Calculation of air mass
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The air mass drawn in is no longer measured directly by the hot film air mass meter and is calculated by the Digital Engine Electronics (DME) instead. A suitable model has been programmed in the Digital Engine Electronics (DME) in order to be able to perform this calculation. The following signals are input into this calculation:
- VANOS setting (load sensing)
- Position of throttle valve
- Intake air temperature (correction of air density)
- Engine speed (cylinder filling levels)
- Intake pipe vacuum (correction during throttling)
- Ambient pressure (air density divided by altitude correction).
The air mass calculated in this way is synchronized with:
- Signal from oxygen sensor (air/fuel ratio)
- Fuel injection period (fuel quantity).
If necessary, the calculated air mass is corrected. If the oxygen sensor fails, a fault is entered in the fault memory of the Digital Motor Electronics (DME) (air mass plausibility check). In such cases, the calculated air mass is no longer compared.