JP2021170475A - Spark plug - Google Patents

Abstract

To provide a spark plug capable of preventing preignition.SOLUTION: A spark plug 1 comprises an insulator 2, a center electrode 3, a housing 4, and a plug cover 5. The plug cover 5 has at least one injection hole 53. The spark plug 1 is configured such that the same can cause electric discharge between an inner wall of a spark formation injection hole 50, which is at least one of the injection holes 53, and an electrode tip part 31. The center electrode 3 has: a central base material 32; and a central core material 33 which is disposed in the central base material 32 and has heat conductivity higher than that of the central base material 32. If a length from a protrusion root 31R of the electrode tip part 31 to a protrusion tip 31T of the electrode tip part 31 in a longitudinal direction of the electrode tip part 31 is defined as a length L, then a tip position of the central core material 33 is located further on the protrusion tip 31T side than a position P which is L/3 away from the projection root 31R to the protrusion tip 31T side.SELECTED DRAWING: Figure 2

Description

The present invention relates to a spark plug.

Spark plugs are used as ignition means in internal combustion engines such as vehicle engines. Patent Document 1 discloses a spark plug in which a center electrode protruding from an insulator is covered with a plug cover. The plug cover is formed with a plurality of through holes that penetrate the plug cover, and the tip of the center electrode is inserted into an insertion hole that is one of the through holes. The spark plug described in Patent Document 1 has a discharge gap for generating a spark discharge between the center electrode and the inner wall of the insertion hole. Further, the spark plug described in Patent Document 1 is configured so that the discharge spark generated in the discharge gap can be extended toward the main combustion chamber side.

Japanese Unexamined Patent Publication No. 2016-95986

The spark plug described in Patent Document 1 has room for improvement from the viewpoint of suppressing the occurrence of pre-ignition.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a spark plug capable of suppressing the occurrence of pre-ignition.

One aspect of the present invention is a tubular insulating insulator (2) and
A central electrode (3) that is held on the inner peripheral side of the insulating insulator and has an electrode tip portion (31) that protrudes from the insulating insulator toward the plug tip side.
A housing (4) arranged on the outer peripheral side of the insulator and
A plug cover (5) provided at a portion on the plug tip side of the housing so as to cover the sub-combustion chamber (100) in which the electrode tip is arranged is provided.
The plug cover is provided with at least one injection hole (53) that communicates the sub-combustion chamber to the outside.
It is configured so that an electric discharge can be formed between the inner wall of the spark forming nozzle (50), which is at least one of the nozzles, and the tip of the electrode.
The center electrode has a central base material (32) and a central core material (33) arranged in the central base material and having a higher thermal conductivity than the central base material.
In the longitudinal direction of the electrode tip, when the length from the protruding root (31R) of the electrode tip to the protruding tip (31T) of the electrode tip is length L, the tip position of the central core material is The spark plug (1) is located at a position closer to the protruding tip side than a position L / 3 away from the protruding root side toward the protruding tip side.

The spark plug of the above aspect is configured to be capable of forming an electric discharge between the tip of the electrode and the inner wall of the spark forming nozzle. Therefore, for example, by appropriately adjusting the ignition timing, the discharge spark can be extended both in the sub-combustion chamber and outside the sub-combustion chamber.

However, when the electrode tip is configured so that a discharge can be formed between the electrode tip and the inner wall of the spark-forming injection hole, the electrode tip must be formed in the vicinity of the spark-forming injection hole. It tends to be necessary to lengthen it, and there is a concern that pre-ignition may occur.

Therefore, in the longitudinal direction of the electrode tip, when the length from the protruding root of the electrode tip to the protruding tip of the electrode tip is length L, the tip position of the central core material is from the protruding root to the protruding tip side. It is located on the protruding tip side of the position L / 3 away. By forming the central core material up to the tip side of the electrode tip to some extent in this way, it is easy to improve the heat dissipation of the electrode tip, and the occurrence of pre-ignition can be suppressed.

As described above, according to the above aspect, it is possible to provide a spark plug capable of suppressing the occurrence of pre-ignition.
The reference numerals in parentheses described in the scope of claims and the means for solving the problem indicate the correspondence with the specific means described in the embodiments described later, and limit the technical scope of the present invention. It's not a thing.

A partial cross-sectional front view of a spark plug attached to an internal combustion engine according to the first embodiment. FIG. 3 is a cross-sectional view of a tip portion of a spark plug according to the first embodiment. The figure which saw the plug cover and the ground electrode in Embodiment 1 from the plug base end side. FIG. 5 is a partially exploded sectional view of a tip portion of a spark plug according to the first embodiment. FIG. 5 is an enlarged cross-sectional view of the periphery of the melt-solidified portion of the spark plug in the first embodiment. FIG. 5 is a cross-sectional view of the tip of a spark plug showing how the discharge spark is stretched in the expansion stroke in the first embodiment. FIG. 5 is a cross-sectional view of a tip portion of a spark plug showing how the discharge spark is stretched in the compression stroke in the first embodiment. FIG. 2 is an enlarged cross-sectional view of the periphery of the melt-solidified portion of the spark plug in the second embodiment. FIG. 3 is an enlarged cross-sectional view of the periphery of the melt-solidified portion of the spark plug in the third embodiment. FIG. 4 is an enlarged cross-sectional view of the periphery of the melt-solidified portion of the spark plug in the fourth embodiment. FIG. 5 is an enlarged cross-sectional view of the periphery of the melt-solidified portion of the spark plug according to the fifth embodiment. FIG. 6 is an enlarged cross-sectional view of the periphery of the melt-solidified portion of the spark plug in the sixth embodiment. FIG. 6 is a cross-sectional view of a tip portion of a spark plug according to the seventh embodiment. 8 is a cross-sectional view of the tip of the spark plug according to the eighth embodiment. FIG. 5 is a cross-sectional view of a tip portion of a spark plug in a modified form of the eighth embodiment. 9 is a cross-sectional view of the tip of the spark plug according to the ninth embodiment. FIG. 5 is a cross-sectional view of the tip of the spark plug according to the tenth embodiment. The front view of the tip part of the spark plug in Embodiment 10. 11 is a cross-sectional view of the tip of the spark plug according to the eleventh embodiment. 12 is a cross-sectional view of the tip of the spark plug according to the twelfth embodiment. FIG. 12 is a cross-sectional view of the tip of a spark plug showing how the discharge spark is stretched in the expansion stroke in the twelfth embodiment. FIG. 3 is a cross-sectional view of the tip of the spark plug according to the thirteenth embodiment. FIG. 13 is a cross-sectional view of the tip of a spark plug showing how the discharge spark is stretched in the expansion stroke in the thirteenth embodiment.

(Embodiment 1)
An embodiment of the spark plug will be described with reference to FIGS. 1 to 7.
As shown in FIG. 2, the spark plug 1 of this embodiment includes an insulator 2, a center electrode 3, a housing 4, and a plug cover 5. The insulating insulator 2 has a tubular shape. The center electrode 3 is held on the inner peripheral side of the insulating insulator 2. The center electrode 3 has an electrode tip portion 31 projecting from the insulating insulator 2 toward the plug tip end side. The housing 4 is arranged on the outer peripheral side of the insulating insulator 2. The plug cover 5 is provided at a portion of the housing 4 on the plug tip side so as to cover the sub-combustion chamber 100 in which the electrode tip 31 is arranged. The plug cover 5 is provided with at least one injection hole 53 that communicates the auxiliary combustion chamber 100 with the outside.

The spark plug 1 is configured to be able to form an electric discharge between the inner wall of the spark forming injection hole 50, which is at least one of the injection holes 53, and the electrode tip portion 31. In this embodiment, which will be described in detail later, an electric discharge is formed between the inner wall of the spark forming injection hole 50 and the electrode tip portion 31 in the expansion stroke of the internal combustion engine.

The center electrode 3 has a center base material 32 and a center core material 33 arranged in the center base material 32 and having a higher thermal conductivity than the center base material 32. In the longitudinal direction of the electrode tip portion 31, when the length from the protruding root 31R of the electrode tip 31 to the protruding tip 31T of the electrode tip 31 is length L, the tip position of the central core material 33 is the protruding root 31R. It is located on the protruding tip 31T side of the position P which is L / 3 away from the protruding tip 31T side.
Hereinafter, this form will be described in detail.

In this embodiment, the central axis of the spark plug 1 is referred to as the plug central axis C. The direction in which the plug central axis C extends is called the Z direction. The Z direction coincides with the axial direction of the cylindrical housing 4 and the axial direction of the tubular insulator 2. Further, as will be described in detail later, the axial direction of the plug central axis C and the spark forming injection hole 50 is the same. The side of the spark plug 1 on which the sub-combustion chamber 100 is formed (for example, the lower side of FIGS. 1 and 2) on one side in the Z direction is referred to as the plug tip end side, and the opposite side is referred to as the plug base end side. .. Further, a direction orthogonal to the Z direction in which the center electrode 3 and the ground electrode 7 described later face each other is referred to as a Y direction. The direction orthogonal to both the Y direction and the Z direction is called the Y direction. The radial direction of the spark plug 1 is referred to as the radial direction of the plug. The circumferential direction of the spark plug 1 is called the plug circumferential direction.

The spark plug 1 can be used as an ignition means in an internal combustion engine such as an automobile or a cogeneration engine, for example. The end of the spark plug 1 on the plug base end side is connected to an ignition coil (not shown), and the end of the spark plug 1 on the plug tip side is arranged in the combustion chamber of the internal combustion engine. As shown in FIG. 1, the combustion chamber is an area surrounded by the cylinder block, the piston, and the cylinder head 11 of the internal combustion engine. Among the combustion chambers, the outer side of the spark plug 1 is the main combustion chamber 12 and the spark plug 1. The inside of the plug cover 5 described later is referred to as an auxiliary combustion chamber 100. The spark plug 1 is attached to the cylinder head 11 of the internal combustion engine in the housing 4.

The housing 4 is formed of a material having conductivity, thermal conductivity, and heat resistance in a cylindrical shape. For example, the housing 4 is made of a nickel-based alloy. As shown in FIGS. 1 and 2, a mounting screw portion 41 is formed on the outer peripheral portion of the housing 4. As shown in FIG. 1, the mounting screw portion 41 is a portion screwed into the female screw hole 111 provided in the cylinder head 11. When the spark plug 1 is attached to the cylinder head 11, the portion of the spark plug 1 on the plug tip side of the mounting screw portion 41 is exposed to the inside of the main combustion chamber 12. As shown in FIG. 1, when the amount of protrusion from the cylinder head 11 is EQ, the amount of protrusion EQ is 5 mm or less. The housing 4 holds an insulating insulator 2 at its inner peripheral portion.

The insulating insulator 2 is formed by forming, for example, a material having electrical insulation in a cylindrical shape. Although not shown, the insulating insulator 2 is locked to the housing 4 in the Z direction. Although not shown, a packing for ensuring a sealing property between the insulating insulator 2 and the housing 4 is provided at the locking portion. As shown in FIG. 2, the insulating insulator 2 has a shaft hole 20 formed through in the Z direction, and holds the center electrode 3 in the inner peripheral portion of the shaft hole 20.

The center electrode 3 is formed of, for example, a metal formed in a long shape in the Z direction. The center electrode 3 includes a central base material 32 and a central core material 33 which is arranged in the central base material 32 and is made of a material having a higher thermal conductivity than the central base material 32. The core base material 32 is made of, for example, a nickel-based alloy. The central core material 33 is made of copper or the like. The central base material 32 has a hollow shape in which the end portion on the plug base end side is open, and the central core material 33 is arranged so as to fill the inner space of the central base material 32. The end of the central core material 33 on the plug base end side is exposed from the opening on the plug base end side of the central base material 32. Further, the central core material 33 has a lower melting point than the central base material 32, and the central core material 33 is formed so as not to be exposed to the sub-combustion chamber 100.

The center electrode 3 includes an electrode tip portion 31 protruding from the insulating insulator 2 toward the plug tip end side. The electrode tip portion 31 has a columnar shape extending in the Z direction. The electrode tip portion 31 projects toward the plug tip side from the end surface of the housing 4 on the plug tip side.

As shown in FIG. 2, the length from the protruding root 31R to the protruding tip 31T of the electrode tip 31 in the longitudinal direction of the electrode tip 31 is defined as the length L. The protruding root 31R is at the same position as the position of the opening end on the plug tip side of the shaft hole 20 of the insulating insulator 2 in the Z direction. At this time, the tip position of the central core material 33 is located on the protruding tip 31T side of the position P L / 3 away from the protruding root 31R on the protruding tip 31T side. In the present embodiment, the tip position of the central core material 33 is located on the protruding tip 31T side rather than the position L / 2 away from the protruding root 31R on the protruding tip 31T side.

The electrode tip portion 31 includes an electrode tip main body 311 composed of a central base material 32 and a central core material 33, and a central tip 312 arranged on the side surface of the electrode tip main body 311. The electrode tip body 311 includes a first portion 311a, a second portion 311b, and a third portion 311c in this order from the plug base end side. The first portion 311a has an outer diameter equivalent to the portion of the center electrode 3 arranged inside the portion on the plug tip side of the shaft hole 20, and has a columnar shape along the Z direction. The second portion 311b is formed so that the diameter is reduced toward the plug tip side from the first portion 311a. The third portion 311c extends from the second portion 311b toward the tip of the plug and has a columnar shape along the Z direction. The third portion 311c is formed so that the outer diameter is smaller than that of the first portion 311a.

In the present embodiment, the position of the end portion of the central core material 33 on the plug tip end side is formed near the boundary portion between the first portion 311a and the second portion 311b in the Z direction. Not limited to this, the position of the end portion of the center electrode 3 on the plug tip side may be located on the plug base end side or on the plug tip side of the boundary portion in the Z direction, for example. good.

As shown in FIGS. 2 and 3, the third portion 311c is formed with flat surface portions 313 on both sides in the X direction. The third portion 311c has a shape in which both ends of a cylinder extending in the Z direction in the X direction are face-cut. In FIG. 3, the tip surface 314 of the electrode tip 31 is projected onto the plug cover 5 in the Z direction by a broken line. The plane portion 313 is formed on a plane orthogonal to the X direction. A central chip 312 is arranged on one of the flat surface portions 313.

The center tip 312 is made of a material having higher wear resistance than the electrode tip body 311 and is made of, for example, a precious metal. The central chip 312 is formed in a rectangular plate shape having a thickness in the normal direction (that is, the X direction) of the flat surface portion 313 on which the central chip 312 is arranged. As shown in FIG. 2, the position of the end portion of the central tip 312 on the plug tip side coincides with the position of the end portion of the electrode tip body 311 on the plug tip side. The central tip 312 forms a discharge gap G with the ground electrode 7. The discharge gap G is a space that forms an initial spark discharge. As will be described later, the discharge spark moves by being pushed by the air flow in the sub-combustion chamber 100, but the initial spark discharge means the discharge spark before moving.

As shown in FIGS. 2 and 4, a plug cover 5 for partitioning the sub-combustion chamber 100 is arranged at the end of the housing 4 on the plug tip side. The plug cover 5 is formed in a cup shape that opens toward the base end side of the plug. That is, the plug cover 5 includes a cover side wall 51 that covers the sub-combustion chamber 100 in the circumferential direction of the plug, and a disk-shaped cover bottom wall 52 that covers the sub-combustion chamber 100 from the plug tip side.

As shown in FIGS. 4 and 5, the portion of the housing 4 on the plug tip end side is provided with a housing protrusion 42 projecting toward the plug tip end on the entire circumference of the housing 4. The plug cover 5 is assembled to the housing 4 so that the inner peripheral surface of the cover side wall 51 is aligned with the outer peripheral surface of the housing protrusion 42. A chamfered portion 421 is formed at a corner portion between the tip surface and the inner peripheral surface of the housing protruding portion 42. This makes it easy to reduce the surface area of the housing 4 facing the sub-combustion chamber 100.

Then, as shown in FIG. 5, the housing 4 and the plug cover 5 are welded from the outer peripheral side on the entire circumference. As a result, the melt-solidified portion 6 in which a part of the housing 4 and a part of the plug cover 5 are melted and solidified is formed in an annular shape. Here, when the width of the surface of the cover side wall 51 of the plug cover 5 on the plug base end side is the width W, the length 6L of the melt-solidified portion 6 in the plug radial direction is larger than W / 2. In this embodiment, the housing 4 and the plug cover 5 are formed separately, but these may be formed by one member. In addition, except for FIG. 5, the melt-solidified portion is not shown.

As shown in FIGS. 2 to 5, the plug cover 5 has a cover base material 54 and a cover core material 55 arranged in the cover base material 54 and having a higher thermal conductivity than the cover base material 54. For example, the cover base material 54 is made of a nickel-based alloy, and the cover core material 55 is made of copper. Most of the plug cover 5 is made of a cover base material 54. The cover base material 54 has a groove portion 56 that opens to the plug base end side at a portion that constitutes the cover side wall 51, and the cover core material 55 fills the region inside the groove portion 56. The cover core material 55 is opened from the cover base material 54 to the plug base end side. The cover core material 55 is arranged all around. Further, the cover core material 55 has a lower melting point than the cover base material 54, and the cover core material 55 is formed so as not to be exposed to the sub-combustion chamber 100 and all the injection holes 53.

As shown in FIGS. 2 and 3, the plug cover 5 has a spark forming injection hole 50 in a region facing the tip surface 314 of the electrode tip portion 31 in the Z direction. The spark forming injection hole 50 is formed so as to penetrate the cover bottom wall 52 in the Z direction. The axial direction of the spark forming injection hole 50 is formed to be the same as the Z direction.

As shown in FIG. 2, the inner wall of the spark forming injection hole 50 covers at least a part of the enlarged surface portion 501 in which the area of the cross section orthogonal to the Z direction increases toward the sub-combustion chamber 100 side in the Z direction. Have in. The area of the cross section of the spark forming injection hole 50 including the enlarged surface portion 501 orthogonal to the Z direction is the area of the inner region of the spark forming injection hole 50 appearing in the cross section. In the present embodiment, the inner wall of the spark forming injection hole 50 includes a cylindrical surface portion 502 and an enlarged surface portion 501 in this order from the plug tip side.

The cylindrical surface portion 502 has a cylindrical shape formed straight in the Z direction. That is, the cylindrical surface portion 502 has a circular shape similar to each other at each position in the Z direction. The end of the cylindrical surface portion 502 on the plug tip side is an outer opening 503 that opens toward the plug tip side. An enlarged surface portion 501 is formed from the end portion of the cylindrical surface portion 502 on the plug base end side to the plug base end side.

The enlarged surface portion 501 is formed in a tapered shape whose diameter increases toward the plug base end side. That is, the enlarged surface portion 501 has a circular shape similar to each other at each position in the Z direction, and the cross-sectional area orthogonal to the Z direction in the inner region of the enlarged surface portion 501 increases toward the plug base end side. .. The end of the enlarged surface portion 501 on the plug base end side is an inner opening 504 that opens on the plug base end side. The spark forming injection hole 50 is configured such that the area of the inner opening 504 on the side of the auxiliary combustion chamber 100 is larger than the area of the outer opening 503 on the outer side of the spark plug 1.

As shown in FIGS. 2 and 3, the inner region of the spark forming injection hole 50 and the tip surface 314 of the electrode tip portion 31 are formed at positions where they overlap each other in the Z direction. The tip surface 314 of the electrode tip portion 31 means the surface of the electrode tip portion 31 on the plug tip side that is closest to the plug tip side. In the present embodiment, the electrode tip body 311 and the center tip 312 constituting the electrode tip 31 have the same end positions on the plug tip side, so that the tip surface 314 of the electrode tip 31 is the electrode tip body 311. It is the tip surface of both the center chip 312 and the center chip 312. The area of the inner opening 504 on the side of the auxiliary combustion chamber 100 in the spark forming injection hole 50 is larger than the tip surface 314 of the electrode tip 31. As shown in FIG. 3, when viewed from the Z direction, at least a part of the inner opening 504 is formed on the outer peripheral side of the tip surface 314 of the electrode tip 31. In the present embodiment, when viewed from the Z direction, the entire inner opening 504 is formed on the outer peripheral side of the tip surface 314 of the electrode tip 31. Further, when viewed from the Z direction, the entire outer opening 503 is formed so as to fit inside the tip surface 314 of the electrode tip 31.

As shown in FIGS. 2 to 4, a ground electrode 7 is provided on the inner wall surface of the plug cover 5 (that is, the surface on the side of the auxiliary combustion chamber 100). The ground electrode 7 has a ground body 71 and a ground tip 72.

The grounding main body 71 is formed in a rectangular plate shape extending in the Z direction. The thickness direction of the grounding main body 71 coincides with the thickness direction of the central chip 312. The end of the grounding main body 71 on the plug tip side is joined to the vicinity of the inner opening 504 on the inner wall surface of the plug cover 5. In the present embodiment, the end of the grounding main body 71 on the plug tip side is joined to a region on the inner wall surface of the plug cover 5 slightly distant from the inner opening 504. The portion of the grounding main body 71 on the plug base end side faces the central chip 312 of the center electrode 3 in the X direction.

As shown in FIGS. 2 and 4, the grounding main body 71 includes a grounding base material 73 and a grounding core material 74 made of a material having a higher thermal conductivity than the grounding base material 73. The grounding base material 73 is made of, for example, a nickel-based alloy, and the grounding core material 74 is made of copper or the like. The grounding base material 73 has a grounding recess 75 recessed from the end edge on the plug tip side to the plug base end side, and the grounding core material 74 fills the region inside the grounding recess 75. The grounding core material 74 is open to the tip end side of the plug from the grounding base material 73, and is connected to the inner surface of the plug cover 5. Further, the grounding core material 74 has a lower melting point than the grounding base material 73, and the grounding core material 74 is formed so as not to be exposed to the sub-combustion chamber 100 and all the injection holes 53. A grounding tip 72 is provided on the surface of the grounding body 71 on the plug base end side on the side of the center electrode 3 so as to face the center tip 312 in the X direction.

The grounding tip 72 is made of a material having a higher wear resistance than the grounding main body 71, and is made of, for example, a precious metal. The grounding tip 72 is formed in a rectangular plate shape, and is arranged so that the thickness direction thereof coincides with the thickness direction of the center tip 312. The position of the end portion of the grounding tip 72 on the plug base end side coincides with the position of the end portion of the grounding main body 71 on the plug base end side. Further, as shown in FIG. 3, the positions of both ends of the grounding tip 72 in the width direction (that is, the Y direction) orthogonal to the Z direction coincide with the positions of both ends of the grounding main body 71 in the Y direction.

As shown in FIG. 3, the dimensions of the grounding chip 72 and the dimensions of the center chip 312 in the Y direction are equivalent to each other. Further, as shown in FIG. 2, the end of the grounding tip 72 on the plug base end side protrudes toward the plug base end side of the center tip 312, and the end of the grounding tip 72 on the plug tip end side is the center tip 312. It is located on the plug base end side of the plug tip end side. A discharge gap G is formed between the grounding tip 72 and the center tip 312. The discharge gap G is a space between the grounding tip 72 and the central tip 312 in the opposite direction (that is, the X direction) between the grounding tip 72 and the central tip 312. As shown in FIG. 3, the discharge gap G is arranged at a position where at least a part thereof overlaps the inner region of the inner opening 504 in the Z direction.

As shown in FIG. 2, the plug cover 5 has a plurality of injection holes 53 penetrating the plug cover 5 in addition to the spark forming injection holes 50. Hereinafter, the term "injection hole 53" means an injection hole 53 other than the spark-forming injection hole 50 unless otherwise specified. The plurality of injection holes 53 are formed on the outer peripheral side in the plug radial direction with respect to the spark formation injection holes 50. Each injection hole 53 is formed so as to be inclined toward the outer peripheral side in the plug radial direction toward the plug tip side. The plurality of injection holes 53 are formed at equal intervals in the circumferential direction of the plug. The number, shape, arrangement location, etc. of the injection holes 53 are appropriately determined upon request.

Next, with reference to FIGS. 6 and 7, a state in which the discharge spark S formed in the discharge gap G in the spark plug 1 of the present embodiment is stretched will be described. The spark plug 1 of the present embodiment is controlled to generate an electric discharge in the expansion stroke (that is, after top dead center; ATDC) or the compression stroke (that is, before top dead center; BTDC) of the internal combustion engine. The way in which the discharge of the spark plug 1 is extended differs depending on whether the discharge is generated in the expansion stroke of the internal combustion engine or the discharge in the compression stroke.

First, with reference to FIG. 6, a case where a spark discharge is generated in the discharge gap G in the expansion stroke will be described. In the expansion stroke, an air flow F1 flowing from the sub-combustion chamber 100 side toward the main combustion chamber 12 side is generated around the spark forming injection hole 50. Further, the initial discharge spark generated in the discharge gap G occurs, for example, between the center chip 312 and the ground chip 72 where the space distance between the center electrode 3 and the ground electrode 7 is the shortest.

The initial discharge spark S is pushed by the above-mentioned airflow F1, and the portion between the two starting points is greatly extended toward the plug tip side, and at the same time, the starting point of the discharge spark S on the ground electrode 7 side is from the ground electrode 7. It moves on the inner wall of the spark forming injection hole 50 toward the tip of the plug, and eventually moves to the vicinity of the end of the inner wall of the spark forming injection hole 50 on the tip side of the plug. In this way, a discharge is formed between the spark forming injection hole 50 and the electrode tip portion 31 of the center electrode 3. Then, the stretched discharge spark S is formed from the spark forming injection hole 50 on the plug tip side, that is, in the main combustion chamber 12, and directly ignites the air-fuel mixture in the main combustion chamber 12. For convenience, FIGS. 6 and 7 below show an initial discharge spark and a stretched state of the initial discharge spark.

At the time of cold start when the internal combustion engine such as an automobile engine is operated in a cold state, the ignition timing may be significantly delayed in order to warm up and activate the catalyst at an early stage. Ignition occurs during the expansion stroke. When a spark discharge is generated in the expansion stroke, there are the following merits. At the time of cold start or the like, the members facing the auxiliary combustion chamber 100 such as the plug cover 5, the housing 4, and the insulating insulator 2 may be at a low temperature. Therefore, especially at the time of cold start or the like, the discharge spark is extended toward the main combustion chamber 12 to suppress the contact area between the initial flame and the plug cover 5 or the like. As a result, it is easy to suppress cold damage in which the heat of the initial flame is taken away by the plug cover 5 and the like. As a result, the ignitability at the time of cold start or the like can be improved.

Next, with reference to FIG. 7, a case where a spark discharge is generated in the discharge gap G in the compression stroke will be described. In the compression stroke, an air flow F2 flowing from the main combustion chamber 12 side to the sub-combustion chamber 100 side is generated around the spark forming injection hole 50. When the airflow F2 flows from the main combustion chamber 12 into the cylindrical surface portion 502 of the spark forming injection hole 50, the flow velocity is locally increased due to the sharp decrease in the cross-sectional area of the flow path. Then, when the airflow F2 flows from the cylindrical surface portion 502 into the enlarged surface portion 501, the flow path cross-sectional area gradually expands, so that the airflow is diffused and the flow velocity decreases. Then, the airflow F2 that has reached the sub-combustion chamber 100 heads toward the plug base end side so as to avoid the center electrode 3, and a part of the airflow F2 passes through the discharge gap G.

Then, the initial discharge spark S generated in the discharge gap G occurs, for example, between the center chip 312 and the ground chip 72 where the space distance between the center electrode 3 and the ground electrode 7 is the shortest. Then, the initial discharge spark S is pushed by the diffused airflow F2 passing through the discharge gap G as described above, and the portion between the two starting points is greatly extended toward the plug base end side. Then, the discharge spark S is greatly extended into the sub-combustion chamber 100 and directly ignites the air-fuel mixture in the sub-combustion chamber 100 to form a flame in the sub-combustion chamber 100. The flame grown in the sub-combustion chamber 100 is ejected as a flame jet from the spark-forming injection hole 50 and the other injection holes 53 into the main combustion chamber 12. Here, since the cross-sectional area of the flow path of the spark-forming injection hole 50 decreases toward the plug tip side, the momentum of the flame jet ejected through the spark-forming injection hole 50 increases. As a result, the combustion period of the internal combustion engine can be shortened.

For example, when the members facing the sub-combustion chamber 100 such as the plug cover 5, the housing 4, the insulator 2, and the center electrode 3 become hot to some extent, a spark discharge is generated in the compression stroke except at the time of cold start. Can be done.

Next, the action and effect of this embodiment will be described in detail.
The spark plug 1 of the present embodiment is configured so that a discharge can be formed between the electrode tip portion 31 and the inner wall of the spark forming injection hole 50. Therefore, for example, by appropriately adjusting the ignition timing, the discharge spark can be extended both inside the sub-combustion chamber 100 and outside the sub-combustion chamber 100.

However, when the electrode tip portion 31 and the inner wall of the spark forming injection hole 50 are configured so that a discharge can be formed, the electrode tip portion 31 needs to be formed in the vicinity of the spark forming injection hole 50. It is likely that the electrode tip 31 needs to be lengthened, and there is a concern that pre-ignition may occur.

Therefore, in the longitudinal direction of the electrode tip portion 31, when the length from the protruding root 31R of the electrode tip portion 31 to the protruding tip 31T of the electrode tip portion 31 is length L, the tip position of the central core material 33 is projected. It is located on the protruding tip 31T side rather than the position L / 3 away from the root 31R on the protruding tip 31T side. By forming the central core material 33 up to the tip end side of the electrode tip portion 31 to some extent in this way, it is easy to improve the heat dissipation of the electrode tip portion 31, and the occurrence of pre-ignition can be suppressed.

Further, the plug cover 5 has a cover base material 54 and a cover core material 55 arranged in the cover base material 54 and having a higher thermal conductivity than the cover base material 54. Therefore, the heat dissipation of the plug cover 5 can be improved, and the occurrence of pre-ignition can also be suppressed.

Further, the cover core material 55 is formed so as not to be exposed to the sub-combustion chamber 100 and all the injection holes 53. Therefore, when the spark plug 1 is used, the temperature of the entire plug cover 5 becomes high, and the cover core material 55 can be prevented from melting to the outside.

As described above, according to this embodiment, it is possible to provide a spark plug capable of suppressing the occurrence of pre-ignition.

(Embodiment 2)
As shown in FIG. 8, this embodiment has a triangular cross section as a whole, with the inner peripheral side surface of the housing protrusion 42 inclined toward the inner peripheral side toward the plug tip side with respect to the first embodiment. It is a form formed in.

Others are the same as in the first embodiment.
In addition, among the codes used in the second and subsequent embodiments, the same codes as those used in the above-described embodiments represent the same components and the like as those in the above-mentioned embodiments, unless otherwise specified.

This embodiment also has the same effect as that of the first embodiment.

(Embodiment 3)
As shown in FIG. 9, this embodiment has a shape in which the corner portion between the tip surface and the inner peripheral surface of the housing protrusion 42 is a rounded portion 422 with respect to the first embodiment. be.
Others are the same as in the first embodiment.

This embodiment also has the same effect as that of the first embodiment.

(Embodiment 4)
As shown in FIG. 10, this embodiment is a form in which the protruding length of the housing protruding portion 42 is changed with respect to the first embodiment. In the present embodiment, the position of the housing protrusion 42 on the plug tip end side is the plug base end side of the boundary portion between the cover side wall 51 and the cover bottom wall 52 (that is, the curved surface portion connecting the cover side wall 51 and the cover bottom wall 52). It is formed at the position of the end of. That is, the housing protrusion 42 is formed so as to face the surface of the cover side wall 51 formed straight along the Z direction.
Others are the same as in the first embodiment.

In this embodiment, it is easy to increase the facing area between the plug cover 5 and the housing 4, and it is easy to promote heat transfer from the plug cover 5 to the housing 4. Therefore, the heat of the plug cover 5 is easily dissipated through the housing 4, and thus the occurrence of pre-ignition is easily suppressed.
In addition, it has the same effect as that of the first embodiment.

(Embodiment 5)
As shown in FIG. 11, this embodiment is a form in which the length of the melt-solidified portion 6 in the plug radial direction is changed with respect to the first embodiment. The melt-solidified portion 6 is formed over the entire surface of the plug cover 5 on the plug base end side in the plug radial direction.
Others are the same as in the first embodiment.

In this embodiment, it is easier to promote heat dissipation from the plug cover 5 to the housing 4, and it is easier to suppress the occurrence of pre-ignition.
In addition, it has the same effect as that of the first embodiment.

(Embodiment 6)
As shown in FIG. 12, this embodiment is a form in which the length of the melt-solidified portion 6 in the plug radial direction is changed with respect to the fifth embodiment. In the present embodiment, the inner peripheral side end portion of the melt-solidified portion 6 is formed up to a part of the housing protruding portion 42.
Others are the same as in the fifth embodiment.

Also in this embodiment, it has the same effect as that of the fifth embodiment.

(Embodiment 7)
As shown in FIG. 13, this embodiment is an embodiment in which the formation range of the central core material 33 in the center electrode 3 is changed with respect to the first embodiment. In the present embodiment, the end portion of the central core material 33 on the plug tip side is formed up to the vicinity of the end portion of the center base material 32 on the plug tip side. In the present embodiment, the tip position of the central core member 33 is located on the protruding tip 31T side rather than the position 3L / 4 away from the protruding root 31R on the protruding tip 31T side. The end portion of the central core material 33 on the plug tip end side is located closer to the plug base end side than the plug tip end side surface of the center base material 32.
Others are the same as in the first embodiment.

In this embodiment, since the end portion of the central core material 33 on the plug tip side is formed up to the vicinity of the end portion of the central base material 32 on the plug tip side, it is easy to further improve the heat dissipation of the entire center electrode 3. As a result, it is easier to suppress the occurrence of pre-ignition.
In addition, it has the same effect as that of the first embodiment.

(Embodiment 8)
As shown in FIG. 14, this embodiment is a form in which the shape of the electrode tip portion 31 is changed from that of the seventh embodiment.

In the present embodiment, the electrode tip main body 311 of the electrode tip 31 (that is, the portion composed of the central base material 32) is the first portion 311a, the second portion 311b, and the third portion in order from the plug base end side, as in the first embodiment. It comprises a site 311c. Similar to the first embodiment, the first portion 311a has an outer diameter equivalent to the portion arranged inside the portion on the plug tip side of the shaft hole 20 in the center electrode 3, and has a columnar shape along the Z direction. It is presented. The surface of the second portion 311b on the ground electrode 7 side in the X direction is inclined so as to be toward the anti-ground electrode 7 side in the X direction toward the plug tip side. The third portion 311c is formed along the Z direction from the portion of the second portion 311b on the plug tip side to the plug tip side. The surface of the third portion 311c on the ground electrode 7 side in the X direction is formed on a flat surface, and the central chip 312 is arranged on the surface.

The central core material 33 is smaller than the central base material 32 and is arranged in the central base material 32 so as to have a similar shape to the central core material 33. That is, the central core material 33 has a shape corresponding to the central base material 32.
Others are the same as in the seventh embodiment.

Also in this embodiment, it has the same effect as that of the seventh embodiment.

In addition, the central core material 33 may have a shape corresponding to the shape of the central base material 32. For example, FIG. 15 shows an example in which the surface 311d on the anti-ground electrode 7 side in the X direction of the third portion 311c becomes a tapered surface that is inclined so as to be toward the ground electrode 7 side in the X direction toward the plug tip side. As shown, even in such a case, the central core material 33 can be formed into a shape similar to that of the central base material 32.

(Embodiment 9)
As shown in FIG. 16, this embodiment is a form in which the shape of the electrode tip main body 311 is changed from that of the first embodiment. In the present embodiment, the second portion 311b is formed in a tapered shape whose diameter decreases toward the plug tip side. The taper angle of the second portion 311b, that is, the angle between one surface of the second portion 311b and the other surface appearing in the cross section passing through the plug central axis C is 45 ° or more and less than 180 °. In the Z direction, the position of the second portion 311b is located closer to the plug tip side than the central position of the electrode tip portion 31.
Others are the same as in the first embodiment.

In this embodiment, a portion having a large outer shape of the center electrode 3 (that is, the first portion 311a) can be formed up to the position on the plug tip side as much as possible, and it is easy to secure the heat capacity of the center electrode 3 and the pre-ignition. It is easier to prevent the occurrence.
In addition, it has the same effect as that of the first embodiment.

(Embodiment 10)
As shown in FIGS. 17 and 18, this embodiment is a form in which the formation range of the cover core material 55 is changed with respect to the first embodiment.

In this embodiment, the cover core material 55 is formed on substantially the entire plug cover 5. The cover core material 55 is formed so as not to be exposed to each injection hole 53 including the sub-combustion chamber 100 and the spark formation injection hole 50. Others are the same as in the first embodiment.

In this embodiment, the heat dissipation of the plug cover 5 is more likely to be improved, and the occurrence of pre-ignition is more likely to be suppressed.
In addition, it has the same effect as that of the first embodiment.

(Embodiment 11)
As shown in FIG. 19, this embodiment is an embodiment in which the configuration of the grounding core material 74 is changed with respect to the tenth embodiment. That is, in this embodiment, the ground core material 74 penetrates the inner surface of the plug cover 5 and is connected to the cover core material 55.
Others are the same as in the tenth embodiment.

In this embodiment, the heat of the ground electrode 7 is easily dissipated through the plug cover 5. Therefore, the occurrence of pre-ignition can be further suppressed.
In addition, it has the same effect as that of the tenth embodiment.

(Embodiment 12)
As shown in FIG. 20, this embodiment is a form in which the longitudinal direction of the ground electrode 7 is the X direction with respect to the first embodiment.

In the present embodiment, the ground electrode 7 is attached to the side wall 51 of the cover and is formed in a rectangular columnar shape extending in the radial direction of the plug. The grounding base material 73 has a grounding recess 75 that opens toward the outer peripheral side, and the grounding core material 74 is filled in the grounding recess 75. A grounding tip 72 is provided on the inner peripheral end surface of the grounding base material 73. The surface of the grounding tip 72 opposite to the grounding base 73 is opposed to the central tip 312 in the X direction.

In this embodiment, as shown in FIG. 21, when a discharge is generated in the discharge gap G in the expansion stroke of the internal combustion engine, the discharge spark S is pushed by the airflow F from the sub-combustion chamber 100 side to the main combustion chamber 12 side to discharge. The starting point of the spark S on the ground electrode 7 side moves to the inner wall of the spark forming injection hole 50, and the portion between the two starting points of the discharge spark S is eventually extended from the spark forming injection hole 50 to the main combustion chamber 12 side.
Others are the same as in the first embodiment.

This embodiment also has the same effect as that of the first embodiment.

(Embodiment 13)
In this embodiment, as shown in FIGS. 22 and 23, the ground electrode 7 is connected to the inner peripheral surface of the housing 4 with respect to the twelfth embodiment. The tip surface 314 of the electrode tip 31 is housed closer to the plug base end than the position of the end of the housing 4 on the plug tip side.

In this embodiment, as shown in FIG. 23, when a discharge is generated in the discharge gap G in the expansion stroke of the internal combustion engine, the discharge spark S is pushed by the airflow from the sub-combustion chamber 100 side to the main combustion chamber 12 side, and the discharge spark is generated. The starting point on the ground electrode 7 side of the above moves to the inner wall of the spark forming injection hole 50, and the portion between the two starting points of the discharge spark is eventually extended from the spark forming injection hole 50 to the main combustion chamber 12 side. If the discharge gap G is too far from the spark forming injection hole 50 toward the plug base end side, it is possible that the discharge spark does not move to the inner wall of the spark forming injection hole 50. Therefore, the discharge gap G is the ground contact of the discharge spark. It is formed near the spark forming injection hole 50 so that the starting point on the electrode 7 side shifts to the inner wall of the spark forming injection hole 50.
Others are the same as in the first embodiment.

This embodiment also has the same effect as that of the first embodiment.

The present invention is not limited to each of the above-described embodiments, and can be applied to various embodiments without departing from the gist thereof.

1 Spark plug 100 Sub-combustion chamber 3 Center electrode 31 Electrode tip 31R Protruding root 31T Protruding tip 32 Center base material 33 Center core material 5 Plug cover 50 Spark formation injection hole

Claims (3)

Cylindrical insulating insulator (2) and
A central electrode (3) that is held on the inner peripheral side of the insulating insulator and has an electrode tip portion (31) that protrudes from the insulating insulator toward the plug tip side.
A housing (4) arranged on the outer peripheral side of the insulator and
A plug cover (5) provided at a portion on the plug tip side of the housing so as to cover the sub-combustion chamber (100) in which the electrode tip is arranged is provided.
The plug cover is provided with at least one injection hole (53) that communicates the sub-combustion chamber to the outside.
It is configured so that an electric discharge can be formed between the inner wall of the spark forming nozzle (50), which is at least one of the nozzles, and the tip of the electrode.
The center electrode has a central base material (32) and a central core material (33) arranged in the central base material and having a higher thermal conductivity than the central base material.
In the longitudinal direction of the electrode tip, when the length from the protruding root (31R) of the electrode tip to the protruding tip (31T) of the electrode tip is length L, the tip position of the central core material is , The spark plug (1) located at a position closer to the protruding tip side than a position L / 3 away from the protruding root side toward the protruding tip side. The plug cover according to claim 1, further comprising a cover base material (54) and a cover core material (55) arranged in the cover base material and having a higher thermal conductivity than the cover base material. Spark plug. The spark plug according to claim 2, wherein the cover core material is not exposed to the sub-combustion chamber and all the injection holes.

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