JP2003163105A - Resistor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resistor element which is improved in pollution resistance by covering the surfaces of a heating resistor, a temperature-sensitive resistor or the like with a protection film having a water-repelling function. <P>SOLUTION: In the resistor element 1 in which a resistor 5 is covered with a glass protection film 6 and exposed to an air flow in use, the protection film 6 is formed of a mixed material composed of glass and titanium oxide. <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 a resistor element suitable for detecting the intake air flow rate of an internal combustion engine.

[0002]

2. Description of the Related Art A conventional technique relating to a heat generating resistor and a temperature sensitive resistor is disclosed in, for example, Japanese Patent Laid-Open No. 5-313617. This is because a lead of about φ0.15 was inserted into a cylindrical alumina pipe with an outer diameter of φ0.5 mm and a length of about 2 mm, and a platinum wire of φ20 μm was spirally wound on the surface of the lead, and then the surface of the resistor It is to coat glass as a protective film.

The resistor element disclosed in Japanese Patent Laid-Open No. 11-230802 has a heating resistor and a temperature sensitive resistor formed on a silicon substrate, and a photocatalyst film, that is, titanium oxide, is formed on the surface of the resistor element for protection. By forming a film and providing a light-emitting body in the vicinity of this protective film, the contaminants adhering to the heat-generating resistor and the temperature-sensitive resistor are removed.

Further, Japanese Patent Application Laid-Open No. 9-17608 discloses a technique of depositing titanium oxide on the surface of a platinum thin film.

[0005]

Among the above-mentioned conventional techniques, the technique described in JP-A-5-313617 has a structure in which a protective film is coated with glass. However, an inorganic substance (oxide) such as glass is used. Is generally known to be close to hydrophilic. In other words, when water adheres to the heat-generating resistor or the temperature-sensitive resistor, the glass shows a hydrophilic property that the water spreads evenly on the coating surface due to the water-repellent action. Attached to the body, dust here,
If fouling substances such as dust adhere, these heating resistors,
There is a possibility that various characteristics such as heat dissipation characteristics of the temperature sensitive resistor may be changed.

On the other hand, the technique disclosed in Japanese Patent Laid-Open No. 11-230802 is to remove the pollutant by the photocatalytic action of the photocatalyst film and the light emitting source even if the pollutant adheres to the protective film. I need.

The technique described in Japanese Patent Laid-Open No. 9-17608, that is, the effect of the titanium oxide film deposited on the surface of the platinum thin film is to prevent diffusion of contaminants other than oxygen into the platinum thin film, that is, Since the platinum thin film does not deteriorate even at a temperature, it differs from the present invention described later in any of its objects, constitutions and effects.

An object of the present invention is to provide a resistor element in which the function of water repellency is added to the protective film itself covering the surface of the heating resistor, the temperature sensitive resistor, etc., and the stain resistance is improved. is there.

[0009]

Means for Solving the Problems The above-mentioned problem is a resistor element which is used by covering the surface of a resistor with a glass protective film and exposing it to an air stream for use. It is achieved by forming a mixed member with titanium.

[0010]

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

FIG. 1 is a sectional view of an embodiment of the resistor element proposed in the present invention.

The resistor element 1 is made of an inexpensive general-purpose inorganic material such as alumina and has an outer diameter of 0.5 to 0.9 mm and a length of 2 to 3 m.
A lead 3 having an outer diameter of 0.2 mm or less is bonded and fixed to a cylindrical pipe 2 of about m by an adhesive 4. The lead 3 is often a platinum wire, a platinum alloy wire, or a lead in which a precious metal material is clad on the surface of a non-precious metal material, and the adhesive 4 is made of a glass-based inorganic material or a precious metal such as platinum or silver. In many cases, a conductive adhesive paste used as a conductor is used. Further, since a platinum thin wire or the like is used as the resistor 5, one end of the resistor 5 is welded to the lead 3, and the pipe 2 is spirally wound with this as a base point, and the winding is finished to a predetermined resistance value. After that, the lead 3 on the opposite side is fixed by welding.
Finally, a protective film 6 is formed of glass to protect the resistor portion.

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

The heating resistor 7 of the thermal air flow meter using the heating resistor 7 and the temperature sensitive resistor 8 is always kept at a constant temperature difference from the temperature sensitive resistor 8 for measuring the air temperature. It is controlled by a feedback circuit at a constant temperature and is constantly heated. Since the heating resistor 7 is installed in the air flow, the surface portion of the heating resistor 7 that radiates heat to this air flow is
That is, it becomes a heat transfer surface. The amount of heat taken by the air flow due to this heat transfer is converted into an electrical signal, and the air flow rate is measured. Reference numeral 9 is an engine body that electrically converts the signal from the heating resistor 7 and holds a drive circuit that converts the signal into an air flow rate signal, and that forms an air passage into which the total intake air flow rate flows. The body 9 has both passages divided into a main passage 10 as one air passage into which most of the intake air flows and a sub passage 11 as the other air passage into which a part of the air flows,
A resistor element 1 including a heating resistor 7 and a temperature sensitive resistor 8 is arranged in a sub passage 11.

In the internal combustion engine, the microcomputer determines the amount of injector injection into the cylinder of the internal combustion engine on the basis of the signal measured by the air flow meter and the signal of another sensor to control combustion of the internal combustion engine. Since the combustion control of the internal combustion engine is performed based on the signal of the air flow rate measurement device, the thermal air flow meter using a heating resistor has the advantage of being able to directly measure the mass flow rate and its reliability, so that many internal combustion Used in engine control systems.

The structure and features of the present invention will be described with reference to FIG. After the lead 3 is bonded and fixed to the cylindrical pipe 2 with the adhesive 4, one end of a platinum thin wire is welded to the lead 3, and the pipe 2 is spirally wound from this as a base point and wound to a predetermined resistance value. After the wiring is completed, the structure and manufacturing process of welding and fixing to the lead 3 on the opposite side and forming the protective film 6 on the resistor portion are the same as the conventional one. The present invention is characterized in that a member having water repellency is adopted as the protective film 6 for protecting the resistor 5, and in this embodiment, this water repellant film is
It was made of glass containing 2 wt% of titanium oxide. Glass is generally formed from silica, alumina, lead oxide, zinc oxide and the like, but in the present invention, silica glass, which is said to have a hydrophilic tendency, by using glass in which titanium oxide is mixed with lead glass, By hindering the regular arrangement of silanol groups (hydroxyl groups) generated on the glass surface and appropriately arranging titanium oxide on the surface of silica glass or lead glass, it becomes possible to impart water repellency. In this case, if the contact angle with the water droplets is at least 90 ° or more, it can be said to be a water-repellent film (the water-repellent film is defined when the contact angle with the water droplets is 90 °, but it is currently clear. There is no boundary line between the water film and the hydrophilic film, and if the contact angle is at least 90 ° or more, it can be said that it is a water-repellent film according to common sense).

Here, the water repellency will be briefly described.
Water repellency refers to an atomic group or molecule that does not dissolve in water molecules and does not easily dissolve in water, but the surface condition that allows water droplets attached to the surface to be repelled is called water repellency. The state in which it is not possible to fit in and is uniformly adapted is called hydrophilic. This can be explained by the magnitude of the surface free energy of the film surface. The surface free energy is extra energy generated on the surface of the film, and if this value is large, the energy for taking in water molecules to the surface of the film is large, so that it tends to be hydrophilic. On the contrary, a film having a small surface free energy tends to have water repellency, and this surface free energy correlates with the surface tension and the contact angle with a water droplet.

Next, the effect of using the protective film 7 of the present invention using titanium oxide will be described. In many cases, the protective film 6 for protecting the resistor 5 in the resistor element 1 is usually made of glass, but it is generally said that glass is hydrophilic with respect to water. . Therefore, when water adheres to the resistor element 1, water droplets tend to uniformly wet the outer circumference of the resistor. In this case, the water that has spread over the entire circumference of the resistor element 1 is unlikely to scatter, and in the case of the heating resistor 7 that is used by being heated to a certain temperature, the heating resistance is affected by the water that has spread over the surface of the heating resistor 7. It becomes a factor that changes various characteristics such as the heat dissipation characteristic of the body 7, which may deteriorate the flow rate measurement accuracy.

Further, when the water droplets evenly spread on the surface of the protective film, the wetted water is less likely to scatter, and when pollutants such as dust and dust flow into the surface, they easily adhere to the surface, resulting in resistance. This may be a factor that accelerates the contamination of the body element 1.

It is generally considered that the protective film on the surface of the resistor element 1 may be coated with a hydrophobic resin, but the heat resistant temperature of these resins is about 200 to 300 ° C. at most, and the heat generating resistor 7 is used. In many cases, heat resistance around 400 ° C. is required, so it cannot be adopted. Further, in many of these cases, there are many cases in which the coating film loses wear and the initial performance is lost over time. On the contrary, glass is effective as an industrial coating capable of maintaining heat resistance of 400 ° C. or higher.
In view of this, in the present invention, by making use of the characteristics of glass and further adding water repellency to the glass to form the coating film of the heating resistor 7, the stain resistance of the surface of the resistor element 1 is improved. Is proposed to improve. Specifically, titanium oxide is added as an additive for glass. In recent years, titanium oxide has been confirmed to have an effect of cleaning the surface of titanium oxide by an excitation action of a photocatalyst, and has been adopted in various fields as a self-cleaning film. It does not mean that. On the contrary, it is characterized by not requiring a photocatalyst. The photocatalytic action of titanium oxide utilizes the excitation action that occurs when light enters titanium oxide.
Since this self-cleaning can be said to be an effect of promoting the uniform diffusion of the liquid attached to the surface hydrophilically, there is a side surface having a greater hydrophilic effect than the water-repellent effect. On the contrary, it has recently been found that titanium oxide has water repellency in the absence of light, and research in this field is currently in progress. That is, in the present invention, attention is paid to the fact that the resistor element 1 of the thermal air flow meter installed in the engine room of the automobile is always installed in a dark place, and the water repellency of titanium oxide in the absence of light is utilized. It was done.

Another embodiment of the present invention will be described below.

In FIG. 2, a resistor 5 is formed of a thin film of platinum or the like on the surface of a cylindrical pipe 2, and spiral resistance trimming is performed on the resistor surface by a laser or the like, and then the lead 3 is attached to a platinum adhesive 4 or the like. This is an example in which the protective film 6 employing the titanium oxide of the present invention is applied to the resistor element 1 having a structure in which the protective film 6 is adhered to form the protective film 6.

In FIG. 3, a thin film is formed on the surface of a solid bobbin 2 of alumina or the like with platinum or the like, and the surface of the resistor 5 is spirally trimmed with a laser or the like.
In this example, the protective film 6 employing the titanium oxide of the present invention is applied to the resistor element 1 having a structure in which the protective film 6 is formed by press-fitting the cap 14 having.

[0024]

According to the present invention, the function of water repellency is added to the protective film by covering the surface of the heating resistor, the temperature sensitive resistor and the like,
It is possible to provide a resistor element having improved stain resistance.

[Brief description of drawings]

FIG. 1 is a sectional view of a resistor element showing a first embodiment of the present invention.

FIG. 2 is a sectional view of a resistor element showing a second embodiment of the present invention.

FIG. 3 is a sectional view of a resistor element showing a third embodiment of the present invention.

FIG. 4 is a cross-sectional view of an air flow rate measuring device using the resistor element of the present invention.

[Explanation of symbols]

1 ... Resistor element, 2 ... Cylindrical pipe, 3 ... Lead, 4 ...
Adhesive, 5 ... Resistor, 6 ... Protective film, 7 ... Cap, 8 ...
Heating resistor, 9 ... Temperature sensitive resistor, 10 ... Engine body,
11 ... Main passage, 12 ... Sub passage.

Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G01K 7/18 F02D 35/00 366E 13/02 366L

Claims (5)

[Claims] 1. A resistor element in which the surface of a resistor is covered with a glass protective film and exposed to an air stream to be used, and the protective film is formed of a mixed member of glass and titanium oxide. A resistor element characterized by the above. 2. The method according to claim 1, wherein lead wires made of a conductive member are adhered to both ends of the cylindrical pipe made of an insulator, and a resistor is formed on the surface of the cylindrical pipe.
A resistor element in which the protective film of the resistor element having a protective film formed on its surface is formed of a mixed member of glass and titanium oxide. 3. The protective film of a thin-film type resistor element according to claim 1, wherein a resistor is formed on a thin plate of an insulator, and the surface of the resistor is covered with a protective film. Resistor element formed. 4. The protective film of the resistor element according to claim 1, wherein the resistor provided on the thin portion formed on the silicon substrate is covered with the protective film, and the protective film is formed of a mixed member of glass and titanium oxide. Resistor element. 5. An internal combustion engine in which the resistor element according to claim 1 is installed in an air duct of an engine room.