WO2010131410A1

WO2010131410A1 - Spark plug

Info

Publication number: WO2010131410A1
Application number: PCT/JP2010/002415
Authority: WO
Inventors: 中川敬太; 安井悟; 柴田勉
Original assignee: 日本特殊陶業株式会社
Priority date: 2009-05-13
Filing date: 2010-04-01
Publication date: 2010-11-18
Also published as: JP2010267425A

Abstract

The center electrode of a spark plug is secured with increased strength within an insulator. A spark plug (100) comprises: a main metal body (50) having a ground electrode (30) at the tip thereof; an insulator (10) provided with a shaft hole (12) having a large inner diameter on the rear end side thereof and a small inner diameter on the tip side thereof with a step section (29) formed therebetween; and a center electrode (20) having a flange section (26) which protrudes outward radially and is in contact, from the rear end side thereof, with the step section (29). The center electrode (20) is provided with: a head section (27) located further toward the rear end side than the flange section (26) and secured within the shaft hole (12) by means of an electrically conductive seal material (4); and a leg section (28) located further toward the tip side than the flange section (26) and forming a spark gap between the leg section and the ground electrode (30). Grooves (35) are formed in the outer periphery of the head section (27) of the center electrode (20).

Description

Spark plug

The present invention relates to a spark plug, and more particularly to a technique for fixing a center electrode in an insulator of a spark plug.

Generally, the center electrode of the spark plug is fixed inside an insulator (insulator) by a glass seal material. However, depending on the state of use of the internal combustion engine to which the spark plug is attached, there is a possibility that the center electrode and the glass sealing material are peeled off due to the influence of heat and vibration. Particularly, in recent years, in spark plugs that have been reduced in diameter, since the center electrode is also reduced in diameter with the reduction in outer diameter, the contact area between the center electrode and the glass sealing material is inevitably reduced. Such a problem becomes remarkable. *

With regard to such a problem, in Patent Document 1, in order to increase the strength of fixing of the center electrode, a plurality of vertical grooves and spiral grooves are formed in the collar portion of the center electrode in contact with the step formed in the shaft hole. Technology is disclosed. However, it has been difficult to form these grooves in the collar portion of the center electrode with stable accuracy. Further, Patent Document 2 discloses a technique for increasing the surface area of the collar portion of the center electrode, but this is intended to prevent pre-ignition by dissipating heat generated in the center electrode. No consideration has been given to increasing the strength of electrode adhesion. In particular, referring to FIG. 2 of Patent Document 2, it can be seen that the glass sealing material is only in contact with the upper surface of the collar portion of the center electrode, so that it is not considered to increase the strength of fixing the center electrode.

JP-A-61-7484 JP-A-62-35481 JP-A-1-292778 Japanese Patent No. 349709

In view of the above-described problems, the problem to be solved by the present invention is to improve the fixing strength of the center electrode provided in the spark plug in the insulator.

SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples. *

Application Example 1 A substantially cylindrical metal shell having a ground electrode at the tip, and a shaft hole held in the metal shell and having a shaft hole having a large diameter on the rear end side and a small diameter on the front end side through a stepped portion. A cylindrical insulator, a hook that is held in the shaft hole of the insulator, has a convex shape toward the outer periphery, contacts the stepped portion from the rear end side, and is disposed on the rear end side of the flange portion. A center electrode having a head portion fixed in the shaft hole by a conductive sealing material, and a leg portion that is disposed on the tip side of the flange portion and forms a spark gap between the ground electrode, and A spark plug comprising: a groove formed on an outer periphery of a head of the center electrode. *

Application Example 2 The spark plug according to Application Example 1, wherein the shortest distance from the outermost periphery of the head to the side wall of the shaft hole is 0.15 mm or more. *

[Application Example 3] The spark plug according to Application Example 1 or Application Example 2, wherein the shortest distance from the outermost periphery of the flange to the side wall of the shaft hole is 0.10 mm or more. Spark plug. *

[Application Example 4] The spark plug according to any one of Application Examples 1 to 3, wherein a groove formed on an outer periphery of the head is formed in a spiral shape. . *

[Application Example 5] The spark plug according to any one of Application Examples 1 to 3, wherein a groove formed on an outer periphery of the head circulates on a surface perpendicular to the axial direction of the center electrode. A spark plug characterized in that it is formed. *

Application Example 6 In the spark plug according to Application Example 4 or Application Example 5, two or more grooves formed on the outer periphery of the head are formed on an arbitrary outer peripheral surface of the head. A spark plug characterized by that. *

[Application Example 7] The spark plug according to any one of Application Examples 1 to 3, wherein a groove formed on an outer periphery of the head is formed in a direction parallel to an axial direction of the center electrode. A spark plug characterized by *

[Application Example 8] The spark plug according to any one of Application Examples 1 to 3, wherein a groove formed on an outer periphery of the head has a knurled shape. *

[Application Example 9] The spark plug according to any one of Application Examples 1 to 8, wherein the diameter of the shaft hole at a position where the head of the center electrode is present is 3.0 mm or less. Features a spark plug. *

[Application Example 10] The spark plug according to any one of Application Examples 1 to 9, wherein the spark plug has a resistor on the rear end side of the conductive sealing material in the shaft hole. plug. *

Application Example 11 The spark plug according to any one of Application Examples 1 to 10, wherein the step portion is formed in a tapered shape. *

[Application Example 12] A spark plug according to any one of Application Examples 1 to 11, wherein the groove on the outer periphery of the head is formed by rolling.

In the spark plug having the configuration of Application Example 1, since the groove is formed on the outer periphery of the head of the center electrode, the contact area between the head and the conductive sealing material can be increased. As a result, the fixing strength of the center electrode in the insulator can be improved.

With the spark plug having the configuration of the application example 2, the conductive sealing material can be satisfactorily fixed to the outer periphery of the head, so that the center electrode can be firmly fixed in the insulator.

With the spark plug having the configuration of the application example 3, the conductive sealing material can be satisfactorily fixed to the outer periphery of the flange portion, so that the center electrode can be firmly fixed in the insulator.

In the spark plug having the configuration of the application example 4, the contact area between the head and the conductive sealing material can be increased by the spiral groove.

In the spark plug having the configuration of the application example 5, the contact area between the head and the conductive sealing material can be increased by the groove formed in the direction perpendicular to the axial direction of the center electrode.

In the spark plug having the configuration of Application Example 6, since a plurality of grooves are formed on an arbitrary outer peripheral surface of the head, the contact area between the head and the conductive sealing material can be increased.

In the spark plug having the configuration of the application example 7, the contact area between the head and the conductive sealing material can be increased by the groove formed in the direction parallel to the axial direction of the center electrode.

With the spark plug having the configuration of the application example 8, the contact area between the head and the conductive sealing material can be increased by the knurled groove.

According to the spark plug having the configuration of the application example 9, even if the diameter of the shaft hole is 3.0 mm or less, according to the above configuration, the groove is formed on the outer periphery of the head of the center electrode. It is possible to improve the adhesion strength in the insulator.

If the spark plug has the configuration of the application example 10, the generation of noise can be suppressed.

If it is a spark plug of the structure of the application example 11, since a collar part can be made to contact a step part favorably, it becomes possible to suppress the wobble of a center electrode.

With the spark plug having the configuration of Application Example 12, since the groove is formed by rolling, the center electrode can be efficiently manufactured at low cost.

It is a fragmentary sectional view of the spark plug 100 as an Example of this invention. 3 is a schematic diagram showing a structure of a center electrode 20. FIG. It is a figure which shows the impact test result of the spark plug 100 which made the groove number A five. It is a figure which shows the impact test result of the spark plug 100 which made the groove number A four. It is a figure which shows the impact test result of the spark plug 100 which made the groove number A three. It is a figure which shows the impact test result of the spark plug 100 which made the groove number A two. It is a figure which shows the impact test result of the spark plug 100 which made the groove number A one. It is a figure which shows the impact test result of the spark plug 100 which made the groove number A zero. It is a graph which shows the relationship between head gap B, buttocks gap C, and an impact test result. FIG. 6 is a view showing an example in which a lateral groove is formed in an electrode head 27. It is a figure which shows the example which formed the vertical groove in the electrode head part. FIG. 5 is a view showing an example in which a knurled groove is formed in an electrode head 27.

Hereinafter, embodiments of the present invention will be described in the following order based on examples. A. Spark plug structure: B. Center electrode structure: C.I. Test results:

A. Spark Plug Structure: FIG. 1 is a partial sectional view of a spark plug 100 as an embodiment of the present invention. In the following description, along the axis O direction in the figure, the lower side is described as the front end side of the spark plug 100 and the upper side is described as the rear end side. The spark plug 100 has a substantially cylindrical metal shell 50 having a ground electrode 30 at its tip, an insulator 10 having an axial hole 12 in the direction of the axis O, and held in the axial hole 12. The center electrode 20 and the terminal fitting 40 provided at the rear end of the insulator 10 are provided. *

As is well known, the insulator 10 is a cylindrical insulator formed by firing alumina or the like and having a shaft hole 12 extending in the direction of the axis O as a center. The shaft hole 12 has a large inner diameter on the rear end side and a small inner diameter on the front end side through the inner stepped portion 29. An insulator flange portion 19 having the largest outer diameter is formed in the central portion of the insulator 10, and a rear end side body portion 18 is formed on the rear end side. 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 from the lever flange portion 19, and further on the front end side than the front end side body portion 17, from the front end side body portion 17. Also, an insulator leg portion 13 having a small outer diameter is formed. The insulator leg portion 13 is reduced in diameter toward the distal end side, and is exposed to the combustion chamber when the spark plug 100 is attached to the engine head 200 of the internal combustion engine. An outer step portion 15 is formed between the insulator leg portion 13 and the distal end side trunk portion 17. *

The center electrode 20 is mainly composed of copper or copper, which is superior in thermal conductivity to the base material, inside the base material formed of nickel or an alloy containing nickel as a main component, such as Inconel (trade name) 600 or 601. This is a substantially rod-shaped electrode having a structure in which a core material made of an alloy is embedded. The tip of the center electrode 20 protrudes from the tip of the insulator 10. On the other hand, the rear end of the center electrode 20 is fixed in the shaft hole 12 by the glass sealing material 4. The rear end of the center electrode 20 is connected to the rear end of the insulator 10 via the glass sealing material 4 and the ceramic resistor 3 (about 5 kΩ) for suppressing noise generation, and further through the glass sealing material 4. It is electrically connected to the terminal fitting 40 arranged. A high voltage cable (not shown) is connected to the terminal fitting 40 via a plug cap (not shown), and a high voltage is applied. *

The center electrode 20 is fixed in the shaft hole 12 by the glass sealing material 4 as follows. First, the center electrode 20 is inserted from the rear end side of the shaft hole 12, and from above, the material powder of the glass sealing material 4 (powder in which copper powder and borosilicate glass powder are mixed 1: 1) is filled, Press with a push rod. Further, the material powder of the ceramic resistor 3 (ZrO 2 powder, alumina powder, carbon black, glass powder, powder mixed with PVA binder, etc.) is filled thereon and pressed with a push rod. Furthermore, after filling the material powder of the glass sealing material 4 again from above and pressing with the push rod, the terminal fitting 40 is inserted into the rear end of the shaft hole 12. Then, the insulator 10 is heated while the terminal fitting 40 is pushed in, so that the material powder of the glass sealing material 4 and the material powder of the ceramic resistor 3 in the shaft hole 12 are melted and then cooled. Then, the glass sealing material 4 and the ceramic resistor 3 are solidified in the shaft hole 12, and the center electrode 20 is fixed in the shaft hole 12. *

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 base 32 welded to the distal end surface 57 of the metal shell 50. The ground electrode 30 is bent so that one side surface of the tip 31 thereof faces the tip of the center electrode 20 on the axis O.

The metal shell 50 is a substantially cylindrical metal fitting for fixing the spark plug 100 to the engine head 200 of the internal combustion engine. The metal shell 50 holds the insulator 10 inside so as to surround a portion extending from a part of the rear end side body portion 18 to the insulator leg portion 13. The metal shell 50 is formed of a low carbon steel material, and a tool engagement portion 51 into which a spark plug wrench (not shown) is fitted, and an attachment screw portion in which a screw thread to be engaged with the attachment screw hole 201 of the engine head 200 is formed. 52. *

Between the tool engaging portion 51 and the mounting screw portion 52 of the metal shell 50, a bowl-shaped seal portion 54 is formed. An annular gasket 5 formed by bending a plate is fitted into a screw neck 59 between the attachment screw portion 52 and the seal portion 54. When the spark plug 100 is attached to the engine head 200, the gasket 5 is crushed and deformed between the seat surface 55 of the seal portion 54 and the engine head 200. Due to the deformation of the gasket 5, the gap between the spark plug 100 and the engine head 200 is sealed, and airtight leakage in the engine through the mounting screw hole 201 is prevented. *

A thin caulking portion 53 is provided on the rear end side of the metal fitting 50 from the tool engaging portion 51. A thin buckled portion 58 is provided between the seal portion 54 and the tool engaging portion 51. 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 arranged. Further, talc (talc) 9 powder is filled between the

ring members

6 and 7. By crimping the crimping portion 53 so as to be bent inward, the insulator 10 is pressed toward the front end side in the metal shell 50 via the

ring members

6, 7 and the talc 9. By this pressing, the metal step 56 formed on the inner periphery of the mounting screw portion 52 of the metal shell 50 and the outer step 15 of the insulator 10 are supported via the iron-made annular plate packing 8, The insulator 10 is fixed to the metal shell 50. *

B. Center Electrode Structure: FIG. 2 is a schematic diagram showing the structure of the center electrode 20. The center electrode 20 includes an electrode flange portion 26 that is in contact with the inner step portion 29 formed in the shaft hole 12 from the rear end side and has a convex shape toward the outer periphery. In addition, the electrode head 27 is disposed on the rear end side of the electrode flange portion 26 and is fixed to the shaft hole 12 by the glass sealing material 4, and the ground electrode 30 is disposed on the front end side of the electrode flange portion 26. And an electrode leg portion 28 that forms a spark gap therebetween. The lower surface on the tip end side of the electrode flange 26 is tapered toward the electrode leg 28 in a tapered shape. The tapered lower surface of the electrode flange 26 is in contact with the inner stepped portion 29 in the shaft hole 12 which is similarly reduced in diameter from the rear end side toward the front end side. As described above, the contact between the lower surface of the electrode flange portion 26 and the inner stepped portion 29 prevents the center electrode 20 from coming off from the front end side of the insulator 10. Further, in the present embodiment, since the inner step portion 29 is tapered, the electrode flange portion 26 and the inner step portion 29 can be satisfactorily brought into contact with each other, and the wobbling of the center electrode 20 can be suppressed. In the present embodiment, the lower surface of the electrode flange portion 26 is formed in a tapered shape, but it may be formed on a flat surface or may be formed in a hook shape. *

In this embodiment, in order to increase the contact area between the center electrode 20 and the glass sealing material 4 and improve the fixing strength of the center electrode 20, a spiral groove 35 is formed on the outer periphery of the electrode head 27 by rolling. is doing. Two or more (preferably three or more) grooves 35 are formed on an arbitrary outer peripheral surface of the electrode head 27 (hereinafter referred to as “groove number A”). The groove 35 has a width of 0.25 mm and a depth of 0.27 mm. In this embodiment, the shortest distance from the outermost periphery of the electrode head 27 to the side wall of the shaft hole 12 (hereinafter referred to as “head gap B”) is secured to 0.15 mm or more. The shortest distance from the outermost periphery of the portion 26 to the side wall of the shaft hole 12 (hereinafter referred to as “gutter gap C”) is ensured to be 0.10 mm or more. *

In addition, in this embodiment, the diameter K1 of the electrode leg portion 28 of the center electrode 20 is 2.0 mm, and the diameter K2 of the shaft hole 12 of the insulator 10 surrounding the periphery is 2.17 mm. The diameter K3 of the shaft hole 12 at the position of the electrode head 27 is 3.0 mm. Further, the rising angle R of the inner step portion 29 reduced in taper from the perpendicular of the axis O is in the range of 25 to 35 °, and is 30 ° in this embodiment. The diameter K3 of the shaft hole 12 at the position of the electrode head 27 is preferably 2.0 mm or more. *

Further, in the present embodiment, the height L1 along the axis O direction of the electrode head 27 is 2.3 mm, and the height L2 along the axis O direction of the electrode flange 26 is 1.2 mm. . The length L3 along the axial direction of the electrode leg 28 is 19.0 mm. The tip end of the electrode leg portion 28 protrudes from the tip end surface of the insulator 10, and its protruding dimension L4 is 0.4 mm. The dimensional tolerance of the protruding dimension L4 can be ± 0.1 mm. *

C. Test result: Subsequently, the test conditions were changed in the range of 0 to 5 grooves A, 0.05 to 0.25 mm in the head gap B, and 0.00 to 0.25 mm in the heel gap C. The results of impact tests in accordance with Section 7.4 of “JIS B 8031” are shown in FIGS. In this impact test, the range was 22 mm, and the number of impacts was 400 per minute. For each test condition, eight spark plugs 100 were prepared and subjected to an impact test, and the test was terminated when one of the plugs was loosened in the center electrode 20. The test time was a maximum of 90 minutes. In FIGS. 3 to 8, the determination result is “◎” for the case where the center electrode 20 did not loosen for 90 minutes, and the case where the looseness did not occur for 50 minutes or more was “◯”, for 20 minutes or more. The case where no looseness occurred was indicated as “Δ”, and the case where looseness occurred in less than 20 minutes was indicated as “x”. When the determination result is “◎” or “◯”, it is determined that the center electrode 20 is fixed with sufficient strength in this embodiment. *

FIG. 3 shows test results of 10 types of spark plugs 100 with five grooves A. The spacing between the grooves when the number of grooves A was 5 was 0.46 mm. Sample No. In the spark plugs 100 of 1 to 6, the head gap B is all 0.25 mm, and the collar gap C is changed from 0.25 mm to 0.00 mm by 0.05 mm. Sample No. The spark plug 100 of No. 7 has a head gap B of 0.20 mm and a buttocks gap C of 0.10 mm. Sample No. The spark plug 100 of No. 8 has a head gap B of 0.15 mm and a buttocks gap C of 0.10 mm. Sample No. The spark plug 100 of No. 9 has a head gap B of 0.10 mm and a heel gap C of 0.10 mm. Sample No. No. 10 has a head gap B of 0.05 mm and a buttocks gap C of 0.05 mm. The conditions for the head gap B and the buttocks gap C for each sample number are the same for FIGS. *

As shown in the test results shown in FIG. 3, when the number of grooves A is 5, when the head gap B is 0.25 mm, the collar gap C should be 0.10 mm or more. Thus, even after 90 minutes from the start of the test, the center electrode 20 did not loosen (Sample Nos. 1 to 4). On the other hand, even when the head gap B is secured to 0.25 mm, if the buttocks gap C is 0.05 mm or less, the center electrode 20 of the center electrode 20 is reached after 20 minutes from the start of the test. Looseness occurred in the fixing (Sample Nos. 5 and 6). Further, when the head gap B is 0.20 mm and the buttocks gap C is 0.10 (sample No. 7), and when the head gap B is 0.15 mm and the buttocks gap C is 0.10 mm ( For sample No. 8), the center electrode 20 did not loosen when 90 minutes passed from the start of the test. However, when the head gap B is 0.10 mm and the heel gap C is 0.10 mm (sample No. 9), and when the head gap B is 0.05 mm and the buttock gap C is 0.05 mm ( In sample No. 10), the center electrode 20 was loosened after 5 minutes from the start of the test. *

4 and 5 show the test results when the number of grooves A is 4 and 3, respectively. When the number of grooves A was 4, the interval between the grooves was 0.57 mm, and when the number of grooves A was 3, it was 0.76 mm. As shown in these figures, when the number of grooves A was 4 and 3, the same test results were obtained as when the number of grooves A was 5. *

FIG. 6 shows the test results when the number of grooves A is two. When the number of grooves A was two, the interval between the grooves was 1.15 mm. As shown in the test results in this figure, when the number of grooves A is two, when the head gap B is secured to 0.25 mm, when the buttock gap C is 0.15 mm or more, At 80 minutes after the start of the test, the center electrode 20 was loosely fixed (Sample Nos. 1 to 3). Further, when the head gap B was 0.25 mm and the heel gap C was 0.10 mm, the center electrode 20 was loosened after 70 minutes from the start of the test (sample No. 4). . On the other hand, even if the head gap B is 0.25 mm, the center electrode 20 can be fixed in less than 20 minutes after the start of the test if the hip gap C is 0.05 mm or less. Looseness occurred (Sample Nos. 5 and 6). Further, when the head gap B is 0.20 mm and the buttocks gap C is 0.10 (sample No. 7), and when the head gap B is 0.15 mm and the buttocks gap C is 0.10 mm ( For sample No. 8), the center electrode 20 was loosened when 60 minutes passed from the start of the test. When the head gap B is 0.10 mm and the buttock gap C is 0.10 mm (sample No. 9), and when the head gap B is 0.05 mm and the buttock gap C is 0.05 mm (sample No. 10), the center electrode 20 was loosened after 5 minutes from the start of the test. *

7 and 8 show test results when the number of grooves A is 1 and 0, respectively. As shown in these figures, when the number of grooves A is 1 or 0, the center electrode can be obtained in less than 50 minutes from the start of the test under any condition of the head gap B and the buttocks gap C. Looseness occurred in the fixing of 20. *

FIG. 9 is a graph showing the relationship between the head gap B, the buttocks gap C, and the test results. In this graph, the horizontal axis represents the size of the head gap B, and the vertical axis represents the size of the buttocks gap C. In each of the test results described above, “◎” or “◯” was obtained as the evaluation result. Is plotted on the coordinates represented by the head gap B and the buttocks gap C. In FIGS. 3 to 6, “×” is plotted at the coordinates represented by the head gap B and the buttocks gap C for the samples for which “x” is obtained as the evaluation result. *

According to the graph shown in FIG. 9 and the test results shown in FIGS. 3 to 8, the spark plug 100 of this example has two or more (preferably, the outer peripheral surface of the electrode head 27 of the center electrode 20 (preferably 3 or more) grooves 35 are formed, and the head gap B is secured to 0.15 mm or more and the collar gap C is secured to 0.10 mm or more, so that the center electrode 20 is firmly placed in the shaft hole 12. It was confirmed that it was fixed. As a result, even if the diameter of the spark plug 100 is reduced, the fixing force of the center electrode 20 can be sufficiently maintained by satisfying these conditions. Furthermore, in this embodiment, since the electrode collar portion 26 is formed on the center electrode 20, it is possible to prevent the center electrode 20 from coming off to the ground electrode 30 side. *

As mentioned above, although one Example of this invention was described, this invention is not limited to such an Example, A various structure can be taken in the range which does not deviate from the meaning. For example, in the above embodiment, the spiral groove 35 is formed on the outer periphery of the electrode head 27 of the center electrode 20, but as shown in FIG. 10, a lateral groove that circulates in a plane perpendicular to the axis O is formed. May be. In addition, as shown in FIG. 11, longitudinal grooves may be formed in a direction parallel to the axis O. In addition, as illustrated in FIG. 12, a knurled groove may be formed on the outer periphery of the electrode head 27. Also according to these aspects, the contact area between the center electrode 20 and the glass sealing material 4 can be increased, so that the fixing strength of the center electrode 20 can be improved. In addition, in the case where a lateral groove, a longitudinal groove, or a knurled groove is formed on the outer periphery of the electrode head 27 as described above, the number of grooves A is 2 or more, the head gap B is 0.15 mm or more, and the collar portion The gap C is preferably set to 0.10 mm or more.

100 ... Spark plug 200 ... Engine head 3 ... Resistor 4 ... Glass seal material 5 ... Gasket 6 ... Ring member 8 ... Plate packing 9 ... Talc 10 ... Insulator 12 ... Shaft hole 13 ... Insulator leg 15 ... Outer step 17 ... tip side body portion 18 ... rear trunk portion 19 ... insulator flange portion 20 ... center electrode 26 ... electrode flange portion 27 ... electrode head 28 ... electrode legs 29 ... inner stepped portion 30 ... ground electrode 35 ... groove 40 ... Terminal fitting 50 ... Main metal fitting 51 ... Tool engaging part 52 ... Mounting screw part 53 ... Clamping part 54 ... Seal part 56 ... Metal step part 58 ... Buckling part

Claims

A substantially cylindrical metal shell having a ground electrode at the tip, and a substantially cylindrical insulator held in the metal shell and having a shaft hole having a large inner diameter on the rear end side and a small inner diameter on the front end side through a stepped portion A flange that is held in the shaft hole of the insulator, has a convex shape toward the outer periphery, contacts the stepped portion from the rear end side, and is disposed closer to the rear end side than the flange, and is a conductive sealing material A spark plug comprising: a head electrode fixed in the shaft hole by a central electrode; and a center electrode having a leg portion that is disposed on a tip side of the flange portion and forms a spark gap with the ground electrode. A spark plug is characterized in that a groove is formed on the outer periphery of the head of the center electrode.
The spark plug according to claim 1, wherein the shortest distance from the outermost periphery of the head to the side wall of the shaft hole is 0.15 mm or more.
The spark plug according to claim 1 or 2, wherein the shortest distance from the outermost periphery of the flange portion to the side wall of the shaft hole is 0.10 mm or more.
The spark plug according to any one of claims 1 to 3, wherein a groove formed on an outer periphery of the head is formed in a spiral shape.
The spark plug according to any one of claims 1 to 3, wherein a groove formed on an outer periphery of the head is formed so as to go around a plane perpendicular to an axial direction of the center electrode. A spark plug characterized by
The spark plug according to claim 4 or 5, wherein two or more grooves formed on an outer periphery of the head are formed on an arbitrary outer peripheral surface of the head. Spark plug.
The spark plug according to any one of claims 1 to 3, wherein a groove formed on an outer periphery of the head is formed in a direction parallel to an axial direction of the center electrode. Features a spark plug.
4. The spark plug according to claim 1, wherein the groove formed on the outer periphery of the head has a knurled shape. 5.
The spark plug according to any one of claims 1 to 8, wherein a diameter of the shaft hole at a position where a head of the center electrode is present is 3.0 mm or less. Spark plug.
The spark plug according to any one of claims 1 to 9, wherein a resistor is provided on a rear end side of the conductive sealing material in the shaft hole.
The spark plug according to any one of claims 1 to 10, wherein the stepped portion is formed in a tapered shape.
The spark plug according to any one of claims 1 to 11, wherein a groove on an outer periphery of the head is formed by rolling.