Spark plug

Abstract

To provide a spark plug capable of suppressing the leakage of a gas in a combustion chamber of an internal combustion engine to the outside.SOLUTION: A spark plug 1 is used for an internal combustion engine which uses a hydrogen gas as a fuel. The spark plug 1 comprises a packing, a filler 6 consisting of a talc powder as a main constituent, and an annular elastic member 43. The filler 6 fills an annular space 60 which is formed closer to a proximal end side Z2 than the packing. The annular elastic member 43 is disposed between the annular space 60 and the packing in a plug axis direction Z. The packing and the annular elastic member 43 seals a gap between a housing 2 and an insulator 3. A proximal end of the housing 2 includes a caulking part 23 which presses the insulator 3 to a distal end side Z1. A gap G1 formed between the caulking part 23 and the insulator 3 is filled with a liquid-state sealing insulation material 42 which seals the gap between the housing 2 and the insulator 3.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a spark plug. [Background technology]

[0002] Spark plugs are used as ignition means in internal combustion engines such as vehicle engines. The spark plug is arranged so that its tip side is exposed to a combustion chamber of the internal combustion engine, where high pressure exists.

[0003] The spark plug described in Patent Document 1 has a step on the tip side of the insulator engaged with a step on the housing, and also has an elastic member interposed between the outer circumferential surface of the insulator and the inner circumferential surface of the housing, in order to prevent airtight leakage of high-pressure gas from the internal combustion engine through the spark plug. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2008-078059 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the case of an internal combustion engine fueled by hydrogen gas, which is easily diffused, there is a risk that leakage of gas in the combustion chamber to the outside cannot be sufficiently prevented even when an elastic member is interposed between the insulator and the housing as in the spark plug described in Patent Document 1. Therefore, it can be said that there is room for further improvement in the spark plug described in Patent Document 1 from the viewpoint of preventing leakage of gas in the combustion chamber to the outside.

[0006] The present invention has been made in view of the above-mentioned problems, and has an object to provide a spark plug that can suppress leakage of gas in the combustion chamber of an internal combustion engine to the outside. [Means for solving the problem]

[0007] A first aspect of the present invention is a spark plug (1) for use in an internal combustion engine fueled by hydrogen gas, A cylindrical insulator (3); A cylindrical housing (2) that holds the insulator on its inner periphery; an annular packing (41) sandwiched in the plug axial direction (Z) by a first housing opposing surface (21) formed on an inner circumferential surface of the housing and a first insulator opposing surface (31) formed on an outer circumferential surface of the insulator at a position closer to a base end (Z2) than the first housing opposing surface, a filler (6) mainly made of talc powder, which is filled in an annular space (60) formed on the base end side of the packing and between an inner peripheral surface of the base end of the housing and an outer peripheral surface of the insulator; an annular elastic member (43) that is sandwiched in the plug axial direction by a second housing opposing surface (22) formed on an inner circumferential surface of the housing and a second insulator opposing surface (32) formed on an outer circumferential surface of the insulator at a position closer to the base end than the second housing opposing surface, and that is disposed between the annular space and the packing in the plug axial direction, the packing and the annular elastic member each provide a seal between the housing and the insulator, the filler is filled between a tip-side annular member (61) disposed at a tip portion of the annular space and a base-side annular member (62) disposed at a base end portion of the annular space, The base end of the housing has a crimping portion (23) that presses the insulator toward the tip side (Z1), the crimping portion presses the base end side annular member directly toward the tip end side, thereby pressing the insulator toward the tip end side via the base end side annular member, the filler, and the tip end side annular member, In the spark plug, a gap (G1) formed between the crimped portion and the insulator is filled with a liquid sealing insulating material (42) that seals between the housing and the insulator.

[0008] A second aspect of the present invention is a spark plug (1) for use in an internal combustion engine fueled by hydrogen gas, A cylindrical insulator (3); A cylindrical housing (2) that holds the insulator on its inner periphery; an annular packing (41) sandwiched in the plug axial direction (Z) by a first housing opposing surface (21) formed on an inner circumferential surface of the housing and a first insulator opposing surface (31) formed on an outer circumferential surface of the insulator at a position closer to a base end (Z2) than the first housing opposing surface, a filler (6) mainly made of talc powder, the filler filling an annular space (60) formed on the base end side of the packing and between an inner peripheral surface of the base end of the housing and an outer peripheral surface of the insulator, The packing seals between the housing and the insulator, the filler is filled between a tip-side annular member (61) disposed at a tip portion of the annular space and a base-side annular member (62) disposed at a base end portion of the annular space, The base end of the housing has a crimping portion (23) that presses the insulator toward the tip side (Z1), the crimping portion presses the base end side annular member directly toward the tip end side, thereby pressing the insulator toward the tip end side via the base end side annular member, the filler, and the tip end side annular member, The gaps between the talc powder constituting the filler are filled with a liquid filler insulating material (420) in the spark plug. Effect of the Invention

[0009] The spark plug of the first aspect includes an annular elastic member and a liquid sealing insulating material that seal between the housing and the insulator, and thus can prevent gas in the combustion chamber of the internal combustion engine from leaking to the outside through the gap between the housing and the insulator.

[0010] In the spark plug of the second aspect, the liquid filling insulating material fills the gaps between the talc powder constituting the filler, thereby making it possible to prevent gas in the combustion chamber of the internal combustion engine from leaking to the outside through a gap between the housing and the insulator.

[0011] As described above, according to the above aspect, it is possible to provide a spark plug that can suppress leakage of gas in the combustion chamber of an internal combustion engine to the outside. 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] 1 is a cross-sectional view of a spark plug according to a first embodiment taken along an axial direction of the spark plug; [Diagram 2] FIG. 3 is a cross-sectional view taken along the axial direction of the plug in the vicinity of the packing in the first embodiment. [Diagram 3] 4 is a cross-sectional view taken along the axial direction of the plug in the vicinity of a crimped portion in the first embodiment. FIG. [Figure 4] 6 is a graph showing the relationship between the width of the annular elastic member and the compression rate and the filling rate in Experimental Example 1. [Diagram 5] FIG. 11 is a cross-sectional view taken along the axial direction of the plug in the vicinity of the crimped portion in the second embodiment. [Figure 6] FIG. 11 is a cross-sectional view taken along the axial direction of the plug in the vicinity of the crimped portion in the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] (Embodiment 1) An embodiment of a spark plug will be described with reference to FIGS. The spark plug 1 of this embodiment is used in an internal combustion engine (not shown) that uses hydrogen gas as fuel. As shown in Figures 1 to 3, the spark plug 1 has a cylindrical insulator 3, a cylindrical housing 2, an annular packing 41, a filler 6 mainly made of talc powder, and an annular elastic member 43. The housing 2 holds the insulator 3 on its inner periphery.

[0014] 1 and 2, the packing 41 is sandwiched in the plug axial direction Z by the first housing opposing surface 21 and the first insulator opposing surface 31 which face each other. The first housing opposing surface 21 is formed on the inner circumferential surface of the housing 2. The first insulator opposing surface 31 is formed on the outer circumferential surface of the insulator 3 on the base end side Z2 from the first housing opposing surface 21.

[0015] 3, the filler 6 is filled in the annular space 60. The annular space 60 is formed on the base end side Z2 of the packing 41, as shown in Fig. 1, and is formed between the inner circumferential surface of the base end of the housing 2 and the outer circumferential surface of the insulator 3. The filler 6 is filled between a tip side annular member 61 arranged at the tip end of the annular space 60 and a base side annular member 62 arranged at the base end of the annular space 60, as shown in Fig. 3.

[0016] The annular elastic member 43 is sandwiched in the plug axial direction Z by the second housing opposing surface 22 and the second insulator opposing surface 32 which face each other. The second housing opposing surface 22 is formed on the inner circumferential surface of the housing 2. The second insulator opposing surface 32 is formed on the outer circumferential surface of the insulator 3 on the base end side Z2 from the second housing opposing surface 22. As shown in FIG. 1 , the annular elastic member 43 is disposed between the annular space 60 and the packing 41 in the plug axial direction Z. The packing 41 and the annular elastic member 43 each seal between the housing 2 and the insulator 3.

[0017] The base end of the housing 2 has a crimping portion 23 that presses the insulator 3 toward the tip side Z1. The crimping portion 23 presses the base end side annular member 62 directly toward the tip side Z1, thereby pressing the insulator 3 toward the tip side Z1 via the base end side annular member 62, the filler 6, and the tip side annular member 61. As shown in Figs. 1 and 3, the gap G1 formed between the crimping portion 23 and the insulator 3 is filled with a liquid sealing insulating material 42 that seals the gap between the housing 2 and the insulator 3.

[0018] The spark plug 1 of this embodiment can be used as an ignition means in an internal combustion engine of an automobile or the like that uses hydrogen gas as fuel, for example. The threaded portion 24 of the housing 2 is screwed into a female threaded portion of a plug hole in a cylinder head (not shown), and the spark plug 1 is attached to the internal combustion engine. One end of the axial direction Z of the spark plug 1 is disposed in a combustion chamber (not shown) of the internal combustion engine. In the axial direction Z of the spark plug 1, the side exposed to the combustion chamber is called the tip side Z1, and the opposite side is called the base side Z2. The axial direction Z of the spark plug 1 is also referred to as the plug axial direction Z as appropriate. The plug central axis C means the central axis C of the spark plug 1. The plug radial direction means the radial direction of a circle centered on the plug central axis C on a plane perpendicular to the plug central axis C. The plug circumferential direction is the direction along the circumference centered on the plug central axis C.

[0019] 1, the spark plug 1 has a center electrode 11 and a ground electrode 12. The center electrode 11 is held on the inner peripheral side of the insulator 3 and is exposed from the insulator 3 to a front end side Z1. The ground electrode 12 forms a discharge gap G2 between itself and the center electrode 11 and is joined to the front end portion of the housing 2. In this embodiment, the plug central axis C is also the central axis of the center electrode 11, the housing 2, and the insulator 3.

[0020] The insulator 3 protrudes toward the base end side Z2 from the crimped portion 23 formed at the base end of the housing 2. The insulator 3 has a tapered tip portion 33 that is tapered toward the tip side Z1 from the packing 41. The tapered tip portion 33 is formed on the tip side Z1 from the first insulator facing surface 31.

[0021] A first glass seal layer 13, a resistor 14, a second glass seal layer 15, and a terminal metal fitting 16 are disposed on the base end side Z2 of the center electrode 11 inside the insulator 3. The first glass seal layer 13 and the second glass seal layer 15 may be made of glass containing copper powder, for example. The resistor 14 may be made of an aggregate in which a conductive material such as a carbon material is dispersed in a base material containing a glass material and an aggregate. The end of the terminal metal fitting 16 on the base end side Z2 is exposed from the insulator 3. The spark plug 1 is electrically connected to an ignition coil (not shown) at the terminal metal fitting 16.

[0022] 1 and 2, an inner protruding portion 210 that protrudes inward in the plug radial direction is formed on the inner circumferential surface of the tip portion of the housing 2. The inner protruding portion 210 is formed in an annular shape. The insulator 3 is engaged with the inner protruding portion 210 in the plug axial direction Z via a packing 41. In other words, a first housing opposing surface 21 is formed at the base end portion of the inner protruding portion 210. The first housing opposing surface 21 engages the insulator 3 from the tip side Z1 via the packing 41.

[0023] The first housing opposing surface 21 is formed so as to follow the first insulator opposing surface 31. The first housing opposing surface 21 and the first insulator opposing surface 31 are each formed so as to extend toward the base end side Z2 as they extend radially outward in the plug radial direction.

[0024] The packing 41 is in pressure contact with both the housing 2 and the insulator 3 over the entire circumference in the circumferential direction of the plug. The packing 41 may be made of a metal such as an alloy containing iron as a main component.

[0025] 3, an insulator protruding portion 34 that protrudes outward in the plug radial direction is formed on the outer circumferential surface of the insulator 3. The insulator protruding portion 34 is formed in an annular shape. The insulator protruding portion 34 covers the tip side Z1 of the annular space 60 and has a second insulator facing surface 32 at its tip.

[0026] The second housing facing surface 22 is formed to follow the second insulator facing surface 32. The second housing facing surface 22 and the second insulator facing surface 32 are each formed to be closer to the base end side Z2 as they move outward in the plug radial direction. In this embodiment, the maximum height Rz of the surface roughness of the second housing facing surface 22 and the second insulator facing surface 32 is 20 μm or less.

[0027] The second housing facing surface 22 and the second insulator facing surface 32 form an elastic member arrangement space 430 in which the annular elastic member 43 is arranged. The annular elastic member 43 is compressed in the plug axial direction Z by the second housing facing surface 22 and the second insulator facing surface 32. The annular elastic member 43 sandwiched between the second housing facing surface 22 and the second insulator facing surface 32 has an elliptical cross section perpendicular to its extending direction. In the cross section of the annular elastic member 43 shown in FIG. 3, the opposing direction between the second housing facing surface 22 and the second insulator facing surface 32 is the minor axis.

[0028] In a free state, the annular elastic member 43 has a circular cross section perpendicular to its extending direction. In this embodiment, the width of the annular elastic member 43 (not shown) in a free state is 0.95 to 1.25 mm. Here, the width of the annular elastic member 43 means the diameter of the cross section perpendicular to the extending direction of the annular elastic member 43.

[0029] The annular elastic member 43 is in pressure contact with both the housing 2 and the insulator 3 over the entire circumference in the plug circumferential direction. The annular elastic member 43 is an elastomer having insulating properties. In this embodiment, the annular elastic member 43 is made of fluororubber. The Young's modulus of the annular elastic member 43 is 0.3 GPa or less.

[0030] The compression ratio of the annular elastic member 43 is 10 to 30%. Here, the compression ratio means the ratio of the difference between the width of the annular elastic member 43 in a free state and the length L3 of the minor axis of the cross section of the annular elastic member 43 in a compressed state shown in FIG. 3 to the width of the annular elastic member 43 in a free state. That is, when the width of the annular elastic member 43 in a free state is 1 mm and the length L3 of the annular elastic member 43 in a compressed state is 0.9 mm, the compression ratio is 10%. The length L3 is also the length of the annular elastic member 43 in a compressed state in the opposing direction between the second housing opposing surface 22 and the second insulator opposing surface 32. The length L3 is also the length of the minor axis of the cross section of the annular elastic member 43 in a compressed state perpendicular to its extending direction.

[0031] In this embodiment, the filling rate of the annular elastic member 43 is 85% or less. Here, the filling rate means the ratio of the area of ​​the annular elastic member 43 to the area of ​​the elastic member arrangement space 430 in a cross section including the plug central axis C as shown in FIG.

[0032] An annular space 60 is formed on the base end side Z2 of the elastic member disposition space 430. The filler 6 filled in the annular space 60 is compressed in the plug axial direction Z by a tip end side annular member 61 and a base end side annular member 62. In this embodiment, the tip end side annular member 61 and the base end side annular member 62 are each made of metal.

[0033] A gap G1 formed on the base end side Z2 of the base end side annular member 62 is filled with an insulating sealing insulator 42. In this embodiment, the gap G1 is formed by being surrounded by the crimped portion 23, the outer circumferential surface of the insulator 3, and the base end side annular member 62. The gap G1 opens to the base end side Z2.

[0034] The sealing insulating material 42 fills the gap G1 over the entire circumference in the plug circumferential direction. A portion of the sealing insulating material 42 is located on the base end side Z2 from the base end of the crimped portion 23 of the housing 2. The sealing insulating material 42 fills the gap G1 so as to cover the entire inner circumferential surface of the crimped portion 23. The base end of the crimped portion 23 and the outer circumferential surface of the insulator 3 face each other in the plug radial direction with the sealing insulating material 42 interposed therebetween.

[0035] The contact portion between the outer circumferential surface of the insulator 3 and the base end side annular member 62 and the contact portion between the housing 2 and the base end side annular member 62 are each covered with a sealing insulating material 42 from the base end side Z2.

[0036] In this embodiment, the sealing insulating material 42 is made of silicone oil. The sealing insulating material 42 is liquid when installed in the internal combustion engine. That is, for example, the sealing insulating material 42 is liquid at the temperature of the sealing insulating material 42 when the internal combustion engine is stopped and at the temperature of the sealing insulating material 42 when the internal combustion engine is operating. In this embodiment, the sealing insulating material 42 is liquid at 0 to 200°C. Furthermore, the sealing insulating material 42 has a viscosity of 1 to 1000 mPa s at 0 to 200°C.

[0037] Moreover, the crimped portion 23 of the housing 2 is formed so as to bend inward in the plug radial direction as it approaches the base end side Z2. The crimped portion 23 is bent inward in the plug radial direction. The crimped portion 23 is provided so that at least a portion of the crimped portion 23 overlaps with the tip side annular member 61, the filler 6, and the base end side annular member 62 when viewed from the plug axial direction Z (not shown). The crimped portion 23 is provided over the entire circumference in the plug circumferential direction.

[0038] As shown in FIG. 1, a minute gap G3 is formed between the annular elastic member 43 and the packing 41 in the plug axial direction Z, and between the inner peripheral surface of the housing 2 and the outer peripheral surface of the insulator 3. The gap G3 communicates with the elastic member arrangement space 430. Also, as shown in FIG. 1 and FIG. 3, a minute gap G4 is formed between the elastic member arrangement space 430 and the annular space 60 in the plug axial direction Z, and between the inner peripheral surface of the housing 2 and the outer peripheral surface of the insulator 3. The gap G4 is formed from the elastic member arrangement space 430 to the annular space 60. The gap G4 communicates with both the elastic member arrangement space 430 and the annular space 60. The width of the gap G3 and the gap G4 in the plug radial direction can be, for example, 0.3 mm or less. Also, the elastic member arrangement space 430 does not include the gap G3 and the gap G4 that communicate with the elastic member arrangement space 430.

[0039] 2, the gap G3 is filled with a liquid gap sealing material 421. The gap sealing material 421 seals the gap between the housing 2 and the insulator 3. In this embodiment, the gap sealing material 421 is made of silicone oil.

[0040] 1, the ratio of length L1 to distance L2 is preferably 1 / 20 to 1 / 4. Length L1 is the length of tapered tip portion 33 in plug axial direction Z. Distance L2 is the distance between packing 41 and crimped portion 23 in plug axial direction Z. More preferably, the ratio of length L1 to distance L2 is 1 / 15 to 1 / 8.

[0041] Next, a method for manufacturing the spark plug 1 of this embodiment will be described. In manufacturing the spark plug 1, first, a rod-shaped ground electrode (not shown) before bending is welded to the tip of the housing 2 (not shown) before the insulator 3 and the like are assembled. Then, as shown in FIG. 1, this rod-shaped ground electrode is bent radially inwardly.

[0042] Next, the insulator 3 and the like are assembled to the housing 2. Specifically, the insulator 3, having the center electrode 11, the first glass seal layer 13, the resistor 14, the second glass seal layer 15, and the terminal fitting 16 arranged on the inside, is inserted into the housing 2 from the base end side Z2. The insulator 3 is inserted into the housing 2 with the gap sealing material 421 applied to a part of its outer circumferential surface. At this time, a packing 41 is disposed between the first housing facing surface 21 and the first insulator facing surface 31, and an annular elastic member 43 is disposed between the second housing facing surface 22 and the second insulator facing surface 32.

[0043] Next, the front end annular member 61, the filler 6, and the base end annular member 62 are arranged in the annular space 60. Thereafter, the pre-bent crimping portion (not shown) erected along the plug axial direction Z is bent toward the inside in the plug radial direction, and the insulator 3 is pressed toward the front end side Z1 via the base end annular member 62 and the like, and crimped. As a result, the insulator 3 moves toward the front end side Z1 with respect to the housing 2, and a load in the plug axial direction Z is applied to each of the packing 41, the annular elastic member 43, and the filler 6. In addition, by crimping the crimping portion 23, each of the packing 41, the annular elastic member 43, and the filler 6 is compressed in the plug axial direction Z, and the gap between the housing 2 and the insulator 3 is sealed by each of the filler 6, the packing 41, and the annular elastic member 43. In addition, the gap between the housing 2 and the insulator 3 is sealed by the gap sealing material 421 applied to the outer circumferential surface of the insulator 3.

[0044] Next, the gap G1 remaining after bending the crimped portion 23 is filled with the sealing insulating material 42. If necessary, the ground electrode 12 fixed to the housing 2 is slightly deformed to finely adjust the discharge gap G2 to an appropriate distance. In this manner, the spark plug 1 of this embodiment can be manufactured as shown in Figs. 1 to 3.

[0045] Next, the effects of this embodiment will be described. The spark plug 1 of this embodiment includes an annular elastic member 43 and a liquid sealing insulating material 42 that seal between the housing 2 and the insulator 3. This makes it possible to prevent gas in the combustion chamber of the internal combustion engine from passing between the housing 2 and the insulator 3 and leaking to the outside.

[0046] Hydrogen gas has a smaller density and molecular diameter than other gases, and is easily diffused. Therefore, an internal combustion engine using hydrogen gas as fuel is required to maintain sufficient airtightness so that flammable hydrogen gas does not leak to the outside through the spark plug 1. In other words, an internal combustion engine using hydrogen gas as fuel needs to have a higher airtightness of the spark plug 1 than an internal combustion engine using gasoline or the like as fuel. Therefore, the spark plug 1 of this embodiment includes an annular elastic member 43 and a liquid sealing insulating material 42. Therefore, it is possible to prevent the gas in the combustion chamber, including hydrogen gas, from leaking to the outside through the gap between the housing 2 and the insulator 3. Therefore, even if the airtightness of the packing 41 is reduced, it is possible to prevent the gas in the combustion chamber, including hydrogen gas and water vapor, from leaking to the outside.

[0047] The filler 6 is mainly composed of flaky talc powder. In the filler 6, the flaky talc powder is arranged so as to be piled up on top of each other. Therefore, in the filler 6 compressed by the crimping portion 23, a minute gap is formed between the talc powder. As a result, when the spark plug 1 receives pressure caused by combustion in the combustion chamber of the internal combustion engine, the filler 6 can expand and contract like a spring, and the stress applied to the crimping portion 23 by the pressure during combustion can be reduced. On the other hand, if gaps are formed between the talc powder to reduce the stress of the crimping portion 23, the airtightness of the filler 6 is likely to decrease by the amount of the gaps formed. On the other hand, if the force applied to the crimping portion 23 is too large in order to reduce the amount of the gaps between the talc powder, the airtightness of the filler 6 is improved, but the filler 6 is difficult to expand and contract. Therefore, it becomes difficult to sufficiently reduce the stress on the crimping portion 23, and the stress is likely to be applied to the housing 2. Therefore, in the spark plug 1 of this embodiment, the gap G1 is filled with the sealing insulating material 42. Therefore, during manufacturing, the sealing insulating material 42 can improve the airtightness between the housing 2 and the insulator 3 without applying too much force to the crimped portion 23. Therefore, it is possible to sufficiently reduce the stress applied to the crimped portion 23 and suppress the gas in the combustion chamber from leaking to the outside.

[0048] In addition, as described above, hydrogen gas is prone to diffusion and may leak even from a small gap. Therefore, the spark plug 1 of this embodiment is provided with a liquid sealing insulating material 42. The liquid sealing insulating material 42 easily penetrates into slight irregularities formed on the inner circumferential surface of the housing 2 and the outer circumferential surface of the insulator 3, and into small gaps between the housing 2 and the insulator 3. This makes it easy to reliably seal the gap between the housing 2 and the insulator 3.

[0049] Furthermore, by filling the gap G1 with the sealing insulating material 42, it is possible to suppress the occurrence of corona discharge between the crimped portion 23 and the insulator 3, and between the housing 2 and a plug cap portion (not shown) of the ignition coil attached to the base end of the spark plug 1. Therefore, even if gas in the combustion chamber leaks to the periphery of the crimped portion 23, it is possible to suppress ignition of hydrogen gas due to corona discharge.

[0050] The sealing insulating material 42 is made of silicone oil. Therefore, the heat resistance of the sealing insulating material 42 can be improved. Therefore, even if the high-temperature gas in the combustion chamber reaches the annular space 60, the sealing insulating material 42 can be prevented from vaporizing and disappearing. As a result, the gap between the housing 2 and the insulator 3 can be sufficiently sealed, and corona discharge can be sufficiently prevented from occurring between the housing 2 and the insulator 3 and between the housing 2 and the plug cap of the ignition coil. Therefore, even if gas in the combustion chamber leaks into a plug hole (not shown) of an internal combustion engine in which the base end of the spark plug 1 is disposed, the gas from the combustion chamber in the plug hole can be prevented from igniting due to corona discharge.

[0051] In this embodiment, the contact portion between the outer circumferential surface of the insulator 3 and the base-end side annular member 62 and the contact portion between the housing 2 and the base-end side annular member 62 are each covered from the base-end side Z2 by the sealing insulating material 42. This makes it possible to further prevent gas in the combustion chamber from leaking to the outside through between the housing 2 and the insulator 3.

[0052] In general, in an internal combustion engine, the temperature of the fastening portion between the threaded portion 24 of the spark plug 1 and the female threaded portion of the plug hole is about 100 to 200°C. Therefore, in the spark plug 1 of this embodiment, the annular elastic member 43 is made of fluororubber. This makes it possible to increase the heat resistance of the annular elastic member 43 located on the base end side Z2 from the threaded portion 24, and to reduce the hydrogen gas permeability of the annular elastic member 43. Therefore, even in an environment of 200°C or higher, it is possible to improve the sealing performance between the housing 2 and the insulator 3 while suppressing deterioration of the annular elastic member 43. In addition, by improving the sealing performance of the annular elastic member 43, it is possible to sufficiently suppress the deterioration of the filler 6 mainly composed of talc powder due to the gas in the combustion chamber.

[0053] Hydrogen gas has a high combustion speed and the gas temperature in the combustion chamber is likely to become high. Therefore, the ratio of the length L1 to the distance L2 is preferably 1 / 20 to 1 / 4. In this case, the length L1 of the tapered tip portion 33 is likely to be short, and the heat dissipation properties of the insulator 3 and the center electrode 11 can be improved. As a result, overheating of the insulator 3 and the center electrode 11 can be suppressed, and the occurrence of pre-ignition, etc. can be suppressed.

[0054] On the other hand, when the length L1 is shortened, the distance L2 tends to be long. In other words, the distance from the crimped portion 23 to the packing 41 tends to be long. And, the longer the distance L2, the less the pressing force toward the tip side Z1 when the crimped portion 23 is crimped is transmitted to the packing 41. Therefore, depending on how the crimped portion 23 is crimped, the airtightness of the packing 41 may be reduced. Therefore, the spark plug 1 of this embodiment includes the annular elastic member 43 and the sealing insulator 42. Therefore, even if the airtightness of the packing 41 is reduced, the leakage of gas from the combustion chamber to the outside can be sufficiently suppressed.

[0055] The compression rate of the annular elastic member 43 is 10 to 30%. Therefore, leakage of gas in the combustion chamber to the outside can be further suppressed, and deterioration of the annular elastic member 43 can be further suppressed. That is, by setting the compression rate of the annular elastic member 43 to 10% or more, the sealing performance of the annular elastic member 43 can be sufficiently ensured. Furthermore, by setting the compression rate of the annular elastic member 43 to 30% or less, excessive deformation of the annular elastic member 43 can be suppressed, and the life of the annular elastic member 43 can be extended. As a result, leakage of gas in the combustion chamber to the outside can be suppressed for a long period of time.

[0056] The filling rate of the annular elastic member 43 is 85% or less. This makes it possible to prevent the annular elastic member 43 from being damaged during, for example, the assembly of the spark plug 1. As a result, the airtightness of the annular elastic member 43 can be sufficiently ensured.

[0057] Furthermore, the gap G3 is filled with a liquid gap sealing material 421. Therefore, leakage of the gas in the combustion chamber to the outside can be further suppressed. Even if the gas in the combustion chamber passes through the packing 41, the gas in the combustion chamber can be suppressed from moving to the annular elastic member 43. Therefore, deterioration of the annular elastic member 43 can be suppressed. As a result, leakage of the gas in the combustion chamber to the outside can be reliably suppressed.

[0058] The Young's modulus of the annular elastic member 43 is equal to or less than 0.3 GPa. This makes it possible to suppress stress generated in the insulator 3 at the pressure-welded portion between the annular elastic member 43 and the insulator 3. As a result, damage to the insulator can be reliably suppressed.

[0059] As described above, according to this embodiment, it is possible to provide the spark plug 1 that can suppress leakage of gas in the combustion chamber of an internal combustion engine to the outside.

[0060] (Experimental Example 1) In this example, as shown in the graph of FIG. 4, in a spark plug having the same basic structure as the spark plug of the first embodiment, the width of the annular elastic member was changed to analyze the relationship between the width of the annular elastic member and the compression rate and the filling rate. In this example, the material of the annular elastic member was fluororubber. In this example, a compression rate of 10 to 30% and a filling rate of 85% or less were set as a standard for suppressing the leakage of gas from the combustion chamber to the outside for a long period of time, and the width of the annular elastic member that satisfies this standard was obtained. In the graph of FIG. 4, the analysis result of the filling rate is shown by a solid line, and the analysis result of the compression rate is shown by a broken line. In addition, in the graph of FIG. 4, the black circles indicate the compression rate and the filling rate when the width of the annular elastic member is 1.0 mm. In addition, the width of the annular elastic member in the graph of FIG. 4 means the width of the annular elastic member in a free state.

[0061] As shown in the graph of FIG. 4, when the width of the annular elastic member in a free state is 0.95 to 1.25 mm, the above criteria are met. Therefore, it is considered that the spark plug 1 of the first embodiment, in which the width of the annular elastic member is 0.95 to 1.25 mm, can suppress leakage of gas in the combustion chamber to the outside for a long period of time. Note that the width of the annular elastic member that satisfies the above criteria varies depending on the shape of the elastic member arrangement space, etc. Therefore, by selecting an annular elastic member with a width that satisfies the above criteria in accordance with the shape of the elastic member arrangement space, etc., leakage of gas in the combustion chamber to the outside can be suppressed for a long period of time.

[0062] (Embodiment 2) In this embodiment, as shown in FIG. 5, gaps in the filler 6 are filled with a liquid filler insulating material 420.

[0063] As shown in Fig. 5, in the spark plug 1 of this embodiment, the gaps between the talc powder constituting the filler 6 are filled with a liquid filling insulating material 420. The filling insulating material 420 fills the gaps between the talc powder over the entire circumferential direction of the plug. The filling insulating material 420 seals the gap between the housing 2 and the insulator 3. In this embodiment, the filling insulating material 420 is made of silicone oil. Also, in this embodiment, the sealing insulating material 42 is not filled in the gap G1.

[0064] The contact portion between the outer circumferential surface of the insulator 3 and the base end side annular member 62 and the contact portion between the housing 2 and the base end side annular member 62 are each covered from the tip end side Z1 with the insulating filling material 420. The contact portion between the outer circumferential surface of the insulator 3 and the tip end side annular member 61 and the contact portion between the housing 2 and the tip end side annular member 61 are each covered from the base end side Z2 with the insulating filling material 420. 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.

[0065] In the spark plug 1 of this embodiment, the liquid filled insulating material 420 is filled into the gaps between the talc powder constituting the filler 6. This makes it possible to prevent gas in the combustion chamber of the internal combustion engine from leaking to the outside through a gap between the housing 2 and the insulator 3.

[0066] Furthermore, by filling the gaps between the talc powder constituting the filler 6 with liquid insulating filler 420, it is possible to improve the airtightness between the housing 2 and the insulator 3 while ensuring the elasticity of the filler 6. As a result, it is possible to reduce the stress on the crimped portion 23 and to suppress the gas in the combustion chamber from leaking to the outside.

[0067] Filler insulating material 420 is made of silicone oil. Therefore, the heat resistance of filler insulating material 420 can be improved. Therefore, even if high-temperature gas in the combustion chamber reaches annular space 60, filling insulating material 420 can be prevented from vaporizing and disappearing. Therefore, the gas in the combustion chamber can be further prevented from leaking to the outside through a gap between housing 2 and insulator 3.

[0068] The contact portion between the outer circumferential surface of the insulator 3 and the base end side annular member 62 and the contact portion between the housing 2 and the base end side annular member 62 are each covered from the tip end side Z1 by the filling insulating material 420. Furthermore, the contact portion between the outer circumferential surface of the insulator 3 and the tip end side annular member 61 and the contact portion between the housing 2 and the tip end side annular member 61 are each covered from the base end side Z2 by the filling insulating material 420. This makes it possible to further prevent gas in the combustion chamber from leaking to the outside through between the housing 2 and the insulator 3. In addition, the same effects as those of the first embodiment are achieved.

[0069] (Embodiment 3) As shown in FIG. 6, this embodiment is provided with both a sealing insulating material 42 and a filling insulating material 420.

[0070] As shown in FIG. 6, in the spark plug 1 of this embodiment, similarly to the spark plug 1 of the first embodiment, the gap G1 is filled with a liquid sealing insulating material 42 that seals between the housing 2 and the insulator 3.

[0071] The abutment portion between the outer peripheral surface of the insulator 3 and the base end side annular member 62, and the abutment portion between the housing 2 and the base end side annular member 62 are each covered from the base end side Z2 by sealing insulating material 42 and from the tip end side Z1 by filling insulating material 420. The rest is the same as in the second embodiment.

[0072] The spark plug 1 of this embodiment includes both the sealing insulating material 42 and the filling insulating material 420. This makes it possible to further prevent gas in the combustion chamber from leaking to the outside.

[0073] The contact portion between the outer circumferential surface of the insulator 3 and the base-end side annular member 62 and the contact portion between the housing 2 and the base-end side annular member 62 are each covered from the base-end side Z2 by the sealing insulating material 42 and from the tip-end side Z1 by the filling insulating material 420. This makes it possible to further prevent gas in the combustion chamber from leaking to the outside. In addition, the same effects as those of the second embodiment are achieved.

[0074] 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]

[0075] Reference Signs List 1...spark plug, 2...housing, 3...insulator, 6...filler, 21...first housing facing surface, 22...second housing facing surface, 23...crimped portion, 31...first insulator facing surface, 32...second insulator facing surface, 41...packing, 42...sealing insulating material, 43...annular elastic member, 60...annular space, 61...tip side annular member, 62...base side annular member, G1...gap, Z...plug axial direction, Z1...tip side, Z2...base side

Claims

1. A spark plug (1) for use in an internal combustion engine fueled by hydrogen gas, A cylindrical insulator (3); A cylindrical housing (2) that holds the insulator on its inner periphery; an annular packing (41) sandwiched in the plug axial direction (Z) between a first housing opposing surface (21) formed on an inner peripheral surface of the housing and a first insulator opposing surface (31) formed on an outer peripheral surface of the insulator at a position closer to the base end (Z2) than the first housing opposing surface, a filler (6) mainly made of talc powder, which is filled in an annular space (60) formed on the base end side of the packing and between an inner peripheral surface of the base end of the housing and an outer peripheral surface of the insulator; and an annular elastic member (43) that is sandwiched in the plug axial direction by a second housing opposing surface (22) formed on an inner circumferential surface of the housing and a second insulator opposing surface (32) formed on an outer circumferential surface of the insulator at a position closer to the base end than the second housing opposing surface, and that is disposed between the annular space and the packing in the plug axial direction, the packing and the annular elastic member each provide a seal between the housing and the insulator, The filler is filled between a tip side annular member (61) arranged at a tip portion of the annular space and a base side annular member (62) arranged at a base end portion of the annular space, The base end of the housing has a crimping portion (23) that presses the insulator toward the tip side (Z1), the crimping portion presses the base end side annular member directly toward the tip end side, thereby pressing the insulator toward the tip end side via the base end side annular member, the filler, and the tip end side annular member, a gap (G1) formed between the crimped portion and the insulator is filled with a liquid sealing insulating material (42) that seals between the housing and the insulator.

2. 2. The spark plug according to claim 1, wherein said annular elastic member is made of fluororubber, and said sealing insulating material is made of silicone oil.

3. A spark plug (1) for use in an internal combustion engine fueled by hydrogen gas, A cylindrical insulator (3); A cylindrical housing (2) that holds the insulator on its inner periphery; an annular packing (41) sandwiched in the plug axial direction (Z) between a first housing opposing surface (21) formed on an inner peripheral surface of the housing and a first insulator opposing surface (31) formed on an outer peripheral surface of the insulator at a position closer to the base end (Z2) than the first housing opposing surface, a filler (6) mainly made of talc powder, which is filled in an annular space (60) formed on the base end side of the packing and between an inner peripheral surface of the base end of the housing and an outer peripheral surface of the insulator, The packing seals between the housing and the insulator, The filler is filled between a tip side annular member (61) arranged at a tip portion of the annular space and a base side annular member (62) arranged at a base end portion of the annular space, The base end of the housing has a crimping portion (23) that presses the insulator toward the tip side (Z1), the crimping portion presses the base end side annular member directly toward the tip end side, thereby pressing the insulator toward the tip end side via the base end side annular member, the filler, and the tip end side annular member, A spark plug, wherein gaps between the talc powder constituting the filler are filled with a liquid filler insulating material (420).

4. 4. The spark plug of claim 3, wherein said filler insulating material is made of silicone oil.

5. 4. The spark plug according to claim 3, wherein a gap (G1) formed between the crimped portion and the insulator is filled with a liquid sealing insulating material (42) that seals between the housing and the insulator.

6. 6. The spark plug according to claim 1, wherein a contact portion between an outer circumferential surface of the insulator and the base end side annular member and a contact portion between the housing and the base end side annular member are each covered from a base end side with the sealing insulating material.

7. 6. The spark plug of claim 5, wherein said sealing insulating material comprises silicone oil.

8. 4. The spark plug according to claim 3, further comprising an annular elastic member (43) that is sandwiched in the plug axial direction by a second housing opposing surface (22) formed on an inner circumferential surface of the housing and a second insulator opposing surface (32) formed on an outer circumferential surface of the insulator at a base end side relative to the second housing opposing surface, and that is disposed between the annular space and the packing in the plug axial direction, and that seals between the housing and the insulator.

9. 9. The spark plug according to claim 8, wherein said annular elastic member is made of fluororubber.

10. 4. The spark plug according to claim 1, wherein the insulator has a tapered tip portion (33) that is tapered in diameter toward the tip side from the packing, and a ratio of a length (L1) of the tapered tip portion in the plug axial direction to a distance (L2) between the packing and the crimped portion in the plug axial direction is 1 / 20 to 1 / 4.

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