Abstract:
The invention relates to a wall or a door of an assembly for cooling electric modules, comprising a wall element provided with ventilation holes and a membrane filter located on the inside of the wall element, in such a way that air entering by means of the ventilation holes is guided through the membrane filter. The invention is characterised in that the wall element has double-sided lamellae arranged one inside the other in an offset manner, so that each path leading through the arrangement of lamellae has a curvature.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is based on and hereby claims priority to PCT Application No. PCT/DE01/00797 filed on Mar. 2, 2001 and German Application No. 100 10 454.1 filed on Mar. 3, 2000, the contents of which are hereby incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The invention relates to an assembly for cooling electrical modules arranged in a housing, in particular for cooling a base station of a mobile radio system or wire-free subscriber access system, and to individual components of an assembly of this type.  
           [0003]    In an electrically operated item of technical equipment, the power loss from modules and components through which current flows causes heating of the equipment. Since standard electrical components for technical equipment have only a limited permissible operating temperature range of, for example, up to 70° C., they are cooled by cooling devices. These cooling devices are, for example, fans which in the housing build up an airflow which flows through the electrical components and modules and which thereby dissipate the thermal output which is generated.  
           [0004]    When the technical equipment is operating outside closed spaces or in adverse conditions within closed spaces, sufficient protection against environmental influences, such as for example dirt and liquids, usually water, is to be provided as well as the dissipation of heat. Protective stipulations according to the specified IP classes are to be observed in order to ensure long-term operation of the technical equipment, i.e. for example of the above-mentioned base station of a mobile radio system.  
           [0005]    EP0654877 has disclosed a door of a switch cabinet with ventilation openings. The ventilation openings can be covered by a cover part, which likewise has ventilation openings. After the door and cover part have been joined together, V-shaped ventilation openings are formed, preventing rectilinear passage into the interior of the switch cabinet.  
           [0006]    DE 29619902U1 has disclosed a filter ventilator for installation in a switch cabinet wall. In this case, a filter mat is arranged behind a cover housing. Both are secured to a base housing with the aid of a quick-acting securing device.  
           [0007]    It is known from DE 19755944 to provide a membrane filter for surface filtering of dirt particles from cooling air which flows in and for separating out liquids in an air inlet of a housing. Compared to a housing which is known, for example, from DE19626778, with an air/heat exchanger which ensures complete separation of an inner cooling circuit from an outer cooling circuit, the use of a membrane filter makes it easy to achieve sufficient protection of the electrical modules for the abovementioned application areas of the technical equipment with the corresponding protective stipulations. At the same time, a temperature difference, which is required for the cooling, between the ambient temperature and the temperature in the interior of the housing is reduced.  
           [0008]    A membrane filter of this type is based, for example, on a membrane which is known for use in items of clothings under the name Goretex (trade name), Sympatex (trade name), etc. The membrane of the filter comprises a fine braided or knitted fabric of fibers which allows a very small pore size. An example of a suitable material for this purpose is PTFE (polytetrafluoroethylene), more commonly known as Teflon. The membrane is generally produced on a textile-like substrate material, for example polyamide, in order to achieve a certain stability of the membrane filter. To obtain the largest possible filter surface area, so that the flow resistance to the cooling air which is produced by the membrane filter remains as low as possible, the membrane which has been laminated onto the substrate material is folded in concertina fashion, so that this large filter surface area can be accommodated within a small frame area.  
           [0009]    Furthermore, protective stipulations with regard to the EMC guidelines (EMC-electromagnetic compatibility) have to be satisfied, specifically on the one hand to protect the equipment arranged in the housing from external radiation and on the other hand to protect the environment from radiation originating from the electrical modules. This is generally achieved by mean of appropriate shielding, for example a suitable braided wire fabric or a braided fabric of electrically conductive material.  
           [0010]    Since in particular base stations of a mobile radio system are arranged in the open air, they are, as has already been mentioned, exposed to the influences of wind and weather, in particular moisture and water, i.e. rain. By way of example, extreme levels of precipitation with corresponding spray water may occur, in which case the membrane filter of an assembly of the generic type cannot be exposed to such an intensive water jet, since there is a risk of the membrane being destroyed. Furthermore, under certain environmental conditions the relative atmospheric humidity of the cooling air within an assembly of the generic type including a base station may rise above a level which is critical for the modules of the base station.  
           [0011]    A further problem is the design of the membrane filter, which is normally arranged in a door or a wall of a cooling assembly of this type. The horizontal folding of the membrane filter means that moisture or condensation or spray water which has penetrated between the door leaf and filter remains in place in the fold in the membrane filter. Furthermore, water which drains out collects on the pedestal, which is located in the door for holding the membrane filter. This water may impair the functioning of the filter, may cause the membrane pedestal to rust if it is made from metal sheet, as is customary, and/or may lead to an increase in the atmospheric humidity in the interior of the housing.  
           [0012]    One aspect of the invention is therefore based on the object of improving the protection for electrical modules which are arranged in a cooling assembly provided with membrane filters, in particular in a base station of a mobile radio system.  
         SUMMARY OF THE INVENTION  
         [0013]    The assembly for cooling electrical modules has a wall which is mounted in front of the electrical modules and comprises a wall element, which is provided with ventilation holes, and a membrane filter, which is arranged on the inner side of the wall element, air which enters through the ventilation holes being guided through the membrane filter.  
           [0014]    According to one aspect of the invention, the membrane filter has a fold with longitudinal folds running substantially vertically. This prevents water or moisture from remaining in the folds of a filter of this type and in this way having disadvantageous effects, for example by increasing the atmospheric humidity of the cooling air which flows in or by slowly rotting the material. Furthermore, a longitudinal fold, i.e. folds in the membrane filter which run vertically, has the advantage that the filter cake which forms at the surface of the filter drops off more easily, since the weight of the filter cake exceeds the adhesive forces of the filter membrane surface at an earlier stage. This advantageously results in longer maintenance or cleaning intervals for the membrane filter.  
           [0015]    In a further preferred embodiment, a frame foot of a frame, which accommodates the membrane filter, of a wall or a door has an outwardly directed inclination, so that water running off the membrane filter is discharged outward. It is preferable for at least one opening for draining the water to be arranged in the vicinity of the frame foot.  
           [0016]    In a further preferred embodiment, the membrane filter, including its filter frame, is inclined with respect to the vertical, so that water can easily drain out of the filter fold. In particular, this embodiment is also suitable for membrane filters with a horizontal fold.  
           [0017]    A wall or door of an assembly for cooling electrical modules has a wall element or door element which is provided with ventilation holes. A membrane filter is arranged on the inner side of the wall or door element, so that the air which enters through the ventilation holes is guided through the membrane filter.  
           [0018]    To prevent water from entering, the wall element or door element has what are known as two-sided lamellae which are set into one another and are arranged so that they are open at the bottom, so that each path leading through the arrangement of lamellae has a curvature. Therefore, a lamella of this type is U-shaped or V-shaped, although it is not intended to restrict the lamella to a U- or V-shape. This ensures that a water jet which impinges on the wall directly cannot apply any pressure to the membrane of the membrane filter arranged behind the wall or door element, since the water jet is broken up or atomized at the lamella and releases its energy to the lamella structure.  
           [0019]    A wall or door element of this type comprises two wall- or door-element halves, each element half being provided with lamellae on one side, so that after the two element halves have been joined a wall or door element with lamellae on two sides is formed. The wall or door element is designed in such a way that the two-sided lamellae are open at the bottom and overlap one another, so that firstly the water can flow away downward and secondly the overlap means that it is impossible for there to be a straight path through the two-sided lamella for a water jet.  
           [0020]    The one-sided lamellae are preferably stamped out of the element half, and the two element halves, which are of identical design, are surface-connected to one another to form a wall or door element on their rear sides, i.e. the sides without the single-sided lamellae produced by the stamping, by joining techniques, such as for example soldering, welding, riveting, screwing and/or adhesive bonding. In this context, the economic production of the wall or door elements is advantageous.  
           [0021]    It is also possible for the wall- or door-element halves to be produced with half-lamellae integrated therein by an injection-molding process and then for the element halves to be joined.  
           [0022]    In a further preferred embodiment, the entire filter block comprising frame and membrane filter arranged therein is designed as a wall or door, the frame having the elements required to fulfill the wall function, such as for example securing elements for modules, seals, door hinges, etc. This allows simple and economic production and allows the wall or door to be exchanged quickly.  
           [0023]    The wall preferably has a filter membrane which is backed by injection-molding on the outer side with a suitable material, such as plastics, corresponding to the desired wall shape, without any material being arranged at the locations of the air inlet. This embodiment results, as it were, in a stable wall or door with integrated membrane filter. Furthermore, the wall or door may be equipped with further elements; by way of example, the air holes may be designed in lamellar form, so that the filter membrane is protected against the direct application of pressure. Furthermore, the wall or door may have a fly screen and/or an EMC shield which is arranged in front of the membrane of the membrane filter, on the inner side of the wall element.  
           [0024]    In a further preferred assembly for cooling electrical modules, a moisture sensor is arranged in the interior of the housing of the assembly. Furthermore, the assembly has a heating element which is arranged in front of the at least one membrane filter, the heating element heating the air which flows in when the moisture sensor detects a moisture content in the interior of the assembly which exceeds a predetermined level. In this way, the relative atmospheric humidity in the interior of the assembly is reduced.  
           [0025]    Features or elements of the various walls or doors may, of course, be combined with one another in an appropriate way.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]    These and other objects and advantages of the present invention will become more apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which:  
         [0027]    [0027]FIG. 1 diagrammatically depicts a cross section through an assembly for cooling electrical modules,  
         [0028]    [0028]FIG. 2 shows a cross section through a door or a wall element according to the related art,  
         [0029]    [0029]FIG. 3 shows a cross section through a door or a wall element according to one aspect of the invention, and  
         [0030]    [0030]FIG. 4 diagrammatically depicts a door or wall element with a membrane which is backed by injection-molding. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0031]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout.  
         [0032]    [0032]FIG. 1 shows an assembly for cooling an item of technical equipment, such as for example a base station of a mobile radio system or wire-free subscriber access system. The item of technical equipment has one or more electrical modules BG which, during operation, release heat to their environment, so that it is necessary to cool them in order not to exceed a maximum permissible operating temperature of the modules BG or individual electrical components.  
         [0033]    The housing G, which is illustrated in side view, of the assembly has at least one suitably designed air inlet LF with a membrane filter MB, the dimensions and arrangement of the air inlet LF being such that the modules are suitably cooled by a corresponding air flow, which is diagrammatically indicated by arrows. Furthermore, the active surface of the membrane filter MB, which may be larger than the air inlet LF, for example by forming a fold, is designed in such a way that the pressure drop of the cooling air which flows in can be compensated for by a cooling device VE arranged in the air outlet LA, for example by a fan, and it is always possible for a sufficient quantity of cooling air to flow in. The air outlet LA may likewise have a membrane filter. Furthermore, air-guide plates LLB, which build up suitable air flows, may be arranged in the housing.  
         [0034]    To prevent a high dynamic pressure, the electrical modules BG and the air-guide plates LLB are arranged in such a manner that passages without bottlenecks, whose curvature is minimized, are formed uniformly. Moreover, a pressure sensor in the interior of the housing G can measure the dynamic pressure and can actuate the cooling device in such a manner that a dynamic pressure which endangers the membrane is avoided.  
         [0035]    The membrane filter MB may be arranged in a frame which allows rapid removal of the membrane filter cartridge, comprising the membrane filter and the frame, for maintenance and cleaning purposes, or for replacement. At the same time, the frame allows folding of the membrane filter MB as described above. To limit the dimensions of the item of technical equipment, the frame may also be integrated in the housing G.  
         [0036]    The membrane filter MB is designed as a surface filter which has the particularly advantageous property of separating dirt particles and liquids out of the ambient atmosphere even at the surface of the membrane, so that, by way of example, sensitive electronic components or circuits in the modules BG are protected against environmental influences of this nature. A membrane filter MB of this type is based, as mentioned above, on a membrane which is known under the name Goretex, Sympatex, etc. for use in items of clothing. The membrane of the filter comprises a fine braided or knitted fabric of fibers. A very small pore size prevents the dirt particles from penetrating in and therefore prevents in some cases irreversible blockage of the membrane. Nevertheless, dirt particles may collect at the surface of the membrane to form what is known as a filter cake. In the same way, liquids cannot pass through the membrane up to a specific pressure per unit area.  
         [0037]    By way of example, PTFE, also known as Teflon, is used as material for the membrane. The membrane is generally applied to a coarsely woven substrate material, such as for example polyamide, in order to achieve a high stability and strength on the part of the membrane filter MB.  
         [0038]    [0038]FIG. 2 shows, in cross section, a known wall or door T which has a wall element or door element TE. This wall element or door element TE is preferably produced from metal. Corresponding plastics may likewise be used. At a suitable location, the wall or door element TE has ventilation openings LF in the form of horizontally running lamellae LME on one side. The one-sided lamellae LME overlap one another in the downward direction in the manner of roof tiles. In this way, a horizontally running water jet cannot penetrate through the lamellae LME, but a water jet WS which is directed obliquely upward and is indicated by an arrow can penetrate through the wall or door element TE. A fly screen FG, an EMC grid EMV and the membrane filter MB are arranged on the rear side of the wall element or door element TE. This membrane filter MB would be damaged or destroyed by the water jet WS beyond a certain water pressure.  
         [0039]    [0039]FIG. 3 shows a wall or door T in cross section, having a wall element or door element TE. The wall element or door element TE is formed by two halves T 1  and T 2  which are surface-connected to one another, for example by welding or adhesive bonding. Each half T 1  and T 2  of the wall element or door element TE has outwardly facing lamellae LME 1  and LME 2  on one side. The halves T 1  and T 2  are joined together to form a wall element or door element TE in such a way that the single lamellae LME 1  and LME 2  are arranged oppositely. As a result, lamellae LMZ which engage over one another, are U- or V-shaped in cross section and in the present context are referred to as two-sided lamellae LMZ are formed. An unimpeded, rectilinear path through the two-sided lamellae LMZ is therefore no longer possible, and consequently the wall element or door element TE is impervious to a direct water jet WS. The other elements of the wall or door in FIG. 3 correspond to those shown in FIG. 2.  
         [0040]    [0040]FIG. 4 shows a perspective illustration of part of a wall element or door element TE with a membrane backed by injection-molding. The figure illustrates a membrane or membrane filter MB, in front of or behind which there is a shell S made from a plastics material or the like, for example by an injection-molding process, in order firstly to stabilize the membrane or membrane filter MB and secondly to form the door or wall T. In other words, the membrane or membrane filter MB is coated on one side, the membrane side of the wall or door T being used as the inner side in a corresponding cooling assembly. The membrane MB is fixedly connected to the shell S by the injection-molding process. A corresponding configuration of the injection mold produces air inlets LF 1  and LF 2  in the wall or door T. The membrane MB may also be coated on both sides with a plastic shell S (not shown), in which case different plastics can be used according to the particular requirement. The air inlets LF 1 , LF 2  may also be designed in the form of the two-sided lamellae described above or may be configured in such a manner that the membrane filter MB can be folded in the region of the air inlets LF 1 , LF 2 .  
         [0041]    The invention has been described in detail with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.