Abstract:
An ignition device for an internal combustion engine, in particular of a motor vehicle, includes at least one pump light source, which provides a pump light. Furthermore, a laser device is provided, which is able to generate a laser light for beaming into a combustion chamber. A waveguide device transmits the pump light from the pump light source to the laser device. The laser device includes at least one refraction device, for example, a lens, which refracts the pump light and is in one piece therewith.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an ignition device for an internal combustion engine. 
       BACKGROUND INFORMATION 
       [0002]    WO 02/081904 describes a generic ignition device, which is designed as a laser ignition device and is situated on a cylinder of an internal combustion engine. The actual laser device is connected to a pump light source, which optically pumps the laser device, via a waveguide device formed by fiberglass. 
       SUMMARY 
       [0003]    Example embodiments of the present invention provide an ignition device of the above-named type in such as to provide it to be mass-produced and used in the most economical possible manner. 
         [0004]    Features of example embodiments of the present invention are also provided in the description that follows and the drawings; the features may also be provided in example embodiments of the present invention in completely different combinations without explicit reference being made thereto. 
         [0005]    The refraction device provided according to example embodiments of the present invention may be manufactured very economically, for example, as an injection-molded part. A complex surface treatment which, for example, would be necessary for a reflector device may be omitted. The manufacturing costs for the ignition device according to example embodiments of the present invention are thus reduced. The single-part design of the refraction device according to example embodiments of the present invention having the laser device also results in simpler handling when the ignition device is installed in the internal combustion engine because the position of the refraction device within the laser device, which is important for the operation of the ignition device, is not modified despite the external forces acting thereon, but is reliably and accurately ensured. In addition, fewer separate parts are to be handled, which also reduces assembly costs and assembly times. 
         [0006]    A first advantageous refinement of the ignition device according to example embodiments of the present invention is characterized by the fact that the laser device includes a laser-active solid and the refraction device includes a lens which is situated on the injection side of the laser-active solid. The pump light refracted by the refraction device may thus be easily injected, mainly transversally, into the laser-active solid. Of course, if the lens is attached directly to the injection side of the laser-active solid, the attachment area on the lens is polished flat to avoid refraction of the pump light arriving in the laser-active solid longitudinally. 
         [0007]    The refraction device may, however, also include a lens which is situated between the laser-active solid and an optical amplifier. The laser-active solid is thus pumped only longitudinally or at least less transversally, whereas the optical amplifier is pumped at least also transversally. 
         [0008]    The refraction device may also include a lens which has an opening and is situated radially outside the laser-active solid. This offers the advantage, mainly when an optical amplifier is provided in series with the laser-active solid, that the laser light transmitted from the laser-active solid to the amplifier is not absorbed by the lens, i.e., the efficiency of the overall ignition device is relatively high. 
         [0009]    Another advantageous embodiment of the ignition device according to example embodiments of the present invention provides that a reflection device be provided, which reflects the pump light refracted by the refraction device to the laser-active solid and/or to the optical amplifier. This increases the degrees of freedom in the design of the ignition device. In particular it makes it possible to use the light refracted by the refraction device for longitudinal pumping of the laser-active solid and/or the optical amplifier. 
         [0010]    A relatively “slim” ignition device is created if the reflection device is situated coaxially with respect to the laser-active solid and/or to the optical amplifier and is at least substantially transparent to laser light. The efficiency is further improved if the reflection device is coaxial with respect to the laser-active solid and/or to the optical amplifier and has an opening through which the laser light may pass because in this case absorption of the laser light by the reflection device is prevented. 
         [0011]    It is advantageous if the laser device, including the laser-active solid, injection mirror, extraction mirror, Q-switch, amplifier, and lens are an overall single piece, optimally forming a monolithic component. 
         [0012]    Example embodiments of the present invention are described below in greater detail with reference to the appended drawing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0013]      FIG. 1  schematically shows an internal combustion engine having an ignition device; 
           [0014]      FIG. 2  schematically shows the ignition device of  FIG. 1 ; 
           [0015]      FIGS. 3 through 8  schematically show different example embodiments of the ignition device of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION  
       [0016]    An internal combustion engine is labeled overall with reference numeral  10  in  FIG. 1 . It is used for driving a motor vehicle. Internal combustion engine  10  includes a plurality of cylinders, only one of which is depicted and labeled with reference numeral  12  in  FIG. 1 . A combustion chamber  14  of cylinder  12  is delimited by a piston  16 . Fuel reaches combustion chamber  14  directly through an injector  18 , which is connected to a pressurized fuel reservoir (“rail”)  20 . 
         [0017]    Fuel  22  injected into combustion chamber  14  is ignited with the help of a laser beam or laser pulse  24 , which is beamed into combustion chamber  14  by an ignition device  27  including a laser device  26 . For this purpose, laser device  26  is supplied with pump light, which is provided by a pump light source  30 , via a waveguide device  28 . Pump light source  30  is controlled by a control and regulating unit  32 , which also activates injector  18 . 
         [0018]    As is apparent from  FIG. 2 , pump light source  30  supplies a plurality of waveguide devices  28  for different laser devices  26 . For this purpose, it has a plurality of individual light sources  34 , which are connected to a pulse current supply  36 . 
         [0019]    Laser device  26  includes a housing  38 , in which, viewed in the direction of the pump light, first a lens  40  forming a refraction device, then an injection mirror  42 , and further a laser-active solid  44 , a passive Q switch  46 , and an extraction mirror  48  are situated. Elements  40  through  48  are designed overall as a single-piece or monolithic component  50 . 
         [0020]    In  FIG. 2 , left of extraction mirror  48 , there is a focusing optical device  52 , which focuses laser beam  24  on a desired point  54 . Furthermore, laser device  26  has a combustion chamber window  56 , which seals housing  38  pressure-tight against combustion chamber  14 . 
         [0021]    Optical components of laser device  26  are depicted in  FIG. 3  in bolder lines, the sides being reversed with respect to  FIG. 2 . It is apparent that the outer diameter of lens  40  is significantly greater than the outer diameter of laser-active solid  44 . Lens  40  is fixedly connected to injection mirror  42 , for example, wrung together or bonded. This creates an overall single-piece monolithic unit  50 , which also includes lens  40 . 
         [0022]    The boundary surface (reference numeral  58  in  FIG. 3 ) connected to injection mirror  42  is polished or ground flat having a surface planarity &lt;X/ 4  (X =wavelength), so that the pump light beams (reference numeral  60  in  FIG. 3 ) introduced from lens  40  into injection mirror  42  and further into laser-active solid  44  reach laser-active solid  44  essentially without further refraction. As a variant, a central hole may also be provided in lens  40 .  FIG. 3  shows that, on the one hand, laser-active solid  44  is pumped longitudinally with pump light  60 , which passes through a central area  62  of lens  40  largely without refraction, and that laser-active solid  44 , on the other hand, is pumped transversally with pump light  64 , which is refracted in a radially outer edge area  66  of lens  40  toward laser-active solid  44 . 
         [0023]    Further example embodiments of the optical components of laser device  26  are shown in greater detail in  FIGS. 4 through 8  that follow. Here and in the following, elements and areas having the same or similar functions as elements and areas of a previously described example embodiment bear the same reference numeral and are not elucidated in detail again. 
         [0024]    The example embodiment shown in  FIG. 4  differs from the one shown in  FIG. 3  in that the former has an additional optical amplifier  68  which is molded onto extraction mirror  48  in one piece. Optical amplifier  68  is, on the one hand, pumped longitudinally by pump light  60 , which is not absorbed by laser-active solid  44 . In addition it is, however, transversally pumped by pump light  70  which is refracted, in an edge area  72  of lens  40  located radially far out, toward optical amplifier  68 . Using an appropriate design of lens  40  the ratio of pump light  60  and  64 , which is injected into laser-active solid  44 , to pump light  70 , which is injected into amplifier  68 , may be set in a simple manner in this example embodiment. 
         [0025]    The example embodiment depicted in  FIG. 5  of the essential optical components of laser device  26  in turn differs from that of  FIG. 4  by the fact that lens  40  is situated between laser-active solid  44  having injection mirror  42 , Q-switch  46 , and extraction mirror  48  on the one hand and amplifier  68  on the other hand. Laser light  24   a  generated in laser-active solid  44  thus passes through lens  40  to reach amplifier  68 . Laser-active solid  44  is also pumped, exclusively longitudinally, by pump light  60  exiting from waveguide device  28 ; lens  40  is thus used exclusively for refracting pump light  70  in radially outer edge area  72  toward optical amplifier  68  and thus pumping the latter transversally. 
         [0026]    Also in this case, an overall single-piece or monolithic component  50  is created by molding extraction mirror  48  on one side of lens  40  and optical amplifier  68  on the other side of lens  40  in one piece, for example, wrung together or bonded. For this purpose, again, the corresponding contact surfaces  58   a  and  58   b  of lens  40  are polished or ground flat, so that laser light  24   a  extracted from extraction mirror  48  reaches optical amplifier  68  unrefracted. Also in this example embodiment, the optical ratios may be set in a simple manner and with high accuracy by dimensioning the individual components. 
         [0027]    In the example embodiment shown in  FIG. 6 , similar to that of  FIG. 4 , optical amplifier  68  is situated directly on extraction mirror  48  on laser-active solid  44 . Lens  40  has a central opening  74 , into which the unit made up of laser-active solid  44  and optical amplifier  68  is inserted. Also in this case, an overall single-piece unit  50  may be created by puttying or gluing together single-piece part  50  made up of laser-active solid  44  and optical amplifier  68  with lens  40 . The example embodiment shown in  FIG. 6  differs from that of  FIG. 5  by increased efficiency because the laser light produced by laser-active solid  44  reaches optical amplifier  68  directly and does not need to pass through lens  40 . 
         [0028]    The example embodiment shown in  FIG. 7  has a design similar to that of  FIG. 6 . However, it also includes a reflection device  76  which in  FIG. 7  is situated to the right of optical amplifier  68  in the axis of laser light beam  24  exiting therefrom. Reflection device  76  is at least essentially transparent to laser light  24  but essentially reflecting for pump light  80  refracted by lens  40 . Lens  40  is designed in such a way that it does not refract pump light  80  or at least does not refract it transversally to optical amplifier  68 , but to reflection device  76 , which pumps pump light  80  longitudinally into optical amplifier  68 . It is understood that the basic system shown in  FIG. 7  could also be combined with those of  FIGS. 4 and 5 . 
         [0029]    The example embodiment of a laser device  26  shown in  FIG. 8  is again based on that of  FIG. 7 . The only difference is that reflection device  76  of the example embodiment of Figure  8  has a central opening  78 , through which laser light  24  emitted by optical amplifier  68  may pass. This has the advantage that reflection device  76  may be provided with a higher efficiency, i.e., higher reflection, and at the same residual absorption of laser light  24  in reflection device  76  is ruled out. 
         [0030]    The reflector (no reference numeral) of reflection devices  76  of  FIGS. 7 and 8  is flat. However, it may also be curved, so that reflection devices  76  would also have a focusing function.