JP7028810B2 - 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 tip 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 and the tip of the ground electrode is the base material and the chip. Intervenes throughout between and. 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. Since the stress generated in the molten portion is inversely proportional to the cross-sectional area of the molten portion, the larger the cross-sectional area of the molten portion, the higher the stress relaxation effect can be.

Japanese Unexamined Patent Publication No. 2013-41754

However, in the above-mentioned conventional technique, if the molten portion is simply thickened in order to increase the cross-sectional area of the molten portion, the amount of melted chips increases, so that the chips become thinner and the chips are likely to be consumed at an early stage.

The present invention has been made to solve this problem, and an object of the present invention is to provide a spark plug capable of ensuring the life of the chip while suppressing the destruction of the chip and the molten portion.

In order to achieve this object, the spark plug of the present invention has a base material, a chip having a discharge surface, a molten portion that is interposed between the chip and the base material as a whole, and a molten portion that joins the chip to the base material. It comprises a grounding electrode comprising, and a center electrode forming a spark gap between the discharge surface and its own tip surface. The molten portion is provided with a thick portion in which the thickness between the chip and the base metal is thicker than the minimum thickness between the chip and the base metal in the outer peripheral portion, at least inside surrounded by the outer peripheral portion of the chip. The thick portion exists outside the range in which the tip surface is projected in the direction perpendicular to the discharge surface.

According to the spark plug according to claim 1, in the molten portion for joining the chip to the base material, the thickness between the chip and the base material is set in the outer peripheral portion of the chip inside surrounded by the outer peripheral portion of the chip. There is a thicker portion thicker than the thickness between the chip and the base metal. Since the stress generated in the chip and the molten portion can be relaxed by the thick portion, the destruction of the chip and the molten portion can be suppressed.

The thick portion exists outside the range in which the tip surface of the center electrode is projected in the direction perpendicular to the discharge surface of the chip. By doing so, it is possible to make a portion of the chip where the thick portion exists in the direction perpendicular to the discharge surface, outside the range. Due to the formation of the thick part, the thickness of the part of the chip where the thick part exists in the direction perpendicular to the discharge surface tends to be thinner than the thickness of the other parts, but this is consumed. Can be placed in difficult places. As a result, it is possible to prevent the chip from being consumed by the electric discharge and the thick portion from being exposed at an early stage. Therefore, the life of the chip can be ensured.

According to the spark plug according to claim 2, since the molten portion includes a plurality of thick portions, the stress generated in the tip and the molten portion can be relieved at a plurality of locations. Therefore, in addition to the effect of claim 1, the destruction of the chip and the molten portion can be further suppressed.

According to the third aspect of the present invention, a molten portion is formed at the first end portion of the base metal, and the second end portion located on the opposite side of the first end portion is joined to the main metal fitting. The thick portion exists in each of the first region on the second end side of the center of the discharge surface of the chip and the second region located on the opposite side of the first region. Therefore, in addition to the effect of claim 2, it is effective in stress relaxation of thermal expansion and contraction that occurs in the direction from the first end portion to the second end portion of the base metal.

According to the spark plug according to claim 4, since the thick portion extends from a part of the outer peripheral portion to a portion other than a part of the outer peripheral portion, the effect of relaxing the stress generated in the chip and the molten portion can be improved. Therefore, in addition to the effect of any one of claims 1 to 3, the destruction of the chip and the molten portion can be further suppressed.

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). It is a rear view of the ground electrode of the spark plug in the 2nd Embodiment.

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 in which a shaft hole 12 penetrating along the axis O is formed, 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 linear expansion coefficient of the chip 44 is different from the linear expansion coefficient 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 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 Pr and further containing Ir are particularly preferable. With such a chemical composition, it is easy to form the thick portion 61 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 61 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. 3). FIG. 2B omits the illustration of the rear end side of the chip 23 of the center electrode 20. 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. 3). The arrow F in FIG. 2B indicates the tip side of the spark plug 10 (see FIG. 1) in the axial direction. 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.

As shown in FIGS. 2A and 2B, in the chip 44, a molten 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 and is joined to the base material 41. Has been done. 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 interface 52 between the tip 44 and the molten portion 51 is raised near the center toward the rear end side (counter-arrow F direction).

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 outer peripheral line 59a and the outer peripheral line in which the outer peripheral 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 miniature drawing 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 thick portion 61 is formed (see FIG. 2B). In the present embodiment, the thick portion 61 extends from a part of the outer peripheral portion 59 (site 62) to the portion 63 of the outer peripheral portion 59 (excluding the portion 62). The thick portion 61 exists outside the range 64 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 64 intersect is inside the outer peripheral edge 54 of the chip 44. The portion 44a of the chip 44 in which the thick portion 61 exists in the direction perpendicular to the discharge surface 45 is thinner than the thickness of other portions of the chip 44 (for example, a portion within the range 64).

The portion 62 of the outer peripheral portion 59 is in contact with the first side 55, and the portion 63 is in contact with the second side 56. The thick portion 61 extends from the first end portion 42 toward the second end portion 43 (see FIG. 1) (in the direction of arrow L). As a result, the thick portion 61 exists in the first region 65 on the second end 43 side of the center 60 of the discharge surface 45 of the chip 44 and in the second region 66 located on the opposite side of the first region 65. do.

The thick portion 61 is 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 shape of the thick portion 61 in each cross section. The overall shape of the thick portion 61 can be estimated from the results of a plurality of cross-sectional observations.

The thickness T1 is the shortest distance between the interfaces 52 and 53 at the outer peripheral portion 59 (excluding the portions 62 and 63) in the cross section of the observed ground electrode 40. The thick portion 61 is a portion thicker between the interfaces 52 and 53 than the thickness T1. The thick portion 61 is specified by comparing the thickness T2 with the thickness T1.

Here, the thickness T3 (not shown) between the tip 44 and the base material 41 at the portions 62 and 63 of the outer peripheral portion 59 is from the thickness T1 of the molten portion 51 at the outer peripheral portion 59 excluding the portions 62 and 63. Is also thick. Therefore, if the thick portion 61 is specified by comparison with the thickness T3, the thick portion 61 becomes too small. Therefore, when estimating the overall shape of the thick portion 61 from the results of a plurality of cross-sectional observations, the positions of the portions 62 and 63 are also specified, and the thickness of the molten portion 51 in the outer peripheral portion 59 (excluding the portions 62 and 63) is specified. T1 is determined, the thickness T2 is evaluated, and the thick portion 61 is specified. When the molten portion 51 has a chemical composition that allows X-rays to pass through, the shape of the thick portion 61 can be specified by a non-destructive inspection using an X-ray transmission device.

The thick 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 boundary portion between the chip 44 and the base material 41 while moving the beam in the direction of the arrow L along the third side 57 of the chip 44. The energy of the beam and the like are adjusted so that the molten portion 51 is formed in the vicinity of the third side 57. Next, the beam is irradiated to the boundary portion between the chip 44 and the base material 41 while moving the beam in the counter-arrow L direction along the fourth side 58 of the chip 44. The energy of the beam and the like are adjusted so that the melted portion overlaps with the melted portion 51 formed earlier. As a result, the portion where the melted portions 51 formed from the two directions overlap each other becomes thicker, and the thickened portion 61 is formed in the melted portion 51.

Since the chip 44 and the base material 41 are fused together in the molten portion 51 of the spark plug 10, the stress generated in the chip 44 and the molten portion 51 due to the difference between the linear expansion coefficient of the base material 41 and the linear expansion coefficient of the chip 44 is applied. ease. As a result, the molten portion 51 suppresses the destruction of the chip 44 and the molten portion 51 due to thermal expansion and contraction. Since the average stress generated in the molten portion 51 is inversely proportional to the cross-sectional area of the molten portion 51, it is desirable that the cross-sectional area of the molten portion 51 is large in order to enhance the stress relaxation effect.

However, if the melted portion is simply thickened in order to increase the cross-sectional area of the melted portion, the amount of melted chips increases, so that the chips become thinner and the chips may be consumed (exposed) at an early stage.

On the other hand, according to the present embodiment, the thick portion 61 is partially present inside the molten portion 51 surrounded by the outer peripheral portion 59 of the chip 44. Since the stress generated in the chip 44 and the molten portion 51 can be relaxed by the thick portion 61, the destruction of the chip 44 and the molten portion 51 can be suppressed.

On the other hand, the thick portion 61 exists outside the range 64 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. By doing so, the portion 44a in which the thick portion 61 exists in the direction perpendicular to the discharge surface 45 of the chip 44 can be present outside the range 64. That is, the thickness of the portion 44a of the chip 44 tends to be thinner than the thickness of the other portions of the chip 44 (particularly the portion within the range 64), but the discharge surface 45 of the chip 44 is the tip surface of the center electrode 20. Since the portion 44a is easily consumed from the portion within the range 64 in which the 24 faces, the portion 44a can be arranged in the portion where it is difficult to be consumed. As a result, the chip 44 is consumed by the electric discharge, and the thick portion 61 can be prevented from being exposed at an early stage. Therefore, the life of the chip 44 can be ensured.

Since the thick portion 61 extends from a part 62 of the outer peripheral portion 59 to the other portion 63 of the outer peripheral portion 59, the volume of the thick portion 61 can be expanded, and the tip 44 and the melting portion 51 can be formed. The effect of relaxing the generated stress can be improved. Therefore, the destruction of the chip 44 and the molten portion 51 can be further suppressed.

The thick portion 61 exists in each of the first region 65 on the second end 43 side of the center 60 of the discharge surface 45 of the chip 44 and the second region 66 located on the opposite side of the first region 65. .. Therefore, it is possible to easily suppress the destruction of the chip 44 and the molten portion 51 due to the thermal expansion and contraction that occurs in the direction from the first end portion 42 to the second end portion 43 (arrow L direction) of the base metal 41.

The second embodiment will be described with reference to FIG. In the second embodiment, a case where a plurality of thick portions 71 are formed in the molten portion 51 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. FIG. 3 is a rear view of the ground electrode 70 when the tip 44 of the spark plug in the second embodiment is viewed from the rear end side. The ground electrode 70 is arranged in place of the ground electrode 40 of the spark plug 10 in the first embodiment.

Inside the molten portion 51 surrounded by the outer peripheral portion 59, the thickness between the chip 44 and the base material 41 is thicker than the thickness between the chip 44 and the base material 41 in the outer peripheral portion 59. A plurality of 71 are formed. The thick portion 71 exists outside the range in which the tip surface 72 of the center electrode 20 is projected in the direction perpendicular to the discharge surface 45 of the chip 44 (the direction perpendicular to the paper surface in FIG. 3). The range in which the tip surface 72 is projected in the direction perpendicular to the discharge surface 45 intersects the outer peripheral edge 54 (fourth side 58) of the chip 44. The fourth side 58 is a portion of the outer peripheral edge 54 that is farthest from the thickest portion 71.

Since the stress generated in the chip 44 and the molten portion 51 can be relaxed by the thick portion 71 formed in the molten portion 51, the destruction of the chip 44 and the molten portion 51 can be suppressed. Since a plurality of thick-walled portions 71 are formed, the volume of the thick-walled portions 71 can be expanded, and the effect of relaxing the stress generated in the chip 44 and the molten portion 51 can be improved.

Since the thick portion 71 exists outside the range in which the tip surface 72 of the center electrode 20 is projected in the direction perpendicular to the discharge surface 45 of the chip 44, the thick portion 71 is outside the range in the direction perpendicular to the discharge surface 45 of the chip 44. A portion where the thick portion 71 is present can be present in the wall. As a result, as in the first embodiment, the chip 44 can be consumed by the electric discharge and the thick portion 71 can be prevented from being exposed at an early stage. Therefore, the life of the chip 44 can be ensured.

Since the range in which the tip surface 72 is projected in the direction perpendicular to the discharge surface 45 intersects the outer peripheral edge 54 of the chip 44, a discharge occurs between the tip surface 72 of the center electrode 20 and the outer peripheral edge 54 of the chip 44. It can be made easy. As a result, it is possible to make it difficult for electric discharge to occur in the vicinity of the thick portion 71, so that it is possible to further lengthen the time until the thick portion 71 is exposed due to the wear of the chip 44. Therefore, the life of the chip 44 can be extended. This effect is remarkable when the range in which the tip surface 72 is projected in the direction perpendicular to the discharge surface 45 intersects the fourth side 48.

The thick portion 71 exists in the first region 65 and the second region 66, respectively. Therefore, it is possible to easily suppress the destruction of the chip 44 and the molten portion 51 due to the thermal expansion and contraction that occurs in the direction from the first end portion 42 to the second end portion 43 (arrow L direction) of the base metal 41.

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 surface 45 of the chip 44 of the ground electrodes 40 and 70 is rectangular has been described, but the present invention is not limited to this. For example, the rectangle may have rounded corners or small chamfers. The shape of the discharge surface 45 may be circular or elliptical. In short, the shape of the discharge surface 45 can be arbitrarily set.

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 first embodiment, both ends of the thick portion 61 reach the outer line of the chip 44 (see FIG. 2A), but the present invention is not necessarily limited to this. If the thick portion 61 extends from a part of the outer peripheral portion 59 to a portion other than a part of the outer peripheral portion 59, the stress relaxation effect of the thick portion 61 can be improved. Therefore, both ends of the thick portion 61 do not need to reach the outer line of the chip 44. Both ends of the thick portion 61 may overlap with the outer peripheral portion 59. That is, it suffices if the thick portion 61 intersects the microcosm 59a.

In the first embodiment, the case where the thick portion 61 extends from the first end portion 42 of the base material 41 toward the second end portion 43 (arrow L direction) has been described, but the present invention is not necessarily limited to this. do not have. Of course, it is possible to form the thick portion 61 so as to extend in a direction intersecting the direction from the first end portion 42 of the base metal 41 toward the second end portion 43 (arrow L direction). The direction in which the thick portion 61 extends can be set by the direction of the high energy beam irradiated when the tip 44 is joined to the base material 41. When the thick portion 61 extends in the direction intersecting the arrow L direction, it is possible to easily suppress the destruction of the tip 44 and the molten portion 51 due to the thermal expansion and contraction that occurs in the direction intersecting the arrow L direction.

10 Spark plug 20 Center electrode 24,72 Tip surface 30 Main metal fittings 40, 70 Ground electrode 41 Base material 42 First end 43 Second end 44 Chip 45 Discharge surface 46 Spark gap 51 Melted part 59 Outer part 60 Discharge surface Central 61, 71 Thick part 64 Projected area of the tip surface 65 1st area 66 2nd area

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 that forms a spark gap between the discharge surface and its own tip surface.
The melted portion is at least inside surrounded by the outer peripheral portion of the chip, and the thickness between the chip and the base material is larger than the minimum thickness between the chip and the base material in the outer peripheral portion. Equipped with a thick thick part,
The thick portion is a spark plug existing outside the range in which the tip surface is projected in a direction perpendicular to the discharge surface. The spark plug according to claim 1, wherein the molten portion includes a plurality of the thick portions. The base material includes a first end portion on which the melted portion is formed, and a second end portion located on the opposite side of the first end portion and joined to the main metal fitting.
The spark according to claim 2, wherein the thick portion exists in each of a first region on the second end side of the center of the discharge surface and a second region located on the opposite side of the first region. plug. The spark plug according to any one of claims 1 to 3, wherein the thick portion extends from a part of the outer peripheral portion to a portion other than the partial portion of the outer peripheral portion.

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