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Mar 08, 2018

The intake pressure sensor transforms the pressure of the intake pipe of the engine into the corresponding electrical signal. The electronic controller of the engine calculates the basic fuel injection time and determines the basic ignition advance angle according to this signal.

There are many forms of pressure sensors. According to the principle of their signal generation, they can be divided into piezoelectric, semiconductor varistor, capacitive, differential transformer and surface elastic wave.

1. semiconductor pressure sensitive resistance intake pressure sensor

(1) semiconductor piezoresistive pressure sensor measurement principle. Semiconductor varistor pressure sensor uses semiconductor piezoresistive effect to transform pressure into corresponding voltage signal.

A semiconductor strain gauge is a sensitive element that changes the resistance value at the time of tension or compression. The strain gauge was attached to the silicon diaphragm, and connected into a Wheatstone bridge, when the silicon diaphragm deformation, the tensile or compressive strain gauge and its resistance to change, the bridge will have corresponding voltage output.

(2) the composition of the structural semiconductor pressure sensitive resistance intake pressure sensor of the pressure sensitive resistance intake pressure sensor is shown in Figure 8-22. The pressure conversion element of the sensor has silicon diaphragm, and the compression deformation of the silicon diaphragm will produce the corresponding voltage signal. One side of the silicon diaphragm is vacuum, and the other side introduces the intake pipe pressure. When the pressure in the intake pipe changes, the deformation of the silicon diaphragm will change, and produce the corresponding voltage signal corresponding to the intake pressure. The greater the inlet pressure, the greater the deformation of the silicon diaphragm and the greater the output pressure of the sensor.

Semiconductor pressure sensitive linear resistor type air pipe pressure sensor is good, and has a small size and high precision, has the advantages of good response characteristics.

2. capacitance intake pressure sensor

(1) capacitive pressure sensor measuring principle of capacitive pressure sensor by using the diaphragm to form a capacitance pressure sensitive element variable, diaphragm deformation, the capacitance value of the corresponding change, change in capacitance by the measuring circuit and pressure corresponding to the sensor will be converted to a corresponding electrical signal. There are two main measuring circuits for capacitive pressure sensors, such as frequency detection and voltage detection, as shown in Figure 8-23.

1) frequency detection: the oscillation frequency of oscillating circuit varies with the size of capacitance of pressure sensitive element. After rectifying and amplifying, the output pulse corresponds to the pressure.

2) voltage detection: the change of capacitance value of pressure sensitive element. After demodulation of carrier and AC amplifying circuit and demodulation circuit, and then filter through filter circuit, output voltage signal corresponding to pressure change is output.

(2) the schematic diagram of the capacitive intake pressure sensor of the capacitive intake pressure sensor is shown in Figure 8-24. The alumina diaphragm and the hollow insulating medium form a capacitive pressure sensitive element which is internally vacuum, and is connected to the sensor hybrid IC.  When the sensor enters the pressure of the intake manifold, the alumina diaphragm will be deformed under the action of the intake pressure, and the capacitance value will be changed. After the mixed integrated circuit is processed, the electrical signal corresponding to the inlet pressure will be changed.

Compared with the intake flow sensor with the same function, the intake pressure sensor has no interference to the intake, and the installation position is flexible. The intake pressure sensor can be installed at the place far away from the intake pipe of the engine through the guidance of the vacuum tube. Therefore, the use of air inlet pressure sensors is increasing in modern engine electronic control systems.