JP2014095619A - Air flow rate measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air flow rate measuring device 1 small in size with an inexpensive configuration and excellent in versatility, capable of reducing pressure loss in an air duct 2, and suitable for measuring an amount of intake air in an internal combustion engine 4.SOLUTION: In an air flow rate measuring device 1, a device body 10 is detachably assembled to an air duct 2, and provided with first and second flow paths 11 and 12 for forming bypass flows B and C of a main flow path 2a and a third flow path 13 for connecting both the flow paths. Then, a throttle 14 enables formation of an air flow B1 reaching the main flow path 2a through the second flow path 12, the third flow path 13, and the first flow path 11. An air flow rate flowing through the third flow path 13 is measured by using a flow sensor 5. Consequently, in the air duct 2, there is no special requirement for processing and a structure (throttle) in accordance with air flow rate characteristics, while accomplishing enhancement of versatility of the air duct 2 and further, reduction of pressure loss in the air duct 2.

Description

  The present invention relates to an air flow rate measuring apparatus suitable for measuring, for example, a flow rate of intake air sucked into an internal combustion engine (hereinafter also referred to as intake air amount).

[Conventional technology]
Conventionally, various types of air flow measuring devices of this type have been proposed and put to practical use. However, since they are arranged in an air duct and measure the air flow, There is known an air flow rate measuring device devised so as not to be affected by backflow caused by dust such as dust or backfire (for example, see Patent Document 1).

The conventional air flow rate measuring device described in Patent Document 1 has a structure as shown in FIG. 6 and has an overall configuration including an air duct 100 as a central functional component.
In other words, the air duct 100 itself is provided with a throttle 101, and an egg-shaped flow meter body 102 is disposed on the upstream side in the immediate vicinity of the throttle 101, and an air passage penetrating in the axial direction around the flow meter main body 102. 103 and a measurement passage 104 branched from the passage 103 in the outer diameter direction, and a flow rate sensor 105 is provided in the measurement passage 104.
As a result, the main flow A (solid arrow) flowing in the air duct 100 is throttled by the throttle portion 101 and the flow meter main body 102, and by this throttle effect, a bypass flow as shown by the arrow S is formed in the measurement passage 104, and the air flow rate Is to measure.
According to the above configuration, the dust entering the air passage 103 penetrates the passage 103 due to its inertia, so that it can be prevented from entering the measurement passage 104, and the backflow D ( A broken line arrow) also flows preferentially through the straight air passage 103, and dust such as soot can be prevented from entering the measurement passage 104.

[Problems of the prior art]
However, since the air flow rate measuring apparatus having the above configuration is provided with the throttle portion 101 in the air duct 100 itself, the pressure loss of the main flow A flowing through the air duct 100 is large, and the flow rate characteristic must be sacrificed accordingly. And since it is the structure by which the apparatus is completed as a whole including the air duct 100, the air duct 100 must be changed according to the flow rate characteristics, and the versatility is poor. In particular, when measuring the intake air amount of an internal combustion engine, the flow characteristics of the internal combustion engine are diverse, so a variety of devices are required, and the mounting space around the internal combustion engine is very strict, so the physique There was a risk that there would be restrictions on mounting.

US Pat. No. 4,776,213

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an air flow measuring device that is excellent in versatility with a small, inexpensive configuration and can reduce pressure loss in an air duct. There is.

[Means of Claim 1]
The invention according to claim 1 (air flow rate measuring device) is assembled with an air duct having a main flow path through which air to be measured flows, and the air duct crossing the main flow path from the outside to the first flow. A flow path forming member having a path, a second flow path, and a third flow path, and a flow rate sensor that is disposed in the third flow path and measures a flow rate of air flowing through the third flow path.
The first flow path and the second flow path form a bypass flow path that takes in part of the air (main flow) flowing through the main flow path and flows as a bypass flow, and the first flow path is located upstream and flows. The first large channel having a large channel cross-sectional area and the first small channel positioned on the downstream side and having a small channel cross-sectional area are configured, and the first small channel has a larger flow velocity than the bypass flow flowing through the second channel. A bypass flow channel for flowing a bypass flow is formed, and the first small flow channel and the second flow channel of the first flow channel are communicated with each other through the third flow channel, so that the main flow channel is connected to the second flow channel, A forward bypass flow that reaches the main flow path through the third flow path and the first flow path is formed.

According to the invention of claim 1 having the above-described configuration, since the air flow rate measurement function can be completed by the flow path forming member and the flow rate sensor, the flow rate forming the central functional component is small and inexpensive. Since the path forming member and the flow sensor can be detachably incorporated in the air duct, the air duct does not require special processing and structure (throttle) according to the air flow characteristics, and the versatility of the air duct is improved. Can do.
Further, since the air duct itself does not have a throttle structure, pressure loss in the air duct can be reduced.
Therefore, an air flow rate measuring device suitable for a device that is used in a severe environment such as an internal combustion engine is provided with a small and inexpensive configuration, excellent versatility, and can reduce pressure loss in an air duct. be able to.

BRIEF DESCRIPTION OF THE DRAWINGS It is typical sectional drawing with which it uses for description of the whole structure of the intake air amount measuring apparatus for internal combustion engines as a representative example of the air flow measuring apparatus of this invention (Example 1). (Example 1) which is a perspective view of the central function part of an air flow measuring device. (Example 2) which is sectional drawing of the center function part of an air flow measuring device. (Example 3) which is sectional drawing of the central function part of an air flow measuring device. (Example 4) which is sectional drawing of the center function part of an air flow measuring device. It is sectional drawing of the conventional air flow measuring device (conventional example).

Hereinafter, the best mode for carrying out the present invention will be described in detail according to four embodiments shown in the drawings.
Each of the embodiments is a representative example of an air flow rate measuring device according to the present invention, and is applied to an air flow rate measuring device (intake air amount measuring device for an internal combustion engine) for measuring an intake air flow rate (intake air amount) of an internal combustion engine. An application example is shown.

In the following description, first, feature points in each embodiment of the present invention and basic functions of the present invention will be described in order, and finally, effects of each feature point of the present invention will be summarized and listed.
In each embodiment, the same or equivalent parts are denoted by the same reference numerals, and redundant description is omitted.

[Example 1]
First, the overall configuration and function of the air flow measuring device of the present invention will be described with reference to FIGS. 1 and 2.

〔Constitution〕
The air flow rate measuring device 1 is disposed in an air duct 2 and measures the flow rate (intake amount) of intake air taken into the internal combustion engine 4 from an air intake 3 such as an air cleaner. A flow sensor 5 for measurement is built in. Then, the intake air amount signal from the flow sensor 5 is supplied as one of the input signals to an electronic device (ECU) 6 that controls the operation state of the internal combustion engine 4, so that the operation state of the internal combustion engine 4 is appropriately set. It is the same as a conventionally known apparatus in that it is controlled.

The air duct 2 connects an air intake 3 such as an air cleaner and an intake manifold of the internal combustion engine 4 and has a main flow path 2a through which air to be measured (intake air) flows as a main flow A (solid arrow). ing.
In the following description, regarding the air flowing through the air duct 2 (main flow path 2a), the flow from the air intake 3 side toward the internal combustion engine 4 side (solid arrow) is referred to as “forward flow” or “forward flow”. The flow in the opposite direction (broken arrow) is referred to as “reverse flow” or “reverse flow”. However, the terms “upstream” and “downstream” are always names based on forward flow. For example, in FIG. 1, the left end (air intake 3 side) is the upstream side and the right end (internal combustion engine 4 side). ) Means the downstream side.

The present invention is characterized in that the air flow rate measuring device 1 is detachably assembled to the air duct 2 so as to cross the main flow path 2a from the outside.
The air flow rate measuring device 1 has the following specific configuration including the arrangement structure of the flow rate sensor 5 described above.

The apparatus main body 10 is formed of a general heat-resistant resin, for example, PBT (polybutylene terephthalate resin). It is comprised from the flow-path formation part (flow-path formation member) 10b protruded inside. Further, in the apparatus main body 10, the flange portion 10a has a disk shape, whereas the flow path forming portion 10b has a rectangular column shape having a rectangular cross section.
The apparatus main body 10 is arranged in the main flow path 2 a so that the long side of the flow path forming portion 10 b is parallel to the main flow A with respect to the air duct 2.

The flow path forming portion 10b is formed with three flow paths, a first flow path 11, a second flow path 12 and a third flow path 13 having a circular cross section.
The 1st flow path 11 and the 2nd flow path 12 are spaced apart up and down along the long side, and each penetrates the flow path formation part 10b. Therefore, the first flow path 11 and the second flow path 12 form a bypass flow path that takes in part of the air (main flow A) flowing through the main flow path 2a and flows it as bypass flows B and C.

In particular, the first flow path 11 includes a first large flow path 11a located on the upstream side and having a large flow cross-sectional area and a first small flow path located on the downstream side and having a small flow cross-sectional area by the tapered throttle 14. 11b. Accordingly, a bypass flow B having a flow velocity larger than that of the bypass flow C flowing through the second flow path 12 due to the narrowing effect of the throttle 14 flows through the first small flow path 11b on the downstream side.
The second channel 12 has the same diameter and the same channel cross-sectional area over the entire length, and only the first small channel 11b has the same diameter and the same flow as the second channel 12 in the first channel 11. It has a road cross-sectional area.

The third flow path 13 is arranged so as to be orthogonal to the first flow path 11 and the second flow path 12, one end being the first small flow path 11 b of the first flow path 11 and the other end being the second flow. The first small flow path 11b and the second flow path 12 are communicated with each other, and open to the path 12 respectively.
The third flow path 13 is provided with a flow rate sensor 5 that measures the flow rate (intake amount) of air passing therethrough. The flow sensor 5 is electrically connected to an electronic device (ECU) 6 via a signal processing unit (not shown) that performs a predetermined process on the measured intake air amount signal.

[Action / Effect]
Next, the operation and effect of the air flow rate measuring apparatus 1 having the above configuration will be described.

During normal operation of the internal combustion engine 4, a forward flow flows in the air duct 2. A part of the main flow A introduced from the air intake 3 and flowing through the main flow path 2a is taken into the first flow path 11 and the second flow path 12 of the air flow rate measuring device 1 to become the bypass flows B and C. Supplied to the engine 4.
Here, the first small channel 11b and the second channel 12 of the first channel 11 have the same diameter and the same channel cross-sectional area. However, the first small channel 11b is bypassed by the throttling effect of the throttle 14. The flow rate of the flow B is larger than that of the bypass flow C that flows through the second flow path 12.
As a result, a forward bypass flow B1 from the main flow path 2a of the air duct 2 to the main flow path 2a through the second flow path 12, the third flow path 13, and the first small flow path 11b of the first flow path 11 is formed. Is done.
Since the bypass flow B1 has a more stable air flow than the main flow A, the flow rate sensor 5 can accurately measure the intake air amount.

Since the first flow path 11 and the second flow path 12 are straight paths parallel to the main flow A, the third flow path 13 is orthogonal to the flow paths 11 and 12, so Dust such as dust that has entered the flow path 11 (first large flow path 11a) and the second flow path 12 does not move toward the third flow path 13 and the flow sensor 5 due to its inertial force. It penetrates through the (first small flow path 11b) and the second flow path 12, and returns to the main flow path 2a.
Further, when backfire or the like is generated in the internal combustion engine 4 and the backflow D is generated, a part of the backflow D enters the first flow path (first small flow path 11b) and the second flow path 12. The dust such as soot contained in the backflow D passes through the first flow path 11 (first large flow path 11a) and the second flow path 12 without being directed toward the third flow path 13 and the flow rate sensor 5 by inertia force. It penetrates and returns to the main flow path 2a.

Accordingly, it is possible to prevent the flow rate sensor 5 from being damaged due to dirt or damage due to dust.
In addition, the air flow rate measuring device 1 can complete the air flow rate measuring function with the device main body 10 (the flow path forming unit 10b and the flow rate sensor 5), and the device main body 10 forming the central part of the device 1 is air-conditioned. Since the air duct 2 can be detachably incorporated into the duct 2, the air duct 2 does not require any special processing or structure (throttle) according to the air flow characteristics, and the versatility of the air duct 2 can be enhanced.
Moreover, since the air duct 2 itself does not have a throttle structure, pressure loss in the air duct 2 can be reduced.

[Example 2]
Next, a second embodiment of the present invention will be described based on FIG. 3 with a focus on differences from the first embodiment.

  The air flow rate measuring device 1 according to the second embodiment is configured such that, when the backflow D is generated, a part of the airflow also actively flows into the third flow path 13. 12 is devised.

The second flow path 12 is provided with a reverse-tapered throttle 15 that increases in diameter toward the downstream side. By this restriction 15, the second flow path 12 is divided into a second small flow path 12a located on the upstream side and having a small cross-sectional area and a second large flow path 12b located on the downstream side and having a large cross-sectional area. Has been.
The second small flow path 12a and the second large flow path 12b have the same diameter and the same cross-sectional area as the first small flow path 11b and the first large flow path 11a of the first flow path 11, respectively. However, when the reverse flow D enters the respective flow paths, the air flow D1 flowing through the second small flow path 12a of the second flow path 12 is caused to flow in the first flow path 11 by the throttling effect by the restriction 15. The flow velocity becomes larger than the air flow D2 flowing through the first small flow path 11b.

Further, the third flow path 13 communicates the first small flow path 11 b of the first flow path 11 and the second small flow path 12 a of the second flow path 12. Therefore, during forward flow in which the main flow A flows, as in the first embodiment, the second flow path 12 (second small flow path 12a) passes through the third flow path 13 to the first small flow path 11b of the first flow path 11. When a reverse flow B1 flowing in the forward direction is generated and a reverse flow D is generated, the second small flow of the second flow path 12 is passed from the first small flow path 11b of the first flow path 11 to the third flow path 13. A reverse flow D3 in the reverse direction flowing in the flow path 12a is generated.
The third flow path 13 is provided with a flow sensor 5A having a backflow detection function (means) as a flow sensor.
For example, a semiconductor chip sensor is known as a flow rate sensor that detects forward flow and reverse flow separately, and such a known sensor can be used as a flow rate sensor 5A with a reverse flow detection function (means). .

According to the above configuration, when the reverse flow D is generated in the air duct 2, a reverse bypass flow D <b> 3 that partially flows from the first flow path 11 through the third flow path 13 to the second flow path 12 is generated. Since the air flows in the third channel 13 in the opposite direction to the forward flow, the flow sensor 5A can detect that the reverse flow has occurred.
Note that dust such as soot entering the first flow path 11 and the second flow path 12 together with the bypass flows D2 and D1 when the reverse flow D is generated is directed toward the third flow path 13 and the flow sensor 5A by inertial force. Without passing through the first flow path 11 and the second flow path 12 and returning to the main flow path 2a, the flow rate sensor 5A is not adversely affected by dust.
Therefore, it is needless to say that the same operation and effect as in the first embodiment can be obtained also in the second embodiment.

[Example 3]
Next, a third embodiment of the present invention will be described based on FIG. 4 with a focus on differences from the first embodiment.

  The air flow rate measuring device 1 according to the third embodiment is configured such that dust during forward flow does not further enter the third flow path 13.

  Specifically, in the first small flow path 11 b and the second flow path 12 of the first flow path 11, the connecting portion with the third flow path 13 is more than the first small flow path 11 b and the second flow path 12. Middle flow path portions 11c and 12c having a slightly larger flow path cross-sectional area are provided. As a result, both end openings of the third flow path 13 (inlet 13a and outlet 13b during forward flow) are opened so as to be directed downstream with respect to the first flow path 11 and the second flow path 12.

According to the above configuration, when the main flow A flows through the main flow path 2 a of the air duct 2, dust entering the first flow path 11 and the second flow path 12 is open at both ends of the third flow path 13. Since (the inlet 13a and the outlet 13b) are directed downstream with respect to the first flow path 11 and the second flow path 12, the first flow path 11 and the first flow path can be vigorously and smoothly by the inertia force. The two flow paths 12 are penetrated.
Therefore, dust is less likely to enter the third flow path 13, and the flow sensor 5 can be more reliably protected from dust.
In the third embodiment, the same actions and effects as those of the first embodiment can be obtained with respect to the expected actions and effects of the air flow measuring device 1.

[Example 4]
Next, a fourth embodiment of the present invention will be described based on FIG. 5 with a focus on differences from the first embodiment.

  The air flow rate measuring apparatus 1 according to the fourth embodiment causes the main passage 2a of the air duct 2 to function as the second flow path 12 according to the first embodiment.

  Specifically, as the first flow path 11, a flow path that is divided into a first large flow path 11 a and a first small flow path 11 b by a tapered restriction 14 as in the first embodiment is used. The first small flow path 11b and the main flow path 2a of the air duct 2 on the downstream side of the air duct 2 are in direct communication with each other through the third flow path 13.

  According to the above configuration, during the forward flow in which the main flow A flows through the main flow path 2 a of the air duct 2, the main flow path of the air duct 2 is reduced by the throttling effect of the restriction 14 with respect to the first small flow path 11 b of the first flow path 11. Since a bypass flow B having a flow velocity larger than that of 2a can be formed, forward stability from the main flow path 2a to the main flow path 2a via the third flow path 13 and the first small flow path 11b of the first flow path 11 is achieved. Air flow A1 can be formed.

  According to the fourth embodiment, the air flow rate measuring device 1 only needs to provide two flow paths of the first flow path 11 and the third flow path 13 in the flow path forming portion (flow path forming member) 10b. As a whole, it is possible to obtain the same operations and effects as those of the first embodiment with an extremely small and simple structure.

[Modification]
As described above, the embodiment of the present invention has been described with respect to four examples. For example, aspects such as the first flow path 11, the second flow path 12, and the third flow path 13 that control the central function of the apparatus of the present invention are as follows. The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

As an example of the modification,
(1) Since the apparatus main body 10 is manufactured by pasting together a pair of resin molded products whose channel portions are halved, the cross-sectional shape of each of the channels 11, 12, 13 is other than circular, for example rectangular Even if it forms, each flow path 11, 12, 13 can be formed, without producing a trouble on a manufacture surface.
(2) As the throttle means for generating the flow velocity difference between the first flow path 11 and the second flow path 12, the tapered throttles 14 and 15 that can expect a rectifying effect are adopted. For example, a step means that simply connects a large-diameter channel portion and a small-diameter channel portion may be employed as the throttle means.
(3) In the second embodiment, the flow rate sensor 5A with a backflow detection function (means) capable of distinguishing and detecting the forward flow and the backflow is used. You may make it use together.
(4) The dust countermeasure at the time of forward flow in Example 3 is also desired by providing the middle flow path portion 12c only on the inlet 13a side of the third flow path 13 in consideration of the air flow of the third flow path 13 at the time of forward flow. The effect of can be obtained.
(5) Although the third flow path 13 is disposed so as to be orthogonal to the first flow path 11 and the second flow path 12 or the main flow path 2a, depending on the desired flow measurement function and dust countermeasure function, for example, Alternatively, the third flow path 13 may be disposed inclined to the downstream side (see FIG. 6), or conversely, inclined to the upstream side.

  The above-described features of the air flow rate measuring device 1 according to the present invention and the functions and effects to be mentioned are summarized and enumerated according to the means described in the claims (especially claims 2 to 4). Then, it is as follows.

(Feature 1 = Means of claim 2)
In the air flow rate measuring device 1 according to claim 1,
The second passage 12 is composed of a second small channel 12a having a small channel cross-sectional area located on the upstream side and a second large channel 12b located on the downstream side and having a large channel cross-sectional area. In the flow path 13, the first small flow path 11b of the first flow path 11 and the second small flow path 12a of the second flow path 12 communicate with each other, and the air flow in the reverse direction flows from the downstream side toward the upstream side. However, the flow path 5A (backflow detection means) with a backflow detection function is provided in the third flow path 13 so as to flow from the second flow path 12 to the first flow path 11 via the third flow path 13. (For example, Example 2).
According to the above means, it is possible to detect the occurrence of the backflow by the flow sensor 5A, and this backflow detection signal can be effectively used for the control of the internal combustion engine 4.

(Feature point 2 = Means of claim 3)
In the air flow rate measuring device 1 according to claim 1 or 2,
Both end openings (inlet 13a and outlet 13b) of the third channel 13 are characterized by opening toward the downstream side with respect to the first channel 11 and the second channel 12 (for example, implementation) Example 3).
According to the above means, the flow sensor 5 can be more reliably protected from dust during forward flow.

(Feature point 3 = Means of claim 4)
The air flow rate measuring device 1 is assembled with an air duct 2 having a main flow path 2a through which air to be measured flows, and the air duct 2 so as to cross the main flow path 2a from the outside. A flow path forming portion (flow path forming member) 10b having three flow paths 13 and a flow rate sensor 5 disposed in the third flow path 13 and measuring the flow rate of air flowing through the third flow path 13 The first flow channel 11 takes in a part of the main flow A flowing through the main flow channel 2a, and is located on the upstream side and has a large flow channel cross-sectional area, and is positioned on the downstream side and the first large flow channel 11a. The first small flow path 11b has a small cross-sectional area, and the first small flow path 11b forms a bypass flow path for flowing a bypass flow B having a flow velocity larger than that of the main flow A flowing through the main flow path 2a. Then, the first small flow path 11b of the first flow path 11 and the main flow path 2a are directly communicated with each other through the third flow path 13, so that the main flow path 2a passes through the third flow path 13 and the first flow path 11. A forward bypass flow reaching the main flow path 2a is formed (for example, Example 4).
According to the above means, it is only necessary to provide the flow path forming portion 10b with two flow paths, ie, the first flow path 11 and the third flow path 13, and the air flow rate measuring device 1 having an extremely small and simple structure is obtained. be able to.

  The air flow rate measuring device 1 of the present invention is not limited to the application example (intake air amount measuring device for an internal combustion engine) of the above-described embodiment, and measures the air flow rate of the measurement target flowing through the main flow path 2a of the air duct 2. Of course, it can be applied to various uses.

  DESCRIPTION OF SYMBOLS 1 ... Air flow measuring device, 2 ... Air duct, 2a ... Main flow path, 5 ... Flow rate sensor, 10 ... Apparatus main body, 10b ... Flow path formation part (flow path formation member), 11 ... 1st flow path, 11a ... 1st 1 large flow path, 11b ... 1st small flow path, 12 ... 2nd flow path, 13 ... 3rd flow path, A ... mainstream, A1, B, B1, C ... bypass flow.

Claims (4)

An air duct (2) having a main flow path (2a) through which air to be measured flows;
The air duct (2) is assembled from the outside so as to cross the main flow path (2a), and has a first flow path (11), a second flow path (12), and a third flow path (13). A flow path forming member (10b);
An air flow rate measuring device (1) comprising a flow rate sensor (5) disposed in the third flow path (13) and measuring a flow rate of air flowing through the third flow path (13),
The first flow path (11) and the second flow path (12) are bypass flow paths that take a part of the main flow (A) flowing through the main flow path (2a) and flow as a bypass flow (B, C). With eggplant,
The first flow path (11) is located on the upstream side and has a first large flow path (11a) having a large flow path cross-sectional area, and the first small flow path (11b) located on the downstream side and having a small flow path cross-sectional area. The first small flow path (11b) is formed of a bypass flow path for flowing the bypass flow (B) having a flow velocity larger than that of the bypass flow (C) flowing through the second flow path (12). And
By connecting the first small flow path (11b) and the second flow path (12) of the first flow path (11) through the third flow path (13), the main flow path (2a) A forward bypass flow (B1) is formed from the second flow path (12), the third flow path (13), and the first flow path (11) to the main flow path (2a). An air flow rate measuring device (1) characterized by the above. In the air flow measuring device (1) according to claim 1,
The second passage (12) includes a second small flow path (12a) located on the upstream side and having a small flow path cross-sectional area, and a second large flow path (12b) located on the downstream side and having a large flow path cross-sectional area. Configured,
The third channel (13) communicates the first small channel (11b) of the first channel (11) and the second small channel (12a) of the second channel (12). Then, the reverse air flow (D) flowing from the downstream side toward the upstream side passes from the second flow path (12) through the third flow path (13) to the first flow path (11). And let it flow,
An air flow rate measuring device (1), wherein a backflow detecting means (5A) is disposed in the third flow path (13). In the air flow rate measuring device (1) according to claim 1 or 2,
Both end openings (13a, 13b) of the third channel (13) are open toward the downstream side with respect to the first channel (11) and the second channel (12). An air flow rate measuring device (1) characterized by An air duct (2) having a main flow path (2a) through which air to be measured flows;
A flow path forming member (10b) having a first flow path (11) and a third flow path (13) assembled to the air duct (2) so as to cross the main flow path (2a) from the outside; ,
An air flow rate measuring device (1) comprising a flow rate sensor (5) disposed in the third flow path (13) and measuring a flow rate of air flowing through the third flow path (13),
The first flow path (11) takes in a part of the main flow (A) flowing through the main flow path (2a), and is located downstream of the first large flow path (11a) having a large flow path cross-sectional area and the downstream. The first small channel (11b) is located on the side and has a small channel cross-sectional area, and the first small channel (11b) has a larger flow velocity than the main flow (A) flowing through the main channel (2a). A bypass flow path for flowing the bypass flow (B) is formed,
The first small channel (11b) and the main channel (2a) of the first channel (11) are communicated with each other by the third channel (13), so that the main channel (2a) An air flow rate measuring device (1) characterized by forming a forward bypass flow (A1) that reaches the main flow path (2a) through the third flow path (13) and the first flow path (11). ).

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