JP2021111513A - Spark plug - Google Patents

Abstract

To provide a spark plug in which the eccentricity of an insulator with respect to a main metal fitting can be suppressed while ensuring the sealing force of a packing.SOLUTION: A spark plug comprises: a cylindrical insulator which has a step part, a center barrel part, and a protruding part; a main metal fitting which has a shelf part, a facing part, and an enlarged diameter part, and which is configured such that the shelf part locks the step part via a packing; and a spacer which is disposed between the center barrel part and the facing part while being spaced apart from the enlarged diameter part. The step part has an outer diameter which increases toward its rear end side. The center barrel part is continuous with the rear end side of the step part. The protruding part, continuous with the rear end side of the center barrel part, protrudes outward in a radial direction. The shelf part has an inner diameter which increases toward its rear end side. The facing part, continuous with the rear end side of the shelf part, faces the center barrel part. The enlarged diameter part, continuous on a further rear end side than the facing part, has an inner diameter which increases toward its rear end side and has an inner peripheral surface which faces a tip-facing surface of the protruding part in an axial direction.SELECTED DRAWING: Figure 2

Description

The present invention relates to a spark plug, and more particularly to a spark plug in which a packing is interposed between a main metal fitting and an insulator.

In a spark plug in which a packing is interposed between a step portion of an insulator and a shelf portion of a main metal fitting, Patent Document 1 (particularly FIG. 3) states that the main metal fitting provided on the rear end side in the axial direction with respect to the shelf portion. A technique for further arranging packing between the inclined surface of the insulator and the inclined surface of the insulator is disclosed. In this technique, when the insulator is held by the main metal fitting, an axial load is applied to the two packings, and a sealing force is obtained by the reaction force of the compressed packings. The reaction force of each of the two packings is proportional to the strain due to the compression of each packing.

Japanese Unexamined Patent Publication No. 2010-231934

However, in the above technique, since an axial load of substantially the same magnitude is applied to the two packings, the strain of one packing affects the strain of the other packing. As a result, the reaction force of each packing is suppressed, so that there is a problem that the sealing force of the packing is lowered. Further, since the packing cannot suppress the eccentricity of the insulator with respect to the main metal fitting, the insulator may be damaged if the insulator hits the main metal fitting due to the eccentricity.

The present invention has been made to solve these problems, and an object of the present invention is to provide a spark plug capable of suppressing the eccentricity of the insulator with respect to the main metal fitting while ensuring the sealing force of the packing.

In order to achieve this object, the spark plug of the present invention has a step portion whose outer diameter increases toward the rear end side, a middle body portion connected to the rear end side of the step portion, and a rear end side of the middle body portion. A tubular insulator that has a continuous radial overhang that projects outward, a shelf that extends in the axial direction, and an inner diameter that increases toward the rear end, and a rear of the shelf. The facing part that is connected to the end side and faces the middle body part, and the inner diameter that is connected to the rear end side of the facing part and becomes larger toward the rear end side, and the inner peripheral surface of itself in the axial direction with the tip facing surface of the overhanging part. A tubular main metal fitting having a diameter-expanded portion facing each other and holding an insulator from the outer peripheral side in a state where a step portion is locked to a shelf portion via a packing, and a middle body portion and an opposing portion. It is provided with a spacer that is arranged between the two and is separated from the enlarged diameter portion.

According to the spark plug according to claim 1, a packing is interposed between the step portion of the insulator and the shelf portion of the main metal fitting. In the insulator, the middle body portion is connected to the rear end side of the step portion, and the overhanging portion is connected to the rear end side of the middle body portion. The inner peripheral surface of the enlarged diameter portion of the main metal fitting faces the tip facing surface of the overhanging portion of the insulator in the axial direction. A spacer is arranged between the middle body portion of the insulator and the facing portion of the main metal fitting connected to the rear end side of the shelf portion. Since the spacer is separated from the enlarged diameter portion, when the insulator is held by the main metal fitting, the axial load is applied to the packing but not to the spacer. Therefore, the sealing force of the packing can be secured. Further, the spacer can suppress the eccentricity of the insulator with respect to the main metal fitting.

According to the spark plug according to claim 2, the Vickers hardness of the spacer is lower than the Vickers hardness of the main metal fitting. Therefore, in addition to the effect of claim 1, damage to the insulator when the spacer hits the insulator can be suppressed.

According to the spark plug according to claim 3, the spacer is arranged on the rear end side of the rear end of the tip facing surface of the step portion and the midpoint at the same distance in the axial direction from the tip of the tip facing surface of the overhanging portion. Has been done. Since the moment when the insulator tilts around the packing is larger on the rear end side than the front end side than the midpoint, by arranging the spacer on the rear end side than the midpoint, in addition to the effect of claim 1 or 2. , It is possible to easily avoid contact between the insulator and the main metal fitting, which may cause the insulator to tilt around the packing.

According to the spark plug according to claim 4, the portion between the fifth thread from the rear end of the male screw formed on the facing portion of the main metal fitting to the rear end of the male screw is the male screw. Compared to other parts, the axial force due to tightening of screws when attached to the engine is large. When the axial force is large, the elongation becomes large, so that portion tends to contract in the radial direction due to thermal expansion and contraction. Since the spacer is arranged between the portion and the middle body portion, in addition to the effect of any one of claims 1 to 3, contact between the insulator and the main metal fitting which may be caused by thermal expansion and contraction of the main metal fitting is established. It can be easily avoided.

It is one side sectional view of the spark plug in 1st Embodiment. It is a partial cross-sectional view of the spark plug which enlarged the part shown by II of FIG. It is a partial cross-sectional view of the spark plug which enlarged the part shown by III of FIG. It is a partial cross-sectional view of the spark plug in the 2nd Embodiment.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a one-sided cross-sectional view of the spark plug 10 in the first embodiment with the axis O as a boundary. FIG. 2 is a partial cross-sectional view of the spark plug 10 in which the portion shown by II in FIG. 1 is enlarged. In FIG. 1, the lower side of the paper surface is referred to as the front end side of the spark plug 10, and the upper side of the paper surface is referred to as the rear end side of the spark plug 10 (the same applies to other drawings). In FIG. 2, the illustration of the intermediate portion in the axial direction is omitted. As shown in FIG. 1, the spark plug 10 includes an insulator 11, a main metal fitting 30, a packing 39 (see FIG. 2), and a spacer 40.

The insulator 11 is a substantially cylindrical member made of alumina or the like, which is excellent in insulating properties and mechanical properties at high temperatures. The insulator 11 is formed with a shaft hole 12 extending along the axis O. In the insulator 11, the tip portion 13, the step portion 14, the middle body portion 15, the overhanging portion 16 and the body portion 17 are connected in this order from the front end side to the rear end side.

The tip portion 13 has the smallest outer diameter among the respective portions of the insulator 11. The outer diameter of the step portion 14 increases toward the rear end side. The middle body portion 15 is connected to the rear end side of the step portion 14. The overhanging portion 16 is an annular portion located between the middle body portion 15 and the body portion 17, and projects outward in the radial direction.

As shown in FIG. 2, the front end facing surface 18 of the step portion 14 is a conical surface whose diameter increases toward the rear end side. The rear end 19 of the tip facing surface 18 is located at the tip of the middle body portion 15. In the present embodiment, the outer peripheral surface of the middle body portion 15 is a cylindrical surface having substantially the same outer diameter of the middle body portion 15 over the entire length in the axial direction. The rear end 19 of the front end facing surface 18 has a portion in which the inclination of the line indicating the front end facing surface 18 with respect to the axis O is different from the inclination of the line indicating the outer peripheral surface of the middle body 15 with respect to the axis O in the cross section including the axis O. This is the rearmost position.

The tip-facing surface 20 of the overhanging portion 16 is a conical surface whose diameter increases toward the rear end side. The tip 21 of the tip facing surface 20 is located at the rear end of the middle body portion 15. In the cross section including the axis O, the tip 21 of the tip facing surface 20 has a portion in which the inclination of the line indicating the tip facing surface 20 with respect to the axis O is different from the inclination of the line indicating the outer peripheral surface of the middle body 15 with respect to the axis O. This is the position on the most tip side.

It will be described back to FIG. The center electrode 23 is arranged on the tip end side of the shaft hole 12 of the insulator 11. The center electrode 23 is a rod-shaped electrode held by the insulator 11 along the axis O. In the center electrode 23, a core material having excellent thermal conductivity is embedded in the base material. The base material is formed of an alloy mainly composed of Ni or a metal material composed of Ni. The core material is formed of copper or an alloy containing copper as a main component. The core material can be omitted. The center electrode 23 is electrically connected to the terminal fitting 24 in the shaft hole 12 of the insulator 11. The terminal fitting 24 is a rod-shaped member to which a high-voltage cable (not shown) is connected, and is made of a conductive metal material (for example, low carbon steel or the like).

The main metal fitting 30 is a substantially cylindrical member made of a conductive metal material (for example, low carbon steel or the like). In the main metal fitting 30, the tip portion 31, the shelf portion 32, the facing portion 33, the diameter-expanded portion 35, the curved portion 36, the tool engaging portion 37, and the rear end portion 38 are connected in this order from the front end side to the rear end side.

As shown in FIG. 2, the tip portion 31 surrounds the tip portion 13 of the insulator 11 with a gap. The shelf portion 32 is arranged on the tip end side of the step portion 14 of the insulator 11. The inner diameter of the shelf portion 32 increases toward the rear end side. The facing portion 33 is connected to the rear end side of the shelf portion 32. The facing portion 33 surrounds the middle body portion 15 of the insulator 11 with a gap. Male screws 34 are formed on the outer circumferences of the tip portion 31, the shelf portion 32, and the facing portion 33. The spark plug 10 is attached to a screw hole of an engine (not shown) by a male screw 34.

The enlarged diameter portion 35 is an annular portion connected to the rear end side of the facing portion 33. The outer diameter of the enlarged diameter portion 35 is larger than the outer diameter of the male screw 34. The enlarged diameter portion 35 regulates the amount of screwing of the male screw 34 into the engine. The inner peripheral surface 35a of the diameter-expanded portion 35 increases in diameter toward the rear end side. The inner peripheral surface 35a of the enlarged diameter portion 35 faces the tip facing surface 20 of the overhanging portion 16 of the insulator 11 in the axial direction. The inner peripheral surface 35a of the enlarged diameter portion 35 is not in contact with the tip facing surface 20 of the overhanging portion 16, and the axial direction is between the inner peripheral surface 35a of the enlarged diameter portion 35 and the tip facing surface 20 of the overhanging portion 16. There is a gap.

A packing 39 is interposed between the tip facing surface 18 of the step portion 14 of the insulator 11 and the shelf portion 32 of the main metal fitting 30. The packing 39 is an annular plate material formed of a metal material such as iron or steel that is softer than the metal material constituting the main metal fitting 30.

The spacer 40 is arranged between the middle body portion 15 of the insulator 11 and the facing portion 33 of the main metal fitting 30 at a position separated from the diameter-expanded portion 35. In the present embodiment, the spacer 40 is an annular member formed of a metal material such as iron or steel, which is softer than the metal material constituting the main metal fitting 30. The Vickers hardness of the spacer 40 is lower than the Vickers hardness of the main metal fitting 30. The Vickers hardness is measured at one point on the opposing portion 33 of the main metal fitting 30 and one point on the spacer 40 in accordance with JIS Z2244: 2009, and the magnitudes thereof are compared. The spacer 40 is arranged on the rear end side of the rear end 19 of the tip facing surface 18 of the step portion 14 and the midpoint 22 located at an equal distance in the axial direction from the tip 21 of the tip facing surface 20 of the overhanging portion 16. ..

The spacer 40 is not limited to metal. For example, it is naturally possible to form the spacer 40 with rubber such as silicone rubber or fluororubber, synthetic resin such as polyphenylene sulfide or polyetheretherketone, flexible mica, or the like.

The shape of the spacer 40 is not limited to an annular shape having a continuous circumference. For example, a C ring having a cut in a part of the circumference, a string shape, a dot shape, and a sheet shape wound around the middle body portion 15 can be mentioned. A plurality of spacers 40 may be arranged. Of course, it is possible to apply an adhesive to one or a plurality of places of the middle body portion 15 and the facing portion 33, and use the cured adhesive as the spacer 40.

It will be described back to FIG. The curved portion 36 of the main metal fitting 30 connects the enlarged diameter portion 35 and the tool engaging portion 37. The tool engaging portion 37 is a portion for engaging a tool such as a wrench when the screw 34 is screwed into the screw hole of the engine. The rear end portion 38 is an annular portion that bends inward in the radial direction. The rear end portion 38 is located on the rear end side of the overhanging portion 16 of the insulator 11. A seal portion 41 filled with powder such as talc is provided between the overhanging portion 16 of the insulator 11 and the rear end portion 38 of the main metal fitting 30 over the entire circumference.

A gasket 42 is arranged between the enlarged diameter portion 35 of the main metal fitting 30 and the male screw 34. The gasket 42 improves the airtightness between the screw holes of the engine and the main metal fitting 30 when the main metal fitting 30 is attached to the engine (not shown). The ground electrode 45 is a rod-shaped metal (for example, nickel-based alloy) member connected to the tip 31 of the main metal fitting 30. The ground electrode 45 forms a spark gap with the center electrode 23.

The spark plug 10 is manufactured by, for example, the following method. First, the center electrode 23 is inserted into the shaft hole 12 of the insulator 11 and arranged so that the tip of the center electrode 23 is exposed to the outside from the shaft hole 12. Next, the terminal fitting 24 is inserted into the shaft hole 12 of the insulator 11, and the terminal fitting 24 and the center electrode 23 are electrically connected. Next, the packing 39 is arranged on the shelf portion 32 of the main metal fitting 30, the spacer 40 is arranged on the inner peripheral surface 35a of the enlarged diameter portion 35 of the main metal fitting 30, and then the insulator 11 is inserted into the main metal fitting 30. When the insulator 11 is inserted into the main metal fitting 30, after the step portion 14 of the insulator 11 comes into contact with the spacer 40, the spacer 40 is sandwiched between the insulator 11 and the main metal fitting 30, so that the spacer 40 has a middle body. It moves between the portion 15 and the facing portion 33, and is separated from the enlarged diameter portion 35. The position of the spacer 40 is maintained by frictional force.

Next, when the seal portion 41 is provided between the main metal fitting 30 and the insulator 11, and the curved portion 36 and the rear end portion 38 are formed on the main metal fitting 30, the shelf portion 32 to the rear end portion 38 of the main metal fitting 30 are formed. In the portion up to, a compressive load in the axial direction is applied to the portion of the insulator 11 from the step portion 14 to the overhanging portion 16 via the packing 39 and the seal portion 41. As a result, the insulator 11 is held by the main metal fitting 30. Next, the ground electrode 45 is bent, and the gasket 42 is attached to obtain the spark plug 10.

Since the enlarged diameter portion 35 and the spacer 40 of the spark plug 10 are separated from each other, the axial load applied to the insulator 11 by the main metal fitting 30 when the insulator 11 is held by the main metal fitting 30 is applied to the packing 39. Does not join the spacer 40. Since the reaction force of the packing 39 is not suppressed by the spacer 40, the sealing force of the packing 39 can be secured.

Further, since the spacer 40 is arranged between the middle body portion 15 and the facing portion 33, when a radial load is applied to the spacer 40 sandwiched between the middle body portion 15 and the facing portion 33, the spacer 40 causes the spacer 40. The eccentricity of the insulator 11 with respect to the main metal fitting 30 can be suppressed. As a result, the insulator 11 can be prevented from hitting the main metal fitting 30 when the spark plug 10 is manufactured (when the main metal fitting 30 is assembled) or when the spark plug 10 is used, so that damage to the insulator 11 can be suppressed.

Since the Vickers hardness of the spacer 40 is lower than the Vickers hardness of the main metal fitting 30, when the spacer 40 hits the insulator 11, the spacer 40 is deformed and damage to the insulator 11 can be suppressed.

The spacer 40 is arranged on the rear end side of the rear end 19 of the tip facing surface 18 of the step portion 14 and the midpoint 22 located at an equal distance in the axial direction from the tip 21 of the tip facing surface 20 of the overhanging portion 16. .. Since the moment when the insulator 11 tilts with respect to the packing 39 is larger on the rear end side than the midpoint 22 than on the front end side, the spacer 40 is arranged on the rear end side of the midpoint 22 to center the packing 39. It is possible to easily avoid contact between the insulator 11 and the main metal fitting 30, which may cause the insulator 11 to tilt.

The spark plug 10 has an axial distance (hereinafter referred to as “screw length”) between the seat surface 43 of the enlarged diameter portion 35 (see FIG. 2) and the tip 44 (see FIG. 2) of the main metal fitting 30 (hereinafter referred to as “screw length”) of 20 mm. The above is suitable. Since the spark plug 10 having a screw length of 20 mm or more has a longer distance between the packing 39 and the enlarged diameter portion 35 than the spark plug having a screw length of less than 20 mm, the insulator 11 is centered on the packing 39. This is because the moment when the screw is tilted becomes large, and when the insulator 11 comes into contact with the main metal fitting 30, the insulator 11 is easily damaged. Therefore, when the screw length is 20 mm or more, the effect of suppressing the eccentricity of the insulator 11 by the spacer 40 becomes large.

FIG. 3 is a partial cross-sectional view of the spark plug 10 in which the portion shown by III in FIG. 2 is enlarged. The spacer 40 is arranged between the facing portion 33 and the middle body portion 15 between the fifth thread 49 counting from the rear end 46 of the male screw 34 and the rear end 46 of the male screw 34. In the present embodiment, the first thread 47 including the rear end 46 of the male screw 34 is an incomplete thread portion, and the thread on the tip side from the second thread 48 is a complete thread portion. However, the number of threads is not limited to this, and the number of threads of the incompletely threaded portion is appropriately set. That is, the fifth thread 49 is the fifth thread counting from the rear end 46 of the male thread 34, regardless of whether the thread is incomplete or completely threaded.

The part between the fifth thread 49 counting from the rear end 46 of the screw 34 of the main metal fitting 30 to the rear end 46 of the male screw 34 is the engine (FIG. 6) as compared with the other parts of the male screw 34. Axial force due to tightening of screws when attached to) is large. When the axial force is large, the elongation becomes large, so that portion tends to contract in the radial direction due to thermal expansion and contraction. Since the spacer 40 is arranged between that portion and the middle body portion 15, contact between the insulator 11 and the main metal fitting 30 which may be caused by thermal expansion and contraction of the main metal fitting 30 is avoided when the spark plug 10 is used. It can be done easily.

The second embodiment will be described with reference to FIG. In the first embodiment, a case where the spacer 40 arranged between the middle body portion 15 of the insulator 11 and the facing portion 33 of the main metal fitting 30 is positioned by friction has been described. On the other hand, in the second embodiment, the case where the spacer 52 is positioned by the step 51 provided on the inner peripheral surface of the facing portion 33 of the main metal fitting 30 will be described. The same parts as those described in the first embodiment are designated by the same reference numerals, and the following description will be omitted. FIG. 4 is a partial cross-sectional view of the spark plug 50 according to the second embodiment. In FIG. 4, the portion shown by II in FIG. 1 is enlarged as in FIG. 2.

As shown in FIG. 4, in the spark plug 50, a step 51 facing the rear end side is formed on the inner peripheral surface of the facing portion 33 of the main metal fitting 30 over the entire circumference. The step 51 is located at a position separated from the enlarged diameter portion 35, and is provided on the rear end side of the midpoint 22. The spacer 52 is arranged on the step 51. In this embodiment, the spacer 52 is an annular metal member. Since the spacer 52 cannot move to the tip side of the step 51, the spacer 52 can be reliably positioned. Instead of the step 51, a recess may be provided on the inner peripheral surface of the facing portion 33, and the spacer 52 may be arranged in the recess. The step 51 and the recess do not have to be continuous over the entire circumference on the inner peripheral surface of the facing portion 33, and may be provided intermittently.

Although the present invention has been described above based on the embodiments, the present invention is not limited to the above embodiments, and various improvements and modifications can be made without departing from the spirit of the present invention. It can be easily inferred.

In the embodiment, the case where the outer peripheral surface of the inner body portion 15 of the insulator 11 is a cylindrical surface has been described, but the present invention is not necessarily limited to this. Of course, it is possible to make the outer peripheral surface of the middle body portion 15 a conical surface in which the outer diameter of the middle body portion 15 increases toward the rear end side. In this case, the tip 21 of the tip facing surface 20 of the overhanging portion 16 is the rear end of a line segment indicating the outer peripheral surface of the middle body portion 15 in the cross section including the axis O.

In the second embodiment, the case where the step 51 is provided on the inner peripheral surface of the facing portion 33 of the main metal fitting 30 and the spacer 52 is arranged on the step 51 has been described, but the present invention is not necessarily limited to this. Instead of providing a step on the main metal fitting 30, it is naturally possible to provide a step or a recess on the outer peripheral surface of the inner body portion 15 of the insulator 11 and arrange a spacer there. The steps and dents do not have to be continuous over the entire circumference on the outer peripheral surface of the middle body portion 15, and may be provided intermittently.

In the embodiment, the case where the gasket 42 is arranged on the tip end side of the enlarged diameter portion 35 has been described, but the present invention is not necessarily limited to this. Of course, it is possible to arrange the spacers 40 and 52 between the main metal fitting 30 of the so-called tapered sheet type spark plug, which omits the gasket 42, and the insulator 11.

In the embodiment, the case where the rear end portion 38 of the main metal fitting 30 applies a load in the axial direction to the overhanging portion 16 of the insulator 11 via the seal portion 41 has been described, but the present invention is not necessarily limited to this. When the seal portion 41 is omitted and the rear end portion 38 of the main metal fitting 30 applies a load in the axial direction to the overhanging portion 16 of the insulator 11, the same effect as that of the present embodiment can be realized.

10,50 Spark plug 11 Insulator 12 Shaft hole 14 Stepped part 15 Middle body part 16 Overhanging part 18 Stepped part tip facing surface 19 Rear end of tip facing surface 20 Overhanging tip facing surface 21 Tip of tip facing surface 22 Midpoint 30 Main metal fittings 32 Shelf 33 Opposing part 34 Male thread 35 Expanded diameter 35a Inner peripheral surface of expanded diameter 39 Packing 40, 52 Spacer 46 Rear end of male thread 49 Fifth thread O axis

Claims (4)

A step portion whose outer diameter increases toward the rear end side, a middle body portion connected to the rear end side of the step portion, and a projecting portion connected to the rear end side of the middle body portion and projecting outward in the radial direction. A tubular insulator that has a portion and extends in the axial direction,
A shelf portion whose inner diameter increases toward the rear end side, a facing portion which is connected to the rear end side of the shelf portion and faces the middle body portion, and a facing portion which is connected to the rear end side of the facing portion and is connected to the rear end side. As the inner diameter increases toward the end, the overhanging portion has a tip-facing surface and an enlarged diameter portion whose inner peripheral surface faces in the axial direction, and the step portion engages with the shelf portion via packing. A spark plug including a tubular main metal fitting that holds the insulator from the outer peripheral side in a stopped state.
A spark plug provided with a spacer arranged between the middle body portion and the facing portion and separated from the enlarged diameter portion. The spark plug according to claim 1, wherein the Vickers hardness of the spacer is lower than the Vickers hardness of the main metal fitting. The spacer is arranged on the rear end side of the rear end of the tip facing surface of the step portion and the midpoint at the same distance in the axial direction from the tip of the tip facing surface of the overhanging portion. Or the spark plug according to 2. The main metal fitting includes a male screw formed on at least a part of the outer periphery of the facing portion.
The spacer is arranged between the facing portion and the middle body portion between the fifth thread from the rear end of the male screw and the rear end of the male screw. The spark plug described in any of 3 to 3.

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