Internal combustion engine and spark plug for internal combustion engine

Abstract

To provide an internal combustion engine and a spark plug therefor which can achieve stable ignitability.SOLUTION: Disclosed is an internal combustion engine 10 equipped with a spark plug 1. The spark plug 1 has an insulator 3, a center electrode 4, a housing 2, a ground electrode 6 forming a first discharge gap G1 between itself and the center electrode 4, and a plug cover 5. The plug cover 5 has an injection hole 51 which brings a sub-combustion chamber 50 into communication with the outside. Viewing in a direction perpendicular to both a plug axis direction Z and an injection hole axis L of the injection hole 51, the first discharge gap G1 is formed at a position overlapping the injection hole axis L or at a position further on tip end side than the injection hole axis L. Between the center electrode 4 and the housing 2, a second discharge gap G2 is formed via a surface of the insulator 3. As a load on the internal combustion engine increases, a discharging position moves from the first discharge gap G1 to the second discharge gap G2.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] A spark plug with an auxiliary 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 auxiliary 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 air-fuel mixture in the main combustion chamber, causing combustion. In the spark plug described in Patent Document 1, the discharge gap is provided at a position 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 auxiliary combustion chamber, making it easy to strengthen the flame jet. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-184435 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, if the discharge gap is located far from the nozzle hole, it is likely to cause flame misfire due to the influence of cooling loss. In particular, when the internal combustion engine is under low load, the temperature of the housing and the plug cover is relatively low, so there is a concern of misfire. On the other hand, when the internal combustion engine is under high load, the temperature of the housing and the plug cover is relatively high, misfire is unlikely to occur. Therefore, it is considered that the position of the discharge gap far from the nozzle hole is advantageous in terms of ignition performance. Thus, there is a concern that the ignition performance of the spark plug described in Patent Document 1 varies depending on the operating state of the internal combustion engine.

[0005] The present invention has been made in view of the above problems, and has as its object to provide an internal combustion engine and a spark plug for an internal combustion engine, which are capable of obtaining stable ignition performance. [Means for solving the problem]

[0006] One aspect of the present invention is an internal combustion engine (10) having 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 a tip end 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 (L) 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.

[0007] 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 a tip end 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, The discharge occurrence position is configured to shift from the first discharge gap to the second discharge gap as the pressure in the auxiliary combustion chamber increases. In a spark plug (1) for an internal combustion engine. Effect of the Invention

[0008] 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.

[0009] In the spark plug for an internal combustion engine, the discharge position is configured to shift 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 the engine is under high load, thereby providing stable ignition performance.

[0010] 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. [Brief description of the drawings]

[0011] [Figure 1] 1 is a cross-sectional explanatory view of an internal combustion engine to which a spark plug is attached according to a first embodiment. [Diagram 2] FIG. 2 is a plan view of the spark plug taken along line II in FIG. 1 . [Diagram 3] 3 is a cross-sectional view of the spark plug taken along line III-III in FIG. 1 . [Figure 4] FIG. 4 is an explanatory diagram of a state in which a discharge occurs in the first discharge gap in the first embodiment. [Diagram 5] FIG. 4 is an explanatory diagram of a state in which a discharge occurs in a second discharge gap in the first embodiment. [Figure 6] 4 is a diagram showing the relationship between the load of the internal combustion engine and the discharge voltage in the first embodiment. [Figure 7] FIG. 11 is a cross-sectional explanatory view of an internal combustion engine to which a spark plug is attached according to a second embodiment. [Figure 8] 8 is a cross-sectional view of the spark plug taken along line VIII-VIII in FIG. 7 . [Figure 9] FIG. 11 is a cross-sectional explanatory view of an internal combustion engine according to a third embodiment. [Figure 10] 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. [Figure 11] FIG. 11 is a cross-sectional explanatory view of an internal combustion engine for explaining an air flow in an auxiliary combustion chamber 50 in a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] (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.

[0013] 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 so as to cover the auxiliary combustion chamber 50 in which the first discharge gap G1 is located.

[0014] 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 at which discharge occurs shifts from the first discharge gap G1 to the second discharge gap G2.

[0015] The spark plug 1 of this embodiment can be used as an ignition means in an internal combustion engine of an automobile, a cogeneration system, or the like. One end of the spark plug 1 in the plug axial direction Z is exposed to a main combustion chamber 101 of an 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.

[0016] The spark plug 1 is attached to the internal combustion engine 10 by screwing an attachment 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 protruding on the inner periphery. The insulator 3 has a step 31 protruding 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.

[0017] A center electrode 4 is inserted and held on the inner periphery side 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.

[0018] The ground electrode 6 is formed so as to protrude from a fixed end 61 fixed to the outer circumferential wall of the auxiliary combustion chamber 50 toward the plug central axis C. A part of the ground electrode 6 and the tip end 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 end of the housing 2 by welding or the like. The ground electrode 6 is inclined so as to extend from the fixed end 61 toward the protruding end toward the tip side.

[0019] 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 circumferential direction of the plug. As shown in Fig. 1, an 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.

[0020] 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 disposed on the tip side of 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.

[0021] The internal combustion engine 10 sequentially repeats an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke in accordance with the reciprocating motion of a piston 74 (see FIG. 9 described later) in a cylinder 70. Then, a voltage is applied to the spark plug 1 at a timing near the top dead center of the piston 74 when the piston switches from the compression stroke to the expansion stroke. This causes a spark discharge to occur in either the first discharge gap G1 or the second discharge gap G2, as shown in FIGS. 4 and 5.

[0022] When a voltage is applied to the spark plug 1, a spark discharge occurs in either the first discharge gap G1 or 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 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.

[0023] In any discharge gap, the higher the ambient pressure, the higher the discharge voltage. The greater the load of 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. Moreover, the relationship between the load B and the discharge voltage in the second discharge gap G2 is shown by line V2.

[0024] As can be seen from the figure, in the first discharge gap G1, the rate of increase in the discharge voltage relative to an increase in the load B 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 increases to a certain extent, the rate of increase in the discharge voltage relative to an increase in the load B decreases (see line V2). In this way, the relationships 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.

[0025] When the internal combustion engine 10 is in the 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 in terms of combustibility.

[0026] 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 it easy for misfires to occur. Therefore, generating a discharge in the first discharge gap G1 close to the injection hole 51 is advantageous in terms of combustibility.

[0027] 6, the discharge voltage V2 of the second discharge gap G2 is lower than the discharge voltage V1 of the first discharge gap G1 in the high load region, and the discharge voltage V1 of the first discharge gap G1 is lower than the discharge voltage V2 of the second discharge gap G2 in the low load region. That is, the discharge voltages of the first discharge gap G1 and the second discharge gap G2 are adjusted so that the line V1 and the line V2 intersect. This adjustment can be performed, for example, by adjusting the distance of the second discharge gap G2. That is, 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.

[0028] 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 the 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 the lines V1 and V2 in Fig. 6 intersect at an appropriate position.

[0029] 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 the discharge in the first discharge gap G1 and the discharge in the second discharge gap G2. That is, when the load is higher than the boundary load B0, the discharge occurs in the second discharge gap G2, and when the load is lower than the boundary load B0, the discharge occurs in the first discharge gap G1. However, in reality, in the vicinity of the boundary load B0, the discharge occurs in the first discharge gap G1 or in the second discharge gap G2.

[0030] Specifically, when the load of the internal combustion engine 10 is lower than a 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 a 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.

[0031] 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 assumed that the first discharge gap G1 gradually expands due to wear of the tip of the center electrode 4. In this case, the discharge voltage in 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.

[0032] Note that "discharge occurs mainly in the first discharge gap G1" may mean, for example, that the probability of discharge in the first discharge gap G1 (i.e., the number of discharges in a certain period or in a certain number of cycles) is 10 times or more the probability of discharge in the second discharge gap G2. Similarly, "discharge occurs mainly in the second discharge gap G2" may mean, for example, that the probability of discharge in the second discharge gap G2 is 10 times or more the probability of discharge in the first discharge gap G1.

[0033] In this manner, the internal combustion engine 10 of this embodiment is configured so that the position at which discharge occurs shifts from the first discharge gap G1 to the second discharge gap G2 as the load on the internal combustion engine 10 increases.

[0034] As described above, the higher the load of the internal combustion engine 10, the higher the atmospheric pressure, i.e., the pressure in the auxiliary combustion chamber 50. Therefore, it can be said that the spark plug 1 of this embodiment is configured such 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.

[0035] 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 a 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 a 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.

[0036] 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 in the chamber is varied. The temperature in the chamber is set to room temperature. In this state, when a voltage is applied to the spark plug 1, it is observed whether a discharge occurs mainly in the first discharge gap G1 or mainly in the second discharge gap G2.

[0037] 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.

[0038] It should be noted 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.

[0039] 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 the line V1 and the line V2 is defined as the boundary pressure P0. The boundary pressure P0, the first reference pressure P1, and the second reference pressure P2 satisfy P1 ≦ P0 ≦ P2.

[0040] Unless otherwise specified, the pressure in the pre-combustion chamber 50 refers to the pressure in the pre-combustion chamber 50 at the time when the spark plug 1 ignites.

[0041] In this embodiment, for example, a nickel alloy can be used as the material of the center electrode 4. 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.

[0042] In this embodiment, no precious metal tip is provided on the portion of either the center electrode 4 or the ground electrode 6 facing the first discharge gap G1. However, a precious metal tip may be provided on at least one of the center electrode 4 and the ground electrode 6 facing the first discharge gap G1. For example, an iridium alloy, a platinum alloy, or the like may be used as the precious metal tip. By providing a precious metal tip on the portion facing the first discharge gap G1, the expansion of the first discharge gap G1 can be suppressed. This makes it possible to suppress a change in the discharge voltage in the first discharge gap G1.

[0043] In addition, in this embodiment, the injection hole 51 is formed so that the injection hole axis L is directed toward the plug central axis C. However, the injection hole may be formed so that the injection hole axis is deviated from the plug central axis. For example, the injection hole may be formed so that the air flow that flows from the injection hole into the auxiliary combustion chamber creates a swirl flow that swirls around the plug in the auxiliary combustion chamber.

[0044] Next, the effects of this embodiment will be described. The internal combustion engine 10 is configured such that the position where 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 where the discharge occurs is the first discharge gap G1, and when the load of the internal combustion engine 10 is relatively high, the position where the discharge occurs is the second discharge gap G2.

[0045] As a result, under relatively low load conditions, as shown in Fig. 4, an initial flame is formed near first discharge gap G1 which is relatively close to nozzle hole 51, and a flame jet can be ejected from nozzle hole 51 while suppressing misfire. Under relatively high load conditions, as shown in Fig. 5, an initial flame is formed near second discharge gap G2 which is relatively far from nozzle hole 51, and a sufficiently grown flame can be ejected from nozzle hole 51 as a flame jet.

[0046] 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.

[0047] When the load of the internal combustion engine 10 is lower than a 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 a second reference load B2, discharge occurs mainly in the second discharge gap G2. This ensures that a flame jet is ejected into the main combustion chamber 101 both at a predetermined low load and at a predetermined high load.

[0048] That is, for example, by adjusting the magnitude 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.

[0049] Furthermore, 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 with an increase in pressure in the auxiliary combustion chamber 50. This allows the flame jet to be effectively ejected into the main combustion chamber 101 whether the internal combustion engine 10 is operating at a low load or a high load.

[0050] Furthermore, 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 makes it possible to reliably eject the flame jet into the main combustion chamber 101 both at a predetermined low load and at a predetermined high load.

[0051] As described above, according to the present embodiment, 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.

[0052] (Embodiment 2) In this embodiment, as shown in FIGS. 7 and 8, the center electrode 4 has a radial protrusion 41. As shown in FIG. 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.

[0053] In this embodiment, the radial protruding portion 41 is formed in an annular shape over the entire circumference in the circumferential direction of the plug, as shown in Fig. 8. However, the radial protruding portion 41 may be configured to protrude only in a part of the circumferential direction of the plug. In addition, the distance between the outer peripheral end of the radial protruding portion 41 and the inner peripheral surface of the housing 2 is longer than the distance of the first discharge gap G1.

[0054] The rest is the same as in embodiment 1. Note that, among the symbols used in embodiment 2 and onwards, the same symbols used in the previous embodiments represent the same components, etc. as in the previous embodiments, unless otherwise specified.

[0055] 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, the length of the second discharge gap G2 can be easily adjusted. In addition, the same effects as those of the first embodiment are achieved.

[0056] (Embodiment 3) In this embodiment, as shown in FIGS. 9 to 11, the fixed end portion 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).

[0057] 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 in 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, and each of the intake port 72 and the exhaust valve 73 is provided. 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 Figs. 9 and 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.

[0058] The intake port 721 and the exhaust port 731 are inclined with respect to the forward and backward movement direction of the piston 74 so that the opening direction of the intake port 721 and the exhaust port 731 is directed toward the central axis of the main combustion chamber 101. In addition, the base end surface of the main combustion chamber 101 is inclined so as to be directed toward the tip side as it moves away from the spark plug 1.

[0059] In the internal combustion engine 10, an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke are repeated in sequence in accordance 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, the gas in the main combustion chamber 101 is exhausted from the exhaust port 731. Due to the way in which the airflow is introduced during the intake stroke, a predetermined airflow is formed in the main combustion chamber 101, and this airflow remains even during the compression stroke.

[0060] 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. In the vicinity of the tip of the spark plug 1 in the main combustion chamber 101, this airflow AF is directed from the intake valve 72 side to the exhaust valve 73 side, 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 intermediate position between the two intake ports 721 to the intermediate position between the two exhaust ports 731 is the main airflow in the vicinity of the tip of the spark plug 1.

[0061] 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, unless otherwise specified, when we say "airflow in the main combustion chamber 101", we mean 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.

[0062] 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 Figs. 9 and 10, the nozzle 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 Fig. 11, the airflow F is mainly introduced from the nozzle 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 opposite side 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 same effects as those of the first embodiment are achieved.

[0063] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments without departing from the gist of the present invention. [Explanation of symbols]

[0064] Reference Signs List 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 axial direction

Claims

1. 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.

2. 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.

3. 3. The internal combustion engine according to claim 1, wherein the center electrode has a radial protrusion (41) that protrudes in a plug radial direction along a tip end surface of the insulator.

4. 4. The internal combustion engine according to claim 1, wherein the ground electrode is formed so as to protrude from a fixed end portion (61) fixed to an outer circumferential wall portion of the auxiliary combustion chamber toward a central axis of the plug, a part of the ground electrode and a tip end portion of the central electrode face each other in the plug axial direction with the first discharge gap interposed therebetween, and the fixed end portion faces an intake valve (72) side as viewed from the plug axial direction.

5. 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).

6. 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.

7. 7. The spark plug for an internal combustion engine according to claim 5, wherein the center electrode has a radial protrusion (41) protruding in a plug radial direction along a tip end surface of the insulator.

Images