JP2013041754A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve ignitability in a spark plug having improved welding strength between an earth electrode and a noble metal chip.SOLUTION: In this spark plug, 80% or more of the area of a noble metal chip projected on a surface parallel to a discharge surface overlaps with a melting part, on a first cross section cut off by a plane perpendicular to the width direction of the earth electrode, a point located at the utmost tip side of the earth electrode in the boundary between the noble metal chip and the melting part is set as A, a portion located at the utmost tip side of the earth electrode between the melting part and the earth electrode is set as an utmost tip part B, the intersection of a virtual straight line LB drawn parallel to an axis line with the utmost tip part B as a reference and a virtual straight line LA drawn perpendicularly to the virtual straight line LB with the point A as a reference is set as C, an angle formed by a first line segment connecting the point A to the intersection C and a second line segment connecting the point A to the utmost tip part B is set as θ1, and a distance from the point A to the intersection C is set as L, 0.05 mm≤L≤1.00 mm, and 5°≤θ1≤85° are satisfied.

Description

  The present invention relates to a spark plug.

  Conventionally, as a method for joining a noble metal tip to a ground electrode of a spark plug, for example, using resistance welding or YAG laser welding is known. Further, it is known that fiber laser welding is used in order to further improve the welding strength of the noble metal tip as the use environment of the spark plug increases due to the recent increase in engine output (for example, Patent Document 1). reference).

Japanese Patent No. 4619443 JP 2011-34826 A JP-A-2005-123166 JP 2002-237365 A

  In the technique of joining the noble metal tip to the ground electrode of the spark plug using fiber laser welding, the welding strength between the ground electrode and the noble metal tip is improved. However, there has been a further demand for spark plugs to improve ignitability in order to improve fuel efficiency and reduce unburned gas.

  An object of the present invention is to further improve ignitability in a spark plug in which the welding strength between a ground electrode and a noble metal tip is improved.

  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.

[Application Example 1]
An insulator having an axial hole penetrating in the axial direction;
A center electrode provided on the tip side of the shaft hole;
A cylindrical metal shell for holding the insulator;
A ground electrode having a base attached to the tip of the metal shell and a tip facing the tip of the center electrode;
A noble metal tip provided at the tip of the ground electrode and having a discharge surface forming a gap with the center electrode;
Provided at least in part between the ground electrode and the noble metal tip, and a melted portion formed by melting the ground electrode and the noble metal tip;
A spark plug comprising:
When projecting the noble metal tip and the melted part onto a plane parallel to the discharge surface, an area of 80% or more of the projected area of the noble metal tip overlaps with the projected melted part,
In a first cross section that is perpendicular to the discharge surface and is cut by a plane that passes through the center of gravity of the noble metal tip and is perpendicular to the width direction of the ground electrode,
Of the boundary between the noble metal tip and the melted portion, the point located on the most distal end side of the ground electrode is A,
Of the melted part and the ground electrode, a portion located closest to the tip of the ground electrode is the most advanced part B,
An intersection of a virtual straight line LB drawn in a direction parallel to the axis with the most advanced portion B as a reference and a virtual straight line LA drawn in a direction perpendicular to the virtual straight line LB with the point A as a reference is C,
An angle formed by a first line segment connecting the point A and the intersection C and a second line segment connecting the point A and the most distal portion B is θ1 [°], When the distance from A to the intersection C is L [mm],
0.05 ≦ L ≦ 1.00
5 ≦ θ1 ≦ 85
A spark plug characterized by satisfying the following conditions.
With such a configuration, an area of 80% or more of the area of the noble metal tip projected on the plane parallel to the discharge surface overlaps the projected melted part, and the horizontal from the noble metal tip to the most advanced part is overlapped. The distance L, which is the distance, is 0.05 mm or more and 1.00 mm or less, and the angle θ1 that is the angle of the end of the ground electrode on the spark gap side is 5 ° or more and 85 ° or less. In the spark plug in which the welding strength of the noble metal tip is improved, the ignitability can be further improved.

[Application Example 2]
A spark plug according to application example 1,
In the first cross section,
D is an end point of the ground electrode located on the tip side of the ground electrode and on the opposite side of the side where the noble metal tip is provided,
Let E be the intersection of the virtual straight line LB and the virtual straight line LD drawn in the vertical direction of the virtual straight line LB with the end point D as a reference.
When an angle formed by a third line segment connecting the endmost part B and the end point D and a fourth line segment connecting the end point D and the intersection point E is θ2 [°],
30 ≦ θ2 ≦ 90
A spark plug characterized by satisfying the following conditions.
With such a configuration, the angle θ2, which is the angle of the outer end portion of the ground electrode, is 30 ° or more and 90 ° or less. Therefore, in the spark plug described in Application Example 1, the ignitability can be further improved. it can.

[Application Example 3]
A spark plug according to application example 1 or 2,
In the first cross section,
Of the melted portion, the hardness of the portion located on the most distal portion B side of the ground electrode from the virtual straight line LO drawn in the axial direction with respect to the point A is A1 [Hv],
Of the melting portion, the hardness of the portion located on the base side of the ground electrode with respect to the virtual straight line LO is A2 [Hv],
When the hardness of a portion of the ground electrode located on the most distal portion B side of the ground electrode from the virtual straight line LO is A3 [Hv],
0.6 ≦ A2 / A1 ≦ 1.7
And the conditions
0.5 ≦ A3 / A1 ≦ 1.8
A spark plug characterized by satisfying the following conditions.
With such a configuration, the hardness A1 of the large diameter portion located on the most distal portion side of the ground electrode in the melted portion, the hardness A2 of the small diameter portion located on the base side of the ground electrode in the melted portion, The hardness A3 of the outer portion located on the most distal portion side of the ground electrode among the ground electrodes is such that 0.6 ≦ A2 / A1 ≦ 1.7 and 0.5 ≦ A3 / A1 ≦ 1.8. Therefore, in the spark plug according to Application Example 1 or 2, the welding strength between the ground electrode and the noble metal tip can be further improved.

[Application Example 4]
The spark plug according to any one of Application Examples 1 to 3,
The spark plug is characterized in that the melted portion is not formed on a surface of the noble metal tip facing the center electrode.
With such a configuration, since the melted portion is not formed on the surface of the noble metal tip that faces the center electrode, the spark plug according to Application Examples 1 to 3 further suppresses a decrease in spark wear resistance. be able to.

[Application Example 5]
The spark plug according to any one of Application Examples 1 to 4,
The spark plug is formed by irradiating a fiber laser or an electron beam to a boundary between the ground electrode and the noble metal tip.
With such a configuration, the melted portion is formed by irradiating the boundary between the ground electrode and the noble metal tip with a fiber laser or an electron beam. The ground electrode and the noble metal tip can be firmly bonded.

  Note that the present invention can be realized in various modes. For example, it can be realized in the form of a spark plug manufacturing method, manufacturing apparatus, manufacturing system, and the like.

It is a fragmentary sectional view of the spark plug as one embodiment of the present invention. It is an enlarged view near the front-end | tip part of the center electrode of a spark plug. It is a projection view with respect to a surface parallel to the discharge surface at the tip of the ground electrode. It is explanatory drawing for demonstrating the horizontal distance from a ground electrode chip | tip to the most advanced part in the XX cross section in FIG. It is explanatory drawing for demonstrating the angle of the front-end | tip part of a ground electrode in the XX cross section in FIG. It is explanatory drawing for demonstrating the hardness of the front-end | tip part vicinity of a ground electrode in the XX cross section in FIG. It is an enlarged view near the front-end | tip part of the center electrode of the spark plug in 2nd Embodiment. It is a projection figure with respect to the surface parallel to the discharge surface of the front-end | tip part of the ground electrode of the spark plug in 3rd Embodiment. It is explanatory drawing for demonstrating the position where the ground electrode chip | tip 80 is provided in the XX cross section of the spark plug in 4th Embodiment. It is a figure which shows the result of the peeling resistance evaluation test regarding the overlapping rate with respect to the fusion | melting part of a ground electrode tip. It is explanatory drawing for demonstrating the oxidation scale generation | occurrence | production ratio. It is a figure which shows the result of the ignitability evaluation test regarding the horizontal distance from a ground electrode tip to the most advanced part. It is a figure which shows the result of the ignitability evaluation test regarding the angle of the spark gap side edge part of a ground electrode. It is a figure which shows the result of the ignitability evaluation test regarding the angle of the outer side edge part of a ground electrode. It is a figure which shows the result of the peeling resistance evaluation test regarding the hardness of the front-end | tip part of a ground electrode.

  Next, an embodiment of a spark plug that is one embodiment of the present invention will be described in the following order.

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

  The spark plug 100 includes an insulator 10, a metal shell 50, a center electrode 20, a ground electrode 30, and a terminal metal fitting 40. The center electrode 20 is held in the insulator 10 in a state extending in the axial direction OD. The insulator 10 functions as an insulator, and the metal shell 50 holds the insulator 10. The terminal fitting 40 is provided at the rear end portion of the insulator 10. The configuration of the center electrode 20 and the ground electrode 30 will be described in detail with reference to FIG.

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

  The metal shell 50 is a cylindrical metal fitting formed of a low carbon steel material, and fixes the spark plug 100 to the engine head 200 of the internal combustion engine. The metal shell 50 holds the insulator 10 inside, and the insulator 10 is surrounded by the metal shell 50 in a portion from a part of the rear end side body portion 18 to the leg length portion 13.

  The metal shell 50 includes a tool engaging portion 51 and a mounting screw portion 52. The tool engaging part 51 is a part into which a spark plug wrench (not shown) is fitted. The mounting screw portion 52 of the metal shell 50 is a portion where a screw thread is formed, and is screwed into a mounting screw hole 201 of the engine head 200 provided in the upper part of the internal combustion engine.

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

  A thin caulking portion 53 is provided on the rear end side of the metal shell 50 from the tool engaging portion 51. In addition, a thin buckled portion 58 is provided between the seal portion 54 and the tool engaging portion 51, similarly to the caulking portion 53. Between the inner peripheral surface of the metal shell 50 from the tool engaging portion 51 to the caulking portion 53 and the outer peripheral surface of the rear end side body portion 18 of the insulator 10, annular ring members 6 and 7 are interposed. Has been. Further, a powder of talc (talc) 9 is filled between the ring members 6 and 7. When the crimping portion 53 is bent inwardly, the insulator 10 is pressed toward the front end side in the metal shell 50 via the ring members 6 and 7 and the talc 9. Thereby, the support part 15 of the insulator 10 is supported by the step part 56 formed in the inner periphery of the metal shell 50, and the metal shell 50 and the insulator 10 are united. At this time, the airtightness between the metal shell 50 and the insulator 10 is maintained by the annular plate packing 8 interposed between the support portion 15 of the insulator 10 and the step portion 56 of the metal shell 50, and is burned. Gas outflow is prevented. The buckling portion 58 is configured to bend outwardly and deform as the compression force is applied during caulking, and increases the airtightness in the metal shell 50 by earning a compression stroke of the talc 9. . A clearance CL having a predetermined dimension is provided between the front end side of the stepped portion 56 of the metal shell 50 and the insulator 10.

  FIG. 2 is an enlarged view of the vicinity of the tip 22 of the center electrode 20 of the spark plug 100. The center electrode 20 is a rod-shaped electrode having a structure in which a core material 25 is embedded in an electrode base material 21. The electrode base material 21 is formed of nickel such as Inconel (registered trademark) 600 or 601 or an alloy containing nickel as a main component. The core material 25 is made of copper or an alloy containing copper as a main component, which is superior in thermal conductivity to the electrode base material 21. Usually, the center electrode 20 is produced by filling a core material 25 inside an electrode base material 21 formed in a bottomed cylindrical shape, and performing extrusion molding from the bottom side and stretching it. The core member 25 has a substantially constant outer diameter at the body portion, but a reduced diameter portion is formed at the distal end side. The center electrode 20 extends in the shaft hole 12 toward the rear end side, and is electrically connected to the terminal fitting 40 (FIG. 1) via the seal body 4 and the ceramic resistor 3 (FIG. 1). Has been. A high voltage cable (not shown) is connected to the terminal fitting 40 via a plug cap (not shown), and a high voltage is applied.

  The tip portion 22 of the center electrode 20 protrudes from the tip portion 11 of the insulator 10. A center electrode tip 90 is bonded to the tip of the tip portion 22 of the center electrode 20. The center electrode tip 90 has a substantially cylindrical shape extending in the axial direction OD, and is formed of a noble metal having a high melting point in order to improve the spark wear resistance. The center electrode tip 90 may be, for example, iridium (Ir), one of the main components of platinum (Pt), rhodium (Rh), ruthenium (Ru), palladium (Pd), and rhenium (Re). It is formed of an Ir alloy to which two or more kinds are added.

  The ground electrode 30 is made of a metal having high corrosion resistance, and is made of, for example, a nickel alloy such as Inconel (registered trademark) 600 or 601. The base 32 of the ground electrode 30 is joined to the tip 57 of the metal shell 50 by welding. Further, the ground electrode 30 is bent, and the distal end portion 33 of the ground electrode 30 is opposed to the distal end portion 22 of the center electrode 20, and is also opposed to the distal end surface 92 of the center electrode tip 90.

  Further, a ground electrode chip 80 is joined to the tip 33 of the ground electrode 30 via a melting portion 85. The discharge surface 82 of the ground electrode tip 80 faces the tip surface 92 of the center electrode tip 90, and a spark gap is formed between the discharge surface 82 of the ground electrode tip 80 and the tip surface 92 of the center electrode tip 90. G is formed. The ground electrode tip 80 can be formed of the same material as the center electrode tip 90. The ground electrode tip 80 corresponds to a “noble metal tip” in the claims.

(A-2) Shape and dimensions of each part:
FIG. 3 is a projection view of the tip 33 of the ground electrode 30 on a surface parallel to the discharge surface 82. FIG. 4 is an explanatory diagram for explaining a horizontal distance from the ground electrode chip 80 to the most distal portion 86 in the XX cross section in FIG. The XX cross section is a plane that passes through the center of gravity of the ground electrode chip 80, is perpendicular to the discharge surface 82, and is perpendicular to the width direction of the ground electrode 30. The XX section corresponds to the “first section” in the claims.

  The ground electrode tip 80 has a quadrangular prism shape and is welded in a state of being embedded in the groove portion 34 (FIG. 4) formed in the ground electrode 30. A melted portion 85 is formed at least partly between the ground electrode tip 80 and the ground electrode 30. The melting portion 85 has a tapered shape that tapers from the tip portion 33 of the ground electrode 30 toward the base portion 32 in the XX cross section. The melting part 85 is formed by melting the ground electrode tip 80 and the ground electrode 30, and has an intermediate composition of the components of the ground electrode tip 80 and the ground electrode 30.

  The melting portion 85 can be formed by irradiating a high energy beam from a direction LL (FIG. 4) substantially parallel to the boundary between the ground electrode 30 and the ground electrode tip 80. In this way, the melted portion 85 is not formed on the surface of the ground electrode tip 80 that faces the center electrode tip 90 (that is, the discharge surface 82). Since the melting part 85 is inferior in spark wear resistance compared to the ground electrode tip 80, it is preferable that the melting part 85 does not exist on the discharge surface from the viewpoint of suppressing the decrease in spark wear resistance. . Moreover, as a high energy beam for forming the fusion | melting part 85, it is preferable to use a fiber laser and an electron beam, for example. In particular, the fiber laser is particularly preferable in that the boundary between the ground electrode 30 and the ground electrode tip 80 can be melted deeply, and the ground electrode 30 and the ground electrode tip 80 can be firmly joined.

  In FIG. 3, the melted portion 85 is shown larger than the actual size for convenience of explanation. In the actual spark plug 100, most of the melted portion 85 cannot be seen from the direction along the axial direction OD. Further, in FIG. 4, for convenience of explanation, a broken line is illustrated at the boundary between the ground electrode chip 80 and the ground electrode 30. In the actual spark plug 100, the ground electrode tip 80 and the ground electrode 30 are fused and integrated in the portion where the melted portion 85 is formed, and the broken line at the boundary disappears. The same applies to the drawings described later.

  Here, as shown in FIG. 3, when the ground electrode chip 80 of the ground electrode 30 is projected onto a plane parallel to the discharge surface 82, the projected area of the ground electrode chip 80 is PD. In addition, regarding the area PD of the ground electrode chip 80, the ratio of the portion overlapping with the melted portion 85 projected on the surface parallel to the discharge surface 82 is “overlap ratio (%) of the ground electrode chip 80 with respect to the melted portion 85”, Alternatively, it is referred to as “melting part overlapping ratio (%)”. At this time, the overlapping ratio of the ground electrode tip 80 to the melted portion 85 is preferably 80% or more. This condition is also referred to as “first condition”.

  The reason why the spark plug 100 preferably satisfies the first condition will be described. Since the melting portion 85 is formed by melting the ground electrode tip 80 and the ground electrode 30, the portion overlapping the melting portion 85 in the ground electrode tip 80 projected onto the surface parallel to the discharge surface 82. That is, it can be regarded as a portion where the ground electrode tip 80 is joined to the ground electrode 30. If 80% or more of the area PD of the ground electrode chip 80 is bonded to the ground electrode 30, even if the spark plug 100 is used in a high-temperature environment of a high-power engine, the ground electrode chip 80 It is possible to secure the welding strength and suppress the peeling of the ground electrode tip 80.

Further, as shown in FIG. 4, the axial direction OD and the melted portion 85 and the ground electrode 30 with respect to the most distal portion 86 (point B) that is the portion located closest to the tip 33 of the ground electrode 30. Let LB be a virtual straight line drawn in a parallel direction. Of the boundary between the ground electrode tip 80 and the melting portion 85, the end point 83 (point A) located closest to the tip 33 of the ground electrode 30 is used as a reference in the vertical direction of the axial direction OD (in other words, the virtual straight line LB). Let LA be a virtual straight line drawn in the vertical direction. At this time, the distance L from the end point 83 (point A) to the intersection C of the virtual straight line LB and the virtual straight line LA is:
0.05mm ≦ L ≦ 1.00mm
It is preferable that This condition is also referred to as “second condition”. The distance L is also referred to as “horizontal distance from the ground electrode tip 80 to the most advanced portion 86”.

  The reason why the spark plug 100 preferably satisfies the second condition will be described. The spark plug 100 generates a spark discharge in the spark gap G by applying a high voltage between the center electrode tip 90 and the ground electrode tip 80 arranged so as to face each other. In the combustion chamber, sparks called spark nuclei are generated in a region near the spark gap G triggered by the spark discharge of the spark plug 100, and the flame nuclei grow to burn the air-fuel mixture. Therefore, in order to improve the ignitability, it is preferable that an appropriate space exists in the vicinity of the ground electrode tip 80 so as not to inhibit the growth of flame nuclei generated in the vicinity of the spark gap G. For the above reasons, the distance L, which is the horizontal distance from the ground electrode tip 80 to the most advanced portion 86, is preferably 0.05 mm or more and 1.00 mm or less.

FIG. 5 is an explanatory diagram for explaining the angle of the distal end portion 33 of the ground electrode 30 in the XX cross section in FIG. 3. The end point 83 (point A), the most advanced portion 86 (point B), and the intersection point C are as described in FIG. As shown in FIG. 5, a line segment LN1 connecting the end point 83 (point A) and the intersection C and a line segment LN2 connecting the end point 83 (point A) and the most advanced portion 86 (point B) are formed. The angle to be set is θ1. At this time, θ1 is
5 ° ≦ (θ1) ≦ 85 °
It is preferable that This condition is also referred to as “third condition”. Further, the angle θ1 is also referred to as “the angle of the end portion of the ground electrode 30 on the spark gap side”.

  The reason why the spark plug 100 preferably satisfies the third condition is the same as the reason why the second condition described above is preferably satisfied. That is, if the angle θ1 at the spark gap side end portion of the ground electrode 30 is set to 5 ° or more and 85 ° or less, an appropriate space can be secured in the vicinity of the ground electrode tip 80. Can be improved.

Further, as shown in FIG. 5, the vertical direction of the axial direction OD is based on the end point 36 (point D) located on the tip 33 side and the side opposite to the side where the ground electrode tip 80 is provided in the ground electrode 30. Let LD be a virtual straight line drawn in other words (in the vertical direction of the virtual straight line LB). Also, let E be the intersection of the virtual straight line LB and the virtual straight line LD. An angle formed by a line segment LN3 connecting the most advanced portion 86 (point B) and the end point 36 (point D) and a line segment LN4 connecting the end point 36 (point D) and the intersection E is defined as θ2. . At this time, θ2 is
30 ° ≦ θ2 ≦ 90 °
Is more preferable. This condition is also referred to as “fourth condition”. The angle θ2 is also referred to as “the angle of the outer end portion of the ground electrode 30”.

  The reason why the spark plug 100 preferably satisfies the fourth condition is the same as the reason why the second condition described above is preferably satisfied. That is, if θ2 is set to 30 ° or more and 90 ° or less, an appropriate space can be secured in the vicinity of the ground electrode chip 80, so that the ignitability of the spark plug 100 can be further improved.

  The line segment LN1 corresponds to a “first line segment” in the claims. Similarly, the line segment LN2 is the “second line segment” in the claims, the line segment LN3 is the “third line segment” in the claims, and the line segment LN4 is the “second line” in the claims. It corresponds to “line segment 4”.

FIG. 6 is an explanatory diagram for explaining the hardness in the vicinity of the tip 33 of the ground electrode 30 in the XX section in FIG. 3. The end point 83 (point A) and the most advanced portion 86 (point B) are as described in FIG. As shown in FIG. 6, of the melting portion 85, the melting portion 85 is located on the most distal portion 86 (point B) side from the virtual straight line LO drawn in the axial direction OD with the end point 83 (point A) as a reference. The hardness of the large-diameter portion AR1 is defined as A1 [Hv]. Moreover, the hardness of the small diameter part AR2 of the fusion | melting part 85 located in the base 32 (FIG. 2) side of the ground electrode 30 rather than the virtual straight line LO among fusion | melting parts 85 is set to A2 [Hv]. Further, the hardness of the outer portion AR3 of the ground electrode 30 located on the most distal portion 86 (point B) side of the virtual straight line LO is A3 [Hv]. At this time, the hardness A1, A2, A3 of each part is as follows.
0.6 ≦ A2 / A1 ≦ 1.7
And the conditions
0.5 ≦ A3 / A1 ≦ 1.8
It is more preferable that the above condition is satisfied. This condition is also referred to as “fifth condition”.

  The hardness [Hv] is Vickers hardness, and is obtained when the test force is set to 1.961 N and the holding time is set to 15 seconds by the hardness measurement method defined in “Z 2244” of the Japanese Industrial Standard (JIS). Value. In addition, the hardness of the large-diameter portion AR1 is preferably determined by measuring the hardness at a plurality of locations included in the large-diameter portion AR1. The same applies to the small-diameter portion AR2 and the outer portion AR3. In FIG. 6, the large-diameter portion AR1 is indicated by hatching, the thin-diameter portion AR2 is indicated by cross-hatching, and the outer portion AR3 is indicated by dotted-line hatching.

  The reason why the spark plug 100 preferably satisfies the fifth condition will be described. In general, when the ground electrode tip 80 and the ground electrode 30 are laser-welded, residual stress is generated near the boundary between the ground electrode tip 80 and the melted portion 85 after welding. In the spark plug 100 of the present embodiment, the shape of the melting portion 85 tapers from the distal end portion 33 of the ground electrode 30 toward the base portion 32 (in other words, from the large diameter portion AR1 toward the small diameter portion AR2). Tapered shape. For this reason, in particular, in the large-diameter portion AR1, the residual stress is concentrated due to the difference in thermal expansion, and the ground electrode tip 80 is easily peeled off. Therefore, if the hardness A1 of the large-diameter portion AR1 of the fusion zone 85, the hardness A2 of the small-diameter portion AR2 and the hardness A3 of the outer portion AR3 of the ground electrode 30 are set as described above, the hardness of each portion is preferably related. And the peeling of the ground electrode tip 80 can be suppressed.

B. Second embodiment:
In the second embodiment of the present invention, a so-called lateral discharge type spark plug will be described. In the following, only portions having a configuration different from that of the first embodiment will be described. In the figure, the same components as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment described above, and detailed description thereof is omitted.

  FIG. 7 is an enlarged view of the vicinity of the tip 22 of the center electrode 20 of the spark plug 100a in the second embodiment. The only difference from the first embodiment shown in FIG. 2 is that a center electrode tip 90 a formed in the body length is provided instead of the center electrode tip 90 and a ground electrode 30 a is provided instead of the ground electrode 30. In other respects, the configuration is the same as that of the first embodiment.

  The base portion 32a of the ground electrode 30a is joined to the distal end portion 57 of the metal shell 50 by welding. The ground electrode 30a is bent, and the tip 33a of the ground electrode 30a faces the side surface 91a of the center electrode tip 90a. That is, the spark plug 100a is a so-called horizontal discharge plug, and the discharge direction is perpendicular to the axial direction OD.

  A ground electrode tip 80a having a quadrangular prism shape is welded to a groove portion 34a formed on the distal end surface 31a of the ground electrode 30a in an embedded state. A melting portion 85a is formed at least at a part between the ground electrode tip 80a and the ground electrode 30a. The melting portion 85a has a tapered shape that tapers from the front end side to the rear end side of the spark plug 100a in the XX cross section. The melting portion 85a is formed by melting the ground electrode tip 80a and the ground electrode 30a, and has an intermediate composition of the components of the ground electrode tip 80a and the ground electrode 30a. In the spark plug 100a of the second embodiment, the relationship between the shape of the melting portion 85a and the shape of the ground electrode 30a is the same as that of the spark plug 100 of the first embodiment, except that the direction is rotated 90 degrees. It is the same. Therefore, the spark plug 100a of the second embodiment satisfies at least the first to third conditions among the conditions shown in the first embodiment.

C. Third embodiment:
In the third embodiment of the present invention, a spark plug including a cylindrical ground electrode tip will be described. In the following, only portions having a configuration different from that of the first embodiment will be described. In the figure, the same components as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment described above, and detailed description thereof is omitted.

  FIG. 8 is a projection view of the tip 33 of the ground electrode 30 of the spark plug 100b according to the third embodiment on a plane parallel to the discharge surface 82b. The only difference from the first embodiment shown in FIG. 3 is that a square-shaped ground electrode chip 80b is provided instead of the square-column-shaped ground electrode chip 80, and the other configurations are the same as those of the first embodiment. is there. In the spark plug 100b of the third embodiment, the relationship between the shape of the melting portion 85 and the shape of the ground electrode 30 is the same as that of the spark plug 100 of the first embodiment. Therefore, the spark plug 100b of the third embodiment satisfies at least the first to third conditions among the conditions shown in the first embodiment.

D. Fourth embodiment:
In the fourth embodiment of the present invention, a description will be given of spark plugs at different positions where the ground electrode tip is provided. In the following, only portions having a configuration different from that of the first embodiment will be described. In the figure, the same components as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment described above, and detailed description thereof is omitted.

  FIG. 9 is an explanatory diagram for explaining a position where the ground electrode tip 80 is provided in the XX cross section of the spark plug 100c according to the fourth embodiment. The only difference from the first embodiment shown in FIG. 4 is that the ground electrode tip 80 is welded to the ground electrode 30c having no groove portion instead of the ground electrode 30 having the groove portion 34. Other configurations are the same as those of the first embodiment. In the spark plug 100c of the fourth embodiment, the relationship between the shape of the melting portion 85 and the shape of the ground electrode 30c is the same as that of the spark plug 100 of the first embodiment. Therefore, the spark plug 100c of the fourth embodiment satisfies at least the first to third conditions among the conditions shown in the first embodiment.

E. Experimental example on the overlap ratio of the ground electrode tip to the fusion zone:
FIG. 10 is a diagram showing the results of a peel resistance evaluation test regarding the overlapping rate of the ground electrode tip 80 with respect to the melted portion 85. FIG. 11 is an explanatory diagram for explaining an oxide scale generation ratio. In the peel resistance evaluation test, a thermal test was conducted in order to examine the relationship between the overlapping rate of the ground electrode tip 80 with respect to the melted portion 85 and the generation ratio of oxide scale. Hereinafter, the “overlap ratio of the ground electrode tip 80 with respect to the melted portion 85” is also referred to as “melted portion overlap ratio”.

  In the peel resistance evaluation test, samples # 11 to # 16 of six spark plugs 100 having different fusion zone overlapping ratios (FIG. 3) were prepared. Samples # 11 to # 15 are the spark plugs 100 shown as the first embodiment (FIGS. 1 to 6), and the distance L (FIG. 4) is 0.05 mm and the angle θ1 (FIG. 5) is 5. ° thing. Sample # 16 is the spark plug 100 shown as the first embodiment (FIGS. 1 to 6), and further has a distance L (FIG. 4) of 0 mm and an angle θ1 (FIG. 5) of 90 °. .

In the peel resistance evaluation test, for each of the samples # 11 to # 16, a crack (fissure) that occurred in the vicinity of the melted portion 85 after repeating 1000 cycles of the following procedure 1a and procedure 2a as one cycle. The length of was measured from a half section. And the oxidation scale generation | occurrence | production ratio was calculated | required from the length of the measured crack.
Procedure 1a) The ground electrode 30 is heated with a burner, and the temperature of the ground electrode 30 is raised to 900 ° C. for 2 minutes.
Procedure 2a) After procedure 1a, the burner is turned off and the ground electrode 30 is slowly cooled for 1 minute.

The oxide scale generation ratio indicates the ratio of the length of cracks (fissures) generated in the vicinity of the melted portion 85 to the length LG of the ground electrode tip 80, and can be obtained by the following equation.
Oxide scale generation ratio (%) = length of crack / length of ground electrode tip 80 LG × 100

  As shown in FIG. 11A, when a plurality of cracks that do not overlap each other occur in the vicinity of the melting portion 85, the “crack length” in the above formula is the sum of the respective lengths of the plurality of cracks. To do. That is, in the case of FIG. 11A, the “crack length” is the length CL1 of the crack CK1 + the length CL2 of the crack CK2. In addition, as shown in FIG. 11B, when a plurality of cracks overlapping in the vicinity of the melting portion 85 occurs, the “crack length” in the above formula is the length of the longer crack among the plurality of cracks. Say it. That is, in the case of FIG. 11B, the “crack length” is the length CL2 of the crack CK2.

  In the results of the peel resistance evaluation test shown in FIG. 10, the horizontal axis represents the overlap ratio (%) of the ground electrode tip 80 with respect to the melted portion 85, and the vertical axis represents the oxide scale generation ratio (%). In this evaluation test, a sample having an oxide scale generation ratio larger than 50% was determined to be “impossible” because the ground electrode tip 80 might be peeled off.

  From the results of this evaluation test, it can be seen that the rate of oxide scale generation decreases as the fusion zone overlap ratio increases. In other words, as the proportion of the area of the portion joined to the ground electrode 30 in the area of the ground electrode tip 80 increases, the ground electrode tip 80 becomes difficult to peel off (that is, the welding strength is reduced). Show improvement). Here, sample # 14 in which the fusion zone overlap ratio is 80%, the distance L (FIG. 4) is 0.05 mm, and the angle θ1 (FIG. 5) is 5 ° has an oxide scale generation ratio of 50% or less, and the determination is “ Yes. On the other hand, Sample # 16, in which the fusion zone overlap rate is also 80%, the distance L (FIG. 4) is 0 mm, and the angle θ1 (FIG. 5) is 90 °, the oxide scale generation rate slightly exceeds 50%. “Not possible”.

  From the above, in order to suppress the peeling of the ground electrode tip of the spark plug and ensure the welding strength of the ground electrode tip, the melting portion overlap ratio (overlap ratio of the ground electrode tip 80 to the melting portion 85) is 80% or more. It can be seen that it is preferable that the first condition is satisfied. Furthermore, it can be seen from the test results of sample # 16 that the welding strength of the ground electrode tip is further improved when the second condition regarding the distance L and the third condition regarding the angle θ1 are satisfied. This point will be described later.

F. Example of the horizontal distance from the ground electrode tip to the most advanced part:
FIG. 12 is a diagram showing the results of an ignitability evaluation test relating to the horizontal distance from the ground electrode tip 80 to the most advanced portion 86. In this ignitability evaluation test, the relationship between the horizontal distance L from the ground electrode tip 80 to the most advanced portion 86 and the ignitability of the air-fuel mixture is examined.

  In the ignitability evaluation test, samples # 21 to # 24 of four spark plugs 100 having different horizontal distances L (FIG. 4) from the ground electrode tip 80 to the most advanced portion 86 were prepared. Samples # 21 to # 24 are the spark plug 100 shown as the first embodiment (FIGS. 1 to 6), and the angle θ1 (FIG. 5) is 5 °.

  In the ignitability evaluation test, the spark plugs shown in Samples # 21 to # 24 were respectively mounted on a 2000 cc, 6-cylinder DOHC type gasoline engine, and an idling operation was performed at an intake pressure of −350 mmHg and 2000 rpm. And the operation | work of measuring the frequency | count that discharge abnormality (misfire etc.) generate | occur | produced during 1000 times of spark discharge was repeatedly implemented, increasing an air fuel ratio gradually. The “air-fuel ratio” is a value (A / F) obtained by dividing the mass of air in the air-fuel mixture by the mass of fuel. In the ignitability evaluation test, the air-fuel ratio when 10 or more discharge abnormalities were measured during 1000 spark discharges as described above was recorded as the limit air-fuel ratio. The higher the limit air-fuel ratio, the better the ignitability of the air-fuel mixture by the spark plug.

  In the results of the ignitability evaluation test shown in FIG. 12, the horizontal axis indicates the distance L (mm), and the vertical axis indicates the limit air-fuel ratio (A / F). From the result of this evaluation test, it can be seen that in the samples # 21, # 22, and # 23 in which the distance L is 1.00 mm or less, the limit air-fuel ratio gradually decreases as the distance L increases. In addition, in sample # 24 where the distance L is 1.50 mm, it can be seen that the critical air-fuel ratio is drastically decreased as compared with the sample where the distance L is 1.00 mm or less. In other words, the smaller the distance L, the larger the space in the vicinity of the ground electrode tip 80, and thus the higher the critical air-fuel ratio (that is, better ignitability).

  From the above, it can be seen that the distance L (horizontal distance from the ground electrode tip 80 to the most advanced portion 86) is preferably 1.00 mm or less in order to improve the ignitability of the spark plug. Further, sample # 21 having a distance L of 0 mm is not preferable because it has excellent ignitability, but the welding strength is insufficient from the test result of sample # 16 in the above-described peel resistance evaluation test (FIG. 10). I understand that. Therefore, in order to improve the ignition strength of the spark plug while improving the welding strength of the ground electrode tip, the horizontal distance L from the ground electrode tip 80 to the most advanced portion 86 is 0.05 mm or more and 1.00 mm or less. That is, it is preferable that the second condition is satisfied.

G. Example of experiment on angle of spark gap side end of ground electrode:
FIG. 13 is a diagram showing the results of an ignitability evaluation test relating to the angle of the end portion of the ground electrode 30 on the spark gap side. In this ignitability evaluation test, the relationship between the angle θ1 of the end portion of the ground electrode 30 on the spark gap side and the ignitability of the air-fuel mixture is examined.

  In the ignitability evaluation test, samples # 31 to # 35 of five spark plugs 100 having different angles θ1 (FIG. 5) of the spark gap side end portion of the ground electrode 30 were prepared. Samples # 31 to # 35 are the spark plug 100 shown as the first embodiment (FIGS. 1 to 6), and the distance L (FIG. 4) is 1.00 mm. In this ignitability evaluation test, the critical air-fuel ratio (A / F) was determined for each of samples # 31 to # 35 using a method similar to the method described in FIG.

  In the results of the ignitability evaluation test shown in FIG. 13, the horizontal axis indicates the angle θ1 (°), and the vertical axis indicates the limit air-fuel ratio (A / F). From the result of this evaluation test, it can be seen that there is almost no difference in the critical air-fuel ratio between sample # 31 where the angle θ1 is 0 ° and sample # 32 where the angle θ1 is 5 °. It can also be seen that the limit air-fuel ratio increases in proportion to the magnitude of the angle θ1 after the angle θ1 exceeds 5 °. In other words, the larger the angle θ1, the larger the space in the vicinity of the ground electrode tip 80, and thus the higher the critical air-fuel ratio (that is, the better the ignitability).

  From the above, it can be seen that the angle θ1 (angle at the spark gap side end of the ground electrode 30) is preferably 5 ° or more in order to improve the ignitability of the spark plug. Further, when the angle θ1 is 90 °, it is presumed that the ignitability is excellent from the test result of FIG. 13, but from the test result of the sample # 16 of the above-described peel resistance evaluation test (FIG. 10), welding is performed. It turns out that it is not preferable because the strength is insufficient. Therefore, in order to improve the ignition strength of the spark plug while improving the welding strength of the ground electrode tip, the angle θ1 of the spark gap side end portion of the ground electrode 30 is 5 ° or more and 85 ° or less. That is, it is understood that it is preferable to satisfy the third condition.

H. Experimental example on the angle of the outer edge of the ground electrode:
FIG. 14 is a diagram illustrating the results of an ignitability evaluation test regarding the angle of the outer end portion of the ground electrode 30. In this ignitability evaluation test, the relationship between the angle θ2 of the outer end portion of the ground electrode 30 and the ignitability of the air-fuel mixture is examined.

  In the ignitability evaluation test, samples # 41 to # 43 of three spark plugs 100 having different angles θ2 (FIG. 5) of the outer end portion of the ground electrode 30 were prepared. Samples # 41 to # 43 are the spark plugs 100 shown as the first embodiment (FIGS. 1 to 6), and the distance L (FIG. 4) is 1.00 mm and the angle θ1 (FIG. 5) is 5. ° thing. In this ignitability evaluation test, the limit air-fuel ratio (A / F) was obtained for each of samples # 41 to # 43 using the same method as described in FIG.

  In the results of the ignitability evaluation test shown in FIG. 14, the horizontal axis indicates the angle θ2 (°), and the vertical axis indicates the limit air-fuel ratio (A / F). From the result of this evaluation test, it can be seen that sample # 41 having an angle θ2 of 30 ° has a slightly higher limit air-fuel ratio than other samples. Further, it can be seen that there is almost no difference in the critical air-fuel ratio between sample # 42 having an angle θ2 of 40 ° and sample # 43 having 90 °. In other words, this indicates that the smaller the angle θ2, the larger the space in the vicinity of the ground electrode tip 80, and thus the higher the critical air-fuel ratio (that is, better ignitability).

  On the other hand, when the angle θ2 is formed to be 90 ° or more, the outer portion of the ground electrode 30 becomes large, and the ignitability deteriorates. When the angle θ2 is set to 30 ° or less, the outer portion of the ground electrode 30 becomes too thin, so that the residual stress due to the difference in thermal expansion cannot be absorbed, and the ground electrode tip 80 is easily peeled off.

  As described above, in order to further improve the ignitability of the spark plug, the angle θ2 (the angle of the outer end portion of the ground electrode 30) is 30 ° or more and 90 ° or less, that is, the fourth condition is satisfied. Is preferable.

I. Experimental example on the hardness of the tip of the ground electrode:
FIG. 15 is a diagram showing the results of a peel resistance evaluation test regarding the hardness in the vicinity of the tip 33 of the ground electrode 30. In the peel resistance evaluation test, a thermal test was conducted in order to investigate the relationship between the hardness near the tip 33 of the ground electrode 30 and the rate of occurrence of oxide scale.

  In the peel resistance evaluation test, the hardness A1 of the large-diameter portion AR1 (FIG. 6) of the melting portion 85, the hardness A2 of the small-diameter portion AR2 (FIG. 6) of the melting portion 85, and the outer portion AR3 of the ground electrode 30 (FIG. Nine spark plug 100 samples # 51 to # 59 having different hardness A3 of 6) were prepared. Samples # 51 to # 59 are the spark plugs 100 shown as the first embodiment (FIGS. 1 to 6). In addition, the hardness in each sample is Vickers hardness as described above, and the hardness A1 employs an average value of the hardness at any three locations included in the large-diameter portion AR1 of the melted portion 85. Similarly, the hardness A2 and the hardness A3 are average values of hardness at arbitrary three locations.

In the peel resistance evaluation test, the length of cracks generated in the vicinity of the melted portion 85 after 1000 cycles of the steps 1b and 2b described below were repeated for each of the samples # 51 to # 59. Was measured from a half section. And the oxidation scale generation | occurrence | production ratio was calculated | required from the length of the measured crack. The method for obtaining the oxide scale generation ratio is as described with reference to FIGS.
Procedure 1b) The ground electrode 30 is heated with a burner and the temperature of the ground electrode 30 is raised to 1000 ° C. for 2 minutes.
Procedure 2b) After procedure 1b, the burner is turned off and the ground electrode 30 is slowly cooled for 1 minute.

  In FIG. 15, for each sample, determination of the sample number, hardness A1, hardness A2, hardness A3, hardness ratio of hardness A1 and hardness A2, hardness ratio of hardness A1 and hardness A3, and oxide scale generation rate The results are shown in tabular form. In this evaluation test, the sample having an oxide scale generation ratio smaller than 30% is judged to be “A” because the possibility that the ground electrode tip 80 is peeled off is extremely small. In addition, the sample having an oxide scale generation ratio of 30% or more and 50% or less is judged as “B” because there is little possibility that the ground electrode tip 80 is peeled off. In addition, the sample having an oxide scale generation ratio larger than 50% might be peeled off from the ground electrode chip 80, and therefore, the determination was “C”.

  From the result of this evaluation test, in sample # 52, the hardness ratio (A2 / A1) between hardness A1 and hardness A2 is 0.6, and the hardness ratio (A3 / A1) between hardness A1 and hardness A3 is 0.4. It can be seen that the oxide scale generation rate exceeds 50% and the C determination is made. On the other hand, in the sample # 53 in which the hardness ratio (A2 / A1) between the hardness A1 and the hardness A2 is 0.6 and the hardness ratio (A3 / A1) between the hardness A1 and the hardness A3 is 0.5, the oxide scale generation ratio Is 50% or less, and it can be seen that B is determined. Therefore, it can be seen that the lower limit of the hardness ratio (A3 / A1) between the hardness A1 and the hardness A3 is preferably 0.5. Further, in sample # 51 in which the hardness ratio (A2 / A1) between hardness A1 and hardness A2 is 0.3 and the hardness ratio (A3 / A1) between hardness A1 and hardness A3 is 0.5, the oxide scale generation ratio Is over 50%, and it is understood that C is determined. On the other hand, in the sample # 53 in which the hardness ratio (A2 / A1) between the hardness A1 and the hardness A2 is 0.6 and the hardness ratio (A3 / A1) between the hardness A1 and the hardness A3 is 0.5, the oxide scale generation ratio Is 50% or less, and it can be seen that B is determined. Therefore, it can be seen that the lower limit of the hardness ratio (A2 / A1) between the hardness A1 and the hardness A2 is preferably 0.6.

Furthermore, in the sample # 57 where the hardness ratio (A2 / A1) of the hardness A1 and the hardness A2 is 1.7 and the hardness ratio (A3 / A1) of the hardness A1 and the hardness A3 is 1.8, the oxide scale generation ratio Is 50% or less, and it can be seen that B is determined. On the other hand, in the sample # 58 in which the hardness ratio (A2 / A1) between the hardness A1 and the hardness A2 is 1.7 and the hardness ratio (A3 / A1) between the hardness A1 and the hardness A3 is 1.9, the oxide scale generation ratio Is over 50%, and it is understood that C is determined. Therefore, it can be seen that the upper limit of the hardness ratio (A3 / A1) between the hardness A1 and the hardness A3 is preferably 1.8. Further, in sample # 57 in which the hardness ratio (A2 / A1) of the hardness A1 and the hardness A2 is 1.7 and the hardness ratio (A3 / A1) of the hardness A1 and the hardness A3 is 1.8, the oxide scale generation ratio Is 50% or less, and it can be seen that B is determined. On the other hand, in sample # 59 in which the hardness ratio (A2 / A1) between hardness A1 and hardness A2 is 2 and the hardness ratio (A3 / A1) between hardness A1 and hardness A3 is 1.8, the oxide scale generation ratio is 50. It can be seen that it exceeds C and becomes C judgment. Therefore, it can be seen that the upper limit of the hardness ratio (A2 / A1) between the hardness A1 and the hardness A2 is preferably 1.7.

  Further, in the peel resistance evaluation test, a sample having a hardness ratio (A2 / A1) of hardness A1 and hardness A2 of 0.9 and a hardness ratio of hardness A1 and hardness A3 (A3 / A1) of 0.8 In sample # 55, in which the hardness ratio (A2 / A1) of hardness A1 and hardness A2 is 1.1 and the hardness ratio (A3 / A1) of hardness A1 and hardness A3 is 1, The scale generation ratio was smaller than 30%, and particularly good results could be obtained. In Samples # 52 and # 58, B determination can be obtained only when the outer tip of the ground electrode 30 is flat, that is, when the angle θ2 of the outer end of the ground electrode 30 is 90 °. did it.

From the above, in order to suppress the peeling of the ground electrode tip of the spark plug and ensure the welding strength of the ground electrode tip, the hardness A1 of the large diameter portion AR1 (FIG. 6) of the melting portion 85 and the thinness of the melting portion 85 are reduced. It can be seen that the hardness A2 of the radial portion AR2 (FIG. 6) and the hardness A3 of the outer portion AR3 (FIG. 6) of the ground electrode 30 preferably satisfy the following fifth condition.
0.6 ≦ A2 / A1 ≦ 1.7
0.5 ≦ A3 / A1 ≦ 1.8

  When the above Experimental Examples E to I are combined, it can be seen that it is preferable to satisfy at least the first to third conditions in order to improve the ignitability while ensuring the welding strength of the ground electrode tip of the spark plug. It can also be seen that it is preferable to satisfy the fourth condition in order to further improve the ignitability of the spark plug. Furthermore, in order to further increase the welding strength of the ground electrode tip of the spark plug, it is understood that it is preferable to satisfy the fifth condition additionally.

J. et al. Variations:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

J1. Modification 1:
In the above embodiment, an example of the configuration of the spark plug has been described by taking the vertical discharge type spark plug and the horizontal discharge type spark plug as examples. However, the positional relationship between the tip of the ground electrode and the tip of the center electrode can be appropriately set according to the application of the spark plug, the required performance, and the like. Moreover, it can also be set as the structure by which a some ground electrode is provided with respect to one center electrode.

J2. Modification 2:
In the above embodiment, the ground electrode chip has been described as having a quadrangular prism shape or a cylindrical shape. However, the shape of the ground electrode chip described above is merely an example, and various shapes can be employed.

DESCRIPTION OF SYMBOLS 3 ... Ceramic resistance 4 ... Sealing body 5 ... Gasket 6 ... Ring member 8 ... Plate packing 9 ... Talc 10 ... Insulator 11 ... Tip part 12 ... Shaft hole 13 ... Leg long part 15 ... Supporting part 17 ... Tip side trunk | drum 18 ... Rear end side body portion 19 ... collar portion 20 ... center electrode 21 ... electrode base material 22 ... tip portion 25 ... core material 30, 30a-c ... ground electrode 31, 31a ... tip end surface 32, 32a ... base portion 33, 33a ... tip Part 34, 34a ... Groove part 36 ... End point 40 ... Terminal metal fitting 50 ... Main metal fitting 51 ... Tool engaging part 52 ... Mounting screw part 53 ... Clamping part 54 ... Seal part 55 ... Seat surface 56 ... Step part 57 ... Tip part 58 ... Buckling portion 59 ... Screw neck 80, 80a-c ... Ground electrode tip 82, 82b ... Discharge surface 83 ... End point 85, 85a ... Melting portion 86 ... Most advanced portion 90, 90a ... Center electrode tip 91a ... Side surface portion 92 …tip 100,100A～c ... spark plug 200: engine head 201 ... hole 205 ... opening edge

Claims (5)

An insulator having an axial hole penetrating in the axial direction;
A center electrode provided on the tip side of the shaft hole;
A cylindrical metal shell for holding the insulator;
A ground electrode having a base attached to the tip of the metal shell and a tip facing the tip of the center electrode;
A noble metal tip provided at the tip of the ground electrode and having a discharge surface forming a gap with the center electrode;
Provided at least in part between the ground electrode and the noble metal tip, and a melted portion formed by melting the ground electrode and the noble metal tip;
A spark plug comprising:
When projecting the noble metal tip and the melted part onto a plane parallel to the discharge surface, an area of 80% or more of the projected area of the noble metal tip overlaps with the projected melted part,
In a first cross section that is perpendicular to the discharge surface and is cut by a plane that passes through the center of gravity of the noble metal tip and is perpendicular to the width direction of the ground electrode,
Of the boundary between the noble metal tip and the melted portion, the point located on the most distal end side of the ground electrode is A,
Of the melted part and the ground electrode, a portion located closest to the tip of the ground electrode is the most advanced part B,
An intersection of a virtual straight line LB drawn in a direction parallel to the axis with the most advanced portion B as a reference and a virtual straight line LA drawn in a direction perpendicular to the virtual straight line LB with the point A as a reference is C,
An angle formed by a first line segment connecting the point A and the intersection C and a second line segment connecting the point A and the most distal portion B is θ1 [°], When the distance from A to the intersection C is L [mm],
0.05 ≦ L ≦ 1.00
5 ≦ θ1 ≦ 85
A spark plug characterized by satisfying the following conditions. The spark plug according to claim 1, wherein
In the first cross section,
D is an end point of the ground electrode located on the tip side of the ground electrode and on the opposite side of the side where the noble metal tip is provided,
Let E be the intersection of the virtual straight line LB and the virtual straight line LD drawn in the vertical direction of the virtual straight line LB with the end point D as a reference.
When an angle formed by a third line segment connecting the endmost part B and the end point D and a fourth line segment connecting the end point D and the intersection point E is θ2 [°],
30 ≦ θ2 ≦ 90
A spark plug characterized by satisfying the following conditions. The spark plug according to claim 1 or 2,
In the first cross section,
Of the melted portion, the hardness of the portion located on the most distal portion B side of the ground electrode from the virtual straight line LO drawn in the axial direction with respect to the point A is A1 [Hv],
Of the melting portion, the hardness of the portion located on the base side of the ground electrode with respect to the virtual straight line LO is A2 [Hv],
When the hardness of a portion of the ground electrode located on the most distal portion B side of the ground electrode from the virtual straight line LO is A3 [Hv],
0.6 ≦ A2 / A1 ≦ 1.7
And the conditions
0.5 ≦ A3 / A1 ≦ 1.8
A spark plug characterized by satisfying the following conditions. The spark plug according to any one of claims 1 to 3,
The spark plug is characterized in that the melted portion is not formed on a surface of the noble metal tip facing the center electrode. The spark plug according to any one of claims 1 to 4,
The spark plug is formed by irradiating a fiber laser or an electron beam to a boundary between the ground electrode and the noble metal tip.

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