Patent Application
20170092416
The present disclosure relates to an inductor assembly comprising at least one inductor coil, a metallic inductor housing at least partially enclosing the inductor coil, and a potting material both contacting the inductor coil and the inductor housing and thermally coupling the inductor coil to the inductor housing.
The electric insulation covering the outer circumference of the inductor winding may be a separate electric insulation, like for example an electrically insulating foil wound around the outer circumference of the inductor winding. The electric insulation covering the outer circumference of the inductor winding, however, may also be provided by an electric insulation wound on the bobbin together with the electric conductor, if this electric insulation of the electric conductor is of a sufficient strength. Often, the electric conductor wound on the bobbin of an inductor coil is provided with a thin layer of an electrically insulating lacquer. Such an electrically insulating lacquer will only be sufficient for providing a sufficient electric insulation of the inductor winding towards each other but not towards the metallic inductor housing. Thus, a separate electric insulation covering the outer circumference of the inductor winding is required.
The metallic housing of the inductor assembly is pot-shaped to receive the potting material. At the open side of the pot-shaped metallic housing, the inductor assembly may end with the potting material at least partially enclosing the inductor coil within the metallic housing, or it may be closed by a metallic closure plate or any other kind of metallic closure.
An inductor assembly as defined at the beginning may, for example, be used as an AC or DC choke, as an AC or DC filter, or as an electric energy storage inductor, for example. In any of these applications, it is required to electrically insulate the inductor winding from the metallic inductor housing. Often, it is also a requirement to electrically insulate the inductor winding from a magnetic core of the inductor assembly on which the bobbin of the at least one inductor coil is arranged. On the other hand, a good thermal coupling of the inductor housing to the inductor coil, and the magnetic core, respectively, is needed to dissipate heat generated both in the inductor coil and the magnetic core by an electric current flowing through the inductor coil. Thus, there are divergent requirements to the potting material, as a potting material providing a good electric insulation normally does not provide for a good thermal coupling. Additionally, potting materials comprising an electrically insulating resin matrix, like for example polyurethane, epoxy or silicone resin, and a filler of thermally conductive particles, like for example ceramic, quartz, AlN or BN particles, to meet both requirements, often display a large viscosity in their fluid state due to the filler. Thus, they are not suited to fill small gaps between the inductor coil and the metallic housing without forming voids. Voids in the potting material, however, reduce the thermal coupling of the inductor coil to the metallic housing and may trigger a breakdown of the electric insulation between the inductor winding and the metallic housing. A breakdown of the electric insulation between the inductor winding and the metallic housing in addition may also be triggered by the filler of thermally conductive particles inside the resin matrix. This is often the case at regions, where a mean distance between the thermally conductive particles is relatively small. Within a typical bulk volume of the potting material at the inside of the metallic housing the distribution of the thermally conductive particles is not ideally homogeneous. Moreover, it varies due to agglomerates, which may be generated during the potting process in particular at small gaps, for instance between the inductor winding and the metallic housing. Within these agglomerates the mean distance between the thermally conductive particles is relatively small and therefore the risk of triggering an electric breakdown is relatively high. Therefore, the thermally conductive filler typically jeopardizes an electric insulation capability of the potting material. Additionally, with small distances between the inductor coil and the metallic housing, it is required to exactly position the inductor coil within the metallic housing so that all gaps between the inductor coil and the metallic housing to be filled with the potting material have a uniform width.
US 2013/0265129 A1 discloses an electromagnetic device including a transformer assembly. The transformer assembly has a core, windings, and a housing disposed around at least a portion of the core and the windings. An enclosure at least partially encloses the transformer assembly. The transformer assembly is mounted to a first portion of the enclosure such that heat is transferred from the transformer assembly to the first portion of the enclosure. A second portion of the enclosure has an extension extending therefrom such that the extension is placed in a thermal contact with the transformer assembly to transfer heat from the transformer assembly to the extension.
DE 10 2011 076 227 A1 discloses an inductive component, like for example a choke, which is used for smoothing the voltage in an electric conductor. The inductive component has an inductor coil comprising at least one inductor winding of an electric wire conductor. The inductor coil is contained in a housing. A thermally conductive pad is arranged between the inductor coil and the housing. The pad may be a thermal pad or it may be made of a phase change material, a material of gel-like consistence or a gap filler material.
WO 2005/052964 A1 discloses a heat conducting bridge for toroidal core inductive resistors. A toroidal core is encircled by at least one winding. A heat conducting bridge is formed by a base element and an element extending from the base element into the center of the toroidal core so that the toroidal core is placed around this element. The base element closes a pot-shaped housing in which the toroidal core is enclosed by a potting material.
DE 35 22 740 A1 discloses a further transformer or choke comprising a toroidal core. Here, a heat conducting element extending into the center of the toroidal core extends from a metallic housing in which the toroidal core and a winding on the toroidal core are enclosed by a granulate material, e.g. quartz sand. The metallic housing comprises cooling ribs for dissipating heat from the winding and the toroidal core.
DE 198 14 897 A1 discloses an inductive component for high powers in which a toroidal core with a winding is arranged in a pot-shaped housing and embedded in a potting material. From the housing, a heat pipe extends into the center of the toroidal core.
Another inductive component comprising a toroidal core and a winding enclosed by a potting material within a metallic housing is known from DE 94 06 996 U1. Here, an element of the housing extending into the center of the toroidal core comprises ring-shaped ribs increasing the surface of this heat transferring element towards the potting material made of resin.
U.S. Pat. No. 4,000,483 A discloses a transformer comprising a laminated magnetic core, an electrically insulating plastic bobbin on which a primary coil is wound, an electrically insulating plastic bobbin on which a secondary coil is wound, and two interengaging electrically insulating plastic covers which enclose the primary coil and provide additional electric insulation between the primary coil and the laminated magnetic core and between the primary and secondary coil. The plastic components are formed to provide 2 mm of electric insulation between the primary and secondary coils, and between the primary coil and the laminated magnetic core. The plastic components are arranged to provide at least 10 mm of creepage distance between the primary and secondary coils and at least 8 mm between the primary coil and the laminated magnetic core. The insulation provided shall allow for mounting the laminated magnetic core directly on the metal frame of an appliance.
US 2008/0079525 A1 discloses an in-line filament transformer for a vacuum device. The filament transformer comprises a core, a primary winding and a secondary winding wound around the core. The secondary winding is biased at a high voltage, and the primary winding is placed in line with the secondary winding. The primary winding and the secondary winding are incorporated in separate bobbins or in a common bobbin. A creepage distance between the primary winding and the secondary winding is provided by a distance between bobbin sections incorporating the primary and the secondary winding. Further, a shield in a primary section of the bobbin is provided for shielding the primary winding from the secondary winding. This shield may be in the form of a shield winding of thin wires. An outer circumference of the secondary winding incorporated within a secondary bobbin section is enclosed by an insulation. Towards a magnetic core, the insulation may be made of an insulating sheet bent in the form of a “C” or of a cap made of an electrically insulating polymeric material. This sheet or cap is anchored in free bobbin sections on both sides of the secondary bobbin section incorporating the secondary winding.
There still is a need of an inductor assembly in which an inductor coil is effectively thermally coupled to but electrically insulated from an inductor housing and which is nevertheless produced at low cost.
An inductor assembly according to the present disclosure comprises at least one inductor coil, a metallic inductor housing at least partially enclosing the inductor coil, and a potting material both contacting the inductor coil and the inductor housing and thermally coupling the inductor coil to the inductor housing. The inductor coil includes a bobbin made of electrically insulating material and an inductor winding made of an electric conductor wound on the bobbin. The inductor winding has an outer circumference and two end faces. An electric insulation covers the outer circumference of the inductor winding. Coil lids also made of electrically insulating material at least partially cover the end faces of the inductor winding and adjacent areas of the electric insulation covering the outer circumference of the inductor winding such that a distance of any point of the end faces of the inductor winding to the metallic housing along any way not passing through the electrically insulating material of the coil lids or the bobbin is at least a required minimum creepage distance.
The disclosure is based on the finding that critical points with regard to the electric insulation between the inductor coil and the metallic inductor housing are those points of the end faces of the inductor winding of the inductor coil which are closest to the metallic inductor housing. Even if these end faces are as such covered by flanges of the bobbin on which the inductor winding is wound, and if the inductor winding, at its outer circumference, is covered by the electric insulation, there will be points of the end faces of the inductor winding which are very close to the metallic inductor housing. Independently on the potting material, the present disclosure ensures that no breakdown of the electric insulation between the inductor coil and the metallic inductor housing takes place at these points by providing the coil lids. These coil lids by at least partially covering the end faces of the inductor winding and adjacent areas of the electric insulation covering the outer circumference of the inductor winding ensure that the required minimum creepage distance is kept between the end faces of the inductor winding and the metallic inductor housing. Here, the relevant ways from the end faces of the inductor winding to the metallic inductor housing are only those not passing through the electrically insulating material of the coil lids or the bobbin, assuming that the electrically insulating material of the coil lids and the bobbin is of a sufficient dielectric strength. Therefore, in the inductor assembly according the present disclosure the design of the coil lids, in particular their overlap with adjacent areas of the electric insulation covering the outer circumference of the inductor winding, influences the creepage distance between the inductor coil and the metallic inductor housing. This in turn generates an option to a targeted modification of the creepage distance via a variation of the coil lid design without a significant increase of an installation space required by the inductor assembly. This will be explained in more detail in the following Figures.
Keeping the required minimum creepage distance, i. e. the minimum distance along insulator surfaces between the end faces of the inductor winding and the metallic inductor housing will ensure that a minimum clearance distance, i. e. a distance via any path through the air is also kept between the end faces of the inductor winding and the metallic inductor, if there is any such path through air in the inductor assembly according to the present disclosure at all.
The present disclosure does not rely on any dielectric strength of the potting material. Instead, by keeping the minimum creepage distances for all points of the end faces of the inductor winding, the potting material only provides an additional electric insulation. Further, keeping the minimum creepage distance by means of the coil lids means that the inductor winding as such may be arranged at a very small distance to the metallic inductor housing. As a result, the small distance between the inductor winding and the metallic inductor housing provides for a good thermal coupling between these components. The present disclosure also does not—at least not significantly—rely on a thermal conductivity of the potting material. This is due to the fact, that the inductor assembly of the present disclosure provides a significant heat transfer to the metallic inductor housing via paths not directed through the potting material, but through heat transfer enhancing interfaces as will be explained in more detail in the following. Therefore, the potting material does not necessarily need a filler of thermally conductive particles in order to provide a sufficient thermal conductivity of the potting material. Without the filler of thermally conductive particles within the potting material the risk of a dielectric breakdown triggered by that filler is eliminated, too. In addition, the potting material typically is cheaper in case it does not have to provide a sufficient thermal conductivity.
Additionally, the coil lids, in several aspects, may aid in producing the inductor assembly of the present disclosure. One of these aspects is arranging the inductor coil with regard to the metallic inductor housing. Another aspect is arranging the inductor coil with regard to other inductor coils and/or a magnetic core of the inductor assembly.
In the inductor assembly according to the present disclosure, the potting material may, for example, be optimized for a low viscosity in its fluid state so that even small gaps between the inductor coil and the metallic inductor housing are securely filled. Due to the small width of these gaps, the thermal conductivity of the potting material is not as important as in case of wider gaps. Of course, one may optimize the gap width and the thermal conductivity of the potting material for an optimum thermal coupling of the inductor coil to the metallic inductor housing considering the cost of the potting material and of the step of filling it into the metallic inductor housing.
In addition to keeping a required minimum creepage distance between all points of the end faces of the inductor winding towards the metallic inductor housing, this required minimum creepage distance may also be kept towards a magnetic core on which the bobbin of the inductor coil is arranged.
The value of the required minimum creepage distance will depend on the actual application of the inductor assembly and several parameters like; e.g., the potential difference between respective components, the impurities within and at the surface of the potting material and/or the environmental conditions which are present during the operation of the respective components typically have to be considered. Suitable values of the required minimum creepage distance are known to those skilled in the art. For example, the absolute value of the required minimum creepage distance between an uninsulated live component and the walls of a metal enclosure may be 1.6 mm, 6.4 mm or 12.7 mm depending on peak values of the potential difference between the component and the metal enclosure.
In the inductor assembly according to the present disclosure, the coil lids may actually contact the metallic inductor housing. In this way, they may be used for aligning the inductor coil within the metallic inductor housing prior to filling in the potting material, for example.
In the inductor assembly according to one embodiment of the present disclosure, the coil lids—or the coil lids together with the bobbin—may completely cover the end faces of the inductor winding, to electrically insulate the entire end faces by the electrically insulating material of the coil lids and the bobbin. It is clear that the coil lids and the bobbin will have to overlap to provide the required minimum creepage distance between the end faces and all points at the outside of this cover. In such an embodiment, an electric contact between the electric conductor of the inductor winding and outer electric or electronic components can be routed between the coil lid and the electric insulation covering the outer circumference of the inductor winding.
In another embodiment of the present disclosure, the coil lids or the coil lids together with the bobbin completely cover the end faces of the inductor winding only except of an electric contact window providing access to the inductor winding. This electric contact window may particularly be used for connecting the electric conductor of the inductor winding to outer electric or electronic components within an appliance in which the inductor assembly according to the present disclosure is used. It is clear that a distance of any point of the electric contact window to the metallic housing, and the magnetic core, if provided, along any path not passing through the electrically insulating material of the coil lids or of the bobbin is also at least the required minimum creepage distance.
This creepage distance of the electric contact window may, for example, be provided in that the electric contact window, particularly towards the magnetic core, is at least partially framed by continuous ribs of the bobbin extending through an opening in the adjacent coil lid. Alternatively or additionally, the electric contact window may be shielded, particularly towards the metallic housing, by a rib of the adjacent coil lid.
In the inductor assembly according to the present disclosure, the coil lids cover areas of the electric insulation covering the outer circumference of the inductor winding that are adjacent to the end faces of the inductor winding. This, however, does not mean that the coil lids completely cover the entire electric insulation covering the outer circumference of the inductor winding. Instead, the coil lids particularly do not cover those areas of the electric insulation which are not close to the end faces but close to the metallic inductor housing. Thus, these uncovered areas of the electric insulation are not thermally decoupled from the metallic inductor housing by the electric insulation material of the coil lids but may be particularly well thermally coupled to the metallic inductor housing for a quick transfer of heat from the inductor winding to the metallic inductor housing. In particular, the thermal coupling can be realized via a direct contact of the uncovered areas of the electric insulation with a heat transfer enhancing element concurrently thermally coupled to the metallic inductor housing.
In one embodiment of the inductor assembly according to the present disclosure, the electric insulation of the outer circumference of the inductor winding is provided by a continuous insulation foil enclosing the outer circumference of the inductor winding. The electric conductor winding may be a conductor foil, and the conductor foil may be wound on the bobbin together with the insulation foil in such a way that the insulation foil extends beyond the conductor foil in axial direction, i.e. at both end faces of the inductor winding, in order to prevent a short circuit of adjacent layers of the inductor winding. The continuous insulation foil may, however, also enclose an inductor winding made of a lacquered electric conductor like for example a lacquered wire. In lower temperature applications, the insulation foil may be a thermoplastic tape of polyvinylchloride, polyethylene or rubber. In higher temperature applications, the insulation foil may be an insulation paper. The thicknesses of a suitable insulation foil will typically be in a range from 25 □m to 100 □m.
To enhance the heat transfer from the outer circumference of the inductor winding to the metallic inductor housing, at least one heat transfer enhancing interface may be provided between an area of the electric insulation covering the outer circumference of the inductor winding—and not covered by the coil lids—, and the metallic inductor housing. This heat transfer enhancing interface may, for example, comprise a metallic belly band wound around the circumference of the inductor winding. Alternatively or additionally, the heat transfer enhancing interface may be of a “C” shape only covering those three sides of the outer circumference of the inductor winding facing inner surfaces of a pot-shaped metallic inductor housing. Alternatively to a metallic belly band also a belly band made out of another material with good thermal conductivity can be used.
When the bobbin of the inductor coil is arranged on a magnetic core, there may, additionally or alternatively, at least be one heat transfer enhancing interface provided between an area of the magnetic core and the metallic inductor housing. If, during an operation of the inductor assembly no potential difference occurs between the metallic inductor housing and the magnetic core, like this is the case, e.g., with a PE-grounded metallic inductor housing and a PE-grounded magnetic core, the at least one heat transfer enhancing interface advantageously can be a metallic element, which directly contacts the magnetic core and the metallic inductor housing and therefore provides an electrical conductivity between the magnetic core and the metallic inductor housing. If, on the other hand, during an operation of the inductor assembly a potential difference between the metallic inductor housing and the magnetic core occurs, an indirect contact ensuring a good thermal coupling is advantageously combined with a sufficient electric insulation between both components. Such an indirect contact prevents an electric connection between the metallic inductor housing and the magnetic core and can be provided by a thin insulation layer like, e.g. a lacquer or a thin insulation foil covering the outer surface of the magnetic core and/or the metallic inductor housing. A small gap between both components, advantageously filled with potting material, can also be used. When the bobbins of two inductor coils are coaxially arranged on the magnetic core, the at least one heat transfer enhancing interface may extend into an axial gap between the facing end faces of the inductor windings of the two inductor coils.
When the bobbins of two inductor coils are arranged on parallel legs of a magnetic core, i. e. side by side, a heat transfer enhancing interface may—alternatively or additionally—be provided between facing areas of the electric insulations covering the outer circumferences of the inductor windings of the two inductor coils. Such a heat transfer enhancing interface is typically plate-shaped.
In the inductor assembly according to the present disclosure, any heat transfer enhancing interface may either be a protrusion or extension of the metallic housing or a separate element located within the metallic inductor housing. Such a separate element may, nevertheless, be attached, mounted or bonded to the metallic inductor housing, or it may be attached, mounted or bonded to the inductor coil or any component placed in the metallic inductor housing together with the inductor coil. For example, it may be a C-shaped element clipped onto the electric insulation covering the outer circumference of the inductor winding of the inductor coil. The material of the separate element may be any material of high thermal conductivity including insulators like, for example, aluminium nitride, aluminium oxide and diamond, and electrical conductors like, for example, aluminium, copper, brass, graphite, etc., or even iron if additional magnetic parameters are desired.
In the inductor assembly of the present disclosure, the two end faces of the inductor winding of each inductor coil are covered by two separate coil lids. However, these two coil lids may also cover the end faces of a second inductor coil arranged side by side with the at least one inductor coil. The facing end faces of two adjacent inductor windings of two coaxially arranged inductor coils, on the other hand, will be covered by two separate coil lids. The separate coil lids, however, may be configured such as to mutually engage each other in a predefined way such as to align the two coaxially arranged inductor coils and/or to keep a predefined distance between them, for example. They may also be configured to hold a section or leg of a magnetic core of the inductor assembly.
Advantageous developments of the disclosure result from the claims, the description and the drawings. The advantages of features and of combinations of a plurality of features mentioned at the beginning of the description only serve as examples and may be used alternatively or cumulatively without the necessity of embodiments according to the disclosure having to obtain these advantages. Without changing the scope of protection as defined by the enclosed claims, the following applies with respect to the disclosure of the original application and the patent: further features may be taken from the drawings, in particular from the illustrated designs and the dimensions of a plurality of components with respect to one another as well as from their relative arrangement and their operative connection. The combination of features of different embodiments of the disclosure or of features of different claims independent of the chosen references of the claims is also possible, and it is motivated herewith. This also relates to features which are illustrated in separate drawings, or which are mentioned when describing them. These features may also be combined with features of different claims. Furthermore, it is possible that further embodiments of the disclosure do not have the features mentioned in the claims.
The number of the features mentioned in the claims and in the description is to be understood to cover this exact number and a greater number than the mentioned number without having to explicitly use the adverb “at least”. For example, if an inductor coil is mentioned, this is to be understood such that there is exactly one inductor coil or there are two inductor coils or more inductor coils. Additional features may be added to these features, or these features may be the only features of the respective product.
The reference signs contained in the claims are not limiting the extent of the matter protected by the claims. Their sole function is to make the claims easier to understand.
In the following, the disclosure is further explained and described with respect to the example embodiments illustrated in the drawings.
The present disclosure relates to an inductor assembly comprising at least one inductor coil, a metallic inductor housing at least partially enclosing the inductor coil, and a potting material both contacting the inductor coil and the inductor housing and thermally coupling the inductor coil to the inductor housing. More particular, the present disclosure relates to such an inductor assembly in which the at least one inductor coil includes a bobbin made of electrically insulating material and an inductor winding made of an electric conductor wound on the bobbin, wherein the inductor winding has an outer circumference and two end faces, and wherein an electric insulation covers the outer circumference of the inductor winding.
The end faces of the inductor windings 4 of each pair of inductor coils 3 arranged side by side on one parallel pair of longitudinal sections of the magnetic core are covered by a pair of coil lids 11 made of electrically insulating material which may be the same as an electrically insulating material of the bobbins of the inductor coils 3. The coil lids 11 also cover areas of the outer circumferences of the inductor windings 4 covered by the electric insulation 5. The coil lids 11 thus ensure that all points of the end faces of the inductor windings 4 keep a required minimum creepage distance and also a minimum clearance distance to the metallic inductor housing 2. Together with the bobbins carrying the inductor windings 4, the coil lids 11 also ensure that the required minimum creepage distance and the minimum clearance distance is kept with regard to the magnetic core 6, particularly with regard to the perpendicular segments 7 of the magnetic core 6.
The coil lids 11, however, do not cover a main part of the electric insulation 5 and thus of the outer circumference of the inductor windings 4. Instead, heat transfer enhancing interfaces 12 thermally couple this main part of the outer circumference of the inductor windings 4 which remains uncovered by the coil lids 11 to the metallic inductor housing 2. Further heat transfer enhancing interfaces 13 extend between each pair of coaxially arranged inductor coils 3 to thermally couple the magnetic core 6 to the metallic inductor housing 2. Additional heat transfer enhancing interfaces 14 extend between the facing outer circumferences of the inductor windings 4 of each pair of inductor coils 3 arranged side by side and thermally couple the adjacent areas of the outer circumferences of the inductor windings 4 to the bottom of the metallic inductor housing 2. The pulling screws 8 extend through and fix these heat transfer enhancing interfaces 14. The coil lids 11 comprise core holding extensions 15 partially enclosing and thus holding the perpendicular sections 7 of the magnetic core 6. The core holding extensions 15 of facing coil lids 11 covering the end faces of axially neighboring inductor coils 3 are configured in such a way that they mutually overlap in axial direction. By designing dedicated form fitting elements on the core holding extensions 15 it is also possible to ensure a predefined distance between axially neighboring inductor coils 3.
The inductor assembly 1 according to
The inductor housing 2 separately depicted in
The perspective bottom view according to
The embodiment of the inductor assembly 1 according to
In
The embodiment of the inductor assembly 1 according to
The creepage distance between two electric-conductor-parts typically is the shortest distance of any possible surface oriented path between these electric-conductor-parts not passing through any insulating bulk material but along insulator surfaces. In
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In the embodiment of the inductor coil 3 of
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| Number | Date | Country | Kind |
|---|---|---|---|
| 14173136.4 | Jun 2014 | EP | regional |
This application claims priority to International Patent Application number PCT/EP2015/06331, filed on Jun. 15, 2015, which claims priority to European Patent Application number 14173136.4, filed on Jun. 19, 2014, and is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2015/006331 | Jun 2015 | US |
| Child | 15375264 | US |
