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 /facelift 12 

MODEL 204.9 with CODE (238) Active Lane Keeping Assist as of model year 2013 

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 to 4.6 m (excepted are track widths of s > 3.9 m, that are driven at a speed of v < 100 km/h)

The electronic ignition lock control unit sends the circuit 15 status over the chassis CAN to the video and radar sensor system control unit and to the multifunction camera.

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

The Active Lane Keeping Assist recognizes the unintended infringement of the lane markings and issues a haptic warning to the driver in specific situations by means of 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. Active Lane Keeping Assist takes the driver's behavior into consideration and decides the point at which a warning is to be issued.

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.

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 (reduced sensitivity, warnings issued later and less often)

If the driver indicates that he/she is "active" before or during 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 antilock braking system (ABS), acceleration skid control (ASR), Brake Assist System (BAS), PRE-SAFE system or the Active Blind Spot Assist system, which requires an intervention by the brake system, a brake intervention by 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.

Active Lane Keeping Assist operation is speed-dependent. The vehicle speed is calculated from the wheel speed signals of the rpm sensors.

The Electronic Stability Program control unit reads in the signals from the rpm sensors directly and sends them over the chassis CAN to the video and radar sensor system control unit, to the instrument cluster and to the multifunction camera. The instrument cluster calculates the vehicle speed to be displayed and sends this over the chassis CAN to the multifunction camera. The video and radar sensor system control unit calculates the vehicle speed itself.

Active Lane Keeping Assist encompasses 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 is mounted at the top center of the windshield and visually records the road space in front of the vehicle. The multifunction camera records lane images.

at a fixed scan rate and makes them available to the integrated control unit.

In addition, the multifunction camera transmits the image data over an LVDS line to the video and radar sensor system control unit.

The multifunction camera measures the lane based on the lane markings.

Schematic of lane recognition by multifunction camera 

Based on the image sequences and the measurement values resulting from the lane markings, the multifunction camera and the video and radar sensor system control unit each calculate a lane independently of each other. These calculations are based on corresponding algorithms.

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 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 Active Lane Keeping Assist function may not be able to issue warnings due to multiple markings.

The current status, especially the warning readiness, is indicated continuously in the multifunction display of the instrument cluster. The multifunction camera sends the corresponding requests over the chassis CAN to the instrument cluster.

Possible displays:

• 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 interventions by the brake system and function errors in the multifunction display
  Fig 4: Screen Display Of Active Lane Keeping Assist (Icon Yellow And Icon Green)

  Courtesy of MERCEDES-BENZ USA

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

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 this over the chassis CAN to the video and radar sensor system control unit and 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 video and radar sensor system control unit and 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 also reads in the data from the yaw rate sensor for lateral and longitudinal acceleration. The yaw rate sensor for lateral and longitudinal acceleration sends the values for longitudinal and lateral acceleration and yaw rate over the dynamics CAN to the Electronic Stability Program control unit.

The Electronic Stability Program control unit sends the values for longitudinal and lateral acceleration, yaw rate and the status of the brake lights switch over the dynamics CAN to the video and radar sensor system control unit and the multifunction camera.

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 video and radar sensor system control unit and the multifunction camera.

If the multifunction camera or the video and radar sensor system control unit detect active corner cutting, crossing of the lane marking at an angle of ∠> 3° or lateral acceleration of g > 4 m/s ² any pending warning or intervention by the brake system is also 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 registered, the Active Lane Keeping Assist 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 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
• 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 front 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 then 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 account 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 systems active

Vehicles up to 31.5.12:

After warning suppression, a warning can only be output again after approx. t = 3 s or after t = 10 s in the case of turn signaling.

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 dependent on vehicle speed) is reached. A warning is then issued.

Additional function requirements for active intervention by the brake system 

• Two lane delimitations present (lines, one of which may be broken)
• The lane delimitation crossed is a continuous line
• Exiting of lane detected (recorded by multifunction camera and video and radar sensor system control unit)
• Active warning by multifunction camera
• No driver activity detected
• Vehicle speed v = 60 to 200 km/h
• Track width s = 2.6 to 4.4 m (excepted are track widths of s > 3.9 m, that are driven at a speed of v < 100 km/h)
• No stationary objects detected by radar sensor system on the vehicle side facing away from the intervention (e.g. warning beacons in construction sites)
• Electronic Stability Program (ESP®) not passively connected (except model 204.077/277/377) or ESP® not shifted to "SPORT HANDLING MODE" (model 204.077/277/377)
• ESP® not in active diagnostic or roller dynamometer mode
• Antilock braking system (ABS), acceleration skid control (ASR), Brake Assist System (BAS), ESP®, PRE-SAFE brake inactive
• Enable for active intervention by the brake system issued by yaw-moment interface

  The yaw moment interface is integrated into the Electronic Stability Program control unit and it issues the enable for a 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 LVDS 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 the calculated lane with the lane data from the multifunction camera. If the comparison matches to a sufficient degree, the video and radar sensor system control unit uses the comparison to generate a "trusted" lane.

If, for example, the vehicle crosses over a continuous line on the right side of the vehicle, the video and radar sensor system control unit decides whether and with which intensity a course-correcting intervention by the brake system is to take place.

If the multifunction camera does not detect any driver activity at the same time and also does not detect any stationary objects on the vehicle side facing away from the intervention, the video and radar sensor system control unit issues approval for the intervention by the brake system.

The video and radar sensor system control unit sends the request for wheel-specific (active) braking of the left side of the vehicle over the dynamics CAN to the Electronic Stability Program control unit. The Electronic Stability Program control unit implements this request and actuates the traction system hydraulic unit accordingly.

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 this activity.

To this end the video and radar sensor system control unit sends the request to issue an information message over the chassis CAN to the multifunction camera.

The multifunction camera sends this request over the chassis CAN to the instrument cluster, which shows it on the multifunction display.

If the driver countersteers against the intervention by the brake system (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, 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 situations occurs:

• Engine switched off
• No forward travel detected
• Lane data cannot be recorded correctly
• Multifunction camera and the video and radar sensor system control unit calculate different lanes
• Driver steers back into the lane
• ESP® passively switched (except model 204.077/277/377)
• ESP® switched to "SPORT HANDLING MODE" (model 204.077/277/377)
• ABS, ASR, BAS, ESP®, PRE-SAFE brake or Active Blind Spot Assist requests intervention by the brake system
• Driver activity recognized:
  • Turn signaling
  • Acceleration
  • Brakes
  • Steering intervention

	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