JP2009146636A - Ignition device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma ignition device with high durability. <P>SOLUTION: In the plasma ignition device 1 in which gas in a discharge space 140 is made into plasma state by impressing high voltage and high current, is injected inside an engine 40 and carries out ignition to an ignition plug 10 with the discharge space 140 partitioned by a center electrode 110, an insulator 120 and a ground electrode 130, the center electrode 110 is formed in an axis shape, the insulator 120 covers an outer side of the center electrode 110 and extends from a lower end face of the center electrode 110 in an axis direction, and is formed in a nearly cylindrical shape with its lower end open, the ground electrode 130 is fitted at outside of the insulator 120 and forms in a nearly circular shape having an opening part 131 communicating with the opening of the lower end of the insulator 120. With the center electrode 110 as an anode side, and the ground electrode 130 as a cathode side, high voltage of positive potential is impressed and a large current is supplied, a discharge space inner diameter ϕD<SB>CHM</SB>, a ground electrode opening inner diameter ϕD<SB>ORF</SB>, an insulator thickness T<SB>INS</SB>, and a surface discharge distance G<SB>PS</SB>are set in predetermined ranges. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an improvement in durability of a plasma ignition device used for ignition of an internal combustion engine.

  In recent years, in internal combustion engines such as automobiles, in order to reduce environmental pollutants in combustion exhaust gas and further improve fuel consumption, combustion by further diluting the air-fuel ratio and supercharging mixing has been attempted. Such lean combustion engines and supercharged mixed combustion engines have low ignitability, and development of an ignition device having excellent ignition performance with high ignitability is strongly desired.

The plasma ignition device 1z as shown in FIG. 14 applies a high voltage from the discharge power source 20z between the center electrode 110z and the ground electrode 130z of the spark plug 10z attached to the engine, and the center electrode 110z and the ground electrode. Immediately after a discharge is generated in the discharge space 140z formed between the discharge space 140z and the plasma generating power source 30z, a large current is supplied to change the gas in the discharge space 140z to a high-temperature and high-pressure plasma state, thereby generating a discharge space. The engine can be ignited from 140z.
Such a plasma ignition device is rich in directivity and can generate an extremely high temperature range of several thousand to several tens of thousands K in a large volume range. It is expected to be applied as an ignition device for use in a combustion engine that is difficult to ignite such as mixed combustion.

  In Patent Document 1, in order to prevent contamination of the center electrode, an insulator provided with an insertion hole extending vertically and holding the center electrode at the center, and an opening covering the insulator and communicating with the insertion hole at the lower end The surface gap type spark plug is disclosed in which a discharge gap is formed in the insertion hole.

  Further, in Patent Document 2, in order to increase the heat value of the plug and improve the self-cleaning property, most of the periphery of the spark gap between the center electrode and the side electrode is surrounded by an electric insulator and has a small volume. In the ignition plug of the internal combustion engine, a plasma gas generated in the discharge space at the time of spark discharge is ejected into the fuel mixture from the ejection hole opened in the discharge space. An ignition plug for an internal combustion engine is disclosed, in which an electrode is disposed apart from the ejection hole.

In Patent Document 3, in order to prevent contamination of the insulator body wall in the discharge space, a small volume discharge space is formed by surrounding the periphery of the spark gap with a porcelain insulator and is generated in the discharge space at the time of spark discharge. In a plasma jet ignition plug in which plasma gas is jetted into a fuel-air mixture in a combustion chamber through an ejection hole formed in the discharge space, the ignition portion of the ceramic insulator that forms the discharge space is defined as a wall surface of the combustion chamber There has been disclosed a plasma jet ignition plug characterized in that it protrudes more appropriately and is formed so that a ground electrode surrounds the ignition portion.
Moreover, in the technique of patent document 3, the center electrode and the ground electrode are formed by forming the thickness of the ignition part of the ceramic insulator protruding into the combustion chamber as thin as possible in the range of 0.2 mm to 2.0 mm. The back electrode effect that generates a strong electric field across the porcelain insulator is added between the two and the discharge gap pressure can be reduced by ionizing the spark gap.
Japanese Patent No. 3581141 Japanese Utility Model Publication No. 55-166092 Japanese Patent Laid-Open No. 57-15378

  However, in the conventional plasma ignition device, as shown in FIG. 14, a negative high voltage is applied with the center electrode on the cathode side and the ground electrode on the anode side. In such a configuration, as shown in FIG. 13, of the high-temperature and high-pressure plasma-like gas generated in the discharge space, a large-mass cation collides with the surface of the central electrode, and the surface gradually erodes. Cathode sputtering occurs. With the progress of cathode sputtering, the distance between the center electrode and the ground electrode, that is, the discharge distance gradually increases, the discharge voltage gradually increases in proportion to the discharge distance, and there is a risk that the engine will eventually be misfired. Further, in a stratified lean burn that attempts to ignite by increasing the fuel concentration of a specific part in the combustion chamber, as disclosed in Patent Document 3, if the ignition portion of the porcelain insulator is projected into the combustion chamber, the combustion There is a possibility that the airflow in the room is disturbed, and the high temperature region cannot be jetted to a specific target site, resulting in misfire.

  Furthermore, in a plasma ignition device that performs energy injection in a temperature range that causes a problem of deposit formation due to cold start or smoldering as disclosed in Patent Document 2 or 3, sparks of a normal spark plug Even if ignition is possible in a lean combustion region that can be ignited even by ignition by discharge, there is a possibility that the engine that is extremely diluted to the extent that it cannot be ignited by a normal spark plug cannot be ignited.

  In addition, as disclosed in Patent Document 3, when the ejection hole provided in the ground electrode is smaller than the inner diameter of the discharge space, the shortest distance between the center electrode and the ground electrode is a portion where both electrodes are directly opposed to each other. Further, the back electrode effect is not sufficiently exhibited, air discharge becomes dominant, and the discharge voltage may be increased. In general, the withstand voltage increases as the gas pressure increases, so there is a possibility that the conventional configuration may not be able to discharge during high compression. In addition, as described in Patent Document 3, when the thickness of the porcelain insulator is set in the range of 0.8 mm to 2.0 mm, the withstand voltage of the porcelain insulator is a very low value. Therefore, even if the back electrode effect is taken into consideration, the discharge voltage that causes dielectric breakdown of the discharge space that occurs prior to the generation of plasma is extremely limited, the applicable discharge distance is extremely short, and low energy is consumed from a narrow electric space. There is a risk that misinjection may occur because sufficient energy cannot be injected into the inflammable combustion engine.

  Therefore, in view of such a situation, the present invention is an electrode by cathode sputtering while maintaining high ignition performance in a plasma ignition device used in a combustion engine with low ignition such as a lean combustion engine and a supercharged mixed combustion engine. It is an object of the present invention to provide a plasma ignition device that suppresses the exhaustion and realizes further improvement in durability.

According to the first aspect of the present invention, there is provided a spark plug mounted on a combustion engine, in which a discharge space is defined by a center electrode, an insulator, and a ground electrode, and for applying a high voltage between the center electrode and the ground electrode. A power source and a plasma generating power source that discharges a large current into the discharge space;
The combustion engine breaks the insulation of the discharge space by applying a high voltage from the discharge power source, and changes the gas in the discharge space to a high temperature, high pressure plasma state by releasing a large current from the plasma generating power source. In the plasma ignition device for injecting into the engine and igniting the engine, the center electrode is formed in an axial shape, and the insulator covers the outside of the center electrode and extends axially from the lower end surface of the center electrode. The ground electrode is formed in a substantially annular shape having an opening that is provided outside the insulator and communicates with the opening at the lower end of the insulator. The application of the positive high voltage and the supply of the large current are performed with the electrode on the anode side and the ground electrode on the cathode side.

According to the invention of claim 1, the positive corona is generated on the lower surface of the center electrode. The positive corona has a slightly higher generated voltage than the negative corona generated on the surface of the center electrode when the conventional center electrode is used as a cathode, but is extremely excellent in progress. Therefore, the required voltage at which the insulation of the discharge space is broken and the discharge can be started between the center electrode and the ground electrode is lower than that in the case where the conventional center electrode is a cathode. By reducing the required voltage, the electric capacity of the discharge high-voltage power supply can be reduced. When the capacity of the high voltage power source for discharge becomes small, the weak current when the high voltage for discharge is applied decreases, and cathode sputtering of the ground electrode due to the weak current becomes difficult to occur.
On the other hand, since the central electrode is an anode, a cation having a large mass among the gas in a plasma state is electrically repelled, so that it is difficult to cause sputtering due to the collision of the cation. Therefore, a highly durable plasma ignition device can be realized while having excellent ignitability in a non-ignitable combustion engine.

  According to a second aspect of the present invention, a housing part is formed in which the ground electrode extends in the direction toward the anti-ground electrode opening, and a portion of the housing part that faces the central electrode is interposed through the insulator. It became the back electrode for the electrode.

  According to the invention of claim 2, a strong electric field is generated between the center electrode and the back electrode, and further generated between the center electrode and the ground electrode disposed at the lower end of the back electrode. The electric flux enters and leaves the discharge space and the insulator, and the electric flux is concentrated on the lower end surface of the center electrode, so that a region having a high potential gradient is formed locally. By such electric field concentration, a positive corona is more likely to be generated on the surface of the center electrode, dielectric breakdown of the discharge space is facilitated, and the required voltage is further reduced. The discharge at this time can be discharged at a lower required voltage than the air discharge penetrating the conventional discharge space, and becomes a creeping discharge that forms a discharge path over the surface of the insulator. Therefore, a plasma type ignition device with higher durability can be realized.

In the invention of claim 3, the relationship of the following formula 1 is satisfied in the relationship between the inner diameter φD _CHM (mm) of the insulator and the inner diameter φD _ORF (mm) of the ground electrode opening.
0.1 ≦ D _ORF −D _CHM・ ・ ・ Equation 1

According to the invention of claim 3, the center electrode and the ground electrode do not directly face each other, and the electric field generated between the center electrode and the ground electrode is always the discharge space and the insulator. As a result, electric field concentration occurs on the surface of the central electrode, and creeping discharge is more likely to occur, and the required voltage can be reduced. Therefore, a plasma ignition device with higher durability can be realized.
On the other hand, when the relationship between the insulator inner diameter φD _CHM and the ground electrode opening inner diameter φD _ORF (mm) is outside the scope of the present invention, the center electrode and the ground electrode are substantially directly opposed to each other. In other words, the air discharge becomes more dominant than the creeping discharge, which may increase the required voltage. In addition, cations having a large mass are likely to collide with the surface of the ground electrode, and there is a possibility that exhaustion due to cathode sputtering becomes severe.

In the invention of claim 4, the relationship of the following formula 2 is satisfied in the relationship between the inner diameter φD _CHM (mm) of the insulator and the inner diameter φD _ORF (mm) of the ground electrode opening.
D _ORF− D _CHM ≦ 1.2 Equation 2

When the inner diameter φD _ORF of the ground electrode opening is much larger than the inner diameter φD _{CHM of the} discharge space, that is, when φD _ORF− φD _CHM > 1.2, the required voltage V due to the positive voltage application and the back electrode effect V than lowering effect of _BDW, surpasses the effect of increasing the required voltage V _BDW due to increased creeping discharge distance G _PS, not exerted the effects of the present invention, there is a risk that can not be discharged.

In invention of Claim 5, in the thickness _TINS (mm) of the said insulator, the relationship of following formula 3 is satisfy | filled.
1.75 ≦ T _INS Formula 3

According to the invention of claim 5, the insulator has a sufficient withstand voltage against the discharge voltage of the plasma ignition device capable of realizing high ignitability. Therefore, a plasma ignition device with higher durability can be realized.
On the other hand, when the thickness T _INS (mm) of the insulator is out of the range of the present invention, it does not have a sufficient withstand voltage with respect to the applied voltage from the discharge power supply, and the insulation breakdown of the insulator The reliability as an ignition device is significantly reduced.

In the invention of claim 6, the following equation 4 is satisfied in the thickness T _INS (mm) of the insulator.
T _INS ≦ 3.5 Equation 4

According to the sixth aspect of the invention, the effect of reducing the required voltage by the back electrode can be exhibited. Therefore, a highly durable plasma ignition device can be realized.
On the other hand, if the thickness T _INS of the insulator is out of the range of the present invention, the back electrode effect may be reduced, and the required voltage may not be reduced.

In the invention of claim 7, the following equation 5 is satisfied in the inner diameter φD _CHM (mm) of the insulator.
0.7 ≦ D _CHM ... Formula 5

According to the invention of claim 7, sufficient durability performance can be secured.
On the other hand, if the inner diameter φD _CHM of the insulator is outside the scope of the present invention,
Since the center electrode is too thin, it can be easily melted by the gas in an extremely high temperature plasma state, and the durability may be significantly reduced.

In invention of Claim 8, in the internal diameter (phi) _DCHM (mm) of the said insulator, the relationship of following formula 6 is satisfy | _filled .
D _CHM ≦ 2.0 Equation 6

According to the eighth aspect of the present invention, when the gas in the discharge space is in a plasma state, high energy can be injected into the combustion chamber of the combustion engine, and ignition of the non-ignitable combustion engine becomes possible.
On the other hand, when the inner diameter φD _CHM of the insulator is outside the scope of the present invention, the volume of the discharge space is large, and even if the gas in the discharge space is in a plasma state, the pressure in the discharge space is There is a risk of misfiring without being injected from the discharge space.

In the invention of claim 9, the creeping discharge distance G _PS (mm) from the lower end of the center electrode to the exit end of the discharge space opening formed by the insulator and the inner diameter φD _CHM (mm) of the insulator The relationship of the following formula 7 is satisfied.
1.8 ≦ G _PS / D _CHM ... Formula 7

By applying a high voltage from the discharge power supply, the insulation of the discharge space is broken, and when a large current is subsequently supplied from the plasma generation power supply, electrons are emitted along the creeping discharge path, The nearby gas is excited and becomes a high-temperature, high-pressure plasma state. According to the ninth aspect of the present invention, it is possible to realize a plasma ignition device capable of injecting energy required for ignition of a hardly ignitable combustion engine.
On the other hand, in a creeping discharge distance G _PS and the inner diameter [phi] D _CHM of the insulator from the center electrode lower end to the outlet end of the discharge space opening formed by the insulator _(mm), when out of the range of the present invention Since the discharge distance is too short, there is a possibility that less gas is excited between the short discharge paths and the energy necessary for ignition cannot be injected.

In the invention of claim 10, the creeping discharge distance G _PS (mm) from the lower end of the center electrode to the exit end of the discharge space opening formed by the insulator and the inner diameter φD _CHM (mm) of the insulator The relationship of the following formula 8 is satisfied.
G _PS / D _CHM ≦ 2.7 ... Formula 8

According to the invention of claim 10, since the insulation of the discharge space can be broken by an appropriate applied voltage, and an appropriate amount of gas in the vicinity of the creeping discharge path can be brought into a plasma state, so that the ignition of the inflammable combustion engine can be performed. A plasma ignition device capable of injecting necessary energy can be realized.
On the other hand, in a creeping discharge distance G _PS and the inner diameter [phi] D _CHM of the insulator from the center electrode lower end to the outlet end of the discharge space opening formed by the insulator _(mm), when out of the range of the present invention Since the discharge distance is too long, the required voltage exceeds the applied voltage, and there is a possibility that no discharge will occur.

In the invention of claim 11, the insulator is made of a dielectric material whose dielectric constant ε satisfies the relationship of the following formula 9.
ε ≧ 7.0 Equation 9

  According to the eleventh aspect of the invention, since the dielectric constant of the insulator is much higher than the dielectric constant of the discharge space, the electric flux of the electric field formed between the center electrode and the ground electrode is large. The portion passes through the insulator. Therefore, the potential gradient at the lower end of the center electrode is further increased, and a positive corona is likely to be generated. Accordingly, the required voltage can be further reduced, and a highly durable plasma ignition device can be realized while having excellent ignitability in a non-ignitable combustion engine.

  According to a twelfth aspect of the present invention, in order to make the lower end surface of the ground electrode substantially the same as the inner wall surface of the combustion engine combustion chamber, a screw is provided on the outer peripheral surface extending from the upper end portion of the rear electrode to the lower end portion of the ground electrode. Forming part.

According to the invention of claim 12, since the ground electrode heated by the extremely high temperature plasma gas generated in the discharge space quickly dissipates heat to the combustion engine combustion chamber wall through the screw portion, the cathode Consumption due to sputtering is less likely to occur. Therefore, a highly durable plasma ignition device can be realized while having excellent ignitability in a non-ignitable combustion engine.
In addition, since the ground electrode does not protrude into the combustion chamber of the combustion engine, it does not disturb the air flow in the combustion chamber, and hardly ignitable combustion regardless of the type of combustion such as stratified combustion or homogeneous mixed combustion. A highly durable plasma ignition device having excellent ignitability in an engine can be realized.

A first embodiment of the present invention will be described with reference to FIG. As shown in FIG. 1, the plasma ignition device 1 according to this embodiment includes a spark plug 10 and a discharge power supply circuit 20 and a plasma generation power supply circuit 30 as a high-voltage power supply.
The spark plug 10 includes a center electrode 110, an insulator 120, and a ground electrode 130, which will be described later.

  The center electrode 110 is formed in a long axis shape. The front end side of the center electrode 110 is formed in a long axis shape by a conductive material made of a noble metal such as iridium or an iridium alloy, and has a highly conductive and highly conductive material such as a Ni material having excellent corrosion resistance and a copper inside. A central electrode middle shaft 111 containing a conductive metal material is formed, and a central electrode terminal portion 113 is formed on the base end side.

The ground electrode 130 has a substantially annular shape, and is formed with a ground electrode opening 130 that communicates with the inner periphery of the insulator 120 that forms the discharge space 140.
On the base end side of the ground electrode 130, the insulator 120 is housed and held, and a back electrode 132 that faces the center electrode 110 through the insulator 120 is integrally formed.
On the outer peripheral surface extending from the base end side of the back electrode 132 to the tip of the ground electrode 130, a threaded portion 133 for screwing to the lean combustion engine 40 is formed.
Further, a housing part 13 is formed on the base end side of the back electrode 132 so as to cover the middle of the insulator 120, and a hexagonal part 134 for screwing the screw part 133 is formed on the outer periphery of the housing part 13. A caulking portion 135 for caulking and fixing the insulator 120 is formed on the base end side of the housing portion 13.
The ground electrode 130 and the housing part 13 are made of a metal material such as nickel or iron.

The insulator 120 is formed in a substantially cylindrical shape that covers the center electrode 110 and extends below the lower end surface of the center electrode 110, and the inside thereof is discharged by the lower end surface of the center electrode 110 and the ground electrode opening 131. A space 140 is formed, and discharge is possible between the center electrode 110 and the ground electrode 130.
The middle of the insulator 120 is fixed by the housing part 13, and a corrugated insulator head 122 is formed on the base end side exposed from the housing part 13, and the center electrode terminal part 113 exposed from the insulator head 122 is formed. Insulation leakage between the housing portion 13 and the housing portion 13 is prevented.

In the present embodiment, the inner diameter φD _CHM (mm) of the discharge space 140 is formed to be φ1.3 mm, and the inner diameter φD _ORF (mm) of the ground electrode opening 131 is formed to be φ1.5 mm. And the relationship of the following formula 2 is satisfied.
0.1 ≦ D _ORF −D _CHM・ ・ ・ Equation 1
D _ORF −D _CHM ≦ 1.2 Formula 2
Furthermore, the wall thickness T _INS (mm) of the insulator 120 is formed to 2.1 mm, which satisfies the relationship of the following formula 3 and the following formula 4.
1.7 ≦ T _INS ... Formula 3
T _INS ≦ 3.5 Equation 4
More preferably, the thickness T _INS of the insulator 120 is set to 2.1 mm or more. The withstand voltage of the insulator 120 is further increased, and the reliability is improved.
In addition, the inner diameter φD _CHM (mm) of the insulator 120 is formed to be φ1.3 mm and satisfies the relationship of the following formula 5 and the following formula 6.
0.7 ≦ D _CHM ... Formula 5
D _CHM ≦ 2.0 Equation 6
The creeping discharge distance G _PS (mm) from the lower end of the center electrode 110 to the outlet end of the opening of the discharge space 140 formed by the insulator 120 is 2.5 mm, and G _PS / D _CHM is 1 .92, which satisfies the relationship of the following formula 7 and the following formula 8.
G _PS / D _CHM ≧ 1.8 Formula 7
G _PS / D _CHM ≦ 2.7 ... Formula 8

By setting the discharge space 140 inner diameter φD _CHM , the ground electrode opening 131 inner diameter φD _ORF , the insulator 120 thickness T _INS , and the creeping discharge distance G _PS to a specific range satisfying any or all of the expressions 1 to 8. Thus, the plasma ignition device 1 having excellent ignitability and high durability can be realized by efficiently using the generated plasma state gas for ignition while effectively reducing the required voltage.

The insulator 120 is made of high-purity alumina, titania, etc. excellent in heat resistance, mechanical strength, dielectric strength at high temperature, thermal conductivity, etc., and an insulating material head 121 is formed on the base end side, and the center Electrical insulation between the electrode terminal portion 111 and the housing 135 is ensured. Further, the dielectric constant ε _Al2O3 of the insulator 120 is 8.5, which satisfies the relationship of the following formula 9.
ε ≧ 7.0 ... Equation 9

The present invention is applied to a combustion engine 40 that is difficult to ignite, such as homogeneous lean burn, stratified lean burn, supercharged mixed combustion, and the like used in a direct injection gasoline engine for automobiles, for example. In the inflammable combustion engine 40, a combustion chamber 400 is defined by a cylinder head 410, a cylinder block (not shown), and a cylinder piston 420, and an intake valve 412 that opens and closes an intake cylinder 411, an exhaust valve 413 that opens and closes an exhaust cylinder 413, A water cooling jacket 415 or the like is provided.
In the plug hole 416 provided in the cylinder head 410, the spark plug 10 is screwed by a screw portion 133 with the ground electrode opening 131 opened in the combustion chamber 400. In the present embodiment, the discharge space 140 is formed inside the cylinder head 410, and the tip of the ground electrode 130 is substantially flush with the inner wall of the cylinder head 410.
The spark plug 10 is mechanically fixed to the cylinder head 410 of the engine 40, the ground electrode 130 and the cylinder head 410 are electrically grounded, and are also thermally coupled to each other. Heat dissipation from the back electrode 132 to the cylinder head 410 is facilitated.

  The discharge power source 20 includes a first power source 21, an ignition switch 22, an ignition coil 23, an ignition coil drive circuit 24, an electronic control unit (ECU) 25, and a first rectifying element 26. The ignition coil drive circuit 24 includes a switching element such as an IGBT (insulated gate bipolar transistor) whose opening and closing is controlled by the ECU 25, and supplies a voltage from the first power supply 21 to the high voltage spark plug 10 that is boosted by the ignition coil 23. The supply is controlled. In the discharge power source 20, when the ignition switch 22 is closed, a low voltage primary voltage is applied from the first power source 21 to the primary coil 231 of the ignition coil 23, and magnetizing energy is stored in the primary coil 231. The ignition coil drive circuit 24 is controlled to open and close in accordance with a command from the ECU 25 according to the operating state of the lean combustion engine 40.

  The plasma generating power source 30 includes a second power source 31, a resistor 32, a plasma generating capacitor 33, and a second rectifying element 34. In the plasma generating power supply 30, the capacitor 33 is charged by the second power supply 31.

The effect of the plasma ignition device of the present invention will be described with reference to FIGS.
As shown in FIG. 2A, when the primary current of the primary coil 231 is cut off by switching of the ignition coil drive circuit 24 in accordance with the ignition signal, the magnetic field of the ignition coil 23 changes, and the primary coil 231 has several hundreds. A primary voltage of V is generated, and a secondary voltage of several to several tens of kV is generated in the secondary coil 232 by self-induction. A positive voltage is applied to the center electrode 110 by the first rectifying element 26, and when this voltage exceeds the dielectric strength voltage of the discharge space 140, the insulation of the discharge space 140 is destroyed, and the center electrode 110 and the ground electrode 130 Discharge occurs between.
At this time, as shown in FIG. 2B, since the center electrode 110 serves as an anode, a positive corona is generated on the lower end surface of the center electrode 110. The positive corona has a slightly higher voltage than the negative corona generated when the conventional center electrode is used as a cathode, but is extremely excellent in progress. Therefore, the required voltage V _{BDW at} which the insulation of the discharge space 140 is broken and the discharge can be started between the center electrode 110 and the ground electrode 130 becomes low.

Furthermore, the material of the insulator 120 is alumina, and the dielectric constant ε _{Al 2 O 3} is 8.5, which is much higher than the dielectric constant ε _AIR of air of 1.0.
Therefore, most of the electric flux of the electric field formed between the end face of the center electrode 110 and the opening 131 of the ground electrode 130 passes through the inside of the insulator 120. For this reason, the discharge path formed between the center electrode 110 and the ground electrode 130 has a higher resistance than the air discharge that penetrates the discharge space 140 that occurs when the conventional center electrode 110 is used as a cathode. The creeping discharge that forms the discharge path so as to crawl the surface becomes dominant.

In addition, a strong electric field is formed between the base electrode side of the ground electrode 130 and the center electrode 110 as the back electrode 132 via the insulator 120, and the electric flux enters and leaves the inside and outside of the insulator 120. The electric flux concentrates on the lower end surface of the electrode 110, and a region having a high potential gradient is formed locally. Due to such electric field concentration, a positive corona is more likely to be generated on the surface of the center electrode, the dielectric breakdown of the discharge space is facilitated, and the required voltage V _BDW required to break the insulation of the discharge space 140 is lowered. ing.

  When a discharge occurs between the center electrode 110 and the ground electrode 130 due to the application of a high voltage from the discharge power supply 20, the energy stored in the capacitor 33 becomes a large current of about 100 A, for example, and the second rectification. The electric current flows while being rectified by the element 34 and is discharged into the discharge space 140 at once, and high energy of about 100 mJ is given to the gas in the discharge space 140.

At this time, as shown in FIGS. 3A and 3B, the gas in the discharge space 140 is ionized to be in a high-temperature / high-pressure plasma state, and the high volume-wise high temperature of the injection length L _PZ from the ground electrode opening 131. A region is injected.
At this time, since the central electrode 110 is an anode, the cation 50 having a large mass among the gas in a plasma state is electrically repelled, and thus the electron 51 having a small mass is formed on the surface of the central electrode 110. Only collide, and sputtering due to the collision of the positive ions 50 is difficult to occur.
Furthermore, since the ground electrode 130 is screwed to the cylinder head 410 via the screw portion 132, the ground electrode 130 heated by the gas in the plasma state quickly radiates heat to the cylinder head 410, so that it is further durable. Improved.
In addition, since the lower end surface of the ground electrode 131 is substantially flush with the inner wall of the cylinder head 410, a gas in a plasma state can be injected to a desired portion without disturbing the airflow in the combustion chamber 400. . In addition to being extremely hot, this high temperature region can grow into a large volume flame kernel and ignite the air-fuel mixture in the non-ignitable combustion chamber 400.

In addition, an induced current remains in the secondary coil 232 of the ignition coil 23 of the discharge power supply 20 even after high-voltage discharge, and this is released into the discharge space 140 as a very weak current after plasma injection. It has been found. At this time, since the ground electrode 130 is heated to a high temperature, there is a possibility that cathode sputtering may occur due to the collision of the cation 50 ionized by the weak current. The weak current emitted from the ignition coil 23 continues for several hundred μsec to 2 msec due to the self-inductance of the ignition coil, and thus has a great influence on the consumption of the ground electrode 130. It is possible to reduce the required voltage V _BDW necessary to destroy the ignition coil 23, and to reduce the self-inductance of the ignition coil 23. When the self-inductance of the ignition coil 23 is reduced, the discharge time of the weak current after the discharge is shortened, and the cathode sputtering of the ground electrode 130 due to the weak current is less likely to occur. Therefore, it is possible to realize the plasma ignition device 1 having high ignitability and high durability in the hardly ignitable lean combustion engine.

In a first embodiment of the present invention in FIG. 4, the embodiment of fixing the creeping discharge distance G _PS to 3.0 mm, in a comparative example in which a negative high voltage is applied to the conventional center electrode, cylinder pressure The change of the discharge voltage when changing is shown. As shown in the figure, according to the present invention, it has been found that the required voltage V _BDW required for discharge can be kept lower than in the prior _art even when the in-cylinder pressure increases.

FIG 5, 2.5 mm creeping discharge distance _{G PS,} the thickness _{T INS} insulator 120 2.1 mm, an inner diameter [phi] D _CHM of the discharge space 140 is fixed to 1.3 mm, the inner diameter of the ground electrode opening 131 The result of having measured the change of the required voltage _VBDW required for the dielectric breakdown of the discharge space 140 in the cylinder pressure _{2MPa when} changing the _difference of ( _{phi) D ORF} and internal diameter ( _{phi) D CHM} from 0 to 1.6 mm is shown. As shown in this figure, the difference between [phi] D _ORF and [phi] D _CHM the horizontal axis, characteristic of the required voltage _{V BDW} and the vertical axis is the collision under the requested voltage _{V BDW} is lowest in the vicinity of 0.5mm curve It turned out to be a relationship drawing. Since the required voltage V _BDW can be lowered by setting φD _ORF −φD _CHM in the range of 0.1 mm to 1.2 mm, it can be expected to improve durability.

FIG. 6 shows a result of measuring a change in the required voltage V _BDW when the inner diameter φD _CHM of the discharge space 140 is fixed and the thickness T _INS of the insulator 120 is changed from 1.5 mm to 4 mm. As shown in this figure, when the thickness T _INS of the insulator 120 is increased, the required voltage V _BDW gradually increases, and particularly when the thickness T _INS of the insulator 120 is greater than 3.5 mm, the required voltage V _BDW is rapidly increased. Turned out to be high. On the other hand, when the thickness T _INS of the insulator 120 is thinner than 1.75 mm, the withstand voltage of the insulator 120 is lowered, which may cause dielectric breakdown.

Figure 7 is an inside diameter [phi] D _CHM of the discharge space 140 is changed from 0.5 mm to 2.0 mm, were measured creeping discharge distance change of the gap enlargement ratio _{G PS} due to wear of the electrode after the durability test Results are shown. Since the center electrode 110 is covered with the insulator 120, the maximum diameter of the center electrode 110 is substantially the same as the inner diameter φD _CHM of the discharge space 140. As shown in the figure, when [phi] D _CHM is thinner than 0.7 mm, rapidly be greater magnification of creeping discharge distance G _PS by electrode wear it was found. When φD _CHM is larger than 2.0 mm, the pressure at which the gas in the plasma state is injected from the discharge space 140 becomes low, and there is a possibility that the engine cannot be ignited.

Figure 8 is a ratio of the creeping discharge distance _{G PS} discharge spaces 140 inside diameter [phi] D _CHM varied from 1.3 to 3.5, when given the energy of 200 mJ, the injection from the discharge space 140 in the atmosphere The result of having photographed and measured the ejection length _LPZ of the plasma state gas to be measured with a high-speed camera is shown. As shown in the figure, the characteristic in which the ratio of G _PS and φD _CHM is the horizontal axis and the jet length L _PZ is the vertical axis is the _maximum jet length when G _PS / φD _CHM is in the vicinity of 1.8 to 2.7. It has been found that the relationship is such that L _PZ becomes longer and a convex curve is drawn.

With reference to FIG. 9, the problem of the conventional plasma ignition device that falls outside the scope of the present invention in relation to the insulator inner diameter φD _CHM (mm) and the ground electrode opening inner diameter φD _ORF (mm) will be described. As shown in FIG. 5A, when the inner diameter φD _ORF of the ground electrode opening 131a is substantially equal to or smaller than the inner diameter φD _CHM of the discharge space 140a, that is, when φD _ORF− φD _CHM <0.1. In this case, the center electrode 110a and the ground electrode 130a are almost directly opposed to each other, so that the air discharge is more dominant than the creeping discharge, which may increase the required voltage V _BDW . In addition, the cation 50 having a large mass is likely to collide with the surface of the ground electrode 130a, and consumption by cathode sputtering becomes severe. Further, as shown in FIG. 5B, when the inner diameter φD _ORF of the ground electrode opening 131b is much larger than the inner diameter φD _CHM of the discharge space 140b, that is, when φD _ORF− φD _CHM > 1.2. the, than lowering effect of the required voltage V _BDW by applying a positive voltage and a back electrode effect, surpasses the effect of increasing the required voltage V _BDW due to increased creeping discharge distance G _PS, not exerted the effects of the present invention, it can be discharged There is a risk of disappearing.

With reference to FIG. 10, the problem of the conventional plasma ignition device in which the thickness T _INS of the insulator 120 falls outside the scope of the present invention will be described. As shown in this figure (a), when the thickness T _INS of the insulator 120c is too thin, that is, when T _INS <1.75, the plasma state necessary for ignition of the non-ignitable combustion engine is reduced. The withstand voltage of the insulator 120c may be insufficient with respect to the required voltage V _BDW required when the discharge space 140c that only injects the gas is formed, and there is a possibility that dielectric breakdown may occur through the insulator 120c. The reliability of the plasma ignition device is significantly reduced. Further, as shown in FIG. 4B, when the thickness T _INS of the insulator 120d is too thick, that is, when T _INS > 3.5, the distance between the center electrode 110 and the back electrode 132 is large. Therefore, the back electrode effect is reduced, and there is a possibility that the required voltage V _BDW cannot be reduced. Therefore, the reliability of the plasma ignition device is significantly reduced.

FIG. 11 illustrates a problem of a conventional plasma ignition device in which the inner diameter φD _CHM of the discharge space 140 is outside the scope of the present invention. As shown in FIG. 5A, when the center electrode 110e is thin and the inner diameter φD _CHM of the discharge space 140e is too small, that is, when φD _CHM <0.7, the center electrode 110e is too thin. Even if the generation of sputtering on the surface of the center electrode 110 is suppressed by being heated to an extremely high temperature by the gas in a high-temperature plasma state and making the polarity of the center electrode positive, the surface of the center electrode 110 is easily May be melted and durability may be significantly reduced. Further, as shown in FIG. 5B, electrons are emitted in the vicinity of the creeping discharge path, and in the discharge space 140, the gas in the vicinity of the creeping discharge path, that is, in the vicinity of the inner peripheral wall surface of the insulator 120 is in a plasma state. Therefore, when the center electrode 110f is thick and the inner diameter φD _CHM of the discharge space 140f is too large, that is, when φD _CHM > 2.0, the discharge space 140f becomes too large and is located away from the creeping discharge path. There is a large amount of gas that is not in a plasma state, and the gas in the discharge space 140 does not reach a pressure sufficient to be injected into the combustion chamber 400, which may lead to misfire.

12, the surface discharge distance G _PS from the center electrode 110 lower end to the outlet end of the discharge space opening formed by the insulator, the problem of the conventional plasma ignition system departing from the scope of the present invention described To do. As shown in FIG. 5A, when the creeping discharge distance G _PS is shorter than the inner diameter φD _CHM of the discharge space 140, that is, when G _PS / D _CHM <1.8, the discharge distance is too short. Therefore, the gas excited between the discharge paths is reduced, and there is a possibility that the energy required for ignition of the combustion engine cannot be injected. Further, as shown in FIG. 4B, when the creeping discharge distance G _PS is longer than the inner diameter φD _CHM of the discharge space 140, that is, when G _PS / D _CHM > 2.7, the discharge distance is Since it is too long, there is a possibility that the required voltage V _BDW exceeds the applied voltage and does not lead to discharge.

  The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the spirit of the present invention. For example, in the above embodiment, the discharge power source and the plasma generation power source are supplied by different power sources. However, a single power source may be used via a Dc-Dc converter or the like.

1 is an overall view showing a configuration of a plasma ignition device according to a first embodiment of the present invention. The effect in the 1st Embodiment of this invention is shown, (a) is a characteristic view which shows a voltage and an electric current change, (b) is principal part sectional drawing which shows the state at the time of discharge. The effect in the 1st Embodiment of this invention is shown, (b) is sectional drawing which shows the state of the plasma-type ignition device which shows the state at the time of plasma generation, (c) is the principal part which shows the state at the time of plasma generation Sectional drawing. The characteristic view which shows the effect of this invention with a comparative example. FIG. 4 is a characteristic diagram showing a change in required voltage due to a difference between the inner diameter of the ground electrode opening and the inner diameter of the discharge space. FIG. 4 is a characteristic diagram showing a change in required voltage due to the insulator thickness. FIG. 6 is a characteristic diagram showing a change in gap enlargement ratio due to the inner diameter of the discharge space. FIG. 4 is a characteristic diagram showing a change in plasma ejection length due to a ratio between a creeping discharge distance and a discharge space inner diameter. (A), (b) is principal part sectional drawing which shows the problem resulting from the ground electrode opening part internal diameter of the conventional plasma ignition apparatus. (A), (b) is principal part sectional drawing which shows the problem resulting from the insulator thickness of the conventional plasma ignition apparatus. (A), (b) is principal part sectional drawing which shows the problem resulting from the discharge space internal diameter of the conventional plasma ignition apparatus. (A), (b) is principal part sectional drawing which shows the problem resulting from the creeping discharge distance of the conventional plasma ignition apparatus. Sectional drawing which shows the principal part which shows the problem of the conventional plasma ignition apparatus. The whole figure which shows the structure of the conventional plasma ignition apparatus.

Explanation of symbols

10 Plasma Spark Plug 110 Center Electrode 120 Insulator 130 Ground Electrode 131 Opening 140 Discharge Space 20 Discharge Power Supply 30 Plasma Generation Power Supply 40 Combustion Engine φD _CHM Discharge Space Inner Diameter φD _ORF Ground Electrode Opening Inner Diameter T _INS Insulator Thickness G _PS creeping discharge distance

Claims (12)

A spark plug that is mounted on a combustion engine and divides a discharge space by a center electrode, an insulator, and a ground electrode, a discharge power source that applies a high voltage between the center electrode and the ground electrode, and the discharge space A power source for generating plasma that emits a large current,
The combustion engine breaks the insulation of the discharge space by applying a high voltage from the discharge power source, and changes the gas in the discharge space to a high temperature, high pressure plasma state by releasing a large current from the plasma generating power source. In a plasma ignition device for injecting into the combustion chamber and igniting the engine,
The center electrode is formed in an axial shape,
The insulator is formed in a substantially cylindrical shape that extends in the axial direction from the lower end surface of the center electrode while covering the outside of the center electrode, and the lower end of the insulator opens.
The ground electrode is provided outside the insulator and is formed in a substantially annular shape having an opening communicating with the opening at the lower end of the insulator.
A plasma ignition device characterized in that application of the positive high voltage and supply of the large current are performed with the central electrode as the anode side and the ground electrode as the cathode side.   A housing portion is formed by extending the ground electrode in the direction toward the opening of the anti-ground electrode, and a portion facing the center electrode of the housing portion via the insulator serves as a back electrode for the center electrode. The plasma ignition device according to claim 1. 3. The plasma according to claim 1, wherein a relationship of the following formula 1 is satisfied in a relationship between an inner diameter φD _CHM (mm) of the insulator and an inner diameter φD _ORF (mm) of the ground electrode opening. Type ignition device.
0.1 ≦ D _ORF −D _CHM・ ・ ・ Equation 1 4. The relationship between the inner diameter φD _CHM (mm) of the insulator and the inner diameter φD _ORF (mm) of the ground electrode opening satisfies the relationship of the following expression (2): 4. The plasma ignition device according to item.
D _ORF −D _CHM ≦ 1.2 Formula 2 _5. The plasma ignition device according to claim 1, wherein a thickness T _INS (mm) of the insulator satisfies a relationship of the following expression (3).
1.75 ≦ T _INS Formula 3 The plasma ignition device according to any one of claims 1 to 5, wherein a thickness T _INS (mm) of the insulator satisfies a relationship of the following expression (4).
T _INS ≦ 3.5 Equation 4 7. The plasma ignition device according to claim 1, wherein an inner diameter φD _CHM (mm) of the insulator satisfies a relationship of the following formula (5).
0.7 ≦ D _CHM ... Formula 5 8. The plasma ignition device according to claim 1, wherein an inner diameter φD _CHM (mm) of the insulator satisfies a relationship of the following formula (6).
D _CHM ≦ 2.0 Equation 6 In the creeping discharge distance G _PS (mm) from the lower end of the center electrode to the exit end of the discharge space opening formed by the insulator and the inner diameter φD _CHM (mm) of the insulator, The plasma ignition device according to any one of claims 1 to 8, wherein the plasma ignition device is satisfied.
1.8 ≦ G _PS / D _CHM ... Formula 7 In the creeping discharge distance G _PS (mm) from the lower end of the center electrode to the exit end of the discharge space opening formed by the insulator and the inner diameter φD _CHM (mm) of the insulator, The plasma ignition device according to any one of claims 1 to 9, wherein the plasma ignition device is satisfied.
G _PS / D _CHM ≦ 2.7 ... Formula 8 The plasma ignition device according to any one of claims 1 to 10, wherein the insulator is made of a dielectric whose dielectric constant ε satisfies the relationship of the following formula (9).
ε ≧ 7.0 ... Formula 9   In order to make the lower end surface of the ground electrode substantially the same as the inner wall surface of the combustion engine combustion chamber, a screw portion is formed on the outer peripheral surface extending from the upper end portion of the back electrode to the lower end portion of the ground electrode. The plasma ignition device according to any one of claims 1 to 11.

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