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

MODEL 207 up to model year 2014 with CODE 238 (Active lane keeping Assist) 

Fig 1: Active Lane Keeping Assist Block Diagram
G10081874Courtesy of MERCEDES-BENZ USA

Function requirements, general 

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

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

The Active 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. 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 2: Overview Of Active Lane Keeping Assist - Shown On Model 221
G07629268Courtesy of MERCEDES-BENZ USA

As of 1.6.12, the driver can select the sensitivity of the Active Lane Keeping Assist in the "Assistance" menu of the instrument cluster.

The following operating modes are available for selection:

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 operation is speed-dependent. The vehicle speed is calculated from the wheel speed signals.

The wheel speeds are recorded by the following sensors:

The Premium Electronic Stability Program control unit reads in the signals from the RPM sensors directly and sends them to the instrument cluster and the video and radar sensor system control unit via the chassis CAN. The instrument cluster calculates the listed vehicle speed and sends this 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 comprises the following subfunctions:

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 pictures of the lane at a fixed scanning rate and makes these pictures available to the integrated control unit. The multifunction camera also sends the picture data to the video and radar sensor system control unit via a low voltage differential signal (LVDS) line. The multifunction camera measures the lane based on the lane markings.

Schematic of lane recognition by multifunction camera 

Fig 3: Schematic Display Of Lane Recognition By Multifunction Camera
G07071998Courtesy of MERCEDES-BENZ USA

Based on the documented 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 of the instrument cluster. The multifunction camera sends the corresponding requests over chassis CAN to the instrument cluster.

Possible displays:

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 signaling:

The steering column tube module control unit reads in the position of the combination switch directly and sends it to the video and radar sensor system control unit and 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 video and radar sensor system control unit and 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 from the yaw rate sensor for lateral and longitudinal acceleration. The yaw rate sensor for lateral and longitudinal acceleration sends the values for vehicle longitudinal and lateral acceleration and yaw rate to the Electronic Stability Program control unit via the vehicle dynamics CAN. The Electronic Stability Program control unit sends the values for vehicle longitudinal and lateral acceleration, yaw rate and the status of the brake light switch to the video and radar sensor system control unit and the multifunction camera via the vehicle dynamics CAN.

Steering intervention:

Steering movements are recorded by the steering angle sensor. 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 multifunction camera or the radar sensors control unit detects active corner cutting, crossing over the lane markings at an angle of ∠ > 3° or a lateral acceleration of a > 4 m/s2 , 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 negatively proportional 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. 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:

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.

IMPORTANT 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 account 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 (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:

Vehicles up to 30.5.12:

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.

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.

Afterwards, a warning is output.

Additional function requirements for active intervention by the brake system 

IMPORTANT The yawing-moment interface is integrated into the Electronic Stability Program control unit and it sends out a status signal to enable 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 is 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 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 a request to issue information over the chassis CAN to the multifunction camera. The multifunction camera sends this request via the chassis CAN to the instrument cluster, which outputs the information message 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 a lateral acceleration of a > 4 m/s2 , any intervention by the brake system is suppressed.

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

  Electrical function schematic for Active Lane Keeping Assist   PE54.71-P-2053-97EAA
  Overview of system components for Active Lane Keeping Assist   GF54.71-P-9996CA 
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