JP2008249635A - Airflow measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an airflow measuring device capable of assuring detection accuracy of the inhalation amount of air flowing through an intake pathway 2 by inhibiting pollution degradation or breakage of heat resistors (flow metering element), thermostatic resistive elements (temperature-compensating resistive element) and the like of a sensing section 4 of the airflow measuring device. <P>SOLUTION: By preparing a sub-bypass channel 13 forming circulating rotational flow of air within a sensor body 3 of the airflow measuring device in addition to a bypass channel 12, the inhaled air flowing into the bypass channel 12 is made it more difficult to flow into the sub-bypass channel 13 from a communicating mouth 29. Thereby, dust contained in inhaling air flowing through the bypass channel 12 toughens to reach a sensing section 4 prepared within the sub-bypass channel 13. Therefore, as pollution degradation or breakage can be inhibited of heat resistors, thermostatic resistive elements and the like of the sensing section 4, detection accuracy can be assured of the inhalation amount of air at the heat resistors of the sensing section 4. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an air flow rate measuring device that measures the flow rate of intake air into an internal combustion engine using a flow rate measuring element such as a heating resistor.

[Conventional technology]
2. Description of the Related Art Conventionally, an air flow meter that measures the flow rate of intake air of an internal combustion engine is known as an air flow measurement device (see, for example, Patent Document 1).
In this air flow meter, a flow rate measuring element (heat generating element) and a temperature sensitive element are installed at predetermined intervals in a bypass flow path disposed in an intake passage of an internal combustion engine, and the heat generating temperature and the temperature sensitive element of the flow rate measuring element are set. The supply current of the flow rate measuring element is controlled so as to keep the temperature difference from the detected temperature (intake air temperature) constant, and the flow rate of the intake air is measured by the supply current value.

[Conventional technical problems]
Incidentally, an air cleaner is provided at the most upstream portion of the intake passage of the internal combustion engine, but dust such as fine dust and filter dust that cannot be captured by the air cleaner (for example, dust having a fine particle diameter of about several μm to several hundred μm). May flow into the air flow meter together with the intake air. If the flow rate measuring element is soiled due to dust adhesion, the amount of heat transfer (heat dissipation) from the flow rate measuring element to the intake air changes, so the output characteristics of the air flow meter change as the amount of dust attached to the flow rate measuring element increases. The measurement error of the flow rate of intake air increases with time.
In addition, when dust having a particle size of about several hundred μm collides with the flow measurement element, the flow measurement element may be damaged. Therefore, if dust that has flowed into the bypass flow path of the air flow meter adheres to or collides with the flow measurement element, the flow measurement element is deteriorated or damaged, and the detection accuracy of the intake air flow rate cannot be secured. Has occurred.
JP 11-118559 A (page 1-4, FIGS. 1 to 4)

  An object of the present invention is to provide an air flow rate measuring device capable of ensuring the detection accuracy of the flow rate of intake air by preventing the deterioration or breakage of the flow rate measuring element.

  According to the first aspect of the present invention, in the communication portion that communicates the air introduction flow path and the air circulation flow path, the air flow flowing through the air introduction flow path comes into contact with the air in the air circulation flow path, and the air introduction A circulating air flow in which air can circulate around the communication portion is generated in the air circulation flow channel by the air flow flowing through the flow channel. And the flow volume of the air supplied to an internal combustion engine is measured by the flow volume measuring element installed in the air circulation flow path.

Here, the air supplied to the internal combustion engine, that is, the dust contained in the air flowing through the air introduction flow path, has a structure in which the air in the air circulation flow path can circulate around the communication part and the flow rate measuring element. Therefore, it is difficult to flow into the air circulation channel.
Therefore, since the flow rate measuring element is installed in the air circulation channel where the dust contained in the air flowing through the air introduction channel is difficult to flow in, it is possible to prevent deterioration in function (performance deterioration) due to contamination of the flow rate measuring element. it can. Further, it is possible to prevent the flow rate measuring element from being damaged due to the collision of dust contained in the intake air with the flow rate measuring element. Further, the accuracy of detecting the flow rate of the intake air can be ensured by preventing the deterioration or breakage of the flow rate measuring element.

According to the second aspect of the present invention, the communication portion is provided with a communication port that opens in a direction orthogonal to the direction of air flow through the air introduction flow path. The communication port is provided in a partition wall that divides the air introduction channel and the air circulation channel. In other words, the communication port is a partition wall and opens so as to communicate the air introduction channel and the air circulation channel.
According to the third aspect of the present invention, the first guide for guiding the air circulating in the air circulation channel to the vicinity of the communication port is provided in the partition wall partitioning the air introduction channel and the air circulation channel, and A second guide is provided for returning the air in the vicinity of the communication port circulated and circulated to the communication portion to the air circulation channel. As a result, the air circulating in the air circulation channel near the communication port and the air flowing in the air introduction channel can easily come into contact with each other, and the air flow circulating in the air circulation channel flows through the air introduction channel. It flows at the same flow rate as the flow rate or at a certain flow rate. Further, since air in the vicinity of the communication port that circulates and circulates in the communication portion easily returns to the air circulation flow path, dust contained in the air flowing through the air introduction flow path is difficult to flow into the air circulation flow path. Therefore, an effect similar to that of the first aspect can be obtained.

  Here, a heating resistor formed in a predetermined pattern on the surface of the circuit board may be employed as the flow rate measuring element. In this case, the heating resistor is connected to a control circuit that controls the amount of current supplied to the heating resistor. The circuit board is installed in a direction perpendicular to the air flow direction circulating in the air circulation flow path.

  The best mode for carrying out the present invention is to prevent the deterioration or breakage of the flow rate measuring element, thereby ensuring the detection accuracy of the flow rate of the intake air. This is realized by providing an air circulation channel through which air can circulate in the communication portion communicating with the road, and installing a flow rate measuring element in the air circulation channel.

[Configuration of Example 1]
FIGS. 1 to 3 show Embodiment 1 of the present invention. FIG. 1 is a view showing an attachment state of an air flow rate measuring device to an intake pipe (intake pipe) of an engine. FIGS. It is the figure which showed the flow measuring device.

  The control device (engine control system) of the internal combustion engine of the present embodiment is a flow rate of intake air (intake air flow rate, intake air amount: hereinafter referred to as intake air amount) sucked into a combustion chamber of an internal combustion engine (engine) such as a gasoline engine. ) And the fuel injection amount based on the intake air amount measured by the air flow measurement device, and the injector energization time (valve open) according to the fuel injection amount. A fuel injection device that variably controls the period), and an engine control unit (engine control device: hereinafter referred to as ECU) that controls the energization time of the injector in association with each system such as an ignition device and an intake control device. Yes.

The air flow rate measuring apparatus according to the present embodiment is used as a thermal air flow meter (hot wire type flow meter) that measures the intake air amount based on the heat radiation amount of the heating resistor (flow rate measuring element) as a heat ray. This air flow rate measuring device is installed inside an intake pipe of an engine, for example, an outlet pipe (intake pipe) 1 of an air cleaner or a throttle body.
The details of the air flow rate measuring device will be described later.

A fuel injection device is a system that injects fuel into an intake port for each cylinder of an engine. This fuel injection device is constituted by an injector or the like that injects fuel pumped up from a fuel tank by an electric fuel pump into an intake port of each cylinder of the engine at an optimal timing.
The ignition device is a system that ignites when the air-fuel mixture in the combustion chamber of each cylinder of the engine is compressed as the piston rises, and burns the air-fuel mixture. The ignition device includes an ignition coil that generates a high voltage for igniting the air-fuel mixture, and a spark plug that ignites the air-fuel mixture by blowing a spark with a high-voltage current generated in the ignition coil.
The injector and the spark plug are mounted on the cylinder head corresponding to each cylinder of the engine.

  The intake control device is an intake passage opening / closing device that opens and closes an intake passage 2 for supplying intake air into a combustion chamber for each cylinder of the engine, and in particular, a throttle corresponding to a valve angle (rotation angle) of a throttle valve. It is a system that controls the amount of intake air sucked into the combustion chamber of each cylinder of the engine according to the opening. This intake control device, that is, the throttle opening control device is installed in the middle of the intake pipe of the engine (airtightly connected downstream of the intake pipe 1 in the intake flow direction), the inside of this throttle body ( A throttle valve that varies the amount of intake air flowing through the throttle bore), an actuator (electric motor) that drives the throttle valve, and the like.

  Here, the air cleaner is installed in the most upstream part of the intake pipe of the engine, and is introduced into the air introduction passage (intake passage 2) from the outside air introduction port opened at the upstream end of the inlet duct (outside air introduction duct) ( It has a filter element (filter element) for filtering outside air). This filter element captures and removes impurities (dust such as dust, dust, sand, etc.) contained in the outside air, so that wear of the sliding parts of the engine caused by hard dust being sucked into the combustion chamber of the engine is reduced. It is an air filter to prevent. The filtration element is accommodated and held inside the air cleaner case.

The air cleaner case is provided with an intake pipe 1 on the downstream side of the filtration element in the intake air flow direction. Inside the intake pipe 1, clean outside air (clean air) filtered by a filter filter of an air cleaner is passed through the throttle body, surge tank, intake manifold, and cylinder head intake port into the combustion chamber of the engine. An intake passage 2 having a circular cross section for supply is formed.
The intake passage 2 refers to the outside air introduced into the inlet duct from the outside air inlet of the air cleaner, inside the air cleaner (filter element), inside the intake pipe 1 of the air cleaner, inside the throttle body, inside the surge tank, and intake manifold This is an intake air introduction path that is introduced into the combustion chamber of each cylinder of the engine via the inside of the cylinder head and the inside of the cylinder head (intake port).
Here, the intake passage 2 of the present embodiment includes a main flow path 11, a bypass flow path 12, a sub bypass flow path 13 and the like, as shown in FIG.

  The air flow rate measuring apparatus of the present embodiment is detachably attached to the intake pipe 1 by a plug-in method. This air flow rate measuring device includes a sensor body (housing, flow rate measuring body) 3 assembled to an intake pipe 1 and a sensing unit in which a heating resistor and a temperature sensitive resistor are formed in a thin film on the surface of a silicon substrate (circuit board). 4 and a circuit incorporating a control circuit for controlling the amount of current supplied to the heating resistor and an output circuit for amplifying the electrical resistance value of the heating resistor (or the voltage value applied to the heating resistor) and outputting the amplified value to the ECU And a module (control module) 5.

  The sensor body 3 is formed in a predetermined shape from a resin material, and is inserted into the intake pipe 1 from the outside of the intake pipe 1 through the attachment hole 6. The sensor body 3 is provided with a flange portion 8 that is fastened and fixed to the intake pipe 1 by a fastening screw 7 or the like. In the sensor body 3, a bypass passage 12 that bypasses a part of the intake air that flows through the intake pipe 1 (intake passage 2) from the main passage 11, and intake air that flows through the bypass passage 12. A sub-bypass channel 13 is formed in which a circulating air flow is generated by the flow (intake flow). In addition, the sensor body 3 includes a partition wall 14 that partitions the bypass flow path 12 and the sub bypass flow path 13, a block 15 for annularizing the sub bypass flow path 13, and a square tubular side wall 16. It is provided integrally.

The bypass flow path 12 bypasses the outside air filtered by the filter element of the air cleaner and bypasses the main flow path 11 of the intake passage 2 to the inside of the throttle body, the inside of the surge tank, the inside of the intake manifold, the inside of the cylinder head. It is an intake air introduction path that is introduced into the combustion chamber of each cylinder of the engine via the (intake port). That is, the bypass flow path 12 is an air introduction flow path for supplying intake air into the combustion chamber of the engine.
The bypass flow path 12 is provided in the vicinity of the central axis of the intake pipe 1 and is in the intake flow direction that flows through the main flow path 11 of the intake passage 2 (the axial direction of the average flow of intake air that flows through the main flow path 11). It is a linear flow path that extends straight in a direction parallel to.

  The sub bypass channel 13 has a communication portion 9 that communicates with the bypass channel 12. The sub-bypass channel 13 is an annular air circulation channel through which air can circulate around the sensing unit 4 and the communication unit 9. That is, the sub-bypass channel 13 is a first straight line 22 extending from the straight part 21 extending in the horizontal direction (horizontal direction) shown in the figure to the first bent part 22 that bends the circulating air flow direction at a right angle to the vertical direction (vertical direction) shown in the figure. Part 23 → first inclined part 24 for inclining the circulating air flow direction with respect to the illustrated vertical direction → communication part 9 → second inclined part 25 for inclining the circulating air flow direction with respect to the illustrated vertical direction The second straight portion 26 extending in the direction) → the annular air circulation flow path returning to the straight portion 21 via the second bent portion 27 that bends the circulating air flow direction at a right angle.

The communication part 9 of the sub-bypass channel 13 is a communication port 29 that opens in a direction orthogonal to the direction of intake air flowing through the bypass channel 12 (the axial direction of the average flow of intake air flowing through the bypass channel 12). have. The communication port 29 is provided in the partition wall portion 14 and opens downward in the figure (for example, the ground direction).
Here, in the partition wall portion 14 of the sensor body 3, the tapered first guide 31 for guiding the circulating air circulating in the sub-bypass flow path 13 to the vicinity of the communication port, and the communication port circulating in the communication unit 9 A tapered second guide 32 for returning the nearby air to the sub-bypass channel 13 is provided.

The sensing unit 4 has a block 15 interposed between the communication port 29 and a position where dust having a small particle diameter contained in the intake air flowing through the bypass passage 12 does not directly hit, that is, inside the sensor body 3 (sub-bypass flow). It is installed in the straight part 21) of the road 13.
The sensing unit 4 has a silicon substrate installed in a direction orthogonal to the axial direction of the average flow of circulating air circulating in the sub-bypass channel 13. In addition, the sensing unit 4 includes a heating resistor and a temperature sensing resistor (temperature sensing element) formed in a predetermined pattern via an insulating film on the surface of the silicon substrate.

The heating resistor is a thermal flow rate measuring element for measuring the amount of intake air flowing through the sub-bypass channel 13, and is electrically connected to a control circuit built in the control module 5 via a wiring portion. ing. The temperature sensitive resistor is a temperature sensing element (temperature compensating resistor) for measuring the temperature of the intake air flowing through the sub-bypass passage 13 (intake air temperature), and is connected to the control circuit via the wiring portion. Electrically connected.
The heating resistor and the temperature-sensitive resistor are formed by depositing (stacking) a heat-sensitive resistor film (thin film) such as platinum on the surface of the insulating film by a vacuum evaporation method or the like, and then removing unnecessary portions by etching. , Each of which is formed in a predetermined pattern.
The insulating film is, for example, a silicon nitride layer, and is formed on the surface of the silicon substrate by sputtering or CVD.
The surfaces of the heating resistor and the temperature sensitive resistor are covered with a protective film made of a silicon nitride layer, for example, like the insulating film.

The control module 5 is disposed at the upper end of the sensor body 3 in the drawing and is disposed outside the attachment hole 6 of the intake pipe 1. The control module 5 has a control circuit and an output circuit on a built-in circuit board.
The control circuit is electrically connected to the heating resistor and the temperature sensitive resistor. Then, the control circuit supplies the amount of supply current (current value, amount of power) supplied to the heating resistor so that the temperature deviation between the heating temperature of the heating resistor and the intake air temperature detected by the temperature sensing resistor becomes a constant value. ) Is controlling. That is, the control circuit is an energization control circuit that controls energization (current) of the heating resistor.

  Here, the heating temperature of the heating resistor is determined on the basis of the electric resistance value of the temperature sensitive resistor, and a substantially constant temperature difference with respect to the ambient temperature (intake air temperature detected by the temperature sensitive resistor) by the control circuit. The energization is controlled so as to be (ΔT). Specifically, when ΔT of the heating resistor is controlled to 200 ° C., for example, when the ambient temperature (intake air temperature) is 20 ° C., energization control is performed so that the temperature of the heating resistor is about 220 ° C., Further, when the ambient temperature (intake air temperature) is 40 ° C., the energization is controlled so that the temperature of the heating resistor is about 240 ° C.

  The output circuit outputs the amount of heat released from the heating resistor to the circulating air flowing around the heating resistor as an electrical signal to the ECU. For example, a heating resistor and a temperature-sensitive resistor are incorporated in a bridge circuit, and even if the heat radiation amount of the heating resistor changes due to the circulating air flow around the heating resistor, a constant electrical resistance value (heating temperature, However, current control is performed so as to maintain temperature compensation), and the current value is converted into a voltage and output to the ECU as an air flow signal.

Here, the intake control device (electric motor that drives the throttle valve), the fuel injection device (injector), and the ignition device (ignition coil, spark plug) are configured to be driven (energization control) by the ECU. .
The ECU is provided with a well-known microcomputer that includes functions such as a CPU that performs control processing and arithmetic processing, a control program or control logic, and a storage device (memory such as ROM and RAM) that stores various data. ing.

  The ECU also inputs sensor signals from various sensors including an electric signal (air flow signal) output from the output circuit of the control module 5 to the microcomputer after the A / D converter performs A / D conversion. It is comprised so that. The microcomputer measures the intake air amount and the flow velocity taken into the combustion chamber of each cylinder of the engine based on the electrical signal (air flow signal) output from the air flow measurement device (thermal air flow meter) ( calculate.

[Operation of Example 1]
Next, the operation of the engine control system provided with the air flow measuring device (thermal air flow meter) of the present embodiment will be briefly described with reference to FIGS.

When the ignition switch is turned on (IG / ON), the ECU controls energization of the electric motor that drives the throttle valve, and also includes an ignition device (ignition coil, spark plug, etc.) and a fuel injection device (electric fuel pump, injector, etc.) Drive). As a result, the engine is operated.
When a specific cylinder of the engine moves from an exhaust stroke to an intake stroke in which the intake valve opens and the piston descends, the negative pressure (pressure lower than atmospheric pressure) in the combustion chamber of the cylinder increases as the piston descends. The air-fuel mixture is sucked from the intake port that is open.

At this time, a flow of intake air is generated in the intake passage 2 communicating with the opened intake port. When a flow of intake air is generated in the intake passage 2, a part of the clean intake air filtered by the filter element of the air cleaner flows into the bypass flow path 12 of the sensor body 3 in the air flow rate measuring device.
Since the bypass flow path 12 and the sub bypass flow path 13 communicate with each other through the communication port 29 inside the sensor body 3, the intake flow flowing through the bypass flow path 12 communicates with the sub bypass flow path 13. The air in the communicating portion 9 of the sub-bypass passage 13 moves to the second inclined portion side by the frictional force of the intake air flow that contacts the air in the portion 9 and flows through the bypass passage 12.
As a result, a circulating air flow in which air can circulate around the sensing unit 4 and the communication unit 9 is generated in the sub-bypass channel 13 as indicated by arrows in FIG. That is, the air in the communication portion 9 of the sub-bypass channel 13 is changed from the second inclined portion 25 → the second straight portion 26 → the second bent portion 27 → the straight portion 21 → the first bent portion 22 → the first straight portion 23 → It circulates through the first inclined portion 24 and circulates to the communicating portion 9.

And in the sensing part 4 installed in the inside of the sensor body 3 (the straight part 21 of the sub-bypass channel 13), when the flow velocity of the circulating air flow circulating through the straight part 21 of the sub-bypass channel 13 is increased, heat is generated. Since the amount of heat released from the resistor increases, the amount of current supplied to the heating resistor from the control circuit of the control module 5 in order to keep the temperature deviation (ΔT) from the intake air temperature measured by the temperature sensitive resistor at a constant value. Becomes larger.
Conversely, when the flow rate of the circulating air flow circulating through the straight portion 21 of the sub-bypass flow path 13 is reduced, the heat dissipation amount of the heating resistor is reduced, so that the supply supplied to the heating resistor from the control circuit of the control module 5 The amount of current is reduced.

  An electric signal (air flow signal) is output from the output circuit of the control module 5 to an external ECU in accordance with the amount of current supplied to the heating resistor, and combustion of each cylinder of the engine is performed by a microcomputer built in the ECU. The amount of intake air (intake amount) introduced into the room is measured (calculated). The microcomputer calculates the basic injection time from the intake air amount (intake air amount to the engine) measured by the air flow measuring device and the engine speed, and sensor signals (for example, throttle opening degree) from various sensors are calculated. Signal, engine coolant temperature signal, engine intake air temperature signal, etc.) are added to calculate the total injection time (fuel injection amount). The microcomputer controls the energization time and injection timing of the injector according to the fuel injection amount.

[Effect of Example 1]
As described above, in the air flow measuring device (thermal air flow meter) of the present embodiment, the sensor body 3 is disposed in the intake passage 2 on the downstream side in the intake flow direction from the filter element of the air cleaner. Part of the new intake air that has passed through the filter element flows into the inside of the sensor body 3 (bypass channel 12) from the inlet of the bypass channel 12. Further, fine dust that could not be captured by the filter element and part of dust such as filter dust (for example, dust having a minute particle diameter of about several μm to several hundred μm) are also taken together with the intake air flowing into the bypass passage 12. It flows into the sensor body 3 of the air flow rate measuring device.

  However, in the air flow rate measuring apparatus of the present embodiment, in addition to the bypass flow path 12, the sensor body 3 communicates with the bypass flow path 12 through a communication port 29 that opens downward in the figure, and An annular sub-bypass passage 13 in which a circulating circulation of air is generated is provided. In other words, since the air in the vicinity of the sensing unit 4 can circulate in the sub-bypass channel 13, the intake air that has flowed into the bypass channel 12 is unlikely to flow into the sub-bypass channel 13 through the communication port 29. It has become.

  Thereby, most of the dust contained in the intake air flowing through the bypass channel 12 does not flow into the sub-bypass channel 13 through the communication port 29, that is, installed in the straight portion 21 of the sub-bypass channel 13. It is difficult to reach the sensing unit 4 and flows out from the outlet of the bypass passage 12 into the intake passage 2 (main passage 11).

  Further, the internal space of the sensor body 3 of the air flow measurement device is divided into a partition wall section 14 that divides the bypass flow path 12 and the sub bypass flow path 13, and the circulating air that circulates in the sub bypass flow path 13 is placed near the communication port. By providing the tapered first guide 31 for guiding, the circulating air circulating in the sub-bypass channel 13 near the communication port and the intake air flowing in the bypass channel 12 are easily brought into frictional contact. The circulating air flow that circulates in the flow path 13 flows at the same flow rate as the flow rate of the intake flow that flows through the bypass flow path 12 or at a certain flow rate.

  As a result, the heat dissipation amount of the heating resistor that changes according to the flow rate of the circulating air flow circulating in the sub-bypass channel 13 communicating with the bypass channel 12 at the communication port 29 also corresponds to the flow rate of the bypass channel 12. The amount of heat released becomes a certain amount of heat released or the flow rate of the bypass flow passage 12, and the amount of intake air flowing through the main flow passage 11 of the intake passage 2 can be measured according to the amount of current supplied to the heating resistor (current value). It becomes.

  Further, a tapered second guide 32 for returning the air in the vicinity of the communication port circulated to the communication portion 9 to the partition wall portion 14 partitioned into the bypass flow channel 12 and the sub bypass flow channel 13 to the sub bypass flow channel 13. Since the circulating air in the vicinity of the communication port that circulates and circulates in the communication portion 9 is easy to return to the second inclined portion 25 of the sub-bypass passage 13 (is easy to flow in), the intake air flowing through the bypass passage 12 Is difficult to flow into the second inclined portion 25 of the sub-bypass passage 13 from the communication port 29.

  Therefore, in the air flow rate measuring apparatus of the present embodiment, the heating resistor and the sensation are formed on the surface of the silicon substrate on the straight portion 21 of the sub-bypass channel 13 where dust contained in the air flowing through the bypass channel 12 is difficult to flow. Since the sensing unit 4 in which the temperature resistor is formed is installed, it is possible to reduce the amount of dust attached to the heating resistor and the like of the sensing unit 4. This makes it difficult for the heating resistor and the like of the sensing unit 4 to be fouled and suppresses a decrease in the amount of heat transfer from the heating resistor to the circulating air (heat radiation amount), so that the output characteristics of the output circuit of the control module 5 Is difficult to change over time, and the measurement error of the intake air amount is reduced. In addition, it is possible to prevent functional degradation (performance degradation) due to fouling of the heating resistor and the temperature sensitive resistor of the sensing unit 4.

Further, since dust contained in the intake air flowing into the bypass channel 12 is difficult to reach the sensing unit 4 installed in the straight portion 21 of the sub-bypass channel 13, for example, the particle size is several hundreds It is possible to prevent damage to the heating resistor, the temperature sensitive resistor, the silicon substrate, and the like due to the dust of about μm colliding with the sensing unit 4.
As described above, in the air flow rate measuring apparatus according to the present embodiment, it is possible to prevent the deterioration and damage of the heating resistor and the like of the sensing unit 4, so that the amount of intake air in the heating resistor of the sensing unit 4 is detected. Accuracy can be ensured.

[Modification]
In this embodiment, a heating resistor formed in a predetermined pattern on the surface of a silicon substrate (circuit board) is used as a flow measuring element, but a cylindrical bobbin is inserted as a flow measuring element at both ends of this bobbin. A pair of lead wires to be formed, a resistance wire wound around the outer periphery of the bobbin and connected to the lead wire, a heating resistor configured to protect the resistance wire and the lead wire, or the like may be used. Further, as the protective film, for example, a glass coating film containing lead oxide that is fired at a high temperature may be used.

In the present embodiment, the sensing unit 4 having at least one heating resistor and at least one temperature compensation resistor (temperature-sensitive resistor) is located farthest from the communication port 29 and dust is intruded by the block 15. Although it is installed in the straight part 21 of the sub bypass flow path (air circulation flow path) 13 that is obstructed, the sensing part 4 is a first bent except for the communication part 9 of the sub bypass flow path (air circulation flow path) 13. You may install in any one of the part 22, the 1st linear part 23, the 1st inclination part 24, the 2nd inclination part 25, the 2nd linear part 26, and the 2nd bending part 27. Further, the sub-bypass channel (air circulation channel) 13 may be a polygonal annular channel such as a mouth shape, or may be an annular, elliptical or oval annular channel.
Also, the direction of opening of the communication port is not only the vertical direction (top and bottom direction) in the figure but also the lower side (ground direction) in the figure, as well as the horizontal direction orthogonal to the top and bottom direction or a direction inclined by a predetermined inclination angle with respect to the top and bottom direction It may be.
Further, in this embodiment, the main flow path 11, the bypass flow path 12 and the sub bypass flow path 13 are provided as the intake passage 2, but the main flow path is abolished and only the air introduction flow path and the air circulation flow path are provided. May be provided.

It is sectional drawing which showed the attachment state of the air flow rate measuring apparatus with respect to an intake pipe (Example 1). (A), (b) is sectional drawing and the side view which showed the air flow measuring device. (A) is AA sectional drawing of Fig.2 (a), (b) is BB sectional drawing of Fig.2 (a), (c) is CC sectional drawing of Fig.2 (a). (D) is DD sectional drawing of Fig.2 (a).

Explanation of symbols

1 Intake pipe (intake pipe, air cleaner outlet pipe, throttle body)
2 Intake passage 3 Sensor body (housing)
4 Sensing part (sensor part)
5 Control module (circuit module)
9 Communication part 11 Main flow path 12 Bypass flow path (air introduction flow path)
13 Sub-bypass channel (air circulation channel)
14 Bulkhead 15 Block 29 Communication Port 31 First Guide 32 Second Guide

Claims (3)

(A) an air introduction flow path for supplying air to the internal combustion engine;
(B) an air circulation channel that has a communication portion that communicates with the air introduction flow channel, and in which air can circulate around the communication portion;
(C) An air flow rate measuring device including a flow rate measuring element installed in the air circulation channel. The air flow rate measuring device according to claim 1,
The communication portion has a communication port that opens in a direction perpendicular to the direction of air flow through the air introduction flow path,
The air flow rate measuring device according to claim 1, wherein the communication port is provided in a partition wall partitioning the air introduction flow path and the air circulation flow path. In the air flow measuring device according to claim 2,
The partition portion returns a first guide for guiding the air circulating in the air circulation channel to the vicinity of the communication port, and the air in the vicinity of the communication port circulated to the communication unit to the air circulation channel. An air flow rate measuring device having a second guide for the purpose.

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