Spark plug

Abstract

To provide a spark plug which can prevent electric field concentration at the end of a tip surface.SOLUTION: A spark plug 1 comprises a ground electrode 11, a center electrode 21, and a main metal fitting 30. The ground electrode 11 has: a base material 12; and an electrode tip 13 bonded to the base material 12. The electrode tip 13 has a tip surface 13a which protrudes from an upper surface 12b of the base material 12 and faces the center electrode 21. Between the base material 12 and the electrode tip 13, a melting part 14 is interposed to bond them together. At least part of an end 13b of the electrode tip 13 located on an end surface 12a side of the base material 12 is covered with the melting part 14. The melting part 14 present at the end of the electrode tip 13b is rounded, and it is present at the same position as the tip surface 13a or is present to a position higher than that of the tip surface 13a.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a spark plug used in an internal combustion engine.

Background Art

[0002] As an ignition means for an internal combustion engine such as an automobile engine, a spark plug is used. The spark plug is provided with a center electrode and a ground electrode as a configuration for generating a spark discharge. An electrode tip is provided on the facing surface of the ground electrode with respect to the center electrode in order to improve the ignitability of the spark plug. The electrode tip is formed of, for example, a columnar body made of a noble metal material and is joined to the base material of the ground electrode by welding or the like.

[0003] For example, Patent Document 1 discloses a spark plug including a ground electrode in which the back side of the tip surface of the electrode tip is joined to the electrode base material by laser welding. In this spark plug, a molten portion formed by laser welding is provided on the back side of the tip surface of the electrode tip.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a ground electrode in which an electrode tip is joined to a base material, the end portion of the electrode tip on the tip surface side of the base material is in an exposed state. For example, when a prismatic electrode tip is joined to a base material, a corner portion of the prism exists on the tip surface side of the base material. When a spark discharge is generated between a ground electrode and a center electrode having such a shape, there is a possibility that electric field concentration occurs at the corner portion of the end of the tip surface, and electrode consumption may be accelerated only at this portion.

[0006] Therefore, an object of the present invention is to provide a spark plug capable of suppressing electric field concentration at an end portion of a chip surface.

Means for Solving the Problems

[0007] A spark plug according to an aspect of the present invention includes a center electrode, a main metal fitting that extends along an axis and insulatively holds the center electrode, a base material having one end connected to the main metal fitting, and a ground electrode having an electrode chip joined to the base material on the other end side of the base material at a position closer to the one end side than a tip surface of the other end. The electrode chip has a chip surface facing the center electrode in the axial direction and protrudes from a facing surface of the base material facing the center electrode in the axial direction. A molten part that joins the base material and the electrode chip is interposed therebetween. In this spark plug, at least a part of an end portion on the tip surface side of the electrode chip is covered with the molten part, and the molten part existing at the end portion is rounded and exists at the same position as the chip surface or at a position higher than the chip surface.

[0008] According to the above configuration, at least a part of the end portion of the electrode chip located on the tip surface side of the base material is covered with the molten part, and since this molten part is rounded, it is possible to suppress electric field concentration at the end portion of the chip surface. Further, since this rounded molten part exists up to the same position as the chip surface, the corner portion at the boundary between the chip surface and the end portion of the electrode chip is not exposed. Thereby, it is possible to suppress electric field concentration at the corner portion of the electrode chip. Further, since this rounded molten part exists up to a position higher than the chip surface, the corner portion at the boundary between the chip surface and the end portion of the electrode chip is covered with the molten part. Thereby, it is possible to suppress electric field concentration at the corner portion of the electrode chip. Therefore, electrode consumption of the ground electrode can be delayed.

[0009] In the spark plug according to the above aspect of the present invention, the molten part existing at the end portion may be at the same position as the chip surface.

[0010] According to the above configuration, since the melting part exists up to the same position as the chip surface, the chip surface of the electrode chip and the surface of the melting part are flush. Thereby, it is possible to suppress the electric field concentration at the corner portion of the electrode chip.

[0011] In the spark plug according to one aspect of the present invention described above, a part of the chip surface may be covered by the melting part.

[0012] According to the above configuration, the corner portion at the boundary between the chip surface and the end portion of the electrode chip is covered and hidden by the melting part. Thereby, it is possible to suppress the electric field concentration at the corner portion of the electrode chip.

[0013] Further, in the spark plug according to one aspect of the present invention, the tip surface of the base material and the melting part may be flush.

[0014] According to the above configuration, the corner portion on the side facing the center electrode at the tip surface of the base material is no longer exposed. Therefore, when spark discharge occurs on the chip surface of the electrode chip, it is possible to suppress the spark from flowing and jumping toward the base material located on the more distal end side, and thus it is possible to suppress a part of the base material from being locally consumed.

Effect of the Invention

[0015] As described above, according to one aspect of the present invention, it is possible to provide a spark plug capable of suppressing the electric field concentration at the end portion of the chip surface.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0017] Hereinafter, each embodiment of the present invention will be described with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated.

[0018] <First Embodiment> The first embodiment of the present invention will be described. In this embodiment, the spark plug 1 will be described as an example.

[0019] (Configuration of Spark Plug) First, the overall configuration of the spark plug 1 will be described with reference to FIG. 1. The spark plug 1 includes an insulator 50 and a main fitting 30. In FIG. 1, the lower side of the paper surface is the one or tip side of the spark plug 1, and the upper side of the paper surface is the other or rear end side of the spark plug 1.

[0020] The insulator 50 is a substantially cylindrical member that extends in the longitudinal direction of the spark plug 1 along the axis O. The insulator 50 is formed of a material excellent in insulation, heat resistance, and thermal conductivity. For example, the insulator 50 is formed of alumina-based ceramics or the like. A center electrode 21 is provided at one end (tip end) 51 of the insulator 50. A terminal fitting 52 is attached to the other end (rear end) of the insulator.

[0021] The center electrode 21 is held in the axial hole of the insulator 50 in a state where its tip end (electrode tip end 22) protrudes from the tip end 51 of the insulator 50. The center electrode 21 has a substantially cylindrical shape, and its tip portion is tapered and reduced in diameter toward the electrode tip end 22. The electrode tip end 22 has a substantially cylindrical shape with the same diameter as the tip portion of the center electrode 21 whose diameter has been reduced.

[0022] The center electrode 21 is formed using a metal material such as a Ni-based alloy containing Ni (nickel) as a main component as a base material. Alloy elements added to the Ni-based alloy include Al (aluminum) and the like. The center electrode 21 may have a core material made of a metal excellent in thermal conductivity, such as a metal material such as Cu (copper) or a Cu alloy, inside thereof.

[0023] An electrode tip end 22 is provided at the tip of the center electrode 21. The electrode tip end 22 can be configured by, for example, a noble metal chip formed in a columnar shape and is joined to the tip of the center electrode 21 by welding or the like. The noble metal chip contains, for example, one kind of noble metal selected from Pt, Rh, Ir, and Ru at a content ratio of 50 wt% or more.

[0024] The main body fitting 30 is a cylindrical member fixed to the screw hole of the internal combustion engine. In the present embodiment, the main body fitting 30 has a substantially cylindrical shape extending along the axis O and is provided so as to partially cover the insulator 50. Thereby, the center electrode 21 provided at the tip end of the insulator 50 is insulated and held by the main body fitting 30.

[0025] The main fitting 30 is formed of a metallic material having electrical conductivity. Examples of such metallic materials include low-carbon steel or metallic materials mainly composed of iron. The main fitting 30 mainly has a caulking part 31, a tool engaging part 32, a bending part 33, a seat part 34, and a body part 36, etc.

[0026] The caulking part 31 is a part that bends toward the insulator 50 side at the rear end side of the main fitting 30. The tool engaging part 32 is a part that is connected to the tip side of the caulking part 31 and engages a tool such as a wrench used when attaching the main fitting 30 to a screw hole of an internal combustion engine (cylinder head). The seat part 34 is located on the tip side of the tool engaging part 32 and protrudes radially outward of the main fitting 30. The bending part 33 is a thin part that connects the tool engaging part 32 and the seat part 34. The body part 36 is located on the tip side of the seat part 34, and a screw part is formed on the outer periphery. An annular gasket is disposed between the seat part 34 and the screw part of the body part 36. When the spark plug 1 is attached to the internal combustion engine, a screw groove (not shown) formed on the outer periphery of the body part 36 is screwed into a screw hole of the internal combustion engine. At this time, the annular gasket is sandwiched between the seat part 34 and the cylinder head, thereby ensuring airtightness in the screw hole.

[0027] Also, a ground electrode 11 is joined to the main fitting 30. The ground electrode 11 is joined to the main fitting 30 by welding or the like.

[0028] The ground electrode 11 mainly has a main body part (base material) 12 and an electrode tip 13. The main body part 12 has a shape bent in a substantially L shape. One end part (also referred to as the base end part) of the main body part 12 is joined to the front end surface of the body part 36 of the main fitting 30. The other end part (also referred to as the tip end part) of the main body part 12 faces the electrode tip part 22 of the center electrode 21.

[0029] The main body part (base material) 12 is formed of a metal material such as a Ni-based alloy containing Ni (nickel) as a main component. Examples of alloying elements added to the Ni-based alloy include Mn (manganese), Cr (chromium), Al (aluminum), etc. The main body part 12 may have, inside thereof, a core material made of a metal excellent in thermal conductivity, such as a metal material like Cu (copper) or a Cu alloy.

[0030] Also, the main body part (base material) 12 may contain, as components other than Ni, at least one element selected from Mn (manganese), Cr (chromium), Al (aluminum), and Ti (titanium).

[0031] The electrode tip 13 is disposed on the tip end side of the main body part 12. The electrode tip 13 is provided so as to protrude toward the electrode tip end 22 side of the center electrode 21. That is, the electrode tip 13 is joined to the main body part 12 on the base end part (one end part) side rather than the tip end surface 12a of the tip end part (the other end part) of the main body part (base material) 12. The tip of the electrode tip 13 is a facing surface facing the electrode tip end 22 of the center electrode 21. The facing surface of this electrode tip 13 with the electrode tip end 22 is referred to as the chip surface 13a (see FIG. 2). The electrode tip 13 is formed of a noble metal material in the same manner as the electrode tip end 22 of the center electrode 21. The electrode tip 13 contains, for example, one kind of noble metal selected from Pt, Rh, Ir, and Ru at a content ratio of 50 wt% or more.

[0032] (Configuration of the tip end of the ground electrode) Subsequently, a more detailed configuration of the tip end of the ground electrode 11 will be described. FIG. 2 shows a cross-sectional configuration of the tip end portion of the ground electrode 11 of the spark plug 1. FIG. 2 is a schematic cross-sectional view when the tip end portion including the electrode tip 13 of the ground electrode 11 is cut in the vertical direction (axial direction) perpendicular to the tip end surface 12a of the main body part 12.

[0033] The electrode chip 13 is welded and joined to the main body part (base material) 12 by, for example, resistance welding. When the electrode chip 13 is welded to the main body part (base material) 12, a molten part 14 obtained by melting a part of the base material and a part of the electrode chip 13 is formed between the main body part 12 and the electrode chip 13. That is, a molten part 14 that joins them is interposed between the main body part 12 and the electrode chip 13. Note that the molten part 14 may also be formed on the contact surface (for example, the bottom surface part 13c of the electrode chip 13, etc.) between the main body part 12 and the electrode chip 13.

[0034] Thereby, an electrode chip 13 is obtained in which at least a part protrudes from the facing surface (in FIG. 2, the upper surface 12b) with the central electrode 21 in the main body part (base material) 12. In the example shown in FIG. 2, a part of the electrode chip 13 (specifically, the part on the bottom surface part 13c side) is embedded in the base material of the main body part 12.

[0035] Also, in another example, the electrode chip 13 may be disposed on the upper surface 12b (the facing surface with the central electrode 21) of the main body part (base material) 12. That is, the upper surface 12b of the main body part (base material) 12 and the bottom surface part 13c of the electrode chip 13 may be in the same plane.

[0036] As shown in FIG. 2, at least a part of the end part 13b of the electrode chip 13 on the tip surface 12a side of the main body part 12 is covered with the molten part 14. And the molten part 14 that exists so as to cover the end part 13b of the electrode chip 13 is rounded. That is, in the cross section of the ground electrode 11 as shown in FIG. 2, the surface of the molten part 14 has a curved R shape. For example, the R value of the rounded part R of the molten part 14 is 30 μm or more and 200 μm or less.

[0037] Also, in the present embodiment, the molten part 14 that exists so as to cover the end part 13b of the electrode chip 13 exists up to the same position as the chip surface 13a. That is, the surface 14a of the molten part 14 on the end part 13b side is flush with the chip surface 13a of the electrode chip 13 (see FIG. 2). Further, the surface 14b of the molten part 14 on the tip surface 12a side of the main body part 12 is flush with the tip surface 12a (see FIG. 2).

[0038] The above-described shape of the tip of the ground electrode 11 can be formed by, for example, shaving the surfaces of the electrode tip 13 and the molten part 14 after welding using a cutting tool or the like.

[0039] (Summary of the First Embodiment) As described above, the spark plug 1 according to the present embodiment includes a center electrode 21, a main body fitting 30, and a ground electrode 11. The ground electrode 11 has a main body portion (base material) 12 and an electrode tip 13 joined to the main body portion 12. The electrode tip 13 protrudes from the upper surface 12b of the main body portion 12 and has a tip surface 13a facing the center electrode 21. A molten part 14 that joins them is interposed between the main body portion 12 and the electrode tip 13. At least a part of the end portion 13b of the electrode tip 13 located on the tip surface 12a side of the main body portion 12 is covered with the molten part 14. The molten part 14 present at the end portion 13b of the electrode tip 13 is rounded and exists up to the same position as the tip surface 13a.

[0040] According to the above configuration, since the molten part 14 that exists so as to cover the end portion 13b of the electrode tip 13 is rounded, it is possible to suppress the concentration of the electric field at the end portion 13b of the tip surface 13a. Further, since this rounded molten part 14 exists up to the same position as the tip surface 13a, the corner portion of the boundary between the tip surface 13a and the end portion 13b in the electrode tip 13 is not exposed. Thereby, it is possible to suppress the concentration of the electric field at the corner portion of the electrode tip 13.

[0041] Further, in the present embodiment, the surface 14b of the molten portion 14 on the tip surface 12a side of the main body portion 12 is flush with the tip surface 12a. As a result, the corner portion on the upper side (the side facing the center electrode 21) of the tip surface 12a of the main body portion 12 is no longer exposed. Therefore, when spark discharge occurs on the chip surface 13a of the electrode chip 13, it is possible to suppress the sparks from concentrating and flowing away at the corner portion of the main body portion 12 located on the more distal end side. Thereby, it is possible to suppress a part (that is, the tip portion) of the main body portion 12 from being locally consumed, and a spark plug 1 with a longer life can be obtained.

[0042] Further, the molten portion 14 contains a trace amount of a noble metal derived from the noble metal component contained in the electrode chip 13. Therefore, the molten portion 14 is less likely to be consumed than the main body portion 12 formed of a metal material such as a nickel-based alloy. By providing such a molten portion 14 up to the tip surface 12a of the main body portion 12, local consumption of the main body portion 12 can be further suppressed.

[0043] <Second Embodiment> Subsequently, a second embodiment of the present invention will be described. In the second embodiment, the configuration of the molten portion interposed between the base material of the ground electrode and the electrode chip is different from that of the first embodiment. For other configurations, the same configurations as those of the first embodiment can be applied. Therefore, in the second embodiment, the description will focus on the differences from the first embodiment.

[0044] FIG. 3 shows a cross-sectional configuration of the tip portion of the ground electrode 11 of the spark plug 1 according to the second embodiment. FIG. 3 is a schematic cross-sectional view when the tip portion including the electrode chip 13 of the ground electrode 11 is cut in the vertical direction (axial direction) perpendicular to the tip surface 12a of the main body portion 12.

[0045] The electrode chip 13 is welded and joined to the main body portion (base material) 12 by, for example, resistance welding. When the electrode chip 13 is welded to the main body portion (base material) 12, a molten portion 114 obtained by melting a part of the base material and a part of the electrode chip 13 is formed between the main body portion 12 and the electrode chip 13.

[0046] As a result, an electrode chip 13 is obtained in which at least a part protrudes from the facing surface (the upper surface 12b in FIG. 3) with the central electrode 21 in the main body portion (base material) 12.

[0047] As shown in FIG. 3, at least a part of the end portion 13b of the electrode chip 13 on the tip surface 12a side of the main body portion 12 is covered with the molten portion 114. And the molten portion 114 existing so as to cover the end portion 13b of the electrode chip 13 is rounded. That is, in the cross section of the ground electrode 11 as shown in FIG. 3, the surface of the molten portion 114 has a curved R shape. The same configuration as that of the first embodiment can be applied to this R shape.

[0048] In the present embodiment, similarly to the first embodiment, the molten portion 114 existing so as to cover the end portion 13b of the electrode chip 13 exists up to the same position as the chip surface 13a. That is, the surface 114a of the molten portion 114 on the end portion 13b side is flush with the chip surface 13a of the electrode chip 13 (see FIG. 3).

[0049] On the other hand, the surface 114b of the molten portion 114 on the tip surface 12a side of the main body portion 12 is provided so as to cover a part of the tip surface 12a of the main body portion 12 (see FIG. 3). This point is different from the first embodiment.

[0050] The above-described shape of the tip portion of the ground electrode 11 can be formed by shaving the surfaces of the electrode chip 13 and the molten portion 114 after welding using, for example, a cutting tool or the like.

[0051] In the present embodiment, since the molten portion 114 existing so as to cover the end portion 13b of the electrode chip 13 is rounded, it is possible to suppress the concentration of the electric field at the end portion 13b of the chip surface 13a.

[0052] Further, in the present embodiment, the surface 114b of the molten portion 114 on the tip surface 12a side of the main body portion 12 is provided so as to cover a part of the tip surface 12a of the main body portion 12. Thereby, the corner portion on the upper side (the side facing the center electrode 21) of the tip surface 12a of the main body portion 12 is covered by the molten portion 114. Therefore, when spark discharge occurs on the chip surface 13a of the electrode chip 13, it is possible to suppress the sparks from flowing toward the main body portion 12 located on the more distal end side. As a result, it is possible to suppress a part of the main body portion 12 (that is, the tip portion) from being locally consumed, and a spark plug 1 with a longer life can be obtained.

[0053] <Third Embodiment> Subsequently, a third embodiment of the present invention will be described. In the third embodiment, the configuration of the molten portion interposed between the base material of the ground electrode and the electrode chip is different from that of the first embodiment. For other configurations, the same configurations as those of the first embodiment can be applied. Therefore, in the third embodiment, the description will be centered on the differences from the first embodiment.

[0054] FIG. 4 shows a cross-sectional configuration of the tip portion of the ground electrode 11 of the spark plug 1 according to the third embodiment. FIG. 4 is a schematic cross-sectional view when the tip portion including the electrode chip 13 of the ground electrode 11 is cut in the vertical direction (axial direction) perpendicular to the tip surface 12a of the main body portion 12.

[0055] The electrode chip 13 is welded and joined to the main body portion (base material) 12 by, for example, resistance welding. When the electrode chip 13 is welded to the main body portion (base material) 12, a molten portion 214 obtained by melting a part of the base material and a part of the electrode chip 13 is formed between the main body portion 12 and the electrode chip 13.

[0056] Thereby, an electrode chip 13 that protrudes at least partially from the facing surface (the upper surface 12b in FIG. 4) with the center electrode 21 in the main body portion (base material) 12 is obtained.

[0057] As shown in Fig. 4, at least a part of the end portion 13b of the electrode chip 13 on the tip surface 12a side of the main body portion 12 is covered by the melting portion 214. And the melting portion 214 existing so as to cover the end portion 13b of the electrode chip 13 is rounded. That is, in the cross section of the ground electrode 11 as shown in Fig. 4, the surface of the melting portion 214 has a curved R shape. The same configuration as that of the first embodiment can be applied to this R shape.

[0058] In the present embodiment, similar to the first embodiment, the melting portion 214 existing so as to cover the end portion 13b of the electrode chip 13 exists up to the same position as the chip surface 13a. That is, the surface 214a of the melting portion 214 on the end portion 13b side is flush with the chip surface 13a of the electrode chip 13 (see Fig. 4).

[0059] On the other hand, the surface 214b of the melting portion 214 on the tip surface 12a side of the main body portion 12 does not cover the tip surface 12a of the main body portion 12. That is, the corner portion 212c on the upper side (the side facing the center electrode 21) of the tip surface 12a is exposed. And the corner portion 212c of the main body portion 12 is rounded. That is, in the cross section of the ground electrode 11 as shown in Fig. 4, the surface of the corner portion 212c of the main body portion 12 has a curved R shape. This point is different from the first embodiment.

[0060] The above-described shape of the tip portion of the ground electrode 11 can be formed by shaving the surfaces of the electrode chip 13, the melting portion 214, and the main body portion 12 after welding using, for example, a cutting tool or the like.

[0061] According to the above configuration, since the molten part 214 that exists so as to cover the end part 13b of the electrode chip 13 is rounded, it is possible to suppress the concentration of the electric field at the end part 13b of the chip surface 13a. Further, since the surface of the corner part 212c of the main body part 12 not covered by the molten part 214 has an R shape, when a spark discharge occurs on the chip surface 13a of the electrode chip 13, it is possible to suppress the spark from flowing and jumping toward the main body part (base material) 12 located on the more tip side. Thereby, it is possible to suppress a part (that is, the tip part) of the main body part 12 from being locally consumed, and it is possible to obtain a spark plug 1 with a longer life.

[0062] <Fourth Embodiment> Subsequently, a fourth embodiment of the present invention will be described. In the fourth embodiment, the configuration of the molten part interposed between the base material of the ground electrode and the electrode chip is different from that of the first embodiment. For other configurations, the same configurations as those of the first embodiment can be applied. Therefore, in the fourth embodiment, the description will be centered on the points different from those of the first embodiment.

[0063] FIG. 5 shows a cross-sectional configuration of the tip part of the ground electrode 11 of the spark plug 1 according to the fourth embodiment. FIG. 5 is a schematic cross-sectional view when the tip part including the electrode chip 13 of the ground electrode 11 is cut in the vertical direction (axial direction) perpendicular to the tip surface 12a of the main body part 12.

[0064] The electrode chip 13 is welded and joined to the main body part (base material) 12 by, for example, resistance welding. When the electrode chip 13 is welded to the main body part (base material) 12, a molten part 314 obtained by melting a part of the base material and a part of the electrode chip 13 is formed between the main body part 12 and the electrode chip 13.

[0065] Thereby, an electrode chip 13 that protrudes at least partially from the facing surface (the upper surface 12b in FIG. 5) with the center electrode 21 in the main body part (base material) 12 is obtained.

[0066] As shown in FIG. 5, at least a part of the end portion 13b of the electrode chip 13 on the tip surface 12a side of the main body portion 12 is covered with a molten portion 314. And the molten portion 314 existing so as to cover the end portion 13b of the electrode chip 13 is rounded. That is, in the cross section of the ground electrode 11 as shown in FIG. 5, the surface of the molten portion 314 has a curved R shape. The same configuration as that of the first embodiment can be applied to this R shape.

[0067] In the present embodiment, the molten portion 314 existing so as to cover the end portion 13b of the electrode chip 13 exists up to a position higher than the chip surface 13a. That is, the surface 314a of the molten portion 314 on the end portion 13b side is provided so as to cover a part of the chip surface 13a of the electrode chip 13 (see FIG. 5). This point is different from the first embodiment.

[0068] On the other hand, the surface 314b of the molten portion 314 on the tip surface 12a side of the main body portion 12 is flush with the tip surface 12a as in the first embodiment (see FIG. 5).

[0069] The above-described shape of the tip portion of the ground electrode 11 can be formed by shaving the surfaces of the electrode chip 13 and the molten portion 314 after welding using, for example, a cutting tool or the like.

[0070] As described above, the spark plug 1 according to the present embodiment includes a center electrode 21, a main body fitting 30, and a ground electrode 11. The ground electrode 11 has a main body portion (base material) 12 and an electrode chip 13 joined to the main body portion 12. The electrode chip 13 protrudes from the upper surface 12b of the main body portion 12 and has a chip surface 13a facing the center electrode 21. A molten portion 314 that joins them is interposed between the main body portion 12 and the electrode chip 13. At least a part of the end portion 13b of the electrode chip 13 located on the tip surface 12a side of the main body portion 12 is covered with the molten portion 314. The molten portion 314 existing at the end portion 13b of the electrode chip 13 is rounded and exists up to a position higher than the chip surface 13a.

[0071] According to the above configuration, the molten part 314 that exists so as to cover the end part 13b of the electrode chip 13 is rounded, thereby suppressing the concentration of the electric field at the end part 13b of the chip surface 13a. Further, since this rounded molten part 14 exists up to a position higher than the chip surface 13a, the corner part of the boundary between the chip surface 13a and the end part 13b in the electrode chip 13 is covered by the molten part 314. Thereby, it is possible to suppress the concentration of the electric field at the corner part of the electrode chip 13.

[0072] <Fifth Embodiment> Next, a fifth embodiment of the present invention will be described. In the fifth embodiment, the configuration of the molten part interposed between the base material of the ground electrode and the electrode chip is different from that of the first embodiment. For other configurations, the same configurations as those in the first embodiment can be applied. Therefore, in the fifth embodiment, the description will be centered on the points different from those in the first embodiment.

[0073] FIG. 6 shows a cross-sectional configuration of the tip portion of the ground electrode 11 of the spark plug 1 according to the fifth embodiment. FIG. 6 is a schematic cross-sectional view when the tip portion including the electrode chip 13 of the ground electrode 11 is cut in the vertical direction (axial direction) perpendicular to the front end surface 12a of the main body portion 12.

[0074] The electrode chip 13 is welded and joined to the main body portion (base material) 12 by, for example, resistance welding. When the electrode chip 13 is welded to the main body portion (base material) 12, a molten part 414 obtained by melting a part of the base material and a part of the electrode chip 13 is formed between the main body portion 12 and the electrode chip 13.

[0075] Thereby, an electrode chip 13 is obtained that protrudes at least partially from the facing surface (the upper surface 12b in FIG. 6) with the center electrode 21 in the main body portion (base material) 12.

[0076] As shown in FIG. 6, at least a part of the end portion 13b of the electrode chip 13 on the tip surface 12a side of the main body portion 12 is covered with the melted portion 414. And the melted portion 414 that exists so as to cover the end portion 13b of the electrode chip 13 has a rounded shape. That is, in the cross section of the ground electrode 11 as shown in FIG. 6, the surface of the melted portion 414 has a curved R shape. The same configuration as that of the first embodiment can be applied to this R shape.

[0077] In the present embodiment, the melted portion 414 that exists so as to cover the end portion 13b of the electrode chip 13 exists up to a position higher than the chip surface 13a. That is, the surface 414a of the melted portion 414 on the end portion 13b side is provided so as to cover a part of the chip surface 13a of the electrode chip 13 (see FIG. 6). This point is different from the first embodiment.

[0078] Further, the surface 414b of the melted portion 414 on the tip surface 12a side of the main body portion 12 is provided so as to cover a part of the tip surface 12a of the main body portion 12 (see FIG. 6). This point is also different from the first embodiment.

[0079] The above-described shape of the tip portion of the ground electrode 11 can be formed by shaving the surfaces of the electrode chip 13 and the melted portion 314 after welding using, for example, a cutting tool or the like.

[0080] According to the above configuration, since the melted portion 414 that exists so as to cover the end portion 13b of the electrode chip 13 has a rounded shape, it is possible to suppress the concentration of the electric field at the end portion 13b of the chip surface 13a. Further, since the surface 414b of the melted portion 414 on the tip surface 12a side of the main body portion 12 is provided so as to cover a part of the tip surface 12a of the main body portion 12, when spark discharge occurs on the chip surface 13a of the electrode chip 13, it is possible to suppress the spark from flowing and flying toward the main body portion 12 located on the more tip side. As a result, it is possible to suppress a part of the main body portion 12 (that is, the tip portion) from being locally consumed, and it is possible to obtain a spark plug 1 with a longer life.

[0081] <Sixth Embodiment> Next, a sixth embodiment of the present invention will be described. In the sixth embodiment, the configuration of the molten portion intervening between the base material of the ground electrode and the electrode chip is different from that of the first embodiment. For other configurations, the same configurations as those of the first embodiment can be applied. Therefore, in the sixth embodiment, the description will focus on the differences from the first embodiment.

[0082] FIG. 7 shows a cross-sectional configuration of a tip portion of the ground electrode 11 of the spark plug 1 according to the sixth embodiment. FIG. 7 is a schematic cross-sectional view when the tip portion including the electrode chip 13 of the ground electrode 11 is cut in a vertical direction (axial direction) perpendicular to the tip surface 12a of the main body portion 12.

[0083] The electrode chip 13 is welded and joined to the main body portion (base material) 12 by, for example, resistance welding. When the electrode chip 13 is welded to the main body portion (base material) 12, a molten portion 514 obtained by melting a part of the base material and a part of the electrode chip 13 is formed between the main body portion 12 and the electrode chip 13.

[0084] As a result, an electrode chip 13 is obtained that at least partially protrudes from the facing surface (the upper surface 12b in FIG. 7) with the center electrode 21 in the main body portion (base material) 12.

[0085] As shown in FIG. 7, at least a part of the end portion 13b of the electrode chip 13 on the tip surface 12a side of the main body portion 12 is covered with the molten portion 514. And the molten portion 514 existing so as to cover the end portion 13b of the electrode chip 13 is rounded. That is, in the cross-section of the ground electrode 11 as shown in FIG. 7, the surface of the molten portion 514 has a curved R shape. The same configuration as that of the first embodiment can be applied to this R shape.

[0086] In the present embodiment, similar to the fourth embodiment and the like, the molten portion 514 existing so as to cover the end portion 13b of the electrode chip 13 exists up to a position higher than the chip surface 13a. That is, the surface 514a of the molten portion 514 on the end portion 13b side is provided so as to cover a part of the chip surface 13a of the electrode chip 13 (see FIG. 7).

[0087] Further, the surface 514b of the molten portion 514 on the tip surface 12a side of the main body portion 12 does not cover the tip surface 12a of the main body portion 12, similar to the third embodiment. That is, the corner portion 212c on the upper side (the side facing the center electrode 21) of the tip surface 12a is exposed. And the corner portion 212c of the main body portion 12 is rounded. That is, in the cross section of the ground electrode 11 as shown in FIG. 7, the surface of the corner portion 212c of the main body portion 12 has a curved R shape.

[0088] The above-described shape of the tip portion of the ground electrode 11 can be formed by machining the surfaces of the electrode tip 13, the molten portion 514, and the main body portion 12 after welding, for example, using a cutting tool or the like.

[0089] According to the above configuration, since the molten portion 514 that exists so as to cover the end portion 13b of the electrode tip 13 is rounded, it is possible to suppress the electric field concentration at the end portion 13b of the chip surface 13a. Further, since the surface of the corner portion 212c of the main body portion 12 not covered by the molten portion 514 has an R shape, when spark discharge occurs on the chip surface 13a of the electrode tip 13, it is possible to suppress the sparks from flowing and flying toward the main body portion (base material) 12 located on the more distal end side. Thereby, it is possible to suppress a part (that is, the tip portion) of the main body portion 12 from being locally consumed, and a spark plug 1 with a longer life can be obtained.

[0090] The embodiments disclosed this time should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included. Also, the configurations obtained by combining the configurations of the respective embodiments described in this specification with each other are also included in the scope of the present invention.

Explanation of Reference Numerals

[0091] 1: Spark plug 11: Ground electrode 12: Main body portion (base material) 12a: Tip surface (of the main body part) 12b: Upper surface (opposing surface to the central electrode of the base material) of the main body part 13: Electrode chip 13a: Chip surface (of the electrode chip) 13b: End part (of the electrode chip) 14: Melting part 21: Central electrode 30: Main body fitting 50: Insulator 114: Melting part 214: Melting part 314: Melting part 414: Melting part 514: Melting part

Claims

Claim 1 a center electrode; a main fitting that extends along an axis and insulatively holds the center electrode; a base material having one end connected to the main fitting, and a ground electrode having an electrode chip joined to the base material on the other end side of the base material at a position closer to the one end side than the tip surface of the other end; comprising: the electrode chip has a chip surface facing the center electrode in the axial direction and protrudes from a facing surface of the base material that faces the center electrode in the axial direction; a spark plug in which a molten part that joins the base material and the electrode chip is interposed between the base material and the electrode chip; at least a part of an end portion on the tip surface side of the electrode chip is covered by the molten part; the molten part present at the end portion has a rounded shape; a part of the chip surface is covered by the molten part, and the molten part exists up to a position higher than the chip surface; a corner portion on the side facing the center electrode at the tip surface of the other end of the base material is not covered by the molten part and is exposed, and the corner portion has a rounded shape; a spark plug.

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