JP6944289B2

JP6944289B2 - Glow plug

Info

Publication number: JP6944289B2
Application number: JP2017130501A
Authority: JP
Inventors: 将憲大坪
Original assignee: NGK Spark Plug Co Ltd
Current assignee: Niterra Co Ltd
Priority date: 2017-07-03
Filing date: 2017-07-03
Publication date: 2021-10-06
Anticipated expiration: 2037-07-03
Also published as: JP2019015409A

Description

本発明は、グロープラグに関するものである。 The present invention relates to glow plugs.

従来から、内燃機関での点火補助に用いられるグロープラグとして、絶縁性材料を主成分とする絶縁性セラミックからなる基体内部に、導電性材料を主成分とする導電性セラミックからなる抵抗体を埋設したセラミックヒータと、セラミックヒータを保持する外筒と、外筒を保持する主体金具と、を備えたグロープラグが提供されている。例えば、特許文献１で開示されるグロープラグは、セラミックヒータを圧入して保持する外筒と、エンジンヘッドに取り付けるためのねじ部を備えた主体金具と、を備えており、主体金具の先端面と外筒の後端面とを接合した構成をなしている。 Conventionally, as a glow plug used for spark plugs in an internal combustion engine, a resistor made of a conductive ceramic having a conductive material as a main component is embedded inside a substrate made of an insulating ceramic containing an insulating material as a main component. A glow plug including a ceramic heater, an outer cylinder for holding the ceramic heater, and a main metal fitting for holding the outer cylinder is provided. For example, the glow plug disclosed in Patent Document 1 includes an outer cylinder for press-fitting and holding a ceramic heater, and a main metal fitting provided with a screw portion for attaching to the engine head, and has a tip surface of the main metal fitting. And the rear end face of the outer cylinder are joined together.

特許第４４２５０１７号公報Japanese Patent No. 442017

特許文献１で開示されるグロープラグをエンジンヘッドに取り付ける場合、エンジンヘッドに形成されたプラグホールにグロープラグを挿入し、主体金具の外表面に形成された雄ねじ部をプラグホールに形成された雌ねじ部にねじ込んで嵌合させることで組み付けることができる。そして、一般的には、グロープラグに形成された雄ねじ部をプラグホールの雌ねじ部にある程度ねじ込むと、外筒の先端側に設けられた当接面（テーパ面）がプラグホール内の当接対象面に当接した状態となり、このような当接状態でグロープラグがエンジンヘッドに固定されることになる。 When the glow plug disclosed in Patent Document 1 is attached to the engine head, the glow plug is inserted into the plug hole formed in the engine head, and the male screw portion formed on the outer surface of the main metal fitting is formed in the plug hole. It can be assembled by screwing it into the part and fitting it. Then, in general, when the male screw portion formed on the glow plug is screwed into the female screw portion of the plug hole to some extent, the contact surface (tapered surface) provided on the tip side of the outer cylinder becomes the contact target in the plug hole. The glow plug is in contact with the surface, and the glow plug is fixed to the engine head in such a contact state.

しかし、グロープラグをエンジンヘッドに組み付ける際に、グロープラグに対して不適切に大きい締付トルクがかけられたり、両部品の接触領域（ねじ領域など）にエンジンオイルなどが入り込むことに起因する過回転（摩擦力の低下に起因する過回転）が生じたりすると、グロープラグをエンジンヘッドにねじ込む際の挿入力（軸方向の力）がより強くなり、グロープラグの一部に変形を生じさせてしまう懸念がある。 However, when assembling the glow plug to the engine head, an improperly large tightening torque is applied to the glow plug, or engine oil or the like gets into the contact area (screw area, etc.) of both parts. When rotation (over-rotation due to a decrease in frictional force) occurs, the insertion force (axial force) when screwing the glow plug into the engine head becomes stronger, causing deformation of a part of the glow plug. There is a concern that it will end up.

具体的には、グロープラグにおいて、ねじ部と当接面（テーパ面）との間で軸方向の強い圧縮力が生じ、主体金具の硬度よりも外筒の硬度のほうが低い一般的な構成では、主体金具よりも外筒のほうが先に変形してしまうことになる。このような変形は、外筒内において主体金具との接合面付近に集中しやすく、変形がセラミックヒータ内に埋め込まれた抵抗体の電極部（外筒の内周部と接触して導通する部分）の近くまで及んでしまうと、外筒の内周部と電極部との間で接触不良が生じてしまい、抵抗体と外筒との間で電気的接続が確保されなくなる虞がある。 Specifically, in a general configuration in which a strong axial compressive force is generated between the threaded portion and the contact surface (tapered surface) in the glow plug, and the hardness of the outer cylinder is lower than the hardness of the main metal fitting. , The outer cylinder will be deformed earlier than the main metal fittings. Such deformation tends to concentrate in the vicinity of the joint surface with the main metal fitting in the outer cylinder, and the deformation is the electrode portion of the resistor embedded in the ceramic heater (the portion that contacts and conducts with the inner peripheral portion of the outer cylinder). ), Poor contact may occur between the inner peripheral portion of the outer cylinder and the electrode portion, and the electrical connection between the resistor and the outer cylinder may not be secured.

本発明は、上述した課題を解決するためになされたものであり、軸線方向の圧縮力が強く加わっても抵抗体と外筒の電気的接続が良好に確保されやすいグロープラグを提供することを目的とするものである。 The present invention has been made to solve the above-mentioned problems, and to provide a glow plug in which a good electrical connection between a resistor and an outer cylinder can be easily secured even when a strong compressive force in the axial direction is applied. It is the purpose.

本発明の一つの解決手段であるグロープラグは、
軸線方向に沿って延びるセラミックヒータと、
前記セラミックヒータの後端側の部位を収容する筒状の主体金具と、
前記セラミックヒータの前端側の部位を露出させつつ前記セラミックヒータと嵌合するとともに自身の後端部が前記主体金具の前端部に接合され、前記主体金具よりも硬度が低い筒状の外筒と、
を備え、
前記セラミックヒータは、
絶縁性セラミックからなり、前記軸線方向に沿って延びる基体と、
導電性セラミックからなり、前記基体に埋設される抵抗体であり、通電によって発熱する発熱部と、前記発熱部と電気的に接続され、前記軸線方向と交差する方向に沿って延びるとともに前記基体の外表面に露出する端面が前記外筒の内周面に接触する接触面として構成された電極部と、を有する抵抗体と、
を備え、
前記外筒は、
所定の外周面を有する小径部と、
前記小径部の後方側に配置されるとともに、前記小径部よりも外周面の径が大きい大径部であり、前記主体金具の前端部と前記軸線方向に対向する大径部と、
を備えるグロープラグであって、
前記接触面の少なくとも一部が前記大径部の内周面と接触しており、
前記外筒において前記主体金具の前端部と対向する対向位置から前記接触面までの前記軸線方向の最短距離が２ｍｍ以上である。 The glow plug, which is one of the solutions of the present invention, is
A ceramic heater that extends along the axial direction,
A cylindrical main metal fitting for accommodating a portion on the rear end side of the ceramic heater,
While exposing the front end side portion of the ceramic heater, the ceramic heater is fitted with the ceramic heater, and the rear end portion of the ceramic heater is joined to the front end portion of the main metal fitting to form a cylindrical outer cylinder having a hardness lower than that of the main metal fitting. ,
With
The ceramic heater is
A substrate made of insulating ceramic that extends along the axial direction,
A resistor made of a conductive ceramic and embedded in the substrate. A heat generating portion that generates heat when energized is electrically connected to the heat generating portion, extends along a direction intersecting the axial direction, and of the substrate. A resistor having an electrode portion whose end surface exposed to the outer surface is configured as a contact surface in contact with the inner peripheral surface of the outer cylinder.
With
The outer cylinder is
A small diameter part with a predetermined outer peripheral surface and
A large-diameter portion that is arranged on the rear side of the small-diameter portion and has a larger outer diameter than the small-diameter portion, and has a large-diameter portion that faces the front end portion of the main metal fitting and the axial direction.
It is a glow plug equipped with
At least a part of the contact surface is in contact with the inner peripheral surface of the large diameter portion.
In the outer cylinder, the shortest distance in the axial direction from the facing position facing the front end portion of the main metal fitting to the contact surface is 2 mm or more.

上記グロープラグでは、セラミックヒータと嵌合する外筒において、肉厚が相対的に大きい大径部のほうが小径部よりもセラミックヒータに対する面圧が確保されやすく、この大径部の内周面に接触するように電極部の接触面を配置しているため、接触面の接触圧がより大きく確保されやすくなる。ゆえに、電極部と外筒の電気的接続が良好に維持されやすい。
また、外筒の硬度を相対的に低くすることで、外筒に嵌合するセラミックヒータにおいて割れなどの不具合を生じにくくすることができる。但し、外筒の硬度が低いと、上述のメリットを享受し得る反面、過剰な締め付け等に起因する軸線方向の圧縮力が加わった場合に、外筒内（特に主体金具の前端部と対向する対向位置付近）で座屈が生じやすくなるという問題がある。そこで、上記グロープラグでは、対向位置から電極部における接触面までの軸線方向の最短距離を２ｍｍ以上としている。このようにすると、主体金具及び外筒に対して軸線方向に過剰な圧縮力が加わってしまい、外筒内の対向位置付近で座屈による変形が生じたとしても、その変形の影響は、電極部の接触面付近には及びにくくなる。よって、上述した軸線方向の圧縮力が加わっても、外筒の内周面と電極部の接触面との間で接触不良が生じにくくなり、電極部と外筒の電気的接続がより確実に維持されやすくなる。 In the above glow plug, in the outer cylinder that fits with the ceramic heater, the large-diameter portion with a relatively large wall thickness is more likely to secure the surface pressure for the ceramic heater than the small-diameter portion, and the inner peripheral surface of the large-diameter portion has a surface pressure. Since the contact surface of the electrode portion is arranged so as to come into contact with each other, it becomes easier to secure a larger contact pressure on the contact surface. Therefore, the electrical connection between the electrode portion and the outer cylinder is likely to be well maintained.
Further, by making the hardness of the outer cylinder relatively low, it is possible to prevent problems such as cracking from occurring in the ceramic heater fitted to the outer cylinder. However, if the hardness of the outer cylinder is low, the above-mentioned merits can be enjoyed, but when a compressive force in the axial direction due to excessive tightening or the like is applied, the inside of the outer cylinder (particularly, it faces the front end portion of the main metal fitting). There is a problem that buckling is likely to occur near the facing position). Therefore, in the glow plug, the shortest distance in the axial direction from the facing position to the contact surface of the electrode portion is set to 2 mm or more. In this way, an excessive compressive force is applied to the main metal fitting and the outer cylinder in the axial direction, and even if deformation due to buckling occurs near the opposite position in the outer cylinder, the influence of the deformation is the electrode. It becomes difficult to reach the vicinity of the contact surface of the part. Therefore, even if the above-mentioned compressive force in the axial direction is applied, poor contact between the inner peripheral surface of the outer cylinder and the contact surface of the electrode portion is less likely to occur, and the electrical connection between the electrode portion and the outer cylinder is more reliable. It will be easier to maintain.

上記グロープラグにおいて、外筒は、軸線方向において大径部と小径部との間に、外周面の径が大径部よりも小さく且つ前方側となるにつれて次第に外周面の径が小さくなるテーパ部を備えていてもよい。そして、接触面の前端側の一部が、軸線方向においてテーパ部が形成された領域内に位置するように構成されていてもよい。 In the glow plug, the outer cylinder is a tapered portion between the large diameter portion and the small diameter portion in the axial direction, in which the diameter of the outer peripheral surface is smaller than that of the large diameter portion and the diameter of the outer peripheral surface gradually decreases toward the front side. May be provided. Then, a part of the front end side of the contact surface may be configured to be located in the region where the tapered portion is formed in the axial direction.

上述した構成のように、電極部の接触面を、軸線方向において大径部とテーパ部とに跨る位置まで対向位置（外筒において主体金具の前端部と対向する位置）から遠ざければ、軸線方向の過剰な圧縮力に起因する変形が対向位置付近で生じても、その変形が接触面に与える影響は一層小さくなる。また、接触面の全部がテーパ部の領域に配置されるのではなく、一部が大径部の領域に配置されるため、接触面の全部がテーパ部の領域に配置される構成と比較すると接触面の接触圧は確保されやすい。 As in the configuration described above, if the contact surface of the electrode portion is far from the facing position (the position facing the front end portion of the main metal fitting in the outer cylinder) to the position straddling the large diameter portion and the tapered portion in the axial direction, the axis line Even if deformation due to excessive compressive force in the direction occurs near the facing position, the influence of the deformation on the contact surface is further reduced. Further, since the entire contact surface is not arranged in the tapered region but a part of the contact surface is arranged in the large diameter region, compared with the configuration in which the entire contact surface is arranged in the tapered region. The contact pressure on the contact surface is easily secured.

上記グロープラグにおいて、接触面の前端を通り軸線方向に直交するグロープラグの断面をみたときのテーパ部の径方向の厚さが、大径部を通り軸線方向に直交するグロープラグの断面をみたときの大径部の径方向の厚さの４０％以上であってもよい。 In the above glow plug, when looking at the cross section of the glow plug passing through the front end of the contact surface and orthogonal to the axial direction, the thickness of the tapered portion in the radial direction is seen from the cross section of the glow plug passing through the large diameter portion and orthogonal to the axial direction. It may be 40% or more of the radial thickness of the large-diameter portion.

このようにすれば、電極部の接触面をテーパ部の位置まで遠ざけて対向位置（外筒において主体金具の前端部と対向する位置）との距離を確保しつつ、接触面の位置において外筒の肉厚を一定程度確保することができる。これにより、肉厚が小さいことに起因する接触圧（外筒の内周面に接触する接触面の面圧）の低下を抑えることができる。また、接触圧が低下すると、外筒の内周面と電極部の接触面の間に空気が入り込む微小な隙間が生じやすくなり、接触領域の付近が酸化しやすくなるという問題があるが、上述した構成とすれば、接触圧の低下に起因する酸化の進展を抑えることができ、酸化に起因する抵抗値の上昇を抑制することができる。 By doing so, the contact surface of the electrode portion is moved away from the position of the tapered portion to secure a distance from the facing position (the position facing the front end portion of the main metal fitting in the outer cylinder), and the outer cylinder is located at the position of the contact surface. It is possible to secure a certain degree of wall thickness. As a result, it is possible to suppress a decrease in the contact pressure (the surface pressure of the contact surface in contact with the inner peripheral surface of the outer cylinder) due to the small wall thickness. Further, when the contact pressure is lowered, there is a problem that a minute gap through which air enters is likely to occur between the inner peripheral surface of the outer cylinder and the contact surface of the electrode portion, and the vicinity of the contact region is likely to be oxidized. With this configuration, the progress of oxidation due to the decrease in contact pressure can be suppressed, and the increase in resistance value due to oxidation can be suppressed.

本発明によれば、軸方向に強い圧縮力が加わっても抵抗体と外筒の電気的接続が良好に確保されやすいグロープラグを実現することができる。 According to the present invention, it is possible to realize a glow plug in which a good electrical connection between the resistor and the outer cylinder can be easily secured even when a strong compressive force is applied in the axial direction.

第１実施形態のグロープラグの一例を示す断面概略図である。It is sectional drawing which shows an example of the glow plug of 1st Embodiment. 図１のグロープラグの一部を拡大して具体的に例示する拡大断面図である。It is an enlarged cross-sectional view which enlarges a part of the glow plug of FIG. 1 and exemplify concretely. 図１のグロープラグにおいて、金属外筒と主体金具を接合する接合部付近を拡大して示す拡大断面図である。FIG. 5 is an enlarged cross-sectional view showing an enlarged view of the vicinity of a joint portion where the metal outer cylinder and the main metal fitting are joined in the glow plug of FIG. 図１のグロープラグを内燃機関に組み付けた状態を示す断面模式図である。FIG. 5 is a schematic cross-sectional view showing a state in which the glow plug of FIG. 1 is assembled to an internal combustion engine. 第１実施形態のグロープラグを過剰に締め付ける過締め付け試験を行ったときの試験結果を示すものであり、試験前のグロープラグと、試験後のグロープラグについて、対向位置からの距離と外径の変形度合いとの関係を示すグラフである。It shows the test result when the overtightening test of overtightening the glow plug of the first embodiment was performed. The distance and outer diameter of the glow plug before the test and the glow plug after the test from the opposite positions are shown. It is a graph which shows the relationship with the degree of deformation.

Ａ．第１実施形態
Ａ１．グロープラグの構成
図１は、第１実施形態のグロープラグの一例を示す概略図である。図２は、図１で示すグロープラグ１のうちのセラミックヒータ４０付近を拡大して示す拡大断面図である。図１、図２において図示されたラインＣＬは、グロープラグ１の中心軸を示している。図１において図示された断面は、中心軸ＣＬを含む断面であり、抵抗体１２０については省略して示している。図２において図示された断面は、中心軸ＣＬを含む断面であり、発熱部１２１、第１導電部１２２、及び第２導電部１２３を通るように抵抗体１２０に沿って切断した切断面を示すものである。図２は、金属外筒７０、接続部材９０、セラミックヒータ４０などを、より詳細に示す断面図である。 A. First Embodiment A1. Configuration of Glow Plugs FIG. 1 is a schematic view showing an example of glow plugs of the first embodiment. FIG. 2 is an enlarged cross-sectional view showing the vicinity of the ceramic heater 40 in the glow plug 1 shown in FIG. 1 in an enlarged manner. The line CL illustrated in FIGS. 1 and 2 indicates the central axis of the glow plug 1. The cross section shown in FIG. 1 is a cross section including the central axis CL, and the resistor 120 is omitted. The cross section shown in FIG. 2 is a cross section including the central axis CL, and shows a cut surface cut along the resistor 120 so as to pass through the heat generating portion 121, the first conductive portion 122, and the second conductive portion 123. It is a thing. FIG. 2 is a cross-sectional view showing the metal outer cylinder 70, the connecting member 90, the ceramic heater 40, and the like in more detail.

以下、中心軸ＣＬのことを「軸線ＣＬ」とも呼び、中心軸ＣＬと平行な方向を「軸線方向」とも呼ぶ。また、軸線方向を前後方向とし、軸線方向においてグロープラグ１におけるセラミックヒータの先端側を前方側、それとは反対側を後方側とする。更に、中心軸ＣＬを中心とする円の径方向を、単に「径方向」とも呼び、中心軸ＣＬを中心とする円の円周方向を「周方向」とも呼ぶ。中心軸ＣＬと平行な方向のうち、図１における下方向を第１方向Ｄ１と呼ぶ。第１方向Ｄ１は、後述する端子部材８０からセラミックヒータ４０に向かう方向である。図中の第２方向Ｄ２と第３方向Ｄ３とは、互いに垂直な方向であり、いずれも、第１方向Ｄ１と垂直な方向である。以下、第１方向Ｄ１を、先端方向Ｄ１とも呼び、第１方向Ｄ１の反対方向を、後端方向Ｄ１ｒとも呼ぶ。また、図１における先端方向Ｄ１側をグロープラグ１の先端側と呼び、図１における後端方向Ｄｒ１側をグロープラグ１の後端側と呼ぶ。 Hereinafter, the central axis CL is also referred to as "axis CL", and the direction parallel to the central axis CL is also referred to as "axis direction". Further, the axial direction is the front-rear direction, and the tip side of the ceramic heater in the glow plug 1 is the front side and the opposite side is the rear side in the axial direction. Further, the radial direction of the circle centered on the central axis CL is also simply referred to as the "diameter direction", and the circumferential direction of the circle centered on the central axis CL is also referred to as the "circumferential direction". Of the directions parallel to the central axis CL, the downward direction in FIG. 1 is called the first direction D1. The first direction D1 is a direction from the terminal member 80, which will be described later, toward the ceramic heater 40. The second direction D2 and the third direction D3 in the figure are directions perpendicular to each other, and both are directions perpendicular to the first direction D1. Hereinafter, the first direction D1 is also referred to as a tip direction D1, and the direction opposite to the first direction D1 is also referred to as a rear end direction D1r. Further, the front end direction D1 side in FIG. 1 is referred to as the front end side of the glow plug 1, and the rear end direction Dr1 side in FIG. 1 is referred to as the rear end side of the glow plug 1.

図１のように、グロープラグ１は、主体金具２０と、中軸３０と、セラミックヒータ４０と、Ｏリング５０と、絶縁部材６０と、金属外筒７０（以下、単に「外筒７０」とも呼ぶ）と、端子部材８０と、接続部材９０と、を含む。 As shown in FIG. 1, the glow plug 1 includes a main metal fitting 20, a center pole 30, a ceramic heater 40, an O-ring 50, an insulating member 60, and a metal outer cylinder 70 (hereinafter, also simply referred to as “outer cylinder 70”). ), The terminal member 80, and the connecting member 90.

主体金具２０は、軸線ＣＬに沿って延びる貫通孔２０Ａを有する筒状の部材であり、後述するセラミックヒータ４０の後端側の部位を収容する部材である。主体金具２０は、導電性材料（例えば、炭素鋼等の金属）で形成されている。主体金具２０は、後端方向Ｄｒ１側の端部に形成された工具係合部２８と、工具係合部２８よりも先端方向Ｄ１側に設けられた雄ネジ部２２と、を含む。工具係合部２８は、グロープラグ１の脱着時に、図示しない工具と係合する部分である。雄ネジ部２２は、公知の雄ネジ構造をなし、例えば、図４のように内燃機関ＥＮの取付孔ＥＨに形成された雌ネジ部ＴＨに螺合する。 The main metal fitting 20 is a tubular member having a through hole 20A extending along the axis CL, and is a member for accommodating a portion on the rear end side of the ceramic heater 40, which will be described later. The main metal fitting 20 is made of a conductive material (for example, a metal such as carbon steel). The main metal fitting 20 includes a tool engaging portion 28 formed at an end portion on the Dr1 side in the rear end direction, and a male screw portion 22 provided on the D1 side in the tip direction direction with respect to the tool engaging portion 28. The tool engaging portion 28 is a portion that engages with a tool (not shown) when the glow plug 1 is attached or detached. The male screw portion 22 has a known male screw structure, and is screwed into, for example, the female screw portion TH formed in the mounting hole EH of the internal combustion engine EN as shown in FIG.

図１のように、主体金具２０の貫通孔２０Ａには、中軸３０が収容されている。中軸３０は、丸棒状の部材である。中軸３０は、導電性材料（例えば、ステンレス鋼）で形成されている。中軸３０の後端方向Ｄｒ１側の端部である後端部３９は、主体金具２０の後端方向Ｄｒ１側の開口部２０Ｂから後端方向Ｄｒ１に向かって突出している。 As shown in FIG. 1, the center pole 30 is housed in the through hole 20A of the main metal fitting 20. The center pole 30 is a round bar-shaped member. The center pole 30 is made of a conductive material (for example, stainless steel). The rear end portion 39, which is the end portion on the rear end direction Dr1 side of the center pole 30, projects from the opening 20B on the rear end direction Dr1 side of the main metal fitting 20 toward the rear end direction Dr1.

開口部２０Ｂの近傍において、中軸３０の外面と、主体金具２０の貫通孔２０Ａの内面と、の間には、Ｏリング５０が設けられている。Ｏリング５０は、弾性材料（例えば、ゴム）で形成されている。主体金具２０の開口部２０Ｂには、リング状の絶縁部材６０が装着されている。絶縁部材６０は、筒状部６２と、筒状部６２の後端方向Ｄｒ１側に設けられたフランジ部６８と、を含む。筒状部６２は、中軸３０の外面と、主体金具２０の開口部２０Ｂを形成する部分の内面と、の間に挟まれている。絶縁部材６０は、例えば、樹脂によって形成されている。主体金具２０は、これらＯリング５０及び絶縁部材６０を介して、中軸３０を支持している。 An O-ring 50 is provided between the outer surface of the center pole 30 and the inner surface of the through hole 20A of the main metal fitting 20 in the vicinity of the opening 20B. The O-ring 50 is made of an elastic material (for example, rubber). A ring-shaped insulating member 60 is attached to the opening 20B of the main metal fitting 20. The insulating member 60 includes a cylindrical portion 62 and a flange portion 68 provided on the Dr1 side in the rear end direction of the tubular portion 62. The tubular portion 62 is sandwiched between the outer surface of the center pole 30 and the inner surface of the portion forming the opening 20B of the main metal fitting 20. The insulating member 60 is made of, for example, a resin. The main metal fitting 20 supports the center pole 30 via the O-ring 50 and the insulating member 60.

絶縁部材６０の後端方向Ｄｒ１側には、端子部材８０が配置されている。端子部材８０は、キャップ状の部材であり、導電性材料（例えば、ニッケル等の金属）で形成されている。端子部材８０と主体金具２０との間には、絶縁部材６０のフランジ部６８が挟まれている。端子部材８０には、中軸３０の後端部３９が挿入されている。端子部材８０が加締められることによって、端子部材８０が後端部３９に固定されている。このような構造により、端子部材８０と中軸３０とが電気的に接続されている。 A terminal member 80 is arranged on the Dr1 side in the rear end direction of the insulating member 60. The terminal member 80 is a cap-shaped member and is made of a conductive material (for example, a metal such as nickel). A flange portion 68 of the insulating member 60 is sandwiched between the terminal member 80 and the main metal fitting 20. The rear end 39 of the center pole 30 is inserted into the terminal member 80. By crimping the terminal member 80, the terminal member 80 is fixed to the rear end portion 39. With such a structure, the terminal member 80 and the center pole 30 are electrically connected.

図１のように、主体金具２０の先端方向Ｄ１側の開口部２０Ｃには、外筒７０が固定されている。外筒７０は、軸線ＣＬに沿って延びる貫通孔７０Ａを有する筒状の部材である。外筒７０は、導電性材料（例えば、ステンレス鋼）によって形成されており、外筒７０の硬度は、主体金具２０の硬度よりも低くなっている。図２のように、外筒７０は、後述するセラミックヒータ４０を保持しており、具体的には、セラミックヒータ４０の前端側の部位を露出させつつセラミックヒータ４０と嵌合している。 As shown in FIG. 1, the outer cylinder 70 is fixed to the opening 20C on the D1 side in the tip direction of the main metal fitting 20. The outer cylinder 70 is a tubular member having a through hole 70A extending along the axis CL. The outer cylinder 70 is made of a conductive material (for example, stainless steel), and the hardness of the outer cylinder 70 is lower than the hardness of the main metal fitting 20. As shown in FIG. 2, the outer cylinder 70 holds the ceramic heater 40 described later, and specifically, the outer cylinder 70 is fitted with the ceramic heater 40 while exposing the front end side portion of the ceramic heater 40.

図２のように、外筒７０は、前端側に形成された小径部７２と、小径部７２の後方側に形成されたテーパ部７６と、テーパ部７６の後方側に形成された大径部７４と、大径部７４の後方側に形成された挿入部７８とを備え、これらが軸線方向に連なって連結されている。貫通孔７０Ａは、小径部７２、テーパ部７６、大径部７４、挿入部７８を全て貫通するように軸線方向に延びており、貫通孔７０Ａの内周面は、軸線ＣＬを中心とする円筒面となっている。 As shown in FIG. 2, the outer cylinder 70 has a small diameter portion 72 formed on the front end side, a tapered portion 76 formed on the rear side of the small diameter portion 72, and a large diameter portion formed on the rear side of the tapered portion 76. A 74 and an insertion portion 78 formed on the rear side of the large diameter portion 74 are provided, and these are connected in a row in the axial direction. The through hole 70A extends in the axial direction so as to penetrate all of the small diameter portion 72, the tapered portion 76, the large diameter portion 74, and the insertion portion 78, and the inner peripheral surface of the through hole 70A is a cylinder centered on the axis CL. It is a face.

図３のように、小径部７２は、円筒状に構成されるとともに外周面の径が相対的に小さくなっている部分である。小径部７２の外周面は、軸線ＣＬを中心とする円筒面となっている。大径部７４は、円筒状に構成されるとともに外周面の径が小径部７２の外周面の径よりも大きくなっている部分である。大径部７４の外周面は、軸線ＣＬを中心とする円筒面となっている。テーパ部７６は、軸線方向において大径部７４と小径部７２との間に介在しており、外周面の径が大径部７４よりも小さく且つ前方側となるにつれて次第に外周面の径が小さくなる構成をなす。テーパ部７６の外周面の前端は、小径部７２の外周面と同程度の径となっており、テーパ部７６の外周面の後端は、大径部７４の外周面と同程度の径となっている。挿入部７８は、大径部７４の後端面７９から後方側に突出した円筒状の形状をなし、主体金具２０の開口部２０Ｃから挿入されて貫通孔２０Ａ内に収容されるように配置される。挿入部７８の外周面は、軸線ＣＬを中心とする円筒面となっている。 As shown in FIG. 3, the small diameter portion 72 is a portion that is formed in a cylindrical shape and has a relatively small outer peripheral surface diameter. The outer peripheral surface of the small diameter portion 72 is a cylindrical surface centered on the axis CL. The large diameter portion 74 is a portion having a cylindrical shape and having a diameter of the outer peripheral surface larger than the diameter of the outer peripheral surface of the small diameter portion 72. The outer peripheral surface of the large diameter portion 74 is a cylindrical surface centered on the axis CL. The tapered portion 76 is interposed between the large diameter portion 74 and the small diameter portion 72 in the axial direction, and the diameter of the outer peripheral surface is smaller than that of the large diameter portion 74 and the diameter of the outer peripheral surface is gradually reduced toward the front side. The composition is as follows. The front end of the outer peripheral surface of the tapered portion 76 has the same diameter as the outer peripheral surface of the small diameter portion 72, and the rear end of the outer peripheral surface of the tapered portion 76 has the same diameter as the outer peripheral surface of the large diameter portion 74. It has become. The insertion portion 78 has a cylindrical shape protruding rearward from the rear end surface 79 of the large diameter portion 74, and is arranged so as to be inserted through the opening 20C of the main metal fitting 20 and accommodated in the through hole 20A. .. The outer peripheral surface of the insertion portion 78 is a cylindrical surface centered on the axis CL.

外筒７０の後端部は圧入や溶接などによって主体金具２０の前端部付近（開口部２０Ｃ付近）に接合されている。外筒７０の後端部のうち、挿入部７８付近は主体金具２０の貫通孔２０Ａ内に挿入され、後端面７９付近の後端部は、溶接によって主体金具２０の前端部（開口部２０Ｃ）に接合されている。図３の例では、大径部７４の外周部の後端側領域と主体金具の外周部の前端側の領域とが溶接されており、外周面からある程度の深さの溶接部１４０が周方向に形成されている。溶接部１４０は、挿入部７８の位置までは到達しておらず、挿入部７８の外側且つ溶接部１４０の内側に、後端面７９が環状に構成されている。主体金具２０の前端部において貫通孔２０Ａ側には、面取り部２４が環状に形成されており、面取り部２４の表面は、軸線方向に対して傾斜した向きのテーパ面となっている。面取り部２４の表面と、後端面７９の間には隙間が構成されている。 The rear end portion of the outer cylinder 70 is joined to the vicinity of the front end portion (near the opening 20C) of the main metal fitting 20 by press fitting or welding. Of the rear end of the outer cylinder 70, the vicinity of the insertion portion 78 is inserted into the through hole 20A of the main metal fitting 20, and the rear end portion near the rear end surface 79 is the front end portion (opening 20C) of the main metal fitting 20 by welding. It is joined to. In the example of FIG. 3, the rear end side region of the outer peripheral portion of the large diameter portion 74 and the front end side region of the outer peripheral portion of the main metal fitting are welded, and the welded portion 140 having a certain depth from the outer peripheral surface is in the circumferential direction. Is formed in. The welded portion 140 has not reached the position of the insertion portion 78, and the rear end surface 79 is formed in an annular shape on the outside of the insertion portion 78 and on the inside of the welded portion 140. A chamfered portion 24 is formed in an annular shape on the through hole 20A side at the front end portion of the main metal fitting 20, and the surface of the chamfered portion 24 is a tapered surface inclined in the axial direction. A gap is formed between the surface of the chamfered portion 24 and the rear end surface 79.

大径部７４の後端面７９は、軸線方向に対して直交する方向の面となっており、主体金具２０の面取り部２４と対向し、面取り部２４よりも外側且つ溶接部１４０よりも内側の前端面にも対向している。軸線方向において後端面７９の位置は「対向位置」（外筒７０において主体金具２０の前端部と対向する位置）の一例に相当する。 The rear end surface 79 of the large diameter portion 74 is a surface in a direction orthogonal to the axial direction, faces the chamfered portion 24 of the main metal fitting 20, and is outside the chamfered portion 24 and inside the welded portion 140. It also faces the front end face. The position of the rear end surface 79 in the axial direction corresponds to an example of the "opposing position" (the position facing the front end portion of the main metal fitting 20 in the outer cylinder 70).

図２のように、外筒７０の貫通孔７０Ａには、通電によって発熱するセラミックヒータ４０が挿入されている。セラミックヒータ４０は、軸線ＣＬに沿って延びるように配置された棒状の部材である。外筒７０は、セラミックヒータ４０の先端部４１付近が露出した状態で、セラミックヒータ４０の中央部分の外周面を、保持している。セラミックヒータ４０の後端部４９は、主体金具２０の貫通孔２０Ａに収容されている。 As shown in FIG. 2, a ceramic heater 40 that generates heat when energized is inserted into the through hole 70A of the outer cylinder 70. The ceramic heater 40 is a rod-shaped member arranged so as to extend along the axis CL. The outer cylinder 70 holds the outer peripheral surface of the central portion of the ceramic heater 40 in a state where the vicinity of the tip portion 41 of the ceramic heater 40 is exposed. The rear end 49 of the ceramic heater 40 is housed in the through hole 20A of the main metal fitting 20.

接続部材９０は、セラミックヒータ４０の後端部４９に固定される部材である。接続部材９０は、軸線ＣＬに沿って延びる貫通孔を有する円筒状の部材であり、導電性材料（例えば、ステンレス鋼）で形成されている。接続部材９０の先端方向Ｄ１側には、セラミックヒータ４０の後端部４９が圧入されている。接続部材９０の後端方向Ｄｒ１側には、中軸３０の先端方向Ｄ１側の端部である先端部３１が圧入されている。このような構造により、中軸３０と接続部材９０とが電気的に接続されている。 The connecting member 90 is a member fixed to the rear end 49 of the ceramic heater 40. The connecting member 90 is a cylindrical member having a through hole extending along the axis CL, and is made of a conductive material (for example, stainless steel). The rear end 49 of the ceramic heater 40 is press-fitted on the D1 side of the connecting member 90 in the tip direction. The tip portion 31, which is the end portion of the center pole 30 on the tip end direction D1 side, is press-fitted onto the Dr1 side in the rear end direction of the connecting member 90. With such a structure, the center pole 30 and the connecting member 90 are electrically connected.

セラミックヒータ４０は、図２のように、後端側から先端側へ軸線ＣＬと平行な方向（軸線方向）に沿って延びる丸棒状の基体１１０と、基体１１０の内部に埋設された略Ｕ字状の発熱抵抗体１２０（以下、単に「抵抗体１２０」と呼ぶ）とを含む。セラミックヒータ４０は、材料を焼成することによって、形成される。 As shown in FIG. 2, the ceramic heater 40 has a round bar-shaped base 110 extending from the rear end side to the front end side along a direction parallel to the axis CL (axis direction), and a substantially U-shape embedded inside the base 110. The heat generating resistor 120 (hereinafter, simply referred to as “resistor 120”) is included. The ceramic heater 40 is formed by firing the material.

基体１１０は、絶縁性セラミック材料によって形成され、軸線方向に沿って延びた形態をなす。本実施形態では、基体１１０を形成するセラミック材料は、窒化珪素（Ｓｉ_３Ｎ_４）から主に成る。他の実施形態としては、基体１１０を構成する窒化珪素（Ｓｉ_３Ｎ_４）のうち、珪素（Ｓｉ）の少なくとも一部がアルミニウム（Ａｌ）で置換され、窒素（Ｎ）の少なくとも一部が酸素（Ｏ）で置換されてもよい。 The substrate 110 is formed of an insulating ceramic material and has a form extending along the axial direction. In the present embodiment, the ceramic material forming the substrate 110 is mainly composed of _{silicon nitride (Si 3} N _4). In another embodiment, of the silicon nitride (Si ₃ N ₄ ) constituting the substrate 110, at least a part of silicon (Si) is replaced with aluminum (Al), and at least a part of nitrogen (N) is oxygen. It may be replaced with (O).

抵抗体１２０は、導電性セラミック材料で形成され、基体１１０に埋設されている。抵抗体１２０を形成する導電性セラミック材料は、通電発熱できる導電性物質であればよく、本実施形態では、炭化タングステン（ＷＣ）と窒化珪素との混合物が用いられる。他の実施形態としては、二珪化モリブデン（ＭｏＳｉ_２）と窒化珪素との混合物等が用いられてもよい。 The resistor 120 is made of a conductive ceramic material and is embedded in the substrate 110. The conductive ceramic material forming the resistor 120 may be a conductive substance capable of generating heat by energization, and in this embodiment, a mixture of tungsten carbide (WC) and silicon nitride is used. As another embodiment, a mixture of molybdenum dissilicate (MoSi ₂ ) and silicon nitride or the like may be used.

基体１１０の先端部（すなわち、セラミックヒータ４０の先端部４１）は、先端側に向かって徐々に細くなっている。抵抗体１２０の電気伝導率は、基体１１０の電気伝導率よりも高い。抵抗体１２０は、通電がなされることによって発熱する。 The tip of the substrate 110 (that is, the tip 41 of the ceramic heater 40) is gradually tapered toward the tip. The electrical conductivity of the resistor 120 is higher than the electrical conductivity of the substrate 110. The resistor 120 generates heat when energized.

図２のように、抵抗体１２０は、２本のリード部として構成される第１導電部１２２、第２導電部１２３と、第１導電部１２２及び第２導電部１２３に接続された発熱部１２１と、電極部１２４、１２５と、を含んでいる。第１導電部１２２、第２導電部１２３は、一部が基体１１０の後端１１０Ａ側に配置されて後端１１０Ａ側から先端１１０Ｂ側に向かって軸線方向に沿って延びる一対の導電部である。第１導電部１２２、第２導電部１２３の各々は、セラミックヒータ４０の後端部４９から先端部４１の近傍まで軸線ＣＬと平行に延びている。第１導電部１２２と第２導電部１２３は、軸線ＣＬを挟んでおおよそ対称な位置に配置されている。第１導電部１２２から第２導電部１２３へ向かう方向が、第３方向Ｄ３である。 As shown in FIG. 2, the resistor 120 has a first conductive portion 122 and a second conductive portion 123 formed as two lead portions, and a heat generating portion connected to the first conductive portion 122 and the second conductive portion 123. 121 and electrode portions 124 and 125 are included. The first conductive portion 122 and the second conductive portion 123 are a pair of conductive portions that are partially arranged on the rear end 110A side of the substrate 110 and extend along the axial direction from the rear end 110A side toward the tip 110B side. .. Each of the first conductive portion 122 and the second conductive portion 123 extends parallel to the axis CL from the rear end portion 49 of the ceramic heater 40 to the vicinity of the front end portion 41. The first conductive portion 122 and the second conductive portion 123 are arranged at positions substantially symmetrical with respect to the axis CL. The direction from the first conductive portion 122 to the second conductive portion 123 is the third direction D3.

発熱部１２１は、上述した導電部からの通電によって発熱する部分であり、第１抵抗部１２１Ａと、第２抵抗部１２１Ｂと、連結部１２１Ｃと、を備える。第１抵抗部１２１Ａは、自身の後端側が一方の導電部（第１導電部１２２）の先端側に接続するとともに、第１導電部１２２から基体１１０の先端側に延びている。第２抵抗部１２１Ｂは、自身の後端側が他方の導電部（第２導電部１２３）の先端側に接続するとともに、第２導電部１２３から基体１１０の先端側に延びている。連結部１２１Ｃは、第１抵抗部１２１Ａ及び第２抵抗部１２１Ｂのそれぞれの先端側を連結する構成をなす。抵抗体１２０は、発熱部１２１と一対の導電部（第１導電部１２２及び第２導電部１２３）とが同一の材料によって形成されている。図２の例では、抵抗体１２０の先端側において相対的に径が細い部分が発熱部１２１であり、相対的に径が太い部分が一対の導電部（第１導電部１２２及び第２導電部１２３）である。 The heat generating portion 121 is a portion that generates heat when energized from the conductive portion described above, and includes a first resistance portion 121A, a second resistance portion 121B, and a connecting portion 121C. The rear end side of the first resistance portion 121A is connected to the tip end side of one of the conductive portions (first conductive portion 122), and extends from the first conductive portion 122 to the tip end side of the substrate 110. The rear end side of the second resistance portion 121B is connected to the tip end side of the other conductive portion (second conductive portion 123), and extends from the second conductive portion 123 to the tip end side of the substrate 110. The connecting portion 121C has a configuration in which the tip ends of the first resistance portion 121A and the second resistance portion 121B are connected to each other. In the resistor 120, the heat generating portion 121 and the pair of conductive portions (first conductive portion 122 and second conductive portion 123) are formed of the same material. In the example of FIG. 2, the portion having a relatively small diameter on the tip side of the resistor 120 is the heat generating portion 121, and the portion having a relatively large diameter is a pair of conductive portions (first conductive portion 122 and second conductive portion). 123).

電極部１２４，１２５は、発熱部１２１と電気的に接続され、軸線方向と交差する方向に沿って延びる構成をなす。電極部１２５は、軸状に構成された第２導電部１２３に連結されるとともに第１導電部１２２及び第２導電部１２３の対向方向（第３方向Ｄ３に沿った方向）に延び、延出側の端面１２５Ａが基体１１０の外表面に露出し、接続部材９０の内周面に接触する。 The electrode portions 124 and 125 are electrically connected to the heat generating portion 121 and extend along a direction intersecting the axial direction. The electrode portion 125 is connected to the second conductive portion 123 configured in a shaft shape, and extends in the opposite direction (direction along the third direction D3) of the first conductive portion 122 and the second conductive portion 123 to extend. The side end surface 125A is exposed on the outer surface of the substrate 110 and comes into contact with the inner peripheral surface of the connecting member 90.

図３のように、電極部１２４は、軸状に構成された第１導電部１２２に連結されるとともに第１導電部１２２及び第２導電部１２３の対向方向（第３方向Ｄ３（図２）に沿った方向）に延び、延出側の端面が基体１１０の外表面に露出し、外筒７０の内周面（貫通孔７０Ａの内壁面）に接触する接触面１２４Ａとして構成されている。電極部１２４の端面（接触面１２４Ａ）は、一部が大径部７４の内周面と接触し、他の一部がテーパ部７６の内周面と接触している。大径部７４の内周面とは、貫通孔７０Ａの内壁面のうち、軸線方向において大径部７４が形成された領域に配置される面であり、テーパ部７６の内周面とは、貫通孔７０Ａの内壁面のうち、軸線方向においてテーパ部７６が形成された領域に配置される面である。つまり、接触面１２４Ａは、軸線方向において大径部７４の領域とテーパ部７６の領域とに跨って配置され、接触面１２４Ａの前端側の一部が、軸線方向においてテーパ部７６が形成された領域内に位置している。 As shown in FIG. 3, the electrode portion 124 is connected to the first conductive portion 122 configured in a shaft shape and is opposed to the first conductive portion 122 and the second conductive portion 123 (third direction D3 (FIG. 2)). The end surface on the extending side is exposed on the outer surface of the substrate 110, and is configured as a contact surface 124A that comes into contact with the inner peripheral surface (inner wall surface of the through hole 70A) of the outer cylinder 70. A part of the end surface (contact surface 124A) of the electrode portion 124 is in contact with the inner peripheral surface of the large diameter portion 74, and the other part is in contact with the inner peripheral surface of the tapered portion 76. The inner peripheral surface of the large diameter portion 74 is a surface of the inner wall surface of the through hole 70A that is arranged in a region where the large diameter portion 74 is formed in the axial direction, and the inner peripheral surface of the tapered portion 76 is defined as a surface. This is a surface of the inner wall surface of the through hole 70A that is arranged in a region where the tapered portion 76 is formed in the axial direction. That is, the contact surface 124A is arranged so as to straddle the region of the large diameter portion 74 and the region of the tapered portion 76 in the axial direction, and a part of the front end side of the contact surface 124A is formed with the tapered portion 76 in the axial direction. Located within the area.

図３のように、グロープラグ１では、外筒７０における上述の「対向位置」（主体金具２０の前端部と対向する後端面７９の位置）から接触面１２４Ａまでは、軸線方向の距離がある程度確保されている。具体的には、対向位置（後端面７９の位置）から接触面１２４Ａの後端までの軸線方向の最短距離Ｌ１が２ｍｍ以上となっている。 As shown in FIG. 3, in the glow plug 1, there is a certain distance in the axial direction from the above-mentioned "opposing position" (the position of the rear end surface 79 facing the front end portion of the main metal fitting 20) on the outer cylinder 70 to the contact surface 124A. It is secured. Specifically, the shortest distance L1 in the axial direction from the facing position (the position of the rear end surface 79) to the rear end of the contact surface 124A is 2 mm or more.

更には、図３のように、接触面１２４Ａの前端Ｐ１を通り軸線方向に直交するグロープラグ１の断面ＣＳ１をみたときのテーパ部７６の径方向の厚さＴ１が、大径部７４を通り軸線方向に直交するグロープラグ１の断面ＣＳ２をみたときの大径部７４の径方向の厚さＴ２の、４０％以上となっている。なお、図３では、大径部７４における軸線方向の任意の一位置の断面を符号ＣＳ２で概念的に示し、この断面での大径部７４の厚さを符号Ｔ２で概念的に示しているが、大径部７４は、軸線方向のいずれの位置でも外周面の径がほぼ同一となっている。 Further, as shown in FIG. 3, the radial thickness T1 of the tapered portion 76 when the cross section CS1 of the glow plug 1 which passes through the front end P1 of the contact surface 124A and is orthogonal to the axial direction is viewed passes through the large diameter portion 74. It is 40% or more of the radial thickness T2 of the large diameter portion 74 when the cross section CS2 of the glow plug 1 orthogonal to the axial direction is viewed. In FIG. 3, the cross section of the large diameter portion 74 at an arbitrary position in the axial direction is conceptually shown by reference numeral CS2, and the thickness of the large diameter portion 74 in this cross section is conceptually shown by reference numeral T2. However, the diameter of the outer peripheral surface of the large diameter portion 74 is substantially the same at any position in the axial direction.

Ａ２．効果
グロープラグ１では、セラミックヒータ４０と嵌合する外筒７０において、肉厚が相対的に大きい大径部７４のほうが小径部７２よりもセラミックヒータ４０に対する面圧が確保されやすく、図３のように、この大径部７４の内周面に接触するように電極部１２４の接触面１２４Ａを配置しているため、接触面１２４Ａの接触圧がより大きく確保されやすくなる。ゆえに、電極部１２４と外筒７０の電気的接続が良好に維持されやすい。 A2. Effect In the glow plug 1, in the outer cylinder 70 fitted with the ceramic heater 40, the large diameter portion 74 having a relatively large wall thickness is more likely to secure the surface pressure on the ceramic heater 40 than the small diameter portion 72, and FIG. As described above, since the contact surface 124A of the electrode portion 124 is arranged so as to come into contact with the inner peripheral surface of the large diameter portion 74, it becomes easier to secure a larger contact pressure of the contact surface 124A. Therefore, the electrical connection between the electrode portion 124 and the outer cylinder 70 is likely to be well maintained.

更に、外筒７０における対向位置（主体金具２０の前端部と対向する位置であり、後端面７９の位置）から接触面１２４Ａまでの軸線方向の最短距離が２ｍｍ以上となっているため、主体金具２０及び外筒７０に対して軸線方向に過剰な圧縮力が加わってしまい外筒７０内において対向位置付近で変形が生じたとしても、その変形の影響は、接触面１２４Ａ付近には及びにくくなる。 Further, since the shortest distance in the axial direction from the facing position of the outer cylinder 70 (the position facing the front end portion of the main fitting 20 and the position of the rear end surface 79) to the contact surface 124A is 2 mm or more, the main fitting. Even if an excessive compressive force is applied to the outer cylinder 70 and the outer cylinder 70 in the axial direction and deformation occurs in the outer cylinder 70 near the opposite position, the influence of the deformation is less likely to reach the vicinity of the contact surface 124A. ..

例えば、図１等で示すグロープラグ１を図４のように内燃機関ＥＮの取付孔ＥＨに取り付ける場合、雄ネジ部２２を取付孔ＥＨの雌ネジ部ＴＨに螺合させ、工具係合部２８に工具を係合させて回転させることで、グロープラグ１を雌ネジ部ＴＨに係合させつつ取付孔ＥＨ内に挿入することができ、挿入が進展すると、テーパ部７６の外面７６Ａを取付孔ＥＨの段差部ＴＳに当てて固定することができる。しかし、テーパ部７６が段差部ＴＳに当接した後にグロープラグ１を過剰に締め付けてしまうと、雄ネジ部２２とテーパ部７６との間で軸線方向の圧縮力が生じ、相対的に硬度が低い外筒７０のほうが先に座屈しやすくなる。このような座屈の影響は対向位置（後端面７９の位置）付近に集中しやすいため、対向位置から接触面１２４Ａまでの軸線方向の最短距離が２ｍｍ以上となるように離しておけば、上述した軸線方向の圧縮力が加わっても、座屈の影響が接触面１２４Ａ付近まで及びにくくなり、外筒７０の内周面と接触面１２４Ａとの間で接触不良が生じにくくなる。よって、電極部１２４と外筒７０の電気的接続がより確実に維持されやすくなる。なお、図４において、符号Ｈ１は、取付孔ＥＨのうち、主体金具２０の一部及び大径部などが収容される孔であり、符号Ｈ２は、小径部７２が収容される孔である。符号ＥＲは、燃焼室の内壁面である。 For example, when the glow plug 1 shown in FIG. 1 or the like is attached to the mounting hole EH of the internal combustion engine EN as shown in FIG. 4, the male screw portion 22 is screwed into the female screw portion TH of the mounting hole EH, and the tool engaging portion 28 The glow plug 1 can be inserted into the mounting hole EH while being engaged with the female screw portion TH by engaging the tool with the mounting hole EH, and as the insertion progresses, the outer surface 76A of the tapered portion 76 is inserted into the mounting hole. It can be fixed by hitting the step portion TS of the EH. However, if the glow plug 1 is excessively tightened after the tapered portion 76 comes into contact with the stepped portion TS, a compressive force in the axial direction is generated between the male screw portion 22 and the tapered portion 76, and the hardness becomes relatively high. The lower outer cylinder 70 is more likely to buckle first. Since the influence of such buckling tends to be concentrated near the facing position (the position of the rear end surface 79), if the shortest distance in the axial direction from the facing position to the contact surface 124A is 2 mm or more, the above-mentioned Even if a compressive force in the axial direction is applied, the influence of buckling is less likely to extend to the vicinity of the contact surface 124A, and poor contact is less likely to occur between the inner peripheral surface of the outer cylinder 70 and the contact surface 124A. Therefore, the electrical connection between the electrode portion 124 and the outer cylinder 70 can be more reliably maintained. In FIG. 4, reference numeral H1 is a hole in the mounting hole EH in which a part of the main metal fitting 20 and a large diameter portion are accommodated, and reference numeral H2 is a hole in which the small diameter portion 72 is accommodated. The symbol ER is the inner wall surface of the combustion chamber.

また、グロープラグ１の外筒７０は、軸線方向において大径部７４と小径部７２との間に、外周面の径が大径部７４よりも小さく且つ前方側となるにつれて次第に外周面の径が小さくなるテーパ部７６を備えており、接触面１２４Ａの前端側の一部が、軸線方向においてテーパ部７６が形成された領域内に位置するように構成されている。このように、電極部１２４の接触面１２４Ａを、軸線方向において大径部７４とテーパ部７６とに跨る位置まで対向位置（後端面７９の位置）から遠ざければ、軸線方向の過剰な圧縮力に起因する変形が対向位置付近で生じても、その変形が接触面１２４Ａに与える影響は一層小さくなる。また、接触面１２４Ａの全部がテーパ部７６の領域に配置されるのではなく、一部は大径部７４の領域に配置されるため、接触面１２４Ａの全部がテーパ部７６の領域に配置される構成と比較すると接触面１２４Ａの接触圧は確保されやすい。 Further, the outer cylinder 70 of the glow plug 1 is located between the large diameter portion 74 and the small diameter portion 72 in the axial direction, and the diameter of the outer peripheral surface gradually becomes smaller than that of the large diameter portion 74 and becomes the front side. The tapered portion 76 is provided so that a part of the contact surface 124A on the front end side is located in the region where the tapered portion 76 is formed in the axial direction. In this way, if the contact surface 124A of the electrode portion 124 is moved away from the facing position (the position of the rear end surface 79) to a position straddling the large diameter portion 74 and the tapered portion 76 in the axial direction, an excessive compressive force in the axial direction is obtained. Even if the deformation caused by the above occurs in the vicinity of the facing positions, the influence of the deformation on the contact surface 124A is further reduced. Further, since the entire contact surface 124A is not arranged in the region of the tapered portion 76 but a part of the contact surface 124A is arranged in the region of the large diameter portion 74, the entire contact surface 124A is arranged in the region of the tapered portion 76. The contact pressure of the contact surface 124A is more likely to be secured as compared with the above configuration.

図３のように、グロープラグ１は、接触面１２４Ａの前端Ｐ１を通り軸線方向に直交するグロープラグ１の断面ＣＳ１をみたときのテーパ部７６の径方向の厚さＴ１が、大径部７４を通り軸線方向に直交するグロープラグ１の断面ＣＳ２をみたときの大径部７４の径方向の厚さＴ２の４０％以上となっている。このようにすれば、電極部１２４の接触面１２４Ａをテーパ部７６の位置まで遠ざけて対向位置（後端面７９の位置）との距離を確保しつつ、接触面１２４Ａの位置において外筒７０の肉厚を一定程度確保することができる。これにより、肉厚が小さいことに起因する接触圧（外筒７０の内周面に接触する接触面１２４Ａの面圧）の低下を抑えることができる。また、接触圧が低下すると、外筒７０の内周面と接触面１２４Ａとの間に空気が入り込む微小な隙間が生じやすくなり、接触領域付近が酸化しやすくなるという問題があるが、上述した構成とすれば、接触圧の低下に起因する酸化の進展を抑えることができ、酸化に起因する抵抗値の上昇を抑制することができる。 As shown in FIG. 3, the glow plug 1 has a large diameter portion 74 having a thickness T1 in the radial direction of the tapered portion 76 when the cross section CS1 of the glow plug 1 passing through the front end P1 of the contact surface 124A and orthogonal to the axial direction is viewed. When the cross section CS2 of the glow plug 1 passing through the above and orthogonal to the axial direction is viewed, the thickness T2 in the radial direction of the large diameter portion 74 is 40% or more. By doing so, the contact surface 124A of the electrode portion 124 is moved away from the position of the tapered portion 76 to secure a distance from the facing position (the position of the rear end surface 79), and the meat of the outer cylinder 70 is formed at the position of the contact surface 124A. A certain degree of thickness can be secured. As a result, it is possible to suppress a decrease in the contact pressure (the surface pressure of the contact surface 124A in contact with the inner peripheral surface of the outer cylinder 70) due to the small wall thickness. Further, when the contact pressure is lowered, there is a problem that a minute gap through which air enters is likely to be generated between the inner peripheral surface of the outer cylinder 70 and the contact surface 124A, and the vicinity of the contact region is easily oxidized. With the configuration, the progress of oxidation due to the decrease in contact pressure can be suppressed, and the increase in resistance value due to oxidation can be suppressed.

Ａ３．評価試験
次に、本発明の効果を検証するために行った試験の結果について説明する。
まず、締付試験について説明する。締付試験を実施するにあたり、第１実施形態のグロープラグ１と同様の構成をなすサンプルを用意し、このグロープラグ１のサンプルを取り付ける取付孔を図４の取付孔ＥＨのような構成で準備した。そして、この取付孔ＥＨにグロープラグ１のサンプルを装着し、ネジ試験機を用いて、グロープラグ１のサンプルを所定トルクで締め付けた。締付トルクは、外筒７０において後端面７９付近で座屈が生じるトルクまで上昇させた。 A3. Evaluation Test Next, the results of a test conducted to verify the effect of the present invention will be described.
First, the tightening test will be described. In carrying out the tightening test, a sample having the same configuration as that of the glow plug 1 of the first embodiment is prepared, and a mounting hole for mounting the sample of the glow plug 1 is prepared with a configuration as shown in the mounting hole EH of FIG. bottom. Then, the sample of the glow plug 1 was mounted on the mounting hole EH, and the sample of the glow plug 1 was tightened with a predetermined torque using a screw tester. The tightening torque was increased to a torque at which buckling occurs in the vicinity of the rear end surface 79 of the outer cylinder 70.

このような締付試験を行った後、試験後のグロープラグ１において対向位置（後端面７９の位置）よりも前方側において、対向位置からの距離ごとに外筒７０の外径を計測した。この計測結果を図５で示す。図５において、横軸は、軸線方向における対向位置からの距離（ｍｍ）を示し、縦軸は、対向位置からの各距離における変化度合いとしている。「各距離における変化度合い」とは、対向位置からの各距離における「試験前の外径に対する試験後の外径の割合」のことであり、外形に変化がなければ０となり、外形の増大量が大きいほど値が大きくなる。また、横軸において「０」は対向位置（後端面７９の位置）を示し、対向位置よりも前方側の距離を正とし、対向位置よりも後方側の距離を負とする。なお、締付試験で用いたグロープラグ１のサンプルでは、対向位置（後端面７９の位置）の前方側及び後方側の所定範囲に溶接部１４０が存在しており、図５では、溶接部が存在する領域の計測結果は省略している。図５で示す試験結果により、対向位置からの軸線方向の距離が２ｍｍ以上であれば、過剰な締め付けがなされても座屈が生じにくくなることが確認された。ゆえに、２ｍｍ以上となる領域に接触面１２４Ａを配置すれば、過剰な締め付けがなされても接触面１２４Ａの接触圧への影響が抑えられると考えられる。 After performing such a tightening test, the outer diameter of the outer cylinder 70 was measured for each distance from the facing position on the front side of the facing position (the position of the rear end surface 79) in the glow plug 1 after the test. The measurement result is shown in FIG. In FIG. 5, the horizontal axis represents the distance (mm) from the facing position in the axial direction, and the vertical axis represents the degree of change at each distance from the facing position. The "degree of change at each distance" is the "ratio of the outer diameter after the test to the outer diameter before the test" at each distance from the opposite position. The larger the value, the larger the value. Further, on the horizontal axis, "0" indicates an opposite position (the position of the rear end surface 79), the distance on the front side of the opposite position is positive, and the distance on the rear side of the opposite position is negative. In the sample of the glow plug 1 used in the tightening test, the welded portion 140 exists in a predetermined range on the front side and the rear side of the facing position (the position of the rear end surface 79), and in FIG. 5, the welded portion is The measurement results of the existing area are omitted. From the test results shown in FIG. 5, it was confirmed that if the distance in the axial direction from the opposite position is 2 mm or more, buckling is less likely to occur even if excessive tightening is performed. Therefore, if the contact surface 124A is arranged in a region of 2 mm or more, it is considered that the influence of the contact surface 124A on the contact pressure can be suppressed even if excessive tightening is performed.

次に、耐久試験について説明する。耐久試験では、第１実施形態のグロープラグ１と同様の構成をなすサンプルをサンプル１〜５（試料番号１〜５）として複数用意した。但し、サンプル１〜５は、軸線方向における接触面１２４Ａの領域での外筒７０の厚さ（肉厚）を種々に変更している。なお、いずれのサンプルも、軸線方向において接触面１２４Ａの領域全体で外筒７０の厚さを一定としている。表１では、サンプル１〜５をそれぞれ試料番号１〜５とし、各サンプルの「肉厚比」を示している。各サンプルの「肉厚比」とは、サンプル５における接触面１２４Ａの領域での外筒７０の厚さ（肉厚）を基準（１００％）とし、この基準に対する各サンプルの対応部分の厚さ（接触面１２４Ａの領域での外筒７０の厚さ（肉厚））の割合を示すものである。 Next, the durability test will be described. In the durability test, a plurality of samples having the same configuration as the glow plug 1 of the first embodiment were prepared as samples 1 to 5 (sample numbers 1 to 5). However, in Samples 1 to 5, the thickness (thickness) of the outer cylinder 70 in the region of the contact surface 124A in the axial direction is variously changed. In each sample, the thickness of the outer cylinder 70 is constant over the entire region of the contact surface 124A in the axial direction. In Table 1, samples 1 to 5 are designated as sample numbers 1 to 5, respectively, and the "thickness ratio" of each sample is shown. The "thickness ratio" of each sample is based on the thickness (thickness) of the outer cylinder 70 in the region of the contact surface 124A in the sample 5 as a reference (100%), and the thickness of the corresponding portion of each sample with respect to this reference. It shows the ratio of (thickness (thickness) of outer cylinder 70 in region of contact surface 124A).

そして、作製した各サンプル１〜５に対して耐久試験を実施した。耐久試験では、サンプルとなるグロープラグを通電してグロープラグの外筒の表面が３００℃になるまで昇温させ、その後、通電を停止して常温となるまで冷却することを１サイクルとした。そして、このサイクルを繰り返し、５００００サイクル実施した。そして、各サンプルについて５００００サイクル実施後に評価を行い、５００００サイクル実施後に試験前よりも抵抗値が１０％以上上昇したサンプルを「×」とし、試験前からの抵抗値の変化が１０％未満であったサンプルを「○」とした。表１にはこの評価結果を示す。 Then, a durability test was carried out on each of the prepared samples 1 to 5. In the durability test, one cycle was to energize the sample glow plug to raise the temperature of the surface of the outer cylinder of the glow plug until it reaches 300 ° C., and then stop the energization to cool it to room temperature. Then, this cycle was repeated, and 50,000 cycles were carried out. Then, each sample is evaluated after 50,000 cycles, and the sample in which the resistance value is increased by 10% or more after the 50,000 cycles is marked with "x", and the change in the resistance value from before the test is less than 10%. The sample was marked with "○". Table 1 shows the evaluation results.

表１の結果により、肉厚比が４０％未満に低下すると、抵抗値が大きく上昇することが確認された。これを踏まえると、図３のような構成の場合、大径部７４の位置での厚さＴ２（肉厚）を基準としたとき、断面ＣＳ１での最小厚さＴ１（肉厚）は、Ｔ２の４０％以上に確保されていることが望ましいといえる。 From the results in Table 1, it was confirmed that the resistance value increased significantly when the wall thickness ratio decreased to less than 40%. Based on this, in the case of the configuration as shown in FIG. 3, the minimum thickness T1 (thickness) in the cross section CS1 is T2 when the thickness T2 (thickness) at the position of the large diameter portion 74 is used as a reference. It can be said that it is desirable that it is secured at 40% or more of.

＜他の実施形態＞
本発明は上記記述及び図面によって説明した実施形態に限定されるものではなく、例えば次のような例も本発明の技術的範囲に含まれる。 <Other embodiments>
The present invention is not limited to the embodiments described in the above description and drawings, and for example, the following examples are also included in the technical scope of the present invention.

第１実施形態の説明では、発熱部と、リード部として機能する一対の導電部とを同一の１種類の材料によって一体的に構成した抵抗体（発熱抵抗体）を例示した。しかし、この例に限定されず、発熱部と一対の導電部とを、電気抵抗率の異なる別々の導電性セラミック材料によってそれぞれ構成してもよい。このように、発熱部と一対の導電部とが異なる材料によって形成されている場合、抵抗体の先端側の材料の部分、即ち、基端側と異なる材料の部分を「発熱部」とし、抵抗体の基端側の材料の部分を「導電部」とすることができる。 In the description of the first embodiment, a resistor (heat generating resistor) in which a heat generating portion and a pair of conductive portions functioning as lead portions are integrally made of the same one kind of material has been exemplified. However, the present invention is not limited to this example, and the heat generating portion and the pair of conductive portions may be formed of different conductive ceramic materials having different electrical resistivitys. In this way, when the heat generating portion and the pair of conductive portions are formed of different materials, the portion of the material on the tip end side of the resistor, that is, the portion of the material different from the base end side is referred to as the "heating portion" and the resistance. The portion of the material on the base end side of the body can be the "conductive portion".

第１実施形態では、大径部の後端面（主体金具の前端部に対向する面）が軸線方向と直交する方向である例を示したが、後端面は、軸線方向に対して多少傾いていてもよく、多少湾曲していてもよい。いずれの場合でも、外筒において主体金具の前端部に対向する面のうちの前端を「対向位置」とすることができ、この「対向位置」から接触面までの軸線方向の最短距離を２ｍｍ以上とすればよい。 In the first embodiment, an example is shown in which the rear end surface of the large diameter portion (the surface facing the front end portion of the main metal fitting) is orthogonal to the axial direction, but the rear end surface is slightly inclined with respect to the axial direction. It may be slightly curved. In either case, the front end of the surface of the outer cylinder facing the front end of the main metal fitting can be set as the "opposing position", and the shortest distance in the axial direction from this "opposing position" to the contact surface is 2 mm or more. And it is sufficient.

第１実施形態では、電極部の接触面が軸線方向において大径部の領域とテーパ部の領域とに跨って配置されていたが、大径部の領域のみに配置されていてもよい。 In the first embodiment, the contact surface of the electrode portion is arranged so as to straddle the region of the large diameter portion and the region of the tapered portion in the axial direction, but it may be arranged only in the region of the large diameter portion.

１…グロープラグ
２０…主体金具
４０…セラミックヒータ
７０…金属外筒（外筒）
７２…小径部
７４…大径部
７６…テーパ部
１１０…基体
１２０…発熱抵抗体（抵抗体）
１２１…発熱部
１２４…第１電極部（電極部）
１２４Ａ…接触面
ＣＬ…中心軸（軸線） 1 ... Glow plug 20 ... Main metal fittings 40 ... Ceramic heater 70 ... Metal outer cylinder (outer cylinder)
72 ... Small diameter part 74 ... Large diameter part 76 ... Tapered part 110 ... Base 120 ... Heat generation resistor (resistor)
121 ... Heat generation part 124 ... First electrode part (electrode part)
124A ... Contact surface CL ... Central axis (axis)

Claims

A ceramic heater that extends along the axial direction,
A cylindrical main metal fitting for accommodating a portion on the rear end side of the ceramic heater,
While exposing the front end side portion of the ceramic heater, the ceramic heater is fitted with the ceramic heater, and the rear end portion of the ceramic heater is joined to the front end portion of the main metal fitting to form a cylindrical outer cylinder having a hardness lower than that of the main metal fitting. ,
With
The ceramic heater is
A substrate made of insulating ceramic that extends along the axial direction,
A resistor made of a conductive ceramic and embedded in the substrate. A heat generating portion that generates heat when energized is electrically connected to the heat generating portion, extends along a direction intersecting the axial direction, and of the substrate. A resistor having an electrode portion whose end surface exposed to the outer surface is configured as a contact surface in contact with the inner peripheral surface of the outer cylinder.
With
The outer cylinder is
A small diameter part with a predetermined outer peripheral surface and
A large-diameter portion that is arranged on the rear side of the small-diameter portion and has a larger outer diameter than the small-diameter portion, and has a large-diameter portion that faces the front end portion of the main metal fitting and the axial direction.
It is a glow plug equipped with
At least a part of the contact surface is in contact with the inner peripheral surface of the large diameter portion.
In the outer cylinder, the shortest distance in the axial direction from the position of the rear end surface facing the front end portion of the main metal fitting to the contact surface is 2 mm or more.
Glow plug.

The outer cylinder has a tapered portion between the large diameter portion and the small diameter portion in the axial direction, in which the diameter of the outer peripheral surface is smaller than that of the large diameter portion and the diameter of the outer peripheral surface gradually decreases toward the front side. With
A part of the front end side of the contact surface is located in the region where the tapered portion is formed in the axial direction.
The glow plug according to claim 1.

When looking at the cross section of the glow plug that passes through the front end of the contact surface and is orthogonal to the axial direction, the radial thickness of the tapered portion passes through the large diameter portion and is orthogonal to the axial direction. Is 40% or more of the radial thickness of the large-diameter portion when viewed.
The glow plug according to claim 2.