JP7203697B2 - Spark plug - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug, and more particularly to a spark plug having a ground electrode with a tip joined to a base material.

A spark plug is known that includes a metal shell fixed to an engine, a ground electrode having a tip joined to a base material connected to the metal shell, and a center electrode insulated and held by the metal shell. In this type of spark plug, when the insulation between the ground electrode and the center electrode is broken, sparks are generated in the discharge path between the tip of the ground electrode and the center electrode. When the flow of the air-fuel mixture in the combustion chamber of the engine stretches the discharge path downstream, the discharge path is formed not only between the tip and the center electrode but also between the base material and the center electrode. The spark consumption of the material becomes intense.

As a technique for suppressing spark consumption of the base material, in the technique disclosed in Patent Document 1 (see FIG. 25B in particular), a part of a rectangular parallelepiped chip is joined to a recess connected to the end surface of the base material, and the chip is The remaining part protrudes from the end face of the base material to form a spark gap between the tip and the center electrode. This makes it easier to form a discharge path between the rest of the tip protruding from the base material and the center electrode, thereby suppressing spark consumption of the base material.

Japanese Patent Application Laid-Open No. 2001-210447

However, in the technique of Patent Document 1, since the four surfaces of the chip are buried in the base material, the ratio of the discharge surface of the chip that contributes to the discharge between the center electrode and the surface area of the chip is the area buried in the base material. There is a problem that it becomes smaller by the amount of . If the protruding length of the chip from the end face of the base material is increased in order to increase the ratio of the discharge surface, the stress concentrates on the protruding part of the chip, making the chip more likely to break or fall off from the base material. There is a problem that

SUMMARY OF THE INVENTION The present invention has been made to solve this problem, and it is an object of the present invention to provide a spark plug capable of increasing the proportion of the discharge surface of the tip while preventing the tip of the ground electrode from being damaged or falling off.

To achieve this object, the spark plug of the present invention comprises a center electrode, a metal shell for insulating and holding the center electrode, a rod-shaped base material having the other end connected to the metal shell, and one end of the base material. and a ground electrode having a ground electrode having a chip disposed on the base member, and one end of the base material has a first surface facing the center electrode and formed with a recess, and the one end side connected to the first surface. a second surface and a third surface extending from the second surface to the other end side, the recess is connected from the second surface to the third surface, the chip is joined to the recess, and the discharge of the center electrode A first discharge surface facing the surface and facing the same direction as the first surface, a second discharge surface facing the same direction as the second surface, and a third discharge surface facing the same direction as the third surface, At least part of the discharge surface of the center electrode exists within a range obtained by projecting the first discharge surface in a direction perpendicular to the first discharge surface, and the first discharge surface smoothly continues to the first surface.

Further, the spark plug of the present invention includes a center electrode, a metal shell for insulating and holding the center electrode, a rod-shaped base material whose other end is connected to the metal shell, and one end of the base material. and a ground electrode having a chip, wherein one end of the base material faces the center electrode and has a first surface formed with a recess, and is connected to the first surface from the one end side to the other end side. a second surface and a third surface extending to the second surface and the third surface, wherein the recess is separated from the end surface of the base material on the one end side and connected from the second surface to the third surface, and the chip is joined to the recess a first discharge surface facing the discharge surface of the center electrode and facing the same direction as the first surface; a second discharge surface facing the same direction as the second surface; and a third discharge surface facing the same direction as the third surface. 3 discharge surfaces, wherein at least part of the discharge surface of the center electrode exists within a range obtained by projecting the first discharge surface in a direction perpendicular to the first discharge surface.

According to the spark plug of claims 1 and 2, the recess formed in the first surface of the base material facing the center electrode extends from the second surface to the third surface of the base material. The chip bonded to the recess has a first discharge surface facing the discharge surface of the center electrode oriented in the same direction as the first surface, and at least a part of the discharge surface of the center electrode oriented in a direction perpendicular to the first discharge surface. It exists within the projected range of the first discharge surface. The second discharge surface of the chip faces in the same direction as the second surface and the third discharge surface faces in the same direction as the third surface. In addition to the first discharge surface, there are the second discharge surface and the third discharge surface that contribute to the discharge with the center electrode, so the proportion of the discharge surface can be increased. Furthermore, although stress tends to concentrate on a portion of the chip that protrudes from the first surface, the first discharge surface is smoothly connected to the first surface to eliminate this portion, so damage to the chip can be suppressed.
Since the length of the side surface of the recess can be made longer than the thickness of the chip from the first surface of the base material, the clutch can be extended to the end of the side surface by the length of the side surface compared to the case where the length of the side surface is equal to the thickness of the chip. It can be difficult to progress. Therefore, it is possible to prevent the chip from coming off due to the cracks starting from the boundary between the first discharge surface and the first surface.

According to the spark plug of claim 3 , the depression formed in the first surface of the base material facing the center electrode is connected to the second surface and the third surface of the base material. The chip bonded to the recess has a first discharge surface facing the discharge surface of the center electrode oriented in the same direction as the first surface, and at least a part of the discharge surface of the center electrode oriented in a direction perpendicular to the first discharge surface. It exists within the projected range of the first discharge surface. The second discharge surface of the chip faces in the same direction as the second surface and the third discharge surface faces in the same direction as the third surface. In addition to the first discharge surface, there are the second discharge surface and the third discharge surface that contribute to the discharge with the center electrode, so the proportion of the discharge surface can be increased. Furthermore, since the recess is separated from the end surface of the base material and a portion of the base material is located closer to the end surface than the chip, the chip is less likely to fall out of the recess.

According to the spark plug of claim 4 , the first discharge surface smoothly continues to the first surface. Stress tends to concentrate on the portion of the chip that protrudes from the first surface, but by eliminating this portion, in addition to the effect of claim 3 , damage to the chip can be suppressed.

According to the spark plug of claim 5 , a diffusion layer or a melted portion is formed between the tip and the side surface of the recess that is continuous with the first surface on the cut surface that is perpendicular to the first discharge surface and parallel to the second surface. be. Cracks tend to propagate along the boundary between the side surface of the dent and the chip, but since the length of the side surface of the dent on the cutting surface is longer than the thickness of the chip from the first surface, The crack that has progressed along the boundary from the dent can be made difficult to grow to the end of the side surface of the dent. Therefore, in addition to the effects of any one of claims 1 to 4 , it is possible to suppress drop-off of chips due to cracks that have progressed along the boundary.

1 is a half sectional view of a spark plug in a first embodiment; FIG. 3 is a perspective view of a center electrode and a ground electrode in the first embodiment; FIG. FIG. 3 is a front view of the center electrode and the ground electrode as seen from the direction of arrow III in FIG. 2; 4 is a cross-sectional view of the center electrode and the ground electrode taken along line IV-IV of FIG. 3; FIG. FIG. 10 is a perspective view of a center electrode and a ground electrode of a spark plug according to a second embodiment; FIG. 10 is a cross-sectional view of a center electrode and a ground electrode in a second embodiment; FIG. 11 is a perspective view of a center electrode and a ground electrode of a spark plug according to a third embodiment; FIG. 10 is a cross-sectional view of a center electrode and a ground electrode in a third embodiment; FIG. 11 is a cross-sectional view of a center electrode and a ground electrode of a spark plug according to a fourth embodiment;

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. FIG. 1 is a half sectional view of the spark plug 10 of the first embodiment taken along the axis O. As shown in FIG. In FIG. 1, the lower side of the page is called the front end side of the spark plug 10, and the upper side of the page is called the rear end side of the spark plug 10 (the same applies to FIGS. 2 to 9). As shown in FIG. 1, the spark plug 10 includes an insulator 11, a center electrode 20, a metal shell 30 and a ground electrode 40. As shown in FIG.

The insulator 11 is a substantially cylindrical member having an axial hole 12 along the axis O, and is made of ceramic such as alumina, which has excellent mechanical properties and high-temperature insulation. The insulator 11 is formed with a rear end-facing surface 13, which is an annular surface facing the rear end side, on the front end side of the inner peripheral surface formed by the shaft hole 12. As shown in FIG. The rear end facing surface 13 is tapered toward the distal end side.

The center electrode 20 is a rod-shaped member whose head portion 21 is engaged with the rear end facing surface 13 , and the shaft portion 22 is disposed in the shaft hole 12 on the distal end side of the rear end facing surface 13 . In the center electrode 20, a bottomed cylindrical base material containing Ni as a main component covers a core material containing copper as a main component. The base material has a composition containing 50 wt % or more of Ni. It is possible to omit the core material. A portion including the tip of the shaft portion 22 of the center electrode 20 is exposed from the shaft hole 12 to the tip side. The center electrode 20 is electrically connected to a terminal fitting 24 inside the shaft hole 12 .

The terminal fitting 24 is a rod-shaped member to which a high-voltage cable (not shown) is connected, and is made of a conductive metal material (such as low-carbon steel, for example). The terminal fitting 24 is fixed to the rear end of the insulator 11 with its tip end inserted into the shaft hole 12 .

The metal shell 30 is a substantially cylindrical member made of a conductive metal material (such as low-carbon steel). The metal shell 30 surrounds the tip side of the insulator 11 and holds the insulator 11 inside. A male thread 32 is formed on the outer peripheral surface of the tip portion 31 of the metallic shell 30 . The male thread 32 is a portion that is screwed into a threaded hole of an engine (not shown). The metal shell 30 includes a seat portion 33 connected to the rear end side of the tip portion 31 and a tool engaging portion 34 connected to the rear end side of the seat portion 33 .

The seat portion 33 is a portion for blocking a gap between a screw hole of an engine (not shown) and the screw 32 , and has an outer diameter larger than that of the tip portion 31 . The tool engaging portion 34 is a portion with which a tool such as a wrench is engaged when tightening the male screw 32 in the threaded hole of the engine. A ground electrode 40 is connected to the distal end portion 31 of the metallic shell 30 .

The ground electrode 40 includes a rod-shaped base material 41 whose main component is Ni, and a tip 60 (see FIG. 2) which is joined to the base material 41 and whose main component is a noble metal. The chip 60 is joined to one end portion 42 of the base material 41 , and the other end portion 43 is connected to the metallic shell 30 . The base material 41 is bent from one end 42 to the other end 43 . The base material 41 has a composition containing 50 wt % or more of Ni. It is possible for the base material 41 to cover a copper-based core material (not shown). The tip 60 has a composition containing 50 wt % or more in total of one or more of noble metals such as Pt, Rh, Ir, and Ru.

FIG. 2 is a perspective view of the center electrode 20 and the ground electrode 40. FIG. 2 shows one end 42 (see FIG. 1) of the base material 41 to which the tip 60 is joined in the ground electrode 40, and the other end 43 (see FIG. 1) of the base material 41 is omitted. there is One end portion 42 of the base material 41 includes a first surface 44 including a first side 45 and a second side 46, a second surface 47 connected to the second side 46 of the first surface 44, and the first surface 44. A third surface 48 connected to the first side 45 and a fourth surface 49 connecting the second surface 47 and the third surface 48 are provided.

The first surface 44 is a surface facing the discharge surface 23 at the tip of the shaft portion 22 of the center electrode 20 . The second surface 47 , the third surface 48 and the fourth surface 49 are connected to the end surface 50 . The first surface 44 , the second surface 47 , the third surface 48 and the fourth surface 49 extend from the one end portion 42 (see FIG. 1 ) side where the end surface 50 is located to the other end portion 43 side. A recess 51 is formed in the first surface 44 of the base material 41 . A recess 51 extends from the second surface 47 to the third surface 48 . The tip 60 has a substantially rectangular parallelepiped shape and is joined to the recess 51 .

3 is a front view of the center electrode 20 and the ground electrode 40 viewed from the direction of arrow III in FIG. 2, and FIG. 4 is a cross-sectional view of the center electrode 20 and the ground electrode 40 along line IV-IV in FIG. As shown in FIG. 4 , the side surface 52 of the recess 51 connects to the first surface 44 and the bottom surface 53 of the recess 51 connects from the side surface 52 to the end surface 50 . In this embodiment, the side surface 52 is an inclined surface that recedes from the end surface 50 as it approaches the bottom surface 53, and the corner formed by the side surface 52 and the bottom surface 53 is rounded.

Returning to FIG. 2, description will be made. The tip 60 has a first discharge surface 61 facing the same direction as the first surface 44 at the one end 42 , a second discharge surface 62 facing the same direction as the second surface 47 , and a third discharge surface 62 facing the same direction as the third surface 48 . A third discharge surface 63 and a fourth discharge surface 64 facing in the same direction as the end surface 50 are provided. The first discharge surface 61 is connected to the second discharge surface 62 , the third discharge surface 63 and the fourth discharge surface 64 .

The fact that each discharge surface of the chip 60 faces in the same direction as each surface of the base material 41 means that when each discharge surface of the chip 60 is viewed from a direction perpendicular to each surface of the base material 41, the discharge surface can be seen. Say things. That is, to explain the relationship between the first surface 44 and the first discharge surface 61 by way of example, a straight line perpendicular to the plane including the first surface 44 on the side of the first discharge surface 61 intersects the first discharge surface 61 . Say. It is not necessary for the first surface 44 and the first discharge surface 61 to be positioned on the same plane, or for the first surface 44 and the first discharge surface 61 to be parallel. The relationship between the other surface of the base material 41 and the other discharge surface of the chip 60 is the same as the relationship between the first surface 44 and the first discharge surface 61 .

In this embodiment, the first discharge surface 61 smoothly connects to the first surface 44, the second discharge surface 62 smoothly connects to the second surface 47, the third discharge surface 63 smoothly connects to the third surface 48, The fourth discharge surface 64 smoothly continues to the end surface 50 . That is, the distance between the second discharge surface 62 and the third discharge surface 63 of the tip 60 is the same as the distance between the second surface 47 and the third surface 48 of the base material 41 . That each discharge surface of the tip 60 is smoothly connected to each surface of the base material 41 means that the step between the discharge surface of the tip 60 and each surface of the base material 41 connected thereto is 20 μm or less. The height of each discharge surface of the chip 60 is the same as the height of each surface of the base material 41 connected to the discharge surface, or higher than each surface of the base material 41 connected to the discharge surface.

As shown in FIGS. 3 and 4, the first discharge surface 61 of the tip 60 of the ground electrode 40 faces the discharge surface 23 of the center electrode 20 with the spark gap G therebetween. At least part of the discharge surface 23 of the center electrode 20 exists within a range 67 obtained by projecting the first discharge surface 61 in a direction perpendicular to the first discharge surface 61 . In this embodiment, the entire discharge surface 23 exists within the range 67 . 3 (the paper surface of FIG. 4) is a plane perpendicular to the first discharge surface 61 and parallel to the second surface 47. As shown in FIG.

As shown in FIG. 4 , the side surface 65 of the chip 60 is an inclined surface that recedes from the fourth discharge surface 64 as it approaches the bottom surface 66 from the first discharge surface 61 , and has a shape that follows the side surface 52 of the recess 51 . The corner formed by the side surface 65 and the bottom surface 66 of the chip 60 is rounded. A diffusion layer 54 is formed between the side surface 52 of the recess 51 of the base material 41 and the side surface 65 of the chip 60 and between the bottom surface 53 of the recess 51 and the bottom surface 66 of the chip 60 . The diffusion layer 54 joins the base material 41 and the tip 60 by diffusion of atoms (atomic bonding) generated between the base material 41 and the tip 60 .

Since the side surface 52 of the recess 51 in FIG. 4 is an inclined surface, the length of the side surface 52 measured along the side surface 52 is equal to the thickness T of the chip 60 from the first surface 44 of the base material 41 (the first surface 44 and the chip 60 to the bottom surface 66). In addition, since the corner formed by the side surface 52 and the bottom surface 53 of the recess 51 is rounded, the length of the side surface 52 measured along the side surface 52 is the length of the chip 60 from the first surface 44 of the base material 41. longer than the thickness T.

The ground electrode 40 is manufactured by, for example, the following method. First, a plate material as a material of the base material 41 is prepared. The top and bottom surfaces of the plate are rectangular. A first surface 44 of the base material 41 is formed by the upper surface of the plate material. A fourth surface 49 of the base material 41 is formed by the lower surface of the plate material. An end surface 50 of the base material 41 is formed by one side surface connecting the upper surface and the lower surface of the plate material.

Next, a recess 51 is formed in the plate member from one side surface thereof to the upper surface thereof. After placing the plate material of the chip 60 on the recess 51 , the plate material of the chip 60 is diffusion-bonded to the plate material of the base material 41 by heating and pressurizing. Next, the diffusion-bonded plate material is cut into rectangular members so that the plate material for the chip 60 and the plate material for the base material 41 are included in the cut rectangular members. A second surface 47 and a third surface 48 of the base material 41 and a second discharge surface 62 and a third discharge surface 63 of the chip 60 are formed by the cut surfaces at this time. Thereby, a strip-shaped ground electrode 40 is obtained.

By appropriately adjusting the size of the plate material that is the material of the base material 41, the length of the obtained strip-shaped member in the longitudinal direction can be adjusted along the longitudinal direction of the base material 41 in the spark plug 10 to be manufactured. can be equal to the length Of course, after obtaining a strip-shaped member, the length in the longitudinal direction may be adjusted.

The spark plug 10 is manufactured by, for example, the following method. First, the center electrode 20 is inserted into the shaft hole 12 of the insulator 11 and arranged so that the discharge surface 23 is exposed to the outside from the shaft hole 12 . Next, while inserting the terminal fitting 24 into the shaft hole 12 , the terminal fitting 24 and the center electrode 20 are electrically connected, and then the metallic shell 30 to which the ground electrode 40 is preliminarily joined is assembled to the outer circumference of the insulator 11 . The strip-shaped base material 41 of the ground electrode 40 is bent so that the first discharge surface 61 of the tip 60 faces the center electrode 20 to obtain the spark plug 10 .

The end surface 50 of the base material 41 of the ground electrode 40 and the fourth discharge surface 64 of the tip 60 heat and heat the plate material that is the material of the base material 41 and the plate material that is the material of the tip 60 when the ground electrode 40 is manufactured. This is the surface that remains under pressure. Since the end surface 50 and the fourth discharge surface 64 are not formed by press cutting using a nipper or the like, the cut surface is crushed and the end surface 50 and the fourth discharge surface 64 do not spread outside the second surface 47 and the third surface 48. can be done. As a result, the flame-extinguishing effect of the end surface 50 and the fourth discharge surface 64 is less likely to occur.

When the spark plug 10 is installed in an engine (not shown), the discharge surface 23 of the center electrode 20 and the ground electrode 40 are exposed to the combustion chamber. The spark plug 10 is arranged in the engine, for example, with the third surface 48 of the base material 41 directed upstream of the airflow of the air-fuel mixture in the combustion chamber, and the second surface 47 directed downstream (exhaust valve side).

When the flow velocity of the air-fuel mixture in the combustion chamber is slow, the discharge path is mainly formed between the discharge surface 23 of the center electrode 20 and the first discharge surface 61 of the tip 60 . On the other hand, when the flow velocity of the air-fuel mixture increases, for example in a lean burn engine, the discharge path is stretched downstream, and a discharge path is formed between the discharge surface 23 of the center electrode 20 and the second discharge surface 62 of the tip 60. obtain. As a result, spark consumption of the base material 41 (second surface 47) can be suppressed.

A side surface 65 and a bottom surface 66 of the chip 60 are buried in the recess 51 of the base material 41, but the second discharge surface 62 and the third discharge surface 63 are exposed together with the first discharge surface 61. FIG. As a result, the proportion of the discharge surface of the tip 60 that contributes to the discharge between the center electrode 20 can be increased. In addition, since there is the fourth discharge surface 64, the proportion of the discharge surface of the tip 60 can be further increased. Furthermore, the portion of the chip 60 that protrudes from the first surface 44 is likely to undergo stress concentration and cracks easily. Therefore, damage to the chip 60 can be suppressed.

Similarly, since the second discharge surface 62 is smoothly connected to the second surface 47, breakage of the portion of the tip 60 protruding from the second surface 47 can be suppressed. In addition, since the third discharge surface 63 is smoothly connected to the third surface 48, breakage of the portion of the tip 60 protruding from the third surface 48 can be suppressed. Furthermore, since the fourth discharge surface 64 is smoothly connected to the end surface 50, damage to the portion of the tip 60 protruding from the end surface 50 can be suppressed.

In the ground electrode 40, the boundary between the first discharge surface 61 and the first surface 44 tends to be the starting point of breakage due to the difference between the coefficient of linear expansion of the tip 60 and the coefficient of linear expansion of the base material 41. FIG. A crack originating from this point tends to propagate along the diffusion layer 54 at the boundary between the side surface 52 of the recess 51 and the side surface 65 of the chip 60 . However, since the length of the side surfaces 52 of the recess 51 is greater than the thickness T of the tip 60 from the first surface 44 , the side surfaces 52 are wider than if the length of the side surfaces 52 were equal to the thickness T of the tip 60 . The longer length makes it difficult for cracks to propagate to the end of the side surface 52 (bottom surface 53). Therefore, it is possible to prevent the chip 60 from coming off due to cracks that have developed along the boundary.

A second embodiment will be described with reference to FIGS. 5 and 6. FIG. In the first embodiment, the case where the recess 51 to which the chip 60 is joined extends from the first surface 44 of the base material 41 to the end surface 50 has been described. On the other hand, in the second embodiment, a case where the recess 81 is separated from the end surface 80 of the base material 72 will be described. The same reference numerals are given to the same parts as those described in the first embodiment, and the following description is omitted.

FIG. 5 is a perspective view of the center electrode 20 and the ground electrode 71 of the spark plug 70 according to the second embodiment. FIG. 6 is a cross-sectional view of the center electrode 20 and the ground electrode 71. As shown in FIG. The ground electrode 71 in the second embodiment is arranged instead of the ground electrode 40 of the spark plug 10 in the first embodiment. 5 and 6 show one end portion 42 (see FIG. 1) of the base material 72 to which the chip 90 is joined in the ground electrode 71, and show the other end portion 43 (see FIG. 1) of the base material 72. FIG. omitted (the same applies to FIGS. 7 to 9).

As shown in FIG. 5, one end portion 42 of the base material 72 has a first surface 74 including a first side 75 and a second side 76 and a second surface 77 connected to the second side 76 of the first surface 74. , a third surface 78 connecting the first side 75 of the first surface 74 and a fourth surface 79 connecting the second surface 77 and the third surface 78 . The first surface 74 is a surface facing the discharge surface 23 at the tip of the shaft portion 22 of the center electrode 20 . The second surface 77 , third surface 78 and fourth surface 79 are connected to the end surface 80 . The first surface 74 , the second surface 77 , the third surface 78 and the fourth surface 79 extend from the one end portion 42 (see FIG. 1 ) side where the end surface 80 is located to the other end portion 43 side. A recess 81 is formed on the first surface 74 of the base material 72 . A recess 81 is spaced apart from the end surface 80 and extends from the second surface 77 to the third surface 78 . The chip 90 has a substantially rectangular parallelepiped shape and is joined to the recess 81 .

As shown in FIG. 6 , side surfaces 82 and 83 of recess 81 are connected to first surface 74 and bottom surface 84 of recess 81 is connected to side surfaces 82 and 83 . In this embodiment, the side surface 82 is an inclined surface that recedes from the end surface 80 as the bottom surface 84 is approached, and the side surface 83 is an inclined surface that approaches the end surface 80 as the bottom surface 84 is approached. The corner formed by the side surface 82 and the bottom surface 84 and the corner formed by the side surface 83 and the bottom surface 84 are rounded.

Returning to FIG. 5, description will be made. The chip 90 has a first discharge surface 91 facing in the same direction as the first surface 74 at the one end 42 (see FIG. 1), a second discharge surface 92 facing in the same direction as the second surface 77, and a third surface 78. and a third discharge surface 93 facing in the same direction. The first discharge surface 91 is connected to the second discharge surface 92 and the third discharge surface 93 . In this embodiment, the first discharge surface 91 smoothly connects to the first surface 74 , the second discharge surface 92 smoothly connects to the second surface 77 , and the third discharge surface 93 smoothly connects to the third surface 78 . That is, the distance between the second discharge surface 92 and the third discharge surface 93 of the chip 90 is the same as the distance between the second surface 77 and the third surface 78 of the base material 72 .

As shown in FIG. 6, the first discharge surface 91 of the tip 90 of the ground electrode 71 faces the discharge surface 23 of the center electrode 20 with the spark gap G therebetween. At least part of the discharge surface 23 of the center electrode 20 exists within a range 97 of the first discharge surface 91 projected in a direction perpendicular to the first discharge surface 91 . In this embodiment, the entire discharge surface 23 exists within the range 97 .

A side surface 94 of the chip 90 is an inclined surface that recedes from the end surface 80 of the base material 72 as it approaches the bottom surface 96 from the first discharge surface 91 , and has a shape that follows the side surface 82 of the recess 81 . The corners formed by the side surface 94 and the bottom surface 96 of the chip 90 are rounded. A side surface 95 of the chip 90 is an inclined surface that approaches the end surface 80 of the base material 72 as it approaches the bottom surface 96 from the first discharge surface 91 , and has a shape that follows the side surface 83 of the recess 81 . The corner formed by the side surface 95 and the bottom surface 96 of the chip 90 is rounded.

between the side surface 82 of the recess 81 of the base material 72 and the side surface 94 of the chip 90, between the side surface 83 of the recess 81 and the side surface 95 of the chip 90, and between the bottom surface 84 of the recess 81 and the bottom surface 96 of the chip 90 , a diffusion layer 85 is formed. The diffusion layer 85 joins the base material 72 and the tip 90 by diffusion of atoms (atomic bonding) generated between the base material 72 and the tip 90 .

Since the side surface 82 of the recess 81 is an inclined surface, the length of the side surface 82 measured along the side surface 82 is equal to the thickness T of the chip 90 from the first surface 74 of the base material 72 (the first surface 74 and the bottom surface of the chip 90 96). Similarly, since the side surfaces 83 of the recess 81 are inclined surfaces, the length of the side surfaces 83 measured along the side surfaces 83 is greater than the thickness T of the tip 90 from the first surface 74 of the base material 72 . In addition, since the corner formed by the side surface 82 and the bottom surface 84 of the recess 81 is rounded, the length of the side surface 82 measured along the side surface 82 is the length of the chip 90 from the first surface 74 of the base material 72 . longer than the thickness T; Similarly, since the corners formed by the side 83 and bottom 84 of the recess 81 are rounded, the length of the side 83 measured along the side 83 is approx. is longer than the thickness T of the

The ground electrode 71 is manufactured by, for example, fitting a plate material for the chip 90 into a recess 81 formed in the upper surface of a plate material for the base material 72, and then heating and pressurizing the chip 90. A plate material as a material is diffusion-bonded to a plate material as a material of the base material 72 . Next, the diffusion-bonded plate material is cut into rectangular members so that the plate material for the chip 90 and the plate material for the base material 72 are included in the rectangular members after cutting. A ground electrode 71 is thus obtained.

Side surfaces 94 , 95 and a bottom surface 96 of the tip 90 of the ground electrode 71 are buried in the recess 81 of the base material 72 , but the second discharge surface 92 and the third discharge surface 93 are exposed together with the first discharge surface 91 . As a result, the proportion of the discharge surface of the tip 90 that contributes to the discharge between the center electrode 20 can be increased. Furthermore, since the recess 81 is separated from the end surface 80 of the base material 72 and a part of the base material 72 is positioned closer to the end surface 80 than the chip 90 , the chip 90 is less likely to fall out of the recess 81 . In particular, since the side surface 95 of the tip 90 is joined to the side surface 83 of the recess 81, the joining area between the tip 90 and the base material 72 can be increased accordingly. Therefore, the bonding strength of the chip 90 can be increased.

The portion of the chip 90 that protrudes from the first surface 74 tends to concentrate stress and crack easily, but the first discharge surface 91 is smoothly connected to the first surface 74 and there is no portion that protrudes from the first surface 74 . Therefore, breakage of the chip 90 can be suppressed. Similarly, since the second discharge surface 92 is smoothly connected to the second surface 77, breakage of the portion of the tip 90 protruding from the second surface 77 can be suppressed. In addition, since the third discharge surface 93 is smoothly connected to the third surface 78, breakage of the portion of the tip 90 protruding from the third surface 78 can be suppressed.

The boundary between the first discharge surface 91 and the first surface 74 of the ground electrode 71 is likely to break due to the difference between the coefficient of linear expansion of the tip 90 and the coefficient of linear expansion of the base material 72 . Cracks originating from this point are along the diffusion layer 85 at the boundary between the side surface 82 of the recess 81 and the side surface 94 of the chip 90 and the diffusion layer 85 at the boundary between the side surface 83 of the recess 81 and the side surface 95 of the chip 90. easy to progress. However, since the length of the side surfaces 82 and 83 of the recess 81 is longer than the thickness T of the chip 90 from the first surface 74, the length of the side surfaces 82 and 83 is equal to the thickness T of the chip 90. , the length of the side surfaces 82 and 83 makes it difficult for cracks to propagate to the ends of the side surfaces 82 and 83 (bottom surface 84). Therefore, it is possible to prevent the chip 90 from coming off due to cracks that have developed along the boundary.

A third embodiment will be described with reference to FIGS. 7 and 8. FIG. In the second embodiment, the case where the first discharge surface 91 of the chip 90 smoothly connects to the first surface 74 of the base material 72 has been described. In contrast, in the third embodiment, the case where there is a step between the first discharge surface 111 of the chip 110 and the first surface 74 of the base material 72 will be described. The same parts as those described in the first embodiment and the second embodiment are given the same reference numerals, and the following description is omitted. FIG. 7 is a perspective view of the center electrode 20 and the ground electrode 101 of the spark plug 100 according to the third embodiment. FIG. 8 is a cross-sectional view of the center electrode 20 and the ground electrode 101. FIG. The ground electrode 101 in the third embodiment is arranged instead of the ground electrode 40 of the spark plug 10 in the first embodiment.

As shown in FIG. 7, base material 102 of ground electrode 101 has depression 103 formed in first surface 74 . The recess 103 is spaced apart from the end surface 80 and extends from the second surface 77 to the third surface 78 . The chip 110 has a substantially rectangular parallelepiped shape and is joined to the recess 103 .

As shown in FIG. 8 , side surfaces 104 and 105 of recess 103 are connected to first surface 74 and bottom surface 106 of recess 103 is connected to side surfaces 104 and 105 . In this embodiment, the side surfaces 104 and 105 are surfaces perpendicular to the first surface 74 respectively. The corner formed by the side surface 104 and the bottom surface 106 and the corner formed by the side surface 105 and the bottom surface 106 are rounded.

Returning to FIG. 7, description will be made. The chip 110 has a first discharge surface 111 facing in the same direction as the first surface 74 at the one end 42 (see FIG. 1), a second discharge surface 112 facing in the same direction as the second surface 77, and a third surface 78. and a third discharge surface 113 facing in the same direction. The first discharge surface 111 is connected to the second discharge surface 112 and the third discharge surface 113 . In this embodiment, there is a step between the first discharge surface 111 and the first surface 74 , the second discharge surface 112 smoothly connects to the second surface 77 , and the third discharge surface 113 smoothly connects to the third surface 78 . connected to That is, the distance between the second discharge surface 112 and the third discharge surface 113 of the chip 110 is the same as the distance between the second surface 77 and the third surface 78 of the base material 72 .

As shown in FIG. 8, the first discharge surface 111 of the tip 110 of the ground electrode 101 faces the discharge surface 23 of the center electrode 20 with the spark gap G therebetween. At least part of the discharge surface 23 of the center electrode 20 exists within a range 117 obtained by projecting the first discharge surface 111 in a direction perpendicular to the first discharge surface 111 . In this embodiment, the entire discharge surface 23 exists within the range 117 . Side surfaces 114 and 115 of the chip 110 are surfaces perpendicular to the first discharge surface 111 and are shaped to follow the side surfaces 104 and 105 of the recess 103, respectively. The corners formed by the side surfaces 114, 115 and the bottom surface 116 of the chip 110 are rounded.

between the side surface 104 of the recess 103 of the base material 102 and the side surface 114 of the chip 110, between the side surface 115 of the recess 103 and the side surface 115 of the chip 110, and between the bottom surface 106 of the recess 103 and the bottom surface 116 of the chip 110 , a diffusion layer 107 is formed. The diffusion layer 107 joins the base material 102 and the tip 110 by diffusion of atoms (atomic bonding) generated between the base material 102 and the tip 110 .

The ground electrode 101 is manufactured by, for example, fitting a plate material for the chip 110 into a depression 103 formed in the upper surface of a plate material for the base material 102, and then heating and pressurizing the chip 110. A plate material as a material is diffusion-bonded to a plate material as a material of the base material 102 . A step is formed between the first discharge surface 111 and the first surface 74 by making the thickness of the plate material that is the material of the chip 110 thicker than the depth of the recess 103 . Next, the diffusion-bonded plate material is cut into rectangular members so that the plate material for the chip 110 and the plate material for the base material 102 are included in the cut rectangular members. A ground electrode 101 is thus obtained.

Since the ground electrode 101 has a step between the first discharge surface 111 of the chip 110 and the first surface 74, the exposed area of the chip 110 from the base material 102 can be increased by the step. Therefore, the proportion of the discharge surface of the chip 110 can be increased by the amount of the step. In addition, since the second discharge surface 112 is smoothly connected to the second surface 77 , damage to the portion of the chip 110 protruding from the second surface 77 can be suppressed. Since the third discharge surface 113 is smoothly connected to the third surface 78, breakage of the portion of the tip 110 protruding from the third surface 78 can be suppressed.

Since the corners formed by the side surfaces 104 and 105 of the recess 103 of the base material 102 and the bottom surface 106 are rounded, the length of the side surfaces 104 and 105 measured along the side surfaces 104 and 105 is equal to the length of the base material 102. is longer than the thickness T of the chip 110 from the first surface 74 of the . Therefore, compared to the case where the length of the side surfaces 104 and 105 is equal to the thickness T of the tip 110 from the first surface 74, the difference between the coefficient of linear expansion of the tip 110 and the coefficient of linear expansion of the base material 102 causes the tip 110 and the tip 110 to be separated from each other. It is possible to make it difficult for a crack that occurs starting from the boundary with the first surface 74 to extend to the edge of the recess 103 (bottom surface 106). Therefore, it is possible to prevent the chip 110 from coming off due to cracks that have developed along the boundary.

A fourth embodiment will be described with reference to FIG. In the third embodiment, the case where the first discharge surface 111 of the chip 110 and the first surface 74 of the base material 102 are connected on the plane of the chip 110 has been described. In contrast, in the fourth embodiment, the case where the first discharge surface 131 of the tip 130 and the first surface 74 of the base material 102 are connected by the curved surfaces 132 and 133 of the tip 130 will be described. The same parts as those described in the first embodiment and the second embodiment are given the same reference numerals, and the following description is omitted. FIG. 9 is a cross-sectional view of the center electrode 20 and the ground electrode 121 of the spark plug 120 according to the fourth embodiment. The ground electrode 121 in the fourth embodiment is arranged instead of the ground electrode 40 of the spark plug 10 in the first embodiment.

As shown in FIG. 9, the base material 122 of the ground electrode 121 has a recess 123 formed in the first surface 74 thereof. A recess 123 is spaced from the end surface 80 and extends from the second surface 77 (see FIG. 5) to the third surface 78 . The chip 130 has a substantially rectangular parallelepiped shape and is joined to the recess 123 . The side surfaces 124 and 125 of the recess 123 are connected to the first surface 74 and the bottom surface 126 of the recess 123 is connected to the side surfaces 124 and 125 . Side surface 124 is an inclined surface that recedes from end surface 80 as bottom surface 126 is approached. Side surface 125 is an inclined surface that approaches end surface 80 as bottom surface 126 is approached.

The tip 130 has a first discharge surface 131 facing in the same direction as the first surface 74 at the one end 42 (see FIG. 1) and a second discharge surface (not shown) facing in the same direction as the second surface 77 (see FIG. 5). ) and a third discharge surface (not shown) facing in the same direction as the third surface 78 (see FIG. 5). There is a step between the first discharge surface 131 and the first surface 74 , and the first discharge surface 131 and the first surface 74 are connected by curved surfaces 132 and 133 . The curved surfaces 132 and 133 are outwardly convex.

The first discharge surface 131 of the tip 130 of the ground electrode 121 faces the discharge surface 23 of the center electrode 20 with the spark gap G therebetween. At least part of the discharge surface 23 of the center electrode 20 exists within a range 137 obtained by projecting the first discharge surface 131 in a direction perpendicular to the first discharge surface 131 . In this embodiment, the entire discharge surface 23 exists within the range 137 . Side surfaces 134 and 135 of chip 130 are inclined surfaces connected to curved surfaces 132 and 133, respectively, and are shaped to follow side surfaces 124 and 125 of recess 123, respectively.

between the side surface 124 of the recess 123 of the base material 122 and the side surface 134 of the chip 130, between the side surface 125 of the recess 123 and the side surface 135 of the chip 130, and between the bottom surface 126 of the recess 123 and the bottom surface 126 of the chip 130 , a diffusion layer 127 is formed. The diffusion layer 127 joins the base material 122 and the tip 130 by diffusion of atoms (atomic bonding) generated between the base material 122 and the tip 130 .

The ground electrode 121 is manufactured by, for example, fitting a plate material for the chip 130 into a depression 123 formed in the upper surface of a plate material for the base material 122, and then heating and pressurizing the chip 130. A plate material as a material is diffusion-bonded to a plate material as a material of the base material 122 . By making the thickness of the plate material of the chip 130 thicker than the depth of the recess 123 and increasing the pressure during bonding, the chip 130 is crushed to form curved surfaces 132 and 133 . Next, the diffusion-bonded plate material is cut into rectangular members so that the plate material for the chip 130 and the plate material for the base material 122 are included in the cut rectangular members. A ground electrode 121 is thus obtained.

Since the ground electrode 121 has a step between the first discharge surface 131 of the chip 130 and the first surface 74, the exposed area of the chip 130 from the base material 122 can be increased by the step. Therefore, the proportion of the discharge surface of the chip 130 can be increased by the amount of the step. Furthermore, since the curved surfaces 132 and 133 connected to the first discharge surface 131 are formed on the chip 130, the curved surfaces 132 and 133 on which the electric field tends to concentrate can be easily formed with the discharge paths.

Since the sides 124 , 125 of the recess 123 of the base material 122 and the sides 134 , 135 of the tip 130 are inclined surfaces, the length of the sides 124 , 125 measured along the sides 124 , 125 is the first surface 74 of the base material 122 . longer than the thickness T of the chip 130 from the Therefore, compared to the case where the length of the side surfaces 124 and 125 is equal to the thickness T of the tip 130 from the first surface 74, the difference between the coefficient of linear expansion of the tip 130 and the coefficient of linear expansion of the base material 122 causes the tip 130 and the tip 130 to be separated from each other. It is possible to make it difficult for a crack that occurs starting from the boundary with the first surface 74 to extend to the end of the recess 123 (bottom surface 126). Therefore, it is possible to prevent the chip 130 from coming off due to cracks that have developed along the boundary.

Although the present invention has been described above based on the embodiments, it should be understood that the present invention is not limited to the above-described embodiments, and that various improvements and modifications are possible without departing from the scope of the present invention. It can be easily guessed.

In the embodiment, the case where the chips 60, 90, 110, 130 are bonded to the entire recesses 51, 81, 103, 123 of the base materials 41, 72, 102, 122 by the diffusion layers 54, 85, 107, 127 will be described. However, it is not necessarily limited to this. For example, diffusion layers 54, 85, 107, and 127 provide diffusion layers 54, 85, 107, and 127 between the bottom surfaces 53, 84, 106, and 126 of the recesses 51, 81, 103, and 123 and the bottom surfaces 66, 96, 116, and 136 of the chips 60, 90, 110, and . Sides 65, 94, 95, 114, 115, 134, 135 of chips 60, 90, 110, 130 and sides 52, 82, 83, 104, 105, 124, 125 of recesses 51, 81, 103, 123 It is naturally possible to join the chips 60, 90, 110, and 130 to parts of the recesses 51, 81, 103, and 123 by contacting or separating from each other. The relationship between the size of the recesses 51, 81, 103, and 123 when manufacturing the ground electrodes 40, 71, 101, and 121 and the size of the plate material of the chips 60, 90, 110, and 130, the temperature and The positions, sizes and thicknesses of the diffusion layers 54, 85, 107 and 127 are appropriately set by setting the pressure.

In the embodiment, plate materials for chips 60, 90, 110, and 130 are placed in recesses 51, 81, 103, and 123 formed in the upper surfaces of plate materials for base materials 41, 72, l02, and 122. Later, the case where the diffusion layers 54, 85, 107, 127 are formed by heating and pressurizing and holding and the chips 60, 90, 110, 130 are joined to the base materials 41, 72, 102, 122 was explained. , but not necessarily limited to this. For example, it is naturally possible to weld the tips 60, 90, 110, 130 to the base materials 41, 72, 102, 122 by resistance welding or the like.

When joining the tips 60, 90, 110, 130 to the base metals 41, 72, 102, 122 by resistance welding, the side surfaces 52, 82, 83, 104, 105, 124, 125 or between bottom surfaces 53, 84, 106, 126 and chips 60, 90, 110, 130 to form diffusion layers 54, 85, 107, 127 or to form fusion zones. can be done. A fusion zone and a diffusion layer may be mixed.

In the first embodiment, the second discharge surface 62 of the tip 60 is smoothly connected to the second surface 47 of the base material 41, and the third discharge surface 63 of the tip 60 is smoothly connected to the third surface 48 of the base material 41. has been described, but it is not necessarily limited to this. For example, when the tip 60 is welded to the base material 41, the second and third discharge surfaces 62 and 47 of the tip 60 are not formed by the cut surfaces. 63 is independent of the distance between the second surface 47 and the third surface 48 of the base material 41 . Therefore, the second discharge surface 62 may protrude from the second surface 47 or the third discharge surface 63 may protrude from the third surface 48 . By making the distance between the second discharge surface 62 and the third discharge surface 63 of the tip 60 longer than the distance between the second surface 47 and the third surface 48 of the base material 41, the first discharge surface 61 area can be made larger. The relationship between the second discharge surface and the second surface and the relationship between the third discharge surface and the third surface described here are the same for the second to fourth embodiments.

In the first embodiment, the case where the fourth discharge surface 64 of the tip 60 is smoothly connected to the end surface 50 of the base material 41 has been described, but it is not necessarily limited to this. Of course, it is possible to protrude the fourth discharge surface 64 from the end surface 50 . The area of the first discharge surface 61 can be increased by protruding the fourth discharge surface 64 from the end surface 50 .

In the first embodiment, the side surface 65 of the chip 60 is an inclined surface that recedes from the fourth discharge surface 64 as it approaches the bottom surface 66 from the first discharge surface 61 . Although the description has been given for the case where the Of course, it is possible to make the side surface 65 of the chip 60 an inclined surface that approaches the fourth discharge surface 64 as it approaches the bottom surface 66 from the first discharge surface 61 . The direction of this inclined surface is the same in the second to fourth embodiments.

Although not described in the embodiment, the angles formed by the first surfaces 44, 74 and the second surfaces 47, 77 of the base materials 41, 72, l02, 122 and the angles formed by the base materials 41, 72, l02, 122 Of course, it is possible to chamfer or round the corners formed by the first surfaces 44 and 74 and the third surfaces 48 and 78 . Similarly, the angles formed by the second surfaces 47, 77 and the fourth surfaces 49, 79 of the base materials 41, 72, l02, 122 and the third surfaces 48, 78 of the base materials 41, 72, l02, 122 Of course, it is possible to chamfer or round the corner formed by the fourth surfaces 49 and 79 .

Although not described in the embodiment, a tip containing a noble metal is joined to the tip of the shaft portion 22 of the center electrode 20, and the tip surface of the tip and the tips 60, 90, 90, 90, 90 of the ground electrodes 40, 71, 101, 121 are connected to each other. Naturally, it is possible to form a spark gap G between 110 and 130 .

In the embodiment, the discharge surface 23 of the center electrode 20 is entirely projected onto the first discharge surfaces 61 , 91 , 111 , 131 in the direction perpendicular to the first discharge surfaces 61 , 91 , 111 , 131 . 117, 137, but the present invention is not necessarily limited to this. A part of the discharge surface 23 of the center electrode 20 should be present within the ranges 67 , 97 , 117 and 137 . This is because discharge paths can be stably formed between the discharge surface 23 of the center electrode 20 and the first discharge surfaces 61 , 91 , 111 , 131 .

In the embodiments, the cases where the base materials 41, 72, 102, 122 of the ground electrodes 40, 71, 101, 121 are bent have been described, but the present invention is not necessarily limited to this. Of course, it is possible to make the base materials 41, 72, 102, 122 linear.

In each embodiment, a part or a plurality of parts of the configuration of another embodiment is added to the embodiment or replaced with a part or a plurality of parts of the configuration of the embodiment. The embodiment may be modified and configured.

For example, the side surface 65 of the tip 60 and the side surface 52 of the recess 51 of the spark plug 10 in the first embodiment may be replaced with the side surface 114 of the tip 110 and the side surface 104 of the recess 103 of the spark plug 100 in the third embodiment. It is of course possible to have a plane perpendicular to the plane 44 . Even if the side surface of the chip and the side surface of the recess are perpendicular to the first surface, the corner formed by the side surface of the chip and the bottom surface is rounded, and the corner formed by the side surface of the recess and the bottom surface is rounded. This is because the length of the boundary between the tip and the base material can be lengthened. Instead of rounding the corner formed by the side surface and bottom surface of the chip or the corner formed by the side surface and bottom surface of the recess, the corner may be chamfered. In this case also, the length of the boundary between the tip and the base material can be lengthened.

Further, the corner formed by the side surface 65 and the bottom surface 66 of the tip 60 of the spark plug 10 in the first embodiment and the corner formed by the side surface 52 and the bottom surface 53 of the recess 51 are rounded as in the fourth embodiment. It is of course possible to omit it. Even if the roundness is omitted, the side 65 of the tip 60 and the side 52 of the recess 51 are inclined surfaces, so the length of the boundary between the tip and the base material can be increased.

Reference Signs List 10, 70, 100, 120 spark plug 20 center electrode 23 discharge surface 30 metal shell 40, 71, 101, 121 ground electrode 41, 72, l02, 122 base material 42 one end 43 other end 44, 74 first surface 47 , 77 second surface 48, 78 third surface 50, 80 end surface 51, 81, 103, 123 recess 52, 82, 83, 104, 105, 124, 125 recess side surface
Bottom of 53,84 dent
54, 85, 107, 127 diffusion layer 60, 90, 110, 130 chip
Sides of 65, 94, 95 chips
Bottom of 66 and 96 chips
61, 91, 111, 131 First discharge surface 62, 92, 112 Second discharge surface 63, 93, 113 Third discharge surface 67, 97, 117, 137 Range T Chip thickness

Claims (5)

a center electrode;
a metal shell that insulates and holds the center electrode;
a ground electrode having a rod-shaped base material, the other end of which is connected to the metal shell, and a tip arranged at one end of the base material;
The one end of the base material has a first surface facing the center electrode and formed with a recess, a second surface connected to the first surface and extending from the one end to the other end, and A spark plug comprising a third surface and an end surface connected to the second surface and the third surface ,
the recess includes a side surface connected to the first surface and a bottom surface connected to the side surface, the side surface and the bottom surface connect from the second surface to the third surface;
The side surface is an inclined surface that moves away from or approaches the end surface as it approaches the bottom surface,
The tip has a first discharge surface that faces the discharge surface of the center electrode and faces the same direction as the first surface, and a second discharge surface that faces the same direction as the second surface. , a third discharge surface facing in the same direction as the third surface, and a side surface following the side surface of the recess ,
at least part of the discharge surface of the center electrode exists within a range obtained by projecting the first discharge surface in a direction perpendicular to the first discharge surface;
The spark plug, wherein the first discharge surface is smoothly connected to the first surface. a center electrode;
a metal shell that insulates and holds the center electrode;
a ground electrode having a rod-shaped base material, the other end of which is connected to the metal shell, and a tip arranged at one end of the base material;
The one end of the base material has a first surface facing the center electrode and formed with a recess, a second surface connected to the first surface and extending from the one end to the other end, and A spark plug comprising a third face,
the recess includes a side surface connected to the first surface and a bottom surface connected to the side surface, and the side surface and the bottom surface connect from the second surface to the third surface;
The tip has a first discharge surface that faces the discharge surface of the center electrode and faces the same direction as the first surface, and a second discharge surface that faces the same direction as the second surface. and a third discharge surface facing in the same direction as the third surface, a side surface following the side surface of the recess, and a bottom surface connected to the side surface of the chip ,
at least part of the discharge surface of the center electrode exists within a range obtained by projecting the first discharge surface in a direction perpendicular to the first discharge surface;
The first discharge surface is smoothly connected to the first surface,
A corner formed by the side surface and the bottom surface of the recess and an angle formed by the side surface and the bottom surface of the chip are chamfered, or a corner formed by the side surface and the bottom surface of the recess and the chip are chamfered. A spark plug in which the corner formed by the side surface and the bottom surface is rounded . a center electrode;
a metal shell that insulates and holds the center electrode;
a ground electrode having a rod-shaped base material, the other end of which is connected to the metal shell, and a tip arranged at one end of the base material;
The one end of the base material has a first surface facing the center electrode and formed with a recess, a second surface connected to the first surface and extending from the one end to the other end, and A spark plug comprising a third face,
the recess is separated from the end surface of the base material on the one end side and is connected from the second surface to the third surface;
The tip has a first discharge surface that faces the discharge surface of the center electrode and faces the same direction as the first surface, and a second discharge surface that faces the same direction as the second surface. and a third discharge surface facing the same direction as the third surface,
A spark plug in which at least part of the discharge surface of the center electrode exists within a range obtained by projecting the first discharge surface in a direction perpendicular to the first discharge surface. 4. The spark plug according to claim 3 , wherein said first discharge surface smoothly connects to said first surface. A diffusion layer or a fusion zone is formed between a side surface of the recess contiguous to the first surface and the chip on a cut surface perpendicular to the first discharge surface and parallel to the second surface,
The spark plug according to any one of claims 1 to 4 , wherein the length of the side surface at the cut surface is longer than the thickness of the tip from the first surface.

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