Patent Publication Number: US-2023136055-A1

Title: Magnetic core and magnetic element comprising same

Description:
TECHNICAL FIELD 
     The present disclosure relates to a magnetic core capable of precisely maintaining the size of a gap and a magnetic element including the same. 
     BACKGROUND ART 
     A magnetic core is an essential component for the functioning of a magnetic circuit for providing a passage for magnetic flux in a magnetic element, such as a transformer or an inductor. Such a magnetic element constitutes an electromagnetic interference (EMI) filter or is widely used for a DC-DC converter for electric vehicles, hybrid electric vehicles, and the like, which have recently been extensively researched and developed. 
       FIG.  1    is a block diagram showing an example of the configuration of a general DC-DC converter. 
     Referring to  FIG.  1   , the DC-DC converter  10  may be disposed between a first battery (Batt  1 )  20  and a second battery (batt  2 )  30 , and may include a drive circuit  11 , a transformer  12 , and an output circuit  13 . 
     The first battery  20  may output DC voltage and DC current, and the transformer  12  may convert AC voltage and AC current. Accordingly, the drive circuit  11  may convert DC current output by the first battery  20  into AC current, which changes over time, and may supply the AC current to a primary coil of the transformer  12  such that the AC current is input to the transformer  12 . To this end, the drive circuit  11  may include a plurality of drive switches constituting a full bridge, and each drive switch may be operated under the control of a controller  40 . 
     The transformer  12  receives AC power from the drive circuit  11 , steps the AC power up or down so as to correspond to the voltage difference between the first battery  20  and the second battery  30 , and outputs the converted power to a secondary coil. In addition, the output circuit  13  may convert AC current output from the transformer  12  into DC current, and may transmit the DC current to the second battery  30 . In addition to this function, the transformer  12  also functions to electrically isolate circuits respectively connected to input terminals and output terminals of the transformer. 
     The magnetic core of the transformer  12  generally includes a Mn—Zn-based ferrite component, and thus may be referred to as a ferrite core. The efficiency of the transformer  12  varies depending on changes in the magnetic flux density of the ferrite core, lost energy is converted into thermal energy, and the thermal energy is released. With regard to the aforementioned DC-DC converter and many other devices to which a magnetic element including a ferrite core is applied, there are demands for miniaturization and reduction in the amount of heat that is generated from the ferrite core during operation. However, since there is a trade-off relationship between the size of the ferrite core and the reduction in the amount of heat that is generated, it is difficult to meet electrical performance requirements only through reducing the size of the ferrite core. Therefore, as an alternative to reducing the size of the ferrite core, it is necessary to modify the shape or structure of the ferrite core. 
     As an alternative thereto, when a magnetic core is composed of two or more core parts, a gap may be formed between center legs or outer legs of the core parts that face each other in order to control heat generation and inductance. 
     However, in the case in which a center gap is formed only between the center legs, the center gap can be easily formed simply by cutting the center legs, but this entails a problem in that heat is concentrated in the center legs. In order to solve this problem, a method of additionally forming an external gap between the outer legs has been proposed. In this case, however, it is difficult to control the size of the gap. 
     DISCLOSURE 
     Technical Problem 
     The present disclosure has been made in order to solve the above problems with the conventional art, and provides a magnetic core that has excellent heat generation characteristics and can be reduced in size and a magnetic element including the same. 
     In particular, the present disclosure provides a magnetic core capable of precisely maintaining the size of a gap between outer legs and a magnetic element including the same. 
     The objects to be accomplished by the disclosure are not limited to the above-mentioned objects, and other objects not mentioned herein will be clearly understood by those skilled in the art from the following description. 
     Technical Solution 
     In order to accomplish the above objects, a magnetic core according to an embodiment of the present disclosure may include an upper core having at least a first outer leg and a second outer leg, a lower core having at least a third outer leg facing the first outer leg and a fourth outer leg facing the second outer leg, and an outer-leg gap portion disposed in each of a region between the first outer leg and the third outer leg and a region between the second outer leg and the fourth outer leg. The outer-leg gap portion may include an adhesive and a plurality of spherical fillers disposed in the adhesive in a distributed form. 
     In an example, the plurality of spherical fillers may not overlap each other in the thickness direction in the outer-leg gap portion. 
     In an example, the upper limit of the content of the spherical fillers in the outer-leg gap portion may be determined in consideration of the planar area of the outer-leg gap portion with respect to the adhesive force of the adhesive, and the lower limit of the content of the spherical fillers in the outer-leg gap portion may be determined in consideration of the length of a short side of each of the first outer leg, the second outer leg, the third outer leg, and the fourth outer leg and the diameters of the spherical fillers. 
     In an example, the spherical fillers may occupy 0.2% to 50% of the planar area of the outer-leg gap portion. 
     In an example, the upper core may further include a first center leg, the lower core may further include a second center leg facing the first center leg, and the first center leg and the second center leg may form a center gap therebetween. 
     In addition, a magnetic element according to an embodiment may include a magnetic core and at least one coil. The magnetic core may include an upper core having at least a first outer leg and a second outer leg, a lower core having at least a third outer leg facing the first outer leg and a fourth outer leg facing the second outer leg, and an outer-leg gap portion disposed in each of a region between the first outer leg and the third outer leg and a region between the second outer leg and the fourth outer leg. The outer-leg gap portion may include an adhesive and a plurality of spherical fillers disposed in the adhesive in a distributed form. 
     Advantageous Effects 
     The effects of the magnetic core according to the present disclosure will be described below. 
     First, since a spherical filler is provided in an external gap, it is possible to accurately control the size of the external gap by changing the diameter of the filler. 
     Second, the size of a center gap may also be maintained through accurate maintenance of the size of the external gap. Accordingly, a target inductance value may be realized, heat may be uniformly generated throughout the magnetic core, and the size thereof may be reduced through control of heat generation. 
     The effects achievable through the disclosure are not limited to the above-mentioned effects, and other effects not mentioned herein will be clearly understood by those skilled in the art from the following description. 
    
    
     
       DESCRIPTION OF DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the disclosure and illustrate embodiments of the disclosure together with the detailed description. However, the technical features of the disclosure are not limited to specific drawings, and the features shown in the drawings may be combined to construct a new embodiment. 
         FIG.  1    is a block diagram showing an example of the configuration of a general DC-DC converter. 
         FIG.  2 A  shows an example of the configuration of a magnetic core according to an embodiment. 
         FIG.  2 B  is an enlarged view of portion ‘A’ in  FIG.  2 A . 
         FIG.  3 A  is a perspective view showing an example of the configuration of a lower core according to an embodiment. 
         FIG.  3 B  shows an example of disposition of fillers for provision of minimum required support on the section of an outer leg according to an embodiment. 
         FIG.  4    shows an example of the configuration of a core according to a comparative example. 
     
    
    
     BEST MODE 
     Hereinafter, devices and methods to which embodiments of the present disclosure are applied will be described in detail with reference to the accompanying drawings. The suffixes “module” and “unit” used herein to describe configuration components are assigned or used in consideration only of convenience in creating this specification, and the two suffixes themselves do not have any distinguished meanings or roles from each other. 
     In the following description of the embodiments, it will be understood that, when each element is referred to as being formed “on” or “under” and “ahead of” or “behind” another element, it can be directly “on” or “under” and “ahead of” or “behind” the other element, or can be indirectly formed with one or more intervening elements therebetween. 
     Additionally, terms such as “first”, “second”, “A”, “B”, “(a)”, “(b)”, etc. may be used herein to describe the components of the embodiments. These terms are only used to distinguish one element from another element, and the essence, order, or sequence of corresponding elements is not limited by these terms. It should be noted that if it is described in the specification that one component is “connected”, “coupled”, or “joined” to another component, the former may be directly “connected”, “coupled”, or “joined” to the latter, or may be indirectly “connected”, “coupled”, or “joined” to the latter via another component. 
     Additionally, the term “comprises”, “includes”, or “has” described herein should be interpreted not to exclude other elements but to further include such other elements since the corresponding elements may be inherent unless mentioned otherwise. Unless otherwise defined, all terms used herein, which include technical or scientific terms, have the same meanings as those generally appreciated by those skilled in the art. Terms such as those defined in common dictionaries should be interpreted as having the same meanings as terms in the context of the pertinent technology, and should not be interpreted as having ideal or excessively formal meanings unless clearly defined in the specification. 
     Hereinafter, a magnetic core according to the embodiment will be described in detail with reference to the accompanying drawings. 
       FIG.  2 A  shows an example of the configuration of a magnetic core according to an embodiment. 
     Referring to  FIG.  2 A , the magnetic core  100  according to the embodiment may include an upper core  110 , which is coupled from above, and a lower core  120 , which is coupled from below. The upper core  110  and the lower core  120  may be vertically symmetrical with each other, or may be asymmetrical. For convenience of explanation, the following description will be made on the assumption that the upper core and the lower core are symmetrical with each other. 
     Each of the upper core  110  and the lower core  120  may include a magnetic material, for example iron or ferrite, but the disclosure is not limited thereto. 
     At least one of the upper core  110  or the lower core  120  that constitute the magnetic core  100 , for example, the upper core  110 , may include a body BD, which has a flat plate shape, and a plurality of legs  111 ,  112 , and  113 , which protrude from the body BD in a thickness direction (i.e. the −Z-axis direction) and extend in a predetermined direction. The plurality of legs may include two outer legs  112  and  113 , which extend in the direction of one axis (here, the y-axis direction) and are spaced apart from each other in the direction of another axis (here, the x-axis direction) on a plane, and one center leg  111 , which is disposed between the two outer legs  112  and  113 . 
     Similarly, the lower core  120  may also include two outer legs  122  and  123  and one center leg  121  disposed therebetween. 
     Each of the upper core  110  and the lower core  120  having the above configurations may be referred to as an “E”-type core according to the external appearance thereof. 
     The lower surface of the center leg  111  of the upper core  110  and the upper surface of the center leg  121  of the lower core  120  may face each other with a predetermined gap therebetween in the thickness direction. The gap between the center legs  111  and  121  may be referred to as a center gap CG. 
     In addition, an outer-leg gap portion  130  may be disposed between each pair of outer legs facing each other, for example, in each of the region between one outer leg  112  of the upper core  110  and one outer leg  122  of the lower core  120  and the region between the other outer leg  113  of the upper core  110  and the other outer leg  123  of the lower core  120 . The concrete configuration of the outer-leg gap portion  130  will be described with reference to  FIG.  2 B . 
       FIG.  2 B  is an enlarged view of portion ‘A’ in  FIG.  2 A . 
     Referring to  FIG.  2 B , the outer-leg gap portion  130  may include an adhesive  131  and a plurality of fillers  132 . The adhesive  131  may include a component that is used for bonding of a general ferrite core, for example, an epoxy resin, but the disclosure is not limited thereto. 
     Each of the fillers  132  may have a spherical shape, and may include an insulating material, such as zirconia, or may include conductive metal. Each of the fillers  132  may be disposed so as not to overlap the other fillers in the thickness direction in the outer-leg gap portion  130 . That is, the fillers  132  may be disposed parallel to each other in a single layer in the outer-leg gap portion  130 . 
     In this case, the diameter D of the filler  132  corresponds to the size of an external gap formed by the outer-leg gap portion  130 , that is, the distance between the lower surface of one outer leg  113  of the upper core  110  and the upper surface of one outer leg  123  of the lower core  120 . Accordingly, in the magnetic core  100  according to the embodiment, it is possible to precisely maintain the size of the external gap, which is determined in consideration of a target inductance or the like, by changing the diameter of the filler  132 . 
     If the lengths of all of the outer legs and the center legs are equal in the Z-axis direction, both the size of the center gap CG and the size of the external gap may correspond to the diameter D of the filler  132 . Depending on the length to which the center legs are cut, the size of the center gap CG may be greater than the diameter D of the filler  132 . Accordingly, in the magnetic core  100  according to the embodiment, it is possible to freely and accurately change the sizes of the center gap CG and the external gap depending on the diameter D of the filler  132 , thus easily achieving a target inductance. In addition, the magnetic core can be manufactured with a low tolerance, and thus the yield and reliability thereof are increased. 
     In order to manufacture the magnetic core  100  according to the embodiment, the upper core  110  and the lower core  120  may be prepared, a gap glue formed such that the plurality of fillers  132  are distributed in the adhesive  131  may be applied in each of the region between the pair of outer legs  112  and  122  and the region between the pair of outer legs  113  and  123 , and the gap glue may be cured in the state in which the upper core and the lower core are pressed in the vertical direction. In the course of pressing, the positions of the fillers may be adjusted such that one filler does not overlap the other fillers in the thickness direction. In addition, in order to control the thickness of the outer-leg gap portion  130  according to the embodiment, that is, the size of the external gap, so as to correspond to the diameter D of the filler  132 , it is preferable for the filler  132  to have a rigidity sufficient to prevent deformation thereof due to pressure applied thereto in the vertical direction or to allow the height thereof to change within a predetermined range (e.g. 5%) after the pressure is applied thereto. 
     If the filler  132  includes a conductive material, the upper core  110  and the lower core  120  are in an electrically shorted state due to the filler  132 . In this case, when the magnetic core  100  is used in a transformer in which there is a large difference between the voltage of a primary coil and the voltage of a secondary coil, a potential difference between parasitic capacitance components generated between the upper core  110  and one coil and between the lower core  120  and the other coil may be eliminated. Accordingly, it is possible to prevent the occurrence of an arc discharge phenomenon due to a large potential difference. 
     Next, the content of the fillers  132  in the outer-leg gap portion  130  will be described with reference to  FIGS.  3 A and  3 B . 
       FIG.  3 A  is a perspective view showing an example of the configuration of the lower core according to an embodiment, and  FIG.  3 B  shows an example of disposition of the fillers for provision of minimum required support on the section of the outer leg according to an embodiment. 
     Referring to  FIG.  3 A , one outer leg  123  of the lower core  120  is formed in the shape of a rectangular column that has a rectangular-shaped plane such that the upper surface SU thereof has a width W and a length L. When the magnetic core  100  according to the embodiment is constructed, the outer-leg gap portion  130  is disposed on the upper surface SU of the outer leg  123 , and the lower surface of the outer leg  113  of the upper core  110 , which is opposite the outer leg  123 , is disposed on the outer-leg gap portion  130 . Here, the theoretical minimum number of fillers  132  for enabling the outer-leg gap portion  130  to support the outer leg  113  of the upper core  110  while preventing distortion of the outer leg  113  is four, and the four fillers  132  are disposed on four respective corners P 1 , P 2 , P 3 , and P 4  of the upper surface SU of the outer leg  123 . However, this is an ideal distribution form. In practice, for support, it is necessary to dispose at least two fillers in the direction in which the short side (i.e. corresponding to “W”) of the upper surface SU extends. 
     For example, assuming that the width W of the upper surface SU is 4.25 mm, that the length L thereof is 28 mm, and that the target size of the external gap is 100 μm, the planar area of the outer-leg gap portion  130  to be disposed on the upper surface SU is 119 mm 2 , and the thickness of the outer-leg gap portion  130 , that is, the diameter D of the filler  132 , is 100 μm. 
     In this case, assuming that the minimal adhesive force required to ensure stable coupling between the upper core  110  and the lower core  120  is 100 kg/cm 2  and that the adhesive force of the adhesive  131  including an epoxy component is 200 kg/cm 2 , if the ratio of the planar area of the adhesive  131  to the total planar area of the outer-leg gap portion  130  is about 50% or more, stable coupling can be ensured. That is, when the planar area occupied by the fillers  132  is 50% or less of 119 mm 2 , which is the planar area of the outer-leg gap portion  130 , the upper core  110  and the lower core  120  can be stably coupled. 
     Meanwhile, the planar area occupied by one filler  132  having a diameter of 100 μm is 0.007850 mm 2  (=0.05×0.05×3.14). 
     As shown in  FIG.  3 B , in order to reliably support the upper core  110 , the short side W of the upper surface SU is formed such that the value obtained by subtracting 50 μm, which is the left radius R 1  of the filler  132 A located on the left-lower corner, and 50 μm, which is the right radius of the filler  132 B located on the right-lower corner, from the length of the short side W is 4.15 μm. This length corresponds to a radius R 2  defining a sector-shaped unit region for minimum required support. Further, in order to reliably support the corresponding unit region, at least three fillers  132 A,  132 B, and  132 C are provided. The area of the sector-shaped unit region having a radius R 2  of 4.15 mm is 13.5 mm 2  (=4.15×4.15×3.14/4), and the value obtained by dividing the planar area of the outer-leg gap portion  130  by the area of the unit region is about 8.8 (i.e. 119 mm 2 /13.5 mm 2 ). Accordingly, the number of fillers  132  that need to be provided for minimum required support in the outer-leg gap portion  130  is 26.4 (=8.8*3), and the planar area of 26.4 fillers is 0.207 mm 2  (=0.00785 mm 2 ×26.4). 
     Consequently, when the fillers occupy a planar area of 0.207 mm 2  in the planar area of 119 mm 2 , the core can be supported. This content of the fillers corresponds to 0.17%, that is, about 0.2%. 
     In summary, the upper limit of the content of the fillers in the outer-leg gap portion  120  is about 50% from the aspect of required adhesive force, and the lower limit thereof is about 0.2% from the aspect of support of the core. That is, the content of the fillers in the outer-leg gap portion  120  may range from 0.2% to 50%. 
     However, this content is calculated based on the adhesive force of the epoxy-based adhesive  131  and the ratio of the diameter of the filler to the planar area of the outer leg. Therefore, it will be apparent to those skilled in the art that the content can vary depending on the components of the adhesive, the target size of the external gap, and the shape and the size of the planar area of the outer leg. 
     Next, the advantages of the magnetic core according to the embodiment compared to a comparative example will be described with reference to  FIG.  4   . 
       FIG.  4    shows an example of the configuration of a core according to a comparative example. 
     The left drawing in  FIG.  4    shows a magnetic core  100 ′ according to a comparative example, and the right drawing in  FIG.  4    is an enlarged view of portion B, corresponding to a pair of outer legs  113 ′ and  123 ′. In the magnetic core  100 ′ according to the comparative example, a spacer layer SPL, which has adhesives AD applied to the upper and lower surfaces thereof, is disposed between the pair of outer legs  113 ′ and  123 ′ facing each other in order to form an external gap. That is, in order to manufacture the magnetic core  100 ′ according to the comparative example, the adhesives AD are applied to the end surfaces of each pair of outer legs that face each other, the spacer layer SPL is inserted between each pair of outer legs, and the magnetic core is pressed. 
     However, the thickness of the adhesive AD may vary depending on the extent to which the magnetic core is pressed. Further, because the spacer layer SPL is generally embodied as a polyimide film, the spacer layer SPL may be compressed when the magnetic core is pressed, thus making it difficult to accurately form an external gap having a desired size. Furthermore, because the spacer layer SPL takes the form of a single sheet corresponding to the planar shape of the outer leg, the spacer layer SPL may escape from the region between a pair of outer legs during a manufacturing process, thus marring the external appearance or, in severe cases, failing to satisfy target specifications. 
     In contrast, in the magnetic core  100  according to the embodiment, since the thickness of the outer-leg gap portion  130  is determined depending on the diameter D of the filler  132 , there is little concern about tolerances or a defective external appearance during a manufacturing process, and it is possible to accurately realize an external gap having any of various sizes by controlling the diameter of the filler  132 . 
     Meanwhile, although the magnetic core  100  composed of two E-type cores has been described above, it will be apparent to those skilled in the art that the above description may also apply to the case in which the magnetic core is configured as a combination of an I-type core and an E-type core or a combination of three or more cores depending on the type of magnetic element to be manufactured. Furthermore, the magnetic core  100  according to the embodiment may also be applied to a transformer, an inductor, and any other magnetic elements to which a magnetic core including a gap is applied through combination with a coil. 
     The technical contents of the above-described embodiments may be combined into various forms as long as they are not incompatible with one another, and thus may be implemented in new embodiments. 
     It will be apparent to those skilled in the art that various changes in form and details may be made without departing from the spirit and essential characteristics of the disclosure set forth herein. Accordingly, the above detailed description is not intended to be construed to limit the disclosure in all aspects and to be considered by way of example. The scope of the disclosure should be determined by reasonable interpretation of the appended claims and all equivalent modifications made without departing from the disclosure should be included in the following claims.