Calculation of air mass

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.