Basic Location Finding, Function
Basic illustration on model 210
The basic location finding function (dead reckoning) is the primary function of continuous location finding. It is performed continuously (approx. once per second) by the navigation
processor integrated into the radio and navigation unit (A2/56) when the ignition is switched on and is independent of the data from the CD-ROM map. After switching off the ignition, the current position remains stored for the duration of the system switch off delay.
The following information can be calculated with the aid of basic location finding:
distance travelled, absolute direction in which vehicle is pointing (compass direction) and direction in which vehicle is driving (forward or reverse).
Calculation of distance travelled
The navigation processor receives the wheel speed signals from
the left rear wheel speed sensor (L6/3) (on model 168) or the left front wheel speed sensor (L6/1) (on model 170) or the right front wheel speed sensor (L6/2) (on models 208 and 210) from the traction systems control module (N47) via a separate line.
On model 203, the wheel speed signal is relayed from the instrument duster (A1) to the radio and navigation unit (A2/56) via the CAN bus (A1 - A2/56).
The distance travelled is obtained from evaluation of the wheel speed signal.
NOTE: The wheel speed signals from the non driven wheels are always used because the slip between the road and tires is lower providing a more precise result when calculating the distance travelled.
NOTE: On model 163, the wheel speed signal is transferred by the traction systems control module (N47) via the CAN bus to the CAN bus adapter. From the CAN bus adapter, the wheel speed signal then travels over a separate lead to the radio and navigation unit (A2/56).
Calculation of vehicle direction
The navigation processor calculates the direction in which the vehicle is moving (compass direction) using the data from the gyrosensor and the sequence of locations calculated with the aid of the global positioning systems (GPS).
The difference between the calculated and actual distance travelled between two turning points is used for automatic recalculation of the tire circumference (required due to tire wear).
Calculation of the direction of motion
The navigation processor recognizes the direction of motion
(forward or backward) from the signal for the reverse gear.
The signal is transferred
model 163 via the reverse lamp lead on
model 168 from the reverse lamp switch (S16/2) (with manual transmission) or the gear recognition module (A61) (with automatic transmission) on;
model 170 from the reverse lamp switch (S16/2) (with automatic transmission) or from the gear recognition switch (S16/10) (with automatic transmission).
via a separate lead in each case.
On models 203,208 and 210 the signal for reverse is transferred to the radio and navigation unit (A2/56) from the instrument cluster (A1) via CAN (A1 - A2/56).
Calibration of wheel circumference
In principle, the navigation system can recalibrate itself while driving as described previously. However, this requires driving a greater distance. For this reason, manual wheel calibration should be performed after changing tires. For this purpose, it is necessary to enter the
tire size (e.g.: 195/050/015) and the information whether the tires are
new (tread depth >approx. 5 mm) or
used (tread depth< approx. 5 mm)
This entry can be made:
with the aid of the hand-held tester (HHT) or
after calling the menu "Navigation RAD" on the radio and navigation unit (A2/56).
NOTE: A special calibration drive via a defined test track is never required.
Possible location finding errors with basic location finding.
Rolling backwards without engaging the reverse gear is evaluated as driving forwards and can lead to temporary errors in the location finding.
Rolling with the ignition switched off or transport of the vehicle also lead to erroneous determination of the location.
However, such errors are corrected automatically by the navigation processor after receiving GPS data.