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

MODEL 230.4 as of 1.7.04 with CODE (494) USA version

Position finding (dead reckoning)

Fig 1: Identifying Basic Position Finding Function

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 (composite positioning):

Distance traveled
Direction of travel (forward or reverse)
Vehicle orientation

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

Distance traveled

Via the controller area network bus class C (engine compartment) (CAN-C), the navigation processor (N41/1) receives the wheel speed signals from the ESP, SPS and BAS control unit (N47-5). These wheel speed signals are evaluated to determine 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 class B (interior) (CAN bus), allows the navigation processor (N41/1) to recognize the direction of travel (forwards or backwards).

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 positions calculated by 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 GPS data.

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 entry is accomplished with 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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