Spark plugs for internal combustion engines

Abstract

To provide a spark plug for an internal combustion engine that can improve ignitability.SOLUTION: In a spark plug 1, a plug cover 5 is formed with a plurality of nozzle holes 51 for communicating a sub-combustion chamber 50 with the outside. A projecting end portion 62 of a ground electrode 6 and an inner wall surface 54 of a plug cover 5 are in contact with each other in the axial direction of a plug. Also, some nozzle holes 51 of the plurality of nozzle holes 51 are ground side nozzle holes 511 whose shortest distance to the projecting end 62 is equal to or less than the inner diameter of the nozzle hole 51. When viewed from the axial direction of the plug, at least a portion of the ground side injection hole 511 overlaps at least one of a ground extension area 6E and a gap extension area GE.SELECTED DRAWING: Figure 4

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 with an auxiliary combustion chamber at its tip is known. In this spark plug, a plug cover covering the auxiliary combustion chamber is formed with multiple nozzle holes. This allows a flame to be ejected from the auxiliary combustion chamber through the nozzle holes 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 2020-009747 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, the spark plug described in Patent Document 1 does not take into consideration the formation of an initial flame. In other words, no consideration is given to improving ignition by extending the discharge generated in the discharge gap. In addition, although ignition by discharge may be performed during the expansion stroke of an internal combustion engine for the purpose of increasing the catalyst temperature of an exhaust gas purification filter, no consideration is given to ignition during the expansion stroke.

[0005] The present invention has been made in view of the above problems, and has an object to provide a spark plug for an internal combustion engine that is capable of improving ignition performance. [Means for solving the problem]

[0006] One aspect of the present invention is a cylindrical insulator (3), a center electrode (4) held on the inner circumferential side of the insulator and exposed from the insulator to the tip side; a cylindrical housing (2) that holds the insulator on its inner periphery; a ground electrode (6) forming a discharge gap (G) between itself and the center electrode; a plug cover (5) fixed to the tip end of the housing so as to cover a sub-combustion chamber (50) in which the discharge gap is disposed, The ground electrode protrudes into the auxiliary combustion chamber from a fixed end (61) fixed to the housing, The plug cover is formed with a plurality of nozzle holes (51) that communicate the auxiliary combustion chamber with the outside, a front end portion of the housing has a housing fixing portion (21) facing a cover base end portion (52) of the plug cover in a plug radial direction, and an opposing surface (22) facing a base end surface (53) of the plug cover in a plug axial direction (Z) on the base end side of the housing fixing portion, The housing fixing portion and the cover base end portion are fixed to each other, the base end surface of the plug cover is disposed at a position spaced apart from the opposing surface in the plug axial direction, the protruding end (62) of the ground electrode and the inner wall surface (54) of the plug cover abut against each other in the plug axial direction, Some of the nozzle holes among the plurality of nozzle holes are ground side nozzle holes (511) whose shortest distance (D1) to the protruding end is equal to or shorter than an inner diameter (D2) of the nozzle hole, When viewed from the plug axial direction, at least a portion of the ground side nozzle hole overlaps with at least one of a ground extension region (6E) in which the ground electrode is extended in a protruding direction and a gap extension region (GE) in which the discharge gap is extended in the protruding direction of the ground electrode. Cage , The plug cover has a protruding portion (55) formed by a part of the inner wall surface protruding toward the base end, and the protruding portion and the protruding end portion abut against each other in the plug axial direction. In a spark plug (1) for an internal combustion engine. Effect of the Invention

[0007] In the above spark plug, the protruding end and the inner wall surface of the plug cover abut against each other in the plug axial direction. Also, when viewed from the plug axial direction, at least a portion of the ground side nozzle overlaps with at least one of the ground extension region and the gap extension region. Therefore, during the expansion stroke of the internal combustion engine, the discharge generated in the discharge gap is easily extended by the air flow toward the ground side nozzle. As a result, ignition performance can be improved.

[0008] As described above, according to the above aspect, it is possible to provide a spark plug for an internal combustion engine that is capable of improving ignition performance. 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 cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. 4 is an explanatory diagram showing the inner diameter of an injection hole in the first embodiment. [Figure 4] FIG. 4 is an explanatory diagram showing a ground extension region and a gap extension region in the first embodiment. [Diagram 5] FIG. 4 is a cross-sectional view illustrating the direction of a swirl flow formed in an auxiliary combustion chamber in the first embodiment. [Figure 6] FIG. 4 is an explanatory diagram showing an extension region of a ground side nozzle hole and the like in the first embodiment. [Figure 7] FIG. 4 is a cross-sectional view showing a line segment L1 in the first embodiment. [Figure 8] 4 is a cross-sectional view showing a state in which the ground electrode and the plug cover are brought into contact with each other in the first embodiment. FIG. [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]4 is a cross-sectional view of the vicinity of the tip of the spark plug in the first embodiment during the expansion stroke and before the discharge is extended. [Figure 11] 4 is a cross-sectional view of the vicinity of the tip of the spark plug according to the first embodiment when the discharge is extended during the expansion stroke. [Figure 12] FIG. 4 is a cross-sectional view of the vicinity of the tip of the spark plug when the starting point of the discharge on the ground electrode side moves to the ground side nozzle hole during the expansion stroke in the first embodiment. [Figure 13] 4 is a cross-sectional view of the vicinity of the tip of the spark plug when the discharge extends to the main combustion chamber during the expansion stroke in the first embodiment. FIG. [Figure 14] FIG. 11 is a cross-sectional view taken along the axial direction of a spark plug in a vicinity of a tip portion of the spark plug according to a second embodiment. [Figure 15] FIG. 11 is a cross-sectional view taken along the axial direction of a spark plug in a vicinity of a tip portion of the spark plug according to a third embodiment. [Figure 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. 4 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 in a first modified embodiment. [Figure 18] FIG. 13 is a cross-sectional view taken along the axial direction of a spark plug in the vicinity of a tip portion of the spark plug according to a fifth embodiment. [Figure 19] FIG. 13 is a cross-sectional view taken along the axial direction of a spark plug in a vicinity of a tip portion of the spark plug according to a sixth embodiment. [Figure 20] FIG. 13 is a cross-sectional view taken along the axial direction of a spark plug in a vicinity of a tip portion of the spark plug according to a seventh embodiment. [Figure 21] FIG. 13 is a cross-sectional view taken along the axial direction of a spark plug in the vicinity of a tip portion of the spark plug according to an eighth embodiment. [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 ninth embodiment. [Figure 23] FIG. 23 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 a tenth embodiment. [Figure 24]24 is a cross-sectional view taken along line XXIV-XXIV in FIG. 25 , showing a portion near the tip end of a spark plug according to an eleventh embodiment, in the axial direction of the plug. [Diagram 25] A cross-sectional view taken along line XXV-XXV in Figure 24. [Figure 26] FIG. 23 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 twelfth embodiment. [Figure 27] FIG. 23 is a cross-sectional view of the tip portion of a spark plug according to a thirteenth embodiment, taken along a line perpendicular to the plug axis direction. [Figure 28] 29 is a cross-sectional view taken along line XXVIII-XXVIII in FIG. 29 , showing a cross-sectional view in the axial direction of the spark plug near the tip portion of the spark plug according to the fourteenth embodiment. [Figure 29] A cross-sectional view taken along line XXIX-XXIX in Figure 28. [Diagram 30] A cross-sectional view taken along line XXX-XXX in Figure 29. [Diagram 31] FIG. 23 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 a fifteenth 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. In this embodiment, a spark plug 1 for an internal combustion engine has a cylindrical insulator 3, a center electrode 4, a cylindrical housing 2, a ground electrode 6, and a plug cover 5, as shown in Fig. 1 and Fig. 2. The center electrode 4 is held on the inner periphery of the insulator 3 and is exposed from the insulator 3 to the tip side. The housing 2 holds the insulator 3 on the 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 of the housing 2 so as to cover the auxiliary combustion chamber 50 in which the discharge gap G is arranged.

[0011] The ground electrode 6 protrudes into the auxiliary combustion chamber 50 from a fixed end portion 61 fixed to the housing 2. In addition, the plug cover 5 is formed with a plurality of injection holes 51 that communicate the auxiliary combustion chamber 50 with the outside.

[0012] 1, the tip end of the housing 2 has a housing fixing portion 21 and an opposing surface 22. The housing fixing portion 21 faces a cover base end portion 52 of the plug cover 5 in the plug radial direction. The opposing surface 22 faces a base end surface 53 of the plug cover 5 in the plug axial direction Z on the base end side of the housing fixing portion 21. The housing fixing portion 21 and the cover base end portion 52 are fixed to each other. The base end surface 53 of the plug cover 5 is located at a position away from the opposing surface 22 in the plug axial direction Z.

[0013] Further, the protruding end portion 62 of the ground electrode 6 and the inner wall surface 54 of the plug cover 5 abut against each other in the plug axial direction Z.

[0014] Also, as shown in Fig. 3, some of the multiple nozzle holes 51 are ground side nozzle holes 511 whose shortest distance D1 to the protruding end 62 is equal to or less than the inner diameter D2 of the nozzle hole 51. As shown in Fig. 4, when viewed from the plug axial direction Z, at least a portion of the ground side nozzle hole 511 overlaps with at least one of the ground extension region 6E and the gap extension region GE. The ground extension region 6E is a region formed by extending the ground electrode 6 in the protruding direction. The gap extension region GE is a region formed by extending the discharge gap G in the protruding direction of the ground electrode 6.

[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 an internal combustion engine 10 by screwing the threaded portion 23 of the housing 2 into the female threaded portion of a plug hole 711 of a cylinder head 71, as shown in FIG.

[0016] The internal combustion engine 10 includes a piston 74 that reciprocates within a cylinder 70. The volume of the main combustion chamber 101 changes due to the reciprocating motion of the piston 74. The internal combustion engine 10 is formed with an intake port 721 and an exhaust port 731, and is provided with an intake valve 72 and an exhaust valve 73, respectively.

[0017] One end of the spark plug 1 in the axial direction Z is disposed in the main combustion chamber 101 of the internal combustion engine 10. In the axial direction Z of the spark plug 1, the side exposed to the main combustion chamber 101 is referred to as the tip side, and the opposite side is referred to as the base side. The axial direction Z of the spark plug 1 is also referred to as the plug axial direction Z or simply as the Z direction, as appropriate. The plug central axis C refers to the central axis C of the spark plug 1. The plug radial direction refers to the radial direction of a circle centered on the plug central axis C on a plane perpendicular to the plug central axis C. The plug circumferential direction refers to the direction along the circumference centered on the plug central axis C. In this embodiment, the plug central axis C is also the central axis of the center electrode 4.

[0018] When the spark plug 1 is attached to the internal combustion engine 10, the plug cover 5 faces the main combustion chamber 101 and separates the auxiliary combustion chamber 50 from the main combustion chamber 101. The injection hole 51 communicates the auxiliary combustion chamber 50 with the main combustion chamber 101.

[0019] In this embodiment, the plug cover 5 has a peripheral wall portion 56, a bottom wall portion 57, and a corner portion 58, as shown in Fig. 1. The peripheral wall portion 56 is a generally cylindrical portion that covers part of the outer periphery of the auxiliary combustion chamber 50. The bottom wall portion 57 is a portion that covers the tip side of the auxiliary combustion chamber 50. The corner portion 58 is a portion that connects the tip of the peripheral wall portion 56 and the outer periphery of the bottom wall portion 57 in a curved shape.

[0020] The peripheral wall portion 56 has a cover base end portion 52 and a base end surface 53. An inner wall surface 54 of the peripheral wall portion 56 is formed along the Z direction.

[0021] Further, a plurality of injection holes 51 are formed in the corner portion 58. As shown in Fig. 2, when viewed from the Z direction, the injection hole 51 formed in the corner portion 58 is an inclined injection hole 512 in which an injection hole axis 512L is inclined at an acute angle with respect to a virtual line VL extending in the plug radial direction passing through the injection hole 51 and the plug central axis C. The inclined injection holes 512 are arranged such that the inclination direction of the injection hole axis 512L with respect to the virtual line VL in each of the inclined injection holes 512 is on the same side in the plug circumferential direction. Further, the inclined injection holes 512 are opened at an inclination with respect to the Z direction so as to move outward in the plug radial direction toward the tip side.

[0022] Due to such a formation mode of the inclined nozzle hole 512, a swirl flow (see dashed arrow SF in FIG. 5) is formed in the auxiliary combustion chamber 50 by the airflow introduced into the auxiliary combustion chamber 50 through the inclined nozzle hole 512. In this embodiment, the swirl flow SF is generated in a counterclockwise spiral shape in FIG. 5 around the plug central axis C.

[0023] Further, a ground side nozzle hole 511 is formed in the bottom wall portion 57. As shown in Fig. 3, an inner diameter D2 of the ground side nozzle hole 511 is 1.2 to 1.4 times an inner diameter D3 of the other nozzle holes 51. In other words, the ground side nozzle hole 511 has a larger opening area than the inclined nozzle hole 512. The opening area of ​​the ground side nozzle hole 511 can be, for example, 1.4 to 2.0 times the opening area of ​​the other nozzle holes 51.

[0024] In this embodiment, the ground side nozzle 511 opens along the Z direction. That is, as shown in FIG. 6, the ground side nozzle 511 opens so that the nozzle hole axis 511L is along the Z direction. The nozzle hole axis 511L is eccentric from the plug central axis C to the outside in the plug radial direction. In this embodiment, the nozzle hole axis 511L does not pass through the ground electrode 6 and the discharge gap G. In addition, an extension region 511E in the opening direction of the ground side nozzle 511 does not overlap with both the discharge gap G and the ground electrode 6.

[0025] 7, a line segment that connects, at the shortest distance, an outer end 514 of the outer opening 513 of the ground side nozzle 511, which is the outermost end in the plug radial direction, to the tip end of the center electrode 4 is defined as a line segment L1. In this case, the line segment L1 does not pass through both the ground electrode 6 and the plug cover 5.

[0026] 2 to 5, when viewed from the plug axial direction Z, the ground side injection hole 511 is formed on the protruding side of the ground electrode 6. As shown in FIG. 1, a protruding end face 621 is formed on the protruding side of the protruding end portion 62. The protruding end face 621 is substantially parallel to the plug axial direction Z, or is inclined toward the protruding side of the ground electrode 6 as it approaches the tip side. In this embodiment, the protruding end face 621 is substantially parallel to the plug axial direction Z.

[0027] 3, when viewed from the Z direction, at least a part of the protruding end face 621 is disposed between the tip end of the center electrode 4 and the ground side nozzle hole 511. In addition, when viewed from the Z direction, at least a part of the protruding end face 621 is disposed between the discharge gap G and the ground side nozzle hole 511.

[0028] 6, a distance D4 from the ground side nozzle hole 511 to the protruding end portion 62 in the plug radial direction is shorter than a distance D5 from the ground side nozzle hole 511 to the inner wall surface 54 of the peripheral wall portion 56 in the plug radial direction. The distance D4 is also shorter than the inner diameter D2 (see FIG. 3). The distance D6 from the ground side nozzle hole 511 to the discharge gap G in the plug radial direction is also shorter than the distance D5.

[0029] As shown in Fig. 4, when viewed from the Z direction, an inner end 516 that is the innermost in the plug radial direction of the inner opening 515 of the ground side nozzle 511 does not overlap with the ground electrode 6 but overlaps with the ground extension region 6E. In this embodiment, the shortest distance from the inner end 516 to the protruding end 62 is distance D1 (see Fig. 3). In addition, the shortest distance from the inner end 516 to the protruding end 62 is shorter than the shortest distance from the inner end 516 to the inner wall surface 54 of the peripheral wall portion 56 in the plug radial direction.

[0030] In this embodiment, when viewed from the Z direction, the ground side nozzle hole 511 entirely overlaps with the ground extension region 6E. When viewed from the Z direction, the ground side nozzle hole 511 also overlaps with the gap extension region GE.

[0031] In this embodiment, the ground electrode 6 is joined by welding or the like to the front end surface of the housing 2. When viewed from the Z direction, the ground electrode 6 is provided along the plug radial direction and protrudes toward the plug central axis C.

[0032] In this embodiment, the ground electrode 6 has a standing portion 64, a bent portion 65, and an extended portion 66, as shown in Fig. 1. The standing portion 64 has a fixed end 61, and stands from the front end of the housing 2 toward the front end along the plug axial direction Z. The bent portion 65 is bent from the front end of the standing portion 64 toward the inside in the plug radial direction. The extended portion 66 extends from the bent portion 65 toward the plug central axis C. A discharge gap G is formed between the extended portion 66 and the center electrode 4.

[0033] The extension portion 66 is inclined in the Z direction so as to move toward the tip side as it approaches the protruding end 62. A tip side surface 661 of the extension portion 66 is also inclined in the Z direction so as to move toward the tip side as it approaches the protruding end 62. In this embodiment, the protruding end 62 is the tip of the ground electrode 6. The protruding end 62 and the inner wall surface 54 of the bottom wall portion 57 abut against each other in the Z direction. The inner wall surface 54 of the bottom wall portion 57 is formed so as to be substantially perpendicular to the Z direction.

[0034] The discharge gap G is formed by the mutual opposition of the tip end of the center electrode 4 and the base end side surface 63 of the ground electrode 6. The base end side surface 63 has a gap forming surface 631 that forms the discharge gap G between it and the center electrode 4. The base end side surface 63 is inclined toward the tip side as it approaches the ground side nozzle 511, at least from the position of the gap forming surface 631 to the protruding end portion 62 in the protruding direction of the ground electrode 6 when viewed from the plug axial direction Z.

[0035] In this embodiment, the gap forming surface 631 and the tip surface 41 of the center electrode 4 face each other to form a discharge gap G. The tip surface 41 of the center electrode 4 is located on the tip side of the tip of the housing 2. In other words, the discharge gap G is formed on the tip side of the tip of the housing 2.

[0036] The discharge gap G is, for example, the area obtained by projecting the tip surface 41 of the center electrode 4 in the Z direction and the area obtained by projecting the tip surface 41 in a direction perpendicular to the base end side surface 63 of the extension portion 66, and is the area between the tip surface 41 and the base end side surface 63.

[0037] In this embodiment, the plug cover 5 is fixed to the housing 2 by welding. Specifically, the cover base end portion 52 is fixed to the housing fixing portion 21 by welding.

[0038] The tip end of the housing 2 is stepped by forming the housing fixing portion 21 and the opposing surface 22. In addition, a cover base end portion 52 is fixed to the outer periphery of the housing fixing portion 21.

[0039] In addition, the base end surface 53 of the plug cover 5 is located on the tip side of the opposing surface 22. The opposing surface 22 and the base end surface 53 face each other in the Z direction without abutting each other. In other words, a gap g1 is formed between the opposing surface 22 and the base end surface 53.

[0040] As shown in Fig. 8, a distance D7 from the opposing surface 22 to the tip of the ground electrode 6 in the Z direction is greater than a distance D8 from the base end surface 53 of the plug cover 5 to the inner wall surface 54 of the bottom wall portion 57 in the Z direction. Since the distance D7 is greater than the distance D8, a gap g1 is formed between the opposing surface 22 and the base end surface 53 of the plug cover 5 when the protruding end 62 is brought into contact with the inner wall surface 54 of the bottom wall portion 57 in the contact step described below, as shown in Fig. 1. In this embodiment, the distance from the base end surface 53 of the plug cover 5 to the tip of the auxiliary combustion chamber 50 in the Z direction is substantially the same as the distance D8.

[0041] Next, a method for manufacturing the spark plug 1 of this embodiment will be described. In manufacturing the spark plug 1, a preparation step, a contact step, and a joining step are performed. In the preparation step, the housing 2 to which the ground electrode 6, the insulator 3, and the center electrode 4 are assembled, and the plug cover 5 to which the injection hole 51 is formed are prepared. In the contact step, after the preparation step, the plug cover 5 is moved toward the base end side with respect to the housing 2 as shown by the arrow M in FIG. 8, so that the protruding end 62 and the inner wall surface 54 of the bottom wall portion 57 are contacted with each other in the Z direction as shown in FIG. 1. In the contact step, the housing fixing portion 21 and the cover base end portion 52 are overlapped in the plug radial direction, and the protruding end 62 and the inner wall surface 54 of the bottom wall portion 57 are contacted with each other in the Z direction. In this embodiment, the protruding end 62 and the inner wall surface 54 of the bottom wall portion 57 are contacted with each other in the Z direction with the plug cover 5 fitted to the housing 2. In the joining step, after the abutting step, the housing fixing portion 21 and the cover base end portion 52 are joined to each other. More specifically, in the joining step, the cover base end portion 52 is joined to the outer periphery of the housing fixing portion 21 by welding while maintaining the protruding end portion 62 and the inner wall surface 54 of the bottom wall portion 57 in abutting contact with each other in the Z direction. This makes it possible to manufacture the spark plug 1 of this embodiment as shown in Figs. 1 and 2.

[0042] Further, the outer peripheral surface of the housing fixing portion 21 and the inner wall surface 54 of the cover base end 52 are each formed to extend along the Z direction. In the abutting step, when the protruding end 62 and the inner wall surface 54 of the bottom wall portion 57 are abutted against each other in the Z direction, the outer peripheral surface of the housing fixing portion 21 and the inner wall surface 54 of the cover base end 52 are in a state of abutting against each other in the plug radial direction. However, a slight clearance may be provided between the outer peripheral surface of the housing fixing portion 21 and the inner wall surface 54 of the cover base end 52 to allow smooth sliding between them.

[0043] Next, the effects of this embodiment will be described. In the above spark plug 1, the protruding end 62 and the inner wall surface 54 of the plug cover 5 abut against each other in the plug axial direction Z. Also, when viewed from the plug axial direction Z, at least a portion of the ground side nozzle hole 511 overlaps with at least one of the ground extension region 6E and the gap extension region GE. Therefore, during the expansion stroke of the internal combustion engine, the discharge generated in the discharge gap G is easily extended by the airflow toward the ground side nozzle hole 511. As a result, the ignition performance can be improved.

[0044] In the expansion stroke, the piston moves toward the tip side, so that the main combustion chamber becomes negative pressure relative to the auxiliary combustion chamber 50. As a result, gas is discharged from the auxiliary combustion chamber 50 to the main combustion chamber through the nozzle hole 51. In addition, as the gas is discharged through the ground side nozzle hole 511, an airflow toward the ground side nozzle hole 511 is formed in the auxiliary combustion chamber 50. Therefore, as shown in FIG. 10, in the expansion stroke, the starting point S1 on the ground electrode 6 side of the discharge S generated in the discharge gap G is likely to move toward the ground side nozzle hole 511 along the base end side surface 63 and the protruding end surface 621 by the airflow A toward the ground side nozzle hole 511, as shown in FIG. 11. Therefore, the discharge S is likely to extend toward the ground side nozzle hole 511. As a result, the ignition performance can be improved. In addition, the protruding end portion 62 and the inner wall surface 54 of the plug cover 5 are in contact with each other in the plug axial direction Z. Therefore, as shown in FIG. 12, the starting point S1 of the discharge S is likely to move from the ground electrode 6 to the inner peripheral surface of the ground side nozzle hole 511 via the inner wall surface 54 of the plug cover 5. Then, the discharge S is further extended, and it is expected that a part of the discharge S will fly out from the ground side nozzle hole 511 to the main combustion chamber side as shown in FIG. 13. Therefore, it is possible to stabilize the combustion in the main combustion chamber during the expansion stroke. This makes it possible to raise the catalyst temperature of the exhaust gas purification filter in a short period of time. As a result, it is expected that fuel efficiency will improve and emissions will be reduced.

[0045] When viewed from the plug axial direction Z, the ground side nozzle hole 511 is formed on the protruding side of the ground electrode 6. The protruding end face 621 is substantially parallel to the plug axial direction Z. Therefore, the airflow A is easily formed in the vicinity of the protruding end face 621 in the auxiliary combustion chamber 50. Therefore, the starting point S1 is easily moved along the protruding end face 621 to the ground side nozzle hole 511. As a result, the discharge can be further extended.

[0046] The inner diameter D2 (see FIG. 3) is 1.2 to 1.4 times the inner diameter D3 (see FIG. 3). This makes it possible to strengthen the airflow A flowing toward the ground side nozzle hole 511. This makes it possible for the discharge S to extend more easily and to fly out from the ground side nozzle hole 511 toward the main combustion chamber more easily. As a result, it is possible to further improve the ignition performance.

[0047] The discharge gap G is formed by opposing the tip end of the center electrode 4 and the base end side surface 63 of the ground electrode 6. The base end side surface 63 is inclined toward the tip end as it approaches the ground side nozzle 511, at least from the position of the gap forming surface 631 to the protruding end portion 62 in the protruding direction of the ground electrode 6 when viewed from the plug axial direction Z. This makes it possible to strengthen the airflow A flowing from the discharge gap G toward the ground side nozzle 511. As a result, the discharge S can be further extended.

[0048] When viewed from the Z direction, at least a part of the protruding end surface 621 is disposed between the discharge gap G and the ground side nozzle hole 511. Therefore, the starting point S1 is more likely to move along the protruding end surface 621 toward the ground side nozzle hole 511. Therefore, the discharge S is more likely to extend and more likely to project from the ground side nozzle hole 511 toward the main combustion chamber.

[0049] Furthermore, the distance D6 (see FIG. 6) is shorter than the distance D5 (see FIG. 6). Therefore, it is easy to reliably and sufficiently form the airflow A in the discharge gap G, and it is easy to shorten the length from the fixed end 61 to the protruding end 62 of the ground electrode 6. Therefore, it is easy to reliably extend the discharge S, and it is easy to shorten the heat dissipation path of the ground electrode 6. As a result, it is possible to reliably improve the ignition performance, and to suppress overheating of the ground electrode 6.

[0050] Line segment L1 (see FIG. 7) does not pass through both the ground electrode 6 and the plug cover 5. Therefore, when the discharge S extends toward the main combustion chamber due to the airflow A, it is unlikely to be short-circuited by the ground electrode 6 and the plug cover 5. Therefore, the discharge easily and reliably extends toward the main combustion chamber. As a result, the ignition ability of the main combustion chamber can be reliably improved.

[0051] In addition, the extension region 511E does not overlap with the discharge gap G. Therefore, during the compression stroke, it is possible to suppress blowing out and short-circuiting of the discharge generated in the discharge gap G due to the airflow flowing into the auxiliary combustion chamber 50 through the ground side nozzle 511. As a result, it is possible to reliably ensure ignition performance during the compression stroke.

[0052] The cover base end portion 52 is fixed to the outer periphery of the housing fixing portion 21. Therefore, the volume of the auxiliary combustion chamber 50 is likely to be large. Therefore, the force of the flame ejected from the auxiliary combustion chamber 50 to the main combustion chamber through the injection hole 51 can be strengthened. As a result, the ignition performance can be improved.

[0053] The spark plug 1 of the present embodiment can be manufactured by performing a preparation step, a contact step, and a joining step. Therefore, the spark plug 1 can be manufactured efficiently. As a result, the productivity of the spark plug 1 can be improved.

[0054] In addition, the protruding end 62 forms the tip of the ground electrode 6. This makes it easier to bring the protruding end 62 into reliable contact with the inner wall surface 54 of the plug cover. This allows the spark plug 1 to be manufactured more efficiently. As a result, the productivity of the spark plug 1 can be further improved.

[0055] Further, the distance D7 is greater than the distance D8 (see FIG. 8). Therefore, in the abutting step, the protruding end 62 can be reliably abutted against the inner wall surface 54 of the bottom wall portion 57. That is, the protruding end 62 can be abutted against the inner wall surface 54 of the bottom wall portion 57 without the base end surface 53 of the plug cover 5 abutting against the opposing surface 22. As a result, the spark plug 1 can be manufactured reliably and efficiently.

[0056] The inclined nozzle hole 512 is formed so that the airflow introduced into the auxiliary combustion chamber 50 through the inclined nozzle hole 512 generates a swirl flow SF in the auxiliary combustion chamber 50. Therefore, the initial flame formed by the discharge generated in the discharge gap G is likely to spread into the auxiliary combustion chamber 50 by the swirl flow SF. Therefore, combustion in the auxiliary combustion chamber 50 is likely to be promoted. As a result, the ignition ability of the auxiliary combustion chamber 50 can be improved.

[0057] The discharge gap G is formed on the tip side of the tip of the housing 2. Therefore, it is easy to check the discharge gap G formed between the ground electrode 6 and the center electrode 4 fixed to the housing 2 before fixing the plug cover 5 to the housing 2. This makes it easy to adjust the discharge gap G. As a result, the spark plug 1 can be manufactured efficiently.

[0058] The ground electrode 6 has an erected portion 64, a bent portion 65, and an extended portion 66. A base end side surface 63 of the extended portion 66 and a tip end portion of the center electrode 4 face each other to form a discharge gap G. Therefore, during manufacture of the spark plug 1, the length of the discharge gap G can be easily adjusted by slightly deforming the ground electrode 6 as necessary. As a result, the spark plug 1 can be manufactured efficiently.

[0059] As described above, according to this embodiment, it is possible to provide a spark plug 1 for an internal combustion engine that can improve ignition performance.

[0060] (Embodiment 2) As shown in FIG. 14, this embodiment is an embodiment in which the shape of the plug cover 5 is modified from that of the first embodiment.

[0061] 14, the plug cover 5 has a protruding portion 55 formed by a part of the inner wall surface 54 protruding toward the base end side. The protruding portion 55 and the protruding end portion 62 abut against each other in the plug axial direction Z.

[0062] The protrusion 55 is formed on the bottom wall 57. The central axis 55L of the protrusion 55 is eccentric to the plug central axis C toward the outside in the plug radial direction. That is, the base end of the protrusion 55 is located toward the outside in the plug radial direction with respect to the plug central axis C. When viewed from the Z direction (not shown), the central axis 55L is on the opposite side to the fixed end 61 across the plug central axis C in the protruding direction of the ground electrode 6. When viewed from the Z direction, the central axis 55L is between the plug central axis C and the ground side injection hole 511 in the protruding direction of the ground electrode 6. In this embodiment, the protrusion 55 is formed integrally with other parts of the plug cover 5.

[0063] The ground side nozzle hole 511 is formed radially outward of the protruding portion 55. The ground side nozzle hole 511 is formed on the tip side of the protruding end portion 62.

[0064] Further, the extension portion 66 is inclined so as to be more inclined toward the base end side as it approaches the protruding end portion 62. The inclination angle θ1 of the extension portion 66 with respect to the Z direction is less than 90°. 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.

[0065] The convex portion 55 and the protruding end portion 62 abut against each other in the plug axial direction Z. Therefore, when manufacturing the spark plug 1, even if the inclination angle θ1 is less than 90°, the protruding end portion 62 and the plug cover 5 can be reliably abutted against each other in the Z direction. As a result, even if the inclination angle θ1 is less than 90°, the discharge can be reliably extended.

[0066] The central axis 55L of the protruding portion 55 is eccentric outward in the plug radial direction with respect to the plug central axis C. Therefore, when manufacturing the spark plug 1, even if the inclination angle θ1 is less than 90°, the protruding end portion 62 can be more reliably brought into contact with the plug cover 5.

[0067] When viewed from the Z direction, the central axis 55L is on the opposite side to the fixed end 61 across the plug central axis C in the protruding direction of the ground electrode 6. Therefore, when manufacturing the spark plug 1, even if the inclination angle θ1 is less than 90°, the protruding end 62 can be more reliably brought into contact with the plug cover 5. In addition, the same effects as those of the first embodiment are achieved.

[0068] (Embodiment 3) As shown in FIG. 15, this embodiment is an embodiment in which the position at which the protrusion 55 is formed is changed from that of the second embodiment.

[0069] 15, the protrusion 55 is formed so that a central axis 55L of the protrusion 55 substantially overlaps with the plug central axis C. The protrusion 55 has a flat base end surface. The base end surface of the protrusion 55 is formed so as to be approximately perpendicular to the Z direction.

[0070] The extension portion 66 is formed so as to extend along the plug radial direction. That is, the extension portion 66 protrudes in a direction substantially perpendicular to the Z direction. A tip side surface 661 of the extension portion 66 is formed so as to be substantially perpendicular to the Z direction. The base end surface of the protrusion 55 is in surface contact with the tip side surface 661. The rest is the same as in the second embodiment.

[0071] The base end surface of the protrusion 55 is in surface contact with the tip side surface 661. Therefore, the starting point on the ground electrode 6 side of the discharge generated in the discharge gap G is likely to reliably move from the ground electrode 6 to the plug cover 5 by the airflow toward the ground side nozzle 511. As a result, the discharge can be reliably extended. In addition, the same effects as those of the second embodiment are achieved.

[0072] (Embodiment 4) As shown in FIG. 16, this embodiment is an embodiment in which the shape of the protruding end portion 62 is modified from that of the first embodiment.

[0073] 16, the protruding end surface 621 is inclined toward the protruding side of the ground electrode 6 as it approaches the tip side. In other words, the protruding end surface 621 is inclined toward the outside in the plug radial direction as it approaches the tip side. The rest is the same as in the first embodiment.

[0074] In this embodiment, the protruding end surface 621 is inclined toward the protruding side of the ground electrode 6 as it approaches the tip side. Therefore, during the expansion stroke, the starting point of the discharge on the ground electrode 6 side is more likely to move toward the ground side nozzle hole 511 on the protruding end surface 621 due to the airflow toward the ground side nozzle hole 511. As a result, the discharge can be further extended.

[0075] Here, as shown in FIG. 17, it is assumed that the protruding end surface 621 is inclined toward the opposite side to the protruding side of the ground electrode 6 as it approaches the tip side. In this case, in the expansion stroke, a stagnation portion 501 where the airflow is relatively weak is likely to be formed near the protruding end surface 621 in the auxiliary combustion chamber 50. Therefore, compared to this embodiment, the starting point of the discharge on the ground electrode 6 side is less likely to move along the protruding end surface 621 to the ground side nozzle hole 511. On the other hand, in this embodiment, as described above, the protruding end surface is inclined toward the protruding side of the ground electrode 6 as it approaches the tip side. Therefore, the airflow toward the ground side nozzle hole 511 is easily formed sufficiently near the protruding end surface 621 in the auxiliary combustion chamber 50. Therefore, the starting point of the discharge on the ground electrode 6 side is likely to move along the protruding end surface 621 to the ground side nozzle hole 511. As a result, the discharge can be further extended. In addition, the same effects as those of the first embodiment are achieved.

[0076] (Embodiment 5) As shown in FIG. 18, this embodiment is an embodiment in which the formation position of the ground side nozzle hole 511 is changed from that of the first embodiment.

[0077] In this embodiment, the ground side nozzle hole 511 is formed at a corner portion 58 as shown in Fig. 18. The ground side nozzle hole 511 is inclined so as to be directed outward in the plug radial direction as it approaches the tip side. The ground side nozzle hole 511 is also an inclined nozzle hole 512.

[0078] In addition, the shortest distance from the protruding end portion 62 to the inner wall surface 54 of the peripheral wall portion 56 is shorter than the shortest distance from the protruding end portion 62 to the plug central axis C. The rest is the same as in the first embodiment.

[0079] The ground side nozzle hole 511 is formed at the corner portion 58. The ground side nozzle hole 511 is inclined so as to be directed outward in the plug radial direction toward the tip side. Therefore, the flame ejected from the auxiliary combustion chamber 50 to the main combustion chamber through the ground side nozzle hole 511 can be ejected along the base end surface of the main combustion chamber. Therefore, the flame is less likely to collide with the base end surface of the main combustion chamber and the piston. Therefore, it is easy to improve the combustibility of the main combustion chamber. As a result, it is expected that knock suppression can be improved during medium and high loads of the internal combustion engine. In addition, the same effects as those of the first embodiment are achieved.

[0080] (Embodiment 6) As shown in FIG. 19, this embodiment is an embodiment in which the shape of the ground electrode 6 is modified from that of the first embodiment.

[0081] In this embodiment, the ground electrode 6 protrudes from the fixed end 61 into the auxiliary combustion chamber 50 without bending, as shown in Fig. 19. In other words, the ground electrode 6 is formed in a rod shape. Also, the ground electrode 6 is inclined toward the tip side as it approaches the protruding end 62. The rest is the same as in the first embodiment.

[0082] The ground electrode 6 protrudes from the fixed end 61 into the auxiliary combustion chamber 50 without bending. This makes it easy to shorten the length of the ground electrode 6 from the fixed end 61 to the protruding end 62. This makes it easy to shorten the heat dissipation path of the ground electrode 6 to the housing 2 and the heat dissipation path to the plug cover 5. This makes it easy to dissipate heat from the ground electrode 6 to the outside. As a result, overheating of the ground electrode 6 can be suppressed. In addition, the same effects as those of the first embodiment are achieved.

[0083] (Embodiment 7) As shown in FIG. 20, this embodiment is an embodiment in which the shape of the ground electrode 6 is modified from that of the sixth embodiment.

[0084] 20, a flat ground contact surface 67 is formed on the tip side of the protruding end portion 62. The ground contact surface 67 is formed so as to be substantially perpendicular to the Z direction. The ground contact surface 67 is also formed so as to be along the inner wall surface 54 of the bottom wall portion 57. The ground contact surface 67 is in surface contact with the inner wall surface 54 of the bottom wall portion 57. The rest is the same as in the sixth embodiment.

[0085] The ground contact surface 67 is in surface contact with the inner wall surface 54 of the bottom wall portion 57. Therefore, the starting point on the ground electrode 6 side of the discharge generated in the discharge gap G is likely to reliably move from the ground electrode 6 to the plug cover 5 by the airflow toward the ground side nozzle hole 511. As a result, the discharge can be reliably extended. In addition, the same effects as those of the sixth embodiment are obtained.

[0086] (Embodiment 8) As shown in FIG. 21, this embodiment is an embodiment in which the opening direction of the ground side nozzle hole 511 is changed from that of the sixth embodiment.

[0087] In this embodiment, the ground side nozzle hole 511 opens at an inclination with respect to the Z direction so as to move outward in the plug radial direction toward the tip side, as shown in Fig. 21. In other words, the nozzle hole axis 511L of the ground side nozzle hole 511 is inclined with respect to the Z direction. The nozzle hole axis 511L passes through the center electrode 4 without passing through the discharge gap G. The rest is the same as in the sixth embodiment.

[0088] The ground side nozzle hole 511 opens at an angle with respect to the Z direction so that it moves radially outward in the plug direction toward the tip side. Therefore, when the discharge generated in the discharge gap G extends toward the main combustion chamber due to the airflow, it is unlikely to be short-circuited by the ground electrode 6 and the plug cover 5. Therefore, the discharge easily and reliably extends toward the main combustion chamber. As a result, it is possible to reliably improve the ignition performance in the main combustion chamber. In addition, the same effects as those of the sixth embodiment are obtained.

[0089] (Embodiment 9) As shown in FIG. 22, this embodiment is an embodiment in which the shape of the ground electrode 6 is modified from that of the first embodiment.

[0090] In this embodiment, the extension portion 66 of the ground electrode 6 is formed so as to extend along the plug radial direction, as shown in Fig. 22. The tip side surface 661 of the extension portion 66 is formed so as to be substantially perpendicular to the Z direction. The tip side surface 661 of the extension portion 66 is formed so as to extend along the inner wall surface 54 of the bottom wall portion 57. The tip side surface 661 is in surface contact with the inner wall surface 54 of the bottom wall portion 57. The rest is the same as in the first embodiment.

[0091] The tip side surface 661 is in surface contact with the inner wall surface 54 of the bottom wall portion 57. Therefore, the starting point on the ground electrode 6 side of the discharge generated in the discharge gap G is likely to reliably move from the ground electrode 6 to the plug cover 5 by the airflow toward the ground side nozzle hole 511. As a result, the discharge can be reliably extended. In addition, the same effects as those of the first embodiment are achieved.

[0092] (Embodiment 10) In this embodiment, as shown in FIG. 23, a cover base end portion 52 is fixed to the inner periphery side of a housing fixing portion 21. As shown in FIG.

[0093] In this embodiment, the abutting step and the joining step are performed in a state in which the inner peripheral surface of the housing fixing portion 21 and the outer peripheral surface of the cover base end portion 52 are in contact with each other in the plug radial direction.

[0094] As shown in FIG. 23, the ground electrode 6 protrudes from the inner circumferential surface 25 of the housing 2 into the auxiliary combustion chamber 50 . The other configurations and effects are the same as those of the first embodiment.

[0095] (Embodiment 11) In this embodiment, as shown in Figs. 24 and 25, a discharge gap G is formed by arranging a center electrode 4 and a ground electrode 6 opposite each other in the plug radial direction.

[0096] As shown in Figs. 24 and 25, the discharge gap G is formed by the center-facing side surface 42 of the center electrode 4 and the ground-facing side surface 68 of the ground electrode 6 facing each other in the plug radial direction.

[0097] The ground electrode 6 is formed in a rod shape. Specifically, the ground electrode 6 is in the shape of a substantially rectangular prism. That is, the ground electrode 6 has four flat side surfaces, one of which is a ground-facing side surface 68. The ground-facing side surface 68 is formed in a continuous flat surface shape from the fixed end portion 61 to the protruding end portion 62. The ground electrode 6 is inclined toward the tip side as it approaches the protruding end portion 62.

[0098] The discharge gap G is, for example, a region between the ground facing side surface 68 and the center facing side surface 42 facing each other in the thickness direction of the ground electrode 6.

[0099] Also, as shown in FIG. 25, when viewed from the Z direction, the ground side nozzle hole 511 does not overlap with the ground extension region 6E but overlaps with the gap extension region GE. The rest is the same as in the first embodiment.

[0100] The discharge gap G is formed by the center facing side surface 42 and the ground facing side surface 68 facing each other in the plug radial direction. Also, when viewed from the Z direction, the ground side nozzle hole 511 overlaps with the gap extension region GE. Therefore, during the expansion stroke, the airflow from the discharge gap G to the ground side nozzle hole 511 is less likely to be blocked by the ground electrode 6, etc. Therefore, the discharge is more likely to extend. Also, when the discharge extends toward the main combustion chamber by the airflow, it is less likely to be short-circuited by the ground electrode 6. Therefore, the discharge is more likely to extend toward the main combustion chamber. As a result, the ignition ability can be further improved.

[0101] The ground electrode 6 has a ground-facing side surface 68. Therefore, the swirl flow formed in the auxiliary combustion chamber 50 is guided by the ground-facing side surface 68 and easily passes through the discharge gap G. Therefore, the discharge formed in the discharge gap G is easily extended. As a result, the ignition performance can be improved. In addition, the same effects as those of the first embodiment are achieved.

[0102] (Embodiment 12) In this embodiment, as shown in FIG. 26, a plug cover 5 is fixed to a housing 2 by screwing.

[0103] In this embodiment, the housing fixing portion 21 and the cover base end portion 52 form a threaded portion that is fixed to each other by threading the male thread portion 11 and the female thread portion 12, as shown in Fig. 26. Specifically, the plug cover 5 is fixed to the housing 2 by threading the female thread portion 12 formed on the cover base end portion 52 with the male thread portion 11 formed on the housing fixing portion 21. In this embodiment, the position of the ground side injection hole 511 in the plug circumferential direction relative to the ground electrode 6 can be adjusted by adjusting the positions at which the threads of the male thread portion 11 and the female thread portion 12 start to be cut.

[0104] Next, a method for manufacturing the spark plug 1 of this embodiment will be described. In the abutting step, with the male threaded portion 11 and the female threaded portion 12 screwed together, the plug cover 5 is rotated in one circumferential direction of the plug relative to the housing 2. As a result, the plug cover 5 is moved toward the base end relative to the housing 2 until the protruding end portion 62 and the inner wall surface 54 of the bottom wall portion 57 abut against each other, as shown in FIG. The other configurations and effects are the same as those of the first embodiment.

[0105] (Embodiment 13) As shown in FIG. 27, this embodiment is an embodiment in which the formation position of the ground side nozzle hole 511 is changed from that of the first embodiment.

[0106] In this embodiment, as shown in FIG. 27, when viewed from the Z direction, a part of the ground side nozzle hole 511 overlaps with the ground extension region 6E. The other configurations and effects are the same as those of the first embodiment.

[0107] (Embodiment 14) In this embodiment, as shown in FIGS. 28 to 30, a base end side protrusion 521 is formed on the cover base end 52. As shown in FIG.

[0108] In this embodiment, the cover base end 52 has a base end side protrusion 521 formed by a part of the base end surface 53 protruding toward the base end side as shown in Figures 28 to 30. In this embodiment, four base end side protrusions 521 are formed on the plug cover 5. Note that, for convenience, the illustration of the ground electrode is omitted in Figure 30.

[0109] 29 and 30, the tip portion of the housing 2 has recesses 24 formed by part of the opposing surface 22 receding toward the base end side. Four recesses 24 are formed in the tip portion of the housing 2. A base end side protrusion 521 is disposed inside the recesses 24. In other words, the base end side protrusion 521 is fitted into the recesses 24. The rest is the same as in the sixth embodiment.

[0110] In this embodiment, the base end side protrusion 521 is disposed inside the recess 24. This makes it easy to determine the position of the plug cover 5 in the plug circumferential direction relative to the housing 2 and the ground electrode 6. This makes it easy to position the ground side injection hole 511 at a desired position during assembly. As a result, the spark plug 1 can be manufactured more efficiently. In addition, the same effects as those of the sixth embodiment are obtained.

[0111] (Embodiment 15) As shown in FIG. 31, this embodiment is an embodiment in which the shape of the ground electrode 6 is modified from that of the first embodiment.

[0112] As shown in FIG. 31, the length of the standing portion 64 in the Z direction is approximately the same as the length of the extending portion 66 in the extending direction.

[0113] The housing 2 has an inner circumferential recess 26 formed by part of the inner circumferential surface 25 receding outward in the plug radial direction. The inner circumferential recess 26 opens to the tip end. A standing portion 64 is fitted into the inner circumferential recess 26. The standing portion 64 is joined to a recess forming surface that forms the inner circumferential recess 26. The rest is the same as in the first embodiment.

[0114] The erected portion 64 is joined to a recess forming surface that forms the inner circumferential recess 26. This makes it easy to increase the joining area of ​​the ground electrode 6 to the housing 2. As a result, the ground electrode 6 can be firmly fixed to the housing 2. In addition, the same effects as those of the first embodiment are achieved.

[0115] In the above embodiments 1 to 15, an inclined injection hole 512 is formed in the corner 58 of the plug cover 5. However, the injection hole formed in the corner can also be formed so that the injection hole axis is aligned along the plug radial direction when viewed from the Z direction.

[0116] In addition, in the above-mentioned embodiments 1 to 4 and 6 to 15, the ground electrode 6 is provided so that the ground electrode 6 and the injection hole 51 do not overlap each other when viewed from the Z direction. However, as in the above-mentioned embodiment 5, the ground electrode 6 can also be provided so that the ground electrode 6 and the injection hole 51 overlap each other when viewed from the Z direction.

[0117] In the above-mentioned second and third embodiments, the protrusion 55 is formed integrally with other portions of the plug cover 5. However, the protrusion can also be formed by joining a separate member to the plug cover.

[0118] The ground electrode can also be arranged so that, when viewed from the Z direction, the innermost end in the plug radial direction of the inner opening of the ground side nozzle hole and the protruding end face of the protruding end portion overlap each other.

[0119] 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.

[0120] 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]

[0121] 1...spark plug, 2...housing, 21...housing fixing portion, 22...opposing surface, 3...insulator, 4...center electrode, 5...plug cover, 50...auxiliary combustion chamber, 51...nozzle hole, 511...ground side nozzle hole, 52...cover base end, 53...base end surface, 54...inner wall surface, 6...ground electrode, 61...fixed end, 62...protruding end, 6E...ground extension region, G...discharge gap, GE...gap extension region, Z...plug axial direction, D1...shortest distance, D2...inner diameter

Claims

1. A cylindrical insulator (3); a center electrode (4) held on the inner circumferential side of the insulator and exposed on the tip side from the insulator; a cylindrical housing (2) that holds the insulator on its inner periphery; a ground electrode (6) forming a discharge gap (G) between itself and the center electrode; a plug cover (5) fixed to the tip of the housing so as to cover a sub-combustion chamber (50) in which the discharge gap is disposed, The ground electrode protrudes into the auxiliary combustion chamber from a fixed end (61) fixed to the housing, The plug cover is formed with a plurality of nozzle holes (51) that communicate the auxiliary combustion chamber with the outside, the front end portion of the housing has a housing fixing portion (21) facing a cover base end portion (52) of the plug cover in the plug radial direction, and an opposing surface (22) facing a base end surface (53) of the plug cover in the plug axial direction (Z) on the base end side of the housing fixing portion, The housing fixing portion and the cover base end portion are fixed to each other, the base end surface of the plug cover is disposed at a position spaced apart from the opposing surface in the plug axial direction, The projecting end portion (62) of the ground electrode and the inner wall surface (54) of the plug cover abut against each other in the plug axial direction, Some of the nozzle holes among the plurality of nozzle holes are ground side nozzle holes (511) whose shortest distance (D1) to the protruding end is equal to or shorter than an inner diameter (D2) of the nozzle hole, when viewed from the plug axial direction, at least a part of the ground side injection hole overlaps with at least one of a ground extension region (6E) in which the ground electrode is extended in a protruding direction and a gap extension region (GE) in which the discharge gap is extended in the protruding direction of the ground electrode, the plug cover has a protrusion (55) formed by a portion of the inner wall surface protruding toward the base end, and the protrusion and the protruding end abut against each other in the plug axial direction.

2. When viewed from the plug axial direction, the ground side injection hole is formed on the protruding side of the ground electrode, 2. A spark plug for an internal combustion engine according to claim 1, wherein a protruding end face (621) is formed on a protruding side of the protruding end portion, and the protruding end face is substantially parallel to an axial direction of the plug or is inclined toward the protruding side of the ground electrode as it extends toward a tip side.

3. 3. The spark plug for an internal combustion engine according to claim 1, wherein an inner diameter of said ground side nozzle hole is 1.2 to 1.4 times an inner diameter (D3) of said other nozzle holes.

4. 4. A spark plug for an internal combustion engine according to claim 1, wherein the discharge gap is formed by opposing a tip portion of the center electrode and a base end side surface (63) of the ground electrode, the base end side surface has a gap forming surface (631) which forms the discharge gap between the center electrode and the base end side surface, and the base end side surface is inclined so as to proceed toward the tip side as it approaches the ground side nozzle hole at least from a position of the gap forming surface to the protruding end in a protruding direction of the ground electrode as viewed in the plug axial direction.

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