Abstract:
An oven light including an attachment sleeve which is attachable in a recess of a cooking cavity wall; a light permeable cover which closes the recess of the cooking cavity wall; an illuminant which is arranged behind the light permeable cover and whose emitted light is used for illuminating the cooking cavity, wherein the illuminant is formed by at least one LED which emits light in a light cone (K), wherein the LED is arranged on a cooling element which dissipates operating heat of the LED, wherein a heat barrier is arranged between the cover and the LED and protects the LED from a cooking temperature, wherein the light cone penetrates an arrangement plane of the heat barrier, characterized in that the heat barrier includes at least one in particular light permeable heat shield with an opening through which light of the LED propagates in a direction towards the cover.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority from German Patent Application DE 10 2015 114 253.8 filed on Aug. 27, 2015 which is incorporated in its entirety by this reference. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to an oven light. 
       BACKGROUND OF THE INVENTION 
       [0003]    Oven lights are known in the art in many configurations. When LEDs are used as illuminants efforts are being made in the art to either effectively dissipate heat that is radiated from the oven cooking chamber in a portion of the LED illuminant effectively or to protect the LED from the heat of the cooking chamber through suitable heat barriers. 
         [0004]    DE 10 2005 044 347 A1 discloses for example the option to fill a gap between the illuminant and the cooking chamber with a silica-aero gel which also insulates against the heat radiation of the cooking chamber. DE 10 2009 02 775 A1 proposes to place a cylindrical element between the cooking chamber and the LED which cylindrical element is configured light permeable and protects the LED from the heat radiation. Additionally this printed document also discloses a ventilation concept for effective heat dissipation. EP 2 233 839 A1 illustrates for example that a gas filled cylinder is useable to offset the LED from the cooking chamber while still putting a sufficient amount of light into the cooking chamber. 
         [0005]    However, it has become apparent that the insulation devices known in the art which protect the LED from heat of the cooking chamber have a disadvantageous effect on the light yield and furthermore render orienting the light for optimum illumination of the cooking chamber very difficult. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    Thus, it is an object of the invention to provide an oven light whose heat barrier protecting the LED substantially does not influence its light emission. 
         [0007]    The object is achieved by an oven light including an attachment sleeve which is attachable in a recess of a cooking chamber wall and includes a light permeable cover which closes the recess of the cooking chamber wall, an illuminant which is arranged behind light permeable cover and whose emitted light illuminates the cooking chamber wherein the illuminant is formed by at least one LED which emits the light in a light cone, wherein the LED is arranged on a cooling element which is used for dissipating operating heat from the LED, wherein a heat barrier is arranged between the cover and the LED and protects the LED from a cooking temperature, wherein the light cone penetrates an arrangement plane of the heat barrier. 
         [0008]    The core idea of the invention is to protect the LED against heat radiation on a surface that is as large as possible and to only configure the heat shield permeable where the light has to pass through. Thus, a rather thin window pane shaped heat shield is used instead of thick insulation layers. The advantageous embodiment provides that the opening of the heat shield with respect to shape and/or width of the light cone essentially corresponds to a contour of the light cone in an arrangement plane of the heat shield. Thus, the invention takes advantage of the fact that the LED emits essentially emits oriented light which has little scattering. This facilitates providing an opening in the heat shield which is similar to the contour of the light cone with respect to diameter and shape. Thus, the opening will be the smaller, the closer the heat shield is arranged to the LED. This facilitates providing unrestricted light passage through the heat barrier and to simultaneously increase the surface of the heat shield that protects against the heat radiation of the cooking chamber. 
         [0009]    In a particularly advantageous embodiment of the invention it is provided that the heat barrier includes plural pane shaped heat shields which are arranged between the LED and the cover and which have a different distance from the LED, wherein the opening of each heat shield with respect to shape and/or width essentially corresponds to a contour of the light cone in the respective arrangement plane. 
         [0010]    The inventors have found that a staggered arrangement of plural heat shields behind one another between the LED and the cover of the oven light provides a very effective reduction of the heat load. Thus, care has to be taken that the openings of the heat shields arranged in different positions relative to the LED providing the light pass through increase in size with a distance from the LED. Each opening essentially corresponds to the light cone in the respective arrangement plane with respect to contour and diameter so that the light pass through can be provided almost unimpeded. Thus, it is also essential that the openings of the heat shields can be configured unfilled so that even light losses through translucent materials provided in the beam path can be avoided. This certainly does not preclude that in particular an opening of one of the staggered heat shields that is proximal to the LED can be provided with a support for a reflector and an optic arrangement. 
         [0011]    When the heat shields are arranged staggered behind one another they are respectively offset from each other by a gap shaped opening. It is provided that an air circulation between the cooking chamber and an outer oven wall providing heat dissipation is run through the gaps between the heat shields and improves heat dissipation in this portion. 
         [0012]    In order to provide a unit that can be mounted easily it is provided that the heat shields are connected with each other and the heat barrier includes support devices for cooling elements at an end of the heat barrier that is oriented away from the cover. 
         [0013]    As stated supra it is provided that an opening proximal to the LED forms a support for a reflector and/or an optics arrangement. 
         [0014]    It is furthermore provided that the attachment sleeve includes support devices for the heat barrier. 
         [0015]    It is a particularly advantageously feature of the invention that the heat barriers are made from materials which have medium to low heat conductivity. Therefore it is conceivable that each heat shield is made from a highly temperature resistant plastic material. Materials from the group of liquid crystal polymers are for example among these highly temperature resistant plastic materials. 
         [0016]    Alternatively it is provided that each heat shield is made from a mineral material, in particular mica. Mineral materials are particularly advantageous when the expected heat load is particularly high. This has to do on the one hand side with the expansion properties which are more advantageous compared to the plastic materials recited supra. Additionally the temperature resistance of mineral materials is much higher than the temperature resistance of plastic materials. Mica has the essential advantage that it already includes reflecting portions. Thus, the mica not only hinders heat pass through towards the LED through its low heat conductivity, but it also reflects heat radiation. 
         [0017]    The reflection of the heat radiation is further improved when a surface of the heat shield that is oriented towards the cover is configured heat reflecting. 
         [0018]    Eventually it is provided that the cover, the attachment sleeve, the heat barrier, the LED and the cooling element form a pre-assembled component. 
         [0019]    In order to provide controlled scattering of the light it is provided that the attachment sleeve includes a light reflecting inner surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    An improved understanding of the invention and additional advantages can be derived from the subsequent description of an advantageous embodiment with reference to drawing figures: 
           [0021]      FIG. 1  illustrates a sketch of an operating principle of a heat barrier in an oven light according to the invention; 
           [0022]      FIG. 2  illustrates an exploded view of the oven light according to the invention in a first embodiment; 
           [0023]      FIG. 3  illustrates a longitudinal sectional view of the oven light according to  FIG. 2 ; 
           [0024]      FIG. 4  illustrates a simplified illustration of the light emission of the oven light according to the invention according to  FIG. 2 ; 
           [0025]      FIG. 5  illustrates an exploded view of a second embodiment of an oven light according to the invention; and 
           [0026]      FIG. 6  illustrates the oven light according to  FIG. 5  in a longitudinal sectional view. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    In the figures an oven light is designated overall with the reference numeral  10 . 
         [0028]    As illustrated in the exploded view in  FIG. 2  the oven light  10  includes an attachment sleeve  11  for the oven light  10  in a recess of a cooking chamber wall. The attachment sleeve  11  is provided with a light permeable cover  12  configured as a cover glass  13  at a side oriented away from the LED  15 . The cover glass  13  includes a shaft  17  that is provided with an external thread  16 . The attachment sleeve  11  includes protrusions  18  directed into an interior space of the attachment sleeve  11  and forming thread path sections. Through an interaction of the exterior thread  16  with the protrusions  18  the cover glass  13  is threadable into the attachment sleeve  11 . Interlocking lobes  19  of the attachment sleeve  11  are offset towards the LED  15  by a flange shaped collar  20 . The interlocking lugs  19  receive an oven wall between themselves and the collar  20  and thus fixate the oven light  10  at the cooking chamber wall. 
         [0029]    Thus, the attachment sleeve  11  has first retaining devices  21  and positioning pins  22  at ends oriented towards the LED  15 . The first retaining devices  21  are used for fixating a heat barrier  14  at the attachment sleeve  11 . The heat barrier  14  includes positioning openings  23  that are associated with the positioning pins  22 . The positioning pins  22  engage the positioning openings  23  in order to fixate the heat barrier  14  at the attachment sleeve  11 . The retaining devices  21  fixate the heat barrier  14  at the attachment sleeve  11 . 
         [0030]    The oven light  10  furthermore includes a cooling element  24  on which the LED  15  is arranged with its circuit board. The cooling element  24  is used for dissipating operating heat from the LED  15  to the ambient air. In order to assure good light yield and in order to influence the light emitted by the LED  15  a reflector  25  and an optical element  26  are provided. 
         [0031]    The heat barrier  14  includes  3  heat shields that are arranged offset from each other and which are designated with reference numerals  27 - 29 . The heat shields  27  and  28  and  28  and  29  are configured pane shaped and attached at one another through spacers  30  so that a respective air gap  31  is formed between the first heat shield  27  and the second heat shield  28  and between the second heat shield  28  and the third heat shield  29 . 
         [0032]    Eventually the heat barrier  14  includes second retaining elements  32  at its end oriented towards the LED  15  wherein the second retaining elements can for example be configured as interlocking elements. The interlocking elements are used for fixating the cooling element  24  at the heat barrier  14 , wherein the LED circuit board is supported between the heat barrier  14  and the cooling element  24 . Thus, a separate attachment of the LED circuit board at the cooling element  24  is not required. 
         [0033]    In the first embodiment of the invention according to  FIGS. 2 and 3  the heat barrier  14  is a one piece injection molded plastic component. 
         [0034]      FIGS. 5 and 6  illustrate a second embodiment of the invention. It differs essentially only through the configuration of the heat barrier  14  which is made in this embodiment from individual pane shaped mineral heat shields  27  through  30 . These heat shields are attached at one another through a support clamp  33  which in turn forms second support devices  32  for arranging the cooling element at the heat barrier  14 . In order to be able to arrange the reflector  25  and/or the optical element  26  in the portion of the LED  15  a separate optical support  34  is provided in this embodiment. In this second embodiment the retaining clamp  36  defines the position of the heat shields  27  through  29  and the distance between them. 
         [0035]    An essential element of the oven light  10  according to the invention is a novel configuration of the heat barrier  14 . This portion of the invention is now described with reference to  FIG. 1 .  FIG. 1  omits a number of elements of the oven light  10  for purposes of clarity. The LED  15  and the heat shields  27 ,  28  and  29  are illustrated. The first heat shield  27  is arranged proximal to the LED  15 , the third heat shield  29  is arranged remote from the LED. The second heat shield  28  is arranged between the first heat shield  27  and the third heat shield  29 . An essential feature of the heat shields  27 ,  28 ,  29  is their pane configuration. Each heat shield  27  through  29  is arranged parallel to the LED circuit board. Each heat shield  27  through  29  is made from a light permeable material and respectively includes an opening. The openings are provided with the reference numerals  35  through  37 . 
         [0036]    LEDs essentially provide oriented light so that the LED  15  emits a cone shaped beam bundle with a defined opening angle. The light cone K in  FIG. 1  is defined by exemplary light beams L. The opening angle of the light cone K is approximately 120°. 
         [0037]    Each heat shield  27  through  29  is arranged respectively in an arrangement plane E 1 -E 3  and the non illustrated cover  12 . The light cone K passes through each of these arrangement planes E 1 -E 3 , wherein its enveloping lines define surfaces in the respective plane E 1 -E 3  that have approximately identical contours but different sizes. The respective surface is an image of the light beam contour in the respective plane E 1 -E 3 . 
         [0038]    In order to provide unimpeded light passage through the heat shields  27 - 29  the openings  35 - 37  are provided in the respective heat shield  27 - 29 . Thus, the opening  35 - 37  of each heat shield  27 - 29  with respect to shape and/or width essentially corresponds to the contour of the light cone K in the respective arrangement plane E 1 -E 3 . Put differently a surface is cut out in a shape of an opening  35 - 37  in the respective heat shields  27 - 29  wherein the opening is defined by the enveloping lines which intersect the respective arrangement plane E 1 -E 3 . 
         [0039]    With an increasing distance of the heat shield  27 - 29  from the LED  15  the respective openings  35 - 37  become larger. Accordingly the opening  35  of the first heat shield  27  is the smallest opening, the opening  36  of the second heat shield  28  is larger corresponding to the expanding light cone. In the embodiment according to  FIG. 1  the opening  37  of the third heat shield  29  has the greatest width. 
         [0040]    When the respective opening  35 - 37  in the respective arrangement plane E 1 -E 3  corresponds to the contour of the light cone K in the respective arrangement plane E 1 -E 3  also the edge beams of the light cone K will run freely through the respective openings  35 - 37 . When statements are made that the openings with respect to contour and/or width essentially correspond to the contour of the light cone in the respective arrangement plane, this means that the applicant has certain latitude when practicing the invention. On the one hand side it is conceivable that the openings  35 - 37  are slightly larger than required corresponding to the dimensions of the light cone K in the respective arrangement plane E 1 -E 3 . This helps to compensate for production tolerances in the LEDs  15  which can lead to slightly varying opening angles of the light cones K. Furthermore this helps to counter arrangement tolerances between the LED  15  and the heat shields  27 - 29  in the sense of a maximum light yield. 
         [0041]    By the same token it is conceivable, however, that the openings  35 - 37  are configured narrower. Thus, a loss of light power occurs through shadowing of the peripheral beams of the light cone K. In turn, however, the heat shielding is improved. It is also well known that LEDs  15  do not necessarily emit light in a shape of a circular cone so that deviations from the cone contour of the LED  15  facilitate influencing the contour of the actually exiting light cone K. When using typical LEDs  15  which emit light in a shape of a circular cone deviations from the circular cone contour can be used to influence a desired exit contour of the light cone K. 
         [0042]    It is apparent from  FIG. 1  how the heat shields are used for heat shielding the LED  15 . The heat radiation is indicated by arrows W. The heat radiation is oriented essentially perpendicular to the circuit board. Each heat shield  27 - 29  absorbs a portion of the heat radiation W. The absorption is thus optimized specific to the arrangement pane. Thus, each heat shield  27 - 29  is opened by the respective opening  35 - 37  just to the extent which is required for optimized light exit. The remaining surface of the heat shields  27 - 29  in the respective arrangement plane E 1 -E 3  is available for absorbing the heat radiation. 
         [0043]    It is provided to produce the heat shields  27 - 29  from a material with low heat conductivity, so that a transfer of heat radiation from a heat shield  27  through  29  to another heat shield  27 - 29  is as small as possible. High temperature resistant plastic materials, for example from the group of liquid crystal polymers have proven suitable. Mineral materials, however, are particularly suitable, in particular layered minerals for example mica. In addition to low heat conductivity of the materials it is furthermore provided that air circulates along the gaps  31  between the heat shields  27 - 29  wherein the air is also used for heat dissipation. Eventually heat shielding can be significantly improved in that surfaces of the heat shields  27 - 29  oriented towards the cover  12  are provided with a heat reflecting coating. 
         [0044]    To sum it all up the advantage of all embodiments of the invention is that contrary to the prior art stacking plural pane shaped heat shields  27 - 29  behind one another in different arrangement planes, E 1 -E 3  minimizes the heat radiation emitted by the cooking cavity in view of maximum light yield. This is achieved by the invention in that each heat shield  27 - 29  is only opened far enough as required by the light cone K emitted by the LED  15 , whereas the remaining surface portions are closed. 
         [0045]    The embodiments of the oven light  10  in  FIGS. 2 and 3 and 5 and 6 , however, are configured differently due to the heat shields  27 - 29  having different configurations. As stated supra the heat barrier  14  in the first embodiment of  FIGS. 2 and 3  is configured as a one piece injection molded plastic component. Selecting plastic as a material for configuring the heat shields  27 - 29  facilitates in a simple manner to configure the first heat shield  27  to support reflectors  25  and optical elements  26 . According to  FIG. 3  the first heat shield  27  forms an annular wall  38  that envelops its opening  35  and that is oriented perpendicular to the LED circuit board. The annular wall  38  is sized with respect to its height so that it can receive a reflector  25  and an optical element  26  configured as a cover glass or a lens. In order to provide a secure support of the reflector  25  and the optical element  36  the annular wall  38  includes an inward oriented support flange  39  at its end oriented towards the cover  12 . Since eventually an inner circumference of the support flange  39  defines the optically effective opening width and opening contour of the opening  35  of the first heat shield this has to be considered in view of maximizing the light yield. 
         [0046]    Using mineral materials for producing the heat shields  27 - 29  necessitates certain configurative changes due to the material properties which are considered in the second embodiment according to  FIGS. 5 and 6 . The heat shields  27 - 29  included therein are respectively configured as individual elements. However, they are attached amongst each other by a metal support clamp  33 . Thus, a separate optics support  34  is provided in order to arrange reflectors  25  or optics elements  26  for example configured as a lens or glass cover in front of the LED  15 . Also the optics support includes an annular wall  38  with a reflector  25  or an optical element  26  arranged therein. This annular wall  38  penetrates the opening  35  of the first heat shield  27  and includes an annular flange  40  with an expanded diameter. The annular flange contacts a bottom side of the first heat shield  27  that is oriented towards the LED  15 , so that a precisely positioned and supported arrangement is provided. Additionally the optical support  34  can be fixated at the cooling element  24  through bars  41 . 
         [0047]      FIGS. 2 and 3  and also  FIGS. 5 and 6  illustrate that the attachment sleeve  11  is the supporting element for the cover  12  and also for the heat barrier  14  and the cooling element  24  arranged thereon. The reflector  25 , the optical element  26  and the LED  15  are also components that are coupled together. This way an oven light  10  is provided that can be pre-assembled and inserted into a recess in the cooking cavity with a few manual steps during the assembly process of an oven. 
         [0048]    It is illustrated based on  FIG. 4  how the light emitted by the LED  15  propagates through the heat barrier  14  and the cover  12  into the cooking cavity. Due to the optimized opening width of the openings  35 - 37  of the heat shields  27 - 29  of the heat barrier  14  the light emissions of the LED  15  reach the portion of the attachment sleeve  11  unimpeded. A portion of the light emission can propagate into the cooking cavity of the oven as direct light dL unimpeded by the light permeable cover  12 . Since the opening in the cooking cavity wall, however, is smaller than the extension of the light cone K in this plane the peripheral beams of the light cone K are deflected by a reflecting inner surface of the attachment sleeve  11  and propagated through the light permeable cover  12  into the cooking cavity. Thus this portion reaches the cooking cavity as indirect light iL. Thus, a distance between the reflection portion of the attachment sleeve  11  for the peripheral beam of the light cone K and the recess of the cooking cavity wall is sized so that the peripheral beams pass through the light permeable cover  12  proximal to the recess edge of the oven wall. This way it is assured that no substantial light losses are to be expected also in this portion. 
       REFERENCE NUMERALS AND DESIGNATIONS 
       [0000]    
       
           10  oven light 
           11  attachment sleeve 
           12  light permeable cone 
           13  cover glass 
           14  heat barrier 
           15  LED 
           16  external thread 
           17  shaft 
           18  protrusion 
           19  interlocking lobe 
           20  collar 
           21  first retaining device 
           22  positioning pin 
           23  positioning opening 
           24  cooling element 
           25  reflector 
           26  optical element 
           27  first heat shield 
           28  second heat shield 
           29  third heat shield 
           30  spacer 
           31  air gap 
           32  second retaining device 
           33  support clamp 
           34  optics support 
           35  openings of  27   
           36  opening of  28   
           37  opening of  29   
           38  annular wall 
           39  support flange 
           40  annular flange 
           41  bar 
         K light cone 
         L light beam 
         dL direct light 
         iL indirect light 
         W heat radiation 
         E 1 -E 3  arrangement planes