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PROBLEM TO BE SOLVED: To prevent an ignition plug from breaking at a rear end part of an insulator more securely even when a rear end-side barrel part is long or when a flat part of the insulator is small in area.
SOLUTION: An ignition plug 1 includes an insulator 2 having a shaft hole 4, main metal fittings 3 arranged at an outer periphery of the insulator 2, and a terminal electrode 6 having a leg part 6A inserted into a rear end side of the shaft hole 4 and a head part 6B exposed from a rear end of the insulator 2. The insulator 2 is formed such that a length L of a region exposed from a rear end of the main metal fittings 3 is 28 to 34 mm and an area of the flat part 2F is 25 mm2 or less. An ignition plug 1 like this is such that a thickness (t) of the thinnest part 2A of an insulator 2 is 1.0 mm or larger within a range of 5.5 mm from the rear end of the insulator 2 to a tip side in the direction of an axis CL1. Further, an area D of a region AR where a projection region PA1 of a flat part 2F and a projection region PA2 of a flat part 6F overlap is 8 mm2 or larger.
COPYRIGHT: (C)2013,JPO&INPIT
【課題】後端側胴部が長かったり、絶縁体の平坦部の面積が小さかったりする場合であっても、絶縁体の後端部における破損をより確実に防止する【解決手段】点火プラグ１は、軸孔４を有する絶縁碍子２と、絶縁碍子２の外周に配設される主体金具３と、軸孔４の後端側に挿通される脚部６Ａ、及び、絶縁碍子２の後端から露出する頭部６Ｂを具備する端子電極６とを備える。また、絶縁碍子２は、主体金具３の後端から露出する部位の長さＬが２８ｍｍ以上３４ｍｍ以下とされたり、平坦部２Ｆの面積が２５ｍｍ2以下とされたりする。このような点火プラグ１において、絶縁碍子２の後端から軸線ＣＬ１方向先端側に５．５ｍｍの範囲内において、絶縁碍子２の最薄肉部２Ａの厚さｔが１．０ｍｍ以上とされる。さらに、平坦部２Ｆの投影領域ＰＡ１と平坦部６Ｆの投影領域ＰＡ２とが重なる領域ＡＲの面積Ｄが８ｍｍ2以上とされる。【選択図】 図１
