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Basic position finding, function - GF82.61-P-3006RM

MODEL 230.467 /474 /475 as of 1.6.04 with CODE (527) COMAND APS (with navigation) 

MODEL 230.476 as of 1.6.04 

Position finding (dead reckoning) 

Fig 1: Identifying Basic Position Finding Function
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Basic position finding, function 

Basic location finding (dead reckoning) is the basic function of continuous location finding. When the ignition is switched on, it is carried out continuously by the navigation processor (N41/1) 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:

IMPORTANT The basic position finding (composite positioning) is performed approximately every 1 s.

Distance traveled 

The navigation processor (N41/1) receives the wheels speed signals from the ESP, SPS [PML] and BAS control unit (N47-5) via the Controller Area Network Bus Class C (engine compartment) (CAN-C). These wheel speed signals are evaluated to determine the distance traveled.

Direction of travel 

Via the signal for reversing that is transmitted by the EIS [EZS] control unit (N73) via the Controller Area Network bus class B (interior) (CAN-B), the navigation processor (N41/1) detects the direction of travel (forward or reverse).

Vehicle orientation 

The navigation processor (N41/1) calculates the orientation (compass direction) of the vehicle from the data of the yaw rate sensor (gyro sensor) and the sequence of the positions calculated using the global positioning system (GPS). The difference in the calculated mileage and the mileage actually covered between 2 turnoff points is used to automatically recalibrate the tire circumference (necessary 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 position finding. Rolling when the ignition is switched off or transporting the vehicle can also distort the position finding.

In both cases the deviation is corrected automatically by the navigation processor (N41/1) upon receipt of the GPS data.

IMPORTANT The driving direction signal (forwards, backwards) 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 do this, the input of tire size and the coding, whether new tires (depth of tread approx. 5 to 10 mm) or worn tires (depth of tread approx.

3 to 5 mm) have been fitted, is necessary. The input takes place via STAR DIAGNOSIS or directly at the COMAND operating, display and control unit (A40/3). A special calibration drive is not required.

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