Spark plug

Abstract

To provide a spark plug capable of inhibiting peeling occurring between a ground electrode and a housing even if hardness of an outer cover layer in the ground electrode is increased.SOLUTION: A base end (51) of a spark plug has an outer cover layer (511), an intermediate layer (512), and a core material layer (513). A junction interface (51a) of the base end (51) joined to the housing (11) is formed only by the core material layer (513). An inner surface (51b) of the base end along an inner surface (11a) of the housing and an outer surface (51c) of the base end along an outer surface (11b) of the housing are formed only by the outer cover layer and the core material layer.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to spark plugs. [Background technology]

[0002] Patent Document 1 below discloses an invention related to a spark plug. In the spark plug described in Patent Document 1 below, the base end of the ground electrode has an outer shell portion disposed on the surface side, an intermediate portion having a higher thermal conductivity than the outer shell portion, and a core portion having a higher hardness than the intermediate portion. At the weld interface between the housing and the ground electrode, only the outer shell portion and the core portion are present, and the intermediate portion is not included. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-27754 A Summary of the Invention [Problem to be solved by the invention]

[0004] In Patent Document 1, it is said that the intermediate portion, whose material strength is inferior to the other two portions, is not included in the welded interface with the housing, thereby preventing the weld strength of the ground electrode from decreasing. In Patent Document 1, the outer shell is made of a metal material that is the hardest and has the highest heat resistance among the ground electrodes, for example, a Ni-based heat-resistant alloy. The outer shell contains a predetermined proportion of aluminum. The intermediate portion is made of, for example, pure Cu or a Cu alloy. The core portion is made of, for example, pure Ni or a Ni alloy.

[0005] In Patent Document 1, elements such as aluminum are added to the material composing the outer cover, which increases the hardness of the outer cover but reduces its ductility. Therefore, when the ground electrode is bent by applying a force in a direction that pulls it away from the housing, there is a concern that peeling may occur at the joint interface between the ground electrode and the housing.

[0006] An object of the present disclosure is to provide a spark plug that can suppress peeling between the ground electrode and the housing even when the hardness of the outer cover layer of the ground electrode is increased. [Means for solving the problem]

[0007] The present disclosure relates to a spark plug, the spark plug comprising an insulator (12) that houses a center electrode (13), a housing (11) that houses the insulator, and a ground electrode (14) having a tip end (52) arranged to form a predetermined gap with respect to the center electrode, and a base end (51) that extends along the center electrode and is joined to the housing. The base end has an outer skin layer (511) arranged on a surface side, an intermediate layer (512) having a higher thermal conductivity than the outer skin layer, and a core layer (513) having a higher hardness than the intermediate layer. In a cross section including the center axis and the base end of the spark plug, a joint interface (51a) of the base end with the housing is composed only of the core layer, and an inner surface (51b) of the base end along the inner surface (11a) of the housing and an outer surface (51c) of the base end along the outer surface (11b) of the housing are composed only of the outer skin layer and the core layer. Effect of the Invention

[0008] According to the present disclosure, it is possible to provide a spark plug that can suppress peeling between the ground electrode and the housing even when the hardness of the outer cover layer of the ground electrode is increased. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a partial cross-sectional view of a spark plug according to the present embodiment. [Diagram 2] FIG. 2 is a perspective view showing the vicinity of the ground electrode of the spark plug according to the present embodiment. [Diagram 3] FIG. 3 is a cross-sectional view showing the ground electrode of the spark plug in this embodiment. [Figure 4]FIG. 4 is a cross-sectional view showing the ground electrode of the spark plug of the present embodiment. [Diagram 5] FIG. 5 is a diagram for explaining a method for manufacturing the spark plug according to this embodiment. [Figure 6] FIG. 6 is a diagram for explaining the method for manufacturing the spark plug in this embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the present embodiment will be described with reference to the accompanying drawings. In order to facilitate understanding of the description, the same components in each drawing are denoted by the same reference numerals as much as possible, and duplicated description will be omitted.

[0011] A schematic configuration of a spark plug 10 according to an embodiment will be described with reference to Fig. 1. The spark plug 10 is attached to, for example, an engine head block. The spark plug 10 ignites an air-fuel mixture in a cylinder of the engine by forming a spark discharge based on application of a voltage. The spark plug 10 includes a housing 11, an insulator 12, a center electrode 13, and a ground electrode 14.

[0012] The housing 11 is formed in a cylindrical shape centered on a plug central axis m10, which is the central axis of the spark plug 10. The housing 11 is formed of a metal material such as carbon steel. The lower end of the insulator 12 is inserted into the inside of the housing 11. A threaded portion 114 is formed on the outer circumferential surface of the lower part of the housing 11. The spark plug 10 can be fastened and fixed to the engine head block by screwing the threaded portion 114 of the housing 11 into a screw hole formed in the engine head block. In the following, the direction along the plug central axis m10 is also referred to as the "plug axial direction Da". The circumferential direction centered on the plug central axis m10 is also referred to as the "plug circumferential direction Dc". The ground electrode 14 side is also referred to as the tip side, and the opposite side is also referred to as the base side.

[0013] The insulator 12 is formed in a cylindrical shape centered on the plug central axis m10. The insulator 12 is made of an insulating material such as alumina. The housing 11 is integrally assembled to the outer periphery of the insulator 12. An axial hole 120 is formed inside the insulator 12. The axial hole 120 is formed so as to penetrate the insulator 12 from the tip end side to the base end side along the plug central axis m10. The center electrode 13, the first seal body 15, the resistor 16, the second seal body 17, and the terminal fitting 18 are inserted in this order from the tip end side into the axial hole 120. The center electrode 13 is inserted into the insulator 12 so as to be exposed from the tip end of the insulator 12.

[0014] The center electrode 13 has a center electrode base material 30 and a center electrode tip 40. The center electrode base material 30 is formed in a cylindrical shape centered on the plug central axis m10. The center electrode base material 30 is made of a nickel (Ni) alloy or the like having excellent heat resistance. The center electrode tip 40 is joined to the tip of the center electrode base material 30. The center electrode tip 40 is formed in a cylindrical shape centered on the plug central axis m10. The center electrode tip 40 is made of an iridium alloy or the like. A first seal body 15, a resistor 16, and a second seal body 17 are sandwiched between the base end side of the center electrode 13 and the tip side of the terminal fitting 18.

[0015] The terminal fitting 18 is formed in a substantially cylindrical shape centered on the plug central axis m10. The terminal fitting 18 is formed of a steel material or the like. A terminal portion 180 is provided on the base end side of the terminal fitting 18. The terminal portion 180 is exposed to the outside from the base end side of the insulator 12.

[0016] The ground electrode 14 has a ground electrode base material 50 and a ground electrode tip 60. The ground electrode base material 50 is made of a nickel alloy or the like. The ground electrode base material 50 is joined to a front end surface 110 of the housing 11. The ground electrode base material 50 is formed so as to extend from the front end surface 110 of the housing 11 to a position facing the center electrode tip 40. The ground electrode tip 60 is joined to a front end portion of the ground electrode base material 50. The ground electrode tip 60 is made of a precious metal alloy such as an iridium alloy or a platinum alloy. The ground electrode tip 60 is disposed so as to face the center electrode tip 40. A gap formed between the center electrode tip 40 and the ground electrode tip 60 is called a spark gap 19.

[0017] In the spark plug 10, an external circuit capable of applying a high voltage is connected to the terminal portion 180 of the terminal fitting 18. When a high voltage is applied to the terminal portion 180 by the external circuit, a spark discharge is generated between the center electrode tip 40 of the center electrode 13 and the ground electrode tip 60 of the ground electrode 14. This spark discharge ignites the air-fuel mixture in the cylinder of the engine, forming a flame, and the mixture is burned.

[0018] Next, the structures of the housing 11 and the ground electrode 14 will be described in detail. As shown in FIG. 2, the ground electrode base material 50 has a base end 51 and a tip end 52. The base end 51 is joined to the tip end surface 110 of the housing 11. The base end 51 is formed so as to extend from the tip end surface 110 of the housing 11 in the plug axial direction Da. The tip end 52 is formed so as to extend from the tip of the base end 51 to a position facing the center electrode tip 40 of the center electrode 13. The ground electrode base material 50 is formed into a substantially L-shape as a whole by being composed of the base end 51 and the tip end 52. In this embodiment, a surface connected to the tip end surface 110 of the housing 11 and on the side of the plug central axis m10 is defined as an inner surface 11a, and an outer side surface opposite to the inner surface 11a is defined as an outer surface 11b.

[0019] As shown in FIG. 3, the base end portion 51 of the ground electrode base material 50 has an outer skin layer 511 , an intermediate layer 512 , and a core layer 513 .

[0020] The outer skin layer 511 is a layer disposed on the outermost side when viewed from the center side of the base end portion 51. The outer skin layer 511 is formed on both the inner surface 11a side and the outer surface 11b side. The outer skin layer 511 is made of, for example, a Ni-based heat-resistant alloy containing nickel (Ni) as a main component. In this specification, the "main component" means the material component with the largest content. Note that the alloy constituting the outer skin layer 511 desirably contains aluminum (Al) at a predetermined ratio.

[0021] The intermediate layer 512 is a layer disposed inside the outer layer 511. The intermediate layer 512 is made of a metal material having a higher thermal conductivity than the outer layer 511. The intermediate layer 512 is desirably made of a metal material having a higher thermal conductivity than the metal material constituting the core layer 513. The intermediate layer 512 is made of, for example, pure Cu or a Cu alloy.

[0022] The core layer 513 is a layer disposed inside the skin layer 511 and / or the intermediate layer 512. The core layer 513 is made of a metal material having a higher hardness than the intermediate layer 512. The core layer 513 is made of, for example, pure Ni or a Ni alloy.

[0023] 3, a joint interface 51a of the base end 51 with the housing 11 is formed only by the core material layer 513. An inner surface 51b of the base end 51 along the inner surface 11a of the housing 11, and an outer surface 51c of the base end 51 along the outer surface 11b of the housing 11 are formed only by the outer skin layer 511 and the core material layer 513.

[0024] The spark plug 10 according to this embodiment includes an insulator 12 that houses a center electrode 13, a housing 11 that houses the insulator 12, and a ground electrode 14 that has a tip end 52 arranged to form a predetermined gap with respect to the center electrode 13, and a base end 51 that extends along the center electrode 13 and is joined to the housing 11. The base end 51 has an outer skin layer 511 arranged on the surface side, an intermediate layer 512 having a higher thermal conductivity than the outer skin layer 511, and a core layer 513 having a higher hardness than the intermediate layer 512.

[0025] In a cross section including the base end 51 and the plug central axis m10, which is the central axis of the spark plug, a joint interface 51a of the base end 51 to the housing 11 is formed only by the core material layer 513. Since the joint interface 51a is formed only by the core material layer 513, the housing 11 and the base end 51 are joined by only one type of material combination, that is, the core material layer 513 and the housing 11, stress concentration is unlikely to occur when an external force is applied, and the joint strength is increased.

[0026] Furthermore, since the inner surface 51b and the outer surface 51c of the base end portion 51 are composed only of the skin layer 511 and the core layer 513, no intermediate layer 512 is interposed on the inner surface 51b side and the outer surface 51c side, and the bonding strength between the skin layer 511 and the core layer 513 is increased.

[0027] In this embodiment, the core layer 513 has a lower hardness than the skin layer 511. Since the core layer 513 has a lower hardness than the skin layer, it is possible to make the core layer 513 a more flexible portion, and when an external bending force is applied to the base end portion 51, the core layer 513 is stretched, and the stress on the skin layer 511 is more reliably reduced.

[0028] In this embodiment, the core material layer 513 and the housing 11 are diffusion bonded. In other words, the core material layer 513 and the housing 11 are solid-state bonded. The material constituting the core material layer 513 and the material constituting the housing 11 are mixed in the bonding region between the core material layer 513 and the housing 11. With this configuration, the bonding strength between the core material layer 513 and the housing 11 can be further increased.

[0029] In this embodiment, the core layer 513 and the skin layer 511 are diffusion bonded. In other words, the core layer 513 and the skin layer 511 are solid-state bonded. The material constituting the core layer 513 and the material constituting the skin layer 511 are mixed in the bonding region between the core layer 513 and the skin layer 511. With this configuration, the bonding strength between the core layer 513 and the skin layer 511 can be further increased.

[0030] In addition, the core layer 513 may have a lower hardness than the outer skin layer 511, the core layer 513 and the housing 11 may be diffusion-bonded, and the core layer 513 and the outer skin layer 511 may be diffusion-bonded in any combination. For example, the core layer 513 may have a lower hardness than the outer skin layer 511, and the core layer 513 and the housing 11 may be diffusion-bonded, but the core layer 513 and the outer skin layer 511 may not be diffusion-bonded. For example, the core layer 513 may have a lower hardness than the outer skin layer 511, and the core layer 513 and the outer skin layer 511 may be diffusion-bonded, but the core layer 513 and the housing ... and the housing 11 may be diffusion-bonded, and the core layer 513 and the outer skin layer 511 may be diffusion-bonded, but the core layer 513 may not have a lower hardness than the outer skin layer 511. Of course, all of the constituent elements may be provided.

[0031] 3, the vicinity of the center of the bonding interface 51a has a concave shape receding from the housing 11, but the shape of the bonding interface 51a is not limited to this. As shown in FIG 4, the vicinity of the center of the bonding interface 51a may have a convex shape protruding toward the housing 11, or may be flat.

[0032] A method for manufacturing the spark plug 10 will be described with reference to Figs. 5 and 6. As shown in Fig. 5, a press table J1, a stopper J2, an upper electrode E1, and a lower electrode E2 are prepared. A housing 11 is placed on the press table J1. The press table J1 is configured to hold the housing 11 and apply pressure in the direction of the arrow in the figure. A ground electrode material 50M, which will become the ground electrode base material 50 after processing, is prepared and held between the upper electrode E1 and the lower electrode E2. One end of the ground electrode material 50M is abutted against the housing 11, and the other end is held by the stopper J2. After being arranged in this manner, current is passed through the upper electrode E1 and the lower electrode E2 to perform resistance welding.

[0033] The joining state between the ground electrode material 50M and the housing 11 during resistance welding will be described with reference to Fig. 6. Fig. 6 is an enlarged view of part VI in Fig. 5 rotated 90° clockwise.

[0034] 6(A), the ground electrode material 50M has an outer cover material 511M, an intermediate material 512M, and a core material 513M. The outer cover material 511M is a portion that will become the outer cover layer 511 after processing, and is made of the same material as the outer cover layer 511. The intermediate material 512M is a portion that will become the intermediate layer 512 after processing, and is made of the same material as the intermediate layer 512. The outer cover material 511M, the intermediate material 512M, and the core material 513M are uniformly configured to abut against the tip surface 110 of the housing 11.

[0035] As shown in FIGS. 6B and 6C, current is passed through the intermediate material 512M and the core material 513M, so that the joining progresses so as to form a gentle concave surface near the center of the housing 11 in the thickness direction.

[0036] As shown in Fig. 6(D), as the joining progresses further, the core material 513M is deformed so as to be pushed outward on both sides. The deformation of the core material 513M ejects the intermediate material 512M, and the outer cover material 511M is also pushed outward. When it is cut along the dashed line in Fig. 6(D), the ground electrode base material 50 joined to the housing 11 is formed as shown in Fig. 6(E).

[0037] The present embodiment has been described above with reference to specific examples. However, the present disclosure is not limited to these specific examples. Any design modifications made by a person skilled in the art to these specific examples are also included within the scope of the present disclosure as long as they have the features of the present disclosure. The elements of each of the above-mentioned specific examples and their arrangements, conditions, shapes, etc. are not limited to those exemplified and can be changed as appropriate. The combination of each of the elements of each of the above-mentioned specific examples can be changed as appropriate as long as no technical contradiction occurs. [Explanation of symbols]

[0038] 11: Housing 11a:Inner surface 11b:Outer surface 12: Insulator 13: Center electrode 14: Ground electrode 51: Proximal end 51a: Bonding interface 511: Outer skin layer 512: Middle class 513: Core layer 52:Tip

Claims

1. A spark plug, comprising: an insulator (12) that houses a center electrode (13); a housing (11) that houses the insulator; a ground electrode (14) having a tip portion (52) arranged such that a predetermined gap is formed with respect to the center electrode, and a base end portion (51) that extends along the center electrode and is joined to the housing; wherein the base end portion has an outer skin layer (511) disposed on the surface side, an intermediate layer (512) having a higher thermal conductivity than the outer skin layer, and a core material layer (513) having a higher hardness than the intermediate layer; and in a cross section including the central axis of the spark plug and the base end portion, a joining interface (51a) of the base end portion with respect to the housing is constituted only by the core material layer, and an inner surface (51b) of the base end portion along the inner surface (11a) of the housing and an outer surface (51c) of the base end portion along the outer surface (11b) of the housing are constituted only by the outer skin layer and the core material layer.

2. The spark plug according to claim 1, wherein the core material layer has a lower hardness than the outer skin layer.

3. The spark plug according to claim 1, wherein the core material layer and the housing are diffusion bonded.

4. The spark plug according to claim 1, wherein the core material layer and the outer skin layer are diffusion bonded.

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