JP2022054246A - Spark plug - Google Patents

Abstract

To provide a spark plug capable of making it less likely that cracks will occur at a bonding interface between an electrode base metal and a metal member.SOLUTION: A spark plug forms a spark discharge by applying a voltage between a center electrode and a ground electrode 14. A ground electrode 14 has an electrode base material 40, a metal member 60 embedded in and bonded to a tip of the electrode base material 40, and a precious metal tip 50 bonded to the electrode base material 40 and the metal member 60. The linear expansion coefficient of the metal member 60 is smaller than the linear expansion coefficient of the electrode base material 40 and is equal to or larger than the linear expansion coefficient of the precious metal tip 50. The metal member 60 has a shape that can constrain the thermal expansion of the electrode base metal 40.SELECTED DRAWING: Figure 4

Description

This disclosure relates to spark plugs.

Conventionally, there is a spark plug that forms a spark discharge between a center electrode and a ground electrode based on the application of a voltage. Some such spark plugs have a precious metal chip bonded to the tip of the electrode base material of the ground electrode in order to meet the demands for extending the life and improving the ignitability. On the other hand, since the electrode base material of the ground electrode and the noble metal chip are made of different materials, the coefficient of linear expansion thereof tends to be different. Specifically, the coefficient of linear expansion of the electrode base material is larger than the coefficient of linear expansion of the precious metal chip. Therefore, when they thermally expand, the thermal expansion amount of the electrode base material tends to be larger than the thermal expansion amount of the noble metal chip, and the stress according to the difference in the thermal expansion amount is between the noble metal chip and the electrode base material. May occur at the junction interface of. Such stress causes cracks and the like to occur at their joint interfaces.

Therefore, conventionally, in the spark plug described in Patent Document 1 below, a metal member having a linear expansion coefficient having a value intermediate to those linear expansion coefficients is provided between the electrode base material of the ground electrode and the noble metal chip. I have to. The metal member has a diameter slightly larger than that of the precious metal chip. In the spark plug described in Patent Document 1, the precious metal chip and the metal member are simultaneously joined to the electrode base material by resistance welding. According to such a configuration, even if there is a difference in the amount of thermal expansion between the electrode base material and the noble metal chip, the difference in the amount of thermal expansion between the members can be absorbed by the metal member. Cracks and the like are less likely to occur at their joint interfaces.

Japanese Patent No. 5068221

In recent vehicles, the temperature environment to which the ground electrode is exposed has become more severe in order to improve the thermal efficiency of the internal combustion engine. Specifically, the ground electrode reaches the maximum temperature when the air-fuel mixture burns in the cylinder of the internal combustion engine. After that, the heat is transferred from the electrode base material of the ground electrode to the housing of the spark plug, so that the temperature of the ground electrode gradually decreases, and when the air-fuel mixture burns thereafter, the temperature of the ground electrode reaches the maximum temperature again. .. Since the temperature of the ground electrode repeatedly rises and falls in this way, it can be said that the ground electrode is exposed to an environment with a large temperature difference.

On the other hand, in recent vehicles, the combustion temperature is higher than before in order to improve the thermal efficiency of the internal combustion engine, so that the temperature difference generated in the ground electrode is larger than before. As the temperature difference generated in the ground electrode increases, the difference in the amount of thermal expansion between the electrode base material and the noble metal chip naturally increases. Therefore, if a metal member is provided between the electrode base material and the noble metal chip as in the spark plug described in Patent Document 1, the difference in the amount of thermal expansion between the members cannot be completely absorbed by the metal member, for example, an electrode. Cracks may occur at the joint interface between the base metal and the metal member. If such cracks frequently occur and further propagate, the metal member may peel off from the electrode base material or the precious metal chip may fall off, which is not preferable.

The present disclosure has been made in view of such circumstances, and an object of the present invention is to provide a spark plug capable of making it difficult for cracks to occur at the bonding interface between an electrode base material and a metal member.

The spark plug (10) that solves the above problems forms a spark discharge by applying a voltage between the center electrode (13) and the ground electrode (14). The ground electrode includes an electrode base material (40), a metal member (60, 100) embedded in the tip of the electrode base material and bonded, and a precious metal chip (60,100) bonded to at least one of the electrode base material and the metal member. 50) and. The coefficient of linear expansion of the metal member is smaller than the coefficient of linear expansion of the electrode base material and is greater than or equal to the coefficient of linear expansion of the noble metal chip. The metal member has a shape capable of restraining the thermal expansion of the electrode base material.

According to this configuration, even in an environment where the electrode base material thermally expands due to a temperature rise, the thermal expansion of the electrode base material is constrained by the metal member, so that the joint interface between the electrode base material and the metal member is cracked. Is less likely to occur.
The reference numerals in parentheses described in the above means and claims are examples showing the correspondence with the specific means described in the embodiments described later.

According to the spark plug of the present disclosure, it is possible to make it difficult for cracks to occur at the joint interface between the electrode base material and the metal member.

FIG. 1 is a cross-sectional view showing a broken cross-sectional structure of the spark plug of the first embodiment. FIG. 2 is a cross-sectional view showing a cross-sectional structure of a tip portion of the ground electrode of the first embodiment. FIG. 3 is a perspective view showing a perspective structure of the metal member of the first embodiment. FIG. 4 is a plan view showing the plan structure of the tip end portion of the ground electrode of the first embodiment. FIG. 5 is a cross-sectional view showing a part of the manufacturing process of the ground electrode of the first embodiment. FIG. 6 is a cross-sectional view showing a part of the manufacturing process of the ground electrode of the first embodiment. FIG. 7 is a diagram schematically showing an operation example of the ground electrode of the first embodiment. FIG. 8 is a plan view showing the plan structure of the tip of the ground electrode of the first modification of the first embodiment. FIG. 9 is a cross-sectional view showing a cross-sectional structure of a tip portion of a ground electrode of a first modification of the first embodiment. FIG. 10 is a perspective view showing a perspective structure of a metal member of a second modification of the first embodiment. FIG. 11 is a plan view showing the plan structure of the tip of the ground electrode of the second modification of the first embodiment. FIG. 12 is a plan view showing the plan structure of the tip of the ground electrode of the second modification of the first embodiment. FIG. 13 is a perspective view showing a perspective structure of a metal member of a third modification of the first embodiment. FIG. 14 is a plan view showing the plan structure of the tip of the ground electrode of the third modification of the first embodiment. FIG. 15 is a plan view showing the plan structure of the tip of the ground electrode of the third modification of the first embodiment. FIG. 16 is a plan view showing the plan structure of the tip end portion of the ground electrode of the second embodiment. FIG. 17 is a plan view showing the plan structure of the tip of the ground electrode of the modified example of the second embodiment. FIG. 18 is a plan view showing the plan structure of the tip of the ground electrode of the modified example of the second embodiment. FIG. 19 is a plan view showing the plan structure of the tip of the ground electrode of the modified example of the second embodiment. FIG. 20 is a cross-sectional view showing a cross-sectional structure of a tip portion of a ground electrode according to a third embodiment. FIG. 21 is a plan view showing the plan structure of the tip end portion of the ground electrode of the third embodiment.

Hereinafter, embodiments of the spark plug will be described with reference to the drawings. In order to facilitate understanding of the description, the same components are designated by the same reference numerals as possible in the drawings, and duplicate description is omitted.
<First Embodiment>
The spark plug 10 of the present embodiment shown in FIG. 1 is arranged in the engine head of an internal combustion engine. The spark plug 10 ignites the air-fuel mixture in the cylinder by forming a spark discharge based on the application of a voltage. The spark plug 10 includes a housing 11, an insulating insulator 12, a center electrode 13, and a ground electrode 14.

The housing 11 is made of a metal material such as carbon steel and is formed in a cylindrical shape around the central axis m10 of the spark plug 10. A threaded portion 11a is formed on the outer periphery of the lower portion of the housing 11. The spark plug 10 can be fixed to the engine head block by screwing the screw portion 11a into a screw hole formed in the engine head block of the internal combustion engine. Inside the housing 11, the lower end of the insulating insulator 12 is coaxially inserted.

The insulating insulator 12 is formed in a cylindrical shape around the central axis m10 by an insulating material such as alumina. A housing 11 is integrally assembled to the outer peripheral portion of the insulating insulator 12. The center electrode 13 is inserted and held in the through hole 12a formed in the lower part of the insulating insulator 12.

The center electrode 13 has an electrode base material 20 and an electrode tip 30. The electrode base material 20 is formed of a nickel (Ni) alloy or the like having excellent heat resistance in a columnar shape centered on the central axis m10. Specifically, the inner material of the electrode base material 20 is made of copper, and the outer material thereof is made of nickel alloy. The tip portion 21 of the electrode base material 20 is exposed from the lower end of the insulating insulator 12. The electrode tip 30 is joined to the tip portion 21 of the electrode base material 20. The electrode tip 30 is formed in a columnar shape about the central axis m10. The electrode chip 30 is made of iridium (Ir), which has a high melting point and excellent wear resistance, as a main material, and is made of an iridium alloy containing rhodium (Rh) in order to suppress high-temperature volatility of iridium. The electrode tip 30 is not limited to the iridium alloy, and may be formed of a precious metal alloy such as a platinum alloy containing platinum (Pt) as a main material.

The ground electrode 14 has an electrode base material 40 and a precious metal chip 50. The electrode base material 40 is made of a nickel alloy or the like. The electrode base material 40 is integrally attached to the lower end surface of the housing 11. The electrode base material 40 is formed so as to be curved and extend from the lower end surface of the housing 11. The tip portion 401 of the electrode base material 40 is located so as to face the electrode tip 30 of the center electrode 13. The precious metal chip 50 is joined to the tip portion 401 of the electrode base material 40. The noble metal chip 50 is formed of a noble metal alloy such as an iridium alloy or a platinum alloy, for example, a Pt-20Ir material. The precious metal chip 50 has a predetermined gap 18 and is arranged so as to face the electrode chip 30. Hereinafter, the gap 18 formed between the electrode tip 30 of the center electrode 13 and the precious metal tip 50 of the ground electrode 14 will be referred to as a “spark discharge gap 18”.

In the spark plug 10, the central shaft member 15 and the terminal portion 16 are electrically connected to the upper portion of the central electrode 13. An external circuit that applies a high voltage is connected to the terminal portion 16. When a high voltage is applied to the terminal portion 16 by an external circuit, a spark discharge is formed between the electrode chip 30 of the center electrode 13 and the noble metal chip 50 of the ground electrode 14. The spark discharge formed by the spark plug 10 ignites the air-fuel mixture in the cylinder of the internal combustion engine, so that the air-fuel mixture burns.

Next, the structure of the ground electrode 14 will be described in detail.
As shown in FIG. 2, the ground electrode 14 further includes a metal member 60 embedded in the tip end portion of the electrode base material 40. As shown in FIG. 3, the metal member 60 has a rectangular parallelepiped portion 61 formed in a rectangular parallelepiped shape, and first end portions 62 and second ends integrally formed at both ends of the rectangular parallelepiped portion 61 in the longitudinal direction, respectively. It has a unit 63. The first end portion 62 and the second end portion 63 are formed in a trapezoidal columnar shape. One side surface 620 of the first end portion 62 and one side surface 630 of the second end portion 63 are arranged so as to face each other in the longitudinal direction of the rectangular parallelepiped portion 61. Further, the other side surface 621 of the first end portion 62 and the other side surface 631 of the second end portion 63 are also arranged so as to face each other in the longitudinal direction of the rectangular parallelepiped portion 61. The metal member 60 is made of a material having a linear expansion coefficient smaller than the linear expansion coefficient of the electrode base material 40 and equal to or higher than the linear expansion coefficient of the noble metal chip 50. Specifically, the metal member 60 is formed of a noble metal alloy such as a platinum alloy mainly composed of platinum, for example, a Pt-20Ni material.

As shown in FIG. 2, the metal member 60 is embedded in the insertion groove 402 formed in the surface 400 of the electrode base material 40. The surface 400 of the electrode base material 40 is an outer surface of the electrode base material 40 facing the center electrode 13. The bottom surface 602 of the metal member 60 is in contact with the bottom surface 402b of the insertion groove 402. At least the bottom surface 602 of the metal member 60 is joined to the bottom surface 402b of the insertion groove 402 by resistance welding. The metal member 60 is embedded in the electrode base material 40 so as to be exposed from the surface 400 of the electrode base material 40. A precious metal chip 50 is bonded to the outer surface 600 of the metal member 60 exposed from the surface 400 of the electrode base material 40. Hereinafter, the outer surface 600 to which the precious metal chip 50 is bonded in the metal member 60 is also referred to as a “joining surface 600”. The metal member 60 is embedded in the electrode base material 40 so that the joint surface 600 thereof is flush with the surface 400 of the electrode base material 40.

As shown in FIG. 4, the tip portion 401 of the electrode base material 40 is formed so that the cross-sectional shape orthogonal to the central axis m10 is rectangular. The direction indicated by the arrow X in the figure indicates the longitudinal direction of the tip portion 401 of the electrode base material 40, and the direction indicated by the arrow Y indicates the lateral direction thereof. A portion 41, which is a part of the electrode base material 40, is sandwiched between one side surface 620 of the first end portion 62 of the metal member 60 and one side surface 630 of the second end portion 63. Similarly, a portion 42 which is a part of the electrode base material 40 is sandwiched between the other side surface 621 of the first end portion 62 of the electrode base material 40 and the other side surface 631 of the second end portion 63.

In the following, the outer surface of the metal member 60 along the circumferential direction around the central axis m10, including the side surfaces 620 and 621 of the first end portion 62 and the side surfaces 630 and 631 of the second end portion 63, is referred to as an “outer peripheral surface”. It is called "601". The metal member 60 may have not only its bottom surface 602 but also its outer peripheral surface 601 joined to the inner peripheral surface 402a of the insertion groove 402 of the electrode base material 40 by resistance welding.

As shown in FIG. 2, the precious metal chip 50 is arranged so that its bottom surface is in contact with the electrode base material 40 and the metal member 60. Specifically, as shown in FIG. 4, the bottom surface of the noble metal chip 50 contacts the rectangular parallelepiped portion 61 of the metal member 60, and also contacts the portions 41 and 42 of the electrode base material 40 and the peripheral portions thereof. It is arranged like this. The bottom surface of the precious metal chip 50 is joined to the electrode base material 40 and the metal member 60 by resistance welding.

Next, a method of joining the electrode base material 40, the precious metal chip 50, and the metal member 60 will be described in detail.
In the spark plug 10 of the present embodiment, in the manufacturing process of the ground electrode 14, after the first joining step of joining the metal member 60 to the electrode base material 40 is performed, the noble metal chip is attached to the electrode base material 40 and the metal member 60. A second joining step of joining 50 is performed.

In the first joining step, first, as shown by an arrow in FIG. 5, the metal member 60 is inserted into the insertion groove 402 of the electrode base material 40. The inner peripheral surface 402a of the insertion groove 402 has a shape slightly larger than the outer peripheral surface 601 of the metal member 60. Further, the depth H11 of the insertion groove 402 is slightly shorter than the thickness H12 of the metal member 60. After fitting the metal member 60 into the insertion groove 402, the resistance welded electrode 80 is brought into contact with the outer surface 600 of the metal member 60, and a current is passed through the metal member 60 and the electrode base material 40 from the resistance welded electrode 80 to the metal member 60. The metal member 60 is pushed into the electrode base material 40 by applying an external force to the electrode base material 40. As a result, they are joined by resistance welding due to Joule heat generated at the contact portion between the bottom surface 602 of the metal member 60 and the bottom surface 402b of the insertion groove 402 of the electrode base material 40. Further, since the electrode base material 40 having a lower melting point is softened by Joule heat, the metal member 60 is gradually embedded in the electrode base material 40 by the external force applied from the resistance welded electrode 80 to the metal member 60. The metal member 60 is pushed into the electrode base material 40 until its outer surface 600 is flush with the surface 400 of the electrode base material 40. The welding burrs generated in this process fill the gap formed between the outer peripheral surface 601 of the metal member 60 and the inner peripheral surface 402a of the insertion groove 402 of the electrode base material 40. At this time, the outer peripheral surface 601 of the metal member 60 and the inner peripheral surface 402a of the insertion groove 402 of the electrode base material 40 may be joined by resistance welding. After embedding the metal member 60 in the electrode base material 40 in this way, a step of removing the welding burrs formed on the outer surface 600 of the metal member 60 is performed, and the metal is formed in the electrode base material 40 as shown in FIG. The molding of the primary molded product 90 in which the member 60 is embedded is completed.

Subsequently, as a second joining step, a step of joining the precious metal chip 50 to the primary molded product 90 shown in FIG. 6 is performed. Specifically, after arranging the noble metal chip 50 in the substantially central portion of the metal member 60 as shown by an arrow in FIG. 6, the noble metal chip 50 is joined to the electrode base material 40 and the metal member 60 by resistance welding.

Next, an operation example of the spark plug 10 of the present embodiment will be described.
When the air-fuel mixture burns in the cylinder of the internal combustion engine, the temperature of the ground electrode 14 exposed in the cylinder rises sharply, so that the electrode base material 40 thermally expands. At this time, in the spark plug 10 of the present embodiment, as shown in FIG. 4, the portions 41 and 42 of the electrode base material 40 are sandwiched between the first end portion 62 and the second end portion 63 of the metal member 60. Moreover, since the linear expansion coefficient of the metal member 60 is smaller than the linear expansion coefficient of the electrode base material 40, the elongation of the portions 41 and 42 of the electrode base material 40 is suppressed by the metal member 60. Therefore, it is difficult for a difference in the amount of elongation to occur between the electrode base material 40 and the metal member 60, and it is difficult for stress to be generated at their joint interfaces. Therefore, cracks and the like are unlikely to occur at the joint interface between the electrode base material 40 and the metal member 60.

Further, since the noble metal chip 50 is bonded to the periphery of the portions 41 and 42 of the electrode base material 40, the elongation of the portions 41 and 42 of the electrode base material 40 is suppressed, so that the noble metal chip 50 and the electrode base material 40 are bonded. It is difficult for stress to be generated at the junction interface with. Therefore, cracks and the like are unlikely to occur at their joint interfaces.

Further, the electrode base material 40 is more likely to extend in the longitudinal direction X than in the lateral direction Y due to thermal expansion. As shown enlarged in FIG. 7, the portion 41 of the electrode base material 40 sandwiched between one side surface 620 of the first end portion 62 of the electrode base material 40 and one side surface 630 of the second end portion 63. Is deformed to extend in the longitudinal direction X, the direction of the elongation changes from a direction parallel to the longitudinal direction X to a direction along one side surface 620 of the first end portion 62 of the metal member 60. Therefore, the amount of elongation of the portion 41 of the electrode base material 40 is smaller than the amount of elongation of the portion 43 located outside the portion 41 of the electrode base material 40. Such a difference in the amount of elongation of the electrode base material 40 is caused by the electrode base material 40 sandwiched between the other side surface 621 of the first end portion 62 of the electrode base material 40 and the other side surface 631 of the second end portion 63. It also occurs between the site 42 and the site 44 located outside the site 42. Due to such a difference in the amount of partial elongation of the electrode base material 40, the side surfaces 620, 621 and the second of the first end portion 62 of the metal member 60 change so that the electrode base material 40 extends in the longitudinal direction X. The electrode base material 40 is pressed against the side surfaces 630 and 631 of the end portion 63. As a result, it is possible to further improve the bonding force between the electrode base material 40 and the metal member 60.

On the other hand, if the noble metal chip 50 is bonded to the metal member 60 and the metal member 60 has the same coefficient of linear expansion as the noble metal chip 50, it is assumed that the temperature of the ground electrode 14 is repeatedly raised and lowered. Also, the metal member 60 and the noble metal chip 50 can easily undergo thermal expansion and contraction integrally. Therefore, stress due to the difference in the amount of thermal expansion between the metal member 60 and the noble metal chip 50 is unlikely to be generated at their joint portions, so that cracks and peeling are unlikely to occur at their joint interfaces.

According to the spark plug 10 of the present embodiment described above, the actions and effects shown in the following (1) to (6) can be obtained.
(1) The ground electrode 14 is a noble metal chip 50 bonded to both the electrode base material 40, the metal member 60 embedded in the tip of the electrode base material 40 and bonded, and the electrode base material 40 and the metal member 60. And have. The coefficient of linear expansion of the metal member 60 is smaller than the coefficient of linear expansion of the electrode base material 40 and is greater than or equal to the coefficient of linear expansion of the noble metal chip 50. The noble metal chip 50 has a shape capable of restraining the thermal expansion of the electrode base material 40. According to this configuration, even in an environment where the electrode base material 40 thermally expands due to a temperature rise, the thermal expansion of the electrode base material 40 is constrained by the metal member 60, so that the electrode base material 40 and the metal member 60 Cracks are less likely to occur at the joint interface of.

(2) The metal member 60 is embedded in the electrode base material 40 so as to be exposed from the surface 400 facing the center electrode 13 in the electrode base material 40. The precious metal chip 50 is joined to the metal member 60. According to this configuration, the stress caused by the difference in the amount of thermal expansion between the members is higher in the portion joined to the metal member 60 than in the portion joined to the electrode base material 40 in the precious metal chip 50. Hard to occur. Therefore, by joining the precious metal chip 50 to the metal member 60, it is possible to prevent cracks and the like from occurring. As a result, it is possible to prevent the precious metal chip 50 from falling off from the electrode base material 40 and the metal member 60, so that the life of the spark plug 10 can be improved.

(3) The electrode base material 40 tends to extend in the longitudinal direction X due to thermal expansion. In consideration of this, as shown in FIG. 2, the length of the metal member 60 along the longitudinal direction X of the electrode base material 40 is longer than the length of the electrode base material 40 along the lateral direction Y. It has a shape. That is, the longitudinal direction of the metal member 60 coincides with the direction in which the electrode base material 40 is easily stretched. According to this configuration, the elongation of the electrode base material 40 can be easily restrained by the metal member 60, so that the generation of cracks and the like can be suppressed more accurately.

(4) The metal member 60 is embedded in the electrode base material 40 so that the joint surface 600 thereof is flush with the surface 400 of the electrode base material 40. According to this configuration, since the noble metal chip 50 can be brought into contact with not only the metal member 60 but also the electrode base material 40, the noble metal chip 50 can be bonded to both the metal member 60 and the electrode base material 40. As a result, the bonding strength of the precious metal chip 50 can be improved.

(5) The metal member 60 may be made of the same material as the precious metal chip 50. According to this configuration, the coefficient of linear expansion of the metal member and the coefficient of linear expansion of the noble metal chip 50 can be made to match each other, so that they are likely to be integrally thermally expanded and contracted. As a result, cracks and the like are less likely to occur at their joint interfaces.

(6) The electrode base material has a structure in which the portions 41 and 42 of the electrode base material 40 are partially sandwiched by the side surfaces 620 and 621 of the first end portion 62 of the metal member 60 and the side surfaces 630 and 631 of the second end portion 63. The thermal expansion of 40 is constrained. According to this configuration, it is possible to easily realize a structure capable of restraining the thermal expansion of the electrode base material 40.

(First modification)
Next, a first modification of the spark plug 10 of the first embodiment will be described.
In the spark plug 10 of this modification, in the second bonding step of the ground electrode 14, the precious metal chip 50 is bonded to the electrode base material 40 and the metal member 60 by resistance welding, and then the precious metal chip 50 is bonded to the electrode base material by laser welding. Further fixed to the 40 and the metal member 60. Specifically, by irradiating the outer peripheral portion of the bottom of the noble metal chip 50 with a laser, the contact portion between the noble metal chip 50 and the metal member 60 and the contact portion between the noble metal chip 50 and the electrode base material 40 are melted. As a result, a molten portion 70 as shown in FIGS. 8 and 9 is formed on the outer peripheral portion of the bottom portion of the precious metal chip 50. The precious metal chip 50 is further joined to the electrode base material 40 and the metal member 60 via the molten portion 70.

According to this configuration, it is possible to further improve the bonding strength of the precious metal chip 50. In particular, since the bonding strength between the electrode base material 40 and the noble metal chip 50 can be improved, cracks and peeling occur at the bonding interface between the electrode base material 40 and the noble metal chip 50 even in an environment of a cold cycle, for example. It becomes difficult to occur.

(Second modification)
Next, a second modification of the spark plug 10 of the first embodiment will be described.
In the metal member 60 of this modification, as shown in FIG. 10, the first end portion 62 and the second end portion 63 are formed in a triangular columnar shape, respectively. One end of the rectangular parallelepiped portion 61 is integrally connected to the central portion of the bottom surface 622 of the first end portion 62, and the other end portion of the rectangular parallelepiped portion 61 is integrated to the central portion of the bottom surface 632 of the second end portion 63. Are linked together. As shown in FIG. 11, the metal member 60 is embedded in the tip portion 401 of the electrode base material 40.

Even when such a metal member 60 is used, as shown in FIG. 11, the electrode base material 40 is formed by the bottom surface 622 of the first end portion 62 of the metal member 60 and the bottom surface 632 of the second end portion 63. Parts 41 and 42 can be sandwiched. Therefore, the same or similar action and effect as the spark plug 10 of the first embodiment can be obtained.

In the spark plug 10 of this modification, in addition to the method of joining the electrode base material 40, the noble metal chip 50, and the metal member 60 by resistance welding, the joining strength between the metal member 60 and the electrode base material 40 is added. In order to further improve the above, the metal member 60 and the electrode base material 40 may be joined by laser welding via the molten portion 71, as shown in FIG.

(Third modification example)
Next, a third modification of the spark plug 10 of the first embodiment will be described.
In the metal member 60 of this modification, as shown in FIG. 13, the first end portion 62 and the second end portion 63 are formed in a rectangular parallelepiped shape, respectively. One end of the rectangular parallelepiped portion 61 is integrally connected to the central portion of the side surface 623 of the first end portion 62, and the other end portion of the rectangular parallelepiped portion 61 is integrated to the central portion of the side surface 633 of the second end portion 63. Is linked. As shown in FIG. 14, the metal member 60 is embedded in the tip portion 401 of the electrode base material 40.

Even when such a metal member 60 is used, as shown in FIG. 14, the electrode base material 40 is formed by the side surface 623 of the first end portion 62 of the metal member 60 and the side surface 633 of the second end portion 63. Parts 41 and 42 can be sandwiched. Therefore, the same or similar action and effect as the spark plug 10 of the first embodiment can be obtained.

In the spark plug 10 of this modification, in addition to the method of joining the electrode base material 40, the noble metal chip 50, and the metal member 60 by resistance welding, the joining strength between the metal member 60 and the electrode base material 40 is added. In order to further improve the above, the metal member 60 and the electrode base material 40 may be joined by laser welding via the molten portion 72, as shown in FIG.

<Second Embodiment>
Next, the spark plug 10 of the second embodiment will be described.
In the spark plug 10 of the present embodiment, instead of the metal member 60, a metal member 100 composed of a pair of metal pieces 110 and 120 as shown in FIG. 16 is used. Each of the metal pieces 110 and 120 is formed so that the cross-sectional shape orthogonal to the central axis m10 is concave. The pair of metal pieces 110 and 120 are arranged so that the openings 111 and 121 face each other with the cross-shaped portion 45 which is a part of the electrode base material 40 interposed therebetween. Notches 112 and 122 are formed on the bottom surfaces of the metal pieces 110 and 120, respectively. The cutouts 112 and 122 are formed so that the width becomes narrower toward the openings 111 and 121, and the cross-sectional shape orthogonal to the central axis m10 is trapezoidal. The cutouts 112 and 122 of the metal pieces 110 and 120 sandwich the portions 46 and 47, which are a part of the electrode base material 40, respectively.

Next, an operation example of the spark plug 10 of the present embodiment will be described.
In the spark plug 10 of the present embodiment, when the electrode base material 40 is thermally expanded, the amount of elongation of the portions 48 and 49 located outside the portions 46 and 47 is larger than the amount of elongation of the portions 46 and 47. Due to these differences in the amount of elongation, as the electrode base material 40 thermally expands, the portions 46 and 47 of the electrode base material 40 press the metal pieces 110 and 120 toward the portion 45 of the electrode base material 40. In this way, the pressing force applied to the metal pieces 110 and 120 suppresses the thermal expansion of the portion 45 of the electrode base material 40 sandwiched between the metal pieces 110 and 120. As a result, similarly to the spark plug 10 of the first embodiment, the actions and effects shown in the above (1), (2), (4), and (5) are exhibited.

Further, according to the spark plug 10 of the present embodiment, the action and effect shown in the following (7) can be further obtained.
(7) The thermal expansion of the electrode base material 40 is suppressed by the structure in which the electrode base material 40 is partially sandwiched by one metal piece 110, 120. According to this configuration, it is possible to easily realize a structure capable of restraining the thermal expansion of the electrode base material 40.

(Modification example)
Next, a modification of the spark plug 10 of the second embodiment will be described.
As shown in FIG. 17, for example, the metal pieces 110 and 120 are formed so that the cross-sectional shape centered on the central axis m10 is concave, but the metal pieces 110 and 120 do not have the notches 112 and 122. It may be formed in. Alternatively, as shown in FIG. 18, the metal pieces 110 and 120 have the same shape as the metal member 60 of the first embodiment, and are arranged so as to line up in the lateral direction Y of the electrode base material 40. You may.

Even when the metal pieces 110 and 120 are formed as shown in FIGS. 17 and 18, if they can partially restrain the thermal expansion of the electrode base material 40, the second It is possible to obtain the same or similar action and effect as the spark plug 10 of the embodiment.
The metal pieces 110 and 120 shown in FIG. 17 may be joined to the electrode base material 40 by laser welding via the melting portion 73 as shown in FIG. The metal pieces 110 and 120 shown in FIG. 16 and the metal pieces 110 and 120 shown in FIG. 18 may also be similarly joined to the electrode base material 40 by laser welding.

<Third Embodiment>
Next, the spark plug 10 of the third embodiment will be described. Hereinafter, the differences from the spark plug 10 of the first embodiment will be mainly described.
As shown in FIGS. 20 and 21, in the spark plug 10 of the present embodiment, the metal member 60 is embedded in the back surface 403 of the tip portion 401 of the electrode base material 40 opposite to the surface 400 facing the center electrode 13. It has been. The metal member 60 is joined to the electrode base material 40 by resistance welding. The bottom surface of the precious metal chip 50 is joined to the surface 400 of the electrode base material 40 by resistance welding. Further, the outer peripheral portion of the bottom portion of the noble metal chip 50 is joined to the electrode base material 40 by laser welding via the molten portion 74.

Even in the spark plug 10 of the present embodiment, since the first end portion 62 and the second end portion 63 of the metal member 60 sandwich the portions 81 and 82 of the electrode base material 40, the thermal expansion of those portions 81 and 82 occurs. It is restrained by the metal member 60. As a result, on the back surface 403 of the electrode base material 40, it is difficult for a difference between the thermal expansion amount of the electrode base material 40 and the thermal expansion amount of the metal member 60 to occur, so that stress is unlikely to be generated at the joint interface between them. Therefore, cracks and the like are less likely to occur at the joint interface between the metal member 60 and the electrode base material 40. Further, on the surface 400 of the electrode base material 40, it is difficult for a difference between the thermal expansion amount of the electrode base material 40 and the thermal expansion amount of the noble metal chip 50 to occur, so that stress is also unlikely to occur at the bonding interface between them. Therefore, cracks and the like are less likely to occur at the joint interface between the electrode base material 40 and the precious metal chip 50.

As described above, the spark plug 10 of the present embodiment can also obtain the same or similar action and effect as the spark plug 10 of the first embodiment.
<Other embodiments>
In addition, each embodiment can also be carried out in the following embodiments.

In the spark plug 10 of the second embodiment, the metal member 100 is not limited to the two metal pieces 110 and 120, but may be composed of three or more metal pieces.
-The shape of the metal member 60 of each embodiment can be changed as appropriate.

In the spark plugs 10 of the first embodiment and the second embodiment, the metal member 60 may be provided so as to protrude from the surface 400 of the electrode base material 40. In this case, the precious metal chip 50 may be joined only to the metal member 60. Similarly, in the spark plug 10 of the third embodiment, the metal member 60 may be provided so as to protrude from the back surface 403 of the electrode base material 40.

-The present disclosure is not limited to the above specific examples. Specific examples described above with appropriate design changes by those skilled in the art are also included in the scope of the present disclosure as long as they have the characteristics of the present disclosure. Each element included in each of the above-mentioned specific examples, and their arrangement, conditions, shape, and the like are not limited to those exemplified, and can be appropriately changed. The combinations of the elements included in each of the above-mentioned specific examples can be appropriately changed as long as there is no technical contradiction.

10: Spark plug 13: Center electrode 14: Ground electrode 50: Noble metal chip 40: Electrode base material 60, 100: Metal member 61: Rectangular parallelepiped part 62: First end 63: Second end 110, 120: Metal piece

Claims (10)

A spark plug (10) that forms a spark discharge by applying a voltage between the center electrode (13) and the ground electrode (14).
The ground electrode is bonded to the electrode base material (40), a metal member (60, 100) embedded and bonded to the tip of the electrode base material, and at least one of the electrode base material and the metal member. With a precious metal chip (50),
The coefficient of linear expansion of the metal member is smaller than the coefficient of linear expansion of the electrode base material and equal to or greater than the coefficient of linear expansion of the noble metal chip.
The metal member is a spark plug having a shape capable of restraining the thermal expansion of the electrode base material. The metal member is embedded in the electrode base material so as to be exposed from the surface of the electrode base material facing the center electrode.
The spark plug according to claim 1, wherein the precious metal chip is joined to the metal member. The tip of the electrode base material is formed so that the cross-sectional shape orthogonal to the central axis of the spark plug is rectangular.
The spark plug according to claim 2, wherein the metal member has a shape in which the length along the longitudinal direction of the electrode base material is longer than the length along the lateral direction of the electrode base material. When the surface of the metal member to which the noble metal chip is joined is used as the joining surface,
The spark plug according to claim 2 or 3, wherein the metal member is embedded in the electrode base material so that the joint surface is flush with the surface of the electrode base material. The spark plug according to any one of claims 2 to 4, wherein the noble metal chip is bonded to both the electrode base material and the metal member. The spark plug according to any one of claims 2 to 5, wherein the metal member is made of the same material as the noble metal chip. The metal member (60) has a rectangular parallelepiped portion (61) formed in a rectangular parallelepiped shape, and a first end portion (62) and a second end portion integrally formed at both ends of the rectangular parallelepiped portion in the longitudinal direction, respectively. (63) and
The first end portion and the second end portion each have a shape having side surfaces arranged so as to face each other with the electrode base material interposed therebetween in the longitudinal direction of the rectangular parallelepiped portion.
Any one of claims 2 to 6 in which the thermal expansion of the electrode base material is constrained by the structure in which the electrode base material is partially sandwiched between the side surface of the first end portion and the side surface of the second end portion. Spark plugs described in section. The metal member (100) is composed of a plurality of metal pieces (110, 120).
The spark plug according to any one of claims 2 to 7, wherein the thermal expansion of the electrode base material is restricted by a structure in which the electrode base material is partially sandwiched by a plurality of the metal pieces. The bottom surface of the metal member is joined to the electrode base material by resistance welding.
The spark plug according to any one of claims 2 to 8, wherein the noble metal chip is joined to the electrode base material and the metal member by resistance welding and laser welding. The spark plug according to claim 1, wherein the metal member is embedded in the back surface of the electrode base material opposite to the surface facing the center electrode.

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