JP2011007163A - Spark-ignition internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve problem of a conventional spark-ignition internal combustion engine wherein when plasma is generated in the combustion chamber and an air-fuel mixture is ignited by a spark discharge between the plasma and an ignition plug, if spark discharge is made by applying a negative high voltage to the center electrode of the ignition plug, electrons tend to be diffused, and the density of the plasma is reduced.SOLUTION: In this spark-ignition internal combustion engine, the electric field generated in the combustion chamber is reacted with a spark discharge by an ignition plug to generate plasma for igniting an air-fuel mixture. The ignition plug 1 includes the center electrode 14 installed in a housing while being insulated and a grounding electrode 15 attached to the bottom end of the housing apart from the center electrode. The spark discharge is made by applying a positive high voltage with respect to the potential of the grounding electrode to the center electrode at each ignition timing.

Description

  The present invention relates to a spark ignition internal combustion engine that reacts an electric field generated in a combustion chamber with a spark discharge by an ignition plug to generate plasma to ignite an air-fuel mixture.

  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 generates plasma by reacting an electric field generated in a combustion chamber with a spark discharge by a spark plug, and ignites an air-fuel mixture. The plug includes 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 apart from the center electrode. A positive high voltage is applied to the center electrode at each ignition timing with respect to the potential of the ground electrode. Is applied to perform 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 plasma is generated by reacting the spark discharge and the electric field, the position for generating the plasma can be easily set.

  As described above, the electric field generating means for generating an electric field includes an electromagnetic wave generator for generating electromagnetic waves of various frequencies, an AC voltage generator for applying an AC voltage to a pair of electrodes arranged in the combustion chamber, and a pair of electrodes. And a pulsating voltage generator for applying a pulsating voltage to the device.

  Examples of the electromagnetic waves generated by the electromagnetic wave generator include microwaves, high frequencies including frequencies used in various wireless communications such as amateur radio, and lasers having wavelengths shorter than those of microwaves. In the case of a laser, a laser oscillation device having a configuration different from that of other electromagnetic wave generation devices is used.

  The AC voltage output from the AC voltage generator has a frequency equal to the above-described high frequency.

  The pulsating voltage generator need only generate a DC voltage whose voltage periodically changes, and the waveform of the DC voltage may be arbitrary. That is, the pulsating voltage in the present application changes from a reference voltage including 0 volt to a pulse voltage that changes to a constant voltage at a constant cycle or a voltage that increases or decreases sequentially at a fixed cycle, for example, AC voltage is half-wave rectified. Such a DC voltage having such a waveform, and a DC voltage obtained by applying a DC bias to the AC are included. In this case, the fixed period may correspond to the frequency at the above-described high frequency. The waveform is not limited to that described above, and may be a sine wave, a sawtooth wave, a triangular wave, or the like.

  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 When the plasma is generated by causing the spark discharge and the electric field to react with each other, the position where the plasma is generated can be easily set.

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. The block diagram which shows the structure of the electromagnetic wave generator which can be used in embodiment of this invention. The block diagram which shows the structure of the alternating voltage generator which can be used in embodiment of this invention. FIG. 6 is a circuit diagram showing an example of an H bridge circuit in FIG. 5.

  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. An ignition plug 1 is attached to the ceiling portion of the combustion chamber 6, and a fuel injection valve for generating an air-fuel mixture supplied to the fuel chamber 6 is provided in the intake port 2. 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 29 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 an electromagnetic wave including a magnetron 24 and a control circuit 25. A microwave generator 26 as a generator is connected via a 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 microwave generator 26 controls the output timing and output power of the microwave output from the magnetron 24 when the control circuit 25 receives the microwave 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). Therefore, the center electrode 14 and the microwave generator 26 constitute an electric field generating means.

  At the time of ignition, spark discharge is generated in the spark plug 1 by an ignition coil (not shown), and an electric field is generated by microwaves almost simultaneously with the start of the spark discharge or immediately after the start of the spark discharge or immediately before the start of the spark discharge. In this configuration, the air-fuel mixture in the combustion chamber 6 is rapidly burned by generating plasma by reacting with an electric field. It should be noted that “immediately after the start of spark discharge” is preferably at the start of induction discharge constituting the spark discharge at the latest.

  Specifically, the spark discharge generated by the spark plug 1 becomes plasma in an electric field, and the flame nucleus at the beginning of flame propagation combustion is larger than ignition by only spark discharge by igniting the mixture with the plasma. In addition, combustion is promoted by generating a large amount of radicals in the combustion chamber 6.

  This is because the flow of electrons due to the spark discharge and the ions and radicals generated by the spark discharge are vibrated and meandered by the influence of the electric field, resulting in a longer path length and a dramatic increase in the number of collisions with surrounding water and nitrogen molecules. This is due to the 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 ignition region for the air-fuel mixture dramatically increases, and the flame kernel that starts the flame propagation combustion also increases.

  As a result, the air-fuel mixture is ignited by the plasma generated by the reaction between the spark discharge and the 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, since 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, electrons can be attracted from a position other than directly below the center axis of the center electrode 14. 14 is released. And since the front-end | tip of the center electrode 14 is small compared with the upper surface of the ground electrode 15, the electron discharge | released from the ground electrode 15 concentrates on the center electrode 14, and a spark discharge arises in the state.

  As a result, when the plasma is generated by reacting the spark discharge and the electric field, if the position where the electric field is generated is the gap 29 between the center electrode 14 and the ground electrode 15 of the spark plug 1, the electron is concentrated at the position. Since an electric field is generated, the reaction between the spark discharge and the electric field is promoted, and plasma is stably generated in the gap 29 between the tip of the center electrode 14 of the spark plug 1 and the ground electrode 15. It is something that can be done.

  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.

  In addition to the magnetron as described above, the microwave generator may be a traveling wave tube or the like, and may further include a semiconductor microwave oscillation circuit.

  In addition, although the center electrode 14 of the spark plug 1 is an antenna in the above-described embodiment, a horn type antenna or a monopole type antenna may be used. In that case, the antenna is provided at a position facing the combustion chamber or the combustion chamber.

  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.

  On the other hand, the frequency of the electromagnetic wave in the electromagnetic wave generator is not limited to the microwave frequency band, and may be any frequency that can generate an electric field in the spark discharge portion of the spark plug 8 to generate plasma. Therefore, as the electromagnetic wave generator, one having a configuration as shown in FIG. 3 is suitable, for example.

  3 includes a transmitter 31 that oscillates an electromagnetic wave of, for example, 300 MHz, a matching tuner (or an antenna tuner) 33 that is connected to the output end of the transmitter 31 by a coaxial cable 32, and a matching tuner 33. A mixer 36 is connected to the output end by an unbalanced cable 34 and is also connected to an igniter 35. In this example, the center electrode 14 of the spark plug 1 functions as an antenna that radiates electromagnetic waves. Therefore, the mixer 36 transmits the electromagnetic waves output from the transmitter 31 via the matching tuner 33 to the spark plug 1. In addition to being applied to the center electrode 14, an ignition signal from the igniter 35 is applied to the center electrode 14. The mixer 36 mixes the electromagnetic wave from the transmitter 31 and the ignition signal from the igniter 35.

  In this example, an electric field is generated between the center electrode 14 and the ground electrode 15 by electromagnetic waves from the transmitter 31. The generated electric field reacts with the spark discharge generated between the center electrode 14 and the ground electrode 15 to generate plasma and ignite the air-fuel mixture.

  Moreover, a laser oscillation apparatus is mentioned as an electromagnetic wave generator. As the laser oscillation device, a combination of a laser diode, a lens assembly including YAG (yttrium, aluminum, garnet) and a cylindrical lens can be used. The laser output from the laser oscillation device is sent to the combustion chamber via an optical fiber. In this case, the optical fiber passes through the inside of the spark plug housing, and its tip is attached toward the gap between the center electrode and the ground electrode. Prior to the spark discharge, the laser is preferably applied to a position where the spark discharge occurs.

  The laser emitted from the optical fiber concentrates in the gap and concentrates the electric field near the gap. Therefore, the electric field can be generated at a desired position due to the directivity of the laser, and the plasma can be generated at the most suitable position for ignition of the air-fuel mixture.

  Instead of the electromagnetic wave generator described above, an AC voltage generator may be used. The AC voltage generator 40 shown in FIG. 4 boosts the voltage of the vehicle battery 41, for example, about 12V (volts) to 300 to 500V by the DC-DC converter 42 which is a booster circuit, and then exemplifies in FIG. The frequency is changed to an alternating current having a frequency of about 1 MHz to 500 MHz, preferably 100 MHz by the H bridge circuit 43, and further boosted to about 4 kVp-p to 8 kVp-p by the step-up transformer 44.

  In such an AC voltage generator 40, for example, when the center electrode 14 and the ground electrode 15 of the spark plug 1 are used as a pair of electrodes for generating an electric field, the AC voltage is generated similarly to the electromagnetic wave generator 30 described above. A mixer is disposed between the step-up transformer 44, the igniter, and the spark plug 1 serving as the output end of the above. Then, by applying a high-voltage AC voltage between the center electrode 14 and the ground electrode 15, an electric field in which the polarity is alternately switched in the frequency band is generated in the gap of the spark plug 1 which is a discharge area. Accordingly, the generated electric field and spark discharge react to generate plasma around the spark plug 1 and ignite the air-fuel mixture. In the case where the pair of electrodes includes the center electrode 14 and the ground electrode 15, a cylinder head, a cylinder block, or a piston may be used instead of the ground electrode 14.

  In addition to using the center electrode 14 and the ground electrode 15 of the spark plug 1 described above, the pair of electrodes may have a configuration in which electrodes are arranged at positions sandwiching the spark plug 1. That is, a pair of electrodes are arranged facing each other at a predetermined distance. In this case, the pair of electrodes are arranged so that the spark plug 1 is positioned between the electrodes. Also in this case, one of the electrodes may be replaced with a ground electrode, a cylinder head, a cylinder block, or a piston.

  Instead of such an AC voltage generator, a pulsating flow generator may be used. That is, instead of applying an alternating current between a pair of electrodes, an electric field is generated between the pair of electrodes by applying a pulsating voltage such as a pulse voltage. In the same way as the AC voltage generator, the pulsating flow generator converts the direct current supplied from the battery to DC? The voltage is boosted by a DC converter, and a pulsating flow is generated by intermittently applying a high-voltage direct current at a predetermined cycle. In the case of a pulsating flow generator, a switching circuit that is periodically turned on and off is used instead of the H-bridge circuit. By using such a pulsating flow generation circuit, an electric field can be generated between the pair of electrodes, and the same effect as in the above-described embodiment can be obtained.

  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.

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 in which an electric field generated in a combustion chamber reacts with a spark discharge by an ignition plug to generate plasma to ignite an air-fuel mixture, wherein the ignition plug is insulated and installed in a housing. Spark ignition type comprising an electrode and a ground electrode provided at the lower end of the housing apart from the center electrode, and applying a positive high voltage to the center electrode at every ignition timing with reference to the potential of the ground electrode Internal combustion engine.

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