JP4482589B2 - Plasma jet ignition plug - Google Patents

Description

  The present invention relates to a plasma jet ignition plug for an internal combustion engine that forms plasma and ignites an air-fuel mixture.

  2. Description of the Related Art Conventionally, spark plugs that ignite an air-fuel mixture by spark discharge are used as ignition plugs of engines that are internal combustion engines for automobiles, for example. In recent years, there has been a demand for higher output and lower fuel consumption of internal combustion engines, as a spark plug with high ignitability that can be ignited reliably even for a lean mixture with a fast combustion spread and a higher ignition limit air-fuel ratio, Plasma jet spark plugs are known.

  Such a plasma jet ignition plug has an insulator (insulator, housing) made of ceramic or the like around a spark discharge gap (gap) between a center electrode and a ground electrode (external electrode) integrated with a metal shell. ) To form a small volume discharge space called a cavity (chamber). Further, a high voltage is applied between the center electrode and the ground electrode to perform a spark discharge, and a current can flow at a relatively low voltage due to the dielectric breakdown generated at this time. Thus, the discharge state is changed, and thereby plasma formed in the cavity is ejected from an opening (external electrode hole) called an orifice to ignite the air-fuel mixture (for example, Patent Document 1). Or refer to Patent Document 2.)

The plasma jet ignition plug described in Patent Document 1 or Patent Document 2 closes the end portion on the front end side of the metal shell formed in a cylindrical shape, opens the orifice in the center with this end portion as a ground electrode, The tip and the cavity of the insulator accommodated in the external electrode are brought into contact with the inner surface of the electrode, so that the orifice and the cavity are coaxially continuous. Also, a separate ground electrode was joined to the tip of the metal shell, an orifice was opened in the center of the ground electrode, and the tip of the insulator was brought into contact with the inner surface (inner side) of the ground electrode. There is also a form (refer FIG. 2 of patent document 1).
Japanese Patent Laid-Open No. 2-72577 JP 2006-294257 A

  However, in manufacturing the plasma jet ignition plug, dimensional control is strictly performed when the insulator, the metal shell, and the ground electrode are manufactured, and the plasma jet ignition plug described in Patent Document 1 and Patent Document 2 is insulated. If the tip of the insulator and the inner surface of the ground electrode are in close contact with each other, if they are affected by the thermal cycle during use, the insulator will be caused by the difference in thermal expansion coefficient between the insulator, the metal shell and the material constituting the ground electrode. Could be damaged. On the other hand, if there is a large gap between the tip surface of the insulator and the inner surface of the ground electrode due to manufacturing tolerances, the plasma energy is reduced when the plasma formed in the cavity is ejected through the orifice. There is a possibility that the gas escapes to the gap and is not ejected in the intended direction, or the ejection amount (ejection length) is small (short). Furthermore, when holding the insulator, it is held by being placed in the metal shell and crimped. However, due to manufacturing tolerances of both the insulator and the metal shell, the tip surface of the insulator is strongly pressed against the inner surface of the ground electrode. When crimped in the applied state, there is a possibility that the insulator is damaged due to an increase in internal stress.

  The present invention was made to solve the above problems, and by separating the insulator and the ground electrode from each other in the axial direction to prevent the insulator from being damaged, and by defining the size of the gap, It is an object of the present invention to provide a plasma jet ignition plug that can reduce energy loss of ejected plasma and suppress deterioration in ignitability.

To achieve the above object, a plasma jet ignition plug according to a first aspect of the present invention has a center electrode and an axial hole extending in the axial direction, and the front end surface of the central electrode is accommodated in the axial hole. An insulator that holds the center electrode; a cavity formed in a concave shape with the inner peripheral surface of the shaft hole and the tip surface of the center electrode on the tip side of the insulator; and a wall of the insulator A metal shell that surrounds and holds the periphery in the radial direction, and an electrode that is joined to the metal shell and is electrically connected to the metal shell, and that is disposed on the tip side of the insulator, and the cavity is surrounded by the outside air A plasma jet ignition plug comprising: a ground electrode having an opening for communication; and plasma generated in the cavity in accordance with a discharge performed between the center electrode and the ground electrode, wherein the insulator The ground electrodes are arranged in a state of being separated from each other in the axial direction. When the size of the gap between the insulator and the ground electrode in the axial direction is a and the volume of the cavity is S , 0 <with a a ≦ 0.5 [mm], Ri ^{0.1 ≦ S ≦ 10 [mm 3} ] der, further, in the formation position of the cavity in the axial direction, the insulator and the metal shell Is arranged in a state of being separated from each other in the radial direction orthogonal to the axial direction, and when the size of the gap between the insulator and the metal shell in the radial direction orthogonal to the axial direction is b , and b ≦ 1.1 [mm] der characterized Rukoto.

The plasma jet ignition plug of the invention according to claim 2 is characterized in that, in addition to the configuration of the invention of claim 1 , the b is 0.1 ≦ b ≦ 1.1 [mm]. .
According to a third aspect of the present invention, in addition to the configuration of the first or second aspect of the present invention, the plasma jet ignition plug is configured such that the size of the gap between the center electrode and the ground electrode in the axial direction is G. In this case, 1.0 ≦ G ≦ 3.0 [mm].

According to a fourth aspect of the present invention, there is provided a plasma jet ignition plug having a center electrode and an axial hole extending in an axial direction. The tip end surface of the central electrode is accommodated in the axial hole and the central electrode is held. Surrounding the insulator, a cavity formed in a concave shape with the inner peripheral surface of the shaft hole and the tip surface of the center electrode on the tip side of the insulator, and the periphery of the insulator in the radial direction A metal shell to be held, an electrode which is joined to the metal shell and is electrically connected to the metal shell, and which is disposed on the tip side of the insulator, and has an opening for communicating the cavity with the outside air. A plasma jet ignition plug that generates plasma in the cavity in accordance with a discharge performed between the center electrode and the ground electrode, wherein the metal shell is in contact with the ground electrode. And at least one of the ground electrode and the insulator are arranged in a state of being separated from each other in the axial direction, and at least one of the joint portion of the metal shell with the ground electrode and the ground electrode A first packing that is in close contact with each other is interposed in a gap between one and the insulator, and at least one of the joint portion of the metal shell with the ground electrode in the axial direction and the ground electrode When the size of the gap between one and the insulator is a and the volume of the cavity is S, 0 <a ≦ 0.8 [mm] and 0.1 ≦ S ≦ 10 [Mm ³ ] and 1.0 ≦ G ≦ 3.0 [mm] where G is the size of the gap between the center electrode and the ground electrode in the axial direction. It is characterized by.

  In addition to the configuration of the invention according to claim 4, the plasma jet ignition plug of the invention according to claim 5 includes a mounting portion provided on the distal end side of the metal shell on the outer peripheral surface of the insulator. A portion accommodated inside the metal shell in the radial direction is formed with a stepped portion having an outer diameter on the rear end side larger than an outer diameter on the front end side, and an inner peripheral surface of the metal shell Is formed with a metal step that bulges inward in the radial direction of the metal shell so that the faces of the metal step and the lever step facing each other. A second packing that is in close contact with both is interposed therebetween, and the second packing has a higher hardness than the first packing.

  In the plasma jet ignition plug according to the first aspect of the present invention, since there is a gap (first gap) between the insulator and the ground electrode in the axial direction, the thermal expansion coefficient is reduced when both are in close contact. There is no risk of breakage due to an increase in internal stress that may arise from the difference. Also in the manufacturing process of the plasma jet ignition plug, the first gap is provided between the insulator and the ground electrode (that is, the size of the gap between the insulator and the ground electrode in the axial direction a> 0 [mm]). If the design is performed in this manner, the insulator is prevented from being held by the metal shell while being pressed against the ground electrode due to the manufacturing tolerance between the two, so that the insulator can be prevented from being damaged.

In the plasma jet ignition plug having such a first gap, the volume S of the cavity satisfies 0.1 ≦ S ≦ 10 [mm ³ ]. Therefore, while ensuring the minimum energy necessary to eject the plasma formed in the cavity from the opening, it is suppressed that the energy spreads and disperses in the cavity, and sufficient energy is emitted from the cavity. A large amount of plasma can be ejected. Further, since the size a of the first gap satisfies 0 <a ≦ 0.5 [mm], the energy of the plasma ejected from the cavity is unlikely to leak into the first gap on the way to the opening. For this reason, plasma of a sufficiently effective size can be ejected outward from the opening, and good ignitability can be obtained.

And, as in the invention according to claim 1 , if the size b of the gap (second gap) between the insulator and the metal shell in the radial direction orthogonal to the axial direction satisfies b ≦ 1.1 [mm] It is possible to prevent the entire volume including the first gap and the second gap from increasing. As a result, plasma energy leaked into the first gap further flows into the second gap in the middle of the plasma ejected from the cavity toward the opening, so that the plasma energy is greatly deprived. Therefore, plasma having a sufficiently effective size can be ejected outward from the opening, and good ignitability can be obtained.

From the viewpoint of heat resistance as a single plasma jet ignition plug, the size b is preferably closer to zero. On the other hand, parts constituting the plasma jet ignition plug expand / contract due to the assembling insertion property between the insulator and the metal shell and the cooling / heating cycle accompanying use. For this reason, the size b is preferably 0.1 [mm] or more as in the invention according to claim 2 . By setting the lower limit value of the size b to 0.1 [mm], damage due to breakage due to expansion / contraction of parts during use can be reduced.
Further, as in the invention according to claim 3, if the size G of the gap (spark discharge gap) between the center electrode and the ground electrode in the axial direction satisfies G ≦ 3.0 [mm]. Good ignitability can be obtained. The reason for this will be described in the test (Example 2) described later. When the spark discharge gap size G exceeds 3.0 mm, the ignitability is remarkably reduced as compared with the case of 3.0 mm or less. It is because it ends. On the other hand, if the size G of the spark discharge gap satisfies 1.0 ≦ G [mm], the cavity depth can be sufficiently secured, and the ejected plasma is effectively frame-shaped. And ignitability can be improved.

In the plasma jet ignition plug of the invention according to claim 4, since the first packing is interposed in the gap (first gap) between the insulator and at least one of the joint portion of the metal shell and the ground electrode, The first gap can be sealed by the first packing. Therefore, since the plasma ejected from the cavity is not leaked toward the soot in the first gap on the way to the opening, it has a sufficiently effective size from the opening to the outside. Plasma can be ejected and good ignitability can be obtained.
If the volume S of the cavity satisfies 0.1 ≦ S ≦ 10 [mm ³ ] as in the invention according to claim 4, the energy of the plasma formed in the cavity spreads and is dispersed in the cavity. Therefore, plasma having a sufficient energy amount can be ejected. Furthermore, if the first gap size “a” satisfies 0 <a ≦ 0.8 [mm], the plasma leaked from the cavity leaks into the first gap on the way to the opening. Hard to do. For this reason, plasma of a sufficiently effective size can be ejected outward from the opening, and good ignitability can be obtained.
Further, as in the invention according to claim 4, when the size G of the gap (spark discharge gap) between the center electrode and the ground electrode in the axial direction satisfies G ≦ 3.0 [mm]. Good ignitability can be obtained.

  Further, as in the invention according to claim 5, if the hardness of the second packing used when holding the insulator with the metal shell is higher than the hardness of the first packing, It does not hinder the deformation of the two packings (deformation that can occur on the surface to enhance the sealing effect). That is, when a force necessary for holding the insulator by the metal shell (holding by caulking) is applied in the manufacturing process of the plasma jet ignition plug, the first packing is easily deformed by the force, and the second packing Since the deformation of the surface is not hindered, the second packing can be brought into close contact with both the metal shell and the insulator, and leakage of combustion gas through the two can be prevented. The first packing can also function as a buffer material between the insulator and the ground electrode when the insulator is caulked and held by the metal shell, and in the process of manufacturing the plasma jet ignition plug, the insulator Can be prevented from being damaged.

  Hereinafter, a first embodiment of a plasma jet ignition plug embodying the present invention will be described with reference to the drawings. First, with reference to FIG. 1 and FIG. 2, the structure of the plasma jet ignition plug 100 as an example is demonstrated. FIG. 1 is a partial cross-sectional view of a plasma jet ignition plug 100 according to the first embodiment. FIG. 2 is an enlarged cross-sectional view of the tip portion of the plasma jet ignition plug 100 according to the first embodiment. In FIG. 1, the axis O direction of the plasma jet ignition plug 100 is the vertical direction in the drawing, the lower side is the front end side (front), and the upper side is the rear end side (rear).

  The plasma jet spark plug 100 according to the first embodiment shown in FIG. 1 is generally held in the insulator 10, a metal shell 50 that holds the insulator 10, and the insulator 10 in the direction of the axis O. The center electrode 20, the ground electrode 30 welded to the front end portion 65 of the metal shell 50, and the terminal metal fitting 40 provided at the rear end portion of the insulator 10 are configured.

  The insulator 10 is a cylindrical insulating member that is formed by firing alumina or the like and has an axial hole 12 in the direction of the axis O as is well known. A flange portion 19 having the largest outer diameter is formed substantially at the center in the direction of the axis O, and a rear end side body portion 18 is formed on the rear end side. The outer peripheral surface on the rear end side of the rear end side body portion 18 is subjected to uneven processing called corrugation for increasing the creepage distance between the metal shell 50 and the terminal metal fitting 40. Further, a distal end side body portion 17 having an outer diameter smaller than that of the rear end side body portion 18 at the front end side from the flange portion 19, and a further outer diameter than the front end side body portion 17 on the front end side from the front end side body portion 17. A small leg length 13 is formed. A stepped portion 14 having a step shape is formed between the leg long portion 13 and the front end side body portion 17. The step 14 corresponds to the “insulator step” in the present invention.

  The inner peripheral portion of the long leg portion 13 of the shaft hole 12 is formed as an electrode housing portion 15 having a diameter smaller than the inner peripheral portions of the front end side body portion 17, the flange portion 19 and the rear end side body portion 18. A center electrode 20 is held inside the electrode housing portion 15. As shown in FIG. 2, the shaft hole 12 is formed as a tip small-diameter portion 61 with the inner circumference further reduced in diameter on the tip side of the electrode housing portion 15. The tip small diameter portion 61 opens at the tip (tip surface) 16 of the insulator 10.

  Next, the center electrode 20 is a cylindrical electrode rod formed of a nickel-based alloy such as Inconel (trade name) 600 or 601, and has a metal core 23 made of copper or the like having excellent thermal conductivity. ing. A disc-shaped electrode tip 25 made of an alloy containing precious metal or W (tungsten) as a main component is welded to the tip 21 of the center electrode 20 so as to be integrated with the center electrode 20. In the first embodiment, the electrode chip 25 integrated with the center electrode 20 is also referred to as “center electrode”.

  Further, as shown in FIG. 1, the rear end side of the center electrode 20 is enlarged in a bowl shape, and this bowl-shaped portion is brought into contact with a stepped portion of the electrode housing portion 15 in the shaft hole 12. The center electrode 20 is positioned in the electrode housing portion 15. As shown in FIG. 2, the distal end surface 26 of the distal end portion 21 of the center electrode 20 (more specifically, the distal end surface 26 of the electrode tip 25 joined integrally with the central electrode 20 at the distal end portion 21 of the central electrode 20). ) Is in contact with a step portion between the electrode housing portion 15 and the tip small-diameter portion 61 having different diameters. With this configuration, a small discharge space having a bottomed cylindrical shape surrounded by the inner peripheral surface of the tip small diameter portion 61 of the shaft hole 12 and the tip surface 26 of the center electrode 20 is formed. In the plasma jet spark plug 100, spark discharge is performed in the spark discharge gap formed between the ground electrode 30 and the center electrode 20, and the path of the spark discharge passes through this discharge space. . This discharge space is called a cavity 60, and plasma is formed in this cavity 60 during spark discharge, and is ejected forward from the opening of the tip 16.

  Further, as shown in FIG. 1, the center electrode 20 is connected to the terminal fitting 40 in the distal end side body portion 17 via the conductive seal body 4 made of a mixture of metal and glass provided in the shaft hole 12. And are electrically connected. The center electrode 20 and the terminal fitting 40 are fixed in the shaft hole 12 while being conducted in the shaft hole 12 by the seal body 4. The terminal fitting 40 extends rearward in the shaft hole 12, and the rear end portion 41 projects outward from the rear end of the insulator 10. A high voltage cable (not shown) is connected to the rear end portion 41 via a plug cap (not shown), and a high voltage is applied from an ignition device (not shown).

  Next, the metal shell 50 will be described. The metal shell 50 is a cylindrical metal fitting for fixing the plasma jet ignition plug 100 to the engine head (not shown) of the internal combustion engine, and extends from the leg long part 13 of the insulator 10 to the front end side of the rear end side body part 18. The insulator 10 is held in its own cylindrical hole 59 so as to surround the periphery of this part. The metal shell 50 is made of a low carbon steel material, and a large-diameter mounting portion 52 is formed from approximately the center to the tip side. A male screw-like thread is formed on the outer peripheral surface of the mounting portion 52, and is screwed into a female screw formed in a mounting hole (not shown) of the engine head. The metal shell 50 places importance on heat resistance and may use stainless steel, Inconel (trade name), or the like.

  A hook-shaped seal portion 54 is formed on the rear end side of the attachment portion 52. An annular gasket 5 formed by bending a plate is inserted into a portion between the seal portion 54 and the attachment portion 52. When the plasma jet ignition plug 100 is attached to the engine head mounting hole (not shown), the gasket 5 is formed between the seat surface 55 which is the surface facing the tip of the seal portion 54 and the peripheral portion of the opening of the mounting hole. By being sandwiched and deformed and sealed between the two, the outflow of combustion gas through the mounting hole is prevented.

  A tool engaging portion 51 into which a plug wrench (not shown) is fitted is formed on the rear end side of the seal portion 54. A thin caulking portion 53 is provided on the rear end side from the tool engagement portion 51, and a thin buckling portion 58 is also provided between the tool engagement portion 51 and the seal portion 54. And annular ring members 6, 7 are interposed between the inner peripheral surface from the tool engaging portion 51 to the caulking portion 53 and the outer peripheral surface of the rear end side body portion 18 of the insulator 10, Further, a powder of talc (talc) 9 is filled between the ring members 6 and 7.

  As shown in FIG. 2, a stepped step portion 56 is formed on the inner peripheral surface of the mounting portion 52, and when holding the insulator 10, the step portion of the insulator 10 is provided on the step portion 56. 14 is supported via an annular second packing 80. For example, a nickel material is used for the second packing 80. Then, as shown in FIG. 1, the insulator 10 is pressed toward the tip end via the ring members 6, 7 and the talc 9 by crimping the end of the crimping portion 53 inwardly. . The buckling portion 58 is heated during the caulking, and is deformed so as to swell with the addition of the compressive force, thereby earning a compression stroke of the caulking portion 53. Thereby, the site | part between the step part 14 and the collar part 19 of the insulator 10 is reliably pinched | interposed between the crimping part 53 and the step part 56 of the metal shell 50, and the insulator 10 is attached to the metal shell 50. It is held together. A gap is provided between the inner peripheral surface of the cylindrical hole 59 of the metal shell 50 and the outer peripheral surface of the leg long portion 13 of the insulator 10. The second packing 80 maintains the airtightness between the metal shell 50 and the insulator 10 and prevents the combustion gas from flowing out through the cylindrical hole 59. The step 56 corresponds to the “metal step” in the present invention.

  In addition, the ground electrode 30 is provided at the distal end portion 65 of the metal shell 50. The ground electrode 30 is made of a metal having excellent heat resistance. As an example, a nickel-based alloy such as Inconel (trade name) 600 or 601 is used. As shown in FIG. 2, the ground electrode 30 is formed in a disk shape having an opening (through-hole in the thickness direction) called an orifice 31 at the center. The ground electrode 30 is aligned with the direction of the axis O, and is disposed in front of the tip 16 of the insulator 10, that is, with a gap between the insulator 10 and the metal shell 50. It is engaged with an engaging portion 57 formed on the inner peripheral surface of the distal end portion 65. In this state, the outer peripheral edge is laser welded to the engaging portion 57 over the entire circumference, and the ground electrode 30 is joined integrally with the metal shell 50. The orifice 31 of the ground electrode 30 is arranged so as to be connected substantially coaxially with the cavity 60 of the insulator 10, and the inside of the cavity 60 communicates with the outside air via the orifice 31. The orifice 31 corresponds to the “opening” in the present invention.

  In the plasma jet ignition plug 100 configured as described above, when a high voltage is applied to the spark discharge gap between the center electrode 20 and the ground electrode 30 with the operation of the internal combustion engine, the ground electrode 30 and the center electrode 20. The insulation between them is broken and spark discharge occurs (also called trigger discharge). When further energy is supplied to the spark discharge gap in this state, high-energy plasma is formed in the cavity 60 formed of a small space surrounded by a wall surface. When the plasma is ejected from the cavity 60, it has a shape like a fire column, that is, a so-called frame shape, and is ejected to the outside, that is, into the combustion chamber through the orifice 31 of the ground electrode 30. Then, the air-fuel mixture in the combustion chamber is ignited, and the formed flame nuclei grow and are combusted.

The plasma jet ignition plug 100 having such a configuration has a gap (hereinafter referred to as “first gap”) between the ground electrode 30 and the tip 16 of the insulator 10. In the first embodiment, when the size of the first gap is a and the volume of the cavity 60 is S, 0 <a ≦ 0.5 [mm] is satisfied based on Example 1 described later. It is specified that 0.1 ≦ S ≦ 10 [mm ³ ] is satisfied while being satisfied. When the volume S of the cavity 60 is larger than 10 [mm ³ ], the energy of the plasma formed is spread and dispersed in the cavity 60, and the amount of plasma energy ejected from the opening side is reduced (the length of the frame). The ignitability may be reduced). On the other hand, if the size a of the first gap is larger than 0.5 mm, the plasma formed in the cavity 60 leaks into the first gap on the way to the orifice 31, and similarly, the amount of plasma jetted is There is a risk that the ignitability may be reduced due to the decrease. As described above, 0 <a ≦ 0.5 [mm] is satisfied, and sufficiently satisfactory ignitability can be obtained if 0.1 ≦ S ≦ 10 [mm ³ ] is satisfied. The result of Example 1 is confirmed.

  The ground electrode 30 is positioned with respect to the metal shell 50 by being joined to the engaging portion 57 of the metal shell 50. The tip 16 of the insulator 10 is positioned with respect to the metal shell 50 when the step 14 of the insulator 10 is supported by the step 56 of the metal shell 50 via the second packing 80. That is, the size a of the first gap between the ground electrode 30 and the tip 16 of the insulator 10 has a manufacturing tolerance depending on the caulking condition of the caulking portion 53 and the thickness and hardness of the second packing 80. Management including it is done.

  Further, the plasma jet ignition plug 100 has a gap (hereinafter referred to as “second gap”) between the outer peripheral surface of the leg long portion 13 of the insulator 10 and the inner peripheral surface of the cylindrical hole 59 of the metal shell 50. "). In the first embodiment, when the size of the second gap is b, it is defined that 0.1 ≦ b ≦ 1.1 [mm] is satisfied based on Example 2 described later. ing. If the size b of the second gap is larger than 1.1 mm, the volume of the entire gap including the first gap and the second gap increases, so that the energy of the plasma leaked into the first gap is increased in the second gap. As a result, there is a risk that the plasma energy will be greatly deprived and the amount of ejection will be reduced, resulting in a decrease in ignitability. From the viewpoint of heat resistance as a single plasma jet ignition plug, the size b of the second gap is preferably closer to 0. However, depending on the assembly / insertability of the insulator 10 and the metal shell 50 and the cooling / heating cycle associated with use. The components constituting the plasma jet ignition plug 100 expand and contract. For this reason, when the size b of the second gap is brought close to 0, there is a risk of damage due to expansion / contraction of the component. As described above, if 0.1 ≦ b ≦ 1.1 [mm] is satisfied, it is possible to obtain sufficiently good ignitability without damaging the plasma jet ignition plug due to expansion / contraction of the parts, This is confirmed from the results of Example 2 described later.

  Furthermore, in the first embodiment, when the size of the spark discharge gap formed between the center electrode 20 and the ground electrode 30 in the axial direction is G, 1 is described based on Example 2 described later. 0.0 ≦ G ≦ 3.0 [mm] is satisfied. This is because if the size G of the spark discharge gap is larger than 3.0 mm, the ignitability is lowered. In order to solve this, the voltage applied to cause a spark discharge between the center electrode 20 and the ground electrode 30 may be made higher. There is also a risk of breaking through. In addition, a more expensive power source must be used. From this point of view, the spark discharge gap size G is preferably set to 3.0 mm or less. On the other hand, when the spark discharge gap size G is less than 1.0 mm, the length of the cavity 60 in the direction of the axis O (depth of the cavity 60) cannot be secured sufficiently, and the ejected plasma has an effective frame shape. In other words, the ignitability may be reduced. As described above, if 1.0 ≦ G ≦ 3.0 [mm] is satisfied, it is confirmed from the results of Example 2 that will be described later that the reliability of spark discharge is improved and sufficiently good ignition performance can be obtained. Has been.

  In the description of the plasma jet ignition plug 100 described above, the structure by so-called heat caulking is described as the holding method of the insulator 10 by the metal shell 50, but the holding method is not limited at all. For example, it may be crimped by cold working without heating, or without using the talc 9, the end of the crimping portion 53 presses the insulator 10 directly or indirectly through packing or the like. The insulator 10 may be held. Furthermore, it is only necessary to be able to hold the insulator 10 regardless of caulking, and the method is not limited. However, when using a method in which the insulator 10 is pressed toward the tip end side in the axis O direction by caulking or the like as a holding method, the configuration by the illustrated heat caulking has an effect of preventing the insulator 10 from being damaged in the manufacturing process. It is effective in terms of having.

  Next, a second embodiment of the plasma jet ignition plug according to the present invention will be described with reference to FIG. FIG. 3 is a partially enlarged cross-sectional view of the plasma jet ignition plug 200 according to the second embodiment. The plasma jet ignition plug 200 of the second embodiment shown in FIG. 3 is between the ground electrode 30 of the plasma jet ignition plug 100 (see FIG. 2) of the first embodiment and the tip 16 of the insulator 10. The first packing 270 is interposed in the gap. The first packing 270 is formed in an annular shape using, for example, a cold rolled steel plate. The inner diameter E of the first packing 270 is configured to be larger than the inner diameter D of the cavity 60, and at least ½ of the diameter difference between the inner diameter E of the first packing 270 and the inner diameter D of the cavity 60 is the size of the first gap a It is specified to be larger. That is, the breakdown voltage value of the creeping discharge that can occur between the center electrode 20 and the first packing 270 is higher than the breakdown voltage value of the creeping discharge and the air discharge that can occur between the center electrode 20 and the ground electrode 30. Is configured to be larger. The structure of the plasma jet ignition plug 200 of the second embodiment differs from the structure of the plasma jet ignition plug 100 of the first embodiment only in the presence or absence of the first packing 270, and the other parts are the same. Therefore, description of the structure of other parts is omitted or simplified.

  In the manufacturing process of the plasma jet ignition plug 200 having such a configuration, the insulator 10 is formed into a cylinder of the metal shell 50 by caulking the caulking portion 53 of the metal shell 50 in the manufacturing process. It is held in the hole 59. At this time, the hardness of the first packing 270 is such that the deformation of the second packing 80 sandwiched between the stepped portions 14 and 56 is not hindered by the first packing 270 sandwiched in the first gap. The material which comprises itself is selected so that it may become lower than hardness of this. As an example, the first packing 270 is a cold rolled steel plate specified by JIS G3141, and has a Vickers hardness of about 110 HV, and the second packing 80 is a nickel material for electron tubes specified by JIS H4501 and has a Vickers hardness. About 200 HV may be used.

  Furthermore, since the first packing 270 seals between the two so that leakage of plasma energy through the first gap can be prevented, the thickness of the first packing 270 before assembling to the plasma jet ignition plug 200 is larger than the first gap. It is configured to be the same as or slightly larger than a. In addition, it is sufficient that the outflow of the combustion gas through the cylindrical hole 59 of the metal shell 50 is prevented by the second packing 80, and the first packing 270 provides a drag force sufficient to seal the leakage of plasma energy. 30 or the tip 16 of the insulator 10 may be provided.

  As described above, in the plasma jet ignition plug 200 according to the second embodiment, the first packing 270 is interposed in the first gap, so that the gap between the ground electrode 30 and the tip 16 of the insulator 10 is surely secured. And having a first gap. Each definition of the volume S of the cavity 60 and the size G of the spark discharge gap is the same as that of the first embodiment, but the first packing 270 is interposed in the first gap, so that the plasma energy is reduced. It does not leak into the two gaps, and the amount of energy leaking into the first gap is also reduced. Therefore, the ignitability of the plasma jet ignition plug 200 is sufficiently maintained even if the size a of the first gap is further expanded. Specifically, it has been confirmed from the results of Example 3 described later that sufficiently good ignitability can be obtained when the size a of the first gap is 0.8 mm or less.

  As described above, the first gap is provided in the plasma jet ignition plug (first embodiment), or the first packing 270 is interposed in the first gap (second embodiment). Confirming that good ignitability can be obtained by prescribing the size of each part as described above, while preventing the insulator 10 from being damaged by the influence of thermal stress during use and stress applied during manufacture. An evaluation test was conducted.

[Example 1]
First, an evaluation test was performed in order to confirm the relationship between the volume S of the cavity 60, the size a of the first gap, and the ignitability. In this evaluation test, four types of insulators with different inner diameters D of the cavities and adjusted so that the volume S is 5, 10, 15, 20 mm ³ are used, and the size a of the first gap is set for each type. Samples of a plurality of plasma jet spark plugs having different diameters in the range of 0.1 to 0.7 mm were prepared. In each sample, the spark discharge gap size G was set to 3.0 mm, and the second gap size b was set to 1.0 mm. Further, the first packing is not interposed in the first gap.

These samples were individually attached to a pressure chamber, and ignitability was confirmed. Specifically, after the sample is first attached to the chamber, the inside of the chamber is filled with an air-fuel mixture with a mixture ratio of air and C ₃ H ₈ gas (air-fuel ratio) of 22, and the atmospheric pressure is set to 0.05 MPa. (Gas filling step). Next, the sample is connected to a power source capable of supplying an energy amount of 150 mJ, a high voltage is applied, ignition is attempted, and whether or not the air-fuel mixture has ignited is confirmed (ignition confirmation step). Whether or not ignition occurred was detected by measuring the pressure in the chamber with a pressure sensor and observing the pressure change in the chamber. This series of steps was tried 100 times to determine the ignition probability. A graph of the results of this evaluation test for each sample is shown in FIG.

As shown in the graph of FIG. 4, the ignition probability tended to decrease as the first gap size a increased. The samples with the cavity volume S of 0.1 mm ³ , 5 mm ³ , and 10 mm ³ each have an ignition probability of 100% when the first gap size a is 0.5 mm or less. It has been confirmed that the ignition probability decreases as the size a becomes larger than 0.5 mm. However, the volume S of the cavity had the 0.05 mm ^3, 15 mm ^3, and respectively the sample of 20 mm ^3, a magnitude a is 0.1mm even ignition probability of the first gap 100%. As a result of this evaluation test, if the size a of the first gap of the plasma jet ignition plug is set to be larger than 0 and 0.5 mm or less and the cavity volume S is set to 0.1 or more and 10 mm ³ or less, plasma jet ignition is performed. It was found that 100% ignition probability can be obtained without damaging the plug.

[Example 2]
Next, an evaluation test was conducted to confirm the relationship between the spark discharge gap size G and the second gap size b and the ignitability. In this evaluation test, the outer diameter of the leg long part is adjusted so that the size b of the second gap is 4 types of 0.5, 1.0, 1.1, and 1.5 mm, and the size of the second gap is set. Samples of plasma jet spark plugs were prepared using a plurality of insulators having different spark discharge gap sizes G in the range of 1.0 to 4.0 for each type of length b. In each sample, the first gap size a was 0.5 mm, and the spark discharge gap size G was adjusted by adjusting the cavity depth. At this time, the inner diameter D of each cavity was adjusted so that the volume S of the cavity was 10 mm ³ . That is, this evaluation test is performed using the value confirmed as the limit value with which 100% ignitability was obtained in Example 1. Further, like the first embodiment, the first packing is not interposed in the first gap.

Each of these samples was individually filled with a mixture of air and C ₃ H ₈ gas in a mixture ratio (air / fuel ratio) of 22 as in Example 1, and attached to a chamber having an atmospheric pressure of 0.05 MPa. It connected to the power supply which can supply the energy amount of 150 mJ, and tried the above-mentioned gas filling process and ignition confirmation process 100 times, and calculated | required the ignition probability. A graph of the results of this evaluation test for each sample is shown in FIG.

  As shown in the graph of FIG. 5, it was found that the ignition probability of all the samples rapidly decreases when the spark discharge gap size G exceeds 3.0 mm. That is, if the size G of the spark discharge gap exceeds 3.0 mm, it can be said that dielectric breakdown in the spark discharge gap hardly occurs. It should be noted that when the spark discharge gap size G is less than 1.0 mm, the cavity depth cannot be sufficiently secured, and effective frame-shaped plasma may not be ejected. From this, it was found that the spark discharge gap size G should be 1.0 mm or more and 3.0 mm or less.

  Further, in the graph of FIG. 5, when the spark discharge gap size G is 3.0 mm or less, it can be confirmed that a sample having a second gap size b of 1.0 mm or less can obtain an ignition probability of 100%. It was. If the size b of the second gap is 1.1 mm as it is, the ignition probability is less than 100%, but the ignition probability is generally 80% or more. Further, when the size b of the second gap was 1.5 mm, the ignition probability was greatly reduced. From the results of this evaluation test, it was confirmed that good ignitability could be obtained if the size b of the second gap of the plasma jet ignition plug was 1.1 mm or less. If the size b of the second gap is 1.0 mm or less, an ignition probability of 100% can be obtained, which is more preferable.

[Example 3]
Next, an evaluation test was performed to confirm whether the ignitability was improved by the presence or absence of the first packing disposed in the first gap. In this evaluation test, the first gap size “a” is in the range of 0.3 to 0.9 mm for each of the two types of the first gap and the one without the first packing. Samples of a plurality of plasma jet ignition plugs prepared in different ways were prepared. In each sample, the size b of the second gap was 1.0 mm. Further, the cavity depth of each sample was adjusted so that the spark discharge gap size G was 3.0 mm regardless of the first gap size a. Furthermore, by adjusting the inner diameter D of the cavity, the cavity volume S of each sample was set to 10 mm ³ . That is, this evaluation test is performed using the value confirmed as the limit value with which 100% ignitability was obtained in Examples 1 and 2 as described above.

In the same manner as in Examples 1 and 2, these samples were individually filled with a mixture of air and C ₃ H ₈ gas in which the mixture ratio (air-fuel ratio) was 22, and the pressure was set to 0.05 MPa. Attached and connected to a power source capable of supplying an energy amount of 150 mJ, the above-described gas filling step and ignition confirmation step were tried 100 times to determine the ignition probability. A graph of the results of this evaluation test for each sample is shown in FIG.

  As shown in the graph of FIG. 6, in the sample in which the first packing is not interposed in the first gap, an ignition probability of 100% is obtained when the size a of the first gap is 0.5 mm or less. It is the same as the result of Example 1 that the ignition probability decreases when the thickness exceeds 0.5 mm. On the other hand, in the sample in which the first packing is interposed in the first gap, the ignition probability of 100% can be maintained until the size a of the first gap exceeds 0.8 mm (if 0.8 mm or less). I knew it was possible.

  Needless to say, the present invention can be modified in various ways. In the first and second embodiments, the opening on the front end side of the cylindrical hole 59 of the metal shell 50 is closed with the ground electrode 30. However, like the plasma jet ignition plug 300 shown in FIG. A joint portion 365 is formed in such a manner that the opening periphery on the tip side of the hole 359 is extended and bent inward in the radial direction, and the ground electrode 330 having the orifice 331 is joined to the opening 357 provided in the center of the joint portion 365. May be. Further, the first packing 370 may be interposed in the gap between the joint portion 365 and the tip 16 of the insulator 10. Of course, the first packing 370 may be in contact with the ground electrode 330. Further, the ground electrode 330 of the plasma jet ignition plug 300 may not be provided, and the central opening 357 of the joint portion 365 of the metal shell 350 may be configured as an orifice as it is. In addition, dimensions, such as the magnitude | size of each gap | interval in the plasma jet ignition plug 300, shall apply to 1st, 2nd embodiment.

  In any of the first and second embodiments, the tip (tip surface) 16 of the insulator 10 and the surface facing the rear end of the ground electrode 30 facing the tip 16 are flat and parallel to each other. The case where it arranged is illustrated. However, the shape and arrangement of the front end 16 of the insulator 10 and the rear end facing surface of the ground electrode 30 can be variously changed. For example, at least one of the front end 16 and the rear end facing surface of the ground electrode 30 may be a curved surface instead of a flat surface, or may have a stepped shape. Further, for example, the front end 16 of the insulator 10 and the rear end facing surface of the ground electrode 30 may not be arranged in parallel to each other. Since the gist of the present invention is to prevent plasma from entering between the tip surface of the insulator and the ground electrode, the size a of the first gap is set to the orifice 31 when the above deformation is applied. It may be measured on the side (innermost in the radial direction of the insulator). Further, the size b of the second gap may be measured at the most distal portion (excluding the C chamfering and R chamfering portions) as shown in FIG.

  Further, in the test for confirming the effect of the present invention, the volume S is changed by changing the depth of the cavity 60 and the diameter of the tip small-diameter portion 61. Is not particularly limited. As shown in the first and second embodiments, the cavity 60 may be formed by the inner peripheral surface of the tip small-diameter portion 61 and the tip surface 26 of the center electrode 20 (see FIGS. 2 and 3). However, the cavity 60 may be configured to include a part of the electrode housing portion 15 whose diameter is larger than the inner diameter of the distal end small diameter portion 61 on the rear end side with respect to the distal end small diameter portion 61. Moreover, you may change the internal diameter of the front-end | tip small diameter part 61 suitably. Of course, in that case, it is needless to say that it is preferable that the opening diameter of the orifice 31 of the ground electrode 30 is larger than the inner diameter of the small-diameter portion 61 because the plasma is less likely to leak into the first gap.

It is a fragmentary sectional view of plasma jet ignition plug 100 of a 1st embodiment. It is sectional drawing to which the front-end | tip part of the plasma jet ignition plug 100 of 1st Embodiment was expanded. It is a partial expanded sectional view of the plasma jet ignition plug 200 of 2nd Embodiment. It is a graph which shows the relationship between the volume S of a cavity, the magnitude | size a of 1st clearance gap, and the ignition probability. It is a graph which shows the relationship between the magnitude | size G of a spark discharge gap, the magnitude | size b of a 2nd gap, and an ignition probability. It is a graph which shows the relationship between the presence or absence of the 1st packing of a 1st clearance gap, the magnitude | size a of 1st clearance gap, and the ignition probability. It is a partial expanded sectional view of the plasma jet ignition plug 300 as a modification.

DESCRIPTION OF SYMBOLS 10 Insulator 12 Shaft hole 14,56 Step part 20 Center electrode 26 Front end surface 30,330 Ground electrode 31,331 Orifice 50 Metal fitting 52 Mounting part 60 Cavity 80 2nd packing 100,200,300 Plasma jet ignition plug 270,370 First packing 331 Orifice 357 Opening 365 Joint

Claims (5)

A center electrode;
An insulator that has an axial hole extending in the axial direction, accommodates the tip surface of the central electrode in the axial hole, and holds the central electrode;
On the tip side of the insulator, a cavity formed in a concave shape with the inner peripheral surface of the shaft hole and the tip surface of the center electrode as wall surfaces;
A metal shell that surrounds and holds the periphery of the insulator in the radial direction;
An electrode which is joined to the metal shell and is electrically connected to the metal shell, and which is disposed on the tip side of the insulator, and has a ground electrode having an opening for communicating the cavity with outside air, and
A plasma jet ignition plug that generates plasma in the cavity in accordance with a discharge performed between the center electrode and the ground electrode;
The insulator and the ground electrode are arranged in a state of being separated from each other in the axial direction,
When the size of the gap between the insulator and the ground electrode in the axial direction is a and the volume of the cavity is S,
0 <with a a ≦ 0.5 [mm], 0.1 ≦ S ≦ 10 [mm 3] der is, furthermore,
At the position where the cavity is formed in the axial direction, the insulator and the metal shell are arranged in a state of being separated from each other in a radial direction perpendicular to the axial direction,
When the size of the gap between the insulator and the metal shell in the radial direction orthogonal to the axial direction is b,
b ≦ 1.1 [mm] plasma jet spark plug according to claim der Rukoto. Said b is
The plasma jet ignition plug according to claim 1 , wherein 0.1 ≦ b ≦ 1.1 [mm]. When the size of the gap between the center electrode and the ground electrode in the axial direction is G,
1.0 ≦ G ≦ 3.0 plasma jet ignition plug according to claim 1 or 2, characterized in that it is [mm]. A center electrode;
An insulator that has an axial hole extending in the axial direction, accommodates the tip surface of the central electrode in the axial hole, and holds the central electrode;
On the tip side of the insulator, a cavity formed in a concave shape with the inner peripheral surface of the shaft hole and the tip surface of the center electrode as wall surfaces;
A metal shell that surrounds and holds the periphery of the insulator in the radial direction;
An electrode which is joined to the metal shell and is electrically connected to the metal shell, and which is disposed on the tip side of the insulator, and has a ground electrode having an opening for communicating the cavity with outside air, and
A plasma jet ignition plug that generates plasma in the cavity in accordance with a discharge performed between the center electrode and the ground electrode;
At least one of the joint portion of the metal shell with the ground electrode and the ground electrode, and the insulator are arranged in a state of being separated from each other in the axial direction,
In a gap between at least one of the joint of the metal shell with the ground electrode and the ground electrode, and the insulator, a first packing that is in close contact with each other is interposed ,
When the size of the gap between the insulator and at least one of the joint of the metal shell with the ground electrode and the ground electrode in the axial direction is a and the volume of the cavity is S In addition,
0 <a ≦ 0.8 [mm], 0.1 ≦ S ≦ 10 [mm ³ ], and
When the size of the gap between the center electrode and the ground electrode in the axial direction is G,
A plasma jet ignition plug, wherein 1.0 ≦ G ≦ 3.0 [mm] . Of the outer peripheral surface of the insulator, the outer diameter of the rear end side of its own rear end side is set on the front end side in the portion of the mounting portion provided on the front end side of the main metal fitting that is accommodated on the radially inner side of the main metal fitting. An insulator step portion configured to be larger than the outer diameter is formed,
On the inner peripheral surface of the metal shell, a metal step is formed that bulges inward in the radial direction of the metal shell so that the surfaces facing the metal shell and the insulator step are opposed to each other.
A second packing that is in close contact with both of the insulator step and the metal step is interposed,
The plasma jet ignition plug according to claim 4, wherein the second packing has a hardness higher than that of the first packing.

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