EP1837964B1 - Zündkerze für einen Verbrennungsmotor - Google Patents

Zündkerze für einen Verbrennungsmotor Download PDF

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Publication number
EP1837964B1
EP1837964B1 EP20070251139 EP07251139A EP1837964B1 EP 1837964 B1 EP1837964 B1 EP 1837964B1 EP 20070251139 EP20070251139 EP 20070251139 EP 07251139 A EP07251139 A EP 07251139A EP 1837964 B1 EP1837964 B1 EP 1837964B1
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EP
European Patent Office
Prior art keywords
ground electrode
electrode
center electrode
face
center
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EP20070251139
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English (en)
French (fr)
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EP1837964A2 (de
EP1837964A3 (de
Inventor
Kazuyoshi c/o NGK Spark Plug Co. Ltd. Torii
Kazumasa C/O Ngk Spark Plug Co. Ltd. Yoshida
Wataru C/O Ngk Spark Plug Co. Ltd. Matsutani
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Niterra Co Ltd
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NGK Spark Plug Co Ltd
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Publication of EP1837964A3 publication Critical patent/EP1837964A3/de
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
    • H01T13/00—Sparking plugs
    • H01T13/20—Sparking plugs characterised by features of the electrodes or insulation
    • H01T13/32—Sparking plugs characterised by features of the electrodes or insulation characterised by features of the earthed electrode
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
    • H01T13/00—Sparking plugs
    • H01T13/20—Sparking plugs characterised by features of the electrodes or insulation
    • H01T13/39—Selection of materials for electrodes

Definitions

  • the present invention relates to a spark plug for use in an internal-combustion engine.
  • a spark plug for use in internal-combustion engines such as the engine of an automobile includes, for example, a center electrode, an insulator provided outside thereof, a cylindrical metal shell disposed outside of said insulator and a ground electrode whose rear portion is joined to a front-end face of said metal shell.
  • the ground electrode assumes a generally rectangular form in the cross-section and is disposed so that a front-end portion inner side face thereof faces the front-end face of the center electrode.
  • a spark discharge gap is formed between the front-end portion of the center electrode and the front-end portion of the ground electrode.
  • a screw portion (not illustrated) is formed on an outer circumferential face of the metal shell.
  • a spark plug is mounted on an engine in such a manner that the screw portion of the metal shell screws into a female thread of a plug opening formed in the engine cylinder head.
  • the spark plug is mounted such that an air-fuel mixture is exposed to a back face of the ground electrode, there is a possibility that the inflow of the air-fuel mixture to the spark discharge gap may be disturbed by the ground electrode. As a result, the ignitability of the spark plug is unlikely to be stable.
  • the conventional art discloses a spark plug having two or more ground electrodes therein in which each ground electrode assumes a columnar form with a generally circular-shape in the cross-section (e.g. Japanese Patent Application Laid-Open (kokai) No. H11-121142 ).
  • each ground electrode assumes a columnar form with a generally circular-shape in the cross-section
  • the air-fuel mixture is unlikely to be exfoliated from the ground electrode and easily reaches the spark discharge gap by flowing to the inner side of the ground electrode, even in a case where the air-fuel mixture is exposed to the back face of the ground electrode.
  • the cross-sectional area of the circular-shaped ground electrode has to be smaller than that of the rectangular-shaped ground electrode.
  • so-called heat sinking ability (heat dispersion) of the ground electrode deteriorates, and the temperature thereof tends to increase at the time of high speed driving or the like. Consequently, the ground electrode suffers considerable erosion which leads to a poor durability thereof.
  • the ground electrode is formed with a two-layer structure comprised of an outer layer comprised of a nickel alloy, which is excellent in oxidation resistance, and an inner layer comprised of a metal having a better thermal conductivity (e.g., copper-system metal) than that of the outer layer.
  • a deformation i.e., "spring back"
  • a defect of the spark plug caused by such deformation is likely to occur when an outer diameter of the ground electrode is relatively small (e.g., 2mm or less).
  • the present invention has been accomplished in view of the above problems, and an object of the invention is to provide a spark plug for use in an internal-combustion engine which is capable of preventing an inflow of an air-fuel mixture to a spark discharge gap so as to prevent poor ignitability, as well as preventing any influence on the spark discharge gap and improving the durability of the spark plug. This is achieved with a spark plug, according to claims 1, 4 and 6 respectively.
  • the present invention provides a spark plug for use in an internal-combustion engine, comprising: a center electrode; an insulator at least partially surrounding the center electrode; a cylindrical metal shell at least partially surrounding the insulator; a ground electrode so disposed that one end thereof is joined to a front-end face of the metal shell and the other end thereof faces the front-end face of the center electrode; and a spark discharge gap formed between the front-end face of the center electrode and a front-end portion of the ground electrode, wherein at least a portion of the ground electrode where sparks are discharged has an outer layer made of a nickel alloy and an inner layer made of pure copper or a copper alloy having a better thermal conductivity than that of the outer layer, and wherein a ratio of a cross-sectional area of the inner layer to the entire cross-sectional area of the ground electrode is 10% or more to 35% or less, characterised in that when the ground electrode and the center electrode are projected from the front-end face side of the ground electrode along the central axis of the center electrode, tang
  • a spark plug according to this composition is comprised of: a center electrode; an insulator provided so as to cover the surroundings of the center electrode; a cylindrical metal shell provided so as to cover the surroundings of the insulator; a ground electrode so disposed that one end thereof is joined to a front-end face of the metal shell and the other end thereof faces the front-end face of the center electrode; and a spark discharge gap formed between the front-end face of the center electrode and a front-end portion of the ground electrode, wherein the ground electrode is constituted so as to reduce its width toward a back face thereof, which is opposed to the center electrode side, at least in a front-end portion thereof located at a front-end side from a center of the spark discharge gap, wherein at least a portion of the ground electrode where sparks are discharged has an outer layer made of a nickel alloy and an inner layer made of pure copper or a copper alloy having a better thermal conductivity than that of the outer layer, and wherein a ratio of a cross-sectional area of the inner layer to the
  • a spark plug according to this composition is comprised of: a center electrode; an insulator provided so as to cover the surroundings of the center electrode; a cylindrical metal shell provided so as to cover the surroundings of the insulator; a ground electrode so disposed that one end thereof is joined to a front-end face of the metal shell and the other end thereof faces the front-end face of the center electrode; and a spark discharge gap formed between the front-end face of the center electrode and a front-end portion of the ground electrode, wherein the ground electrode has a width of 2mm or less at least in the front-end portion thereof located at a front-end side from a center of the spark discharge gap and a convex-shaped curved face at a back face thereof located opposed to the center electrode side, wherein at least a portion of the ground electrode where sparks are discharged has an outer layer made of a nickel alloy and an inner layer made of pure copper or a copper alloy having a better thermal conductivity than that of the outer layer, and wherein a ratio of a cross-sectional
  • a noble metal tip may be provided on at least either the ground electrode or the center electrode.
  • the spark discharge gap is formed between the noble metal tip and the ground electrode which are opposed to each other.
  • the spark discharge gap is formed between the noble metal tip and the center electrode which are opposed to each other.
  • the spark discharge gap is formed between the noble metal tips which are opposed to each other.
  • no noble metal tip is provided on the center electrode or the ground electrode, the spark discharge gap is formed between the front-end face of the center electrode and an inner side face of the ground electrode which are opposed to each other.
  • the ground electrode does not necessary assume a circular form in the cross-section, but may be constituted so as to reduce its width toward the back face thereof, which is opposed to the center electrode side, at least in the front-end portion thereof located at the front-end side from the center of the spark discharge gap.
  • the convex-shaped curved face may be formed at the back face of the ground electrode which is opposed to the center electrode side.
  • reduced width means that it is not a constitution where a corner of the ground electrode is simply chamfered, but a constitution where 1/4 or more of the width is reduced along a direction perpendicular to the width (i.e., a thickness of the ground electrode).
  • a "width” referred to in this document means a width in a direction perpendicular to the longitudinal direction of the spark plug (i.e., the direction parallel to the front-end face of the metal shell) and is a projection width when the ground electrode is viewed from the center electrode (the front-end face of the ground electrode).
  • a "copper alloy” in this document is an alloy containing over 50% by mass of copper.
  • the ground electrode is constituted so as to reduce its width toward the back face thereof at least in the front-end portion thereof located at the front-end side from the center of the spark discharge gap (in the composition 2, particularly, the ground electrode has a width of 2mm or less and a convex-shaped curved face at the back face thereof which is opposed to the center electrode side).
  • the air-fuel mixture can easily reach the spark discharge gap by flowing to the inner side of the ground electrode, even in a case where the air-fuel mixture is directly exposed to the back face of the ground electrode. As a result, a poor ignitability of the spark plug can be prevented.
  • At least a portion of the ground electrode where sparks are discharged has an outer layer made of a nickel alloy and an inner layer made of pure copper or a copper alloy having a better thermal conductivity than that of the outer layer. Having such an outer layer, durability against oxidization is improved. Also, having such an inner layer, heat sinking ability becomes favorable and it is possible to prevent a failure due to a temperature rise of the ground electrode at the time of high-speed driving, such as an increment of the spark discharge gap due to an erosion of the ground electrode.
  • a ratio of a cross-sectional area of the inner layer to the entire cross-sectional area of the ground electrode is 10% or more to 35% or less. In the case where the ratio of the cross-sectional area of the inner layer to the entire cross-sectional area of the ground electrode is less than 10%, heat sinking ability is not sufficient and a magnitude of the erosion of the ground electrode becomes large.
  • the ratio of the cross-sectional area of the inner layer to the entire cross-sectional area of the ground electrode exceeds 35%, a deformation (i.e., "spring back") of the ground electrode tends to occur due to a difference in the coefficient of thermal expansion between the outer layer and the inner layer, thereby possibly having an influence on a spark discharge gap.
  • the composition 1 where the ratio of a cross-sectional area of the inner layer to the entire cross-sectional area of the ground electrode is 10% or more to 35% or less, heat sinking ability becomes favorable and a spring back of the ground electrode can be prevented, thereby preventing the erosion of the ground electrode and the influence on the spark discharge gap due to the spring back.
  • the durability of the spark plug can be improved.
  • a spark plug according to this composition is comprised of: a center electrode; an insulator provided so as to cover the surroundings of the center electrode; a cylindrical metal shell provided so as to cover the surroundings of the insulator; a ground electrode so disposed that one end thereof is joined to a front-end face of the metal shell and the other end thereof faces the front-end face of the center electrode; and a spark discharge gap formed between the front-end face of the center electrode and a front-end portion of the ground electrode, wherein the ground electrode has a width of 2mm or less and is constituted so as to reduce its width toward a back face thereof, which is opposed to the center electrode side, at least in the front-end portion thereof located at a front-end side from a center of the spark discharge gap, wherein at least a portion of the ground electrode where sparks are discharged has an outer layer made of a nickel alloy and an inner layer made of pure copper or a copper alloy having a better thermal conductivity than that of the outer layer, and wherein a ratio of a cross-
  • Composition 4 A spark plug according to this composition is comprised of: a center electrode; an insulator provided so as to cover the surroundings of the center electrode; a cylindrical metal shell provided so as to cover the surroundings of the insulator; and a ground electrode disposed so that one end thereof is joined to a front-end face of the metal shell and the other end thereof faces the front-end face of the center electrode.
  • the spark plug further comprises: a spark discharge gap formed between the front-end face of the center electrode and a front-end portion of the ground electrode, wherein the ground electrode has a width of 2mm or less at least in the front-end portion thereof located at a front-end side from a center of the spark discharge gap and a convex-shaped curved face at a back face thereof located opposed to the center electrode side, wherein at least a portion of the ground electrode where sparks are discharged has an outer layer made of a nickel alloy and an inner layer made of a nickel alloy or pure nickel having a higher purity and a better thermal conductivity than that of the outer layer, in which a ratio of a cross-sectional area of the inner layer to the entire cross-sectional area of the ground electrode is 20% or more, and a thickness of the outer layer is 0.2mm or more.
  • the compositions 3 and 4 can obtain a similar effect as that of the composition 1.
  • at least a portion of the ground electrode where sparks are discharged has an outer layer made of a nickel alloy and an inner layer made of pure nickel or a nickel alloy having a higher purity and a better thermal conductivity than that of the outer layer. Having such an outer layer, durability against oxidization is improved. Also, having such an inner layer, heat sinking ability becomes favorable, and it is possible to prevent a failure due to a temperature rise of the ground electrode at the time of high-speed driving, such as an increment of the spark discharge gap due to an erosion of the ground electrode.
  • the ratio of a cross-sectional area of the inner layer to the entire cross-sectional area of the ground electrode is 20% or more, and a thickness of the outer layer is 0.2mm or more.
  • the ratio of the cross-sectional area of the inner layer to the entire cross-sectional area of the ground electrode is less than 20%, heat sinking ability is not favorable and a magnitude of the erosion of the ground electrode becomes large.
  • the ratio of the cross-sectional area of the inner layer to the entire cross-sectional area of the ground electrode is made larger to some degree than that of the composition 1, an influence on the ground electrode due to a difference in the coefficient of thermal expansion between the outer layer and the inner layer is small, because both layers contains nickel.
  • the ratio of the cross-sectional area of the inner layer to the entire cross-sectional area of the ground electrode is made considerably large, the thickness of the outer layer becomes small. The thin outer layer may cause a fracture.
  • composition 2 which has the ratio of a cross-sectional area of the inner layer to the entire cross-sectional area of the ground electrode is 20% or more, and a thickness of the outer layer is 0.2mm or more, heat sinking ability becomes favorable, thereby preventing the erosion of the ground electrode and the fracture of the outer layer. As a result, the durability of the spark plug can be improved.
  • the thickness of the outer layer it is desirable to provide the following composition 5.
  • composition 5 In any one of the compositions 1 to 4, a spark plug according to a composition 5, provided that the distance of the spark discharge gap is taken as G (mm), the diameter of the front-end portion of the center electrode is taken as D (mm) and the distance between a point nearest to the center electrode in the outer layer and a point nearest to the center electrode in the inner layer is taken as T0 (mm) when the ground electrode is projected from the front-end face side thereof along a central axis of the center electrode, wherein the distance T0 satisfies the expression 0.2mm ⁇ T0 ⁇ 0.5mm within a range of ⁇ [(D/2)+G] from the central axis of the center electrode.
  • the range of ⁇ [(D/2)+G] is a range mainly corresponding to "a portion where the spark discharge is performed" i.e., a range where the spark discharge is easily generated in any one of compositions 1 to 4.
  • the distance T0 satisfies the expression 0.2mm ⁇ T0 ⁇ 0.5mm.
  • the distance T0 is less than 0.2mm, there is a possibility that the thin outer layer might suffer a tear (fracture).
  • the inner layer may be made eccentric with respect to the ground electrode. In this case, it is desirable to have the following composition 6.
  • composition 6 In any one of the compositions 1 to 5, a spark plug according to a composition 6, provided that the ground electrode and the center electrode are projected from the front-end face side of the ground electrode along the central axis of the center electrode, tangent lines are drawn from two outer rims of the front-end of the center electrode, respectively, so as not to intersect with each other with respect to a periphery line of the ground electrode, and the periphery line is divided in two parts by contact points to define one part as a center electrode side and the other part as a back face side, wherein the inner layer is made eccentric so that a thinnest portion of the outer layer is located at the back face side of the ground electrode.
  • the inner layer is made eccentric so that the thinnest portion of the outer layer is located at the back face side of the ground electrode.
  • more effective heat sinking ability can be expected because the inner layer having an excellent heat dispersion is made eccentric at the back face side of the ground electrode where a combustion chamber is closely disposed.
  • the fracture of the portion where the spark discharge is generated can be prevented and the effective heat sinking ability in the combustion chamber is facilitated because the inner layer is not made extremely eccentric but is made eccentric to some extent.
  • the inner layer may be made eccentric with respect to the ground electrode as follows.
  • Composition 7 A spark plug according to this composition, provided that an outer edge of a front-end portion of the ground electrode, an inner layer formed in the ground electrode and the center electrode are projected from the front-end face side of the ground electrode along the central axis of the center electrode, tangent lines are drawn from two outer rims of the front-end of the center electrode, respectively so as not to intersect with each other with respect to a periphery line of the ground electrode, and the front-end portion of the ground electrode are divided by, including a segment which connects both contact points of the tangent lines, a planar face perpendicular to the front-end face of the ground electrode into two portions: an inner side portion serving as a center electrode side; and an outer side portion serving as an opposed side to the center electrode, wherein, in the front-end portion of the ground electrode, a volume Vo of an outer side inner layer with respect to the outer side portion is larger than a volume Vi of an inner side inner layer with respect to the inner side portion.
  • the inner layer formed in the front-end portion of the ground electrode is made eccentric toward outer side, as well as disposed at the inner side.
  • the outer side inner layer of the front-end portion of the ground electrode actively conducts heat from a portion near the center of a combustion chamber to a metal shell.
  • the front-end portion of the ground electrode has the inner side inner layer, it is possible to avoid releasing heat, which is received by the outer side outer layer from the center of the combustion chamber, through the inner side of the front-end portion of the ground electrode, thereby resulting in preventing any ignitability failure caused by drawing significant heat from an initial flame kernel formed between the spark discharge gap.
  • a noble metal tip joined to the ground electrode is exposed in the spark discharge gap, it is possible to avoid an extreme heat cycle in use, thereby improving the durability of the tip.
  • Fig. 1 is a partially sectional front view showing an entire composition of a spark plug according to this embodiment
  • Fig. 2 is a partially sectional front view showing a composition of a main portion.
  • the present invention will be described with reference to mainly Fig. 2 .
  • a spark plug 100 is comprised of a metal shell 1, an insulator 2, a center electrode 3 and a ground electrode 4. There is also provided a contact terminal or the like electrically connected to the center electrode 3 through a resistor or a glass seal portion at a rear-end side of the insulator 2, even though no numeral is particularly attached thereto.
  • the metal shell 1 assumes a cylindrical form and holds the insulator 2 therein through talc, a packing or the like.
  • a front-end portion of the insulator 2 projects from the metal shell 1.
  • the center electrode 3 is disposed inside the insulator 2 so that a noble-metal tip 31 formed at a front-end of the center electrode 3 projects from the insulator 2.
  • a rear-end face of the ground electrode 4 is welded to a front-end face of the metal shell 1 and a bent portion 5 positioned in a middle section of the ground electrode 4 in the longitudinal direction is bent toward the central direction.
  • the ground electrode 4 is arranged so that a front-end portion inner side face thereof faces the front-end face of the center electrode 3.
  • a noble metal tip 32 facing the noble metal tip 31 is formed in the inner side face of the ground electrode 4. Furthermore, a gap formed between the noble metal tip 31 and the noble metal tip 32 serves as a spark discharge gap 33.
  • the insulator 2 is comprised of a ceramic sintered compact made of, for example, alumina, and a pore 6 for accommodating the center electrode 3 is formed therein along the axial direction of the insulator 2.
  • the metal shell 1 assumes a cylindrical form and is made of a metal, such as low carbon steel. Further, the metal shell 1 constitutes a housing of the spark plug 100, and has an outer circumference face forming a screw portion 7 for mounting the spark plug 100 on a cylinder head of the engine (not illustrated).
  • the main body of the ground electrode 4 has a two-layer structure comprised of an outer layer 4A and an inner layer 4B.
  • the outer layer 4A in this embodiment is comprised of a nickel alloy, such as Inconel 600 and Inconel 601 (registered trademark).
  • the inner layer 4B is comprised of pure copper having a better thermal conductivity than that of the nickel alloy. Such an inner layer 4B can facilitate a heat sinking ability of the ground electrode 4 (later described in detail).
  • the main body of the center electrode 3 also has a two-layer structure comprised of an outer layer and an inner layer.
  • the noble metal tip 31 formed on the center electrode 3 is comprised of a noble alloy that contains, for example, iridium as a main component, platinum-10% by mass, rhodium- 3% by mass and nickel-1% by mass.
  • the noble metal tip 32 formed on the ground electrode 4 is comprised of a noble alloy that contains, for example, platinum as a main component, iridium-20% by mass and rhodium-5% by mass.
  • a predetermined shape e.g., a columnar shape
  • the noble metal tip 31 and 32 are formed on the center electrode 3 and the ground electrode 4, respectively, in this embodiment, the noble metal tip may be provided on either the ground electrode 4 or the center electrode 3.
  • the spark discharge gap is formed between the noble metal tip 31 and the ground electrode 4 which are opposed to each other.
  • the noble metal tip 32 is formed only on the ground electrode 4
  • the spark discharge gap is formed between the noble metal tip 32 and the center electrode 3 which are opposed to each other.
  • the spark discharge gap is formed between the front-end face of the center electrode 3 and an inner side face of the ground electrode 4 which are opposed to each other.
  • the ground electrode 4 has the two-layer structure in which a main body portion is comprised of the outer layer 4A and the inner layer 4B as mentioned above. As shown in Figs. 2 , 3 and 4 , the ground electrode 4 assumes a circular form in the cross-section and an outer diameter L thereof is 2mm or less (e.g., 1.7mm) [i.e., the width in the direction perpendicular to the longitudinal direction of the spark plug 100 (the direction parallel to the front-end face of the metal shell) which is a projection width when the ground electrode 4 is viewed from the center electrode 3 (front-end face of the ground electrode 4)].
  • an outer diameter L thereof is 2mm or less (e.g., 1.7mm) [i.e., the width in the direction perpendicular to the longitudinal direction of the spark plug 100 (the direction parallel to the front-end face of the metal shell) which is a projection width when the ground electrode 4 is viewed from the center electrode 3 (front-end face of the ground electrode 4)].
  • the outer layer 4A is comprised of the nickel alloy
  • the inner layer 4B is comprised of pure copper.
  • the inner layer 4B reaches (is exposed to) the front-end face of the ground electrode 4 and the ratio of the cross-sectional area of the inner layer 4B to the entire cross-sectional area of the ground electrode 4 falls within the range of 10% or more to 35% or less (e.g., 25% in this embodiment).
  • the distance of the spark discharge gap 33 is taken as G (mm)
  • the diameter of the front-end portion (the noble metal tip 31 in this embodiment) of the center electrode 3 is taken as D (mm)
  • the distance between a point P2 nearest to the center electrode 3 in the outer layer 4A and a point P1 nearest to the center electrode 3 in the inner layer 4B is taken as T0 (mm) when the ground electrode 4 is projected from the front-end face side thereof along a central axis C1 of the center electrode 3
  • the distance T0 is greater than or equal to 0.2mm and less than or equal to 0.5mm within a range of ⁇ [(D/2)+G] from the central axis C1 of the center electrode 3 (i.e., within the range where the spark discharge is easily generated).
  • the metal shell 1 is prepared beforehand. That is, a through-hole is provided in a columnar-shaped metal material (e.g., iron-system material or a stainless steel material, such as S15C or S25C) using a cold forging processing to produce a primary body of the metal shell 1. Then, an outer shape of thus-produced body is arranged by a cutting process to form a metal shell intermediate body.
  • a columnar-shaped metal material e.g., iron-system material or a stainless steel material, such as S15C or S25C
  • the ground electrode 4 is joined to the front-end portion of the metal shell intermediate body by a resistance welding.
  • the ground electrode 4 welded at this time assumes a straight rod-like shape and has not been bent yet.
  • the ground electrode 4 may be obtained as follows.
  • the copper core constituting the inner layer 4B is disposed in a nickel alloy cup, which constitutes the outer layer 4A, or inserted in a cylindrical nickel alloy body to thereby form a cup-shape assembly or a cylindrical assembly having a core-in-sheath structure.
  • thus-formed assembly is subjected to an extrusion molding using a mold or the like so as to thin down somewhat with a diameter being a little larger than that of a final diameter.
  • the intermediate material is subjected to a swaging process to thin down the diameter thereof.
  • a wire drawing process using a die or the like may be employed to thin down the intermediate material, instead of the swaging process.
  • the straight rod-like ground electrode 4 comprised of the outer layer 4A and the inner layer 4B is produced.
  • the noble metal tip 32 is joined to the front-end portion of the ground electrode 4 by resistance welding, laser welding or the like.
  • plating in a welded area is removed prior to the welding process, or alternatively, a masking is applied to an area for welding in the plating process. Further, the tip welding may be performed after an assembly process (later described).
  • the insulator 2 is formed by molding process, separately from the metal shell 1.
  • a raw granulated body for molding is prepared using a raw powder mixture of alumina as a main component and a binder or the like.
  • the granulated body is subjected to a rubber pressing to form a cylindrical mold.
  • thus-formed mold is subject to a grinding process so as to machine the exterior thereof.
  • the thus-ground mold is sintered in a furnace to complete the insulator 2.
  • the center electrode 3 is manufactured separately from the metal shell 1 and the insulator 2. That is, the forging process is performed to a nickel alloy, and a copper core is disposed in the center of thus-forged alloy in order to improve heat dispersion. Then, the noble metal tip 31 is joined to the front-end portion of the core by a resistance welding, a laser welding or the like.
  • the thus-formed center electrode 3 having the noble metal tip 31 and a terminal fitting (not illustrated) are disposed and fixed in the pore 6 of the insulator 2 through the glass seal material (not illustrated).
  • a mixture of borosilicate glass and metallic powder is used as a glass seal.
  • the prepared glass seal is charged into the pore 6 of the insulator 2.
  • the terminal fitting is pressed into the pore 6 from the rear side, and the thus-assembled body is fired in the furnace.
  • a glaze layer formed on a surface of a drum portion of the insulator 2 at the rear-end side may be simultaneously fired, or the glaze layer may be formed beforehand.
  • the thus-formed center electrode 3, the thus-formed insulator 2 provided with the terminal fitting and the metal shell 1 including the ground electrode 4 are assembled. More particularly, the rear-end portion of the metal shell 1 relatively formed thin is subjected to a cold caulking or a hot caulking so that a part of the insulator 2 is enclosed and held by the metal shell 1 from the circumferential direction.
  • the spark discharge gap 33 formed between the center electrode 3 (the noble metal tip 31) and the ground electrode 4 (the noble metal tip 32) is formed and defined by bending the ground electrode 4.
  • the spark plug 100 having the above-mentioned composition is manufactured.
  • Samples (the spark plugs) with three types of ground electrodes with an outer diameter L of 1.7mm, 1.5mm and 1.3mm were prepared. Also, each type of the samples had a different inner layer diameter (cross-sectional area). The sample was mounted on an inline four-cylinder engine having a displacement of 2000 cc, and a durability test with a 100,000km run was conducted. It is noted that a diameter D of the noble metal tip of the center electrode was 0.6mm, and the iridium alloy (Ir-5Pt) was employed as a material for the noble metal tip.
  • Ir-5Pt iridium alloy
  • an increment of a spark discharge gap (hereinafter referred to as a "gap" for the sake of convenience) are shown in Tables 1, 2 and 3, when the outer diameter L is 1.7mm, 1.5mm and 1.3mm, respectively. Further, the relationship between the increment of the gap and the ratio of the cross-sectional area of the inner layer to the cross-sectional area of the ground electrode is shown in Fig. 6 .
  • the ratio of the cross-sectional area of the inner layer to the cross-sectional area of the ground electrode was measured as follows. First, an image of the ground electrode was taken from the front-end direction to measure the cross-sectional area thereof. After conducting the durability test, the cross-section of the center line (the direction where the front-end portion extends) of the ground electrode including the center line of the center electrode was observed so as to measure the cross-sectional area of the inner layer. Here, based on these two values, the ratio of the inner layer cross-sectional area was calculated.
  • the above-described method is only adoptable when the ground electrode has a uniform diameter. However, when a cross-sectional area of the ground electrode differs along the longitudinal direction, a method such as a three-dimensional transmission imaging (so-called CT scan) may be adopted.
  • the heat sinking ability becomes favorable, and the spring back of the ground electrode can be prevented, thereby preventing the erosion of the ground electrode 4, as well as preventing the influence on the spark discharge gap due to the spring back.
  • the durability of the spark plug can be improved.
  • the spark plug according to this embodiment is also comprised of a metal shell 1, an insulator 2, a center electrode 3 and a ground electrode 4.
  • the composition of the ground electrode 4 is different from that of the first embodiment.
  • a main body of the ground electrode 4 has a two-layer structure comprised of an outer layer 4A and an inner layer 4B, and the outer layer 4A in this embodiment is also comprised of a nickel alloy, such as Inconel 600 or the like.
  • the inner layer 4B in the second embodiment is comprised of high purity nickel (e.g., pure nickel: including indispensable components) having a better thermal conductivity than that of the outer layer 4A.
  • the ground electrode 4 according to the second embodiment also assumes a circular form in the cross-section and an outer diameter L [i.e., the width in the direction perpendicular to the longitudinal direction of the spark plug 100 (the direction parallel to the front-end face of the metal shell) which is a projection width when the ground electrode 4 is viewed from the center electrode 3 (front-end face of the ground electrode 4)] thereof is 2mm or less (e.g., 1.7mm).
  • the ratio of the cross-sectional area of the inner layer 4B to the entire cross-sectional area of the ground electrode 4 is set to be 20% or more (e.g., 25% in this embodiment).
  • a thickness T (refer to Fig. 5B ) of the outer layer 4A is set to be 0.2mm or more.
  • the distance between a point P2 nearest to the center electrode 3 in the outer layer 4A and a point P 1 nearest to the center electrode 3 in the inner layer 4B is taken as T0 (mm) when the ground electrode 4 is projected from the front-end face side thereof along a central axis C1 of the center electrode 3, the distance T0 is greater than or equal to 0.2mm and less than or equal to 0.5mm within a range of ⁇ [(D/2)+G] from the central axis C1 of the center electrode 3 (i.e., within the range where the spark discharge is easily generated).
  • Samples (the spark plugs) with three types of ground electrodes with an outer diameter L of 1.7mm, 1.5mm and 1.3mm were prepared. Each type of the samples had a different inner layer diameter (cross-sectional area).
  • the sample was mounted on an inline four-cylinder engine having a displacement of 2000 cc, and a durability test of a 100,000km run was conducted. It is noted that a diameter D of the noble metal tip of the center electrode was 0.6mm, and the iridium alloy (Ir-5Pt) was employed as a material for the noble metal tip.
  • the evaluation result (regarding a presence/absence of an outer layer fracture and an increment of the gap) is shown in Table 4, 5 and 6, when the outer diameter L is 1.7mm, 1.5mm and 1.3mm, respectively. Further, the relationship between the increment of the gap and the ratio of the cross-sectional area of the inner layer to the cross-sectional area of the ground electrode is shown in Fig. 7 .
  • the heat sinking ability becomes favorable, thereby preventing an influence on the spark discharge gap due to the erosion of the ground electrode. As a result, the durability of the spark plug can be improved.

Claims (8)

  1. Zündkerze (100) zum Betrieb in einem Verbrennungsmotor, umfassend:
    eine Mittelelektrode (3);
    einen Isolator (2), welcher die Mittelelektrode (3) zumindest teilweise umgibt;
    ein zylindrisches Metallgehäuse (1), welches den Isolator (2) zumindest teilweise umgibt;
    eine Massenelektrode (4), welche so angeordnet ist, dass ein Ende davon mit einer vorderendigen Fläche des Metallgehäuses (1) verbunden ist und dass das andere Ende davon der vorderendigen Fläche der Mittelelektrode (3) gegenüberliegt; und
    einen Funkenentladungs-Zwischenraum (33), welcher zwischen der vorderendigen Fläche der Mittelelektrode (3) und einem vorderendigen Abschnitt der Massenelektrode (4) ausgebildet ist,
    wobei zumindest ein Abschnitt der Massenelektrode (4), wo Funken entladen werden, eine äußere Schicht (4A), welche aus einer Nickellegierung hergestellt ist, und eine innere Schicht (4B), welche aus reinem Kupfer oder einer Kupferlegierung mit einer besseren Wärmeleitfähigkeit als derjenigen der äußeren Schicht (4A) hergestellt ist, aufweist, und
    wobei ein Verhältnis eines Querschnittsbereichs der inneren Schicht (4B) zu dem gesamten Querschnittsbereich der Massenelektrode (4) 10 % oder mehr bis 35 % oder weniger beträgt,
    dadurch gekennzeichnet,
    dass, wenn die Massenelektrode (4) und die Mittelelektrode (3) von der Seite der vorderendigen Fläche der Massenelektrode (4) entlang der Mittelachse (C1) der Mittelelektrode (3) hervorragen, Tangenten (m1, m2) von zwei äußeren Rändern des vorderen Endes der Mittelelektrode (3) gezogen werden, um sich nicht miteinander bezüglich einer Umfangslinie der Mittelelektrode (4) zu schneiden, und wobei die Umfangslinie durch Berührungspunkte (PM1, PM2) in zwei Teile geteilt wird, um einen Teil als eine Seite (α1) und den anderen Teil als eine Seite (β1) einer hinteren Fläche der Mittelelektrode (3) zu definieren,
    wobei dann die innere Schicht (4B) exzentrisch ist, so dass der dünnste Abschnitt der äußeren Schicht (4A) an der Seite (β1) der hinteren Fläche der Massenelektrode (4) angeordnet ist.
  2. Zündkerze nach Anspruch 1, dadurch gekennzeichnet, dass die Massenelektrode (4) ausgestaltet ist, um eine verringerte Breite einer hinteren Fläche davon aufzuweisen, wobei die hintere Fläche am weitesten von der Mittelelektrode (3), zumindest in einem vorderendigen Abschnitt der Massenelektrode (4), welcher vor einer Mitte des Funkenentladungs-Zwischenraumes (33) angeordnet ist, entfernt ist.
  3. Zündkerze nach Anspruch 1, dadurch gekennzeichnet, dass die Massenelektrode (4) eine Breite von 2 mm oder weniger zumindest in dem vorderendigen Abschnitt davon, welcher vor einer Mitte des Funkenentladungs-Zwischenraumes (33) angeordnet ist, und eine konvex geformte gekrümmte Fläche an einer hinteren Fläche davon, welche am weitesten von Seite der Mittelelektrode (3) entfernt ist, aufweist.
  4. Zündkerze (100) zum Betrieb in einem Verbrennungsmotor, umfassend:
    eine Mittelelektrode (3);
    einen Isolator (2), welcher die Mittelelektrode (3) zumindest teilweise umgibt;
    ein zylindrisches Metallgehäuse (1), welches den Isolator (2) zumindest teilweise umgibt;
    eine Massenelektrode (4), welche so angeordnet ist, dass ein Ende davon mit einer vorderendigen Fläche des Metallgehäuses (1) verbunden ist und dass das andere Ende davon der vorderendigen Fläche der Mittelelektrode (3) gegenüberliegt; und
    einen Funkenentladungs-Zwischenraum (33), welcher zwischen der vorderendigen Fläche der Mittelelektrode (3) und einem vorderendigen Abschnitt der Massenelektrode (4) ausgebildet ist,
    wobei zumindest ein Abschnitt der Massenelektrode (4), wo Funken entladen werden, eine äußere Schicht (4A), welche aus einer Nickellegierung hergestellt ist, und eine innere Schicht (4B), welche aus reinem Kupfer oder einer Kupferlegierung mit einer besseren Wärmeleitfähigkeit als derjenigen der äußeren Schicht (4A) hergestellt ist, aufweist, und
    wobei ein Verhältnis eines Querschnittsbereichs der inneren Schicht (4B) zu dem gesamten Querschnittsbereich der Massenelektrode (4) 20 % oder mehr beträgt,
    dadurch gekennzeichnet,
    dass die Massenelektrode eine Breite von 2 mm oder weniger aufweist, und
    dass die äußere Schicht (4A) eine Dicke von 0,2 mm oder mehr aufweist.
  5. Zündkerze nach Anspruch 4, dadurch gekennzeichnet, dass die Massenelektrode (4) eine Breite von 2 mm oder weniger aufweist und ausgestaltet ist, so dass ihre Breite zu einer hinteren Fläche davon abnimmt, wobei die hintere Fläche am weitesten von der Seite der Mittelelektrode (3) der Massenelektrode (4), zumindest in dem vorderendigen Abschnitt der Massenelektrode (4), welcher vor einer Mitte des Funkenentladungs-Zwischenraumes (33) angeordnet ist, entfernt ist.
  6. Zündkerze (100) zum Betrieb in einem Verbrennungsmotor, umfassend:
    eine Mittelelektrode (3);
    einen Isolator (2), welcher die Mittelelektrode (3) zumindest teilweise umgibt;
    ein zylindrisches Metallgehäuse (1), welches den Isolator (2) zumindest teilweise umgibt;
    eine Massenelektrode (4), welche so angeordnet ist, dass ein Ende davon mit einer vorderendigen Fläche des Metallgehäuses (1) verbunden ist und dass das andere Ende davon der vorderendigen Fläche der Mittelelektrode (3) gegenüberliegt; und
    einen Funkenentladungs-Zwischenraum (33), welcher zwischen der vorderendigen Fläche der Mittelelektrode (3) und einem vorderendigen Abschnitt der Massenelektrode (4) ausgebildet ist,
    dadurch gekennzeichnet,
    dass die Massenelektrode (4) eine Breite von 2 mm oder weniger zumindest in dem vorderendigen Abschnitt davon, welcher vor einer Mitte des Funkenentladungs-Zwischenraumes (33) angeordnet ist, und eine konvex geformte gekrümmte Fläche an einer Fläche davon, welche von der Seite der Mittelelektrode (3) der Massenelektrode (4) am weitesten entfernt ist, aufweist,
    dass zumindest ein Abschnitt der Massenelektrode (4), wo Funken entladen werden, eine äußere Schicht (4A), welche aus einer Nickellegierung hergestellt ist, und eine innere Schicht (4B), welche aus einer Nickellegierung oder aus reinem Nickel mit einer höheren Reinheit und einer besseren Wärmeleitfähigkeit als derjenigen der äußeren Schicht (4A) hergestellt ist, aufweist, und
    dass ein Verhältnis eines Querschnittsbereichs der inneren Schicht (4B) zu dem gesamten Querschnittsbereich der Massenelektrode (4) 20 % oder mehr beträgt, und
    dass eine Dicke der äußeren Schicht (4A) 0,2 mm oder mehr beträgt.
  7. Zündkerze (100) zum Betrieb in einem Verbrennungsmotor nach einem der Ansprüche 1 bis 6,
    dadurch gekennzeichnet,
    dass, wenn ein Abstand des Funkenentladungs-Zwischenraumes (33) G entspricht, ein Durchmesser des vorderendigen Abschnitts der Mittelelektrode (3) D entspricht und ein Abstand zwischen einem Punkt, welcher der Mittelelektrode (3) in der äußeren Schicht (4A) am nächsten liegt, und einem Punkt, welcher der Mittelelektrode (3) in der inneren Schicht (4B) am nächsten liegt, T0 entspricht, wenn die Massenelektrode (4) von einer Seite der vorderendigen Fläche davon entlang einer Mittelachse (C1) der Mittelelektrode (3) hervorragt,
    dass dann der Abstand T0 der Ungleichung 0,2 mm ≤ T0 ≤ 0,5 mm innerhalb eines Bereiches von ±[(D/2) + G] von der Mittelachse (C1) der Mittelelektrode (3) genügt.
  8. Zündkerze (100) nach einem der Ansprüche 1 bis 7,
    dadurch gekennzeichnet,
    dass, wenn die Massenelektrode (4) und die Mittelelektrode (3) von der Seite der vorderendigen Fläche der Massenelektrode (4) entlang der Mittelachse (C1) der Mittelelektrode (3) hervorragen, Tangenten (m1, m2) von zwei äußeren Rändern des vorderen Endes der Mittelelektrode (3) gezogen werden, um sich nicht miteinander bezüglich einer Umfangslinie der Massenelektrode (4) zu schneiden und wobei der vorderendige Abschnitt der Massenelektrode (4) durch eine ebene Fläche (HM) senkrecht zu der vorderendigen Fläche der Massenelektrode (4), wobei ein Segment, welches beide Berührungspunkte (PM1, PM2) der Tangenten verbindet, eingeschlossen ist, in zwei Abschnitte geteilt ist: einen inneren Seitenabschnitt, welcher als eine Seite der Mittelelektrode (3) dient; und einen äußeren Seitenabschnitt, welcher als eine der Mittelelektrode (3) gegenüberliegende Seite dient,
    dass dann in dem vorderendigen Abschnitt der Massenelektrode (4) ein Volumen Vo der inneren Schicht (4BOS), welches in dem äußeren Seitenabschnitt angeordnet ist, größer als ein Volumen Vi der inneren Schicht (4BIS), welches in dem inneren Seitenabschnitt angeordnet ist, ist.
EP20070251139 2006-03-20 2007-03-19 Zündkerze für einen Verbrennungsmotor Active EP1837964B1 (de)

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JP4719191B2 (ja) * 2007-07-17 2011-07-06 日本特殊陶業株式会社 内燃機関用スパークプラグ
JPWO2009153927A1 (ja) * 2008-06-18 2011-11-24 日本特殊陶業株式会社 スパークプラグ
CN102138260B (zh) * 2008-09-02 2013-07-31 日本特殊陶业株式会社 火花塞
US8207657B2 (en) * 2008-11-04 2012-06-26 Ngk Spark Plug Co., Ltd. Spark plug and method of manufacturing the same
US8519606B2 (en) * 2009-08-26 2013-08-27 Ngk Spark Plug Co., Ltd. Spark plug for internal combustion engine and method of manufacturing spark plug
EP2621035B1 (de) * 2010-09-24 2018-11-21 Ngk Spark Plug Co., Ltd. Zündkerzenelektrode, herstellungsverfahren dafür, zündkerze und verfahren zur herstellung der zündkerze
WO2012039229A1 (ja) * 2010-09-24 2012-03-29 日本特殊陶業株式会社 スパークプラグの電極及びその製造方法、並びにスパークプラグ及びスパークプラグの製造方法
JP2015133243A (ja) * 2014-01-14 2015-07-23 日本特殊陶業株式会社 スパークプラグ
DE102018125456A1 (de) * 2018-10-15 2020-04-16 Bayerische Motoren Werke Aktiengesellschaft Zündkerze sowie Verfahren zum Herstellen einer Elektrode
CN110792515B (zh) * 2019-11-08 2022-05-06 陕西航空电气有限责任公司 一种大推力发动机点火电嘴

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US4331899A (en) * 1979-03-09 1982-05-25 Nippon Soken, Inc. Spark plug
US5210457A (en) * 1990-09-07 1993-05-11 Ngk Spark Plug Co., Ltd. Outer electrode for spark plug and a method of manufacturing thereof
FR2726864B1 (fr) * 1994-11-15 1996-12-27 Sagem Allumage Organe d'allumage pour moteur a combustion interne
JPH08213149A (ja) * 1995-02-01 1996-08-20 Ngk Spark Plug Co Ltd スパークプラグ
JP2002343533A (ja) * 2001-03-15 2002-11-29 Denso Corp 内燃機関用スパークプラグ
DE10129040A1 (de) * 2001-06-15 2003-01-02 Bosch Gmbh Robert Zündkerze

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