JP6715600B2 - Spark plug for internal combustion engine - Google Patents

Description

The present invention relates to a spark plug for an internal combustion engine.

2. Description of the Related Art Some ignition plugs that ignite an air-fuel mixture filled in a combustion chamber of an internal combustion engine are ignited by high frequency electric energy. As an example of such a spark plug, Patent Document 1 discloses a coaxial cable having an inner conductor as a center electrode, an outer conductor as a ground electrode, and a packing as a dielectric provided between the two at the tips of the two. A spark plug including a waveguide structure is disclosed. In the configuration disclosed in Patent Document 1, the tip of the coaxial waveguide structure is projected into the combustion chamber of the internal combustion engine. Then, a high-frequency voltage is applied to the coaxial waveguide structure to concentrate the electric field at the tip of the inner conductor, whereby free plasma consisting of microwave plasma is formed at the tip. A discharge is formed at the tip of the coaxial waveguide structure by the free plasma, so that the air-fuel mixture in the combustion chamber is ignited.

Japanese Patent No. 4404770

However, in the configuration disclosed in Patent Document 1, it is difficult to form a discharge in a high pressure field because the discharge is formed only by the electric field concentration by the microwave. For example, when a microwave oscillator with an output of 500 W is used, the discharge formation limit pressure at room temperature is about 2 atm. Further, even when the end portion of the inner conductor (that is, the center electrode) as the antenna reaches a high temperature (for example, about 900° C. which is a knock limit) due to heating by high frequency or heating by combustion in the engine cylinder, The discharge formation limit pressure is at most about 8 atm. On the other hand, the internal pressure of the combustion chamber in an internal combustion engine of an automobile or the like is 20 atmospheric pressure or more in the high load region, which is higher than the discharge formation limit pressure described above. Therefore, in an internal combustion engine such as an automobile, it is difficult to generate a discharge only by the electric field concentration of microwaves in a high load region.

In order to facilitate the discharge formation by the electric field concentration of microwaves in such a high load region, the electric field strength is increased by using a high-power microwave oscillator as the first method, and the spark discharge is used as the second method. It is conceivable to use a discharge forming assist such as a laser together. However, in the first method, since the electric field strength is proportional to the square root of the input power, there is a problem in that increasing the electric field strength causes a large increase in energy consumption. In addition, the use of a high-power microwave oscillator causes a problem of an increase in cost and an increase in size. In the second method, there are problems that the ignition system becomes complicated, the entire apparatus becomes large, and the cost increases due to an increase in the number of parts. Therefore, none of them is suitable for use in an internal combustion engine equipped in an automobile or the like.

The present invention has been made in view of such a background, and an object thereof is to provide an ignition plug for an internal combustion engine, which is suitable for an internal combustion engine provided in an automobile or the like.

One aspect of the present invention includes a cylindrical outer conductor (10),
A tubular shape that is held inside the outer conductor (10) and has a dielectric tip (21, 210, 211, 212) exposed on the tip side (Y1) in the plug axial direction (Y) of the outer conductor. A dielectric (20, 200, 201, 202),
A center electrode (30, 300, 301) which is held inside the tubular dielectric and has an electrode tip (31, 310, 311) exposed on the tip side in the plug axial direction of the tubular dielectric. ,
Equipped with
A spark plug (1) for an internal combustion engine, which is configured to apply a high-frequency voltage to the center electrode to form a discharge from a tip portion of the electrode toward a tip side in a plug axial direction,
Between the electrode tip and the dielectric tip, when a high-frequency voltage is applied to the center electrode, the electrode is provided between the electrode tip and the dielectric tip prior to the discharge. Space portions (50, 500, 501, 502, 503, 504, 505) are formed to separate the two so that a partial discharge is generated from the tip portion,
The space portion includes a region inside the outer conductor, which is located closer to the base end side (Y2) in the plug axial direction than the end portion (121) in the plug axial direction in the outer conductor , and the plug shaft. The front end of the center electrode is heated by lowering the gas density of the fuel in the space by applying a high-frequency voltage to the center electrode. A spark plug (1) for an internal combustion engine, characterized in that the starting voltage is lowered to cause the partial discharge.

In the above ignition plug for an internal combustion engine, when a high frequency voltage is applied to the center electrode, first, the center electrode is heated, and the gas density in the space formed between the center electrode and the tubular dielectric is increased. made and the decrease in the child. As a result, the discharge starting voltage in the space decreases, so that partial discharge easily occurs in the space. Then, by further applying a high frequency voltage, a partial discharge is formed in the space from the tip of the electrode. The formed partial discharge extends from the electrode tip toward the tip side in the plug axial direction by absorbing the high frequency energy emitted from the electrode tip of the center electrode due to the application of the high frequency voltage. The discharge is formed toward the tip side.

That is, the above-mentioned partial discharge becomes a trigger discharge of the discharge formed from the electrode tip of the center electrode toward the tip side in the plug axis direction, and from the electrode tip to the tip side with smaller energy (that is, low electric field strength). A discharge can be formed toward the discharge. As a result, even under a high pressure condition of, for example, 20 atmospheres or more, discharge formation by electric field concentration based on application of a high frequency voltage becomes easy. As a result, the ignition limit (so-called EGR limit) under high EGR conditions in the internal combustion engine and the ignition limit (so-called lean limit) under lean fuel conditions (ie, lean combustion) are improved to improve the thermal efficiency in the internal combustion engine. It is possible to improve the fuel efficiency.

In the spark plug for the internal combustion engine, since it is not necessary to use a high-power microwave oscillator, it is possible to reduce energy consumption and cost, and it is possible to suppress an increase in size and a complicated ignition system. .. Therefore, the spark plug for an internal combustion engine is more suitable for use in an internal combustion engine for an automobile or the like.

As described above, according to the above aspect, it is possible to provide a spark plug for an internal combustion engine, which is more suitable for use in an internal combustion engine for an automobile or the like.
The reference numerals in parentheses described in the claims and the means for solving the problems indicate the corresponding relationship with the specific means described in the examples described later, and limit the technical scope of the present invention. Not a thing.

3 is a perspective view of an ignition plug for an internal combustion engine in Embodiment 1. FIG. FIG. 3 is a sectional view of the tip of the spark plug for the internal combustion engine in the first embodiment. 3 is a schematic diagram showing discharge formation in an ignition plug for an internal combustion engine in Embodiment 1. FIG. FIG. 3 is a diagram showing discharge formation in the spark plug for the internal combustion engine in the first embodiment. FIG. 5 is a diagram showing the results of a discharge test in Example 1. 6 is a perspective view of an ignition plug for an internal combustion engine in Embodiment 2. FIG. 6 is a sectional view of the tip of an ignition plug for an internal combustion engine in Embodiment 2. FIG. 6 is a schematic diagram showing discharge formation in an ignition plug for an internal combustion engine in Example 2. FIG. FIG. 6 is a sectional view of a tip of an ignition plug for an internal combustion engine according to a third embodiment. 8 is a sectional view of the tip of an ignition plug for an internal combustion engine in Embodiment 4. FIG. FIG. 9 is a sectional view of the tip of an ignition plug for an internal combustion engine in a fifth embodiment. FIG. 10 is a sectional view of the tip of an ignition plug for an internal combustion engine in a sixth embodiment. FIG. 13 is a sectional view of the tip of an ignition plug for an internal combustion engine in a seventh embodiment. FIG. 5 is a sectional view of the tip of an ignition plug for an internal combustion engine in a reference example .

The spark plug for an internal combustion engine of the present invention can be used as an ignition means in an internal combustion engine provided in an automobile or the like.
In the above spark plug for an internal combustion engine, the side inserted into the combustion chamber is referred to as the tip side, and the end portion on the tip side is referred to as the tip. Further, the side opposite to the tip side is referred to as the base end side, and the end portion on the base end side is referred to as the base end.
Further, in the present specification, the plug axial direction means the axial direction of the spark plug.
Further, in the present specification, the space portion is such that an air layer is interposed between the electrode tip portion and the dielectric tip portion, and the outer edge portion of the electrode tip portion and the inner edge portion of the dielectric tip portion are formed. It is defined as a space including a virtual line segment connecting with.

(Example 1)
An embodiment of the spark plug for the internal combustion engine will be described with reference to FIGS.
The spark plug 1 for an internal combustion engine of the first embodiment includes an outer conductor 10, a tubular dielectric 20, and a center electrode 30, as shown in FIGS. 1 and 2.
The outer conductor 10 has a tubular shape.
The tubular dielectric 20 is held inside the outer conductor 10 and has a dielectric tip portion 21 exposed on the tip side Y1 of the outer conductor 10 in the plug axis direction Y.
The center electrode 30 is held inside the tubular dielectric 20, and has an electrode tip portion 31 exposed on the tip side Y1 of the tubular dielectric 20 in the plug axis direction Y.
Then, in the spark plug 1 for an internal combustion engine, as shown in FIG. 3, a high frequency voltage is applied to the center electrode 30 to form a discharge S2 from the electrode tip 31 toward the tip side Y1 in the plug axis direction Y. Is configured. A discharge S2 formed between the electrode tip 31 and the dielectric tip 21 from the electrode tip 31 toward the tip side Y1 in the plug axis direction Y when a high frequency voltage is applied to the center electrode 30. Prior to the above, a space 50 is formed between the electrode tip 31 and the dielectric tip 21 so as to separate them so that a partial discharge S1 is generated from the electrode tip 31.
In this example, the direction of the tip in the plug axis direction Y is the tip side Y1, and the side opposite to the tip side Y1 is the base side Y2.

Hereinafter, the spark plug 1 for the internal combustion engine of this example (hereinafter, also simply referred to as “spark plug 1”) will be described in detail.
As shown in FIG. 1, in the present example, the outer conductor 10 includes a cylindrical first outer conductor 11 and a cylindrical second outer conductor provided inside the first outer conductor 11 so as to share a central axis. And a conductor 12. A gap 10 a is formed between the first outer conductor 11 and the second outer conductor 12. The first outer conductor 11 also serves as the housing 13 of the ignition plug 1, and a mounting screw portion 131 for screwing into the internal combustion engine is formed on the outer peripheral surface of the housing 13.

As shown in FIG. 2, the tubular dielectric 20 is provided inside the second outer conductor 12 so as to share the central axis with the first outer conductor 11 and the second outer conductor 12. The dielectric tip portion 21, which is the tip on the tip side Y1 of the tubular dielectric 20, is located closer to the tip side Y1 than the outer conductor tip portion 121, which is the tip portion on the tip side Y1 of the second outer conductor 12. That is, the dielectric tip 21 of the tubular dielectric 20 projects toward the tip side Y1. As the material of the cylindrical dielectric 20, it is preferable to adopt a material that improves the electric field strength of the electrode tip portion 31. By improving the electric field strength of the electrode tip portion 31, a partial discharge is easily formed between the electrode tip portion 31 and the dielectric tip portion 21. A material having a high dielectric constant (eg, alumina) can be used as the material of the cylindrical dielectric body 20 that improves the electric field strength of the electrode tip portion 31.

The center electrode 30 has a columnar shape, and is provided inside the tubular dielectric 20 so as to share the central axis with the tubular dielectric 20. The outer diameter of the center electrode 30 is smaller than the inner diameter of the cylindrical dielectric 20, and the outer peripheral surface 31b of the center electrode 30 and the inner peripheral surface 21b of the cylindrical dielectric 20 are separated from each other. The electrode tip portion 31, which is the end portion on the tip side Y1 of the center electrode 30, is located closer to the base end side Y2 than the dielectric tip portion 21. The outer conductor tip 121 of the second outer conductor 12 and the position in the plug axis direction Y are the same.

As the material of the center electrode 30, in order to facilitate heating of the electrode tip portion 31 of the center electrode 30, a material having a relatively low conductivity or a material partially containing the material can be used. As such a material, for example, a material having a conductivity lower than that of copper can be used. Note that only the electrode tip portion 31 may be made of such a material. Also in this case, the electrode tip portion 31 can be easily heated.

Further, as the material of the center electrode 30, in order to facilitate heating of the electrode tip portion 31 of the center electrode 30, a material that easily absorbs high frequency energy or a material containing a part of the material can be used. Alternatively, by coating the outer peripheral surface 31b of the center electrode 30 or the inner peripheral surface 21b of the cylindrical dielectric body 20 with a material that easily absorbs high-frequency energy, the electrode tip portion 31 of the center electrode 30 may be easily heated. Good. As a material that easily absorbs high frequency energy, for example, carbon can be used. For example, stainless steel (SUS) can be used as a material that partially contains a material that easily absorbs high-frequency energy.

As shown in FIG. 2, the space 50 is formed as a space surrounded by the inner peripheral surface 21b of the tubular dielectric 20, the electrode tip 31 of the center electrode 30, and the outer peripheral surface 31b. The space 50 is a space including a virtual line segment L connecting the outer edge 31 a of the electrode tip 31 and the inner edge 21 a of the dielectric tip 21. That is, the space 50 separates the electrode tip 31 from the dielectric tip 21. The length of the coaxial tube formed of the outer conductor 10, the tubular dielectric 20, and the center electrode 30 in the plug axis direction Y can be set to a value at which the electric field strength of the electrode tip portion 31 is maximized. The size can be set to 1/4 of the wavelength of the applied high frequency.

The spark plug 1 is connected to a high frequency (for example, microwave) generator (not shown), and is configured so that the high frequency power output from the high frequency generator is input to the center electrode 30.

Next, the function and effect of this example will be described.
In the spark plug 1 for an internal combustion engine of this example, when a high-frequency voltage is applied to the center electrode 30, first, the center electrode 30 is heated to cause a gap between the electrode tip 31 and the dielectric tip 21. The gas density in the formed space 50 is reduced. As a result, the discharge start voltage is lowered, so that partial discharge easily occurs in the space 50. Then, when a high frequency voltage is further applied, as shown in FIG. 3, a partial discharge S1 is generated in the space 50 from the electrode tip 31. In the partial discharge S1, the high frequency (eg, microwave) energy emitted from the electrode tip 31 of the center electrode 30 by the application of the high frequency voltage is input, and the tip side Y1 in the plug axis direction Y from the electrode tip 31 is input. To form an open electrode, that is, an antenna, and a discharge S2 is formed from the electrode tip portion 31 toward the tip side Y1 in the plug axis direction Y. As a result, high frequency energy is emitted from the center electrode 30 to the space 50.

That is, the above-described partial discharge S1 becomes a trigger discharge of the discharge S2 from the center electrode 30 toward the tip side Y1 in the plug axis direction Y, and with smaller energy (that is, low electric field strength) from the center electrode 30 to the tip in the plug axis direction Y. It is possible to form the discharge S2 toward the side Y1. This facilitates the discharge formation based on the application of the high frequency voltage even under a high pressure condition of, for example, 20 atmospheres or more. As a result, the internal combustion engine is improved by improving the ignition limit under high EGR conditions (so-called EGR limit) and the combustion limit under lean fuel conditions (that is, lean combustion) (so-called lean limit). It is possible to improve the thermal efficiency in the fuel cell and to contribute to the improvement of fuel efficiency.

In the spark plug 1 for the internal combustion engine, since it is not necessary to use a high-power microwave oscillator, it is possible to reduce energy consumption and cost, and suppress the increase in size and the complexity of the ignition system. it can. Therefore, the spark plug 1 for an internal combustion engine is more suitable for use in the internal combustion engine provided in an automobile or the like.

Further, in the present example, the electrode tip end portion 31 is located closer to the base end side Y2 than the dielectric tip end portion 21. As a result, the space 50 is formed inside the tubular dielectric 20. Thereby, the space 50 can be sufficiently secured, and formation of partial discharge can be promoted. Further, the partial discharge formed in the space 50 is less likely to be affected by the gas flow of the mixed gas in the combustion chamber of the internal combustion engine, and the partial discharge can be promoted to be extended by the input of the high frequency energy. As a result, it becomes possible to form the discharge S2 from the center electrode 30 toward the tip side Y1 in the plug axis direction Y with smaller energy, that is, with lower electric field strength, and is more suitable for use in an internal combustion engine provided in an automobile or the like. It becomes the ignition plug 1 for an internal combustion engine.

Further, in the present example, the electrode tip portion 31 is located at the same position as the end portion 121 on the tip side Y1 of the outer conductor 10 in the plug axis direction Y. As a result, the electrode tip portion 31 is located at the open end of the coaxial tube formed of the outer conductor 10, the tubular dielectric body 20, and the center electrode 30, and the space between the electrode tip portion 31 and the tubular dielectric body 20 is set. It is possible to maximize the electric field strength in the vicinity of the electrode tip portion 31, and partial discharge between them is likely to occur.

Further, in the present example, the dielectric tip 21 of the tubular dielectric 20 projects from the tip 121 of the second outer conductor 12 to the tip side Y1. Thereby, the space 50 can be sufficiently secured, and formation of partial discharge can be promoted. As a result, the formation of the discharge S2 from the center electrode 30 toward the tip side Y1 in the plug axial direction Y can be promoted, and the ignition plug for an internal combustion engine more suitable for use in the internal combustion engine provided in an automobile or the like. It becomes 1.

As described above, according to this example, it is possible to provide the ignition plug 1 for an internal combustion engine, which is more suitable for use in the internal combustion engine provided for an automobile or the like.

(Discharge test)
Next, the spark plug 1 for the internal combustion engine of Example 1 was subjected to a discharge test.
The pressure of the air-fuel mixture in the combustion chamber in which the spark plug 1 is installed (hereinafter referred to as the atmospheric pressure) is changed from 0.6 MPa to 5 MPa, and is formed from the electrode tip 31 toward the tip side Y1 in the plug axial direction Y. The discharge length of the generated discharge S2 was observed. In this test, as shown in FIG. 3, the length from the dielectric tip 21 to the tip Y1 of the discharge S2 in the plug axis direction Y is the discharge length M of the discharge S2.

As shown in FIG. 4(1), at the atmospheric pressure of 0.6 MPa, after 0.55 ms has elapsed from the application of the high frequency voltage to the center electrode 30, the electrode tip portion 31 is discharged toward the tip side Y1 in the plug axis direction Y. S2 started to form. Then, after the passage of 0.75 ms shown in FIG. 4(2) and the state of 1.06 ms shown in FIG. 4(3), after the passage of 2.95 ms shown in FIG. It was confirmed that S2 was formed sufficiently long. Then, as shown in FIG. 5, the length M of the discharge S2 at an atmospheric pressure of 0.6 MPa was 6.0 mm. The length M of the discharge S2 is 6.0 mm at an atmospheric pressure of 1.0 MPa, 3.8 mm at an atmospheric pressure of 2.0 MPa, 2.6 mm at an atmospheric pressure of 3.0 MPa, 1.8 mm at an atmospheric pressure of 4.0 MPa, It was 1.4 mm at an atmospheric pressure of 5.0 MPa.

As described above, in the ignition plug 1 for the internal combustion engine of the first embodiment, after the high frequency voltage is applied to the center electrode 30, a sufficiently long discharge S2 from the electrode tip 31 toward the tip side Y1 in the plug axis direction Y is performed. Was confirmed to be formed.

(Example 2)
The spark plug 1 for an internal combustion engine of the second embodiment includes a ground electrode 40 as shown in FIGS. 6, 7, and 8. The ground electrode 40 extends from the outer conductor 10 and forms a gap with the electrode tip portion 31. Then, in the ignition plug 1 for the internal combustion engine of this example, as shown in FIG. 8, a high frequency voltage is applied to the center electrode 30 to form a discharge S2 between the electrode tip 31 and the ground electrode 40. It is configured. Between the electrode tip portion 31 and the dielectric tip portion 21, when a high frequency voltage is applied to the center electrode 30, the electrode tip portion 31 and the ground electrode 40 are discharged before the discharge between the electrode tip portion 31 and the ground electrode 40. A space 50 is formed between the dielectric tip 21 and the dielectric tip 21 so as to separate the electrode tip 31 from each other so that a partial discharge S1 is generated.
Other configurations are the same as those in the first embodiment.

According to this example, the same operational effects as those of the above-described first example are achieved. In this example, the ground electrode 40 is provided that extends from the first outer conductor 11 and forms a gap between the center electrode 30 and the electrode tip portion 31 so that the discharge S2 is formed in the gap. Is configured. This can be expected to promote the formation of the discharge S2 toward the ground electrode 40 after the formation of the partial discharge S1.

According to this example, similarly to the case of the first example, it is possible to provide the ignition plug 1 for an internal combustion engine, which is more suitable for use in the internal combustion engine provided for an automobile or the like.

(Example 3)
The spark plug 1 for an internal combustion engine of this example includes a center electrode 300 shown in FIG. 9 instead of the center electrode 30 (FIG. 7) of the second embodiment. The other components are the same as in the case of the second embodiment, and the same reference numerals as those in the case of the second embodiment are used in this example as well, and the description thereof is omitted.

The center electrode 300 has a columnar shape, and as shown in FIG. 9, is provided inside the tubular dielectric 20 so as to share the central axis with the tubular dielectric 20. The electrode tip portion 310, which is the end portion on the tip side Y1 of the center electrode 300, is located on the base end side Y2 with respect to the dielectric tip portion 21, and is more proximal than the outer conductor tip portion 121 of the second outer conductor 12. It is located on the end side Y2.

A space portion 500 is formed as a space surrounded by the inner peripheral surface 21b of the tubular dielectric 20, the electrode tip portion 310 of the center electrode 300, and the outer peripheral surface 310b. The space 500 is a space including a virtual line segment L connecting the outer edge 310a of the electrode tip 310 and the inner edge 21a of the dielectric tip 21. That is, the space 500 separates the electrode tip 310 from the dielectric tip 21.

The spark plug 1 of the present example is also the same as that of the second embodiment except that the dielectric tip 21 is located at the same position as the outer conductor tip 121 in the plug axis direction Y in the case of the second embodiment. Produces the effect of. In this example, the ground electrode 40 is provided, but instead of this, the ground electrode 40 may not be provided as in the case of the first embodiment. In this case as well, the same operational effect as this example is obtained.

(Example 4)
The spark plug 1 for an internal combustion engine of this example includes a tubular dielectric 200 shown in FIG. 10 instead of the tubular dielectric 20 (FIG. 9) in the third embodiment. As shown in FIG. 10, the dielectric tip 210, which is the tip Y1 end of the cylindrical dielectric 200, is located at the position in the plug axis direction Y that is the tip Y1 end of the second outer conductor 12. It is the same as the conductor tip 121. That is, the dielectric tip 210 of the tubular dielectric 200 is flush with the outer conductor tip 121 in the plug axis direction Y.

As shown in FIG. 10, a space 501 is formed as a space surrounded by the inner peripheral surface 210b of the cylindrical dielectric 200, the electrode tip 310 of the center electrode 300, and the outer peripheral surface 310b. The space 501 is a space including a virtual line segment L connecting the outer edge 310a of the electrode tip 310 and the inner edge 210a of the dielectric tip 210. That is, the space 501 separates the electrode tip 310 from the dielectric tip 210.
The other components are the same as in the case of the second embodiment, and the same reference numerals as those in the case of the second embodiment are used in this example as well, and the description thereof is omitted.

Also in the spark plug 1 of this example, the same operational effects as in the case of the third embodiment are exhibited. In this example, the ground electrode 40 is provided, but instead of this, the ground electrode 40 may not be provided as in the case of the first embodiment. In this case as well, the same operational effect as this example is obtained.

(Example 5)
As shown in FIG. 11, the spark plug 1 for an internal combustion engine of the present example has a tubular dielectric body 200 (FIG. 10) of the fourth embodiment in place of the tubular dielectric body 20 (FIG. 7) of the second embodiment. Prepare That is, in this example, the dielectric tip 210 of the cylindrical dielectric 200, the electrode tip 31 of the center electrode 30, and the tip 121 of the outer conductor 10 (that is, the second outer conductor 12 in this example) are flush with each other. Has become.

As shown in FIG. 11, a space portion 502 is formed as a space surrounded by the inner peripheral surface 210b of the cylindrical dielectric 200 and the outer peripheral surface 31b of the center electrode 30. The space 502 is a space including a virtual line segment L connecting the outer edge 31a of the electrode tip 31 and the inner edge 210a of the dielectric tip 210. That is, the space 502 separates the electrode tip 31 from the dielectric tip 210.
The other components are the same as those in the case of the third embodiment, and the same reference numerals as those in the case of the third embodiment are used in this example as well, and the description thereof is omitted.

According to the spark plug 1 for the internal combustion engine of this example, the function and effect of the electrode tip portion 31 being located closer to the base end side Y2 than the dielectric tip portion 21 in the case of the second embodiment, and the tubular dielectric Except for the effect of the dielectric tip 21 of the body 20 protruding from the tip 121 of the second outer conductor 12 to the tip side Y1, the same effect as that of the second embodiment is achieved. In this example, the ground electrode 40 is provided, but instead of this, the ground electrode 40 may not be provided as in the case of the first embodiment. In this case as well, the same operational effect as this example is obtained.

(Example 6)
In the spark plug 1 for the internal combustion engine of the present example, as shown in FIG. 12, the electrode tip 310 is closer to the tip side Y1 than the dielectric tip 210 with respect to the center electrode 30 (FIG. 11) of the fifth embodiment. It has a protruding center electrode 301.

As shown in FIG. 12, a space 503 is formed as a space between the outer peripheral surface 311b of the center electrode 301 and the inner edge 210a of the tubular dielectric 200. The space portion 503 is a space including an imaginary line segment L connecting the outer edge portion 311a of the electrode tip portion 311 and the inner edge portion 210a of the dielectric tip portion 210. That is, the space 503 separates the electrode tip 311 from the dielectric tip 210. The other components are the same as in the case of the fifth embodiment, and the same reference numerals as those in the case of the fifth embodiment are used in this example as well, and the description thereof is omitted.

According to the spark plug 1 for the internal combustion engine of the present example, in the case of the second embodiment shown in FIG. 7, the function and effect obtained by locating the electrode tip portion 31 on the base end side Y2 with respect to the dielectric tip portion 21 are obtained. , The action and effect of the electrode tip 31 being located at the same position as the tip 121 of the second outer conductor 12 in the plug axis direction Y, and the dielectric tip 21 of the tubular dielectric 20 being the second outer conductor. The same operational effect as that of the second embodiment is achieved, except for the operational effect obtained by projecting from the distal end portion 121 of No. 12 to the distal end side Y1. In this example, the ground electrode 40 is provided, but instead of this, the ground electrode 40 may not be provided as in the case of the first embodiment. In this case as well, the same operational effect as this example is obtained.

(Example 7)
The spark plug 1 for an internal combustion engine of the present example includes a tubular dielectric body 201 as shown in FIG. 13, instead of the tubular dielectric body 200 (FIG. 11) of the fifth embodiment. The inner diameter of the tubular dielectric 201 is substantially the same as the outer diameter of the center electrode 30, and the inner peripheral surface 211b of the tubular dielectric 201 is in contact with the outer peripheral surface 31b of the center electrode 30.

As shown in FIG. 13, a conical cutout portion 221 centered on the center electrode 30 is formed on the tip side Y1 of the cylindrical dielectric body 201. A space portion 504 is formed as a space surrounded by the wall surface 221a of the cutout portion 221 and the outer peripheral surface 31b of the center electrode 30. The space portion 504 is a space including a virtual line segment L that connects the outer edge portion 31a of the electrode tip portion 31 and the inner edge portion 211a of the dielectric tip portion 211. That is, the space 504 separates the electrode tip 31 from the dielectric tip 211.

The other components are the same as in the case of the fifth embodiment, and the same reference numerals as those in the case of the fifth embodiment are used in this example as well, and the description thereof is omitted. Also in the spark plug 1 of this example, the same operational effect as in the case of the fifth example is achieved.

In addition, in the present example, the notch portion 221 is formed in a conical shape, but the present invention is not limited to this, and a space portion around the electrode tip portion 31 of the center electrode 30 is formed of a space capable of forming partial discharge. It should be formed. Further, although the ground electrode 40 is provided in the present example, it may be replaced with a configuration in which the ground electrode 40 is not provided as in the case of the first embodiment. In this case as well, the same operational effect as this example is obtained.

( Reference example )
The spark plug 1 for an internal combustion engine of the reference example includes a tubular dielectric body 202 as shown in FIG. 14, instead of the tubular dielectric body 201 (FIG. 13) of the seventh embodiment. The inner diameter of the cylindrical dielectric 202 is substantially the same as the outer diameter of the center electrode 30, and the inner peripheral surface 212b of the cylindrical dielectric 201 and the outer peripheral surface 31b of the center electrode 30 are in contact with each other. The dielectric tip 212 of the tubular dielectric 202 is located on the tip side Y1 with respect to the electrode tip 31 of the center electrode 30 and the tip 121 of the outer conductor 10 (first outer conductor 12).

As shown in FIG. 14, a space portion 505 is formed as a space surrounded by the inner peripheral surface 212b of the tubular dielectric 202 and the electrode tip portion 31 of the center electrode 30. The space portion 505 is a space including a virtual line segment L that connects the outer edge portion 31 a of the electrode tip portion 31 and the inner edge portion 212 a of the dielectric tip portion 212.

The other components are the same as in the case of the seventh embodiment, and the same reference numerals as those in the case of the seventh embodiment are used in this example as well, and the description thereof is omitted. Also in the spark plug 1 of this example, the same operational effects as in the case of the seventh embodiment are exhibited. In this example, the ground electrode 40 is provided, but instead of this, the ground electrode 40 may not be provided as in the case of the first embodiment. In this case as well, the same operational effect as this example is obtained.

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

1 Spark Plug for Internal Combustion Engine 10 External Conductor 20, 200, 201, 202 Cylindrical Dielectric 21, 210, 211, 212 Derivative Tip Section 30, 300, 301 Center Electrode 31, 310, 311 Electrode Tip Section 40 Ground Electrode 50 , 500, 501, 502, 503, 504, 505 Space

Claims (5)

A cylindrical outer conductor (10),
A tubular shape that is held inside the outer conductor (10) and has a dielectric tip (21, 210, 211, 212) exposed on the tip side (Y1) in the plug axial direction (Y) of the outer conductor. A dielectric (20, 200, 201, 202),
A center electrode (30, 300, 301) which is held inside the tubular dielectric and has an electrode tip (31, 310, 311) exposed on the tip side in the plug axial direction of the tubular dielectric. ,
Equipped with
A spark plug (1) for an internal combustion engine, which is configured to apply a high-frequency voltage to the center electrode to form a discharge from a tip portion of the electrode toward a tip side in a plug axial direction,
Between the electrode tip and the dielectric tip, when a high-frequency voltage is applied to the center electrode, the electrode is provided between the electrode tip and the dielectric tip prior to the discharge. Space portions (50, 500, 501, 502, 503, 504, 505) are formed to separate the two so that a partial discharge is generated from the tip portion,
The space portion includes a region inside the outer conductor, which is located closer to the base end side (Y2) in the plug axial direction than the end portion (121) in the plug axial direction in the outer conductor , and the plug shaft. The front end of the center electrode is heated by lowering the gas density of the fuel in the space by applying a high-frequency voltage to the center electrode. An ignition plug (1) for an internal combustion engine, characterized in that the starting voltage is lowered to cause the partial discharge. The spark plug for an internal combustion engine according to claim 1, wherein the electrode tip portion is located closer to the base end side (Y2) in the plug axial direction than the dielectric tip portion. The spark plug for an internal combustion engine according to claim 1 or 2, wherein the electrode tip portion is located at the same position as the tip end portion (121) of the outer conductor in the plug axial direction. .. The internal combustion engine according to any one of claims 1 to 3, wherein the dielectric tip end portion is located closer to the tip end side than an end portion of the outer conductor on the tip end side in the plug axial direction. Spark plug for. A ground electrode (40) extending from the outer conductor and forming a gap with the electrode tip portion is provided, and the discharge is formed in the gap. An ignition plug for an internal combustion engine according to any one of claims 1 to 4.