Patent Grant
8624474
The present invention relates to a spark plug used for igniting fuel through generating a spark electrically in an internal combustion engine.
A conventional spark plug typically has a metal shell that is fixed by caulking to an outer circumference of a ceramic insulator that holds a center electrode therein (See, for example, Japanese Patent Application Laid-Open (kokai) No. 11-345676). Such metal shell of the spark plug has a pair of flanges projecting in an outer circumference direction. During a “caulking process,” a cylindrical groove, bulging out in the outer circumference direction, is formed between the flanges. Examples of the flanges in the metal shell are a tool engagement portion assuming a polygonal-shape for engaging with a tool for mounting a spark plug to an engine head, or a trunk portion for compressing a gasket towards an engine head.
Recently, a reduction in size of a spark plug is considered as one of the various resolutions of fuel efficiency improvement in an internal combustion engine and of emission gas reduction. However, deterioration in strength of the metal shell has not been considered in connection with the miniaturization of the spark plug. For example, when the metal shell is miniaturized with the same reduction ratio as that of the spark plug, the strength of a groove in the metal shell could not fully be achieved, which may lead to a crack due to impact or stress corrosion.
In light of the above-described problems, an object of the present invention is to provide a technique capable of reducing the size of a spark plug while securing the integrity of the groove in the metal shell.
The present invention has been conceived to solve, at least partially, the above problem and can be embodied in the following modes or application examples.
Aspect 1
In accordance with a first aspect of the present invention, there is provided a spark plug comprising: a rod-like center electrode; a ceramic insulator electrically insulating an outer circumference of the center electrode; and a metal shell fixed by caulking to an outer circumference of the ceramic insulator. The metal shell includes a cylindrical groove that bulges out in an outer circumference direction. A polygonal tool engagement portion adjoins one end of the groove and bulges out in the outer circumference direction with respect to the groove. A trunk portion adjoins another end (which is different to the one end) of the groove and bulges out in the outer circumference direction with respect to the groove. A ground electrode is joined to the metal shell and forms a spark gap with the center electrode, wherein an opposite side distance “S” between opposing two sides of the polygonal tool engagement portion is 12 mm or less, wherein a section modulus “Z1” and a section modulus “Z2” satisfy a relationship: Z1<=Z2, where “Z1” represents a section modulus in the one end of the groove, and where “Z2” represents a section modulus in the other end of the groove.
Aspect 2
In accordance with another aspect of the present invention, there is provided a spark plug according to Aspect 1, wherein the section modulus “Z1” preferably satisfy a relationship Z1>=49 mm3.
Aspect 3
In accordance with another aspect of the present invention, there is provided a spark plug as described above according to Aspects 1 or 2, wherein a distance A, a distance B and the section modulus “Z2” preferably satisfy the following relationship:
if A>B,Z2>=62 mm3,
if A<=B,Z2>=53 mm3,
where the distance “A” represents a distance from the one end to an outermost portion having a largest outer diameter in the groove, and where the distance “B” represents a distance from the other end to the outermost portion.
Aspect 4
In accordance with another aspect of the present invention, there is provided a spark plug as described above according to any one of Aspects 1 to 3, wherein a thickness “C” preferably satisfy the relationship:
C>=3 mm,
where the thickness “C” represents a thickness of the trunk portion along an axis of the center electrode from a region adjoining the other end of the groove.
Aspect 5
In accordance with another aspect of the present invention, there is provided a spark plug as described above according to any one of Aspects 1 to 4, wherein a distance “D” and a distance “H” preferably satisfy the following relationship:
(H/D)<=0.17,
where the distance “D” represents a distance from the one end to the other end of the groove, and
where the distance “H” represents a distance from the outermost portion to a straight line that connects the one end to the other end of the groove.
Aspect 6
In accordance with another aspect of the present invention, there is provided a spark plug as described above according to any one of Aspects 1 to 5, wherein the metal shell may be plated with nickel.
Aspect 7
In accordance with another aspect of the present invention, there is provided a spark plug as described above according to any one of Aspects 1 to 6, wherein the fixation by caulking may be conducted through a cold caulking.
The present invention can be implemented in various forms. For example, the present invention can be implemented not only in a spark plug but also, for example, in a metal shell of a spark plug, an internal combustion engine in which the spark plug is mounted, and in a method for manufacturing a spark plug. Further, the present invention is not limited to the above-described aspects, but may be embodied in various other forms without departing from the gist of the invention.
According to a spark plug of Aspect 1, the impact resistance of the groove is securable, i.e., obtainable, even though the opposite side distance of the tool engagement portion is 12 mm or less. Therefore, the spark plug can be miniaturized while securing the strength of the groove of the metal shell.
According to the spark plug of Aspect 2, the impact resistance of the groove is fully securable.
According to the spark plug of Aspect 3, the impact resistance of the groove is fully securable corresponding to the relationship between the distance A that is from the outermost portion to the one end of the groove and the distance B that is from outermost portion to the other end of the groove.
According to the spark plug of Aspect 4, impact exerted on the groove can be alleviated.
According to the spark plug of Aspect 5, resistance to stress corrosion cracking can be improved.
According to the spark plug of Aspect 6, although the metal shell is plated by nickel that tends to cause cracks due to stress corrosion, the spark plug can be miniaturized while securing the intensity, i.e., strength, of the groove of the metal shell.
According to the spark plug of Aspect 7, the spark plug can be miniaturized while maintaining the strength of the groove of the metal shell, even though the cold caulking, which tends to cause an asymmetry of the bulging of the groove across the outermost portion, is adopted for fixing the metal shell.
In order to further define the configuration and the effect of the present invention described above, a spark plug according to the present invention will next be described with reference to specific embodiments.
In the spark plug 100, an outer circumference of the rod-like center electrode 10 is insulated by the ceramic insulator 20. One end of the center electrode 10 projects from one end of the ceramic insulator 20 and the other end of the center electrode 10 is electrically connected to the other end of the ceramic insulator 20. An outer circumference of the ceramic insulator 20 is held by the metal shell 30 through caulking. with being Metal shell 30 is electrically insulated from the center electrode 10. The ground electrode 40 is electrically connected to the metal shell 30 and forms a spark gap for generating sparks, in cooperation with the center electrode 10. The spark plug 100 is mounted on a mounting threaded hole 210 provided in an engine head 200 of an internal combustion engine (not shown) with the metal shell 30 being engaged with the mounting threaded hole 210. When a high voltage of 20,000 volts to 30,000 volts is applied to the center electrode 10, a spark is generated across the spark gap formed between the center electrode 10 and the ground electrode 40.
The center electrode 10 of the spark plug 100 is a rod-like electrode having a structure in which a core 14 is embedded within an electrode base metal 12 to have a closed-bottomed tubular shape. Core 14 is superior in thermal conductivity to the electrode base metal 12. In the present embodiment, the center electrode 10 is held by the ceramic insulator 20 with one end of the electrode base metal 12 projecting from the one end of the ceramic insulator 20 and electrically connected to the other end of the ceramic insulator 20 through a sealing body 16, a ceramic resistance 17, a sealing body 18 and a terminal fitting 19. In a preferred embodiment, the electrode base metal 12 is formed of a nickel alloy, such as INCONEL (registered trademark), which contains nickel as a main component. The core 14 of the center electrode 10 is formed of copper or an alloy which contains copper as a main component.
The ground electrode 40 of the spark plug 100 is welded to the metal shell 30 and bent in a direction perpendicular to the axis O-O of the center electrode 10 so as to face a front end of the center electrode 10. In the present embodiment, the ground electrode 40 is formed of a nickel alloy, such as INCONEL (registered trademark), which contains nickel as a main component.
The ceramic insulator 20 of the spark plug 100 is formed from a ceramic material, such as alumina, by firing. The ceramic insulator 20 is a tubular member having therein an axial bore 28 for accommodating the center electrode 10. The ceramic insulator 20 has an insulator nose 22, a first trunk portion 24, a flange 25 and a second trunk portion 26 in this order along the axis O-O from a side where the center electrode 10 projects. The insulator nose 22 of the ceramic insulator 20 assumes a tubular form whose outer diameter reduces towards the side where the center electrode 10 projects. The first trunk portion 24 of the ceramic insulator 20 assumes a tubular form whose outer diameter is larger than that of the insulator nose 22. The flange 25 of the ceramic insulator 20 assumes a tubular form whose outer diameter is larger than that of the first trunk portion 24. The second trunk portion 26 of the ceramic insulator 20 assumes a tubular form whose outer diameter is smaller than that of the flange 25 and provides a sufficient distance between the metal shell 30 and the terminal fitting 19.
Although the metal shell 30 of the spark plug 100 is made of nickel-plated low-carbon steel in this embodiment, it may be zinc-plated low-carbon steel or a non-plated-nickel alloy in other embodiments. In this embodiment, although the metal shell 30 was fixed by caulking to the ceramic insulator 20 through cold caulking, it may be fixed through thermal caulking in other embodiments.
The metal shell 30 has an end face 31, a threaded portion 32, a trunk portion 34, a groove 35, a tool engagement portion 36 and a caulking portion 38 in this order along the axis O-O from the side where the center electrode 10 projects. The end face 31 of the metal shell 30 is a hollow cylindrical face formed at the front end of the threaded portion 32. The ground electrode 40 is joined to the end face 31, and the center electrode 10 surrounded by the insulator nose 22 of the ceramic insulator 20 projects from the center of the end face 31. The cylindrical threaded portion 32 of the metal shell 30 has a screw thread on its outer circumference which is threadingly engaged with the mounting threaded hole 210 of the engine head 200. The caulking portion 38 of the metal shell 30 is subjected to plastic working and is located adjacent to the tool engagement portion 36 so as to fit with the second trunk portion 26 of ceramic insulator 20 when the metal shell 30 is caulked to the ceramic insulator 20. A filled-up portion 63, that is filled with talc powder, is formed in a region between the caulking portion 38 of the metal shell 30 and the flange 25 of the ceramic insulator 20. The filled-up portion 63 is sealed by packings 62 and 64.
The groove 35 of the metal shell 30 is provided between the trunk portion 34 and the tool engagement portion 36. The groove 35 bulges out in an outer circumference direction when the metal shell 30 is fixed by caulking to the ceramic insulator 20. In this embodiment, the bulging groove 35 assumes a curving shape in the outer circumference direction due to cold caulking. When the thermal caulking is adopted, this shape is resulted from compression. The trunk portion 34 of the metal shell 30 is provided adjacent to the groove 35 and assumes a flange-like shape projecting in the outer circumference direction with respect to the groove 35 so as to compress the gasket 50 towards the engine head 200. The tool engagement portion 36 of the metal shell 30 is provided adjacent to the groove 35 and assumes a flange-like shape projecting in the outer circumference direction with respect to the groove 35. The tool engagement portion 36 assumes a polygonal shape so as to allow a tool (not shown) to be engaged therewith for mounting the spark plug 100 to the engine head 200. Although the tool engagement portion 36 assumes a hexagonal shape in this embodiment, it may assume a polygonal shape, such as quadrangular and octagonal shapes, in other embodiments.
The relationship between a section modulus “Z1” and a section modulus “Z2” preferably satisfy the following relationship:
Z1<=Z2,
where the section modulus “Z1” relates to the axis O-O in the first groove end 353 of the groove 35, and
where the section modulus “Z2” relates to the axis O-O in the second groove end 357 of the groove 35.
In addition, the section modulus “Z1” is represented by the following expression 1, and the section modulus “Z2” is represented by the following expression 2.
[Z1=(π/32)·[{(d2)4−(d1)4}/(d2)] (1)
Z2=(π/32)·[{(d4)4−(d3)4}/(d4)] (2)
The “d1” in the expression 1 shows an inner diameter of the first groove end 353, and the “d2” shows an outer diameter of the first groove end 353. The “d3” in the expression 2 shows an inner diameter of the second groove end 357, and the “d4” shows an outer diameter of the second groove end 357.
The section modulus Z1 in the first groove end 353 of the groove 35 preferably satisfies a relationship: Z1>=49 mm3. The section modulus Z2 in the second groove end 357 of the groove 35 preferably satisfies a relationship:
if A>B,Z2>=62 mm3; and
if A<=B,Z2>=53 mm3,
where “A” represents a distance along the axis O-O from the first groove end 353 to the outermost portion 355 of the groove 35, and where “B” represents a distance along the axis O-O from the outermost portion 355 of the groove 35 to the second groove end 357. Evaluated value of the section modulus Z1 and that of Z2 will be mentioned later.
Regarding the shape of trunk portion 34, a thickness C from a portion adjacent to the second groove end 357 of the groove 35 to the trunk portion 34 along the axis O-O preferably satisfies a relationship: C>=3.0 mm. An evaluated value of the thickness C of the trunk portion 34 will be mentioned later.
The relationship between a distance “D” and a distance “H” preferably satisfies:
(H/D)<=0.17,
where “D” represents a distance from the first groove end 353 to the second groove end 357 of the groove 35 along the axis O-O, and
where “H” represents a distance from the outermost portion 355 to a straight line connecting the first groove end 353 to the second groove end 357 of the groove 35. An evaluated value of a bulging ratio (H/D) of the groove 35 that bulges out in the outer circumference direction will be mentioned later.
In the impact resistance test of
According to the evaluation result in
Further, according to the evaluation result in
According to the evaluation result in
According to the evaluation result in
According to the evaluation result in
According to the evaluation result of
According to the spark plug 100 described above, when the section modulus Z1, Z2 of the groove 35 satisfy the relationship Z1<=Z2, the impact resistance of the groove 35 may be secured, i.e., achieved, even if the opposite side distance of the tool engagement portion is 12 mm or less. Thus, the spark plug 100 can be miniaturized while maintaining the strength and integrity of the groove 35 of the metal shell 30. Further, when the section modulus Z1 of the groove 35 satisfies the relationship Z1>=49 mm3, the impact resistance of the groove 35 may be fully secured. Furthermore, when the section modulus Z2 of the groove 35 satisfies the relationship: “if A>B, Z2>=62 mm3” or “if A<=B, Z2>=53 mm3”, the impact resistance of the groove 35 is fully securable corresponding to the relationship between the distance A and the distance B. Moreover, when the thickness C of the trunk portion 34 satisfies the relationship C>=3 mm, the impact exerted on the groove 35 can be alleviated. When the bulging ratio (H/D) of the groove 35 satisfies the relationship (H/D)<=0.17, the stress corrosion cracking resistance can be improved.
Further, the spark plug 100 can be miniaturized while maintaining the intensity of the groove 35 of the metal shell 30 even though the metal shell 30 is plated by nickel that tends to cause cracks due to stress corrosion. Furthermore, the spark plug 100 can be miniaturized while maintaining the intensity of the groove 35 of the metal shell 30, even though the cold caulking, which tends to cause an asymmetry of the bulging of the groove 30 across the outermost portion 355, is adopted for fixing the metal shell 30.
The present invention is not limited to the above-described embodiments or modes, but may be embodied in various other forms without departing from the gist of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-041755 | Feb 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/005809 | 9/28/2010 | WO | 00 | 8/21/2012 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2011/104785 | 9/1/2011 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20020024160 | Sugimoto | Feb 2002 | A1 |
| 20060022566 | Ishiguro | Feb 2006 | A1 |
| 20060284535 | Ozeki et al. | Dec 2006 | A1 |
| 20100096968 | Ban et al. | Apr 2010 | A1 |
| 20110043094 | Suzuki | Feb 2011 | A1 |
| 20110304256 | Nakamura et al. | Dec 2011 | A1 |
| Number | Date | Country |
|---|---|---|
| 11-345676 | Dec 1999 | JP |
| 2006-66385 | Mar 2006 | JP |
| Entry |
|---|
| Form PCT/ISA/210—Int'l Search Report (from corresponding Int'l Patent App. No. PCT/JP2010/005809—English version only); 1 page. |
| Number | Date | Country | |
|---|---|---|---|
| 20120306346 A1 | Dec 2012 | US |
