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

GF54.30-P-0012LE Speed Limit Assist, Function
- with CODE (513) Speed Limit Assist
- refinement package
- as of model year 2010

Function requirements, general
^ Engine running (circuit 61 ON)
^ Vehicle moving forward

The CDI control unit (N3/9) (with diesel engine) or ME-SFI control unit (N3/10) (with gasoline engine) transmits the status "Engine running" to the multifunction camera (A40/11) via the chassis CAN (CAN E).

Speed Limit Assist, general
The Speed Limit Assist function records shown speed limits for the stretch driven on by the vehicle. These are displayed in the form of a traffic sign in the multifunction display (A1p13) of the instrument cluster (A1).

The area in front of the vehicle is recorded with the aid of the multifunction camera which is located at the top of the windshield. The Speed Limit Assist function is currently available for the following countries: Belgium, Denmark, Germany, France, Italy, Luxembourg, Netherlands, Austria, Switzerland and 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 by the COMAND controller unit (A40/3), evaluated and provided to the multifunction camera via the central CAN (CAN F), central gateway control unit (N93) and chassis CAN.

The Speed Limit Assist function is not available in the event of failure of the COMAND controller unit.

The Speed Limit Assist function is maintained for a travel distance of s = 30 km only in the event of a temporary failure.

The Speed Limit Assist function is activated via the "Assistance" menu in the instrument cluster.
The instrument cluster transmits the corresponding status to the multifunction camera via the chassis CAN.

The Speed Limit Assist function consists of the following partial functions:
^ Picture recognition and evaluation function sequence
^ Display concept function sequence

Picture recognition and evaluation function sequence
While driving, the multifunction camera records pictures of the area in front of the vehicle.
The recording angle of the multifunction camera is a = 32°. The pictures recorded are transmitted to the integrated picture recognition module which compares these with the stored data records and thus assigns the traffic signs to the respective valid road traffic regulations.

The national regulations for the design and attachment of traffic signs are taken into account for this. The picture recognition module assigns credibility to all results.

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
- The vehicle's own movement and yaw behavior provided by the ESP control unit via the chassis CAN (N47-5) (without model 221.095/195) or by the regenerative braking system control unit (N30/6) (model 221.095/195)

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. Generally valid speed limits in built-up areas, on expressways and freeways are not displayed.

Information on the vehicle' own movement is derived from the wheel speeds as an indicator of vehicle speed

The instrument cluster also transmits information on vehicle speed. This is used as a substitute value.

The yaw rate sensor for lateral and longitudinal acceleration (B24/15) provides information on the yaw behavior of the vehicle and transmits this via the vehicle dynamics CAN (CAN H) to the ESP control unit or to the regenerative braking system control unit which passes on this information to the multifunction camera via the chassis CAN.

After evaluating the data the multifunction camera transmits a corresponding request to the instrument cluster for controlling the display of the currently recognized speed limit via the chassis CAN, central gateway control unit and central CAN. 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.

Component Identification:

The multifunction camera in fact records all picture objects, however only evaluates circular contours Therefore speed limit signs and derestriction signs are recorded in countries which have signs in accordance with the Vienna Convention.

Traffic signs with additional restrictions are recognized and displayed although they are not relevant possibly due to additional restrictions.

Situations are listed as an example in the following, in which pictures recorded by the multifunction camera are not usable and are not used for the display in the multifunction display.

The multifunction camera cannot record square traffic signs.
Speed limits marked by town/village entry and town/village exit signs or by freeway start and finish signs are not recorded.

The horizontal angle of vision of the multifunction camera is limited.

Traffic signs erected immediately after junctions, turn-offs which the vehicle takes, can be "missed" by the multifunction camera.

The horizontal recording angle of the multifunction camera is a = 32°.

Evaluation window at vehicle speed v = 144 km/h (b)
Evaluation window at vehicle speed v = 72 km/h (c)

The vertical angle of vision of the multifunction camera is limited.
Traffic signs on sign bridges 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 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 light in front of one's eyes or light from behind
- 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 viewing direction 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.

Electronically actuated changing traffic signs can be "missed" or interpreted incorrectly.
With these changing traffic signs, differences can occur between the duration of the display and the fixed cycle time of the picture recording. This results in only a part of the segments of the changing traffic sign being visible or the appearance of the changing traffic sign changing from one recording to the next. These are "missed" if the operating time of electronically actuated changing traffic signs is outside the observation time window.

Unfavorably designed back-end sections of commercial vehicles may be interpreted as destriction 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 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.
Since the town/village borders do not always coincide with the markings for buildings on the navigation map, it may happen that the display of the last identified speed limit is either removed too early or continues to show inside the official town/village area.

Situations resulting in the display not being removed or being removed unnecessarily are shown in the following pictures.

Component Identification:

Display concept function sequence
The display concept distinguishes between the following modes:
- Information mode
- Display mode

Information mode:
In information mode the recognized speed limit can be displayed in the form of a traffic sign for a period of t = 5 s. The information can be acknowledged within this period. The information mode can be switched on or off by the driver. The status is displayed by a symbol.

Display mode:
In display mode the recognized speed limit is displayed permanently until one of the following events occurs:
- Recognition of a new speed limit
- Recognition of a derestriction sign
- No renewed recognition of a relevant traffic sign within a route depending on the type of road
- Passing recognized local limits
- Recognition of turning off process
- Change in type of road