JP2014107084A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain flash-over while maintaining durability of an electrical insulator.SOLUTION: A spark plug comprises: an electric insulator having a shaft hole penetrating in an axial line direction, and having a step part projecting outward in a radial direction on its own outer periphery; a center electrode provided on a tip side of the shaft hole; a cylindrical main metal fitting having a receiving part projecting inward in the radial direction on its own inner periphery, and holding the electric insulator while the step part is locked with the receiving part; and a packing arranged between the step part and the receiving part and contacting them. In the electric insulator, arithmetic average roughness Raof an outer surface of a portion nearer the tip side than a position contacting the packing is 3 μm or more and 15 μm or less.

Description

  The present invention relates to a spark plug.

  In recent years, the discharge voltage required for the spark plug has been on the rise with the demand for higher engine output and lower fuel consumption. For this reason, a phenomenon (so-called flashover) in which electricity is discharged along the creeping surface of the insulator provided in the spark plug may occur.

  In order to suppress the flashover, in Patent Document 1, irregularities called corrugation are formed on the ignition portion side (electrode side) of the insulator, and in Patent Document 2, provided between the insulator and the metal shell. The surface average roughness of the portion of the insulator that is in contact with the packing is 10 μm or less.

Japanese Utility Model Publication No. 50-59428 JP 2003-303661 A Japanese Unexamined Patent Publication No. 01-221879

  However, in the spark plug described in Patent Document 1, stress is likely to be concentrated in the concave portion of the corrugation, which may damage the insulator. In the spark plug described in Patent Document 2, no consideration is given to the processing of the insulator surface from the tip of the insulator to the contact portion with the packing, so the possibility of flashover still remains. Therefore, a technology for suppressing flashover while maintaining durability of an insulator in a spark plug is desired.

  The present invention has been made to solve the above-described problems, and can be realized as the following forms.

(1) According to one aspect of the present invention, a spark plug is provided. The spark plug has an axial hole penetrating in the axial direction, and has an insulator having a stepped portion projecting radially outward on an outer periphery thereof; a center electrode provided on a distal end side of the axial hole; A cylindrical metal shell provided on the outer periphery of the insulator, having a receiving portion protruding radially inward on its inner periphery, and holding the insulator in a state where the step portion is locked to the receiving portion; A packing disposed between the stepped portion and the receiving portion and in contact with both; and an arithmetic average roughness of an outer surface of a portion of the insulator that is closer to the tip than a position in contact with the packing Ra ₁ is 3 μm or more and 15 μm or less. According to this form of the spark plug, the arithmetic average roughness Ra ₁ of the outer surface of the insulator on the tip side with respect to the position in contact with the packing is 3 μm or more. Over is suppressed. In addition, according to the spark plug of this embodiment, the arithmetic average roughness Ra ₁ of the outer surface of the portion of the insulator that is closer to the tip than the position in contact with the packing is 15 μm or less, so that it is formed on the surface of the insulator. It is possible to reduce the stress acting on the concave and convex portions of the concave and convex, and to suppress damage to the insulator such as breakage and cracking of the insulator, and to improve the durability of the spark plug.

(2) In the spark plug of the above aspect, the distance between the insulator and the metal shell in a direction orthogonal to the axial direction is 0.5 mm or less at a tip side from a position where the insulator and the packing are in contact with each other. The arithmetic average roughness Ra ₂ of the outer surface of the insulator in a part may be 3 μm or more and 15 μm or less. Generally, the smaller the distance between the insulator and the metal shell, the easier the creeping discharge of the insulator occurs. According to the spark plug of this embodiment, the arithmetic average roughness Ra ₂ of the outer surface of the insulator at a portion where the distance between the insulator and the metal shell is narrow can be set to 3 μm or more and 15 μm or less. It can be suppressed and the durability of the spark plug can be improved.

(3) In the spark plug of the above aspect, the length along the axial direction from the tip of the insulator to the position where the insulator and the packing are in contact may be 10 mm or less. When the length from the tip of the insulator to the position where the insulator and the packing are in contact is as short as 10 mm or less, flashover is more likely to occur. In this regard, according to the spark plug of the above aspect, flashover can be suppressed even when the length from the tip of the insulator to the position where the insulator and the packing are in contact is relatively short.

(4) When the length along the axial direction from the tip of the insulator to the position where the insulator and the packing are in contact is L, the spark plug of the above aspect is the packing of the insulator. The arithmetic average roughness Ra ₃ of the outer surface of the insulator in a portion from the position in contact with the tip to the tip side by L / 3 along the axial direction may be 15 μm or less. Insulator parts that come in contact with the packing are formed in a shelf shape. In this case, the electric field can easily concentrate and flashover can occur, and stress can easily concentrate on the shelf and the insulator can be damaged. May increase. According to this form of the spark plug, the arithmetic average roughness Ra ₃ of the outer surface of the insulator in the vicinity of the packing (near the shelf) can be reduced to 15 μm or less, so that flashover can be suppressed and the durability of the spark plug is improved. it can.

(5) The spark plug of the above aspect may have a screw diameter of M10 or less. Generally, a spark plug having a screw diameter of M10 or less is easily damaged because the insulator is thin. According to the spark plug of this embodiment, flashover can be suppressed while maintaining durability even in a spark plug having a screw diameter of M10 or less and a thin insulator.

(6) The spark plug of the above aspect includes a ground electrode that is fixed to a tip portion of the metal shell and forms a gap with the tip portion of the center electrode, and the gap is 0.9 mm or more. Also good. According to the spark plug of this embodiment, flashover can be suppressed and a high voltage can be applied to a spark plug having an interval of 0.9 mm or more while maintaining durability.

  The present invention can be realized in various forms other than the apparatus. For example, the present invention can be realized in the form of a spark plug manufacturing method, a spark plug control method, a computer program for realizing the control method, a non-temporary recording medium on which the computer program is recorded, and the like.

The fragmentary sectional view of the spark plug 100 in 1st Embodiment. The elements on larger scale explaining the front-end | tip part of the spark plug 100 in 1st Embodiment.

A. First embodiment:
A1. Spark plug schematic configuration:
FIG. 1 is a partial cross-sectional view of a spark plug 100 according to the first embodiment. As shown in FIG. 1, the spark plug 100 has an elongated shape along the axis O. In FIG. 1, the right side of the axis OO indicated by a one-dot broken line shows an external front view, and the left side of the axis OO shows a cross-sectional view of the spark plug 100 cut along a cross section passing through the central axis of the spark plug 100. ing. In the following description, the lower side in FIG. 1 that is parallel to the axis O is called the front end side, and the upper side in FIG. 1 is called the rear end side.

  The spark plug 100 includes an insulator 10, a center electrode 20, a ground electrode 30, a terminal fitting 40, and a metal shell 50. The rod-shaped center electrode 20 protruding from one end of the insulator 10 is electrically connected to a terminal fitting 40 provided at the other end of the insulator 10 through the inside of the insulator 10. The outer periphery of the center electrode 20 is held by the insulator 10, and the outer periphery of the insulator 10 is held by the metallic shell 50 at a position away from the terminal fitting 40. The ground electrode 30 electrically connected to the metal shell 50 forms a spark gap, which is a gap for generating a spark, between the tip of the center electrode 20. The spark plug 100 is attached to a mounting screw hole 201 provided in the engine head 200 of the internal combustion engine via a metal shell 50. When a high voltage of 20,000 to 30,000 volts is applied to the terminal fitting 40, a spark is generated in a spark gap formed between the center electrode 20 and the ground electrode 30. The insulator 10 corresponds to an “insulator” in the claims.

  The insulator 10 is an insulator formed by firing a ceramic material such as alumina. The insulator 10 is a cylindrical member having a shaft hole 12 that accommodates the center electrode 20 and the terminal fitting 40 formed at the center. A central body 19 having a large outer diameter is formed at the axial center of the insulator 10. A rear end side body portion 18 that insulates between the terminal metal fitting 40 and the metal shell 50 is formed on the terminal metal fitting 40 side of the central body portion 19. 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 center electrode 20 side with respect to the central body portion 19, and a front end side body portion 17 is provided further ahead of the front end side body portion 17. A leg length portion 13 having an outer diameter equal to or smaller than the outer diameter and having a diameter reduced toward the distal end side is formed. In addition, the leg long part 13 is good also as a straight shape which has a fixed outer diameter, a shape which has a step part, etc.

  The metal shell 50 is a cylindrical metal fitting that surrounds and holds a portion extending from a part of the rear end side body portion 18 of the insulator 10 to the long leg portion 13. In the present embodiment, the metal shell 50 is made of low carbon steel, and is subjected to a plating process such as nickel plating or zinc plating. The metal shell 50 includes a tool engaging portion 51, a mounting screw portion 52, and a seal portion 54. A tool (not shown) for attaching the spark plug 100 to the engine head 200 is fitted into the tool engaging portion 51 of the metal shell 50. The mounting screw portion 52 of the metal shell 50 has a thread that is screwed into the mounting screw hole 201 of the engine head 200. The seal portion 54 of the metal shell 50 is formed in a hook shape at the base of the mounting screw portion 52, and an annular gasket 5 formed by bending a plate is inserted between the seal portion 54 and the engine head 200. . The front end surface 57 of the metal shell 50 has a hollow circular shape, and the center electrode 20 projects from the long leg portion 13 of the insulator 10 at the center thereof.

  A thin caulking portion 53 is provided on the rear end side of the metal fitting 50 from the tool engaging portion 51. In addition, a thin compression deformation portion 58 is provided between the seal portion 54 and the tool engagement portion 51 as in the caulking portion 53. 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, annular ring members 6 and 7 are interposed. Further, talc (talc) 9 powder is filled between the ring members 6 and 7. When the spark plug 100 is manufactured, the compression deformable portion 58 is compressed and deformed by pressing the caulking portion 53 inward so as to be bent toward the inner side. The insulator 10 is pressed toward the front end side in the metal shell 50 through the talc 9. By this pressing, the talc 9 is compressed in the direction of the axis O, and the airtightness in the metal shell 50 is enhanced.

  Further, on the inner periphery of the metal shell 50, a member located at the base end of the leg long portion 13 of the insulator 10 is connected to the metal inner step portion 56 formed at the position of the mounting screw portion 52 via the annular plate packing 8. The stop part 300 is pressed. The plate packing 8 is a member that maintains the airtightness between the metal shell 50 and the insulator 10 and prevents combustion gas from flowing out.

  The center electrode 20 is a rod-like member in which a core material (not shown) having better thermal conductivity than the electrode base material is embedded in an electrode base material (not shown). In this embodiment, the electrode base material is made of a nickel alloy containing nickel as a main component, and the core member is made of copper or an alloy containing copper as a main component. The rear end portion of the center electrode 20 is electrically connected to the terminal fitting 40 via the ceramic resistor 3 and the seal body 4.

  The ground electrode 30 is made of a metal having high corrosion resistance, and a nickel alloy is used as an example. The proximal end of the ground electrode 30 is welded to the distal end surface 57 of the metal shell 50. The tip side of the ground electrode 30 is bent in a direction intersecting the axis O, and the tip of the ground electrode 30 faces the tip surface of the center electrode 20 on the axis O. Note that the ground electrode 30 may be formed of a rod-like member in which a core material having better thermal conductivity than the electrode base material is embedded inside the electrode base material, like the center electrode 20.

A2. Detailed configuration of the insulator 10:
FIG. 2 is a partially enlarged view for explaining a tip portion of the spark plug 100 according to the first embodiment. FIG. 2 shows the frame X in FIG. 1 in an enlarged manner. The long leg portion 13 of the insulator 10 includes a locking portion 300 that is locked to the metal inner step portion 56, and a body portion 302 that is formed on the distal end side of the locking portion 300. The trunk | drum 302 is formed so that an outer diameter may reduce toward the front end side. The locking part 300 corresponds to a “step part” in the claims.

  The metal inner step 56 of the metal shell 50 is formed on the front end side of the first step portion 400 and the first step portion 400 whose inner diameter is reduced from the rear end side toward the front end side. The second step portion 402 extends so as to face 302, and the third step portion 404 is formed on the front end side of the second step portion 402 and has an inner diameter that increases from the rear end side toward the front end side. The second step portion 402 is formed in a tapered shape so that the inner diameter increases from the rear end side toward the front end side. The bracket inner step portion 56 corresponds to a “receiving portion” in the claims.

  As shown in FIG. 2, the leg length portion 13 of the insulator 10 and the metal inner step portion 56 of the metal shell 50 are arranged so as to be separated by a predetermined distance.

Among the insulators 10, the arithmetic average roughness Ra ₁ of the outer surface of the portion on the tip side with respect to the position PA on the tip side where the packing 8 and the insulator 10 are in contact is 3 μm or more and 15 μm or less. It should be noted that the arithmetic average roughness Ra of the outer surface of the insulator 10 where the distance Da between the insulator 10 and the metal shell 50 in the direction orthogonal to the axis O direction is 0.5 mm or less on the tip side of the position PA. ₂ is preferably 3 μm or more and 15 μm or less.

  In this specification, the arithmetic average roughness (surface roughness) of the outer surface of the insulator 10 is determined according to JIS B 0601 using a non-contact three-dimensional measuring device NH-3 (manufactured by Mitaka Kouki Co., Ltd.). It has been measured.

In the first embodiment, the roughness of the outer surface of the insulator 10 is defined by adjusting the grain size and cutting speed of a grindstone for polishing the outer surface of the insulator 10. In order to make the arithmetic average roughness Ra ₁ of the outer surface of the insulator 10 3 μm or more and 15 μm or less, it is preferable that the average particle size of the grindstone is 50 μm or more and 150 μm or less. This is because when the average particle size of the grindstone is less than about 50 μm, there is a problem that clogging is likely to occur, and when the average particle size of the grindstone is greater than about 150 μm, there is a problem that the cutting trace becomes large and rough cutting occurs. Further, from the viewpoint of improving productivity and extending the service life of the grindstone, it is preferable that the cutting speed for cutting the molded body (insulator 10) is 0.5 g / sec or more and 2.0 g / sec or less. . This is because when the cutting speed is less than 0.5 g / sec, there is a problem that productivity is lowered, and when the cutting speed is higher than 2.0 g / sec, there is a high possibility that the life of the grindstone is reduced. In addition, for example, the outer surface of the insulator 10 is roughly cut using a grindstone having a high average particle size, and then the outer surface of the insulator 10 is polished using a grindstone having a low average particle size so as to have a desired roughness. Also good.

The length L along the axis O direction from the tip 10a of the insulator 10 to the position PA where the insulator 10 and the packing 8 contact is 10 mm or less. Further, the arithmetic average roughness Ra ₃ of the outer surface of the insulator 10 in a portion from the position PA in contact with the packing 8 to the tip side by L / 3 along the axis O direction in the insulator 10 is 15 μm or less.

  In the first embodiment, the spark plug 100 has a screw diameter of M10 or less. In the spark plug 100, the distance Db (so-called spark distance) between the tip 20a of the center electrode 20 and the metal tip 31 of the ground electrode 30 is 0.9 mm or more.

A3. Evaluation results:
The result of having tested and evaluated about the anti-flash over performance, bending strength, and antifouling property about the spark plug 100 provided with the conditions demonstrated above is shown. Table 1 shows test results of flashover resistance and bending strength, and Table 2 shows test results of antifouling properties.

In Table 1, each item is shown as follows.
Screw diameter: Screw diameter of the metal shell 50 Gap: Spark distance Db between the center electrode 20 and the ground electrode 30
L: Length along the axis O direction from the tip 10a of the insulator 10 to the position PA where the insulator 10 and the packing 8 contact Ra ₁ : The length of the insulator 10 at the tip side of the position PA that contacts the packing 8 Arithmetic average roughness Ra _{2 of the} outer surface Ra ₂ : Arithmetic average roughness of the outer surface of the insulator 10 where the distance Da between the insulator 10 and the metal shell 50 is 0.5 mm or less Ra ₃ : From the position PA in contact with the packing 8 Arithmetic mean roughness of the outer surface of the insulator 10 in the portion up to the tip side by L / 3 along the axis O direction

In the test for evaluating the flashover resistance, a spark plug was attached to a visible chamber, and the discharge was observed by synchronizing the discharge and the discharge waveform, thereby evaluating the flashover occurrence rate (unit:%). In Test 1, the occurrence rate of flashover when a voltage of 60 kH and 25 kV is applied for 30 seconds under a pressure of 0.6 Mp and the determination result are shown in “FO resistance performance” of Table 1. In Table 1, the determination results are as follows, where Fr is the flashover occurrence rate.
A: Fr ≦ 0.1%
B: 0.1% <Fr ≦ 0.5%
C: 0.5% <Fr ≦ 1.0%
D: 1.0% <Fr ≦ 3.0%
E: 3.0% <Fr ≦ 10.0%
F: Fr> 10.0%

In the test for evaluating the bending strength, an impact resistance test according to “JIS B 8031 — 7.4” is performed, and the determination result is shown in “Bending strength” in Table 1. The outline of the impact resistance test is as follows. After being attached to the L-shaped bush, an impact was applied to the tip of the sample at a rate of 400 times per minute as an impact 22 mm by an impact tester specified in 7.4 of JIS B8031. And after 3 hours progress, while checking the presence or absence of the crack in a leg long part, the number (number of cracks) which the crack generate | occur | produced was measured. In Table 1, the determination results are as follows.
A: Crack generation rate ≦ 1%
B: ≦ 3%
C: ≦ 10%
D: ≧ 10%

As shown in Table 1, in the spark plug of the comparative example, when the arithmetic average roughness Ra ₁ of the outer surface of the insulator 10 is less than 0.3 μm, the bending strength is good, but the flashover occurs. When the rate Fr exceeds 0.5% and the arithmetic average roughness Ra ₁ exceeds 15.0, the flashover resistance is good at 1.0% or less, but the strength decreases. This is because the spark plug in which the arithmetic average roughness Ra ₁ of the outer surface of the insulator 10 at the tip side of the position PA in contact with the packing 8 is less than 3.0 μm has less unevenness on the outer surface, and thus flashover occurs. For spark plugs whose arithmetic average roughness Ra ₁ of the outer surface of the insulator 10 at the tip side of the position PA in contact with the packing 8 exceeds 15.0 μm, This is probably because the recesses of the recesses and recesses are relatively deep and stress tends to concentrate on the recesses. In the spark plugs of Examples 1 to 12 that satisfy various conditions of the spark plug 100 of the first embodiment, the arithmetic average roughness Ra ₁ of the outer surface of the insulator 10 at the tip side of the position PA in contact with the packing 8. Is 3.0 μm or more and 15 μm or less, and as shown in Table 1, both the flashover resistance and the bending strength are good.

In addition, as shown in Table 1, the arithmetic average roughness Ra ₂ of the outer surface of the insulator 10 where the distance Da between the insulator 10 and the metal shell 50 is 0.5 mm or less is 3.0 μm or more, and The spark plugs of Examples 4 to 12 having a size of 15 μm or less can further improve the flashover resistance.

Further, as shown in Table 1, if the arithmetic average roughness Ra ₃ of the outer surface of the insulator 10 in the portion from the position PA to the tip side by L / 3 along the axis O direction is 15 μm or less, the insulation The effect of improving the bending strength of the insulator 10 is high.

  Further, as shown in Table 1, a spark plug having a length L of 10 mm or less along the axis O direction from the tip 10a of the insulator 10 to a position PA where the insulator 10 and the packing 8 are in contact, and the screw diameter is M10 In the following spark plugs, the arithmetic average roughness of the outer surface of the insulator 10 is set to 3.0 μm or more and 15 μm or less, thereby increasing the degree of the effect of improving the flashover resistance and the bending strength.

  In addition, as shown in Table 1, the spark plug having an interval of 0.9 mm or more has durability by setting the arithmetic average roughness of the outer surface of the insulator 10 to 3.0 μm or more and 15 μm or less. While maintaining the above, flashover can be suppressed and a high voltage can be applied.

The fouling property evaluation test is a “smoldering fouling test” defined in JIS standard D1606. For the spark plug having various conditions shown in Table 2, a coating layer made of an insulating oil is provided on the surface of the leg portion 13, and a displacement of 1500 cc is provided on a chassis dynamometer in a low temperature test chamber (−10 ° C.). A test vehicle having a cylinder engine is placed, and four spark plugs are assembled to the engine of the test vehicle corresponding to each cylinder. Examples of the “insulating oil” include a mixed liquid containing silicon oil, fluorine-based oil or the like as a main component and containing paraffin or the like. After performing idling three times, the vehicle travels for 40 seconds at a third speed of 35 km / h, and again travels for 40 seconds at a third speed of 35 km / h with an idling of 90 seconds. Then stop and cool the engine once. Next, after performing idling three times, traveling for 20 seconds at a speed of 15 km / h is performed a total of three times, with the engine stopped for 30 seconds, and then the engine is stopped. This series of test patterns was taken as one cycle, and a plurality of cycles were repeatedly tested. At the end of each cycle, the insulation resistance value between the metal shell and the connection terminal is measured for a given sample, and the number of cycles when the insulation resistance value reaches 10 MΩ (the number of cycles reaching 10 MΩ) is confirmed. did. In Table 2, the determination results are as follows, where N is the number of cycles reaching 10 MΩ.
A: N ≧ 7
B: N = 6
C: N ≦ 5

表２に示されるように、絶縁碍子１０の外表面の算術平均粗さＲａ₁が３．０μｍ以上、かつ、１５μｍ以下であるスパークプラグでは、フラッシュオーバーが抑制されるので、絶縁碍子１０の高温化を抑制でき、比較的長期間に亘って、脚長部の基端部側の表面に十分な厚みの被膜層を存在させておくことができる。その結果、脚長部１３の表面に絶縁油からなる被膜層を設けた場合において、より優れた絶縁性能（耐汚損性の向上）を実現することができる。

As shown in Table 2, in the spark plug in which the arithmetic average roughness Ra ₁ of the outer surface of the insulator 10 is 3.0 μm or more and 15 μm or less, flashover is suppressed. The coating layer having a sufficient thickness can be kept on the surface of the leg end portion on the base end side for a relatively long period of time. As a result, in the case where a coating layer made of insulating oil is provided on the surface of the leg long portion 13, it is possible to achieve better insulating performance (improvement of stain resistance).

B. Variations:
・ Modification 1:
In the first embodiment, a portion where the distance Da between the insulator 10 and the metal shell 50 in the direction orthogonal to the direction of the axis O is 0.5 mm or less on the tip side of the position PA where the insulator 10 and the packing 8 are in contact with each other. The arithmetic average roughness Ra ₂ of the outer surface of the insulator 10 is 3 μm or more and 15 μm or less, but the arithmetic average roughness of the outer surface of the insulator 10 in the interval Da is 0.5 mm or less. Ra ₂ may not be 3 μm or more and 15 μm or less.

Modification 2
Moreover, in 1st Embodiment, the length L along the axis O direction from the front-end | tip 10a of the insulator 10 to the position PA where the insulator 10 and the packing 8 contact is 10 mm or less. Further, the arithmetic average roughness Ra ₃ of the outer surface of the insulator 10 in a portion from the position PA in contact with the packing 8 to the front end side by L / 3 along the axis O direction in the insulator 10 is 15 μm or less. The arithmetic average roughness Ra ₃ of the outer surface of the insulator 10 may not be 15 μm or less.

・ Modification 3:
In the first embodiment, the spark plug 100 has a screw diameter of M10 or less, but the screw diameter may be larger than M10.

-Modification 4:
In the first embodiment, in the spark plug 100, the distance Db between the tip 20a of the center electrode 20 and the metal tip 31 of the ground electrode 30 is 0.9 mm or more, but the distance Db is 0.9 mm. It may be less.

  The present invention is not limited to the above-described embodiments, examples, and modifications, and can be realized with various configurations without departing from the spirit thereof. For example, the technical features in the embodiments, examples, and modifications corresponding to the technical features in each embodiment described in the summary section of the invention are to solve some or all of the above-described problems, or In order to achieve part or all of the above effects, replacement or combination can be performed as appropriate. Further, if the technical feature is not described as essential in the present specification, it can be deleted as appropriate.

DESCRIPTION OF SYMBOLS 3 ... Ceramic resistance 4 ... Sealing body 5 ... Gasket 6 ... Ring member 8 ... Packing 9 ... Talc 10 ... Insulator 10a ... Tip 12 ... Shaft hole 13 ... Leg long part 17 ... Tip side trunk | drum 18 ... Rear end side trunk | drum 19 ... center barrel 20 ... center electrode 20a ... tip 30 ... ground electrode 31 ... metal tip 40 ... terminal fitting 50 ... metal shell 51 ... tool engaging portion 52 ... mounting screw portion 53 ... caulking portion 54 ... seal portion 56 ... Metal fitting inner step 57 ... distal end surface 58 ... compression deformation portion 100 ... spark plug 200 ... engine head 201 ... mounting screw hole 300 ... locking portion 302 ... trunk portion 400 ... first step portion 402 ... second step portion 404 ... first 3 steps

Claims (6)

An insulator having a shaft hole penetrating in the axial direction and having a stepped portion projecting radially outward on its outer periphery;
A center electrode provided on a tip side of the shaft hole;
A cylindrical metal shell provided on the outer periphery of the insulator, having a receiving portion protruding radially inward on the inner periphery thereof, and holding the insulator in a state where the step portion is locked to the receiving portion. When,
A spark plug provided between the stepped portion and the receiving portion and in contact with the packing,
The spark plug according to claim ₁ , wherein an arithmetic mean roughness Ra1 of an outer surface of a portion of the insulator closer to a tip side than a position in contact with the packing is 3 μm or more and 15 μm or less. The spark plug according to claim 1,
Arithmetic of the outer surface of the insulator at a portion where the distance between the insulator and the metal shell in the direction orthogonal to the axial direction is 0.5 mm or less on the tip side of the position where the insulator and the packing are in contact with each other A spark plug having an average roughness Ra ₂ of 3 μm or more and 15 μm or less. The spark plug according to claim 1 or 2, wherein
The length along the axial direction from the tip of the insulator to the position where the insulator and the packing are in contact with each other is 10 mm or less. The spark plug according to any one of claims 1 to 3, wherein
When the length along the axial direction from the tip of the insulator to the position where the insulator and the packing contact is L,
Among the insulators, an arithmetic average roughness Ra ₃ of an outer surface of the insulator in a portion from the position in contact with the packing to the tip side by L / 3 along the axial direction is 15 μm or less. And spark plug. The spark plug according to any one of claims 1 to 4, wherein
A spark plug having a screw diameter of M10 or less. The spark plug according to any one of claims 1 to 5, wherein
A ground electrode fixed to the tip of the metal shell and forming a gap with the tip of the center electrode;
The spark plug is characterized in that the distance is 0.9 mm or more.

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