Spark plug

Abstract

The purpose of the present invention is to provide a spark plug (10) configured so that a gasket (24) will not catch on a threaded part (16). This spark plug comprises: a main metal fitting (15) disposed on the outer periphery of an insulator (11) and extending along a center line (C) from the distal end to the proximal end; and a gasket positioned on the outer periphery of the main metal fitting. The main metal fitting includes: a threaded part (16) composed of a male thread centered on a center line; a head part (18) including a seat surface (17) provided toward the proximal end of the threaded part; and a neck part (19) disposed between the head part and the screw part. The neck part includes a flange part (20) protruding radially outward. The gasket is positioned between the head part and the flange part. An outer diameter (D3) of the flange part is lesser than an outer diameter (D2) of the threaded part, but larger than the minimum value of an inner diameter (D6) of the gasket.

Description

Spark plug

[0001] The present invention relates to a spark plug including a gasket disposed on the outer periphery of a metal shell.

[0002] The spark plug gasket is sandwiched between the seating surface of the metal shell and the engine when the spark plug is installed in the engine, preventing gas leakage. The prior art disclosed in Patent Document 1 includes a metal shell including a threaded portion that is coupled to the female thread of the engine plug hole, a head including the seating surface, and a neck portion sandwiched between the head and the threaded portion, and a gasket arranged on the outer periphery of the neck, the outer diameter of which is larger than the outer diameter of the threaded portion.

[0003] Japanese Patent Application Laid-Open No. 2008-4267

[0004] In the prior art, if the gasket gets caught on the threaded portion and the catch does not come off when the threaded portion is tightened to the engine, there is a problem that gas leaks from the gap that forms between the spark plug seat and the engine.

[0005] The present invention has been made to solve this problem, and has as its object to provide a spark plug that can prevent the gasket from getting caught on the threaded portion.

[0006] A first aspect for achieving this object comprises a metal shell that is disposed on the outer periphery of an insulator and extends along a center line from the front end to the rear end, and a gasket that is disposed on the outer periphery of the metal shell, wherein the metal shell includes a threaded portion consisting of a male thread centered on the center line, a head including a seat 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 that protrudes radially outward, and the gasket is disposed between the head and the flange, and the outer diameter of the flange is smaller than the outer diameter of the threaded portion and larger than the minimum value of the inner diameter of the gasket.

[0007] In the second aspect, the gasket of the first aspect comprises a ring portion that is continuous around the center line and a plurality of protrusions that protrude radially inward from the ring portion, and the dimensions, arranged in descending order, 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 protrusions.

[0008] In a third aspect of the second aspect, when a first point is set at the rearmost position of the portion of the metal shell where the outer diameter of the flange is largest in a cross section including the center line, and a second point is set at a portion of the neck that is rearward of the flange and closest to the first point across the center line, the distance between the second point and the first point is greater than the inner diameter of the convex portion.

[0009] In a fourth aspect, in any one of the first to third aspects, the length of the threaded portion is equal to or greater than half the distance between the tip of the metallic shell and the seat surface.

[0010] According to the present invention, the neck portion sandwiched between the head and threaded portion of the metal shell includes a flange portion that projects radially outward, and the gasket is disposed between the head and flange portion. The outer diameter of the flange portion is smaller than the outer diameter of the threaded portion and larger than the minimum value of the inner diameter of the gasket, so that the movement of the gasket is restricted by the flange portion. This prevents the gasket from getting caught on the threaded portion.

[0011] Fig. 1 is a half-sectional view of the spark plug according to a first embodiment; Fig. 2 is a bottom view of a gasket; Fig. 3 is a side view of the spark plug in which a portion indicated by III in Fig. 1 is enlarged; Fig. 4 is a cross-sectional view of a metallic shell; Fig. 5 is a half-sectional view of the spark plug attached to an engine; Fig. 6 is a bottom view of a gasket of a spark plug according to a second embodiment;

[0012] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a half-sectional view of a spark plug 10 according to a first embodiment, combining an outline view and a full cross-sectional view along a center line C. In Fig. 1, the lower side of the page is the leading end side of the spark plug 10, and the upper side is the trailing end side of the spark plug 10 (the same applies to Figs. 3, 4, and 5).

[0013] 1, a spark plug 10 includes an insulator 11, a metal shell 15 disposed on the outer periphery of the insulator 11, and a gasket 24 disposed on the outer periphery of the metal shell 15. The insulator 11 is a cylindrical member made of a ceramic such as alumina, which has excellent mechanical properties and insulating properties at high temperatures. The insulator 11 is provided with an axial hole 12 extending along a center line C.

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

[0015] The metal terminal 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 metal terminal 14 is fixed to the rear end of the insulator 11 with its front end inserted into the axial hole 12 and its rear end protruding from the insulator 11. A metal shell 15 is fixed to the outer periphery of the insulator 11.

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

[0017] The metal shell 15 is provided with a tool engaging portion 21 on the rear end side of the head portion 18. When the spark plug 10 is attached to an engine 32 (see FIG. 5 ), a tool such as a wrench is engaged with the tool engaging portion 21 to tighten the threaded portion 16 onto the internal threads of the spark plug hole 33. In the spark plug 10 of this embodiment, the length L1 of the threaded portion 16 is equal to or greater than half the distance L2 between the tip end 22 of the metal shell 15 and the seating surface 17. This improves the thermal conductivity from the metal shell 15 to the engine 32 when the spark plug 10 is attached to the engine 32 by tightening the threaded portion 16 onto the internal threads of the spark plug hole 33, compared to when the length L1 is less than half the distance L2.

[0018] The ground electrode 23 is connected to the tip 22 of the metallic shell 15. The ground electrode 23 is a conductor extending from the metallic shell 15 toward the center line C. A spark gap is formed between the ground electrode 23 and the center electrode 13. The ground electrode 23 is, for example, made of a metal primarily composed of Ni with a core material primarily composed of copper embedded therein. The core material may be omitted. The gasket 24 is an annular metallic member and is disposed between the head 18 and the flange 20.

[0019] 2 is a bottom view of the gasket 24 as viewed from the tip 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 that protrude radially inward from the annular portion 25. In this embodiment, there are eight protrusions 26, but this is merely an example and is not limiting. The inner diameter D4 of the protrusions 26 is the diameter of an imaginary cylinder that contacts the radial tip of the protrusions 26. The inner diameter D1 of the annular portion 25 is the inner diameter of the annular portion 25 excluding the protrusions 26. The inner diameter D4 of the protrusions 26 is smaller than the inner diameter D1 of the annular portion 25. The inner diameter D4 of the protrusions 26 is the minimum inner diameter of the gasket 24.

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

[0021] The flange 20 is located at a position away from the seat 17 of the head 18 toward the tip. The gasket 24 is disposed between the flange 20 and the seat 17. The outer diameter D3 of the flange 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 an imaginary cylinder that contacts the crest of the male thread. The outer diameter D3 of the flange 20 is the diameter of an imaginary cylinder that contacts the crest of the flange 20. In descending order of dimensions, the inner diameter D1 of the ring portion 25, the outer diameter D2 of the threaded portion 16, the outer diameter D3 of the flange 20, and the inner diameter D4 of the convex portion 26 are in that order.

[0022] The gasket 24 is provided between the flange 20 of the metal shell 15 and the seating surface 17 during the manufacturing process of the spark plug 10. First, the metal shell 15, which has the threaded portion 16 and the flange 20, is inserted into the ring portion 25, which does not have the protrusion 26, from the front end 22. Because the inner diameter D1 of the ring portion 25 is larger than the outer diameter D2 of the threaded portion 16 and the outer diameter D3 of the flange 20, the ring portion 25 can be moved between the seating surface 17 and the flange 20.

[0023] Next, the metal shell 15 is inserted, tip end 22 first, 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 vicinity of the inner edge of the ring portion 25. The ring portion 25 is sandwiched between the claws and the head portion 18, and a 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. Because the inner diameter D4 of the protrusion 26 is smaller than the outer diameter D3 of the flange portion 20, the protrusion 26 comes into contact with the flange portion 20, restricting the movement of the gasket 24. The protrusion 26 holds the gasket 24 between the head portion 18 and the flange portion 20, preventing the gasket 24 from getting caught on the threaded portion 16.

[0024] 4 is a cross-sectional view of the metallic shell 15 including the center line C. The neck portion 19 includes a flange portion 20, a front end 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 front end 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 front end portion 28 and larger than the root diameter of the threaded portion 16. The outer diameter of the rear end portion 29 is smaller than the inner diameter D4 of the protrusion 26 of the gasket 24. The front end 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 portion of the flange 20 that has the largest outer diameter. The outer diameter of the top portion 27 is equal to the outer diameter D3 of the flange 20. The outer diameter of the flange 20 gradually decreases from the top portion 27 toward the front end portion 28, and gradually decreases from the top portion 27 toward the rear end portion 29.

[0026] A first point 30 is set at the rearmost point on the outer circumference of the apex 27, and a second point 31 is set at a position opposite the first point 30 across the center line C and closest to the first point 30. The second point 31 is a point on the outer circumference of the rear end 29 of the neck 19, rearward of the flange 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 29 and the flange 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. This prevents the tip of the protrusion 26 of the gasket 24 from contacting the apex 27 when the gasket 24 is tilted relative to the neck 19 as shown in FIG. 3 , thereby preventing the gasket 24 from getting caught on the flange 20.

[0027] Figure 5 is a half-sectional view of the spark plug 10, including the center line C, attached to an engine 32. Figure 5 shows the vicinity of the gasket 24 of the spark plug 10, and other parts are omitted. Figure 5 shows the engine 32 in cross section.

[0028] The spark plug 10 is attached to the engine 32 by fastening the threaded portion 16 to the internal thread of the spark plug hole 33. The ring portion 25 of the gasket 24 sandwiched between the head portion 18 and the engine 32 tightly contacts the head portion 18 and the engine 32 to prevent gas leakage from between the spark plug hole 33 and the spark plug 10.

[0029] If the shortest distance D5 between the first point 30 (see FIG. 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 installation in the engine 32, the tip of the protrusion 26 of the gasket 24 may contact or climb over the crest 27, causing the gasket 24 to become caught on the flange 20. If the tightening torque of the screws used to install the spark plug 10 in the engine 32 is small, the spark plug 10 may be installed in the engine 32 with the gasket 24 remaining caught on the flange 20. In this case, the ring 25 of the gasket 24 cannot be tightly fitted to the head 18 and the engine 32, which may result in gas leakage from between the spark plug hole 33 and the spark plug 10.

[0030] In contrast, in 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, so that the gasket 24 does not get 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 tightly attached to the head 18 and the engine 32.

[0031] Because the outer diameter D3 of the flange 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 than when the outer diameter D3 of the flange 20 is larger than the outer diameter D2 of the threaded portion 16. This is because the ring portion 25 needs to pass over the flange 20, and therefore the inner diameter D1 of the ring portion 25 must be larger than the outer diameter D3 of the flange 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. This increases the contact area between the head portion 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 portion 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, the spark plug 10 was described as having a gasket 24 including a protrusion 26 that protrudes radially inward. In contrast, in the second embodiment, a spark plug 10 will be described as having a gasket 34 that does not have a protrusion. The same parts as those described in the first embodiment are designated by the same reference numerals, and the following description will be omitted.

[0034] 6 is a bottom view of the gasket 34 as seen from the tip end side of the spark plug 10. The gasket 34 replaces the gasket 24 of the spark plug 10 and is disposed between the head 18 and the flange 20 of the metallic shell 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 20 and the seating surface 17 of the metal shell 15 during the manufacturing process of the spark plug 10. First, the metal shell 15, provided with the threaded portion 16 and flange 20, is inserted, from the tip 22, into a metal ring (not shown) that will become the gasket 34. Because 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 20, the ring can be moved between the seating surface 17 and the flange 20.

[0036] Next, the metal shell 15 is inserted, tip 22 first, into a cylindrical tool (not shown) with cylindrical teeth protruding in the axial direction, and the teeth of the tool are placed near the inner edge of the ring. The ring is sandwiched between the teeth and the head 18, and axial force is applied, plastically deforming the ring with the pressure of the teeth until the inner diameter D6 becomes smaller than the outer diameter D3 of the flange 20, thereby forming the gasket 34. Because the inner diameter D6 of the gasket 34 is smaller than the outer diameter D3 of the flange 20, the flange 20 restricts the movement of the gasket 34.

[0037] The dimensions, arranged in descending order, are the outer diameter D2 of the threaded portion 16, the outer diameter D3 of the flange 20, and the inner diameter D6 of the gasket 34. If the shape of the inner edge of the gasket 34 is elliptical or oval, the inner diameter D6 of the gasket 34 is the minor axis (the smallest value of the inner diameter). The gasket 34 fits between the head 18 and the flange 20, preventing the gasket 34 from getting caught on the threaded portion 16.

[0038] The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments, and it can be easily inferred that various improvements and modifications are possible within the scope of the present invention.

[0039] In the embodiment, the cross section of the flange portion 20 in the cross section of the metallic shell 15 including the center line C is trapezoidal, but this is not limited to this. The cross section of the flange portion 20 may be set to any suitable shape, such as triangular or semicircular.

[0040] Although not described in the embodiment, it is of course possible to dispose a cap covering the center electrode 13 and the ground electrode 23 on the metallic shell 15 and provide a hole penetrating the cap. In a spark plug with a cap disposed on the metallic shell 15, fuel flows from the engine's combustion chamber through the hole and into the inside of the cap when the engine valve is operated. A flame kernel is generated by 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 burns the fuel. Expansion pressure generated by the combustion of the fuel generates a gas flow containing a flame. The spark plug injects the gas containing the flame from the hole into the combustion chamber, and the flame jet burns the fuel in the combustion chamber.

[0041] REFERENCE SIGNS LIST 10 Spark plug 11 Insulator 15 Metal shell 16 Threaded portion 17 Bearing surface 18 Head portion 19 Neck portion 20 Flange portion 22 Tip portion 24, 34 Gasket 25 Annular portion 26 Convex portion 27 Top portion (portion of flange portion with largest outer diameter) 29 Rear end portion (portion of neck portion rearward of flange portion) 30 First point 31 Second point C Center line D1 Inner diameter of ring portion (inner diameter of gasket) D2 Outer diameter of threaded portion D3 Outer diameter of flange portion D4 Inner diameter of convex portion (minimum inner diameter of gasket) D5 Distance between first point and second point D6 Inner diameter of gasket L1 Length of threaded portion L2 Distance between tip portion of metal shell and bearing surface

Claims

1. A spark plug comprising: a metal shell arranged on the outer periphery of an insulator and extending along a center line from the front end to the rear end; and a gasket arranged on the outer periphery of the metal shell, wherein the metal shell includes a threaded portion consisting of a male thread centered on the center line, a head including a seat provided on the rear end side of the threaded portion, and a neck portion sandwiched between the head and the threaded portion, wherein the neck portion includes a flange portion extending radially outward, and the gasket is arranged between the head and the flange portion, and the outer diameter of the flange portion is smaller than the outer diameter of the threaded portion and larger than the minimum value of the inner diameter of the gasket.

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

3. The spark plug according to claim 2, wherein, in a cross section of the metallic shell including the center line, a first point is set at the rearmost position of a portion of the collar portion where the outer diameter is largest, and a second point is set at a portion of the neck portion that is rearward of the collar portion and closest to the first point across the center line, the distance between the second point and the first point is larger than the inner diameter of the convex portion.

4. A spark plug according to any one of claims 1 to 3, wherein the length of the threaded portion is at least half the distance between the tip of the metallic shell and the seating surface.

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