Speed Limit Assist, Function - GF54.30-P-0012GR
MODEL 166 up to model year 2016 with CODE 513 (Speed Limit Assist)
Function requirements, general
- Engine running or drive train operational
- Vehicle moving forward
The CDI control unit or the ME-SFI control unit sends the "Engine running" status or the "Drive train operational" signal via chassis CAN 1, the electronic ignition lock control unit and chassis CAN 2 to the multifunction camera.
The vehicle speed is calculated from the wheel speeds, the direction of travel is defined by the wheel rotation direction. The Electronic Stability Program control unit sends the wheel speed and wheel direction signals via chassis CAN 1, the electronic ignition lock control unit and chassis CAN 2 to the multifunction camera.
Speed Limit Assist, general
The Speed Limit Assist detects the speed limits as declared by the traffic signs for the stretch of road covered by the vehicle.
The following traffic signs are recorded and evaluated on the stretch of road being driven on by the vehicle:
- Speed limits
- Supplementary sign
- Derestriction sign
The attributes verified in the navigation system's digital map (speed limits, location boundaries) are also evaluated. The corresponding traffic signs are shown in the multifunction display and in color in the Audio/COMAND display.
With vehicles as of 01.07.2012, the multifunction display is shown in color.
As a result information on the current permissible speed is available to the driver. The Speed Limit Assist is continuously active in the background. In other words, the corresponding traffic signs are permanently recorded and evaluated by the multifunction camera [MFK]. The way in which traffic symbols are displayed depends on the settings of the "Speed limit" menu of the IC Limit" menu in instrument cluster. The instrument cluster sends the status of the Speed Limit Assist via chassis CAN 2 to the multifunction camera.
The Speed Limit Assist is currently available for the following countries:
- Andorra
- Belgium
- Denmark
- Germany
- Great Britain
- Gibraltar
- France
- Italy
- Ireland
- Luxembourg
- Liechtenstein
- Monaco
- Netherlands
- Austria
- San Marino
- Switzerland
- Spain
In which of the listed countries the vehicle is located is defined by global positioning system (GPS) signals. These are received and evaluated by the COMAND controller unit. The COMAND controller unit transmits the map data via interior CAN, the electronic ignition lock control unit and chassis CAN 2 to the multifunction camera.
If the COMAND controller unit fails, the Speed Limit Assist is no longer available.
In the event of a temporary failure only, the function of the Speed Limit Assist can be maintained for a travel distance of s = 30 km.
Function sequence of Speed Limit Assist
The Speed Limit Assist consists of the following subfunctions:
- Picture recognition and evaluation function sequence
- Function sequence for control and display concept
Picture recognition and evaluation function sequence
During a journey, the multifunction camera records, at a horizontal detection angle of ∠ = 34°, pictures of traffic signs mounted above or at the side of the road. The recorded pictures are sent to the integrated picture recognition module which compares them against the stored data records and assigns the traffic signs to the respective valid road traffic regulations. The picture recognition module assigns credibility to all results.
The national regulations for the design and attachment of traffic signs are taken into account for this.
In addition the multifunction camera evaluates information on the area around the vehicle and on the vehicle's own movement.
These include:
- The multifunction camera records the distance and the angle to other road users and objects
- Map data on the COMAND controller unit
- Vehicle movement and yaw behavior, sent via chassis CAN 1 from Electronic Stability Program control unit
Information about the vehicle's own movement is derived from the wheel speed signal.
The yaw rate sensor for lateral and longitudinal acceleration sends information on the yaw characteristics of the vehicle via vehicle dynamics CAN, Electronic Stability Program control unit, chassis CAN 1, electronic ignition lock control unit and chassis CAN 2 to the multifunction camera.
The map data serves the plausibility check of objects recorded by the multifunction camera as well as the fading out of speed limits displayed when driving into built-up areas. If the camera does not detect any speed limits, the values verified in the digital card of the navigation system are displayed. It is not necessary to activate navigation mode (navigation system "sleep-mode").
Because speed limits are subject to alteration, the digital map data has to be regularly updated.
Generally valid speed limits in built-up areas, on expressways and freeways are not displayed.
After evaluation of the data, the multifunction camera transmits a corresponding request to control the display of currently detected road signs via chassis CAN 2 to the instrument cluster and via chassis CAN 2, electronic ignition lock control unit and interior CAN to the COMAND controller unit. The COMAND controller unit then activates the Audio/COMAND display via telematics CAN and sends the corresponding picture data over the low voltage differential signal (LVDS) line to the Audio/COMAND display.
The multifunction camera also combines the information about speed limit to form an event if the information is contradictory.
Traffic signs recognized by the multifunction camera
The MFK records all picture objects and evaluates circular as well as square contours. Speed limits and derestriction symbols including additional restrictions in countries with signage according to the Vienna convention are accordingly recorded. Non-relevant signs (supplementary signs that, e.g. are relevant for a turnoff lane) are suppressed. If the navigation system is active, supplementary signs will be shown immediately if they are relevant for the currently active navigation. Supplementary signs not relevant for passenger cars (e.g. speed limits for trucks) will not be shown. The number of these traffic signs amounts to approx. 10% of all traffic signs.
Situations are listed by way of example below, in which the pictures recorded by the multifunction camera cannot be evaluated and cannot be used for display.
Speed limits marked by town/village entry and town/village exit signs or by freeway start and finish signs are not recorded. These traffic signs however, are filed through the road definition feature (e.g. freeway) in the digital navigation map.
Electronically actuated changing traffic signs can be "missed" or interpreted incorrectly. In the event of changing traffic signs that are actuated by pulses or flashes, there may be difference to the picture recording's permanent cycle time, depending on the actuated frequency of the changing traffic signs. As a result only fragments of the changing traffic signs will be recognized.
If the picture cannot be fully recognized as a traffic sign it is not shown on the display.
Changing traffic signs on which the outer circle is missing are not shown either.
The horizontal angle of vision of the multifunction camera is limited. Traffic signs erected immediately after junctions, turnoffs which the vehicle takes, can be "missed" by the multifunction camera.
The horizontal detection angle of the multifunction camera is ∠ a = 34°.
The vertical angle of vision of the multifunction camera is limited.
Traffic signs on sign gantries are only interpreted reliably up to a vehicle speed of v = 160 km/h.
In order to keep recognition certainty homogeneous over all vehicle speed ranges, the evaluation window of the multifunction camera is downsized as the vehicle speed increases. The consequence of limiting the evaluation window of the multifunction camera is that traffic signs installed low down, as used, e.g. in construction sites, are "missed" if they are passed at high speed.
The resolution of the multifunction camera is limited.
Traffic signs on wide or multilane roads can be "missed" as they do not reach the size required for clear identification in the evaluation window of the multifunction camera.
The sensitivity and dynamics of the multifunction camera are limited.
This results in traffic signs not being recognized under the following conditions:
- Traffic signs with low contrast
- Extreme oncoming lights or lights from the rear
- Low levels of lighting, darkness
The focus and alignment of the multifunction camera are fixed. As a result recorded objects are represented with a movement blur depending on the exposure time.
This movement blur and sensitivity of the multifunction camera limit its usefulness at night. The fixed focus and static alignment mean that the traffic signs to be recorded must be completely visible in a small observation time window.
Recognition is not possible if the traffic sign is concealed by other objects within this observation window.
Unfavorably designed back-end sections of commercial vehicles may be interpreted as derestriction signs by mistake (left picture). Signage on the back-end section of commercial vehicles may be interpreted as traffic signs by mistake (right picture).
Information on the classification of roads and regional development are deduced from the map data provided by COMAND controller unit. By this means the system recognizes that the vehicle is leaving a road for which a speed limit identified earlier was displayed. Since the picture recognition is unable to cancel the display of a speed limit identified outside a town/village when passing a town/village entry sign, use is made of the map data. With a change from a non-built-up area to a built-up area as defined by the markings for buildings on the navigation map, the display of the last identified speed limit is canceled. As the town/village limits do not always match the built-up area markings on the navigation map, the result of this is that possibly the display of the last detected speed limit is either masked out too soon or continues to remain displayed in the built-up area.
Situations resulting in the display not being removed or being removed unnecessarily are shown in the following pictures.
Function sequence for control and display concept
The Speed Limit Assist is shown graphically on the multifunction display and the Audio/COMAND display.
The control and display concept includes the following subfunctions:
- Operating concept
- Display concept
Operating concept
Operation takes place via the "Speed limit" menu level of the IC via the following controls:
- Left multifunction steering wheel button group
- Scroll forward/back button
- System selection button
- OK button
The steering wheel electronics directly reads in the control signals from the left multifunction steering wheel button group and transmits this via the steering LIN to the steering column tube module. The steering column tube module control unit transmits them via chassis CAN 1, the electronic ignition lock control unit and interior CAN to the instrument cluster.
The Speed Limit Assist is selected in the menu structure of the instrument cluster as follows:
- "Assist" main menu selection
- "Speed Limit" submenu selection
- Possibility of selecting between activate and deactivate information mode
Display concept
The display concept in the multifunction display differentiates between the following variants:
- Information mode
- Permanent display
- Fault messages
Information mode:
In information mode, the detected traffic sign is shown on an optional menu level on the instrument cluster for a period of t = 5 s and can be acknowledged during this period using the OK button. The information mode can be switched on and off via the "Speed limit" [speed limit] submenu in the "Assist" menu. The status is displayed by the fading in of the appropriate pictogram.
Permanent display:
When selecting the "Speed limit" submenu in the "Assist" menu in the IC the recognized traffic sign is displayed until this submenu is exited again.
The display in the Audio/COMAND display is shown irrespective of the display selected in the multifunction display.
In the "Speed limit information" navigation menu on the COMAND controller unit, the display in the map view can be activated or deactivated.
The following events induce a display change or cancellation:
- Recognition of a new speed limit
- Recognition of a derestriction sign
- No identification of a new road sign for a certain distance, depending on the type of road.
- Passing recognized local limits
- Change of road type (turnoff procedure)
Following this, a maximum speed for the navigation system's digital road map is shown (if available).
Fault messages:
If the Speed Limit Assist fails, a message indicating the cause, i.e. "Speed Limit Assist currently unavailable" (e.g. fogging of the multifunction camera) or "System nonfunctional" (e.g. failure of the multifunction camera or navigation system), is output on the multifunction display.
In countries where Speed Limit Assist is not available, the following message is output: "Speed Limit Assist unavailable in this country".
Shown on multifunction display, shown on multifunction display up to 30.06.2012
With model 166.8 and with model 166.0 as of 01.07.2012 the display is in color.
Shown in Audio/COMAND display
Shown on multifunction display, shown on multifunction display up to 30.06.2012
Visual output of derestriction sign
The following events cause the derestriction sign to be displayed (picture F):
- Passing by a derestriction sign (picture F)
- Passing by a derestriction sign with a speed value (picture G), if previously no traffic sign with a speed value has been recognized. The following events cause the derestriction sign to be displayed (picture G):
- Passing by a derestriction sign with a speed value (picture G)
- Passing by a derestriction sign restricted by a supplementary sign (picture G1) with speed value. The following event leads to the display of a derestriction sign (picture H):
- Passing a derestriction sign with speed value (picture G) which deviates from the speed value of the traffic sign recorded in prior history (picture H1)
| Electrical function schematic, Speed Limit Assist | PE54.30-P-2059-97NAA | ||
| Overview of system components for driver assistance systems | GF54.00-P-9998GR |