Spark plug for internal combustion engine and manufacturing method thereof

Abstract

To provide a spark plug for an internal combustion engine that can improve productivity, and a manufacturing method for the same.SOLUTION: In a spark plug 1, a plug cover 5 is provided at an end part of a housing 2 so as to cover a sub-combustion chamber 50 where a discharge gap G is disposed. A ground electrode 6 includes, on a base end side, a ground inclined surface 611 that is inclined toward an end side as extending in a protruding direction. The discharge gap G is formed by an end part of a center electrode 4 and the ground inclined surface 611 facing each other. In addition, the discharge gap G is formed on the base end side relative to the end of the housing 2. A line L1 exists on a line L2 or on the end side relative to the line L2. A line L3 exists on the base end side relative to the line L1. A line L4 exists on the line L3 or on the base end side relative to the line L3.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] For example, a spark plug having a sub-combustion chamber in which a discharge gap is arranged is known, as disclosed in Patent Document 1. In this spark plug, a ground electrode is fixed to a tip end of a housing, and after a discharge gap is formed, a plug cover that covers the sub-combustion chamber can be joined to the housing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-184435 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the spark plug described in Patent Document 1, the discharge gap is formed by the center electrode and the ground electrode facing each other in the plug axial direction, and is formed closer to the base end than the tip end of the housing. Therefore, it is difficult to directly visually check the discharge gap before the plug cover is fixed to the housing. This makes it difficult to adjust the discharge gap to a desired length, which tends to reduce productivity.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to provide a spark plug for an internal combustion engine and a method for manufacturing the same, which are capable of improving productivity. [Means for solving the problem]

[0006] One aspect of the present invention is a cylindrical insulator (3), a center electrode (4) held on the inner circumferential side of the insulator and 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) provided at the tip of the housing so as to cover a sub-combustion chamber (50) in which the discharge gap is disposed, The plug cover is formed with a nozzle hole (51) that communicates the auxiliary combustion chamber with the outside, The ground electrode projects into the auxiliary combustion chamber from a fixed end portion (62) fixed to the housing, and has a ground inclined surface (611) on a base end side, the ground inclined surface being inclined toward a tip end side as it projects, the discharge gap is formed by the front end of the center electrode and the ground inclined surface of the ground electrode facing each other, and is formed on the base end side of the front end of the housing, In a cross section including a plug central axis (PC) and along a protruding direction of the ground electrode, a point on the ground inclined surface closest to the center electrode is defined as point A, a point on the center electrode closest to the ground inclined surface is defined as point B, a point on a base end surface (61) of the ground electrode closest to a front end surface (21) of the housing on the opposite side of the plug central axis from the fixed end is defined as point C, a point on the front end surface of the housing on the opposite side of the plug central axis from the fixed end and closest to point C is defined as point D, a point on the center electrode closest to point D is defined as point E, a line segment connecting point C and point D is defined as line segment L1, a line segment connecting point A and point D is defined as line segment L2, a line segment connecting point B and point D is defined as line segment L3, and a line segment connecting point E and point D is defined as line segment L4, The line segment L1 is located on the line segment L2 or is located on the tip side of the line segment L2, The line segment L3 is located on the base end side of the line segment L1, The line segment L4 is located on the line segment L3 or on the proximal side of the line segment L3. Cage , The housing has a fixing recess (26) formed by recessing a part of an inner wall surface (22) outward in a plug radial direction, and the fixing recess (26) of the housing is open to a tip end side, The ground electrode is fixed to a recess forming surface (261) that forms the fixing recess. In a spark plug (1) for an internal combustion engine.

[0007] Another aspect of the present invention is a spark plug comprising: 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; a ground electrode (6) that forms a discharge gap (G) between the center electrode; and a plug cover (5) provided at the tip of the housing so as to cover an auxiliary combustion chamber (50) in which the discharge gap is arranged. The plug cover has an injection hole (51) that communicates the auxiliary combustion chamber with the outside. The ground electrode protrudes into the auxiliary combustion chamber from a fixed end (62) fixed to the housing, and has a ground inclined surface (611) on the base end side that is inclined toward the tip side as it protrudes. The discharge gap is formed by the tip of the center electrode and the ground inclined surface of the ground electrode facing each other, and is formed on the base end side of the tip of the housing. the housing has a fixing recess (26) formed by recessing a part of an inner wall surface (22) outward in a plug radial direction, the fixing recess in the housing is open on a tip side, and the ground electrode is fixed to a recess forming surface (261) that forms the fixing recess. A method for manufacturing a spark plug (1) for an internal combustion engine, comprising the steps of: The ground electrode is fixed to the housing, and the length of the discharge gap is adjusted to a desired length. Then, the plug cover is fixed to the front end of the housing. When the ground electrode is fixed to the housing, the fixed end portion is fitted into the fixed recess portion, and then welding is performed. The method for manufacturing a spark plug for an internal combustion engine allows the entire discharge gap to be directly and visually confirmed when viewed from the tip side of the housing and from the protruding side of the ground electrode before the plug cover is provided. Effect of the Invention

[0008] The spark plug is configured so that the line segments L1 to L4 are located at the above positions. Therefore, before the plug cover is provided, the entire discharge gap can be easily and directly visually confirmed when viewed from the tip side of the housing and from the protruding side of the ground electrode. Therefore, the discharge gap can be easily adjusted. Therefore, a discharge gap having a desired length can be easily formed. As a result, the productivity of the spark plug can be improved.

[0009] In the above-mentioned method for manufacturing a spark plug, the entire discharge gap of the spark plug before the plug cover is attached can be directly and visually confirmed when viewed from the tip side of the housing and from the protruding side of the ground electrode. This makes it easy to adjust the discharge gap. As a result, the spark plug can be manufactured efficiently.

[0010] As described above, according to the above aspect, it is possible to provide a spark plug for an internal combustion engine 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]

[0011] [Figure 1] 2. FIG. 3 is a cross-sectional view taken along the line II in FIG. 2, showing a portion of the spark plug in the axial direction of the plug in the vicinity of the tip portion of the spark plug in the first embodiment. [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Diagram 3] 4 is a cross-sectional view showing lines L1 to L4 in the first embodiment. FIG. [Figure 4] 4 is a cross-sectional view showing a state in which an assembly jig is brought into contact with a center electrode in the first embodiment. FIG. [Diagram 5] 4 is a cross-sectional view showing a state in which a ground electrode is welded to an inner wall surface in the first embodiment. FIG. [Figure 6] 4 is a cross-sectional view showing lines L5 and L6 in the first embodiment. FIG. [Figure 7] FIG. 4 is a cross-sectional view showing a state in which the plug cover is brought into contact with the housing in the first embodiment. [Figure 8] 1 is a cross-sectional view of an internal combustion engine in which a spark plug is installed according to a first 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 the spark plug according to a second embodiment. [Figure 10] 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 third embodiment. [Figure 11] 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 fourth embodiment. [Figure 12] 12 is a cross-sectional view taken along the line XII-XII in FIG. 13 , showing a portion of a spark plug in a fifth embodiment in the axial direction of the plug, and FIG. [Figure 13] FIG. 13 is a cross-sectional view taken along line XIII-XIII in FIG. [Figure 14] 13 is a cross-sectional view of the tip portion of a spark plug according to a sixth embodiment, taken along a line perpendicular to the axial direction of the plug, as viewed from the tip side. FIG. [Figure 15] 17 is a cross-sectional view taken along the axial direction of a spark plug in the vicinity of a tip portion of the spark plug according to the seventh embodiment, and corresponds to a cross-sectional view taken along the line XV-XV in FIG. [Figure 16] FIG. 16 is a cross-sectional view taken along line XVI-XVI in FIG. [Figure 17] FIG. 13 is a cross-sectional view taken along the axial direction of a spark plug in the vicinity of a tip portion of the spark plug according to an eighth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] (Embodiment 1) DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A spark plug for an internal combustion engine and a manufacturing method thereof will be described with reference to FIGS. As shown in Fig. 1 and Fig. 2, a spark plug 1 for an internal combustion engine according to this embodiment has a cylindrical insulator 3, a center electrode 4, a cylindrical housing 2, a ground electrode 6, and a plug cover 5. The center electrode 4 is held on the inner periphery of the insulator 3 and 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 at the tip of the housing 2 so as to cover the auxiliary combustion chamber 50 in which the discharge gap G is arranged. The plug cover 5 has an injection hole 51 that communicates the auxiliary combustion chamber 50 with the outside.

[0013] The ground electrode 6 protrudes into the auxiliary combustion chamber 50 from a fixed end 62 fixed to the housing 2. The ground electrode 6 also has a ground inclined surface 611 on the base end side that is inclined toward the tip side in the protruding direction.

[0014] The discharge gap G is formed by opposing the tip end of the center electrode 4 and the ground inclined surface 611 of the ground electrode 6. The discharge gap G is formed on the base end side of the tip end of the housing 2.

[0015] 3, in a cross section including the plug central axis PC and along the protruding direction of the ground electrode 6, a point on the ground inclined surface 611 closest to the center electrode 4 is designated as point A, and a point on the center electrode 4 closest to the ground inclined surface 611 is designated as point B. In addition, in a cross section including the plug central axis PC and along the protruding direction of the ground electrode 6, a point on the base end surface 61 of the ground electrode 6 closest to the front end surface 21 of the housing 2 on the opposite side of the plug central axis PC from the fixed end portion 62 is designated as point C. In addition, in a cross section including the plug central axis PC and along the protruding direction of the ground electrode 6, a point on the front end surface 21 of the housing 2 on the opposite side of the plug central axis PC from the fixed end portion 62 is designated as point D, and a point on the center electrode 4 closest to point D is designated as point E.

[0016] The line segment connecting point C and point D is line segment L1, and the line segment connecting point A and point D is line segment L2. Furthermore, the line segment connecting point B and point D is line segment L3, and the line segment connecting point E and point D is line segment L4. In this case, line segment L1 is located on line segment L2 or is located further distal than line segment L2. Furthermore, line segment L3 is located further proximal than line segment L1. Furthermore, line segment L4 is located on line segment L3 or is located further proximal than line segment L3.

[0017] 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 a threaded portion 23 formed on the outer circumferential surface of a housing 2 into a female threaded portion of a plug hole 711 of a cylinder head 71, as shown in Fig. 8 .

[0018] 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.

[0019] 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 PC refers to the central axis PC of the spark plug 1. In the spark plug 1 of this embodiment, the plug central axis PC is also the central axis of the center electrode 4, as shown in Figs. 1 and 2.

[0020] In this embodiment, the plug cover 5 is joined by welding or the like to the tip of the housing 2. As shown in Fig. 8, when the spark plug 1 is attached to the internal combustion engine 10, the plug cover 5 separates the auxiliary combustion chamber 50 from the main combustion chamber 101. An injection hole 51 formed in the plug cover 5 connects the auxiliary combustion chamber 50 and the main combustion chamber 101.

[0021] 1, the discharge gap G disposed in the auxiliary combustion chamber 50 is formed by the front end surface 42 of the center electrode 4 and the ground inclined surface 611 of the ground electrode 6 facing each other. The front end surface 42 and the ground inclined surface 611 are both flat surfaces.

[0022] 2, when viewed from the Z direction, the tip surface 42 of the center electrode 4 and the ground inclined surface 611 overlap with each other. In detail, when viewed from the Z direction, the entire tip surface 42 and a part of the ground inclined surface 611 overlap with each other.

[0023] In this embodiment, points B and E are on the front end surface 42 of the center electrode 4, as shown in FIG.

[0024] 1, a small diameter portion 43 having an outer diameter smaller than that of the other portions is formed at the tip of the center electrode 4. The tip surface 42 is formed at the small diameter portion 43. The discharge gap G is, for example, a region obtained by projecting the tip surface 42 of the center electrode 4 in the Z direction and a region obtained by projecting the tip surface 42 in a direction perpendicular to the ground inclined surface 611, and is the region between the tip surface 42 and the ground inclined surface 611.

[0025] In this embodiment, the ground electrode 6 has a substantially rectangular prism shape. The ground electrode 6 is inclined toward the tip side in the protruding direction. The ground electrode 6 has four flat side surfaces, one of which is a base end surface 61. In other words, the base end surface 61 of the ground electrode 6 is entirely flat. In this embodiment, the base end surface 61 of the ground electrode 6 is entirely a ground inclined surface 611.

[0026] In this embodiment, the ground electrode 6 is fixed to the inner wall surface 22 of the housing 2. In addition, the tip of the ground electrode 6 is located closer to the base end than the tip of the housing 2.

[0027] Next, a method for manufacturing the spark plug 1 of this embodiment will be described. 4 to 7, in this embodiment, the ground electrode 6 is fixed to the housing 2, the length of the discharge gap G is adjusted to a desired length, and then the plug cover 5 is fixed to the tip of the housing 2. As shown in Figures 6 and 7, before the plug cover 5 is provided, the entire discharge gap G can be directly seen when viewed from the tip side of the tip of the housing 2 and from the protruding side of the ground electrode 6.

[0028] That is, as shown in Fig. 6, when the spark plug 1 before the plug cover 5 is provided is viewed from, for example, the position of point F, the entire discharge gap G can be directly seen. Note that point F is a point on the tip side of the tip of the housing 2 and on the protruding side of the ground electrode 6.

[0029] In a cross section including the plug central axis PC and along the protruding direction of the ground electrode 6, a line segment connecting points A and F is defined as line segment L5. Also, a line segment connecting points B and F is defined as line segment L6. In this case, line segments L5 and L6 do not pass through the ground electrode 6, the center electrode 4, or the housing 2, respectively.

[0030] Furthermore, when fixing the ground electrode 6 to the housing 2 before the plug cover 5 and the ground electrode 6 are fixed, the protruding end 63 opposite the fixed end 62 of the ground electrode 6 is held by an assembly jig 11, as shown in Figures 4 and 5. Then, as shown in Figure 5, the fixed end 62 of the ground electrode 6 is abutted against the inner wall surface 22 of the housing 2 and welded.

[0031] The assembly jig 11 has a base end support part 111 and a tip end support part 112 that sandwich the ground electrode 6 from the base end side and the tip end side. When the fixed end part 62 is welded to the inner wall surface 22, a base end surface 113 of the base end support part 111 is brought into contact with the tip of the center electrode 4.

[0032] In this embodiment, the base end surface 113 of the base end support part 111 is a flat surface. The tip surface of the base end support part 111 is also a flat surface. The tip surface of the base end support part 111 is inclined with respect to the Z direction. The base end surface of the tip side support part 112 is approximately parallel to the tip surface of the base end support part 111.

[0033] In this embodiment, the base end support part 111 and the tip end support part 112 sandwich the protruding end part 63 of the ground electrode 6 in the thickness direction of the ground electrode 6. At this time, the tip surface of the base end support part 111 and the ground inclined surface 611 of the ground electrode 6 abut against each other. The base end surface of the tip end support part 112 and the tip surface of the ground electrode 6 abut against each other. As a result, the ground electrode 6 is inclined at a predetermined angle with respect to the Z direction.

[0034] 7. Moreover, the length D1 in the Z direction of the base end support portion 111 shown in FIG. 4 is equal to the length D2 in the Z direction of the discharge gap G shown in FIG.

[0035] As shown in Figs. 4 and 5, the assembly jig 11 has a base end support portion 111 and a tip end support portion 112 disposed on a jig body portion 114. The base end support portion 111 is fixed to the base end portion of the jig body portion 114 and protrudes from the base end portion in a direction perpendicular to the axial direction of the jig body portion 114. The width of the base end support portion 111 in the Z direction decreases as it moves away from the jig body portion 114. The tip end support portion 112 is attached to the tip side of the base end support portion 111 in a state in which it can slide relative to the jig body portion 114. This allows the protruding side end portion 63 of the ground electrode 6 to be sandwiched between the tip end support portion 112 and the base end support portion 111.

[0036] Next, the manufacturing method of this embodiment will be described in detail. In assembling the ground electrode 6, the assembling jig 11 holding the ground electrode 6 is moved toward the tip of the center electrode 4 as shown by the arrow M in Fig. 4. Then, as shown in Fig. 5, the base end surface 113 of the base end support part 111 and the tip surface 42 of the center electrode 4 are brought into contact with each other in the Z direction, and the fixed end part 62 of the ground electrode 6 and the inner wall surface 22 of the housing 2 are brought into contact with each other. At this time, the tip surface 42 of the center electrode 4 and the ground inclined surface 611 of the ground electrode 6 face each other in the Z direction with the base end support part 111 in between.

[0037] Next, the fixed end 62 of the ground electrode 6 is joined to the inner wall surface 22 by laser welding. Specifically, the ground electrode 6 is welded to the inner wall surface 22 by irradiating the laser light L toward the abutting portion where the fixed end 62 and the inner wall surface 22 abut against each other. After welding, the assembly jig 11 is removed from the ground electrode 6.

[0038] Next, as shown in Fig. 6, the spark plug 1 before the plug cover 5 is attached is photographed by a camera, for example, from the tip side of the tip of the housing 2 and from the protruding side of the ground electrode 6. In other words, the discharge gap G is photographed by a camera from outside the spark plug 1. Then, the length of the discharge gap G is confirmed based on the photographed image. After confirming the length of the discharge gap G, the ground electrode 6 fixed to the housing 2 is slightly deformed as necessary to fine-tune the discharge gap G to an appropriate distance.

[0039] Next, the plug cover 5 is moved toward the tip end of the housing 2 as shown by the arrow M in Fig. 7, so that the base end of the plug cover 5 and the tip end of the housing 2 are brought into contact with each other in the Z direction. Then, the tip end of the housing 2 and the base end of the plug cover 5 are welded to each other. In this way, the spark plug 1 of this embodiment can be obtained as shown in Figs. 1 and 2.

[0040] Next, the effects of this embodiment will be described. The spark plug 1 is configured so that the line segments L1 to L4 are located at the above positions. Therefore, before the plug cover 5 is provided, the entire discharge gap G can be easily and directly seen when viewed from the tip side of the housing 2 and from the protruding side of the ground electrode 6. Therefore, the discharge gap G is easy to adjust. 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.

[0041] Furthermore, discharge gap G is formed closer to the base end than to the tip of housing 2. Therefore, the distance between discharge gap G and nozzle hole 51 tends to be long. Therefore, it is expected that the flame will spread from a position sufficiently far away from nozzle hole 51, and that the flame jet will be ejected from nozzle hole 51 into the main combustion chamber under a condition of sufficiently high internal pressure. As a result, the flame jet is strengthened, and improvements in the power output and fuel efficiency of the internal combustion engine can be expected.

[0042] The tip of the ground electrode 6 is located closer to the base end than the tip of the housing 2. This tends to make the distance between the discharge gap G and the nozzle hole 51 longer. As a result, the flame jet can be further strengthened.

[0043] In the above-described method for manufacturing the spark plug 1, the spark plug 1 before the plug cover 5 is provided can have its entire discharge gap G directly visible when viewed from the tip side of the housing 2 and from the protruding side of the ground electrode 6. This makes it easy to adjust the discharge gap G. As a result, the spark plug 1 can be manufactured efficiently.

[0044] In the manufacturing method of the spark plug 1 of this embodiment, the ground electrode 6 is fixed to the housing 2, and then the plug cover 5 is fixed to the housing 2. Here, the spark plug 1 before the plug cover 5 is provided can be directly and entirely seen from the tip side of the housing 2 and the protruding side of the ground electrode 6. That is, the entire discharge gap G can be directly and entirely seen from the outside of the spark plug 1. Therefore, it is easy to check whether the length of the discharge gap G is a desired length. Therefore, after the ground electrode 6 is fixed to the housing 2, the discharge gap G can be easily adjusted. That is, even if there is a variation in the dimensions of each component of the spark plug 1 or a variation during assembly, the discharge gap G can be easily fine-tuned to an appropriate distance by slightly deforming the ground electrode 6 fixed to the housing 2. As a result, the spark plug 1 can be efficiently manufactured.

[0045] As described above, according to the present embodiment, it is possible to provide a spark plug for an internal combustion engine and a manufacturing method thereof that can improve productivity.

[0046] (Embodiment 2) As shown in FIG. 9, this embodiment is an embodiment in which the shape of the tip portion of the center electrode 4 is modified from that of the first embodiment. That is, the center electrode 4 has a central inclined surface 41 that is inclined toward the tip side as it approaches the protruding end 63 opposite to the fixed end 62 of the ground electrode 6. The central inclined surface 41 is inclined along the ground inclined surface 611. In this embodiment, the entire tip surface 42 of the center electrode 4 forms the central inclined surface 41.

[0047] In this embodiment, the line segment L4 is located on the line segment L3 as shown in FIG.

[0048] Moreover, the central inclined surface 41 is parallel to the ground inclined surface 611. Here, parallel does not necessarily mean parallel in the strict sense, but also includes a slight angular difference of, for example, 5° or less from parallel in the strict sense.

[0049] In this embodiment, the central inclined surface 41 of the center electrode 4 and the ground inclined surface 611 of the ground electrode 6 are each a flat surface. The respective flat surfaces are arranged parallel to each other and face each other, thereby forming a discharge gap G. 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] The center electrode 4 has a central inclined surface 41. The central inclined surface 41 is inclined along the ground inclined surface 611. This makes it easy to disperse the starting positions of discharges on the center electrode 4 side. This makes it possible to suppress localized wear of the center electrode 4 and to suppress an increase in the distance of the discharge gap G. As a result, the life of the spark plug 1 can be extended.

[0051] The line segment L4 is located on the line segment L3. Therefore, the central inclined surface 41 and the ground inclined surface 611 tend to be substantially parallel to each other. Therefore, the starting points of discharge on the side of the center electrode 4 tend to be further dispersed. As a result, the life of the spark plug 1 can be further extended.

[0052] The central inclined surface 41 is parallel to the ground inclined surface 611. This makes it easier to disperse the starting points of discharge on the side of the central electrode 4. As a result, the life of the spark plug 1 can be further extended. In addition, the same effects as those of the first embodiment are achieved.

[0053] (Embodiment 3) As shown in FIG. 10, this embodiment is an embodiment in which the shape of the ground electrode 6 is modified from that of the first embodiment.

[0054] In this embodiment, as shown in Fig. 10, the ground electrode 6 has a fixed side portion 64 including a fixed end portion 62, and an inclined portion 65 having a ground inclined surface 611. The fixed side portion 64 is formed along the plug radial direction. The inclined portion 65 is inclined with respect to the Z direction so as to move toward the tip side as it approaches the protruding side end portion 63. Note that the plug radial direction means the radial direction of a circle centered on the central axis PC of the spark plug 1 on a plane perpendicular to the central axis PC of the spark plug 1. The other configurations and effects are the same as those of the first embodiment.

[0055] (Embodiment 4)

[0056] As shown in FIG. 11, this embodiment is an embodiment in which the shape of the ground electrode 6 is modified from that of the first embodiment.

[0057] In this embodiment, the ground electrode 6 is fixed to the housing 2 so as to extend along the plug radial direction, as shown in FIG.

[0058] The thickness of the portion of the ground electrode 6 near the protruding end portion 63 in the Z direction decreases toward the protruding direction of the ground electrode 6. A ground inclined surface 611 is formed in the tapered portion of the ground electrode 6. The other configurations and effects are the same as those of the first embodiment.

[0059] (Embodiment 5) In this embodiment, as shown in FIGS. 12 and 13, the ground electrode 6 is fixed to a flat surface 221 of the housing 2. In the embodiment shown in FIG. That is, the inner wall surface 22 has a flat surface 221. The ground electrode 6 is fixed to the flat surface 221.

[0060] 12, the housing 2 has a support portion 24 formed by a part of the inner wall surface 22 protruding inward in the plug radial direction. The support portion 24 is formed in an annular shape. The support portion 24 supports the insulator 3 in the Z direction.

[0061] In this embodiment, the flat surface 221 is formed along the Z direction. The flat surface 221 is formed from the tip of the housing 2 to the support portion 24.

[0062] The length D3 of the flat surface 221 in the Z direction is equal to or greater than the length D4 of the joint surface of the fixed end portion 62 in the Z direction. In addition, in the width direction of the ground electrode 6 perpendicular to the longitudinal direction of the ground electrode 6, the width D5 of the flat surface 221 is equal to or greater than the width D6 of the ground electrode 6, as shown in FIG. The rest is the same as in the first embodiment.

[0063] The fixed end 62 of the ground electrode 6 is fixed to the flat surface 221. Therefore, the joining surface of the fixed end 62 to be joined to the inner wall surface 22 can be made flat. Therefore, the ground electrode 6 before being fixed to the inner wall surface 22 can be efficiently manufactured. That is, for example, the ground electrode 6 can be manufactured by cutting a metal wire or the like to a predetermined length so that the cut surface is a flat surface. As a result, the productivity of the spark plug 1 can be improved. In addition, the same effects as those of the first embodiment are achieved.

[0064] (Embodiment 6) As shown in FIG. 14, in this embodiment, compared to the fifth embodiment, a flat surface 221 of a housing 2 protrudes inward in the plug radial direction.

[0065] In this embodiment, the housing 2 has a protrusion 25 formed by a part of the inner wall surface 22 protruding inward in the plug radial direction, as shown in Fig. 14. The protrusion 25 has a flat surface 221 facing inward in the plug radial direction. The fixed end 62 of the ground electrode 6 is welded to the flat surface 221 formed on the protrusion 25.

[0066] Moreover, the protrusion 25 is formed from the tip of the housing 2 to the support portion 24 (not shown). The other configurations and effects are the same as those of the fifth embodiment.

[0067] (Embodiment 7) In this embodiment, as shown in FIGS. 15 and 16, the ground electrode 6 is fixed to a recess forming surface 261. As shown in FIG.

[0068] 15 and 16, the housing 2 has a fixing recess 26 formed by recessing a part of the inner wall surface 22 radially outward. The fixing recess 26 is formed from a position on the base end side of the tip of the discharge gap G in the plug axial direction Z to the tip of the housing 2. The fixing recess 26 is open on the tip side. The ground electrode 6 is fixed to a recess forming surface 261 that forms the fixing recess 26.

[0069] 15 and 16, the recess-forming surface 261 has two circumferentially opposed surfaces 262 that face the ground electrode 6 in the plug circumferential direction, and one radially opposed surface 263 that faces the ground electrode 6 in the plug radial direction. In this embodiment, the circumferentially opposed surfaces 262 and the radially opposed surface 263 are also flat surfaces 221. The plug circumferential direction is a direction along a circumference centered on the plug central axis PC.

[0070] In this embodiment, the ground electrode 6 and each of the two circumferentially opposed surfaces 262 are joined to each other. The ground electrode 6 and the radially opposed surface 263 are also joined to each other.

[0071] In this embodiment, when joining the ground electrode 6 to the housing 2, the fixed end portion 62 is fitted into the fixed recess 26 and then welding is performed. The rest is the same as in the fifth embodiment.

[0072] The ground electrode 6 is fixed to the recess forming surface 261. This makes it possible to increase the joint area of ​​the ground electrode 6 with respect to the housing 2. As a result, the strength of the joint between the housing 2 and the ground electrode 6 can be increased.

[0073] Furthermore, since the bonding area of ​​the ground electrode 6 with respect to the housing 2 is increased, heat from the ground electrode 6 is more likely to be efficiently transferred to the housing 2. This makes it possible to prevent overheating of the ground electrode 6. As a result, pre-ignition can be suppressed. Moreover, the ground electrode 6 can be easily positioned relative to the housing 2 in the plug circumferential direction.

[0074] Moreover, the fixing recess 26 is open to the tip side. Therefore, the fixing end 62 of the ground electrode 6 can be inserted along the Z direction from the tip side of the fixing recess 26. Therefore, the ground electrode 6 can be easily disposed at a desired position. As a result, the productivity can be improved.

[0075] Also, by forming the fixing recess 26 at a predetermined position relative to the threading start of the threaded portion 23 in the housing 2, it is easy to determine the position of the injection hole 51 relative to the ground electrode 6 and the position of the injection hole 51 relative to the threading start of the threaded portion 23. That is, for example, a protrusion is provided at the base end of the plug cover 5. Also, the formation position of the protrusion relative to the injection hole 51 is determined. Then, when the plug cover 5 is fixed to the housing 2, this protrusion is fitted into the fixing recess 26 opening at the tip side. This makes it easy to determine the threading start of the threaded portion 23 and the position of the injection hole 51 relative to the ground electrode 6. Therefore, it is easy to arrange the injection hole 51 so that the airflow introduced into the auxiliary combustion chamber 50 through the injection hole 51 is not easily obstructed by the ground electrode 6. Also, it is easy to arrange the injection hole 51 so that the outer opening 511 of the injection hole 51 faces the upstream side of the airflow of the main combustion chamber. Therefore, it is easy to strengthen the airflow in the auxiliary combustion chamber 50. Therefore, the initial flame formed by the discharge is easily carried by the airflow to the base end side of the auxiliary combustion chamber 50. Therefore, the flame is easily developed from the base end side of the auxiliary combustion chamber 50. As a result, the flame jet ejected into the main combustion chamber can be strengthened. In addition, the same effects as those of the fifth embodiment are achieved.

[0076] (Embodiment 8) In this embodiment, as shown in FIG. 17, the ground electrode 6 is inserted into and fixed to an insertion hole 27 formed in the housing 2. As shown in FIG.

[0077] In this embodiment, as shown in Fig. 17, the housing 2 is formed with an insertion hole 27 through which the ground electrode 6 is inserted. The insertion hole 27 is formed from the threaded portion 23 to the inner wall surface 22 of the housing 2. The insertion hole 27 is formed so as to communicate between the outside and the auxiliary combustion chamber 50 before the ground electrode 6 is inserted and fixed.

[0078] The insertion hole 27 is opened at an incline with respect to the Z direction so as to be closer to the plug center axis PC and toward the tip side. The ground electrode 6 is joined to the inner circumferential surface of the insertion hole 27. The rest is the same as in the first embodiment.

[0079] The ground electrode 6 is inserted and fixed in the insertion hole 27. Therefore, by forming the insertion hole 27 so that the opening direction is in a predetermined direction, the ground electrode 6 can be easily fixed in a desired position. In other words, the ground electrode 6 can be easily and stably fixed to the housing 2 so that the inclination angle of the ground electrode 6 and its position relative to the center electrode 4 are at a desired angle or position. As a result, productivity can be improved.

[0080] In addition, the ground electrode 6 is fixed to the inner circumferential surface of the insertion hole 27. Therefore, the joint area of ​​the ground electrode 6 with respect to the housing 2 can be increased. As a result, the strength of the joint between the housing 2 and the ground electrode 6 can be increased. Furthermore, the increased joint area of ​​the ground electrode 6 with respect to the housing 2 can suppress pre-ignition. In addition, the same effects as those of the first embodiment are achieved.

[0081] In the above-mentioned embodiments 1 to 8, four injection holes 51 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.

[0082] In the above-mentioned embodiments 1 to 8, the injection hole 51 is formed so that the central axis (not shown) of the injection hole 51 is along the plug radial direction when viewed from the Z direction. However, the injection hole can also be formed so that the central axis of the injection hole is inclined with respect to a virtual line (not shown) that passes through the injection hole and the plug central axis and extends in the plug radial direction when viewed from the Z direction. In other words, the injection hole can also be formed so that a swirl flow is generated in the auxiliary combustion chamber by introducing an air flow into the auxiliary combustion chamber through the injection hole.

[0083] 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.

[0084] In the above-mentioned embodiments 1, 2, and 5 to 8, the ground electrode 6 has a substantially quadrangular prism shape. However, the ground electrode may also have, for example, a substantially cylindrical shape.

[0085] 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]

[0086] 1...spark plug, 2...housing, 21...tip surface, 3...insulator, 4...center electrode, 5...plug cover, 50...auxiliary combustion chamber, 51...nozzle hole, 6...ground electrode, 61...base end surface, 611...ground inclined surface, 62...fixed end, G...discharge gap, PC...plug center axis

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) provided at the tip of the housing so as to cover a sub-combustion chamber (50) in which the discharge gap is disposed, The plug cover is formed with a nozzle hole (51) that communicates the auxiliary combustion chamber with the outside, The ground electrode protrudes into the auxiliary combustion chamber from a fixed end portion (62) fixed to the housing, and has a ground inclined surface (611) on the base end side that is inclined toward the tip side as it protrudes, the discharge gap is formed by the front end of the center electrode and the ground inclined surface of the ground electrode facing each other, and is formed on the base end side of the front end of the housing, In a cross section including the plug central axis (PC) and along the protruding direction of the ground electrode, a point on the ground inclined surface closest to the center electrode is defined as point A, a point on the center electrode closest to the ground inclined surface is defined as point B, a point on a base end surface (61) of the ground electrode closest to a front end surface (21) of the housing on the opposite side of the plug central axis from the fixed end is defined as point C, a point on the front end surface of the housing on the opposite side of the plug central axis from the fixed end and closest to point C is defined as point D, a point on the center electrode closest to point D is defined as point E, a line segment connecting point C and point D is defined as line segment L1, a line segment connecting point A and point D is defined as line segment L2, a line segment connecting point B and point D is defined as line segment L3, and a line segment connecting point E and point D is defined as line segment L4, The line segment L1 is located on the line segment L2 or is located on the tip side of the line segment L2, The line segment L3 is located on the base end side of the line segment L1, The line segment L4 is located on the line segment L3 or is located on the proximal side of the line segment L3, The housing has a fixing recess (26) formed by recessing a part of an inner wall surface (22) outward in a plug radial direction, and the fixing recess in the housing is open toward a tip end side, The ground electrode is fixed to a recess forming surface (261) that forms the fixed recess.

2. The recess-forming surface has two circumferentially opposed surfaces (262) opposed to the ground electrode in the plug circumferential direction, and one radially opposed surface (263) opposed to the ground electrode in the plug radial direction, 2. A spark plug for an internal combustion engine according to claim 1, wherein the ground electrode and each of the two circumferentially opposed surfaces are joined to each other, and the ground electrode and each of the radially opposed surfaces are joined to each other.

3. 3. A spark plug for an internal combustion engine according to claim 1, wherein the center electrode has a central inclined surface (41) inclined toward a tip side as it approaches a protruding end (63) opposite to the fixed end of the ground electrode, and the central inclined surface is inclined along the ground inclined surface.

4. 4. The spark plug for an internal combustion engine according to claim 3, wherein said line segment L4 is located on said line segment L3.

5. 5. The spark plug for an internal combustion engine according to claim 3, wherein said central inclined surface is parallel to said ground inclined surface.

6. 6. The spark plug for an internal combustion engine according to claim 1, wherein a tip end of said ground electrode is located closer to a base end than a tip end of said housing.

7. The spark plug has 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 side, a ground electrode (6) that forms a discharge gap (G) between itself and the center electrode, and a plug cover (5) provided at the tip of the housing so as to cover an auxiliary combustion chamber (50) in which the discharge gap is arranged, and a nozzle hole (51) that communicates the auxiliary combustion chamber with the outside is formed in the plug cover, and the ground electrode protrudes into the auxiliary combustion chamber from a fixed end (62) fixed to the housing, and is oriented in the direction of protrusion. a ground inclined surface (611) on a base end side inclined so as to extend toward a tip end as the center electrode approaches the tip end, the discharge gap is formed by opposing a tip end portion of the center electrode and the ground inclined surface of the ground electrode to each other, and is formed on the base end side of the tip of the housing, the housing has a fixing recess (26) recessed by receding a part of an inner wall surface (22) toward an outer side in a plug radial direction, the fixing recess in the housing is open to the tip end side, and the ground electrode is fixed to a recess forming surface (261) that forms the fixing recess, The ground electrode is fixed to the housing, and the length of the discharge gap is adjusted to a desired length. Then, the plug cover is fixed to the front end of the housing. When the ground electrode is fixed to the housing, the fixed end portion is fitted into the fixed recess portion, and then welding is performed. a spark plug cover for connecting the ground electrode to the housing and the housing tip, the spark plug cover being disposed on the ground electrode side of the housing, the ground electrode protruding side of the housing, and the spark plug cover being disposed on the housing tip side of the housing, the ground electrode protruding ... ground electrode protruding side of the ground electrode, the spark plug cover being disposed on the housing tip side of the housing, the ground electrode protruding side of the ground electrode, the ground electrode protruding side of the ground

8. The recess forming surface has two circumferentially opposed surfaces (262) opposed to the ground electrode in the plug circumferential direction, and one radially opposed surface (263) opposed to the ground electrode in the plug radial direction, 8. The method for manufacturing a spark plug for an internal combustion engine according to claim 7, wherein when fixing the ground electrode to the housing, the ground electrode and each of the two circumferentially opposed surfaces are joined to each other, and the ground electrode and each of the radially opposed surfaces are joined to each other.

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