JP2015088364A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug whose electrode chip has both peeling resistance and consumption resistance.SOLUTION: In a spark plug, when defining a direction from a fused part toward an electrode chip side as a first direction, and a direction from a fused part toward an electrode body side as a second direction, the fused part contacts with a surface of the electrode chip on the second direction side at an axis line of the electrode chip. In the fused part, in a cross-section including the axis line and a point A, which is a point positioned on the most toward the second direction side of a portion exposing on the side surface of the electrode chip, an intersection of the axis line and a borderline between the fused part and the electrode chip is defined as a point X, a point positioned on the most toward the second direction side on a borderline between the fused part and the electrode body is defined as a point B, and an intersection of the axis line and the borderline between the fused part and the electrode body is defined as a point Y. Then, an angle θ1 formed between a line segment AX and a straight line, which passes through the point X and perpendicularly intersects with the axis line, satisfies a relationship of 0<θ1≤10 (in a unit of degrees), and an angle θ2 formed between a line segment BY and a straight line, which passes through the point Y and perpendicularly intersects with the axis line of the electrode chip, satisfies a relationship of 0<θ2≤5 (in a unit of degrees).

Description

  The present invention relates to a spark plug, and more particularly, to a spark plug including an electrode tip in an electrode gap forming portion.

  A spark plug is known in which, for example, an electrode tip made of a noble metal having excellent wear resistance is disposed at a portion where a spark gap of an electrode (a center electrode or a ground electrode) is formed. One surface of the electrode tip in the axial direction (the surface opposite to the surface forming the spark gap) is joined to the base material of the electrode by laser welding, for example. During laser welding, between the electrode tip and the electrode base material, the electrode tip and the electrode base material are melted to form a melted portion.

  Here, if the depth in the direction perpendicular to the axial direction of the melted portion is insufficient, the electrode tip may be easily peeled off, that is, the peel resistance may be lowered. In addition, if there is a portion with a large width in the axial direction of the melted portion, the width in the axial direction of the electrode tip after bonding is relatively small in that portion, so wear resistance may be reduced. From such characteristics, it is desired to achieve both peeling resistance and wear resistance by optimizing the shape of the fusion zone and the width in the axial direction.

  For example, in the spark plug disclosed in Patent Document 1, the area of the boundary surface between the electrode tip and the electrode is relative to the cross-sectional area perpendicular to the axis of the electrode tip at the portion closest to the melted portion of the outer surface of the electrode tip. And 5% or less. When the length along the axis of the part exposed on the outer surface of the melted part is P (mm) and the diameter of the electrode tip is Q (mm), P ≦ 0.6 and Q / P In addition to satisfying ≦ 6, the portion of the melted portion having a length along the axis of P / 1.5 is located on the radially outer side from the position inside Q / 4 from the outer peripheral surface of the electrode tip. As described above, a melting portion is formed.

JP 2011-34826 A

  In view of the above circumstances, an object of the present invention is to provide a new technology capable of achieving both peeling resistance and wear resistance of an electrode tip of a spark plug.

  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 application examples.

[Application Example 1]
A rod-shaped center electrode;
An insulator having a through hole into which the center electrode is inserted;
A metal shell disposed on the outer periphery of the insulator;
A ground electrode that is in electrical communication with the metal shell and forms a spark gap with the center electrode;
A spark plug comprising:
At least one of the center electrode and the ground electrode is
Columnar electrode tips forming the spark gap;
An electrode body in which the electrode tip is laser welded to an end; and
A fusion zone formed between the electrode body and the electrode tip by the laser welding, wherein the component of the electrode body and the component of the electrode tip are melted,
Of the two directions along the axis of the electrode tip, the direction on the electrode tip side as viewed from the melting portion is the first direction, and the direction on the electrode body side as viewed from the melting portion is the second direction. When
The melting portion is in contact with the surface of the electrode tip in the second direction side at the position of the axis of the electrode tip,
Of the melted portion, the point located on the second direction side of the portion exposed on the side surface of the electrode tip is a point A,
In a cross section including the point A and the axis of the electrode tip,
The intersection of the axis of the electrode tip and the boundary line between the melted portion and the electrode tip is a point X,
The point located on the second direction side most on the boundary line between the melting part and the electrode body is a point B,
When the intersection of the axis of the electrode tip and the boundary line between the melted part and the electrode body is a point Y,
The point A is located closer to the first direction than the point X,
An acute angle θ1 formed by a line segment AX connecting the point A and the point X and a straight line passing through the point X and perpendicular to the axis of the electrode tip satisfies 0 <θ1 ≦ 10 (unit is degree). ,
The point B is located on the second direction side from the point Y,
An acute angle θ2 formed by a line segment BY connecting the point B and the point Y and a straight line passing through the point Y and perpendicular to the axis of the electrode tip satisfies 0 <θ2 ≦ 5 (unit is degree). ,Spark plug.

  According to the above configuration, the melting part is in contact with the electrode tip at the position of the axis of the electrode tip. That is, the melted part is formed over a relatively wide range in the contact area between the electrode main body and the electrode tip before the melted part is formed (before laser welding is performed). As a result, the welding strength is improved, and the suppression of peeling of the metal tip, that is, the improvement of peeling resistance can be realized.

  Further, in the cross section including the point A and the axis of the electrode chip (hereinafter also simply referred to as the chip cross section), the point located in the second direction side of the part exposed on the side surface of the electrode chip in the melted portion is the point A. When the intersection of the axis of the electrode tip and the boundary between the melted portion and the electrode tip is point X, point A is located on the first direction side from point X and is a line connecting point A and point X An acute angle θ1 formed by the minute AX and a straight line passing through the point X and orthogonal to the axis of the electrode tip satisfies 0 <θ1 ≦ 10 (unit is degree). As a result, the melted portion is not formed in the vicinity of the side surface of the electrode tip, that is, in the vicinity of the outer surface of the melted portion, so that the melted portion extends excessively toward the electrode tip. Therefore, it is possible to prevent the length (also referred to as thickness) of the electrode tip in the axial direction from becoming excessively small in the vicinity of the side surface of the electrode tip. As a result, the thickness of the electrode tip can be secured and the wear resistance of the electrode can be improved.

  Here, if the thickness of the melted part is uneven and the melted part is excessively thin, the stress caused by the difference in thermal expansion coefficient between the electrode body and the electrode tip cannot be sufficiently relaxed at that part. There is a possibility that peeling of the electrode tip is likely to occur. According to the above configuration, further, in the chip cross-section, the point located on the most second direction side on the boundary line between the melted part and the electrode main body in the melted part is the point B, the axis of the electrode chip, the melted part, When the intersection of the boundary line with the electrode body is the point Y, the point B is located on the second direction side from the point Y, the line BY connecting the point B and the point Y, and the electrode passing through the point Y The acute angle θ2 formed by the straight line perpendicular to the axis of the chip satisfies 0 <θ2 ≦ 5 (the unit is degrees). As a result, the melted portion is not formed in the vicinity of the outer surface due to excessive expansion of the melted portion toward the electrode body. Therefore, the uniformity of the thickness of the melting part can be improved. As a result, it is possible to effectively relieve the stress generated during use and further improve the peel resistance.

  Thus, the spark plug having the above-described configuration can realize both the wear resistance and the peel resistance of the electrode tip.

[Application Example 2]
The spark plug according to application example 1,
In the cross section,
The boundary line between the melting part and the electrode tip includes a first orthogonal part having an acute angle of less than ± 2 degrees between the orthogonal direction orthogonal to the axis of the electrode chip,
The boundary line between the melting part and the electrode body includes a second orthogonal part having an acute angle between the orthogonal direction of less than ± 2 degrees,
Of the melted portion, a point that is located closest to the second direction side of a portion in contact with the side surface opposite to the side surface of the electrode tip with which the point A is in contact is referred to as a point A ′,
When the point located in the second direction side of the part exposed on the outer surface opposite to the outer surface where the point B is located in the melting part is the point B ′,
The ratio of the length in the orthogonal direction of the first orthogonal portion to the length in the orthogonal direction between the point A and the point A ′ is 70% or more,
The spark plug, wherein a ratio of the length in the orthogonal direction of the second orthogonal portion to the length in the orthogonal direction between the point B and the point B ′ is 70% or more.

  If there is a variation in the content ratio between the component of the electrode tip and the component of the electrode body in the melting part, the part of the melting part is relatively close to the electrode chip and the coefficient of thermal expansion is relatively close to the electrode body. There is a possibility that stress generated during use cannot be sufficiently relieved. According to the above configuration, the first orthogonal part at the boundary line between the melting part and the electrode tip and the second orthogonal part at the boundary line between the melting part and the electrode body are provided over a relatively wide range. Thus, the uniformity of the content of each component in the melted part can be improved. As a result, it is possible to further effectively relieve the stress generated during use and further improve the peel resistance.

[Application Example 3]
The spark plug according to Application Example 1 or Application Example 2,
In the cross section,
When the length in the first direction between the point A and the point B is E,
A spark plug satisfying E ≦ 0.4 mm (millimeters).

  According to the said structure, it can suppress that the thickness of an electrode tip becomes thin in the vicinity of the side surface of an electrode tip. As a result, the wear resistance of the electrode can be further improved.

[Application Example 4]
The spark plug according to any one of Application Example 1 to Application Example 3,
In the cross section,
When the length in the first direction between the point X and the point Y is F,
A spark plug satisfying F ≧ 0.15 mm (millimeters).

  According to the above configuration, the thickness of the melted portion can be sufficiently ensured even at a portion that intersects the axis of the electrode tip. As a result, it is possible to further effectively relieve the stress generated during use and further improve the peel resistance.

[Application Example 5]
The spark plug according to any one of Application Example 1 to Application Example 4,
The spark plug, wherein a content rate of the component of the electrode tip in the melting part is 40% by weight or more and 80% by weight or less.

  According to the said structure, the coefficient of thermal expansion of a fusion | melting part can be optimized by optimizing the content rate of the component of the electrode tip in a fusion | melting part. As a result, it is possible to more effectively relieve the stress generated during use and further improve the peel resistance.

  It should be noted that the present invention can be realized in various aspects, for example, in aspects such as a spark plug and an internal combustion engine equipped with the spark plug.

It is sectional drawing of the spark plug 100 of this embodiment. 3 is an enlarged perspective view of a tip portion of a center electrode 20. FIG. It is a figure which shows the cross section CS1 containing the point A1 and the axis line CO of the electrode tip 29. FIG. It is a figure explaining the welding method of the base part 27 and the electrode tip 29. FIG. It is explanatory drawing which shows the measuring method of generation | occurrence | production ratio SA of an oxide scale. It is a graph which shows the evaluation result of a 3rd evaluation test. It is a graph which shows the evaluation result of a 4th evaluation test. It is a graph which shows the evaluation result of a 5th evaluation test. It is an expansion perspective view of the front-end | tip part of the ground electrode 30B of the spark plug of 2nd Embodiment. It is a figure which shows the cross section CS2 containing the point A12 and the axis line CO of the electrode tip 39. FIG.

A. First embodiment:
A-1. Spark plug configuration:
Hereinafter, embodiments of the present invention will be described based on the embodiments. FIG. 1 is a cross-sectional view of a spark plug 100 of the present embodiment. The dashed line in FIG. 1 indicates the axis CO (also referred to as axis CO) of the spark plug 100. A direction parallel to the axis CO (vertical direction in FIG. 1) is also referred to as an axis direction. The radial direction of the circle centered on the axis CO is simply referred to as “radial direction”, and the circumferential direction of the circle centered on the axis CO is also simply referred to as “circumferential direction”. The lower direction in FIG. 1 is referred to as a front end direction FD, and the upper direction is also referred to as a rear end direction BD. The lower side in FIG. 1 is called the front end side of the spark plug 100, and the upper side in FIG. 1 is called the rear end side of the spark plug 100. The spark plug 100 includes an insulator 10 as an insulator, a center electrode 20, a ground electrode 30, a terminal fitting 40, and a metal shell 50.

  The insulator 10 is formed by firing alumina or the like. The insulator 10 is a substantially cylindrical member that extends along the axial direction and has a through hole 12 (shaft hole) that penetrates the insulator 10. The insulator 10 includes a flange part 19, a rear end side body part 18, a front end side body part 17, a step part 15, and a leg length part 13. The rear end side body portion 18 is located on the rear end side of the flange portion 19 and has an outer diameter smaller than the outer diameter of the flange portion 19. The front end side body portion 17 is located on the front end side from the flange portion 19 and has an outer diameter smaller than the outer diameter of the rear end side body portion 18. The long leg portion 13 is positioned on the distal end side from the distal end side body portion 17 and has an outer diameter smaller than the outer diameter of the distal end side body portion 17. The long leg portion 13 is reduced in diameter toward the distal end side, and is exposed to the combustion chamber when the spark plug 100 is attached to an internal combustion engine (not shown). The step portion 15 is formed between the leg long portion 13 and the distal end side body portion 17.

  The metal shell 50 is formed of a conductive metal material (for example, a low carbon steel material) and is a cylindrical metal fitting for fixing the spark plug 100 to an engine head (not shown) of an internal combustion engine. The metal shell 50 is formed with an insertion hole 59 penetrating along the axis CO. The metal shell 50 is disposed on the outer periphery of the insulator 10. That is, the insulator 10 is inserted and held in the insertion hole 59 of the metal shell 50. The tip of the insulator 10 is exposed from the tip of the metal shell 50, and the rear end of the insulator 10 is exposed from the rear end of the metal shell 50.

  The metal shell 50 is formed between a hexagonal column-shaped tool engagement portion 51 with which a spark plug wrench engages, an attachment screw portion 52 for attachment to an internal combustion engine, and the tool engagement portion 51 and the attachment screw portion 52. And a bowl-shaped seal portion 54. Here, the nominal diameter of the mounting screw portion 52 is, for example, one of M8 (8 mm (millimeters)), M10, M12, M14, and M18.

  An annular gasket 5 formed by bending a metal plate is fitted between the mounting screw portion 52 and the seal portion 54 of the metal shell 50. The gasket 5 seals a gap between the spark plug 100 and the internal combustion engine (engine head) when the spark plug 100 is attached to the internal combustion engine.

  The metal shell 50 further includes a thin caulking portion 53 provided on the rear end side of the tool engaging portion 51, and a thin compression deformation portion 58 provided between the seal portion 54 and the tool engaging portion 51. And. An annular region formed between the inner peripheral surface of the portion of the metal shell 50 from the tool engaging portion 51 to the crimping portion 53 and the outer peripheral surface of the rear end side body portion 18 of the insulator 10 has an annular shape. Ring members 6 and 7 are arranged. Between the two ring members 6 and 7 in the region, talc (talc) 9 powder is filled. The rear end of the crimped portion 53 is bent radially inward and fixed to the outer peripheral surface of the insulator 10. The compression deformation portion 58 of the metal shell 50 is compressed and deformed when the crimping portion 53 fixed to the outer peripheral surface of the insulator 10 is pressed toward the distal end side during manufacture. The insulator 10 is pressed toward the front end side in the metal shell 50 through the ring members 6 and 7 and the talc 9 by the compression deformation of the compression deformation portion 58. A step portion 15 (insulator side step portion) of the insulator 10 is formed by a step portion 56 (metal side step portion) formed at the position of the mounting screw portion 52 on the inner periphery of the metal shell 50 through the annular plate packing 8. ) Is pressed. As a result, the gas in the combustion chamber of the internal combustion engine is prevented by the plate packing 8 from leaking outside through the gap between the metal shell 50 and the insulator 10.

  The center electrode 20 is a rod-like member extending along the axis CO, and is inserted into the through hole 12 of the insulator 10. The center electrode 20 has a structure including an electrode main body 21, a core material 22 embedded in the electrode main body 21, and an electrode tip 29. The electrode body 21 is made of nickel or an alloy containing nickel as a main component (such as Inconel 600 (the alphabetical INCONEL is a registered trademark)). The core material 22 is formed of copper or an alloy containing copper as a main component, which is superior in thermal conductivity to the alloy forming the electrode body 21. The tip of the center electrode 20 is exposed from the tip of the insulator 10 in the tip direction FD.

  The center electrode 20 has a flange portion 24 (also referred to as an electrode flange portion or a flange portion) provided at a predetermined position in the axial direction, and a head portion 23 (electrode head) that is a portion on the rear end side of the flange portion 24. Part) and a leg part 25 (electrode leg part) which is a part on the tip side of the collar part 24. The flange 24 is supported by the step 16 of the insulator 10. An electrode tip 29 is joined to the tip portion of the leg portion 25 of the center electrode 20 by, for example, laser welding. The configuration of the tip portion of the leg portion 25 of the center electrode 20 will be described later with reference to FIGS.

  The ground electrode 30 is joined to the tip of the metal shell 50. The electrode body of the ground electrode 30 is formed of a metal having high corrosion resistance, for example, a nickel alloy such as Inconel 600. The base material base end portion 32 of the ground electrode 30 is joined to the front end surface of the metal shell 50 by welding. As a result, the ground electrode 30 is electrically connected to the metal shell 50. The base material tip 31 of the ground electrode 30 is bent, and one side surface of the base material tip 31 faces the electrode tip 29 of the center electrode 20 in the axial direction on the axis CO. An electrode tip 33 is welded to the one side surface of the base material tip 31 at a position facing the electrode tip 29 of the center electrode 20. As the electrode tip 33, for example, Pt (platinum) or an alloy containing Pt as a main component, specifically, a Pt-20Ir alloy (a platinum alloy containing 20% by mass of iridium) or the like is used. A spark gap is formed between the electrode tip 29 of the center electrode 20 and the electrode tip 33 of the ground electrode 30.

  The terminal fitting 40 is a rod-shaped member that extends along the axis CO. The terminal fitting 40 is formed of a conductive metal material (for example, low carbon steel), and a metal layer (for example, a Ni layer) for corrosion protection is formed on the surface thereof by plating or the like. The terminal fitting 40 includes a collar part 42 (terminal jaw part) formed at a predetermined position in the axial direction, a cap mounting part 41 located on the rear end side of the collar part 42, and a leg part 43 on the distal side of the collar part 42. (Terminal leg). The cap mounting part 41 including the rear end of the terminal fitting 40 is exposed on the rear end side of the insulator 10. The leg portion 43 including the tip of the terminal fitting 40 is inserted (press-fitted) into the through hole 12 of the insulator 10. A plug cap to which a high voltage cable (not shown) is connected is mounted on the cap mounting portion 41, and a high voltage for generating a spark is applied.

  In the through hole 12 of the insulator 10, a resistor 70 for reducing radio noise when a spark is generated is disposed in a region between the front end of the terminal fitting 40 and the rear end of the center electrode 20. The resistor is made of, for example, a composition containing glass particles as a main component, ceramic particles other than glass, and a conductive material. A gap between the resistor 70 and the center electrode 20 in the through hole 12 is filled with a conductive seal 60, and a gap between the resistor 70 and the terminal fitting 40 is filled with a conductive seal 80 of glass and metal. ing.

A-2. Configuration of the tip of the center electrode:
FIG. 2 is an enlarged perspective view of the tip portion of the center electrode 20. In FIG. 2, contrary to FIG. 1, the upper side of the figure is the front end direction FD, and the lower side of the figure is the rear end direction BD. The same applies to FIGS. 3 and 4 described later.

  The distal end portion of the leg portion 25 (electrode body 21) of the center electrode 20 has a reduced diameter portion 26 whose outer diameter decreases from the rear end side toward the distal end direction FD, and a circle positioned on the distal end side of the reduced diameter portion 26. A columnar pedestal 27 is formed. A cylindrical electrode tip 29 is joined to the distal end side of the pedestal portion 27 by laser welding. As the material of the electrode tip 29, for example, iridium (Ir) or an alloy containing Ir as a main component is used. Specifically, an Ir-5Pt alloy (iridium alloy containing 5% by mass of platinum) or the like is used. Used. By laser welding, a melted portion 28 in which the components of the pedestal 27 and the components of the electrode tip 29 are melted is formed between the electrode tip 29 and the pedestal 27. In the present embodiment, the axis CO of the spark plug 100 and the axis of the electrode tip 29 coincide. Therefore, the axis CO can also be referred to as the axis CO of the electrode tip 29. The diameter of the electrode tip 29 is not limited to this, but is preferably 0.3 mm or more and 3.5 mm or less, and more preferably 0.4 mm or more and 2.6 mm or less.

  The diameter of the pedestal portion 27 is larger than the diameter of the electrode tip 29. For this reason, the outer peripheral surface (also referred to as the outer surface) of the melting portion 28 has a truncated cone shape with a diameter reduced from the rear end side toward the front end direction FD. And the outer peripheral surface of the fusion | melting part 28 contains the exposed part 28C exposed on the outer peripheral surface (it is also called side surface) 29C of the electrode tip 29 as shown by hatching at the front end side. This exposed portion 28 </ b> C includes a so-called weld dripping (sagging) located on the distal direction FD side from the rear end of the outer peripheral surface 29 </ b> C of the electrode tip 29. When the outer peripheral surface of the electrode tip 39 is viewed once in the circumferential direction, a point that is located closest to the rear end direction BD in the exposed portion 28C is defined as A1 (FIG. 2). This point A1 can also be said to be the most distal portion FD side portion of the outer peripheral surface of the melted portion 28, except for the portion where welding droop occurs. This point A1 can also be said to be the point located on the outermost surface 29C of the electrode tip 29 on the line OL1 indicating the front end of the outer circumferential surface of the melting portion 28 and located in the rearmost direction BD. it can.

  FIG. 3 is a diagram showing a cross-section CS1 including the point A1 and the axis CO of the electrode tip 29. The cross section CS1 passes through the center point OC1 of the tip surface (gap forming surface) 29A of the electrode tip 29. As can be seen from FIG. 3, in the present embodiment, the rear end surface of the electrode tip 29 is in contact with the melting portion 28 throughout. In other words, since the sufficiently deep melted portion 28 is formed by laser welding, there is no portion where the electrode tip 29 and the pedestal portion 27 are in direct contact. In the cross section CS1 of FIG. 3, the intersection of the axis CO of the electrode tip 29 and the boundary line BL1 between the electrode tip 29 and the melting part 28 is defined as a point X1. The point X1 can also be said to be the intersection of the axis CO and the rear end surface of the electrode tip 29.

  In the cross section CS1 of FIG. 3, a point located on the most rear end direction BD side of the boundary line BJ1 between the melting portion 28 and the pedestal portion 27 (electrode body 21) is defined as B1. Since the diameter of the pedestal portion 27 is larger than the diameter of the electrode tip 29, no welding dripping occurs on the outer peripheral surface of the pedestal portion 27. In the cross section CS1 of FIG. 3, the intersection of the axis CO of the electrode tip 29 and the boundary line BJ1 between the melting part 28 and the pedestal part 27 is defined as a point Y1. The point Y1 can also be said to be an intersection of the axis CO and the tip surface of the pedestal portion 27.

  In order to perform laser welding from the outer peripheral surface side, the point A1 is located on the tip direction FD side from the point X1. Further, the point B1 is located on the rear end direction BD side from the point Y1. That is, in the melted portion 28, the axial length (also referred to simply as thickness) E1 of the outer peripheral surface is longer than the thickness F1 on the axis CO.

  Here, the acute angle formed by the line AX1 connecting the points A1 and X1 and the straight line HL1 passing through the point X1 and orthogonal to the axis CO of the electrode tip 29 is defined as θ11 (unit is degree). The larger the angle θ11, the wider the outer peripheral surface of the melted portion 28 is on the electrode tip 29 side. An acute angle formed by a line segment BY1 connecting the point B1 and the point Y1 and a straight line HJ1 passing through the point Y1 and orthogonal to the axis CO of the electrode tip 29 is θ12 (unit is degree). The larger the θ12 is, the wider the outer peripheral surface of the melting part 28 is on the pedestal part 27 side. As described above, since the point A1 is located on the tip direction FD side from the point X1, θ11 does not become 0 degree (0 <θ11). Similarly, since the point B1 is located on the rear end direction BD side from the point Y1, θ12 does not become 0 degree (0 <θ12).

  In the cross section CS1 of FIG. 3, the boundary line BL1 between the melted portion 28 and the electrode tip 29 has an acute angle between the orthogonal direction orthogonal to the electrode tip 29, that is, an acute angle with the straight line HL1 is less than ± 2 degrees. A certain orthogonal part PL1 is included. The part from the point C1 to the point C1 ′ in FIG. 3 is the orthogonal part PL1 of the boundary line BL1.

  Further, the boundary line BJ1 between the melting part 28 and the pedestal part 27 (electrode body 21) has an acute angle with the orthogonal direction orthogonal to the electrode tip 29, that is, an acute angle with the straight line HJ1 is less than ± 2 degrees. A certain orthogonal part PJ1 is included. The part from the point D1 to the point D1 ′ in FIG. 3 is the orthogonal part PJ1 of the boundary line BJ1.

  The orthogonal part PL1 of the boundary line BL1 is also referred to as a first orthogonal part PL1, and the orthogonal part PJ1 of the boundary line BJ1 is also referred to as a second orthogonal part PJ1. The length of the first orthogonal part PL1 (the length from the point C1 to the point C1 ′) in the cross section of FIG. 3 is L1. Further, the length of the second orthogonal portion PJ1 (the length from the point D1 to the point D1 ′) in the cross section of FIG.

  Further, in the cross section CS1 of FIG. 3, the melted portion 28 that is in contact with the outer peripheral surface (right side surface in FIG. 3) opposite to the outer peripheral surface (left side surface in FIG. 3) of the electrode tip 29 on the side in contact with the point A1. A point located closest to the rear end direction BD among the parts is defined as a point A1 ′. In the example of FIG. 3, since the welding droop 28C (exposed portion 28C on the side surface) is generated on the outer peripheral surface on the opposite side, the point A1 ′ is the position of the rear end of the welding dripping 28C. The length between the point A1 and the point A1 ′ in the direction orthogonal to the axis CO is M1. The length M1 is substantially equal to the diameter of the electrode tip 29. A ratio (L1 / M1) of the length L1 of the first orthogonal part PL1 to the length M1 between the point A1 and the point A1 ′ is also referred to as a first orthogonal ratio (L1 / M1).

  Moreover, let the point located in the most back end direction BD side of the site | part exposed in the outer peripheral surface on the opposite side to the outer peripheral surface in which the point B1 is located among the fusion | melting parts 28 as point B1 '. The length between the point B1 and the point B1 ′ in the direction orthogonal to the axis CO is defined as K1. The length K1 is substantially equal to the diameter of the tip of the pedestal 27. The ratio (J1 / K1) of the length J1 of the second orthogonal part PJ1 to the length K1 between the point B1 and the point B1 ′ is also referred to as a second orthogonal ratio (J1 / K1).

  It can be said that the thickness F1 of the melted portion 28 on the axis CO is the length in the axial direction between the point X1 and the point Y1. Further, the thickness E1 on the outer peripheral surface of the melted portion 28 can be said to be the length in the axial direction between the points A1 and B1.

A-2. Method of welding the pedestal 27 (electrode body 21) and the electrode tip 29:
FIG. 4 is a diagram for explaining a welding method between the pedestal 27 and the electrode tip 29. In the present embodiment, the pedestal 27 and the electrode tip 29 are welded using a fiber laser that is thinner than a YAG laser and can form a deep melted part.

  FIG. 4 shows a state in which the electrode tip 290 before welding is fixed to the base portion 270 before welding. Using a predetermined jig (not shown), the axis of the pedestal 270 and the axis of the electrode tip 290 are fixed so as to coincide with each other. The length (thickness) H1 ′ in the axial direction of the electrode tip 29 before welding is not limited to this, but is preferably 0.2 mm to 3.5 mm, for example, 0.3 mm to 2 More preferably, it is 2 mm or less.

  In this state, the laser LZ is irradiated from the fiber laser irradiation device 300 to the irradiation position LP on the contact surface between the electrode tip 290 and the pedestal portion 270. The laser LZ is irradiated along a direction perpendicular to the axis CO. In the example of FIG. 4, the irradiation position LP is located on the contact surface between the rear end surface 290 </ b> B of the electrode tip 290 and the front end surface 270 </ b> U of the base portion 270. Then, the electrode tip 290 and the pedestal portion 270 are rotated relative to the fiber laser irradiation apparatus 300 around the axis CO with respect to the electrode tip 290 and the pedestal portion 270 (also referred to as a workpiece). The laser LZ is irradiated over the entire circumference of the outer edge of the contact surface. In the present embodiment, the laser LZ is irradiated continuously rather than intermittently. As a result, the melting portion 28 shown in FIG. 3 is formed between the electrode tip 29 and the pedestal portion 27.

  Here, the thickness F1 on the axis CO of the melting part 28 can be increased. As the irradiation position LP of the laser LZ is shifted to the tip side (electrode tip 29 side), the content of the component of the electrode tip 29 in the melting portion 28 can be increased, and the content of the component of the pedestal portion 27 can be reduced. Further, the thickness F1 on the axis CO of the melting part 28 can be reduced.

  By changing the irradiation condition of the laser LZ, it is possible to form the melted portion 28 having various shapes. For example, the faster the workpiece rotation speed with respect to the fiber laser irradiation apparatus 300, the smaller the thickness F1 on the axis CO of the melted portion 28 can be made. As the energy of the laser LZ is larger, the thickness F1 on the axis CO of the melted portion 28 can be increased. Further, the thickness F1 on the axis CO of the melting portion 28 can be increased as the condensing position GP of the laser LZ is further away from the irradiation position LP in FIG.

  Further, by increasing the rotation speed of the workpiece and increasing the energy of the laser LZ, the thickness E1 of the outer peripheral surface of the melting portion 28 becomes larger than the thickness F1 on the axis CO of the melting portion 28. Can be suppressed. By suppressing the increase in the thickness E1 of the outer peripheral surface of the melting portion 28 with respect to the thickness F1 on the axis CO of the melting portion 28, the above-described angles θ11 and θ12 can be suppressed from increasing. it can. Further, for example, by bringing the condensing position GP of the laser LZ closer to the workpiece, the lengths of the first orthogonal part PL1 and the second orthogonal part PJ1 can be increased, and the first orthogonal ratio (L1 / M1) ) And the second orthogonal ratio (J1 / K1) can be increased. Increasing the rotational speed of the workpiece is most effective for suppressing the thickness E1 of the outer peripheral surface of the melting portion 28 and for suppressing the angles θ11 and θ12. Further, as the irradiation position LP is shifted toward the electrode body 21 (pedestal portion 27), θ11 increases with respect to θ12, and as the irradiation position LP is shifted toward the electrode tip 29, θ11 decreases with respect to θ12.

  In the spark plug 100 having the above configuration, the melting portion 28 is in contact with the electrode tip 29 at the position of the axis CO of the electrode tip 29 (point X1 in FIG. 3). That is, the melted portion 28 is formed over a relatively wide range between the base 27 (electrode body 21) and the contact area with the electrode tip 29 before the melted portion is formed (before laser welding is performed). Yes. As a result, the welding strength is improved, and the suppression of peeling of the electrode tip 29, that is, the improvement of peeling resistance can be realized.

  As can be seen from FIG. 3, of the two directions along the axis CO of the electrode tip 29, the direction on the electrode tip 29 side when viewed from the melting portion 28 is the tip direction FD in the first embodiment. Further, the direction on the pedestal portion 27 (electrode body 21) side when viewed from the melting portion 28 is the rear end direction BD in the first embodiment. Therefore, in the center electrode 20 of the first embodiment, the front end direction FD corresponds to the first direction in the claims, and the rear end direction BD corresponds to the second direction in the claims.

A-4: First evaluation test:
Fifteen types of samples 1-1 to 1-15 in which the shapes of the melted portions 28 of the spark plug 100 in the first embodiment are different from each other were created and evaluated (Table 1). In each sample, the angles of θ11 and θ12 described above are made different from each other by changing the laser irradiation conditions of the laser welding described above. The above-described Ir-5Pt alloy (iridium alloy containing 5% by mass of platinum) is used as the material of the electrode tip 29 of each sample, and the above-described material is used as the material of the electrode body 21 (pedestal portion 27). Inconel 600 was used.

The dimensions common to the spark plug 100 common to each sample are as follows.
Diameter of electrode tip 29: 0.6 mm
Thickness H1 ′ before welding of the electrode tip 29: 0.5 mm
Diameter of tip of pedestal 27 before welding: 0.9 mm

  Table 1 shows the angles of θ11 and θ12 described above for each sample. As shown in Table 1, in each sample, θ11 is any one of 6 degrees, 8 degrees, 10 degrees, 12 degrees, and 14 degrees. In each sample, θ12 is any one of 3 degrees, 5 degrees, and 7 degrees.

  Each sample was subjected to a spark test as a wear resistance evaluation test and a cold test as a peel resistance evaluation test. In the spark test, each sample was subjected to a spark test for generating spark discharge 100 times per second for 250 hours in a chamber filled with nitrogen pressurized to 0.4 MPa. At the time of discharging, a predetermined power supply device (for example, a full transistor ignition device) was used.

  Then, after the spark test, the outer shape of the electrode tip 29 of each sample is enlarged and projected using a projector, and the maximum amount of consumption (reduced length from the original size) of the electrode tip 29 in the axial direction is measured. did. Normally, the amount of wear in the vicinity of the outer peripheral surface of the electrode tip 29 is maximized. And the evaluation result of the sample whose consumption amount exceeds 0.25 mm was set to "x", and the evaluation result of the sample whose consumption amount is 0.25 mm or less was set to "(circle)". The smaller the consumption amount, the better the wear resistance.

  In the cold test, the cycle of heating and cooling near the tip of each sample of the spark plug 100 (near the spark gap) was repeated 1000 times. Specifically, one cycle is such that the vicinity of the tip of each sample is heated with a burner for 2 minutes and then cooled in air for 1 minute. The intensity | strength of the burner was adjusted so that the temperature of the front-end | tip part of the metal shell 50 may reach a predetermined target temperature by heating for 2 minutes. In the first evaluation test, the target temperature is 900 degrees Celsius.

  After the thermal test, the center electrode 20 of each sample was cut along the cross section including the axis CO of the electrode tip 29, and the oxide scale generation ratio SA (unit:%) was measured. Below, the measuring method of the generation rate SA of an oxide scale is demonstrated.

  FIG. 5 is an explanatory diagram showing a method of measuring the oxide scale generation ratio SA. FIG. 5 is the same cross section as the cross section shown in FIG. In the cross section of FIG. 5, it is assumed that oxide scales OS1 to OS3 indicated by thick solid lines are generated. The oxide scale OS1 is generated on the boundary line BL1 between the rear end surface of the electrode tip 29 and the front end surface of the melting part 28. The oxide scales OS2 and OS3 are generated on the boundary line BL2 between the rear end surface of the melting portion 28 and the front end surface of the pedestal portion 27. It means that the smaller the generation ratio SA of oxide scale, the better the peel resistance.

  The length in the direction perpendicular to the axial direction of the electrode tip 29 in the cross section of FIG. The oxide scale generation ratio SA is a ratio of the length of the range where the oxide scale is generated on either of the boundary lines BL1 and BL2 in the range of the length LG perpendicular to the axial direction shown in FIG. FIG. 5 shows the range of the length LNa where the oxide scale is generated and the range of the length LNb. In this case, the oxide scale generation ratio SA can be calculated by the following formula: SA = {(LNa + LNb) / LG} × 100.

  An evaluation result of a sample having an oxide scale generation rate SA exceeding 50% was set to “x”, and an evaluation result of a sample having an oxide scale generation rate SA of 50% or less was set to “◯”.

  In samples 1-1 to 1-6 in which θ11 exceeds 10 degrees, the evaluation results of the spark test are all “x”, and in samples 1-7 to 1-15 in which θ11 is 10 degrees or less, the sparks The evaluation results of the tests were all “◯”. The reason is estimated as follows. That is, θ11 is sufficiently small that the melted portion 28 does not spread excessively toward the electrode tip 29 in the vicinity of the outer peripheral surface of the electrode tip 29, that is, in the vicinity of the outer peripheral surface of the melted portion. means. In this case, it is considered that the thickness H1 (FIG. 3) in the vicinity of the outer peripheral surface of the electrode tip 29 can be suppressed from becoming excessively small. If the thickness H1 (FIG. 3) in the vicinity of the outer peripheral surface of the electrode tip 29 becomes excessively small, the electrode tip 29 is consumed in the vicinity of the outer peripheral surface of the electrode tip 29 and the melted portion 28 is exposed to the front end side. Consumability is reduced. This is because the melted portion 28 is significantly inferior in wear resistance as compared with the electrode tip 29. Therefore, when θ11 is 10 degrees or less, it is possible to secure the thickness H1 in the vicinity of the outer peripheral surface of the electrode tip 29 and improve wear resistance.

  In Samples 1-1, 1-4, 1-7, 1-10, and 1-13 in which θ12 exceeds 5 degrees, the evaluation results of the cooling test are all “x”, and θ12 is 5 degrees. In the following samples 1-2, 1-3, 1-5, 1-6, 1-8, 1-9, 1-11, 1-12, 1-14, 1-15, the evaluation result of the cooling test Were all “◯”. The reason is estimated as follows. When the thickness of the melted portion 28 is not uniform, for example, a portion where the melted portion 28 is excessively thin may occur. In some cases, the stress caused by the difference in coefficient of thermal expansion between the electrode main body 21 (pedestal portion 27) and the electrode tip 29 cannot be sufficiently relaxed, and the electrode tip 29 tends to peel off. The reason why θ12 is sufficiently small is that the melted portion 28 is excessively spread toward the electrode body 21 (pedestal portion 27) in the vicinity of the outer peripheral surface of the electrode tip 29, that is, in the vicinity of the outer peripheral surface of the melted portion. Means no. Therefore, it is considered that the uniformity of the thickness of the melted portion 28 is improved. Therefore, when θ12 is 5 degrees or less, the uniformity of the thickness of the melted portion 28 is improved, the stress between the electrode body 21 and the electrode tip 29 is effectively relieved, and peeling resistance is improved. Can be further improved.

  Furthermore, as an additional test of the first evaluation test, four types of samples 1-16 to 1-19 having θ11 of 10 degrees and θ12 of 5 degrees were prepared, and a spark test and a thermal test were performed. As shown in Table 2, in these four types of samples 1-16 to 1-19, the first orthogonal ratio (L1 / M1) described with reference to FIG. 3 and the second orthogonal ratio (J1 / K1) ) And are different. For example, in the four types of samples 1-16 to 1-19, the first orthogonal ratio (L1 / M1) is 27%, 59%, 65%, and 81%, respectively, and the second orthogonal ratio (J1 / K1) is 41%, 64%, 73%, 87%.

  Thus, as shown in Table 2, in these four types of samples 1-16 to 1-19, both the evaluation result of the spark test and the evaluation result of the cooling test were “◯”. From this test result, θ11 is 10 degrees or less and θ12 is 5 degrees or less regardless of the values of the first orthogonal ratio (L1 / M1) and the second orthogonal ratio (J1 / K1). If it exists, it turned out that both wear resistance and peeling resistance can be achieved.

  From the results of the first evaluation test described above, it was found that θ11 is preferably 10 degrees or less and θ12 is preferably 5 degrees or less from the viewpoint of achieving both wear resistance and peel resistance. As described above, since 0 <θ11 and 0 <θ12, in other words, the angles θ11 and θ12 are 0 <θ11 ≦ 10 (unit is degree) and 0 <θ12 ≦ 5 (unit is degree) ) Is preferably satisfied. By doing so, it is possible to achieve both wear resistance and peeling resistance of the electrode tip 29. In addition, since the wear resistance of the electrode tip 29 can be improved, it is not necessary to increase the axial length of the electrode tip 29 in order to ensure the wear resistance of the electrode tip 29. As a result, the length of the electrode tip 29 in the axial direction can be reduced, and the amount of a material such as a noble metal used can be reduced.

A-5: Second evaluation test:
Next, 49 samples 2-1 to 2-49 satisfying a preferable range of θ11 and θ12 that were clarified in the first evaluation test were prepared, and a cooling test was performed under conditions more severe than the first evaluation test. . Specifically, in the cooling test of the second evaluation test, the target temperature described above is set to 950 degrees Celsius. The other conditions for the cooling test and other dimensions common to each sample are the same as those in the first evaluation test.

  As shown in Table 3, in this evaluation test, while satisfying 0 <θ11 ≦ 10 (unit is degree) and 0 <θ12 ≦ 5 (unit is degree), the first orthogonal ratio (L1 / M1 ) And the second orthogonal ratio (J1 / K1) are changed to 7 levels of 40%, 50%, 60%, 70%, 80%, 90%, and 95%, respectively, to obtain 49 types (7 X7 types) of samples were prepared. Table 3 shows the generation rate SA (unit:%) of oxide scale as the evaluation results of 49 types of samples.

  In the first sample group (outside the bold frame) in which at least one of the first orthogonal ratio (L1 / M1) and the second orthogonal ratio (J1 / K1) is less than 70%, the generation ratio of oxide scale SA was 50% or more in all cases. Specifically, the first sample group is Samples 2-1 to 2-24, 2-29 to 2-31, 2-36 to 2-38, and 243 to 2-45.

  In the second sample group (within the bold line frame) in which the first orthogonal ratio (L1 / M1) is 70% or more and the second orthogonal ratio (J1 / K1) is 70% or more, Oxidation scale generation ratio SA was less than 50% in all cases. That is, the second sample group had better peel resistance than the first sample group. Specifically, the second sample group is Samples 2-25 to 2-28, 2-32 to 2-35, 2-39 to 2-42, and 2-46 to 2-49.

  More specifically, among the second sample groups, the larger the first orthogonal ratio (L1 / M1), the smaller the oxide scale generation rate SA, and the better the peel resistance. Similarly, in the second sample group, the larger the second orthogonal ratio (J1 / K1), the smaller the oxide scale generation ratio SA, and the better the peel resistance. Specifically, the first orthogonal ratio (L1 / M1) and the second orthogonal ratio (J1 / K1) are more preferably 80% from 70%, more preferably 90% from 80%, and 95% or more. Is most preferred.

  The reason is estimated as follows. When the first orthogonal ratio (L1 / M1) is 70% or more and the second orthogonal ratio (J1 / K1) is 70% or more, the first orthogonal part PL1 Two orthogonal portions PJ1 can be provided over a relatively wide range. As a result, it is possible to prevent a large amount of one of the components of the electrode tip 29 and the electrode main body 21 (pedestal portion 27) from being taken into the melting portion 28. Therefore, the uniformity of the content rate of each component in the melting part 28 can be improved. Here, if there is a variation in the content ratio between the component of the electrode tip 29 and the component of the electrode body 21 in the melting part 28, the thermal expansion coefficient of the melting part 28 is relatively close to that of the electrode tip 29. There is a possibility that the rate is relatively close to the electrode body 21 and the stress generated when the spark plug 100 is used cannot be sufficiently relaxed. As can be understood from the above description, the first orthogonal ratio (L1 / M1) is 70% or more and the second orthogonal ratio (J1 / K1) is 70% or more, so that the spark plug can be used. The stress generated during the use of 100 can be more effectively relaxed, and the peel resistance can be further improved.

  From the above results of the second evaluation test, from the viewpoint of improving peel resistance, the first orthogonal ratio (L1 / M1) is 70% or more, and the second orthogonal ratio (J1 / K1) is 70% or more was found to be more preferable. In this way, the peel resistance of the electrode tip 29 can be further improved.

A-6. Third evaluation test:
Next, six types of samples that satisfy the preferable range revealed in the second evaluation test were prepared, and the spark test was performed under conditions more severe than the first evaluation test. Specifically, in the spark test of the third evaluation test, a spark test for generating 100 spark discharges per second in a chamber filled with nitrogen pressurized to 0.8 MPa was performed for 200 hours. Then, every 25 hours, a sample was taken out and the consumption amount of the electrode tip 29 was measured. In a plurality of samples, θ11 is fixed at 10 degrees and θ12 is fixed at 5 degrees, and the first orthogonal ratio (L1 / M1) and the second orthogonal ratio (J1 / K1) are fixed at 70%, respectively. It was done. Other dimensions common to each sample are the same as those in the first evaluation test.

  FIG. 6 is a graph showing the evaluation results of the third evaluation test. As shown in FIG. 6, in this evaluation test, the axial length E1 of the outer peripheral surface of the electrode tip 29 (the axial length E1 from the point A1 to the point B1 (FIG. 3)) is 0.3 mm, Six types of samples 3-1 to 3-6, which were changed in six stages of 0.35 mm, 0.4 mm, 0.45 mm, 0.5 mm, and 0.55 mm, were prepared.

  In the graph of FIG. 6, for each sample, the consumption amount of the sample after 25 to 200 hours has been plotted every 25 hours.

  As shown in FIG. 6, at the time when 200 hours passed, the samples 3-1 to 3-3 having the length E1 of 0.4 mm or less were suppressed in the consumption amount to less than 0.25 mm. On the other hand, in samples 3-4 to 3-6 in which the length E1 exceeds 0.4 mm, the consumption amount greatly exceeds 0.25 mm and reaches 0.3 mm or more. That is, samples 3-1 to 3-3 having a length E1 of 0.4 mm or less have better wear resistance than samples 3-4 to 3-6 having a length E1 of 0.4 mm or less. Met.

  Comparing samples 3-1 to 3-3, which had good wear resistance, sample 3-2 having a length E1 of 0.35 mm and sample 3-1 having a length E1 of 0.3 mm were There was no difference in the amount of wear, indicating the same level of wear resistance. Compared with these samples 3-1, 3-2, the sample 3-3 having a length E1 of 0.4 mm has a slightly large consumption amount and is slightly inferior in wear resistance.

  The reason is estimated as follows. When the length E1 becomes excessively large, the thickness H1 of the electrode tip 29 in the vicinity of the outer peripheral surface of the electrode tip 29 may be shortened. As described above, when the electrode chip 29 is excessively thin, the wear resistance of the center electrode 20 is lowered. This can be suppressed. When the length E1 is 0.4 mm or less (E ≦ 0.4 mm), it is possible to suppress the thickness in the vicinity of the outer peripheral surface of the electrode tip 29 from becoming excessively thin. As a result, the wear resistance of the center electrode 20 can be further improved.

  From the results of the third evaluation test described above, it was found that the axial length E1 from the point A1 to the point B1 of the melted portion 28 is more preferably 0.4 mm or less. In this way, the wear resistance of the electrode tip 29 can be further improved.

A-7. Fourth evaluation test:
Next, a plurality of samples satisfying a preferable range revealed in the second evaluation test were prepared, and a cooling test was performed under conditions more severe than those in the second evaluation test. Specifically, in the cooling test of the fourth evaluation test, the target temperature described above is set to 1000 degrees Celsius. The other conditions for the cooling test are the same as those for the second evaluation test. The dimensions common to each sample are as described in the first evaluation test. In a plurality of samples, θ11 is fixed at 10 degrees and θ12 is fixed at 5 degrees, and the first orthogonal ratio (L1 / M1) and the second orthogonal ratio (J1 / K1) are 70%, respectively. Fixed to.

  FIG. 7 is a graph showing the evaluation results of the fourth evaluation test. As shown in FIG. 7, in this evaluation test, the length F1 (FIG. 3) in the axial direction from the point X1 to the point Y1 described above is set to 0.05 mm, 0.1 mm, 0.15 mm, 0.2 mm, 0, Seven types of samples 4-1 to 4-7, which were changed in seven stages of .25 mm, 0.3 mm, and 0.35 mm, were prepared.

  In FIG. 7, the generation ratio SA of the oxide scale of each sample is plotted.

  As shown in FIG. 7, in Samples 4-1 and 4-2 having a length F1 of less than 0.15 mm, the oxide scale generation rate SA greatly exceeded 50% and reached 80%. On the other hand, in Samples 4-3 to 4-7 having a length F1 of 0.15 mm or more, the oxide scale generation ratio SA was significantly lower than 50% and was 30% or less. That is, Samples 4-3 to 4-7 having a length F1 of 0.15 mm or more have better peel resistance than Samples 4-1 and 4-2 having a length F1 of less than 0.15 mm. Met.

  When samples 4-3 to 4-7, which had good peel resistance, were compared, the larger the length F1, the smaller the generation rate SA of oxide scale, and the better the peel resistance. That is, the length F1 is preferably 0.2 mm from 0.15 mm, more preferably 0.25 mm from 0.2 mm, more preferably 0.3 mm from 0.25 mm, and most preferably 0.35 mm or more.

  The reason is estimated as follows. If the thickness of the melted portion 28 can be sufficiently ensured even at a portion that intersects the axis CO of the electrode tip 29, the stress generated when the spark plug 100 is used can be more effectively relieved to further improve the peel resistance. be able to. Therefore, when the length F1 is 0.15 mm or more, the peel resistance of the center electrode 20 can be further improved.

  From the result of the fourth evaluation test described above, the axial length F1 from the point X1 to the point Y1, that is, the axial length F1 of the portion that intersects the axial line CO of the melting portion 28 is 0.15 mm or more. Has been found to be more preferable. If it carries out like this, the peeling resistance of the electrode tip 29 can be improved more.

A-8. Fifth evaluation test:
Next, seven types of samples satisfying the preferable range revealed in the fourth evaluation test were prepared, and a cooling test was performed under conditions more severe than the fourth evaluation test. Specifically, in the cooling test of the fifth evaluation test, the target temperature described above is set to 1020 degrees Celsius. The other conditions for the cooling test are the same as those for the fourth evaluation test. In the seven types of samples, θ11 is fixed at 10 degrees and θ12 is fixed at 5 degrees, and the first orthogonal ratio (L1 / M1) and the second orthogonal ratio (J1 / K1) are 70%, respectively. Fixed to. Moreover, the length F1 on the axis CO of the melting part 28 was fixed to 0.3 mm.

  FIG. 8 is a graph showing the evaluation results of the fifth evaluation test. As shown in FIG. 8, seven types of samples 5-1 to 3, in which the content of the component (iridium alloy) of the electrode tip 29 in the melting part 28 was changed from 30 wt% to 90 wt% in increments of 10%. -7 was prepared. In addition, the content rate of the component of the electrode tip 29 in the fusion | melting part 28 is reduced by shifting the irradiation position of the laser LZ to the rear end side (pedestal part 27 side) from the irradiation position LP of FIG. By shifting the irradiation position of the laser LZ from the irradiation position LP in FIG. 4 to the tip side (electrode tip 29 side), the content rate of the component of the electrode tip 29 in the melting part 28 is increased.

  As shown in FIG. 8, in the sample 5-1 in which the content of the component of the electrode tip 29 is 30% by weight and the sample 5-7 in which the content of the component of the electrode tip 29 is 90% by weight, The generation rate SA greatly exceeded 50% and reached 60% or more. On the other hand, in the samples 5-2 to 5-6 in which the content of the component of the electrode tip 29 is 40% by weight or more and 80% by weight or less, the generation ratio of oxide scale is significantly lower than 50%. That is, samples 5-2 to 5-6 in which the component content of the electrode tip 29 is 40 wt% or more and 80 wt% or less are samples in which the content of the component of the electrode tip 29 is 30 wt% or 90 wt%. Compared with 5-1, 5-7, the peel resistance was good.

  When Samples 5-2 to 5-6, which had good peel resistance, were compared, Sample 5-4 in which the content of the component of the electrode tip 29 was 60% by weight had the smallest oxide scale generation rate SA. . And in the range whose content rate of the component of the electrode tip 29 is 60 weight% or more, the generation rate SA of the oxide scale became large, so that the said content rate was large. Further, in the range where the component content of the electrode tip 29 is 60% by weight or less, the smaller the content rate, the larger the generation rate SA of the oxide scale. Therefore, from the viewpoint of peel resistance, the content of the components of the electrode tip 29 is preferably 40% by weight to 50% by weight, and more preferably 50% by weight to 60% by weight. Further, the content of the components of the electrode tip 29 is preferably 80% by weight to 70% by weight, and more preferably 70% by weight to 60% by weight.

  The reason is estimated as follows. If the content of the component of the electrode tip 29 in the melting part 28 is excessively large, the coefficient of thermal expansion of the melting part 28 is too close to the coefficient of thermal expansion of the electrode tip 29. Further, if the content of the component of the electrode tip 29 in the melting part 28 is excessively small, the thermal expansion coefficient of the melting part 28 becomes too close to the thermal expansion coefficient of the electrode body 21. In any case, there is a possibility that the stress caused by the difference in coefficient of thermal expansion between the electrode tip 29 and the electrode body 21 cannot be relaxed appropriately. When the content rate of the component of the electrode tip 29 is 40% by weight or more and 80% by weight or less, the coefficient of thermal expansion of the melted portion 28 is increased by optimizing the content rate of the component of the electrode tip 29 in the melted portion 28 Can be optimized. As a result, the stress generated during use of the spark plug 100 can be more effectively relaxed, and the peel resistance can be further improved.

  From the results of the fifth evaluation test described above, it was found that the content of the component of the electrode tip 29 in the melted portion 28 is more preferably 40% by weight or more and 80% by weight or less. If it carries out like this, the peeling resistance of the electrode tip 29 can be improved more.

B. Second embodiment:
FIG. 9 is an enlarged perspective view of the tip portion of the ground electrode 30B of the spark plug according to the second embodiment. In FIG. 9, as in FIG. 1 and opposite to FIGS. 2 and 3, the lower side of the figure is the front end direction FD, and the upper side of the figure is the rear end direction BD. The overall configuration of the spark plug of the second embodiment is the same as the overall configuration of the spark plug 100 of the first embodiment of FIG.

  The base material base end portion (not shown) of the ground electrode 30B is joined to the front end of the metal shell 50 in the same manner as the base material base end portion 32 shown in FIG. A columnar pedestal 37 is formed on the surface of the rear end side of the base end 31 of the ground electrode 30B. A columnar electrode tip 39 is joined to the rear end side of the pedestal portion 37 by laser welding. For this reason, between the columnar electrode tip 39 and the pedestal portion 37, the component of the pedestal portion 37 and the component of the electrode tip 39 are the same as the central electrode 20 (FIG. 3) of the spark plug 100 of the first embodiment. A melted part 38 is formed by melting and. In the second embodiment, the axis CO of the spark plug 100 and the axis of the electrode tip 39 coincide with each other. Therefore, the axis CO can also be referred to as the axis CO of the electrode tip 39.

  The diameter of the pedestal portion 37 is larger than the diameter of the electrode tip 39. For this reason, the outer peripheral surface of the fusion | melting part 38 has a truncated cone shape diameter-reduced toward the rear end direction BD from the front end side. And the outer peripheral surface of the fusion | melting part 38 contains the exposed part 38C exposed on the outer peripheral surface 29C of the electrode chip 39 in the rear end side, as shown by hatching (FIG. 9). The exposed portion 38 </ b> C includes a so-called weld droop that is positioned in the rear end direction BD from the front end of the outer peripheral surface 39 </ b> C of the electrode tip 39. When the outer peripheral surface of the electrode tip 39 is viewed once in the circumferential direction, a point located on the most distal direction FD side in the exposed portion 38C is defined as A2. In other words, this point A2 can also be said to be the most rear end direction BD side portion of the outer peripheral surface of the melted portion 28, except for the portion where the welding is generated. This point A2 can also be said to be the point located on the outermost surface 39C of the electrode tip 39 and the point on the line OL2 indicating the rear end of the outer circumferential surface of the melting portion 38, which is located in the most distal direction FD. it can.

  FIG. 10 is a diagram showing a cross section CS2 including the point A2 and the axis CO of the electrode tip 39. As shown in FIG. The cross section CS2 passes through the center point OC2 of the rear end surface (gap forming surface) 39A of the electrode tip 39. As can be seen from FIG. 10, in the present embodiment, the tip surface of the electrode tip 39 is in contact with the melting portion 38 throughout. In the cross section CS2 of FIG. 10, the intersection of the axis CO of the electrode tip 39 and the boundary line BL2 between the electrode tip 39 and the melting part 38 is defined as a point X2. In the cross section CS2 of FIG. 10, the point located in the most distal direction FD among the boundary line BJ2 between the melting part 38 and the pedestal part 37 (electrode body) is defined as B2. In the cross section CS2 of FIG. 3, an intersection of the axis CO of the electrode tip 39, the boundary line BJ2 of the melting part 38, and the pedestal part 37 is defined as a point Y2.

  In order to perform laser welding from the outer peripheral surface side, the point A2 is located on the rear end direction BD side from the point X2. Further, the point B2 is located on the tip direction FD side from the point Y2. The thickness E2 on the outer peripheral surface of the melting part 38 is longer than the thickness F2 on the axis CO.

  Here, an acute angle formed by the line AX2 connecting the point A2 and the point X2 and the straight line HL2 passing through the point X2 and orthogonal to the axis CO of the electrode tip 39 is θ21 (unit is degree). In addition, an acute angle formed by a line segment BY2 connecting the point B2 and the point Y2 and a straight line HJ2 passing through the point Y2 and orthogonal to the axis CO of the electrode tip 39 is θ22 (unit is degree).

  In the cross section CS2 of FIG. 10, the boundary line BL2 between the melting portion 38 and the electrode tip 39 has an acute angle between the orthogonal direction orthogonal to the electrode tip 39, that is, an acute angle with the straight line HL2 is less than ± 2 degrees. A certain orthogonal part PL2 is included. The part from the point C2 to the point C2 ′ in FIG. 10 is the orthogonal part PL2 of the boundary line BL2.

  Further, the boundary line BJ2 between the melting portion 38 and the pedestal portion 37 (electrode body) has an acute angle with the orthogonal direction orthogonal to the electrode tip 39, that is, an acute angle with the straight line HJ2 is less than ± 2 degrees. The orthogonal part PJ2 is included. The part from the point D2 to the point D2 ′ in FIG. 10 is the orthogonal part PJ2 of the boundary line BJ2.

  The length of the orthogonal part PL2 in the cross section CS2 of FIG. 10 is L2, and the length of the orthogonal part PJ2 is J2. In the cross section CS2 in FIG. 10, the outer peripheral surface (the right side surface in FIG. 10) opposite to the outer peripheral surface (the left side surface in FIG. 10) of the electrode tip 39 on the side in contact with the point A2 and the melting portion 28 are A point located closest to the distal direction FD among the contacted parts is defined as a point A2 ′. The length between the point A2 and the point A2 ′ in the direction orthogonal to the axis CO is M2.

  Further, in the melted portion 38, the point located on the most distal direction FD side of the portion exposed on the outer peripheral surface opposite to the outer peripheral surface where the point B2 is located is defined as a point B2 ′, and the point B2 and the point B2 ′ The length in the direction perpendicular to the axis CO is K2.

  It can be said that the thickness F2 on the axis CO of the melting part 38 is the length in the axial direction between the point X2 and the point Y2. Moreover, the thickness E3 on the outer peripheral surface of the melting part 38 can be said to be the length in the axial direction between the points A2 and B2.

  In the ground electrode 30B of the spark plug according to the second embodiment described above, the melting portion 38 is formed by the welding method using the fiber laser described with reference to FIG. 4 as with the center electrode 20 according to the first embodiment. Has been.

  In the spark plug of the second embodiment, the melting part 38 is in contact with the electrode tip 39 at the position of the axis CO of the electrode tip 39 (point X2 in FIG. 10). That is, the melted portion 38 is formed over a relatively wide range of the contact portion between the pedestal portion 37 (electrode body) and the electrode tip 39 before the melted portion is formed (before laser welding is performed). . As a result, the welding strength is improved, and suppression of peeling of the electrode tip 39, that is, improvement of peeling resistance can be realized.

  In addition, the peel resistance and wear resistance characteristics of the ground electrode 30B of the spark plug of the second embodiment are the same as the peel resistance and wear resistance characteristics of the center electrode 20 of the spark plug 100 of the first embodiment. Can think. Therefore, based on the results of the first to fifth evaluation tests performed on the center electrode 20 of the spark plug 100 of the first embodiment, the ground electrode 30B of the spark plug of the second embodiment is Similar to the center electrode 20 of the spark plug 100 of one embodiment, it is preferable to satisfy the following relationship.

  Specifically, it is preferable that the angles θ21 and θ22 satisfy 0 degree <θ21 ≦ 10 degrees and 0 degree <θ22 ≦ 5 degrees. By doing so, it is possible to achieve both wear resistance and peel resistance of the electrode tip 39.

  Furthermore, the ratio (L2 / M1) of the length L2 of the orthogonal part PL2 to the length M2 is 70% or more, and the ratio (J2 / K2) of the length J2 of the orthogonal part PJ2 to the length K2 is 70% or more is more preferable. By so doing, the peel resistance of the electrode tip 39 can be further improved.

  Furthermore, the length E2 in the axial direction from the point A2 to the point B2 of the melting part 38 is more preferably 0.4 mm or less (E2 ≦ 0.4 mm). In this way, the wear resistance of the electrode tip 39 can be further improved.

  Furthermore, the axial length F2 from the point X2 to the point Y2, that is, the axial length F2 of the portion that intersects the axial line CO of the melting portion 38 is more preferably 0.15 mm or more (F2 ≧ 0). .15 mm). By so doing, the peel resistance of the electrode tip 39 can be further improved.

  Further, the content of the component of the electrode tip 39 in the melting part 38 is more preferably 40 wt% or more and 80 wt% or less. By so doing, the peel resistance of the electrode tip 39 can be further improved.

  As can be seen from FIG. 10, of the two directions along the axis CO of the electrode tip 39, the direction on the electrode tip 39 side when viewed from the melting portion 38 is the rear end direction BD in the second embodiment. . In addition, the direction on the pedestal portion 37 (electrode body) side when viewed from the melting portion 38 is the front end direction FD in the second embodiment. Therefore, in the ground electrode 30B of the second embodiment, the front end direction FD corresponds to the second direction in the claims, and the rear end direction BD corresponds to the first direction in the claims.

C. Variation:
(1) In the first embodiment and the second embodiment, as shown in FIG. 1, a spark plug of the type in which the axis CO of the spark plug 100 and the axes of the electrode tip 29 and the ground electrode 30 are the same. Take as an example. Instead, a spark plug of a type in which the axis CO of the spark plug 100 and the axis of the electrode tip 29 or the ground electrode 30 intersect, for example, an orthogonal type may be employed.

(2) In the first embodiment, the melted portion 28 that contacts the entire rear end surface 29 is formed by continuously irradiating the fiber laser. Instead of this, for example, the melted portion 28 may be formed by intermittently irradiating a fiber laser. Even in this case, it is preferable that laser welding is performed at a sufficient depth so that the electrode tip 29 and the melted portion 28 come into contact with each other on the axis CO of the electrode tip 29 (point X1 in FIG. 3). .

(3) The spark plug has both the center electrode 20 (FIG. 3) having the configuration described as the first embodiment and the ground electrode 30B (FIG. 10) having the configuration described as the second embodiment. You may prepare. The spark plug may include the center electrode 20 (FIG. 3) having the configuration described as the first embodiment and a ground electrode having a known configuration. Further, the spark plug may include the ground electrode 30B (FIG. 10) having the configuration described as the second embodiment and a center electrode having a known configuration.

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

  5 ... gasket, 6 ... ring member, 8 ... plate packing, 9 ... talc, 10 ... insulator, 13 ... leg length, 15 ... step, 16 .... Step part, 17 ... Front end side body part, 18 ... Rear end side body part, 19 ... Gutter part, 20 ... Center electrode, 21 ... Electrode body, 22 ... Core material , 23 ... head, 24 ... buttocks, 25 ... legs, 26 ... reduced diameter part, 27 ... pedestal part, 28 ... melting part, 29 ... electrode tip 30 ... ground electrode, 30B ... ground electrode, 30B ... center electrode, 37 ... pedestal part, 38 ... melting part, 39 ... electrode tip, 40 ... terminal fitting, 41 ... Cap mounting part, 42 ... Bridge part, 43 ... Leg part, 50 ... Metal fitting, 51 ... Tool engaging part, 52 ... Mounting screw part, 53 ... Caulking part, 54 ... seal part, 56 ... step part, 58 ... compression deformation part, 59 ... insertion hole, 60 ... conductive seal, 70 ... resistor, 80. .. Conductive seal, 100 ... spark plug, 00 ... fiber laser irradiation apparatus

Claims (5)

A rod-shaped center electrode;
An insulator having a through hole into which the center electrode is inserted;
A metal shell disposed on the outer periphery of the insulator;
A ground electrode that is in electrical communication with the metal shell and forms a spark gap with the center electrode;
A spark plug comprising:
At least one of the center electrode and the ground electrode is
Columnar electrode tips forming the spark gap;
An electrode body in which the electrode tip is laser welded to an end; and
A fusion zone formed between the electrode body and the electrode tip by the laser welding, wherein the component of the electrode body and the component of the electrode tip are melted,
Of the two directions along the axis of the electrode tip, the direction on the electrode tip side as viewed from the melting portion is the first direction, and the direction on the electrode body side as viewed from the melting portion is the second direction. When
The melting portion is in contact with the surface of the electrode tip in the second direction side at the position of the axis of the electrode tip,
Of the melted portion, the point located on the second direction side of the portion exposed on the side surface of the electrode tip is a point A,
In a cross section including the point A and the axis of the electrode tip,
The intersection of the axis of the electrode tip and the boundary line between the melted portion and the electrode tip is a point X,
The point located on the second direction side most on the boundary line between the melting part and the electrode body is a point B,
When the intersection of the axis of the electrode tip and the boundary line between the melted part and the electrode body is a point Y,
The point A is located closer to the first direction than the point X,
An acute angle θ1 formed by a line segment AX connecting the point A and the point X and a straight line passing through the point X and perpendicular to the axis of the electrode tip satisfies 0 <θ1 ≦ 10 (unit is degree). ,
The point B is located on the second direction side from the point Y,
An acute angle θ2 formed by a line segment BY connecting the point B and the point Y and a straight line passing through the point Y and perpendicular to the axis of the electrode tip satisfies 0 <θ2 ≦ 5 (unit is degree). ,Spark plug. The spark plug according to claim 1,
In the cross section,
The boundary line between the melting part and the electrode tip includes a first orthogonal part having an acute angle of less than ± 2 degrees between the orthogonal direction orthogonal to the axis of the electrode chip,
The boundary line between the melting part and the electrode body includes a second orthogonal part having an acute angle between the orthogonal direction of less than ± 2 degrees,
Of the melted portion, a point that is located closest to the second direction side of a portion in contact with the side surface opposite to the side surface of the electrode tip with which the point A is in contact is referred to as a point A ′,
When the point located in the second direction side of the part exposed on the outer surface opposite to the outer surface where the point B is located in the melting part is the point B ′,
The ratio of the length in the orthogonal direction of the first orthogonal portion to the length in the orthogonal direction between the point A and the point A ′ is 70% or more,
The spark plug, wherein a ratio of the length in the orthogonal direction of the second orthogonal portion to the length in the orthogonal direction between the point B and the point B ′ is 70% or more. The spark plug according to claim 1 or 2, wherein
In the cross section,
When the length in the first direction between the point A and the point B is E,
A spark plug satisfying E ≦ 0.4 mm (millimeters). The spark plug according to any one of claims 1 to 3,
In the cross section,
When the length in the first direction between the point X and the point Y is F,
A spark plug satisfying F ≧ 0.15 mm (millimeters). The spark plug according to any one of claims 1 to 4, wherein
The spark plug, wherein a content rate of the component of the electrode tip in the melting part is 40% by weight or more and 80% by weight or less.

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