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

MODEL 218 as of model year 2015 with CODE 238 (Active lane keeping Assist) 

Function requirements, general 

• Engine running or drive train operational
• Soiling and function test on radar sensor system completed successfully

  Object recording (e.g. vehicle ahead) via the radar sensor system is based on the radar measuring procedure.

  The front long range radar sensor and the front bumper DISTRONIC (DTR) sensors perform a soiling and function test after each engine start to ensure that they are functioning correctly. The function test requires an object to be located in the respective detection area (this object is used as a reference value). If a malfunction is detected or no objects (for the function test) are present in the detection range, the Active Lane Keeping Assist cannot be activated. The radar sensors control unit receives the sensor signals from the front bumper DISTRONIC (DTR) sensors via radar CAN 1 and sends them via the chassis FlexRay to the front long range radar sensor. The front long range radar sensor evaluates them in combination with its own signals and, when all the radar sensors are functioning correctly, sends the "Radar sensor system operational" status via suspension FlexRay to the radar sensors control unit.

The CDI control unit or the ME-SFI control unit sends the "Engine running" or "Drivetrain operational" signal to the stereo multifunction camera and to the radar sensors control unit via chassis CAN 1, the chassis gateway control unit and chassis FlexRay.

Shown on model 205.0 

Active Lane Keeping Assist, general 

The Active Lane Keeping Assist detects when the vehicle crosses lane markings, and issues a haptic warning to the driver in certain situations by initiating vibrations on the steering wheel.

Crossing over lane markings is optically recorded and processed by the stereo 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 this warning, the radar sensors control unit initiates specific interventions by the brake system to return the vehicle to the traffic lane.

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.

During active control of the anti-lock braking system (ABS), acceleration skid control (ASR) and Brake Assist System (BAS), or during brake intervention by PRE-SAFE® or by the Active Blind Spot Assist, brake intervention by the Active Lane Keeping Assist is suppressed or canceled immediately.

Warnings are issued as soon as the vehicle is in the direct vicinity of a broken or solid line or crosses over it.

Interventions by the brake system only occur when the vehicle crosses a continuous line (lane delimitation) at an angle of ∠ < 3°, when the lane is delimited by two lane markings or, in the case of a broken line, when there is a vehicle in the oncoming lane or on a lane running in parallel in a collision-critical area.

The Active Lane Keeping Assist comprises the following subfunctions:

• Function sequence for Active Lane Keeping Assist ON and OFF 
• Function sequence for lane recognition 
• Function sequence for recognition of oncoming traffic/parallel traffic 
• 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 Active Lane Keeping Assist ON and OFF 

The Active Lane Keeping Assist can be switched off and on via the "Assistance" menu of the instrument cluster. The instrument cluster sends the status of the Active Lane Keeping Assist via chassis CAN 2, the chassis gateway control unit and chassis FlexRay to the radar sensors control unit and to the multifunction camera.

The driver also has to option of configuring the sensitivity of the Active Lane Keeping Assist in the instrument cluster's "Assistance" menu.

The following operating modes are available for selection:

• Standard (Sensitivity increased, warnings issued earlier and more frequently)
• Adaptive (reduced sensitivity, warnings issued later and less often)

The instrument cluster sends the selected operating mode via chassis CAN 2, chassis gateway control unit and chassis FlexRay to the stereo multifunction camera.

Active Lane Keeping Assist operation is speed-dependent. The vehicle speed is calculated from the wheel speed. The Electronic Stability Program control unit sends them to the radar sensors control unit and to the stereo multifunction camera via chassis CAN 1, chassis gateway control unit and chassis FlexRay. In addition, the Electronic Stability Program control unit sends the wheel speed to the instrument cluster via chassis CAN 1, the front SAM control unit and chassis CAN 2. The instrument cluster calculates the vehicle speed to be displayed and sends this via chassis CAN 2, chassis gateway control unit and chassis FlexRay to the stereo multifunction camera. The radar sensors control unit calculates the vehicle speed itself.

Additional function requirements for lane recognition 

• Detectable lane marking present on both sides (no construction site markings (ambiguous markings), no snow, not covered etc., i.e. not enough contrast)
• Forward travel recognized and gear range "D" selected
• Two lane dividers present

The direction of travel is defined using the wheel rotation direction. The Electronic Stability Program control unit sends corresponding information to the radar sensors control unit and to the stereo multifunction camera via chassis CAN 1, the chassis gateway control unit and chassis FlexRay.

The fully integrated transmission control unit sends information about the engaged gear range to the radar sensors control unit and the stereo multifunction camera via the drive train CAN, CDI control unit or ME-SFI control unit, chassis CAN 1, chassis gateway control unit and chassis FlexRay.

Function sequence for lane recognition 

The stereo multifunction camera is mounted at the top center of the windshield and records the road space in front of the vehicle. The stereo multifunction camera documents images of the lane at a fixed scanning rate and makes these available to the integrated control unit. Additionally, the stereo multifunction camera sends processed lane data to the radar sensors control unit via the chassis FlexRay.

Schematic of lane recognition by stereo multifunction camera 

The stereo multifunction camera calculates the lane on the basis of two different lane algorithms that are implemented in the stereo multifunction camera. If a comparison of the two lane algorithms results in a match, the stereo multifunction camera uses it to generate a safe lane.

The stereo multifunction camera uses this data to calculate 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. If there are several markings present (e.g. in construction site zones), the Active Lane Keeping Assist may not be ready to issue a warning. If tar joints in the road surface are interpreted as lane markings, a warning is suppressed.

Function sequence for recognition of oncoming traffic/parallel traffic 

Vehicles in the oncoming lane or the lane running parallel are recognized by the long range and/or short range sensor system. The radar sensors control unit receives the signals of the corresponding radar sensors, checks their plausibility and evaluates them, taking the data of the stereo multifunction camera into account.

The radar sensors control unit reads in the signals of the front long-range radar sensor via the chassis FlexRay. The sensor signals from the front bumper DISTRONIC (DTR) sensors are read in by the radar sensors control unit via radar CAN 1.

The stereo multifunction camera determines values for the width and the course of the lane and sends these to the radar sensors control unit via the chassis FlexRay.

Based on values such as the speed of the two vehicles, the respective relative position on the lane and the course of the lane, the radar sensors control unit determines whether a course-correcting wheel-specific brake intervention is required.

The following situations can lead to a course-correcting brake intervention when changing to the parallel lane/oncoming lane:

• Approaching vehicle in the oncoming lane
• Slower vehicle to be passed in the parallel lane
• Passing vehicle in the parallel lane
• Vehicle in the parallel lane (at approximately the same level)

Further information on intervention by the brake system can be found in "Function sequence for active brake intervention".

The following representations illustrate the situations described above:

Approaching vehicle in the oncoming lane 

Vehicles in the oncoming lane are detected by the following radar sensors depending on the distance and angle to the vehicle with Active Lane Keeping Assist:

• Front long-range radar sensor
• DISTRONIC sensor (DTR)/left front bumper

Slow vehicle to be passed in the parallel lane 

Vehicles in the right or left parallel lane in the area ahead are detected by the following radar sensors depending on which lane and on the distance and angle to the vehicle with Active Lane Keeping Assist:

• Front long-range radar sensor
• Right front bumper DISTRONIC (DTR) sensor and left front bumper DISTRONIC (DTR) sensor

Passing vehicle in the parallel lane 

Vehicles approaching from behind the vehicle with Active Lane Keeping Assist at a high relative speed are detected by the following radar sensors depending on which lane and on the distance and angle to the vehicle with Active Lane Keeping Assist:

• Center rear bumper radar sensor
• Left rear bumper radar sensor or right rear bumper radar sensor

Vehicle in the parallel lane is at approx. the same level as the vehicle with Active Lane Keeping Assist 

Vehicles in the right or left parallel lane level with the vehicle with Active Lane Keeping Assist are detected by the following radar sensors depending on which lane and on the distance and angle to the vehicle with Active Lane Keeping Assist:

• DISTRONIC sensor (DTR)/right front bumper
• DISTRONIC sensor (DTR)/left front bumper
• Left rear bumper radar sensor or right rear bumper radar sensor

The following situations can lead to a cancellation of the course-correcting brake intervention:

• Vehicle detected with short distance in the rear area in own lane (tailgating scenario)
• Obstacle detected in own lane (e.g. bicycle)
• Driving obstacle detected behind the lane delimitation (hard shoulder) with narrow lane

Function sequence for recognition of driver activity 

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

• Clearly active steering (steering intervention), braking or accelerating
• Turn signals
• Sporty driving (high cornering speeds or heavy acceleration)
• Cutting a tight corner

Steering:

Steering movements are recorded by the steering wheel angle sensor.

The steering column tube module control unit reads in the signals from the steering wheel angle sensor directly and sends information about the steering angle and the steering wheel velocity to the radar sensors control unit and to the stereo multifunction camera via chassis CAN 1, the chassis gateway control unit and chassis FlexRay.

Brakes:

The Electronic Stability Program control unit sends the status of the brake pedal via chassis CAN 1, the chassis gateway control unit and chassis FlexRay to the radar sensors control unit and the stereo multifunction camera.

Acceleration:

The CDI control unit or the ME-SFI control unit sends information about the accelerator pedal position via chassis CAN 1, the chassis gateway control unit and chassis FlexRay to the radar sensors control unit and to the stereo multifunction camera.

Turn signaling:

The steering column tube module control unit reads in the switch position of the combination switch directly and sends it to the radar sensors control unit and the stereo multifunction camera via chassis CAN 1, the chassis gateway control unit and chassis FlexRay.

Turn rate, lateral acceleration and longitudinal acceleration (sporty driving):

The acceleration/yaw rate is detected by the yaw rate sensor for lateral and longitudinal acceleration. The yaw rate sensor for lateral and longitudinal acceleration sends corresponding values via the vehicle dynamics CAN and Electronic Stability Program control unit. The Electronic Stability Program control unit evaluates the data and sends it to the radar sensors control unit and to the stereo multifunction camera via chassis CAN 1, the chassis gateway control unit and chassis FlexRay.

If the stereo multifunction camera and the radar sensors control unit detect active corner cutting, crossing of the lane markings at an angle of ∠ > 3° or a lateral acceleration of a > 4 m/s² , a pending warning or intervention by the brake system is also suppressed here.

Function sequence for recognition of control interventions 

Controls located in close proximity of the driver and that affect the attention of the driver when they are operated are monitored. If a control intervention is registered, the Active Lane Keeping Assist deems the driver to be "distracted". Control interventions are evaluated by the stereo multifunction camera. The warning threshold is adjusted to match the actuation frequency of the controls, i.e. the Active Lane Keeping Assist warns earlier and possibly more often. An active warning is output as soon as the vehicle is in the direct proximity of or crosses over the lane marking.

The following controls are monitored:

• Audio system controls
• Comfort function controls:
  • Cruise control lever
  • Steering column adjustment switch (without code (443) Steering wheel heater) or steering column adjustment switch and steering wheel heater (with code (443) Steering wheel heater)
  • Left multifunction steering wheel button group or right multifunction steering wheel button group
  • Driver-side power window and outside mirror adjustment switch group (only the outside mirror adjustment is monitored)
• Interior illumination controls:
  • Interior lamp automatic function button
  • Left front reading lamp button
  • Right front reading lamp button

Control interventions on audio system:

The control interventions at the Audio/COMAND control panel are received via the telematics CAN from the radio (with code (505) 20 NTG5 radio without navigation capability or code (522) Audio 20 radio) or the COMAND controller unit (with code (531) COMAND APS). The radio or the COMAND controller unit sends information about audio system control interventions to the stereo multifunction camera via the interior CAN, front SAM control unit, chassis CAN 1, chassis gateway control unit and chassis FlexRay.

Control interventions on comfort functions:

The steering column tube module control unit sends information about control interventions at the cruise control lever, the steering column adjustment switch and the multifunction steering wheel button groups to the stereo multifunction camera via chassis CAN 1, the chassis gateway control unit and chassis FlexRay.

The steering wheel electronics reads in the control signals 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 the control signals from the power window and outside mirror adjustment switch group over the left front door LIN and sends them to the stereo multifunction camera over the interior CAN, front SAM control unit, chassis CAN 1, chassis gateway control unit and the chassis FlexRay.

Interior illumination control interventions:

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

The overhead control panel control unit reads in the control signals from the front dome lamp switch and the front reading lamp switch directly and sends them via the interior CAN, front SAM control unit, chassis CAN 1, chassis gateway control unit and chassis FlexRay to the stereo multifunction camera.

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

The front SAM control unit reads in the control signals from the front dome lamp switch and the front reading lamp switch directly via the overhead control panel electronics. The front SAM control unit sends these status signals to the stereo multifunction camera via chassis CAN 1, the chassis gateway control unit and chassis FlexRay.

Additional function requirements for warning output 

• Lane recognition by the stereo multifunction camera
• Vehicle speed v = 60 to 200 km/h
• Radius of curve = r > 150 m
• Exiting of lane detected (detected by stereo multifunction camera)
• Oncoming traffic, overtaking vehicles or parallel traffic detected in critical area by the radar sensor system when the vehicle crosses a broken line

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 stereo multifunction camera sends the request to actuate the steering wheel vibration motor to the steering column tube module control unit via the chassis FlexRay, the chassis gateway control unit and chassis CAN 1. The steering column tube module control unit sends this request over the steering LIN to the steering wheel electronics, which then actuates 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 in order to allow for the perceivable effects of the suspension at high speeds.

The warning is suppressed when the triggering conditions are no longer given or when driver activity is detected (braking, accelerating, steering and/or turn signaling).

In "Standard" mode, a haptic warning is suppressed under the following prerequisites:

• Turn signaling recognized (the warnings are suppressed for a certain period of time)
• Intervention of a driving safety system recognized (e.g. by Electronic Stability Program (ESP®), PRE-SAFE® brake or Active Blind Spot Assist)

In "Adaptive" mode, a haptic warning is suppressed under the following prerequisites:

• Turn signaling recognized (the warnings are suppressed for a certain time period)
• Intervention by a driving safety system detected (e.g. by ESP®, PRE-SAFE® brake or Active Blind Spot Assist)
• Heavy acceleration (e.g. kickdown)
• Strong braking
• Rapid steering movement (e.g. during an evasive maneuver or during a rapid lane change)
• Corner cutting recognized

Following suppression (driver activity, triggering condition not given), a new 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.

By means of lane recognition and the current vehicle position, the stereo 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.

The corresponding information for suppression of the warning is received by the stereo multifunction camera via the chassis FlexRay. 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.

When the "Lane Keeping Assist" menu is activated, a visual warning message is shown in the multifunction display of the instrument cluster in addition to the haptic warning. The stereo multifunction camera sends the request to issue a warning to the instrument cluster via the chassis FlexRay, chassis gateway control unit, chassis CAN 1, front SAM control unit and interior CAN.

Illustration showing warning indication, shown on 205.0 

Additional function requirements for active intervention by the brake system 

• Active warning by stereo multifunction camera
• No driver activities recognized following a warning
• The lane delimitation crossed is a continuous line
• The lane delimitation crossed is a broken line and oncoming traffic/parallel traffic is recognized by the radar sensor system or the stereo multifunction camera
• Lane width s = 2.6 to 4.4 m (vehicle speed v = 60 to 200 km/h) (exceptions are lane widths of s > 3.9 m where a speed of v < 100 km/h is permitted)
• Radius of curve = r > 500 m (inner radius), r > 150 m (outer radius)
• No stationary objects detected by radar sensor system on the vehicle side opposite the intervention (e.g. warning beacons in construction sites)
• ESP® not switched passively
• ESP® not in active diagnostic or roller dynamometer mode
• No autonomous brake interventions recognized (e.g. by ESP®, PRE-SAFE® brake or Active Blind Spot Assist)
• Tire pressure of all wheels within the tolerance range (run-flat mode not active) (with code (475) Tire pressure monitor (premium) or code (477) Tire pressure loss warning)
• No driving with a trailer recognized (with code (550) Trailer hitch)
• Approval issued for active intervention by the brake system for yawing moment interface

  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.

The Electronic Stability Program control unit sends the status of the ESP® to the stereo multifunction camera and the radar sensors control unit via chassis CAN 1, the chassis gateway control unit and chassis FlexRay.

On vehicles with code (475) Tire pressure monitor (premium), the tire pressure monitor control unit sends the information about the respective tire pressure to the stereo multifunction camera and to the radar sensors control unit via chassis CAN 1, the chassis gateway control unit and chassis FlexRay.

In vehicles with code (477) Tire pressure loss warning (RDW), the tire pressure is determined based on the rolling circumference. The tire pressure loss warning (RDW) system is functionally integrated in the Electronic Stability Program control unit. The Electronic Stability Program control unit sends the information about the tire pressure to the stereo multifunction camera and to the radar sensors control unit via chassis CAN 1, the chassis gateway control unit and chassis FlexRay.

When a trailer is detected, the trailer recognition control unit (with code (550) Trailer hitch) sends the "Trailer detected" status to the stereo multifunction camera and to the radar sensors control unit via the interior CAN, the front SAM control unit, chassis CAN 1, the chassis gateway control unit and chassis FlexRay.

Function sequence for active intervention by the brake system 

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

If the stereo 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 radar sensors control unit issues approval for the intervention by the brake system. The radar sensors control unit sends the request for wheel-specific (active) deceleration of the left side of vehicle to the Electronic Stability Program control unit via the chassis FlexRay, chassis gateway control unit and chassis CAN 1. 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.

The stereo multifunction camera sends the corresponding request to the instrument cluster via the chassis FlexRay, chassis gateway control unit, chassis CAN 1, front SAM control unit and chassis CAN 2.

The brake intervention is canceled immediately as soon as driver activity is detected (e.g. if the driver steers against the brake intervention (overrides the brake intervention)) or if the above-mentioned function requirements are no longer given.

Electrical function schematic for Active Lane Keeping Assist	PE54.71-P-2053-97XAC
Overview of system components for driver assistance systems	GF54.00-P-9998FQM