Display speed, function - GF54.30-P-3025GZ
MODEL 164
Shown on model 164.1
The electronic speedometer (A1p8) displays the vehicle speed. The electronic speedometer (A1p8) is driven by a stepper motor. In addition the vehicle speed can also be displayed digitally in the 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):
- Left front rpm sensor (L6/1)
- Right front rpm sensor (L6/2)
- Left rear rpm sensor (L6/3)
- Right rear rpm sensor (L6/4)
The instrument cluster (A1) receives the wheel speeds as rpm from the ESP control unit (N47-5) over 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 multifunction display (A1p13). The display of vehicle speed in km/h or mph is stored country-specific nonvolatile memory and can be changed in the "settings" menu. The digital speed display is matched to the electronic speedometer (A1p8) by a performance map.
Evaluating the wheel speed signals
Since the wheels do not always rotate at the same speed, all 4 wheel speeds must be evaluated. The actual process is relatively complex, which is why only a general description is provided here:
- The individual wheel speeds are compared and submitted to a plausibility check. 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) ascertains by means of suitable comparisons (lateral comparisons) of the wheel speeds that the vehicle is cornering, the vehicle speed is calculated from the mean value of the front wheel speeds.
- 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, an appropriate error message is stored in the memory.
If fault messages are received for all wheel speeds, the speed 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 limiter function status is displayed over the LIM (variable speed limiter) function lamp (A1e33) in the multifunction display (A1p13).
| Instrument cluster, component description | GF54.30-P-6000GZ |