Spark plug for internal combustion engine

Abstract

To provide a spark plug for an internal combustion engine, which is capable of improving the strength of a fixed end of a ground electrode and also of improving the welding strength of the ground electrode to a housing.SOLUTION: In a spark plug, a ground electrode 6 includes an outer skin layer 611, an intermediate layer 612, and a core material layer 613. At least a portion of the intermediate layer 612 is disposed inside the outer skin layer 611 and has a higher thermal conductivity than the outer skin layer 611. At least a portion of the core material layer 613 is disposed inside the intermediate layer 612. The outer skin layer 611 and the core material layer 613 have a higher hardness than the intermediate layer 612. A fixed end portion 62 of the ground electrode 6 welded to a housing front end surface 21 has an end weld layer 5 that welds the outer skin layer 611, the intermediate layer 612, and the core material layer 613 to each other. The end weld layer 5 covers the intermediate layer 612 from a base end side Z2. At least a portion of the end weld layer 5 is located closer to the base end side Z2 than the housing front end surface 21.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a spark plug for an internal combustion engine. [Background technology]

[0002] For example, as disclosed in Patent Document 1, there is known a spark plug for an internal combustion engine that includes a ground electrode having an outer skin layer, an intermediate layer that is disposed inside the outer skin layer and has a higher thermal conductivity than the outer skin layer, and a core material layer disposed inside the intermediate layer. This spark plug aims to increase the welding strength of the ground electrode to the housing by suppressing the intermediate layer from being included in the welding interface between the ground electrode and the housing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6170526 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the spark plug described in Patent Document 1, no consideration is given to the mutual welding strength between the outer cover layer, the intermediate layer, and the core layer at the fixed end of the ground electrode welded to the housing. Therefore, it can be said that there is room for further improvement in the spark plug described in Patent Document 1 from the viewpoint of ensuring the strength of the fixed end.

[0005] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a spark plug for an internal combustion engine which can improve the strength of the fixed end of the ground electrode and can improve the welding strength of the ground electrode to the housing. [Means for solving the problem]

[0006] One aspect of the present invention is a cylindrical insulator (3), a center electrode (4) held on the inner circumferential side of the insulator and exposed from the insulator to a tip side (Z1); A cylindrical housing (2) that holds the insulator on its inner periphery; a ground electrode (6) welded to the housing and forming a discharge gap (G) between the ground electrode and the center electrode, The ground electrode has an outer skin layer (611), an intermediate layer (612) at least a portion of which is disposed inside the outer skin layer and has a thermal conductivity higher than that of the outer skin layer, and a core layer (613) at least a portion of which is disposed inside the intermediate layer, The skin layer and the core layer have a higher hardness than the intermediate layer, The fixed end portion (62) of the ground electrode welded to a housing front end surface (21), which is a front end surface of the housing, stands upright from the housing front end surface toward the front end side along the plug axial direction (Z), The fixed end portion has an end welding layer (5) that welds the outer skin layer, the intermediate layer, and the core material layer together, At the fixed end portion, the end weld layer covers the intermediate layer from the base end side (Z2), At least a portion of the end weld layer is located on the base end side of the housing tip end surface of a spark plug (1) for an internal combustion engine. Effect of the Invention

[0007] In the above spark plug, the fixed end of the ground electrode has an end weld layer that welds the outer cover layer, the intermediate layer, and the core layer together. In addition, in the fixed end, the end weld layer covers the intermediate layer from the base end side. Therefore, it is possible to improve the mutual welding strength between the outer cover layer, the intermediate layer, and the core layer. As a result, it is possible to improve the strength of the fixed end of the ground electrode.

[0008] In addition, at least a portion of the end weld layer is located closer to the base end than the front end surface of the housing, which makes it easier to widen the joint area between the housing and the ground electrode, thereby improving the weld strength of the ground electrode to the housing.

[0009] As described above, according to the above aspect, it is possible to provide a spark plug for an internal combustion engine which can improve the strength of the fixed end of the ground electrode and can also improve the welding strength of the ground electrode to the housing. In addition, the symbols in parentheses described in the claims and the means for solving the problems indicate a correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present invention. [Brief description of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view of a spark plug according to a first embodiment taken along an axial direction of the spark plug; [Diagram 2] FIG. 2 is a cross-sectional view taken along the axial direction of the plug in the vicinity of the discharge gap in the first embodiment. [Diagram 3] 3 is a view of the spark plug according to the first embodiment, seen from the tip end side, taken along the line III in FIG. 2. [Figure 4] 4 is a cross-sectional view taken along the end axial direction near the fixed end in the first embodiment, taken along line IV-IV in FIG. 3. [Diagram 5] 4 is a cross-sectional view taken along the end axial direction near the fixed end in the first embodiment, taken along line VV in FIG. 3. [Figure 6] VI-VI line cross-sectional view of FIG. 2. [Figure 7] FIG. 2 is a perspective view of a first member and the like constituting an electrode member in the first embodiment. [Figure 8] FIG. 3 is a perspective view of an electrode member before being stretched in the first embodiment. [Figure 9] FIG. 4 is a perspective view of the electrode member after stretching in the first embodiment. [Figure 10] 5 is a diagram showing a state in which the ground electrode before being bent is resistance-welded to the housing in the first embodiment. FIG. [Figure 11] FIG. 2 is a diagram showing a state of a destructive test in Experimental Example 1. [Figure 12] 4 is a cross-sectional view of each sample before destructive testing in Experimental Example 1, taken along line VV in FIG. 3. [Figure 13] 4 is a cross-sectional view of each sample after the destructive test in Experimental Example 1, taken along line VV in FIG. 3. [Figure 14] 4 is a graph showing the relationship between the magnitude of a current flowing during resistance welding and the tensile strength of a ground electrode in Experimental Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] (Embodiment 1) An embodiment of a spark plug for an internal combustion engine will be described with reference to Figs. A spark plug 1 for an internal combustion engine according to this embodiment has a cylindrical insulator 3, a center electrode 4, a cylindrical housing 2, and a ground electrode 6, as shown in Fig. 1. The center electrode 4 is held on the inner periphery side of the insulator 3 and is exposed from the insulator 3 on a tip side Z1. The housing 2 holds the insulator 3 on its inner periphery side. The ground electrode 6 is welded to the housing 2 and forms a discharge gap G between itself and the center electrode 4.

[0012] 2 and 4 to 6, the ground electrode 6 has an outer skin layer 611, an intermediate layer 612, and a core layer 613. At least a portion of the intermediate layer 612 is disposed inside the outer skin layer 611, and has a higher thermal conductivity than the outer skin layer 611. At least a portion of the core layer 613 is disposed inside the intermediate layer 612. The outer skin layer 611 and the core layer 613 have a higher hardness than the intermediate layer 612.

[0013] 4 and 5, the fixed end 62 of the ground electrode 6 welded to the housing front end surface 21, which is the front end surface of the housing 2, stands from the housing front end surface 21 toward the front end side Z1 along the plug axial direction Z. The fixed end 62 has an end weld layer 5 that welds the outer skin layer 611, the intermediate layer 612, and the core layer 613 to one another. In the fixed end 62, the end weld layer 5 covers the intermediate layer 612 from the base end side Z2. At least a part of the end weld layer 5 is located on the base end side Z2 of the housing front end surface 21.

[0014] The spark plug 1 of this embodiment can be used, for example, as an ignition means in an internal combustion engine of an automobile, etc. The spark plug 1 is attached to an internal combustion engine (not shown) by screwing a threaded portion 22 (see FIG. 1) of a housing 2 into a female threaded portion of a plug hole in a cylinder head (not shown).

[0015] One end of the spark plug 1 in the axial direction Z is disposed in a combustion chamber (not shown) of an internal combustion engine. In the axial direction Z of the spark plug 1, the side exposed to the combustion chamber is referred to as a tip side Z1, and the opposite side is referred to as a base side Z2. The axial direction Z of the spark plug 1 is also referred to as a plug axial direction Z as appropriate. The plug central axis PC means the central axis PC of the spark plug 1. The plug radial direction means the radial direction of a circle centered on the central axis PC of the spark plug 1 on a plane perpendicular to the central axis PC of the spark plug 1. The plug circumferential direction is a direction along the circumference of a circle centered on the plug central axis PC. In this embodiment, the central axis PC is also the central axis of the housing 2, the insulator 3, and the center electrode 4. In the spark plug 1 of this embodiment, the ground electrode 6 is provided so that the central axis GC of the fixed end 62 is aligned with the plug axial direction Z, as shown in FIG. 1 and FIG. 2. In this embodiment, the plug central axis PC and the central axis GC of the fixed end 62 are parallel to each other. In this specification, the direction parallel to the central axis GC of the fixed end portion 62 is referred to as the end portion axis direction Y.

[0016] As shown in Fig. 1, a first glass seal layer 11, a resistor 12, a second glass seal layer 13, and a terminal metal fitting 14 are disposed on the base end side Z2 of the center electrode 4 inside the insulator 3. The first glass seal layer 11 and the second glass seal layer 13 may be made of glass containing copper powder, for example. The resistor 12 may be made of an aggregate in which a conductive material such as a carbon material is dispersed in a base material containing a glass material and an aggregate. The end of the terminal metal fitting 14 on the base end side Z2 is exposed from the insulator 3. The spark plug 1 is electrically connected to an ignition coil (not shown) at the terminal metal fitting 14.

[0017] In this embodiment, the ground electrode 6 has a standing portion 63, a bent portion 64, and an extended portion 65, as shown in Fig. 2. The standing portion 63 has a fixed end portion 62, and stands from the housing front end surface 21 toward the front end side Z1 along the plug axial direction Z. The bent portion 64 is bent from the front end of the standing portion 63 toward the inside in the plug radial direction. The extended portion 65 extends from the bent portion 64 toward the inside in the plug radial direction, and has a ground side tip 67 joined to its base end side surface.

[0018] The fixed end 62 of the standing portion 63 is fixed to the housing front end surface 21 by resistance welding. In this embodiment, the housing front end surface 21 is a flat surface and is formed so as to be perpendicular to the plug axial direction Z.

[0019] A ground side tip 67 is welded to a protruding end 66 of the extension portion 65. The ground side tip 67 is welded to an outer cover layer 611 of the extension portion 65. A center side tip 41 is joined to a tip end of the center electrode 4. The ground side tip 67 and the center side tip 41 face each other in the plug axial direction Z, thereby forming a discharge gap G. The ground side tip 67 and the center side tip 41 may be made of a precious metal such as platinum or iridium, or an alloy containing these as a main component.

[0020] In the ground electrode 6, the outer skin layer 611, the intermediate layer 612, and the core layer 613 are each provided from the fixed end 62 of the standing portion 63 to the extension portion 65. The outer skin layer 611 and the core layer 613 may be made of, for example, nickel or a nickel alloy containing nickel as a main component. In this embodiment, the outer skin layer 611 is made of a nickel alloy containing aluminum or the like, and the core layer 613 is made of nickel. The intermediate layer 612 may be made of, for example, copper or an alloy containing copper as a main component. In this embodiment, the intermediate layer 612 is made of copper.

[0021] In this embodiment, the cross section perpendicular to the extending direction of the ground electrode 6 is rectangular as shown in FIG. 6. The width W1 of the ground electrode 6 is larger than the thickness T1 of the ground electrode 6. The ground electrode 6 has a multi-layer structure in which an outer skin layer 611, an intermediate layer 612, and a core layer 613 are overlapped in both the thickness direction and the width direction of the ground electrode 6. As shown in FIG. 3, the direction in which the plug center axis PC and the center axis GC of the fixed end 62 are aligned when viewed from the plug axial direction Z is the thickness direction of the fixed end 62. The direction perpendicular to both the end axial direction Y and the thickness direction of the fixed end 62 is the width direction of the fixed end 62.

[0022] 4, in a cross section including the plug center axis PC and the center axis GC, a distance D1 from the housing front end surface 21 to the base end of the fixed end 62 in the end axial direction Y is greater than a thickness T2 of the outer skin layer 611 of the extension portion 65 located on the front end side Z1 of the end welded layer 5. In the cross section shown in FIG 4, the distance D1 is greater than a thickness T3 of the intermediate layer 612 of the extension portion 65 located on the front end side Z1 of the end welded layer 5. In the cross section shown in FIG 4, the distance D1 is also the distance from the housing front end surface 21 to the base end of the core layer 613 in the end axial direction Y.

[0023] The end weld layer 5 is an alloy layer containing copper and nickel, which is formed by melting and mixing a part of the intermediate layer 612, a part of the skin layer 611, and a part of the core layer 613 during welding, and then solidifying again. When viewed from the end axial direction Y, the intermediate layer 612 and the end weld layer 5 of the fixed end 62 overlap each other.

[0024] The fixed end 62 has two end weld layers 5 formed along the width direction of the fixed end 62 and two end weld layers 5 formed along the thickness direction of the fixed end 62. As shown in FIG. 4, the two end weld layers 5 formed along the width direction of the fixed end 62 are formed to sandwich the core material layer 613 in the thickness direction of the fixed end 62. Also, as shown in FIG. 5, the two end weld layers 5 formed along the thickness direction of the fixed end 62 are formed to sandwich the core material layer 613 in the width direction of the fixed end 62. The two end weld layers 5 formed along the width direction of the fixed end 62 and the two end weld layers 5 formed along the thickness direction of the fixed end 62 each cover the intermediate layer 612 from the base end side Z2. In the fixed end 62, the intermediate layer 612 and the end weld layers 5 covering the intermediate layer 612 from the base end side Z2 each surround the core material layer 613 over the entire circumference.

[0025] The end welded layer 5 is formed between the outer skin layer 611 and the core material layer 613 in the radial direction of the core material layer 613. The end welded layer 5 is covered by at least one of the outer skin layer 611 and the core material layer 613 from the base end side Z2.

[0026] As shown in Fig. 4, in a cross section including the plug central axis PC and the central axis GC of the fixed end 62, an extension line VL1 of the housing front end surface 21 overlaps with the end weld layer 5. Also, as shown in Fig. 5, in a cross section that is perpendicular to a plane including the plug central axis PC and the central axis GC of the fixed end 62 and that includes the central axis GC of the fixed end 62, an extension line VL2 of the housing front end surface 21 overlaps with the end weld layer 5.

[0027] 4, in a cross section including the plug center axis PC and the center axis GC of the fixed end 62, the area of ​​the end weld layer 5 located on the base end side Z2 of the housing front end surface 21 is larger than the area of ​​the end weld layer 5 located on the front end side Z1 of the housing front end surface 21. In other words, in the cross section shown in Fig. 4, the area of ​​the end weld layer 5 located on the base end side Z2 of the extension line VL1 is larger than the area of ​​the end weld layer 5 located on the front end side Z1 of the extension line VL1.

[0028] 5, in a cross section perpendicular to a plane including the plug center axis PC and the center axis GC of the fixed end 62 and including the center axis GC of the fixed end 62, the area of ​​the end welded layer 5 located on the base end side Z2 of the housing front end surface 21 is larger than the area of ​​the end welded layer 5 located on the front end side Z1 of the housing front end surface 21. In other words, in the cross section shown in FIG 5, the area of ​​the end welded layer 5 located on the base end side Z2 of the extension line VL2 is larger than the area of ​​the end welded layer 5 located on the front end side Z1 of the extension line VL2.

[0029] 4 and 5, the base end of the core layer 613 at the fixed end 62 is located on the base end side Z2 relative to the end welded layer 5. As shown in FIG.

[0030] In this embodiment, as shown in Fig. 4, the base end of the core material layer 613 at the fixed end 62 covers the end weld layer 5 from the base end side Z2 at least in a cross section including the plug central axis PC and the central axis GC of the fixed end 62. Also, the end weld layer 5 formed between the skin layer 611 and the core material layer 613 in the thickness direction of the fixed end 62 is covered from the base end side Z2 by the base end of the core material layer 613. That is, the end weld layer 5 formed along the width direction of the fixed end 62 is covered from the base end side Z2 by the base end of the core material layer 613. When viewed from the end axial direction Y, the end weld layer 5 formed between the skin layer 611 and the core material layer 613 in the thickness direction of the fixed end 62 overlaps with the base end of the core material layer 613.

[0031] In the cross section shown in Fig. 4, the base end of the core material layer 613 at the fixed end 62 protrudes both inward and outward in the plug radial direction. In the cross section shown in Fig. 4, the base end of the core material layer 613 at the fixed end 62 protrudes inward in the plug radial direction more than the end weld layer 5, and protrudes outward in the plug radial direction more than the end weld layer 5. In the cross section shown in Fig. 4, the base end of the core material layer 613 at the fixed end 62 is welded to the housing 2 at a position on the base end side Z2 more than the end weld layer 5.

[0032] Next, a method for manufacturing the ground electrode 6 will be described. In this embodiment, the ground electrode 6 before being welded to the housing 2 has a rectangular prism shape. In manufacturing the ground electrode 6, first, as shown in FIG. 7, a bottomed tubular first member 601 which becomes the outer skin layer 611, a cylindrical second member 602 which becomes the intermediate layer 612, and a third member 603 which becomes the core layer 613 are manufactured. The third member 603 has a cylindrical shaft portion 604 and a flange portion 605 which is provided at one end of the shaft portion 604 and protrudes outward from the shaft portion 604. Then, as shown by an arrow M1 in FIG. 7, the shaft portion 604 of the third member 603 is inserted into an insertion hole formed in the second member 602. Then, as shown by an arrow M2 in FIG. 7, the third member 603 to which the second member 602 is assembled is disposed inside the first member 601, thereby manufacturing the electrode member 60 before being stretched as shown in FIG. 8. In the electrode member 60, the first member 601, the second member 602, and the third member 603 are not joined to one another.

[0033] Next, the electrode member 60 is stretched by cold forging. Specifically, a part of the electrode member 60 is passed through a die (not shown) having a rectangular opening, and is formed into a quadrangular prism shape as shown in FIG. 9. Then, the part of the electrode member 60 formed into a quadrangular prism shape is cut along a plane VP perpendicular to the longitudinal direction of the electrode member 60 as shown in FIG. 9. At this time, the electrode member 60 is cut at a portion where the first member 601, the second member 602, and the third member 603 are layered and overlapped. In this way, the ground electrode 6 having a quadrangular prism shape is manufactured before being welded to the housing 2 and before being bent. In the ground electrode 6 before being welded to the housing 2, the outer skin layer 611, the intermediate layer 612, and the core layer 613 are not joined to each other.

[0034] Next, a method for manufacturing the spark plug 1 will be described. In the method for manufacturing the spark plug 1 of this embodiment, first, the ground electrode 6 before being bent is welded to the housing front end surface 21. In this embodiment, the housing front end surface 21 before the ground electrode 6 is welded is formed over the entire plug circumferential direction. The housing 2 to which the ground electrode 6 is welded is the housing 2 before the insulator 3 holding the center electrode 4 is assembled. When welding the ground electrode 6 to the housing 2, as shown in FIG. 10, current is passed between the housing front end surface 21 and the cut surface of the ground electrode 6 while the longitudinal direction of the ground electrode 6 is aligned with the longitudinal direction of the housing 2. The ground electrode 6 is welded to the housing front end surface 21 by passing current between two ground side electrode portions 711 and 712 that hold the ground electrode 6 in the thickness direction and an electrode portion (not shown) that is in contact with the housing 2.

[0035] The electrode portion to be brought into contact with the housing 2 is provided on a fixed base 73 that fixes the housing 2. A recess is formed in the fixed base 73 to accommodate a part of the housing 2 inside. The fixed base 73, which accommodates a part of the housing 2 inside the recess, is pressed in the direction of the arrow P in FIG. 10 to apply current while the ground electrode 6 is pressed by the housing front end surface 21. In addition, a stopper portion 72 is used to suppress the movement of the ground electrode 6 when pressed so that the ground electrode 6 can be sufficiently pressed by the housing front end surface 21. That is, the stopper portion 72 is brought into contact with the protruding end surface of the protruding end portion 66 to support the ground electrode 6. In addition, resistance welding is performed while the housing 2 is pressed toward the ground electrode 6, so that the base end of the ground electrode 6 moves toward the base end side Z2 from the housing front end surface 21. In addition, by performing welding in this manner, an end weld layer 5 that covers the base end side Z2 of the intermediate layer 612 is formed, and an end weld layer 5 is formed at a position on the base end side Z2 from the housing front end surface 21. When performing resistance welding, for example, a rod-shaped member (not shown) can be used to insert inside the housing 2, and the housing 2 can be pushed toward the ground electrode 6 using this rod-shaped member, thereby pressing the ground electrode 6 with the housing tip surface 21.

[0036] After the ground electrode 6 is welded to the housing 2, a part of the outer skin layer 611 protruding from the housing front end surface 21 to the front end side Z1 is removed as necessary.

[0037] Next, the ground side tip 67 is welded to the outer layer 611 of the ground electrode 6. Thereafter, the square prism-shaped ground electrode 6 is bent to form the standing portion 63, the bent portion 64, and the extended portion 65.

[0038] After bending the ground electrode 6, the insulator 3 holding the center electrode 4 on its inner periphery is assembled into the housing 2. Thereafter, if necessary, the ground electrode 6 is slightly deformed to finely adjust the discharge gap G to an appropriate distance. In this manner, the spark plug 1 of this embodiment can be manufactured as shown in Figs. 1 to 3.

[0039] Next, the effects of this embodiment will be described. In the above spark plug 1, the fixed end 62 has an end weld layer 5 that welds the outer cover layer 611, the intermediate layer 612, and the core layer 613 together. In the fixed end 62, the end weld layer 5 covers the intermediate layer 612 from the base end side Z2. This improves the mutual welding strength between the outer cover layer 611, the intermediate layer 612, and the core layer 613. As a result, the strength of the fixed end 62 can be improved.

[0040] Moreover, at least a portion of the end weld layer 5 is located on the base end side Z2 relative to the housing front end surface 21. This makes it easier to widen the joining area between the housing 2 and the ground electrode 6. As a result, the welding strength of the ground electrode 6 to the housing 2 can be improved.

[0041] Moreover, the ground electrode 6 includes an intermediate layer 612 having a higher thermal conductivity than the outer layer 611. This improves the heat dissipation from the ground electrode 6 to the housing 2. As a result, in the spark plug 1 provided in the internal combustion engine, even if the ground electrode 6 is exposed to high temperatures, overheating of the ground electrode 6 can be suppressed.

[0042] When manufacturing the spark plug 1, the ground electrode 6 is welded to the housing 2 in a state where the outer skin layer 611, the intermediate layer 612, and the core material layer 613 are not joined to each other. Therefore, in order to sufficiently ensure the strength of the fixed end 62 and the heat dissipation of the ground electrode 6, it is necessary to sufficiently join the intermediate layer 612 to the outer skin layer 611 and the core material layer 613. In other words, if the intermediate layer is not sufficiently joined to the outer skin layer and the core material layer at the fixed end 62, the intermediate layer may peel off from the outer skin layer and the core material layer due to stress applied to the fixed end when the ground electrode is bent. If the intermediate layer peels off from the outer skin layer and the core material layer, a space is likely to be formed between the intermediate layer and the outer skin layer and the core material layer, and a space is also likely to be formed between the intermediate layer and the housing, and the heat dissipation of the ground electrode to the housing may not be sufficiently ensured. Therefore, in this embodiment, the fixed end 62 has an end weld layer 5 that covers the intermediate layer 612 from the base end side Z2. Therefore, the mutual welding strength between the outer skin layer 611, the intermediate layer 612, and the core material layer 613 can be improved, and the strength of the fixed end 62 can be improved. As a result, even if a strong stress is generated in the fixed end 62 when the ground electrode 6 welded to the housing 2 is bent to form the discharge gap G, for example, the intermediate layer 612 can be sufficiently suppressed from peeling off from the outer skin layer 611 and the core material layer 613. Therefore, it is possible to sufficiently suppress the formation of a space between the intermediate layer 612 and the outer skin layer 611, the housing 2, etc. Therefore, it is possible to sufficiently ensure the heat dissipation of the ground electrode 6 to the housing 2. As a result, it is possible to suppress overheating of the ground electrode 6, and it is possible to suppress oxidation of the outer skin layer 611 and the ground side tip 67. As a result, it is possible to suppress the wear of the ground electrode 6, and it is possible to extend the life of the ground electrode 6.

[0043] In a cross section including the plug center axis PC and the center axis GC of the fixed end 62, the area of ​​the end weld layer 5 located on the base end side Z2 of the housing front end surface 21 is larger than the area of ​​the end weld layer 5 located on the front end side Z1 of the housing front end surface 21. Therefore, the joint area between the housing 2 and the ground electrode 6 is likely to be wider. Therefore, the welding strength of the ground electrode 6 to the housing 2 can be further improved. As a result, even if a strong stress is generated in the fixed end 62 when the ground electrode 6 is bent, peeling of the ground electrode 6 from the housing 2 can be further suppressed.

[0044] In a cross section perpendicular to a plane including the plug center axis PC and the center axis GC of the fixed end 62, and including the center axis GC of the fixed end 62, the area of ​​the end weld layer 5 located on the base end side Z2 of the housing front end surface 21 is larger than the area of ​​the end weld layer 5 located on the front end side Z1 of the housing front end surface 21. Therefore, the joint area between the housing 2 and the ground electrode 6 is likely to be wider.

[0045] The base end of the core material layer 613 at the fixed end 62 is located on the base end side Z2 further than the end weld layer 5. Therefore, the ground electrode 6 can be firmly fixed to the housing 2. In other words, the base end of the core material layer 613 is welded to the housing 2 in a state where it is embedded deeper on the base end side Z2 than the end weld layer 5, so that the ground electrode 6 can be firmly fixed to the housing 2. As a result, the welding strength of the ground electrode 6 to the housing 2 can be further improved.

[0046] At the fixed end 62, the intermediate layer 612 and the end welded layer 5 covering the intermediate layer 612 from the base end side Z2 each surround the entire periphery of the core material layer 613. In addition, the base end of the core material layer 613 at the fixed end 62 covers the end welded layer 5 from the base end side Z2 at least in a cross section including the plug center axis PC and the central axis GC of the fixed end 62. Therefore, the mutual welding strength between the outer cover layer 611, the intermediate layer 612, and the core material layer 613 can be further improved, and the ground electrode 6 can be firmly fixed to the housing 2.

[0047] Specifically, since the end weld layer 5 surrounds the core material layer 613 over the entire circumference, even if stress occurs in the fixed end 62 when the ground electrode 6 is bent, the intermediate layer 612 can be further suppressed from peeling off from the outer cover layer 611 and the core material layer 613. In addition, since the base end of the core material layer 613 covers the end weld layer 5 from the base end side Z2 at least in a cross section including the plug central axis PC and the central axis GC, the intermediate layer 612 can be further suppressed from peeling off from the core material layer 613 when the ground electrode 6 is bent. In other words, the intermediate layer 612 can be firmly fixed to the core material layer 613 via the end weld layer 5 at a location where high stress is likely to occur when the ground electrode 6 is bent. Therefore, the strength of the fixed end 62 can be further improved. As a result, the intermediate layer 612 can be further suppressed from peeling off from the core material layer 613, etc. In addition, since the joint area between the core material layer 613 and the housing 2 tends to be wide, the welding strength of the ground electrode 6 to the housing 2 can be further improved.

[0048] When viewed from the end axial direction Y, the end weld layer 5 formed between the outer skin layer 611 and the core material layer 613 in the thickness direction of the fixed end 62 overlaps with the base end of the core material layer 613. Therefore, the intermediate layer 612 can be firmly fixed to the core material layer 613 via the end weld layer 5 formed along the width direction of the fixed end 62. As a result, it is possible to further suppress peeling of the intermediate layer 612 from the core material layer 613. In addition, since the joint area between the core material layer 613 and the housing 2 is likely to be wider, the welding strength of the ground electrode 6 to the housing 2 can be further improved.

[0049] In a cross section including the plug central axis PC and central axis GC, the distance D1 (see FIG. 4) is greater than the thicknesses T2 and T3. Therefore, the fixed end 62 can be welded to the housing 2 in a state where it is deeply inserted into the base end side Z2. As a result, the ground electrode 6 can be firmly joined to the housing 2.

[0050] At the fixed end 62, the end welded layer 5 is formed between the outer skin layer 611 and the core material layer 613 in the radial direction of the core material layer 613. Therefore, the mutual welding strength between the outer skin layer 611, the intermediate layer 612, and the core material layer 613 can be further improved.

[0051] The end welded layer 5 is covered from the base end side Z2 by at least one of the outer skin layer 611 and the core material layer 613. Therefore, the mutual welding strength between the outer skin layer 611, the intermediate layer 612, and the core material layer 613 can be further improved, and the fixed end 62 can be fixed to the housing 2 more firmly.

[0052] The third member 603 has a flange portion 605. Therefore, in the portion of the ground electrode 6 near the discharge gap G, spaces are unlikely to be formed between the intermediate layer 612 and the outer skin layer 611, and between the intermediate layer 612 and the core material layer 613. Therefore, high heat dissipation from the ground electrode 6 to the housing 2 can be sufficiently ensured.

[0053] As described above, according to this embodiment, it is possible to provide a spark plug 1 for an internal combustion engine which can improve the strength of the fixed end portion 62 and the welding strength of the ground electrode 6 to the housing 2.

[0054] In the above-described first embodiment, a portion of the end weld layer 5 is located on the tip side Z1 of the housing tip surface 21. However, the entire end weld layer may be located on the base end side of the housing tip surface.

[0055] (Experimental Example 1) In this example, a destructive test was performed using a plurality of samples in which the current values ​​when the ground electrode 6 was resistance-welded to the housing 2 were different from each other, and the relationship between the structure of the fixed end 62 and the welding strength of the fixed end 62 to the housing 2 was examined. The sample used in this example was the housing 2 to which the ground electrode 6 before bending was welded, as shown in FIG. 11. In this example, the basic structures of the ground electrode 6 and the housing 2 were the same as those of the ground electrode 6 and the housing 2 of the first embodiment. In this example, the housing 2 with the nominal diameter of the threaded portion 22 being M12 was used, and the ground electrode 6 with the width W1 (see FIG. 6) being 2.6 mm and the thickness T1 (see FIG. 6) being 1.3 mm was used. In addition, when the ground electrode 6 was welded to the housing 2, the load with which the housing 2 pressed the ground electrode 6 was set to 500 N. The rest was the same as the manufacturing method of the first embodiment.

[0056] In this example, in carrying out the destructive test, first, as shown in Fig. 11, the housing 2 is inserted into an insertion hole 740 formed in the fixing jig 74 and fixed to the fixing jig 74. Then, as shown by an arrow M3 in Fig. 11, the tensile strength of the ground electrode 6 is evaluated by pulling the ground electrode 6 toward one side in the end axial direction Y using a pulling jig 75 until the ground electrode 6 breaks.

[0057] Fig. 12 shows a cross-sectional view of the fixed end 62 of each sample before the destructive test, and Fig. 13 shows a cross-sectional view of the fixed end 62 of each sample after the destructive test. Figs. 12(a) and 13(a) are cross-sectional views of sample a, in which the current value during resistance welding was 0.8 kA, and Figs. 12(b) and 13(b) are cross-sectional views of sample b, in which the current value during resistance welding was 1.0 kA. Figs. 12(c) and 13(c) are cross-sectional views of sample c, in which the current value during resistance welding was 1.4 kA, and Figs. 12(d) and 13(d) are cross-sectional views of sample d, in which the current value during resistance welding was 2.0 kA.

[0058] The graph in Figure 14 shows the relationship between the magnitude of the current flowing during resistance welding and the tensile strength for each sample. In the graph in Figure 14, the white circles represent plots of the results for each sample. The white circles also represent plots of the average values ​​of the results for five samples.

[0059] As shown in the graph of FIG. 14, it can be seen that the tensile strength increases significantly as the current flow increases until the current flow reaches 1.2 kA. In addition, it was confirmed that sample a had a tensile strength lower than 0.8 kN and did not have sufficient tensile strength. Sample b had a tensile strength significantly higher than sample a, and had a sufficient tensile strength of about 1.4 kN. In addition, samples with current flow values ​​of 1.2 to 1.8 kA had a tensile strength of 2.0 kN or more. In particular, samples with current flow values ​​of 1.4 to 1.8 kA had tensile strengths of about the same level as each other and had high tensile strength. In addition, the cross sections of the fixed end 62 in the samples with current flow values ​​of 1.6 kA and 1.8 kA were equivalent to the cross section of sample c in FIG. 12(c). In addition, it was confirmed that sample d had a tensile strength of 1.8 kN or more and had sufficient tensile strength, but had a lower tensile strength than samples with current flow values ​​of 1.4 to 1.8 kA. In this manner, it was found that the tensile strength of the ground electrode 6 is determined by the magnitude of the current flowing during resistance welding of the ground electrode 6.

[0060] Next, each sample will be specifically described. As shown in Fig. 12(a), the formation of the end weld layer 5 was not confirmed for sample a. Moreover, as shown in Fig. 13(a), after the destructive test, the ground electrode 6 peeled off at the weld interface between the housing 2 and the ground electrode 6. From this result, it is considered that since the end weld layer 5 was not formed for sample a, the weld strength of the ground electrode 6 to the housing 2 could not be sufficiently ensured, resulting in a low tensile strength.

[0061] It was confirmed that, as shown in Fig. 12(b), sample b had an end welded layer 5 formed to cover the base end side Z2 of the intermediate layer 612. As shown in Fig. 13(b), after the destructive test, sample b had some peeled off areas at the welded interface between the housing 2 and the ground electrode 6, but the ground electrode 6 was broken with a part of the fixed end 62 including the intermediate layer 612 and the end welded layer 5 remaining on the housing 2. From this result, it is considered that sample b had the end welded layer 5 formed to cover the base end side Z2 of the intermediate layer 612, thereby ensuring sufficient strength of the fixed end 62 and the welded strength of the ground electrode 6 to the housing 2.

[0062] As shown in FIG. 12(c), it was confirmed that the end weld layer 5 of sample c is larger than that of sample b, and that the core layer 613 is welded to the housing 2 in a state where it is more deeply embedded in the base end side Z2. The amount of embedment of the core layer 613 into the base end side Z2 of the housing 2 increases in the order of the core layer 613, the skin layer 611, and the intermediate layer 612. That is, the core layer 613 is embedded in the housing 2 the most. On the other hand, the intermediate layer 612 is embedded in the housing 2 the least. The end weld layer 5 was formed between the core layer 613 and the skin layer 611 in the radial direction of the core layer 613. It was also confirmed that the end weld layer 5 covering the intermediate layer 612 from the base end side Z2 surrounds the core layer 613 over the entire circumference. In addition, as shown in FIG. 13(c), in the sample c, after the destructive test, no peeling was observed at the welded interface between the housing 2 and the ground electrode 6, and fracture of the ground electrode 6 was confirmed at a location away from the location where the end weld layer 5 was formed in the end axial direction Y. From these results, it is considered that the core material layer 613 of the sample c is welded deep into the housing 2, thereby further improving the weld strength of the ground electrode 6 to the housing 2. In addition, since the end weld layer 5 surrounds the core material layer 613 over the entire circumference, it is considered that the strength of the fixed end 62 is further improved and the weld strength of the ground electrode 6 to the housing 2 is further improved. Furthermore, since the end weld layer 5 is formed so as to be sandwiched between the core material layer 613 and the outer skin layer 611 in the radial direction of the core material layer 613, it is considered that the mutual weld strength of the intermediate layer 612, the core material layer 613, and the outer skin layer 611 is improved, and the strength of the fixed end 62 is further increased. Therefore, it is considered that the tensile strength of the sample c is increased as shown in FIG. 14.

[0063] As shown in FIG. 12(d), the fixed end 62 of sample d was confirmed to have a structure similar to that of the fixed end 62 of sample c. However, unlike sample c, air bubbles 69 were formed between the intermediate layer 612 and the end welded layer 5 of sample d. It is believed that the air bubbles 69 were formed by the material constituting the ground electrode 6 vaporizing during welding. From these results, it is believed that the fixed end 62 of sample d has a structure similar to that of the fixed end 62 of sample c, and therefore has a high tensile strength. On the other hand, as shown in FIG. 13(d), sample d was broken at the location where the air bubbles 69 were formed after the destructive test. From this, it is believed that the strength of the fixed end 62 of sample d was reduced by the amount of the air bubbles 69 formed, and the tensile strength was reduced in comparison with sample c.

[0064] From the above results, it is considered that by setting the energizing current value to 1.0 kA or more, the end weld layer 5 covering the intermediate layer 612 from the base end side Z2 is formed, and the strength of the fixed end 62 and the welding strength of the ground electrode 6 to the housing 2 can be sufficiently ensured. Also, by setting the energizing current value to 1.4 kA or more, the end weld layer 5 is formed over a wide area, and the amount of penetration of the ground electrode 6 into the housing 2 increases, and it is considered that the strength of the fixed end 62 and the welding strength of the ground electrode 6 to the housing 2 can be further improved. Furthermore, by setting the energizing current value to 1.4 kA or more and smaller than 2.0 kA, it is possible to suppress the formation of bubbles 69 while forming the end weld layer 5 over a wide area, and it is considered that the strength of the fixed end 62 and the welding strength of the ground electrode 6 to the housing 2 can be further improved.

[0065] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments without departing from the gist of the present invention. [Explanation of symbols]

[0066] 1...spark plug, 2...housing, 3...insulator, 4...center electrode, 5...end welded layer, 6...ground electrode, 21...housing tip surface, 62...fixed end, 611...outer layer, 612...intermediate layer, 613...core layer, G...discharge gap, Z...plug axial direction, Z1...tip side, Z2...base side

Claims

1. A cylindrical insulator (3); a center electrode (4) held on the inner circumferential side of the insulator and exposed from the insulator to a tip side (Z1); A cylindrical housing (2) that holds the insulator on its inner periphery; a ground electrode (6) welded to the housing and forming a discharge gap (G) between the ground electrode and the center electrode, The ground electrode has an outer skin layer (611), an intermediate layer (612) at least a portion of which is disposed inside the outer skin layer and has a higher thermal conductivity than the outer skin layer, and a core layer (613) at least a portion of which is disposed inside the intermediate layer, The skin layer and the core layer have a higher hardness than the intermediate layer, a fixed end portion (62) of the ground electrode welded to a housing front end surface (21), which is a front end surface of the housing, is erected from the housing front end surface toward the front end side along the plug axial direction (Z), The fixed end portion has an end welding layer (5) that welds the outer skin layer, the intermediate layer, and the core layer together, At the fixed end portion, the end weld layer covers the intermediate layer from the base end side (Z2), At least a portion of the end weld layer is located on a base end side relative to the housing tip surface.

2. 2. The spark plug for an internal combustion engine according to claim 1, wherein, in a cross section including a plug center axis (PC) and a center axis (GC) of the fixed end, an area of ​​the end weld layer located on a base end side relative to the housing front end surface is larger than an area of ​​the end weld layer located on a tip end side relative to the housing front end surface.

3. 3. The spark plug for an internal combustion engine according to claim 1, wherein, in a cross section perpendicular to a plane including a plug center axis (PC) and a center axis (GC) of the fixed end and including the center axis of the fixed end, an area of ​​the end weld layer located on a base end side relative to the housing front end surface is larger than an area of ​​the end weld layer located on a tip end side relative to the housing front end surface.

4. 3. The spark plug for an internal combustion engine according to claim 1, wherein a base end portion of said core material layer in said fixed end portion is located closer to the base end than said end weld layer.

5. At the fixed end portion, the intermediate layer and the end welding layer covering the intermediate layer from the base end side each surround the core material layer over the entire circumference, 3. The spark plug for an internal combustion engine according to claim 1, wherein a base end of the core material layer at the fixed end covers the end weld layer from the base end side at least in a cross section including a plug center axis (PC) and a center axis (GC) of the fixed end.

Images