JPH07282959A - Heater element - Google Patents

Abstract

PURPOSE:To obtain a heater element, of which resistance value and temperature coefficient of resistance can k easily set. CONSTITUTION:Conductive grain parts 113 form a conductive route as an electrical resistor. Insulating large grains parts 114 have the electrical insulating characteristic, and the relative increase thereof in relation to the conductive grain parts 113 increases the resistance value of the conductive route. Since the coefficient of linear expansion of the insulating large grain parts 114 is smaller than that of the conductive grain parts 113 because of the large grain diameter thereof, the contact resistance value of the resistance value of the conductive route is reduced with heating. The relative increase of the insulating large grain parts 114 in relation to the conductive grain parts 113 shifts the temperature coefficient of resistance to the negative direction. Insulating small grain parts 115, of which diameter is smaller than that of the insulating large grain parts 114, are distributed between the conductive grain parts, namely, in the conductive route. Electric resistance value of an electrical route can be thereby remarkably changed by relatively increasing the insulating small grain parts 115 in relation to the conductive grain parts 113.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic heater and is applied to, for example, a ceramic glow plug of a diesel engine.

[0002]

2. Description of the Related Art A rod-shaped base made of an electrically insulating ceramic member, a heating element made of an electric resistor embedded in one end of the base, and a heating element embedded in the base and individually connected to both ends of the heating element. And a heating element, wherein the heating element is a ceramic heater made of a sintered body in which insulating particles made of electrically insulating ceramic powder and conductive particles having conductivity are dispersed. Known from the past.

For example, Japanese Patent Application Laid-Open No. 63-63, filed by the present applicant.
No. 96883 discloses a heating element and a substrate by changing the particle size of a mixed powder composed of insulating particles (Si ₃ N ₄ ) and conductive particles (MoSi ₂ ). That is, the heating element is composed of large-diameter insulating particles and small-sized conductive particles. By doing so, a structure in which the conductive particles are continuous so that the conductive particles are wrapped around the insulating particles and a desired resistivity can be obtained. On the other hand, the substrate is composed of insulating grain portions and conductive grain portions having almost the same grain size. By doing so, the conductive grain portions are separated from each other by the insulating grain portions, and become electrically insulating.

By thus constructing the heating element and the base with the same material, it is possible to perform integral sintering under optimum conditions, reduce the difference in linear expansion coefficient, and improve reliability by integrating the heating element and the base. . In addition, Japanese Patent Application Laid-Open No. 64-61
No. 356, additive particles composed of island-shaped aggregated ceramic additive particles dispersed in insulating ceramic matrix particles, and the matrix particles individually surrounding the additive particles, We propose a ceramic body that divides the space.

[0005]

However, the characteristics of the heating element are determined by the resistance value and the resistance temperature coefficient (ratio of the resistance value at room temperature to the resistance value at high temperature).
In the configuration of the 6883 publication, as shown in FIG. 5, when the mixing ratio of the conductive particles is large, the resistance value is low and the temperature coefficient of resistance is high. When the mixing ratio of the conductive particles is small, the resistance value is high and the resistance is low. There is a problem that it becomes a temperature coefficient and limits the range of realizable heating element characteristics.

That is, it is extremely difficult to set the resistance value and the temperature coefficient of resistance to arbitrary values depending on the mixing ratio of the insulating particles and the conductive particles, and the specific resistance value and resistance on the line shown in FIG. Only a heater with a temperature coefficient can be supplied. Here, the relationship between the compounding amount of the conductive particle portion, the resistance value, and the temperature coefficient of resistance will be described below.

The resistance value of the heating element can be regarded as a combined resistance value in which a large number of specific resistance values of the conductive particles themselves and contact resistance values between the conductive particles are arranged in series and parallel, and It is greatly affected by the arrangement state of the sex grain parts. The contact resistance values of the conductive particles (MoSi ₂ ) having a large linear expansion coefficient and the insulating particles (S
A microscopic view of a heating element composed of i ₃ N ₄ ) causes a tensile force to act on the conductive particles, so that the contact resistance value at room temperature is the value in this state.

Here, when the heating element generates heat by energization, this tensile force is alleviated and the contact property is improved, so it is considered that the contact resistance value at the time of heat generation is reduced. It is presumed that the larger the particle size of the insulating particles and the larger the amount of the insulating particles, the greater the tensile force at room temperature and the more remarkable the decrease in contact resistance due to heat generation. After all, it can be seen that the temperature coefficient of resistance of this type of heating element is determined by the increase in specific resistance value and the decrease in contact resistance value due to heat generation.

Next, the relationship between the amount of conductive particles and the resistance value will be described. It is considered that when the amount of the conductive particles increases, the cross-sectional area of the conductive part in the conductive ceramic body increases, resulting in a low resistance value. In addition, when the amount of conductive particles increases, the tensile force at room temperature is small and the relaxation of the tensile force due to heat generation is small, and it is greatly affected by the increase in the specific resistance value of the conductive particles themselves. It is considered that the temperature coefficient of resistance of (MoSi ₂ ) itself approaches.

The present invention has been made in view of the above problems,
It is an object of the present invention to provide a ceramic heater in which the resistance value and resistance temperature coefficient of a heating element can be easily set.

[0011]

The first structure of the present invention is as follows.
Between the insulating large-grain portion and the insulating large-grain portion composed of the large-grain size electrically insulating ceramic granules, and the conductive large-grain portion having a smaller grain diameter and a larger linear expansion coefficient than the insulating large-grain portion. An electrically conductive grain portion that intervenes to form a conductive path and an electrically insulating ceramic grain body having a particle size smaller than that of the insulating large grain portion, and that is interposed between the electrically conductive paths to increase the electrical resistance of the electrically conductive path. A heating element comprising a sintered body including an insulating small grain portion to be increased.

In a second structure of the present invention, in addition to the first structure, the insulating small particle portion and the conductive particle portion have an average particle diameter of ⅕ or less of that of the insulating large particle portion. Characterized by points. In the third structure of the present invention, in addition to the above first to third structures, the insulating small particle portion is 1/3 to the conductive particle portion.
It is characterized by having an average particle size of 3 times.

According to a fourth structure of the present invention, in addition to the above-mentioned first to fourth structures, the insulating small particle portion is a conductive particle portion of 5 to 5.
It is characterized in that it is mixed by 200% by volume. A fifth structure of the present invention is characterized in that, in addition to the first to fifth structures, the insulating large grain portion and the insulating small grain portion are made of the same material. A sixth structure of the present invention is, in addition to the above-mentioned sixth structure, a base made of conductive particles and insulating particles made of the same material as the conductive particles and the insulating small particles, and a base. It is a ceramic heater provided with the heating element of the said 1st-5th structure embedded, and the electrode wire which is embedded in the said base | substrate and consists of a high melting point metal member connected to the edge part of the said heating element.

In a seventh aspect of the present invention, when the linear expansion coefficient of the base is A / ° C., the linear expansion coefficient of the heating element 2 is B / ° C., and the linear expansion coefficient of the electrode wire is C / ° C. , A ≦ B,
Further, it is characterized in that the relation of 0 ≦ (C−A) ≦ 1.5 × 10 ⁻⁶ is satisfied.

[0015]

In the first structure of the heating element of the present invention, the conductive particles form a conductive path as an electric resistor. The insulating large grain portion is electrically insulating, and its increase relative to the conductive grain portion causes an increase in the resistance value of the conductive path. Further, since the insulating large grain portion has a larger grain size and a smaller linear expansion coefficient than the conductive grain portion, the contact resistance value of the resistance value of the conductive path decreases with heat generation. Therefore, its relative increase with respect to the conductive particles causes the temperature coefficient of resistance to shift in the negative direction.

In particular, in the present invention, the insulating small particle portion having a smaller particle size than the insulating large particle portion is dispersed between the conductive particle portions, that is, in the conductive path. By doing so, the electrical resistance value of the electrical path can be significantly changed by the relative increase of the insulating small grain portion with respect to the conductive grain portion. On the other hand, the insulating small-grain portion has a small particle diameter, and a tensile stress is applied to the conductive small-grain portion adjacent to the insulating small-grain portion so that the temperature coefficient of resistance of the conductive path becomes negative as in the insulating large-grain portion. Although it is shifted in the direction, the degree of its influence is much smaller than the degree of change in the electric resistance value of the electric path.

After all, the resistance temperature coefficient can be adjusted by increasing or decreasing the insulating large grain portion with respect to the conductive particle portion, and further adjusting the resistance value by increasing or decreasing the insulating small grain portion. The degree of freedom in adjusting the temperature coefficient of resistance and the resistance value is remarkably increased as compared with the conventional one. FIG. 5 shows a model diagram of this heating element. 113 is a conductive grain part, 114 is an insulating large grain part,
Reference numeral 115 is an insulating small grain portion.

The conductive grain portion 113 surrounds the insulating small grain portion 115, and the conductive grain portion 113 and the insulating small grain portion 115 surround the insulating large grain portion 114. It is possible to set the resistance value by changing the tensile force of the conductive particles by setting the amount of insulating large particles, setting the temperature coefficient of resistance, and changing the cross-sectional area of the conductive path by the amount of insulating small particles. I understand.

According to the second structure of the present invention, the above effects can be further improved. That is, when the average particle size of the insulating small particles is more than the above range, the insulating small particles do not disperse in the conductive path formed of the conductive particles, and thus the target resistance value and the temperature coefficient of resistance cannot be obtained. . Further, if the average particle diameter of the conductive particle portion is equal to or more than the above range, it becomes difficult for the conductive particle portion to surround the large insulating particle portion, so that there is a problem that the conductive path is not formed.

According to the third structure of the present invention, the above effects can be further improved. That is, if the average particle size of the insulating small particle portion is less than the above range, the insulating small particle portion is surrounded by the conductive particle portion, which causes a problem that the conductive path is cut off. If the value exceeds the above range, the insulating small particle portions are hard to disperse in the conductive path, so that there is a problem that the target resistance value and the temperature coefficient of resistance cannot be obtained.

According to the fourth structure of the present invention, the above effects can be further improved. That is, when the volume of the insulating small grain portion is equal to or more than the above range, the insulating small grain portion is too much, and the conductive path is broken. According to the fifth configuration of the present invention, since the bondability of the heating element is improved, the operational effect of improving reliability can be achieved.

According to the sixth aspect of the present invention, the heating element comprises insulating particles and conductive particles made of the same material as the insulating small particles and the conductive particles of the heating element. The small particles are embedded in the substrate that blocks the conductive path. With this, not only the bondability between the heating element and the base body is improved, but also the thermal stress generated by the difference in linear expansion can be reduced.

After all, with the above configuration, the resistance value and the temperature coefficient of resistance can be adjusted in a wide range.

[0024]

EXAMPLES The present invention will be described below with reference to specific examples. FIG. 1 is a sectional view showing an embodiment of a ceramic heater 1 of the present invention, and FIG. 2 is an enlarged view of a main part thereof. The ceramic heater 1 includes a base 3 having a circular rod shape, a U-shaped heating element 2 embedded in the tip of the base 3, and an electrode wire 4 having a circular cross section embedded in the base end and the center of the base 3. It consists of 5 and 5.

The substrate 3 is made of an insulating ceramic sintered body having a circular cross section in which a small amount of a conductive ceramic powder made of MoSi ₂ is dispersed in an insulating ceramic powder made of Si ₃ N ₄ . The heating element 2 is a conductive ceramic sintered body having a circular cross section containing a conductive ceramic powder made of MoSi ₂ and an insulating ceramic powder made of Si ₃ N ₄ .

The base ends of the electrode wires 4 and 5 are exposed at the outer periphery of the base body 1 to form partial cylindrical surfaces 4c and 5c, and their tip portions 4a and 5a extend from both end surfaces of the heating element 2 to the heating element 2. It is buried inside. The electrode wires 4 and 5 are made of a refractory metal such as tungsten or molybdenum or an alloy thereof, but are tungsten wires having a circular cross section here. The radii of curvature of the partial cylindrical surfaces 4c and 5c are made equal to the radius of the base body 3.

FIG. 3 shows an example in which the ceramic heater 1 of this embodiment is used in a glow plug of a diesel engine.
Substrate 3 in which the partial cylindrical surfaces 4c and 5c of the electrode wires 4 and 5 are exposed
The sides of the are plated with nickel. A metal hollow pipe 6 is fitted and brazed to the central portion of the base body 3 through this nickel plating layer. The hollow pipe 6 holds the ceramic heater 1 and is electrically connected to the partial cylindrical surface 4c of the electrode wire 4. Connected to each other. On the outer periphery of the hollow pipe 6, a tip end portion of a metal housing 10 having a cylindrical shape with both ends having an attachment screw 10a for mounting on an engine (not shown) is fitted.
It is brazed.

On the other hand, a metal cap 7 is brazed to the partial cylindrical surface 5c of the electrode wire 5 led out to the base end of the base 3, and one end of the metal wire 8 is welded to the metal cap 7. The other end of the metal wire 8 is welded to the tip of the center shaft 9.
The male screw portion 91 formed at the base end of the center shaft 9 is connected to a power source (not shown). The center shaft 9 is fitted in the housing 10, the center shaft 9 is electrically insulated from the housing 10 by the glass seal 11 and the insulating bush 12, and the glass seal 11 and the insulating bush 12 are screwed to the male screw portion 91. It is fixed by a nut 13.

With such a configuration, the power source (not shown), the center shaft 9, the metal wire 8, the metal cap 7, the electrode 5, the heating element 2, the electrode 4, the hollow pipe 6, and the housing 10 are provided.
A current can be passed through an engine block (not shown) via the. Explaining the method of manufacturing the ceramic heater 1, the heating element 2 is injection-molded with the electrode wires 4, 5 set at predetermined positions in the mold, and then the electrode wires 4,
A molded product obtained by injection molding of the base body 3 is sintered with the integrated body 5 and the heating element 2 set at a predetermined position in the mold by hot pressing. After that, the outer periphery is ground to form.

FIG. 4 shows an enlarged schematic sectional view (model diagram) of the base body 3. The base 3 is a mixed powder of MoSi ₂ having an average particle diameter of 1 μm as the conductive particle portion 111 and Si ₃ N ₄ having an average particle diameter of 1 μm as the insulating particle portion 112, Y ₂ O ₃ as an additive, A sintered body of a mixture in which Al ₂ O ₃ is added in an amount of 3% by mass and 5% by mass with respect to the total mass of MoSi ₂ and Si ₃ N ₄ , and a structure in which MoSi ₂ particles are surrounded by Si ₃ N ₄ particles It has become.

An enlarged schematic sectional view (model diagram) of the heating element 2 is shown in FIG. The heating element 2 has MoSi ₂ having an average particle diameter of 1 μm as the conductive grain portion 113 and an average particle diameter of 17 μm as the first insulating grain portion (insulating large grain portion in the present invention) 114.
The Si ₃ N ₄ and the second insulating grain portion the powder mixture the top of the Si ₃ N ₄ having an average particle diameter of 1μm as (insulating small portion of the present invention) 115, as an additive Y ₂ O _3, This is a sintered body of a mixture in which Al ₂ O ₃ is added in an amount of 3% by mass and 5% by mass with respect to the total mass of MoSi ₂ and Si ₃ N ₄ , respectively, and the second insulating particles 115 are conductive particles 113. The first insulating grain portion 114 is surrounded by the second insulating grain portion 115 and the conductive grain portion 113.

FIG. 6 shows the relationship between the weight ratio of the conductive particles of the heating element and the resistance value and the temperature coefficient of resistance of JP-A-63-96883. Here, the temperature coefficient of resistance is represented by the ratio of change in resistance value when the heating element is heated from 20 ° C to 900 ° C. The materials are shown in the model diagram of FIG. It can be seen from FIG. 6 that the resistance value decreases and the resistance temperature coefficient increases as the blending amount of MoSi ₂ increases.
For example, 40 wt% MoSi ₂ has a resistance value of 0.1Ω.
The resistance temperature coefficient is 4.0, and the required specifications of the heating element are such that the heater having a resistance value of 1.0Ω and a resistance temperature coefficient of 4.0 is manufactured unless the material of the conductive particles is changed. I see that I can't do it.

Next, the heating element 2 of this embodiment will be described. The material is the one shown in the model diagram of FIG. 5, and the content of the conductive particles 113 (MoSi ₂ ) is kept constant at 40 wt%,
For the remaining 60 wt, the relationship between the resistance value and the resistance temperature coefficient of the heating element 2 manufactured by variously changing the compounding amount (wt%) of the first insulating grain portion 114 and the second insulating grain portion 115 is shown. Figure 7
Shown in.

From FIG. 7, the composition of the second insulating grain portion 115 is shown.
When the amount is 0 wt%, MoSi in FIG. ₂Is a value of 40 wt%
However, the compounding amount of the first insulating grain portion 114 is reduced.
And increase the compounding amount of the second insulating grain portion 115.
And the resistance value increases, and the temperature coefficient of resistance decreases slightly. So
And various MoSi₂Second insulating grain part with the compounding amount of
This relationship is established by changing the compounding amount of 115.
I confirmed that. In addition, the resistance value is 1.0Ω,
The heating element 2 having a temperature coefficient of resistance of 4.0 is MoSi₂Is 45
wt%, the first insulating grain portion 114 is 20 wt%, the second
The insulating particle portion 115 can be manufactured at 35 wt%.
I was able to confirm that.

As described above, the conductive particles 113 have an average particle size of 1 μm.
MoSi ₂ , the first insulating grain portion 114 has an average grain size of 17
An example in which Si ₃ N _{4 of} μm and the second insulating grain portion 115 is Si ₃ N ₄ having an average particle size of 1 μm was described. It shows in Table 1.
In the test, the average grain size of the conductive grain portion 113, the first insulating grain portion 114, and the second insulating grain portion 115 was changed, and FIG.
It was confirmed whether or not the effect of this example shown in FIG.

[0036]

[Table 1]

From Table 1, when the average particle size of the conductive particles 113 is 1 μm and the average particle size of the first insulating particles 114 is 17 μm, the average particle size of the second insulating particles 115 is The effect of this example is recognized when the average particle size of the first insulating particles 114 is 9 μm or less, and the average particle size of the second insulating particles 115 is 5 μm or less when the average particle size of the first insulating particles 114 is 9 μm. Was recognized.

From the above results, the second insulating grain portion 115
It is understood that the effect of the present invention can be recognized when the particle diameter is about 1/2 or less of the first insulating particle portion 114. Further, although the test results in which the average particle diameter of the conductive particle portion 113 is changed are also shown, it can be seen that the effect of the present invention is not affected by the average particle diameter of the conductive particle portion 113. Next, the conductive particles 11
3, first insulating grain portion 114, second insulating grain portion 115
Was tested with various materials.
Is conductive, the effect of the present embodiment can be obtained with members other than MoSi ₂ , and if the first insulating grain portion 114 and the second insulating grain portion 115 have insulating properties, Si ₃ N ₄ It was also confirmed that the effects of the present example can be obtained with other members.

Furthermore, the same effect was obtained even if the first insulating grain portion 114 and the second insulating grain portion 115 were made of different materials. However, the following attention should be paid to the required heater life when selecting the above materials. Since the heating element 2 is heated to a high temperature by energization, the base 3 and the conductive particle portion 1
Cracks may occur due to large repeated thermal stress caused by the difference in linear expansion coefficient between the electrode 3 and the electrode wires 4, 5. That is, if the difference in the linear expansion coefficient between the base 3 and the heating element 2 is large, cracks occur in the base 3 or the heating element,
If the difference in the linear expansion coefficient between the base 3 and the electrode wires 4 and 5 is large, cracks occur in the base 3. These cracks develop during long-term use and fail to function as a heater.

Therefore, the substrate 3, the heating element 2, the electrode wires 4, 5
The linear expansion coefficient of the base material 3 was A / ° C., the linear expansion coefficient of the heating element 2 was B / ° C., the linear expansion of the electrode wires 4 and 5 was tested by changing the linear expansion coefficient of Coefficient is C /
C, A ≦ B and 0 ≦ (C−A) ≦ 1.
It was also found that it was necessary to satisfy the relationship of 5 × 10 ⁻⁶ .

Although an example of a conductive ceramic body has been described above as the heating element 2, a green sheet of the substrate 3 is formed, and a print pattern constituting the heating element 2 is formed on the green sheet, and the electrode wire is further formed on the green sheet. It goes without saying that the same effects as the above-mentioned effects can be obtained even when 4, 5 are arranged and the above green sheets are laminated in appropriate amounts and then fired and ground to form a ceramic heater.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a ceramic heater of the present invention.

FIG. 2 is an enlarged sectional view of a main part of the heater shown in FIG.

FIG. 3 is a cross-sectional view showing an embodiment in which the ceramic heater of FIG. 1 is adopted in a ceramic glow plug.

FIG. 4 is a model diagram showing an example of a substrate.

FIG. 5 is a model diagram showing an example of a heating element.

FIG. 6 is a diagram showing the relationship between the blending ratio of the conductive particles of the heating element of JP-A-63-96883, the resistance value, and the temperature coefficient of resistance.

FIG. 7 is a diagram showing a relationship between a blending ratio of a heating element of the present embodiment, a resistance value, and a temperature coefficient of resistance.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramic glow plug 2 Heating element 3 Base material 4 Electrode wire 5 Electrode wire 113 Conductive grain part 114 First insulating grain part (insulating large grain part) 115 Second insulating grain part (insulating small grain part)

Claims (6)

[Claims] 1. An insulating large grain part made of a large grain size electrically insulating ceramic grain body, and a conductive grain body having a smaller grain size and a larger linear expansion coefficient than the insulating large grain part, and having the insulating property. The conductive particles that are interposed between the large particles to form a conductive path, and the electrically insulating ceramic particles that have a smaller particle size than the insulating large particles, and the conductive particles that are interposed between the conductive paths A heating element comprising a sintered body including an insulating small grain portion that increases electric resistance of a path. 2. The insulating small grain portion and the conductive grain portion are
The heating element according to claim 1, which has an average particle diameter of ⅕ or less of that of the insulating large grain portion. 3. The small insulating particles are 1/3 of the conductive particles.
The heating element according to any one of claims 1 to 3, which has an average particle size of 3 to 3 times. 4. The insulating small-grain portion is 5 to 2 of the conductive grain portion.
The heating element according to any one of claims 1 to 4, which is mixed in an amount of 00% by volume. 5. The heating element according to claim 1, wherein the insulating large grain portion and the insulating small grain portion are made of the same material. 6. A base body comprising a conductive grain portion and an insulating grain portion made of the same material as that of the conductive grain portion and the insulating small grain portion, and embedded in the base body. 2. A ceramic heater comprising: the heat generating element; and an electrode wire that is embedded in the base body and is connected to an end of the heat generating element and is made of a high melting point metal member.