JP7390241B2 - Spark plug - Google Patents

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. A plurality of through holes are formed in the plug cover, and the tip of the center electrode is inserted into one of the through holes, which is an insertion hole. The spark plug described in Patent Document 1 has a discharge gap between the center electrode and the inner wall of the insertion hole for generating spark discharge. Further, the spark plug described in Patent Document 1 is configured so that discharge sparks generated in the discharge gap can be extended toward the main combustion chamber side.

JP2016-95986A

In the spark plug described in Patent Document 1, there is room for improvement from the viewpoint of improving ignition performance.

The present invention has been made in view of this problem, and aims to provide a spark plug that can improve ignition performance.

One aspect of the present invention includes a sub-combustion chamber (2), at least one injection hole (33) that communicates the sub-combustion chamber with the outside, and a center in which an electrode tip (41) is disposed within the sub-combustion chamber. An electrode (4), and a spark plug ( 1),
The inner wall of the spark forming nozzle hole has an enlarged surface portion (301) in which the area of a cross section perpendicular to the hole axis direction increases toward the sub-combustion chamber side in the hole axis direction (X) of the spark forming nozzle hole. , the spark plug has the spark plug in at least a part of the region in the direction of the hole axis.

The spark plug of the above embodiment is configured to be able to generate an electric discharge between the electrode tip and the inner wall of the spark-forming nozzle hole. Therefore, for example, by appropriately adjusting the ignition timing, it is possible to extend the discharge sparks both inside and outside the sub-combustion chamber. The inner wall of the spark-forming nozzle hole has an enlarged surface portion in which the area of a cross section perpendicular to the hole axis direction increases toward the sub-combustion chamber side in the hole axis direction, in at least a part of the hole axis direction. Therefore, when extending the discharge spark toward the sub-combustion chamber side, the following effects are achieved.

In the enlarged surface portion, the flow passage cross-sectional area increases from the outside of the spark plug toward the sub-combustion chamber. Therefore, the airflow that passes through the spark-forming nozzle hole and heads into the sub-combustion chamber is diffused at the enlarged surface portion, and the flow velocity is reduced. This can prevent discharge sparks from easily blowing out.

As described above, according to the above aspect, it is possible to provide a spark plug that can improve ignitability.
Note that the numerals in parentheses described in the claims and means for solving the problem indicate correspondence with specific means described in the embodiments described later, and do not limit the technical scope of the present invention. It's not a thing.

1 is a partially sectional front view of a spark plug attached to an internal combustion engine in Embodiment 1. FIG. 1 is a cross-sectional view of the tip of a spark plug in Embodiment 1. FIG. A sectional view taken along the line III-III in FIG. 2. A sectional view taken along the line IV-IV in FIG. 3. FIG. 3 is a cross-sectional view of the tip of the spark plug showing how discharge sparks are elongated during the compression stroke in Embodiment 1. FIG. FIG. 3 is a cross-sectional view of the tip of the spark plug showing how discharge sparks are elongated during the expansion stroke in Embodiment 1; FIG. 3 is a cross-sectional view of the tip of a spark plug in Embodiment 2. FIG. 7 is a cross-sectional view of the tip of a spark plug in Embodiment 3. FIG. 4 is a cross-sectional view of the tip of a spark plug in Embodiment 4. 5 is a cross-sectional view of the tip of a spark plug in Embodiment 5. FIG. FIG. 7 is a cross-sectional view of the tip of a spark plug in Embodiment 6. FIG. 7 is a sectional view of the tip of a spark plug in a modification of Embodiment 6. FIG. 7 is a cross-sectional view of the tip of a spark plug in Embodiment 7. FIG. 8 is a cross-sectional view of the tip of a spark plug in Embodiment 8. 9 is a cross-sectional view of the tip of a spark plug in Embodiment 9. FIG. 10 is a cross-sectional view of the tip of a spark plug in Embodiment 10. FIG. FIG. 7 is a cross-sectional view of the tip of a spark plug in Embodiment 11. FIG. 7 is a cross-sectional view of the tip of a spark plug in Embodiment 12. FIG. 7 is a cross-sectional view of the tip of a spark plug in Embodiment 13. FIG. 14 is a cross-sectional view of the tip of a spark plug in Embodiment 14. 15 is a cross-sectional view of the tip of a spark plug in Embodiment 15. FIG. A sectional view taken along the line XXII-XXII in FIG. 21. 16 is a cross-sectional view of the tip of a spark plug in Embodiment 16. FIG. 17 is a cross-sectional view of the tip of a spark plug in Embodiment 17. FIG. A sectional view taken along the line XXV-XXV in FIG. 24. 26 is a sectional view corresponding to FIG. 25 in a modified form of the seventeenth embodiment; FIG. FIG. 9 is a cross-sectional view of the tip of a spark plug in Embodiment 18. 19 is a cross-sectional view of the tip of a spark plug in Embodiment 19. FIG. A sectional view taken along the line XXIX-XXIX in FIG. 28. FIG. 7 is a cross-sectional view of the tip of a spark plug in Embodiment 20. FIG. 7 is a cross-sectional view of the tip of a spark plug in Embodiment 21. FIG. 22 is a cross-sectional view of the tip of a spark plug in Embodiment 22. FIG. 4 is a cross-sectional view corresponding to FIG. 3 in a first modified form. FIG. 5 is a cross-sectional view corresponding to FIG. 4 in a second modified form. FIG. 5 is a cross-sectional view corresponding to FIG. 4 in a third modified form.

(Embodiment 1)
Embodiments of the spark plug will be described using FIGS. 1 to 6.
As shown in FIG. 2, the spark plug 1 of this embodiment includes a sub-combustion chamber 2, at least one nozzle hole 33 that communicates the sub-combustion chamber 2 with the outside of the spark plug 1, and an electrode tip inside the sub-combustion chamber 2. 41 is arranged. The spark plug 1 is configured to be able to generate a discharge between the inner wall of the spark-forming nozzle hole 30, which is at least one of the nozzle holes 33, and the electrode tip 41. In this embodiment, although details will be described later, an electric discharge is formed between the inner wall of the spark-forming nozzle hole 30 and the electrode tip 41 during the expansion stroke of the internal combustion engine.

The inner wall of the spark forming nozzle hole 30 has an enlarged surface portion 301 whose cross-sectional area perpendicular to the hole axis direction X increases toward the sub-combustion chamber 2 side in the hole axis direction X, in at least a part of the area in the hole axis direction X. has. The area of the cross section of the spark forming nozzle hole 30 including the enlarged surface portion 301 orthogonal to the hole axis direction X is the area of the inner region of the spark forming nozzle hole 30 appearing in the cross section. The hole axis direction X is the direction in which the central axis of the spark forming nozzle hole 30 extends.
Hereinafter, this embodiment will be explained in detail.

In this embodiment, the central axis of the spark plug 1 is referred to as a plug central axis C. The direction in which the plug center axis C extends is referred to as the plug axis direction Y. The plug axial direction Y coincides with the axial direction of the cylindrical housing 5 and the axial direction of the cylindrical insulator 6. Further, although details will be described later, the plug axial direction Y and the hole axial direction X are the same direction. One side in the plug axial direction Y, on which the auxiliary combustion chamber 2 of the spark plug 1 is formed (for example, the lower side of FIGS. 1 and 2) is called the plug tip side, and the opposite side is called the plug base end. It's called the side. The radial direction of the spark plug 1 is referred to as the plug radial direction. The circumferential direction of the spark plug 1 is referred to as the plug circumferential direction.

The spark plug 1 can be used, for example, as an ignition means in an internal combustion engine such as an automobile or a cogeneration engine. The end of the spark plug 1 on the proximal side of the plug is connected to an ignition coil (not shown), and the end on the tip side of the plug is disposed within a combustion chamber of an internal combustion engine. As shown in FIG. 1, the combustion chamber is an area surrounded by the cylinder block, piston, and cylinder head 11 of an internal combustion engine. The inside of the plug cover 3, which will be described later, is called an auxiliary combustion chamber 2. A spark plug 1 is mounted in a housing 5 to a cylinder head 11 of an internal combustion engine.

As shown in FIGS. 1 and 2, the housing 5 is made of a material having electrical conductivity, thermal conductivity, and heat resistance and is formed into a cylindrical shape. A mounting screw portion 51 is formed on the outer periphery of the housing 5 . As shown in FIG. 1, the mounting screw portion 51 is a portion that is screwed into a female screw hole 111 provided in the cylinder head 11. When the spark plug 1 is attached to the cylinder head 11 , a portion of the mounting screw portion 51 of the spark plug 1 on the plug tip side is exposed to the inside of the main combustion chamber 12 . The housing 5 holds an insulator 6 at its inner periphery.

The insulator 6 is made of, for example, an electrically insulating material formed into a cylindrical shape. Although not shown, the insulator 6 is locked to the housing 5 in the plug axial direction Y. Although not shown, the locking portion between the insulator 6 and the housing 5 is provided with a packing that ensures sealing between them. The insulator 6 holds the center electrode 4 at its inner circumference.

The center electrode 4 is made of, for example, metal and is formed to be elongated in the plug axis direction Y. As shown in FIG. 2, the center electrode 4 includes an electrode tip portion 41 that protrudes from the insulator 6 toward the plug tip side. The electrode tip portion 41 has a cylindrical shape extending in the plug axial direction Y. The electrode tip portion 41 projects further toward the plug tip side than the end surface of the housing 5 on the plug tip side.

The electrode tip portion 41 includes an electrode tip body 411 integrally formed of the same material as the center electrode 4 disposed inside the insulator 6, and a center tip 412 disposed on the side surface of the electrode tip body 411. Equipped with. As shown in FIGS. 2 and 3, a tip placement surface 411a is formed on the side surface of the electrode tip body 411. The chip arrangement surface 411a faces outward in the radial direction of the plug and is formed in a planar shape orthogonal to the radial direction of the plug. A center chip 412 is arranged on the chip arrangement surface 411a.

The center tip 412 is made of a material with higher wear resistance than the electrode tip main body 411, for example, made of a noble metal. The center chip 412 is formed into a rectangular plate shape having a thickness in the normal direction of the chip arrangement surface 411a. The position of the end of the center tip 412 on the plug tip side matches the position of the end of the electrode tip body 411 on the plug tip side. A discharge gap G is formed between the center tip 412 and a ground electrode 7, which will be described later. The discharge gap G is a space in which an initial spark discharge is formed. As will be described later, the discharge sparks S are pushed by the airflow in the auxiliary combustion chamber 2 and move, but the initial spark discharge refers to the discharge sparks S before they move.

As shown in FIGS. 1 and 2, a plug cover 3 that partitions the sub-combustion chamber 2 is disposed at the end of the housing 5 on the plug tip side. The plug cover 3 is made of a material that has electrical conductivity, thermal conductivity, and heat resistance. The plug cover 3 is formed into a cup shape that opens toward the proximal end of the plug. That is, the plug cover 3 includes a cover side wall 31 that covers the sub-combustion chamber 2 in the circumferential direction of the plug, and a disk-shaped cover bottom wall 32 that covers the sub-combustion chamber 2 from the plug tip side. An end portion of the plug cover 3 on the proximal end side of the plug is joined to the housing 5 around the entire circumference, and is electrically and thermally connected to the housing 5. In this embodiment, the housing 5 and the plug cover 3 are constructed separately, but they may be constructed as a single member.

As shown in FIGS. 2 and 3, the plug cover 3 has a spark forming nozzle hole 30 in a region facing the tip surface 413 of the electrode tip portion 41 in the plug axial direction Y. As shown in FIGS. The spark forming nozzle hole 30 is formed to penetrate the cover bottom wall 32 in the plug axial direction Y. The hole axis direction X, which is the axial direction of the spark forming nozzle hole 30, is formed to be the same direction as the plug axis direction Y.

As described above, the inner wall of the spark forming nozzle hole 30 has an enlarged surface portion 301 whose cross-sectional area perpendicular to the hole axis direction X increases toward the auxiliary combustion chamber 2 side in the hole axis direction X. In some areas. In this embodiment, the inner wall of the spark forming nozzle hole 30 includes a cylindrical surface portion 302 and an enlarged surface portion 301 in this order from the plug tip side.

As shown in FIG. 2, the cylindrical surface portion 302 has a cylindrical shape that is straight in the plug axial direction Y. As shown in FIG. That is, the cylindrical surface portion 302 has the same circular shape at each position in the plug axial direction Y. The end of the cylindrical surface portion 302 on the plug tip side forms an outer opening 303 that opens toward the plug tip side. An enlarged surface portion 301 is formed from the end of the cylindrical surface portion 302 on the plug proximal end side to the plug proximal end side.

The enlarged surface portion 301 is formed in a tapered shape whose diameter increases toward the proximal end of the plug. That is, the enlarged surface portion 301 has a similar circular shape at each position in the plug axial direction Y, and the area of the cross section of the enlarged surface portion 301 perpendicular to the plug axial direction Y decreases toward the proximal end of the plug. growing. The end of the enlarged surface portion 301 on the proximal end of the plug forms an inner opening 304 that opens toward the proximal end of the plug. The spark forming nozzle hole 30 is configured such that the area of the inner opening 304 on the side of the sub-combustion chamber 2 is larger than the area of the outer opening 303 on the outside of the spark plug 1.

As shown in FIG. 3, the inner region of the spark-forming nozzle hole 30 and the tip surface 413 of the electrode tip portion 41 are formed at positions that overlap with each other in the hole axis direction X. Note that the tip surface 413 of the electrode tip portion 41 refers to the surface of the electrode tip portion 41 on the plug tip side that is closest to the plug tip side. In this embodiment, as shown in FIG. 2, the electrode tip main body 411 and the center tip 412 that constitute the electrode tip section 41 have the same end positions on the plug tip side, so that the tip surface 413 of the electrode tip section 41 are the tip surfaces of both the electrode tip body 411 and the center tip 412. As shown in FIGS. 2 and 3, the area of the inner opening 304 of the spark forming nozzle hole 30 on the sub-combustion chamber 2 side is larger than the tip surface 413 of the electrode tip 41. When viewed from the hole axis direction X, at least a portion of the inner opening 304 is formed on the outer peripheral side of the tip surface 413 of the electrode tip 41. In this embodiment, when viewed from the hole axis direction X, the entire inner opening 304 is formed on the outer peripheral side of the tip surface of the electrode tip body 411. Furthermore, when viewed from the hole axis direction X, the entire outer opening 303 is formed to fit inside the tip surface of the electrode tip body 411.

As shown in FIGS. 2 and 4, a ground electrode 7 is provided on the inner wall surface of the plug cover 3 (ie, the surface on the side of the auxiliary combustion chamber 2). The ground electrode 7 has a ground main body portion 71 and a ground tip 72.

The grounding main body portion 71 is formed into a rectangular plate shape extending in the hole axis direction X. As shown in FIGS. 2 and 3, the thickness direction of the grounding main body portion 71 coincides with the thickness direction of the center chip 412. As shown in FIGS. The end of the grounding main body portion 71 on the plug tip side is joined to the inner wall surface of the plug cover 3 near the inner opening 304 . In this embodiment, the end of the grounding main body portion 71 on the plug tip side is joined to an area of the inner wall surface of the plug cover 3 that is slightly away from the inner opening 304 . A portion of the grounding main body portion 71 on the proximal end side of the plug faces the tip placement surface 411a of the center electrode 4. A grounding tip 72 is provided on the surface of the grounding main body portion 71 on the center electrode 4 side in a portion on the proximal end of the plug so as to face the center tip 412 .

The grounding tip 72 is made of a material with higher wear resistance than the grounding main body portion 71, and is made of a noble metal, for example. The grounding chip 72 is formed into a rectangular plate shape, and is arranged so that its thickness direction coincides with the thickness direction of the center chip 412. As shown in FIG. 2, the position of the end of the grounding tip 72 on the proximal end of the plug matches the position of the end of the grounding main body 71 on the proximal end of the plug. Further, as shown in FIGS. 3 and 4, the positions of both ends of the grounding chip 72 in the width direction (for example, the left-right direction in FIG. 4) perpendicular to the hole axis direction X are the positions of both ends of the grounding main body portion 71 in the width direction. is consistent with Note that in FIG. 4, the grounding chip 72 is hatched for convenience.

As shown in FIG. 3, the dimensions of the grounding tip 72 and the center tip 412 in the width direction (that is, the vertical direction in FIG. 3) are equal to each other. As shown in FIG. 2, in this embodiment, the end of the grounding tip 72 on the proximal end of the plug protrudes further toward the proximal end of the plug than the center tip 412; The tip 412 is located closer to the proximal end of the plug than the end of the tip 412 that is closer to the plug tip. A discharge gap G is formed between the ground tip 72 and the center tip 412. As shown in FIGS. 2 and 3, the discharge gap G is arranged at a position where at least a portion thereof overlaps the inner region of the inner opening 304 in the hole axis direction X.

As shown in FIGS. 1 and 2, the plug cover 3 has a plurality of nozzle holes 33 that penetrate the plug cover 3 in addition to the spark-forming nozzle holes 30. Hereinafter, when the nozzle hole 33 is simply referred to, it means the nozzle hole 33 other than the spark-forming nozzle hole 30 unless otherwise specified. The plurality of nozzle holes 33 are formed closer to the outer periphery of the spark-forming nozzle hole 30 in the plug radial direction. Each nozzle hole 33 is formed so as to be inclined toward the outer circumferential side in the radial direction of the plug as it goes toward the plug tip side. The plurality of nozzle holes 33 are formed at equal intervals in the circumferential direction of the plug. Note that the number, shape, location, etc. of the nozzle holes 33 are determined as appropriate according to requests.

Next, the manner in which the discharge sparks formed in the discharge gap G are extended in the spark plug 1 of this embodiment will be explained using FIGS. 5 and 6. The spark plug 1 of this embodiment is controlled to generate discharge during the compression stroke (that is, before top dead center; BTDC) or the expansion stroke (that is, after top dead center; ATDC) of the internal combustion engine. The way in which the discharge of the spark plug 1 is extended is different depending on whether the discharge is caused during the compression stroke of the internal combustion engine or when the discharge is caused during the expansion stroke.

First, the case where spark discharge is caused to occur in the discharge gap G during the compression stroke will be explained using FIG. 5. In the compression stroke, an airflow F1 flows from the main combustion chamber 12 side toward the auxiliary combustion chamber 2 side around the spark forming nozzle hole 30. When the airflow F1 flows from the main combustion chamber 12 into the cylindrical surface portion 302 of the spark-forming nozzle hole 30, the cross-sectional area of the flow path decreases rapidly, so that the flow velocity locally increases. When the airflow F1 flows into the enlarged surface section 301 from the cylindrical surface section 302, the cross-sectional area of the flow path gradually expands, so that the airflow is diffused and the flow velocity decreases. Then, the airflow that has reached the sub-combustion chamber 2 heads toward the plug base end side so as to avoid the center electrode 4, and a portion thereof passes through the discharge gap G.

The initial discharge spark S generated in the discharge gap G occurs, for example, between the center tip 412 and the ground tip 72, where the spatial distance between the center electrode 4 and the ground electrode 7 is the closest. Then, the initial discharge spark S is pushed by the diffused airflow F1 passing through the discharge gap G as described above, and the region between the two starting points is greatly stretched toward the proximal end of the plug. Then, the discharge spark S is greatly elongated into the sub-combustion chamber 2, directly ignites the air-fuel mixture within the sub-combustion chamber 2, and forms a flame within the sub-combustion chamber 2. The flame grown in the sub-combustion chamber 2 is ejected from the spark-forming nozzle hole 30 and other nozzle holes 33 into the main combustion chamber 12 as a flame jet. Here, since the flow path cross-sectional area of the spark-forming nozzle hole 30 decreases toward the plug tip side, the momentum of the flame jet ejected through the spark-forming nozzle hole 30 increases. Thereby, the combustion period of the internal combustion engine can be shortened. For convenience, FIG. 5 shows two states: an initial discharge spark S and a state in which the initial discharge spark S is stretched.

For example, spark discharge may be caused during the compression stroke when members facing the sub-combustion chamber 2, such as the plug cover 3, housing 5, insulator 6, and center electrode 4, reach a certain level of high temperature, other than during a cold start. Can be done.

Next, the case where spark discharge is caused in the discharge gap G during the expansion stroke will be explained using FIG. 6. In the expansion stroke, an airflow F2 flows from the sub-combustion chamber 2 side toward the main combustion chamber 12 side around the spark-forming nozzle hole 30. The initial discharge spark S generated in the discharge gap G occurs, for example, between the center tip 412 and the ground tip 72, where the spatial distance between the center electrode 4 and the ground electrode 7 is the closest.

The initial discharge spark S is pushed by the above-mentioned airflow F2, and the region between the two starting points is greatly stretched toward the plug tip, and at the same time, the starting point on the grounding tip 72 side moves from the grounding tip 72 to the spark forming nozzle. 30 toward the plug tip side, and eventually moves to near the end of the inner wall of the spark forming nozzle hole 30 on the plug tip side. In this way, a discharge is formed between the spark-forming nozzle hole 30 and the electrode tip 41 of the center electrode 4. Then, the elongated discharge spark S is formed from the spark forming nozzle hole 30 toward the tip end of the plug, that is, within the main combustion chamber 12, and directly ignites the air-fuel mixture within the main combustion chamber 12.

When starting a cold internal combustion engine such as an automobile engine, the ignition timing may be significantly retarded in order to quickly warm up and activate the catalyst. Ignition occurs during the expansion stroke. Generating spark discharge during the expansion stroke has the following advantages: During a cold start, members facing the sub-combustion chamber 2, such as the plug cover 3, housing 5, and insulator 6, may be at a low temperature. Therefore, especially during a cold start, the discharge sparks S are extended toward the main combustion chamber 12 to suppress the contact area between the initial flame and the plug cover 3 and the like. Thereby, it is easy to suppress cooling loss due to the heat of the initial flame being taken away by the plug cover 3 and the like. As a result, it is possible to improve the ignition performance during cold starting and the like.

Next, the effects of this embodiment will be explained.
The spark plug 1 of this embodiment is configured to be able to generate a discharge between the electrode tip 41 and the inner wall of the spark-forming nozzle hole 30. Therefore, for example, by appropriately adjusting the ignition timing, the discharge sparks S can be extended both inside and outside the sub-combustion chamber 2. The inner wall of the spark forming nozzle hole 30 has an enlarged surface portion 301 whose cross-sectional area perpendicular to the hole axis direction X increases toward the sub-combustion chamber 2 side in the hole axis direction X, at least in part in the hole axis direction X. in the area of Therefore, when extending the discharge spark S toward the sub-combustion chamber 2 side, the following effects are achieved.

The enlarged surface portion 301 has a passage cross-sectional area that increases from the outside of the spark plug 1 toward the sub-combustion chamber 2 side. Therefore, the airflow that passes through the spark-forming nozzle hole 30 and heads into the sub-combustion chamber 2 is diffused at the enlarged surface portion 301, and the flow velocity is reduced. This makes it possible to prevent the discharge spark S from easily blowing out and causing frequent re-discharge.

Further, the enlarged surface portion 301 has a flow passage cross-sectional area that decreases from the sub-combustion chamber 2 side toward the outside of the spark plug 1. Therefore, the flame generated by being ignited by the discharge spark S in the sub-combustion chamber 2 grows within the sub-combustion chamber 2, and eventually ejects to the outside of the spark plug 1 through the nozzle hole 33, but As the airflow passes through the enlarged surface section 301 of No. 30, the flow path cross-sectional area of the enlarged surface section 301 decreases as it advances, so that it is compressed and the flow velocity increases. Therefore, the momentum of the flame jet ejected from the spark-forming nozzle hole 30 toward the main combustion chamber 12 is increased, and the ignitability is easily improved.

Further, in the spark forming nozzle hole 30, the area of the inner opening 304 on the side of the sub-combustion chamber 2 is larger than the area of the outer opening 303 on the outside of the spark plug 1. It is easy to diffuse the airflow going from the main combustion chamber 12 side to the sub-combustion chamber 2 side, and it is easy to increase the flow velocity of the airflow going from the sub-combustion chamber 2 side to the main combustion chamber 12 side.

Furthermore, the inner region of the spark-forming nozzle hole 30 and the tip surface 413 of the electrode tip portion 41 are formed at positions that overlap with each other in the hole axis direction X. The area of the inner opening 304 on the sub-combustion chamber 2 side of the spark-forming nozzle hole 30 is larger than the tip surface 413 of the electrode tip 41. When viewed from the hole axis direction X, at least a portion of the inner opening 304 is formed on the outer peripheral side of the tip surface 413 of the electrode tip 41. Therefore, it is possible to suppress the formation of initial discharge sparks S in the spark-forming nozzle hole 30 due to the inner opening 304 of the spark-forming nozzle hole 30 coming too close to the electrode tip 41. Therefore, it is possible to prevent the spark forming nozzle hole 30 from being worn out.

As described above, according to this embodiment, it is possible to provide a spark plug that can improve ignitability.

(Embodiment 2)
In this embodiment, as shown in FIG. 7, the shape of the spark forming nozzle hole 30 is changed from the first embodiment.

In this embodiment, the entire spark forming nozzle hole 30 in the hole axis direction X is an enlarged surface portion 301. That is, the spark forming nozzle hole 30 is generally formed in a tapered shape such that the area of the cross section perpendicular to the hole axis direction X increases as it goes toward the plug base end side.

The rest is the same as in the first embodiment.
Note that among the symbols used in the second embodiment and subsequent embodiments, the same symbols as those used in the previously described embodiments represent the same components as those in the previously described embodiments, unless otherwise specified.

In this embodiment, the spark-forming nozzle holes 30 can be easily formed.
Other than that, it has the same effects as Embodiment 1.

(Embodiment 3)
In this embodiment, as shown in FIG. 8, the shape of the spark forming nozzle hole 30 is changed from the second embodiment. In this embodiment, the spark-forming nozzle hole 30 is curved so that the central portion in the hole axis direction X protrudes toward the inner circumferential side, and has a trumpet shape.
The rest is the same as in the second embodiment.

This embodiment also has the same effects as the second embodiment.

(Embodiment 4)
In this embodiment, as shown in FIG. 9, the shape of the spark forming nozzle hole 30 is changed from the second embodiment. In this embodiment, the spark forming nozzle hole 30 is curved so that the center portion in the hole axis direction X protrudes toward the outer circumferential side.
The rest is the same as in the second embodiment.

This embodiment also has the same effects as the second embodiment.

(Embodiment 5)
In this embodiment, as shown in FIG. 10, the shape of the spark forming nozzle hole 30 is changed from the first embodiment.

In this embodiment, the spark-forming nozzle hole 30 is formed in a stepped shape such that the area of the cross section perpendicular to the hole axis direction X becomes larger toward the proximal end of the plug. In this embodiment, the spark forming nozzle holes 30 are formed in three stages. The entire spark forming nozzle hole 30 in the hole axis direction X is an enlarged surface portion 301.
The rest is the same as in the first embodiment.

This embodiment also has the same effects as the first embodiment.

(Embodiment 6)
In this embodiment, as shown in FIG. 11, the shape of the spark forming nozzle hole 30 is changed from the fifth embodiment.

In this embodiment, the spark forming nozzle hole 30 is formed in two steps. A circular deburring recess 34 is formed around the outer opening 303 in the cover bottom wall 32 . The spark-forming nozzle hole 30 of the plug cover 3 is formed, for example, by punching from the auxiliary combustion chamber 2 side toward the outside of the spark plug 1, and a burr that protrudes to the outside of the spark plug 1 is formed around the outer opening 303 of the spark-forming nozzle hole 30. may be formed. Therefore, deburring work is performed, but traces thereof may remain on the plug cover 3 as deburring recesses 34. The deburring recess 34 is formed to have a thickness that is 1/5 or less of the thickness of the cover bottom wall 32. In this way, the concave portion formed to have a thickness of 1/5 or less of the maximum thickness of the cover bottom wall 32 does not substantially affect the diffusion of airflow, etc., and is not called a spark-forming nozzle hole 30.
The rest is the same as in the fifth embodiment.

This embodiment also has the same effects as the first embodiment.

Note that when deburring is performed using a drill, the deburring recess 34 is formed in a tapered shape that increases in diameter toward the tip end of the plug, as shown in FIG. In such a case, if the thickness of the deepest part of the deburring recess 34 (that is, the inner circumferential end) is less than or equal to 1/5 of the thickness of the cover bottom wall 32, the deburring recess 34 can be removed. 34 does not refer to the spark-forming nozzle 30.

(Embodiment 7)
In this embodiment, as shown in FIG. 13, the formation range of the grounding tip 72 in the hole axis direction X is changed from the first embodiment.

In this embodiment, the formation range of the grounding tip 72 in the hole axis direction X is the same as the formation range of the center tip 412 in the hole axis direction X. That is, in the hole axis direction It is located at the same position as the end of the tip 412 on the proximal end of the plug.
The rest is the same as in the first embodiment.

This embodiment also has the same effects as the first embodiment.

(Embodiment 8)
In this embodiment, as shown in FIG. 14, the formation range of the grounding tip 72 in the hole axis direction X is changed from the first embodiment.

In this embodiment, the formation range of the grounding tip 72 in the hole axis direction X is larger than the formation range of the center tip 412 in the hole axis direction X. In the hole axis direction It stands out.
The rest is the same as in the first embodiment.

In this embodiment, the movement of the starting point of the discharge spark S on the ground tip 72 side toward the plug tip side and toward the plug base end side is easily promoted. Thereby, the ignitability of the spark plug 1 can be easily improved. Furthermore, wear of the ground electrode 7 can be suppressed.
Other than that, it has the same effects as Embodiment 1.

(Embodiment 9)
In this embodiment, as shown in FIG. 15, the formation range of the grounding tip 72 in the hole axis direction X is changed from the eighth embodiment.

A portion of the grounding tip 72 on the proximal end of the plug protrudes further toward the proximal end of the plug than the center tip 412 . A portion of the grounding tip 72 on the plug tip side faces the center tip 412 in the plug radial direction.
The rest is the same as in the first embodiment.

In this embodiment, the movement of the starting point of the discharge spark S on the ground tip 72 side toward the plug base end is easily promoted.
Other than that, it has the same effects as Embodiment 1.

(Embodiment 10)
As shown in FIG. 16, in this embodiment, the formation range of the grounding tip 72 in the hole axis direction X is changed from the eighth embodiment. The grounding tip 72 is formed and arranged over the entire area of the grounding main body portion 71 in the hole axis direction X. A portion of the grounding tip 72 on the proximal end of the plug protrudes further toward the proximal end of the plug than the center tip 412 , and a portion on the distal end of the plug protrudes further toward the distal end of the plug than the center tip 412 . The center portion of the grounding tip 72 in the hole axis direction X faces the center tip 412 in the plug radial direction.
The rest is the same as in the eighth embodiment.

In this embodiment, the movement of the starting point of the discharge spark S on the ground tip 72 side toward the plug tip side and toward the plug base end side is easily promoted.
Other than that, it has the same effects as Embodiment 1.

(Embodiment 11)
In this embodiment, as shown in FIG. 17, the formation range of the grounding tip 72 in the hole axis direction X is changed from the eighth embodiment.

The spark plug 1 of this embodiment includes two grounding tips 72 that are spaced apart from each other in the hole axis direction X. One of the grounding tips 72 is arranged at the end of the grounding main body section 71 on the plug proximal end side, and the other grounding tip 72 is arranged at the end of the grounding main body section 71 on the plug distal end side. In the region between the two grounding tips 72 in the hole axis direction X, the grounding main body portion 71 and the center tip 412 face each other in the plug radial direction.
The rest is the same as in the eighth embodiment.

In this embodiment, the amount of the grounding tip 72 made of noble metal or the like is reduced while promoting the movement of the origin of the discharge spark S on the grounding tip 72 side toward the tip end of the plug and toward the base end of the plug. This can prevent high costs.
Other than that, it has the same effects as Embodiment 1.

(Embodiment 12)
In this embodiment, as shown in FIG. 18, the dimensions of the ground electrode 7 in the hole axis direction X are changed from the first embodiment.

In this embodiment, the end of the ground electrode 7 on the proximal end of the plug is located at the same position as the end of the center electrode 4 on the end of the plug, or closer to the end of the plug than the end of the center electrode 4 on the end of the plug. are doing. The dimension of the grounding tip 72 in the hole axis direction X is smaller than the dimension of the grounding body part 71 in the hole axis direction X. The grounding chip 72 is arranged only at the end of the grounding main body 71 on the proximal end of the plug.
The rest is the same as in the first embodiment.

This embodiment also has the same effects as the first embodiment.

(Embodiment 13)
In this embodiment, as shown in FIG. 19, the formation range of the grounding tip 72 in the hole axis direction X is changed from the twelfth embodiment. That is, in the hole axis direction X, the grounding tip 72 is formed over the entire grounding main body portion 71.
The rest is the same as in the eleventh embodiment.

This embodiment also has the same effects as the first embodiment.

(Embodiment 14)
As shown in FIG. 20, this embodiment is an embodiment in which a grounding tip 72 is bonded to the end surface of the grounding main body portion 71 on the plug base end side. The grounding tip 72 is formed in a region facing the center tip 412 in the plug radial direction. In this embodiment, the entire grounding tip 72 is formed so as to overlap the grounding main body portion 71 in the hole axis direction X.
The rest is the same as in the first embodiment.

This embodiment also has the same effects as the first embodiment.

(Embodiment 15)
As shown in FIGS. 21 and 22, this embodiment is different from the first embodiment in that the ground electrode is eliminated.

In this embodiment, the electrode tip 41 of the center electrode 4 is formed so that the spatial distance between it and the inner opening 304 of the spark forming nozzle hole 30 is the shortest. Therefore, an initial spark discharge is formed between the electrode tip 41 and the spark-forming nozzle 30.

The electrode tip portion 41 of the center electrode 4 is composed only of an electrode tip body 411 and does not include a center tip. As shown in FIG. 22, the electrode tip portion 41 is formed so that the cross-sectional shape perpendicular to the hole axis direction X is circular. That is, the electrode tip portion 41 does not need to form a flat surface on the outer circumferential surface for arranging the center tip 412, and is formed to have a circular cross section. When viewed from the hole axis direction X, the entire inner opening 304 is formed on the outer peripheral side of the tip surface 413 of the electrode tip 41. When viewed from the hole axis direction X, the entire outer opening 303 is formed on the inner peripheral side of the tip surface 413 of the electrode tip 41.
The rest is the same as in the first embodiment.

This embodiment also has the same effects as the first embodiment.

(Embodiment 16)
As shown in FIG. 23, this embodiment is different from the fifteenth embodiment in that a center tip 412 is provided on the end surface of the electrode tip body 411 of the center electrode 4 on the plug tip side. The center tip 412 has a circular shape similar to the tip surface of the electrode tip body 411, and is arranged over substantially the entire end surface of the electrode tip body 411 on the plug tip side.
The rest is the same as the fifteenth embodiment.

This embodiment also has the same effects as the first embodiment.

(Embodiment 17)
As shown in FIGS. 24 and 25, this embodiment is different from the first embodiment in that the center chip and the ground chip are eliminated. That is, the electrode tip portion 41 of the center electrode 4 is made up of only the electrode tip body 411, and the ground electrode 7 is made up of only the ground body portion 71.

The electrode tip main body 411 of the center electrode 4 is formed to have a circular cross section as in the twelfth embodiment. Further, as shown in FIG. 24, the ground electrode 7 is formed to have a rectangular cross section.
The rest is the same as in the first embodiment.

This embodiment also has the same effects as the first embodiment.

Note that in this embodiment, since no grounding chip is provided in the grounding main body portion 71, there is no need to form a plane facing the center electrode 4 side in the grounding main body portion 71. Therefore, for example, the grounding main body portion 71 may be formed to have a circular cross section as shown in FIG. 26.

(Embodiment 18)
As shown in FIG. 27, this embodiment is different from the seventeenth embodiment in that a center tip 412 is provided on the end surface of the electrode tip body 411 of the center electrode 4 on the plug tip side.

The center tip 412 has a circular shape similar to the end surface of the electrode tip body 411 on the plug tip side, and is arranged over substantially the entire end surface of the electrode tip body 411 on the plug tip side. The length of the center tip 412 in the hole axis direction X is larger than the diameter of the center tip 412. The outer peripheral surface of the center tip 412 faces the ground electrode 7 in the plug radial direction.
The rest is the same as in the seventeenth embodiment.

This embodiment also has the same effects as the first embodiment.

(Embodiment 19)
In this embodiment, as shown in FIGS. 28 and 29, a center chip 412 is provided in contrast to the seventeenth embodiment, and the way in which the center chip 412 is provided is improved.

In this embodiment, the electrode tip main body 411 of the center electrode 4 has an electrode tip recess 414 at a portion on the ground electrode 7 side in the plug radial direction. The electrode tip recess 414 is formed so that the side surface of the electrode tip main body 411 is recessed toward the inner circumference, and is open toward the plug tip side. The bottom surface 414a of the electrode tip recess 414 is formed to be a flat surface facing the ground electrode 7 side.

A central tip 412 is disposed within the electrode tip recess 414 . The center tip 412 is formed into a plate shape having a thickness in the plug radial direction, and faces the ground electrode 7 in the plug radial direction. When viewed from the hole axis direction X, a portion of the center tip 412 is disposed within the electrode tip recess 414, and the other portion is disposed outside the electrode tip recess 414. In addition, in FIG. 29, the outline of the electrode tip recess 414 in the direction perpendicular to the hole axis direction X is represented by a two-dot chain line.
The rest is the same as in the seventeenth embodiment.

This embodiment also has the same effects as the seventeenth embodiment.

(Embodiment 20)
As shown in FIG. 30, this embodiment is different from the first embodiment in that it does not include a grounding chip. In this embodiment, an initial spark discharge is formed between the center tip 412 and the grounded body portion 71.
The rest is the same as in the first embodiment.

This embodiment also has the same effects as the first embodiment.

(Embodiment 21)
As shown in FIG. 31, this embodiment is an embodiment in which the entire ground electrode 7 is constituted by a ground tip 72 made of noble metal, in contrast to embodiment 20. In this embodiment, the maximum width of the ground electrode 7 in the opposing direction between the ground electrode 7 and the center electrode 4 is equal to or less than 1/2 of the length of the ground electrode 7 in the hole axis direction X.
The rest is the same as the 20th embodiment.

This embodiment also has the same effects as the first embodiment.

(Embodiment 22)
As shown in FIG. 32, this embodiment is different from the first embodiment in that the ground electrode 7 is attached to the cover side wall 31.

The ground electrode 7 is formed to be elongated in the plug radial direction. The end surface of the ground electrode 7 on the inner peripheral side faces the center electrode 4 side. The ground electrode 7 consists of only the ground main body part 71 and does not include the ground tip 72, but is not limited thereto.

The electrode tip portion 41 of the center electrode 4 includes an electrode tip body 411 and a center tip 412 attached to a side surface of the electrode tip body 411. The center tip 412 is provided on the side surface of the electrode tip main body 411 so as to form a discharge gap G so as to face the end surface on the inner peripheral side of the ground electrode 7 in the plug radial direction.

In this embodiment, among all the nozzle holes 33, the nozzle hole that is spatially closest to the discharge gap G is the spark-forming nozzle hole 30. In this embodiment, the spark-forming nozzle hole 30 is formed near the corner between the cover bottom wall 32 and the cover side wall 31, and is arranged in the plug axial direction Y so as to move toward the inner circumference toward the plug base end. tilted against. Along with this, the hole axis direction X is also inclined with respect to the plug axis direction Y so that the closer it goes to the plug base end, the more the hole goes toward the inner peripheral side. The spark forming nozzle hole 30 is formed so that the area of the cross section perpendicular to the hole axis direction X increases as it goes toward the sub-combustion chamber 2 side in the hole axis direction X. At least a portion of the discharge gap G is arranged on an extension line of the spark forming nozzle hole 30 in the hole axis direction X.

In this embodiment, when spark discharge is caused in the discharge gap G during the compression stroke of the internal combustion engine, the airflow is diffused from the main combustion chamber 12 side through the spark formation nozzle holes 30 and reaches the sub-combustion chamber 2 . The discharge sparks S generated in the discharge gap G of the spark plug 1 are pushed by the diffused airflow as described above and are stretched within the sub-combustion chamber 2.

In addition, when a discharge is generated in the discharge gap G during the expansion stroke of the internal combustion engine, the discharge spark S is pushed by the airflow that goes from the auxiliary combustion chamber 2 side to the main combustion chamber 12 side, and the discharge spark S starts at the ground electrode 7 side. moves to the spark-forming nozzle hole 30, and eventually the region between the two starting points of the discharge spark S is extended from the spark-forming nozzle hole 30 toward the main combustion chamber 12 side.
The rest is the same as in the first embodiment.

This embodiment also has the same effects as the first embodiment.

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

For example, as shown in FIG. 33, in contrast to Embodiment 1, the cross-sectional shape of the ground electrode 7 perpendicular to the hole axis direction X can be made approximately semicircular, as if a part of the circle was cut straight. In this case, by arranging the grounding tip 72 on the straight portion 73 in the cross-sectional shape of the grounding electrode 7, the arrangement of the grounding tip 72 becomes easy.

Further, as shown in FIG. 34, the arrangement range of the grounding chip 72 may be modified with respect to the first embodiment. In the example shown in FIG. 34, the grounding tip 72 is formed to fit inside the grounding main body portion 71 when viewed from the center electrode side. Further, as shown in FIG. 35, the shape of the grounding tip 72 when viewed from the center electrode side may be circular.

1 Spark plug 2 Sub-combustion chamber 30 Spark forming nozzle hole 301 Enlarged surface portion 33 Nozzle hole 4 Center electrode 41 Electrode tip X Hole axial direction

Claims (3)

A sub-combustion chamber (2), at least one injection hole (33) communicating the sub-combustion chamber with the outside, and a center electrode (4) having an electrode tip (41) disposed within the sub-combustion chamber. A spark plug (1) comprising: a spark plug (1) configured to be able to generate an electric discharge between an inner wall of at least one of the spark-forming nozzle holes (30) and the tip of the electrode;
The inner wall of the spark forming nozzle hole has an enlarged surface portion (301) in which the area of a cross section perpendicular to the hole axis direction increases toward the sub-combustion chamber side in the hole axis direction (X) of the spark forming nozzle hole. , a spark plug having the spark plug in at least a partial region in the axial direction of the hole. The spark plug according to claim 1, wherein the area of the inner opening (304) on the side of the sub-combustion chamber of the spark-forming nozzle hole is larger than the area of the outer opening (303) on the outside side of the spark plug. . The inner region of the spark-forming nozzle hole and the tip surface (413) of the electrode tip portion are formed at positions overlapping each other in the hole axial direction, and the inner opening of the spark-forming nozzle hole on the sub-combustion chamber side The area of the portion (304) is larger than the tip surface of the electrode tip, and when viewed from the hole axis direction, at least a part of the inner opening is on the outer peripheral side of the tip surface of the electrode tip. The spark plug according to claim 1 or 2, wherein the spark plug is formed in a.

Images