Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: A connection structure between a center electrode and a metal terminal of a spark plug having a composite part that contains a plurality of secondary particles each formed of a plurality of primary particles of iron-containing oxide as a magnetic substance, and a conductive material coating the plurality of secondary particles. The iron-containing oxide includes at least one of an oxide represented by M1+AOFe2?AO3 (where ?0.5?A?0.5; and M is at least one kind of element selected from the group consisting of Mn, Fe, Co, Ni, Cu, Mg, Zn and Ca) and an oxide represented by Q3Fe5O12 (where Q is at least one kind of element selected from the group consisting of Y, Lu, Yb, Tm, Er, Ho, Dy, Tb, Gd and Sm). In cross section, an average particle size of the primary particles is 0.5 ?m to 100 ?m, an average particle size of the secondary particles is 0.5 mm to 2.0 mm, and a porosity of the inside of the secondary particles is 5% or lower.

Abstract: A spark plug includes a cylindrical metallic shell having a ground electrode at a forward end of the cylindrical metallic shell, a cylindrical insulator held in the metallic shell, a center electrode disposed in the insulator, a resistor element disposed in the insulator and having a forward end located rearward of a rear end of the center electrode, a forward-end-side electrically conductive seal layer disposed in the insulator to be located between the center electrode and the resistor element, and a rear-end-side electrically conductive seal layer disposed in the insulator to be located rearward of the resistor element. The forward end of the resistor element is located forward of the rear end of the metallic shell, and the rear end of the resistor element is located rearward of the rear end of the metallic shell.

Abstract: The spark plug includes: an insulator having a through hole that penetrates therethrough along an axial direction; a center electrode disposed on one end side of the through hole; a metal terminal disposed on the other end side of the through hole; and a conductive seal layer connected to at least one of the center electrode and the metal terminal. The conductive seal layer contains glass and a Cu—Zn alloy. A volumetric percentage of the Cu—Zn alloy in the conductive seal layer is greater than or equal to 44% and not greater than 55%.

Abstract: An electrically-conductive seal portion of a spark plug includes a large-diameter seal portion, a small-diameter seal portion having an outer diameter smaller than an outer diameter of the large-diameter seal portion, and a tapered seal portion disposed between the large-diameter seal portion and the small-diameter seal portion. An insulator includes a flange portion, a first middle-body portion having an outer diameter smaller than an outer diameter of the flange portion, a second middle-body portion having an outer diameter smaller than an outer diameter of the first middle-body portion, and a leg portion having an outer diameter that tapers toward a tip end of the spark plug. The tapered seal portion is disposed inside the first middle-body portion.

Abstract: 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.

Abstract: A spark plug includes a cylindrical metallic shell having a ground electrode at a forward end of the cylindrical metallic shell, a cylindrical insulator held in the metallic shell, a center electrode disposed in the insulator, a resistor element disposed in the insulator and having a forward end located rearward of a rear end of the center electrode, a forward-end-side electrically conductive seal layer disposed in the insulator to be located between the center electrode and the resistor element, and a rear-end-side electrically conductive seal layer disposed in the insulator to be located rearward of the resistor element. The forward end of the resistor element is located forward of the rear end of the metallic shell, and the rear end of the resistor element is located rearward of the rear end of the metallic shell.

Abstract: 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.

Abstract: The spark plug includes: an insulator having a through hole that penetrates therethrough along an axial direction; a center electrode disposed on one end side of the through hole; a metal terminal disposed on the other end side of the through hole; and a conductive seal layer connected to at least one of the center electrode and the metal terminal. The conductive seal layer contains glass and a Cu—Zn alloy. A volumetric percentage of the Cu—Zn alloy in the conductive seal layer is greater than or equal to 44% and not greater than 55%.

Abstract: 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.

Abstract: 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 MSiO2, MMgO, MBaO, and MCaO, respectively, and a sum of MSiO2, MMgO, MBaO, and MCaO is represented by Mt, the grain boundary phase contains these components so as to satisfy conditions (1) to (4) as follows: (1) 0.17?MSiO2/Mt?0.47; (2) 0.005?MMgO/Mt?0.07; (3) 0.29?MBaO/Mt?0.77; (4) 0.03?MCaO/Mt?0.19.

Abstract: An electrically-conductive seal portion of a spark plug includes a large-diameter seal portion, a small-diameter seal portion having an outer diameter smaller than an outer diameter of the large-diameter seal portion, and a tapered seal portion disposed between the large-diameter seal portion and the small-diameter seal portion. An insulator includes a flange portion, a first middle-body portion having an outer diameter smaller than an outer diameter of the flange portion, a second middle-body portion having an outer diameter smaller than an outer diameter of the first middle-body portion, and a leg portion having an outer diameter that tapers toward a tip end of the spark plug. The tapered seal portion is disposed inside the first middle-body portion.

Abstract: 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 MSiO2, MMgO, MBaO, and MCaO, respectively, and a sum of MSiO2, MMgO, MBaO, and MCaO is represented by Mt, the grain boundary phase contains these components so as to satisfy conditions (1) to (4) as follows: (1) 0.17?MSiO2/Mt?0.47; (2) 0.005?MMgO/Mt?0.07; (3) 0.29?MBaO/Mt?0.77; (4) 0.03?MCaO/Mt?0.19.

Abstract: 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.

Abstract: 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. 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 member and the second member. The third conductive sealing portion is disposed on a rear end side of the second member and is in contact therewith.

Abstract: 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.

Abstract: 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 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 member and the second member. The third conductive sealing portion is disposed on a rear end side of the second member and is in contact therewith.