Abstract:
A secondary transformer unit for mounting on a vehicle having an electric drive includes at least one secondary core, and at least one secondary coil that is arranged on the secondary core. At least one outer skin is provided to envelope the secondary core and contains reinforcing fibers. The outer skin is configured to retain inside the at least one outer skin fragments produced when the at least one secondary core breaks.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is the U.S. National Stage of International Application No. PCT/EP2012/004174, filed Oct. 5, 2012, which designated the United States and has been published as International Publication No. WO 2013/056791 and which claims the priority of German Patent Application, Serial No. 10 2011 116 250.3, filed Oct. 18, 2011, pursuant to 35 U.S.C. 119(a)-(d). 
     BACKGROUND OF THE INVENTION 
     The invention relates to a secondary transformer unit for attachment to a vehicle with an electric drive having at least one secondary core and at least one secondary coil arranged on the secondary core, and to a vehicle with an electric drive. 
     Motor vehicles with an electric drive, such as hybrid cars and pure electric cars, which have traction batteries for supplying electric power to an electric motor, are known in the art. These conventional motor vehicles are equipped with a system for inductive energy transfer, which also allows a frequent recharging of the batteries with ease of use. This system works like a transformer and includes a primary transformer unit installed on the infrastructure side, for example on the rear wall of a garage, and a secondary transformer unit that is integrated at the front of the motor vehicle behind the front license plate. 
     The document DE 10 2009 023 409 A1 relates to a system for electric power transmission and forms the basis for the preamble of claim  1 . This document discloses a secondary transformer unit or secondary transformer which is mounted at the bow or at the front of an electric vehicle and includes a U-shaped half transformer core and a coil winding wound thereon at an oblique angle. This secondary transformer unit is mounted at the front bumper of the electric vehicle, and the front license plate of the electric vehicle is mounted on the secondary transformer unit. 
     Since this conventional secondary transformer unit is mounted at the bow of the vehicle, it must be integrated in an area of the vehicle that has a high influence on the crash behavior in accidents involving pedestrians. In particular, the front of the vehicle becomes harder due to the additionally installed components, in particular the half-transformer core usually composed of magnetic steel sheets or ferrite; however, a well-defined and smooth vehicle front is necessary to minimize the risk of injury to pedestrians. Since the conventional secondary transformer unit is mounted at the front bumper behind the front license plate, less space remains available for deformation elements made of foam arranged between the bumper and the passenger compartment, requiring a reduction of their thickness, i.e. its extent in the direction of travel. This leads to a further increase of the hardness of the vehicle front. 
     DE 24 34 890 B1 describes an apparatus for connecting a charger arranged in a motor vehicle with an AC power grid or three-phase power grid. The apparatus is composed of a transformer divided into two parts, wherein the two parts each have a core on which the respective primary and secondary windings are arranged. The transformer part connected to an AC power grid and having the primary windings is arranged in a charging board of a parking space, whereas the transformer part connected to the secondary windings is located in a bumper of the motor vehicle. The transformer parts are provided with a plastic cover for corrosion protection. 
     DE 37 18 676 A1 discloses a molded article made of composite material, in particular of a hybrid material of fiber reinforced plastic and metal with a film-like or layer-like or spongy or network-like core which is embedded in plastic. The reinforcing fibers may be made of aramide, carbon and/or glass. 
     SUMMARY OF THE INVENTION 
     It is the object of the invention to improve a secondary transformer unit and a vehicle with an electric drive with such a secondary transformer unit with respect to crash behavior in accidents involving pedestrians. 
     The invention is based on the realization that the half-transformer core, which typically consists of laminated magnetic steel sheets or ferrite, may break or tear in an accident, producing sharp-edged, hard fragments that increase the risk of injury especially for an involved pedestrian. 
     According to a first aspect, the invention relates to a secondary transformer unit for attachment to a vehicle having an electric drive, including
         at least one secondary core;   at least one secondary coil arranged on the secondary core, and   at least one outer skin which at least partially surrounds at least the secondary core and contains the reinforcing fibers and which is configured to retain fragments within the outer skin when the secondary core breaks.       

     Since the outer skin at least partially envelops the secondary core, it can catch and retain sharp-edged, hard fragments of, for example, the secondary core containing magnetic steel sheet and/or electrical steel and/or ferrite which breaks apart or is torn in an accident, thereby reducing the risk of injury in particular for an involved pedestrian. 
     The outer skin may be formed in any way depending on the requirements, for example, it may only partially surround the secondary core or may not cover a portion of the secondary core or may envelop the entire secondary core or may completely envelop the secondary core. 
     When the outer skin only partially envelops the secondary core, it may be formed, for example, as a band or as a sleeve that is open on two opposite sides, or as a bag that is open on one side. Preferably, the band or the sleeve may cover a front side and a rear side of the secondary core that delimit the secondary core in an x-direction, as well as a top side and a bottom side of the secondary core that delimit the secondary core in a z-direction, while leaving a left side and a right side of the secondary core that delimit the secondary core in a y-direction uncovered. In this case, the x-direction corresponds to the direction of travel or longitudinal direction of the vehicle on which the secondary transformer unit is to be mounted, the y-direction corresponds to the transverse direction of this vehicle, and the z-direction corresponds to the vertical direction of this vehicle. The bag may preferably cover the front, back, top, bottom and the left or right side of the secondary core, while leaving the respective other side, i.e. the right or left side of the secondary core uncovered. 
     When the outer skin completely envelops the secondary core, it may be, for example, formed as an envelope that is open on neither side, or is closed on all sides. The envelope may preferably cover the front side, rear side, top side, bottom side, the left side and the right side of the secondary core or may leave no side of the secondary core uncovered. 
     It may be provided that the outer skin is at least partially attached to the secondary core. 
     In this way, catching, retaining and holding together fragments of the secondary core is further improved. 
     The attachment may be carried out, as required, in any desired manner, for example by gluing and/or welding. 
     The outer skin may be formed, as required, in any desired manner, for example so as to at least partially enveloping only the secondary core or in addition also the secondary coil. 
     When the outer skin envelops the secondary core and the secondary coil, it may advantageously press the secondary coil against the secondary core. 
     The secondary core may be constructed, as required, in any manner and is preferably substantially plate-shaped and has, for example, a thickness in the x-direction, a width in the y-direction and a height in the z direction, wherein the thickness is less than the height and the height is less than the width. 
     Such a substantially plate-shaped secondary core can be easily deformed, in particular bent or broken through, in the x-direction in the event of a collision, and requires little installation space between the bumper and the passenger compartment, so that foam deformation elements to be mounted in this area which is important for the frontal crash performance can have a greater thickness, i.e. dimension in the direction of travel. 
     It may be provided that the outer skin is tear-resistant and/or cut-resistant. 
     Such outer skin is able to also catch and retain sharp fragments of the secondary core in its interior. 
     The outer skin may be formed, as necessary, in any manner and may have, for example, a woven fabric and/or knit fabric and/or a network and/or a film. 
     The materials for the woven fabric, the knit fabric, the network and the film may be selected arbitrarily as required, and contain, for example, at least one metal and/or at least one rubber material and/or at least one plastic material and/or carbon and/or at least one silicone and/or at least one glass and/or at least one ceramic. 
     The reinforcing fibers may be formed, as needed, in any number of ways and preferably contain aramide fibers and/or glass fibers and/or carbon fibers and/or metal fibers. 
     According to a second aspect of the invention proposes, a vehicle with an electric drive is proposed, including at least one of the proposed secondary transformer units. 
     It may be provided that one of the secondary transformer units is arranged at the front of the vehicle and/or one of the secondary transformer units is arranged at the rear of the vehicle and/or one of the secondary transformer units is arranged at the left side of the vehicle and/or one of the secondary transformer units is arranged at the right side of the vehicle and/or one of the secondary transformer units is arranged at the bottom of the vehicle and/or one of the secondary transformer units is arranged on the roof of the vehicle. 
     Each proposed vehicle may further include a front license plate arranged in front of a secondary transformer unit at the front in the direction of travel, and/or a rear license plate arranged in the direction of travel behind a secondary transformer unit mounted at the rear. 
     The discussions relating to one aspect of the invention, in particular to individual features of this aspect, apply mutatis mutandis similarly for the other aspects of the invention. 
     Embodiments of the invention will now be described in more detail with reference to the accompanying drawings. The resulting individual features, however, are not limited to the individual embodiments, but may be combined with several of the above-described individual features and/or with features of other embodiments. The details in the drawings are to be understood as only illustrative, but not as limiting. The reference symbols included in the claims are not intended to limit the scope of the invention in any way, but merely refer to the embodiments shown in the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The drawings show in: 
         FIG. 1  a front view of a secondary transformer unit in a first embodiment, which can be arranged at a front of a vehicle having an electric drive; 
         FIG. 2  the plan view of  FIG. 1 ; 
         FIG. 3  a front view of a secondary transformer unit in a second embodiment; and 
         FIG. 4  a front view of a vehicle with an electric drive in a preferred embodiment. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIGS. 1 and 2  show schematically a first embodiment of a secondary transformer unit  10  according to the invention for installation on a vehicle  11  with an electric drive ( FIG. 4 ). This secondary transformer unit  10  includes a secondary core  12 , a secondary coil  13  arranged on the secondary core  12 , and an outer skin  14  enveloping the secondary core  12 . 
     In this first embodiment, the secondary core  12  is plate-shaped, is made of ferrite, and has a top side  15 , a bottom side  16 , a left side  17 , a right side  18 , a front side  19  and a rear side  20 . The top side  15  and bottom side  16  delimit the secondary core  12  in a z-direction, which points in  FIG. 1  toward the top side and in  FIG. 2  toward the front side of the drawing plane. The left side  17  and the right side  18  delimit the secondary core  12  in a y-direction, which points in  FIGS. 1 and 2  to the right. The front side  19  and the rear side  20  delimit the secondary core  12  in an x-direction, which points in  FIG. 1  toward the front out of the drawing plane and in  FIG. 2  downwards. The x-direction corresponds to the direction of travel or the longitudinal direction of the vehicle  11 , the y-direction corresponds to the transverse direction of the vehicle  11 , and the z-direction corresponds to the vertical direction of the vehicle  11 . In addition, the secondary core  12  has a width in the y direction that corresponds to the distance between the left side  17  and the right side  18 , a height in the z direction that corresponds to the distance between the top side  15  and bottom side  16  and significantly smaller than the width, and in the x direction a thickness that corresponds to the distance between the front side  19  and the rear side  20  and is significantly smaller than the height. 
     In this first embodiment, the outer skin  14  has a tear-proof fabric of aramide fibers and envelops only the secondary core  12 , but not the secondary coil  13 . The outer skin  14  is closed on all sides, much like an envelope or a bubble, covers the top side  15 , the bottom side  16 , the left side  17 , the right side  18 , the front side  19  and the rear side  20  and is glued to the front side  19  and the rear side  20  with an unillustrated adhesive. 
     In this first embodiment, the secondary coil  13  is arranged in three substantially rectangular turns on the front side  19  of the secondary core  12 . An unillustrated primary transformer unit which includes a primary core and a primary coil arranged on the primary core is configured to generate a magnetic field when being placed at a small distance in front of the front side  19  and when an alternating current flows through its primary coil, with the field lines indicated in  FIG. 1  by the circles with a dot and the circles with a cross. Field lines enter, for example, the front face  19  of the secondary core  12  at locations marked by the circles with a cross and exit the secondary core  12  at locations marked by the circles with a dot and extend inside the secondary core  12  from the circles with a cross to the circles with a dot. These field lines thus envelop the turns of the secondary coil  13  and induce therein an AC voltage which is supplied to an unillustrated high-voltage onboard electrical system of the vehicle  11  for charging its traction batteries. 
     In this first embodiment, the turns of the secondary coil  13  are glued to the front side of the outer skin  14  which faces forward in the x-direction. 
       FIG. 3  illustrates a secondary transformer unit  10  according to the invention in a second embodiment. This second embodiment is similar to the first embodiment, so in the following only the differences will be described in detail. 
     In this second embodiment, the outer skin  14  envelops not only the secondary core  12 , but also the secondary coil  13 , and is glued only to the rear side  20  with an unillustrated adhesive. 
     In this second embodiment, the turns of the secondary coil  3  are glued to the front side  19  of the secondary core  12 . 
       FIG. 4  shows schematically a preferred embodiment of a vehicle  11  according to the invention with an electric drive in the form of a hybrid car. This vehicle  11  includes a secondary transformer unit  10  in the first embodiment, a front license plate  21  and a front bumper  22 . 
     In this preferred embodiment, the secondary transformer unit  10  is arranged at the front of the vehicle  11  and attached with the rear side of the outer skin  14  facing rearward in the x-direction to a front side to the front side of bumper  22  facing forward in to the x direction. Also, the license plate  21  is arranged in the x-direction in front of the secondary transformer unit  10  and fastened with its rear side facing rearward opposite to the x-direction to the front of the outer skin  14 . In this case, the license plate  21  is arranged and the turns of the secondary coil  13  are placed on the front side of the outer skin  14  such that the license plate  21  abuts the partial area of the front side enveloped by the secondary coil  13  and the secondary coil  13  surrounds the license plate  21  without touching it.