JP2010096144A - Spark-ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem of the plasma density decline due to the electron diffusion tendency at the spark discharge by applying a negative high voltage to the central electrode of the ignition plug in the case of igniting a fuel/air mixture with plasma and spark discharge of the ignition plug by producing plasma in a combustion chamber. <P>SOLUTION: The spark-ignition internal combustion engine is 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. The ignition plug comprises a central electrode mounted in a housing with insulation, and a grounding electrode provided at the lower end of the housing away from the central electrode. Spark discharge is carried out by applying a positive high voltage to the central electrode for each ignition period on the basis of the electric potential of the grounding electrode. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to 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 an ignition 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 plasma is generated in the combustion chamber using a magnetron, an electrode for radiating microwaves from a magnetron, that is, an antenna such as the auxiliary electrode of the above-mentioned Patent Document 1, or an antenna, or an antenna is provided around the spark plug. It is conceivable to use the center electrode as an antenna.

  In general, a spark plug has a cylindrical or needle-shaped center electrode, whereas a ground electrode has a square cross section, for example, the width and length of the surface facing the center electrode is the tip of the center electrode. It is bigger than the surface. In ignition, spark discharge is performed by applying a negative high voltage to the center electrode with the ground electrode as a reference potential. Therefore, discharge occurs when electrons are emitted from the center electrode to the ground electrode.

  However, when electrons are emitted from the center electrode toward the ground electrode in this way, the electrons diffuse, so that when plasma is generated using the above-described center electrode as an antenna for microwaves, the density of the plasma decreases. There is a tendency that the ignition performance of the air-fuel mixture is reduced accordingly.

  Therefore, the present invention aims to eliminate such problems.

  That is, the spark ignition internal combustion engine of the present invention is a spark ignition internal combustion engine that ignites an air-fuel mixture by reacting plasma generated in a combustion chamber by electromagnetic waves and spark discharge by an ignition plug, the ignition plug being It has a center electrode that is insulated and installed in the housing, and a ground electrode that is provided at the lower end of the housing away from the center electrode. A positive high voltage is applied to the center electrode at each ignition timing based on the potential of the ground electrode. And performing a spark discharge.

  According to such a configuration, at the time of spark discharge, since the center electrode becomes a positive high voltage, electrons are emitted from the ground electrode toward the center electrode. That is, electrons emitted from the ground electrode are concentrated on the center electrode. As a result, when the spark discharge and the plasma are reacted, it is possible to easily set the position for generating the plasma.

  The present invention is configured as described above, and at the time of spark discharge, since the central electrode becomes a positive high voltage, electrons are emitted from the ground electrode toward the central electrode, and the electrons emitted from the ground electrode are By concentrating on the center electrode, when the spark discharge and the plasma are caused to react, the position for generating the plasma can be easily set.

  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. A spark plug 1 is attached to the ceiling portion of the combustion chamber 6. The engine 100 itself excluding the spark plug 1 may be a spark ignition type that is known in this field.

  The spark plug 1 of this embodiment 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 apart 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 is electrically connected by the center electrode 14 protruding from the lower end of the housing 13 and the center shaft (not shown). The ground electrode 15 is integrally provided on the housing 13 at a position that is connected to the housing 13 and extends from the lower end of the housing 13 to a position facing the lower end of the center electrode 14. 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.

  The housing 13 has a cylindrical shape with an internal space sufficient to accommodate the insulator 16, and is made of, for example, stainless steel, which is a conductive material. The upper end portion of the housing 13 is squeezed inward in order to keep the insulator 16 in tight contact and maintain airtightness. Further, a male screw portion 18 for attachment to the cylinder head 8 is formed on the outer periphery of the lower portion from the central portion in the longitudinal direction. In addition, between the male screw part 18 and the upper end part, a metal shell 19 serving as a mounting base part when attached is formed with a larger outer diameter than the male screw part 18.

  The center electrode 14 is formed of, for example, a cylindrical metal material, and the lower end thereof is exposed from the insulator 16 and is exposed from the lower end of the housing 13. The tip of the center pole 14 is a substantially flat circular surface and faces the upper surface of the ground electrode 15 substantially in parallel.

  With respect to such a center electrode 14, the ground electrode 15 is substantially L-shaped in a side view formed integrally with the lower end surface of the housing 13, and the tip thereof has a gap 30 from the center axis of the center electrode 14. It extends to the open position. Since the ground electrode 15 has a long upper surface as compared with the center electrode 14 in this way, the upper surface becomes an electron emission surface having a larger area than the tip of the center electrode 14. Since the ground electrode 15 is integrally provided in the housing 13 as described above, the ground electrode 15 is maintained at the same potential as that of the housing 13, that is, at the ground potential in use.

  As shown in FIG. 2, an ignition device 22 including an igniter 20 and an ignition coil 21 is connected to such a spark plug 1 via a mixer 23, and a high pressure including a magnetron 24 and a control circuit 25. An AC generator 26 is connected via the mixer 23. When an ignition signal is input at each ignition timing from an electronic control device (not shown) for controlling the operation of the engine 100, the ignition device 22 excites the ignition coil 21 by the igniter 20, and the center electrode of the ignition plug 1 14 is configured to apply a positive high voltage.

  The high-voltage AC generator 26 controls the output timing and output power of the microwave output from the magnetron 24 when the control circuit 25 receives the high-voltage AC generation signal from the electronic control device. The microwave output from the magnetron 24 is applied to the center electrode 14 of the spark plug 1 via a waveguide and a coaxial cable (not shown).

  In this engine 100, the microwave generated by the high-voltage AC generator 26 in a normal operation state is radiated from the central electrode 14 into the combustion chamber 6 almost simultaneously with or immediately after the spark discharge, and is generated thereby. The mixture is ignited by reacting the plasma and the spark discharge generated by the spark plug 1.

  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 this case, the spark plug 1 emits electrons from the ground electrode 15 toward the center electrode 14 because the center electrode 14 becomes a positive high voltage during spark discharge. In this embodiment, the upper surface of the ground electrode 15 facing the center electrode 14 has a larger area than the tip of the center electrode 14, so that electrons are transmitted from a position other than directly below the center axis of the center electrode 14. Is released towards Since the tip of the pole 14 has a small area at the center as compared with the upper surface of the ground electrode 15, electrons emitted from the ground electrode 15 are concentrated on the center electrode 14, and spark discharge occurs in that state.

  As a result, when spark discharge and plasma are reacted, the plasma is generated at the gap 30 between the center electrode 14 and the ground electrode 15 of the spark plug 1, and the plasma is generated at a position where electrons are concentrated. The reaction between the spark discharge and the plasma is promoted. Thus, plasma can be stably generated in the gap 30 between the tip of the center electrode 14 of the spark plug 1 and the ground electrode 15.

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

  In the above-described embodiment, the tip of the center electrode 14 is a substantially flat circular surface, but it may be pointed like a needle toward one point of the ground electrode.

  The high-voltage AC generator may be a traveling wave tube or the like in addition to the magnetron as described above, and may further include a microwave oscillation circuit made of a semiconductor.

  In addition, although the center electrode 14 of the spark plug 1 is an antenna in the above-described embodiment, it may be a beam type antenna or a monopole type antenna.

  Furthermore, when the center electrode 14 of the spark plug 1 is made to function as an antenna and is used as a high-frequency power feeding unit, if the high frequency is continuously applied to the center electrode at a constant voltage, the temperature of the center electrode excessively increases. The high frequency voltage is controlled so as to be lower than the upper limit temperature set based on the heat resistant temperature of the center electrode.

  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 block diagram which shows the electric structure centering on the ignition plug of the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Spark plug 13 ... Housing 14 ... Center electrode 15 ... Ground electrode 20 ... Igniter 21 ... Ignition coil 22 ... Ignition device 24 ... Magnetron 25 ... Control circuit 26 ... High voltage alternating current generator

Claims (1)

  A spark ignition type internal combustion engine that ignites an air-fuel mixture by reacting plasma generated in a combustion chamber by electromagnetic waves and spark discharge by an ignition plug, wherein the ignition plug is insulated and installed in the housing; A spark ignition internal combustion engine comprising a ground electrode provided at a lower end of a housing apart from the center electrode, and applying a positive high voltage to the center electrode at each ignition timing with reference to the potential of the ground electrode to perform a spark discharge.

Images