JP2021012857A - Ignition plug - Google Patents

Abstract

To provide an ignition plug that improves ignitability.SOLUTION: An ignition plug 1 includes a center electrode 10, an insulator 20, a housing 30, an insulating layer 40, and a floating electrode 50. The center electrode 10 includes a center electrode tip portion 11 that is arranged coaxially with the insulator 20 inside the tubular insulator 20, and protrudes toward a tip side Y1 in a plug axial direction from the insulator 20. The housing 30 includes a sub chamber 2 formed on the tip side Y1 in the plug axial direction of the insulator 20, and includes a through hole 32 for communicating the sub chamber 2 and a main combustion chamber 3. The floating electrode 50 is provided inside the housing 30. The insulating layer 40 is provided inside the housing 30 and insulates the floating electrode 50 from the housing 30. The floating electrode 50 forms a first discharge gap G1 that causes a discharge between itself and the center electrode 10, and a second discharge gap G2 that causes a discharge between itself and a through hole forming portion 31 that forms the through hole 32 in the housing 30.SELECTED DRAWING: Figure 2

Description

The present invention relates to a spark plug.

Conventionally, a spark plug of an internal combustion engine having an auxiliary chamber has been used. For example, in the configuration disclosed in Patent Document 1, a sub chamber is provided in the structure of the spark plug, and the tip of the center electrode is located in the sub chamber. An internal electrode is provided in the sub chamber, and one end of the internal electrode faces the tip of the center electrode at a position on the back side of the sub chamber to form a first discharge gap. Then, the flame generated by igniting the fuel gas in the sub chamber due to the discharge in the first discharge gap is ejected into the main combustion chamber from one injection hole provided in the sub chamber, and becomes the fuel gas in the main combustion chamber. It is configured to ignite. Further, the other end of the internal electrode penetrates the bottom of the sub chamber from a position different from the injection hole provided in the sub chamber and protrudes into the main combustion chamber to form the external electrode. The external electrode forms a second discharge gap facing the ground electrode formed so as to project from the housing toward the main combustion chamber. The discharge in the second discharge gap is configured to directly ignite the fuel gas in the main combustion chamber.

In the configuration disclosed in Patent Document 1, when the operating state of the internal combustion engine is in the partial load or high load region, a sufficient amount of fuel gas exists in the sub chamber, so that the first one located in the back side of the sub chamber. In the flame generated by the discharge of the discharge gap, the ratio of heat loss to the inner wall of the auxiliary chamber is small. Therefore, the flame grows sufficiently in the sub chamber and is ejected from the injection hole into the main combustion chamber to improve the ignitability of the fuel gas in the main combustion chamber. Further, when the operating state of the internal combustion engine is in the low load region or when the internal combustion engine is operated under the catalyst warming condition, the fuel gas in the sub chamber is relatively small, so that the first discharge gap located at the back side of the sub chamber is used. The generated flame has a large rate of heat loss to the inner wall of the sub-chamber, and the flame growth is hindered, so that sufficient flame ejection cannot be obtained. However, since the second discharge gap is located at a position protruding toward the main combustion chamber, the fuel gas in the main combustion chamber is directly ignited by the discharge of the second discharge gap, and the fuel gas in the main combustion chamber is ignitable. Is increasing.

European Patent No. 6694542

However, in the configuration disclosed in Patent Document 1, when the operating state of the internal combustion engine is in the partial load or high load region, the flame generated by the discharge of the first discharge gap reaches the injection hole and is ejected into the main combustion chamber. There is room for improvement in promoting flame eruption and improving ignitability. On the other hand, when the operating state of the internal combustion engine is in the low load region or when the internal combustion engine is operated under the warm-up condition of the catalyst, the fuel gas in the main combustion chamber is discharged by the discharge in the second discharge gap at the position protruding toward the main combustion chamber. Although it is ignited directly, the discharge is formed at the position of the second discharge gap and reaches only a very narrow area in the main combustion chamber, so it is improved to improve the ignitability of the fuel gas in the main combustion chamber. There is room for.

The present invention has been made in view of such a problem, and an object of the present invention is to provide an ignition plug capable of improving ignitability.

One aspect of the present invention includes a tubular insulator (20) and
A center electrode (10) which is arranged coaxially with the insulating insulator inside the insulating insulator and has a central electrode tip portion (11) protruding toward the tip side in the plug axial direction from the insulating insulator.
A housing (30) having a sub chamber (2) formed on the tip side of the insulator in the plug axial direction and having a through hole (32) for communicating the sub chamber and the main combustion chamber (3).
A floating electrode (50) provided inside the housing and
An insulating layer (40) provided inside the housing and insulating the floating electrode and the housing,
Have,
The floating electrode forms a first discharge gap (G1) that causes a discharge with the center electrode, and discharges with a through hole forming portion (31) that forms a through hole in the housing. It is in the spark plug (1), which is configured to form a second discharge gap (G2) to be generated.

In the spark plug, discharge is generated in both the first discharge gap in the sub chamber and the second discharge gap formed in the through hole of the housing. When the operating state of the internal combustion engine is in a partial load or high load region, a sufficient amount of fuel gas exists in the sub chamber, so that heat loss to the inner wall of the sub chamber or the like in the flame generated by the discharge of the first discharge gap is caused. The ratio is getting smaller. Therefore, the flame can grow sufficiently in the sub chamber, and a sufficient amount of flame is ejected from the through hole into the main combustion chamber. Further, the discharge in the second discharge gap will occur in or around the through hole of the housing. Therefore, the discharge of the second discharge gap is subordinated by the inflow airflow from the main combustion chamber to the sub chamber, which is generated by the fuel gas flowing from the main combustion chamber into the sub chamber as the piston rises in the main combustion chamber. It will be stretched to the indoor side. As a result, the discharge gives energy to the fuel gas in the sub-chamber and promotes combustion in the sub-chamber. At the same time, the downdraft toward the main combustion chamber generated in the sub-chamber due to the flame growth due to the discharge of the first discharge gap in the sub-chamber and the inflow air flow flowing into the sub-chamber from the through hole collide with each other in the sub-chamber. Therefore, the turbulence of the airflow in the sub-chamber is promoted, and the combustion in the sub-chamber is further promoted. As a result, the ejection of flame is promoted and the ignitability of the fuel gas on the main combustion chamber side can be improved.

On the other hand, when the operating state of the internal combustion engine is in the low load region or when the internal combustion engine is operated under the catalyst warm-up condition, the fuel gas in the sub-chamber is relatively small, so that the flame growth in the sub-chamber is hindered and sufficient flame ejection occurs. I can't get it. However, as the piston in the main combustion chamber descends, an outflow airflow from the sub-chamber toward the main combustion chamber side is generated through the through hole, and the outflow airflow extends the discharge of the second discharge gap toward the main combustion chamber side. .. As a result, the electric discharge spreads in the main combustion chamber, and the ignitability of the fuel gas on the main combustion chamber side can be improved. Further, since the flame spreads in the main combustion chamber, heat loss to the inner wall of the sub chamber and the like is suppressed, so that the ignitability of the fuel gas can be further improved.

As described above, according to the above embodiment, it is possible to provide a spark plug with improved ignitability.

The reference numerals in parentheses described in the scope of claims and the means for solving the problem indicate the correspondence with the specific means described in the embodiments described later, and limit the technical scope of the present invention. It's not a thing.

The front view of the spark plug in Embodiment 1. FIG. 1 is an enlarged cross-sectional view of the position of line II-II. FIG. 2 is a partially enlarged view of the vicinity of the tip of the center electrode. FIG. 2 is a partially enlarged view of the vicinity of the tip of the floating electrode. Bottom view of the spark plug in the first embodiment In the first embodiment, (a) a conceptual diagram showing discharge generation, and (b) a conceptual diagram showing flame growth. In the first embodiment, (a) a conceptual diagram showing flame growth, and (b) a conceptual diagram showing flame ejection. In the first embodiment, (a) a conceptual diagram showing discharge generation, and (b) a conceptual diagram showing flame growth. In the first embodiment, (a) a conceptual diagram showing flame growth, and (b) a conceptual diagram showing flame ejection. In the simulation test, (a) a diagram showing the results of a test example, and (b) a diagram showing the results of a comparative example. The figure which shows the result of the test example and the comparative example in the simulation test. A front view of a conventional spark plug as a comparative example in a comparative test. The figure which shows the test example and the result of the comparative example in the comparative test. A partially enlarged view of a cross section in the modified form 1. A partially enlarged view of a cross section in the modified form 2. A partially enlarged view of a cross section in the modified form 3. A partially enlarged view of a cross section in the modified form 4. A partially enlarged view of a cross section in the modified form 5. FIG. 6 is an enlarged view of a part of a cross section in the modified form 6. FIG. 6 is an enlarged view of a part of a cross section in the modified form 7. FIG. 5 is an enlarged view of a part of a cross section in the modified form 8. A partially enlarged view of a cross section in the modified form 9. FIG. 5 is an enlarged view of a part of a cross section in the modified form 10. FIG. 23 is an enlarged cross-sectional view of the position of the XXIV-XXIV line. 11 is an enlarged view of a part of a cross section in the modified form 11.

(Embodiment 1)
An embodiment of the spark plug device will be described with reference to FIGS. 1 to 13.
As shown in FIG. 2, the spark plug 1 of the present embodiment shown in FIG. 1 has a center electrode 10, an insulating insulator 20, a housing 30, an insulating layer 40, and a floating electrode 50.
The insulating insulator 20 has a tubular shape.
The center electrode 10 is arranged coaxially with the insulating insulator 20 inside the insulating insulator 20, and has a center electrode tip portion 11 protruding toward the tip side Y1 in the plug axial direction from the insulating insulator 20.
The housing 30 has a sub chamber 2 formed on the tip side Y1 of the insulating insulator 20 in the plug axial direction, and has a through hole 32 for communicating the sub chamber 2 and the main combustion chamber 3.
The floating electrode 50 is provided inside the housing 30.
The insulating layer 40 is provided inside the housing 30 and insulates the housing 30 and the floating electrode 50.
Then, the floating electrode 50 forms a first discharge gap G1 that generates an electric discharge with the center electrode 10, and also generates an electric discharge with the through hole forming portion 31 that forms the through hole 32 in the housing 30. It is configured to form a second discharge gap G2.

Hereinafter, the spark plug 1 of the present embodiment will be described in detail.
As shown in FIG. 1, in the spark plug 1 of the present embodiment, the housing 30 has a tubular shape with the plug axial direction Y as the longitudinal direction. An insulating insulator 20 is arranged coaxially with the housing 30 in the housing 30, and the insulating insulator 20 has a tubular shape.

Inside the insulating insulator 20, the center electrode 10 is arranged coaxially with the insulating insulator 20. The center electrode 10 is provided at the end of Y1 on the tip side in the plug axial direction, and has a center electrode tip 11 exposed in the housing 30. The tip portion 11 of the center electrode extends in the tip side Y1 in the plug axial direction and is bent in the radial direction X.

As shown in FIG. 2, an insulating layer 40 is provided inside the housing 30. In the present embodiment, the insulating layer 40 is formed separately from the insulating insulator 20. Further, the insulating layer 40 has a tubular shape, and the outer peripheral surface of the insulating layer 40 has a shape along the inner peripheral surface of the housing 30. A base end through hole 41 formed through is provided at the end of the plug axial direction base end side Y2 in the insulating layer 40, and a tip through hole 42 is formed at the end of the plug shaft direction front end side Y1. There is. Both the base end through hole 41 and the tip end through hole 42 are located on the plug axis 20a. Then, the tip end portion 11 of the center electrode has entered the inside of the insulating layer 40 through the base end through hole 41.

As shown in FIG. 2, a floating electrode 50 is provided inside the housing 30. In the present embodiment, the floating electrode 50 is a linear metal member and extends in the plug axial direction Y along the inner wall of the insulating layer 40. The floating electrode tip 51, which is the end of the plug axial tip side Y1 of the floating electrode 50, protrudes from the tip through hole 42 of the insulating layer 40 to the first through hole 321 in the bottom wall 35 of the sub chamber 2, which will be described later. It has reached. On the other hand, as shown in FIG. 3, the floating electrode base end 52, which is the end of the plug axial base end side Y2 of the floating electrode 50, is located inside the insulating layer 40. The base end portion 52 of the floating electrode and the tip end portion 11 of the center electrode of the center electrode 10 face each other in a state of being separated from each other. The space between the floating electrode base end portion 52 and the center electrode tip end portion 11 is the first discharge gap G1 that generates the discharge S1. As shown in FIG. 2, the first discharge gap G1 is located in the sub chamber 2 on the Y2 side in the plug axial direction, that is, on the back side of the sub chamber 2.

As shown in FIG. 2, the space inside the housing 30 forms the sub chamber 2. As shown in FIG. 4, the housing 30 has a bottom wall portion 35 forming the bottom portion of the sub chamber 2, a side wall portion 36 forming the side portion of the sub chamber 2, and a bottom wall portion 35 on the tip side Y1 in the plug axial direction. It has a connecting portion 37 that connects the side wall portion 36 and the side wall portion 36. The bottom wall portion 35, the side wall portion 36, and the connecting portion 37 form a cup-shaped Y1 on the tip side in the plug axial direction of the housing 30. The housing 30 is made of metal and has conductivity. The cup-shaped portion including the bottom wall portion 35, the side wall portion 36, and the connecting portion 37 may be separated from the housing 30 to form a separate body. Further, the cup-shaped portion may be formed integrally with the cylinder head forming the main combustion chamber.

As shown in FIGS. 1 and 2, a through hole 32 is provided in the tip side Y1 of the housing 30 in the plug axial direction. Then, the portion of the bottom wall portion 35 that forms the wall surface and the opening of the through hole 32 is referred to as the through hole forming portion 31. In the present embodiment, the through hole 32 includes a first through hole 321 and a second through hole 322. Further, in the present embodiment, the portion forming the wall surface and the opening of the first through hole 321 is designated as the first through hole forming portion 311, and the portion forming the wall surface and the opening of the second through hole 322 is formed as the second through hole. Let's call it part 312. As shown in FIG. 4, in the present embodiment, the first through hole 321 is provided on the plug axis 20a in the bottom wall portion 35, and is a through hole formed parallel to the plug axis direction Y.

As shown in FIG. 4, the floating electrode tip portion 51 is located inside the first through hole 321. In the present embodiment, the tip surface 51a of the floating electrode tip 51 and the surface of the bottom wall 35 on the main combustion chamber 3 side are on the same plane. Then, the space between the floating electrode tip portion 51 and the first through hole forming portion 311 forming the first through hole 321 becomes the second discharge gap G2 that causes the discharge S2.

As shown in FIG. 4, the second through hole 322 is provided in the connecting portion 37. The second through hole 322 is formed along a virtual axis 322a inclined with respect to the plug axial direction Y. The virtual axis 322a is inclined at a predetermined angle with respect to the plug axis 20a so as to be separated from each other toward the tip side Y1 in the plug axis direction. As shown in FIG. 5, in this embodiment, four second through holes 322 are provided. The four second through holes 322 are located at equal intervals in the circumferential direction about the plug axis 20a when viewed from the plug axis direction Y. As shown in FIG. 4, in the present embodiment, the inclination angles of the virtual axis 322a with respect to the plug axis 20a are the same.

As shown in FIG. 3, a protrusion 41a protruding inward in the radial direction is formed on the wall surface of the base end through hole 41 of the insulating layer 40. As a result, the shortest creepage distance L2 between the floating electrode base end portion 52 via the surface of the insulating layer 40 and the inner surface of the housing 30 is longer than that in the case where the protruding portion 41a is not provided. The shortest distance L1 between the floating electrode base end portion 52 and the center electrode tip portion 11 in the first discharge gap G1 is shorter than the shortest creepage distance L2. This prevents creeping discharge from occurring through the surface of the insulating layer 40.

Further, as shown in FIG. 4, a protruding portion 42a projecting inward in the radial direction is formed on the wall surface of the tip through hole 42 of the insulating layer 40. As a result, the shortest creepage distance L4 between the floating electrode 50 and the inner surface of the housing 30 via the surface of the insulating layer 40 is longer than that in the case where the protruding portion 42a is not provided. Then, as shown in FIG. 4, the shortest distance L3 between the floating electrode tip portion 51 and the first through hole forming portion 311 in the second discharge gap G2 is shorter than the shortest creepage distance L4. This prevents creeping discharge from occurring through the surface of the insulating layer 40.

Next, a usage mode of the spark plug 1 of the present embodiment will be described.
First, when the load of the internal combustion engine is in the partial load to high load region, a sufficient amount of fuel gas is present in the sub chamber 2. Therefore, as shown in FIG. 6 (a), the electric discharge generated in the first discharge gap G1 located at the back of the sub chamber 2 causes an initial flame on the back side of the sub chamber 2 as shown in FIG. 6 (b). As shown in FIG. 6B, F0 grows toward the tip side Y1 in the plug axial direction in the sub chamber 2. Heat loss occurs due to the housing 30 forming the sub chamber 2 with respect to the initial flame F0, but as described above, since a sufficient amount of fuel gas exists in the sub chamber 2, the fuel gas is easily burned and is generated. There is a lot of heat. As a result, the ratio of heat loss to the amount of heat generated is relatively small, so that sufficient flame growth is achieved in the sub chamber 2.

In the partial load to high load region in the present embodiment, the ignition timing in the internal combustion engine is set to BTDC (Before Top Dead Center), and as shown in FIG. 7A, the main ignition timing occurs as the piston rises. The inflow airflow P1 flowing from the combustion chamber into the sub chamber 2 extends the discharge S2 generated in the second discharge gap G2 into the sub chamber 2. As a result, the amount of energy given to the fuel gas in the sub chamber 2 by the discharge S2 is increased, and combustion in the sub chamber 2 is promoted. Further, as the initial flame F0 generated on the back side of the sub chamber 2 grows, a downdraft P2 toward the tip side Y1 in the plug axial direction is generated in the sub chamber 2. Then, the inflow airflow P1 and the downdraft P2 collide with each other in the sub-chamber 2, so that the turbulence of the airflow increases in the sub-chamber 2. As a result, the combustion of the fuel gas in the sub chamber 2, that is, the growth of the flame is promoted, and as shown in FIG. 6B, the flame F1 is vigorously ejected from the second through hole 322 into the main combustion chamber. It will be. Along with this, the flame F2 is ejected from the first through hole 321 and the discharge S2 is extended to the main combustion chamber 3 side.

On the other hand, under catalyst warm-up conditions such as when the load of the internal combustion engine is in the low load region or when the internal combustion engine is started, the amount of fuel gas existing in the sub chamber 2 is small, so that the fuel gas is less than in the high load region. The combustion of fuel gas is reduced, and the amount of heat generated is also small. As a result, the ratio of heat loss to the amount of heat generated becomes relatively large, so even if discharge S1 occurs in the first discharge gap G1 as shown in FIG. 8 (a), it is high as shown in FIG. 8 (b). Sufficient growth of flame cannot be expected compared to the case of the load region. However, in the low load region such as at the time of cold start in the present embodiment, the ignition timing is set to ATDC (After Top Dead Center), and as shown in FIG. 9A, the secondary generated as the piston descends. An outflow airflow P3 from the inside of the chamber 2 toward the main combustion chamber 3 is generated. Then, the discharge S2 generated in the second discharge gap G2 at the tip of the sub chamber 2 is extended to the main combustion chamber 3 side by the outflow airflow P3. As a result, the flame can be spread to the main combustion chamber side. Especially at the time of cold start, the surface temperature of the housing 30 and the insulating insulator 20 is low, but since the flame is positively expanded to the main combustion chamber 3 side, the contact area between the flame and the housing 30 and the insulating insulator 20 is reduced. Therefore, the energy loss in the flame can be suppressed and the combustion of the fuel gas in the main combustion chamber 3 can be promoted.

Next, a simulation test of flame ejection was performed on the spark plug 1 of the present embodiment. In this simulation test, based on CFD (Computational Fluid Dynamics), as a test example, in the spark plug 1 of the present embodiment, the temperature when discharge is generated in both the first discharge gap G1 and the second discharge gap G2. Changes and changes in in-cylinder pressure were analyzed. Further, as a comparative example, the spark plug 1 of the present embodiment does not have the insulating layer 40 and the floating electrode 50, and the tip of the center electrode 10 reaches the first through hole 321 to form the second discharge gap G2. The temperature change when a discharge was generated in the second discharge gap G2 was analyzed. The test conditions of this simulation test were that 25 mJ of energy was consumed in each of the discharge gaps G1 and G2 in the test example, and 50 mJ of energy was consumed in the discharge gap G2 in the comparative example. The other conditions were an ignition pressure of 0.6 MPa, a fuel type propane, and a stoichiometric condition.

From the results of the temperature change in the present simulation test shown in FIGS. 10 (a) and 10 (b), it was shown that the amount of flame ejected in the test example increased with time as compared with the comparative example. Further, from the analysis result of the in-cylinder pressure change shown in FIG. 11, it was shown that the in-cylinder pressure increased earlier in the test example than in the comparative example.

Next, in the spark plug 1 of the present embodiment, a comparative test of combustion volatility was conducted.
In this comparative test, the spark plug 1 of the first embodiment was used as a test example. Further, as a comparative example, the conventional spark plug 9 shown in FIG. 12 was used. The conventional spark plug 9 includes a center electrode 91, an insulating insulator 92, a housing 93, and a ground electrode 94, and a discharge gap G9 is formed between the tip of the center electrode 91 and the end of the ground electrode 94. The conventional spark plug 9 does not have an auxiliary chamber.

In this comparative test, the combustion volatility at the time of ATDC ignition was calculated and the test example and the comparative example were compared. The test conditions were an engine speed of 1200 r / m, a stoichiometric condition, and a load of 150 kPa.

According to this comparative test, as shown in FIG. 13, the spark plug 1 of the test example had a lower combustion volatility than the spark plug 9 of the comparative example. This is because, in the ignition plug 1 of the test example, in ATDC ignition, as shown in FIGS. 9 (a) and 9 (b), the outflow airflow P3 from the sub chamber 2 toward the main combustion chamber 3 side as the piston descends. It is presumed that this is because the discharge S2 of the second discharge gap G2 is extended to the main combustion chamber 3 side, which improves the ignitability.

Next, the action and effect of the spark plug 1 of the present embodiment will be described in detail.
In the spark plug 1 of the present embodiment, discharges S1 and S2 are generated in both the first discharge gap G1 in the sub chamber 2 and the second discharge gap G2 formed in the first through hole 321. When the operating state of the internal combustion engine is in a partial load or high load region, a sufficient amount of fuel gas exists in the sub chamber 2, so that the inner wall of the sub chamber 2 or the like in the flame generated by the discharge S1 of the first discharge gap G1 The rate of heat loss to is small. Therefore, the flame can sufficiently grow in the sub chamber 2, and a sufficient amount of flame is ejected from the through hole 32 into the main combustion chamber 3. Further, as the piston in the main combustion chamber 3 rises, fuel gas flows from the main combustion chamber 3 into the sub chamber 2 through the through hole 32, and an inflow air flow P1 from the main combustion chamber 3 to the sub chamber 2 is generated. .. Then, the discharge S2 of the second discharge gap G2 located in the first through hole 321 of the housing 30 is extended to the inside of the sub chamber 2 by the inflow airflow P1. As a result, energy is given to the fuel gas in the sub chamber 2 by the discharge S2, and combustion in the sub chamber 2 is promoted. At the same time, the flame generated by the discharge S1 of the first discharge gap G1 grows in the sub chamber 2, and a downdraft P2 toward the main combustion chamber 3 side is generated in the sub chamber 2. Then, the downdraft P2 and the inflow airflow P1 flowing into the sub-chamber 2 from the through hole 32 collide with each other in the sub-chamber 2, and the turbulence of the air flow in the sub-chamber 2 is promoted to cause combustion in the sub-chamber 2. Further promoted. As a result, the ejection of flame is promoted, and the ignitability of the fuel gas on the main combustion chamber 3 side can be improved.

On the other hand, when the operating state of the internal combustion engine is in the low load region or when the internal combustion engine is operated under the catalyst warming condition, the fuel gas in the sub chamber 2 is relatively small, so that the flame growth in the sub chamber 2 is sufficiently inhibited. I can't get a good flame spout. However, as the piston descends in the main combustion chamber 3, an outflow airflow P3 is generated from the sub-chamber 2 toward the main combustion chamber 3 side through the through hole 32, and the outflow airflow P3 causes the discharge S2 of the second discharge gap G2. Is extended to the main combustion chamber 3 side. As a result, the fuel gas on the main combustion chamber 3 side can be ignited. As a result, compared to the case where the discharge S2 is only formed in the second discharge gap G2, the discharge S2 is more likely to spread in the main combustion chamber 3, so that heat loss to the inner wall of the sub chamber 2 is suppressed and the fuel is fueled. The ignitability of gas can be improved.

Further, in this example, the housing 30 is located on the tip side Y1 in the plug axial direction, and has a bottom wall portion 35 forming the bottom portion of the sub chamber 2, a side wall portion 36 forming the side wall of the sub chamber 2, and a bottom wall. It has a connecting portion 37 that connects the portion 35 and the side wall portion 36. The through hole 32 includes a first through hole 321 provided on the plug axis 20a in the bottom wall portion 35 and a second through hole 322 provided in the connecting portion 37. The floating electrode 50 is configured to form a second discharge gap G2 with the first through hole forming portion 311 forming the first through hole 321. As a result, the discharge S2 generated in the second discharge gap G2 is likely to be extended to the tip end side Y1 in the plug axial direction or the proximal end side Y2 in the plug axial direction by the ascent or descent of the piston, so that the fuel gas is ignited. The sex can be further improved.

Further, in the present embodiment, the insulating insulator 20 and the insulating layer 40 are separate bodies from each other. When the insulating insulator 20 is extended to the tip side Y1 in the plug axial direction to form the insulating layer 40 and the two are integrated, the inner diameter of the insulating layer 40 becomes smaller. Therefore, the cold loss due to the insulating layer 40 against the flame formed in the sub chamber 2 increases, and the ignitability deteriorates. In the present embodiment, as described above, since the insulating insulator 20 and the insulating layer 40 are separate bodies from each other, the inner diameter of the insulating layer 40 can be relatively increased. As a result, cold loss due to the insulating layer 40 can be reduced.

Further, in the present embodiment, the insulator is formed into a tubular shape as the insulating layer 40, but instead of this, the insulating layer 40 is inside the housing 30 as shown in the modified form 1 shown in FIG. It may consist of a film formed on the wall surface. The insulating layer 40 can be formed by spraying, plating, vapor deposition, or the like on the inner wall surface of the housing 30, and in the modified form 1, the insulating layer 40 is formed on the entire inner wall surface of the housing 30. According to the modified form 1, it is possible to further prevent creepage discharge from occurring between the floating electrode 50 and the housing 30. As in the modified form 2 shown in FIG. 15, the tip of the central electrode formed linearly by extending the base end portion 52 of the floating electrode toward the plug axis 20a and bending it toward the base end side Y2 in the plug axis direction. It may face the portion 11.

Further, in the present embodiment, the floating electrode 50 is made of a linear metal member, but instead of this, the floating electrode 50 is formed inside the insulating layer 40 as shown in the modified form 3 shown in FIG. It may have a film portion 50a. The film portion 50a in the modified form 2 can be formed by spraying, plating, vapor deposition, or the like on the inner wall surface of the insulating layer 40 with a conductive material. In the modified form 3, the film portion 50a is formed in a tubular shape on the inner wall surface of the insulating layer 40. Further, the floating electrode 50 includes a floating electrode tip 51 extending from the end of the plug axial tip side Y1 of the membrane portion 50a toward the first through hole 321 and a plug axial proximal end side of the membrane portion 50a. It has a floating electrode base end 52 extending from the end of Y2 toward the center electrode tip 11. According to the modified embodiment 3, the same effect as that of the present embodiment can be obtained, and the floating electrode 50 can be easily held.

Further, as in the modified form 4 shown in FIG. 17, the insulating layer 40 is formed of a film formed on the inner wall surface of the housing 30, and the floating electrode 50 is further formed on the inner wall surface of the insulating layer 40. Has. A ring member 53 having a floating electrode tip portion 51 is inserted into the floating electrode 50 at the tip end side Y1 in the plug axial direction. The floating electrode base end portion 52 is formed by the end portion of the membrane portion 50a on the base end side Y2 in the plug axial direction. According to the modified form 4, the insulating layer 40 can prevent an unintended creeping discharge and easily hold the floating electrode 50. It should be noted that the modified form 4 also has the same effect as that of the present embodiment.

Further, as in the modified form 5 shown in FIG. 18, the floating electrode 50 includes a tip side ring member 54 inserted in the region of the plug axial tip side Y1 of the insulating layer 40 and a plug axial direction group of the insulating layer 40. It is composed of a base end side ring member 55 inserted in the region of the end side Y2, and a connecting portion 56 provided between the two and connected to the both and formed along the inner side surface of the insulating layer 40. May be. According to the modified embodiment 5, the same effect as that of the present embodiment is obtained, and the floating electrode 50 is not formed between the distal end side ring member 54 and the proximal end side ring member 55, so that the weight is reduced. Can be achieved.

Further, as in the modified form 6 shown in FIG. 19, a floating electrode 50 made of a tubular member made of metal may be inserted inside the tubular insulating layer 40. In the modified form 6, the floating electrode tip 51 extends from the plug axial tip of the tubular portion of the floating electrode 50 toward the plug axis 20a and bends to the plug axial tip side Y1 to form the first through hole 321. It is extended and formed toward. On the other hand, the floating electrode base end portion 52 is formed by the end portion of the tubular portion forming the floating electrode 50 on the plug axial direction base end side Y2. The modified form 6 also has the same effect as that of the present embodiment. As in the modified form 7 shown in FIG. 20, the floating electrode base end 52 is extended toward the plug axis 20a and bent toward the plug axis direction base end side Y2 so as to face the center electrode tip 11. You may.

Further, as in the modified form 8 shown in FIG. 21, the center electrode tip portion 11 and the floating electrode base end portion 52 may be formed of a noble metal having a high melting point. As such a precious metal, for example, Ir, Pt, Rh, W, Ta and the like can be used. Further, as in the modified form 9 shown in FIG. 22, the floating electrode tip portion 51 and the first through hole forming portion 311 may be formed of a noble metal having a high melting point. The first through-hole forming portion 311 can be formed, for example, by inserting a tubular member having a collar portion 311a from a high melting point precious metal into the through hole formed in the bottom wall portion 35 of the housing 30. According to the modified form 8 and the modified form 9, wear of the electrode can be suppressed.

Further, as in the modified form 10 shown in FIG. 23, a groove portion 45 extending in the plug axial direction Y is provided on the inner wall surface of the tubular insulating layer 40. Then, as shown in FIG. 24, the width of the groove portion 45 of the modified form 10 is the same as the width of the rod-shaped floating electrode 50, and the floating electrode 50 is inserted into the groove portion 45 to form the floating electrode 50. Is retained. This facilitates the holding and positioning of the floating electrode 50.

Further, as in the modified form 11 shown in FIG. 25, the floating electrode 50 may be formed into a spiral shape extending in the plug axial direction Y and inserted inside the tubular insulating layer 40. According to the modified form 11, the assembling property of the floating electrode 50 is improved. The modified embodiment 11 also has the same effect as that of the first embodiment.

As described above, according to the present embodiment and the modified form, it is possible to provide an ignition plug capable of improving ignitability.

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

1 Spark plug 2 Sub chamber 3 Main combustion chamber 10 Center electrode 20 Insulator 30 Housing 31 Through hole forming part 311 First through hole forming part 312 Second through hole forming part 32 Through hole 321 First through hole 322 Second through hole 35 Bottom wall 36 Side wall 37 Connecting 40 Insulating layer 50 Floating electrode G1 First discharge gap G2 Second discharge gap

Claims (5)

Cylindrical insulator (20) and
A center electrode (10) which is arranged coaxially with the insulating insulator inside the insulating insulator and has a central electrode tip portion (11) protruding toward the tip side in the plug axial direction from the insulating insulator.
A housing (30) having a sub chamber (2) formed on the tip side of the insulator in the plug axial direction and having a through hole (32) for communicating the sub chamber and the main combustion chamber (3).
A floating electrode (50) provided inside the housing and
An insulating layer (40) provided inside the housing and insulating the floating electrode and the housing,
Have,
The floating electrode forms a first discharge gap (G1) that causes a discharge with the center electrode, and discharges with a through hole forming portion (31) that forms a through hole in the housing. A spark plug (1) configured to form a resulting second discharge gap (G2). The housing is located on the tip side in the plug axial direction, and has a bottom wall portion (35) forming the bottom portion of the sub chamber, a side wall portion (36) forming the side wall of the sub chamber, and the bottom wall portion. It has a connecting portion (37) that connects the side wall portion and
The through hole includes a first through hole (321) provided on the plug axis in the bottom wall portion and a second through hole (322) provided in the connecting portion.
The spark plug according to claim 1, wherein the floating electrode is configured to form the second discharge gap with the first through hole forming portion (311) forming the first through hole. The spark plug according to claim 1 or 2, wherein the insulating insulator and the insulating layer are separate from each other. The spark plug according to any one of claims 1 to 3, wherein the insulating layer is made of a film formed on the inner wall surface of the housing. The spark plug according to any one of claims 1 to 4, wherein the floating electrode has a film portion formed inside the insulating layer.