Spark plug for internal combustion engine and internal combustion engine equipped with same

Abstract

To provide a spark plug for an internal combustion engine that can suppress overheating of a plug cover and improve ignitability, and provide an internal combustion engine having the same.SOLUTION: In a spark plug 1, a plug cover 5 has an injection hole 51 and a tip flat surface 52. The injection hole 51 opens so as to extend outward in the radial direction of a plug as going to the tip side. The length from a tip 211 of a screw portion 21 to the tip of the plug cover 5 in an axial direction Z of the plug is equal to 6.5 mm or less. The distance in the axis direction Z of the plug from an intersection point P1 between an outer peripheral surface of a virtual tube VT1 obtained by extending the tip 211 of the screw portion 21 in the axial direction Z of the plug and an extension line 511L of a base end surface 511 of the injection hole 51 to the tip 211 of the screw portion 21 is defined as a distance h2. The inclination angle of the center axis of the injection hole 51 with respect to the axial direction Z of the plug is defined as an angle θ1. At this time, the spark plug 1 satisfies the following formula (1): h2×sinθ1>1.5 mm.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a spark plug for an internal combustion engine and an internal combustion engine equipped with the same. [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. The spark plug described in Patent Document 1 specifies the ratio of the total surface area of ​​the inner wall surfaces of the housing and plug cover facing the pre-combustion chamber to the surface area of ​​the outer circumferential surface of the insulator facing the pre-combustion chamber. This is intended to prevent the pre-combustion chamber from becoming too hot, 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 2020-184435 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the spark plug described in Patent Document 1, the tip surface of the plug cover has a convex curved shape that is curved so as to be convex toward the tip side. Therefore, the plug cover is likely to protrude a large amount into the main combustion chamber and is likely to receive heat from the combustion in the main combustion chamber. Therefore, from the viewpoint of suppressing overheating of the plug cover and suppressing pre-ignition, it can be said that there is room for further improvement.

[0005] The present invention has been made in consideration of the above problems, and aims to provide a spark plug for an internal combustion engine that is capable of suppressing overheating of the plug cover and improving ignition performance, and an internal combustion engine equipped with the same. [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 and has a threaded portion (21) formed on its outer 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 has a nozzle hole (51) that communicates the auxiliary combustion chamber with the outside, and has a tip flat surface (52) whose normal direction is oriented in the plug axial direction (Z), The injection hole opens at an incline with respect to the plug axial direction so as to move outward in the plug radial direction toward the tip side, The length (h1) from the tip (211) of the threaded portion to the tip of the plug cover in the plug axial direction is 6.5 mm or less, When the distance in the plug axial direction between the tip of the threaded portion and an intersection (P1) between the outer circumferential surface of a virtual cylinder (VT1) obtained by extending the tip of the threaded portion in the plug axial direction and an extension line (511L) of the base end surface (511) of the injection hole is a distance h2, and the inclination angle of the central axis of the injection hole with respect to the plug axial direction is an angle θ1, the following formula (1) is satisfied: death , The plug cover has a peripheral wall portion (53) covering an outer periphery side of the auxiliary combustion chamber, a bottom wall portion (54) covering a tip side of the auxiliary combustion chamber, and a corner portion (55) connecting a tip of the peripheral wall portion and an outer periphery of the bottom wall portion in a curved shape, A base end portion of the peripheral wall portion is joined to a tip end portion of the housing, The tip flat surface is formed on the bottom wall portion, The nozzle hole is formed in the corner portion. In a spark plug (1) for an internal combustion engine. h2×sinθ1>1.5mm (1)

[0007] Another aspect of the present invention is a combustion chamber comprising: A plug hole (12) communicating with the main combustion chamber; An internal combustion engine (10) having a spark plug (1) inserted and fixed in the plug hole, The spark plug includes a cylindrical insulator (3), a center electrode (4) held on the inner periphery of the insulator and protruding from the insulator toward a tip side, a cylindrical housing (2) holding the insulator on its inner periphery and having a threaded portion (21) formed on its outer periphery, a ground electrode (6) forming a discharge gap (G) between itself and the center electrode, and a plug cover (5) provided at a tip portion of the housing so as to cover a sub-combustion chamber (50) in which the discharge gap is located, The spark plug is attached to the internal combustion engine by screwing the threaded portion into a female threaded portion (121) formed on an inner circumferential surface of the spark plug hole, The tip of the spark plug is disposed so as to face the main combustion chamber, the plug cover has a nozzle hole (51) that communicates the auxiliary combustion chamber with the main combustion chamber, and has a tip flat surface (52) whose normal direction is oriented in the plug axial direction (Z), and the nozzle hole opens at an angle with respect to the plug axial direction so as to move outward in the plug radial direction toward the tip side, a length (H1) from a tip (131) of a screw-in portion (13) between the screw portion and the female screw portion to a tip of the plug cover in the plug axial direction is 6.5 mm or less; When a distance in the plug axial direction between an intersection (P2) of an outer circumferential surface of an imaginary cylinder (VT2) obtained by extending an opening end (122) on the tip side of the spark plug hole in the plug axial direction and an extension line (511L) of the base end surface (511) of the injection hole and the opening end is defined as a distance H2, and an inclination angle of the central axis of the injection hole with respect to the plug axial direction is defined as an angle θ1, the following formula (2) is satisfied: death , The plug cover has a peripheral wall portion (53) covering an outer periphery side of the auxiliary combustion chamber, a bottom wall portion (54) covering a tip side of the auxiliary combustion chamber, and a corner portion (55) connecting a tip of the peripheral wall portion and an outer periphery of the bottom wall portion in a curved shape, A base end portion of the peripheral wall portion is joined to a tip end portion of the housing, The tip flat surface is formed on the bottom wall portion, The nozzle hole is formed in the corner portion. It is found in internal combustion engines. H2×sinθ1>1.5mm (2) Effect of the Invention

[0008] In the above spark plug, the plug cover has a flat tip surface. Also, the length from the tip of the threaded portion to the tip of the plug cover in the plug axial direction is 6.5 mm or less. This makes it easy to reduce the amount of protrusion of the plug cover into the main combustion chamber. As a result, overheating of the plug cover can be suppressed.

[0009] In addition, the spark plug satisfies the above formula (1). Therefore, the flame jet ejected into the main combustion chamber through the nozzle hole is not easily cooled by the base end face of the main combustion chamber. As a result, ignition performance can be improved.

[0010] In the above internal combustion engine, the plug cover of the spark plug has a flat tip surface. Also, the length from the tip of the threaded portion to the tip of the plug cover in the plug axial direction is 6.5 mm or less. This makes it easy to reduce the amount of protrusion of the plug cover into the main combustion chamber. As a result, overheating of the plug cover can be suppressed.

[0011] In addition, the internal combustion engine satisfies the above formula (2). Therefore, the flame jet ejected into the main combustion chamber through the nozzle hole is not easily cooled by the base end face of the main combustion chamber. As a result, ignition performance can be improved.

[0012] As described above, according to the above aspect, it is possible to provide a spark plug for an internal combustion engine that can suppress overheating of the plug cover and improve ignition performance, and an internal combustion engine equipped with the spark plug. 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]

[0013] [Figure 1] 2 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, and corresponds to a cross-sectional view taken along line II in FIG. [Diagram 2] 4 is a cross-sectional view showing the angle θ1 and the length of each portion in the first embodiment. FIG. [Diagram 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. [Figure 4] IV arrow view of FIG. 2. [Diagram 5] 1 is a cross-sectional view of an internal combustion engine according to a first embodiment. [Figure 6] 1 is a cross-sectional view of a spark plug installed in an internal combustion engine according to a first embodiment. [Figure 7] FIG. 4 is a cross-sectional view showing a length H1 in the first embodiment. [Figure 8] 4 is a cross-sectional view showing angles θ1 and θ2 in the first embodiment. FIG. [Figure 9] 6 is a graph showing the relationship between length H1 and the ignition timing at which pre-ignition occurs in Experimental Example 1. [Figure 10] FIG. 13 is a CFD analysis diagram showing a flame jet ejected from the pre-combustion chamber to the main combustion chamber through a nozzle hole in Experimental Example 2. [Figure 11] 11 is a graph showing the relationship between the crank angle and the length of the flame jet in Experimental Example 2. [Figure 12] 11 is a graph showing the relationship between the crank angle and the flame jet speed in Experimental Example 2. [Figure 13] FIG. 13 is a CFD analysis diagram of the flame jet showing angle θ3 in Experimental Example 2. [Figure 14] FIG. 7 is a cross-sectional view of a spark plug installed in an internal combustion engine according to a second embodiment. [Figure 15] FIG. 11 is a cross-sectional view showing the distance h2 and the distance H2 in the second embodiment. [Figure 16] FIG. 11 is a cross-sectional view of a spark plug installed in an internal combustion engine according to a third embodiment. [Figure 17] FIG. 11 is a cross-sectional view showing the distance h2 and the distance H2 in the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] (Embodiment 1) DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a spark plug for an internal combustion engine and an internal combustion engine equipped with the same will be described with reference to FIGS. As shown in Figs. 1 to 4, 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 and has a threaded portion 21 formed on its outer 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 arranged.

[0015] The plug cover 5 has an injection hole 51 that connects the auxiliary combustion chamber 50 with the outside, and has a tip flat surface 52 whose normal direction faces the plug axial direction Z. The injection hole 51 opens at an angle with respect to the plug axial direction Z so that it becomes more outward in the plug radial direction as it approaches the tip side.

[0016] As shown in FIG. 2, a length h1 from the tip 211 of the threaded portion 21 to the tip of the plug cover 5 in the plug axial direction Z is 6.5 mm or less.

[0017] 1, an intersection point P1 is defined as an intersection between the outer circumferential surface of an imaginary cylinder VT1 obtained by extending the tip 211 of the threaded portion 21 in the plug axial direction Z and an extension line 511L of the base end surface 511 of the injection hole 51. A distance h2 is defined as a distance in the plug axial direction Z between the intersection point P1 and the tip 211 of the threaded portion 21. Also, as shown in FIG. 2, an inclination angle of the central axis of the injection hole 51 with respect to the plug axial direction Z is defined as an angle θ1. At this time, the spark plug 1 satisfies the following formula (1). h2×sinθ1>1.5mm (1)

[0018] 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. 5, the spark plug 1 is attached to an internal combustion engine 10 by screwing a threaded portion 21 of a housing 2 into a female threaded portion 121 of a spark plug hole 12 of a cylinder head 120. When the spark plug 1 is attached to the internal combustion engine 10, the housing 2 is in thermal contact with the cylinder head 120.

[0019] The internal combustion engine 10 has a piston 17 that reciprocates in a cylinder 16. The volume of the main combustion chamber 11 changes due to the reciprocating motion of the piston 17. The internal combustion engine 10 is formed with an intake port 141 and an exhaust port 151, and is equipped with an intake valve 14 and an exhaust valve 15, respectively.

[0020] One end of the spark plug 1 in the axial direction Z is disposed in the main combustion chamber 11 of the internal combustion engine 10. In the axial direction Z of the spark plug 1, the side exposed to the main combustion chamber 11 is referred to as the tip side, and the opposite side is referred to as the base side. The axial direction Z of the spark plug 1 is also referred to as the plug axial direction Z or simply as the Z direction, as appropriate. The plug central axis C 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.

[0021] In this embodiment, the plug cover 5 is joined by welding or the like to the tip of the housing 2. As shown in Fig. 5 to Fig. 8, when the spark plug 1 is attached to the internal combustion engine 10, the plug cover 5 separates the auxiliary combustion chamber 50 from the main combustion chamber 11. Further, the injection hole 51 communicates between the auxiliary combustion chamber 50 and the main combustion chamber 11.

[0022] In this embodiment, the plug cover 5 has a peripheral wall portion 53, a bottom wall portion 54, and a corner portion 55, as shown in FIG. 2. The peripheral wall portion 53 is a substantially cylindrical portion that covers part of the outer periphery of the auxiliary combustion chamber 50. The bottom wall portion 54 is a portion that covers the tip side of the auxiliary combustion chamber 50. The corner portion 55 is a portion that connects the tip of the peripheral wall portion 53 and the outer periphery of the bottom wall portion 54 in a curved shape. A base end portion of the peripheral wall portion 53 is joined to the tip portion of the housing 2. The plug cover 5 is in thermal contact with the housing 2.

[0023] Further, a tip flat surface 52 is formed on the bottom wall portion 54. The tip flat surface 52 is formed so as to be perpendicular to the Z direction. In this embodiment, the entire tip surface of the bottom wall portion 54 forms the tip flat surface 52.

[0024] In this embodiment, the length in the Z direction from the tip 211 of the threaded portion 21 to the tip flat surface 52 is a length h1. In this embodiment, the length h1 is 3.3 mm or less.

[0025] In addition, in the plug cover 5, the injection hole 51 is formed in a corner portion 55. The injection hole 51 is formed in a substantially cylindrical shape.

[0026] In this embodiment, the injection hole 51 is formed such that an extension line 51L of the central axis of the injection hole 51 is aligned along the plug radial direction when viewed from the Z direction as shown in Fig. 4. The injection hole 51 is formed such that the extension line 51L substantially passes through the plug central axis C.

[0027] 2, the inclination angle of the extension line 51L with respect to the plug central axis C is an angle θ1. The angle θ1 is, for example, 45° to 75°.

[0028] In this embodiment, an extension line 511L of the base end surface 511 of the nozzle hole 51 includes the central axis of the nozzle hole 51 and is substantially parallel to the extension line 51L in a cross section along the Z direction, as shown in FIG.

[0029] 1, in a cross section including the central axis of the injection hole 51 and taken along the Z direction, a straight line that is parallel to the central axis of the injection hole 51 and passes through the tip 211 of the threaded portion 21 is defined as a straight line L1. In this case, the angle at which the outer circumferential surface of the imaginary cylinder VT1 and the straight line L1 intersect is angle θ1, which is the angle on the tip side of the straight line L1.

[0030] In a cross section including the central axis of the injection hole 51 and along the Z direction, a straight line that is perpendicular to the central axis of the injection hole 51 and passes through the intersection point P1 is defined as a straight line L2. The intersection point between the straight lines L1 and L2 is defined as an intersection point P3. At this time, the distance from the intersection point P1 to the intersection point P3 is h2×sinθ1.

[0031] 2, the housing 2 has a step-shaped supporting side step 22. The insulator 3 has a step-shaped supported side step 31. The base end surface of the supporting side step 22 supports the supported side step 31 in the Z direction via an annular gasket (not shown).

[0032] The insulator 3 has leg portions 32 whose diameter decreases toward the tip side. In this embodiment, the portion of the insulator 3 that is on the tip side of the supported side step portion 31 becomes the leg portion 32. The outer peripheral surface of the leg portion 32 faces the auxiliary combustion chamber 50. In this embodiment, the length D1 of the leg portion 32 in the Z direction is 11 mm or more.

[0033] Next, the internal combustion engine 10 of this embodiment will be described. 5 to 8, the internal combustion engine 10 has a main combustion chamber 11, a spark plug hole 12 communicating with the main combustion chamber 11, and a spark plug 1. The spark plug 1 is inserted into the spark plug hole 12 and fixed therein.

[0034] The spark plug 1 is attached to the internal combustion engine 10 by screwing a threaded portion 21 into a female threaded portion 121 formed on the inner circumferential surface of a spark plug hole 12. The tip portion of the spark plug 1 is disposed so as to face the main combustion chamber 11.

[0035] As shown in FIG. 7, a length H1 from a tip 131 of the screw engagement portion 13 between the threaded portion 21 and the female threaded portion 121 to the tip of the plug cover 5 in the plug axial direction Z is 6.5 mm or less.

[0036] 6, an intersection point P2 is defined as the point of intersection between the outer circumferential surface of an imaginary cylinder VT2 obtained by extending the open end 122 on the tip side of the spark plug hole 12 in the plug axial direction Z and an extension line 511L of the base end surface 511 of the injection hole 51. A distance H2 is defined as the distance between the intersection P2 and the open end 122 in the plug axial direction Z. At this time, the internal combustion engine 10 satisfies the following formula (2). H2×sinθ1>1.5mm (2)

[0037] In this embodiment, the tip 211 of the screw portion 21 and the tip 131 of the screw portion 13 are positioned at the same position in the Z direction as shown in Fig. 7. In addition, the opening end 122 and the tip 211 of the screw portion 21 are positioned at the same position in the Z direction as well. Therefore, in this embodiment, H1 = h1 and H2 = h2. In addition, the tip 131 of the screw portion 13 and the base end of the base end surface 111 of the main combustion chamber 11 are positioned at the same position in the Z direction as well.

[0038] 6, in a cross section including the central axis of the injection hole 51 and taken along the Z direction, a straight line L3 is parallel to the central axis of the injection hole 51 and passes through the inner circumferential surface of the opening end 122. In this case, the angle at which the outer circumferential surface of the imaginary cylinder VT2 and the straight line L3 intersect is angle θ1, which is the angle on the tip side of the straight line L3.

[0039] In a cross section including the central axis of the injection hole 51 and along the Z direction, a straight line that is perpendicular to the central axis of the injection hole 51 and passes through the intersection point P2 is defined as a straight line L4. The intersection point between the straight lines L3 and L4 is defined as an intersection point P4. At this time, the distance from the intersection point P2 to the intersection point P4 is H2×sinθ1.

[0040] 7, the length in the Z direction from the tip 131 of the screw portion 13 to the tip flat surface 52 is a length H1. In this embodiment, the length H1 is 3.3 mm or less.

[0041] 5 to 8, the base end surface 111 of the main combustion chamber 11 is inclined with respect to the plug axial direction Z so as to move toward the tip side as it moves away from the spark plug 1. The inclination angle of the base end surface 111 of the main combustion chamber 11 with respect to the plug axial direction Z is defined as angle θ2. Here, angle θ2 is greater than angle θ1. The difference between angle θ2 and angle θ1 is greater than 15°.

[0042] As shown in FIG. 8, in a cross section including the plug central axis C, the inclination angle of an extension line 111L of the base end face 111 with respect to the plug central axis C is an angle θ2.

[0043] Next, the effects of this embodiment will be described. In the above spark plug 1, the plug cover 5 has a tip flat surface 52. In addition, the length h1 is 6.5 mm or less. Therefore, it is easy to reduce the amount of protrusion of the plug cover 5 into the main combustion chamber 11. As a result, overheating of the plug cover 5 can be suppressed.

[0044] 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 11 through the nozzle hole 51. This causes the flame to propagate to the main combustion chamber 11 and combust the mixture. Here, the temperature of the main combustion chamber 11 during combustion is likely to be highest near the center of the combustion, that is, the center of the main combustion chamber 11, due to the effect of cooling by the cylinder 16 and the piston 17. In addition, among the parts of the plug cover 5, the tip is the part that protrudes most into the main combustion chamber 11, that is, the part closest to the center of the main combustion chamber 11. Therefore, the shorter the length h1 is and the larger the distance between the tip of the plug cover 5 and the center of the main combustion chamber 11 is, the easier it is to suppress the plug cover 5 from receiving heat due to the combustion in the main combustion chamber 11. In other words, the smaller the amount of protrusion of the plug cover 5 into the main combustion chamber 11, the easier it is to suppress the plug cover 5 from receiving heat and to suppress overheating. On the other hand, if the plug cover 5 is made too small to make the auxiliary combustion chamber 50 too small, it becomes difficult to strengthen the flame jet ejected from the auxiliary combustion chamber 50 into the main combustion chamber 11. Therefore, the plug cover 5 of the spark plug 1 of this embodiment is formed with a tip flat surface 52. This makes it possible to reduce the amount of protrusion of the plug cover 5 into the main combustion chamber 11 while ensuring the volume of the auxiliary combustion chamber 50. As a result, it is possible to suppress overheating of the plug cover 5 while ensuring ignition performance.

[0045] Furthermore, by setting the length h1 to 6.5 mm or less, it is easy to shorten the heat dissipation path from the tip end of the plug cover 5 to the screwing portion 13 when the spark plug 1 is installed in the internal combustion engine 10. Therefore, the heat of the plug cover 5 is easily dissipated to the internal combustion engine 10 via the screwing portion 13. As a result, overheating of the plug cover 5 can be suppressed.

[0046] Moreover, the spark plug 1 satisfies the above formula (1). Therefore, the flame jet ejected into the main combustion chamber 11 through the nozzle hole 51 is not easily cooled by the base end surface 111 of the main combustion chamber 11. As a result, the ignition performance can be improved.

[0047] The flame jet ejected into the main combustion chamber 11 extends along the opening direction of the nozzle hole 51, and tends to expand larger than the diameter of the nozzle hole 51 in a direction perpendicular to the central axis of the nozzle hole 51. Therefore, when the value of h2×sinθ1 is smaller than a predetermined value, the flame jet is likely to be cooled by the base end surface 111 of the main combustion chamber 11. Thus, the spark plug 1 of this embodiment satisfies the above formula (1). Therefore, the flame jet is unlikely to be cooled by the base end surface 111 of the main combustion chamber 11. As a result, ignition performance can be improved.

[0048] In this embodiment, the length h1 is 3.3 mm or less. This makes it easier to further reduce the amount of protrusion of the plug cover 5 into the main combustion chamber 11. As a result, overheating of the plug cover 5 can be further suppressed.

[0049] The shorter the length h1, the more the plug cover 5 can be prevented from overheating. On the other hand, if the length h1 is too short, the flame jet is more likely to be cooled by the base end face 111. Therefore, the spark plug 1 of this embodiment has a length h1 of 6.5 mm or less and satisfies the above formula (1). Therefore, it is possible to prevent the plug cover 5 from overheating while preventing the flame jet from being cooled by the base end face 111. In other words, the spark plug 1 can achieve both prevention of overheating of the plug cover 5 and improvement of ignition performance.

[0050] In the above-described internal combustion engine 10, the plug cover 5 of the spark plug 1 has a tip flat surface 52. Also, the length H1 is 6.5 mm or less. Therefore, it is easy to reduce the amount of protrusion of the plug cover 5 into the main combustion chamber 11. As a result, overheating of the plug cover 5 can be suppressed.

[0051] Furthermore, by setting the length H1 to 6.5 mm or less, it is easy to shorten the heat dissipation path from the tip of the plug cover 5 to the screw-fitting portion 13. Therefore, heat from the plug cover 5 is easily dissipated to the internal combustion engine 10 via the screw-fitting portion 13. As a result, overheating of the plug cover 5 can be suppressed.

[0052] Moreover, the internal combustion engine 10 satisfies the above formula (2). Therefore, the flame jet ejected into the main combustion chamber 11 through the nozzle hole 51 is not easily cooled by the base end surface 111 of the main combustion chamber 11. As a result, the ignition performance can be improved.

[0053] In this embodiment, the length H1 is 3.3 mm or less. This makes it easier to further reduce the amount of protrusion of the plug cover 5 into the main combustion chamber 11. As a result, overheating of the plug cover 5 can be further suppressed.

[0054] The shorter the length H1, the more the plug cover 5 can be prevented from overheating. On the other hand, if the length H1 is too short, the flame jet is more likely to be cooled by the base end face 111. Therefore, in the internal combustion engine 10 of this embodiment, the length H1 is 6.5 mm or less and satisfies the above formula (2). Therefore, the flame jet can be prevented from being cooled by the base end face 111 while preventing the plug cover 5 from overheating. In other words, the internal combustion engine 10 can achieve both prevention of overheating of the plug cover 5 and improvement of ignition performance. As a result, the output and fuel efficiency of the internal combustion engine 10 can be improved while preventing knocking during high load of the internal combustion engine 10.

[0055] The base end surface 111 of the main combustion chamber 11 is inclined with respect to the plug axial direction Z so as to move toward the tip side as it moves away from the spark plug 1. Moreover, the angle θ2 is greater than the angle θ1. Moreover, the difference between the angles θ2 and θ1 is greater than 15°. Therefore, the flame jet ejected into the main combustion chamber 11 through the nozzle hole 51 is even less likely to be cooled by the base end surface 111 of the main combustion chamber 11. In other words, even when the spread of the flame jet in the main combustion chamber 11 is taken into consideration, the collision of the flame jet with the base end surface 111 can be prevented. As a result, the ignition performance can be further improved.

[0056] The nozzle hole 51 opens at an angle with respect to the Z direction, and is formed at a corner 55. Therefore, the opening direction of the nozzle hole 51 can be easily aligned with the expansion direction of gas caused by combustion in the auxiliary combustion chamber 50. As a result, the flame jet can be ejected with force along the opening direction of the nozzle hole 51.

[0057] As described above, according to the present embodiment, it is possible to provide a spark plug for an internal combustion engine that can suppress overheating of the plug cover and improve ignition performance, and an internal combustion engine equipped with the spark plug.

[0058] (Experimental Example 1) In this example, as shown in the graph of FIG. 9, a relationship between the length H1 and the ignition timing at which pre-ignition occurs was analyzed using a plurality of internal combustion engines having the same basic structure as in the first embodiment but different values ​​of the length H1 (see FIG. 7). Generally, the more the ignition timing is advanced, the more likely pre-ignition occurs. Therefore, in this example, the ignition timing was gradually advanced for each internal combustion engine, and the ignition timing at which pre-ignition occurs was analyzed. The test conditions were that the internal combustion engine was a single-cylinder engine, the throttle was fully opened, and the rotation speed was 6500 rpm. In addition, the length of the leg of the insulator of the spark plug installed in the internal combustion engine was 11 mm. In addition, the internal combustion engine used in this example has H1=h1. Therefore, in this example, the length H1 will be mainly described.

[0059] Here, the ignition timing at which pre-ignition occurs is BTDC (abbreviation for top dead center) 29° CA (abbreviation for crank angle) or more, which is set as the standard for sufficient suppression of pre-ignition when used as a general automobile engine. From the above analysis results, a length H1 that satisfies this standard was determined. In addition, the ignition timing at which pre-ignition occurs is BTDC 37° CA or more, which is set as the standard for sufficient suppression of pre-ignition when used as a high-efficiency engine such as an automobile engine with a high compression ratio or an automobile engine equipped with a turbocharger. From the above analysis results, a length H1 that satisfies this standard was also determined.

[0060] In the graph of Fig. 9, the circles represent plots of the analysis results of each internal combustion engine. The graph of Fig. 9 also shows straight lines approximating these plots.

[0061] From the graph in Figure 9, it can be seen that the shorter the length H1, the more advanced the ignition timing at which pre-ignition occurs. From this result, it is believed that the shorter the length H1, the more the plug cover can be prevented from overheating, and therefore pre-ignition can be prevented.

[0062] Also, from the approximation line shown in the graph of FIG. 9, the length H1 at which the ignition timing at which pre-ignition occurs is BTDC 29° CA or more is estimated to be 6.5 mm or less. Also, the length H1 at which the ignition timing at which pre-ignition occurs is BTDC 37° CA or more is estimated to be 3.3 mm or less. From this result, in the internal combustion engine used in this example, it is considered that pre-ignition can be suppressed when used as a general automobile engine by setting the length H1 and the length h1 to 6.5 mm or less. Also, it is considered that pre-ignition can be suppressed by setting the length H1 and the length h1 to 3.3 mm or less, even if the engine is used as a high-efficiency engine such as an automobile engine with a high compression ratio or an automobile engine equipped with a supercharger.

[0063] (Experimental Example 2) In this example, as shown in Figs. 10 to 13, a CFD analysis (short for "Computational Fluid Dynamics analysis") was performed on the extension of a flame jet F1 ejected from a spark plug 1 installed in an internal combustion engine 10. Specifically, using an internal combustion engine having a basic structure similar to that of the first embodiment, the relationship between the elapsed time from ignition by the spark plug and the extension of the flame jet ejected into the main combustion chamber was analyzed. The test conditions were: internal combustion engine speed 4000 rpm, equivalence ratio 1, EGR rate (i.e. exhaust gas recirculation rate) 0%, ignition timing by the spark plug 714° CA, and ignition energy 60 mJ. In addition, the internal combustion engine used in this example has H2=h2.

[0064] Figure 10 shows the analysis results of flame jet F1 at 723° CA, 9° CA after ignition by the spark plug. From this result, it can be seen that flame jet F1 extends along the opening direction of nozzle hole 51, and expands larger than the diameter of nozzle hole 51 in the direction perpendicular to the central axis of nozzle hole 51. The flame jet F1 shown in the figure is a flame of 2300 K or more.

[0065] The length of the flame jet F1 ejected into the main combustion chamber 11 in the opening direction of the nozzle hole 51 is defined as D2. As shown in the graph of Figure 11, it can be seen that the rate of increase of the length D2 decreases as the crank angle advances.

[0066] As shown in the graph of Figure 12, the flame jet speed decreases as the crank angle advances. Also, it can be seen that the rate of decrease in the flame jet speed from 722° CA to 723° CA is significantly lower than before 722° CA. In other words, the flame jet spread slows down from 722° CA to 723° CA compared to before 722° CA. And, from the analysis results of this example, it was found that the expansion of the combustion range in the main combustion chamber after 723° CA is mainly due to the expansion of the combustion range caused by the flame propagation from the flame jet (not shown).

[0067] Here, in order to promote combustion in the main combustion chamber, it is considered important to suppress the cooling of the flame jet, which is the ignition source of the mixture in the main combustion chamber, by the base end face of the main combustion chamber. In particular, it is important to suppress the collision of the flame jet with the base end face of the main combustion chamber before the flame jet spread slows down. With this in mind, the spread of the flame jet will be explained below.

[0068] As shown in FIG. 10, in a cross section including the central axis of the nozzle hole 51 and along the Z direction, the direction perpendicular to the central axis of the nozzle hole 51 is defined as the Y direction. A straight line passing through a part F2 of the outer periphery of the flame jet F1 closest to the base end face 111 of the main combustion chamber 11 in the Y direction and parallel to the central axis of the nozzle hole 51 is defined as a straight line L5. In a cross section including the central axis of the nozzle hole 51 and along the Z direction, the straight line L5 and the extension line 511L are substantially parallel to each other. Note that the flame portion F3 extending toward the base end face 111 side from the straight line L5 in the Y direction is not a part of the flame jet F1 ejected into the main combustion chamber 11 through the nozzle hole 51, but indicates a flame formed by igniting the mixture in the main combustion chamber 11 by the flame jet F1. In other words, the flame portion F3 indicates a flame formed by flame propagation from the flame jet.

[0069] The distance between extension line 511L in the Y direction and straight line L5 is set to distance D3. In other words, the maximum spread length of flame jet F1 from extension line 511L in the Y direction toward base end surface 111 is distance D3.

[0070] As shown in Fig. 10, in the analysis result at 723°CA immediately after the extension of the flame jet slowed down, distance D3 was 1.5 mm. Therefore, by making the distance between extension line 511L and base end face 111 longer than 1.5 mm, it is believed that the collision of the flame jet with base end face 111 is suppressed and the cooling loss of the flame jet is suppressed. Therefore, it is believed that the cooling loss of the flame jet can be suppressed by making the values ​​of H2 × sinθ1 (see Fig. 6) and h2 × sinθ1 (see Fig. 1) longer than 1.5 mm.

[0071] Also, Fig. 13 is an analysis diagram of flame jet F1 at 723°CA, similar to Fig. 10. As shown in Fig. 13, in a cross section including the central axis of nozzle hole 51 and along the Z direction, the center of outer opening 512 of nozzle hole 51 is set as center P5. Also, a line segment connecting part F2 of the outer periphery of flame jet F1 to center P5 is set as line segment L6. In this case, the inclination angle θ3 of line segment L6 with respect to an extension line 51L of the central axis of nozzle hole 51 is 15°.

[0072] An imaginary cone VT3 has the extension line 51L as its central axis, the center P5 as its apex, and the line segment L6 as its side. At this time, it is considered that the flame jet F1 mainly ejects so as to pass through the space inside the imaginary cone VT3. Therefore, by making the angle θ2 (see FIG. 8) larger than 15° with respect to the angle θ1 (see FIG. 8), it is considered that the flame jet is less likely to collide with the base end surface 111 of the main combustion chamber 11, and is more difficult to cool.

[0073] (Embodiment 2) In this embodiment, as shown in Figs. 14 and 15, the distance H2 is shorter than the distance h2.

[0074] 14 and 15, the tip 131 of the screw portion 13 is located on the base end side of the opening end 122 on the tip side of the spark plug hole 12. In addition, the tip 211 of the threaded portion 21 is located on the base end side of the base end surface 111 and the opening end 122 of the main combustion chamber 11. 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.

[0075] In this embodiment, the tip 131 of the screw portion 13 is located closer to the base end than the open end 122. This makes it easier to further reduce the amount of protrusion of the plug cover 5 into the main combustion chamber 11. As a result, overheating of the plug cover 5 can be further suppressed. In addition, the same effects as those of the first embodiment are achieved.

[0076] (Embodiment 3) In this embodiment, as shown in Figs. 16 and 17, the distance H2 is longer than the distance h2.

[0077] 16 and 17, in this embodiment, the tip 211 of the threaded portion 21 is located further forward than the open end 122 and the tip 131 of the screw portion 13. In addition, the tip 211 of the threaded portion 21 is located further forward than the base end of the base end surface 111 of the main combustion chamber 11.

[0078] As shown in FIG. 16, the length H1 is longer than the length h1. The rest is the same as in the first embodiment.

[0079] In this embodiment, the distance H2 is longer than the distance h2. Therefore, the flame jet is even less likely to be cooled by the base end surface 111 of the main combustion chamber 11. As a result, the ignition performance can be further improved. In addition, the same effects as those of the first embodiment are achieved.

[0080] In the above-mentioned embodiments 1 to 3, the injection hole 51 is formed so that the central axis of the injection hole 51 is along the plug radial direction when viewed from the Z direction. However, the injection hole can also be formed so that the central axis of the injection hole is inclined with respect to a virtual line (not shown) that passes through the injection hole and the plug central axis and extends in the plug radial direction when viewed from the Z direction. In other words, the injection hole can also be formed so that a swirl flow is generated in the auxiliary combustion chamber by introducing an air flow into the auxiliary combustion chamber through the injection hole.

[0081] In the above-mentioned embodiments 1 to 3, four injection holes 51 are formed in the plug cover 5. However, the plug cover may have five or more injection holes. Also, the number of injection holes formed in the plug cover may be three or less.

[0082] In the above-mentioned embodiments 1 to 3, the discharge gap G is formed by the center electrode 4 and the ground electrode 6 facing each other in the Z direction. However, the discharge gap can also be formed, for example, by making the center electrode and the ground electrode face each other in the plug radial direction.

[0083] In the above-mentioned embodiments 1 to 3, one injection hole is formed so as to overlap with the ground electrode when viewed from the Z direction. However, the injection hole 51 can also be formed so as not to overlap with the ground electrode 6 when viewed from the Z direction.

[0084] 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]

[0085] 1...spark plug, 2...housing, 21...threaded portion, 211...tip of threaded portion, 3...insulator, 4...center electrode, 5...plug cover, 50...auxiliary combustion chamber, 51...nozzle hole, 511...base end surface of nozzle hole, 511L...extension line of base end surface of nozzle hole, 52...tip flat surface, 6...ground electrode, G...discharge gap, Z...plug axial direction

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 and has a threaded portion (21) formed on its outer 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 has a nozzle hole (51) that communicates the auxiliary combustion chamber with the outside, and has a tip flat surface (52) whose normal direction is oriented in the plug axial direction (Z), The injection hole opens at an incline with respect to the plug axial direction so as to move outward in the plug radial direction toward the tip side, a length (h1) from a tip (211) of the threaded portion to a tip (h1) of the plug cover in the plug axial direction is 6.5 mm or less; When a distance in the plug axial direction between an intersection (P1) of an outer circumferential surface of a virtual cylinder (VT1) obtained by extending the tip of the threaded portion in the plug axial direction and an extension line (511L) of the base end surface (511) of the injection hole and the tip of the threaded portion is defined as a distance h2, and an inclination angle of the central axis of the injection hole with respect to the plug axial direction is defined as an angle θ1, the following formula (1) is satisfied, The plug cover has a peripheral wall portion (53) covering the outer periphery side of the auxiliary combustion chamber, a bottom wall portion (54) covering the tip side of the auxiliary combustion chamber, and a corner portion (55) connecting the tip of the peripheral wall portion and the outer periphery of the bottom wall portion in a curved shape, A base end portion of the peripheral wall portion is joined to a tip end portion of the housing, The tip flat surface is formed on the bottom wall portion, The spark plug (1) for an internal combustion engine, wherein the nozzle hole is formed in the corner portion. h2×sinθ1>1.5mm...(1)

2. 2. The spark plug for an internal combustion engine according to claim 1, wherein a length from a tip of said threaded portion to a tip of said plug cover in an axial direction of said plug is 3.3 mm or less.

3. A main combustion chamber (11); A plug hole (12) communicating with the main combustion chamber; An internal combustion engine (10) having a spark plug (1) inserted and fixed in the plug hole, The spark plug includes a cylindrical insulator (3), a center electrode (4) held on the inner periphery of the insulator and protruding from the insulator toward a tip side, a cylindrical housing (2) holding the insulator on its inner periphery and having a threaded portion (21) formed on its outer periphery, a ground electrode (6) forming a discharge gap (G) between itself and the center electrode, and a plug cover (5) provided at the tip of the housing so as to cover an auxiliary combustion chamber (50) in which the discharge gap is located, The spark plug is attached to the internal combustion engine by screwing the threaded portion into a female threaded portion (121) formed on an inner circumferential surface of the spark plug hole, The tip of the spark plug is disposed so as to face the main combustion chamber, the plug cover has a nozzle hole (51) that communicates the auxiliary combustion chamber with the main combustion chamber, and has a tip flat surface (52) whose normal direction faces the plug axial direction (Z), and the nozzle hole opens at an angle with respect to the plug axial direction so as to move outward in the plug radial direction toward the tip side, a length (H1) from a tip (131) of a screw-threaded portion (13) between the screw portion and the female screw portion to a tip of the plug cover in the plug axial direction is 6.5 mm or less; When a distance in the plug axial direction is defined as a distance H2, which is a distance between an intersection (P2) of an outer circumferential surface of an imaginary cylinder (VT2) obtained by extending an opening end (122) on the tip side of the plug hole in the plug axial direction and an extension line (511L) of the base end surface (511) of the injection hole, and the opening end, and when a tilt angle of the central axis of the injection hole with respect to the plug axial direction is defined as an angle θ1, the following formula (2) is satisfied, The plug cover has a peripheral wall portion (53) covering the outer periphery side of the auxiliary combustion chamber, a bottom wall portion (54) covering the tip side of the auxiliary combustion chamber, and a corner portion (55) connecting the tip of the peripheral wall portion and the outer periphery of the bottom wall portion in a curved shape, A base end portion of the peripheral wall portion is joined to a tip end portion of the housing, The tip flat surface is formed on the bottom wall portion, The nozzle hole is formed in the corner portion. H2×sinθ1>1.5mm...(2)

4. An internal combustion engine as described in claim 3, wherein when the distance in the plug axial direction between the tip of the threaded portion and the intersection (P1) of the outer peripheral surface of a virtual cylinder (VT1) obtained by extending the tip (211) of the threaded portion in the plug axial direction and an extension line of the base end surface of the nozzle hole, the distance H2 is longer than the distance h2.

5. 5. The internal combustion engine according to claim 3, wherein a base end surface (111) of the main combustion chamber is inclined with respect to a plug axial direction so as to move toward a tip side as it moves away from the spark plug, and when an inclination angle of the base end surface of the main combustion chamber with respect to the plug axial direction is defined as an angle θ2, the angle θ2 is larger than the angle θ1, and a difference between the angle θ2 and the angle θ1 is larger than 15°.

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