JP2003161652A - Flow rate measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flow rate measuring device capable of achieving high performance, high degree of reliability, and low cost in the environments where pollutants or water droplets come by air, and vibration is applied or the like. <P>SOLUTION: An inlet of a bypass passage where a heat generating resistive element is provided is arranged with an angle. The flow rate measuring device itself is also arranged with an angle which is neither perpendicular to nor parallel to the flow direction of a fluid flowing through a main passage. As a result, water droplets or the like have difficulty in intruding the bypass, providing high-precision measurements of fluid flow rate. Breakdowns due to resonance or the like are also prevented. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a device for measuring a flow rate. In particular, the present invention relates to a general sensor for measuring a fluid flow rate and various control systems including various sensors used for air-fuel consumption control of an internal combustion engine.

[0002]

2. Description of the Related Art A structure in which a bypass passage is inclined and installed is
It is known from German Application No. DE19547915A1 and a technique has been clarified in which the critical point of the characteristic variation is avoided and the characteristic variation is suppressed by preliminarily inclining the bypass passage to an insensitive region.

In addition, a heating resistor is installed in the shadow of the flow,
D has a structure that avoids fouling substances and water droplets by inertial separation.
It is revealed by E19815654A1.

However, if both are combined and the installation position of the heat-generating resistor or the temperature-sensitive resistor is devised, it is possible to avoid flying of pollutants and water droplets, and the temperature caused by heat generation of the control circuit board can be avoided. It is possible to solve all of the problems of characteristics, the problem of vibration resistance, and the problem of flow rate measurement error in the flow path where the backflow occurs. There is no description about these in the above-mentioned known example.

[0005]

The flow measuring device used in an internal combustion engine or the like, which has a particularly severe environment, has the following problems. (1) Avoid the arrival of fouling substances and water droplets. (2) To solve the temperature characteristic problem caused by the heat generation of the circuit. (3) To solve the problem of vibration resistance due to downsizing of the flow rate measuring device. (4) Suppress flow rate measurement error when backflow occurs. (5) Achieve cost reduction.

A main object of the present invention is to solve (1).

[0007]

The above object can be achieved by the inventions described in the claims. For example, (1) The opening of the bypass passage member in which the heating resistor is installed, that is, the bypass inlet has a rectangular cross section.
One surface that is arranged at an angle that is neither vertical nor horizontal with respect to the surface and that has a rectangular cross section also has a vertical or horizontal direction with respect to the flow direction of the fluid flowing through the main flow path. Place it at an angle. (2) The metal base member is mounted so as to be tilted in the direction in which the metal base member comes into direct contact with the fluid most than other components. (3) When mounting the structure by inclining it and inserting the structure, such as a metal base member or a bypass member, from the insertion hole, maintain a sufficient clearance with the insertion hole, and when mounting by screwing or the like, the clearance is 4 mm. Wear it so that the sides are not even. (4) The heating resistor is installed inside the bypass passage, and the temperature sensitive resistor and the intake air temperature sensor are installed outside the bypass passage. (5) The heat-generating resistor and the temperature-sensitive resistor, and the intake air temperature sensor are placed in the forward flow flowing from the upstream side of the main flow path and the reverse flow flowing from the downstream side, and the heat-generating resistor is placed at a position where it is well exposed to the forward flow. The resistor is placed at a position well exposed to backflow, and the intake air temperature sensor is placed at a position well exposed to both forward and reverse flows. (6) The bypass passage outlet installed on the bypass passage member side is offset to the downstream side with respect to the bypass passage outlet and the bypass passage inlet on the metal base member side. (7) Arrange the connectors at the same angle as the rectangular cross section, that is, in parallel.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a front view showing a preferred embodiment of the present invention applied to a heating resistance type air flow rate measuring device and a sectional view taken along line AA. A heating resistor 1 for detecting the flow rate of a fluid, a temperature sensitive resistor 2 for detecting the temperature of intake air and performing temperature compensation, and a thermistor 3 for independently detecting the intake air temperature are integrated in a housing member 4. It is fixed to the molded metal terminal member 5. The housing member 4 and the circuit board 6, the cover member 7 for protecting the circuit board 6, and the sub-passage member 8 for forming a bypass passage are stacked and assembled on a metal base 9,
The metal terminal member 5 provided on the housing member 4 and the circuit board 6 are electrically connected to each other, and further, the connector terminal 10 provided on the housing member 4 for inputting and outputting an electric signal is electrically connected to the circuit board 6. Then, a heating resistance type air flow rate measuring device is established.

Actually, an insertion hole is provided in the main passage 11 or the like through which air flows, and the insertion hole is used for insertion. However, when used in an internal combustion engine of an automobile or the like, the intake air actually contains fine particle dust, and further air containing water and oil components also flows. If these fouling substances adhere to the heat-generating resistor 1, the measured flow rate value may change instantly and may change over time. In particular, when water droplets are scattered, the measured flow rate value greatly changes instantaneously, so countermeasures against such water droplet scattering have become an important issue.

Therefore, as shown in FIG. 1, the air intake 12 to the bypass passage is not opened so as to face the air flow direction 13, but is arranged at an angle. Further, the air flow rate measuring device itself was rotated and the bypass passage was attached so as to be oblique to the air flow direction 13. This configuration makes it difficult for water droplets to enter the bypass,
The air flow rate can be accurately measured even when water droplets are scattered.

Further, this method is a special attachment in the case where measures against water droplets and fouling substances are particularly required, and when there is no such a concern, the air intake port 12 is arranged in the air flow direction 13. On the other hand, it is desirable that the opening be vertical, that is, toward the front. Since it is not possible to reduce the cost by manufacturing a special product against water droplets or scattering of pollutants, it is preferable to use a structure capable of achieving the problem simply by replacing the sub passage member 8 and mounting it at an angle as in the present invention.

The diagonal mounting has a great effect in addition to avoiding the scattering of water droplets and pollutants. As shown in the cross-sectional view taken along the line A-A in FIG. 1, the rectangular cross section has a shape close to a plate in which the long side length is three times or more the short side length and is used in an internal combustion engine such as an automobile. When the product of the present invention is applied, insufficient mechanical strength is feared, and in particular, failure due to resonance or the like is considered. Therefore, as described above, the air flow rate measuring device itself is rotated and the bypass passage is attached so as to be oblique to the air flow direction 13. Then, if the long side length of the rectangular cross section is about 3a to 5a, the region where the resonance occurs is a relatively high engine speed region, that is, the region where the air velocity is high, and the bypass passage with respect to the air flow direction 13 is formed. Since it is installed diagonally, large lift and drag can be generated. That is, a force that suppresses the tip portion that is most likely to shake at the time of resonance is applied, and it becomes possible to prevent a failure due to resonance.

FIG. 2 is a top view showing an embodiment in which the present invention is applied to a heating resistance type air flow rate measuring device. In order to reduce the manufacturing cost, the connector 14 for inputting / outputting an electric signal is arranged in parallel with the rectangular cross section. Therefore, when the air flow rate measuring device itself is rotated and the bypass passage is attached so as to be inclined with respect to the air flow direction 13, the connector 14 is also attached at the same angle.

FIG. 3 is a sectional view showing an embodiment in which the present invention is applied to a heating resistance type air flow rate measuring device. When the bypass passage is attached so as to be inclined with respect to the air flow direction 13, the metal base 9 is inclined in the direction most exposed to air. The circuit board 6 is fixed to the metal base 9, and the metal base 9 has a role of radiating the heat generated by the circuit board 6. With this configuration, the heat generated by the circuit board 6 can be radiated more efficiently.

The heating resistor 1 is inside the bypass passage, the temperature sensing resistor 2 is upstream of the heating resistor 1, and outside the bypass passage, the thermistor 3 is upstream of the temperature sensing resistor 2, and They are located outside the bypass passages. At this time, the thermistor 3 is well exposed to the air flow from both the forward flow 15 and the reverse flow 16 flowing in the main passage 11, the position where the temperature sensitive resistor 2 is well exposed to the reverse flow 16, and the heating resistor 1 is good to the forward flow. The bypass passage is inclined so that it is exposed. With this configuration, it is possible to reduce the error of the heating resistance type air flow rate measuring device due to the pulsating flow of the engine.

Here, the pulsation influence error in the heating resistance type air flow rate measuring device will be described.

The air flowing in the intake pipe of the engine becomes a pulsating flow as the intake valve opens and closes. The magnitude of this pulsation is small when the throttle valve is relatively closed, and increases as the throttle valve is near full opening. When the pulsation amplitude further increases, the flow in the intake pipe becomes a flow accompanied by backflow. However, it is difficult for the heating resistor to detect the flow direction due to its structure, and the forward flow or the reverse flow is simply detected as the flow velocity. Therefore, when a backflow occurs, the heating resistor simply detects it as a flow velocity, and as a result, a positive error occurs.

This positive output error can be partly divided by utilizing the operation of controlling the temperature between the heating resistor 1 and the temperature sensitive resistor 2 to a constant temperature. Specifically, the temperature sensitive resistor 2 is slightly heated, and the temperature sensitive resistor 2 is attached at an angle so that the air hits the temperature sensitive resistor 2 only when backflow occurs. Then, only when the backflow occurs, the slightly heated temperature sensitive resistor 2 is cooled, and as a result, the heating temperature of the heat generating resistor 1 whose temperature difference from the temperature sensitive resistor 2 is kept constant is lowered. That is, the heating current of the heating resistor 1 is reduced only when the backflow occurs, that is, a signal indicating that the air flow rate is reduced is output, and the plus error can be cut by that amount. By this principle, as described above, the error of the heat generation resistance type air flow measuring device due to the engine pulsating flow can be reduced, and it can be achieved by mounting the device at an angle.

FIG. 4 is a front view showing an embodiment of the present invention applied to a heating resistance type air flow rate measuring device and its cross section B.
FIG. The bypass passage structure in which the heating resistor 1 is installed has a detour structure that bypasses once, and its outlet is provided at one location on the metal base 9 side and at one location on the sub-passage member 8 side. As described above, the pulsation influence error in the heating resistance type air flow rate measuring device causes a plus error due to the backflow from the engine. When it becomes a pulsating flow region with a certain large amplitude that does not lead to backflow, the relationship between the heating resistor 1 and the air flow rate is non-linear.
Due to the response delay of the heating resistor 1 itself, a minus error occurs with respect to the true air flow rate. These positive and negative output errors can be reduced by attenuating the intake pulsation that has reached the inside of the bypass passage, and when a backflow occurs, the backflow is less likely to enter the bypass passage. These can be achieved by increasing the inertia of the air flow flowing inside the bypass passage. Specifically, with respect to the distance between the entrance and the exit of the bypass passage seen in the air flow direction 13,
Ideally, the entire length of the bypass passage is configured to be long, that is, this bypass structure is used.

FIG. 5 is a side view showing an embodiment in which the present invention is applied to a heating resistance type air flow rate measuring device and its cross section C.
FIG. The bypass outlet 17 is diverted in two directions via the diverter guide 18. A larger opening area of the bypass outlet 17 is more effective in improving the bypass flow velocity. However, if the bypass outlet 17 is opened at one place, the entire length of the bypass passage is shortened and the bypass flow is easily affected. Therefore, the flow is divided into two directions to improve the bypass flow velocity and reduce the pulsation error.

FIG. 6 is a side view showing an embodiment of the present invention applied to a heating resistance type air flow rate measuring device and its cross section D.
FIG. The bypass outlet 17 on the side of the sub-passage member 8 is offset downstream from the bypass outlet 17 on the side of the metal base 9. When the heat generation resistance type air flow rate measuring device is tilted and attached, the pulsation error can be adjusted by the position of the bypass outlet 17 on the side of the sub passage member 8. Since the influence of pulsation varies greatly depending on the type of engine and the shape of the intake system, it is possible to individually adjust the pulsation error for each model.

FIG. 7 is a front view showing an embodiment in which the present invention is applied to a heating resistance type air flow rate measuring device and its cross section E.
FIG. Main path for heating resistance type air flow measuring device 1
1, the main passage 11, the metal base 9 and the main passage 1 when inserted
1 and the housing member 4, the clearance amount formed between the main passage 11 and the cover member 7 is arbitrarily set. Especially when the downstream side clearance 19 is set to zero, that is, contact or small, when the bypass passage receives wind pressure,
Each component is pressed against the main passage 11, and the proof strength against resonance is further improved. Further, when the main passage or each component is provided with a contacting protrusion or the like, it becomes a point contact or a line contact from the surface contact, and the mountability when the heating resistance type air flow rate measuring device is inserted into the main passage 11 is improved.

FIG. 8 is a sectional view showing an embodiment in which the present invention is applied to a heating resistance type air flow rate measuring device. If the heating resistance type air flow rate measuring device is installed at an angle, the pressure loss of the intake system will increase slightly. For this reason, the shape on the most upstream side is rounded.

Finally, referring to FIG. 9, an embodiment in which the product of the present invention is applied to an electronic fuel injection type internal combustion engine as a heating resistance type air flow rate measuring device will be shown. The intake air 52 sucked from the air cleaner 51 is sucked into the engine cylinder 57 via an intake duct 53, a throttle body 54, and an intake manifold 56 including an injector 55 to which fuel is supplied. On the other hand, the gas generated in the engine cylinder 58
Are discharged through the exhaust manifold 59.

The air flow rate signal and pressure signal output from the circuit module 60 of the heating resistance type air flow rate measuring device, the intake air temperature signal from the intake air temperature sensor 61, the throttle valve angle signal output from the throttle angle sensor 62, and the exhaust gas. Oxygen concentration meter 63 provided on the manifold 59
A control unit 65 for inputting the oxygen concentration signal output from the engine and the engine rotation speed signal output from the engine tachometer 64, etc., sequentially calculates these signals to optimize the fuel injection amount and the idle air control valve. The opening is obtained, and the injector 55 and the idle air control valve 66 are controlled using the values.

Next, another embodiment will be briefly described (see FIG. 1). A thermal type flow rate measuring device, comprising: a sub-passage forming member (4) that forms a sub-passage inserted in a main passage through which gas flows; and a heating resistor (1) provided in the sub-passage. And a flow measuring device in which the sub passage is installed so as to be inclined with respect to the main passage so that an inlet of the sub passage cannot be directly seen from an upstream side of the main passage. Further, the flow rate measuring device is characterized in that the heating resistor is not directly visible from the upstream side of the main passage.

The effects of this embodiment will be described below. (1) The air intake port to the bypass passage is not opened so as to be in front of the air flow direction, but is arranged at an angle, and the air flow rate measuring device itself is rotated to move the bypass passage in the air flow direction. It is possible to make it difficult for water droplets to enter the bypass by installing it at an angle to the
The air flow rate can be accurately measured even when water droplets are scattered. (2) Since the structure is such that the problem can be achieved simply by replacing the sub-passage member and mounting it at an angle, cost reduction can be achieved even with a special product. (3) When the air flow rate measuring device itself is rotated and the bypass passage is obliquely attached to the air flow direction, a large lift and drag force can be obtained, and a force that suppresses the tip end portion that easily shakes at the time of resonance is added. As a result, it becomes possible to prevent a failure due to resonance. (4) When the bypass passage is mounted so as to be oblique to the air flow direction, the metal base is tilted in the direction most exposed to air. With this configuration, the heat generated by the circuit board can be radiated more efficiently. (5) The heating resistor is arranged inside the bypass passage, the temperature sensing resistor is arranged upstream of the heating resistor and outside the bypass passage, and the thermistor is arranged upstream of the temperature sensing resistor and outside the bypass passage. , The thermistor is a forward flow through the main passage,
Pulsating flow of the engine by tilting the bypass passage so that it is well exposed to air flow from both directions of backflow, the temperature sensitive resistor is well exposed to backflow, and the heat generating resistor is well exposed to forward flow. It is possible to reduce the error of the heating resistance type air flow rate measuring device due to the above. (6) When the heating resistance type air flow rate measuring device is inserted into the main passage, the amount of clearance formed between the main passage and the metal base, between the main passage and the housing member, and between the main passage and the cover member is arbitrarily set. In particular, by setting the clearance on the downstream side to be zero or small, each component is pressed against the main passage when the bypass passage receives wind pressure, and the proof strength against resonance is further improved. Further, when the main passage or each component is provided with a contacting protrusion or the like, the surface contact becomes a point or line contact, and the mountability at the time of inserting the heating resistance type air flow rate measuring device into the main passage is improved.

[0028]

According to the present invention, it is possible to reduce deterioration in accuracy due to fouling substances and water droplets.

[Brief description of drawings]

FIG. 1 is a front view showing an embodiment of the present invention and an AA sectional view thereof.

FIG. 2 is a top view showing an embodiment of the present invention.

FIG. 3 is a sectional view showing an embodiment of the present invention.

FIG. 4 is a front view showing a first embodiment of the present invention and a BB sectional view thereof.

FIG. 5 is a side view showing the embodiment of the present invention and a cross-sectional view taken along the line CC.

FIG. 6 is a side view showing the embodiment of the present invention and a sectional view taken along the line D-D thereof.

7A and 7B are a front view and an EE cross-sectional view showing an embodiment of the present invention.

FIG. 8 is a sectional view showing an embodiment of the present invention.

FIG. 9 is a front view showing an embodiment of the present invention.

[Explanation of symbols]

1 ... Heating resistor, 2 ... Temperature sensitive resistor, 3 ... Thermistor, 4
... Housing member, 5 ... Metal terminal member, 6 ... Circuit board, 7 ... Cover member, 8 ... Sub passage member, 9 ... Metal base, 10 ... Connector terminal, 11 ... Main passage, 12
... air intake port, 13 ... air flow direction, 14 ... connector, 15 ... forward flow, 16 ... backflow, 17 ... bypass outlet,
18 ... Diversion guide, 19 ... Downstream clearance, 51 ...
Air cleaner, 52 ... Intake air, 53 ... Intake duct, 5
4 ... Throttle body, 55 ... Injector, 56 ... Intake manifold, 57 ... Engine cylinder, 58 ... Gas, 59 ... Exhaust manifold, 60 ... Circuit module,
61 ... Intake air temperature sensor, 62 ... Throttle angle sensor,
63 ... Oxygen concentration meter, 64 ... Tachometer, 65 ... Control unit, 66 ... Idle air control valve.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02D 33/00 318J (72) Inventor Hiroshi Onikawa 2477 Takaba, Hitachinaka City, Ibaraki Stock Company Hitachi Car Engineering Co., Ltd. Inner F term (reference) 2F035 AA02 EA00

Claims (19)

[Claims] 1. A thermal type flow rate measuring device comprising: a sub-passage forming member that forms a sub-passage inserted in a main passage through which gas flows; and a heating resistor provided in the sub-passage. A flow rate measuring device in which the sub passage is installed so as to be inclined with respect to the main passage so that an inlet of the sub passage cannot be directly seen from an upstream side of the main passage. 2. The flow measuring device according to claim 1, wherein the heating resistor is not directly visible from the upstream side of the main passage. 3. A device which is used by being inserted into a fluid flow path to cause a heating current to flow through a resistor to generate heat, and which outputs a signal according to the fluid flow rate from the amount of heat radiated to a fluid to be measured. The shape of the portion to be inserted into the fluid flow path, such as the bypass passage member for protecting the resistor internally and guiding the fluid, the housing member for supporting each component such as the control circuit board, or protecting the interior, is roughly In a flow rate measuring device having a rectangular cross-section and having a length-to-length ratio with respect to the short side being three times or more and having a more plate-like aspect ratio, the opening of the bypass passage member in which the heating resistor is installed, that is, A flow measuring device, wherein the bypass inlet is opened at a certain angle which is not vertical or horizontal with respect to a certain surface constituting the rectangular cross section. 4. The flow direction of fluid according to claim 3, immediately after the fluid has passed through the opening of the bypass passage member, that is, the bypass inlet, and the flow direction of the fluid is vertical or horizontal to the flow direction of the fluid flowing through the main flow path. A flow measuring device characterized by flowing at an angle that is not a direction. 5. The fluid according to claim 3 or 4, wherein the fluid passing through the heating resistor portion flows at a certain angle, not in the vertical or horizontal direction with respect to the flow direction of the fluid flowing in the main flow path. A flow measuring device characterized by. 6. A device which is used by inserting it into a fluid flow path to cause a heating current to flow through a resistor to generate heat, and which outputs a signal according to the fluid flow rate from the amount of heat released to the fluid to be measured. The shape of the portion to be inserted into the fluid flow path, such as the bypass passage member for protecting the resistor internally and guiding the fluid, the housing member for supporting each component such as the control circuit board, or protecting the interior, is roughly In a flow rate measuring device having a rectangular cross-section and having a length-to-length ratio with respect to the short side being three times or more and having a more plate-like aspect ratio, the opening of the bypass passage member in which the heating resistor is installed, that is, The bypass inlet is arranged at an angle that is not vertical or horizontal with respect to one surface forming the rectangular cross section, and the one surface forming the rectangular cross section also flows through the main flow path. Fluid flow Flow measuring apparatus characterized by being arranged at an angle, i.e. with an inclination not vertically or horizontally with respect to the direction. 7. The connector according to any one of claims 3 to 6, wherein the connectors for inputting and outputting electric signals and the like are arranged at the same angle as the rectangular cross section, that is, in a parallel relationship. Flow rate measuring device. 8. A metal base member for fixing a control circuit board, a housing member for internally protecting the control circuit board, and a connector for electric signal input / output, a heating resistor for fluid detection, and a temperature. It consists of a temperature sensing resistor for compensation, a bypass passage member for internally protecting the thermistor type intake air temperature sensor and the like, and a cover member for protecting the control circuit board with the housing member as a closed space, which are superposed. It has a laminated structure that can be assembled by
In addition, after assembly, in a flow rate measuring device in which the cross-sectional shape of the metal base in the direction perpendicular to the longitudinal direction has a substantially rectangular cross section in which the long side is three times or more the short side, the metal base is better than other components. A flow measuring device, wherein the member is attached so as to be inclined in a direction in which it comes into direct contact with the fluid most. 9. The flow rate measuring device according to claim 8, wherein the heating resistor is installed inside the bypass passage, and the temperature sensitive resistor and the intake air temperature sensor are installed outside the bypass passage. 10. The heating resistor and the temperature-sensitive resistor according to claim 8, wherein the intake air temperature sensor is placed in a forward flow flowing from an upstream side of the main flow path and a reverse flow flowing from a downstream side of the main flow path. The heating resistor is disposed at a position well exposed to forward flow, the temperature-sensitive resistor is disposed at a position well exposed to backflow, and the intake air temperature sensor is disposed at a position well exposed to both forward and reverse flows. A characteristic flow measurement device. 11. A flow rate measuring device according to claim 10, wherein an intake air temperature sensor, a temperature sensitive resistor, and a heat generating resistor are arranged in this order from the upstream side of the main flow path. 12. The bypass passage structure according to any one of claims 8 to 11, wherein the bypass passage structure has a bypass structure, and the outlet of the bypass passage is located at one location on the metal base side and the bypass passage member side. A flow rate measuring device, characterized in that it is provided at one location. 13. The flow rate according to claim 12, wherein the outlet of the bypass passage is divided into two parts at the most upstream side of the main passage after bypassing the bypass passage, that is, at the tip of the structure. measuring device. 14. The bypass passage outlet installed on the side of the bypass passage member according to any one of claims 12 to 13, wherein the bypass passage outlet on the side of the metal base member is offset from the bypass passage outlet on the side of the metal base member or on the downstream side. A flow measuring device characterized by the above. 15. A metal base member for fixing a control circuit board, a housing member for internally protecting the control circuit board, and a connector for integrating an electric signal input / output, a heating resistor for detecting a fluid, and a temperature. It consists of a temperature sensing resistor for compensation, a bypass passage member for internally protecting the thermistor type intake air temperature sensor and the like, and a cover member for protecting the control circuit board with the housing member as a closed space, which are superposed. It has a laminated structure that can be assembled by
In addition, after assembly, the metal base has a cross-sectional shape in a direction perpendicular to the longitudinal direction of the metal base, which has a substantially rectangular cross section in which the long side is three times or more the short side, and the cross section is opened in the main channel through which the fluid flows. In a flow rate measuring device that is used by inserting the metal base member into a rectangular insertion hole to a position where the metal base member is sufficiently exposed to fluid, the metal base member is attached so as to be tilted in a direction in which the metal base member comes into direct contact with the fluid most than other components, When inserting a structure such as a metal base member or a bypass member through the insertion hole, maintain a necessary and sufficient clearance with the insertion hole, and at the end of mounting by screwing or the like, the clearance becomes uneven on four sides. A flow rate measuring device, characterized in that it is mounted as described above. 16. The flow rate according to claim 15, wherein the metal base member and the insertion hole have a large clearance and the clearance is almost zero between the cover member and the insertion hole. measuring device. 17. The flow rate measuring device according to claim 15, wherein the flow path measuring device is mounted in the main flow path in such a state that a clearance on the upstream side is wide and a clearance on the downstream side is almost zero. 18. The flow rate measuring device according to claim 3, wherein the shape of the structure on the most upstream side is a rounded streamlined shape. 19. A control system for an internal combustion engine, which controls the internal combustion engine by using the flow rate measuring device according to any one of claims 3 to 18.