Basic position finding, function - GF82.61-P-3006PME
MODELS 203.0 /2 /7 as of 24.4.04 with CODE (525) MB Audio 50 APS radio
Basic location finding (dead reckoning) is the basic function of continuous location finding. This is performed by the navigation processor in the radio and navigation unit (A2/56) continuously when the ignition is on and is independent of the CD read in. After the ignition is switched off, the current position of the vehicle is stored in the navigation processor.
The following information is calculated with the aid of basic position finding:
- Distance traveled
- Direction of travel (forward or reverse)
- Vehicle orientation
Basic position finding is performed approx. once a second.
Distance traveled
Via the Controller Area Network bus class C (engine compartment) (CAN-C) the navigation processor receives the wheel speed signals from the ESP and BAS control unit (N47-5). The evaluation of these signals gives the distance traveled.
Direction of travel
The signal for recognizing reversing for the navigation processor comes from the electronic ignition switch control unit (N73) via the Controller Area Network bus class B (interior) (CAN-B).
Vehicle orientation
From the data of the yaw rate sensor and the sequence of the vehicle locations calculated with the Global Positioning System (GPS), the navigation processor calculates the orientation (compass direction) of the vehicle. The difference between the calculated and actual travel distance between 2 turn-off points is used for automatic recalibration of the tire circumference.
This is necessary because of tire wear.
Position finding errors
Rolling backwards without the transmission being shifted into reverse gear is evaluated as moving forwards and can lead to temporary errors in location finding. Rolling with "circuit 15C" or transport of the vehicle also make the location finding result erroneous.
In both cases, the deviation of the position finding is automatically corrected by the navigation processor on receipt of GPS signals.
The travel direction signal (forward or reverse) is generated by the wheel speed sensors. This makes possible an exact recording of the distance traveled.
Calibration
Wheel calibration is necessary following a tire change. To this end, it is necessary to enter the tire size and the coding, regarding whether new or used tires have been fitted.
The entry is made via STAR DIAGNOSIS or directly via the radio and navigation unit (A2/56). A trip is not required.
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