Ngk Spark Plug Company, Limited

Hirokazu Kurono

Toshitaka Honda

Kuniharu Tanaka

Katsuya Takaoka

Hironori Uegaki

Haruki Yoshida

Kazuhiro Kurosawa

Takeshi Mitsuoka

Hiroki Takeuchi

Yutaka Yokoyama

Toshimasa Saji

Kengo Fujimura

Jumpei Isasa

Shun Kondo

Tomoaki Kato

Makoto Kuribayashi

Yusuke Nomura

Seiji Nakano

Nobuyoshi Araki

Hiroyuki Hazama

Kota Yokoyama

Akira Suzuki

Masahiro Konishi

Hisashi Kozuka

Takashi Kasashima

Jumpei Kita

Toshiki Kon

Toshinori Takeichi

Kazumichi Hirose

Kazuya Matsui

Hiroyuki Kawaji

Mitsushiro Kondo

Kazunari Miyata

Hiroshi Nishihara

Ryuji Nagae

Syuuichiro Wakizoe

Junpei Kita

Mitushiro Kondo

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.

Spark plug

An employed rear mold is comprised of a plurality of mold pieces. The plurality of mold pieces include a first mold piece which forms a first partial internal surface of the internal surface of the rear mold along the entire circumference of the internal surface, and a second mold piece which is located axially forward of the first mold piece and forms a second partial internal surface of the internal surface of the rear mold along the entire circumference of the internal surface. Releasing the molded body includes starting to move the first mold piece rearward in relation to a rear molded portion, and, subsequently to starting to move the first mold piece, starting to move the second mold piece rearward in relation to the rear molded portion, thereby disassembling the rear mold into the plurality of mold pieces.

Spark plug insulator production method, insulator, molding die

A method for manufacturing an insulator for a spark plug includes a molding process of forming a cylindrical molded product having an axial hole that extends in a direction of an axial line, by means of injection molding using a mold that has a columnar cavity therein and a bar-shaped member disposed in the cavity and extending in the direction of the axial line. In this method, the molding process includes an injection step of injecting a material containing a ceramic. In the injection step, the material is injected into the cavity from a plurality of injection openings that are opened at an inner circumferential surface, of the mold, that forms the cavity. The plurality of injection openings include two or more injection openings located at different positions in the direction of the axial line, or two or more injection openings located at different positions in a circumferential direction.

Method for manufacturing insulator for spark plug

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.

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.

A spark plug having a connection portion disposed between a metal terminal and a center electrode. The connection portion includes: a magnetic substance formed from a Fe-containing oxide; a conductor which is a wire helically disposed on an outer periphery of the magnetic substance and electrically connected to the metal terminal and the center electrode; and an intermediate member which is in contact with the magnetic substance, the conductor, and an inner peripheral surface of the insulator, is disposed between the magnetic substance and the conductor, and the inner peripheral surface of the insulator, and has lower electrical conductivity than the conductor. The conductor is made of one or more of an oxide conductor, carbon, and a carbon compound.

Spark plug including a magnetic substance and a conductor disposed thereon

A spark plug having a connection portion disposed in the axial hole and between a metal terminal and a center electrode. The connection portion includes: a magnetic substance formed from a Fe-containing oxide; a conductor helically disposed on an outer periphery of the magnetic substance and electrically connected to the metal terminal and the center electrode; and an intermediate member disposed between the magnetic substance and the conductor, and an inner peripheral surface of the insulator and having lower electrical conductivity than the conductor. The conductor includes a base and a conductive layer disposed on an outer periphery of the base and having higher electrical conductivity than the base, and the conductive layer has a thickness of larger than 0.1 &#x3bc;m and equal to or smaller than 25 &#x3bc;m.

A spark plug including a metal shell having a ground electrode, a cylindrical ceramic insulator held in the metal shell and having therein an axial hole having a small-diameter portion, and a large-diameter portion larger in diameter than the small-diameter portion and connected to a rear end of the small-diameter portion via a stepped portion, a resistor arranged in the large-diameter portion, a center electrode having: a flange portion projecting in a radial direction in the large-diameter portion to contact with the stepped portion; and a leg portion arranged in the small-diameter portion so as to extend from the flange portion toward the front end side, and a seal body arranged in the large-diameter portion and electrically connecting between the center electrode and the resistor. The seal body includes an insulating seal body that comes into contact with the ceramic insulator, and a conductive seal body.

An alumina-based sintered body includes 92 mass % to 96 mass % of Al in terms of an oxide, and at least three elements selected from Group II elements, one of the at least three elements being 1.90 mass % or more of Ba in terms of an oxide. The alumina-based sintered body includes the following phases in a grain boundary phase present between alumina crystal grains: a first crystal phase containing Si and at least one of the Group II elements, and a second crystal phase containing Al and at least one of the Group II elements. In X-ray diffraction of the alumina-based sintered body, the maximum relative intensity of the first crystal phase and the maximum relative intensity of the second crystal phase are both 2 or above relative to the maximum diffraction intensity of the alumina crystal.

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.

Disclosed is a spark plug capable of suppressing high-frequency noise by improving the material of an electrical connection part between a center electrode and a metal terminal within an axial hole of an insulator. A spark plug has an electrical connection part arranged in an axial hole of an insulator to establish electrical connection between a center electrode and a metal terminal. The electrical connection part includes a conductor having a first crystal phase formed of a Fe-containing oxide and a second crystal phase formed of a conductive metal oxide of perovskite crystal structure.

A spark plug including a metallic shell having a ground electrode, an insulator held inside the metallic shell and having an axial hole having a small diameter portion, an intermediate diameter portion connected to a rear end of the small diameter portion via a step portion, and a large diameter portion disposed on the rear side of the intermediate diameter portion, a resistor disposed inside the large diameter portion, a center electrode having a flange portion which bulges in a radial direction inside the intermediate diameter portion and comes into contact with the step portion and a leg portion which extends forward from the flange portion and is disposed inside the small diameter portion, and a seal disposed on the rear side of the step portion and electrically connecting the center electrode and the resistor. The rear end of the seal is located inside the intermediate diameter portion.

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 including an insulator containing not less than 92 mass % and not greater than 96 mass % of Al component in terms of oxide, wherein the insulator is formed from an alumina sintered body comprising alumina crystal and a grain boundary phase present between crystal grains of the alumina crystal. Assuming that mass contents of an Si component, an Mg component, a Ba component, and a Ca component in terms of oxide are represented by M, M, M, and M, respectively, and a sum of M, M, M, and Mis represented by Mt, the grain boundary phase contains these components so as to satisfy conditions (1) to (4) as follows: (1) 0.17&#x2266;M/Mt&#x2266;0.47; (2) 0.005&#x2266;M/Mt&#x2266;0.07; (3) 0.29&#x2266;M/Mt&#x2266;0.77; (4) 0.03&#x2266;M/Mt&#x2266;0.19.

A connection portion connecting a center electrode and a terminal metal fixture together in a through hole of the insulator includes a resistor and a magnetic substance structure including a magnetic substance and a conductor and being disposed on a leading end side or a rear end side of the resistor while being positioned away from the resistor. The connection portion further includes a first conductive sealing portion, a second conductive sealing portion and a third conductive sealing portion. The first conductive sealing portion is disposed on a leading end side of a first member and is in contact therewith. The second conductive sealing portion is disposed between the first member and a second member and is in contact with the first and second members. The third conductive sealing portion is disposed on a rear end side of the second member and is in contact therewith.

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Nagoya, Japan

Hirokazu Kurono