Magnetic circuit for carrying at least one coil

Abstract

The invention relates to a magnetic circuit (2) for carrying at least one coil (3), the circuit (2) comprising: at least one inner leg (6) and at least two outer legs (4), and a connecting part (7) for guiding the magnetic flux of the inner leg (6) towards each outer leg (4), none of the outer legs (4) having a gap width and the inner leg (6) being at least partially formed from at least one material having a relative magnetic permeability lower than that of the material(s) forming the outer legs.

Claims

1. A magnetic circuit for carrying at least one coil, the circuit comprising: at least one inner leg and at least two outer legs; and a connecting part serving to guide the magnetic flux from the inner leg to each outer leg, each outer leg having no non-magnetic gap and the inner leg being at least partially made from one or more materials that have a relative magnetic permeability that is lower than that of the material or materials of which the outer legs are formed, each outer leg being made as a single piece in one and the same material from one outer leg to the other and the relative magnetic permeability of the material of a portion of the inner leg being lower than the relative magnetic permeability of the material of the outer legs, the ratio between the relative magnetic permeability of the material of said portion of the inner leg and the relative magnetic permeability of the material of the outer legs being comprised between 0.001 and 0.033, and wherein the inner leg comprises a plurality of successive transverse sections that are homothetic images of one another, having a ratio of less than one from one section to an adjacent section of the plurality of successive transverse sections with increasing proximity to the connecting part.

2. The magnetic circuit as claimed in claim 1, the material of said portion of the inner leg being a magnetic powder.

3. The magnetic circuit as claimed in claim 1, the connecting part comprising at least one portion made from the same material or materials as said portion of the inner leg.

4. An assembly comprising: a magnetic circuit as claimed in claim 1, and at least one electrically conducting coil carried by the magnetic circuit.

5. The assembly as claimed in claim 4, the coil being formed by winding an electrically conducting wire or by a metal strip that is electrically insulated on one of its two faces.

6. The magnetic circuit as claimed in claim 1, each one of the inner leg and outer legs extending parallel to one and the same longitudinal axis between a first end and a second end, and the connecting part comprising a first part connecting the first ends together and a second part connecting the second ends together.

7. The magnetic circuit as claimed in claim 6, each outer leg being formed from a magnetic tape wound about an axis.

8. The magnetic circuit as claimed in claim 7, said axis of winding being perpendicular to the longitudinal axis and not simultaneously intersecting the inner leg and either one of the outer legs.

9. The magnetic circuit as claimed in claim 6, each outer leg being formed of a stack of magnetic laminations.

10. The magnetic circuit as claimed in claim 9, said laminations being stacked along an axis of stacking perpendicular to the longitudinal axis and not simultaneously intersecting the inner leg and either one of the outer legs.

11. The assembly as claimed in claim 10, the coil being wound around a zone of the inner leg.

12. A static electrical energy convertor comprising at least one assembly as claimed in claim 10.

13. The assembly as claimed in claim 10, comprising several distinct coils.

14. The assembly as claimed in claim 13, the coils being wound around one of the following zones of the magnetic circuit: a zone of one of the outer legs or a zone of the connecting part.

Description

(1) The invention may be better understood from reading the following description of one nonlimiting exemplary embodiment thereof and from studying the attached drawing in which:

(2) FIG. 1 has already been described,

(3) FIG. 2 is a schematic and not-to-scale depiction of one example of an assembly according to the invention in a depiction similar to that of FIG. 1,

(4) FIGS. 3 to 7 depict an assembly according to a first exemplary embodiment of the invention, FIG. 3 depicting the assembly face-on, FIG. 4 depicting a detail of the coil of the assembly of FIG. 3, FIG. 5 being a view on V of the assembly of the figure, FIG. 6 being a view of part of the outer leg of the assembly of FIG. 3, and FIG. 7 is a section on A-A of the assembly of FIG. 3,

(5) FIGS. 8 to 12 depict an assembly according to a second exemplary embodiment of the invention, FIG. 8 depicting the assembly face-on, FIG. 9 depicting a detail of the coil of the assembly of FIG. 8, FIG. 10 being a view on X of the assembly of FIG. 8, FIG. 11 being a view of part of the outer leg of the assembly of FIG. 8, and FIG. 12 is a section on A-A of the assembly of FIG. 8,

(6) FIGS. 13 to 17 depict alternative forms of embodiment of the assembly depicted in FIG. 8, and

(7) FIGS. 18 to 20 depict an assembly according to another exemplary embodiment of the invention.

(8) FIG. 2 very schematically and not to scale depicts one example of an assembly 1 according to the invention, for the purposes of comparing it with that depicted in FIG. 1.

(9) The assembly 1 comprises a magnetic circuit 2 and one single coil 3 in the example described. As may be seen, the magnetic circuit 2 comprises two outer legs 4 and an inner leg 6 which is positioned between the two outer legs 4. A connecting part 7 guides the magnetic flux from the inner leg 6 toward each outer leg 4. As depicted in this FIG. 2, each outer leg 4 is produced here as a single piece, with no non-magnetic gap.

(10) As can be seen in FIG. 2, each outer leg 4 and the inner leg 6 may extend parallel to one and the same straight longitudinal axis X, between two ends 10 and 11 in the case of the outer legs 4, and 12 and 13 in the case of the inner leg 6.

(11) The connecting part 7 may then comprise a first connecting part 14 connecting the first ends 10 and 12 together and a second connecting part 15 connecting the second ends 11 and 13 together. In the example considered, the first connecting part 14 and second connecting part 15 extend transversely with respect to the axis X, notably perpendicular to this axis X.

(12) The inner leg 6 comprises a portion 16 made from a material different from that used to make the rest of the magnetic circuit 2 depicted in FIG. 2.

(13) The portion 16 is made for example of a magnetic powder. The powder may have been molded then compacted beforehand in order to create this portion 16. By way of powder use is made for example of the powder marketed by the company Magnetics under the reference XFlux 60. The magnetic powder may have a relative magnetic permeability comprised between a few units and a few hundreds of units, for example between 6 and 100. The rest of the magnetic circuit 2 is made of magnetic laminations, for example marketed by the company JFE under the reference 10JNHF600. There is a ratio comprised between 0.1 and 0.01, for example, between the relative magnetic permeability of the portion 16 and that of the material used to make the outer legs 4 and the connecting part 7 of the magnetic circuit 2 of FIG. 2.

(14) The coil 3 is a single coil in the example of FIG. 2 and is wound around the inner leg 6. The coil 3 in this example is of the foil type, which means to say that it is made of a strip 18, one of the faces of which is covered with an insulating layer 19. The strip 18 is made for example of copper or of aluminum.

(15) The assembly 1 is placed in a casing, not depicted, used both to cool the assembly 1 and to protect it against attack from the external environment.

(16) As may be seen in FIG. 2 very schematically, because of the absence of a non-magnetic gap in the outer legs 4 and because of the presence of the portion 16 in the inner leg 6, the magnetic flux remains well contained within the outer legs 4, stray magnetic flux outside of these legs being reduced very significantly.

(17) An assembly 1 according to a first exemplary embodiment of the invention will now be described with reference to FIGS. 3 to 7.

(18) This assembly 1, viewed face-on in FIG. 3, comprises a single coil 3 wound around the inner leg 6. In this example, the coil 3 is formed of an electrically conducting strip 20 coated with an electrical insulator 22, as can be seen in FIG. 4 which depicts in detail part of the coil 3 of the assembly of FIG. 3. As depicted in FIG. 3, the coil 3 in this example is not encapsulated in the magnetic circuit 2.

(19) Still according to the example of FIG. 3, the portion 16 defines the entirety of the inner leg 6, which means to say that the inner leg 6 is wholly formed by the portion 16.

(20) It may also be seen in FIG. 3 that the ends 12 and 13 of the inner leg 6 are free, not being covered by the coil 3.

(21) According to this first exemplary embodiment of the invention, the rest of the magnetic circuit 2 is obtained from two soft magnetic strips 22. Once shaped, these two strips are C-shaped, one of the strips forming an outer leg 4 and having: a return extending transversely to said outer leg to form that fraction of the first connecting part 14 that is situated between said outer leg 4 and the inner leg 6, and a return extending transversely to said outer leg 4 to form that fraction of the second connecting part 15 that is situated between said outer leg 4 and the inner leg 6.

(22) The other strip forms the other outer leg 4 and likewise has: a return extending transversely to said outer leg 4 to form that fraction of the first connecting part 14 that is situated between said other outer leg 4 and the inner leg 6, and a return extending transversely to said outer leg 4 to form that fraction of the second connecting part 15 that is situated between said other outer leg 4 and the inner leg 6.

(23) Each outer leg 4 as well as the fraction of the first connecting part 14 and the fraction of the second connecting part 15 that is positioned between said outer leg 4 and the inner leg 6 is obtained by winding a soft magnetic tape 22 around an axis Z situated in a plane perpendicular to the longitudinal axis X and not simultaneously intersecting both the inner leg 6 and either of the outer legs 4.

(24) As may be seen in FIG. 5, which is a side view on V of the assembly 1 of FIG. 3, each outer leg 4 extends beyond the coil 3 via its first 10 and second 11 ends. By contrast, the coil 3 may extend beyond the outer legs 4 on each side thereof on either side of the longitudinal axis X, as depicted in FIG. 5.

(25) FIG. 6 depicts a detail of FIG. 3 showing the makeup of the outer legs 4 and of the connecting parts 14 and 15 according to this first exemplary embodiment of the invention, these being made up of layers of magnetic material 23 alternating with non-magnetic layers 24.

(26) An assembly 1 according to a second exemplary embodiment of the invention will now be described with reference to FIGS. 8 to 12.

(27) This second exemplary embodiment differs from the one that has just been described with reference to FIGS. 3 to 7 through the configuration of the outer legs 4 and of the connecting parts 14 and 15.

(28) The outer legs 4 and the first 14 and second 15 connecting parts are obtained here by stacking magnetic laminations in a direction perpendicular to the axis X and not simultaneously intersecting the inner leg 6 and either of the outer legs 4, this direction being the axis Z in FIG. 8.

(29) The outer legs 4 and the first 14 and second 15 connecting parts are therefore formed by layers of magnetic material 23 alternating with layers of magnetic insulator 24.

(30) The assembly 1 according to this second exemplary embodiment of the invention has a shape that is parallelepipedal overall.

(31) Various alternative forms according to the second exemplary embodiment of the invention will now be described with reference to FIGS. 13 to 17.

(32) In FIGS. 13 and 14, each end 12 and 13 of the inner leg 6 comprises successive transverse sections that decrease with increased proximity to the corresponding connecting part 14 or 15.

(33) In the example of FIG. 13, the first connecting part 14 comprises three sections: a first section 30 facing the first end 12 of the inner leg 6, a second section 31 forming one end of the first connecting part 14 and belonging to a component that also forms an outer leg 4 and one end of the second connecting part 15, and a third section 32 that forms the other end of the first connecting part 14 and belongs to a component that also forms the other outer leg 4 and the other end of the second connecting part 15,

(34) the first section 30 being positioned between the sections 31 and 32.

(35) In the example of FIG. 14, the first connecting part 14 also comprises three sections 30 to 32 but these are straight, having the form of bars with no return.

(36) As depicted in FIGS. 15 to 17, the first 14 and second 15 connecting parts may have portions 40 facing the ends 12 and 13 of the inner leg 6 which are made from a material different from the material used to form the rest of said parts 14 or 15. When magnetic powder is used to form the inner leg 6, these portions 40 may be made of powder likewise, notably using the same powder. There may therefore be continuity between the portion 16 of the inner leg 6 and the portions 40 of the connecting parts 14 and 15.

(37) The portions 40 may extend along the axis X, from one edge of each connecting part 14 or 15 to the other, or otherwise.

(38) In the example of FIG. 15, each end 12 or 13 of the inner leg 6 has a transverse section that varies with increasing proximity to the adjacent connecting part 14 or 15. The transverse section may vary in decreasing steps with increased proximity to the corresponding connecting part, forming a staircase appearance visible in FIG. 15. The portion 40 of each connecting part 14 or 15 in this example has a transverse section that is constant, this transverse section being equal to the final transverse section of the end 12 or 13 of the inner leg 6.

(39) In the example of FIG. 16, unlike that of FIG. 15, the portion 40 has a transverse section that decreases continuously to zero, having a pyramid shape when viewed at right angles to the axis X.

(40) In the example of FIG. 17, the portion 40 comprises, in succession, with decreasing proximity to the inner leg 6, a first section 41, the transverse section of which is the same as that of the end 12 or 13 of the inner leg 6 and a second section 42, the transverse section of which is a homothetic image with a ratio of less than one of that of the section 41.

(41) In other alternative forms which have not been depicted, the first 14 and second 15 connecting parts have no portion 40 and the end 12 or 13 of the inner leg 6 is made of the same material as the outer legs 4 and as the connecting parts 14 and 15.

(42) In the examples that have just been described, just one coil 3 is carried by the magnetic circuit 2 and this coil is wound around all or part of the length of the inner leg 6.

(43) However, the invention is not restricted to these examples as will now be seen.

(44) FIGS. 18 and 19 illustrate another example of an assembly 1. In these figures, four coils 3 are carried by the magnetic circuit 2. None of these coils 3 is wound around the inner leg 6.

(45) In FIG. 18, one of the coils 3.sub.1 is wound around a zone 50 of the first connecting part 14 between the first end 12 of the inner leg 6 and one of the outer legs 4, another coil 3.sub.2 is wound around a zone 51 of the first connecting part 7 between the first end 12 of the inner leg 6 and the other outer leg 4, another coil 3.sub.3 is wound around a zone 53 of the second connecting part 15 between the second end 13 of the inner leg 6 and the outer leg 4 adjacent to the coil 3.sub.1 and the last coil 3.sub.4 is wound around a zone 53 of the second connecting part 15 between the second end 13 of the inner leg 6 and said other outer leg 4.

(46) As depicted in FIG. 19, the coils 3.sub.1 and 3.sub.3 are electrically connected to one another to form just one single inductor and the coils 3.sub.2 and 3.sub.4 are likewise electrically connected to one another.

(47) The assembly 1 according to FIGS. 18 and 19 therefore forms two inductors. The assembly 1 may be as described with reference to FIGS. 14 to 16 of the application filed in the name of the applicant company at the European patent office under number EP 11 188922.6. The content of this application is incorporated by reference into the present application, at least insofar as FIGS. 14 to 16 of this application are concerned.

(48) In another alternative form depicted in FIG. 20, six coils 3.sub.1 to 3.sub.6 may be carried by the magnetic circuit 2 which then comprises two inner legs 6. Of these six coils, three are electrically connected in series to form one inductor, just like the three remaining coils which form another inductor. Three coils 3.sub.1 to 3.sub.3 are, for example, carried by the first connecting part 14 and electrically connected in series while the other three coils 3.sub.4 to 3.sub.6 are carried by the second connecting part 15 and electrically connected in series.

(49) In yet another alternative form similar to the one depicted in FIG. 20, three inductors are formed by connecting the coils 3.sub.1 to 3.sub.6 in series in pairs.

(50) The assembly 1 that has just been described may, when the magnetic circuit 2 carries just one single coil, have an inductor having an inductance of around 450 H. This inductor may be incorporated into a DC/DC voltage convertor operating at a chopping frequency of 20 kHz with a duty cycle of 0.66 in order to convert a voltage of 300 V into a voltage of 800 V, for example. The voltage convertor for example forms part of an electric vehicle inverter/charging circuit, for example as disclosed in application WO 2010/057893.

(51) The invention is not restricted to the examples that have just been described.

(52) The expression comprising a/an is to be understood as being synonymous with the expression comprising at least a/an/one unless specified to the contrary.