Basic location finding, function - GF82.61-P-3006D
MODELS 163, 168, 170, 203.0 /2 /7, 208, 209.3 /4, 210 with CODE (353) Audio 30 APS
Basic representation of the basic location finding shown on model 210
Basic location finding (dead reckoning) is the basic function of continuous location finding. It is permanently carried out by the navigation processor that is integrated in the radio (A2) when the ignition is switched on (approx. once per second) and is irrespective of the data of the DVD map. After switching off the ignition, the current position is stored for the duration of the system shut-off delay time.
The following information is calculated with the aid of basic location finding:
- Distance traveled
- Absolute vehicle direction (compass direction)
- Direction of travel (forward or reverse)
Calculation of distance traveled
The navigation processor receives the wheel speed signal of the following components:
- Left rear rpm sensor (L6/3) (model 168)
- Wheel speed sensor, left front (L6/1)
- Right front rpm sensor (L6/2) (model 208, 210)
- Left front rpm sensor (L6/1) and right front rpm sensor (L6/2) (models 203, 209)
The evaluation of the wheel speed signals reveals the mileage covered.
The wheel speed signals of the not driven wheels are evaluated, since their slip between the roadway and tire is lower, which results in a more accurate result when calculating the mileage.
Calculation of the vehicle orientation
The navigation computer calculates the direction in which the vehicle is traveling (compass direction) from the data from the gyrosensor and the sequence of locations calculated with the aid of the global positioning system (GPS). The difference in the calculated mileage and the mileage actually covered between 2 turn-off points is used to automatically recalibrate the tire circumference (necessary due to tire wear).
Calculation of the direction of motion
The navigation processor recognizes the direction of motion (forward or reverse) from the reverse signal.
Calibration of tire circumference
As a matter of principle, the navigation system recalibrates itself while driving as described. However, this may require driving a longer distance. After changing tires, manual recalibration should therefore be accomplished. To do this, it is necessary to enter the tire size (e.g.:195/050/015) and possibly the following information:
- new tires (tread depth > approx. 5 mm)
- used tires (tread depth < approx. 5 mm)
The entry can be done two different ways:
- With aid of STAR DIAGNOSIS.
- By calling the "Navigation → TIRE" menu at the radio (A2)
Errors due to vehicle movement with switched off ignition lead to an inaccurate basic location finding. Rolling backwards without the reverse gear engaged is evaluated as forwards motion, and may lead to an error in the location finding. Rolling with the ignition switched off or vehicle transportation also falsify map matching.
The errors are, however, corrected automatically after a short time by the navigation processor after receiving GPS data.
A special calibration drive by driving around a defined test path is not ever required.
| Map-supported location finding, function | GF82.61-P-3008C |