Basic position finding, function - GF82.61-P-3006PM
MODEL 203.0 /2 /7 as of 24.4.04 with CODE (527) COMAND APS with single DVD drive (with navigation)
Position finding (dead reckoning)
Basic position finding, function
Basic location finding (dead reckoning) is the basic function of continuous location finding. This is performed by the navigation processor in the COMAND operating, display and control unit (A40/3) continuously when the ignition is switched on and is independent of the Digital Versatile Disk (DVD) map. The current position is stored after the ignition is switched off.
The following information is calculated with the aid of basic position finding:
- Distance traveled
- Direction of travel (forward or reverse)
- Vehicle orientation
The basic position finding is performed approx. every 1 s.
Distance traveled
The integrated navigation processor receives the wheel speed signals from the ESP and BAS control unit (N47-5) via the Controller Area Network bus class C (engine compartment) (CAN-C).
The evaluation of the wheel speed signals gives the distance traveled.
Direction of travel
The signal for backing up which is transferred by the EIS control unit (N73) via the Controller Area Network bus (interior compartment), allows the navigation processor to recognize the direction of motion (forwards or backwards).
Vehicle orientation
The data of the yaw rate sensor (gyrosensor) and the sequence of locations as calculated with the global positioning system (GPS), are used by the navigation processor to calculate the orientation (compass direction) of the vehicle. The difference in the calculated and actual distance traveled between 2 turning points is used to automatically recalibrate the tire circumference (required due to tire wear).
Errors with basic position finding
Rolling backwards without the transmission being shifted into reverse gear is evaluated as moving forwards and can lead to temporary errors in location finding. Any rolling with the ignition switched off or vehicle transportation also falsify position finding.
In both cases, this deviation is automatically corrected by the navigation processor on receipt of GPS data.
The vehicle direction signal (forwards or backwards) will be 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 as to whether new (depth of tread approx. 5 to 10 mm) or used tires (depth of tread approx. 3 to 5 mm) have been fitted.
Entry is made using the STAR DIAGNOSIS or directly on the COMAND operating, display and control unit (A40/3). A special calibration drive is not required.
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