Ngk Spark Plug Company, Limited

Niterra Co., Ltd.

Haruki Yoshida

Kuniharu Tanaka

Toshitaka Honda

Hirokazu Kurono

Hironori Uegaki

Yutaka Yokoyama

Katsuya Takaoka

Takamitsu Mizuno

Hiroki Shimada

Kazuhiro Kurosawa

Yusuke Nomura

Jumpei Isasa

Nobuyoshi Araki

Jumpei Kita

Takuto Koba

Shun Kondo

Toshiki Kon

Yoshitomo Iwasaki

Kengo Fujimura

Michitaka Yamada

Takeshi Sakuma

Toshimasa Saji

Atsushi Tsukada

Noriyuki Tamura

Tomoya Kukino

Toshinori Takeichi

Akira Suzuki

Yuichi Yamada

Tsutomu Shibata

Hisashi Kozuka

Hideto Yamada

Takashi Kasashima

Satoru Ochiai

Seiji Nakano

Keita Nakagawa

Satoshi Yano

Shota Takaenoki

Masaaki Kumagai

Houju Fukushima

Shoma Tsumagari

Naoya Harata

Ayato Kawabe

A spark plug includes a sealing material disposed around a center electrode in an insulator. On a cross section including a center line of an axial hole, one of long sides of a rectangle is set into the insulator along the center line. The rectangle is divided into 20 equal regions in the insulator by dividing each of short sides of the rectangle into two equal parts and dividing each of the long sides of the rectangle into 10 equal parts. The rectangle has a porosity of 5% or less. Among pores that appear in each of the regions, 10 pores having largest areas are selected as specific pores. The specific pores have an average area of 26.3 μmor less. The specific pores include no more than 30 pores having areas of 37 μmor more and no less than eight pores having areas of 51 μmor more.

Spark plug

When a force to bend a spark plug insulator is applied to the spark plug insulator to fracture the spark plug insulator, for a range including a starting point of the fracture out of two ranges into which a fracture surface created by the fracture is divided by a plane which is a plane perpendicular to a direction of the force and includes the axial line, an average of areas of particles appearing in a planar image of the range is 4.4 μmor larger and 8.0 μmor smaller, and a maximum area of the particles is 600 μmor smaller. The particles include large particles having an area of 60 μmor larger and 600 μmor smaller, and, as the large particles, 0.1 particles/mmor more are present per unit area of the planar image.

Spark plug insulator and spark plug

A spark plugof the present invention includes an insulatormade from an alumina-based sintered body and including: a leg portionprovided on a front end side; a middle trunk portionprovided on a rear end side of the leg portionand having a larger diameter than the leg portion; and a flange portionprovided on the rear end side of the middle trunk portionand having a larger diameter than the middle trunk portion. In the spark plug, in a state where a cut surfaceobtained by cutting the middle trunk portionin a direction perpendicular to an axial line AX direction at an arbitrary position in the axial line AX direction is mirror-polished, when 20 observation regions X each being 185 μm×250 μm are set so as not to overlap each other, and with respect to each of a plurality of pores included in the 20 observation regions X, a square value P[μm] of a length P [μm] of a circumference of the pore is obtained, an average value of the square values P[μm] of top 20 pores having the largest square values P[μm] is not greater than 2200 μm, and a proportion T [%] of a total area of all pores included in the 20 observation regions X relative to a total area (100%) of the 20 observation regions X is not greater than 5%.

In a spark plugof the present invention, in a mirror-polished surfaceobtained by mirror-polishing a cut surfaceobtained by cutting an insulatorin a direction perpendicular to an axial line AX direction, at a position separated by 2 mm from a portion having a maximum diameter of a diameter-enlarged portionto a rear end side along the axial line AX direction, when 20 first observation regions X each being 192 μm×255 μm are set so as to each overlap a reference position mbeing a position 0.2 mm in a radial direction from an inner peripheral surfaceside of the insulatorand so as not to overlap each other, a proportion (porosity) of an area of all of pores included in the 20 first observation regions X relative to a total area (100%) of the 20 first observation regions X is not greater than 3.5%, and in a thermally etched surfaceobtained by subjecting the mirror-polished surfaceto thermal etching, when 20 second observation regions Y each being 32 μm×43 μm are set so as to each overlap the reference position mand so as not to overlap each other, a particle size distribution of alumina particles included in the 20 second observation regions Y is regarded as a normal distribution, an average particle diameter of the alumina particles is defined as A, and a standard deviation of a particle diameter of the alumina particles is defined as σ, A is not less than 1.9 μm and not greater than 2.8 μm, and (A+3σ) is not greater than 3.0 μm.

A spark plugof the present invention includes: an insulatormade from an alumina-based sintered body; a center electrode being a bar-like electrode inserted in the insulatorand having, on a rear end side of the center electrode, a diameter-enlarged portion enlarged in a radial direction and engaged with an inner wall of the insulator; and a conductive sealing material provided on the rear end side of the center electrodeinside the insulator. In a mirror-polished surface obtained by mirror-polishing a cut surface obtained by cutting the insulator in a direction perpendicular to the axial line direction, at a position 2 mm from a portion having a maximum diameter of the diameter-enlarged portion to the rear end side along the axial line direction, when 20 observation regions each being 192 μm×255 μm are set so as to each overlap a reference position being a center position between an inner peripheral surface and an outer peripheral surface of the insulator and so as not to overlap each other, an average of a proportion (porosity) of pores included in each observation region is not greater than 3.5% and, with respect to a variation in the proportion (porosity), when a standard deviation is defined as σ, σ is not greater than 0.36.

A spark plug which includes an insulator having an axial hole extending along an axial line, a metallic shell disposed around the insulator, and a center electrode disposed in the axial hole to be located on the forward end side of the axial line is provided. The insulator has a step portion provided on the outer circumferential surface thereof and facing toward the forward end side. The metallic shell has a receiving surface provided on the inner circumferential surface thereof and facing toward the rear end side and with which the step portion is engaged via a packing. A portion of the step portion on the outer circumferential side is a first curved surface being convex toward the forward end side, and a portion of the step portion on the inner circumferential side of the first curved surface is a second curved surface being convex toward the rear end side.

A spark plug according to one embodiment of the present invention includes an insulator formed of an alumina-based sintered body, wherein the insulator contains 90 wt % or more of an aluminum component in terms of oxide, and wherein crystal grains of the insulator has an average grain size of 1.5 mm or smaller and a grain size standard deviation of 1.2 &#x3bc;m or smaller.

An insulator for a spark plug including a first portion; a second portion located on the rear side of the first portion, an outer diameter F at a front end of the second portion being smaller than an outer diameter of the first portion; a third portion located on the front side of the first portion, an outer diameter D at a rear end of the third portion being smaller than the outer diameter of the first portion and the outer diameter F at the front end of the second portion; a first slope portion connecting the first portion and the second portion; and a second slope portion connecting the first portion and the third portion. A length A of the second slope portion and a length B of the first slope portion satisfy 2.0&#x2264;A/B&#x2264;3.9, and 0.50&#x2264;D/F&#x2264;0.88 is satisfied.

Spark plug that has an insulator less likely to be damaged

A spark plug having an insulator with a leg portion whose outer circumferential surface has an arithmetic mean roughness Ra of 0.5 &#x3bc;m or less. The leg portion has a first section, a second section, and a third section. The first section has an outer diameter that decreases toward the forward end of the first section. The second section is located forward of and adjacent to the first section and its outer diameter decreases toward the forward end of the second section. The outer circumferential surface of the second section is located inward of a first straight line passing through the base and forward ends of the outer circumferential surface of the first section. The third section is located forward of and adjacent to the second section. The outer diameter of the third section is equal to or less than a forward end outer diameter Ds of the second section over the entire third section.

The spark plug includes an insulator made from an alumina-based sintered body, and the insulator contains 90 to 98 wt % of an Al component in oxide equivalent. The insulator contains 1 to 5 wt % of an Si component, 0.1 to 1 wt % of an Mg component, 2 wt % or less of a Ca component, 0.3 to 6 wt % of a Ba component, and 0.11 to 5 wt % of a rare earth component, in oxide equivalent. In analysis using a scanning transmission electron microscope with a probe diameter of an electron beam set at 1 nm, Si and a rare earth element are detected at a crystal grain boundary having a thickness of 15 nm or less, and an alkaline earth metal at the crystal grain boundary is less than a detection limit.

Provided is a spark plug capable of ensuring fouling resistance with a simple configuration. An insulator includes a step portion formed on an outer circumferential surface thereof. A center electrode is arranged in an axial hole of the insulator. A cylindrical metal shell having a shelf portion formed on an inner circumferential surface thereof is arranged radially outside the insulator. The insulator further includes a front end portion located frontward of the step portion. An outer circumferential surface of the front end portion has an arithmetic average roughness of 0.5 &#x3bc;m or smaller in a circumferential direction. A recess is formed with a depth of 3 to 20 &#x3bc;m in at least part of an end surface and the outer circumferential surface of the front end portion so as to extend from the front toward the rear.

The spark plug includes an insulator formed of an alumina-based sintered body, and the insulator contains Si, Ba, and a rare earth element. In an analysis of the insulator by using a scanning transmission electron microscope having an electron-probe diameter of 1 nm, Si and a rare earth element are detected at a crystal grain boundary having a thickness of 15 nm or less, a content of an alkaline earth metal is less than a detection limit at the crystal grain boundary, and a diffraction spot is present in an electron diffraction pattern of a portion where Ba is detected.

A spark plug having a resistor disposed between a metal terminal and a center electrode so as to be electrically connected to the metal terminal and the center electrode, wherein the resistor is in contact with an inner circumferential surface of the insulator. On a cross section taken along the axial line so as to include the axial line, in a case where a plurality of points are plotted at predetermined intervals in a direction of the axial line so as to be present on a partial boundary line, within an arbitrary range in the direction of the axial line, of a boundary line between the insulator and the resistor, and a regression line is drawn by a least-squares method with use of the plurality of points, an average value of distances in a direction perpendicular to the regression line between the regression line and the partial boundary line is 0.1 to 0.3 &#x3bc;m.

Disclosed is a spark plug including: an insulator having an axial hole formed along an axis of the spark plug; a center electrode disposed in a front end side of the axial hole; and a metal shell fixed around an outer circumference of the insulator, with a front end portion of the insulator protruding frontward from a front end of the metal shell. The front end portion of the insulator consists only of a first section and a second section located adjacent to and frontward of the first section and having an inner diameter larger than that of the first section. The second section has a chamfered area formed on an inner circumferential surface thereof so as to continue to a front end of the insulator.

Spark plug including an insulator with a front end portion having first and second sections

A spark plug having a center electrode that is formed by joining a conductive portion made of a conductive material and an insulating portion made of an insulating material. A sealing member electrically connects the conductive portion to a resistor. The insulating portion includes a protruding portion at a location on the back side of a back end of the sealing member. The protruding portion is embedded in the resistor.

Growing community of inventors

Tajimi, Japan

Haruki Yoshida