GB2201840A

GB2201840A - Noise absorber for absorbing electrically generated noise

Info

Publication number: GB2201840A
Application number: GB08801084A
Authority: GB
Inventors: Kazuhiro Matsui
Original assignee: Kitagawa Industries Co Ltd
Current assignee: Kitagawa Industries Co Ltd
Priority date: 1987-01-20
Filing date: 1988-01-19
Publication date: 1988-09-07
Anticipated expiration: 2008-01-19
Also published as: JPS63179604A; GB8801084D0; DE8800494U1; GB2201840B; JP2589685B2; DE3801188A1

Description

1 2201840 1 NOISE ABSORBER FOR ABSORBING ELECTRICALLY GENERATED NOISE The

present invention relates to a noise absorber and, in particular, to a noise absorber which can be attached to a cord or cable of an electronic device for absorbing electrically generated noise which is generated within the device or which is transmitted into or from the device through the cord or cable.

As a method for absorbing such a noise, it is well known to attach a magnetic ferrite device to a cord or cable. In this known method, two half-ring parts'of a ferrite are simply attached to the cord or cable by winding adhesive tape around the ferrite device, therefore, the ferrite can easily become detached from the cord or cable. Moreover, it is troublesome to attach the separate parts of the device to, and to remove them from, the cord or cable. When a conductive ferrite device is employed, it may create a short circuit or may generate an electrical contact in the electronic device. Furthermore, a closed magnetic circuit formed by the two half -ring shaped ferrite parts is liable to be broken at abutment surfaces of the two parts. When an air gap is created between the abutment surfaces of the ferrite parts, there arises a problem that the noise absorbing effect deteriorates due to the increase of magnetic resistance.

According to the present invention there is provided a noise absorber for absorbing electrically generated noise, comprising a body formed of a magnetic material having therein a through hole for receiving an electric cord or cable and divided longitudinally into two parts, each of said two parts including part of said through hole and two abutment surfaces, each of said abutment surfaces being larger in surface area than the minimum cross-section of each part of said magnetic body, and a holding device for receiving and holding said magnetic body so that said two parts of said magnetic body abut each other through said abutment surfaces.

In such a noise absorber, manganese-zinc or nickel-zinc ferrite is preferable as the material for the magnetic body. A metallic core formed of sifficone steel or a powder such as molybdenum may also be used. The magnetic body is divided into two parts for clamping around the cord or 1 2 cable and is ring-shaped, disc-shaped or cylinder- shaped, including a through hole for receiving the cord or cable in the centre thereof. The abutment surfaces of the magnetic body are so formed as to be larger in area than the minimum cross-section (a normal cross-section through a plane passing through the axis of the through hole and this section has a minimum area compared with all other sections of the magnetic body) for passing the magnetic flux in order to decrease the magnetic resistance as much as possible. The abutment surfaces are flat, curved or bent to make the area of the abutment surface larger. A holding case having two case parts for holding the two parts of the magnetic body therein is preferably made of synthetic resin, the case parts being interlocked. On at leat one of the ends of one case part are provided engaging projections to interlock the case parts. Further, the two case parts can be interconnected via a hinge which is provided on the one end of each case part.

Some embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a perspective view of a magnetic body constituting a first embodiment of the invention; Figure 2 is a perspective view illustrating a cross-section and an abutment surface of the magnetic body of Figure 1; Figure 3 is a perspective view of a holding case for holding the magnetic body of Figure 1 therein; Figure 4 is a cross-sectional view illustrating the first embodiment of noise absorber; Figure 5 is a perspective view of the noise absorber of Figure 4 attached to a cord or cable; Figure 6 is a perspective view of a magnetic body constituting a second embodiment of the invention; Figure 7 is a perspective view illustrating a basic cross-section and an abutment surface of the magnetic body of Figure 6; Figure 8 is a perspective view of a holding case for holding the magnetic body of Figure 6 therein; Figure 9 is a cross-sectional view of the second embodiment of noise absorber; Figure 10 s a front view of a magnetic body constituting a third embodiment of the invention; tll 3 Figure 11 is an exploded perspective view of the magnetic body of Figure 10; Figure 12 is a perspective view of a holding case for holding the magnetic body of Figure 10 therein; Figure 13 is a sectional view of the third embodiment of a noise absorber; Figure 14 is a front view of a magnetic body constituting a fourth embodiment of the invention; Figure 15 is an exploded perspective view of the magnetic body shown in Figure 14; Figure 16 is a front view of a magnetic body constituting a fifth embodiment of the invention; Figure 17 is an exploded perspective view of the magnetic body shown in Figure 16; Figure 18 is a front view of a magnetic body constituting a sixth embodiment of the invention; and Figure 19 is an exploded perspective view of the magnetic body shown n Figure 18.

Referring to Figure 1, there is shown a magnetic body 1 of a noise absorber constituting a first embodiment which is in the form of a substantially elliptical disc formed of a ferrite. The magnetic body 1 is divided along a cutting plane 8, which lies on the major axis of the elliptical magnetic body 1, into two parts comprising an upper part la and a lower part lb. In the centre of the magnetic body 1, is formed a through hole 2 for receiving a cord or cable 30 of an electronic device. As shown in Figure 2, each abutment surface 3 of the upper and lower parts la and lb is larger in area than a basic cross-section 4 for passing magnetic flux, that is, a criDss-section taken along the minor axis of the elliptical magnetic body 1. Therefore, when a closed magnetic circuit is formed by the magnetic body 1, magnetic resistance can be decreased at the abutment surfaces 3, where usually magnetic resistance tends to be increased. Further, the upper and lower parts la and lb may be formed by combined ferrites having a different noise absorbing range to extend the noise absorbing range.

Figure 3 shows a holding case 5 for holding the magnetic body 1 therein, which has a substantially elliptical shape and includes an upper case part 5b for respectively holding the upper and lower parts la and lb of the 1 4 magnetic body 1 therein, each being made of a resilient synthetic resin (for example, nylon or polyethylene). On both ends of the upper case 5a are provided engaging tabs 5t in which rectangular apertures 6 are formed. Engaging projections 7 are provided on both end walls of the lower case 5b. They engage in the associated rectangular apertures 6 to securely interlock the upper case part 5a and the lower case part 5b when the parts 5a and 5b are brought together. In the centre of the holding case 5, is a hole for receiving the cord or cable 30.

As shown in Figure 4, the both case parts 5a and 5b are interlocked by engaging the rectangular apertures 6 with the respective engaging projection 7 and the upper and lower parts la and lb of the magnetic body 1 are held in the upper and lower case parts 5a and 5b, respectively. At this time, the abutment surfaces 3 are abutted against each other substantially without any clearance therebetween, resulting to a secure holding of the magnetic body 1 in the holding case 5. Alternatively, each of the case parts 5a and 5b may have an engaging tabe 5t on one end and an engaging projection 7 on the other end. As shown in Figure 5, such a noise absorber is attached to the cord or cable 30 of an electronic device so as to surround it in ofder to absorb noise generated by the electric current flowing through the cord or cable 30. The area of the abutment surfaces 3 of the magnetic body 1 of the noise absorber is so large that the magnetic resistance is not increased at the abutment surfaces 3. As a result, sufficient magnetic induction is generated to effectively absorb noise created by the electrical current. The most suitable number of noise absorbers which are attached to the cord or cable 30, and their location, are determined by measuring the noise- absorbing efficiency with a noise-measuring device.

Figures 6 to 9 show a second embodiment of a noise absorber of the present invention. A magnetic body 11, as shown in Figure 6, is in the form of a substantially annular disc made of ferrite and including diametrically opposed lugs 11c, and is longitudinally divided along a cutting plane 18 extending through the axis of the circular magnetic body 11 into an upper part 11a and lower part 11b. In the centre of the magnetic body 11, is provided a through hole 12 for receiving the cord or cable 30. On both the side surfaces of the upper and lower parts 11a and 11b, are provided holding recesses 11d which can be engaged with projections 15d provided inside a holding case 15, which will be described later. The magnetic body 11 is thus k, a substantially ring-shaped disc including lugs 11c on the both ends, which is divided into two parts. The abutment surfaces 13 of the magnetic body 11 are sufficiently larger in area than the basic cross-section 14. Therefore, when a closed magnetic circuit 'is formed, the magnetic resistance is decreased at the abutment surfaces where the magnetic resistance is usually liable to be increased.

Figure 8 shows the holding case 15 for holding the magnetic body 11 therein, which includes an upper case part 15a and a lower case part 15b for receiving the respective upper and lower parts 11a and 11b of the magnetic body 11 therein, each being made of a resilient synthetic resin. On both end portions of the upper part 15a where the lugs 11c of the magnetic body 11 is received therein are provided engaging tabs 15t in which rectangular apertures 16 are formed. On both end portions of the lower case part 15b are provided engaging projections 17 which engage with the associated rectangular apertures 16 to securely interlock the upper case part 15a and the lower case part 15b when teh both case parts 15a and 15b are brought together. The projections 15d which engaged with the recesses 11d formed on the both side surfaces of the magnetic body 11 are provided inside the holding case 15.

As shown in Figure 9, both case parts 15a and 15b are interlocked by engaging the rectangular apertures 16 with the engaging projections 17 when the upper and lower parts 11a and 11b of the magnetic body 11 are received in the upper and lower case Parts 15a and 15b, respectively. At this time, the abutment surfaces 13 of the magnetic body 11 are abutted substantially against each other without any clearance therebetween, resulting in a secure holding of the magnetic body 11 in the holding case 15. Alternatively, each of the case parts 15a and 15b may have an engaging tab 15t on one end and an engaging projection 17 on the other end.

Such a noise absorber, as well as that of the first embodiment, is attached to the cord or cable 30 of an electronic device so as to surround the cord or cable 30 for absorbing noise generated by electrical current flowing through the cord or cable 30 by means of the magnetic body 11. The abutment surfaces 13 of the magnetic body 11 of the noise absorber are formed so large that magnetic resistance is not increased at the abutment surf aces 13. As a result, sufficient magnetic induction is generated to effectively absorb noise generated by the electrical current.

k, 6 Figures 10 to 13 show a third embodiment of a noise absorber of the present invention. A magnetic body 21, as shown in Figure 10, is in the form of a circular ring-shaped member formed of a ferrite and is divided along two parallel cutting planes 21c and 21d into an upper part 21a and a lower part 21b. Parallel abutment surfaces 23 are formed along lines tangential to the periphery of a through hole 22. As shown in Figure 11, the abutment surfaces 23 of the magnetic body 21 are sufficiently larger in area than a basic cross-section 24. As a result, when a closed magnetic circuit is formed, the magnetic resistance is decreased at the abutment surfaces 23 where the magnetic resistance is usually apt to be increased.

Figure 12 shows a holding case 25 for holding the magnetic body 21 therein, which includes an upper case part 25a and a lower case part 25b for holding the upper and lower parts 21a and 21b of the magnetic body 21, respectively. The upper and lower case parts 25a and 25b are integrally made of a synthetic resin and are hingedly connected at one end by a hine 28 so as to be opened and closed. On the opposite end of the upper case part 25a to that of the hinge 28 is provided an engaging tab 25t which has a rectangular aperture 26. An engaging projection 27 which can be engaged with the aperture 26 is provided on the lower case part 25b. Further, as shown in Figure 13, cushion members 29 are attached to the inside surface of the upper case part 25a and to the inside bottom surface of the lower case part 25b by means of an adhesive.

As shown in Figure 13, in such holding case 25, the upper and lower case parts 25a and 25b are interlocked by engaging the aperture 26 at a free end of the upper case part 25a with the engaging projection 27 at the free end of the lower case part 25b when the respective upper and lower parts 21a and 21b are received therein. The abutment surfaces 23 of the magnetic body 21 are abutted against each other substantially without any clearance therebetween with the help of the cushion members 29, resulting in a secure holding of the magnetic body 21 in the holding case 25.

Such a noise absorber is attached to the cord or cable 30 of an electronic device so as to surround the cord or cable 30 for absorbing noise generated by electrical current flowing through the cord or cable 30 by means of the magnetic body 21. The abutment surfaces 23 of the magnetic body 21 of the noise absorber are formed so large that the magnetic resistance is not increased at the abutment surface 23. As a result, 1 7 sufficient magnetic induction is generated to effectively absorb noise generated by electrical current.

Figures 14 to 19 show modified forms of magne tic bodies 31, 41 and 51 which can be used in place of the magnetic body 21 of the third embodiment. As shown in Figure 14, two dividing planes 35 and 36 of the magnetic body 31 are formed at an angle relative to each other and extend from a through hole 32 of a circular ring-shaped magnetic body 31. A small-sized upper part 31a is abutted on the central upper surface of a larged-sized part 31b. As shown in Figure 15, the abutment surfaces 33 of the magnetic body 31. are sufficiently larger in area than a minimum cross-section 34. Therefore, the magnetic resistance which is apt to be increased at the abutment magnetic surfaces 33 is decreased. Further, in the magnetic body 31 shown in Figure 14, the upper and lower parts 31a and 31b are difficult to dislocate. Even if they become dislocated, they can be restored automatically.

As shown in Figure 16, a V-shaped and inverted V-shaped dividing surfaces 45 and 46 of an annular magnetic body 41 are provided which extend in the opposite direction to each other from a through hole 42 in the circular ring-shaped magnetic body 41. Therefore, as shown in Figure 17, inclined abutment surfaced 43 are formed so that an upper part 41a and a lower part 41b of the magnetic body 41 may not be dislocated. The separate abutment surfaces 43 are sufficiently larger in area than the crosssection 44 to prevent the magnetic resistance at the abutment surfaces 43 from being increased. Furthermore, as shown in Figure 18, upwardly arcuate and downwardly arcuate and partially planar surfaces 55 and 56 are formed in magnetic body 51 and extend in the opposite direction to each other from a through hole 52. Accordingly, as shown in Figure 19, some abutment surfaces 53 have an outwardly curved part abutted with abutment surfaces 53 having a curved recess so that an upper part 51a and a lower part 51b of the body 51 may not be easily dislocated. The abutment surfaces 53 are sufficiently larger in area than a cross- section 54 to prevent the magnetic resistance at the abutment surface 53 from being increased.

k 8

Claims

1. A noise absorber for absorbing electrically generated noise, comprising a body formed of a magnetic material having therein a through hole for receiving an electric cord or cable and divided longitudinally into two parts, each of said two parts including part of said through hole and two abutment surfaces, each of said abutment surfaces being larger in surface area than the minimum cross-section of each part of said magnetic body, and a holding device for receiving and holding said magnetic body so that said two parts of said magnetic body abut each other through said abutment surfaces.

2. A noise absorber as claimed in claim 1, in which said holding device comprises two casing parts for housing said magnetic body, said casing parts being detachably connected together at leat at one end.

3. A noise absorber as claimed in claim 1 or claim 2, in which siad magnetic body is of elliptical shape and said body is divided along a plane extending along the major axis of said elliptical body.

4. A noise absorber as claimed in claim 3, in which said holding device has an elliptical shape and is divided into two casing parts along a plane extending along the major axis of said elliptical device, one easing part having a locking aperture at one end thereof and the other casing part having an engaging projection at one end thereof, said projections being engaged with said locking aperture when said casing parts are brought together.

5. A noise absorber as claimed in claim 1 or claim 2, in which said magnetic body is substantially circular in shape and has diametrically opposed outwardly extending lugs, said magnetic body being divided along a plane extending through the axis of said circular shape and through said lugs.

6. A noise absorber as claimed in claim 5, in which said holding device has a substantially circular shape and is divided along a plane containing the j 9 1 i axis of said circular shape into two casing parts, each casing part having flange portions extending outwardly and between which said lugs of said body are received, at least one casing part having a locking aperture at one end of a said flange and the other casing part having an engaging projection at one end of a said flange, said engaging projection being engaged with said lacking aperture when said two casing parts are brought together.

7. A noise absorber as claimed in any preceding claim, in which said two parts of said magnetic body are each provided with at least one holding recess and said holding device is provided with projections which engage in said recesses when said holding device receives said magnetic body therein.

8. A noise absorber as claimed in claim 1 or claim 2, in which said magnetic body has a circular shape and is divided along two parallel planes disposed tangential to the periphery of said through hole and extending oppositely and outwardly from each contact point with the periphery of said hole.

9. A noise absorber as claimed in claim 1 or claim 2, in which said magnetic body has a circular shape and is divided into two parts along two planes which are not parallel and intersect the periphery of said through hole.

10. A noise absorber as claimed in claim 1 or claim 2, in which said magnetic body has a circular shape and is divided into two parts along Vshaped and inverted V-shaped surfaces which intersect the periphery of said through hole.

11. A noise absorber as claimed in claim 1 or claim 2, in which said magnetic body has a circular shape and is divided into two parts along a partially planar surface having outwardly curved parts and which intersects the perhiphery of said through hole.

12. A noise absorber as claimed in any one of claims 8 to 11, in which said holding device has a circular shape and is divided along a plane including the axis of said circular shape into two casing parts, said casing parts being connected together at one end thereof by a hinge and detachably connected together by an engaging projection and a locking aperture at the other end.

13. A noise absorber as claimed in any preceding claim, in which cushion members are disposed between said magnetic body and said holding device.

14. A noise absorber for absorbing electrically generated noise comprising a tubular body formed of a magnetic material having a through hole for receiving an electric cord or cable and divided longitudinally along a dividing plane into two parts, each of said two parts including half of said through hole and two abutment surfaces, each of said abutment surfaces being larger in surface area than the minimum cross- section of each part of said magnetic body, and a holding device for receiving and holding said magnetic body so that said two parts of said magnetic body abut each other through said abutment surfaces.

15. A noise absorber for absorbing electrically generated noise substantially as hereinbefore described with reference to and as illustrated in Figures 1 to 5 or Figures 6 to 9 or Figures 10 to 13 or Figures 14 and 15 or Figures 16 and 17 or Figures 18 and 19 of the accompanying drawings.

1 Published 1988 at The Patent Office, State House, 66171 High Holborn, London WCIR 4TP. Further copies 3nay be obtained from The Patent Office, Sales Branch, St Maxy Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. 1187.