Spark plug for internal combustion engine and internal combustion engine

Abstract

To provide a spark plug for an internal combustion engine which enables improvement of productivity while securing heat radiation performance of a plug cover, and to provide the internal combustion engine.SOLUTION: A spark plug 1 for an internal combustion engine has: an insulator 3; a center electrode 4; a housing 2; a ground electrode 6; and a plug cover 5. The plug cover 5 fits in the inner periphery side of a tip part of the housing 2. A fitting protrusion part 71 and a fitting recessed part 72 which fit with each other are respectively formed at one and the other of an outer peripheral surface of the plug cover 5 and an inner peripheral surface of the housing 2. A fitting part 7, where the fitting protrusion part 71 and the fitting recessed part 72 are fitted, is formed at the base end side relative to a tip 231 of an attachment screw part 23 of the housing 2.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] A spark plug equipped with an auxiliary combustion chamber is disclosed in, for example, Patent Document 1. In such a spark plug, a plug cover is welded to a housing. In consideration of the fixing strength of the plug cover to the housing, welding is generally performed over the entire circumference of the plug. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-184433 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, the process of welding the plug cover to the housing over the entire circumference takes time, and therefore there is room for improvement in terms of productivity of the spark plug. Furthermore, if welding is not performed over the entire circumference of the plug, there is a concern that the heat dissipation ability of the plug cover will decrease.

[0005] The present invention has been made in consideration of the above-mentioned problems, and has an object to provide a spark plug for an internal combustion engine and an internal combustion engine that can improve productivity while ensuring the heat dissipation properties of the plug cover. [Means for solving the problem]

[0006] One aspect of the present invention is a cylindrical insulator (3), a center electrode (4) held on the inner circumferential side of the insulator and protruding from the insulator toward the tip side; a cylindrical housing (2) that holds the insulator on its inner periphery; 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 plug cover is fitted onto the inner periphery of the tip end of the housing, An engaging protrusion (71) and an engaging recess (72) that engage with each other are formed on one and the other of an outer peripheral surface of the plug cover and an inner peripheral surface of the housing, The fitting portion (7) where the fitting protrusion and the fitting recess are fitted together is formed on the base end side of the tip end (231) of the mounting screw portion (23) of the housing. And, The fitting recess is formed over the entire circumferential circumference of the plug. , in spark plugs for 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 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 plug cover is fitted onto the inner periphery of the tip end of the housing, An engaging protrusion (71) and an engaging recess (72) that engage with each other are formed on one and the other of an outer peripheral surface of the plug cover and an inner peripheral surface of the housing, The fitting portion (7) in which the fitting protrusion and the fitting recess are fitted together is formed on the base end side relative to the tip end (231) of the mounting screw portion (23) of the housing, The plug cover is located on a spark plug for an internal combustion engine, the plug cover having a linear expansion coefficient greater than that of the housing.

[0007] The present invention moreover Another aspect is an internal combustion engine (10) equipped with the above-mentioned spark plug for an internal combustion engine, the mounting thread portion is screwed into a female thread portion (82) formed in a plug hole (81) of the internal combustion engine, The fitting portion is located on the base end side of the tip (231) of the screw-fitting portion (83) between the mounting screw portion and the female screw portion, in the internal combustion engine. Effect of the Invention

[0008] In the spark plug for an internal combustion engine, a mating protrusion and a mating recess that fit into each other are formed on one and the other of the outer peripheral surface of the plug cover and the inner peripheral surface of the housing. Therefore, by mating the mating protrusion and the mating recess, the plug cover can be fixed to the housing without welding or the like over the entire circumference. This improves the productivity of the spark plug.

[0009] In addition, the fitting portion is formed closer to the base end than the tip of the mounting screw portion of the housing, which improves the heat dissipation of the plug cover and thus suppresses the temperature rise of the plug cover.

[0010] The internal combustion engine is an internal combustion engine to which the spark plug is attached. Therefore, the productivity of the internal combustion engine can be improved. Furthermore, the fitting portion is located on the base end side relative to the tip end of the threaded portion. This improves the heat dissipation of the plug cover.

[0011] As described above, according to the above aspect, it is possible to provide a spark plug for an internal combustion engine and an internal combustion engine that can improve productivity while ensuring the heat dissipation properties of the plug cover. 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]

[0012] [Figure 1] 4 is an explanatory sectional view of the spark plug for an internal combustion engine according to the first embodiment, taken along line II in FIG. 3; [Diagram 2] FIG. 4 is an explanatory cross-sectional view of a fitting portion in the first embodiment. [Diagram 3] FIG. 3 is a view taken along the line III in FIG. [Figure 4] 4 is a cross-sectional view taken along line IV-IV in FIG. 3 . [Diagram 5]FIG. 4 is an explanatory cross-sectional view of a tip portion of a housing in the first embodiment. [Figure 6] FIG. 4 is a plan view of the tip portion of the housing according to the first embodiment, as viewed from the tip side. [Figure 7] FIG. 4 is an explanatory cross-sectional view showing a state immediately before the plug cover is attached to the housing in the first embodiment. [Figure 8] FIG. 4 is a partially enlarged cross-sectional explanatory view showing a state immediately before the plug cover is attached to the housing in the first embodiment. [Figure 9] FIG. 1 is a cross-sectional explanatory view of an internal combustion engine according to a first embodiment. [Figure 10] FIG. 2 is a partially enlarged cross-sectional explanatory view of the internal combustion engine according to the first embodiment. [Figure 11] FIG. 11 is a plan view of the tip portion of the housing according to the second embodiment, as viewed from the tip side. [Figure 12] FIG. 11 is an explanatory cross-sectional view of a spark plug for an internal combustion engine according to a third embodiment. [Figure 13] FIG. 11 is another explanatory sectional view of the spark plug for an internal combustion engine according to the third embodiment. [Figure 14] FIG. 11 is a cross-sectional explanatory view of an internal combustion engine according to a third embodiment. [Figure 15] FIG. 11 is an explanatory cross-sectional view of a fitting portion in a third embodiment. [Figure 16] FIG. 11 is a partially enlarged cross-sectional explanatory view showing a state immediately before the plug cover is attached to the housing in the third embodiment. [Figure 17] FIG. 11 is an explanatory cross-sectional view of a spark plug according to a fourth embodiment. [Figure 18] FIG. 13 is an explanatory sectional view of another spark plug according to the fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] (Embodiment 1) An embodiment of a spark plug for an internal combustion engine and an internal combustion engine will be described with reference to Figs. A spark plug 1 for an internal combustion engine according to this embodiment includes a cylindrical insulator 3, a center electrode 4, a cylindrical housing 2, a ground electrode 6, and a plug cover 5, as shown in FIGS.

[0014] 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.

[0015] The plug cover 5 is fitted into the inner periphery of the tip portion of the housing 2. A fitting protrusion 71 and a fitting recess 72 that fit into each other are formed on one and the other of the outer periphery of the plug cover 5 and the inner periphery of the housing 2. The fitting portion 7 in which the fitting protrusion 71 and the fitting recess 72 fit into each other is formed on the base end side of the tip 231 of the mounting screw portion 23 of the housing 2.

[0016] In this embodiment, a fitting protrusion 71 is formed on the inner peripheral surface of the housing 2, and a fitting recess 72 is formed on the outer peripheral surface of the plug cover 5. The protruding height of the fitting protrusion 71 is not particularly limited, but may be, for example, about 10 to 50 μm. As shown in FIG. 2, the fitting protrusion 71 may have a substantially semicircular cross-sectional shape taken along a plane including the plug axial direction Z. The dimensions and shape of the fitting recess 72 may be such that they fit the fitting protrusion 71.

[0017] The fitting recess 72 is formed over the entire circumference in the plug circumferential direction. That is, in this embodiment, the fitting recess 72 is formed over the entire circumference in the plug circumferential direction on the outer circumferential surface of the plug cover 5.

[0018] The fitting protrusion 71 is also formed over the entire circumference in the circumferential direction of the plug. That is, in this embodiment, the fitting protrusion 71 is formed over the entire circumference in the circumferential direction of the plug on the inner circumferential surface of the housing 2 as shown in Fig. 6. However, when the fitting recess 72 is formed over the entire circumference in the circumferential direction of the plug, the fitting protrusion 71 may be formed only partially in the circumferential direction of the plug (see Fig. 11).

[0019] 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 disposed in the main combustion chamber of the internal combustion engine. In the plug axial direction Z, the side exposed to the main combustion chamber 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.

[0020] The housing 2 has a mounting thread portion 23 on its outer circumferential surface. The spark plug 1 is attached to the internal combustion engine by screwing the mounting thread portion 23 into a female thread portion 82 formed in a plug hole 81 of the internal combustion engine, as shown in Fig. 9. The mounting thread portion 23 forms a part of a heat dissipation path from the spark plug 1 to peripheral members (such as an engine head 84).

[0021] 5 and 6, in this embodiment, a step portion 22 is formed on the inner periphery side of the tip portion of the housing 2 over the entire circumference in the plug circumferential direction. The width of the step portion 22 in the plug radial direction is approximately equal to the thickness of the plug cover 5. As shown in FIGS. 1 and 2, the base end portion of the plug cover 5 is fitted into this step portion 22. The inner diameter of the inner periphery of the plug cover 5 is approximately equal to the inner diameter of the inner periphery of the housing 2 at the base end side of the step portion 22.

[0022] A fitting convex portion 71 is formed on the inner circumferential surface of the housing 2 at the stepped portion 22. The base end of the stepped portion 22 is located closer to the base end than the tip of the mounting screw portion 23 in the plug axial direction Z. As described above, the fitting convex portion 71 is located closer to the base end than the tip of the mounting screw portion 23 in the plug axial direction Z. In this embodiment, the fitting convex portion 71 is formed at the stepped portion 22 closer to the base end than the middle position in the plug axial direction.

[0023] 1, 2 and 4, with the mating protrusion 71 and the mating recess 72 mated, a part of the base end side of the plug cover 5 is fitted into the step portion 22 of the housing 2. The housing 2 and the plug cover 5 are fixed to each other without being welded. The plug cover 5 is pressed against the housing 2 at the mating portion 7 and a portion adjacent to the base end side thereof. Also, the outer circumferential surface of the plug cover 5 is in contact with the inner circumferential surface of the housing 2 even on the tip side of the mating portion 7.

[0024] The distance in the plug axial direction Z between the base end of the stepped portion 22 and the fitting convex portion 71 is equal to or greater than the distance in the plug axial direction Z between the base end of the plug cover 5 and the fitting concave portion 72. In Figures 1, 2, etc., the distance in the plug axial direction Z between the base end of the stepped portion 22 and the fitting convex portion 71 is shown as being equal to the distance in the plug axial direction Z between the base end of the plug cover 5 and the fitting concave portion 72.

[0025] 1, 3 and 4, the plug cover 5 has a plurality of injection holes 51. The plug cover 5 is generally cup-shaped, and its open end is fitted into the tip end of the housing 2. The plug cover 5 has a cylindrical peripheral wall portion 53 that runs along the open end. A fitting recess 72 is formed on the outer circumferential surface of the base end (i.e., the portion on the open end side) of the peripheral wall portion 53, over the entire circumference in the plug circumferential direction. The fitting recess 72 has a groove shape.

[0026] The plug cover 5 has a larger linear expansion coefficient than the housing 2. In this embodiment, the plug cover 5 is made of nickel or an alloy mainly composed of nickel. The housing 2 is made of an alloy mainly composed of iron. More specifically, the plug cover 5 is made of, for example, a nickel alloy. The housing 2 is made of, for example, low carbon steel. The ground electrode 6 is made of, for example, a nickel alloy.

[0027] Next, a method for manufacturing the spark plug 1 of this embodiment will be described. First, as shown in Figures 5 and 6, a housing 2 having a step portion 22 at its tip portion is prepared. The step portion 22 can be formed by cutting the housing 2 or the like. In addition, a recess 24 is provided in a portion of the plug circumferential direction, cut further from the step portion 22 toward the base end side. Figure 6 is a view of the tip surface of the housing 2 as viewed from the tip side.

[0028] 7, a sub-assembly is prepared in which the center electrode 4, the insulator 3, and the ground electrode 6 are assembled inside the housing 2. The fixed end 61 of the ground electrode 6 is placed in the recess 24 of the housing 2 and joined to the housing 2 by laser welding or the like (see FIG. 4). After that, the size of the discharge gap G between the ground electrode 6 and the center electrode 4 is adjusted.

[0029] Next, the plug cover 5 is attached to the housing 2. As shown in Figures 7 and 8, the above-mentioned fitting recess 72 is formed over the entire circumference in the plug radial direction on the outer circumferential surface of the plug cover 5. In addition, a chamfered portion 52 is formed on the outer circumferential edge of the base end of the plug cover 5.

[0030] 7, 8, and 1, the base end of the plug cover 5 is inserted into the inner periphery of the tip end of the housing 2. At this time, the plug cover 5 is moved toward the base end side relative to the housing 2 along the plug axial direction Z. The outer periphery of the plug cover 5 slides against the inner periphery of the stepped portion 22 of the housing 2. Then, the plug cover 5 is pushed into the housing 2 until the fitting recess 72 of the plug cover 5 fits into the fitting protrusion 71 of the housing 2. As a result, the housing 2 and the plug cover 5 are fitted together as shown in FIGS. 1 to 3, and the spark plug 1 is obtained.

[0031] Next, an internal combustion engine 10 equipped with the spark plug 1 will be described with reference to FIGS. In the internal combustion engine 10, the mounting thread portion 23 is screwed into a female thread portion 82 formed in a spark plug hole 81 of the internal combustion engine. The fitting portion 7 is located on the base end side of a tip end 831 of a screw-in portion 83 between the mounting thread portion 23 and the female thread portion 82.

[0032] In an internal combustion engine 10 equipped with a spark plug 1, a plug cover 5 protrudes into a main combustion chamber 11. The auxiliary combustion chamber 50 and the main combustion chamber 11 communicate with each other through a nozzle hole 51. The plug cover 5 receives heat from the main combustion chamber 11 and the auxiliary combustion chamber 50. The heat of the plug cover 5 is dissipated to an engine head 84 through a screw-fitting portion 83.

[0033] Next, the effects of this embodiment will be described. In the spark plug 1 for an internal combustion engine, a mating protrusion 71 and a mating recess 72 that fit into each other are formed on the inner circumferential surface of the housing 2 and the outer circumferential surface of the plug cover 5, respectively. Therefore, by mating the mating protrusion 71 and the mating recess 72 with each other, the plug cover 5 can be fixed to the housing 2 without welding or the like over the entire circumference. Therefore, the productivity of the spark plug 1 can be improved.

[0034] In addition, the fitting portion 7 is formed on the base end side relative to the tip 231 of the mounting screw portion 23 of the housing 2. This improves the heat dissipation properties of the plug cover 5. This makes it possible to suppress a rise in temperature of the plug cover 5. This makes it easier to suppress pre-ignition of the spark plug 1.

[0035] That is, in the above-described internal combustion engine 10, the fitting portion 7 can be positioned closer to the base end than the tip 831 of the screw portion 83. This improves the heat dissipation of the plug cover 5 and suppresses the occurrence of pre-ignition. Therefore, knocking and the like can be suppressed, particularly during high-load operation, which contributes to improving the output and fuel efficiency of the internal combustion engine.

[0036] In addition, since the fitting portion 7 is formed closer to the base end than the tip 831 of the screw portion 83, it also helps to suppress a rise in temperature of the fitting portion 7 itself. Furthermore, the outer periphery of the fitting portion 7 is supported and reinforced by the engine head 84, which has high strength. This makes it possible to suppress the occurrence of excessive thermal stress in the fitting portion 7. In particular, it is possible to suppress the tensile stress acting on the housing 2 in the vicinity of the fitting portion 7 in the circumferential direction of the plug.

[0037] In this embodiment, in particular, the fitting protrusion 71 is formed on the inner peripheral surface of the housing 2, and the fitting recess 72 is formed on the outer peripheral surface of the plug cover 5. Therefore, the housing 2 and the plug cover 5 can be easily brought into contact over a wider range. As a result, the heat dissipation of the housing 2 can be easily improved. That is, in this embodiment, unlike the third embodiment described later, no gap (see reference numeral 250 in FIG. 15) is provided between the tip of the housing 2 and the fitting protrusion 71. This is easily achieved because the fitting recess 72 is formed in the plug cover 5. When the plug cover 5 has the fitting protrusion 71 as in the third embodiment described later, the above gap is provided in order to suppress interference between the fitting protrusion 71 and the inner peripheral surface of the housing 2 and enable smooth fitting. In this embodiment, it is possible to reduce such a gap as much as possible, and as a result, it is easier to improve the heat dissipation of the plug cover 5.

[0038] In addition, the fitting recess 72 is formed over the entire circumference in the plug circumferential direction. This eliminates the need for circumferential alignment of the plug when assembling the plug cover 5 to the housing 2. This makes it even easier to manufacture the spark plug 1. In addition, by forming both the fitting recess 72 and the fitting protrusion 71 over the entire circumference in the plug circumferential direction, it is possible to improve the fitting strength between the housing 2 and the plug cover 5 and further improve the heat dissipation properties of the plug cover 5.

[0039] The plug cover 5 has a linear expansion coefficient larger than that of the housing 2. The environment in which the spark plug 1 is used is a high-temperature environment, and both the plug cover 5 and the housing 2 thermally expand from their assembled states. Here, since the linear expansion coefficient of the plug cover 5 is larger than that of the housing 2, the plug cover 5 thermally expands more than the housing 2 when the spark plug 1 is used. As a result, the pressure contact force between the plug cover 5 and the housing 2 is stronger near the fitting portion 7. Therefore, the fitting strength between the two can be made stronger during use than when assembled, and vibration resistance and the like can be improved. In addition, the heat dissipation of the plug cover 5 is improved, and therefore the temperature rise of the plug cover 5 during use of the spark plug 1 can be more easily suppressed.

[0040] As described above, according to the present embodiment, it is possible to provide a spark plug for an internal combustion engine and an internal combustion engine that can improve productivity while ensuring the heat dissipation properties of the plug cover.

[0041] (Embodiment 2) In this embodiment, as shown in Fig. 11, the fitting protrusions 71 are scattered in a part of the plug circumferential direction of the housing 2. In this case, the fitting portion 7 is scattered in a part of the plug circumferential direction. In the figure, the fitting protrusions 71 are formed at equal intervals in four places in the plug circumferential direction.

[0042] In this embodiment, the fitting recesses 72 may be formed on the outer peripheral surface of the plug cover 5 over the entire circumferential direction of the plug, as in embodiment 1. The fitting recesses 72 may also be partially scattered at locations corresponding to the fitting protrusions 71.

[0043] The rest is the same as in embodiment 1, and the same effects can be obtained. 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.

[0044] (Embodiment 3) In this embodiment, as shown in FIGS. 12 to 16, a fitting recess 72 is formed on the inner circumferential surface of the housing 2, and a fitting protrusion 71 is formed on the outer circumferential surface of the plug cover 5. As shown in FIG. In this embodiment, the housing 2 has an inner circumferential surface formed with an expanded diameter portion 25 having an inner diameter larger than the periphery of the fitting recess 72 .

[0045] 15 , the inner circumferential surface of the housing 2 has a base end abutment surface 261 and a tip end abutment surface 262 that abut the outer circumferential surface of the plug cover 5 at a position adjacent to the fitting recess 72 in the plug axial direction Z. An expanded diameter portion 25 is formed on the tip side of the tip end abutment surface 262. The expanded diameter portion 25 is formed parallel to the plug axial direction Z up to the tip of the housing 2. A gap 250 is formed in an annular shape between the inner circumferential surface of the expanded diameter portion 25 and the outer circumferential surface of the plug cover 5.

[0046] In this embodiment, when assembling the plug cover 5 to the housing 2, as shown in Fig. 16, the base end of the plug cover 5 is fitted into the inner periphery of the tip end of the housing 2. Because the enlarged diameter portion 25 is provided on the inner periphery of the housing 2, the portion of the plug cover 5 from which the fitting convex portion 71 protrudes can also be easily inserted into the inner periphery of the housing 2. Even if the fitting convex portion 71 slides along the inner periphery of the housing 2, the sliding resistance can be reduced.

[0047] When the fitting convex portion 71 of the plug cover 5 reaches the tip-side abutment surface 262 of the housing 2 (i.e., the base-end side of the enlarged diameter portion 25), at least one of the housing 2 and the plug cover 5 is slightly elastically deformed. This causes the fitting convex portion 71 to climb over the tip-side abutment surface 262 and fit into the fitting recess 72. As a result, as shown in Figures 12 and 13, the fitting convex portion 71 and the fitting recess 72 are fitted together, and the plug cover 5 is assembled to the housing 2. The rest is the same as in the first embodiment, and the same effects as in the first embodiment can be obtained.

[0048] (Embodiment 4) In this embodiment, as shown in FIGS. 17 and 18, a part of the plug cover 5 serves as the ground electrode 6. That is, in this embodiment, a ground electrode (see reference numeral 6 in FIGS. 1 and 4) as a separate member from the housing 2 and the plug cover 5 is not provided.

[0049] 17, a tip portion of the center electrode 4 is disposed close to a bottom wall portion 54 of a plug cover 5, thereby forming a discharge gap G between the center electrode 4 and the bottom wall portion 54. In this case, a part of the bottom wall portion 54 functions as a ground electrode 6.

[0050] 18, a bottom wall portion 54 of a plug cover 5 is provided with a protruding portion 541 protruding from the base end side in the plug axial direction Z. A discharge gap G is formed between the protruding portion 541 and the center electrode 4. In this case, the protruding portion 541 functions as the ground electrode 6. The rest is the same as in the first embodiment.

[0051] In this embodiment, the number of parts can be reduced, and therefore the spark plug 1 can be manufactured with even greater productivity. In addition, the same effects as those of the first embodiment are achieved.

[0052] In the above-mentioned first to fourth embodiments, for example, the housing 2 and the plug cover 5 may be partially welded together. For example, laser welding or the like may be used. However, even in this case, since the spark plug 1 has the fitting portion 7, it is not necessary to perform welding over the entire circumference of the plug in the circumferential direction, and it is sufficient to provide a welded portion only in a part of the circumferential direction of the plug.

[0053] 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]

[0054] 1...spark plug for internal combustion engine, 2...housing, 23...mounting screw portion, 231...tip of (mounting screw portion), 3...insulator, 4...center electrode, 5...plug cover, 50...auxiliary combustion chamber, 6...ground electrode, 71...fitting protrusion, 72...fitting recess

Claims

1. A cylindrical insulator (3); a center electrode (4) held on the inner circumferential side of the insulator and protruding from the insulator toward the tip side; a cylindrical housing (2) that holds the insulator on its inner periphery; 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 plug cover is fitted onto the inner periphery of the tip end of the housing, A mating protrusion (71) and a mating recess (72) that fit into each other are formed on one and the other of an outer peripheral surface of the plug cover and an inner peripheral surface of the housing, respectively; The fitting portion (7) in which the fitting protrusion and the fitting recess are fitted together is formed on the base end side relative to the tip end (231) of the mounting screw portion (23) of the housing, The spark plug for an internal combustion engine, wherein the fitting recess is formed over the entire circumference in the circumferential direction of the plug.

2. 2. The spark plug for an internal combustion engine according to claim 1, wherein the plug cover has a linear expansion coefficient greater than that of the housing.

3. 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 plug cover is fitted onto the inner periphery of the tip end of the housing, A mating protrusion (71) and a mating recess (72) that fit into each other are formed on one and the other of an outer peripheral surface of the plug cover and an inner peripheral surface of the housing, respectively; The fitting portion (7) in which the fitting protrusion and the fitting recess are fitted together is formed on the base end side relative to the tip end (231) of the mounting screw portion (23) of the housing, A spark plug for an internal combustion engine, wherein the plug cover has a linear expansion coefficient greater than that of the housing.

4. 4. The spark plug for an internal combustion engine according to claim 1, wherein the fitting protrusion is formed on an inner circumferential surface of the housing, and the fitting recess is formed on an outer circumferential surface of the plug cover.

5. An internal combustion engine (10) equipped with a spark plug for an internal combustion engine according to any one of claims 1 to 4, The mounting screw portion is screwed into a female screw portion (82) formed in a plug hole (81) of the internal combustion engine, The fitting portion is located on the base end side relative to a tip (831) of a screw-threaded portion (83) between the mounting screw portion and the female screw portion.

Images