JPH11118556A - Air flow rate-measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce measurement errors because of installation displacements by generating the flow rate signal of an air path from the output of a flow rate-measuring element set in a bypass passage of the air path and curving an outer wall face of the bypass passage in a flow direction. SOLUTION: A part of the air flowing in a suction pipe 11 is separated and introduced to a bypass passage 18 and a Venturi tube part 16. The air entering the bypass passage 18 joins at the downstream side where a flow of the air of the Venturi tube part 16 becomes fast, and accelerates a bypass flow by the suction force of an outflow opening 22. A temperature difference to the detected temperature of a heat-sensitive element 30 is controlled to be constant by a current of a heat-generating element 29 exposed to the bypass flow. A flow rate of the sucked air is measured from a current value of the heat-generating element 29. At this time, the size relationship of the sectional areas A1, A2, A3 of an upstream path 18a, a bend part 18b, a downstream path 18c of the bypass passage 18 is set to hold A1<A2 and A1<A3. A vena contracta brought about at the lower stream side than the bend part 18b is restricted. Measurement accuracy for the flow rate is improved accordingly.

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 an air flow rate in an air passage by measuring an air flow rate flowing through a bypass flow passage arranged in the air passage.

[0002]

2. Description of the Related Art Conventionally, this type of air flow measuring device has been used for measuring the intake air flow rate of an internal combustion engine. For example, a flow measuring pipe protruding in the center direction is assembled to an intake pipe of an internal combustion engine, and a space inside the flow measuring pipe is partitioned into an upstream side and a downstream side by a partition wall except for an upper part, so that the inside of the flow measuring pipe is reversed. Forming a U-shaped bypass flow path,
An air flow measuring device that allows a part of the air flowing in the intake pipe to flow into the bypass flow path from the inlet on the upstream side of the flow measurement pipe and flows out into the intake pipe from the outlet on the downstream side of the flow measurement pipe is known. Have been. Then, a flow rate measuring element (heating element) and a temperature sensing element are installed in the bypass flow path, and the bypass flow rate and, accordingly, the intake air flow rate are determined based on the power supplied to the flow rate measuring element and the temperature detected by the temperature sensing element. Measure. In this device, by forming the bypass flow path in an inverted U-shape, the overall length of the bypass flow path is lengthened to increase the inertia of the air in the bypass flow path, thereby pulsating the air flow in the intake pipe. The pulsation of the bypass flow due to the pulsation is reduced, and the flow measurement accuracy is prevented from lowering due to the pulsation.

[0003]

In recent years, there has been a demand for an improvement in measurement accuracy in a low flow rate region due to the expansion of the intake flow rate measurement range and the tightening of emission regulations accompanying the increase in output of an internal combustion engine. Therefore, it is necessary to increase the flow rate of the bypass flow even in a low flow rate region. However, when the bypass flow path is formed in an inverted U-shape as in the above-described air flow measurement device, the bypass flow is curved. Due to the rapid 180 ° turn at the section, the flow inertia during the turn causes a strong contraction immediately after the bend, increasing the flow resistance and reducing the flow velocity of the bypass flow. For this reason, in the low flow rate region, the flow velocity of the bypass flow cannot be sufficiently secured, and the flow rate measurement accuracy deteriorates.

In order to solve this drawback, a shell-shaped flow rate measuring member is arranged at the center of the intake pipe, a bypass flow path is formed at the center of the flow rate measuring member, and the outlet of the bypass flow path is connected to the flow rate outlet. 2. Description of the Related Art There is known an air flow measuring device that opens on an outer peripheral surface of a measuring member. In this case, since the flow path cross-sectional area of the intake pipe is narrowed by the flow rate measuring member, the flow velocity of the air flowing along the outer peripheral surface of the flow rate measuring member increases, and the suction force (negative pressure) is applied to the outlet of the bypass flow path. In order to increase the flow rate of the bypass flow.

However, in the above-mentioned air flow measuring device, in order to increase the suction force acting on the outlet of the bypass flow passage, the outer diameter of the flow measuring member is increased to narrow the flow passage cross-sectional area of the intake pipe. ing. For this reason, the ventilation resistance of the intake pipe increases, and the intake efficiency decreases. Therefore, in the air flow measuring device disclosed in Japanese Patent Application Laid-Open No. 8-327422, the circuit section and the bypass flow path section are formed as an integrated module, and the support section connecting the circuit section and the bypass flow path section is provided with a bypass flow path section. The shape is such that the dynamic pressure generated by the air flow in the intake pipe is smaller than that of the inlet face, thereby reducing the ventilation resistance of the intake pipe and improving the intake efficiency. Specifically, the width of the support portion in the direction perpendicular to the air flow direction is made smaller than the width of the portion forming the inlet portion of the bypass flow passage, or the shape of the support portion is cylindrical or in the air flow direction. Streamlined according to

However, in the air flow measuring device disclosed in Japanese Patent Application Laid-Open No. 8-327422, since the side surface of the bypass flow path constituting the bypass flow path has a planar shape, the air flow measurement device when the module is mounted on the intake pipe is not provided. There is a problem that a measurement error due to a variation in the mounting angle with respect to the module rotation direction is large. The present invention has been made in order to solve such a problem, and an object of the present invention is to provide an air flow measuring device capable of reducing a measurement error due to a mounting displacement.

Another object of the present invention is to provide an air flow measuring device capable of increasing the speed of a bypass flow without increasing airflow resistance and suppressing output fluctuation.

[0008]

According to the air flow measuring device of the first aspect of the present invention, a bypass is provided in an air passage and forms a bypass flow passage through which a part of air flowing through the air passage flows. A curved surface portion is provided on at least the outer wall surface of the air passage in the air flow direction of the air passage. For this reason, separation of the air flow near the bypass passage in the air passage can be suppressed, and the air flow can be smoothed. Therefore, it is possible to reduce a measurement error due to a variation in the mounting angle with respect to the module rotation direction when the module including the bypass flow path and the circuit is installed in the air passage.

Further, by suppressing separation of the air flow near the bypass passage in the air passage, the pressure loss in the air passage can be reduced. Furthermore, since the bypass flow is stabilized by smoothing the air flow near the bypass passage in the air passage, output fluctuations can be suppressed. According to the air flow measuring device according to the second aspect of the present invention, the curved surface portion is provided from the outer wall surface in the air flow direction to the outer wall surface on the inlet side and the outlet side in the direction perpendicular to the air flow in the air passage of the bypass flow passage portion. Therefore, the measurement error due to the mounting displacement can be further reduced, the pressure loss in the air passage can be further reduced, and the output fluctuation can be further suppressed.

According to the air flow measuring device of the third aspect of the present invention, the outermost outermost wall of the outer wall in the air flow direction and the innermost innermost wall of the outer wall in the airflow direction are separated. Since the vertical distance between the air flow and the air flow in the air passage is within a predetermined range, measurement errors due to misalignment can be reliably reduced, pressure loss in the air passage is reliably reduced, and output fluctuation is reliably suppressed. be able to.

According to the air flow measuring device of the present invention, the bypass flow path is formed into an inverted U-shaped flow path in which two adjacent parallel flow paths are connected by a bent portion. By increasing the total length of the bypass passage, pulsation of the bypass flow due to pulsation of the air flow in the air passage can be reduced.
Furthermore, by forming the curved portion of the bypass flow passage and the downstream flow passage in a shape that suppresses the contraction flow that occurs downstream of the bend portion, the flow velocity is prevented from decreasing due to the contraction flow, and the flow velocity of the bypass flow is reduced even in a low flow rate region. As a result, the flow measurement accuracy can be improved.

In this case, even if the cross-sectional area of the flow path near the boundary between the bent portion and the downstream flow path is made larger than the cross-sectional area of the upstream flow path, and the cross-sectional area of the flow path is gradually changed. Good.
This effectively suppresses the contraction that occurs downstream of the bend. Also, the flow path cross-sectional area of the entire downstream flow path of the bypass flow path may be larger than the flow path cross-sectional area of the upstream flow path. In other words, since the contraction occurs in the downstream flow path, the effect of suppressing the contraction can be obtained even if the flow path cross-sectional area of the entire downstream flow path is increased.

Alternatively, the cross-sectional area of the bent portion of the bypass flow path may be larger than the cross-sectional area of the upstream flow path. As described above, when the flow path cross-sectional area of the bent portion is increased,
The direction change of the flow in the bend becomes gentle, and the contraction generated by the inertia of the flow immediately after the bend is reduced. Further, it is preferable that the flow rate measuring element is installed in a place where the cross-sectional area of the bypass flow path is small. That is, in a place where the cross-sectional area of the bypass flow passage is small, the flow velocity of the bypass flow is increased, and stable flow measurement can be performed.

[0014] Further, the flow rate measuring element may be provided in the upstream flow path of the bypass flow path. Because the flow rate of the bypass flow is faster and more stable in the upstream flow path compared to other parts,
If a flow measurement element is installed in the upstream flow path, stable flow measurement can be performed.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 5 show an air flow measuring device according to an embodiment of the present invention. As shown in FIGS. 2 and 3, a module 13 of the air flow measuring device is assembled in a mounting hole 12 formed at a predetermined position of an intake pipe 11 as an air passage of the internal combustion engine by a plug-in method. The module 13 includes a circuit module 14 as a circuit section and a flow rate measuring body 15 as a bypass flow path section.
Consists of The flow rate measuring body 15 is attached to the mounting hole 12 as a whole.
, And is formed in a cylindrical shape extending to near the central axis C of the intake pipe 11.

As shown in FIG. 1, the flow rate measuring body 15 has an outer wall surface 150 in the air flow direction in the intake pipe 11 and an intake pipe 1.
1, an outer wall surface 156 on the inlet side in the vertical direction with respect to the air flow in
Outer wall surface 1 on the outlet side in the vertical direction with respect to the air flow in intake pipe 11
55. Outer walls 150, 155 and 15
6 are each formed in a convex curved shape. The outer wall surface 150 is provided in the entire axial direction of the flow measurement body 15,
A curved surface shape is formed in the entire area in the axial direction. Outer wall 1
56 is provided from a flange portion 20 to be described later of the flow rate measuring body 15 to an inflow port 19 to be described later.
Are formed in the entire area in the axial direction. Outer wall 15
Numeral 5 is provided from a flange portion 20 of the flow rate measuring body 15 to an outlet 22 to be described later, and a curved surface shape is formed on the entire outer wall surface 155 in the axial direction. Furthermore, the outer wall 150
A connecting portion 151 between the outer wall surface 156 and the outer wall surface 156 is formed in a convex curved shape, and a connecting portion 153 between the outer wall surface 150 and the outer wall surface 155 is also formed in a convex curved surface shape. Outer wall 15
0, 155 and 156, and connecting parts 151 and 153
And constitute a curved surface portion. The outer wall surface 150 is provided with an outermost portion 152 located at the outermost position on the outer wall surface 150 at a substantially central portion in the air flow direction in the intake pipe 11. The outermost portion 152 is farthest away from the connection portions 151 and 153 on the outer wall surface 150 in a direction perpendicular to the airflow in the intake pipe 11. The connection parts 151 and 153 constitute the innermost part located on the outermost part on the outer wall surface 150.

As shown in FIGS. 2 and 3, the flow measuring body 15 is configured such that two pipes extending along the rear direction of the intake pipe 11 are arranged side by side along the air flow direction of the intake pipe 11, and the joining wall 17 is provided.
The two parallel flow paths 18a adjacent to each other
An inverted U-shaped bypass flow path 18 is formed by connecting the bent portions 18c with the bent portions 18b. The relationship between the cross-sectional area A1 of the upstream flow path 18a, the cross-sectional area A2 of the bent portion 18b, and the cross-sectional area A3 of the downstream flow path 18c of the bypass flow path 18 is represented by A1 <A2 and A1 < By setting A3, the contraction generated downstream of the bent portion 18b is suppressed.

An inflow port 19 through which a part of the air (main flow) flowing in the intake pipe 11 flows into the bypass flow path 18 is provided on the upstream side surface of the flow measurement body 15.
Is formed to be adjacent to. In addition, the flow measurement body 1
A flange portion 20 is formed on the outer peripheral portion of the upper end of 5, and this flange portion 20 is locked (stopped) on the upper surface of the peripheral portion of the mounting hole 12.

On the other hand, a venturi tube 16 is integrally formed at the lower end of the flow measuring body 15 in parallel with the main flow direction, and the inlet 21 of the venturi tube 16 and the inlet 19 of the bypass passage 18 are connected to each other by the intake pipe. 11 are close to each other with the central axis C interposed therebetween. An outlet 22 of the bypass flow path 18 is formed on the downstream peripheral wall of the Venturi tube 16, and the Venturi tube 1
The flow (bypass flow) of the bypass flow path 18 is merged with the flow (Venturi flow) in the Venturi pipe part 16 on the downstream side of 6, ie, near the throat.

Further, on the downstream side peripheral wall of the Venturi tube section 16, a flow path enlarging section 23 for enlarging the flow path cross-sectional area of the Venturi tube section 16 at a portion where the bypass flow from the bypass flow path 18 joins is provided in the circumferential direction. It is formed to extend. By forming the upstream end face of the enlarged flow path portion 23 into a slope shape, a guide portion 24 for guiding the bypass flow toward the downstream side of the venturi tube 16 is formed at the outlet 22 of the bypass flow passage 18. Have been.

The venturi pipe portion 16 is formed so that the outer diameter increases toward the downstream side, and the air flow path between the outer peripheral surface of the venturi pipe portion 16 and the inner peripheral surface of the intake pipe 11 It becomes narrower on the downstream side. As a result, the airflow in the intake pipe 11 becomes faster toward the downstream side of the Venturi pipe 16, and the main flow increases the suction force acting on the outlet of the Venturi pipe 16, so that the Venturi pipe 1
The flow velocity of the air in 6 increases.

On the other hand, the upper end opening of the flow measuring body 15 is closed by the circuit module 14. On the lower surface of the circuit module 14, a heating element 29 as a flow rate measuring element is provided.
The heating element 29 and the temperature sensing element 30 are assembled at predetermined intervals by supporting members 31 and 32, respectively.
a. Here, the reason why the heating element 29 is installed in the upstream flow path 18a is that the flow path cross-sectional area A1 of the upstream flow path 18a in the bypass flow path 18 is the smallest, and the flow velocity of the bypass flow in the upstream flow path 18a is small. This is because the flow rate is the highest, and the flow rate measurement accuracy is improved when the flow velocity of the bypass flow is high. In addition, the temperature sensing element 30 is preferably installed near the heating element 29 within a range that is not affected by the heat radiation of the heating element 29 in order to measure the temperature of the air touching the heating element 29.

Inside the circuit module 14, there is provided a circuit board 33 for controlling the energization of the heating element 29 and the temperature sensing element 30, and a side portion of the circuit module 14 for connecting a wire harness (not shown). The connector 34 is insert-molded. An intake air temperature sensor 35 is insert-molded on the lower surface side of the circuit module 14 so as to protrude downward.
5, the temperature of the air flowing through the intake pipe 11 (intake temperature) is detected.

The flange portion 20 at the upper end of the flow measurement body 15 is joined to the fitting protrusion 36 on the lower surface of the circuit module 14 by fusion or adhesion or the like, and an O-ring 37 attached to the outer periphery of the fitting protrusion 36 is provided. This seals the inner part of the mounting hole 12. Then, the screw 39 is inserted into the screw insertion hole of the fixing piece 38 formed on the side of the circuit module 14 and screwed into the screw hole of the mounting flange 40 formed on the intake pipe 11, so that the air flow measuring device 13 is used. It is assembled to the mounting hole 12 of the intake pipe 11 by a plug-in method.

The air flow measuring device 1 configured as described above
In 3, a part of the air flowing in the intake pipe 11 flows into the bypass flow path 18 and the venturi pipe section 16 separately. The air (bypass flow) that has flowed into the bypass flow path 18 is located on the downstream side of the venturi tube 16 where the flow velocity of the air is high,
It merges with the air flow (Venturi flow) in the Venturi tube section 16. At this junction, a suction force acts on the outlet 22 of the bypass passage 18 by the Venturi flow, thereby increasing the flow velocity of the bypass flow. Then, the bypass flow rate and thus the intake air flow rate are measured based on the power supplied to the heating element 29 exposed to the bypass flow and the temperature detected by the temperature sensing element 30. That is, the current (heating temperature) of the heating element 29 is controlled so that the temperature difference from the detected temperature (intake temperature) of the temperature-sensitive element 30 becomes constant. Measure.

In this case, it is necessary to increase the flow velocity of the bypass flow touching the heating element 29 in order to improve the flow measurement accuracy. Since the bypass flow path 18 is formed in an inverted U-shape, it is unavoidable that contraction occurs immediately after the bent portion 18b due to the inertia of the flow when the bypass flow is changed in direction at the bent portion 18b. When the contraction becomes strong, the flow resistance increases, and the flow velocity of the bypass flow decreases.

Therefore, in this embodiment, the bypass passage 18
The relationship between the cross-sectional area A1 of the upstream flow path 18a, the cross-sectional area A2 of the curved path 18b, and the cross-sectional area A3 of the downstream flow path 18c is set as Al <A2 and A1 <A3. This suppresses the contraction that occurs downstream of the bent portion 18b. That is, as compared with the cross-sectional area A1 of the upstream flow path 18a, the cross-sectional area A of the bent portion 18b and the downstream flow path 18c is compared.
2. When A3 is increased, the direction change when flowing from the upstream flow path 18a to the downstream flow path 18c via the curved portion 18b becomes gentle, and the contraction generated by the inertia of the flow immediately after the curved portion 18b causes Bends 18b
And the pressure loss due to the friction between the inner wall surface of the downstream flow passage 18c and the air are also reduced by the increase in the cross-sectional area of the flow passage.
The flow from 8b to the outlet 22 via the downstream flow path 18c becomes smoother, and the flow velocity of the bypass flow touching the heating element 29 becomes higher than before. In addition, the bypass passage 18
Is formed in an inverted U-shape, the overall length of the bypass flow path 18 is increased, the pulsation of the bypass flow due to the pulsation of the air flow in the intake pipe 11 can be reduced, and the speed of the bypass flow is increased. In addition, the flow measurement accuracy can be improved.

Next, as shown in FIG.
The distance between the air flow in the intake pipe 11 and the vertical direction to the connection parts 151 and 153 is represented by L, and the L dimension, the output fluctuation width of the heating element 29, and the module of the air flow measuring device in the intake pipe 11 FIG. 5 shows the relationship between the pressure loss and the pressure loss due to the pressure loss. FIG. 6 shows that the L dimension is zero and the intake pipe 1
1 is a module 13 of an air flow measurement device provided with a flow measurement body 115 having an outer wall surface 159 in the air flow direction in the inside 1 as a plane.
0 is shown as a comparative example. Other components that are substantially the same as those in this embodiment are denoted by the same reference numerals.

In the comparative example shown in FIG. 6, since the outer wall surface 159 is flat, the air flow near the flow rate measuring body 115 in the intake pipe 11 is separated, and the air flow is disturbed. For this reason, as shown in FIG. 5, the pressure loss in the intake pipe 11 becomes relatively large. Furthermore, the flow rate measuring body 11 in the intake pipe 11
5 is disturbed, the flow measurement body 11
5, the bypass flow becomes unstable, and as shown in FIG.
The fluctuation range of the output of the heating element 29 is relatively large. Furthermore, when the module 130 is installed in the intake pipe 11, a measurement error due to a variation in the mounting angle with respect to the rotation direction of the module 130 becomes relatively large.

On the other hand, in the present embodiment, the outer wall surface 150 and the connecting portions 151 and 153 are formed into a curved shape, and the L dimension is set to a predetermined range of 1 mm to 3 mm as shown by a dotted line in FIG. The separation of the air flow near the flow measurement body 15 in the inside can be suppressed, and the air flow can be smoothed. Therefore, it is possible to reduce a measurement error due to a variation in the mounting angle with respect to the rotation direction of the module 13 when the module 13 is installed in the intake pipe 11.
Further, by suppressing the separation of the air flow near the flow measurement body 15 in the intake pipe 11, the pressure loss in the intake pipe 11 can be reduced as shown in FIG. Therefore, the output of the internal combustion engine can be improved. Further, by smoothing the air flow near the flow measurement body 15 in the intake pipe 11, the bypass flow in the bypass flow path 18 in the flow measurement body 15 is stabilized, and as shown in FIG. 29 can be suppressed from varying.

In the embodiment of the present invention described above, the venturi tube 16 is formed at the lower end of the flow measuring body 15, and the outlet 22 of the bypass flow path 18 is opened to the downstream peripheral wall of the venturi tube 16. As a result, the suction force can be efficiently applied to the outlet 22 of the bypass flow channel 18 by the high-speed air flow flowing in the venturi tube section 16, and the flow velocity of the bypass flow can also be increased.

The means for applying a suction force to the outlet 22 of the bypass passage 18 is not limited to the venturi tube section 16, and various structures can be considered. Therefore, according to the present invention, the suction force may be applied to the outlet of the bypass flow path without using the venturi tube. In the present embodiment, the heating element 29 is installed in the upstream flow path 18a in consideration of the fact that the upstream flow path 18a has the smallest flow passage cross-sectional area and the bypass flow velocity is the fastest among the bypass flow paths 18. To improve the flow measurement accuracy. However, the location of the heating element 29 is not limited to the upstream channel 18a. If there is a location where the downstream channel 18c has a small channel cross-sectional area and a high flow velocity, the heating element 29 is installed there. You may.

In the present embodiment, since the module 13 can be assembled by the plug-in method, the place where the module 13 is assembled is not limited to the intake pipe 11, but may be an air cleaner, a throttle body or the like. If a mounting hole of a predetermined size is formed in another member constituting a part, the module 13 can be assembled very easily, and the module 13 can be shared and the cost can be reduced.

The present invention is not limited to a device for measuring an intake air amount of an internal combustion engine, but can be used as a device for measuring a flow rate of air flowing through various air passages.

[Brief description of the drawings]

1A and 1B are diagrams showing a module of an air flow measuring device according to an embodiment of the present invention, wherein FIG. 1A is a sectional view taken along line AA of FIG. 1B, and FIG. 1B is a front view.

FIG. 2 is a longitudinal left side view showing an assembled state of the air flow measuring device according to one embodiment of the present invention.

FIG. 3 is a vertical sectional front view showing an assembled state of the air flow measuring device according to one embodiment of the present invention.

FIG. 4 is an enlarged view of FIG.

FIG. 5 is a data diagram showing a relationship between an L dimension of a curved surface of a side surface portion of the flow measurement body, an output fluctuation width of a heating element, and a pressure loss by an air flow measurement device in an intake pipe.

6A and 6B are diagrams showing a module of an air flow measuring device according to a comparative example, wherein FIG. 6A is a sectional view taken along line AA of FIG. 6B, and FIG. 6B is a front view.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Intake pipe (intake passage) 13 Module 14 Circuit module (Circuit part) 15 Flow rate measuring body (Bypass flow path part) 16 Venturi pipe part 17 Joining wall 18 Bypass flow path 18a Upstream flow path 18b Bent part 18c Downstream flow path Reference Signs List 19 inflow port 20 flange section 22 outflow port 29 heating element (flow rate measurement element) 30 temperature sensing element 150, 155, 156 outer wall surface (curved surface portion) 151, 152 connection portion (innermost portion) 152 outermost portion

Claims (4)

[Claims] 1. A bypass passage provided in an air passage and configured to allow a part of air flowing through the air passage to flow therein,
A bypass flow path unit including a flow rate measurement element for measuring an air flow rate provided in the bypass flow path; and a circuit for outputting a signal related to an air flow rate flowing through the air passage based on an output signal of the flow rate measurement element. And a curved surface portion provided on an outer wall surface of at least the air passage in the air flow direction of the bypass flow passage portion. 2. The air conditioner according to claim 1, wherein the curved surface portion is provided from an outer wall surface in the air flow direction to an outer wall surface on an inlet side and an outlet side in a direction perpendicular to an air flow in the air passage of the bypass flow passage portion. Item 7. An air flow measuring device according to Item 1. 3. A distance in a direction perpendicular to the air flow of the air passage between an outermost outermost surface of the outer wall surface in the air flow direction and an innermost innermost surface of the outer wall surface in the air flow direction. 3. The air flow measuring device according to claim 2, wherein the distance is within a predetermined range. 4. The device according to claim 1, wherein the bypass passages are adjacent to each other.
Are formed in an inverted U-shaped flow path in which the two flow paths are connected by a bent portion, one of which is disposed on the upstream side, the other flow path is disposed on the downstream side, and the bent portion and the downstream side flow path are 4. The air flow measuring device according to claim 1, wherein the air flow measuring device is formed in a shape that suppresses a contraction generated downstream of the bent portion.