JP4950266B2 - Sealing member for spark plug and spark plug - Google Patents

Description

  The present invention relates to a spark plug sealing member and a spark plug that are used by being mounted on a metal shell of a spark plug that is attached to an attachment hole of an internal combustion engine and seals airtight leakage through the attachment hole.

  A general spark plug is attached to an internal combustion engine by screwing a thread formed on the outer periphery of a metal shell into a female screw in a mounting hole provided in an engine head of the internal combustion engine. In such a spark plug, an annular sealing member (gasket) is attached to the outer periphery of the metal shell in order to prevent airtight leakage in the combustion chamber through the mounting hole. A general gasket is produced by folding a plate material formed in an annular shape from a steel strip for cold rolling (hereinafter referred to as “Fe”), for example, in a radial direction so that the cross section has an S shape. When the spark plug is attached to the attachment hole, the gasket is sandwiched between the overhanging portion of the metal shell and the opening peripheral portion of the attachment hole and compressed, and the axial force (according to tightening) is improved while improving adhesion. A reaction force acting in the axial direction due to compression is generated, and airtight leakage in the combustion chamber is sealed through the mounting hole.

  In recent years, downsizing and higher performance of internal combustion engines have been achieved, engine vibrations tend to be intense, and the temperature in the combustion chamber is also increasing. For this reason, a conventional gasket made of Fe has a relatively low durability against creep deformation caused by a heating / cooling cycle that accompanies driving / resting of the engine, so that it may loosen and cause a reduction in axial force. Therefore, the use of a gasket made of stainless steel, which is higher in rigidity than Fe and hardly causes creep deformation, maintains airtightness (see, for example, Patent Document 1).

JP 2004-134120 A

  However, as the internal combustion engine is reduced in size, the spark plug is also reduced in size, and the strength of the metal shell decreases as the thickness of the metal shell is reduced. Therefore, the recommended tightening torque of the spark plug is set low. Highly rigid gaskets made of stainless steel are less prone to plastic deformation, so if the tightening torque is low, sufficient axial force cannot be obtained after tightening, which may result in insufficient sealing of the airtight leak in the combustion chamber. there were. On the other hand, if the tightening torque is increased so as to cause sufficient plastic deformation of the gasket, the burden on the screw neck of the metal shell whose strength has been reduced due to downsizing increases, which may cause breakage or the like.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a spark plug sealing member and a spark plug capable of obtaining a sufficient axial force even with a low tightening torque.

A sealing member for the spark plug according to a 請 Motomeko 1, giving the process of folding the sheet material in the radial direction on a single plate material forming the annular made of austenitic stainless steel or ferritic stainless steel, at least the The plate member is formed so as to have a portion where two or more layers are overlapped in the axial direction, and is used by being mounted on the outer periphery of a metallic shell of a spark plug having a cylindrical shape and having a thread. A projecting portion that is provided on the outer periphery of the metal shell and extends outwardly from the outer periphery of the metal shell, and forms a round in the circumferential direction, and an opening peripheral portion of the mounting hole. Is a sealing member for a spark plug that seals between the projecting portion and the peripheral edge portion of the opening by being compressed in the axial direction. The number of layers of the plate material in the most multiplexed portion where the number of layers of the plate material constituting the sealing member is the largest in the axial direction in a state before being attached to the metal shell and being attached to the internal combustion engine which is 0 or less N, the average thickness of the plate material is l [mm], the total thickness of each layer of the plate material at the most multiplexed portion is L [mm], and the thickness of the sealing member in the axial direction before compression is x [mm] when a, and 0.2 ≦ l [mm] ≦ 0.5 , and 2 ≦ n ≦ 5, 1.1L ≦ x ≦ 1.4L ··· above, fulfills and (2), the plate Is a portion that is folded and connected between two portions that are arranged to overlap in the axial direction, and the curvature radius of the portion having the smallest curvature radius in one of the plurality of the bent portions , The minimum radius of curvature R at the bent portion Further, the minimum curvature radii R of the plurality of bent portions are compared with each other, the minimum radius of curvature R of the first bent portion having the largest minimum curvature radius R is set to R1 [mm], and When the minimum curvature radius R of the second bent portion having the smallest minimum curvature radius R is R2 [mm], 0.2 ≦ R1 ≦ 0.8 (3) and 0.05 ≦ R2 ≦ 0.2 (4) and R1> R2 (5) are satisfied .

Moreover, the sealing member for a spark plug of the invention according to claim 2 is the structure of the invention according to claim 1 , wherein the radius of curvature of the first bent portion becomes the minimum radius of curvature R <b> 1. When the thickness of the plate material is t1 [mm] and the thickness of the plate material in the portion where the radius of curvature is the minimum curvature radius R2 in the second bent portion is t2 [mm], t2 <t1. (6) is satisfied.

A spark plug of the invention according to claim 3 is characterized in that the spark plug sealing member according to claim 1 or 2 is mounted.

Since the sealing member for a spark plug of the invention according to claim 1 is made of austenitic stainless steel or ferritic stainless steel, the rigidity is higher than that of a sealing member made of a generally used cold rolling steel strip. High durability against creep deformation caused by heating / cooling during engine operation / rest. When this sealing member is attached to a spark plug having a nominal diameter of M10 or less, it is defined that the (total) thickness x of the sealing member in the axial direction satisfies the expression (2). That is, since the thickness x in the axial direction is smaller than that of a generally used sealing member, even if the spark plug is compressed in the axial direction, the elastic deformation reaches the limit and the plastic deformation does not occur. As soon as it occurs, the plate materials constituting the sealing member can be brought into close contact with each other. In the relationship between the tightening torque of the spark plug and the axial force generated in the sealing member, the sealing member is elastically deformed and the axial force is increased as the tightening torque is increased. When plastic deformation occurs, the axial force may not increase even when the tightening torque is increased. Even in such a case, the sealing member according to claim 1 can continuously increase the axial force because the plate members are in close contact with each other during elastic deformation or immediately after plastic deformation occurs as described above. .

  When the thickness x of the sealing member is larger than 1.4 L, the axial force with respect to the tightening torque may be smaller than that of a sealing member made of a generally used cold rolling steel strip. In addition, the sealing member is formed with a portion projecting inward by lightly crushing the whole or a part of the inner hole side to prevent dropping after being attached to the metal shell. When the thickness x of the sealing member is smaller than 1.1 L, there is a possibility that a projecting portion having a size sufficient to prevent the dropout may not be formed even if the sealing member is crushed.

By the way, the 1st bending part of a sealing member is a site | part with the largest minimum curvature radius R1, and the plastic deformation which occurs when an elastic deformation reaches a limit and elastic deformation which applies a fastening torque to a sealing member The state of depends on the size of the minimum curvature radius R1. That is, there is a correlation between the magnitude of the minimum curvature radius R1 and the magnitude of the axial force. Therefore, when a certain compressive force is applied to the sealing member, the degree of deformation of the sealing member can be adjusted by the size of the minimum curvature radius R1, and the axial force generated in the sealing member is the sealing member. It can be adjusted according to the degree of deformation. When a spark plug is attached without using a torque wrench and tightening is performed at a rotation angle (90 degrees to 270 degrees) generally employed, the range of compressive force applied to the sealing member is a certain range. The size of the minimum curvature radius R1 can be adjusted in accordance with the range so that a target axial force can be obtained . Satisfy the minimum radius of curvature R1 of that is the formula (3), when performing tightening by the rotational angle, it is possible to obtain the axial force can obtain sufficient sealing effect by the sealing member.

Further, since the second bent portion its minimum radius of curvature R2 of having most small minimum radius of curvature R2 satisfies the formula (4), at the time of compression, the elastic deformation and plastic deformation in the second bent portion is smoothly It is performed and the adhesiveness at the time of contact of each layer of the board | plate material which comprises a sealing member can be improved.

Thus, when producing a highly rigid sealing member made of stainless steel, as in the invention according to claim 2 , the second bent portion needs to have a higher degree of bending than the first bent portion. If thickness t2 of this is made thinner than thickness t1 of the 1st bending part, processing can be performed easily.

Moreover, in the spark plug of the invention according to claim 3 , by mounting the sealing member for the spark plug according to claim 1 or 2 , a sufficient sealing effect can be obtained even if the size and diameter are reduced. Obtainable.

FIG. 3 is a partial cross-sectional view of the spark plug 100 as viewed in a state attached to the engine head 150. FIG. 3 is a cross-sectional view in which the vicinity of a gasket 80 of a spark plug 100 attached to an engine head 150 is enlarged. It is sectional drawing in the circumferential direction before deforming the gasket 80 by compression. It is a graph which shows the relationship between fastening torque and axial force. It is a graph which shows the relationship between the thickness of the whole gasket, and the frequency | count of omission occurrence. It is a graph which shows the relationship between the thickness of the whole gasket, and axial force. It is a graph which shows the relationship between the thickness of the whole gasket, and axial force. It is a graph which shows the relationship between the thickness of the whole gasket, and axial force. It is a graph which shows the relationship between the thickness of the whole gasket, and axial force. It is a graph which shows the relationship between the thickness of the whole gasket, and axial force. It is a graph which shows the relationship between the rotation angle by the difference in minimum curvature radius R1, and axial force. It is a graph which shows the relationship between the minimum curvature radius R1 in which the axial force of 10 kN is obtained, and a rotation angle.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a spark plug embodying the present invention and an embodiment of a manufacturing method thereof will be described with reference to the drawings. First, with reference to FIGS. 1-3, the structure of the spark plug 100 which mounted | wore with the gasket 80 as an example of the sealing member which concerns on this invention is demonstrated. FIG. 1 is a partial cross-sectional view of the spark plug 100 as viewed in a state attached to the engine head 150. FIG. 2 is an enlarged cross-sectional view of the vicinity of the gasket 80 of the spark plug 100 attached to the engine head 150. FIG. 3 is a cross-sectional view in the circumferential direction before the gasket 80 is deformed by compression. In FIG. 1, the axis O direction of the spark plug 100 will be described as the vertical direction in the drawing, the lower side will be described as the front end side, and the upper side will be described as the rear end side.

  As shown in FIG. 1, the spark plug 100 roughly includes an insulator 10 that holds the center electrode 20 on the front end side in its own shaft hole 12 and holds the terminal fitting 40 on the rear end side. The outer periphery in the circumferential direction is surrounded by the metal shell 50 and held in the circumferential direction. Further, the ground electrode 30 is joined to the front end surface 57 of the metal shell 50, and the front end portion 31 side is bent so as to face the center electrode 20.

  First, the insulator 10 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 an axial hole 12 extending in the direction of the axis O is formed at the axial center. 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 side body portion 18 is formed on the rear end side (the 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 distal end side, and exposed to the combustion chamber 151 when the spark plug 100 is attached to the engine head 150 of the internal combustion engine. A step portion 15 is formed between the leg length portion 13 and the front end side body portion 17.

  Next, the center electrode 20 will be described. The center electrode 20 is formed of 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 distal end portion 21 of the center electrode 20 protrudes from the distal end surface of the insulator 10 and is formed so as to become smaller in diameter toward the distal end side. A tip 90 made of a noble metal is joined to the tip surface of the tip portion 21 in order to improve the spark wear resistance. Further, 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. An ignition coil (not shown) is connected to the terminal fitting 40 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 perpendicular to its longitudinal direction, and the base 32 is joined to the distal 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 21 of the center electrode 20.

  Next, the metal shell 50 will be described. The metal shell 50 is a cylindrical metal fitting for fixing the spark plug 100 to the engine head 150 of the internal combustion engine. Inside the metal shell 50 is a portion extending from a part of the rear end side body portion 18 of the insulator 10 to the leg length portion 13. The insulator 10 is held so as to surround the part. The metal shell 50 is made of a low carbon steel material, and a tool engaging portion 51 to which a spark plug wrench (not shown) is fitted, and a mounting portion 52 in which a screw thread to be screwed into the female screw of the mounting hole 155 of the engine head 150 is formed. And have. The metal shell 50 of the present embodiment is manufactured in accordance with a standard in which the nominal diameter of the thread of the mounting portion 52 is M12.

  Between the tool engaging portion 51 and the attachment portion 52 of the metal shell 50, an overhanging portion 54 is formed. A portion between the attachment portion 52 and the overhang portion 54 is referred to as a screw neck 55 and is formed to have a smaller diameter than the outer diameter of the overhang portion 54 and the outer diameter of the attachment portion 52. When the spark plug 100 is attached to the engine head 150, a gasket 80 (described later) for sealing an airtight leak in the combustion chamber 151 via the attachment hole 155 is fitted into the screw neck 55.

  Further, a thin caulking portion 53 is provided on the rear end side of the metal fitting 50 from the tool engaging portion 51, and between the overhang portion 54 and the tool engaging portion 51, similarly to the caulking portion 53. A thin buckling portion 58 is provided. Annular ring members 6, 7 are interposed 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. Further, a powder of talc (talc) 9 is filled between the ring members 6 and 7. Then, the insulator 10 is pressed toward the front end side in the metal shell 50 through the ring members 6 and 7 and the talc 9 by bending the crimping portion 53 inwardly. Thereby, the step portion 15 of the insulator 10 is supported by the step portion 56 formed at the position of the mounting portion 52 on the inner periphery of the metal shell 50 via the annular plate packing 8, so that the metal shell 50 and the insulator 50 are supported. 10 is integrated. At this time, the airtightness between the metal shell 50 and the insulator 10 is maintained by the plate packing 8, and the outflow of combustion gas is prevented. The above-described buckling portion 58 is configured to bend outwardly and deform with the addition of compressive force during caulking, and increase the compression length of the talc 9 in the direction of the axis O to improve airtightness. ing.

  Next, the gasket 80 will be described. The gasket 80 shown in FIG. 2 and FIG. 3 is produced by performing a process of turning itself back in the radial direction of a plate made of austenitic stainless steel or ferritic stainless steel. It is. When the spark plug 100 is attached to the engine head 150, the gasket 80 is compressed and deformed between the opening peripheral edge portion 156 of the attachment hole 155 and the overhanging portion 54 of the metal shell 50, and adheres to both. Thus, an airtight leak in the combustion chamber 151 via the mounting hole 155 is sealed. 2 shows a sectional shape of the gasket 80 after being deformed by compression, and FIG. 3 shows a sectional shape of the gasket 80 before being deformed.

  The gasket 80 has a portion in which at least two layers overlap each other in the axis O direction. Although not shown, the gasket 80 has an inner diameter slightly larger than the outer diameter of the mounting portion 52 in a state before compression. When mounting to the spark plug 100, the gasket 80 is fitted into the screw neck 55 from the front end side of the metal shell 50. Then, the entire portion of the gasket 80 or a part on the inner hole side is lightly crushed in a state where it is in contact with the overhanging portion 54, so that the gasket 80 has a portion protruding inward from the tip of the thread of the metal shell 50. Is formed, and the screw neck 55 is prevented from coming off.

  In the spark plug 100 of the present embodiment having such a structure, as described above, even if the tightening torque at the time of attachment decreases as the size and diameter of the spark plug 100 are reduced, airtight leakage in the combustion chamber 151 is prevented. The material of the gasket 80 is defined so that a sufficient axial force can be obtained. Specifically, as a material of the gasket 80, for example, stainless steel (SUS) having the following standard number defined in JIS (Japanese Industrial Standard) can be used. Examples of austenitic stainless steels include SUS201, SUS202, SUS301, SUS301J, SUS302, SUS302B, SUS304, SUS304L, SUS304N1, SUS304N2, SUS304LN, SUS305, SUS309S, SUS310S, SUS316, US3316L, S3316L, S3316L, S3316L, S3316L, S3316L, S3316L, S3316L SUS317L, SUS317J1, SUS321, SUS347, SUSXM15J1, etc. can be used. Examples of ferritic stainless steel include SUS405, SUS410L, SUS429, SUS430, SUS430LX, SUS430JIL, SUS434, SUS436L, SUS436JIL, SUS444, SUS445J1, SUS445J2, SUS447J1, and SUS447M27. The gaskets 80 made of stainless steel such as these have higher rigidity than the commonly used gaskets made of Fe, and are resistant to creep deformation caused by heating and cooling associated with engine driving and stopping. Is expensive.

  The gasket 80 is sandwiched between the overhanging portion 54 of the metallic shell 50 and the opening peripheral edge portion 156 of the mounting hole 155 when the spark plug 100 is attached, is compressed, and is deformed to improve the adhesion, thereby improving the sealing performance. A stopping effect is obtained. For this purpose, when using the austenitic stainless steel or the ferritic stainless steel, the average thickness of the plate material constituting the gasket 80 is preferably 0.2 to 0.5 mm. If the average thickness of the plate material is less than 0.2 mm, the gasket 80 is crushed by a relatively small compressive force when the spark plug 100 is attached, and a sufficient axial force cannot be obtained within an appropriate range of tightening torque. There is a fear. On the other hand, when the average thickness exceeds 0.5 mm, it is necessary to increase the compression force for causing deformation of the gasket 80. When the spark plug 100 is tightened by applying a stronger compression force, There is a possibility that the screw neck 55 may be damaged or the thread of the mounting portion 52 may be crushed. The average thickness is an average thickness of different portions (for example, ten different portions) in the plate material.

  However, the recommended tightening torque when attaching the spark plug to the engine head is determined according to the standard (nominal diameter) of the spark plug in JIS B8031, and the tightening torque is smaller as the nominal diameter is smaller. Is small. In the spark plug 100 having a small diameter of M12 or less, when the gasket 80 made of stainless steel (SUS) is replaced with a conventional gasket made of Fe as it is, the axial force generated during tightening is made of Fe. Reduced compared to gaskets. This will be described with reference to FIG.

  When a spark plug with a gasket is attached to an engine head, if the tightening torque is increased, the gasket first undergoes elastic deformation and the axial force increases. As shown in FIG. 4, the gasket made of stainless steel (shown by a two-dot chain line) is higher in rigidity than the gasket made of Fe (shown by a solid line), so that elastic deformation becomes a limit as the tightening torque increases. The tightening torque at which plastic deformation (so-called buckling) begins to occur is large. While the buckling is occurring, even if the tightening torque is increased, the plastic deformation only increases, and the increase in the axial force is almost flat and the axial force is lost. When the tightening torque is further increased and the folded plate materials are brought into close contact with each other in the axial direction and further plastic deformation becomes difficult, the axial force starts to rise again. A gasket made of Fe, which has a lower rigidity than stainless steel, causes sufficient plastic deformation at a relatively low tightening torque. Therefore, the range of tightening torque during the buckling (hereinafter referred to as “buckling region”). Is smaller than a gasket made of stainless steel. In the spark plug having a nominal diameter of M12, the tightening torque recommended in the above JIS B8031 is 15 to 25 N · m. In that range, the axial force generated in the stainless steel gasket is the same as that in the Fe gasket. It does not reach the resulting axial force. That is, a high tightening torque is required to obtain an axial force equivalent to that of a gasket made of Fe in a stainless steel gasket.

  The gasket 80 of the present embodiment (shown by a one-dot chain line in FIG. 4) is made of stainless steel that is more rigid than Fe and resistant to creep deformation, while reducing the buckling region. An axial force for a tightening torque equivalent to that of the gasket is obtained. Specifically, in the process of increasing the tightening torque, during the elastic deformation or immediately after the plastic deformation occurs, the plates are brought into close contact with each other so that the loss of axial force can be reduced (tightening). Regulations are provided for the overall thickness of the gasket 80 in the previous state.

  As shown in FIG. 3, the number of plate layers in the portion where the layers of the plate material constituting the gasket 80 overlap most in the direction of the axis O (the most multiplexed portion) is n. For example, in the gasket 80 shown in FIG. 3, the number of layers of the plate material constituting the gasket 80 is the largest on the one-dot chain line P along the axis O direction, and the number of layers is four. Further, the average thickness of the plate material is l [mm], the total thickness of each layer of the plate material in the most multiplexed portion is L [mm], and the total thickness of the gasket 80 in the axis O direction is x [mm].

  In defining the thickness x [mm] of the entire gasket 80, two virtual planes orthogonal to the axis O are assumed. Since the gasket 80 has an annular shape that makes a continuous round in the circumferential direction, the virtual planes are in contact with the gasket 80 over the entire circumference on both sides of the gasket 80 in the axis O direction. The distance between the two virtual planes at this time corresponds to the thickness x of the entire gasket 80.

  As described above, the appropriate range of the tightening torque at the time of attachment is determined according to the nominal diameter of the thread formed on the attachment portion 52 of the metal shell 50. Therefore, the gasket 80 is defined differently depending on the nominal diameter so that the gasket 80 can obtain a sufficient axial force within an appropriate range of the tightening torque according to the nominal diameter.

As in the case of the gasket 80 according to the present embodiment, when the metal fitting 50 having a nominal diameter of M12 is attached,
0.2 ≦ l ≦ 0.5
When,
2 ≦ n ≦ 5
When,
1.1L ≦ x ≦ 1.45L (1)
It is prescribed to satisfy.

On the other hand, when attaching a gasket to a metal shell whose nominal diameter is M10 or less,
0.2 ≦ l ≦ 0.5
When,
2 ≦ n ≦ 5
When,
1.1L ≦ x ≦ 1.4L (2)
It is prescribed to satisfy.

  As described above, in the process of manufacturing the spark plug 100, after the gasket 80 is fitted into the screw neck 55, the entire gasket 80 or a part on the inner hole side is lightly crushed, so A portion projecting inward is also formed, so that the screw neck 55 is prevented from coming off (dropping out). When forming this protruding portion, if x is less than 1.1 L, the amount of protrusion due to crushing sufficient to prevent the dropout cannot be obtained, and the dropout from the screw neck 55 may not be sufficiently prevented. This has been confirmed from the results of Example 1 described later.

  On the other hand, if x is increased, the gap between the layers of the plate material constituting the gasket is widened, and the amount of elastic deformation and plastic deformation required to bring the layers into close contact with each other during compression increases, so the buckling shown in FIG. The area expands. When the spark plug is attached to the attachment hole with the recommended tightening torque, x is preferably 1.45L or less when the nominal diameter of the metal shell is M12, and x is 1 when M10 or less. .4L or less is preferable. It will be described later that when the upper limit of x is exceeded, the axial force obtained by the gasket becomes smaller than the axial force obtained when a spark plug using a conventional gasket made of Fe is similarly attached. This is confirmed from the results of Examples 2 to 4 and Examples 5 and 6.

  In the present embodiment, provision is made for the radii of curvature of the bent portions 83, 86, 89 of the gasket 80 shown in FIG. The bent portion refers to a portion where the two plate portions constituting the gasket overlap each other in the direction of the axis O in the circumferential cross section of the gasket. Specifically, the bent portion 83 is folded and connected between a portion 81 and a portion 82 arranged on a one-dot chain line Q along the axis O direction at a portion on the plate material. The bent portion 86 is connected between the portion 84 and the portion 85 that are disposed on the one-dot chain line S along the axis O direction at the portion on the plate. The bent portion 89 is connected by folding back between a portion 87 and a portion 88 arranged on the one-dot chain line P along the axis O direction at a portion on the plate material.

Next, in each of the bent portions 83, 86, and 89, the curvature radius of the smallest portion of the curvature radii of the contour that is inside the fold at the contour of the circumferential cross section (shown by a dotted line in FIG. 3). Let the radius of the circle) be the minimum radius of curvature R of each. Then, the respective minimum curvature radii R in the respective bent portions 83, 86, 89 are compared, and the minimum curvature radius R of the bent portion 83 having the largest minimum curvature radius R is defined as R1 [mm], and the smallest minimum curvature radius. The minimum curvature radius R of the bent portion 86 having R is R2 [mm]. At this time, in this embodiment,
0.2 ≦ R1 ≦ 0.8 (3)
When,
0.05 ≦ R2 ≦ 0.2 (4)
When,
R1> R2 (5)
And that is satisfied. The bent portion 83 corresponds to the “first bent portion” in the present invention, and the bent portion 86 corresponds to the “second bent portion” in the present invention.

  When attaching the spark plug 100 to the attachment hole 155, it is necessary to use a torque wrench to tighten with the recommended tightening torque, but if the torque wrench is not ready, adjust the rotation angle when tightening. Designed to obtain the required axial force. Specifically, when the gasket 80 is brought into contact with the opening peripheral edge 156 of the mounting hole 155 at the time of tightening, tightening at a preset rotation angle is equivalent to the case of tightening with the recommended tightening torque. Axial force can be obtained. Since the bent portion 83 has the largest minimum curvature radius R1 (that is, R1> R2), when the gasket 80 is compressed and deformed, the degree of deformation of the entire gasket 80 is greatly affected. That is, depending on the minimum curvature radius R1 of the bent portion 83, the state of elastic deformation caused by applying a tightening torque to the gasket 80 and the state of plastic deformation caused when the elastic deformation reaches the limit differ. For this reason, it can be said that there is a correlation in the relationship between the rotation angle at the time of tightening and the obtained axial force. Therefore, when a certain compressive force is applied to the gasket 80, the degree of deformation of the gasket 80 can be adjusted by the size of the minimum radius of curvature R1, and the axial force generated in the gasket 80 is the deformation of the gasket 80. It can be adjusted according to the degree. In other words, when tightening is performed at a rotation angle (90 degrees to 270 degrees) that is generally employed when the spark plug 100 is attached, the range of the compressive force applied to the gasket 80 is a certain range. Accordingly, it is possible to adjust the size of the minimum curvature radius R1 so that a target axial force can be obtained. Therefore, in the present embodiment, the minimum curvature radius R1 of the bent portion 83 is set to 0.2 mm or more and 0.8 mm or less. Based on the result of Example 7 to be described later, if the minimum radius of curvature R1 of the bent portion 83 is set in the above range, tightening is performed in a range of a rotation angle (90 degrees to 270 degrees) generally employed. In this case, it was possible to obtain a minimum axial force of 10 kN, which is considered to cause no loosening due to engine vibration or the like.

  Further, unlike the bent portion 83, the bent portion 86 has the smallest minimum radius of curvature R2, so that the smoothness of the elastic deformation and plastic deformation in the bent portion 86 is due to the layers of the plate material constituting the gasket. It affects the adhesion at the time of contact. Therefore, in the present embodiment, the minimum curvature radius R2 of the bent portion 86 is set to 0.05 mm or more and 0.2 mm or less. If the minimum curvature radius R2 of the bent portion 86 is less than 0.05 mm, the bent portion 86 may crack when the gasket 80 is compressed. Further, if the minimum curvature radius R2 of the bent portion 86 is larger than 0.2 mm, adhesion between the layers of the plate material may not be obtained when the gasket 80 is compressed, and there is a possibility that loosening due to engine vibration or the like may occur. This was found from the results of Example 8 described later.

Further, in the present embodiment, the thickness of the plate material in the portion of the bent portion 83 where the curvature radius is the minimum curvature radius R1 is t1 [mm], and the curvature radius of the bent portion 86 is the minimum curvature radius R2. When the thickness of the plate material in the part is t2 [mm],
t2 <t1 (6)
It stipulates that

  As described above, the bent portion 86 having the minimum radius of curvature R2 smaller than the minimum radius of curvature R1 of the bent portion 83 needs to be bent more than the bent portion 83 during manufacture. Considering the ease of processing when manufacturing the gasket 80 made of stainless steel, it is preferable to make the thickness t2 of the bent portion 86 having a large degree of bending smaller than the thickness t1 of the bent portion 83.

  As described above, when the gasket 80 made of stainless steel having higher rigidity than the conventional gasket made of Fe is used for the spark plug 100, the gasket 80 has a sealing effect equivalent to that of the gasket made of Fe. Various evaluation tests were conducted in order to set the size specification.

  First, an evaluation test for confirming the lower limit of the thickness x of the entire gasket was performed. In this evaluation test, a plurality of plate materials having an average thickness l of 0.3 mm were prepared by punching plate-shaped stainless steel into an annular shape. Then, as shown in FIG. 3, each plate was subjected to bending using a mold so that the number n of plate layers in the portion overlapping most in the axis O direction was 4. At this time, the mold is adjusted so that the total thickness x of the gasket formed after the bending process changes in the range of 1.0 L to 1.65 L, and 50 pieces each for the total thickness x are for M12. A gasket sample was prepared.

  Each of the prepared samples was fitted into a test spark plug, and a part projecting inward was formed by lightly crushing a part of the inner hole side to prevent disconnection. Then, vibration was applied to the spark plug on which each sample was mounted, and the number of samples in which dropout occurred was counted among the 50 samples prepared for each different gasket thickness x. The result of this test is shown in the graph of FIG.

  As shown in FIG. 5, none of the samples in which the thickness x of the entire gasket was 1.1 L or more dropped out by the vibration test. However, in all samples in which the total thickness x was less than 1.1 L, dropping occurred. From this, it was confirmed that the entire thickness x should be 1.1 L or more in order for the portion protruding inward to have a size sufficient to prevent the removal.

  Next, an evaluation test for confirming the upper limit of the thickness x of the entire gasket was performed. In this evaluation test, as in Example 1, a plurality of plate materials made of stainless steel (SUS) having an average thickness 1 of the plate material constituting itself of 0.3 mm are prepared, and the plate material in the portion that overlaps most in the axis O direction is prepared. Bending was performed so that the number n of layers was 4. And the whole thickness x after a bending process was changed in the range of 1.0L-1.85L, and several types of samples of the gasket for M12 were produced. For comparison, a sample of a gasket having the same shape and an overall thickness of 1.8 L (2.16 mm) was prepared using a plate made of Fe having an average thickness of 0.3 mm.

  Each prepared sample is attached to a test spark plug, and this spark plug is attached to an aluminum bush made using the same aluminum material as the engine head with a tightening torque of 20 N · m. It was measured. In the aluminum bush, a female screw corresponding to a spark plug having a nominal diameter of M12 described in JIS B8031 is formed by NC machining in a mounting hole opened in an aluminum bar material. Further, the axial force was measured by sandwiching a load cell between the peripheral edge of the opening of the aluminum bush and the gasket and electrically detecting the compressive force after tightening. The result of this test is shown in the graph of FIG.

  As described above, the gasket made of stainless steel has higher resistance to plastic deformation than the gasket made of Fe, and the axial force generated at a tightening torque of 20 N · m is small (see FIG. 4). As shown in FIG. 6, the axial force generated in the gasket decreased as the thickness x of the entire gasket increased. In the conventional gasket of the size (shape) made of Fe (the total thickness is 1.8 L), an axial force of about 9.5 kN was obtained at a tightening torque of 20 N · m. With the gasket made of stainless steel having a shape, only an axial force of about 4.8 kN was obtained. In the gasket made of stainless steel, it was confirmed that the total thickness x should be 1.45L or less in order to achieve the same axial force as that of the conventional gasket made of Fe.

  Next, an evaluation test was conducted for the same M12 gasket as in Example 2 where the maximum number of layers was three. In this evaluation test, a sample of a gasket for M12 made of stainless steel in which the average thickness l of the plate material constituting itself is 0.4 mm and the number n of the plate material layers in the portion overlapping most in the direction of the axis O is 3. In the same manner as described above, the total thickness x after bending was changed in the range of 1.0 L to 1.85 L. For comparison, a sample of a conventional gasket made of Fe having the same shape with an average thickness of 0.4 mm and an overall thickness of 1.8 L (2.16 mm) was prepared. Then, when an evaluation test was performed in the same manner as in Example 2, as shown in FIG. 7, the same tendency as in the four-layer gasket evaluated in Example 2 was observed in the gasket with the maximum number of layers being three. It was confirmed that Similarly, in order to achieve the same axial force as that of the conventional gasket made of Fe in the gasket made of stainless steel, it has been found that the total thickness x should be 1.45 L or less.

  Furthermore, an evaluation test was conducted for the case where the maximum number of layers was set to 5 with the same gasket for M12 as in Example 2. In this evaluation test, a sample of a gasket for M12 made of stainless steel in which the average thickness l of the plate material constituting itself is 0.25 mm and the number n of the plate material layers in the portion that overlaps most in the direction of the axis O is 5. In the same manner as described above, the total thickness x after bending was changed in the range of 1.0 L to 1.85 L. Then, an evaluation test was performed in the same manner as in Example 2 together with a conventional gasket made of Fe having an average thickness of 0.25 mm and an overall thickness of 1.8 L (2.25 mm) prepared for comparison. went. The result of this test is shown in FIG. 8, and it was confirmed that the gasket having the maximum number of layers of 5 showed the same tendency as the 4-layer gasket evaluated in Example 2. Similarly, in order to achieve the same axial force as that of the conventional gasket made of Fe in the gasket made of stainless steel, it has been found that the total thickness x should be 1.45 L or less.

  Similarly, an evaluation test for confirming the upper limit of the thickness x of the entire gasket was performed on the gasket for M10. In this evaluation test, a sample of a gasket for M10 made of stainless steel in which the average thickness l of the plate material constituting itself is 0.3 mm and the number n of the plate material layers in the portion overlapping most in the direction of the axis O is 4. In the same manner as described above, the total thickness x after bending was changed in the range of 1.0 L to 1.85 L. For comparison, a conventional gasket made of Fe having the same shape with an average thickness of 0.3 mm and an overall thickness of 1.8 L (2.16 mm) is prepared. An evaluation test was conducted to measure the axial force when attached to an aluminum bush with a tightening torque of 5 N · m. The result of this test is shown in FIG. 9, and also in the M10 gasket, the axial force generated in the gasket tended to decrease as the thickness x of the entire gasket increased. It was confirmed that the overall thickness x should be 1.4 L or less in order to realize the axial force equivalent to that of the conventional gasket made of Fe with the gasket made of stainless steel with the gasket for M10.

  Further, the same evaluation test was performed on the gasket for M8. This is a sample of M8 gasket made of stainless steel with an average thickness l of the plate material constituting itself of 0.4 mm and a number n of the plate material layers at the most overlapping portion in the direction of the axis O, which is 3 as above. What changed the whole thickness x after a process in the range of 1.0L-1.85L was prepared. For comparison, a conventional gasket made of Fe having the same shape with an average thickness of 0.4 mm and an overall thickness of 1.8 L (2.16 mm) is prepared. An evaluation test was performed to measure the axial force when attached to an aluminum bush with a tightening torque of m. The result of this test is shown in FIG. 10, and in the M8 gasket, the same tendency that the axial force generated in the gasket decreases as the thickness x of the entire gasket increases is shown. And in order to realize the axial force equivalent to the conventional gasket made of Fe with the gasket made of stainless steel with the gasket for M8, if the total thickness x is 1.4L or less like the gasket for M10 It was confirmed that it was good.

  Next, an evaluation test for defining the size of the minimum curvature radius R1 of the bent portion having the largest minimum curvature radius R1 was performed. As described above, when the gasket is compressed and deformed, the size of the minimum curvature radius R1 of the bent portion having the largest minimum curvature radius R1 greatly affects the degree of deformation of the entire gasket, and consequently the gasket. This affects the axial force obtained. As indicated by the one-dot chain line in the graph of FIG. 4, the gasket satisfying the expression (1) has almost no buckling region in which the increase of the axial force is flat with respect to the increase of the tightening torque, and the tightening torque. And the axial force are almost proportional. Therefore, the largest minimum radius of curvature R1 is evaluated from the relationship between the rotation angle when the spark plug is attached to the attachment hole and the axial force obtained by the gasket.

  In this evaluation test, the average thickness l of the plate material constituting itself is 0.3 mm, the number n of the plate material layers in the portion overlapping most in the direction of the axis O is 4, and the minimum radius of curvature R1 is 0.1 mm to 1.0 mm. A plurality of samples of M12 gaskets made of stainless steel were prepared so that the total thickness x after bending was adjusted to 1.33 L (1.6 mm). Each of these samples is mounted on a test spark plug, and the spark plug is attached to an aluminum bush at different rotation angles in the range of 30 to 360 degrees for each type of gasket. The axial force was measured in the same manner as in Example 2. The result of this evaluation test is shown in the graph of FIG.

  As a result of this evaluation test, as shown in FIG. 11, although the coefficient varies depending on the size of the minimum radius of curvature R1, it was confirmed that there is a proportional relationship between the rotation angle and the axial force. Here, since the minimum required axial force at which no loosening due to engine vibration or the like does not occur is 10 kN, a proportional straight line (solid line) for estimating the rotation angle when an axial force of 10 kN is obtained in FIG. The relationship between the rotation angle and the minimum radius of curvature R1 is shown in the graph of FIG. Generally, the range of 90 to 270 degrees (1/4 to 3/4 rotation) that is easy to understand intuitively is adopted as the rotation angle when tightening the spark plug. From the graph of FIG. 12, it was found that the value of the minimum curvature radius R1 that satisfies the rotation angle range of 90 to 270 degrees was found to be 0.2 mm to 0.8 mm.

  Next, an evaluation test for defining the size of the minimum curvature radius R2 of the bent portion having the smallest minimum curvature radius R2 was performed. As described above, the smoothness of elastic deformation or plastic deformation in the bent portion having the minimum radius of curvature R2 affects the adhesion at the time of contact between the layers of the plate material constituting the gasket. Therefore, the average thickness l of the plate material constituting itself is 0.3 mm, the number n of the plate material layers in the portion overlapping most in the direction of the axis O is 4, and the minimum curvature radius R2 is in the range of 0.03 mm to 0.25 mm. A plurality of samples of M12 gaskets made of stainless steel, which were adjusted so that the total thickness x after bending was 1.33 L (1.6 mm) while being changed, were prepared. At this time, in the sample in which the minimum curvature radius R2 was 0.03 mm, a crack was generated in the bent portion. Therefore, the sample was evaluated as x because it was inferior in formability, and excluded from the following evaluation tests.

  Each sample was mounted on a test spark plug, and the spark plug was attached to an aluminum bush with a tightening torque of 20 N · m, and a vibration test shown in ISO11565 was performed. Specifically, with the aluminum bush attached with the spark plug heated to 200 degrees, the vibration of acceleration 30G ± 2G, frequency 50-500Hz, sweep rate 1 octave / min, the axial direction of the spark plug and its orthogonal direction For 8 hours each. Then, after the vibration test, a torque (return torque) necessary for removing the metal shell was measured. When the return torque is 10 N · m or more (50% or more when tightening), the resistance to looseness (loose resistance) is evaluated as “good”, and those with less than 10 N · m are resistant to looseness. X was rated as low. The results of this evaluation test are shown in Table 1.

  As shown in Table 1, the gasket having a minimum radius of curvature R2 of 0.05 mm to 0.20 mm was good in terms of loosening resistance, but the gasket of 0.25 mm could be confirmed to have a problem in loosening resistance. It was. From the results of this test, it was found that the minimum radius of curvature R2 should be 0.05 mm to 0.20 mm.

  Needless to say, the present invention can be modified in various ways. For example, the gasket 80 may be a plate material having a uniform thickness or a gradient in the shape of an annular plate material before bending. In addition, the gasket 80 has been described as an example in which the number n of the plate material layers in the portion that overlaps most in the direction of the axis O is 4, but it may be of 2 to 5 layers. In this embodiment, the gasket 80 attached to the spark plug 100 having a nominal diameter of M12 has been described. However, the gasket used for the spark plug having a nominal diameter of M10 or less, such as for M10 and M8, is also in the form. The same applies to.

DESCRIPTION OF SYMBOLS 50 Metal shell 54 Overhang | projection part 80 Gasket 81 Part 82 Part 83 Bent part 84 Part 85 Part 86 Bent part 87 Part 88 Part 89 Bent part 100 Spark plug 150 Engine head 155 Mounting hole 156 Opening peripheral part

Claims (3)

An annular plate made of austenitic stainless steel or ferritic stainless steel is subjected to a process in which the plate is folded back in the radial direction so that at least the plate has an area where two or more layers overlap in the axial direction. In the state where the metal shell is mounted and used on the outer periphery of the metal shell of the spark plug having a cylindrical shape and having a thread, the metal shell is attached to the mounting hole of the internal combustion engine by screwing. It is compressed in the axial direction between a protruding portion provided on the outer periphery and extending outward from the outer periphery and making a round in the circumferential direction, and an opening peripheral portion of the mounting hole. A sealing member for a spark plug that seals between a protruding portion and the peripheral edge of the opening,
In a state before being attached to the metal shell having a nominal diameter of M10 or less and being attached to the internal combustion engine,
In the axial direction, the number of layers of the plate material in the most multiplexed portion where the number of layers of the plate material constituting the sealing member is the largest is n, the average thickness of the plate material is l [mm], and the plate material in the most multiplexed portion is When the total thickness of each layer is L [mm], and the thickness in the axial direction of the sealing member before compression is x [mm],
0.2 ≦ l [mm] ≦ 0.5
When,
2 ≦ n ≦ 5
When,
1.1L ≦ x ≦ 1.4L (2)
With satisfy the door,
The portion where the plate member is folded and connected between the two portions arranged in the axial direction is defined as a bent portion, and the portion having the smallest radius of curvature in one of the plurality of bent portions. The curvature radius is set to the minimum curvature radius R in the bent portion, and the minimum curvature radius R is compared between the plurality of bent portions, and the first bent portion having the largest minimum curvature radius R is compared. When the minimum curvature radius R is R1 [mm], and the minimum curvature radius R of the second bent portion with the smallest minimum curvature radius R is R2 [mm],
0.2 ≦ R1 ≦ 0.8 (3)
When,
0.05 ≦ R2 ≦ 0.2 (4)
When,
R1> R2 (5)
And a spark plug sealing member characterized by satisfying the above . The thickness of the plate member at the portion where the radius of curvature is the minimum radius of curvature R1 in the first bent portion is t1 [mm], and the portion of the second bent portion where the radius of curvature is the minimum radius of curvature R2 When the thickness of the plate material at t2 [mm],
t2 <t1 (6)
The spark plug sealing member according to claim 1 , wherein: A spark plug comprising the sealing member for a spark plug according to claim 1 or 2 attached thereto.

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