DE102023200929A1 - Coil structure for inductive energy transfer - Google Patents

Abstract

A coil structure for wireless energy transmission is specified, which
a base plate which supports an arrangement with a flat magnetic core material, and which further comprises a flat winding of an electrical conductor which comprises one or more wires and is arranged on the arrangement with magnetic core material, the electrical conductor comprising a material surrounding the wires which is rigid at room temperature and softened at a second temperature above room temperature, the coil structure further comprising a potting compound surrounding the flat winding.

Description

Regardless of the grammatical gender of a particular term, persons with male, female or other gender identity are included.

The invention relates to a coil structure for inductive energy transmission, which comprises a flat coil made of an electrical conductor. The invention further relates to a method for producing such a coil structure.

There are two opposing systems for recharging the accumulators of electric vehicles, commonly referred to as batteries: wired charging and wireless charging.

With wired charging, a charging cable is plugged into a corresponding socket on the vehicle and the electrical energy is transferred via cable. With wireless charging, also known as WPT for "wireless power transfer", the electrical energy is transferred inductively, i.e. via magnetic fields. It is not yet clear which charging system will prevail or whether both charging systems will exist side by side in the long term.

Wireless charging systems typically have a coil system that is used to generate an alternating magnetic field. The coil system is powered by an inverter. It is located roughly centrally in or on the floor of a charging bay so that a vehicle to be charged can park in the charging bay in the normal way. The vehicle has a suitable receiving coil arrangement in its underbody with which the electrical energy from the magnetic field can be absorbed.

Planar coils are typically used in base coil units for inductive energy transmission. A magnetic core material such as ferrite is arranged on a base plate. A holder (strand holder) is then arranged on top of this. Due to the magnetic fields, the holder is typically made of non-electrically conductive plastics. These in turn have a low thermal conductivity, which makes it difficult to dissipate heat from the coil structure.

It is the object of the invention to provide a coil structure which reduces the disadvantages mentioned at the outset. A further object is to provide a method for producing such a coil structure.

This object is achieved by a coil structure having the features specified in claim 1. A further solution consists in the method for producing the coil structure having the features of claim 10.

The coil structure according to the invention for wireless energy transmission comprises a base plate which carries an arrangement with a magnetic core material. It further comprises a flat winding of an electrical conductor which comprises one or more wires and is arranged on the arrangement with magnetic core material.

The electrical conductor comprises a material surrounding the wires that is softened at a second temperature above room temperature and below 200 °C. Finally, the coil structure comprises a potting compound surrounding the flat winding.

In the method according to the invention for producing a coil structure for wireless energy transmission, a housing with a base plate is provided,
a magnetic core material is introduced into the housing and an electrical conductor is provided.

Furthermore, the electrical conductor is heated, which softens a material surrounding the wires, the conductor is formed into a flat coil, and the conductor is cooled, which solidifies the material so that the flat coil becomes self-supporting.

Finally, the flat coil is inserted into the housing and a potting material is inserted into the housing and hardened.

The material is preferably designed in such a way that after heating to a temperature above room temperature, in particular between 100 °C and 200 °C and subsequent cooling back to room temperature, it solidifies and becomes dimensionally stable. The material is in particular a baking varnish.

The solution according to the invention advantageously eliminates the need for a carrier that carries the electrical conductor, for example a high-frequency strand, keeps it in shape and protects it mechanically. This makes the structure simpler and more cost-effective. Furthermore, the thermal connection of a casting compound to the electrical conductor is better than the thermal connection of a carrier of a known type, since the casting compound surrounds the electrical conductor on all sides in a materially bonded manner. This improves the heat dissipation of the electrical conductor.

• In einer vorteilhaften Ausgestaltung ist der Wicklungsdraht eine Litze. Die Litze ist insbesondere als Bündel von gegeneinander elektrisch isolierten Einzeldrähten ausgeführt. Die Litze kann Rundlitze sein, bei der das Bündel einen im Wesentlichen runden Querschnitt aufweist. Diese Litze ist vorteilhaft eine einfache und kostengünstige Form von Wicklungsdraht.

Advantageous embodiments of the coil structure according to the invention emerge from the dependent claims. The embodiment of the independent claims can be combined with the features of one of the subclaims or preferably also with those of several subclaims. Accordingly, the following features can also be provided:

• In an advantageous embodiment, the winding wire is a stranded wire. The stranded wire is designed in particular as a bundle of individual wires that are electrically insulated from one another. The stranded wire can be a round stranded wire, in which the bundle has a substantially round cross-section. This stranded wire is advantageously a simple and cost-effective form of winding wire.

The winding wire particularly preferably consists of a bundle of individual wires that are electrically insulated from one another, i.e. it is a high-frequency stranded wire. The high-frequency stranded wire can comprise at least 500 individual wires, in particular at least 2000 or at least 4000 individual wires. The individual wire diameters of the high-frequency stranded wire can be at most 0.1 mm, in particular at most 0.05 mm. The existing and emerging industrial standards in the field of charging electric vehicles provide for operation at frequencies in the range between 50 kHz and 100 kHz. At such frequencies, the use of high-frequency stranded wire is particularly advantageous because it has thin individual conductors with which lower line losses can be achieved than with other conductor types.

The casting compound can be an epoxy resin. These are easy to process and widely available. The properties can be advantageously adjusted by choosing the material.

The potting compound can, for example, be selected so that it has a thermal conductivity of at least 1 W/mK. This thermal conductivity is significantly higher than the approximately 0.3 W/mK of a typical plastic such as POM (polyoxymethylene), from which the strand carrier is made. This significantly improves the heat dissipation of the coil compared to solutions in which the coil is arranged in a strand carrier.

In addition to the electrical conductor, the potting compound can also enclose the magnetic core material. In other words, in this case the electrical conductor and the magnetic core material are potted together. This also improves the cooling of the magnetic core material, as it is also surrounded by the potting compound in a material-locking manner. It is useful if the potting compound has a sufficiently low viscosity of less than 1000 mPas, in particular less than 100 mPas, in the liquid state in order to be able to flow around the magnetic core material sufficiently well.

The base plate can comprise a frame into which the magnetic core material and the electrical conductor are placed and which is designed in such a way that the potting compound can be filled in so as to enclose the electrical conductor. Such a frame as an integral part of the base plate simplifies the manufacture of the coil structure.

The material, especially the baking varnish, can be heated by external heating, especially in an autoclave. In this case, the heating is uniform. Alternatively, the material can be heated by applying current to the electrical conductor.

If a base plate with a frame is used, the casting compound can be poured in and is limited by the frame when it is filled in. Alternatively, the casting compound can be injected through the frame, i.e. from the side.

• 1 eine Bodenspulen-Einheit mit einer flachen Spule als Explosionsgrafik
• 2 ein Herstellungsverfahren für die Bodenspulen-Einheit

In the following, the invention is described and explained in more detail using the embodiments shown in the figures. They show:

• 1 a ground coil unit with a flat coil as exploded view
• 2 a manufacturing process for the ground coil unit

1 shows a ground coil unit 10 according to an embodiment of the invention. Such a ground coil unit 10 serves as a transmitting station for the wireless transmission of electrical energy, for example to an electrically powered vehicle (eCar). The ground coil unit is shown in the form of an exploded diagram, since the essential elements would not be visible in the cast state.

The wireless transmission occurs inductively by means of a magnetic field that is generated by a coil 11. The coil 11 is formed from a high-frequency strand. In this example, the high-frequency strand has 2000 individual wires with an individual wire diameter of 0.05 mm.

The coil 11 is, as in 1 As can be seen, it is made up of two partial windings 111, 112. This achieves a more homogeneous magnetic field than would be possible with a single winding. The two partial windings 111, 112 run into each other, which leads to a slightly different inductance of the two partial windings 111, 112.

A base plate 12 serves as the basis and support for the construction of the base coil unit 10. In this example, the base plate 12 is made of plexiglass and includes a frame that encloses the other elements that are applied to the base plate 12. A ferrite layer 13 is placed on the base plate 12 in the frame. The ferrite layer 13 can have individual ferrite plates, in other words it can be divided.

The coil 11 is arranged on the ferrite layer 13. While in known arrangements of this type a strand carrier made of plastic is used to carry the sensitive strand and to keep it in its shape, in this embodiment a high-frequency strand is used in which the individual wires are coated with a baked enamel.

The exemplary steps used to manufacture the ground coil unit 10 are shown in 2 shown schematically.

In a first step 21, the base plate 12 is provided. In a second step 22, the ferrite layer 13 is inserted into the base plate 12.

In a third step 23, the high-frequency strand is provided with the baking varnish. In a fourth step 24, this is placed in a molded body so that it takes on the shape of the coil.

In a fifth step 25, heating takes place to, for example, 150 °C, which softens the baked enamel. The heating can take place, for example, in an autoclave or otherwise by external heating.

In a sixth step 26, a controlled and slow cooling takes place, after which the resulting coil 11 made of the high-frequency strand is self-supporting and dimensionally stable and can be removed from the molded body.

It is understood that steps 21, 22 on the one hand and steps 23 to 26 on the other hand can be carried out in parallel and no order has to be followed.

In a seventh step, the coil 11 is placed on the ferrite layer 13 in the base plate 12 or inserted into the frame. In an eighth step 28, the casting compound 14 is poured into the frame of the base plate. Once it has hardened, the process described here is complete. The base plate 12 and its frame form a basin for the casting compound 14, so that the casting compound 14, for example an epoxy resin, can be poured in without further ado. Alternatively, the casting compound 14 can also be injected from the side.

In this example, the potting compound 14 is filled in such a way that it also surrounds the ferrite layer 13. For this purpose, it is expedient if the viscosity of the potting compound 14 in the liquid state is sufficiently low to be able to penetrate through the gaps in the ferrite layer 13.

The solidified casting compound 14 protects the coil 11 from mechanical stress. The heat dissipation in this structure, in which the coil 11 is directly surrounded by the casting compound 14, is advantageously better than in a structure in which the coil 11 rests on a coil carrier.

The baking varnish is a material that is initially malleable at room temperature and softens at elevated temperatures in the range of 100 °C to 200 °C. After heating and subsequent cooling, the baking varnish solidifies.

The two partial windings 111, 112 each have two contacts 141...143, with one of the contacts 141, 142 being guided outwards in a straight line from the inner end of the partial winding 111, 112. While the partial windings 111, 112 are in principle completely flat, i.e. they form an essentially two-dimensional shape, this contact 141, 142 runs outside the plane, since it has to cross the path of the partial windings 111, 112.

To improve the magnetic properties, it is possible to provide crossing points at which the two conductors of the partial windings swap positions. At these crossing points, one or both of the conductors must also leave the plane that would otherwise be maintained.

In other designs, only a single winding can be used. In this case, there are only two contacts.

Reference symbols

10

Coil construction

11

Kitchen sink

12

Base plate

13

Ferrite layer

14

Casting compound

111, 112

Partial winding

141...143

Contact

21...28

first to eighth step

Claims (15)

Coil structure (10) for wireless energy transmission, with - a base plate (12) which carries an arrangement with a magnetic core material (13), - a flat winding (11) of an electrical conductor which comprises one or more wires and which is arranged on the arrangement with magnetic core material (13), the electrical conductor having a material surrounding the wires which is softened at a second temperature which is above room temperature and below 200 °C, - a casting compound (14) surrounding the flat winding (11). Coil structure (10) according to Claim 1 , in which the electrical conductor is a high-frequency strand. Coil structure (10) according to Claim 2 , in which the high-frequency strand comprises at least 500 individual cores, in particular at least 2000 or at least 4000. Coil structure (10) according to Claim 2 or 3 , in which the single wire diameter of the high-frequency strand is not more than 0.1 mm, in particular not more than 0.05 mm. Coil assembly (10) according to one of the preceding claims, wherein the material is a baked enamel. Coil assembly (10) according to one of the preceding claims, wherein the potting compound (14) is an epoxy resin. Coil structure (10) according to one of the preceding claims, wherein the potting compound (14) has a thermal conductivity of at least 1 W/mK. Coil structure (10) according to one of the preceding claims, wherein the potting compound (14) encloses the electrical conductor and the magnetic core material (13). Coil structure (10) according to one of the preceding claims, in which the base plate (12) comprises a frame into which the magnetic core material (13) and the electrical conductor are inserted and which is designed such that the potting compound (14) can be filled in so as to enclose the electrical conductor. Method for producing a coil structure (10) for wireless energy transmission, in which - a base plate (12) is provided, - magnetic core material (13) is introduced onto the base plate (12), - an electrical conductor is provided, - the electrical conductor is heated, whereby a material surrounding the wires is softened, - the conductor is formed into a flat coil (11), - the conductor is cooled, whereby the material solidifies so that the flat coil (11) becomes self-supporting, - the flat coil (11) is introduced onto the magnetic core material (13), - a potting compound is applied to the base plate (12) surrounding the flat coil (11) and hardened. Procedure according to Claim 10 in which the material is heated by external heating, especially in an autoclave. Procedure according to Claim 10 , in which the material is heated by energizing the electrical conductor. Method according to one of the Claims 10 until 12 , in which the potting compound (14) is applied such that it encloses the electrical conductor and the magnetic core material (13). Method according to one of the Claims 10 until 13 , in which a base plate (12) with a frame is used and the casting compound (14) is limited by the frame during filling. Method according to one of the Claims 10 until 14 , in which the casting compound (14) is injected through the frame.

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