EP2324234A1

EP2324234A1 - Ignition device for a laser ignition of an internal combustion engine

Info

Publication number: EP2324234A1
Application number: EP09780773A
Authority: EP
Inventors: Martin Weinrotter; Pascal Woerner; Juergen Raimann; Dieter Wolz
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2008-08-08
Filing date: 2009-07-17
Publication date: 2011-05-25
Also published as: DE102008041130A1; JP5216143B2; WO2010015500A1; US8607755B2; JP2011530665A; US20110203542A1

Abstract

An ignition laser for an internal combustion engine is proposed in which the combustion chamber window (58) is connected to a housing (38) of the ignition laser in a manner that is resistant to gas, pressure and temperature. Moreover, a pressure relief hole (67) is provided which effectively prevents a pressure increase in the housing (38) of the ignition laser.

Description

description

title

Ignition device for a laser ignition of an internal combustion engine

State of the art

From WO 2005/066488 Al a so-called laser ignition is known. This laser ignition comprises an ignition laser, which projects into the combustion chamber of an internal combustion engine. The ignition laser is optically pumped by a light source from a pump light source.

At a combustion chamber facing the end of the ignition laser, a so-called combustion chamber window is present, which is transmissive to the laser beams generated in the ignition laser. This combustion chamber window must be sealingly received in a housing of the ignition laser. High demands are placed on the seal between the combustion chamber window and the housing because surface temperatures of over 600 ° C. can occur on the combustion chamber window during operation of the internal combustion engine. In addition, intermittent pressure loads of up to approx. 250 bar are added. If a firing laser is used to ignite a gas turbine, prevail in the combustion chamber of the gas turbine, although lower pressures, however, the surface of the combustion chamber window can reach temperatures of up to 1,000 ° C, in any case, uncontrolled Glühzündungen must be prevented. It is obvious that the inside of the ignition laser against the extremely high

Temperatures and pressures must be securely sealed. If exhaust gases should get inside the ignition laser, this leads to the failure of the ignition laser.

From the subsequently published DE 102007041528.3 an ignition laser is known, in which the combustion chamber window and the housing are sealed so that over the entire life of the internal combustion engine and the pressure prevailing in the combustion chamber of an internal combustion engine, a reliable and reliable sealing of the combustion chamber window and housing is ensured , Disclosure of the invention

The invention is based on the object to provide an ignition laser with further improved lifetime and reliability.

This object is achieved with a laser ignition device for an internal combustion engine comprising a laser active solid, a combustion chamber window and a housing with an inner sleeve and an outer sleeve, wherein the inner sleeve and the outer sleeve define a gap, achieved in that the housing has a pressure compensation device, and that the Pressure equalization device connects the gap and the environment with each other. The pressure compensation device according to the invention is intended as a kind of backup system for the sealing concept of the laser ignition device. If, during operation of the laser ignition device, only minimal leaks should occur, this can lead to the pressure in the intermediate space rising significantly above the ambient pressure and, as a result, severely stressing the sealing surface between the combustion chamber window and the inner sleeve of the housing. The pressure equalization device according to the invention ensures that even with small minimum leakage flows between the outer housing and the combustion chamber window, the sealing surface between the combustion chamber window and the inner sleeve is not claimed in unauthorized manner, so that the interior of the housing is reliably protected against flue gases and the impurities contained in the flue gases is.

By means of the pressure compensation device according to the invention, the sealing of the housing interior is still maintained even if the first-mentioned sealing surface, which is naturally exposed to higher thermal and chemical stresses, should leak in the course of the operating life of the internal combustion engine or the laser ignition device. By means of the pressure compensation device according to the invention, an amount of exhaust gas flowing into the intermediate space due to a leak between outer sleeve and combustion chamber window can be removed. As a result, the pressure in the space does not increase and the operating conditions of the second seal between the combustion chamber window and inner sleeve do not change. Also, an impermissible pressurization of the gap is avoided.

A manufacturing technology very simple variant of a printing device according to the invention is designed as a pressure equalization hole, which is mounted in the outer sleeve. In this case, the pressure equalization hole is positioned on the outer sleeve, that the pressure equalization hole in the installed state of the laser ignition device opens into a shaft of the cylinder head of the internal combustion engine in which Laser ignition device is mounted. This shaft corresponds to the so-called plug shaft in the cylinder head of conventional internal combustion engines in which the ignition is triggered by a spark plug.

In order to prevent contaminants from passing through the pressure compensation bore from the said shaft into the space between outer sleeve and inner sleeve, it is further provided that the pressure compensation bore has a minimum diameter at its exit from the housing, and that the diameter increases in the direction of the intermediate space , So it is for example possible to perform the pressure equalization hole as a stepped bore or run as a cylindrical bore and then to reduce the outer diameter of the outer surface partially by a forming process, the diameter of the pressure compensation hole.

Furthermore, it is also possible to accommodate a filter element in the pressure compensation bore. This filter element has the task of preventing the penetration of particles and other contaminants and can for example be made of a temperature-resistant foam, be it plastic, metal or a sintered material. Furthermore, it is also possible to form the filter element as a wire mesh or another knitted fabric.

A further advantageous embodiment of the invention provides for closing the pressure compensation bore, for example, by means of a plug made of a hardenable plastic material which performs the function of a seal. A particularly suitable material is polyimide, due to its high temperature resistance. Another suitable material is silicone, due to its high gas permeability, but particle and liquid tightness.

By closing the pressure equalization bore with a plug, it is firstly ensured that in normal operation, i. if the sealing between the outer sleeve and the combustion chamber window is completely leakproof, the pressure compensation bore is closed and thus no dirt can get into the intermediate space. However, if the pressure in the space increases, for example to 4 bar above ambient pressure, the plug is forced out by these pressure forces from the pressure equalization hole and the pressure equalization hole allows pressure equalization between the space and the environment. This ensures that no inadmissibly high pressures can occur in the intermediate space.

A further advantageous embodiment of the invention provides that the pressure compensation device is designed as Druckentlastungsnut, preferably on a bolt thread and / or a female thread of the housing Laser ignition device is mounted. This pressure relief groove is preferably mounted in the axial direction, so that the pressure relief groove ends at the end of the laser ignition device remote from the combustion chamber window.

By separating the housing into an inner sleeve and an outer sleeve, an embodiment of the outer sleeve and the inner sleeve which is optimally adapted to the respective task can likewise be achieved. It is also possible to provide a further optimized ignition laser by choosing different materials for outer sleeve and inner sleeve. Alternatively, it is possible to materially connect a membrane with the outer sleeve and the combustion chamber window or with the inner sleeve and the combustion chamber window.

Further advantages and advantageous embodiments of the invention are the following drawings, the description and the claims removable. All of the features disclosed in the drawing, the description and the claims can be essential to the invention both individually and in any combination with one another.

Brief description of the drawings In the drawing:

Figure Ia is a schematic representation of an internal combustion engine with a laser-based ignition device; Figure Ib is a schematic representation of the ignition device of Figure 1 and

Figures 2 to 7 embodiments of the invention ignition laser.

An internal combustion engine carries in FIG. 1a overall the reference numeral 10. It can be used to drive a motor vehicle, not shown. The internal combustion engine 10 usually comprises a plurality of cylinders, of which only one is designated by the reference numeral 12 in FIG. A combustion chamber 14 of the cylinder 12 is limited by a piston 16. Fuel enters the combustion chamber 14 directly through an injector 18, which is connected to a designated also as a rail fuel pressure accumulator 20. Alternatively, the fuel-air mixture can also be formed outside the combustion chamber 14, for example in the intake manifold.

The present in the combustion chamber 14 fuel-air mixture 22 is ignited by means of a laser pulse 24 which is emitted from an ignition laser 26 comprehensive ignition device 27 into the combustion chamber 14. For this purpose, the laser device 24 fed via a light guide device 28 with a pumping light, which is provided by a pumping light source 30. The pumping light source 30 is controlled by a control unit 32, which can also control the injector 18.

As can be seen from FIG. 1 b, the pumping light source 30 feeds a plurality of optical waveguide devices 28 for different ignition lasers 26, which are each assigned to a cylinder 12 of the internal combustion engine 10. For this purpose, the pumping light source 30 has a plurality of individual laser light sources 340, which are connected to a pulse power supply 36. Due to the presence of a plurality of individual laser light sources 340, the pumping light is distributed as it were "dormant" to the various laser devices 26, so that no optical distributor or the like between the pumping light source 30 and the ignition lasers 26 are required.

The ignition laser 26 has, for example, a laser-active solid 44 with a passive Q-switching circuit 46, which forms an optical resonator together with a coupling mirror 42 and a Auskoppelspiegel 48. Upon application of pumping light generated by the pumping light source 30, the ignition laser 26 generates a laser pulse 24 in a manner known per se, which is focused by focusing optics 52 onto an ignition point ZP located in the combustion chamber 14 (FIG. The components present in the housing 38 of the ignition laser 26 are separated from the combustion chamber 14 by a combustion chamber window 58.

In Figure 2, the detail X of Figure Ib is greatly enlarged in partial longitudinal section shown. In this embodiment, the housing 38 is formed in two parts. It comprises an inner sleeve 62 and an outer sleeve 64. The outer sleeve 64 has a shoulder 66 on a combustion chamber 14 (see FIG. 1a). The paragraph 66 has essentially two functions. First, it shields a portion of the combustion chamber window 58 from the combustion chamber and the pressures and temperatures prevailing there, so that the thermal load of the combustion chamber window 58 is reduced.

Furthermore, it is possible with the help of paragraph 66, the combustion chamber window 58 to press against the inner sleeve 62 and thereby increase the tightness in the joints 60 and 70. For this purpose, a female thread is provided on the outer sleeve 64, which cooperates with a corresponding bolt thread of the inner sleeve 62. This thread, consisting of nut thread and bolt thread, is in its

Entity characterized by the reference numeral 68. Furthermore, instead of the thread, the inner sleeve 62 can be pressed onto the outer sleeve 64 with a predetermined contact pressure and the connection can be produced by welding or another cohesive method or by a non-positive or positive-locking method (flanging). As an alternative to the described embodiment of a cohesive connection of window and sleeve, the sealing effect can be generated by clamping. In this case, the surfaces with the reference numerals 60 and 70 are the sealing surfaces.

The combustion chamber window 58 is integrally connected to an end face (without reference numeral) of the inner sleeve 62 of the housing 38. The joint is in Figure 2 with the

Reference numeral 60 provided. The cohesive connection between combustion chamber window 58 and housing 38 can be effected by soldering, in particular brazing, soft soldering, gluing, vitrification or welding. In the exemplary embodiment illustrated in FIG. 2, the housing 38 preferably has a thermal expansion coefficient which approximates the coefficient of thermal expansion of the combustion chamber window 58. As a result, thermal stresses are avoided and as a result, the joint 60 relieved. At the same time, however, care must be taken that the housing 38 is made of a heat-resistant material and as a result also has sufficient fatigue strength at the operating temperatures prevailing in the combustion chamber. Particularly advantageous in this embodiment is their low space requirement.

In the embodiment shown in FIG. 2, all pressure forces are transmitted via the joint 60 from the combustion chamber window 58 into the housing 38 or the inner sleeve 62 of the housing 38.

By separating the housing 38 into an inner sleeve 62 and an outer sleeve 64, the designer has more degrees of freedom for functionally optimized design of the two components mentioned and the joint 60 are available. Thus, for example, the material of the outer sleeve 64 can be optimized in terms of heat resistance and fatigue strength, while the material of the inner sleeve 62 is chosen so that its thermal expansion coefficient as much as possible corresponds to the coefficient of thermal expansion of the combustion chamber window 58, if a material connection is preferred. If a frictional connection is selected, different coefficients of thermal expansion can be at least partially compensated. As a result, the thermal stresses are reduced and the joint 60 relieved. Furthermore, it is of course also possible to select the material of the inner sleeve 62 so that the inventive claimed cohesive connection between the combustion chamber window 58 and inner sleeve 62 can be made as safe, simple and durable.

Due to the bracing of the outer sleeve 64 and the inner sleeve 62, a sealing surface 70 is formed between the shoulder 66 and the combustion chamber window, which thus constitutes a redundant seal which, as it were, precedes the joint 60 and This either causes a complete separation of the combustion chamber 14 and the interior of the ignition laser 26 or at least reduces the temperature and pressure stress of the joint 60 and as a result relieves the joint 60.

In order to optimize the sealing surface 70 with respect to its sealing effect, it may be advantageous, for example, to provide the shoulder 66 or the combustion chamber window 58 with the area of the sealing surface 70 with a coating of a ductile material, such as copper. As a result, the smallest unevennesses of the contact surfaces between combustion chamber window 58 and outer sleeve 64 are equalized and the sealing effect is improved. This coating may, for example, be 5 μm to 100 μm thick. Alternatively, it would also be possible to exchange the positions of the joint 60 and the sealing surface 70. This would mean that the combustion chamber window 58 is materially connected to the shoulder 66 of the outer sleeve 64 and the combustion chamber window 58 is pressed sealingly against the end face of the inner sleeve. However, it should be noted that the thermal load in the area of the contact surface between the shoulder 66 and the combustion chamber window 58 is higher than between the combustion chamber window 58 and the inner sleeve 62.

The inner sleeve 62, the outer sleeve 64 and the combustion chamber window 58 define a gap 65. When the sealing surface 70 between the shoulder 66 and the combustion chamber window 58 is completely sealed, the pressure in the gap 65 remains approximately equal to the ambient pressure. 2 shows a first embodiment of an inventive

Pressure relief device in the form of a pressure relief hole 67 shown. This pressure relief bore 67 connects the outer of the outer sleeve 64 with the gap 65, which is bounded by the outer sleeve 64 and the inner sleeve 62 substantially. The pressure relief bore 67 is axially spaced from the combustion chamber window 58, so that in the laser ignition device, the pressure relief hole 67 not in the combustion chamber, but in a shaft of the cylinder head of the internal combustion engine (not shown) opens, in which the laser ignition device is used. This shaft corresponds to the well known in conventional internal combustion engine plug hole is used in the spark plug and is fastened via the plug thread in the cylinder head. In the exemplary embodiment illustrated in FIG. 3, a membrane 72 is provided, which is integrally connected to the combustion chamber window 58 at one end in the region of the joint 60. At its other end, it is integrally connected to the outer sleeve 64. This second joint is provided in Figure 3 by the reference numeral 74. With its side facing away from the combustion chamber window, the membrane 72 rests on the inner sleeve 62 and is additionally characterized by the pressure prevailing in the combustion chamber 14 or pressed by the tension of the inner sleeve 62 with the outer sleeve 64 against the inner sleeve 62. A gas-tight connection between the diaphragm 72 and the inner sleeve 62 is not necessary in the region of the joint 60, since the membrane is connected at its other end to the second joint 64 in a gastight manner with the outer sleeve 64. In Figure 3, the pressure relief hole is formed as a frusto-conical bore, the minimum diameter of outer diameter of the outer sleeve 64 is present. This prevents the penetration of dirt particles from the outside into the gap 64. At the same time the production cost and the flow resistance is also reduced. It is also possible to form the pressure relief bore 67 as stepped bores (not shown) or the pressure relief bore on

Outer diameter of the outer sleeve 64 to narrow locally after manufacture by a forming or upsetting process, so that in this way the penetration of dirt and other particles is effectively suppressed in the space. If the cross-section of the pressure relief device has a diameter of approximately 0.1 to 0.3 mm, then leakage quantities which occur at the sealing surface 70 between the shoulder 66 and the combustion chamber window 58 can be dissipated. However, if this seal fails completely, so that large pressure surges enter the space 65, the opening of the through hole must have a multi-square millimeter opening cross-section.

In the exemplary embodiment illustrated in FIG. 4, the membrane 72 is connected to the inner sleeve 62 in the region of the second joint 74. Also, the use of the membrane 72 causes relative movements between the combustion chamber window 58 and housing 38 can be compensated without major mechanical stresses and with respect to the materials and a degree of freedom in the selection of materials of inner sleeve 62, outer sleeve 64 and membrane 72 is obtained. FIG. 4 shows an exemplary embodiment of a pressure relief bore 67 according to the invention, in which the pressure relief bore is inserted through a filter insert 71 into the pressure relief bore 67. The filter element can be made of an open-cell foam made of plastic, ceramic or metal wires or metal fabric. Main task of the filter element 71 is to prevent the ingress of contaminants into the gap.

In Figure 5, the pressure relief hole 67 is closed by a plug 69. This plug 69 may be formed by a hot melt adhesive or other adhesive. By the plug 69 it is ensured that in normal operation no exchange between the gap 65 and the environment takes place. Only when a maximum permissible pressure in the intermediate space 65 is exceeded, the gas forces acting through the pressure relief hole on the plug 69, this push out of the bore 67 and the pressure relief hole is released. In the exemplary embodiments according to FIGS. 6a to 6c, further configurations of inner sleeve 62, outer sleeve 64 and pressure relief bores 67 are illustrated.

FIG. 7 shows a further exemplary embodiment of a pressure relief device according to the invention. In this embodiment, a longitudinal groove 73 is milled into the bolt thread of the inner sleeve 62, which allows a controlled pressure equalization between the gap 65 and the environment. Of course, it is also possible, in the nut thread of the outer sleeve 64 a longitudinal groove (not shown) to introduce.

Claims

claims

A laser ignition device for an internal combustion engine (10) comprising a laser active solid (44), a combustion chamber window (58) and a housing (38) with an inner sleeve (62) and an outer sleeve (64), wherein the inner sleeve (62) and an outer sleeve (64) delimiting a gap (65), characterized in that the housing (38) has a pressure compensation device (67), and in that the pressure compensation device (67, 73) connects the intermediate space (65) and the surroundings.

2. laser ignition device according to claim 1, characterized in that in the outer sleeve (64) has a pressure compensation bore (67) is provided, and that the pressure compensating bore (67) spaced from the combustion chamber window (58) from the housing (38) exits.

3. laser ignition device according to one of the preceding claims, characterized in that the pressure compensation bore (67) at its exit from the housing (38) has a minimum diameter, and that the diameter increases in the direction of the intermediate space (65).

4. Laser ignition device according to one of the preceding claims, characterized in that in the pressure compensation bore (67), a filter element (71) is provided.

5. laser ignition device according to one of the preceding claims, characterized in that the pressure compensation bore (67) by a plug (69), in particular of polyimide or silicone, is closed.

6. laser ignition device according to one of the preceding claims, characterized in that the outer sleeve (64) at its the combustion chamber (14) facing the end has a shoulder (66), and that the shoulder (66), the combustion chamber window (58) partially covered.

7. laser ignition device according to one of the preceding claims, characterized in that the outer sleeve (64) at its combustion chamber (14) facing away from the end has a female thread that the inner sleeve (62) has a with the female thread of the outer sleeve (64) cooperating bolt thread, and that a pressure relief groove (73) is formed in the nut thread and / or the bolt thread.