JPH11142200A - Air flow rate measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a measuring apparatus which enhances a shieldability and a dust resistant property by a method wherein a metal or resin mesh which covers a heating resistor and a thermosensitive resistor is built in a small passage near the heating resistor and the thermosensitive resistor. SOLUTION: A body 4 holds a drive circuit 2 by which a signal from a heating resistor 1 is converted electrically into an air flow rate signal, and it forms an air passage into which the whole air flow rate flows and which is composed of a main passage 5 and of an auxiliary passage 6. A straightening lattice 7 which stabilizes the flow of the intake air, which enhances the measuring accuracy of an air flow rate and which reduces a noise is formed of a metal mesh to be a tube shape, and it is built in the body 4 together with a module 8 which is composed of the heating resistor 1, of the drive circuit 2 and of a thermosensitive resistor 3. In addition, the straightening lattice 7 is arranged near the heating resistor 1 and the thermosensitive resistor 3. By this structure, the dust resistant property and the radio frequency noise resistant property of a measuring apparatus can be enhanced together with the straightening effect of the intake air as the intrinsic function of the straightening lattice 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rectifying grid suitable for an air flow meter for measuring the flow rate of air taken into an internal combustion engine. The improvement structure.

[0002]

2. Description of the Related Art Conventionally, in order to fix a mesh to a body as disclosed in Japanese Patent Application Laid-Open No. 62-232517, a mesh edge is swaged with a frame at a mesh edge, and the outer periphery of the frame is used as a reference. Was built into the body. Therefore, the rectifying grid has no function other than the rectifying grid.

[0003]

However, since the rectifying grid described in the above-mentioned prior art has no function other than the rectifying grid, the rectifying grid is provided at the intake air introduction portion of the body holding the heating resistor and the temperature-sensitive resistor. It was often installed in.

The present invention has been devised in order to make the rectification grid multifunctional by adding a value other than the rectification grid by changing the shape and installation structure of the rectification grid. A metal or resin mesh in the form of a rectifying grid can also serve as a shield covering the heating resistor by being arranged near the heating resistor and the temperature-sensitive resistor. The influence on the heat generating resistor from dust flowing in with the intake air may be reduced.

[0005]

The rectifying grid structure of the present invention which solves the above-mentioned problems has a structure in which a commonly used metal mesh is formed so as to cover the entire circumference or a part of a heating resistor and a temperature sensing resistor. Molding. At this time, the mesh is achieved by forming into a cylindrical shape that covers the heating resistor and the temperature-sensitive resistor by the deep drawing of a press or the usual punching press.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a sectional view of the air flow measuring device provided with the rectifying grid of the present invention, and FIG. 2 is a front view of the air flow measuring device provided with the rectifying grid of the present invention shown in FIG. is there.

First, the structure and operating principle of the air flow measuring device will be described with reference to FIGS.

In the present invention, a thermal air flow measuring device will be described as a model. The thermal type air flow measuring device includes a drive circuit 2 having a feedback circuit for heating the heating resistor 1 to a predetermined temperature, and a temperature sensing resistor 3 for measuring the temperature of intake air.
And a body 4 for holding these. The heating resistor 1 is heated so as to be always maintained at a constant temperature difference from the temperature sensing resistor 3 for measuring the air temperature. Since the heating resistor 1 is installed in the airflow, the surface portion of the heating resistor 1 that radiates heat to the airflow serves as a heat dissipation surface, that is, a heat transfer surface. This heat transfer converts the amount of heat taken by the air flow into an electrical signal to measure the air flow.

Next, the configuration of the air flow measuring device will be described. Reference numeral 4 denotes a body that holds a drive circuit 2 that converts a signal from the heating resistor 1 into an air flow signal by electrically converting the signal, and forms an air passage into which the total intake air flow flows. The body 4 has two passages divided into a main passage 5 as one air passage into which most of the intake air flows, and a sub passage 6 as the other air passage into which a part of the air flows. .

Usually, a rectifying grid that promotes stabilization of the flow of intake air, improves air flow measurement accuracy, and reduces output signal noise (hereinafter referred to as noise) has a structure that is installed in an air flow intake portion of the body 4. Almost. In the present invention, the rectifying grid 7 is formed into a tubular shape with a metal mesh, and is assembled into the body 4 together with the module 8 including the heating resistor 1 and the temperature-sensitive resistor 3 including the driving circuit, and the rectifying grid 7. It is characterized in that it is arranged near the heating resistor 1 and the temperature-sensitive resistor 3.

FIG. 3 is an assembly structure diagram in which the rectifying grid 7 of the present invention is installed in an air flow measuring device. An embodiment of the present invention will be described with reference to FIG. The module 8 including the drive circuit 2 for electrically controlling the heating resistor 1 and the temperature-sensitive resistor 3 is usually
The structure is such that it is inserted into the bypass passage 9 forming the sub passage 6 and further incorporated into the body 4.

In the present invention, the module 8 and the bypass passage 9
And a mesh formed by metal or resin, that is, a rectifying grid 7 is inserted between them. The rectifying grid 7 shown in FIG. 3A can be formed from a single mesh in a deep drawing manner by pressing. Since the rectifying grid of this form has a brim portion 12 attached to a mesh formed in a cylindrical shape, the rectifying grid has good handling properties and is a shape advantageous in automatic assembly. If the shape of the rectifying grid 7 shown in FIG. 3A cannot be obtained, a single mesh sheet as shown in FIGS. 3B and 3C may be punched and formed into a round shape.

By arranging the rectifying grid 7 in the vicinity of the heating resistor 1 and the temperature-sensitive resistor 3 according to the present invention, not only the rectification effect of the intake air, which is the original purpose, but also the dust resistance of the heating resistor 1 is improved. There is a possible effect. Dust flowing in with the intake air gradually accumulates on the surface of the heating resistor 1 and eventually changes the heat transfer from the heating resistor 1 to the air as shown in FIG. This is a factor that deteriorates the accuracy.

In the present invention, dust accumulated on the surface of the heating resistor 1 can be reduced by the rectifying grid 7 arranged near the heating resistor 1. This is because the intake air that has flowed into the body 4 comes into contact with the mesh lines of the rectifying grid, so that Karman vortices are generated behind the respective contact portions, and thereafter the air flow branches. The branched air flow contacts the heating resistor 1 at a certain angle instead of being horizontal with respect to the heating resistor 1.

Dust tends to accumulate in the horizontal direction with respect to the heating resistor 1, but when the air stream contacts at a certain angle, the dust and the surface of the heating resistor 1 contact each other. During this time, a slip phenomenon occurs, and dust hardly accumulates. As shown at 11 in FIG. 4, it is clear that the dust characteristics of the product of the present invention can be improved as compared with the conventional product.

The rectifying grid 7 disposed near the heating resistor 1 and the temperature-sensitive resistor 3 shown in FIG. 5 is preferably formed of a conductive metal mesh. The rectifying grid 7 of the present invention is characterized in that a screw fastening hole 13 is provided in the collar portion 12 and the rectifying grid 7 is fixed to the body 4 with screws together with the rectifying grid 7 provided between the module 8 and the bypass passage 9. This structure is such that the inside of the rectifying grid 7 formed into a cylindrical shape is shielded by the metal fastening of the screw tightening portion and the brim section 12 of the rectifying grid 7 with the body 4 (when made of metal) or the metal base of the module 8. Create an effect. In other words, the rectifying grid 7 covering the entire circumference of the heating resistor 1 and the temperature-sensitive resistor 3 has a shielding effect obtained by making metal contact with the ground of the metal body 4 and the module 8, so that the heat-generating resistor 1 and the temperature-sensitive resistor 3 can be obtained. 3 has the effect of reducing the influence of the propagated radio wave that propagates from the control circuit 3 and enters the drive circuit 2.

That is, the propagating radio wave that normally floats enters the driving circuit 2 electrically through the heating resistor 1 and the temperature-sensitive resistor 3 which are conductive members without a shield portion. Since the rectifying grid 7 covers the entire circumference of the heating resistor 1 and the temperature-sensitive resistor 3 to form a shield, the floating radio wave propagates to the rectifying grid 7 and falls to the ground. There is no possibility that the drive circuit 2 will malfunction due to electrical intrusion from the temperature-sensitive resistor 3.

FIG. 6 shows a radio interference resistance characteristic 14 when the rectifying grating 7 of the present invention is disposed and a radio interference resistance characteristic 15 when it is not disposed. It can be seen that there is an effect of improving the anti-electromagnetic interference performance from the shielding effect of the rectifying grid covering the heating resistor 1 and the temperature-sensitive resistor 3 in the low frequency region.

[0020]

According to the present invention, it is possible to provide a high quality air flow measuring device which has a rectifying effect on the intake air, which is an original function of the rectifying grid, and is effective in improving dust resistance and electromagnetic interference resistance. Has an effect.

[Brief description of the drawings]

FIG. 1 is a side sectional view of an air flow measuring device according to an embodiment of the present invention.

FIG. 2 is a front view of FIG. 1;

FIG. 3 is an exploded structural view of FIG. 1;

FIG. 4 is a dust characteristic diagram of the air flow measuring device.

FIG. 5 is a perspective view showing another embodiment of the rectifying grating shown in FIG. 3;

FIG. 6 is a characteristic diagram showing radio wave resistance of the air flow measuring device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heating resistor, 2 ... Drive circuit, 3 ... Temperature sensitive resistor, 4 ...
Body, 5: Main passage, 6: Sub passage, 7: Rectifying grid, 8:
Module, 9: Bypass passage, 10: Dust characteristics of conventional product, 11: Dust characteristics of present product, 12 ... Collar, 13 ...
Screw tightening holes, 14: Electromagnetic interference resistance characteristics of the product of the present invention, 15: Electromagnetic interference resistance characteristics of conventional products.

Claims (4)

[Claims] 1. A structure provided with a small passage provided in a main passage through which a part of the total air flow rate flows, and a heating resistor and a temperature-sensitive resistor element for measuring an air flow amount are installed in the small passage. In the air flow measuring device having, the metal or resin mesh that covers the heating resistor and the temperature-sensitive resistor element is formed into a tubular shape or a shape that covers the entire heating resistor and the temperature-sensitive resistor element, and An air flow measuring device, wherein the air flow measuring device is incorporated in the small passage and arranged near a heating resistor and a temperature-sensitive resistor element. 2. A method according to claim 1, wherein a part of the mesh covering the heating resistor and the temperature-sensitive resistor element incorporated in the small passage into which a part of the intake air flow rate flows is metal-touched to the body or the circuit module to ground. An air flow measurement device, wherein a radio wave resistant shield covering the heating resistor and the temperature-sensitive resistor is formed by electrically connecting the heating resistor and the temperature-sensitive resistor. 3. The intake air comes into contact with the flow straightening grid to generate a Karman vortex downstream of the flow straightening grid. Then, the air flow flows backward while branching. An air flow measuring device characterized in that a heating resistor or a temperature-sensitive resistor is arranged at a position where there is. 4. An air flow measuring device for measuring an air flow using the rectifying grid according to any one of claims 1, 2 and 3.