JP2021170476A - Spark plug - Google Patents

Abstract

To provide a spark plug which allows improvement in ignitability.SOLUTION: A spark plug 1 comprises: a sub-combustion chamber 2; at least one injection hole 33 which brings the sub-combustion chamber 2 into communication with an outside; a center electrode 4 which has an electrode tip part 41 disposed inside the sub-combustion chamber 2; and a ground electrode 5 which forms a discharge gap G between itself and the center electrode 4. The spark plug 1 is configured such that the spark plug can cause electric discharge between an inner wall of a spark generation injection hole 30, which is at least one of the injection holes 33, and the electrode tip part 41. The discharge gap G is formed between a center discharge surface 410 facing an outer peripheral side of the electrode tip part 41 and a ground discharge surface 50 facing the outer peripheral side of the ground electrode 5. The discharge gap G and the spark generation injection hole 30 are formed at positions overlapping each other in a direction along the ground discharge surface 50.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 improving ignitability.

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 improving ignitability.

One aspect of the present invention is a center in which a sub-combustion chamber (2), at least one injection hole (33) communicating the sub-combustion chamber to the outside, and an electrode tip portion (41) are arranged in the sub-combustion chamber. The inner wall of the spark-forming injection hole (30), which is at least one of the injection holes, and the ground electrode (5) for forming a discharge gap (G) between the electrode (4) and the center electrode. A spark plug (1) configured to form a discharge between the tip of the electrode and the tip of the electrode.
The discharge gap is formed between the central discharge surface (410) facing the outer peripheral side of the electrode tip and the ground discharge surface (50) facing the outer peripheral side of the ground electrode.
The discharge gap and the spark forming injection hole are located in a spark plug formed at a position where they overlap each other in a direction along the grounding discharge surface.

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.

The discharge gap is formed between the central discharge surface of the tip of the electrode facing the outer peripheral side and the ground discharge surface of the ground electrode facing the outer peripheral side. Further, the discharge gap and the spark forming injection hole are formed at positions where they overlap each other in the direction along the ground discharge surface. Therefore, the airflow passing through the discharge gap and the spark forming nozzle is likely to be formed smoothly. Therefore, regardless of whether the discharge spark is extended into the sub-combustion chamber or the discharge spark is extended outside the sub-combustion chamber, the discharge spark can be easily extended and the ignitability of the spark plug can be improved.

As described above, according to the above aspect, it is possible to provide a spark plug capable of improving ignitability.
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. FIG. 2 is a cross-sectional view taken along the line III-III. The perspective view of the electrode tip portion in Embodiment 1. FIG. The perspective view of the ground electrode in Embodiment 1. FIG. 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. The perspective view of the ground electrode in the modified form of Embodiment 1. FIG. 2 is a cross-sectional view of a tip portion of a spark plug according to a second embodiment. FIG. 9 is a cross-sectional view taken along the line AA. The perspective view of the electrode tip portion in Embodiment 2. The perspective view of the electrode tip portion in Embodiment 3. The perspective view of the electrode tip portion in Embodiment 4. The perspective view of the electrode tip portion in Embodiment 5. FIG. 6 is a cross-sectional view of the tip of the spark plug according to 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. 17 is a cross-sectional view taken along the line XVIII-XVIII. The perspective view of the ground electrode in Embodiment 8. The perspective view of the ground electrode in Embodiment 9. The perspective view of the ground electrode in Embodiment 10. 11 is a perspective view of the ground electrode according to the eleventh embodiment. 12 is a cross-sectional view of the tip of the spark plug according to the twelfth embodiment. The perspective view of the ground electrode in Embodiment 12. The perspective view of the ground electrode in Embodiment 13. FIG. 4 is a cross-sectional view of a tip portion of a spark plug according to a fourteenth embodiment. FIG. 15 is a cross-sectional view of the tip of the spark plug according to the fifteenth embodiment. 16 is a cross-sectional view of the tip of the spark plug according to the sixteenth embodiment. FIG. 6 is a cross-sectional view of the tip of the spark plug according to the seventeenth 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 the present embodiment has a sub-combustion chamber 2, at least one injection hole 33 that communicates the sub-combustion chamber 2 to the outside, and an electrode tip 41 arranged in the sub-combustion chamber 2. A ground electrode 5 that forms a discharge gap G between the center electrode 4 and the center electrode 4 is provided. The spark plug 1 is configured to be able to form an electric discharge between the inner wall of the spark forming injection hole 30, which is at least one of the injection holes 33, and the electrode tip portion 41. 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 30 and the electrode tip portion 41 in the expansion stroke of the internal combustion engine.

As shown in FIGS. 2 and 3, the discharge gap G is formed between the central discharge surface 410 of the electrode tip portion 41 facing the outer peripheral side and the ground discharge surface 50 of the ground electrode 5 facing the outer peripheral side. The discharge gap G and the spark forming injection hole 30 are formed at positions where they overlap each other in the direction along the ground discharge surface 50.
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 plug axis direction X. The plug axial direction X coincides with the axial direction of the cylindrical housing 6 and the axial direction of the tubular insulator 7. Further, as will be described in detail later, the plug central axis C and the hole axis direction in which the central axis of the spark forming injection hole 30 extends are the same directions. One side of the plug axial direction X, the side of the spark plug 1 where the auxiliary combustion chamber 2 is formed (for example, the lower side of FIGS. 1 and 2) is referred to as the plug tip side, and the opposite side is referred to as the plug base end. Called the side. 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 as shown in FIG. 1, the end of the spark plug 1 on the plug tip side is arranged in the combustion chamber of the internal combustion engine. The combustion chamber is an area surrounded by a cylinder block, a piston, and a cylinder head 11 of an internal combustion engine. Among the combustion chambers, the outer side of the spark plug 1 is the main combustion chamber 12, and the plug cover 3 of the spark plug 1 described later. The inside is called the sub-combustion chamber 2. The spark plug 1 is attached to the cylinder head 11 of the internal combustion engine in the housing 6.

The housing 6 is formed of a material having conductivity, thermal conductivity, and heat resistance in a cylindrical shape. As shown in FIGS. 1 and 2, a mounting screw portion 61 is formed on the outer peripheral portion of the housing 6. As shown in FIG. 1, the mounting screw portion 61 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 61 is exposed to the inside of the main combustion chamber 12. The housing 6 holds an insulating insulator 7 at its inner peripheral portion.

The insulating insulator 7 is formed by forming, for example, a material having electrical insulation in a cylindrical shape. Although not shown, the insulating insulator 7 is locked to the housing 6 in the plug axial direction X. Although not shown, a packing for ensuring a sealing property between the insulating insulator 7 and the housing 6 is provided at the locking portion. The insulating insulator 7 holds the center electrode 4 at its inner peripheral portion.

The center electrode 4 is formed of, for example, a metal formed in a long length in the plug axial direction X. As shown in FIG. 2, the center electrode 4 includes an electrode tip portion 41 protruding from the insulator 7 toward the plug tip side. As shown in FIGS. 2 and 4, the electrode tip portion 41 has a columnar shape extending in the plug axial direction X. As shown in FIG. 2, the electrode tip portion 41 projects toward the plug tip side from the end surface of the housing 6 on the plug tip side. The central discharge surface 410, which is a part of the outer peripheral surface of the electrode tip portion 41, forms a discharge gap G with the outer peripheral surface of the ground electrode 5. 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 2, but the initial spark discharge means the discharge spark before moving.

As shown in FIG. 2, a plug cover 3 for partitioning the sub-combustion chamber 2 is arranged at the end of the housing 6 on the plug tip side. The plug cover 3 is made of a material having conductivity, thermal conductivity, and heat resistance. The plug cover 3 is formed in a cup shape that opens toward the base end side of the plug. That is, the plug cover 3 includes a cover side wall 31 that covers the sub-combustion chamber 2 in the peripheral direction of the plug, and a disk-shaped cover bottom wall 32 that covers the sub-combustion chamber 2 from the plug tip side. The end of the plug cover 3 on the plug base end side is joined to the housing 6 all around, and is electrically and thermally connected to the housing 6.

As shown in FIG. 2, the thickness t2 of the end surface of the plug cover 3 on the plug base end side is smaller than the thickness t1 of the portion of the housing 6 on the plug tip side. The entire end surface of the plug cover 3 on the plug base end side faces the surface of the housing 6 on the plug end side. In this embodiment, the housing 6 and the plug cover 3 are formed separately, but these may be formed by one member.

As shown in FIGS. 2 and 3, the plug cover 3 has a spark forming injection hole 30 in a region facing the tip surface 411 of the electrode tip portion 41 and the plug axial direction X. The spark forming injection hole 30 is formed so as to penetrate the cover bottom wall 32 in the plug axial direction X. The hole axial direction, which is the axial direction of the spark forming injection hole 30, is formed to be the same as the plug axial direction X.

The inner wall of the spark forming injection hole 30 has an enlarged surface portion 301 in at least a part of the hole axis direction in which the area of the cross section orthogonal to the hole axis direction increases toward the side of the auxiliary combustion chamber 2 in the hole axis direction. The area of the cross section of the spark forming injection hole 30 including the enlarged surface portion 301 orthogonal to the hole axis direction is the area of the inner region of the spark forming injection hole 30 appearing in the cross section. In the present embodiment, the inner wall of the spark forming injection hole 30 includes a cylindrical surface portion 302 and an enlarged surface portion 301 in this order from the plug tip side.

The cylindrical surface portion 302 has a cylindrical shape formed straight in the plug axial direction X. That is, the cylindrical surface portion 302 has a circular shape similar to each other at each position in the plug axial direction X. The end of the cylindrical surface portion 302 on the plug tip side is an outer opening 303 that opens toward the plug tip side. An enlarged surface portion 301 is formed from the end portion of the cylindrical surface portion 302 on the plug base end side to the plug base end side.

The enlarged surface portion 301 is formed in a tapered shape whose diameter increases toward the plug base end side. That is, the enlarged surface portion 301 has a circular shape similar to each other at each position in the plug axial direction X, and the cut toward the plug base end side is orthogonal to the plug axial direction X in the inner region of the enlarged surface portion 301. The area becomes large. The end of the enlarged surface portion 301 on the plug base end side is an inner opening 304 opened on the plug base end side. The spark forming injection hole 30 is configured such that the area of the inner opening 304 on the side of the auxiliary combustion chamber 2 is larger than the area of the outer opening 303 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 30 and the tip surface 411 of the electrode tip portion 41 are formed at positions where they overlap each other in the hole axis direction. The area of the inner opening 304 on the side of the auxiliary combustion chamber 2 in the spark forming injection hole 30 is larger than the tip surface 411 of the electrode tip 41. When viewed from the hole axis direction, at least a part of the inner opening 304 is formed on the outer peripheral side of the tip surface 411 of the electrode tip 41. In the present embodiment, when viewed from the hole axis direction, the entire inner opening 304 is formed on the outer peripheral side of the tip surface 411 of the electrode tip 41. Further, when viewed from the hole axis direction, the entire outer opening 303 is formed so as to fit inside the tip surface 411 of the electrode tip 41.

As shown in FIGS. 2 and 5, a ground electrode 5 is provided on the inner wall surface of the plug cover 3 (that is, the surface on the side of the auxiliary combustion chamber 2). The ground electrode 5 is formed in a columnar shape extending in the hole axis direction. The ground electrode 5 may have another shape such as a polygonal prism shape as shown in FIG. Here, in FIGS. 5 and 8, the illustration of the spark forming injection hole is omitted.

As shown in FIGS. 2 and 3, the end of the ground electrode 5 on the plug tip side is joined to the vicinity of the inner opening 304 on the inner wall surface of the plug cover 3. In the present embodiment, the end of the ground electrode 5 on the plug tip side is joined to a region of the inner wall surface of the plug cover 3 slightly distant from the inner opening 304.

A part of the outer peripheral surface of the ground electrode 5 on the plug base end side is a ground discharge surface 50 facing the central discharge surface 410 of the electrode tip portion 41 of the center electrode 4 in the plug radial direction, and is a central discharge surface. A discharge gap G is formed between the 410 and the ground discharge surface 50. The discharge gap G is arranged at a position where at least a part thereof overlaps the inner region of the inner opening 304 in the hole axis direction.

The plug cover 3 has a plurality of injection holes 33 penetrating the plug cover 3 in addition to the spark forming injection holes 30. Hereinafter, the term "injection hole 33" means an injection hole 33 other than the spark-forming injection hole 30 unless otherwise specified. The plurality of injection holes 33 are formed on the outer peripheral side in the plug radial direction with respect to the spark formation injection holes 30. Each injection hole 33 is formed so as to be inclined toward the outer peripheral side in the plug radial direction toward the plug tip end side. The plurality of injection holes 33 are formed at equal intervals in the circumferential direction of the plug. The number, shape, arrangement location, etc. of the injection holes 33 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 2 side to the main combustion chamber 12 side is generated around the spark forming injection hole 30. Further, the initial discharge spark S generated in the discharge gap G occurs, for example, between the central discharge surface 410 and the ground discharge surface 50 where the space distance between the center electrode 4 and the ground electrode 5 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 on the ground electrode 5 side of the discharge spark S is from the ground electrode 5. It moves on the inner wall of the spark forming injection hole 30 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 30 on the tip side of the plug. In this way, a discharge is formed between the spark forming injection hole 30 and the electrode tip portion 41 of the center electrode 4. Then, the stretched discharge spark S is formed from the spark forming injection hole 30 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 2 such as the plug cover 3, the housing 6, and the insulating insulator 7 may be at a low temperature. Therefore, especially at the time of cold start, the discharge spark is extended toward the main combustion chamber 12 to suppress the contact area between the initial flame and the plug cover 3 and 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 3 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 2 side is generated around the spark forming injection hole 30. When the airflow F2 flows from the main combustion chamber 12 into the cylindrical surface portion 302 of the spark forming injection hole 30, 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 302 into the enlarged surface portion 301, 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 inside of the sub-combustion chamber 2 faces the plug base end side so as to avoid the center electrode 4, 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 central discharge surface 410 and the ground discharge surface 50 where the space distance between the center electrode 4 and the ground electrode 5 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 2 and directly ignites the air-fuel mixture in the sub-combustion chamber 2 to form a flame in the sub-combustion chamber 2. The flame grown in the sub-combustion chamber 2 is ejected as a flame jet from the spark-forming injection hole 30 and the other injection holes 33 into the main combustion chamber 12. Here, since the cross-sectional area of the flow path of the spark-forming injection hole 30 decreases toward the plug tip side, the momentum of the flame jet ejected through the spark-forming injection hole 30 increases. As a result, the combustion period of the internal combustion engine can be shortened.

For example, a spark discharge is generated in the compression stroke when the members facing the auxiliary combustion chamber 2, such as the plug cover 3, the housing 6, the insulator 7, and the center electrode 4, become hot to some extent, except during a cold start. Can be done.

Next, the action and effect of this embodiment will be described.
The spark plug 1 of the present embodiment is configured so that a discharge can be formed between the electrode tip portion 41 and the inner wall of the spark forming injection hole 30. Therefore, for example, by appropriately adjusting the ignition timing, the discharge spark can be extended both inside the sub-combustion chamber 2 and outside the sub-combustion chamber 2.

The discharge gap G is formed between the central discharge surface 410 facing the outer peripheral side of the electrode tip 41 and the ground discharge surface 50 facing the outer peripheral side of the ground electrode 5. Further, the discharge gap G and the spark forming injection hole 30 are formed at positions where they overlap each other in the direction along the ground discharge surface 50. Therefore, the airflow passing through the discharge gap G and the spark forming injection hole 30 is likely to be smoothly formed. Therefore, regardless of whether the discharge spark is stretched inside the sub-combustion chamber 2 or outside the sub-combustion chamber 2, the discharge spark is easily stretched and the ignitability of the spark plug 1 is improved. be able to.

As described above, according to this embodiment, it is possible to provide a spark plug capable of improving ignitability.

(Embodiment 2)
As shown in FIGS. 9 to 11, this embodiment is an embodiment in which the configuration of the electrode tip portion 41 of the center electrode 4 is changed from that of the first embodiment.

The electrode tip portion 41 includes an electrode tip body 412 integrally formed of the same material as the portion of the center electrode 4 arranged inside the insulating insulator 7, and a center tip 413 arranged on the electrode tip body 412. .. The electrode tip body 412 has an electrode tip recess 412a at a portion on the ground electrode 5 side in the plug radial direction. The electrode tip recess 412a is formed so that the outer peripheral surface of the electrode tip body 412 is recessed inward and is open to the plug tip side. The bottom surface 412b of the electrode tip recess 412a is formed so as to be a flat surface facing the ground electrode 5 side. A central tip 413 is arranged in the electrode tip recess 412a.

The center tip 413 is made of a material having higher wear resistance than the electrode tip body 412, and is made of, for example, a precious metal. The center chip 413 is formed in a disk shape or an elliptical plate shape having a thickness in the plug radial direction, and faces the ground electrode 5 in the plug radial direction. The position of the end portion of the center tip 413 on the plug tip side coincides with the position of the end portion of the electrode tip body 412 on the plug tip side. As shown in FIG. 10, when viewed from the hole axis direction, a part of the central tip 413 is arranged inside the electrode tip recess 412a, and another part is arranged outside the electrode tip recess 412a. In FIG. 28, the contour of the electrode tip recess 412a in the direction orthogonal to the hole axis direction is represented by a two-dot chain line. The surface of the central chip 413 opposite to the bottom surface 412b constitutes a central discharge surface 410 formed in a plane shape orthogonal to the plug radial direction.

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.

In this embodiment, the central discharge surface 410 is formed in a flat shape. Therefore, the airflow passing through the discharge gap G can be smoothed. As a result, regardless of whether the discharge spark is stretched inside the sub-combustion chamber 2 or toward the main combustion chamber 12, the discharge spark is easily stretched and the ignitability of the spark plug 1 is easily improved.

Further, since the central discharge surface 410 is composed of the central tip 413 having higher wear resistance than the electrode tip main body 412, electrode wear can be suppressed.
In addition, it has the same effect as that of the first embodiment.

(Embodiment 3)
As shown in FIG. 12, this embodiment is an embodiment in which the shape of the central chip 413 is changed with respect to the second embodiment.

In the present embodiment, the central tip 413 is formed in the shape of a rectangular plate having a thickness in the normal direction of the bottom surface 412b of the electrode tip concave portion 412a.
Others are the same as in the second embodiment.

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

(Embodiment 4)
As shown in FIG. 13, this embodiment is an embodiment in which the shape of the central chip 413 is changed with respect to the third embodiment.

In the present embodiment, the central chip 413 is a polygon having a pentagonal or higher cross-sectional shape orthogonal to the hole axis direction. In the cross-sectional shape, the surface of the central tip 413 on the ground electrode 5 side has a corner portion E protruding toward the ground electrode 5 side in the plug radial direction. The corner portion E forms a discharge gap G with the ground electrode 5. The two surfaces forming the corner portion E form the central discharge surface 410 facing the ground electrode 5 side.
Others are the same as in the third embodiment.

In this embodiment, the starting point of the initial discharge spark can be formed at the corner E of the central chip 413, and the starting point position of the initial discharge spark can be easily specified.
This embodiment also has the same effect as that of the second embodiment.

(Embodiment 5)
As shown in FIG. 14, this embodiment is an embodiment in which the shape of the central chip 413 is changed with respect to the third embodiment.

In the present embodiment, the central chip 413 is a polygon having a pentagonal or higher cross-sectional shape orthogonal to the hole axis direction. In the cross-sectional shape, the surface of the central tip 413 on the ground electrode 5 side has a tip recess D recessed toward the anti-ground electrode 5 side in the plug radial direction. The two surfaces forming the tip recess D form the central discharge surface 410. Then, in the cross-sectional shape, the surface of the central chip 413 on the ground electrode 5 side has a pair of corner portions E protruding toward the ground electrode 5 on both sides of the chip recess D. The pair of corner portions E form a discharge gap G with the ground electrode 5.
Others are the same as in the third embodiment.

In the present embodiment, the starting point of the initial discharge spark can be formed on the pair of corners E of the central chip 413, and the starting point position of the initial discharge spark can be easily specified. Further, by forming the discharge gap G with the pair of corner portions E, the discharge spark can be arbitrarily generated at any of the pair of corner portions E, but the pair of corner portions E are consumed substantially evenly. , It is easy to prevent the progress of electrode wear due to local wear of the central chip 413.
In addition, it has the same effect as that of the third embodiment.

(Embodiment 6)
As shown in FIG. 15, this embodiment is a form in which the electrode tip main body 412 is not provided with the electrode tip concave portion and the central tip 413 is arranged on the outer peripheral surface of the electrode tip main body 412, as shown in FIG. As a result, the central chip 413 projects toward the outer peripheral side of the outer peripheral surface of the electrode tip main body 412 from the surface portion adjacent to the surface portion on which the central chip 413 is arranged.
Others are the same as in the second embodiment.

In the present embodiment, the central tip 413 projects toward the outer peripheral side of the outer peripheral surface of the electrode tip main body 412 from the surface portion adjacent to the surface portion on which the central chip 413 is arranged. Therefore, the starting point of the initial discharge spark can be reliably formed on the central tip 413. Therefore, it is easy to suppress electrode wear.
In addition, it has the same effect as that of the second embodiment.

(Embodiment 7)
In this embodiment, as shown in FIG. 16, the end portion 413a on the plug tip side of the central tip 413 projects toward the plug tip side from the plug tip side surface of the electrode tip body 412, as compared with the sixth embodiment. It is a form.
Others are the same as in the sixth embodiment.

In this embodiment, it is easy to prevent the starting point of the discharge spark from being formed on the surface of the electrode tip body 412 on the plug tip side or the like.
In addition, it has the same effect as that of the sixth embodiment.

(Embodiment 8)
As shown in FIGS. 17 to 19, this embodiment is an embodiment in which the configuration of the ground electrode 5 is changed with respect to the first embodiment.

The grounding electrode 5 includes a grounding main body 51 and a grounding tip 52 arranged on the grounding main body 51. The grounding main body 51 is formed in a columnar shape extending in the hole axis direction. The grounding main body 51 has a grounding recess 511 at a portion on the center electrode 4 side in the radial direction of the plug. The grounding recess 511 is formed so that the outer peripheral surface of the grounding main body 51 is recessed inward and is open to the plug base end side. The bottom surface 511a of the ground contact recess 511 is formed so as to be a flat surface facing the center electrode 4 side. A grounding tip 52 is arranged in the grounding recess 511.

The grounding tip 52 is made of a material having higher wear resistance than the grounding main body 51, and is made of, for example, a precious metal. The grounding tip 52 is formed in a disk shape or an elliptical plate shape having a thickness in the plug radial direction, and faces the center electrode 4 in the plug radial direction. As shown in FIG. 17, the grounding tip 52 makes the position of the end portion on the plug base end side coincide with the position of the end portion on the plug base end side of the grounding main body 51. As shown in FIG. 18, when viewed from the hole axis direction, a part of the grounding tip 52 is arranged inside the grounding recess 511, and another part is arranged outside the grounding recess 511. The surface of the grounding tip 52 opposite to the bottom surface 511a constitutes a grounding discharge surface 50 formed in a plane shape orthogonal to the plug radial direction.

Others are the same as in the first embodiment.

In this embodiment, the ground discharge surface 50 is formed in a flat shape. Therefore, the airflow passing through the discharge gap G can be smoothed. As a result, regardless of whether the discharge spark is stretched inside the sub-combustion chamber 2 or toward the main combustion chamber 12, the discharge spark is easily stretched and the ignitability of the spark plug 1 is easily improved.

Further, since the grounding discharge surface 50 is composed of the grounding tip 52 having higher wear resistance than the grounding main body 51, electrode wear can be suppressed.
In addition, it has the same effect as that of the first embodiment.

(Embodiment 9)
As shown in FIG. 20, this embodiment is an embodiment in which the shape of the grounding tip 52 is changed from that of the eighth embodiment.

In the present embodiment, the grounding tip 52 is formed in the shape of a rectangular plate having a thickness in the normal direction of the bottom surface 511a of the grounding recess 511.
Others are the same as in the eighth embodiment.

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

(Embodiment 10)
As shown in FIG. 21, this embodiment is an embodiment in which the shape of the grounding tip 52 is changed from that of the ninth embodiment.

In the present embodiment, the grounding tip 52 is a polygon having a pentagonal or higher cross-sectional shape orthogonal to the hole axis direction. In the cross-sectional shape, the surface of the grounding tip 52 on the center electrode 4 side has a corner portion E protruding toward the center electrode 4 side in the plug radial direction. The corner portion E forms a discharge gap G with the center electrode 4. The two surfaces forming the corner portion E form the ground discharge surface 50 facing the center electrode 4 side.
Others are the same as in the ninth embodiment.

In the present embodiment, the starting point of the initial discharge spark can be formed at the corner E of the grounding tip 52, and the starting point position of the initial discharge spark can be easily specified.
Also in this embodiment, it has the same effect as that of the eighth embodiment.

(Embodiment 11)
As shown in FIG. 22, this embodiment is an embodiment in which the shape of the grounding tip 52 is changed from that of the ninth embodiment.

In the present embodiment, the grounding tip 52 is a polygon having a pentagonal or higher cross-sectional shape orthogonal to the hole axis direction. In the cross-sectional shape, the surface of the grounding tip 52 on the center electrode 4 side has a tip recess D recessed toward the anti-center electrode 4 side in the plug radial direction. The two surfaces forming the tip recess D form the ground discharge surface 50. Then, in the cross-sectional shape, the surface of the grounding tip 52 on the grounding electrode 5 side has a pair of corner portions E protruding toward the grounding electrode 5 side on both sides of the tip recess D. The pair of corner portions E form a discharge gap G with the ground electrode 5.
Others are the same as in the ninth embodiment.

In the present embodiment, the starting point of the initial discharge spark can be formed on the pair of corners E of the grounding tip 52, and the starting point position of the initial discharge spark can be easily specified. Further, by forming the discharge gap G with the pair of corner portions E, the discharge spark can be arbitrarily generated at any of the pair of corner portions E, but the pair of corner portions E are consumed substantially evenly. , It is easy to prevent the progress of electrode wear due to local wear of the grounding tip 52.
In addition, it has the same effect as that of the ninth embodiment.

(Embodiment 12)

As shown in FIGS. 23 and 24, this embodiment is an embodiment in which the configurations of the grounding main body 51 and the grounding tip 52 are changed from those of the ninth embodiment.

The grounding main body 51 is formed in a square columnar shape extending in the hole axis direction. The chip arranging surface 512, which is one of the side surfaces of the grounding main body 51, faces the center electrode 4, and the grounding chip 52 is arranged on the chip arranging surface 512. As a result, the grounding chip 52 protrudes toward the outer peripheral side of the grounding electrode 5 from the surface portion of the chip arrangement surface 512 adjacent to the surface portion on which the grounding chip 52 is arranged.
Others are the same as in the ninth embodiment.

In the present embodiment, the grounding chip 52 projects toward the outer periphery of the chip arranging surface 512 of the grounding main body 51 with respect to the surface portion adjacent to the surface portion on which the grounding chip 52 is arranged. Therefore, the starting point of the initial discharge spark can be reliably formed on the grounding tip 52. Therefore, it is easy to suppress electrode wear.
In addition, it has the same effect as that of the ninth embodiment.

(Embodiment 13)
As shown in FIG. 25, this embodiment is an embodiment in which the grounding main body 51 and the grounding tip 52 are modified from the embodiment 12.

The grounding main body 51 extends in the hole axis direction and has a substantially semicircular cross-sectional shape orthogonal to the hole axis direction. A chip arranging surface 512 is formed on the outer peripheral surface of the grounding main body 51 on the center electrode 4 side. The chip arrangement surface 512 faces the center electrode 4 side and is formed in a plane shape orthogonal to the plug radial direction. In the hole axis direction, the chip arranging surface 512 is formed on the entire grounding main body 51. As a result, the grounding main body 51 has a shape in which a part of the columnar shape is cut off in the axial direction. A grounding chip 52 is arranged on the chip arranging surface 512. In the hole axis direction, the grounding chip 52 is formed to have a length equivalent to that of the chip arranging surface 512.
Others are the same as in the twelfth embodiment.

In the present embodiment, when the expansion stroke of the internal combustion engine is ignited and the spark is extended to the main combustion chamber 12 side, it is possible to prevent the starting point of the discharge spark from being formed on the grounding main body 51.
In addition, it has the same effect as that of the twelfth embodiment.
(Embodiment 14)
In this embodiment, as shown in FIG. 26, with respect to the eighth embodiment, the end portion 521 of the grounding tip 52 on the plug base end side protrudes toward the plug tip side from the surface of the grounding main body 51 on the plug base end side. It is an embodiment. Further, the electrode tip portion 41 of the center electrode 4 has the same configuration as the electrode tip portion 41 of the second embodiment. That is, the electrode tip portion 41 includes an electrode tip main body 412 and a central tip 413.

The position of the end of the grounding tip 52 on the plug base end side is located closer to the plug tip than the end of the center tip 413 on the plug base end side.
Others are the same as in the eighth embodiment.

In this embodiment, for example, when ignition is performed in the compression stroke of the internal combustion engine and the discharge spark is extended to the side of the auxiliary combustion chamber 2, it is easy to prevent the starting point of the discharge spark from shifting from the center electrode 4 chip to the electrode tip body 412. , It is easy to suppress electrode wear.
In addition, it has the same effects as those of Embodiments 2 and 8.

(Embodiment 15)
As shown in FIG. 27, this embodiment is a form in which the configuration of the ground electrode 5 is the configuration of the ground electrode shown in the thirteenth embodiment with respect to the fourteenth embodiment.
Others are the same as in the 14th embodiment.

In the present embodiment, the discharge spark is formed on the electrode tip main body 412 and the ground main body 51 of the center electrode 4 regardless of whether the discharge spark is stretched into the sub-combustion chamber 2 or toward the main combustion chamber 12. It is easy to prevent this, and it is easier to suppress electrode wear.
In addition, it has the same effect as that of the 14th embodiment.

(Embodiment 16)
In this embodiment, as shown in FIG. 28, the more the central discharge surface 410 and the ground discharge surface 50 constituting the discharge gap G are farther from the spark forming injection hole 30 in the hole axis direction, the more toward the outer peripheral side in the plug radial direction. It is a form that is inclined toward it.

The portion of the electrode tip portion 41 of the center electrode 4 on the plug tip side is reduced toward the plug tip side, and a part of the outer peripheral surface thereof constitutes the central discharge surface 410. Further, the ground electrode 5 is formed in a square columnar shape extending in the hole axis direction, and the surface facing the central discharge surface 410 is inclined toward the outer peripheral side in the plug radial direction toward the plug base end side. The ground discharge surface is 50. The central discharge surface 410 and the ground discharge surface 50 are formed in parallel with each other.

The end of the ground electrode 5 on the plug tip side is adjacent to the inner opening 304 of the spark forming injection hole 30. The inclination angle of the ground discharge surface 50 and the central discharge surface 410 with respect to the hole axis direction is smaller than the inclination angle of the enlarged surface portion 301 of the spark forming injection hole 30 with respect to the hole axis direction.
Others are the same as in the first embodiment.

In this embodiment, the enlarged surface portion 301 and the grounding discharge surface 50 can be smoothly connected, and the air flow can easily pass through the spark forming injection hole 30 and the discharge gap G.
In addition, it has the same effect as that of the first embodiment.

(Embodiment 17)
As shown in FIG. 29, this embodiment has the same basic structure as that of the 16th embodiment, but the shape of the ground electrode 5 is changed.

In the present embodiment, the ground electrode 5 has an extension portion extending to the inside of the spark forming injection hole 30. The extension portion is formed on the enlarged surface portion 301 of the spark forming injection hole 30. The ground discharge surface 50 of the ground electrode 5 is connected to the cylindrical surface portion 302 of the spark forming injection hole 30.
Others are the same as in the 16th embodiment.

In this embodiment, for example, when a discharge is generated in an expansion stroke in an internal combustion engine and a discharge spark is extended to the main combustion chamber 12 side, the starting point of the discharge spark from the ground discharge surface 50 of the ground electrode 5 to the spark forming injection hole 30 Easy to move. Therefore, when a discharge is generated in the expansion stroke of the internal combustion engine, the discharge spark is easily extended to the main combustion chamber 12 side.
In addition, it has the same effect as that of the 16th 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. For example, embodiments 2 to 7 characterized by the shape of the center electrode and embodiments 8 to 13 characterized by the shape of the ground electrode can be appropriately combined. Further, in the configurations described in the 16th and 17th embodiments, the center electrode and the grounding electrode may be provided with the center tip and the grounding tip as in the second to thirteenth embodiments. It is also possible to provide the hole axis direction in a direction inclined with respect to the plug axis direction.

1 Spark plug 2 Sub-combustion chamber 30 Spark formation injection hole 33 Injection hole 4 Center electrode 41 Electrode tip 410 Center discharge surface 5 Ground electrode 50 Ground discharge surface G Discharge gap

Claims (3)

The sub-combustion chamber (2), at least one injection hole (33) communicating the sub-combustion chamber to the outside, a center electrode (4) in which the electrode tip portion (41) is arranged in the sub-combustion chamber, and the above. A ground electrode (5) that forms a discharge gap (G) with the center electrode is provided, and between the inner wall of the spark-forming nozzle (30), which is at least one of the nozzles, and the tip of the electrode. A spark plug (1) configured to form an electric discharge.
The discharge gap is formed between the central discharge surface (410) facing the outer peripheral side of the electrode tip and the ground discharge surface (50) facing the outer peripheral side of the ground electrode.
A spark plug in which the discharge gap and the spark forming injection hole are formed at positions where they overlap each other in a direction along the grounding discharge surface. The spark plug according to claim 1, wherein at least one of the central discharge surface and the ground discharge surface forming the discharge gap is formed in a planar shape. The inner wall of the spark-forming injection hole has an enlarged surface portion (301) in which the area of the cross section orthogonal to the hole-axis direction is expanded toward the sub-combustion chamber side in the hole-axis direction (X) of the spark-forming injection hole. The central discharge surface and the ground discharge surface, which are present in at least a part of the region in the hole axis direction and form the discharge gap, are plugged as they move away from the spark-forming injection hole in the hole axis direction. The spark plug according to claim 1, which is inclined toward the outer peripheral side in the radial direction.

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