Abstract:
A cladding (cover) element ( 32 ) includes a reception unit which is integrated therein. The reception unit contains a receiving coil ( 10 ) for the contactless transfer of electric energy and a plurality of flux-conducting elements ( 15   a,    15   b;    16   a,    16   b ) that are associated with the receiving coil ( 10 ) for concentrating the field strength. The cover element ( 32 ) is made of a fiber-reinforced plastic. The flux-conducting elements ( 15   a,    15   b;    16   a,    16   b ) and the receiving coil ( 10 ) are arranged in a base body ( 18 ) that is used to position the elements and coil and are embedded with the base body ( 18 ) in the cladding element ( 32 ). A process is also provided for producing the cladding element ( 32 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a United States National Phase application of International Application PCT/DE2007/001576 and claims the benefit of priority under 35 U.S.C. §119 of German Patent Application DE 10 2006 048 831.8 filed Oct. 11, 2006, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention pertains to a cover element with a receiving unit, which is integrated in same and which contains a receiver coil for the contactless transmission of electric power and a plurality of flux-conducting elements, which are associated with the receiving coil and are intended to concentrate the field intensity, and which are formed of a material having high permeability compared to that of air and further relates to a process for manufacturing a cover element 
       BACKGROUND OF THE INVENTION 
       [0003]    Cover elements (cladding elements) of this type are known especially in magnetic levitation vehicles (DE 10 2004 056 439 A1). The receiving unit having a receiver coil is used for the contactless, inductive transmission of electric power from a track to a vehicle. At least one primary conductor, which is connected to a power source and is designed as a transmitting coil, is provided for this purpose at the track and at least one secondary receiver coil is provided at the vehicle. The receiving unit including the contacting elements belonging to it in the form of plug-type connectors or the like is mounted on a shell-like cover element, which covers a magnetic back box on a side facing the track or is integrated in same. Among other things, carrier magnets for the magnetic levitation vehicle and the means needed for controlling same, which can be operated with the electric power supplied by the receiver coil, are accommodated in the magnetic back box, which is connected via frame straps to an undercarriage or body of the vehicle. An autonomous assembly unit for the “carrying” function is thus obtained. 
         [0004]    To improve the magnetic coupling between the primary conductor and the receiver coil and to avoid eddy current losses, the receiver coil is provided with means for concentrating the lines of magnetic flux generated by the primary conductor on its side facing away from the primary conductor. These means contain flux-conducting elements in the form of strips and connection elements connecting the ends thereof, which said connection elements are made of a material with high permeability and high electric resistance, preferably a ferrite, especially a soft ferrite. The strips and connection elements are connected into a grid frame, which is to be placed on the receiver coil, by bonding or according to another method. 
         [0005]    The manufacture of flux-conducting elements from a material such as ferrite or the like is carried out by pressing and subsequent sintering of a powder prepared from this material. The flux-conducting elements obtained hereby are comparatively brittle, mechanically delicate and poorly processable. In addition, the joining of the flux-conducting elements into a grid frame is very labor-intensive. 
         [0006]    For the same reason, the usual fastening of the receiver coil and of the flux-conducting elements to the cover element by screwing, bonding or the like is not simple. In addition, there is a risk that the flux-conducting elements will be destroyed or become separated because of the mechanical vibrations and shocks occurring during the operation of the magnetic levitation vehicle, which makes undesired maintenance and repair work necessary. 
       SUMMARY OF THE INVENTION 
       [0007]    Based on this, the basic technical object of the present invention is to design the cover element of the class described in the introduction such that its manufacture is simplified, the flux-conducting elements are securely integrated in the cover element and long service life is therefore attained even when they consist of a brittle, easily breakable material. 
         [0008]    The present invention offers the advantage that a receiving unit, which comprises the basic body with the flux-conducting elements and the receiver coil, is preferably completely embedded in the cover element manufactured from a fiber-reinforced plastic. Additional means for fastening the receiving unit at or in the cover element are not therefore necessary. In addition, not only are the flux-conducting elements positioned based on their arrangement in the basic body, but they are also held securely and protected against mechanical shocks. This is especially true when the basic body is manufactured from a foam with damping action, which is preferred. 
         [0009]    The present invention will be explained in more detail below in connection with the attached drawings on the basis of exemplary embodiments. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    In the drawings: 
           [0011]      FIG. 1  is a schematic view showing a partial section through a usual magnetic levitation vehicle in the area of a track provided with a long stator; 
           [0012]      FIG. 2  is a schematic perspective and greatly enlarged view of a part of a receiving unit; 
           [0013]      FIG. 3  is a schematic view showing a cross section through the receiving unit and the primary conductor according to  FIG. 2 ; 
           [0014]      FIG. 4  is a perspective view of a basic body according to the present invention which can be used to manufacture the receiving unit according to  FIGS. 2 and 3 ; 
           [0015]      FIG. 5  is a sectional view showing enlarged sections along line V-V in  FIG. 4 ; 
           [0016]      FIG. 6  is a sectional view showing enlarged sections along line VI-VI in  FIG. 4 ; 
           [0017]      FIG. 7  is a sectional view through the basic body corresponding to  FIG. 5  after mounting a receiver coil and inserting flux-conducting element; 
           [0018]      FIG. 8  is a schematic exploded perspective view showing the formation of an assembly unit according to the present invention that can be used in the manufacture of the receiving unit; 
           [0019]      FIG. 9  shows a perspective view of an outer shell of a cover element according to the present invention, which said outer shell is intended for receiving the basic body according to  FIGS. 7 and 8 ; 
           [0020]      FIG. 10  is a cross sectional view approximately along line X-X in  FIG. 9  through a complete cover element according to the present invention; and 
           [0021]      FIG. 11  is a schematic view showing a device for manufacturing the cover element according to the present invention according to  FIG. 10 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    Referring to the drawings in particular,  FIG. 1  schematically shows a cross section through a magnetic levitation vehicle  1 , which is mounted in the usual manner in such a way that it is able to travel on a track, which extends in the longitudinal direction of a line and which contains carriers  2  manufactured from steel and/or concrete and track panels  3  mounted thereon. The magnetic levitation vehicle  1  is driven by means of a long-stator motor, which has stator packages  4  that are fastened under the track panel  3  and follow each other in the longitudinal direction thereof. The energizing field of the long-stator motor is generated by at least one magnet array provided with carrier magnets, which has magnet poles facing the grooves of the stator packages  4 , which said grooves are open downwardly in  FIG. 1 . Not only does the carrier magnet  5  provide the energizing field, but it also assumes the carrying and levitating function by maintaining a preset gap between the carrier magnet  5  and the stator packages  4  during the operation of the magnetic levitation vehicle  1 . The magnet array containing the carrier magnets  5  is otherwise accommodated in a magnetic back box  6 , which is fastened to the magnetic levitation vehicle  1  via laterally arranged frame straps. 
         [0023]    A primary conductor  7 , which is designed as a transmitting coil, preferably contains a line section  7   a ,  7   b  running back and forth and preferably extends over the entire length of the track, is provided along the track. The two line sections  7   a ,  7   b  are fastened to the carrier  2 , e.g., by means of a bracket  8  consisting of an insulator. The primary conductor  7  is connected, in addition, to a power source  9  of, e.g., 200 A, which is preferably a high-frequency power source and is shown only schematically. 
         [0024]    A receiving unit with a receiver coil  10  is mounted on the magnetic levitation vehicle  1 . This receiver coil  10  is preferably designed such that it does not extend around the primary conductor  7  but is located opposite same at a short distance only. The receiver coil  10  preferably comprises a plurality of parallel conductors, which are arranged relative to the primary conductor  7  such that they are passed through by the lines of magnetic flux generated by this primary conductor  7  or the line sections  7   a ,  7   b  and the current of approx. 200 A supplied by the primary conductor  7  can be uncoupled at the terminal ends thereof, not shown. The two terminal ends, not shown, of the receiver coil  10  are connected in the known manner, e.g., with a voltage transformer, which is part of a usual power supply unit, which supplies the magnetic levitation vehicle  1  with the electric power necessary for its operation. It is clear that corresponding primary conductors  7  are preferably installed on both sides of the carrier  2  when the magnetic levitation vehicles  1  are provided with carrier magnets  5  on both longitudinal sides and that as many receiving units are provided in the longitudinal direction of the magnetic levitation vehicles  1  as are necessary for the operation of the magnetic levitation vehicles  1  or desirable for reasons of redundancy. 
         [0025]    The receiver coil  10  is preferably manufactured as a prefabricated assembly unit together with the necessary contacting elements, e.g., plug-type connectors, and mounted on the magnetic back box  6 . It is especially advantageous to accommodate the receiver coil  10  at or in a shell-like cover element  11 , which is fastened to a rear side of the magnetic back box  6 , which said rear side faces the primary conductor  7 . 
         [0026]    The receiver coil  10  is preferably designed in the manner of a so-called layer winding. As is shown in  FIG. 2 , it contains a plurality of layers located in one plane. The individual layers are preferably made of a conductor with round or square cross section and have essentially straight first and second longitudinal sections  10   a ,  10   b , which extend in parallel to one another and along the magnet array, as well as end windings  10   c , which connect the ends thereof. The longitudinal sections  10   a ,  10   b  extend in parallel to the line sections  7   a ,  7   b  of the primary conductor  7  and are used to generate voltage. The first longitudinal sections  10   a  are associated with line section  7   a  and the second longitudinal sections  10   b  are associated with line section  7   b  of the primary conductor  7  such that the line sections  7   a ,  7   b  are arranged approximately in the middle of the layer part formed by the associated longitudinal sections  10   a ,  10   b , as is shown especially in  FIG. 3 . By contrast, the conductors of the receiver coil  10  extend in the area of the end windings  10   c  essentially at right angles to the line sections  7   a  and  7   b , respectively. 
         [0027]    To increase the magnetic coupling between the primary conductor  7  and the receiver coil  10  and to avoid eddy current losses, the receiving unit has, furthermore, on the side of the receiver coil  10  facing away from the primary conductor  7 , a means for concentrating the field intensity generated by the primary conductor  7 , as it is schematically indicated by lines of magnetic flux  14   a ,  14   b  in  FIG. 3 . This means contains flux-conducting elements, which consist of a material with high permeability and high electrical resistivity. An especially preferred material for this purpose is ferrite, especially soft ferrite, which is, however, comparatively brittle, mechanically delicate and therefore poorly processable because it is manufactured from ferromagnetic powders by pressing and subsequent sintering. The flux-conducting elements are therefore composed of many, comparatively small strips of material and connection elements, which are connected to one another by bonding or according to other methods to form grid frames. 
         [0028]    A plurality of first material strips  15   a , which are arranged essentially at right angles to the line section  7   a  and in parallel to the winding plane formed by the longitudinal sections  10   a , are provided, e.g., on a side of the receiver coil  10  facing away from line section  7   a  in a construction likewise shown in  FIGS. 2 and 3 . A plurality of second material strips  15   b , which are preferably located in the same plane as the first material strips  15   a , are provided in a corresponding arrangement on a side of the receiver coil  10  facing away from line section  7   b . Both material strips  15   a ,  15   b  have a length that is somewhat greater than the height of the layer parts formed by the longitudinal sections  10   a ,  10   b , without overlapping with the ends facing each other. The individual material strips  15   a ,  15   b  are arranged in a grid-like pattern and in parallel to one another at preselected distances. 
         [0029]    The ends of the first material strips  15   a  are connected to one another by first connection elements  16   a , which are arranged essentially in parallel to line section  7   a . The ends of the second material strips  15   b  are correspondingly connected by second connection elements  16   b . Components designed in the manner of grid frames are formed as a result. 
         [0030]    Both the material strips  15   a ,  15   b  and the connection elements  16   a  and  16   b  preferably consist of a ferrite. In addition, they are arranged close behind the longitudinal sections  10   a ,  10   b  and are arranged such that they bring about a concentration of the lines of flux  14   a  and  14   b  generated by the line sections  7   a ,  7   b , as this is schematically indicated in  FIG. 3 . It is assumed in  FIG. 3  that the current flows through line section  7   a  momentarily in a direction exiting from the drawing plane and it flows through line section  7   a  momentarily in a direction entering the drawing plane. Because of the high permeability of the material strips  15   a ,  15   b , the lines of flux  14   a ,  14   b  are closed directly behind the line sections  10   a ,  10   b , as is schematically indicated by arrows, as a result of which the magnetic coupling is greatly increased. Higher eddy current losses are at the same time prevented from developing because the material strips  15   a ,  15   b  and connection elements  16   a ,  16   b  magnetically shield the parts of the magnetic back box  6  located behind them because of their high permeability. Finally, the connection elements  16   a ,  16   b  shall bring about an extensively uniform distribution of the magnetic flux within the grid frame structure. The length of the material strips  15   a ,  15   b  and of the connection elements  16   a ,  16   b  is therefore preferably selected to be such that the largest possible number of lines of flux  14   a ,  14   b  are collected or concentrated. 
         [0031]    The connection elements  16   a ,  16   b  are preferably fastened on the sides of the material strips  15   a ,  15   b  facing the line sections  7   a ,  7   b . This leads to the advantage that they come to lie essentially in the same plane as the longitudinal sections  10   a ,  10   b  of the receiver coil  10 , as is shown especially in  FIG. 3 . As a result, no additional space is required for them, especially if their thickness, which is sufficient from a magnetic point of view, is approximately equal to the thickness of the longitudinal sections  10   a ,  10   b.    
         [0032]    Receiving units of the type described are known from the document DE 10 2004 056 439 A1, which is made into the subject of the present disclosure by reference to avoid further repetitions. 
         [0033]    To simplify the manufacture of the grid frame comprising the strips  15   a ,  15   b  and connection elements  16   a ,  16   b , a basic body  18  ( FIG. 4 ) is used according to the present invention as a starting component, which is provided with depressions in the form of grooves or the like wherever the flux-conducting elements are to come to lie and can therefore be considered to be an organizing auxiliary means. Webs left in place between the depressions are designed such that their surfaces can also be used, at least partially, as contact surfaces for the receiver coil  10 . 
         [0034]    As is apparent from  FIGS. 4 through 7 , the basic body  18  is manufactured in the exemplary embodiment from an originally plane-parallel panel, which has, like the receiver coil  10 , an essentially rectangular outer contour and has accordingly two long longitudinal sides  18   a  arranged in parallel to one another and two short, likewise essentially parallel front sides  18   b  arranged at right angles thereto. In addition, the basic body  18  is divided by a middle web  19  extending in parallel to the longitudinal sides  18   a  into two halves, which are essentially mirror-symmetrical in relation to this. 
         [0035]    To mount the strips  15   a ,  15   b  ( FIG. 2 ), each half of the basic body  18  is provided, from its broad side that is the upper broad side in  FIGS. 4 through 7 , with a plurality of first depressions  20 , whose lower limitations or bottoms are indicated by broken lines in  FIGS. 5 and 7 . The depressions  20  extend into a first plane  21  of the basic body  18  and are arranged at right angles to the longitudinal sides  18   a  and to the middle web  19 , on the one hand, and in parallel to one another, on the other hand. The number and size of these depressions  20  correspond to the number and size of the strips  15   a  and  15   b  to be mounted. 
         [0036]    Webs  22  left in place between the depressions  20  are provided according to  FIGS. 5 and 6 , at their ends adjoining the longitudinal sides  18   a  and the middle web  19 , with second depressions  23 , which likewise extend into the first plane  21  and are thus connected to the first depressions  20 . 
         [0037]    In one exemplary embodiment, which is considered to be the best so far and is shown in  FIGS. 4 through 7 , the height of the parts  22   a  of the webs  22  ( FIG. 5 ) that remain after the second depressions  23  have been formed and face the longitudinal sides  18   a  is reduced, so that these parts reach only a second plane  24 , which has a distance that corresponds to the thickness of the strips  15   a  and  15   b  from the first plane  21 . Third depressions  25 , which are used to mount the longitudinal sections  10   a ,  10   b  of the receiver coil  10 , are formed as a result. Depressions  25  extend at right angles to the longitudinal sides  18   a  of the basic body  18  from the second depressions  23  to the steps  22   b  of the webs  22  and have a length in the direction of extension that corresponds to the width of the receiver coil  10  to be inserted, whose longitudinal sections  10   a ,  10   b  can be seen in  FIG. 7 . 
         [0038]    The surfaces of parts  22   c  of the webs  22 , whose height is reduced, are located in a third plane  26  of the basic body  18 . The surfaces of an edge section  27  of the basic body  18 , which extends all around, as well as of the middle web  19  are also located in this plane  16 , which has a distance from the second plane  24  that corresponds essentially to the thickness of the receiver coil  10 . 
         [0039]    The basic body  18  is provided with additional depressions  28  ( FIG. 4 ) extending into the second plane  24  in an area each adjoining the front sides  18   b . The size of these depressions is selected to be such that they can receive the end windings  10   c  ( FIG. 2 ) of the receiver coil  10 . In addition, the height of the different layers of the receiver coil  10  is selected to be such that after it has been placed on the upper surfaces or bottoms of the depressions  25  and  28 , it closes flush with the third plane  26 , as is shown in  FIG. 7 . 
         [0040]    The receiving unit is advantageously manufactured in the manner shown in FIG.  8  as follows: 
         [0041]    The basic body  18  is first provided with the depressions  20 ,  23 ,  25  and  28  and webs  22  shown in  FIGS. 4 through 6  by subjecting a plane-parallel panel, e.g., to a machining process, especially various milling steps. The depressions  25  and  28  then form a space intended for receiving the receiver coil  10 . This space is dimensioned such that, on the one hand, the receiver coil  10  comes into contact with step  22   b  with its inner contour  10   d  when it is inserted into the basic body  18  ( FIG. 7 ) and is hereby positioned in the transverse direction of the basic body  18  and, on the other hand, it abuts against the free ends of the middle web  19  and is thus oriented in the longitudinal direction of the basic body  18 . This state is shown in the lowermost picture in  FIG. 8 . In other words, steps  22   b  and the ends of the middle web  19  form stop and positioning means for exactly positioning the receiver coil  10  in the basic body  18 . 
         [0042]    The flux-conducting elements  15   a ,  15   b  and  16   a ,  16   b  are prepared in another process step. They are prepared, e.g., by pressing and subsequent sintering from a material such as ferrite, especially a soft ferrite, and this preparation may also be carried out fully independently from the manufacture of the cover element according to the present invention. In particular, the material strips  15   a ,  15   b  are prepared, on the one hand, corresponding to  FIG. 2  such that they exactly fit into the first depressions  20 , which are visible in the right-hand part of  FIG. 6 . On the other hand, the connection elements  16   a ,  16   b  are prepared such that they exactly fit into the second depressions  23 , which are visible in  FIGS. 5 and 6 . To avoid premature rupture of the connection elements  16   a ,  16   b , individual pieces thereof are prepared, which have, analogously to  FIG. 2 , such a length that they extend over a small number of material strips  15   a ,  15   b  only (cf.  FIG. 8 ) and are essentially only as long as the material strips  15   a ,  15   b . The material strips  15   a ,  15   b  and connection elements  16   a ,  16   b  can subsequently be connected, corresponding to  FIG. 8 , second picture from the top, by means of a mounting adhesive or the like into a grid frame, which fits exactly into the depressions  20  and  23  of the basic body  18 . 
         [0043]    Regardless of whether the flux-conducting elements  15   a ,  15   b  and  16   a ,  16   b  are integrated into such a grid frame or not, they are now inserted into the depressions  20 ,  23  of the basic body  18 . As is schematically shown in the left-hand part of  FIG. 6 , the material strips  15   a  and  15   b  come to lie in a depression  20  each and fill this out over the entire length. By contrast, the connection elements  16   a  and  16   b  are arranged, as is shown in  FIG. 7 , in the depressions  23  of the basic body  18 , and they are in contact with the ends of the material strips  15   a ,  15   b . As in the case of the grid frame, a connection of the connection elements  16   a ,  16   b  can be established with the material strips  15   a ,  15   b  by means of a mounting adhesive or the like in this case as well. 
         [0044]    Subsequent to the insertion of the flux-conducting elements  15   a ,  15   b ,  16   a ,  16   b , the receiver coil  10  is placed on the basic body  18 , as is shown in  FIGS. 7 and 8  (lowermost picture) such that their longitudinal sections  10   a ,  10   b  come to lie in the third depressions  25  and hence on the surfaces of the web parts  22   a  and their end windings  10   c  in the depressions  28 . 
         [0045]    According to a first exemplary embodiment of the manufacturing process according to the present invention, the receiving unit, which comprises the basic body  18 , the flux-conducting elements  15   a ,  15   b  and  16   a ,  16   b  as well as the receiver coil  10  and is still joined together loosely, is now placed into an outer shell  30  ( FIG. 9 ) of a cover element corresponding to the cover element  11  in  FIG. 1 , which said outer shell was prepared in advance and was manufactured from a fiber-reinforced plastic. This outer shell  30  forms a component defining the outer contour of the cover element in the exemplary embodiment and at the same time a mold for manufacturing the complete cover element. The receiving unit prepared in advance is now inserted into the outer shell  30  preferably such that the receiver coil  10  comes to lie on its bottom  30   a . The receiving unit is subsequently enveloped with a fiber-reinforced plastic. An inner shell  31 , which is shown in  FIG. 10  and is firmly connected to the outer shell  30 , is formed as a result, while the receiving unit is arranged at the same time in a sandwich-like pattern between the two shells  30 ,  31 . On the whole, a cover element  32 , in which the receiving unit is integrated captively and essentially also indestructibly, is thus obtained. 
         [0046]    The cover element  32  may contain additional components besides the receiving unit. These include, e.g., a tunable capacitor block, not shown, which is connected to the receiver coil  10 , forms a resonant circuit with this and is used to tune this resonant circuit to a natural frequency of, e.g., 20 kHz, which corresponds to the frequency of the current of the primary conductor  7  ( FIG. 1 ). In addition, additional components, which are useful or necessary for the operation of the carrier magnets  5  ( FIG. 1 ), may be accommodated in a space  33  of the cover element  32 . In addition, the basic body  18  may be provided, which is not shown, with the necessary connection contacts for the receiver coil  10 , and additional components may, of course, also be arranged on the basic body  18 . 
         [0047]    A mold  34  ( FIG. 11 ), whose cavity defines the outer contour of the cover element  32  or of the outer shell  30 , is used to manufacture the cover element  32  in a second exemplary embodiment of the present invention. At least one first fiber mat  35  is first inserted, preferably in the dry state, into this mold  34  to prepare the outer shell  30 . The receiving unit prepared corresponding to  FIG. 8  is then placed on this fiber mat, after which at least one second, preferably likewise dry fiber mat  36  is placed on this receiving unit. The arrangement is preferably selected such that the two fiber mats  35 ,  36  have edge sections  35   a ,  36   a , which lie one on top of another and extend all around, so that the receiving unit is surrounded by the fiber mats  35 ,  36  on all sides. 
         [0048]    The mold  34  is now lined on its top side with a film  37  or the like, which covers and seals its cavity and is connected to a vacuum pump, not shown, through a channel  38  extending into the bottom of the cavity. The fiber mats  35 ,  36  and the basic body  18  with its components are hereby pressed tightly against the bottom of the cavity and against one another and the edge sections  35   a ,  36   a  are brought together. A casting resin is then pressed into the cavity through a gate  39 , which likewise opens, e.g., at the bottom of the mold, in order to impregnate the fiber mats  35 ,  36  with the casting resin, as this is commonly practiced in the manufacture of shaped parts from fiber-reinforced plastics. 
         [0049]    The casting resin is then cured or allowed to cure, optionally at elevated temperature, after which the film  37  is peeled off and the finished cover element is removed from the mold  34 . To facilitate this operation, the mold  34  may have been previously coated with a mold release agent and at least one insert part  40  (cf.  FIG. 10 ), which makes it possible to slightly raise the finished cover element, may have been provided between the two fiber mats  35 ,  36 . The cover element removed from the mold  34  corresponds, in turn, to the cover element  11  in  FIG. 1 . 
         [0050]    One advantage of the process described is that the bottom of the outer shell  30  is made comparatively thin and the receiver coil  10  can therefore be arranged very close to the primary conductor  7  ( FIG. 1 ), which increases the efficiency of said coil. In addition, analogously to a double-T beam, the basic body  18  forms the middle web between the two shells  30  and  31  and as a result a spacing element, which ensures high rigidity of the cover element. 
         [0051]    The manufacture of the fiber-reinforced cover element  32  may otherwise also be carried out by means of other processes commonly used in the manufacture of fiber-reinforced and especially glass fiber-reinforced plastic parts. Besides the manual lamination and the vacuum injection described, for example, the injection molding and pressing technique and especially the use of prepregs, i.e., mats already impregnated with hot-curing resins, which are subjected to further processing by hot or cold pressing, are suitable. Furthermore, it is possible to combine a plurality of mats possessing different properties, e.g., to arrange Aramide fiber mats for sufficiently securing joints, glass fiber mats for high strength and nonwoven mats for obtaining a good optical appearance one on top of another in layers in the process described on the basis of  FIGS. 10 and 11 . 
         [0052]    To simplify the manufacture of the receiving unit comprising the basic body  18 , the flux-conducting elements  15   a ,  15   b  and  16   a ,  16   b  as well as the receiver coil  10 , it is possible according to another preferred embodiment of the present invention to manufacture the flux-conducting elements  15   a ,  15   b  and  16   a ,  16   b  by a casting operation. The receiver coil  10  is preferably placed for this onto the finished basic body  18  preferably in the manner shown in  FIG. 8  (lowermost picture) without individual flux-conducting elements  15   a ,  15   b  and  16   a ,  16   b  having been introduced before. The receiver coil  10  is then in contact with the steps  22   b  ( FIGS. 5 and 7 ) and with the ends of the middle web  19 , while the depressions  20 ,  23  remain free. 
         [0053]    A liquid mixture, which contains a curable casting resin and a powder, which consists of a material having high permeability, is prepared in another process step. A powder of ferrite, preferably a soft ferrite, is used for this, in particular. This mixture may, of course, also have been prepared already before the manufacture of the basic body  18  and/or before the insertion of the receiver coil  10  into this. 
         [0054]    The finished mixture, which preferably contains a multicomponent casting resin provided with a curing agent, is now poured into the depressions  23  left free by the receiver coil  10  by means of pouring nozzles, not shown. As an alternative, a pouring spout, which passes over the length of the depressions  23 , may be used for this as well. The casting resin penetrates during the casting operation not only into the depressions  23 , but also into the depressions  20 , which extend between these and are partly under the receiver coil  10 , and fills these completely. The basic body  18  is thus used as a casting mold. The casting resin is prevented from running out into the depressions  28  by raised webs  22   a  at the lateral ends of the web rows. 
         [0055]    The casting operation is concluded when the level of casting resin has reached the third plane  26  ( FIG. 7 ). As a result, the casting resin can rise up to level  26  in the areas located between the parts  22   c  of the webs  22 , as this is indicated in  FIG. 3  by a broken line  41 . However, this does not compromise the function of the strips  15   a ,  15   b  as flux-conducting elements. 
         [0056]    One advantage of the process described is that a shaped part of the type of a grid form is formed, which contains the strips  15   a ,  15   b  and connection elements  16   a ,  16   b  shown in  FIGS. 2 and 3  with the difference that these are manufactured in one piece and form a one-piece, contiguous grid frame, which is arranged recessed in the basic body  18 . Special measures for connecting the strips  15   a ,  15   b  and connection elements  16   a ,  16   b  are therefore unnecessary. Furthermore, it is advantageous that the receiver coil  10  is also already inserted into the basic body  18  and is firmly embedded in same by the casting operation. The basic body  18 , the receiver coil  10  and the flux-conducting elements  15   a ,  15   b ,  16   a ,  16   b  therefore form a structural and receiving unit, which is completely preassembled or can be completely preassembled and which is embedded as a whole in the cover  11  ( FIG. 1 ) of the magnetic back box  6 . Finally, it is also advantageous that the cast flux-conducting elements have a higher ductility than the ferrite elements used otherwise, which are manufactured as compression moldings. 
         [0057]    The basic body  18  is preferably manufactured from a plastic, especially a foam, e.g., polyurethane with highly damping properties. As an alternative to machining, it is possible, besides, to manufacture the basic body  18  as a whole by casting, foaming or pressing with the use of a corresponding die, in which case the depressions  25 ,  28  for the receiver coil  10  can be kept free, e.g., by a correspondingly shaped displacement body. 
         [0058]    The present invention is not limited to the exemplary embodiment described, which can be varied in many different ways. This applies, in particular, to the grid frame-like structure of the flux-conducting elements shown in  FIGS. 2 and 3 , because these may also be arranged in other advantageous patterns and can be made larger or smaller than described. It may be advantageous, above all in case of the use of the casting process described on the basis of  FIGS. 5 through 7 , to design the flux-conducting elements  15   a ,  15   b  ( FIG. 2 ) as panels passing over the length of the receiver coil  10 . The webs  22  ( FIGS. 5 through 7 ) could be eliminated altogether in this case and the depressions  20  could be made continuous in the longitudinal direction of the basic body  18 . It would be possible now, e.g., to fill in a first step the entire lower space of the basic body  18  up to level  24  ( FIG. 6 ) with the casting resin mixture, then to insert the receiver coil  10  and finally to fill the space occupied by the flux-conducting elements  16   a  and  16   b  in  FIG. 7  with the casting resin mixture. The shape of the cover element  32  may be different as well, because this depends mainly on whether it is to be provided with additional components or the like or whether it is to cover such additional components. Furthermore, it is clear that the receiver coil  10  is provided with connection contacts, not shown, at suitable points and the depressions  28  ( FIG. 4 ) may also be absent altogether, especially when it is desirable to bend off the end windings  10   c  to the rear analogously to DE 10 2004 056 439 A1. The cover element  32  would have to be provided with correspondingly shaped side parts in this case. Instead of flux-conducting elements made of ferrite, it would also be possible to provide flux-conducting elements consisting of other materials, e.g., soft iron, especially when the power transmission takes place at such low frequencies that the losses generated thereby are tolerable. Finally, it is obvious that the various features can also be used in combinations other than those described and shown. 
         [0059]    While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.