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

MODEL 212 as of model year 2014 with CODE 238 (Active lane keeping Assist) 

Function requirements, general 

• Engine running or drive train operational
• Active Lane Keeping Assist switched on

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

Shown on model 221 

Active Lane Keeping Assist, general 

The Active Lane Keeping Assist function detects any unintentional driving across lane markings and issues a haptic warning to the driver in certain situations by means of vibrations at 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.

An option is available to the driver to configure the Active Lane Keeping Assist sensitivity 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)

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), the acceleration skid control (ASR), the Brake Assist System PLUS (BAS+) and/or the Brake Assist System PLUS crossing traffic (BAS+Q) and/or during brake interventions by PRE-SAFE or Active Blind Spot Assist, a brake intervention of the Active Lane Keeping Assist is suppressed and/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 restricted through two lane markings or, with a broken line, when there is a vehicle in the oncoming lane or on a lane running in parallel in a collision-critical area.

Active Lane Keeping Assist operation is speed-dependent. The vehicle speed is calculated on the basis of the wheel speeds. The Electronic Stability Program control unit or the regenerative braking system control unit sends this over the chassis CAN 1, chassis gateway control unit and the chassis FlexRay to the radar sensors control unit and to the stereo multifunction camera. The Electronic Stability Program control unit or the regenerative braking system control unit sends the wheel speeds over chassis CAN 1, the front SAM control unit and chassis CAN 2 to the instrument cluster. The instrument cluster calculates the vehicle speed to be displayed and sends it to the stereo multifunction camera via chassis CAN 2, the front SAM control unit, chassis CAN 1, the chassis gateway control unit and chassis FlexRay. The radar sensors control unit calculates the vehicle speed itself.

The Active Lane Keeping Assist consists of the following subfunctions:

• 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 

Additional function requirements for lane recognition 

• Recognizable lane markings 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 or the regenerative braking system control unit sends corresponding information over the chassis CAN 1, chassis gateway control unit and the chassis FlexRay to the radar sensors control unit and to the stereo multifunction camera.

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 multiple markings (e.g. in construction zones), the Active Lane Keeping Assist may not be able to issue warnings. Tar joints in the road surface might be interpreted as lane markings, which can also lead to a suppression of the readiness to output a warning.

Possible displays in the multifunction display of instrument cluster 

Additional function requirements for recognition of oncoming traffic/parallel traffic 

• Long range radar soiling and function test completed successfully

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 radar sensors control unit reads in the signals of the front bumper radar sensor via radar CAN 1. The radar sensors control unit reads in the signals of the rear bumper radar sensor via radar CAN 2.

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
• Slow 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 the brake intervention can be found in "Function sequence for active brake intervention".

The following representations illustrate the situations described above:

Approaching vehicle in the oncoming lane, shown on model 222 

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

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

Slow vehicle to be passed in the parallel lane, shown on model 222 

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

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

Passing vehicle in the parallel lane, shown on model 222 

Vehicles approaching from behind with a high relative speed compared to the vehicle with Active Lane Keeping Assist are recognized by the following radar sensors depending on the side of the lane, the distance and the angle to the vehicle with Active Lane Keeping Assist:

• Center rear bumper radar sensor
• Left rear bumper radar sensor (recognized vehicle is located to the left of the vehicle with Active Lane Keeping Assist)
• Right rear bumper radar sensor (recognized vehicle is located to the right of the vehicle with Active Lane Keeping Assist)

Vehicle in the parallel lane is at approximately the same level as the vehicle with Active Lane Keeping Assist, shown on model 222 

Vehicles in the right or left parallel lane at the level of the vehicle with Active Lane Keeping Assist are recognized by the following radar sensors depending on the side of the lane, the distance and the 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 (recognized vehicle is located to the left of the vehicle with Active Lane Keeping Assist)
• Right rear bumper radar sensor (recognized vehicle is located to the right of the vehicle with Active Lane Keeping Assist)

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, braking or accelerating
• Cutting a tight corner
• Turn signals
• Sporty driving at high cornering speeds or with high acceleration

Steering intervention:

Steering movements are detected by the steering angle sensor. The steering column tube module control unit reads in the signals from the steering angle sensor directly and sends them to the radar sensors control unit and the stereo multifunction camera via chassis CAN 1, the chassis gateway control unit and chassis FlexRay.

Brakes:

Operation of the brake pedal is detected by the brake lights switch. The Electronic Stability Program control unit or the regenerative braking system control unit reads in the status of the brake lights switch directly and sends this over the chassis CAN 1, chassis gateway control unit and the chassis FlexRay to the radar sensors control unit and the stereo multifunction camera.

Acceleration:

The accelerator pedal sensor registers any accelerator pedal actuation. The CDI control unit or the ME-SFI control unit reads in the signals from the accelerator pedal sensor directly and sends them via chassis CAN 1, the chassis gateway control unit and chassis FlexRay to the radar sensors control unit and 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.

Rotational speed, lateral and longitudinal acceleration:

The yaw rate sensor for lateral and longitudinal acceleration sends the longitudinal and lateral acceleration vales and the yaw velocity to the Electronic Stability Program control unit or the regenerative braking system control unit over the vehicle dynamics CAN. The Electronic Stability Program control unit or the regenerative braking system control unit evaluates the data and sends the data over chassis CAN 1, the chassis gateway control unit and the chassis FlexRay to the radar sensors control unit, and the stereo multifunction camera.

If the stereo multifunction camera and the radar sensors control unit detect active corner cutting by the driver, crossing over 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 control actuating frequency, 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
  • 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:
  • Front dome lamp switch
  • Left front reading lamp switch
  • Right front reading lamp switch

Control interventions on audio system:

The control interventions at the Audio/COMAND control panel are received by the radio or the COMAND controller unit via the telematics CAN. 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.

Comfort function controls:

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 interior illumination (with code (414) Power glass tilting/sliding roof): The status of the front dome lamp switch and the front reading lamp switch is read in directly by the overhead control panel control unit and it is then sent over the interior CAN, front SAM control unit, chassis CAN 1, chassis Gateway control unit and the chassis FlexRay to the stereo 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 read in directly by the front SAM control unit 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, to account for perceptible influences from 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).

It is possible to choose between "Standard" or "Adaptive" mode using the corresponding menu in the instrument cluster. As a result, the warning threshold can be configured as follows:

• 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 of a driving safety system recognized (e.g. by ESP®, PRE-SAFE brake or Active Blind Spot Assist)
  • Strong acceleration (e.g. kickdown)
  • Strong braking
  • Rapid steering movement (e.g. during an evasive maneuver or during a rapid lane change)
  • Corner cutting recognized

    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 instrument cluster sends the information about the selected mode to the stereo multifunction camera via chassis CAN 2, the front SAM control unit, chassis CAN 1, the chassis gateway control unit and chassis FlexRay.

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.

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.

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 km/h 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 facing away from the intervention (e.g. warning beacons in construction sites)
• ESP® not switched to passive
• 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 inflation 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 in the Electronic Stability Program control unit or the regenerative braking system control unit and issues the approval for a course-correcting braking torque.

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

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. In terms of its function, the RDW is integrated into the Electronic Stability Program control unit or into the regenerative braking system control unit. The Electronic Stability Program control unit or the regenerative braking system control unit sends the information on tire pressure over chassis CAN 1, the chassis gateway control unit and the chassis FlexRay to the stereo multifunction camera, and to the radar sensors control unit.

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 (assets) deceleration of the left side of vehicle over the chassis FlexRay, chassis gateway control unit and chassis CAN 1 to the Electronic Stability Program control unit or the regenerative braking system control unit. The Electronic Stability Program control unit or the regenerative braking system 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 a driver activity is recognized (for example if the driver steers against the brake intervention (overrides the brake intervention) or if the above function requirements are no longer given.

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