阅读说明：本技术 火花塞 (Spark plug ) 是由 伴谦治 于 2020-04-08 设计创作，主要内容包括：本发明提供一种能够使火焰核容易生长的火花塞。火花塞具备：筒状的主体配件,从前端侧朝向后端侧沿轴线延伸；中心电极,绝缘保持于主体配件的内侧；接地电极,与主体配件电连接,在中心电极与所述接地电极自身的端部之间形成火花间隙；以及盖部,在主体配件的前端侧,将中心电极和接地电极的端部从前端侧进行覆盖,并且形成有贯通孔,比接地电极的端部的后端靠前端侧的盖部的内表面及贯通孔的内表面的算术平均粗糙度为6.3μm以下。(The invention provides a spark plug capable of facilitating the growth of flame nuclei. The spark plug is provided with: a cylindrical metal shell extending along an axis from a front end side to a rear end side; a center electrode held in an insulated manner inside the metal shell; a ground electrode electrically connected to the metallic shell, a spark gap being formed between the center electrode and an end of the ground electrode; and a cover portion that covers the ends of the center electrode and the ground electrode from the distal end side, and that has a through hole formed therein, wherein the arithmetic average roughness of the inner surface of the cover portion and the inner surface of the through hole on the distal end side of the rear end of the ground electrode is 6.3 [ mu ] m or less.)

1. A spark plug, comprising:

a cylindrical metal shell extending along an axis from a front end side to a rear end side;

a center electrode held in an insulated manner inside the main body fitting;

a ground electrode electrically connected to the metallic shell, a spark gap being formed between the center electrode and an end of the ground electrode itself; and

a lid portion that covers end portions of the center electrode and the ground electrode from a distal end side thereof and that has a through hole formed therein,

the arithmetic mean roughness of the inner surface of the lid portion and the inner surface of the through hole on the front end side of the rear end of the end portion of the ground electrode is 6.3 [ mu ] m or less.

2. The spark plug of claim 1,

the arithmetic average roughness of the inner surface of the lid and the inner surface of the through hole is 1.6 [ mu ] m or less.

3. The spark plug of claim 1,

the arithmetic average roughness of the inner surface of the lid and the inner surface of the through hole is 0.8 [ mu ] m or less.

4. The spark plug according to any one of claims 1 to 3,

the metal shell has a male screw formed on a rear end side of an outer surface thereof, and is welded to a rear end portion of the lid portion on a front end side of the male screw,

the arithmetic mean roughness of the outer surface of the lid portion excluding the welded portion to be welded to the metal shell is 6.3 μm or less.

5. The spark plug according to any one of claims 1 to 3,

a male screw is formed on the rear end side of the outer surface of the cap portion,

the arithmetic average roughness of the outer surface of the cover portion on the tip side of the tip of the male screw is 6.3 [ mu ] m or less.

6. The spark plug according to claim 4 or 5,

the arithmetic average roughness of the outer surface of the cover portion is 1.6 [ mu ] m or less.

7. The spark plug according to claim 4 or 5,

the arithmetic average roughness of the outer surface of the cover portion is 0.8 [ mu ] m or less.

8. The spark plug according to any one of claims 1 to 7,

the arithmetic mean roughness is measured on an intersection of a plane parallel to the axis and the surface of the lid portion.

Technical Field

The present invention relates to a spark plug for forming a sub-chamber in a combustion chamber of an engine.

Background

There is known a spark plug in which a sub-chamber is formed in a combustion chamber of an engine (for example, patent document 1). Such a spark plug has a through hole formed in a lid portion connected to a metal shell. The cover portion exposed to the combustion chamber forms a sub-chamber in the combustion chamber. The combustible mixture flows from the combustion chamber into the lid portion through the through hole. The spark plug ignites the fuel-air mixture reaching the spark gap, and injects an airflow including a flame from the through hole into the combustion chamber by an expansion pressure generated by combustion of the fuel-air mixture. The combustible mixture in the combustion chamber is burned by the flame jet.

Disclosure of Invention

Problems to be solved by the invention

However, in the technique disclosed in patent document 1, if the variation in the turbulence of the fuel-air mixture flowing from the combustion chamber to the cover portion through the through-hole becomes large, the fuel-air mixture hardly reaches the spark gap as designed, and the growth of the flame kernel generated in the spark gap is suppressed, and the combustion may become unstable.

The present invention has been made to solve the above-described problems, and an object thereof is to provide a spark plug capable of facilitating growth of a flame kernel.

Means for solving the problems

In order to achieve the object, a spark plug according to the present invention includes: a cylindrical metal shell extending along an axis from a front end side to a rear end side; a center electrode held in an insulated manner inside the metal shell; a ground electrode electrically connected to the metallic shell, a spark gap being formed between the center electrode and an end of the ground electrode; and a cover portion that covers the ends of the center electrode and the ground electrode from the distal end side, and that has a through hole formed therein, wherein the arithmetic average roughness of the inner surface of the cover portion and the inner surface of the through hole on the distal end side of the rear end of the ground electrode is 6.3 [ mu ] m or less.

Effects of the invention

According to the spark plug of the present invention, since the arithmetic mean roughness of the inner surface of the cover portion and the inner surface of the through hole on the front end side with respect to the rear end of the end portion of the ground electrode is 6.3 μm or less, it is possible to reduce the variation in flow disturbance of the fuel-air mixture reaching the spark gap from the combustion chamber along the inner surface of the cover portion through the through hole. As a result, the combustible mixture easily reaches the spark gap as designed, and thus the flame kernel can easily grow.

In addition, when the arithmetic mean roughness of the inner surface of the lid portion and the inner surface of the through hole is 1.6 μm or less, the variation in the flow disturbance of the combustible mixture can be further reduced, and therefore, the flame kernel can be more easily grown. The effect is further enhanced when the arithmetic average roughness of the inner surface of the lid portion and the inner surface of the through hole is 0.8 μm or less.

When a male screw is formed on the rear end side of the outer surface of the metal shell and the rear end of the cover portion is welded to the metal shell on the front end side of the male screw, if the arithmetic average roughness of the outer surface of the cover portion excluding the welded portion to the metal shell is 6.3 μm or less, the variation in flow disturbance of the fuel-air mixture flowing from the combustion chamber to the through-hole along the outer surface of the cover portion can be reduced. As a result, the variation in the turbulence of the flow of the fuel-air mixture reaching the spark gap through the through-hole can be further reduced, and therefore, the flame kernel can be more easily grown.

When the male screw is formed on the rear end side of the outer surface of the cover portion, if the arithmetic average roughness of the outer surface of the cover portion on the front end side of the front end of the male screw is 6.3 μm or less, the variation in flow disturbance of the fuel-air mixture flowing from the combustion chamber to the through-hole along the outer surface of the cover portion can be reduced. As a result, the variation in the turbulence of the flow of the fuel-air mixture reaching the spark gap through the through-hole can be further reduced, and therefore, the flame kernel can be more easily grown.

In addition, when the arithmetic mean roughness of the outer surface of the lid portion is 1.6 μm or less, the variation in flow disturbance of the combustible mixture can be further reduced, and therefore, the flame kernel can be more easily grown. The effect is greater when the arithmetic average roughness of the outer surface of the cover portion is 0.8 μm or less.

When the arithmetic mean roughness measured on the intersection of the plane parallel to the axis and the surface of the cover portion is in the above range, the effect of reducing the variation in flow disturbance from the through hole to the spark gap can be further increased. As a result, the flame kernel can be more easily grown.

Drawings

Fig. 1 is a partial sectional view of a spark plug in a first embodiment.

Fig. 2 is a cross-sectional view of the spark plug enlarged from a portion shown in II of fig. 1.

Fig. 3 is a perspective view of the cover cut by a plane parallel to the axis.

Fig. 4 is a partial sectional view of a spark plug in a second embodiment.

Fig. 5 is a cross-sectional view of the spark plug enlarged from a portion indicated by V in fig. 4.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Fig. 1 is a partial sectional view of a spark plug 10 in a first embodiment. In fig. 1, the lower side of the paper surface is referred to as the front end side of the spark plug 10, and the upper side of the paper surface is referred to as the rear end side of the spark plug 10 (the same applies to fig. 2, 4, and 5). Fig. 1 shows a cross section including the axis O at a portion on the tip end side of the spark plug 10. As shown in fig. 1, the spark plug 10 includes an insulator 11, a center electrode 13, a metallic shell 20, a ground electrode 30, and a cover 40.

The insulator 11 is a substantially cylindrical member having a shaft hole 12 formed along the axis O, and is formed of a ceramic such as alumina having excellent mechanical properties and high-temperature insulation properties. A center electrode 13 is disposed on the tip end side of the axial hole 12 of the insulator 11. The center electrode 13 is electrically connected to the terminal fitting 14 in the axial hole 12. The terminal fitting 14 is a rod-shaped member connected to a high-voltage cable (not shown), and is formed of a metal material having electrical conductivity (e.g., mild steel or the like). The terminal fitting 14 is fixed to the rear end of the insulator 11.

The metallic shell 20 is a substantially cylindrical member formed of a conductive metal material (for example, mild steel). The metal shell 20 includes: a tip portion 22 having a male screw 21 formed on an outer peripheral surface thereof; a seat portion 23 adjacent to the rear end side of the front end portion 22; and a tool engagement portion 24 formed on the rear end side of the seat portion 23. The external thread 21 is threadedly engaged with the threaded hole 2 of the engine 1. The seat portion 23 is a portion for closing a gap between the screw hole 2 and the male screw 21 of the engine 1, and has an outer diameter larger than that of the male screw 21. When the male screw 21 is fastened to the screw hole 2 of the engine 1, a tool such as a wrench is engaged with the tool engagement portion 24.

The ground electrode 30 is a rod-shaped member formed of a metal material containing Pt or the like as a main component. In the present embodiment, the ground electrode 30 is disposed at the position of the male screw 21, and penetrates the distal end portion 22 to protrude inside the distal end portion 22. One end 31 of the ground electrode 30 faces the center electrode 13. A cap 40 is connected to the distal end side of the male screw 21 at the distal end portion 22 of the metal shell 20. The main component element of the ground electrode 30 is not limited to this, and other elements may be used as the main component. Examples of the other element include Ni and Ir.

The lid 40 covers the center electrode 13 and the one end 31 of the ground electrode 30 from the distal end side. The lid 40 is formed of a metal material containing Fe or the like as a main component. The lid 40 has a through hole 41 formed on the front end side of the ground electrode 30. The cover 40 is exposed to the combustion chamber 3 of the engine 1 in a state where the spark plug 10 is attached to the screw hole 2 of the engine 1 via the male screw 21. The through hole 41 communicates a sub-chamber 42 surrounded by the metallic shell 20 and the lid 40 with the combustion chamber 3. In the present embodiment, a plurality of through holes 41 are formed in the lid 40. The main component element of the lid 40 is not limited to this, and other elements may be used as the main component. Examples of the other element include Ni and Cu.

Fig. 2 is a cross-sectional view of the spark plug 10 including the axis O, which is an enlarged view of a portion shown in II in fig. 1. A recess 25 recessed radially inward is formed in the distal end portion 22 of the metal shell 20 at the position of the male thread 21. At the distal end portion 22, a hole 26 that is narrower than the recess 25 is formed radially inside the recess 25. The hole 26 penetrates the front end portion 22 in the radial direction. The other end portion 32 of the ground electrode 30 inserted into the hole 26 is joined to the leading end portion 22 by the weld 27. A spark gap 33 is formed between one end 31 of the ground electrode 30 and the center electrode 13. Since the ground electrode 30 is engaged with the region of the male screw 21 of the metallic shell 20, heat of the ground electrode 30 is transmitted from the male screw 21 to the engine 1.

An outer opening end 44 is formed in the outer surface 43 of the lid 40 through the through hole 41, and an inner opening end 46 is formed in the inner surface 45 of the lid 40 through the through hole 41. In the present embodiment, the entire inner surface 45 of the cover portion 40 formed in a conical shape is located on the front end side of the rear end 34 of the one end portion 31 of the ground electrode 30. The cross-sectional area of the sub-chamber 42 surrounded by the inner surface 45 of the cover 40, which is perpendicular to the axis O, increases from the front end side toward the rear end side.

The inner opening end 46 of the through hole 41 is located on the front end side of the rear end 34 of the one end portion 31 of the ground electrode 30. The inner surface 47 of the through hole 41 is inclined toward the distal end side as approaching from the inner open end 46 to the outer open end 44. The rear end portion 48 of the cover 40 is joined to the front end portion 22 of the metal shell 20 by a weld 49.

Fig. 3 is a perspective view of the lid 40 cut by a plane 50 parallel to the axis O (see fig. 1). Fig. 3 shows a part of the circumference of the cover 40. The surface roughness of the outer surface 43, the inner surface 45, and the inner surface 47 of the through hole 41 is adjusted by magnetic fluid polishing, buffing polishing, or the like in the lid portion 40. The arithmetic average roughness Ra of the outer surface 43 and the inner surface 45 of the lid portion 40 and the inner surface 47 of the through hole 41 is measured on an intersection line 51 of the plane 50 parallel to the axis O and the surface of the lid portion 40.

The intersection 51 is detected by, for example, a noncontact surface roughness meter using light, and the cross section is measured in accordance with JISB 0601: 2013, the arithmetic average roughness Ra is obtained by passing the curve (not shown) obtained by a filter for cutting off the short wavelength component or the long wavelength component. The evaluation length of the arithmetic average roughness is based on JIS B0633: 2001.

The arithmetic mean roughness of the outer surface 43, the inner surface 45 of the lid 40 and the inner surface 47 of the through hole 41 are each 6.3 μm or less. Preferably, the arithmetic mean roughness of the outer surface 43, the inner surface 45 of the lid 40 and the inner surface 47 of the through hole 41 are each set to 1.8 μm or less. More preferably, the arithmetic mean roughness of the outer surface 43, the inner surface 45 of the lid 40 and the inner surface 47 of the through hole 41 are each set to 0.8 μm or less. The roughness of the outer surface 43 and the inner surface 45 of the lid 40 is the roughness of the portions other than the welded portion 49.

In the ignition plug 10 attached to the engine 1 (see fig. 1), the combustible mixture flows from the combustion chamber 3 through the through hole 41 into the inside of the cover portion 40 by the valve operation of the engine 1. The spark plug 10 generates a flame kernel in the spark gap 33 by the discharge between the center electrode 13 and the ground electrode 30. The flame kernel ignites the combustible mixture inside the cover portion 40 after growth, so that the combustible mixture is burned. The ignition plug 10 injects an air flow containing flame from the through hole 41 into the combustion chamber 3 by the expansion pressure generated by the combustion. The combustible mixture in the combustion chamber 3 is burned by the flame jet.

In the spark plug 10, the arithmetic mean roughness of the inner surface 45 of the cover portion 40 and the inner surface 47 of the through hole 41 on the front end side of the rear end 34 of the one end portion 31 of the ground electrode 30 is 6.3 μm or less, and therefore, the variation in turbulence of the flow of the fuel mixture flowing from the combustion chamber 3 to the cover portion 40 along the inner surface 47 of the through hole 41 and reaching the spark gap 33 along the inner surface 45 of the cover portion 40 can be reduced. As a result, the fuel-air mixture easily reaches the spark gap 33 from the combustion chamber 3 through the through-hole 41 as designed, and the flame kernel generated in the spark gap 33 easily grows. As a result, the combustible mixture can be ignited as designed.

Since the cross-sectional area of the sub-chamber 42 surrounded by the inner surface 45 of the cover 40, which is perpendicular to the axis O, increases from the front end side toward the rear end side, the flow velocity of the fuel-air mixture flowing from the combustion chamber 3 into the cover 40 in the vicinity of the rear end portion 48 of the cover 40 can be made slower than the flow velocity in the vicinity of the front end of the cover 40. The slower the flow velocity, the weaker the turbulence of the flow, and therefore the variation in the turbulence of the fuel-air mixture flowing through the spark gap 33 can be further reduced. As a result, the flame kernel generated in the spark gap 33 can be more easily grown.

Since the arithmetic mean roughness of the outer surface 43 of the cover portion 40 excluding the welded portion 49 between the metallic shell 20 and the cover portion 40 is 6.3 μm or less, the variation in the flow disturbance of the fuel-air mixture flowing from the combustion chamber 3 into the through-hole 41 along the outer surface 43 of the cover portion 40 can be reduced. As a result, the variation in the turbulence of the flow of the fuel-air mixture reaching the spark gap 33 through the through-hole 41 can be further reduced, and therefore, the flame kernel generated in the spark gap 33 can be more easily grown.

A second embodiment will be described with reference to fig. 4 and 5. In the first embodiment, a case where the lid portion 40 is welded to the metallic shell 20 is described. In contrast, in the second embodiment, a case will be described in which the cylindrical member 70 having the lid portion 75 formed at the distal end thereof is connected to the metal shell 61. Note that the same portions as those described in the first embodiment are denoted by the same reference numerals, and the following description is omitted. Fig. 4 is a partial sectional view of a spark plug 60 according to a second embodiment, and fig. 5 is a sectional view of the spark plug 60 in which a portion indicated by V in fig. 4 is enlarged.

The spark plug 60 includes an insulator 11, a center electrode 13, a metallic shell 61, a ground electrode 64, and a lid 75. The metallic shell 61 is a substantially cylindrical member formed of a conductive metal material (for example, mild steel). The metal shell 61 includes a tip end portion 63 having a male screw 62 formed on an outer peripheral surface thereof. A seat portion 23 and a tool engagement portion 24 are provided on the rear end side of the front end portion 63. The ground electrode 64 is a rod-shaped member formed of a metal material containing Pt, Ni, Ir, or the like as a main component. In the present embodiment, the ground electrode 64 is disposed on the distal end side of the male screw 62 of the distal end portion 63. One end 65 (see fig. 5) of the ground electrode 64 faces the center electrode 13.

The tubular member 70 is a closed-end tubular member, and includes: a main body portion 71; a flange portion 74 adjacent to the rear end side of the body portion 71; and a lid portion 75 adjacent to the front end side of the body portion 71. The distal end portion 63 of the metal shell 61 is disposed inside the body portion 71. A female screw 72 is formed on the inner peripheral surface of the body portion 71, and a male screw 73 is formed on the outer peripheral surface of the body portion 71. The internal thread 72 of the body 71 is coupled to the external thread 62 of the metallic shell 61. The male screw 73 of the body portion 71 is coupled to the screw hole 2 of the engine 1. The outer diameter of the flange portion 74 is larger than the outer diameter of the male screw 73. The seat portion 23 of the metal shell 61 is disposed radially inward of the flange portion 74.

The lid 75 covers the center electrode 13 and the one end 65 of the ground electrode 64 from the distal end side. The lid portion 75 has a through hole 76 formed on the front end side of the ground electrode 64. The lid portion 75 is exposed to the combustion chamber 3 of the engine 1 in a state where the cylindrical member 70 of the ignition plug 60 is attached to the screw hole 2 of the engine 1 via the male screw 73. The through hole 76 communicates a sub-chamber 77 surrounded by the metallic shell 61 and the cover 75 with the combustion chamber 3. In the present embodiment, a plurality of through holes 76 are formed in the lid portion 75.

As shown in fig. 5, the other end 66 of the ground electrode 64 is joined to the distal end 63 of the metallic shell 61 on the distal end side of the male screw 62. A spark gap 67 is formed between one end portion 65 of the ground electrode 64 and the center electrode 13. An outer open end 79 is formed in the outer surface 78 of the lid portion 75 through the through hole 76, and an inner open end 81 is formed in the inner surface 80 of the lid portion 75 through the through hole 76. The inner surface 80 of the cap 75 is formed in a spherical crown shape. The inner opening end 81 of the through hole 76 is located on the front end side of the rear end 68 of the one end portion 65 of the ground electrode 64. The inner surface 82 of the through hole 76 is inclined toward the distal end side as approaching from the inner open end 81 to the outer open end 79.

A part (a portion on the front end side) of the inner surface 80 of the cover portion 75 is positioned on the front end side of the rear end 68 of the one end portion 65 of the ground electrode 64. The arithmetic average roughness of the inner surface 80 of the cover 75 on the front end side of the rear end 68 of the one end 65 of the ground electrode 64 and the arithmetic average roughness of the inner surface 82 of the through hole 76 are each 6.3 μm or less. The arithmetic mean roughness of the outer surface 78 of the cover 75 on the tip side of the tip of the male screw 73 is 6.3 μm or less. As a result, the spark plug 60 of the second embodiment can achieve the same operational effects as the spark plug 10 of the first embodiment. As described in the first embodiment, the arithmetic mean roughness is measured on the intersection of a plane (not shown) parallel to the axis O and the surface of the lid portion 75.