JP2019012677A

JP2019012677A - Spark plug

Info

Publication number: JP2019012677A
Application number: JP2017130205A
Authority: JP
Inventors: 俊介津荷; Shunsuke Tsuga
Original assignee: NGK Spark Plug Co Ltd
Current assignee: Niterra Co Ltd
Priority date: 2017-07-03
Filing date: 2017-07-03
Publication date: 2019-01-24
Anticipated expiration: 2037-07-03
Also published as: JP6767938B2

Abstract

To provide a spark plug capable of improving preignition inhibitory effect.SOLUTION: A spark plug includes an insulation extending from the tip side to the rear end side in the axial direction, and having a radially outward protruding part, and a cylindrical main body metal fitting arranged on the outer peripheral side of the insulation, where the main body metal fitting includes a shelf part having a locking part where the protruding part of the insulation is locked. When dividing a space formed between a tip, which is a part of the main body metal fitting closer to the tip side than the locking part, and the insulation into two by a plane along the axis line including the axis line, the volume of the first space is larger than the volume of the remaining second space.SELECTED DRAWING: Figure 1

Description

本発明はスパークプラグに関し、特にプレイグニッションを抑制できるスパークプラグに関するものである。 The present invention relates to a spark plug, and more particularly to a spark plug that can suppress pre-ignition.

スパークプラグが装着された内燃機関では、スパークプラグの絶縁体と主体金具との間の空間に滞留した混合気が受熱して、プレイグニッション（過早着火）が発生することがある。この種のプレイグニッションを抑制するため、特許文献１には、主体金具のうち軸線方向の先端側の部分の内径を全周に亘って拡大する技術が開示されている。 In an internal combustion engine equipped with a spark plug, the air-fuel mixture staying in the space between the spark plug insulator and the metal shell may receive heat and preignition (pre-ignition) may occur. In order to suppress this kind of pre-ignition, Patent Literature 1 discloses a technique for enlarging the inner diameter of a portion on the distal end side in the axial direction of the metal shell over the entire circumference.

特開２０１４−１３６６７号公報JP 2014-13667 A

しかし、上記従来の技術ではプレイグニッションの抑制効果が不十分である。 However, the effect of suppressing pre-ignition is not sufficient with the above conventional technique.

本発明は上述した問題点を解決するためになされたものであり、プレイグニッションの抑制効果を向上できるスパークプラグを提供することを目的としている。 The present invention has been made to solve the above-described problems, and an object thereof is to provide a spark plug capable of improving the pre-ignition suppression effect.

この目的を達成するために本発明のスパークプラグは、先端側から後端側へと軸線方向に延び、径方向外側へ張り出す張出部を備える絶縁体と、絶縁体の外周側に配置される筒状の主体金具と、を備える。主体金具は、絶縁体の張出部が直接または他部材を介して係止される係止部を有する棚部を備える。主体金具のうち係止部よりも先端側の部位である先端部と絶縁体との間にできる空間を、軸線を含み軸線に沿う平面で二分したときに、その一方の第１空間の体積は、残りの第２空間の体積よりも大きい。 In order to achieve this object, the spark plug of the present invention is disposed on the outer peripheral side of the insulator, which has an overhang extending in the axial direction from the front end side to the rear end side and projecting radially outward. A cylindrical metal shell. The metal shell includes a shelf portion having a locking portion to which the protruding portion of the insulator is locked directly or via another member. When the space formed between the front end portion and the insulator, which is a portion on the front end side of the locking portion of the metal shell, is divided into two by a plane including the axis and along the axis, the volume of the first space of the one is The volume of the remaining second space is larger.

請求項１記載のスパークプラグによれば、内燃機関の吸気行程における気流の上流側に第１空間を配置すると、吸気行程において、先端部の内側に進入した混合気は第２空間から第１空間へ流れる。第１空間の体積は第２空間の体積よりも大きいので、第１空間に混合気を滞留させ難くできる。その結果、第１空間に滞留した混合気が受熱して生じるプレイグニッションを抑制できるので、プレイグニッションの抑制効果を向上できる。 According to the spark plug of the first aspect, when the first space is arranged on the upstream side of the air flow in the intake stroke of the internal combustion engine, the air-fuel mixture entering the inside of the tip portion in the intake stroke is transferred from the second space to the first space. To flow. Since the volume of the first space is larger than the volume of the second space, it is difficult for the air-fuel mixture to stay in the first space. As a result, the pre-ignition generated when the air-fuel mixture staying in the first space receives heat can be suppressed, so that the pre-ignition suppression effect can be improved.

請求項２記載のスパークプラグによれば、軸線と直交し先端部を通る断面において、径方向外側に凹んだ凹部が、先端部の内周に設けられる。また、軸線から凹部の両端に対して引かれた２つの直線のなす角は６０〜１８０°の所定角度に設定される。そのため、請求項１の効果に加え、先端部の内周に凹部を設けることによって第１空間の体積を簡易に拡大できる。 According to the spark plug of the second aspect, in the cross section orthogonal to the axis and passing through the tip portion, the concave portion recessed radially outward is provided on the inner periphery of the tip portion. The angle formed by two straight lines drawn from the axis to both ends of the recess is set to a predetermined angle of 60 to 180 °. Therefore, in addition to the effect of the first aspect, the volume of the first space can be easily enlarged by providing the concave portion on the inner periphery of the tip portion.

請求項３記載のスパークプラグによれば、主体金具に接合された接地電極は、主体金具のうち、２つの直線および軸線を含み凹部を挟む２つの平面によって切り取られる部分以外の部分に接合されている。これにより、接地電極が、吸気行程における混合気の流れを妨げ難くできるので、請求項２の効果に加え、プレイグニッションの抑制効果をさらに向上できる。 According to the spark plug of claim 3, the ground electrode joined to the metal shell is joined to a portion of the metal shell other than a portion cut by two planes including two straight lines and an axis and sandwiching the recess. Yes. Thereby, since the ground electrode can make it difficult to prevent the flow of the air-fuel mixture in the intake stroke, in addition to the effect of claim 2, the effect of suppressing pre-ignition can be further improved.

請求項４記載のスパークプラグによれば、絶縁体のうち先端部に取り囲まれる部分は、先端側へ向かうにつれて外径が縮径する縮径部と、縮径部の先端に連接されると共に外径が一定の第１直線部と、を備えている。第１直線部が設けられているので、第１直線部が設けられていない場合に比べて、先端部と絶縁体との径方向の隙間を大きくできる。一方、第１直線部と先端部との径方向の隙間に比べて、縮径部と先端部との径方向の隙間は小さいので、先端部のうち縮径部を取り囲む部分に凹部を少なくとも設けることにより、縮径部と先端部との間に混合気を滞留させ難くできる。よって、請求項２又は３の効果に加え、混合気の受熱に起因するプレイグニッションをより生じ難くできる。 According to the spark plug of the fourth aspect, the portion surrounded by the tip portion of the insulator is connected to the diameter-reduced portion whose outer diameter is reduced toward the tip side, and is connected to the tip of the diameter-reduced portion and is externally connected. A first straight portion having a constant diameter. Since the first straight portion is provided, the radial gap between the tip portion and the insulator can be increased as compared with the case where the first straight portion is not provided. On the other hand, since the radial gap between the reduced diameter portion and the tip portion is smaller than the radial gap between the first straight portion and the tip portion, at least a recess is provided in the portion surrounding the reduced diameter portion of the tip portion. This makes it difficult for the air-fuel mixture to stay between the reduced diameter portion and the tip portion. Therefore, in addition to the effect of the second or third aspect, pre-ignition caused by heat reception of the air-fuel mixture can be made more difficult to occur.

請求項５記載のスパークプラグによれば、断面は、先端部の任意の断面なので、先端部の軸線方向の一部に凹部が形成されている場合に比べて、混合気を滞留させ難くできる。よって、請求項２から４のいずれかの効果に加え、混合気の受熱に起因するプレイグニッションをより生じ難くできる。 According to the spark plug of the fifth aspect, since the cross section is an arbitrary cross section of the tip portion, the air-fuel mixture can be made difficult to stay as compared with the case where the concave portion is formed in a part of the tip portion in the axial direction. Therefore, in addition to the effect of any one of claims 2 to 4, preignition caused by heat reception of the air-fuel mixture can be made less likely to occur.

請求項６記載のスパークプラグによれば、絶縁体のうち先端部に取り囲まれる部分は、外径が一定の第２直線部と、第２直線部の先端に連接されると共に先端側へ向かうにつれて外径が縮径する縮径部と、を備えている。断面は、先端部のうち絶縁体の縮径部の後端よりも先端側の部分の任意の断面なので、先端部の一部に凹部が形成されている場合に比べて、混合気を滞留させ難くできる。よって、請求項２又は３の効果に加え、混合気の受熱に起因するプレイグニッションをより生じ難くできる。 According to the spark plug of claim 6, the portion surrounded by the tip portion of the insulator is connected to the second straight portion having a constant outer diameter and the tip of the second straight portion, and toward the tip side. A reduced diameter portion whose outer diameter is reduced. Since the cross section is an arbitrary cross section of the tip portion of the tip portion of the reduced diameter portion of the insulator, the air-fuel mixture is retained as compared with a case where a recess is formed in a part of the tip portion. It can be difficult. Therefore, in addition to the effect of the second or third aspect, pre-ignition caused by heat reception of the air-fuel mixture can be made more difficult to occur.

請求項７記載のスパークプラグによれば、軸線と直交し先端部を通る断面において、絶縁体のうち先端部に取り囲まれる部分は、先端部の内周との径方向の距離が、他の部位と比較して大きな小径部を備えている。軸線から小径部の両端に対して引かれた２つの直線のなす角は６０〜１８０°の所定角度に設定される。従って、請求項１の効果に加え、絶縁体に小径部を設けることによって第１空間の体積を簡易に拡大できる。 According to the spark plug of claim 7, in the cross section orthogonal to the axis and passing through the tip portion, the portion surrounded by the tip portion of the insulator has a radial distance from the inner periphery of the tip portion to other parts. Compared with, it has a large diameter part. An angle formed by two straight lines drawn from the axis to both ends of the small diameter portion is set to a predetermined angle of 60 to 180 °. Therefore, in addition to the effect of the first aspect, the volume of the first space can be easily expanded by providing the insulator with the small diameter portion.

本発明の第１実施の形態におけるスパークプラグの部分断面図である。It is a fragmentary sectional view of the spark plug in a 1st embodiment of the present invention. スパークプラグの先端側の部分断面図である。It is a fragmentary sectional view by the side of the tip of a spark plug. 図１のＩＩＩ−ＩＩＩ線におけるスパークプラグの断面図である。It is sectional drawing of the spark plug in the III-III line of FIG. 第２実施の形態におけるスパークプラグの断面図である。It is sectional drawing of the spark plug in 2nd Embodiment. 第３実施の形態におけるスパークプラグの断面図である。It is sectional drawing of the spark plug in 3rd Embodiment. 第４実施の形態におけるスパークプラグの断面図である。It is sectional drawing of the spark plug in 4th Embodiment. （ａ）は比較例におけるスパークプラグの断面図であり、（ｂ）は実施例１におけるスパークプラグの断面図であり、（ｃ）は実施例２におけるスパークプラグの断面図であり、（ｄ）は実施例３におけるスパークプラグの断面図である。(A) is sectional drawing of the spark plug in a comparative example, (b) is sectional drawing of the spark plug in Example 1, (c) is sectional drawing of the spark plug in Example 2, (d) These are sectional drawings of the spark plug in Example 3. FIG. 実施例１から３及び比較例におけるスパークプラグのクランク角と空間の平均温度との関係を示す図である。It is a figure which shows the relationship between the crank angle of the spark plug in Examples 1-3 and a comparative example, and the average temperature of space.

以下、本発明の好ましい実施形態について添付図面を参照して説明する。図１は本発明の第１実施の形態におけるスパークプラグ１０の部分断面図であり、図２はスパークプラグ１０の先端側の部分断面図である。図１及び図２では、紙面下側をスパークプラグ１０の先端側、紙面上側をスパークプラグ１０の後端側という。図１に示す矢印Ｆは、スパークプラグ１０が装着された内燃機関（図示せず）の吸気行程において生じる気流（タンブル流）の向きである。 Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a partial cross-sectional view of the spark plug 10 according to the first embodiment of the present invention, and FIG. 2 is a partial cross-sectional view of the tip side of the spark plug 10. 1 and 2, the lower side of the drawing is referred to as the front end side of the spark plug 10, and the upper side of the drawing is referred to as the rear end side of the spark plug 10. An arrow F shown in FIG. 1 indicates the direction of an air flow (tumble flow) generated in an intake stroke of an internal combustion engine (not shown) to which the spark plug 10 is attached.

図１に示すようにスパークプラグ１０は、絶縁体１１及び主体金具３０を備えている。絶縁体１１は、高温下の絶縁性や機械的特性に優れるアルミナ等により形成された略円筒状の部材である。絶縁体１１は、先端側から後端側へ順に、軸線Ｏに沿って第１直線部１２、縮径部１３、第２直線部１４、張出部１５、係合部１６及び後端部１７が連接されている。絶縁体１１は軸線Ｏに沿って軸孔１８が貫通する。軸孔１８の先端側の張出部１５の内周には、先端側に向かって縮径する後端向き面１９が形成されている。 As shown in FIG. 1, the spark plug 10 includes an insulator 11 and a metal shell 30. The insulator 11 is a substantially cylindrical member formed of alumina or the like that is excellent in insulation at high temperatures and mechanical properties. The insulator 11 has a first straight portion 12, a reduced diameter portion 13, a second straight portion 14, an overhang portion 15, an engagement portion 16, and a rear end portion 17 along the axis O in order from the front end side to the rear end side. Are connected. The insulator 11 has a shaft hole 18 extending along the axis O. A rear end-facing surface 19 that is reduced in diameter toward the front end side is formed on the inner periphery of the protruding portion 15 on the front end side of the shaft hole 18.

第１直線部１２は、絶縁体１１のうち最も先端側に位置する部位である。第１直線部１２の外径は、軸線Ｏ方向の全長に亘って略同一である。第１直線部１２の後端側に、縮径部１３を介して、第１直線部１２よりも外径の大きい第２直線部１４が連接されている。縮径部１３は先端側に向かって縮径している。第２直線部１４の外径は、軸線Ｏ方向の全長に亘って略同一である。 The first straight portion 12 is a portion located on the most distal side of the insulator 11. The outer diameter of the first straight portion 12 is substantially the same over the entire length in the axis O direction. A second straight line portion 14 having an outer diameter larger than that of the first straight line portion 12 is connected to the rear end side of the first straight line portion 12 via a reduced diameter portion 13. The reduced diameter portion 13 is reduced in diameter toward the distal end side. The outer diameter of the second straight portion 14 is substantially the same over the entire length in the direction of the axis O.

第２直線部１４の後端側に、径方向外側へ向かって張り出す張出部１５が連接されている。張出部１５の外径は、軸線Ｏ方向の全長に亘って略同一である。張出部１５の先端面１５ａは、先端側に向かって縮径している。係合部１６は、張出部１５の後端側に連接されている。係合部１６は、絶縁体１１のうち外径が最も大きい円環状の部分である。係合部１６の後端側に、後端部１７が連接されている。後端部１７の外径は、軸線Ｏ方向の全長に亘って略同一であり、係合部１６の外径よりも小さい。 An overhanging portion 15 that projects outward in the radial direction is connected to the rear end side of the second linear portion 14. The outer diameter of the overhanging portion 15 is substantially the same over the entire length in the direction of the axis O. The distal end surface 15a of the overhanging portion 15 is reduced in diameter toward the distal end side. The engaging portion 16 is connected to the rear end side of the overhang portion 15. The engaging portion 16 is an annular portion having the largest outer diameter in the insulator 11. A rear end portion 17 is connected to the rear end side of the engaging portion 16. The outer diameter of the rear end portion 17 is substantially the same over the entire length in the direction of the axis O, and is smaller than the outer diameter of the engaging portion 16.

中心電極２０は、軸孔１８の先端側に配置され軸線Ｏに沿って絶縁体１１に保持される棒状の電極である。中心電極２０は、軸孔１８に形成された後端向き面１９に係止されている。中心電極２０は、熱伝導性に優れる芯材が電極母材に埋設されている。電極母材は、Ｎｉを主体とする合金またはＮｉからなる金属材料で形成されており、芯材は銅または銅を主成分とする合金で形成されている。端子金具２１は、高圧ケーブル（図示せず）が接続される棒状の部材であり、導電性を有する金属材料（例えば低炭素鋼等）によって形成されている。端子金具２１は軸孔１８に挿入され、軸孔１８内で中心電極２０に電気的に接続されている。 The center electrode 20 is a rod-shaped electrode that is disposed on the distal end side of the shaft hole 18 and is held by the insulator 11 along the axis O. The center electrode 20 is locked to a rear end facing surface 19 formed in the shaft hole 18. The center electrode 20 has a core material excellent in thermal conductivity embedded in the electrode base material. The electrode base material is made of an alloy mainly composed of Ni or a metal material made of Ni, and the core material is made of copper or an alloy mainly composed of copper. The terminal fitting 21 is a rod-like member to which a high voltage cable (not shown) is connected, and is formed of a conductive metal material (for example, low carbon steel). The terminal fitting 21 is inserted into the shaft hole 18 and is electrically connected to the center electrode 20 in the shaft hole 18.

主体金具３０は、導電性を有する金属材料（例えば低炭素鋼等）によって形成された略円筒状の部材である。主体金具３０は、後端側から先端側へ順に、屈曲部３１、工具係合部３２、連絡部３３、座部３４及び胴部３５が連接されている。胴部３５の外周にはおねじ３６が形成されている。屈曲部３１は、絶縁体１１の係合部１６の後端側に配置される部位である。工具係合部３２は、内燃機関（図示せず）のねじ穴におねじ３６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。連絡部３３は、主体金具３０を絶縁体１１に組み付けるときに、塑性変形（屈曲）させて加締め固定するための部位である。座部３４は、内燃機関（図示せず）のねじ穴とおねじ３６との隙間を塞ぐための部位であり、胴部３５の外径よりも外径が大きく形成されている。 The metal shell 30 is a substantially cylindrical member formed of a conductive metal material (for example, low carbon steel). In the metal shell 30, a bent part 31, a tool engaging part 32, a connecting part 33, a seat part 34, and a body part 35 are connected in order from the rear end side to the front end side. A male screw 36 is formed on the outer periphery of the body portion 35. The bent portion 31 is a portion disposed on the rear end side of the engaging portion 16 of the insulator 11. The tool engaging portion 32 is a portion that engages a tool such as a wrench when the screw 36 is tightened in a screw hole of an internal combustion engine (not shown). The connecting portion 33 is a portion for plastically deforming (bending) and fixing by caulking when the metal shell 30 is assembled to the insulator 11. The seat portion 34 is a portion for closing a gap between the screw hole of the internal combustion engine (not shown) and the external screw 36, and has an outer diameter larger than the outer diameter of the body portion 35.

図２に示すように胴部３５の内周には、径方向の内側へ突出する棚部３７が、全周に亘って形成されている。絶縁体１１の張出部１５と棚部３７との間にパッキン３８が介在する。パッキン３８は、主体金具３０を構成する金属材料よりも軟質の軟鋼板等の金属材料で形成される円環状の板材である。棚部３７は、パッキン３８を介して張出部１５を先端側から係止する係止部３９を備えている。係止部３９は、棚部３７のうちパッキン３８が接触する部位である。棚部３７の後端面３７ａは、先端側に向かうにつれて縮径している。胴部３５のうち係止部３９の先端よりも先端側の部位である先端部４０は、径方向の隙間をあけて、絶縁体１１の第１直線部１２、縮径部１３及び第２直線部１４を取り囲む。第１直線部１２の一部（先端側）は、先端部４０から先端側に突出する。 As shown in FIG. 2, a shelf 37 that protrudes inward in the radial direction is formed on the inner circumference of the body 35 over the entire circumference. A packing 38 is interposed between the overhanging portion 15 of the insulator 11 and the shelf portion 37. The packing 38 is an annular plate formed of a metal material such as a mild steel plate that is softer than the metal material constituting the metal shell 30. The shelf portion 37 includes a locking portion 39 that locks the overhanging portion 15 from the distal end side via a packing 38. The locking portion 39 is a portion of the shelf portion 37 that contacts the packing 38. The rear end surface 37a of the shelf portion 37 is reduced in diameter toward the front end side. The distal end portion 40 which is a portion on the distal end side of the distal end of the locking portion 39 in the body portion 35 is spaced apart in the radial direction so that the first straight portion 12, the reduced diameter portion 13 and the second straight portion of the insulator 11. Enclose part 14. A part (front end side) of the first straight portion 12 protrudes from the front end portion 40 to the front end side.

棚部３７は、棚部３７よりも先端側の先端部４０の内周面４１と軸線Ｏとの距離が、棚部３７の内周面３７ｂと軸線Ｏとの距離よりも長くなるように、先端部４０の軸線Ｏ方向の一部に設けられている。棚部３７は、絶縁体１１の第２直線部１４の径方向の外側に位置する。先端部４０のうち棚部３７よりも先端側の内周面４１と絶縁体１１との径方向の隙間は、棚部３７と絶縁体１１との径方向の隙間よりも大きい。先端部４０の内周の一部には、径方向の外側に凹んだ凹部４２が形成されている。 The shelf portion 37 is configured such that the distance between the inner peripheral surface 41 of the distal end portion 40 on the front end side of the shelf portion 37 and the axis O is longer than the distance between the inner peripheral surface 37b of the shelf 37 and the axis O. It is provided in a part of the tip portion 40 in the axis O direction. The shelf portion 37 is located on the outer side in the radial direction of the second straight portion 14 of the insulator 11. The radial gap between the inner peripheral surface 41 and the insulator 11 on the distal end side of the shelf portion 37 in the distal end portion 40 is larger than the radial gap between the shelf portion 37 and the insulator 11. A concave portion 42 that is recessed outward in the radial direction is formed on a part of the inner periphery of the distal end portion 40.

本実施の形態では、凹部４２の後端面４３は、縮径部１３の後端１３ａよりも後端側（図２上側）に位置する。凹部４２は、棚部３７から先端部４０の先端まで軸線Ｏ方向に延びている。絶縁体１１と先端部４０との間にできる空間を、軸線Ｏを含む平面４７（図３参照）で二分したときにできる第１空間４４及び第２空間４５は、凹部４２に臨む第１空間４４の体積が、残りの第２空間４５の体積よりも大きい。 In the present embodiment, the rear end surface 43 of the recess 42 is located on the rear end side (upper side in FIG. 2) than the rear end 13 a of the reduced diameter portion 13. The recess 42 extends in the direction of the axis O from the shelf 37 to the tip of the tip 40. The first space 44 and the second space 45 formed when the space formed between the insulator 11 and the tip portion 40 is divided into two by a plane 47 (see FIG. 3) including the axis O, the first space facing the recess 42. The volume of 44 is larger than the volume of the remaining second space 45.

主体金具３０の先端に接地電極４６が接合されている。接地電極４６は、棒状の金属製（例えばニッケル基合金製）の部材であり、先端部が、中心電極２０と間隙（火花ギャップ）を介して対向する。本実施の形態では、接地電極４６は屈曲している。 A ground electrode 46 is joined to the tip of the metal shell 30. The ground electrode 46 is a rod-shaped metal member (for example, a nickel-base alloy member), and a tip portion thereof faces the center electrode 20 via a gap (spark gap). In the present embodiment, the ground electrode 46 is bent.

主体金具３０の屈曲部３１と絶縁体１１の係合部１６との間に、タルク等の充填材４７が介在する。主体金具３０は、屈曲部３１及び棚部３７が、充填材４７及びパッキン３８を介して係合部１６及び張出部１５に軸線Ｏ方向の荷重を加える。これにより主体金具３０は、棚部３７と絶縁体１１の張出部１５との間（第１空間４４及び第２空間４５の後端側）を密閉し、第１空間４４及び第２空間４５の先端側を開放した状態で、絶縁体１１を保持する。 A filler 47 such as talc is interposed between the bent portion 31 of the metal shell 30 and the engaging portion 16 of the insulator 11. In the metal shell 30, the bent portion 31 and the shelf portion 37 apply a load in the axis O direction to the engaging portion 16 and the overhanging portion 15 via the filler 47 and the packing 38. Thereby, the metal shell 30 seals the space between the shelf portion 37 and the overhanging portion 15 of the insulator 11 (the rear end side of the first space 44 and the second space 45), and the first space 44 and the second space 45. The insulator 11 is held in a state in which the tip end side is opened.

図３は図１のＩＩＩ−ＩＩＩ線におけるスパークプラグ１０の断面図である。図３では、軸線Ｏと直交し縮径部１３及び先端部４０を通る切断面によって切断されたスパークプラグ１０の断面が図示されている。 FIG. 3 is a cross-sectional view of the spark plug 10 taken along line III-III in FIG. In FIG. 3, a cross section of the spark plug 10 cut by a cut surface that is orthogonal to the axis O and passes through the reduced diameter portion 13 and the distal end portion 40 is illustrated.

本実施の形態では、先端部４０（主体金具３０）と縮径部１３（絶縁体１１）との間にできる空間を第１空間４４と第２空間４５とに二分する平面４７は、接地電極４６の対称面（軸線Ｏを含み図３紙面に垂直な面）である。第１空間４４の体積を第２空間４５の体積より大きくするため、先端部４０の内周の一部（第１空間４４に臨む部分）に、径方向の外側に凹んだ凹部４２が形成される。本実施の形態では、凹部４２の径方向の深さは、先端部４０の内周の仮想円ｖ（軸線Ｏを中心とする円）に対して周方向に亘って同一に設定されている。 In the present embodiment, the plane 47 that bisects the space formed between the tip portion 40 (the metal shell 30) and the reduced diameter portion 13 (the insulator 11) into the first space 44 and the second space 45 is the ground electrode. 46 symmetry planes (planes including the axis O and perpendicular to the plane of FIG. 3). In order to make the volume of the first space 44 larger than the volume of the second space 45, a recess 42 that is recessed outward in the radial direction is formed in a part of the inner periphery of the tip portion 40 (portion facing the first space 44). The In the present embodiment, the depth in the radial direction of the recess 42 is set to be the same in the circumferential direction with respect to the virtual circle v (a circle centered on the axis O) on the inner periphery of the tip end portion 40.

スパークプラグ１０は、内燃機関（図示せず）の吸気行程における気流Ｆの上流側に第１空間４４が位置するように、内燃機関に配置される。内燃機関の吸気行程において、気流Ｆ（混合気）は第２空間４５を経て第１空間４４に進入する。第１空間４４の体積は第２空間４５の体積より大きいので、第１空間４４に混合気が滞留しないようにできる。その結果、第１空間４４に滞留した混合気が受熱して生じるプレイグニッション（過早着火）を抑制できる。 The spark plug 10 is disposed in the internal combustion engine such that the first space 44 is positioned on the upstream side of the airflow F in the intake stroke of the internal combustion engine (not shown). In the intake stroke of the internal combustion engine, the air flow F (air mixture) enters the first space 44 through the second space 45. Since the volume of the first space 44 is larger than the volume of the second space 45, the air-fuel mixture can be prevented from staying in the first space 44. As a result, pre-ignition (premature ignition) generated when the air-fuel mixture staying in the first space 44 receives heat can be suppressed.

凹部４２は、先端部４０のうち第１空間４４に臨む部分に切削等を施すことによって形成される。凹部４２の周方向の両端に対して軸線Ｏから引かれた２つの直線４８，４９のなす角θは、６０〜１８０°の所定角度に設定される。直線４８，４９と先端部４０の内周とが交わる２点間の沿面距離は、直線４８，４９と縮径部１３（絶縁体１１）の外周とが交わる２点間の沿面距離より長いので、先端部４０に凹部４２を形成することによって、絶縁体１１の外径を部分的に小さくする場合に比べて、第１空間４４の体積を効率良く拡大できる。 The recess 42 is formed by cutting or the like in the portion of the tip 40 that faces the first space 44. An angle θ formed by two straight lines 48 and 49 drawn from the axis O with respect to both ends in the circumferential direction of the recess 42 is set to a predetermined angle of 60 to 180 °. The creepage distance between the two points where the straight lines 48 and 49 intersect the inner periphery of the tip 40 is longer than the creepage distance between the two points where the straight lines 48 and 49 intersect with the outer periphery of the reduced diameter portion 13 (insulator 11). By forming the recess 42 in the distal end portion 40, the volume of the first space 44 can be efficiently expanded as compared with the case where the outer diameter of the insulator 11 is partially reduced.

接地電極４６は、主体金具３０のうち、２つの直線４８，４９及び軸線Ｏを含み凹部４２を挟む２つの平面４８，４９（図３紙面に垂直な面）によって切り取られる扇形状の部分（角度θの部分）以外の部分（３６０°−θの部分）に接合されている。これにより、第１空間４４から気流Ｆ（混合気）が出やすくなる。よって、プレイグニッションの抑制効果をさらに向上できる。 The ground electrode 46 is a fan-shaped portion (angle) cut out by two flat surfaces 48 and 49 (surfaces perpendicular to the paper surface of FIG. 3) including two straight lines 48 and 49 and the axis O and sandwiching the recess 42 in the metal shell 30. It is joined to a portion (360 ° -θ portion) other than (θ portion). As a result, the air flow F (air mixture) is easily emitted from the first space 44. Therefore, the pre-ignition suppression effect can be further improved.

絶縁体１１（図２参照）は、張出部１５よりも先端側に、第２直線部１４、縮径部１３及び第１直線部１２が連接されている。棚部３７は、第２直線部１４の径方向の外側に配置されている。第２直線部１４の先端側に縮径部１３及び第１直線部１２が連接されているので、第２直線部１４から絶縁体１１の先端までの部分が円錐台状に形成される場合に比べて、先端部４０と絶縁体１１との径方向の隙間を大きくできる。よって、先端部４０と絶縁体１１との間の気流（混合気）を流れ易くできる。 In the insulator 11 (see FIG. 2), the second straight portion 14, the reduced diameter portion 13, and the first straight portion 12 are connected to the distal end side of the overhang portion 15. The shelf portion 37 is disposed on the outer side in the radial direction of the second linear portion 14. Since the reduced diameter portion 13 and the first linear portion 12 are connected to the distal end side of the second linear portion 14, when the portion from the second linear portion 14 to the distal end of the insulator 11 is formed in a truncated cone shape. In comparison, the radial gap between the tip 40 and the insulator 11 can be increased. Therefore, the airflow (air mixture) between the tip 40 and the insulator 11 can be easily flowed.

第１直線部１２と先端部４０との径方向の隙間に比べて、縮径部１３と先端部４０との径方向の隙間は小さいが、凹部４２が、先端部４０のうち、少なくとも縮径部１３の径方向の外側の部分に形成されているので、縮径部１３と先端部４０との間に混合気を滞留させ難くできる。よって、混合気の受熱に起因するプレイグニッションを生じ難くできる。 The radial gap between the reduced diameter portion 13 and the distal end portion 40 is smaller than the radial clearance between the first straight portion 12 and the distal end portion 40, but the concave portion 42 is at least reduced in diameter in the distal end portion 40. Since it is formed in the radially outer portion of the portion 13, it is difficult to retain the air-fuel mixture between the reduced diameter portion 13 and the tip portion 40. Therefore, pre-ignition caused by the heat reception of the air-fuel mixture can be made difficult to occur.

凹部４２の後端面４３（図２参照）は、縮径部１３の後端１３ａよりも後端側に位置するので、第２直線部１４の先端側の一部と凹部４２との隙間を大きくできる。その結果、第１空間４４の軸線Ｏ方向の長さを長くできる。なお、凹部４２の後端面４３の位置は、棚部３７の軸線Ｏ方向の厚さが薄くなり過ぎないように、棚部３７の機械的強度を考慮して設定される。 Since the rear end surface 43 (see FIG. 2) of the concave portion 42 is located on the rear end side with respect to the rear end 13a of the reduced diameter portion 13, a gap between a portion on the front end side of the second linear portion 14 and the concave portion 42 is increased. it can. As a result, the length of the first space 44 in the axis O direction can be increased. The position of the rear end surface 43 of the recess 42 is set in consideration of the mechanical strength of the shelf 37 so that the thickness of the shelf 37 in the direction of the axis O is not too thin.

さらに、凹部４２は、棚部３７から先端部４０の先端まで軸線Ｏ方向に延びているので、先端部４０の軸線Ｏ方向の一部に凹部４２が形成される場合に比べて、先端部４０の内側に混合気を滞留させ難くできる。よって、第１空間４４内の混合気の受熱に起因するプレイグニッションを生じ難くできる。 Furthermore, since the recess 42 extends in the axis O direction from the shelf 37 to the tip of the tip 40, the tip 40 is compared to the case where the recess 42 is formed in a part of the tip 40 in the axis O direction. The air-fuel mixture can be made difficult to stay inside. Therefore, preignition caused by heat reception of the air-fuel mixture in the first space 44 can be made difficult to occur.

凹部４２の後端面４３は、棚部３７の先端側の部分を軸線Ｏに垂直に切断するので、後端面４３が棚部３７を切断しない場合に比べて、その分だけ第１空間４４を軸線Ｏ方向に広げることができる。第１空間４４の体積を軸線Ｏ方向に広げることにより、第１空間４４の体積を径方向の外側に広げなくて済むので、その分だけ胴部３５の径方向の厚さ（肉厚）を大きくできる。その結果、胴部３５の機械的強度を確保できる。 Since the rear end surface 43 of the recess 42 cuts the portion on the front end side of the shelf 37 perpendicular to the axis O, the first space 44 is axially increased by that amount compared to the case where the rear end surface 43 does not cut the shelf 37. Can be expanded in the O direction. By expanding the volume of the first space 44 in the direction of the axis O, it is not necessary to expand the volume of the first space 44 outward in the radial direction, so that the thickness (wall thickness) of the body portion 35 in the radial direction is increased accordingly. Can be big. As a result, the mechanical strength of the trunk portion 35 can be ensured.

次に図４を参照して第２実施の形態について説明する。第１実施の形態では、仮想円ｖに対する凹部４２の径方向の深さが、周方向に亘って同一の場合について説明した。これに対し第２実施の形態では、仮想円ｖに対する凹部５１の径方向の深さが異なる場合について説明する。なお、第１実施の形態で説明した部分と同一の部分については、同一の符号を付して以下の説明を省略する。図４は第２実施の形態におけるスパークプラグ５０の断面図である。図４では、図３と同様に、軸線Ｏと直交し縮径部１３及び先端部４０を通る切断面によって切断されたスパークプラグ５０の断面が図示されている（図５から図７においても同じ）。 Next, a second embodiment will be described with reference to FIG. In 1st Embodiment, the case where the depth of the radial direction of the recessed part 42 with respect to the virtual circle v was the same over the circumferential direction was demonstrated. On the other hand, in the second embodiment, a case will be described in which the radial depth of the recess 51 with respect to the virtual circle v is different. In addition, about the part same as the part demonstrated in 1st Embodiment, the same code | symbol is attached | subjected and the following description is abbreviate | omitted. FIG. 4 is a cross-sectional view of the spark plug 50 in the second embodiment. 4, as in FIG. 3, a cross section of the spark plug 50 cut by a cut surface that is orthogonal to the axis O and passes through the reduced diameter portion 13 and the tip portion 40 is shown (the same applies to FIGS. 5 to 7). ).

図４に示すようにスパークプラグ５０は、先端部４０のうち第１空間４４に臨む部分に凹部５１が形成されている。凹部５１の径方向の深さは、凹部５１の周方向の両端から中央へ向かうにつれて、先端部４０の内周の仮想円ｖ（軸線Ｏを中心とする円）に対して次第に増している。これにより、凹部５１によって第１空間４４の体積を第２空間４５の体積より大きくできると共に、凹部５１がなめらかに連なるので、凹部５１が切り欠きとなって先端部４０の機械的強度を低下させないようにできる。 As shown in FIG. 4, the spark plug 50 has a recess 51 formed in a portion of the tip portion 40 facing the first space 44. The depth in the radial direction of the recess 51 gradually increases with respect to the virtual circle v (a circle centered on the axis O) on the inner periphery of the tip 40 as it goes from the circumferential ends of the recess 51 toward the center. As a result, the volume of the first space 44 can be made larger than the volume of the second space 45 by the concave portion 51 and the concave portion 51 is smoothly connected, so that the concave portion 51 is notched and the mechanical strength of the distal end portion 40 is not reduced. You can

次に図５を参照して第３実施の形態について説明する。第１実施の形態および第２実施の形態では、凹部４２，５１が先端部４０の一か所に形成される場合について説明した。これに対し第３実施の形態では、先端部４０の複数か所に凹部６１が形成される場合について説明する。なお、第１実施の形態で説明した部分と同一の部分については、同一の符号を付して以下の説明を省略する。図５は第３実施の形態におけるスパークプラグ６０の軸線Ｏに垂直な断面図である。 Next, a third embodiment will be described with reference to FIG. In 1st Embodiment and 2nd Embodiment, the case where the recessed parts 42 and 51 were formed in one place of the front-end | tip part 40 was demonstrated. On the other hand, 3rd Embodiment demonstrates the case where the recessed part 61 is formed in several places of the front-end | tip part 40. FIG. In addition, about the part same as the part demonstrated in 1st Embodiment, the same code | symbol is attached | subjected and the following description is abbreviate | omitted. FIG. 5 is a cross-sectional view perpendicular to the axis O of the spark plug 60 in the third embodiment.

図５に示すようにスパークプラグ６０は、先端部４０のうち第１空間４４に臨む部分に凹部６１が形成されている。凹部６１は、軸線Ｏ方向（図５紙面に垂直な方向）に延びる溝状に各々が形成され、それらが周方向の複数か所（本実施の形態では５か所）に離れて形成されている。凹部６１が形成された領域の周方向の両端に対して軸線Ｏから引かれた２つの直線４８，４９のなす角θは、６０〜１８０°の所定角度に設定されている。第３実施の形態におけるスパークプラグ６０においても、第１実施の形態と同様の作用効果を実現できる。さらに、先端部４０の内面の表面積を拡大できるので、先端部４０の内面の放熱効果を向上できる。 As shown in FIG. 5, the spark plug 60 has a recessed portion 61 formed in a portion of the tip portion 40 facing the first space 44. The recesses 61 are each formed in a groove shape extending in the direction of the axis O (the direction perpendicular to the paper surface of FIG. 5), and are formed separately at a plurality of locations in the circumferential direction (5 locations in the present embodiment). Yes. An angle θ formed by two straight lines 48 and 49 drawn from the axis O with respect to both ends in the circumferential direction of the region where the recess 61 is formed is set to a predetermined angle of 60 to 180 °. In the spark plug 60 according to the third embodiment, the same function and effect as the first embodiment can be realized. Furthermore, since the surface area of the inner surface of the tip portion 40 can be increased, the heat dissipation effect of the inner surface of the tip portion 40 can be improved.

次に図６を参照して第４実施の形態について説明する。第１実施の形態から第３実施の形態では、先端部４０（主体金具３０）に凹部４２，５１，６１が形成される場合について説明した。これに対し第４実施の形態では、絶縁体１１の外径を小さくする小径部７１が形成される場合について説明する。なお、第１実施の形態で説明した部分と同一の部分については、同一の符号を付して以下の説明を省略する。図６は第４実施の形態におけるスパークプラグ７０の軸線Ｏに垂直な断面図である。 Next, a fourth embodiment will be described with reference to FIG. In the first to third embodiments, the case where the concave portions 42, 51, and 61 are formed in the distal end portion 40 (the metal shell 30) has been described. On the other hand, in the fourth embodiment, a case will be described in which the small diameter portion 71 that reduces the outer diameter of the insulator 11 is formed. In addition, about the part same as the part demonstrated in 1st Embodiment, the same code | symbol is attached | subjected and the following description is abbreviate | omitted. FIG. 6 is a cross-sectional view perpendicular to the axis O of the spark plug 70 in the fourth embodiment.

図６に示すようにスパークプラグ７０は、絶縁体１１のうち第１空間４４に臨む部分に小径部７１が形成されている。小径部７１は、軸線Ｏと直交する断面（図６参照）において、小径部７１と先端部４０との径方向の距離が、絶縁体１１のうち小径部７１以外の他の部位と先端部４０との径方向の距離に比べて大きい部分である。軸線Ｏから小径部７１の周方向の両端に対して引かれた２つの直線７２，７３のなす角θは、６０〜１８０°の所定角度に設定されている。 As shown in FIG. 6, the spark plug 70 has a small-diameter portion 71 formed in a portion of the insulator 11 that faces the first space 44. In the cross section perpendicular to the axis O (see FIG. 6), the small-diameter portion 71 has a radial distance between the small-diameter portion 71 and the distal end portion 40 that is other than the small-diameter portion 71 in the insulator 11 and the distal end portion 40. It is a part larger than the distance in the radial direction. An angle θ formed by two straight lines 72 and 73 drawn from the axis O to both ends in the circumferential direction of the small diameter portion 71 is set to a predetermined angle of 60 to 180 °.

本実施の形態では、小径部７１は、第２直線部１４（図２参照）から縮径部１３にかけて軸線Ｏ方向に延びている。これにより、第１空間４４の体積を拡大するために、絶縁体１１のうち径方向の厚さ（肉厚）が最も薄い第１直線部１２の厚さを薄くしなくて良いので、第１直線部１２の機械的強度が低下しないようにできる。 In the present embodiment, the small diameter portion 71 extends in the axis O direction from the second straight portion 14 (see FIG. 2) to the reduced diameter portion 13. Thereby, in order to expand the volume of the first space 44, the thickness of the first linear portion 12 having the smallest radial thickness (thickness) in the insulator 11 does not have to be reduced. The mechanical strength of the straight line portion 12 can be prevented from decreasing.

なお、中心角が同じであれば絶縁体１１の弧の長さは先端部４０の弧の長さより短いので、先端部４０に凹部４２（図３参照）を形成する方が、小径部７１を形成するよりも第１空間４４の体積を拡大し易い。しかし、第４実施の形態によれば、それ以外は第１実施の形態と同様の作用効果を実現できる。 If the central angles are the same, the length of the arc of the insulator 11 is shorter than the length of the arc of the tip portion 40. Therefore, forming the concave portion 42 (see FIG. 3) in the tip portion 40 causes the small diameter portion 71 to be formed. It is easier to expand the volume of the first space 44 than to form it. However, according to the fourth embodiment, the same operational effects as those of the first embodiment can be realized otherwise.

図７及び図８を参照して、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。なお、第１実施の形態で説明した部分と同一の部分については、同一の符号を付して以下の説明を省略する。図７（ａ）は比較例におけるスパークプラグ８０の断面図であり、図７（ｂ）は実施例１におけるスパークプラグ９０の断面図であり、図７（ｃ）は実施例２におけるスパークプラグ１００の断面図であり、図７（ｄ）は実施例３におけるスパークプラグ１１０の断面図である。図７（ａ）から図７（ｄ）では、図３と同様に、軸線Ｏと直交し縮径部１３及び先端部４０を通る切断面によって切断された断面が図示されている。 The present invention will be described in more detail with reference to FIG. 7 and FIG. 8, but the present invention is not limited to this example. In addition, about the part same as the part demonstrated in 1st Embodiment, the same code | symbol is attached | subjected and the following description is abbreviate | omitted. 7A is a cross-sectional view of the spark plug 80 in the comparative example, FIG. 7B is a cross-sectional view of the spark plug 90 in the first embodiment, and FIG. 7C is a spark plug 100 in the second embodiment. FIG. 7D is a cross-sectional view of the spark plug 110 according to the third embodiment. 7A to 7D, a cross section cut by a cut surface that is orthogonal to the axis O and passes through the reduced diameter portion 13 and the distal end portion 40 is shown, as in FIG.

（比較例）
図７（ａ）に示す比較例におけるスパークプラグ８０は、先端部４０に凹部４２（図１参照）が形成されていないことを除き、第１実施の形態で説明したスパークプラグ１０と同一である。スパークプラグ８０は、平面４７で二分された第１空間４４及び第２空間４５の体積が同一である。 (Comparative example)
The spark plug 80 in the comparative example shown in FIG. 7A is the same as the spark plug 10 described in the first embodiment, except that the concave portion 42 (see FIG. 1) is not formed in the distal end portion 40. . In the spark plug 80, the volumes of the first space 44 and the second space 45 divided by the plane 47 are the same.

（実施例１）
図７（ｂ）に示す実施例１におけるスパークプラグ９０は、先端部４０に凹部９１が形成されている。凹部９１は、棚部３７から先端部４０の先端まで軸線Ｏ方向（紙面に垂直な方向）に延びている。軸線Ｏ周りの凹部９１の角度θ（直線４８，４９のなす角）は６０°である。角度θの二等分線は平面４７に垂直である。第１空間４４の体積は、凹部９１の分だけ第２空間４５の体積より大きい。 Example 1
The spark plug 90 in the first embodiment shown in FIG. 7B has a concave portion 91 formed at the tip end portion 40. The recess 91 extends from the shelf 37 to the tip of the tip 40 in the direction of the axis O (direction perpendicular to the paper surface). The angle θ (angle formed by the straight lines 48 and 49) of the recess 91 around the axis O is 60 °. The bisector of the angle θ is perpendicular to the plane 47. The volume of the first space 44 is larger than the volume of the second space 45 by the amount of the recess 91.

（実施例２）
図７（ｃ）に示す実施例２におけるスパークプラグ１００は、先端部４０に凹部１０１が形成されている。凹部１０１は、棚部３７から先端部４０の先端まで軸線Ｏ方向（紙面に垂直な方向）に延びている。軸線Ｏ周りの凹部１０１の角度θ（直線４８，４９のなす角）は９０°である。角度θの二等分線は平面４７に垂直である。第１空間４４の体積は、凹部１０１の分だけ第２空間４５の体積より大きい。 (Example 2)
The spark plug 100 according to the second embodiment shown in FIG. 7C has a concave portion 101 formed at the distal end portion 40. The recess 101 extends from the shelf 37 to the tip of the tip 40 in the direction of the axis O (direction perpendicular to the paper surface). The angle θ (angle formed by the straight lines 48 and 49) of the recess 101 around the axis O is 90 °. The bisector of the angle θ is perpendicular to the plane 47. The volume of the first space 44 is larger than the volume of the second space 45 by the amount of the recess 101.

（実施例３）
図７（ｄ）に示す実施例３におけるスパークプラグ１１０は、先端部４０に凹部１１１が形成されている。凹部１１１は、棚部３７から先端部４０の先端まで軸線Ｏ方向（紙面に垂直な方向）に延びている。軸線Ｏ周りの凹部１１１の角度θ（直線４８，４９のなす角）は９０°である。凹部１１１の周方向の端の一方と軸線Ｏとを通る直線４９は平面４７に重なり、凹部１１１の他方の端と軸線Ｏとを通る直線４８は平面４７と垂直である。第１空間４４の体積は、凹部１１１の分だけ第２空間４５の体積より大きい。 (Example 3)
The spark plug 110 according to the third embodiment shown in FIG. 7D has a recess 111 at the tip 40. The recess 111 extends from the shelf 37 to the tip of the tip 40 in the direction of the axis O (direction perpendicular to the paper surface). The angle θ (angle formed by the straight lines 48 and 49) of the recess 111 around the axis O is 90 °. A straight line 49 passing through one of the circumferential ends of the recess 111 and the axis O overlaps the plane 47, and a straight line 48 passing through the other end of the recess 111 and the axis O is perpendicular to the plane 47. The volume of the first space 44 is larger than the volume of the second space 45 by the amount of the recess 111.

実施例１から３及び比較例におけるスパークプラグ８０，９０，１００，１１０の平面４７と内燃機関の吸気行程における気流Ｆ（タンブル流）とが直交するように、気流Ｆの上流側に第１空間４４を配置した内燃機関について、燃焼シミュレーションを行った。各部の寸法などのシミュレーションの条件は以下のとおりであった。内燃機関のクランク軸の回転数２０００ｒｐｍ、内燃機関の吸気圧力２００ｋＰａ、スパークプラグの第２直線部１４の外径５．７ｍｍ、第１直線部１２の外径３．４ｍｍ、第１直線部１２の軸線Ｏ方向の長さ７．５ｍｍ、先端部４０の内周面４１と軸線Ｏとの距離３．６ｍｍ、凹部９１，１０１，１１１と軸線Ｏとの距離３．９ｍｍ。 The first space on the upstream side of the airflow F so that the plane 47 of the spark plugs 80, 90, 100, 110 in the first to third embodiments and the comparative example and the airflow F (tumble flow) in the intake stroke of the internal combustion engine are orthogonal to each other. A combustion simulation was performed on the internal combustion engine in which 44 is disposed. The simulation conditions such as the dimensions of each part were as follows. The internal combustion engine crankshaft rotation speed is 2000 rpm, the internal combustion engine intake pressure is 200 kPa, the outer diameter of the second straight portion of the spark plug is 5.7 mm, the outer diameter of the first straight portion is 3.4 mm, the first straight portion is The length in the direction of the axis O is 7.5 mm, the distance between the inner peripheral surface 41 of the tip 40 and the axis O is 3.6 mm, and the distance between the recesses 91, 101, 111 and the axis O is 3.9 mm.

図８は実施例１から３及び比較例におけるスパークプラグ８０，９０，１００，１１０のクランク角（°ＢＴＤＣ）と空間（第１空間４４及び第２空間４５）の平均温度（Ｋ）との関係を示す図である。図中、ａは比較例におけるスパークプラグ８０の平均温度の曲線であり、ｂ，ｃ，ｄはそれぞれ実施例１，２，３におけるスパークプラグ９０，１００，１１０の平均温度の曲線である。横軸は上死点前のクランク角であり、平均温度が急激に上昇する部分（各曲線が立ち上がる部分）のクランク角が小さいほどプレイグニッション（過早着火）が発生し難いことを示している。 FIG. 8 shows the relationship between the crank angle (° BTDC) of the spark plugs 80, 90, 100, and 110 and the average temperature (K) of the space (first space 44 and second space 45) in Examples 1 to 3 and the comparative example. FIG. In the figure, a is a curve of the average temperature of the spark plug 80 in the comparative example, and b, c, d are curves of the average temperature of the spark plugs 90, 100, 110 in Examples 1, 2, and 3, respectively. The horizontal axis is the crank angle before top dead center, and the smaller the crank angle of the part where the average temperature rises rapidly (the part where each curve rises), the less pre-ignition (pre-ignition) occurs. .

図８に示すように、ａの立ち上がりのクランク角に比べてｂ，ｃ，ｄの立ち上がりのクランク角が小さいことから、第１空間４４の体積を第２空間４５の体積よりも大きくすることにより、プレイグニッションを発生し難くできることがわかった。また、ｂの立ち上がりのクランク角に比べてｃの立ち上がりのクランク角が小さいことから、凹部９１，１０１の角度θが大きい方がプレイグニッションを発生し難くできることがわかった。第１空間４４の体積と第２空間４５の体積との差が大きい方が、第１空間４４に混合気を滞留させ難くできるので、混合気の受熱に起因するプレイグニッションを抑制できると推察される。 As shown in FIG. 8, since the rising crank angle of b, c, d is smaller than the rising crank angle of a, the volume of the first space 44 is made larger than the volume of the second space 45. , It was found that it is difficult to generate pre-ignition. In addition, since the crank angle at which c rises is smaller than the crank angle at which b rises, it was found that preignition is less likely to occur when the angle θ of the recesses 91 and 101 is larger. It is presumed that the larger the difference between the volume of the first space 44 and the volume of the second space 45, the harder the air-fuel mixture stays in the first space 44, so that it is possible to suppress preignition caused by heat reception of the air-fuel mixture. The

さらに、図８に示すように、ｃの立ち上がりのクランク角に比べてｄの立ち上がりのクランク角が小さいことから、凹部１１１と接地電極４６とが離れている方がプレイグニッションを発生し難くできることがわかった。凹部１１１と接地電極４６とが離れている方が、第１空間４４の気流を接地電極４６が妨げ難くできるので、混合気の受熱に起因するプレイグニッションを抑制できると推察される。 Furthermore, as shown in FIG. 8, since the rising crank angle of d is smaller than the rising crank angle of c, pre-ignition can be less likely to occur when the recess 111 and the ground electrode 46 are separated. all right. Since the ground electrode 46 can hardly prevent the airflow in the first space 44 when the concave portion 111 and the ground electrode 46 are separated from each other, it is presumed that preignition caused by heat reception of the air-fuel mixture can be suppressed.

図示はしていないが、図７（ｄ）に示すスパークプラグ１１０において、凹部１１１の周方向の端の両端（直線４８，４９）が平面４７に重なるようにすると、直線４８，４９のなす角θは１８０°となる。この場合は、第１空間４４の体積と第２空間４５の体積との差が最も大きくなるので、第１空間４４の気流をさらに滞留させ難くできる。よって、混合気の受熱に起因するプレイグニッションをより抑制できる。 Although not shown, in the spark plug 110 shown in FIG. 7D, if both ends (straight lines 48, 49) of the circumferential end of the recess 111 overlap the plane 47, the angle formed by the straight lines 48, 49 θ is 180 °. In this case, since the difference between the volume of the first space 44 and the volume of the second space 45 is the largest, the airflow in the first space 44 can be further prevented from staying. Therefore, the pre-ignition resulting from the heat reception of the air-fuel mixture can be further suppressed.

また、この実施例によれば、凹部の両端に対して引かれた２つの直線４８，４９のなす角θは、６０〜１８０°の所定角度に設定されるのが好ましいことがわかった。同様に、絶縁体１１に形成される小径部７１（図６参照）の両端に対して引かれた２つの直線７２，７３のなす角θも、６０〜１８０°の所定角度に設定されるのが好ましいと推察される。 Further, according to this embodiment, it was found that the angle θ formed by the two straight lines 48 and 49 drawn with respect to both ends of the recess is preferably set to a predetermined angle of 60 to 180 °. Similarly, an angle θ formed by two straight lines 72 and 73 drawn with respect to both ends of the small diameter portion 71 (see FIG. 6) formed in the insulator 11 is also set to a predetermined angle of 60 to 180 °. Is presumed to be preferable.

以上、実施の形態に基づき本発明を説明したが、本発明は上記実施の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。 The present invention has been described above based on the embodiments. However, the present invention is not limited to the above embodiments, and various improvements and modifications can be made without departing from the spirit of the present invention. It can be easily guessed.

上記各実施の形態では、絶縁体１１と先端部４０との間にできる空間を、接地電極４６の対称面である平面４７で二分して第１空間４４と第２空間とを作ったが、必ずしもこれに限られるものではない。空間を第１空間４４と第２空間とに二分する平面４７は、凹部４２，５１，６１，９１，１０１，１１１や小径部７１の周方向の中心と軸線Ｏとを含む平面以外の平面であれば、接地電極４６と無関係に、任意に設定できる。第２空間４５の体積よりも体積の大きい第１空間４４を、内燃機関（図示せず）の吸気行程における気流Ｆの上流側に配置することより、第１空間４４に混合気を滞留させ難くすることができ、混合気の受熱に起因するプレイグニッションを抑制できるからである。但し、気流Ｆに対する接地電極４６の位置を考慮すれば、プレイグニッションの抑制効果をさらに高めることができる。 In each of the embodiments described above, the space formed between the insulator 11 and the tip portion 40 is divided into two by the plane 47 that is the plane of symmetry of the ground electrode 46 to form the first space 44 and the second space. It is not necessarily limited to this. The plane 47 that divides the space into the first space 44 and the second space is a plane other than the plane including the center in the circumferential direction of the concave portions 42, 51, 61, 91, 101, 111 and the small diameter portion 71 and the axis O. If there is, it can be arbitrarily set regardless of the ground electrode 46. By arranging the first space 44 having a volume larger than the volume of the second space 45 on the upstream side of the air flow F in the intake stroke of the internal combustion engine (not shown), it is difficult for the air-fuel mixture to stay in the first space 44. This is because it is possible to suppress preignition caused by heat reception of the air-fuel mixture. However, if the position of the ground electrode 46 with respect to the airflow F is taken into consideration, the effect of suppressing preignition can be further enhanced.

上記各実施の形態では、第１空間４４の体積を第２空間４５の体積より大きくするために、第１実施の形態から第３実施の形態では先端部４０に凹部４２，５１，６１を形成し、第４実施の形態では絶縁体１１に小径部７１を形成したが、これらを組み合わせることは当然可能である。先端部４０に凹部４２，５１，６１を形成すると共に、絶縁体１１に小径部７１を形成することにより、第１空間４４の体積と第２空間４５の体積との差をより大きくできる。 In each of the above embodiments, in order to make the volume of the first space 44 larger than the volume of the second space 45, the recesses 42, 51, 61 are formed in the tip 40 in the first to third embodiments. And although the small diameter part 71 was formed in the insulator 11 in 4th Embodiment, it is naturally possible to combine these. The difference between the volume of the first space 44 and the volume of the second space 45 can be further increased by forming the concave portions 42, 51, 61 in the tip portion 40 and forming the small diameter portion 71 in the insulator 11.

上記各実施の形態では、主体金具３０の棚部３７と絶縁体１１の張出部１５との間にパッキン３８（他部材）が介在す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。パッキン３８を省略して、棚部３７と張出部１５とを密着させ、棚部３７が張出部１５を直接係止することは当然可能である。この場合、係止部３９は、棚部３７のうち張出部１５が接触する部位である。 In each of the embodiments described above, the case where the packing 38 (other member) is interposed between the shelf portion 37 of the metal shell 30 and the overhanging portion 15 of the insulator 11 is not necessarily limited thereto. . Of course, it is possible that the packing portion 38 is omitted, the shelf portion 37 and the overhang portion 15 are brought into close contact with each other, and the shelf portion 37 directly locks the overhang portion 15. In this case, the locking portion 39 is a portion of the shelf portion 37 that contacts the overhang portion 15.

上記各実施の形態では、主体金具３０の屈曲部３１と絶縁体１１の係合部１６との間に充填材４７を配置す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。充填材４７を省略することは当然可能である。 In each of the above embodiments, the case where the filler 47 is disposed between the bent portion 31 of the metal shell 30 and the engaging portion 16 of the insulator 11 has been described. However, the present invention is not necessarily limited thereto. Of course, the filler 47 can be omitted.

上記各実施の形態では、棚部３７よりも先端側の先端部４０の内周面４１と軸線Ｏとの距離が、棚部３７の内周面３７ｂと軸線Ｏとの距離よりも長くなるように、先端部４０の軸線Ｏ方向の一部に棚部３７が設け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。軸線Ｏを含む断面（図２参照）において、内周面４１と棚部３７の内周面３７ｂとが同一直線上に位置するように、先端部４０の軸線Ｏ方向の全長に亘って棚部３７を設けることは当然可能である。この場合も、絶縁体１１に第１直線部１２及び縮径部１３が設けられているので、第２空間４５を確保できる。 In each of the above embodiments, the distance between the inner peripheral surface 41 of the tip 40 on the tip side of the shelf 37 and the axis O is longer than the distance between the inner periphery 37b of the shelf 37 and the axis O. In addition, although the case where the shelf 37 is provided in a part of the tip portion 40 in the axis O direction has been described, it is not necessarily limited thereto. In the cross section including the axis O (see FIG. 2), the shelf portion extends over the entire length of the tip portion 40 in the axis O direction so that the inner peripheral surface 41 and the inner peripheral surface 37b of the shelf portion 37 are located on the same straight line. It is naturally possible to provide 37. Also in this case, since the first linear portion 12 and the reduced diameter portion 13 are provided in the insulator 11, the second space 45 can be secured.

上記各実施の形態では、主体金具３０に接合された接地電極４６を屈曲させる場合について説明した。しかし、必ずしもこれに限られるものではない。屈曲した接地電極４６を用いる代わりに、直線状の接地電極４６を用いることは当然可能である。この場合には、主体金具３０の先端側を軸線Ｏ方向に延ばし、直線状の接地電極４６を主体金具３０に接合して、接地電極４６の先端部を中心電極２０と対向させる。 In each of the above embodiments, the case where the ground electrode 46 joined to the metal shell 30 is bent has been described. However, it is not necessarily limited to this. Instead of using the bent ground electrode 46, it is naturally possible to use a straight ground electrode 46. In this case, the front end side of the metal shell 30 is extended in the direction of the axis O, the linear ground electrode 46 is joined to the metal shell 30, and the front end portion of the ground electrode 46 is opposed to the center electrode 20.

上記各実施の形態では、接地電極４６の先端部と中心電極２０とを軸線Ｏ上で対向するように接地電極４６を配置する場合について説明した。しかし、必ずしもこれに限られるものではなく、接地電極４６と中心電極２０との位置関係は適宜設定できる。接地電極４６と中心電極２０との他の位置関係としては、例えば、中心電極２０の側面と接地電極４６の先端部とが対向するように接地電極４６を配置すること等が挙げられる。 In each of the above embodiments, the case where the ground electrode 46 is arranged so that the tip of the ground electrode 46 and the center electrode 20 face each other on the axis O has been described. However, the present invention is not necessarily limited to this, and the positional relationship between the ground electrode 46 and the center electrode 20 can be set as appropriate. Other positional relationships between the ground electrode 46 and the center electrode 20 include, for example, arranging the ground electrode 46 so that the side surface of the center electrode 20 and the tip of the ground electrode 46 face each other.

１０，５０，６０，７０，９０，１００，１１０スパークプラグ
１１絶縁体
１２第１直線部
１３縮径部
１３ａ縮径部の後端
１４第２直線部
１５張出部
３０主体金具
３７棚部
３８パッキン（他部材）
３９係止部
４０先端部
４２，５１，６１，９１，１０１，１１１凹部
４４第１空間
４５第２空間
４６接地電極
４７平面
４８，４９平面（直線）
７１小径部
７２，７３直線
Ｏ軸線 10, 50, 60, 70, 90, 100, 110 Spark plug 11 Insulator 12 First straight portion 13 Reduced diameter portion 13a Rear end of reduced diameter portion 14 Second straight portion 15 Overhang portion 30 Metal shell 37 Shelf portion 38 Packing (other parts)
39 Locking portion 40 Tip portion 42, 51, 61, 91, 101, 111 Recess 44 First space 45 Second space 46 Ground electrode 47 Plane 48, 49 Plane (straight line)
71 Small-diameter portion 72, 73 Straight O-axis

Claims

An insulator having an overhang extending in the axial direction from the front end side to the rear end side and projecting radially outward;
A cylindrical metal shell disposed on the outer peripheral side of the insulator, and
The metal shell is a spark plug including a shelf portion having a locking portion to which the protruding portion of the insulator is locked directly or via another member,
When the space formed between the front end portion of the metal shell and the insulator, which is a portion closer to the front end than the locking portion, is bisected by a plane that includes the axis and extends along the axis, A spark plug in which the volume of one space is larger than the volume of the remaining second space.

In a cross section perpendicular to the axis and passing through the tip,
The tip portion is provided with a concave portion that is recessed radially outward on its inner periphery,
The spark plug according to claim 1, wherein an angle formed by two straight lines drawn from the axis to both ends of the concave portion is set to a predetermined angle of 60 to 180 °.

A ground electrode joined to the metal shell,
The spark plug according to claim 2, wherein the ground electrode is joined to a portion of the metal shell other than a portion cut out by two planes including the two straight lines and the axis and sandwiching the concave portion.

Of the insulator, the portion surrounded by the tip portion has a reduced diameter portion whose outer diameter decreases toward the tip side, and a first straight portion connected to the tip of the reduced diameter portion and having a constant outer diameter. And comprising
The spark plug according to claim 2 or 3, wherein the concave portion is provided at least in a portion surrounding the reduced diameter portion of the tip portion.

The spark plug according to any one of claims 2 to 4, wherein the cross section is an arbitrary cross section of the tip portion.

Of the insulator, the portion surrounded by the tip portion is connected to the tip of the second straight portion having a constant outer diameter and the outer diameter is reduced toward the tip side. And comprising
4. The spark plug according to claim 2, wherein the cross section is an arbitrary cross section of a portion of the front end portion that is closer to a front end side than a rear end of the reduced diameter portion of the insulator.

In a cross section perpendicular to the axis and passing through the tip,
The portion surrounded by the tip portion of the insulator includes a small-diameter portion whose radial distance from the inner periphery of the tip portion is larger than that of other portions.
The spark plug according to claim 1, wherein an angle formed by two straight lines drawn from the axis to both ends of the small diameter portion is set to a predetermined angle of 60 to 180 °.