Abstract: An improved structure of a spark plug which provides higher durability of a joint of a noble metal chip to an electrode such as a center or a ground electrode. The joint is formed by laser welding. A fused portion made of materials of the noble metal chip and the electrode fused together by the laser welding is formed in the joint so that it may continue over at least half a circumference of a contact between the noble metal chip and the electrode without interfaces of welds, thereby enhancing the activity of the fused portion as a thermal stress absorber. A welding method is also provided.

Abstract: Noble metallic tips, made of a Pt alloy or an Ir alloy, are fixed to electrode base materials. The electrode base materials are an alloy containing a chief element selected from the group consisting of Ni, Fe, and Co and a plurality of additive elements. At least two kinds of additive elements contained in this alloy have a standard free energy of formation smaller than that of the chief element.

Abstract: A spark plug and manufacturing method are disclosed having a center electrode and a ground electrode to which a center-electrode noble metal chip and a ground-electrode noble metal chip are secured, respectively, by welding. The center-electrode noble metal chip has a bending strength defined by a coefficient of linear expansion of the center electrode, a coefficient of linear expansion of the center-electrode noble metal chip, a Young's modulus, a tensile strength, a chip diameter, a chip protruding length and a thickness of a fused portion, and the ground-electrode noble metal chip has a bending strength defined by a coefficient of linear expansion of the ground electrode, a coefficient of linear expansion of the ground-electrode noble metal chip, a Young's modulus, a tensile strength of the second noble metal chip, a chip diameter, a chip protruding length and a thickness of a fused portion.

Abstract: A small-sized spark plug is provided which ensures the stability in the location of production of sparks between center and ground electrodes. The center and ground electrodes have joined thereon cylindrical members such as noble metal chips which are opposed to each other through a spark gap. The cylindrical members are so oriented to have longitudinal center lines extend parallel in misalignment with each other. This orientation results in shorter and longer intervals between end surfaces of the cylindrical members. The sparks are concentrated between portions of edges of cylindrical members located apart the shorter interval, thereby resulting in the stability in the location of production of the sparks.

Abstract: An improved structure of a spark plug which provides higher durability and ignitability of a gaseous fuel. The spark plug consists of a center electrode, a ground electrode, a noble metal chip joined to a center electrode-opposed surface of the ground electrode by laser welding, and a fused portion that forms a weld of the noble metal chip and the ground electrode formed by materials of the ground electrode and the noble metal chip melted together. A sectional area of the noble metal chip traversing a length thereof is between 0.1 mm2 and 0.6 mm2. An unfused sectional area percentage that is a percentage of a sectional area of an unfused portion of a joined end of the noble metal chip within a range of a sectional area of the noble metal chip closest to the fused portion traversing the length of the noble metal chip is less than or equal to 50%.

Abstract: A spark plug is provided which ensures the reliability of a weld between a noble metal chip and a ground electrode as well as higher durability and ignitability of fuel. The ground electrode is joined to a metal shell, after which the noble metal chip is laser-welded to the ground electrode. The laser welding is achieved by emitting laser beams around an interface between the noble metal chip and the ground electrode outside a given angular range within which the metal shell will be an obstruction to the traveling of the laser beams. Specifically, the laser beams are emitted without any optical interference with the metal shell. This permits the angle between the orientation of each of the laser beams and the surface of the ground electrode to be minimized regardless of the metal shell, thus ensuring a desired depth of the fused portions in the noble metal chip.

Abstract: A noble metal chip of which one end is welded to an earth electrode by laser has a sectional area of not less than 0.12 mm2 and not more than 1.15 mm2 at the other end. A length from the surface of the earth electrode to the top surface of the noble metal chip is not less than 0.3 mm and not more than 1.5 mm. An outer surface of the fused junction layer obtained by laser welding between the noble metal chip and the earth electrode has a concave surface, wherein the slope on the plane including the axis of the noble metal chip is curved with a radius R.

Abstract: Reliability in connection between a chip and a base material (at least one of the central electrode and the ground electrode) of a spark plug is improved by forming a plurality of welding layers at connection between the chip and the base material in a distance increasing direction from the central electrode with overlap. With respect to section along the connection surface the sum of the sectional area of the first weld layer and the second weld layer at the overlap portion between the first and second weld layers is equal to or greater than 1.4 times the sectional are of the chip. A stress releasing layer of which linear expansion coefficient is between those of the chip and the base material may be provided between the chip and the base material for welding.

Abstract: A spark plug and a production method thereof is provided which is designed to improve the high temperature oxidation resistance of a ground electrode without sacrificing the mechanical strength of a weld of the ground electrode with a metal shell. The ground electrode is made of a Ni-based alloy containing 10% or more by weight of Cr and 1.5% or more by weight of Al and joined to the metal shell by resistance welding in a substantially oxygen free atmosphere.

Abstract: At least one of a center electrode and a ground electrode of an engine spark plug is a Ni-base alloy containing, in weight percentage, 0.5˜2.5% Si, 0.1˜1.2% Mn, 3.2˜5.0% Al, 0.9˜2.8% Cr, 0.001˜0.025% C in addition to Ni and unavoidable impurities. And, a value S/V is in a range from 1.7 mm−1 to 3.9 mm−1 when ‘S’ represents a surface area of the ground electrode and ‘V’ represents a volume of the ground electrode.

Abstract: A spark plug is composed of a main metal fitting having a cylindrical structure, an insulator disposed inside the cylindrical main metal fitting, a center electrode fitted in the insulator in a manner that a front end portion of the center electrode projects outward over one end of the insulator, and a grounding electrode mounted to the main metal fitting and having one end portion opposing to the front end portion of the center electrode through a discharge gap therebetween. The front end portion of the center electrode includes a conical portion having a tapered surface having a taper angle of less than 80°, and a columnar portion formed to a top end portion of the conical portion so as to have a diameter in a range of 0.4 mm to 0.8 mm.

Abstract: A noble metallic tip of a ground electrode protrudes from an opposed surface of the ground electrode by a protrusion amount ‘t’ not less than 0.3 mm. The noble metallic tip of the ground electrode possesses excellent oxidative and volatile resistance compared with a noble metallic tip of a center electrode.

Abstract: A spark plug for an engine comprises a mounting member to be mounted to an engine, an insulator disposed inside the mounting member and formed with an axial hole, a center electrode formed of a metal material and disposed in the axial hole of the insulator in a manner insulated from the mounting member, and an earth electrode disposed so as to oppose to the center electrode. At least one of the center electrode and earth electrode is formed as a base material having one surface to which a tip composed, as a discharge member, of a noble metal or alloy thereof is welded and fixed thereto through a fused portion. The fused portion between the tip and the base material has an area of a maximum sectional area portion of a size of not more than 1.5 times a sectional area of a portion of the tip positioned at a boundary portion to the fused portion, and the sectional area of the tip positioned at the boundary portion is not less than 2 mm2 and not more than 7 mm2.

Abstract: Carbon fouling adhered on an insulator tip of a spark plug of the present invention is burnt down by a leak current during an inductive discharge period, due to a promoted ionization before beginning a capacitive discharge, in such an arrangement of a central electrode that a border portion of a body and narrowed portion is positioned in an insulator. The carbon burning-down effect is further improved by a narrow projection provided with an earth electrode, due to increased inductive energy and extended inductive discharge time period. This is because an electric field in a discharge gap is raised, thereby decreasing a discharge voltage and suppressing an energy emitted from a coil during the capacitive discharge.

Abstract: A noble metallic tip of a ground electrode protrudes from an opposed surface of the ground electrode by a protrusion amount ‘t’ not less than 0.3 mm. The noble metallic tip of the ground electrode possesses excellent oxidative and volatile resistance compared with a noble metallic tip of a center electrode.

Abstract: A noble metal tip of a grounding electrode is inclinedly disposed with respect to a noble metal chip of a central electrode by an angle &agr; so that a discharging gap is narrow at a side closer to one end of the grounding electrode and wide at the opposite side closer to the other side of the grounding electrode. When the discharging gap has expanded to a certain extent due to exhaustion of the noble metal tips of the electrodes, the re-gapping adjustment is performed to decline or push the noble metal tip of the grounding electrode toward the noble metal tip of the central electrode so as to decrease the angle &agr;. Thus, the discharging gap can be adjusted to an adequate value.

Abstract: A spark plug and a production method thereof is provided which is designed to improve the high temperature oxidation resistance of a ground electrode without sacrificing the mechanical strength of a weld of the ground electrode with a metal shell. The ground electrode is made of a Ni-based alloy containing 10% or more by weight of Cr and 1.5% or more by weight of Al and joined to the metal shell by resistance welding in a substantially oxygen free atmosphere.

Abstract: At least one of a center electrode and a ground electrode of an engine spark plug is a Ni-base alloy containing, in weight percentage, 0.5˜2.5% Si, 0.1˜1.2% Mn, 3.2˜5.0% Al, 0.9˜2.8% Cr, 0.001˜0.025% C in addition to Ni and unavoidable impurities. And, a value S/V is in a range from 1.7 mm−1 to 3.9 mm−1 when ‘S’ represents a surface area of the ground electrode and ‘V’ represents a volume of the ground electrode.

Abstract: An improved structure of a spark plug which provides higher durability of a joint of a noble metal chip to an electrode such as a center or a ground electrode. The joint is formed by laser welding. A fused portion made of materials of the noble metal chip and the electrode fused together by the laser welding is formed in the joint so that it may continue over at least half a circumference of a contact between the noble metal chip and the electrode without interfaces of welds, thereby enhancing the activity of the fused portion as a thermal stress absorber. A welding method is also provided.

Abstract: Noble metallic tips, made of a Pt alloy or an Ir alloy, are fixed to electrode base materials. The electrode base materials are an alloy containing a chief element selected from the group consisting of Ni, Fe, and Co and a plurality of additive elements. At least two kinds of additive elements contained in this alloy have a standard free energy of formation smaller than that of the chief element.