The working principle of hot film air flow sensor is very simple.

The working principle of hot-film air flow sensor, the core of simple hot-film air flow sensor is a thin (hot-mode) heating element. Attached with heat sink.

Control the temperature of the heating element to be constant (the simple sensor thermal module itself has the function of temperature stability). When the temperature is high, reducing the heating current will bring the temperature down, and vice versa.

Air takes away heat through the hot film, and the heat taken away is related to the air flow.

In order to keep the temperature of the hot film stable, when the temperature of the hot film changes, the heating current must be changed accordingly. The temperature is related to the air flow, so the heating current is related to the air flow.

Check the heating current and know the air flow.

Briefly describe the working principle of vane air flow sensor 1, throttle position sensor?

Function: The throttle position sensor is used to monitor the throttle opening, determine the idle speed, full load and acceleration and deceleration, so as to realize the throttle opening state.

Various corresponding fuel injection quantity control. Fault impact: the idle speed is high and low, or the overspeed phenomenon is caused. ?

2. Intake valve pressure sensor?

Function: The intake pressure sensor provides engine load information, that is, it is connected with the engine.

When measuring the pressure of the intake pipe, the intake air quantity entering the engine is indirectly measured, and then the intake air quantity is converted into an electrical signal through the internal circuit and provided to the computer. Fault effect: the engine is not easy to start, or the idle speed is unstable. ?

3. air temperature sensor?

Function: Provide air temperature information to correct fuel injection quantity and ignition timing. ? Fault effect: low idle speed and easy flameout. ?

4. Crankshaft angle sensor?

Function: Provide information of speed and crankshaft phase, and provide reference points for fuel injection timing and ignition timing. Fault effect: the engine can't start or the engine suddenly shuts down after starting. ?

5. Coolant temperature sensor?

Function: Monitor the temperature of engine coolant, convert it into voltage signal and send it to computer. ECU controls fuel injection, ignition timing and idle speed control according to this signal. ? Fault effect: low idle speed. ?

6. oxygen sensor?

Function: The main component that provides the concentration information of the mixer, which is used to correct the fuel injection quantity, realize the closed-loop control of air-fuel ratio and ensure that the actual air-fuel ratio of the engine is close to the theoretical air-fuel ratio. ? Failure impact: unstable idle speed and excessive consumption. ?

7. Knock sensor?

Function: To provide knock information for correcting ignition timing and realizing knock closed-loop control. ? Fault influence: When knocking is about to happen, it is impossible to provide the knock signal point, the computer can't receive the signal "peak value", and the ignition advance angle can't be reduced, so knocking occurs. ?

8. Three-way catalyst?

Function: the three-way catalytic converter is installed in front of the muffler in the exhaust pipe, which can simultaneously reduce the contents of three pollutants (carbon monoxide co, unburned carbon oxide HC and oxide Nox) in the exhaust gas. When the air-fuel ratio of the engine approaches the theoretical air-fuel ratio, the conversion efficiency of the three-way catalytic converter is the highest. When the high temperature of 300℃ ~ 800℃ passes through the center of the three-way catalyst, the harmful gas is oxidized and reduced by the expensive catalyst attached to the ceramic monomer and converted into harmless gas. ? Failure impact: Exhaust gas can't reach the standard.

The working principle of Jiangling air flow sensor This automobile air flowmeter belongs to thermal type. Air flows through the sensor, and the sensor changes its heating resistance to calculate the temperature change value, thus calculating the air flow. If there is something wrong with the car, ask the car master. 4S shop professional technician, 10 minutes to solve.

Working principle of automobile air flow sensor Working principle of air flow sensor: intake air flow conversion

The basic signal sent to the electronic control unit (ECU) for fuel injection decision is used to measure the air flow drawn into the engine.

Electrical control

Various operations

It is necessary to accurately measure the amount of air inhaled into the engine at every moment as the main basis for ECU to calculate (control) the fuel injection amount.

Or the circuit is faulty, the ECU can control the fuel injection quantity by confirming the intake signal, so that the mixture becomes rich or thin, and the engine runs, thereby electronically controlling the gasoline injection system.

Transducer/sensor (English name: transducer/sensor) is a detection device that can sense the measured information, and can convert the sensed information into electrical signals or other required forms of information output according to certain rules to meet the requirements of information transmission, processing, storage, display, recording and control.

The characteristics of sensors include miniaturization, digitalization, intelligence, multifunction, systematization and networking. This is the first step to realize automatic detection and automatic control. The existence and development of sensors make objects have senses such as touch, taste and smell, and make them come alive slowly. Generally, according to its basic sensing function, it can be divided into ten categories: heat sensitive element, light sensitive element, gas sensitive element, force sensitive element, magnetic sensitive element, humidity sensitive element, sound sensitive element, radiation sensitive element, color sensitive element and taste sensitive element.

In order to get information from the outside world, people must use sensory organs. However, it is not enough to study natural phenomena and laws and their functions in production activities only by people's own sensory organs. In order to adapt to this situation, sensors are needed. Therefore, it can be said that the sensor is an extension of the human five senses, also known as the electric five senses.

With the advent of the new technological revolution, the world began to enter the information age. In the process of using information, the first thing to be solved is to obtain accurate and reliable information, and sensors are the main ways and means to obtain information in nature and production fields.

In the modern industrial production process, especially in the automatic production process, various sensors should be used to monitor and control various parameters in the production process, so that the equipment can work in the normal state or the best state and the products can achieve the best quality. Therefore, it can be said that without many excellent sensors, modern production will lose its foundation.

Structure and working principle of hot-wire air flow sensor? The basic structure of the hot-wire air flow sensor consists of a platinum hot wire (platinum wire) for sensing air flow, a temperature compensation resistor (cold wire) for correcting according to the intake temperature, a control circuit board for controlling the current of the hot wire and generating an output signal, and an air flow sensor housing. According to the different installation parts of platinum hot wire in the shell, the hot wire air flow sensor is divided into two structural forms: mainstream measurement and bypass measurement. Structure diagram of hot-wire air flow sensor using mainstream measurement method. There are metal protective nets at both ends, and the sampling tube is placed in the center of the main air duct. The sampling tube consists of two plastic sheaths and a hot wire support ring. The platinum wire (RH) with a hot wire diameter of 70μm is arranged in the support ring, and its resistance changes with temperature, which is an arm of the Wheatstone bridge circuit. A platinum film resistor is installed in the plastic sheath at the front end of the hot wire support ring, and its resistance value changes with the inlet temperature, which is called temperature compensation resistor (RK), which is the other arm of Wheston bridge circuit. The precision resistor (RA) is bonded to the plastic sheath at the back end of the hot wire support ring. This resistor can be fine-tuned by laser, and it is also an arm of the Wheston bridge. The voltage drop across the resistor is the output signal voltage of the hot wire air flow sensor. The Whiston bridge also has an arm resistor RB mounted on the control circuit board.

The working principle of the hot-wire air flow sensor is to keep the temperature of the hot-wire through the hybrid integrated circuit A, so that there is a certain difference between the temperature of the hot-wire and the temperature of the inhaled air. When the air mass flow rate increases, the hybrid integrated circuit A increases the current through the hot wire, and vice versa. In this way, the current through the hot wire RH is a single function of the air mass flow, that is, the hot wire current IH increases or decreases with the increase of the air mass flow, generally within the range of 50- 120mA. Bosch LH gasoline injection system and some high-end cars use this kind of air flow sensor, such as Buick, Nissan Maxima and Volvo.

How to repair the hot-wire or hot-film air flow sensor ① Check the output signal voltage. Unplug the plug of the air flow sensor, remove the air flow sensor, as shown in Figure 2, apply the battery voltage between the D and E terminals of the air flow sensor, and then measure the voltage between the B and D terminals of the sensor with a multimeter. Its standard voltage should be1.6 0.5v. If the voltage is not within the specified range, replace the air flow sensor.

After the above inspection, as shown in Figure 2(b), blow the air inlet of the air flow sensor and measure the voltage between terminals B and D at the same time. When blowing, the voltage should be raised to 2 ~ 4V. If the voltage does not meet the requirements, replace the air flow sensor.

② Inspection of self-cleaning function. Install the air flow sensor, remove the dust screen of the sensor, start the engine, and accelerate to more than 2500 rpm. When the engine stops running for 5s, it can be seen from the air inlet of the air flow sensor that the hot wire emits light (the heating temperature is about1000 C) about1s.. If the platinum wire does not glow, check the self-cleaning signal of the sensor or replace the air flow sensor.

Check the hot-wire air flow sensor of Nissan CA 18E engine as follows:

(1) On-board inspection. Remove the air flow sensor coupler and check the voltage between terminal B on one side of the harness and the ground, which should be12v; ; After that, check the voltage between terminal 3 1 and ground, as shown in Figure 2.

② One-piece inspection. As shown in fig. 3(a), a voltage of 12V is applied between terminals B and C, and then the output voltage between terminals B and C is checked ... As shown in fig. 3(b), the change of sensor output voltage is measured when blowing air. When air is not blown, the voltage is 0.8V；; When blowing, the voltage should be 2.0V.

What types of hot-wire and hot-film air flow sensors belong to? Common air flow sensors can be divided into vane (wing plate) type, core measuring type, hot wire type, hot film type, Carmen vortex street type and so on according to their structural types.

Air flow sensor

Answer: The air flow sensor converts the inhaled air into an electrical signal and sends it to the electronic control unit (ECU) as one of the basic signals for determining fuel injection. It is a sensor used to measure the air flow sucked into the engine. In order to obtain the best mixture concentration under various working conditions, the electronically controlled gasoline injection engine must correctly measure the intake air entering the engine at each moment, which is the main basis for ECU to calculate (control) the fuel injection quantity. If the air flow sensor or circuit fails, the ECU can't get the correct intake signal, so it can't control the fuel injection normally, which will cause the mixture to be too rich or too lean and make the engine run abnormally. There are many types of air flow sensors in electronically controlled gasoline injection system. At present, the common air flow sensors can be divided into vane (wing plate) type, wick type, hot wire type, hot film type, Carmen vortex type and so on according to their structural types.

What is the principle of air flow sensor? It is a sensor, which measures the air flow into the engine. In order to obtain the best mixture concentration under various working conditions, the electronically controlled gasoline injection engine must correctly measure the intake air entering the engine at each moment, which is the main basis for ECU to calculate (control) the fuel injection quantity. If the air flow sensor or circuit fails, the ECU can't get the correct intake signal, so it can't control the fuel injection normally, which will cause the mixture to be too rich or too lean and make the engine run abnormally. There are many types of air flow sensors in electronically controlled gasoline injection system. At present, the common air flow sensors can be divided into vane (wing plate) type, wick type, hot wire type, hot film type, Carmen vortex type and so on according to their structural types. Structure and working principle of vane air flow sensor This vane air flow sensor is used in the traditional Bosch L gasoline injection system and some mid-range vehicles, such as Toyota Camry, Toyota Previa and Mazda MPV multi-purpose vehicles. It consists of an air flowmeter and a potentiometer. The air flow meter has a rotating wing (measuring blade) that can swing around the shaft in the air inlet channel, and the coil spring acting on the shaft can make the measuring blade close the air inlet channel. When the engine is working, the intake air flows through the air flow meter to push the measuring piece to deflect and make it open. The opening angle of the measuring blade depends on the balance between the thrust of the inhaled airflow on the measuring blade and the elastic force of the spiral spring on the measuring blade shaft. The air intake is changed by the driver manipulating the throttle. The greater the air intake, the greater the thrust of air flow on the measuring piece and the greater the opening angle of the measuring piece. A potentiometer is connected to the shaft of the measuring piece. The sliding arm of potentiometer rotates synchronously with the measuring piece, which converts the change of the opening angle of the measuring piece (that is, the change of air intake) into the change of resistance value. The potentiometer is connected with the ECU through wires and connectors. ECU measures the air intake of the engine according to the change of potentiometer resistance or the change of voltage acting on it. The vane air flow sensor usually has an electric gasoline pump switch. When the engine starts running, the measuring piece deflects, the switch contacts are closed, and the electric gasoline pump is electrified to run; After the engine is turned off, the measuring piece is turned to the off position, and the switch of the electric gasoline pump is turned off. At this time, even if the ignition switch is in the on position, the electric gasoline pump will not work. There is also a air temperature sensor in the flow sensor, which is used to measure the intake air temperature and compensate the intake air temperature. The wire connector of vane air flow sensor generally has 7 terminals. However, there are also five terminals after the control contact switch of the electric gasoline pump in the potentiometer is cancelled. Marking of terminal blocks for Nissan and Toyota blade air flow sensors. Terminal marks are generally marked on the sheath of the coupler. Structure and working principle of Carmen vortex street air flow sensor There is a linear or triangular vortex generator in the middle of the intake pipe. When the air flows through the vortex generator, a series of asymmetric but very regular air vortices will be produced in the air flow behind the vortex generator, which is called Carmen vortex. According to Karman vortex theory, this vortex array moves in disorder along the direction of air flow, and its moving speed is proportional to the air speed, that is, the number of vortices passing through a point behind the vortex generator per unit time is proportional to the air speed. Therefore, the velocity and flow rate of air can be calculated by measuring the number of vortices per unit time. There are two methods to measure the number of eddy currents per unit time: mirror detection and ultrasonic detection. There is a light-emitting diode and a photosensitive diode in the mirror image detection Carmen vortex flow sensor. The light beam emitted by the LED is reflected by the reflector to the photodiode, so that the photodiode is turned on. The reflector is mounted on a very thin metal reed. The metal reed vibrates under the pressure of intake vortex, and its vibration frequency is the same as the number of vortex generated in unit time. Because the mirror vibrates with the reed, the reflected light beam also changes at the same frequency, which causes the photodiode to turn on and off at the same frequency with the light beam. The ECU can calculate the air intake according to the switching frequency of the photodiode. This Carmen vortex street air flow sensor is used in Lexus LS400 car. Ultrasonic detection of Carmen vortex street air flow sensor There is an ultrasonic transmitter and an ultrasonic receiver on both sides of the back half. When the engine is running, the ultrasonic transmitter continuously sends out ultrasonic waves with a certain frequency to the ultrasonic receiver. When the ultrasonic wave reaches the receiver through the intake airflow, the phase of the ultrasonic wave changes due to the influence of the vortex in the airflow. The ECU calculates the number of eddy currents generated per unit time according to the corresponding change frequency measured by the receiver, so as to obtain the speed and flow rate of air, and then determines the reference air volume and the reference ignition advance angle according to this signal. Inspection structure and working principle of hot-wire air flow sensor The basic structure of hot-wire air flow sensor is composed of platinum hot wire (platinum wire) for sensing air flow, temperature compensation resistor (cold wire) for correcting air intake temperature, control circuit board for controlling hot-wire current and generating output signal, and air flow sensor housing. According to the different installation parts of platinum hot wire in the shell, the hot wire air flow sensor is divided into two structural forms: mainstream measurement and bypass measurement. Structure diagram of hot-wire air flow sensor using mainstream measurement method. There are metal protective nets at both ends, and the sampling tube is placed in the center of the main air duct. The sampling tube consists of two plastic sheaths and a hot wire support ring. The platinum wire (RH) with a hot wire diameter of 70μm is arranged in the support ring, and its resistance changes with temperature, which is an arm of the Wheatstone bridge circuit. A platinum film resistor is installed in the plastic sheath at the front end of the hot wire support ring, and its resistance value changes with the inlet temperature, which is called temperature compensation resistor (RK), which is the other arm of Wheston bridge circuit. The precision resistor (RA) is bonded to the plastic sheath at the back end of the hot wire support ring. This resistor can be fine-tuned by laser, and it is also an arm of the Wheston bridge. The voltage drop across the resistor is the output signal voltage of the hot wire air flow sensor. The Whiston bridge also has an arm resistor RB mounted on the control circuit board. The working principle of the hot-wire air flow sensor is to keep the temperature of the hot-wire through the hybrid integrated circuit A, so that there is a certain difference between the temperature of the hot-wire and the temperature of the inhaled air. When the air mass flow rate increases, the hybrid integrated circuit A increases the current through the hot wire, and vice versa. In this way, the current through the hot wire RH is a single function of the air mass flow, that is, the hot wire current IH increases or decreases with the increase of the air mass flow, generally within the range of 50- 120mA.