Ngk Spark Plug Company, Limited

Kengo Fujimura

Toshitaka Honda

Hirokazu Kurono

Seiji Nakano

Haruki Yoshida

Takeshi Mitsuoka

Kuniharu Tanaka

Hironori Uegaki

Katsuya Takaoka

Hiroki Takeuchi

Yutaka Yokoyama

Toshimasa Saji

Shota Takaenoki

Shoma Tsumagari

Kimihiro Nishizono

Hiroki Ota

Ryuji Nagae

To prevent a sealant from intruding between a flange and a stepped portion during manufacture of a spark plug and to prevent cracking of an insulator during use of the spark plug, a spark plug includes a center electrode including a flange, an insulator having a through-hole extending in an axial-line direction and holding the center electrode, and a sealant filled in the through-hole to fix the flange and the insulator to each other; the insulator including a stepped portion in which the through-hole reduces a diameter toward a front end side and that supports the flange, and a small-diameter portion that is continuous with a front end side of the stepped portion and in which the diameter of the through-hole is smaller than in the stepped portion; an angle &#x3b8;formed by the stepped portion and a plane perpendicular to the axial line and an angle &#x3b8;formed by the plane perpendicular to the axial line and an opposing surface of the flange opposing the stepped portion satisfies &#x3b8;&#x2265;6&#xb0;, and in a cross section including the axial line, a maximum diameter Dof the flange and a diameter Dof the through-hole at a rear end of the small-diameter portion in the axial-line direction satisfy 0.15 mm&#x2264;(D&#x2212;D)/2.

Spark plug

An ignition plug comprising: an insulator having a through hole extending from a rear-end side toward a forward-end side; a center electrode inserted at least partially into a portion of the through hole on the forward-end side; a metal terminal member inserted at least partially into a portion of the through hole on the rear-end side; and a seal disposed within the through hole and in contact with the center electrode and an inner circumferential surface of the insulator. The seal contains a glass and an electrically conductive substance, and the glass contained in the seal contains Si in an amount of 50 mass % or more as reduced to SiOand Na in an amount of 0.1 mass % or more and less than 1 mass % as reduced to NaO.

Ignition plug

A spark plug enabling suppression of reduction in the strength of an insulator. In the spark plug, a rear end portion of an engagement portion formed on an outer peripheral surface of a tubular insulator extending along an axial line from a front side to a rear side, is engaged with a to-be-engaged portion of a tubular metal shell disposed on the outer peripheral surface of the insulator. The insulator is made from ceramic such as alumina. On at least a part of the outer peripheral surface of the insulator, a projected and recessed portion is formed on the front side relative to the engagement portion so as to helically extend in a circumferential direction of the insulator.

An insulator is rendered less breakable. A spark plug insulator is a tube-shaped spark plug insulator having a through hole extending in a direction of an axial line. The spark plug insulator contains alumina as a main component and mullite at at least part of the insulator. Mullite is contained in only an inner circumferential surface of the tube-shaped spark plug insulator and in at least part of the inner circumferential surface of the spark plug insulator in an area extending toward a distal end from a portion having a largest outer diameter.

Spark plug insulator containing mullite and spark plug including same

A spark plug with an insulator that includes: a first portion having a first inner diameter with a front end of a trunk portion of a metal terminal disposed therein; a second portion having a second inner diameter larger than the first inner diameter, and including a portion 1 mm or more forward of a rear end of the insulator; and a third portion disposed between the first portion and the second portion and having a third inner diameter larger than the first inner diameter and smaller than the second inner diameter. The trunk portion of the metal terminal includes: a front trunk portion and a rear trunk portion with a front end of the rear trunk portion positioned forward of a rear end of the third portion of the insulator, the rear trunk portion having an outer diameter larger than the outer diameter of the front trunk portion.

An insulator used in a spark plug having improved strength and dielectric strength performance. The insulator comprises a sintered compact whose main constituent is alumina. In the sintered compact, a content ratio of a rare earth element (R. E.) and a group 2 element (2A) satisfies 0.1&#x2266;R. E./2A &#x2266;1.4, and the content ratio of the R. E. and barium oxide (BaO) satisfies 0.2&#x2266;BaO/R. E.&#x2266;0.8. At least one virtual rectangular frame of 7.5 &#x3bc;m&#xd7;50 &#x3bc;m surrounding crystals containing the rare earth element lies within a region of 630 &#x3bc;m&#xd7;480 &#x3bc;m in any cross section of the sintered compact.

Insulator and spark plug

An insulator for spark plug with a main constituent of alumina and containing silicon includes a grain boundary phase positioned between alumina particles. The grain boundary phase contains: a group 2A element; a rare earth element; and at least one kind of zirconium, titanium, chrome, niobium, manganese, and iron (a first element). Assuming that a total amount of the rare earth element is X (mass %), a total amount of the group 2A element is Y (mass %), and a total amount of the first element is Z (mass %), the following are met:0.40&#x2266;20.10&#x2266;0.40.

Insulator for spark plug and spark plug

A spark plug includes: a center electrode including a rod portion and a head portion and having a diameter larger than the diameter of the rod portion; an insulator having an axial bore, the center electrode being disposed in the axial bore at its front end; and a seal portion for fixing the center electrode in the axial bore. The insulator comprises: a leg portion inner circumferential surface; a cylindrical trunk portion inner circumferential surface which surrounds the head portion; and a support surface which supports the head portion. The seal portion has: a seal portion outer circumferential surface; a seal portion abutment surface; and a connecting surface. In a cross section of the seal portion, a curve, which is part of the contour of the seal portion and is included in the connecting surface, has a radius of curvature R of 0.1 mm or more.

Growing community of inventors

Ichinomiya, Japan

Kengo Fujimura