Spark plug for internal combustion engine and method for manufacturing the same

Abstract

To provide a spark plug for an internal combustion engine superior in productivity, and a manufacturing method thereof.SOLUTION: A spark plug for an internal combustion engine 1 includes an insulator 3, a center electrode 4, a housing 2, a ground electrode 6, and a plug cover 5. On one and the other of the base end of the plug cover 5 and the tip of the housing 2, there are multiple fitting protrusions 71 and multiple fitting recesses 72 that fit together in the axial direction of the plug. The fitting protrusion 71 and the fitting recess 72 are provided at regular intervals in the circumferential direction of the plug. The number of fitting portions 7 between the fitting protrusion 71 and the fitting recess 72 is a divisor of the number of injection holes 51 formed in the plug cover 5 at equal intervals in the circumferential direction of the plug.SELECTED DRAWING: Figure 1

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 Art

[0002] A spark plug having a sub-combustion chamber is disclosed in, for example, Patent Document 1. In such a spark plug, a plug cover having injection holes is joined to the tip of a housing. And when fixing the plug cover to the housing, it may be necessary to perform positioning in the circumferential direction of the plug between the two. That is, when attaching the plug cover to the housing with members such as a ground electrode attached, it may be desirable to set the positional relationship between each part of the housing (for example, the attachment position of the ground electrode, etc.) and the injection holes to a specific positional relationship. In the spark plug described in Patent Document 1, it is described that positioning between each part of the housing and the plug cover in the circumferential direction of the plug is achieved by the ground electrode provided on the housing engaging with a groove formed in the plug cover.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the spark plug disclosed in Patent Document 1, the positioning means between the housing and the plug cover is formed only at one location in the circumferential direction of the plug. Therefore, when aligning the plug cover with the housing, the angle by which the plug cover is rotated in the circumferential direction of the plug with respect to the housing can be up to about 180°. As a result, the assembly time between the housing and the plug cover tends to be long. Therefore, it can be said that there is room for improvement in the productivity of the spark plug.

[0005] The present invention has been made in view of such problems, and aims to provide a spark plug for an internal combustion engine with excellent productivity and a method for manufacturing the same.

Means for Solving the Problems

[0006] One aspect of the present invention is a spark plug (1) for an internal combustion engine, including a cylindrical insulator (3), a center electrode (4) held on the inner peripheral side of the insulator and protruding from the insulator toward the tip side, a cylindrical housing (2) that holds the insulator on the inner peripheral side, a ground electrode (6) that forms a discharge gap (G) with the center electrode, and a plug cover (5) provided at the tip of the housing so as to cover a sub-combustion chamber (50) where the discharge gap is disposed. The spark plug (1) for an internal combustion engine has: a plurality of fitting convex portions (71) and fitting concave portions (72) that fit together in the plug axial direction are respectively provided on one and the other of the base end portion of the plug cover and the tip end portion of the housing, the fitting convex portions and the fitting concave portions are respectively provided at equal intervals in the plug circumferential direction, the number of fitting portions of the fitting convex portions and the fitting concave portions is a divisor of the number of spray holes (51) formed at equal intervals in the plug circumferential direction in the plug cover, and The fitting convex portion and the fitting concave portion are configured to be able to perform positioning in the plug circumferential direction of the housing and the plug cover by fitting with each other. , and is in a spark plug 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, where the spark plug includes a cylindrical insulator (3), a center electrode (4) held on the inner peripheral side of the insulator and protruding from the insulator toward the tip side, a cylindrical housing (2) that holds the insulator on the inner peripheral side, a ground electrode (6) that forms a discharge gap (G) with the center electrode, and a plug cover (5) provided at the tip of the housing so as to cover a sub-combustion chamber (50) where the discharge gap is disposed. A spark plug for an internal combustion engine, comprising a plug cover (5) provided at a tip end portion of the housing so as to cover a sub combustion chamber (50) in which the discharge gap is disposed. Before joining the tip end portion of the housing and the base end portion of the plug cover. A plurality of fitting convex portions (71) and a plurality of fitting concave portions (72) that can be fitted to each other in the plug axis direction (Z) are provided on one and the other of the base end portion of the plug cover and the tip end portion of the housing, respectively. The fitting convex portions and the fitting concave portions are provided at equal intervals in the circumferential direction of the plug, respectively. The number of the fitting convex portions and the number of the fitting concave portions are divisors of the number of injection holes (51) formed at equal intervals in the circumferential direction of the plug. When joining the tip end portion of the housing and the base end portion of the plug cover, a plurality of the fitting convex portions and a plurality of the fitting concave portions are fitted to each other. to perform positioning in the plug circumferential direction of the housing and the plug cover , It is a method for manufacturing a spark plug for an internal combustion engine.

Advantages of the Invention

[0008] In the spark plug for an internal combustion engine, a plurality of fitting convex portions and a plurality of fitting concave portions that are fitted to each other in the plug axis direction are provided on one and the other of the base end portion of the plug cover and the tip end portion of the housing, respectively. And the fitting convex portions and the fitting concave portions are provided at equal intervals in the circumferential direction of the plug, respectively. Therefore, positioning between the housing and the plug cover can be performed at a plurality of positions in the circumferential direction of the plug. Then, from a state where the tip end of the housing and the base end of the plug cover are opposed to each other at an arbitrary relative position in the circumferential direction of the plug, alignment between the fitting concave portion and the fitting convex portion can be performed by a relative rotation within 90°. Therefore, the assembly time between the housing and the plug cover can be reduced. As a result, the productivity of the spark plug can be improved.

[0009] In addition, the number of fitting portions between the fitting convex portions and the fitting concave portions is a divisor of the number of injection holes formed at equal intervals in the circumferential direction of the plug. Therefore, no matter which combination of the plurality of fitting convex portions and the plurality of fitting concave portions is fitted to form the fitting portions, the relative positions of the plurality of injection holes with respect to each part of the housing are the same. Therefore, the positional relationship between each part of the housing and the injection holes is determined to be a predetermined positional relationship without being affected by various factors during assembly. Therefore, the productivity of the spark plug can be ensured.

[0010] In the method for manufacturing the spark plug for an internal combustion engine described above, the plurality of fitting convex portions and the plurality of fitting concave portions described above are fitted to each other. Thereby, as described above, the productivity of the spark plug can be improved.

[0011] As described above, according to the above aspect, it is possible to provide a spark plug for an internal combustion engine and a method for manufacturing the same, which are excellent in productivity. Note that the reference numerals in parentheses described in the claims and the means for solving the problems indicate the correspondence with the specific means described in the embodiments described later, and do not limit the technical scope of the present invention.

Brief Description of Drawings

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Embodiments for Carrying Out the Invention

[0013] (Embodiment 1) An embodiment of a spark plug for an internal combustion engine will be described with reference to FIGS. 1 to 9. The spark plug 1 for an internal combustion engine of this embodiment has a cylindrical insulator 3, a center electrode 4, a cylindrical housing 2, a ground electrode 6, and a plug cover 5, as shown in FIGS. 1 to 4.

[0014] The center electrode 4 is held on the inner peripheral side of the insulator 3 and protrudes from the insulator 3 toward the tip side. The housing 2 holds the insulator 3 on the inner peripheral side. The ground electrode 6 forms a discharge gap G with the center electrode 4. The plug cover 5 is provided at the tip of the housing 2 so as to cover the sub-combustion chamber 50 in which the discharge gap G is arranged.

[0015] A plurality of fitting convex portions 71 and fitting concave portions 72 that fit with each other in the plug axial direction Z are provided on one and the other of the base end portion of the plug cover 5 and the tip portion of the housing 2, respectively. The fitting convex portions 71 and the fitting concave portions 72 are provided at equal intervals in the plug circumferential direction. The number of fitting portions 7 of the fitting convex portions 71 and the fitting concave portions 72 is a divisor of the number of spray holes 51. Here, the number of spray holes 51 is the number of spray holes 51 formed at equal intervals in the plug circumferential direction in the plug cover 5.

[0016] The spark plug 1 of this embodiment can be used, for example, as an ignition means in an internal combustion engine such as an automobile or cogeneration. One end of the spark plug 1 in the plug axial direction Z is exposed to the main combustion chamber of the internal combustion engine. In the plug axial direction Z, the side exposed to the main combustion chamber is referred to as the tip side, and the opposite side is referred to as the base end side. Also, the direction orthogonal to the central axis of the spark plug 1 (that is, the plug central axis C) is referred to as the plug radial direction. Also, the direction along the circumference centered on the plug central axis C is referred to as the plug circumferential direction.

[0017] In this embodiment, four fitting convex portions 71 are formed at the base end portion of the plug cover 5, and four fitting concave portions 72 are provided at the tip end portion of the housing 2. The fitting convex portions 71 and the fitting concave portions 72 are provided at a 90° pitch in the circumferential direction of the plug, respectively. The plurality of fitting convex portions 71 have the same shape, and the plurality of fitting concave portions 72 have the same shape.

[0018] Any of the plurality of fitting convex portions 71 can be fitted with any of the plurality of fitting concave portions 72. Therefore, in this embodiment, there are four mounting angles in the circumferential direction of the plug of the plug cover 5 with respect to the housing 2.

[0019] Also, in this embodiment, the plug cover 5 has four spray holes 51 at equal intervals in the circumferential direction of the plug. Therefore, the four spray holes 51 are provided at a 90° pitch. The four spray holes 51 have the same size and the same shape as each other.

[0020] As shown in FIG. 2, the number of fitting portions 7 is the same as the number of spray holes 51 formed at equal intervals in the circumferential direction of the plug. That is, in this embodiment, as described above, the number of fitting portions 7 and the number of spray holes 51 are both four. In addition, when other spray holes are formed in addition to the spray holes 51 formed at equal intervals in the circumferential direction of the plug, those spray holes are not counted as the "number of spray holes 51 formed at equal intervals in the circumferential direction of the plug". For example, when a spray hole is formed on the plug central axis on the tip end surface of the plug cover 5, that spray hole is not counted as the "number of spray holes 51 formed at equal intervals in the circumferential direction of the plug".

[0021] The spray holes 51 are formed at positions in the circumferential direction of the plug corresponding to the center of the fitting portion 7 as viewed from the plug axis direction Z. Also, the width of the fitting portion 7 in the circumferential direction of the plug is substantially equal to the interval between adjacent fitting portions 7 in the circumferential direction of the plug.

[0022] The fitting concave portion 72 is formed in a part on the outer peripheral side at the tip end portion of the housing 2. Therefore, the inner peripheral side surface, the two circumferential side surfaces, and the base end surface of the fitting convex portion 71 face the respective surfaces constituting the fitting concave portion 72.

[0023] As shown in FIGS. 2 and 4, the ground electrode 6 is joined to the tip of the housing 2. In this embodiment, the ground electrode 6 protrudes from the fixed end 61 fixed to the housing 2 toward the plug central axis C and is inclined toward the tip side. A part of the ground electrode 6 faces the tip of the central electrode 4 in the plug axis direction Z to form a discharge gap G. Further, the fixed end 61 of the ground electrode 6 is disposed at an intermediate position between two fitting portions 7 adjacent to each other in the plug circumferential direction. In other words, as shown in FIG. 2, when viewed from the plug axis direction Z, the fixed end 61 of the ground electrode 6 is disposed at an intermediate position between two nozzle holes 51 adjacent to each other in the plug circumferential direction.

[0024] Note that the tip of the housing 2 and the base end of the plug cover 5 have an annular shape centered on the plug central axis C in a cross section perpendicular to the plug axis direction Z, as shown in FIGS. 2 and 5.

[0025] Next, the manufacturing method of the spark plug 1 of this embodiment will be described. The state before joining the tip of the housing 2 and the base end of the plug cover 5 is shown in FIGS. 5 to 9. In this state, a plurality of fitting convex portions 71 and fitting concave portions 72 that can be fitted to each other in the plug axis direction are provided on one and the other of the base end of the plug cover 5 and the tip of the housing 2, respectively. In this embodiment, a plurality of fitting convex portions 71 are formed on the base end of the plug cover 5, and a plurality of fitting concave portions 72 are formed on the tip of the housing 2.

[0026] The fitting convex portions 71 and the fitting concave portions 72 are provided at equal intervals in the plug circumferential direction, respectively. The number of the fitting convex portions 71 and the number of the fitting concave portions 72 are divisors of the number of the nozzle holes 51 formed at equal intervals in the plug circumferential direction. In this embodiment, as described above, the number of the fitting convex portions 71 and the number of the fitting concave portions 72 are the same as the number of the nozzle holes 51.

[0027] When joining the tip of the housing 2 and the base end of the plug cover 5, as shown in FIGS. 8, 9, 1 to 4, a plurality of fitting convex portions 71 and a plurality of fitting concave portions 72 are fitted to each other.

[0028] When joining the plug cover 5 to the housing 2, as shown in FIG. 9, the center electrode 4, the insulator 3, and the ground electrode 6 are assembled to the housing 2 in advance. The base end of the plug cover 5 is brought into contact with the tip of the housing 2 in this state and joined. The base end of the plug cover 5 is brought into contact with the tip of the housing 2 and joined.

[0029] When bringing the base end of the plug cover 5 into contact with the tip of the housing 2, for example, as shown in FIGS. 7 to 9, the tip surface of the housing 2 is oriented upward in the vertical direction. Then, the plug cover 5 with the base surface facing vertically downward is opposed to the tip surface of the housing 2. In FIGS. 7 to 9, the tip surface of the housing 2 and the base surface of the plug cover 5 are opposed to each other in a separated state, but the plug cover 5 may be placed on the tip surface of the housing 2. Also, in FIGS. 7 and 8, the ground electrode 6 and the like are omitted.

[0030] However, when arranging the plug cover 5 with respect to the housing 2, if the alignment in the circumferential direction of the plug is not accurately performed, for example, as shown in FIG. 7, the fitting concave portion 72 of the housing 2 and the fitting convex portion 71 of the plug cover 5 are in a misaligned state with respect to each other. The state shown in FIG. 7 is the state where the misalignment is the largest in the circumferential direction of the plug.

[0031] Therefore, for example, from the state as shown in FIG. 7, by rotating the plug cover 5 with respect to the housing 2 in the plug circumferential direction, the state where the fitting concave portion 72 and the fitting convex portion 71 face each other can be achieved as shown in FIG. 8. In this state, all the fitting concave portions 72 and all the fitting convex portions 71 face each other. By setting such a positional relationship, as shown in FIG. 3, the fitting concave portion 72 and the fitting convex portion 71 can be fitted to each other, and the fitting portion 7 can be formed. That is, it is assembled in a state where the plug cover 5 is aligned with respect to the housing 2 in the plug circumferential direction.

[0032] Thereafter, the tip of the housing 2 and the base end of the plug cover 5 are joined by welding or the like. Thereby, the spark plug 1 as shown in FIGS. 1 to 4 can be obtained.

[0033] Next, the operation and effect of this embodiment will be described. In the spark plug 1, a plurality of fitting convex portions 71 and fitting concave portions 72 that fit with each other in the plug axial direction Z are provided at the base end of the plug cover 5 and the tip of the housing 2, respectively. The fitting convex portions 71 and the fitting concave portions 72 are provided at equal intervals in the plug circumferential direction, respectively. Therefore, positioning between the housing 2 and the plug cover 5 can be performed at a plurality of positions in the plug circumferential direction. Then, from the state where the tip of the housing 2 and the base end of the plug cover 5 face each other at an arbitrary relative position in the plug circumferential direction, the fitting concave portion 72 and the fitting convex portion 71 can be aligned by a relative rotation within 90°. Particularly in the case of this embodiment, from the state where the tip of the housing 2 and the base end of the plug cover 5 face each other at an arbitrary relative position in the plug circumferential direction (for example, the state shown in FIG. 7), the state where the fitting concave portion 72 and the fitting convex portion 71 are aligned (the state shown in FIG. 8) can be achieved by a relative rotation within 45°. Therefore, the assembly time between the housing 2 and the plug cover 5 can be reduced. As a result, the productivity of the spark plug 1 can be improved.

[0034] In addition, the number of fitting portions 7 of the fitting convex portions 71 and the fitting concave portions 72 (four in this embodiment) is a divisor of the number of injection holes 51 formed at equal intervals in the circumferential direction of the plug (four in this embodiment). Therefore, no matter which combination of the plurality of fitting convex portions 71 and the plurality of fitting concave portions 72 is fitted to form the fitting portion 7, the relative positions of the plurality of injection holes 51 with respect to each part of the housing 2 (for example, the mounting position of the ground electrode 6, etc.) are the same. Therefore, the positional relationship between each part of the housing 2 and the injection holes 51 is determined to be a predetermined positional relationship without being affected by various factors during assembly. Therefore, the productivity of the spark plug 1 can be ensured.

[0035] Note that by setting the positional relationship between the ground electrode 6 and the injection holes 51 to a predetermined positional relationship, for example, the relationship between the airflow in the sub-combustion chamber 50 and the ground electrode 6 and the discharge gap G can be maintained in an appropriate positional relationship. As a result, good ignitability and suppression of overheating of the ground electrode 6 can be ensured.

[0036] In addition, the positional relationship between the injection holes 51 and the starting position of the mounting screw portion 23 provided on the housing 2 can also be maintained in an appropriate positional relationship. As a result, when the spark plug 1 is attached to the internal combustion engine, the positional relationship between the airflow in the main combustion chamber and the injection holes 51 can be set to an appropriate positional relationship. As a result, good ignitability can be ensured.

[0037] In addition, the number of fitting portions 7 is the same as the number of injection holes 51 formed at equal intervals in the circumferential direction of the plug. Therefore, while maintaining the positional relationship between the ground electrode 6 etc. and the injection holes 51 in a predetermined positional relationship, the number of fitting portions 7 can be increased as much as possible. As a result, the alignment in the circumferential direction of the plug between the housing 2 and the plug cover 5 can be performed in a short time.

[0038] As described above, according to this embodiment, it is possible to provide a spark plug for an internal combustion engine and a method for manufacturing the same, which are excellent in productivity.

[0039] (Embodiment 2) This embodiment is a form in which the widths of the fitting convex portion 71 and the fitting concave portion 72 in the circumferential direction of the plug are reduced as shown in FIGS. 10 to 12. As shown in FIG. 12, in a state where the plug cover 5 is joined to the housing 2, the width of the fitting portion 7 in the circumferential direction of the plug is small. In Embodiment 1, the width of the fitting portion 7 in the circumferential direction of the plug is substantially equal to the width between the fitting portions 7. In contrast, in this embodiment, the width of the fitting portion 7 in the circumferential direction of the plug is smaller than the width between the fitting portions 7.

[0040] Other aspects are the same as those of Embodiment 1. Among the reference numerals used in Embodiments 2 and later, those that are the same as the reference numerals used in the previously described embodiments represent the same components and the like as those in the previously described embodiments unless otherwise specified. This embodiment also has the same operational effects as those of Embodiment 1.

[0041] (Embodiment 3) This embodiment is a form in which the shape of the fitting portion 7 as viewed from the radial direction of the plug is substantially trapezoidal as shown in FIG. 13. The shapes of the fitting convex portion 71 and the fitting concave portion 72 as viewed from the radial direction of the plug are substantially trapezoidal. In this embodiment, the contour of the fitting convex portion 71 is inclined such that the width in the circumferential direction of the plug gradually decreases toward the protruding side (i.e., the base end side). The contour of the fitting concave portion 72 is inclined such that the width in the circumferential direction of the plug gradually decreases toward the bottom side (i.e., the base end side). Other aspects are the same as those of Embodiment 1.

[0042] In this embodiment, the fitting between the fitting concave portion 72 and the fitting convex portion 71 can be easily performed. Therefore, the productivity of the spark plug can be further improved. Other aspects have the same operational effects as those of Embodiment 1.

[0043] (Embodiment 4) In this embodiment, as shown in FIGS. 14 to 18, the fitting convex portion 71 and the fitting concave portion 72 have a triangular shape when viewed from the radial direction of the plug. The circumferential length of the fitting projection 71 and the fitting recess 72 in the plug circumferential direction is 1 / N of the entire circumference in the plug circumferential direction at the joint between the tip of the housing 2 and the base end of the plug cover 5. N is the number of fitting portions 7.

[0044] In this embodiment, N is 4. Therefore, the circumferential length a of each fitting projection 71 and each fitting recess 72 in the plug circumferential direction is the length corresponding to a central angle of 90° in the plug circumferential direction. Note that the phrase "the shape as viewed from the plug radial direction is triangular" means that, as shown in FIGS. 16 to 18, the developed shape that appears when a plurality of fitting projections 71 and a plurality of fitting recesses 72 formed over the entire circumference in the plug circumferential direction are developed in a planar shape is triangular. Also, in this developed shape, the top 711 of the triangular peak and the bottom 721 of the valley may be chamfered. In this case, the developed shape is not a geometrically exact triangle, but such a substantially triangular case is also included in the above-mentioned "triangular shape".

[0045] In this embodiment, when joining the base end of the plug cover 5 to the tip of the housing 2, as shown in FIGS. 16 to 18, alignment between the two can be performed. First, the base end of the plug cover 5 is opposed to the tip of the housing 2. At this time, unless alignment or the like is performed in particular, usually, as shown in FIG. 16 for example, the fitting recess 72 of the housing 2 and the fitting projection 71 of the plug cover 5 are in a positional relationship shifted in the plug circumferential direction (the left-right direction in the figure).

[0046] With this positional relationship in the plug circumferential direction maintained, the plug cover 5 is brought closer to the housing 2 in the plug axial direction Z. Then, as shown in FIG. 17, a part of the base end of the plug cover 5 abuts on a part of the tip of the housing 2. In other words, a part of the slope of the fitting projection 71 abuts on a part of the slope of the fitting recess 72. These abutting portions are formed at a plurality of locations in the plug circumferential direction.

[0047] From this state (i.e., the state shown in FIG. 17), when a force in the direction of approaching the plug cover 5 in the plug axis direction Z is applied to the housing 2 (for example, a load that is not particularly large, such as the self-weight of the plug cover 5), the abutted inclined surfaces slide against each other. At this time, the plug cover 5 moves in the plug circumferential direction (left direction in FIG. 7) with respect to the housing 2 in a direction approaching the top 711 of the fitting convex portion 71 at the bottom 721 of the fitting concave portion 72. That is, the plug cover 5 rotates in the plug circumferential direction (left direction in the figure) with respect to the housing 2. Then, as shown in FIG. 18, the plurality of fitting concave portions 72 and the plurality of fitting convex portions 71 are fitted to each other. Other aspects are the same as those of the first embodiment.

[0048] In this embodiment, as described above, after the base end portion of the plug cover 5 is abutted against the tip end portion of the housing 2, by simply applying a load in the direction in which both approach each other in the plug axis direction Z, the fitting state between the fitting convex portion 71 and the fitting concave portion 72 can be accurately obtained. That is, for example, in a state where the plug cover 5 is placed on the tip end portion of the housing 2 facing upward in the vertical direction, by applying appropriate vibration to these, the self-weight of the plug cover 5 can accurately align the positions of the fitting concave portion 72 and the fitting convex portion 71 in the plug circumferential direction. Other than that, it has the same effects as those of the first embodiment.

[0049] (Embodiment 5) In this embodiment, as shown in FIGS. 19 to 21, the relationship between the depth h of the fitting concave portion 72 and the thickness t of the fitting convex portion 71 is shown. The depth h is the depth of the fitting concave portion 72 in the plug axis direction Z. The thickness t is the thickness of the fitting convex portion 71 in the plug diameter direction. In this embodiment, the depth h and the thickness t satisfy h ≤ t. More preferably, the depth h and the thickness t satisfy h ≤ t / 2. Other aspects are the same as those of the first embodiment.

[0050] In this embodiment, the joining of the housing 2 and the plug cover 5 can be performed more easily. That is, it is conceivable to join the two by laser welding in a state where the tip end portion of the housing 2 and the base end portion of the plug cover 5 are fitted together. At this time, if the depth h is too large, for example, it is necessary to move the irradiation position of the laser light in the circumferential direction of the plug while moving it up and down in the plug axis direction Z with respect to the assembly of the housing 2 and the plug cover 5, or to make it go around a plurality of times.

[0051] On the other hand, if the depth h is made small, the welding of the joint portion can be achieved by making the irradiation position of the laser beam L with respect to the assembly go around once in the circumferential direction of the plug without moving it in the plug axis direction Z (see FIG. 21). The melted portion 101 shown in FIG. 21 is a melted portion obtained when the irradiation position of the laser beam is made to go around once in the circumferential direction of the plug with respect to the assembly.

[0052] Here, generally, the width w of the melted portion 101 by laser welding is substantially equal to the depth d of the melted portion 101 (see FIG. 20). And the depth d of the melted portion 101 should be equal to or more than the thickness t of the fitting convex portion 71 from the viewpoint of the joining strength. Therefore, by making the depth h of the fitting concave portion 72 about the thickness t of the fitting convex portion 71 or smaller than that, the joining surface between the fitting concave portion 72 and the fitting convex portion 71 can be welded over the entire circumference by one-time laser welding (see FIG. 21).

[0053] In consideration of the irradiation position accuracy etc. of the laser beam L, it is more preferable from the viewpoint of productivity to make the depth h equal to or less than half of the thickness t of the fitting convex portion 71 (that is, h ≤ t / 2). In addition, it has the same operational effects as those of the first embodiment.

[0054] (Embodiment 6) In this embodiment, as shown in FIGS. 22 and 23, the number of fitting portions 7 is less than the number of spray holes 51. In Embodiments 1 to 5, a form was shown in which the number of fitting portions 7 was the same as the number of injection holes 51 formed at equal intervals in the circumferential direction of the plug. In contrast, in the spark plug 1 of the present embodiment, the number of fitting portions 7 is less than the number of injection holes 51. In the form shown in FIGS. 22 and 23, the number of fitting portions 7 is half the number of injection holes 51.

[0055] Specifically, in the spark plug 1 shown in FIG. 22, the number of injection holes 51 is eight, and the number of fitting portions 7 is four. The eight injection holes 51 are formed at equal intervals in the circumferential direction of the plug. That is, the arrangement pitch between adjacent injection holes 51 in the circumferential direction of the plug is 45° in central angle. The number and arrangement of the fitting portions 7 are the same as those in Embodiment 1 (see FIG. 2).

[0056] In the spark plug 1 shown in FIG. 23, the number of injection holes 51 is four, and the number of fitting portions 7 is two. The two fitting portions 7 are arranged on opposite sides with the plug central axis interposed therebetween. That is, the arrangement pitch between the two fitting portions 7 is 180° in central angle. The number and arrangement of the injection holes 51 are the same as those in Embodiment 1 (see FIG. 2).

[0057] Thus, even when the number of fitting portions 7 is less than the number of injection holes 51, if the number of fitting portions 7 is a divisor of the number of injection holes 51 formed at equal intervals in the circumferential direction of the plug, the same operational effects as in Embodiment 1 can be obtained. Therefore, the combination of the number of fitting portions 7 and the number of injection holes 51 may be other than the above, as long as the number of fitting portions 7 is plural and is a divisor of the number of injection holes 51 formed at equal intervals in the circumferential direction of the plug.

[0058] In addition, in the above-described embodiment, the form in which the fitting recess 72 is provided in the housing 2 and the fitting projection 71 is provided in the plug cover 5 is shown. However, it is also possible to adopt a mode in which the fitting projection is provided in the housing and the fitting recess is provided in the plug cover. Note that the fitting projection and the fitting recess are convenient expressions for representing the portions where both are fitted to each other. That is, for example, also in each of the above-described embodiments, a portion between the fitting projections 71 adjacent to each other in the circumferential direction of the plug can be defined as the fitting recess, and a portion between the fitting recesses 72 adjacent to each other in the circumferential direction of the plug can be defined as the fitting recess.

[0059] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments without departing from the gist thereof.

Explanation of reference numerals

[0060] 1... Spark plug for internal combustion engine, 2... Housing, 3... Insulator, 4... Central electrode, 5... Plug cover, 50... Sub-combustion chamber, 51... Injection hole, 6... Ground electrode, 7... Fitting portion, 71... Fitting projection, 72... Fitting recess, G... Discharge gap, Z... Plug axial direction

Claims

1. A cylindrical insulator (3), A center electrode (4) held on the inner peripheral side of the insulator and protruding from the insulator toward the tip side, A cylindrical housing (2) that holds the insulator on the inner peripheral side, A ground electrode (6) that forms a discharge gap (G) with the center electrode, A spark plug (1) for an internal combustion engine, comprising a plug cover (5) provided at the tip of the housing so as to cover a sub-combustion chamber (50) where the discharge gap is disposed, A plurality of fitting convex portions (71) and fitting concave portions (72) that fit together in the plug axial direction are provided on one and the other of the base end portion of the plug cover and the tip end portion of the housing, respectively, The fitting convex portions and the fitting concave portions are provided at equal intervals in the circumferential direction of the plug, The number of fitting portions is a divisor of the number of injection holes (51) formed at equal intervals in the circumferential direction of the plug cover, The fitting convex portion and the fitting concave portion are configured to be able to position the housing and the plug cover in the circumferential direction of the plug by fitting together with each other. A spark plug for an internal combustion engine.

2. The spark plug for an internal combustion engine according to claim 1, wherein the number of the fitting portions is the same as the number of the injection holes formed at equal intervals in the circumferential direction of the plug.

3. The spark plug for an internal combustion engine according to claim 1 or 2, wherein the fitting convex portion and the fitting concave portion have a triangular shape when viewed from the radial direction of the plug.

4. The spark plug for an internal combustion engine according to claim 3, wherein the circumferential length of the fitting convex portion and the fitting concave portion in the circumferential direction of the plug is 1 / N of the entire circumference in the circumferential direction of the joint portion between the tip end portion of the housing and the base end portion of the plug cover, and N is the number of the fitting portions.

5. When the depth of the fitting recess in the plug axial direction is h and the thickness of the fitting projection in the plug radial direction is t, the spark plug for an internal combustion engine according to any one of claims 1 to 4, which satisfies h≤t.

6. A method for manufacturing a spark plug (1) for an internal combustion engine, The spark plug includes a cylindrical insulator (3), a center electrode (4) held on the inner peripheral side of the insulator and protruding from the insulator toward the tip side, a cylindrical housing (2) that holds the insulator on the inner peripheral side, a ground electrode (6) that forms a discharge gap (G) with the center electrode, and a plug cover (5) provided at the tip of the housing so as to cover a sub-combustion chamber (50) where the discharge gap is disposed. In a state before joining the tip of the housing and the base end of the plug cover, a plurality of fitting projections (71) and fitting recesses (72) that can be fitted to each other in the plug axial direction (Z) are provided on one and the other of the base end of the plug cover and the tip of the housing, respectively. The fitting projections and the fitting recesses are provided at equal intervals in the plug circumferential direction, respectively. The number of the fitting projections and the number of the fitting recesses are divisors of the number of the injection holes (51) formed at equal intervals in the plug circumferential direction. When joining the tip of the housing and the base end of the plug cover, the housing and the plug cover are positioned in the plug circumferential direction by fitting the plurality of fitting projections and the plurality of fitting recesses to each other. A method for manufacturing a spark plug for an internal combustion engine.

7. The method for manufacturing a spark plug for an internal combustion engine according to claim 6, wherein the number of each of the fitting projections and the fitting recesses is the same as the number of the injection holes formed at equal intervals in the plug circumferential direction.

8. The method for manufacturing a spark plug for an internal combustion engine according to claim 6 or 7, wherein the fitting convex portion and the fitting concave portion have a triangular shape when viewed from the plug radial direction.

9. The method for manufacturing a spark plug for an internal combustion engine according to claim 8, wherein the length of the fitting convex portion and the fitting concave portion in the plug circumferential direction is 1 / N of the entire circumference in the plug circumferential direction of the joint portion between the tip end portion of the housing and the base end portion of the plug cover, and N is the number of each of the fitting convex portion and the fitting concave portion.

10. The method for manufacturing a spark plug for an internal combustion engine according to any one of claims 6 to 9, when the depth of the fitting concave portion in the plug axial direction is h and the thickness of the fitting convex portion in the plug radial direction is t, h ≤ t is satisfied.

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