Interpret the structure principle of air flow sensor
The air flow sensor is a sensor used to measure the air flow of the intake engine. The product has the advantages of safe and reliable use, stable performance, flexible use, easy maintenance, and high reliability. What is the structural principle of the air flow sensor?
Structure principle of air flow sensor:
On the electronically controlled fuel injection device, a sensor that measures the amount of air sucked by the engine, that is, the air flow sensor is one of the important components that determines the control accuracy of the system. When the control accuracy of the air-fuel ratio (A/F) of the air and air mixture sucked by the engine is specified as ±1.0, the allowable error of the system is ±6%-7%, and this allowed error is distributed to each component of the system When on, the error allowed by the air flow sensor is ±2%-3%.
The ratio of the maximum and minimum values ??of the intake air flow of the gasoline engine, max/min, is 40-50 in the natural air intake system, and 60-70 in the system with supercharging. In this range, the air flow The sensor should be able to maintain a measurement accuracy of ±2-3%. The air flow sensor used on the electronically controlled fuel injection device should not only maintain the measurement accuracy over a wide range of measurement, but also have excellent measurement responsiveness and be able to measure pulsation. Air flow and output signal processing should be simple.
According to the different characteristics of the air flow sensor, the fuel control system is divided into the L-type control for directly measuring the intake air amount and the D-type control for indirectly measuring the intake air amount (according to the negative pressure of the intake manifold and the engine) The intake speed is indirectly measured by the rotation speed of the engine. In the ROM of the D-type control mode, the intake air volume in various states with the engine speed and the pressure in the intake pipe as parameters is stored in advance, and the microcomputer operates according to the measured The intake air pressure and speed in the state can be calculated by referring to the intake air volume memorized by the ROM. The air flow meter used by the L-type control is basically the same as the general industrial flow sensor, but it can adapt to the harsh environment of the car. The response to sudden changes in flow rate when the accelerator is depressed and the requirement for high-precision detection even in uneven airflow caused by the shape of the intake manifold before and after the sensor.
The original electronic fuel injection control system did not use a microcomputer. It is an analog circuit. At that time, a valve-type air flow sensor was used, but as microcomputers were used to control fuel injection, several other air flow sensors also appeared.