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

MODEL 212.0/2 up to 28.2.13 with CODE (238) Active Lane Keeping Assist as of model year 2011 /AEJ 10 

Function requirements, general 

IMPORTANT The status of circuit 15 is sent by the electronic ignition lock control unit (N73) over the chassis CAN (CAN E) to the multifunction camera (A40/11) and the video and radar sensor system control unit (N62/2).

IMPORTANT Interventions by the brake system only ever take place when:

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

The Active 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 (M99). 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.

Fig 1: Overview Of Active Lane Keeping Assist System
G07629268Courtesy of MERCEDES-BENZ USA

For vehicles 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:

(Sensitivity reduced, 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.

IMPORTANT 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 operates on a speed-dependent basis and therefore requires the vehicle speed to be calculated. This is defined by the wheel speeds.

The wheel speeds are recorded by the following components:

The regenerative braking system control unit (N30/6) (model 212.095/098/298) or the Premium Electronic Stability Program control unit (N30/7) (except model 212.095/098/298) directly reads in the rpm sensor signals and sends them over the chassis CAN to the video and radar sensor system control unit and to the instrument cluster. The video and radar sensor system control unit calculates the vehicle speed internally. The instrument cluster calculates vehicle speed and sends it over the chassis CAN to the multifunction camera.

The video and radar sensor system control unit calculates the vehicle speed itself.

The Active Lane Keeping Assist function includes the following subfunctions:

Function sequence for lane recognition 

The multifunction camera is mounted at the top center of the windshield and it records the road space in front of the vehicle. The multifunction camera then measures the lane based on the lane markings.

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 multifunction camera also sends the picture data over a low voltage differential signal (LVDS) line to the video and radar sensor system control unit.

Schematic of lane recognition by multifunction camera 

Fig 2: Schematic Of Lane Recognition By Multifunction Camera
G07071998Courtesy of MERCEDES-BENZ USA

Based on the recorded video 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.

IMPORTANT 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 (A1p13) of the instrument cluster.

The multifunction camera sends the corresponding requests over chassis CAN to the instrument cluster.

Possible displays for vehicles up to 31.5.11:

Possible displays for vehicles as of 1.6.11:

Function sequence for recognition of driver activity 

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

Deliberate driver activity is recorded as follows:

Turn signaling:

The steering column tube module control unit (N80) directly reads in the switch position of the combination switch (S4) and sends this over the chassis CAN to the video and radar sensor system control unit and to the multifunction camera.

Acceleration:

The accelerator pedal sensor (B37) registers any operation of the accelerator pedal.

The CDI control unit (N3/9) (for diesel engine) or the ME-SFI [ME] control unit (N3/10) (for gasoline engine) directly reads in the signals from the accelerator pedal sensor and sends them over 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 (S9/1). The brake system control unit or the Electronic Stability Program control unit directly reads in the status of the brake lights switch.

The data of the yaw rate sensor for lateral and longitudinal acceleration (B24/15) are recorded, and then sent over the dynamics CAN (CAN H) to the brake system control unit or to the Electronic Stability Program control unit.

The brake system control unit or the Electronic Stability Program control unit sends the data on the vehicle's self-movement along with the status of the brake lights switch over the chassis CAN to the video and radar sensor system control unit and to the multifunction camera.

Steering intervention:

Steering movements are recorded by the steering angle sensor (N49). The steering column tube module control unit reads in the signals from the steering angle sensor and transmits this via the chassis CAN to the video and radar sensor system control unit and to the multifunction camera.

IMPORTANT If 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 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 match 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 function 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 function warns earlier and possibly more often.

The following controls are monitored:

Control interventions are recorded as follows:

Control interventions on audio system:

The control interventions on the audio system control buttons are sent by the radio or the radio with autopilot system or the COMAND controller unit over the interior CAN (CAN B), front SAM control unit with fuse and relay module (N10/1) and the chassis CAN to the multifunction camera.

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.

IMPORTANT The steering wheel electronics (N135) directly read in the control interventions at the multifunction steering wheel button groups, and send them over the steering LIN (LIN E1) to the steering column tube module control unit.

The control interventions on the driver-side electric window lifting mechanism and outside mirror adjustment switch group (outside mirror adjustment only) are registered by the left front door control unit (N69/1) over the left front door-(LIN B5).

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

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

The status of the front dome lamp switch and the front reading lamp switch are directly read in by the overhead control panel control unit (N70) and it sends them 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 and the front reading lamp switch is directly read in by the front SAM control unit over the electronic OCP (N70/3). The front SAM control unit then sends them over 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 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.

IMPORTANT The warning is terminated when the triggering conditions are no longer given or when driver activity is detected (accelerating and braking 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:

Vehicles up to 31.5.12:

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.

Vehicles as of 1.6.12:

After a warning is suppressed, the next possible warning can be issued in "Standard" mode after approx. t = 3 s, in the "Adaptive" mode after approx. t = 5 s and following turn signaling always after t = 10 s.

IMPORTANT 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.

Additional function requirements for active intervention by the brake system 

IMPORTANT The yawing moment interface, which is integrated in the brake system control unit or the Electronic Stability Program control unit, internally issues an enabling signal for 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 the vehicle, for example, 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 vehicle over the dynamics CAN to the brake system control unit or to the Electronic Stability Program control unit.

The brake system control unit or the Electronic Stability Program control unit implements this request and actuates the traction system hydraulic unit (A7/3) 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 a request to issue information over the chassis CAN to the multifunction camera.

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

IMPORTANT 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 conditions occurs:

  Active Lane Keeping Assist, location of components   GF54.71-P-0004-01FL 
REFER TO SYSTEM WIRING DIAGRAMS Electrical function schematic for Active Lane Keeping Assist   PE54.71-P-2053-97DAA
  Active Lane Keeping Assist, block diagram   GF54.71-P-0004-02FL 
  Overview of system components for Active Lane Keeping Assist   GF54.71-P-9996FL 
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