Spark plugs for internal combustion engines

Abstract

To provide a spark plug which can be efficiently manufactured.SOLUTION: In a spark plug 1, a plug cover 5 is fixed to a tip end of a housing 2 such that it covers a sub-combustion chamber 10 in which a discharge gap G is located. At a tip end of the spark plug 1, there is formed an injection hole 7 for bringing the sub-combustion chamber 10 into communication with the outside. The injection hole 7 is formed by the tip end of the housing 2 and an outer circumferential end 51 of the plug cover 5 both surrounding the injection hole. At the tip end of the spark plug 1, there is formed at least one of a housing groove 22 and a cover groove 52. An injection hole formation surface 70 forming the injection hole 7 has at least one of the following: a housing groove formation surface 220 forming the housing groove 22; and a cover groove formation surface 520 forming the cover groove 52.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] For example, as disclosed in Patent Document 1, a spark plug for an internal combustion engine having an auxiliary combustion chamber at its tip is known. In this spark plug, a nozzle hole is formed in a plug cover covering the auxiliary combustion chamber. This allows a flame to be ejected from the auxiliary combustion chamber through the nozzle hole into the main combustion chamber, thereby combusting the air-fuel mixture in the main combustion chamber. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] 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 injection hole is provided so as to penetrate the plug cover, which may make it difficult to form the injection hole. Therefore, from the viewpoint of efficient production of spark plugs, it can be said that there is room for further improvement.

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

[0006] The present invention First The embodiment includes 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 a sub-combustion chamber (10) in which the discharge gap is disposed, A nozzle hole (7) that connects the auxiliary combustion chamber to the outside is formed at the tip of the spark plug, The injection hole is formed by being surrounded by both the tip end portion of the housing and the outer peripheral end portion (51) of the plug cover, At least one of a housing groove (22) formed by part of a front end face (21) of the housing receding toward a base end and a cover groove (52) formed by part of a base end face (510) of the outer circumferential end portion receding toward the front end is formed in the front end of the spark plug, The nozzle hole forming surface (70) forming the nozzle hole has at least one of a housing groove forming surface (220) forming the housing groove and a cover groove forming surface (520) forming the cover groove. death , a tip of the auxiliary combustion chamber and a tip of the central electrode are each located on the tip side of a tip of the insulator, and the discharge gap is formed on the tip side of the tip of the insulator, An outer opening (72) of the injection hole opens to an outer circumferential surface of the tip end of the spark plug. Found in spark plugs for internal combustion engines. The 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 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 a sub-combustion chamber (10) in which the discharge gap is disposed, A nozzle hole (7) that connects the auxiliary combustion chamber to the outside is formed at the tip of the spark plug, The injection hole is formed by being surrounded by both the tip end portion of the housing and the outer peripheral end portion (51) of the plug cover, At least one of a housing groove (22) formed by part of a front end face (21) of the housing receding toward a base end and a cover groove (52) formed by part of a base end face (510) of the outer circumferential end portion receding toward the front end is formed in the front end of the spark plug, a nozzle hole forming surface (70) that forms the nozzle hole has at least one of a housing groove forming surface (220) that forms the housing groove and a cover groove forming surface (520) that forms the cover groove, The tip surface of the housing has a housing side fixing surface (23) inclined with respect to the plug axial direction (Z) so as to move toward the tip side as it moves radially outward, and the base end surface of the outer circumferential end has a cover side fixing surface (53) inclined with respect to the plug axial direction so as to move toward the tip side as it moves radially outward, and the housing side fixing surface and the cover side fixing surface are fixed to each other in this spark plug for an internal combustion engine. Effect of the Invention

[0007] In the above spark plug, the injection hole is formed by being surrounded by both the tip end of the housing and the outer circumferential end of the plug cover. Also, the injection hole forming surface has at least one of the housing groove forming surface and the cover groove forming surface. Therefore, the injection hole can be easily formed. As a result, the spark plug can be efficiently manufactured.

[0008] As described above, according to the above aspect, it is possible to provide a spark plug that can be efficiently manufactured. 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]

[0009] [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 view taken along the arrow II in FIG. [Diagram 3] 3 is a cross-sectional view taken along the line III-III in FIG. 2, showing an enlarged cross-sectional view of the vicinity of a joint between a housing and an outer peripheral end portion. [Figure 4] 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. [Diagram 5] 5 is a view of the tip portion of the housing in the first embodiment as seen from the tip side, taken along the line V in FIG. 4. [Figure 6] 6 is a view of the plug cover in the first embodiment as seen from the base end side, taken along the line VI in FIG. 4. [Figure 7] 4 is a cross-sectional view showing a line segment L1 and a line segment L2 in the first embodiment. FIG. [Figure 8] FIG. 4 is a cross-sectional view showing line segments L3 and L4 in the first embodiment. [Figure 9] 1 is a cross-sectional view of an internal combustion engine in which a spark plug is installed according to a first embodiment. [Figure 10]12 is a cross-sectional view taken along line XX in FIG. 11 , showing a portion near the tip end of a spark plug according to a second embodiment of the present invention. [Figure 11] XI arrow view of FIG. 10 . [Figure 12] 12 is a cross-sectional view taken along line XII-XII in FIG. 13 , showing a portion near the tip end of a spark plug according to a third embodiment, taken along an axial direction of the plug. [Figure 13] FIG. 13 is a view taken along the arrow XIII in FIG. [Figure 14] 14 is a cross-sectional view taken along line XIV-XIV in FIG. 15 , showing a portion near the tip end of the spark plug according to the fourth embodiment, taken along an axial direction of the plug. [Figure 15] 15 is a view taken along the arrow XV in FIG. 14 . [Figure 16] 16 is a cross-sectional view taken along line XVI-XVI in FIG. 15, showing an enlarged cross-sectional view of the vicinity of a joint between a housing and an outer peripheral end portion. [Figure 17] 13 is a cross-sectional view showing a state in which the plug cover is brought into contact with the housing in the fourth embodiment. FIG. [Figure 18] 18 is a view of the tip portion of the housing according to the fourth embodiment as viewed from the tip side, taken along the arrow XVIII in FIG. 17. [Figure 19] 19 is a view of the plug cover in the fourth embodiment as seen from the base end side, taken along the line XIX in FIG. 17. [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 fifth embodiment. [Figure 21] 13 is an enlarged cross-sectional view of the vicinity of a joint between a housing and an outer peripheral end portion in embodiment 5. FIG. [Figure 22] 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. [Diagram 23] 13 is an enlarged cross-sectional view of the vicinity of a joint between a housing and an outer peripheral end portion in a sixth embodiment. [Figure 24] 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 seventh embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] (Embodiment 1) An embodiment of a spark plug for an internal combustion engine will be described with reference to Figs. A spark plug 1 for an internal combustion engine according to this embodiment has a cylindrical insulator 3, a center electrode 4, a cylindrical housing 2, a ground electrode 6, and a plug cover 5, as shown in Fig. 1 and Fig. 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 its inner periphery. The ground electrode 6 forms a discharge gap G between itself and the center electrode 4. The plug cover 5 is fixed to the tip portion of the housing 2 so as to cover the auxiliary combustion chamber 10 in which the discharge gap G is located.

[0011] An injection hole 7 that connects the auxiliary combustion chamber 10 to the outside is formed at the tip of the spark plug 1. The injection hole 7 is surrounded by both the tip of the housing 2 and the outer circumferential end 51 of the plug cover 5.

[0012] At least one of a housing groove 22 and a cover groove 52 is formed in the tip end of the spark plug 1. The housing groove 22 is formed by receding a part of the tip end surface 21 of the housing 2 toward the base end side. The cover groove 52 is formed by receding a part of the base end surface 510 of the outer circumferential end portion 51 toward the tip end side.

[0013] The nozzle hole forming surface 70 that forms the nozzle hole 7 has at least one of a housing groove forming surface 220 that forms the housing groove 22 and a cover groove forming surface 520 that forms the cover groove 52 .

[0014] The spark plug 1 of this embodiment can be used, for example, as an ignition means in an internal combustion engine of an automobile, etc. As shown in Fig. 9, the threaded portion 24 of the housing 2 is screwed into a female threaded portion of a plug hole 811 of a cylinder head 81, so that the spark plug 1 is attached to the internal combustion engine 8. The housing 2 is in thermal contact with the cylinder head 81.

[0015] The internal combustion engine 8 is equipped with a piston 84 that reciprocates in a cylinder 85. The volume of the main combustion chamber 80 changes due to the reciprocating motion of the piston 84. The internal combustion engine 8 is formed with an intake port 821 and an exhaust port 831, each of which is equipped with an intake valve 82 and an exhaust valve 83. In addition, a base end surface 801 of the main combustion chamber 80 is inclined so that the further away from the spark plug 1 it is, the closer it is to the piston 84.

[0016] One end of the spark plug 1 in the axial direction Z is disposed in the main combustion chamber 80 of the internal combustion engine 8. In the axial direction Z of the spark plug 1, the side exposed to the main combustion chamber 80 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. The plug radial direction refers to the radial direction of a circle centered on the plug central axis PC on a plane perpendicular to the plug central axis PC. The plug circumferential direction refers to the direction along the circumference centered on the plug central axis PC. In this embodiment, the plug central axis PC is also the central axis of the center electrode 4.

[0017] In this embodiment, the outer periphery of the auxiliary combustion chamber 10 is covered by a housing 2 as shown in Fig. 1. The tip of the auxiliary combustion chamber 10 is covered by a plug cover 5. When the spark plug 1 is installed in an internal combustion engine 8, the nozzle hole 7 connects the auxiliary combustion chamber 10 and the main combustion chamber 80.

[0018] 2, four injection holes 7 are formed in the tip portion of the spark plug 1. When viewed from the Z direction, the injection holes 7 are formed at equal intervals in the circumferential direction of the plug.

[0019] 1, the nozzle hole 7 opens at an incline with respect to the Z direction so that the more it moves outward in the plug radial direction, the more it moves toward the tip side. That is, the nozzle hole axis 7L of the nozzle hole 7 is inclined with respect to the Z direction. Also, as shown in FIG. 2, when viewed from the Z direction, the nozzle hole 7 is formed so that the nozzle hole axis 7L is along the plug radial direction.

[0020] As shown in FIG. 9, in a cross section that includes the nozzle hole axis 7L and is along both the Z direction and the arrangement direction of the intake valve 82 and the exhaust valve 83, the inclination angle α1 of the nozzle hole axis 7L with respect to the Z direction is less than or equal to the inclination angle α2 of the base end surface 801 of the main combustion chamber 80 with respect to the Z direction.

[0021] 1, the nozzle hole 7 is surrounded by both the housing groove forming surface 220 and the cover groove forming surface 520. In other words, the nozzle hole forming surface 70 that forms the nozzle hole 7 has both the housing groove forming surface 220 and the cover groove forming surface 520.

[0022] The plug cover 5 is joined to the front end of the housing 2 by welding or the like. In this embodiment, the plug cover 5 is made of nickel or an alloy mainly composed of nickel, which has a higher thermal conductivity than low carbon steel etc. The plug cover 5 is in thermal contact with the front end of the housing 2.

[0023] 1, 2, 4 and 6, the plug cover 5 is plate-shaped. More specifically, the plug cover 5 is substantially disk-shaped.

[0024] In this embodiment, four cover grooves 52 are formed in the outer circumferential end portion 51 of the plug cover 5. The cover grooves 52 are formed so that the width in the Z direction increases toward the outside in the plug radial direction.

[0025] The tip of the housing 2 has a substantially cylindrical shape. As shown in Fig. 5, four housing grooves 22 are formed in the tip of the housing 2. As shown in Figs. 1 and 4, the housing grooves 22 are formed so that the width in the Z direction decreases toward the outside in the plug radial direction. The housing 2 is made of a metal such as low carbon steel or stainless steel. In this embodiment, the housing 2 is made of low carbon steel.

[0026] At least one of the housing groove forming surface 220 and the cover groove forming surface 520 is formed extending from the inner opening 71 to the outer opening 72 of the nozzle hole 7. In this embodiment, the housing groove forming surface 220 is formed extending from the inner opening 71 to the outer opening 72 as shown in Fig. 1. In other words, the housing groove 22 is formed extending from the inner opening 71 to the outer opening 72 of the nozzle hole 7. The housing groove 22 is formed extending from the inner circumferential surface to the outer circumferential surface of the housing 2.

[0027] In this embodiment, the housing groove 22 and the cover groove 52 are formed by performing cutting on the tip end portion or the outer circumferential end portion 51 of the housing 2, respectively.

[0028] 7, in a cross section including the nozzle hole axis 7L and along the Z direction, the housing groove forming surface 220 and the cover groove forming surface 520 are each inclined with respect to the Z direction so as to move toward the tip side as they move toward the outside in the plug radial direction. Also, in a cross section including the nozzle hole axis 7L and along the Z direction, the housing groove forming surface 220 and the cover groove forming surface 520 are substantially parallel to each other. That is, in a cross section including the nozzle hole axis 7L and along the Z direction, the housing groove forming surface 220 and the cover groove forming surface 520 are each substantially parallel to the nozzle hole axis 7L.

[0029] In this embodiment, the ground electrode 6 protrudes from a fixed end 61 fixed to the housing 2 toward the plug central axis PC. A base end surface 62 of the ground electrode 6 is inclined toward the tip side as it approaches the plug central axis PC. The base end surface 62 of the ground electrode 6 is a flat surface.

[0030] 2, the ground electrode 6 is provided so as to extend along the plug radial direction when viewed from the Z direction. Furthermore, one injection hole 7 is formed on the protruding side of the ground electrode 6. Hereinafter, the injection hole 7 formed on the protruding side of the ground electrode 6 will be referred to as the protruding-side injection hole 73.

[0031] 1, the discharge gap G is formed by the front end surface 41 of the center electrode 4 and the base end surface 62 of the ground electrode 6 facing each other. The discharge gap G is, for example, a region obtained by projecting the front end surface 41 of the center electrode 4 in the Z direction and a region obtained by projecting the front end surface 41 in a direction perpendicular to the base end surface 62 of the ground electrode 6, and is the region between the front end surface 41 and the base end surface 62.

[0032] 7, in a cross section including the plug center axis PC and along the protruding direction of the ground electrode 6, a point on the base end surface 62 of the ground electrode 6 that is closest to the center electrode 4 is designated as point A, and a point on the center electrode 4 that is closest to the base end surface 62 is designated as point B. In addition, in a cross section including the plug center axis PC and along the protruding direction of the ground electrode 6, a point on the housing groove forming surface 220 that forms the protrusion-side injection hole 73 and that is the most distal point is designated as point C.

[0033] Moreover, the line segment connecting point A and point C is defined as line segment L1, and the line segment connecting point B and point C is defined as line segment L2. In this case, line segment L1 and line segment L2 do not pass through any of the ground electrode 6, the center electrode 4, and the housing 2, respectively.

[0034] Next, a method for manufacturing the spark plug 1 of this embodiment will be described. First, a method for adjusting the discharge gap G will be described. In this embodiment, before the plug cover 5 is fixed to the housing 2 in which the insulator 3 and the center electrode 4 are assembled, the ground electrode 6 is fixed to the housing 2 and the length of the discharge gap G is adjusted to a desired length. Specifically, before the plug cover 5 is fixed to the housing 2, the ground electrode 6 is joined to the housing 2 by welding. Then, after checking 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.

[0035] As shown in Fig. 8, in the spark plug 1 of this embodiment, before the plug cover 5 is fixed to the housing 2, both points A and B can be directly seen when viewed from the protruding side of the ground electrode 6 and from the outside of the spark plug 1. In other words, when the spark plug 1 before the plug cover 5 is provided is viewed from, for example, the position of point D in Fig. 8, both points A and B can be directly seen. Note that point D is a point on the protruding side of the ground electrode 6 and outside the spark plug 1.

[0036] Furthermore, in this embodiment, before the plug cover 5 is fixed to the housing 2, the entire discharge gap G can be directly seen from the protruding side of the ground electrode 6 and from the outside of the spark plug 1.

[0037] 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 D is defined as line segment L3. Also, a line segment connecting points B and D is defined as line segment L4. In this case, line segments L3 and L4 do not pass through the ground electrode 6, the center electrode 4, or the housing 2, respectively.

[0038] Next, the fixing of the plug cover 5 to the housing 2 after the discharge gap G is adjusted will be described. In this embodiment, as shown in FIG. 3, the tip end surface 21 of the housing 2 and the base end surface 510 of the outer circumferential end 51 are brought into contact with each other, and then the housing 2 and the outer circumferential end 51 are joined to each other by welding. Specifically, the plug cover 5 is moved toward the tip of the housing 2 as shown by the arrow M in FIG. 4, and the base end surface 510 of the outer circumferential end 51 and the tip end surface 21 of the housing 2 are brought into contact with each other in the Z direction. Also, at this time, the plug cover 5 and the housing 2 are brought into contact with each other so that the cover groove portion 52 and the housing groove portion 22 overlap each other as viewed from the Z direction. Next, the abutting portion where the tip end surface 21 of the housing 2 and the base end surface 510 of the outer circumferential end 51 are brought into contact with each other is welded by laser welding. As a result, the spark plug 1 of this embodiment can be obtained, in which the injection hole forming surface 70 has both the cover groove forming surface 520 and the housing groove forming surface 220. 4 may be oriented vertically downward. In this case, the housing 2 and the plug cover 5 may be arranged so that the plug cover 5 can be placed on the tip of the housing 2 when the base end surface 510 of the outer circumferential end portion 51 and the tip surface 21 of the housing 2 are brought into contact with each other.

[0039] Next, the effects of this embodiment will be described. In the above spark plug 1, the injection hole 7 is formed by being surrounded by both the tip end portion of the housing 2 and the outer peripheral end portion 51 of the plug cover 5. The injection hole forming surface 70 has at least one of the housing groove forming surface 220 and the cover groove forming surface 520. This makes it possible to easily form the injection hole 7. As a result, the spark plug 1 can be efficiently manufactured.

[0040] In this embodiment, the nozzle hole 7 opens at an incline with respect to the Z direction so that the further outward in the plug radial direction the closer to the tip side. Therefore, it is possible to prevent the flame jet ejected into the main combustion chamber 80 through the nozzle hole 7 from colliding with the base end surface 801 of the main combustion chamber 80 and the piston 84. Therefore, it is possible to prevent the flame jet from being cooled. In addition, it is possible to eject the flame jet so as to reach the end of the main combustion chamber 80. As a result, it is possible to improve the ignition performance in the main combustion chamber 80.

[0041] The spark plug 1 of this embodiment ignites the mixture in the auxiliary combustion chamber 10 and forms a flame by generating a discharge in the discharge gap G. The flame generated in the auxiliary combustion chamber 10 is then ejected as a flame jet into the main combustion chamber 80 through the nozzle hole 7. This causes the flame to propagate to the main combustion chamber 80 and combust the mixture. Here, in the spark plug 1 of this embodiment, the opening direction of the nozzle hole 7 is inclined with respect to the Z direction as described above.

[0042] Consider a case where a nozzle hole is formed in a bottomed cylindrical, i.e., cup-shaped plug cover with an opening direction inclined with respect to the Z direction. In this case, since the outer surface of the plug cover is a convex curved surface protruding outward, when cutting with a drill or pressing with a punch, the tip of the drill or punch is likely to slip, making it difficult to form the nozzle hole. Furthermore, when the plug cover is made of a metal with high hardness such as nickel, it is even more difficult to form the nozzle hole. Also, when the nozzle hole is opened by laser processing, electric discharge processing, or the like, the number of processing steps increases, and productivity is likely to decrease. Therefore, in the spark plug 1 of this embodiment, the nozzle hole 7 is formed so that the nozzle hole forming surface 70 has at least one of the housing groove forming surface 220 and the cover groove forming surface 520. Therefore, the nozzle hole 7 can be easily formed. In other words, compared to the case where the nozzle hole is opened so as to penetrate the plug cover, the groove portion can be easily formed in the tip portion and the outer circumferential end portion 51 of the housing 2 by cutting processing or the like. Then, by forming at least one of the housing groove 22 and the cover groove 52 and joining the front end portion and the outer circumferential end portion 51 of the housing 2 to each other, the injection hole 7 can be easily formed. As a result, the spark plug 1 can be efficiently manufactured.

[0043] In addition, the plug cover 5 is plate-shaped. Therefore, the plug cover 5 can be manufactured efficiently. As a result, the spark plug 1 can be manufactured more efficiently.

[0044] Let us assume that the plug cover has a cup shape. In this case, bending, drawing, and the like are required to form the plug cover from a plate-shaped member. On the other hand, in this embodiment, the plug cover 5 is plate-shaped. Therefore, the plug cover 5 can be easily manufactured from a plate-shaped member without bending or drawing. As a result, the spark plug 1 can be manufactured more efficiently.

[0045] In particular, nickel or an alloy mainly composed of nickel has a higher hardness than low carbon steel and the like, and is therefore difficult to bend, draw, or otherwise process. Therefore, when the plug cover 5 is made of nickel or an alloy mainly composed of nickel as in this embodiment, the productivity can be further improved by forming the plug cover 5 in a plate shape. As a result, the spark plug 1 can be manufactured more efficiently. Nickel is a metal that has a higher thermal conductivity and is good at dissipating heat than low carbon steel and the like.

[0046] Furthermore, by forming the plug cover 5 in a plate shape, it is possible to reduce the amount of nickel used in the entire spark plug 1. This makes it possible to conserve resources.

[0047] In addition, since the plug cover 5 is made of nickel or an alloy mainly composed of nickel, which has a higher thermal conductivity than low carbon steel and the like, the heat received by the combustion of the air-fuel mixture can be easily dissipated to the outside via the housing 2. This makes it possible to prevent the plug cover 5 from overheating, and as a result, it is possible to prevent pre-ignition.

[0048] At least one of the housing groove forming surface 220 and the cover groove forming surface 520 is formed across the nozzle hole 7 from the inner opening 71 to the outer opening 72. This makes it possible to form the nozzle hole 7 more easily. As a result, the spark plug 1 can be manufactured more efficiently.

[0049] In the spark plug 1 of this embodiment, before the plug cover 5 is provided, both points A and B (see FIG. 8) can be directly seen from the protruding side of the ground electrode 6 and from the outside of the spark plug 1. This makes it easy to adjust the discharge gap G while checking its length. This makes it easy to form the discharge gap G with a desired length. As a result, the spark plug 1 can be efficiently manufactured.

[0050] The spark plug 1 also has a protruding-side nozzle hole 73. The line segments L1 and L2 (see FIG. 7) do not pass through the ground electrode 6, the center electrode 4, or the housing 2, respectively. Therefore, when viewed from the protruding side of the ground electrode 6, both points A and B can be directly seen through the housing groove portion 22. This makes it easy to adjust the discharge gap G. As a result, the spark plug 1 can be manufactured efficiently.

[0051] As described above, according to the present embodiment, it is possible to provide the spark plug 1 that can be efficiently manufactured.

[0052] (Embodiment 2) As shown in Figs. 10 and 11, this embodiment is an embodiment in which the position where the discharge gap G is formed is changed from that of the first embodiment.

[0053] In this embodiment, the ground electrode 6 protrudes toward the tip end of the center electrode 4 as shown in Figures 10 and 11. The ground electrode 6 is provided along the plug radial direction.

[0054] The discharge gap G is formed by an end face 63 on the protruding side of the ground electrode 6 and an outer circumferential surface of the tip portion of the center electrode 4 facing each other in the plug radial direction. 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.

[0055] This embodiment also has the same effects as the first embodiment.

[0056] (Embodiment 3) In this embodiment, as shown in Figs. 12 and 13, a side surface 64 of the ground electrode 6 and an outer circumferential surface of the tip portion of the center electrode 4 face each other in the plug radial direction, thereby forming a discharge gap G.

[0057] 12 and 13, the ground electrode 6 protrudes into the auxiliary combustion chamber 10 so as to be perpendicular to the Z direction. A side surface 64 of the ground electrode 6 forming the discharge gap G is formed in a flat shape. The normal direction of the side surface 64 is substantially perpendicular to the protruding direction of the ground electrode 6. The other configurations and effects are the same as those of the second embodiment.

[0058] (Embodiment 4) As shown in Figs. 14 to 19, this embodiment is an embodiment in which the shapes of the tip end portion and the outer circumferential end portion 51 of the housing 2 are changed from those of the first embodiment.

[0059] 16 and 17, the tip end surface 21 of the housing 2 has a housing side fixing surface 23 inclined with respect to the plug axial direction Z so as to approach the tip side as it moves outward in the plug radial direction. In addition, the base end surface 510 of the outer circumferential end portion 51 has a cover side fixing surface 53 inclined with respect to the plug axial direction Z so as to approach the tip side as it moves outward in the plug radial direction. The housing side fixing surface 23 and the cover side fixing surface 53 are fixed to each other.

[0060] In this embodiment, the entire tip end surface 21 of the housing 2 serves as the housing side fixing surface 23. In addition, four housing side fixing surfaces 23 are formed as shown in Fig. 18. When viewed from the Z direction, each housing groove portion 22 is formed so as to be sandwiched between the housing side fixing surfaces 23 in the plug circumferential direction.

[0061] In this embodiment, no cover groove portion is formed in the plug cover 5 as shown in Fig. 19. The shape of the plug cover 5 is substantially symmetrical about an axis. That is, different cross sections including the central axis of the plug cover 5 have the same shapes.

[0062] 16, the cover-side fixing surface 53 is inclined with respect to the Z direction so as to be aligned with the housing-side fixing surface 23. As shown in FIG. The rest is the same as in the first embodiment.

[0063] The tip surface 21 of the housing 2 has a housing side fixing surface 23. The base end surface 510 of the outer circumferential end portion 51 has a cover side fixing surface 53. The housing side fixing surface 23 and the cover side fixing surface 53 are fixed to each other. Therefore, when fixing the plug cover 5 to the housing 2, it is easy to determine the position of the plug cover 5 relative to the housing 2 in the plug radial direction. As a result, the spark plug 1 can be manufactured more efficiently.

[0064] Moreover, the shape of the plug cover 5 is substantially symmetrical about the axis. Therefore, the plug cover 5 can be easily manufactured. Furthermore, the plug cover 5 can be fixed to the housing 2 without having to determine the position of the plug cover 5 relative to the housing 2 in the plug circumferential direction. As a result, the spark plug 1 can be manufactured even more efficiently.

[0065] The cover side fixing surface 53 is inclined with respect to the Z direction so as to follow the housing side fixing surface 23. Therefore, when the plug cover 5 is moved toward the tip end of the housing 2 as shown by the arrow M in Fig. 17 and brought into contact with the housing 2, the contact area between the cover side fixing surface 53 and the housing side fixing surface 23 can be made large. This can reliably increase the strength of the joint between the housing 2 and the plug cover 5. As a result, a spark plug 1 having high strength can be manufactured. In addition, the same effects as those of the first embodiment are achieved.

[0066] (Embodiment 5) As shown in Figs. 20 and 21, this embodiment is an embodiment in which the ratio of the thickness of the tip portion of the housing 2 to the thickness of the plug cover 5 is changed from that of the fourth embodiment.

[0067] In this embodiment, as shown in Fig. 21, the thickness D1 of the tip portion of the housing 2 is thicker than the thickness D2 of the plug cover 5. More specifically, the thickness D1 is 1.5 times or more the thickness D2. In this embodiment, the thickness D1 is the thickness in the plug radial direction of a part of the housing 2 located on the tip side of the threaded portion 24. Moreover, the thickness D2 is the thickness of the plug cover 5 in the Z direction.

[0068] In addition, in a cross section including the plug center axis PC, the length D3 of the joint between the housing side fixing surface 23 and the cover side fixing surface 53 is longer than the thickness D2. More specifically, the length D3 is 1.5 times or more the thickness D2. In this embodiment, the joint between the housing side fixing surface 23 and the cover side fixing surface 53 is performed by laser welding. The rest is the same as in the fourth embodiment.

[0069] The thickness D1 is 1.5 times or more the thickness D2. Furthermore, the length D3 is 1.5 times or more the thickness D2. Therefore, the heat of the plug cover 5 is easily transferred to the housing 2 via the joint between the housing side fixing surface 23 and the cover side fixing surface 53. Therefore, the heat of the plug cover 5 is easily dissipated to the outside via the housing 2. As a result, overheating of the plug cover 5 can be suppressed.

[0070] In this embodiment, the plug cover 5 is made of nickel or an alloy mainly composed of nickel. The housing 2 is made of low carbon steel. Therefore, the thermal conductivity of the plug cover 5 is approximately 1.5 times that of the housing 2. Therefore, if the thicknesses D1 and D2 are equal to each other, there is a risk that the transfer of heat from the plug cover 5 to the housing 2 will not be performed efficiently. Therefore, in this embodiment, the thickness D1 is set to be 1.5 times or more the thickness D2. Therefore, the heat of the plug cover 5 is easily transferred to the housing 2. As a result, the heat of the plug cover 5 is easily dissipated to the outside via the housing 2.

[0071] Furthermore, even if the thickness D1 is 1.5 times or more the thickness D2, if the length D3 is not sufficiently secured, there is a risk that heat will not be transferred efficiently through the joint between the housing side fixing surface 23 and the cover side fixing surface 53. Therefore, in this embodiment, the length D3 is set to be 1.5 times or more the thickness D2. Therefore, the heat of the plug cover 5 is easily transferred to the housing 2. As a result, the heat of the plug cover 5 is easily dissipated to the outside through the housing 2. In addition, the same effects as those of the fourth embodiment are achieved.

[0072] (Embodiment 6) In this embodiment, as shown in Figs. 22 and 23, the tip of the housing 2 is formed in a stepped shape.

[0073] 23, the front end of the housing 2 has an inclined portion 25 formed so that the thickness in the plug radial direction decreases toward the front end, and a protruding portion 26 protruding toward the front end from the front end of the inclined portion 25. The front end of the housing 2 has a stepped shape due to the formation of the inclined portion 25 and the protruding portion 26.

[0074] In this embodiment, the plug cover 5 is fixed to the housing 2 by first placing the plug cover 5 on the stepped front end of the housing 2 so that the outer circumferential end 51 fits therein, and then welding is performed. When the plug cover 5 is brought into contact with the front end of the housing 2, the inclined portion 25 and the convex portion 26 each come into contact with the outer circumferential end 51.

[0075] Further, the inclined portion 25 has a housing side fixing surface 23. That is, the cover side fixing surface 53 of the outer peripheral end portion 51 is joined to the inclined portion 25. Further, the outer peripheral surface of the outer peripheral end portion 51 is joined to the inner peripheral surface of the protrusion portion 26. The rest is the same as in the fourth embodiment.

[0076] In this embodiment, the tip end of the housing 2 has an inclined portion 25 and a convex portion 26. Therefore, when the plug cover 5 is fixed to the housing 2, the plug cover 5 can be easily disposed at a desired position relative to the housing 2. As a result, the spark plug 1 can be efficiently manufactured. In addition, the same effects as those of the fourth embodiment are achieved.

[0077] (Embodiment 7) In this embodiment, as shown in FIG. 24, the tip portion of the housing 2 is tapered.

[0078] In this embodiment, the tip end of the housing 2 has a tapered section 27 formed so as to decrease in diameter toward the tip end as shown in Fig. 24. The tapered section 27 extends inward in the plug radial direction as it approaches the tip end. Also, due to the tapered section 27 being formed, the tip end of the auxiliary combustion chamber 10 decreases in diameter so that the width in the plug radial direction decreases toward the tip end.

[0079] In a cross section including the nozzle hole axis 7L and along the Z direction, the nozzle hole 7 is formed so that the nozzle hole axis 7L is substantially perpendicular to the extension direction of the tapered portion 27. In other words, in a cross section including the nozzle hole axis 7L and along the Z direction, the nozzle hole axis 7L is substantially perpendicular to the inner circumferential surface of the tapered portion 27. The rest is the same as in the fourth embodiment.

[0080] In a cross section including the nozzle hole axis 7L and along the Z direction, the nozzle hole 7 is formed so that the nozzle hole axis 7L is substantially perpendicular to the extension direction of the tapered portion 27. Therefore, the length of the nozzle hole 7 in the opening direction can be shortened. Therefore, the area of ​​the nozzle hole forming surface 70 can be reduced. Therefore, the amount of heat received by the nozzle hole forming surface 70 by the flame ejected from the auxiliary combustion chamber 10 to the main combustion chamber through the nozzle hole 7 can be reduced. Therefore, it is possible to prevent the nozzle hole forming surface 70 and the area nearby from becoming hot. As a result, pre-ignition can be suppressed.

[0081] In addition, in a cross section including the nozzle hole axis 7L and along the Z direction, the nozzle hole axis 7L is substantially perpendicular to the inner peripheral surface of the tapered portion 27. Here, the internal pressure of the auxiliary combustion chamber 10 generated when the mixture in the auxiliary combustion chamber 10 is burned tends to be applied in the normal direction of the inner wall surface 101 of the auxiliary combustion chamber 10. Therefore, the opening direction of the nozzle hole 7 tends to be a direction along the direction in which the internal pressure of the auxiliary combustion chamber 10 is applied. Therefore, a flame can be forcefully ejected into the main combustion chamber through the nozzle hole 7. As a result, the ignition ability in the main combustion chamber can be improved. In addition, the same effects as those of the fourth embodiment are achieved.

[0082] In the above-mentioned embodiments 1 to 7, four injection holes 7 are formed in the tip portion of the spark plug 1. However, five or more injection holes may be formed in the tip portion of the spark plug. Also, the number of injection holes may be three or less.

[0083] In the above-mentioned embodiments 1 to 7, the cross section of the nozzle hole 7 perpendicular to the nozzle hole axis 7L is substantially rectangular. However, the housing groove and the cover groove can be formed so that the cross section of the nozzle hole perpendicular to the nozzle hole axis is, for example, circular, elliptical, semicircular, or a polygonal shape other than a rectangle.

[0084] In the above-mentioned embodiments 1 to 7, when viewed from the Z direction, some of the nozzle holes 7 are formed so that the nozzle hole axis 7L is aligned with the protruding direction of the ground electrode 6. However, for example, when viewed from the Z direction, the nozzle holes may be formed so that the nozzle hole axes of all the nozzle holes are inclined with respect to the protruding direction of the ground electrode.

[0085] In the above embodiments 1 to 7, the nozzle hole 7 is formed so that the nozzle hole axis 7L is along the plug radial direction when viewed from the Z direction. However, the nozzle hole can also be formed so that the nozzle hole axis is inclined with respect to a virtual line (not shown) that passes through the nozzle hole and the plug central axis and extends in the plug radial direction when viewed from the Z direction. In other words, the nozzle 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 nozzle hole.

[0086] 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.

[0087] The nozzle hole may also be formed so that the area of ​​the cross section perpendicular to the nozzle hole axis decreases from the inner opening to the outer opening of the nozzle hole, for example. In this case, the ejection speed of the flame jet can be improved.

[0088] 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]

[0089] Reference Signs List 1...spark plug, 10...auxiliary combustion chamber, 2...housing, 21...tip surface, 22...housing groove, 220...housing groove forming surface, 3...insulator, 4...center electrode, 5...plug cover, 51...outer periphery end, 510...base end surface, 52...cover groove, 520...cover groove forming surface, 6...ground electrode, 7...nozzle hole, 70...nozzle hole forming surface, G...discharge gap

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 a tip end portion of the housing so as to cover a sub-combustion chamber (10) in which the discharge gap is disposed, A nozzle hole (7) that connects the auxiliary combustion chamber to the outside is formed at the tip of the spark plug, The injection hole is formed by being surrounded by both the tip end of the housing and the outer peripheral end (51) of the plug cover, At least one of a housing groove (22) formed by a part of a tip end surface (21) of the housing receding toward a base end side and a cover groove (52) formed by a part of a base end surface (510) of the outer circumferential end portion receding toward a tip end side is formed in the tip end portion of the spark plug, a nozzle hole forming surface (70) that forms the nozzle hole has at least one of a housing groove forming surface (220) that forms the housing groove and a cover groove forming surface (520) that forms the cover groove, a tip of the auxiliary combustion chamber and a tip of the central electrode are each located on the tip side of a tip of the insulator, and the discharge gap is formed on the tip side of the tip of the insulator, A spark plug for an internal combustion engine, wherein an outer opening (72) of the nozzle hole opens onto an outer circumferential surface of a tip portion of the spark plug.

2. 2. A spark plug for an internal combustion engine according to claim 1, wherein the tip surface of the housing has a housing side fixing surface (23) inclined with respect to the plug axial direction (Z) so as to move toward the tip side as it moves outward in the plug radial direction, and the base end surface of the outer circumferential end portion has a cover side fixing surface (53) inclined with respect to the plug axial direction so as to move toward the tip side as it moves outward in the plug radial direction, and the housing side fixing surface and the cover side fixing surface are fixed to each other.

3. 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 a sub-combustion chamber (10) in which the discharge gap is disposed, A nozzle hole (7) that connects the auxiliary combustion chamber to the outside is formed at the tip of the spark plug, The injection hole is formed by being surrounded by both the tip end of the housing and the outer peripheral end (51) of the plug cover, At least one of a housing groove (22) formed by a part of a tip end surface (21) of the housing receding toward a base end side and a cover groove (52) formed by a part of a base end surface (510) of the outer circumferential end portion receding toward a tip end side is formed in the tip end portion of the spark plug, a nozzle hole forming surface (70) that forms the nozzle hole has at least one of a housing groove forming surface (220) that forms the housing groove and a cover groove forming surface (520) that forms the cover groove, a plug having a housing side fixed surface (23) inclined with respect to the plug axial direction (Z) so as to extend toward the tip side as it extends outward in the plug radial direction, and a base end surface of the outer circumferential end portion has a cover side fixed surface (53) inclined with respect to the plug axial direction so as to extend toward the tip side as it extends outward in the plug radial direction, and the housing side fixed surface and the cover side fixed surface are fixed to each other.

4. 4. The spark plug for an internal combustion engine according to claim 1, wherein the plug cover is plate-shaped.

Images