JP2010182536A - Plasma ignition device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent insulation breakdown of a tip in the vicinity of an injection hole at insulator sidewalls to form a chamber in a plasma ignition device. <P>SOLUTION: In the plasma ignition device which includes the chamber 1 formed by the insulator sidewall 2, the center electrode 3 arranged on the base end side of the chamber, and a ground electrode 4 arranged on the tip side of the chamber, and changes gas in the chamber into plasma by discharge generated by application of a voltage between the center electrode and the ground electrode, and injects gas changed into plasma in the chamber from the injection hole 5 formed in the ground electrode, around the tip 2a of the insulautor sidewall, an air layer 8 is formed between a metal housing 4a to surround the tip. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a plasma ignition device.

  In an internal combustion engine, it is necessary to reliably ignite a homogeneous mixture in the entire cylinder or a mixture existing in a part of the cylinder by an ignition device. However, a general ignition device that generates a spark in the ignition gap ignites one point of the air-fuel mixture and does not have a very high ignitability.

  As an ignition device having excellent ignitability, a plasma ignition device that injects a plasma jet has been proposed (see, for example, Patent Document 1). The plasma ignition device includes a chamber formed by an insulator side wall, a central electrode disposed on the proximal end side of the chamber, and a ground electrode disposed on the distal end side of the chamber. The gas in the chamber is turned into plasma by the discharge generated by applying a voltage between them, and thus the ground electrode is formed so that the chamber and the cylinder communicate with each other using the high-temperature and high-pressure plasma gas in the chamber as a plasma jet. Highly ignitable can be realized because the air-fuel mixture is simultaneously ignited in the portion that comes into contact with the substantially cylindrical plasma jet having a relatively large surface area immediately after the injection. .

JP 2006-294257 A JP 2008-153190 A JP2008-186743 Special table 2007-507060 US Pat. No. 5,367,871 Special table 2008-529229

  In the plasma ignition device described above, the tip of the insulator side wall that forms the chamber is located in the vicinity of the nozzle hole formed in the ground electrode, and all the plasma in the chamber always comes into contact immediately before being injected from the nozzle hole. Will be. As a result, the distal end portion of the insulator side wall becomes higher in temperature than the base end portion, the withstand voltage performance is lowered, and damage such as dielectric breakdown may occur and a through hole may be formed may occur.

  Accordingly, an object of the present invention is to suppress the occurrence of dielectric breakdown at the tip portion near the nozzle hole of the insulator side wall forming the chamber in the plasma ignition device.

  The plasma ignition device according to claim 1 according to the present invention includes a chamber formed by an insulator side wall, a center electrode disposed on a proximal end side of the chamber, and a ground electrode disposed on a distal end side of the chamber. The gas in the chamber is turned into plasma by the discharge generated by applying a voltage between the center electrode and the ground electrode, and the plasma in the chamber is turned into the plasma from the nozzle hole formed in the ground electrode. In the plasma ignition device for injecting the generated gas, an air layer is formed around the distal end portion of the insulator side wall and a metal housing surrounding the distal end portion.

  The plasma ignition device according to claim 2 according to the present invention is the plasma ignition device according to claim 1, wherein the nozzle hole formed in the ground electrode has an inner diameter concentric with the cylindrical chamber, A portion around the nozzle hole of the ground electrode is divided into at least three parts by at least three notches extending radially from the nozzle hole, and is elastically deformed outward to come into contact with the end face of the tip of the insulator side wall. Features.

  According to the plasma ignition device of the first aspect of the present invention, since the air layer is formed around the tip of the insulator side wall and the metal housing surrounding the tip, the insulator side wall is formed. Even if the tip of the metal becomes high temperature and the withstand voltage performance decreases, the insulation between the metal housing and the metal housing is enhanced by the air layer. it can.

  According to a second aspect of the present invention, there is provided the plasma ignition device according to the first aspect, wherein the nozzle hole formed in the ground electrode has an inner diameter concentric with the cylindrical chamber. The portion around the nozzle hole is divided into at least three parts by at least three cuts extending radially from the nozzle hole, elastically deformed outward, and comes into contact with the end face of the tip of the insulator side wall. Even if the tip of the side wall becomes hot, it is difficult to maintain it at a high temperature due to good heat dissipation to the ground electrode side, which can prevent a significant drop in the withstand voltage performance. Occurrence can be further suppressed.

It is a schematic longitudinal cross-sectional view which shows embodiment of the plasma ignition apparatus by this invention. It is a P arrow view of the plasma ignition device of FIG.

  FIG. 1 is a schematic longitudinal sectional view showing an embodiment of a plasma ignition device according to the present invention. In the figure, 1 is a cylindrical chamber that is formed by a side wall of an insulator 2 so as to extend in the axial direction of the ignition device and generates plasma, and 3 is a center disposed on the base end side of the chamber 1. Reference numeral 4 denotes a ground electrode which is located on the front end side of the chamber 1 and is integral with the metal housing 4a. Of course, the ground electrode 4 may be electrically and mechanically integrated with the housing 4a as a separate member from the housing 4a. An injection hole 5 communicates the chamber 1 with the inside of the cylinder. The injection hole 5 has the same inner diameter D as the chamber 1 and is formed in the ground electrode 4.

  The center electrode 3 and the ground electrode 4 can be made of a metal having heat resistance and high conductivity, for example, an iron-based metal such as stainless steel, a nickel-based metal, an iridium-based metal, or an iridium alloy. The material of the insulator 2 for insulating the ground electrode 4 from the center electrode 3 is preferably ceramics (for example, alumina ceramics). Reference numeral 6 denotes a conductor for applying a voltage to the center electrode 3, and reference numeral 7 denotes a conductive adhesive for electrically connecting the conductor 6 and the center electrode 3.

  In order to turn the gas in the chamber 1 into plasma, first, a high voltage is applied between the center electrode 3 and the ground electrode 4 to generate a creeping discharge S 1 on the inner surface of the side wall of the insulator 2. Thus, when the gas (air mixture) in the vicinity of the creeping discharge in the chamber 1 is turned into plasma and ions and electrons are generated, air discharge at a relatively low voltage becomes possible through the plasmaized gas, Next, this air discharge S2 is generated.

  Thus, when most of the gas in the chamber 1 is converted into plasma by the air discharge S2, the gas in the chamber 1 becomes high temperature and pressure and is injected as a plasma jet from the nozzle hole 5 to ignite the air-fuel mixture in the cylinder. Let Of course, instead of using the creeping discharge and the air discharge in combination as described above, the gas in the chamber 1 may be converted into a plasma by only the creeping discharge or the air discharge.

  By the way, the tip 2a of the insulator side wall forming the chamber 1 is located in the vicinity of the injection hole 5 formed in the ground electrode 4, and all the plasma in the chamber is always in contact immediately before being injected from the injection hole 5. Will be. As a result, the distal end portion 2a of the insulator side wall becomes higher in temperature than the base end portion, the withstand voltage performance is lowered, and damage such as dielectric breakdown may occur and a through hole may be formed may occur. .

  In the plasma ignition device of the present embodiment, an air layer 8 extending in the circumferential direction is formed around the tip portion 2a of the insulator side wall and the metal housing 4a surrounding the tip portion 2a. Thereby, even if the end portion 2a of the insulator side wall becomes high temperature and the withstand voltage performance is lowered, the insulation between the metal housing 4a and the metal housing 4a is enhanced by the air layer 8; Occurrence of dielectric breakdown from the inner surface of the tip portion 2a to the metal housing 4a can be suppressed.

  1, the nozzle hole 5 formed in the ground electrode 4 has an inner diameter D concentric with the cylindrical chamber 1, and a portion around the nozzle hole of the ground electrode 4. 4b is divided into eight by eight incisions 5a extending radially from the nozzle hole 5 at equal angular intervals, and the respective parts thus divided into eight by the notches 5a are outward from the ends of the notches 5a on both sides. It is easy to elastically deform. In the present embodiment, the cuts 5a are eight at equal angular intervals. However, at least three cuts are formed even if the angular cuts are not equal, and the angle between the two cuts is 180 degrees. If the size is reduced, each divided part can be easily elastically deformed outward with the root between the ends of the cuts on both sides.

  In this embodiment, the insulator 2 has a frustoconical outer surface 2b in the vicinity of the center electrode 3, and this frustoconical outer surface 2b faces the frustoconical inner surface 4c of the housing 4a. A seal 9 is arranged to seal a gap between the insulator 2 and the housing 4a.

  In such a configuration, in general, in order to allow the metal seal 8 to be sufficiently pressed by the truncated conical outer surface 2b of the insulator 2 and the truncated conical inner surface 4c of the housing 4a, the insulator 2 and the housing 4a. The ground electrode 4 is not brought into contact with the ground electrode 4, and it is difficult to dissipate heat to the ground electrode 4 even when the tip 2 a of the insulator 2 is at a high temperature.

  However, in this embodiment, the nozzle hole surrounding portion 4b of the ground electrode 4 is easily elastically deformed outward by the notch 5a, and the metal seal 9 has the truncated conical outer surface 2b of the insulator 2 and the truncated portion of the housing 4a. When sufficiently pressed by the conical inner surface 4c, the end surface of the tip 2a of the insulator 2 comes into contact with the ground electrode 4 to elastically deform the nozzle hole surrounding portion 4b outward. As a result, the tip 2a of the insulator 2 and the ground electrode 4 are in close contact with each other, and if the tip 2a on the side wall of the insulator becomes high temperature, good heat dissipation to the ground electrode 4 side is realized, and the tip 2a. Can hardly be maintained at a high temperature, and the withstand voltage performance can be prevented from greatly deteriorating.

  By the way, the edge portion of the ground electrode 4 is used for creeping discharge and air discharge in the chamber 1. Accordingly, if the inner diameter D of the nozzle hole 5 is made smaller than the inner diameter of the chamber 1 and the nozzle hole side portion of the cut 5a is exposed in the chamber 1, the edge portion of the ground electrode 4 used for discharge is lengthened. As a result, the wear of the edge portion due to the discharge can be dispersed, so that the life of the ground electrode 4 can be extended.

DESCRIPTION OF SYMBOLS 1 Chamber 2 Insulator 3 Center electrode 4 Ground electrode 5 Injection hole 5a Notch 8 Air layer

Claims (2)

  A chamber formed by an insulator side wall; a center electrode disposed on a proximal end side of the chamber; and a ground electrode disposed on a distal end side of the chamber, the space between the center electrode and the ground electrode In the plasma ignition device, the gas in the chamber is turned into plasma by the discharge generated by applying a voltage to the plasma, and the plasmad gas in the chamber is ejected from the nozzle hole formed in the ground electrode. An air layer is formed around a front end portion of the side wall between the side wall and a metal housing surrounding the front end portion.   The nozzle hole formed in the ground electrode has an inner diameter that is concentric with the cylindrical chamber, and a portion around the nozzle hole of the ground electrode is formed by at least three notches extending radially from the nozzle hole. 2. The plasma ignition device according to claim 1, wherein the plasma ignition device is divided into at least three parts and elastically deforms outward to come into contact with an end face of a tip portion of the insulator side wall.

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