NL2019416B1 - Topology of a ferrite shield for inductive coils - Google Patents

Abstract

Topology of a ferrite shield for inductive coils Assembly (10), comprising a first inductive coil (11) comprising one or more windings of an electric wire forming one or more coil loops, an arrangement of ferrite tiles (14) disposed on one side of the first inductive coil, characterised in that the ferrite tiles are disposed such that they form one or more tile loops corresponding to the one or more coil loops and such that spaces between adjacent ones of the ferrite tiles are aligned locally perpendicular to the electric wire. (FIG 1)

Description

Technical field [0001] The present invention is related to an assembly comprising a ferrite shield for an inductive coil, in particular for contactless power transfer applications, such as in the automotive field. The present invention is equally related to an arrangement or disposition of the ferrite shield for such applications.

Background art [0002] For inductive coils, in particular for inductive power transfer, e.g. for charging car batteries, it is known to use ferrite not only to shield the magnetic field induced by the inductive coil, but also to improve the efficiency of power transfer between a sending and a receiving coil. The ferrite guides the magnetic field generated by the sending coil along preferred paths, enabling to reduce the volume in which the magnetic field generated by the inductive coil is significant and increase the intensity of the magnetic field in the area of interest (i.e. near the receiving coil). This can improve the coupling between the coils and thereby reduce the energy losses during inductive power transfer.

[0003] One drawback of ferrite is its high mass density and cost. Using ferrite therefore tends to lead to high costs and bulky assemblies.

Summary of the invention [0004] In automotive inductive power transfer applications, it would be desirable to reduce weight, bulkiness and cost of the assemblies for inductive power transfer. However, since high power is transferred in such applications, the efficiency of the inductive power transfer must remain high. It is therefore an aim of the present invention to provide assemblies which overcome one or more of the above problems.

[0005] It is also an aim of the present invention to provide assemblies for inductive power transfer having improved power density.

[0006] According to a first aspect of the invention, there is therefore provided an assembly as set out in the appended claims.

[0007] Assemblies according to aspects described herein comprise a first inductive coil comprising one or more windings of an electric wire or cable forming one or more coil loops, and an arrangement offerrite tiles disposed on one side (e.g., top or bottom) of the first inductive coil. According to one aspect, the coil loops are disposed in, or form a first plane. The ferrite tiles are disposed in a second plane substantially parallel to the first plane. According to a second aspect, the ferrite tiles are disposed such that they form one or more tile loops corresponding to the one or more coil loops. Tiles arranged at opposite sides of the coil are advantageously spaced apart a distance substantially equal to an internal diameter of the coil. According to another aspect, spaces between adjacent ferrite tiles are aligned locally perpendicular to an axial orientation of the electric wire.

[0008] Assemblies according to aspects described herein hence can ensure that the gaps (spaces) between adjacent tiles run parallel with the direction ofthe magnetic field and therefore the path of the magnetic field remains practically undisturbed by the tile arrangement.

[0009] Furthermore, advantageously, the area of the tiles and the area of the coil substantially fully overlap. As a result, a central area is obtained with sufficient volume that can be used for accommodating additional components. As the tiles do not substantially extend beyond the area ofthe coil, weight and cost can be saved.

[0010] Further advantageous aspects are described in the dependent claims.

Brief description of the figures [0011] Aspects of the invention will now be described in more detail with reference to the appended drawings, wherein same reference numerals illustrate same features and wherein:

[0012] Figure 1 represents a partially exploded perspective view of an assembly according to aspects described herein;

[0013] Figure 2 represents an exploded perspective view of an assembly according to aspects described herein.

Description of embodiments [0014] Referring to Fig. 1, an assembly 10 according to aspects described herein comprises an inductive coil 11, which can comprise an electric wire or cable which is wound in one or more turns forming a loop. In the configuration of Fig. 1, the loop is a single loop having an “0” configuration, even though other configurations, such as double loops (e.g. having the shape of an “8”) or multiple loops are possible.

[0015] Advantageously, the coil 11 is accommodated in a housing 12 which can comprise pre-formed paths or tracks 121 accommodating the electric wire. The paths 121 may run spirally to form the turns of the electric wire or cable and thereby form the coil 11.

[0016] The housing 12 may further comprise mounts 122 for mounting ferrite tiles 14 thereon. Mounts 122 may have any suitable shape and may allow for maintaining a relative position between the coil 11 and the ferrite tiles 14. Tile support members 13, e.g. made of a resilient material, such as an elastomeric material, may be provided on mounts 122 for supporting and securing the tiles 14. Useful examples of mounts 122 and tile support members 13 are described in Dutch co-pending application No. 2019414 filed 14 August 2014, the contents of which are incorporated herein by reference.

[0017] Support members 13 and mounts 122 may ensure that tiles 14 are spaced apart from the coil 11 at any suitable distance.

[0018] According to one aspect, a plurality offerrite tiles 14 are disposed so as to cover the coil 11. The tiles 14 are advantageously made of ferrite, in particular soft ferrite. They may be made of other magnetic (e.g. ferromagnetic or ferrimagnetic) materials. The magnetic material is advantageously used to improve magnetic coupling between the coils of the primary side and of the secondary side. Therefore, it is advantageous to choose a composition that has low losses at the power transfer frequency of interest (e.g. <500 kW/m³ at 100 kHz, 200 mT and 25 °C). Typically, power transfer frequencies range between 50 and 100 kHz for automotive applications.

[0019] It will be convenient to note that in use, the ferrite tiles may be disposed on one side of the coil 11 only, e.g. either above, or below the coil 11. In the present disposition, a combination of rectangular tiles 141 and tiles 142 having the shape of a disc segment, e.g. a 45° segment, are advantageously used. By way of example, as shown in Fig. 1, between each 90° segment formed with tiles 142, at least one rectangular tile 141 is disposed. The tiles 14 are disposed such that they form a loop corresponding to the loop of the coil 11. The tiles 14 overlap the windings ofcoil 11 and advantageously provide a substantially 1/1 overlap with the area of the coil 11, i.e. the area of tiles 14 and the area of coil 11 is substantially identical.

[0020] As shown in Fig. 1, the spaces between adjacent tiles 14 are perpendicular to the local orientation (axis) of the wire of coil 11. Such a disposition ensures that the gaps (spaces) between adjacent tiles run parallel with the main direction of the magnetic field and therefore the magnetic field is not negatively affected by the tile arrangement. As a result, any number of ferrite tiles 14 may be used, as long as the spaces (gaps) between the tiles are oriented perpendicular to the coil windings. This allows to tailor the dimensions of the tiles on the basis of material properties in order to prevent breaking of tiles. This furthermore also allows to provide appropriate mounting and securing of the tiles.

[0021] Each tile advantageously comprises four edges. Two opposite edges 143 are arranged such that they are aligned with the wire of the coil 11. The other two opposite edges 144 run perpendicular to the wire of the coil. This is also advantageously the case for the segment-shaped tiles 142. The edges 144 advantageously have a length substantially corresponding to a breadth ofthe coil 11, i.e. the tile 14 extends continuously over a breadth of coil 11.

[0022] A central area 15 is completely enclosed by the coil 11.

Advantageously, central area 15 is also fully enclosed by the loop of tiles 14. That is, tiles arranged at opposite sides of the coil 11 are spaced apart over a distance substantially equal to, or slightly smaller than an internal diameter of coil 11. The central area advantageously accommodates electronic circuitry, e.g. driving circuitry for the coil

11. Useful examples of electric circuitry that can be accommodated in central area 15 are: inverter circuitry and rectifier circuitry [0023] Referring to Fig. 2, in order to shield the electronic circuitry arranged in central area 15, a shielding layer 16 of an electrically conductive material can be arranged between the central area on the one hand and the coil 11 and ferrite tiles 14 on the other hand. Layer 16 may advantageously be made of a thermally conductive material in order to form a thermal path with low thermal resistance to facilitate heat spreading. Advantageously, layer 16 overlaps at least partially with the ferrite tiles 14, at a side opposite the coil 11. Within central area 15, layer 16 advantageously forms a bulge 161. Bulge 161 advantageously increases a space in central area 15. Additionally, bulge 161 advantageously protrudes in a direction of the coil 11 which may facilitate heat transfer to the environment from a side 101. This is particularly useful where assembly 20 is a ground assembly of an automotive inductive power transfer system and the assembly 20 rests with side 102 on ground level. In such a case, side 101 will form the top side.

[0024] It will be convenient to note that the assembly 20 of Fig. 2 is inversed with respect to the assembly 10 of Fig. 1, i.e. in Fig. 2 the tiles 14 are located underneath the coil 11. Additionally, electronic circuitry in central area 15 would be located underneath layer 16 (e.g., underneath bulge 161).

[0025] A conductive loop 17 may be provided at a periphery of layer 16.

Conductive loop 17 advantageously has a higher conductivity than layer 16. By way of example, layer 16 may be made of aluminium and conductive loop 16 may be formed of copper. A relatively high conductivity for loop 17 advantageously decreases power dissipation within the housing 12. The conductive loop 17 may comprise a wire arranged in a single turn or a plurality of turns and may or may not be constrained to a single plane. Conductive loop 17 may be terminated by a fixed or variable impedance, which can be resistive, capacitive, or inductive, or any suitable combination thereof. By way of example, conductive loop 17 can be made of (separately insulated) stranded copper wire, solid copper plate or any other material with a relatively low AC resistance.

[0026] The central area 15 may additionally or alternatively be covered with a layer 18 made of a material having a relative magnetic permeability μ_Γ > 10. The material of layer 18 advantageously has a low electrical conductivity σ « 1000 S/m, e.g. ferrite material (σ » 1Ί0'⁵ S/m). The ferrite can be either flexible or solid and may be relatively thin due to the low magnetic flux density in this location. Layer 18 advantageously has a thickness which is less than or equal to half the thickness of the tiles 14, advantageously less than or equal to 0.2 times the thickness of tiles 14. The layer 18 is advantageously applied to shield the layer 16 which reduces the power dissipation due to eddy currents that are induced by the coil. Layer 18 advantageously has some overlap with the tiles 14.

[0027] Referring back to Fig. 1, a second type of coil 19 can be provided in addition to coil 11. Four such coils 19 are provided in Fig. 1, at 90° distance from one another, and more or less coils 19 may be provided as desired. For example, only two or three coils 19 may be provided, at least two of which may have perpendicular axes. Each coil 19 is wound about a tile 14, in particular a rectangular tile 141. Optionally, coils 19 may be wound about a plurality of tiles 14. Coils 19 may be used for inducing/sensing additional magnetic fields distinct from the magnetic field induced by coil 11, e.g. for position sensing. By spatially separating the different coils 19, less coils are required and/or a better accuracy can be obtained for such purposes. Typically, the coils 19 are wound perpendicular to the main direction of the magnetic field generated by power transfer coil 11. This leads to an improved decoupling of the magnetic fields of coils 11 and 19, with improves signal to noise ratio and reduced coupling of higher harmonics. As a result less stringent insulation requirements for coil 19 are needed.

Claims (17)

CONCLUSIONS Assembly (10, 20), comprising: a first inductive coil (11) comprising one or more turns of an electrical wire forming one or more coil loops defining a plane, an arrangement of ferrite tiles (14) disposed substantially parallel to the plane on one side of the first inductive coil, characterized in that the ferrite tiles are arranged to form one or more tile loops corresponding to the one or more coil loops and so that spaces between adjacent ferrite tiles are aligned locally perpendicular to the electrical wire. The assembly of claim 1, wherein the ferrite tiles (14) are continuous in a direction locally perpendicular to the electrical wire and along a length corresponding to a width of the inductive coil (11). The assembly of claim 1 or 2, wherein an extension region of the ferrite tiles (14) and an extension region of the first inductive coil (11) are substantially identical. The assembly of any one of claims 1 to 3, wherein at least one of the one or more coil loops and corresponding tile loop enclose a central region (15) not covered by the ferrite tiles (14). Assembly according to claim 4, comprising one or more inductive coil driving circuits placed in the central region (15). Assembly according to claim 4 or 5, comprising a thermally conductive layer (16) covering the central region (15) and the respective coil loop and tile loop. The assembly of claim 6, wherein the thermally conductive layer (16) is electrically conductive. The assembly of claim 6 or 7, wherein the thermally conductive layer forms a bulge (161) in the central region. Assembly according to any one of claims 4 to 8, comprising a ferrite containing layer covering the central region (15), the ferrite containing layer overlapping at least partially with the ferrite tiles. The assembly of claim 9, wherein the ferrite containing layer is formed as a continuous sheet. Assembly according to claim 9 or 10, wherein the ferrite containing layer has a thickness that is at least 20% smaller than the thickness of the ferrite tiles. Assembly according to any of the preceding claims, comprising at least one second inductive coil (19), wherein each of the at least one second inductive coil is wound around one or more of the ferrite tiles (14) so that an axis of the first inductive coil (11) and an axis of the second inductive coil are perpendicular to each other. The assembly of claim 12, comprising a plurality of the second inductive coil (19), each of the plurality of the second inductive coil located in a different quadrant from the respective coil loop. An assembly according to any one of the preceding claims, wherein at least one of the tile loops consists of a combination of rectangular tiles (141) and tiles formed as a disc segment (142). Assembly according to any one of the preceding claims, wherein the first inductive coil (11) is a coil for inductive transfer of electrical energy. A base station (20) for the transfer of inductive power to a vehicle, comprising the assembly of claim 15. Vehicle assembly (10) for receiving electric energy transmitted by inductive power transmission, comprising the assembly according to claim 15. Vo 212