Method for manufacturing spark plug for internal combustion engine

Abstract

To provide a spark plug for an internal combustion engine that can improve productivity, and a manufacturing method for the same, as well as the internal combustion engine.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. In the plug cover 5, an injection hole 51 for communicating between the sub-combustion chamber 50 and the outside is formed. The ground electrode 6 is fixed to an inner wall surface 21 of the housing 2. The ground electrode 6 protrudes into the sub-combustion chamber 50 from a fixed end part 62 fixed to the inner wall surface 21. The discharge gap G is formed by an end part of a center electrode 4 and a base end surface 61 of the ground electrode 6 facing each other in a plug axis direction Z. In addition, the discharge gap G is formed on the base end side relative to the end of the housing 2.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a spark plug for an internal combustion engine. Gu's Manufacturing method By law Regarding. [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, a through hole is provided in the housing that penetrates in the plug radial direction, and the ground electrode is inserted into the through hole. Meanwhile, the discharge gap is formed by the center electrode and the ground electrode facing each other in the plug axial direction. Therefore, it is difficult to adjust the discharge gap to a desired length. This tends to result in low productivity.

[0005] The present invention has been made in view of the above problems, and provides a spark plug for an internal combustion engine that can improve productivity. Gu's Manufacturing method Law It is what we intend to provide. [Means for solving the problem]

[0007] The present invention One aspect teeth , insideSpark plugs for combustion engines (1) A method for producing The above spark plugs are 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 is fixed to an inner wall surface (21) of the housing and protrudes into the auxiliary combustion chamber from a fixed end (62) fixed to the inner wall surface, the discharge gap is formed by a front end portion of the center electrode and a base end surface (61) of the ground electrode facing each other in the plug axial direction (Z), and is formed on the base end side of the front end of the housing, When the ground electrode is fixed to the housing before the plug cover and the ground electrode are fixed, A protruding end (63) of the ground electrode opposite to the fixed end is held by an assembly jig (14), and the fixed end of the ground electrode is abutted against the inner wall surface of the housing and welded to the inner wall surface of the housing; The assembly jig has a base end side support portion (141) and a tip end side support portion (142) that sandwich the ground electrode from the base end side and the tip end side, In the method for manufacturing a spark plug for an internal combustion engine, when the fixed end is welded to the inner wall surface, the base end surface (143) of the base end support portion is brought into contact with the tip of the center electrode. Effect of the Invention

[0009] In the above spark plug, the ground electrode is fixed to the inner wall surface of the housing. This makes it easy to adjust the position of the ground electrode relative to the housing. This makes it easy to adjust the discharge gap, thereby improving the productivity of the spark plug.

[0010] In the method for manufacturing the spark plug, the ground electrode is fixed to the inner wall surface of the housing using the assembly jig. Therefore, a discharge gap having a desired length can be easily formed. As a result, the spark plug can be efficiently manufactured.

[0011] As described above, according to the above aspect, a spark plug for an internal combustion engine capable of improving productivity is provided. Gu's Manufacturing method Law can be provided. 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]

[0012] [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] 1 is a cross-sectional view of an internal combustion engine according to a first embodiment. [Figure 4] FIG. 2 is a diagram showing the internal combustion engine according to the first embodiment, as viewed from the front end side. [Diagram 5] 1 is a diagram showing a spark plug installed in an internal combustion engine according to a first embodiment, as viewed from the tip side. [Figure 6] FIG. 4 is a cross-sectional explanatory view illustrating the relationship between an extension region, which is an extension of the nozzle hole in the opening direction, and the discharge gap in the first embodiment. [Figure 7] 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. [Figure 8] 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 9] 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 10] 4 is a cross-sectional view of the vicinity of the tip of the spark plug in the first embodiment during the compression stroke and before the discharge extends. [Figure 11] 4 is a cross-sectional view of the vicinity of the tip of the spark plug when the discharge is extended during the compression stroke in the first embodiment. FIG. [Figure 12]12 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 second embodiment, and corresponds to a cross-sectional view taken along line XII-XII in FIG. [Figure 13] FIG. 13 is a cross-sectional view taken along line XIII-XIII in FIG. [Figure 14] FIG. 11 is a cross-sectional view of the tip portion of a spark plug according to a third embodiment, taken along a line perpendicular to the axial direction of the plug, as viewed from the tip side. [Figure 15] FIG. 11 is a view of the ground electrode according to the third embodiment, as viewed from the protruding side of the ground electrode. [Figure 16] 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 17] FIG. 11 is a view of the ground electrode according to the fourth embodiment, as viewed from the protruding side of the ground electrode. [Figure 18] FIG. 13 is a cross-sectional view of the tip portion of a spark plug according to a fifth embodiment, taken along a line perpendicular to the axial direction of the plug, as viewed from the tip side. [Figure 19] 21 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, and corresponds to a cross-sectional view taken along the line XIX-XIX in FIG. 20. [Figure 20] FIG. 20 is a cross-sectional view taken along line XX-XX in FIG. 19. [Figure 21] 13 is a cross-sectional view of the tip portion of a spark plug according to a seventh embodiment, taken along a line perpendicular to the axial direction of the plug, as viewed from the base end side. FIG. [Figure 22] 13 is a cross-sectional view of the tip portion of a spark plug according to an eighth embodiment, taken along a line perpendicular to the axial direction of the plug, as viewed from the base end side. FIG. [Figure 23] FIG. 13 is a cross-sectional view taken along the plug axis direction of a spark plug installed in an internal combustion engine according to a ninth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] (Embodiment 1) A spark plug for an internal combustion engine, a manufacturing method thereof, and an internal combustion engine according to embodiments will be described with reference to FIGS. 1 to 11. FIG. 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.

[0014] The ground electrode 6 is fixed to the inner wall surface 21 of the housing 2. The ground electrode 6 protrudes into the auxiliary combustion chamber 50 from a fixed end 62 fixed to the inner wall surface 21. A discharge gap G is formed by the tip end of the center electrode 4 and a base end surface 61 of the ground electrode 6 facing each other in the plug axial direction Z. The discharge gap G is formed on the base end side relative to the tip of the housing 2, as shown in FIG.

[0015] 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 the internal combustion engine 10 by screwing a threaded portion 23 formed on the outer circumferential surface of the housing 2 into a female threaded portion of a plug hole 171 of a cylinder head 17, as shown in FIG.

[0016] One end of the spark plug 1 in the axial direction Z is disposed in the main combustion chamber 11 of the internal combustion engine 10. In the axial direction Z of the spark plug 1, the side exposed to the main combustion chamber 11 is referred to as the tip side, and the opposite side is referred to as the base side. The axial direction Z of the spark plug 1 is also referred to as the plug axial direction Z or simply as the Z direction, as appropriate. The plug central axis C means the central axis C of the spark plug 1. In this embodiment, the plug central axis C also means the central axis of the central electrode 4 and the central axis of the main combustion chamber 11. The plug radial direction means the radial direction of a circle centered on the central axis C of the spark plug 1 on a plane perpendicular to the central axis C of the spark plug 1.

[0017] In this embodiment, the plug cover 5 is joined by welding or the like to the tip end of the housing 2. As shown in Figures 6, 10 and 11, 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 11.

[0018] 10 and 11, the auxiliary combustion chamber 50 includes a space on the inner circumferential side of the tip portion of the housing 2 around the center electrode 4 protruding from the insulator 3 toward the tip side. The auxiliary combustion chamber 50 also includes a pocket portion 501, which is an annular space formed between the outer circumferential surface of the insulator 3 and the inner wall surface 21 of the housing 2.

[0019] The injection hole 51 formed in the plug cover 5 connects the auxiliary combustion chamber 50 and the main combustion chamber 11. In this embodiment, the injection hole 51 is formed such that an extension line 51L of the central axis of the injection hole 51 is aligned along the plug radial direction when viewed from the Z direction as shown in Fig. 2. The extension line 51L of the central axis of the injection hole 51 substantially passes through the plug central axis C.

[0020] In this embodiment, as shown in Fig. 1, the discharge gap G is formed on the base end side of an extension line 51L of the central axis of the nozzle hole 51. As shown in Fig. 6, the discharge gap G is formed on the base end side of an extension region 51E that extends the nozzle hole 51 in the opening direction.

[0021] In this embodiment, the discharge gap G is formed by the leading end surface 42 of the center electrode 4 and the base end surface 61 of the ground electrode 6 facing each other in the Z direction. The leading end surface 42 and the base end surface 61 are each flat. The leading end surface 42 is formed along the base end surface 61. Moreover, the leading end surface 42 and the base end surface 61 are each approximately perpendicular to the Z direction.

[0022] The center electrode 4 has a small diameter portion 41 at its tip end, the small diameter portion 41 having a smaller outer diameter than the other portions. The small diameter portion 41 has a tip end surface 42. The discharge gap G is, for example, a region obtained by projecting the small diameter portion 41 of the center electrode 4 in the Z direction, and is a region between the tip end surface 42 of the center electrode 4 and the base end surface 61 of the ground electrode 6.

[0023] In this embodiment, the ground electrode 6 has a substantially rectangular prism shape and is provided along the plug radial direction, as shown in Figs.

[0024] 10 and 11, the housing 2 has a support portion 24 formed by a part of the inner wall surface 21 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.

[0025] An inner wall surface 21 of the housing 2 is formed into a substantially cylindrical shape on the tip side of the support portion 24 .

[0026] Next, a method for manufacturing the spark plug 1 of this embodiment will be described. 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 14, as shown in Fig. 7. Then, the fixed end 62 of the ground electrode 6 is abutted against the inner wall surface 21 of the housing 2 and welded to it, as shown in Fig. 8.

[0027] The assembly jig 14 has a base end support part 141 and a tip end support part 142 that sandwich the ground electrode 6 from the base end side and the tip end side. When welding the fixed end part 62 to the inner wall surface 21, a base end surface 143 of the base end support part 141 is brought into contact with the tip of the center electrode 4.

[0028] In this embodiment, the base end support part 141 and the tip end support part 142 sandwich the protruding end part 63 of the ground electrode 6 in the Z direction. At this time, the tip surface of the base end support part 141 and the base end surface 61 of the ground electrode 6 abut against each other. The base end surface of the tip end support part 142 and the tip surface of the ground electrode 6 abut against each other.

[0029] In this embodiment, the base end surface 143 of the base end support portion 141 is a flat surface. The base end surface 143 is approximately perpendicular to the Z direction. In addition, the tip surface of the base end support portion 141 and the base end surface of the tip end support portion 142 are also flat surfaces and are approximately perpendicular to the Z direction.

[0030] As shown in FIG. 7, the thickness L1 of the base end support portion 141 in the Z direction is equal to the length L2 of the discharge gap G in the plug axial direction Z shown in FIG.

[0031] 7 and 8, the assembly jig 14 has a base end support portion 141 and a tip end support portion 142 disposed on a jig body portion 144. The base end support portion 141 is fixed to the base end portion of the jig body portion 144 and protrudes from the base end portion in a direction perpendicular to the axial direction of the jig body portion 144. The tip end support portion 142 is attached to the tip side of the base end support portion 141 in a state in which it can slide relative to the jig body portion 144. This allows the protruding end portion 63 of the ground electrode 6 to be sandwiched between the tip end support portion 142 and the base end support portion 141. In this embodiment, the assembly jig 14 holds the ground electrode 6 with the protruding end surface of the protruding end portion 63 abutting against the jig body portion 144.

[0032] Next, the manufacturing method of this embodiment will be described in detail. In assembling the ground electrode 6, the assembling jig 14 holding the ground electrode 6 is moved toward the tip of the center electrode 4 as shown by the arrow M in Fig. 7. Then, as shown in Fig. 8, the base end surface 143 of the base end support part 141 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 62 of the ground electrode 6 and the inner wall surface 21 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 base end surface 61 of the ground electrode 6 face each other in the Z direction with the base end support part 141 in between.

[0033] Next, the fixed end 62 of the ground electrode 6 is joined to the inner wall surface 21 by laser welding. Specifically, the ground electrode 6 is welded to the inner wall surface 21 by irradiating the laser light L toward the abutting portion where the fixed end 62 and the inner wall surface 21 abut against each other. After welding, the assembly jig 14 is removed from the ground electrode 6. Note that, for example, it is also possible to temporarily fix the ground electrode 6 to the inner wall surface 21 by resistance welding or the like, and then remove the assembly jig 14 from the ground electrode 6, and then perform laser welding.

[0034] Next, the plug cover 5 is moved toward the tip end of the housing 2 as shown by the arrow M in Fig. 9, 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.

[0035] Next, the internal combustion engine 10 of this embodiment will be described. 3 and 4, an internal combustion engine 10 includes the above-mentioned spark plug 1. The internal combustion engine 10 also includes a main combustion chamber 11, and an intake valve 12 and an exhaust valve 13 provided in the main combustion chamber 11. The tip of the spark plug 1 is disposed so as to face the main combustion chamber 11.

[0036] As shown in FIGS. 4 and 5, when viewed in the plug axial direction Z, the ground electrode 6 protrudes from a position closer to the intake valve 12 than the tip of the center electrode 4 toward the tip of the center electrode 4.

[0037] At least one of the injection holes 51 is an intake-side injection hole 510 formed such that an outer opening 511 faces the intake valve 12 when viewed from the plug axial direction Z. As shown in Fig. 6, the intake-side injection hole 510 opens at an angle with respect to the plug axial direction Z so as to move outward in the plug radial direction toward the tip side.

[0038] As shown in Fig. 3, the internal combustion engine 10 includes a piston 16 that reciprocates in a cylinder 15. The volume of the main combustion chamber 11 changes due to the reciprocating motion of the piston 16. The internal combustion engine 10 also includes an intake port 121 and an exhaust port 131, each of which includes an intake valve 12 and an exhaust valve 13. In this specification, the direction in which the intake valve 12 and the exhaust valve 13 are arranged when the internal combustion engine 10 is viewed from the Z direction as shown in Fig. 4, and which is perpendicular to the Z direction, is referred to as the Y direction as appropriate.

[0039] 3 and 4, the spark plug 1 is disposed in a position in the cylinder head 17 surrounded by the intake port 121 and the exhaust port 131. As shown in Fig. 4, two intake ports 121 and two exhaust ports 131 are provided for each main combustion chamber 11.

[0040] The two intake ports 121 and the two exhaust ports 131 are arranged circumferentially around the spark plug 1. The two intake ports 121 are adjacent to each other around the spark plug 1, and the two exhaust ports 131 are adjacent to each other around the spark plug 1. As shown in Fig. 3, the intake ports 121 and the exhaust ports 131 are inclined with respect to the forward and backward movement direction of the piston 16 so that their opening directions are toward the central axis of the main combustion chamber 11. In addition, the base end surface of the main combustion chamber 11 is inclined so as to be toward the tip side as it moves away from the spark plug 1.

[0041] Furthermore, the internal combustion engine 10 sequentially repeats an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke in accordance with the reciprocating motion of the piston 16. During the intake stroke, gas is introduced into the main combustion chamber 11 through the two intake ports 121, and during the exhaust stroke, gas within the main combustion chamber 11 is exhausted through the two exhaust ports 131.

[0042] In the main combustion chamber 11, a tumble flow is formed, which is an airflow around an axis perpendicular to the sliding direction of the piston 16, as shown by an arrow A1 in Fig. 3. This airflow is directed from the intake valve 12 toward the exhaust valve 13, i.e., along the Y direction, near the tip of the spark plug 1 in the main combustion chamber 11. More specifically, as shown in Fig. 4, when viewed from the plug axial direction Z, the main airflow near the tip of the spark plug 1 is an airflow that runs from the midpoint between the two intake ports 121 toward the midpoint between the two exhaust ports 131.

[0043] The airflow in the main combustion chamber 11 is not always constant, but may vary between cycles or between different timings within one cycle. However, the direction of the main airflow, particularly the airflow at the ignition timing, is roughly fixed, and the above-mentioned airflow refers to the main airflow at the ignition timing. And, when we say "airflow in the main combustion chamber 11," we mean the airflow near the tip of the spark plug 1 at the above-mentioned ignition timing, unless otherwise specified. And, when we simply say "upstream side" and "downstream side," we mean the upstream side and downstream side of the above-mentioned "airflow in the main combustion chamber 11," unless otherwise specified.

[0044] In this embodiment, there is one intake side nozzle 510. As shown in Fig. 3 to Fig. 6, in the Y direction, the intake side nozzle 510 is formed closer to the intake valve 12 than the other nozzles 51. Also, an outer opening 511 of the intake side nozzle 510 faces upstream of the airflow of the main combustion chamber 11.

[0045] 4 and 5, when viewed from the Z direction, the intake side nozzle 510 is formed such that an extension line 51L of the central axis of the intake side nozzle 510 is aligned with the protruding direction of the ground electrode 6. When viewed from the Z direction, the intake side nozzle 510 is formed such that an extension line 51L of the central axis of the intake side nozzle 510 is aligned with the Y direction. Also, the ground electrode 6 is fixed such that the protruding direction of the ground electrode 6 is aligned with the Y direction.

[0046] Next, the effects of this embodiment will be described. In the spark plug 1, the ground electrode 6 is fixed to the inner wall surface 21 of the housing 2. This makes it easy to adjust the position of the ground electrode 6 with respect to the housing 2. This makes it easy to adjust the discharge gap G, and the productivity of the spark plug 1 can be improved.

[0047] That is, the ground electrode 6 is fixed to the inner wall surface 21. Therefore, when the ground electrode 6 is fixed to the housing 2, one end of the ground electrode 6 (i.e., the end that becomes the fixed end 62) can be slid along the inner wall surface 21 while being in contact with the inner wall surface 21. Therefore, the position of the ground electrode 6 relative to the housing 2 can be finely adjusted. Therefore, even if there is a variation in the dimensions of each component of the spark plug 1, the distance between the tip of the center electrode 4 and the base end surface 61 of the ground electrode 6 can be easily set to a desired length by adjusting the fixed position of the ground electrode 6 relative to the inner wall surface 21. As a result, a discharge gap G having a desired length can be easily formed.

[0048] Furthermore, the discharge gap G is formed on the base end side of an extension line 51L of the central axis of the injection hole 51. Therefore, even if the flow speed of the airflow introduced into the auxiliary combustion chamber 50 through the injection hole 51 is relatively fast, the fast airflow is unlikely to flow into the discharge gap G. This makes it possible to suppress the discharge generated in the discharge gap G from being blown out and short-circuited by the airflow. This makes it easier to ignite the air-fuel mixture in the auxiliary combustion chamber 50 by the discharge. As a result, ignition performance can be improved.

[0049] Furthermore, the discharge gap G is formed closer to the base end than the extension region 51E that extends the nozzle hole 51 in the opening direction. Therefore, even if the flow speed of the airflow introduced into the auxiliary combustion chamber 50 through the nozzle hole 51 is relatively fast, the fast airflow is less likely to flow into the discharge gap G. As a result, the blowing out of the discharge and the short circuit caused by the airflow can be further suppressed.

[0050] In addition, because the ground electrode 6 is fixed to the inner wall surface 21 of the housing 2, the position where the discharge gap G is formed can be easily located closer to the base end of the auxiliary combustion chamber 50. In other words, the position where the discharge gap G is formed can be easily located away from the nozzle hole 51. Therefore, it can be expected that the flame will spread from a position sufficiently away from the nozzle hole 51, and that the flame jet will be ejected from the nozzle hole 51 into the main combustion chamber under a condition where the internal pressure is sufficiently high. As a result, the flame jet is strengthened, which can be expected to suppress knocking during high load of the internal combustion engine 10, and to improve the output and fuel efficiency of the internal combustion engine 10.

[0051] In the method for manufacturing the spark plug 1, the ground electrode 6 is fixed to the inner wall surface 21 of the housing 2 by using an assembly jig 14. Therefore, the discharge gap G having a desired length can be easily formed. As a result, the spark plug 1 can be efficiently manufactured.

[0052] The thickness L1 (see FIG. 7) of the base end support portion 141 in the Z direction is equal to the length L2 (see FIG. 9) of the discharge gap G in the Z direction. Then, the fixed end portion 62 of the ground electrode 6 is welded to the inner wall surface 21 with the base end surface 143 of the base end support portion 141 in contact with the tip of the center electrode 4. Therefore, the length L2 can be made equal to the thickness L1. Therefore, the discharge gap G can be made to a desired length without adjusting the length of the discharge gap G after the ground electrode 6 is fixed to the housing 2. Therefore, even if it is difficult to directly check the discharge gap G, the discharge gap G of a desired length can be easily formed. As a result, the productivity can be improved.

[0053] Furthermore, by using the assembly jig 14, the discharge gap G having a desired length can be easily formed closer to the base end of the auxiliary combustion chamber 50, i.e., at a position away from the injection hole 51. Therefore, the spark plug 1 having improved ignition performance can be easily formed.

[0054] In addition, since the ground electrode 6 is fixed to the inner wall surface 21, there is no need to provide a through hole or the like in the housing 2 for inserting the ground electrode 6. This can improve productivity.

[0055] In the above internal combustion engine 10, the spark plug 1 has an intake-side nozzle 510. When viewed from the Z direction, the ground electrode 6 protrudes from a position closer to the intake valve 12 than the tip of the center electrode 4 toward the tip of the center electrode 4. This makes it easier for the airflow introduced into the auxiliary combustion chamber 50 through the intake-side nozzle 510 to flow toward the discharge gap G by being guided by the base end surface 61 of the ground electrode 6. This makes it easier for the discharge formed in the discharge gap G to extend. As a result, it is possible to improve ignition performance.

[0056] In this embodiment, the outer opening 511 of the intake side nozzle 510 faces the intake valve 12 side when viewed from the Z direction. That is, the outer opening 511 of the intake side nozzle 510 faces the upstream side of the airflow of the main combustion chamber 11. Therefore, during the compression stroke, the airflow introduced into the auxiliary combustion chamber 50 through the intake side nozzle 510 tends to be stronger than the airflow introduced into the auxiliary combustion chamber 50 through the other nozzles 51. Also, the intake side nozzle 510 opens at an incline with respect to the Z direction so as to move outward in the plug radial direction toward the tip side. Therefore, as shown in FIG. 10 and FIG. 11, the airflow A2 introduced into the auxiliary combustion chamber 50 through the intake side nozzle 510 tends to move toward the downstream side of the auxiliary combustion chamber 50 and toward the base end side of the auxiliary combustion chamber 50. The airflow A2 heading toward the base end side flows into the pocket portion 501, changes direction in the pocket portion 501, and tends to head toward the tip side on the upstream side. That is, an airflow (i.e., a tumble flow) around an axis perpendicular to the Z direction is likely to be formed in the auxiliary combustion chamber 50. The airflow A2 heading toward the tip side is guided by the base end surface 61 of the ground electrode 6 located upstream of the tip of the center electrode 4, and tends to head toward the discharge gap G. Therefore, as shown in FIG. 10, the discharge S generated in the discharge gap G tends to be extended by the airflow A2 as shown in FIG. 11. As a result, the ignition performance can be improved.

[0057] In addition, the initial flame generated by the discharge is easily carried toward the base end of the auxiliary combustion chamber 50 by the airflow A2 flowing toward the base end. This allows the flame to spread from a position sufficiently distant from the nozzle hole 51, and it is expected that the flame jet will be ejected from the nozzle hole 51 into the main combustion chamber 11 with the internal pressure being sufficiently high. As a result, it is expected that knocking during high load of the internal combustion engine 10 will be suppressed, and that the output and fuel efficiency of the internal combustion engine 10 will be improved.

[0058] As described above, according to the present invention, it is possible to provide a spark plug for an internal combustion engine, a manufacturing method thereof, and an internal combustion engine, which are capable of improving productivity.

[0059] (Embodiment 2) In this embodiment, as shown in FIGS. 12 and 13, the ground electrode 6 is fixed to a flat surface 211 of the housing 2. In the embodiment shown in FIG. That is, the inner wall surface 21 has a flat surface 211. The ground electrode 6 is fixed to the flat surface 211.

[0060] In this embodiment, the flat surface 211 is formed along the Z direction as shown in Figures 12 and 13. The flat surface 211 is formed from the tip of the housing 2 to the support portion 24.

[0061] 12, the length L3 of the flat surface 211 in the Z direction is equal to or greater than the thickness L4 of the ground electrode 6 in the Z direction. In addition, as shown in Fig. 13, in the width direction of the ground electrode 6 perpendicular to the longitudinal direction of the ground electrode 6, the width L5 of the flat surface 211 is equal to or greater than the width L6 of the ground electrode 6. 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.

[0062] The fixed end 62 of the ground electrode 6 is fixed to the flat surface 211. Therefore, the surface of the fixed end 62 that is joined to the inner wall surface 21 can be made flat. Therefore, the ground electrode 6 can be efficiently manufactured before being fixed to the inner wall surface 21. 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.

[0063] The flat surface 211 is formed from the tip of the housing 2 to the support portion 24. Therefore, the housing 2 having the flat surface 211 formed thereon can be easily manufactured by cold forging. As a result, productivity can be improved. In addition, the same effects as those of the first embodiment are achieved.

[0064] (Embodiment 3) As shown in Figs. 14 and 15, this embodiment is an embodiment in which the shape of the ground electrode 6 is modified from that of the second embodiment.

[0065] In this embodiment, as shown in Figs. 14 and 15, the fixed end portion 62 of the ground electrode 6 has a width that increases toward the outside in the plug radial direction. The rest is the same as in the second embodiment.

[0066] The fixed end 62 of the ground electrode 6 becomes wider as it goes outward in the plug radial direction. This makes it possible to increase the bonding area of ​​the ground electrode 6 with respect to the housing 2. This makes it possible to increase the strength of the bonded portion between the housing 2 and the ground electrode 6. This makes it possible to manufacture a spark plug 1 with high strength.

[0067] In addition, since the bonding area of ​​the ground electrode 6 with respect to the housing 2 is increased, heat from the ground electrode 6 is easily and efficiently transferred to the housing 2. This makes it possible to prevent the ground electrode 6 from becoming too hot. As a result, pre-ignition can be suppressed. In addition, the same effects as those of the second embodiment are achieved.

[0068] (Embodiment 4) As shown in Figs. 16 and 17, this embodiment is an embodiment in which the shape of the ground electrode 6 is modified from that of the second embodiment.

[0069] In this embodiment, as shown in Figs. 16 and 17, the fixed end portion 62 of the ground electrode 6 has a thickness in the Z direction that increases toward the outer side in the plug radial direction. The rest is the same as in the second embodiment.

[0070] The fixed end 62 of the ground electrode 6 has a thickness in the Z direction that increases toward the outside in the plug radial direction. This makes it possible to increase the joint area of ​​the ground electrode 6 with the housing 2. As a result, it is possible to increase the strength of the joint between the housing 2 and the ground electrode 6 and to suppress pre-ignition. In addition, the same effects as those of the second embodiment are achieved.

[0071] (Embodiment 5) As shown in FIG. 18, in this embodiment, compared to the second embodiment, a flat surface 211 of a housing 2 protrudes inward in the plug radial direction.

[0072] In this embodiment, the housing 2 has a protrusion 25 formed by a part of the inner wall surface 21 protruding inward in the plug radial direction, as shown in Fig. 18. The protrusion 25 has a flat surface 211 facing inward in the plug radial direction. The fixed end 62 of the ground electrode 6 is welded to the flat surface 211 formed on the protrusion 25.

[0073] 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 second embodiment.

[0074] (Embodiment 6) In this embodiment, as shown in FIGS. 19 and 20, the ground electrode 6 is fixed to the recess forming surface 221. As shown in FIG.

[0075] 19 and 20, the housing 2 has a fixing recess 22 formed by recessing a part of the inner wall surface 21 radially outward. The fixing recess 22 is formed from the position of the tip of the discharge gap G in the plug axial direction Z, or from a position on the base end side of the tip of the discharge gap G to the tip of the housing 2. The fixing recess 22 is open on the tip side. The ground electrode 6 is fixed to a recess forming surface 221 that forms the fixing recess 22.

[0076] In this embodiment, as shown in Fig. 19, the fixing recess 22 is formed from a position on the base end side of the tip of the discharge gap G to the tip of the housing 2. Also, as shown in Fig. 20, the width L7 of the fixing recess 22 in the width direction of the ground electrode 6 is approximately the same as the width L6 of the ground electrode 6.

[0077] 19 and 20, the recess-forming surface 221 has two circumferentially opposed surfaces 222 that face the ground electrode 6 in the plug circumferential direction, and one radially opposed surface 223 that faces the ground electrode 6 in the plug radial direction. In this embodiment, the circumferentially opposed surfaces 222 and the radially opposed surface 223 are also flat surfaces 211. The plug circumferential direction is a direction along a circumference centered on the plug central axis C.

[0078] In this embodiment, the ground electrode 6 and each of the two circumferentially opposed surfaces 222 are joined to each other. The ground electrode 6 and the radially opposed surface 223 are also joined to each other.

[0079] In this embodiment, when joining the ground electrode 6 to the housing 2, the fixed end portion 62 is fitted into the fixed recess 22 and then welding is performed. The rest is the same as in the second embodiment.

[0080] The ground electrode 6 is fixed to the recess forming surface 221. This makes it possible to further 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 further increased.

[0081] Furthermore, the bonding area of ​​the ground electrode 6 with respect to the housing 2 is increased, so that heat from the ground electrode 6 is more efficiently transferred to the housing 2. Therefore, pre-ignition can be further suppressed. Moreover, the ground electrode 6 can be easily positioned relative to the housing 2 in the plug circumferential direction.

[0082] Moreover, the fixing recess 22 is open to the tip side. Therefore, the fixing end 62 of the ground electrode 6 can be inserted from the tip side of the fixing recess 22 along the Z direction. Therefore, the ground electrode 6 can be easily disposed at a desired position. As a result, the productivity can be improved.

[0083] In addition, by forming the fixing recess 22 at a predetermined position relative to the threading start of the threaded portion 23 in the housing 2, 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 can be easily determined. 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 22 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 directed toward the base end surface 61 of 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, the discharge generated in the discharge gap G is easily extended by the airflow. Furthermore, the initial flame formed by the discharge is easily carried by the airflow toward 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, ignition performance can be improved. In addition, the same effects as those of the second embodiment are achieved.

[0084] (Embodiment 7) As shown in FIG. 21, this embodiment is an embodiment in which the shapes of the ground electrode 6 and the fixing recess 22 are changed from those of the sixth embodiment.

[0085] As shown in FIG. 21, in the width direction of the ground electrode 6, a width L8 of a portion of the fixed end portion 62 is smaller than a width L9 of the ground electrode 6 at another portion.

[0086] A width L7 of the fixing recess 22 in the width direction of the ground electrode 6 is approximately the same as the width L8. The other configurations and effects are the same as those of the sixth embodiment.

[0087] (Embodiment 8) As shown in FIG. 22, this embodiment is an embodiment in which the shapes of the ground electrode 6 and the fixing recess 22 are changed from those of the sixth embodiment.

[0088] As shown in FIG. 22, the fixed end 62 of the ground electrode 6 has a width that decreases toward the outside in the plug radial direction.

[0089] The fixing recess 22 also has a width in the width direction of the ground electrode 6 that decreases toward the outer side in the plug radial direction. The other configurations and effects are the same as those of the sixth embodiment.

[0090] (Embodiment 9) In this embodiment, as shown in FIG. 23, the opening area of ​​the intake side nozzle hole 510 is increased.

[0091] 23, the plug cover 5 is formed with an intake side nozzle 510 and nozzle holes 51 other than the intake side nozzle 510. The intake side nozzle 510 has a larger opening area than the other nozzle holes 51. The inner diameter L10 of the intake side nozzle 510 may be set to be 1.2 to 1.4 times the inner diameter L11 of the other nozzle holes 51, for example. The opening area of ​​the intake side nozzle 510 may be set to be 1.5 to 2.0 times the opening area of ​​the other nozzle holes 51, for example. The rest is the same as in the first embodiment.

[0092] The intake side nozzle 510 has a larger opening area than the other nozzles 51. Therefore, the airflow introduced into the auxiliary combustion chamber 50 through the intake side nozzle 510 can be strengthened. Therefore, the tumble flow in the auxiliary combustion chamber 50 can be strengthened. Therefore, the airflow toward the discharge gap G can be strengthened. Therefore, the discharge generated in the discharge gap G can be further extended. As a result, the ignition performance can be further improved. In addition, the same effects as those of the first embodiment are achieved.

[0093] In the above-mentioned embodiments 1 to 9, the ground electrode 6 has a substantially rectangular prism shape. However, the ground electrode may also have, for example, a substantially cylindrical shape.

[0094] In the above-mentioned embodiments 1 to 9, 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.

[0095] In the above-mentioned embodiments 1 to 9, the injection hole 51 is formed so that an extension line 51L of the central axis 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.

[0096] 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.

[0097] 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]

[0098] 1...spark plug, 2...housing, 21...inner wall surface, 3...insulator, 4...center electrode, 5...plug cover, 50...auxiliary combustion chamber, 51...nozzle hole, 6...ground electrode, 61...base end surface, 62...fixed end, G...discharge gap, Z...plug axial direction

Claims

1. A method for manufacturing a spark plug (1) for an internal combustion engine, comprising the steps of: The above spark plugs are 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 is fixed to an inner wall surface (21) of the housing and protrudes into the auxiliary combustion chamber from a fixed end (62) fixed to the inner wall surface, the discharge gap is formed by a front end portion of the center electrode and a base end surface (61) of the ground electrode facing each other in the plug axial direction (Z), and is formed on the base end side of the front end of the housing, When the ground electrode is fixed to the housing before the plug cover and the ground electrode are fixed, A protruding end (63) of the ground electrode opposite to the fixed end is held by an assembly jig (14), and the fixed end of the ground electrode is abutted against the inner wall surface of the housing and welded to the inner wall surface of the housing; The assembly jig has a base end side support portion (141) and a tip end side support portion (142) that sandwich the ground electrode from the base end side and the tip end side, a base end surface (143) of the base end support portion is brought into contact with the tip of the center electrode when the fixed end portion is welded to the inner wall surface.

2. 2. The method for manufacturing a spark plug for an internal combustion engine according to claim 1, wherein the inner wall surface has a flat surface (211), and the ground electrode is fixed to the flat surface.

3. 3. The method for manufacturing a spark plug for an internal combustion engine according to claim 1, wherein the housing has a fixing recess (22) formed by receding a part of the inner wall surface outward in the plug radial direction, the fixing recess (22) being formed from a position of a tip of the discharge gap in the plug axial direction or from a position base end side of the tip of the discharge gap to a tip of the housing and opening to the tip side, and the ground electrode is fixed to a recess forming surface (221) that forms the fixing recess.

4. 4. The method for manufacturing a spark plug for an internal combustion engine according to claim 1, wherein the discharge gap is formed on a base end side of an extension line (51L) of a central axis of the injection hole.

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