JP6762008B2 - Spark plug device - Google Patents

Description

The present invention relates to a spark plug device.

For example, Patent Document 1 discloses a spark plug (spark plug device) in which a sub-combustion chamber (ignition chamber) is formed by a housing and a plug cover fixed in contact with the housing. Such a spark plug is attached to the combustion chamber of an internal combustion engine, and by applying a high voltage to the center electrode provided inside the housing, between the center electrode and the ground electrode provided on the plug cover. Generates a flame nucleus. The spark plug ignites the mixture of fuel and air filled in the combustion chamber by this flame nucleus.

Japanese Unexamined Patent Publication No. 2015-130302

By the way, in recent years, it has been proposed to perform lean burn with a lean mixture in order to improve the fuel efficiency of an internal combustion engine. The dilute air-fuel mixture has lower ignitability than the normal air-fuel mixture. Therefore, in the case of lean burn, it is necessary to pass a larger current through the center electrode in the spark plug device to generate a flame nucleus having a high energy density. However, when a large current is passed through the center electrode, a large load is applied to the center electrode, which may accelerate the replacement cycle of the spark plug.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to reduce the load applied to the center electrode and extend the life of the spark plug device.

In order to achieve the above object, in the present invention, as a first means, a spark plug device including a center electrode through which an electric current is passed and a ground electrode arranged with a gap between the tip of the center electrode. Therefore, a configuration is adopted in which the inner wall surface is set to a three-dimensional shape having at least one focal point, and the plug cover is provided so that the focal point is aligned with the gap.

As the second means, in the first means, the inner wall surface of the plug cover is formed by at least a part of a spherical surface centered on the focal point.

As the third means, in the second means, the inner wall surface of the plug cover is formed by a range exceeding at least half of the spherical surface.

As a fourth means, in the second or third means, the inner wall surface of the plug cover and the ground electrode are connected, and only the ground electrode is arranged between the gap and the inner wall surface of the plug cover. Adopt the configuration that is.

As a fifth means, in any of the first to fourth means, the housing is provided with the center electrode being held and the shape of the end face facing the gap is set so that the focal point is aligned with the gap. , Is adopted.

As the sixth means, in the fifth means, a configuration is adopted in which the diameter of the housing is set to be equal to or larger than the bolt diameter of M14 specified in the Japanese Industrial Standards.

As a seventh means, in any of the first to fourth means, the plug cover adopts a configuration in which openings are formed at intervals of 120 ° in the circumferential direction centered on the apex.

According to the present invention, the inner wall surface of the plug cover has a three-dimensional shape having a focal point, and the focal point of the plug cover is arranged in the gap between the center electrode and the ground electrode. When the center electrode is energized, energy due to electric discharge is released into the gap between the center electrode and the ground electrode, and a shock wave is generated. When this shock wave is reflected in the focal direction on the inner wall surface of the plug cover, adiabatic compression of the air-fuel mixture occurs at the focal point, and the temperature of the air-fuel mixture rises. As a result, the air-fuel mixture becomes more easily ignited, so that ignition is possible even when the energy density of the flame nucleus is small. Therefore, the current flowing through the center electrode can be reduced as compared with the conventional case, and the life of the spark plug device can be extended by reducing the load applied to the center electrode.

It is a partial sectional view of the spark plug device which concerns on one Embodiment of this invention. It is an enlarged sectional view including the plug cover of the spark plug device which concerns on one Embodiment of this invention. It is a front view including the plug cover of the spark plug device which concerns on one Embodiment of this invention. It is an enlarged sectional view including a plug cover in the modification of the spark plug device which concerns on one Embodiment of this invention. It is an enlarged sectional view including a plug cover in the modification of the spark plug device which concerns on one Embodiment of this invention.

Hereinafter, an embodiment of the spark plug device according to the present invention will be described with reference to the drawings. In the drawings below, the scale of each member is appropriately changed in order to make each member recognizable.

[First Embodiment]
FIG. 1 is a partial cross-sectional view of the spark plug device 1 according to the present embodiment. Further, FIG. 2 is an enlarged cross-sectional view including the plug cover 4 of the spark plug device 1 according to the present embodiment.
The spark plug device 1 according to the present embodiment is provided in a combustion chamber of, for example, an internal combustion engine, and as shown in FIGS. 1 and 2, a housing portion 2, an insulating porcelain 3, a plug cover 4, and a center electrode 5 are provided. A ground electrode 6 and a terminal 7 are provided. In this spark plug device 1, an ignition chamber A is formed inside the plug cover 4. The ignition chamber A is a space centered on the focal point A1 and is arranged inside the combustion chamber of the internal combustion engine.

The housing portion 2 is provided on the outer periphery of the center electrode 5 and is a member that holds the center electrode 5. The housing portion 2 has a housing 2a and a gasket 2b fixed to the outer periphery of the housing 2a. The housing 2a has an outer peripheral diameter substantially equal to that of the M18 bolt specified in the Japanese Industrial Standards, has a cylindrical shape centered on the central axis L, and has a plug cover 4 attached to one end.
Further, the other end side of the housing 2a has an enlarged diameter, and as shown in FIG. 2, has a substantially hexagonal shape when viewed from the central axis L direction. The gasket 2b is a member that seals a gap with respect to the internal combustion engine when the spark plug device 1 is attached to the internal combustion engine.

As shown in FIG. 1, the insulating insulator 3 is arranged between the housing 2a and the center electrode 5, has a substantially cylindrical shape centered on the central axis L, and is a member formed of ceramic or the like. Such an insulator 3 insulates between the housing 2a and the center electrode 5 and between the housing 2a and the terminal 7.

The plug cover 4 is a hemispherical dome-shaped metal member, and its open end is fixed to the end of the housing 2a. Further, the plug cover 4 is formed with an ignition opening 4a. FIG. 3 is a front view including the plug cover 4 of the spark plug device 1 according to the present embodiment. As shown in FIG. 3, the ignition openings 4a are formed at three locations at intervals of 120 ° about the apex of the central axis L. The ignition opening 4a is an opening for allowing the air-fuel mixture filled in the combustion chamber of the internal combustion engine to flow into the ignition chamber A.

The inner wall surface 4b of the plug cover 4 has a spherical shape centered on the focal point A1 formed on the central axis L. A substantially spherical ignition chamber A centered on the focal point A1 is formed by the spherical inner wall surface 4b of the plug cover 4, the end surface 2a1 of the housing 2a, and the end surface 3a of the insulating insulator 3. Further, the inner wall surface 4b has a spherical shape up to a position beyond the focal point A1 and in contact with the housing 2a. That is, the inner wall surface 4b is formed by a range exceeding at least half of the spherical surface centered on the focal point A1.
The plug cover 4 is arranged so that the focal point A1 and the gap between the center electrode 5 and the ground electrode 6 are aligned with each other. Such an ignition chamber A is a space in which members other than the ground electrode 6 do not exist in the range from the focal point A1 to the plug cover 4.

The center electrode 5 is a tapered metal member having a substantially cylindrical shape provided inside the insulating insulator 3 on the central axis L, and the tapered tip portion 5a protrudes from the end portion of the insulating insulator 3. That is, the tip portion 5a of the center electrode 5 projects toward the ignition chamber A. The tip portion 5a is arranged on the insulating insulator 3 side with respect to the focal point A1. Further, the center electrode 5 has an end portion opposite to the tip portion 5a in contact with the terminal 7. When a current flows through the center electrode 5 via the terminal 7, a discharge phenomenon occurs between the center electrode 5 and the ground electrode 6.

The ground electrode 6 is an inner wall surface 4b of the plug cover 4 and is a metal member arranged on the central axis L. The ground electrode 6 and the center electrode 5 face each other on the central axis L with the ignition chamber A interposed therebetween in a state of forming a gap. Such a ground electrode 6 is an electrode on the negative electrode side with respect to the center electrode 5. The current flowing through the ground electrode 6 is discharged to the cylinder head of the internal combustion engine via the plug cover 4 and the housing 2a.

The terminal 7 is a terminal that comes into contact with the end portion of the center electrode 5 opposite to the tip portion 5a and is arranged inside the insulating insulator 3 on the central axis L. The terminal 7 is connected to an ignition coil or the like (not shown), and a current generated by the ignition coil or the like is passed through the center electrode 5.

The ignition operation of the spark plug device 1 according to the present embodiment will be described.
The current generated by the ignition coil or the like flows to the center electrode 5 via the terminal 7. As a result, a discharge phenomenon occurs between the center electrode 5 and the ground electrode 6, and a flame nucleus is formed. At this time, in the ignition chamber A, a shock wave is generated radially around the focal point A1 in the gap between the center electrode 5 and the ground electrode 6. This shock wave is reflected by the inner wall surface 4b of the plug cover 4, the end surface 2a1 of the housing 2a, and the end surface 3a of the insulating insulator 3, and returns to the focal point A1 direction again. As a result, in the ignition chamber A, the energy of the shock wave is concentrated around the focal point A1, the air-fuel mixture is adiabatically compressed, and the temperature rises sharply. The period until the temperature rises is extremely short as compared with the discharge period. Therefore, the air-fuel mixture in the ignition chamber A becomes easier to ignite as the temperature rises. Therefore, it is possible to ignite even if the energy density of the flame nucleus is small.

Further, in the combustion chamber of the internal combustion engine, the air-fuel mixture is flowing violently. On the other hand, by providing the spark plug device 4 with the plug cover 4, the plug cover 4 functions as a windshield, so that the flow of the air-fuel mixture in the ignition chamber A can be suppressed. Therefore, a flame nucleus is likely to be generated in the gap between the center electrode 5 and the ground electrode 6.

According to the spark plug device 1 according to the present embodiment, since the inner wall surface 4b of the plug cover 4 is hemispherical, the energy of the shock wave generated inside the ignition chamber A is concentrated on the focal point A1. The air-fuel mixture around the focal point A1 is adiabatically compressed, so that the temperature rises and it becomes easy to ignite. That is, the spark plug device 1 according to the present embodiment can ignite the air-fuel mixture even if the current flowing through the center electrode 5 is reduced. Therefore, it is possible to reduce the load on the center electrode 5 and extend the service life.

Further, according to the spark plug device 1 according to the present embodiment, the inner wall surface 4b of the plug cover 4 is formed in a range exceeding half of the spherical surface centered on the focal point A1. Therefore, the inner wall surface 4b of the plug cover 4 can reflect the shock wave in a range exceeding half of the spherical surface centered on the focal point A1.

Further, in the ignition chamber A, there is no member that inhibits the reflection of the shock wave between the focal point A1 and the plug cover 4. As a result, more shock waves are reflected by the inner wall surface 4b of the plug cover 4, and the temperature of the air-fuel mixture at the focal point A1 can be raised. Therefore, the air-fuel mixture can be ignited efficiently, and the life of the center electrode 5 can be further extended.

Further, in the spark plug device 1 according to the present embodiment, the diameter of the housing 2a is M18. Therefore, the surface area of the plug cover 4 can be increased. Therefore, more shock waves generated in the ignition chamber A can be reflected, and the life of the center electrode 5 can be extended.

Further, according to the spark plug device 1 according to the present embodiment, three ignition openings 4a of the plug cover 4 are formed at intervals of 120 °. Therefore, the spark plug device 1 according to the present embodiment can maximize the effect of reflecting the shock wave energy and suppressing the heat loss of the plug cover 4 when the combustion is performed using the dilute mixture. Therefore, the air-fuel mixture can be ignited more efficiently, the load on the center electrode 5 can be reduced, and the life of the spark plug device 1 can be further extended.

[Second Embodiment]
Subsequently, a modified example of the spark plug device according to the present invention will be described as a second embodiment. In the spark plug device 1 according to the present embodiment, the same reference numerals are used for the parts common to the first embodiment, and the description thereof will be omitted. FIG. 4 is an enlarged cross-sectional view including the plug cover 4 of the spark plug device 1 according to the present embodiment.

As shown in FIG. 4, the housing portion 2 in the present embodiment is shaped so that the annular end surface 2a1 of the end portion to which the plug cover 4 is attached has a curved surface having a center on the central axis L. The housing portion 2 is arranged so that the center of the end surface 2a1 overlaps the focal point A1. Further, the insulating insulator 3 is shaped like a curved surface in which the end surface 3a of the end portion on the plug cover 4 side has a center on the central axis L, similarly to the housing portion 2. The insulating insulator 3 is arranged so that the center of the end surface 3a overlaps the focal point A1.

According to the spark plug device 1 according to the present embodiment, the end surface 2a1 of the housing 2a arranged facing the ignition chamber A and the end surface 3a of the insulating insulator 3 face the inner wall surface 4b of the plug cover 4. It is processed into a curved surface in the direction. As a result, the shock wave generated in the ignition chamber A is also reflected in the focal point A1 direction on the end surface 2a1 of the housing 2a and the end surface 3a of the insulating insulator 3. Therefore, since more energy can be concentrated on the focal point A1, the air-fuel mixture can be ignited more efficiently, and the life of the center electrode 5 can be further extended.

[Third Embodiment]
A modification of the spark plug device according to the present invention will be described as a third embodiment. In the spark plug device 1 according to the present embodiment, the same reference numerals are used for the parts common to the first embodiment, and the description thereof will be omitted. FIG. 5 is an enlarged cross-sectional view including the plug cover 4 of the spark plug device 1 according to the present embodiment.

As shown in FIG. 5, the ground electrodes 6a and 6b in the present embodiment project toward the focal point A1 from two positions at equal distances with the central axis L in between. With such a configuration, even if one ground electrode 6a does not function, the spark plug device 1 can be operated by the other ground electrode 6b functioning. Therefore, it is possible to extend the life of the spark plug device 1.

The present invention is not limited to the above embodiment, and for example, the following modifications can be considered.
(1) In the second embodiment, the end surface 2a1 of the housing 2a adopts a curved surface, but the present invention is not limited thereto. The end surface 2a1 of the housing 2a may be a flat surface perpendicular to the straight line connecting the edge of the end surface 2a1 and the focal point A1. In this case, it is easier to manufacture than the case where the end face 2a1 is a curved surface.
Similarly, the end surface 3a of the insulating insulator 3 can also be a flat surface that is perpendicular to the straight line connecting the edge of the end surface 3a and the focal point A1.

(2) Further, in the first to third embodiments, the outer diameter of the housing 2a is M18, and the ignition openings 4a of the plug cover 4 are formed at three places at 120 ° intervals. The invention is not limited to this. The number and size of the ignition openings 4a of the plug cover 4 can be appropriately changed based on the correlation between the reflected amount of the shock wave and the heat loss amount, depending on the outer diameter of the housing.

(3) Further, the center electrode 5 can have a curved end surface of the tip portion 5a. In this case, since the shock wave can be reflected even at the end face of the center electrode 5, more shock wave energy can be concentrated on the focal point A1. Therefore, the temperature of the air-fuel mixture can be raised further.

(4) Further, in the first to third embodiments, the inner wall surface 4b of the plug cover 4 has a curved surface shape, but the present invention is not limited to this. The inner wall surface 4b of the plug cover 4 may have a three-dimensional polyhedral shape.

1 …… Spark plug device 2 …… Housing 2a …… Housing 2a 1 …… End face 4 …… Plug cover 5 …… Center electrode 6 …… Ground electrode A …… Ignition chamber A1 …… Focus L …… Center axis

Claims (9)

A spark plug device including a center electrode through which an electric current is passed and a ground electrode arranged with a gap between the tip of the center electrode.
The inner wall surface is set to a three-dimensional shape having at least one focal point, and the plug cover is provided so that the focal points are aligned with the gap .
The plug cover is an ignition plug device that covers the gap from the side opposite to the center electrode . The spark plug device according to claim 1, wherein the inner wall surface of the plug cover is formed by at least a part of a spherical surface centered on the focal point. The spark plug device according to claim 2, wherein the inner wall surface of the plug cover is formed by a range exceeding at least half of the spherical surface. The inner wall surface of the plug cover and the ground electrode are connected to each other.
The spark plug device according to any one of claims 1 to 3, wherein only the ground electrode is arranged between the gap and the inner wall surface of the plug cover. The ignition according to any one of claims 1 to 4, wherein the center electrode is held and the housing is provided with a housing in which the shape of the end face facing the gap is set so that the focus is aligned with the gap. Plug device. The spark plug device according to claim 5, wherein the diameter of the housing is set to be equal to or larger than the bolt diameter of M14 specified in the Japanese Industrial Standards. The spark plug device according to any one of claims 1 to 6, wherein the plug cover is formed with openings at intervals of 120 ° in the circumferential direction centered on the apex. A spark plug device including a center electrode through which an electric current is passed and a ground electrode arranged with a gap between the tip of the center electrode.
The inner wall surface is set to a three-dimensional shape having at least one focal point, and the plug cover is provided so that the focal points are aligned with the gap .
An ignition plug device characterized in that the inner wall surface of the plug cover is formed by at least a part of a spherical surface centered on the focal point . A spark plug device including a center electrode through which an electric current is passed and a ground electrode arranged with a gap between the tip of the center electrode.
The inner wall surface is set to a three-dimensional shape having at least one focal point, and the plug cover is provided so that the focal points are aligned with the gap .
The plug cover is an ignition plug device characterized in that openings are formed at intervals of 120 ° in the circumferential direction centered on the apex .

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