JPH06267711A - Resistor element - Google Patents

Abstract

PURPOSE:To improve stability of a resistance value of a resistor element by composing leads of noble metal of one end of the lead and a low heat conductive part connected to the metal and disposed at the other end of the lead, and fixing the metal to an electric insulator. CONSTITUTION:Leads 14 are each formed of noble metal 14a at one end of the lead 14 and a low heat conductive part 14b at the other end of the lead 14. The metal 14a contains noble metal or alloy containing the noble metal as a main ingredient. As a material of the metal 14a, main ingredient is platinum or metal containing the platinum. The part 14b is formed of metal having lower heat conductivity than that of a material for forming the metal 14a. As a material of the part 14b, stainless steel, iron-nickel alloy is preferable. The metal 14a of the lead 14 is inserted fixedly via an electric insulator. In this case, the metal 14a is preferably extended from a part in which the metal 14 is fixed to the insulator 12 to the part 14b side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistor element having an improved lead. Such a resistor element can be suitably used for a thermal type flow meter that measures the flow rate of intake air or the like in an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, a thermal type flow meter for measuring a fluid flow rate by a resistor element whose resistance value changes according to temperature is known as a kind of flow meter for measuring a fluid flow rate when a fluid temperature changes. There is. This type of thermal flow meter, for example,
JP-A-55-43447, JP-A-56-7771
6 and JP-A-60-91121.

As a resistor element used in a thermal type flow meter, there is one that uses a tubular base body, and its general structure is such that a metal resistor is formed around the outer surface of a tubular electrical insulator. The surface of the metal resistor is covered with a glass layer, and leads are inserted and fixed to both ends of the tubular electrical insulator, and the metal resistor is electrically connected to each of the leads. This metal resistance has a resistance value that changes according to temperature, but a thin film type in which a thin metal film such as platinum is used for the metal resistance and a thin film is formed on the outer surface of the tubular body,
A wire-wound type is known in which a thin metal wire such as platinum is used for metal resistance and is wound around the outer surface of a ceramic cylindrical body. In either case, a protective film such as glass covers the cylindrical body containing the metal resistor or the thin metal wire.

In such a thermal type flow meter, a pair of leads of the resistor element is supported by a pair of support rods projecting from the wall of the insulating member forming the fluid flow path, whereby such a resistor element is formed. Over a pair of support rods, and the resistor element is arranged in the fluid flow path. That is, the resistor element is fixed to a metal having a large mechanical strength such as tensile strength, for example, a support rod made of stainless steel or the like by a welded portion in which leads at both ends are spot-electrically welded, and the support rod is made of resin. It is fixed to an insulating member such as.

When measuring the fluid flow rate, one of such resistor elements is used as a temperature compensating element for keeping the same temperature as the fluid temperature. In addition, another resistor element should be kept at about 100 to 100% more than the temperature compensating element.
The fluid flow rate is measured by using as a heating element that is heated by energizing so that the temperature becomes higher than about 200 ° C., and detecting the amount of energization to this heating element.

[0006]

Conventionally, platinum wires have been used as leads for such resistor elements. However, since the tensile strength of platinum wire is limited, when the lead of the resistor element is spot-welded to the above-mentioned support rod during the step of inserting the lead into the cylindrical ceramic, or when the resistor element is heat-sensitive. When used as a component of a flow meter, if the lead is subjected to tensile stress, the lead may break. Further, when a stainless wire is used as the lead, the tensile strength is improved as compared with the platinum wire, but it is sometimes exposed to high temperature air during the manufacturing process of the resistor element, so that it may be oxidized.

As a means for solving this, Japanese Patent Laid-Open No. 3683/1983
In No. 02, the inventors of the present application have proposed a resistor element using a wire material in which a core material is coated with a precious metal coating such as platinum or a platinum alloy. However, in the resistor element using such a noble metal coated wire for the lead, since the core material has a large rigidity, when a force is applied in the bending direction of the lead, as shown in FIG.
A crack may be generated in the bonding portion 16 for bonding the lead to the tubular body or in the noble metal coating 14z of the lead. The adhesive portion plays a role of electrically connecting the lead and the metal resistor depending on the type of the resistor element, and such a crack changes the electrical resistance of the adhesive portion, and the resistance of the resistor element is changed. Change the value. Further, cracks in the noble metal coating on the leads also change the electrical resistance of the noble metal coating, and change the resistance value of the resistor element. Such a change in the resistance value of the resistor element hinders stable operation of the resistor element and is not preferable in practice.

When a resistor element using such a noble metal coating wire as a lead is joined to the insulating support through the lead by welding, as shown in FIG. 7, the noble metal component forming the noble metal coating is formed. And the components such as iron constituting the support bar do not melt well at the interface 8 between the lead 14 and the support bar 5, and the welding conditions must be strictly controlled.
There is a possibility that variations in the welding strength between the lead and the support may become large.

Therefore, the present invention aims to provide a resistor element having a high stability of resistance value even when a bending stress is applied to the lead, and is an improvement of the lead of the conventional resistor element. . It is also an object that the resistor element has a lead for improving the welding strength between the lead and the support rod.

[0010]

That is, according to the present invention,
A metal resistor is formed on an electric insulator, a surface of the metal resistor is covered with a glass layer, and a lead is fixed to the electric insulator, and the metal resistor is electrically connected to each of the leads in a resistor element. , The lead is composed of a noble metal part at one end of the lead and a low heat conducting part bonded to the noble metal part at the other end of the lead, and the noble metal part is a noble metal or a noble metal. Characterized in that the low thermal conductive part is composed of a metal having a lower thermal conductivity than the material forming the noble metal part, and the noble metal part is fixed to the electrical insulator. A resistive element is provided.

In the present invention, it is preferable that the noble metal portion extends to the surface of the lead and the low heat conducting portion extends to the inside of the lead at the joining portion between the noble metal portion and the low heat conducting portion. Further, the noble metal portion is further closer to the low heat conduction portion side than the portion where the noble metal portion is fixed to the electric insulator,
It is preferably extended.

Further, it is preferable that the noble metal portion and the low thermal conductive portion are joined by heat treatment. Furthermore, it is preferable that the noble metal portion is made of platinum or an alloy containing platinum as a main component. Furthermore, it is preferable that the low thermal conductive portion is made of stainless steel or an alloy containing iron and nickel as main components.

[0013]

In the resistor element of the present invention, as shown in FIG.
The lead 14 is composed of a noble metal portion 14 a at one end of the lead 14 and a low heat conduction portion 14 b at the other end of the lead 14.

The noble metal portion 14a is made of a noble metal or an alloy containing a noble metal as a main component. As the material of the noble metal portion 14a, platinum, rhodium, silver, palladium, or an alloy containing these as main components can be used. It is preferable to use platinum or an alloy containing platinum as a main component. An example of this is an alloy consisting of 80% by weight platinum and 20% by weight rhodium. In addition, such precious metal part 14
The material of "a" is more plastic than the material of the low thermal conductive portion 14b.

The low thermal conductive portion 14b is made of a metal having a lower thermal conductivity than the material forming the noble metal portion 14a. Examples of the material of the low thermal conductive portion 14b include stainless steel, nickel iron alloy, molybdenum, tungsten, tin bronze, monel metal and the like. As a material of the low thermal conductive portion 14b, a metal material having high mechanical strength such as tensile strength and strong against oxidation is preferable. For example, stainless steel, iron-nickel alloy, particularly stainless steel is preferable.

The noble metal portion 14a and the low heat conductive portion 14b are
Although they are joined, this joining method does not matter. In order to improve the bonding strength, the noble metal portion 14a and the low heat conducting portion 1
4b preferably undergoes a heat treatment. The heat treatment conditions will be described later.

In the resistor element 10 of the present invention, the lead 14
The noble metal part 14 a of the above is inserted and fixed to the electric insulator 12. At this time, the precious metal portion 14a is
It is preferable that a extends further from the portion fixed to the electrical insulator 12 toward the low heat conductive portion 14b. That is, as shown in FIG.
Not only extending from one end face to the adhesive portion 16,
Furthermore, it is preferable to extend beyond the adhesive portion 16 toward the low heat conduction portion 14b side. The noble metal portion 14a is the adhesive portion 1
6 as well as beyond the glass layer 19 and further toward the low heat conductive portion 14b side.

As described above, in the joining of the lead 14 and the electric insulator 12 in the resistor element 10 of the present invention, the noble metal portion 14a which is more plastic than the low thermal conductive portion 14b is inserted into the electric insulator 12 and fixed. Therefore, when a bending stress is applied to the lead, the noble metal portion 14a can be bent without cracking the adhesive portion 16, so that the resistance value of the resistor element itself does not change, and The stability can be improved.

Further, the resistor element 10 of the present invention is fixed to the supporting rod via the lead 14, and when the thermal type flow meter is manufactured, the low heat conducting portion 14b is fixed in contact with the supporting rod. Therefore, the welding strength between the lead 14 and the support rod 5 can be improved by making the material of the low thermal conductive portion 14b and the material of the support rod 5 well melt each other. Therefore,
In order to improve the welding strength between the lead 14 and the support rod 5,
It is preferable that the low thermal conductive portion 14b of the lead 14 and the support rod 5 are made of a material that is well melted with each other. That is, lead 1
It is preferable that the low thermal conductive portion 14b of No. 4 and the support rod 5 are made of the same material or relatively similar materials. For example, it is preferable that at least one metal contained in the low thermal conductive portion 14b is also contained in the support rod 5. Also, lead 1
It is preferable that the materials of the low thermal conductive portion 14b of 4 and the supporting rod 5 are stainless steel. The material of the support rod 5 is preferably a metal having high mechanical strength such as tensile strength.
For example, stainless steel and iron-nickel alloy are preferable.

In the present invention, the noble metal portion 14a is connected to the lead 14 at the joining portion of the noble metal portion 14a and the low thermal conductive portion 14b.
It is preferable that the low thermal conductive portion 14b extends to the surface and extends inside the lead 14. That is, as shown in FIG. 1, it is preferable that the joining portion between the noble metal portion 14a and the low heat conducting portion 14b has a shape such that the noble metal portion 14a covers around the low heat conducting portion 14b. Also, the precious metal part 14
a is preferably 40 to 80% of the length of the lead 14, and more preferably 50 to 75%.

Further, when the noble metal portion 14a has such a shape as to cover the periphery of the low thermal conductive portion 14b at the joint portion, the noble metal portion 14a is perpendicular to the axial direction of the lead. It is not necessary to cover the cross section once. For example, as shown in FIG. 2 (d), in the joint portion of the lead having a rectangular cross section, the noble metal portion 14 is formed on all sides of the joint portion.
It is not necessary for a to cover the low thermal conductive portion 14b, and only two sides may be covered with the noble metal portion 14a. The portion of the low thermal conductive portion 14b covered with the noble metal portion 14a is subjected to heat treatment at a high temperature in the manufacturing process of the resistor element,
This is because oxidation can be prevented. In this connection, it is preferable that the noble metal portion 14a covers the low thermal conductive portion 14b so as to surround the cross section perpendicular to the axial direction of the lead.
This is because the surface that can prevent the oxidation of the low thermal conductive portion 14b increases.

A method of making the leads 14 used in the present invention will be described below. As shown in FIGS. 2A and 2B, the flat plate 2 that becomes the noble metal portion 14a and the low heat conduction portion 14b.
And the flat plate 3a to be formed side by side, and a noble metal film having an appropriate thickness such as platinum is pressure-welded from both sides of the flat plates 2 and 3a such that the noble metal film having a suitable thickness crosses the joint portion of both flat plates. For example, 200 μm thick SUS403 stainless steel can be used as the flat plate 2, a 200 μm thick platinum plate can be used as the flat plate 3a, and a 10 μm thick platinum film can be used as the noble metal film 3b. At this time, as shown in FIG. 2B, rectangular portions not covered by the noble metal coating are formed on both sides of the flat plate 2 along one side of the flat plate. The thickness of the flat plate after pressure welding is, for example, about 150 μm.

As another method, without using the flat plate 3a in FIG. 2 (a) and otherwise changing it, a noble metal film having an appropriate thickness such as platinum is pressure-welded from both sides of the flat plate 2 to form a noble metal portion. It is possible to form a precursor plate that will become 14a and the low thermal conductive portion 14b. Since the noble metal film is rich in plasticity and easily deformed, it can be formed by such a method.

After such pressure welding, a heat treatment is performed to strengthen the adhesion between the noble metal portion 3 and the low heat conductive portion 2. This is because the heat treatment causes the components of the low heat conductive portion to diffuse into the noble metal portion and the components of the noble metal coating to diffuse into the low heat conductive portion, thereby strengthening the bonding between the noble metal portion and the low heat conductive portion.

As such heat treatment conditions, for example,
It is preferably 600 to 900 ° C. and 60 minutes or less.

After the heat treatment as described above, FIG.
As shown in FIG. 2, this plate is cut so that the noble metal coating intersects with the uncoated side, and a lead is obtained as shown in FIG. The cross-sectional shape of this lead is, for example, a square with each side of 150 μm.

After cutting in this way, the cross section of the lead becomes a quadrangle, but it is preferable to be edged like C chamfering or R chamfering. This is because the stress on the edge can be reduced. The edging can be performed, for example, by pressing in a direction in which the edge is crushed as shown in FIG.

Hereinafter, a method of manufacturing the resistor element 10 will be described. As shown in FIG. 1, as a material of the electric insulator 12, an electrically insulating ceramic such as alumina or quartz is preferably used. When the electric insulator 12 has a tubular shape, an outer diameter of about 0.3 to 1 mm is practically preferable. The length is preferably around 2 to 3 mm. For example, outer diameter 0.5mm, inner diameter 0.3mm, length 2-3m
Alumina pipe of about m is used. The electrical insulator is
As shown in FIG. 9, it is also possible to take a plate shape. Also,
The shapes of the electric insulator and the resistor element are described in JP-A-64-18.
It may have a plate shape as described in Japanese Patent Application No. 023 and Japanese Patent Application Laid-Open No. 4-123401.

In the method of manufacturing the thin film resistor element, the metal thin film 18 is formed on the electric insulator 12 such as ceramics by a known method such as sputtering, physical vapor deposition (PVD), chemical vapor deposition (CVD), plating and the like. . As shown in FIG. 1, the metal thin film 18 does not necessarily have to adhere to the surface of the electric insulator 12, and an intermediate layer made of glass or the like can be interposed between the electric insulator 12 and the metal thin film 18.

Next, this metal thin film is formed into an appropriate shape such as a spiral shape or a meandering shape by laser trimming or the like to form a thin film resistor 18 having a specific resistance value. The metal is preferably platinum or an alloy containing platinum. The thickness of the thin film is preferably 0.5 to 3 μm. By adjusting the thickness of the thin film and, for example, the spiral pitch, the resistance value of the thin film resistor can be adjusted from several ohms to 1000 ohms.

The step of inserting the lead 14 into the electrical insulator 12 may be carried out before the final glass coating step. Before the thin film forming step, between the thin film forming step and the trimming step, the trimming step and the glass coating step are performed. It may be performed at any time in between.

The lead 14 is a metal wire having a diameter of about 0.1 to 0.3 mm and is as described above.
Insert the lead 14 from the noble metal portion 14a into the electrical insulator,
The lead 14 of the electrical insulator 12 is bonded and fixed using a conductive adhesive such as a mixed paste of platinum and glass. Thus, the conductive adhesive forms the adhesive portion 16 that electrically connects the lead 14 and the platinum thin film 18.

It is not always necessary to use a conductive adhesive, and the electrical insulator 12 and the lead 14 are fixed with an adhesive having no conductivity, and the lead 14 and the platinum thin film 18 are electrically conductive paste. May be applied for electrical connection.

Finally, a glass layer 19 made of glass or the like is formed so as to cover the metal thin film 18 and the electrical connection portion 16 formed around the electrical insulator 12. For example, lead borosilicate glass powder is made into a slurry, and this slurry is attached to the surface of the electrical insulator 12 by dipping, blade coating, spray coating, or the like. After drying the slurry adhering to this surface, it is baked to form the glass layer 19.

The method for manufacturing the wire wound resistor element is basically the same as the method for manufacturing the thin film resistor element. However, instead of forming a metal thin film, a highly conductive wire such as a platinum wire is wound around the electrical insulator 12 and the wire is connected to the lead 14 by welding. In a wire wound resistor element, the bond 16 need not be conductive. For example, when a platinum wire having a diameter of 0.5 mm and a length of 2 mm and a platinum wire having a diameter of 20 μm are wound at a pitch of 35 μm, a resistance of about 20 ohm is obtained.

The low heat conductive portions 14a of the leads 14 at both ends of the resistor element 10 thus obtained are fixed to the support bar 5 made of stainless steel or the like by spot electric welding or the like. Noble metal coating is not formed on the lead portion where the lead 14 is welded to the support rod 5. Further, as shown in FIG. 4, two portions of the low thermal conductive portion 14b of the lead 14 may be welded to the support rod 5. This is because by increasing the number of welded portions in this manner, the welding strength between the resistor element 10 and the support rod 5 is increased and the reliability of durability is improved. Thus, the lead 14 having a shape in which the low thermal conductive portion 14b has a skirt wider than the noble metal portion 14a can be obtained by, for example, the method shown in FIG. By aligning the flat plate that will become the low heat conduction part and the flat plate that will become the noble metal part side by side so that the shape as shown in FIG.
Join these flat plates. The noble metal portion 3 and the low heat conductive portion of this joint plate are machined into a shape as shown in FIG. 8B by machining such as grinding. It is preferable that the noble metal portions 3 protruding in a rectangular parallelepiped shape are periodically arranged at regular intervals. Next, the noble metal part 3 protruding adjacently
The lead 1 having a desired shape as shown in FIG. 8C is cut along the BB cross section in FIG.
4 can be obtained.

A circuit diagram of the drive circuit of the thermal type flow meter is shown in FIG. A thermal type flow meter usually has two resistor elements 10 as one set, one is a fluid temperature compensating element 21, and the other is a heating element 22, and a fluid flow path 24 for passing a fluid to be measured.
It is arranged inside. The temperature compensating element 21 and the heating element 22 form a bridge together with the other resistors 30 and 32. The temperature compensating element 21 is set to the same temperature as the fluid to be measured, while the temperature of the heating element 22 is higher than that of the temperature compensating element 21 by a predetermined temperature of about 100 to 200 ° C. Feedback control is performed by the differential amplifier 26. At this time, the temperature compensating element 21 is made to flow a minute current such that heat generation can be ignored, and is used for compensating the heat generation amount of the heat generating element 22 with the temperature of the fluid to be measured.

Under such energization control,
When the air flow rate changes, the current amount of the heating element 22 and the resistor 30 connected in series with it and the voltage applied thereto change. Therefore, the amount of current flowing through the heating element 22, the amount of current flowing through the resistor 30 as illustrated, or the output terminals 28, 28.
The voltage output during this allows the power required to heat the heating element 22 to be known, and thus the amount and velocity of the fluid passed through the fluid passage 24 can be calculated and measured. It is preferable that the fluid passage 24 is provided separately from the main fluid passage.

The insulating member for fixing the support 5 is not limited as long as it is insulating and retains mechanical strength at a high temperature to some extent, but synthetic resin can be preferably used. For example, polyethylene terephthalate or polybutylene terephthalate can be mentioned.

[0040]

EXAMPLES The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the following examples. Leads were prepared by the method shown in FIG. As the flat plate 2a, a platinum plate having a thickness of 200 μm and a width of 10 mm,
As the flat plate 2b, SUS403 having a thickness of 200 μm and a width of 10 mm
Of 10 μm thick on both sides of
A platinum film having a width of 15 mm was pressure-welded. Then, heat treatment was performed at 800 ° C. Then, as shown in FIG. 2 (c), this plate is cut to form a lead as shown in FIG. 2 (d).
Pressed and trimmed as in.

An alumina pipe having an outer diameter of 0.5 mm, an inner diameter of 0.22 mm and a length of 2 mm was used as the electric insulator 12.
A platinum thin film having a thickness of 0.4 μm was formed on the outer surface by a known spattering method. Next, this platinum thin film was trimmed into a spiral shape by a laser, and a platinum thin film 18 was formed so that the resistance value was 20 ohms.

Then, at both ends of the bobbin having the platinum thin film 18 formed thereon, a diameter of 0.15 mm manufactured as described above is provided.
Insert the lead of 60% by volume of platinum and 40% by volume of glass
It was adhered with a platinum adhesive. 6 in the air
The lead and the bobbin were fixed by firing at 00 ° C. for 10 minutes.
Glass having a melting point of about 580 ° C. was applied to the bobbin portion of this element precursor, and baked in air at 580 ° C. for 5 minutes to form a glass layer, and a resistor element 10 was obtained. The resistor element 10 is attached to a pair of support rods 5 made of stainless steel having a diameter of 1.0 mm.
Was fixed by projection welding, and the resistor element was bridged. The stability of the resistance value and the welding strength of this resistor element were satisfactory.

[0043]

As described above, in the resistor element,
Since the noble metal part of the lead is fixed to the electrical insulator, when the bending stress is applied to the lead, the noble metal part can be bent without cracks in the adhesive part, etc., so the resistance value of the resistor element is stable. The property is improved. Further, when the resistor element of the present invention is used in a thermal type flow meter, the low heat conductive portion, not the precious metal portion of the lead, contacts and fixes to the support rod, so that the welding strength of the lead and the support rod can be improved. it can.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a specific example of a resistor element of the present invention.

FIG. 2 is a perspective view illustrating a specific example of a lead manufacturing method that can be used in the present invention.

FIG. 3 is a cross-sectional explanatory view showing a specific example of the edging of the lead that can be used in the present invention.

FIG. 4 is a schematic explanatory view showing a specific example of a method for fixing the resistor element of the present invention to a support rod.

FIG. 5 is a circuit diagram of a drive circuit of a thermal type flow meter to which the present invention is applied.

FIG. 6 is a cross-sectional explanatory view for explaining a case where a bending effect is applied to a lead of a conventional resistor element.

FIG. 7 is a cross-sectional view illustrating when a conventional resistor element is fixed to a support rod.

FIG. 8 is a perspective view illustrating a specific example of a lead manufacturing method that can be used in the present invention.

FIG. 9 is a cross-sectional explanatory view showing a specific example of a resistor element to which the present invention is applied.

[Explanation of symbols]

 2 Low heat conduction plate 3a Noble metal plate 3b Noble metal film 5 Support rod 10 Resistor element 12 Electrical insulator 14 Lead 14a Noble metal part 14b Low heat conduction part 16 Adhesive part 18 Metal thin film 19 Glass layer 20 Drive circuit 21 Temperature compensation element 22 Heating element 26 differential amplifier 28 output terminal 30 resistance 32 resistance

Claims (6)

[Claims] 1. A metal resistor is formed on an electric insulator, a surface of the metal resistor is covered with a glass layer, and a lead is fixed to the electric insulator, and the metal resistor is electrically connected to each of the leads. In the resistor element to be connected, the lead is composed of a noble metal part at one end of the lead and a low heat conduction part joined to the noble metal part and at the other end of the lead. The noble metal part is made of a noble metal or an alloy containing a noble metal as a main component, the low thermal conductivity part is made of a metal having a thermal conductivity lower than that of the material forming the noble metal part, and the noble metal part is made of the above-mentioned electrical material. A resistor element characterized by being fixed to an insulator. 2. The noble metal portion extends to the surface of the lead at the joint between the noble metal portion and the low heat conductive portion, and the low heat conductive portion extends inside the lead.
The resistor element according to 1. 3. The noble metal portion further extends toward the low heat conduction portion side from the portion where the noble metal portion is fixed to the electrical insulator.
The resistor element according to 1. 4. The noble metal portion and the low heat conductive portion are
The resistor element according to claim 1, 2 or 3, which is joined by heat treatment. 5. The noble metal part is made of platinum or an alloy containing platinum as a main component.
4. The resistor element according to any one of 4 above. 6. The resistor element according to claim 1, wherein the low thermal conductive portion is made of stainless steel or an alloy containing iron and nickel as main components.