JP2010121482A - Ignition device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ignition device showing excellent ignitability even for a lean combustion engine, or ignition retardant engine in light load combustion or the like, and having both of excellent durability and easy manufacturing properties. <P>SOLUTION: This ignition device 1 is installed on an internal combustion engine 60 and ignites the internal combustion engine 60. The ignition device 1 includes at least a discharge part 11 comprising a discharge electrode 110 and a ground electrode 130 opposing to the discharge electrode 110 through an insulator 120 as a discharge means as an discharge means for discharging in a combustion chamber 600, and a laser oscillation circuit 40 and a laser collection part 15 as a laser oscillation means oscillating laser beam, and collects laser beam on discharge route generated by the discharge means. Plasma generated by discharge efficiently absorbs laser beam, further generation of plasma is induced, and flame core is generated with low energy. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an ignition device that is mounted on an internal combustion engine and ignites the internal combustion engine.

  In an internal combustion engine such as an automobile engine, in order to reduce environmental load substances contained in combustion exhaust gas and further improve fuel efficiency, fuel dilution, high supercharging, and the like have been attempted. In general, a lean combustion engine and a high supercharged air-fuel mixture combustion engine are difficult to ignite, and therefore an ignition device with better ignitability is desired.

As an ignition device capable of exhibiting excellent ignitability even in such a non-ignitable engine, a high-energy laser beam is condensed in an engine combustion chamber by a condensing lens facing the combustion chamber to generate a flame nucleus, and an air-fuel mixture Various proposals have been made on laser ignition devices that perform the ignition of (see, for example, Patent Document 1).
JP 2005-42591 A

However, in order to cause the laser break to focus the laser beam in the low-density air-fuel mixture and generate flame nuclei, for example, high energy such as several tens of mJ is supplied and several to several hundred GW It is said that the light needs to be condensed to a high energy density of about / cm ² . For this reason, there exists a possibility that an apparatus may enlarge, or the condensing lens which condenses a laser beam may be damaged.
In order to use such laser light for ignition of an internal combustion engine, high accuracy, performance, and durability are required for a condenser lens used in a laser oscillator. Further, there is a high demand for laser quality represented by M ² value indicating the condensing property of the laser beam output from the laser oscillator. Using such a high-quality laser oscillator may increase the manufacturing cost of the ignition device.
Also, since the laser beam is condensed in the space, if there is a small amount of gas that absorbs energy around the condensing point, such as during lean combustion, the collected energy is collected without being absorbed by the gas. There is also a possibility that the energy that has passed through the light spot is dissipated in the engine combustion chamber and the input energy is wasted.

  Therefore, in view of such circumstances, the present invention shows excellent ignitability even in a hardly ignitable engine such as a lean combustion engine or low load combustion, is easy to downsize, and has excellent durability and ease of manufacture. The purpose of the present invention is to provide an ignition device.

  According to the first aspect of the present invention, there is provided an ignition device that is mounted on an internal combustion engine and ignites the internal combustion engine, and includes at least discharge means that discharges in the combustion chamber of the internal combustion engine, and laser oscillation means that oscillates laser light. The laser oscillating unit includes a condensing unit that condenses the laser beam on the discharge path of the discharging unit.

When ignition is performed by condensing laser light into the space of a conventional internal combustion engine combustion chamber, if the gas density where the condensing point exists is low, the energy of the laser light is not absorbed and passes through the condensing point. However, according to the invention of claim 1, the laser oscillation means is provided by the presence of plasma having better laser light absorption than ordinary gas. The energy of the laser beam oscillated from is absorbed by the plasma existing around the condensing point, prompting the generation of further plasma, and the growth of the flame kernel proceeds promptly.
Therefore, even if the energy density is lower than the conventional one, the energy of the laser beam condensed in the combustion chamber is effectively utilized for the growth of the flame kernel, and the internal combustion engine can be ignited with certainty. In addition, since the energy required for ignition can be reduced, the size of the discharge means and the laser oscillation means can be reduced.
Further, since the energy of the oscillated laser beam is small, the laser oscillating unit and the condensing unit receive less damage from the oscillated laser beam, and the durability of the laser oscillating unit and the condensing unit is improved. . In addition, since it is possible to ignite at a lower energy density than before, it is possible to reduce the demand for laser quality such as M ² value. Therefore, the discharge unit and the laser beam oscillation unit can be easily manufactured, and the manufacturing cost can be reduced.

  Specifically, as in the invention of claim 2, the discharge means includes a discharge electrode, a ground electrode opposed to the discharge electrode via an insulator, a power supply, and a voltage of the power supply boosted to a high voltage. And a high voltage application circuit applied between the discharge electrode and the ground electrode.

According to the invention of claim 2, according to the invention, the plasma generated by the discharge efficiently absorbs the high-density laser energy condensed at the condensing point of the laser beam, and the rapid generation of the flame kernel is achieved. An ignition device that promotes growth and exhibits excellent ignitability can be realized.
Further, instead of directly igniting the air-fuel mixture in the combustion chamber by spark discharge as in the conventional ignition device using a spark plug that performs ignition by arc discharge, the discharge means according to the present invention concentrates on the discharge path. In addition, since the minimum discharge necessary for generating plasma for improving the energy absorption of the laser beam is performed, the necessary power source capacity can be reduced. Therefore, the size of the power source and the high voltage application circuit can be reduced.

  Further, the laser oscillation means is constituted by a power source and a laser oscillation circuit that oscillates by converting electric energy from the power source into laser light.

  According to the invention of claim 3, according to the invention, the plasma generated by the discharge efficiently absorbs the high-density laser energy condensed at the condensing point of the laser beam, and the rapid generation of the flame kernel is achieved. An ignition device that promotes growth and exhibits excellent ignitability can be realized.

  According to a fourth aspect of the invention, there is provided an electronic control device that controls the discharge means and the laser oscillation means in accordance with an operating condition of the internal combustion engine, and the electronic control device is configured to emit laser light from the laser oscillation means. Prior to oscillation, discharge from the discharge means is performed, and control is performed to oscillate laser light within a predetermined period after discharge.

  According to the invention of claim 4, since high-energy laser light can be condensed at a high density with respect to the state in which plasma is generated in advance by the discharge means, flame nuclei are quickly generated and grown, Even when the internal combustion engine is in a difficult-to-ignite operation state, ignition can be reliably performed. Therefore, an ignition device that exhibits excellent ignitability can be realized.

The ignition device of the present invention is an ignition device used for ignition of an automobile engine or the like, and a lean combustion engine with a high air-fuel ratio, a lean combustion with a low load, or a high air-fuel ratio and compression ratio by a supercharger. The ignition device exhibits good ignitability even in a non-ignitable engine such as a high-supercharged mixed combustion engine.
Prior to laser oscillation, the ignition device of the present invention generates plasma by discharge in the vicinity of the laser condensing point, increases the absorption efficiency of laser energy, reduces the energy required for laser break, and suppresses lens damage. At the same time, the greatest feature is that it is possible to reduce the cost by reducing the requirements for lens performance and laser quality.

  With reference to FIG. 1, the outline | summary of the ignition device 1 in the 1st embodiment of this invention is demonstrated. The ignition device 1 is attached to the internal combustion engine 60, and is connected to the ignition plug 10, which is a main part of the present invention, the power source 20, and the power source 20, and the voltage of the power source 20 is boosted to a high voltage and applied to the ignition plug 10. The high voltage application circuit 30 is connected to the power source 20, the laser oscillation circuit 30 that converts electric energy from the power source 20 into laser light and oscillates in the ignition plug 10, and the high voltage application circuit 20 according to the operating conditions of the internal combustion engine 60. And an electronic control unit ECU 50 that controls the laser oscillation circuit 30.

The spark plug 10 includes a discharge portion 11, a laser oscillation portion 15, and a housing portion 14 that houses these and is fixed to the internal combustion engine 60.
The discharge part 11 includes a discharge electrode terminal part 112 connected to the high voltage application circuit 30, a substantially long discharge electrode middle shaft part 111 connected to the discharge electrode terminal part 112, a discharge electrode 110 connected to the discharge electrode middle shaft part 111, A substantially cylindrical insulator 120 that covers the discharge electrode middle shaft portion 111 and a part of the discharge electrode 110 and insulates the discharge electrode middle shaft portion 111 from the discharge electrode 110 and the housing portion 14, and extends to the tip of the housing portion 14. And a ground electrode 130 provided.
The discharge electrode 110 and the ground electrode 130 are opposed to each other with a predetermined discharge distance. The ground electrode 130 is in a grounded state with the cylinder head 61 of the internal combustion engine 60 via the housing portion 14.
In the present embodiment, the case where a pair of the discharge electrode 110 and the ground electrode 130 is provided is shown, but a plurality of pairs of the discharge electrode 110 and the ground electrode 130 may be provided.

The laser oscillation unit 15 is connected to the laser beam transmission unit 150 such as an optical fiber that transmits the laser beam oscillated from the laser oscillation circuit 40 and the laser beam transmission unit 150, and transmits the laser beam to the axis of the laser oscillation unit 15. The energy of the laser beam oscillated in parallel to the axis of the laser oscillation unit 15 via the group lens 151 and the group lens 151 formed by combining a plurality of lenses to be parallel light is stored in the engine combustion chamber 600. A condensing lens 152 that condenses light at the condensing point FP, a protective cover 153 that protects the condensing lens 152, and a substantially cylindrical lens housing portion 160 that houses them, together with the discharge portion 11, the housing portion 14. It is stored inside.
Note that a diffraction grating may be used instead of the condenser lens 152.

  The high voltage application circuit 30 includes, for example, an ignition coil that boosts the voltage of the power supply voltage 20 to a high voltage and an igniter that includes a switching element that opens and closes the ignition coil.

As the laser oscillation circuit 40, a known laser oscillation circuit can be appropriately employed. For example, the laser oscillation circuit 40 includes a laser medium such as a semiconductor laser serving as a laser oscillation source, an excitation source that gives energy to the laser medium, and a laser amplification unit that amplifies the oscillated laser light.
As the laser medium, a solid-state laser can be used in addition to a semiconductor laser.
The laser amplifying unit includes a shutter element (Q switch), a reflecting mirror, and an output mirror. Both the solid-state laser and the shutter element are excited by laser light oscillated from the pumping semiconductor laser, When the energy exceeds a certain threshold determined by the physical properties of the shutter element itself, the shutter opens and resonates and is amplified every time the laser beam reciprocates between the reflecting mirror and the output mirror. High density laser light can be extracted.

In the internal combustion engine 60, a combustion chamber 600 is defined by a cylinder head 61, a substantially cylindrical cylinder 63, and a piston 64 that freely moves up and down in the cylinder 63. The cylinder head 61 is provided with an intake cylinder 610 and an exhaust cylinder 620, which are opened and closed by an intake valve 611 and an exhaust valve 621, respectively. The air introduced from the intake cylinder 610 into the combustion chamber 600 and the fuel supplied into the fuel chamber 600 by a fuel injection device (not shown) are mixed, compressed by the piston 64, and at a predetermined crank angle, When a laser break with extremely high energy density is generated in the combustion chamber 600 by the ignition device 1, combustion / explosion of the air-fuel mixture is induced by the flame kernel, and the pressure P _CYL in the combustion chamber 600 rises at once, and the piston is caused by the pressure. 64 is pushed down, and the power of the internal combustion engine 60 is obtained.

With reference to FIG. 2, the effect of the ignition device 1 in the 1st Embodiment of this invention is demonstrated. FIG. 5A is a time chart schematically showing changes in the discharge voltage V _DC , the discharge current I _DC , the laser oscillation energy E _LZR , and the in-cylinder pressure P _CYL during ignition of the ignition device 1 in the present embodiment. FIG. 4B is a cross-sectional view of the main part schematically showing a state where arc discharge _VARRC and laser oscillation are generated.
As shown in FIG. 2 (a), when an ignition signal is transmitted from the ECU 50 in accordance with the operating condition of the internal combustion engine 60, a high voltage is applied from the high voltage application circuit 20 to the discharge electrode 110 of the spark plug 10, and the discharge is performed. When the voltage V _DC (kV) reaches a predetermined required voltage exceeding the withstand voltage between the discharge electrode 110 and the ground electrode 130, the insulation is broken, and as shown in FIG. 2 (b), the discharge electrode 110 and the ground electrode Arc discharge _VARRC occurs between the first electrode 130 and the plasma region A _{PLZ in} a very small region.
Arcing _{V ARC} continues about several tens μs The formed discharge path from the discharge current _{I DC} flows 1μs between the discharge electrode 110 and the ground electrode 130.

During this time, when laser light is oscillated from the laser oscillation circuit 40 in accordance with the oscillation command from the ECU 50, the energy E _LZR oscillated instantaneously from the laser oscillation circuit 40 is collected in an extremely short time of about 0.1 ns to 20 ns. Concentrate on the light spot FP. The condensing point FP is located on a discharge path formed between the discharge electrode 110 and the ground electrode 130.
Incidentally, the spot diameter of the focal point FP is about Fai10myuemu, there several tens μm about the discharge path φ of the arc discharge V _ARC, the size of the generated plasma region A _PLZ the range of about ambient φ1mm discharge path Therefore, even if the discharge position varies, the condensing point FP is always located on the discharge path.
The gas in the plasma state absorbs laser energy better than normal air, and the laser beam with extremely high energy density collected at the condensing point FP is efficiently absorbed by the gas in the plasma state. A laser break occurs in which very high energy flame nuclei are generated.
In the present invention, the discharge is avoided between the edge of the discharge electrode 110 and the housing portion 14 and the discharge is surely generated between the discharge electrode 110 and the ground electrode 130 as shown in FIG. As shown, the distance D _GP from the edge of the discharge electrode 110 to the edge of the ground electrode 130 is preferably set shorter than the distance _DH between the discharge electrode 110 and the edge of the housing portion 14.

The effects of the present invention will be described with reference to FIG.
In the conventional laser ignition device, since the laser irradiation target is a gas, if there is not enough gas to absorb the laser energy at the condensing point FP, the laser break does not occur and the laser light is collected. There is a possibility that the light passes through the light spot FP and is dissipated in the combustion chamber 600 and is wasted.
Further, the energy E _BRK 2 necessary for laser break when laser oscillation is performed without conventional discharge shown as Comparative Example 1 is used, and the ignition device 1 of the present invention shown as Example 1 is used prior to laser oscillation. If the energy E _BRK 1 required for laser break in the case of discharge is set to be equal to the conventional energy, the difference (ΔE _BRK = E _BRK 2−E _BRK 1) is the flame after the laser break. It can be used for nuclear growth.
Therefore, according to the present invention, plasma is generated in the vicinity of the condensing point FP, so that laser energy can be easily absorbed and flame nuclei due to laser break can be reliably generated. In addition, since a part of the incident energy can be used for the growth of the flame kernel after the laser break, the flame kernel grows quickly and the mixture is easily ignited.

According to the inventors' diligent tests, an energy density of about 4.6 GW / cm ² was required when a laser break was generated only by conventional laser oscillation. For example, it has been found that a laser break can be generated at an energy density of about 3.5 GW / cm ^{2, which is} about 24% lower than in the past.
Accordingly, it is possible to reduce the requirements for the laser quality such as the lens accuracy, performance, durability, and M ² value used in the laser oscillation circuit 40, and it is possible to reduce the cost.
Further, in the conventional ignition device using only laser oscillation, it is necessary to use an expensive aspherical lens as the condensing lens in order to reduce the condensing diameter of the condensing point FP as much as possible to increase the energy density. In the ignition device 1 of the invention, the plasma generated in the vicinity of the condensing point FP can be efficiently absorbed even at a low energy density. Therefore, it is possible to use a cheaper spherical lens.
Furthermore, since the laser intensity can be reduced, the coating on the lens surface of the condenser lens 152 is omitted, or when a protective cover 153 is provided, a lens having low heat resistance is used as the condenser lens 152, It is expected that laser beam parallelism and low intensity distribution performance can be used.

In particular, at the time of lean combustion or low load combustion, the gas density around the condensing point FP is low, and the absorption of the laser beam is further deteriorated. Therefore, according to the ignition device 1 of the present invention, even in such an inflammable internal combustion engine, the gas around the condensing point FP is used as the plasma region A _PLZ to improve the laser energy absorbability, thereby reliably igniting. can do.

In addition, in a conventional ignition device using a spark plug, a flame kernel is generated by arc discharge generated between the center electrode and the ground electrode to ignite the mixture, so that the discharge path is as thick as possible and the arc has a long life. Discharge is required.
For this reason, a conventional ignition device using a spark plug requires a high energy of about 30 mJ, and a coil having a large inductance is used as an ignition coil for boosting the applied voltage in order to lengthen the discharge time.
On the other hand, in the high voltage circuit 30 and the discharge unit 11 used in the ignition device of the present invention, the air-fuel mixture is not directly ignited by the arc discharge _VARC , but is oscillated from the laser oscillation unit 15 and collected in the combustion chamber 600. Since it is only necessary to generate a plasma in the vicinity of the condensing point FP to absorb the laser beam to be emitted, it is not necessary to supply high energy as in the case of ignition by a conventional spark plug.
Therefore, when the high voltage application circuit 30 is formed by a circuit using, for example, an ignition coil, a coil having a small inductance can be used, and thus the size of the high voltage application circuit 30 can be reduced.
Furthermore, since the high voltage applied to the discharge unit 11 also has a small amount of energy, consumption due to sputtering of the discharge electrode 110 and the ground electrode 130 during discharge is suppressed, and a highly durable ignition device 1 can be realized.

With reference to FIG. 4, the ignition device 1a in the 2nd Embodiment of this invention is demonstrated. In addition, about the part similar to the said embodiment, since the same code | symbol was attached | subjected, description is abbreviate | omitted and only the characteristic part in this embodiment is demonstrated.
In the present embodiment, the laser oscillation unit 15a uses a group lens 151a and a condensing lens 152a having a long condensing distance, and further, a mirror surface 641 is provided on the top surface of the piston 64a, and the laser light reflected by the mirror surface 641 is a discharge electrode. In this configuration, light is condensed at a light condensing point FP located between 110 and the ground electrode 130.
Even in such a configuration, a high voltage is applied between the discharge electrode 110 and the ground electrode 130 prior to laser oscillation as in the above embodiment, and an arc discharge is generated between the discharge electrode 110 and the ground electrode 130. V _ARC is generated, gas in the vicinity of the condensing point FP is turned into plasma, and laser oscillation is performed in a state where the laser energy is easily absorbed, so that a laser break can be generated with lower energy.
The mirror surface 641 may be formed in a flat shape as shown in the figure, or may be formed in a concave shape by denting the top surface of the piston 64a. In this case, the position of the condensing point FP is closer to the mirror surface 641.

An ignition device 1b according to a third embodiment of the present invention will be described with reference to FIG. In the above embodiment, the case where the discharge part and the laser oscillation part are integrally housed in the housing part has been shown. However, in this embodiment, the discharge part 11b and the laser oscillation part 15b are provided separately. Different points.
When the discharge part and the laser oscillation part are provided separately, the discharge electrode needs to be formed shorter than the outer diameter of the discharge part in order to mount the discharge part on the cylinder head. For this reason, if the central axis of the discharge part and the central axis of the laser oscillation part are arranged parallel to each other, the distance between the discharge electrode and the ground electrode becomes longer, and the ground electrode and the equipotential housing part or cylinder head There is a risk that arc discharge will occur between the discharge electrodes and the gas in the vicinity of the focal point will not be converted into plasma.
Therefore, in the present embodiment, the discharge electrode 110b is discharged so that the distance between the tip of the discharge electrode 110b and the ground electrode 130b is as short as possible and the condensing point FP is positioned on the discharge path. It is inclined and bent toward the combustion chamber 600 side so as to be an obtuse angle rather than a right angle with respect to the axis of the portion 11b.
Even in such a configuration, a high voltage is applied between the discharge electrode 110 and the ground electrode 130 prior to laser oscillation as in the above embodiment, and an arc discharge V _ARC is applied between the discharge electrode 110 and the ground electrode 130. Is generated, the gas in the vicinity of the condensing point FP is turned into plasma, and laser oscillation is performed in a state where the laser energy is easily absorbed, and a laser break can be generated with lower energy.

The present invention is not limited to the above embodiment. For example, in the above embodiment, a configuration in which a protective cover is provided to protect the condenser lens or the diffraction grating is shown. When an optical lens or a diffraction grating is used, a configuration without a protective cover may be employed.
Further, the ignition device of the present invention does not limit the type of fuel injected to the internal combustion engine to be applied and the fuel injection method.

The block diagram which shows the outline | summary of the ignition device in the 1st Embodiment of this invention. The operation | movement of the ignition device in the 1st Embodiment of this invention is shown, (a) is a time chart figure, (b) is principal part sectional drawing which shows the mode at the time of laser oscillation typically. The characteristic view which shows the effect of this invention with a comparative example. The principal part sectional drawing which shows the outline | summary of the ignition device in the 2nd Embodiment of this invention. The principal part sectional drawing which shows the outline | summary of the ignition device in the 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ignition device 10 Spark plug 11 Discharge part 110 Discharge electrode 111 Discharge electrode center shaft part 112 Discharge electrode terminal part 120 Insulator 130 Ground electrode 140 Housing 141 Housing hexagon part 142 Housing screw part 15 Laser oscillation part 150 Laser light transmission means 151 Group lens 152 Condensing Lens 153 Protective Cover 160 Lens Housing 20 Power Supply 30 High Voltage Application Circuit 40 Laser Oscillation Circuit 50 Electronic Control Unit (ECU)
60 Internal combustion engine 600 Combustion chamber 61 Cylinder head 610 Intake cylinder 611 Intake valve 620 Exhaust cylinder 621 Exhaust valve 63 Cylinder 64 Piston

Claims (4)

An ignition device mounted on an internal combustion engine for igniting the internal combustion engine,
At least discharge means for discharging in the combustion chamber of the internal combustion engine;
Laser oscillation means for oscillating laser light,
The ignition device according to claim 1, wherein the laser oscillating means includes a condensing means for condensing the laser light on a discharge path of the discharging means.   The discharge means includes a discharge electrode, a ground electrode opposed to the discharge electrode through an insulator, a power source, and a voltage of the power source is increased to a high voltage and applied between the discharge electrode and the ground electrode. The ignition device according to claim 1, further comprising a high voltage application circuit.   3. The ignition device according to claim 1, wherein the laser oscillation means includes a power source and a laser oscillation circuit that oscillates by converting electric energy from the power source into laser light. Comprising an electronic control device for controlling the discharge means and the laser oscillation means in accordance with the operating status of the internal combustion engine;
The electronic control unit performs discharge from the discharge unit prior to oscillation of the laser beam from the laser oscillation unit, and performs control to oscillate the laser beam within a predetermined period after discharge. The ignition device according to any one of claims 1 to 3.

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