Abstract:
An inductance component includes a magnetic core ( 11, 12 ) forming a magnetic circuit having a magnetic gap, an exciting coil ( 14 ) wound around the magnetic core, and a permanent magnet ( 13 ) disposed in the magnetic gap. The permanent magnet is greater in sectional area than the magnetic core.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an inductance component which is a magnetic device such as a transformer and an inductor and, in particular, to an inductance component comprising a permanent magnet disposed in a magnetic gap formed in a magnetic core. 
     In order to reduce the size and the weight of an inductance component, it is effective to reduce the volume of a magnetic core comprising a magnetic material. Generally, the magnetic core reduced in size easily reaches magnetic saturation so that a current level handled by a power supply is inevitably decreased. In order to solve the above-mentioned problem, there is known a technique in which the magnetic core is provided with a magnetic gap formed at a part thereof. With this structure, a magnetic resistance of the magnetic core is increased so that the decrease in current level is prevented. In this case, however, the magnetic core is decreased in magnetic inductance. 
     In order to prevent the decrease in magnetic inductance, proposal is made of a technique related to such a structure that the magnetic core comprises a permanent magnet for generating a magnetic bias. In this technique, a d.c. magnetic bias is given to the magnetic core by the use of the permanent magnet. As a consequence, the number of magnetic lines of flux which can pass through the magnetic gap is increased. 
     However, the existing inductance component using the permanent magnet is disadvantageous in the following respect. That is, the insertion amount or volume of the permanent magnet disposed in the magnetic gap is determined by a sectional area of a middle leg portion of the magnetic core and the dimension of the magnetic gap. Thus, the magnetic bias given to the magnetic core is inevitably restricted. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of this invention to provide an inductance component capable of increasing the insertion amount of a permanent magnet to thereby obtain an appropriate magnetic biasing effect without varying the dimension of a magnetic gap. 
     According to this invention, there is provided an inductance component comprising a magnetic core forming a magnetic circuit having a magnetic gap, an exciting coil wound around the magnetic core, and a permanent magnet disposed in the magnetic gap and greater in sectional area than the magnetic core. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a perspective view of an inductance component according to a first embodiment of this invention with a part seen through; 
     FIG. 2 is an exploded perspective view of the inductance component illustrated in FIG. 1; 
     FIG. 3 is a side sectional view of the inductance component illustrated in FIG. 3; 
     FIG. 4 is a perspective view of an inductance component as a first comparative example with a part seen through; 
     FIG. 5 is a graph showing a d.c. superposition inductance characteristic of the inductance component illustrated in FIG. 1 in comparison with those of the first comparative example in FIG.  4  and another example without using a magnetic bias; 
     FIG. 6 is a perspective view of a modification of the inductance component illustrated in FIG. 1 with a part seen through; 
     FIG. 7 is a perspective view of an inductance component according to a second embodiment of this invention with a part seen through; 
     FIG. 8 is a side sectional view of the inductance component illustrated in FIG. 7; 
     FIG. 9 is a graph showing a d.c. superposition inductance characteristic of the inductance component illustrated in FIG. 7 in comparison with those of the first comparative example in FIG.  4  and another example without using a magnetic bias; 
     FIGS. 10A to  10 D are side sectional views showing various modifications of the inductance component illustrated in FIGS. 1 to  3 ; 
     FIG. 11 is a perspective view of an inductance component according to a third embodiment of this invention; 
     FIG. 12 is an exploded perspective view of the inductance component illustrated in FIG. 11; 
     FIG. 13 is a side sectional view of the inductance component illustrated in FIG. 11; 
     FIG. 14 is a side sectional view of an inductance component as a second comparative example; 
     FIG. 15 is a side sectional view of an inductance component as a third comparative example; and 
     FIG. 16 is a graph showing a d.c. superposition inductance characteristic of the inductance component illustrated in FIG. 11 in comparison with those of the second comparative example in FIG.  14  and the third comparative example in FIG.  15 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 through 3, description will be made of an inductance component according to a first embodiment of this invention 
     The inductance component illustrated in FIGS. 1 through 3 is adapted to be used as a magnetic device such as a transformer and an inductor. The inductance component comprises a magnetic core composed of first and second core members  11  and  12  faced to each other. The first core member  11  has a cylindrical leg portion  11   a  at its center. The second core member  12  has a flat or plate-like portion  12   a  faced to one end of the leg portion  11   a  through a magnetic gap t 1 . The first core member  11  further has a flange portion  11   b  radially outwardly expanding from the other end of the leg portion  11   a . The second core member  12  further has a tubular portion  12   b  extending from an outer peripheral end of the plate-like portion  12   a  to surround the leg portion  11   a  and connected to the flange portion  11   b.    
     To the magnetic gap t 1  of the magnetic core, a disc-shaped permanent magnet  13  is fitted. Between the leg portion  11   a  and the tubular portion  12   b , an exciting coil  14  is arranged to surround the leg portion  11   a . The permanent magnet  13  is arranged so that a magnetic field  16  generated by the permanent magnet  13  is opposite or reverse to a magnetic field  15  generated by the exciting coil  14 . Thus, the magnetic field  16  by the permanent magnet  13  and the magnetic field  15  by the exciting coil  14  are opposite to each other. A terminal  17  is attached to an outer peripheral end of the flange portion  11   b  and connected to the exciting coil  14 . 
     The magnetic core used herein defines a magnetic path having a magnetic path length of 1.75 cm, an effective sectional area of 0.237 cm 2 , and a gap t 1  of 230 μm. The exciting coil  14  has 10 turns and a d.c. resistance of 23 m Ω. The permanent magnet  13  has a thickness of 220 μm and a sectional area of 50.3 mm 2 . Thus, the permanent magnet  13  is greater in sectional area than the magnetic path of the magnetic core. 
     As illustrated in FIG. 4, preparation is made of an inductance component as a first comparative example which comprises a magnetic core having a middle leg portion  18  and a circular permanent magnet  19  having a sectional area of 23.8 mm 2  substantially similar to that of the middle leg portion  18 . In addition, preparation is also made of an inductance component without using a permanent magnet. 
     For the inductance component in FIGS. 1 through 3, the inductance component in FIG. 4, and the inductance component without using the magnetic bias, d.c. superposition inductance characteristics are measured. The result is shown in FIG.  5 . In FIG. 5, a solid line  21 , a broken line  22 , and a solid line  23  represent the d.c. superposition inductance characteristics of the inductance component in FIGS. 1 through 3, the inductance component in FIG. 4, and the inductance component without using the magnetic bias, respectively. As is obvious from FIG. 5, the inductance component in FIGS. 1 through 3 is improved in d.c. superposition inductance characteristic by 23% or more as compared with the inductance component in FIG.  4 . 
     In FIG. 6, a modification of the inductance component in FIG. 1 is shown. As illustrated in the figure, the permanent magnet  13  has a circular section while the middle leg portion  11   a  of the first core member  11  has a rectangular section. 
     Referring to FIGS. 7 and 8, description will be made of an inductance component according to a second embodiment of this invention. Parts similar in function to those of the inductance component illustrated in FIGS. 1 through 3 are designated by like reference numerals and detailed description thereof will be omitted. 
     The magnetic core used in this embodiment defines a magnetic path having a magnetic path length of 1.75 cm, an effective sectional area of  0.237 cm   2 , and a gap t 2  of 230 m Ω. The exciting coil  14  has 10 turns and a d.c. resistance of 23 m Ω. The leg portion  11   a  of the first core member  11  has a circular section. The permanent magnet  13  has a thickness of 220 μm and a rectangular shape (square shape) with an area of 30.25 mm 2 . 
     For the inductance component in FIGS. 7 and 8, the inductance component in FIG. 4, and the inductance component without using the magnetic bias, d.c. superposition inductance characteristics are measured. The result is shown in FIG.  9 . In FIG. 9, a solid line  26 , a broken line  27 , and a solid line  28  represent the d.c. superposition inductance characteristics of the inductance component in FIGS. 7 and 8, the inductance component in FIG. 4, and the inductance component without using the magnetic bias, respectively. As is obvious from FIG. 9, the inductance component in FIGS. 7 and 8 is improved in d.c. superposition inductance characteristic by 8% or more as compared with the inductance component in FIG.  4 . Furthermore, since the permanent magnet  13  has a rectangular section, it is possible to effectively utilize the material as compared with the circular section. 
     In each of the foregoing embodiment, the permanent magnet  13  preferably comprises (1) at least one resin selected from polyamide imide resin, polyimide resin, epoxy resin, polyphenylene sulfide resin, silicone resin, polyester resin, aromatic polyamide resin, and liquid crystal polymer and (2) rare earth magnet powder dispersed therein, having an intrinsic coercive force of 10 kOe or more, Tc of 500° C. or more, and an average particle size of 2.5-25 μm, and coated with at least one metal selected from Zn, Al, Bi, Ga, In, Mg, Pb, Sb, and Sn or alloy thereof. Preferably, the resin has a content of 30% or more in volumetric ratio and a specific resistance of 0.1 Ωcm or more. 
     The rare earth magnet powder preferably has a composition of Sm(Co bal .Fe 0.15-0.25 Cu 0.05-0.06 Zr 0.02-0.03 ) 7.0-8.5 . 
     Preferably, the rare earth magnet powder is coated with an inorganic glass having a softening point between 220° C. and 550° C. Preferably, the metal or the alloy coating the rare earth magnet powder is further coated with a nonmetallic inorganic compound having a melting point not lower than 300° C. The amount of the metal or the alloy, the inorganic glass, or a combination of the metal or the alloy and the nonmetallic inorganic compound preferably falls within a range between 0.1 and 10% in volume. 
     During production of the permanent magnet, the rare earth metal powder is oriented in a thickness direction in a magnetic field of 25T or more so that the permanent magnet is provided with magnetic anisotropy. The permanent magnet desirably has a center line average roughness of 10 μm or less. 
     Each of the above-mentioned inductance component can be modified in various manners as illustrated in FIGS. 10A through 10D. Parts having similar functions are designated by like reference numerals. Thus, the shape of the first and the second core members  11  and  12  as well as the shape and the size of the permanent magnet  13  can be modified in various manners. 
     Referring to FIGS. 11 through 13, description will be made of an inductance component according to a third embodiment of this invention. 
     The inductance component illustrated in FIGS. 11 through 13 is also adapted to be used as a magnetic device such as a transformer and an inductor. The inductance component comprises a magnetic core composed of first and second core members  31  and  32  faced to each other. The first core member  31  comprises an E-shaped magnetic core having a cylindrical leg portion  31   a  at its center. The second core member  32  comprises an I-shaped magnetic core having a plate-like portion  32   a  faced to one end of the leg portion  31   a  through a magnetic gap. The first core member  31  further has a flange portion  31   b  radially outwardly expanding from the other end of the leg portion  31   b  and a pair of side plate portions  31   c  extending from opposite ends of the flange portion  31   b  in parallel to the leg portion  31   a  and connected to the plate-like portion  32   a.    
     To the magnetic gap, a permanent magnet  33  is fitted. Between the leg portion  31   a  and the side plate portions  31   c , an exciting coil  34  is arranged to surround the leg portion  31   a . The permanent magnet  33  is arranged so that a magnetic field  36  generated by the permanent magnet  33  is opposite or-reverse to a magnetic field  35  generated by the exciting coil  34 . Thus, the magnetic field  36  by the permanent magnet  33  and the magnetic field  35  by the exciting coil  34  are opposite to each other. 
     An insulating base  36  is attached to the plate-like portion  32   a . The insulating base  36  is a resin molded product. The exciting coil  34  has a portion  34   a  extending on or over the insulating base  36  to serve as a terminal known in the art. 
     The first and the second core members  31  and  32  are made of Mn—Zn ferrite and define a magnetic path having a magnetic path length of 12.3 mm and an effective sectional area, i.e., a sectional area of the leg portion  31   a , of 8.0 mm 2 . The magnetic path has a magnetic gap t 3  equal to 200 μm. The permanent magnet  33  has a disc shape with a thickness of 150 μm and a diameter of 5 mm. Therefore, the permanent magnet  33  is greater in sectional area than the magnetic path of the magnetic core. The exciting coil  34  has 3 turns. 
     Comparison will be made between the inductance component in FIGS. 11 to  13  and the inductance component in FIGS. 1 to  3 . The leg portion  31   a , the flange portion  31   b , the side plate portions  31   c , the plate-like portion  32   a , the permanent magnet  33 , and the exciting coil  34  correspond to the leg portion  11   a , the flange portion  11   b , the tubular portion  12   b , the plate-like portion  12   a , the permanent magnet  13 , and the exciting coil  14 , respectively. Therefore, the inductance component in FIGS. 11 to  13  may be modified in the manner similar to those mentioned in conjunction with the first embodiment. 
     As a second comparative example, an inductance component illustrated in FIG. 14 is prepared. In the inductance component in FIG. 14, the permanent magnet  33  is replaced by a permanent magnet  43  having an area (8.0 mm 2 ) equal to that of the leg portion  31   a  of the inductance component in FIGS. 11 to  13 . The permanent magnet  43  is equal in thickness to the permanent magnet  33 . 
     As a third comparative example, an inductance component illustrated in FIG. 15 is prepared. The inductance component illustrated in FIG. 15 has nothing equivalent or corresponding to the permanent magnet  33  of the inductance component in FIGS. 11 to  13 . 
     For the inductance components in FIGS. 11 to  13 , FIG. 14, and FIG. 15, d.c. superposition inductance characteristics are measured. The result is shown in FIG.  16 . In FIG. 16, a solid line  46 , a broken line  47 , and a solid line  48  represent the d.c. superposition inductance characteristics of the inductance components in FIGS. 11 to  13 , FIG. 14, and FIG. 15, respectively. As is obvious from FIG. 16, the inductance component in FIGS. 11 to  13  is improved in d.c. superposition inductance characteristic by 25% or more as compared with the inductance component in FIG.  14 .