JP2011007155A - Ignition plug of spark-ignition internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve problem of a conventional ignition plug wherein when microwave is emitted from the center electrode of the ignition plug to generate plasma in the case of generating plasma by reacting an electric field with a spark ignition and igniting an air-fuel mixture, if the direction of a high-frequency field by the microwave is aligned with the center axis direction of the center electrode, namely, the discharge direction of a spark discharge, the action of the field on the spark discharge becomes small, and predetermined effects cannot be expected.SOLUTION: This ignition plug of a spark-ignition internal combustion engine includes a 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 plasma is generated by reacting the spark discharge generated between the center electrode and the grounding electrode with the electric field generated in a combustion chamber to ignite the air-fuel mixture. The grounding electrode is disposed so that the end thereof is positioned apart from the center axis of the center electrode. The grounding electrode includes a specific surface 21 which causes the direction of the electric field in the direction crossing the direction of the spark discharge produced between the center electrode and the grounding electrode.

Description

  The present invention relates to an ignition plug for a spark ignition type internal combustion engine that reacts an electric field generated in a combustion chamber with spark discharge by an ignition plug to generate plasma and 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, for example, a method using a magnetron is considered. When plasma is generated in a combustion chamber by a magnetron, an antenna that radiates microwaves is required. In this case, the center electrode of the spark plug can be used as an antenna.

  A general spark plug has a structure in which a ground electrode having a substantially square cross section is provided with a gap in the vicinity of a position immediately below the center electrode with respect to the center electrode. In such an electrode structure, when a microwave is applied to the central electrode, the direction of the high-frequency electric field by the microwave is directed to the central axis direction of the central electrode.

  However, when the direction of the high-frequency electric field is the same as the direction of the central axis of the center electrode, that is, the discharge direction of the spark discharge, the effect of the high-frequency electric field on the spark discharge is small and the expected effect cannot be expected.

  Therefore, the present invention aims to eliminate such problems.

  That is, the spark plug of the spark ignition internal combustion engine of the present invention includes a center electrode that is insulated and attached in the housing, and a ground electrode that is provided at the lower end of the housing apart from the center electrode. A spark plug of a spark ignition type internal combustion engine that generates plasma by reacting a spark discharge generated between and an electric field generated in a combustion chamber to ignite an air-fuel mixture, and a ground electrode is a center axis of a center electrode And a specific surface for generating a direction of an electric field in a direction intersecting with a direction of a spark discharge generated between a center electrode and a ground electrode. To do.

  According to such a configuration, when the electric field and the spark discharge react, the electric field direction, that is, the direction occurs in a direction intersecting with the spark discharge by the specific plane. For this reason, the electric field and the spark discharge react to generate plasma efficiently, so that the spark discharge is amplified and good ignition can be obtained.

  Specifically, the specific surface is an inclined surface provided on the lower surface of the ground electrode facing away from the center electrode. In such a configuration, in order to form the direction of the electric field in a desired direction, it is preferable that the ground electrode has an inclined side surface that obliquely crosses the extension axis of the ground electrode that intersects the center axis of the center electrode.

  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 and high-frequency waves including frequencies used in various wireless communications such as amateur radio.

  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 an electric field and a spark discharge react to generate plasma efficiently, whereby the spark discharge is amplified and good ignition can be obtained.

1 is an enlarged sectional view showing a main part of an engine to which an embodiment of the present invention is applied. The front view of the embodiment. The principal part enlarged front view of the embodiment. The bottom view of the embodiment. The principal part expansion perspective view 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. 8 is a circuit diagram showing an example of an H bridge circuit in FIG. 7.

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

  An engine 100, which is a spark ignition type internal combustion engine, showing an enlarged mounting portion of the spark plug 1 in FIG. 1, is of a double overhead camshaft (DOHC) type, and has an intake port 2 opening 3 and an exhaust port 4 opening 5. However, they are opposed to each other centering on a spark plug 1 attached to substantially the center of the ceiling portion of the combustion chamber 6 and open 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, and a fuel injection valve for generating an air-fuel mixture supplied to the combustion 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.

  As shown in FIGS. 2 to 5, 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 housing 13 separated from the center electrode 14. And a ground electrode 15 provided at the lower end. 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 columnar metal material, and the lower end thereof is exposed from the insulator 16 and is exposed from the lower end of the housing 13.

  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 20 from the center axis of the center electrode 14. It extends to the open position. Since the ground electrode 15 is integrally provided in the housing 13 as described above, it is maintained at the same potential as the housing 13 during use. The ground electrode 15 includes a specific surface 21 that is inclined in a direction of retreating from the tip when viewed from the front. That is, the specific surface 21 is an inclined surface provided on the lower surface of the ground electrode 15 facing away from the center electrode 14 and has an acute angle with respect to the upper surface 22 of the ground electrode 15. In addition, the ground electrode 15 includes an inclined side surface that obliquely crosses the extended axis 24 of the ground electrode 15 that intersects the central axis 23 of the center electrode 14. That is, the ground electrode 15 has an inclined side surface 25 whose front side surface is inclined toward the back side.

  In such a configuration, the spark plug 1 is attached to each cylinder of the engine 100 and functions as an antenna for generating plasma, which will be described later, in addition to the original function of performing spark discharge. That is, the engine 100 generates plasma by reacting the spark discharge of the spark plug 1 with the electric field generated in the combustion chamber 6 when the air-fuel mixture in the combustion chamber 6 is ignited using the spark plug 1. Compared to ignition by spark discharge when plasma is not generated, the ignition region is enlarged. For this purpose, the center electrode 14 of the spark plug 1 is connected to an ignition coil for spark discharge, and is an electromagnetic wave generating device including a magnetron that outputs a microwave that is an electromagnetic wave for generating an electric field. A wave generator (not shown) is connected. Accordingly, as described below, the microwave output from the magnetron is applied to the center electrode 14 of the spark plug 1.

  As described above, since the ground electrode 15 has the specific surface 21 that is separated from the central axis 23 of the center electrode 14 by the gap 20 and is inclined with respect to the central axis 23, microwaves are applied to the central electrode 14. In this case, the direction of the electric field (electric field lines) generated between the center electrode 14 and the ground electrode 15 is perpendicular to the specific surface 21 on the surface of the specific surface 21. That is, when the state of the electric field generated between the center electrode 14 and the ground electrode 15 is represented by lines of electric force, the tip surface of the center electrode 14 and the specific surface 21 of the ground electrode 15 intersect each other vertically, and the center electrode 14 In many cases, the tip surface of the electrode and the specific surface 21 of the ground electrode 15 are connected in a curved shape. For this reason, the direction of the electric field in the space between the center electrode 14 and the ground electrode 15 of the spark plug 1 does not align with the direction of the center axis 23 of the center electrode 14, but becomes distorted. Thereby, the strength of the electric field of the direction component orthogonal to the spark discharge generated between the center electrode 14 and the ground electrode 15 is increased, and the flow of electrons due to the spark discharge can be efficiently meandered, so that the specific surface 21 Compared to the case where there is no plasma, the generated plasma increases. Similarly, since the direction of the electric field is also perpendicular to the inclined side surface 25 formed on the front surface of the ground electrode 15, the intensity of the electric field in the direction component perpendicular to the spark discharge is increased toward the inclined side surface 25. This further increases the plasma generation.

  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.

  Since the ground electrode 15 includes the specific surface 21 and the inclined side surface 25, the direction of the electric field is different from the direction of the spark discharge. Acts, the flow of electrons due to the spark discharge can be efficiently meandered, and the generated plasma can be increased. Since the electric field strength can be adjusted by controlling the direction of the electric field in this way, the output of the magnetron that outputs the microwave can be suppressed. Therefore, power consumption for generating plasma can be reduced.

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

  As described in the above embodiment, the present invention provides a specific surface that causes the electric field formed by the microwave radiated from the center electrode 14 to distort in the space between the center electrode 14 and the ground electrode 15. It is characterized by being provided at the tip portion of the ground electrode 15, and the shape of the specific surface is not limited to the above-described embodiment. That is, the specific surface may be provided in consideration of the direction of the electric field penetrating perpendicularly to the metal surface. In the above-described embodiment, the specific surface 21 is a flat surface. However, the specific surface 21 may be a curved surface such as a concave surface or a convex surface, or a wavy curved surface with a continuous uneven surface.

  In the above-described embodiment, the inclined side surface is provided only on the front side of the ground electrode 15, but may be provided on the back side. That is, the ground electrode has a structure in which the side surfaces on both sides are inclined in the direction in which the side surfaces are close to each other and the specific surface is provided on the lower surface. Therefore, the tip portion of the ground electrode facing the center electrode is a triangular pyramid tip formed by three surfaces concentrated toward one point.

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

  In addition, the center electrode is not used as an antenna as in the above-described embodiment, and an antenna separate from the spark plug may be used. In this case, for example, a horn type or monopole type antenna can be used. These antennas are preferably provided around the center electrode 14 of the spark plug 1. Further, it may be attached to the spark plug 1 itself around the center electrode 14 of the spark plug 1.

  Further, when the center electrode of the spark plug 1 functions as an antenna, 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 to be set.

  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 1 to generate plasma. Therefore, as the electromagnetic wave generator, one having a configuration as shown in FIG. 6 is suitable, for example.

  6 includes, for example, a transmitter 31 that oscillates an electromagnetic wave of 300 MHz, a matching tuner (or antenna tuner) 33 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.

  Instead of the electromagnetic wave generator described above, an AC voltage generator may be used. The AC voltage generator 40 shown in FIG. 7 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.

  Instead of such an AC voltage generator, a pulsating flow generator may be used. That is, instead of applying an alternating current between the pair of electrodes described above, a pulsating voltage such as a pulse voltage is applied to generate an electric field between the electrodes. 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 electrodes, and an effect similar to that of 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 6 ... Combustion chamber 13 ... Housing 14 ... Center electrode 15 ... Ground electrode 21 ... Specific surface 23 ... Center axis 24 ... Extension axis 25 ... Inclined side surface

Claims (3)

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, spark discharge generated between the center electrode and the ground electrode, and an electric field generated in the combustion chamber Is a spark ignition type internal combustion engine for generating plasma and igniting an air-fuel mixture,
The ground electrode is arranged so that its tip is located at a position away from the center axis of the center electrode, and the direction of the electric field is generated in a direction intersecting with the direction of the spark discharge generated between the center electrode and the ground electrode. A spark plug of a spark ignition type internal combustion engine having a specific surface.   The spark plug for a spark ignition type internal combustion engine according to claim 1, wherein the specific surface is an inclined surface provided on a lower surface of the ground electrode facing away from the center electrode. The spark plug of the spark ignition type internal combustion engine according to claim 2, wherein the ground electrode has an inclined side surface that obliquely crosses the extended axis of the ground electrode that intersects the central axis of the center electrode.

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