Abstract: A method of manufacturing a spark plug including a cylindrical tubular metallic shell having a screw portion on an outer surface thereof and a ground electrode attached to an end surface at one end of the metallic shell in the direction of the center axis thereof comprises a measurement step of measuring a surface of the screw portion which passes through a measurement region located at a predetermined position in the direction of the center axis, while rotating the metallic shell about the center axis thereof; an attachment position calculation step of calculating, on the basis of information obtained in the measurement step, an attachment position at which the ground electrode is attached to the end surface; and a joining step of joining the ground electrode to the end surface at the attachment position, wherein the measurement step includes a step of measuring a displacement of the surface of the screw portion by using a non-contact-type displacement sensor.

Abstract: A method of manufacturing a spark plug including a cylindrical tubular metallic shell having a screw portion on an outer surface thereof and a ground electrode attached to an end surface at one end of the metallic shell in the direction of the center axis thereof comprises a measurement step of measuring a surface of the screw portion which passes through a measurement region located at a predetermined position in the direction of the center axis, while rotating the metallic shell about the center axis thereof; an attachment position calculation step of calculating, on the basis of information obtained in the measurement step, an attachment position at which the ground electrode is attached to the end surface; and a joining step of joining the ground electrode to the end surface at the attachment position, wherein the measurement step includes a step of measuring a displacement of the surface of the screw portion by using a non-contact-type displacement sensor.

Abstract: A method for manufacturing a spark plug includes an assembling step of assembling an insulator into a metallic shell by insertion of the insulator into the metallic shell from an axially rear end opening portion of the metallic shell. The assembling step includes a displacement restricting step of restricting a relative positional displacement between the metallic shell and the insulator in a radial direction intersecting with the axial direction so as to reduce eccentricity between the axis of the metallic shell and the axis of the insulator to a predetermined value or less, while allowing a relative positional displacement between the metallic shell and the insulator in the axial direction. In the assembling step, whether or not the insulator is cracked in the assembling step is judged by detecting acoustic emission from the insulator.

Abstract: A spark plug includes a metal shell formed with a mounting male thread portion and a radially outwardly protruding seat portion and a solid annular gasket disposed between the male thread portion and the seat portion. The gasket has a recessed portion formed with a depth in the direction of an axis such that the recessed portion has an opening at a front end surface of the gasket (18) located opposite to the seat portion. The front end surface of the gasket includes an inner peripheral front end surface region decreasing in thickness toward an inner periphery of the gasket and an outer peripheral front end surface region formed radially outside the inner peripheral front end surface region. The opening of the recessed portion is located radially inside an innermost periphery of the outer peripheral front end surface region.

Abstract: A method for inspecting a spark plug that includes a tubular insulator having an axial hole, a center electrode inserted into the axial hole at a front end side thereof, a tubular metallic shell disposed around the insulator, an annular space defined by an outer circumferential surface of the insulator, and an inner circumferential surface of the metallic shell and opened frontward. The method includes steps of: inspecting insulation performance of the insulator based on whether dielectric breakdown is caused in the insulator when a voltage is applied to the center electrode; photographing an area including at least the center electrode, the insulator, and the annular space from a front end side in the direction of the axis when the voltage is applied to the center electrode; and determining whether the dielectric breakdown has occurred based on the photographed image.

Abstract: A spark plug includes a metal shell formed with a mounting male thread portion and a radially outwardly protruding seat portion and a solid annular gasket disposed between the male thread portion and the seat portion. The gasket has a recessed portion formed with a depth in the direction of an axis such that the recessed portion has an opening at a front end surface of the gasket located opposite to the seat portion. The front end surface of the gasket includes an inner peripheral front end surface region decreasing in thickness toward an inner periphery of the gasket and an outer peripheral front end surface region formed radially outside the inner peripheral front end surface region. The opening of the recessed portion is located radially inside an innermost periphery of the outer peripheral front end surface region.

Abstract: A spark plug includes a tubular insulator and a tubular metal shell secured to an outer peripheral surface of the insulator by crimping. The tubular metal shell includes: an inner peripheral surface where powder for sealing is filled between the outer peripheral surface and the inner peripheral surface; a tool engagement portion overhanging in a polygonal shape; and a crimped lid disposed at an end portion of the metal shell coupled to the tool engagement portion, the end portion being bent toward the outer peripheral surface of the insulator by crimping. A relationship between a length L and a thickness t satisfies 2.50?L/t?3.10, the length L being a length along a shape of the crimped lid from the tool engagement portion to the insulator in a planar surface that passes through the axis, the thickness t being a thickness at an intermediate portion of the crimped lid.

Abstract: A method for manufacturing a spark plug includes: a preparation step of preparing a specimen provided with a center electrode, an insulator, a metal shell, and a ground electrode; and an inspection step of applying a predetermined voltage between the ground electrode and the center electrode of the prepared specimen, and determining whether dielectric breakdown is caused in the insulator. The inspection step includes a calculation step and a judgment step. The calculation step involves receiving an oscillating wave generated from the specimen upon application of the predetermined voltage to the specimen, obtaining a power spectrum by subjecting an oscillating wave signal representing the oscillating wave to fast Fourier transform, and then calculating an integral of a predetermined frequency range in the power spectrum. In the judgment step, whether discharge is caused by dielectric breakdown of the insulator is judged by utilizing the integral.

Abstract: A spark plug includes a ceramic insulator extending in the direction of an axis (CL1) and a metallic shell provided around the ceramic insulator. Talc is pressed charged between the ceramic insulator and the metallic shell and a crimp portion is formed for fixing the metallic shell and the ceramic insulator while the metallic shell having the ceramic insulator inserted thereinto is supported by a tubular receiving member. The receiving member is made movable in relation to a pressing jig in its radial direction. Thus, at the time of pressing of the talc, etc., the eccentricity between the center axis (CL2), (CL3) of the pressing jig and the axis (CL1) in the radial direction can be reduced, whereby the misalignment between the axis (CL1) and the center axis of the metallic shell or the like assembly error can be suppressed.

Abstract: A method for manufacturing a spark plug includes: a preparation step of preparing a specimen provided with a center electrode, an insulator, a metal shell, and a ground electrode; and an inspection step of applying a predetermined voltage between the ground electrode and the center electrode of the prepared specimen, and determining whether dielectric breakdown is caused in the insulator. The inspection step includes a calculation step and a judgment step. The calculation step involves receiving an oscillating wave generated from the specimen upon application of the predetermined voltage to the specimen, obtaining a power spectrum by subjecting an oscillating wave signal representing the oscillating wave to fast Fourier transform, and then calculating an integral of a predetermined frequency range in the power spectrum. In the judgment step, whether discharge is caused by dielectric breakdown of the insulator is judged by utilizing the integral.

Abstract: A method for inspecting a spark plug that includes a tubular insulator having an axial hole, a center electrode inserted into the axial hole at a front end side thereof, a tubular metallic shell disposed around the insulator, an annular space defined by an outer circumferential surface of the insulator, and an inner circumferential surface of the metallic shell and opened frontward. The method includes steps of: inspecting insulation performance of the insulator based on whether dielectric breakdown is caused in the insulator when a voltage is applied to the center electrode; photographing an area including at least the center electrode, the insulator, and the annular space from a front end side in the direction of the axis when the voltage is applied to the center electrode; and determining whether the dielectric breakdown has occurred based on the photographed image.

Abstract: A spark plug comprises an insulator and a metal shell. The insulator includes a nose length portion at the forward end, and a tapered portion, extending from the rear end of the nose length portion toward the rear end of the insulator, increased in diameter toward the rear end. The metal shell includes a shoulder portion, protruding inward and having a retaining surface by which the tapered portion is retained, and a male thread portion on the outer peripheral side of the shoulder portion, and the thread diameter of the male thread portion is set to M12 or less. When the insulator's cross-sectional area, perpendicular to an axis, passing through the boundary between the nose length section and tapered portion is B (mm2), and the metal shell's cross-sectional area, perpendicular to the axis, passing through the tip of the retaining surface is C (mm2), 2.80?C/B?3.50 is satisfied.

Abstract: A spark plug includes a ceramic insulator having a tapered rear end stepped portion whose diameter decreases from front to rear and a metal shell having a crimp portion which crimps the rear end stepped portion from the rear end. An area defined by an outer edge of the rear end stepped portion and an inner edge of the crimp portion is 5-25 mm2 when the spark plug is projected on a plane perpendicular to an axial line. An angle formed by a tapered surface of the rear end stepped portion and a plane perpendicular to the axial line is 20-60 degrees. A distance along the axial line from a front end of a proximal portion of the crimp portion to a frontmost position of a contact portion between an inner surface of the crimp and the rear end stepped portion is 0.4-1.8 mm.

Abstract: A park plug includes a tubular insulator extending along and centered on an axis, and a tubular metal shell secured to an outer peripheral surface of the insulator by crimping, in which powder for sealing is filled between the outer peripheral surface of the insulator and an inner peripheral surface of the metal shell. A relationship between a minimum outer diameter d of the insulator and a maximum inner diameter D of the metal shell in a filling-up area where the powder is filled between the metal shell and the insulator satisfies 1.12?D/d?1.16.

Abstract: A spark plug includes a tubular insulator and a tubular metal shell secured to an outer peripheral surface of the insulator by crimping. The tubular metal shell includes: an inner peripheral surface where powder for sealing is filled between the outer peripheral surface and the inner peripheral surface; a tool engagement portion overhanging in a polygonal shape; and a crimped lid disposed at an end portion of the metal shell coupled to the tool engagement portion, the end portion being bent toward the outer peripheral surface of the insulator by crimping. A relationship between a length L and a thickness t satisfies 2.50?L/t?3.10, the length L being a length along a shape of the crimped lid from the tool engagement portion to the insulator in a planar surface that passes through the axis, the thickness t being a thickness at an intermediate portion of the crimped lid.

Abstract: A method for manufacturing a spark plug includes an assembling step of assembling an insulator into a metallic shell by insertion of the insulator into the metallic shell from an axially rear end opening portion of the metallic shell. The assembling step includes a displacement restricting step of restricting a relative positional displacement between the metallic shell and the insulator in a radial direction intersecting with the axial direction so as to reduce eccentricity between the axis of the metallic shell and the axis of the insulator to a predetermined value or less, while allowing a relative positional displacement between the metallic shell and the insulator in the axial direction. In the assembling step, whether or not the insulator is cracked in the assembling step is judged by detecting acoustic emission from the insulator.

Abstract: A spark plug having an insulator with improved breakage resistance. The spark plug has a cross-section that satisfies the following relationship: 0.6 mm<=L, where “A” represents a connection point between a support portion of the insulator and an insulator trunk portion formed at a front end side with respect to the support portion, where “B” represents a position closer to the outer circumference side among the positions of (a) an innermost position of a contact portion where the support portion and a packing are in contact with each other and (b) an intersection of the support portion and a virtual straight line that is parallel to an axial line of the spark plug and extends from an innermost circumferential end of a stepped portion of a metal shell, and where “L” represents a length of a path from point “A” to point “B” along a surface of the insulator.

Abstract: Provided is a technique for limiting the radial displacement between a metal shell and an insulator in a spark plug. At the time of manufacturing a spark plug with a metal shell and an insulator, the metal shell and the insulator are assembled together by, while allowing relative positional displacement between the metal shell and the insulator in an axial direction (O-O), limiting relative positional displacement between the metal shell and the insulator in a radial direction intersecting with the axial direction in such a manner that the amount of deviation between an axis of the metal shell and an axis of the insulator becomes less than or equal to a predetermined level.

Abstract: [Objective] To provide a spark plug which is configured such that an insulation member, from which a center electrode projects, is pressed frontward and held in a metallic shell, and is fixed by means of crimping the rear end of the metallic shell, and which can prevent a drop in gas tightness between the metallic shell and the insulation member due to a difference in thermal expansion therebetween. [Means for Solution] In a spark plug in which a mating shaft portion (10) of an insulation member (1) is loose-fitted into a mating hole portion (30) of a metallic shell (21), a filler (41) for maintaining gas tightness is charged between the outer circumferential surface of the mating shaft portion (10) and the inner circumferential surface of the mating hole portion (30). Despite the thermal expansion difference, the gas tightness is maintained, because the filler (41) for maintaining gas tightness is charged between the inner and outer circumferential surfaces.

Abstract: Disclosed is a spark plug having an insulator with good breakage resistance. A spark plug 1 contains a ceramic insulator 2, a plate packing 22 and a metal shell 3. The ceramic insulator 2 has, on an outer circumferential surface thereof, a step portion 14, a leg portion 13 and a curved surface portion 31 between the step portion 14 and the leg portion 13. The metal shell 3 has, on an inner circumferential surface thereof, a taper portion 21. The ceramic insulator 2 is fixed in the metal shell 3 with the step portion 14 retained on the taper portion 21 via the plate packing 22. Herein, 50% or more of an inner circumferential edge portion IP of the plate packing 22 is in contact with a part of the ceramic insulator 2 located front of a middle region CP of the curved surface portion 31.