GF82.61-P-2010CAJ Position Finding and Destination-Oriented Navigation, Function
GF82.61-P-2010CAJ Position Finding and Destination-Oriented Navigation, Function
MODEL 207.3 /4
- with CODE ( 498) Japan version
- with CODE (527) COMAND APS with single DVD drive (with navigation system)
Function requirements for position finding and the destination-oriented navigation function
^ Circuit 30g ON or circuit 15R ON
^ The Cockpit Management and Data System (COMAND) is authorized and working correctly.
^ Signals are available from at least three global positioning system (GPS) satellites.
^ COMAND controller unit (A40/3) activated via "ON" button
Position finding and destination-oriented navigation, general
The position finding and destination-oriented navigation function is divided into the following subareas:
^ Function sequence for GPS position finding
^ Function sequence for basic position finding
^ Function sequence for calibration
^ Function sequence for destination-oriented navigation
Function sequence for GPS position finding
The GPS is a satellite-based positioning system. It is available worldwide. The GPS satellites permanently transmit time and position data (longitude and latitude). GPS position finding is irretrievable after vehicle transport (e.g. by train or ferry or after towing). A new GPS position (after interruption of the satellite reception) can take several minutes (up to t = 20 minutes when the equipment is commissioned). The accuracy of the position finding and the actual calculation is essentially based on the measurement of the runtimes of the signals transmitted synchronously by the various satellites.
A vital precondition is the synchronicity of the clocks in the satellites and in the receiver. To this end the receiver is equipped with an automatic time correction, which in turn is made possible with the aid of the satellite signals. GPS signals are received by the GPS receiver integrated into the COMAND controller unit directly from the multifunction antenna (A28/11). The GPS signals are used by the COMAND control unit to calculate the current vehicle position (receiver). In addition, the vehicle's direction of travel is determined with the aid of the sequence of the locations calculated with GPS.
Since GPS operates in the gigahertz range (microwave) and the signals are weak, reception interference can occur as the result of the following events:
- Atmospheric interference, e.g. inclement weather, water vapor, fog
- Multi-path reception due to signal reflections, e.g. from building walls
- Signal shadowing, e.g. in built-up areas and in tunnels, by high buildings, by trees
Function sequence for basic position finding
Basic position finding runs parallel to GPS position finding. For basic position finding the COMAND controller unit requires the following information:
- Wheel speed signals
- Distance traveled data
- Vehicle alignment (cardinal points)
- Direction of travel data (forwards or backwards)
For basic position finding, the COMAND controller unit requires signals from the following components:
- Wheel speeds provided by the Electronic Stability Program control unit (N30/4):
- Left front axle rpm sensor (L6/1)
- Right front axle rpm sensor (L6/2)
- Left rear axle rpm sensor (L6/3)
- Right rear axle rpm sensor (L6/4)
- Turn rate sensor (gyro sensor), integrated into COMAND controller unit, for determining the vehicle orientation (compass direction)
- Front SAM control unit with fuse and relay module (N10/1), for detecting data about the direction of travel
- Steering angle sensor (N49), for detecting the steering angle signals
The turn rate sensor (gyro sensor) data in the COMAND controller unit are forwarded within the COMAND controller unit.
The wheel speed signals are received by the COMAND controller unit from the listed rpm sensors in the following way:
- Direct line
- Electronic Stability Program control unit
- Chassis CAN (CAN E)
- Front SAM control unit
- Interior CAN (CAN B)
The data about the direction of travel (forwards or backwards) is received by the COMAND controller unit in the following way:
- Front SAM control unit
- Interior CAN
After this the COMAND controller unit uses the distance traveled, the vehicle alignment and the direction of travel to calculate the vehicle position (degree of longitude and degree of latitude) at any given time.
The steering angle signal is read in by the steering column tube module control unit (N80) and forwarded via the chassis CAN to the front SAM control unit and from there via the interior CAN to the COMAND controller unit.
The basic position finding calculation is performed approx. once per second.
Error during position finding
Basic position finding is falsified when a vehicle rolls backwards with "circuit 15 OFF" (ignition switched off) or if it is transported somewhere. In both instances the deviation is automatically corrected by the COMAND controller unit's integrated navigation processor upon reception of GPS data.
Function sequence for calibration
The calibration following a tire replacement is performed automatically.
Because of the tire abrasion, a constant recalibration of the tire circumference is required. It is carried out automatically and uses the difference between the calculated and actually traveled distance between turning points calculated with the aid of map- based position finding.
Function sequence for destination-oriented navigation
The navigation consists of the following subfunctions:
^ Function sequence for destination-oriented navigation through voice output
^ Function sequence for destination-oriented navigation through visual display
^ Function sequence for Vehicle Information and Communication System (VICS) over FM multiplexer
^ Function sequence for dynamic route guidance, VICS (dealer option)
Function sequence for destination-oriented navigation through voice output
The integrated navigation processor continuously compares the route calculation data with the position finding data and uses the data to deduce measures for further destination-oriented navigation.
For vehicles with code (810) Sound system the audio signals are output by the COMAND controller unit via MOST to the sound system amplifier control unit (N40/3) and from there via direct lines to the following speakers:
- Left door tweeter (H4/1h1)
- Left door bass speaker (H4/1h2)
- Right door tweeter (H4/2h1)
- Right door bass speaker (H4/2h2)
- Center dashboard speaker (H4/27)
On vehicles without code (810) Sound system, the audio signals are output over direct lines by the COMAND controller unit to the following speakers:
- Left door tweeter
- Left door bass speaker
- Right door tweeter
- Right door bass speaker
Function sequence for destination-oriented navigation through visual display
The signals for visual display of the navigation (map navigation) are generated by the COMAND controller unit and transmitted to the Audio/COMAND display (A40/8) via a low voltage differential signaling (LVDS) line. The Audio/COMAND display switch-on request is generated by the COMAND controller unit via the telematics CAN (CAN A).
Function sequence for VICS over FM multiplexer
The driver is provided with vital information by the VICS on the current traffic situation. Traffic impairments and traffic jams are shown on the map, however they are not incorporated into the dynamic route guidance. The radio antenna signal travels to the COMAND controller unit as follows:
Model 207.3:
- Rear window antenna structure
- Direct line
- FM, AM and CL [ZV] antenna amplifier (A2/18)
- Direct line
Model 207.4:
- Front window antenna amplifier
- Direct line
- FM, AM and CL [ZV] antenna amplifier (A2/55)
- Direct line
The VICS information is processed in the FM multiplexer integrated into the COMAND controller unit. The information is then displayed on the Audio/COMAND display by means of the low voltage differential signaling line. In addition, the FM multiplexer can also receive additional information, e.g. on the weather or earthquakes.
Function sequence for dynamic route guidance, VICS (dealer option)
Dynamic route guidance requires the VICS control unit (A2/37).
The VICS control unit contains both the receiver and the antenna.
The antenna communicates with the VICS beacons (transmitter masts) installed on the road, which transmit microwave or infrared signals within a 2.5 Gigahertz reception range. Received signals are sent directly to the COMAND control unit where they are decoded. The traffic messages are stored and relayed to the navigation processor.
The traffic data recorder decodes the traffic information and forwards this to the navigation processor upon request. The navigation processor makes the decision whether the route should be changed. If necessary, a voice message saying that the route was changed is output.
