JP2010096145A - Wave guide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem of possible generation of electric discharge between an antenna and a wave guide wall by application of discharge voltage to the antenna inside the wave guide for each ignition period due to a coaxial cable connected with the ignition plug at supplying the microwave output by the magnetron to a central electrode of the ignition plug using the coaxial cable in the case of reacting plasma produced in a combustion chamber and spark discharge of an ignition plug using a magnetron. <P>SOLUTION: The wave guide for guiding the electromagnetic wave output by a high frequency generating device into the combustion chamber is assembled to a spark-ignition type internal combustion engine for igniting a fuel/air mixture by reacting plasma produced in a combustion chamber by an electromagnetic wave and spark discharge by an ignition plug. One end part is connected with the high frequency generating device, and the wave guide comprises an antenna for connecting a coaxial cable with insulation inside the vicinity of the other end part. The internal pressure is maintained higher than the pressure in the combustion chamber. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a waveguide used in a spark ignition internal combustion engine that generates plasma in a combustion chamber and ignites an air-fuel mixture by plasma and spark discharge by a spark plug.

  2. Description of the Related Art Conventionally, in a spark ignition internal combustion engine mounted on a vehicle, particularly an automobile, an air-fuel mixture in a combustion chamber is ignited at each ignition timing by spark discharge between a center electrode and a ground electrode of a spark plug. In such ignition by an ignition plug, for example, in an internal combustion engine of a type in which fuel is directly injected into a cylinder, if the injected fuel is not distributed at the spark discharge position of the ignition plug, it rarely occurs.

For this reason, in such an internal combustion engine, a plasma atmosphere is generated in the discharge region of the spark plug, for example, as described in Patent Document 1, in order to compensate for the spark discharge of the spark plug, and an arc is generated in the plasma atmosphere. It is known that the discharge is performed to surely ignite the air-fuel mixture in the combustion chamber without applying a higher voltage than in the past and to obtain a stable flame.
JP 2007-32349 A

  By the way, as a method for generating plasma under atmospheric pressure, a method using a magnetron is considered. When using a magnetron, the output microwave is radiated into the combustion chamber through a conductor serving as an antenna. In this case, since there is a spark plug as a conductor located in the combustion chamber, the center electrode of the spark plug may be an antenna. As described above, when the spark plug is an antenna for microwaves, the microwave is supplied to the center electrode of the spark plug using the waveguide and the coaxial cable.

  Since the waveguide directly connected to the magnetron cannot be directly connected to the spark plug, the microwave is extracted by a coaxial cable that can be connected to the spark plug. The coaxial cable is connected to an antenna attached to the waveguide wall via an insulator.

  In such a configuration, since the coaxial cable is connected to the ignition plug, a discharge voltage is applied to the antenna at each ignition timing. For this reason, there was a possibility of discharge between the antenna and the waveguide wall.

  Therefore, the present invention aims to eliminate such problems.

  In other words, the waveguide according to the present invention is assembled in a spark ignition internal combustion engine that ignites an air-fuel mixture by reacting plasma generated in the combustion chamber by electromagnetic waves and spark discharge by the spark plug, and output from the high frequency generator. A waveguide that guides electromagnetic waves into the combustion chamber, with a high-frequency generator connected to one end, and an insulated antenna connected to the coaxial cable inside the other end. Is maintained at a pressure higher than the pressure in the combustion chamber.

  According to such a configuration, even when the spark plug is used as an electromagnetic wave supply conductor, the discharge between the antenna and the inner wall of the tube is suppressed by maintaining the high pressure in the tube. Therefore, it is possible to reliably cause a spark discharge in the spark plug at the ignition timing.

  Specifically, the spark plug is provided with a center electrode and a ground electrode disposed opposite to the center electrode via a discharge gap, and the antenna is provided between the inner wall with an insulator having a predetermined thickness. In addition, it is preferable to set the in-pipe pressure based on the ratio of the in-cylinder pressure, the discharge gap, and the predetermined thickness when the spark ignition internal combustion engine is motored.

  The present invention is configured as described above, and even when the spark plug is used as an electromagnetic wave supply conductor, the internal pressure of the tube is maintained at a high level. Discharge can be suppressed, and spark discharge can surely occur in the spark plug at the ignition timing.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 shows an engine 100, which is a spark ignition type internal combustion engine, showing an enlarged mounting portion of a spark plug 1 in one cylinder, for example, of a three-cylinder double overhead camshaft (DOHC) type. 3 and the opening 5 of the exhaust port 4 are arranged opposite to each other centering on a spark plug 1 attached to substantially the center of the ceiling portion of the combustion chamber 6 and are opened at two locations per cylinder. That is, the engine 100 is attached to the cylinder block 7, and the camshafts 9 and 10 are attached to the intake side and the exhaust side of the cylinder head 8 forming the ceiling portion of the combustion chamber 6, respectively. The intake port 2 of the cylinder head 8 is opened and closed by an intake valve 11 that reciprocates when the camshaft 9 rotates, and the exhaust port 4 is opened and closed by an exhaust valve 12 that reciprocates when the camshaft 10 rotates. Is.

  The spark plug 1 includes a housing 13 made of a conductive material, a center electrode 14 that is insulated and attached in the housing 13, and a ground electrode 15 that is provided at the lower end of the housing 13 away from the center electrode 14. That is, in the spark plug 1, the housing 13 supports the substantially cylindrical insulator 16, and the connection terminal 17 attached to the upper end of the insulator 16 has a center electrode 14 protruding from the lower end of the insulator 16 and a center shaft (not shown). The ground electrode 15 is integrally provided in the housing 13 at a position that is electrically connected and extends from the lower end of the housing 13 to a position facing the lower end of the center electrode 14. A discharge gap for spark discharge is formed between the center electrode 14 and the ground electrode 15. The insulator 16 insulates the center electrode 14 and the housing 13 that is an attachment portion to the engine 100, and also insulates the central shaft that is a connecting member between the center electrode 14 and the connection terminal 17, and has a substantially cylindrical shape. ing.

  For such an engine 100, the ignition plug 1 has an ignition coil (not shown) integrally provided with an igniter, for example, attached to its connection terminal 17 and electromagnetic waves with respect to the center electrode 14 of the ignition plug 1. The coaxial cable 18 is electrically connected so that microwaves can be supplied. The coaxial cable 18 is also electrically connected to the waveguide 19. That is, in this embodiment, the antenna that supplies the microwave to the combustion chamber 6 is not provided alone, but the microwave is supplied to the combustion chamber 6 using the center electrode 14 of the spark plug 1 as an antenna. .

  As shown in FIG. 2, the waveguide 19 is provided with a magnetron 20 as a high-frequency generator at one end thereof, and an in-pipe antenna provided in the vicinity of the other end and insulated from the tube wall 21. 22. Further, in this configuration, the waveguide 19 is hermetically boosted in a state in which the pressure in the tube is filled with an inert gas such as helium or argon or a nitrogen gas to a tube pressure Pin described later. The waveguide 19 has a hollow cross-sectional shape made of, for example, aluminum die cast and has a rectangular shape, and is fixed to the ground potential similarly to the ground electrode 15.

  As shown in FIG. 3, the in-pipe antenna 22 is attached to a through hole 23 formed in the pipe wall 21 via an insulator 24 such as polytetrafluoroethylene, and is fixed to the outer surface of the pipe wall 21. It is electrically connected to a coaxial cable connector 25. The in-tube antenna 22 is provided at a position closer to the magnetron 20 by ¼ wavelength from the end wall 26 of the waveguide 19. The in-pipe antenna 22 is a so-called monopole antenna, and is composed of a conductor having a length of about ¼ of the wavelength of the received microwave. The gap between the inner surface of the tube wall 21 and the in-tube antenna 22 affects the in-tube pressure of the waveguide 19 and is determined based on the desired in-tube pressure Pin.

The desired in-pipe pressure Pin includes an antenna gap dimension Gat of a gap between the inner surface of the pipe wall 21 and the in-pipe antenna 22, a maximum compression pressure value Pmax at the time of motoring of the engine 100 where the piston 27 is located at the top dead center, Based on the discharge gap dimension Gsp of the discharge gap of the spark plug 1, the following equation is used.
Pin = Pmax · Gsp / Gat

  In the above, the maximum compression pressure value Pmax is determined by the compression ratio of the engine 100 and the like, and the discharge gap dimension Gsp is also determined by the spark plug that uses it. In this case, since the antenna gap dimension Gat can be about three times as large as the discharge gap dimension Gsp, the desired in-tube pressure Pin should be about 1/3 of the maximum compression pressure value Pmax. Can do. In this way, after determining the desired pipe pressure Pin, the inert gas is pressurized to the determined pipe pressure Pin or higher and sealed. Thereby, the in-tube pressure of the waveguide 19 is maintained at a desired in-tube pressure Pin.

  By making the in-tube pressure Pin higher than the atmospheric pressure in this way, even if a discharge voltage is applied to the in-tube antenna 22 at each ignition timing, the occurrence of discharge between the in-tube antenna 22 and the tube wall 24 is suppressed. can do. Therefore, even when the antenna gap Gat is reduced by increasing the microwave frequency and reducing the size of the waveguide 19, discharge can be prevented. Further, the discharge voltage from the ignition coil can be prevented from entering the magnetron 20.

  In addition, when this engine 100 ignites the air-fuel mixture in the combustion chamber 6 using the spark plug 1, the spark plug 1 reacts with the plasma generated in the combustion chamber 6 by causing the spark discharge of the spark plug 1 to react with the spark plug 1. This spark discharge is larger than the spark discharge when not reacting with plasma.

  At the time of ignition, a spark discharge is generated in the spark plug 1 by an ignition coil (not shown), and a high-frequency electric field is generated by microwaves almost simultaneously with or immediately after the spark discharge to generate plasma, whereby the combustion chamber 6 It is the structure which burns the inside air-fuel mixture rapidly.

  Specifically, the spark discharge by the spark plug 1 becomes plasma in a high-frequency electric field, and the flame becomes large.

  This is because the flow of electrons due to the spark discharge and the ions and radicals generated by the spark discharge oscillate and meander due to the influence of the high-frequency electric field, resulting in a longer path length and the number of collisions with surrounding water and nitrogen molecules. This is due to a dramatic increase. Water molecules and nitrogen molecules that have been struck by ions and radicals become OH radicals and N radicals, and the surrounding gas that has been struck by ions and radicals is ionized, in other words, a plasma state. The flame will increase dramatically.

  As a result, the air-fuel mixture is ignited by the spark discharge increased by reacting with the high-frequency electric field, so that the ignition region is expanded and the two-dimensional ignition of only the spark plug 1 is changed to the three-dimensional ignition. Therefore, the initial combustion is stabilized, and the combustion rapidly propagates into the combustion chamber 6 as the radicals increase, and the combustion expands at a high combustion rate.

  In addition, this invention is not limited to the above-mentioned embodiment.

  In the above-described embodiment, a magnetron that is a high-frequency generator has been described. However, in addition to the magnetron, a traveling wave tube or the like may be used, and even if the high-frequency generator includes a microwave oscillation circuit made of a semiconductor. Good.

  In addition, the specific configuration of each part is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

  As an application example of the present invention, it can be used for a spark ignition type internal combustion engine that uses gasoline or liquefied natural gas as fuel and requires spark discharge by an ignition plug for ignition.

1 is an enlarged sectional view showing a main part of an engine to which an embodiment of the present invention is applied. The perspective view in the state which connected the coaxial cable of the embodiment. Sectional drawing which expands and shows the principal part of the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Spark plug 14 ... Center electrode 15 ... Ground electrode 18 ... Coaxial cable 19 ... Waveguide 20 ... Magnetron 22 ... In-pipe antenna

Claims (2)

This is a waveguide that guides the electromagnetic waves output from the high-frequency generator into the combustion chamber, which is assembled in a spark ignition internal combustion engine that ignites the air-fuel mixture by reacting the plasma generated in the combustion chamber with electromagnetic waves and the spark discharge from the spark plug. There,
A waveguide that has a high frequency generator connected to one end and an insulated antenna that connects a coaxial cable in the vicinity of the other end, and maintains the pressure inside the tube higher than the pressure in the combustion chamber .   The spark plug includes a center electrode and a ground electrode disposed opposite to the center electrode via a discharge gap, the antenna is provided between the inner wall and an insulator having a predetermined thickness, and the pressure in the tube is reduced. 2. The waveguide according to claim 1, wherein the waveguide is set based on a ratio of an in-cylinder pressure, a discharge gap, and a predetermined thickness when the spark ignition internal combustion engine is motored.

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