JP2016142183A - Ignition device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure airtightness in an ignition plug applying an electromagnetic wave resonance structure.SOLUTION: An ignition device includes an input portion to which electromagnetic wave from an external circuit is input, a step-up portion for boosting electromagnetic wave by an electromagnetic wave resonance structure, and having an axial length set to be 1/4 of wavelength of the electromagnetic wave, a discharge portion disposed at an output side of the step-up portion, a connecting portion for impedance matching of the electromagnetic wave transmitted in the external circuit and the electromagnetic wave transmitted in the step-up portion, and a seal material for holding airtightness, and the seal material is disposed near a boundary of the step-up portion and the connecting portion.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an ignition device, and more particularly to an ignition plug having an electromagnetic wave resonance structure having airtightness.

  The applicant has developed a technique for improving the air-fuel ratio by applying microwave technology to combustion in an internal combustion engine (for example, Patent Document 1). Patent Document 1 discloses a technique for expanding a flame ignited by irradiating a microwave after igniting fuel using a spark plug.

  Further, the applicant has developed a spark plug using a microwave resonance structure that boosts the input microwave to generate discharge (Patent Documents 2 and 3). In this spark plug, since microwaves are used as a power source, high-speed and continuous discharge can be generated, and non-equilibrium plasma can be generated at an arbitrary timing. This cannot be realized by the conventional spark plug, and the air-fuel ratio can be improved by using this new spark plug.

Japanese Patent No. 4876217 Japanese Patent Application No. 2013-171781 Japanese Patent Application No. 2014-168540 Japanese Patent Application 2014-247500 US Pat. No. 7,963,262

  However, in order to use the spark plugs of Patent Documents 2 to 4 in an internal combustion engine having a high compression ratio, the airtightness is insufficient. In particular, since the above spark plug employs a microwave resonance structure, it is necessary to determine the arrangement of the sealing material in consideration of electrical characteristics.

  The present invention has been made in view of the above points.

  The ignition device of the present invention includes an input unit to which an electromagnetic wave from an external circuit is input, and a booster unit that boosts the electromagnetic wave by an electromagnetic resonance structure, and whose axial length is set to a quarter of the wavelength of the electromagnetic wave. A discharge part disposed on the output side of the booster part, an electromagnetic wave that transmits the external circuit, a coupling part that performs impedance matching of the electromagnetic wave that is transmitted through the booster part, and a sealing material that maintains hermeticity, Is arranged in the vicinity of the boundary between the boosting unit and the coupling unit.

  According to the present invention, airtightness can be ensured in a spark plug employing an electromagnetic resonance structure.

1 is a front view of a partial cross section showing a configuration of an ignition device 1. FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the following embodiment is a preferable illustration, Comprising: It does not intend restrict | limiting the range of this invention, its application thing, or its use.

(First embodiment)
FIG. 1 is a diagram showing the configuration of the ignition device 1. The ignition device 1 functions as a kind of spark plug that is inserted into a mounting port of a cylinder head of an internal combustion engine such as a gasoline engine or a diesel engine and ignites fuel. The ignition device 1 is disposed at the center of the cylinder head, like a normal spark plug. When used as an auxiliary ignition device for multi-point ignition for the purpose of shortening the flame propagation distance, initial combustion period, main combustion period, etc. (see, for example, Patent Document 4 by the present applicant), the ignition device 1 is A plurality of cylinder heads may be provided in the periphery (for example, between exhaust / intake ports, between exhaust / exhaust ports, and between intake / intake ports). Referring to FIG. 1, ignition device 1 is roughly divided into input unit 1a, coupling unit 1b, and resonance unit 1c. A microwave is input to the input unit 1a from an external circuit such as an oscillator. The coupling unit 1b performs impedance matching between the external circuit and the resonance unit 1c. In particular, capacitive coupling is performed for the purpose of impedance matching in the microwave frequency band. The resonating unit 1c has a microwave resonance structure and is divided into a resonating unit 1c that boosts microwaves. A discharge electrode 16 is provided at the tip of the resonance part 1c. Each part of the ignition device 1 is accommodated in the case 11. The case 11 also serves as a ground electrode, and the ignition device 1 is configured to discharge between the discharge electrode 16 and the case 11 by the microwave boosted by the resonance unit 1 c.

  The input unit 1a includes an input terminal 12 to which a coaxial cable that transmits a microwave generated by an external oscillation circuit is joined, and a first center electrode 13 that transmits the microwave input from the input terminal 12 to the tip. Provided. A dielectric 21 is provided between the first center electrode 13 and the case 11.

  A first center electrode 13 and a second center electrode 14 are provided in the coupling portion 1b. The second center electrode 14 has a cylindrical part 18 whose bottom is on the resonance part 1 c side, and the first central electrode 13 is inserted into the cylindrical part 18. That is, the cylindrical inner walls of the rod-shaped first central electrode 13 and the cylindrical second central electrode 14 are opposed to each other, and the microwave from the first central electrode 13 is capacitively coupled to the second central electrode 14 in this opposed portion. Is transmitted to. A dielectric 22 is also provided between the second center electrode 14 and the case 11. If the impedance of the external circuit (the coaxial cable is 50Ω and the impedance of the resonance part 1c is 10Ω, and the imaginary component is ignored and simply considered, the impedance of the coupling part 1b is designed to be about 20Ω. Good.

  Here, the impedance of the coupling portion 1b is (1) the positional relationship between the inner wall of the cylindrical portion of the second central electrode 14 and the first central electrode 13 inserted into the cylindrical portion (the distance between the two electrodes or (Opposite area), (2) positional relationship between the second center electrode 14 and the case 11 (distance between the two companies and the opposing area), (3) material of the dielectric 23 filled between the second center electrode 14 and the case 11 It is determined by.

  A third center electrode 15 is provided in the resonating unit 1c. A cylindrical dielectric 23 is provided around the tip side of the third center electrode 15. On the other hand, the dielectric 23 or the like is not provided between the rear end side of the third center electrode 15 and the case 11 and is an annular space. The third center electrode 15 is connected to the second center electrode 14 and transmits the microwave of the second center electrode 14 to the discharge electrode 16. The third center electrode 15 is designed to have a length of about a quarter wavelength of the microwave. Here, the quarter wavelength of the microwave does not simply indicate the length of a quarter of the value obtained by dividing the speed of light by the frequency, but the refractive index of the third center electrode 15 or the third center electrode. The length of the microwave that propagates through the third center electrode 15 is substantially a quarter wavelength, taking into account the refractive index of the dielectric 23 that is the adjacent member 15. In other words, when the microwave node comes to the rear end side of the third center electrode 15 and the antinode of the microwave is located on the tip side of the third center electrode 15, the third center electrode It can be said that the length of 15 corresponds to a quarter wavelength of the microwave. Again, if the design is such that the microwave node is located on the rear end side of the third central electrode 15 and the antinode of the microwave is on the front end side, it is arranged on the front end side of the third central electrode 15. The potential of the discharge electrode 16 can be increased, and a high voltage can be generated between the discharge electrode 16 and the case 11 to cause discharge.

  In the resonance part 1c, the reactance component L is mainly defined by the coil component of the third center electrode 15, and the capacitance component C is a capacitance mainly formed by the third center electrode 15, the discharge electrode 16 and the case 11. It is considered that Specifically, (1) the shape and size of the discharge electrode 16 and the distance between the case 11, (2) the distance between the third center electrode 15 and the case 11, and (3) the third center electrode 15 and the case 11. It is considered that it is determined by the gap ratio (air layer) 17 provided between them, the length ratio of the dielectric 24, and the like. The resonating unit 1c is designed so that the virtual equivalent circuit defined by L and C resonates in the microwave frequency band.

  As described above, the ignition device 1 generates the voltage Vc3 higher than the power supply voltage (the microwave voltage V1 input to the ignition device 1) by the boosting method using the resonator. As a result, discharge occurs between the discharge electrode 16 and the ground electrode (case 11). When the discharge voltage exceeds the breakdown voltage of the gas molecules in the vicinity, electrons are emitted from the gas molecules, non-equilibrium plasma is generated, and the fuel is ignited.

  In the ignition device 1, the case 11 and the center electrodes 12, 13, and 14 can be made of a conductive metal such as tungsten, molybdenum, brass, stainless steel (SUS), yellow tantalum, and beryllium copper. In addition, for example, the same material (for example, tungsten) may be used for all these members, or may be appropriately used depending on the application. However, whatever material is used, it belongs to the category of the present invention.

  The dielectrics 21, 22, and 23 can be made of ceramic (alumina), steatite, silicon nitride, or the like.

  Sealing materials 31, 32, and 33 for ensuring the airtightness of the ignition device 1 are provided on the distal end side of the coupling portion 1b. The sealing material 31 is provided between the dielectric 22 and the case 11 so as to surround the outer periphery of the pipe-shaped dielectric 22. The sealing material 32 is disposed on the bottom surface of the second center electrode 14 and has a ring shape surrounding the outer periphery of the third center electrode 15. In addition, as a material of the sealing material, a brazing material (gold brazing, silver brazing, etc.), a metallized material, an adhesive, a glass material, or the like can be used. In order to prevent the sealing material from falling off or coming off, the electrode surface or the dielectric surface on which the sealing material is disposed may be rough or groove-shaped, and the sealing material may be filled therein.

  As described above, in the ignition device 1, the sealing material is disposed on the distal end side of the coupling portion 1b, that is, in the vicinity of the boundary between the coupling portion 1b and the resonance portion 1c. As described above, in the ignition device 1, a microwave node comes near the boundary between the coupling portion 1 b and the resonance portion 1 c so that the potential becomes low (zero). Therefore, if a sealing material is disposed in this region, the influence on the characteristics (loss and phase) of the microwave can be reduced.

  Further, if the sealing material is disposed on the tip side from this position, there is a problem of heat resistance of the sealing material. For example, even when using silver solder that can handle high temperatures of 600 ° C, it may be exposed to temperatures exceeding 1000 ° C instantaneously on the tip side, which is insufficient in terms of heat resistance. . On the other hand, if it is in the vicinity of the coupling portion 1b and the resonance portion 1c, it is considered that it is only necessary to be able to cope with a temperature of about 300 ° C., so that the selection range of materials is widened. If a sealing material is further arranged on the rear side, the heat-resistant hurdle is lowered. However, since bubbles invade into the ignition device 1, particularly the inside of the coupling portion 1 b, the electrical characteristics (frequency) of the ignition device 1 are reduced. Characteristics). Furthermore, due to the intrusion of bubbles, the pressure between the members of the coupling portion 1b (between the dielectric and the electrode) becomes high, and the ignition device 1 itself may be damaged. Therefore, it is suitable to dispose a sealing material on the distal end side of the coupling portion 1b from the viewpoint of heat resistance and electrical / mechanical characteristics.

  In addition, since the frequency in the 2.45 GHz band is used, the capacitance of the capacitor is small, and the ignition device 1 is advantageous for downsizing. In addition, as a result of employing the boosting method, only the vicinity of the discharge electrode 16 in the ignition device 1 has a high potential, which is excellent in terms of isolation. In these respects, the ignition device of the present invention is superior to a conventional ignition device having a resonance structure (for example, Patent Document 5).

  In addition, since the ignition device 1 is driven by microwaves, discharge is also performed at a cycle of microwaves (GHz). Therefore, since the next discharge is performed before the generated radicals are killed, the generated OH radicals are maintained without being killed. On the other hand, since the conventional spark plug cannot turn on / off the spark at a high frequency, the radical generated once is immediately killed. Therefore, when a conventional spark plug is used, the above-described effects cannot be achieved.

  The embodiment of the present invention has been described above. The scope of the present invention is determined based on the invention described in the claims, and should not be limited to the above embodiment.

  For example, the ignition device targeted by the present invention is not limited to the ignition device 1 described above, and may be another mode as long as the ignition device adopts an electromagnetic resonance structure. Moreover, although the ignition device 1 shall operate | move with a microwave, you may use the electromagnetic waves which have another zone | band.

DESCRIPTION OF SYMBOLS 1 Ignition device 1a Input part 1b Coupling part 1c Resonance part 11 Case (ground electrode)
12 Microwave input terminal 13 1st center electrode 14 2nd center electrode 15 3rd center electrode 16 Discharge electrode 17, 18 Space 21, 22, 23 Dielectric material

1 is a front view of a partial cross section showing a configuration of an ignition device 1. FIG. FIG. 2 is an enlarged view of FIG. 1, and is an enlarged view of the vicinity of a distal end side of a coupling portion 1 b of the ignition device 1.

Referring also to FIG. 2 , seal materials 31, 32, 33 for ensuring the airtightness of the ignition device 1 are provided on the distal end side of the coupling portion 1 b. The sealing material 31 is provided between the dielectric 22 and the case 11 so as to surround the outer periphery of the pipe-shaped dielectric 22. The sealing material 32 is disposed on the bottom surface of the second center electrode 14 and has a ring shape surrounding the outer periphery of the third center electrode 15. In addition, as a material of the sealing material, a brazing material (gold brazing, silver brazing, etc.), a metallized material, an adhesive, a glass material, or the like can be used. In order to prevent the sealing material from falling off or coming off, the electrode surface or the dielectric surface on which the sealing material is disposed may be rough or groove-shaped, and the sealing material may be filled therein.

Claims (1)

An input unit for receiving electromagnetic waves from an external circuit;
An electromagnetic wave is boosted by an electromagnetic wave resonance structure, and a pressure increasing unit in which an axial length is set to a quarter of the wavelength of the electromagnetic wave;
A discharge unit arranged on the output side of the boost unit;
A coupling unit that performs impedance matching between the electromagnetic wave transmitted through the external circuit and the electromagnetic wave transmitted through the booster;
Equipped with a sealing material that maintains hermeticity,
An ignition device characterized in that a sealing material is provided in the vicinity of a boundary between a boosting portion and a coupling portion.

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