Line filter assembly

Abstract: A line filter assembly adapted to be inserted in an electric power supply circuit of various electronic appliances for avoiding an invasion and leakage of noises comprises first and second core members each having a pair of opposite arms connected together through a common bridge. Coils are formed on the arms of each of the core members in such a manner that directions of magnetic fluxes produced in the closed magnetic circuit as a result of flow of line currents can be counteracted while the same coils are so arranged that the magnetic fluxes produced in the closed magnetic circuit as a result of the flow of the line currents can be oriented in the same direction.

Description: The invention relates to a line filter assembly which comprises a magnetic core means forming a closed magnetic circuit and including first and second arm means opposite to each other and connected together through a common bridge means, a first coil means having a portion thereof wound around the first arm means and the remaining portion wound around the second arm means, a second coil means having a portion wound around the first arm means and the remaining portion wound around the second arm means, said first and second coil means being so designed that directions of magnetic fluxes produced in the closed magnetic circuit as a result of flow of line currents counteract while said coil means are so arranged that common-mode noise components in the flow of the line currents are prevented. Line filter assemblies are mainly used to prevent common-mode noise components which appear between a pair of lines and ground in electric power supply circuits. From JP-A-60-14515 a noise filter is known having partial windings with different diameters in order to optimize the magnetic fluxes and the winding structure. From IBM Technical Disclosure Bulletin, Vol. 32, No.1, June 1989, pages 99, 100 a common-mode noise rejection filter is known using a toroid core. Such a toroid core assembly is difficult to manufacture. Furthermore, from US-A-4,835,497 an AC line filter is known using two cores for each line and an additional auxiliary core for coupling the two main cores. It is an object of the present invention to optimize the assembly of the closed magnetic circuit and the windings of such a line filter assembly to obtain a good space factor and a compact size including reduced height. According to the invention, a line filter assembly as defined in the preamble of claim 1 is characterized by a casing of generally U-shaped section accommodating an assembly of the magnetic core means having the first and second coil means mounted on the first and second arm means, a substantially elastic metal clamp of generally U-shaped configuration exteriorly encircling the casing with free ends thereof engaged with opposite side faces of the magnetic core means. Preferable embodiments are defined in the dependent claims. Details and features of the present invention will become clear from the following description taken in conjunction with preferred embodiments thereof with reference to the accompanying drawings, in which: Fig. 1 is a perspective view, with a portion cut away, of a line filter assembly according to a first preferred embodiment of the present invention; Fig. 2 is a sectional view of the line filter assembly of Fig. 1; Fig. 3 is a side view of the line filter assembly of Fig. 1; Fig. 4 is a perspective view of a coil bobbin assembly used in the line filter assembly of Fig. 1; Fig. 5 is a perspective view of the coil bobbin assembly of Fig. 4 bent to form juxtaposed coil bobbins; Fig. 6 is a sectional view of the line filter assembly according to a second preferred embodiment of the present invention; Fig. 7 is a perspective view of a casing used in the line filter assembly of Fig. 6; Fig. 8 is a perspective view, with a portion cut away, of the line filter assembly according to a third preferred embodiment of the present invention; and Fig. 9 is a bottom plan view of the line filter assembly of Fig. 8. Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings. Figs. 1 to 5 pertain to a first preferred embodiment of the present invention. In Fig. 4, there is shown a multi-linked winding bobbin assembly made of synthetic resin. The multi-linked winding bobbin assembly shown therein comprises first and second bobbins 10 which have respective hollows 8 defined therein and are linked together in an in-line fashion by means of a thin-walled portion 9 of 0.5 to 2 mm in wall thickness. A copper wire having its peripheral surface coated with an electrically insulating material is wound around the first bobbin 10 so as to extend from one end of the first bobbin 10 towards the opposite end thereof adjacent the thin-walled portion 9 thereby to form a first coil 11, and then around the second bobbin 10 so as to extend from one end of the second bobbin 10 adjacent the thin-walled portion 9 towards the opposite end thereof thereby to form a second coil 12. The copper wire so wound around the multi-linked winding bobbin assembly has its opposite ends soldered to respective metallic terminal members 13 secured rigidly to the first and second bobbins 10. Third and fourth coils 14 and 15 are also formed on another multi-linked winding bobbin assembly of similar construction in a similar manner as shown in Fig. 4. However, the direction of turn of the copper wire used to form the third and fourth coils 14 and 15 is opposite to the direction of turn of the copper wire used to form the first and second coils 11 and 12, while the total number of turns of the third and fourth coils 14 and 15 is equal to that of the first and second coils 11 and 12. Each bobbin assembly is folded 180° inwardly about the respective thin-walled portion 9 as shown in Fig. 5 to allow the first and second coils 11 and 12, or the third and fourth coils 14 and 15, to be juxtaposed relative to each other. While the first and second bobbins 10 having the first and second coils 11 and 12 are juxtaposed to each other as shown in Fig. 5, a generally U-shaped first core member 17 having a pair of arms is mounted on the juxtaposed bobbins 10 with the arms thereof inserted into the respective hollows 8 in the bobbins 10 with the first and second coils 11 and 12 thereby to complete a first coil unit. Similarly, while the first and second bobbins 10 having the third and fourth coils 14 and 15 are juxtaposed to each other in a manner similar to that shown in Fig. 5, a generally U-shaped second core member 17 having a pair of arms is mounted on the juxtaposed bobbins 10 with the arms thereof inserted into the respective hollows 8 in the bobbins 10 with the third and fourth coils 14 and 15 thereon thereby to complete a first coil unit. Thereafter, the first and second coil units are coupled with each other, with the arms of the first core member 17 abutted end-to-end with the arms of the second core member 17, by means of a generally U-shaped elastic metal clamp 18 that tightly embraces the first and second core members 17 together as shown in Fig. 2, thereby completing the line filter assembly with the first and second core members 17 defining a closed magnetic circuit. It is to be noted that the elastic metal clamp 18 is preferably made of stainless steel and that each of the first and second core members 17 is made of ferrite. It is also to be noted that each of the first and second coils 11 and 12 and each of the third and fourth coils 14 and 15 should be so arranged and so positioned that the directions of flow of magnetic fluxes developed in the respective core members 17 as a result of flow of line currents can be counteracted to each other whereas the first and second coils 11 and 12 and the third and fourth coils 14 and 15 should be so arranged and so positioned that the directions of flow of magnetic fluxes developed in the respective core members 17 as a result of flow of the line currents can remain the same with respect to each other. In the line filter assembly of the construction described hereinabove, a leakage inductance brought about by a leakage of the magnetic fluxes from the core members 17 to the outside thereof caused by each of the coils 11 and 12, 14 and 15 is rendered to be 1 to 1.5% of the inductance of each of the coils 11 and 12, 14 and 15, which is of a value lower than one half of that of the prior art line filter assembly. Because of this, a magnetic saturation of the core material resulting from the line current can hardly take place and the line filter assembly can be manufactured of a size 20 to 30% smaller than that of the prior art line filter assembly for a given inductance with the same line current. According to the first preferred embodiment of the present invention, the line filter assembly can give a reduced leakage inductance resulting from a leakage of the magnetic fluxes; is less susceptible to magnetic saturation of the material for the core member during the flow of the line current and can have an increased number of turn of the coils as compared with those used in the prior art line filter assembly. However, the coils of an increased number of turns tends to emit heat as a result of the flow of the line current and, therefore, the number of turns available is limited by an increase in temperature. This can be substantially suppressed when portions of the line filter assembly where the coils are formed are filled with resinous material such as epoxy resin, silicone resin or urethane resin and it has been found that the temperature increase could be suppressed about 50%. When in the line filter assembly shown in and described with reference to Figs. 1 to 5 those portions of the line filter assembly exteriorly of the coils are filled with epoxy resin by the use of a dipping method, the size of the resultant line filter assembly could have been reduced further 20 to 30% to exhibit the same inductance at the same temperature increase when the same line current is passed. The line filter assembly according to a second preferred embodiment of the present invention is shown in Fig. 6 in sectional representation and is designed to withstand external vibrations to ensure a highly reliable performance. Referring now to Fig. 6, two multi-linked winding bobbins 10 all made of synthetic resin and each having the hollow defined therein are employed, and coils 11 and 14 are formed on one of the bobbins 10 while the coils 12 and 15 are formed on the other of the bobbins 10. Those bobbins 10 are housed within the casing 16 comprised of a pair of side walls 16a and 16b and an intermediate partition wall 16c and, thereafter, the opposite arms 17b of the first and second core members 17 are inserted into the hollows of the bobbins 10 until free ends of the arms 17b of the first core member 17 are brought into abutment with free ends of the arms 17b of the second bore member 17 within the hollows 8 of the bobbins 10. Each of the first and second core members 17 is made of ferrite or the like and is of a type comprising the pair of the opposite arms 17b connected together by means of a bridge 17a to render the respective core member 17 to represent a generally U-shaped configuration. Thereafter, the first and second core members 17 are clamped together by means of an elastic metal clamp 18 that embraces them thereby to complete the line filter assembly. It is to be noted that the elastic metal clamp 18 is preferably made of stainless steel and is of a generally U-shaped configuration having a pair of opposite bent fingers 18a engageable respective side portions of the first and second core members 17 to clamp the first and second core members 17 together and also having a bent tip 18b continued from each finger 18a so as to extend perpendicular thereto. The bent end 18b integral with each finger 18a of the elastic metal clamp 18 is so designed and so dimensioned that the tip thereof can be brought into engagement with an inner surface of the side wall 16b of the casing 16 while the bent end 18b itself is held in contact with a corresponding one of the opposite ends of the bobbin 10. In this construction, in the event that external vibrations are applied to the line filter assembly constructed as shown in Fig. 6, the ends 18b of the respective fingers 18a of the elastic metal clamp 18 cooperate with the side walls of the casing 16 and the adjacent ends of the bobbin 10 to absorb the vibrations thereby to avoid any possible collision between the core members 17 and the bobbins 10. Accordingly, not only damages to the closed magnetic circuit defined by the core members 17, but also any possible reduction in magnetic permeability can be advantageously avoided to render the resultant line filter assembly to operate in a stabilized and reliable manner. The casing 16 used in the line filter assembly may be modified as shown in Fig. 7. The casing 16 shown in Fig. 7 comprises the pair of the side walls 16a and 16b and the partition wall 16c positioned intermediate between the side walls 16a and 16b. The partition wall 16c has its opposite ends formed with respective core guide recesses 25, a bottom face of each of said core guide recesses 25 having a deformable projection 26 formed integrally therewith. The deformable projection 26 in each of the core guide recesses 25 is capable of being deformed in contact with the associated bridge 17a of each of the core members 17 when the elastic metal clamp 18 is encircled to clamp the core members 17 together. To cause the closed magnetic circuit, defined by the core members 17, to be sandwiched between the elastic metal clamp 18 and the deformable projections 26 is effective to substantially eliminate any possible rattling of some component parts of the line filter assembly which would occur during and after the assembly thereof and also to eliminate the need of use of any bonding agent, thereby to avoid a reduction in performance and to improve the reliability. The size of each of the deformable projection 26 in the partition wall 16c of the casing 16 is so selected as to be of a value which is greater than the difference between the maximum size thereof available or permissible within the tolerance in dimension of the core members 17, forming the closed magnetic circuit, and the minimum size thereof available or permissible within the tolerance in dimension of the partition wall 16c of the casing 16 and, also, as to be of such a value that the limit in size thereof attainable by the respective deformable projection 26 when deformed can be smaller than the difference between it and the maximum size thereof available or permissible within the tolerance in dimension of the core members 17 forming the closed magnetic circuit. However, it is to be noted that, instead of the use of the deformable projections- 26 in the partition wall 16c of the casing, the casing 16 may be either integrally formed with thin-walled portions during the molding of the casing 16 or fitted with cushioning elements, such as silicone rubber pieces, subsequent to the molding of the casing. A third preferred embodiment of the present invention will now be described with reference to Figs. 8 and 9. The bobbin assembly shown in Fig. 8 and made of synthetic resin comprises two bobbins 10 which have respective hollows 8 defined therein. Each of the bobbins 10 has a plurality of radially outwardly flanged end collars 20 formed integrally therewith at its opposite ends and also a plurality of radially outwardly flanged intermediate collars 19 at a generally intermediate portion thereof. The coils 11 and 14 are formed on one of the bobbins 10 and the coils 12 and 15 are formed on the other of the bobbins 10. The bobbins 10 with the coils 11, 14 and 12, 15 mounted thereon respectively are subsequently housed within the casing 16 of a generally E-shaped cross-section, followed by a fitting of a bottom plate 27 to the casing 16. Thereafter, the arms of the generally U-shaped first core member 17 and the arms of the generally U-shaped second core member 17 are inserted into the respective hollows 8 of the bobbins 10 from opposite directions until free ends of the arms of the first core member 17 are brought into abutment with free ends of the arms of the second bore member 17 within the hollows 8 of the bobbins 10. The first and second core members 17 are subsequently clamped together by means of the elastic metal-clamp 18 that embraces them. In this embodiment, each of the end collars 20 of each of the bobbins 10 has its opposite sides formed with respective engagement grooves 28 which open towards the side walls 16a and 16b and the partition wall 16c of the casing 16. On the other hand, a portion of each of the side walls 16 and 16b and the partition wall 16c of the casing 16, which confronts the associated engagement groove 28 in the corresponding end collar 20 is formed with an engagement rib 29 which is engageable into the associated engagement groove 28 as the assembly of bobbins 10 with coils thereon is housed within the casing 16. Also, respective lower edges of the side walls 16a and 16b of the casing 16 are formed with retainer pawls 31 for retaining in position the multi-linked bobbins 10. The side walls 16a and 16b of the casing 16 is further formed with hook pawls 31 which can be snapped into respective detent holes defined in the bottom plate 27 to secure the latter to the casing 16 with the filter assembly housed therein in the form as sandwiched between the casing 16 and the bottom plate 27. The assembly shown in Figs. 8 and 9 is advantageous in that no bonding agent is employed to fix the component parts in position, thereby minimizing the number of manufacturing steps and that the component parts can be tightly fixed in position within the casing thereby to improve the reliability considerably. From the foregoing description of the preferred embodiments of the present invention, it is clear that substantial portion of magnetic leakage fluxes from one of the coils and also from the other of the coils can be counterbalanced to make a magnetic saturation difficult to occur. Also. the core members forming the closed magnetic circuit may be small in size for the resultant line filter assembly to operate with the same line current to give the same inductance and, therefore, the line filter assembly as a whole can be manufactured compact in size, low in height and at a reduced manufacturing cost. Also, any possible influence which may be brought by the line filter assembly on peripheral component parts can be minimized. Thus, the present invention has a significant utility.

Claims: A line filter assembly which comprises: a magnetic core means (17) forming a closed magnetic circuit and including first and second arm means opposite to each other and connected together through a common bridge means; a first coil means (11, 12) having a portion thereof wound around the first arm means and the remaining portion wound around the second arm means; a second coil means (14, 15) having a portion wound around the first arm means and the remaining portion wound around the second arm means; said first and second coil means (11, 12; 14, 15) being so designed that directions of magnetic fluxes produced in the closed magnetic circuit as a result of flow of line currents counteract while said coil means are so arranged that common-mode noise components in the flow of the line currents are prevented; characterized by a casing (16) of generally U-shaped section accommodating an assembly of the magnetic core means (17) having the first and second coil means mounted on the first and second arm means; a substantially elastic metal clamp (18) of generally U-shaped configuration exteriorly encircling the casing (16) with free ends thereof engaged with opposite side faces of the magnetic core means (17). The line filter assembly as claimed in claim 1, wherein each free end of the metal clamp (18) comprises a finger and a pawl defined at and protruding outwardly from a free end of the finger for abutment with corresponding ends of respective bobbins (10) and also with an inner wall of the casing (16). The line filter assembly as claimed in claim 1, wherein said casing (16) includes a pair of opposite side walls (16a, 16b) and a partition wall (16c) positioned intermediate between the opposite side walls, said partition wall (16c) having a deformable element (26) provided at any one of opposite ends thereof, said deformable element (26) being deformed when the core means (17) is clamped by the elastic metal clamp (18). The line filter assembly as claimed in Claim 1, wherein said casing (16) includes a pair of opposite side walls (16a, 16b) and a partition wall (16c) positioned intermediate between the opposite side walls, and wherein respective portions of collars (20) provided at opposite ends of each of bobbins (10), which confront the side walls (16a, 16b) and the partition wall (16c), are formed with engagement grooves (28), and respective portions of the side walls (16a, 16b) and the partition wall (16c) of the casing are formed with engagement ribs (29) cooperable with the associated engagement grooves (28).

Inventors: HASHIMOTO SHUNJI, MORI TATSUYA, ODA TOSHINORI, HASHIMOTO, SHUNJI, MORI, TATSUYA, ODA, TOSHINORI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1991
Main classification: H03H1
IPC codes: H03H1