Abstract: A spark plug for an internal combustion engine is provided which includes a housing, a porcelain insulator, a center electrode, and an annular ground electrode. The housing has a small-diameter portion which has a smaller inner diameter and defines a front end thereof. The ground electrode is secured to a front end surface of the small-diameter portion and forms a spark gap between itself and an outer periphery of the center electrode. A pocket is formed between the inner periphery of the housing and a portion of the porcelain insulator which is located closer to a front end of the porcelain insulator than the mounting shoulder is. An air vent extends from outside the ground electrode in a radial direction of the spark plug to the pocket to establish communication between the pocket and the combustion chamber of the internal combustion engine.

Abstract: A spark plug for an internal combustion engine is provided which includes a housing, a porcelain insulator, a center electrode, and an annular ground electrode. The housing has a small-diameter portion which has a smaller inner diameter and defines a front end thereof. The ground electrode is secured to a front end surface of the small-diameter portion and forms a spark gap between itself and an outer periphery of the center electrode. A pocket is formed between the inner periphery of the housing and a portion of the porcelain insulator which is located closer to a front end of the porcelain insulator than the mounting shoulder is. An air vent extends from outside the ground electrode in a radial direction of the spark plug to the pocket to establish communication between the pocket and the combustion chamber of the internal combustion engine.

Abstract: A spark plug includes a tubular housing, a tubular insulator retained in the housing, a center electrode secured in the insulator with a distal end portion of the center electrode protruding outside the insulator, and an annular ground electrode fixed to a distal end of the housing. The housing has, at the distal end thereof, a small-inner diameter portion that has a smaller inner diameter than other portions of the housing. The annular ground electrode is arranged on a distal end surface of the small-inner diameter portion of the housing so that an inner circumferential surface of the ground electrode faces an outer circumferential surface of the distal end portion of the center electrode through a spark gap formed therebetween. The outer diameter of the ground electrode is less than the outer diameter of the distal end surface of the small-inner diameter portion of the housing.

Abstract: A spark plug includes a tubular housing, a tubular insulator retained in the housing, a center electrode secured in the insulator with a distal end portion of the center electrode protruding outside the insulator, and an annular ground electrode fixed to a distal end of the housing. The housing has, at the distal end thereof, a small-inner diameter portion that has a smaller inner diameter than other portions of the housing. The annular ground electrode is arranged on a distal end surface of the small-inner diameter portion of the housing so that an inner circumferential surface of the ground electrode faces an outer circumferential surface of the distal end portion of the center electrode through a spark gap formed therebetween. The outer diameter of the ground electrode is less than the outer diameter of the distal end surface of the small-inner diameter portion of the housing.

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: 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 first gap discharge gap is located between a front end of a center electrode and a front side of a first ground electrode of a spark plug. A second discharge gap is located between a front end of a second ground electrode and a front side of the center electrode. Respective dimensional relationships between various of these elements are established to promote self-cleaning of the spark plug.

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: In a spark plug having a center electrode, first and second ground electrodes, an insulator and a metal housing, a first discharge gap is constituted between a front end of the center electrode and a front side of the first ground electrode and a second discharge gap is constituted between a front end of the second electrode and a front side of the center electrode. Respective dimensional relationships of A, B, C, H, F and L1 are defined where A is a distance of the first discharge gap, Bis a shortest distance between the front end of the second ground electrode and the insulator, C is an axial length from a leading end of the metal housing and a front end of the insulator, H is an axial length from the front end of the insulator and the front end of the center electrode, F is an axial length from the front end of the insulator to the front end edge of the second electrode and L1 is a shortest axial length from the leading end of the metal housing to the front end of the second ground electrode.

Abstract: A spark plug including an insulation porcelain having a throughhole; a center electrode held at one end of the throughhole; a housing holding the insulation porcelain; a ground electrode disposed at a front end of the housing and facing the center electrode; a spark gap defined by the center electrode and the ground electrode; and at least one of the center and ground electrodes having a nobel metal member bonded to a discharging spot of its front end, wherein the nobel metal member consists of 90 wt % or more of an Ir—Rh alloy containing 1 to 60 wt % Rh and the balance substantially consisting of at least one of Pt, Pb, Ru, Au and Ni.

Abstract: A spark plug for an internal combustion engine comprises a noble metallic firing tip laser welded on the opposing surface of either a central electrode or a grounded electrode. A fused junction layer, formed between the noble metallic firing tip and the base electrode member, contains 40˜70 wt % noble metallic firing tip component. The noble metallic firing tip has a non-fused portion axially extending by a length “L”, where 0.2 mm ≦L≦0.7 mm. The fused junction layer axially extends by a length “M”, where 0.2 mm ≦M≦0.7 mm. And, the relationship B≧1.3A is established when “A” represents the diameter of the noble metallic firing tip and “B” represents the diameter of a contact area at the boundary between the fused junction layer and the base electrode member, where 0.3 mm ≦A≦0.6 mm.

Abstract: A spark plug with a plug screw outer diameter D of 10 mm-12 mm, wherein the length A of the discharge gap 6, the width B of the gas volume 7, the protruding length C of the insulator 2 with respect to the fitting piece 1, the diameter F of the center electrode 3, the end diameter G of the noble metal tip 51 and the protruding height H of the noble metal tip 51 with respect to the center electrode 3 are within the following ranges:0.9 mm.ltoreq.A.ltoreq.1.35 mm, (10/9)A.ltoreq.B, 1.0 mm.ltoreq.C.ltoreq.2.5 mm, 10 mm.ltoreq.D.ltoreq.12 mm, 2.0 mm.ltoreq.F.ltoreq.2.7 mm, 0.6 mm.ltoreq.G.ltoreq.0.9 mm, and 0.3 mm.ltoreq.H.ltoreq.1.0 mm.

Abstract: A process of producing a spark plug having an improved consumption resistance is provided. The spark plug comprises a noble metal chip composed of an Iridium (Ir) alloy material and includes an insulator enclosing a center electrode and a ground electrode, which has a facing portion facing the tip of the center electrode. The chip may be disposed on the tip of the center electrode, the facing portion of the ground electrode or both. The Ir alloy material consists of Ir and a metal that has a higher oxidation resistance than Ir and forms a solid solution with Ir at all proportions to prevent oxidation evaporation of Ir. In order to prevent surface cracking, the chip is produced by elongating an ingot of the Ir alloy material through hot forging to form a bar having a fine fiber texture. Then, the chip is hot rolled, hot wire drawn and cut to the desired length.

Abstract: To improve the consumption resistance and lifetime, a spark plug for an internal combustion engine comprises: an insulation porcelain having a throughhole; a center electrode held at one end of the throughhole; a housing holding the insulation porcelain; a ground electrode disposed at an front end of the housing and facing the center electrode; a spark gap defined by the center electrode and the ground electrode; and at least one of the center electrode and the ground electrode having a noble metal chip bonded to a discharging spot of an front end thereof, wherein the noble metal chip consisting of an Ir-Rh alloy contains Rh in an amount of from 1 wt % to 60 wt %.

Abstract: To provide a spark plug having an improved consumption resistance and producible through a simple process, a spark plug comprises a noble metal chip composed of an Ir alloy material and disposed on at least one of the tip of the center electrode and the facing portion of the ground electrode, the Ir alloy material is composed of Ir and a metal having a higher oxidation resistance than Ir and forming solid solution with Ir at all proportions to prevent oxidation evaporation of Ir, and the chip is produced by elongating an ingot of the Ir alloy material through hot forging to a bar having a fine fiber texture to prevent surface cracking during elongation, followed by hot rolling, hot wire drawing and cutting to the chip length.

Abstract: Center and earth electrodes are melted at the predetermined regions on the tip thereof where noble metallic chips are fixed. Then, the noble metallic chips are sunk in the melted portions of these center and earth electrodes so as to form protruding portions along outer peripheries of the noble metallic chips. Thus, the noble metallic chips are fixed to the electrodes through the protruding portions. Next, the noble metallic chips are irradiated by energy-condensing light through the protruding portions thus formed. With this irradiation, the center electrode is welded to one noble metallic chip, while the earth electrode is welded to the other noble metallic chip.

Abstract: A spark plug for an Internal combustion engine is provided. When it is assumed that the distance of a first spark gap (g1) defined by a central electrode (8) and a first grounding electrode (16) whose width is "A" and which is axially opposed to the central electrode, and a second spark gap (g2) defined by the central electrode and at least one second grounding electrode (21) whose width is "B" and which is opposed to the side surface of the central electrode, the relationship defined by 0.5.ltoreq..SIGMA.Bn/A.ltoreq.1.5 is established, wherein "n" represents the number of the second grounding electrode to reduce the discharge voltage of the spark plug and maintain a high heat resistance. Preferably, the spark plug satisfies the relationship defined by 0.1 mm.ltoreq.g2-g1.ltoreq.0.4 mm to improve the ignitability of the spark plug.