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1. (WO2018029942) SPARK PLUG

Pub. No.:    WO/2018/029942    International Application No.:    PCT/JP2017/019934
Publication Date: Fri Feb 16 00:59:59 CET 2018 International Filing Date: Tue May 30 01:59:59 CEST 2017
IPC: H01T 13/20
Applicants: NGK SPARK PLUG CO., LTD.
日本特殊陶業株式会社
Inventors: TAKEDA Yohei
竹田 蓉平
UEGAKI Hironori
上垣 裕則
Title: SPARK PLUG
Abstract:
The objective of the invention is to improve the durability of a spark plug. This spark plug comprises an insulator having a shaft hole extending along an axial line direction, a central electrode extending along the axial line direction and having a rear end positioned inside the shaft hole, a terminal metal fitting extending along the axial line direction and having a forward end positioned more toward the rear end of the shaft hole than the rear end of the central electrode therein, a resistance body disposed between the terminal metal fitting and the central electrode inside the shaft hole, and a conductive seal layer filling the space between the central electrode and the resistance body inside the shaft hole, thereby separating the central electrode from the resistance body. The conductive seal layer comprises a first layer positioned toward the central electrode and a second layer positioned between the first layer and the resistance body. The thermal expansion coefficients of the resistance body, the first layer, and the second layer are different from one another. The thermal expansion coefficient of the second layer has a value between the thermal expansion coefficient of the first layer and the thermal expansion coefficient of the resistance body.