JP2002357465A - Air flow rate measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air flow rate measurement device capable of reducing the occurrence of output fluctuation and a measurement error due to turbulence of intake air flow and improving measurement precision. SOLUTION: In this air flow rate measurement device, a flow rate detection element measuring an air flow rate is arranged inside a bypass flow passage into which a part of air flowing through an intake passage is let flow. The cross section area of the bypass flow passage is shaped so that it is the widest in an inflow port part and gradually reduced three-dimensionally from the inflow port part to the detection element arrangement site arranged on the downstream side inside the air flow passage. The bypass flow passage is provided with an air restriction part in which the cross sectional shape of the bypass flow passage is gradually and gently increased around the arrangement center of the flow rate detection element in the upstream and downstream directions, and the restriction part is arranged only in the parallel direction to the left and right sides of the flow detection element. When height of the restriction part, a restriction length in the upstream part, and that in the downstream part are represented by h, L1, and L2 respectively, they satisfy the following relationship: 1<=L1/h, 1<=L2/h, and 2.5<a/h<=20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air flow measuring device for measuring the amount of intake air in an intake passage, and more particularly, to a bypass passage in the intake passage for introducing a part of air flowing through the intake passage of an automobile engine. The present invention relates to an air flow measuring device having the same.

[0002]

2. Description of the Related Art As a conventional technique for improving the detection accuracy of an air flow measuring device, for example, those disclosed in Japanese Patent Application Laid-Open No. H10-14020 and Japanese Patent Application Laid-Open No. H11-511262 are known. Those disclosed in these publications have a shape in which the cross section is narrowed two-dimensionally so that the side surface of the measurement flow path is tapered in the axial direction when viewed from the flow direction, and the upstream side of the narrowest part of the measurement flow path or the measurement is performed. The detection element is arranged upstream of the outlet in the flow path. The taper of the flow path in the direction of flow ensures that a uniform parallel flow of intake air is created in the area where the detection element is present, with as little disturbance as possible.

[0003]

However, according to the technique disclosed in the above publication, the measurement flow path has a shape in which only the direction perpendicular to the flow direction of the intake air is narrowed two-dimensionally. The fluctuation of the air can be reduced, but the fluctuation of the intake air on the non-throttled side cannot be suppressed. Therefore, there is a problem that the effect on the detection accuracy is not sufficient.

Further, in the above-mentioned prior art, since the detecting element is disposed at a position that can be seen from the inlet of the intake air,
If foreign matter such as dust is mixed in the intake air, the foreign matter may be reflected on the side surface (slope) of the diaphragm and hit the detection element. In the worst case, the detection element may be broken by the reflected foreign matter. There is a problem that there is. SUMMARY OF THE INVENTION In view of the above-described problems in the related art, an object of the present invention is to reduce at least a part of a bypass flow path three-dimensionally to reduce output fluctuation due to turbulence of a flow of intake air flowing into a measuring device and occurrence of a measurement error. An object of the present invention is to provide an air flow measuring device capable of suppressing the measurement and improving the measurement accuracy.

Another object of the present invention is to prevent the detection element from being damaged due to collision of foreign matter with the detection element by forming the inflow port so that the detection element cannot be seen from the inlet of the intake air. is there.

[0006]

Means for Solving the Problems To solve the above problems, the means described in claim 1 can be adopted. According to this means, the cross-sectional area of the bypass flow passage is the largest at the air inlet, and the cross-section from the air inlet to the bypass flow passage to the detection element arrangement site disposed in the downstream air passage is Has a shape gradually narrowed three-dimensionally, so that the output fluctuation of the flow detection element due to the turbulence of the flow of the intake air flowing into the air flow measuring device is smaller than the conventional bypass flow path narrowed only two-dimensionally. In addition, the occurrence of measurement errors is suppressed, and as a result, measurement accuracy can be improved.

[0007] By adopting the means of claim 2,
Fluctuation of the output of the flow rate detection element and occurrence of measurement error due to turbulence of the air to the downstream side of the detection element arrangement position are suppressed.
In addition, the cross-sectional shape of the bypass passage defined in claim 3 suppresses the output fluctuation and the measurement error of the flow rate detecting element due to the turbulence of the air around the detecting element arrangement position.

According to the fourth aspect of the present invention, by adopting the throttle shape in which the backflow is difficult to enter, it is possible to use the sensor which cannot detect the backflow. Further, according to the means of claim 5, by forming a throttle shape capable of rectifying both the forward flow and the backward flow, it is possible to use a sensor capable of detecting the backward flow. further,
According to the sixth aspect of the present invention, by adopting a shape in which the degree of restriction rapidly changes in the vicinity of the position where the detection element is disposed, it can be used when the turbulence of the upstream air flow is large.

Further, according to the means of the present invention, the diaphragm height is made different depending on the location, such as above and below the position where the detecting element is disposed, so that it can be used for controlling a system which requires tuning of pulsation characteristics. Further, according to the means of claim 8, the cross-sectional area of the bypass flow path in a predetermined range on the downstream side of the detection element arrangement site is fixed or reduced, so that it is used for controlling a system requiring a high response sensor. it can.

According to the ninth aspect of the present invention, since the flow rate detecting element cannot be seen through the inlet, the probability that the flow rate detecting element is damaged by foreign matter in the air is reduced. Further, according to the ninth to fourteenth aspects, the throttle portion is provided only in a direction parallel to the left and right sides of the sensor, the height of the throttle portion is h, the length of the upstream throttle is L1, and the length of the downstream throttle is L1. Where L2 and the width of the bypass channel are a, 1 ≦ L1
/ H, 1 ≦ L2 / h, and 2.5 <a / h ≦ 20, so that foreign matter hardly hits the sensor,
The sensor is hardly damaged even at a large flow rate, and the air flow rate can be detected with high accuracy even at a backflow.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. Throughout the drawings, the same reference numeral indicates the same thing, and the same reference numeral indicates the letter a,
Those marked with b, c, etc. represent similar ones. FIG. 1 is a schematic sectional view of a part of an intake passage of an automobile engine according to an embodiment of the present invention. In the figure, 1 is a duct through which intake air passes, 2 is a bypass passage provided in the duct 1 for measuring the amount of intake air and passes a part of the intake air, and 3 is an amount of air flowing through the bypass passage , A sensing part of the sensor 3, a sensor support member 5, a circuit for processing the output of the sensor 3, and an air inlet part 7 to the bypass passage 2. According to the embodiment of the present invention, the inlet 7 is provided at a position where the sensor 3 cannot be seen from the inlet 7. Thus, even if foreign matter is mixed in the air flowing from the inflow port 7, the probability that the foreign matter is reflected on the wall of the bypass flow path and collides with the sensor 3 can be reduced. The sensor 3 utilizes the resistance temperature characteristics of the heating resistor. The sensor 3 is mounted on the sensor support member 5 at the sensor placement site. The intake air flow rate measured by the sensor 3 is used in a system for controlling optimal air-fuel efficiency and ignition timing by a fuel injection control means.

It is desirable that the air flow in the vicinity of the sensing unit 4 be a uniform parallel flow as little as possible. In order to realize this, in the embodiment of the present invention, at least a part of the cross section of the bypass flow passage is formed in a three-dimensionally narrowed shape as described below. FIG. 2 is a perspective view of the conventional bypass flow passage 2x viewed from the air inlet. As shown in the drawing, conventionally, the throttle portions 21 and 2 are formed only on the side walls that are vertically located with respect to the sensor support member 5 in the bypass flow path 2x.
2 was provided.

FIG. 3 is a perspective view of the bypass passage according to the embodiment of the present invention, as viewed from the upstream port. As shown,
In the present embodiment, the throttle portions 21 ′ and 22 ′ of the side walls of the bypass flow passage located above and below the sensor support member 5.
In addition to the above, throttle portions 31 and 32 are also provided on the side walls of the bypass flow passage at the left and right positions of the sensor support member 4. In addition,
In the examples shown in FIGS. 2 and 3, the cross-sectional shape of the bypass passage is rectangular. Hereinafter, the left and right directions of the rectangle in the drawing are referred to as a vertical direction of the sensor or a direction parallel to the top and bottom of the sensor, and the vertical direction in the drawing is referred to as a left and right direction of the sensor or a direction parallel to the left and right of the sensor. Further, the inflow side of the bypass flow path is upstream of the air flow, and the opposite side is downstream of the air flow. Various examples of the aperture shape of the aperture section can be considered according to the specifications of the sensor.

Various examples in the embodiment of the present invention will be described with reference to FIG. However, in the example after FIG. 4,
Although the inflow port 7 is illustrated as being located at a position where the sensor 3 can be seen, it is preferable that the inflow port 7 is located at a position where the sensor 1 cannot be actually seen as shown in FIG. A first example of the present invention will be described with reference to FIGS.

FIG. 4A shows the bypass passage of FIG.
It is the figure which looked at the section cut in the A line from the direction of the illustrated arrow.
As can be seen from the figure, of the inner wall of the bypass flow passage 2a, the wall in the vertical direction of the sensor 3 is located on the side of the inlet 7 (FIG. 4).
In (A), the inlet 7 of the sensor supporting member is made thinner.
There are provided throttle portions 21a and 22a having an air flow rate gradually increasing in the downstream direction, which is the opposite side.

FIG. 4B shows the bypass passage of FIG.
It is the figure which looked at the terminal surface cut by the B line from the direction of the arrow shown. As can be seen from FIG. 5, among the inner walls of the bypass flow passage 2a, the wall in the left and right direction of the sensor 3 is thinned on the side of the inflow port 7 (left side in FIG. Throttling portions 31a and 32a of an air flow rate gradually increasing toward the side opposite to the inflow portion 7 are provided.

More specifically, in the example of FIG. 4, the throttle portions 21a, 22a, 31a, and 32a are
The aperture start position coincides with the position of the upstream end of the sensor support member 5, and the aperture end position is the position of the downstream end of the sensor support member 5. Matches. Further, the shape of the throttle portion at the throttle end portion is such that it is difficult for the backflow of air to enter the upstream side (shape in which the throttle amount suddenly becomes zero). Thus, when the sensor 3 is a sensor that cannot detect backflow, the air flow measuring device according to this embodiment can be used.

FIG. 5 is an exploded perspective view showing the bypass passage shown in FIG. 4 for easy understanding. In the figure, hatched portions are stuck together to form a bypass flow path. As can be seen from the figure, the cross section of the bypass flow path is narrowed three-dimensionally. In the following example, an exploded perspective view is omitted for simplification, but an exploded perspective view similar to FIG. 5 can be considered.

FIG. 6 is a view for explaining a second example of the embodiment of the present invention. FIG. 6 (A) shows the bypass passage of FIG.
Sectional view of a bypass flow path according to a second example of the embodiment of the present invention, in which a cross section taken along a line is viewed from a direction of an illustrated arrow;
FIG. 4B is a cross-sectional view of the bypass flow path according to a second example of the embodiment of the present invention, in which a cross-section of the bypass flow path of FIG. The difference from the example of FIG. 4 is that the diaphragms 21b, 22b, 31b,
Reference numeral 32b indicates that the restriction is started from the position of the inlet port 7. The other configuration is the same as that of FIG. As in this example, depending on the specifications of the sensor, the detection accuracy may be improved by setting the throttle start position from the position of the inflow port 7.

FIG. 7 is a view for explaining a third example of the embodiment of the present invention. FIG.
Sectional view of a bypass flow path according to a third example of the embodiment of the present invention, in which a cross section taken along a line is viewed from a direction of an arrow shown in the drawing;
FIG. 4B is a cross-sectional view of the bypass flow path according to a third example of the embodiment of the present invention, in which a cross-section of the bypass flow path of FIG. 3 taken along line BB is viewed from the direction of the illustrated arrow. The difference from the example of FIG. 6 is that in the example of FIG.
The stop by c and 32c is started from the position where the sensor 3 is arranged. Other configurations are the same as those in FIG. Thereby, the cross section from the inlet 7 of the bypass flow passage to the position immediately before the position where the sensor 3 is disposed has a shape that is gradually narrowed two-dimensionally in a direction parallel to the flow direction of the inflow air, and the position where the sensor is disposed. The cross section of only the peripheral portion has a shape gradually narrowed three-dimensionally. By adopting this configuration according to the specifications of the sensor, it is possible to suppress the output fluctuation, measurement, and occurrence of errors due to turbulence of the flow of the intake air flowing into the air flow measurement device, and improve the measurement accuracy in some cases. is there.

FIG. 8 is a view for explaining a fourth example of the embodiment of the present invention. FIG. 8 (A) shows the bypass passage of FIG.
Sectional view of a bypass passage according to a fourth example of the embodiment of the present invention, the sectional view taken along the line viewed from the direction of the illustrated arrow;
FIG. 4B is a cross-sectional view of the bypass flow path according to a fourth example of the embodiment of the present invention, in which a cross-section of the bypass flow path of FIG. The difference from the example of FIG. 4 is that the aperture portions 21d, 22d, and 31 in FIG.
d and 32d are that the contour along the direction of the air flow changes in a curved shape. Other configurations are the same as those in FIG. By adopting this configuration according to the specifications of the sensor, output fluctuations due to turbulence of the flow of intake air flowing into the air flow measuring device, measurement and generation of errors are suppressed,
In some cases, measurement accuracy can be improved.

FIG. 9 is a cross-sectional view of a bypass flow path according to a fifth example of the embodiment of the present invention, in which a cross section of the bypass flow path of FIG. B-
The cross-sectional view taken along the line B can be inferred from the above-described example, and is not shown. In this example, the throttle units 21e and 2e
The contour of 2e along the air flow direction is a curve as in the example of FIG. 8, and the throttle amount is gradually reduced in a curve further downstream from a position corresponding to the downstream end of the sensor support member 5. I have less. Other configurations are the same as those in FIG. With this configuration, it is possible to rectify both the forward flow and the backward flow, and as a result, it is possible to use a sensor of the backflow detection type.

FIG. 10 is a cross-sectional view of a bypass flow path according to a sixth example of the embodiment of the present invention, in which a cross-section of the bypass flow path of FIG. B
Since the cross-sectional view taken along line -B can be inferred from the above example,
Illustration is omitted. In this example, the contour of the throttle portions 21f and 22f along the air flow direction is the sensor support member 5
Is a curve that changes rapidly in the vicinity of. That is, the diaphragms 21f and 22f start the diaphragm in the vicinity of the position corresponding to the upstream end of the sensor support member 5, the diaphragm amount becomes maximum near the sensor 3, and then the diaphragm amount decreases toward the downstream. The throttle amount is zero near the position corresponding to the downstream end of the sensor support member 5. With such a configuration, even when the turbulence of the air flow in the upstream is large, it is possible to suppress the output fluctuation, the measurement, and the generation of the error due to the turbulence, and to improve the measurement accuracy.

FIG. 11 is a cross-sectional view of a bypass flow path according to a seventh example of the embodiment of the present invention, in which a cross-section of the bypass flow path of FIG. B
Since the cross-sectional view taken along line -B can be inferred from the above example,
Illustration is omitted. In this example, the aperture height h1 of the aperture section 21g and the aperture height h2 of the aperture section 22g are different. The aperture heights of the aperture portions 31g and 32g (not shown) may be different. By varying the aperture height in this way, it is possible to tune the pulsation characteristics.

FIG. 12 is a sectional view of the bypass flow path according to an eighth embodiment of the present invention, in which a cross section of the bypass flow path of FIG. B
Since the cross-sectional view taken along line -B can be inferred from the above example,
Illustration is omitted. In this example, the contours of the throttle portions 21h and 22h on the upstream side are the same as those shown in FIGS. 4 to 10, but the downstream side of the sensor support member 5 from the position corresponding to the sensor 3 on the downstream side. The diaphragm height is constant up to the position corresponding to the end. Then, the throttle amount is gradually reduced further downstream from a position corresponding to the downstream end of the sensor support member 5. The notches 31h and 32h (not shown) also have the same outline as the notches 21h and 22h. With this configuration, the cross-sectional area of the air flow portion of the bypass flow path is constant near the sensor 3 and there is no increase in the cross-sectional area immediately downstream of the sensor. The occurrence of measurement errors can be suppressed, and the measurement accuracy can be improved. FIG. 13 is a diagram showing a cross section of a bypass flow channel according to an example of the second embodiment of the present invention. In this embodiment, the narrowed portion 22i in the bypass channel 2i has a gentle shape in the upstream and downstream directions as in FIGS. The difference from the embodiment shown in FIGS. 9 to 12 is that, in FIG. 13, a diaphragm is not provided in a direction perpendicular to the sensor 3 and a diaphragm 22i is provided only in a direction parallel to the left and right of the sensor 3. Is provided. In FIG. 13, the height of the radial stop of the bypass flow path 2i from the throttle start position S of the bypass flow path 2i to the position P of the maximum height of the throttle is defined as h, and the elevation from the throttle start position S of the bypass flow path 2i. Bypass flow path 2 to the highest height position P of the throttle
The length of i (the length of the throttle in the upstream portion) is L1, and the length of the bypass channel 2i from the position P at the highest height of the throttle to the end position E of the throttle (the length of the throttle in the downstream portion). Is L2.
The width of the bypass channel 2i is a. FIG. 14 is a graph showing a relationship obtained by an experiment of the above h, L2, and the amount of noise at the time of pulsation. If the amount of noise at the time of pulsation is indicated by hatching in the figure, it cannot be put to practical use as an air flow measuring device. As shown, L2 / h is 1
As described above, the pulsation noise is suppressed to a value lower than a value that can be put to practical use. Therefore, it is necessary to satisfy 1 ≦ L2 / h on the downstream side. Similarly, on the upstream side, 1 ≦ L1 /
h must be satisfied. FIG. 15 is a graph showing the relationship obtained from the above experiments a and h and the detection accuracy. In the figure, if the detection accuracy is lower than the hatched portion, the device cannot be put to practical use as an air flow measuring device. As shown in the figure, it was found that the detection accuracy was higher than a practically usable value when a / h was greater than 2.5 and 20 or less. Therefore, a relationship of 2.5 <a / h ≦ 20 is required.
FIG. 13 shows an example in which the length L1 on the upstream side is asymmetric with respect to the longitudinal direction of the bypass flow path which is shorter than the length L2 on the downstream side, but it is desirable that the length L1 be symmetric (L1 = L2). FIG. 16 is a diagram showing a cross section of a bypass flow channel according to a second example of the second embodiment of the present invention. In this example, the throttle portion 22j has a symmetrical shape in the longitudinal direction of the bypass flow path, and has a cross section obtained by cutting off a part of a sphere. FIG. 17 is a diagram showing a cross section of a bypass flow channel according to a third example of the second embodiment of the present invention. In this example, the aperture portion 22k is symmetrical, and has a trapezoidal cross section. FIG. 18 is a diagram showing a cross section of a bypass flow channel according to a fourth example of the second embodiment of the present invention. In this example, the throttle section 221 has a symmetrical shape, and has a triangular cross section. FIG. 19 is a diagram showing a cross section of a bypass flow channel according to a fifth example of the second embodiment of the present invention.
In this example, the aperture portion 22m has a symmetrical shape, and has a substantially trapezoidal cross section with a longer upper side than that of the example in FIG. Since L1 = L2 = L in any of the aperture shapes shown in FIGS. 16 to 19, it is desirable to satisfy the following relationship: 1 ≦ L / h2.5 <a / h ≦ 20. FIG. 20 is a sectional view taken along line AA ′ of the bypass passage shown in FIGS. 16 to 19. that's all,
According to the embodiment shown in FIGS. 13 to 20, it is difficult for foreign matter to hit the sensor 3, and the probability of the sensor 3 being damaged even at a high flow velocity is reduced. Further, a parallel flow of the intake air can be created in the area where the sensor 3 exists, and the backflow can be rectified well, so that the air flow rate can be accurately detected. FIG. 21 is a graph showing an experimental result of the relationship between the air flow velocity and the presence or absence of breakage in the second embodiment. As shown in the figure, according to the second embodiment of the present invention, it was found that there was no breakage even if the flow velocity was higher than in the past. In the figure, the mark x indicates the case where the sensor was damaged, and the mark ○ indicates the case where the sensor was not damaged. If the flow velocity is lower than the shaded area, it cannot be used as an air flow measuring device. FIG. 22 is a graph of an experimental result in which the relationship between the output flow rate conversion value and time in the second embodiment is compared with the actual air amount, the second embodiment of the present invention, and the conventional example. . As shown in the figure, it has been found that the output flow conversion amount at the time of backflow is closer to the actual air flow rate in the second embodiment of the present invention than in the related art.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a part of an intake passage of an automobile engine according to an embodiment of the present invention.

FIG. 2 is a perspective view of a conventional bypass passage 2 viewed from an air inlet.

FIG. 3 is a perspective view seen from an air inlet of a bypass flow channel according to the embodiment of the present invention.

4A is a view of a cross section of the bypass flow path of FIG. 3 taken along the line AA viewed from the direction of the arrow shown in FIG. 3, and FIG. 4B is a view of the bypass flow path of FIG. It is the figure which looked at the terminal surface from the direction of the illustration arrow.

FIG. 5 is an exploded perspective view showing the bypass flow path shown in FIG. 4 for easy understanding.

FIG. 6 is a diagram illustrating a second example of the embodiment of the present invention.

FIG. 7 is a diagram illustrating a third example of an embodiment of the present invention.

FIG. 8 is a diagram illustrating a fourth example of an embodiment of the present invention.

FIG. 9 is a diagram illustrating a fifth example of an embodiment of the present invention.

FIG. 10 is a diagram illustrating a sixth example of an embodiment of the present invention.

FIG. 11 is a diagram illustrating a seventh example of the embodiment of the present invention.

FIG. 12 is a diagram illustrating an eighth example of the embodiment of the present invention.

FIG. 13 is a diagram showing a cross section of a bypass flow channel according to an example of the second embodiment of the present invention.

FIG. 14 is a graph showing a relationship obtained by an experiment of h, L2, and a noise amount during pulsation.

FIG. 15 is a graph showing a relationship obtained by experiments of a and h and detection accuracy.

FIG. 16 is a diagram showing a cross section of a bypass flow channel according to a second example of the second embodiment of the present invention.

FIG. 17 is a diagram showing a cross section of a bypass flow channel according to a third example of the second embodiment of the present invention.

FIG. 18 is a diagram showing a cross section of a bypass flow channel according to a fourth example of the second embodiment of the present invention.

FIG. 19 is a diagram showing a cross section of a bypass flow channel according to a fifth example of the second embodiment of the present invention.

FIG. 20 is a diagram illustrating the bypass flow path A- shown in FIGS. 16 to 19;
FIG. 3 is a sectional view taken along line A ′.

FIG. 21 is a graph showing an experimental result of a relationship between an air flow velocity and the presence or absence of breakage in the second embodiment.

FIG. 22 is a graph of experimental results comparing the relationship between the output flow rate conversion value and time in the second embodiment with the actual air amount, the second embodiment of the present invention, and a conventional example. .

[Explanation of symbols]

2a to 2j: bypass flow path 3: sensor (detection element) 4: sensing part 5: sensor support member 7: inflow part 21a to 21h, 22a to 22m: throttle part 31a to 31d, 32a to 32d: throttle part h1, h2: height of the diaphragm h: height of the diaphragm in the second embodiment L1: length of the bypass flow path from the start position of the diaphragm to the top position of the diaphragm L2: bypass from the top position of the diaphragm to the end position of the diaphragm Length of flow path a ... Width of bypass flow path

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Takao Iwaki 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Inside Denso Corporation (72) Inventor Yasushi Goka 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Denso Corporation F term (for reference) 2F030 CC14 CE11 CF01 CF02 2F035 AA02 EA03

Claims (14)

[Claims] 1. An air flow measuring device in which a flow detecting element for measuring an air flow is disposed inside a bypass flow passage through which a part of air flowing through an intake passage flows, wherein a cross-sectional area of the bypass flow passage is smaller than that of the bypass flow passage. The cross section from the inflow port to the detection element disposed in the air passage on the downstream side is maximum at the inflow port of the air into the flow path, and has a shape gradually narrowed three-dimensionally. Characteristic air flow measurement device. 2. The air flow measuring device according to claim 1, wherein the cross section of the bypass flow path has a shape gradually narrowed to a predetermined position on the downstream side of the air with respect to the detection element arrangement site. 3. A cross section from the inlet of the bypass flow passage to a position immediately before the detection element disposition portion has a shape gradually narrowed two-dimensionally in a direction parallel to a flowing direction of the inflowing air. 3. The air flow measuring device according to claim 1, wherein a cross section of only a peripheral portion of the part has a shape gradually narrowed three-dimensionally. 4. The air flow measurement device according to claim 1, wherein a throttle shape of a cross section of the bypass flow path around the detection element disposition portion has a throttle shape in which a backflow is difficult to enter. 5. The throttle shape of a cross section of the bypass flow path around the detection element arrangement site is a throttle shape capable of rectifying both forward flow and reverse flow.
An air flow measurement device as described. 6. The throttle shape of a cross section of the bypass flow path in the vicinity of the detection element disposition portion is a shape in which the degree of restriction changes rapidly near the detection element disposition portion. 3. The air flow measuring device according to 1 or 2. 7. The throttle shape of the cross section of the bypass flow path in the vicinity of the detection element disposition portion is such that the throttle height on one side wall of the bypass flow path is different from the throttle height on the other side wall. 3. The method according to claim 1, wherein
An air flow measurement device as described. 8. The throttle shape of the cross section of the bypass flow path around the detection element arrangement site is a shape in which the cross-sectional area up to a predetermined position on the downstream side of the detection element installation region is constant or reduced. The air flow measuring device according to claim 1 or 2, wherein 9. The air flow measuring device according to claim 1, wherein the inlet is located at a position where the flow detecting element cannot be seen from the inlet. 10. An air flow measuring device in which a flow rate detecting element for measuring an air flow rate is arranged inside a bypass flow path through which a part of air flowing through an intake passage flows, wherein the bypass flow path has a cross-sectional shape. A throttle portion for air that gradually increases in the upstream and downstream directions around the arrangement position of the flow rate detection element, and the throttle section is provided only in a direction parallel to the left and right sides of the flow rate detection element, The height of the throttle unit is h, the length of the bypass channel from the throttle start position to the vertex position of the throttle unit is L1, the length of the bypass channel from the vertex position of the throttle unit to the throttle end position is L2, An air flow measuring device characterized by satisfying 1 ≦ L1 / h1 ≦ L2 / h2.5 <a / h ≦ 20, where a width of the bypass channel is a. 11. The air flow measuring device according to claim 10, wherein the throttle portion has an asymmetric shape with respect to a longitudinal direction of the bypass flow path with respect to the vertex position. 12. The air flow measuring device according to claim 10, wherein the throttle portion has a shape symmetrical with respect to a longitudinal direction of the bypass flow path with respect to the vertex position. 13. The air flow measuring device according to claim 12, wherein the throttle portion has a shape of a part of a sphere. 14. The air flow measuring device according to claim 12, wherein the throttle section has a trapezoidal shape.