JP2010086758A - Spark plug and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve long life improvement of a spark plug which uses a rare-metal chip member at a part of spark discharge. <P>SOLUTION: The spark plug includes a central electrode extending through an axis direction of the spark plug and a grounded electrode forming a spark gap between the central electrode and the same. At least either the central electrode or the grounded electrode includes an electrode matrix, a rare-metal chip member, and a medium member with its first face in contact with the rare-metal chip member and a second face which is the opposite side of the first face in contact with the electrode matrix, as well as a laser-melted part formed on the side face of the rare-metal chip member and the medium member formed by laser welding at least a portion of an outer rim of a contact part of the rare-metal chip member and the medium member. At least a portion of the laser melted part is embedded in the electrode matrix. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a spark plug and a method for manufacturing the spark plug.

  There is known a spark plug in which a noble metal tip member such as iridium (Ir) excellent in spark wear resistance and oxidation wear resistance is joined to a spark discharge portion in a center electrode or a ground electrode of the spark plug. In such a spark plug, a technique for fixing a noble metal tip member to an electrode base material by laser welding is known. (For example, patent document 1).

JP 2005-183167 A JP 2002-93547 A JP-A-8-298178 Koji Nakayama and two others, “Development of long-life iridium plugs for 190 gas engines”, Preprint of Academic Lecture, Japan Society for Automotive Engineers, 2004, No. 37-04, p. 7-12

  However, since the laser melting portion between the noble metal tip member and the electrode base material is difficult to control the components, there is a possibility that corrosion occurs in the laser melting portion. The corrosion may cause the noble metal tip member to peel off and shorten the life of the spark plug.

  An object of the present invention is to realize a long life of a spark plug in a spark plug using a noble metal tip member at a spark discharge site.

  In order to solve at least a part of the problems described above, the present invention can take the following forms or application examples.

Application Example 1 A central electrode extending in the axial direction;
A ground electrode that forms a spark gap with the center electrode;
A spark plug having
At least one of the center electrode and the ground electrode is
An electrode base material;
A precious metal tip member;
An intermediate member in which a first surface is in contact with the noble metal tip member, and a second surface opposite to the first surface is in contact with the electrode base material;
By laser welding at least a part of the outer edge of the contact portion between the noble metal tip and the intermediate member, a laser melting portion formed on a side surface of the noble metal tip member and the intermediate member,
With
A spark plug, wherein at least a part of the laser melting portion is buried in the electrode base material.
In this way, since at least a part of the laser melting portion is buried in the electrode base material, corrosion of the laser welding portion can be suppressed and the life of the spark plug can be extended.

[Application Example 2] The spark plug according to Application Example 1,
A spark plug, which is resistance-welded between the intermediate member and the electrode base material.
If it carries out like this, a laser fusion part can be further covered by the welding droop by resistance welding. As a result, the corrosion of the laser weld can be further suppressed, and the life of the spark plug can be extended.

[Application Example 3] The spark plug according to Application Example 1 or Application Example 2,
A spark plug in which 50% or more of the laser melting portion is buried in the electrode base material.
In this way, the corrosion of the laser weld can be further suppressed, and the life of the spark plug can be extended.

[Application Example 4] The spark plug according to Application Example 1 or Application Example 2,
A spark plug in which 100% of the laser melting portion is buried in the electrode base material.
In this way, the corrosion of the laser weld can be further suppressed, and the life of the spark plug can be extended.

[Application Example 5] The spark plug according to any one of Application Examples 1 to 4,
The electrode base material is a spark plug having a recess for burying the laser melting portion.
In this way, the laser weld can be easily embedded in the electrode base material.

[Application Example 6] The spark plug according to Application Example 5,
A spark plug, wherein resistance welding is performed between an upper surface of the recess and a bottom surface of the intermediate member.
If it carries out like this, it can suppress more reliably that a laser welding part touches external air by resistance welding. As a result, the corrosion of the laser weld can be further suppressed, and the life of the spark plug can be extended.

Application Example 7 The spark plug according to any one of Application Example 2 to Application Example 6,
A spark plug provided on the upper surface of the electrode base material with a protruding portion protruding from the upper surface of the electrode member along a side surface of the noble metal tip member.

[Application Example 8] The spark plug according to Application Example 7,
The protruding portion is a spark plug that covers at least a part of the laser melting portion.
If it carries out like this, it will be suppressed that a laser fusion part touches external air by a protrusion part. As a result, the corrosion of the laser weld can be further suppressed, and the life of the spark plug can be extended.

[Application Example 9] The spark plug according to Application Example 7 or Application Example 8,
Between the intermediate member and the electrode base material, resistance welding is performed,
The protrusion is a spark plug, which is a welding sag of the resistance welding.
By so doing, the laser welded portion is covered by welding sagging, so that the corrosion of the laser welded portion can be further suppressed and the life of the spark plug can be extended. Further, since the welding sag naturally occurs by resistance welding, a protruding portion for covering the laser welded portion can be easily formed.

[Application Example 10] The spark plug according to any one of Application Examples 1 to 9,
A spark plug in which a linear expansion coefficient of the intermediate member is larger than a linear expansion coefficient of the noble metal tip member and smaller than a linear expansion coefficient of the electrode base material.
In this case, the linear expansion coefficient of the intermediate member is larger than the linear expansion coefficient of the noble metal tip member and smaller than the linear expansion coefficient of the electrode base material, and therefore, between the intermediate member and the noble metal tip member, and between the intermediate member and the electrode base member. The stress which generate | occur | produces between materials can be suppressed. As a result, separation between the intermediate member and the noble metal tip member and separation between the intermediate member and the electrode base material can be suppressed.

[Application Example 11] The spark plug according to any one of Application Examples 1 to 10,
The intermediate member is
i) Palladium (Pd)
ii) Gold (Au)
iii) Gold palladium alloy (AuPd alloy)
iv) A spark plug formed of a material mainly containing any one of platinum-nickel alloys.
In this way, an intermediate member that satisfies the conditions of the Young's modulus and the linear expansion coefficient can be formed.

[Application Example 12] The spark plug according to any one of Application Example 1 to Application Example 11,
A spark plug in which a melting point of the noble metal tip member is higher than a melting point of the electrode base material.
By doing so, it is difficult to resistance weld the noble metal tip member and the electrode base material. Therefore, a configuration in which the noble metal tip member and the intermediate member are welded using laser welding is more effective.

[Application Example 13] The spark plug according to Application Example 12,
The noble metal tip member is
i) Iridium (Ir)
ii) Iridium alloy
iii) Platinum (Pt)
iv) A spark plug formed of a material mainly composed of any one of platinum alloys.
In this case, since the melting point of the noble metal tip is relatively high, it is difficult to resistance weld the noble metal tip member and the electrode base material. For this reason, the structure which welds a noble metal tip member and an intermediate member using laser welding is more effective.

[Application Example 14] The spark plug according to any one of Application Examples 1 to 13,
A spark plug, wherein at least one of the center electrode and the ground electrode is the ground electrode.
In this case, since the corrosion of the ground electrode that is inserted deeply into the combustion chamber of the engine and becomes high temperature can be suppressed, the life of the spark plug can be extended.

[Claim 15] The spark plug according to any one of claims 1 to 9, wherein
The spark plug is formed of the same material as the nickel alloy or the ground electrode base material.

Application Example 16 A spark plug manufacturing method having a center electrode extending in the axial direction and a ground electrode that forms a spark gap between the center electrode,
(A) laser welding at least part of the outer edge of the contact portion between the noble metal tip member and the first surface of the intermediate member;
(B) fixing a second surface side opposite to the first surface of the intermediate member to at least one electrode base material of the center electrode and the ground electrode;
With
The step (b) is performed such that at least a part of the laser melting portion formed on the side surfaces of the noble metal tip member and the intermediate member in the step (a) is buried in the electrode base material. A method for manufacturing a spark plug.
By doing so, it is possible to manufacture a spark plug in which at least a part of the laser melting portion is buried in the electrode base material and corrosion of the laser welding portion can be suppressed.

[Application Example 17] A spark plug manufacturing method according to Application Example 15,
The step (b)
(B1) forming a buried hole in the electrode base material;
(B2) fixing the noble metal member and the intermediate member to the buried hole with the second surface side down;
A method for manufacturing a spark plug, comprising:
In this way, it is possible to easily manufacture a spark plug in which at least a part of the laser melting portion is buried in the electrode base material.

A. First embodiment:
Hereinafter, embodiments of the present invention will be described based on examples. FIG. 1 is a partial cross-sectional view of a spark plug 100 as an embodiment of the present invention. In FIG. 1, the axial direction OD of the spark plug 100 will be described as the vertical direction in the drawing, the lower side will be described as the front end side, and the upper side will be described as the rear end side.

  As shown in FIG. 1, the spark plug 100 includes an insulator 10 as an insulator, a metal shell 50 that holds the insulator 10, a center electrode 20 that is held in the insulator 10 in the axial direction OD, A ground electrode 30 and a terminal fitting 40 provided at the rear end of the insulator 10 are provided.

  As is well known, the insulator 10 is formed by firing alumina or the like, and has a cylindrical shape in which an axial hole 12 extending in the axial direction OD is formed at the axial center. A flange portion 19 having the largest outer diameter is formed substantially at the center in the axial direction OD, and a rear end side body portion 18 is formed on the rear end side (upper side in FIG. 1). A front end side body portion 17 having a smaller outer diameter than the rear end side body portion 18 is formed on the front end side from the flange portion 19 (lower side in FIG. 1), and further, on the front end side from the front end side body portion 17, A leg length portion 13 having an outer diameter smaller than that of the distal end side body portion 17 is formed. The long leg portion 13 is reduced in diameter toward the tip side, and is exposed to the combustion chamber when the spark plug 100 is attached to the engine head 200 of the internal combustion engine. A step portion 15 is formed between the long leg portion 13 and the front end side body portion 17.

  The metal shell 50 is a cylindrical metal fitting for fixing the spark plug 100 to the engine head 200 of the internal combustion engine. The metal shell 50 holds the insulator 10 inside so as to surround a portion from a part of the rear end side body part 18 to the leg long part 13. The metal shell 50 is formed of a low carbon steel material, and has a thread engaging with a tool engaging portion 51 into which a spark plug wrench (not shown) is fitted and a mounting screw hole 201 of the engine head 200 provided at the upper part of the internal combustion engine. And a formed mounting screw portion 52. In this embodiment, the mounting screw 52 is M14 whose outer diameter M (nominal diameter) is a standard outer diameter, or M10 to M18 having a smaller or larger diameter.

  Between the tool engaging portion 51 and the mounting screw portion 52 of the metal shell 50, a bowl-shaped seal portion 54 is formed. An annular gasket 5 formed by bending a plate is fitted into a screw neck 59 between the mounting screw portion 52 and the seal portion 54. When the spark plug 100 is attached to the engine head 200, the gasket 5 is crushed and deformed between the seat surface 55 of the seal portion 54 and the opening peripheral edge portion 205 of the attachment screw hole 201. Due to the deformation of the gasket 5, the gap between the spark plug 100 and the engine head 200 is sealed, and airtight leakage in the engine through the mounting screw hole 201 is prevented.

  A thin caulking portion 53 is provided on the rear end side of the metal fitting 50 from the tool engaging portion 51. Further, a thin buckled portion 58 is provided between the seal portion 54 and the tool engaging portion 51, similarly to the caulking portion 53. Between the inner peripheral surface of the metal shell 50 from the tool engagement portion 51 to the crimping portion 53 and the outer peripheral surface of the rear end side body portion 18 of the insulator 10, annular ring members 6 and 7 are interposed. Further, talc (talc) 9 powder is filled between the ring members 6 and 7. By crimping the crimping portion 53 so as to be bent inward, the insulator 10 is pressed toward the front end side in the metal shell 50 via the ring members 6, 7 and the talc 9. As a result, the step portion 15 of the insulator 10 is supported by the step portion 56 formed at the position of the mounting screw portion 52 on the inner periphery of the metal shell 50 via the annular plate packing 8 so as to be insulated from the metal shell 50. The insulator 10 is integrated. At this time, the airtightness between the metal shell 50 and the insulator 10 is maintained by the plate packing 8, and the outflow of combustion gas is prevented. The buckling portion 58 is configured to bend outwardly and deform as the compression force is applied during caulking. The compression length in the axial direction OD of the talc 9 is increased to increase the airtightness in the metal shell 50. Increases sex. A clearance having a predetermined dimension is provided between the metal shell 50 and the insulator 10 on the tip side of the step portion 56.

  FIG. 2 is an enlarged view of the vicinity of the tip of the center electrode 20 of the spark plug 100 in the first embodiment. The center electrode 20 is mainly made of copper or copper having higher thermal conductivity than the electrode base material 21 inside the electrode base material 21 made of nickel or an alloy containing nickel as a main component, such as Inconel (trade name) 600. It is a rod-shaped electrode having a structure in which a core material 25 made of an alloy as a component is embedded. Usually, the center electrode 20 is produced by filling a core material 25 inside an electrode base material 21 formed in a bottomed cylindrical shape, and performing extrusion molding from the bottom side and stretching it. The core member 25 has a substantially constant outer diameter at the body portion, but is formed in a tapered shape at the distal end side.

  The center electrode 20, more specifically, the electrode base material 21, includes a tapered electrode base material base 22, a melting portion 23, and an electrode tip 90 having a small diameter toward the front end. The portion on the tip side of the electrode base material pedestal 22 is protruded from the tip portion 11 of the insulator 10. The electrode tip 90 is formed with a high melting point noble metal as a main component in order to improve spark wear resistance. Examples of the electrode chip 90 include iridium (Ir) and one type of platinum (Pt), rhodium (Rh), ruthenium (Ru), palladium (Pd), and rhenium (Re) mainly containing Ir. Alternatively, an Ir alloy to which two or more kinds are added is used, and an Ir-5Pt alloy (iridium alloy containing 5% by mass of platinum) or the like is frequently used. The electrode tip 90 may be made of platinum or a platinum alloy containing one or more of Ir, Ru, palladium, and rhenium with platinum as a main component.

  The melting part 23 is formed through welding of the electrode tip 90 to the electrode base pedestal 22, for example, laser welding in which a laser is irradiated and the electrode base pedestal 22 and the electrode tip 90 are melted by the heat. That is, in a state where the electrode tip 90 is disposed on the tip surface of the electrode base material pedestal 22, while irradiating a laser aiming at the boundary surface between the electrode base material base 22 and the electrode tip 90, the irradiated portion is arranged around the entire boundary surface. Make one round. In this laser welding, since both materials (the constituent material of the electrode base material base 22 and the noble metal of the electrode tip 90) are melted and mixed by laser irradiation, the electrode tip 90 and the electrode base material base 22 are firmly joined. At the same time, a melting portion 23 that connects the electrode base material base 22 and the electrode tip 90 is formed. The melting portion 23 is formed as an alloy of both materials by melting the both materials.

  The center electrode 20 extends in the shaft hole 12 toward the rear end side, and is electrically connected to the terminal fitting 40 on the rear side (upper side in FIG. 1) via the seal body 4 and the ceramic resistor 3 (see FIG. 1). It is connected to the. A high voltage cable (not shown) is connected to the terminal fitting 40 via a plug cap (not shown), and a high voltage is applied.

  The electrode base material of the ground electrode 30 is made of a metal having high corrosion resistance. As an example, a nickel alloy is used. In this embodiment, a nickel alloy called Inconel (trade name) 600 (INC600) is used. The ground electrode 30 has a substantially rectangular cross section in a direction orthogonal to its longitudinal direction. A proximal end portion (one end portion) 32 of the ground electrode 30 is joined to the distal end surface 57 of the metal shell 50 by welding. One side surface of the tip end portion (other end portion) 31 of the ground electrode 30 is bent so as to face the electrode tip 90 of the center electrode 20 on the axis O in the axial direction OD. A spark gap is formed between one side surface of the electrode base material tip 31 of the ground electrode 30 and the tip surface of the electrode tip 90. This spark gap is, for example, about 0.2 to 0.6 mm.

  A two-layer member 300 is resistance-welded to the electrode base material on the side surface facing the electrode tip 90 at the electrode base material tip 31 of the ground electrode 30. The two-layer member 300 includes a noble metal tip member 310 and an intermediate member 320. The noble metal tip member 310 and the intermediate member 320 are stacked in a direction facing the electrode tip 90 (in the first embodiment, the axial direction OD). For the noble metal tip member 310, for example, Pt (platinum) or an alloy containing Pt as a main component is used. In this embodiment, a Pt-20Ir alloy (a platinum alloy containing 20% by mass of iridium) is used. The intermediate member 320 includes Pd (palladium) or an alloy containing Pd as a main component, Au (gold) or an alloy containing Au as a main component, AuPd alloy, Pt alloy, platinum nickel alloy (for example, Pt-20Ni (20 mass) % Platinum-containing platinum alloy)). In this embodiment, Pd is used. Further, the intermediate member 320 may be formed of the same material as the electrode base material of the ground electrode 30 including a nickel alloy such as INC600.

  FIG. 3 is an enlarged view of a portion centering on the two-layer member 300. In the noble metal tip member 310 and the intermediate member 320 stacked on each other, the lower surface of the noble metal tip member 310 and the upper surface of the intermediate member 320 are in contact with each other. The outer edge of the contact surface is joined by laser welding over the entire circumference. The laser melting part 350 formed by laser welding does not reach the center of the contact surface between the noble metal tip member 310 and the intermediate member 320, but has a depth (width in the direction perpendicular to the stacking direction) L and an outer diameter. d, formed in a ring shape having a thickness t3. The two-layer member 300 is buried in the electrode base material tip 31 by the thickness t2 of the intermediate member 320, and protrudes above the electrode base material tip 31 by the thickness t1 of the noble metal tip member 310. That is, the contact surface between the intermediate member 320 and the noble metal tip member 310 is located on the same plane as the upper surface HL of the electrode base material tip 31.

  In this embodiment, the diameter d of the noble metal tip member 310 and the intermediate member 320 is 1.5 mm. The diameter d is preferably in the range of about 0.4 mm to 3.5 mm. In the present embodiment, the thickness t1 of the noble metal tip member 310 is 0.4 mm. The thickness t1 of the noble metal tip member 310 is preferably in the range of about 0.1 mm to 0.8 mm. In this embodiment, the thickness t2 of the intermediate member 320 is 0.4 mm. The thickness t1 of the intermediate member 320 is preferably in the range of about 0.1 mm to 2.5 mm. In the present embodiment, the depth L of the laser melting part 350 is set to about 1/6 of the diameter d of the noble metal tip member 310 and the intermediate member 320. The depth L of the laser melting part 350 is preferably in the range of about 1/10 to 1/2 of the diameter d of the noble metal tip member 310 and the intermediate member 320. In this embodiment, the thickness t3 of the laser melting part 350 is 0.3 mm. The thickness t3 of the laser melting part 350 is preferably in the range of about 0.1 mm to 0.8 mm.

  In the laser melting part 350, 50% of the thickness t3 is buried in the tip end part 31 of the electrode base material. That is, in the laser melting part 350, the upper half in the axial direction OD direction protrudes above the upper surface HL of the electrode base material tip 31, and the lower half is buried below the upper surface HL of the electrode base material tip 31. . Between the lower surface of the two-layer member 300 (the lower surface of the intermediate member 320) and the electrode base material tip 31 (FIG. 3: reference numeral BS portion), the side surface of the two-layer member 300 (the side surface of the intermediate member 320), and the electrode base material tip The portion 31 and the portion 31 (FIG. 3: reference sign SS portion) are joined by resistance welding. A welding sag 311 is formed on the upper surface HL of the electrode base material tip 31 along the side surface of the two-layer member 300 over the entire circumference of the two-layer member 300. The welding sag 311 protrudes upward from the electrode base material tip 31 in a ring shape. The welding sag 311 covers the upper half of the laser melting part 350 in the axial direction OD direction. The laser melting part 350 is in a state where the lower half is buried in the electrode base material tip 31 and the upper half is covered with the welding sag 311 so that the whole is not in contact with the outside air.

  The spark plug 100 described above can be manufactured, for example, by the following manufacturing method. First, the center electrode 20, the insulator 10, the metal shell 50, and the ground electrode 30 in which the above-described electrode tip 90 is joined to the electrode base material base 22 with the melting part 23 interposed therebetween are prepared. Next, the center electrode 20 is assembled to the insulator 10 so as to cover the outer periphery of the center electrode 20 while exposing the tip of the center electrode 20 (specifically, the electrode tip 90, the melting portion 23, and the electrode base material base 22). Thereafter, the metal shell 50 is assembled on the outer periphery of the insulator 10 so that the tip of the insulator 10 protrudes from the tip surface of the metal shell 50 by about 1.5 mm or more, and the base end of the base electrode of the ground electrode 30 The part 32 is joined to the front end surface 57 of the metal shell 50. The two-layer member 300 is welded to the electrode base material tip 31 of the ground electrode 30 that has been joined. Thereafter, the ground electrode 30 is bent so that the electrode base material tip 31 of the ground electrode 30 faces the tip of the center electrode 20.

  FIG. 4 is a flowchart showing a process of welding the noble metal tip member 310 and the intermediate member 320 to the electrode base material tip 31. FIGS. 5 and 6 are diagrams for explaining welding of the noble metal tip member 310 and the intermediate member 320 to the electrode base material tip 31.

  In step S10, the noble metal tip member 310 and the intermediate member 320 are laser-welded to produce a two-layer member 300 (FIG. 5A). Laser welding of the noble metal tip member 310 and the intermediate member 320 irradiates a laser aiming at the contact surface between the noble metal tip member 310 and the intermediate member 320, similarly to the laser welding of the electrode base material base 22 and the electrode tip 90. However, the irradiation part is made to make one turn over the entire contact surface. By this laser welding, the above-described ring-shaped laser melting portion 350 is formed, and the noble metal tip member 310 and the intermediate member 320 are firmly joined. The laser melting part 350 is difficult to control the composition because the materials of the noble metal tip member 310 and the intermediate member 320 are melted and mixed, and compared with the noble metal tip member 310 and the intermediate member 320, corrosion occurs. It is easy to become an easy material.

  In step S20, an electrode base material for the ground electrode 30 is prepared. In step S30, the buried hole 312 for installing the two-layer member 300 is formed in the electrode base material tip 31 (FIG. 5B). The buried hole 312 is formed in a size that allows the intermediate member 320 to be fitted with almost no gap. That is, the intermediate member 320 is a cylinder having a shape that is substantially the same as the intermediate member 320 when viewed from above. The buried hole 312 is formed by cutting with a drill, for example. The depth of the buried hole 312 is formed to be the same as the thickness t2 of the intermediate member 320 described above.

  In step S <b> 40, the two-layer member 300 is resistance-welded to the buried hole 312 formed in the electrode base material tip 31. Specifically, first, the electrode base material tip 31 is installed on the installation table with the surface opposite to the surface on which the buried hole 312 is formed, and is electrically grounded via the installation table. (Not shown). Then, the two-layer member 300 is fitted into the buried hole 312 with the intermediate member 320 facing down (FIG. 6). In this state, about 50% of the lower side of the laser melting part 350 is buried in the buried hole 312. Further, the upper end surface in the stacking direction of the noble metal tip member 310 is pressed downward in the stacking direction by the resistance welding electrode 500 (FIG. 6). The resistance welding electrode 500 has a circular cylindrical cross section perpendicular to the stacking direction and a rectangular cross section in the stacking direction. The cylindrical diameter of the resistance welding electrode 500 is larger than the cylindrical diameter of the noble metal tip member 310. For this reason, when the resistance welding electrode 500 descends from above in the stacking direction of the noble metal tip member 310, the lower end surface of the resistance welding electrode 500 contacts the entire upper end surface of the noble metal tip member 310. Touch. In the state of FIG. 6, the resistance welding electrode 500 presses the upper end surface of the noble metal tip member 310 substantially uniformly with a predetermined pressure.

  Resistance welding is performed in a state where the resistance welding electrode 500 presses the upper end surface of the noble metal tip member 310. Specifically, the potential of the resistance welding electrode 500 is set higher than the ground potential of the electrode base material tip 31, and as a result, the noble metal tip member 310 and the intermediate member 320 are connected via the resistance welding electrode 500. A large current flows through the electrode base material tip 31. The lower surface of the intermediate member 320 and the bottom surface of the buried hole 312 of the electrode base material tip 31 in contact with the lower surface are resistance welded. Further, resistance welding is performed between the side surface of the intermediate member 320 and the inner wall surface of the buried hole 312. When resistance welding is performed in this manner, a welding sag mainly composed of the electrode base material tip 31 (INC 600 in this embodiment) whose melting point is lower than that of the intermediate member 320 is formed on the opening edge of the buried hole 312 and the two-layer member 300. The above-mentioned welding sag 311 is formed by overflowing from between the two (FIG. 3). When the resistance welding is completed, the resistance welding electrode 500 is raised and the two-layer member 300 is released from the pressed state.

    The characteristics of the electrode base material (INC 600) of the ground electrode 30, the material of the noble metal tip member 310 (Pt-20Ir), and the material of the intermediate member 320 (Pd or Pt-20Ni) are shown below.

  As can be seen from Table 1, the Young's modulus of the intermediate member 320 is smaller than the Young's modulus of the noble metal tip member 310 and the electrode base material of the ground electrode 30. The linear expansion coefficient of the intermediate member 320 is larger than the linear expansion coefficient of the noble metal tip member 310 and smaller than the linear expansion coefficient of the electrode base material of the ground electrode 30.

  FIG. 7 is a graph showing the stress generated on the lower surface of the noble metal tip member 310. This graph is a value calculated by simulation. In this simulation, the diameter d of the noble metal tip member 310 was calculated for each of 0.6 mm, 1.5 mm, and 3.0 mm. This simulation was calculated for a steady state at 950 ° C. Pt-20Ir is used as the material characteristic of the noble metal tip member 310, and the INC600 characteristic value is used as the material characteristic of the electrode base material of the ground electrode 30. In this simulation, calculation was performed for two types of materials for the intermediate member 320: palladium (Pd (triangle)) and platinum alloy (Pt-20Ni (circle)) containing 20% by mass of nickel. Further, as a comparative example, the calculation was performed for the case where the noble metal tip member 310 was directly welded to the electrode base material tip 31 (INC 600) without using the intermediate member 320 (square mark).

  As can be seen from the simulation results shown in FIG. 7, when the intermediate member 320 having the material characteristics described in paragraph 0035 is used, the stress generated on the lower surface of the noble metal tip member 310 is suppressed. In particular, when palladium (Pd) is used for the intermediate member 320, compared to the case where Pt-20Ni is used as the material of the intermediate member 320 or the case where the noble metal tip member 310 is directly welded to the electrode base material tip 31. The stress generated on the lower surface of the noble metal tip member 310 is significantly suppressed. As a result, peeling between the noble metal tip member 310 and the intermediate member 320 can be suppressed.

  Further, in the first embodiment, the laser melting part 350 is not entirely in contact with the outside air because the lower half is buried in the electrode base material tip 31 and the upper half is covered with the welding sag 311. It has become. As a result, corrosion of the laser melting part 350 is suppressed, and peeling of the noble metal tip member 310 due to the corrosion is suppressed. Therefore, the life extension of the spark plug 100 is realized.

  FIG. 8 is a graph showing the experimental results of examining the occurrence of corrosion in the laser melting part 350. In this experiment, the depth of the buried hole 312 was changed, and the ratio of the thickness of the laser melting portion 350 buried in the electrode base material tip 31 was 25% or 50% (corresponding to the first embodiment). ) And 100% (corresponding to a second embodiment to be described later), a spark plug was produced and an experiment was conducted. In the experiment, 10 samples were prepared for one type of spark plug. Each sample was attached to the engine and continuously operated for 1000 hours under the conditions of 1500 revolutions per minute (rpm) and an output of 400 kw. Thereafter, the laser melting part 350 of the spark plug was visually inspected to determine the presence or absence of corrosion. As a result, it was found that the higher the burying rate of the laser melting portion 350 with respect to the tip end portion 31 of the electrode base material, the more the occurrence of corrosion is suppressed. In particular, when the burying rate of the laser melting part 350 with respect to the electrode base material tip 31 is 50% or more, the occurrence of corrosion is remarkably suppressed, and further, when the burying rate is 100%, it is further remarkable. It was found that the occurrence of corrosion was suppressed.

  Furthermore, in the present embodiment, since the welding sag 311 protrudes from the electrode base material tip portion 31 and covers the laser melting portion 350, corrosion of the laser melting portion 350 can be further suppressed. Further, since the lower part of the two-layer member 300 (the part of the intermediate member 320) is buried in the electrode base material tip 31, the dimension in which the noble metal tip member 310 protrudes from the electrode base material tip 31 (FIG. 3, t1). ) Can be reduced. As a result, in the noble metal tip member 310, the heat generated by the discharge can easily escape via the electrode base material tip 31. That is, the heat pulling of the spark plug 100 is improved.

B. Second embodiment:
FIG. 9 is a view showing the vicinity of the two-layer member 300 of the spark plug in the second embodiment. The spark plug according to the second embodiment corresponds to a sample in which the burying rate of the laser melting portion 350 with respect to the tip portion 31 of the electrode base material is 100% among the experimental results in FIG. 8 described above. As shown in FIG. 9, in the spark plug according to the second embodiment, the entire laser melting portion 350 is positioned below the upper surface HL of the electrode base material tip portion 31, and the laser melting portion 350 is almost complete. Further, it is buried in the electrode base material tip 31. Further, a welding sag 311 is formed over the entire circumference of the side surface of the noble metal tip member 310 along the side surface of the noble metal tip member 310 above the electrode base material tip 31.

  According to the spark plug in the second embodiment configured as described above, as understood from the experimental results of FIG. 8, the corrosion resistance of the laser melting portion 350 is further improved, and the life of the spark plug is extended. it can. Moreover, the dimension which the noble metal tip member 310 protrudes from the electrode base material front-end | tip part 31 can be made still smaller than 1st Example. As a result, the heat extraction of the spark plug is further improved.

C. Variation:
・ First modification:
In the above embodiment, the two-layer member 300 is disposed on the ground electrode, but it may be disposed on the center electrode or on both the ground electrode and the center electrode.

・ Second modification:
In the above embodiment, the noble metal tip member 310 and the intermediate member 320 constituting the two-layer member 300 are circular in shape when viewed from the stacking direction, but are not limited thereto. For example, the noble metal tip member 310 and the intermediate member 320 may be a polygon such as a rectangle or a hexagon, or may be an ellipse. Regardless of the shape, the noble metal tip member 310 and the intermediate member 320 have substantially the same shape as viewed from the stacking direction, and the laser melting portion 350 has the inner wall surface formed substantially vertically on the noble metal tip member 310. What is necessary is just to be buried in the burial hole.

・ Third modification:
As in the above embodiment, it is preferable that the Young's modulus of the intermediate member 320 is smaller than the Young's modulus of the noble metal tip member 310 and the Young's modulus of the electrode base material tip 31, and the linear expansion coefficient of the intermediate member 320 is noble metal tip member. It is preferably larger than the linear expansion coefficient of 310 and smaller than the linear expansion coefficient of the electrode base material tip 31. When the noble metal tip member 310 is platinum or an alloy containing platinum as a main component and the electrode base material is a nickel alloy, the material of the intermediate member 320 that satisfies such conditions is i) palladium. There is a material whose main component is any one of (Pd), ii) gold (Au), and iii) gold palladium alloy (AuPd alloy).

-Fourth modification:
In the above embodiment, the vertical discharge type has been described as an example, but a horizontal discharge type may be used. The positional relationship between the distal end portion of the ground electrode and the distal end portion of the center electrode 20 can be appropriately set according to the use of the spark plug, the required performance, and the like. A plurality of ground electrodes may be provided for one central electrode.

-5th modification:
In the above embodiment, the noble metal tip member 310 and the intermediate member 320 are laser welded over the entire circumference of the outer edge of the contact surface, but may be partially laser welded. For example, the noble metal tip member 310 and the intermediate member 320 may be laser-welded at a plurality of locations at predetermined intervals on the outer edge of the contact surface, or one half of the outer surface of the contact surface is laser-welded. Also good. Alternatively, the noble metal tip member 310 and the intermediate member 320 may be laser welded continuously at 75% of the outer edge, and the remaining 25% may not be laser welded. In these cases, of the outer edge of the contact surface between the noble metal tip member 310 and the intermediate member 320, the ratio of the portion that is laser-welded and the portion that is not is appropriately changed according to the required bonding strength. Is possible.

-6th modification:
In the embodiment described above, the spark plug 350 in which the laser melting portion 350 is buried with respect to the electrode base material tip 31 (first embodiment) and 100% spark plug (second embodiment). However, this ratio can be changed as appropriate, and if at least a part of the laser melting part 350 is buried, the occurrence of corrosion can be suppressed in the part where the laser melting part 350 is buried. it can. As can be seen from the experimental results shown in FIG. 8, this ratio is preferably 50% or more, more preferably as high as possible, and even more preferably 100% or more.

  As mentioned above, although the Example and modification of this invention were demonstrated, this invention is not limited to these Example and modification at all, and implementation in a various aspect is possible within the range which does not deviate from the summary. It is.

The fragmentary sectional view of the spark plug as one example of the present invention. The enlarged view near the front-end | tip of the center electrode of the spark plug in 1st Example. The enlarged view of the part centering on a two-layer member. The flowchart which shows the process of welding a noble metal tip member and an intermediate member to an electrode base material front-end | tip part. The 1st figure for demonstrating welding of the noble metal tip member and intermediate member with respect to the electrode base material front-end | tip part. The 2nd figure for demonstrating welding of the noble metal tip member and intermediate member with respect to the electrode base material front-end | tip part. The graph which shows the stress which generate | occur | produces in the lower surface of a noble metal tip member. The graph which shows the experimental result investigated about generation | occurrence | production of the corrosion in a laser melting part. The figure which shows the vicinity part of the two-layer member of the spark plug in 2nd Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Ceramic resistance 4 ... Sealing body 5 ... Gasket 6 ... Ring member 8 ... Plate packing 9 ... Talc 10 ... Insulator 11 ... Tip part 12 ... Shaft hole 13 ... Leg long part 15 ... Step part 17 ... Tip side trunk | drum 18 ... Rear end side body part 19 ... collar part 20 ... center electrode 21 ... electrode base material 22 ... electrode base material base 23 ... melting part 25 ... core material 30 ... ground electrode 31 ... electrode base material tip part 32 ... base material base end part DESCRIPTION OF SYMBOLS 40 ... Terminal metal fitting 50 ... Main metal fitting 51 ... Tool engaging part 52 ... Mounting screw part 53 ... Clamping part 54 ... Sealing part 55 ... Seat surface 56 ... Step part 57 ... Tip end surface 58 ... Buckling part 59 ... Screw neck 90 DESCRIPTION OF SYMBOLS ... Electrode tip 100 ... Spark plug 200 ... Engine head 201 ... Mounting screw hole 205 ... Opening peripheral part 300 ... Two-layer member 310 ... Precious metal tip member 311 ... Welding sag 312 ... Buried hole 320 ... Intermediate member 350 ... Laser -Melting zone 500 ... Resistance welding electrode

Claims (17)

A central electrode extending in the axial direction;
A ground electrode that forms a spark gap with the center electrode;
A spark plug having
At least one of the center electrode and the ground electrode is
An electrode base material;
A precious metal tip member;
An intermediate member in which a first surface is in contact with the noble metal tip member, and a second surface opposite to the first surface is in contact with the electrode base material;
By laser welding at least a part of the outer edge of the contact portion between the noble metal tip and the intermediate member, a laser melting portion formed on a side surface of the noble metal tip member and the intermediate member,
With
A spark plug, wherein at least a part of the laser melting portion is buried in the electrode base material. The spark plug according to claim 1,
A spark plug, which is resistance-welded between the intermediate member and the electrode base material. The spark plug according to claim 1 or 2, wherein
A spark plug in which 50% or more of the laser melting portion is buried in the electrode base material. The spark plug according to claim 1 or 2, wherein
A spark plug in which 100% of the laser melting portion is buried in the electrode base material. The spark plug according to any one of claims 1 to 4, wherein
The electrode base material is a spark plug having a recess for burying the laser melting portion. The spark plug according to claim 5, wherein
A spark plug, wherein resistance welding is performed between an upper surface of the recess and a bottom surface of the intermediate member. The spark plug according to any one of claims 2 to 6,
A spark plug provided on the upper surface of the electrode base material with a protruding portion protruding from the upper surface of the electrode member along a side surface of the noble metal tip member. The spark plug according to claim 7, wherein
The protruding portion is a spark plug that covers at least a part of the laser melting portion. The spark plug according to claim 7 or claim 8,
Between the intermediate member and the electrode base material, resistance welding is performed,
The protrusion is a spark plug, which is a welding sag of the resistance welding. The spark plug according to any one of claims 1 to 9,
A spark plug in which a linear expansion coefficient of the intermediate member is larger than a linear expansion coefficient of the noble metal tip member and smaller than a linear expansion coefficient of the electrode base material. The spark plug according to any one of claims 1 to 10,
The intermediate member is
i) Palladium (Pd)
ii) Gold (Au)
iii) Gold palladium alloy (AuPd alloy)
iv) A spark plug formed of a material mainly containing any one of platinum-nickel alloys. The spark plug according to any one of claims 1 to 11, wherein
A spark plug in which a melting point of the noble metal tip member is higher than a melting point of the electrode base material. The spark plug according to claim 12, wherein
The noble metal tip member is
i) Iridium (Ir)
ii) Iridium alloy
iii) Platinum (Pt)
iv) A spark plug formed of a material mainly composed of any one of platinum alloys. The spark plug according to any one of claims 1 to 13,
A spark plug, wherein at least one of the center electrode and the ground electrode is the ground electrode. The spark plug according to any one of claims 1 to 9,
The spark plug is formed of the same material as the nickel alloy or the ground electrode base material. A spark plug manufacturing method comprising a center electrode extending in the axial direction and a ground electrode forming a spark gap between the center electrode,
(A) laser welding at least part of the outer edge of the contact portion between the noble metal tip member and the first surface of the intermediate member;
(B) fixing a second surface side opposite to the first surface of the intermediate member to at least one electrode base material of the center electrode and the ground electrode;
With
The step (b) is performed such that at least a part of the laser melting portion formed on the side surfaces of the noble metal tip member and the intermediate member in the step (a) is buried in the electrode base material. A method for manufacturing a spark plug. A method for producing a spark plug according to claim 15,
The step (b)
(B1) forming a buried hole in the electrode base material;
(B2) fixing the noble metal member and the intermediate member to the buried hole with the second surface side down;
A method for manufacturing a spark plug, comprising:

Images