Abstract:
A hermetically sealed and/or ignition protection housing is provided with heat bridges at discreet points. The heat bridges form mounting faces in the interior space of the housing and also on the outer side. Heat from the interior of the housing generated by an item on the interior mounting faces is dissipated outwardly at the corresponding points by means of the heat bridges.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is the national phase of PCT/EP2006/011396, filed Nov. 28, 2006, which claims the benefit of German Patent Application No. DE 102006013017.0, filed Mar. 20, 2006. 
     FIELD OF THE INVENTION 
     The present invention relates generally to hermetically sealed and/or ignition protective housings, and more particularly, to housings of such type which are adapted to dissipate heat outwardly from heat generating components mounted within the housing. 
     BACKGROUND OF THE INVENTION 
     Housings of the flameproof protection enclosure type Ex-d are used for accommodating electric and electronic components that themselves do not conform to any type of explosion protection regulations. Except for very narrow flashover-proof gaps in the region of mechanical lead-throughs in the housings of this type, they are hermetically sealed. The width of such gaps in Ex-d housings is such that ignition of an explosive gas mixture in the interior of the housing does not result in the release of any particles that could ignite an explosive mixture in the surroundings of the housing. The gap width is in the range of tenths of a millimeter. Accordingly, it is difficult to cool individual semiconductors having high power loss within such a housing. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a flame-proof protection housing of the foregoing type which permits easy cooling of heat generating devices within the housing. 
     The inventive housing features an essentially hermetically sealed interior that is surrounded by housing walls. At least one of the housing walls contains a thermal bridge that makes it possible to dissipate heat outwardly from the interior. This thermal bridge includes an elevation that protrudes inwardly from the housing wall and has a mounting face for the component to be cooled. Another elevation with a mounting face for a cooling element is arranged on the outside of the housing wall such that it is aligned with the inwardly protruding elevation. By use of individual elevations on both inner and outer sides of the housing wall, the formation of the mounting faces is considerably simplified. 
     In order to achieve a low thermal resistance, the mounting faces for the component to be cooled and for the cooling element usually need to be planar. If the housing is made of cast iron, the surfaces naturally are relatively rough. The processing required for effecting planar mounting faces results in a material weakening at the respective location of the wall, which usually is unacceptable for reasons of explosion protection unless the remainder of the wall is formed with such excess dimensions that it remains sufficiently thick after the processing in the region of the mounting faces. 
     In the context of the present invention, the wall is made thicker in the region in which the thermal bridge is produced than in the remainder of the wall. This makes it possible to remove material in the region of the thermal bridge without impairing the stability or pressure resistance of the housing. This furthermore makes it possible to easily provide thermal bridges on different walls such that they are spatially separated from one another. Consequently, the cooling elements or cooling devices provided on the outside of the housing can also be spatially separated from one another in order to largely preclude a mutual impairment of the cooling effect. 
     Finally, forming thermal bridges by utilizing locally defined elevations on the inner and the outer wall provides the advantage of inducing a lower heat distortion in the housing wall. This is also important, particularly with respect to larger housings, because a significant distortion can cause the housing cover, under certain circumstances, to no longer satisfy the explosion requirements. The gap between the cover and the housing frame can become impermissibly large due to such a distortion. The massive and spatially concentrated thermal bridge makes it possible to effect a concentrated heat dissipation from the housing at its designated location and largely keeps the heat away from the remainder of the wall. In addition, the elevations also make it possible to eliminate an impairment caused by any type of reinforcing ribs provided on the wall. 
     The housing is advantageously provided with at least one essentially flat housing wall. The inventive solution is suitable for use with round housings, as well as square or cuboid housings. The housing wall containing the thermal bridge preferably consists of a material with adequate thermal conductivity. The elevations on the inner side and the outer side can then be directly formed integrally out of the wall material. 
     It is furthermore possible to arrange the thermal bridge in a corresponding opening in the housing wall, for example, in the form of a bolt that extends through the housing wall in a sealed fashion. Openings for this purpose may be threaded openings into which the bolt in the form of a threaded bolt is screwed and adhered to the bore thread. Instead of the adhesion, it also would be possible to insert the bolt such that an Ex gap is formed. In this case, a correspondingly designed thread may serve as the Ex gap. 
     Favorable conditions are achieved if the elevations have the shape of a truncated cone or a truncated pyramid. In this case, the, elevations on the inner and the outer side respectively face one another with their largest cross-sectional surface. Advantageous mounting options also are achieved if the mounting face consists of a plane face. 
     If a larger amount of heat needs to be transferred, it would be easily possible to arrange several of the thermal bridges adjacent to one another, wherein each thermal bridge respectively carries either a group of components or an individual component. All thermal bridges can be connected to a common cooling element on the outer side. 
     In order to mount the cooling element and the components, the thermal bridges may contain threaded bores in the mounting faces or plane faces, respectively. These bores preferably are in the form of blind holes in order to avoid undesirable passages in the region of the bores. 
     Basic embodiments of the invention are described below with reference to the figures. When reading through the description of the figures, it becomes clear that the individual characteristics of the embodiments can be arbitrarily combined with one another. A description of all subcombinations of the individual embodiments would unnecessarily inflate the volume of this application. 
     In other respects, additional refinements of the invention form the objects of the dependent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded fragmentary perspective of a protective housing having thermal bridges in accordance with the invention; and 
         FIG. 2 , a representation similar to  FIG. 1 , of an alternative embodiment with a different variation of the thermal bridge. 
     
    
    
     While the invention is susceptible of various modifications and alternative constructions, certain illustrative embodiments thereof have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now more particularly to  FIG. 1  of the drawings, there is shown an illustrative housing of the flame proof encapsulated Ex-d type in accordance with the invention. The illustrated housing  1  includes a housing base body  2  that is closed with a cover  3 . The cover  3  and contact surface on the housing base body  2  form an Ex-d type gap  4 . 
     The housing base body  1  is formed by a housing rear wall  5  and a frame that surrounds the rear wall  5  consisting of a bottom wall  6 , a housing side wall  7  (particularly visible in  FIG. 1 ), a housing roof  8 , and a second housing side wall that is cut away from view in  FIG. 1  and extends parallel to the other housing side wall  7 . Pairs of the individual walls respectively extend parallel to one another such that the housing base body as a whole has a cuboid shape. 
     The housing bottom wall  6 , the two housing side walls  7  and the housing roof  8  form a closed ring-shaped cover contact surface  9 , which forms one side of the Ex-d gap  4 . The housing rear wall  5 , the bottom wall  6  and the housing side walls  7 , as well as the housing roof  8 , consist of essentially planar structures with approximately parallel planar sides that face the housing interior and essentially planar faces that are directed outward. 
     The housing cover  3  also has essentially a shell or planar faxed shape with a contact surface  11  for mating with the housing base body  2  on its shell-shaped cover edge  11 . The contact surface  12  is complementary to the cover contact surface  9  and forms the other side of the Ex-d gap  4 . 
     In the region of the cover contact surface  9 , the housing base body  2  is provided with a number of integrally cast beads  13  that extend perpendicular to the Ex-d gap  4  and correspond to complementary beads  14  or thickenings on the cover  3 . These beads  13  contain threaded bores for screwing in screws that are inserted into stepped holes  15  in the beads  14  and serve for screwing the cover  3  to the housing base body  2 . 
     The housing  1  serves to accommodate electronic components, one of which is illustrated in the form of a power transistor  16  in the SOT  220  housing. In order to dissipate heat generated from the electronic component  16  or other electronic components, several thermal bridges  17  extend through the housing wall  5  such that they are spatially separated from one another. The thermal bridges serve for thermally coupling the heat-generating components  16  to an externally mounted rib-type cooling element  18 . 
     Each of the illustrated thermal bridges  17  is composed of a projection  19  in the shape of a truncated cone that protrudes into the housing interior and a corresponding projection  21  in the shape of a truncated cone that protrudes from the outside of the housing rear wall. The two projections  19 ,  21  of each thermal bridge  17 , which in this case are in the shape of truncated cones, are aligned with one another in such a way that they lie on a common axis that extends perpendicular to the housing rear wall  5 . 
     The inner projection in the shape of a truncated cone ends in a planar face  22  that serves as the mounting face for the power semiconductor  16 . A threaded blind hole  23  extends through the mounting face  22 . In the embodiment shown, all mounting or plateau faces  22  in the interior of the housing lie in a common plane such that it is also possible to mount larger heat-emitting components on several thermal bridges  17 . 
     The projection  21  on the outer side also has the shape of a truncated cone and similarly has an outwardly directed mounting or planar face  24 , through which a threaded blind hole  25  extends coaxially. The thermal bridges  17  on the outer side are identically formed such that the plateau faces or mounting faces  24  on the outer side also lie in the same plane. This makes it possible to utilize the cooling element  18  for several thermal bridges  17 . At each thermal bridge  17 , the corresponding projections in the shape of truncated cones face one another with their base surfaces. 
     The cooling element  18  has a plane mounting face  26  from which cooling ribs  27  extend toward the opposite side. Through-bores  28  for mounting screws  29  are situated between the corresponding cooling ribs, wherein said mounting screws serve for mounting the cooling element  18  on the two visible thermal bridges  17  shown in  FIG. 1 . 
     The illustrated thermal bridges  17 , which form an integral part of a housing wall, are particularly suitable for housings that consist of a metal alloy with adequate thermal conductivity, for example, an aluminum alloy. Since the thermal bridges  17  are raised on the inner side, the plane faces or mounting faces  22  can be easily produced without weakening the housing wall during the production process. This is particularly advantageous if the housing is made of cast iron housing which is common practice with housings of this type. Due to the casting technique, such mounting faces would be rough and also have significant tolerances. In the embodiment shown, the integrally cast projections  19  in the shape of truncated cones can be readily machined on their mounting face side. 
     The thermal bridges  17  can be selectively located at desirable positions. It is also easily possible to form the thermal bridges  17  with mounting faces that lie in a common plane as indicated above. This makes it possible to mount large-volume heat-generating elements on several thermal bridges  17 . However, it further is possible to position a thermally conductive plate on several thermal bridges  17 , wherein the thermally conductive plate accommodates several individual power semiconductors  16  or other heat-generating components. The heat is transferred outward to the cooling element  18  in a concentrated fashion via the thermal bridges  17 . 
     A similar production technique applies to the projections of thermal bridges  17  that are in the shape of truncated cones situated on the outer side. The processing of the housing is significantly simplified. Only little material needs to be removed in order to create a planar mounting face for the large cooling element  18 . 
     The tightness of the housing is preserved because the mounting bores are in the form of blind holes. The elevations in the shape of truncated cones also facilitates the formation of blind holes with a sufficient screw-in depth. 
     While the invention has been described in connection with a housing of the “protection type flameproof enclosure,” it should be understood that the inventive solution can also be advantageously utilized with housings of the “protection type powder filling.” In that application, one also encounters the problem of having to dissipate the heat of heat-generating electronic or electric components outward. Sand is a relatively inferior thermal conductor and thermally insulates the components quite well. It is therefore correspondingly difficult to dissipate the heat of the components outwardly. However, this can be easily effected with the inventive solution. 
       FIG. 2  shows another embodiment of the thermal bridges  17 . In this case, the thermal bridges consist of individual cylindrical bolts  17   a  that are inserted into corresponding through-bores  31  in the housing rear wall. 
       FIG. 2  shows a housing in a form similar to that of  FIG. 1 . In contrast to  FIG. 1 , it is assumed that the housing wall has an inferior thermal conductivity, for example, because the housing wall  5  consists of a fiber-reinforced plastic material. In order to still dissipate heat outwardly through such a relatively well-insulating material, the aforementioned through-holes  31  are provided in the housing rear wall  5 . It suffices to merely provide these openings if the housing rear wall has a corresponding material thickness. However, if the material thickness is insufficient, it is advantageous to provide the housing rear wall  5  with thickened portions  32  in the shape of truncated cones in the vicinity of the bores  31 , as shown in  FIG. 2 . The thermal bridge  17 , for example, in the form of a copper bolt is inserted into this opening  31  in a sealed fashion. As illustrated in the enlarged detail, this can be effected by providing the copper bolts  17   a  with an external thread  33  that engages a corresponding internal thread in the bore  31 . 
     The copper bolt again has the blind holes  23 ,  25  for rigidly screwing and securing on the heat-generating semiconductor  16 . If a uniform height is desired, the copper bolts  17  are machined on the face side as described following the insertion. 
     As another variation, it is possible to insert the thermal bridge  17  in the form of a bolt into a smooth opening  31  and to tighten the bolt against the housing with corresponding nuts from both sides. In that case, however, the surfaces adjacent to the through-opening have to be processed accordingly. Such a preparation is not required if the thermal bridge  17  is screwed into a corresponding thread and adhered therein. It suffices to process the thermal bridges  17  on the face sides after the adhesion or securement process in order to produce the mounting faces. 
     From the foregoing, it can be seen that a hermetically sealed or protective housing is provided that has heat dissipation thermal bridges at discrete points. The thermal bridges form mounting faces in the interior of the housing, as well as mounting faces on the outer side. Heat from the interior of the housing is dissipated outwardly at the corresponding points via the thermal bridges.