JP2021051840A

JP2021051840A - Ceramic heater and glow plug

Info

Publication number: JP2021051840A
Application number: JP2019172386A
Authority: JP
Inventors: 僚平林田; Ryohei Hayashida
Original assignee: NGK Spark Plug Co Ltd
Current assignee: Niterra Co Ltd
Priority date: 2019-09-23
Filing date: 2019-09-23
Publication date: 2021-04-01
Anticipated expiration: 2039-09-23
Also published as: JP7236970B2

Abstract

To provide a ceramic heater and a glow plug that can prevent increase in processing time while ensuring the accuracy of polishing-based processing.SOLUTION: A ceramic heater 10 includes a substrate 11 made of an insulating ceramic containing silicon nitride as a main component and containing silicon carbide, and a heating element 15 which is embedded in the substrate and made of a conductive ceramic. When the longest length of a line connecting two points on the outer shape of one of silicon carbide particles appearing on a cross-section of the substrate is defined as a particle length and the longest particle length of the particle lengths of one or more particles appearing on the cross-section is defined as a maximum particle length L, the maximum length L is 2.0 μm or more and 5.0 μm or less.SELECTED DRAWING: Figure 1

Description

本発明は、窒化珪素を主成分とし炭化珪素を含有するセラミックヒータ及びそれを備えるグロープラグに関するものである。 The present invention relates to a ceramic heater containing silicon nitride as a main component and containing silicon carbide, and a glow plug including the same.

窒化珪素を主成分とし炭化珪素を含有する絶縁性セラミックからなる基体に導電性セラミックからなる発熱体を埋設した焼結体を得た後、焼結体に研磨加工を施してセラミックヒータを得る技術が特許文献１に開示されている。特許文献１の表６に、基体の断面に現出する炭化珪素の粒子の最大粒径が１．６μｍ，８．８μｍ，１８．８μｍのセラミックヒータが記載されている。 A technique for obtaining a ceramic heater by obtaining a sintered body in which a heating element made of a conductive ceramic is embedded in a substrate made of an insulating ceramic containing silicon carbide as a main component and then polishing the sintered body. Is disclosed in Patent Document 1. Table 6 of Patent Document 1 describes ceramic heaters having maximum particle sizes of 1.6 μm, 8.8 μm, and 18.8 μm of silicon carbide particles appearing on the cross section of the substrate.

国際公開第２００７／１３５７７３号明細書WO 2007/135773

しかしながら、基体の断面に現出する炭化珪素の粒子の最大粒径が１．６μｍであると、炭化珪素による砥粒の劈開が研磨加工中に生じ難くなるので、砥粒の切れ刃が鈍化し、砥石の切れ味が低下して加工時間が長くなるという問題点がある。 However, if the maximum particle size of the silicon carbide particles appearing on the cross section of the substrate is 1.6 μm, cleavage of the abrasive grains due to the silicon carbide is unlikely to occur during the polishing process, so that the cutting edge of the abrasive grains becomes dull. However, there is a problem that the sharpness of the grindstone is lowered and the processing time is lengthened.

また、基体の断面に現出する炭化珪素の粒子の最大粒径が８．８μｍ，１８．８μｍであると、炭化珪素によって砥粒の劈開が部分的に過度に生じたり、砥粒が部分的に脱落したりして、砥石面が荒れてしまう。そのような状態で研磨を続けると、加工精度が低下するという問題点がある。 Further, when the maximum particle size of the silicon carbide particles appearing on the cross section of the substrate is 8.8 μm or 18.8 μm, the silicon carbide partially causes the cleavage of the abrasive grains to be partially excessive, or the abrasive grains are partially formed. The grindstone surface becomes rough due to falling off. If polishing is continued in such a state, there is a problem that the processing accuracy is lowered.

本発明はこれらの問題点を解決するためになされたものであり、研磨による加工精度を確保しつつ加工時間が長くなるのを抑制できるセラミックヒータ及びグロープラグを提供することを目的とする。 The present invention has been made to solve these problems, and an object of the present invention is to provide a ceramic heater and a glow plug capable of suppressing a long processing time while ensuring processing accuracy by polishing.

この目的を達成するために本発明のセラミックヒータは、窒化珪素を主成分とし炭化珪素を含有する絶縁性セラミックからなる基体と、基体に埋設され導電性セラミックからなる発熱体と、を備え、基体の断面に現出する炭化珪素の粒子の１つの外形上の２点間を結ぶ線分のうち最も長い長さを粒子長さとし、その断面に現出する１又は複数の粒子の粒子長さのうち最も長い粒子長さを最大長さＬとしたとき、最大長さＬが２．０μｍ以上５．０μｍ以下である。 In order to achieve this object, the ceramic heater of the present invention includes a substrate made of an insulating ceramic containing silicon carbide as a main component and containing silicon carbide, and a heating element embedded in the substrate and made of a conductive ceramic. The longest length of the line connecting two points on one outer shape of the silicon carbide particles appearing in the cross section is defined as the particle length, and the particle length of one or more particles appearing in the cross section. When the longest particle length is the maximum length L, the maximum length L is 2.0 μm or more and 5.0 μm or less.

本発明のグロープラグは、上記セラミックヒータと、基体のうち発熱体を埋設した部分を少なくとも露出させつつセラミックヒータを保持する筒状部材と、を備え、セラミックヒータと筒状部材とは圧入構造をなし、セラミックヒータは、筒状部材に圧入された部分の外周面に、発熱体に電気的に接続される電極取出部を備える。 The glow plug of the present invention includes the ceramic heater and a tubular member that holds the ceramic heater while exposing at least the portion of the substrate in which the heating element is embedded, and the ceramic heater and the tubular member have a press-fitting structure. None, the ceramic heater is provided with an electrode extraction portion electrically connected to the heating element on the outer peripheral surface of the portion press-fitted into the tubular member.

請求項１記載のセラミックヒータによれば、基体の断面に現出する炭化珪素の粒子の最大長さＬは２．０μｍ以上５．０μｍ以下である。最大長さＬが２．０μｍ以上であると研磨（又は研削）中に炭化珪素による砥粒の劈開が生じ易くなるので、砥粒に新しい切れ刃が発生し、砥石の切れ味を維持できる。その結果、加工時間が長くならないようにできる。さらに最大長さＬが５．０μｍ以下であると、炭化珪素の粒子による部分的な砥粒の劈開や砥石からの砥粒の脱落を抑制できるので、砥石面の荒れを抑制できる。その結果、セラミックヒータの仕上げ面粗さを小さくできるので、加工精度を確保できる。 According to the ceramic heater according to claim 1, the maximum length L of the silicon carbide particles appearing on the cross section of the substrate is 2.0 μm or more and 5.0 μm or less. When the maximum length L is 2.0 μm or more, cleavage of the abrasive grains by silicon carbide is likely to occur during polishing (or grinding), so that a new cutting edge is generated in the abrasive grains and the sharpness of the grindstone can be maintained. As a result, the processing time can be prevented from becoming long. Further, when the maximum length L is 5.0 μm or less, partial cleavage of the abrasive grains due to the silicon carbide particles and dropping of the abrasive grains from the grindstone can be suppressed, so that roughness of the grindstone surface can be suppressed. As a result, the roughness of the finished surface of the ceramic heater can be reduced, so that the processing accuracy can be ensured.

請求項２記載のセラミックヒータによれば、発熱体は炭化タングステンを主成分とし、基体は窒化珪素を主成分とし炭化珪素を含有する。基体の断面の所定の領域において、粒子長さが２．０μｍ以上５．０μｍ以下の炭化珪素の粒子の面積の総和の、領域の面積に対する割合は１０％以下なので、基体に含まれる炭化珪素によって、基体の線膨張係数が発熱体の線膨張係数より著しく大きくならないようにできる。その結果、請求項１の効果に加え、発熱体が基体に加える熱応力を抑制できる。 According to the ceramic heater according to claim 2, the heating element contains tungsten carbide as a main component, and the substrate contains silicon nitride as a main component and contains silicon carbide. In a predetermined region of the cross section of the substrate, the ratio of the total area of the silicon carbide particles having a particle length of 2.0 μm or more and 5.0 μm or less to the area of the region is 10% or less. , The coefficient of linear expansion of the substrate can be prevented from being significantly larger than the coefficient of linear expansion of the heating element. As a result, in addition to the effect of claim 1, the thermal stress applied to the substrate by the heating element can be suppressed.

請求項３記載のグロープラグによれば、セラミックヒータが、基体のうち発熱体を埋設した部分を少なくとも露出させて筒状部材に保持される。セラミックヒータと筒状部材とは圧入構造をなす。セラミックヒータは、筒状部材に圧入された部分の外周面に、発熱体に電気的に接続される電極取出部を備えるので、セラミックヒータの外周面の加工精度の確保により、電極取出部と筒状部材との電気的な接続の信頼性を確保できる。 According to the glow plug according to claim 3, the ceramic heater is held by the tubular member by exposing at least the portion of the substrate in which the heating element is embedded. The ceramic heater and the tubular member form a press-fitting structure. Since the ceramic heater is provided with an electrode extraction portion electrically connected to the heating element on the outer peripheral surface of the portion press-fitted into the tubular member, the electrode extraction portion and the cylinder can be ensured by ensuring the processing accuracy of the outer peripheral surface of the ceramic heater. The reliability of the electrical connection with the shape member can be ensured.

一実施の形態におけるセラミックヒータの断面図である。It is sectional drawing of the ceramic heater in one Embodiment. （ａ）は基体の断面の模式図であり、（ｂ）は基体の断面に現出する炭化珪素の粒子の模式図である。(A) is a schematic view of a cross section of the substrate, and (b) is a schematic diagram of silicon carbide particles appearing on the cross section of the substrate. グロープラグの断面図である。It is sectional drawing of the glow plug.

以下、本発明の好ましい実施の形態について添付図面を参照して説明する。図１は本発明の一実施の形態におけるセラミックヒータ１０の軸線Ｏを含む断面図である。図１では、紙面下側をセラミックヒータ１０の先端側、紙面上側をセラミックヒータ１０の後端側という。図１に示すようにセラミックヒータ１０は、基体１１と、基体１１に埋設された発熱体１５と、を備えている。 Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view including the axis O of the ceramic heater 10 according to the embodiment of the present invention. In FIG. 1, the lower side of the paper surface is referred to as the front end side of the ceramic heater 10, and the upper side of the paper surface is referred to as the rear end side of the ceramic heater 10. As shown in FIG. 1, the ceramic heater 10 includes a base 11 and a heating element 15 embedded in the base 11.

基体１１は絶縁性セラミックからなり、本実施形態では先端が球冠状の略円柱状に形成されている。基体１１を構成する絶縁性セラミックは窒化珪素を主成分とし、炭化珪素を含有する。主成分とは、絶縁性セラミックを構成する複数の化合物の中で窒化珪素の質量が最も大きいことを意味する。絶縁性セラミックに含まれる窒化珪素および炭化珪素以外の化合物としては、例えば希土類元素の酸化物、Ｗ，Ａｌ，Ｃｒの各酸化物、炭化物、珪化物、窒化物などから選ばれる１種または２種以上が挙げられる。希土類元素としては、例えばＥｒ，Ｙｂ，Ｙ等が挙げられる。 The substrate 11 is made of an insulating ceramic, and in the present embodiment, the tip is formed in a substantially cylindrical shape having a spherical crown shape. The insulating ceramic constituting the substrate 11 contains silicon nitride as a main component and silicon carbide. The principal component means that the mass of silicon nitride is the largest among the plurality of compounds constituting the insulating ceramic. Examples of compounds other than silicon nitride and silicon carbide contained in the insulating ceramic include one or two selected from rare earth element oxides, W, Al, and Cr oxides, carbides, silices, and nitrides. The above can be mentioned. Examples of rare earth elements include Er, Yb, Y and the like.

発熱体１５は、導電性セラミックからなる導体１４の一部である。導体１４は、基体１１の先端近くに埋設されたＵ字状の発熱体１５と、発熱体１５の後端に接続され軸線Ｏに沿って延びる一対の棒状のリード部１６と、リード部１６の後端近くにそれぞれ設けられた電極取出部１７，１８と、を備えている。電極取出部１７，１８は基体１１の外周面に露出している。電極取出部１８は電極取出部１７よりも後端側に位置する。電極取出部１７，１８は、リード部１６を介して発熱体１５に電力を供給する部位である。 The heating element 15 is a part of a conductor 14 made of conductive ceramic. The conductor 14 is a U-shaped heating element 15 embedded near the tip of the substrate 11, a pair of rod-shaped lead portions 16 connected to the rear end of the heating element 15 and extending along the axis O, and a lead portion 16. It is provided with electrode take-out portions 17, 18 provided near the rear end, respectively. The electrode extraction portions 17 and 18 are exposed on the outer peripheral surface of the substrate 11. The electrode extraction portion 18 is located on the rear end side of the electrode extraction portion 17. The electrode extraction portions 17 and 18 are portions for supplying electric power to the heating element 15 via the lead portion 16.

発熱体１５の断面積はリード部１６の断面積より狭いので、発熱体１５を構成する導電性セラミックの材質がリード部１６を構成する導電性セラミックの材質と同じでも、発熱体１５の抵抗をリード部１６の抵抗よりも大きくできる。その結果、発熱体１５の発熱量をリード部１６の発熱量よりも大きくできるので、発熱体１５を選択的に発熱させることができる。なお、発熱体１５及びリード部１６の断面積を異ならせるのではなく、比抵抗がリード部１６の比抵抗よりも大きい材質を発熱体１５に採用して、発熱体１５を選択的に発熱させることは当然可能である。 Since the cross-sectional area of the heating element 15 is narrower than the cross-sectional area of the lead portion 16, even if the material of the conductive ceramic constituting the heating element 15 is the same as the material of the conductive ceramic constituting the lead portion 16, the resistance of the heating element 15 is increased. It can be larger than the resistance of the lead portion 16. As a result, the amount of heat generated by the heating element 15 can be made larger than the amount of heat generated by the lead portion 16, so that the heating element 15 can be selectively generated. Instead of making the cross-sectional areas of the heating element 15 and the lead portion 16 different, a material having a specific resistance larger than the specific resistance of the lead portion 16 is used for the heating element 15 to selectively generate heat of the heating element 15. Of course it is possible.

発熱体１５を構成する導電性セラミックは炭化タングステン（ＷＣ）を主成分とする。主成分とは、導電性セラミックを構成する複数の化合物の中で炭化タングステンの質量が最も大きいことを意味する。導電性セラミックに含まれる炭化タングステン以外の化合物としては、窒化珪素、焼結助剤が挙げられる。 The conductive ceramic constituting the heating element 15 contains tungsten carbide (WC) as a main component. The principal component means that the mass of tungsten carbide is the largest among the plurality of compounds constituting the conductive ceramic. Examples of the compound other than tungsten carbide contained in the conductive ceramic include silicon nitride and a sintering aid.

図２（ａ）は基体１１の断面の模式図である。基体１１の断面は、任意の平面（切断面）で基体１１が切断された面である。図２（ａ）に示す矩形の領域２０は、走査型電子顕微鏡（ＳＥＭ）の視野である。領域２０の大きさは、本実施形態では、縦Ｈ＝３０μｍ、横Ｗ＝４５μｍである。領域２０には基体１１の断面の画像が示される。基体１１の断面観察の前にプラズマエッチング等のエッチングを施し、断面に現出する粒界をはっきりさせる。粒子の外形を識別し易くするためである。 FIG. 2A is a schematic view of a cross section of the substrate 11. The cross section of the substrate 11 is a surface on which the substrate 11 is cut on an arbitrary plane (cut surface). The rectangular region 20 shown in FIG. 2A is the field of view of a scanning electron microscope (SEM). In the present embodiment, the size of the region 20 is vertical H = 30 μm and horizontal W = 45 μm. An image of a cross section of the substrate 11 is shown in the region 20. Before observing the cross section of the substrate 11, etching such as plasma etching is performed to clarify the grain boundaries appearing on the cross section. This is to make it easier to identify the outer shape of the particles.

領域２０には、絶縁性セラミックを構成する粒子、粒界および気孔が現出する。絶縁性セラミックを構成する粒子には、炭化珪素の粒子２１，２４が含まれる。図２（ａ）では断面に現出する炭化珪素のうち、粒子長さ（後述する）が２．０μｍ以上の粒子のみを図示している。なお、図２（ａ）では、粒子長さ（後述する）が２．０μｍよりも小さい粒子や、気孔は図示が省略されている。本実施形態では、粒子長さ（後述する）が２．０μｍ以上の２つの粒子２１，２４が領域２０に現出する場合について説明するが、これは一例である。領域２０に現出する粒子長さが２．０μｍ以上の炭化珪素の粒子の数はいくつでも構わない。基体１１の断面の組織に存在する炭化珪素の粒子２１，２４は、例えばＳＥＭ及びエネルギー分散型Ｘ線分光（ＥＤＸ）を用いて特定できる。 Particles, grain boundaries and pores that make up the insulating ceramic appear in the region 20. The particles constituting the insulating ceramic include silicon carbide particles 21 and 24. FIG. 2A shows only the particles having a particle length (described later) of 2.0 μm or more among the silicon carbides appearing in the cross section. In FIG. 2A, particles having a particle length (described later) smaller than 2.0 μm and pores are not shown. In the present embodiment, a case where two particles 21 and 24 having a particle length (described later) of 2.0 μm or more appear in the region 20 will be described, but this is an example. The number of silicon carbide particles appearing in the region 20 and having a particle length of 2.0 μm or more may be any number. The silicon carbide particles 21 and 24 present in the cross-sectional structure of the substrate 11 can be identified using, for example, SEM and energy dispersive X-ray spectroscopy (EDX).

図２（ｂ）は基体１１の断面に現出する炭化珪素の粒子２１の模式図である。粒子長さは、１つの粒子２１の外形２２上の２点間を結ぶ線分２３のうち最も長い長さのことである。粒子２４も同様にして、領域２０に現出する炭化珪素の全ての粒子の粒子長さを求める。最大長さＬは、領域２０内の断面に現出する粒子２１，２４（図２（ａ）参照）の粒子長さのうち最も長い粒子長さのことである。 FIG. 2B is a schematic view of silicon carbide particles 21 appearing on the cross section of the substrate 11. The particle length is the longest length of the line segment 23 connecting two points on the outer shape 22 of one particle 21. Similarly for the particles 24, the particle lengths of all the particles of silicon carbide appearing in the region 20 are obtained. The maximum length L is the longest particle length among the particle lengths of the particles 21 and 24 (see FIG. 2A) appearing in the cross section in the region 20.

本実施形態では、粒子２１の粒子長さＬは粒子２４の粒子長さＫより長いので、粒子２１の粒子長さが最大長さＬである。粒子２１，２４の粒子長さＫ，Ｌは、断面の画像を基に画像解析ソフト等を用いることにより算出される。セラミックヒータ１０は、基体１１の断面に現出する炭化珪素の粒子２１，２４の粒子長さＫ，Ｌのうち最も長い粒子長さＬ（最大長さ）が２．０μｍ以上５．０μｍ以下である。 In the present embodiment, the particle length L of the particles 21 is longer than the particle length K of the particles 24, so that the particle length of the particles 21 is the maximum length L. The particle lengths K and L of the particles 21 and 24 are calculated by using image analysis software or the like based on the image of the cross section. In the ceramic heater 10, the longest particle length L (maximum length) among the particle lengths K and L of the silicon carbide particles 21 and 24 appearing on the cross section of the substrate 11 is 2.0 μm or more and 5.0 μm or less. is there.

また、領域２０に現出する粒子長さＫ，Ｌが２．０μｍ以上５．０μｍ以下の粒子２１，２４の面積の総和の、領域２０の面積（本実施形態では３０×４５μｍ^２）に対する割合は１０％以下である。粒子長さが２．０μｍ未満の炭化珪素の粒子は領域２０内に存在するが、粒子長さが２．０μｍ以上５．０μｍ以下の粒子２１，２４の面積に着目して、炭化珪素の粒子の面積の総和を求める。粒子２１，２４の面積の総和は、断面の画像を基に画像解析ソフト等を用いることにより算出される。 Further, the ratio of the total area of the particles 21 and 24 having particle lengths K and L appearing in the region 20 to 2.0 μm or more and 5.0 μm or less with respect to the area of the region 20 (30 × 45 μm ² in this embodiment). Is less than 10%. Silicon carbide particles having a particle length of less than 2.0 μm exist in the region 20, but focusing on the areas of the particles 21 and 24 having a particle length of 2.0 μm or more and 5.0 μm or less, the silicon carbide particles. Find the sum of the areas of. The total area of the particles 21 and 24 is calculated by using image analysis software or the like based on the image of the cross section.

セラミックヒータ１０は、例えば以下のような方法によって製造される。まず、窒化珪素を主成分とし炭化珪素を含有する絶縁性セラミックの原料粉末を湿式で混合粉砕し、バインダを添加後、スプレードライを施し基体１１の原料を調製する。この原料をプレス成形することにより、軸線Ｏを含む切断面で基体１１を二つ割りにしたような、基体１１の半分を構成する成形体を得る。 The ceramic heater 10 is manufactured by, for example, the following method. First, a raw material powder of an insulating ceramic containing silicon nitride as a main component and containing silicon carbide is mixed and pulverized in a wet manner, a binder is added, and then spray drying is performed to prepare a raw material for the substrate 11. By press-molding this raw material, a molded product that constitutes half of the substrate 11 is obtained, as if the substrate 11 was split in half on the cut surface including the axis O.

これとは別に、炭化タングステンを主成分とする導電性セラミックの原料粉末を湿式で混合粉砕し、スプレードライを施し粉末を得る。この粉末にバインダ、可塑剤、分散剤等を加えて混練し、導体１４の原料を調製する。導体１４の原料を射出成形することにより、導体１４の成形体を得る。 Separately from this, a raw material powder of a conductive ceramic containing tungsten carbide as a main component is mixed and pulverized in a wet manner and spray-dried to obtain a powder. A binder, a plasticizer, a dispersant and the like are added to this powder and kneaded to prepare a raw material for the conductor 14. A molded body of the conductor 14 is obtained by injection molding the raw material of the conductor 14.

基体１１の成形体に導体１４の成形体を置いたものを金型に配置した後、残りの基体１１の原料をプレス成形することにより、基体１１の成形体に導体１４の成形体が埋め込まれた棒状の成形体を得る。成形体を所定の温度で脱脂し、ホットプレス焼成を行うことにより焼成体が得られる。 A molded body of the conductor 14 placed on the molded body of the base 11 is placed in a mold, and then the remaining raw material of the base 11 is press-molded to embed the molded body of the conductor 14 in the molded body of the base 11. Obtain a rod-shaped molded product. A fired body is obtained by degreasing the molded body at a predetermined temperature and performing hot press firing.

必要に応じて焼成体に切断加工が施される。次いで、ダイヤモンドホイール等の砥石を用いて焼結体の表面に研磨（研削）加工を施し、セラミックヒータ１０が得られる。寸法精度を向上させるためである。電極取出部１７，１８が基体１１に埋没している場合には、基体１１の表面の研磨により、電極取出部１７，１８を基体１１の表面に露出させることができる。 If necessary, the fired body is cut. Next, the surface of the sintered body is polished (ground) using a grindstone such as a diamond wheel to obtain a ceramic heater 10. This is to improve the dimensional accuracy. When the electrode extraction portions 17 and 18 are embedded in the substrate 11, the electrode extraction portions 17 and 18 can be exposed on the surface of the substrate 11 by polishing the surface of the substrate 11.

セラミックヒータ１０は、基体１１の断面に現出する炭化珪素の粒子２１，２４の最大長さＬが２．０μｍ以上なので、研磨加工中に、炭化珪素による砥粒の劈開が生じ易くなる。その結果、研磨加工中に砥粒に新しい切れ刃が発生し、砥石の切れ味を維持できるので、加工時間が長くならないようにできる。さらに最大長さＬは５．０μｍ以下なので、炭化珪素の粒子２１，２４による部分的な砥粒の劈開や砥石からの砥粒の脱落を抑制できる。これにより砥石面の荒れを抑制できる。その結果、セラミックヒータ１０の仕上げ面粗さを小さくできるので、基体１１及び電極取出部１７，１８の加工精度を確保できる。 In the ceramic heater 10, since the maximum length L of the silicon carbide particles 21 and 24 appearing on the cross section of the substrate 11 is 2.0 μm or more, cleavage of the abrasive grains by the silicon carbide is likely to occur during the polishing process. As a result, a new cutting edge is generated in the abrasive grains during the polishing process, and the sharpness of the grindstone can be maintained, so that the processing time can be prevented from becoming long. Further, since the maximum length L is 5.0 μm or less, partial cleavage of the abrasive grains by the silicon carbide particles 21 and 24 and dropping of the abrasive grains from the grindstone can be suppressed. As a result, the roughness of the grindstone surface can be suppressed. As a result, the roughness of the finished surface of the ceramic heater 10 can be reduced, so that the processing accuracy of the substrate 11 and the electrode extraction portions 17 and 18 can be ensured.

発熱体１５は、窒化珪素よりも線膨張係数が大きい炭化タングステン（ＷＣ）を主成分とする。基体１１は、窒化珪素を主成分とし炭化珪素を含有する。粒子長さが２．０μｍ以上５．０μｍ以下の炭化珪素の粒子２１，２４の面積の総和の、領域２０の面積に対する割合は１０％以下なので、基体１１に含まれる炭化珪素によって、基体１１の線膨張係数が発熱体１５の線膨張係数より著しく大きくならないようにできる。その結果、発熱体１５が基体１１に加える熱応力を抑制できる。 The heating element 15 is mainly composed of tungsten carbide (WC) having a coefficient of linear expansion larger than that of silicon nitride. The substrate 11 contains silicon nitride as a main component and silicon carbide. Since the ratio of the total area of the silicon carbide particles 21 and 24 having a particle length of 2.0 μm or more and 5.0 μm or less to the area of the region 20 is 10% or less, the silicon carbide contained in the substrate 11 causes the substrate 11 to be affected. The coefficient of linear expansion can be prevented from being significantly larger than the coefficient of linear expansion of the heating element 15. As a result, the thermal stress applied to the substrate 11 by the heating element 15 can be suppressed.

図３を参照して、セラミックヒータ１０を備えるグロープラグ３０について説明する。図３はグロープラグ３０の軸線Ｏを含む断面図である。図３では、紙面下側をグロープラグ３０の先端側、紙面上側をグロープラグ３０の後端側という。 The glow plug 30 including the ceramic heater 10 will be described with reference to FIG. FIG. 3 is a cross-sectional view including the axis O of the glow plug 30. In FIG. 3, the lower side of the paper surface is referred to as the front end side of the glow plug 30, and the upper side of the paper surface is referred to as the rear end side of the glow plug 30.

グロープラグ３０は、セラミックヒータ１０と、セラミックヒータ１０を保持する筒状部材５０と、を備えている。筒状部材５０は、セラミックヒータ１０のうち発熱体１５を埋設した部分を少なくとも露出させて基体１１を保持する。セラミックヒータ１０と筒状部材５０とは圧入構造をなしている。筒状部材５０は、略円筒状の金属製（例えばステンレス鋼等）の部材である。セラミックヒータ１０のうち筒状部材５０に圧入された部分１９に電極取出部１７が位置し、電極取出部１７は筒状部材５０に接続されている。セラミックヒータ１０のうち電極取出部１８を含む後端側の部分が筒状部材５０から突出している。 The glow plug 30 includes a ceramic heater 10 and a tubular member 50 that holds the ceramic heater 10. The tubular member 50 holds the substrate 11 by exposing at least the portion of the ceramic heater 10 in which the heating element 15 is embedded. The ceramic heater 10 and the tubular member 50 have a press-fitting structure. The tubular member 50 is a substantially cylindrical metal member (for example, stainless steel or the like). The electrode take-out portion 17 is located in the portion 19 of the ceramic heater 10 that is press-fitted into the tubular member 50, and the electrode take-out portion 17 is connected to the tubular member 50. A portion of the ceramic heater 10 on the rear end side including the electrode extraction portion 18 protrudes from the tubular member 50.

筒状部材５０は、筒部５１の後端側に厚肉部５２及び係合部５３が形成されている。係合部５３は厚肉部５２よりも後端側に配置され、係合部５３の外径は厚肉部５２の外径よりも小さい。筒状部材５０は、係合部５３が主体金具３１の軸孔３２に嵌められ、厚肉部５２が主体金具３１の先端に突き当てられている。筒状部材５０は主体金具３１の先端に固定されている。 The tubular member 50 has a thick portion 52 and an engaging portion 53 formed on the rear end side of the tubular portion 51. The engaging portion 53 is arranged on the rear end side of the thick portion 52, and the outer diameter of the engaging portion 53 is smaller than the outer diameter of the thick portion 52. In the tubular member 50, the engaging portion 53 is fitted into the shaft hole 32 of the main metal fitting 31, and the thick portion 52 is abutted against the tip of the main metal fitting 31. The tubular member 50 is fixed to the tip of the main metal fitting 31.

主体金具３１は、軸線Ｏに沿う軸孔３２が形成された略円筒状の金属製（例えば炭素鋼やステンレス鋼等）の部材である。主体金具３１は、軸線方向の略中央の外周面にねじ部３３が形成され、ねじ部３３よりも後端側の外周面に工具係合部３４が形成されている。ねじ部３３は、エンジン（図示せず）に形成されたねじ穴に係合する部位である。工具係合部３４は、エンジンのねじ穴にねじ部３３を締め付けるときに、レンチ等の工具を係合させる部位である。 The main metal fitting 31 is a member made of a substantially cylindrical metal (for example, carbon steel, stainless steel, etc.) in which a shaft hole 32 along the axis O is formed. The main metal fitting 31 has a threaded portion 33 formed on the outer peripheral surface substantially at the center in the axial direction, and a tool engaging portion 34 formed on the outer peripheral surface on the rear end side of the threaded portion 33. The screw portion 33 is a portion that engages with a screw hole formed in an engine (not shown). The tool engaging portion 34 is a portion for engaging a tool such as a wrench when the screw portion 33 is tightened in the screw hole of the engine.

中軸３５は金属製の円柱状の部材である。中軸３５の先端側は軸孔３２に収容され、中軸３５の後端側は主体金具３１から突出する。絶縁部材３７は中軸３５を囲むリング状の部材であり、主体金具３１の軸孔３２に配置されている。絶縁部材３７は主体金具３１に中軸３５を固定する。絶縁部材３７は、主体金具３１と中軸３５との間を電気的に絶縁すると共に、主体金具３１と中軸３５との間を気密封止する。 The center pole 35 is a metal columnar member. The tip end side of the center pole 35 is housed in the shaft hole 32, and the rear end side of the center pole 35 projects from the main metal fitting 31. The insulating member 37 is a ring-shaped member that surrounds the center pole 35, and is arranged in the shaft hole 32 of the main metal fitting 31. The insulating member 37 fixes the center pole 35 to the main metal fitting 31. The insulating member 37 electrically insulates between the main metal fitting 31 and the center pole 35, and airtightly seals between the main metal fitting 31 and the center pole 35.

絶縁部材３８は中軸３５を囲む筒状部３９及びフランジ部４０を備える部材であり、絶縁部材３７よりも後端側の軸孔３２に配置されている。フランジ部４０は、筒状部３９よりも後端側において中軸３５を囲んで配置されている。絶縁部材３８は、主体金具３１と中軸３５との間、及び、主体金具３１とスリーブ４１との間を電気的に絶縁する。 The insulating member 38 is a member including a tubular portion 39 and a flange portion 40 surrounding the center pole 35, and is arranged in a shaft hole 32 on the rear end side of the insulating member 37. The flange portion 40 is arranged so as to surround the center pole 35 on the rear end side of the tubular portion 39. The insulating member 38 electrically insulates between the main metal fitting 31 and the center pole 35 and between the main metal fitting 31 and the sleeve 41.

スリーブ４１は略円筒状の金属製の部材であり、フランジ部４０に接した状態で、主体金具３１の後端から突出した中軸３５を取り囲む。スリーブ４１は塑性変形され、中軸３５に加締め固定されている。スリーブ４１は絶縁部材３８の脱落を防止する。 The sleeve 41 is a substantially cylindrical metal member, and surrounds the center pole 35 protruding from the rear end of the main metal fitting 31 in a state of being in contact with the flange portion 40. The sleeve 41 is plastically deformed and crimped and fixed to the center pole 35. The sleeve 41 prevents the insulating member 38 from falling off.

セラミックヒータ１０の後端側は、筒状部材５０から突出して主体金具３１の軸孔３２に収容される。電極リング５４はセラミックヒータ１０を囲む金属製の部材であり、セラミックヒータ１０の電極取出部１８に接触する。中軸３５の先端部３６と電極リング５４との間はリード線５５によって電気的に接続される。グロープラグ３０の中軸３５と主体金具３１との間に電圧が印加されると、セラミックヒータ１０の電極取出部１７，１８から発熱体１５に通電される。セラミックヒータ１０は、筒状部材５０に圧入された部分１９の外周面に電極取出部１７が形成されているので、セラミックヒータ１０の外周面の加工精度の確保により、電極取出部１７と筒状部材５０との電気的な接続の信頼性を確保できる。 The rear end side of the ceramic heater 10 protrudes from the tubular member 50 and is housed in the shaft hole 32 of the main metal fitting 31. The electrode ring 54 is a metal member that surrounds the ceramic heater 10, and comes into contact with the electrode extraction portion 18 of the ceramic heater 10. The tip 36 of the center pole 35 and the electrode ring 54 are electrically connected by a lead wire 55. When a voltage is applied between the center pole 35 of the glow plug 30 and the main metal fitting 31, the heating element 15 is energized from the electrode extraction portions 17 and 18 of the ceramic heater 10. In the ceramic heater 10, the electrode extraction portion 17 is formed on the outer peripheral surface of the portion 19 press-fitted into the tubular member 50. Therefore, the electrode extraction portion 17 and the tubular shape can be ensured by ensuring the processing accuracy of the outer peripheral surface of the ceramic heater 10. The reliability of the electrical connection with the member 50 can be ensured.

本発明を実施例によりさらに詳しく説明するが、本発明はこの実施例に限定されるものではない。 The present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

（サンプルの作製）
窒化珪素（平均粒径０．７μｍ）８０ｗｔ％、炭化珪素、焼結助剤の各粉末を湿式で混合粉砕し、バインダを添加後、スプレードライを施し基体１１の原料を調製した。粒度分布の異なる炭化珪素の粉末を配合することにより、種々の基体１１の原料を得た。なお、基体１１の原料中の炭化珪素の配合量はサンプル間で一定にした。 (Preparation of sample)
80 wt% of silicon nitride (average particle size 0.7 μm), silicon carbide, and sintering aid powders were mixed and pulverized in a wet manner, a binder was added, and then spray drying was performed to prepare a raw material for the substrate 11. By blending silicon carbide powders having different particle size distributions, raw materials for various substrates 11 were obtained. The amount of silicon carbide blended in the raw material of the substrate 11 was kept constant between the samples.

これとは別に、ＷＣ７０ｗｔ％、窒化珪素、焼結助剤の各粉末を湿式で混合粉砕し、スプレードライを施し粉末を得た。この粉末にバインダ、可塑剤、分散剤等を加えて混練し、導体１４の原料を調製した。導体１４の原料を射出成形することにより、導体１４の成形体を得た。 Separately from this, each powder of WC 70 wt%, silicon nitride, and a sintering aid was mixed and pulverized in a wet manner, and spray-dried to obtain a powder. A binder, a plasticizer, a dispersant and the like were added to this powder and kneaded to prepare a raw material for the conductor 14. A molded body of the conductor 14 was obtained by injection molding the raw material of the conductor 14.

基体１１の原料をプレス成形することにより、二つ割りにした導体１４の成形体を得た。その後、基体１１の成形体に導体１４の成形体を置いたものを金型に配置し、残りの基体１１の原料をプレス成形することにより、基体１１の成形体に導体１４の成形体が埋め込まれた棒状の成形体を得た。成形体を所定の温度で脱脂した後、ホットプレス焼成を行い、異なる大きさの炭化珪素の粒子が基体１１に配された焼結体のサンプル１−７を得た。 By press-molding the raw material of the substrate 11, a molded body of the conductor 14 divided into two was obtained. After that, a molded body of the conductor 14 placed on the molded body of the base 11 is placed in a mold, and the remaining raw material of the base 11 is press-molded to embed the molded body of the conductor 14 in the molded body of the base 11. A rod-shaped molded product was obtained. After degreasing the molded product at a predetermined temperature, hot press firing was performed to obtain a sintered sample 1-7 in which particles of silicon carbide having different sizes were arranged on the substrate 11.

（炭化珪素の粒子の最大長さＬの測定）
サンプル１−７の基体１１の断面をプラズマエッチングした後、ＳＥＭの画像を用いて、断面に現出する炭化珪素の粒子の最大長さＬを測定した。具体的には、縦Ｈ＝３０μｍ、横Ｗ＝４５μｍの矩形の領域（視野）を任意に１０個選択し、その１０領域（１０視野）の断面に現出する炭化珪素の粒子の粒子長さのうち最も長い粒子長さ（最大長さＬ）を測定した。サンプル１−７の最大長さＬ（μｍ）を表１に記した。なお、サンプル２−７は、粒子長さが２．０μｍ以上５．０μｍ以下の炭化珪素の粒子の面積の総和の、領域の面積に対する割合は１０％以下であった。 (Measurement of maximum length L of silicon carbide particles)
After plasma etching the cross section of the substrate 11 of the sample 1-7, the maximum length L of the silicon carbide particles appearing on the cross section was measured using the SEM image. Specifically, 10 rectangular regions (fields of view) having a length of H = 30 μm and a width of W = 45 μm are arbitrarily selected, and the particle lengths of the silicon carbide particles appearing in the cross section of the 10 regions (10 fields of view). The longest particle length (maximum length L) was measured. The maximum length L (μm) of Sample 1-7 is shown in Table 1. In Sample 2-7, the ratio of the total area of the silicon carbide particles having a particle length of 2.0 μm or more and 5.0 μm or less to the area of the region was 10% or less.

（加工試験）
＃２７０の篩を通過し＃４００の篩に残る大きさの砥粒（ダイヤモンド）を保持したビトリファイドダイヤモンドホイール（砥石）を用いて、サンプル１−７の焼結体にセンタレス研磨を施す試験を行った。この試験を実施した研磨機には自動ドレス機構が備えられており、焼結体の研削３００本ごとに、研磨機の運転中に自動ドレスを実施した。試験は、砥石に加わる研削抵抗を略一定にし、焼結体の研削によって砥石面が荒れるまでの本数、１０００本の焼結体の研削に要した加工時間を測定した。

(Processing test)
A test was conducted in which the sintered body of sample 1-7 was centerlessly polished using a vitrified diamond wheel (grinding stone) holding abrasive grains (diamonds) of a size that passed through the # 270 sieve and remained on the # 400 sieve. It was. The grinding machine that carried out this test was equipped with an automatic dressing mechanism, and automatic dressing was carried out during the operation of the grinding machine for every 300 grindings of the sintered body. In the test, the grinding resistance applied to the grindstone was made substantially constant, and the number of grindstones until the surface of the grindstone was roughened by grinding the sintered body and the processing time required for grinding 1000 sintered bodies were measured.

なお、「砥石面の荒れ」は、接触式表面粗さ計を用いて研磨後の焼結体の表面粗さを測定して評価した。焼結体の表面に接触させた表面粗さ計の触針を軸線Ｏに沿って４ｍｍ走査し、算術平均粗さＲａが０．４μｍ以上、又は、最大谷深さＲｖが２．５μｍ以上のものが発生したときに、研磨機の運転を停止して、砥石のドレッシング（目直し）を作業者が行った。表１に記した「砥石面が荒れるまでの数」はドレッシングの間隔に等しい。算術平均粗さＲａ及び最大谷深さＲｖの測定は、ＪＩＳＢ０６０１：２０１３に準拠した。 The "roughness of the grindstone surface" was evaluated by measuring the surface roughness of the sintered body after polishing using a contact type surface roughness meter. The stylus of the surface roughness meter brought into contact with the surface of the sintered body was scanned 4 mm along the axis O, and the arithmetic mean roughness Ra was 0.4 μm or more, or the maximum valley depth Rv was 2.5 μm or more. When something happened, the operation of the polishing machine was stopped and the worker dressed the grindstone. The "number until the grindstone surface becomes rough" shown in Table 1 is equal to the dressing interval. Arithmetic mean roughness Ra and maximum valley depth Rv were measured according to JIS B0601: 2013.

頻繁にドレッシングが必要になると、研磨機の運転をその都度停止しなければならないので、研磨加工の作業性が低下する。従って作業性の観点から、「砥石面が荒れるまでの数」は１０００００以上が望ましい。表１によればサンプル１−５がこの条件を満たす。サンプル６，７は、基体１１の断面に現出する炭化珪素の粒子長さが５．０μｍを超える大きな粒子によって、砥粒を保持しているボンドブリッジが折損して砥粒が脱落したり、砥粒が部分的に劈開したりしたと推察される。サンプル６，７では、砥石の切れ味は良いので加工時間は短くなるが、仕上げ面粗さが大きくなり、加工精度が低下する。 If dressing is required frequently, the operation of the polishing machine must be stopped each time, which reduces the workability of the polishing process. Therefore, from the viewpoint of workability, it is desirable that the "number until the grindstone surface becomes rough" is 100,000 or more. According to Table 1, Samples 1-5 satisfy this condition. In Samples 6 and 7, the bond bridge holding the abrasive grains was broken by the large particles of silicon carbide appearing on the cross section of the substrate 11 and the particle length exceeded 5.0 μm, and the abrasive grains fell off. It is presumed that the abrasive grains were partially cleaved. In Samples 6 and 7, since the sharpness of the grindstone is good, the processing time is short, but the finished surface roughness is large and the processing accuracy is lowered.

また、１０００本の研削に要する加工時間が長くなると加工の作業性が低下するので、作業性の観点から、加工時間は６時間以内が望ましい。表１によればサンプル２−７がこの条件を満たす。サンプル１は、基体１１の断面に現出する炭化珪素の粒子長さが２．０μｍ未満であり炭化珪素の粒子が小さいので、砥石の気孔が切り屑で塞がれたり砥粒の切れ刃が鈍化したりして、砥石の切れ味が低下し加工時間が長くなったと推察される。 Further, if the machining time required for grinding 1000 pieces becomes long, the machining workability decreases. Therefore, from the viewpoint of workability, the machining time is preferably 6 hours or less. According to Table 1, Sample 2-7 satisfies this condition. In sample 1, since the particle length of silicon carbide appearing on the cross section of the substrate 11 is less than 2.0 μm and the particles of silicon carbide are small, the pores of the grindstone are blocked with chips and the cutting edge of the abrasive grains is broken. It is presumed that the sharpness of the grindstone decreased and the processing time became longer due to the blunting.

これに対し、基体１１の断面に現出する炭化珪素の粒子の最大長さＬが２．０μｍ以上５．０μｍ以下のサンプル２−５は、砥粒に新しい切れ刃が適度に発生し、砥石の切れ味を維持できたと推察される。さらに、炭化珪素の粒子による砥粒の砥石からの脱落や部分的な砥粒の劈開を抑制できたので、砥石面の荒れを抑制し、仕上げ面粗さを小さくすることができ、加工精度を確保できたと推察される。よって、基体１１の断面に現出する炭化珪素の粒子の最大長さＬが２．０μｍ以上５．０μｍ以下であると、加工精度を確保しつつ加工時間が長くなるのを抑制できることが明らかになった。 On the other hand, in Sample 2-5 in which the maximum length L of the silicon carbide particles appearing on the cross section of the substrate 11 is 2.0 μm or more and 5.0 μm or less, a new cutting edge is appropriately generated in the abrasive grains, and the grindstone It is presumed that the sharpness of the was maintained. Furthermore, since the silicon carbide particles can prevent the abrasive grains from falling off from the grindstone and the partial cleavage of the abrasive grains can be suppressed, the roughness of the grindstone surface can be suppressed, the roughness of the finished surface can be reduced, and the processing accuracy can be improved. It is presumed that it was secured. Therefore, it is clear that when the maximum length L of the silicon carbide particles appearing on the cross section of the substrate 11 is 2.0 μm or more and 5.0 μm or less, it is possible to suppress a long processing time while ensuring processing accuracy. became.

以上、実施の形態に基づき本発明を説明したが、本発明は上記実施形態に何ら限定されるものではなく、本発明の趣旨を逸脱しない範囲内で種々の改良変形が可能であることは容易に推察できるものである。 Although the present invention has been described above based on the embodiments, the present invention is not limited to the above embodiments, and it is easy that various improvements and modifications can be made without departing from the spirit of the present invention. It can be inferred from.

実施形態では、セラミックヒータ１０の基体１１が円柱状に形成される場合について説明したが、必ずしもこれに限られるものではない。基体１１の形状は用途に応じて適宜設定できる。例えば、基体の軸線Ｏに直交する断面を楕円状、多角状等の形状にすることは当然可能である。また、セラミックヒータは棒状の基体をもつものに限られない。例えば、板状の基体間に導体を挟み込んだいわゆる板状のセラミックヒータとすることは当然可能である。この場合は平面研削によるセラミックヒータの加工のときに、加工精度を確保しつつ加工時間が長くなるのを抑制できる。 In the embodiment, the case where the substrate 11 of the ceramic heater 10 is formed in a columnar shape has been described, but the present invention is not necessarily limited to this. The shape of the substrate 11 can be appropriately set according to the application. For example, it is naturally possible to make the cross section orthogonal to the axis O of the substrate into an elliptical shape, a polygonal shape, or the like. Further, the ceramic heater is not limited to the one having a rod-shaped substrate. For example, it is naturally possible to use a so-called plate-shaped ceramic heater in which a conductor is sandwiched between plate-shaped substrates. In this case, when machining the ceramic heater by surface grinding, it is possible to suppress a long machining time while ensuring machining accuracy.

実施形態では、プレス成形によってセラミックヒータ１０の基体１１の成形体を製造する場合について説明したが、これは一例であり、公知の他の製造方法を採用できる。例えば、プレス成形ではなく、基体１１の原料粉末の射出成形により基体１１の成形体を得ることは当然可能である。また、プレス成形によって導体１４の成形体を得ることは当然可能である。 In the embodiment, the case where the molded body of the base 11 of the ceramic heater 10 is manufactured by press molding has been described, but this is an example, and other known manufacturing methods can be adopted. For example, it is naturally possible to obtain a molded product of the substrate 11 by injection molding of the raw material powder of the substrate 11 instead of press molding. Further, it is naturally possible to obtain a molded body of the conductor 14 by press molding.

実施形態では、セラミックヒータ１０がグロープラグ３０に用いられる場合について説明したが、必ずしもこれに限られるものではない。セラミックヒータ１０の用途には制限がない。例えばバーナーの着火用ヒータ、ガスセンサの加熱用ヒータ、Diesel particulate filter（ＤＰＦ）にセラミックヒータ１０を用いることは当然可能である。 In the embodiment, the case where the ceramic heater 10 is used for the glow plug 30 has been described, but the present invention is not necessarily limited to this. There are no restrictions on the use of the ceramic heater 10. For example, it is naturally possible to use the ceramic heater 10 for the ignition heater of the burner, the heating heater of the gas sensor, and the Diesel particulate filter (DPF).

実施形態ではセラミックヒータ１０と筒状部材５０とが圧入構造をなし、筒状部材５０に圧入されたセラミックヒータ１０の電極取出部１７に筒状部材５０が直接接続される場合について説明したが、必ずしもこれに限られるものではない。例えばセラミックヒータ１０を金属部材の中に入れて、セラミックヒータ１０の電極取出部１７と金属部材との間をワイヤやろう材等の導電材料によって接続することは当然可能である。また、導電性セラミックからなる発熱体が埋設された絶縁性セラミックからなる基体の表面に、印刷等によって、発熱体に電気的に接続したリードを設けた後、金属部材の中に基体を入れ、ろう材等の導電材料によって基体のリードと金属部材とを接続することは当然可能である。 In the embodiment, the case where the ceramic heater 10 and the tubular member 50 form a press-fitting structure and the tubular member 50 is directly connected to the electrode extraction portion 17 of the ceramic heater 10 press-fitted into the tubular member 50 has been described. It is not necessarily limited to this. For example, it is naturally possible to put the ceramic heater 10 in the metal member and connect the electrode extraction portion 17 of the ceramic heater 10 and the metal member with a conductive material such as a wire or a brazing material. Further, after providing a lead electrically connected to the heating element by printing or the like on the surface of the substrate made of an insulating ceramic in which a heating element made of a conductive ceramic is embedded, the substrate is placed in a metal member. Of course, it is possible to connect the lead of the substrate and the metal member with a conductive material such as a brazing material.

実施形態では、セラミックヒータ１０を保持する筒状部材５０が主体金具３１に固定されたグロープラグ３０について説明したが、必ずしもこれに限られるものではない。例えば、セラミックヒータ１０が筒状部材と共に変位可能となるように主体金具に保持されるグロープラグ（いわゆるヒータ付き圧力センサ）とすることは当然可能である。 In the embodiment, the glow plug 30 in which the tubular member 50 holding the ceramic heater 10 is fixed to the main metal fitting 31 has been described, but the present invention is not necessarily limited to this. For example, it is naturally possible to use a glow plug (so-called pressure sensor with a heater) held in the main metal fitting so that the ceramic heater 10 can be displaced together with the tubular member.

１０セラミックヒータ
１１基体
１５発熱体
１７，１８電極取出部
１９筒状部材に圧入された部分
２０領域
２１，２４炭化珪素の粒子
２２外形
２３線分
３０グロープラグ
５０筒状部材
Ｋ，Ｌ粒子長さ 10 Ceramic heater 11 Base 15 Heating element 17, 18 Electrode extraction part 19 Part pressed into the tubular member 20 Region 21,24 Silicon carbide particles 22 Outer shape 23 Line segment 30 Glow plug 50 Cylindrical member K, L Particle length

Claims

A ceramic heater comprising a substrate made of an insulating ceramic containing silicon nitride as a main component and containing silicon carbide, and a heating element embedded in the substrate and made of a conductive ceramic.
In the cross section of the substrate, the longest length of the line segments connecting two points on the outer shape of the silicon carbide particles appearing in the cross section is defined as the particle length, and one or more appearing in the cross section. A ceramic heater having the longest particle length of the particles, where the maximum length L is 2.0 μm or more and 5.0 μm or less.

The heating element contains tungsten carbide as a main component and
The ceramic heater according to claim 1, wherein the ratio of the total area of the particles having a particle length of 2.0 μm or more and 5.0 μm or less to the area of the region in a predetermined region of the cross section is 10% or less.

The ceramic heater according to claim 1 or 2,
A tubular member that holds the ceramic heater while exposing at least the portion of the substrate in which the heating element is embedded is provided.
The ceramic heater and the tubular member form a press-fitting structure.
The ceramic heater is a glow plug having an electrode extraction portion electrically connected to the heating element on the outer peripheral surface of a portion press-fitted into the tubular member.