Spark plugs for internal combustion engines

Abstract

To provide a spark plug for an internal-combustion engine, capable of suppressing an overheat of a plug cover.SOLUTION: In a spark plug 1, an injection hole 51 for communicating a sub combustion chamber 50 and an external part is formed in a plug cover 5. The plug cover 5 includes an annular notched surface 52 connected to an external side open part 511 of the injection hole 51 at the circumference of at least one injection hole 51. The annular notched surface 52 is formed along the entire circumference of the external side open part 511 so as to be adjacent to the external side open part 511. Also, in a cross section containing an injection hole shaft 51L, an angle formed by an inner peripheral surface 512 of the injection hole 51 and the annular notched surface 52 is 225° or more. In addition, a part where the annular notched surface 52 is formed in the plug cover 5 is formed so that a thickness increases as it goes away from the external side open part 511.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] For example, as disclosed in Patent Document 1, a spark plug for an internal combustion engine having a pre-combustion chamber at its tip is known. In this spark plug, the plug cover covering the pre-combustion chamber has a thin tip. This is intended to reduce the amount of heat received by the tip, and to prevent the air-fuel mixture from igniting before the spark plug generates a discharge (i.e., pre-ignition). [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 takes into consideration the heat received from the combustion in the main combustion chamber, but does not take into consideration the heat received from the flame ejected from the auxiliary combustion chamber to the main combustion chamber through the nozzle hole formed in the plug cover. In other words, it does not take into consideration the prevention of the inner circumferential surface of the nozzle hole and its surrounding areas from becoming too hot due to the flame. Therefore, there is a concern about pre-ignition starting from the inner circumferential surface of the nozzle hole and its surrounding areas, and it can be said that there is room for further improvement.

[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 preventing overheating of the plug cover. [Means for solving the problem]

[0006] One aspect of the present invention is a cylindrical insulator (3), a center electrode (4) held on the inner circumferential side of the insulator and protruding from the insulator toward the tip side; a cylindrical housing (2) that holds the insulator on its inner periphery; a ground electrode (6) forming a discharge gap (G) between itself and the center electrode; a plug cover (5) provided at the tip of the housing so as to cover a sub-combustion chamber (50) in which the discharge gap is disposed, The plug cover is formed with a nozzle hole (51) that communicates the auxiliary combustion chamber with the outside, The plug cover has an annular cutout surface (52) around at least one of the nozzle holes, the cutout surface (52) being connected to an outer opening (511) of the nozzle hole, the annular cutout surface is formed adjacent the outer opening around the entire periphery of the outer opening; In a cross section including an injection hole axis (51L) of the injection hole, an angle (θ1) between an inner circumferential surface (512) of the injection hole and the annular cut surface is 225° or more, The plug cover has a portion where the annular cutout surface is formed so that the thickness of the portion increases with increasing distance from the outer opening. Cage , The annular cutout surface and the outer opening are formed to be located on the same plane. In a spark plug (1) for an internal combustion engine. Effect of the Invention

[0007] The above spark plug has an annular cutout surface that satisfies the above conditions. Therefore, the area of ​​the inner peripheral surface of the injection hole can be reduced while ensuring the thickness of the plug cover. Therefore, the amount of heat received by the inner peripheral surface of the injection hole by the flame ejected from the auxiliary combustion chamber to the main combustion chamber through the injection hole can be reduced while ensuring the heat dissipation to the outside of the plug cover. As a result, overheating of the plug cover can be suppressed.

[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 suppressing overheating of the plug cover. 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. 3 is a view taken along the line III in FIG. [Figure 4] 4 is an enlarged cross-sectional view of the vicinity of the nozzle hole, showing angles θ1 and θ2 in the first embodiment. FIG. [Diagram 5] FIG. 4 is an enlarged cross-sectional view of the vicinity of the nozzle hole, showing the length of each part in the first embodiment. [Figure 6] 1 is a cross-sectional view of an internal combustion engine in which a spark plug is installed according to a first embodiment. [Figure 7] 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 comparative embodiment 1. [Figure 8] FIG. 11 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 Comparative Example 2. [Figure 9] FIG. 2 is an analytical diagram showing a state in which a flame jet is ejected from a spark plug of Comparative Example 1 in Experimental Example 1. [Figure 10] An enlarged view of the nozzle area in Figure 9. [Figure 11] FIG. 4 is an analytical diagram showing a state in which a flame jet is ejected from the spark plug of the first embodiment in the experimental example 1. [Figure 12] An enlarged view of the nozzle area in Figure 11. [Figure 13] 4 is a graph showing the relationship between the crank angle and the temperature of the inner circumferential surface of the injection hole in the first embodiment and the first comparative example in the first experimental example. [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 an enlarged cross-sectional view of the vicinity of the nozzle hole, showing the angle θ1, in the second embodiment. [Figure 16] FIG. 16 is a view taken along the arrow XVI in FIG. [Figure 17] FIG. 11 is an analytical diagram showing a state in which a flame jet is ejected from the spark plug of the second embodiment in the experimental example 2. [Figure 18] An enlarged view of the nozzle area in Figure 17. [Figure 19] 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. 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. As shown in Fig. 1 and Fig. 2, a spark plug 1 for an internal combustion engine according to this embodiment has a cylindrical insulator 3, a center electrode 4, a cylindrical housing 2, a ground electrode 6, and a plug cover 5. The center electrode 4 is held on the inner periphery of the insulator 3 and protrudes from the insulator 3 toward the tip side. The housing 2 holds the insulator 3 on the inner periphery side. The ground electrode 6 forms a discharge gap G between itself and the center electrode 4. The plug cover 5 is provided at the tip of the housing 2 so as to cover the auxiliary combustion chamber 50 in which the discharge gap G is arranged. The plug cover 5 has an injection hole 51 that communicates the auxiliary combustion chamber 50 with the outside.

[0011] The plug cover 5 also has an annular cutout surface 52 around at least one nozzle hole 51, the cutout surface 52 being connected to the outer opening 511 of the nozzle hole 51. As shown in FIG 3, the annular cutout surface 52 is formed adjacent to the outer opening 511 over the entire periphery of the outer opening 511.

[0012] As shown in FIG. 4, in a cross section including the nozzle hole axis 51L of the nozzle hole 51, the angle θ1 between the inner circumferential surface 512 of the nozzle hole 51 and the annular cutout surface 52 is 225° or more.

[0013] Moreover, the portion of the plug cover 5 where the annular cutout surface 52 is formed is formed so that the thickness increases as it gets farther away from the outer opening 511 .

[0014] The spark plug 1 of this embodiment can be used, for example, as an ignition means in an internal combustion engine of an automobile, etc. As shown in Fig. 6, the threaded portion 21 of the housing 2 is screwed into a female threaded portion of a plug hole 711 of a cylinder head 71, so that the spark plug 1 is attached to the internal combustion engine 10. When the spark plug 1 is attached to the internal combustion engine 10, the housing 2 is in thermal contact with the cylinder head 71.

[0015] The internal combustion engine 10 also 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.

[0016] 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. In this embodiment, the plug central axis C is also the central axis of the center electrode 4.

[0017] When the spark plug 1 is attached to the internal combustion engine 10, the plug cover 5 separates the auxiliary combustion chamber 50 from the main combustion chamber 101. The injection hole 51 connects the auxiliary combustion chamber 50 and the main combustion chamber 101.

[0018] In this embodiment, the plug cover 5 has a peripheral wall portion 54, a bottom wall portion 55, and a corner portion 56, as shown in Fig. 1. The peripheral wall portion 54 is a generally cylindrical portion that covers part of the outer periphery of the auxiliary combustion chamber 50. The bottom wall portion 55 is a portion that covers the tip side of the auxiliary combustion chamber 50. The corner portion 56 is a portion that connects the tip of the peripheral wall portion 54 and the outer periphery of the bottom wall portion 55 in a curved shape.

[0019] A base end of the peripheral wall portion 54 is joined to a tip end of the housing 2. The plug cover 5 is in thermal contact with the housing 2.

[0020] Further, the corner portion 56 is formed with an injection hole 51 and an annular cutout surface 52. The injection hole 51 is formed in a substantially cylindrical shape. As shown in FIG. 2, the injection hole 51 is formed such that an injection hole axis 51L is along the plug radial direction when viewed from the Z direction. As shown in FIG. 1, the injection hole 51 opens at an angle with respect to the Z direction so as to move outward in the plug radial direction toward the tip side. Moreover, an annular cutout surface 52 is formed around all the injection holes 51.

[0021] 5, the length L1 of the nozzle hole 51 in the opening direction, around which the annular cutout surface 52 is formed, is equal to or greater than 1 / 2 and equal to or less than 2 / 3 of the nozzle hole diameter L2 of the nozzle hole 51. The nozzle hole diameter L2 may be, for example, 0.7 to 1.5 mm.

[0022] Moreover, the length L1 is ½ or more and ⅔ or less of the thickness L3 of the plug cover 5. The thickness L3 is, for example, 0.75 mm or more. Moreover, in this embodiment, the length L4 of the annular cutout surface 52 in the opening direction of the injection hole 51 is ½ or more of the length L1.

[0023] 3, the annular cutout surface 52 is formed in an annular shape. In this embodiment, the annular cutout surface 52 is formed so as to have a smaller diameter as it approaches the outer opening 511, as shown in FIGS. 1, 4, and 5. In other words, the annular cutout surface 52 is formed so as to have a larger diameter as it moves outward from the outer opening 511 in the opening direction of the injection hole 51. The annular cutout surface 52 is formed from the outer opening 511 to the outer surface 53 of the injection hole 51.

[0024] 4 is preferably greater than or equal to 240° and less than or equal to 270°. In a cross section including the nozzle hole axis 51L, the inclination angle θ2 of the extension line 52L of the annular cutout surface 52 with respect to the nozzle hole axis 51L is greater than or equal to 45°.

[0025] The annular cutout surface 52 can be formed, for example, by performing cutting with a drill or electric discharge machining on the plug cover 5 after the nozzle hole 51 is opened. In this embodiment, the annular cutout surface 52 is formed by cutting with a drill. Furthermore, the plug cover 5 before the nozzle hole 51 is opened can be formed, for example, by plastic processing a plate-shaped member with a uniform thickness.

[0026] Next, the effects of this embodiment will be described. The spark plug 1 has the annular cutout surface 52 that satisfies the above conditions. Therefore, the area of ​​the inner circumferential surface 512 of the injection hole 51 can be reduced while ensuring the thickness of the plug cover 5. Therefore, the amount of heat received by the inner circumferential surface 512 of the injection hole 51 by the flame ejected from the auxiliary combustion chamber 50 to the main combustion chamber through the injection hole 51 can be reduced while ensuring the heat dissipation to the outside of the plug cover 5. As a result, overheating of the plug cover 5 can be suppressed.

[0027] The spark plug 1 of this embodiment ignites the mixture in the auxiliary combustion chamber 50 by generating a discharge in the discharge gap G, and forms a flame. Then, the flame generated in the auxiliary combustion chamber 50 is ejected as a flame jet into the main combustion chamber through the nozzle hole 51. As a result, the flame is propagated to the main combustion chamber to combust the mixture. At this time, the inner circumferential surface 512 of the nozzle hole 51 receives heat from the flame ejected into the main combustion chamber. The inner circumferential surface 512 is more likely to receive heat from the flame as the area increases. Therefore, the spark plug 1 of this embodiment has the annular cutout surface 52. Therefore, the length L1 (see FIG. 5) of the nozzle hole 51 is likely to be short. Therefore, the area of ​​the inner circumferential surface 512 is likely to be small, and the amount of heat received by the inner circumferential surface 512 by the flame can be suppressed. Therefore, it is possible to suppress the inner circumferential surface 512 and the area around it from becoming too hot, and to suppress overheating of the plug cover 5. Therefore, in an internal combustion engine of an automobile or the like equipped with the spark plug 1, pre-ignition can be suppressed even during high-load operation, etc. As a result, the fuel efficiency and output of the internal combustion engine can be improved.

[0028] 7, if the plug cover 5 does not have the annular cutout surface 52, the length L1 is likely to be longer than that of the first embodiment. Therefore, the amount of heat received by the inner circumferential surface 512 of the injection hole 51 is likely to be greater than that of the first embodiment.

[0029] 8, a spark plug 92 of Comparative Example 2 is considered in which an inner cutout surface 57 that is connected to an inner opening 513 of the nozzle hole 51 is formed around the nozzle hole 51. The inner cutout surface 57 is formed adjacent to the inner opening 513 over the entire periphery of the inner opening 513. The inner cutout surface 57 is also formed so as to increase in diameter as it moves away from the inner opening 513. In this case, although the length L1 tends to be short, the inner cutout surface 57 is also likely to receive heat from the flame ejected into the main combustion chamber in addition to the inner circumferential surface 512 of the nozzle hole 51. Therefore, in Comparative Example 2, the amount of heat received near the nozzle hole 51 by the flame ejected into the main combustion chamber tends to be large.

[0030] On the other hand, the spark plug 1 of this embodiment has annular cutout surface 52 that satisfies the above conditions. Therefore, the length L1 is easily shortened, and the amount of heat received by the inner circumferential surface 512 of the nozzle hole 51 due to the flame can be reduced. Also, when the flame jet is ejected from the nozzle hole 51 into the main combustion chamber, the flame jet is easily detached from the annular cutout surface 52. Therefore, the amount of heat received by the flame jet at the annular cutout surface 52 can be reduced. Therefore, the amount of heat received by the flame near the nozzle hole 51 can be easily reduced. As a result, overheating of the plug cover 5 can be suppressed.

[0031] Also, consider the case where the thickness of the plug cover is thinned. In this case, the length L1 is likely to be short, so the amount of heat received by the inner circumferential surface of the injection hole due to the flame can be suppressed. Here, the thicker the plug cover is, the more easily the heat of the plug cover moves to the housing and is likely to be dissipated to the outside through the housing. Therefore, when the thickness of the plug cover is thinned, the amount of heat dissipated by the plug cover is likely to be small, and the plug cover may become hot. On the other hand, the spark plug 1 of this embodiment has the annular cutout surface 52 as described above. Therefore, the area of ​​the inner circumferential surface 512 of the injection hole 51 can be reduced while ensuring the thickness of the plug cover 5. Therefore, the amount of heat received by the inner circumferential surface 512 due to the flame can be suppressed while ensuring the heat dissipation to the outside of the plug cover 5. As a result, overheating of the plug cover 5 can be suppressed.

[0032] The annular cutout surface 52 is formed by performing cutting processing with a drill on the plug cover 5 after the injection hole 51 is opened. Therefore, the annular cutout surface 52 adjacent to the outer opening 511 can be easily formed. As a result, the spark plug 1 capable of suppressing overheating of the plug cover 5 can be efficiently manufactured.

[0033] Moreover, angle θ1 is equal to or greater than 225°. Therefore, the flame jet easily separates from annular cutout surface 52. This makes it possible to reduce the heat received by annular cutout surface 52 from the flame jet. As a result, overheating of plug cover 5 can be suppressed.

[0034] Also, it is preferable that angle θ1 is 240° or more. This makes it easier for the flame jet to separate from the annular cutout surface 52. This makes it possible to more sufficiently ensure the momentum of the flame jet, and more reliably suppress the heat received by the annular cutout surface 52 from the flame jet. As a result, it is possible to more sufficiently ensure ignition performance in the main combustion chamber, and more reliably suppress overheating of the plug cover 5.

[0035] Moreover, it is preferable that the angle θ1 is equal to or less than 270°. This allows the annular cutout surface 52 to be easily formed by cutting. As a result, the spark plug 1 capable of suppressing overheating of the plug cover 5 can be efficiently manufactured.

[0036] The annular cutout surface 52 is formed adjacent to the outer opening 511 over the entire periphery of the outer opening 511. Therefore, the length of the inner circumferential surface 512 of the injection hole 51 in the opening direction can be shortened over the entire inner circumferential surface 512 of the injection hole 51. Therefore, it is possible to prevent the amount of heat received by the inner circumferential surface 512 from becoming locally large. Therefore, it is possible to prevent the inner circumferential surface 512 and the area therearound from becoming locally hot. As a result, it is possible to prevent the plug cover 5 from overheating.

[0037] The portion of the plug cover 5 where the annular cutout surface 52 is formed is formed so that its thickness increases with increasing distance from the outer opening 511. This makes it easier to dissipate heat from the inner circumferential surface 512 of the injection hole 51 and its surrounding areas to the outside. As a result, overheating of the plug cover 5 can be suppressed.

[0038] In addition, an annular cutout surface 52 is formed around all of the injection holes 51. This makes it possible to reliably prevent overheating of the plug cover 5. As a result, pre-ignition can be reliably prevented.

[0039] The length L1 of the nozzle hole 51 around which the annular cutout surface 52 is formed is equal to or greater than 1 / 2 and equal to or less than 2 / 3 of the nozzle hole diameter L2. Therefore, the flame to be ejected into the main combustion chamber can be reliably guided by the inner circumferential surface 512 of the nozzle hole 51, and the amount of heat received by the inner circumferential surface 512 can be reliably reduced. Therefore, the momentum of the flame jet can be sufficiently ensured while overheating of the plug cover 5 can be reliably suppressed. As a result, pre-ignition can be reliably suppressed while adequately ensuring ignition performance.

[0040] As described above, according to this embodiment, it is possible to provide the spark plug 1 for an internal combustion engine, which is capable of suppressing overheating of the plug cover 5.

[0041] (Experimental Example 1) In this example, as shown in Figs. 9 to 13, a CFD analysis (abbreviation of "Computational Fluid Dynamics analysis") was performed on the temperature of the inner peripheral surface 512 of the nozzle hole 51 when a flame jet F was ejected from the spark plug 1, 91 installed in the internal combustion engine 10, 910. In this example, the analysis was performed using the spark plug 1 of the first embodiment and the spark plug 91 of the comparative embodiment 1. The test conditions were: the internal combustion engine speed was 4000 rpm, the equivalence ratio was 1.013, the EGR rate (i.e., exhaust gas recirculation rate) was 0%, the ignition timing by the spark plug was 723° CA (abbreviation of crank angle), and the ignition energy was 60 mJ. In addition, the spark plug 1 of the first embodiment used in this example had an angle θ1 (see Fig. 4) of 225°. In addition, Figs. 9 and 10 show the analysis results of the comparative embodiment 1, and Figs. 11 and 12 show the analysis results of the first embodiment.

[0042] 9 and 10, in the case of comparative embodiment 1, it was found that the flame ejects so as to come into contact with the inner circumferential surface 512 of the nozzle hole 51 from the inner wall surface 58 to the outer surface 53 of the plug cover 5. That is, in the case of comparative embodiment 1, it was found that the flame ejects so as to come into contact with the entire inner circumferential surface 512 in the opening direction of the nozzle hole 51. On the other hand, as shown in FIGS. 11 and 12, in the case of embodiment 1, it was found that the flame ejects so as to come into contact with the entire inner circumferential surface 512 in the opening direction of the nozzle hole 51, but separates from the annular cutout surface 52.

[0043] The graph in FIG. 13 is a graph showing the relationship between the crank angle and the temperature of the inner circumferential surface 512 of the nozzle hole 51 in the first embodiment and the first comparative embodiment. From this graph, it can be seen that the temperature of the inner circumferential surface 512 rises immediately after ignition in both the first embodiment and the first comparative embodiment. It can also be seen that the peak temperature after ignition is lower in the first embodiment than in the first comparative embodiment. Here, the first embodiment has an annular cutout surface 52. Therefore, the area of ​​the inner circumferential surface 512 in the first embodiment is smaller than that in the first comparative embodiment. In addition, in the first embodiment, the flame jet F separates from the annular cutout surface 52. Therefore, it is considered that the first embodiment can suppress the amount of heat received near the nozzle hole 51 more than the first comparative embodiment. As a result, it is considered that the first embodiment can suppress the temperature of the inner circumferential surface 512 more than the first comparative embodiment.

[0044] (Embodiment 2) In this embodiment, as shown in FIGS. 14 to 16, a recess 59 is formed adjacent to an outer opening 511. As shown in FIG.

[0045] As shown in FIGS. 14 to 16, the recess 59 is formed by recessing a part of the outer surface 53 of the plug cover 5 towards the auxiliary combustion chamber 50 side.

[0046] The diameter of the recess 59 is larger than the diameter of the injection hole 51. The recess 59 is formed adjacent to the outer opening 511 over the entire periphery of the outer opening 511, as shown in Fig. 16. By providing the recess 59 adjacent to the outer opening 511, an annular cutout surface 52 is formed around the outer opening 511. In other words, a part of the surface forming the recess 59 becomes the annular cutout surface 52.

[0047] In this embodiment, the annular cutout surface 52 is formed so as to be perpendicular to the injection hole axis 51L. Moreover, the annular cutout surface 52 and the outer opening 511 are formed so as to be positioned on substantially the same plane.

[0048] 15, in this embodiment, the angle θ1 is greater than 225°. More specifically, the angle θ1 is 270°. 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.

[0049] In this embodiment, angle θ1 is greater than 225°. This ensures that the flame jet can easily separate from annular cutout surface 52. This ensures sufficient momentum for the flame jet, and also ensures that the heat received by annular cutout surface 52 from the flame jet is suppressed. As a result, it is possible to ensure sufficient ignition performance in the main combustion chamber, and also to reliably prevent overheating of plug cover 5.

[0050] In addition, the annular cutout surface 52 and the outer opening 511 are formed to be positioned substantially on the same plane. This makes it easier for the flame jet to separate from the annular cutout surface 52. As a result, it is possible to more sufficiently ensure ignition performance and more reliably prevent overheating of the plug cover 5. In addition, the same effects as those of the first embodiment are achieved.

[0051] (Experimental Example 2) In this example, as shown in Figs. 17 and 18, the state of the flame jet F ejected into the main combustion chamber 101 from the spark plug 1 of the second embodiment was analyzed. The other test conditions were the same as those in Experimental Example 1.

[0052] From the analysis diagrams of FIG. 17 and FIG. 18, it can be seen that when the flame jet F is ejected from the spark plug 1 of the second embodiment, the flame jet F completely separates from the annular cutout surface 52 and ejects vigorously along the opening direction of the nozzle hole 51. Here, in the second embodiment, the angle θ1 is greater than 225°. Therefore, it is considered that the flame jet F completely separates from the annular cutout surface 52. This is considered to reliably suppress the heat received by the annular cutout surface 52 from the flame jet F. In addition, it is considered that the flame jet F can be ejected vigorously into the main combustion chamber 101 by completely separating from the annular cutout surface 52. This is considered to ensure sufficient ignition performance in the main combustion chamber 101.

[0053] (Embodiment 3) As shown in FIG. 19, this embodiment is an embodiment in which the range in which the annular cutout surface 52 is formed is changed from that of the second embodiment.

[0054] In this embodiment, the annular cutout surface 52 and the outer opening 511 are formed to be positioned substantially on the same plane as in the second embodiment, as shown in Fig. 19. The annular cutout surface 52 is formed from the outer opening 511 to the outer surface 53. The rest is the same as in the second embodiment.

[0055] The annular cutout surface 52 and the outer opening 511 are formed to be positioned substantially on the same plane. Moreover, the annular cutout surface 52 is formed from the outer opening 511 to the outer surface 53. Therefore, the annular cutout surface 52 can be easily formed by performing a cutting process on the plug cover 5 after the injection hole 51 is opened. As a result, the spark plug 1 capable of suppressing overheating of the plug cover 5 can be efficiently manufactured. In addition, the same effects as those of the second embodiment are achieved.

[0056] In the above-mentioned embodiments 1 to 3, the injection hole 51 is formed in the corner portion 56. However, the injection hole can also be formed in, for example, the bottom wall portion. That is, an annular cutout surface can be formed adjacent to the outer opening of the injection hole formed in the bottom wall portion.

[0057] In the above-mentioned first to third embodiments, the injection hole 51 is formed so that the injection hole axis 51L is aligned with the plug radial direction when viewed from the Z direction. However, the injection hole can also be formed so that the injection hole axis is inclined with respect to the plug radial direction when viewed from the Z direction. In other words, the injection hole can also be formed so that a swirl flow is generated in the auxiliary combustion chamber by introducing an air flow into the auxiliary combustion chamber through the injection hole.

[0058] 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]

[0059] 1...spark plug, 2...housing, 3...insulator, 4...center electrode, 5...plug cover, 50...auxiliary combustion chamber, 51...nozzle hole, 511...outer opening, 512...inner circumferential surface, 51L...nozzle hole axis, 52...annular notched surface, 6...ground electrode, G...discharge gap, θ1...angle

Claims

1. A cylindrical insulator (3); a center electrode (4) held on the inner circumferential side of the insulator and protruding from the insulator toward the tip side; a cylindrical housing (2) that holds the insulator on its inner periphery; a ground electrode (6) forming a discharge gap (G) between itself and the center electrode; a plug cover (5) provided at the tip of the housing so as to cover a sub-combustion chamber (50) in which the discharge gap is disposed, The plug cover is formed with a nozzle hole (51) that communicates the auxiliary combustion chamber with the outside, The plug cover has an annular cutout surface (52) around at least one of the nozzle holes, the cutout surface (52) being connected to an outer opening (511) of the nozzle hole; the annular cutout surface is formed adjacent the outer opening around the entire periphery of the outer opening; In a cross section including the nozzle hole axis (51L) of the nozzle hole, an angle (θ1) between an inner circumferential surface (512) of the nozzle hole and the annular cutout surface is 225° or more, a portion of the plug cover where the annular cutout surface is formed is formed so as to have a thickness that increases with increasing distance from the outer opening, The spark plug (1) for an internal combustion engine, wherein the annular cutout surface and the outer opening are formed to be positioned on the same plane.

2. A spark plug for an internal combustion engine as described in claim 1, wherein the annular cutout surface, formed to be positioned on the same plane as the outer opening, is formed from the outer opening to the outer surface (53) of the plug cover.

3. 3. The spark plug for an internal combustion engine according to claim 1, wherein the annular cut surface is formed around all of the nozzle holes.

4. 4. A spark plug for an internal combustion engine according to claim 1, wherein the nozzle hole having the annular cutout surface formed around it has a length (L1) in an opening direction of the nozzle hole that is equal to or greater than ½ and equal to or less than ⅔ of a nozzle hole diameter (L2) of the nozzle hole.

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