Patent Publication Number: US-2007120636-A1

Title: Magnetic coupling device for contactless energy transmission systems

Description:
FIELD OF THE INVENTION  
      The present invention relates to a detachable transformer for a contactless energy transmission system, in particular, the magnetic coupling device structure design of the detachable transformer can decrease leakage magnetic flux and improve electrical energy transmission efficiency.  
     DESCRIPTION OF PRIOR ART  
      The contactless energy transmission system generally utilizes magnetic coupling to transfer the electrical energy from the primary to the secondary by means of magnetism concept. The contactless energy transmission system is extensively used for the charging devices of electric vehicles, electric toothbrushes, portable telephones, the power supplies of automated cranes . . . and so on.  FIG. 1  shows a circuit diagram of a prior art contactless energy transmission system, where a detachable transformer is used to separate at least two different power sources. The detachable transformer transmits electrical energy based on the principle of magnetic induction. Therefore, the magnetic coupling effect of the detachable transformer has impact on the electrical energy conversion efficiency for overall system.  
      There are many types of prior art detachable transformers  1 , for example,  FIG. 2  shows a detachable transformer with U-type cores  2 . The U-type cores  2  are wound with coils  3  to form a primary side and a secondary side. Moreover, the two U-type cores  2  are placed in proximity with a gap therebetween to couple the electrical energy of the primary side to the secondary side. Related researches and analyses show that the magnetic coupling effect of the detachable transformer depends on the air gap. The magnetic coupling efficiency of the detachable transformer is around 80% when the air gap between the primary side and the secondary side is zero. The magnetic coupling efficiency of the detachable transformer is less than 50% when the air gap between the primary side and the secondary side is more than 2 mm.  
     SUMMARY OF THE INVENTION  
      It is the object of the present invention to provide a detachable transformer for a contactless energy transmission system to decrease leakage magnetic flux and improve electrical energy transmission efficiency, where the detachable transformer comprises magnetic coupling element with concave portion and convex portion, respectively. The magnetic coupling element contains a core and windings. The specific slant air gap design has the effect of cover.  
      Accordingly, the present invention provides a detachable transformer for contactless power system. The detachable transformer contains a first magnetic coupling element comprising a plurality of coupling legs as an opened end, where the first magnetic coupling element being wound with coil to form a primary side. The detachable transformer further contains a second magnetic coupling element comprising a plurality of coupling legs as an opened end. The second magnetic coupling element is wound with coil to form a secondary side. The opened end of the first magnetic coupling element faces the opened end of the second magnetic coupling element in contactless way to provide contactless power coupling. The coupling leg of the first magnetic coupling element comprises at least one bump on a facing surface thereof. The coupling leg of the second magnetic coupling element comprises at least one dent on a facing surface thereof, where wherein the bump can be fit into the dent in contactless manner.  
      Accordingly, the present invention provides a detachable transformer for contactless power system. The detachable transformer comprises a primary-side core wound with coil and a secondary-side core wound with coil, wherein an electrical power being able to couple to the secondary-side core; wherein at least one concave portion and at least one convex portion are formed on facing surfaces of the primary-side core and the secondary-side core. 
    
    
     BRIEF DESCRIPTION OF DRAWING  
      The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself however may be best understood by reference to the following detailed description of the invention, which describes certain exemplary embodiments of the invention, taken in conjunction with the accompanying drawings in which:  
       FIG. 1  shows a circuit diagram of a prior art contactless energy transmission system.  
       FIG. 2  shows a detachable transformer with U-type cores.  
       FIG. 3  shows the sectional view of a detachable transformer according to a preferred embodiment of the present invention.  
       FIGS. 4   a  and  4   b  show the magnetic flux in the prior art detachable transformer and the detachable transformer according to a preferred embodiment of the present invention, respectively.  
       FIG. 5  shows the measurement result by impedance analyzer. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIG. 3  shows the sectional view of a detachable transformer according to a preferred embodiment of the present invention. The detachable transformer also comprises two cores for magnetic coupling. The two cores are wound with coils to form the primary side and the secondary side. According to the present invention, each core comprises facing surface with concave or convex shapes to form more confined magnetic coupling path and to reduce magnetic loss.  FIGS. 4   a  and  4   b  show the magnetic flux in the prior art detachable transformer and the detachable transformer according to a preferred embodiment of the present invention, respectively. When the prior art detachable transformer and the detachable transformer according to a preferred embodiment of the present invention have the same air gap (d mm), the magnetic flux area of the detachable transformer according to the present invention is larger than that of the prior art detachable transformer, and part of the magnetic flux path length of the detachable transformer according to the present invention is less than that of the prior art detachable transformer.  
      With reference again to  FIG. 3 , the detachable transformer  10  according to the present invention comprises a first core  11  and a second core  12  with a plurality of coupling legs  111  and  121 , respectively. The first core  11  and the second core  12  can be of U shape or E shape. The coupling legs  111  and  121  of the first core  11  and the second core  12  are in close proximity and have symmetrical shape to provide contactless magnetic coupling effect.  
      The coupling leg  111  of the first core  11  comprises a facing surface  112  with at least one bump  113 . The coupling leg  121  of the second core  12  comprises a facing surface  122  with at least one dent  123 . The bump  113  and the dent  123  have such shapes that the bump  113  can be fit with the dent  123  in contactless way. Therefore, the magnetic coupling path can be more confined.  
      To evaluate the enhancement on the magnetic coupling effect and the reduction on magnetic loss, a test is conducted with following formula for magnetic coupling coefficient:  
             L   =       L     1   ⁢   p       +     L     2   ⁢   p       +     2   ⁢           ⁢   M               (   1   )               k   =     M         L     1   ⁢   p       ⁢     L     2   ⁢   p                     (   2   )             
 
      where k is the magnetic coupling coefficient, L, M, L 1p  and L 2p  are the total inductance, the mutual inductance, the self inductance of primary side and the self inductance of secondary side. The measurement result by impedance analyzer is shown in  FIG. 5 . As can be seen from this figure, the magnetic coupling coefficient of the detachable transformer according to the present invention is higher than that of prior art detachable transformer.  
      As can be verified by simulation and experiment, the core structure according to the present invention can enhance the confinement of magnetic flux and increase coupling efficiency.  
      Although the present invention has been described with reference to the preferred embodiment thereof, it will be understood that the invention is not limited to the details thereof. Various substitutions and modifications have suggested in the foregoing description, and other will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.