JP2012037465A - Heating resistor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heating resistor element whose yield is improved, and whose shape is stabilized.SOLUTION: In this heating resistor element including: a cylindrical insulator 6; a lead wire 7 inserted into the both ends of the insulator; a silica-based glass adhesive layer 8 provided on the internal face of the insulator and to fix the insulator and the lead wire; a heating resistor 9 wound around the outer peripheral face of the insulator so as to be deposited to the lead wire; and an insulating protection film 11 covering a portion of the insulator, the heating resistor and the lead wire, a filler 17 is dispersed to the glass adhesive layer.

Description

  The present invention relates to an air flow rate measuring apparatus suitable for detecting an intake air flow rate of an internal combustion engine, and more particularly to a heating resistor element for detecting an air flow rate.

  As a flow meter for detecting an intake air amount of an internal combustion engine such as an automobile, a thermal air flow meter capable of directly measuring a mass flow rate is a mainstream.

  Heating resistor elements used in thermal air flowmeters have long been applied to winding-type elements in which a heating resistor is wound in a spiral on the surface of a cylindrical insulator made of alumina. Yes. On the other hand, in recent years, it has been proposed to manufacture an element of a thermal flow meter on a semiconductor substrate such as silicon using a micromachine technique. Since the size of the heating resistor is as small as several hundred microns and is formed in a thin film shape, it has a small heat capacity, a high-speed response, and low power consumption. When classified by the heating resistor element, these two types are applied, but the winding type and the silicon type have their respective characteristics and are properly used depending on the use environment and destination (region).

  Patent Document 1 discloses a conventional technique for stabilizing the shape of a wound heating resistor element and improving the accuracy of air flow rate detection. Patent Document 1 describes a technique in which an end portion of an insulator around which a heating resistor is wound is a conical surface.

JP-A-8-110256

  An air flow meter mounted on an internal combustion engine such as an automobile has a heating resistor element installed in a sub-passage that takes in a part of the airflow flowing through the main passage in order to improve flow detection accuracy and antifouling properties. It has a configuration. The sub-passage is provided with a restriction in the flow path where the heating resistor element is disposed, and contrivances are made for ensuring flow rate detection accuracy and expanding the flow rate detection range.

  The basic principle of the measurement of the thermal flow meter is based on the use of the amount of heat taken away by the air flowing through the heated resistor, that is, the heat radiation characteristics. From this basic principle, the variation in the restriction of the portion where the heating resistor element described above is installed and the variation in the shape of the heating resistor element itself that becomes the basis of the flow rate detection affect the detection accuracy of the air flow meter.

  In JP-A-8-110256, regarding the cause of the flow rate detection accuracy and yield deterioration as an air flow meter, “the bobbin end face is formed in the radial direction, and, for example, glass slurry is applied or dipped on this end face, When the protective film is formed by drying and baking, the end surface covering portion that covers the end surface of the protective film becomes a substantially conical shape that becomes thicker at the inner peripheral end of the end surface of the bobbin and becomes thinner at the outer peripheral end of the end surface of the bobbin. However, the variation in the thickness is large, and the end surface covering portion of the protective film is thickened, so that air bubbles are easily mixed therein, and the gap between the bobbin hole and the lead wire from the end surface covering portion of the protective film The amount of the liquid protective film material that intrudes into the substrate increases and the amount of the material changes. Here, the bobbin refers to a cylindrical insulator. Furthermore, a method for improving the problem by disposing an end portion of the insulator around which the heating resistor is wound as a conical surface is disclosed.

  In this way, if air bubbles are generated inside the protective film located at the end of the insulator of the winding-type heating resistor element or the shape of the end of the element varies, the output characteristics of the air flow meter will be bent, which is detected. This leads to deterioration of accuracy and productivity.

  In the prior art, it is not an idea to take measures against the root cause of the problem, but only to improve the result. Although the root cause will be described later, the present invention devised an idea from the root cause of the problem and disclosed a permanent countermeasure.

  Accordingly, it is an object of the present invention to provide a heating resistor element that improves the yield and has a stable shape by sealing both ends of the glass adhesive layer of the heating resistor element.

  In order to achieve the above object, the heating resistor element of the present invention has a conductive lead wire inserted into both ends of a cylindrical insulator, and the insulator and the lead wire are fixed by a silica-based glass adhesive layer. A structure in which a resistor is formed in a spiral shape on the outer peripheral surface of the insulator, and the insulator surface on which the resistor is formed on the outer peripheral surface and part of the lead wires at both ends of the insulator are covered with an insulating protective film In the heating resistor element, the filler is dispersed in the glass adhesive layer, and by making the glass with high thixotropy, holes formed in the glass adhesive layer in the lead wire insertion step and the glass adhesive layer firing step ( It is possible to completely seal both ends of the closed space in the insulator and the outside air), so that it is possible to form a uniform protective film that protects both ends of the insulator. Become.

  According to the present invention, since both ends of the glass adhesive layer of the heating resistor element can be sealed, it is possible to provide a heating resistor element that can improve the yield and has a stable shape.

It is a figure which shows the basic composition of the heating resistor element vicinity of a thermal type flow meter. It is a figure which shows the cross-section of a heating resistor element. It is a figure which shows the production process outline | summary of a heating resistive element. It is a figure which shows the state of the glass contact bonding layer and insulation protective film of the heating resistor element which is the conventional inferior goods. It is a figure which shows the AA cross section of FIG. It is a figure which shows the state of the glass contact bonding layer and insulation protective film of the heating resistor element which is the conventional inferior goods. It is a figure which shows the output characteristic of the air flowmeter to which the heating resistive element of FIG. 6 is applied. It is a figure which shows the state of the glass contact bonding layer and insulation protective film of the heating resistor element which is the conventional good product. It is a figure which shows embodiment of this invention. It is a figure which shows the optimal volume mixing ratio of the glass and filler in this invention.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  FIG. 1 shows a basic configuration in the vicinity of a heating resistor element of a thermal type flow meter according to the present invention. The heating resistor element 1 is fixedly installed by welding to a metal terminal 2 protruding from a housing 3 in which a metal terminal 2 is insert-molded in resin. A resistance thermometer element 5 is arranged upstream of the air flow of the heating resistor element 1 installed in the sub-passage 4. The temperature measuring resistor element 5 detects the temperature of the air and the heating resistor element 1. The mass flow rate of air flowing around is measured. The heating resistor element 1 and the resistance temperature detector element 5 are connected to a control circuit via a metal terminal 2 that supports them. The control circuit performs feedback control so that the heating temperature of the heating resistor element 1 is always constant by adjusting the current flowing through the heating resistor element in response to the temperature change of the heating resistor element due to the generation of air flow. Is going.

  Next, the structure of the heating resistor element 1 will be described.

  FIG. 2 shows a cross-sectional structure of the heating resistor element of the present invention. The base material of the heating resistor element which is the subject of the present invention is a cylindrical insulator 6, for example, an alumina pipe in which lead wires 7 made of a noble metal alloy such as platinum, iridium or palladium are inserted at both ends of an alumina pipe. 6 and a lead wire 7 are fixed by a silica-based glass adhesive layer 8. A heating resistor 9 made of a material such as platinum is formed in a spiral shape on the outer peripheral surface of the alumina pipe 6 of the base material, and both ends of the heating resistor 9 are welded 10 to the lead wires 7 respectively. Is fixed. Further, on the outer peripheral surface, the surface of the alumina pipe 6 on which the heating resistor 9 is formed and a part of the lead wire 7 at both ends of the alumina pipe 6 are covered with an insulating protective film 11. The inside of the alumina pipe 6 surrounded by the alumina pipe 6, the lead wire 7, and the glass adhesive layer 8 is a space and air 12 is sealed.

  Here, the production process of the heating resistor element will be briefly described with reference to FIG.

  First, in the process of producing the base material of FIG. 3A, after the lead wire 7 is dipped into the glass paste 13 and pulled out, the lead wire 7 is inserted into the alumina pipe 6 and both ends are inserted at a predetermined temperature. Firing is completed. The glass paste 13 is a mixture of a so-called silica-based glass powder having a composition such as barium mainly composed of silica and a solvent. The firing temperature is set from the characteristic temperature of the glass. In the winding process shown in FIG. 3 (b) with respect to the base material manufactured in this way, one end of the heating resistor 9 is welded 10a to the lead wire 7 on one side, and then the alumina pipe 6 at a constant pitch. And finally, the heating resistor 9 is formed by welding 10b to the other lead wire 7. Further, after the winding, the insulating protective film 11 is formed in the coating process shown in FIG. 3C, and the heating resistor element is completed. The insulating protective film 11 is dipped into a glass paste and baked in the same manner as the glass adhesive layer 8 to form a substantially uniform glass film.

  Mixing of bubbles 14 in the insulating protective film 11 located at the end of the alumina pipe 6 (FIG. 4) and variations in the film thickness (element shape) of the insulating protective film 11 (FIG. 6: example of end) ) Is a phenomenon and a result that occur in the final coating process in the above process. The root cause of this problematic phenomenon is variations in the base material.

  This will be specifically described below with reference to FIGS. As will be described in detail later, a gap (hole) is formed in the glass adhesive layer 8 as shown in FIG. Thus, when the gap (hole) 15 is generated in the glass adhesive layer 8, the glass paste flows into the hole 15 generated in the glass adhesive layer 8 when dipping the glass paste for the protective film 16. Or when the air 12 sealed inside the alumina pipe 6 expands during the firing process by dipping the glass paste for insulation protection, and through the holes 15 formed in the glass adhesive layer 8 to the outside. In order to escape, the air bubbles 14 are not completely removed and remain as bubbles 14 at the end of the alumina pipe 6. If the insulating protective film 11 is formed on the glass adhesive layer 8 in which the holes 15 are formed, the film thickness of the insulating protective film 11 at both ends of the alumina pipe 6 tends to be insufficient, as shown in FIG. The variation in the film thickness of the insulating protective film 11 depends on the size of the hole 15, and if the hole 15 is large, the film thickness becomes extremely thin.

  In the air flow meter to which the element having an extremely thin glass film thickness shown in FIG. 6 is applied, the output characteristics are bent. An example is shown in FIG. When the output average of an air flow meter to which a standard element having a moderate insulating protective film is applied is zero, the output of the air flow meter to which an element having a thin protective film at the end is applied as shown in FIG. In the low flow rate region and the high flow rate region, the characteristic curve (bounce) occurs. From this, it can be seen that if the insulating protective film of the element, that is, the shape of the heat generating portion varies, the heat dissipation characteristics change and adversely affect the output characteristics.

  FIG. 8 shows an example of a non-defective heating resistor element. In this way, if the glass adhesive layer 8 can be securely sealed at both ends, bubbles are not generated, and the insulating protective film 11 at the end can be stably formed. Accordingly, suppressing the generation of the holes 15 generated in the glass adhesive layer 8 is an essential measure.

  The holes 15 generated in the glass adhesive layer 8 are generated in the process of producing the base material. There are two generation factors. One is a phenomenon that may occur due to the insertion pressure when the glass paste 13 is dipped into the lead wire 7 and inserted into the alumina pipe 6. The other is a phenomenon that may occur due to the expansion of the sealed air in the alumina pipe 6 as the temperature rises during the firing process after insertion. The viscosity of the glass paste greatly affects the former phenomenon, and the characteristics of the glass are the dominant factors for the latter phenomenon. Since the former can be reduced by the arrangement and insertion method of the lead wires, it can be said that the essence of the problem lies in the latter phenomenon. The present invention discloses an embodiment for solving the latter problem described above.

  As described above, the conventional glass adhesive layer is silica-based glass. In the firing process, first, the solvent volatilizes in a low temperature region and changes to a state of only glass powder. As the temperature rises and exceeds the softening point of the glass, the glass begins to melt and eventually becomes a film. Holes are formed in the glass adhesive layer 8 in the course of this change of state, while the glass melts and becomes a film, the air in the alumina pipe becomes sealed, and further the temperature rises to the holding temperature. is there. When the glass melts, it becomes a low viscosity state like a water tank. At that time, when the air 12 in the alumina pipe 6 expands and pressure is applied to the inner surface of the glass, defoaming is performed. At this time, if the glass opens the hole, that is, if the glass is leveled, no defoaming trace will eventually remain, but the surface tension applied to the surface of the glass film and the flow of the glass itself will eventually Acts in the direction of spreading. In other words, once the holes generated by defoaming are generated, they are not blocked by glass leveling. Therefore, the above-described problem occurs in the conventional glass adhesive layer.

  Therefore, in this example, glass powder and a small amount of filler 17 were added to the glass paste for glass bonding. FIG. 9 shows a cross section of the heating resistor element of the present invention. As shown in FIG. 9, the filler 17 is dispersed in the glass adhesive layer 8 after firing. The filler is generally called an aggregate, and when the filler 17 is added, the thixotropy (shape maintaining property) of the material is improved. That is, the thixotropy of the glass adhesive layer 8 in the molten state is superior by mixing the filler 17 against the pressure applied to the inner surface of the glass caused by the expansion of the air 12 in the alumina pipe 6 during the firing process of the glass adhesive layer 8. Then, the air 12 can be confined in the alumina pipe 6 without defoaming during firing.

  As described above, in this embodiment, the filler is dispersed in the glass adhesive layer, and the glass having a high thixotropy causes the glass adhesive layer in the lead wire insertion process and the glass adhesive layer firing process. It is possible to completely seal the hole at both ends. This makes it possible to uniformly form the thickness of the insulating protective film that protects both ends of the insulator.

  Next, the specification of the filler 17 suitable for the application will be described. The composition of the filler 17 is alumina, and the shape is preferably spherical. The thermal expansion characteristics of silica-based glass 18 (hereinafter referred to as “glass 18”) used for conventional bonding are determined from the thermal expansion of alumina pipe 6 and lead wire 7 to be bonded. Since the composition of the alumina pipe 6 to be bonded is alumina, alumina is suitable as the composition of the filler 17. Thereby, generation | occurrence | production of the crack at the time of baking and a crack can be suppressed, and the excessive reaction with glass does not occur at the time of high temperature baking, but a filler can exhibit the role as an aggregate at the time of baking. However, since the thermal expansion changes depending on the size of the filler 17 and the blending ratio with the glass, it is necessary to consider these sensitive parameters. On the other hand, the reason why the shape is preferably spherical is to improve the sliding of the glass paste when the lead wire coated by dipping the glass paste is inserted. The gap D between the alumina pipe 6 and the lead wire 7 is inevitably narrow in order to ensure the quality as an element. In order to reliably arrange the glass paste in the narrow gap, it is effective to make the filler 17 spherical.

  Still another preferred embodiment will be described. The maximum particle diameter dmax of the filler 17 is preferably set to D or less with respect to the gap D between the alumina pipe 6 and the lead wire 7 shown in FIG. By applying the filler 17 having such a dimensional size, even if the insertion of the lead wire 7 is deviated from the central axis of the alumina pipe 6, the filler 17 can be surely inserted into the gap D.

  Next, it is preferable that the glass adhesive layer 8 after firing has a reaction layer 19 by a chemical reaction having a composition contained in those materials at the interface between the glass 18 and the filler 17. Silica-based glass 18 has a relatively high firing temperature due to the characteristics of the composition. The bonded state at the interface between the silica-based glass 18 and the filler 17 is basically that when the glass 18 is baked at an appropriate temperature, the filler 17 reacts with the glass 18 and a reaction layer 19 is generated at the interface between them. The This reaction layer 19 is an oxide layer of alumina and barium, and is so-called barium aluminate. As described above, when the filler 17 and the glass 18 are bonded together by a chemical reaction in a completely bonded state, peeling at the interface or generation of cracks starting from the interface after use does not occur. Further, even if a crack occurs for some reason, extension can be prevented by the presence of the filler 17 that is an aggregate. Thereby, the quality as an element can be improved.

  Next, the compounding ratio of the glass 18 and the filler 17 will be described. The optimum blending ratio of the inorganic components of the glass 18 and the filler 17 is determined from a condition that satisfies both the generation rate of the holes of the glass adhesive layer 8 which is the essence of the problem and the adhesive strength which is the original purpose of the glass adhesive layer 8. . Here, as for the adhesive strength, the optimum mixing ratio of the glass 18 and the filler 17 in this embodiment is shown in FIG. 10 on the outer periphery of the alumina pipe 6 in the winding process of FIG. The unit is expressed by volume notation wt%. The solid line in FIG. 10 represents the relationship between the volume mixing ratio of the glass with respect to the inorganic content and the adhesive strength, and the alternate long and short dash line represents the relationship between the volume mixing ratio of the glass with respect to the inorganic content and the incidence of holes.

  In the case of only glass to which a conventional filler is not added, the bonding strength can be sufficiently secured, but the holes 15 are generated in the glass adhesive layer 8. The probability is almost equal to 100%. In the state where the proportion of the glass 18 is reduced and a small amount of the filler 17 is blended (the proportion of the glass is about 90% to 85%, and the rest is a filler), the strength tends to be remarkably lowered. This is because if only a small amount of filler 17 is blended, there is an unstable state of reaction between the glass 18 and the filler 17, and the blending of the filler 17 also reduces the glass component itself. For this reason, the strength is lowered as a whole. However, when the ratio of the glass 18 is further reduced and the blending of the filler 17 is increased, the reaction state between the glass 18 and the filler 17 starts to stabilize, and if the ratio is 80% to 60%, the result of satisfying the predetermined required strength described above is obtained. can get. On the other hand, it can be seen that the incidence of the holes 15 in the glass adhesive layer 8 decreases as the proportion of the filler 17 increases.

  The occurrence rate of the holes 15 in the glass adhesive layer 8 is preferably 0%, but is not limited thereto, and about 5% is sufficient. Further, regarding the required strength, it is sufficient that the lead wire 7 does not come out of the alumina pipe 6 when a tensile force is applied to the lead wire 7 in the winding step of FIG.

  In view of these, it can be said that the optimal volume ratio of glass and filler is preferably in the range of glass: filler = 80%: 20% to glass: filler = 60%: 40%.

  As a result, it is possible to more reliably satisfy both the sealing of the adhesive layer at both ends of the insulator by improving the thixotropy of the glass and the adhesive strength between the insulator and the lead wire. Stability can be obtained, the detection accuracy of the air flow meter can be improved, and the production yield can be improved.

  In this example, specifications of suitable fillers are described. However, if the requirements regarding other specifications such as the composition of the filler, the maximum particle diameter, the blending ratio of glass and filler, and the like are satisfied, the shape is unsatisfactory. There is no problem even if a regular (debris-like) filler is used.

DESCRIPTION OF SYMBOLS 1 Heating resistor element 2 Metal terminal 3 Housing | casing 4 Subpassage | path 5 Resistance thermometer element 6 Insulator (alumina pipe)
7 Lead wire 8 Glass adhesive layer 9 Heating resistor 10, 10a, 10b Welding part 11 Insulating protective film 12 Air 13 Glass paste 14 Bubble 15 Hole 16 Flow of glass paste 17 Filler 18 Silica glass 19 Reaction layer

Claims (7)

A cylindrical insulator, lead wires inserted at both ends of the insulator, a silica-based glass adhesive layer for fixing the insulator and the lead wire provided on the inner surface of the insulator; A heating resistor having a heating resistor wound around the outer peripheral surface of the insulator and welded to the lead wire, an insulator, the heating resistor, and an insulating protective film covering a part of the lead wire In the body element,
A heating resistor element, wherein a filler is dispersed in the glass adhesive layer. The heating resistor element according to claim 1,
The heating resistor element, wherein the insulator is made of alumina. The heating resistor element according to claim 1 or 2,
The heating resistor element, wherein the filler is composed of alumina. The heating resistor element according to any one of claims 1 to 3,
The heating resistor element, wherein the filler is spherical. The heating resistor element according to any one of claims 1 to 4,
The heating resistor element, wherein a maximum particle diameter of the filler is equal to or less than a thickness of the adhesive layer between the inner surface of the insulator and the lead wire. The heating resistor element according to any one of claims 1 to 5,
A heating resistor element, wherein an oxide layer of aluminum and barium produced by reaction with glass is present on the surface layer of the filler. The heating resistor element according to any one of claims 1 to 6,
In the heating resistor element, the glass adhesive layer has a glass occupying ratio of 60 to 80 wt% and a filler occupying ratio of 40 to 20 wt% with respect to the total volume of the glass adhesive layer.

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