JP7655209B2 - Spark plug for internal combustion engine and internal combustion engine - Google Patents

Description

The present invention relates to a spark plug for an internal combustion engine and an internal combustion engine.

A spark plug equipped with a secondary combustion chamber is disclosed, for example, in Patent Document 1. In the spark plug disclosed in Patent Document 1, the direction of the nozzle hole formed in the plug cover is specified taking into account the direction of the flame jet.

JP 2020-9747 A

However, the spark plug described in Patent Document 1 does not take any measures to consider the combustibility in both the low-load and high-load operating ranges of the internal combustion engine.

The present invention was made in consideration of these problems, and aims to provide a spark plug for an internal combustion engine and an internal combustion engine that can obtain stable combustion characteristics in the operating range of the internal combustion engine, from low load to high load.

One aspect of the present invention is a cylindrical insulator (3),
a center electrode (4) held on the inner circumferential side of the insulator and protruding from the insulator toward the tip side;
a cylindrical housing (2) that holds the insulator on its inner periphery;
a ground electrode (6) forming a discharge gap (G) between itself and the center electrode;
a plug cover (5) provided at a tip end of the housing so as to cover a sub-combustion chamber (50) in which the discharge gap is disposed,
The ground electrode protrudes into the auxiliary combustion chamber from a fixed end portion (61) fixed to the housing or the plug cover on the outer circumferential side of the auxiliary combustion chamber,
The plug cover is formed with three or more nozzle holes (51) that communicate the auxiliary combustion chamber with the outside,
The nozzle hole axes (511L, 512L) of the nozzle holes are inclined with respect to the plug axial direction (Z) so as to be outward in the plug radial direction toward the tip side,
When the spark plug is divided into two parts, a first plug portion (11) and a second plug portion (12), by a virtual plane (P) which includes the plug center axis (C) and is perpendicular to the extending direction of the ground electrode as viewed in the plug axial direction, the side on which the fixed end is arranged is defined as the first plug portion, the injection hole formed in the first plug portion is defined as a first injection hole (511), and the injection hole formed in the second plug portion is defined as a second injection hole (512),
the number of the first nozzle holes is greater than the number of the second nozzle holes,
an inner diameter of the first nozzle hole is smaller than an inner diameter of the second nozzle hole,
at least one of the second nozzle holes is a protruding-side nozzle hole (52) through which a central axis (C6) of the ground electrode passes when viewed from the plug axial direction, a protruding end portion (63) of the ground electrode is disposed between the central electrode and the protruding-side nozzle hole when viewed from the plug axial direction, the protruding end portion is disposed at a position closer to the protruding-side nozzle hole than to the central electrode when viewed from the plug axial direction, and the protruding end portion is disposed on the tip side of a straight line (L1) connecting, at the shortest distance, a base end of an outer opening portion (522) of the protruding-side nozzle hole and a tip end portion of the central electrode .
Found in spark plugs for internal combustion engines.

In the spark plug for the internal combustion engine, the number of the first nozzle holes is greater than the number of the second nozzle holes, and the inner diameter of the first nozzle holes is smaller than the inner diameter of the second nozzle holes. As a result, by appropriately mounting the spark plug to the internal combustion engine, stable combustion can be achieved in the operating range of the internal combustion engine, from low load to high load.

As described above, according to the above aspects, it is possible to provide a spark plug for an internal combustion engine and an internal combustion engine that can obtain stable combustion characteristics in an operating range of the internal combustion engine ranging from low load to high load.
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.

FIG. 3 is a cross-sectional view of the spark plug according to the first embodiment taken along line II of FIG. 2; FIG. 2 is a cross-sectional view taken along line II-II of FIG. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2 . FIG. 2 is a cross-sectional explanatory view of an internal combustion engine according to the first embodiment ; FIG. 5 is an explanatory diagram corresponding to a cross section taken along line VV in FIG. 4 . FIG. 11 is a cross-sectional view illustrating the operation and effect of the first embodiment. FIG. 11 is an explanatory diagram of a flame jet as viewed from the plug axial direction in the case of a relatively low load in the first embodiment; FIG. 11 is an explanatory diagram of a flame jet as viewed from the plug axial direction in the case of a relatively high load in the first embodiment. FIG. 11 is a cross-sectional explanatory view of an internal combustion engine according to a second embodiment . FIG. 11 is a cross-sectional explanatory view of an internal combustion engine according to a third embodiment . FIG. 13 is a cross-sectional view of a spark plug according to a fourth embodiment taken along a central axis of the plug; FIG. 13 is an explanatory cross-sectional view of a spark plug according to a fifth embodiment , taken along a line perpendicular to the center axis of the plug. FIG. 13 is an explanatory cross-sectional view of a spark plug according to a sixth embodiment, taken along line XIII-XIII in FIG. 14 . A cross-sectional view taken along line XIV-XIV in Figure 13. FIG. 13 is a cross-sectional view illustrating the operation and effect of the sixth embodiment. FIG. 13 is a cross-sectional view of a spark plug according to a seventh embodiment of the present invention ;

( Reference Form 1 )
A reference embodiment of a spark plug for an internal combustion engine will be described with reference to Figs.
As shown in FIGS. 1 to 3, the spark plug 1 of this embodiment includes 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. The ground electrode 6 forms a discharge gap G between the center electrode 4 and the ground electrode 6. The plug cover 5 is provided at the tip of the housing 2 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 61 fixed to the housing 2 or the plug cover 5 on the outer periphery of the auxiliary combustion chamber 50. The plug cover 5 has three or more nozzle holes 51 that connect the auxiliary combustion chamber 50 to the outside. The nozzle hole axes 511L, 512L of the nozzle holes 51 are inclined with respect to the plug axial direction Z so that they move outward in the plug radial direction as they approach the tip side.

Imagine an imaginary plane P that includes the plug center axis C and is perpendicular to the extension direction of the ground electrode 6 when viewed from the plug axial direction Z. This imaginary plane P divides the spark plug 1 into two parts: a first plug portion 11 and a second plug portion 12. The side where the fixed end portion 61 is arranged is the first plug portion 11. The injection hole 51 formed in the first plug portion 11 is the first injection hole 511. The injection hole 51 formed in the second plug portion 12 is the second injection hole 512. In this case, the number of first injection holes 511 is greater than the number of second injection holes 512. The inner diameter of the first injection hole 511 is smaller than the inner diameter of the second injection hole 512.

The spark plug 1 of this embodiment can be used as an ignition means in internal combustion engines of automobiles, cogeneration systems, etc. As shown in FIG. 4, one end of the spark plug 1 in the plug axial direction Z is disposed in the main combustion chamber 101 of the internal combustion engine 10. In the plug axial direction Z, the side exposed to the main combustion chamber 101 is referred to as the tip side, and the opposite side is referred to as the base side. Also, the direction perpendicular to the central axis of the spark plug 1 (i.e., the plug central axis C) is referred to as the plug radial direction. Also, the direction along the circumference centered on the plug central axis C is referred to as the plug circumferential direction.

As shown in FIG. 2, in this embodiment, three injection holes 51 are formed. Two of the three injection holes 51 are first injection holes 511 formed in the first plug portion 11. In this embodiment, the injection hole axes 511L of the two first injection holes 511 are aligned along the plug radial direction when viewed from the plug axial direction Z. In other words, the injection hole axes 511L of the first injection holes 511 essentially intersect with the plug central axis C. When viewed from the plug axial direction Z, the first injection holes 511 are arranged on both sides of the fixed end portion 61 of the ground electrode 6. In this embodiment, the ground electrode 6 is joined to the tip of the housing 2 by welding or the like.

In this embodiment, the other of the three injection holes 51 is a second injection hole 512 formed in the second plug portion 12. The second injection hole 512 also extends along the plug radial direction when viewed from the plug axial direction Z. In other words, the injection hole axis 512L of the second injection hole 512 also essentially intersects with the plug central axis C.

When viewed from the plug axial direction Z, the multiple first injection holes 511 are arranged in positions that are symmetrical with respect to the central axis C6 of the ground electrode 6. When viewed from the plug axial direction Z, the second injection hole 512 is arranged on the central axis C6 of the ground electrode 6. When viewed from the plug axial direction Z, the central axis C6 of the ground electrode 6 and the injection hole axis 512L of the second injection hole 512 overlap with each other.

As shown in FIG. 1, the ground electrode 6 is inclined with respect to the plug axial direction Z so as to move toward the tip side from the fixed end 61 toward the plug central axis C. In other words, the ground electrode 6 is inclined toward the tip side of the plug axial direction Z as it moves from the fixed end 61 toward the protruding end.

The discharge gap G is located further forward than the tip 21 of the housing 2. The tip surface of the center electrode 4 is located further forward in the plug axial direction Z than the tip 21 of the housing 2.

In this embodiment, the inner diameter of the second nozzle hole 512 is approximately 1.4 times the inner diameter of the first nozzle hole 511. The opening area of the second nozzle hole 512 is approximately twice the opening area of the first nozzle hole 511. As a result, the sum of the opening areas of the two first nozzle holes 511 and the opening area of one second nozzle hole 512 are approximately equal.

However, as long as the number of first injection holes 511 is greater than the number of second injection holes 512, these numbers are not particularly limited. For example, there may be three first injection holes 511 and one or two second injection holes 512. Alternatively, there may be four first injection holes 511 and one, two, or three second injection holes 512. In any case, it is considered that the sum of the opening areas of all the first injection holes 511 and the opening areas of all the second injection holes 512 are approximately equal.

An internal combustion engine 10 equipped with the spark plug 1 of this embodiment will be described with reference to FIGS.
The internal combustion engine 10 has a main combustion chamber 101, and an intake valve 72 and an exhaust valve 73 provided in the main combustion chamber 101. When viewed from the plug axial direction Z, the first plug portion 11 faces the intake valve 72 side.

That is, the spark plug 1 is attached to the internal combustion engine 10 so that the first plug portion 11 faces the intake valve 72.

As shown in FIG. 4, the internal combustion engine 10 includes a cylinder head 76, a cylinder block 75, and a piston 74 that reciprocates within the cylinder 70. The cylinder head 76, the cylinder block 75, and the piston 74 form a main combustion chamber 101. The cylinder head 76 is formed with an intake port 721 and an exhaust port 731, each of which is provided with an intake valve 72 or an exhaust valve 73. The spark plug 1 is attached between the intake port 721 and the exhaust port 731 in the cylinder head 76. That is, as shown in FIG. 4 and FIG. 5, 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.

The intake port 721 and 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 101. In addition, the base end surface of the main combustion chamber 101 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, gas (mainly air) is introduced into the main combustion chamber 101 from the intake port 721, and during the exhaust stroke, gas in the main combustion chamber 101 is exhausted from the exhaust port 731. Due to the way the airflow is introduced during the intake stroke, a certain airflow is formed in the main combustion chamber 101, and this airflow remains even during the compression stroke.

In the main combustion chamber 101, as shown in FIG. 4, a tumble flow, that is, an air flow AF1 around an axis perpendicular to the sliding direction of the piston 74, is mainly formed. In addition, as shown in FIG. 4 and FIG. 5, this air flow AF1 is directed from the intake valve 72 side to the exhaust valve 73 side near the tip of the spark plug 1 in the main combustion chamber 101. More specifically, as shown in FIG. 5, when viewed from the plug axial direction Z, the air flow AF1 along the direction from the midpoint between the two intake ports 721 to the midpoint between the two exhaust ports 731 is the main air flow near the tip of the spark plug 1.

The airflow in the main combustion chamber 101 is not always constant, but may vary between cycles or between different timings within 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 AF1 refers to the main airflow at the ignition timing. And, when we say "airflow in the main combustion chamber 101," unless otherwise specified, we mean the above-mentioned airflow AF1 near the tip of the spark plug 1 at the ignition timing.

Next, the effects of this embodiment will be described.
In the spark plug 1 for an internal combustion engine, the number of the first injection holes 511 is greater than the number of the second injection holes 512, and the inner diameter of the first injection holes 511 is smaller than the inner diameter of the second injection holes 512. Thus, by appropriately mounting the spark plug 1 to the internal combustion engine 10, it is possible to obtain stable combustibility in an operating range of the internal combustion engine ranging from low load to high load.

In other words, by mounting the spark plug 1 on the internal combustion engine 10 so that the first plug portion 11 faces the intake valve 72, the following phenomena can be expected in both a relatively low-load operating range and a relatively high-load operating range.

In the relatively low load operating range, as shown in Figures 4 and 5, an airflow AF1 is formed in the main combustion chamber 101 near the tip of the spark plug 1, flowing from the intake valve 72 side to the exhaust valve 73 side. As a result, as shown in Figure 6, an airflow AF2 flows from the first nozzle hole 511 into the auxiliary combustion chamber 50.

This airflow AF2 creates a tumble flow in the auxiliary combustion chamber 50, which flows toward the base end of the second plug portion 12 and then flows toward the tip end of the first plug portion 11. The airflow AF3 then passes through the discharge gap G along the base end side of the ground electrode 6 and flows toward the second nozzle hole 512. This causes the discharge S in the discharge gap G to be elongated.

Therefore, the combustion in the auxiliary combustion chamber 50 diffuses from a position close to the second nozzle hole 512. Here, since the inner diameter of the second nozzle hole 512 is large, the flame jet injected from the second nozzle hole 512 is less susceptible to cooling loss from the plug cover 5. Therefore, as shown in FIG. 7, the flame jet J2 from the second nozzle hole 512 is more easily injected, improving ignition performance. For example, ignition performance can be more easily ensured even in an EGR (i.e., exhaust gas recirculation) environment.

In the relatively high load operating range, the fuel concentration is high and the temperature is also high. Therefore, the combustion diffusion in the auxiliary combustion chamber 50 is fast, and the difference in the arrival time of the flame to the multiple nozzle holes 51 is unlikely to occur. In other words, there is no large difference in the arrival time of the flame between the first nozzle hole 511 and the second nozzle hole 512. In addition, the flame is also prevented from suffering cooling loss. Therefore, the flame jets J1 and J2 are sufficiently injected from both the first nozzle hole 511 and the second nozzle hole 512.

Since the first nozzle holes 511 have a small inner diameter, the penetration force of the flame jet J1 is high, and the flame jet J1 is sprayed from the first nozzle holes 511 with great force. Also, since there are a large number of first nozzle holes 511, the flame jet J1 sprayed from the first nozzle holes 511 tends to diffuse widely in the area of the main combustion chamber 101 on the intake valve 72 side. In other words, combustion can be promoted in the main combustion chamber 101 on the intake valve 72 side, which has a relatively low temperature. This improves the combustion balance in the main combustion chamber 101 and suppresses knocking in the internal combustion engine.

As shown in FIG. 2, the first nozzle holes 511 are arranged in line symmetry with respect to the central axis C6 of the ground electrode 6 when viewed from the plug axial direction Z. This allows the airflows flowing in from the first nozzle holes 511 to merge with each other and flow toward the second plug portion 12. This strengthens the tumble flow (see arrow AF3 in FIG. 6) in the auxiliary combustion chamber 50, and further improves combustibility in the relatively low load operating range.

As shown in FIG. 6, the ground electrode 6 is inclined with respect to the plug axial direction Z so that it is inclined from the fixed end 61 toward the tip side as it approaches the plug center axis C. This allows the airflow AF3 in the auxiliary combustion chamber 50 to be guided more smoothly to the discharge gap G.

The discharge gap G is also positioned closer to the tip than the tip 21 of the housing 2. This makes it possible to suppress cooling loss of the initial flame. It also makes it easier to extend the discharge S toward the second nozzle hole 512. As a result, it is possible to further improve combustibility in the relatively low load operating range.

As described above, this embodiment can provide a spark plug for an internal combustion engine and an internal combustion engine that can obtain stable combustion characteristics in the operating range of the internal combustion engine from low load to high load.

( Reference Form 2 )
As shown in FIG. 9, this embodiment is an internal combustion engine 10 having an injector 71 that directly injects fuel into a main combustion chamber 101.
The spark plug 1 is disposed so that an injection flow F containing fuel injected from the injector 71 is directed toward the second nozzle hole 512 .

At any time between the intake stroke and the compression stroke of the internal combustion engine 10, fuel is injected from the injector 71 into the main combustion chamber 101. An injection flow F containing this fuel is formed in the main combustion chamber 101 and directed toward the outer opening of the second injection hole 512.

The arrow F in FIG. 9 indicates the direction of the injection flow immediately after fuel injection, and does not necessarily coincide with the airflow in the main combustion chamber 101 during the intake stroke, compression stroke, or expansion stroke. In addition, the state in which the injection flow F is directed toward the second injection hole 512 is a state in which the outer opening of the second injection hole 512 is visible from the direction of the injection flow F near the plug cover 5.

The injector 71 is provided adjacent to the intake port 721. The injector 71 is installed in such a position that it injects fuel toward the central axis of the main combustion chamber 101.

The fuel injected into the main combustion chamber 101 forms an injection flow F with the air in the main combustion chamber 101, for example as shown in FIG. 9, 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 second nozzle hole 512 of the spark plug 1.

The injected flow F is a mixture with a relatively large fuel ratio. Therefore, the vicinity of the second nozzle hole 512 where the injected flow F reaches becomes a mixture containing a large amount of fuel. This mixture is introduced into the auxiliary combustion chamber 50 through the second nozzle hole 512. And, because the second nozzle hole 512 has a larger inner diameter than the first nozzle hole 511, the mixture is more easily introduced into the auxiliary combustion chamber 50 through the second nozzle hole 512.

The rest is the same as in Reference Form 1. In addition, among the symbols used in Reference Form 2 and the following, the same symbols as those used in the above-mentioned forms indicate the same components, etc. as those in the above-mentioned forms , unless otherwise specified.

In this embodiment of 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 second nozzle hole 512. This makes it easier for a high-fuel-density mixture to be introduced from the second nozzle hole 512 into the auxiliary combustion chamber 50. As a result, the ignition performance in the auxiliary combustion chamber 50 is improved, and the ignition performance in the main combustion chamber 101 is also improved.

For example, the effect of improving ignition when retard injection and retard ignition are performed during high load operation of the internal combustion engine can be expected. During the compression stroke in which retard injection is performed, the atmosphere in the main combustion chamber 101 is compressed, and air flows into the auxiliary combustion chamber 50 through the nozzle hole 51. This causes the pressure in the auxiliary combustion chamber 50 to increase. Therefore, while it is relatively difficult for the mixture to flow into the auxiliary combustion chamber 50 at the timing of retard ignition, according to this embodiment, it is easy to introduce a high concentration mixture into the auxiliary combustion chamber 50 via the second nozzle hole 512. Alternatively, it can be said to be particularly effective in improving ignition when starting the internal combustion engine, where the air flow is relatively weak and unevenness in the fuel concentration is likely to occur.
In addition, the present embodiment has the same effects as those of the first embodiment .

( Reference Form 3 )
As shown in FIG. 10, this embodiment is an embodiment in which the orientation of the spark plug 1 installed in the internal combustion engine 10 is changed from that of the second embodiment.

The internal combustion engine 10 of this embodiment is configured so that a portion of the injection flow F injected from the injector 71 heads directly toward the spark plug 1. Therefore, in this embodiment, the spark plug 1 is disposed in such a direction that a portion of the injection flow F heads directly toward the second nozzle hole 512. In other words, the injector 71 injects fuel into the main combustion chamber 101 so that the injection flow F containing fuel heads directly toward the outer opening of the second nozzle hole 512.

In this embodiment, the spark plug 1 is arranged such that, when viewed from the Z direction, the outer opening of the second nozzle hole 512 faces the intake valve 72 side (not shown).
The rest is the same as in the second embodiment .

The spark plug 1 is positioned so that the injection flow F injected from the injector 71 is directed directly toward the second nozzle hole 512. This ensures that a mixture with high fuel density is easily introduced into the auxiliary combustion chamber 50 from the second nozzle hole 512. In addition, since the second nozzle hole 512 has a larger inner diameter than the first nozzle hole 511, the mixture is more easily introduced into the auxiliary combustion chamber 50 through the second nozzle hole 512.
In addition, it has the same effects as the second embodiment .

( Reference Form 4 )
In this embodiment, the first injection hole 511 and the second injection hole 512 are formed so that the extension region 511E and the extension region 512E do not overlap the discharge gap G, as shown in FIG.

The extension region 511E is a region obtained by extending the first nozzle hole 511 along the nozzle hole axis 511L. The extension region 512E is a region obtained by extending the second nozzle hole 512 along the nozzle hole axis 512L.
The first injection hole 511 and the second injection hole 512 are further formed such that the extension region 511E and the extension region 512E do not intersect with each other.

In this embodiment, the inclination angle of the injection hole axis 511L of the first injection hole 511 and the inclination angle of the injection hole axis 512L of the second injection hole 512 relative to the plug axis direction Z are made different from each other, so that the extension region 511E and the extension region 512E do not intersect with each other.

In this embodiment, the inclination angle of the injection hole axis 511L of the first injection hole 511 with respect to the plug axial direction Z is larger than the inclination angle of the injection hole axis 512L of the second injection hole 512 with respect to the plug axial direction Z.
The rest is similar to the first embodiment .

In this embodiment, the first injection hole 511 and the second injection hole 512 are formed so that the extension region 511E and the extension region 512E do not intersect with each other. This makes it difficult for the airflow flowing from the first injection hole 511 into the auxiliary combustion chamber 50 to be obstructed by the airflow flowing from the second injection hole 512. This makes it easier to form a tumble flow (see arrow AF3 in FIG. 6) in the auxiliary combustion chamber 50. As a result, it becomes easier to extend the discharge S formed in the discharge gap G toward the second plug portion 12.

In addition, the extension region 511E and the extension region 512E do not overlap with the discharge gap G. As a result, the airflow passing through the discharge gap G due to the above-mentioned tumble flow is less likely to be disturbed by the airflow flowing into the auxiliary combustion chamber 50 from the first injection hole 511 and the second injection hole 512. As a result, the discharge S formed in the discharge gap G can be easily extended toward the second plug portion 12.
In addition, the present embodiment has the same effects as those of the first embodiment .

( Reference Form 5 )
In this embodiment, the first injection hole 511 and the second injection hole 512 are formed so that the extension region 511E and the extension region 512E do not overlap the discharge gap G, as shown in FIG.
Also in this embodiment, the first injection hole 511 and the second injection hole 512 are formed such that the extension region 511E and the extension region 512E do not intersect with each other.

In this embodiment, the inclination angle of the ground electrode 6 with respect to the central axis C6 when viewed from the plug axial direction Z is different between the nozzle hole axis 511L of the first nozzle hole 511 and the nozzle hole axis 512L of the second nozzle hole 512.

In this embodiment, the number of first injection holes 511 is three, and the number of second injection holes 512 is two. One of the three first injection holes 511 is formed at a position overlapping the fixed end portion 61 of the ground electrode 6 when viewed from the plug axial direction Z. The injection hole axis 511L of this first injection hole 511 is aligned along the plug radial direction when viewed from the plug axial direction Z.

On the other hand, the other two of the three first injection holes 511 are formed on opposite sides of the ground electrode 6 when viewed from the plug axial direction Z. The injection hole axes 511L of these first injection holes 511 are offset from the plug radial direction when viewed from the plug axial direction Z, and intersect with the central axis C6 of the ground electrode 6 at the second plug portion 12.

In addition, the nozzle hole axes 512L of the two second nozzle holes 512 also intersect with the central axis C6 of the ground electrode 6 in the second plug portion 12 when viewed from the plug axial direction Z.

The rest is similar to the first embodiment .
In this embodiment, the same effects as those of the second embodiment can be obtained.

(Embodiment 6)
In this embodiment, as shown in FIGS. 13 to 15, the ground electrode 6 protrudes significantly toward the second plug portion 12 side.

In this embodiment, at least one second nozzle hole 512 is a protruding side nozzle hole 52 through which the center axis C6 of the ground electrode 6 passes when viewed from the plug axial direction Z. When viewed from the plug axial direction Z, the protruding end portion 63 of the ground electrode 6 is disposed between the center electrode 4 and the protruding side nozzle hole 52.

As shown in FIG. 14, when viewed from the plug axial direction Z, the protruding end 63 is positioned closer to the protruding side nozzle hole 52 than to the center electrode 4. As shown in FIG. 13, the protruding end 63 is positioned closer to the tip side than the straight line L1. The straight line L1 is the straight line that connects the base end of the outer opening 522 of the protruding side nozzle hole 52 and the tip end of the center electrode 4 at the shortest distance.

The ground electrode 6 has a thickness in the plug axial direction Z of a portion closer to the protruding end 63 than the fixed end 61 in the longitudinal direction of the ground electrode 6. The tapered portion of the ground electrode 6 has a tip surface formed along the inner surface of the bottom wall of the plug cover 5.
The rest is similar to the first embodiment .

In this embodiment, especially during the expansion stroke, the airflow discharged from the auxiliary combustion chamber 50 through the ejection side nozzle hole 52 is guided to the ground electrode 6 and easily passes through the discharge gap G.

In this regard, let us consider the expansion stroke of an internal combustion engine 10 (see FIG. 4) equipped with the spark plug 1 of this embodiment. During the expansion stroke, the piston 74 moves toward the tip end, causing the main combustion chamber 101 to have a negative pressure relative to the auxiliary combustion chamber 50. This causes gas to be discharged from the auxiliary combustion chamber 50 to the main combustion chamber 101 through the nozzle hole 51. The airflow AF4 formed in the auxiliary combustion chamber 50 as the gas is discharged through the ejection side nozzle hole 52 is guided to the ground electrode 6 and heads toward the ejection side nozzle hole 52, as shown in FIG. 15. The airflow AF4 guided to the ground electrode 6 then passes through the discharge gap G.

Therefore, during the expansion stroke, the discharge S generated in the discharge gap G is easily extended toward the protruding side nozzle hole 52 by the airflow AF4 as shown in FIG. 15, improving ignition in the auxiliary combustion chamber 50. In addition, since the ignition position can be easily brought closer to the protruding side nozzle hole 52, for example, under operating conditions where the temperature of the auxiliary combustion chamber 50 is low, cold loss is suppressed and the flame jet to the main combustion chamber 101 can be strengthened. Furthermore, since the discharge S or discharge plasma or initial flame generated in the discharge gap G is easily ejected from the protruding side nozzle hole 52, ignition in the main combustion chamber 101 can be improved.

In addition, during the expansion stroke, the starting point of the discharge S generated in the discharge gap G on the ground electrode 6 side is likely to move toward the protrusion side nozzle hole 52 due to the airflow AF4 that is guided through the protrusion side nozzle hole 52. Therefore, the discharge S is likely to extend toward the protrusion side nozzle hole 52. As a result, ignition performance can be improved.

When viewed from the plug axial direction Z, the protruding end 63 is positioned closer to the protruding side nozzle hole 52 than to the center electrode 4. Therefore, during the expansion stroke, the airflow AF4 guided by the ground electrode 6 is more likely to flow toward the protruding side nozzle hole 52. Therefore, the discharge S generated in the discharge gap G is more likely to extend toward the protruding side nozzle hole 52. As a result, ignition performance can be further improved.

The protruding end 63 is positioned further forward than the straight line L1. Therefore, during the expansion stroke, the discharge S 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 52 and the main combustion chamber. As a result, ignition performance can be reliably improved.

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 52 is likely to be short-circuited by the protruding end 63 when it tries to extend further toward the protruding side nozzle hole 52 than the protruding end 63. On the other hand, in this embodiment, the protruding end 63 is disposed in the above-mentioned position. Therefore, during the expansion stroke, the discharge S generated in the discharge gap G is unlikely to be short-circuited by the protruding end 63 even if it extends further toward the protruding side nozzle hole 52 than the protruding end 63, as shown in FIG. 15. As a result, ignition performance can be improved.

In addition, by arranging the protruding end portion 63 in the above-mentioned position, the starting point of the discharge S on the ground electrode 6 side is likely to move to the inner surface of the protruding side nozzle hole 52, as shown in Fig. 15. Furthermore, the starting point is likely to move toward the outer opening 522 of the protruding side nozzle hole 52. Therefore, the discharge S is more likely to extend toward the main combustion chamber 101. As a result, the ignition ability of the main combustion chamber 101 can be further improved.
In addition, the present embodiment has the same effects as those of the first embodiment .

( Reference Form 7 )
In this embodiment, as shown in FIG. 16, the shape of the ground electrode 6 is modified.
That is, in this embodiment, the ground electrode 6 has a portion along the plug axial direction Z on the fixed end 61 side, and is bent from that portion toward the plug central axis C. The surface of the ground electrode 6 facing the center electrode 4 is a surface that is approximately perpendicular to the plug axial direction Z.
The rest is the same as in the first embodiment , and has the same effects.

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, 10...internal combustion engine, 11...first plug part, 12...second plug part, 2...housing, 3...insulator, 4...center electrode, 5...plug cover, 50...auxiliary combustion chamber, 51...nozzle hole, 511...first nozzle hole, 512...second nozzle hole, 511L, 512L...nozzle hole axis, 6...ground electrode, 61...fixed end, C...plug center axis, G...discharge gap, P...imaginary plane, Z...plug axis direction

Claims (8)

A cylindrical insulator (3);
a center electrode (4) held on the inner circumferential side of the insulator and protruding from the insulator toward the tip side;
a cylindrical housing (2) that holds the insulator on its inner periphery;
a ground electrode (6) forming a discharge gap (G) between itself and the center electrode;
a plug cover (5) provided at a tip end of the housing so as to cover a sub-combustion chamber (50) in which the discharge gap is disposed,
The ground electrode protrudes into the auxiliary combustion chamber from a fixed end portion (61) fixed to the housing or the plug cover on the outer circumferential side of the auxiliary combustion chamber,
The plug cover is formed with three or more nozzle holes (51) that communicate the auxiliary combustion chamber with the outside,
The nozzle hole axes (511L, 512L) of the nozzle holes are inclined with respect to the plug axial direction (Z) so as to be outward in the plug radial direction toward the tip side,
When the spark plug is divided into two parts, a first plug portion (11) and a second plug portion (12), by a virtual plane (P) which includes the plug center axis (C) and is perpendicular to the extending direction of the ground electrode as viewed in the plug axial direction, the side on which the fixed end is arranged is defined as the first plug portion, the injection hole formed in the first plug portion is defined as a first injection hole (511), and the injection hole formed in the second plug portion is defined as a second injection hole (512),
the number of the first nozzle holes is greater than the number of the second nozzle holes,
an inner diameter of the first nozzle hole is smaller than an inner diameter of the second nozzle hole,
at least one of the second nozzle holes is a protruding-side nozzle hole (52) through which a central axis (C6) of the ground electrode passes when viewed from the plug axial direction, a protruding end portion (63) of the ground electrode is disposed between the central electrode and the protruding-side nozzle hole when viewed from the plug axial direction, the protruding end portion is disposed at a position closer to the protruding-side nozzle hole than to the central electrode when viewed from the plug axial direction, and the protruding end portion is disposed on the tip side of a straight line (L1) connecting, at the shortest distance, a base end of an outer opening portion (522) of the protruding-side nozzle hole and a tip end portion of the central electrode .
Spark plugs for internal combustion engines. The spark plug for an internal combustion engine according to claim 1, wherein the first nozzle hole and the second nozzle hole are formed so that an extension region (511E) of the first nozzle hole extended along the nozzle hole axis and an extension region (512E) of the second nozzle hole extended along the nozzle hole axis do not overlap the discharge gap and do not intersect with each other. The spark plug for an internal combustion engine according to claim 1 or 2, wherein the first nozzle holes are arranged in line symmetry with respect to the central axis of the ground electrode when viewed in the plug axial direction. 4. The spark plug for an internal combustion engine according to claim 1 , wherein the ground electrode is inclined with respect to the axial direction of the plug so as to move from the fixed end toward a tip side as the ground electrode approaches a central axis of the plug. 5. The spark plug for an internal combustion engine according to claim 1 , wherein the discharge gap is disposed on a tip side of the tip (21) of the housing. An internal combustion engine (10) equipped with the spark plug for an internal combustion engine according to any one of claims 1 to 5 ,
The present invention has a main combustion chamber (101), and an intake valve (72) and an exhaust valve (73) provided in the main combustion chamber,
the first plug portion faces the intake valve side when viewed from the plug axial direction. An internal combustion engine (10) equipped with the spark plug for an internal combustion engine according to any one of claims 1 to 5 ,
A main combustion chamber (101);
an injector (71) for injecting fuel directly into the main combustion chamber;
The spark plug is disposed so that an injection flow (F) containing the fuel injected from the injector is directed toward the second nozzle hole. 8. The internal combustion engine according to claim 7 , further comprising an intake valve (72) and an exhaust valve (73) provided in the main combustion chamber, and the first plug portion faces the intake valve side when viewed from a plug axial direction.

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