JP7045340B2 - Spark plug - Google Patents

Description

The present invention relates to a spark plug, and more particularly to a spark plug in which a tip is bonded to a base material of a ground electrode.

In a spark plug in which a spark gap is formed between the discharge surface of the chip of the ground electrode and the center electrode, in the technique disclosed in Patent Document 1, the molten portion formed by melting the base material of the ground electrode and the chip is the mother. Intervenes throughout between the material and the chip. The molten portion relaxes the stress caused by the difference between the linear expansion coefficient of the base metal and the linear expansion coefficient of the chip, and suppresses the destruction of the chip and the molten portion due to thermal expansion and contraction.

Japanese Unexamined Patent Publication No. 2013-41754

In this type of spark plug, when an electric field is concentrated on the outer peripheral edge of the discharge surface of the chip of the ground electrode or sparks are blown off, the spark discharge generated between the outer peripheral edge of the discharge surface and the center electrode causes the chip to be discharged. The outer peripheral edge is more likely to be consumed than the center of the discharge surface. When the outer peripheral edge of the discharge surface of the chip is consumed and the outer periphery of the molten portion is exposed, and the outer periphery of the molten portion is consumed and the cross-sectional area of the fused portion becomes smaller, the molten portion is destroyed by the stress generated by thermal expansion and contraction. The chip may fall off. Therefore, the spark plug whose tip is worn and the outer periphery of the molten portion is exposed is replaced with a new one. The average consumer prefers spark plugs that are replaced infrequently.

The present invention has been made to meet this demand, and an object of the present invention is to provide a spark plug that can be replaced less frequently.

In order to achieve this object, the spark plug of the present invention includes a base metal, a chip having a discharge surface, a molten portion that intervenes throughout between the chip and the base material, and joins the chip to the base material. A ground electrode is provided, and a center electrode whose tip surface faces the discharge surface is provided. The chip has a thick portion on its outer peripheral portion in which the distance between the discharge surface and the molten portion is longer than the distance between the discharge surface and the molten portion in the center of the discharge surface, and the thick portion has an outer peripheral portion. It is provided over the entire circumference of the portion, and the chip overlaps the molten portion and the base metal over the entire circumference in the projection region in the thickness direction of the chip .

According to the spark plug according to claim 1, the distance between the discharge surface and the melted portion of the thick portion existing over the entire circumference of the outer peripheral portion of the chip is the distance between the discharge surface and the melted portion in the center of the discharge surface. Longer than the distance between. As a result, it is possible to prolong the period until the outer periphery of the molten portion is exposed due to the consumption of the thick portion due to the discharge between the outer peripheral edge of the discharge surface of the chip and the center electrode. Therefore, the frequency of replacing the spark plug can be reduced.

According to the spark plug according to claim 2, the distance between the discharge surface of the chip and the tip surface of the center electrode is g, and the shortest distance between the outer peripheral edge of the discharge surface of the chip and the outer peripheral edge of the tip surface of the center electrode. When L is satisfied, the relationship of g ≦ 0.6 mm and L / g ≦ 1.1 is satisfied. Thereby, in addition to the effect of claim 1, it is possible to easily generate a discharge between the outer peripheral edge of the discharge surface of the chip and the outer peripheral edge of the tip surface of the center electrode.

According to the spark plug according to claim 3, the thickness of the molten portion between the chip and the base material is larger than the thickness between the chip and the base material on the inner side surrounded by the outer peripheral portion of the chip. It also has a thick central part. Since the cross-sectional area of the molten portion can be secured by the central portion and the stress generated in the chip or the molten portion can be relaxed, in addition to the effect of claim 1 or 2, the destruction of the chip or the molten portion can be suppressed.

According to the spark plug according to claim 4, the central portion exists within the range where the tip surface of the center electrode is projected in the direction perpendicular to the discharge surface of the chip. This makes it difficult to expose the central portion due to wear of the chip due to discharge between the outer peripheral edge of the discharge surface of the chip and the center electrode. By making it difficult to expose the central portion, it is possible to suppress the consumption of the central portion, so that in addition to the effect of claim 3, the stress relieving effect of the central portion can be ensured.

It is one side sectional view of the spark plug in 1st Embodiment. (A) is a rear view of the ground electrode, and (b) is a cross-sectional view of the ground electrode and the center electrode in the line IIb-IIb of FIG. 2 (a). (A) is a rear view of the ground electrode of the spark plug in the second embodiment, and (b) is a cross-sectional view of the ground electrode and the center electrode in the line IIIb-IIIb of FIG. 3 (a).

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a one-sided cross-sectional view of the spark plug 10 with the axis O as a boundary in the first embodiment. In FIG. 1, the lower side of the paper surface is referred to as the front end side of the spark plug 10, and the upper side of the paper surface is referred to as the rear end side of the spark plug 10. As shown in FIG. 1, the spark plug 10 includes an insulator 11, a center electrode 20, a main metal fitting 30, and a ground electrode 40.

The insulator 11 is a substantially cylindrical member having a shaft hole 12 penetrating along the axis O, and is made of ceramics such as alumina having excellent mechanical properties and insulating properties at high temperatures. In the insulator 11, a rear end facing surface 13 which is an annular surface facing the rear end side is formed on the tip end side of the inner peripheral surface formed by the shaft hole 12. The diameter of the rear end facing surface 13 is reduced toward the tip side.

The center electrode 20 is a rod-shaped member in which the head portion 21 is locked to the rear end facing surface 13, and the shaft portion 22 is arranged 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. It is possible to omit the core material. A chip 23 is bonded to the tip of the base material of the center electrode 20. The chip 23 contains one or more of noble metals such as Pt, Rh, Ir, and Ru, and has a chemical composition containing 50 wt% or more of one of these noble metals. The center electrode 20 is electrically connected to the terminal fitting 25 in the shaft hole 12.

The terminal fitting 25 is a rod-shaped member to which a high-voltage cable (not shown) is connected, and is made of a conductive metal material (for example, low carbon steel or the like). The terminal fitting 25 is fixed to the rear end of the insulator 11 with the tip end side inserted into the shaft hole 12.

The main metal fitting 30 is a substantially cylindrical member made of a conductive metal material (for example, low carbon steel or the like). The main metal fitting 30 surrounds the tip end side of the insulator 11 and holds the insulator 11 inside. The main metal fitting 30 has a screw 32 formed on the outer peripheral surface of the body portion 31 on the tip end side of the main metal fitting 30. The male screw 32 is a portion to be screwed into a screw hole of an engine (not shown). The main metal fitting 30 includes a seat portion 33 connected to the rear end side of the body portion 31, and a rear end portion 34 connected to the rear end side of the seat portion 33.

The seat portion 33 is a portion for closing the gap between the screw hole of the engine (not shown) and the male screw 32, and is formed to have an outer diameter larger than the outer diameter of the body portion 31. The rear end portion 34 is formed with a tool engaging portion to which a tool such as a wrench engages when the screw 32 is tightened in the screw hole of the engine. The main metal fitting 30 has a ground electrode 40 connected to the body portion 31.

The ground electrode 40 includes a base material 41 formed of a conductive metal material (for example, a Ni-based alloy or the like), and a chip 44 bonded to the base material 41. The base material 41 is a rod-shaped member including a first end portion 42 to which the tip 44 is joined and a second end portion 43 to which the main metal fitting 30 is joined. The material of the chip 44 is different from the material of the base material 41, and the coefficient of linear expansion of the chip 44 is different from the coefficient of linear expansion of the base material 41.

The chip 44 contains one or more of noble metals such as Pt, Rh, Ir, and Ru, and has a chemical composition containing 50 wt% or more of one or more of these noble metals. Among these, a chemical composition containing 50 wt% or more of Ir and a chemical composition containing 50 wt% or more of Pt and further containing Ir are particularly preferable. With such a chemical composition, it is easy to form the thick portion 62 described later.

A spark gap 46 is formed between the discharge surface 45 of the chip 44 facing the rear end side and the center electrode 20 (tip surface 24 of the chip 23). The discharge surface 45 is preferably a rectangular shape having a side length of 2.5 mm or more, or a circular shape having an equivalent size. With such a shape, it is easy to form the thick portion 62 described later.

FIG. 2A is a rear view of the ground electrode 40 when the chip 44 is viewed from the rear end side, and FIG. 2B is a cross-sectional view of the ground electrode 40 and the center electrode 20 in the line IIb-IIb of FIG. 2A. Is. FIG. 2A shows the first end portion 42 of the base material 41, and the second end portion 43 (see FIG. 1) is not shown (the same applies to FIG. 3A). FIG. 2B omits the illustration of the rear end side of the chip 23 of the center electrode 20 (the same applies to FIG. 3B).

The arrow L in FIG. 2A indicates the longitudinal direction of the base material 41 extending from the first end portion 42 of the base material 41 to the second end portion 43 (the same applies to FIG. 3A). The arrow F in FIG. 2B indicates the tip side of the spark plug 10 (see FIG. 1) in the axial direction (the same applies to FIG. 3B). In the present embodiment, the chip 44 has a discharge surface 45 formed in a rectangular plate shape. The area of the discharge surface 45 of the chip 44 is larger than the area of the tip surface 24 of the chip 23 of the center electrode 20. The shape of the tip surface 24 of the chip 23 (center electrode 20) is circular.

As shown in FIGS. 2A and 2B, a melting portion 51 in which the base material 41 and the chip 44 are fused is formed at the first end portion 42 of the base material 41. The chip 44 is joined to the base material 41 by the molten portion 51. Due to the formation of the melting portion 51, the entire surface of the chip 44 on the opposite side of the discharging surface 45 is melted and disappears.

The outer peripheral edge 54 of the discharge surface 45 of the chip 44 is composed of a first side 55 and a second side 56 facing each other, and a third side 57 and a fourth side 58 intersecting the first side 55 and the second side 56, respectively. .. The third side 57 and the fourth side 58 face each other. The first side 55 is located on the second end 43 (see FIG. 1) side of the base material 41 in the longitudinal direction (arrow L direction) with respect to the second side 56.

In the rear view of the first end portion 42 viewed from the direction perpendicular to the discharge surface 45 of the chip 44 (see FIG. 2A), the molten portion 51 extends to the periphery of the outer peripheral edge 54 of the chip 44. In the present embodiment, since the discharge surface 45 of the chip 44 has a rectangular plate shape, the outline of the portion of the chip 44 that is visible from the direction perpendicular to the discharge surface 45 is the outer peripheral edge of the discharge surface 45 of the chip 44. Equal to 54.

The outer peripheral portion 59 of the chip 44 is a region between the outline 59a and the outer line in which the outer line of the chip 44 (the outer peripheral edge 54 in the present embodiment) is reduced to 60%. The outline of the chip 44 and the miniature 59a are similar. The center of the outline of the chip 44 and the center of the miniature 59a coincide with the center 60 of the discharge surface 45. The width of the outer peripheral portion 59 is the distance between the microcosm 59a arranged inside the outer line of the chip 44 and the outer line. The width of the portion of the outer peripheral portion 59 in contact with the first side 55 and the second side 56 is 20% of the distance between the first side 55 and the second side 56, respectively. The width of the portion of the outer peripheral portion 59 in contact with the third side 57 and the fourth side 58 is 20% of the distance between the third side 57 and the fourth side 58, respectively.

The melting portion 51 has a thickness T2 between the chip 44 and the base material 41 inside the molten portion 51 surrounded by the outer peripheral portion 59 of the chip 44, and a thickness T1 between the chip 44 and the base material 41 in the outer peripheral portion 59. A thicker central portion 61 is formed (see FIG. 2B). The central portion 61 exists within the range 63 in which the tip surface 24 of the center electrode 20 (see FIG. 1) is projected in the direction perpendicular to the discharge surface 45 of the chip 44. The portion where the discharge surface 45 of the chip 44 and the range 63 intersect is inside the outer peripheral edge 54 of the chip 44.

Due to the central portion 61 formed in the melting portion 51, the interface 52 is raised near the center toward the rear end side (in the direction of the counter arrow F). In the chip 44, the distance D1 between the discharge surface 45 of the chip 44 and the molten portion 51 (interface 52) on the outer peripheral portion 59 is the distance D1 between the discharge surface 45 and the molten portion 51 (interface 52) at the center 60 of the discharge surface 45. A thick portion 62 longer than the distance D2 is formed on the outer peripheral portion 59. The thick portion 62 is provided over the entire circumference of the outer peripheral portion 59.

The central portion 61 and the thick portion 62 are specified based on the result of cutting the ground electrode 40 perpendicular to the discharge surface 45 of the chip 44 and observing the cross section thereof with a microscope or the like. For example, at intervals of 20% of the distance between the first side 55 and the second side 56 of the chip 44 (dividing the chip 44 into five equal parts), the cross sections are sequentially formed from the second side 56 toward the first side 55. Make and observe the shapes of the interfaces 52 and 53 in each cross section. The overall shape of the interfaces 52 and 53 is estimated from the results of a plurality of cross-sectional observations, and the positions, sizes and ranges of the central portion 61 and the thick portion 62 are specified.

When the chip 44 and the molten portion 51 have a chemical composition that allows X-rays to pass through, the central portion 61 and the thick portion 62 can be identified by a non-destructive inspection using an X-ray transmission device.

The thickness T1 is the longest distance between the interfaces 52 and 53 at the outer peripheral portion 59 in the cross section of the observed ground electrode 40. The central portion 61 is a portion thicker between the interfaces 52 and 53 than the thickness T1. The central portion 61 is identified by comparing the thickness T2 with the thickness T1.

The distance D2 is the distance between the discharge surface 45 and the molten portion 51 (interface 52) at the center 60 of the discharge surface 45 in the observed cross section of the ground electrode 40. In the outer peripheral portion 59, the portion where the distance D1 between the discharge surface 45 and the melting portion 51 (interface 52) is longer than the distance D2 is the thick portion 62. The thick portion 62 is identified by comparing the distance D1 with the distance D2.

The central portion 61 can be formed by irradiating the boundary portion between the chip 44 and the base material 41 with a high energy beam such as a laser beam from a direction substantially parallel to the discharge surface 45 of the chip 44. For example, first, the beam is irradiated to the center of the third side 57 of the chip 44, which is the boundary portion between the chip 44 and the base material 41, and then from the end of the third side 57 in the direction of the arrow L along the third side 57. While moving the beam, the beam is irradiated to the boundary portion between the chip 44 and the base material 41. The energy of the beam and the like are adjusted so that the molten portion 51 is formed at the center of the third side 57 beyond the center 60 of the discharge surface 45.

Next, after irradiating the center of the fourth side 58 of the chip 44 at the boundary between the chip 44 and the base material 41 with a beam, the beam is radiated from the end of the fourth side 58 in the counter-arrow L direction along the fourth side 58. While moving the beam, the beam is irradiated to the boundary portion between the chip 44 and the base material 41. At the center 60 of the discharge surface 45, the energy of the beam and the like are adjusted so that the molten portion overlaps with the previously formed fused portion 51. As a result, the amount of melting near the center 60 where the melting portions 51 formed from the two directions overlap each other increases, and the central portion 61 is formed in the melting portion 51.

In the present embodiment, the distance g between the discharge surface 45 of the chip 44 and the tip surface 24 of the center electrode 20 is set to 0.6 mm or less. The distance g is the distance between the spark gaps 46. The relationship between the distance g and the shortest distance L between the outer peripheral edge 54 of the discharge surface 45 and the outer peripheral edge 26 of the tip surface 24 of the center electrode 20 satisfies L / g ≦ 1.1. The outer peripheral edge 54 of the discharge surface 45 is a straight line where the side surface 44a of the chip 44 and the discharge surface 45 intersect. The outer peripheral edge 26 of the tip surface 24 is a curve where the side surface 23a of the chip 23 and the tip surface 24 intersect. When g ≦ 0.6 mm and L / g ≦ 1.1 are satisfied, it is possible to easily generate a discharge between the outer peripheral edge 54 of the discharge surface 45 of the chip 44 and the outer peripheral edge 26 of the tip surface 24 of the center electrode 20. As a result, the discharge start voltage can be lowered.

The distance g is preferably g ≧ 0.2. This is to ensure ease of manufacture and prevent deterioration of ignitability. Further, L / g ≧ 1.0 can be set. The lengths of the first side 55, the second side 56, the third side 57, and the fourth side 58 of the chip 44 are all preferably 2.5 mm or more. This is because the portion (outer peripheral edge 26) where the chip 44 is likely to be discharged can be lengthened.

An electric field is concentrated on the outer peripheral edge 54 of the discharge surface 45 of the chip 44, or sparks are blown off by an air flow in a combustion chamber (not shown), so that between the outer peripheral edge 54 of the discharge surface 45 and the center electrode 20. When spark discharge is likely to occur, the chip 44 consumes more outer peripheral edges 54 than the vicinity of the center 60 of the discharge surface 45. When the outer peripheral edge 54 of the discharge surface 45 is consumed and the outer periphery of the molten portion 51 is exposed, and the outer periphery of the molten portion 51 is further consumed and the cross-sectional area of the molten portion 51 becomes smaller, the stress generated by the thermal expansion and contraction causes the molten portion 51 to be exposed. May be destroyed and the chip 44 may fall off. Therefore, the spark plug whose chip 44 is worn out and the outer periphery of the molten portion 51 is exposed is replaced with a new one.

According to the present embodiment, on the outer peripheral portion 59 of the chip 44, the distance D1 between the discharge surface 45 of the outer peripheral portion 59 and the melting portion 51 (interface 52) is the same as the discharge surface 45 at the center 60 of the discharge surface 45. There is a thick portion 62 longer than the distance D2 between the molten portion 51 (interface 52). Since the thick portion 62 exists over the entire circumference of the outer peripheral portion 59, the outer periphery of the molten portion 51 is consumed due to the consumption of the thick portion 62 due to the discharge between the outer peripheral edge 54 of the discharge surface 45 of the chip 44 and the center electrode 20. Can be lengthened until it is exposed. Therefore, the replacement frequency of the spark plug 10 can be reduced.

Here, if the entire melting portion 51 is simply thinned, the amount of melting of the portion of the chip 44 opposite to the discharge surface 45 is reduced, so that the melting portion 51 is exposed due to the consumption of the chip 44 from the outer peripheral edge 54 of the discharge surface 45. It is possible to lengthen the period until the discharge. However, if the entire molten portion 51 is thinned, the stress relaxing effect of the molten portion 51 is reduced, so that the tip 44 and the molten portion 51 may be easily broken.

In the molten portion 51 of the present embodiment, the thickness T2 (thickness between the interfaces 52 and 53) between the chip 44 and the base metal 41 is located inside the outer peripheral portion 59 surrounded by the outer peripheral portion 59 of the chip 44. A central portion 61 thicker than the maximum value of the thickness T1 (thickness between the interfaces 52 and 53) between the chip 44 and the base material 41 is provided. Since the cross-sectional area of the molten portion 51 can be secured by the central portion 61 and the stress generated in the chip 44 and the molten portion 51 can be relaxed, the breakage of the chip 44 and the molten portion 51 can be suppressed.

The central portion 61 exists within the range 63 in which the tip surface 24 of the center electrode 20 is projected in the direction perpendicular to the discharge surface 45 of the chip 44. Since it is difficult to expose the central portion 61 due to the wear of the chip 44 due to the discharge between the outer peripheral edge 54 of the discharge surface 45 of the chip 44 and the center electrode 20, the wear of the central portion 61 can be suppressed. Therefore, even if the outer peripheral edge 54 of the discharge surface 45 is consumed and the outer periphery of the molten portion 51 is exposed and the outer periphery of the molten portion 51 is further consumed, the stress relaxation effect can be ensured by the central portion 61. As a result, the destruction of the molten portion 51 can be suppressed and the chip 44 can be suppressed from falling off.

The second embodiment will be described with reference to FIG. In the second embodiment, the ground electrode 70 having a chip 71 having a circular discharge surface 72 will be described. The same parts as those described in the first embodiment are designated by the same reference numerals, and the following description will be omitted. 3 (a) is a rear view of the ground electrode 70 of the spark plug in the second embodiment, and FIG. 3 (b) is a cross section of the ground electrode 70 and the center electrode 20 in the line IIIb-IIIb of FIG. 3 (a). It is a figure. The ground electrode 70 is arranged in place of the ground electrode 40 of the spark plug 10 in the first embodiment.

In the ground electrode 70, the tip 71 is bonded to the first end portion 42 of the base metal 41 via the molten portion 76. The melting portion 76 is formed by melting the base material 41 and the chip 71. Due to the formation of the molten portion 76, the entire surface of the disk-shaped chip 71 opposite to the discharge surface 72 is melted and disappears. The shape of the outer peripheral edge 73 of the discharge surface 72 of the chip 71 is circular.

In the rear view of the first end portion 42 viewed from the direction perpendicular to the discharge surface 72 of the chip 71 (see FIG. 3A), the molten portion 76 extends to the periphery of the outer peripheral edge 73 of the chip 71. In the present embodiment, the outline of the chip 71 representing the shape of the portion of the chip 71 that is visible from the direction perpendicular to the discharge surface 72 is equal to the outer peripheral edge 73 of the discharge surface 72 of the chip 71.

In this embodiment, the corners where the side surface 71a of the chip 71 and the discharge surface 72 intersect are rounded. In this case, a virtual surface 81 parallel to the surface 41a is set at a height 90% of the height H from the surface 41a of the base material 41 to which the chip 71 is joined to the discharge surface 72, and the virtual surface 81 is set. The curve at which the side surface 71a and the side surface 71a intersect is defined as the outer peripheral edge 73. Even when chamfering is applied instead of rounding, the virtual surface 81 is set in the same manner as in the case of rounding. As a result, the shortest distance L when the corner where the side surface 71a of the chip 71 and the discharge surface 72 intersect is rounded or chamfered can be uniquely determined.

The outer peripheral portion 74 of the chip 71 is a region between the outline of the chip 71 and the outline of the chip 71 (the outer peripheral edge 73 in the present embodiment) reduced to 60%. The outline of the chip 71 and the miniature 74a are similar. The center of the outline of the chip 71 and the center of the miniature 74a coincide with the center 75 of the discharge surface 72. The width of the outer peripheral portion 74 is the distance between the microcosm 74a arranged inside the outer line of the chip 71 and the outer line, and is 20% of the diameter of the discharge surface 72.

In the molten portion 76, the thickness T2 between the chip 71 and the base material 41 is inside the molten portion 76 surrounded by the outer peripheral portion 74 of the chip 71, and the maximum thickness between the chip 71 and the base material 41 in the outer peripheral portion 74. A central portion 79 thicker than T1 is formed (see FIG. 3 (b)). The central portion 79 exists in the range 82 where the tip surface 24 of the center electrode 20 (see FIG. 1) is projected in the direction perpendicular to the discharge surface 45 of the chip 44. The portion where the discharge surface 72 of the chip 71 and the range 82 intersect is inside the outer peripheral edge 73 of the chip 71.

Due to the central portion 79 formed in the molten portion 76, the interface 77 is raised near the center toward the rear end side (in the direction of the counter arrow F). In the chip 71, the distance D1 between the discharge surface 72 of the chip 71 and the molten portion 76 (interface 77) on the outer peripheral portion 74 is the distance D1 between the discharge surface 72 and the molten portion 76 (interface 77) at the center 75 of the discharge surface 72. A thick portion 80 longer than the distance D2 is formed on the outer peripheral portion 74. The thick portion 80 is provided over the entire circumference of the outer peripheral portion 74.

The distance g between the discharge surface 72 of the chip 71 and the tip surface 24 of the center electrode 20 is set to 0.6 mm or less. The relationship between the distance g and the shortest distance L between the outer peripheral edge 73 of the discharge surface 72 and the outer peripheral edge 26 of the tip surface 24 of the center electrode 20 satisfies L / g ≦ 1.1.

As a result, the spark plug in the second embodiment can realize the same effect as that in the first embodiment. The diameter of the discharge surface 72 of the chip 71 is preferably 2.5 mm or more. This is because the portion (outer peripheral edge 73) where the chip 71 is likely to be discharged can be lengthened.

Although the present invention has been described above based on the embodiments, the present invention is not limited to the above embodiments, and various improvements and modifications can be made without departing from the spirit of the present invention. It is easy to guess.

In the embodiment, the case where the discharge surfaces 45 and 72 of the chips 44 and 71 of the ground electrodes 40 and 70 are rectangular or circular has been described, but the present invention is not limited to this. For example, the shapes of the discharge surfaces 45 and 72 can be arbitrarily set, such as making the shape of the discharge surface 45 a polygon other than a rectangle such as a hexagon or an ellipse.

In the embodiment, the case where the chip 23 containing a precious metal or the like is provided on the center electrode 20 has been described, but the present invention is not limited to this. Of course, it is possible to omit the chip 23 of the center electrode 20. When the chip 23 is omitted, the tip surface of the center electrode 20 means the tip surface of the base metal.

In the embodiment, the case where the thick central portions 61 and 79 having the thickness T2 are formed in the molten portions 51 and 76 has been described, but the present invention is not limited to this. This is because even if the central portions 61 and 79 are not formed, the thick portions 62 and 80 can be formed on the chips 44 and 71 if the vicinity of the center of the interfaces 52 and 77 is raised toward the discharge surfaces 45 and 72. ..

10 Spark plug 20 Center electrode 24 Tip surface 26 Outer peripheral edge of tip surface 40,70 Ground electrode 41 Base material 44,71 Chip 45,72 Discharge surface 51,76 Melting part 54,73 Outer peripheral edge of discharge surface 59,74 Outer peripheral part 60,75 Central part of the discharge surface 61,79 Central part 62,80 Thick part 63,82 Projected range of the tip surface

Claims (4)

A ground electrode comprising a base material, a chip having a discharge surface, and a molten portion that is interposed between the chip and the base material and joins the chip to the base material.
A spark plug comprising a center electrode whose tip surface faces the discharge surface.
The chip is provided with a thick portion on its outer peripheral portion in which the distance between the discharge surface and the melted portion is longer than the distance between the discharge surface and the melted portion at the center of the discharge surface. ,
The thick portion is provided over the entire circumference of the outer peripheral portion.
The tip is a spark plug that overlaps the melted portion and the base metal over the entire projection region in the thickness direction of the tip . When the distance between the discharge surface and the tip surface is g and the shortest distance between the outer peripheral edge of the discharge surface and the outer peripheral edge of the tip surface is L, g ≦ 0.6 mm and L / g. The spark plug according to claim 1, which satisfies the relationship of ≤1.1. The molten portion has a central portion inside the outer peripheral portion in which the thickness between the chip and the base material is thicker than the thickness between the chip and the base material in the outer peripheral portion. The spark plug according to claim 1 or 2. The spark plug according to claim 3, wherein the central portion exists within a range in which the tip surface is projected in a direction perpendicular to the discharge surface.

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