Abstract:
An electrical device having a housing and moisture-sensitive electrical structural units situated in the housing, having a pressure compensation element situated in a housing part, which avoids, preferably prevents, the ingress of moisture, the pressure compensation element including a diaphragm which is permeable to gas, having an impact protection element situated in front of the diaphragm, which at least avoids spraying a liquid directly onto the diaphragm, wherein the impact protection element is in one piece part of the housing part.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an electrical device having a pressure compensation element. 
     BACKGROUND INFORMATION 
     An electrical device having a pressure compensation element is described in German Patent Application No. DE 38 17 227, in which the pressure compensation element is inserted into an opening in a housing. A disadvantage of this design is that on the one hand the pressure compensation element is composed of numerous individual parts, and on the other hand an additional joining process is necessary for fastening the pressure compensation element in the housing. 
     SUMMARY OF THE INVENTION 
     The electrical device according to the present invention has the advantage that the design of the impact protection element as a part connected in one piece to the housing part results overall in an electrical device having a pressure compensation element which on the one hand is very effective and on the other hand is very easy to manufacture. 
     According to a further embodiment of the present invention, the impact protection element is situated in a recess and extends or rises above a base of the recess. As a result of these measures it is very difficult for the liquid impinging on the electrical device, for example during high-pressure cleaning using a compact high-speed liquid jet, to, on the one hand, deflect this liquid jet onto the impact protection element, and on the other hand, to exert high pressure on the surfaces at that location. These measures on the one hand avoid liquid even reaching the region of the pressure compensation element, and on the other hand avoid liquid striking the surfaces at a high momentum. As a result of these measures, very little liquid reaches a diaphragm at all. If the impact protection element is fastened to the base of the above-mentioned recess via individual supports, it is possible to provide openings which enable air exchange with the interior of the housing for the electrical device. When the outer sides of the supports form an enveloping surface in the shape of a truncated cone, this results, on the one hand, in the above-mentioned surface which is hardly exposable to a direct liquid jet, and on the other hand this design allows this contour of the pressure compensation element to be easily demolded from an injection mold. This injection mold is necessary for manufacturing the housing part having the contour of the pressure compensation element. 
     As the result of providing openings between the supports which are oriented essentially perpendicular to the outwardly facing surface of the impact protection element, the openings are hardly impacted directly by the above-mentioned liquid jet, so that there is little or no impingement by the liquid jet on the diaphragm located therebeneath. This allows the diaphragm to reliably remain fixed in place; i.e., the diaphragm is not detachable under liquid pressure. If the preferably circular diaphragm is fastened to a back side of the base facing the interior of the housing, preferably by use of an integral jointing process, on the one hand the diaphragm is particularly well protected from the outside and on the other hand a particularly large annular surface on the back side of the base is obtained which is used to fasten the diaphragm. Thus, the diaphragm surface is also independent of the surface area of the openings between the surroundings of the electrical device and the diaphragm. 
     When an annular ridge extends between the base and the impact protection element, this allows further deflection of a surge of water which could possibly penetrate this region, i.e., into the recess, thereby further reducing the kinetic energy of the water. The pressure on the diaphragm is thus further reduced. The reliability and durability of the diaphragm or the diaphragm fastening is increased. 
     A further possibility for improving the fastening of the diaphragm is to provide on the back side of the impact protection element a pin which extends from the base into the housing interior. The pin preferably ends in the plane of the above-mentioned annular surface to which the diaphragm is fastened, so that the diaphragm may be additionally fastened, without tension, on a cylindrical end face of the pin. 
     According to a further embodiment of the present invention, the recess in which the impact protection element is situated is formed by a truncated cone-shaped ring. This allows the housing part manufactured by the injection molding process, for example, to be easily demolded from both sides of the housing part. 
     Furthermore, the truncated cone-shaped ring projects beyond an outer surface of the housing part. This results in a type of annular wall which at least partially ensures that a liquid flowing along the surface of the housing part does not flow into the recess. 
     In addition, the truncated cone-shaped ring projecting beyond the surface of the housing part extends beyond an essentially funnel-shaped outer surface of the housing part. When, for example, a specified cuboidal dimension is not to be exceeded for the control unit or electrical device, this still allows the surface to be formed by this ring, which then projects far enough so that ultimately the ring at best is in flush abutment with the housing surface—which usually forms a surface—adjoining the funnel-shaped surface. 
     The pressure compensation element is composed of two parts, namely a housing shell bearing the impact protection element and the diaphragm itself. These requirements ultimately result in a particularly easily manufactured and assembled, and therefore economical, housing part together with a pressure compensation element or a corresponding electrical device. 
     The geometry of the housing part which avoid a penetration of liquid may be produced from two molding tools. This results in an overall reduction of the tool costs and therefore the manufacturing costs. 
     In addition, the liquid-repellent geometry or contour may be produced without so-called cross slides in the injection mold. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic cross-sectional illustration of an electrical device together with a pressure compensation element. 
         FIG. 2  shows a cross section of the pressure compensation element and the housing part for the electrical device from  FIG. 1 . 
         FIG. 3  shows a cutaway three-dimensional illustration of the pressure compensation element from  FIG. 2  in a view from the underside. 
         FIG. 4  shows a cross section of two parts of an injection mold which with regard to the contour of the pressure compensation element is free of cross slides, having a liquid-repellent geometry or contour of the pressure compensation element incorporated therein. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a cross section of an electrical device  10 . Electrical device  10  has a housing  13  composed of a lower housing part  16  and an upper housing part  19 . Both housing parts  16  and  19  together form housing  13  having joint  22 . In housing  13  itself a printed circuit board  25  is provided, to which the moisture-sensitive electrical modules, for example electrical module  28 , are fastened. Upper housing part  19  has a pressure compensation element  31  which allows gas exchange through a surface  34  of housing part  19 . This gas exchange is necessary so that housing  13  is not exposed to excessive mechanical stresses at various external temperatures. The aim is to avoid leaks from occurring in the housing or that external or internal air pressure even destroys the housing. 
       FIG. 2  shows a three-dimensional view of a section of pressure compensation element  31  mentioned above. In this case the line of vision is directed on outer surface  34  of housing  13 . On its upper surface  34  housing part  19  has pressure compensation element  31 . This pressure compensation element is composed of at least one opening  37  and a diaphragm  40  situated downstream from opening  37  in the direction facing the housing interior. An impact protection element  43  is provided so that a liquid jet which externally strikes housing part  19  cannot directly apply pressure on diaphragm  40  via opening or openings  37 . In the example according to  FIG. 2 , this impact protection element  43  has a surface  44  which has essentially the same orientation as surface  34  of housing part  19 . Impact protection element  43  is designed as one piece with housing part  19 , and is therefore a part of housing part  19 . 
     The outwardly facing surface of impact protection element  43  terminates considerably below surface  34  of housing part  19 . 
     An electrical device  10  is thus provided having a housing  13 , moisture-sensitive electrical modules  28  being situated in housing  13 , and a pressure compensation element  31  being provided in a housing part  13  which avoids or prevents penetration of moisture. Pressure compensation element  31  has a diaphragm  40  which is permeable to gas, and has an impact protection element  43  situated in front of diaphragm  40  which at least prevents liquid from splattering directly on diaphragm  40 . Impact protection element  43  is designed as one piece with housing part  13 . 
     Impact protection element  43  is designed so that it may be impinged on relatively little by a direct liquid jet, for which reason impact protection element  43  is situated in a recess  46 . This recess  46  has a base  49 , and impact protection element  43  rises or extends above the level of the base in the manner of a pedestal. Impact protection element  43 , which as such is an approximately circular plate having surface  44 , is thus fastened in one piece to base  49  via individual supports  52 . The outer sides of supports  52  form a prismatic enveloping surface  55  which, as illustrated in  FIG. 2 , preferably has the exterior shape of a perforated truncated cone due to opening or openings  37 . Ideally this enveloping surface  55  would have a cylindrical design, but in practice this has not proven to be satisfactory because of process engineering constraints (demolding). 
     Recess  46  facilitates the runoff of liquid and contaminants on surface  44  of impact protection element  43 , which is oriented transversely or in the direction of gravity. 
     Furthermore, openings  37  are provided between supports  52 . Because of the orientation of the above-mentioned enveloping surface  55 , these openings  37  are oriented essentially perpendicular to the outwardly facing surface  44  of impact protection element  43 . In this regard also see  FIG. 3 , in which openings  37  are more easily identifiable. 
     Each individual opening  37  preferably has a compact surface area of approximately 4 mm 2  or greater, but at least 3 mm 2 . A “compact” surface area means that the length of the circumferential border of an individual opening  37  is as short as possible; i.e., opening  37  has a round or rectangular, ideally square, area, for example. Oppositely situated border edges of opening  37  should be at least 2 mm apart. 
     An annular ridge  58 , which is also adjoined by an annular surface  61  (see  FIG. 3 ), extends on the back side of base  49  into the interior of housing  13 . As shown in  FIG. 2  but also identifiable in  FIG. 3 , this annular ridge  58  forms a boundary inside which diaphragm  40 , which in the exemplary embodiment is circular, is or becomes fastened to annular ridge  61 . 
     Whereas supports  52  mentioned above extend radially inward from base  49  and to the outside, a truncated cone-shaped ring  64  extends radially outward from the edge of base  49 . Here as well a cylindrical ring would be ideal, but in this case the same constraints previously mentioned for enveloping surface  55  apply. Truncated cone-shaped ring  64  begins at base  49  and extends in the direction of surface  34  of housing part  19 . This truncated cone-shaped ring  64  forms pot-shaped recess  46 . At this location truncated cone-shaped ring  64  projects beyond outer surface  34  of housing part  19  and terminates in an annular wall  67  which forms a collar-like protective element or wall and thus partially prevents the penetration of liquid into recess  46 . In the exemplary embodiment, this annular wall  67  ends in a funnel-shaped surface  70  which is lowered with respect to further surface  34 , so that annular wall  67  does not project beyond, for example, a cuboidal surface of housing  13 . However, annular wall  67  can still extend beyond surface  34  without exceeding the cuboidal boundary.  FIG. 3  shows the manner in which diaphragm  40  rests on annular surface  61 . This back side of base  49  facing the interior of housing  13  bears the preferably circular diaphragm  40 , which likewise is preferably fastened at that location via an integral jointing process. Examples of integral jointing processes used here include a welding process (ultrasonic welding) or a gluing process. 
     To better support diaphragm  40 , the diaphragm may be additionally supported by a pin  73 . This pin  73  extends on the back side of base  49  toward the interior of the housing and ends at the level of annular surface  61 . In this case, diaphragm  40  may likewise be fastened or fixed using an integral jointing process. 
     As clearly shown in  FIG. 3 , an annular ridge  76  extends between base  49  and impact protection element  43 . This annular ridge  76  acts as part of a labyrinth for a water jet which surges into recess  46  from below, as shown in  FIG. 3 , thereby reducing the kinetic energy of the water jet. Annular ridge  76  thus acts as a type of barrier and prevents excessive wetting of diaphragm  40 . In addition, diaphragm  40  is preferably made of polytetrafluoroethylene (PTFE) film. 
     Annular ridge  76  at least partially prevents water or liquid rebounding from the wall of recess  46  from directly striking diaphragm  40 . 
     It is easily seen that pressure compensation element  31  is composed of two parts, namely a housing part  19  which supports impact protection element  43  and diaphragm  40 . A liquid-repellent geometry (recess  46 , base truncated cone-shaped ring  64 , base  49 , supports  52 , opening  37 , impact protection element  43 ; also optionally pin  73 , annular ridge  76 , annular ridge  58 , annular wall  67 , funnel-shaped surface  70 ) may be produced from two molds (also see  FIG. 4 ). In the region of pressure compensation element  31  the molds constitute an upper molding part  79  and a lower molding part  82 , which may be supplemented by the fact that the liquid-repellent geometry may be represented without cross slides. Openings  37  are situated in a dividing surface  85  formed by the two molds. 
     In addition, the liquid-repellent geometry (see above) may be produced without cross slides in the injection mold (see  FIG. 4 ). 
     If, for example, a liquid jet directly strikes recess  46 , a portion of the liquid jet is diverted by impact protection element  43 . Part of the liquid which flows down to base  49  is compressed into opening  37 , but at that location it is at least slightly decelerated by an annular ridge  76  which may be present. This labyrinth-like design of the flow path down to diaphragm  40  results in an increase in the flow resistance from surface  34  to diaphragm  40 . This necessarily causes the quantity of liquid ultimately reaching diaphragm  40  to be smaller than it would otherwise be. 
     Pressure compensation element  31  functions as follows: When a liquid jet obliquely strikes housing part  19 , a portion of this jet is diverted by annular wall  67  which may be present, and does not travel even as far as recess  46 . As a result of the oblique impact by the liquid jet which occurs anyway, the liquid jet is practically prevented from directly striking openings  37 , since impact protection element  43  is located too far below surface  34 . The oblique liquid jet is diverted and decelerated at the surface of truncated cone-shaped ring  64  facing impact protection element  43 . Further deceleration is then achieved as a result of the deflection into openings  37 . The portion of the jet which enters is then decelerated once again at this location by annular ridge  76  which may be present. Here as well, therefore, there is very little impingement by the liquid on gas-permeable diaphragm  40 .