Ngk Spark Plug Company, Limited

Naoyuki Mukoyama

Keiji Ozeki

Tomoaki Kato

Hiroyuki Kameda

Daisuke Kasahara

Yuichi Yamada

Tsutomu Kobayashi

Hirotaka Saito

Masahiro Nishida

A spark plug having an insulator with a front end portion having an annular groove opened to a front side around an axial line. The groove has a width of greater than or equal to 0.2 mm in a radial direction. In a cross section including the axial line, a value D/L obtained by dividing, by a length L, a creepage distance D, from a position P on the frontmost side of a region in which a clearance distance between an outer surface of a front end portion and an inner circumferential surface of a metal shell is less than or equal to 0.1 mm to a connection position between an outer surface of the front end portion and the axial hole, is greater than or equal to 1.1.

Spark plug

A spark plug including a bottomed tubular insulator, a tubular metal shell, a conductive layer, and a terminal. The insulator extends along an axial line from a front end side to a rear end side and is closed at a front end. The metal shell has a ledge portion that projects radially inward and locks the insulator from the front end side. The metal shell holds the insulator from an outer peripheral side. The conductive layer covers at least a part of an inner peripheral surface of a portion of the insulator which is located on the front end side with respect to a locking portion locked by the ledge portion. The terminal is electrically connected to the conductive layer and is insulated from the metal shell.

A plasma jet plug includes a rod-shaped central electrode, an insulator having an axial hole, a metal shell disposed around the insulator, an orifice electrode electrically connected to the metal shell and located at a distal end side of the insulator, and a gasket that contacts an outer surface of the insulator and an inner surface of the metal shell. The insulator includes a first member, a second member and an inorganic seal layer. The first member has the axial hole and includes a large-diameter portion and a small-diameter portion. The second member has a through hole into which the small-diameter portion is inserted. The second member has an outer surface that contacts the gasket. The inorganic seal layer seals a gap between the first member and the second member. In a section including the axis, the sum of seal lengths is greater than or equal to 3 mm.

Plasma jet plug

A plasma jet plug has a cavity defined by a surface of a center electrode, an inner surface of an insulator, and a surface of a ground electrode. When a volume of a portion of the cavity on a front side of a front portion of the center electrode is a first volume Vand a volume of a portion of the cavity on a rear side of the front end of the center electrode is a second volume V, the following expression is satisfied:1/2&#x2267;0.20.

Plasma jet spark plug

A spark plug includes a center electrode, an insulator, a metallic shell, and a seal member for providing a seal between the insulator and the metallic shell. The insulator includes a first portion, a second portion located axially forward of the first portion and being smaller than the first portion, and an insulator first-diameter-reducing-portion whose outside diameter reduces forward and which connects the first portion and the second portion. The metallic shell includes a protrusion that includes a metallic shell diameter-reducing-portion whose inside diameter reduces forward. The seal member is disposed between the insulator first-diameter-reducing-portion and the metallic shell diameter-reducing-portion. A relationship &#x3b8;is satisfied, where the angle &#x3b8;is an angle between a straight line orthogonal to the axial line and the outline of the metallic shell diameter-reducing-portion, and the angle &#x3b8;is an angle between the straight line and an outline of the insulator first-diameter-reducing-portion.

A spark plug includes a ceramic insulator having an engagement portion, and a metallic shell provided around the ceramic insulator and having a protrusion. The protrusion has a diameter-decreasing portion, which seats on the engagement portion via an annular seat packing. On a cross section including an axial line, &#x3b8;s&#x3e;&#x3b8;p is satisfied, where &#x3b8;p represents an acute angle (&#xb0;) between a straight line orthogonal to the axial line and the contour of the engagement portion, and &#x3b8;s represents an acute angle (&#xb0;) between a straight line orthogonal to the axial line and the contour of the diameter-decreasing portion. In the aforementioned cross section, Hvo&#x3e;Hvi is satisfied, where Hvo represents the Vickers hardness (Hv) of the seat packing at the midpoint of a first line segment, and Hvi represents the Vickers hardness (Hv) of the seat packing at the midpoint of a second line segment.

Spark plug, and production method therefor

A spark plug includes an insulator, and a metal shell disposed at an outer periphery of the insulator and including a shoulder. The insulator includes a trunk portion, and a leg formed at the tip end side of the trunk portion. The shoulder of the metal shell includes a first shoulder, and a second shoulder formed at the tip end side of the first shoulder. A distance Da between the tip end of the second shoulder and the leg and a distance Db between the tip end of the trunk portion and the second shoulder satisfy a relationship of Da/Db&#x2267;1.1. A distance T between the rear end of the first shoulder and the tip end of the second shoulder and a distance L between the rear end of the first shoulder and a tip end face of the metal shell satisfy a relationship of T/L&#x2266;0.5.

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Nisshin, Japan

Naoyuki Mukoyama