an air flow sensor, air flow meter, also known, is one of the sensor EFI engine. It sucked air flow into an electric signal to the electronic control unit (the ECU), as one of the basic fuel injection signal determined, is a sensor measuring the intake air flow rate of the engine.
1. Overview of the air flow sensor
an electronic control air flow sensor for a gasoline injection engine can obtain optimal concentration gas mixture in various operating conditions, it must be determined accurately for each instantaneous intake air amount of the engine, as the main basis for calculation ECU (control) fuel injection quantity. If the air flow sensor or line failure, the ECU the intake air amount signal is not correct, it can not normally perform the fuel injection amount control, will cause the mixture too thick or too thin, so that the engine does not operate properly. Electronically controlled fuel injection system of the air flow sensor has a variety of types, common air flow sensor according to the structure type can be divided blade (blade) type, amount of the core type, a hot wire, the hot film, such as several Karman vortex type species.
2. The air flow sensor principle structure
In the electronically controlled fuel injection device, a sensor measuring the amount of air sucked into the engine, i.e. the air flow sensor is one of the important components of the control system determines the accuracy. When a predetermined air sucked into the engine, air fuel ratio (A / F) control accuracy of ± 1.0, the system’s tolerance of ± 6 ~ 7, this allows the error distribution to the various system components , air flow sensor allowable error of ± 2 ~ 3.
The air sucked into a gasoline engine of the maximum and minimum flow rate ratio of max / min in a natural intake system, 40 to 50, in the supercharger system 60 to 70, within this range , air flow sensor should be able to maintain measurement accuracy ± 2 to 3, an air flow sensor electronically controlled fuel injection device used in a wide measurement range should not only be able to maintain measurement accuracy, and also excellent responsiveness measurement, measure process air flow, the pulsation of the output signal should be simple.
Depending on the characteristics of the air flow sensor, the fuel control system into a metered manner to control the intake air amount of L-type and D indirectly measured intake air amount control direct measurement of the intake air amount (intake manifold negative tube according the rotational speed control type .D indirectly measured pressure and the intake air amount of the engine in the microcomputer ROM, the intake air amount is stored in advance in various states to the pressure in the intake pipe and engine rotational speed as parameters, the microcomputer in accordance with the measured intake pressure and rotational speed of each operation state, the intake air amount with reference to the ROM memory, the amount of fuel can be calculated using the L-shaped control meter and an air flow sensor for general industrial substantially the same, but it can adapt to the harsh automotive environment, However, dramatic changes in response to a request to occur when the flow rate of the accelerator pedal and the sensorBefore and after the intake manifold due to the uneven shape of the air flow can be detected with high accuracy requirements.
The microcomputer is not the first electronic fuel injection control system. Instead analog circuit, is employed when the shutter-type air flow sensor, but with the microcomputer for controlling the fuel injection, there have been several other air flow sensor.
The structure of the shutter type air flow sensor.
type air flow sensor flap is mounted on a gasoline engine, is mounted between the air cleaner and the throttle valve, its function is to detect the intake air amount of the engine, and converts the detection result into an electrical signal, and then input the microcomputer. The sensor is a potentiometer by the airflow meter two parts.
look at the work process air flow sensor. From the air cleaner toward the intake air valve, the valve to the intake air amount and the return spring stop position of the equilibrium, that is, the opening degree of the shutter to be proportional to the intake amount. The rotational shaft of the shutter is also equipped with a potentiometer, the potentiometer slide arm synchronous rotation with the shutter, the voltage drop by the sliding resistance of the sheet measured opening degree conversion into an electrical signal and then input to the control circuit.
Karman’s vortex type air flow sensor
To overcome the air flow sensor flap disadvantage, i.e. to ensure accuracy in the premise, extend the measurement range, and cancels the sliding contact, there is the development of small, lightweight air flow sensor, i.e., the Karman vortex air flow sensor. Karman vortex is a physical phenomenon, vortex detection method, the detection accuracy of the electronic control circuit with nothing to do, change the size of the passage area of the air column of the vortex generator determines the detection accuracy. And because the output of such a sensor is an electronic signal (frequency), so the control circuitry of the input signal, the AD converter may be omitted. Thus, the essence, the Karman vortex air flow sensor is suitable for computer processing of the signal. Such a sensor has the following three advantages: high precision, may output a linear signal, the signal processing is simple; long-term use, the performance does not change; because there is no need for detecting the volume flow and the temperature of the atmospheric pressure correction.
Such a flow schematic circuit for detecting the air flow sensor, when a Karman vortex is generated, and on the rate of change with pressure, the basic principle is to use the flow rate detection in which rate of change. A square wave signal, a digital signal. The more the intake air amount, the higher the frequency of the Karman’s vortex, the air flow sensor output signal frequency is higher.
gentle air flow sensor and pressure compensation, mainly used for a variety of fluid media flow measurement industry medium conduit, such as a gas, liquid, vapor, etc.. Characterized by a pressure loss is small, a large measurement range, high accuracy, almost independent of the fluid density, pressure, temperature, viscosity and other parameters when measuring actual volume flow. No moving mechanical parts, so high reliability and low maintenance. Instrument parameters can be long-term stability. This instrument uses piezoelectric stress sensors, high reliability, operates in the operating temperature range of -10 ℃ ~ + 300 ℃ of. Standard analog signals, digital pulse signal output, easy to use and supporting computers and other digital systems, is a more advanced, the ideal flow rate. The biggest advantage of
the air flow sensor is the effect of the medium was measured from the meter factor, it can be extended from one medium to another exemplary media. However, due to the liquid flow rate range and gas vary greatly, resulting in very different frequency ranges also. Vortex amplifier circuit for processing a signal, the filter pass band different circuit parameters are also different, and therefore, the same circuit can be used to measure parameters different media. .
3 air flow sensor measuring range
and measuring instruments pass through the air flow sensor range as follows:
Instrumentation path
Code
Standard Range [ 123] Code
extended range
DN25 (1quot;)
S
2.5-25 m3 / h
W
4-40 m3 / h
DN40 (1.5quot; )
S
5-50 m3 / h
W
6-60 m3 / h
DN50 (2quot;)
S1
6-65 m3 / h
W1
5-70 m3 / h
S2
10-100 m3 / h
W2
8-100 m3 / h
DN80 (3quot;)
S1
13-250 m3 / h
W1 [123 ] 10-160 m3 / h
S2
20-400 m3 / h
W2
DN100 (4quot;)
S1
20-400 m3 / h
W1 [ 123] 13-250 m3 / h
S2
32-650 m3 / h
W2
DN150 (6quot;)
S1
32-650 m3 / h
W1
80-1600 m3 / h
S2
50-1000 m3 / h
W2
DN200 (8quot;)
S1
80-1600 m3 / h
W1
50-1000 m3 / h
S2
130-2500 m3 / h
W2
DN 250 (10quot;)
S1
130-2500 m3 / h [ 123] W1
80-1600 m3 / h
S2
200-4000 m3 / h
W2
DN 300 (12quot;)
S
200-4000 m3 / h
W1
130-2500 m3 / h
detection principle
field of the aerial line will be blown when the audible hum. The higher the wind speed higher frequency sound, this is because the vortex formation caused by the flow of air through the wire, liquid, gas and other fluids in both This can occur, this phenomenon may be made using the vortex flow sensor. After vortex forming two pillars disposed in the pipeline, there scrollThe frequency can be measured flows. Because scroll shape into two parallel and alternating left and right, along the street lights and the like, it is known vortex. Because this phenomenon is first found Kaman, so also called Karman vortex street ultrasonic flow sensor Karman vortex air flow sensor is provided with two ultrasonic air intake passage, the main passage and the bypass passage is detected, the intake air flow rate portion is located in the main channel, the channel is disposed next to the object to be able to adjust the flow rate of the main channel, so that the detection characteristic of the main channel was ideal. That is, different displacement engines, by varying the passage section of the air flow sensor method size, one size can be used to cover a variety of air-flow rate sensor of the engine. A triangular prism and several vortex amplifier board constituting the main passage Karman vortex generator. On both sides of the Karman’s vortex generated at the oppositely disposed ultrasonic transmitter and an ultrasonic receiver belonging to the electronic detection device, these two components may be included in the sensor, the two electrical signals generated by the electronic sensor air a flow sensor control circuit (hybrid IC) shaping into the desired waveform amplified, and then inputted to the microcomputer. In order to use ultrasound scroll, the scroll on the inner wall of the channel sound absorbing materials are glued, in order to prevent irregular reflection of ultrasonic.
a pressure change detecting Karman’s vortex type air flow sensor
is alternately from both ends of the vortex swirl generator occurs, thus alternately generated at both ends of the vortex generator, so both ends of the vortex generator pressure is also alternately changes, changes in this pressure chamber is guided to the mirror through the pressure guide hole tapered vortex generators on the downstream side of the column, the mirror cavity with a fine mirror is tensioned tension band, Therefore, the tension band distortion and vibration occurs, in addition, to using the plate spring tension band with appropriate tension, whereby, in addition to vibration and pressure and changes in pressure in the vortex impact is difficult to obtain the stable and torsional vibration.
pressure caused by the vortex occurrence pressure guiding holes formed into the mirror cavity, the change is synchronized with the reflected pressure chamber, a mirror belt to form a tensioned torsion vibration. The mirror is very light, even at low flow rates, pressure conditions change is very small, the action will be. In the upper portion of the mirror, the optical sensor is arranged corresponding configuration of a light emitting diode and phototransistor, etc., the mirror reflected light is emitted by the diode, and when incident on the phototransistor, the current will become, after the waveform output circuit.
4. The air flow sensor maintenance essentials
air flow signal is engine control unit (ECU) to control the vapor concentration of the primary mixed signal, if the intake air amount is increased, the fuel injection quantity controlled by the ECU too big, and vice versa.