JP2010116909A - Internal combustion engine having plasma igniter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the melting loss of a nozzle hole formed at the end of a plasma igniter by well cooling in an internal combustion engine having the plasma igniter. <P>SOLUTION: This internal combustion engine includes the plasma igniter 100 which has a chamber 1 formed of the side wall of an insulator 2, an earth electrode 3 disposed at one end of the chamber, and a center electrode 4 disposed at the other end of the chamber and in which the nozzle hole 6 allowing the chamber to communicate with the inside of a cylinder is formed at the end 100a thereof. The plasma igniter is attached to a cylinder head 108. Squish generating parts 107a, 108a are formed by the cylinder head and the top surface of a piston. The front end of the plasma igniter is cooled by the squish flow S generated by the squish generating parts. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an internal combustion engine including 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 a side wall of an insulator, a ground electrode disposed at one end of the chamber, and a center electrode disposed at the other end of the chamber. A high-temperature and high-pressure plasma is generated in the chamber by a discharge generated by applying a voltage between the two. The plasma thus generated is injected as a plasma jet from a nozzle hole formed at the tip of the plasma ignition device and communicating the inside of the cylinder and the chamber, and simultaneously ignites a predetermined area of the air-fuel mixture corresponding to the cross-sectional area of the plasma jet. Therefore, high ignitability is realized.

JP 2006-294257 A Japanese Patent Laid-Open No. 11-324681 JP 2006-183512 A JP2008-151000 JP2002-4863

  In such a plasma ignition device, the nozzle hole formed at the tip becomes extremely high temperature due to the passage of plasma, and may be melted if not sufficiently cooled.

  Accordingly, an object of the present invention is to satisfactorily cool the nozzle hole formed at the tip of the plasma ignition device and suppress melting damage in an internal combustion engine equipped with the plasma ignition device.

  An internal combustion engine comprising the plasma ignition device according to claim 1 according to the present invention includes a chamber formed by a side wall of an insulator, a ground electrode disposed on one end side of the chamber, and a second end side of the chamber. An internal combustion engine having a plasma ignition device having a nozzle hole formed at a tip portion communicating with the chamber and the cylinder, the plasma ignition device being attached to a cylinder head, A squish generating part is formed by a cylinder head and a piston top surface, and the tip part of the plasma ignition device is cooled by a squish flow generated by the squish generating part.

  An internal combustion engine comprising the plasma ignition device according to claim 2 according to the present invention is the internal combustion engine comprising the plasma ignition device according to claim 1, wherein the nozzle hole is formed on an end face of the tip portion of the plasma ignition device. The end face is not parallel to the traveling direction of the squish flow so that the squish flow collides with the end face.

  An internal combustion engine comprising the plasma ignition device according to claim 3 according to the present invention is the internal combustion engine comprising the plasma ignition device according to claim 1, wherein a side surface of the tip portion of the plasma ignition device leads to the chamber. An inflow hole is formed, and the squish flow flows into the chamber through the inflow hole.

  According to the internal combustion engine comprising the plasma ignition device according to the first aspect of the present invention, the plasma ignition device is attached to the cylinder head, and the squish generating portion is formed by the cylinder head and the piston top surface. The tip of the plasma igniter is cooled by the squish flow, so that the nozzle hole formed at the tip of the plasma igniter is cooled well by the squish flow, and the melting of the nozzle is prevented. It is suppressed.

  According to the internal combustion engine comprising the plasma ignition device according to claim 2 of the present invention, in the internal combustion engine comprising the plasma ignition device according to claim 1, an injection hole is formed at the end face of the tip portion of the plasma ignition device, The end surface of the tip is not parallel to the direction of travel of the squish so that the squish flow collides with the end surface of the tip. Thereby, not only the nozzle hole is reliably cooled by the squish flow, but also the squish flow flows into the chamber from the nozzle hole, and the chamber is also cooled by the squish flow.

  According to the internal combustion engine having the plasma ignition device according to claim 3 of the present invention, in the internal combustion engine having the plasma ignition device according to claim 1, the side surface of the tip portion of the plasma ignition device has an inflow leading to the chamber. A hole is formed so that the squish flow flows into the chamber through the inflow hole. Thereby, not only the nozzle hole is cooled by the squish flow, but also the inside of the chamber is cooled by the squish flow flowing into the chamber.

  FIG. 1 is a sectional view showing an embodiment of an internal combustion engine provided with a plasma ignition device according to the present invention. In the figure, reference numeral 100 denotes a plasma ignition device, which is disposed at the substantially upper center of the cylinder of the cylinder head 108. Reference numeral 101 denotes a pair of intake ports that communicate into the cylinder via a pair of intake valves 102, and 103 denotes a pair of exhaust ports that communicates into the cylinder via a pair of exhaust valves 104.

  Reference numeral 105 denotes a first fuel injection valve disposed in one intake port 101. Further, 106 is arranged around the upper part of the cylinder, preferably between a pair of intake ports 101 around the upper part of the cylinder having a relatively low temperature, and is used for injecting fuel directly into the cylinder. Two fuel injection valves.

  This internal combustion engine performs, for example, homogeneous combustion, determines the required fuel amount based on the engine operating state (engine load and engine speed), and the required fuel amount is mainly determined by the second fuel injection valve 106. It is injected into the cylinder during the intake stroke. When the required fuel amount becomes large, vaporization of the injected fuel may be insufficient by the ignition timing, so that a part of the required fuel amount is injected into the intake port 101 by the first fuel injection valve.

  However, the internal combustion engine is not limited to such a fuel system, and even if the second fuel injection valve 106 is omitted and the fuel is injected only by the first fuel injection valve 105, the first fuel injection is performed. The valve 105 may be omitted and fuel may be injected only by the second fuel injection valve 106. On the engine low load side, stratified combustion may be performed in which fuel is injected into the cylinder by the second fuel injection valve 106 in the compression stroke to form a stratified mixture, and this is ignited and combusted.

  FIG. 1 shows the compression top dead center immediately after the ignition timing. At this time, the intake valve side portion 107a on the top surface of the piston 107 and the intake valve side portion 108a on the cylinder upper surface of the cylinder head 108 are substantially parallel. And a squish generating part is generated to generate a squish flow that flows into a relatively large space between the exhaust valve side portion 107b on the top surface of the piston 107 and the exhaust valve side portion 108b on the cylinder upper surface of the cylinder head 108. To do. In the intake valve side portion 108a of the cylinder upper surface of the cylinder head 108, the squish flow S generated particularly when the portion between the two intake ports 101 approaches the intake valve side portion 107a on the top surface of the piston 107 is: It collides with the tip of the plasma ignition device 100 disposed at the approximate center of the cylinder top of the cylinder head 108, and cools the nozzle hole formed at the tip. Of course, the squish generating part is not limited to the intake valve side, and may be formed on the exhaust valve side.

  FIG. 2 is an enlarged cross-sectional view of the vicinity of the tip of the plasma ignition device 100 of FIG. In the plasma ignition device 100, the chamber 1 for generating plasma is formed by the cylindrical tip 2 a of the insulator 2. A ground electrode 3 is disposed on one end side of the chamber 1, and a center electrode 4 is disposed on the other end side of the chamber 1. A housing 5 covers the insulator 2 and integrally fixes the ground electrode 3 by welding or the like. A nozzle hole 6 that communicates between the chamber 1 and the inside of the cylinder is formed at the distal end portion 100 a of the plasma ignition device 100.

  In the plasma ignition device 100 of the present embodiment, the ground electrode 3 has a structure facing the chamber 1 and the cylinder, and the nozzle hole 6 is formed through the ground electrode 3. Further, depending on the structure of the ground electrode, there may be a housing portion facing the inside of the chamber 1 and the cylinder, and in this case, an injection hole can be formed so as to penetrate the housing portion. . Further, when the ground electrode is opposed to the chamber but is covered by the housing and is not opposed to the inside of the cylinder, the injection hole can be formed so as to penetrate the ground electrode and the housing.

  The ground electrode 3 and the center 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 3 from the center electrode 4 is preferably ceramics (for example, alumina ceramics). 7 is a conductor (for example, nickel) for applying a voltage to the center electrode 4, and 8 is a conductive adhesive for electrically connecting the conductor 7 and the center electrode 4. G1 is a metal gasket for sealing the gap between the insulator 2 and the housing 5, and G2 is a metal gasket for sealing the gap between the housing 5 and the mounting hole of the cylinder head 108.

  FIG. 3 shows a power supply control circuit of the plasma ignition device. In FIG. 3, 10 is a transistor controlled by the electronic control unit ECU, 11 is a first battery, and 12 is an ignition coil. Reference numeral 13 denotes a capacitor, and reference numeral 14 denotes a control circuit for the second battery 15.

  In the power supply control circuit configured as described above, the ECU first amplifies the voltage of the first battery 11 by the ignition coil 12 by switching of the transistor 10 and applies it between the center electrode 4 and the ground electrode 3. Thus, a high voltage acting between the center electrode 4 and the ground electrode 3 generates a creeping discharge on the inner surface of the cylindrical tip 2a of the insulator 2, and a gas (mixture) in the vicinity of the creeping discharge in the chamber 1 is generated. ) Into plasma. In this way, a part of the gas in the chamber 1 is turned into plasma and ions and electrons are generated, and at the same time, the voltage stored in the capacitor is released, and an air discharge is generated in the chamber 1. The control circuit applies a relatively low voltage of the second battery 15 between the center electrode 4 and the ground electrode 3 so that the air discharge continues, but a relatively large current can flow.

  Thus, when most of the gas in the chamber 1 is turned into plasma by the air discharge, the gas in the chamber 1 becomes high temperature and high pressure and is injected from the nozzle hole 6 as a plasma jet, and the mixture in the cylinder is improved. Ignite.

  When the gas in the chamber 1 is turned into plasma, the creeping discharge can be generated at a lower voltage than the air discharge. However, it is not efficient to make most of the gas in the chamber 1 into plasma only by the creeping discharge because the creeping discharge must be sustained for a long time on the inner surface of the side wall of the insulator 2. It is necessary to generate an air discharge. As described above, the voltage necessary for generating the air discharge can be lowered by converting some of the gas into plasma by creeping discharge. Thus, by generating a creeping discharge first and then generating an air discharge, most of the gas in the chamber 1 can be made into plasma without requiring a very high voltage.

  By the way, since the nozzle hole 6 becomes high temperature when plasma is ejected, it may be melted if it is not sufficiently cooled. Even when the nozzle hole 6 is formed not in the housing 5 but in the ground electrode 3 having high heat resistance as in this embodiment, the ground electrode 3 is caused by creeping discharge and air discharge when generating plasma. In order to increase the temperature, sufficient cooling is still necessary.

  In the present embodiment, as described above, the plasma ignition device 100 injects plasma at the ignition timing, and the squish flow S generated by the squish generation unit in the vicinity of the compression top dead center immediately after the ignition timing causes The tip portion 100a is cooled, so that the nozzle hole 6 formed in the tip portion 100a of the plasma ignition device 100 is cooled well by the squish flow S, and the melt damage of the nozzle hole 6 is suppressed. .

  Further, in the present embodiment, the nozzle hole 6 is formed in the end surface 100b of the tip end portion 100a of the plasma ignition device 100, and the end surface 100b of the tip end portion 100a is made to collide with the end surface 100b of the tip end portion 100a. The squish flow S is not parallel to the traveling direction. In the present embodiment, in particular, the central axis of the plasma ignition device 100 is inclined toward the exhaust valve so that the squish flow collides with the end surface 100b at a relatively large acute angle (or relatively small obtuse angle). As a result, the squish flow S not only reliably cools the nozzle hole 6 but also flows into the chamber 1 from the nozzle hole 6 and is heated in the chamber 1 at the time of plasma generation, that is, in the insulator. The cylindrical tip 2a and the center electrode 4 are also cooled by the squish flow. In order to facilitate the flow of the squish flow S into the chamber 1, in this embodiment, a chamfer 6 a (or a circular chamfer may be used) is formed on the outer edge of the nozzle hole 6.

  FIG. 4 is an enlarged cross-sectional view of the vicinity of the tip of a plasma ignition device 100 ′ showing a second embodiment of an internal combustion engine equipped with the plasma ignition device according to the present invention. Only differences from the first embodiment shown in FIGS. 1 and 2 will be described below. The central axis of the plasma ignition device 100 ′ of this embodiment is parallel to the cylinder central axis and is not inclined. However, since the cylinder upper surface of the cylinder head 108 has a pent roof shape formed by the intake valve side portion 108a and the exhaust valve side portion 108b, the traveling direction of the squish flow S along the intake valve side portion 108a of the cylinder head 108 The squish flow S collides with the end surface 100b ′ of the tip end 100a ′ and cools the nozzle hole 6 well without being parallel to the end surface 100b ′ of the tip end portion 100a ′ of the plasma ignition device 100 ′.

  Further, in the present embodiment, an inflow hole 5a ′ communicating with the chamber 1 is formed on the side surface 100c ′ of the tip 100a ′ of the plasma ignition device 100 ′, and the squish flow S ′ is passed through the inflow hole 5a ′. It flows into the inside. As a result, the squish flow S ′ flowing into the chamber 1 from the inflow hole 5a ′ also cools the inside of the chamber 1 that is at a high temperature when plasma is generated, that is, the cylindrical tip 2a and the center electrode 4 of the insulator. The

It is sectional drawing which shows 1st embodiment of an internal combustion engine provided with the plasma ignition apparatus by this invention. It is an expanded sectional view of the front-end | tip part vicinity of the plasma ignition apparatus of FIG. It is a power supply control circuit of a plasma ignition device. It is an expanded sectional view of the front-end | tip part vicinity of the plasma ignition apparatus which shows 2nd embodiment of an internal combustion engine provided with the plasma ignition apparatus by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Chamber 2 Insulator 3 Ground electrode 4 Center electrode 5a 'Inflow hole 6 Injection hole S, S' Squish flow 100, 100 'Plasma ignition apparatus 100a, 100a' Tip part

Claims (3)

  A chamber formed by a side wall of an insulator; a ground electrode disposed at one end of the chamber; and a center electrode disposed at the other end of the chamber; An internal combustion engine having a plasma ignition device having a nozzle hole formed at a tip thereof, wherein the plasma ignition device is attached to a cylinder head, and a squish generating portion is formed by the cylinder head and a piston top surface, thereby generating the squish An internal combustion engine comprising a plasma ignition device, wherein the tip portion of the plasma ignition device is cooled by a squish flow generated by a portion.   The nozzle hole is formed in an end surface of the tip portion of the plasma ignition device, and the end surface is not parallel to the traveling direction of the squish flow so that the squish flow collides with the end surface. An internal combustion engine comprising the plasma ignition device according to claim 1.   An inflow hole leading to the chamber is formed in a side surface of the tip portion of the plasma ignition device, and the squish flow flows into the chamber through the inflow hole. An internal combustion engine comprising the plasma ignition device according to Item 1.

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