Speed Limit Assist, Function - GF54.30-P-0012CE

MODEL 204.0/2 with CODE (513) Speed Limit Assist as of model year 2012/AEJ 11 model refinement package

MODEL 204.3 with CODE (513) Active Lane Keeping Assist

MODEL 204.9 with CODE (513) Speed Limit Assist as of model year 2013/facelift 12

Fig 1: Speed Limit Assist - Block Diagram

Function requirements, general

Engine running or drivetrain operational
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 uses the mulifunction camera to record the speed limits indicated by the traffic signs for the stretch of road covered by the vehicle.

The following traffic signs are detected by the multifunction camera and evaluated:

Speed limits
Supplementary sign
Derestriction sign

The attributes verified in the digital card of the navigation system are also evaluated.

The corresponding traffic signs are shown in color 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 are read in and evaluated by the COMAND controller unit.

The COMAND controller unit sends the navigation data over the interior CAN, front SAM control unit and the chassis CAN to the multifunction camera.

In the event of a COMAND controller unit malfunction the Speed Limit Assist function is no longer available. The Speed Limit Assist function remains available in the event of a temporary malfunction for a travel distance of

s = 30 km.

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 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 COMAND controller unit
Vehicle movement and yaw behavior sent over chassis CAN from Electronic Stability Program control unit

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").

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.

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, code (237) Active Blind Spot Assist or code (238) Active Lane Keeping Assist, model 204.077/277/377) provides information on the yaw behavior of the vehicle and sends this information via the vehicle dynamics CAN, the Electronic Stability Program control unit and the chassis CAN to the multifunction camera.

On vehicles without code (233) DISTRONIC PLUS and without code (237) Active Blind Spot Assist and without code (238) Active Lane Keeping Assist and except model 204.077/277/377, the yaw rate sensor for lateral and longitudinal acceleration is integrated in the Electronic Stability Program control unit.

After evaluation of the data, the multifunction camera sends a corresponding request to control the display of the currently detected road sign over the chassis CAN to the instrument cluster and over the chassis CAN, front SAM control unit and the interior CAN to the COMAND controller unit.

The COMAND controller unit receives this request, activates the Audio/COMAND display over the telematics CAN and then generates the picture signals for displaying the speed limit.

For vehicles without code (255) AMG Performance Media, the COMAND controller unit sends the picture signals over the low voltage differential signaling (LVDS) line to the Audio/COMAND display.

For vehicles with code (255) AMG Performance Media, the COMAND controller unit sends the picture signals over the low voltage differential signaling (LVDS) line to the AMG Performance Media control unit.

The AMG Performance Media control unit over another low voltage differential signaling (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

Fig 2: Screen Display - Speed Limit Assist (Traffic Signs By 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.

Listed below are some examples of situations in which the pictures recorded by the multifunction camera cannot be evaluated and cannot be used for display in the multifunction display or in the Audio/COMAND 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.

Fig 3: Screen Display - Speed Limit Assist Marked (Town/Village Entry And Town/Village Exit Signs)

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.

Fig 4: Screen Display - Speed Limit Assist (60)

Changing traffic signs on which the outer circle is missing are not shown either.

Fig 5: Screen Display - Speed Limit Assist (70)

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 ∠ = 34°.

Fig 6: Screen Display - Speed Limit Assist (Multifunction Camera Horizontal Angle)

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.

Fig 7: Screen Display - Speed Limit Assist (Multifunction Camera Horizontal Angle)

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.

Fig 8: Screen Display - Speed Limit Assist (Traffic Signs On Wide And Multilane Roads Missed)

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).

Fig 9: Screen Display - Speed Limit Assist (Unfavorably Designed Back-End Sections Of Commercial Vehicles)

Fig 10: Screen Display - Speed Limit Assist (Signage On Back-End Section Of Commercial Vehicles)

Information on the classification of roads and regional development are deduced from the navigation 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 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.

Fig 11: Screen Display - Speed Limit Assist (Vehicles Road Map)

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
- 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 forwards the control signals 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
- Selection option between activate and deactivate information mode

The instrument cluster sends the status of the Speed Limit Assist function over the chassis CAN to the multifunction camera.

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 function malfunctions a "System currently unavailable" message is shown (e.g. fogging of multifunction camera) or "System nonfunctional" (e.g. failure of multifunction camera or the navigation system) in the multifunction display. For this purpose the multifunction camera sends corresponding requirements over the chassis CAN to the instrument cluster.

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)

Fig 12: Screen Display - Speed Limit Assist (60)

Display in Audio/COMAND display, system language German (display of detected traffic sign on country-specific basis)

Fig 13: Screen Display - Speed Limit Assist (Detected Traffic Sign On Country-Specific Basis)

Shown in multifunction display, English GUI language

Fig 14: Screen Display - Speed Limit Assist (English GUI Language)

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)

Fig 15: Screen Display - Speed Limit Assist (Visual Output Of Derestriction Sign)

	Electrical function schematic, Speed Limit Assist		PE54.30-P-2059-97FAA
	Overview of system components for driver assistance systems		GF54.00-P-9998CE