JP2009194076A - Laser ignition device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser ignition device that allows desired pulse energy adjustment without manipulation of the inside of a resonator. <P>SOLUTION: The laser ignition device is required for ignition of the fuel stored in the combustion chamber of an internal combustion engine. This laser ignition device is characterized by an excitation optical system for condensing the excited light to an amplifying medium, a resonator system including the amplifying medium and a saturable absorber, an output optical system for condensing the laser beam output from the resonator system into the combustion chamber, and an incident light diameter adjusting means for changing the diameter of incident light to the amplifying medium of the excited light. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a laser ignition device, and more particularly to a laser ignition device capable of adjusting pulse energy as desired without operating the inside of a resonator.

  A spark plug is generally used as an ignition device for an internal combustion engine. A spark plug is a device that ignites an air-fuel mixture by applying a high voltage between electrodes to generate a discharge between the electrodes. Since the spark plug has a relatively simple structure and has practically sufficient durability, it has long been used as an ignition device in an internal combustion engine.

  In recent years, higher compression ratios have been desired for internal combustion engines in order to reduce fuel consumption and harmful emissions. In general, the lower the pressure, the easier the discharge, so a high compression ratio is a disadvantageous condition for ignition by a spark plug. In order to discharge reliably even at a high compression ratio, it is necessary to change the electrode shape and increase the applied voltage. However, these may cause a decrease in durability, a decrease in ignitability, a dielectric breakdown, or an increase in cost.

  Further, ignition position control and ignition from a plurality of locations are being studied in order to end combustion in a shorter time and at a lower temperature. However, since the spark plug is ignited in the vicinity of the inner wall surface of the combustion chamber, it is disadvantageous for the requirement of controlling the ignition point.

  Laser ignition devices have attracted attention as ignition means that meet these requirements. The laser ignition device condenses a pulse laser with a lens, and ignites the plasma generated at the condensing point as a starting point. In contrast to the spark plug, the laser ignition device improves the ignitability as the compression ratio increases. Further, by adjusting the condensing point position, there is an advantage that ignition from a single or a plurality of arbitrary ignition points in the combustion chamber is possible. In addition, there are advantages such as no generation of electrical noise, no short circuit due to attached dirt, and no protrusions that obstruct flame propagation in the combustion chamber.

  Although the concept of laser ignition devices has been around for a long time, many problems remain to be put into practical use. However, due to the ever-increasing demand for advanced combustion control of internal combustion engines and the high output and low price of laser diodes, diode-pumped solid-state lasers can be made smaller and cheaper than before. In recent years, it has been in the spotlight again.

  In order to ignite the air-fuel mixture with a laser, it is necessary to generate a pulse having a very large energy of several mJ to several tens of mJ and a pulse width of about ns. Among several methods for generating such a giant pulse, it is possible to generate a giant pulse relatively easily and to operate with relatively high energy efficiency. A pumped solid state laser is expected.

  By the way, the pulse energy required for igniting the fuel in the internal combustion engine varies depending on the operating state of the internal combustion engine. It is preferable that the laser ignition device attached to the internal combustion engine can oscillate a pulse laser having a desired pulse energy according to the operating condition, since power consumption can be suppressed. In passive Q switching, the pulse energy is known to be determined by the initial transmittance of the saturable absorber, etc., so that the initial transmittance differs from the initial saturable absorber in order to change the pulse energy. A method of exchanging with a saturable absorber is conceivable.

  Further, in claim 1 of Patent Document 1, “a saturable absorber functioning as a Q switch is disposed on the optical path of light in a laser resonator in which a laser medium is disposed, and the laser resonator is disposed in the laser resonator. The saturable absorber is moved relative to the optical path of the light to change an initial transmittance of the saturable absorber when the light passes through the saturable absorber. According to such a pulse width variable laser oscillation method, “the light in the saturable absorber of light passing through the saturable absorber disposed in the laser resonator” is described. The initial transmittance of the saturable absorber can be changed in accordance with the change in the optical path length at the time, and thus the light transmittance in the saturable absorber is changed and the timing of the shutter operation is changed. For this reason, the pulse width of the pulsed laser beam to be output which could not be realized without replacing the saturable absorber arranged as the Q switch element in the laser resonator until now or The stepwise change can be realized by a single saturable absorber arranged as a Q-switch element in the laser resonator. ”(See paragraph number 0014 of Patent Document 1) Yes.

  However, replacement of an optical component such as a saturable absorber and driving of the optical component inside the resonator are not preferable for a laser oscillation device that requires high precision. Moreover, producing a saturable absorber having a special shape as described in Patent Document 1 or providing a means for driving it with high accuracy complicates the apparatus configuration and leads to an increase in cost.

JP 2006-179724 A

  The subject of this invention is providing the laser ignition device which can adjust pulse energy as desired, without operating the inside of a resonator.

As means for solving the problems,
Claim 1
A laser ignition device for igniting fuel in a combustion chamber of an internal combustion engine, an excitation optical system for condensing excitation light on an amplification medium, a resonator system having an amplification medium and a saturable absorber, and the resonator A laser ignition device comprising: an output optical system that condenses laser light output from a system in the combustion chamber; and an incident diameter adjusting unit that changes an incident diameter of the excitation light to the amplification medium. Yes,
Claim 2
2. The laser ignition device according to claim 1, wherein the incident diameter adjusting unit includes an excitation optical system driving device that drives the excitation optical system to change a distance of the excitation optical system with respect to the amplification medium. And
Claim 3
The incident diameter adjusting means condenses at least one of the lens and the input unit in the amplification medium in the excitation optical system including at least one lens and an input unit to which excitation light is input. 3. The laser ignition device according to claim 1, further comprising a lens input unit driving device that drives in an optical axis direction formed by the input unit and the condensing point without changing a point position. 4. And
Claim 4
A laser ignition device comprising: the laser ignition device according to any one of claims 1 to 3; and an excitation light source that supplies the excitation light to the excitation optical system.

  A laser ignition device according to the present invention is a laser ignition device that ignites fuel in a combustion chamber of an internal combustion engine, and includes an excitation optical system that condenses excitation light on an amplification medium, an amplification medium, and a saturable absorber. A resonator system, an output optical system for condensing laser light output from the resonator system in the combustion chamber, and an incident diameter adjusting means for changing an incident diameter of the excitation light to the amplification medium. . In this laser ignition device, the incident diameter of the excitation light to the amplification medium can be changed by the incident diameter adjusting means, and the pulse energy output from the laser ignition device varies depending on the incident diameter of the excitation light to the amplification medium. To do. Therefore, it is possible to provide a laser ignition device capable of adjusting the pulse energy output from the laser ignition device as desired.

  Further, the incident diameter adjusting means includes an excitation optical system driving device that drives the excitation optical system to change the distance of the excitation optical system with respect to the amplification medium, so that the excitation optical system driving device amplifies the excitation light. The incident diameter to the medium can be changed. Therefore, it is possible to provide a laser ignition device capable of adjusting the pulse energy output from the laser ignition device as desired.

  Further, the incident diameter adjusting means is configured to collect at least one of the lens and the input unit in the amplification medium in the excitation optical system including at least one lens and an input unit to which excitation light is input. A lens input unit driving device that drives in the direction of the optical axis formed by the input unit and the condensing point without changing the position of the light spot is provided. The incident diameter can be changed. Therefore, the pulse energy output from the laser ignition device can be adjusted as desired, and the loss of excitation light energy can be suppressed and the pulse laser can be oscillated with high efficiency.

  First, a laser ignition device which is an embodiment of a laser ignition device according to the present invention will be described with reference to FIG. FIG. 1A is a configuration explanatory diagram of a laser ignition device according to an embodiment of the present invention. The laser ignition device 1 of the present embodiment condenses the excitation light 2 on a semiconductor laser 3 that is an example of an excitation light source that outputs the excitation light 2, an optical fiber 4 that transmits the excitation light 2, and an amplification medium 5. A resonator system 10 having an amplifying medium 5 and a saturable absorber 9 between an excitation optical system 6 to be performed, a total reflection mirror 7 and a partial reflection mirror 8, and a laser beam 11 output from the resonator system 10. Output optical system 12 for condensing the light in the combustion chamber of the internal combustion engine, and incident diameter adjusting means 13 for changing the incident diameter R1 of the excitation light 2 to the amplification medium 5.

  The semiconductor laser 3, which is an example of an excitation light source, outputs pulse energy having desired energy from the resonator system 10 by irradiating the amplification medium 5 in the resonator system 10 with the excitation light 2 and exciting the amplification medium 5. As long as it can be used, a known semiconductor laser can be employed.

  The optical fiber 4 transmits the excitation light output from the semiconductor laser 3, irradiates the amplification medium 5 in the resonator system 10 with the excitation light 2, and excites the amplification medium 5 to thereby generate a desired signal from the resonator system 10. As long as pulse energy having energy can be output, a known optical fiber can be employed. The pumping light output from the semiconductor laser 3 may be collected by the pumping optical system 6 without passing through the optical fiber 4 and irradiated to the amplification medium 5. However, the pumping light from the input unit 14 through the optical fiber 4 may be used. It is preferable that 2 is made incident on the excitation optical system 6 because the semiconductor laser 3 can be set apart from the internal combustion engine and is less susceptible to the heat of the internal combustion engine.

  The excitation optical system 6 includes an input unit 14 to which excitation light is supplied and at least one lens 15 and 16, condenses the excitation light output from the semiconductor laser 3, and amplifies the light with a desired incident diameter R <b> 1. The light can enter the medium 5. In the present embodiment, the excitation optical system 6 includes two plano-convex lenses 15 and 16, collects the excitation light 2 using the two plano-convex lenses 15 and 16, and the entire resonator system 10. The light passes through the reflecting mirror 7 and enters the amplification medium 5.

  The input unit 14 in the laser ignition device of the present embodiment is formed by, for example, a cylindrical part 23 and a disk-like part 24 that holds the cylindrical part 23, and the cylindrical part 23 accommodates the lenses 15 and 16. It is installed so as to be fitted in the housing. An optical fiber 4 is fitted into the cylindrical portion 23, and excitation light transmitted through the optical fiber 4 is supplied to the excitation optical system 6 via the input portion 14. When the optical fiber 4 is not used, excitation light is supplied to the excitation optical system 6 via the input unit 14 from the semiconductor laser 3 which is an example of the excitation light source. In the laser ignition device shown in FIGS. 3 and 4, which is another embodiment to be described later, the input units 314 and 414 may be driven by the lens input unit driving devices 313 and 413. At this time, the cylindrical portions of the input portions 314 and 414 are expanded or contracted, or the input portions 314 and 414 or the housing end portions to which the input portions 314 and 414 are fixed are driven by appropriate moving means. The positions of the input units 314 and 414 in the optical systems 306 and 406, that is, the output positions of the excitation light with respect to the amplification media 305 and 405 are determined.

  The pumping light 2 only needs to be able to irradiate the pumping light 2 to a region including the optical axis of the resonator system 10 in the amplification medium 5. In the laser ignition device 1 according to this embodiment, the light of the resonator 10 is used. An excitation optical system 6 is disposed on the extension line of the axis, and the excitation light 2 collected by the excitation optical system 6 passes through the total reflection mirror 7 and is irradiated perpendicularly to the surface of the plate-like amplification medium 5. ing. In addition, for example, the excitation optical system 6 may be arranged at a position where the excitation light 2 is incident obliquely with respect to the surface of the amplification medium 5 on which the excitation light 2 is incident.

  The resonator system 10 is formed by a total reflection mirror 7, an amplification medium 5, a saturable absorber 9, and a partial reflection mirror 8, and the total reflection mirror 7, the amplification medium 5, the saturable absorber 9, and the partial reflection mirror. As long as the optical component such as 8 can output a pulse laser having a desired energy, a known optical component can be adopted. As a configuration of the resonator system 10, for example, as shown in FIG. 1A, the surface of the amplification medium 5 on the side on which the excitation light 2 is incident is coated with a substance having the function of a total reflection mirror. A total reflection mirror 7 is formed, a saturable absorber 9 is disposed between the total reflection mirror 7 and the partial reflection mirror 8, and a Fabry-Perot resonator is formed between the total reflection mirror 7 and the partial reflection mirror 8. The The saturable absorber 9 is usually disposed between the amplifying medium 5 and the partial reflection mirror 8, but when the saturable absorber 9 is a material that does not absorb the excitation light 2, It can also be arranged between the amplification medium 5.

  The total reflection mirror 7 reflects the oscillation wavelength 21 with a reflectivity greater than 99% (approximately 100% reflectivity) and transmits light of other wavelengths. The partial reflection mirror 8 has a characteristic of reflecting the oscillation wavelength 21 with a reflectance of 10 to 98%, preferably 60 to 90% and transmitting the remaining oscillation wavelength 21. As shown in FIG. 1A, in the laser ignition device 1 of the present embodiment, the surface of the amplification medium 5 on which the excitation light 2 is incident is coated with a substance having the function of the total reflection mirror 7. However, the total reflection mirror 7 and the partial reflection mirror 8 may be arranged as independent components, or the amplification medium 5 in the saturable absorber 9 is arranged. The partial reflection mirror 8 may be formed by coating a surface having a function of the partial reflection mirror 8 on the surface opposite to the side. Further, the total reflection mirror 7, the amplifying medium 5, the saturable absorber 9, and the partial reflection mirror 8 may be arranged in close contact with each other, or only some optical components may be arranged in close contact with each other. good.

  The amplification medium 5 is a material that is excited and emits stimulated light when irradiated with the excitation light 2 output from the semiconductor laser 3. For example, a single crystal such as Nd: YAG, Yb: YAG, or ceramics is used. Preferably used. The shape of the amplifying medium 5 is a plate shape in the example shown in FIG. 1A, but the shape of the amplifying medium 5 is such that light reciprocating inside the resonator system 10 is generated, and the laser is emitted from the resonator system 10 to the laser. The light 11 is not particularly limited as long as it can be output, and may have a convex lens shape, a concave lens shape, or the like. The size of the amplifying medium 5 is not particularly limited as long as the light reciprocating inside the resonator system 10 is generated and the laser beam 11 can be output from the resonator system 10. What is necessary is just to adjust suitably according to it.

The saturable absorber 9 has a function as a Q switch by changing the transmittance with respect to the oscillation wavelength 11. The saturable absorber 9 is not particularly limited as long as it is a crystal body that can change the light transmittance by absorbing light stimulated and emitted from the amplification medium 5. For example, Cr ⁴⁺ : YAG is preferable. Used for.

  The output optical system 12 has at least one lens, and can focus the pulse laser 11 output from the resonator system 10 at a desired position in the combustion chamber of the internal combustion engine. In the present embodiment, there are two plano-convex lenses 17 and 18 and an output window 19 that has no optical effect and isolates the combustion chamber from the output optical system 12.

  The incident diameter adjusting means 13 can employ any incident diameter adjusting means 13 as long as the incident diameter R1 of the excitation light 2 output from the semiconductor laser 3 to the amplification medium 5 can be changed. For example, in the laser ignition device 1 of the present embodiment, as shown in FIG. 1A, an excitation optical system drive device 13 is employed, and this excitation optical system drive device 13 drives the excitation optical system 6. In addition, the distance of the excitation optical system 6 with respect to the amplification medium 5 can be changed. By changing the distance between the amplification medium 5 and the excitation optical system 6, the position of the condensing point 20 of the excitation light 2 collected by the excitation optical system 6 is changed, so that the incident diameter R1 to the amplification medium 5 is Variable.

  As a method of adjusting the energy per pulse of a pulse laser oscillated from a resonator system including a saturable absorber, that is, a pulse energy as in the laser ignition device according to the present invention, It is conceivable to change the incident diameter. The incident diameter is, for example, the diameter of a circle when the amplification light is irradiated on the surface of the amplification body in a circular shape when the amplification medium is plate-shaped and the surface of the amplification medium on which the excitation light is incident is flat. It is. In addition, when the amplification medium has a shape such as a spherical shape or a lens shape, or when the surface on which the excitation light is incident is not flat but has a undulation, the incident diameter is the excitation light on the amplification medium. This is the diameter when the area of the shape formed when the incident surface is projected is converted into a circle. In other words, the pulse energy depends on the projected area of the excitation light incident on the surface of the amplification medium. The excitation light irradiated to the amplification medium usually has an intensity distribution with respect to the incident surface, and the intensity distribution varies depending on the distribution of the excitation light intensity in the excitation light source and the position of the focal point of the excitation light with respect to the amplification medium. Generally, the central part is high and the end part is low. In the present invention, the weak excitation region where the intensity of excitation light sufficient to oscillate the pulse laser is not irradiated is not included in the projected area of the excitation light, that is, the incident diameter.

  The reason why the pulse energy changes depending on the incident diameter of the excitation light with respect to the amplification medium, that is, the projected area will be described below. The pulse energy per unit projected area of the excitation light incident on the surface of the amplifying medium has a transmittance (sometimes referred to as initial transmittance) with respect to an oscillation wavelength which is a characteristic value inherent to the saturable absorber. It depends on internal loss such as reflectivity of the reflector. Here, since the internal loss is usually constant in the resonator system, the pulse energy per unit projected area of the excitation light incident on the surface of the amplifying medium is constant in the appropriately designed resonator system. . Therefore, when the projected area of the excitation light incident on the surface of the amplification medium is increased, the pulse energy increases. Therefore, the pulse energy of the pulse laser can be adjusted as desired by adjusting the incident diameter of the excitation light to the amplification medium.

  In the laser ignition device 1 of the present embodiment shown in FIG. 1A, the condensing point 20 of the excitation light 2 condensed by the excitation optical system 6 is located at the middle point in the thickness direction of the amplification medium 5. . FIG. 1B is an enlarged explanatory view of a portion where the excitation light is incident on the amplification medium, and shows the spot diameter of the excitation light. On the other hand, FIG. 2A shows an example in the case where the distance between the excitation optical system and the amplification medium is made closer than in the laser ignition device in FIG. FIG. 2B is an enlarged explanatory view of a portion where the excitation light is incident on the amplification medium, and shows the spot diameter of the excitation light. In the laser ignition device 201 of the present embodiment shown in FIG. 2A, the excitation optical system 206 is driven in the optical axis direction by the excitation optical system driving device 213, and the distance between the excitation optical system 206 and the amplification medium 205 is increased. It is approaching. As a result, the condensing point 220 of the excitation light 202 shifts in a direction away from the total reflection mirror 207 on the optical axis of the amplification medium 205, so that the incident diameter R 2 of the excitation light 202 incident on the surface of the amplification medium 205 is As compared with the cases of FIGS. 1 (a) and 1 (b). When the incident diameter R2 of the excitation light 202 to the amplification medium 205 increases, the pulse energy of the pulse laser oscillated from the laser ignition device of the present embodiment increases.

  3 (a) and 4 (a) are explanatory views of the configuration of a laser ignition device according to another embodiment of the present invention. FIG. 3B and FIG. 4B are enlarged explanatory views of a portion where the excitation light of the amplification medium is incident, and show the spot diameter of the excitation light. The laser ignition devices 301 and 401 of the present embodiment shown in FIGS. 3A and 4A are lenses instead of the excitation optical system driving devices 13 and 213 in FIGS. 1A and 2A. Input unit driving devices 313 and 413 are provided. The excitation optical systems 306 and 406 include convex lenses 321 and 421, plano-convex lenses 315 and 415 in which the downstream sides of the excitation lights 302 and 402 are convex, and plano-convex lenses 416 and 416 in which the upstream sides of the excitation lights 302 and 402 are convex. They are arranged in a line in this order to form a zoom lens. Except for the lens input unit driving devices 313 and 413 and the excitation optical systems 306 and 406, the configuration is the same as that shown in FIGS. The laser ignition devices 301 and 401 according to this embodiment shown in FIGS. 3A and 4A are provided with an excitation optical system 306 by lens input unit driving devices 313 and 413 including appropriate means such as a pinion and a rack. , 406, at least one of the input units 314 and 414 for inputting excitation light and the lenses 321, 421, 315, 415, 316 and 416 is driven to input units 314 to the amplification media 305 and 405. 414 and the lens 321, 421, 315, 415, 316, 416, by changing the distance between the lens 321, 421, 315, 415, 316, 416 without changing the position of the condensing points 320, 420 in the amplification media 305, 405 The incident diameters R3 and R4 of the light 302 and 402 on the surfaces of the amplification media 305 and 405 are changed. The laser ignition devices 301 and 401 of the present embodiment shown in FIGS. 3A and 4A both have the condensing points 320 and 320 of the excitation lights 302 and 402 collected by the excitation optical systems 306 and 406, respectively. Reference numeral 420 denotes a midpoint in the thickness direction of the amplification media 305 and 405. The laser ignition device 301 shown in FIGS. 3A and 3B drives the lenses 321, 315, and 316 in the excitation optical system 306 by the lens input unit driving device 310, so that FIGS. The excitation light 302 is incident on the surface of the amplifying medium 305 with the same incident diameter as in the case of FIG. On the other hand, the laser ignition device 401 shown in FIGS. 4A and 4B condenses light more than in the case of FIGS. 3A and 3B without changing the position of the condensing point in the amplification medium 405. This is an example of increasing the spot diameter of a point. Therefore, the incident diameter R4 of the excitation light 402 incident on the surface of the amplification medium 405 in FIGS. 4 (a) and 4 (b) is larger than that in FIGS. 3 (a) and 3 (b). When the incident diameter R4 of the excitation light 402 to the amplification medium 405 is increased, the pulse energy is increased as compared with the cases of FIGS. 3 (a) and 3 (b). In the example of the laser ignition device shown in FIGS. 3A, 3B, 4A, and 4B, the condensing point of the excitation light is located at the middle point in the thickness direction of the amplification medium. However, what is necessary is just to set suitably according to the shape and material characteristic of amplification medium, such as the surface of the amplification medium in which excitation light injects, or the surface vicinity.

  The incident diameter R2 of the excitation light 202 to the amplification medium 205 in the laser ignition device 201 shown in FIGS. 2 (a) and 2 (b) and the excitation light 402 in the laser ignition device 401 shown in FIGS. 4 (a) and 4 (b). When the incident diameter R4 to the amplification medium 405 is the same, the oscillated pulse energy is the same. However, the excitation light 402 incident on the surface of the amplification medium 405 in FIGS. 4A and 4B is more than the excitation light 202 incident on the surface of the amplification medium 205 in FIGS. Since it is close to the condensing point, the ratio of energy contributing to oscillation is high in the total energy of the excitation light. Therefore, the laser ignition device 401 shown in FIGS. 4 (a) and 4 (b) can obtain a pulse laser with higher efficiency than the laser ignition device 201 shown in FIGS. 2 (a) and 2 (b). .

  This will be described in more detail with reference to FIGS. FIGS. 5A to 5D are irradiated on the surface of the amplification medium corresponding to each of the laser ignition devices shown in FIGS. 1A and 1B and FIGS. 4A and 4B. It is the figure which represented typically the relationship between the incident diameter of excitation light, and intensity | strength. The vertical axis indicates the intensity of the excitation light on the surface of the amplification medium on which the excitation light is incident, and the broken line indicates the intensity of the excitation light necessary for oscillating the pulse laser, that is, the laser oscillation threshold. The diameter of the surface exceeding the laser oscillation threshold on the surface of the amplification medium on which the excitation light is incident is the incident diameter. The laser ignition device shown in FIGS. 1A, 1B, 3A, 3B, 4A, and 4B has excitation light at a midpoint in the thickness direction of the amplification medium. 5 and the surface of the amplifying medium is close to the condensing point, the intensity of the excitation light irradiated on the surface of the amplifying medium is shown in FIGS. 5 (a), (c), and (d). As shown in FIG. 5B, the surface of the amplifying medium irradiated sharply rises compared to FIG. Therefore, out of the total energy of the pumping light, the energy of the pumping light that does not contribute to the pulse oscillation and is less than the laser oscillation threshold (broken line) is small. On the other hand, in the laser ignition device shown in FIGS. 2A and 2B, the condensing point of the excitation light is shifted to a position away from the total reflection mirror on the optical axis, and the surface of the amplification medium is the condensing point. As shown in FIG. 5B, the intensity of the excitation light on the surface of the amplifying medium has a shape of a gentle mountain shape on the surface irradiated to the amplifying medium. Therefore, out of the total energy of the excitation light, the energy of the excitation light that does not contribute to the pulse oscillation is less than the laser oscillation threshold (broken line). Therefore, rather than the laser ignition device having the excitation optical system driving device shown in FIGS. 1A, 1B and 2A, 2B, FIGS. The laser ignition device having the lens input unit driving device shown in a) and (b) can oscillate a pulse laser having desired pulse energy with high efficiency by suppressing the loss of excitation light energy. This is preferable because it is possible.

  FIG. 6 shows a schematic diagram of a cylinder when the laser ignition device of this embodiment is mounted on a cylinder of an internal combustion engine. A cylinder 600 of the internal combustion engine is formed by a cylinder block 601, a cylinder head 602, and a piston 603. A space surrounded by the cylinder block 601, the cylinder head 602, and the piston 603 is a combustion chamber 604. A suction pipe 605 for supplying a mixture of fuel and air is connected to the cylinder head 602, and the supply of the mixture is adjusted by opening and closing the suction valve 606. The cylinder head 602 is connected to an exhaust pipe 607 for discharging the air-fuel mixture so that the exhaust of the air-fuel mixture is adjusted by opening and closing the exhaust valve 608. The laser ignition device 1 of the present embodiment can be installed at an arbitrary position as long as the air-fuel mixture in the combustion chamber 604 can be ignited. For example, as shown in FIG. The laser ignition device of this embodiment can be installed between the exhaust valve 608 and the exhaust valve 608. The pulse laser output from the laser ignition device causes breakdown in the combustion chamber 604, and the air-fuel mixture in the combustion chamber 604 is combusted starting from the imaging point of the pulse laser. Although an example of a cylinder in an internal combustion engine has been described, the configuration of the cylinder is not limited to the above configuration. The laser ignition device of the present embodiment can adjust the pulse energy as desired when the ratio of the fuel in the air-fuel mixture changes according to the operating state of the internal combustion engine. Therefore, it is possible to provide a laser ignition device with reduced power consumption.

  FIG. 7 is a configuration diagram for explaining the control device of the laser ignition device of the present embodiment. The laser ignition device of the present embodiment analyzes signals obtained by various sensors attached to the cylinders of the internal combustion engine, and controls the power source of the semiconductor laser and the lens input unit driving device based on the analysis result Is preferably controlled by. The control device 700 is formed by a calculation unit 701 and a control unit 702, and various sensors 703 attached to the cylinders of the internal combustion engine, for example, the pressure in the combustion chamber, the concentration of fuel in the combustion chamber, the exhaust temperature in the exhaust pipe, A signal transmitted from a sensor that detects an oxygen concentration, a residual fuel concentration, and the like in the exhaust gas in the exhaust pipe is analyzed in the calculation unit 701. The analyzed result is transmitted to the control unit 702, and the control unit 702 generates a control signal and outputs the control signal to the incident diameter adjusting unit 704 such as a lens input unit driving device. With this control signal, the lens input unit driving device 704 controls the position of at least one of the lens and the input unit in the excitation optical system with respect to the amplification medium so that the excitation light irradiated to the amplification medium has a desired incident diameter. To do. After that, after starting the operation of the semiconductor laser, a control signal is output to the power source 705 of the semiconductor laser at a timing considering the time until the pulse laser is output from the laser ignition device, and the power of the semiconductor laser is turned on and off. To. By repeating the above steps, the air-fuel mixture in the cylinder of the internal combustion engine can be ignited at an appropriate timing, so that the cylinder can be operated as desired according to the operating status of the internal combustion engine. When the excitation optical system driving device is used instead of the lens input unit driving device to adjust the incident diameter of the excitation light applied to the amplification medium, the control device controls the excitation optical system driving device. .

  Next, the operation of the laser ignition device 1 will be described with reference to FIG. As shown in FIG. 1A, the pumping light 2 output from the semiconductor laser 3 is transmitted through the optical fiber 4 and input from the input unit 14 to the pumping optical system 6. The input excitation light 2 is condensed by two plano-convex lenses 15 and 16 in the excitation optical system 6, passes through the total reflection mirror 7 of the resonator system 10, and enters the amplification medium 5. The incident excitation light 2 is absorbed by the amplifying medium 5 and excited with time to increase the inversion distribution density, and stimulated emission occurs. In the process in which the light oscillated from the amplification medium 5 reciprocates in the resonator formed by the partial reflection mirror 8 and the total reflection mirror 7, the saturable absorber 9 absorbs the light reciprocating in the resonator, Since the transmittance of the saturable absorber increases, the Q value, which is the ratio between the energy stored in the resonator and the lost energy, rapidly increases, and the oscillation wavelength 21 and the partial reflector that reciprocate inside the resonator. The laser beam 11 passing through 8 increases rapidly. As the output increases rapidly, the inversion distribution density of the amplification medium decreases rapidly, so that the oscillation wavelength 21 that reciprocates in the resonator and the laser beam 11 that passes through the partial reflection mirror 8 start to decrease in a short time. The output is a giant pulse. Here, when the excitation optical system 6 is brought close to the resonator system 10 by the excitation optical system driving device 13, the condensing point of the excitation light 2 is shifted in a direction away from the surface on which the excitation light 2 is incident on the amplification medium 5. To do. Therefore, since the incident diameter R1 of the excitation light 2 incident on the amplification medium 5 is increased, the pulse energy of the pulse laser oscillated from the laser ignition device 1 is increased.

  When the excitation light 2 from the semiconductor laser 3 is continuously irradiated, the above process is repeated, so that the pulse laser 11 is output at a predetermined interval from the laser ignition device 1 of the present embodiment. On the other hand, when the inversion distribution density of the amplification medium 5 reaches the threshold value, when the excitation light 2 output from the semiconductor laser 3 is quickly stopped, a single pulse laser 11 is obtained.

  The pulse laser 11 output from the partial reflection mirror 8 is condensed by two plano-convex lenses 17 and 18 in the output optical system 12, and an imaging point 22 is formed in the combustion chamber of the cylinder isolated by the output window 19. Is done. A high electric field is generated at the image point 22. When the electric field density is higher than a threshold value determined by various conditions, breakdown occurs, and the air-fuel mixture in the combustion chamber burns starting from the imaging point 22.

  The laser ignition device according to the present invention is not limited to the above embodiment, and various modifications can be made. For example, the type and number of lenses in the excitation optical system are not particularly limited as long as the incident diameter of the excitation light with respect to the amplification medium can be adjusted as desired. Further, the type and number of lenses in the output optical system are not particularly limited as long as they can be adjusted so that the imaging point of the pulse laser is provided at a desired position in the combustion chamber of the internal combustion engine.

FIG. 1A is a configuration explanatory diagram of a laser ignition device according to an embodiment of the present invention. FIG. 1B is an enlarged explanatory view of a portion where the excitation light is incident on the amplification medium. FIG. 2A is an example in the case where the distance between the excitation optical system and the amplification medium is made closer than that of the laser ignition device in FIG. FIG. 2B is an enlarged explanatory view of a portion where the excitation light is incident on the amplification medium. FIG. 3A is a diagram for explaining the configuration of a laser ignition device according to another embodiment of the present invention. FIG. 3B is an enlarged explanatory view of a portion where excitation light is incident on the amplification medium. FIG. 4A shows an example in which the spot diameter of the condensing point is increased as compared with the case of FIG. 3A without changing the position of the condensing point in the amplification medium. FIG. 4B is an enlarged explanatory view of a portion where the excitation light is incident on the amplification medium. FIGS. 5A to 5D are irradiated on the surface of the amplification medium corresponding to each of the laser ignition devices shown in FIGS. 1A and 1B and FIGS. 4A and 4B. It is the figure which represented typically the relationship between the incident diameter of excitation light, and intensity | strength. FIG. 6 is a block diagram for explaining a control device for a laser ignition device according to an embodiment of the present invention. FIG. 7 is a schematic view of a cylinder when a laser ignition device according to an embodiment of the present invention is mounted on a cylinder of an internal combustion engine.

Explanation of symbols

1, 201, 301, 401 Laser ignition device 2, 202, 302, 402 Excitation light 3, 203, 303, 403 Semiconductor laser 4, 204, 304, 404 Optical fiber 5, 205, 305, 405 Amplifying medium 6, 206, 306, 406 Excitation optical system 7, 207, 307, 407 Total reflection mirror 8, 208, 308, 408 Partial reflection mirror 9, 209, 309, 409 Saturable absorber 10, 210, 310, 410 Resonator system 11, 211 311, 411 Laser light 12, 212, 312, 412 Output optical system 13, 213, 313, 413 Incident diameter adjusting means, excitation optical system drive device, lens input unit drive device 14, 214, 314, 414 input unit 15, 16, 17, 18, 215, 216, 217, 218, 315, 316, 317, 318, 415, 416, 417, 418 Plano-convex lens 19, 219, 319, 419 Output window 20, 220, 320, 420 Condensing point 21, 221, 321, 421 Oscillation wavelength 22, 222, 322, 422 Imaging point 321, 421 Convex lens 600 Cylinder 601 Cylinder block 602 Cylinder head 603 Piston 604 Combustion chamber 605 Suction pipe 606 Suction valve 607 Exhaust pipe 608 Exhaust valve 700 Controller 701 Calculation section 702 Control section 703 Sensor 704 Incident diameter adjusting means 705 Power supply R1, R2, R3, R4 Incident Diameter

Claims (4)

  A laser ignition device for igniting fuel in a combustion chamber of an internal combustion engine, an excitation optical system for condensing excitation light on an amplification medium, a resonator system having an amplification medium and a saturable absorber, and the resonator A laser ignition device comprising: an output optical system that condenses laser light output from a system in the combustion chamber; and an incident diameter adjusting unit that changes an incident diameter of the excitation light to the amplification medium.   2. The laser ignition device according to claim 1, wherein the incident diameter adjusting unit includes an excitation optical system driving device that drives the excitation optical system to change a distance of the excitation optical system with respect to the amplification medium. .   The incident diameter adjusting means condenses at least one of the lens and the input unit in the amplification medium in the excitation optical system including at least one lens and an input unit to which excitation light is input. 3. The laser ignition device according to claim 1, further comprising a lens input unit driving device that drives in an optical axis direction formed by the input unit and the condensing point without changing a point position. 4. .   A laser ignition device comprising: the laser ignition device according to claim 1; and an excitation light source that supplies the excitation light to the excitation optical system.

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