Spark plug for internal combustion engine and manufacturing method thereof

Abstract

To provide a spark plug capable of improving productivity, and a manufacturing method of the same.SOLUTION: In a spark plug 1, a plug cover 5 is provided with a ground electrode 6. A discharge gap G is formed by a center discharge surface 41 of a center electrode 4 and a ground discharge surface 61 of the ground electrode 6 opposite to each other in a plug axial direction Z. A tip end part of a housing 2 includes a housing fixing part 21 and an opposite surface 22. The housing fixing part 21 is opposite to a cover base end part 51 of the plug cover 5 in a plug radial direction. The opposite surface 22 is opposite to a base end surface 52 of the plug cover 5 in the plug axis direction Z on a side closer to the base end than the housing fixing part 21. The housing fixing part 21 and the cover base end part 51 are bonded to each other. Further, the base end surface 52 of the plug cover 5 is arranged at a position separated from the opposite surface 22 in the plug axis direction Z.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 technology]

[0002] For example, there is known a spark plug for an internal combustion engine that is provided with an auxiliary combustion chamber at its tip, as disclosed in Patent Document 1. In the spark plug disclosed in Patent Document 1, the ground electrode is fixed to the tip of the housing, and after the discharge gap is adjusted, the spark plug can be assembled so that the discharge gap is located inside the plug cover that covers the auxiliary combustion chamber. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-009747 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the spark plug described in Patent Document 1, when the ground electrode is deformed to form the discharge gap, so-called spring back may occur in the ground electrode. Therefore, it may be difficult to adjust the discharge gap to a desired length. This poses a problem in terms of productivity of the spark plug.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to provide a spark plug and a manufacturing method thereof that can improve productivity. [Means for solving the problem]

[0006] The first aspect of the present invention is a cylindrical insulator (3), a center electrode (4) held on the inner circumferential side of the insulator and protruding from the insulator toward the tip side; a cylindrical housing (2) that holds the insulator on its inner periphery; a ground electrode (6) forming a discharge gap (G) between itself and the center electrode; a plug cover (5) fixed to a tip end portion of the housing so as to cover the auxiliary combustion chamber (50) in which the ground electrode is provided and in which the discharge gap is disposed, The ground electrode protrudes from an inner wall surface (53) of the plug cover into the auxiliary combustion chamber, and is provided along a plug radial direction when viewed from a plug axial direction (Z). The discharge gap is formed by a central discharge surface (41) of the central electrode and a ground discharge surface (61) of the ground electrode facing each other in the plug axial direction, a front end portion of the housing has a housing fixing portion (21) facing a cover base end portion (51) of the plug cover in the plug radial direction, and an opposing surface (22) facing a base end surface (52) of the plug cover in the plug axial direction on the base end side of the housing fixing portion, The housing fixing portion and the cover base end portion are joined to each other, The base end surface of the plug cover is disposed at a position spaced apart from the opposing surface in the plug axial direction. Cage , the cover base end portion has a plurality of protruding portions (54) formed by a portion of the base end surface protruding toward the base end side, the opposing surface has a stepped portion (23) formed in a stepped shape along the plug circumferential direction, and the protruding portions abut against portions of the stepped portions in the plug axial direction. In a spark plug (1) for an internal combustion engine.

[0007] A second aspect of the present invention is a cylindrical insulator (3), a center electrode (4) held on the inner circumferential side of the insulator and protruding from the insulator toward the tip side; a cylindrical housing (2) that holds the insulator on its inner periphery; a plug cover (5) that forms a discharge gap (G) between itself and the central electrode and is fixed to the tip end of the housing so as to cover a sub-combustion chamber (50) in which the discharge gap is disposed, the discharge gap is formed by a central discharge surface (41) of the central electrode and a ground discharge surface (611) which is a part of an inner wall surface (53) of the plug cover facing each other in the plug axial direction (Z); a front end portion of the housing has a housing fixing portion (21) facing a cover base end portion (51) of the plug cover in a plug radial direction, and an opposing surface (22) facing a base end surface (52) of the plug cover in a plug axial direction on the base end side of the housing fixing portion, The housing fixing portion and the cover base end portion are joined to each other, The base end surface of the plug cover is located at a position away from the opposing surface in the plug axial direction in a spark plug (1) for an internal combustion engine.

[0008] A third aspect of the present invention is a method for manufacturing a spark plug (1) for an internal combustion engine, comprising the steps of: The spark plug includes a cylindrical insulator (3), a center electrode (4) held on the inner periphery of the insulator and protruding from the insulator toward a tip side, a cylindrical housing (2) holding the insulator on its inner periphery, a ground electrode (6) forming a discharge gap (G) between the center electrode, and a plug cover (5) in which the ground electrode is provided and which is fixed to a tip portion of the housing so as to cover an auxiliary combustion chamber (50) in which the discharge gap is located, The ground electrode protrudes from an inner wall surface (53) of the plug cover into the auxiliary combustion chamber, and is provided along a plug radial direction when viewed from a plug axial direction (Z). The discharge gap is formed by a central discharge surface (41) of the central electrode and a ground discharge surface (61) of the ground electrode facing each other in the plug axial direction, a front end portion of the housing has a housing fixing portion (21) facing a cover base end portion (51) of the plug cover in the plug radial direction, In manufacturing the above spark plugs, a preparation step of preparing the housing having the insulator and the center electrode assembled thereto, and the plug cover having the ground electrode provided thereon; a gap abutment step of, after the preparation step, placing the plug cover relative to the housing such that the central discharge surface and the ground discharge surface abut against each other in the plug axial direction while overlapping the housing fixing portion and the cover base end portion in the plug radial direction; a separating step of separating the ground discharge surface from the center discharge surface by moving the plug cover relative to the housing in an axial direction of the plug after the gap abutting step; After the separating step, a joining step is performed in which the housing fixing portion and the cover base end portion are joined to each other. stomach , a front end portion of the housing has an opposing surface (22) facing a base end surface (52) of the plug cover in the plug axial direction on the base end side of the housing fixing portion, the cover base end portion has a plurality of convex portions (54) formed by a part of the base end surface protruding toward the base end side, and the opposing surface has a stepped portion (23) formed in a stepped shape along the plug circumferential direction, After the separating step and before the bonding step, a cover abutting step of rotating the plug cover in a plug circumferential direction relative to the housing to bring the protrusion into abutment with the stepped portion in the plug circumferential direction, and then moving the plug cover toward a base end side along a plug axial direction relative to the housing to bring the protrusion into abutment with the stepped portion in the plug axial direction; The present invention relates to a method for manufacturing a spark plug for an internal combustion engine.

[0009] A fourth aspect of the present invention is a method for manufacturing a spark plug (1) for an internal combustion engine, comprising the steps of: The spark plug includes a cylindrical insulator (3), a center electrode (4) held on the inner periphery of the insulator and protruding from the insulator toward a tip side, a cylindrical housing (2) holding the insulator on the inner periphery, and a plug cover (5) fixed to a tip portion of the housing so as to form a discharge gap (G) between the central electrode and the plug cover and to cover an auxiliary combustion chamber (50) in which the discharge gap is located, the discharge gap is formed by a central discharge surface (41) of the central electrode and a ground discharge surface (611) which is a part of an inner wall surface (53) of the plug cover facing each other in the plug axial direction (Z); a front end portion of the housing has a housing fixing portion (21) facing a cover base end portion (51) of the plug cover in a plug radial direction; In manufacturing the above spark plugs, a preparation step of preparing the housing having the insulator and the center electrode assembled thereto, and the plug cover; a gap abutment step of, after the preparation step, placing the plug cover relative to the housing such that the central discharge surface and the ground discharge surface abut against each other in the plug axial direction while overlapping the housing fixing portion and the cover base end portion in the plug radial direction; a separating step of separating the ground discharge surface from the center discharge surface by moving the plug cover relative to the housing in an axial direction of the plug after the gap abutting step; In the method for manufacturing a spark plug for an internal combustion engine, a joining step of joining the housing fixing portion and the cover base end portion to each other is carried out after the separating step. Effect of the Invention

[0010] In the spark plug of the first aspect, the discharge gap is formed by opposing the central discharge surface and the ground discharge surface of the ground electrode provided on the plug cover in the plug axial direction. In addition, the base end surface of the plug cover is located at a position spaced apart from the opposing surface in the plug axial direction. Therefore, the discharge gap can be adjusted without deforming the ground electrode. Therefore, a discharge gap having a desired length can be easily formed. As a result, the productivity of the spark plug can be improved.

[0011] In the spark plug of the second aspect, the discharge gap is formed by the central discharge surface and the ground discharge surface of the plug cover facing each other in the plug axial direction. In addition, the base end surface of the plug cover is located at a position spaced apart from the facing surface in the plug axial direction. Therefore, a discharge gap having a desired length can be easily formed. As a result, the productivity of the spark plug can be improved.

[0012] The method for manufacturing a spark plug according to the third aspect includes a preparation step, a gap contact step, a separation step, and a joining step. Therefore, the discharge gap can be adjusted without deforming the ground electrode. As a result, the discharge gap can be easily adjusted, and the spark plug can be efficiently manufactured.

[0013] The method for producing a spark plug according to the fourth aspect includes a preparation step, a gap contact step, a separation step, and a joining step. Therefore, the discharge gap can be easily adjusted. As a result, the spark plug can be efficiently produced.

[0014] As described above, according to the above aspect, it is possible to provide a spark plug and a manufacturing method thereof that can improve productivity. In addition, the symbols in parentheses described in the claims and the means for solving the problems indicate a correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present invention. [Brief description of the drawings]

[0015] [Figure 1] 2 is a cross-sectional view taken along line II in FIG. 2, showing a portion near the tip end of the spark plug according to the first embodiment, taken along an axial direction of the plug; [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Diagram 3] 3 is a cross-sectional view showing the length of a discharge gap and the like in the first embodiment. FIG. [Figure 4] 6 is a cross-sectional view showing how the plug cover is moved toward the base end side with respect to the housing in the gap abutment step in the first embodiment. FIG. [Diagram 5] 4 is a cross-sectional view showing a state in which the central discharge surface and the ground discharge surface are in contact with each other in the first embodiment. FIG. [Figure 6] 1 is a cross-sectional view of an internal combustion engine in which a spark plug is installed according to a first embodiment. [Figure 7] FIG. 11 is a cross-sectional view taken along the axial direction of a spark plug in a vicinity of a tip portion of the spark plug according to a second embodiment. [Figure 8] FIG. 11 is a cross-sectional view showing a state in which the central discharge surface and the ground discharge surface are in contact with each other in the second embodiment. [Figure 9] FIG. 11 is a cross-sectional view taken along the axial direction of a spark plug in a vicinity of a tip portion of a spark plug according to a third embodiment. [Figure 10]FIG. 11 is a cross-sectional view showing a state in which the central discharge surface and the ground discharge surface are in contact with each other in the third embodiment. [Figure 11] FIG. 11 is a view of the vicinity of the tip portion of a spark plug according to a fourth embodiment, as viewed from a direction perpendicular to the plug axial direction. [Figure 12] 12 is a view of the plug cover according to the fourth embodiment, seen from the base end side, taken along the line XII in FIG. 15. [Figure 13] 13 is a view of the housing according to the fourth embodiment as seen from the tip end side, taken along the arrow XIII in FIG. 15. [Figure 14] FIG. 13 is an enlarged view of the vicinity of a staircase portion in the fourth embodiment. [Figure 15] 13 is a view showing a state in which the plug cover is moved toward the base end side with respect to the housing in the gap abutment process in the fourth embodiment. FIG. [Figure 16] FIG. 13 is a diagram showing a state in which the central discharge surface and the ground discharge surface are in contact with each other in the fourth embodiment. [Figure 17] FIG. 13 is a view showing a state in which the plug cover has been moved toward the tip side relative to the housing in the separating process in the fourth embodiment. [Figure 18] 13 is a view showing a state in which the protrusion is brought into contact with the stepped portion in the plug circumferential direction in a cover abutting step in a fourth embodiment. FIG. [Figure 19] FIG. 13 is a cross-sectional view taken along the axial direction of a spark plug in a vicinity of a tip portion of the spark plug according to a fifth embodiment. [Figure 20] FIG. 13 is a cross-sectional view taken along the axial direction of a spark plug in a vicinity of a tip portion of the spark plug according to a sixth embodiment. [Figure 21] FIG. 13 is a cross-sectional view of the tip portion of a spark plug according to a seventh embodiment, taken perpendicular to the axial direction of the plug. [Figure 22] FIG. 13 is a cross-sectional view illustrating the direction of a swirl flow formed in an auxiliary combustion chamber in the seventh embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] (Embodiment 1) An embodiment of a spark plug for an internal combustion engine and a manufacturing method thereof will be described with reference to Figs. In this embodiment, a spark plug 1 for an internal combustion engine 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 and 2. The center electrode 4 is held on the inner periphery of the insulator 3 and protrudes from the insulator 3 toward the tip side. The housing 2 holds the insulator 3 on the inner periphery side. The ground electrode 6 forms a discharge gap G between itself and the center electrode 4. The plug cover 5 is provided with the ground electrode 6. The plug cover 5 is fixed to the tip portion of the housing 2 so as to cover the auxiliary combustion chamber 50 in which the discharge gap G is arranged.

[0017] The ground electrode 6 protrudes from an inner wall surface 53 of the plug cover 5 into the auxiliary combustion chamber 50. The ground electrode 6 is provided so as to extend along the plug radial direction when viewed from the plug axial direction Z, as shown in Fig. 2. The discharge gap G is formed by the central discharge surface 41 of the center electrode 4 and the ground discharge surface 61 of the ground electrode 6 facing each other in the plug axial direction Z, as shown in Fig. 1.

[0018] The tip end of the housing 2 has a housing fixing portion 21 and an opposing surface 22. The housing fixing portion 21 faces a cover base end portion 51 of the plug cover 5 in the plug radial direction. The opposing surface 22 faces a base end surface 52 of the plug cover 5 in the plug axial direction Z on the base end side of the housing fixing portion 21. The housing fixing portion 21 and the cover base end portion 51 are joined to each other. The base end surface 52 of the plug cover 5 is located at a position away from the opposing surface 22 in the plug axial direction Z.

[0019] The spark plug 1 of this embodiment can be used, for example, as an ignition means in an internal combustion engine of an automobile, etc. The spark plug 1 is attached to an internal combustion engine 10 by screwing the threaded portion 24 of the housing 2 into the female threaded portion of a plug hole 711 of a cylinder head 71, as shown in FIG.

[0020] The internal combustion engine 10 includes 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, and is provided with an intake valve 72 and an exhaust valve 73, respectively.

[0021] 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 centered on the plug central axis C. In this embodiment, the plug central axis C is also the central axis of the center electrode 4.

[0022] When the spark plug 1 is attached to the internal combustion engine 10, the plug cover 5 faces the main combustion chamber 101 and separates the auxiliary combustion chamber 50 from the main combustion chamber 101.

[0023] Further, the plug cover 5 is formed with a nozzle hole 55 that communicates the auxiliary combustion chamber 50 with the outside. In this embodiment, as shown in FIG. 2, the plug cover 5 is formed with four nozzle holes 55. When viewed from the Z direction, the nozzle hole axis 55L is formed along the plug radial direction. Further, the nozzle hole 55 opens at an angle with respect to the Z direction so as to move outward in the plug radial direction toward the tip side. When the spark plug 1 is attached to the internal combustion engine 10, the nozzle hole 55 communicates the auxiliary combustion chamber 50 with the main combustion chamber 101.

[0024] In addition, the ground electrode 6 is joined to the plug cover 5 by welding or the like. The ground electrode 6 has a substantially rectangular prism shape. The ground electrode 6 has four flat side surfaces, one of which serves as a base end side surface 62. The base end side surface 62 of the ground electrode 6 faces the central discharge surface 41 of the center electrode 4 in the Z direction. In other words, a part of the base end side surface 62 serves as the ground discharge surface 61.

[0025] The ground discharge surface 61 and the central discharge surface 41 are each flat and formed to be substantially perpendicular to the Z direction. As shown in Fig. 1, the central discharge surface 41 is located on the tip side of the tip of the housing 2. In other words, the discharge gap G is formed on the tip side of the tip of the housing 2.

[0026] The tip end of the housing 2 is formed in a stepped shape and has a housing fixing portion 21 and an opposing surface 22. A cover base end portion 51 is joined to the outer periphery of the housing fixing portion 21.

[0027] In addition, the base end surface 52 of the plug cover 5 is located on the tip side of the opposing surface 22. The opposing surface 22 and the base end surface 52 face each other in the Z direction without abutting each other. In other words, a gap g1 is formed between the opposing surface 22 and the base end surface 52. As shown in Fig. 3, a distance D1 from the opposing surface 22 to the base end surface 52 of the plug cover 5 in the plug axial direction Z is equal to or greater than a length D2 of the discharge gap G in the plug axial direction Z.

[0028] Further, a distance D3 from the opposing surface 22 to the central discharge surface 41 in the Z direction is equal to or greater than a distance D4 from the base end surface 52 of the plug cover 5 to the ground discharge surface 61 in the Z direction.

[0029] Next, a method for manufacturing the spark plug 1 of this embodiment will be described with reference to FIGS. In manufacturing the spark plug 1, a preparation step, a gap contact step, a separation step, and a joining step are performed. In the preparation step, the housing 2 to which the insulator 3 and the center electrode 4 are assembled, and the plug cover 5 to which the ground electrode 6 is provided are each prepared. In the gap contact step, after the preparation step, the plug cover 5 is placed on the housing 2 such that the central discharge surface 41 and the ground discharge surface 61 are abutted against each other in the plug axial direction Z while the housing fixing portion 21 and the cover base end portion 51 are overlapped in the plug radial direction, as shown in FIG. 5. In the separation step, after the gap contact step, the plug cover 5 is moved in the plug axial direction Z relative to the housing 2 to separate the ground discharge surface 61 from the central discharge surface 41. In the joining step, after the separation step, the housing fixing portion 21 and the cover base end portion 51 are joined to each other. The steps will be described in detail below.

[0030] In this embodiment, the outer circumferential surface of the housing fixing portion 21 and the inner circumferential surface of the cover base end 51 are each formed to extend along the Z direction. The gap abutment step to the joining step are performed in a state in which the plug cover 5 is fitted to the housing 2. That is, each step is performed in a state in which the outer circumferential surface of the housing fixing portion 21 and the inner circumferential surface of the cover base end 51 are in contact with each other in the plug radial direction. However, a slight clearance may be provided between the outer circumferential surface of the housing fixing portion 21 and the inner circumferential surface of the cover base end 51 to enable smooth sliding between them.

[0031] First, in a preparation step, the ground electrode 6, which is a separate member from the plug cover 5, is joined to the plug cover 5, thereby producing the plug cover 5 provided with the ground electrode 6.

[0032] Next, in the gap abutment step, the plug cover 5 is fitted to the housing 2 to which the center electrode 4 and the like are assembled. Then, as shown by the arrow M in Fig. 4, the plug cover 5 is slid toward the base end side relative to the housing 2 using a robot arm, so that the central discharge surface 41 and the ground discharge surface 61 are brought into contact with each other, as shown in Fig. 5. That is, in the gap abutment step, a state is created in which no discharge gap G is formed between the central discharge surface 41 and the ground discharge surface 61. In addition, with the ground discharge surface 61 in contact with the central discharge surface 41, a gap g2 is formed between the base end surface 52 of the plug cover 5 and the opposing surface 22.

[0033] Next, in the separating step, the plug cover 5 is slid toward the tip end in the Z direction relative to the housing 2 using a robot arm, as shown by arrow M in FIG. 5 , so that the ground discharge surface 61 moves away from the central discharge surface 41. At this time, the plug cover 5 is slid in the Z direction relative to the housing 2 by the length of the discharge gap G. This makes it possible to set the length of the discharge gap G to a desired length. In other words, the amount of movement of the plug cover 5 relative to the housing 2 in the separating step corresponds to the length of the discharge gap G.

[0034] Next, in the joining process, the housing fixing portion 21 and the cover base end portion 51, which are in contact with each other in the plug radial direction, are joined to each other by welding or the like. Also, in the joining process, the cover base end portion 51 is joined to the outer periphery of the housing fixing portion 21. In this manner, the spark plug 1 of this embodiment can be manufactured as shown in Figs. 1 and 2.

[0035] Next, the effects of this embodiment will be described. In the spark plug 1 of this embodiment, the discharge gap G is formed by the central discharge surface 41 and the ground discharge surface 61 of the ground electrode 6 provided on the plug cover 5 facing each other in the plug axial direction Z. In addition, the base end surface 52 of the plug cover 5 is disposed at a position separated from the facing surface 22 in the plug axial direction Z. This makes it possible to adjust the discharge gap G without deforming the ground electrode 6. This makes it possible to easily form the discharge gap G having a desired length. As a result, the productivity of the spark plug 1 can be improved.

[0036] That is, the spark plug 1 of this embodiment can be manufactured by performing a preparation step, a gap contact step, a separation step, and a joining step. Therefore, the discharge gap G can be adjusted without deforming the ground electrode 6. Therefore, the discharge gap G of a desired length can be formed without readjusting the discharge gap G. As a result, the productivity of the spark plug 1 can be improved. In addition, the defective rate of the spark plug 1 can be reduced.

[0037] Moreover, the distance D1 is equal to or greater than the length D2 (see FIG. 3). Therefore, when manufacturing the spark plug 1, the ground discharge surface 61 can be reliably brought into contact with the central discharge surface 41 in the gap contacting step. Therefore, the discharge gap G having a desired length can be reliably and easily formed. As a result, the productivity of the spark plug 1 can be reliably improved.

[0038] In addition, the cover base end 51 is joined to the outer periphery of the housing fixing part 21. Therefore, the width of the plug cover 5 in the plug radial direction can be increased. Therefore, the volume of the inner space in the plug cover 5 can be increased. Therefore, the volume of the auxiliary combustion chamber 50 can be increased. Therefore, the flame jet ejected from the auxiliary combustion chamber 50 to the main combustion chamber through the injection hole 55 can be strengthened. As a result, ignition performance can be improved.

[0039] The method for manufacturing the spark plug 1 of this embodiment includes a preparation step, a gap contact step, a separation step, and a joining step. Therefore, the discharge gap G can be adjusted without deforming the ground electrode 6. As a result, the discharge gap G can be easily adjusted, and the spark plug 1 can be efficiently manufactured.

[0040] In this embodiment, the steps from the gap abutment step to the joining step are performed with the plug cover 5 fitted to the housing 2. Therefore, when performing each step, the position of the plug cover 5 in the plug radial direction relative to the housing 2 is unlikely to shift. This makes it possible to manufacture the spark plug 1 more efficiently.

[0041] The outer circumferential surface of the housing fixing portion 21 and the inner circumferential surface of the cover base end 51 are each formed to extend along the Z direction. Therefore, with the cover base end 51 fitted into the housing fixing portion 21, the plug cover 5 can be slid in the Z direction relative to the housing 2. Therefore, the housing fixing portion 21 and the cover base end 51 can be formed in simple shapes, and the processes from the gap abutment step to the joining step can be performed efficiently. Therefore, the spark plug 1 can be manufactured even more efficiently.

[0042] In this embodiment, the movement distance of the plug cover 5 in the Z direction relative to the housing 2 in the separating step is the length D2 of the discharge gap G. Therefore, by adjusting the movement distance of the plug cover 5 in the Z direction relative to the housing 2, the length of the discharge gap G can be adjusted without directly checking the discharge gap G.

[0043] In the joining step, the cover base end portion 51 is joined to the outer periphery of the housing fixing portion 21. Therefore, the plug cover 5 can be attached to the housing 2 so as to increase the volume of the auxiliary combustion chamber 50. As a result, it is possible to manufacture a spark plug 1 with improved ignition performance.

[0044] The ground electrode 6 is provided along the plug radial direction when viewed from the plug axial direction Z. The injection hole 55 opens at an angle with respect to the Z direction so as to move outward in the plug radial direction toward the tip side. Therefore, the airflow introduced into the auxiliary combustion chamber 50 through the injection hole 55 is guided to the base end side surface 62 of the ground electrode 6 and tends to move toward the discharge gap G. Therefore, the discharge formed in the discharge gap G tends to extend. As a result, ignition performance can be improved.

[0045] As described above, according to the present embodiment, it is possible to provide the spark plug 1 and the manufacturing method thereof that can improve productivity.

[0046] (Embodiment 2) In this embodiment, as shown in FIGS. 7 and 8, a part of the plug cover 5 constitutes the ground electrode 6.

[0047] 7, the plug cover 5 forms a discharge gap G between itself and the center electrode 4. The discharge gap G is formed by the central discharge surface 41 of the center electrode 4 and a ground discharge surface 611, which is a part of the inner wall surface 53 of the plug cover 5, facing each other in the plug axial direction Z.

[0048] In this embodiment, the tip of the center electrode 4 extends close to the inner wall surface 53 of the plug cover 5, thereby forming a discharge gap G between the inner wall surface 53. In other words, in this embodiment, the ground electrode 6 does not protrude into the auxiliary combustion chamber 50 from the inner wall surface 53.

[0049] Next, a method for manufacturing the spark plug 1 of this embodiment will be described. In the preparation step, the housing 2 to which the insulator 3 and the center electrode 4 are assembled, and the plug cover 5 are each prepared. In the gap abutment step, as shown in Fig. 8, the plug cover 5 is placed on the housing 2 such that the central discharge surface 41 and the ground discharge surface 611 abut against each other in the plug axial direction Z while the housing fixing portion 21 and the cover base end portion 51 are overlapped in the plug radial direction. In the separation step, the plug cover 5 is moved in the plug axial direction Z relative to the housing 2, as shown by the arrow M in Fig. 8, to separate the ground discharge surface 611 from the central discharge surface 41. The rest is the same as in embodiment 1. Note that, among the symbols used in embodiment 2 and onwards, the same symbols used in the previous embodiments represent the same components, etc. as in the previous embodiments, unless otherwise specified.

[0050] In the spark plug 1 of this embodiment, the discharge gap G is formed by the central discharge surface 41 and the ground discharge surface 611 of the plug cover 5 facing each other in the plug axial direction Z. In addition, the base end surface 52 of the plug cover 5 is disposed at a position spaced apart from the facing surface 22 in the plug axial direction Z. Therefore, the discharge gap G having a desired length can be easily formed. As a result, the productivity of the spark plug 1 can be improved.

[0051] The method for manufacturing the spark plug 1 of this embodiment includes a preparation step, a gap contact step, a separation step, and a joining step. Therefore, it is possible to easily adjust the discharge gap G. As a result, it is possible to efficiently manufacture the spark plug 1.

[0052] In this embodiment, a part of the plug cover 5 constitutes the ground electrode 6. Therefore, the spark plug 1 can be manufactured without fixing the ground electrode to the plug cover 5. As a result, the spark plug 1 can be manufactured more efficiently. In addition, the same effects as those of the first embodiment are achieved.

[0053] (Embodiment 3) In this embodiment, as shown in Figs. 9 and 10, a plug cover 5 is fixed to a housing 2 by screwing.

[0054] 9, the housing fixing portion 21 and the cover base end portion 51 form a threaded portion that is fixed to each other by threaded engagement between the male threaded portion 11 and the female threaded portion 12 that threads with the male threaded portion 11. Specifically, the plug cover 5 is fixed to the housing 2 by threaded engagement between the female threaded portion 12 formed on the cover base end portion 51 and the male threaded portion 11 formed on the housing fixing portion 21.

[0055] Next, a method for manufacturing the spark plug 1 of this embodiment will be described. In the gap abutment process, with the male thread portion 11 and the female thread portion 12 screwed together, the plug cover 5 is rotated in one circumferential direction of the plug relative to the housing 2. This causes the plug cover 5 to move toward the base end relative to the housing 2 until the central discharge surface 41 and the ground discharge surface 61 abut against each other, as shown in Fig. 10.

[0056] In the separating step, with the male threaded portion 11 and the female threaded portion 12 screwed together, the plug cover 5 is rotated in the other circumferential direction of the plug relative to the housing 2 as shown by the arrow M in Fig. 10. This moves the plug cover 5 toward the tip side relative to the housing 2, separating the ground discharge surface 61 from the central discharge surface 41. The rest is the same as in the first embodiment.

[0057] The housing fixing portion 21 and the cover base end portion 51 form a screw engagement portion. Therefore, the plug cover 5 can be efficiently assembled to the housing 2. That is, when performing the joining step after the discharge gap G is set to a desired length in the separating step, the cover base end portion 51 can be joined to the housing fixing portion 21 by welding or the like without holding the plug cover 5 by a robot arm or the like. Therefore, the tact time of the work performed by the robot arm can be shortened. As a result, the productivity of the spark plug 1 can be improved.

[0058] The manufacturing method of the spark plug 1 of this embodiment includes the gap contact step and the separation step described above. Therefore, the discharge gap G can be easily adjusted. That is, for example, the pitch of the male thread portion 11 and the female thread portion 12 is 1.25 mm, and the length D2 (see FIG. 3) of the discharge gap G is 0.6 mm. In this case, the plug cover 5 is rotated 0.48 times in the plug circumferential direction relative to the housing 2 in the separation step, so that the length D2 can be set to 0.6 mm. As a result, the spark plug 1 can be efficiently manufactured. In addition, the same effects as those of the first embodiment are achieved.

[0059] (Embodiment 4) As shown in Figs. 11 to 18, this embodiment is an embodiment in which the shapes of a cover base end portion 51 and an opposing surface 22 are changed from those of the first embodiment.

[0060] As shown in Fig. 11, Fig. 12, and Fig. 15 to Fig. 18, the cover base end 51 has a plurality of protruding portions 54 formed by a part of the base end face 52 protruding toward the base end side. As shown in Fig. 11, Fig. 13 to Fig. 18, the opposing surface 22 has a stepped portion 23 formed in a stepped shape along the plug circumferential direction. Also, as shown in Fig. 11, the protruding portion 54 abuts against a part of the stepped portion 23 in the plug axial direction Z.

[0061] In this embodiment, as shown in Fig. 12, two protrusions 54 are formed on the cover base end 51. The two protrusions 54 are formed to face each other in the plug radial direction. Moreover, each protrusion 54 is disposed to be sandwiched between the two base end faces 52 in the plug circumferential direction.

[0062] 11, the protrusion 54 has a protrusion side surface 541 that faces the plug circumferential direction and is formed along the Z direction, and a protrusion base end surface 542 that is formed substantially perpendicular to the Z direction. The protrusion base end surfaces 542 of the two protrusions 54 abut against the stepped portion 23 in the Z direction. In this embodiment, the protrusion base end surfaces 542 are positioned at the same positions as each other in the Z direction.

[0063] Further, two stepped portions 23 are formed at the tip end of the housing 2 in accordance with the number of the protrusions 54. As shown in Fig. 13, when the tip end of the housing 2 is viewed from the Z direction, the two stepped portions 23 are formed to be point symmetrical with respect to the plug central axis C. In this embodiment, the stepped portion 23 is formed at a part of the opposing surface 22.

[0064] The stepped portion 23 has a plurality of stepped portions 231. Each of the stepped portions 231 has a circumferential contact surface 232 that faces the plug circumferential direction and is formed along the Z direction, and an axial contact surface 233 that is formed substantially perpendicular to the Z direction.

[0065] As shown in Fig. 14, the length D5 of each step 231 in the Z direction is equal to or less than the tolerance of the discharge gap G. That is, for example, the reference value of the length D2 (see Fig. 3) of the discharge gap G is 0.6 mm, the maximum allowable value of the length D2 is 0.65 mm, and the minimum allowable value of the length D2 is 0.55 mm. In this case, since the tolerance of the discharge gap G is 0.1 mm, the length D5 is equal to or less than 0.1 mm. In this embodiment, the length D5 is equal to the tolerance of the discharge gap G. The length D5 is also the length of the circumferential contact surface 232 in the Z direction.

[0066] 15, the length D6 of the stepped portion 23 in the Z direction is longer than the length D2. As shown in Fig. 11, the distance D7 from the central discharge surface 41 in the Z direction to the opposing surface 22 located at the most base end side is longer than the distance D8 from the ground discharge surface 61 to the protruding-portion base end surface 542 of the protruding portion 54 in the Z direction.

[0067] Next, a method for manufacturing the spark plug 1 of this embodiment will be described with reference to FIGS. In this embodiment, the gap abutment step is performed so that the protrusion 54 and the stepped portion 23 do not abut against each other in the Z direction. Specifically, the plug cover 5 is placed on the housing 2 so that the protrusion 54 does not overlap the stepped portion 23 when viewed from the Z direction (not shown), and the plug cover 5 is slid toward the base end side with respect to the housing 2 as shown by the arrow M in Fig. 15. Note that the direction of the arrow M in Fig. 15 is vertically downward.

[0068] In the separating process, the plug cover 5 is slid toward the tip side relative to the housing 2 as shown by the arrow M in Fig. 16. Also, in the separating process, the plug cover 5 is moved toward the tip side relative to the housing 2 in the Z direction by a distance equivalent to the maximum allowable value of the length D2.

[0069] In this embodiment, the cover abutting step is performed after the separating step and before the joining step. In the cover abutting step, the plug cover 5 is rotated in the plug circumferential direction relative to the housing 2, as shown by the arrow M in Fig. 17, so that the protrusions 54 abut against the stepped portion 23 in the plug circumferential direction. Thereafter, the plug cover 5 is moved toward the base end along the plug axial direction Z relative to the housing 2, as shown by the arrow M in Fig. 18, so that the protrusions 54 abut against the stepped portion 23 in the plug axial direction Z.

[0070] Specifically, in the cover abutting step, while maintaining the position of the plug cover 5 in the Z direction relative to the housing 2, the plug cover 5 is rotated in the plug circumferential direction relative to the housing 2 as shown by the arrow M in Fig. 17. As a result, as shown in Fig. 18, the convex side surface 541 of the convex portion 54 is brought into contact with the circumferential contact surface 232 of the step portion 231 in the plug circumferential direction. Thereafter, as shown by the arrow M in Fig. 18, the plug cover 5 is moved toward the base end side relative to the housing 2, and the convex base end surface 542 of the convex portion 54 is brought into contact with the axial contact surface 233 of the step portion 231 in the Z direction as shown in Fig. 11. Here, the length D5 (see Fig. 14) is equal to or less than the tolerance of the discharge gap G. Therefore, the amount of movement of the plug cover 5 toward the base end side relative to the housing 2 in the cover abutting step is equal to or less than the tolerance of the discharge gap G. As described above, in the separating step, the plug cover 5 is moved toward the tip side in the Z direction relative to the housing 2 by a distance equivalent to the maximum allowable value of the length D2. Therefore, when the protruding portion base end surface 542 is brought into contact with the axial contact surface 233 in the cover contacting step, the distance in the Z direction from the central discharge surface 41 to the ground discharge surface 61 is within the allowable range of the length D2 of the discharge gap G. In other words, the discharge gap G can be set to a desired length. The rest is the same as in the first embodiment.

[0071] The cover base end 51 has a plurality of protrusions 54. The opposing surface 22 has a stepped portion 23. The protrusions 54 abut against parts of the stepped portion 23 in the plug axial direction Z. This makes it possible to efficiently form the discharge gap G having a desired length. As a result, the productivity of the spark plug 1 can be further improved.

[0072] In this embodiment, the cover abutting step is performed after the separating step and before the joining step, which allows the spark plug 1 to be manufactured more efficiently.

[0073] Specifically, in the cover abutting step, the plurality of protrusions 54 are brought into contact with the stepped portion 23 in the Z direction, so that the plug cover 5 can be placed on the tip of the housing 2 while maintaining the length of the discharge gap G at a desired length. That is, even if the robot arm is released from the plug cover 5 after the cover abutting step, the plug cover 5 can be maintained in a state in which it is placed on the housing 2 while maintaining the length of the discharge gap G at a desired length. Therefore, in the joining step, the plug cover 5 can be joined to the housing 2 without being held by the robot arm. Therefore, the tact time of the work performed by the robot arm can be shortened. As a result, the productivity of the spark plug 1 can be further improved.

[0074] The length D6 (see FIG. 15) is longer than the length D2. Therefore, even if there is variation in the position of the central discharge surface 41 relative to the housing 2 in the Z direction, the protrusion 54 can be reliably brought into contact with the stepped portion 23 in the cover abutting step. Therefore, the discharge gap G having a desired length can be reliably formed. As a result, the spark plug 1 can be reliably and efficiently manufactured.

[0075] The distance D7 (see FIG. 11) is equal to or greater than the distance D8 (see FIG. 11). Therefore, in the gap contact step, the ground discharge surface 61 can be reliably contacted with the central discharge surface 41. As a result, the spark plug 1 can be manufactured reliably and efficiently. In addition, the same effects as those of the first embodiment are achieved.

[0076] In the fourth embodiment, the cover base end 51 has two protrusions 54. However, three or more protrusions may be formed on the cover base end. In this case, by forming a step portion corresponding to the number of protrusions, the plug cover can be stably placed on the tip end of the housing when the joining process is performed.

[0077] (Embodiment 5) In this embodiment, as shown in FIG. 19, a cover base end portion 51 is joined to the inner periphery side of the housing fixing portion 21. As shown in FIG.

[0078] In this embodiment, the steps from the gap abutment step to the joining step are performed in a state in which the inner circumferential surface of the housing fixing portion 21 and the outer circumferential surface of the cover base end portion 51 are in contact with each other in the plug radial direction. The other configurations and effects are the same as those of the first embodiment.

[0079] (Embodiment 6) As shown in FIG. 20, this embodiment is an embodiment in which the shape of the cover base end portion 51 is changed from that of the fifth embodiment.

[0080] 20, the cover base end 51 has a cylindrical thin-walled portion 511. The thickness of the thin-walled portion 511 is thinner than other portions of the plug cover 5. Here, "thinner than other portions" means that the average thickness of the thin-walled portion 511 is thinner than the average thickness of portions of the plug cover 5 other than the thin-walled portion 511.

[0081] Furthermore, the plug cover 5 is fixed to the housing 2 by joining the thin portion 511 to the inner periphery side of the housing fixing portion 21 .

[0082] The plug cover 5 also has a cover facing surface 56 that faces the housing fixing part 21 in the Z direction. The cover facing surface 56 is formed along the tip of the outer circumferential surface of the thin-walled part 511. The rest is the same as in the fifth embodiment.

[0083] The cover base end portion 51 has a thin portion 511. This makes it possible to increase the volume of the auxiliary combustion chamber 50. As a result, it is possible to improve ignition performance. In addition, the same effects as those of the fifth embodiment are achieved.

[0084] (Embodiment 7) As shown in Figs. 21 and 22, this embodiment is an embodiment in which the opening direction of the nozzle hole 55 is changed from that of the first embodiment.

[0085] 21, when viewed from the Z direction, the injection hole 55 is formed so that the injection hole axis 55L is inclined at an acute angle with respect to an imaginary line VL extending in the plug radial direction and passing through the injection hole 55 and the plug central axis C. The inclination directions of the injection hole axes 55L of the multiple injection holes 55 with respect to the imaginary line VL are on the same side in the plug circumferential direction.

[0086] Due to such a formation mode of the nozzle hole 55, a swirl flow (see dashed arrow SF in FIG. 22) is formed in the auxiliary combustion chamber 50 by the airflow introduced into the auxiliary combustion chamber 50 through the nozzle hole 55. In this embodiment, the swirl flow SF is generated in a counterclockwise spiral shape in FIG. 22 around the plug central axis C. The rest is the same as in the first embodiment.

[0087] The nozzle hole 55 is formed so that the airflow introduced into the auxiliary combustion chamber 50 through the nozzle hole 55 generates a swirl flow SF in the auxiliary combustion chamber 50. Therefore, the initial flame formed by the discharge generated in the discharge gap G is likely to spread into the auxiliary combustion chamber 50 by the swirl flow SF. Therefore, combustion in the auxiliary combustion chamber 50 is likely to be promoted. As a result, the ignition ability of the auxiliary combustion chamber 50 can be improved. In addition, the same effects as those of the first embodiment are achieved.

[0088] In the above-mentioned embodiments 1 to 7, four injection holes 55 are formed in the plug cover 5. However, the plug cover may have five or more injection holes. Also, the number of injection holes formed in the plug cover may be three or less.

[0089] In the above-mentioned embodiments 1 and 3 to 7, the ground electrode 6, which is a separate member from the plug cover 5, is fixed to the plug cover 5. However, the plug cover and the ground electrode may be formed integrally.

[0090] In the above-described embodiments 1 and 3 to 7, when viewed from the Z direction, the nozzle hole axes 55L of all the nozzle holes 55 are inclined with respect to the protruding direction of the ground electrode 6. However, for example, when viewed from the Z direction, the nozzle holes may be formed such that the nozzle hole axes of some of the nozzle holes are aligned with the protruding direction of the ground electrode.

[0091] Also, a tip can be joined to each of the tip of the center electrode and the ground electrode that form the discharge gap. That is, a discharge gap can be formed between the tip joined to the tip of the center electrode and the tip joined to the ground electrode. The tip can be made of a precious metal such as iridium or platinum, or an alloy containing these as a main component.

[0092] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments without departing from the gist of the present invention. [Explanation of symbols]

[0093] 1...spark plug, 2...housing, 21...housing fixing portion, 22...facing surface, 3...insulator, 4...center electrode, 41...center discharge surface, 5...plug cover, 50...auxiliary combustion chamber, 51...cover base end portion, 52...base end surface, 53...inner wall surface, 6...ground electrode, 61...ground discharge surface, G...discharge gap, Z...plug axial direction

Claims

1. A cylindrical insulator (3); a center electrode (4) held on the inner circumferential side of the insulator and protruding from the insulator toward the tip side; a cylindrical housing (2) that holds the insulator on its inner periphery; a ground electrode (6) forming a discharge gap (G) between itself and the center electrode; a plug cover (5) fixed to the tip end of the housing so as to cover the auxiliary combustion chamber (50) in which the ground electrode is provided and in which the discharge gap is disposed, The ground electrode protrudes from an inner wall surface (53) of the plug cover into the auxiliary combustion chamber, and is provided along a plug radial direction when viewed from a plug axial direction (Z). The discharge gap is formed by a central discharge surface (41) of the central electrode and a ground discharge surface (61) of the ground electrode facing each other in the plug axial direction, the front end portion of the housing has a housing fixing portion (21) facing a cover base end portion (51) of the plug cover in the plug radial direction, and an opposing surface (22) facing a base end surface (52) of the plug cover in the plug axial direction on the base end side of the housing fixing portion, The housing fixing portion and the cover base end portion are joined to each other, the base end surface of the plug cover is disposed at a position spaced apart from the opposing surface in the plug axial direction, the cover base end has a plurality of protrusions (54) formed by a portion of the base end face protruding toward the base end, the opposing surface has a stepped portion (23) formed in a stepped shape along the plug circumferential direction, and the protrusions abut against portions of the stepped portions in the plug axial direction.

2. A cylindrical insulator (3); a center electrode (4) held on the inner circumferential side of the insulator and protruding from the insulator toward the tip side; a cylindrical housing (2) that holds the insulator on its inner periphery; a plug cover (5) which forms a discharge gap (G) between the central electrode and the plug cover and is fixed to the tip of the housing so as to cover a sub-combustion chamber (50) in which the discharge gap is disposed, The discharge gap is formed by a central discharge surface (41) of the central electrode and a ground discharge surface (611) which is a part of an inner wall surface (53) of the plug cover facing each other in the plug axial direction (Z), the front end portion of the housing has a housing fixing portion (21) facing a cover base end portion (51) of the plug cover in a plug radial direction, and an opposing surface (22) facing a base end surface (52) of the plug cover in a plug axial direction on the base end side of the housing fixing portion, The housing fixing portion and the cover base end portion are joined to each other, The base end surface of the plug cover is disposed at a position spaced apart from the opposing surface in the plug axial direction.

3. 3. The spark plug for an internal combustion engine according to claim 2, wherein the cover base end has a plurality of convex portions (54) formed by a portion of the base end face protruding toward the base end, the opposing surface has a stepped portion (23) formed in a stepped shape along the circumferential direction of the plug, and the convex portions abut against portions of the stepped portions in the axial direction of the plug.

4. 3. The spark plug for an internal combustion engine according to claim 2, wherein the housing fixing portion and the cover base end portion form a threaded portion in which the housing fixing portion and the cover base end portion are fixed to each other by threaded engagement of a male thread portion (11) and a female thread portion (12) that threadably engages with the male thread portion.

5. 5. The spark plug for an internal combustion engine according to claim 1, wherein a distance (D1) from the opposing surface to the base end surface of the plug cover in the plug axial direction is equal to or greater than a length (D2) of the discharge gap in the plug axial direction.

6. 6. The spark plug for an internal combustion engine according to claim 1, wherein the base end portion of the cover is joined to an outer circumferential side of the housing fixing portion.

7. A method for manufacturing a spark plug (1) for an internal combustion engine, comprising the steps of: The spark plug includes a cylindrical insulator (3), a center electrode (4) held on the inner periphery of the insulator and protruding from the insulator toward a tip side, a cylindrical housing (2) that holds the insulator on its inner periphery, a ground electrode (6) that forms a discharge gap (G) between the center electrode, and a plug cover (5) in which the ground electrode is provided and which is fixed to a tip portion of the housing so as to cover an auxiliary combustion chamber (50) in which the discharge gap is arranged, The ground electrode protrudes from an inner wall surface (53) of the plug cover into the auxiliary combustion chamber, and is provided along a plug radial direction when viewed from a plug axial direction (Z). The discharge gap is formed by a central discharge surface (41) of the central electrode and a ground discharge surface (61) of the ground electrode facing each other in the plug axial direction, a front end portion of the housing has a housing fixing portion (21) facing a cover base end portion (51) of the plug cover in the plug radial direction, In manufacturing the above spark plugs, a preparation step of preparing the housing having the insulator and the center electrode assembled thereto, and the plug cover having the ground electrode provided thereon; a gap abutment step of, after the preparation step, placing the plug cover relative to the housing such that the central discharge surface and the ground discharge surface abut against each other in the plug axial direction while overlapping the housing fixing portion and the cover base end portion in the plug radial direction; a separating step of separating the ground discharge surface from the center discharge surface by moving the plug cover relative to the housing in an axial direction of the plug after the gap abutting step; a joining step of joining the housing fixing portion and the cover base end portion to each other is performed after the separating step; the front end portion of the housing has an opposing surface (22) opposing a base end surface (52) of the plug cover in the plug axial direction on the base end side of the housing fixing portion, the cover base end portion has a plurality of convex portions (54) formed by a part of the base end surface protruding toward the base end side, and the opposing surface has a stepped portion (23) formed in a stepped shape along the plug circumferential direction, After the separating step and before the bonding step, A method of manufacturing a spark plug for an internal combustion engine, comprising the steps of: rotating the plug cover in a plug circumferential direction relative to the housing to abut the convex portion against the stepped portion in the plug circumferential direction; and then moving the plug cover toward the base end along the plug axial direction relative to the housing to abut the convex portion against the stepped portion in the plug axial direction.

8. A method for manufacturing a spark plug (1) for an internal combustion engine, comprising the steps of: The spark plug includes a cylindrical insulator (3), a center electrode (4) held on the inner periphery of the insulator and protruding from the insulator toward the tip side, a cylindrical housing (2) that holds the insulator on the inner periphery, and a plug cover (5) that forms a discharge gap (G) between the central electrode and the plug cover and is fixed to the tip portion of the housing so as to cover an auxiliary combustion chamber (50) in which the discharge gap is located. The discharge gap is formed by a central discharge surface (41) of the central electrode and a ground discharge surface (611) which is a part of an inner wall surface (53) of the plug cover facing each other in the plug axial direction (Z), The front end of the housing has a housing fixing portion (21) facing a cover base end portion (51) of the plug cover in a plug radial direction, In manufacturing the above spark plugs, a preparation step of preparing the housing having the insulator and the center electrode assembled thereto, and the plug cover; a gap abutment step of, after the preparation step, placing the plug cover relative to the housing such that the central discharge surface and the ground discharge surface abut against each other in the plug axial direction while overlapping the housing fixing portion and the cover base end portion in the plug radial direction; a separating step of separating the ground discharge surface from the center discharge surface by moving the plug cover relative to the housing in an axial direction of the plug after the gap abutting step; the separating step is followed by a joining step of joining the housing fixing portion and the cover base end portion to each other.

9. the front end portion of the housing has an opposing surface (22) opposing a base end surface (52) of the plug cover in the plug axial direction on the base end side of the housing fixing portion, the cover base end portion has a plurality of convex portions (54) formed by a part of the base end surface protruding toward the base end side, and the opposing surface has a stepped portion (23) formed in a stepped shape along the plug circumferential direction, After the separating step and before the bonding step, 9. The method of manufacturing a spark plug for an internal combustion engine according to claim 8, further comprising the steps of: rotating the plug cover in a plug circumferential direction relative to the housing to bring the convex portion into contact with the stepped portion in the plug circumferential direction; and then moving the plug cover toward a base end along a plug axial direction relative to the housing to bring the convex portion into contact with the stepped portion in the plug axial direction.

10. The housing fixing portion and the cover base end portion form a threaded portion that is fixed to each other by threading a male threaded portion (11) and a female threaded portion (12) that threadably engages with the male threaded portion, In the gap abutment step, the plug cover is rotated in one circumferential direction of the plug relative to the housing with the male thread portion and the female thread portion screwed together, thereby moving the plug cover toward the base end side relative to the housing until the center discharge surface and the ground discharge surface abut against each other, 9. The method of manufacturing a spark plug for an internal combustion engine according to claim 8, wherein in the separating step, the plug cover is rotated in the other circumferential direction of the plug relative to the housing with the male threaded portion and the female threaded portion screwed together, thereby moving the plug cover toward a tip side relative to the housing and separating the ground discharge surface from the center discharge surface.

11. 11. The method for manufacturing a spark plug for an internal combustion engine according to claim 7, wherein in the joining step, the base end portion of the cover is joined to an outer circumferential side of the housing fixing portion.

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