Patent Grant
8674592
This application is a U.S. National Phase Application under 35 U.S.C. §371 of International Patent Application No. PCT/JP2011/004617, filed Aug. 18, 2011, and claims the benefit of Japanese Patent Application No. 2010-243037, filed Oct. 29, 2010, all of which are incorporated by reference herein. The International Application was published in Japanese on May 3, 2012 as International Publication No. WO/2012/056618 under PCT Article 21(2).
The present invention relates to a spark plug, particularly to a technique for fitting a metal shell to a ceramic insulator.
Recently, there has been a demand for reduction in size (diameter) of a spark plug in order to attain a higher degree of engine design flexibility for improvement in engine performance, such as engine output and efficiency. For example, the diameter reduction of the spark plug leads to the formation of a smaller plug hole and permits the arrangement of a larger water jacket and intake/exhaust ports in the engine.
It is, however, undesirable to simply reduce the diameter of the spark plug because a crimp portion formed in an end portion of a metal shell for fitting the insulator to the metal shell is made small. As a result, a problem, such as air leakage and the ceramic insulator falling out from the metal shell, tends to occur (refer to Japanese Patent Application Laid-Open (kokai) No. 2007-258142).
The present invention has been conceived to solve the above-mentioned conventional problem, and an object of the invention is to provide a technique for firmly holding a ceramic insulator by a crimp portion of a metal shell even though a diameter of a spark plug is reduced in size.
In order to solve, at least partially, the above problem, the present invention can be embodied in the following modes or application examples.
[Aspect 1]
A spark plug comprising:
a generally cylindrical ceramic insulator including an axial bore extending along an axial line, a front end stepped portion whose diameter tapering from a rear end side to a front end side and a tapered rear end stepped portion positioned rearward of the front end stepped portion and whose diameter tapering from the front end side to the rear end side, both the front end stepped portion and the rear end stepped portion formed on an outer circumferential surface of the ceramic insulator;
a generally cylindrical metal shell including an engaging stepped portion that is formed on an inner circumferential surface thereof and engaged with the front end stepped portion of the ceramic insulator from the rear end side and a crimp portion that is formed in a rear end portion of the metal shell and crimps the rear end stepped portion of the ceramic insulator from the rear end side, the metal shell fitted to the outer circumferential surface of the ceramic insulator, wherein
an area S defined by an outer edge of the rear end stepped portion and an inner edge of the crimp portion falls within a range of 5 mm2 to 25 mm2 when the spark plug is projected on a plane perpendicular to the axial line,
an angle θ1 formed by a tapered surface of the rear end stepped portion and a plane perpendicular to the axial line falls within a range of 20 degrees to 60 degrees, and
a distance L along the axial line from a front end of a proximal portion of the crimp portion to a frontmost position of a contact portion between an inner surface of the crimp portion and the rear end stepped portion falls within a range of 0.4 mm to 1.8 mm.
[Aspect 2]
The spark plug according to Aspect 1, wherein the angle θ1 falls within a range of 20 degrees to 50 degrees, and the distance L falls within a range of 0.8 mm to 1.4 mm.
[Aspect 3]
The spark plug according to Aspect 1 or 2, wherein, when the tapered surface of the rear end stepped portion is extended in an outer circumferential direction, an angle θ2 defined by the tapered surface and an outer surface of the crimp portion falls within a range of 15 degrees to 50 degrees.
[Aspect 4]
The spark plug according to any one of Aspects 1 to 3, wherein a diameter D of an outermost circumferential portion of the rear end stepped portion falls within a range of 7 mm to 10 mm.
[Aspect 5]
The spark plug according to any one of Aspects 1 to 4, wherein the rear end stepped portion and the inner surface of the crimp portion are in contact with each other through a packing.
The present invention can be implemented not only in the above-described spark plug, but also in a method for manufacturing a spark plug and an internal combustion engine provided with a spark plug.
The spark plug of Aspect 1 having the area S falling within the range of 5 mm2 to 25 mm2, the angle θ1 falling within the range of 20 degrees to 60 degrees and the distance L falling within the range of 0.4 mm to 1.8 mm is capable of firmly holding the ceramic insulator by the crimp portion that is formed in the rear end portion of the metal shell, even though the spark plug diameter is reduced in size.
According to the spark plug of Aspect 2, the ceramic insulator is further firmly held by the crimp portion formed in the rear end portion of the metal shell.
According to the spark plug of Aspect 3, it is possible to improve loosening-proof properties of the crimp portion.
According to the spark plug of Aspect 4, the ceramic insulator may be firmly held by the crimp portion of the metal shell, even though the spark plug has a relatively small diameter such that the diameter of the outermost circumferential portion of the rear end stepped portion falls within a range of 7 mm to 10 mm.
According to the spark plug of Aspect 5, since the friction between the rear end stepped portion of the ceramic insulator and the inner surface of the crimp portion develops, the ceramic insulator is further firmly held by the crimp portion of the metal shell.
These and other features and advantages of the present invention will become more readily appreciated when considered in connection with the following detailed description and appended drawings, wherein like designations denote like elements in the various views, and wherein:
[Mode for Carrying Out the Invention]
A. Embodiment
The spark plug 100 includes a ceramic insulator 10 serving as an insulator, a metal shell 50, a center electrode 20, a ground electrode 30, and a metal terminal 40. An insertion hole 501 extending in the axial direction. OD is formed in the metal shell 50. The ceramic insulator 10 is inserted and held in this insertion hole 501. The center electrode 20 is held in an axial bore 12 formed in the ceramic insulator 10 in the axial direction OD. A front end portion of the center electrode 20 is exposed at the front end side of the ceramic insulator 10. The ground electrode 30 is joined to a front end portion (downward end in
As it is widely known, the ceramic insulator 10 is formed from alumina, etc. through firing and has a cylindrical tubular shape, and its axial bore 12 extends coaxially along the axial direction OD. The ceramic insulator 10 has a flange portion 19 having the largest outer diameter and located approximately at the center with respect to the axial direction OD and a rear trunk portion 18 located rearward (upward in
The metal shell 50 is a cylindrical metallic member and is adapted to fix the spark plug 100 to the engine head 200 of the internal combustion engine. The metal shell 50 holds the ceramic insulator 10 therein while surrounding the ceramic insulator 10 in a region extending from a portion of the rear trunk portion 18 to the insulator nose 13. That is, the ceramic insulator 10 is inserted in the insertion hole 501 of the metal shell 50 so that the front end and the rear end of the ceramic insulator 10 are exposed from the front end and the rear end of the metal shell 50, respectively. The metal shell 50 is formed from low-carbon steel, and nickel plating is applied to the entire metal shell 50. The metal shell 50 has a hexagonal tool engagement portion 51 and a mounting threaded portion 52. The tool engagement portion 51 allows a spark wrench (not shown) to be fitted thereto. The mounting threaded portion 52 of the metal shell 50 has a thread formed thereon, and is screwed into amounting threaded hole 201 of the engine head 200 provided at an upper portion of the internal combustion engine. In addition, although the nickel plating is employed to the entire metal shell 50 in this embodiment, zinc plating may be also employed thereto.
The metal shell 50 has a flange-like seal portion 54 formed between the tool engagement portion 51 and the mounting threaded portion 52. An annular gasket 5 formed by folding a sheet is fitted to a screw neck 59 between the mounting threaded portion 52 and the seal portion 54. When the spark plug 100 is mounted to the engine head 200, the gasket 5 is crushed and deformed between a seat surface 55 of the seal portion 54 and a peripheral surface 205 around the opening of the mounting threaded hole 201. The deformation of the gasket 5 provides a seal between the spark plug 100 and the engine head 200, thereby preventing air leakage from the interior of the engine via the mounting threaded hole 201.
The metal shell 50 has a thin-walled crimp portion 53 located rearward of the tool engagement portion 51. The metal shell 50 also has a contractive deformation portion 58, which is thin-walled similar to the crimp portion 53, between the seal portion 54 and the tool engagement portion 51. The crimp portion 53 is bent inward so that the inner surface of the crimp portion 53 is brought into contact with the rear end stepped portion 15 of the ceramic insulator 10 during the crimping operation. The ceramic insulator 10 is pressed forward within the metal shell 50 due to the deformation of the contractive deformation portion 58 to which a compression force is applied. As a result of the pressing, the front end stepped portion 14 of the ceramic insulator 10 is compressed towards the step portion 56 formed on the inner circumference of the metal shell 50 through the sheet packing 8, whereby the ceramic insulator 10 is held by and accommodated in the metal shell 50.
The center electrode 20 is a rod-like electrode having a structure in which a core 25 is embedded within an electrode base member 21. The electrode base member 21 is formed of nickel or an alloy, such as INCONEL (trademark) 600, which contains Ni as a predominant component. The core 25 is formed of copper or an alloy which contains Cu as a predominant component, copper and the alloy being superior in thermal conductivity to the electrode base member 21. Normally, the center electrode 20 is fabricated as follows: the core 25 is placed within the electrode base member 21 which is formed into a closed-bottomed tubular shape, and the resultant assembly is drawn by extrusion from the bottom side. The core 25 is formed such that, while its trunk portion has a substantially constant outer diameter, its front end portion is tapered. A front end portion of the center electrode 20 assumes a tapered shape that tapers towards the front end. An electrode tip 90 is joined to a front end of the tapered shape portion. The electrode tip 90 is formed of noble metal as a predominant component with a high-melting point so as to improve spark erosion resistance. The electrode tip 90 contains, for example, iridium (Ir) and an Ir alloy containing Ir as a predominant component.
The center electrode 20 disposed in the axial bore 12 of the ceramic insulator 10 extends toward the rear end side, and is electrically connected to the metal terminal 40 via a seal member 4 and a ceramic resistor 3. A high-voltage cable (not shown) is connected to the metal terminal 40 via a plug cap (not shown) so as to apply high voltage to the metal terminal 40.
A base material of the ground electrode 30 is formed of a metal having high corrosion resistance; for example, a Ni alloy. In this embodiment, a Ni alloy called INCONEL (trademark) 600 (INC600) is employed. A proximal end portion 32 of the ground electrode 30 is joined to a front end surface of the metal shell 50 through welding. The ground electrode 30 is bent such that a surface of a distal end portion 31 of the ground electrode 30 faces, on the axial line O, the electrode tip 90 of the center electrode 20 in the axial direction OD. A spark gap is formed between the surface of the distal end portion 31 of the ground electrode 30 and a front end surface of the electrode tip 90.
In this embodiment, as shown in
Each conditions described in the above embodiment will be summarized.
Hereafter, the basis of the above conditions will be described with reference to the results of various evaluations.
B. Various Evaluations:
(B1) Conditions 1 to 3
Regarding the conditions 1 and 2, in order to evaluate the projection area S shown in
As shown in Table 1, the spark plugs having the projection area S of 3, 5, 10, 15, 20, 25 and 30 mm2 and the shoulder angle θ1 varying between 10 and 80 degrees in steps of 10 degrees were prepared and tested. A spark plug which showed the air leakage through the crimp portion 53 was indicated with “x”, and a spark plug which showed no air leakage was indicated with “◯”.
As shown in Table 1, the spark plugs having the projection area S of 3 mm2 showed the air leakage at every shoulder angle θ1. On the other hand, the spark plugs having the projection area S of 30 mm2 showed no air leakage. That is, when the projection area S is kept at 30 mm2, it is possible to prevent the air leakage regardless of the shoulder angle θ1. Further, although the spark plugs having the projection area S between 5 and 25 mm2 showed no air leakage at the shoulder angle θ1 of between 10 and 60 degrees, the air leakage was observed at the shoulder angle θ1 of between 70 and 80 degrees.
Thus, it was confirmed that the spark plugs having the projection area S ranging from 5 mm2 to 25 mm2 and the shoulder angle θ1 ranging from 10 degrees to 60 degrees were effective against the air leakage.
Next, in order to evaluate whether or not any crack was visually observed in the crimp portion 53, the spark plugs having the projection area S of either 5 mm2 or 25 mm2 as in Table 1 and varying in the shoulder angle θ1 between 0 to 40 degrees in steps of 5 degrees were prepared. The results are shown in Table 2.
As shown in Table 2, both the spark plugs having the projection area S of 5 mm2 and the spark plugs having the projection area S of 25 mm2 showed cracks in each crimp portion 53 at the shoulder angle θ1 of 15 degrees or less. However, no crack was observed in the spark plugs having the shoulder angle θ1 of 20 degrees or more. In view of the crack in the crimp portion 53, the shoulder angle θ1 is preferably 20 degrees or more as in the condition 2. A spark plug which showed the air leakage through the crimp portion 53 was indicated with “x”, and a spark plug which showed no air leakage was indicated with “◯”.
In addition, as the shoulder angle θ1 becomes smaller, a load A cos θ that the crimp portion 53 presses the rear end stepped portion 15 corresponding to a crimping load A during the manufacturing process becomes greater (see
Next, in order to evaluate the distance L of the condition 3, the spark plugs having the projection area S of either 5 mm2 or 25 mm2 as in Table 1 and varying in the distance L (see
As shown in Table 3, both the spark plugs having the projection area S of 5 mm2 and the spark plugs having the projection area S of 25 mm2 showed cracks in the crimp portion 53 when the distance L was 0.3 mm or less. However, no crack was observed in the spark plugs having the distance L of 0.4 mm or more. When the distance L is too short, the crimp portion 53 is drastically bent during the manufacturing process, which tends to cause a crack in the crimp portion 53. In view of the crack in the crimp portion 53, the distance L of the condition 3 is preferably 0.4 mm or more. A spark plug which showed the air leakage through the crimp portion 53 was indicated with “x”, and a spark plug which showed no air leakage was indicated with “◯”.
In the case where the distance L is too long, a moment applied to the crimp portion 53 increases when a force pushing up the ceramic insulator 10 from the spark gap side is applied. As a result, the durability of the crimp portion 53 deteriorates. In order to evaluate the upper limit of the distance L, the spark plugs varying in the distance L between 0.4 mm and 2.4 mm in steps of 0.2 mm and in the shoulder angle θ1 between 20 degrees and degrees in steps of 10 degrees were prepared for the airtightness test. The results are shown in
(B2) Condition 4
In the condition 4, the cover angle θ2 (refer to
(B3) Condition 5
In the condition 5, the diameter D of the ceramic insulator (see
According to the results of the tests, the spark plug 100 of the embodiments can secure the strength, airtightness and durability of the contact area of the rear end stepped portion 15 and the crimp portion 53 by fulfilling the conditions 1-3. Furthermore, as in the condition 5, even though the ceramic insulator diameter D is small, the sufficient strength is securable as long as the conditions 1-3 are fulfilled. Furthermore, when the condition 4 is fulfilled, the spark plug having suitable loosening proof properties is achievable.
As mentioned above, although the embodiment of this invention was described, this invention is not limited to such an embodiment, but can take various compositions in the area which does not deviate from the point.
As shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-243037 | Oct 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/004617 | 8/18/2011 | WO | 00 | 3/6/2013 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2012/056618 | 5/3/2012 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20030168955 | Suzuki | Sep 2003 | A1 |
| 20070046162 | Moribe et al. | Mar 2007 | A1 |
| Number | Date | Country |
|---|---|---|
| 2003-257583 | Sep 2003 | JP |
| 2007-258142 | Oct 2007 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20130162135 A1 | Jun 2013 | US |
