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.