JP2009176525A - Spark plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spark plug in which anti-fouling property is improved by utilizing a cleaning effect by corona discharge. <P>SOLUTION: When a distance between the outer side end part 68 of diameter direction in a fittings face 61 facing toward the rear end and a first edge angle part region 65 is L, the distance X between a ring-shaped packing 8 and the first edge corner part region 65 of the rear end side in a fittings reduced diameter part 60 of the body fittings 50 is arranged to be 0.05 L or more and 0.3 L or less. By this, since the angle of the first edge corner part region 65 becomes exposed without being covered by the packing 8, electric field intensity in the vicinity of the first edge corner part region 65 becomes intensified so that the corona discharge occurs. Since the carbon adhered to the surface of the insulating insulator 10 is cleaned by this corona discharge, the anti-fouling property of the spark plug is improved. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a spark plug that is assembled in an internal combustion engine and ignites an air-fuel mixture.

  Conventionally, spark plugs for ignition are used in internal combustion engines. A typical spark plug has a center electrode that forms an electrode for spark discharge on its tip side, an insulator that holds the center electrode in the shaft hole, and surrounds the periphery of the insulator in the radial direction. And a metal shell. One end of the ground electrode is joined to the metal shell, and a spark discharge gap is formed between the other end and the tip of the center electrode. This spark discharge gap becomes an ignition part, and spark discharge is performed, whereby the air-fuel mixture is ignited.

  By the way, in the structure of such a spark plug, the diameter of the leg long part at the tip end side of the insulator is smaller than the diameter of the trunk part in the intermediate part in the axial direction of the insulator, and between the leg long part and the trunk part. A step portion is formed in the. The step portion of the insulator is locked to the reduced diameter portion provided in the cylindrical hole of the metal shell through an annular packing, so that the gap between the step portion of the insulator and the reduced diameter portion of the metal shell is reduced. The insulator is held in the metal shell with a predetermined gap therebetween. In recent years, a spark plug in which the gap is narrowed to a predetermined distance or less has been proposed (see, for example, Patent Document 1). In the spark plug having such a configuration, the outer diameter of the metal shell can be reduced, so that the spark plug itself can be reduced in size, and thus, the degree of freedom in designing an engine head to which the spark plug is attached can be increased. Can do. In addition, compared with the case where the gap between the insulator and the metal shell is wide, the thermal conductivity (heat pull) from the insulator to the metal shell is improved, so that it spontaneously ignites before ignition of the spark plug. The possibility of pre-ignition (pre-ignition) is reduced. Furthermore, since the amount of unburned gas entering the gap is reduced, the amount of carbon adhering to the surface of the insulator is reduced, and the occurrence of smoldering contamination is suppressed.

However, since the gap between the insulator and the metal shell becomes narrow, when the insulator is fouled by the adhesion of carbon, a leak (leakage) phenomenon in which sparks fly through this gap is likely to occur. This leakage phenomenon tends to occur as the ambient electric field strength increases. Accordingly, a spark plug has been proposed in which the radius of curvature is 0.2 mm or more at the corner of the reduced diameter portion provided inside the metal shell to round the corner to reduce the electric field strength near the reduced diameter portion. (For example, refer to Patent Document 2).
JP 2005-183177 A Japanese Patent Laid-Open No. 9-283259

  However, in the spark plug described in Patent Document 2, the occurrence of corona discharge is suppressed because the electric field strength in the vicinity of the reduced diameter portion of the metal shell is reduced, and it is difficult to clean the insulators using this corona discharge. There was a problem of becoming. Further, even when the rounded corners are not rounded, if the packing disposed in the gap covers the corners, there is a problem that the electric field strength is lowered and corona discharge is difficult to occur.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a spark plug that can improve the stain resistance by utilizing the cleaning effect of corona discharge.

  In order to achieve the above object, a spark plug according to a first aspect of the present invention includes an axial center electrode that forms an electrode for spark discharge on its tip side, and an axial hole that extends in the axial direction of the center electrode. And an insulator that holds the center electrode inside the shaft hole, a cylindrical hole that extends in the axial direction, and holds the insulator inside the cylinder hole, and the insulator And an annular packing interposed therebetween so as to be in contact with the metal shell, and the insulator is an insulator body portion which is a rear end side portion of the insulator, and a front end side portion of the insulator, A leg length part having a diameter smaller than the outer diameter of the insulator body part, and an insulator step part that connects the insulator body part and the leg length part and has an insulator tip-facing surface that is a surface facing the tip side in the axial direction; The cylindrical hole of the metallic shell is formed in the cylindrical hole. A reduced-diameter portion of the metal fitting having a diameter smaller than the diameter is formed, and the reduced-diameter portion of the metal fitting is an inward-facing surface that faces the rear end side of the metal fitting that faces the rear end side in the axial direction and a surface that faces the inner side in the radial direction. A spark plug disposed between the insulator tip-facing surface of the insulator and the metal-facing end-facing surface of the metal shell, wherein the packing has a reduced diameter portion. The distance between the first ridge angle part formed by the metal rear end facing surface and the inward surface and the packing is the distance between the radially outer end of the metal rear end surface and the first ridge angle part. L is 0.05 L or more and 0.3 L or less.

  Moreover, the spark plug of the invention according to claim 2 has the first ridge angle part in the contour line of the cross section when the cross section of the metal shell including the axis is viewed in addition to the configuration of the invention of claim 1. The radius of curvature of is 0.2 mm or less.

  According to a third aspect of the present invention, there is provided a spark plug according to the first or second aspect, wherein the first ridge angle portion and the insulator are spaced apart by a distance of 0.3 mm or less. It is characterized by.

  In addition to the configuration of the invention according to any one of claims 1 to 3, the spark plug of the invention according to claim 4 has a reduced diameter portion when the cross-section of the metal shell including the axis is viewed. An angle between the surface facing the rear end of the metal fitting and a plane orthogonal to the axis of the metal shell is 20 degrees or more and 30 degrees or less.

  According to a fifth aspect of the present invention, in the spark plug of the invention, in addition to the structure of the first aspect of the invention, the metal fitting diameter-reduced portion is a metal tip which is a surface facing the tip side in the axial direction. A second ridge angle portion formed by the inward surface of the reduced-diameter portion of the metal fitting and the metal fitting tip-facing surface in a contour line of the cross-section when the cross-section of the metal shell including the axis is included. The curvature radius of is larger than the curvature radius of the first ridge angle portion.

  In the spark plug according to the first aspect of the present invention, the distance X between the first ridge angle portion and the packing is set to 0. 0 with respect to the distance L between the radially outer end portion and the first ridge angle portion on the metal rear end facing surface. Since the positional relationship is determined to be 05L or more, the first ridge angle portion can be exposed without being covered with the packing. Thereby, the electric field strength in the vicinity of the first ridge angle portion becomes stronger than the surrounding area, and corona discharge can be easily generated. If corona discharge occurs, the carbon adhering to the surface of the insulator can be burned off and cleaned, so that the risk of occurrence of a leak phenomenon can be reduced. That is, by increasing the electric field strength in the vicinity of the first ridge angle portion, corona discharge can be positively generated and a carbon cleaning effect can be obtained. Therefore, according to the spark plug of the invention of claim 1, since the occurrence of the leak phenomenon can be suppressed even if the distance between the metal shell and the insulator is reduced, the spark plug can be reduced in size and Heat extraction to the metal shell can be improved. Further, by setting the distance between the first ridge angle portion and the packing to 0.3 L or less, it is possible to prevent the strength in the radial direction of the annular packing from being reduced and the strength from being lowered. Therefore, deterioration of the performance of the spark plug due to excessive deformation of the packing can be prevented.

  As described above, when the corona discharge is generated in the vicinity of the first ridge angle portion, the sharper the corner of the first ridge angle portion, the stronger the electric field strength and the easier the corona discharge occurs. Therefore, in the invention according to claim 2, when looking at the cross-section of the metal shell including the axis, because the radius of curvature of the first ridge corner portion in the outline of the cross-section is 0.2mm or less, the corner is sharpened, The carbon cleaning effect by corona discharge can be obtained more reliably.

  Further, although the distance that the corona discharge can reach is limited, as in the invention according to claim 3, the first ridge angle portion and the insulator are separated by a distance of 0.3 mm or less, so that the first Since the corona discharge generated in the vicinity of the ridge portion reliably reaches the surface of the insulator and cleans the carbon, the occurrence of a leak phenomenon can be suppressed. And, as the distance between the first ridge angle portion and the insulator is reduced, the inner diameter of the metal shell can be reduced without changing the outer diameter of the insulator, and the outer diameter of the spark plug can be reduced. When designing the engine head to be mounted, the degree of freedom can be increased. Furthermore, since the insulator and the metal shell are close to each other, the heat conduction efficiency is improved, the heat sink from the insulator to the metal shell is improved, and the occurrence of pre-ignition can be suppressed.

  In addition, as in the invention according to claim 4, it is desirable that the angle θ of the metal fitting rear end facing surface of the metal reduced diameter portion with respect to a plane perpendicular to the axis of the metal shell is 20 degrees or more and 30 degrees or less. By setting the value of θ to 20 degrees or more, the spark plug can be easily assembled by aligning the axis of the metal shell and the axis of the insulator, and deterioration of performance due to eccentricity can be prevented. And, by setting the value of θ to 30 degrees or less, sufficient force is applied to the packing, so that a gap is generated between the metal shell and the packing, or between the insulator and the packing, and the airtightness is deteriorated. Can be prevented. Furthermore, since the angle of the first ridge angle part is sharpened by setting θ to 30 degrees or less, the electric field strength in the vicinity of the first ridge angle part can be increased.

  Further, when the second ridge angle portion is formed on the distal end side in the reduced-diameter portion of the metal fitting, when the cross-section of the metal shell including the axis is viewed as in the invention according to claim 5, the outline of the cross-section It is desirable to make the curvature radius of the second ridge angle part larger than the curvature radius of the first ridge angle part. By doing so, the electric field strength in the cylinder of the metal shell is distributed between the vicinity of the first ridge angle portion and the vicinity of the second ridge angle portion, so that the electric field strength near the second ridge angle portion closer to the spark discharge gap is weakened. It is possible to make the leak phenomenon difficult to occur. And since it becomes difficult to generate | occur | produce a leak phenomenon, a higher voltage can be applied to a spark plug. That is, the withstand voltage of the spark plug can be improved. Moreover, since the electric field strength in the vicinity of the first ridge angle portion is increased, the carbon cleaning effect by corona discharge can be improved.

  Hereinafter, an embodiment of a spark plug embodying the present invention will be described with reference to the drawings. First, the structure of the spark plug 100 as an example will be described with reference to FIGS. 1 and 2. FIG. 1 is a partial cross-sectional view of the spark plug 100, and FIG. 2 is an enlarged cross-sectional view of a main part near the packing 8. In FIG. 1, the spark plug 100 will be described with the axial direction as the vertical direction in the drawing, the lower side as the front end side of the spark plug 100, and the upper side as the rear end side.

  As shown in FIG. 1, the spark plug 100 generally includes an insulator 10, a metal shell 50 that holds the insulator 10, a center electrode 20 that is held in the insulator 10 in the direction of the axis O, and a metal shell. 50 is provided at the rear end portion of the insulator 10 and the ground electrode 30 which is bent so that the inner end 33 of the front end portion 31 faces the front end portion 22 of the center electrode 20. Terminal metal fitting 40.

  First, the insulator 10 constituting the insulator of the spark plug 100 will be described. As is well known, the insulator 10 is formed by firing alumina or the like, and has a cylindrical shape in which a shaft hole 12 extending in the direction of the axis O is formed at the center of the shaft. A flange portion 19 having the largest outer diameter is formed substantially at the center in the direction of the axis O, and a rear end body portion 18 is formed on the rear end side (upper side in FIG. 1). A front end side body portion 17 having an outer diameter smaller than that of the rear end side body portion 18 is formed on the front end side (lower side in FIG. 1) from the flange portion 19. A long leg portion 13 having an outer diameter smaller than that of the side body portion 17 is formed. The long leg portion 13 is reduced in diameter toward the tip side, and when the spark plug 100 is attached to the engine head (not shown) of the internal combustion engine, it is exposed to the combustion chamber. And between the leg long part 13 and the front end side trunk | drum 17, it is formed as the insulator step part 15 which has the insulator tip direction surface 14 (refer FIG. 2) which is a surface which faces the front end side of an axis line O direction. In addition, the part of the rear end side from the insulator step part 15 including the front end side body part 17, the rear end side body part 18, and the flange part 19 corresponds to the "insulator body part" in the present invention.

  Next, the center electrode 20 is formed in a substantially cylindrical shape from a nickel-based alloy such as Inconel (trade name) 600 or 601, and has a metal core 23 made of copper or the like having excellent thermal conductivity. The center electrode 20 is held on the distal end side in the shaft hole 12 of the insulator 10 so that the axis thereof coincides with the axis O of the spark plug 100. The distal end side of the center electrode 20 protrudes from the distal end surface of the distal end portion 11 of the insulator 10, and the protruding portion is formed so that the diameter decreases toward the distal end side. A noble metal tip 91 for improving the spark wear resistance is joined to the tip of the protruding portion, and a small-diameter tip 22 is formed integrally with the center electrode 20 body. In the present embodiment, the noble metal tip 91 integrated with the center electrode 20 is referred to as a “center electrode”.

  The center electrode 20 is electrically connected to the upper terminal fitting 40 via the seal body 4 and the ceramic resistor 3 provided in the shaft hole 12. A high voltage cable (not shown) is connected to the terminal fitting 40 via a plug cap (not shown) so that a high voltage is applied.

  Next, the ground electrode 30 will be described. The ground electrode 30 is made of a metal having high corrosion resistance. As an example, a nickel alloy such as Inconel (trade name) 600 or 601 is used. The ground electrode 30 has a substantially rectangular cross section in the longitudinal direction, and the base end portion 32 is joined to the front end surface 57 of the metal shell 50 by welding. The tip 31 of the ground electrode 30 is bent so that one side faces the tip 22 of the center electrode 20, and the inner surface 33 and the tip 21 of the center electrode 20 (in this embodiment, the noble metal tip 91). A spark discharge gap is formed between the tip surface 21).

  Next, the metal shell 50 will be described. As shown in FIG. 1, the metal shell 50 is a cylindrical metal fitting for fixing the spark plug 100 to an engine head of an internal combustion engine (not shown), and the tip portion 11 of the insulator 10 is connected to the tip surface 57 of the metal shell 50. In the protruding state, the insulator 10 is held inside so as to surround a portion from the leg long part 13 to the rear end side body part 18. The metal shell 50 is formed of a low carbon steel material, and includes a tool engaging portion 51 into which a spark plug wrench (not shown) is fitted, and a male screw-like screw portion 52 that is screwed into an engine head provided at the upper part of the internal combustion engine. I have. A flange-like seal portion 54 is formed between the tool engaging portion 51 and the screw portion 52, and a gasket for preventing airtight leakage in the engine at a position between the seal portion 54 and the screw portion 52. 5 is inserted.

  A thin caulking portion 53 is provided on the rear end side of the metal fitting 50 from the tool engagement portion 51, and a thin buckling portion 58 is provided between the seal portion 54 and the tool engagement portion 51. Is provided. The buckling portion 58 is configured so as to bend outwardly and deform with the addition of a compressive force when the crimping portion 53 is crimped, thereby improving airtightness. An annular ring is formed between the inner peripheral surface of the metal shell 50 from the tool engaging portion 51 to the caulking portion 53 and the outer peripheral surface of the rear end side body portion 18 of the insulator 10 held inside. Members 6 and 7 are interposed, and a powder of talc (talc) 9 is filled between the ring members 6 and 7.

  Then, as shown in FIG. 2, the metal fitting 50 has a reduced diameter that protrudes radially inwardly into the cylindrical hole 55 of the metallic shell 50 on the distal end side in the axis O direction of the metallic shell 50 and makes one round of the inner circumference of the cylindrical hole 55. A portion 60 is provided. The metal fitting reduced diameter portion 60 extends from the metal rear end facing surface 61 which is a surface facing the rear end side (upward in FIG. 2) and the radially inner end of the metal rear end facing surface 61 toward the front end side. And an inwardly facing surface 62 facing radially inward, and a fitting distally facing surface 63 extending from the end of the inwardly facing surface 62 toward the radially outer side and facing the distal end side (downward in FIG. 2). ing. A first ridge angle portion 65 is formed by the metal rear end facing surface 61 and the inward surface 62, and a second ridge angle portion 66 is formed by the inward surface 62 and the metal tip facing surface 63.

  With such a configuration, as shown in FIG. 1, the insulator 8 of the insulator 10 inserted in the cylindrical hole 55 is arranged with the packing 8 on the metal rear end facing surface 61 of the metal diameter reduced portion 60 of the metal shell 50. The step portion 15 is supported. Furthermore, the ring members 6, 7 and the talc 9 are disposed between the metal shell 50 and the insulator 10, and in this state, the end of the crimping portion 53 is bent inward, and the insulator 10 is thus crimped. Is pressed toward the front end side in the metal shell 50. Then, as shown in FIG. 2, the insulator tip-facing surface 14 of the insulator step portion 15 of the insulator 10 is annularly formed on the metal rear end-facing surface 61 of the metal diameter-reduced portion 60 formed in the cylindrical hole 55 of the metal shell 50. The metal shell 50 and the insulator 10 are integrated with each other through the packing 8. The packing 8 is made by punching a copper plate having a high thermal conductivity, and can efficiently transfer the heat of the insulator 10 to the metal shell 50 and let it escape to the engine head via the metal shell 50. Therefore, the heat resistance of the spark plug 100 is improved. In addition, the airtightness between the metal shell 50 and the insulator 10 is maintained by the packing 8, and the gap 70 between the outer peripheral surface of the leg long portion 13 of the insulator 10 and the inner peripheral surface of the metal shell 50. The unburned gas that has entered is configured not to flow out to the rear end side (upper side in FIG. 2) from the packing 8.

  Next, the positional relationship and shape of the insulator 10, the metal shell 50, and the packing 8 will be described with reference to FIG. As described above, the first ridge angle portion 65 is formed on the rear end side of the metal fitting reduced diameter portion 60 formed in the cylindrical hole 55 of the metal shell 50 by the metal rear end facing surface 61 and the inward surface 62. Yes. When a high voltage is applied to the metal shell 50, the electric field strength in the vicinity of the first ridge angle portion 65 becomes stronger in the gap 70 between the insulator 10 and the metal shell 50 than in other portions, and corona discharge is generated. Can occur. In the present invention, by actively generating corona discharge in the vicinity of the first ridge angle portion 65, carbon adhering to the surface of the leg portion 13 of the insulator 10 is burned and cleaned, and a leak (leakage) phenomenon occurs. The possibility can be reduced.

  In the present embodiment, the packing 8 is disposed on the metal rear end facing surface 61 to expose the first ridge angle portion 65. Here, when the first ridge angle portion 65 is covered with the packing 8, the electric field strength in the vicinity of the first ridge angle portion 65 is weaker than that in the case where the first ridge angle portion 65 is exposed. There is a possibility that the cleaning effect cannot be obtained. On the other hand, as the distance between the first ridge angle portion 65 and the packing 8 is increased, the radial width of the annular packing 8 is narrowed, so that the rigidity of the packing 8 may be reduced and deformation may occur. When the packing 8 is deformed, an excessive force is applied to the insulator 10 when the metal shell 50 is caulked, and the insulator 10 may be cracked. In addition, the airtightness may be reduced. Therefore, in the present embodiment, based on the results of the analysis shown in Example 1 described later and the test shown in Example 2, the first ridge angle portion 65 and the end portion 68 on the outer side in the radial direction of the metal fitting rear end facing surface 61. The layout position of the packing 8 is defined so that 0.05L ≦ X ≦ 0.3L, where L is the distance between and the first ridge angle portion 65 and the packing 8 is X. Yes.

  Next, the shape of the first ridge angle portion 65 will be described. Since the electric field strength increases as the corner of the metal becomes sharper, corona discharge is more likely to occur as the corner of the first ridge angle portion 65 becomes sharper, and a carbon cleaning effect is obtained. Therefore, in the present embodiment, when the cross section of the metal shell 50 including the axis O is viewed based on the result of Example 3 described later, the curvature radius r of the first ridge angle portion 65 in the contour line of the cross section is 0. It is configured to be 2 mm or less, and the first ridge angle portion 65 is sharpened. In addition, when the curvature radius r is seen over the entire circumference of the first ridge angle portion 65, the maximum value and the minimum value of the curvature radius r are within the range of 0.05 mm to 0.25 mm, and the curvature over the entire circumference. If the average value of the radius r is 0.2 mm or less, a good cleaning effect of carbon can be obtained.

  Further, as the angle θ formed by the plane orthogonal to the axis O and the metal fitting rear end facing surface 61 in the metal fitting reduced diameter portion 60 is reduced, the first ridge angle portion 65 becomes sharper, so that corona discharge occurs. It becomes easy. Furthermore, since the force applied to the packing 8 is increased, a gap is hardly generated between the insulator 10 and the packing 8 or between the metal shell 50 and the packing 8, and the airtightness is improved. On the other hand, if the angle θ is too small, the axis of the cylindrical metal shell 50 and the axis of the insulator 10 held by the metal shell 50 cannot be aligned with each other, and the spark plug 100 is eccentric. There is a risk of lowering the heat resistance and leakage resistance. Therefore, in the present embodiment, the angle θ formed by the plane orthogonal to the axis O and the metal fitting rear end facing surface 61 is 20 degrees based on the analysis results shown in Example 4 described later and the test results shown in Example 5. As described above, it is configured to be 30 degrees or less.

  Next, the distance between the first ridge angle portion 65 and the insulator 10 will be described. In the present embodiment, as described above, the carbon adhering to the surface of the insulator 10 is cleaned by generating a corona discharge in the vicinity of the first ridge angle portion 65. However, if the distance Y between the first ridge angle portion 65 and the insulator 10 is too large, corona discharge does not reach the insulator 10 and a cleaning effect cannot be obtained. Further, as the distance Y is increased, the amount of unburned gas flowing from the gap 70 between the metal shell 50 and the insulator 10 to the vicinity of the first ridge angle portion 65 increases, and thus adheres to the surface of the insulator 10. The amount of carbon increases, and cleaning by corona discharge becomes difficult. Therefore, in the present embodiment, the first ridge angle portion 65 and the insulator 10 are separated by a distance of 0.3 mm or less based on the result of the test shown in Example 6 described later. Further, as the distance Y is shortened, the effect of improving the heat conductivity from the insulator 10 to the metal shell 50 and improving the heat resistance of the spark plug 100 can be obtained. In addition, when the distance between the first ridge angle part 65 and the insulator 10 is viewed over the entire circumference, the maximum value and the minimum value of this distance are within the range of 0.1 mm to 0.35 mm, and this If the average value over the entire circumference of the distance is 0.3 mm or less, a good effect can be obtained.

  Next, the shape of the second ridge angle portion 66 will be described. The second ridge angle part 66 is closer to the spark discharge gap than the first ridge angle part 65. Therefore, since the creepage distance on the surface of the insulator 10 is shorter when the leakage occurs at the second ridge angle portion 66 than when the leakage phenomenon occurs at the first ridge angle portion 65, the second ridge angle portion 66 leaks. The phenomenon is easy to occur. In addition, as the electric field strength increases, the possibility of a leak phenomenon occurring at that location increases. Therefore, if the electric field strength near the second ridge angle portion 66 is increased, the frequency of occurrence of a leak phenomenon at the second ridge angle portion 66 increases, so that the number of times of sparks in the regular spark discharge gap is reduced and the performance of the spark plug 100 is improved. Deteriorates. Therefore, when the cross section of the metal shell 50 including the axis O is viewed, the curvature radius R of the second ridge angle portion 66 is larger than the curvature radius r of the first ridge angle portion 65 in the outline of the cross section. Thereby, the electric field strength in the cylinder of the metal shell 50 is distributed between the vicinity of the first ridge angle portion 65 and the vicinity of the second ridge angle portion 66, thereby preventing the occurrence of a leak phenomenon.

  In order to confirm the effect of this invention about the spark plug comprised in this way, the evaluation test shown below was done.

[Example 1]
First, a simulation analysis was performed on the relationship between the distance between the first ridge angle part 65 and the packing 8 and the electric field strength in the vicinity of the first ridge angle part 65 and the second ridge angle part 66. In this simulation, software for obtaining electric field strength by a known FEM analysis method was used. And, the distance between the first ridge angle portion 65 and the radially outer end 68 of the metal rear end facing surface 61 is L, and the distance between the first ridge angle portion 65 and the packing 8 is X. When the value is 0, 0.05L, and 0.10L, various conditions are set in three patterns to analyze the electric field strength, and the analysis results are shown in FIG. The horizontal axis of the graph shown in FIG. 3 indicates the position of the spark plug in the axial direction, the left side corresponds to the rear end side of the spark plug, and the right side corresponds to the front end side. The vertical axis indicates the electric field strength, and the electric field strength is higher toward the upper side.

  As shown in FIG. 3, when the value of X is 0 (when the first ridge angle portion 65 and the packing 8 are in contact) as a result of this analysis, the electric field strength in the vicinity of the first ridge angle portion 65 is There was not much difference from the surroundings, and it was confirmed that the electric field strength near the second ridge angle portion 66 was significantly stronger than the surroundings. On the other hand, when the value of X was 0.05 L, the electric field strength near the first ridge angle portion 65 was strong, and the electric field strength near the second ridge angle portion 66 was weak. That is, it was confirmed that the electric field strength is dispersed in the first ridge angle part 65 and the second ridge angle part 66. When the value of X is 0.10 L, the electric field strength near the first ridge angle portion 65 is further increased, and the electric field strength of the second ridge angle portion 66 is further decreased. From this result, it was found that the value of X is desirably 0.05 L or more in order to increase the electric field strength in the vicinity of the first ridge angle portion 65 and obtain a cleaning effect by corona discharge.

[Example 2]
Next, an evaluation test was performed on the relationship between the distance between the first ridge angle portion 65 and the packing 8 and the thickness of the packing 8. In this evaluation test, the distance between the first ridge angle portion 65 and the radially outer end 68 of the metal rear end facing surface 61 is L, and the distance between the first ridge angle portion 65 and the packing 8 is X. Samples of a plurality of spark plugs differing by 0.1 L from 0 to 0.5 L only in the value of X. Here, the larger the value of X, the narrower the radial width of the annular packing 8. And the thickness of the packing 8 when each sample exhibited the same airtightness was measured, and the measurement result is shown in FIG.

  As shown in FIG. 4, as a result of this evaluation test, when the value of X is increased (the radial width of the packing 8 is narrowed), the thickness of the packing is almost equal when X is 0 to 0.2L. Although it did not change, it was confirmed that the packing 8 was slightly deformed and thinned at 0.3L, and that the thickness of the packing 8 was suddenly thinned at 0.4L or more. As described above, when the packing 8 is deformed, there is a possibility that the insulator 10 may be cracked or the like or the airtightness may be lowered. Therefore, in order to prevent the deformation of the packing 8 and ensure the performance of the spark plug 100, it can be said that the value of X is preferably set to 0.3 L or less. Then, when the two results of Example 1 and Example 2 were integrated, it was found that the value of X is preferably 0.05L ≦ X ≦ 0.3.

[Example 3]
Next, a simulation analysis was performed on the relationship between the radius of curvature of the corner of the first ridge angle portion 65 and the electric field strength near the first ridge angle portion 65. In this simulation, software for obtaining electric field strength by a known FEM analysis method was used. The distance between the first ridge angle portion 65 and the packing 8 is fixed to 0.1 L, and only the radius of curvature of the corner of the first ridge angle portion 65 is changed from 0 mm to 0.5 mm. Conditions were set and the electric field strength was analyzed. The analysis results are shown in FIG.

  As shown in FIG. 5, as a result of this analysis, it was confirmed that the electric field strength in the vicinity of the first ridge angle portion 65 becomes weaker as the radius of curvature is increased (rounded corners). When the radius of curvature is greater than 0.2 mm, the electric field strength remains a small value and does not change much. However, when the radius of curvature is 0.2 mm or less, it can be confirmed that the electric field strength increases as the radius of curvature decreases. Therefore, in order to obtain a cleaning effect by corona discharge, it can be said that the radius of curvature of the corner of the first ridge angle portion 65 is desirably 0.2 mm or less.

[Example 4]
Next, a simulation analysis was performed on the relationship between the angle of the metal fitting rear end facing surface 61 with respect to a plane orthogonal to the axis O and the electric field strength near the first ridge angle portion 65. In this simulation, software for obtaining electric field strength by FEM analysis was used. Then, the distance between the first ridge angle portion 65 and the packing 8 is fixed to 0.1 L, various conditions are set by changing only the angle θ of the metal fitting rear end facing surface 61 with respect to the plane orthogonal to the axis O, The electric field strength was analyzed. The analysis results are shown in FIG.

  As shown in FIG. 6, when the value of θ is larger than 40 degrees as a result of this analysis, the electric field strength in the vicinity of the first ridge angle portion 65 remains weak but does not change much, but the value of θ is 40 degrees or less. In this case, it was confirmed that the electric field strength increased as the value of θ was decreased. From this, it was found that the value of θ is desirably 40 degrees or less.

[Example 5]
Next, an evaluation test was performed on the relationship between the angle of the metal fitting rear end facing surface 61 with respect to a plane orthogonal to the axis O, airtightness, and assembly eccentricity. In this evaluation test, a plurality of spark plugs were produced by changing only the angle θ of the metal fitting rear end facing surface 61 with respect to the plane orthogonal to the axis O. And the shift | offset | difference (assembly eccentricity) of the axial center of the metal shell 50 in each spark plug and the axial center of the insulator 10 was measured. Further, in order to evaluate the airtightness, air is sent from the front end side of each spark plug to the gap 70 (see FIG. 2) between the metal shell 50 and the insulator 10 at an air pressure of 2 MPa, and the packing is passed through the gap. The amount of outflow (cc) per minute of the air flowing out to the rear end side of 8 is measured using an air flow meter. This operation was performed a plurality of times while changing the temperature of the spark plug, and the temperature of the metal shell 50 in the vicinity of the packing 8 when 10 cc of air flowed out in one minute was measured. The measurement results are shown in FIG. In addition, air becomes easy to flow out to the rear end side of the packing 8 as the temperature increases. Therefore, it can be said that the higher the temperature (leakage seating temperature) of the metal shell 50 when 10 cc of air flows out in one minute, the better the airtight spark plug.

  As shown in FIG. 7, as a result of this evaluation test, when the value of θ is increased, good airtightness can be obtained up to 30 degrees, but when it exceeds 30 degrees, the airtightness deteriorates rapidly. I was able to confirm. As for assembly eccentricity, it is confirmed that as the value of θ is increased, the amount of eccentricity rapidly decreases up to 20 degrees, and the amount of eccentricity decreases gradually when it exceeds 20 degrees. did it. Therefore, it can be said that the value of θ is preferably 20 degrees or more and 30 degrees or less in consideration of airtightness and assembly eccentricity.

[Example 6]
Next, an evaluation test was performed on the relationship between the distance between the first ridge angle portion 65 and the insulator 10 and the smoldering contamination of the spark plug. In this evaluation test, the distance between the first ridge angle part 65 and the packing 8 is fixed to 0.1 L, and only the distance Y between the first ridge angle part 65 and the insulator 10 is 0.1 mm and 0.3 mm. The spark plug was subjected to a smoldering stain test for each spark plug. This test was performed based on a predetermined operation pattern defined by JIS D1606. In this operation pattern, in a temperature state of minus 10 degrees, the insulation resistance of the insulator 10 after being operated in a state where the insulator 10 is easily contaminated and the insulation after being operated in a state in which the attached carbon is easily cleaned. The insulation resistance of the insulator 10 was measured, and this was regarded as one cycle, and a total of 10 cycles were repeated. The measurement results are shown in FIG. In addition, if the speed of cleaning cannot keep up with the speed of fouling, and the insulation resistance of the insulator 10 cannot be maintained, the graph is lowered to the right.

  As shown in FIG. 8, when the distance Y is 0.1 mm and 0.3 mm as a result of this evaluation test, the insulation resistance of the insulator 10 is maintained even after 10 cycles. However, it was confirmed that the insulation resistance could not be maintained when the value of Y was 0.4 mm. Further, when the insulator 10 and the metal shell 50 are in contact with each other, the insulation resistance of the insulator 10 cannot be ensured. Therefore, in order to obtain a cleaning effect by corona discharge, it has been found desirable to separate the first ridge angle portion 65 and the insulator 10 from each other with a distance of 0.3 mm or less.

  Needless to say, the present invention can be modified in various ways. For example, unlike the metal fitting reduced diameter portion 60 of the present embodiment, the metal fitting reduced diameter portion 60 may be extended to the front end surface 57 of the metal shell 50. Moreover, it is not limited to the material of packing, You may use not only copper but iron, stainless steel, etc.

1 is a partial cross-sectional view of a spark plug 100. FIG. It is sectional drawing to which the principal part of packing 8 vicinity was expanded. 6 is a graph showing a result of analysis on a relationship between a distance between a first ridge angle portion 65 and a packing 8 and an electric field strength in the vicinity of the reduced diameter portion 60 of the metal shell 50. It is a graph which shows the result of the evaluation test about the relationship between the distance between the 1st ridge angle site | part 65 and the packing 8, and the thickness of the packing 8. FIG. It is a graph which shows the result of the analysis about the relationship between the curvature radius of the angle | corner of the 1st ridge angle site | part 65, and the electric field strength of the 1st ridge angle site | part 65 vicinity. It is a graph which shows the result of the analysis about the relationship between the angle of the metal fitting rear end surface 61 with respect to the plane orthogonal to the axis line O, and the electric field strength of the 1st ridge angle part 65 vicinity. It is a graph which shows the result of the evaluation test about the relationship of the angle of the metal fitting rear end surface 61 with respect to the plane orthogonal to the axis line O, airtightness, and assembly eccentricity. It is a graph which shows the result of the evaluation test about the relationship between the distance between the 1st ridge angle site | part 65 and the insulator 10, and the smoldering stain of a spark plug.

Explanation of symbols

8 Packing 10 Insulator 12 Shaft hole 13 Leg long part 14 Insulator tip-facing surface 15 Insulator step 17 End-side trunk 18 Rear-end trunk 20 Central electrode 50 Main metal fitting 55 Cylindrical hole 60 Fitting reduced diameter part 61 Fitting rear end Surface 62 Inward surface 63 Metal tip-facing surface 65 First ridge angle portion 66 Second ridge angle portion 68 End portion 100 Spark plug

Claims (5)

An axial center electrode that forms an electrode for spark discharge on its tip side;
An insulator having an axial hole extending in the axial direction of the central electrode, and holding the central electrode inside the axial hole;
A metal shell having a cylindrical hole extending in the axial direction and holding the insulator inside the cylindrical hole;
An annular packing interposed between the insulator and the metal shell so as to contact the insulator,
The insulator is an insulator body part which is a part on the rear end side of the insulator, a part on the tip side of the insulator, a leg length part whose diameter is smaller than an outer diameter of the insulator body part, and the insulator body part, The leg long portion is connected, and is configured to include an insulator step portion having an insulator tip facing surface that is a surface facing the tip end side in the axial direction.
A metal fitting diameter-reduced portion is formed in the cylindrical hole of the metal shell, and the metal fitting reduced-diameter portion is a surface facing the rear end side in the axial direction. A rear end facing surface and an inward facing surface that is a surface facing radially inward,
The packing is a spark plug disposed between the insulator tip-facing surface of the insulator and the metal rear-facing surface of the metal shell,
A distance between a first ridge angle portion formed by the metal rear end facing surface and the inward surface in the metal reduced diameter portion and the packing is a radially outer end of the metal rear end facing surface and the first A spark plug, wherein the distance from the ridge angle portion is L and is 0.05L or more and 0.3L or less.   2. The spark plug according to claim 1, wherein when the cross section of the metallic shell including the axis is viewed, a radius of curvature of the first ridge angle portion in the outline of the cross section is 0.2 mm or less.   The spark plug according to claim 1 or 2, wherein the first ridge angle part and the insulator are spaced apart by a distance of 0.3 mm or less.   When the cross section of the metal shell including the axis is viewed, the angle between the surface facing the rear end of the metal fitting and the plane perpendicular to the axis of the metal shell is 20 degrees or more and 30 degrees or less. The spark plug according to any one of claims 1 to 3, wherein: The metal fitting reduced diameter portion has a metal fitting tip-facing surface which is a surface facing the tip side in the axial direction,
When the cross section of the metal shell including the axis is viewed, the curvature radius of the second ridge angle portion formed by the inward surface of the reduced diameter portion of the metal fitting and the surface of the metal fitting tip in the contour line of the cross section is The spark plug according to any one of claims 1 to 4, wherein the spark plug is larger than a radius of curvature of the first ridge angle portion.

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