Ngk Spark Plug Company, Limited

Takamitsu Mizuno

Haruki Yoshida

Toshitaka Honda

Jumpei Kita

Atsushi Tsukada

Satoshi Yano

Tsutomu Shibata

Satoru Ochiai

Shinichi Sakurai

Yoshitomo Iwasaki

Masaaki Kumagai

Hoju Fukushima

A spark plug includes an insulator having an axial hole, a center electrode inserted into a forward portion of the axial hole, a terminal electrode inserted into a rear portion of the axial hole, and an interelectrode insert which contains glass and electrically conductive carbon and is disposed in the axial hole between the center electrode and the terminal electrode. The interelectrode insert has a resistance of 1.0 k&#x3a9; to 3.0 k&#x3a9;, and the interelectrode insert has a carbon content of 1.5% by mass to 4.0% by mass at a forward portion located forward of a center point between the rear end of the center electrode and the forward end of the terminal electrode. Furthermore, the forward portion is lower in resistance than a rear portion of the interelectrode insert located rearward of the center point.

Spark plug

A spark plug includes an insulator with a through hole, a center electrode disposed at a tip end side of the through hole, a metal terminal nut disposed at a rear end side of the through hole, a resistor disposed in a position between the center electrode and the metal terminal nut inside of the through hole and apart from the center electrode, and a conductive seal that is disposed between the resistor and the center electrode inside of the through hole and contacts both the center electrode and the resistor. A contact surface between the resistor and the conductive seal includes at least one point where a distance in the central axis direction from a virtual plane that includes a rear end of the resistor and is vertical to the central axis is local maximum, and include at least one point where the distance is local minimum.

A spark plug having a resistor containing SiOand BO. The glass is a phase-separated glass having aggregate phase and an intervening phase. In a cross section of the resistor, when a plurality of imaginary lines perpendicular to an axial line CLare drawn at intervals of 0.1 mm in the direction of the axial line CL, the number of aggregate phase located on each of the imaginary lines is determined, and the average number of aggregate phase per imaginary line is determined for each of a plurality of line groups each comprised of five consecutive imaginary lines, there are three or more consecutive line groups which satisfy the condition that the average number of aggregate phase per imaginary line is larger, by 5 or more, than the minimum average number of aggregate phase per imaginary line among the plurality of line groups.

A spark plug, comprised of: an insulator having an axial bore extending in the direction of an axis, a first inner circumferential surface extending at a forward side of the axial bore, a second inner circumferential surface extending at a rear side of the axial bore and having a diameter greater than that of the first inner circumferential surface, and a ledge connecting the first inner circumferential surface and the second inner circumferential surface; a center electrode having a head supported by the ledge and extending in a space surrounded by the second inner circumferential surface, and a circular columnar leg extending continuously from the forward end of the head in a space surrounded by the first inner circumferential surface; and a seal material for holding the center electrode in the axial bore.

A spark plug having a connecting portion that electrically connects a center electrode with a metal terminal within an axial bore in an insulator. The connecting portion of the spark plug includes a resistor. A center electrode-side resistance, which is the resistance of a portion of the resistor that extends from the center thereof toward the center electrode in the axial direction, is larger than a metal terminal-side resistance, which is the resistance of a portion of the resistor that extends from the center thereof toward the metal terminal.

A spark plug includes an insulator having an axial hole, a metal terminal member having an insert portion and a depression formation zone existing on the insert portion and having depressions, and a metallic shell. The spark plug satisfies the following conditions: (1) the insert portion has a length H of 35 mm or more; (2) the depression formation zone has a length F of 13 mm or more; (3) the insert portion has a smooth surface zone on its outer circumferential surface; (4) the ratio (A/B) between diameter A of a forward end of the insert portion and inside diameter B of the insulator measured at the forward end satisfies the relational expression 0.9&#x2266;A/B&#x2266;0.98; and (5) Vickers hardness of the insert portion measured at the center of a cross section of the insert portion is 150 Hv or more to 350 Hv or less.

A spark plug includes an insulator, a terminal electrode, a center electrode, a resistor, and a glass seal layer. The terminal electrode has: a recess part opened to the front end side and having a depth in a center axis direction of the terminal electrode; and a flat part neighboring the recess part at its outer circumference side. The relationship 0.52&#x2266;B/A&#x2266;0.91 is satisfied, wherein A (mm) represents an area of a region surrounded by an outline of an outer circumference surface of the terminal electrode, and B (mm) which represents an area of a region of the terminal electrode surrounded by an outline of an inner surface of the recess part, in a cross section orthogonal to the center axis and located 0.1 mm away from a front end along the center axis to the rear end side.

A spark plug includes an insulator having an axial hole, a first inner circumferential surface, a second inner circumferential surface whose diameter is greater than that of the first inner circumferential surface, and a ledge portion connecting the first and the second inner circumferential surfaces. The spark plug also includes a center electrode having a large-diameter portion, a projection portion, and a circular columnar leg portion that projects into a space surrounded by the first inner circumferential surface. The spark plug includes a seal portion which fixes the center electrode within the axial hole. When C&#x3c;A, A&#x2212;C&#x2266;B&#x2212;A, where A represents a diameter of an imaginary cylinder having the minimum diameter required for surrounding the projection portion, B represents a maximum diameter of the large-diameter portion, and C represents an average diameter of the leg portion present in the space surrounded by the first inner circumferential surface.

A method for manufacturing an insulator for a spark plug is provided. The method includes: a preparing step; a press pin arranging step; a powder filling step after the press pin arranging step; a cavity blocking step after the powder filling step; a compression molding step after the cavity blocking step; a die releasing step after the compression molding step; and a press pin removing step after the die releasing step.

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Hashima, Japan

Takamitsu Mizuno