Spark plug for internal combustion engine and manufacturing method thereof

Abstract

To provide a spark plug for an internal combustion engine capable of reliably forming a discharge gap in desired length, and a manufacturing method for the same.SOLUTION: In a spark plug 1, a ground electrode 6 is fixed to an end part of a housing 2. The plug cover 5 is welded at an end of the housing 2. A welding part 11 of the plug cover 5 and the housing 2 is continuously formed all over a circumference in a plug circumferential direction. An area which is nearer on the fixed end 61 side than a plug central axis C in the direction in which the fixed end 61 and the plug central axis C are arranged seen from a plug axis direction and between a straight line L1 and a straight line L2 seen from the plug axis direction is a ground side area R. Then, outside the ground area R, a welding start part 111 and a welding completion part 112 are formed in the welding part 11.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a spark plug for an internal combustion engine and a method for manufacturing the same. [Background technology]

[0002] For example, as disclosed in Patent Document 1, a spark plug with a pre-combustion chamber at its tip is known. In this spark plug, a plug cover covering the pre-combustion chamber is formed with multiple injection holes. This allows flames to be ejected from the pre-combustion chamber through the injection holes into the main combustion chamber, thereby combusting the air-fuel mixture in the main combustion chamber. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-184435 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the spark plug described in Patent Document 1, the ground electrode and the plug cover are each fixed to the front end of the housing. Therefore, when the plug cover is fixed to the housing by welding after adjusting the discharge gap, the length of the discharge gap after welding may differ from the length of the discharge gap before welding depending on the welding method. Therefore, it can be said that there is room for further improvement from the viewpoint of discharge gap formation.

[0005] The present invention has been made in view of the above-mentioned problems, and aims to provide a spark plug for an internal combustion engine that can reliably form a discharge gap of a desired length, and a method for manufacturing the same. [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 to the tip side from the insulator; a cylindrical housing (2) that holds the insulator on its inner periphery; a ground electrode (6) fixed to the tip of the housing and forming a discharge gap (G) between itself and the center electrode; a plug cover (5) welded to the tip of the housing so as to cover the auxiliary combustion chamber (50) in which the discharge gap is arranged, The ground electrode protrudes into the auxiliary combustion chamber from a fixed end (61) fixed to the housing, The welded portion (11) between the plug cover and the housing is formed continuously around the entire circumference of the plug, When a ground side region (R) is defined as a region closer to the fixed end than the plug central axis (C) in the direction of arrangement of the fixed end and the plug central axis (C) as viewed from the plug axial direction (Z), and as a region between a straight line (L1) connecting the plug central axis and one end (611) of the fixed end in the circumferential direction of the plug and a straight line (L2) connecting the plug central axis and the other end (612) of the fixed end in the circumferential direction of the plug, A welding start portion (111) and a welding end portion (112) of the welded portion are formed outside the ground contact region. Crate , a base end of the plug cover faces the front end of the housing in both the plug axial direction and the plug radial direction and has a cover fitting portion (52) formed along the plug circumferential direction, and a front end of the housing faces the cover fitting portion in both the plug axial direction and the plug radial direction and has a housing fitting portion (21) formed along the plug circumferential direction, the cover fitting portion and the housing fitting portion have axially opposing portions (12) at a plurality of locations in the radial direction of the plug, where the cover fitting portion and the housing fitting portion are opposed to each other in the plug axial direction, the welded portion is formed at some of the axially opposing portions, and a heat-conducting member (13) having a higher thermal conductivity than the plug cover and the housing is interposed at at least some of the axially opposing portions where the welded portion is not formed, and the heat-conducting member is in close contact with the front end portion of the housing and the base end portion of the plug cover; In a spark plug (1) for an internal combustion engine.

[0007] Another aspect of the present invention is a method for manufacturing a spark plug (1) for an internal combustion engine, the spark plug (1) comprising: a cylindrical insulator (3); a center electrode (4) held on the inner periphery of the insulator and exposed from the insulator toward a tip end thereof; a cylindrical housing (2) holding the insulator on the inner periphery; a ground electrode (6) fixed to a tip end of the housing and forming a discharge gap (G) between the center electrode and the ground electrode; and a plug cover (5) welded to the tip end of the housing so as to cover an auxiliary combustion chamber (50) in which the discharge gap is disposed, the ground electrode protruding into the auxiliary combustion chamber from a fixed end (61) fixed to the housing, When welding the plug cover to the housing, a weld (11) between the plug cover and the housing is formed continuously around the entire circumference of the plug, When a ground side region (R) is defined as a region closer to the fixed end than the central axis of the plug in the direction of arrangement of the fixed end and the central axis of the plug (C) as viewed from the axial direction of the plug, and as viewed from the axial direction of the plug, between a straight line (L1) connecting the central axis of the plug and one end (611) of the fixed end in the circumferential direction of the plug and a straight line (L2) connecting the central axis of the plug and the other end (612) of the fixed end in the circumferential direction of the plug, Welding is started from the outside of the ground side area and is finished outside the ground side area. death , a base end of the plug cover faces the front end of the housing in both the plug axial direction and the plug radial direction and has a cover fitting portion (52) formed along the plug circumferential direction, and the front end of the housing faces the cover fitting portion in both the plug axial direction and the plug radial direction and has a housing fitting portion (21) formed along the plug circumferential direction, and the cover fitting portion and the housing fitting portion face each other in the plug axial direction, and have axially opposing portions (12) at a plurality of locations in the plug radial direction; Before welding the plug cover to the housing, a heat-conducting member (13) having a higher thermal conductivity than the plug cover and the housing is disposed on some of the axially opposing portions of the plurality of axially opposing portions, and the plug cover is pressed against the housing along the plug axial direction to bring the heat-conducting member and the housing, and the heat-conducting member and the plug cover, into close contact with each other; When welding the plug cover to the housing, welding is performed to the axially opposing portion where the heat conduction member is not disposed. The present invention relates to a method for manufacturing a spark plug for an internal combustion engine. [Effects of the Invention]

[0008] In the above spark plug, the weld start portion and the weld end portion are formed outside the ground-side region. Therefore, the length of the discharge gap after welding the plug cover to the housing can be prevented from changing from the length of the discharge gap before welding. As a result, a discharge gap of the desired length can be reliably formed.

[0009] In the above-described method for manufacturing a spark plug, when welding the plug cover to the housing, welding is started from outside the ground-side region and finished outside the ground-side region. This prevents the length of the discharge gap after welding the plug cover to the housing from changing from the length of the discharge gap before welding. As a result, a discharge gap of the desired length can be reliably formed.

[0010] As described above, according to the above-described aspect, it is possible to provide a spark plug for an internal combustion engine, which can reliably form a discharge gap of a desired length, and a method for manufacturing the same. In addition, the symbols in parentheses in the claims and the means for solving the problems indicate the correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present invention. [Brief explanation of the drawings]

[0011] [Figure 1] 2. FIG. 3 is a cross-sectional view of the vicinity of the tip end portion of the spark plug according to the first embodiment, taken along the axial direction of the plug, and is a cross-sectional view taken along the line II in FIG. [Figure 2] Arrow II view of Figure 1. [Figure 3] 3 is a view of the spark plug according to the first embodiment, showing a straight line L1 and a straight line L2, as viewed from the front end side. FIG. [Figure 4] IV arrow view of Figure 2. [Figure 5] FIG. 4 is a cross-sectional view showing how the plug cover is fitted to the housing in the first embodiment. [Figure 6] VI arrow view of Figure 5. [Figure 7] FIG. 4 is a cross-sectional view of the vicinity of the axially opposing portion before the plug cover is welded to the housing in the first embodiment. [Figure 8] FIG. 3 is a diagram showing the direction in which the irradiation position of the laser light moves in the first embodiment. [Figure 9] 1 is a cross-sectional view of an internal combustion engine in which a spark plug is installed according to a first embodiment. [Figure 10]FIG. 10 is a cross-sectional view taken along the axial direction of a spark plug in the vicinity of a tip portion of the spark plug according to a second embodiment. [Figure 11] FIG. 11 is a cross-sectional view taken along the axial direction of a spark plug in the vicinity of a tip portion of the spark plug according to a third embodiment. [Figure 12] 10 is a CT image of the spark plug of the third embodiment in Experimental Example 1. [Figure 13] 1 is a CT image of a spark plug of Comparative Example 1 in Experimental Example 1. [Figure 14] 10 is a photograph showing the appearance of the spark plug of Example 3 near the welding end portion in Experimental Example 1. [Figure 15] 13 is a photograph of the appearance of the spark plug of the third embodiment in Experimental Example 1, seen from the opposite side to that of FIG. 12. [Figure 16] FIG. 10 is a cross-sectional view taken along the axial direction of a spark plug in the vicinity of its tip end in a fourth embodiment. [Figure 17] FIG. 11 is a cross-sectional view taken along the axial direction of a spark plug in the vicinity of a tip portion of the spark plug according to a fifth embodiment. [Figure 18] FIG. 13 is a cross-sectional view of the vicinity of a welded portion in a sixth embodiment. [Figure 19] FIG. 13 is a cross-sectional view of the vicinity of the axially opposing portion before the plug cover is welded to the housing in the sixth embodiment. [Figure 20] FIG. 13 is a cross-sectional view taken along the axial direction of a spark plug in the vicinity of its tip end in a seventh embodiment. [Figure 21] FIG. 13 is an enlarged cross-sectional view of the heat conduction member and its vicinity in the seventh embodiment. [Figure 22] FIG. 13 is a cross-sectional view showing a state in which the plug cover is pressed against the housing in the seventh embodiment. [Figure 23] FIG. 13 is a cross-sectional view taken along the axial direction of a spark plug in the vicinity of a tip portion of the spark plug according to an eighth embodiment. [Figure 24] 13 is a cross-sectional view of the vicinity of a welded portion in embodiment 9. FIG. [Figure 25] FIG. 13 is a cross-sectional view of the vicinity of the axially opposing portion before the plug cover is welded to the housing in the ninth embodiment. [Figure 26] 13 is a cross-sectional view of the vicinity of a welded portion in embodiment 10. FIG. [Figure 27] FIG. 20 is a cross-sectional view of the vicinity of the axially opposing portion before the plug cover is welded to the housing in the tenth embodiment. [Figure 28] 12 is a cross-sectional view of the vicinity of the welded portion in embodiment 11. FIG. [Figure 29] FIG. 23 is a cross-sectional view of the vicinity of the axially opposing portion before the plug cover is welded to the housing in the eleventh embodiment. [Figure 30] 23 is a cross-sectional view of the vicinity of the welded portion in the twelfth embodiment. [Figure 31] FIG. 23 is a cross-sectional view of the vicinity of the contact portion between the base end portion of the plug cover and the front end portion of the housing before the plug cover is welded to the housing in a twelfth embodiment. [Figure 32] 23 is a cross-sectional view of the vicinity of the welded portion in the thirteenth embodiment. [Figure 33] FIG. 23 is a cross-sectional view of the vicinity of the contact portion between the base end of the plug cover and the front end of the housing before the plug cover is welded to the housing in the thirteenth embodiment. [Figure 34] 34 is a cross-sectional view of the vicinity of the tip end portion of the spark plug according to the fourteenth embodiment, taken along the axial direction of the plug, and taken along the line XXXIV-XXXIV in FIG. 35. [Figure 35] XXXV arrow view of Figure 34. DETAILED DESCRIPTION OF THE INVENTION

[0012] (Embodiment 1) An embodiment of a spark plug for an internal combustion engine and a method for manufacturing the same will be described with reference to FIGS. As shown in FIGS. 1 and 2 , 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, a ground electrode 6, and a plug cover 5. The center electrode 4 is held on the inner periphery of the insulator 3 and is exposed from the insulator 3 toward the tip. The housing 2 holds the insulator 3 on the inner periphery. The ground electrode 6 is fixed to the tip of the housing 2 and forms a discharge gap G between it and the center electrode 4. The plug cover 5 is welded to the tip of the housing 2 so as to cover the auxiliary combustion chamber 50 in which the discharge gap G is located. The ground electrode 6 protrudes into the auxiliary combustion chamber 50 from a fixed end 61 fixed to the housing 2.

[0013] As shown in Figures 2 and 3, the weld 11 between the plug cover 5 and the housing 2 is formed continuously around the entire circumferential circumference of the plug. As shown in Figure 3, as viewed from the axial direction Z, a line connecting the central axis C of the plug and one end 611 of the fixed end 61 in the circumferential direction is designated as line L1. As viewed from the axial direction Z, a line connecting the central axis C of the plug and the other end 612 of the fixed end 61 in the circumferential direction is designated as line L2. As viewed from the axial direction Z, a region closer to the fixed end 61 than the central axis C in the direction of alignment of the fixed end 61 and the central axis C is designated as a ground side region R. A weld start portion 111 and a weld end portion 112 of the weld 11 are formed outside the ground side region R.

[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. As shown in Fig. 9, the spark plug 1 is attached to an internal combustion engine 10 by threading the threaded portion 23 of the housing 2 into the female threaded portion of a plug hole 711 in a cylinder head 71. The cylinder head 71 and the housing 2 are in thermal contact with each other.

[0015] The internal combustion engine 10 has a piston 74 that reciprocates within a cylinder 70. The volume of the main combustion chamber 101 changes due to the reciprocating motion of the piston 74. The internal combustion engine 10 is formed with an intake port 721 and an exhaust port 731, each of which is equipped with an intake valve 72 or an exhaust valve 73.

[0016] One end of the spark plug 1 in the axial direction Z is disposed in the main combustion chamber 101 of the internal combustion engine 10. In the axial direction Z of the spark plug 1, the side exposed to the main combustion chamber 101 is referred to as the tip side, and the opposite side is referred to as the base side. The axial direction Z of the spark plug 1 is also referred to as the plug axial direction Z or simply as the Z direction, as appropriate. The plug central axis C refers to the central axis C of the spark plug 1. The plug radial direction refers to the radial direction of a circle centered on the plug central axis C on a plane perpendicular to the plug central axis C. The plug circumferential direction refers to the direction along the circumference of a circle centered on the plug central axis C. In this embodiment, the plug central axis C also corresponds to the central axis of the center electrode 4.

[0017] When the spark plug 1 is attached to the internal combustion engine 10 , the plug cover 5 separates the auxiliary combustion chamber 50 from the main combustion chamber 101 .

[0018] Further, the plug cover 5 is formed with a nozzle hole 51 that connects the auxiliary combustion chamber 50 to the outside. When the spark plug 1 is attached to the internal combustion engine 10, the nozzle hole 51 connects the auxiliary combustion chamber 50 to the main combustion chamber 101.

[0019] 1, the base end of the plug cover 5 has a cover fitting portion 52. The cover fitting portion 52 faces the front end of the housing 2 in both the plug axial direction Z and the plug radial direction, and is formed along the plug circumferential direction. The front end of the housing 2 has a housing fitting portion 21. The housing fitting portion 21 faces the cover fitting portion 52 in both the plug axial direction Z and the plug radial direction, and is formed along the plug circumferential direction.

[0020] In this embodiment, the housing fitting portion 21 is formed by recessing a portion of the outer peripheral surface of the housing 2 radially inward. The housing fitting portion 21 opens toward the tip end. A cover fitting portion 52 is fitted into the housing fitting portion 21.

[0021] The spark plug 1 of this embodiment has an axially opposing portion 12 where the cover fitting portion 52 and the housing fitting portion 21 face each other in the plug axial direction Z. In this embodiment, the axially opposing portion 12 is formed over the entire circumferential direction of the plug. In other words, the axially opposing portion 12 is formed in an annular shape.

[0022] A weld 11 is formed at the axially opposing portion 12. The housing 2 and the plug cover 5 are in thermal contact with each other via the weld 11. The plug cover 5 and the housing 2 are made of a material such as iron, nickel, an alloy of iron or nickel, or stainless steel.

[0023] The front end of the housing 2 has a front end protrusion 24 formed by a portion of the front end side surface 22 protruding toward the front end. The front end protrusion 24 is formed along the inner circumferential surface of the housing 2 and is formed radially inward of the base end of the plug cover 5. As shown in FIG. 6 , the front end protrusion 24 is formed on a portion of the front end of the housing 2 in the circumferential direction of the plug.

[0024] As shown in Fig. 1, the ground electrode 6 is fixed by welding to the surface of the front-side protruding portion 24 facing inward in the plug radial direction. The ground electrode 6 protrudes inward in the plug radial direction from the front-side protruding portion 24. The ground electrode 6 is provided along the plug radial direction without bending. A discharge gap G is formed by the protruding end portion 63 of the ground electrode 6 and the front end portion of the center electrode 4 facing each other in the plug radial direction.

[0025] In this embodiment, the fixed end 61 of the ground electrode 6 is located closer to the tip end than the welded portion 11 in the Z direction. The shortest distance D1 from the welded portion 11 to the fixed end 61 in the Z direction is shorter than three times the width W2 of the welded portion 11 in the Z direction. In addition, the shortest distance D1 is shorter than twice the width W2. In this embodiment, the shortest distance D1 is shorter than the width W2.

[0026] The welded portion 11 is formed in both the ground side region R and in a region of the spark plug 1 other than the ground side region R. As shown in FIG. 3 , a weld start portion 111 and a weld end portion 112 of the welded portion 11 are each formed at a position at least the width W1 of the ground electrode 6 away from the ground side region R in the circumferential direction of the plug. The welded start portion 111 and the weld end portion 112 are each formed at a position at least twice the width W1 away from the ground side region R in the circumferential direction of the plug. The welded start portion 111 and the weld end portion 112 are each formed at a position at least three times the width W1 away from the ground side region R in the circumferential direction of the plug. In this embodiment, the width W1 is the length of the ground electrode 6 in a direction perpendicular to both the Z direction and the protruding direction of the ground electrode 6.

[0027] Furthermore, a weld overlap portion 113 is formed between the weld start portion 111 and the weld end portion 112 in the circumferential direction of the plug. The weld overlap portion 113 is formed by welding the opposing portions of the plug cover 5 and the housing 2 multiple times. In this embodiment, the weld overlap portion 113 is formed by welding two times to a portion of the axially opposing portion 12. The weld overlap portion 113 is not formed in the ground contact region R, but is formed outside the ground contact region R. In this embodiment, the range of the weld 11 from the weld start portion 111 to the weld end portion 112 forms the weld overlap portion 113.

[0028] The weld overlap portion 113 is formed at a position that is at least width W1 away from the ground side region R in the circumferential direction of the plug. The weld overlap portion 113 is formed at a position that is at least twice width W1 away from the ground side region R in the circumferential direction of the plug. The weld overlap portion 113 is formed at a position that is at least three times width W1 away from the ground side region R in the circumferential direction of the plug.

[0029] Next, a method for manufacturing the spark plug 1 will be described. In the manufacturing method of this embodiment, when welding the plug cover 5 to the housing 2, a weld 11 is formed between the plug cover 5 and the housing 2 continuously around the entire circumference of the plug. Welding is started from the outside of the ground side region R and finished outside the ground side region R. This will be described in detail below.

[0030] First, before welding the plug cover 5 to the housing 2, the insulator 3 and the center electrode 4 are assembled to the housing 2. Then, the ground electrode 6 is welded to the housing 2, and the length of the discharge gap G is adjusted to achieve the desired length.

[0031] Next, as shown by arrow M in Fig. 5, the plug cover 5 is moved toward the base end relative to the tip end of the housing 2, thereby fitting the cover fitting portion 52 into the housing fitting portion 21. As shown in Fig. 7, with the cover fitting portion 52 fitted into the housing fitting portion 21, the outer peripheral surface of the tip end of the housing 2 and the outer peripheral surface of the base end of the plug cover 5 are flush with each other. Then, with the base end surface of the cover fitting portion 52 abutting in the Z direction against the fitting portion forming surface that forms the housing fitting portion 21, the plug cover 5 is welded to the tip end of the housing 2. In this embodiment, the housing 2 and the plug cover 5 are welded by laser welding.

[0032] Specifically, the tip end of the housing 2 and the cover fitting portion 52 are welded together by irradiating the axially opposing portion 12 with laser light L from the outer periphery. Furthermore, the irradiating position of the laser light L on the axially opposing portion 12 is moved in the plug circumferential direction as shown by the arrow IP in FIG. 8 , while continuously welding. The irradiating position of the laser light L is then moved to a position slightly past the welding start position SP. This allows the weld 11 to be formed continuously around the entire circumferential direction of the plug. Furthermore, as shown in FIGS. 2 to 4 , a weld start portion 111 is formed at the welding start position SP, and a weld end portion 112 is formed at the welding end position. Furthermore, this welding forms a weld overlap portion 113 extending from the weld start portion 111 to the weld end portion 112.

[0033] In this embodiment, the weld overlap portion 113 is formed by irradiating the weld portion 11 formed by one irradiation of the laser light L with another irradiation of the laser light L. That is, as shown by the arrow IP in Fig. 8 , the irradiation position of the laser light L on the axial facing portion 12 is moved by more than one revolution in the circumferential direction of the plug, so that the same location on the axial facing portion 12 is irradiated with the laser light L twice.

[0034] The number of times that the axially opposing portions 12 in the ground side region R are welded is equal to or less than the number of times that the axially opposing portions 12 in regions other than the ground side region R. The number of times that the axially opposing portions 12 in the ground side region R are welded with the laser light L is one.

[0035] The welding start position and welding end position are each spaced apart from the ground side region R in the circumferential direction of the plug by at least the width W1 of the ground electrode 6 (see FIG. 3). The welding start position and welding end position are each spaced apart from the ground side region R in the circumferential direction of the plug by at least twice the width W1 of the ground electrode 6. The welding start position and welding end position are each spaced apart from the ground side region R in the circumferential direction of the plug by at least three times the width W1 of the ground electrode 6.

[0036] Next, the effects of this embodiment will be described. The spark plug 1 has a weld start portion 111 and a weld end portion 112 formed outside the ground side region R. This prevents the length of the discharge gap G after the plug cover 5 is welded to the housing 2 from changing from the length of the discharge gap G before the welding. As a result, the discharge gap G can be reliably formed to have the desired length.

[0037] Here, let us assume that a weld start portion and a weld end portion are formed in the ground side region. In this case, if a weld is formed continuously around the entire circumferential direction of the axially opposing portion to ensure airtightness of the auxiliary combustion chamber, an overlapping weld portion will be formed in the ground side region. That is, the number of welds performed on at least a portion of the axially opposing portion in the ground side region is greater than the number of welds performed on the axially opposing portion in regions other than the ground side region. As a result, the amount of heat received by welding near the axially opposing portion in the ground side region is likely to be relatively large. This may result in a risk of heat deformation of a portion of the ground electrode located in the ground side region or a portion of the housing near the fixed end of the ground electrode. This may result in a risk of the length of the discharge gap after welding being easily changed from the length of the discharge gap before welding. Therefore, in the spark plug 1 of this embodiment, a weld start portion 111 and a weld end portion 112 are formed outside the ground side region R. This allows the number of welds performed on the axially opposing portion 12 in the ground side region R to be less than the number of welds performed on the axially opposing portion 12 in regions other than the ground side region R. This reduces the amount of heat received by welding near the axially opposing portion 12 in the ground-side region R. This reliably prevents parts of the housing 2 near the ground electrode 6 and the fixed end 61 from being deformed by heat. This prevents the length of the discharge gap G after welding the plug cover 5 to the housing 2 from changing from the length of the discharge gap G before welding. As a result, it is possible to reliably form the discharge gap G of the desired length.

[0038] The weld start portion 111 and the weld end portion 112 are each formed at a position at least twice the width W1 (see FIG. 3) away from the ground side region R in the circumferential direction of the plug. This more reliably prevents parts of the housing 2 near the ground electrode 6 and the fixed end portion 61 from being deformed by heat during welding. This more reliably prevents the length of the discharge gap G after the plug cover 5 is welded to the housing 2 from changing from the length of the discharge gap G before welding. As a result, the discharge gap G of the desired length can be more reliably formed.

[0039] In the method for manufacturing the spark plug 1, when welding the plug cover 5 to the housing 2, welding is started from outside the ground side region R and finished outside the ground side region R. This makes it possible to prevent the length of the discharge gap G after welding the plug cover 5 to the housing 2 from changing from the length of the discharge gap G before welding. As a result, it is possible to reliably form the discharge gap G of the desired length.

[0040] The welding start position and welding end position are each at least twice the width W1 away from the ground side region R in the circumferential direction of the plug. This makes it possible to further reduce the amount of heat received near the joint between the housing 2 and the ground electrode 6 when the housing 2 and the plug cover 5 are welded together. This further reduces the change in the length of the discharge gap G after the plug cover 5 is welded to the housing 2 from the length of the discharge gap G before the welding.

[0041] Furthermore, the welded portion 11 is formed continuously around the entire circumference of the axially opposing portion 12 in the circumferential direction of the plug. This ensures airtightness of the auxiliary combustion chamber 50. This allows a powerful flame to be ejected from the auxiliary combustion chamber 50 to the main combustion chamber through the injection hole 51. As a result, ignition performance can be improved.

[0042] A weld overlap portion 113 is formed in the axially opposing portion 12. This ensures reliable airtightness of the auxiliary combustion chamber 50. That is, to ensure reliable airtightness of the auxiliary combustion chamber 50, the weld 11 needs to be reliably and continuously formed around the entire circumferential circumference of the plug in the axially opposing portion 12. Therefore, in this embodiment, the irradiation position of the laser light L on the axially opposing portion 12 is moved by more than one circumferential circumference of the plug. This ensures reliable formation of the weld 11 around the entire circumferential circumference of the plug, and also forms the weld overlap portion 113. This ensures reliable airtightness of the auxiliary combustion chamber 50 and improves ignition performance.

[0043] As described above, according to the present embodiment, it is possible to provide the spark plug 1 for an internal combustion engine and the manufacturing method thereof, which can reliably form the discharge gap G of a desired length.

[0044] (Embodiment 2) In this embodiment, as shown in FIG. 10, the ground electrode 6 is provided so as to be inclined with respect to the radial direction of the plug.

[0045] In this embodiment, as shown in Fig. 10, the ground electrode 6 protrudes from the fixed end 61 into the auxiliary combustion chamber 50 without being bent. The ground electrode 6 is inclined so that it approaches the tip side as it approaches the plug central axis C. In addition, the base end side surface 62 of the ground electrode 6 is also inclined so that it approaches the tip side as it approaches the plug central axis C.

[0046] The discharge gap G is formed by the base end side surface 62 of the ground electrode 6 and the tip end of the center electrode 4 facing each other. The discharge gap G is formed on the tip side of the tip of the housing 2. Other aspects are the same as those of embodiment 1. Note that, among the symbols used in embodiment 2 and onwards, the same symbols as those used in the previous embodiments represent the same components, etc. as those in the previous embodiments, unless otherwise specified.

[0047] The discharge gap G is formed closer to the tip of the housing 2 than the tip of the housing 2. Therefore, it is easy to check the discharge gap G formed between the ground electrode 6 and the center electrode 4 fixed to the housing 2 before welding the plug cover 5 to the housing 2. This makes it easy to adjust the discharge gap G. As a result, the spark plug 1 can be manufactured efficiently. In addition, the same effects as those of the first embodiment are achieved.

[0048] (Embodiment 3) As shown in FIG. 11, this embodiment is an embodiment in which the shape of the ground electrode 6 is changed from that of the first embodiment.

[0049] In this embodiment, the protruding end 63 of the ground electrode 6 is formed so that its width in the Z direction decreases toward the plug central axis C, as shown in Fig. 11. The ground electrode 6 is formed so that the outline of the protruding end 63 fits along the outer circumferential surface of the tip end of the center electrode 4 in a cross section that includes the plug central axis C and is taken along the protruding direction of the ground electrode 6.

[0050] The fixed end 61 of the ground electrode 6 is fixed to the front side surface 22 of the housing 2. The welded portion 11 is formed so that a part of the welded portion 11 and a part of the fixed end 61 overlap each other when viewed from the protruding direction of the ground electrode 6 (not shown). The other configurations and effects are the same as those of the first embodiment.

[0051] (Experimental Example 1) In this example, as shown in Figs. 12 to 15, the relationship between the length D2 of the discharge gap G after welding the plug cover 5 to the housing 2 and the length of the discharge gap G before welding was examined for the spark plug 1 of Embodiment 3 and the spark plug 9 of Comparative Example 1. As shown in Figs. 14 and 15, the spark plug 1 of Embodiment 3 used in this example has a weld finish portion 112 that protrudes slightly outward in the plug radial direction. That is, in the spark plug 1 of Embodiment 3, at least a portion of the weld finish portion 112 is located further outward in the plug radial direction than other portions of the welded portion 11. Furthermore, the spark plug 9 of Comparative Example 1 shown in Fig. 13 has the same basic structure as that of Embodiment 3 except for the welded portion 11, but the weld start portion, weld finish portion, and weld overlap portion 113 are each formed in the ground-side region R.

[0052] Fig. 12 is a CT (computed tomography) image of the spark plug 1 of embodiment 3 after the plug cover 5 has been welded to the housing 2. Regarding the spark plug 1 of embodiment 3, the length of the discharge gap G before and after welding was examined. As a result, it was confirmed that the length of the discharge gap G before welding the plug cover 5 to the housing 2 and the length D2 after the formation of the welded portion 11 shown in Fig. 12 were substantially the same. Specifically, the length of the discharge gap G before welding was 0.700 mm, and the length D2 after welding was 0.702 mm, and it was confirmed that there was almost no change before and after welding. The length of the discharge gap G before welding was measured with a pin gauge, and the length D2 after welding was measured from a CT image.

[0053] 13 is a CT image of the spark plug 9 of Comparative Form 1 after the plug cover 5 has been welded to the housing 2. As a result of examining the length of the discharge gap G before and after welding for the spark plug 9 of Comparative Form 1, it was confirmed that the length D2 shown in FIG. 13 was shorter than the length of the discharge gap G before welding the plug cover 5 to the housing 2. Specifically, the length of the discharge gap G before welding was 0.72 mm, and the length D2 after welding was 0.06 mm, and a change in the length of the discharge gap G before and after welding was observed.

[0054] In the case of the spark plug 9 of Comparative Example 1 shown in FIG. 13 , as described above, the weld start portion, the weld finish portion, and the weld overlap portion 113 are each formed in the ground side region R. Therefore, it is considered that the amount of heat received by the ground electrode 6 and the housing 2 in the ground side region R during welding is greater in the spark plug 9 of Comparative Example 1 than in the spark plug 1 of Embodiment 3. Therefore, it is considered that the ground electrode 6 or the housing 2 is deformed by the heat during welding, and the length D2 of the discharge gap G after welding is shorter than the length of the discharge gap G before welding. On the other hand, in the case of the spark plug 1 of Embodiment 3 shown in FIGS. 12 , 14 , and 15 , the weld start portion and the weld finish portion 112 are formed outside the ground side region R. Therefore, it is considered that the amount of heat received by the ground electrode 6 and the housing 2 in the ground side region R during welding is smaller in the spark plug 1 of Embodiment 3 than in Comparative Example 1. Therefore, it is considered that deformation of the ground electrode 6 and the housing 2 due to the heat during welding was suppressed. Therefore, it is considered that the length of the discharge gap G was substantially unchanged before and after welding. That is, the spark plug 1 in which the weld start portion 111 and the weld end portion 112 are formed outside the ground side region R can reliably form a discharge gap G of a desired length.

[0055] (Embodiment 4) As shown in FIG. 16, this embodiment is different from the second embodiment in that the joining location of the ground electrode 6 is changed.

[0056] In this embodiment, the ground electrode 6 is joined to an inclined surface provided on the front end side surface 22 of the housing 2, as shown in Fig. 16. This inclined surface is formed on a part of the front end side surface 22 of the housing 2 in the plug circumferential direction. In addition, the fixed end portion 61 is disposed so as to contact the inner circumferential surface of the plug cover 5. The other configurations and effects are the same as those of the second embodiment.

[0057] (Embodiment 5) In this embodiment, as shown in FIG. 17, an insertion recess 53 for inserting the ground electrode 6 is formed at the base end of the plug cover 5.

[0058] In this embodiment, as shown in Fig. 17, an insertion recess 53 is formed at the base end of the plug cover 5 by retracting a portion of the base end side surface of the plug cover 5 toward the tip end. The insertion recess 53 is formed to penetrate in the protruding direction of the ground electrode 6. A fixed end 61 of the ground electrode 6 is disposed inside the insertion recess 53.

[0059] The front end of the housing 2 has a ground-side protrusion 26 formed by part of its inner circumferential surface protruding radially inward along the protruding direction of the ground electrode 6. The ground-side protrusion 26 is formed on part of the front end of the housing 2 in the circumferential direction of the plug.

[0060] The ground electrode 6 is joined to the ground-side protrusion 26. The ground electrode 6 is also fixed to the tip of the housing 2 via a welded portion 11. The rest is the same as in the fourth embodiment.

[0061] The fixed end 61 is disposed inside the insertion recess 53. This increases the bonding area between the housing 2 and the ground electrode 6. This facilitates transfer of heat from the ground electrode 6 to the housing 2. As a result, overheating of the ground electrode 6 can be suppressed.

[0062] The ground electrode 6 is also joined to the ground-side protrusion 26. This further increases the joining area between the housing 2 and the ground electrode 6. As a result, overheating of the ground electrode 6 can be further suppressed.

[0063] The ground electrode 6 is fixed to the tip of the housing 2 via the welded portion 11. Therefore, heat from the ground electrode 6 is easily transferred to the housing 2 via the welded portion 11. As a result, overheating of the ground electrode 6 can be reliably prevented. In addition, the same effects as those of the fourth embodiment are achieved.

[0064] (Embodiment 6) In this embodiment, as shown in FIGS. 18 and 19, the base end of the plug cover 5 and the front end of the housing 2 are each formed in a stepped shape.

[0065] 18 and 19, the spark plug 1 of this embodiment has axially opposing portions 12 at a plurality of locations in the plug radial direction, where the cover fitting portion 52 and the housing fitting portion 21 face each other in the plug axial direction Z. The spark plug 1 of this embodiment has the axially opposing portions 12 formed at two locations in the plug radial direction.

[0066] As shown in Figure 19, when the housing fitting portion 21 and the cover fitting portion 52 are fitted together before welding the plug cover 5 to the housing 2, the housing 2 and the plug cover 5 abut against each other in the Z direction at both of the axially opposing portions 12 formed in the two locations. The other configurations and effects are the same as those of the first embodiment.

[0067] (Embodiment 7) In this embodiment, as shown in FIGS. 20 to 22, a heat conduction member 13 is interposed between the axially opposing portions 12. As shown in FIG.

[0068] 20 to 22 , in the spark plug 1 of this embodiment, welded portions 11 are formed on some of the axially opposing portions 12 among the plurality of axially opposing portions 12. Furthermore, among the axially opposing portions 12 not having welded portions 11, at least some of the axially opposing portions 12 have a heat-conducting member 13 interposed therein, the heat-conducting member 13 having a higher thermal conductivity than the plug cover 5 and the housing 2. The heat-conducting member 13 is in close contact with the front end portion of the housing 2 and the base end portion of the plug cover 5.

[0069] The heat conducting member 13 is provided over the entire circumference of the plug in the circumferential direction. The heat conducting member 13 is in close contact with the tip end surface of the housing fitting portion 21 and also with the base end side surface of the cover fitting portion 52.

[0070] The heat conducting member 13 is mainly composed of copper and is annealed. In this embodiment, the copper content of the heat conducting member 13 can be, for example, 99 mass % or more.

[0071] In this embodiment, the axially opposing portions 12 are formed at two locations in both the plug radial direction and the Z direction. A welded portion 11 is formed in one of the axially opposing portions 12, and a heat-conducting member 13 is interposed in the other axially opposing portion 12. The axially opposing portion 12 in which the welded portion 11 is formed is located on the outer side in the plug radial direction of the axially opposing portion 12 in which the heat-conducting member 13 is interposed.

[0072] The ground electrode 6 is fixed to the inner circumferential surface of the tip of the housing 2. The welded portion 11 is formed so that a part of the welded portion 11 and a part of the fixed end portion 61 overlap each other when viewed from the protruding direction of the ground electrode 6 (not shown).

[0073] Next, a method for manufacturing the spark plug 1 of this embodiment will be described. In this embodiment, before welding the plug cover 5 to the housing 2, the heat conduction members 13 are placed on some of the axially opposing portions 12, and the plug cover 5 is pressed against the housing 2 in the plug axial direction Z, as shown by the arrow P in Fig. 22. This brings the heat conduction members 13 and the housing 2, and the heat conduction members 13 and the plug cover 5, into close contact with each other.

[0074] Furthermore, when the plug cover 5 is welded to the housing 2, the welding is performed to the axially opposing portion 12 where the heat conducting member 13 is not arranged.

[0075] In this embodiment, before welding the plug cover 5 to the housing 2, the heat conductive member 13 is placed on the axially opposing portion 12 on the auxiliary combustion chamber 50 side. Then, as shown by arrow P in FIG. 22 , the plug cover 5 is pressed against the housing 2 toward the base end. This compresses and deforms the heat conductive member 13, causing the housing 2 and the plug cover 5 to abut against each other at the axially opposing portion 12 on the outer periphery where the heat conductive member 13 is not disposed. Then, in this pressed state, laser light L is irradiated onto the axially opposing portion 12 on the outer periphery. This welds the plug cover 5 to the front end of the housing 2. The rest is the same as in the sixth embodiment.

[0076] The spark plug 1 of this embodiment has axially opposing portions 12 at multiple locations in the plug radial direction. Welded portions 11 are formed in some of the axially opposing portions 12. Furthermore, heat-conducting members 13 are interposed in at least some of the axially opposing portions 12 where no welded portions 11 are formed. The heat-conducting members 13 are in close contact with the front end portion of the housing 2 and the base end portion of the plug cover 5. Therefore, heat from the plug cover 5 can be transferred to the housing 2 via the heat-conducting members 13 in addition to the welded portions 11. In other words, the heat from the plug cover 5 can be efficiently transferred to the housing 2 at the axially opposing portions 12 where the heat-conducting members 13 are interposed, without forming welded portions 11. Therefore, heat from the plug cover 5 can be efficiently dissipated to the outside via the housing 2 while reliably suppressing deformation of the ground electrode 6 and portions of the housing 2 near the fixed end 61 due to heat generated during welding. As a result, the discharge gap G of the desired length can be reliably formed, and overheating of the plug cover 5 can be reliably prevented.

[0077] The spark plug 1 of this embodiment has axially opposing portions 12 formed at two locations in the plug radial direction. Therefore, if a heat-conducting member is not interposed at the axially opposing portions, a gap may occur at one of the axially opposing portions even if the housing and the plug cover are designed to abut against each other at the two axially opposing portions. That is, a gap may occur at one of the axially opposing portions due to machining tolerances of the cover fitting portion and the housing fitting portion. Therefore, if a gap occurs at an axially opposing portion where no weld is formed, an air layer is interposed between the plug cover and the housing at this axially opposing portion, making it difficult for heat from the plug cover to be transferred to the housing. Furthermore, if welds are formed at both axially opposing portions to improve the heat dissipation of the plug cover, the number of welds in the ground side region will be increased. Therefore, the ground electrode 6 and portions of the housing 2 near the fixed end 61 may be easily deformed by heat during welding. Therefore, the spark plug 1 of this embodiment has a heat-conducting member 13 interposed at the axially opposing portion 12 where no weld is formed. Therefore, it is possible to reliably prevent the ground electrode 6 and a portion of the housing 2 near the fixed end 61 from being deformed by heat during welding, while also reliably preventing overheating of the plug cover 5. As a result, it is possible to reliably form a discharge gap G of the desired length, and it is also possible to reliably prevent pre-ignition even during high-load operation of the internal combustion engine.

[0078] In the method for manufacturing the spark plug 1 of this embodiment, before welding the plug cover 5 to the housing 2, the heat conduction member 13 and the housing 2, and the heat conduction member 13 and the plug cover 5 are brought into close contact with each other. Furthermore, when welding the plug cover 5 to the housing 2, welding is performed to the axially opposing portion 12 where the heat conduction member 13 is not disposed. This makes it possible to reliably form the discharge gap G of the desired length and to reliably prevent the plug cover 5 from overheating.

[0079] The heat conduction member 13 is primarily composed of copper and is annealed. This allows the hardness of the heat conduction member 13 to be relatively low. This makes it easier to bring the heat conduction member 13 into closer contact with the plug cover 5 and the housing 2. This makes it easier to transfer heat from the plug cover 5 to the housing 2 more efficiently. As a result, overheating of the plug cover 5 can be further suppressed. In addition, the same effects as those of the sixth embodiment are obtained.

[0080] (Embodiment 8) As shown in FIG. 23, this embodiment is an embodiment in which the shape of the ground electrode 6 is changed from that of the sixth embodiment.

[0081] In this embodiment, as shown in FIG. 23 , the ground electrode 6 is joined to the front end side surface 22 of the housing 2 by welding. The ground electrode 6 has an erect portion 64, a bent portion 65, and an extended portion 66. The erect portion 64 has a fixed end portion 61 and extends from the front end side surface 22 of the housing 2 toward the front end along the plug axial direction Z. The bent portion 65 bends from the front end of the erect portion 64 toward the inside in the plug radial direction. The extended portion 66 extends from the bent portion 65 toward the plug central axis C. The extended portion 66 and the front end of the center electrode 4 face each other in the Z direction, thereby forming a discharge gap G.

[0082] The plug cover 5 also has an inner recess 55 formed by recessing a portion of its inner circumferential surface outward in the plug radial direction. The inner recess 55 is formed on a portion of the plug cover 5 in the plug circumferential direction. The inner recess 55 is also formed so as to open on the base end side. At least a portion of the erected portion 64 of the ground electrode 6 is located inside the inner recess 55. The rest is the same as in the sixth embodiment.

[0083] At least a portion of the standing portion 64 is disposed inside the inner recess 55. This makes it easy to increase the joint area between the housing 2 and the ground electrode 6. In other words, since the standing portion 64 is disposed inside the inner recess 55, the joint area between the tip side surface 22 and the ground electrode 6 can be increased accordingly. This makes it easy for heat from the ground electrode 6 to transfer to the housing 2. As a result, overheating of the ground electrode 6 can be suppressed. In addition, the same effects as those of the sixth embodiment are obtained.

[0084] (Embodiment 9) As shown in FIGS. 24 and 25, this embodiment is an embodiment in which the shape of the tip of the housing 2 is changed from that of the sixth embodiment.

[0085] 24 and 25, in this embodiment, the thickness of the base end side of the housing fitting portion 21 at the tip end of the housing 2 and the thickness of the tip end side of the cover fitting portion 52 at the base end of the plug cover 5 are equal to each other. Also, the inner circumferential surface of the tip end of the housing 2 and the inner circumferential surface of the base end of the plug cover 5 are flush with each other. The other configurations and effects are the same as those of the sixth embodiment.

[0086] (Embodiment 10) 26 and 27, in this embodiment, the axially opposing portion 12 where the welded portion 11 is formed is located on the tip side relative to the other axially opposing portion 12. In other words, the axially opposing portion 12 on the outer periphery side is located on the tip side relative to the axially opposing portion 12 on the auxiliary combustion chamber 50 side. The other configurations and effects are the same as those of the ninth embodiment.

[0087] (Embodiment 11) As shown in FIGS. 28 and 29, this embodiment is an embodiment in which the shapes of the base end portion of the plug cover 5 and the tip end portion of the housing 2 are changed from those of the ninth embodiment.

[0088] 28 and 29, the front end portion of the housing 2 has a groove 27 formed by part of the front end side surface 22 of the housing 2 being recessed toward the base end side. The groove 27 is formed outside the inner circumferential surface of the front end portion of the housing 2 in the radial direction of the plug and inside the outer circumferential surface of the front end portion of the housing 2. The groove 27 is formed over the entire circumferential direction of the plug.

[0089] A cover fitting portion 52 is fitted into the groove portion 27. The axially opposing portions 12 are formed at three locations in the plug radial direction. The other configurations and effects are the same as those of the ninth embodiment.

[0090] (Embodiment 12) As shown in FIGS. 30 and 31, this embodiment is an embodiment in which the shapes of the base end portion of the plug cover 5 and the tip end portion of the housing 2 are changed from those of the ninth embodiment.

[0091] 31 , before the plug cover 5 is welded to the housing 2, the front end of the housing 2 has a housing inclined portion 28 formed so that its width in the plug radial direction decreases toward the front end. The housing inclined portion 28 has a housing inclined surface 281 that inclines inward in the plug radial direction toward the front end. The housing inclined portion 28 and the housing inclined surface 281 are each formed over the entire circumferential direction of the plug.

[0092] Furthermore, before the plug cover 5 is welded to the housing 2, the base end of the plug cover 5 has a cover inclined portion 56 formed so that its width in the plug radial direction decreases toward the base end. The cover inclined portion 56 has a cover inclined surface 561 that inclines inward in the plug radial direction toward the tip end. The cover inclined portion 56 and the cover inclined surface 561 are each formed over the entire circumferential circumference of the plug.

[0093] In the method for manufacturing the spark plug 1 of this embodiment, when welding the plug cover 5 to the housing 2, the housing inclined surface 281 and the cover inclined surface 561 are welded in a state in which they are in contact with each other. Also, in this embodiment, the plug cover 5 is welded to the housing 2 in a state in which the housing inclined surface 281 and the cover inclined surface 561 are in surface contact with each other. The other configurations and effects are the same as those of the ninth embodiment.

[0094] (Embodiment 13) As shown in FIGS. 32 and 33, this embodiment is an embodiment in which the shapes of the base end portion of the plug cover 5 and the tip end portion of the housing 2 are changed from those of the ninth embodiment.

[0095] In this embodiment, as shown in Figures 32 and 33, the housing 2 does not have a housing fitting portion 21. As shown in Figure 33, before the plug cover 5 is welded to the housing 2, the tip side surface 22 of the housing 2 is formed so as to be perpendicular to the Z direction.

[0096] Furthermore, the plug cover 5 does not have a cover fitting portion 52. Before the plug cover 5 is welded to the housing 2, the base end side surface of the plug cover 5 is formed so as to be perpendicular to the Z direction.

[0097] When welding the plug cover 5 to the housing 2, as shown in Figure 33, the base end side surface of the plug cover 5 and the tip end side surface 22 of the housing 2 are abutted against each other in the Z direction, and laser light is irradiated from the outer periphery. The other configurations and effects are the same as those of the ninth embodiment.

[0098] (Embodiment 14) As shown in FIGS. 34 and 35, this embodiment is an embodiment in which the shape of the tip of the housing 2 is changed from that of the first embodiment.

[0099] 34 and 35 , the front end side surface 22 of the housing 2 is formed continuously around the entire circumferential direction of the plug. The ground electrode 6 is joined to the front end side surface 22. The fixed end portion 61 of the ground electrode 6 is disposed so as to contact the inner circumferential surface of the plug cover 5. The other configurations and effects are the same as those of the first embodiment.

[0100] In the spark plugs 1 of the above-described first to fourteenth embodiments, the weld start portion 111, the weld end portion 112, and the weld overlap portion 113 are each formed in a region closer to the fixed end portion 61 than the plug central axis C in the direction of alignment of the fixed end portion 61 and the plug central axis C when viewed from the Z direction. However, the weld start portion, the weld end portion, and the weld overlap portion can also each be formed in a region on the opposite side of the plug central axis from the fixed end portion in the direction of alignment of the fixed end portion and the plug central axis when viewed from the Z direction.

[0101] In the spark plug 1 of the above-described Embodiments 1 to 14, the ground electrode 6 is fixed to the front end portion of the housing 2. Here, "the ground electrode 6 is fixed to the front end portion of the housing 2" includes, for example, the case where the ground electrode and the housing are integrally formed.

[0102] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments within the scope of the present invention. [Explanation of symbols]

[0103] 1...spark plug, 11...weld, 111...weld start portion, 112...weld end portion, 2...housing, 3...insulator, 4...center electrode, 5...plug cover, 50...auxiliary combustion chamber, 6...ground electrode, 61...fixed end portion, 611, 612...end portion, C...plug center axis, G...discharge gap, L1, L2...straight line, R...ground side region, Z...plug axial direction

Claims

1. A cylindrical insulator (3), a center electrode (4) held on the inner circumferential side of the insulator and exposed to the tip side from the insulator; a cylindrical housing (2) that holds the insulator on its inner periphery; a ground electrode (6) fixed to the tip of the housing and forming a discharge gap (G) between itself and the center electrode; a plug cover (5) welded to the tip of the housing so as to cover the auxiliary combustion chamber (50) in which the discharge gap is arranged, The ground electrode protrudes into the auxiliary combustion chamber from a fixed end (61) fixed to the housing, The welded portion (11) between the plug cover and the housing is formed continuously around the entire circumference of the plug, When a ground side region (R) is defined as a region closer to the fixed end than the central axis of the plug in the arrangement direction of the fixed end and the central axis of the plug (C) as viewed from the axial direction of the plug, and as viewed from the axial direction of the plug, between a straight line (L1) connecting the central axis of the plug and one end (611) of the fixed end in the circumferential direction of the plug, and a straight line (L2) connecting the central axis of the plug and the other end (612) of the fixed end in the circumferential direction of the plug, A welding start portion (111) and a welding end portion (112) of the weld are formed outside the ground contact region, a base end portion of the plug cover faces the front end portion of the housing in both the plug axial direction and the plug radial direction and has a cover fitting portion (52) formed along the plug circumferential direction, and a front end portion of the housing faces the cover fitting portion in both the plug axial direction and the plug radial direction and has a housing fitting portion (21) formed along the plug circumferential direction, a spark plug (1) for an internal combustion engine, wherein the cover fitting portion and the housing fitting portion have axially opposing portions (12) at a plurality of locations in the radial direction of the plug, where the cover fitting portion and the housing fitting portion are opposed to each other in the plug axial direction, the welded portion being formed in some of the axially opposing portions, and a heat-conducting member (13) having a higher thermal conductivity than the plug cover and the housing being interposed in at least some of the axially opposing portions where the welded portion is not formed, and the heat-conducting member is in close contact with a tip end of the housing and a base end of the plug cover.

2. 2. The spark plug for an internal combustion engine according to claim 1, wherein the welding start portion and the welding end portion are each formed at a position at least twice the width (W1) of the ground electrode from the ground side region in the circumferential direction of the plug.

3. 3. The spark plug for an internal combustion engine according to claim 1, wherein said heat conducting member is mainly composed of copper and is annealed.

4. A method for manufacturing a spark plug (1) for an internal combustion engine, the spark plug (1) comprising: a cylindrical insulator (3); a center electrode (4) held on the inner periphery of the insulator and exposed from the insulator to a tip end thereof; a cylindrical housing (2) holding the insulator on the inner periphery; a ground electrode (6) fixed to a tip end of the housing and forming a discharge gap (G) between the center electrode and the ground electrode; and a plug cover (5) welded to the tip end of the housing so as to cover an auxiliary combustion chamber (50) in which the discharge gap is disposed, the ground electrode protruding into the auxiliary combustion chamber from a fixed end (61) fixed to the housing, When welding the plug cover to the housing, a weld (11) between the plug cover and the housing is formed continuously around the entire circumference in the plug circumferential direction, When a ground side region (R) is defined as a region closer to the fixed end than the central axis of the plug in the arrangement direction of the fixed end and the central axis of the plug (C) as viewed from the axial direction of the plug, and as viewed from the axial direction of the plug, between a straight line (L1) connecting the central axis of the plug and one end (611) of the fixed end in the circumferential direction of the plug and a straight line (L2) connecting the central axis of the plug and the other end (612) of the fixed end in the circumferential direction of the plug, Welding is started from outside the ground side region and finished outside the ground side region; a base end of the plug cover faces the front end of the housing in both the plug axial direction and the plug radial direction and has a cover fitting portion (52) formed along the plug circumferential direction, and the front end of the housing faces the cover fitting portion in both the plug axial direction and the plug radial direction and has a housing fitting portion (21) formed along the plug circumferential direction, and axially opposing portions (12) where the cover fitting portion and the housing fitting portion face each other in the plug axial direction are provided at a plurality of locations in the plug radial direction; Before welding the plug cover to the housing, a heat-conducting member (13) having a higher thermal conductivity than the plug cover and the housing is disposed on some of the axially opposing portions among the plurality of axially opposing portions, and the plug cover is pressed against the housing along the plug axial direction to bring the heat-conducting member and the housing, and the heat-conducting member and the plug cover, into close contact with each other; a plug cover welded to the housing, the plug cover being welded to the axially opposing portion where the heat conduction member is not disposed;

5. 5. The method for manufacturing a spark plug for an internal combustion engine according to claim 4, wherein a welding start position and a welding end position are each spaced apart from the ground side region in the circumferential direction of the plug by at least twice the width (W1) of the ground electrode.

6. 6. The method for manufacturing a spark plug for an internal combustion engine according to claim 4, wherein the heat conducting member is mainly composed of copper and is annealed.

Images