Abstract: 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 ?m or smaller.

Abstract: Disclosed is a spark plug including: an insulator having an axial through hole formed with a first hole region and a second hole region larger in inner diameter than the first hole region; a center electrode having a collar portion disposed in the second hole region; a resistor disposed in the second hole region, with a front end of the resistor being located apart from a rear end of the center electrode; and a conductive seal material arranged at least between the center electrode and the resistor within the second hole region, wherein the center electrode has a recess recessed from the rear end thereof toward the front, wherein the recess is provided at least at a location of a maximum outer diameter section of the collar portion, and wherein the conductive seal material is filled into the recess from the rear end of the center electrode.

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 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: 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 ?m or smaller.

Abstract: Disclosed is a spark plug including: an insulator having an axial through hole formed with a first hole region and a second hole region larger in inner diameter than the first hole region; a center electrode having a collar portion disposed in the second hole region; a resistor disposed in the second hole region, with a front end of the resistor being located apart from a rear end of the center electrode; and a conductive seal material arranged at least between the center electrode and the resistor within the second hole region, wherein the center electrode has a recess recessed from the rear end thereof toward the front, wherein the recess is provided at least at a location of a maximum outer diameter section of the collar portion, and wherein the conductive seal material is filled into the recess from the rear end of the center electrode.

Abstract: A spark plug includes: an insulator having an axial hole formed therein in an axial direction; a center electrode extending in the axial direction and having a rear end located within the axial hole; a metal terminal extending in the axial direction and having a front end located rearward of the rear end of the center electrode within the axial hole; a resistor arranged between the center electrode and the metal terminal within the axial hole; and a conductive seal layer that fills a space between the resistor and the center electrode in the axial. The conductive seal layer has a first layer portion located adjacent to the center electrode and a second layer portion located between the first layer portion and the resistor. The second layer portion has a thermal expansion coefficient different from and falling between those of the first layer portion and the resistor.

Abstract: 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 ?m.

Abstract: A spark plug includes: an insulator having an axial hole formed therein in an axial direction; a center electrode extending in the axial direction and having a rear end located within the axial hole; a metal terminal extending in the axial direction and having a front end located rearward of the rear end of the center electrode within the axial hole; a resistor arranged between the center electrode and the metal terminal within the axial hole; and a conductive seal layer that fills a space between the resistor and the center electrode in the axial. The conductive seal layer has a first layer portion located adjacent to the center electrode and a second layer portion located between the first layer portion and the resistor. The second layer portion has a thermal expansion coefficient different from and falling between those of the first layer portion and the resistor.

Abstract: 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.

Abstract: 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 ?m and equal to or smaller than 25 ?m.

Abstract: 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 ?m.

Abstract: 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.

Abstract: 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 ?m and equal to or smaller than 25 ?m.

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: The present invention allows reduction in high frequency noise of a spark plug. A Fe-containing oxide layer is formed on the surface of a beneath-flange rod-shaped portion, of a metal terminal of the spark plug, between a terminal flange portion and an upper end of a metal shell. The surface area of the Fe-containing oxide layer is not less than 10% of the surface area of the beneath-flange rod-shaped portion.

Abstract: A spark plug has an insulator, a rod-shaped electrode member disposed in an axial hole of the insulator, and a cylindrical magnetic member disposed on an outer circumference of the electrode member within the axial hole. The insulator includes a large inner diameter region, a middle inner diameter region located frontward of the large inner diameter region and having an inner diameter smaller than that of the large inner diameter region, and a small inner diameter region located frontward of the middle inner diameter region and having an inner diameter smaller than that of the middle inner diameter region. The electrode member is retained on a step portion of the insulator between the middle inner diameter region and the small inner diameter region. The magnetic member is positioned in the axial hole at a location within the large inner diameter region.

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 has an insulator, a rod-shaped electrode member disposed in an axial hole of the insulator, and a cylindrical magnetic member disposed on an outer circumference of the electrode member within the axial hole. The insulator includes a large inner diameter region, a middle inner diameter region located frontward of the large inner diameter region and having an inner diameter smaller than that of the large inner diameter region, and a small inner diameter region located frontward of the middle inner diameter region and having an inner diameter smaller than that of the middle inner diameter region. The electrode member is retained on a step portion of the insulator between the middle inner diameter region and the small inner diameter region. The magnetic member is positioned in the axial hole at a location within the large inner diameter region.

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.