Abstract:
A coil unit for an electric vehicle for the inductive transfer of electrical energy between the coil unit and a stationary charging station. The coil unit includes at least one coil and a flux guide unit for guiding a magnetic flux occurring during operation of the coil. Also disclosed is an electric vehicle having a coil unit for the inductive transfer of electrical energy between a secondary coil of the coil unit and a primary coil of a charging station. The disclosed coil solves the problem of allowing the safe use of the inductive electrical energy transfer in electric vehicles, in particular motor vehicles, by proposing a coil unit, in which the flux guide unit has material weakenings, and an electric vehicle having such a coil unit.

Description:
FIELD OF THE INVENTION 
     The invention concerns a coil unit and an electric vehicle. 
     BACKGROUND OF THE INVENTION 
     In the area of the transfer of inductive energy to movable consumers, for example, electric land vehicles, such as automobiles or trucks, a method is known for charging its vehicle battery via a stationary primary coil of a charging station and a secondary coil located on the bottom of the vehicle. The primary coil is thereby located on or in the traveling lane, for example, on publicly accessible parking lots, charging areas of filling stations, or in the garage of the owner of the vehicle. For the charging operation, the electric vehicle is driven over the primary coil, so that the secondary coil that is located in the vehicle is aligned on the primary coil. 
     DE 10 2009 033 236 A1 discloses an example for this, in which the secondary coil is located, together with a ferrite plate as a flux guide unit, in a housing on the bottom of an electric vehicle. 
     DE 10 2008 029 200 A1 discloses a body of a motor vehicle with at least one structure area formed from a plate element. The plate element is located on the bottom of the vehicle body and, in the longitudinal direction, has longitudinal hollow chambers located in the transverse direction of the motor vehicle, next to one another, into which energy storage elements, in particular, accumulator batteries, or other components of an energy storage device are placed. In order to reduce damage or destruction of the energy storage device with the resulting endangerment of the vehicle occupants in case of an accident of the motor vehicle, the energy storage elements, for example, are located only in areas which cannot be deformed excessively in case of an accident, for example, only under the driver&#39;s seat, located centrally. In this way, not only the front and rear structures, but also the lateral areas of the passenger compartment, can be deformed for the energy absorption, whereas the energy storage elements are not located in these areas. 
     DE 10 2007 040 770 A1 discloses a passenger car with a vehicle bottom with a middle tunnel, which extends in the longitudinal direction of the vehicle. The middle tunnel has at least one weak site, where the middle tunnel is deformed under the effect of force caused by an accident after a stress limit has been exceeded. No indication is made there of a coil unit with a flux guide unit for the inductive transfer of electrical energy between the coil unit and a stationary charging station. 
     DE 10 2010 035 634 A1 discloses a transfer system for charging the traction batteries of an electric vehicle with a coupling device that is attachable thereon, with a transformer part, by means of which the electrical energy can be transferred inductively to a transformer part on the vehicle. The transformer part, which is integrated in the vehicle license plate, has a coupling body made of a flexible plastic material, which surrounds an electrical coil arrangement with a ferrite arrangement, consisting of plate- or yoke-like ferrites, separated from one another. The ferrites, separated from one another, worsen the magnetic flux guidance and thus the coupling between the transformer parts. 
     With the known coil units, the disadvantage is that the magnetic flux guide unit, as a rule, is made of a massive, rigid, and heavy material, for example, a ferrite plate. Since the coil unit is usually arranged, parallel to the surface, on the bottom of the vehicle and exhibits a great inertia because of its heavy weight, the danger with a rear-end collision is that the flux guide unit will be hurled in the direction of the impact zone and the coil unit will be thereby destroyed and perhaps travel from its anchorage on the bottom of the vehicle and will damage the vehicle and endanger the vehicle occupants as well as persons found outside the vehicle. Since the flux guide unit is also very rigid, as a rule, it will also transfer the impact energy, more or less undiminished, in case of a collision. 
     SUMMARY OF THE INVENTION 
     A coil unit and electric unit as disclosed herein make possible the safe use of the inductive electrical energy transfer with electric vehicles, in particular, motor vehicles. 
     Advantageous developments and appropriate refinements are also disclosed herein. 
     This goal is attained by the invention with a coil unit with the features of Claim  1  and an electric vehicle with the features of Claim  13 . Advantageous developments and appropriate refinements of the invention are indicated in the subclaims. 
     A coil unit mentioned in the beginning is characterized, in accordance with the invention, in that the flux guide unit exhibits material weaknesses. 
     Preferably, the material weaknesses can essentially run transverse to the longitudinal direction of the vehicle, where this includes slight deviations by a few centimeters, preferably, by a few millimeters, from the course exactly transverse to the longitudinal direction. Preferably, the material weaknesses can also run essentially concentric to a center of the flux guide unit. Also preferably, the material weaknesses can essentially run in the direction of the magnetic field lines of the magnetic flux guided in the flux guide unit, so that the magnetic flux is hardly impaired in the flux guide unit. 
     In an advantageous development of the invention, the material weaknesses can be designed, completely or partially, as predetermined breaking points, so that in case of an accident, the impact energy damages or completely destroys the predetermined breaking points. 
     In an embodiment which is favorable for manufacturing technology, the material weaknesses in the flux guide unit can be provided as grooves. Furthermore, the material weaknesses can be provided on various flat sides of the flux guide unit so they are favorable for operational technology, in order to reduce a deformation of the flux guide unit in a preferred direction. 
     Preferably, the material weaknesses can run in a plane of the flux guide unit, parallel to the longitudinal direction of the vehicle, inclined—preferably, at an incline to the plane. Thus, parts of the flux guide unit, broken apart in case of an accident, do not collide against one another with their impact edges and in this way, transfer the impact energy, but rather the parts of the flux guide unit, which have broken part, are pushed from the plane against one another—that is, they move past one another. 
     Preferably, the material weaknesses can be partial or complete breaks of the flux guide unit. In a favorable embodiment, the breaks can be filled, partially or completely, with an adhesive and/or bonding material, so that they are affixed to one another, in their position. The adhesive and/or the bonding material can thereby have ferromagnetic or ferrimagnetic characteristics, so as to make available a good magnetic conductance and thus a good flux guidance in the flux guide unit in spite of the breaks. 
     An electric vehicle, mentioned in the beginning, is characterized, in accordance with the invention, in that the coil unit is designed as described above and below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiment examples of the invention are described in detail, below, with the aid of the appended drawings. The figures show the following: 
         FIG. 1 , a lateral sectional view of an inductive energy transfer device with a first embodiment of a coil unit in accordance with the invention; 
         FIG. 2 , a schematic top view of the coil unit from  FIG. 1 ; 
         FIG. 3 , a lateral sectional view of a second coil unit in accordance with the invention; 
         FIG. 4 , a lateral sectional view of a third coil unit in accordance with the invention; 
         FIG. 5 , a lateral sectional view of the coil unit from  FIG. 4 , after it was destroyed; 
         FIG. 6 , a lateral sectional view of a fourth coil unit in accordance with the invention; 
         FIGS. 7   a - c , schematic top views of other coil units in accordance with the invention, with a circular disk-shaped flux guide unit; 
         FIGS. 8   a - c , schematic top views of other coil units in accordance with the invention, with a square flux guide unit. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows, schematically, a lateral sectional view of an energy transfer device  1  for the inductive transfer of electrical energy between a primary coil unit  3 , installed on a lane bottom  2 , which is, in fact, known, and a secondary coil unit  6  in accordance with the invention, placed on a vehicle bottom  4  of an electric vehicle  5 . The longitudinal and forward traveling direction of the electric vehicle  5  is marked with an arrow L in  FIG. 1 . 
     The primary coil unit  3  thereby comprises, in a manner which is, in fact, known, a primary coil housing  7  with a primary coil  8  located therein, with primary coil windings  9  and a primary coil-flux guide unit  10 . 
     The secondary coil unit  6 , which is also only designated, below, as the coil unit  6 , has—in a manner which is, in fact, known—a housing  11  with a coil  12 , integrated therein, with coil windings  13 . In order to attain as good as possible a guidance of the magnetic flux for the inductive energy transfer, the coil unit  6  has a flux guide unit in accordance with the invention, which is also integrated into the housing  11 , in the form of a circular ferrite plate  14 . Since the material of the ferrite plate  14 , which is a good magnetically conducting material, is rather heavy, the ferrite plate  14  forms a massive and rigid object. Since the coil unit  6  is essentially placed parallel to the surface of the vehicle bottom  4  and exhibits a great inertia because of its heavy weight, the danger, in case of a rear-end collision, is that the ferrite plate  14  is hurled in the direction of the impact site and thereby destroys the coil unit  6  and perhaps travels from its anchorage on the vehicle bottom  4 . Since the ferrite plate  14  is also very rigid, it also transfers—in the case of an impact—the impact energy in its longitudinal direction L, more or less undiminished. 
     It is precisely when using the coil unit  6  in electric vehicles that measures must therefore be taken so that in case of an accident, especially a rear-end collision, the ferrite plate  14 , if possible, causes no damage or only slight damage, and, if possible, does not pass on undiminished impact energy, but rather, if possible, absorbs a large amount of the impact energy. 
     In this regard, the invention makes provision so that the ferrite plate  14  has material weaknesses which, in particular, with a rear-end collision, provide for the targeted breakage of the ferrite plate  14 , wherein the impact energy is absorbed, and/or parts of the ferrite plate  14  can move against one another so much that the impact energy is not passed on directly, but rather the energy flow is interrupted. 
     In the embodiment of the invention shown in  FIGS. 1 and 2 , the ferrite plate  14  essentially has, as material weaknesses, grooves  15 , running transverse to the longitudinal direction L. The grooves  15  or the crosslinks  16  of the ferrite plate  17  remaining there are particularly used, in case of a collision, as predetermined breaking points, where the ferrite plate  14  breaks in a defined manner. As shown in  FIGS. 1 and 2 , in a preferred embodiment, the grooves  15  are arranged on different flat sides  17 ,  18  of the ferrite plate  14 , so that the ferrite plate  14  easily breaks in the case of a collision, since the frontally introduced impact energy is conducted, at an incline, via the crosslinks  16 , wherein a fraction of the impact energy running in the longitudinal direction L then leads to the zigzag breaking of the ferrite plate  14 . In this way, not only the direct passing on of the impact energy is reduced, but rather the individual broken parts of the ferrite plate then escape laterally. 
     In an embodiment of the invention shown in  FIG. 3 , the ferrite plate  14  has breaks  19 , running transverse to the longitudinal direction L—that is, it is subdivided so that the result is four plate parts  14   a - d . In order to reduce the disadvantages of the breaks  19  for the magnetic flux guidance through the thus produced material break or even the air gap, provision can be advantageously made so that impact sites between adjacent partial elements  14   a - d  are very narrow—that is, for example, the impact sites are pressed against one another by a mechanical holding device. Alternatively, by the casting of the plate parts  14   a - d , preferably pressed against one another during the casting process, a good magnetically conducting connection can also be attained in the housing  11 , and a high magnetic resistance, in particular, an air gap, can be prevented. 
     Alternatively or additionally, the breaks  19  can also be advantageously filled with an adhesive or bonding material, which is preferably elastic, and in case of a collision, can be easily destroyed, for example, rubber or a soft-elastic plastic. Preferably, the adhesive or the bonding material can have a good magnetic conductance, for example, by the addition of an additive with a good magnetic conductance, such as ferrite powder. In a favorable continuation of the invention, the adhesive or the bonding material can have a poor electric conductance, so as to reduce or completely prevent any eddy currents from appearing in the ferrite plate  14 . 
     In order to further improve the desired break behavior of the ferrite plate  14 , the embodiment of the invention shown in  FIGS. 4 and 5  provide for the provision of inclined breaks  20 , running at an incline to the plane E, instead of the breaks  19  from  FIG. 3 , in the longitudinal direction L, running perpendicular to the plane E of the ferrite plate  14 . These inclined breaks  20  can also be designed in such a way that they do not divide the ferrite plate  14  into individual partial elements  14   a - d , but rather that the ferrite plate  14  remains, partially or completely, also connected to the inclined breaks  20 , via crosslinks similar to the embodiment shown in  FIG. 1 . 
     Preferably, the inclined breaks  20  are so inclined that with a collision of  FIG. 6 , to the left, indicated in  FIG. 6  with the large arrow, the inner plates  14   b  and  14   c , closer to the center, slide toward the traveling lane  2  and away from the vehicle bottom  4 , if they are pushed together by the front most plate part  14   a  and, perhaps, the plate part  14   d  furthest in the rear. This ensures that in the case of an accident, the ferrite plate  14  or one or more of its plate parts  14   a - d  are, if possible, not pushed toward the electric vehicle  5  and, in the worst case, into its passenger space. 
     In another advantageous development of the invention according to  FIG. 6 , provision can also be made to incorporate a protection element  21  into the housing  11 ; this additionally prevents that, in case of destruction, the ferrite plate  14  or its plate parts  14   a - d  can also not get from the housing  11  to the outside of the vehicle  5 , so as not to endanger the outside area of the vehicle. Preferably, the protection element  21  can be produced from a material which does not impair the magnetic and/or electric characteristics of the coil unit  6 , for example, a preferably flat Kevlar or aramid fabric or paper. 
     In  FIGS. 7 a - c  and 8 a - c   , schematic top views of other coil units, in accordance with the invention, with a circular disk-shaped or square ferrite plate  14  are shown, wherein the invention can also be implemented with other configurations, for example, rectangular, octagonal, polygonal, etc. With these drawings, it is assumed that the forward traveling direction and the longitudinal direction of the electric vehicle  5  point to the left, as defined in  FIG. 1 . 
     In the embodiments according to  FIGS. 7 a  and 8 a   , material weaknesses  22  and  23  run in the shape of rays from the center of the ferrite plate  14  to the outside, wherein the material weaknesses  22  completely interrupt the ferrite plate  14 , including its thickness, whereas the material weaknesses  23  do not extend to the periphery of the ferrite plate  14 . In these embodiments, the material weaknesses  22 ,  23  essentially run in the main direction of the magnetic flux, which is produced, in the embodiment shown in  FIG. 7 a   , by nondepicted coil windings  13 , arranged in the form of a spiral on the ferrite plate  14 , and, in the embodiment shown in  FIG. 8 a   , by nondepicted coil windings  13 , arranged in the form of a spiral in the square. 
     In the embodiments according to  FIGS. 7 b  and 8 b   , material weaknesses  24  and  25  run in a circular or square shape—that is, interrupt the main direction of the magnetic flux. If the material weaknesses  24  and  25 , as indicated in  FIGS. 7 b  and 8 b   , are complete breaks of the ferrite plate  14 , then they can be filled with an adhesive or bonding material, described above in  FIG. 3 , so as to reduce its magnetic resistance. In this way, the break behavior of the ferrite plate  14  can be improved in the case of an inclined or lateral rear-end accident, so that the ferrite plate  14 , if possible, breaks in the transverse direction to the rear-end collision. 
     In the embodiment of the invention according to  FIG. 7 c   , material weaknesses  26  run in the shape of rays and not entirely to the periphery of the ferrite plate  14 , similar to the embodiment shown in  FIG. 8 a   , wherein in  FIG. 7 c   , the material weaknesses  26  only break the ferrite plate  14  linearly. 
     An embodiment of the invention shown in  FIG. 8 c    corresponds to the embodiment shown in  FIG. 3 , with the difference that the ferrite plate  14  is square here and not round. 
     Instead of the material weaknesses, described above and shown in the figures, in the form of grooves or complete breaks, the material weaknesses can also be designed differently, for example, by holes, stampings, or embossings, extending, completely or partially, through the thickness of the ferrite plate  14 . Also, the material weaknesses can be advantageously produced by deliberately caused inhomogeneities of the material forming the ferrite plate  14 , so that, for example, the thickness of the ferrite plate  14  remains the same at the points of the desired material weaknesses, but the density of the material is reduced. Also, the different types of material weaknesses can be combined with one another. 
     LIST OF REFERENCE SYMBOLS 
       1  Energy transfer device 
       2  Lane bottom 
       3  Primary coil unit 
       4  Bottom of the electric vehicle 
       5  Electric vehicle 
       6  Secondary coil unit 
       7  Primary coil housing 
       8  Primary coil 
       9  Primary coil windings of the primary coil 
       10  Flux guide unit of the primary coil unit 
       11  Housing of the secondary coil 
       12  Secondary coil 
       13  Coil windings of the secondary coil unit 
       14  Ferrite plate as a flux guide unit of the secondary coil unit 
       15  Grooves 
       16  Crosslinks 
       17  Upper, inner flat side 
       18  Lower, outer flat side 
       19  Breaks 
       20  Inclined breaks 
       21  Protection element 
       22  Ray-shaped material weaknesses 
       23  Ray-shaped material weaknesses 
       24  Circular material weaknesses 
       25  Square-shaped material weaknesses 
       26  Ray-shaped, linear material weaknesses