JP7585986B2 - Spark plug for internal combustion engine and internal combustion engine equipped with same - Google Patents

Description

The present invention relates to a spark plug for an internal combustion engine and an internal combustion engine equipped with the same.

For example, as disclosed in Patent Document 1, a spark plug with a secondary combustion chamber at the tip is known. In this spark plug, a cover portion covering the secondary combustion chamber is formed with multiple nozzle holes. This allows a flame to be ejected from the secondary combustion chamber through the nozzle holes into the main combustion chamber, thereby combusting the mixture in the main combustion chamber.

JP 2020-009747 A

However, the spark plug described in Patent Document 1 does not take into consideration the ignition of the mixture in the auxiliary combustion chamber, i.e., the formation of the initial flame itself. In other words, no consideration is given to extending the discharge in the auxiliary combustion chamber to improve ignition performance.

The present invention was made in consideration of these problems, and aims to provide a spark plug for an internal combustion engine that can improve ignition performance, and an internal combustion engine equipped with the same.

The first 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 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 and is inclined with respect to the plug radial direction when viewed from the plug axial direction (Z),
Some of the plurality of nozzle holes are protruding side nozzle holes (510) formed on the protruding side of the protruding end portion (63) of the ground electrode,
At least a portion of the protruding end is located in a spark plug (1) for an internal combustion engine, the distance (D2) to the protruding side nozzle hole being closer than the distance (D1) to the plug center axis (C).

A second aspect of the present invention is an internal combustion engine (10) including the above-mentioned spark plug for an internal combustion engine,
A main combustion chamber (11);
an intake valve (72) and an exhaust valve (73) provided in the main combustion chamber;
The spark plug is disposed so that an outer surface (52) of the plug cover faces the main combustion chamber,
The spark plug is arranged such that, when viewed from the plug axial direction, an outer opening (511) of at least one of the projection-side nozzle holes faces the intake valve side,
The projection side nozzle hole is located in the internal combustion engine and has a larger opening area than the other nozzle holes.

A third aspect of the present invention is an internal combustion engine (10) including the above-mentioned spark plug for an internal combustion engine,
A main combustion chamber (11);
The spark plug is disposed so that an outer surface (52) of the plug cover faces the main combustion chamber;
an injector (71) for injecting fuel directly into the main combustion chamber;
The spark plug is disposed so that an injection flow (F) including the fuel injected from the injector during a compression stroke of the internal combustion engine is directed toward an outer opening (511) of the projection-side nozzle hole,
The projection side nozzle hole is located in the internal combustion engine and has a larger opening area than the other nozzle holes.

In the spark plug for an internal combustion engine according to the first aspect, the extension line of the central axis of the injection hole does not pass through the discharge gap and is inclined with respect to the plug radial direction when viewed from the plug axial direction. This allows the airflow introduced into the auxiliary combustion chamber through the injection hole to form a swirl flow in the auxiliary combustion chamber. The swirl flow formed in the auxiliary combustion chamber can then extend the discharge formed in the discharge gap. As a result, ignition performance can be improved.

In addition, at least a portion of the protruding end is positioned closer to the protruding side nozzle hole than to the plug center axis. Therefore, the airflow flowing out of the auxiliary combustion chamber through the protruding side nozzle hole is guided to the base end surface of the ground electrode and easily passes through the discharge gap. Therefore, the discharge formed in the discharge gap easily extends toward the protruding side nozzle hole. As a result, ignition performance can be improved.

In the internal combustion engine according to the second aspect, the spark plug has a protruding side nozzle having a larger opening area than the other nozzles. The spark plug is arranged so that the outer opening of at least one protruding side nozzle faces the intake valve side when viewed from the plug axial direction. This allows a large flame to be ejected from the auxiliary combustion chamber to the intake valve side of the main combustion chamber through the protruding side nozzle when viewed from the plug axial direction. This makes it possible to improve the ignition of the mixture on the intake valve side of the main combustion chamber when viewed from the plug axial direction. This makes it possible to burn the mixture in the entire main combustion chamber in a balanced manner. As a result, it is possible to suppress combustion abnormalities that cause knocking, etc.

In the internal combustion engine according to the third aspect, the spark plug is positioned so that the injection flow from the injector is directed toward the outer opening of the protruding side nozzle hole, which has a larger opening area than the other nozzle holes. This makes it easier for a high-fuel-density mixture to be introduced from the protruding side nozzle hole into the auxiliary combustion chamber. As a result, the high-fuel-density mixture can more easily reach the discharge gap, improving ignition performance.

As described above, according to the above aspect, it is possible to provide a spark plug for an internal combustion engine capable of improving ignition performance, and an internal combustion engine including 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.

3 is a cross-sectional view of the spark plug in the axial direction of the plug in the vicinity of the tip portion of the spark plug according to the first embodiment, which is equivalent to a cross-sectional view taken along line II in FIG. 2 . FIG. FIG. 2 is a cross-sectional view taken along line II-II of FIG. FIG. 4 is an explanatory diagram showing the distance from the protruding end to the central axis of the plug and the distance from the protruding end to the protruding-side nozzle hole in the first embodiment. FIG. 4 is an explanatory cross-sectional view taken along the plug axial direction, illustrating the position of a protruding end portion in the first embodiment. FIG. 4 is a cross-sectional view illustrating the positional relationship between an extension region of the projection-side nozzle hole and a base end surface of the ground electrode in the first embodiment. FIG. 4 is a cross-sectional view illustrating a positional relationship between an extension region of the ground electrode and a projection-side nozzle hole in the first embodiment. 1 is a cross-sectional explanatory diagram of an internal combustion engine according to a first embodiment. FIG. 4 is a diagram illustrating the direction of an airflow formed in a main combustion chamber in the first embodiment, as viewed from the front end side of the internal combustion engine. FIG. 2 is a cross-sectional view of a tip portion of the spark plug according to the first embodiment, during a compression stroke and before a discharge extends. 4 is a cross-sectional view of the tip portion of the spark plug according to the first embodiment when the discharge is extended during the compression stroke. FIG. 4 is a cross-sectional view of the vicinity of the tip portion of the spark plug according to the first embodiment during the expansion stroke and before the discharge is extended. 4 is a cross-sectional view of the vicinity of the tip portion of the spark plug according to the first embodiment when the discharge is extended during the expansion stroke. 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. 11 is a cross-sectional view of an internal combustion engine according to a second embodiment. FIG. 11 is a cross-sectional view illustrating the direction of an injection flow relative to a spark plug in a second embodiment. 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. 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 fourth embodiment. 13 is a schematic diagram of airflow in a pocket portion in the fourth embodiment. 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. FIG. 13 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 sixth embodiment. FIG. 13 is a cross-sectional view of a tip portion of a spark plug according to a seventh embodiment, taken perpendicular to the plug axial direction. 22 arrow view of Figure 21 (illustration of the plug cover and housing is omitted). FIG. 13 is a view of the ground electrode according to the seventh embodiment, viewed from the protruding direction of the ground electrode. 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. FIG. 13 is a cross-sectional view of a tip portion of a spark plug according to a ninth embodiment, taken perpendicular to the plug axial direction. FIG. 13 is a cross-sectional view illustrating the positional relationship between the extension region of the ground electrode and the center of the projection-side nozzle hole in the ninth embodiment. 27 is a view taken along the arrow XXVII in FIG. 26 (illustration of the plug cover and housing is omitted). FIG. 13 is a cross-sectional view of the ninth embodiment when the discharge is extended during the expansion stroke. FIG. 13 is a cross-sectional view of the ninth embodiment when the discharge extends to the ejection side nozzle hole during the expansion stroke. FIG. 13 is a cross-sectional view of the ninth embodiment when the discharge extends to the main combustion chamber during the expansion stroke.

(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.
1 and 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 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.

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. The discharge gap G is formed by the tip of the tip protrusion 41 and the base end surface 61 of the ground electrode 6 facing each other.

The plug cover 5 has a plurality of injection holes 51 that communicate the auxiliary combustion chamber 50 with the outside. As shown in FIG. 2, the extension line 51L of the central axis of the injection hole 51 does not pass through the discharge gap G and is inclined with respect to the plug radial direction when viewed from the plug axial direction Z. Some of the injection holes 51 are protruding side injection holes 510 formed on the protruding side of the protruding end 63 of the ground electrode 6. As shown in FIG. 3, at least a part of the protruding end 63 is disposed at a position where the distance D2 to the protruding side injection hole 510 is closer than the distance D1 to the plug central axis C. In this embodiment, the entire protruding end 63 is disposed at a position where the distance D2 to the protruding side injection hole 510 is closer than the distance D1 to the plug central axis C.

The spark plug 1 of this embodiment can be used as an ignition means in an internal combustion engine of an automobile, cogeneration, or the like. As shown in FIG. 7, the mounting screw portion 22 formed on the outer peripheral surface of the housing 2 is screwed into the female screw portion of the plug hole 761 of the cylinder head 76, and the spark plug 1 is attached to the internal combustion engine 10. One end of the axial direction Z of the spark plug 1 is placed 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 called the tip side, and the opposite side is called the base side. The axial direction Z of the spark plug 1 is also referred to as the plug axial direction Z or simply the Z direction as appropriate. The plug central axis C means the central axis C of the spark plug 1. In this embodiment, the plug central axis C is also the central axis of the center electrode 4. The plug radial direction means the radial direction of a circle centered on the central axis C of the spark plug 1 on a plane perpendicular to the central axis C of the spark plug 1.

As shown in FIG. 1, the plug cover 5 is joined to the tip of the housing 2 by welding or the like. When the spark plug 1 is attached to the internal combustion engine, the plug cover 5 separates the auxiliary combustion chamber 50 from the main combustion chamber.

The auxiliary combustion chamber 50 includes a space on the inner periphery of the tip of the housing 2 around the tip protrusion 41 of the center electrode 4. The auxiliary combustion chamber 50 also includes a pocket portion 501, which will be described later.

The insulator 3 has a tapered tip 30 that tapers toward the tip. The insulator 3 is disposed inside the housing 2 and is supported in the Z direction by the housing 2. That is, a latched portion 32 provided on the outer peripheral surface of the insulator 3 is latched from the tip side in the Z direction to a latching portion 23 provided on the inner peripheral surface of the housing 2. The portion of the insulator 3 on the tip side of the latched portion 32 forms the tapered tip 30.

The auxiliary combustion chamber 50 has a pocket portion 501, which is an annular space, between the outer peripheral surface of the insulator 3 and the inner peripheral surface of the housing 2. In other words, the pocket portion 501 is a space formed between the tapered tip portion 30 and the housing 2 in the plug radial direction.

In this embodiment, the plug cover 5 has a peripheral wall portion 53 that covers a part of the outer periphery of the auxiliary combustion chamber 50, a bottom wall portion 54 that covers the tip side of the auxiliary combustion chamber 50, and a corner portion 55 that connects the peripheral wall portion 53 and the bottom wall portion 54. The injection hole 51 is formed in the corner portion 55. In the spark plug 1 installed in an internal combustion engine, the injection hole 51 formed in the plug cover 5 connects the auxiliary combustion chamber 50 and the main combustion chamber.

During the compression stroke of the internal combustion engine, airflow is introduced from the main combustion chamber to the auxiliary combustion chamber 50 through the injection hole 51. The injection hole 51 is formed so that the airflow introduced into the auxiliary combustion chamber 50 through the injection hole 51 generates a swirl flow (see dashed arrows Asd and Asu in Figures 9 and 10) in the auxiliary combustion chamber 50. Specifically, as shown in Figure 2, when viewed from the Z direction, the extension line 51L of the injection hole's central axis is inclined at an acute angle to the imaginary line VL that extends in the plug radial direction passing through the injection hole 51 and the plug central axis C. For the multiple injection holes 51, the inclination direction of the extension line 51L of the injection hole's central axis with respect to the imaginary line VL in each injection hole 51 is on the same side in the plug circumferential direction. The plug circumferential direction is the direction along the circumference centered on the plug central axis C.

By forming the nozzle hole 51 in this manner, as shown in Figures 9 and 10, the airflow introduced into the auxiliary combustion chamber 50 through the nozzle hole 51 creates a swirl flow in the auxiliary combustion chamber 50. In this embodiment, the swirl flow is generated in a counterclockwise spiral shape in Figures 9 and 10 around the plug center axis C.

In addition, during the expansion stroke of the internal combustion engine, gas flows from the auxiliary combustion chamber 50 to the main combustion chamber through each nozzle hole 51, forming a swirl flow in the opposite direction to the swirl flow formed during the compression stroke.

In this embodiment, the injection holes 51 formed in the plug cover 5 have a generally cylindrical shape as shown in Figs. 1 and 2. As shown in Fig. 2, the injection holes 51 are formed at equal intervals in the plug circumferential direction when viewed from the Z direction. Also, as shown in Fig. 1, the injection holes 51 open at an angle to the Z direction so that they move radially outward toward the tip side.

As shown in FIG. 2, in this embodiment, the plug cover 5 has four nozzle holes 51, one of which is the protruding side nozzle hole 510.

As shown in FIG. 2, when viewed from the Z direction, in the protruding direction of the ground electrode 6, at least a portion of the protruding side nozzle hole 510 and the discharge gap G are located on opposite sides of the protruding end portion 63 of the ground electrode 6.

When viewed from the Z direction, in the protruding direction of the ground electrode 6, at least a portion of the protruding side nozzle hole 510 and the fixed end 62 of the ground electrode 6 are located on opposite sides of the protruding end 63.

In addition, the distance from the protruding end 63 to the protruding side nozzle hole 510 is shorter than the distance from the protruding end 63 to the nozzle holes 51 other than the protruding side nozzle hole 510.

In this embodiment, as shown in FIG. 6, when viewed from the Z direction, the extension region 6E, which extends the ground electrode 6 in the protruding direction, and a portion of the protruding side nozzle hole 510 overlap each other. The extension region 6E also passes through at least a portion of the protruding side nozzle hole 510. Note that the protruding side nozzle hole 510 can also be formed so that the extension region 6E and the entire protruding side nozzle hole 510 overlap each other when viewed from the Z direction.

In this embodiment, as shown in FIG. 5, when viewed from the Z direction, the extension region 510E extending the projection side nozzle hole 510 in the opening direction and the base end surface 61 of the ground electrode 6 overlap each other. Also, when viewed from the Z direction, the extension region 510E and the projection end portion 63 overlap each other.

As shown in FIG. 2, when viewed from the plug axial direction Z, the extension line 51L of the central axis of the protruding side nozzle hole 510 and the base end surface 61 of the ground electrode 6 overlap each other. When viewed from the Z direction, the extension line 51L of the central axis of the protruding side nozzle hole 510 and the protruding end portion 63 of the ground electrode 6 overlap each other.

In addition, in this embodiment, the projection side nozzle hole 510 has a larger opening area than the other nozzle holes 51, as shown in Figures 1 to 6.

The inner diameter of the protruding side nozzle hole 510 can be, for example, 1.2 to 1.4 times the inner diameter of the nozzle holes 51 other than the protruding side nozzle hole 510. Also, the opening area of the protruding side nozzle hole 510 can be, for example, 1.4 to 2.0 times the opening area of the nozzle holes 51 other than the protruding side nozzle hole 510.

As shown in FIG. 4, the straight line connecting the base end of the outer opening 511 of the projection side nozzle hole 510 and the tip end of the tip projection portion 41 at the shortest distance is defined as line L1. In a cross section including line L1 and taken along the plug axial direction Z, the projection end portion 63 is positioned on the tip side of line L1.

The straight line connecting the center of the outer opening 511 of the projection side nozzle hole 510 and the tip of the tip projection 41 at the shortest distance is defined as line L2. As shown in FIG. 4, in a cross section that includes line L2 and is taken along the plug axial direction Z, the projection end 63 is positioned on the tip side of line L2.

The straight line connecting the tip of the inner opening 512 of the projection side nozzle hole 510 and the tip of the tip projection portion 41 at the shortest distance is defined as line L3. As shown in FIG. 4, in a cross section including line L3 and taken along the plug axial direction Z, the projection end portion 63 is positioned on the tip side of line L3.

In addition, in this embodiment, the base end surface 61 of the ground electrode 6 has a ground inclined surface 611 in the longitudinal direction of the ground electrode 6, at least from the portion that forms the discharge gap G to the protruding end 63, as shown in FIG. 1. The ground inclined surface 611 is inclined with respect to the plug axial direction Z so as to move 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 ground inclined surface 611.

In this embodiment, the ground electrode 6 has a cross section (not shown) perpendicular to the longitudinal direction of the ground electrode 6 that is a flattened rectangle. In addition, the thickness of the ground electrode 6 in the direction perpendicular to the longitudinal direction of the ground electrode 6 from the portion that forms the discharge gap G in the longitudinal direction of the ground electrode 6 to the protruding end 63 decreases as the thickness approaches the protruding end 63. The ground inclined surface 611 of the tapered portion of the ground electrode 6 has a larger inclination angle with respect to the plane perpendicular to the Z direction than the ground inclined surface 611 of the other portion of the ground electrode 6.

In addition, in this embodiment, the fixed end 62 of the ground electrode 6 is fixed to 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.

In this embodiment, the discharge gap G is formed by the tip protrusion 41 and the ground electrode 6 facing each other in the plug axial direction Z.

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, forming a discharge gap G. It is also possible to join tips to 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, a discharge gap G can 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.

Next, an internal combustion engine 10 equipped with the above-mentioned spark plug 1 is shown in FIGS.
The internal combustion engine 10 has a main combustion chamber 11, an intake valve 72 and an exhaust valve 73 provided in the main combustion chamber 11, and a spark plug 1. The spark plug 1 is arranged so that the outer surface 52 of the plug cover 5 faces the main combustion chamber 11. As shown in Figure 8, the spark plug 1 is arranged so that an outer opening 511 of at least one projection-side injection hole 510 faces the intake valve 72 side when viewed from the plug axial direction Z.

As shown in FIG. 7, the internal combustion engine 10 of this embodiment includes a cylinder head 76, a cylinder block 75, and a piston 74 that reciprocates within the cylinder 70. The main combustion chamber 11 is formed by the cylinder head 76, the cylinder block 75, and the piston 74. The cylinder head 76 is formed with an intake port 721 and an exhaust port 731, each of which is provided with an intake valve 72 or an exhaust valve 73. A 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. 8.

As shown in FIG. 7, the intake port 721 and the exhaust port 731 are inclined with respect to the direction of movement of the piston 74 so that their opening direction faces the central axis of the main combustion chamber 11. In addition, the base end surface of the main combustion chamber 11 is inclined so that it faces the tip side as it moves away from the spark plug 1.

In the internal combustion engine 10, the intake stroke, compression stroke, expansion stroke, and exhaust stroke are repeated in sequence with the reciprocating motion of the piston 74. During the intake stroke of the internal combustion engine 10, gas is introduced into the main combustion chamber 11 from the two intake ports 721, and during the exhaust stroke, gas in the main combustion chamber 11 is exhausted from the two exhaust ports 731. Due to the way the airflow is introduced during the intake stroke, a certain airflow is formed in the main combustion chamber 11, and this airflow remains even during the compression stroke.

In the main combustion chamber 11, a tumble flow is formed, which is an airflow around an axis perpendicular to the sliding direction of the piston 74, as shown by the arrow A1 in FIG. 7. This airflow A1 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 11, as shown in FIG. 7 and FIG. 8. More specifically, as shown in FIG. 8, when viewed from the plug axial direction Z, the airflow A1 along the direction from the midpoint between the two intake ports 721 to the midpoint between the two exhaust ports 731 is the main airflow near the tip of the spark plug 1.

The airflow in the main combustion chamber 11 is not always constant, but may vary between cycles or between different times during 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 A1 refers to the main airflow at the ignition timing.

Next, the effects of this embodiment will be described.
In the above spark plug 1 for an internal combustion engine, an extension line 51L of the central axis of the injection hole does not pass through the discharge gap G and 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. The swirl flow formed in the auxiliary combustion chamber 50 can then extend the discharge formed in the discharge gap G. As a result, ignition performance can be improved.

In addition, at least a portion of the protruding end 63 is positioned at a distance D2 to the protruding side nozzle hole 510 that is closer than the distance D1 to the plug center axis C. Therefore, the airflow flowing out of the auxiliary combustion chamber 50 through the protruding side nozzle hole 510 is guided by the base end surface 61 of the ground electrode 6 and easily passes through the discharge gap G. Therefore, as shown in Figures 11 and 12, the discharge formed in the discharge gap G easily extends toward the protruding side nozzle hole 510. As a result, ignition performance can be improved.

That is, in the compression stroke, as shown in FIG. 9 and FIG. 10, an ascending swirl flow Asu and a descending swirl flow Asd are formed. The ascending swirl flow Asu rotates mainly near the inner peripheral wall of the auxiliary combustion chamber 50 toward the base end while rotating in the plug circumferential direction. The descending swirl flow Asd mainly rotates in the plug circumferential direction toward the tip end at a position close to the plug central axis C. The descending swirl flow Asd is also formed on the outer periphery side of the discharge gap G. As a result, the gas in the discharge gap G and its periphery is easily drawn into the descending swirl flow Asd. Therefore, as shown in FIG. 9 and FIG. 10, an air flow A21 toward the descending swirl flow Asd is easily formed in the discharge gap G and its periphery. Therefore, as shown in FIG. 9, the discharge S formed in the discharge gap G is easily extended by the air flow A21 as shown in FIG. 10. As a result, the ignition performance can be improved.

Furthermore, the ignited initial flame is carried to the base end side of the auxiliary combustion chamber 50 by the ascending swirl flow Asu. This allows the flame to spread from a position sufficiently far away 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. 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, improving fuel efficiency and reducing emissions.

In addition, during the expansion stroke, the piston moves toward the tip side, causing the main combustion chamber to have a 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 Figures 11 and 12, the airflow A22 formed in the auxiliary combustion chamber 50 as the gas is discharged through the protruding side nozzle hole 510 is guided by the base end surface 61 of the ground electrode 6, passes through the discharge gap G, and heads toward the protruding side nozzle hole 510. Therefore, as shown in Figure 11, the discharge S generated in the discharge gap G during the expansion stroke is easily extended toward the protruding side nozzle hole 510 by the airflow A22, as shown in Figure 12, and the ignition ability in the auxiliary combustion chamber 50 can be improved. In addition, since the ignition position is easily brought close to the protruding side nozzle hole 510, for example, under operating conditions in which the temperature of the auxiliary combustion chamber 50 is low, the cold loss is also suppressed, and the flame jet to the main combustion chamber can be strengthened. Furthermore, the discharge S or discharge plasma, or initial flame generated in the discharge gap G, is easily ejected from the ejection side nozzle hole 510, improving ignition performance in the main combustion chamber.

Also, as shown in FIG. 11, during the expansion stroke, the starting point SP of the discharge S generated in the discharge gap G on the ground electrode 6 side is likely to move toward the protruding side nozzle hole 510 due to the airflow A22 as shown in FIG. 12. Therefore, the discharge S is likely to extend toward the protruding 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 protruding end portion 63 of the ground electrode 6 to the inner surface of the protruding side nozzle hole 510. This will further extend the discharge S, and it is expected that part of the discharge S will fly out from the protruding side nozzle hole 510 toward the main combustion chamber. This will further improve the ignition performance of the internal combustion engine.

The base end surface 61 of the ground electrode 6 has a ground inclined surface 611 in the longitudinal direction of the ground electrode 6, at least from the portion that forms the discharge gap G to the protruding end 63. Therefore, during the expansion stroke, the airflow discharged from the auxiliary combustion chamber 50 through the protruding side nozzle 510 is more easily guided by the base end surface 61 having the ground inclined surface 611. Therefore, the discharge formed in the discharge gap G is more easily extended toward the protruding side nozzle 510. As a result, ignition performance can be further improved.

In a cross section that includes the straight line L1 (see FIG. 4) and is along the plug axial direction Z, the protruding end 63 is located further forward than the straight line L1. Therefore, during the expansion stroke, the discharge generated in the discharge gap G is not short-circuited by the protruding end 63, and is likely to reliably extend toward the protruding side nozzle hole 510 and the main combustion chamber. As a result, ignition performance can be reliably improved.

In other words, let us assume that the protruding end 63 is located closer to the base end than the straight line L1. In this case, the discharge extending toward the protruding side nozzle hole 510 is likely to be short-circuited by the protruding end 63 when it tries to extend further toward the protruding side nozzle hole 510 than the protruding end 63. On the other hand, in this embodiment, the protruding end 63 is disposed in the above-mentioned position. 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 protruding end 63 even if it extends further toward the protruding side nozzle hole 510 than the protruding end 63, as shown in FIG. 12 and FIG. 13. As a result, ignition performance can be improved.

In addition, because the protruding end 63 is positioned as described above, the starting point SP of the discharge S on the ground electrode 6 side is likely to move to the inner surface of the protruding 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 protruding side nozzle hole 510. This makes it easier to extend the discharge S toward the main combustion chamber. As a result, the ignition ability of the main combustion chamber can be further improved.

In addition, in a cross section that includes the straight line L2 (see FIG. 4) and is along the plug axial direction Z, the protruding end 63 is disposed on the tip side of the straight line L2. Therefore, the discharge generated in the discharge gap G is not short-circuited by the protruding end 63, and is more likely to extend toward the protruding side nozzle hole 510 and the main combustion chamber.

In addition, in a cross section that includes the straight line L3 (see FIG. 4) and is along the plug axial direction Z, the protruding end 63 is disposed on the tip side of the straight line L3. Therefore, the discharge generated in the discharge gap G is not short-circuited by the protruding end 63, and is more likely to extend toward the protruding side nozzle hole 510 and the main combustion chamber.

When viewed from the plug axial direction Z, the extension line 51L of the central axis of the protruding side nozzle hole 510 and the base end surface 61 of the ground electrode 6 overlap each other. Therefore, the airflow discharged from the auxiliary combustion chamber 50 via the protruding side nozzle hole 510 is easily and reliably guided by the base end surface 61 of the ground electrode 6. Therefore, the discharge formed in the discharge gap G is easily and reliably extended toward the protruding side nozzle hole 510.

The protruding side nozzle hole 510 has a larger opening area than the other nozzle holes 51. Therefore, during the expansion stroke, the airflow guided from the auxiliary combustion chamber 50 through the protruding side nozzle hole 510 tends to be stronger. Therefore, the airflow guided by the base end surface 61 of the ground electrode 6 tends to be stronger. Therefore, the discharge generated in the discharge gap G tends to extend further toward the protruding side nozzle hole 510. As a result, ignition performance can be further improved.

In addition, the extension line 51L of the central axis of the nozzle hole 51 does not pass through the discharge gap G. Therefore, the airflow introduced into the auxiliary combustion chamber 50 through the nozzle hole 51 is unlikely to flow directly into the discharge gap G. As a result, it is possible to suppress the discharge from being blown out and short-circuited by the airflow.

In the internal combustion engine 10, the spark plug 1 has a protruding side nozzle 510 with a larger opening area than the other nozzle holes 51. The spark plug 1 is arranged so that the outer opening 511 of at least one protruding side nozzle 510 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 11 through the protruding side nozzle 510 when viewed from the plug axial direction Z. Therefore, the ignition ability of the mixture on the intake valve 72 side in the main combustion chamber 11 when viewed from the plug axial direction Z can be improved. Therefore, the mixture in the entire main combustion chamber 11 can be burned in a balanced manner. As a result, it is possible to suppress combustion abnormalities that cause knocking, etc.

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 11, tends 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 in the main combustion chamber 11. Therefore, when viewed from the Z direction, the combustion of the mixture on the intake valve 72 side in the main combustion chamber 11 is delayed compared to the mixture on the exhaust valve 73 side, which may cause the balance of the combustion of the mixture in the main combustion chamber 11 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 11. Therefore, the mixture in the entire main combustion chamber 11 can be burned in a balanced manner, and the local residue of unburned fuel can be suppressed. As a result, it is possible to suppress combustion abnormalities that cause knocking, etc.

As described above, this embodiment provides a spark plug 1 for an internal combustion engine that can improve ignition performance, and an internal combustion engine 10 equipped with the same.

(Embodiment 2)
In this embodiment, as shown in FIGS. 14 and 15 , the spark plug 1 is disposed in the internal combustion engine 10 so that the injection flow F injected from the injector 71 is directed toward the outer opening 511 of the projection side nozzle hole 510.

The internal combustion engine 10 of this embodiment has an injector 71 that injects fuel directly into the main combustion chamber 11, as shown in FIG. 14. 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 is directed toward the outer opening 511 of the ejection side nozzle hole 510. Note that the arrow F shown in FIG. 14 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 11 during the compression stroke or expansion stroke. In addition, the state in which the injection flow F is directed toward the outer opening 511 of the ejection side nozzle hole 510 is a state in which the outer opening 511 of the ejection side nozzle hole 510 is visible from the direction of the injection flow F near the plug cover 5 shown in FIG. 15.

In this embodiment, the spark plug 1 is positioned so that the outer opening 511 of the protruding side nozzle hole 510 faces the exhaust valve 73 when viewed from the Z direction (not shown).

As shown in FIG. 14, an injector 71 is provided 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 11.

During the compression stroke, the atmosphere in the main combustion chamber 11 is compressed, and air flows into the auxiliary combustion chamber 50 through the nozzle hole 51. This creates a swirl flow in the auxiliary combustion chamber 50, and the pressure in the auxiliary combustion chamber 50 also rises. Then, for example, during the compression stroke, the injector 71 injects fuel directly into the main combustion chamber 11.

The fuel injected into the main combustion chamber 11 forms an injection flow F together with the air in the main combustion chamber 11, as shown in FIG. 14, 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 heads 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 protruding side nozzle hole 510 in the spark plug 1, as shown in FIG. 15.

The injected flow F is a mixture with a relatively high fuel ratio. Therefore, the vicinity of the outer opening 511 of the ejection side nozzle 510 where the injected flow F reaches becomes a mixture containing a large amount of fuel. This mixture is then drawn into the auxiliary combustion chamber 50, where a swirl flow is formed, via the ejection side nozzle 510. The mixture with high fuel density drawn in from the ejection side nozzle 510 is directed toward the discharge gap G.

Then, near the top dead center of the compression stroke, a discharge is generated in the discharge gap G 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 embodiment 1. Note that, among the reference symbols used in embodiment 2 and onwards, the reference symbols that are the same as those used in the above-mentioned embodiments represent the same components, etc. as those in the above-mentioned embodiments, unless otherwise specified.

In the internal combustion engine 10, the spark plug 1 is positioned so that the injection flow F injected from the injector 71 is directed toward the outer opening 511 of the protruding side injection hole 510, which has a larger opening area than the other injection holes 51. This makes it easier for a high-fuel-density mixture to be introduced from the protruding side injection hole 510 into the auxiliary combustion chamber 50. As a result, the high-fuel-density mixture can more easily reach the discharge gap G, improving ignition performance.

For example, when an internal combustion engine is operating at high load, 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 later timing than normal fuel injection and ignition. In other words, the fuel injection timing from the injector 71 is set to, for example, the timing just before the piston 74 reaches top dead center during the compression stroke. Specifically, fuel is injected at, for example, 30° BTDC. BTDC stands for Before Top Dead Center, and indicates how many crank angles before the compression top dead center the timing is. The ignition of the spark plug 1 is set to be substantially at the compression top dead center.

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 11, a certain amount of air has already filled the auxiliary combustion chamber 50, and the airflow within the main combustion chamber 11 is also weakened. This results in a situation in which the amount of fuel introduced into the auxiliary combustion chamber 50 from the injection hole 51 formed in the plug cover 5 is relatively small.

However, the spark plug 1 of this embodiment is disposed so that the injection flow injected from the injector 71 is directed toward the outer opening 511 of the protruding side injection hole 510, which has a larger opening area than the other injection holes 51. Therefore, a mixture with a high fuel density is easily introduced from the protruding side injection hole 510 into the auxiliary combustion chamber 50. As a result, the ignition ability in the auxiliary combustion chamber 50 is improved, and the ignition ability in the main combustion chamber 11 is also improved.
In addition, the second embodiment has the same effects as the first embodiment.

In the above internal combustion engine 10, the spark plug 1 is arranged so that the outer opening 511 of the protruding side nozzle 510 faces the exhaust valve 73 when viewed from the Z direction. However, as in the first embodiment, the spark plug can also be arranged so that the outer opening of at least one protruding side nozzle faces the intake valve when viewed from the Z direction. In this case, too, the spark plug and the injector are arranged so that the injection flow containing fuel injected from the injector during the compression stroke is directed toward the outer opening of the protruding side nozzle. This allows a large flame to be ejected from the auxiliary combustion chamber to the intake valve side of the main combustion chamber through the protruding side nozzle when viewed from the Z direction.

(Embodiment 3)
As shown in FIG. 16, this embodiment is an embodiment in which the position of the discharge gap is changed from that of the first embodiment.

In this embodiment, the discharge gap G is formed on the tip side of the tip of the housing 2. In other words, the tip protrusion 41 of the center electrode 4 protrudes on the tip side of the tip of the housing 2.

16 , the thickness of the ground electrode 6 in a direction perpendicular to the longitudinal direction of the ground electrode 6 at a portion 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 54 of the plug cover 5.
The rest is the same as in the first embodiment.

The discharge gap G is formed further toward the tip side than 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.
In addition, the second embodiment has the same effects as the first embodiment.

(Embodiment 4)
As shown in Figs. 17 and 18, this embodiment is an embodiment in which the shape of a pocket portion 501 is changed from that of the first embodiment.

In this embodiment, as shown in Figures 17 and 18, the outer peripheral surface of the insulator 3 has an insulator inclined surface 31 that tapers toward the tip side at the portion facing the pocket portion 501. The inner peripheral surface of the housing 2 has a housing inclined surface 21 that tapers toward the base end at the portion facing the pocket portion 501.

In this embodiment, the insulator 3 has an insulator inclined surface 31 provided on almost the entire portion of the outer circumferential surface thereof facing the pocket portion 501. Also, in this embodiment, the housing 2 has an inclined surface 21 provided on almost the entire portion of the inner circumferential surface thereof facing the pocket portion 501.
The rest is the same as in the first embodiment.

The spark plug 1 of this embodiment has an insulator inclined surface 31 and a housing inclined surface 21 at the portion facing the pocket portion 501. This makes it easier for the swirl flow formed in the auxiliary combustion chamber 50 to be formed as an air flow of sufficient strength on the outer periphery side of the discharge gap G.

That is, the airflow introduced into the auxiliary combustion chamber 50 from the nozzle hole 51 moves toward the base end while forming an ascending swirl flow along the inner wall of the auxiliary combustion chamber 50. The ascending swirl flow then rotates while moving toward the base end along the inner surface of the housing 2 in the pocket portion 501. Here, as shown in FIG. 18, since the inner surface of the housing 2 has the housing inclined surface 21, the ascending swirl flow Asu moving toward the base end gradually approaches the plug central axis C as it moves toward the base end of the pocket portion 501. The symbol Asu in FIG. 18 shows an image of the main flow of the ascending swirl flow toward the base end in the pocket portion 501.

Then, the swirl flow that bounces off the base end of the pocket 501 rotates toward the tip. At this time, the downward swirl flow Asd still has a vector component that moves toward the plug central axis C. Therefore, it rotates toward the tip along the outer circumferential surface of the insulator 3. The symbol Asd in Figure 18 shows an image of the main flow of the downward swirl flow in the pocket 501, moving toward the tip.

Since the outer peripheral surface of the insulator 3 has an insulator slope 31, the downward swirl flow Asd moving toward the tip side gradually approaches the plug central axis C. That is, the swirl flow gradually approaches the plug central axis C both when moving toward the base end side and when moving thereafter toward the tip side. This ensures that an airflow of sufficient strength is formed on the outer peripheral side of the central electrode 4 and the discharge gap G. As a result, the discharge formed in the discharge gap G can be easily and reliably extended, improving the ignition performance in the auxiliary combustion chamber 50.
In addition, the second embodiment has the same effects as the first embodiment.

(Embodiment 5)
As shown in FIG. 19, this embodiment is an embodiment in which the shape of the tip portion of the center electrode 4 is modified from that of the first embodiment.
That is, the tip surface 411 of the center electrode 4 is inclined along the ground inclined surface 611 of the ground electrode 6 .

In this embodiment, the tip surface 411 of the center electrode 4 and the ground inclined surface 611 of the ground electrode 6 are each flat. As shown in Fig. 19, 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 first embodiment.

The tip end surface 411 of the center electrode 4 is inclined along the ground inclined surface 611 of the ground electrode 6. Therefore, the tip end surface 411 of the center electrode 4 and the ground 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 second embodiment has the same effects as the first embodiment.

(Embodiment 6)
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.

In this embodiment, the tip of the center electrode 4 has a tapered shape with a diameter that decreases toward the tip side, as shown in FIG. 20. The tip of the center electrode 4 having a tapered shape has a substantially truncated cone shape. The tip of the center electrode 4 can be substantially conical, substantially square pyramidal, substantially square pyramidal, etc.

The tapered surface 412 at the tapered tip of the center electrode 4 is formed in an annular shape. A part of the tapered surface 412 is inclined along the ground inclined surface 611 of the ground electrode 6. A discharge gap G is formed between the tapered surface 412 and the ground inclined surface 611 of the ground electrode 6.
The rest is the same as in the fifth embodiment.

In this embodiment, a discharge gap G is formed between the tapered surface 412 and the ground 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 second embodiment has the same effects as the fifth embodiment.

(Embodiment 7)
As shown in Figs. 21 to 23, this embodiment is an embodiment in which the shape of the ground electrode 6 is modified from that of the first embodiment.

In this embodiment, as shown in Figures 21 to 23, the base end surface 61 of the ground electrode 6 has a protruding side inclined surface 612 at least on the protruding end 63 side of the portion facing the tip surface 411 of the center electrode 4 in the Z direction in the longitudinal direction of the ground electrode 6. As shown in Figure 23, when viewed from the protruding direction of the ground electrode 6, the protruding side inclined surface 612 is inclined in the Z direction so as to move toward the tip side as it approaches the protruding side nozzle hole.

In other words, as shown in Figures 21 to 23, the protruding side inclined surface 612 gradually moves toward the tip side in the width direction of the ground electrode 6, which is a direction perpendicular to the longitudinal direction of the ground electrode 6, as it approaches the protruding side nozzle hole 510.

As shown in FIG. 21, when viewed from the Z direction, the extension line 51L of the central axis of the projection-side nozzle hole 510 and the projection-side inclined surface 612 overlap each other.
The rest is the same as in the first embodiment.

The ground electrode 6 in this embodiment has a protruding side inclined surface 612. Therefore, the airflow discharged from the auxiliary combustion chamber 50 through the protruding side nozzle hole 510 is more easily guided by the base end surface 61 having the protruding side inclined surface 612. Therefore, the discharge formed in the discharge gap G is more easily extended toward the protruding side nozzle hole 510. As a result, the ignition performance can be further improved.

In addition, the starting point of the discharge generated in the discharge gap G on the ground electrode 6 side is more likely to move toward the projection side nozzle hole 510 due to the airflow discharged from the auxiliary combustion chamber 50 through the projection side nozzle hole 510. Therefore, the discharge is more likely to extend toward the projection side nozzle hole 510.
In addition, the second embodiment has the same effects as the first embodiment.

(Embodiment 8)
As shown in FIG. 24, this embodiment is an embodiment in which the shape of the ground electrode 6 is modified from that of the first embodiment.
That is, 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 having a ground 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.

In this embodiment, the fixed end 62 of the ground electrode 6 is joined to the front end surface 24 of the housing 2 as shown in Fig. 24. The ground electrode 6 can also be joined to the inner circumferential surface of the front end of the housing 2.
The rest is the same as in the first embodiment.

In this embodiment, the ground electrode 6 has the fixed side portion 64 and the inclined portion 65. Therefore, the ground electrode 6 can be easily stably fixed to the tip portion of the housing 2 while arranging the protruding end portion 63 near the protruding side injection hole 510. As a result, the productivity of the spark plug 1 can be easily improved.
In addition, the second embodiment has the same effects as the first embodiment.

(Embodiment 9)
As shown in Figs. 25 to 30, this embodiment is an embodiment in which the fixing position of the ground electrode 6 is changed from that of the first embodiment.

In this embodiment, the projection side nozzle hole 510 has a larger opening area than the other nozzle holes 51, as shown in Figures 25, 26, and 28 to 30. As shown in Figure 25, when viewed from the plug axial direction Z, the extension line 51L of the central axis of the projection side nozzle hole 510 is aligned along the projection direction of the ground electrode 6 so as not to overlap with the ground electrode 6. Also, as shown in Figure 26, when viewed from the plug axial direction Z, the center 510C of the projection side nozzle hole 510 is located outside the extension region 6E that extends the ground electrode 6 in the projection direction.

The ground electrode 6 is fixed to the housing 2 so as to be aligned along the plug radial direction when viewed from the Z direction. The ground electrode 6 also has two circumferential side surfaces 66 that face in the plug circumferential direction, as shown in Figures 25 to 30.

As shown in Figures 25, 26, 28, and 29, the spark plug 1 of this embodiment has an adjacent injection hole 513 as an injection hole 51 other than the protruding side injection hole 510. As shown in Figure 26, the adjacent injection hole 513 is an injection hole adjacent to the protruding side injection hole 510 in the plug circumferential direction, with the extension region 6E of the ground electrode 6 sandwiched between them, as viewed from the Z direction.

The protruding side nozzle hole 510 and the adjacent nozzle hole 513 are formed at positions offset from each other by 90° in the plug circumferential direction. When viewed from the Z direction, the ground electrode 6 protrudes toward the gap between the protruding side nozzle hole 510 and the adjacent nozzle hole 513 in the plug circumferential direction.

When viewed from the Z direction, the distance between the protruding end 63 of the ground electrode 6 and the protruding side nozzle hole 510 is shorter than the distance between the protruding end 63 and the adjacent nozzle hole 513. In other words, of the multiple nozzle holes 51 formed in the plug cover 5, the protruding end 63 is closest to the protruding side nozzle hole 510.

The inner diameter of the protrusion side nozzle hole 510 can be, for example, 1.2 to 1.4 times the inner diameter of the other nozzle holes 51. By setting the inner diameter of the protrusion side nozzle hole 510 within this range, it becomes easier to make the airflow flowing out from the protrusion side nozzle hole 510 sufficiently strong. In this embodiment, all the nozzle holes 51 other than the protrusion side nozzle hole 510, including the adjacent nozzle hole 513, have the same inner diameter.
The rest is the same as in the first embodiment.

In this embodiment, the projection side nozzle hole 510 has a larger inner diameter than the other nozzle holes 51. Therefore, especially during the expansion stroke, a large amount of gas is discharged from the auxiliary combustion chamber 50 to the main combustion chamber through the projection side nozzle hole 510, and as shown in Figures 28 to 30, an airflow A22 is formed in the auxiliary combustion chamber 50 toward the projection side nozzle hole 510. The airflow A22 is also formed so as to flow from the discharge gap G toward the projection side nozzle hole 510. Therefore, the discharge S generated by the expansion stroke ignition is stretched toward the projection side nozzle hole 510 by the airflow A22.

In addition, in this embodiment, the extension line 51L of the central axis of the protruding side nozzle 510 is aligned along the protruding direction of the ground electrode 6 so as not to overlap with the ground electrode 6 when viewed from the Z direction. Also, when viewed from the Z direction, the center 510C of the protruding side nozzle 510 is located outside the extension region 6E (see FIG. 26). Therefore, in the expansion stroke, the airflow A22 along the circumferential side surface 66 of the ground electrode 6 on the protruding side nozzle 510 side is also easily formed effectively. Therefore, the starting point SP of the discharge S on the ground electrode 6 side is easily moved toward the protruding end 63 along the circumferential side surface 66 on the protruding side nozzle 510 side, as shown in FIG. 28. Therefore, the discharge S is more easily extended, and the ignition ability in the expansion stroke can be further improved.

In addition, because the projection side nozzle hole 510 and the ground electrode 6 are positioned as described above, the starting point SP of the discharge S is easily moved by the airflow A22 to the inner surface of the projection side nozzle hole 510, as shown in FIG. 29. Therefore, as shown in FIG. 30, a part of the discharge S is easily ejected from the projection side nozzle hole 510 toward the main combustion chamber. As a result, the ignition performance in the main combustion chamber can be improved.

In addition, when starting the engine, ignition may be performed early in the expansion stroke immediately after the piston passes top dead center in order to raise the catalyst temperature in the exhaust gas purification filter installed in the exhaust system. Therefore, by improving ignition performance during the expansion stroke as described above, the catalyst temperature of the exhaust gas purification filter can be raised in a short period of time when starting the engine, etc. This can be expected to improve fuel efficiency and reduce emissions.

In addition, when viewed from the Z direction, the distance between the protruding end 63 and the protruding side injection hole 510 is shorter than the distance between the protruding end 63 and the adjacent injection hole 513. Therefore, during the expansion stroke, the discharge formed in the discharge gap G is more likely to extend toward the protruding side injection hole 510. As a result, it is possible to further improve the ignition performance during the expansion stroke.
In addition, the second embodiment has the same effects as the first embodiment.

The present invention is not limited to the above-described embodiments, and can be applied to various embodiments without departing from the spirit of the present invention.

1...spark plug, 2...housing, 3...insulator, 4...center electrode, 41...tip protrusion, 5...plug cover, 50...auxiliary combustion chamber, 51...nozzle hole, 510...protruding side nozzle hole, 6...ground electrode, 61...base end face, 62...fixed end, 63...protruding end, 51L...extension of the central axis of the nozzle hole, C...plug central axis, G...discharge gap, Z...plug axial direction, D1...distance from the protruding end to the plug central axis, D2...distance from the protruding end to the protruding side nozzle hole

Claims (11)

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 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 and is inclined with respect to the plug radial direction when viewed from the plug axial direction (Z),
Some of the plurality of nozzle holes are protruding side nozzle holes (510) formed on the protruding side of the protruding end portion (63) of the ground electrode,
At least a part of the protruding end portion is disposed at a position where a distance (D2) to the protruding side nozzle hole is closer than a distance (D1) to a plug center axis (C). The spark plug for an internal combustion engine according to claim 1, wherein the base end surface of the ground electrode has a ground inclined surface (611) that is inclined with respect to the plug axial direction from at least the portion that forms the discharge gap to the protruding end in the longitudinal direction of the ground electrode toward the tip side as it approaches the protruding end. A spark plug for an internal combustion engine according to claim 1 or 2, in which the protruding end is located on the tip side of the straight line (L1) in a cross section along the plug axial direction, the straight line (L1) connecting the base end of the outer opening (511) of the protruding side nozzle hole and the tip end of the tip protruding portion by the shortest distance. A spark plug for an internal combustion engine according to any one of claims 1 to 3, wherein the discharge gap is formed on the tip side of the housing. The auxiliary combustion chamber has a pocket portion (501) that is an annular space between the outer peripheral surface of the insulator and the inner peripheral surface of the housing, the outer peripheral surface of the insulator has an insulator inclined surface (31) that narrows toward the tip side at a portion facing the pocket portion, and the inner peripheral surface of the housing has a housing inclined surface (21) that narrows toward the base end at a portion facing the pocket portion. A spark plug for an internal combustion engine according to any one of claims 1 to 4. A spark plug for an internal combustion engine according to any one of claims 1 to 5, wherein an extension of the central axis of the projection side nozzle hole and the base end surface of the ground electrode overlap each other when viewed in the plug axial direction. 7. The spark plug for an internal combustion engine according to claim 1, wherein the projection side nozzle hole has an opening area larger than those of the other nozzle holes.
The projection side nozzle has a larger opening area than the other nozzles,
6. A spark plug for an internal combustion engine according to claim 1, wherein, when viewed in a plug axial direction, an extension line of a central axis of the projection-side injection hole is along the projection direction of the ground electrode so as not to overlap with the ground electrode, and a center (510C) of the projection-side injection hole is located outside an extension region (6E) formed by extending the ground electrode in the projection direction. An internal combustion engine (10) comprising a spark plug for an internal combustion engine according to claim 7 or 8,
A main combustion chamber (11);
an intake valve (72) and an exhaust valve (73) provided in the main combustion chamber;
The spark plug is disposed so that an outer surface (52) of the plug cover faces the main combustion chamber,
The spark plug is arranged such that an outer opening (511) of at least one of the projection-side nozzle holes faces the intake valve side when viewed from the plug axial direction. An internal combustion engine (10) comprising a spark plug for an internal combustion engine according to claim 7 or 8,
A main combustion chamber (11);
The spark plug is disposed so that an outer surface (52) of the plug cover faces the main combustion chamber;
an injector (71) for injecting fuel directly into the main combustion chamber;
The spark plug is arranged so that an injection flow (F) containing the fuel injected from the injector during a compression stroke of the internal combustion engine is directed toward an outer opening (511) of the projection side nozzle hole. The main combustion chamber has an intake valve (72) and an exhaust valve (73),
11. The internal combustion engine according to claim 10, wherein the spark plug is disposed such that, when viewed in a plug axial direction, the outer opening of at least one of the projection side nozzle holes faces the intake valve side.

Images