Spark plug

Abstract

To provide a spark plug capable of preventing a gasket from being caught on a threaded part.SOLUTION: A spark plug includes: a main metal tool disposed on an outer circumference of an insulator and extending from a tip end to a rear end along a center line; and a gasket disposed on the outer circumference of the main metal tool. The main metal tool includes a screw part formed of a male screw centered on the center line, a head part including a seat surface provided on the rear end side of the screw part, and a neck part sandwiched between the head part and the screw part, and the neck part includes a flange part protruding outward in a radial direction. The gasket is disposed between the head part and the flange part, and an outer diameter of the flange part is smaller than an outer diameter of the threaded part and larger than a minimum value of an inner diameter of the gasket.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD

[0001] The present invention relates to a spark plug including a gasket disposed on an outer periphery of a metallic shell. BACKGROUND ART

[0002] A gasket of a spark plug is sandwiched between a seating surface of a metallic shell and an engine when the spark plug is attached to the engine, to prevent gas leakage. The prior art disclosed in Patent Document 1 includes a metallic shell including a threaded portion coupled to a female thread of a plug hole of the engine, a head portion including a seating surface, and a neck portion sandwiched between the head portion and the threaded portion, and a gasket disposed on an outer periphery of the neck portion, wherein an outer diameter of the neck portion is larger than an outer diameter of the threaded portion. PRIOR ART DOCUMENTS PATENT DOCUMENTS

[0003] PATENT DOCUMENT 1 Japanese Unexamined Patent Application Publication No. 2008-4267 SUMMARY OF INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0004] In the prior art, there is a problem that the gasket catches on the threaded portion, and if the catch is not released when the threaded portion is tightened to the engine, gas leaks from a gap formed between the seating surface of the spark plug and the engine.

[0005] The present invention has been made to solve this problem, and an object thereof is to provide a spark plug that can prevent the gasket from catching on the threaded portion. MEANS FOR SOLVING THE PROBLEMS

[0006] A first aspect of the present invention for achieving this objective comprises a main fitting disposed on the outer circumference of an insulator and extending along a center line from the front to the rear end, and a gasket disposed on the outer circumference of the main fitting, wherein the main fitting includes a threaded portion consisting of an external thread centered on the center line, a head including a seating surface provided on the rear end side of the threaded portion, and a neck portion sandwiched between the head and the threaded portion, the neck portion including a flange portion that protrudes radially outward, the gasket disposed between the head and the flange portion, the outer diameter of the flange portion being smaller than the outer diameter of the threaded portion and larger than the minimum inner diameter of the gasket.

[0007] In the second embodiment, the gasket comprises a ring portion continuous around a center line and a plurality of protrusions projecting radially inward from the ring portion, arranged in descending order of size as follows: the inner diameter of the ring portion, the outer diameter of the threaded portion, the outer diameter of the flange portion, and the inner diameter of the protrusions.

[0008] In the third embodiment, in the second embodiment, when a first point is set at the rearmost end of the portion with the largest outer diameter of the flange in the cross section of the main fitting including the center line, and a second point is set at the portion of the neck that is further rear than the flange and closest to the first point on the opposite side of the center line from the first point, the distance between the second point and the first point is greater than the inner diameter of the convex portion.

[0009] The fourth aspect is that, in any of the first to third aspects, the length of the threaded portion is at least half the distance between the tip of the main fitting and the seating surface. [Effects of the Invention]

[0010] According to the present invention, the neck portion sandwiched between the head and threaded portion of the main fitting includes a flange portion that protrudes radially outward, and the gasket is positioned between the head and the flange portion. Since the outer diameter of the flange portion is smaller than the outer diameter of the threaded portion and larger than the minimum inner diameter of the gasket, the movement of the gasket is restricted by the flange portion. Therefore, the gasket can be prevented from getting caught on the threaded portion. [Brief explanation of the drawing]

[0011] [Figure 1]This is a cross-sectional view of one side of the spark plug in the first embodiment. [Figure 2] This is a bottom view of the gasket. [Figure 3] This is a side view of the spark plug, enlarged from the section indicated by III in Figure 1. [Figure 4] This is a cross-sectional view of the main metal fitting. [Figure 5] This is a cross-sectional view of one side of a spark plug installed in an engine. [Figure 6] This is a bottom view of the spark plug gasket in the second embodiment. [Modes for carrying out the invention]

[0012] Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Figure 1 is a one-sided cross-sectional view combining an outline view and a full cross-sectional view with respect to the center line C of the spark plug 10 in the first embodiment. In Figure 1, the lower side of the paper is the tip side of the spark plug 10, and the upper side of the paper is the rear end side of the spark plug 10 (the same applies to Figures 3, 4, and 5).

[0013] As shown in Figure 1, the spark plug 10 comprises an insulator 11, a main body fitting 15 arranged on the outer circumference of the insulator 11, and a gasket 24 arranged on the outer circumference of the main body fitting 15. The insulator 11 is a cylindrical member made of ceramic such as alumina, which has excellent mechanical properties and insulation properties at high temperatures. The insulator 11 is provided with an axial hole 12 extending along the center line C.

[0014] The central electrode 13 is a rod-shaped conductor positioned within the axial hole 12 of the insulator 11, extending along the center line C. The tip of the central electrode 13 protrudes from the tip of the insulator 11 along the center line C. The central electrode 13 is electrically connected to the terminal fitting 14 within the axial hole 12.

[0015] The terminal fitting 14 is a rod-shaped member to which an ignition device (not shown) is connected, and is made of a conductive metal material (such as low-carbon steel). The terminal fitting 14 is fixed to the rear end side of the insulator 11, with its distal end side inserted into the axial hole 12 and its rear end side protruding from the insulator 11. A main metal fitting 15 is fixed to the outer periphery of the insulator 11.

[0016] The main metal fitting 15 is a cylindrical member made of a metal material (such as low-carbon steel). The main metal fitting 15 includes a threaded portion 16 formed of a male thread centered on the center line C, a head portion 18 including a seating surface 17 provided on the rear end side of the threaded portion 16, and a neck portion 19 sandwiched between the head portion 18 and the threaded portion 16. The neck portion 19 includes a flange portion 20 protruding radially outward. The threaded portion 16, the head portion 18, and the flange portion 20 are formed by forging or cutting a metal material.

[0017] In the main metal fitting 15, a tool engagement portion 21 is provided on the rear end side of the head portion 18. When attaching the spark plug 10 to the engine 32 (see FIG. 5), a tool such as a wrench is engaged with the tool engagement portion 21 to tighten the threaded portion 16 into the female thread of the plug hole 33. In the spark plug 10 of the present embodiment, the length L1 of the threaded portion 16 is 1 / 2 or more of the distance L2 between the distal end 22 of the main metal fitting 15 and the seating surface 17. Thereby, compared with the case where the length L1 is less than 1 / 2 of the distance L2, the thermal conductivity from the main metal fitting 15 to the engine 32 when the spark plug 10 is attached to the engine 32 by tightening the threaded portion 16 into the female thread of the plug hole 33 can be improved.

[0018] The ground electrode 23 is connected to the distal end 22 of the main metal fitting 15. The ground electrode 23 is a conductor extending from the main metal fitting 15 toward the center line C. A spark gap is formed between the ground electrode 23 and the center electrode 13. An example of the ground electrode 23 is one in which a core material containing copper as a main component is embedded in a metal containing Ni as a main component. It is possible to omit the core material. The gasket 24 is an annular member made of metal, and is disposed between the head portion 18 and the flange portion 20.

[0019] Figure 2 is a bottom view of the gasket 24 as viewed from the front end side of the spark plug 10. The gasket 24 includes an annular portion 25 that is continuous around the center line C, and a plurality of protrusions 26 protruding radially inward of the annular portion 25 from the annular portion 25. In the present embodiment, there are eight protrusions 26, but this is an example and the number is not limited thereto. The inner diameter D4 of the protrusion 26 is the diameter of a virtual cylinder that is in contact with the radial tip of the protrusion 26. The inner diameter D1 of the annular portion 25 is the inner diameter of the annular portion 25 in the portion excluding the protrusions 26. The inner diameter D4 of the protrusion 26 is smaller than the inner diameter D1 of the annular portion 25. The inner diameter D4 of the protrusion 26 is the minimum value of the inner diameter of the gasket 24.

[0020] Figure 3 is an enlarged side view of the spark plug 10 showing the part indicated by III in Figure 1. Figure 3 shows the gasket 24 in a cross-sectional view including the center line C. The annular portion 25 of the gasket 24 is thicker than the protrusion 26, and the cross-sectional area of the annular portion 25 is larger than the cross-sectional area of the protrusion 26.

[0021] The flange portion 20 is provided at a position spaced apart from the seating surface 17 of the head portion 18 toward the front end side. The gasket 24 is arranged between the flange portion 20 and the seating surface 17. The outer diameter D3 of the flange portion 20 is smaller than the outer diameter D2 of the threaded portion 16. The outer diameter D2 of the threaded portion 16 is the diameter of a virtual cylinder that is in contact with the crests of the external thread. The outer diameter D3 of the flange portion 20 is the diameter of a virtual cylinder that is in contact with the top of the flange portion 20. When arranged in descending order of dimension, the order is the inner diameter D1 of the annular portion 25, the outer diameter D2 of the threaded portion 16, the outer diameter D3 of the flange portion 20, and the inner diameter D4 of the protrusion 26.

[0022] The gasket 24 is provided between the flange portion 20 and the seating surface 17 of the metallic shell 15 in the manufacturing process of the spark plug 10. First, the metallic shell 15 provided with the threaded portion 16 and the flange portion 20 is inserted from the front end 22 into the annular portion 25 where the protrusions 26 are not provided. Since the inner diameter D1 of the annular portion 25 is larger than the outer diameter D2 of the threaded portion 16 and the outer diameter D3 of the flange portion 20, the annular portion 25 can be moved between the seating surface 17 and the flange portion 20.

[0023] Next, the main fitting 15 is inserted from the tip 22 into a cylindrical tool (not shown) with multiple claws protruding in the axial direction, and the claws of the tool are brought into contact with the inner edge of the ring portion 25. The ring portion 25 is sandwiched between the claws and the head 18, and force is applied in the axial direction, causing the ring portion 25 to plastically deform due to the pressure of the claws, forming a protrusion 26 on the ring portion 25. Since the inner diameter D4 of the protrusion 26 is smaller than the outer diameter D3 of the flange portion 20, the protrusion 26 contacts the flange portion 20, restricting the movement of the gasket 24. Because the gasket 24 is contained between the head 18 and the flange portion 20 by the protrusion 26, the gasket 24 can be prevented from getting caught on the threaded portion 16.

[0024] Figure 4 is a cross-sectional view of the main fitting 15 including the center line C. The neck portion 19 includes a flange portion 20, a tip portion 28 between the flange portion 20 and the threaded portion 16, and a rear end portion 29 between the flange portion 20 and the head portion 18. The outer diameter D3 of the flange portion 20 is larger than the outer diameter of the tip portion 28 and larger than the outer diameter of the rear end portion 29. The outer diameter of the rear end portion 29 is smaller than the outer diameter of the tip portion 28 and larger than the diameter of the groove of the threaded portion 16. The outer diameter of the rear end portion 29 is smaller than the inner diameter D4 of the convex portion 26 of the gasket 24. The tip portion 28 may be omitted so that the flange portion 20 contacts the rear end of the threaded portion 16.

[0025] The top portion 27 is the part of the flange portion 20 with the largest outer diameter. The outer diameter of the top portion 27 is equal to the outer diameter D3 of the flange portion 20. The outer diameter of the flange portion 20 gradually decreases as it approaches the tip portion 28 from the top portion 27, and gradually decreases as it approaches the rear end portion 29 from the top portion 27.

[0026] A first point 30 is set at the rearmost end of the outer circumference of the top portion 27, and a second point 31 is set on the opposite side of the center line C from the first point 30, and at the position closest to the first point 30. The second point 31 is a point on the outer circumference of the rear end portion 29 of the neck portion 19, which is at the rear end of the flange portion 20. The second point 31, where the distance between the first point 30 and the second point 31 is shortest, is located at the boundary between the rear end portion 29 and the flange portion 20. The distance D5 between the first point 30 and the second point 31 is greater than the inner diameter D4 of the protrusion 26 of the gasket 24. As a result, when the gasket 24 is tilted relative to the neck portion 19 as shown in Figure 3, the tip of the protrusion 26 of the gasket 24 does not come into contact with the top portion 27, and the gasket 24 does not get caught on the flange portion 20.

[0027] Figure 5 is a cross-sectional view of one side of the spark plug 10, including the center line C, attached to the engine 32. Figure 5 shows the area around the gasket 24 of the spark plug 10, with other parts omitted. Figure 5 shows a cross-sectional view of the engine 32.

[0028] The spark plug 10 is attached to the engine 32 by tightening its threaded portion 16 into the female thread of the plug hole 33. The ring portion 25 of the gasket 24, sandwiched between the head 18 and the engine 32, is in close contact with the head 18 and the engine 32 to prevent gas leakage from between the plug hole 33 and the spark plug 10.

[0029] If the shortest distance D5 between the first point 30 (see Figure 4) and the second point 31 is smaller than the inner diameter D4 of the protrusion 26 of the gasket 24, when the gasket 24 is tilted relative to the neck 19 of the spark plug 10 before it is installed in the engine 32, the tip of the protrusion 26 of the gasket 24 may come into contact with or go over the top 27, causing the gasket 24 to catch on the flange 20. If the tightening torque of the screws when installing the spark plug 10 in the engine 32 is small, the gasket 24 may remain caught on the flange 20 while the spark plug 10 is installed in the engine 32. In this case, the ring portion 25 of the gasket 24 cannot make tight contact with the head 18 and the engine 32, and gas may leak from between the plug hole 33 and the spark plug 10.

[0030] In contrast, with respect to the spark plug 10, the shortest distance D5 between the first point 30 and the second point 31 is greater than the inner diameter D4 of the protrusion 26 of the gasket 24, thus preventing the gasket 24 from getting caught on the flange 20. Therefore, even if the tightening torque of the screws when attaching the spark plug 10 to the engine 32 is small, the ring portion 25 of the gasket 24 sandwiched between the head 18 and the engine 32 can be made to be in close contact with the head 18 and the engine 32.

[0031] Since the outer diameter D3 of the flange portion 20 is smaller than the outer diameter D2 of the threaded portion 16, the inner diameter D1 of the ring portion 25 of the gasket 24 can be made smaller compared to the case where the outer diameter D3 of the flange portion 20 is larger than the outer diameter D2 of the threaded portion 16. This is because the inner diameter D1 of the ring portion 25 must be larger than the outer diameter D3 of the flange portion 20, since the ring portion 25 must pass over the flange portion 20.

[0032] If the outer diameter of the ring portion 25 is constant, the smaller the inner diameter D1 of the ring portion 25, the longer the radial length of the ring portion 25 can be. This increases the contact area between the head 18 and the ring portion 25, and the contact area between the engine 32 and the ring portion 25, when the ring portion 25 is in close contact with the head 18 and the engine 32. Since a larger contact area is advantageous for the airtightness of the gasket 24, making the outer diameter D3 of the flange portion 20 smaller than the outer diameter D2 of the threaded portion 16 is expected to improve the airtightness of the gasket 24.

[0033] A second embodiment will be described with reference to Figure 6. In the first embodiment, a spark plug 10 was described that includes a gasket 24 with a protrusion 26 projecting radially inward. In contrast, in the second embodiment, a spark plug 10 is described that includes a gasket 34 without a protrusion. Parts identical to those described in the first embodiment are denoted by the same reference numerals and their descriptions are omitted below.

[0034] Figure 6 is a bottom view of the gasket 34 as seen from the tip side of the spark plug 10. The gasket 34 replaces the gasket 24 of the spark plug 10 and is placed between the head 18 and the flange 20 of the main fitting 15. The gasket 34 is an annular metal member that is continuous around the center line C.

[0035] The gasket 34 is provided between the flange portion 20 and the seating surface 17 of the main fitting 15 during the manufacturing process of the spark plug 10. First, the main fitting 15, which has a threaded portion 16 and a flange portion 20, is inserted from its tip 22 into a metal ring (not shown) that will become the gasket 34. Since the inner diameter of the ring is larger than the outer diameter D2 of the threaded portion 16 and the outer diameter D3 of the flange portion 20, the ring can be moved between the seating surface 17 and the flange portion 20.

[0036] Next, the main body fitting 15 is inserted from the tip 22 into a cylindrical tool (not shown) with cylindrical teeth protruding in the axial direction, and the teeth of the tool are brought into contact with the inner edge of the ring. The ring is sandwiched between the teeth and the head 18, and force is applied in the axial direction, causing the ring to plastically deform with the pressure of the teeth until the inner diameter D6 becomes smaller than the outer diameter D3 of the flange portion 20, thereby forming the gasket 34. Since the inner diameter D6 of the gasket 34 is smaller than the outer diameter D3 of the flange portion 20, the movement of the gasket 34 is restricted by the flange portion 20.

[0037] When arranged in descending order of dimensions, the order is: outer diameter D2 of the threaded portion 16, outer diameter D3 of the flange portion 20, and inner diameter D6 of the gasket 34. If the shape of the inner edge of the gasket 34 is elliptical or oblong, the inner diameter D6 of the gasket 34 is the minor axis (minimum value of the inner diameter). Since the gasket 34 fits between the head 18 and the flange portion 20, it is possible to prevent the gasket 34 from getting caught on the threaded portion 16.

[0038] Although the present invention has been described above based on embodiments, it can be easily inferred that the present invention is not limited in any way to the above embodiments, and that various improvements and modifications are possible without departing from the spirit of the present invention.

[0039] In the embodiment, the case where the cross-section of the flange portion 20 is trapezoidal in the cross-sectional view of the main fitting 15 including the center line C has been described, but it is not limited to this. The cross-section of the flange portion 20 can be set as appropriate, such as triangular or semicircular.

[0040] Although not described in the embodiment, it is of course possible to place a cap covering the center electrode 13 and the ground electrode 23 on the main fitting 15 and to provide a hole through the cap. In a spark plug with a cap placed on the main fitting 15, fuel flows from the engine's combustion chamber through the hole into the inside of the cap when the engine's valves are operated. A flame kernel is generated by the discharge between the center electrode 13 and the ground electrode 23, and as the flame kernel grows, it ignites the fuel inside the cap and the fuel burns. The expansion pressure generated by the combustion of the fuel creates a gas flow containing the flame. The spark plug injects the gas containing the flame from the hole into the combustion chamber, and the jet of flame burns the fuel inside the combustion chamber. [Explanation of symbols]

[0041] 10 Spark plugs 11 Insulator 15 Main fittings 16 Threaded part 17 Seat 18 head 19 Neck 20 Guard section 22 Tip 24,34 Gasket 25 Ring part 26 Convex part 27. Top (the part with the largest outer diameter of the flange) 29. Rear end (the part of the neck that is further back from the flange) 30 First point 31. Second point C center line D1 Inner diameter of the ring portion (inner diameter of the gasket) D2 Outer diameter of the threaded portion D3 Outer diameter of the flange D4 Inner diameter of the protrusion (minimum inner diameter of the gasket) D5 Distance between the first point and the second point D6 gasket inner diameter L1 Length of the threaded portion L2 Distance between the tip of the main fitting and the seat surface

Claims

1. A main fitting is positioned on the outer circumference of the insulator and extends along the center line from the tip to the rear end, The main fitting comprises a gasket positioned on the outer circumference of the main fitting, The main fitting comprises a threaded portion consisting of a male thread centered on the center line, The head includes a seating surface provided on the rear end side of the threaded portion, A spark plug comprising a neck portion sandwiched between the head and the threaded portion, The neck portion includes a flange portion that protrudes radially outward, The gasket is positioned between the head and the flange. A spark plug in which the outer diameter of the flange portion is smaller than the outer diameter of the threaded portion and larger than the minimum inner diameter of the gasket.

2. The gasket has an annular portion that is continuous around the center line, It comprises a plurality of protrusions that project radially inward from the ring portion, The spark plug according to claim 1, wherein the dimensions, when arranged in descending order of size, are the inner diameter of the ring portion, the outer diameter of the threaded portion, the outer diameter of the flange portion, and the inner diameter of the protrusion portion.

3. In the cross-section of the main fitting including the center line, The first point is set at the rearmost end of the portion of the flange with the largest outer diameter, When the second point is located in the part of the neck portion that is at the rear end of the flange portion, and is set on the opposite side of the center line from the first point, and is the closest to the first point, The spark plug according to claim 2, wherein the distance between the second point and the first point is greater than the inner diameter of the protrusion.

4. The spark plug according to any one of claims 1 to 3, wherein the length of the threaded portion is 1 / 2 or more of the distance between the tip of the main fitting and the seating surface.

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