Patent Application
20180212405
The present invention relates to a spark plug.
A spark plug used for ignition in an internal combustion engine such as a gasoline engine or the like includes a metallic shell for attaching the spark plug to an engine head. The metallic shell has a generally tubular shape. In a state in which a ceramic insulator having a center electrode is inserted into the metallic shell, a crimp portion of the metallic shell is crimped, whereby the metallic shell is assembled to the ceramic insulator (for example, refer to Japanese Patent Application Laid-Open (kokai) No. 2002-164147).
In internal combustion engines, pressures in the combustion chambers thereof have been increased due to higher degree of supercharging and higher compression ratio. Therefore, the ceramic insulator of a spark plug is pressed with a larger force in a direction from a forward end side of the spark plug (the side where a spark gap is formed) toward a rear (proximal) end side thereof. As a result, there is a possibility that the ceramic insulator comes off the metallic shell. To solve this problem, it has been desired to enhance the ceramic insulator retaining performance of the metallic shell.
The present invention has been accomplished to address the above-mentioned problem and can be realized as the following modes.
(1) According to one aspect of the present invention, there is provided a spark plug is provided comprised of a ceramic insulator having a generally tubular shape and a through hole extending in a direction of an axial line, the ceramic insulator including a center electrode on a forward end side of the through hole in the direction of the axial line; and a metallic shell formed in a generally tubular shape and having a crimp portion at a rear end of the metallic shell in the direction of the axial line, the crimp portion being crimped in a state in which the ceramic insulator is inserted into the metallic shell so that the ceramic insulator is held by the metallic shell, wherein the crimp portion satisfies a relation of A≥1.7 mm and a relation of t≥1.20 mm in a cross section of the crimp portion taken along a plane containing the axial line, where A is a distance between a closest point which is a point within the cross section closest to the ceramic insulator and a point of intersection at which a first orthogonal line passing through the closest point and orthogonal to the axial line intersects with an outer circumference of the crimp portion, and t is a thickness of a proximal end of the crimp portion. In the spark plug of this mode, the crimp strength of the crimp portion is increased. Therefore, it is possible to decrease the possibility that when the pressure within a combustion chamber of an internal combustion engine in which a forward end portion of the spark plug is disposed increases, the ceramic insulator comes off the metallic shell due to the pressure within the combustion chamber.
(2) In accordance with a second aspect of the present invention, there is provided a spark plug as described above, wherein the crimp portion may satisfy a relation of 0.7≤C/B≤1.5, where C/B is the ratio of a distance C to a distance B in the cross section, the distance B being a distance between the closest point and a parallel line which passes through a proximal point of the outer circumference of the crimp portion and which is parallel to the axial line, and the distance C being a maximum distance between the outer circumference of the crimp portion and a second orthogonal line which passes through the proximal point of the outer circumference of the crimp portion and which is orthogonal to the axial line. In this case as well, the crimp strength of the crimp portion is increased. Therefore, it is possible to decrease the possibility that the ceramic insulator comes off the metallic shell.
The present invention can be realized in various other forms. For example, the present invention can be realized as a method of manufacturing a spark plug or as a metallic shell or the like.
The spark plug 100 includes a ceramic insulator 10 serving as an insulator, a center electrode 20, the ground electrode (external electrode) 30, the metallic terminal member 40, and the metallic shell 50. The ceramic insulator 10 is a tubular insulator having an axial hole 12 which is centrally located and which accommodates the center electrode 20 and the metallic terminal member 40. The ceramic insulator 10 is formed, for example, by firing a ceramic material such as alumina. The center electrode 20 is a generally rod-shaped electrode, and has a covering member 21 which is formed into the shape of a tube with a bottom, and a core member 25 embedded in the covering member 21. The core member 25 is higher in thermal conductivity than the covering member 21. The center electrode 20 is held by the ceramic insulator 10, and the ceramic insulator 10 is held by the metallic shell 50. The ground electrode 30 is a generally rod-shaped bent electrode, and is attached to the forward end of the metallic shell 50. The metallic terminal member 40 is attached to the rear end of the ceramic insulator 10. A spark gap G is formed between the free end of the ground electrode 30 and the forward end of the center electrode 20.
The metallic shell 50 is mainly composed of a crimp portion 53, a tool engagement portion 51, a compressible and deformable portion 55, a seal portion 54, and a screw portion 52 provided in this order from the rear end side in the axial direction.
The crimp portion 53 is generally annular and has a straight taper (with a taper angle of θ0) such that the thickness of the crimp portion 53 decreases from the root (hereinafter also referred to as “the crimp portion proximal end”) where the crimp portion 53 is connected with the tool engagement portion 51 toward the crimp portion distal end 536 (the rear end in the axial direction). More specifically, the thickness t1 of the crimp portion proximal end 534 (hereinafter also referred to as the crimp portion proximal end thickness t1) is larger than the thickness t2 of the crimp portion distal end 536. In this embodiment, the thickness t1 of the crimp portion proximal end 534 is set to 1.20 mm or greater. As shown in
The tool engagement portion 51 has a generally hexagonal shape in a plan view. A tool (spark plug wrench) is engaged with the tool engagement portion 51 when the spark plug 100 is attached to the engine head.
On the outer surface of the screw portion 52, there is formed a screw thread which comes into screw engagement with the screw hole of the engine head when the spark plug 100 is attached to the engine head. Also, an inwardly projecting step portion 56 is formed on the inner circumference of the screw portion 52. As will be described later, a diameter-reduced portion 15 of the ceramic insulator 10 is supported by the step portion 56 (see
The seal portion 54 is formed between the screw portion 52 and the tool engagement portion 51 such that the seal portion 54 is continuous with the screw portion 52. When the spark plug 100 is attached to the engine head, the seal portion 54 prevents leakage of a gas in the engine through the screw hole formed on the engine head. When the spark plug 100 is attached to the engine head, as shown in
The compressible and deformable portion 55 is provided between the tool engagement portion 51 and the seal portion 54. The compressible and deformable portion 55 has a small thickness such that the compressible and deformable portion 55 deflects and deforms outward (see
When the crimp portion 53 is crimped, the ceramic insulator 10 is inserted into the through hole 59 of the metallic shell 50, and the crimp portion 53 in an uncrimped state (see
(1) Distance A: In the case where a point in the crimp portion 53 closest to the ceramic insulator 10 is defined as a closest point N and a line passing through the closest point N and orthogonal to the axial line OL is defined as a first orthogonal line Lv1, the distance between the closest point N and a point of intersection I between the first orthogonal line Lv1 and the outer circumference 532 of the crimp portion 53 is defined as the distance A.
(2) Distance B: In the case where the proximal end of the outer circumference 532 of the crimp portion 53 is defined as an outer circumference proximal point E1, the distance between the closest point N and a parallel line Lh which passes through the outer circumference proximal point E1 and is parallel to the axial line OL is defined as the distance B.
(3) Distance C: The maximum distance between the outer circumference 532 of the crimp portion 53 and a second orthogonal line Lv2 which passes through the outer circumference proximal point E1 and is orthogonal to the axial line OL is defined as the distance C.
(4) Curved portion angle θ1: The angle between the first orthogonal line Lv1 and a tangent line Lt at a curved portion proximal point E2 which is the proximal end of the curved portion of the outer circumference 532 of the crimp portion 53 is defined as the curved portion angle θ1. In
(5) Crimp portion proximal end thickness t1: The thickness of the crimp portion proximal end 534 is defined as the crimp portion proximal end thickness t1. The crimp portion proximal end thickness t1 in the present embodiment corresponds to the thickness t at the proximal end of the crimp portion in claims.
In the present embodiment, in order to increase the crimp strength of the crimp portion 53, the crimp portion proximal end thickness t1 is set to 1.20 mm or greater (t1≥1.20 mm), and the distance A is set to 1.7 mm or greater (A≥1.7 mm). Further, it is preferred that a relation of 0.7≤C/B≤1.5 be satisfied. Also, it is preferred that a relation of 50°≤the curved portion angle θ1≤85° be satisfied. The angle of the crimp portion proximal end 534 (the angle between the tangent line at the outer circumference proximal point E1 and the second orthogonal line Lv2) was set to fall within a range of 70° to 90°. This is because when the angle of the crimp portion proximal end 534 is smaller than 70°, the tool engagement portion 51 may deflect and deform outward. Notably, it is preferred to render the distance A equal to or smaller than the distance B (the distance A≤the distance B) for the following reason. The distance A becomes greater than the distance B (the distance A>the distance B) when the angle of the crimp portion proximal end 534 is greater than 90°, and in such a case, the tool engagement portion 51 may deflect and deform outward as described above.
Samples having the structure of the above-described embodiment in which the metallic shell 50 is assembled to the ceramic insulator 10 (the crimp portion 53 was crimped) were prepared, and two types of evaluation tests were performed to evaluate the crimp strength of the crimp portion 53. The first evaluation test is a test for evaluating the influence of the above-mentioned distance A on the crimp strength, and a second evaluation test is a test for evaluating the influence of C/B on the crimp strength. In these evaluation tests, a compressive load was applied to the ceramic insulator 10 of each sample from the forward end side thereof by using a compression testing machine (Autograph AG-X series, product of Shimadzu Corporation), and the maximum load (N) indicated by the Autograph machine was monitored. The maximum value of the compressive load (N) applied to the ceramic insulator 10 was used as the crimp strength (N).
The crimp portions 53 of the metallic shells 50 of the plurality of samples used for the first evaluation test have the same inner diameter (17.87 mm) and different outer diameters D to thereby have different thicknesses t1. The crimp portions 53 have the same height h (
In the range of the distance A shown in Table 1, the crimp strength which changed with the distance A had no local maximum and increased as the distance A increased. When the distance A was 1.7 mm or greater, the crimp strength was 17,000 N or greater. These results show that when the distance A is 1.7 mm or greater, a crimp strength of 17,000 N or greater is obtained.
In the second evaluation test, the crimp strength was evaluated for a plurality of samples in which the distance A was fixed to 1.7 mm, 2.3 mm, or 2.9 mm, and the ratio of the distance C to the distance B, i.e., C/B shown in
As shown in Table 2, in the case where the value of C/B is fixed, the crimp strength increases with the distance A. In the case where the distance A is fixed, the crimp strength becomes maximum when the value of C/B is 0.8 and the crimp strength decreases as the value of C/B increases from 0.8. This is because the degree of bending of the crimp portion 53 near the crimp portion distal end 536 decreases as the value of C/B increases as described above. In addition, when the value of C/B is excessively small, crimping fails. In the case where the distance A was 1.7 mm, the crimp strength was 17,000 N or greater when the relation of 0.7≤C/B≤1.5 was satisfied. In the case where the distance A was 2.3 mm or 2.9 mm, the crimp strength was 17,000 N or greater when the relation of 0.6≤C/B was satisfied. These results demonstrate that the crimp strength of 17,000 N or greater is also obtained when the distance A is 1.7 mm or greater and the relation of 0.7≤C/B≤1.5 is satisfied. Notably, in the second evaluation test, the crimp strength became 17,000 N or greater when the curved portion angle θ1 fell within the range of 50° to 85°.
The above-described test results shows that when the distance A of the crimp portion 53 of the metallic shell 50 is 1.7 mm or greater, a crimp strength of 17,000 N or greater is highly likely to be obtained. Thus, the ceramic insulator retaining performance of the metallic shell 50 is enhanced, and the ceramic insulator 10 is prevented from coming off the metallic shell 50. In addition, when the relation of 0.7≤C/B≤1.5 is satisfied, the possibility that a crimp strength of 17,000 N or greater is obtained increases.
The present invention is not limited to the above-described embodiment, but may be embodied in various other forms without departing from the spirit of the invention. For example, in order to solve, partially or entirely, the above-mentioned problem or yield, partially or entirely, the above-mentioned effects, technical features of the embodiments corresponding to technical features of the modes described in the section “SUMMARY OF THE INVENTION” can be replaced or combined as appropriate. Also, the technical feature(s) may be eliminated as appropriate unless the present specification mentions that the technical feature(s) is essential. For example, the following modifications are possible.
The diameter of the ceramic insulator 10 of the spark plug 100, and the thickness and height of the crimp portion 53 of the metallic shell 50 of the spark plug 100 are not limited to the values employed in the above-described embodiment. The minimum requirement is that the distance A (
The above-described embodiment shows the example in which the annular ring members 6 and 7 are interposed between the outer circumferential surface of the ceramic insulator 10 and a portion of the inner circumferential surface of the metallic shell 50, which portion extends from the tool engagement portion 51 to the crimp portion 53, and powder of talc 9 is charged between the two ring members 6 and 7. However, the ring members 6 and 7 and the talc 9 may be omitted. In other words, the spark plug 100 may be configured such that the crimp portion 53 of the metallic shell 50 directly presses the ceramic insulator 10.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-085181 | Apr 2015 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/001788 | 3/28/2016 | WO | 00 |
