Function of air flowmeter
The air flow meter measures the fresh air quantity and intake temperature entering the engine intake manifold, and ECU performs fuel injection quantity correction, smoke limit and EGR opening control according to these information.
2. Installation position
The sensor is installed on the intake pipe of the engine, at the rear end of the air filter.
3. Working principle
3. 1. The principle of air flowmeter
The air flow sensor integrates some electronic components on the ceramic substrate. When the engine works normally, the diaphragm is heated first, and some heat will be taken away when fresh air flows through the sensor. At this time, the ECU will control the Whiston bridge on the diaphragm to supplement the heat, which will cause the change of the electrical signal. When the signal is transmitted to the ECU, the ECU will calculate the intake air volume according to this change.
3.2. Principle of air temperature sensor
The air temperature sensor is a negative temperature coefficient resistor. When the intake air temperature changes, the resistance of this resistor will change, which will lead to the change of the signal voltage at the ECU end. The ECU calculates the intake air temperature according to this change.
3.3. Judgment of airflow direction
There are constant temperature resistors at both ends of the hot film of the air flowmeter. When air flows through the hot film, it will take away some heat, so the temperature at the front end of the hot film is lower than that at the back end. ECU judges the direction of airflow according to this signal!
4. Circuit diagram of air flowmeter
5. Control strategy
The ECU will always monitor the working state of the air flow meter, and take corresponding control when the ECU judges that the air flow meter is out of order, as follows.
4. 1. When the MIL light of the engine lights up, the EGR system will quit working, and the exhaust gas will no longer participate in the system work;
4.2. The engine speed will be limited to a certain speed, and the power will be limited;
4.3. When the air flowmeter fails, the engine can be started normally without being affected;
Second, the air flow meter detection:
Fault codes related to air flow meters