GF82.61-P-3006RJ Basic Position Finding, Function
GF82.61-P-3006RJ Basic Position Finding, Function
- with CODE (498) Japan version
Basic determination of location, function
Basic location finding (dead reckoning) is the basic function of continuous location finding. It is performed constantly by the navigation processor in the COMAND operating, display and control unit (A40/3) when the ignition is switched on, irrespective 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 motion (forward or reverse).
^ Vehicle orientation
The basic position finding (composite positioning) is performed approximately every 1 s.
Distance traveled
The navigation processor in the COMAND operating, display and control unit (A40/3) receives the wheel speed signals from the ESP, SPS 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 reversing, which is sent by the EIS control unit (N73) via the Controller Area Network bus Class B (interior) (CAN-B), enables the navigation processor in the COMAND operating, display and control unit (A40/3) to recognize the direction of travel (forwards or backwards).
Vehicle orientation
The navigation processor in the COMAND operating, display and control unit (A40/3) calculates the orientation (compass direction) of the vehicle using data from the yaw rate sensor (gyro sensor) and the sequence of positions calculated on the basis of the data received by the global positioning system.
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.
Rolling when the ignition is switched off or transporting the vehicle can also distort the position finding. In both cases, the deviation is automatically corrected by the navigation processor in the COMAND operating, display and control unit (A40/3) when GPS data are received.
To enable extremely accurate recording of the travel distance, the direction of travel signal (forwards, backwards) is generated by the following components:
^ Left front rpm sensor (L6/1)
^ Right front rpm sensor (L6/2)
^ Left rear rpm sensor (L6/3)
^ Right rear rpm sensor (L6/4)
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.
Post calibration
Post calibration of the tire circumference is necessary because of tire wear. This is done automatically and uses the difference calculated with the aid of the map-based position finding regarding the calculated and actually traveled distance between 2 turnoff points.
