JP5744763B2 - Spark plug - Google Patents

Description

  The present invention relates to a spark plug in which a noble metal tip is attached to an electrode.

  A spark plug is known in which a noble metal tip is attached to an electrode in order to increase the durability of the electrode. The noble metal tip used for the electrode of the spark plug is a noble metal (for example, platinum, iridium, ruthenium, rhodium, etc.) having superior durability against spark discharge and oxidation than the electrode base material, or such noble metal as a main component. It is formed of an alloy and is attached to the electrode using fusion welding (for example, laser welding, arc welding, gas welding, etc.).

  As one of the structures for attaching the noble metal tip to the electrode, there has been proposed a structure in which the outer periphery of the noble metal tip is laser-welded from the outside of the electrode base material, biased toward the tip of the electrode where laser irradiation is relatively easy (For example, see Patent Document 1). In addition, a structure in which laser welding is performed almost uniformly over the entire circumference of the noble metal tip by interposing an intermediate base material with the electrode base material has been proposed (see, for example, Patent Document 2).

  The noble metal tip and the base material (electrode base material or intermediate base material) are joined to each other through a fusion part by fusion welding. A thermal stress is generated in the melted portion joining the noble metal tip and the base material due to a difference in thermal expansion between the noble metal tip and the base material. This thermal stress causes a crack in the melted portion, and the noble metal tip may fall off the electrode depending on the progress of the crack.

JP 2005-183167 A JP 2009-283262 A

  Conventionally, sufficient consideration has not been made to prevent the noble metal tip from falling off by considering the arrangement of the melted portion joining the noble metal tip and the base material.

  In view of the above-described problems, an object of the present invention is to provide a spark plug with improved electrode durability.

SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.
One aspect of the present invention includes a center electrode extending in the axial direction, and a ground electrode having a base end portion and a tip end portion, and a noble metal tip is attached to a side surface of the ground electrode on the tip end side using fusion welding. Provide spark plugs. In this spark plug, the noble metal tip has a fusion zone formed by fusion welding formed in a range between an outer periphery of the noble metal tip and a central axis of the noble metal tip parallel to the axis of the center electrode; In the plane perpendicular to the central axis while passing through the deepest point of the molten part closest to the central axis, the overall shape of the molten part appearing on the plane is such that the center of gravity of the overall shape is more The shape is located on the end side; the melting portion is continuous in the range of 5% to 40% of the outer periphery along the outer periphery on the base end side with respect to the central axis in the plane. . According to this aspect, since the melted portion is biased toward the base end side, which has better heat dissipation than the tip end side, in the ground electrode, the melted portion is formed biased toward the tip end side, or the noble metal tip Compared with the case where the melted part is formed almost uniformly over the entire circumference, the thermal stress generated in the melted part is reduced, and as a result, the noble metal tip can be prevented from falling off. As a result, the durability of the ground electrode in the spark plug can be improved. Moreover, it can suppress that a fusion | melting part ruptures over the whole region by the crack by a thermal stress, and can prevent the drop of a noble metal tip.

[Application Example 1] A spark plug according to Application Example 1 includes a ground electrode having a base end portion and a tip end portion, and a spark in which a noble metal tip is attached to a side surface on the tip end side of the ground electrode using fusion welding. The noble metal tip has a melted portion formed by fusion welding formed in a range between an outer periphery of the noble metal tip and an axis of the noble metal tip, and is the deepest point of the melted portion closest to the axis. In the plane orthogonal to the axis while passing through, the overall shape of the melted portion appearing on the plane is a shape in which the center of gravity of the overall shape is located closer to the base end side than the axis . According to this application example, in the ground electrode, the melting part is biased toward the base end part side, which has better heat dissipation than the tip end side. Compared with the case where the melted portion is formed almost uniformly over the entire circumference, the thermal stress generated in the melted portion is reduced, and thus the noble metal tip can be prevented from falling off. As a result, the durability of the ground electrode in the spark plug can be improved.

Application Example 2 The noble metal tip may be joined to the intermediate base material surrounding the outer periphery by the fusion welding, and may be attached to the ground electrode via the intermediate base material. According to this application example, it is possible to easily form a melted portion that is biased toward the base end side.

Application Example 3 The melting portion may be continuous in the range of 5% or more and 40% or less of the outer periphery along the outer periphery on the base end side with respect to the axis in the plane. According to this application example, it is possible to suppress the melted portion from being torn across the entire area due to cracks due to thermal stress, and to prevent the noble metal tip from falling off.

Application Example 4 In the plane, an outer peripheral surface constituting the outer periphery may exist on the opposite side of the shaft with respect to the deepest point. According to this application example, it is possible to suppress the thermal stress from mutually affecting the opposite side of the shaft with respect to the deepest point, and to reduce the thermal stress generated in the melted portion on the deepest point side.

Application Example 5 In the plane, an outer peripheral surface constituting the outer periphery may exist on the opposite side of the shaft with respect to each part of the melting portion. According to this application example, it is possible to suppress the thermal stress from affecting each part of the melted part and the opposite side across the shaft, and to reduce the thermal stress generated in each part of the melted part.

Application Example 6 The ground electrode includes an outer layer portion that constitutes the side surface, and a core portion that is formed inside the outer layer portion and closer to the base end portion side than the noble metal tip. May have a higher thermal conductivity than the outer layer portion. According to this application example, since the heat extraction of the ground electrode on the base end side than the noble metal tip is improved, the thermal stress generated in the melted portion can be further reduced.

Application Example 7 The melting portion may be formed by performing the fusion welding from the outer peripheral side toward the shaft. According to this application example, the noble metal tip can be easily attached by fusion welding.

  The form of the present invention is not limited to the form of a spark plug, and can be applied to various forms such as an electrode of a spark plug, an internal combustion engine having a spark plug, and a method of manufacturing a spark plug. Further, the present invention is not limited to the above-described embodiments, and it is needless to say that the present invention can be implemented in various forms without departing from the spirit of the present invention.

It is a fragmentary sectional view showing a spark plug. It is explanatory drawing which expands and shows the ground electrode of a spark plug. It is explanatory drawing which shows the attachment structure of a noble metal tip. It is explanatory drawing which shows the cross section of a noble metal tip. It is process drawing which shows the manufacturing process of a spark plug. It is a graph which shows the evaluation result regarding the attachment structure of a noble metal tip. It is a graph which shows the evaluation result regarding the attachment structure of a noble metal tip. It is explanatory drawing which shows the attachment structure of the noble metal chip | tip in a 1st modification. It is explanatory drawing which shows the attachment structure of the noble metal chip | tip in a 2nd modification. It is explanatory drawing which shows the attachment structure of the noble metal chip | tip in a 3rd modification. It is explanatory drawing which shows the attachment structure of the noble metal chip | tip in a 4th modification. It is explanatory drawing which shows the attachment structure of the noble metal chip | tip in a 5th modification. It is explanatory drawing which shows the attachment structure of the noble metal chip | tip in a 6th modification. It is explanatory drawing which shows the attachment structure of the noble metal chip | tip in a 7th modification. It is explanatory drawing which shows the attachment structure of the noble metal chip | tip in an 8th modification. It is explanatory drawing which shows the attachment structure of the noble metal chip | tip in a 9th modification. It is explanatory drawing which shows the attachment structure of the noble metal chip | tip in a 10th modification. It is explanatory drawing which shows the attachment structure of the noble metal chip | tip in 2nd Embodiment. It is process drawing which shows the manufacturing process of the spark plug in 2nd Embodiment. It is explanatory drawing which shows the attachment structure of the noble metal chip | tip in 3rd Embodiment.

A. First embodiment:
A-1. Spark plug configuration:
FIG. 1 is a partial cross-sectional view showing a spark plug 100. FIG. 1 illustrates the external shape of the spark plug 100 on the right side of the drawing with the axis CA1 being the axis of the spark plug 100 as a boundary, and the cross-sectional shape of the spark plug 100 on the left side of the drawing. In the following description, the lower side of the spark plug 100 is referred to as “front end side”, and the upper side of the paper is referred to as “rear end side”.

  The spark plug 100 includes a center electrode 10, an insulator 20, a metal shell 30, and a ground electrode 40. A noble metal tip 450 is attached to the ground electrode 40 of the spark plug 100. In the present embodiment, the axis CA1 of the spark plug 100 is also the axis of each member of the center electrode 10, the insulator 20, and the metal shell 30.

  The center electrode 10 of the spark plug 100 is a rod-shaped electrode body. In the present embodiment, the center electrode 10 is made of a nickel alloy mainly composed of nickel such as Inconel (registered trademark). The outer surface of the center electrode 10 is electrically insulated from the outside by an insulator 20. The tip side of the center electrode 10 protrudes from the tip side of the insulator 20. The rear end side of the center electrode 10 is electrically connected to the rear end side of the insulator 20. In the present embodiment, the rear end side of the center electrode 10 is electrically connected to the rear end side of the insulator 20 through the seal body 16, the ceramic resistor 17, the seal body 18, and the terminal fitting 19.

  The insulator 20 of the spark plug 100 is a cylindrical insulator. In this embodiment, the insulator 20 is formed by firing an insulating ceramic material such as alumina. The insulator 20 includes a shaft hole 28 that is a through hole along the axis CA1. The center hole 10 is accommodated in the shaft hole 28.

  The metal shell 30 of the spark plug 100 is a cylindrical metal body. In the present embodiment, the metallic shell 30 is a nickel-plated low carbon steel metal body. In other embodiments, the metal shell 30 may be a zinc-plated low-carbon steel metal body or an unplated (non-plated) nickel alloy metal body. The metal shell 30 is caulked and fixed to the outer surface of the insulator 20 while being electrically insulated from the center electrode 10.

  The metal shell 30 includes an end surface 31 and a mounting screw portion 32. The end surface 31 of the metal shell 30 is a hollow circular surface that forms the tip side of the metal shell 30. A ground electrode 40 is joined to the end face 31. The insulator 20 and the center electrode 10 protrude from the center of the end surface 31. The mounting screw portion 32 of the metal shell 30 is a cylindrical portion having a thread formed on the outer surface. In the present embodiment, the spark plug 100 can be attached to the internal combustion engine 200 by screwing the attachment screw portion 32 of the metal shell 30 into the screw hole 210 of the internal combustion engine 200.

  FIG. 2 is an explanatory view showing the ground electrode 40 of the spark plug 100 in an enlarged manner. In FIG. 2A, the ground electrode 40 as viewed from the direction orthogonal to the axis CA1 is shown together with the distal end side of the center electrode 10. FIG. 2B illustrates the ground electrode 40 viewed from the arrow F2b-F2b in FIG. The ground electrode 40 of the spark plug 100 includes an electrode base material 410, an intermediate base material 430, and a noble metal tip 450.

  The electrode base material 410 of the ground electrode 40 is a bent rod-shaped electrode body. The electrode base material 410 extends in a direction along the axis CA1 from the end surface 31 of the metal shell 30, and is bent in a direction intersecting the axis CA1. The base end portion 401 of the electrode base material 410 is joined to the end surface 31 of the metal shell 30. The tip portion 402 of the electrode base material 410 faces the direction intersecting the axis CA1.

  The side surface 403 of the electrode base material 410 faces the tip of the center electrode 10 on the tip portion 402 side. A noble metal tip 450 is attached to the side surface 403 on the distal end portion 402 side by fusion welding. In the present embodiment, the noble metal tip 450 is attached to the electrode base material 410 via the intermediate base material 430. In this embodiment, the fusion welding used to attach the noble metal tip 450 is laser welding, but in other embodiments, arc welding or gas welding may be used.

  A spark gap SG, which is a gap for generating a spark, is formed between the center electrode 10 and the noble metal tip 450. A spark can be generated in the spark gap SG by applying a high voltage of 20,000 to 30,000 volts to the center electrode 10 through the terminal fitting 19 with the spark plug 100 attached to the internal combustion engine 200. is there.

  In this embodiment, the electrode base material 410 has a square cross section, and has side surfaces 404, 405, and 406 in addition to the side surface 403 as four side surfaces adjacent to the base end portion 401 and the distal end portion 402. The side surface 404 of the electrode base material 410 is a back surface with respect to the side surface 403. The side surfaces 405 and 406 are surfaces adjacent to the side surfaces 403 and 403, respectively.

  The electrode base material 410 has an outer layer portion 412 and a core portion 414. The outer layer portion 412 of the electrode base material 410 constitutes the outer surface of the ground electrode 40. In the present embodiment, the outer layer portion 412 constitutes the tip portion 402 and the side surfaces 403, 404, 405, 406 as the outer surface of the ground electrode 40. The core portion 414 of the electrode base material 410 is formed inside the outer layer portion 412 and closer to the base end portion 401 than the noble metal tip 450.

  The thermal conductivity TCi of the core portion 414 is larger than the thermal conductivity TCe of the outer layer portion 412. In the present embodiment, the outer layer portion 412 is made of a nickel alloy containing nickel as a main component including Inconel (registered trademark). In the present embodiment, the core portion 414 is made of copper. In another embodiment, the material of the core portion 414 may be an alloy containing copper as a main component or another metal having a higher thermal conductivity than the outer layer portion 412.

  The intermediate base material 430 of the ground electrode 40 is a member that surrounds the outer periphery of the noble metal tip 450, and is embedded in the electrode base material 410 together with the noble metal tip 450. In the present embodiment, the intermediate base material 430 has a cylindrical shape. A noble metal tip 450 is inserted into the hollow portion of the intermediate base material 430. The intermediate base material 430 is joined to the noble metal tip 450 and also joined to the electrode base material 410. As a result, the noble metal tip 450 is attached to the electrode base material 410 via the intermediate base material 430.

  In the present embodiment, the intermediate base material 430 is made of a nickel alloy containing nickel as a main component including Inconel (registered trademark). In the present embodiment, the material of the intermediate base material 430 is the same material as the outer layer portion 412 of the electrode base material 410, but may be a different material from the outer layer portion 412 in other embodiments.

  The noble metal tip 450 of the ground electrode 40 is a metal body containing a noble metal that is more resistant to spark discharge and oxidation than the electrode base material 410. In this embodiment, the noble metal tip 450 is made of an alloy containing platinum as a main component and 20% by mass of rhodium. The noble metal tip 450 may be a metal body made of a noble metal (for example, platinum, iridium, ruthenium, rhodium, etc.) having superior durability against spark discharge or oxidation than the electrode base material 410, or such noble metal. The metal body which consists of an alloy which has as a main component may be sufficient.

  In the present embodiment, the shape of the noble metal tip 450 is a columnar shape. In the present embodiment, the axis CAc of the noble metal tip 450 is on an extension line of the axis CA1.

  FIG. 3 is an explanatory view showing a mounting structure for the noble metal tip 450. FIG. 3A illustrates a structure for attaching the noble metal tip 450 as viewed from the front end side of the center electrode 10. FIG. 3B illustrates a cross section of the noble metal tip 450 viewed from the arrow F3b-F3b in FIG. In the following description, the base end 401 side from the axis CAc of the noble metal tip 450 is referred to as “base end side region Sbs”, and the tip end 402 side from the axis CAc of the noble metal tip 450 is referred to as “tip end side region Stp”. Call it.

  As shown in FIG. 3B, the side surface 403 of the electrode base material 410 is formed with a recess 416 that is recessed in substantially the same shape as the outer shape of the intermediate base material 430. A noble metal tip 450 and an intermediate base material 430 are attached inside the recess 416.

  The recess 416 of the electrode base material 410 is constituted by a recess bottom surface 417 and a recess side surface 418. The concave bottom surface 417 of the electrode base material 410 is a surface that intersects the axis CAc of the noble metal tip 450. The concave side surface 418 of the electrode base material 410 is a surface along the axis CAc of the noble metal tip 450.

  The intermediate base material 430 has a first end surface 431, a second end surface 432, an outer peripheral surface 435, and an inner peripheral surface 438. The first end surface 431 and the second end surface 432 of the intermediate base material 430 are surfaces that intersect the axis CAc of the noble metal tip 450 and face each other. The outer peripheral surface 435 and the inner peripheral surface 438 of the intermediate base material 430 are surfaces along the axis CAc of the noble metal tip 450.

  The noble metal tip 450 has a first tip end surface 451, a second tip end surface 452, and a tip outer peripheral surface 455. The first tip end surface 451 and the second tip end surface 452 in the noble metal tip 450 are surfaces that intersect the axis CAc of the noble metal tip 450 and face each other. Chip outer peripheral surface 455 of intermediate base material 430 is a surface along axis CAc of noble metal tip 450.

  The first end surface 431 of the intermediate base material 430 is located on the same plane as the side surface 403 of the electrode base material 410. The second end surface 432 of the intermediate base material 430 is in contact with the concave bottom surface 417 of the electrode base material 410. The outer peripheral surface 435 of the intermediate base material 430 is in contact with the concave side surface 418 of the electrode base material 410. The inner peripheral surface 438 of the intermediate base material 430 is in contact with the chip outer peripheral surface 455 of the noble metal tip 450.

  The first tip end surface 451 of the noble metal tip 450 is positioned closer to the center electrode 10 than the side surface 403 of the electrode base material 410 and faces the tip side of the center electrode 10. The second tip end surface 452 of the noble metal tip 450 is in contact with the concave bottom surface 417 of the electrode base material 410. The chip outer peripheral surface 455 on the first chip end surface 451 side protrudes from the side surface 403 of the electrode base material 410, and the chip outer peripheral surface 455 on the second chip end surface 452 side is on the inner peripheral surface 438 of the intermediate base material 430. It is in contact.

  As shown in FIG. 3, the ground electrode 40 has a melting part 420 and a melting part 440. The melting portion 420 is a portion formed by melting the electrode base material 410 and the intermediate base material 430 when the electrode base material 410 and the intermediate base material 430 are joined by fusion welding. The melting part 440 is a part formed by melting the intermediate base material 430 and the noble metal tip 450 when the intermediate base material 430 and the noble metal tip 450 are joined by fusion welding. In the present embodiment, the melted portion 440 is formed by melt welding of the intermediate base material 430 and the noble metal tip 450 before the melted portion 420 is formed by melt welding of the electrode base material 410 and the intermediate base material 430. In the present embodiment, the fusion welding that forms the fusion parts 420 and 430 is laser welding.

  When the electrode base material 410 and the intermediate base material 430 are joined by laser welding, the intermediate base material 430 to which the noble metal tip 450 is joined is inserted into the recess 416 of the electrode base material 410, and the electrode base material 410 Laser is irradiated along the axis CAc of the noble metal tip 450 to the boundary between the concave side surface 418 and the outer peripheral surface 435 of the intermediate base material 430. As a result, as shown in FIG. 3, the shape of the melted portion 420 by laser welding of the electrode base material 410 and the intermediate base material 430 becomes a columnar shape from the side surface 403 of the electrode base material 410 along the concave side surface 418. In the present embodiment, as shown in FIG. 3A, the melting part 420 is formed at a plurality of locations that do not interfere with the melting part 440.

  When the intermediate base material 430 and the noble metal tip 450 are joined by laser welding, the noble metal is inserted from the outer peripheral surface 435 of the intermediate base material 430 with the noble metal tip 450 inserted inside the inner peripheral surface 438 of the intermediate base material 430. Laser is irradiated toward the axis CAc of the chip 450. As a result, as shown in FIG. 3, the shape of the melted portion 440 by laser welding between the intermediate base material 430 and the noble metal tip 450 is a convex shape from the outer peripheral surface 435 of the intermediate base material 430 toward the axis CAc of the noble metal tip 450. Become. In the present embodiment, as shown in FIG. 3A, melted portions 440 are formed at four locations.

  A fusion zone 440 obtained by laser welding between the intermediate base material 430 and the noble metal tip 450 has a base material region 443 and a tip region 445. The base material region 443 of the melting part 440 is formed from the outer periphery to the inner periphery of the intermediate base material 430. The tip region 445 of the melting part 440 is formed from the outer periphery of the noble metal tip 450 toward the inside. In FIG. 3, the base material region 443 is subjected to single hatching, and the chip region 445 is subjected to cross hatching.

  FIG. 4 is an explanatory view showing a cross section of the noble metal tip 450 viewed from the arrow F4-F4 in FIG. A plane PL indicated by arrows F4-F4 in FIG. 3B passes through the deepest point Pdp closest to the axis CAc of the noble metal tip 450 in the melting part 440 formed in the noble metal tip 450, and the axis CAc of the noble metal tip 450 is obtained. It is a plane orthogonal to.

  As shown in FIG. 4, in the plane PL passing through the deepest point Pdp of the melting part 440, the center of gravity Gmt of the entire shape of the tip region 445 in the melting part 440 appearing on the plane PL is more proximal than the axis CAc of the noble metal tip 450. It is located on the part 401 side, that is, on the base end side region Sbs. That is, in the plane PL passing through the deepest point Pdp of the melted portion 440, the overall shape of the melted portion 440 that appears on the plane PL is such that the center of gravity Gmt of the overall shape is located closer to the base end 401 side than the axis CAc of the noble metal tip 450. Shape. In the example shown in FIG. 4, the center of gravity Gmt is the center of gravity of the entire chip region 445 appearing at four locations on the plane PL. In FIG. 3A, the melted portion 440, the deepest point Pdp, and the center of gravity Gmt appearing on the plane PL are shown superimposed.

  The melted part 440 in the noble metal tip 450 is continuous in the range of 5% to 40% of the outer periphery of the noble metal tip 450 along the outer periphery of the noble metal tip 450 in the base end side region Sbs on the plane PL. That is, when the continuous length of the melted portion 440 continuous along the outer periphery of the noble metal tip 450 in the base end region Sbs on the plane PL is “Lmt” and the outer peripheral length of the noble metal tip 450 is “Lcf”, the outer peripheral length The continuous length ratio Rct, which is a percentage of the continuous length Lmt with respect to Lcf, is 5% or more and 40% or less. The evaluation of the continuous length ratio Rct will be described later.

  In the present embodiment, as shown in FIG. 4, the melting part 440 does not exist on the straight line LN passing through the axis CAc of the noble metal tip 450 from the deepest point Pdp of the melting part 440 in the plane PL. That is, in the plane PL, the tip outer peripheral surface 455 of the noble metal tip 450 exists on the opposite side of the deepest point Pdp of the melting portion 440 with the axis CAc of the noble metal tip 450 interposed therebetween.

A-2. Spark plug manufacturing process:
FIG. 5 is a process diagram showing the manufacturing process of the spark plug 100. In the manufacturing process of the spark plug 100, an electrode base material 410, an intermediate base material 430, and a noble metal tip 450 are prepared to manufacture the ground electrode 40 (process P110). In the present embodiment, the electrode base material 410 prepared prior to the attachment of the noble metal tip 450 is a wire extending straight and is not bent like the electrode base material 410 in the finished spark plug 100.

  After preparing each member of the ground electrode 40 (process P110), a chip joined body formed by laser welding the intermediate base material 430 and the noble metal tip 450 is created (process P120). Specifically, after the noble metal tip 450 is inserted inside the intermediate base material 430, a laser is irradiated from the outer peripheral surface 435 of the intermediate base material 430 toward the axis CAc of the noble metal tip 450, and the center of gravity Gmt of the melting part 440 is obtained. Is laser welded to the intermediate base material 430 and the noble metal tip 450 so that the position is shifted from the axis CAc of the noble metal tip 450. As a result, a melting portion 440 is formed in the intermediate base material 430 and the noble metal tip 450.

  After creating the chip assembly (process P120), the chip assembly and the electrode base material 410 are resistance-welded (process P130). Specifically, after inserting the chip assembly into the recess 416 of the electrode base material 410 so that the center of gravity Gmt of the melting part 440 is closer to the base end part 401 side of the electrode base material 410 than the axis CAc of the noble metal tip 450, The chip assembly is resistance-welded to the concave bottom surface 417 of the electrode base material 410 by applying a current to the chip joint and the electrode base material 410 while pressurizing the chip joint and the electrode base material 410. In other embodiments, resistance welding (process P130) may be omitted.

  After resistance welding the chip assembly and the electrode base material 410 (process P130), the chip assembly and the electrode base material 410 are laser-welded (process P140). Specifically, the boundary between the concave side surface 418 of the electrode base material 410 and the outer peripheral surface 435 of the intermediate base material 430 is irradiated with a laser along the axis CAc of the noble metal tip 450, so that the electrode base material 410 and the intermediate base material 430 and laser welding. As a result, a melting portion 420 is formed in the electrode base material 410 and the intermediate base material 430.

  After the chip assembly and the electrode base material 410 are laser-welded (process P140), the spark plug 100 is completed through assembly of each member constituting the spark plug 100 (process P150). In the present embodiment, an electrode intermediate product obtained by laser welding the chip assembly and the electrode base material 410 is welded to the metal shell 30, and then another member is assembled to the metal shell 30 and finally welded to the metal shell 30. The ground electrode 40 is completed by bending the electrode intermediate product.

A-3. Evaluation of precious metal tip mounting structure:
6 and 7 are graphs showing the evaluation results regarding the mounting structure of the noble metal tip 450. In the evaluation tests of FIGS. 6 and 7, the shape characteristics and durability were evaluated for a plurality of samples having different centroids Gmt and continuous length ratios Rct of the melted portion 440.

  In the evaluation of the shape characteristics in the evaluation tests of FIGS. 6 and 7, for each sample, the intermediate base material 430 and the noble metal tip 450 are joined by laser welding, and then the intermediate base material 430 is deformed by heat during laser welding. The presence or absence of welding sag was confirmed visually. The welding sag of the intermediate base material 430 forms a gap between the intermediate base material 430 and the electrode base material 410 and becomes a factor that hinders heat extraction of the noble metal tip 450. In addition, the welding sag of the intermediate base material 430 also hinders the attachment of the noble metal tip 450 to the electrode base material 410 and becomes a factor of reducing the ignitability of the spark plug 100.

  In the durability evaluation in the evaluation tests of FIGS. 6 and 7, each sample was attached to a 6-cylinder cogeneration engine, and after 1000 hours of operation (durability test) at the rated output, the deepest point Pdp of the melting part 440 was determined. The noble metal tip 450 was polished until the passing plane PL appeared, and the plane PL, which is the polished cross section, was observed with a microscope. In the observation of the plane PL with a microscope, it was confirmed whether or not there was complete fracture in which cracks along the outer periphery of the noble metal tip 450 were completely included in the entire melted portion 440. The complete tearing of the melting part 440 becomes a factor that the noble metal tip 450 falls off.

  In the evaluation test of FIG. 6, the center of gravity Gmt of the melting part 440 is in the proximal end side region Sbs, and the continuous length ratio Rct of the melting part 440 is “3%”, “5%”, “10%”, “ Thirty samples each having values of “25%”, “40%”, and “45%” were prepared.

  In each sample of FIG. 6, the melted portions 440 that satisfy the continuous length ratio Rct of each value are arranged at a plurality of locations around the axis CAc of the noble metal tip 450. The number of melted portions 440 in each sample of FIG. 6 is 25 for the sample having the continuous length ratio Rct of “3%”, 16 for the sample of “5%”, 8 for the sample of “10%”, “25” 3 for the “%” sample, 2 for the “40%” sample, and 2 for the “45%” sample.

  In the evaluation test of FIG. 7, the center of gravity Gmt of the melting portion 440 is substantially the same position as the axis CAc of the noble metal tip 450, and the continuous length ratio Rct of the melting portion 440 is “3%”, “5%”, “10 30 samples each having values of “%”, “25%”, “40%”, and “45%” were prepared.

  In each sample in FIG. 7, melting portions 440 satisfying the continuous length ratio Rct of each value are arranged at a plurality of locations at equal intervals around the axis CAc of the noble metal tip 450. The number of the melted portions 440 in each sample in FIG. 7 is 25 for the sample with the continuous length ratio Rct of “3%”, 16 for the sample with “5%”, and “10%” as in each sample in FIG. 8 samples, 3 samples of “25%”, 2 samples of “40%”, and 2 samples of “45%”.

6 and 7 show the number of samples in which welding sag occurs in the intermediate base material 430 and the number of samples in which complete tearing occurs in the fusion zone 440 for each continuous length ratio Rct. The criteria for comprehensive evaluation in FIGS. 6 and 7 are as follows.
○ (excellent): Number of occurrences of both welding sag and complete tearing is 5 or less △ (good): Number of occurrences of either welding sag and complete tearing is 5 or less × (impossible): Both welding sag and complete tearing Number of occurrences of 6 or more

  According to the evaluation results of FIG. 6 and FIG. 7, from the viewpoint of suppressing welding sag of the intermediate base material 430, the continuous length ratio Rct is preferably 40% or less, more preferably 25% or less, and even more preferably 10% or less. I understand that. The cause of this result is that as the continuous length ratio Rct decreases, the continuous length Lmt of the fusion zone 440 decreases, and the time for continuously irradiating the intermediate base material 430 with laser during laser welding also decreases. It is conceivable that the temperature rise of the intermediate base material 430 can be suppressed.

  According to the evaluation results of FIG. 6 and FIG. 7, from the viewpoint of preventing complete tearing of the fusion zone 440, the continuous length ratio Rct is preferably 5% or more, more preferably 10% or more, and even more preferably 25% or more. I understand. The cause of this result is considered to be that the continuous length Lmt of the melted part 440 becomes longer as the continuous length ratio Rct increases, and the progress of cracks reaching both ends of the melted part 440 can be suppressed.

  Comparing the evaluation result of FIG. 6 and the evaluation result of FIG. 7, the sample of FIG. 6 in which the center of gravity Gmt of the melting part 440 is in the proximal end side region Sbs is obtained at any melting length at any continuous length ratio Rct. It can be seen that the number of occurrences of complete tearing in the melted portion 440 is smaller than that of the sample of FIG. As one of the factors of this result, the melting portion 440 is arranged almost evenly on the outer periphery of the noble metal tip 450, and the thermal stress is generated almost uniformly over the entire area of the melting portion 440, than the sample of FIG. It is conceivable that the sample of FIG. 6 in which the melting part 440 is biased can alleviate the interaction of thermal stress generated in each part of the melting part 440. Another factor is that the base end portion side region Sbs where heat is transferred to the metal shell 30 via the base end portion 401 is superior in heat sinking to the tip end portion side region Stp. It can be considered that the sample of FIG. 6 that is biased toward the end side region Sbs can effectively reduce the thermal stress generated in the melting portion 440.

  Accordingly, as shown in FIG. 6 and FIG. 7 as a comprehensive evaluation, the spark plug 100 preferably satisfies the condition that the center of gravity Gmt of the melting portion 440 is located in the base end side region Sbs. It is more preferable that the continuous length ratio Rct satisfies the condition of 5% to 40%.

A-4. effect:
According to the spark plug 100 of the first embodiment described above, the melting portion 440 is biased toward the base end portion 401 side with better heat dissipation than the distal end portion 402 side in the ground electrode 40, and thus is biased toward the distal end portion 402 side. Compared with the case where the melted portion 440 is formed and the case where the melted portion 440 is formed almost uniformly over the entire circumference of the noble metal tip 450, the thermal stress generated in the melted portion 440 is reduced, and consequently the noble metal The chip 450 can be prevented from falling off. As a result, the durability of the ground electrode 40 in the spark plug 100 can be improved.

  In addition, since the noble metal tip 450 is attached to the ground electrode 40 via the intermediate base material 430, the melted portion 440 that is biased toward the base end portion 401 side can be prepared.

  Further, since the continuous length ratio Rct of the melted portion 440 is 5% or more and 40% or less, it is possible to suppress the melted portion from being broken all over by cracks due to thermal stress and to prevent the noble metal tip from falling off. .

  Further, as shown in FIG. 4, in the plane PL, the tip outer peripheral surface 455 of the noble metal tip 450 is present on the opposite side of the deepest point Pdp of the melted portion 440 with the axis CAc of the noble metal tip 450 therebetween. It is possible to suppress the thermal stress from affecting the deepest point Pdp of the melting portion 440 and the opposite side of the noble metal tip 450 across the axis CAc, thereby reducing the thermal stress generated in the melting portion 440 on the deepest point Pdp side. be able to.

  Further, since the ground electrode 40 has a core portion 414 having a higher thermal conductivity than the outer layer portion 412 on the base end portion 401 side with respect to the noble metal tip 450, the ground electrode 40 on the base end portion 401 side with respect to the noble metal tip 450. Therefore, the thermal stress generated in the melting part 440 can be further reduced.

  Moreover, since the fusion | melting part 440 is formed by irradiating a laser toward the axis | shaft CAc from the 2nd tip end surface 452 side in the noble metal tip 450, the noble metal tip 450 can be attached easily by laser welding.

A-5. Variation:
FIGS. 8 to 17 are explanatory views respectively showing the attachment structure of the noble metal tip 450 in the first to tenth modified examples. 8 to 17, similarly to FIG. 3A, the noble metal tip mounting structure viewed from the front end side of the center electrode 10 is shown superimposed on the center of gravity Gmt appearing on the plane PL. In FIG. 8 to FIG. 17, illustration of the melted portion by fusion welding of the electrode base material and the intermediate base material is omitted.

  The spark plug 100 of the first modified example having the mounting structure illustrated in FIG. 8 is different from the first embodiment in that a melted portion 440a having a shape different from that of the melted portion 440 is formed instead of the melted portion 440 of the first embodiment. This is the same as in the first embodiment. As shown in FIG. 8, in the first modified example, melted portions 440a are formed at four locations on the plane PL. The largest melting part 440a among them is formed in the base end part side region Sbs. The other three melted portions 440a are formed along the outer periphery of the noble metal tip 450 with a gap therebetween. Also in the first modification, the center of gravity Gmt of the melting part 440a is located in the base end part side region Sbs.

  The spark plug 100 of the second modified example having the mounting structure illustrated in FIG. 9 is different from the first embodiment in that a melted portion 440b having a shape different from that of the melted portion 440 is formed instead of the melted portion 440 of the first embodiment. This is the same as in the first embodiment. As shown in FIG. 9, in the second modified example, melted portions 440b are formed at six locations on the plane PL. These six melted portions 440b are arranged at equal intervals with substantially the same size in a ratio of four in the proximal end side region Sbs and two in the distal end side region Stp. Also in the second modified example, the center of gravity Gmt of the melting part 440b is located in the base end part region Sbs.

  The spark plug 100 of the third modified example having the mounting structure illustrated in FIG. 10 is different from the first embodiment in that a melting part 440c having a shape different from that of the melting part 440 is formed instead of the melting part 440 of the first embodiment. This is the same as in the first embodiment. As shown in FIG. 10, in the third modification example, a melting portion 440 c is formed at one location so as to concentrate on the base end side region Sbs on the plane PL. Therefore, on the plane PL, the chip outer peripheral surface 455 of the noble metal tip 450 exists on the opposite side of the melted portion 440c with the axis CAc of the noble metal tip 450 interposed therebetween. Also in the third modified example, the center of gravity Gmt of the melting part 440c is located in the base end part region Sbs.

  The spark plug 100 of the fourth modified example having the mounting structure illustrated in FIG. 11 is different from the first embodiment in that a melted portion 440d having a shape different from that of the melted portion 440 is formed instead of the melted portion 440 of the first embodiment. This is the same as in the first embodiment. As shown in FIG. 11, in the fourth modified example, the melted portion 440 d is continuously formed over almost the entire outer periphery of the noble metal tip 450 in the base end side region Sbs on the plane PL. Therefore, on the plane PL, the tip outer peripheral surface 455 of the noble metal tip 450 exists on the opposite side of the melted portion 440d with the axis CAc of the noble metal tip 450 interposed therebetween. Also in the fourth modified example, the center of gravity Gmt of the melting portion 440d is located in the base end portion side region Sbs.

  The spark plug 100 of the fifth modified example having the mounting structure illustrated in FIG. 12 is different from the first embodiment in that a melting portion 440e having a shape different from that of the melting portion 440 is formed instead of the melting portion 440 of the first embodiment. This is the same as in the first embodiment. As shown in FIG. 12, in the fifth modified example, one melting portion 440e is formed in the base end side region Sbs and two locations in the tip end side region Stp. Also in the fifth modification, the center of gravity Gmt of the melting portion 440e is located in the base end portion side region Sbs. In FIG. 12, a region that is axially symmetric with respect to each portion of the melting portion 440e is illustrated by a one-dot chain line. In the fifth modification, each part of the melting part 440e is formed avoiding a position that is axially symmetric with respect to the other part of the melting part 440e and the axis CAc of the noble metal tip 450. Therefore, on the plane PL, the chip outer peripheral surface 455 of the noble metal tip 450 exists on the opposite side of the melted portion 440e with the axis CAc of the noble metal tip 450 interposed therebetween.

  The spark plug 100 of the sixth modified example having the mounting structure illustrated in FIG. 13 includes an intermediate base material 430f having a shape different from that of the intermediate base material 430 in place of the intermediate base material 430 of the first embodiment, and It is the same as that of 1st Embodiment except the point which is replaced with the fusion | melting part 440 of 1 embodiment, and the melting part 440f from which a shape differs from the fusion | melting part 440 is formed. The intermediate base material 430f of the sixth modification is the same as the intermediate base material 430 of the first embodiment except that the outer periphery is a quadrangle. As shown in FIG. 13, in the sixth modified example, there are two places in the base end side area Sbs, one place in the tip end side area Stp, and two places across the base end side area Sbs and the tip end side area Stp. , Melting portions 440f are respectively formed. Also in the sixth modification, the center of gravity Gmt of the melting portion 440f is located in the base end portion side region Sbs.

  The spark plug 100 of the seventh modified example having the mounting structure shown in FIG. 14 includes an intermediate base material 430g having a shape different from that of the intermediate base material 430 in place of the intermediate base material 430 of the first embodiment. A melting part 440g having a shape different from that of the melting part 440 is formed instead of the melting part 440 of the embodiment, and a noble metal chip 450g having a shape different from that of the noble metal chip 450 instead of the noble metal chip 450 of the first embodiment. Except for the point provided with, it is the same as the first embodiment. The intermediate base material 430g of the seventh modified example is the same as the intermediate base material 430 of the first embodiment, except that it is a quadrangular cylindrical shape. The noble metal tip 450g of the seventh modification is the same as the noble metal tip 450 of the first embodiment except that it is a quadrangular prism shape. As shown in FIG. 14, in the seventh modified example, there are two places in the base end side area Sbs, one place in the tip end side area Stp, and two places across the base end side area Sbs and the tip end side area Stp. The melted portions 440g are respectively formed. Also in the seventh modification, the center of gravity Gmt of the melting portion 440g is located in the base end portion side region Sbs.

  The spark plug 100 of the eighth modified example having the mounting structure illustrated in FIG. 15 includes an intermediate base material 430h having a shape different from that of the intermediate base material 430 in place of the intermediate base material 430 of the first embodiment. A melted portion 440h having a shape different from that of the melted portion 440 is formed instead of the melted portion 440 of the embodiment, and a noble metal tip 450h having a shape different from that of the noble metal tip 450 instead of the noble metal tip 450 of the first embodiment. Except for the point provided with, it is the same as the first embodiment. The intermediate base material 430h of the eighth modification is the same as the intermediate base material 430 of the first embodiment, except that it is triangular. The noble metal tip 450h of the eighth modification is the same as the noble metal tip 450 of the first embodiment except that it has a triangular prism shape. As shown in FIG. 15, in the eighth modification, one of the triangular corners of the intermediate base material 430 and the noble metal tip 450 h is directed to the side surface 406. As shown in FIG. 15, in the eighth modified example, three melting portions 440h are formed in the base end portion side region Sbs and one portion in the tip end portion region Stp, respectively. Also in the eighth modification, the center of gravity Gmt of the melting portion 440h is located in the base end portion side region Sbs.

  The spark plug 100 of the ninth modification having the mounting structure illustrated in FIG. 16 includes an intermediate base material 430i having a shape different from that of the intermediate base material 430 in place of the intermediate base material 430 of the first embodiment, and It is the same as that of 1st Embodiment except the point which is replaced with the fusion | melting part 440 of 1 embodiment, and the fusion | melting part 440i from which a shape differs from the fusion | melting part 440 is formed. As shown in FIG. 16, in the ninth modification, the axis CAc of the noble metal tip 450 is in a position biased toward the tip end portion 402 side with respect to the center of the intermediate base material 430i. In the ninth modification, the noble metal tip 450 is in contact with the electrode base material 410 on the distal end portion 402 side. As shown in FIG. 16, in the ninth modified example, melted portions 440i are formed at three locations. Among them, the largest melted portion 440i is formed in the base end portion side region Sbs. The other two melted portions 440 i are formed along the outer periphery of the noble metal tip 450 with a gap therebetween. Also in the ninth modification, the center of gravity Gmt of the melting portion 440i is located in the base end portion side region Sbs.

  The spark plug 100 of the tenth modification having the mounting structure illustrated in FIG. 17 includes an intermediate base material 430j having a shape different from that of the intermediate base material 430 in place of the intermediate base material 430 of the first embodiment. Except for the point that a melted part 440j having a shape different from that of the melted part 440 is formed instead of the melted part 440 of the embodiment and a noble metal tip 450j having a shape different from that of the noble metal tip 450 of the first embodiment, This is the same as in the first embodiment. As shown in FIG. 17, the intermediate base material 430j of the tenth modification is the same as the intermediate base material 430 of the first embodiment except that it is U-shaped. The noble metal tip 450j of the tenth modification is the same as the noble metal tip 450 of the first embodiment except that it is a quadrangular prism shape. In the tenth modified example, the axis CAc of the noble metal tip 450j is in a position biased toward the tip end portion 402 side with respect to the center of the intermediate base material 430j. In the tenth modification, the noble metal tip 450j is in contact with the electrode base material 410 on the distal end portion 402 side. As shown in FIG. 17, in the tenth modified example, the melted portions 440j are formed at two locations in the base end portion side region Sbs and at two locations straddling the base end portion side region Sbs and the tip end portion side region Stp, respectively. Yes. Also in the tenth modification, the center of gravity Gmt of the melting portion 440j is located in the base end portion side region Sbs.

  According to the spark plug 100 of the first to tenth modified examples (FIGS. 8 to 17) described above, as in the first embodiment, the base end portion of the ground electrode 40 that has better heat dissipation than the end portion 402 side. Since the melted portions 440a to 440j are biased toward the 401 side, the melted portions are formed biased toward the distal end portion 402 side, or the melted portions are formed almost uniformly over the entire circumference of the noble metal tip 450. In comparison, the thermal stress generated in the melted portions 440a to 440j is reduced, so that the noble metal tip 450 can be prevented from falling off. Also in the first to tenth modified examples (FIGS. 8 to 17), it is preferable that the continuous length ratio Rct of the melted portions 440a to 440j is 5% to 40%.

  Further, according to the spark plug 100 of the third to fifth modified examples (FIGS. 10 to 12), on the plane PL, on the opposite side of the melted portions 440c to 440e with the axis CAc of the noble metal tip 450 interposed therebetween. Since the chip outer peripheral surface 455 of the noble metal tip 450 is present, it is possible to suppress the thermal stress from affecting each other of the melted portions 440c to 440e and the opposite side across the axis CAc of the noble metal tip 450, The thermal stress generated in each part of the melting parts 440c to 440e can be reduced.

B. Second embodiment:
B-1. Spark plug configuration:
FIG. 18 is an explanatory diagram showing a mounting structure for the noble metal tip 450s in the second embodiment. In FIG. 18A, the attachment structure of the noble metal tip 450s viewed from the side surface 403 side is shown superimposed on the deepest point Pdp and the center of gravity Gmt appearing on the plane PL. FIG. 18B illustrates a cross section of the noble metal tip 450s viewed from the arrow F18b-F18b in FIG.

  The spark plug 100 according to the second embodiment having the mounting structure shown in FIG. 18 is the first embodiment except that the noble metal tip 450s is directly attached to the electrode base material 410 without the intermediate base material 430. It is the same as the form. The noble metal tip 450s of the second embodiment is the same as the noble metal tip 450 of the first embodiment except that the tip outer peripheral surface 455 on the second tip end face 452 side is in contact with the concave side surface 418 of the electrode base material 410. It is. The melting part 440s of the second embodiment is a part formed by melting the electrode base material 410 and the noble metal tip 450s when the electrode base material 410 and the noble metal tip 450s are joined by fusion welding. In the present embodiment, the fusion welding that forms the fusion zone 440s is laser welding.

  When joining the electrode base material 410 and the noble metal tip 450s by laser welding, the side surface 403 of the electrode base material 410 and the outer periphery of the tip of the noble metal tip 450s in a state where the noble metal tip 450s is inserted into the recess 416 of the electrode base material 410. Laser irradiation is performed toward the boundary with the surface 455. Accordingly, as shown in FIG. 18, the melted portion 440s by laser welding between the electrode base material 410 and the noble metal tip 450s is directed from the boundary between the electrode base material 410 and the noble metal tip 450s toward the axis CAc of the noble metal tip 450s. It becomes an inclined convex shape. In the present embodiment, as shown in FIG. 18A, melted portions 440s are formed at five locations in the base end side region Sbs.

  A melted portion 440 s by laser welding between the electrode base material 410 and the noble metal tip 450 s has a base material region 441 s and a tip region 445 s. The base material region 441 s of the melting part 440 s is formed at a part including the boundary between the side surface 403 and the concave side surface 418 in the electrode base material 410. The tip region 445s of the melting part 440s is formed from the outer periphery to the inside of the noble metal tip 450s. In FIG. 18, the base material region 441s is single-hatched and the chip region 445s is cross-hatched.

  As shown in FIG. 18, in the plane PL passing through the deepest point Pdp of the melting part 440s, the center of gravity Gmt of the entire shape of the chip region 445s in the melting part 440s appearing on the plane PL is more proximal than the axis CAc of the noble metal tip 450s. It is located on the part 401 side, that is, on the base end side region Sbs. In the example shown in FIG. 18, the center of gravity Gmt is the center of gravity of the entire chip region 445s appearing at five locations on the plane PL.

  The melted portion 440s in the noble metal tip 450s is continuous in the range of 5% or more and 40% or less of the outer periphery of the noble metal tip 450s along the outer periphery of the noble metal tip 450s in the base end side region Sbs on the plane PL. That is, the continuous length ratio Rct, which is a percentage of the continuous length Lmt of the fusion zone 440s with respect to the outer peripheral length Lcf of the noble metal tip 450s, is 5% or more and 40% or less.

  In the present embodiment, as shown in FIG. 18 (a), melted portions 440s are formed at five locations concentrated on the base end portion side region Sbs. Therefore, on the plane PL, the tip outer peripheral surface 455 of the noble metal tip 450s exists on the opposite side of the melted portion 440s with respect to the axis CAc of the noble metal tip 450s.

B-2. Spark plug manufacturing process:
FIG. 19 is a process diagram showing a manufacturing process of the spark plug 100 according to the second embodiment. In the manufacturing process of the spark plug 100, in order to manufacture the ground electrode 40, an electrode base material 410 and a noble metal tip 450s are prepared (process P210). In this embodiment, the electrode base material 410 prepared prior to the attachment of the noble metal tip 450s is a straight wire that is not bent like the electrode base material 410 in the finished spark plug 100.

  After preparing each member of the ground electrode 40 (process P210), the electrode base material 410 and the noble metal tip 450s are resistance-welded (process P230). Specifically, by inserting the noble metal tip 450s into the recess 416 of the electrode base material 410, and then applying a current to the electrode base material 410 and the noble metal tip 450s while applying pressure to the electrode base material 410 and the noble metal tip 450s, A noble metal tip 450 s is resistance welded to the concave bottom surface 417 of the electrode base material 410. In other embodiments, resistance welding (process P230) may be omitted.

  After the electrode base material 410 and the noble metal tip 450s are resistance welded (process P230), the electrode base material 410 and the noble metal tip 450s are melt welded (process P240). Specifically, the side surface 403 of the electrode base material 410 and the chip outer peripheral surface of the noble metal tip 450s so that the center of gravity Gmt of the melting portion 440s is closer to the base end portion 401 side of the electrode base material 410 than the axis CAc of the noble metal tip 450s. A laser is irradiated toward the boundary with 455, and the electrode base material 410 and the noble metal tip 450s are laser welded. As a result, a melting part 440s is formed in the electrode base material 410 and the noble metal tip 450s. In the present embodiment, the fusion welding used for attaching the noble metal tip 450s is laser welding, but in other embodiments, arc welding or gas welding may be used.

  After the electrode base material 410 and the noble metal tip 450s are laser-welded (process P240), the spark plug 100 is completed through the assembly of the members constituting the spark plug 100 (process P250). In this embodiment, an electrode intermediate product obtained by laser welding the electrode base material 410 and the noble metal tip 450 s is welded to the metal shell 30, and then another member is assembled to the metal shell 30 and finally welded to the metal shell 30. The ground electrode 40 is completed by bending the electrode intermediate product.

B-3. effect:
According to the spark plug 100 of the second embodiment described above, the melting portion 440s is biased toward the base end portion 401 side with better heat sinking than the tip end portion 402 side in the ground electrode 40, so that the melting portion 440s is generated. Thermal stress is reduced, and as a result, the noble metal tip 450s can be prevented from falling off. As a result, the durability of the ground electrode 40 in the spark plug 100 can be improved.

  In addition, since the continuous length ratio Rct of the melted part 440s is 5% or more and 40% or less, it is possible to prevent the melted part from being broken all over due to cracks due to thermal stress, and to prevent the noble metal tip from falling off. .

  Further, as shown in FIG. 18, in the plane PL, the chip outer peripheral surface 455 of the noble metal tip 450 s exists on the opposite side of each part of the fusion portion 440 s with the axis CAc of the noble metal tip 450 s. It is possible to suppress the thermal stress from affecting each part of 440 s and the opposite side across the axis CAc of the noble metal tip 450 s, thereby reducing the thermal stress generated in each part of the melting part 440 s.

C. Third embodiment:
FIG. 20 is an explanatory diagram showing a mounting structure for the noble metal tip 450t in the third embodiment. FIG. 20A illustrates a cross section of the noble metal tip 450t viewed from the arrow F20a-F20a in FIG. FIG. 20B shows a mounting structure for the noble metal tip 450t as viewed from the side surface 404 side.

  The spark plug 100 of the third embodiment having the mounting structure illustrated in FIG. 20 includes an electrode base material 410t instead of the electrode base material 410, a point including a noble metal tip 450t instead of the noble metal tip 450, and a second feature. The second embodiment is the same as the second embodiment except that a melted portion 440t having a shape different from that of the melted portion 440s is formed instead of the melted portion 440s of the embodiment. The electrode base material 410t of the third embodiment is the same as the electrode base material 410 of the second embodiment except that the electrode base material 410t includes a through-hole side surface 419 that is a surface that forms a through-hole, instead of the recess 416 of the second embodiment. It is the same. The noble metal tip 450t of the third embodiment is the same as the noble metal tip 450 of the second embodiment except that the noble metal tip 450t has a cylindrical shape that is longer in the axis CAc direction than the thickness between the side surface 403 and the side surface 404 of the electrode base material 410. It is. The manufacturing process of the spark plug 100 in the third embodiment is the same as that of the second embodiment except that the welding position is different.

  In the third embodiment, the first tip end surface 451 of the noble metal tip 450t is located closer to the center electrode 10 than the side surface 403 of the electrode base material 410t, and faces the tip side of the center electrode 10. The second tip end surface 452 of the noble metal tip 450t is located on the same plane as the side surface 404 of the electrode base material 410t. The chip outer peripheral surface 455 on the first chip end surface 451 side protrudes from the side surface 403 of the electrode base material 410t, and the chip outer peripheral surface 455 on the second chip end surface 452 side is on the through-hole side surface 419 of the electrode base material 410t. It is in contact.

  When the electrode base material 410t and the noble metal tip 450t are joined by fusion welding, the through hole side surface 419 of the electrode base material 410t is inserted with the noble metal tip 450t inside the through hole side surface 419 of the electrode base material 410t. A laser is irradiated along the axis CAc of the noble metal tip 450 t to the boundary between the noble metal tip 450 t and the chip outer peripheral surface 455. As a result, as shown in FIG. 20, a melted portion 440t formed by fusion welding of the electrode base material 410t and the noble metal tip 450t has a cylindrical shape extending from the side surface 403 of the electrode base material 410t along the through-hole side surface 419. In the present embodiment, as shown in FIG. 20B, melted portions 440t are formed at five locations in the base end portion side region Sbs.

  A fusion zone 440t by fusion welding of the electrode base material 410t and the noble metal tip 450t has a base material region 441t and a tip region 445t. The base material region 441t of the melting part 440t is formed along the through-hole side surface 419. The chip region 445 t of the melting part 440 t is formed along the chip outer peripheral surface 455. In FIG. 20, the base material region 441t is subjected to single hatching, and the chip region 445t is subjected to cross hatching.

  In the third embodiment, as shown in FIG. 18, the plane PL passing through the deepest point Pdp of the melting part 440t is flush with the side surface 404 of the electrode base material 410t and the second tip end surface 452 of the noble metal tip 450t. . In the plane PL, the center of gravity Gmt of the entire shape of the tip region 445t in the melting portion 440t appearing on the plane PL is located on the base end portion 401 side, that is, the base end portion side region Sbs from the axis CAc of the noble metal tip 450t. In the example shown in FIG. 20, the center of gravity Gmt is the center of gravity of the entire chip region 445t appearing at five locations on the plane PL.

  The melted portion 440t in the noble metal tip 450t is continuous in the range of 5% to 40% of the outer circumference of the noble metal tip 450t along the outer circumference of the noble metal tip 450t in the base end side region Sbs on the plane PL. That is, the continuous length ratio Rct, which is a percentage of the continuous length Lmt of the fusion zone 440t with respect to the outer peripheral length Lcf of the noble metal tip 450t, is 5% or more and 40% or less.

  In the present embodiment, as shown in FIG. 20 (b), melted portions 440t are formed at five locations concentrated on the base end portion side region Sbs. Therefore, in the plane PL, the tip outer peripheral surface 455 of the noble metal tip 450t exists on the opposite side of the melted portion 440t with respect to the axis CAc of the noble metal tip 450t.

  According to the spark plug 100 of the third embodiment described above, the melting portion 440t is biased toward the base end portion 401 side with better heat dissipation than the tip end portion 402 side in the ground electrode 40, and thus the same as in the second embodiment. In addition, the thermal stress generated in the melting part 440t is reduced, and as a result, the noble metal tip 450t can be prevented from falling off. As a result, the durability of the ground electrode 40 in the spark plug 100 can be improved.

D. Other embodiments:
As mentioned above, although embodiment of this invention was described, this invention is not limited to such embodiment at all, Of course, it can implement with various forms within the range which does not deviate from the meaning of this invention. is there. For example, the noble metal tip mounting structure in each of the above embodiments may be applied to another electrode different from the ground electrode 40.

  The cross-sectional shape of the electrode base material is not limited to a square shape, and can be implemented in various shapes such as a circular shape, an elliptical shape, a triangular shape, and an n-corner shape (n ≧ 5). In addition, the electrode base material is not limited to a multilayer structure including the outer layer portion 412 and the core portion 414, and may be a structure composed of a single material or a multilayer structure of three or more layers.

  The intermediate base material is not limited to a cylindrical shape, a triangular cylindrical shape, a rectangular cylindrical shape, or a U-shape, and can be implemented in various shapes such as an elliptical cylindrical shape and an n-square cylindrical shape (n ≧ 5). .

  Further, the noble metal tip is not limited to a columnar shape, a triangular prism shape, or a quadrangular prism shape, and can be implemented in various shapes such as an elliptical column shape and an n prism shape (n ≧ 5).

  In addition, instead of forming the melted portion by fusion welding between the intermediate base material and the noble metal tip from the outer peripheral surface of the intermediate base material toward the axis CAc of the noble metal tip, the inner peripheral surface of the intermediate base material and the tip of the noble metal tip You may form along a boundary with an outer peripheral surface.

  Further, the continuous length ratio Rct of the melted part in the noble metal tip is preferably 5% or more and 40% or less. However, if the center of gravity Gmt of the melted part in the noble metal tip is located in the base end side region Sbs, the continuous length ratio Rct is It may be less than 5% or may exceed 40%.

  Further, on the plane PL, the tip outer peripheral surface of the noble metal tip preferably exists on the opposite side of the noble metal tip axis CAc with respect to the deepest point Pdp of the melted portion in the noble metal tip. On the other hand, it is more preferable that the tip outer peripheral surface of the noble metal tip exists on the opposite side of the noble metal tip axis CAc. However, if the center of gravity Gmt of the melted part in the noble metal tip is located in the proximal end side region Sbs, there is another melted part on the opposite side of the noble metal tip across the axis CAc with respect to at least a part of the melted part. You may do it.

DESCRIPTION OF SYMBOLS 10 ... Center electrode 16 ... Sealing body 17 ... Ceramic resistance 18 ... Sealing body 19 ... Terminal metal fitting 20 ... Insulator 28 ... Shaft hole 30 ... Main metal fitting 31 ... End face 32 ... Mounting screw part 40 ... Ground electrode 100 ... Spark plug 200 ... Internal combustion engine 210 ... Screw hole 401 ... Base end portion 402 ... Tip end portion 403, 404, 405, 406 ... Side surface 410 ... Electrode base material 412 ... Outer layer portion 414 ... Core portion 416 ... Concave portion 417 ... Concave bottom surface 418 ... Concave side surface 419 ... Through-hole side surface 420 ... Melting portion 430 ... Intermediate base material 431 ... First end surface 432 ... Second end surface 435 ... Outer peripheral surface 438 ... Inner peripheral surface 440, 440a to 440j, 440s, 440t ... Melting portion 441, 443 ... Base material region 445 ... Chip region 450 ... Precious metal chip 451 ... First chip end face 452 ... Second chip end face 455 ... Chip Peripheral surface SG ... spark gap CA1 ... axis CAc ... axial Gmt ... centroid PL ... plan Pdp ... deepest point Sbs ... base end region Stp ... tip side region

Claims (6)

A spark plug having a center electrode extending in the axial direction, a ground electrode having a base end portion and a tip end portion, and a noble metal tip attached to the side surface on the tip end side of the ground electrode using fusion welding ,
The melted portion by the fusion welding the noble metal tip, and the outer circumference of the noble metal tip is formed in the range between the central axis of the axis parallel to the noble metal tip of the center electrode,
In a plane perpendicular to the closest the said central axis while through the deepest point of the molten portion on the central axis, the overall shape of the molten portion appearing on the plane, the base than the center of gravity is the center axis of the該全body shape Ri shape der positioned on the end,
The spark plug is characterized in that the molten part is continuous in the range of 5% to 40% of the outer periphery along the outer periphery on the base end side of the central axis in the plane .   2. The noble metal tip is bonded to the intermediate base material surrounding the outer periphery by the fusion welding, and is attached to the ground electrode through the intermediate base material. Spark plug. 3. The spark plug according to claim 1, wherein an outer peripheral surface constituting the outer periphery is present on the opposite side of the deepest point across the central axis in the plane. The outer surface which comprises the said outer periphery exists in the said plane in the other side which pinched | interposed the said central axis with respect to each part of the said fusion | melting part, The Claim 1 thru | or 3 characterized by the above-mentioned. The described spark plug. The spark plug according to any one of claims 1 to 4 , wherein
The ground electrode is
An outer layer portion constituting the side surface;
A core portion formed inside the outer layer portion and closer to the base end side than the noble metal tip, and
The spark plug according to claim 1, wherein the core portion has a thermal conductivity larger than that of the outer layer portion. The spark plug according to any one of claims 1 to 5 , wherein the fusion part is formed by performing the fusion welding from the outer peripheral side toward the central axis.

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