The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Feb. 20, 2001
Filed:
Aug. 26, 1998
Yutaka Tanaka, Aichi, JP;
Makoto Sugimoto, Aichi, JP;
NGK Spark Plug Co., Ltd., Aichi, JP;
Abstract
In a spark plug, a resistor is placed between a terminal and a center electrode within a through hole of an insulator. The through hole of the insulator has a first portion which allows the center electrode to be inserted therethrough, and a second portion which is formed on a rear side of the first portion so as to be larger in diameter than the first portion and which accommodates the resistor therein, where the second portion is connected to the first portion via a connecting portion including a two- or more-stepped reduced-diameter portion. Then, an electrically conductive glass seal layer is placed at a position corresponding to the connecting portion between the resistor and the center electrode. When the glass seal layer is formed by filling electrically conductive glass powder and its heating and compression, the pressurizing cross-sectional area in the axial direction is reduced to an extent of diameter reduction by the reduced-diameter portion of the connecting portion, so that a sufficient compressing force can be ensured in the event that the pressurizing force is lost, for example, due to friction between the upper filler material (e.g., resistor material powder) and the wall surface of the through hole. By virtue of this arrangement, the sintering of the glass seal layer progresses sufficiently so that the burns of carbon in the glass seal portion and the oxidization of metal components become unlikely to occur. Thus, such trouble as increase in conduction resistance can be avoided over a long term.