Displaying speed, function - GF54.30-P-3025SK
MODELS 171.4
The electronic speedometer (A1p8) is used to display vehicle speed. The electronic speedometer (A1p8) is driven by a stepper motor.
In addition the vehicle speed can also be displayed digitally in the upper multifunction display (A1p13).
Measuring the vehicle speed
To calculate the vehicle speed the wheel speeds of the following sensors are evaluated by the instrument cluster (A1):
- Rpm sensor, left front (L6/1)
- Rpm sensor, right front (L6/2)
- Left rear rpm sensor (L6/3)
- Right rear Rpm sensor (L6/4)
The instrument cluster (A1) receives from the ESP and BAS control unit (N47-5) the wheel speeds in rpm via the Controller Area Network bus class C (CAN-C).
As the tire circumference differs only very slightly among all the approved tires, no coding of the tire circumference is necessary.
Digital speedometer
The vehicle speed is displayed digitally in the upper multifunction display (A1p13). The display of vehicle speed in m/h or mph is stored country-specific in a non-volatile memory and can be changed in the "adjustments" menu. The digital speed display is compared by a performance map in the electronic speedometer (A1p8).
Evaluating the wheel speed signals
As all the wheels do not have the same speeds, all 4 wheel speeds must be evaluated. As this is relatively complex, the procedure will only be described here in simplified form:
- The individual wheel speeds are compared and checked for plausibility. If no significant deviations of individual wheel speed signals are to be detected, the vehicle speed is detected from the rpm of the left front wheel.
- If the individual wheel speed signals differ considerably, the speed signals may be faulty or the vehicle may be cornering.
- If the instrument cluster (A1) establishes by means of suitable comparisons (side comparisons) of wheel speeds, that the vehicle is cornering, the vehicle speed is determined from the mean value of the speeds of the front wheels.
- If the comparisons indicate one or more incorrect wheel speeds, the speed is calculated from the highest wheel speed. This also applies if an error message is received instead of a rotational wheel speed. In this case in addition a corresponding error message is set.
If error messages are received for all wheel speeds, the speed of 0 km/h or 0 mph is displayed.
This evaluation of the wheel speed signals also applies for evaluating the distance traveled since the distance is calculated from the vehicle speed.
Speed limiting with winter tires
A permanent speed limit (adjustable in 10-km/h steps of 160 km/h to 240 km/h) can be activated and adjusted with the right multifunction steering wheel button group (S111) and left multifunction steering wheel button group (S110).
LIMITER
The status of the limiter function is displayed in the lower multifunction display (A1p15).
| Instrument cluster (IC), location/task | GF54.30-P-3039SK |