Spark plug for internal combustion engine

Abstract

To provide a spark plug for an internal combustion engine capable of suppressing preignition.SOLUTION: In a spark plug 1, a packing 5 is held in a plug axis direction Z between a housing opposite face 22 and an insulator opposite face 32 which are opposed to each other. An insulator 3 includes a tapered distal end portion 31. The spark plug 1 includes a pocket part 7 which is an annular space formed between an outer peripheral surface 311 of the tapered distal end portion 31 and an inner peripheral surface of a housing 2. A distal end of the insulator 3 is disposed at the same position as a distal end of the housing 2 or a position closer to a proximal end side Z2 than the distal end of the housing 2 in the plug axis direction Z. The distal end portion of the housing 2 includes an inner protrusion 21. The housing opposite face 22 is formed in a proximal end portion of the inner protrusion 21. The pocket part 7 is formed between the outer peripheral surface 311 of the tapered distal end portion 31 and an inner peripheral surface 211 of the inner protrusion 21.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] For example, a spark plug is known that includes an insulator having a tapered tip portion that decreases in diameter toward the tip side, as disclosed in Patent Document 1. In this spark plug, a pocket portion that is an annular space is formed between the outer circumferential surface of the tapered tip portion and the inner circumferential surface of the housing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4623880 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the spark plug described in Patent Document 1 does not particularly consider the scavenging performance of the pocket. Therefore, depending on how the pocket is formed, the scavenging performance of the pocket may be reduced. If the scavenging performance of the pocket is reduced, pre-ignition may occur in an internal combustion engine equipped with the spark plug. Therefore, it can be said that there is room for improvement in the spark plug described in Patent Document 1 from the viewpoint of suppressing pre-ignition.

[0005] The present invention has been made in view of the above problems, and has an object to provide a spark plug for an internal combustion engine that is capable of suppressing pre-ignition. [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 exposed from the insulator to a tip side (Z1); 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; and an annular packing (5) sandwiched in the plug axial direction (Z) by a housing facing surface (22) formed on the inner circumferential surface of the housing and an insulator facing surface (32) formed on the outer circumferential surface of the insulator at a position closer to the base end (Z2) than the housing facing surface, The packing seals between the housing and the insulator, The insulator has a tapered tip portion (31) that is tapered toward the tip side and is formed on the tip side of the insulator facing surface, a pocket portion (7) that is open to the tip side and is an annular space formed between an outer peripheral surface (311) of the tapered tip portion and an inner peripheral surface of the housing; a tip end of the insulator is disposed at the same position as a tip end of the housing or at a position closer to a base end than the tip end of the housing in a plug axial direction, The front end portion of the housing has an inner protruding portion (21) that is formed around the entire circumference of the front end portion of the housing and protrudes toward the inside in the plug radial direction, The housing-facing surface is formed at a base end of the inner protrusion, The pocket is in a spark plug (1) for an internal combustion engine, the pocket being formed between an outer circumferential surface of the tapered tip and an inner circumferential surface of the inward projection (211). Effect of the Invention

[0007] In the above spark plug, the pocket portion is formed between the outer peripheral surface of the tapered tip portion and the inner peripheral surface of the inner protrusion formed at the tip portion of the housing. The housing-facing surface is formed at the base end portion of the inner protrusion. Therefore, the volume of the pocket portion is easily reduced, and the scavenging performance of the pocket portion is easily improved. As a result, pre-ignition can be suppressed.

[0008] In addition, the tip of the insulator is disposed at the same position as the tip of the housing in the axial direction of the plug, or at a position closer to the base end than the tip of the housing. This makes it possible to prevent overheating of the tip of the insulator, thereby making it possible to prevent pre-ignition.

[0009] As described above, according to the above aspect, it is possible to provide a spark plug for an internal combustion engine that is capable of suppressing pre-ignition. 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]

[0010] [Figure 1] 1 is a half cross-sectional view of a spark plug according to a first embodiment. [Diagram 2] 2 is a half cross-sectional view of the vicinity of the tip portion of the spark plug according to the first embodiment. [Diagram 3] 3 is a view of the spark plug according to the first embodiment, seen from the tip end side, taken along the line III in FIG. 2. [Figure 4] 4 is a cross-sectional view of the vicinity of the tip portion of the spark plug according to the first embodiment, showing the radius of the thread portion, etc., taken along line IV-IV in FIG. [Diagram 5] 6 is a graph showing the relationship between length C and the occurrence frequency of pre-ignition in Experimental Example 1. [Figure 6] 4 is a graph showing the relationship between the value of C / X and the occurrence frequency of pre-ignition in an internal combustion engine fueled by hydrogen gas in Experimental Example 1. [Figure 7] 13 is a graph showing the relationship between the value of C / X and the occurrence frequency of pre-ignition in an internal combustion engine fueled by gasoline in Experimental Example 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] (Embodiment 1) An embodiment of a spark plug for an internal combustion engine will be described with reference to Figs. As shown in Figs. 1 to 4, the spark plug 1 for an internal combustion engine of this embodiment has a cylindrical insulator 3, a center electrode 4, a cylindrical housing 2, a ground electrode 6, and an annular packing 5. The center electrode 4 is held on the inner periphery side of the insulator 3 and is exposed from the insulator 3 to the tip side Z1. The housing 2 holds the insulator 3 on the inner periphery side. The ground electrode 6 forms a discharge gap G between the center electrode 4. As shown in Figs. 2 and 4, the packing 5 is sandwiched in the plug axial direction Z by a housing facing surface 22 and an insulator facing surface 32 that face each other. The housing facing surface 22 is formed on the inner periphery surface of the housing 2. The insulator facing surface 32 is formed on the outer periphery surface of the insulator 3 at a position closer to the base end side Z2 than the housing facing surface 22. The packing 5 seals between the housing 2 and the insulator 3.

[0012] The insulator 3 has a tapered tip portion 31 whose diameter decreases toward the tip side Z1. The tapered tip portion 31 is formed on the tip side Z1 beyond the insulator facing surface 32. The spark plug 1 also has a pocket portion 7 which is an annular space formed between an outer circumferential surface 311 of the tapered tip portion 31 and an inner circumferential surface of the housing 2. The pocket portion 7 opens to the tip side Z1.

[0013] The tip of the insulator 3 is disposed at the same position as the tip of the housing 2 in the plug axial direction Z, or at a position closer to the base end side Z2 than the tip of the housing 2.

[0014] The tip end of the housing 2 has an inner protrusion 21. The inner protrusion 21 is formed around the entire circumference of the tip end of the housing 2 and protrudes inward in the plug radial direction. The housing opposing surface 22 is formed at the base end of the inner protrusion 21. The pocket portion 7 is formed between the outer peripheral surface 311 of the tapered tip end 31 and the inner peripheral surface 211 of the inner protrusion 21.

[0015] The spark plug 1 can be used as an ignition means in an internal combustion engine of an automobile or the like. The spark plug 1 of this embodiment is used in an internal combustion engine (not shown) that uses hydrogen gas as fuel. The threaded portion 23 formed on the outer circumferential surface 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 of the internal combustion engine. In the axial direction Z of the spark plug 1, the side exposed to the combustion chamber is referred to as a tip side Z1, and the opposite side is referred to as a base side Z2. The axial direction Z of the spark plug 1 is also referred to as a plug axial direction Z as appropriate. The plug center axis PC means the center axis PC of the spark plug 1. The plug radial direction means the radial direction of a circle centered on the plug center axis P on a plane perpendicular to the plug center axis PC. The plug circumferential direction is a direction along the circumference centered on the plug center axis PC. In this embodiment, the plug central axis PC is also the central axis of the center electrode 4 , the housing 2 , and the insulator 3 .

[0016] In this embodiment, the tip surface of the center electrode 4 is located on the tip side Z1 from the tip of the housing 2 as shown in Fig. 2 and Fig. 4. Also, as shown in Fig. 1, a first glass seal layer 11, a resistor 12, a second glass seal layer 13, and a terminal metal fitting 14 are arranged on the base end side Z2 of the center electrode 4 inside the insulator 3. The first glass seal layer 11 and the second glass seal layer 13 may be made of glass containing copper powder, for example. The resistor 12 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 base end side Z2 of the terminal metal fitting 14 is exposed from the insulator 3. The spark plug 1 is electrically connected to an ignition coil (not shown) at the terminal metal fitting 14.

[0017] An annular space 150 is formed between the inner peripheral surface of the base end of the housing 2 and the outer peripheral surface of the insulator 3. The annular space 150 is filled with a filler 15 mainly made of talc powder. The filler 15 is filled between a tip side annular member 151 arranged at the tip end of the annular space 150 and a base side annular member 152 arranged at the base end of the annular space 150.

[0018] The base end of the housing 2 has a crimping portion 24 that presses the insulator 3 toward the tip side Z1. The crimping portion 24 is bent toward the inside in the plug radial direction. The crimping portion 24 presses the base end side annular member 152 directly toward the tip side Z1, thereby pressing the insulator 3 toward the tip side Z1 via the base end side annular member 152, the filler 15, and the tip side annular member 151.

[0019] 2 and 4, the housing facing surface 22 is formed to follow the insulator facing surface 32. The housing facing surface 22 and the insulator facing surface 32 are each formed to extend toward the base end side Z2 as they extend radially outward in the plug radial direction. The housing facing surface 22 formed on the inner protruding portion 21 engages the insulator 3 from the tip side Z1 via a packing 5.

[0020] The packing 5 is in pressure contact with both the housing 2 and the insulator 3 over the entire circumference in the circumferential direction of the plug. In this embodiment, the tip of the packing 5 is located on the tip side Z1 from the threaded portion 23. The packing 5 may be made of a metal such as an alloy mainly composed of iron.

[0021] In this embodiment, the tip of the inner protrusion 21 forms the tip of the housing 2. The inner protrusion 21 protrudes toward the plug central axis PC and is formed in an annular shape. As shown in Fig. 4, the length L3 of the inner protrusion 21 in the plug axial direction Z is equal to or less than the radius R of the threaded portion 23 of the housing 2. In this embodiment, the nominal diameter of the threaded portion 23 is equal to or less than M12.

[0022] A ground electrode 6 is fixed to the inner protrusion 21. The ground electrode 6 is joined to the tip surface of the inner protrusion 21 by resistance welding. As shown in Figs. 2 and 4, the ground electrode 6 protrudes from a fixed portion 61 fixed to the inner protrusion 21 toward the plug central axis PC without bending. In other words, the ground electrode 6 is formed in a rod shape. The ground electrode 6 is inclined toward the tip side Z1 as it approaches the plug central axis PC.

[0023] The base end side surface 62 of the ground electrode 6 is a flat surface entirely. As shown in Fig. 4, in a cross section including the plug central axis PC and along the protruding direction of the ground electrode 6, the base end side surface 62 is formed in a straight line and is inclined with respect to the inner circumferential surface 211 of the inner protruding portion 21. A discharge gap G is formed between the base end side surface 62 and the tip end of the center electrode 4.

[0024] Further, the spark plug 1 has an inner space 70 which is a space on the inner peripheral side of the inner protruding portion 21. The inner space 70 has a pocket portion 7. In this embodiment, a part of the inner space 70 is formed on the tip side Z1 with respect to the tapered tip portion 31. A part of the inner space 70 formed on the tip side Z1 with respect to the tapered tip portion 31 is formed between the inner peripheral surface 211 of the inner protruding portion 21 and the outer peripheral surface of the center electrode 4, and opens to the tip side Z1. In this embodiment, the inner space 70 is composed of a portion formed on the tip side Z1 with respect to the tapered tip portion 31 and the pocket portion 7.

[0025] The pocket portion 7 is formed on the tip side Z1 with respect to the screw portion 23. That is, the inner space 70 is formed on the tip side Z1 with respect to the screw portion 23. Further, the pocket portion 7 is formed such that the width in the plug diameter direction increases toward the tip side Z1.

[0026] In this embodiment, the volume V of the inner space 70 is 36 mm 3 or less. The volume V is preferably 29.6 mm 3 or less. Further, the volume V is more preferably 22.5 mm 3 or less.

[0027] In this embodiment, the entire tapered tip portion 31 faces the inner space 70. Further, the tapered tip portion 31 has a flat tip surface 312 formed in an annular shape. In this embodiment, the tip surface 312 is formed so as to be orthogonal to the plug axis direction Z.

[0028] As shown in FIG. 2, let the length in the plug axis direction Z of the tapered tip portion 31 be length C. At this time, the length C is 2.6 mm or less. Further, let the distance from the base end of the tapered tip portion 31 to the tip of the housing 2 in the plug axis direction Z be distance X. At this time, the length C and the distance X satisfy the relationship of 0 < C / X ≤ 0.74.

[0029] The length C is also the length of the pocket portion 7 in the plug axial direction Z. In this embodiment, the length C is equal to or less than the radius R of the thread portion 23 (see FIG. 4). The length C is preferably equal to or less than 1.6 mm, and more preferably equal to or less than 0.6 mm. The distance X is also equal to or less than the radius R of the thread portion. The value of C / X is preferably equal to or less than 0.64, and more preferably equal to or less than 0.40.

[0030] 2, the distance from the tip of the insulator 3 to the tip of the housing 2 in the plug axial direction Z is defined as distance L1. In this case, distance L1 satisfies 0 mm≦L1≦1 mm. In this embodiment, distance L1 is also the distance from the tip of the tapered tip portion 31 to the tip of the inner protrusion 21 in the plug axial direction Z. In this embodiment, the tip of the insulator 3 is located on the base end side Z2 relative to the tip of the housing 2.

[0031] 3, the distance L2 in the plug radial direction from the inner circumferential surface 211 of the inner protrusion 21 to the outer periphery of the tip surface 312 of the tapered tip portion 31 is 2.3 mm or less. The distance L2 is half the length obtained by subtracting the outer diameter D1 of the tip surface 312 of the tapered tip portion 31 from the inner diameter D2 of the inner protrusion 21.

[0032] Next, the effects of this embodiment will be described. In the above spark plug 1, the pocket portion 7 is formed between the outer peripheral surface 311 of the tapered tip portion 31 and the inner peripheral surface 211 of the inner protrusion portion 21 formed at the tip portion of the housing 2. The housing-opposing surface 22 is formed at the base end portion of the inner protrusion portion 21. Therefore, the volume of the pocket portion 7 is easily reduced, and the scavenging performance of the pocket portion 7 is easily improved. As a result, pre-ignition can be suppressed.

[0033] In general, the larger the volume of the pocket, the lower the scavenging performance of the pocket, and the more likely high-temperature gas is to remain inside the pocket. If high-temperature gas remains in the pocket, the insulator is likely to overheat, which may cause pre-ignition. In this embodiment, the spark plug 1 forms the pocket 7 between the outer circumferential surface 311 of the tapered tip portion 31 and the inner circumferential surface 211 of the inner protrusion 21 formed at the tip portion of the housing 2, and forms the housing-facing surface 22 at the base end of the inner protrusion 21. This makes it easy to reduce the volume of the pocket 7. In addition, the length of the pocket 7 in the plug axial direction Z is easily shortened, and the entire pocket 7 can be brought closer to the tip of the housing 2. Therefore, the scavenging performance of the entire pocket 7 can be improved. As a result, pre-ignition can be suppressed.

[0034] Furthermore, the tip of the insulator 3 is disposed in the plug axial direction Z at the same position as the tip of the housing 2 or at a position on the base end side Z2 of the tip of the housing 2. This makes it possible to prevent overheating of the tip of the insulator 3. As a result, pre-ignition can be suppressed.

[0035] In general, the more the insulator protrudes into the combustion chamber of the internal combustion engine, the more heat it is likely to receive from the combustion chamber. Therefore, if the insulator protrudes too much from the housing, there is a risk of overheating at the tip of the insulator. Therefore, in the spark plug 1 of this embodiment, the tip of the insulator 3 is disposed in the plug axial direction Z at the same position as the tip of the housing 2, or at a position Z2 on the base end side of the tip of the housing 2. This makes it possible to suppress the protrusion of the insulator 3 into the combustion chamber. Therefore, it is possible to suppress overheating at the tip of the insulator 3. As a result, it is possible to suppress pre-ignition.

[0036] The length C is 2.6 mm or less. Also, the length C and the distance X satisfy the relationship of 0 < C / X ≤ 0.74. Therefore, the volume of the pocket portion 7 can be further reduced, and the tip of the insulator 3 can be disposed at a position away from the combustion chamber of the internal combustion engine. Thereby, overheating of the insulator 3 can be further suppressed. As a result, pre-ignition can be further suppressed.

[0037] Also, the length C is preferably 1.6 mm or less. In this case, pre-ignition can be further suppressed. Further, the length C is more preferably 0.6 mm or less. In this case, pre-ignition can be further suppressed.

[0038] The value of C / X is preferably 0.64 or less. In this case, pre-ignition can be further suppressed. Further, the value of C / X is more preferably 0.40 or less. In this case, pre-ignition can be further suppressed.

[0039] The distance L1 satisfies 0 mm ≤ L1 ≤ 1 mm. Therefore, while suppressing the protrusion of the insulator 3 into the combustion chamber, the volume of the inner space 70 can be reduced. Therefore, overheating of the insulator 3 can be sufficiently suppressed. As a result, pre-ignition can be sufficiently suppressed.

[0040] The spark plug 1 of the present embodiment is used in an internal combustion engine using hydrogen gas as fuel. Also, as described above, the spark plug 1 of the present embodiment can improve the scavenging performance of the pocket portion 7 and suppress overheating of the tip portion of the insulator 3. Therefore, even if the spark plug 1 is installed in an internal combustion engine using hydrogen gas, which has a smaller minimum ignition energy compared to gasoline or the like, as fuel, pre-ignition can be sufficiently suppressed.

[0041] Moreover, the pocket portion 7 is formed on the tip side Z1 relative to the threaded portion 23. Therefore, the entire pocket portion 7 can be brought even closer to the tip of the housing 2. As a result, the scavenging performance of the pocket portion 7 can be further improved.

[0042] The length C is equal to or less than the radius R of the threaded portion 23. Therefore, the volume of the pocket portion 7 can be made sufficiently small. As a result, the scavenging performance of the pocket portion 7 can be improved, and overheating of the insulator 3 can be sufficiently suppressed.

[0043] Moreover, the distance X is equal to or less than the radius R. Therefore, the volume of the inner space 70 can be made sufficiently small, and the entire pocket portion 7 can be brought sufficiently close to the tip of the housing 2. As a result, the scavenging performance of the inner space 70 can be improved, and overheating of the insulator 3 can be sufficiently suppressed.

[0044] In this embodiment, the volume V of the inner space 70 is 36.0 mm 3 Therefore, the scavenging performance of the inner space 70 can be improved. As a result, pre-ignition can be further suppressed. In addition, the volume V is 29.6 mm 3 In this case, the scavenging performance of the inner space 70 can be further improved. 3 It is more preferable that the above-mentioned condition be satisfied. In this case, the scavenging performance of the inner space 70 can be further improved.

[0045] The ground electrode 6 protrudes from the fixed portion 61 toward the plug center axis PC without bending. This makes it possible to shorten the heat dissipation path from the protruding end of the ground electrode 6 to the housing 2. In addition, it is easy to suppress the amount of protrusion of the ground electrode 6 into the combustion chamber. This makes it possible to suppress overheating of the ground electrode 6. As a result, pre-ignition can be suppressed.

[0046] In this embodiment, the tip of the insulator 3 is located on the base end side Z2 relative to the tip of the housing 2. This makes it possible to reduce the amount of protrusion of the ground electrode 6 and the center electrode 4 from the tip of the housing 2 toward the tip side Z1. This makes it possible to reduce the amount of protrusion of the ground electrode 6 and the center electrode 4 into the combustion chamber. This makes it possible to sufficiently prevent overheating of the ground electrode 6 and the center electrode 4. As a result, it is possible to sufficiently prevent pre-ignition.

[0047] As described above, according to this embodiment, it is possible to provide the spark plug 1 for an internal combustion engine that is capable of suppressing pre-ignition.

[0048] (Experimental Example 1) In this example, as shown in the graph of FIG. 5, a relationship between the length C and the occurrence frequency of pre-ignition was analyzed using a plurality of spark plugs having the same basic structure as the spark plug of the first embodiment but different lengths C of the tapered tip portion. As an experimental condition, the spark plug was installed in an internal combustion engine using hydrogen gas as fuel. In addition, in each spark plug, the outer diameter D1 (see FIG. 3) of the tip surface of the tapered tip portion was 3.7 mm, and the inner diameter D2 (see FIG. 3) of the inner protrusion was 5.2 mm. In addition, in each spark plug, the distance L1 (see FIG. 2) was 0.9 mm, and the tip of the tapered tip portion was disposed on the base end side from the tip of the housing. In addition, the plurality of spark plugs used in this example had the same value of distance L1 as described above, but the distances from the tip of the housing to the packing in the plug axial direction were different from each other, so that the lengths C were different from each other. In other words, the spark plug in which the packing is farther away from the tip of the housing toward the base end has a longer length C and a larger volume of the pocket portion. Therefore, the longer the length C, the larger the volume V of the inner space. In this example, the occurrence frequency of pre-ignition means the ratio of the number of occurrences of pre-ignition to the number of combustion cycles of the internal combustion engine in a predetermined period of time.

[0049] As shown in the graph of Figure 5, it can be seen that the shorter the length C, the lower the frequency of pre-ignition. In particular, when the length C is 2.6 mm or less, the frequency of pre-ignition is significantly lower than when the length C is 3.6 mm. Also, when the length C is 0.6 mm, the frequency of pre-ignition is significantly lower than when the length C is 1.6 mm. It can also be seen that the smaller the volume V, the lower the frequency of pre-ignition. In particular, when the volume V is 36.0 mm or less, the frequency of pre-ignition is significantly lower than when the length C is 1.6 mm. 3 If the volume V is set to 43.0 mm 3 The frequency of pre-ignition is significantly lower than when the volume V is 22.5 mm 3 In this case, the volume V is 29.6 mm 3 From these results, it is considered that the spark plug of the first embodiment, in which the length C is 2.6 mm or less, can sufficiently suppress pre-ignition. 3 It is believed that the spark plug of the following embodiment 1 can sufficiently suppress pre-ignition.

[0050] The graph in FIG. 6 shows the relationship between the value of C / X and the frequency of pre-ignition. As shown in the graph in FIG. 6, it can be seen that the smaller the value of C / X, the lower the frequency of pre-ignition. In particular, when the value of C / X is 0.74 or less, the frequency of pre-ignition is significantly lower than when the value of C / X is 0.80. Furthermore, when the value of C / X is 0.40, the frequency of pre-ignition is significantly lower than when the value of C / X is 0.64. From these results, it is considered that the spark plug of embodiment 1, which has a value of C / X of 0.74 or less, can sufficiently suppress pre-ignition.

[0051] (Experimental Example 2) In this example, the relationship between the insulator protrusion value and the frequency of pre-ignition was analyzed using a plurality of spark plugs having the same basic structure as the spark plug of embodiment 1, but with different values ​​obtained by subtracting distance X from length C (hereinafter referred to as insulator protrusion value) as shown in Table 1 below. The plurality of spark plugs used in this example each had a length C of 2.6 mm. Furthermore, the plurality of spark plugs used in this example had different distances from the tip of the housing to the packing in the plug axial direction, thereby giving them different insulator protrusion values.

[0052] [Table 1]

[0053] In Table 1, an insulator protrusion value of "0 mm" indicates that the tip of the insulator is at the same position as the tip of the housing in the plug axial direction. In addition, in Table 1, a positive insulator protrusion value indicates that the tip of the insulator is located on the tip side of the tip of the housing. In other words, an insulator protrusion value of "+1 mm" means that the insulator protrudes 1 mm from the tip of the housing toward the tip side. In addition, in Table 1, a negative insulator protrusion value indicates that the tip of the insulator is located on the base side of the tip of the housing. In other words, when the insulator protrusion value is negative, the tip of the insulator is disposed within the inner space. In addition, in Table 1, a circle symbol indicates that pre-ignition did not occur, and a cross symbol indicates that pre-ignition occurred.

[0054] In this example, the spark plugs with an insulator protrusion value of 0 mm were verified under the operating conditions of the internal combustion engine in which pre-ignition does not occur. The other conditions were the same as those in Experimental Example 1.

[0055] As shown in Table 1, pre-ignition was not observed in spark plugs with an insulator protrusion value of "-1 mm". On the other hand, pre-ignition was observed in spark plugs with a positive insulator protrusion value. In other words, pre-ignition was observed in spark plugs in which the tip of the insulator protrudes from the tip of the housing toward the tip side. From this result, it is considered that the tip of the insulator of the spark plug with a positive insulator protrusion value protrudes into the combustion chamber, so the amount of heat received by the tip of the insulator is greater than that of a spark plug with an insulator protrusion value of "0 mm". As a result, it is considered that the tip of the insulator overheated, causing pre-ignition. In contrast, it is considered that the spark plugs with insulator protrusion values ​​of "0 mm" and "-1 mm" were able to suppress the heat received by the tip of the insulator because the tip of the insulator did not protrude into the combustion chamber, and therefore were able to suppress pre-ignition. However, it was confirmed that pre-ignition occurred in the spark plug with the insulator protrusion value of "-2 mm". Here, the length C is the same for each spark plug. Therefore, the smaller the insulator protrusion value, the larger the volume of the inner space and the more the pocket portion is disposed on the base end side. Therefore, it is considered that the spark plug with the insulator protrusion value of "-2 mm" has a larger volume of the inner space and the pocket portion is disposed in a recessed position on the base end side, and the scavenging performance of the pocket portion is lowered, compared with the spark plugs with the insulator protrusion values ​​of "0 mm" and "-1 mm". As a result, it is considered that pre-ignition occurred. From these results, it is considered that the spark plug of embodiment 1 that satisfies 0 mm ≦ L1 ≦ 1 mm can sufficiently suppress pre-ignition.

[0056] (Experimental Example 3) In this example, a plurality of spark plugs having the same basic structure as the spark plug of the first embodiment but different distances L2 (see FIG. 3) were used to analyze the relationship between the distance L2 and the occurrence frequency of pre-ignition. In this example, the length C of each spark plug was set to 1.6 mm. Also, in this example, a spark plug having a distance L2 of 2.3 mm and a spark plug having a distance L2 of 2.0 mm were used. The other experimental conditions were the same as those of Experimental Example 1.

[0057] As a result of the experiment of this example, the occurrence frequency of pre-ignition was 1% in both the spark plug with the distance L2 of 2.3 mm and the spark plug with the distance L2 of 2.0 mm. From this result, it is considered that even if the distance L2 is changed in the range of 2.0 to 2.3 mm, it is difficult to affect the occurrence frequency of pre-ignition. In other words, when the distance L2 is increased, the volume of the pocket portion is increased, but the opening of the pocket portion is increased, and the scavenging performance of the pocket portion is improved accordingly. On the other hand, when the distance L2 is decreased, the opening of the pocket portion is decreased, but the volume of the pocket portion is decreased, and the scavenging performance of the pocket portion is improved accordingly. Therefore, it is considered that there was no clear difference in the occurrence frequency of pre-ignition even if the distance L2 was changed in the range of 2.0 to 2.3 mm. Therefore, from the results of Experimental Examples 1 to 3, it is considered that the length C and the insulator protrusion value are more likely to affect the occurrence frequency of pre-ignition than the distance L2.

[0058] (Experimental Example 4) In this example, the relationship between the C / X value and the occurrence frequency of pre-ignition in a gasoline-fueled internal combustion engine was analyzed using a plurality of spark plugs with different C / X values ​​as shown in the graph of Fig. 7. The other experimental conditions were the same as those in Experimental Example 1.

[0059] As shown in the graph in Figure 7, even when gasoline is used as fuel for an internal combustion engine, the smaller the C / X value, the lower the frequency of pre-ignition. In particular, when the C / X value is 0.74 or less, the frequency of pre-ignition is significantly lower than when the C / X value is 0.80.

[0060] On the other hand, in this example, unlike the result of Experimental Example 1 in which hydrogen gas was used as fuel for the internal combustion engine, almost no difference was observed in the frequency of pre-ignition between a spark plug with a C / X value of 0.64 and a spark plug with a C / X value of 0.40. From the results of Experimental Example 4 and Experimental Example 1, it is presumed that when the C / X value is less than 0.64, the effect of the difference in the value of C / X and the length C on the frequency of pre-ignition is greater when the spark plug is used in an internal combustion engine fueled by hydrogen gas than when the spark plug is used in an internal combustion engine fueled by gasoline. In other words, it is presumed that when the spark plug is used in an internal combustion engine fueled by hydrogen gas, the frequency of pre-ignition is more susceptible to the effect of high-temperature gas remaining in the pocket portion than when the spark plug is used in an internal combustion engine fueled by gasoline. Therefore, it is presumed that it is important for the spark plug used in an internal combustion engine fueled by hydrogen gas to improve the scavenging performance of the pocket portion in order to suppress pre-ignition, compared to the spark plug used in an internal combustion engine fueled by gasoline. In particular, from the results of Experimental Example 1, it is considered that in a spark plug used in an internal combustion engine that uses hydrogen gas as fuel, the scavenging performance of the pocket portion improves as the values ​​of C / X and length C are reduced, making it easier to suppress pre-ignition.

[0061] 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]

[0062] 1...spark plug, 2...housing, 3...insulator, 4...center electrode, 5...packing, 6...ground electrode, 7...pocket portion, 21...inner protrusion, 22...housing facing surface, 31...tapered tip portion, 32...insulator facing surface, 211...inner circumferential surface, 311...outer circumferential surface, G...discharge gap, Z...plug axial direction, Z1...tip side, Z2...base end side

Claims

1. A cylindrical insulator (3); a center electrode (4) held on the inner circumferential side of the insulator and exposed from the insulator to a tip side (Z1); 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; and an annular packing (5) sandwiched in the plug axial direction (Z) between a housing facing surface (22) formed on an inner peripheral surface of the housing and an insulator facing surface (32) formed on an outer peripheral surface of the insulator at a position closer to the base end (Z2) than the housing facing surface, The packing seals between the housing and the insulator, The insulator has a tapered tip portion (31) that is tapered toward the tip side and is formed on the tip side of the insulator facing surface, a pocket portion (7) that is an annular space formed between an outer peripheral surface (311) of the tapered tip portion and an inner peripheral surface of the housing and that opens to the tip side; a tip end of the insulator is disposed at the same position as a tip end of the housing or at a position closer to a base end than the tip end of the housing in a plug axial direction, The tip end of the housing has an inner protruding portion (21) that is formed around the entire circumference of the tip end of the housing and protrudes toward the inside in the plug radial direction, The housing-facing surface is formed at a base end of the inner protrusion, A spark plug (1) for an internal combustion engine, wherein the pocket portion is formed between an outer circumferential surface of the tapered tip portion and an inner circumferential surface of the inner protrusion portion.

2. 2. The spark plug for an internal combustion engine according to claim 1, wherein, when a length of the tapered tip portion in an axial direction of the plug is defined as a length C, the length C is equal to or less than 2.6 mm, and when a distance in the axial direction of the plug from a base end of the tapered tip portion to a tip of the housing is defined as a distance X, the length C and the distance X satisfy a relationship of 0<C / X≦0.

74.

3. 3. The spark plug for an internal combustion engine according to claim 1, wherein, when a distance L1 from a tip of the insulator to a tip of the housing in an axial direction of the plug is defined as 0 mm≦L1≦1 mm.

4. 3. The spark plug for an internal combustion engine according to claim 1, wherein the spark plug is used in an internal combustion engine that uses hydrogen gas as fuel.

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