Speed Limit Assist, function - GF54.30-P-0012FL
MODEL 212.0/2 up to 28.2.13 with CODE (513) USA version
Function requirements, general
- Engine running or drivetrain operational
- Vehicle moving forward
The CDI control unit (N3/9) (with diesel engine) or ME-SFI [ME] control unit (N3/10) (with gasoline engine) transmits the engine running or drivetrain ready status to the multifunction camera (A40/11) over the chassis CAN (CAN E).
Speed Limit Assist, general
The Speed Limit Assist function uses the multifunction camera to detect the speed limits declared by 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
- Speed limits, restricted through supplementary signs (as of 1.6.10)
- Derestriction signs (as of 1.6.10)
The attributes verified in the digital card of the navigation system are also evaluated.
The corresponding traffic signs are shown in color the multifunction display (A1p13) and on the audio/COMAND display (A40/8).
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.
Function sequence of Speed Limit Assist
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
During a journey, the multifunction camera records - at a horizontal detection angle of ∠ = 45° - pictures of the 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 multifunction camera's 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:
- Distance and angle to other road users and objects recorded by the multifunction camera itself
- Navigation data of radio with autopilot system (A2/56) or the COMAND controller unit (A40/3)
- Vehicle self-movement and yaw behavior over the chassis CAN, sent on model and equipment-specific basis by the following control units:
- Electronic Stability Program control unit (N30/4) (model 212 (except 212.074/077/095/098/274/277/298) without code (233) DISTRONIC PLUS)
- RBS control unit (N30/6) (model 212.095/098/298)
- Premium Electronic Stability Program control unit (N30/7) (model 212 (except 212.095/098/298) with code (233) DISTRONIC PLUS, model 212.074/077/274/277)
Information on the vehicle's own movement is derived from the wheel speeds as an indicator of vehicle speed.
Information on the vehicle's longitudinal acceleration and lateral acceleration as well as the yaw rate is recorded by the yaw rate sensor for lateral and longitudinal acceleration (B24/15).
The yaw rate sensor for lateral and longitudinal acceleration sends the corresponding information over the dynamics CAN (CAN H) to the Electronic Stability Program control unit.
The Electronic Stability Program control unit sends the values for vehicle longitudinal and lateral acceleration, yaw rate and information on the wheel speeds over the chassis CAN (CAN E) to the multifunction camera.
The navigation data serve 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 actuate the navigation function (navigation system "sleep-mode").
The navigation data are also used to evaluate the national availability. The national availability may be able to be extended and therefore it matches the current software release. If the navigation data are not available (e.g. no GPS signals), the Speed Limit Assist is switched off following a travel distance of s = 30 km.
The navigation data are sent by the radio with autopilot system (with code (511) Audio 50 APS incl. DVD changer or code (525) MB Audio 50 APS radio) or the COMAND controller unit (with code (512) COMAND APS incl. DVD changer or code (527) COMAND APS with single DVD drive (with navigation)) over the interior CAN, front SAM control unit and the chassis CAN to the multifunction camera.
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.
The multifunction camera also combines the information about speed limit to form an event if the information is contradictory.
After evaluating the data, the multifunction camera sends a corresponding request to actuate the display of the currently recognized speed limitation over chassis CAN to the instrument cluster and to the front SAM control unit.
The front SAM control unit forwards the request over the body CAN to the radio with autopilot system or to the COMAND controller unit.
The radio with autopilot system or the COMAND controller unit processes this information and sends a switch-on request over the telematics CAN to the audio/COMAND display.
The picture signals for displaying speed limitation are generated by the COMAND controller unit and sent over a low voltage differential signaling line to the audio/COMAND display.
Traffic signs recognized by the multifunction camera
The multifunction camera 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 multifunction camera cannot be evaluated and therefore cannot be used for display in the multifunction 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 recording angle of the multifunction camera is ∠ a = 45°.
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 the recognition safety homogenous over all speed ranges, the evaluation window is reduced in size as the vehicle speed reduces. The consequence of limiting the evaluation window of the multifunction camera is that traffic signs installed low down, as used 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 multi-lane 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 is 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 result of the fixed focus and static alignment 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.
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 on built-up areas is derived from the radio with Auto-Pilot-System or from the navigation data provided by the 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 system 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 navigation 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 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 (S110)
- Scroll back and forward button (S110s1)
- System selection button (S110s3)
- OK button (S110s6)
The steering wheel electronics (N135) directly read in the control signals from the multifunction steering wheel button group and sends them over the steering LIN (LIN E1) to the steering column tube module control unit.
The steering column tube module control unit forwards the control signals via the chassis CAN to the instrument cluster.
The Speed Limit Assist function is selected as follows in the instrument cluster:
- "Assist" main menu selection
- "Speed Limit" submenu selection
- Selection option between activate and deactivate information mode
Display concept
The display concept in the multifunction display differentiates between the following variants:
- Information mode
- Permanent display
- Error messages
Information mode
In the information mode a recognized traffic sign can be shown on any menu level on the instrument cluster for a duration of t = 5 s and it can be acknowledged within this period by pressing 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 limit of the navigation system's digital road map is shown where available.
Error messages
If the system malfunctions a message is shown to match the cause such as "System currently unavailable" (e.g. fogging of multifunction camera) or "System nonfunctional" (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".
Shown in multifunction display (display of detected traffic sign on country-specific basis)
With vehicles as of 1.6.11, the multifunction display is shown in color.
Display in Audio/COMAND display, system language German (display of detected traffic sign on country-specific basis)
Shown in multifunction display up to 31.5.10, GUI language English
Shown on multifunction display as of 1.6.10, as of 1.6.11 shown in color, GUI language English
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)
| Speed Limit Assist, location of components | GF54.30-P-0012-01FL | ||
| Electrical function schematic, Speed Limit Assist | PE54.30-P-2059-97DAA | ||
| Speed Limit Assist, block diagram | GF54.30-P-0012-02FL | ||
| Overview of system components, Speed Limit Assist | GF54.30-P-9990FL |