JP2023060426A - spark plug - Google Patents

Abstract

To provide a spark plug which can prevent outflow of combustion gas.SOLUTION: A main body metal fitting 50 of a spark plug 10 has a sheet surface 530 which is a surface to be pressure-welded to an internal combustion engine EG, and whose cross section obtained by cutting the main body metal fitting in a direction perpendicular to a center axis CX of an axial hole 200 has an outer diameter that increases, along the center axis CX, toward the opposite side to a center electrode 30. At a position, on the main body metal fitting 50, away from the sheet surface 530 along the center axis CX, there is formed a deformed groove 520 which extends in the circumferential direction around the center axis CX.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to spark plugs.

For example, an internal combustion engine mounted on a vehicle is provided with a spark plug for igniting fuel. A spark plug has a center electrode and a ground electrode, and ignites fuel by generating spark discharge between these electrodes. When attaching the spark plug to the internal combustion engine, the spark plug is fastened and fixed so that the seat surface of the spark plug is pressed against the seat surface of the internal combustion engine. By bringing the respective seat surfaces into pressure contact with each other, the outflow of combustion gas from the internal combustion engine to the outside is suppressed. For convenience of explanation, the seat surface provided in the internal combustion engine is hereinafter also referred to as the "receiving side seat surface". Further, the seat surface provided on the spark plug is hereinafter also referred to as "plug-side seat surface".

By the way, the taper angle of the receiving side sheet surface is specified as 60°+0°/−1° in the international standard ISO28741:2013. On the other hand, the taper angle of the plug-side seat surface is specified as 63°±1° in the same standard. That is, the receiving side seat surface and the plug side seat surface are not parallel to each other. The range of the portion of the plug-side seat surface that is pressed against the receiving-side seat surface is a narrow range that can be generally regarded as a "line". Therefore, if a scratch is formed in this range for some reason, there is a possibility that the combustion gas from the internal combustion engine may flow out through the scratch.

Therefore, in the ignition plug disclosed in Patent Document 1, the shape of the plug-side seat surface is devised so that the area of the plug-side seat surface that is pressed against the receiving-side seat surface is replaced with the end portion where scratches are likely to be formed. have different ranges.

JP 2020-119687 A

However, even in the spark plug described in Patent Document 1, the range of the portion of the plug-side seat surface that is pressed against the receiving-side seat surface is still a narrow range that can be generally regarded as a "line". . For this reason, there is still the possibility that scratches will be formed in the range of the plug-side seat surface that is pressed against the receiving-side seat surface during the spark plug manufacturing process or the like. Thus, from the viewpoint of suppressing the outflow of combustion gas, the spark plug described in Patent Document 1 has room for improvement.

An object of the present disclosure is to provide a spark plug capable of suppressing outflow of combustion gas.

A spark plug according to the present disclosure is a spark plug (10) attached to an internal combustion engine (EG), comprising an insulator (20) formed with a shaft hole (200) and a central axis (CX) of the shaft hole. A center electrode (30) held by an insulator, a metal shell (50) holding the insulator from the outer peripheral side, and a center electrode extending from the metal shell at a position corresponding to one end along the and partially opposed ground electrodes (60). The metal shell is a surface that is pressed against the internal combustion engine, and is a sheet whose outer diameter of a cross section when cut perpendicular to the central axis increases toward the side opposite to the center electrode along the central axis. face (530). A deformed groove (520) extending in the circumferential direction surrounding the central axis is formed in the metal shell at a position spaced apart from the seat surface along the central axis.

When the spark plug having such a configuration is attached to the internal combustion engine, the portion of the metal shell between the seat surface (the plug-side seat surface) and the deformed groove is pressed against the internal combustion engine. It deforms elastically. As a result, the seat surface comes into contact with the internal combustion engine over a relatively wide range, so that the possibility of the seat surface being scratched across the range can be extremely reduced. As a result, the outflow of combustion gas can be further suppressed than in the conventional art.

According to the present disclosure, there is provided a spark plug capable of suppressing outflow of combustion gas.

FIG. 1 is a diagram showing the configuration of a spark plug according to this embodiment. FIG. 2 is a diagram showing the configuration of the seat surface and the vicinity thereof of the spark plug according to the present embodiment. FIG. 3 is a diagram for explaining deformation when the spark plug according to the present embodiment is attached to the internal combustion engine. FIG. 4 is a diagram showing a range in which the spark plug according to this embodiment is pressed against the internal combustion engine. FIG. 5 is a diagram showing the configuration of a spark plug according to a modification of this embodiment. FIG. 6 is a diagram showing the configuration of a spark plug according to another modification of the present embodiment.

Hereinafter, this embodiment will be described with reference to the accompanying drawings. In order to facilitate understanding of the description, the same constituent elements in each drawing are denoted by the same reference numerals as much as possible, and overlapping descriptions are omitted.

A configuration of a spark plug 10 according to this embodiment will be described with reference to FIG. In FIG. 1, the left side portion shows a cross section of the ignition plug 10 taken along a plane including a central axis CX, which will be described later. However, of the members constituting the spark plug 10, the appearance of the terminal fitting 40 is shown instead of the cross section.

The spark plug 10 is attached to each cylinder of an internal combustion engine (not shown) and is a device for igniting fuel in the combustion chamber of the cylinder. The spark plug 10 includes an insulator 20 , a center electrode 30 , a terminal fitting 40 , a metal shell 50 and a ground electrode 60 .

The insulator 20 is a cylindrical member made of an insulating material such as alumina. A shaft hole 200 is formed in the insulator 20 . Axial hole 200 is a through hole formed to penetrate insulator 20 along its central axis. A central axis of the shaft hole 200 coincides with a central axis of the insulator 20 . The central axis of the shaft hole 200 is hereinafter also referred to as "central axis CX". In a cross section of the insulator 20 taken perpendicular to the central axis CX, the shaft hole 200 has a circular shape.

The center electrode 30 is a metal member held by the insulator 20 at a position corresponding to one end (lower end in FIG. 1) of the shaft hole 200 along the center axis CX. be. The center electrode 30 is a rod-shaped member, most of which is arranged inside the shaft hole 200 . A portion of the center electrode 30 protrudes from the shaft hole 200 to the outside of the insulator 20, and a discharge tip 31 is attached to the tip of the protruding portion. The insulator 20 described above can be said to be a member that holds the center electrode 30 from the outer peripheral side.

The terminal fitting 40 is a metal member held by the insulator 20 at the other end (upper end in FIG. 1) of the shaft hole 200 along the central axis CX. be. The terminal fitting 40 is a rod-shaped member, and most of it is arranged inside the shaft hole 200 . A portion of the terminal fitting 40 protrudes from the shaft hole 200 to the outside of the insulator 20 . This projecting portion serves as an electrode terminal to which a voltage is applied from an external power source (not shown).

The insulator 20 to which the center electrode 30 is attached along the central axis CX is hereinafter also referred to as the "tip side". In the insulator 20, the side of the insulator 20 to which the terminal fitting 40 is attached along the central axis CX is hereinafter also referred to as the "rear end side."

A resistor 71 is arranged in the shaft hole 200 between the terminal fitting 40 and the center electrode 30 . The resistor 71 is a member arranged to adjust the electric resistance of the electric circuit from the terminal fitting 40 to the center electrode 30 . The resistor 71 is made of a material obtained by adding a predetermined amount of carbon powder to powdered glass and zirconia. The electrical resistance of the resistor 71 is adjusted by the amount of carbon added. By arranging the resistor 71 in the electric path from the terminal fitting 40 to the center electrode 30 , generation of electromagnetic noise due to spark discharge of the spark plug 10 is suppressed. The resistor 71 and the center electrode 30 are electrically connected via a conductive sealing layer 72 . Similarly, the terminal fitting 40 and the resistor 71 are electrically connected via a conductive sealing layer 73 . Both of the conductive sealing layers 72 and 73 are conductive layers made of powdered glass to which copper powder is added.

The metal shell 50 is a tubular member that holds a portion of the insulator 20 from the outer peripheral side. The metal shell 50 is entirely made of metal. The metal shell 50 is fixed to the insulator 20 by crimping, and holds the insulator 20 in that state. The metal shell 50 has a fitting portion 52 and an insertion portion 56 .

The fitting portion 52 is provided at a rear end portion of the metallic shell 50 . The fitting portion 52 is a portion that is fitted with a tool such as a plug wrench when attaching the spark plug 10 to the internal combustion engine. The shape of the fitting portion 52 when viewed along the central axis CX is, for example, a hexagon.

The insertion portion 56 is provided in a portion of the metallic shell 50 on the distal end side. The insertion portion 56 is a portion that is inserted into an insertion hole (not shown) formed in the internal combustion engine. A male screw 561 is formed on the outer peripheral surface of the insertion portion 56 . When the spark plug 10 is attached to the internal combustion engine, the fitting portion 52 rotates around the central axis CX due to the force received from the tool. As a result, the female thread formed on the inner peripheral surface of the insertion hole and the male thread 561 of the insertion portion 56 are screwed together. Thereby, the ignition plug 10 is fastened and fixed to the internal combustion engine. When the spark plug 10 is attached to the internal combustion engine, the metal shell 50 has the same ground potential as the internal combustion engine.

A cylindrical portion 510 and a seat surface 530 are provided in the metal shell 50 at a position between the fitting portion 52 and the insertion portion 56 along the central axis CX.

The columnar portion 510 is a portion whose outer shape is formed in a substantially columnar shape. The central axis of cylindrical portion 510 coincides with central axis CX. The outer diameter of cylindrical portion 510 is slightly larger than the inner diameter of the insertion hole provided in the internal combustion engine. A deformed groove 520 is formed in the cylindrical portion 510, which will be described later.

A portion of the metallic shell 50 closer to the distal end side than the columnar portion 510 along the central axis CX has a tapered shape in which the diameter decreases toward the distal end side. The seat surface 530 is the outer surface of such a tapered portion. Such a seat surface 530 is a portion adjacent to the columnar portion 510 along the central axis CX, and the outer diameter of the cross section when cut perpendicularly to the central axis CX is equal to that of the central electrode along the central axis CX. It can be said that the portion 30 is formed so as to become larger toward the opposite side (that is, the rear end side). The outer diameter of the portion of the seat surface 530 closest to the tip is smaller than the inner diameter of the insertion hole provided in the internal combustion engine. The seat surface 530 is a surface that is pressed against the internal combustion engine when the spark plug 10 is attached to the internal combustion engine. The seat surface 530 is provided over the entire circumference along the tip end of the cylindrical portion 510 .

The ground electrode 60 is a metal member formed so as to extend from the end surface S on the tip side of the metal shell 50 toward the tip side. The ground electrode 60 is bent, and a portion thereof faces the discharge tip 31 of the center electrode 30 along the central axis CX. That is, the ground electrode 60 has one end connected to the end surface S of the metal shell 50 and the other end facing the center electrode 30 . A discharge tip 61 is attached to a portion of the ground electrode 60 that faces the center electrode 30 . As a result, the discharge tip 61 and the discharge tip 31 are aligned along the central axis CX and face each other. A gap formed between the discharge tip 61 and the discharge tip 31 facing each other serves as a discharge gap GP in which spark discharge occurs.

During operation of the internal combustion engine, a pulse-like high voltage is applied between the terminal fitting 40 of the spark plug 10 and the body of the internal combustion engine. This high voltage is applied between the discharge tip 61 and the discharge tip 31 facing each other, causing spark discharge in the discharge gap GP. Either one or both of the discharge tip 61 and the discharge tip 31 may be omitted.

A detailed configuration of the seat surface 530 and its vicinity portion of the metal shell 50 will be described with reference to FIG. 2 . FIG. 2 shows an enlarged view of a portion of the spark plug 10 attached to the internal combustion engine EG.

An angle θ1 shown in FIG. 2 indicates the taper angle of the seat surface 530 . The taper angle of the seat surface 530 is defined as the angle between the straight line indicating the seat surface 530 and the central axis CX in a cross section including the central axis CX. In international standard ISO28741:2013, the angle θ1, which is the taper angle of the seat surface 530, is defined as 63°±1°.

A seat surface SS shown in FIG. 2 is a seat surface provided on the internal combustion engine EG side, that is, a surface against which a seat surface 530 is pressed when the spark plug 10 is attached. The seat surface SS is provided along the entire circumference at the edge of an insertion hole provided in the internal combustion engine EG.

An angle θ2 shown in FIG. 2 indicates a taper angle of the seat surface SS. The taper angle of the seat surface SS is defined as the angle between the straight line indicating the seat surface SS and the central axis CX in a cross section including the central axis CX. In the international standard ISO28741:2013, the angle θ2, which is the taper angle of the seat surface SS, is defined as 60°+0°/−1°.

Since the respective taper angles are different from each other in this manner, the seat surface 530 and the seat surface SS are not parallel to each other. Therefore, in a spark plug having a general configuration, the range of the portion of the seat surface 530 that is pressed against the seat surface SS is a narrow range that can be generally regarded as a "line" at or near the end on the rear end side. It has become.

By the way, in the process of manufacturing the spark plug 10 or the like, scratches may be formed in a part of the metal shell 50 made of metal. For example, in a barrel plating process for plating the surfaces of metal shells 50, a large number of metal shells 50 placed inside a barrel, which is a bucket-shaped container, easily collide with each other. As a result of the collision, a scratch may be formed on a portion of the metallic shell 50 .

The range of the portion of the seat surface 530 that is pressed against the seat surface SS is narrow enough to be regarded as a "line" as described above in a general configuration. In such a narrow pressure welding range, if a scratch that straddles the range is formed in the barrel plating process or the like, there is a possibility that the combustion gas from the internal combustion engine EG will flow out through the scratch. be.

As a method for solving such a problem, for example, as in the spark plug described in Japanese Patent Application Laid-Open No. 2020-119687, scratches are formed in the range of the seat surface 530 that is pressed against the seat surface SS. It is also conceivable to devise the shape of the seat surface 530 so that it is in a range different from the rear end side portion where it is easy to move.

However, even if such an arrangement is made, the area of the seat surface 530 that is pressed against the seat surface SS remains a narrow range that can be regarded as a "line". Therefore, there is still a possibility that scratches will be formed in the range of the seat surface 530 that is pressed against the seat surface SS in the spark plug manufacturing process or the like.

Therefore, in the spark plug 10 according to the present embodiment, the deformed groove 520 is formed in the metal shell 50 to solve the problem that the combustion gas may flow out through the scratches on the seat surface 530 .

As shown in FIG. 2 , the deformation groove 520 is formed in the cylindrical portion 510 of the metal shell 50 at a position near the seat surface 530 . The deformed groove 520 is formed so as to extend along the circumferential direction surrounding the central axis CX at a position slightly spaced from the seat surface 530 toward the rear end side along the central axis CX. In addition, the deformed groove 520 is formed so as to extend along the entire circumference of the cylindrical portion 510 along the circumferential direction (that is, as an endless annular groove).

Of the two inner surfaces facing each other inside the deformed groove 520, the inner surface on the side of the seat surface 530 (that is, the tip side) is hereinafter also referred to as the "first inner surface 521". In addition, the inner surface on the side opposite to the seat surface 530 (that is, on the rear end side) is hereinafter also referred to as the "second inner surface 522". As indicated by the dotted line in FIG. 2, the depth direction of the deformed groove 520 is tilted with respect to the central axis CX so that the depth direction of the deformation groove 520 approaches the distal end side.

FIG. 3A shows the state at the time when the seat surface 530 comes into contact with the seat surface SS in the process of attaching the spark plug 10 to the internal combustion engine EG. In this state, the magnitude of the force that presses the seat surface 530 and the seat surface SS against each other is approximately zero. Therefore, the shape of the metal shell 50 including the portion near the deformed groove 520 remains the original shape before attachment. At this time, that is, before the spark plug 10 is attached to the internal combustion engine EG, the first inner surface 521 and the second inner surface 522 are parallel to each other. Both the first inner surface 521 and the second inner surface 522 are parallel to the seat surface 530 . Therefore, the portion of the metal shell 50 between the first inner surface 521 and the seat surface 530 has a thin plate shape with a uniform thickness as a whole.

From the state shown in FIG. 3(A), as the fitting portion 52 is further tightened using a tool, that is, as the spark plug 10 is rotated around the central axis CX, the spark plug 10 is The whole moves to the tip side. At this time, the seat surface 530 is strongly pressed against the seat surface SS. A thin plate portion of the metal shell 50 between the first inner surface 521 and the seat surface 530 is elastically deformed by the force received from the seat surface SS. As a result, the width dimension of the entrance portion of the deformed groove 520 becomes narrower than the original width dimension.

FIG. 3(B) shows a state where the installation of the spark plug 10 is completed. In this state, as a result of the elastic deformation of the thin plate portion, substantially the entire portion of the seat surface 530 in which the deformation grooves 520 are formed is brought into contact with the seat surface SS. there is As described above, when the ignition plug 10 according to the present embodiment is attached to the internal combustion engine EG, the range of the portion of the seat surface 530 that is pressed against the seat surface SS is the same as when the deformed groove 520 is not formed. is wider than As a result, it is possible to ensure a wide range that functions as a "seal portion" for suppressing leakage of combustion gas. The deformation groove 520 can be said to be a groove provided to facilitate elastic deformation of the portion of the metallic shell 50 where the seat surface 530 is formed along the seat surface SS. Note that the first inner surface 521 and the seat surface 530 are parallel to each other even in the state of FIG. 3B.

The thickness between the first inner surface 521 and the seat surface 530 can be appropriately set within a thickness range that allows elastic deformation of the portion to easily occur. The “thickness that allows elastic deformation to occur easily” means that the work of rotating the fitting portion 52 around the central axis CX using a tool such as a plug wrench can be performed manually without hindrance. It's about thickness.

A hatched range 530A in FIG. 4 represents a range of the seat surface 530 in which elastic deformation as described above can occur, that is, a range in which the deformation grooves 520 are formed on the back side. As described above, when the ignition plug 10 is completely attached to the internal combustion engine EG, substantially the entire area 530A is in contact with the seat surface SS, and the seal portion for suppressing the outflow of combustion gas is formed. function as

As shown in FIG. 4, a scratch SC may be formed in a portion of range 530A. If such a scratch SC were formed to straddle the entire range 530A from the front end side to the rear end side, the combustion gas would flow out through the scratch SC. However, since the range 530A is a range formed widely in the depth direction of the deformation groove 520, the possibility of forming a scratch SC that causes combustion gas to flow out is extremely small. In other words, in most cases, as in the example shown in FIG. 4, the scratch SC is wholly within the range 530A, or is in a state where it covers only one end of the range 530A. As described above, in the spark plug 10 according to the present embodiment, by forming the deformation groove 520 in the metal shell 50, the possibility of forming a scratch that straddles the entire range 530A is reduced, thereby reducing combustion. It is possible to sufficiently suppress the outflow of gas as compared with the conventional art.

As for the shape of the deformed groove 520, various shapes other than the shapes described above can be employed.

In the modification shown in FIG. 5A, the depth direction of the deformation groove 520 is perpendicular to the central axis CX. That is, the deformed groove 520 in this modified example is formed so as to recede in a concave shape toward the central axis CX along the direction perpendicular to the central axis CX. Even in such a mode, the same effects as in the present embodiment can be obtained.

In the modification shown in FIG. 5A, the first inner surface 521 and the second inner surface 522 are parallel to each other, as in the present embodiment. Instead of such a mode, a configuration as shown in FIG. 5B may be adopted. In the modified example shown in FIG. 5B, the distance between the first inner surface 521 and the second inner surface 522 (that is, the width dimension of the deformed groove 520) gradually decreases toward the far side of the deformed groove 520. . Even in such a mode, the same effects as in the present embodiment can be obtained.

Yet another modified example will be described with reference to FIG. In the modification shown in FIG. 6, the taper angle of the seat surface 530 is not uniform throughout. The seat surface 530 in this modified example has a first portion 531 with a taper angle of θ11 and a second portion 532 with a taper angle of θ12. θ11 is greater than θ12. Also, the taper angle (θ2) of the seat surface SS is smaller than θ11 and larger than θ12.

The first portion 531 is a portion of the seat surface 530 on the leading end side, and the second portion 532 is a portion of the seat surface 530 on the rear end side. An edge E<b>1 is formed at the boundary between the first portion 531 and the second portion 532 . An edge E2 is formed at the boundary between the second portion 532 and the cylindrical portion 510. As shown in FIG.

In such a configuration, the position of the edge E1, which is the portion of the seat surface 530 that is first pressed against the seat surface SS, is different from the position of the edge E2, which is the portion of the seat surface 530 that is most likely to be scratched. can be a position. As a result, it is possible to reduce the possibility that a scratch is formed at the position of the edge E1, like the spark plug described in Japanese Patent Application Laid-Open No. 2020-119687.

In this modified example, by further forming modified grooves 520 similar to those of the present embodiment, the possibility of outflow of combustion gas is further reduced. Note that the first inner surface 521 is parallel to the first portion 531 of the seat surface 530 before the spark plug 10 is attached to the internal combustion engine EG. Thus, even in a mode in which the first inner surface 521 is parallel to only a portion of the seat surface 530 instead of the entire seat surface 530, the same effects as in the present embodiment can be obtained.

The present embodiment has been described above with reference to specific examples. However, the present disclosure is not limited to these specific examples. Design modifications to these specific examples by those skilled in the art are also included in the scope of the present disclosure as long as they have the features of the present disclosure. Each element included in each specific example described above and its arrangement, conditions, shape, etc. are not limited to those illustrated and can be changed as appropriate. As long as there is no technical contradiction, the combination of the elements included in the specific examples described above can be changed as appropriate.

EG: Internal combustion engine 10: Spark plug 20: Insulator 30: Center electrode 50: Metal shell 60: Ground electrode 200: Shaft hole 520: Deformation groove 530: Seat surface

Claims (5)

A spark plug (10) mounted in an internal combustion engine (EG), comprising:
an insulator (20) having a shaft hole (200);
a center electrode (30) held by the insulator at a position corresponding to one end along the central axis (CX) of the axial hole;
a metal shell (50) that holds the insulator from the outer peripheral side;
a ground electrode (60) extending from the metal shell and partially facing the center electrode;
The metal shell is
A sheet that is a surface that is pressed against the internal combustion engine and that has an outer diameter of a cross section when cut perpendicular to the central axis that increases toward the opposite side of the central electrode along the central axis. a face (530),
A spark plug, wherein a deformed groove (520) extending in a circumferential direction surrounding the central axis is formed in the metal shell at a position spaced apart from the seat surface along the central axis. 2. The spark plug according to claim 1, wherein an inner surface of said deformation groove on the side of said seat surface and at least a portion of said seat surface are parallel to each other. Before being attached to the internal combustion engine,
2. A first inner surface (521), which is an inner surface on the side of the seat surface, and a second inner surface (522), which is an inner surface on the side opposite to the seat surface, of the deformed groove are parallel to each other. The spark plug described in . The deformed groove is
2. The spark plug according to claim 1, wherein the spark plug is recessed toward the central axis along a direction perpendicular to the central axis. 5. The spark plug according to any one of claims 1 to 4, wherein the deformation groove is formed over the entire circumference of the metallic shell along the circumferential direction.

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