Abstract: A spark plug including an insulator having an axial hole, a center electrode held at one end side and a terminal electrode held at the other end side of the axial hole, an electrical connection portion electrically connecting the center electrode and the terminal electrode inside the axial hole, wherein the electrical connection portion includes a conductor including a ceramic phase and a metal wire having a spiral structure portion, wherein the metal wire has a wire diameter of 0.1 mm or greater and 0.5 mm or smaller, and wherein the spiral structure portion of the metal wire is configured such that an outer diameter thereof is 1.0 mm or greater and 3 mm or smaller, a pitch thereof is 0.3 mm or greater and 1 mm or smaller, and a height thereof is 8 mm or greater and 30 mm or smaller.

Abstract: A spark plug having an insulator with a through hole formed therein in a direction of an axis, a center electrode disposed in a front side of the through hole, a metal terminal disposed in a rear side of the through hole, an electrical connection part arranged in the through hole to establish electrical connection between the center electrode and the metal terminal and a metal shell holding therein the insulator. The electrical connection part has a conductor including a conductive material and at least one kind of Fe-containing oxide material. The Fe-containing oxide material contains at least FeO. The conductor satisfies a relationship of 0.06?S1/(S1+S2)?0.46 where, in a cross section taken along the axis, S1 is an area occupied by the conductive material and S2 is an area occupied by the Fe-containing oxide material.

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: A spark plug having an insulator formed of an alumina-based sintered material which contains an Si component and a rare earth element component that satisfy the following conditions (1) and (2): (1) an oxide-reduced amount of the Si component (mass %) is greater than or equal to 0.05 and less than or equal to 0.45; and (2) a ratio of an oxide-reduced amount of the rare earth element component to an oxide-reduced amount of the Si component is greater than or equal to 2.5 and less than or equal to 4.5, and which has alumina grains and an alumina grain boundary phase including a complex oxide crystal phase satisfying the following condition (3): (3) the complex oxide crystal phase contains at least two components selected from among an Al component, an Si component, a Group 2 element component, and a rare earth element component.

Abstract: A spark plug including an insulator containing an Al component, in terms of oxides, 89 mass % or more and a Ti component, in terms of oxides, more than 0 mass % and 0.2 mass % or less, characterized in that the insulator is formed of an alumina-based sintered material which contains, in a grain boundary phase present between alumina crystal grains, a first crystal phase containing at least one species selected from among an La component, an Nd component, a Pr component, a Y component, an Er component, a Yb component, and an Lu component, and a second crystal phase containing at least one species of Group 2 element components, an Al component and an Si component.

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 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: An ignition plug includes an insulator having an axial hole extending therethrough in the direction of an axis, a center electrode inserted into a forward end portion of the axial hole, and a metallic shell disposed externally of the insulator. The insulator includes a step portion engaged with an inner circumferential portion of the metallic shell and a leg portion extending forward from the forward end of the step portion. The porosity of the leg portion is 3.0% or less. Among three regions of the leg portion that are radially trisected in a cross section perpendicular to the axis, the outermost region is defined as a first region and the innermost region is defined as a second region. The porosity of the first region is equal to or more than 1.20 times the porosity of the second region.

Abstract: A spark plug exhibiting excellent withstand voltage characteristics and mechanical strength at high temperature, which are comparable to those at ambient temperature. The spark plug having an insulator formed of an alumina-based sintered material containing: an Al component, an Si component, a Group 2 element component, and a rare earth element component. The amounts of such components satisfy a condition (1): 0.25? oxide-reduced amount (mass %) of the Si component ?1.25, and a condition (2): 1.35?[(oxide-reduced amount of the Si component)/((oxide-reduced amount of the Group 2 element component)/(oxide-reduced amount of the rare earth element component))]?7.5. The alumina-based sintered material includes alumina grains, and a glass phase including a crystal phase that satisfies a condition (3) that the crystal phase includes at least one of an aluminate crystal phase and a silicate crystal phase, each having a grain size of 20 to 350 nm.

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: 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: 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 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 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 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 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”.