Air mass meter

This mass air flow sensor is designed as a hot-film air mass meter.

A heated surface of the hot-film air mass sensor in the flow of intake air is controlled to a constant temperature with respect to the intake air. The intake air flowing past this surface cools this heated surface and thus changes its resistance. The heating current which is necessary in order to maintain the constant temperature is the measurement variable for the air mass drawn in. The DME control unit uses it to calculate the load signal and thus the basic variable for the injection timing.

Important advantages:

  • Changes in air pressure (air density) are recorded
  • Temperature influences are compensated
  • No moving parts
  • Large measuring range
  • Low pressure drop in the intake pipe due to low air resistance. This improves the efficiency of the engine.

In contrast to the hot-wire mass air sensor, clear-burning of the sensor is no longer necessary after the engine has been turned off. Any dirt deposits on the surface do not influence the sensor signals directly since the protective film cleans itself due to the constant overtemperature.


Intake air temperature sensor

The intake air temperature sensor is integrated in the mass air flow sensor on vehicles with engine management system MS45. A precision ballast resistor (NTC resistor) is used to convert the temperature into a measurement value which can be evaluated electrically by the DME control unit.

The intake air temperature sensor is not required for correction of the fuel injection period, as the intake-air temperature is automatically taken into account in the air mass metering. The intake air temperature sensor is set at the start procedure in conjunction with the engine coolant temperature sensor. The resistance values of both sensors supply exact information for calculating the fuel injection period. In this way hot start problems in particular are avoided.

The air column in the mass air flow sensor can oscillate during a start procedure. For this reason, the value output by the mass air flow sensor cannot be used as a correct value for fuel injection period. The temperature sensors are therefore used as a measured variable up to a freely programmable engine speed threshold.


Wiring, Air Mass Meter & IAT:

Air Mass Meter_IAT