JP7722285B2 - Spark plug and method for manufacturing the same - Google Patents

Description

This disclosure relates to spark plugs and methods for manufacturing spark plugs.

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 located 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. The weld interface between the housing and the ground electrode only contains the outer shell portion and the core portion, and does not include the intermediate portion.

JP 2017-27754 A

Patent Document 1 claims that by not including the middle portion, whose material strength is weaker than the other two portions, at the weld interface with the housing, it is possible to prevent a decrease in the weld strength of the ground electrode. In Patent Document 1, the outer shell is made of a metal material with the highest hardness and heat resistance among the ground electrodes, such as a Ni-based heat-resistant alloy. The outer shell contains a specified proportion of aluminum. The middle 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.

In Patent Document 1, elements such as aluminum are added to the material that makes up the outer sheath, which increases the hardness of the outer sheath but reduces its ductility. As a result, there is a concern that peeling may occur at the joint interface between the ground electrode and the housing if the ground electrode is bent by applying force in a direction that pulls it away from the housing.

The objective 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 coating layer on the ground electrode is increased.

The present disclosure relates to a 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) positioned 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) disposed on the surface side, an intermediate layer (512) that has a higher thermal conductivity than the outer skin layer, and a core material layer (513) that has a higher hardness than the intermediate layer. In a cross section including the center axis of the spark plug and the base end, the joint interface (51a) of the base end with the housing is composed only of the core material layer, and a first angle (θ1) formed by a tangent line (L1) that passes through an intersection (P1) of the outer surface (11b) of the housing and is tangent to the joint interface and an outer line (11bL) along the outer surface is an acute angle.

The present disclosure relates to a method for manufacturing a spark plug, which includes preparing a housing (11) that houses an insulator including a center electrode; preparing a ground electrode material (50M) that is joined to the housing to form a ground electrode, the ground electrode material having an outer cover material (511M) disposed on the surface side, an intermediate material (512M) that has a higher thermal conductivity than the outer cover material, and a core material (513M) that is harder than the intermediate material; forming the mating surface of the ground electrode material with the housing to have a first surface (50Ma) that is aligned with the leading edge surface (110) of the housing and a second surface (50Mb) that is disposed from the first surface toward the outer cover material; inclining the second surface toward the outer surface (11b) of the housing so that it is away from the leading edge surface; and abutting the mating surface of the ground electrode material against the leading edge surface of the housing and resistance welding the ground electrode material to form the ground electrode by joining the ground electrode material to the housing.

This disclosure provides a spark plug that can suppress peeling between the ground electrode and the housing, even when the hardness of the outer coating layer on the ground electrode is increased.

FIG. 1 is a partial cross-sectional view of a spark plug according to this embodiment. FIG. 2 is a perspective view showing the vicinity of the ground electrode of the spark plug according to this embodiment. FIG. 3 is a cross-sectional view showing the ground electrode of the spark plug according to this embodiment. FIG. 4 is a cross-sectional view showing the ground electrode of the spark plug according to this embodiment. FIG. 5 is a cross-sectional view showing the ground electrode of the spark plug according to this embodiment. FIG. 6 is a diagram for explaining a method for manufacturing a spark plug according to this embodiment. FIG. 7 is a diagram for explaining a method for manufacturing a spark plug according to this embodiment. FIG. 8 is a diagram for explaining a method for manufacturing a spark plug according to this embodiment. FIG. 9 is a diagram for explaining a method for manufacturing a spark plug according to this embodiment.

This embodiment will now be described with reference to the accompanying drawings. To facilitate understanding, identical components in each drawing will be designated by the same reference numerals whenever possible, and duplicate explanations will be omitted.

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

The housing 11 is cylindrically shaped and centered on the plug central axis m10, which is the central axis of the spark plug 10. The housing 11 is made of a metal material such as carbon steel. The lower end of the insulator 12 is inserted into the housing 11. A threaded portion 114 is formed on the outer peripheral 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 threaded hole formed in the engine head block. Note that, below, the direction along the plug central axis m10 is also referred to as the "plug axial direction Da." The circumferential direction about the plug central axis m10 is also referred to as the "plug circumferential direction Dc." The side facing the ground electrode 14 is also referred to as the tip side, and the opposite side is also referred to as the base side.

The insulator 12 is cylindrically formed around 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 to penetrate the insulator 12 from the tip end to the base end along the plug central axis m10. The center electrode 13, first seal body 15, resistor 16, second seal body 17, and terminal fitting 18 are inserted into the axial hole 120 in this order from the tip end. The center electrode 13 is inserted into the insulator 12 so that it is exposed from the tip end of the insulator 12.

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, which has 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.

The terminal fitting 18 is formed in a generally cylindrical shape centered on the plug central axis m10. The terminal fitting 18 is made of steel or other material. A terminal portion 180 is provided at the base end of the terminal fitting 18. The terminal portion 180 is exposed to the outside from the base end of the insulator 12.

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 bonded to the leading end surface 110 of the housing 11. The ground electrode base material 50 is formed so as to extend from the leading end surface 110 of the housing 11 to a position opposite the center electrode tip 40. The ground electrode tip 60 is bonded to the leading end 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 positioned so as to face the center electrode tip 40. The gap formed between the center electrode tip 40 and the ground electrode tip 60 is called the spark gap 19.

In the spark plug 10, an external circuit capable of applying high voltage is connected to the terminal portion 180 of the terminal fitting 18. When high voltage is applied to the terminal portion 180 by the external circuit, a spark discharge is formed 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 engine cylinder, forming a flame and causing the mixture to combust.

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 to extend from the tip end surface 110 of the housing 11 in the plug axial direction Da. The tip end 52 is formed 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 generally L-shape overall by being composed of the base end 51 and the tip end 52. In this embodiment, the surface connected to the tip end surface 110 of the housing 11 and facing the plug center axis m10 is referred to as the inner surface 11a, and the outer surface opposite the inner surface 11a is referred to as the outer surface 11b.

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

The outer skin layer 511 is the outermost layer when viewed from the center of the base end 51. The outer skin layer 511 is formed on both the inner surface 11a and the outer surface 11b. The outer skin layer 511 is made of, for example, a Ni-based heat-resistant alloy whose main component is nickel (Ni). In this specification, "main component" refers to the material component with the largest content. It is desirable that the alloy that makes up the outer skin layer 511 also contains aluminum (Al) at a specified ratio.

The intermediate layer 512 is a layer disposed inside the outer skin layer 511. The intermediate layer 512 is made of a metal material with a higher thermal conductivity than the outer skin layer 511. It is also desirable that the intermediate layer 512 be made of a metal material with a higher thermal conductivity than the metal material that makes up the core layer 513. The intermediate layer 512 is made of, for example, pure Cu or a Cu alloy.

The core layer 513 is a layer disposed inside the outer layer 511 and/or the intermediate layer 512. The core layer 513 is made of a metal material that is harder than the intermediate layer 512. The core layer 513 is made of, for example, pure Ni or a Ni alloy.

In the example shown in Figure 3, the bonding interface 51a of the base end 51 with the housing 11 is composed only of the core material layer 513.

The first angle θ1 is an acute angle formed by a tangent line L1 that passes through the intersection P1 between the outer surface 11b of the housing 11 and the joint interface 51a and is tangent to the joint interface 51a, and an outer line 11bL along the outer surface 11b. The second angle θ2 is an acute angle formed by a tangent line L2 that passes through the intersection P2 between the inner surface 11a of the housing 11 and the joint interface 51a and is tangent to the joint interface 51a, and an inner line 11aL along the inner surface 11a. In the example shown in Figure 3, both the first angle θ1 and the second angle θ2 are acute angles, but only one of them may be an acute angle.

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 that is positioned 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 that is positioned on the surface side, an intermediate layer 512 that has a higher thermal conductivity than the outer skin layer 511, and a core material layer 513 that has a higher hardness than the intermediate layer 512. In a cross section that includes the plug center axis m10, which is the central axis of the spark plug, and the base end 51, the joint interface 51a of the base end 51 with the housing 11 is composed only of the core material layer 513.

The first angle θ1, which is the angle between the tangent line L1 that passes through the intersection point P1 between the outer surface 11b of the housing 11 and the joint interface 51a and is tangent to the joint interface 51a, and the outer line 11bL along the outer surface 11b, is an acute angle. For example, when an external force that bends the base end 51 from the outer surface 11b side of the housing 11 toward the inner surface 11a is applied to the base end 51, tensile stress is generated at the joint interface 51a on the outer surface 11b side because the first angle θ1 is an acute angle. Tensile stress is stress along the direction that runs from the housing 11 to the base end 51 and intersects with the joint interface 51a. Therefore, compared to the shear stress that would occur if the first angle θ1 were an obtuse angle, stress is generated in a direction that increases the joint strength between the housing 11 and the base end 51, thereby suppressing delamination.

In the spark plug 10 according to this embodiment, the second angle θ2 formed by the tangent line L2 that passes through the intersection P2 between the inner surface 11a of the housing and the joint interface 51a and is tangent to the joint interface 51a, and the inner line 11aL along the inner surface 11a, is an acute angle. For example, when an external force that bends the base end 51 from the inner surface 11a of the housing 11 toward the outer surface 11b is applied to the base end 51, tensile stress is generated at the joint interface 51a on the inner surface 11a side because the second angle θ2 is an acute angle. Tensile stress is stress that runs along the direction from the housing 11 to the base end 51 and intersects with the joint interface 51a. Therefore, compared to the shear stress that would occur when the second angle θ2 is an obtuse angle, stress is generated in a direction that increases the joint strength between the housing 11 and the base end 51, thereby suppressing the occurrence of peeling.

When the first angle θ1 and the second angle θ2 are both acute angles as shown in Figure 3, the effects achieved when the first angle θ1 is an acute angle and the effects achieved when the second angle θ2 is an acute angle are both achieved.

In the example shown in FIG. 4, a portion of the joint interface 51a of the base end 51 relative to the housing 11 is composed of a core material layer 513 and an outer skin layer 511. More specifically, on the outer surface 11b side of the housing 11, the joint interface 51a is composed of the core material layer 513 and the outer skin layer 511.

In the example shown in FIG. 4, as in the example shown in FIG. 3, the base end portion 51 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 511, and a core material layer 513 having a higher hardness than the intermediate layer 512. In the example shown in FIG. 4, in a cross section including the plug central axis m10, which is the central axis of the spark plug, and the base end portion 51, the joint interface 51a of the base end portion 51 with the housing 11 is composed of the core material layer 513 and the outer skin layer 511.

In the example shown in FIG. 4 , the third angle θ3 formed by the tangent line L3 that passes through the intersection P3 between the outer surface 11b of the housing 11 and the bonded interface 51a and is tangent to the bonded interface 51a, and the outer line 11bL along the outer surface 11b, is an acute angle. For example, when an external force that bends the base end 51 from the outer surface 11b side of the housing 11 toward the inner surface 11a is applied to the base end 51, tensile stress is generated at the bonded interface 51a on the outer surface 11b side because the third angle θ3 is an acute angle. Tensile stress is stress along the direction from the housing 11 to the base end 51 and intersects with the bonded interface 51a. Therefore, compared to the shear stress that would occur if the third angle θ3 were an obtuse angle, stress is generated in a direction that increases the bond strength between the housing 11 and the base end 51, thereby suppressing peeling.

In the example shown in Figure 5, the joint interface 51a of the base end 51 with the housing 11 is also composed of a core material layer 513 and an outer skin layer 511. More specifically, on both the outer surface 11b and the inner surface 11a of the housing 11, the joint interface 51a is composed of a core material layer 513 and an outer skin layer 511.

In the example shown in Figure 5, in addition to the third angle θ3, the fourth angle θ4 is also an acute angle. The third angle θ3 is the same as that explained with reference to Figure 4. In the example shown in Figure 5, the fourth angle θ4, which is the angle formed by the tangent line L4 that passes through the intersection P4 between the inner surface 11a of the housing 11 and the joint interface 51a and is tangent to the joint interface 51a, and the inner line 11aL along the inner surface 11a, is an acute angle.

For example, when an external force is applied to the base end 51 so as to bend it from the outer surface 11b of the housing 11 toward the inner surface 11a, the effect is the same as that described with reference to FIG. 4. On the other hand, when an external force is applied to the base end 51 so as to bend it from the inner surface 11a of the housing 11 toward the outer surface 11b, tensile stress is generated at the bonded interface 51a on the inner surface 11a side because the fourth angle θ4 is an acute angle. Tensile stress is stress along the direction from the housing 11 to the base end 51, intersecting the bonded interface 51a. Therefore, compared to the shear stress that occurs when the fourth angle θ4 is an obtuse angle, for example, stress is generated in a direction that increases the bond strength between the housing 11 and the base end 51, thereby suppressing the occurrence of delamination. In the example shown in FIG. 5, both the third angle θ3 and the fourth angle θ4 are acute angles, but only one of them may be an acute angle.

A method for manufacturing the spark plug 10 will be described with reference to Figures 6, 7, and 8. As shown in Figure 6, a presser J1, a stopper J2, an upper electrode E1, and a lower electrode E2 are prepared. The housing 11 is placed on the presser J1. The presser 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 this arrangement, current is passed through the upper electrode E1 and the lower electrode E2 to perform resistance welding.

The joining state between the ground electrode material 50M and the housing 11 during resistance welding will be explained with reference to Figure 7. Figure 7 is an enlarged view of portion VII in Figure 6 rotated 90 degrees clockwise.

As shown in FIG. 7(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 the part 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 the part 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, intermediate material 512M, and core material 513M are uniformly configured to abut against the housing 11.

The outer cover material 511M is inclined so as to move away from the tip surface 110 of the housing 11. Meanwhile, the intermediate material 512M and core material 513M abut against the tip surface 110 of the housing 11. The abutting surface of the ground electrode material 50M with the housing 11 has a first surface 50Ma that is aligned with the tip surface 110 of the housing 11, and a second surface 50Mb that is positioned from the first surface 50Ma toward the outer cover material 511M.

As shown in Figures 7(B) and 7(C), current is passed through the intermediate material 512M and the core material 513M, so the joining progresses in such a way that a gentle concave surface is formed near the center of the housing 11 in the thickness direction.

As shown in Figure 7(D), as the joining progresses further, the core material 513M is deformed so that it is 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 cut along the dashed line in Figure 7(D), the ground electrode base material 50 joined to the housing 11 is formed, as shown in Figure 7(E).

Figure 8 shows the contact state between the upper electrode E1 and lower electrode E2 and the ground electrode material 50M at the stage corresponding to Figure 7(D). As shown in Figure 8, a rectangular melted portion is formed between the corner of the lower electrode E2 and the housing 11. By tilting the lower electrode E2A in a direction away from the housing 11, as in Figure 9, the melted portion can be oriented in a direction away from the housing 11.

As described above, the method for manufacturing the spark plug 10 begins with preparing a housing 11 that houses the insulator 12, including the center electrode 13. Next, a ground electrode material 50M is prepared, which will be joined to the housing 11 to form the ground electrode 14. The ground electrode material 50M includes an outer cover material 511M disposed on the surface side, an intermediate material 512M having a higher thermal conductivity than the outer cover material 511M, and a core material 513M having a higher hardness than the intermediate material 512M. The mating surface of the ground electrode material 50M with the housing 11 is then formed to have a first surface 50Ma that is aligned with the front end surface 110 of the housing and a second surface 50Mb that is disposed on the outer cover material 511M side from the first surface 50Ma, and the second surface 50Mb is inclined toward the outer surface 11b of the housing 11 so as to be spaced apart from the front end surface 110. Next, the butt surface of the ground electrode material 50M is brought into contact with the tip surface 110 of the housing 11 and resistance welded to join the ground electrode material 50M to the housing 11, forming the ground electrode 14.

In the manufacturing method of the spark plug 10 of this embodiment, the second surface 50Mb formed on the ground electrode material 50M is inclined so as to be away from the tip surface 110 on the outer surface 11b side of the housing 11, making it possible to achieve a joining state in which the first angle θ1 is an acute angle as described with reference to Figure 3, and a joining state in which the third angle θ3 is an acute angle as described with reference to Figures 4 and 5.

In the manufacturing method of the spark plug 10 of this embodiment, the second surface 50Mb is inclined so as to be away from the tip surface 110 on the inner surface 11a side of the housing 11. By inclining the second surface 50Mb in this manner, it is possible to achieve a joining state in which the second angle θ2 is an acute angle, as described with reference to Figure 3, or a joining state in which the fourth angle θ4 is an acute angle, as described with reference to Figure 5.

The inclination of the second surface 50Mb may be provided only on the inner surface 11a of the housing 11, or only on the outer surface 11b of the housing 11.

The present embodiment has been described above with reference to specific examples. However, the present disclosure is not limited to these specific examples. Design modifications to these specific examples made by a person skilled in the art as appropriate are also included within the scope of the present disclosure as long as they comprise the features of the present disclosure. The elements of the above-mentioned specific examples, as well as their arrangement, conditions, shape, etc., are not limited to those exemplified and can be modified as appropriate. The elements of the above-mentioned specific examples can be combined in different ways as appropriate, as long as no technical contradictions arise.

11: Housing 11a: Inner surface 11b: Outer surface 12: Insulator 13: Center electrode 14: Ground electrode 51: Base end 51a: Bonding interface 511: Outer layer 512: Intermediate layer 513: Core layer 52: Tip end

Claims (9)

A spark plug,
an insulator (12) that houses a center electrode (13);
a housing (11) for accommodating the insulator;
a ground electrode (14) having a tip end (52) disposed so as to form a predetermined gap with respect to the center electrode, and a base end (51) extending along the center electrode and joined to the housing,
The base end portion is
An outer skin layer (511) disposed on the surface side;
an intermediate layer (512) having a higher thermal conductivity than the outer skin layer;
a core layer (513) having a higher hardness than the intermediate layer;
and
In a cross section including a center axis and the base end portion of the spark plug,
a bonding interface (51a) of the base end portion with respect to the housing is formed only by the core material layer,
a first angle (θ1) formed by a tangent (L1) that passes through an intersection (P1) between the outer surface (11b) of the housing and the joint interface and is in contact with the joint interface, and an outer line (11bL) that follows the outer surface, is an acute angle. A spark plug,
an insulator (12) that houses a center electrode (13);
a housing (11) for accommodating the insulator;
a ground electrode (14) having a tip end (52) disposed so as to form a predetermined gap with respect to the center electrode, and a base end (51) extending along the center electrode and joined to the housing,
The base end portion is
An outer skin layer (511) disposed on the surface side;
an intermediate layer (512) having a higher thermal conductivity than the outer skin layer;
a core layer (513) having a higher hardness than the intermediate layer;
and
In a cross section including a center axis and the base end portion of the spark plug,
a bonding interface (51a) of the base end portion with respect to the housing is formed only by the core material layer,
a second angle (θ2) formed by a tangent (L2) that passes through an intersection (P2) between the inner surface (11a) of the housing and the joint interface and is in contact with the joint interface, and an inner line (11aL) that runs along the inner surface, is an acute angle. 2. The spark plug according to claim 1,
In a cross section including a center axis and the base end portion of the spark plug,
a bonding interface between the base end portion and the housing is formed only by the core material layer,
a second angle formed by a tangent line passing through an intersection of the inner surface of the housing and the joint interface and contacting the joint interface, and an inner line along the inner surface, is an acute angle. A spark plug,
an insulator (12) that houses a center electrode (13);
a housing (11) for accommodating the insulator;
a ground electrode (14) having a tip end (52) disposed so as to form a predetermined gap with respect to the center electrode, and a base end (51) extending along the center electrode and joined to the housing,
The base end portion is
An outer skin layer (511) disposed on the surface side;
an intermediate layer (512) having a higher thermal conductivity than the outer skin layer;
a core layer (513) having a higher hardness than the intermediate layer;
and
In a cross section including a center axis and the base end portion of the spark plug,
a joint interface (51a) of the base end portion with respect to the housing is formed by the core material layer and the outer skin layer,
a third angle (θ3) formed on the inside of the housing (11), which is an acute angle, is formed between a tangent (L3) that passes through an intersection (P3) between the outer surface (11b) of the housing and the joint interface and is tangent to the joint interface, and an outer line (11bL) along the outer surface. A spark plug,
an insulator (12) that houses a center electrode (13);
a housing (11) for accommodating the insulator;
a ground electrode (14) having a tip end (52) disposed so as to form a predetermined gap with respect to the center electrode, and a base end (51) extending along the center electrode and joined to the housing,
The base end portion is
An outer skin layer (511) disposed on the surface side;
an intermediate layer (512) having a higher thermal conductivity than the outer skin layer;
a core layer (513) having a higher hardness than the intermediate layer;
and
In a cross section including a center axis and the base end portion of the spark plug,
a joint interface (51a) of the base end portion with respect to the housing is formed by the core material layer and the outer skin layer,
a fourth angle (θ4) formed inside the housing (11), which is an acute angle, is formed between a tangent (L4) that passes through an intersection (P4) between the inner surface (11a) of the housing and the joint interface and is in contact with the joint interface, and an inner line (11aL) that runs along the inner surface . 5. The spark plug according to claim 4,
In a cross section including a center axis and the base end portion of the spark plug,
a joint interface between the base end portion and the housing is formed by the core material layer and the outer skin layer,
a fourth angle formed on the inside of the housing (11), which is an acute angle, formed between a tangent line that passes through an intersection of the inner surface of the housing and the joint interface and is in contact with the joint interface, and an inner line along the inner surface. A method for manufacturing a spark plug, comprising:
A housing (11) is provided to accommodate an insulator including a center electrode;
a ground electrode material (50M) to be joined to the housing and serving as a ground electrode, the ground electrode material (50M) having an outer cover material (511M) disposed on a surface side, an intermediate material (512M) having a higher thermal conductivity than the outer cover material, and a core material (513M) having a higher hardness than the intermediate material;
The abutting surface of the ground electrode material with the housing is formed to have a first surface (50Ma) along the tip surface (110) of the housing and a second surface (50Mb) disposed on the outer cover material side from the first surface,
The second surface is inclined so as to be spaced apart from the tip surface on the outer surface (11b) side of the housing,
abutting a mating surface of the ground electrode material against a front end surface of the housing and resistance welding the ground electrode material to form the ground electrode by joining the ground electrode material to the housing. A method for manufacturing a spark plug, comprising:
A housing (11) is provided to accommodate an insulator including a center electrode;
a ground electrode material (50M) to be joined to the housing and serving as a ground electrode, the ground electrode material (50M) having an outer cover material (511M) disposed on a surface side, an intermediate material (512M) having a higher thermal conductivity than the outer cover material, and a core material (513M) having a higher hardness than the intermediate material;
The abutting surface of the ground electrode material with the housing is formed to have a first surface (50Ma) along the tip surface (110) of the housing and a second surface (50Mb) disposed on the outer cover material side from the first surface,
The second surface is inclined so as to be spaced apart from the tip surface on the inner surface (11a) side of the housing,
abutting a mating surface of the ground electrode against a front end surface of the housing and resistance welding the abutting surface to form the ground electrode by joining the ground electrode material to the housing. 8. A method for manufacturing a spark plug according to claim 7, comprising:
the second surface is inclined so as to be spaced apart from the tip surface on the inner surface side of the housing.