JP2001033288A - Air flow rate measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the change with time of the output characteristic caused by adhesion of a foreign matter, by preventing the foreign matter in the air from adhering to a flow rate measuring element with an extremely simple structure. SOLUTION: A reversely U-shaped bypass passage 18 is installed in an intake pipe 11, and a flow rate measuring element 29 and a temperature sensing element 30 are installed in the upper part of an upstream-side passage 18a of the bypass passage 18. An air inflow opening 19 is formed on the side face of the upstream-side passage 18a, and a foreign matter passing opening 23 is formed on a part, facing the upper-side part of the air inflow opening 19, of a partition 17 of the bypass passage 18. Thereby, the foreign matter in the air flowing into the upstream-side passage 18a of the bypass passage 18 is sent to a downstream-side passage 18c through the foreign matter passing opening 23. A guide wall 24 for guiding the air passing through the foreign matter passing opening 23 toward the downstream side of the downstream-side passage 18c is formed on the surface on the downstream-side passage 18c side of the partition 17, and the air flow passing through the foreign matter passing opening 23 is joined smoothly to a bypass flow in the downstream-side passage 18c.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air flow measuring device in which a bypass flow path is arranged in an air passage, and the flow rate of air is measured by a flow measuring element arranged in the bypass flow path.

[0002]

2. Description of the Related Art Conventionally, this type of air flow measuring device has been used as an air flow meter for measuring an intake air flow rate of an internal combustion engine. In addition, a flow rate measuring element (heating element) and a temperature sensing element are installed at a predetermined interval, and the flow rate is adjusted so that the temperature difference between the heating temperature of the flow rate measuring element and the detection temperature (intake temperature) of the temperature sensing element is kept constant. The supply current of the measuring element is controlled, and the intake air flow rate is measured based on the supply current value.

[0003] Usually, an air cleaner is provided at the most upstream portion of the intake passage. However, foreign matters such as fine dust and oil particles which cannot be caught by the air cleaner, filter dust of the air cleaner, and the like are taken into the air flow measuring device together with the intake air. May flow in. When such foreign matter adheres to the flow measuring element,
Since the amount of heat transfer (radiation) from the flow measuring element to the air decreases, the output characteristics of the air flow measuring device change with time due to the attachment of foreign matter to the flow measuring element, and the measurement error of the intake air flow rate decreases. It gets bigger.

In Japanese Patent Laid-Open Publication No. Hei 6-18303, a flow rate measuring element and a catching means for catching foreign matter on the downstream side of the flow rate measuring element are provided in a sub air passage arranged in the air passage. Separation vortices are generated in the auxiliary air passage by the trapping means, and the flow path resistance due to the separation vortices is configured to decrease as the amount of foreign matter adhering to the trapping means increases. To compensate for the decrease in heat dissipation capability due to the decrease in flow path resistance (increased air flow velocity) due to foreign matter adhering to the capturing means, thereby preventing the output characteristics from changing over time due to foreign matter adhering to the flow rate measuring element. I have.

In Japanese Patent Laid-Open Publication No. Hei 10-197308, two sub air passages are crossed in an air passage, and a flow measuring element is arranged at the crossing portion, and the flow of air in the two sub air passages is periodically changed. By switching the air flow alternately from different directions to the flow measuring element, thereby eliminating foreign substances adhering to the flow measuring element and preventing the output characteristics from changing over time due to foreign substances adhering to the flow measuring element. Like that.

[0006]

However, the former (Japanese Patent Application Laid-Open No. 6-18303) has difficult problems such as the estimation of the amount of adhered foreign matter and the setting of the shape and size of the trapping means for generating the separation vortex in accordance therewith. Therefore, it is very difficult to accurately compensate for the decrease in the heat radiation capability of the flow rate measuring element due to the adhesion of the foreign matter by the decrease in the flow path resistance (increase in the air flow velocity) by the capturing means. Therefore, it is very difficult to prevent output characteristics from changing with time using this technique.

On the other hand, in the latter case (JP-A-10-197308), a change in output characteristics is unavoidable because the adhering matter remains in a portion of the flow rate measuring element where the air flow does not hit. Measurement accuracy decreases over time.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances. Therefore, the object of the present invention is to prevent foreign substances in the air from adhering to the flow rate measuring element with a very simple structure, and to prevent the foreign substances from adhering. It is an object of the present invention to provide an air flow measuring device that can more reliably prevent the output characteristics from changing with time than the conventional technology and can improve the measurement accuracy of the air flow.

[0009]

In order to achieve the above-mentioned object, an air flow measuring device according to a first aspect of the present invention is arranged such that a bypass flow path provided in an air passage is provided with respect to a direction of air flow in the air passage. The upstream flow path and the downstream flow path arranged at a substantially right angle are formed in an inverted U-shaped flow path connected by a bent portion, and the partition wall that separates the upstream flow path and the downstream flow path is formed. A foreign matter passage port is formed at a position facing the air inlet of the upstream flow path or in the vicinity thereof.

In this configuration, the air that has flowed from the air inlet into the upstream flow path of the bypass flow path changes direction substantially at right angles to the air flow direction in the air flow path, and the air flows into the bypass flow path (the upstream flow path). Flow → bend → downstream flow path). At this time, foreign substances such as dust, oil particles, and filter dust of an air cleaner contained in the air flowing from the air inlet port have a large inertia compared to the air flow and tend to flow linearly. If a foreign substance passage port is formed at or near the air inlet of the partition wall (that is, a place where the air flow changes direction at a substantially right angle), the foreign substances in the air will be removed by the inertia together with some air. Shortcut the bypass flow path through the passage port and flow to the downstream flow path. This makes it possible to prevent foreign matter in the air from adhering to the flow rate measuring element in the bypass flow path, and to achieve an output characteristic due to foreign matter adhesion with a very simple structure in which a foreign matter passage opening is formed in the partition wall of the bypass flow path. The change with time can be more reliably prevented than in the prior art, and the measurement accuracy of the air flow rate can be improved.

In this case, a guide wall for guiding air passing through the foreign matter passage port toward the downstream side of the downstream flow path is provided in the downstream flow path of the bypass flow path. Good. In this way, the flow of air (shortcut flow) passing through the foreign matter passage can be smoothly merged with the bypass flow flowing in the downstream flow path, and the turbulence (flow rate) Fluctuation of the flow velocity of the bypass flow hitting the measuring element) can be reduced, and output fluctuation of the flow measuring element can be reduced.

In consideration of the fact that the air flowing from the air inlet into the upstream flow path changes direction at a substantially right angle toward the flow measuring element and flows, the foreign matter passage port is provided as in claim 3 Is preferably formed so as to straddle a position facing the air inlet and a position closer to the flow measuring element than the position. In this way, even foreign substances flowing on the flow measurement element side from the position opposite to the air inlet on the bypass flow toward the flow measurement element side can pass through the foreign substance passage port, and Can be more reliably prevented from adhering.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an air flow meter (air flow meter) for an internal combustion engine will be described below with reference to the drawings. As shown in FIG. 1, an air flow measuring device 13 is mounted in a mounting hole 12 formed at a predetermined position in an intake pipe 11 (air passage) of an internal combustion engine by a plug-in method. The air flow measuring device 13 includes a circuit module 14 and a flow measuring unit 15. The flow rate measuring unit 15 has the mounting hole 1 as a whole.
It is formed in the shape of a rectangular tube extending from 2 to the vicinity of the central axis C of the intake pipe 11. This flow measurement unit 15 is provided with the intake pipe 1
The two pipes extending in the radial direction of 1 are arranged along the air flow direction of the intake pipe 11 and joined by the partition wall 17, so that the upstream flow path 18a and the downstream flow path 18c are connected by a bent portion 18b. An inverted U-shaped bypass flow path 18 is formed.
The flow path cross-sectional area A1 of the upstream flow path 18a of the bypass flow path 18 is formed to be smaller than the flow path cross-sectional area A2 of the downstream flow path 18c.

An air inlet 19 through which a part of the air (main flow) flowing through the intake pipe 11 flows into the flow measurement unit 15 is formed on the upstream side surface of the flow measurement unit 15. At the lower end of the flow measurement unit 15, a Venturi tube 16 is integrally formed in parallel with the main flow direction. An air outlet 22 of the bypass flow path 18 is formed on the downstream side of the Venturi pipe section 16, and the air flow (bypass flow) of the bypass flow path 18 passes through the Venturi pipe section 16 on the downstream side of the Venturi pipe section 16. It merges with the flow of air (venturi flow).

Further, in the partition 17, a foreign substance passage 23 is formed at a portion facing the upper part of the air inlet 19, at the downstream side flow path 1.
8c. The upper part of the foreign substance passage port 23 projects upward (toward the flow measuring element 29) from the upper end of the air inlet 19, and the lateral width of the foreign substance passage port 23 is
The width is substantially the same as the width of the air inlet 19 (FIG. 2).
reference). A guide wall 24 that guides the flow of air (shortcut flow) passing through the foreign matter passage 23 toward the downstream side of the downstream flow passage 18c is provided on the surface of the partition wall 17 on the downstream flow passage 18c side. The mouth 23 is formed to extend downward from the upper edge.

On the other hand, the opening at the upper end of the flow measuring unit 15 is closed by the circuit module 14. On the lower surface of the circuit module 14, a flow rate measuring element 29 (heating element) and a temperature sensing element 30 are assembled at predetermined intervals by supporting members 31, 32, respectively.
9 and the temperature sensing element 30 are installed above the upstream flow path 18 a of the bypass flow path 18. Here, the reason for installing the flow rate measuring element 29 in the upstream flow path 18a is that the flow path cross-sectional area A1 of the upstream flow path 18a is smaller than the flow path cross-sectional area A2 of the downstream flow path 18c, This is because the flow velocity is higher in the upstream flow path 18a, and the flow measurement accuracy is higher when the flow velocity of the bypass flow is higher. Since the temperature sensing element 30 measures the temperature of the air that comes into contact with the flow measurement element 29, it is preferable that the temperature sensing element 30 is installed near the flow measurement element 29 within a range that is not affected by heat radiation of the flow measurement element 29.

A circuit board (not shown) for controlling the flow of electricity to the flow measuring element 29 and the temperature sensing element 30 is housed inside the circuit module 14, and a wire harness (FIG. (Not shown) is insert-molded. An intake air temperature sensor 35 (see FIG. 2) is disposed on the lower surface side of the circuit module 14 so as to protrude downward. Detects the temperature of the air flowing inside (intake air temperature).

The flange 20 at the upper end of the flow measuring unit 15 is fitted with a fitting projection 36 on the lower surface of the circuit module 14.
The inner peripheral portion of the mounting hole 12 is sealed by an O-ring 37 mounted on the outer periphery of the fitting convex portion 36. Then, with the lower surface of the circuit module 14 in contact with the upper surface of the peripheral edge of the mounting hole 12, as shown in FIG.
The screw 39 is inserted into the screw insertion hole of the intake pipe 11 and screwed into the screw hole of the attachment portion 40 of the intake pipe 11, whereby the air flow measuring device 13
Is assembled in the mounting hole 12 of the intake pipe 11 by a plug-in method.

The air flow measuring device 1 configured as described above
In 3, a part of the air flowing through the intake pipe 11 flows into the upstream flow path 18 a of the bypass flow path 18 and the Venturi pipe part 16 from the air inlet 19 separately. Bypass channel 18
The air that has flowed into the upstream flow path 18a changes direction at a substantially right angle to the air flow direction in the intake pipe 11, and the bypass flow path 18 (the upstream flow path 18a → the bent portion 18b → the downstream flow) Flows along road 18c). This bypass flow merges with the flow of air (Venturi flow) passing through the Venturi tube 16 on the downstream side of the Venturi tube 16. At the junction, a suction force (negative pressure) acts on the air outlet 22 of the bypass passage 18 by the Venturi flow, thereby increasing the flow velocity of the bypass flow. Then, the current (heat generation temperature) of the flow measurement element 29 is controlled by the circuit module 14 so that the temperature difference from the detected temperature (intake air temperature) of the temperature sensing element 30 becomes constant, and the current of the flow measurement element 29 at that time is controlled. The bypass flow rate and thus the intake air flow rate are measured according to the value.

In this case, most of the air that has flowed in from the upper portion of the air inlet 19 turns upward at substantially right angles to the main flow direction and flows through the upstream flow passage 18a of the bypass flow passage 18. In the embodiment, since the foreign matter passage port 23 is formed in a portion of the partition wall 17 of the bypass passage 18 facing the upper side of the air inlet 19, a part of the air flowing from the upper side of the air inlet 19 is formed. Cuts off the bypass passage 18 through the foreign matter passage 23 and makes the downstream passage 18
Flows to c. If foreign matter such as dust, oil particles, and filter dust of an air cleaner is included in the air flowing from the air inlet 19, the foreign matter tends to flow linearly with a large inertia as compared with the flow of air. Along with a part of the air, it flows through the foreign matter passage 23 to the bypass flow path 18 to flow to the downstream flow path 18c. This prevents foreign substances in the air from reaching and adhering to the flow measurement element 29.

As is apparent from the above description, in the present embodiment, the air is formed by a very simple method of forming the foreign substance passage 23 in the portion of the partition 17 of the bypass passage 18 opposite to the air inlet 19. Foreign matter in the inside can be prevented from adhering to the flow rate measuring element 29, and a change over time in the output characteristics due to the foreign matter adhering can be suppressed, and the measurement accuracy of the air flow rate can be improved.

In this embodiment, the air flow (shortcut flow) passing through the foreign substance passage 23 is guided by the guide wall 24 toward the downstream side of the downstream flow path 18c. The shortcut flow that has passed through 23 can be smoothly merged with the bypass flow in the downstream flow passage 18c. Accordingly, disturbance of the bypass flow due to the merging of the shortcut flows can be prevented, fluctuation in the flow velocity of the bypass flow impinging on the flow measurement element 29 can be reduced, and output fluctuation of the flow measurement element 29 can be reduced.

In order to evaluate the output fluctuation of the flow rate measuring element 29 caused by the foreign matter passage 23, the present inventors have compared the air flow measurement device 13 of this embodiment (with the foreign matter passage 23) with the conventional air flow measurement device. (Without the foreign matter passage port 23), a test was performed to compare the fluctuation range of the output with respect to the air flow rate of both, and the test result is shown in FIG. This test was performed without any foreign matter adhering to the flow rate measuring element 29 in any case. According to the test results, even in the air flow measuring device 13 of the present embodiment (with the foreign matter passage port 23),
By providing the guide wall 24, the fluctuation range of the output with respect to the air flow rate can be reduced by a conventional air flow rate measuring device (without the foreign substance passage port 23).
It was confirmed that it could be at almost the same level as.

Also, in the present embodiment, the upper part of the foreign matter passage opening 23 is taken into consideration in consideration that most of the air flowing from the upper part of the air inlet 19 turns upward and flows through the bypass passage 18. Since the projection is made to protrude above the upper end of the air inlet 19, the foreign matter that flows on the bypass flow toward the flow measuring element 29 and flows upward (toward the flow measuring element 29) from the position facing the air inlet 19. Also, the foreign matter can pass through the foreign matter passage port 23, and the foreign matter can be more reliably prevented from adhering to the flow rate measuring element 29.

It should be noted that the present invention is not limited to the foreign matter passage port 23 or the guide wall 2.
The position and shape of 4 and the shape of the venturi tube section 16 may be changed as appropriate. In addition, the present invention is not limited to a device for measuring an intake air amount of an internal combustion engine, but can be used as a device for measuring an air flow rate flowing through various air passages.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional front view showing an assembled state of an air flow measuring device according to an embodiment of the present invention.

FIG. 2 is a longitudinal left side view showing an assembled state of the air flow measuring device.

FIG. 3 is a characteristic diagram of the output fluctuation width showing a comparison between the output fluctuation width of the air flow measurement device of the present embodiment and the output fluctuation width of the conventional air flow measurement device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 ... Intake pipe (air passage), 12 ... Mounting hole, 13 ... Air flow measurement device, 14 ... Circuit module, 15 ... Flow measurement unit, 16 ... Venturi pipe part, 17 ... Partition wall, 18 ...
Bypass flow path, 18a ... upstream flow path, 18b ... bent portion,
18c: Downstream flow path, 19: Air inlet, 22: Air outlet, 23: Foreign matter passage, 24: Guide wall, 29: Flow measuring element, 30: Thermosensitive element.

Claims (3)

[Claims] 1. An air flow rate, wherein a bypass flow path through which a part of air flowing through the air flow path flows is arranged in an air flow path, and an air flow rate is measured by a flow rate measuring element disposed in the bypass flow path. In the measurement device, the bypass flow path is an inverted U-shaped flow path in which an upstream flow path and a downstream flow path that are disposed at substantially right angles to the air flow direction in the air passage are connected by a bent portion. A foreign matter passage opening is formed at a position facing the air inlet of the upstream flow path or in the vicinity thereof, of the partition partitioning the upstream flow path and the downstream flow path that is formed. Characteristic air flow measurement device. 2. A guide wall provided in the downstream flow passage for guiding air passing through the foreign matter passage opening toward a downstream side of the downstream flow passage. An air flow measuring device according to item 1. 3. The foreign matter passage port is formed so as to straddle a position facing the air inlet and a position closer to the flow measuring element than the position. 3. The air flow measuring device according to 1 or 2.