JPH0272577A - Ignition plug of internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent abrasion of an electrode, by continuously equipping a bottom wall at the end of a cylindrical insulator to cover the bottom inner side of an outer electrode upto a vicinity of an orifice thereof. CONSTITUTION:A bottom wall 4a is continuously equipped at the end of an insulator 4, an outlet 7 of approximately same diameter as that of an orifice 6 is provided in the center thereof, and a discharging space 8 is produced across a gap G between a center electrode 2 and an outer electrode 5. Since a volume produced by this gap G and the discharging space 8 must be arranged at a specified level determined by a voltage and a required plasma gas generating volume, the shape of the discharging space 8 is made flat in a large diameter by projecting the bottom wall 4a of the insulator 4 and the center electrode 2 in a large diameter is employed. Therefore an electric current density in the center electrode 2 is lowered and abrasion of the discharging surface may be reduced. Thereby the abrasion of both electrodes 2 and 5 may be prevented.

Description

【発明の詳細な説明】 （産業上の利用分野） 本発明は、内燃機関の点火に使用されプラズマジェット
で点火する点火プラグに関する。DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a spark plug used for ignition of an internal combustion engine and ignited by a plasma jet.

（従来の技術） この種の点火プラグは、一般に第４図に示すように中心
電極ａ１絶縁体す、外側電極Ｃとこれらで囲まれる放電
空間ｄ１外側電極の底部ｅに設けたオリフィスｆを備え
、両電極間にギャップＧをもつものであり、両電極間の
放・電によって生成する高温のプラズマガスをオリフィ
スｆから噴出させて混合気に点火する（特開昭５７−１
５３７８）。(Prior Art) As shown in FIG. 4, this type of spark plug generally includes a center electrode a1, an insulator, an outer electrode C, a discharge space d1 surrounded by these, and an orifice f provided at the bottom e of the outer electrode. , which has a gap G between both electrodes, and the high-temperature plasma gas generated by the discharge between the two electrodes is ejected from the orifice f to ignite the air-fuel mixture (Japanese Patent Laid-Open No. 57-1
5378).

（発明が解決しようとする課題） この点火プラグは、陽イオンの入る中心電極側に電極の
摩耗が生じ易く、一方、外側電極側では該電極が高温の
プラズマガスとシリンダ内の燃焼ガスで内外から加熱さ
れるため、混合気中の酸素により酸化摩耗が生じ易い。(Problems to be Solved by the Invention) In this spark plug, electrode wear tends to occur on the center electrode side, where positive ions enter, while on the other hand, on the outer electrode side, the electrode is exposed to high temperature plasma gas and combustion gas in the cylinder. Since the fuel is heated from the ground, oxidative wear is likely to occur due to the oxygen in the air-fuel mixture.

したがって、本発明は、このような電極の摩耗を防止す
ることを課題とす′る。Therefore, it is an object of the present invention to prevent such electrode wear.

（課題を解決するための手段） 本発明の前記課題の解決手段は、中心電極と底部にオリ
フィスを設けた有底筒状の外側電極の間に円筒状絶縁体
を介設し、両電極の間に放電空間を形成したプラズマジ
ェット式の内燃機関の点火プラグにおいて、円筒状絶縁
体の端部に、外側電極の底部内面をオリフィス付近まで
覆う底壁を連設したことを特徴とする特（作　用） 前記の構成であるから、一定のプラズマガスを発生させ
るために両電極間のギャップ及び放電空間の容積を一定
の値にすると、放電空間が扁平形になるため中心電極の
断面積を太き（することができて、電流密度が小さくな
り摩耗が少なくなる。また、外側電極の内面側は、絶縁
体の底壁で覆われているため、放電空間内のプラズマガ
スからの加熱は抑制され、外側電極の酸化摩耗も少なく
なる。(Means for Solving the Problems) A means for solving the above problems of the present invention is to interpose a cylindrical insulator between the center electrode and a bottomed cylindrical outer electrode having an orifice at the bottom, and to In a spark plug for a plasma jet internal combustion engine in which a discharge space is formed between, a special feature ( Effect) With the above configuration, if the gap between both electrodes and the volume of the discharge space are set to constant values in order to generate a constant plasma gas, the discharge space will become flat, so the cross-sectional area of the center electrode will be reduced. The inner surface of the outer electrode is covered with an insulating bottom wall, so heating from the plasma gas in the discharge space is prevented. oxidative wear of the outer electrode is also reduced.

（実施例） 以下、図面を参照して実施例を説明する。第１図、第２
図において１は点火プラグ、２は中心電極、３は中心電
極２に接続する端子、４は絶縁体、５は外側電極、５ａ
は外側電極と一体の底部で中心にオリフィス６を備え、
画電極２゜５間にはギャップＧを有する。絶縁体４の端
部には底壁４ａが連設されてその中心にオリフィス６と
略等しい径の出ロアが設けられ、ギャップＧの間で放電
空間８が形成されている。(Example) Hereinafter, an example will be described with reference to the drawings. Figures 1 and 2
In the figure, 1 is a spark plug, 2 is a center electrode, 3 is a terminal connected to the center electrode 2, 4 is an insulator, 5 is an outer electrode, 5a
is equipped with an orifice 6 in the center at the bottom integrated with the outer electrode,
There is a gap G between the picture electrodes 2.5. A bottom wall 4a is connected to the end of the insulator 4, and a lower outlet having a diameter substantially equal to that of the orifice 6 is provided at the center thereof, and a discharge space 8 is formed between the gap G.

このギャップＧと放電空間８の容積は、電圧及び必要と
するプラズマガス発生量より決まる一定の値にしなけれ
ばならないから、絶縁体４の底壁４ａを張出したことに
より、放電空間８の形状は、従来のものに比べて扁平か
つ大径になり、中心電極２として大径のものが使用でき
る。This gap G and the volume of the discharge space 8 must be set to constant values determined by the voltage and the required amount of plasma gas generation, so by extending the bottom wall 4a of the insulator 4, the shape of the discharge space 8 can be changed. , it is flatter and has a larger diameter than the conventional one, and a large diameter one can be used as the center electrode 2.

これにより中心電極２の電流密度は低くなり、放電面の
摩耗が軽減される。This lowers the current density of the center electrode 2 and reduces wear on the discharge surface.

一方、外側電極５の底部５ａは、底壁４ａによって覆わ
れているから、放電空間８内のプラズマガスから受ける
熱量は抑制されて高温にならない。このため該電極５が
混合気中の酸素で酸化されて摩耗する量も減少される。On the other hand, since the bottom portion 5a of the outer electrode 5 is covered by the bottom wall 4a, the amount of heat received from the plasma gas in the discharge space 8 is suppressed and does not reach a high temperature. Therefore, the amount of wear of the electrode 5 due to oxidation by oxygen in the air-fuel mixture is also reduced.

第２図のプラグのオリフィス６は、絶縁体との開ロアよ
り仁かに小径であるが、これを同径としてもよいし、第
３図のようにオリフィス６を開口・７より大径にしても
放電に支障は生じることな（同一の効果を奏する。The orifice 6 of the plug shown in Figure 2 has a slightly smaller diameter than the open lower part of the insulator, but it may be the same diameter, or the orifice 6 can be made larger in diameter than the opening 7 as shown in Figure 3. However, there is no problem with discharge (the same effect is produced).

（発明の効果） 以上のように、本発明は、絶縁体の底壁で外側電極の底
部を覆うことにより、外側電極の高温化を防止して酸化
摩耗を減少させ、また放電空間の大径化により中心電極
を大径にしてその放電面の摩耗を減少し、簡単な手段で
画電極の摩耗が防止でき、低コストですぐれた効゛果を
奏する。(Effects of the Invention) As described above, the present invention prevents the temperature of the outer electrode from increasing and reduces oxidative wear by covering the bottom of the outer electrode with the bottom wall of the insulator, and also reduces the oxidation wear due to the large diameter of the discharge space. By increasing the diameter of the center electrode, the wear of the discharge surface is reduced, and the wear of the picture electrode can be prevented by a simple means, resulting in excellent effects at low cost.

【図面の簡単な説明】[Brief explanation of the drawing]

第１図は本発明の実施例の正面図、第２図は第１図のＡ
部拡大図、第３図は変形例の要部断面図、第４図は従来
例の断面図である。 ２・・・中心電極　　　　４・・・絶縁体４ａ・・・底
壁　　　　　　５・・・外部電極５ａ・・・底部　　　
　　　６・・・オリフィス第２図Figure 1 is a front view of an embodiment of the present invention, and Figure 2 is A of Figure 1.
FIG. 3 is a sectional view of a main part of a modified example, and FIG. 4 is a sectional view of a conventional example. 2... Center electrode 4... Insulator 4a... Bottom wall 5... External electrode 5a... Bottom part
6... Orifice diagram 2

Claims (1)

【特許請求の範囲】[Claims] 中心電極と底部にオリフィスを設けた有底筒状の外側電
極の間に円筒状絶縁体を介設し、両電極の間に放電空間
を形成したプラズマジェット式の内燃機関の点火プラグ
において、円筒状絶縁体の端部に、外側電極の底部内面
をオリフィス付近まで覆う底壁を連設したことを特徴と
する、内燃機関の点火プラグ。In spark plugs for plasma jet internal combustion engines, a cylindrical insulator is interposed between a center electrode and a bottomed cylindrical outer electrode with an orifice at the bottom to form a discharge space between the two electrodes. A spark plug for an internal combustion engine, characterized in that a bottom wall covering the bottom inner surface of an outer electrode up to the vicinity of an orifice is connected to an end of a shaped insulator.