JPH11118558A - Air flow rate measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus for measuring the air flow rate with high accuracy by suppressing disturbance of air flow in a bypath through a simple structure. SOLUTION: A bypath 34 comprises an upstream channel 34a for passing the air from an intake port 31d in one radial direction of an air channel 2, a downstream channel 34b for passing the air in the opposite radial direction to the upstream channel 34a disposed in parallel with the upstream channel 34a on the downstream side thereof, and a channel 34c communicating between the upstream channel 34a and the downstream channel 34b. A corner part 35 facing the joint between the upstream channel 34a and the downstream channel 34b is formed into a smooth concave face having arcuate cross-section. Since generation of vortexes in the air flow passing a heat-sensitive resistor 25 and a heating resistor 26 arranged in the vicinity of the corner part 35 or disturbance of the air flow can be suppressed, fluctuation in the output of air flow rate being detected by the heat-sensitive resistor 25 and the heating resistor 26 can be suppressed and the air flow rate can be detected with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air flow measuring device for measuring a flow rate of air flowing through an air flow path by providing a bypass flow path in an air flow path and measuring the flow rate of air flowing through the bypass flow path.

[0002]

2. Description of the Related Art Conventionally, a bypass flow path is provided in an air flow path, and the flow rate of the air flowing through the bypass flow path is measured by a flow rate measuring element disposed in the bypass flow path. BACKGROUND ART An air flow measuring device for measuring a flow rate is known. In this way, the air flow rate in the air flow path is indirectly measured by the flow rate measurement element disposed in the bypass flow path. Depending on the shape of the bypass flow path, eddy currents, air density, etc. may be present in the vicinity of the flow rate measurement element. In some cases, the fluctuation of the air flow detected by the flow measuring element unit becomes large due to the turbulence of the air flow. If the difference between the air flow actually flowing in the air flow passage and the air flow detected by the flow measurement element disposed in the bypass flow passage is large, for example, the fuel injection amount in which the measured air flow is a control factor Cannot be optimally controlled in accordance with the operating state of the engine, resulting in a problem that harmful substances discharged into the exhaust gas increase. Particularly, in the thermal type flow rate measuring device using a heating resistor in the flow rate measuring element portion, the heating resistor is minute and quickly responds to the fluctuation of the flow rate, so that it responds sensitively to the turbulence of the air flow. Therefore, the measured flow rate tends to fluctuate due to turbulence in the air flow.

In the air flow measuring device disclosed in Japanese Patent Application Laid-Open No. Hei 8-5428, the corner of the body is formed in a circular arc shape at the connection between the axial bypass and the radial bypass, so that the bypass flow passage is formed. An attempt is made to reduce turbulence such as eddy currents and air density in an air flow flowing through the inside, thereby reducing the fluctuation range of a measured flow rate.

[0004]

However, in the air flow measuring device disclosed in Japanese Patent Application Laid-Open No. 8-5428, a heating resistor and a temperature-sensitive resistor as flow measuring elements disposed in the axial bypass are used. The air in the air flow path collides directly. Therefore, the adhesive foreign matter in the air flow path directly collides with the heating resistor and the temperature-sensitive resistor and adheres to each resistor, so that the control current of each resistor changes and the measured flow rate changes with time. There is.

In order to generally use an air flow measuring device mounted on various intake pipes, it is desirable to have a bypass flow passage inlet near the center of the duct where the flow velocity is stable. In the L-shaped bypass flow passage, it is difficult to arrange the bypass flow passage inlet at the center of the duct. The purpose of the present invention is
It is an object of the present invention to provide an air flow measuring device that has a simple configuration, reduces turbulence in the air flow in a bypass flow path, and accurately measures an air flow.

[0006]

According to the air flow measuring device according to the first aspect of the present invention, in the U-shaped bypass flow passage, the communication portion between the upstream flow passage and the communication flow passage, and the downstream flow passage. The corner of the bypass member facing at least one of the communicating portions between the flow path and the communication flow path is formed in a curved shape. Therefore, the air flow flowing through the bypass flow path is smoothed, and the occurrence of turbulence such as eddy currents and air density is reduced in the air flow. Therefore, the air flow rate can be detected with high accuracy in the flow rate measuring element section, and the air flow rate can be measured with high accuracy based on the detection signal.

Further, since the bypass flow path is formed in a U-shape, the air flowing from the air flow path collides with the inner wall of the bypass member before colliding with the flow rate measuring element portion, and the air in the air having an adhesive force is formed. Foreign matter adheres to the inner wall and is removed. This reduces foreign substances in the air flow path from directly colliding with the flow rate measuring element and adhering to the flow rate measuring element, so that the measured flow rate can be prevented from changing over time.

Further, since the bypass passage formed in a U-shape can arrange the bypass passage entrance near the center of the duct, a stable flow can be measured, and the air flow rate can be measured with high accuracy. Can be. According to the air flow measuring device according to the second aspect of the present invention, by forming both the upstream and downstream corners of the communication flow path in a curved shape, the air flow flowing through the bypass flow path is further increased. It is smoothed and reduces the occurrence of turbulence such as eddies and air density in the air flow.

According to the air flow measuring device according to the third aspect of the present invention, by disposing the flow measuring element in the vicinity of one of the corners formed in a curved surface, the bypass flow surrounded by the bypass member is provided. Since the flow measuring element is disposed in the back of the road, foreign matter in the air is less likely to adhere to the flow measuring element.
Furthermore, even if the flow rate measuring element is arranged near the corner where the air flow direction changes, the air flow near the corner may be disturbed by eddy currents and air density due to the curved corner. That has been reduced. Therefore, the air flow rate can be measured with high accuracy.

According to the air flow measuring device according to the fourth aspect of the present invention, since the flow measuring element is composed of the heating resistor and the temperature-sensitive resistor, the air flow can be quickly responded to the fluctuation of the air flow and the air can be precisely measured. The flow rate can be measured.

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a first embodiment of the present invention; (First Embodiment) FIGS. 1 and 2 show an example in which an air flow measuring device according to a first embodiment of the present invention is attached to an intake pipe of an internal combustion engine.
Shown in

[0012] As shown in FIG.
Consists of a circuit module 20 and a bypass member 30. The bypass member 30 is inserted into a mounting hole 1 a provided in the intake pipe 1 and disposed in the air flow path 2. The circuit module 20 is attached to the intake pipe 1 with bolts 29.
The circuit module 20 and the bypass member 30 are connected by bonding or welding.

The circuit module 20 has a circuit section and a flow measuring element section. In addition, the circuit module 20 includes a thermistor 27 as an air temperature measuring element for measuring the air temperature in the air flow path 2. The circuit section has a housing 21, a control circuit 22, a heat sink 23, a connector 24, and a cover 28, and the flow measuring element section has a temperature-sensitive resistor 25 and a heating resistor 26 shown in FIG.

As shown in FIG. 2, the control circuit 22 is accommodated in a resin housing 21 and is held by an aluminum heat radiating plate 23 as a heat radiating member for radiating heat generated from the control circuit 22. I have. The heat radiating plate 23 may be formed of another metal material instead of aluminum. The circuit module 20 is mounted on the intake pipe 1 by fastening the mounting portion 23 a provided on the heat sink 23 to the intake pipe 1 with a bolt 29. Since the circuit module 20 and the bypass member 30 are modularized, the air flow measuring device 10 is attached to the intake pipe 1 by attaching the circuit module 20 to the intake pipe 1.

As shown in FIGS. 1 and 2, the control circuit 2
2 is electrically connected to the temperature-sensitive resistor 25, the heating resistor 26, and the thermistor 27 via support members 25a, 26a, 27a. The control circuit 22 controls energization of the temperature-sensitive resistor 25 and the heat-generating resistor 26, and detects air detected by the temperature-sensitive resistor 25 and the heat-generating resistor 26 in accordance with the flow rate of air flowing through a bypass passage 34 described later. The detection signal of the flow rate and the detection signal of the air temperature detected by the thermistor 27 are output from the connector 24.

The temperature-sensitive resistor 25 and the heating resistor 26 are
The bypass passage 34 is provided near a communicating portion between an upstream passage 34a and a communication passage 34c described later. Temperature sensitive resistor 2
In order to measure the temperature of the air that touches the heating resistor 26, it is preferable to install the heater 5 near the heating resistor 26 within a range that is not affected by the heat radiation of the heating resistor 26. The bypass member 30 has an outer tube 31 and a venturi tube 32 formed integrally with the outer tube 31. The outer tube 31 and the venturi tube 32 are arranged parallel to the air flow. The Venturi tube 32 is located at the bottom of the outer tube 31 on the side opposite to the circuit module 20, and is connected to the circuit module 20 from the Venturi tube 32.
The partition wall 33 extends toward. The partition wall 33 partitions an upstream channel 34a and a downstream channel 34b, which will be described later.

The bypass passage 34 is defined by the inner wall of the outer tube 31 and the partition wall 33. The inner wall surface of the outer tube 31 has an upstream flat surface 31a extending in the cross-sectional direction of the air flow channel 2 and a downstream flat surface 31b located downstream of the upstream flat surface 31a and expanding in the cross-sectional direction of the air flow channel 2. And a bottom plane 31c located at the bottom of the bypass flow path 34 and perpendicular to each of the upstream plane 31a and the upstream plane 31a. Upstream plane 3
The corner 35 connecting the first flat surface 1a and the bottom flat surface 31c is formed in a smooth concave curved surface having an arc-shaped cross section, and the downstream flat surface 31b
36, which intersects with the bottom plane 31c, are formed at right angles. If it is a smooth concave curved surface, the cross-sectional shape of the corner portion 35 is not limited to an arc shape. The partition wall 33 is formed in a thin plate shape, and the end on the side of the communication flow path 34c is rounded into a convex curved shape.

The bypass flow passage 34 has an upstream flow passage 34a in which air flowing from the intake inlet 31d flows in one radial direction of the air flow passage 2, and an upstream flow passage 34 downstream of the upstream flow passage 34a.
and a communication flow path as a bent portion of a bypass flow path which connects the upstream flow path and the downstream flow path, the flow path being provided in parallel with the downstream flow path and flowing air in a radial direction opposite to the upstream flow path a. 34c. The flow direction of the air flowing from the upstream flow path 34a toward the downstream flow path 34b changes in the communication flow path 34c.

The flow passage area of the upstream flow passage 34a is
b, the flow velocity of the air flow flowing through the upstream flow path 34a is faster than the flow velocity of the air flow flowing through the downstream flow path 34b. As described above, since the temperature-sensitive resistor 25 and the heat-generating resistor 26 are disposed near the communication portion between the upstream flow path 34a and the communication flow path 34c, that is, at a location where the flow velocity is high in the bypass flow path 34, The air flow rate can be detected with high accuracy by the temperature-sensitive resistor 25 and the heating resistor 26, and the air flow rate can be measured with high accuracy based on the detection signal.

Next, the operation of the air flow measuring device 10 will be described with reference to FIG. The air flowing from the intake passage 2 into the intake inlet 31 d of the outer pipe 31 is divided into a flow toward the upstream passage 34 a of the bypass passage 34 and a flow toward the Venturi passage 32 a in the Venturi tube 32. The air flow flowing in the upstream flow path 34a smoothly flows to the communication flow path 34c along the concave curved corner 35. Communication channel 34c
The airflow flowing from the airflow to the downstream flow path 34b merges with the air passing through the venturi flow path 32a on the downstream side of the venturi pipe 32, and flows out to the air flow path 2 from the intake outlet 31e. On the downstream side of the Venturi tube 32, a negative pressure is generated because the flow velocity of the air increases. The air in the bypass passage 34 is sucked by the negative pressure, and the flow velocity of the air in the bypass passage 34 is increased.

The control circuit 22 controls the heating resistor 26 so that the difference between the temperature of the heating resistor 26 calculated from the current value supplied to the heating resistor 26 and the air temperature detected by the temperature-sensitive resistor 25 becomes constant. Control the current value supplied to the
Output this current value as a flow rate detection signal. Here, the effect of the air flow measuring device 10 of the first embodiment will be described in comparison with a comparative example shown in FIG.

In the comparative example, two corners 42 and 43 formed on the upstream side and the downstream side of the communication channel 34c are both formed at right angles where planes intersect. The other configuration is the same as that of the first embodiment. Therefore, the corner 4 where the temperature-sensitive resistor 25 and the heat-generating resistor 26 are disposed is provided.
In the vicinity of 2, the air flow is likely to be disturbed such as a vortex or air density. Due to the turbulence of the air flow, as shown in FIG.
In addition, the fluctuation range of the output of the air flow rate detected by the heating resistor 26 increases.

On the other hand, in the air flow measuring device 10 of the first embodiment, the corner 35 located near the position where the temperature-sensitive resistor 25 and the heat-generating resistor 26 are disposed is formed in a concave curved surface. Therefore, turbulence such as a vortex generated in the air flow and air density is suppressed. Therefore, even when the air flow rate increases, the fluctuation range of the output of the air flow rate detected by the temperature-sensitive resistor 25 and the heating resistor 26 is smaller than that in the comparative example. The flow rate can be detected with high accuracy, and the air flow rate can be measured with high accuracy based on the detection signal.

In the first embodiment, the thermistor 27 for detecting the temperature of the air in the air flow path 2 is provided. However, a configuration without the thermistor may be adopted. (Second Embodiment) FIG. 5 shows a second embodiment of the present invention. First
Components that are substantially the same as those in the embodiment are denoted by the same reference numerals.

In the second embodiment, the temperature-sensitive resistor 25 and the heat-generating resistor 26
The corner 53 formed downstream of the communication flow path 34c as well as the corner 52 at which is disposed is formed in an arcuate concave curved surface. Therefore, the bypass flow path 3 is larger than in the first embodiment.
Since the turbulence such as the vortex and the density of the air is suppressed from occurring in the air flow flowing through the inside 4, the fluctuation range of the output of the air flow rate detected by the temperature-sensitive resistor 25 and the heating resistor 26 is further reduced, Air flow rate can be measured with high accuracy.

In the embodiments described above, at least the corners where the temperature-sensitive resistor 25 and the heat-generating resistor 26 are disposed in the vicinity are formed in an arcuate concave curved surface.
The turbulence such as eddy currents and air density is suppressed from occurring in the airflow flowing through the temperature-sensitive resistor 25 and the heating resistor 26. Therefore, by measuring the air flow rate flowing in the vise flow path 34, the air flow rate flowing in the air flow path 2 can be measured with high accuracy.

Further, since the vise flow path 34 is formed in a U-shape, the foreign matter having an adhesive force contained in the air flow path 2 does not directly collide with the temperature-sensitive resistor 25 and the heat-generating resistor 26. Since it collides with and adheres to the partition wall 33, the temperature-sensitive resistor 25
In addition, the adhesion of foreign matter to the heating resistor 26 can be reduced. Therefore, the temperature-sensitive resistor 25 and the heating resistor 26
Since it is possible to suppress the foreign matter from adhering to the surface, it is possible to reduce a change in the flow rate output with time due to a change in the heat generation temperature.

Further, since the bypass flow path inlet can be arranged near the center of the duct, a stable flow can be measured, and the air flow rate can be measured with high accuracy. In the above embodiments, the temperature-sensitive resistor 25 and the heating resistor 26 are disposed on the upstream side of the communication channel 34c.
It may be arranged downstream of c. In this case, the communication channel 34
The corner located on the downstream side of c is formed into a circular arc-shaped smooth concave curved surface. The corner located on the upstream side of the communication flow path 34c may be formed in any shape of a right angle or a concave curved surface.

Further, the temperature-sensitive resistor 2 may be located at any position in the bypass flow path, not in the vicinity of the corner formed in the concave curved shape.
5 and the heating resistor 26 may be provided. Further, in the above-described plurality of embodiments, the end of the thin plate-like partition 33 on the side of the communication channel 34c is rounded to form a convex curved surface. However, when the thickness of the partition is thick, the upstream of the end of the partition 33 on the side of the communication channel 34c. It is desirable that, of the convex corners formed on the side and the downstream side, the corners where the temperature-sensitive resistor 25 and the heating resistor 26 are disposed in the vicinity are formed in a convex curved shape.

The present invention is not limited to an apparatus for measuring the air flow rate of an internal combustion engine, but can be used as an apparatus for measuring an air flow rate flowing through various air flow paths.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a state in which an air flow measuring device according to a first embodiment of the present invention is attached to an intake pipe.

FIG. 2 is a view in the direction of arrow II in FIG. 1;

FIG. 3 is a characteristic diagram showing a relationship between a flow rate and an output fluctuation width in the first embodiment and a comparative example.

FIG. 4 is a longitudinal sectional view showing a comparative example of the first embodiment.

FIG. 5 is a longitudinal sectional view showing a state in which an air flow measuring device according to a second embodiment of the present invention is attached to an intake pipe.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Intake pipe 2 Air flow path 10 Air flow measuring device 20 Circuit module 22 Control circuit 23a Attachment part 25 Temperature sensitive resistor 26 Heating resistor 27 Thermistor 30 Bypass member 31 Outer pipe 32 Venturi pipe 33 Partition wall 34 Bypass flow path 34a Upstream flow Road 34b Downstream flow path 34c Communication flow path 35, 36, 52, 53 Corner

Claims (4)

[Claims] 1. An air flow measuring device for measuring an air flow rate flowing through an air flow path, a bypass member disposed in the air flow path, and a part of the air flowing through the air flow path. A bypass member that forms a U-shaped bypass flow path into which a fluid flows, a flow rate measurement element section disposed in the bypass flow path, and an electrical connection with the flow rate measurement element section, wherein the flow rate measurement element section A control circuit that outputs a detection signal of the air flow rate detected in the above, wherein the bypass flow path is provided on an upstream flow path through which air flows in one radial direction of the air flow path, and on a downstream side of the upstream flow path. A downstream flow path in which air flows in a radial direction opposite to the upstream flow path, and a communication flow path that communicates the upstream flow path and the downstream flow path, the upstream flow path and the communication flow path And a small number of communication parts between the downstream flow path and the communication flow path. Ku even air flow rate measuring apparatus characterized by forming the corners of the bypass member facing either a curved surface. 2. The air flow measuring device according to claim 1, wherein both the corners located on the upstream side and the downstream side of the communication flow path are formed in a curved shape. 3. The air flow measuring device according to claim 1, wherein the flow measuring element is provided near one of the corners formed in a curved shape. 4. The air flow measuring device according to claim 1, wherein the flow measuring element has a heating resistor and a temperature-sensitive resistor.