions on the interior illumination are registered by the front SAM control unit and it then sends the signals over the chassis CAN.

The multifunction camera receives the information on the control interventions on the audio system, the comfort functions and the interior illumination over 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 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 and the driver feels the vibration. The intensity of the vibration is adapted to the vehicle speed, to cover for perceptible influences from the suspension at high speeds.

The warning is terminated by the discontinuity of the triggering conditions or when driver activity is recognized (braking, accelerating and braking or turn signaling). If during a warning a driver response is detected, e.g. steering back into the lane or turn signaling, the warning is also terminated.

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 systems active

The next possible warning output, after a warning output has been suppressed, takes place after approx. t = 3 s and generally after turn signaling for 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 recognized a warning period delay occurs, until a defined threshold (lateral acceleration dependent on ground speed) is reached, whereupon a warning is then issued.

Additional function requirements for active intervention by the brake system 

• Two lane barriers (lines, one of which may be broken) must be present
• A crossed over lane barrier must be a lane divider line
• Recognition that a lane has been exited (calculated in multifunction camera and video and radar sensor system control unit)
• Driver warning by multifunction camera currently pending
• No driver activity detected
• No stationary object detected on the side away from the intervention between the vehicle and the lane marking through the radar sensor system of the DISTRONIC PLUS or Active Blind Spot Assist systems (e.g. warning beacons in construction sites)
• Approval for active intervention by the brake system issued by yawing moment interface

The yawing moment interface, which is integrated into the Electronic Stability Program control unit, uses a status signal to issue approval for the course-correcting braking torque.

Function sequence for active intervention by the brake system 

The video and radar sensor system control unit receives the pictures from the multifunction camera over the low voltage differential signaling line. The picture data are used by the video and radar sensor system control unit to calculate a lane.

Parallel to this the multifunction camera also calculates its own lane. The multifunction camera sends the lane data over the chassis CAN to the video and radar sensor system control unit.

The video and radar sensor system control unit compares its calculated lane with the multifunction camera pictures of the lane. If the comparison of the lanes matches to a sufficient degree, the video and radar sensor system control unit uses the comparison to generate a secured lane.

If the vehicle, for example, crosses over a dividing line on the right side of the vehicle, the video and radar sensor system control unit uses a defined algorithm to decide whether and with which intensity a track-aligning intervention by the brake system is to take place.

If the multifunction camera does not detect any driver activity at the same time, and if there are no stationary objects on the vehicle side averted from the intervention, the video and radar sensor system control unit internally issues approval for the intervention by the brake system. The video and radar sensor system control unit then sends a corresponding request over the vehicle dynamics CAN for wheel-specific (active) braking of the left side of the vehicle to the Electronic Stability Program control unit.

The Electronic Stability Program control unit then initiates the corresponding wheel-specific interventions by the brake system, which are then implemented by the hydraulic unit traction system. The vehicle is "guided back" into the lane. At the same time as the wheel-specific intervention by the brake system, the driver is visually notified of the activity. To this end, the video and radar sensor system control unit sends a corresponding request to issue information over the chassis CAN to the multifunction camera.

The multifunction camera sends this request over chassis CAN for visual output in the multifunction display on the instrument cluster.

If during an intervention by the brake system the driver steers opposite to the intervention by the brake system (i.e. overrides the intervention by the brake system), the intervention by the brake system is immediately canceled.

Information on active intervention by the brake system function: If the video and radar sensor system control unit detects active corner cutting by the driver, any crossing over of the lane marking at an angle of ∠ >3° or any lateral acceleration of a > 4 m/s ² an intervention by the brake system is suppressed.

Active interventions by the brake system are canceled, when one of the following conditions occurs:

• Driver steers back into the lane
• Engine switched off
• No forward travel detected
• Lane data not recorded properly
• Multifunction camera and the video and radar sensor system control unit calculate different lane data
• Driver activity recognized:
  • Turn signaling
  • Acceleration
  • Brakes
  • Steering intervention
• the ESP is shifted to passive (without model 204.077/277/375)
• ESP shifted to the "SPORT HANDLING MODE" (model 204.077/277/375)
• ABS, ASR, BAS, ESP, PreSafe or Active Blind Spot Assist request an intervention by the brake system

	Electrical function schematic for Active Lane Keeping Assist		PE54.71-P-2053-97FAA
	Overview of system components for Active Lane Keeping Assist		GF54.00-P-9998CE