JP7600959B2 - Internal combustion engine and spark plug for internal combustion engine - Google Patents

Description

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

A spark plug with a secondary combustion chamber is disclosed in, for example, Patent Document 1. In such a spark plug, an initial flame generated in the discharge gap grows in the secondary combustion chamber and ejects a flame jet from the nozzle hole. As a result, the flame jet ejected into the main combustion chamber ignites the mixture in the main combustion chamber, causing combustion. In the spark plug described in Patent Document 1, the discharge gap is located far from the nozzle hole. Therefore, unless flame misfire occurs, the flame will be ejected from the nozzle hole after having grown sufficiently in the secondary combustion chamber, making it easy to strengthen the flame jet.

JP 2020-184435 A

However, if the discharge gap is located far from the nozzle hole, it is likely to cause flame misfire due to the effects of cooling loss. Misfire is a concern especially when the internal combustion engine is running at low load because the temperatures of the housing and plug cover are relatively low. On the other hand, misfire is less likely to occur when the temperature of the housing and plug cover is relatively high, such as when the internal combustion engine is running at high load. For this reason, it is considered advantageous in terms of ignition performance to have the discharge gap located far from the nozzle hole. Thus, there is a concern that the ignition performance of the spark plug described in Patent Document 1 may vary depending on the operating state of the internal combustion engine.

The present invention was made in consideration of these problems, and aims to provide an internal combustion engine and a spark plug for an internal combustion engine that can achieve stable ignition.

One aspect of the present invention is an internal combustion engine (10) equipped with a spark plug (1),
The above spark plugs are
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 first discharge gap (G1) 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 first discharge gap is disposed,
The plug cover has a nozzle hole (51) that communicates the auxiliary combustion chamber with the outside,
the first discharge gap is formed at a position overlapping with the nozzle hole axis or at a position on the tip side of the nozzle hole axis when viewed from a direction perpendicular to both the plug axial direction (Z) and the nozzle hole axis (L),
A second discharge gap (G2) is provided between the center electrode and the housing via a surface of the insulator,
a discharge occurrence position is shifted from the first discharge gap to the second discharge gap as the load of the internal combustion engine increases.
It is found in internal combustion engines.

Another 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 first discharge gap (G1) 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 first discharge gap is disposed,
The plug cover has a nozzle hole (51) that communicates the auxiliary combustion chamber with the outside,
the first discharge gap is formed at a position overlapping with an injection hole axis (L) of the injection hole or at a position on the tip side of the injection hole axis,
A second discharge gap (G2) is provided between the center electrode and the housing via a surface of the insulator,
With an increase in pressure in the auxiliary combustion chamber, a discharge occurrence position is shifted from the first discharge gap to the second discharge gap.
A spark plug (1) for an internal combustion engine.

In the above internal combustion engine, the discharge occurrence position is configured to shift from the first discharge gap to the second discharge gap as the load of the internal combustion engine increases. Therefore, when the load of the internal combustion engine is relatively low, the discharge occurrence position is the first discharge gap, and when the load of the internal combustion engine is relatively high, the discharge occurrence position is the second discharge gap. As a result, in a relatively low load state, an initial flame is formed near the first discharge gap, which is relatively close to the nozzle hole, and a flame jet can be ejected from the nozzle hole while suppressing misfire. In addition, in a relatively high load state, an initial flame is formed near the second discharge gap, which is relatively far from the nozzle hole, and a sufficiently grown flame can be ejected from the nozzle hole as a flame jet.
In this way, the flame jet can be effectively ejected both at low load and at high load, and stable ignition performance can be obtained.

The spark plug for the internal combustion engine is configured so that the discharge position shifts from the first discharge gap to the second discharge gap as the pressure in the auxiliary combustion chamber increases. This allows the flame jet to be ejected effectively both when the internal combustion engine is under low load and when it is under high load. This allows stable ignition to be achieved.

As described above, according to the above aspect, it is possible to provide an internal combustion engine and a spark plug for an internal combustion engine that are capable of obtaining stable ignition performance.
In addition, the symbols in parentheses described in the claims and the means for solving the problems indicate a correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present invention.

1 is a cross-sectional explanatory diagram of an internal combustion engine to which a spark plug is attached according to a first embodiment. FIG. 2 is a plan view of the spark plug, taken along line II in FIG. 1 . 3 is a cross-sectional view of the spark plug taken along line III-III in FIG. 1 . FIG. 4 is an explanatory diagram of a state in which a discharge occurs in a first discharge gap in the first embodiment. FIG. 4 is an explanatory diagram of a state in which a discharge occurs in a second discharge gap in the first embodiment. 4 is a diagram showing the relationship between the load of the internal combustion engine and the discharge voltage in the first embodiment. FIG. 11 is a cross-sectional view of an internal combustion engine to which a spark plug is attached according to a second embodiment. 8 is a cross-sectional view of the spark plug taken along line VIII-VIII in FIG. 7 . FIG. 11 is a cross-sectional explanatory view of an internal combustion engine according to a third embodiment. FIG. 11 is an explanatory diagram illustrating the direction of an airflow formed in a main combustion chamber in a third embodiment, as viewed from the front end side of the internal combustion engine. FIG. 11 is a cross-sectional view of an internal combustion engine illustrating an air flow in an auxiliary combustion chamber 50 in a third embodiment.

(Embodiment 1)
An embodiment of an internal combustion engine 10 and a spark plug 1 for an internal combustion engine will be described with reference to FIGS.
The internal combustion engine 10 of this embodiment is an internal combustion engine equipped with a spark plug 1 .
As shown in FIGS. 1 to 3, the spark plug 1 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 first discharge gap G1 between itself and the center electrode 4. The plug cover 5 is provided at the tip of the housing 2 to cover the auxiliary combustion chamber 50 in which the first discharge gap G1 is located.

The plug cover 5 has a nozzle hole 51 that connects the auxiliary combustion chamber 50 to the outside. As shown in Fig. 1, the first discharge gap G1 is formed at a position overlapping with the nozzle hole axis L of the nozzle hole 51 or at a position further forward than the nozzle hole axis L. A second discharge gap G2 is provided between the center electrode 4 and the housing 2, with the surface of the insulator 3 interposed therebetween.
As the load of the internal combustion engine 10 increases, the position where discharge occurs shifts from the first discharge gap G1 to the second discharge gap G2.

The spark plug 1 of this embodiment can be used as an ignition means in internal combustion engines of automobiles, cogeneration systems, etc. One end of the spark plug 1 in the plug axial direction Z is exposed to 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. 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. The direction along the circumference centered on the plug central axis C is referred to as the plug circumferential direction.

The spark plug 1 is attached to the internal combustion engine 10 by screwing a mounting thread portion 23 formed on the outer periphery of the housing 2 into a female thread portion formed in the plug hole 71 .
The housing 2 is a generally cylindrical body made of metal. As shown in Fig. 1, a generally cylindrical insulator 3 is held on the inner periphery of the housing 2. The housing 2 has a locking protrusion 21 that protrudes on the inner periphery. The insulator 3 has a step 31 that protrudes on the outer periphery. The step 31 of the insulator 3 is locked to the locking protrusion 21 of the housing 2, whereby the insulator 3 is held on the inner periphery of the housing 2. The insulator 3 is made of a ceramic such as alumina.

The center electrode 4 is inserted and held on the inner periphery of the insulator 3. The center electrode 4 protrudes further toward the tip side than the tip of the insulator 3. The central axis of the center electrode 4 coincides with the plug central axis C. A second discharge gap G2 is formed between the side surface of the center electrode 4 at the tip of the insulator 3 and the locking protrusion 21 of the housing 2. The second discharge gap G2 is a creepage gap along the surface of the insulator 3.

The ground electrode 6 is formed so as to protrude from a fixed end 61 fixed to the outer peripheral wall of the auxiliary combustion chamber 50 toward the plug central axis C. A part of the ground electrode 6 and the tip of the central electrode 4 face each other in the plug axial direction Z via a first discharge gap G1. The ground electrode 6 is joined to the tip of the housing 2 by welding or the like. The ground electrode 6 is inclined so as to move toward the tip side from the fixed end 61 toward the protruding end.

A plug cover 5 is joined to the tip of the housing 2. A plurality of injection holes 51 are formed in the plug cover 5. As shown in FIG. 2, in this embodiment, four injection holes 51 are formed at equal intervals in the plug circumferential direction. As shown in FIG. 1, the injection hole axis L, which is the central axis of the injection hole 51, is inclined so as to approach the outer periphery as it approaches the tip. When viewed from a direction perpendicular to both the injection hole axis L and the plug axial direction Z, the first discharge gap G1 is located at a position overlapping with the injection hole axis L or on the tip side of the injection hole axis L.

In this embodiment, when viewed from a direction perpendicular to both the injection hole axis L and the plug axial direction Z, the first discharge gap G1 is located further forward than the injection hole axis L. In other words, when viewed from a direction perpendicular to both the injection hole axis L and the plug axial direction Z, the injection hole axis L intersects with the plug central axis C on the base end side of the first discharge gap G1.

The internal combustion engine 10 repeats the intake stroke, compression stroke, expansion stroke, and exhaust stroke in sequence with the reciprocating motion of the piston 74 (see FIG. 9 described later) in the cylinder 70. Then, at the timing near the top dead center of the piston 74 when the compression stroke switches to the expansion stroke, a voltage is applied to the spark plug 1. This causes a spark discharge to occur in either the first discharge gap G1 or the second discharge gap G2, as shown in FIG. 4 and FIG. 5.

When a voltage is applied to the spark plug 1, a spark discharge occurs in one of the first discharge gap G1 and the second discharge gap G2, whichever has a lower discharge voltage.
As described above, the first discharge gap G1 is formed in the space between the tip end of the center electrode 4 and the ground electrode 6. On the other hand, the second discharge gap G2 is a creepage gap along the surface of the insulator 3.

In any discharge gap, the higher the ambient pressure, the higher the discharge voltage. The greater the load on the internal combustion engine 10, the higher the ambient pressure. The relationship between the load B of the internal combustion engine and the discharge voltage is generally as shown in FIG. 6. In the figure, the relationship between the load B and the discharge voltage in the first discharge gap G1 is shown by line V1. The relationship between the load B and the discharge voltage in the second discharge gap G2 is shown by line V2.

As can be seen from the figure, the rate of increase in the discharge voltage relative to an increase in the load B in the first discharge gap G1 is roughly constant throughout the entire operating range (see line V1). In contrast, in the second discharge gap G2, which is a creeping discharge gap, when the load B becomes large to a certain extent, the rate of increase in the discharge voltage relative to an increase in the load B becomes small (see line V2). Thus, the relationship between the load B and the discharge voltage in the first discharge gap G1 and the second discharge gap G2 show different trends, as shown in FIG. 6.

When the internal combustion engine 10 is operating in a high load range, the temperatures of the housing 2 and the plug cover 5 are high, making it difficult for misfires to occur. Therefore, generating a discharge in the second discharge gap G2, which is far from the injection hole 51, is advantageous from the standpoint of combustibility.

On the other hand, when the internal combustion engine 10 is operating in a low load range, the temperatures of the housing 2 and the plug cover 5 are low, making misfires more likely to occur. Therefore, generating a discharge in the first discharge gap G1, which is close to the injection hole 51, is advantageous from the standpoint of combustibility.

Therefore, as shown in FIG. 6, in the high load region, the discharge voltage V2 of the second discharge gap G2 is lower than the discharge voltage V1 of the first discharge gap G1, and in the low load region, the discharge voltage V1 of the first discharge gap G1 is lower than the discharge voltage V2 of the second discharge gap G2. In other words, the discharge voltages in the first discharge gap G1 and the second discharge gap G2 are adjusted so that the lines V1 and V2 intersect. This adjustment can be made, for example, by adjusting the distance of the second discharge gap G2. In other words, by shortening the second discharge gap G2, the discharge voltage V2 can be lowered, and by lengthening the second discharge gap G2, the discharge voltage V2 can be increased.

In addition, in a typical spark plug, the length of the portion corresponding to the second discharge gap G2 is made sufficiently long so that discharge occurs only in the discharge gap corresponding to the first discharge gap G1 (in other words, so that lines V1 and V2 in FIG. 6 do not intersect). In contrast, in the spark plug 1 of this embodiment, the second discharge gap G2 is intentionally made somewhat short so that lines V1 and V2 in FIG. 6 intersect at an appropriate position.

In FIG. 6, the load corresponding to the intersection of line V1 and line V2 (hereinafter referred to as boundary load B0) is theoretically the boundary between discharging in the first discharge gap G1 and discharging in the second discharge gap G2. That is, when the load is higher than the boundary load B0, discharging occurs in the second discharge gap G2, and when the load is lower than the boundary load B0, discharging occurs in the first discharge gap G1. However, in reality, in the vicinity of the boundary load B0, discharging occurs in the first discharge gap G1 or in the second discharge gap G2.

Specifically, when the load of the internal combustion engine 10 is lower than the first reference load B1, discharge occurs mainly in the first discharge gap G1, and when the load of the internal combustion engine 10 is higher than the second reference load B2, discharge occurs mainly in the second discharge gap G2. The first reference load B1 is equal to or smaller than the second reference load B2. For example, the first reference load B1 can be set to 1/4 of the full load, and the second reference load B2 can be set to 3/4 of the full load.

To achieve this, for example, the length of the second discharge gap G2 is adjusted so that the boundary load B0 is a value between the first reference load B1 and the second reference load B2. It is also possible that the first discharge gap G1 gradually expands due to wear at the tip of the center electrode 4. In this case, the discharge voltage at the first discharge gap G1 gradually increases, and the line V1 in FIG. 6 shifts upward. At this time, the boundary load B0 approaches the first reference load B1. In this way, taking into consideration that the boundary load B0 may fluctuate, it is preferable to maintain the relationship B1≦B0≦B2 even when it fluctuates.

Note that "discharge occurs mainly in the first discharge gap G1" can mean, for example, that the discharge probability in the first discharge gap G1 (i.e., the number of discharges within a certain period or in a certain number of cycles) is 10 times or more the discharge probability in the second discharge gap G2. Similarly, "discharge occurs mainly in the second discharge gap G2" can mean, for example, that the discharge probability in the second discharge gap G2 is 10 times or more the discharge probability in the first discharge gap G1.

In this manner, the internal combustion engine 10 of this embodiment is configured so that the discharge occurrence position shifts from the first discharge gap G1 to the second discharge gap G2 as the load on the internal combustion engine 10 increases.

As mentioned above, the higher the load on the internal combustion engine 10, the higher the atmospheric pressure, i.e., the pressure in the auxiliary combustion chamber 50. Therefore, the spark plug 1 of this embodiment is configured so that the discharge occurrence position shifts from the first discharge gap G1 to the second discharge gap G2 as the pressure in the auxiliary combustion chamber 50 increases.

The spark plug 1 of this embodiment is configured as follows. That is, at room temperature, when the pressure P in the auxiliary combustion chamber 50 is lower than the first reference pressure P1, discharge occurs mainly in the first discharge gap G1, and when the pressure P in the auxiliary combustion chamber 50 is higher than the second reference pressure P2, discharge occurs mainly in the second discharge gap G2. The first reference pressure P1 is equal to or lower than the second reference pressure P2.

The configuration of the spark plug 1 can be confirmed, for example, by the following test. That is, the spark plug 1 is attached to a chamber simulating a main combustion chamber, and the pressure inside the chamber is varied. The temperature inside the chamber is set to room temperature. In this state, when a voltage is applied to the spark plug 1, it is observed whether discharge occurs mainly in the first discharge gap G1 or mainly in the second discharge gap G2.

At this time, if it can be confirmed that "when the pressure in the chamber (i.e., the pressure in the auxiliary combustion chamber 50) is lower than the first reference pressure P1, discharge occurs mainly in the first discharge gap G1, and when the pressure in the chamber (i.e., the pressure in the auxiliary combustion chamber 50) is higher than the second reference pressure P2, discharge occurs mainly in the second discharge gap G2," it can be confirmed that the above requirement is met.

Note that the phrase "at room temperature" refers solely to the assumption that the above-mentioned tests are conducted at room temperature, and does not mean that the spark plug 1 will be used at room temperature in practice.

Here, for example, the first reference pressure P1 can be 0.5 MPa, and the second reference pressure can be 1.5 MPa. In addition, in FIG. 6, the pressure P corresponding to the intersection of line V1 and line V2 is set as boundary pressure P0. The boundary pressure P0, the first reference pressure P1, and the second reference pressure P2 satisfy P1≦P0≦P2.

Unless otherwise specified, the pressure in the auxiliary combustion chamber 50 refers to the pressure in the auxiliary combustion chamber 50 at the time when the spark plug 1 ignites.

In this embodiment, the material of the center electrode 4 may be, for example, a nickel alloy. In particular, it is preferable to use an alloy containing 93% or more of nickel and 3% or less of chromium, from the viewpoint of suppressing channeling of the center electrode 4 due to discharge in the second discharge gap G2.

In addition, in this embodiment, no precious metal tip is provided on the portion of either the center electrode 4 or the ground electrode 6 that faces the first discharge gap G1. However, a precious metal tip can be provided on at least one of the center electrode 4 and the ground electrode 6 in the portion that faces the first discharge gap G1. For example, an iridium alloy, a platinum alloy, or the like can be used as the precious metal tip. By providing a precious metal tip in the portion that faces the first discharge gap G1, the expansion of the first discharge gap G1 can be suppressed. This makes it possible to suppress changes in the discharge voltage in the first discharge gap G1.

In addition, in this embodiment, the nozzle hole 51 is formed so that the nozzle hole axis L is directed toward the plug central axis C. However, the nozzle hole can also be formed so that the nozzle hole axis is offset from the plug central axis. For example, the nozzle hole can be formed so that the airflow flowing from the nozzle hole into the auxiliary combustion chamber creates a swirl flow in the plug circumferential direction in the auxiliary combustion chamber.

Next, the effects of this embodiment will be described.
The internal combustion engine 10 is configured such that the position at which the discharge occurs shifts from the first discharge gap G1 to the second discharge gap G2 as the load of the internal combustion engine increases. Therefore, when the load of the internal combustion engine 10 is relatively low, the position at which the discharge occurs is the first discharge gap G1, and when the load of the internal combustion engine 10 is relatively high, the position at which the discharge occurs is the second discharge gap G2.

As a result, under relatively low load conditions, as shown in FIG. 4, an initial flame is formed near the first discharge gap G1, which is relatively close to the nozzle hole 51, and a flame jet can be ejected from the nozzle hole 51 while suppressing misfires. Under relatively high load conditions, as shown in FIG. 5, an initial flame is formed near the second discharge gap G2, which is relatively far from the nozzle hole 51, and a fully grown flame can be ejected as a flame jet from the nozzle hole 51.

In this way, the flame jet can be effectively ejected at both low and high loads. This allows for stable ignition.

When the load of the internal combustion engine 10 is lower than the first reference load B1, discharge occurs mainly in the first discharge gap G1, and when the load of the internal combustion engine 10 is higher than the second reference load B2, discharge occurs mainly in the second discharge gap G2. This makes it possible to reliably eject a flame jet into the main combustion chamber 101, both at a specified low load and at a specified high load.

That is, for example, by adjusting the size of the second discharge gap G2, the boundary load B0 is adjusted to be between the first reference load B1 and the second reference load B2. This makes it possible to ensure that when the load of the internal combustion engine 10 is lower than the first reference load B1, discharge occurs mainly at least in the first discharge gap G1, and when the load of the internal combustion engine 10 is higher than the second reference load B2, discharge occurs mainly at least in the second discharge gap G2.

In addition, the spark plug 1 of this embodiment is configured so that the discharge position shifts from the first discharge gap G1 to the second discharge gap G2 as the pressure in the auxiliary combustion chamber 50 increases. This allows the flame jet to be effectively ejected into the main combustion chamber 101, whether the internal combustion engine 10 is under low load or high load.

In addition, at room temperature, when the pressure in the auxiliary combustion chamber 50 is lower than the first reference pressure P1, discharge occurs mainly in the first discharge gap G1, and when the pressure in the auxiliary combustion chamber 50 is higher than the second reference pressure P2, discharge occurs mainly in the second discharge gap G2. This allows the flame jet to be reliably ejected into the main combustion chamber 101 both at a specified low load and at a specified high load.

As described above, this embodiment can provide an internal combustion engine and a spark plug for an internal combustion engine that can provide stable ignition.

(Embodiment 2)
In this embodiment, as shown in FIGS. 7 and 8, the center electrode 4 has a radial protrusion 41.
The radial protruding portion 41 protrudes in the plug radial direction along the tip end surface of the insulator 3. The radial protruding portion 41 is formed by causing a part of the portion of the center electrode 4 protruding from the tip end of the insulator 3 to protrude in the plug radial direction.

In this embodiment, as shown in FIG. 8, the radial protrusion 41 is formed in an annular shape around the entire circumference of the plug. However, the radial protrusion 41 may be configured to protrude only in a portion of the circumference of the plug. In addition, the distance between the outer peripheral end of the radial protrusion 41 and the inner peripheral surface of the housing 2 is longer than the distance of the first discharge gap G1.

Otherwise, it is the same as in embodiment 1. Note that, among the symbols used in embodiment 2 and onwards, the same symbols used in the previous embodiments represent the same components, etc. as in the previous embodiments, unless otherwise specified.

In this embodiment, it is possible to easily make the second discharge gap G2 not pass through the tip corner of the insulator 3. This makes it possible to suppress localized damage (i.e., channeling) caused by discharge in the second discharge gap G2 at the tip corner of the insulator 3. In addition, by adjusting the protruding length of the radial protruding portion 41, it is also possible to easily adjust the length of the second discharge gap G2.
In addition, the second embodiment has the same effects as the first embodiment.

(Embodiment 3)
In this embodiment, as shown in FIGS. 9 to 11, the fixed end 61 of the ground electrode 6 faces the intake valve 72 side when viewed in the plug axial direction Z.
The ground electrode 6 is formed to protrude from the fixed end 61 toward the plug central axis C (see FIG. 11 ). A part of the ground electrode 6 and the tip end of the center electrode 4 face each other in the plug axial direction Z with a first discharge gap G1 interposed therebetween (see FIG. 11 ).

As shown in FIG. 9, 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. A 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. 9 and FIG. 10, 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, 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 AF in FIG. 9. This airflow AF is directed from the intake valve 72 side to the exhaust valve 73 side near the tip of the spark plug 1 in the main combustion chamber 101, as shown in FIG. 9 and FIG. 10. More specifically, as shown in FIG. 10, when viewed from the plug axial direction Z, the airflow AF 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 101 is not always constant, but may vary between cycles or between different timings in one cycle. However, the direction of the main airflow, particularly the direction of the airflow at the ignition timing, is roughly fixed, and the above-mentioned airflow AF means the main airflow at the ignition timing. And, when we say "airflow in the main combustion chamber 101", unless otherwise specified, it means the above-mentioned airflow AF near the tip of the spark plug 1 at the ignition timing.
The rest is the same as in the first embodiment.

In the internal combustion engine 10 of this embodiment, the fixed end 61 of the ground electrode 6 faces the intake valve 72 side as viewed from the plug axial direction Z. Therefore, as shown in Figures 9 and 10, the injection hole 51 on the fixed end 61 side of the ground electrode 6 faces the upstream side of the airflow AF in the main combustion chamber 101. Then, as shown in Figure 11, the airflow F is mainly introduced from the injection hole 51 on the fixed end 61 side. As a result, in the auxiliary combustion chamber 50, as shown by the arrow F, a tumble flow is formed that moves toward the base end side along the inner wall surface on the side opposite to the fixed end 61, and then moves toward the tip side along the inner wall surface on the fixed end 61 side. Then, the airflow F is guided to the first discharge gap G1 by the base end side of the ground electrode 6. As a result, the discharge formed in the first discharge gap G1 is easily extended, and ignition performance can be improved.
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, 10...internal combustion engine, 2...housing, 3...insulator, 4...center electrode, 5...plug cover, 50...auxiliary combustion chamber, 51...nozzle hole, 6...ground electrode, G1...first discharge gap, G2...second discharge gap, L...nozzle hole axis, Z...plug axis direction

Claims (7)

An internal combustion engine (10) equipped with a spark plug (1),
The above spark plugs are
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 first discharge gap (G1) 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 first discharge gap is disposed,
The plug cover has a nozzle hole (51) that communicates the auxiliary combustion chamber with the outside,
the first discharge gap is formed at a position overlapping with the nozzle hole axis or at a position on the tip side of the nozzle hole axis when viewed from a direction perpendicular to both the plug axial direction (Z) and the nozzle hole axis (L),
A second discharge gap (G2) is provided between the center electrode and the housing via a surface of the insulator,
a discharge occurrence position is shifted from the first discharge gap to the second discharge gap as the load of the internal combustion engine increases.
Internal combustion engine. when a load (B) of the internal combustion engine is lower than a first reference load (B1), discharge occurs mainly in the first discharge gap, and when a load of the internal combustion engine is higher than a second reference load (B2), discharge occurs mainly in the second discharge gap;
The first reference load is equal to or less than the second reference load.
2. The internal combustion engine of claim 1. The internal combustion engine according to claim 1 or 2, wherein the center electrode has a radial protrusion (41) that protrudes in the plug radial direction along the tip surface of the insulator. The internal combustion engine according to any one of claims 1 to 3, wherein the ground electrode is formed so as to protrude from a fixed end (61) fixed to the outer peripheral wall of the auxiliary combustion chamber toward the plug center axis, a part of the ground electrode and a tip of the central electrode face each other in the plug axial direction via the first discharge gap, and the fixed end faces the intake valve (72) as viewed from the plug axial direction. 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 first discharge gap (G1) 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 first discharge gap is disposed,
The plug cover has a nozzle hole (51) that communicates the auxiliary combustion chamber with the outside,
the first discharge gap is formed at a position overlapping with an injection hole axis (L) of the injection hole or at a position on the tip side of the injection hole axis,
A second discharge gap (G2) is provided between the center electrode and the housing via a surface of the insulator,
With an increase in pressure in the auxiliary combustion chamber, a discharge occurrence position is shifted from the first discharge gap to the second discharge gap.
A spark plug for an internal combustion engine (1). a discharge is generated mainly in the first discharge gap when the pressure in the auxiliary combustion chamber (P) is lower than a first reference pressure (P1) at room temperature, and a discharge is generated mainly in the second discharge gap when the pressure in the auxiliary combustion chamber is higher than a second reference pressure (P2);
The first reference pressure is equal to or less than the second reference pressure.
6. A spark plug for an internal combustion engine according to claim 5. A spark plug for an internal combustion engine according to claim 5 or 6, wherein the center electrode has a radial protrusion (41) that protrudes in the plug radial direction along the tip surface of the insulator.

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