JP2003270017A - Sealing structure for thermal flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a corrosive gas from permeating to the inside of a thermal flowmeter. <P>SOLUTION: The thermal flowmeter has a structure wherein a base is bonded to a body having an auxiliary passage in which a heating resistor and a temperature-sensitive resistor are installed or to a housing molded integrally with the auxiliary passage, an electronic circuit used to control the heating resistor and the temperature-sensitive resistor is installed inside the housing and the housing is covered with a cover. The structure is achieved in such a way that, when the base used to hold the electronic circuit is bonded to the housing, it is bonded by combining an elastic adhesive such as a silicone adhesive or the like and an adhesive of low gas permeability such as a nylon adhesive, an epoxy adhesive, a polyurethane adhesive or the like or a seal member, and that a gas-permeation shielding layer is formed. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adhesive sealing structure for a thermal type flow meter, and more particularly to an air flow rate measuring device suitable for detecting the intake air flow rate of an internal combustion engine.

[0002]

2. Description of the Related Art As disclosed in Japanese Patent Application Laid-Open No. 11-125551, a conventional sealing structure for a thermal type flow meter has a metal part inserted in a resin member inside a module in which an electronic circuit is installed. There is disclosed a structure in which a counterbore is provided in the minute gap generating part, and a sealing member such as a silicone adhesive is applied to the counterbore part to fill the gap between the resin and the inserted metal member.

[0003]

In the airtight structure in the above-mentioned prior art, the silicone gel for protecting the electronic circuit parts and the wires for transmitting electric signals flows out from the inside of the module in which the electronic circuit is installed to the outside. For the purpose of prevention, a silicone adhesive is mainly used as an adhesive member that seals the gap between the resin member and the inserted metal member.

However, since a silicone adhesive generally has high gas permeability and does not prevent liquid from leaking, it does not have a shielding property against gas. Therefore, in an environment where corrosive gas is prevalent, the silicone adhesive is used. There is a risk that corrosive gases will penetrate into the module through the adhesive and corrode electronic circuits.

[0005]

A sealing structure for a thermal type flow meter according to the present invention which achieves the above objects will be described. A thermal type flow meter has a base bonded to a body having a sub-passage in which a heat-generating resistor and a temperature-sensitive resistor are installed, or to a housing integrally formed with the sub-passage, and the heat-generating resistor and the temperature-sensing body inside the housing. An electronic circuit for controlling the resistor is installed, and the housing is covered with a cover. When the base for holding the electric circuit and the housing are bonded,
This can be achieved by forming a gas permeation shield layer by combining and bonding an elastic adhesive such as a silicone adhesive and an adhesive having low gas permeability such as nylon, epoxy, polyurethane, or a sealing member in combination.

[0006]

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

Before specifically describing the present invention, a thermal type flow meter in which the present invention will be most effectively used will be described with reference to FIG.

The heat generating resistor 1 of the thermal type flow meter using the heat generating resistor 1 and the temperature sensitive resistor 2 is always constant with the temperature sensitive resistor 2 for measuring the air temperature when the fluid to be measured is air, for example. A constant temperature is controlled by an electronic circuit 3 that is feedback-controlled so as to maintain a temperature difference, and is constantly heated. Since the heating resistor 1 is installed in the air flow, the surface portion of the heating resistor 1 that radiates heat to the air flow serves as a heat radiation 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 rate. Reference numeral 4 is a body 4 that holds an electronic circuit 3 that electrically converts the signal from the heating resistor 1 into an air flow rate signal and that forms an air passage into which the total intake air flow rate flows. The body 4 has both 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, and heat is generated. The resistor element including the resistor 1 and the temperature sensitive resistor 2 is arranged in the sub passage 6.

Particularly when used in an internal combustion engine for automobiles, a microcomputer determines the amount of injector injection into the cylinder of the internal combustion engine based on the signal measured by the air flow meter and the signals of other sensors to control combustion of the internal combustion engine. However, since the combustion control of the internal combustion engine is performed based on the signal of the air flow meter, the thermal type flow meter using the heating resistor 1 and the temperature sensitive resistor 2 can directly measure the mass flow rate. With the advantages,
It is used in more control systems of internal combustion engines because of its reliability.

FIG. 1 shows the sealing structure of the thermal type flow meter proposed by the present invention.

The thermal type flow meter has a heating resistor 1 and a temperature sensing resistor 2.
And is connected to an electronic circuit 3 for electrically controlling a constant temperature based on the electric signals of the heating resistor 1 and the temperature sensitive resistor 2. The electronic circuit 3 for controlling the constant temperature is formed by a ceramic or a multilayer ceramic firing plate,
In many cases, the hybrid IC substrate 7 has an electronic circuit formed between layers or on the surface thereof.
The circuit conductor formed on the C substrate 7 is often made of silver or a silver alloy. However, since the circuit conductor formed on the hybrid IC substrate 7 is formed of silver or a silver alloy, when exposed to a corrosive gas such as sulfur gas, the circuit conductor has high corrosion reactivity and does not corrode. There is a risk that Therefore, in order to secure the reliability against corrosive gas, a sealing structure in which these corrosive gas does not enter the inside of the housing is important.

In the structure of a general thermal type flow meter, a silicone adhesive is often used for bonding the hybrid IC substrate 7 and the base 9 holding the housing 8. This is because there is a background that a silicone adhesive, which is an elastic rubber adhesive, is selected from the viewpoint of reliability for adhesion between the base 9 made of a metal having a large linear expansion coefficient and the housing 8 made of resin. When the silicone adhesive has high gas permeability and is exposed to a corrosive gas environment, it has extremely high gas permeability as compared with other polymer members.For example, when exposed to a corrosive gas-filled environment, Adhesive part 1 of silicone adhesive
0, or a corrosive gas permeates from the filling part to reach the inside of the housing 8, and eventually the conductor part of silver or silver alloy formed on the hybrid IC substrate 7 inside the housing 8 may be corroded. .

Therefore, although it suffices to use a silicone adhesive having high gas permeability for bonding the base 9 and the housing 8, the environment in which the thermal type flow meter is used is -4.
It is assumed that the product will be used in a severe temperature environment from 0 ° C to 130 ° C, and when used in such a severe environment, it is the only silicone adhesive that can maintain adhesion reliability. Is. In the present invention, in order to protect the conductor formed of silver or silver alloy of the hybrid IC substrate 7 inside the housing 8 from corrosion due to permeation of corrosive gas, the gas from the bonding portion 10 of the silicone adhesive or the filling portion is filled. The present invention proposes a sealing structure using an adhesive that prevents penetration and has high adhesion reliability.

A combination sealing structure using an adhesive having different properties will be specifically described with reference to FIG.

First, the base 9 and the housing 8 are bonded and fixed using an elastic rubber adhesive such as a silicone adhesive.
Further, the housing 8 surrounding the electronic circuit 3 inside the housing 8
The combination adhesive sealing structure is characterized in that the gas permeation shielding layer 11 is formed by applying an adhesive having low gas permeability to the interface between the inner wall portion and the base 9 and curing it. Further, the opening of the housing 8 is covered with the cover 14 and sealed with an adhesive. In this case, the important feature of the sealing structure according to the present invention is that the end portion of the adhesive or coating agent having low gas permeability is surely applied to or coated on the inner wall of the housing 8. It is possible to form the gas permeation-shielding layer 11 by applying a coating that exerts adhesive strength at the other end and by reliably applying or coating the contact surface with the base 9 at the other end to form an adhesive surface. Become.

The adhesive 10 having low gas permeability is polyamide (nylon) or polyester.
It is possible to form the gas permeation shielding layer as an adhesive agent for the hot melt 12 by forming a blanking sheet according to the dimensions of the housing in advance. The hot melt 12 has good productivity and can be automated. It will be easy.

As a measure from a different viewpoint, there is also a measure of using an adhesive containing silver as a gas permeation shielding layer. When the corrosive gas is a corrosive gas containing sulfur such as sulfurous acid gas or hydrogen sulfide gas, even if the corrosive gas permeates through the silicone adhesive, the corrosive gas that has permeated through the adhesive layer containing this silver is
By chemically reacting with the silver compounded in the adhesive, corrosive gas stays as a sulfide in the silver compound adhesive, and the housing 8
There is also a method that can prevent the corrosive gas from flowing inside.

Generally, an elastic rubber adhesive such as silicone has a high adhesion reliability, but it has a feature of high gas permeability. On the contrary, the group of adhesives having low gas permeability has a drawback that adhesion reliability is low. In the present invention, by combining the advantages and advantages of both adhesives, the adhesive reliability of elastic rubber adhesives such as silicone adhesives and nylon-based, polyurethane-based or epoxy-based adhesives with low gas permeability are obtained. By combining the gas shielding properties possessed by the above, a suitable sealing structure can be obtained in which the adhesion reliability and the gas permeation shielding layer are simultaneously formed to enhance the reliability of the hermetically sealed structure.

A silicone adhesive is representative of the elastic rubber adhesive exhibiting adhesion reliability. The high adhesive reliability of silicone adhesives is well known and need not be described here. However, the gas permeability coefficient is based on the data of oxygen (O ₂ ) as the target gas. Silicon: 60 × 10 ⁻⁹ (cm ³ gas (RTP), cm / s · c)
m ² · cmHg) Natural rubber: 2.4 × 10 ⁻⁹ (cm ³ gas (RTP), cm / s · cm
² · cmHg) Polyethylene: 0.8 × 10 ⁻⁹ (cm ³ gas (RTP), cm / s
・ Cm ²・ cmHg) Polyvinyl chloride: 0.014 × 10 ^-9 (cm ³ gas (RTP),
cm / s · cm ² · cmHg) Polyamide: 0.004 × 10 ^-9 (cm ³ gas (RTP), cm /
s ・ cm ²・ cmHg) Polyester: 0.0019 × 10 ^-9 (cm ³ gas (RTP),
^{cm / s · cm 2 · cmHg} ) and it is understood that the gas permeability of the silicone is large compared to the other polymer member. The high gas permeability of silicone adhesives is a characteristic and physical property of silicone polymers. Improving this is almost impossible, and it is a proposition that should be a future issue.

Adhesives and sealants having poor gas permeability include vinyl polymerization systems such as polyvinyl chloride and polyethylene, and polycondensation and polyaddition systems such as polyester, polyamide (nylon) and polyimide. Thermosetting resins such as epoxy, polyurethane and acrylic, and rubbers such as fluororesin and modified silicone are also effective. The gas permeability of these adhesives or coating agents having low gas permeability is to be used as a corrosive gas for sulfur dioxide gas, hydrogen sulfide gas, carbon disulfide gas, Sx gas containing S8, chlorine gas, hydrocarbon gas, When a corrosive gas such as a mixed gas of nitrogen oxide gas and the above-mentioned corrosive gases is used, 20 × 10 ^-9 (c
A resin member having the following physical property values of m ³ gas (RTP), cm / s · cm ² · cmHg) is suitable.

Further, a mixed system in which a plurality of resins such as epoxy and nylon, polyurethane and epoxy are blended is also effective.

FIG. 2 shows another embodiment of the present invention shown in FIG.

A method of bonding the housing 8 and the base 9 with an elastic rubber adhesive 10 such as silicone, and then applying an adhesive or a coat having low gas permeability to the outer periphery of the housing 8. By providing the base 9 with a groove serving as a reference when applying an adhesive or a coating member having low gas permeability, it is possible to form a coating film with less work variation. In this case, the dimension of the base 9 requires a dimensional margin for applying an adhesive having low gas permeability, and there is a drawback that the overall dimension becomes large.

FIG. 3 is also an embodiment of another embodiment of the present invention shown in FIG.

A partition 13 is formed in advance in the housing 8 to prevent both the elastic adhesive 10 such as a silicone adhesive and the adhesive having low gas permeability from coming into contact with each other. Since both adhesives can be applied and cured at the same time, the structure has excellent productivity. In general, different types of adhesives are often in a paste state or a grease state before curing, and become a cured product by heating. At this time, when contacting with a different type of adhesive, many adhesives cause curing inhibition and often do not cure. Therefore, in the case of the embodiment shown in FIGS. 1 and 2, a step of temporarily adhering and curing the base 9 and the housing 8 with the silicone adhesive 10 and then applying and curing an adhesive or sealing material having a lower gas permeability is performed. Although it is necessary to step on, the embodiment shown in FIG. 3 has an advantage that productivity can be improved because simultaneous coating and simultaneous curing can be performed by the partition 13 provided so as not to contact with each other. This partition 13
It is not an absolute requirement to provide the housing 8 on the housing 8, and the same effect can be obtained even if a partition is formed on the base 9.

FIG. 4 shows a combination example most suitable for mass production.

First, a hot melt sheet 12 of polyamide (nylon), polyester, or the like is placed on the bonding portion between the base 9 and the housing 8. By heating, the hot melt sheet 12 can form the gas permeation shielding layer 11 having low gas permeation on the adhesive portion on the surface of the base 9. Further, it is a structure in which a silicone adhesive, an epoxy adhesive, or the like is applied to the adhesive portion of the housing 8 and is adhered to the base 9.
For this structure, it is important to use a silicone adhesive or an epoxy adhesive that can adhere to the surface of the gas permeation shielding layer 11 formed of polyamide (nylon) or the like. In recent years, silicone adhesives have also been listed on the market that can bond with polyamide (nylon), which was previously impossible, and there is a high possibility that even better silicone adhesives will be listed in the future. .

FIG. 5 is also an embodiment of another embodiment of the present invention shown in FIG.

The embodiment shown in FIG. 5 is not a combination of adhesives but a structure in which a resin member having low gas permeability is coated on the entire outer periphery including the adhesive filling portion of the thermal type flow meter. Fluororesin, nylon, polyurethane, acryl, modified silicone, etc. are promising for the resin member to be coated, and it is effective to spray the resin member to be coated on the entire circumference of the thermal type flow meter and then heat-harden it. It is also effective to apply powder coating by spraying fine powder resin such as epoxy, epoxy urethane, polyester, polyamide (nylon) on the surface. Especially in the case of powder coating, since the firing temperature is relatively high, the polymer resin material that forms the housing member is bonded by chemical bonding, and the adhesion reliability between the coated surface and the housing that is the object to be coated is high. There is an effect that a high gas permeation shielding layer can be formed.

[0030]

According to the present invention, an elastic rubber adhesive such as a silicone adhesive having excellent adhesion reliability and an adhesive having a low gas permeability, or an adhesive in which a coating member is combined is used to seal a gas. There is an effect that it is possible to provide a thermal type flow meter in which a shielding layer is formed and which has high airtightness and reliability.

[Brief description of drawings]

FIG. 1 is a sealing structure of a thermal type flow meter of the present invention.

FIG. 2 is another embodiment of the sealing structure shown in FIG.

FIG. 3 is another embodiment of the sealing structure shown in FIG.

4 is another embodiment of the sealing structure shown in FIG.

5 is another embodiment of the sealing structure shown in FIG.

FIG. 6 is a sectional structural view of a thermal type flow meter.

[Explanation of symbols]

1 ... Heating resistor, 2 ... Temperature sensitive resistor, 3 ... Electronic circuit, 4 ...
Body, 5 ... Main passage, 6 ... Sub passage, 7 ... Hybrid I
C substrate, 8 ... Housing, 9 ... Base, 10 ... Elastic rubber adhesive bonding portion, 11 ... Gas permeation shielding layer, 12 ... Hot melt seal, 13 ... Partition, 14 ... Cover.

Claims (9)

[Claims] 1. A heat generating resistor and a temperature sensitive resistor installed in a passage forming an intake passage of an internal combustion engine, and a constant temperature control electronic circuit electrically connected to the heat generating resistor and the temperature sensitive resistor. In a thermal type flow meter comprising: a base for holding the electronic circuit and a housing for covering the circuit part, or a housing and a cover for sealing the housing. Characterized in that an elastic rubber adhesive having a high degree of elasticity and an adhesive having a low gas permeability or a sealing member are combined to form a gas permeation shielding layer, and an adhesive sealing structure of the housing covering the base and the circuit part is formed. Thermal flow meter. 2. The adhesive as claimed in claim 1, wherein the gas permeability of the adhesive or the sealing member is sulfur dioxide, hydrogen sulfide gas, carbon disulfide gas, Sx gas containing S8, chlorine gas, hydrocarbon gas. 20 × 10 ^-9 (cm ³ g for mixed gas of nitrogen oxide gas and each corrosive gas presented above
A thermal type flow meter having a gas permeability of as (RTP), cm / s · cm ² · cmHg) or less. 3. An adhesive having low gas permeability according to claim 1, wherein the polyvinyl polymerization system such as polyvinyl chloride and polyvinyl alcohol, the polycondensation system of polyester, polyamide (nylon), polyimide, etc., the polyaddition system, epoxy and polyurethane. A thermal flowmeter characterized by being a thermosetting resin system such as acrylic, a rubber system such as a fluorine resin and a modified silicone resin, and a mixed system such as epoxy nylon and fluorine group-containing silicone. 4. The thermal type flow meter according to claim 1, wherein an adhesive layer made of hot melt is formed in the case of nylon, polyester or epoxy as an adhesive agent for lowering gas permeability. 5. A thermal type flow meter according to claim 1, wherein an adhesive such as epoxy compounded with silver is used as the adhesive having particularly poor gas permeability. 6. A heat generating resistor and a temperature sensitive resistor installed in a passage forming an intake passage of an internal combustion engine, and an electronic circuit electrically connected to the heat generating resistor and the temperature sensitive resistor. In the thermal type flow meter, the outer periphery of the thermal type air flow meter including a base holding the electronic circuit and a housing covering the electronic circuit is coated with a member having low gas permeability. Flowmeter. 7. The surface coating having low gas permeability according to claim 6, wherein the member for coating the outer periphery of the thermal type flow meter is formed by powder coating of polyamide (nylon), polyester, epoxy urethane or the like. Characteristic thermal type flow meter. 8. A thermal type flow meter installed in an intake passage of an internal combustion engine, comprising: a heating resistor; a control circuit for the heating resistor; and a case having the control circuit provided therein. A thermal flowmeter, wherein the eyes are bonded by using a first adhesive and a second adhesive having a gas permeability lower than that of the first adhesive. 9. A thermal type flow meter installed in an intake passage of an internal combustion engine, comprising: a heating resistor; a control circuit for the heating resistor; and a case that houses the control circuit. A thermal type flow meter, comprising: an adhesive that adheres eyes; and a coating material that has a lower gas permeability than the adhesive and that coats the adhesive.