Abstract: An ignition plug, wherein, when a relative density of a portion of an insulator, which is positioned between a radial virtual plane including a front end of the insulator and a radial virtual plane including a front end of a portion of the insulator which is in contact with a metal shell or the plate packing, is referred to as A (%), and a relative density of a portion of the insulator, which is positioned between the radial virtual plane including the front end of the portion of the insulator which is in contact with the metal shell or the plate packing and a radial virtual plane including a center of a resistor in an axial direction, is referred to as B (%), the following equations are satisfied: 93.90?A, and 0.10?A?B?0.90.

Abstract: An insulator for spark plug with a main constituent of alumina and containing silicon includes a grain boundary phase positioned between alumina particles. The grain boundary phase contains: a group 2A element; a rare earth element; and at least one kind of zirconium, titanium, chrome, niobium, manganese, and iron (a first element). Assuming that a total amount of the rare earth element is X (mass %), a total amount of the group 2A element is Y (mass %), and a total amount of the first element is Z (mass %), the following are met: 0.40?Y/X?2.00 0.10?Z/X?0.40.

Abstract: An insulator used in a spark plug having improved strength and dielectric strength performance. The insulator comprises a sintered compact whose main constituent is alumina. In the sintered compact, a content ratio of a rare earth element (R. E.) and a group 2 element (2A) satisfies 0.1?R. E./2A?1.4, and the content ratio of the R. E. and barium oxide (BaO) satisfies 0.2?BaO/R. E.?0.8. At least one virtual rectangular frame of 7.5 ?m×50 ?m surrounding crystals containing the rare earth element lies within a region of 630 ?m×480 ?m in any cross section of the sintered compact.

Abstract: A spark plug includes: a center electrode including a rod portion and a head portion and having a diameter larger than the diameter of the rod portion; an insulator having an axial bore, the center electrode being disposed in the axial bore at its front end; and a seal portion for fixing the center electrode in the axial bore. The insulator comprises: a leg portion inner circumferential surface; a cylindrical trunk portion inner circumferential surface which surrounds the head portion; and a support surface which supports the head portion. The seal portion has: a seal portion outer circumferential surface; a seal portion abutment surface; and a connecting surface. In a cross section of the seal portion, a curve, which is part of the contour of the seal portion and is included in the connecting surface, has a radius of curvature R of 0.1 mm or more.

Abstract: A spark plug having excellent load life performance even when the spark plug receives an impact or vibration. The spark plug includes an accommodated portion of a metallic terminal, which is accommodated in an axial hole of an insulator, having a plurality of bent portions formed as a result of proper bending of the accommodated portion. The bent portions are in close vicinity to an inner circumferential surface of the insulator at three or more locations, and are present without localizing in the radial direction of the axial hole.

Abstract: An ignition plug includes a ceramic insulator having an axial bore, a metallic shell, and a terminal electrode. The terminal electrode has a leg portion inserted into a rear side of the axial bore, and a head portion formed on a rear side of the leg portion and having an outside diameter greater than that of the leg portion. The insulator includes a rear trunk portion exposed from the rear end of the metallic shell, which has a maximum outside diameter of 9.5 mm or less. The insulator has an end-surface seat portion located forward of its rear end and being in contact with the forward end surface of the head portion, and an outer circumferential portion into which at least a forward end portion of the head portion is inserted and which is located externally of the outer circumference of the head portion.

Abstract: A task of this invention is to provide a spark plug that is superior in withstand voltage characteristics at high temperatures. A spark plug of this invention is equipped with a center electrode, an insulator, and a metal shell, and is characterized by that the insulator is equipped with an alumina-based sintered body containing silicon component (Si component), magnesium component (Mg component), at least one component of calcium component, strontium component, and barium component, and a rare earth element component (RE component), that a grain boundary phase of the alumina-based sintered body has a hexaaluminate crystal containing the RE component, that, in the alumina-based sintered body, the weight ratio of the RE component to the Mg component is 5.4?RE oxide/MgO?17.5, and that the content of an alkali metal component in terms of oxide in a spot having a diameter of 0.

Abstract: A spark plug having improved load life performance and fixing strength of a metallic terminal to an insulator, and which reduces the incidence of breakage of the insulator when the metallic terminal is inserted into the axial hole of the insulator. The spark plug of the present invention is characterized in that the distance ((B?A)/2) between the forward end portion of the metallic terminal and the wall surface of an intermediate diameter portion of the axial hole of the insulator falls within a range of 0.02 mm to 0.2 mm, the shrinkage amount (D?C) of a connecting portion falls within a range of 6 mm to 27 mm, and the Vickers hardness of the metallic terminal at ordinary temperature falls within a range of 100 Hv to 430 Hv.

Abstract: An ignition plug, wherein, when a relative density of a portion of an insulator, which is positioned between a radial virtual plane including a front end of the insulator and a radial virtual plane including a front end of a portion of the insulator which is in contact with a metal shell or the plate packing, is referred to as A (%), and a relative density of a portion of the insulator, which is positioned between the radial virtual plane including the front end of the portion of the insulator which is in contact with the metal shell or the plate packing and a radial virtual plane including a center of a resistor in an axial direction, is referred to as B (%), the following equations are satisfied: 93.90?A, and 0.10?A?B?0.90.

Abstract: A spark plug with both improved load life performance and improved radio-noise-preventing property, wherein the spark plug has a resistor containing a Ti component. The spark plug includes a circular columnar insulator having a through hole; a center electrode; a terminal shell; and a resistor provided in the through hole and between the terminal shell and the center electrode. The resistor contains glass, a Ti component, a Zr component, and a non-metallic electrically conductive material.

Abstract: A spark plug manufacturing method providing a spark plug equipped with an insulator having dielectric strength by means of judging whether or not the insulator has a defect. A defect judgement step judges whether or not the insulator has a defect, by generating an electric potential difference between the center electrode and the metallic shell under conditions such that an assembly of the center electrode, metallic shell, and insulator is disposed within a pressure vessel; a high-pressure atmosphere higher in pressure than the atmospheric pressure is established within the pressure vessel; a space allowing the presence of insulating oil is a space surrounded by the packing, the metallic shell, the insulator, and an imaginary plane containing a forward end surface of the metallic shell; and the insulating oil is present at least in a region of the space where the distance between the ledge and insulator becomes shortest.

Abstract: A spark plug that prevents a sharp increase in resistance of a resistor and materializes an excellent load life performance. The spark plug has a resistor formed by heat-sealing of a resistor composition that contains, at least, a conductive material and glass powder. The glass powder contains between 35.0 mol % and 69.8 mol % SiO2, between 15.0 mol % and 49.8 mol % B2O3, between 5.0 mol % and 20.0 mol % Li2O, and at least one additive selected from MgO, CaO, SrO, BaO, Na2O, K2O, ZnO, and ZrO2 in a total of between 2.6 mol % and 25.0 mol %. Further, the total content of Li2O and the additive(s) in the glass powder is between 15.2 mol % and 45.0 mol %, and the ratio of the Li2O content to the total content of the additive(s) is between 1.3 and 5.0.

Abstract: A spark plug manufacturing method providing a spark plug equipped with an insulator having dielectric strength by means of judging whether or not the insulator has a defect. A defect judgement step judges whether or not the insulator has a defect, by generating an electric potential difference between the center electrode and the metallic shell under conditions such that an assembly of the center electrode, metallic shell, and insulator is disposed within a pressure vessel; a high-pressure atmosphere higher in pressure than the atmospheric pressure is established within the pressure vessel; a space allowing the presence of insulating oil is a space surrounded by the packing, the metallic shell, the insulator, and an imaginary plane containing a forward end surface of the metallic shell; and the insulating oil is present at least in a region of the space where the distance between the ledge and insulator becomes shortest.

Abstract: A spark plug that is equipped with an insulator that has a stem portion on a front end side, a center electrode, and a main metal member that retains the insulator at an engaging projection portion, wherein an inner diameter DIN of the engaging projection portion, the maximum outer diameter dOUT of the stem portion, which faces an inner circumferential surface of the engaging projection portion, its inner diameter dIN, and dielectric constant ? of the insulator satisfy the condition of “(DIN?dOUT)/2?0.40 (mm)”, “(dOUT?dIN)/2?1.65 (mm)”, and “??9.4”.

Abstract: A spark plug having a center electrode, an insulator and a metal shell and satisfying conditions (1) to (5) as defined herein. Also disclosed is a method of manufacturing a spark plug including the step of producing an insulator by preparing a raw material powder in such a manner that the particle size distribution ratio (90% volume diameter/10% volume diameter) between particles of 10% volume diameter and particles of 90% volume diameter in the raw material powder is 3.6 to 5.2, and then, press-forming and sintering the prepared raw material powder.

Abstract: A spark plug having a connecting portion that electrically connects a center electrode with a metal terminal within an axial bore in an insulator. The connecting portion of the spark plug includes a resistor. A center electrode-side resistance, which is the resistance of a portion of the resistor that extends from the center thereof toward the center electrode in the axial direction, is larger than a metal terminal-side resistance, which is the resistance of a portion of the resistor that extends from the center thereof toward the metal terminal.

Abstract: A spark plug manufacturing method provides a reduction in the cost of raw material preparation and the cost of the disposal of unused powder by recycling powder not used in forming a filler layer of another spark plug. The method is used to make a spark plug that includes a metal shell having a through hole, and an insulating body held inside the through hole, and a filler layer containing talc in a space surrounded by an inner peripheral surface of the through hole and an outer peripheral surface of the insulating body. The powder not used in a process of forming a filler layer of another spark plug is recycled for forming the filler layer of the present spark plug, where the forming process is performed after talc and a binder are mixed.

Abstract: An isolation portion (P) of an insulator (10) of a spark plug (100) electrically insulatively isolates a front end portion (22) of a center electrode (20) and a holding portion (56) of a metallic shell (50) from each other and has an intermediate portion (P2) which extends while its outside diameter varies, thereby ensuring an insulation distance between the two portions. The ratio (S/V) of the surface area (S) of the outer surface (14) of the isolation portion (P) to the volume (V) of the isolation portion (P) satisfies the relation 1.26 mm?1?S/V, whereby the insulation distance between the front end portion (22) and the holding portion (56) is sufficiently ensured while existing dimensional conditions are held unchanged. Through satisfaction of the relation S/V?1.

Abstract: A spark plug having improved load life performance and fixing strength of a metallic terminal to an insulator, and which reduces the incidence of breakage of the insulator when the metallic terminal is inserted into the axial hole of the insulator. The spark plug of the present invention is characterized in that the distance ((B?A)/2) between the forward end portion of the metallic terminal and the wall surface of an intermediate diameter portion of the axial hole of the insulator falls within a range of 0.02 mm to 0.2 mm, the shrinkage amount (D?C) of a connecting portion falls within a range of 6 mm to 27 mm, and the Vickers hardness of the metallic terminal at ordinary temperature falls within a range of 100 Hv to 430 Hv.

Abstract: A spark plug having excellent load life performance, and a method of manufacturing the same, the spark plug having a connecting portion which electrically connects a center electrode and a metallic terminal within the axial hole of an insulator, the connecting portion including a resistor whose porosity is 5.0% or less.