JPH05126611A - Air flow meter and internal combustion engine therewith - Google Patents

Abstract

(57) [Summary] [Purpose] In an air flow meter, any drift in the cross section of the air passage can be reduced, accurate measurement can be performed, and a simple configuration is realized, which is practical and versatile in structural design. Improve. A main air passage (2) and an auxiliary air passage (3) having an axial auxiliary air passage (3a) protruding into the main air passage (2) parallel to the air flow direction and a radial sub air passage (3b) orthogonal to the air flow direction are formed. In the air flow meter having the main body 1 and the air flow rate detecting elements 4 and 5 arranged in the auxiliary air passage 3a in the axial direction for detecting the intake air amount, the main body 1 is arranged from the arrangement portion of the air flow rate detecting elements 4 and 5. Also has a curved pipe portion 1a on the upstream side, and the inlet opening of the axial sub air passage 3a in which the air flow rate detecting elements 4 and 5 are arranged has a diameter on the opposite side of the curved pipe portion from the central position of the main air passage 2. Located outside the direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air flow meter for detecting the intake air flow rate of an internal combustion engine for automobiles.

[0002]

2. Description of the Related Art An air flow meter for detecting the intake air flow rate of an internal combustion engine for an automobile has a structure in which an air cleaner in an upstream passage or a duct with a large angle is connected,
When the upstream passage and the duct are eccentrically connected to each other, the flow velocity distribution in the cross section of the air passage largely changes, and the degree of the uneven flow increases. In particular, the air cleaner element used to remove dust and the like contained in the intake air in the air cleaner upstream of the air flow meter is gradually polluted by dust and the like, so the flow velocity distribution in the air passage cross-section tends to change. .. If such a drift exists, the measurement error of the measured flow rate value of the air flow meter with respect to the true air flow rate value becomes large, and it has a significant adverse effect on engine control when mounted on an internal combustion engine of an automobile or the like. There was a problem.

In order to solve the above problems, it is necessary to provide a means for making the flow velocity distribution in the cross section of the air flow meter uniform. As an example of this means, it is conceivable to make the length of the upstream side passage 3 to 10 times the diameter of the passage, but in this case, from the point of view of the structural design of the air flow meter and also the layout in the engine room. Also from the point of view, it is difficult to secure a space for arranging such a large air flow meter, and it is not practical.

Another means for reducing the uneven flow in the cross section of the air passage of the air flow meter as described above is disclosed in JP-A-61-65053.
Japanese Patent Laid-Open Publication No. 64-26112. First, in the air flow meter described in JP-A-61-65053, a block body is installed in the main air passage, and a sub air passage having an inlet at the center of the main air passage is arranged in the block body.
It is configured to install an air flow rate detection element in this sub air passage, and by measuring the flow rate flowing in the sub air passage,
Measure the air flow rate through the main air passage. Thus, when the inlet of the sub air passage is located in the center of the main air passage, it is relatively insensitive to the drift.

Next, the air flow meter disclosed in Japanese Patent Laid-Open No. 64-26112 is provided with a rectifying body for correcting a drift in the upstream side of the main air passage. Normally, the structure of this rectifying body has a uniform mesh, but in this conventional example, by changing the roughness, size, depth, etc. of the rectifying body, it is possible to prevent uneven flow. It adopts the means to correct the drift by matching the ventilation resistances which are almost proportional to the flow velocity distribution.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the air flow meter described in Japanese Patent No. 053, when the degree of deviation of the air passage cross section of the air flow meter is small, the inlet of the sub air passage is located at the center of the main air passage, so the influence of the deviation is relatively small. However, this effect can no longer be expected when the degree of drift is increased, and it is easily affected. Also,
In the air flow meter described in Japanese Patent Laid-Open No. 64-26112, the drift can be reduced regardless of the degree, but a rectifying body that matches the drifts of various patterns is necessary, which hinders the standardization of the air flow meter. Become.

In view of the above problems, it is an object of the present invention to reduce any drift in the cross section of an air passage, enable accurate measurement, and have a simple structure, practicality in structure design and general purpose. It is to provide an air flow meter having high performance.

[0008]

In order to achieve the above-mentioned object, the present invention is provided with a main air passage for supplying air to an engine and a projecting opening in the main air passage, which is installed parallel to the air flow direction. A main body forming an axial sub air passage and a sub air passage having a radial sub air passage opening to the main air passage which is installed orthogonally to the air flow direction, and an axial sub air of the sub air passage. An air flow rate detection element for detecting the amount of intake air disposed in the passage, and the radial sub air passage is formed by closing the groove portion of the bridge portion provided in the main body with a plate-like passage cover. In the air flow meter, the main body has a bent pipe portion upstream of the air flow rate detection element arrangement portion, and the axial auxiliary air passage in which the air flow rate detection element is arranged is the center of the main air passage. The bent pipe from the position And it is located radially outward of the opposite side of the.

Further, it may be characterized in that an inlet cross-sectional area of the bent pipe portion is larger than a cross-sectional area of an air flow rate detecting element arrangement portion of the main body.

Further, the main body can be constructed by combining two main body portions divided by a plane parallel to the plane including the radial direction of the curved pipe section.

The main body is composed of a bent pipe portion and a straight pipe portion.
It can be configured by combining two pipe parts.

The main body may be integrated with a throttle body located downstream of the main body.

Further, in an air flow meter having a main body forming a main air passage for supplying air to the engine and an air flow rate detecting element arranged in the main air passage for detecting an intake air amount, the main body is An inlet flow section of the bent tube section is larger than an air flow rate detection element placement section of the main body of the main body, and the air flow rate is further increased. The detection element may be located radially outside of the central position of the main air passage opposite to the curved pipe portion.

Further, the main body can be constructed by combining two main body portions divided in the circumferential direction of the curved pipe portion.

Furthermore, the internal combustion engine according to the invention comprises at least one of the air flow meters according to the invention.

[0016]

According to the present invention, since the main body of the air flow meter has the curved pipe portion upstream of the portion where the inlet opening of the axial auxiliary air passage is arranged, the flow velocity distribution of the air in the curved pipe portion is the secondary flow. Due to the occurrence of the flow velocity, the flow is corrected to a constant flow velocity that is slow on the inner side in the radial direction on the same side as the curved pipe section and has a high velocity distribution on the outer side on the opposite side to the curved pipe section. Also, the range of the fast flow velocity distribution on the outside is wide, and the inlet opening of the axial auxiliary air passage in which the air flow rate detecting element is installed is located on the outside in the radial direction on the side opposite to the bent pipe portion. The intake air amount in a portion where the flow velocity is stable can be detected in a wide range, and the output characteristic is also stable. Therefore, even if a change occurs in the flow state on the upstream side of the air flow meter and a drift occurs on the upstream side of the air flow meter, the flow rate can be accurately measured without being affected by the change.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An air flow meter according to an embodiment of the present invention will be described below with reference to FIGS.
Will be described in detail with reference to.

First, the structure of the air flow meter according to this embodiment will be described. FIG. 1 is a sectional view of an air flow meter according to this embodiment. The main body 1 of this air flow meter has a bent pipe portion 1a in which an air introduction portion on the upstream side is bent at about 90 °, and a straight pipe portion 1b is arranged on the downstream side thereof. The main body 1 has a main air passage 2 for supplying air to the engine.
And an L-shaped sub air passage 3 that has an axial sub air passage 3a that projects into the main air passage 2 and is parallel to the air flow direction, and a radial sub air passage 3b that is orthogonal to the air flow direction. The sub air passage outlet 6 is formed at the most downstream portion of the radial air passage 3b. Radial air passage 3b
Is formed by closing the groove portion of the bridge portion 3A provided in the main body 1 with the plate-shaped member 7, and the plate-shaped member 7 is fixed to the bridge portion 3A by tightening with the set screw 8. In such a structure, air enters from the left side of the bent pipe portion 1a in the figure and passes through the main air passage 2 composed of the bent pipe portion 1a and the straight pipe portion 1b, and a part of the air flows through the sub air passage 3. Flows downward through the figure.

In the axial sub air passage 3a, as a flow rate detecting element, a heat generating resistor 4 for detecting the flow rate of air,
A heat-sensitive resistor 5 for detecting the intake air temperature is arranged, and these are supported by support pins 4a and 5a, respectively. An electronic control module 10 is installed on the outside of the straight pipe portion 1b via an O-ring 9. The electronic control module 10 is provided with a heating resistor 4 and a thermosensitive resistor 5 via the instruction pins 4a and 5a. Each is connected. The electronic control module 10 converts the air flow rate detected by the heating resistor 4 and the air temperature detected by the heat-sensitive resistor 5 into a voltage output, and controls the electronic fuel injection device as information on the intake air flow rate and the intake air temperature. It has the function of sending to the device. Further, the inlet opening of the axial sub air passage 3a in which the air flow rate detecting elements 4 and 5 are arranged is located radially outside of the center position of the main air passage 2 on the side opposite to the curved pipe portion.

In the above structure, the inlet opening of the axial sub air passage 3a for the air flowing into the straight pipe portion 1b from the curved pipe portion 1a upstream of the inlet opening of the axial sub air passage 3a is arranged. The velocity distribution in the cross section at the position is corrected so as to be faster inside the bend. Further, the flow velocity distribution in the radial outside position of the curved pipe portion is stable in a wide range from the center of the straight pipe portion 1b in which the inlet opening of the axial sub air passage 3a is arranged, and the flow velocity can be measured in this range. In this case, the output noise of the air flow meter can be suppressed to a low level.

Next, regarding the principle that the flow velocity distribution of the air supplied to the air flow meter is corrected by the curved pipe section,
This will be described with reference to FIGS. 2 and 3. 2 is a diagram schematically showing a state of the air flow in the bent pipe portion when the air flow having a constant flow velocity is supplied to the bent pipe portion.
FIG. 2A is a diagram showing a flow velocity in a cross section along a plane including the radial direction of the curved pipe portion, and FIG. 2B is a diagram showing a flow velocity in a transverse cross section in the middle of the curved pipe portion. Further, FIG. 3 is a diagram for explaining the flow velocity distribution in the cross section of the straight pipe portion, FIG. 3 (a) is a schematic view showing the cross-sectional position of the main body, and FIG. 3 (b) is in FIG. 3 (a). BB cross section,
That is, FIG. 3C shows the flow velocity distribution by the constant flow velocity line in the cross section immediately after the end of the bent portion, and FIG.
It is a figure which shows the flow velocity distribution by the constant flow velocity line in the cross section further downstream than (b). The flow in the bent pipe portion 1a is regarded as a swirling flow around the center of the bend, and therefore centrifugal force acts. The magnitude of this centrifugal force is affected by the flow velocity of air,
Since the centrifugal force acting on the fluid part in the central part where the flow velocity is high becomes larger than the centrifugal force acting on the fluid part in which the flow velocity is slow near the wall surface, the fluid in the center part is pushed outward in the radial direction on the side opposite to the curved pipe part. , It bends along the pipe wall and wraps around inward in the radial direction on the same side as the pipe portion. Therefore, a secondary flow as shown in FIG. 2A can be made in the cross section of the bent pipe portion. In the curved pipe portion, due to the secondary flow and the separation of the flow caused by the sudden increase in pressure along the radially inner wall surface on the same side as the curved pipe portion, the main flow in the central portion is outward. When pushed, the position of the maximum velocity is corrected so as to be biased toward the radially outer side opposite to the curved pipe portion at the end of the curved pipe portion as shown in FIG. 2 (b). In addition, the bent pipe section 1 located upstream
3 (b) and 3 (c) show the cross-sectional flow velocity distribution of the air that has entered the straight pipe portion 1b of the main body 1 from a in the straight pipe portion 1b in which the inlet opening of the axial auxiliary air passage 3a is arranged. As shown in FIGS. 3B and 3C, at the radially outer position on the side opposite to the curved pipe portion with respect to the center of the main air passage 2 in which the inlet opening of the axial sub air passage 3a is arranged. As shown in the range (1) in the figure of c), the isovelocity lines are not complicated, and the flow velocity distribution is stable in a wide range. Therefore,
When the flow velocity is measured in the vicinity of this, the influence of the output noise of the air flow meter and the pulsating flow from the engine can be suppressed to a small level, and the accurate air flow rate can be measured.

Next, the results of experiments conducted by the present inventors using the air flow meter shown in FIG. 1 will be described with reference to FIG. In FIG. 4, an air cleaner attached to an actual vehicle is installed on the upstream side of the air flow meter according to the present embodiment, and the air cleaner is rotated 180 ° with respect to the initial reference angle to impart a drift, thereby measuring the air flow rate ( It is a figure showing how much an error occurs to a measured value when output voltage) is a standard angle. In addition, this is the result when the air cleaner is attached at the angle that shows the maximum change in the output voltage error.
The horizontal axis represents the air flow rate, and the vertical axis represents the output voltage error of the air flow rate detection element. In the figure, the solid line (this embodiment) is the value in the air flow meter according to the present embodiment shown in FIG. 1, and the broken line (conventional example) is obtained by removing the bent pipe portion 1a from the main body 1 of this embodiment. It is a value obtained by an air flow meter having a structure having only the straight pipe portion 1b. According to FIG. 4, the air flow meter according to the conventional example has a large output error especially on the low flow rate side, but the air flow meter according to the present embodiment has a small output voltage error regardless of the magnitude of the air flow rate and has excellent performance. Is shown.

Next, a modification of the air flow meter according to this embodiment will be described with reference to FIGS. 5 to 9. First,
The air flow meter shown in FIG. 5 gradually reduces the cross-sectional area from the entrance portion of the bent pipe portion 1c of the main body 1A to the straight pipe portion so that the air flow rate is more inward than the cross-sectional area of the entrance portion of the bent pipe portion 1c. The configuration is such that the cross-sectional area of the portion where the inlet opening of the axial sub air passage 3a in which the detection elements 4 and 5 are installed is arranged is made small. According to this modified example, since the throttling action is applied when the air passes through the curved pipe portion 1c, the difference in velocity between the radially outer side and the inner side of the curved pipe portion after passing is shown in FIG. Is larger than when using an air flow meter. That is, the correction amount by the bent pipe portion is increased, and more accurate and stable air flow measurement can be performed.

FIGS. 6 and 7 are views for explaining an example of manufacturing an air flow meter main body having a bent pipe portion as shown in FIG. 1 or 5. Since it is very difficult to remove a main body having a bent pipe portion such as used in the air flow meter according to the present invention by a mold, it is common to divide the body into several main body portions (pieces) to produce the body. Is considered to be. In the manufacturing example shown in FIG. 6, the two main body portions 11a, 1 divided by a plane parallel to the plane including the radial direction of the bent pipe section.
This is a manufacturing example in which 1b is combined and bonded by ultrasonic welding or the like. In this case, since there is a bridge portion 3A for forming a sub air passage inside the main body and it is difficult to divide the main body in the circumferential direction of the curved pipe portion, as shown in FIG. It is desirable to divide by a plane parallel to the plane including the radial direction. According to this production example, the main body can be easily produced, and it is particularly effective when the main body is made of plastic. On the other hand, the manufacturing example shown in FIG. 7 is a manufacturing example in which the main body is bent and two pipe parts divided into a straight pipe part 12a and a straight pipe part 12b are combined. In the air flow meter manufactured according to this manufacturing example, the bent pipe portion can be easily removed, so that the body can be standardized. That is, when the influence of uneven flow is large, the one provided with the bent pipe portion 12a is attached, and when it is attached to an air cleaner or the like having a small influence of the uneven flow, the bent pipe portion 12a is removed and only the straight pipe portion 12b is attached. ..

FIG. 8 is a view showing a modified example in which the main body of the air flow meter according to the present invention and the throttle body located downstream thereof are integrated. 8, the main body 1B of the air flow meter shown in FIG. 1 and the throttle main body 13 are integrally formed. The throttle main body 13 includes a throttle shaft 14, a throttle valve 15 for adjusting the air flow rate, and a throttle lever 16. It is installed. According to this modification, the structure can be simplified by integrating the air flow meter main body 1B and the throttle main body 13.

Further, FIG. 9 is a diagram showing a modified example in which the air flow meter shown in FIG. 1 is applied to an electronic fuel injection type internal combustion engine. In FIG. 9, the air 18 sucked from the air cleaner 17 is an air flow meter main body 1 and a throttle main body 13 having an idle control valve 19 for controlling the air flow rate at idle and the throttle valve 15 described above.
Is mixed with the fuel supplied from the injector 20, passes through the intake valve 21, and is then sucked into the engine cylinder 22. Piston 23 in engine cylinder 22
The mixed gas of fuel and air compressed by is exploded by the spark ignited by the spark plug 24 to rotate the engine, and thereafter, the exhaust gas 2 is discharged from the exhaust valve 25.
It is discharged as 6. The oxygen concentration of the exhaust gas 26 is detected by the O ₂ sensor 27, and the signal is feed-hacked to the control device 28. This signal is compared with the signal from the electronic control module 10 of the air flow meter by the control device 28, and based on this result, the opening degree of the idle control valve 19 and the injector 20.
Of the fuel injection amount and the ignition timing of the spark plug 23 are controlled. According to this modification, in the electronic fuel injection type internal combustion engine, the accurate air flow rate is measured by the air flow meter, and the measured value and the oxygen amount by the O ₂ sensor 27 are compared and processed to obtain the optimum ignition condition. The opening degree of the idle control valve 19, the fuel injection amount of the injector 20, and the ignition timing of the spark plug 23 can be adjusted so that In this modification,
Although the air flow meter shown in FIG. 1 is applied, it goes without saying that any of the air flow meters shown in FIGS. 5 to 8 can be applied in addition to this.

Next, an air flow meter according to another embodiment of the present invention will be described with reference to FIGS. 10 to 12. The embodiment shown in FIG. 10 is similar to the embodiment shown in FIG. 5 from the inlet portion of the curved pipe portion 1e of the main body 1C to the straight pipe portion 1e.
The cross-sectional area of the curved pipe section 1 is gradually reduced toward f
Air flow rate detection element 4, 5 rather than the cross-sectional area of the inlet of e
The cross-sectional area of the portion where the is installed is reduced. However, in the present embodiment, the sub-air passage 3 as in the embodiment shown in FIG. 5 is not provided, and the air flow rate detecting elements 4, 4 are directly located on the radially outer side of the main air passage 2 opposite to the curved pipe portion. 5 and an electronic control module 10 are provided. According to the present embodiment, as in the embodiment of FIG. 5, when the air passes through the bent pipe portion 1e, the throttling action is added, and the bent pipe portion 1e is increased.
As a result, the correction amount is increased, and more accurate and stable air flow measurement becomes possible. In addition, this does not require providing a bridge portion forming a sub air passage in the main body 1C or attaching a plate-like member, so that the structure is simple and the assembly is easy, and the influence of uneven flow is relatively large. It is effective when installed in an institution that does not have it.

In the embodiment shown in FIG. 11, the air flow rate detecting elements 4 and 5 and the electronic control module 10 of the air flow meter shown in FIG. 10 are arranged inside the bent pipe portion 1g. In this case, the heating resistor 4 and the temperature sensitive resistor 5
The supporting pins 5a and 5b for supporting the respective members are made longer than in the case of the embodiment shown in FIG. 10, and the heat generating resistor 4 and the temperature sensitive resistor 5 are bent pipe portions from the center of the main air passage 2 as described above. It is installed at a position where the velocity distribution on the outer side in the radial direction on the opposite side is stable over a wide range. According to the present embodiment, the electronic control module 10 is installed on the inner side in the radial direction on the same side as the bent pipe portion, so that it is not necessary to secure a large installation space. Therefore, when it is mounted in the engine room, it is suitable when the structure of the embodiment shown in FIGS. 1 and 5 has no space.

Next, FIG. 12 is a view for explaining an example of manufacturing the air flow meter main body of the embodiment shown in FIG. 10 or FIG. 11, in which FIG. 12 (a) is a front view and FIG. 12 (b) is FIG. In this case as well, it is very difficult to remove the main body having the bent tube portion by the mold, and therefore it is considered that it is common to manufacture the body by dividing it into several main body portions (pieces). In the manufacturing example shown in FIG. 12, the two main body portions 11c and 11 are divided in the circumferential direction of the bent pipe portion.
This is a manufacturing example in which d is combined and bonded by ultrasonic welding or the like. According to this production example, the main body can be easily produced, and it is particularly effective when the main body is made of plastic. In this case, since there is no bridge portion or the like for forming the sub air passage inside the main body, not only the circumferential direction of the bent pipe portion but also the radial direction of the bent pipe portion is included as shown in FIG. It can also be manufactured by combining two body parts divided by a plane parallel to the plane. Further, as shown in FIG. 7, it is also possible to manufacture it by combining two pipe parts of a bent pipe part and a straight pipe part.
According to the above two manufacturing examples, the same effects as those described in the manufacturing examples of FIGS. 6 and 7 can be expected.

Further, the air flow meter according to the embodiment shown in FIGS. 10 to 12 can be applied to an internal combustion engine of electronic fuel injection type as shown in FIG.

[0031]

According to the present invention, a bent pipe portion is provided on the upstream side of the main body of an air flow meter, and the air passing through the bent pipe portion is slower on the inner side in the radial direction on the same side as the bent pipe portion and is opposite to the bent pipe portion. Since it is corrected to a constant drift that causes a fast and stable flow velocity distribution on the outer side in the radial direction on the side, the influence of the drift before entering the air flow meter is reduced, and accurate measurement can be performed. Moreover, it is possible to provide an air flow meter having a simple structure and high practicality and versatility in structural design.

[Brief description of drawings]

FIG. 1 is a sectional view of an air flow meter according to an embodiment of the present invention.

FIG. 2 is a diagram showing a state of the air flow in the bent pipe portion when an air flow having a constant flow velocity is supplied to the bent pipe portion, and FIG. 2 (a) is a view showing a surface including a radial direction of the bent pipe portion. A sectional view taken along the line (b) is a transverse sectional view in the middle of the bent pipe portion.

3A and 3B are views for explaining a flow velocity distribution in a straight pipe section, wherein FIG. 3A is a schematic diagram showing a cross-sectional position of a main body, and FIG. 3B is a diagram showing a flow velocity distribution in a BB cross section by iso-velocity lines. , (C) are diagrams showing the flow velocity distribution of the C-C cross section by the constant flow velocity lines.

FIG. 4 is a diagram comparing experimentally the influence of drift in one example according to the present invention and in the conventional example.

5 is a diagram showing a modification of the air flow meter shown in FIG.

FIG. 6 is a view showing one example of manufacturing the air flow meter main body shown in FIG. 1 or FIG.

FIG. 7 is a view showing another example of manufacturing the air flow meter main body shown in FIG. 1 or FIG.

FIG. 8 is a view showing a modified example in which a main body of an air flow meter according to the present invention and a throttle body located downstream thereof are integrally structured.

9 is a diagram showing a modified example in which the air flow meter shown in FIG. 1 is applied to an electronic fuel injection type internal combustion engine.

FIG. 10 is a sectional view of an air flow meter according to another embodiment of the present invention.

FIG. 11 is a diagram showing a modification of the air flow meter shown in FIG.

12A and 12B are views showing a manufacturing example of the air flow meter main body shown in FIG. 10 or FIG. 11, in which FIG. 12A is a front view and FIG.

[Explanation of symbols]

 1, 1A, 1B, 1C, 1D Main body 1a, 1c, 1e, 1g Curved pipe portion 1b, 1d, 1f, 1h Straight pipe portion 2 Main air passage 3 Sub air passage 3A Bridge portion 3a Axial sub air passage 3b Radial direction Sub-air passage 4 Heat-generating resistor 5 Heat-sensitive resistor 6 Sub-air passage outlet 7 Plate-like member 10 Electronic control module 11a, 11b, 11c, 11d Main body portion 12a Bent pipe portion 12b Straight pipe portion 13 Throttle body

Claims (8)

[Claims] 1. A main air passage for supplying air to an engine, an axial auxiliary air passage projecting in the main air passage and opened to be parallel to the air circulation direction, and installed orthogonally to the air circulation direction. And a main body having a sub air passage having a radial sub air passage opening to the main air passage, and an air flow rate detecting element arranged in the axial sub air passage of the sub air passage to detect an intake air amount. In an air flow meter having
The main body has a bent pipe portion upstream of the air flow rate detection element arrangement portion, and an inlet opening of the axial sub air passage in which the air flow rate detection element is arranged is located from a central position of the main air passage. An air flow meter, which is located radially outside of the curved pipe portion. 2. The air flow meter according to claim 1, wherein an inlet cross-sectional area of the bent pipe portion is larger than a cross-sectional area of a portion of the main body where the air flow rate detecting element is arranged. 3. The body according to claim 1, wherein the body is constructed by combining two body portions divided by a plane parallel to a plane including a radial direction of the curved pipe section. Air flow meter. 4. The air flow meter according to claim 1, wherein the main body is configured by combining two pipe portions, a curved pipe portion and a straight pipe portion. 5. The air flow meter according to claim 1, wherein the main body is integrated with a throttle body located downstream of the main body. 6. An air flow meter, comprising: a main body that forms a main air passage for supplying air to an engine; and an air flow rate detection element that is disposed in the main air passage and detects an intake air amount, wherein the main body is the An inlet flow section of the bent tube section is larger than an air flow rate detection element placement section of the main body of the main body, and the air flow rate is further increased. The air flow meter, wherein the detection element is located radially outside of the central position of the main air passage opposite to the curved pipe portion. 7. The air flow meter according to claim 7, wherein the main body is configured by combining two main body portions that are divided in the circumferential direction of the bent pipe portion. 8. An internal combustion engine equipped with the air flow meter according to claim 1. Description: