阅读说明：本技术 火花塞 (Spark plug ) 是由 今井奖 于 2020-03-31 设计创作，主要内容包括：本发明提供一种火花塞,能够抑制火花塞的松动。火花塞的特征在于,具备：筒状的主体金属件,具有在外周形成有外螺纹的安装螺纹部；绝缘体,配置于上述主体金属件的内周,并具有轴孔；及中心电极,配置于上述轴孔,在沿着上述主体金属件的轴线的方向上,上述外螺纹的有效直径为极大值的有效直径极大部存在于比上述中心电极的后端靠前端侧。(The invention provides a spark plug, which can inhibit the loosening of the spark plug. The spark plug is characterized by comprising: a cylindrical main body metal fitting having a mounting screw portion with an external screw formed on an outer periphery thereof; an insulator disposed on an inner periphery of the main body metal piece and having a shaft hole; and a center electrode disposed in the axial hole, wherein an effective diameter maximum portion where an effective diameter of the male screw is maximum is present on a front end side of a rear end of the center electrode in a direction along an axis of the body metal.)

1. A spark plug is characterized by comprising:

a cylindrical main body metal fitting having a mounting screw portion with an external screw formed on an outer periphery thereof;

an insulator disposed on an inner periphery of the main body metal member and having a shaft hole; and

a center electrode disposed in the axial hole,

in a direction along the axis of the body metal piece,

an effective diameter maximum portion in which the effective diameter of the male screw is maximum is present on the front end side of the rear end of the center electrode.

2. The spark plug of claim 1,

the effective diameter of the external thread is largest at the effective diameter-enlarged portion.

3. The spark plug according to claim 1 or 2,

the insulator has an insulator stepped portion protruding to an outer periphery,

the main metal piece is provided with a metal piece inner step part protruding towards the inner periphery,

the insulator step portion is in contact with the metal piece inner step portion via a seal,

in the direction along the said axis, the axis of the shaft,

the large effective diameter portion is located on the front end side of the rear end of the step portion in the metal member.

4. The spark plug of claim 3,

in the direction along the said axis, the axis of the shaft,

the major portion of the effective diameter is present at a location of a step portion within the metal piece.

5. The spark plug according to any one of claims 1 to 4,

the length of the mounting thread portion in the direction along the axis is 26.5mm or more.

Technical Field

The present invention relates to a spark plug.

Background

The attachment operation of the ignition plug to an internal combustion engine, for example, a gasoline engine, is performed by screwing a threaded portion formed on an outer surface of a main metal of the ignition plug into an internal thread provided in an engine head. Also, the effective diameter of the threaded portion is generally uniform (for example, patent document 1).

Patent document 1: japanese laid-open patent publication No. 2015-225774

Disclosure of Invention

Problems to be solved by the invention

In general, it is preferable to make the screw portion longer because the degree of freedom of the place where the water jacket of the engine is disposed is higher. However, in the case where the effective diameter of the threaded portion is made uniform, the longer the length of the threaded portion is, the larger the area of contact between the threaded portion and the engine head is, with the result that the surface pressure per unit area decreases. Therefore, there are problems as follows: when receiving vibration generated by a combustion cycle of the engine, the longer the screw portion is, the more easily the spark plug becomes loose.

Means for solving the problems

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

(1) According to one aspect of the present invention, a spark plug is provided. The spark plug is characterized by comprising: a cylindrical main body metal fitting having a mounting screw portion with an external screw formed on an outer periphery thereof; an insulator disposed on an inner periphery of the main body metal piece and having a shaft hole; and a center electrode disposed in the axial hole, wherein an effective diameter maximum portion where an effective diameter of the male screw is maximum is present on a front end side of a rear end of the center electrode in a direction along an axis of the body metal. According to the spark plug of this aspect, the surface pressure increases at the extremely large effective diameter portion by contact with the engine cylinder head, so that the wobble of the spark plug is suppressed, and as a result, the looseness of the spark plug can be suppressed.

(2) In the spark plug of the above aspect, the effective diameter of the male screw may be the largest in the extremely large effective diameter portion. According to the spark plug of this aspect, heat from the inside of the engine is efficiently released from the main metal fitting through the extremely large effective diameter portion, and therefore heat is favorably conducted.

(3) In the spark plug according to the above aspect, the insulator may include an insulator stepped portion that protrudes outward, the main metal fitting may include a metal fitting inner stepped portion that protrudes inward, the insulator stepped portion may be in contact with the metal fitting inner stepped portion via a seal, and the portion having the extremely large effective diameter may be located on a front end side of a rear end of the metal fitting inner stepped portion in a direction along the axis. According to the spark plug of this aspect, heat from the inside of the engine is efficiently released from the main metal fitting through the extremely large effective diameter portion, and therefore heat is favorably conducted.

(4) In the spark plug according to the above aspect, the extremely large effective diameter portion may be present at a position of the step portion in the metal fitting in a direction along the axis. According to the spark plug of this aspect, heat from the inside of the engine is efficiently released from the main metal fitting through the extremely large effective diameter portion, and therefore heat is favorably conducted.

(5) In the spark plug according to the above aspect, the length of the mounting screw portion in the direction along the axis may be 26.5mm or more. According to the spark plug of the present embodiment, it is possible to suitably use the spark plug of the embodiment in which the length of the mounting screw portion, which is generally prone to be loosened, is long.

The present invention can be realized in various forms, for example, in the form of an engine head to which a spark plug is attached.

Drawings

Fig. 1 is an explanatory view showing a partial cross section of a spark plug.

Fig. 2 is a diagram showing displacement of the effective diameter of the male screw of the mounting screw portion.

Fig. 3 is a diagram illustrating a positional relationship of the effective diameter maximum portion of the spark plug.

Fig. 4 is a diagram showing displacement of the effective diameter of the male screw in the second embodiment.

Fig. 5 is a diagram showing displacement of the effective diameter of the male screw in the third embodiment.

Fig. 6 is a diagram showing displacement of the effective diameter of the male screw in the fourth embodiment.

Detailed Description

A. The first embodiment:

fig. 1 is an explanatory diagram showing a cross section of a spark plug 100. In fig. 1, the outer shape of the spark plug 100 is shown on the right side of the drawing, and the cross-sectional shape of the spark plug 100 is shown on the left side of the drawing, with the axis CA as the axial center of the spark plug 100 as the boundary. In the description of the present embodiment, the lower side in fig. 1 will be referred to as the front end side of the spark plug 100, and the upper side in fig. 1 will be referred to as the rear end side of the spark plug 100.

The spark plug 100 includes: an insulator 10 having a shaft hole 12 along an axis CA; a center electrode 20 provided in the axial hole 12; a cylindrical body metal fitting 50 disposed on the outer periphery of the insulator 10; and a ground electrode 30, a base end of the ground electrode 30 being fixed to the main body metal 50.

The insulator 10 is an insulator formed by firing a ceramic material mainly composed of alumina. The insulator 10 is a member disposed on the inner periphery of the metal shell 50, and is a cylindrical member having a center formed with a shaft hole 12 that accommodates a part of the center electrode 20 on the front end side and a part of the terminal fitting 40 on the rear end side. A central body portion 19 having a large outer diameter is formed at the axial center of the insulator 10. A rear-end body portion 18 having an outer diameter smaller than that of the central body portion 19 is formed on the rear end side of the central body portion 19. A distal-side body 17 having an outer diameter smaller than that of the rear-side body 18 is formed on the distal end side of the central body 19. Further, the distal-side main body portion 17 has a long leg portion 13 formed at a distal end thereof, the long leg portion having a smaller outer diameter toward the center electrode 20.

The main metal fitting 50 is a cylindrical metal fitting that surrounds and holds a portion from a part of the rear end side main body portion 18 of the insulator 10 to the thigh portion 13. The main body metal 50 is formed of, for example, low carbon steel, and is entirely subjected to plating treatment such as nickel plating or zinc plating. The main body metal fitting 50 includes a tool engagement portion 51, a seal portion 54, and an attachment screw portion 52 in this order from the rear end side. A tool for attaching the spark plug 100 to the engine head 90 is fitted to the tool engagement portion 51. The mounting screw portion 52 is a portion having a male screw formed on the entire periphery of the metal shell 50, and is screwed into the mounting screw hole 93 of the engine head 90. The seal portion 5 is formed in a flange shape at the root of the mounting screw portion 52. An annular gasket 65 formed by bending a plate body is inserted between the seal portion 54 and the engine head 90. An end surface 57 on the tip side of the main body metal 50 is hollow and round, and the tip of the long leg 13 of the insulator 10 and the tip of the center electrode 20 protrude from the center thereof.

A caulking portion 53 having a small thickness is provided on the rear end side of the body metal fitting 50 with respect to the tool engagement portion 51. Further, a compression deformation portion 58 having a small thickness similar to the caulking portion 53 is provided between the sealing portion 54 and the tool engagement portion 51. Annular ring members 66 and 67 are interposed between the inner circumferential surface of the body metal 50 from the tool engagement portion 51 to the caulking portion 53 and the outer circumferential surface of the rear end side body portion 18 of the insulator 10, and a space between the ring members 66 and 67 is filled with a powder of talc 69. When manufacturing the spark plug 100, the caulking portion 53 is bent inward and pressed against the tip end side, so that the compression deformation portion 58 is compressed and deformed. By the compression deformation of the compression-deformable portion 58, the insulator 10 is pressed toward the distal end side in the main metal 50 via the ring members 66, 67 and the talc 69. By this pressing, the talc 69 is compressed in the axis CA direction, thereby improving the airtightness inside the body metal 50.

A metal inner step portion 56 protruding toward the inner periphery is formed in the main body metal 50. In addition, the position of the rear end of the metal piece inner step portion 56 in the direction along the axis CA is P2. Further, an insulator stepped portion 15 is formed on the insulator 10 so as to be located at the rear end of the long leg portion 13 and project outward. The metal fitting inner step portion 56 is in contact with the insulator step portion 15 via an annular seal 68 on the inner periphery of the main body metal fitting 50. The seal 68 is a member for maintaining airtightness between the metal shell 50 and the insulator 10, and prevents outflow of combustion gas. In the present embodiment, a plate seal is used as the seal.

The center electrode 20 is a rod-shaped member in which a core member 22 having a thermal conductivity superior to that of the electrode member 21 is embedded in the electrode member 21. The electrode member 21 is formed of a nickel alloy containing nickel as a main component, and the core member 22 is formed of copper or an alloy containing copper as a main component. A noble metal tip formed of, for example, an iridium alloy or the like may be joined to the tip end portion of the center electrode 20 on the tip end side.

A flange 23 protruding outward is formed near the end of the center electrode 20 on the rear end side. The flange portion 23 contacts the shaft hole inner step portion 14 protruding toward the inner peripheral side in the shaft hole 12 of the insulator 10 from the rear end side, and positions the center electrode 20 in the insulator 10. The center electrode 20 is electrically connected to the terminal fitting 40 through the sealing body 64 and the ceramic resistor 63 at the rear end side of the center electrode 20. In the direction along the axis CA, the position of the rear end of the center electrode is P1.

The ground electrode 30 is formed of an alloy containing nickel as a main component. The base end of the ground electrode 30 is fixed to the end surface 57 of the main metal 50. The ground electrode 30 extends from the base end 32 toward the tip end side along the axis CA, and the intermediate portion is bent so that one side surface of the tip end portion 33 faces the tip end surface of the center electrode 20. A noble metal tip 31 is provided on a surface of the leading end 33 of the ground electrode 30 facing the center electrode 20. A gap for spark discharge is formed between the noble metal tip 31 and the center electrode 20. The noble metal tip 31 is formed of, for example, platinum, iridium, ruthenium, rhodium, or an alloy thereof.

Fig. 2 is a diagram showing displacement of the effective diameter of the male screw of the mounting screw portion 52. In fig. 2, the displacement of the effective diameter is indicated by a dashed line, and for reference the shape of the thread ridge of the external thread is indicated by a solid line. From the viewpoint of easy understanding of the contents, the displacement of the effective diameter indicated by the broken line is larger than the actual displacement amount, and does not have a meaning as an absolute value. In fig. 2, the vertical axis represents the effective diameter of the male screw, and the horizontal axis represents the position in the direction along the axis CA. Here, in the present specification, "effective diameter of male screw" means a value specified in JIS B0205.

As shown in fig. 2, in the spark plug 100 of the present embodiment, there is an effective diameter extremely large portion PA that is a portion where the effective diameter of the male screw is maximum. Here, the "extremely large effective diameter portion" refers to a portion having an effective diameter larger than the front end side and the rear end side of the portion. In the present embodiment, the effective diameter at the very large effective diameter portion PA is 11.100 mm.

Fig. 3 is a diagram illustrating a positional relationship of the effective-diameter extremely large portion PA of the spark plug 100. In the present embodiment, the effective diameter extremely large portion PA is located on the front end side of the rear end P1 (see also fig. 1) of the center electrode 20 in the direction along the axis CA.

According to the spark plug 100 of the present embodiment, the looseness of the spark plug 100 can be suppressed when the spark plug 100 is fixed to the engine head 90. This mechanism will be explained below.

When the spark plug 100 is fixed to the engine head 90, the front end side is generally more likely to receive heat from the inside of the engine than the rear end side of the spark plug 100. Specifically, in the main body metal 50 of the spark plug 100, the temperature of the front end side is increased to about 600 ℃, whereas the temperature of the rear end side of the main body metal 50 is increased to only about 100 ℃. As a result, the front end side of the main body metal fitting 50 expands more by heat than the rear end side.

In the spark plug 100 of the present embodiment, the effective diameter extremely large portion PA is present on the front end side of the rear end P1 of the center electrode 20, and therefore the amount of thermal expansion is larger than in the case where the effective diameter extremely large portion PA is present on the rear end side of the rear end P1 of the center electrode 20. As a result, the contact with the engine cylinder head 90 increases the surface pressure at the effective diameter extremely large portion PA, so that the wobble of the spark plug 100 is suppressed, and as a result, the looseness of the spark plug 100 can be suppressed.

The effective diameter of the spark plug 100 of the present embodiment is larger at the effective diameter extremely large portion PA than at the tip end side of the effective diameter extremely large portion PA. Therefore, it is possible to suppress damage to the mounting screw hole 93 of the engine head 90 due to excessive thermal expansion occurring in the portion on the front end side of the effective diameter extremely large portion PA.

In addition, the spark plug 100 of the present embodiment has the largest effective diameter of the male screw at the extremely large effective diameter portion PA. Here, when the metal shell 50 receives heat from inside the engine, the heat is conducted to the engine head 90 through the extremely large effective diameter portion PA in contact with the engine head 90, and is released from the metal shell 50. According to the present embodiment, the effective diameter extremely large portion PA is present on the front end side of the rear end P1 of the center electrode 20, and therefore, heat is efficiently released from the main metal fitting 50 through the effective diameter extremely large portion PA as compared with the case where the effective diameter extremely large portion PA is present on the rear end side of the rear end P1 of the center electrode 20. Therefore, according to the spark plug 100 of the present embodiment, the heat conduction is good.

In addition, the spark plug 100 of the present embodiment has the largest effective diameter of the male screw at the extremely large effective diameter portion PA. According to the present embodiment, when the spark plug 100 is fixed to the engine head 90, the surface pressure is concentrated on the effective diameter extremely large portion PA by being in contact with the engine head 90 at the effective diameter extremely large portion PA. In this way, as compared with the case where the effective diameters are uniformly the same, the looseness of the spark plug 100 can be effectively suppressed.

In addition, as shown in fig. 3, in the present embodiment, the effective diameter extremely large portion PA exists at the same position as the rear end P2 of the metal inner step portion 56 in the direction along the axis CA. That is, in the present embodiment, the effective diameter maximum portion PA exists at the position of the step portion 56 in the metal member in the direction along the axis CA. When the insulator 10 or the center electrode 20 receives heat from the inside of the engine, the heat is conducted to the main metal 50 through the seal 68 and the metal inner step portion 56, and then conducted to the engine head 90 through the extremely large effective diameter portion PA. According to the present embodiment, since the effective diameter enlargement portion PA is present at the position of the step portion 56 in the metal fitting in the direction along the axis CA, heat is efficiently released from the main body metal fitting 50 via the effective diameter enlargement portion PA. Therefore, according to the spark plug 100 of the present embodiment, the heat conduction is good.

In the present embodiment, the length of the mounting screw portion 52 in the direction along the axis CA is 26.5mm or more. Here, "the length of the mounting screw portion 52" indicates the length from the thread ridge at the leading end to the surface on the leading end side of the seal portion 54. In general, as the length of the mounting screw portion 52 is longer, the larger the area of contact between the male screw of the mounting screw portion 52 and the female screw of the engine head 90 is, the more the looseness tends to be generated. The lower limit of the length of the mounting screw portion 52 in the direction along the axis CA is not limited to this, and may be 18mm or more, for example. The upper limit of the length of the mounting thread portion 52 in the direction along the axis CA is not particularly limited, but is preferably 70mm or less, and more preferably 50mm or less, from the viewpoint of ease of manufacturing the spark plug 100.

B. Second embodiment

Fig. 4 is a diagram showing displacement of the effective diameter of the male screw in the second embodiment. In fig. 4, as in fig. 2, the displacement of the effective diameter is indicated by a broken line, and the shape of the thread ridge of the male screw is indicated by a solid line for reference. From the viewpoint of easy understanding of the contents, the displacement of the effective diameter indicated by the broken line is larger than the actual displacement amount, and does not have a meaning as an absolute value. In fig. 4, the vertical axis represents the effective diameter of the male screw, and the horizontal axis represents the position in the direction along the axis CA. The same applies to fig. 5 and 6 below.

The second embodiment is different from the first embodiment in the form of displacement of the effective diameter of the male screw, but is otherwise identical in structure. In the second embodiment, the effective diameter maximum portion PA is present on the tip side of the rear end P2 of the metal fitting inner step portion 56. In this way, when the main body metal fitting 50 receives heat from the engine, heat is efficiently released from the main body metal fitting 50 via the extremely large effective diameter portion PA, as compared to a case where the extremely large effective diameter portion PA is present on the rear end side of the rear end P2 of the metal fitting inner step portion 56. Therefore, according to the present embodiment, the heat of the main body metal 50 is well conducted.

C. Third embodiment

Fig. 5 is a diagram showing displacement of the effective diameter of the male screw in the third embodiment. The third embodiment is different from the first embodiment in the form of displacement of the effective diameter of the male screw, but is otherwise identical in structure.

In the third embodiment, the effective diameter of the male screw on the rear end side of the vicinity of the rear end P1 of the center electrode 20 is uniformly the same, and the effective diameter gradually increases from the vicinity of the rear end P1 of the center electrode 20 to the effective diameter extremely large portion PA, and gradually decreases from the effective diameter extremely large portion PA to the tip. In such an embodiment, the looseness of the spark plug 100 can be suppressed.

D. Fourth embodiment

Fig. 6 is a diagram showing displacement of the effective diameter of the male screw in the fourth embodiment. The fourth embodiment is different from the first embodiment in the form of displacement of the effective diameter of the male screw, but is otherwise identical in configuration.

In the fourth embodiment, the effective diameter of the male screw on the rear end side of the vicinity of the rear end P1 of the center electrode 20 is uniformly the same, and the effective diameter gradually increases from the vicinity of the rear end P1 of the center electrode 20 to the vicinity of the rear end P2 of the metal fitting inner step portion 56, and an extremely large effective diameter portion PA having a constant width is provided from the vicinity of the rear end P2 of the metal fitting inner step portion 56. In such an embodiment, the looseness of the spark plug 100 can be suppressed.

E. Other embodiments are as follows:

the present invention is not limited to the above-described embodiments, and can be realized in various configurations without departing from the spirit thereof. For example, in order to solve part or all of the above-described problems or to achieve part or all of the above-described effects, the technical features in the embodiments corresponding to the technical features in the respective aspects described in the summary of the invention may be appropriately replaced or combined. Note that, as long as the technical features are not described as indispensable in the present specification, the technical features can be appropriately deleted.

In the above embodiment, the effective diameter is the largest at the most significant portion PA of the effective diameter, but is not limited thereto. The effective diameter may be maximized in a portion other than the effective diameter maximum portion PA.

In the above embodiment, the effective diameter extremely large portion PA is present at the same position as the rear end P2 of the metal piece inner step portion 56 or at the front end side of the rear end P2 of the metal piece inner step portion 56 in the direction along the axis CA. However, the present invention is not limited to this, and the effective diameter maximum portion PA may be present on the rear end side of the rear end P2 of the metal fitting inner step portion 56 in the direction along the axis CA.

In the above-described embodiment, as shown in fig. 3, the metal fitting inner step portion 56 protrudes inward from the portion on the front end side and the portion on the rear end side of the metal fitting inner step portion. However, it is not limited thereto. The metal fitting inner step portion 56 may protrude inward from a portion closer to the rear end side than itself.

In the above embodiment, the insulator stepped portion 15 is present on the tip end side of the shaft-hole inner stepped portion 14 in the direction along the axis CA. However, the insulator stepped portion 15 may be present at the same position as the shaft-hole inner stepped portion 14 or may be present on the rear end side of the shaft-hole inner stepped portion 14 in the direction along the axis CA. From the viewpoint of manufacturing the spark plug 100, it is preferable that the insulator stepped portion 15 be present on the tip end side of the shaft-hole inner stepped portion 14 in the direction along the axis CA.

Description of reference numerals

10 … insulator

12 … axle hole

13 … Long leg

14 … step in axle hole

15 … insulator step

17 … front end side body part

18 … rear end side body part

19 … Central body section

20 … center electrode

21 … electrode component

22 … core material

23 … flange portion

30 … ground electrode

31 … noble metal tip

32 … base end

33 … front end

40 … terminal fitting

50 … main body metal piece

51 … tool engaging part

52 … installation screw part

53 … riveting part

54 … seal

56 … step in metal piece

57 … end face

58 … compression deformation

63 … ceramic resistor

64 … sealing body

65 … gasket

66, 67 … Ring component

68 … sealing member

69 … Talc

90 … engine cylinder head

93 … mounting screw hole

100 … spark plug

CA … axis

P1 … rear end

P2 … rear end

The effective diameter of PA … is very large.