Abstract:
A power capacitor is described herein. The power capacitor includes a housing and at least one capacitor winding. The power capacitor also includes at least one mechanical spring element between the housing and the at least one capacitor winding.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Pursuant to 35 USC §120, this application claims the benefit of PCT/DE2006/000663 filed Nov. 1, 2007 which claims the benefits of German Patent Application No. 102005020320.5 filed May 2, 2005, 102005031366.3 filed Jul. 5, 2005 and 102005031367.1 filed Jul. 5, 2006. Each of these applications is incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     A power capacitor will be specified. 
     A capacitor is known from the publication EP 0 598 256 B1. 
     BACKGROUND 
     A problem to be solved consists in specifying a power capacitor that is protected against vibrations. 
     SUMMARY 
     A power capacitor will be specified that has a capacitor winding and a housing. The capacitor winding can be constructed, for example, using MPM film winding technology. The dielectric for the film winding can be, for example, polyester, PEN, PPS, or also polypropylene. Flat windings and round windings can also come into consideration. 
     In an example embodiment, a dielectric made from polyester can have a dielectric constant of 3.3. A dielectric made from polyester can be very stable thermally. 
     A power capacitor will be specified that is suitable for absorbing a large electrical current. The maximum current can equal preferably between 50 and 300 Amperes. 
     The nominal voltage of the power capacitor preferably equals between 150 and 600 Volts. 
     In the housing of the capacitor, one or also several capacitor windings can be provided, which contribute to the capacitance of the capacitor. For example, two capacitor windings each with a capacitance of one millifarad can be stacked one above the other and connected by means of a parallel circuit to form a nominal capacitance of C Nenn =2 mF. The capacitance, however, can also assume other values. 
     The film thickness of the dielectric contained in the film winding preferably equals a few micrometers, especially preferred around 3 μm. Therefore, an especially large capacitance can be achieved with low space requirements and still adequate electric strength. 
     In a special embodiment of the power capacitor, a capacitor winding is provided, which is provided on two side surfaces with a Schoop layer. Here, it can preferably involve a flame-sprayed or arc-sprayed metallic layer that preferably contains zinc or a film construction containing a film with zinc and another film with zinc and also a film with copper. 
     Through a suitable selection of the geometries of the capacitor winding, Schoop layer, and housing, a capacitance can be set between the capacitor elements and the housing (also terminal-housing capacitance), which is suitable for suppressing interference in a voltage-system converter and which has generally favorable properties in terms of EMV (electromagnetic compatibility). 
     In one embodiment of the power capacitor, it is provided that a winding is contacted by means of two contact films arranged on opposing sides of the film winding. These contact films can be, for example, Schoop layers. 
     In one embodiment of the power capacitor, several capacitor windings are contained in the capacitor housing, with each contact film of the individual windings to be connected to a common external pole lying on the same side of the power capacitor. 
     In addition, a power capacitor will be specified, in which a capacitor housing is provided. In addition, at least one capacitor winding is provided in the interior of the housing. A mechanical, elastic element is provided between a capacitor winding and the housing. Such an elastic element can help to absorb the volume expansion of the capacitor winding during heating. On the other hand, however, such an elastic element also has the advantage that vibrations, like those appearing, for example, during the operation of a motor vehicle, can be damped. 
     In a preferred embodiment of the capacitor, mechanical, elastic elements are arranged on two opposing sides of a capacitor winding, so that the mechanical fixing of the capacitor winding can be realized especially well. The elastic elements could also be arranged on all sides in a peripheral direction. 
     In an especially preferred way, a so-called “spring pad” is used as the mechanical, elastic element. A spring pad is preferably produced from a plastic foam, with the individual pores of the foam forming gas-tight, enclosed cells that are filled with a gas, for example CO 2 . A “spring pad” produced in this way has the advantage that it is very insensitive relative to material fatigue. The spring properties are caused primarily not by the compression and decompression of a solid body, but instead by the enclosed gas bubbles and thus through compression or decompression of a gas volume. Such elastic elements have a service life of many years, without losing their elastic properties due to aging or other processes. 
     With the help of one or more elastic elements between the capacitor winding and housing, a fixed positioning of the capacitor winding in the housing can be achieved. For the case that the housing is an electrical conductor, an essentially constant capacitance between a contact film of a capacitor winding and the housing and thus a constant and relatively exactly adjustable terminal-housing capacitance can be provided, which has the advantage of very favorable properties in terms of EMV or which can be used for suppressing interference in a voltage-system converter. 
     In an especially preferred embodiment of the capacitor, it is provided that the housing has the shape of a trough, with the trough having a base and, for example, four side walls, and also an open upper end. On the side surfaces of the trough, mounting eyelets or mounting elements can be provided, with whose help the power capacitor can be mounted on another electronic element. On the upper side of the housing, a peripheral groove can also be provided for receiving a sealing ring. 
     For fixing a capacitor winding in the housing, an insulating shell can be provided, which is inserted—to some extent as a second trough—into the lower region of the housing. In the insulating trough, the capacitor winding is then inserted. For closing the capacitor in an insulating way at the open end of the housing, a second insulating shell is placed on the upper side. 
     In a preferred embodiment, the lower and the upper shells are expanded to form an essentially enclosed housing. 
     According to a special embodiment of the capacitor, it can be provided that the upper shell has openings, through which the outer contact elements or pairs of contact elements can pass. Electrically insulating collars, which are used for insulating the outer contact elements, are arranged at the openings of the upper shell. 
     In another embodiment of the capacitor, it can be provided that the lower insulating shell has a structured or profiled section on its outer side or also a structured or profiled section on its inner side, by means of which the friction between the insulating shell and a mechanical, elastic element can be increased. Thereby, the positional stability of the mechanical, elastic element (e.g., spring pad) can be improved. The structured or profiled section of the shell makes it more difficult for the spring element to slip. 
     In an especially preferred embodiment of the capacitor, a cooling surface that can be used for cooling the capacitor is provided on the upper side. Such a cooling surface can be formed in an especially preferred way by a sheet-metal strip or a ribbon cable. Such a ribbon cable can be formed, e.g., from two overlapping sheet-metal strips, which are insulated from each other and which are connected to outer contacts of the capacitor and which are used for energizing the capacitor winding. For example, the upper of two electrically conductive sheets can be used as a cooling element. Through a suitable construction, care can be taken that the upper of the electrically conductive sheets is closed sufficiently well with the upper edge of the housing, with which a good mechanical contact can be provided, preferably a good thermo-mechanical contact of the upper sheet to another housing to be mounted on the upper side—which provides, e.g., a cooling plate. 
     In order to reduce the risk of a short circuit, it is advantageous if electrical insulation is arranged on the surface of the cooling element. For example, such insulation can be formed by a transparent, insulating film, which is, for example, only a few micrometers thick and which thus only insignificantly prevents heat transport. In a different embodiment, the electrical insulation is guaranteed by the upper of two insulating shells, which is possible essentially in that the wall thickness of the insulating shell is selected sufficiently thin. The wall thickness can equal, for example, 0.3 mm. 
     In addition, an electrical module is described, wherein a first unit of the module concerns an electronic system containing, e.g., IGBT modules. In general, the first unit can be an electrical device for power electronics. Another unit of the module is the capacitor described here. Preferably, the upper side of the capacitor or the housing of the capacitor is connected over an area to the bottom side of the first unit. The outer contacts of the capacitor here project into the housing of the first unit and are connected there, for example, by means of a threaded connection, to the IGBTs located there. The first unit does not necessarily have to contain IGBTs; it can also contain other electronic components or also mechanical components. 
     Preferably, the bottom side of the first unit, that is, the side of the first unit in contact with the capacitor, is equipped with a device for heat dissipation. Such a device can be, for example, a metal plate provided with holes. Such a device, however, can also be constructed in the form of cooling ribs. 
     Preferably, there is a good planar contact between the upper current rail in the capacitor and the cooling device of the first unit. Therefore, in an advantageous way, heat generated in the capacitor can be easily dissipated to the outside. In one embodiment of the capacitor, the upper side of the capacitor is formed by a thin insulating film, which has only a low heat resistance and which thus provides for good heat transport from the capacitor to the first unit of the electronic module. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The subject matter described here will be explained in more detail below with reference to the figures. 
         FIG. 1  shows a capacitor in a perspective view. 
         FIG. 2  shows as an example the construction of the capacitor from  FIG. 1 . 
         FIG. 3  shows the upper part of an insulating shell as a construction drawing. 
         FIG. 4  shows the lower part of an insulating shell as a construction drawing. 
         FIG. 5  shows an electrical module in a schematic cross section. 
     
    
    
     The dimensional information specified in the figures is to be understood only as an example. It does not limit the subject matter described here. The same elements or elements with the same function are labeled with the same reference symbols. 
     DETAILED DESCRIPTION 
       FIG. 1  shows a capacitor with a housing  1 , on whose upper side several mounting eyelets  2  are arranged in the peripheral direction. The mounting eyelets  2  can help mount the capacitor on another electronic unit. Such a unit is shown, for example, in  FIG. 5 . 
       FIG. 2  shows the housing as a construction drawing. The housing  1  can be made, for example, from aluminum or can contain aluminum. The length of the housing equals approximately 25 cm. The width of the housing equals around 12 cm. 10 mounting eyelets are arranged on the periphery of the housing. The number of mounting eyelets, however, can vary according to how large the housing is and what type of mechanical stability is required for the connection of the housing to another electronic unit. The depth of the trough-shaped housing equals approximately 6 cm. A peripheral groove  1   a , which is used for receiving a sealing compound or a sealing ring, is arranged on the upper side of the housing. 
       FIG. 3  shows the upper part of an insulating shell, which can be arranged between the capacitor winding or windings and the housing of the capacitor. The shell is preferably made from insulating material, for example, polycarbonate or PP with a preferred thickness of 0.3 to 0.5 mm. The upper half shell  13  is shaped so that it can be placed somewhat like a cover over the capacitor winding. It is provided with longitudinal holes  14 , through which the outer contacts of the current supply elements can project. In the region of the holes  14 , preferred collars  15  can be arranged, which insulate the lower region of the outer connections. 
     The wall thickness of the upper half shell  15  should be relatively thin at least in the upper (cover) region, in order to guarantee good cooling from the upper side of the capacitor. 
       FIG. 4  shows a lower half shell  16 , which is preferably inserted into the housing before the insertion of the capacitor winding. It is preferably made from insulating material like the upper half shell  13 . 
     The lower half shell is equipped with a surface profiled section  17  shown in  FIG. 4 . The surface profiled section can correspond both to the outer side and also to the inner side of the insulating shell. 
     The surface profiled section has the advantage that a mechanical, elastic element, which presses against the lower half shell and consequently against the surface structure, cannot easily slip due to the increased friction. Therefore, slipping of the spring element can be stopped. Here, the spring element can lie both on the outer wall of the shell  16  and also on the inner wall of the shell  16 . 
       FIG. 5  shows a capacitor as a component of an electronic unit, which can be, for example, a voltage-system converter. The electronic unit  21  here contains several IGBT modules in one housing  21   a . On the bottom side of the housing  21   a , a capacitor is arranged, which is fixed, for example, by screws, to the housing  21   a  by means of the mounting eyelets  2 . 
     The outer connections  3   a  or  3   b  project through holes in the housing  21   a  into the interior of the electronic unit  21 . On the lower side of the housing  21   a , a cooling plate  20  is provided, which is suitable for heat transport. The lower side of the cooling plate  20  is in direct thermal contact with the elements of the capacitor, especially with the upper side of the upper half shell according to  FIG. 5  forming the upper seal of the capacitor. The upper side of the capacitor, however, can also be formed by a transparent, insulating film according to  FIG. 1 , especially for the case that no insulating half shells are arranged in the capacitor, but instead the capacitor winding is held by a sealing compound in the housing of the capacitor. 
     In  FIG. 5 , the capacitance of the capacitor is formed essentially by two capacitor windings  18   a ,  18   b , which are placed in the housing one above the other. An insulating half shell  16  in the form of a lower half shell is arranged between the capacitor windings and the housing  1  of the capacitor. Spring elements are installed between the lower half shell  16  and the capacitor windings. Here, the spring element  19   a  is installed on the side of the base and the spring element  19   b  is installed on the side of the wall. In an especially preferred embodiment of the capacitor, the spring elements are installed on all sides. 
     The capacitor windings can be held with low vibrations in the housing by the spring elements. The base-side spring element  19   a  here fulfills another function. Because it presses the capacitor windings  18   a ,  18   b  and the elements located above upward, it can provide improved heat contact of the cooling plate  20  with the elements forming the upper seal of the capacitor. This improves the dissipation of waste heat of the capacitor.