JPH0572012A - Heat wire type air flowmeter - Google Patents

Abstract

PURPOSE:To enable both electric wave interference resistance characteristics and the measures against electric wave interference of a heat wire type air flowmeter to be compatible. CONSTITUTION:Heat wires 5 for measuring an air flowrate and a temperature- sensing resistor 6 for compensating temperature are incorporated into a body 1 with an intake passage 2 through a support pin 4. The body 1 is made of a non-conductive synthetic resin, an annular conductive band 9 is fitted to at least one portion of the outer wall so that an outer periphery of the body may be surrounded, thus enabling the heat wire 5, the temperature-sensing resistor 6, and the support pin 4 to be surrounded. In stead of the conductive bond 9, a conductive pattern according to plating or paint may be formed on an outer wall of the body 1 or at least one part of the body 1 may be formed by a conductive synthetic resin. These conductive members are grounded to a low-potential terminal or a GND terminal of a heat wire drive circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot wire type air flow meter for detecting the flow rate of air supplied to an engine, and more particularly to a technique for preventing radio wave interference of the hot wire type air flow meter.

[0002]

2. Description of the Related Art Conventionally, a technique of providing a hot-wire air flow meter on a body forming a part of an intake passage of an engine has been widely known. Recently, it has been proposed that the body be made of synthetic resin to reduce its weight.

When the body is made of synthetic resin as described above, the heat ray type air flow meter is easily affected by external noise (electromagnetic waves), and it is necessary to prevent this. This electromagnetic wave propagates through a harness to a module composed of a heating resistor (heat wire), a temperature-sensing resistor for temperature compensation, and a drive circuit, and when the radiation causes the heating resistor, the temperature-sensitive resistor, and these. In some cases, the support pins of the above may propagate as an antenna. Electromagnetic waves propagating from the harness are taken as countermeasures by a through capacitor and a shield structure in the connector section.

On the other hand, the propagation by radiation is disclosed in, for example, Japanese Patent Laid-Open No.
As disclosed in Japanese Patent Application Laid-Open No. 9-159020, a conductive coating portion is provided on a passage wall for measuring an air flow rate to cover a heating element and its support, and is disclosed in Japanese Patent Laid-Open No. 63-229327. As described above, it has been proposed to cover the heating resistor and its support with a conductive cap to take measures for electromagnetic shielding.

[0005]

Among the above-mentioned radio wave interference resistant techniques, in the method of forming the conductive coating on the passage wall for measuring the air flow rate, the passage for measuring the air flow rate has the main intake passage on the side wall of the body. When it is provided by bypass, it is necessary to apply a conductive coating to the inner wall of the narrow bypass passage by, for example, insert, mixing with resin, plating, painting or the like, and a high level coating technique is required. On the other hand, in the method of covering the periphery of the heating resistor and its support with a conductive cap, if a step is formed between the cap and the inner wall of the passage in which it is mounted, turbulent flow occurs and the accuracy of measuring the air flow rate is adversely affected. , Strict accuracy is required for cap mounting.

The present invention has been made in view of the above points, and an object thereof is to provide means for easily taking measures against radio wave interference with respect to a heat wire type air flow meter, and yet not impairing flow rate measurement accuracy. To do.

[0007]

In order to achieve the above object, the present invention basically proposes the following problem solving means.

That is, in a hot wire type air flow meter in which a heating resistor for measuring an air flow rate and a temperature sensitive resistor for temperature compensation are incorporated inside a body having an intake passage through a support pin, the body is a cylinder. Shaped synthetic resin, at least part of the outer wall of the body surrounds the outer circumference of the body,
(A) A ring-shaped conductive band is attached, (b) a conductive pattern is formed by plating or paint, or at least a part of the body is (c) formed by a conductive synthetic resin. An annular conductive band, a conductive pattern, or a conductive resin is used to surround the heat generating resistor, the temperature sensitive resistor, and the support pin, and the conductive band,
The conductive pattern or conductive resin was grounded to the low potential terminal or GND terminal of the drive circuit for the heating resistor.

[0009]

As described above, the propagation of external noise (electromagnetic waves) from the heat ray type air flow meter by radiation becomes particularly large when the body of the intake passage is made of synthetic resin.

As a countermeasure against this problem, the present invention provides the outer wall of the body with a conductive member according to any one of the above (a) to (b), whereby the module of the heating resistor, the temperature sensitive resistor and the support pin is provided. Since the impedance of the conductive member is smaller than the impedance, the electromagnetic wave propagates not through the module side but through the conductive member and falls to the GND or the low potential terminal of the drive circuit. As a result, malfunction due to electromagnetic waves is eliminated, and radio wave interference resistance is improved.

Further, in order to prevent the above-mentioned radio wave interference, an annular conductive band is fitted to the outer wall of the body, plated or coated, or at least a part of the body is made of a conductive synthetic resin. Compared with the technique of coating the inner wall of the passage inside the body, the forming technique can be performed easily and does not require detailed work, and the simple passage structure inside the body can be maintained. Will not be adversely affected.

[0012]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a vertical sectional view of a hot wire type air flow meter according to a first embodiment of the present invention, and FIG. 2 is a front view thereof.

In these figures, a body 1 is made of non-conductive synthetic resin, and a main intake passage 2 for supplying air to the engine and a passage 3 for measuring an air flow rate are provided inside. The passage 3 for measuring the air flow rate is arranged on the side wall of the body 1 so as to bypass the main intake passage 2.

A heat generating resistor (hereinafter referred to as a heat wire) for measuring an air flow rate is provided in the bypass passage 3 via each support pin 4.
5 and a temperature sensitive resistor (cold wire) 6 for temperature compensation are arranged. More specifically, on the outer wall of the body 1, a case 7 accommodating the drive circuit part of the hot wire air flow meter is attached together with a base 8 made of a conductive member, and the support pins 4 are attached from inside the case 7 to the base 8 and the body. Hole 1
By passing a, the heat generating resistor 5 and the temperature sensitive resistor 6 previously welded to the tip of the support pin 4 are positioned in the bypass passage 3.
As the heating wire 1, a platinum wire is wound on an alumina bobbin and the surface thereof is coated with a glass material. The temperature sensitive resistor 6 has the same structure as the heating wire 5.

A conductive band 9 is attached to the outer wall of the body 1 so as to surround the outer periphery thereof. The conductive band 9 is fitted to a position on the outer wall of the body 1 that surrounds the heat ray 5 and the temperature-sensitive resistor 6, and has an annular band shape that fits the outer wall at the surrounding position.

3 and 4 show specific examples of these conductive bands 9, in which both ends 9a and 9b of the band 9 are fitted into the groove 13a formed on the mounting surface 13 of the base 8 and the screw 1
The base 8 and the band 9 are fastened to the outer wall of the body 1 by 2. The band 9 is attached to the base 8 via the screw 12.
It is grounded to the (GND terminal of the drive circuit). Band 9 is
For example, when using a metal material, a plated brass plate C280
1R1 / 44, t0.5, Cu underlayer 0.5 to 1.8μ
m, Sn plating 1 to 2 μm, etc. are effective, a screw hole 11 having a width of 5 mm or more for passing a screw 12 is provided at an end, and an external mounting metal fitting 10 is provided at an appropriate position.

In the above structure, a current is supplied from the drive circuit to the heating wire 5 arranged in the bypass passage 3 for heating the heating wire to a constant temperature regardless of the increase / decrease in the air flow rate. The constant temperature is a temperature at which the heating temperature of the heating wire 5 maintains a constant temperature difference with respect to the air temperature, and the air temperature is corrected by the temperature sensing resistor 6 for temperature compensation. There is a monotonically increasing function relationship between the current flowing through the heating wire 5 and the air flow rate, whereby the air flow rate is detected.

The conductive band 9 formed on the outer wall of the body is grounded to the ground while surrounding the heat ray 5, the temperature sensitive resistor 6 and its support pin 4, and the heat ray 5, the temperature sensitive resistor 6 and the support pin 4 are connected. Since the impedance of the conductive band 9 is smaller than the module impedance, the electromagnetic wave that is external noise propagates through the conductive band 9 and falls to GND, not on the module side. As a result, erroneous measurement due to external noise is eliminated, and radio wave interference resistance is improved.

FIG. 11 shows a conventional resin body only,
The anti-jamming characteristics of the present invention are compared with those of the present invention.
It was greatly improved in the vicinity of 0 MHz to 550 MHz.

FIG. 12 shows the relationship between the electric field strength at a frequency of 80 MHz and the width of the conductive member (band). When the width is 5 mm or more, the electric field strength is 3 V / m or more.

Further, according to the radio wave resistant means of the present embodiment, it is only necessary to fit the conductive band 9 to the outer wall of the body 1 and fix it with screws, and it is difficult to mount the conductive band 9 inside the body as compared with the outside. Since it is not necessary to provide any anti-interference measures,
It is possible to guarantee the accuracy improvement of the hot wire type air flow meter by a simple mounting work and without adversely affecting the flow of the bypass passage 3.

FIG. 5 shows a second embodiment of the present invention, in which the module including the heat ray, the temperature sensitive resistor, the support pins of these, and the driving circuit is not attached, but is the same as the first embodiment. It is the installation of. Further, the same reference numerals as those in the first embodiment indicate the same or common elements (the same applies to FIG. 5 and subsequent figures).

In this embodiment, most of the body 1 is made of non-conductive synthetic resin, and a part of its outer wall layer is made of conductive synthetic resin 9-1. That is, in this embodiment, the resin body 1 and
A ring-shaped conductive resin 9-1 having a width of 5 mm or more was molded on the outer periphery thereof. The conductive resin 9-1 is in contact with the conductive base or the like of the module of the hot-wire type air flow meter and grounded to GND as in the first embodiment.

FIG. 6 shows a third embodiment of the present invention. In this embodiment as well, the module including the heat wire, the temperature-sensitive resistor, the support pins for these elements, and the drive circuit is not mounted, but the module is mounted in the same manner as in the first embodiment.

In the present embodiment, the non-conductive synthetic resin forming the body 1 is used as the resin element 1A to which plating is hard to adhere.
And a resin element 1B to which plating is easily attached. The resin element 1B forms a part of the passage walls of the main intake passage 2 and the bypass passage 3 while surrounding the heat ray, the temperature sensitive resistor and the support pins thereof, and the resin element 1B and the resin element 1A around it. Is injection-molded by a two-stage mold. After this two-stage molding, plating 9-2 was applied to the entire outer circumference of the resin element 1B. The plating 9-2 is also grounded to GND.

Also in the above second and third embodiments, the heat generating resistor and the temperature sensitive resistor in which the conductive resin 9-1 and the plating 9-2 are arranged in the bypass passage 3 at the position of the outer wall of the body 1. Also, by surrounding the support pins and the support pins, the anti-jamming characteristics of the first embodiment can be obtained.

FIG. 7 is a front view of a hot wire type air flow meter according to a fourth embodiment of the present invention, and FIG. 8 is a partial sectional view thereof.

In this embodiment, as a countermeasure against electromagnetic interference, a conductive band 9 is attached to the outer wall of a non-conductive synthetic resin body 1 as in the case of the first embodiment. A large number of small protrusions 20 were provided in the above, and the small protrusions 20 were fitted into the small holes 20 provided in the band 9, and then the small protrusions 20 were caulked by thermal deformation.

FIG. 9 is a front view of a hot wire type air flow meter according to a fifth embodiment of the present invention, and FIG. 10 is a partial sectional view thereof.

This embodiment is a modification of the fourth embodiment.
Two projections 20-1 extending in the circumferential direction are provided on the outer wall of the non-conductive synthetic resin body 1, and a conductive band 9 having an annular shape is fitted between the projections 20-1. 20-
1 is heat-deformed and the conductive band 9 is attached to the body 1.
Attached to the outer wall of the.

FIG. 13 is a front view of a hot wire type air flow meter according to a sixth embodiment of the present invention. In this embodiment, a part 9c of the conductive band 9 mounted on the outer wall of the body 1 is used as a drive circuit. The low potential portion 8 was welded and electrically connected.

FIG. 14 is a sectional view of a hot wire type air flow meter according to a seventh embodiment of the present invention, and FIG. 15 is a front view thereof. In the present embodiment, the heat wire 5 and the temperature sensitive resistor 6 are arranged in the center of the main intake passage 2, and in this case as well, the conductive band 9 and the conductive resin as described above are provided on the outer wall of the body 1. 9-
By setting either 1 or plating 9-2, it is possible to take measures against radio waves. Although not shown, even if a rectifying cylinder is provided in the center of the main intake passage 2 and a heat wire, a temperature sensitive resistor, and a support pin are arranged in this rectifying cylinder, the same conductivity as in the seventh embodiment is obtained. It is possible to improve the resistance to electromagnetic interference by applying a conductive member.

[0034]

As described above, according to the present invention, in the hot-wire type air flow meter, it is possible to take measures against radio waves more easily than in the past, and further, such measures against radio waves are taken. Since it does not hinder the flow of the air flow rate measurement passage, it is possible to maintain good measurement accuracy of the air flow rate.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a first embodiment of the present invention.

FIG. 2 is a front view of the first embodiment.

FIG. 3 is a perspective view of a conductive band used in the above embodiment.

FIG. 4 is a perspective view of a conductive band used in the above embodiment.

FIG. 5 is a vertical sectional view of a second embodiment of the present invention.

FIG. 6 is a vertical sectional view of a third embodiment of the present invention.

FIG. 7 is a front view of the fourth embodiment of the present invention.

FIG. 8 is a partial cross-sectional view of the fourth embodiment.

FIG. 9 is a vertical sectional view of a fifth embodiment of the present invention.

FIG. 10 is a partial cross-sectional view of the fifth embodiment.

FIG. 11 is an explanatory view showing the radio interference resistance characteristics of the product of the present invention and the conventional product in comparison.

FIG. 12 is an explanatory diagram showing the relationship between the width of a conductive member used in each of the above examples and the electric field strength.

FIG. 13 is a partial front view showing a sixth embodiment of the present invention.

FIG. 14 is a vertical sectional view showing a seventh embodiment of the present invention.

FIG. 15 is a front view of the seventh embodiment.

[Explanation of symbols]

1 ... Body, 2 ... Intake passage, 3 ... Bypass passage, 4 ... Support pin, 5 ... Heating resistor (heat wire), 6 ... Temperature sensitive resistor, 8
... Base, 9 ... Conductive band, 9-1 ... Conductive resin, 9
-2 ... Plating, 20, 20-1 ... Protrusion for heat crimping.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadao Suzuki 2520 Takaba, Katsuta-shi, Ibaraki, Sawa Plant, Hitachi Ltd. (72) Inventor Motoyuki Takeda 2477 Kashima Yatsu, Katsuta-shi, Ibaraki 3477 Hitachi Automotive Engineering Co., Ltd. (72) Inventor Masatoshi Sugiura 2477 Kashima Yatsu Kashima, Katsuta City, Ibaraki Prefecture 3 Hitachi Automotive Engineering Co., Ltd.

Claims (8)

[Claims] 1. A hot wire type air flow meter in which a heating resistor for measuring an air flow rate and a temperature sensing resistor for temperature compensation are incorporated inside a body having an intake passage via a support pin, wherein the body is a cylinder. -Shaped synthetic resin, a ring-shaped conductive band is attached to at least a part of the outer wall of the body so as to surround the outer circumference of the body, and the conductive band surrounds the heating resistor, the temperature-sensitive resistor, and the support pin. The heat wire type air flow meter, wherein the conductive band is grounded to the low potential terminal or the GND terminal of the drive circuit for the heating resistor. 2. A hot wire type air flow meter in which a heating resistor for measuring an air flow rate and a temperature sensing resistor for temperature compensation are incorporated through a support pin inside a body having an intake passage, wherein the body is a cylinder. -Like synthetic resin is used to form a conductive pattern by plating or paint on at least a part of the outer wall of the body so as to surround the outer circumference of the body, and the conductive pattern forms the heating resistor, the temperature-sensitive resistor and the support pin. A heat wire type air flow meter, characterized in that the conductive pattern is surrounded, and the conductive pattern is grounded to a low potential terminal or a GND terminal of a drive circuit for the heating resistor. 3. A hot wire type air flow meter in which a heating resistor for measuring an air flow rate and a temperature sensing resistor for temperature compensation are incorporated through a support pin inside a body having an intake passage, wherein the body is a cylinder. -Shaped synthetic resin, at least a part of the body is made of conductive synthetic resin, and the conductive synthetic resin surrounds the heating resistor, the temperature sensitive resistor and the support pin. A heat wire type air flow meter characterized in that a synthetic resin is grounded to a low potential terminal or a GND terminal of the drive circuit for the heating resistor. 4. The hot wire type air flow meter according to claim 1, wherein the conductive band is attached to the outer wall of the body by screwing. 5. The hot-wire air flowmeter according to claim 1, wherein the conductive band is mounted by crimping a protrusion formed on the body by thermal deformation. 6. The hot wire type air flow meter according to claim 3, wherein the body is injection-molded of a non-conductive synthetic resin and a conductive synthetic resin by a two-step molding method. 7. The heat-generating resistor and the temperature-sensitive resistor according to claim 1, wherein the heat-generating resistor and the temperature-sensitive resistor are arranged in a bypass passage provided in a side wall of the body so as to bypass the intake passage. A hot wire air flow meter. 8. The hot wire type air flow meter according to claim 1, wherein the heat generating resistor and the temperature sensitive resistor are arranged in a central portion of the intake passage.