Spark plugs for internal combustion engines

Abstract

To provide a spark plug for an internal combustion engine which allows improvement in ignitability.SOLUTION: In a spark plug 1 for an internal combustion engine, a plug cover 5 is provided at a tip end of a housing 2 such that it covers a sub-combustion chamber 50 where a discharge gap G is located. The plug cover 5 has a plurality of injection holes 51 formed thereon. An extension line 51L of the central axis of each of the injection holes does not pass through the discharge gap G. One injection hole 51 of the plurality of injection holes 51 is an axis-side injection hole 510 formed at a position where a distance D2 to a plug central axis C in a plug radius direction is shorter than a distance D1 to an inner circumferential surface 21 of the tip end of the housing 2 in the plug radius direction. The axis-side injection hole 510 is formed such that an extension region extending from the axis-side injection hole 510 in its opening direction does not pass through the discharge gap G. Viewing from the opening direction of the axis-side injection hole 510, the axis-side injection hole 510 is formed such that at least part of the axis-side injection hole 510 does not overlap a ground electrode 6.SELECTED DRAWING: Figure 3

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 cover portion covering the auxiliary combustion chamber is formed with a plurality of 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 ignition of the mixture in the pre-combustion chamber, i.e., the formation of an initial flame itself. In other words, no consideration is given to improving ignition by extending the discharge in the pre-combustion chamber.

[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 having a tip protrusion (41) protruding toward the tip side of 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) provided at the tip of the housing so as to cover the auxiliary combustion chamber (50) in which the discharge gap is disposed. A spark plug (1) for an internal combustion engine, The ground electrode protrudes into the auxiliary combustion chamber from a fixed end (62) fixed to the housing or the plug cover, The discharge gap is formed by the tip end of the tip protrusion and the base end surface (61) of the ground electrode facing each other, The plug cover is formed with a plurality of nozzle holes (51) that communicate the auxiliary combustion chamber with the outside, An extension line (51L) of the central axis of the nozzle hole does not pass through the discharge gap, some of the plurality of injection holes are shaft-side injection holes (510) formed at positions where a distance (D2) to a plug central axis (C) in the plug radial direction is closer than a distance (D1) to an inner circumferential surface (21) of a tip portion of the housing in the plug radial direction, The shaft side nozzle hole is formed such that an extension region (510E) extending the shaft side nozzle hole in an opening direction does not pass through the discharge gap, and at least a part of the shaft side nozzle hole does not overlap the ground electrode when viewed from the opening direction of the shaft side nozzle hole. Cage , the nozzle hole has an outer nozzle hole (514) formed radially outward of the shaft-side nozzle hole, the outer nozzle hole having at least two large nozzle holes (515) and a small nozzle hole (516) having an opening area smaller than that of the large nozzle hole, the large nozzle hole opens at an angle with respect to the plug axial direction (Z) so as to move radially outward toward the tip side, when the spark plug is divided into a first plug portion (11) and a second plug portion (12) by a predetermined plane (P) including a plug central axis, both of the at least two large nozzle holes are formed in the first plug portion, a fixed end of the ground electrode is fixed to the housing or the plug cover in the first plug portion, the shaft-side nozzle hole is formed in the second plug portion, and when viewed from the plug axial direction, the fixed end of the first plug portion is disposed between extensions of central axes of the at least two large nozzle holes in the plug circumferential direction. Spark plug for internal combustion engine Gu be. Effect of the Invention

[0007] The spark plug for an internal combustion engine has an axial-side nozzle hole as one of a plurality of nozzle holes. Therefore, the airflow introduced into the auxiliary combustion chamber through the axial-side nozzle hole and the airflow discharged from the auxiliary combustion chamber through the axial-side nozzle hole tend to pass near the discharge gap. The airflow passing near the discharge gap has an attraction effect, which can extend the discharge generated in the discharge gap. As a result, the 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. FIG. 3 is a cross-sectional view of the spark plug in the axial direction in the vicinity of the tip portion of the spark plug according to the first embodiment, which corresponds to a cross-sectional view taken along line II in FIG. [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. 4 is an explanatory cross-sectional view taken along the plug axial direction, illustrating the position where an axis-side injection hole is formed in the first embodiment. [Figure 4] FIG. 4 is an explanatory cross-sectional view for explaining the positional relationship between an extension region, which is an extension of an axis-side nozzle hole in an opening direction, and a discharge gap in the first embodiment. [Diagram 5] FIG. 3 is an explanatory cross-sectional view illustrating the positional relationship between an axis-side nozzle hole, a center electrode, and a ground electrode in the first embodiment. [Figure 6] FIG. 4 is an explanatory cross-sectional view perpendicular to the plug axial direction, illustrating the position at which an axis-side injection hole is formed in the first embodiment. [Figure 7] FIG. 4 is a cross-sectional view illustrating the direction of a swirl flow formed in the auxiliary combustion chamber during the compression stroke in the first embodiment. [Figure 8] FIG. 1 is a cross-sectional explanatory view of an internal combustion engine according to a first embodiment. [Figure 9] 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 10] 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 11] 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 12]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 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 a spark plug according to a second embodiment. [Figure 15] FIG. 11 is an explanatory cross-sectional view illustrating the positional relationship between an axis-side nozzle hole, a center electrode, and a ground electrode in a second 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 a spark plug according to a third embodiment. [Figure 17] 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 18] FIG. 13 is a cross-sectional view taken along the axial direction of a spark plug in a vicinity of a tip portion of the spark plug according to a fifth embodiment. [Figure 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 an eighth embodiment, showing the vicinity of a tip portion of the spark plug. [Figure 22] 13 is a cross-sectional view of the tip portion of a spark plug according to a ninth embodiment, taken along a line perpendicular to the axial direction of the plug. FIG. [Figure 23] FIG. 23 is a cross-sectional view taken along line XXIII-XXIII in FIG. 22. [Figure 24] FIG. 23 is a cross-sectional view of the tip portion of a spark plug according to a tenth embodiment, taken perpendicular to the plug axial direction. [Diagram 25] FIG. 25 is a cross-sectional view taken along line XXV-XXV in FIG. 24. [Figure 26] FIG. 23 is a view of the ground electrode in the tenth embodiment, viewed from the protruding direction of the ground electrode. [Figure 27] FIG. 23 is a cross-sectional view of the tip portion of a spark plug according to an eleventh embodiment, taken along a plane perpendicular to the plug axis direction. [Figure 28] FIG. 28 is a cross-sectional view taken along line XXVIII-XXVIII in FIG. 27. [Figure 29] FIG. 23 is an explanatory cross-sectional view of an internal combustion engine according to an eleventh embodiment. [Diagram 30] FIG. 23 is a view of the internal combustion engine from the front end side, illustrating the direction of the airflow formed in the main combustion chamber in the eleventh embodiment. [Diagram 31] FIG. 23 is a cross-sectional view of the vicinity of the tip of a spark plug in an eleventh embodiment during the compression stroke and before the discharge extends. [Diagram 32] FIG. 23 is a cross-sectional view of the vicinity of the tip of a spark plug in an eleventh embodiment when the discharge is extended during the compression stroke. [Diagram 33] FIG. 2 is a CFD analysis diagram of the spark plug of the eleventh embodiment in the compression stroke in the experimental example 1. [Diagram 34] FIG. 23 is a cross-sectional explanatory view of an internal combustion engine according to a twelfth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] (Embodiment 1) An embodiment of a spark plug for an internal combustion engine will be described with reference to Figs. A spark plug 1 for an internal combustion engine according to this embodiment has a cylindrical insulator 3, a center electrode 4, a cylindrical housing 2, a ground electrode 6, and a plug cover 5, as shown in Fig. 1 and Fig. 2. The center electrode 4 is held on the inner periphery of the insulator 3, and has a tip projection 41 projecting from the tip side of the insulator 3. The housing 2 holds the insulator 3 on its inner periphery. The ground electrode 6 forms a discharge gap G between itself and the center electrode 4. The plug cover 5 is provided at the tip of the housing 2 so as to cover the auxiliary combustion chamber 50 in which the discharge gap G is located.

[0011] The ground electrode 6 protrudes into the auxiliary combustion chamber 50 from a fixed end 62 fixed to the housing 2 or the plug cover 5. A discharge gap G is formed by the tip of the tip protrusion 41 and a base end surface 61 of the ground electrode 6 facing each other.

[0012] The plug cover 5 is formed with a plurality of injection holes 51 that communicate the auxiliary combustion chamber 50 with the outside. An extension line 51L of the central axis of the injection hole does not pass through the discharge gap G. Some of the injection holes 51 are shaft-side injection holes 510 that are formed at a position where a distance D2 to the plug central axis C in the plug radial direction is closer than a distance D1 to the inner circumferential surface 21 of the tip of the housing 2 in the plug radial direction, as shown in FIG. 3. The shaft-side injection hole 510 is formed so that an extension region 510E extending the shaft-side injection hole 510 in the opening direction does not pass through the discharge gap G, as shown in FIG. 4. In addition, the shaft-side injection hole 510 is formed so that at least a part of the shaft-side injection hole 510 does not overlap with the ground electrode 6 when viewed from the opening direction of the shaft-side injection hole 510, as shown in FIG. 2.

[0013] The spark plug 1 of this embodiment can be used, for example, as an ignition means in an internal combustion engine of an automobile, cogeneration, etc. The spark plug 1 is attached to an internal combustion engine 10 by screwing a mounting thread portion 22 formed on the outer circumferential surface of a housing 2 into a female thread portion of a plug hole 761 of a cylinder head 76, as shown in Fig. 8 .

[0014] 8, the internal combustion engine 10 includes a piston 74 that reciprocates in 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.

[0015] 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. In this embodiment, the plug central axis C also refers to the central axis of the central electrode 4. The plug radial direction refers to 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.

[0016] 1, the plug cover 5 is joined by welding or the like to the tip of the housing 2. When the spark plug 1 is attached to an internal combustion engine, the plug cover 5 separates the auxiliary combustion chamber 50 from the main combustion chamber.

[0017] The plug cover 5 has a peripheral wall portion 52 that covers a part of the outer periphery of the auxiliary combustion chamber 50, a bottom wall portion 53 that covers the tip side of the auxiliary combustion chamber 50, and a corner portion 54 that connects the peripheral wall portion 52 and the bottom wall portion 53. An axis-side injection hole 510 is formed in the bottom wall portion 53.

[0018] 1 to 7, the injection hole 51 has an outer injection hole 514 formed radially outward of the shaft-side injection hole 510. The outer injection hole 514 is formed in the corner portion 54 as shown in FIG.

[0019] In a spark plug 1 installed in an internal combustion engine, a nozzle hole 51 formed in a plug cover 5 connects the auxiliary combustion chamber 50 and the main combustion chamber. During a compression stroke or the like of the internal combustion engine, airflow is introduced from the main combustion chamber to the auxiliary combustion chamber 50 through the nozzle hole 51. Here, the nozzle hole 51 is formed so that the airflow introduced into the auxiliary combustion chamber 50 through the nozzle hole 51 generates a swirl flow (see dashed arrow AF10 in FIG. 7) in the auxiliary combustion chamber 50.

[0020] 2, at least the extension lines 51L of the central axes of the injection holes 51 other than the shaft-side injection hole 510 are inclined with respect to the plug radial direction when viewed from the plug axial direction Z. That is, in this embodiment, when viewed from the Z direction, the extension lines 51L of the central axes of the outer injection holes 514 are inclined at an acute angle with respect to a virtual line VL that passes through the outer injection hole 514 and the plug central axis C and extends in the plug radial direction. The outer injection holes 514 are on the same side in the plug circumferential direction, with the extension lines 51L of the central axes of the outer injection holes 514 inclined with respect to the virtual line VL in each of the outer injection holes 514. The plug circumferential direction is a direction along a circumference centered on the plug central axis C.

[0021] By forming the outer nozzle hole 514 in this manner, as shown in Fig. 7, a swirl flow is formed in the auxiliary combustion chamber 50 by the airflow introduced into the auxiliary combustion chamber 50 through the outer nozzle hole 514. In this embodiment, the swirl flow AF10 is generated in a counterclockwise spiral shape in Fig. 7 around the plug central axis C.

[0022] During the expansion stroke of the internal combustion engine, gas flows from the auxiliary combustion chamber 50 to the main combustion chamber through each outer nozzle hole 514, forming a swirl flow in the opposite direction to the swirl flow formed during the compression stroke.

[0023] The outer injection holes 514 are formed at equal intervals in the circumferential direction of the plug when viewed from the Z direction, as shown in Figures 2, 6 and 7. Moreover, the outer injection holes 514 open at an incline with respect to the Z direction so as to move outward in the radial direction of the plug toward the tip side, as shown in Figures 1 and 3 to 5. Moreover, an extension region (not shown) of the outer injection hole 514 extended in the opening direction does not pass through the discharge gap G.

[0024] 1 to 7, in this embodiment, the shaft side injection hole 510 has a larger opening area than the other injection holes 51. That is, the shaft side injection hole 510 has a larger opening area than the outer injection hole 514.

[0025] The inner diameter of the shaft side nozzle hole 510 can be, for example, 1.2 to 1.4 times the inner diameter of the outer nozzle hole 514. The opening area of ​​the shaft side nozzle hole 510 can be, for example, 1.4 to 2.0 times the opening area of ​​the outer nozzle hole 514.

[0026] In addition, the distance from the discharge gap G to the shaft side nozzle hole 510 is shorter than the distance from the discharge gap G to the outer nozzle hole 514 .

[0027] 6, a virtual circle VC has a diameter half the maximum diameter D4 of the auxiliary combustion chamber 50 and is centered on the plug central axis C. In this embodiment, the shaft-side injection hole 510 is formed at a position closer to the discharge gap G than the outer periphery of the virtual circle VC when viewed from the Z direction.

[0028] 3, in this embodiment, the distance D2 is equal to or less than half the distance D1. Moreover, the distance D2 is equal to or less than the maximum diameter D3 of the tip protrusion 41. Strictly speaking, the distance D1 can be the distance from the shaft side injection hole 510 to the inner circumferential surface 21 of the tip of the housing 2 in the plug radial direction. Moreover, the distance D2 can be the distance from the shaft side injection hole 510 to the plug center axis C in the plug radial direction.

[0029] 1, the shaft side injection hole 510 is formed so that an extension line 51L of the central axis of the shaft side injection hole 510 is along the Z direction. The shaft side injection hole 510 is formed so that the extension line 51L of the central axis of the shaft side injection hole 510 does not pass through the tip protruding portion 41.

[0030] In this embodiment, the shaft side nozzle hole 510 is formed so that the entire shaft side nozzle hole 510 does not overlap the ground electrode 6 when viewed from the opening direction of the shaft side nozzle hole 510 as shown in FIG.

[0031] In this embodiment, the shaft-side injection hole 510 is formed on the protruding side of the protruding end portion 63 of the ground electrode 6 when viewed from the Z direction.

[0032] When viewed from the Z direction, the shaft-side injection hole 510 and the discharge gap G are located on opposite sides of the protruding end 63 of the ground electrode 6. In addition, when viewed from the Z direction, in the protruding direction of the ground electrode 6, the shaft-side injection hole 510 and the fixed end 62 of the ground electrode 6 are located on opposite sides of the discharge gap G.

[0033] As shown in FIG. 5 , a line segment L1 that connects, in the plug radial direction, the outermost outer end 513 of the outer opening 511 of the shaft-side nozzle 510 to the tip of the tip protrusion 41 over the shortest distance does not pass through both the ground electrode 6 and the plug cover 5.

[0034] In addition, the line segment L2 connecting the center of the outer opening 511 of the shaft side nozzle hole 510 and the tip end of the tip protrusion 41 at the shortest distance does not pass through both the ground electrode 6 and the plug cover 5.

[0035] A line segment L3 connecting the inner opening 512 of the shaft side nozzle hole 510 and the tip end of the tip protrusion 41 at the shortest distance does not pass through the ground electrode 6.

[0036] 1, the tip protrusion 41 has a large diameter portion 413 and a small diameter portion 412. The small diameter portion 412 is formed on the tip side of the large diameter portion 413 and has an outer diameter smaller than that of the large diameter portion 413. A discharge gap G is formed between the small diameter portion 412 and the ground electrode 6.

[0037] In this embodiment, the discharge gap G is formed by the leading end projection 41 and the ground electrode 6 facing each other in the plug axial direction Z.

[0038] Specifically, the tip surface 411 of the center electrode 4 and the base end surface 61 of the ground electrode 6 face each other in the Z direction, thereby forming a discharge gap G. It is also possible to join tips to each of the tip surface 411 of the center electrode 4 and the base end surface 61 of the ground electrode 6, which face each other in the Z direction (not shown). In other words, the discharge gap G can also be formed between the tip joined to the tip surface 411 of the center electrode 4 and the tip joined to the base end surface 61 of the ground electrode 6. The tip can be made of a precious metal such as iridium or platinum, or an alloy mainly composed of these metals.

[0039] The discharge gap G is, for example, a region obtained by projecting the small diameter portion 412 of the center electrode 4 in the Z direction, and is a region between the tip end surface 411 of the small diameter portion 412 and the base end surface 61 of the ground electrode 6. In this embodiment, the plug central axis C passes through the discharge gap G.

[0040] In this embodiment, the discharge gap G is formed on the tip side of the tip of the housing 2. That is, the tip protruding portion 41 of the center electrode 4 protrudes further on the tip side than the tip of the housing 2.

[0041] Furthermore, the fixed end 62 of the ground electrode 6 is fixed to the tip end of the housing 2. After the ground electrode 6 is fixed to the housing 2, the plug cover 5 is fixed to the housing 2, thereby manufacturing the spark plug 1 of this embodiment.

[0042] In this embodiment, the ground electrode 6 is fixed so as to extend along the plug radial direction when viewed from the Z direction, as shown in Figures 2, 6, and 7. In this embodiment, the ground electrode 6 is substantially in the shape of a quadrangular prism. That is, the ground electrode 6 has four flat side surfaces, one of which is the base end surface 61. That is, the entire base end surface 61 is a flat surface.

[0043] The base end surface 61 of the ground electrode 6 has an inclined surface 611 in the longitudinal direction of the ground electrode 6, at least from a portion that forms the discharge gap G to the protruding end 63 of the ground electrode 6. As shown in Fig. 1, the inclined surface 611 is inclined toward the tip side as it approaches the protruding end 63. In this embodiment, the entire base end surface 61 of the ground electrode 6 is the inclined surface 611.

[0044] Next, the effects of this embodiment will be described. The spark plug 1 for an internal combustion engine has the shaft-side nozzle hole 510 as a part of the multiple nozzle holes 51. Therefore, the airflow introduced into the auxiliary combustion chamber 50 through the shaft-side nozzle hole 510 and the airflow discharged from the auxiliary combustion chamber 50 through the shaft-side nozzle hole 510 tend to pass near the discharge gap G. The airflow passing near the discharge gap G has an attraction effect, which can extend the discharge generated in the discharge gap G. As a result, the ignition performance can be improved.

[0045] That is, the shaft-side nozzle hole 510 is formed at a position where the distance D2 (see FIG. 3) is closer than the distance D1 (see FIG. 3). Therefore, during the compression stroke, the airflow introduced into the auxiliary combustion chamber 50 through the shaft-side nozzle hole 510 is likely to pass near the discharge gap G. Therefore, the gas in the discharge gap G and its periphery is likely to be drawn into the airflow introduced into the auxiliary combustion chamber 50 through the shaft-side nozzle hole 510. Therefore, as shown in FIG. 9 and FIG. 10, an airflow AF12 is likely to be formed in the discharge gap G and its periphery toward the airflow AF11 introduced into the auxiliary combustion chamber 50 through the shaft-side nozzle hole 510. Therefore, as shown in FIG. 9, the discharge S formed in the discharge gap G is likely to be extended by the airflow AF12 as shown in FIG. 10. As a result, the ignition performance can be improved.

[0046] Furthermore, the discharge S stretched by the airflow AF12 and the initial flame formed by the discharge S are easily carried by the airflow AF11 to the base end side of the auxiliary combustion chamber 50. 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 with the internal pressure being sufficiently high. As a result, it is expected that knocking at high loads of the internal combustion engine will be suppressed, and the EGR rate (i.e., exhaust gas recirculation rate) will be improved at low or medium loads, leading to improved fuel efficiency and reduced emissions.

[0047] In addition, in the expansion stroke, the piston moves to 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. As shown in Figs. 11 to 13, the airflow AF13 formed in the auxiliary combustion chamber 50 with the discharge of gas through the shaft-side nozzle hole 510 is likely to pass near the discharge gap G. Therefore, in the discharge gap G and its periphery, an airflow AF14 is likely to be formed toward the airflow AF13 discharged through the shaft-side nozzle hole 510. Therefore, as shown in Fig. 11, the discharge S formed in the discharge gap G is likely to be extended by the airflow AF14 as shown in Fig. 12. As a result, the ignition performance can be improved.

[0048] Moreover, the discharge S stretched by the airflow AF14 is likely to be further stretched toward the shaft-side nozzle hole 510 by the airflow AF13. Also, since the ignition position can be easily brought close to the shaft-side nozzle hole 510, for example, under operating conditions in which the temperature of the auxiliary combustion chamber 50 is low, cold loss is suppressed and the flame jet to the main combustion chamber can be strengthened. Furthermore, the discharge S or discharge plasma, or the initial flame generated in the discharge gap G is likely to be ejected from the shaft-side nozzle hole 510, so that the ignition performance in the main combustion chamber can be improved.

[0049] Also, as shown in FIG. 11, in the expansion stroke, the starting point SP on the ground electrode 6 side of the discharge S generated in the discharge gap G is likely to move toward the shaft-side nozzle hole 510 by the airflows AF13 and AF14 as shown in FIG. 12. Therefore, the discharge S is likely to extend toward the shaft-side nozzle hole 510. As a result, the ignition performance can be improved. In some cases, as shown in FIG. 13, the starting point SP of the discharge S may move from the ground electrode 6 to the inner surface of the shaft-side nozzle hole 510. Then, the discharge S is further extended, and it is expected that a part of the discharge S will fly out from the shaft-side nozzle hole 510 toward the main combustion chamber. This can improve the ignition performance of the main combustion chamber.

[0050] The line segment L1 (see FIG. 5) does not pass through both the ground electrode 6 and the plug cover 5. Therefore, during the expansion stroke, the discharge generated in the discharge gap G is less likely to be short-circuited by the ground electrode 6 and the plug cover 5. This ensures that the discharge extends toward the shaft-side injection hole 510 and the main combustion chamber. As a result, ignition performance can be reliably improved.

[0051] That is, it is assumed that the line segment L1 passes through the ground electrode 6 and the plug cover 5. In this case, the discharge extending toward the shaft-side nozzle hole 510 is likely to be short-circuited by the ground electrode 6 when it tries to extend toward the shaft-side nozzle hole 510 beyond the ground electrode 6. Also, when the discharge tries to extend outward beyond the inner opening 512 of the shaft-side nozzle hole 510, it is likely to be short-circuited by the plug cover 5. On the other hand, in this embodiment, the line segment L1 does not pass through both the ground electrode 6 and the plug cover 5. Therefore, as shown in FIG. 11, the discharge S generated in the discharge gap G during the expansion stroke is unlikely to be short-circuited by the ground electrode 6 even if it extends toward the shaft-side nozzle hole 510 beyond the ground electrode 6, as shown in FIG. 12 and FIG. 13. Also, as shown in FIG. 13, even if the discharge extends outward beyond the inner opening 512 of the shaft-side nozzle hole 510, it is unlikely to be short-circuited by the plug cover 5. As a result, it is possible to improve ignition performance.

[0052] In addition, because the line segment L1 does not pass through both the ground electrode 6 and the plug cover 5, the starting point SP of the discharge S on the ground electrode 6 side is likely to move to the inner surface of the shaft-side nozzle hole 510, as shown in Fig. 13. Furthermore, the starting point SP is likely to move toward the outer opening 511 of the shaft-side nozzle hole 510. This makes it easier to extend the discharge S toward the main combustion chamber. As a result, the ignition performance of the main combustion chamber can be further improved.

[0053] Moreover, the line segment L2 (see FIG. 5) does not pass through both the ground electrode 6 and the plug cover 5. Therefore, during the expansion stroke, the discharge generated in the discharge gap G is less likely to be short-circuited by the ground electrode 6 and the plug cover 5. This makes it possible to more reliably extend the discharge toward the shaft-side injection hole 510 and the main combustion chamber.

[0054] The line segment L3 (see FIG. 5) does not pass through the ground electrode 6. Therefore, during the expansion stroke, the discharge generated in the discharge gap G is less likely to be short-circuited by the ground electrode 6. This makes it possible to more reliably extend the discharge toward the shaft side injection hole 510 and the main combustion chamber.

[0055] The base end surface 61 of the ground electrode 6 has an inclined surface 611 from at least a portion forming the discharge gap G to the protruding end 63 of the ground electrode 6 in the longitudinal direction of the ground electrode 6. Therefore, as shown in Figs. 11 to 13, during the expansion stroke, the airflow AF14 formed in and around the discharge gap G is easily guided by the inclined surface 611 toward the airflow AF13 led out from the auxiliary combustion chamber 50 via the shaft side nozzle hole 510. Therefore, the discharge S generated in the discharge gap G is more easily extended toward the shaft side nozzle hole 510. As a result, the ignition performance can be further improved.

[0056] Furthermore, at least an extension line 51L of the central axis of the injection holes 51 other than the shaft-side injection hole 510 is inclined with respect to the plug radial direction when viewed from the plug axial direction Z. This makes it possible to form a swirl flow in the auxiliary combustion chamber 50 by the airflow introduced into the auxiliary combustion chamber 50 through the injection hole 51. Therefore, the initial flame formed by the discharge is likely to spread into the auxiliary combustion chamber 50 by the swirl flow. As a result, the combustion in the auxiliary combustion chamber 50 is promoted, and the flame jet to the main combustion chamber can be strengthened.

[0057] Furthermore, during the compression stroke, the initial flame is likely to be carried by the swirl flow toward the base end of the auxiliary combustion chamber 50. 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 at a sufficiently high internal pressure.

[0058] In addition, an extension line 51L of the central axis of the injection hole 51 does not pass through the discharge gap G. Therefore, even if the flow velocity 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. As a result, it is possible to suppress blowing out and short-circuiting of the discharge generated in the discharge gap G due to the fast airflow.

[0059] In addition, an extension region of the nozzle hole 51 in the opening direction does not pass through the discharge gap G. 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. In addition, the airflow introduced into the auxiliary combustion chamber 50 through the nozzle hole 51 is less likely to form a turbulent flow in the discharge gap G. As a result, it is possible to suppress the blowing out and short circuit of the discharge caused by the airflow, and it is possible to reliably extend the discharge by the airflow introduced through the shaft-side nozzle hole 510.

[0060] The shaft-side nozzle hole 510 has a larger opening area than the other nozzle holes 51. Therefore, the airflow introduced into the auxiliary combustion chamber 50 through the shaft-side nozzle hole 510 and the airflow discharged from the auxiliary combustion chamber 50 through the shaft-side nozzle hole 510 tend to be strong. This makes it possible to strengthen the drawing-in effect of the airflow passing near the discharge gap G. As a result, the discharge generated in the discharge gap G can be reliably extended.

[0061] 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 easily.

[0062] 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.

[0063] (Embodiment 2) As shown in Figs. 14 and 15, this embodiment is an embodiment in which the opening direction of the shaft side injection hole 510 is changed from that of the first embodiment. That is, an extension line 51L of the central axis of the shaft-side injection hole 510 is inclined with respect to the plug axial direction Z and passes through the base end side of the discharge gap G.

[0064] 14 and 15, an extension line 51L of the central axis of the shaft side nozzle hole 510 passes through the tip protruding portion 41. In addition, the extension line 51L of the central axis of the shaft side nozzle hole 510 substantially passes through the plug central axis C. 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] An extension line 51L of the central axis of the shaft-side injection hole 510 is inclined with respect to the plug axis direction Z and passes through the base end side of the discharge gap G. Therefore, the airflow introduced into the pre-combustion chamber 50 via the shaft-side injection hole 510 and the airflow discharged from the pre-combustion chamber 50 via the shaft-side injection hole 510 can easily pass near the discharge gap G. This can strengthen the effect of drawing in the airflow to the discharge generated in the discharge gap G. As a result, the discharge can be reliably extended.

[0066] 15, by forming the shaft-side injection hole 510 as described above, the line segments L1 and L2 are unlikely to pass through both the ground electrode 6 and the plug cover 5. Therefore, during the expansion stroke, the discharge is unlikely to be short-circuited by the ground electrode 6 and the plug cover 5. As a result, the discharge can be effectively extended during the expansion stroke. In addition, the same effects as those of the first embodiment are achieved.

[0067] (Embodiment 3) As shown in FIG. 16, this embodiment is an embodiment in which the shape of the ground electrode 6 is modified from that of the first embodiment.

[0068] 16 , the thickness of the ground electrode 6 in a direction perpendicular to the longitudinal direction of the ground electrode 6 at a part closer to the protruding end 63 than the fixed end 62 gradually decreases toward the protruding end 63. The surface on the tip side of the tapered portion of the ground electrode 6 is formed along the inner wall surface of the bottom wall 53 of the plug cover 5. The other configurations and effects are the same as those of the first embodiment.

[0069] (Embodiment 4) As shown in FIG. 17, this embodiment is an embodiment in which the shape of the base end surface 61 of the ground electrode 6 is modified from that of the first embodiment.

[0070] 17, a portion of the base end surface 61 of the ground electrode 6 that is closer to the protruding end portion 63 than the fixed end portion 62 has a larger inclination angle with respect to a plane perpendicular to the Z direction than other portions of the base end surface 61. A discharge gap G is formed between the portion of the base end surface 61 and the center electrode 4. The other configurations and effects are the same as those of the first embodiment.

[0071] (Embodiment 5) As shown in FIG. 18, this embodiment is an embodiment in which the shape of the ground electrode 6 is modified from that of the first embodiment.

[0072] In this embodiment, as shown in Fig. 18, the ground electrode 6 is fixed to the tip end of the housing 2, and has a fixed side portion 64 including a fixed end portion 62, and an inclined portion 65 with an inclined surface 611. The fixed side portion 64 is formed along the plug radial direction. The inclined portion 65 is inclined in the Z direction toward the tip side as it approaches the protruding end portion 63. The other configurations and effects are the same as those of the first embodiment.

[0073] (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.

[0074] 19, the ground electrode 6 includes a fixed inclined portion 66 having an inclined surface 611 and a fixed end portion 62, and a gap forming portion 67 that forms a discharge gap G. The fixed inclined portion 66 is inclined with respect to the Z direction toward the base end side as it approaches the fixed end portion 62. The gap forming portion 67 is formed along the plug radial direction.

[0075] In this embodiment, the tip surface 411 of the center electrode 4 is formed to follow the base end surface 61 of the gap forming portion 67. The tip surface 411 of the center electrode 4 and the base end surface 61 of the gap forming portion 67 are both flat surfaces. The respective flat surfaces are disposed substantially parallel to each other and opposed to each other, thereby forming a discharge gap G. The rest is the same as in the first embodiment.

[0076] The discharge gap G is formed by arranging the tip end surface 411 of the center electrode 4 and the base end surface 61 of the gap forming portion 67 facing each other in approximately parallel relation. This makes it easy to disperse the starting points of discharge on the center electrode 4 side. This makes it possible to suppress localized wear of the center electrode 4 and to suppress the increase in the distance of the discharge gap G. As a result, the life of the spark plug 1 can be extended. In addition, the same effects as those of the first embodiment are achieved.

[0077] (Embodiment 7) As shown in FIG. 20, this embodiment is an embodiment in which the shape of the tip portion of the center electrode 4 is modified from that of the fifth embodiment. That is, the tip surface 411 of the center electrode 4 is inclined along the inclined surface 611 of the ground electrode 6 .

[0078] In this embodiment, the tip surface 411 of the center electrode 4 and the inclined surface 611 of the ground electrode 6 are each flat. As shown in Fig. 20, the flat surfaces are arranged substantially parallel to each other and face each other, thereby forming a discharge gap G. The rest is the same as in the fifth embodiment.

[0079] The tip end surface 411 of the center electrode 4 is inclined along the inclined surface 611 of the ground electrode 6. Therefore, the tip end surface 411 of the center electrode 4 and the inclined surface 611 of the ground electrode 6 can be made substantially parallel to each other. This makes it easy to disperse the starting points of discharge on the center electrode 4 side. This makes it possible to suppress localized wear of the center electrode 4 and to suppress the increase in the distance of the discharge gap G. As a result, the life of the spark plug 1 can be extended. In addition, the same effects as those of the fifth embodiment are achieved.

[0080] (Embodiment 8) As shown in FIG. 21, this embodiment is an embodiment in which the shape of the tip portion of the center electrode 4 is modified from that of the seventh embodiment.

[0081] In this embodiment, the tip of the center electrode 4 has a tapered shape with a diameter decreasing toward the tip side as shown in Fig. 21. The tip of the tapered center electrode 4 has a substantially truncated cone shape. The tip of the center electrode 4 may have a substantially conical shape, a substantially truncated square pyramid shape, a substantially square pyramid shape, or the like.

[0082] The tapered surface 414 of the tapered tip of the center electrode 4 is formed in an annular shape. A part of the tapered surface 414 is inclined along the inclined surface 611 of the ground electrode 6. A discharge gap G is formed between the tapered surface 414 and the inclined surface 611 of the ground electrode 6. The rest is the same as in the seventh embodiment.

[0083] In this embodiment, a discharge gap G is formed between the tapered surface 414 and the inclined surface 611. Therefore, in this embodiment as well, local wear of the center electrode 4 can be suppressed, and the distance of the discharge gap G can be suppressed from increasing. In addition, the same effects as those of the seventh embodiment are obtained.

[0084] (Embodiment 9) As shown in Figs. 22 and 23, this embodiment is an embodiment in which the position at which the shaft side nozzle hole 510 is formed is changed from that of the first embodiment.

[0085] In this embodiment, the shaft-side nozzle hole 510 and the discharge gap G are aligned in the width direction of the ground electrode 6 when viewed from the Z direction, as shown in FIG.

[0086] 22 and 23, the ground electrode 6 has two circumferential side surfaces 68 facing in the plug circumferential direction. As shown in Fig. 22, when viewed from the Z direction, the axis-side injection hole 510 and the discharge gap G are located on opposite sides to each other with one of the circumferential side surfaces 68 in between.

[0087] The ground electrode 6 is fixed to the housing 2 with a central axis 6C extending along the longitudinal direction of the ground electrode 6 deviated from the plug radial direction when viewed from the Z direction. In other words, the central axis 6C of the ground electrode 6 does not pass through the plug central axis C.

[0088] Further, a part of the base end surface 61 of the ground electrode 6 on the shaft side nozzle hole 510 side in the width direction of the ground electrode 6 forms a discharge gap G between itself and the center electrode 4 . The other configurations and effects are the same as those of the first embodiment.

[0089] (Embodiment 10) As shown in Figs. 24 to 26, this embodiment is an embodiment in which the shape of the ground electrode 6 and the like are modified from those of the ninth embodiment.

[0090] 24 to 26, the ground electrode 6 has a nozzle hole-side inclined surface 612. The nozzle hole-side inclined surface 612 is inclined with respect to the Z direction in the arrangement direction of the discharge gap G and the shaft side nozzle 510 as viewed from the Z direction, so as to move toward the tip side as it approaches the shaft side nozzle 510.

[0091] In this embodiment, the nozzle hole-side inclined surface 612 is inclined with respect to the Z direction so as to move toward the tip side as it approaches the shaft-side nozzle hole 510 when viewed from the protruding direction of the ground electrode 6, as shown in Fig. 26. In other words, the nozzle hole-side inclined surface 612 gradually moves toward the tip side in the width direction of the ground electrode 6 as it approaches the shaft-side nozzle hole 510, as shown in Figs. 24 to 26. Note that the ground electrode may be provided with a surface inclined with respect to the Z direction in the width direction of the ground electrode, on a portion opposite to the side on which the nozzle hole-side inclined surface is formed, so as to move toward the tip side as it moves away from the shaft-side nozzle hole.

[0092] 24, when viewed from the Z direction, the nozzle hole-side inclined surface 612 is formed in a portion of the ground electrode 6 that is sandwiched between at least the shaft-side nozzle 510 and the tip end of the tip protrusion 41. In this embodiment, the nozzle hole-side inclined surface 612 is formed over the entire ground electrode 6 in the longitudinal direction.

[0093] Moreover, the ground electrode 6 is provided along the plug radial direction when viewed from the Z direction. The rest is the same as in the ninth embodiment.

[0094] The ground electrode 6 has a nozzle-hole-side inclined surface 612. Therefore, during the expansion stroke, the discharge generated in the discharge gap G is not short-circuited by the ground electrode 6, and tends to reliably extend toward the shaft-side nozzle hole 510 and the main combustion chamber. In addition, the same effects as those of the ninth embodiment are obtained.

[0095] (Embodiment 11) As shown in Figs. 27 to 32, this embodiment is an embodiment in which the opening direction of the injection hole 51 and the like are changed from the first embodiment.

[0096] 27 and 28, the outer injection hole 514 has at least two large injection holes 515 and a small injection hole 516 having an opening area smaller than that of the large injection hole 515. The large injection hole 515 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.

[0097] 27 , when the spark plug 1 is divided into a first plug portion 11 and a second plug portion 12 by a predetermined plane P including the plug center axis C, at least two large injection holes 515 are formed in the first plug portion 11. A fixed end portion 62 of the ground electrode 6 is fixed to the housing 2 or the plug cover 5 of the first plug portion 11. The shaft side injection hole 510 is formed in the second plug portion 12.

[0098] When viewed from the plug axial direction Z, in the first plug part 11, the fixed end 62 is disposed between extension lines 51L of the respective central axes of the at least two large injection holes 515 in the plug circumferential direction.

[0099] In this embodiment, as shown in FIG. 27, two large injection holes 515 and three small injection holes 516 are formed in the plug cover 5. The inner diameter of the large injection hole 515 can be, for example, 1.2 to 1.4 times the inner diameter of the small injection hole 516. The opening area of ​​the large injection hole 515 can be, for example, 1.4 to 2.0 times the opening area of ​​the small injection hole 516. In this embodiment, the opening areas of the multiple large injection holes 515 are equal to each other. The opening area of ​​the large injection hole 515 and the opening area of ​​the shaft-side injection hole 510 are equal to each other.

[0100] 27, when the spark plug 1 is divided into two by a plane P, the side where the large injection hole 515 is formed and where the fixed end portion 62 of the ground electrode 6 is located constitutes the first plug portion 11. In other words, when viewed from the Z direction, the multiple large injection holes 515 are formed biased toward the first plug portion 11 side.

[0101] The large nozzle hole 515 is formed so that an extension line 51L of the central axis of the large nozzle hole 515 does not pass through the tip protrusion 41. When viewed from the plug axial direction Z, the intersection point of the extension lines 51L of the central axes of at least two large nozzle holes 515 is defined as intersection point A. When viewed from the plug axial direction Z, intersection point A and the large nozzle hole 515 are located on opposite sides of each other in the protruding direction of the ground electrode 6, with the tip protrusion 41 in between.

[0102] When viewed from the Z direction, the small injection hole 516 is formed so that an extension line 51L of the central axis of the small injection hole 516 is along the plug radial direction. In other words, the small injection hole 516 is formed so that the extension line 51L of the central axis of the small injection hole 516 substantially passes through the plug central axis C. In addition, as shown in Fig. 28, the extension line 51L of the central axis of the small injection hole 516 does not pass through the discharge gap G, but passes through the base end side of the discharge gap G.

[0103] The auxiliary combustion chamber 50 also includes a space on the inner circumferential side of the tip portion of the housing 2, around the tip protruding portion 41 of the center electrode 4. The auxiliary combustion chamber 50 also includes a pocket portion 501, which will be described later.

[0104] As shown in FIG. 28, the insulator 3 has a tapered tip portion 31 that is tapered toward the tip side. The insulator 3 is disposed inside the housing 2 and is supported in the Z direction by the housing 2. That is, the locked portion 32 provided on the outer peripheral surface of the insulator 3 is locked from the tip side in the Z direction to the locking portion 23 provided on the inner peripheral surface of the housing 2. The portion of the insulator 3 on the tip side of the locked portion 32 is the tapered tip portion 31. An annular pocket portion 501 is formed between the outer surface of the tapered tip portion 31 and the inner surface of the housing 2. That is, the pocket portion 501 is an annular space formed between the tapered tip portion 31 and the housing 2 in the plug radial direction.

[0105] Next, an internal combustion engine 10 equipped with the above-described spark plug 1 is shown in FIGS. The spark plug 1 is arranged so that the outer surface 55 of the plug cover 5 faces the main combustion chamber 101. As shown in Figure 30, the spark plug 1 is arranged so that the outer opening 511 of at least one large injection hole 515 faces the intake valve 72 when viewed from the plug axial direction Z.

[0106] As shown in FIG. 29, the internal combustion engine 10 of this embodiment includes a cylinder head 76, a cylinder block 75, and a piston 74 that reciprocates in the cylinder 70. The cylinder head 76, the cylinder block 75, and the piston 74 form a main combustion chamber 101. The cylinder head 76 is formed with an intake port 721 and an exhaust port 731, and each of the intake port 72 and the exhaust valve 73 is provided. The spark plug 1 is attached between the intake port 721 and the exhaust port 731 in the cylinder head 76. In detail, the spark plug 1 is disposed in a position surrounded by the two intake ports 721 and the two exhaust ports 731 in the cylinder head 76, as shown in FIG.

[0107] 29, the intake port 721 and the exhaust port 731 are inclined with respect to the forward and backward movement direction of the piston 74 so that the opening direction of the intake port 721 and the exhaust port 731 is directed toward the central axis of the main combustion chamber 101. In addition, the base end surface of the main combustion chamber 101 is inclined so as to be directed toward the tip side as it moves away from the spark plug 1.

[0108] In the internal combustion engine 10, an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke are repeated in sequence with the reciprocating motion of the piston 74. In the intake stroke of the internal combustion engine 10, gas is introduced into the main combustion chamber 101 from the two intake ports 721, and in the exhaust stroke, gas in the main combustion chamber 101 is exhausted from the two exhaust ports 731. Due to the way in which the airflow is introduced in the intake stroke, etc., a predetermined airflow is formed in the main combustion chamber 101, and this airflow remains in the compression stroke.

[0109] In the main combustion chamber 101, a tumble flow is formed, which is an airflow around an axis perpendicular to the sliding direction of the piston 74, as shown by an arrow AF2 in Fig. 29. This airflow AF2 is directed from the intake valve 72 side to the exhaust valve 73 side near the tip of the spark plug 1 in the main combustion chamber 101, as shown in Fig. 29 and Fig. 30. More specifically, as shown in Fig. 30, when viewed from the plug axial direction Z, the airflow AF2 along the direction from the intermediate position between the two intake ports 721 to the intermediate position between the two exhaust ports 731 becomes the main airflow near the tip of the spark plug 1.

[0110] The airflow in the main combustion chamber 101 is not always constant, but may vary between cycles or between different timings in one cycle. However, the direction of the main airflow, particularly the direction of the airflow at the ignition timing, is roughly fixed, and the above-mentioned airflow AF2 means the main airflow at the ignition timing. And, when we say "airflow in the main combustion chamber 101", we mean the airflow AF2 near the tip of the spark plug 1 at the 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 101" unless otherwise specified.

[0111] In the internal combustion engine 10 configured as described above, during the compression stroke, gas in the main combustion chamber 101 is introduced into the auxiliary combustion chamber 50 through the injection hole 51. Here, the large injection hole 515 has a larger opening area than the small injection hole 516, and as shown in Figures 29 and 30, the outer opening 511 of the large injection hole 515 faces upstream of the airflow AF2 of the main combustion chamber 101. Therefore, more gas is introduced into the auxiliary combustion chamber 50 through the large injection hole 515 than through the small injection hole 516.

[0112] In the compression stroke, the main flow of the gas introduced into the auxiliary combustion chamber 50 through the large nozzle hole 515, as shown by the arrow AF15 in Figs. 31 and 32, moves toward the inner wall surface 502 on the downstream side of the auxiliary combustion chamber 50, moves toward the base end side along the inner wall surface 502, and is introduced into the downstream pocket portion 501. The main flow of the gas that has entered the downstream pocket portion 501 turns toward the upstream side in the pocket portion 501, and moves toward the tip side along the upstream pocket portion 501. That is, an airflow (i.e., a tumble flow) around an axis in a direction perpendicular to the Z direction is formed. The airflow AF15 moving toward the tip side is guided by the base end surface 61 of the ground electrode 6 and moves toward the discharge gap G. The above airflow AF15 is merely the main flow, and not all gas necessarily flows in this way.

[0113] In other words, the airflow AF15 introduced into the auxiliary combustion chamber 50 through the large injection hole 515 flows toward the inner wall surface 502 of the second plug portion 12 and is introduced into the pocket portion 501 of the second plug portion 12. The airflow AF15 introduced into the pocket portion 501 changes direction toward the first plug portion 11 and flows in the direction of the base end surface 61 of the ground electrode 6, i.e., toward the tip side. The airflow AF15 is then guided by the base end surface 61 of the ground electrode 6 toward the discharge gap G. The rest is the same as in the first embodiment.

[0114] In the spark plug 1 of this embodiment, when viewed from the plug axial direction Z, the fixed end 62 of the ground electrode 6 is disposed in the first plug portion 11 between the extension lines 51L of the central axes of at least two large injection holes 515 in the plug circumferential direction. As a result, the airflow formed in the auxiliary combustion chamber 50 is easily guided to the base end surface 61 of the ground electrode 6 and directed toward the discharge gap G. Therefore, the discharge formed in the discharge gap G is easily extended. In addition, the shaft-side injection hole 510 is formed in the second plug portion 12. Therefore, the discharge extended by the airflow guided to the base end surface 61 is easily extended further toward the base end side by the airflow introduced into the auxiliary combustion chamber 50 through the shaft-side injection hole 510. As a result, the ignition performance can be further improved.

[0115] That is, the opening area of ​​the large injection hole 515 is larger than the opening area of ​​the small injection hole 516. Therefore, during the compression stroke, the airflow introduced into the auxiliary combustion chamber 50 through the large injection hole 515 is likely to be stronger than the airflow introduced into the auxiliary combustion chamber 50 through the small injection hole 516. In addition, the large injection hole 515 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 Figures 31 and 32, the airflow AF15 introduced into the auxiliary combustion chamber 50 through the large injection hole 515 tends to move toward the inner wall surface 502 of the auxiliary combustion chamber 50 of the second plug portion 12 and toward the base end side of the auxiliary combustion chamber 50. The airflow AF15 that moves toward the base end side of the auxiliary combustion chamber 50 changes direction and tends to move toward the tip side on the first plug portion 11 side. Therefore, the airflow AF15 is guided by the base end surface 61 of the ground electrode 6 of the first plug part 11 and is likely to flow toward the discharge gap G. Therefore, the discharge S generated in the discharge gap G is likely to extend toward the second plug part 12. As a result, the ignition performance can be improved.

[0116] In addition, the discharge S extending toward the second plug portion 12 is likely to be further extended toward the base end side by the airflow AF11 introduced into the auxiliary combustion chamber 50 through the shaft-side nozzle 510 and the airflow AF15 toward the base end side of the second plug portion 12, as shown in FIG. 32. The formed initial flame is also likely to be carried toward the base end side by these airflows AF11 and AF15. Therefore, the combustion of the mixture grows from a region closer to the base end side in the auxiliary combustion chamber 50, so that the pressure in the auxiliary combustion chamber 50 can be increased when the flame reaches the nozzle hole 51. As a result, the flame jet to the main combustion chamber 101 can be strengthened.

[0117] Moreover, the large nozzle hole 515 is formed so that an extension line 51L of the central axis of the large nozzle hole 515 does not pass through the tip protrusion 41. Moreover, when viewed from the Z direction, the intersection point A and the large nozzle hole 515 are located on opposite sides of the tip protrusion 41 in the protruding direction of the ground electrode 6. Therefore, the airflow introduced into the auxiliary combustion chamber 50 through the large nozzle hole 515 is less likely to be blocked by the tip protrusion 41, and a tumble flow is more likely to be formed. Therefore, the airflow guided to the base end surface 61 of the ground electrode 6 can be strengthened. As a result, the discharge formed in the discharge gap G can be further extended.

[0118] In the above internal combustion engine 10, the spark plug 1 is arranged such that the outer opening 511 of at least one large injection hole 515 faces the intake valve 72 side when viewed from the plug axial direction Z. This allows a large flame to be ejected from the auxiliary combustion chamber 50 to the intake valve 72 side of the main combustion chamber 101 through the large injection hole 515 when viewed from the plug axial direction Z. This makes it possible to improve the ignition ability of the mixture on the intake valve 72 side in the main combustion chamber 101 when viewed from the plug axial direction Z. This makes it possible to burn the mixture in the entire main combustion chamber 101 in a well-balanced manner. As a result, it is possible to suppress abnormal combustion that causes knocking and the like.

[0119] That is, when viewed from the Z direction, the intake valve 72 side, which is provided with the intake port 721 that introduces relatively low-temperature gas into the main combustion chamber 101, is likely to be at a low temperature compared to the exhaust valve 73 side, which is provided with the exhaust port 731 that discharges high-temperature gas. Therefore, when viewed from the Z direction, the combustion of the mixture on the intake valve 72 side in the main combustion chamber 101 is delayed compared to the mixture on the exhaust valve 73 side in the main combustion chamber 101, which may cause the balance of the combustion of the mixture in the main combustion chamber 101 to be poor. However, in this embodiment, as described above, when viewed from the Z direction, a large flame can be ejected from the auxiliary combustion chamber 50 to the intake valve 72 side of the main combustion chamber 101. Therefore, the mixture in the entire main combustion chamber 101 can be burned in a balanced manner, and localized residual unburned fuel can be suppressed. As a result, it is possible to suppress combustion abnormalities that cause knocking and the like.

[0120] Furthermore, the outer opening 511 of the large nozzle hole 515 faces the intake valve 72 side when viewed from the Z direction. Therefore, the outer opening 511 of the large nozzle hole 515 tends to face the upstream side of the airflow in the main combustion chamber 101. Therefore, gas is easily introduced into the auxiliary combustion chamber 50 through the large nozzle hole 515. Therefore, a strong airflow is easily generated in the auxiliary combustion chamber 50. As a result, the discharge generated in the discharge gap G can be further extended. Other than the effects achieved by the formation of a swirl flow, the second embodiment has the same effects as the first embodiment.

[0121] (Experimental Example 1) In this example, as shown in Fig. 33, the airflow in the auxiliary combustion chamber 50 of the spark plug 1 having substantially the same configuration as that of the embodiment 11 was analyzed. The analysis of the airflow was calculated using computational flow dynamics (hereinafter referred to as CFD). That is, a general simulation analysis was performed using CFD, assuming the airflow generated when the spark plug 1 of the embodiment 11 is attached to the internal combustion engine 10 and used as an actual automobile engine. The spark plug 1 was installed in the internal combustion engine 10 such that the outer opening 511 of the large nozzle hole 515 faces the intake valve side when viewed from the plug axial direction Z.

[0122] Figure 33 shows the analysis results at BTDC (abbreviation for top dead center of compression) and 35° CA (abbreviation for crank angle) during the compression stroke. In this figure, each of the many arrows indicates the direction of the airflow at each point.

[0123] 33, it was confirmed that the airflow AF15 introduced into the auxiliary combustion chamber 50 through the large injection hole 515 heads toward the base end of the auxiliary combustion chamber 50 at the second plug portion 12. It was also confirmed that the airflow AF15 headed toward the base end of the auxiliary combustion chamber 50 changes direction at the pocket portion 501 and heads toward the tip end at the first plug portion 11 side. The airflow AF15 headed toward the tip end is guided by the base end surface 61 of the ground electrode 6 of the first plug portion 11 and heads toward the discharge gap G. It is believed that this makes it easier for the discharge generated in the discharge gap G to extend toward the second plug portion 12 side.

[0124] Also, it was confirmed that the airflow AF11 introduced into the auxiliary combustion chamber 50 through the shaft-side nozzle 510 passes near the discharge gap G and heads toward the base end. This suggests that the discharge extended toward the second plug portion 12 by the airflow AF15 is likely to be further extended toward the base end by the airflows AF11 and AF15.

[0125] (Embodiment 12) As shown in FIG. 34, this embodiment is an internal combustion engine 10 in which a spark plug 1 is arranged so that the injection flow F injected from an injector 71 is directed toward the outer opening 511 of the large injection hole 515 in the spark plug 1 of embodiment 11.

[0126] The internal combustion engine 10 of this embodiment has an injector 71 that injects fuel directly into the main combustion chamber 101, as shown in Fig. 34. The spark plug 1 is arranged so that the injection flow F containing fuel injected from the injector 71 during the compression stroke of the internal combustion engine 10 heads toward the outer opening 511 of the large injection hole 515. Note that the arrow F shown in Fig. 34 indicates the direction of the injection flow immediately after fuel injection, and does not necessarily coincide with the air flow in the main combustion chamber 101 during the compression stroke or expansion stroke. Also, the state in which the injection flow F heads toward the outer opening 511 of the large injection hole 515 is a state in which the outer opening 511 of the large injection hole 515 is visible from the direction of the injection flow F near the plug cover 5.

[0127] In this embodiment, the spark plug 1 is disposed so that, when viewed from the Z direction, the outer opening 511 of the large nozzle hole 515 faces the exhaust valve 73 side (not shown).

[0128] Furthermore, an injector 71 is provided at a position adjacent to the intake port 721. The injector 71 is attached in such a position that it injects fuel toward the central axis of the main combustion chamber 101.

[0129] During the compression stroke, the atmosphere in the main combustion chamber 101 is compressed, and the air flows into the auxiliary combustion chamber through the nozzle hole 51. This increases the pressure in the auxiliary combustion chamber. Then, for example, during the compression stroke, the injector 71 injects fuel directly into the main combustion chamber 101.

[0130] As shown in Fig. 34, the fuel injected into the main combustion chamber 101 forms an injection flow F together with the air in the main combustion chamber 101 and hits the base end face of the piston 74. In this embodiment, the base end face of the piston 74 has a concave surface. The injection flow F that hits the base end face of the piston 74 changes its trajectory and travels toward the base end side, i.e., the spark plug 1 side. At this time, the injection flow F reaches the vicinity of the outer opening 511 of the large injection hole 515 in the spark plug 1.

[0131] The injection flow F is a mixture with a relatively high fuel ratio. Therefore, the vicinity of the outer opening 511 of the large injection hole 515 where the injection flow F reaches becomes a mixture containing a large amount of fuel. This mixture is then introduced into the auxiliary combustion chamber via the large injection hole 515. The mixture with high fuel density introduced via the large injection hole 515 is directed toward the discharge gap.

[0132] Then, near the top dead center of the compression stroke, a discharge is generated in the discharge gap of the spark plug 1. This efficiently ignites the air-fuel mixture. Note that the above-mentioned fuel injection timing and the discharge ignition timing of the spark plug 1 can be changed in various ways depending on the situation, purpose, etc., as described later. The rest is the same as in the eleventh embodiment.

[0133] In the internal combustion engine 10 of this embodiment, the spark plug 1 is disposed so that the injection flow F injected from the injector 71 is directed toward the outer opening 511 of the large injection hole 515. This makes it easier for a high-fuel-density mixture to be introduced into the auxiliary combustion chamber from the large injection hole 515. As a result, the high-fuel-density mixture can more easily reach the discharge gap, improving ignition performance.

[0134] Furthermore, for example, in high-load operation of an internal combustion engine, retarded injection and retarded ignition may be performed to suppress pre-ignition. Retarded injection and retarded ignition are fuel injection and ignition performed at a timing later than the timing of general fuel injection and ignition. In other words, the fuel injection timing from the injector 71 is set to, for example, the timing immediately before the piston 74 reaches the top dead center during the compression stroke. Specifically, fuel is injected at, for example, a timing of 30° BTDC. And the ignition of the spark plug 1 is set to the timing substantially at the top dead center of the compression stroke.

[0135] By injecting fuel and igniting at such timing, it is possible to suppress ignition earlier than the desired timing, i.e., early ignition, and to suppress pre-ignition. On the other hand, when retarded injection is performed, when fuel is supplied to the main combustion chamber 101, a certain amount of air has already filled the auxiliary combustion chamber, and the airflow in the main combustion chamber 101 is also weakened. This leads to a situation in which the amount of fuel introduced into the auxiliary combustion chamber from the injection hole 51 formed in the plug cover 5 is likely to be relatively small.

[0136] However, the spark plug 1 of this embodiment is disposed so that the injection flow F injected from the injector 71 is directed toward the outer opening 511 of the large injection hole 515. Therefore, a mixture with high fuel density is easily introduced into the auxiliary combustion chamber through the large injection hole 515. Therefore, a mixture with high fuel density is easily able to reach the discharge gap. As a result, the ignition performance in the auxiliary combustion chamber is improved, and the ignition performance in the main combustion chamber 101 is improved. In addition, the same effects as those of the eleventh embodiment are obtained.

[0137] 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]

[0138] 1...spark plug, 2...housing, 3...insulator, 4...center electrode, 41...tip protrusion, 5...plug cover, 50...auxiliary combustion chamber, 51...nozzle hole, 510...shaft-side nozzle hole, 6...ground electrode, 61...base end surface, 62...fixed end, 51L...extension of central axis of nozzle hole, 510E...extension area of ​​shaft-side nozzle hole extended in the opening direction, C...plug central axis, G...discharge gap

Claims

1. A cylindrical insulator (3); a center electrode (4) held on the inner circumferential side of the insulator and having a tip protrusion (41) protruding toward the tip side of 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) provided at a 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 (62) fixed to the housing or the plug cover, The discharge gap is formed by the tip end of the tip protrusion and the base end surface (61) of the ground electrode facing each other, The plug cover is formed with a plurality of nozzle holes (51) that communicate the auxiliary combustion chamber with the outside, An extension line (51L) of the central axis of the injection hole does not pass through the discharge gap, some of the plurality of nozzle holes are shaft-side nozzle holes (510) formed at positions where a distance (D2) to a plug central axis (C) in a plug radial direction is closer than a distance (D1) to an inner circumferential surface (21) of a tip portion of the housing in the plug radial direction, the shaft side nozzle hole is formed such that an extension region (510E) extending from the shaft side nozzle hole in an opening direction does not pass through the discharge gap, and such that at least a portion of the shaft side nozzle hole does not overlap with the ground electrode when viewed from the opening direction of the shaft side nozzle hole, a plug cover for supporting the ground electrode in a plug circumferential direction, the plug cover being disposed in a direction parallel to the plug axis, and the plug cover being disposed in a direction parallel to the plug axis, the plug cover being disposed in a direction parallel to the plug axis, and the plug cover being disposed in a direction parallel to the plug axis, the plug cover being disposed in a direction parallel to the plug axis, the plug cover being disposed in a direction parallel to the plug axis, the plug cover being disposed in a direction parallel to the plug axis, the plug cover being disposed in a direction parallel to the plug axis, the plug cover being disposed in a direction parallel to the plug axis, the plug cover being disposed in a direction parallel to the plug axis, the plug cover being disposed in a direction parallel to the plug axis, the plug cover being disposed in a direction parallel to the plug axis, the plug cover being disposed in a direction parallel to the plug axis, the plug cover being disposed in a direction parallel to the plug axis, the plug cover being disposed in a direction parallel to the plug axis, the plug cover being disposed in a direction parallel to the plug axis, the plug cover being disposed in a direction parallel to the plug axis, the plug cover being disposed in a direction parallel to the plug axis,

2. 2. A spark plug for an internal combustion engine according to claim 1, wherein a line segment (L1) connecting, in a plug radial direction, an outermost end (513) of an outer opening (511) of said shaft-side nozzle hole to the tip end of said tip projection portion at the shortest distance does not pass through both said ground electrode and said plug cover.

3. 3. A spark plug for an internal combustion engine according to claim 2, wherein a line segment (L2) connecting, at the shortest distance, a center of an outer opening of said shaft side nozzle hole and the tip end of said tip projection portion does not pass through both said ground electrode and said plug cover.

4. 4. The spark plug for an internal combustion engine according to claim 3, wherein a line segment (L3) connecting an inner opening (512) of said shaft side nozzle hole and the tip end of said tip projection at the shortest distance does not pass through said ground electrode.

5. 5. A spark plug for an internal combustion engine according to claim 1, wherein an extension line of a central axis of the shaft-side injection hole is inclined with respect to a plug axial direction (Z) and passes through a base end side of the discharge gap.

6. 6. The spark plug for an internal combustion engine according to claim 1, wherein the discharge gap is formed on a tip side of the tip of the housing.

7. 7. A spark plug for an internal combustion engine according to claim 1, wherein a base end surface of the ground electrode has an inclined surface (611) that is inclined toward a tip side as it approaches the protruding end (63) from at least a portion that forms the discharge gap in a longitudinal direction of the ground electrode to the protruding end (63) of the ground electrode.

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