Speed Limit Assist, Function - GF54.30-P-0012RD
Model 172.4 up to model year 2017
with code 513 (Speed Limit Assist)
Shown on model 172.4
Function requirements, general
- "Engine running" or "Drive train operational" signal on
- Vehicle moving forward
The CDI control unit or the ME-SFI [ME] control unit sends the "Engine running" or the "Drivetrain operational" signal over the chassis CAN to the multifunction camera.
Speed Limit Assist, general
The Speed Limit Assist function records the speed limits as declared by traffic signs for the stretch of road covered by the vehicle.
The speed limits are shown in the multifunction display of the instrument cluster and in the Audio/COMMAND display in the form of traffic signs.
The following traffic signs are recorded by the multifunction camera and evaluated:
- Speed limits
- Supplementary sign
- Derestriction signs
The attributes verified in the navigation system's digital map (speed limits, location boundaries) are also evaluated.
As a result information on the current permissible speed is available to the driver.
The function Speed Limit Assist is permanently 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 function 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 the GPS signals (global positioning system).
These are read in and evaluated by the COMMAND controller unit.
The COMMAND controller unit sends the map data and navigation data over the interior CAN, front SAM control unit and the chassis CAN to the multifunction camera.
The Speed Limit Assist function is not available in the event of failure of the COMMAND controller unit.
The Speed Limit Assist function is only maintained for a travel distance of s = 30 km in the event of a temporary failure.
The Speed Limit Assist function includes the following subfunctions:
- Picture recognition and evaluation function sequence
- Function sequence for control and display concept Picture recognition and evaluation function sequence
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
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.
around the vehicle and on the vehicle's own movement.
These include:
- Distance and angle to other road users and objects recorded by the multifunction camera
- Map data and the navigation data of the COMMAND controller unit
- Vehicle movement and yaw behavior sent via the chassis CAN by the Electronic Stability Program control unit
Information on the vehicle's own movement is derived from the wheel speeds as an indicator of vehicle speed.
The yaw rate sensor for lateral and longitudinal acceleration (with code 233 (DISTRONIC PLUS) up to and including model year 2015 or code 239 (DISTRONIC PLUS) model year 2016 or model 172.475) provides information on the vehicle's yaw behavior and sends this over the vehicle dynamics CAN to the Electronic Stability Program control unit.
The Electronic Stability Program control unit transmits this information via the chassis CAN to the multifunction camera.
On model 172 (except 172.475) without code 233 (DISTRONIC PLUS) up to and including model year 2015 or without code 239 (DISTRONIC PLUS) model year 2016, the yaw rate sensor for lateral and longitudinal acceleration is integrated into the Electronic Stability Program control unit.
The map data and the navigation data are required for the plausibility test of the object detected 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 the request to control the display of currently detected road sign via the chassis CAN to the instrument cluster and via the chassis CAN, the front SAM control unit and the interior CAN to the COMMAND controller unit.
The COMMAND controller unit then sends this request to the Audio/COMMAND display over the telematics CAN.
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.
Situation are listed as an example in the following, in which the pictures recorded by the MFK cannot be evaluated and cannot be used for display in the multifunction display.
Place-name signs, freeway signs
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
Electronically actuated changing traffic signs can be "missed" or interpreted incorrectly. In the event of changing traffic signs that are actuated in pulses or flashes, depending on the actuated frequency of the display there may be difference to the fixed cycle time for picture recording. 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 without circular ring
Changing traffic signs on which the outer circle is missing are not shown either.
Horizontal angle of vision of multifunction camera
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°.
Vertical angle of vision of multifunction camera
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, for example signs used in construction sites, are "missed" if they are passed at high speed.
Resolution of multifunction camera
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
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 result of the fixed focus and static alignment
- Low levels of lighting, darkness is 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.
Misinterpretation of back-end sections of commercial vehicles
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 and navigation data sent by the COMMAND 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.
Representation of town/village limits and built-up area limits
Function sequence for control and display concept
The Speed Limit Assist is shown graphically on the multifunction display and the Audio/COMMAND display.
The control and display concept is split up into 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 read in the control signals on the multifunction steering wheel button group directly and transmit them to the steering column tube module control unit over the steering LIN.
The steering column tube module control unit transmits the control signals of the multifunction steering wheel button group via the chassis CAN to the instrument cluster.
The Speed Limit Assist function 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/COMMAND display is shown irrespective of the display selected in the multifunction display.
In the "Speed limit information" navigation menu on the COMMAND 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 speed limit from the digital road map of the navigation system is shown (if available).
Fault messages
If the Speed Limit Assist function fails, a message is shown to match the cause such as "System currently unavailable" (e.g. fogging of multifunction camera) or "System inoperative" (e.g. failure of multifunction camera or the navigation system) in the multifunction display.
In countries in which the function Speed Limit Assist is basically not available the following message is issued: "Speed limit assist not available in this country".
Display in multifunction display (depiction of the detected traffic sign is country-specific)
Shown on Audio/COMMAND display, system language German (the detected traffic signs are shown on a country-specific basis)
Shown in multifunction display
Indication 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 by 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-2059-97TAA | ||
| Overview of system components for driver assistance systems | GF54.00-P-9998RD |