JP7689934B2 - Spark plug - Google Patents

Description

The present invention relates to a spark plug for use in an internal combustion engine.

Spark plugs are used as an ignition means for internal combustion engines such as automobile engines. Spark plugs are provided with a center electrode and a ground electrode as components for generating spark discharge. An electrode tip is provided on the surface of the ground electrode facing the center electrode to improve the ignition performance of the spark plug. The electrode tip is formed, for example, from a columnar body made of a precious metal material, and is joined to the base material of the ground electrode by welding or the like.

For example, Patent Document 1 discloses a spark plug having 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 fusion zone formed by laser welding is provided on the back side of the tip surface of the electrode tip.

International Publication No. 2015/098007

In a ground electrode where the electrode tip is joined to the base material, the end of the electrode tip on the tip surface side of the base material is exposed. For example, when a rectangular electrode tip is joined to the base material, the corners of the rectangular column are present on the tip surface side of the base material. If a spark discharge occurs between a ground electrode of this shape and a center electrode, the electric field may concentrate on the corners of the end of the tip surface, which may accelerate the wear of the electrode only in this part.

Therefore, the present invention aims to provide a spark plug that can suppress electric field concentration at the end of the tip surface.

The spark plug according to one aspect of the present invention includes a center electrode, a metal shell extending along an axis and insulating the center electrode, a base metal shell having one end connected to the metal shell, and a ground electrode having an electrode tip at the other end of the base metal, the electrode tip being joined to the base metal on the one end side of the tip surface of the other end. The electrode tip has a tip surface facing the center electrode in the axial direction, and protrudes from the surface of the base metal facing the center electrode in the axial direction, and a fusion zone is interposed between the base metal and the electrode tip to join them. In this spark plug, at least a portion of the end of the electrode tip on the tip surface side is covered with the fusion zone, and the fusion zone at the end is rounded and is at the same position as the tip surface or even higher than the tip surface.

According to the above configuration, at least a part of the end of the electrode tip located on the tip surface side of the base material is covered with a molten part, and this molten part is rounded, so that it is possible to suppress electric field concentration at the end of the tip surface. In addition, since this rounded molten part exists at the same position as the tip surface, the corner part of the boundary between the tip surface and the end of the electrode tip is not exposed. This makes it possible to suppress electric field concentration at the corner part of the electrode tip. In addition, since this rounded molten part exists at a position higher than the tip surface, the corner part of the boundary between the tip surface and the end of the electrode tip is covered by the molten part. This makes it possible to suppress electric field concentration at the corner part of the electrode tip. Therefore, it is possible to delay the electrode wear of the ground electrode.

In the spark plug according to one aspect of the present invention described above, the molten portion at the end may be located at the same position as the tip surface.

According to the above configuration, the molten part is located at the same position as the tip surface, so that the tip surface of the electrode tip and the surface of the molten part are flush with each other. This makes it possible to suppress electric field concentration at the corners of the electrode tip.

In the spark plug according to one aspect of the present invention described above, a portion of the tip surface may be covered by the molten portion.

With the above configuration, the corners of the boundary between the tip surface and the end of the electrode tip are covered and hidden by the molten part. This makes it possible to suppress electric field concentration at the corners of the electrode tip.

In addition, in a spark plug according to one aspect of the present invention, the tip surface of the base material and the molten portion may be flush with each other.

With the above configuration, the corners of the tip surface of the base material facing the center electrode are not exposed. Therefore, when a spark discharge occurs on the tip surface of the electrode tip, the sparks are prevented from flowing toward the base material located closer to the tip, and localized wear of a portion of the base material is prevented.

As described above, one aspect of the present invention provides a spark plug that can suppress electric field concentration at the end of the tip surface.

1 is a side view showing an external configuration of a spark plug according to an embodiment of the present invention; 1 is a schematic cross-sectional view showing a configuration of a tip portion of a ground electrode of a spark plug according to a first embodiment. FIG. 10 is a schematic cross-sectional view showing the configuration of a tip portion of a ground electrode of a spark plug according to a second embodiment. FIG. FIG. 11 is a schematic cross-sectional view showing the configuration of a tip portion of a ground electrode of a spark plug according to a third embodiment. FIG. 13 is a schematic cross-sectional view showing the configuration of a tip portion of a ground electrode of a spark plug according to a fourth embodiment. FIG. 13 is a schematic cross-sectional view showing the configuration of a tip portion of a ground electrode of a spark plug according to a fifth embodiment. FIG. 13 is a schematic cross-sectional view showing the configuration of a tip portion of a ground electrode of a spark plug according to a sixth embodiment.

Each embodiment of the present invention will be described below with reference to the drawings. In the following description, identical parts are given the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated.

First Embodiment
A first embodiment of the present invention will be described below. In this embodiment, a spark plug 1 will be described as an example.

(Spark plug configuration)
First, the overall configuration of a spark plug 1 will be described with reference to Fig. 1. The spark plug 1 includes an insulator 50 and a metal shell 30. In Fig. 1, the lower side of the drawing refers to one side or the leading end side of the spark plug 1, and the upper side of the drawing refers to the other side or the trailing end side of the spark plug 1.

The insulator 50 is a generally cylindrical member that extends in the longitudinal direction of the spark plug 1 along the axis O. The insulator 50 is made of a material that has excellent insulating properties, heat resistance, and thermal conductivity. For example, the insulator 50 is made of alumina-based ceramics. 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.

The center electrode 21 is held in the axial hole of the insulator 50 with its tip (electrode tip 22) protruding from the tip 51 of the insulator 50. The center electrode 21 has a roughly cylindrical shape, and its tip portion tapers in diameter toward the electrode tip 22. The electrode tip 22 has a roughly cylindrical shape with the same diameter as the tip portion of the center electrode 21 that has been reduced in diameter.

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

The tip of the center electrode 21 is provided with an electrode tip portion 22. The electrode tip portion 22 can be formed, for example, of a precious metal tip formed into a cylindrical shape, and is joined to the tip of the center electrode 21 by welding or the like. The precious metal tip contains, for example, one type of precious metal selected from Pt, Rh, Ir, and Ru at a content of 50 wt% or more.

The metal shell 30 is a tubular member that is fixed to a screw hole in an internal combustion engine. In this embodiment, the metal shell 30 has a generally cylindrical shape that extends along the axis O, and is arranged to partially cover the insulator 50. As a result, the center electrode 21 provided at the tip of the insulator 50 is insulated and held by the metal shell 30.

The metal shell 30 is made of a conductive metal material. Examples of such metal materials include low carbon steel and metal materials whose main component is iron. The metal shell 30 mainly includes a crimping portion 31, a tool engagement portion 32, a curved portion 33, a seat portion 34, and a body portion 36.

The crimping portion 31 is a portion that is bent toward the insulator 50 at the rear end side of the metal shell 30. The tool engagement portion 32 is a portion that is connected to the tip side of the crimping portion 31 and engages a tool such as a wrench that is used when attaching the metal shell 30 to a screw hole of an internal combustion engine (cylinder head). The seat portion 34 is located on the tip side of the tool engagement portion 32 and protrudes radially outward from the metal shell 30. The curved portion 33 is a thin-walled portion that connects the tool engagement portion 32 and the seat portion 34. The body portion 36 is located on the tip side of the seat portion 34 and has a threaded portion formed on its outer periphery. An annular gasket is disposed between the seat portion 34 and the threaded portion of the body portion 36. When the spark plug 1 is attached to an internal combustion engine, a thread groove (not shown) formed on the outer periphery of the body portion 36 is screwed into the screw hole of the internal combustion engine. At this time, the annular gasket is sandwiched between the seat portion 34 and the cylinder head, thereby ensuring airtightness in the screw hole.

The ground electrode 11 is joined to the metal shell 30. The ground electrode 11 is joined to the metal shell 30 by welding or the like.

The ground electrode 11 mainly has a main body (base material) 12 and an electrode tip 13. The main body 12 is bent into a generally L-shape. One end (also called the base end) of the main body 12 is joined to the tip surface of the trunk 36 of the metal shell 30. The other end (also called the tip) of the main body 12 faces the electrode tip 22 of the center electrode 21.

The main body (base material) 12 is formed of a metal material such as a Ni-based alloy containing Ni (nickel) as the main component. Examples of alloy elements added to the Ni-based alloy include Mn (manganese), Cr (chromium), and Al (aluminum). The main body 12 may have a core material inside that is made of a metal with excellent thermal conductivity, such as a metal material such as Cu (copper) or a Cu alloy.

The main body (base material) 12 may also contain at least one element selected from Mn (manganese), Cr (chromium), Al (aluminum), and Ti (titanium) as a component other than Ni.

The electrode tip 13 is disposed on the tip side of the main body 12. The electrode tip 13 is provided so as to protrude toward the electrode tip 22 side of the center electrode 21. That is, the electrode tip 13 is joined to the main body 12 on the base end (one end) side of the tip surface 12a of the tip (other end) of the main body (base material) 12. The tip of the electrode tip 13 is an opposing surface facing the electrode tip 22 of the center electrode 21. The opposing surface of the electrode tip 13 with the electrode tip 22 is called the tip surface 13a (see FIG. 2). The electrode tip 13 is formed of a precious metal material, similar to the electrode tip 22 of the center electrode 21. The electrode tip 13 contains, for example, one precious metal selected from Pt, Rh, Ir, and Ru at a content of 50 wt% or more.

(Configuration of tip of ground electrode)
Next, a more detailed configuration of the tip portion of the ground electrode 11 will be described. Fig. 2 shows a cross-sectional configuration of the tip portion of the ground electrode 11 of the spark plug 1. Fig. 2 is a schematic cross-sectional view of the tip portion including the electrode tip 13 of the ground electrode 11 cut in a vertical direction (axial direction) perpendicular to the tip surface 12a of the body portion 12.

The electrode tip 13 is welded to the main body (base material) 12 by, for example, resistance welding. When the electrode tip 13 is welded to the main body (base material) 12, a molten portion 14 is formed between the main body 12 and the electrode tip 13, which is obtained by melting a part of the base material and a part of the electrode tip 13. In other words, the molten portion 14 that joins the main body 12 and the electrode tip 13 is interposed between them. The molten portion 14 may also be formed on the contact surface between the main body 12 and the electrode tip 13 (for example, the bottom surface portion 13c of the electrode tip 13, etc.).

This results in an electrode tip 13 that at least partially protrudes from the surface of the main body (base material) 12 that faces the center electrode 21 (top surface 12b in FIG. 2). In the example shown in FIG. 2, a portion of the electrode tip 13 (specifically, the portion on the bottom surface 13c side) is embedded in the base material of the main body 12.

In another example, the electrode tip 13 may be disposed on the upper surface 12b (opposing surface to the center electrode 21) of the main body portion (base material) 12. In other words, the upper surface 12b of the main body portion (base material) 12 and the bottom surface 13c of the electrode tip 13 may be located on the same plane.

As shown in FIG. 2, at least a portion of the end 13b of the electrode tip 13 on the tip surface 12a side of the main body 12 is covered with a molten part 14. The molten part 14 that covers the end 13b of the electrode tip 13 is rounded. That is, in the cross section of the ground electrode 11 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.

In addition, in this embodiment, the molten portion 14 that covers the end portion 13b of the electrode tip 13 is present at the same position as the tip surface 13a. That is, the surface 14a of the molten portion 14 on the end portion 13b side is flush with the tip surface 13a of the electrode tip 13 (see FIG. 2). Furthermore, 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 (see FIG. 2).

The above-described shape of the tip of the ground electrode 11 can be formed by cutting the surface of the electrode tip 13 and the molten part 14 after welding, for example, using a cutting tool.

(Summary of the first embodiment)
As described above, the spark plug 1 according to this embodiment includes the center electrode 21, the metallic shell 30, and the ground electrode 11. The ground electrode 11 includes a body portion (base material) 12 and an electrode tip 13 joined to the body portion 12. The electrode tip 13 protrudes from an upper surface 12b of the body portion 12 and has a tip surface 13a facing the center electrode 21. A fusion zone 14 that joins the body portion 12 and the electrode tip 13 is interposed between the body portion 12 and the electrode tip 13. At least a portion of an end portion 13b of the electrode tip 13 located on the front end surface 12a side of the body portion 12 is covered with the fusion zone 14. The fusion zone 14 present at the end portion 13b of the electrode tip 13 is rounded and is present at the same position as the tip surface 13a.

According to the above configuration, the molten portion 14 that covers the end 13b of the electrode tip 13 is rounded, which makes it possible to suppress electric field concentration at the end 13b of the tip surface 13a. In addition, since the rounded molten portion 14 is present at the same position as the tip surface 13a, the corner portion of the boundary between the tip surface 13a and the end 13b of the electrode tip 13 is not exposed. This makes it possible to suppress electric field concentration at the corner portion of the electrode tip 13.

In addition, in this embodiment, the surface 14b of the fusion zone 14 on the tip surface 12a side of the body 12 is flush with the tip surface 12a. This prevents the corners on the upper side (the side facing the center electrode 21) of the tip surface 12a of the body 12 from being exposed. Therefore, when a spark discharge occurs on the tip surface 13a of the electrode tip 13, it is possible to prevent sparks from concentrating on the corners of the body 12 located closer to the tip and flying away. This prevents localized wear of a portion of the body 12 (i.e., the tip portion), resulting in a spark plug 1 with a longer life.

The molten portion 14 also contains a small amount of precious metal derived from the precious metal components contained in the electrode tip 13. Therefore, the molten portion 14 is less susceptible to wear 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, localized wear of the main body portion 12 can be further suppressed.

Second Embodiment
Next, a second embodiment of the present invention will be described. In the second embodiment, the configuration of the fusion zone between the base metal of the ground electrode and the electrode tip is different from that of the first embodiment. Other configurations can be applied similarly to those of the first embodiment. Therefore, in the second embodiment, the differences from the first embodiment will be mainly described.

Figure 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. Figure 3 is a schematic cross-sectional view of the tip portion including the electrode tip 13 of the ground electrode 11 cut in a vertical direction (axial direction) perpendicular to the tip surface 12a of the body portion 12.

The electrode tip 13 is welded to the main body (base material) 12 by, for example, resistance welding. When the electrode tip 13 is welded to the main body (base material) 12, a molten zone 114 is formed between the main body 12 and the electrode tip 13, where a part of the base material and a part of the electrode tip 13 are melted.

This results in an electrode tip 13 that protrudes at least partially from the surface of the main body (base material) 12 that faces the center electrode 21 (top surface 12b in Figure 3).

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

In this embodiment, as in the first embodiment, the molten part 114 that covers the end 13b of the electrode tip 13 is present at the same position as the tip surface 13a. In other words, the surface 114a of the molten part 114 on the end 13b side is flush with the tip surface 13a of the electrode tip 13 (see FIG. 3).

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

The above-described shape of the tip of the ground electrode 11 can be formed by cutting the surface of the electrode tip 13 and the molten part 114 after welding, for example, using a cutting tool.

In this embodiment, the molten portion 114 that covers the end 13b of the electrode tip 13 is rounded, which makes it possible to prevent electric field concentration at the end 13b of the tip surface 13a.

In addition, in this embodiment, the surface 114b of the fusion zone 114 on the tip surface 12a side of the body portion 12 is provided so as to cover a part of the tip surface 12a of the body portion 12. As a result, the corner portion on the upper side (the side facing the center electrode 21) of the tip surface 12a of the body portion 12 is covered by the fusion zone 114. Therefore, when a spark discharge occurs on the tip surface 13a of the electrode tip 13, it is possible to prevent sparks from flowing toward the body portion 12 located closer to the tip side. This prevents a part of the body portion 12 (i.e., the tip portion) from being locally worn out, and a spark plug 1 with a longer life can be obtained.

Third Embodiment
Next, a third embodiment of the present invention will be described. In the third embodiment, the configuration of the fusion zone between the base metal of the ground electrode and the electrode tip is different from that of the first embodiment. Other configurations can be applied similarly to those of the first embodiment. Therefore, in the third embodiment, the differences from the first embodiment will be mainly described.

Figure 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. Figure 4 is a schematic cross-sectional view of the tip portion including the electrode tip 13 of the ground electrode 11 cut in a vertical direction (axial direction) perpendicular to the tip surface 12a of the body portion 12.

The electrode tip 13 is welded to the main body (base material) 12 by, for example, resistance welding. When the electrode tip 13 is welded to the main body (base material) 12, a molten zone 214 is formed between the main body 12 and the electrode tip 13, where a part of the base material and a part of the electrode tip 13 are melted.

This results in an electrode tip 13 that protrudes at least partially from the surface of the main body (base material) 12 that faces the center electrode 21 (top surface 12b in Figure 4).

As shown in FIG. 4, at least a portion of the end 13b of the electrode tip 13 on the tip surface 12a side of the main body 12 is covered with a molten portion 214. The molten portion 214 that covers the end 13b of the electrode tip 13 is rounded. That is, in the cross section of the ground electrode 11 shown in FIG. 4, the surface of the molten portion 214 has a curved R-shape. The same configuration as in the first embodiment can be applied to this R-shape.

In this embodiment, as in the first embodiment, the molten part 214 that covers the end 13b of the electrode tip 13 is present at the same position as the tip surface 13a. In other words, the surface 214a of the molten part 214 on the end 13b side is flush with the tip surface 13a of the electrode tip 13 (see FIG. 4).

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

The above-described shape of the tip of the ground electrode 11 can be formed by cutting the surfaces of the electrode tip 13, the molten part 214, and the main body 12 after welding, for example, using a cutting tool.

According to the above configuration, the molten part 214 covering the end 13b of the electrode tip 13 is rounded, which makes it possible to suppress electric field concentration at the end 13b of the tip surface 13a. In addition, the surface of the corner 212c of the body part 12 that is not covered by the molten part 214 is rounded, which makes it possible to suppress sparks from flowing toward the body part (base material) 12 located closer to the tip when a spark discharge occurs on the tip surface 13a of the electrode tip 13. This prevents localized wear of a part of the body part 12 (i.e., the tip part), resulting in a spark plug 1 with a longer life.

Fourth Embodiment
Next, a fourth embodiment of the present invention will be described. In the fourth embodiment, the configuration of the fusion zone between the base metal of the ground electrode and the electrode tip is different from that of the first embodiment. Other configurations can be applied similarly to those of the first embodiment. Therefore, in the fourth embodiment, the differences from the first embodiment will be mainly described.

Figure 5 shows a cross-sectional configuration of the tip portion of the ground electrode 11 of the spark plug 1 according to the fourth embodiment. Figure 5 is a schematic cross-sectional view of the tip portion including the electrode tip 13 of the ground electrode 11 cut in a vertical direction (axial direction) perpendicular to the tip surface 12a of the body portion 12.

The electrode tip 13 is welded to the main body (base material) 12 by, for example, resistance welding. When the electrode tip 13 is welded to the main body (base material) 12, a molten zone 314 is formed between the main body 12 and the electrode tip 13, where a part of the base material and a part of the electrode tip 13 are melted.

This results in an electrode tip 13 that protrudes at least partially from the surface of the main body (base material) 12 that faces the center electrode 21 (top surface 12b in Figure 5).

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

In this embodiment, the molten part 314 that covers the end 13b of the electrode tip 13 is located at a position higher than the tip surface 13a. In other words, the surface 314a of the molten part 314 on the end 13b side is provided so as to cover a part of the tip surface 13a of the electrode tip 13 (see FIG. 5). This is different from the first embodiment.

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 Figure 5).

The above-described shape of the tip of the ground electrode 11 can be formed by cutting the surface of the electrode tip 13 and the molten part 314 after welding, for example, using a cutting tool.

As described above, the spark plug 1 according to this embodiment includes the center electrode 21, the metal shell 30, and the ground electrode 11. The ground electrode 11 includes the body portion (base material) 12 and the electrode tip 13 joined to the body portion 12. The electrode tip 13 protrudes from the upper surface 12b of the body portion 12 and has a tip surface 13a facing the center electrode 21. Between the body portion 12 and the electrode tip 13, there is a fusion zone 314 that joins them. At least a portion of the end portion 13b of the electrode tip 13 located on the tip surface 12a side of the body portion 12 is covered with the fusion zone 314. The fusion zone 314 present at the end portion 13b of the electrode tip 13 is rounded and exists at a position higher than the tip surface 13a.

According to the above configuration, the molten part 314 that covers the end 13b of the electrode tip 13 is rounded, which makes it possible to suppress electric field concentration at the end 13b of the tip surface 13a. In addition, since this rounded molten part 14 is located at a position higher than the tip surface 13a, the corner part of the boundary between the tip surface 13a and the end 13b of the electrode tip 13 is covered by the molten part 314. This makes it possible to suppress electric field concentration at the corner part of the electrode tip 13.

Fifth embodiment
Next, a fifth embodiment of the present invention will be described. In the fifth embodiment, the configuration of the fusion zone between the base metal of the ground electrode and the electrode tip is different from that of the first embodiment. Other configurations can be applied similarly to those of the first embodiment. Therefore, in the fifth embodiment, the differences from the first embodiment will be mainly described.

Figure 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. Figure 6 is a schematic cross-sectional view of the tip portion including the electrode tip 13 of the ground electrode 11 cut in a vertical direction (axial direction) perpendicular to the tip surface 12a of the body portion 12.

The electrode tip 13 is welded to the main body (base material) 12 by, for example, resistance welding. When the electrode tip 13 is welded to the main body (base material) 12, a molten part 414 is formed between the main body 12 and the electrode tip 13, where a part of the base material and a part of the electrode tip 13 are melted.

This results in an electrode tip 13 that protrudes at least partially from the surface of the main body (base material) 12 that faces the center electrode 21 (top surface 12b in Figure 6).

As shown in FIG. 6, at least a portion of the end 13b of the electrode tip 13 on the tip surface 12a side of the main body 12 is covered with a molten portion 414. The molten portion 414 that covers the end 13b of the electrode tip 13 is rounded. That is, in the cross section of the ground electrode 11 shown in FIG. 6, the surface of the molten portion 414 has a curved R-shape. The same configuration as in the first embodiment can be applied to this R-shape.

In this embodiment, the molten part 414 that covers the end 13b of the electrode tip 13 is located at a position higher than the tip surface 13a. In other words, the surface 414a of the molten part 414 on the end 13b side is provided so as to cover a part of the tip surface 13a of the electrode tip 13 (see FIG. 6). This is different from the first embodiment.

The surface 414b of the fusion zone 414 on the tip end surface 12a side of the body 12 is provided so as to cover a portion of the tip end surface 12a of the body 12 (see FIG. 6). This is also different from the first embodiment.

The above-described shape of the tip of the ground electrode 11 can be formed by cutting the surface of the electrode tip 13 and the molten part 314 after welding, for example, using a cutting tool.

According to the above configuration, the molten portion 414 covering the end 13b of the electrode tip 13 is rounded, which makes it possible to suppress electric field concentration at the end 13b of the tip surface 13a. In addition, the surface 414b of the molten portion 414 on the tip surface 12a side of the body portion 12 is provided to cover a part of the tip surface 12a of the body portion 12, which makes it possible to suppress sparks from flowing toward the body portion 12 located closer to the tip when a spark discharge occurs on the tip surface 13a of the electrode tip 13. This prevents a part of the body portion 12 (i.e., the tip portion) from being locally worn out, making it possible to obtain a spark plug 1 with a longer life.

Sixth Embodiment
Next, a sixth embodiment of the present invention will be described. In the sixth embodiment, the configuration of the fusion zone between the base metal of the ground electrode and the electrode tip is different from that of the first embodiment. Other configurations can be applied similarly to those of the first embodiment. Therefore, in the sixth embodiment, the differences from the first embodiment will be mainly described.

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

The electrode tip 13 is welded to the main body (base material) 12 by, for example, resistance welding. When the electrode tip 13 is welded to the main body (base material) 12, a molten zone 514 is formed between the main body 12 and the electrode tip 13, where a part of the base material and a part of the electrode tip 13 are melted.

This results in an electrode tip 13 that protrudes at least partially from the surface of the main body (base material) 12 that faces the center electrode 21 (top surface 12b in Figure 7).

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

In this embodiment, as in the fourth embodiment, the molten portion 514 that covers the end portion 13b of the electrode tip 13 is located at a position higher than the tip surface 13a. In other words, the surface 514a of the molten portion 514 on the end portion 13b side is provided so as to cover a portion of the tip surface 13a of the electrode tip 13 (see FIG. 7).

In addition, the surface 514b of the fusion zone 514 on the tip surface 12a side of the main body 12 is not covered by the tip surface 12a of the main body 12, as in the third embodiment. That is, the corner 212c on the upper side of the tip surface 12a (the side facing the center electrode 21) is exposed. And the corner 212c of the main body 12 is rounded. That is, in the cross section of the ground electrode 11 as shown in FIG. 7, the surface of the corner 212c of the main body 12 has a curved R shape.

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

According to the above configuration, the molten portion 514 covering the end 13b of the electrode tip 13 is rounded, which makes it possible to suppress electric field concentration at the end 13b of the tip surface 13a. In addition, the surface of the corner 212c of the body portion 12 that is not covered by the molten portion 514 is rounded, which makes it possible to suppress sparks from flowing toward the body portion (base material) 12 located closer to the tip when a spark discharge occurs on the tip surface 13a of the electrode tip 13. This prevents localized wear of a portion of the body portion 12 (i.e., the tip portion), resulting in a spark plug 1 with a longer life.

The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not by the above description, and is intended to include all modifications equivalent to the claims and within the scope thereof. Furthermore, configurations obtained by combining the configurations of the embodiments described in this specification are also included in the scope of the present invention.

1: Spark plug 11: Ground electrode 12: Main body (base material)
12a: tip surface (of the main body) 12b: upper surface (of the main body) (surface facing the center electrode of the base material)
13: Electrode tip 13a: (Electrode tip) tip surface 13b: (Electrode tip) end portion 14: Melted portion 21: Center electrode 30: Metal shell 50: Insulator 114: Melted portion 214: Melted portion 314: Melted portion 414: Melted portion 514: Melted portion

Claims (1)

A center electrode;
a metal shell extending along an axis and insulating and holding the center electrode;
a base metal having one end connected to the metallic shell; and a ground electrode having an electrode tip at the other end of the base metal, the electrode tip being joined to the base metal on the one end side of a tip surface of the other end,
the electrode tip has a tip surface facing the center electrode in the axial direction and protrudes from an opposing surface of the base material facing the center electrode in the axial direction,
A spark plug in which a fusion zone is interposed between the base material and the electrode tip, the fusion zone joining the base material and the electrode tip,
At least a portion of the end of the electrode tip on the tip surface side is covered with the fusion zone,
The fusion zone at the end is rounded,
a part of the tip surface is covered with the molten portion, and the molten portion is present at a position higher than the tip surface;
a corner portion of the tip surface of the other end portion of the base material facing the center electrode is not covered by the molten portion and is exposed, and the corner portion is rounded;
Spark plug.

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