Intake pressure sensor output characteristics
When the engine is working, with the change of throttle opening, the vacuum, absolute pressure and output signal characteristic curve in the intake manifold are changing.
The injection system detects the absolute pressure in the intake manifold behind the throttle. The rear of the throttle valve reflects both vacuum and absolute pressure, so some people think that vacuum and absolute pressure are a concept. In fact, this understanding is one-sided. Under the condition of constant atmospheric pressure (standard atmospheric pressure is 101.3kPa), the higher the vacuum in the manifold, the lower the absolute pressure in the manifold. The vacuum is equal to the difference between atmospheric pressure minus the absolute pressure in the manifold. The higher the absolute pressure in the manifold, the lower the vacuum in the manifold. The absolute pressure in the manifold is equal to the difference between the atmospheric pressure outside the manifold and the vacuum. That is, atmospheric pressure is equal to the sum of vacuum and absolute pressure. After understanding the relationship between atmospheric pressure, vacuum and absolute pressure, the output characteristics of the intake pressure sensor are clear.
During engine operation, the smaller the throttle opening, the greater the vacuum of the intake manifold, the smaller the absolute pressure in the manifold, and the smaller the output signal voltage. The greater the throttle opening, the smaller the vacuum of the intake manifold, the greater the absolute pressure in the manifold, and the greater the output signal voltage. The output signal voltage is inversely proportional to the vacuum degree in the manifold, and proportional to the absolute pressure in the manifold.
Principle of intake pressure sensor
The intake pressure sensor detects the absolute pressure of the intake manifold behind the throttle. It detects the absolute pressure change in the manifold according to the engine speed and load, and then converts it into a signal voltage to send to the engine control unit (ECU). The ECU controls the size of the basic fuel injection amount according to the magnitude of this signal voltage.
There are many types of intake pressure sensors, including varistor type and capacitive type. Because the varistor type has the advantages of fast response time, high detection accuracy, small size and flexible installation, it is widely used in injection systems.