JP2003238252A - Ceramic structure and glow plug using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ceramic structure capable of appropriately improving electrical insulation and heat resistance with an inexpensive configuration, and to provide a glow plug using the structure. <P>SOLUTION: In the ceramic structure 30 in a glow plug G1, an electrically insulative ceramic support 35 for supporting a U-shaped heating element 33 while enwrapping it is obtained by sintering a material in which Si<SB>3</SB>N<SB>4</SB>and a metal silicide are contained as base materials and ≥1 wt.% SiO<SB>2</SB>and 5 to 20 wt.% rare earth oxide are added as additives, with the proviso that the amount of the rare earth oxide added is not less than that of SiO<SB>2</SB>added. <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 ceramic structure in which a heating element that generates heat when energized is surrounded by an electrically insulating ceramic support, and the ceramic structure is, for example, a ceramic glow plug or the like. Used for.

[0002]

2. Description of the Related Art For example, FIG. 5 shows a general sectional structure of a ceramic structure in a ceramic glow plug.
A ceramic structure J30 is held in a metal sleeve 20 held by the housing 10 with its tip portion protruding.

The ceramic structure J30 is U in the illustrated example.
The heating element 33 is made of a conductive ceramic and has a pair of lead wires 34 that are electrically connected to the heating element 33 and electrically connect the heating element 33.
And the lead wire 34 is an electrically insulating ceramic support J
It is embedded in 35.

Conventionally, the ceramic support J35 has a mixture of silicon nitride (Si ₃ N ₄ ) and metal silicide (MoSi ₂ ) as a base material, and alumina (Al ₂ O ₃ ) or a rare earth oxide added thereto. It consists of a sintered body obtained by sintering a material. Here, alumina or a rare earth oxide is added to crystallize the grain boundary phase and improve the insulating property.

[0005]

At present, there is a demand from users to further improve the electric insulation and heat resistance of the ceramic structure.

For example, in the case of glow plugs, direct injection of diesel engines is progressing, and glow plugs are required to have a more elongated shape. Therefore, if the ceramic structure J30 shown in FIG. 5 is further thinned, the U-shaped space t of the U-shaped heating element 33 is narrowed, and there is a concern that the electrical insulation property is deteriorated at the space. In terms of temperature, heat resistance of 1200 ° C. or higher is required.

As described above, in order to further improve the electric insulation and heat resistance of the ceramic structure, the conventional ceramic support J35 has the following problems.

For example, at a high temperature of 1200 ° C. or higher, alumina reacts with impurities contained in the base material in an uncontrollable manner to form a low-melting glass phase, which is an obstacle to improving heat resistance. Further, since the rare earth oxide is expensive, it is difficult to add a large amount thereof even when trying to promote crystallization of the grain boundary phase.

In view of the above problems, it is an object of the present invention to provide a ceramic structure capable of appropriately improving electrical insulation and heat resistance with an inexpensive structure and a glow plug using the same.

[0010]

In order to achieve the above object, as a result of examining a multi-component system phase diagram of a base material (silicon nitride etc.) and additives constituting a ceramic support, a relatively inexpensive SiO ₂ was found. We paid attention to the fact that it has the property of replacing alumina.

Then, the composition ratio of the base material made of a mixture of silicon nitride and metal silicide, which constitutes the ceramic support, and the additive made of SiO 2 and rare earth oxide is changed to change the electrical insulation and heat resistance of the ceramic structure. The experiment was examined. The present invention was obtained as a result of this experimental study.

That is, according to the first aspect of the invention, the heating element (33) which generates heat when energized and the electrically insulating ceramic support (35) which surrounds and supports the heating element.
In the ceramic structure including, the ceramic support has 1% by weight of Si ₃ N ₄ and metal silicide as a base material.
The above SiO ₂ and 5 to 20% by weight of a rare earth oxide added as an additive, and a material obtained by sintering a material in which the amount of the rare earth oxide added is equal to or more than the addition amount of SiO _2. Is characterized in that.

The present invention has been experimentally confirmed to be effective. Further, if a ceramic support body obtained by sintering a material having the above composition is used, a ceramic structure capable of appropriately improving electric insulation and heat resistance with a cheaper structure than the conventional one. The body can be provided.

Further, the effect of the present invention is that, as in the ceramic structure according to claim 2, the heating element (33) has a U-shape, and the shortest distance (t) between the U-shapes is 0.2 mm. ~
It can be effectively used even for objects having a thickness of 1.5 mm.

According to the study by the present inventor, in the conventional ceramic structure, a short-circuiting distance between U-shapes is as short as 1.5 mm or less, and a short heating element is likely to cause a short circuit at a high temperature.
By using the ceramic support of the present invention, electrical insulation can be ensured. Also, the shortest distance between U-shapes is 0.2
If it is less than mm, it is too narrow to be manufactured.

Even when the heating element (33) has a maximum temperature of 1200 ° C. or higher when generating heat, as in the invention of claim 3, the effect of the invention of claim 1 described above. Is effectively demonstrated.

Further, as in the invention described in claim 4, Y ₂ O ₃ can be used as the rare earth oxide.

Furthermore, the invention described in claim 5 provides a glow plug comprising the ceramic structure (30) according to any one of claims 1 to 4. Accordingly, it is possible to provide a glow plug using a ceramic structure that can appropriately improve electrical insulation and heat resistance with an inexpensive structure.

The reference numerals in parentheses for each means described above are examples showing the correspondence with specific means described in the embodiments described later.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) The present invention will be described below with reference to the embodiments shown in the drawings. FIG. 1 is a vertical sectional view showing the overall configuration of a glow plug G1 for a diesel engine according to a first embodiment of the present invention.

The glow plug G1 is attached to a plurality (for example, four cylinders) of engine heads (not shown) in a direct injection diesel engine of an automobile, and is applied to promote ignition and combustion of fuel when the engine is started.

The housing 10 has a cylindrical shape that can be attached to the engine, and is made of a conductive material (for example, iron-based material). On the outer peripheral surface between the one end 11 and the other end 12 of the housing 10, a mounting screw portion 13 for mounting to the engine head and a nut portion 14 for screw tightening are formed.

The housing 10 can be made, for example, by using carbon steel or the like, the inner surface and the outer surface of which are processed by cold forging, and then the mounting screw portion 13 is formed by cutting or the like. Further, as the size of the mounting screw portion 13, for example, a size of M8 or less standardized by JIS (Japanese Industrial Standard) can be adopted.

A cylindrical sleeve 20 made of a heat resistant / corrosion resistant alloy (for example, stainless steel) is housed in the inner hole of the housing 10. The other end 22 of the sleeve 20 is inserted into the housing 10 with one end 21 thereof protruding from the one end 11 of the housing 10. Here, the housing 10 is press-fitted or brazed at the insertion portion.
The inner surface of the sleeve 20 and the outer surface of the sleeve 20 are fixed without a gap, and the sleeve 20 is held by the housing 10.

A ceramic rod-shaped ceramic structure 30 is housed in the inner hole of the sleeve 20. The ceramic structure 30 has one end 31 side protruding from the one end 21 of the sleeve 20 and the other end 32 side being the sleeve 20.
Has been inserted into. Here, the ceramic structure 30 is fixed and held to the sleeve 20 by brazing the insertion portion or the like.

The ceramic structure 30 is a U-shaped heating element 33 made of a conductive ceramic (for example, one containing silicon nitride and molybdenum silicide) which generates heat when energized.
A pair of lead wires 34, which are electrically connected to the heating element 33 and are made of tungsten or the like, for energizing the heating element 33.
With.

The ceramic structure 30 is a sintered body in which the heating element 33 and the lead wire 34 are embedded in a ceramic support 35 made of an insulating ceramic.
Thus, the ceramic support 35 causes the heating element 33 to
Is supported to be wrapped up.

Further, in the illustrated example, the ceramic structure 30
Has a step portion 36 in the middle thereof, and the one end 31 side has a small diameter portion 3
7, the other end 32 side is the large diameter portion 38, and the one end 31 is spherical.

Here, in the present embodiment, the ceramic support 35 of the ceramic structure 30 is made of Si ₃ N ₄ and a metal silicide as a base material and contains 1 wt% or more of SiO ₂ and 5 to 20 wt% of a rare earth oxide. That is added as an additive and the amount of the rare earth oxide added is SiO 2.
_The main feature is that a material having an addition amount of ₂ or more is sintered.

In other words, the weight ratio of the base material and the additive is 6 to 40 when the base material is 100. That is, with the base material as 100% by weight, a material having SiO ₂ of 1% by weight or more, rare earth oxide of 5 to 20% by weight, and the addition amount of the rare earth oxide being the addition amount of SiO ₂ or more is sintered. What is formed is a ceramic support 35.

In the present example, but not limited to, the metal silicide of ceramic support 35 is MoSi ₂ and the rare earth oxide is Y ₂ O ₃ . Further, the heat generating element 33 has a maximum temperature of 1200 ° C. or higher when generating heat, and the shortest distance t between U-shaped portions is 0.2 mm to 1.5 mm.

A rod-shaped middle shaft 40 made of carbon steel machined by cutting and cold forging is housed in the inner hole of the housing 10 on the side of the other end 12 of the housing 10. A cap lead 50 made of a conductive metal such as stainless steel is fitted to one end 41 side of the center shaft 40.

Then, one lead wire 34 of the ceramic structure 30 is electrically connected to the center shaft 40 by being connected to the cap lead 50 by brazing or the like at a portion exposed from the ceramic support body 35. There is. The other lead wire 34 is grounded to the housing 10 via the sleeve 20 by being connected to the sleeve 20 at the portion exposed from the ceramic support 35 by brazing or the like.

The other end 42 side of the center shaft 40 projects from the other end 12 of the housing 10.
A terminal screw portion 43 is formed to which an external wiring member (not shown) electrically connected to a power source (not shown) is screwed.

Here, between the other end 42 side of the center shaft 40 and the housing 10, a cylindrical insulating bush 60 and a center shaft 40 are provided.
An electrically insulating member such as an annular welded glass 62 and an insulator 64 for holding, fixing, and centering is interposed. Welded glass 62 and insulator 64
Is fastened and fixed by a nut 44 provided on the terminal screw portion 43 via an insulating bush 60.

Next, based on the above structure, the glow plug G
The manufacturing method of No. 1 will be specifically described. For the ceramic structure 30, first, the raw material of the heating element 33 and the raw material of the ceramic support 35 are prepared.

For example, regarding the heating element 33, when the base material composed of 30% by weight of Si ₃ N ₄ and 70% by weight of MoSi ₂ is taken as 100% by weight, 10% by weight of Y ₂ O ₃ and 7% by weight. A material is compounded with an additive consisting of% SiO ₂ . On the other hand, regarding the ceramic support 35,
Additives consisting of 10% by weight Y ₂ O ₃ and 7% by weight SiO ₂ were mixed, with the base material consisting of 90% by weight Si ₃ N ₄ and 10% by weight MoSi ₂ as 100% by weight. Blend the ingredients.

The heating element material and the ceramic support material are powders, which are agitated and mixed in a pot mill. For example, 150 ingredients in a 5 liter pot
Add 0 g and 5 kg of boulders and stir for 8 hours.

Then, the respective raw materials mixed by the mill are injection molded. Injection molding is mainly performed in three stages. First, as shown in FIG. 2A, a heating element material is injection-molded in a mold in which the lead wires 34 are arranged to form a U-shaped temporary molded body 30 a integrated with the lead wires 34.

Next, the primary molded body 30a is placed in a molding die, and a ceramic support material is injection-molded to mold half of the ceramic support 35 as shown in FIG. 2 (b). The secondary molded body 30b is made. Next, the secondary molded body 30b is placed in a molding die, and the ceramic support material is injection-molded to mold the other half of the ceramic support 35, as shown in FIG. 2 (c).
A tertiary molded body 30c having an almost final shape is produced.

Next, as shown in FIG. 2 (d), the molded tertiary molded body 30c is placed in the carbon mold K1 and hot press firing is performed in which it is fired at a predetermined temperature and time while applying pressure. . Then, by grinding the fired sintered body, the final shape of the ceramic structure 30 is finished.
In this way, the ceramic structure 30 is completed.

Next, the center rod 4 is inserted through the cap lead 50.
0 and one lead wire 34 of the ceramic structure 30 are fixed by brazing. Further, the ceramic structure 30 is inserted into the sleeve 20, and the lead wire 34 on the insertion portion and the other side and the sleeve 20 are fixed by brazing. In this way, an integrated member in which the ceramic structure 30, the center shaft 40, and the sleeve 20 are integrated is completed.

Then, the integrated member is attached to the housing 10.
The housing 10 and the sleeve 20 are fixed to each other by brazing. Note that the insertion portion may be fixed by press fitting.

Subsequently, the insulating bush 60 and the fused glass 6
While arranging 2 and the insulator 64 around the center shaft 40, the nut 44 is tightened along the terminal screw portion 43.
The welding glass 62 is put in a powder form and heated to be welded. In this way, the glow plug G1 shown in FIG. 1 is completed.

This glow plug G1 has a mounting screw portion 13
It is screwed and attached to the hole portion of the engine head (not shown) through. And the ceramic structure 3
One end 31 of 0 is exposed to the combustion chamber of the engine.

Further, with the glow plug G1 attached to the engine head, the terminal screw portion 43 is tightened with a terminal nut (not shown) by the external wiring member electrically connected to the power source. It can be assembled.
As a result, with the housing 10 and the engine head on the ground side, it is possible to energize the heating element 33 of the ceramic structure 30 from the power source through the external wiring member and the center shaft 40.

In the glow plug G1, when the heating element 33 is energized, the heating element 33 generates heat,
The heat ignites the fuel in the combustion chamber. In this way, ignition and combustion of fuel at the time of engine start are promoted.

By the way, as described above, in the present embodiment, in the ceramic structure 30, the ceramic support 35 includes 1 wt% or more of SiO ₂ and 5 to 20 containing Si ₃ N ₄ and a metal silicide as a base material. The main characteristic is that the rare earth oxide is added by weight% as an additive, and a material in which the amount of the rare earth oxide added is equal to or more than the added amount of SiO ₂ is sintered. .

The ceramic support 35 having such a composition is based on the result of the experiment conducted by the present inventor. Next, an example of the experiment result will be described with reference to FIG.

The table shown in FIG. 3 shows the ceramic support 35.
90% by weight of Si as a sintering raw material ₃N_FourAnd 10 weight
% MoSi₂When the base material consisting of 100% by weight
And the additive Y₂O₃Weight ratio (wt%), SiO₂
When materials with various weight ratios (% by weight) of are used,
The electrical insulation, sinterability and durability of the ceramic structure 30
It shows the results of the examination.

Here, the shortest distance between the U-shapes of the U-shaped heating element 33 is 0.4 mm, but the shortest distance is 0.2 mm.
The same result as in FIG. 3 is obtained in the range of mm to 1.5 mm.

Regarding the insulating property, the ceramic structure 30
In, a heating element 33 having a configuration in which the U-shaped bent portion is removed to divide the heating element 33 into two linear portions,
When the resistance value between the pair of lead wires 34 is 5 MΩ or more when this is placed at a temperature of 1200 ° C.,
It was determined that good insulation could be ensured.

Regarding the sinterability, pores (air bubbles)
No grain boundary material (Y₂O₃And SiO ₂) There is no aggregation
It was determined that good sinterability could be ensured. Also resistant
For durability, the heating element 33 is energized for 6 minutes and 140
0 ° C temperature (1400 ° C in about 30 seconds after energization)
Then, turn off the power for 1 minute, cool it down, and return it to room temperature.
The heat generation performance can be maintained by performing over 10,000 cycles.
If so, it was determined that good durability could be ensured.

In FIG. 3, "○" means that each performance can be reliably ensured for a plurality of samples,
“Δ” means that the performance could not be ensured for some of the samples, and “x” means that the performance could not be secured for most of the samples. Then, "determination" in FIG.
In the above, those that meet the purpose of the present invention are marked with "○", and those that do not meet are marked with "X".

[0055] As can be seen from FIG. 3, when the addition amount of Y ₂ O ₃ is less than the added amount of SiO _2, when the additive amount of SiO ₂ is less than 1 wt%, the addition amount of Y ₂ O ₃ of 5 wt If less than%,
When the amount of Y ₂ O ₃ added is more than 20% by weight, any of the insulating property, the sinterability and the durability cannot be secured.

For example, if the added amount of Y ₂ O _{3 or} the added amount of SiO ₂ is too small, the ceramic support 35, which is a sintered body, will be used.
On the other hand, the amount of Y ₂ O ₃ added and SiO ₂
If the addition amount of is too large, they are aggregated and the sinterability deteriorates.

Therefore, from the result of the examination as shown in FIG. 3, as the sintering raw material of the ceramic support 35, Si ₃
1% by weight or more of Si using N ₄ and a metal silicide as a base material
Be those O ₂ and 5-20% by weight of rare earth oxide is added as an additive, and adopted as the addition amount of the rare earth oxide is formed by sintering the material is more than the added amount of SiO ₂ To do.

Further, according to the present embodiment, the ceramic support member 35 obtained by sintering the material having the above composition.
With the ceramic structure 30 having the above, it is possible to provide the ceramic structure 30 that can appropriately improve the electrical insulating property and the heat resistance with an inexpensive structure as compared with the related art, and the glow plug G1 using the ceramic structure 30.

(Second Embodiment) FIG. 4 is a vertical sectional view showing the overall structure of a glow plug G2 for a combustion heater according to a second embodiment of the present invention. This glow plug G2 is
It is used as a heat source to assist ignition of a combustion type heater that uses light oil as fuel and is used for heating. Differences from the first embodiment will be described.

In this glow plug G2, the structure of the ceramic structure 30 is basically the same as that shown in FIG. 1, and the difference is that the diameter is almost uniform and one end 31 is It is a flat end surface rather than a spherical surface. That is, the ceramic structure 30 of the present embodiment
Also, the heating element 33 and the pair of lead wires 34 are supported so as to be wrapped by the ceramic support 35, and the composition of the ceramic support 35 is the same as above.

The ceramic structure 30 is inserted into a housing 110 made of stainless steel or the like and fixed by brazing. This glow plug G2 is provided in the combustion chamber with one end 31 of the ceramic structure 30 with respect to the combustion heater body.
Are attached by press-fitting the housing 110 so that the protrusions protrude.

Further, an annular insulating ring 120 made of alumina or the like and a cylindrical sleeve 130 made of stainless steel or the like are provided on the outer periphery of the ceramic structure 30 closer to the other end 32 than the housing 110. The other end 32 of the ceramic structure 30 is covered with a cap 140 made of stainless steel or the like.

Further, one lead wire 34 is electrically connected to the cap 140 by brazing or the like, and the other lead wire 34 is electrically connected to the sleeve 130 at the portion exposed from the ceramic support 35 by brazing or the like. Connected to each other. The cap 140 side is positive and the sleeve 130 side is negative, and the power source 150 is connected to the heat source 33. The heat generating element 33 is energized to generate heat.

Also in the present embodiment as described above, the ceramic structure 30 capable of appropriately improving the electric insulating property and the heat resistance with the inexpensive structure as compared with the conventional structure and the glow plug G2 using the same are provided. be able to.

According to the study by the present inventor, in the conventional ceramic structure, a short-circuiting distance between U-shapes of 1.5 mm or less and a narrow heating element is likely to cause a short circuit at a high temperature. In the above embodiment, the shortest distance t between U-characters is in the range of 0.2 mm to 1.5 mm because the shortest distance between the letters is less than 0.2 mm and it is difficult to manufacture. It is preferable to use 33. However, the shortest distance t between U-shapes is not limited to the above range.

In the ceramic structure of the present invention, the heating element may have a shape other than the U-shape shown in the above embodiment.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing the overall configuration of a glow plug for a diesel engine according to a first embodiment of the present invention.

FIG. 2 is an explanatory view showing a method for manufacturing a ceramic support.

FIG. 3 is a table showing the results of examining the composition of a ceramic support.

FIG. 4 is a vertical sectional view showing the overall structure of a glow plug for a combustion heater according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a general cross-sectional structure of a ceramic structure in a ceramic glow plug.

[Explanation of symbols]

30 ... Ceramic structure, 33 ... Heating element, 35 ... Ceramic support, t ... Shortest distance between U-shaped U-shaped heating elements.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H05B 3/48 C04B 35/58 102K 102Y F term (reference) 3K092 PP16 QA01 QB11 QB13 QB32 QB41 QB62 QC02 QC16 QC27 QC38 QC43 QC44 QC64 RA02 RB22 RB27 RD02 RD09 RD38 TT06 TT37 UB02 VV06 VV34 4G001 BA04 BA09 BA32 BA49 BB04 BB09 BB32 BB49 BD23

Claims (5)

[Claims] 1. A heating element (33) which generates heat when energized,
A ceramic structure provided with an electrically insulating ceramic support (35) for enclosing and supporting the heating element, wherein the ceramic support contains Si ₃ N ₄ and a metal silicide as a base material in an amount of 1% by weight or more. SiO ₂ and 5 to 20% by weight of a rare earth oxide are added as additives, and a material obtained by sintering a material in which the amount of the rare earth oxide added is equal to or more than the amount of SiO ₂ added. A ceramic structure characterized by being present. 2. The heating element (33) is U-shaped,
The shortest distance (t) between the U-shapes is 0.2mm-1.5mm
The ceramic structure according to claim 1, wherein 3. The ceramic structure according to claim 1, wherein the heating element (33) has a maximum temperature of 1200 ° C. or higher when generating heat. 4. The ceramic structure according to claim 1, wherein the rare earth oxide is Y ₂ O ₃ . 5. A glow plug comprising a ceramic structure (30) according to any one of claims 1 to 4.