JP6767936B2 - Spark plug and ignition device - Google Patents

Description

The present invention relates to a spark plug and an ignition device, and more particularly to an ignition plug and an ignition device capable of suppressing penetration of an insulator.

As an ignition plug that ignites the air-fuel mixture sucked into the combustion chamber of an internal combustion engine, there is one that uses unbalanced plasma (Patent Document 1). In the spark plug disclosed in Patent Document 1, a bottomed tubular insulator encloses the tip of the center electrode, and the main metal fitting extends the insulator from the outer peripheral side so that the tip of the insulator protrudes from its own tip. Hold. The spark plug generates plasma in the space at the tip of the insulator and ignites the air-fuel mixture. The gap between the insulator and the main metal fitting should be as narrow as possible in order to secure the amount of plasma generated from the tip of the insulator and to facilitate the transfer of heat from the tip to the main metal fitting to prevent abnormal overheating of the tip. Is preferable.

Japanese Unexamined Patent Publication No. 2014-22341

However, a certain size of gap is provided between the insulator and the main metal fitting in consideration of the variation in the dimensions of the main metal fitting and the main metal fitting, the assembly accuracy, and the linear expansion difference between the insulator and the main metal fitting. ing. Since strong plasma is likely to be generated at the tip of the main metal fitting having a high electric field strength, the insulator may penetrate (dielectric breakdown).

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a spark plug and an ignition device capable of suppressing penetration of an insulator.

In order to achieve this object, the spark plug of the present invention extends from the front end side to the rear end side along the axis, and has a bottomed tubular insulator with a closed tip and its own tip included in the insulator. It is provided with a central electrode and a tubular main metal fitting that holds the insulator from the outer peripheral side in a state where the tip of the insulator protrudes from its own tip. It is provided with an insulating layer that covers at least a part of the inner surface of the main metal fitting from the tip end side to the rear end side of the inner surface over the entire circumference.

According to the spark plug according to claim 1, since the insulating layer covers at least a part of the inner surface of the main metal fitting from the tip of the inner surface to the rear end side over the entire circumference, the electric field strength of the tip of the inner surface of the main metal fitting is strong. Can be lowered. As a result, it is possible to make it difficult to generate plasma at the tip of the inner surface of the main metal fitting, so that penetration of the insulator can be suppressed. Further, by reducing the amount of plasma generated at the tip of the inner surface of the main metal fitting, the amount of plasma generated from the tip of the insulator can be relatively increased.
The thickness of the insulating layer is 0.1 times or more the distance in the direction perpendicular to the axis between the insulating layer and the insulator at the tip of the inner surface. Therefore, the effect of the insulating layer that lowers the electric field strength can be ensured.

According to the spark plug according to claim 2, the insulating layer further covers at least a part of the tip surface of the main metal fitting from the tip of the inner surface to the outer side in the radial direction over the entire circumference. The length from the tip of the inner surface to the outer edge in the radial direction in the direction orthogonal to the axis of the insulating layer is 4.2 times the distance in the direction perpendicular to the axis between the insulating layer and the insulator at the tip of the inner surface. That is all. Therefore, the effect of the insulating layer that lowers the electric field strength can be ensured.

According to the spark plug according to claim 3, the insulating layer further covers at least a part of the tip surface of the main metal fitting from the tip of the inner surface to the outer side in the radial direction over the entire circumference. Therefore, in addition to the effect of claim 1, the effect of the insulating layer that lowers the electric field strength can be improved.

According to the spark plug according to claim 4, the length from the tip of the inner surface to the outer end in the radial direction in the direction orthogonal to the axis of the insulating layer is the axis between the insulating layer and the insulator at the tip of the inner surface. It is more than 4.2 times the distance in the direction perpendicular to. Therefore, in addition to the effect of claim 3, the effect of the insulating layer that lowers the electric field strength can be ensured.

According to the spark plug according to claim 5, the length of the insulating layer from the tip of the inner surface in the axial direction is equal to or greater than the distance between the insulating layer and the insulator at the tip of the inner surface in the direction perpendicular to the axis. .. Therefore, in addition to the effect of any one of claims 1 to 4, the effect of the insulating layer that lowers the electric field strength can be ensured.

According to the ignition device according to claim 6, a voltage application unit that applies an AC voltage or a plurality of pulse voltages to the center electrode causes a plasma on the outer surface of the tip end portion of the spark plug according to any one of claims 1 to 5. Occurs. Therefore, any of the effects of claims 1 to 5 can be obtained.

It is a schematic diagram of the ignition device in the 1st Embodiment of this invention. It is one side sectional view of the spark plug. It is one side sectional view of the spark plug which enlarged the tip part of an insulator. (A) is a cross-sectional view of the spark plug shown by enlarging the portion shown by IVa in FIG. 3, and (b) is a cross-sectional view showing a part of the spark plug according to the second embodiment in an enlarged manner. , (C) is an enlarged cross-sectional view showing a part of the spark plug according to the third embodiment. (A) is an enlarged sectional view showing a part of the spark plug in the fourth embodiment, and (b) is an enlarged sectional view showing a part of the spark plug in the fifth embodiment. Yes, (c) is an enlarged cross-sectional view showing a part of the spark plug in the sixth embodiment. (A) is a diagram showing the relationship between the ratio of the length of the insulating layer in the axial direction to the distance from the insulating layer to the insulator and the reduction rate of the electric field strength, and (b) is formed on the inner surface of the main metal fitting. It is a figure which compared the reduction rate of the electric field strength by the insulating layer, and the reduction rate of the electric field strength by the insulating layer formed on the inner surface and the tip surface of the main metal fitting. (A) is a diagram showing the relationship between the ratio of the length of the insulating layer in the direction perpendicular to the axis to the distance from the insulating layer to the insulator and the reduction rate of the electric field strength, and (b) is a diagram showing the relationship from the insulating layer to the insulator. It is a figure which shows the relationship between the ratio of the thickness of the insulating layer with respect to the distance, and the reduction rate of the electric field strength.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic view of the ignition device 10 according to the first embodiment of the present invention. The ignition device 10 includes a spark plug 11 and a voltage application unit 12. The spark plug 11 is attached to the screw hole 15 of the internal combustion engine 13 with the tip exposed inside the combustion chamber 14. The rear end of the spark plug 11 is electrically connected to the voltage application unit 12. The voltage application unit 12 applies an AC voltage or a plurality of pulse voltages to the spark plug 11 by using the electric power supplied from the battery (not shown). As a result, the spark plug 11 generates non-equilibrium plasma and ignites the air-fuel mixture in the combustion chamber 14.

The spark plug 11 will be described with reference to FIGS. 2 and 3. FIG. 2 is a one-sided cross-sectional view of the spark plug 11 with the axis O as a boundary, and FIG. 3 is a one-sided cross-sectional view of the spark plug 11 with the tip 48 of the insulator 40 enlarged. In FIGS. 2 and 3, the lower side of the paper surface is referred to as the front end side of the spark plug 11, and the upper side of the paper surface is referred to as the rear end side of the spark plug 11 (FIGS. 4 (a), 4 (b), 4 (c), 5). The same applies to (a) and FIG. 5 (b)). As shown in FIG. 2, the spark plug 11 includes a main metal fitting 20, an insulator 40, and a center electrode 50.

As shown in FIG. 2, the main metal fitting 20 is a substantially cylindrical member fixed to the screw hole 15 of the internal combustion engine 13 (see FIG. 1), and is formed of a conductive metal material (for example, low carbon steel). Has been done. The main metal fitting 20 is connected in this order from the rear end side to the front end side along the axis O in the order of the crimping portion 21, the tool engaging portion 22, the curved portion 23, the seat portion 24, and the body portion 25. A screw portion 26 is formed on the outer peripheral surface of the body portion 25.

The crimping portion 21 and the curved portion 23 are portions for fixing the main metal fitting 20 to the insulator 40. The tool engaging portion 22 is a portion for engaging a tool such as a wrench when connecting the screw portion 26 to the screw hole 15 (see FIG. 1). The seat portion 24 is located on the rear end side of the body portion 25 and is a portion that projects radially outward in an annular shape. An annular gasket 53 is arranged between the seat portion 24 and the body portion 25. When the screw portion 26 is fitted into the screw hole 15, the gasket 53 is sandwiched between the seat portion 24 and the internal combustion engine 13 to seal the gap between the screw hole 15 and the screw portion 26. A shelf portion 27 (see FIG. 3) is formed on the inner circumference of the body portion 25.

The insulator 40 is a bottomed cylindrical member made of alumina or the like, which has excellent mechanical properties and heat insulating properties at high temperatures. In the insulator 40, a hole 41 that is open at the rear end of the insulator 40 and has a closed tip is formed along the axis O. The insulator 40 includes a body portion 42 extending in the axis O direction, an annular overhanging portion 43 extending radially outward from the center of the body portion 42 in the axis O direction, and a body portion 42 via a locking portion 44. It is provided with a leg portion 45 connected to the tip end side of the. The outer diameter of the leg portion 45 is set to be smaller than the outer diameter of the body portion 42, and the outer diameter of the locking portion 44 is reduced toward the tip side.

The insulator 40 is inserted into the main metal fitting 20. A packing 54 (see FIG. 3) is interposed between the locking portion 44 of the insulator 40 and the shelf portion 27 of the main metal fitting 20. The packing 54 is an annular plate material formed of a metal material such as a mild steel plate that is softer than the metal material constituting the main metal fitting 20.

A filler 56 such as talc sandwiched between the ring member 55 and the tool engaging portion 22 of the main metal fitting 20 is provided between the body portion 32 on the rear end side of the overhanging portion 43 of the insulator 40 and the tool engaging portion 22 of the main metal fitting 20. Be placed. When the crimping portion 21 of the main metal fitting 20 is crimped inward in the radial direction toward the insulator 40, the insulator 40 presses against the shelf portion 27 of the main metal fitting 20 via the ring member 55 and the filler 56. Will be done. As a result, the main metal fitting 20 fixes the insulator 40 via the packing 54, the ring member 55, and the filler 56.

The center electrode 50 is a rod-shaped electrode formed of a conductive metal material (for example, a nickel-based alloy or the like). The center electrode 50 is locked in the hole 41 of the insulator 40 and extends along the axis O from the front end side to the rear end side.

The terminal fitting 51 is a rod-shaped member to which the voltage applying portion 12 (see FIG. 1) is connected, and is made of a conductive metal material (for example, low carbon steel or the like). The tip end side of the terminal fitting 51 is arranged in the hole 41 of the insulator 40. A conductive sealing material 52 is arranged between the terminal fitting 51 and the center electrode 50. The center electrode 50 and the terminal fitting 51 are electrically connected to each other in the hole 41 by the sealing material 52.

As shown in FIG. 3, the leg portion 45 of the insulator 40 has a first portion 46 connected to the tip end side of the locking portion 44 and a second portion 47 connected to the tip end side of the first portion 46. I have. The outer diameters of the first part 46 and the second part 47 are set to be the same over the axis O direction. The outer diameter of the second part 47 is set to be smaller than the outer diameter of the first part 46. The body portion 25 of the main metal fitting 20 is arranged on the outer side in the radial direction of the first portion 46, and the tip end side and the second portion 47 of the first portion 46 project from the body portion 25 toward the tip end side. The tip portion 48 is a portion of the insulator 40 that exists on the tip side in the axis O direction with respect to the main metal fitting 20. Plasma is generated at the tip 48.

The body portion 25 of the main metal fitting 20 is arranged outside the first portion 46 of the insulator 40 in the radial direction. When the gap between the inner surface 28 of the body portion 25 and the first portion 46 becomes large, plasma is likely to be generated between the body portion 25 and the first portion 46, energy loss occurs, and the amount of plasma generated at the tip portion 48. Is reduced and ignitability is reduced. Further, when the gap between the inner surface 28 of the body portion 25 and the first portion 46 becomes large, it becomes difficult for the heat of the leg portion 45 to be transferred to the main metal fitting 20, so that the tip portion 48 overheats abnormally and the tip portion 48 becomes a heat source. It is easy for problems to ignite. Therefore, it is preferable to make the gap between the body portion 25 and the first portion 46 as narrow as possible.

However, in consideration of the variation in dimensions of the main metal fitting 20 and the insulator 40, the assembly accuracy, the linear expansion difference between the insulator 40 and the main metal fitting 20, and the like, the distance between the body portion 25 and the first portion 46 is constant. A sized gap (for example, about 0.2 to 0.5 mm) is provided. Since strong plasma is likely to be generated at the tip (edge) of the main metal fitting 20 where the electric field is easily concentrated, the insulator 40 (first part 46) may penetrate (dielectric breakdown). Since an AC voltage or a plurality of pulse voltages is applied to the spark plug 11, plasma is superimposed on a portion having a high electric field strength, and the insulator 40 easily penetrates. Therefore, an insulating layer 31 is provided to cover the inner surface 28 of the main metal fitting 20.

The insulating layer 31 will be described with reference to FIG. 4A. FIG. 4A is a cross-sectional view of the spark plug 11 in which the portion shown by IVa in FIG. 3 is enlarged. The spark plug 11 has an insulating layer 31 that covers a part of the inner surface 28 of the main metal fitting 20 (body portion 25) from the tip 29 to the rear end side (upper side of FIG. 4A) of the inner surface 28 over the entire circumference. It is provided.

The inner surface 28 of the main metal fitting 20 refers to a surface facing the outer circumference of the insulator 40. In the present embodiment, the inner surface 28 has the same diameter from the tip of the shelf 27 (lower side in FIG. 3) to the tip 29 in the axis O direction. The tip 29 of the inner surface 28 means the angle at which the tip surface 30 of the main metal fitting 20 and the inner surface 28 intersect. The tip surface 30 of the main metal fitting 20 means a surface facing the tip side of the main metal fitting 20.

The insulating layer 31 has a volume resistivity of about 1 × 10 ⁷ to 1 × 10 ¹⁵ Ω · m. The insulating layer 31 is formed on the main metal fitting 20 by well-known means such as chemical vapor deposition (CVD), coating and baking of an insulating paint, plating, and thermal spraying. With the insulating layer 31, the electric field strength of the tip 29 of the inner surface 28 can be lowered as compared with the case without the insulating layer 31, so that plasma can be less likely to be generated between the tip 29 and the leg 45. As a result, the penetration of the insulator 40 (leg portion 45) can be suppressed, the energy loss due to the generation of plasma at the tip portion 29 can be suppressed, and the amount of plasma generated from the tip portion 48 can be relatively increased. ..

The length L from the tip 29 to the rear end 32 in the axis O direction of the insulating layer 31 is the direction perpendicular to the axis O (see FIG. 3) between the insulating layer 31 and the insulator 40 at the tip 29. The length is set to a distance D or more, that is, L / D ≧ 1. If the vicinity of the tip 29 is covered with an insulating layer 31 having a length L of a distance D or more, the electric field strength of the tip 29 where the electric field is concentrated can be suppressed.

The thickness T of the insulating layer 31 is set to 0.1 times or more the distance D. It is not necessary for the insulating layer 31 to have a uniform thickness T. This is because the effect can be obtained if the thickness of the thin portion of the insulating layer 31 is 0.1 times or more the distance D.

Next, a second embodiment will be described with reference to FIG. 4 (b). The same parts as those described in the first embodiment are designated by the same reference numerals, and the following description will be omitted. FIG. 4B is an enlarged cross-sectional view showing a part of the spark plug 60 according to the second embodiment. Note that FIG. 4 (b) shows the same portion as that of FIG. 4 (a) (the same applies to FIGS. 4 (c), 5 (a), 5 (b), and 5 (c)).

The spark plug 60 is chamfered at a portion of the tip surface 62 of the main metal fitting 61 that communicates with the inner surface 28. The spark plug 60 has an insulating layer 31 that covers a part of the inner surface 28 on the rear end side (upper side of FIG. 4B) from the tip 29 where the front end surface 62 and the inner surface 28 of the main metal fitting 61 intersect. It is provided. According to the spark plug 60 of the second embodiment, the same effect as that of the first embodiment can be obtained by the insulating layer 31.

The third embodiment will be described with reference to FIG. 4 (c). In the first embodiment and the second embodiment, the case where a part of the inner surface 28 is covered with the insulating layer 31 has been described. On the other hand, in the third embodiment, a case where a part of the inner surface 28 and the tip surface 30 is covered with the insulating layer 71 will be described. The same parts as those described in the first embodiment are designated by the same reference numerals, and the following description will be omitted. FIG. 4C is an enlarged cross-sectional view showing a part of the spark plug 70 according to the third embodiment.

The spark plug 70 includes an insulating layer 71 that covers the vicinity of the tip 29 of the inner surface 28 of the main metal fitting 20. The insulating layer 71 includes an inner surface portion 72 that covers a part of the inner surface 28 of the main metal fitting 20 from the tip end 29 to the rear end side (upper side of FIG. 4C) over the entire circumference, and the outer surface (from the tip end 29 to the tip surface 30). An end face portion 73 that covers a part of FIG. 4C (left side) over the entire circumference is provided. By providing the end surface portion 73 in addition to the inner surface portion 72, the concentration of the electric field at the tip 29 can be further suppressed, so that the effect of suppressing the penetration of the insulator 40 by the insulating layer 71 can be improved.

The length L from the tip 29 to the rear end 74 in the axis O direction of the inner surface portion 72 is the direction perpendicular to the axis O (see FIG. 3) between the inner surface portion 72 and the insulator 40 at the tip 29. The length is set to be equal to or greater than the distance D, that is, L / D ≧ 1.

The length M of the insulating layer 71 (the length excluding the thickness T of the inner surface portion 72) from the tip 29 to the radial outer end 75 in the direction orthogonal to the axis O (see FIG. 3) is the distance D. It is set to 4.2 times or more of. Further, the thickness T of the inner surface portion 72 and the end surface portion 73 is set to 0.1 times or more the distance D.

Next, a fourth embodiment will be described with reference to FIG. 5 (a). The same parts as those described in the first embodiment are designated by the same reference numerals, and the following description will be omitted. FIG. 5B is an enlarged cross-sectional view showing a part of the spark plug 80 according to the fourth embodiment.

The spark plug 80 has a rounded portion of the tip surface 82 of the main metal fitting 81 that communicates with the inner surface 28. The spark plug 80 is provided with an insulating layer 83 that covers the tip 29 where the tip surface 82 and the inner surface 28 of the main metal fitting 81 intersect. The insulating layer 83 includes an inner surface portion 84 and an end surface portion 85. The inner surface portion 84 is a portion that covers a part of the inner surface 28 from the front end 29 to the rear end side (upper side in FIG. 5A) over the entire circumference. The end surface portion 85 is a portion that covers a part of the outside (left side in FIG. 5A) from the tip end 29 to the tip end surface 82 over the entire circumference.

The length L from the tip 29 to the end 86 on the rear end side of the inner surface portion 84 in the axis O direction is the direction perpendicular to the axis O (see FIG. 3) between the inner surface portion 84 and the insulator 40 at the tip 29. The length is set to be equal to or greater than the distance D, that is, L / D ≧ 1.

The length M (the length excluding the thickness T of the inner surface portion 84) of the insulating layer 83 from the tip 29 to the radial outer end 87 in the direction orthogonal to the axis O (see FIG. 3) is 4 of the distance D. . Set to 2 times or more. According to the spark plug 80 of the fourth embodiment, the same effect as that of the third embodiment can be obtained by the insulating layer 83.

The fifth embodiment will be described with reference to FIG. 5 (b). In the first to fourth embodiments, the case where the thickness T of the insulating layers 31, 71, and 83 is substantially uniform has been described. On the other hand, in the fifth embodiment, the insulating layer 91 whose thickness gradually becomes thinner as it approaches the ends 94 and 95 of the insulating layer 91 will be described. The same parts as those described in the first embodiment are designated by the same reference numerals, and the following description will be omitted. FIG. 5B is an enlarged cross-sectional view showing a part of the spark plug 90 according to the fifth embodiment.

The spark plug 90 includes an insulating layer 91 that covers the vicinity of the tip 29 of the inner surface 28 of the main metal fitting 20. The insulating layer 91 includes an inner surface portion 92 and an end surface portion 93. The inner surface portion 92 is a portion that covers a part of the inner surface 28 from the front end 29 to the rear end side (upper side in FIG. 5B) over the entire circumference. The end face portion 93 is a portion that covers a part of the outside (left side of FIG. 5B) from the tip 29 to the tip surface 30 over the entire circumference.

The length L from the tip 29 to the rear end 94 of the insulating layer 91 in the axis O direction is the direction perpendicular to the axis O (see FIG. 3) between the insulating layer 91 and the insulator 40 at the tip 29. The length of the distance D or more, that is, L ≧ D is set. The end 95 is a portion where the thickness T of the inner surface portion 92 is 0.1 times the distance D. Therefore, the thickness T of the inner surface portion 92 is set to 0.1 times or more the distance D.

Further, the length M of the insulating layer 91 from the tip 29 to the radial outer end 95 in the direction orthogonal to the axis O (see FIG. 3) (the length not including the thickness T of the inner surface portion 92 of the tip 29) is , It is set to 4.2 times or more of the distance D. The end 95 is a portion where the thickness T of the end face portion 93 is 0.1 times the distance D. Therefore, the thickness T of the end face portion 93 is set to 0.1 times or more the distance D. According to the spark plug 90 of the fifth embodiment, the same effect as that of the third embodiment can be obtained by the insulating layer 91.

The sixth embodiment will be described with reference to FIG. 5 (c). In the fifth embodiment, the case where the thickness T of the insulating layer 91 gradually becomes thinner as it approaches the ends 94 and 95 of the insulating layer 91 has been described. On the other hand, in the sixth embodiment, the insulating layer 101 in which a portion whose thickness gradually decreases as it approaches the ends 104 and 105 of the insulating layer 101 and a portion whose thickness is substantially uniform coexist will be described. The same parts as those described in the first embodiment are designated by the same reference numerals, and the following description will be omitted. FIG. 5C is an enlarged cross-sectional view showing a part of the spark plug 100 according to the sixth embodiment.

The spark plug 100 includes an insulating layer 101 that covers the vicinity of the tip 29 of the inner surface 28 of the main metal fitting 20. The insulating layer 101 includes an inner surface portion 102 and an end surface portion 103. The inner surface portion 102 is a portion that covers a part of the inner surface 28 from the front end 29 to the rear end side (upper side in FIG. 5C) over the entire circumference. The end face portion 103 is a portion that covers a part of the outside (left side of FIG. 5C) from the tip 29 to the tip surface 30 over the entire circumference.

The length L from the tip 29 to the rear end 104 of the insulating layer 101 in the axis O direction is the direction perpendicular to the axis O (see FIG. 3) between the insulating layer 101 and the insulator 40 at the tip 29. The length of the distance D or more, that is, L ≧ D is set. The end 104 is a portion where the thickness T of the inner surface portion 102 is 0.1 times the distance D. Therefore, the thickness T of the inner surface portion 102 is set to 0.1 times or more the distance D.

Further, the length M of the insulating layer 101 from the tip 29 to the radial outer end 105 in the direction orthogonal to the axis O (see FIG. 3) (the length not including the thickness T of the inner surface portion 102 at the tip 29) is , It is set to 4.2 times or more of the distance D. The end 105 is a portion where the thickness T of the end face portion 103 is 0.1 times the distance D. Therefore, the thickness T of the end face portion 103 is set to 0.1 times or more the distance D. According to the spark plug 100 of the sixth embodiment, the same effect as that of the third embodiment can be obtained by the insulating layer 101.

The present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

(Example 1)
For the spark plug 11 on which the insulating layer 31 was formed described in the first embodiment, the relationship between the length L of the insulating layer 31 and the electric field strength was simulated (electrostatic field analysis) using a computer. The software used was ANSYS Mechanical APDL (ANSYS, Inc.), and the simulation target was a 2D axisymmetric model.

The dimensions of each part of the model were as follows (see FIG. 3). The outer diameter D1 of the center electrode 50 = Φ1.7 mm, the outer diameter D2 of the second part 47 of the insulator 40 = Φ4.1 mm, the outer diameter D3 of the first part 46 of the insulator 40 = Φ7.2 mm, the first part 46 Of these, the length L1 = 1.0 mm of the portion protruding from the main metal fitting 20, the length L2 = 11.3 mm of the portion of the center electrode 50 protruding from the main metal fitting 20, and the length L3 of the tip 48 of the insulator 40. = 12.7 mm, thickness T of insulating layer 31 = 0.1 mm, distance D from insulating layer 31 to insulator 40 = 0.25 mm.

The relative permittivity of the insulator 40 and the insulating layer 31 was 9.5, and the volume of air (relative permittivity was 1.0) surrounding the tip 48 was Φ104 mm × 62.7 mm. When the length L of the insulating layer 31 is changed in the range of 0.2 to 5.3 mm and a voltage of 20 kV is applied between the inner surface of the hole 41 of the insulator 40 and the main metal fitting 20 by the center electrode 50. The electric field strength (V / m) of was calculated.

FIG. 6A is a diagram showing the relationship between the ratio (L / D) of the axial length L of the insulating layer 31 to the distance D from the insulating layer 31 to the insulator 40 and the reduction rate (%) of the electric field strength. Is. The reduction rate (%) of the electric field strength is how much the electric field strength of the surface (particularly the edge portion) of the insulating layer 31 is reduced with respect to the electric field strength of the tip 29 of the inner surface 28 when the insulating layer 31 is not present. It is an index to show. When the insulating layer 31 is not provided, the outer diameter D3 = Φ7.4 mm of the first portion 46 of the insulator 40 is set in order to make the distance from the tip 29 of the inner surface 28 to the insulator 40 0.25 mm.

From FIG. 6A, it was found that the slope of the graph changed significantly with L / D = 1 as the boundary. It has been clarified that by setting the insulating layer 31 to L / D ≧ 1, the effect of lowering the electric field strength near the tip 29 of the inner surface 28 of the main metal fitting 20 can be enhanced.

(Example 2)
A simulation was performed to compare the effect of the insulating layer 31 described in the first embodiment with the effect of the insulating layer 71 described in the third embodiment. The length L of the insulating layer 31 and the length L of the inner surface portion 72 and the length M of the end surface portion 73 of the insulating layer 71 are set to 5.3 mm, and the thickness T of the insulating layer 31, the inner surface portion 72 and the end surface portion 73 is set. The electric field strength was calculated under the same conditions as in Example 1 except that the variation was made in the range of 0.01 to 0.8 mm.

When the end face portion 73 is provided on the main metal fitting 20, the length of the main metal fitting 20 in the axis O direction is shortened by the thickness T of the end face portion 73. When the insulating layer is provided on the inner surface of the main metal fitting 20, the distance from the insulating layer to the insulator 40 is 0.25 mm, so that the first part 46 of the insulator 40 is provided according to the thickness T of the insulating layer. The outer diameter D3 was adjusted.

FIG. 6B shows the reduction rate of the electric field strength by the insulating layer 31 formed on the inner surface 28 of the main metal fitting 20, and the reduction rate of the electric field strength by the insulating layer 71 formed on the inner surface 28 and the tip surface 30 of the main metal fitting 20. It is a figure comparing with and. In FIG. 6B, the horizontal axis represents the ratio of the thickness T to the distance D (T / D), and the vertical axis represents the reduction rate (%) of the electric field strength. The broken line is a graph of the insulating layer 31, and the solid line is a graph of the insulating layer 71. From FIG. 6B, it was clarified that the reduction rate of the electric field strength can be increased by providing the insulating layer 71 (end face portion 73) on the main metal fitting 20.

(Example 3)
A simulation was performed to investigate the relationship between the length M and the distance D of the insulating layer 71 described in the third embodiment. The length L of the inner surface portion 72 of the insulating layer 71 is 5.3 mm, the thickness T of the inner surface portion 72 and the end face portion 73 is 0.1 mm, and the length M of the end face portion 73 is in the range of 0.4 to 4.45 mm. The electric field strength was calculated under the same conditions as in Example 1 except that it was changed in.

FIG. 7A shows the relationship between the ratio (M / D) of the length M of the insulating layer 71 in the direction perpendicular to the axis to the distance D from the insulating layer 71 to the insulator 40 and the reduction rate (%) of the electric field strength. It is a figure. From FIG. 7A, it was found that the slope of the graph changes with M / D = 4.2 as a boundary. It has been clarified that by setting the insulating layer 71 to M / D ≧ 4.2, the effect of lowering the electric field strength near the tip 29 of the inner surface 28 of the main metal fitting 20 can be enhanced.

(Example 4)
A simulation was performed to investigate the relationship between the thickness T of the insulating layer 31 and the distance D described in the first embodiment. Except that the length L of the insulating layer 31 was 5.3 mm, the distance D was changed in the range of 0.15 to 0.5 mm, and the thickness T of the insulating layer 31 was changed in the range of 0.01 to 0.8 mm. The electric field strength was calculated under the same conditions as in Example 1.

FIG. 7B is a diagram showing the relationship between the ratio (T / D) of the thickness T of the insulating layer 31 to the distance D from the insulating layer 31 to the insulator 40 and the reduction rate (%) of the electric field strength. From FIG. 7B, it was found that the reduction rate when T / D ≥ 0.1 can be about 3 times or more the reduction rate when T / D <0.1. Therefore, it has become clear that the insulating layer 31 is desirable if it has a thickness T of 1/10 or more of the distance D.

Although the present invention has been described above based on the embodiments, the present invention is not limited to the above-described embodiments, and various improvements and modifications can be made without departing from the spirit of the present invention. It is easy to infer.

In each of the above embodiments, the case where the inner surface 28 of the main metal fitting 20 has the same diameter from the tip of the shelf 27 (lower side in FIG. 3) to the tip 29 in the axis O direction has been described, but this is not necessarily the case. It is not something that can be done. The shape and diameter of the inner surface 28 of the main metal fitting 20 can be appropriately set in consideration of the heat dissipation property and the assembly accuracy of the main metal fitting 20.

In each of the above embodiments, the case where the leg portion 45 on the distal end side of the locking portion 44 of the insulator 40 has a smaller diameter of the second portion 47 on the distal end side than the diameter of the first portion 46 at the root will be described. However, it is not necessarily limited to this. Of course, it is possible to make the diameters of the legs 45 the same over the axis O direction. Further, it is naturally possible to make the diameter of the portion of the leg portion 45 of the insulator 40 protruding toward the tip side from the main metal fitting 20 larger than the diameter of the portion of the leg portion 45 existing inside the main metal fitting 20. ..

In each of the above embodiments, the case where the diameter of the portion of the center electrode 50 arranged inside the leg portion 45 is the same over the axis O direction has been described, but the present invention is not necessarily limited to this. Of course, it is possible to make the diameter of the portion arranged on the tip side of the leg portion 45 larger than the diameter of the base portion of the center electrode 50. By appropriately setting the diameter of the leg portion 45 and the diameter of the center electrode 50, the surface area and the thickness in the radial direction of the tip portion 48 of the insulator 40 are set, and the amount of plasma generated around the tip portion 48 is determined. Can be set as appropriate.

In each of the above embodiments, the case where the insulator 40 is formed of one member has been described, but the present invention is not necessarily limited to this. Of course, it is possible to divide the insulator 40 into a plurality of members and join the members with adhesives, screws, or the like to form the insulator 40.

10 Ignition device 11, 60, 70, 80, 90, 100 Ignition plug 12 Voltage application part 20, 61, 81 Main metal fittings 28 Inner surface of main metal fittings 29 Inner surface tip 30, 62, 82 Tip surface of main metal fittings 31, 71, 83,91,101 Insulator layer 40 Insulator 48 Insulator tip 50 Center electrode 75,87,95,105 End D Distance L, M Length O Axis T Thickness

Claims (6)

A bottomed tubular insulator that extends from the front end side to the rear end side along the axis and has a closed tip.
A center electrode whose tip is included in the insulator,
A spark plug including a tubular main metal fitting that holds the insulator from the outer peripheral side in a state where the tip portion of the insulator protrudes from its own tip.
An insulating layer is provided which covers at least a part of the inner surface of the main metal fitting from the tip end side to the rear end side of the inner surface over the entire circumference .
A spark plug in which the thickness of the insulating layer is 0.1 times or more the distance in the direction perpendicular to the axis between the insulating layer and the insulator at the tip of the inner surface . A bottomed tubular insulator that extends from the front end side to the rear end side along the axis and has a closed tip.
A center electrode whose tip is included in the insulator,
A spark plug including a tubular main metal fitting that holds the insulator from the outer peripheral side in a state where the tip portion of the insulator protrudes from its own tip.
An insulating layer is provided which covers at least a part of the inner surface of the main metal fitting from the tip end side to the rear end side of the inner surface over the entire circumference .
The insulating layer further covers at least a part of the tip surface of the main metal fitting radially outward from the tip of the inner surface over the entire circumference.
The length from the tip of the inner surface to the outer end in the radial direction in the direction orthogonal to the axis of the insulating layer is the direction perpendicular to the axis between the insulating layer and the insulator at the tip of the inner surface. Spark plug that is more than 4.2 times the distance of . The spark plug according to claim 1, wherein the insulating layer further covers at least a part of the tip surface of the main metal fitting radially outward from the tip of the inner surface over the entire circumference. The length from the tip of the inner surface to the outer end in the radial direction in the direction orthogonal to the axis of the insulating layer is the direction perpendicular to the axis between the insulating layer and the insulator at the tip of the inner surface. The spark plug according to claim 3, which is 4.2 times or more the distance of. The length from the tip of the inner surface in the axial direction of the insulating layer, of claims 1 to is the direction perpendicular distance above the axis between the insulating layer and said insulator in said tip of said inner surface The spark plug according to any one of 4 . The spark plug according to any one of claims 1 to 5.
An ignition device including a voltage application unit that generates non-equilibrium plasma on the outer surface of the tip portion by applying an AC voltage or a plurality of pulse voltages to the center electrode.

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