Types of Air Flow Sensors

October 22,2021

If your beloved car has occurred the following problems such as engine backfired sharply, driving hardly with dark smoke and repeat a few days later after a basic repairing we can definitely tell you that it is likely the problem of air flow sensor. And today we are going to talk about the definition of this item its working principle and types.


AUDI air flow sensor


The definition of air flow sensor


It is used to check the amount of air inhaled by the engine as it can transmit the amount of air into an electrical signal and record on ECU which could be used to calculated fuel injection time and ignition time.


The types of air flow sensor


Now the market mainstream on two types of mass flow type: hot wire air flow sensor, hot mode air flow sensor. Other volume flow vane type, Karman vortex type has been eliminated. The theoretical air-fuel ratio, or air-fuel mass ratio, is 14.7:1.


🔢hot wire air flow sensor


This type sensor suits for Nissan (Chollima), GM (Buick Regal), Mercedes Benz, etc. The hot-wire air flow sensor measuring element is a platinum wire wound on ceramic.


  • The principle of hot wire air flow sensor


When the air stream overheats the wire, the heat of the hot wire is absorbed by the air and cools it. The more air flows through the hot wire, the more heat is taken away. Hot wire air flowmeter is used to measure air mass flow rate by heat transfer between hot wire and air. Its working principle is to keep the temperature difference between the hot wire and the suction air at 100℃, and the temperature of the hot wire is controlled by the hybrid integrated circuit. As the quality of air entering the engine increases, so does the amount of heat taken away by the air. In a hybrid integrated circuit, the current through the hot wire resistance increases in order to maintain the hot wire temperature; Conversely, the current through the hot wire resistor will decrease. In this way, the current through the hot wire resistance is a single function of air mass flow rate, that is, the hot wire current increases with the increase of air mass flow rate and decreases with the decrease of air mass flow rate.


As the air flow increases, the temperature of the platinum wire wire resistance RH decreases, the RH resistance decreases, and the heating current IH increases to maintain a certain temperature of the wire (100℃ higher than the air flow temperature). The signal resistance RA is in series with RH, so the voltage V2 at both ends of the resistance RA increases. V2 is the signal voltage that our air meter needs to give the ECU.


  • Self-cleaning function


after the sensor has been used for a period of time, the hot wire surface will be polluted by air dust, which will reduce its thermal radiation capacity and affect the measurement accuracy.


  • Self-cleaning mode 


ECU receives flameout instruction, controls the self-cleaning circuit to be connected, heats the hot wire to 1000℃ and holds it for 1S, then burns off the dust.


🔢Hot mode air flow sensor


It is currently as the mainstream development direction of air flow meter, so it is very widely used, better than the hot wire type. This sensor suits for more cars such as AUDI, Volkswagen, BMW.


  • Structure


the structure of hot film air flowmeter is shown in figure. The heating body is not a hot wire, but a hot film, consisting of hot metal platinum fixed on a thin layer of resin film. This structure can make the heating element not directly bear the force produced by the air flow, improve the strength of the heating element, improve the reliability of the air flow meter. The platinum film is plated on a ceramic substrate.


The principle of hot mode air flow sensor is the same as the hot wire air flow sensor.


  • The benefits of hot mode air flow sensor


Hot film is not easy to damage with good stain resistance. It doesn’t need the function of self-cleaning and its cost is very low.


If you are looking for a AUDI air flow sensor supplier, we are looking forward to be your first choice. YASEN is a professional air flow sensor supplier, providing all sorts of air flow sensors fitting with all kinds of auto. If you have any need please feel free to contact us.