Speed Limit Assist, function - GF54.30-P-0012CA

MODEL 207.3 as of model year 2010 up to model year 2014 with CODE 513 (Speed Limit Assist) 

MODEL 207.4 up to model year 2014 with CODE 513 (Speed Limit Assist) 

Function requirements, general 

• Circuit 61 ON
• Vehicle moving forward

The "circuit 61 ON" status is sent by the CDI control unit (with diesel engine) or the ME-SFI control unit (with gasoline engine) to the multifunction camera via the chassis CAN.

Speed Limit Assist, general 

The following traffic signs are recorded and evaluated on the stretch of road being driven on by the vehicle.:

• Speed limits
• Speed limits, restricted by additional signs (model 207.3 as of 1.6.10 and model 207.4)
• Derestriction signs (model 207.3 as of 1.6.10 and model 207.4)

In addition the attributes verified in the digital card of the navigation system are evaluated. The corresponding traffic signs are shown in the multifunction display and in the audio/COMAND display. 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 countries listed the vehicle is located is defined by way of Global Positioning System (GPS) signals. These signals are read in and evaluated by the radio with auto pilot system (with code (511) Audio 50 APS incl. DVD changer or code (525) MB Audio 50 APS radio) or by the COMAND controller unit (with code (512) COMAND APS incl. DVD changer or code (527) COMAND APS with single DVD drive (with navigation)). The radio or the COMAND controller unit sends the navigation data to the multifunction camera via the interior CAN, front SAM control unit with fuse and relay module and chassis CAN.

The Speed Limit Assist function is not available if the radio or the COMAND controller unit fails. 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 

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:

• Distance and angle to other road users and objects recorded by the multifunction camera itself
• Navigation data from radio or COMAND controller unit
• Inherent motion and yaw behavior of the vehicle via the chassis CAN, provided by the Electronic Stability Program control unit (without code (233) DISTRONIC PLUS) or by the Premium Electronic Stability Program control unit (with code (233) DISTRONIC PLUS)

Information on the vehicle' own movement is derived from the wheel speeds as an indicator of vehicle speed. The yaw rate sensor for lateral and longitudinal acceleration supplies information about the yaw behavior of the vehicle and sends this information via the vehicle dynamics CAN to the Electronic Stability Program control unit which forwards the information via the chassis CAN 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 multifunction camera does not detect any speed limits, the verified values in the navigation system's digital map are then shown. It is not necessary to actuate the navigation function (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 evaluating the data the multifunction camera transmits a corresponding request to control the display of the currently recognized traffic sign over the chassis CAN to the instrument cluster and the front SAM control unit. The front SAM control unit sends the request to the radio or to the COMAND controller unit via the interior CAN. The radio or the COMAND controller unit then actuates via the telematics CAN and via a low voltage differential signal line the Audio/COMAND display to show the currently detected traffic sign. If a data source (picture recognition, vehicle data or navigation data) fails, the most credible result is deduced from the remaining data together with the stored past history data.

The multifunction camera also combines this information into a result when the individual information on the speed limit contradicts.

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.

Below is a list of example situations 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 in pulses or flashes, depending on the actuated frequency of the changing traffic sign there may be a difference to the fixed cycle time for picture recording which results in only fragments of the changing traffic sign being detected.

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 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 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 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. Detection 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 about the classification of roads and regional development is derived from the navigation data provided by the radio or 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.

If you switch from a non-built-up area to a built-up area, as defined by the built-up area marking on the navigation map the display of the last speed limit detected 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 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 control signals from the multifunction steering wheel button group are read in directly by the steering wheel electronics and transmitted to the steering column tube module control unit via the steering LIN. 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 in the menu 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 displayed at every menu level of the instrument cluster for t = 5 s and can be acknowledged within this time with 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. If the information mode is switched off, recognized traffic signs are not shown permanently either.

The display in the Audio/COMAND display is shown irrespective of the display selected in the multifunction display.

The display in the map view can be activated or deactivated in the "Speed limit information" navigation menu of the radio or the COMAND controller unit.

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 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 

Shown in Audio/COMAND display 

Detected speed limit (poss. on model 207.3 as of 1.6.10 and model 207.4 including supplementary signs)

Shown in multifunction display up to 31.5.10 

Shown in multifunction display as of 1.6.10 

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 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-2059-97EAA
	Overview of system components, Speed Limit Assist		GF54.30-P-9990CA