Abstract:
An inductive energy transmission system including: a primary coil connectible to an electrical useful voltage source, the primary coil being connected to a first capacitor, the first capacitor being connected to a local ground potential of the energy transmission system; and a secondary coil inductively coupled to the primary coil; wherein a second capacitor is situated between the primary coil and the local ground potential of the energy transmission system.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an inductive energy transmission system. Furthermore, the present invention relates to a method for manufacturing an inductive energy transmission system. 
       BACKGROUND INFORMATION 
       [0002]    In inductive energy transmission, a spatial separation is fundamentally provided between a primary coil and a secondary coil. This spatial separation is primarily due to a freedom of positioning the contactless inductive energy transmission process or charging. Said spatial separation, however, may result in disadvantages especially for electromagnetic compatibility (EMC). This is essentially the result of the open type of construction of the transformer with the primary coil and the secondary coil. This is to be seen in contrast to a conventional transformer, which is well encapsulated and whose primary and secondary coils are situated as close to each other as possible. 
         [0003]    This open type of construction results in the problem explained in the following with reference to  FIG. 1 .  FIG. 1  shows a fundamental situational equivalent circuit diagram of the mentioned conventional “open construction type” during an EMC test scenario. A primary side resonant circuit may be seen that is formed by a primary coil  10 , whose winding produces a resonant inductance, and a first capacitor  15 , which produces a resonant capacitance. First capacitor  15  is connected to a local ground potential  16  of inductive energy transmission system  100 . The primary-side resonant circuit is supplied by an exciting electrical useful voltage source U Ex . The exciting useful voltage source U Ex  provides an electrical useful signal for the inductive energy transmission system  100 . The useful voltage source U Ex  is overlaid with an electrical noise voltage source U S , which represents all noise signals of the inductive energy transmission system  100 . A noise signal in the sense of the present invention is to be understood primarily as common-mode noise. Generally, noise signals are understood both as common-mode noise and as differential-mode noise. 
         [0004]    In terms of circuit technology, the two coils  10  and  20  respectively also form an electrode. With the primary coil and the secondary coil  10 ,  20 , two electrodes are thus facing each other, between which a parasitic mutual capacitance  11  is situated. The parasitic mutual capacitance  11  is low primarily due to the wall thicknesses of the two housings of the coils  10 ,  20 , common values of mutual capacitance  11  being between approximately 5 pF and approximately 25 pF. The two electrodes of coils  10 ,  20  respectively form a parasitic ground capacitance  12 ,  13  with respect to ground. Usual values for ground capacitances  12 ,  13  are in the range of approximately 20 pF to approximately 40 pF. 
         [0005]    The secondary side of inductive energy transmission system  100  has an electronic load that is represented by a resistor  60  that is connected in parallel to secondary coil  20 . The load may be for example an ohmic consumer (e.g. an incandescent lamp) or, as is usual in inductive chargers, an accumulator. The entire secondary system furthermore has another ground capacitance  14 , which is connected to load  60  and to the ground potential. 
         [0006]      FIG. 1  further shows a measuring resistor  40  of a radio measuring receiver that is required for EMC measurement. Measuring resistor  40  may be configured as a 50 ohm terminal resistor. The electrical voltage dropping on measuring resistor  40  is designated by U m  and represents the electromagnetic noises on the radio measuring receiver. 
         [0007]    The circuit configuration from  FIG. 1  thus shows that the above-mentioned common-mode noise may cause electrical displacement currents that flow via ground capacitors  12 ,  13 ,  14  to ground. This is indicated by three closed circuits via ground capacitors  12 ,  13 ,  14  that are represented as dashed lines. The displacement currents flow on the ground via the radio measuring receiver back to noise voltage source U S . The equivalent circuit diagram from  FIG. 1  thus illustrates a coupling path of the noise via the ground capacitors  12 ,  13 ,  14 . 
       SUMMARY OF THE INVENTION 
       [0008]    It is thus an objective of the present invention to provide an improved inductive energy transmission system. 
         [0009]    According to a first aspect, the objective is achieved by an inductive energy transmission system, having:
       a primary coil that is connectible to an electrical useful voltage source, the primary coil being connected to a first capacitor, the first capacitor being connected to a local ground potential of the energy transmission system; and   a secondary coil inductively coupled to the primary coil; wherein a second capacitor is developed between the primary coil and the local ground potential of the energy transmission system.       
 
         [0012]    In this manner, a bypass capacitor is implemented in terms of circuit engineering, as a result of which the aforementioned noise is hardly measurable anymore because an alternative path is created for the noise. This results in the creation of a very effective noise suppression method that advantageously allows for a standard-conforming design of the inductive energy transmission system. 
         [0013]    According to a second aspect, the objective is achieved by a method for manufacturing an inductive energy transmission system, having the steps:
       providing a primary coil;   connecting the primary coil to a first capacitor;   connecting the first capacitor to a local ground potential of the energy transmission system;   providing a secondary coil; and   providing a second electrode of a second capacitor, the second electrode of the second capacitor being connected to the local ground potential.       
 
         [0019]    Advantageous developments of the inductive energy transmission system and of the method are the subject matter of descriptions herein. 
         [0020]    One advantageous development of the inductive energy transmission system is characterized by the fact that a first electrode of the second capacitor is formed by the primary coil and that a second electrode of the second capacitor is connected to the ground potential. This allows for the noise-suppressing bypass capacitor to be technically implemented in a simple manner. 
         [0021]    Another advantageous development of the inductive energy transmission system is characterized by the fact that the second electrode of the second capacitor is developed in a layered manner, a conductive layer being respectively covered on opposite surfaces by an insulating layer. This advantageously makes it possible to increase an electrical breakdown strength of the second electrode. 
         [0022]    Another advantageous development of the inductive energy transmission system is characterized by the fact that the conductive layer of the second capacitor is developed in a fleece-like manner from a carbon material. A conductive layer having a good noise-suppressing effect is thus provided. 
         [0023]    Another advantageous development of the inductive energy transmission system is characterized by the fact that the conductive layer is developed to be woven or pressed. This provides alternative possibilities for the technical construction of the conductive layer. This supports a diverse freedom of design for the bypass capacitor. 
         [0024]    Another advantageous development of the inductive energy transmission system provides for the conductive layer to be connected to the local ground potential by way of conductive reinforcement elements. This advantageously makes it possible to implement a mechanical reinforcement for the conductive layer and a possibility of an electrical contact between the conductive layer and the local ground potential. 
         [0025]    Another advantageous development of the inductive energy transmission system provides for the second capacitor to have a capacitance value that is at least approximately twice, particularly approximately three times to approximately five times, even more particularly approximately six times to approximately ten times as great as a parasitic ground capacitance of the inductive energy transmission system. In this manner, favorable technical capacitance values are realized for the bypass capacitor. 
         [0026]    In the following, the present invention is described in detail with additional advantages and features on the basis of several figures. In this connection, all described features are the subject matter of the present invention, irrespective of their representation in the specification and in the figures and irrespective of their antecedent reference in the descriptions herein. The figures are specifically intended to illustrate the principles that are essential to the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  shows a basic block diagram of a conventional inductive energy transmission system. 
           [0028]      FIG. 2  shows a specific embodiment of an inductive energy transmission system according to the invention. 
           [0029]      FIG. 3  shows a simplified representation of a possible implementation of a second electrode of the bypass capacitor. 
           [0030]      FIG. 4  shows a basic sequence of one specific embodiment of the method according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    As an effective noise suppression measure, the present invention provides for the insertion of a bypass capacitor in the form of a second capacitor  50  into the primary circuit so as in this manner to keep the noises within the primary circuit. Second capacitor  50  conducts the noises directly back to the noise voltage source U S  and thus effectively prevents an unwanted indirect coupling path of the noises. In order to achieve a significant bypass effect by way of second capacitor  50 , its capacitance should be approximately twice, more particularly approximately three to approximately five times, particularly approximately six to approximately ten times as great as a ground capacitance of the entire system formed from parasitic ground capacitances  12 ,  13 ,  14 . 
         [0032]      FIG. 2  shows a current path of the noise following the insertion of the bypass capacitor fundamentally as a closed circuit represented by a dashed line. The current path in effect forms a closed path via the useful voltage source U Ex , the noise voltage source U S , the primary coil  10  and second capacitor  50 . The current path thus essentially no longer runs via measuring resistor  40 , which allows the measurable noise to be reduced significantly. 
         [0033]    In order to implement the bypass capacitor, a technical implementation of a second electrode  50   a  is required, after the first electrode of the bypass capacitor is formed by the winding of primary coil  10 . For this purpose, it is provided to mount a conductive layer  90  in direct proximity to primary winding  10 . It is furthermore important to design the capacitance of the bypass capacitor to be as high as possible, two essential factors that may influence said capacity being a maximization of the electrode surface and a minimization of the distance of the two electrodes with respect to each other. 
         [0034]      FIG. 3  shows in a greatly simplified manner a fundamental technical specific embodiment of a second electrode  50   a  of second capacitor  50 . The present invention may provide for two layers of insulating foils to be situated one upon the other, between which a conductive graphite or carbon layer is situated. The arrangement layered in this manner thus forms the second electrode  50   a,  which is conductively connected to the local ground terminal of first capacitor  15 . In combination with the primary electrode of primary coil  10 , the noise suppressing bypass capacitor is implemented in this manner. 
         [0035]    In principle, any conductive material may be used for conductive layer  90  of electrode  50   a  with the exception of metallic, in particular ferromagnetic material since this material would produce unwanted eddy current and hysteresis losses. 
         [0036]    Test series have shown that using a conductive layer or electrode in the form of a graphite or carbon layer as conductive layer  90  provides the best results for an optimized noise-suppression effect of second capacitor  50 . For this purpose, the graphite layer may be developed advantageously by a lacquer. Particularly advantageously, the graphite layer is configured as a carbon fiber weave or a fleece-like fiber fabric, it being possible for conductive layer  90  to be woven or pressed in a fleece-like manner as a fleece-like carbon material. The second electrode  50   a  of the bypass capacitor formed in this manner is connected in an electrically conductive manner to a fixed reference point, normally the local ground potential  16  of first capacitor  15  of inductive energy transmission system  100 . 
         [0037]    As a mechanical reinforcement of conductive layer  90 , it is possible to use electrically conductive reinforcement rings  91 , which are made of aluminum or copper and which are provided for a mechanical reinforcement of conductive layer  90  and an improved electrical contact between electrode  50   a  and ground potential  16 . 
         [0038]      FIG. 4  shows in principle a sequence of a specific embodiment of the method of the present invention. 
         [0039]    A primary coil  10  is provided in a first step  200 . 
         [0040]    In a second step  210 , primary coil  10  is connected to a first capacitor  15 . 
         [0041]    In a third step  220 , first capacitor  15  is connected to a local ground potential  16  of energy transmission system  100 . 
         [0042]    In a fourth step  230 , a secondary coil  20  is provided. 
         [0043]    Finally, in a fifth step  240 , a second electrode  50   a  of a second capacitor  50  is provided, second electrode  50   a  of second capacitor  50  being connected to local ground potential  16 . 
         [0044]    Advantageously, inductive energy transmission system  100  may be used in any technical systems in which contactless inductive charging occurs, for example in an electric toothbrush, an electric car etc. 
         [0045]    In summary, the present invention provides an improved inductive energy transmission system that advantageously returns electromagnetic noises essentially to the source of the noise and thereby optimizes the efficiency of the inductive energy transmission system. 
         [0046]    One skilled in the art, in proceeding, will implement specific embodiments of the present invention that are not described, or only partially described, without deviating from the core of the present invention.