DE102022210135A1 - Transformer for a DC-DC converter - Google Patents

Abstract

A transformer (200) for mounting on a circuit board (205) comprises a primary winding (215) and a secondary winding (220), which are wound coaxially around a common, straight winding axis (235), the winding axis (235) being parallel to the circuit board (235). 205) is oriented.

Description

The present invention relates to a DC-DC converter in a motor vehicle. In particular, the invention relates to a transformer in such a DC-DC converter.

A motor vehicle includes an electric drive train with a battery, a power converter and an electric drive machine. The current converter is set up to convert a direct voltage provided by the battery into a plurality of mutually phase-shifted alternating currents for the drive machine in order to control a torque provided by the machine or a speed adopted.

An electrical system on board the motor vehicle is traditionally operated with a direct voltage of approximately 12 V. This means that consumers on board the motor vehicle can be supplied with energy, for example various control devices or lighting devices or an entertainment or communication system. In order to supply the on-board electrical system with electrical energy from the battery, a DC-DC converter is required. A voltage provided by the battery is usually around 400 or around 800 V, so a large voltage difference has to be bridged with a single-stage conversion.

The DC-DC converter should be compact and efficient, cost-effective and thermally stable. Active and passive electronic components are used for conversion, which are usually arranged on a circuit board. Many well-known DC-DC converters use a planar transformer in which a secondary winding is designed as a conductor track on the circuit board. Heat that arises on the conductor tracks when operating such a transformer is usually difficult to dissipate. Other transformers available for DC-DC applications use a primary winding made of high-frequency stranded wire, which is more expensive and difficult to process than solid wire. In addition, several connections to a housing or a heat sink often have to be provided to dissipate the heat generated, so that installation or service can be complex.

An object underlying the present invention is to provide an improved transformer, an improved transformer arrangement, an improved DC-DC converter and an improved method for providing a transformer. The invention solves this problem by means of the subject matter of the independent claims. In addition, an improved motor vehicle is specified. Subclaims give preferred embodiments.

According to a first aspect of the present invention, a transformer for mounting on a circuit board includes a primary winding and a secondary winding coaxially wound around a common, straight winding axis, the winding axis being oriented parallel to the circuit board.

Due to the winding axis being parallel to the circuit board, the primary winding and the secondary winding can be attached to one another in an improved manner. A thermal coupling between the windings can be improved, so that heat that occurs in the area of one of the coils during operation of the transformer can be better dissipated to the outside.

In a particularly preferred embodiment, the transformer is set up to transmit electrical energy at a frequency of approximately 80 - 120 kHz. In particular, the transformer can be set up for use in a DC-DC converter. A ratio of an input voltage to an output voltage of the DC-DC converter can be large, so that a turns ratio between the primary winding and the secondary winding can also be large. The frequency used for conversion can be generated using an external circuit and is preferably chosen so that efficient conversion is possible with inexpensive and easy-to-use components.

The secondary winding can be formed from a sheet of metal. The sheet metal can conduct a large current and only heat up slightly to moderately. Due to the large surface area, any heat that occurs can be easily dissipated into the surroundings. The sheet metal can be of a simple shape and the secondary winding can be easily manufactured and handled independently before being mounted on the transformer.

The finished transformer can form a complete, independent component that can be used directly in a circuit. This makes it easier for the transformer to be used in an electrical or electronic circuit. The circuit board (circuit board) preferably does not form an integral component of the transformer, so that the circuit board or a layout of conductor tracks located thereon can be easily developed independently of the transformer.

The secondary winding preferably comprises no more than one turn. This allows the transformer to be adapted to a circuit, which requires a large conversion ratio. Such a requirement may exist in particular on a DC-DC converter on board a motor vehicle. In a first variant, the secondary winding is U-shaped and can comprise less than one complete turn. This design is particularly easy to assemble and can support attachment of the secondary winding to the primary winding in such a way that the coils are thermally coupled to one another. In a second variant, the secondary winding is O-shaped and comprises practically exactly one full turn. Terminals of the secondary winding may extend perpendicular to a plane in which the O-shape is formed. To scale the transformer, the material thickness of the secondary winding can be increased or decreased.

The primary winding is further preferably wound from a solid conductor. The conductor is preferably electrically insulated radially on the outside and can be, for example, a copper wire or a lacquered copper wire. Due to the good heat dissipation of the transformer due to its design, the use of a high-frequency stranded wire may not be necessary. A high-frequency stranded wire comprises a large number of fine, mutually insulated wires that are interwoven in a predetermined manner. The solid conductor is less expensive and can be installed much more easily. For example, removing the insulation at the end of the conductor in order to connect it electrically can be much easier than with a high-frequency stranded wire. This can reduce the production and handling costs of the transformer. To scale the transformer, the number of turns or the wire cross-section of the primary winding can be increased or decreased.

More preferably, the primary winding is located radially on the inside and the secondary winding is located radially on the outside of the transformer. Due to its closed surface, the secondary winding can absorb heat from the primary winding radially on the inside and release it radially on the outside to an environment. A conductor of the secondary winding preferably comprises a stronger material than a conductor of the primary winding, so that the secondary winding is more durable. The secondary winding can protect the primary winding mechanically, for example against accidental damage during manufacture or assembly of the transformer.

It is particularly preferred that the primary winding is thermally coupled to the secondary winding. In a first embodiment, the transformer can for this purpose comprise a thermal coupling material that lies between the coils. The thermal interface material (TIM) may comprise any thermally conductive material, such as a paste, an adhesive, a filler, a sheet material, an adhesive tape, or a phase change material (PCM). The TIM is designed to fit as closely as possible to a surface of an adjacent material in order to keep thermal resistance low. Pores or unevenness in the adjacent material can be closed or bridged. The TIM can be inserted or filled into a radial gap between the coils.

In a second embodiment, the primary winding and the secondary winding can at least partially rest against each other in order to ensure good heat transfer. A carrier to which the coils are attached can have a recess in an area between the coils to promote heat transfer. the two embodiments can advantageously be connected to one another. For example, a liquid or pasty TIM can pass through a recess to further improve the thermal contact between the coils.

The transformer can further comprise an external transformer core. The transformer core is preferably designed as a shell core and can be made from a material such as ferrite. A magnetic field of the transformer can thus have improved low-scattering. Because the primary and secondary windings lie flat against one another, the transformer's leakage inductance can be low. Due to the flat structure, a capacitive coupling between the primary and secondary coils can be increased. Conversely, external electric or magnetic fields can be better kept away from currents flowing in the coils. The electromagnetic compatibility of the transformer or a device constructed with it can be improved. The transformer core can have good thermal conductivity, so that any heat that occurs can be easily dissipated to an external element or environment. A surface of the transformer core can be shaped in such a way that heat transfer to another element is promoted.

The transformer core is preferably in two parts so that it can be easily assembled onto the adjacent windings. The parts are also preferably identical in shape so that the transformer core can be manufactured from two identical parts. Inventory and assembly costs can thus be kept low.

According to a further aspect of the present invention, a method of manufacturing a transformer adapted to be mounted on a circuit board includes steps of axial mounting pushing a finished, straight primary winding onto a carrier; and pushing a fully wound, straight secondary winding onto the carrier such that the coils are coaxial and wound around a common winding axis that is straight and oriented parallel to the circuit board. Depending on the shape of the secondary winding, it can also be attached axially along the winding axis or in a direction perpendicular to the winding axis.

A transformer described herein can be easily manufactured using the method and does not require any special joining or assembly techniques. Features or advantages of the method and the transformer may be mutually transferable.

A thermal coupling material can be applied between the primary winding and the secondary winding. For example, a pasty TIM can be used, which is introduced between the coils during assembly. In particular, the TIM can be provided on the carrier or on one of the coils before the coils are attached to each other or to the carrier. By axially pushing the coils into or onto the carrier, the TIM can advantageously be evenly distributed and penetrate into a gap or unevenness. Excess TIM can be easily removed after pushing on. In another embodiment, for example, a plate-shaped TIM can also be used, which is easier to handle and does not need to be further processed after the coils have been attached.

According to yet another aspect of the present invention, a transformer assembly includes a transformer described herein and a cooling element, the cooling element having a recess to receive a portion of the transformer remote from the circuit board. A TIM can also be provided between the transformer and the cooling element. More preferably, the TIM used is pasty at the time of assembly, so that it can better fill a space between the recess and the transformer. It is preferred that the cooling element lies parallel to the circuit board. In a further embodiment, a flat cooling element without a recess can also be provided, which rests on the transformer. The cooling element can comprise a heat sink, a closed fluid channel for a cooling fluid or a housing of a circuit in which the transformer is inserted.

According to yet another aspect of the present invention, a DC-DC converter, in particular for use on board an electrically driven motor vehicle, comprises a transformer described herein or a transformer arrangement described herein. The DC-DC converter is preferably set up to convert a high DC voltage of approximately 400 or approximately 800 V into a significantly lower on-board voltage of, for example, approximately 12 V, approximately 24 V or approximately 48 V. Any converter circuit that requires a transformer can be used for this purpose. In particular, the DC-DC converter can be designed as a push-pull converter, for example with half-bridge or full-bridge control. Other converter principles are also conceivable.

According to yet another aspect of the present invention, a motor vehicle comprises an electrical energy storage device, an electric drive machine and a DC-DC converter described herein. The energy storage is set up to provide a driving voltage for the electric drive machine and the DC-DC converter is set up to feed a low-voltage vehicle electrical system. The motor vehicle can in particular include a motor vehicle, a passenger car, a truck or a bus.

• 1 ein Kraftfahrzeug mit einem Gleichstromwandler;
• 2 einen Transformator in einer ersten Ausführungsform;
• 3 ein erstes Verfahren zur Herstellung eines Transformators;
• 4 weitere Ansichten eines Transformators;
• 5 einen Transformator in einer zweiten Ausführungsform;
• 6 ein zweites Verfahren zur Herstellung eines Transformators; und
• 7 weitere Ansichten eines Transformators

darstellt.The invention will now be described in more detail with reference to the accompanying figures, in which:

• 1 a motor vehicle with a DC converter;
• 2 a transformer in a first embodiment;
• 3 a first method for producing a transformer;
• 4 further views of a transformer;
• 5 a transformer in a second embodiment;
• 6 a second method of manufacturing a transformer; and
• 7 further views of a transformer

represents.

1 shows in an upper area a system 100 with a motor vehicle 105. The motor vehicle 105 includes a drive train 110, which includes an electric drive machine 115, which is fed from a battery 125 by means of a current converter 120. The battery 125 is designed as a high-voltage battery and usually has a nominal voltage of several 100 volts. For example, the battery 125 on a mid-range vehicle 105 can provide approximately 400 V and the Battery on a sedan or sports car approx. 800 V.

In addition, the motor vehicle 105 has an on-board electrical system 125, which is symbolically shown as an interface. One or more electrical consumers can be connected to the on-board network 125 and can be operated on board the motor vehicle 105. Example consumers include actuators, control devices, a lighting system, interior lighting or even sensors. The vehicle electrical system 125 can be powered from the battery 125 by a DC-DC converter 130. A nominal voltage of the vehicle electrical system 125 is usually approximately 12 V or a small integer multiple thereof. The DC-DC converter 120 is set up to reduce a DC voltage provided by the battery 125 to the nominal voltage of the vehicle electrical system 125. A usable power can be in the range of several 100 watts to several kW.

The DC-DC converter 120 can operate in any manner, for example as a forward converter, a flyback converter, or a resonant converter. In a preferred embodiment, the DC-DC converter 120 is designed as a push-pull converter. In a lower area of 1 a basic circuit diagram of the DC-DC converter 120 is shown in an exemplary embodiment with full-bridge control. In another embodiment, the push-pull flux converter could also be designed using a half bridge or with a parallel feed. In the middle of the circuit diagram you can see a transformer, the advantageous design of which is described in more detail here.

2 shows an exploded view of a transformer 200 for a DC-DC converter 120 in a first embodiment. The transformer 200 is designed to be attached to a circuit board 205 and optionally to a cooling element 210. The circuit board 205 and the cooling element 210 or a surface facing the circuit board 205 preferably run parallel to one another.

The transformer 200 includes a primary winding 215 and a secondary winding 220, which are preferably attached to a carrier 225. In the illustrated embodiment, the carrier 225 can be closed on one side by means of a separate closure element 230 after the coils 215, 220 are attached to it. The carrier 225 can be made from a plastic, for example by injection molding.

The coils 215, 220 are wound around a common winding axis 235, which preferably extends parallel to the circuit board 205 when the transformer 200 is attached to the circuit board 205. Ends of the secondary winding 220 preferably extend laterally away from the transformer 200, so that the transformer can be flexibly placed relative to a power semiconductor of the DC-DC converter 130. Ends of the primary winding 215 and the secondary winding 220 preferably point in the same direction. Ends of the primary winding 215 or the secondary winding 220 can be attached to the circuit board 205, for example using a through-hole method, or on its surface (surface mounted) and electrically contacted. Alternatively, one of the windings 215, 220 can be contacted by means of a welded or screwed connection. In further embodiments, the windings 215 or 220 can, for example, also be provided for connection to cables or assembled with cables, or the transformer 200 can be provided with a plug contact for electrical connection.

The primary winding 215 typically includes multiple turns, which are preferably wound from a solid conductor, which may include, for example, a copper wire. In the representation of 2 the copper wire has a round cross-section and the primary winding 215 is wound in one layer; In other embodiments, a different conductor cross section and/or a multi-layer structure can also be selected. A cross section of the primary winding 215 is also, for example, essentially rectangular, but in another embodiment it can also be, for example, round or oval.

The secondary winding 220 is also wound from a solid conductor, but preferably from a sheet metal. The secondary winding 220 may comprise no more than one turn and in the embodiment shown, the secondary winding 220 is U-shaped with less than one turn. Ends of the secondary winding 220 are cut narrower to facilitate mounting on the circuit board 205.

After the transformer 200 has been assembled, the secondary winding 220 is arranged concentrically to the primary winding 215 and radially on the outside. To improve heat transfer between the coils 215, 220, a first thermal coupling material TIM 240 can be provided. The first TIM 240 is, for example, plate-shaped and is located between the two upward-pointing legs of the U-shaped sheet metal, which forms the secondary winding 220. In another embodiment, for example, a liquid or pasty first TIM 240 can be used.

The carrier 225 with the end element 230 is preferably designed to carry an external transformer core 245. The transformer core 245 is preferably designed in two parts, although in one embodiment both parts can be shaped the same. The transformer core 245 can preferably be made from a ferrite. If the transformer core 245 is attached to the carrier 225, it includes a middle leg which extends along the winding axis 235 through the primary winding 215 and the secondary winding 220, as well as two further legs which are on different sides of the middle leg and outside the coils 215 and 220 lie.

A fastening device 250 can be formed on the carrier 225 in order to attach the transformer 200, for example, to the circuit board 205 or the cooling element 210. In the exemplary embodiment shown, a fastening device 250 comprises a flange with a recess for a screw and a spacer bolt 255 is formed on the cooling element 210 into which the screw can be screwed. In another embodiment, a spacer bolt 255 may also be attached to the circuit board 205.

For improved dissipation of heat from the transformer 200 into the cooling element 210, a second thermal coupling material TIM 260 can be provided. The second TIM 260 preferably rests on one side on the cooling element 210 and on the other side on the secondary winding 220 and/or the transformer core 245. The usual options apply to the choice of the second TIM 260; in the embodiment shown, a plate-shaped second TIM 260 is shown as an example.

3 shows a first method 300 for producing a transformer 200 according to FIG 2 illustrated embodiment. In a step 305, the primary winding 215 can be pushed onto the carrier 225. In addition, the end element 230 can be attached to the carrier 225, so that a separately manageable unit is created.

In a step 310, this unit can be combined with the secondary winding 220. For this purpose, the first TIM 240 can be attached to the secondary winding 220 before the two legs of the secondary winding 220 are inserted through corresponding recesses in the carrier 225. The secondary winding 220 is thus pushed radially into the carrier 225 with respect to its winding axis 235. If the secondary winding 220 is positioned correctly, the winding axes 235 of both coils 215, 220 coincide. The result of step 310 is in 3 can be seen in a lower right area.

In a step 315, the magnet 245 can be attached to the carrier 225. For this purpose, two shells of the transformer core 245 can be brought together on the carrier 225 from different axial sides of the winding axis 235. The shells of the transformer core 245 can be glued to one another or to the carrier 225.

4 shows further embodiments of a transformer 200 in the manner of 2 . In an upper area, a view is shown in which the winding axis 235 runs perpendicular to the plane of the drawing. It can be seen how the circuit board 205 and the cooling element 210 lie essentially parallel to one another on different sides of the transformer 200. The fastening elements 250 can be attached to the spacer bolts 245 of the cooling element 210 using screws or other elements symbolized by block arrows. Ends of the coils 215 and 220 protrude through corresponding recesses in the circuit board 205 and can be soldered or welded there, for example.

In a lower area of 4 a side of the transformer 200 faces the viewer, which side faces away from the side of the circuit board 205 and which can be set up to rest on the cooling element 210. The secondary winding 220 and the transformer core 245 are not shown. It can be seen that the primary winding 405 is not surrounded on all sides by the carrier 225 in the radial direction. Rather, one or more recesses 405 are provided in a section of the carrier 225 located between the coils 215 and 220. A first recess 405 facing the viewer can accommodate the first TIM 240 at least in sections. To the side of this, a total of six further recesses 405 are shown on the right and left, which can serve to improve thermal exchange between the coils 215 and 220 through heat radiation or through convection. In one embodiment, the first TIM 240 may be present in one of these recesses. Several first TIM 240s can also be used.

5 shows a transformer 200 in a second embodiment. In an upper area, a view is shown in which one side of the transformer 200, which usually rests on the circuit board 205, faces the viewer. Ends of the primary winding 215 face the viewer. The secondary winding 220 can again be made from sheet metal, but compared to the embodiment of 2 preferred further closed, so that essentially an O-shape results along the winding axis 235. Ends of the primary development 220 lie flat in a plane that is perpendicular to the O-shape and in which the circuit board 205 can extend. The ends can be connected electrically or mechanically to the circuit board 205, for example by soldering or welding.

In the lower area of 5 a cross section through a transformer 200 is shown, which is attached to a cooling element 210. For this purpose, two screws 505 are guided through recesses in the fastening devices 250. The screws 505 are screwed into a material of the cooling element 210, which has a recess 510 in which a lower section of the transformer 200 is received. The second TIM 260 is accommodated in a space between the transformer 200 and the cooling element 210. In this embodiment, a pasty or liquid second TIM 260 can advantageously be used, which can optionally harden after the transformer 200 has been mounted on the cooling element 210.

6 shows a flow chart of a second method 600 for assembling a transformer 200 of the embodiment of 4 . Essentially, steps 605-615 described below correspond in pairs to steps 305-315 of the first method 300.

In a first step 605, the primary winding 215 is attached to the carrier 225. In a step 610, the secondary winding 220 can be attached to the carrier 225. Both coils 215, 220 can be inserted axially into the carrier 225 along their winding axis 235. It should be noted that here, in contrast to the one in 2 In the embodiment shown, the secondary winding 220 is attached axially with respect to its winding axis 235 (see step 310 of the first method 300). Steps 605 and 610 can be performed in any order or simultaneously. The end element 230 can then be attached to the carrier 225. The coils 215, 220 are preferably locked on the carrier 225, so that a separately manageable unit results.

In a step 615, the transformer core 245 can be attached to the carrier 225 from the outside. For this purpose, the shells of the transformer core 245 are preferably pushed axially onto the carrier 225 from different sides with respect to the winding axis 235. Optionally, the shells of the transformer core 245 can be glued in this position. The finished transformer 200 is in a lower left area of 6 shown.

7 shows further views of a transformer 200 of the embodiment of 5 . In an upper area there is a representation similar to that in the upper area of 4 and in a lower area a view similar to that in the lower area of 4 shown. In the illustration below, the transformer 200 is fully assembled and also includes the secondary winding 220 and the transformer core 245. The secondary winding 220 has an optional recess that may be on a side opposite its ends. A pasty or liquid first TIM 240 can pass through the recess and be distributed between the coils 215, 220. Conversely, the first TIM 240 can also be provided between the coils 215, 220 before the coils 215, 220 are pushed together axially. In this case, excess first TIM can exit through the recess and be removed if necessary. In a further embodiment, the exited first TIM 240 can also serve as a second TIM 260 by being placed between the cooling element 210 and the secondary winding 220 during assembly.

Reference symbols

100

system

105

motor vehicle

110

Drivetrain

115

electric machine

120

Power converter

125

battery

130

DC-DC converter

135

On-board electrical system

200

transformer

205

Circuit board

210

Cooling element

215

primary winding

220

Secondary winding

225

carrier

230

Closing element

235

winding axis

240

first thermal coupling material, first TIM

245

Transformer core

250

Fastening device

255

Standoffs

260

second thermal coupling material, second TIM

300

first procedure

305

Attach primary winding to carrier

310

Attach secondary winding to carrier

315

Attach transformer core to support

405

recess

505

Screw, bolt, rivet

510

deepening

600

second procedure

605

Attach primary winding to carrier

610

Attach secondary winding to carrier

615

Attach transformer core to support

Claims (14)

A transformer (200) for mounting on a circuit board (205), the transformer (200) comprising: a primary winding (215) and a secondary winding (220) coaxially wound around a common straight winding axis (235), the winding axis (235) being oriented parallel to the circuit board (205). Transformer (200). Claim 1 , wherein the transformer (200) is set up to transmit electrical energy at a frequency of approximately 80 - 120 kHz. Transformer (200) to Claim 1 or 2 , wherein the secondary winding (220) is formed from a sheet metal. Transformer (200) according to one of the preceding claims, wherein the secondary winding (220) comprises no more than one turn. A transformer (200) according to any one of the preceding claims, wherein the primary winding (215) is wound from a solid conductor. Transformer (200) according to one of the preceding claims, wherein the primary winding (215) lies radially inside and the secondary winding (220) lies radially outside. Transformer (200) according to one of the preceding claims, wherein the primary winding (215) is thermally coupled (240) to the secondary winding (220). Transformer (200) according to one of the preceding claims, further comprising an external transformer core (245). Transformer (200). Claim 8 , whereby the transformer core (245) is in two parts. Method (300, 600) for producing a transformer (200) which is designed to be mounted on a printed circuit board (205), the method comprising the following steps: - axially pushing (305) a fully wound, straight primary winding (215) onto a carrier (225); - Pushing (310) a fully wound, straight secondary winding (220) onto the carrier (225); - so that the coils (215, 220) are coaxial and are wound around a common winding axis (235) which is oriented straight and parallel to the circuit board (205). Procedure (300, 600). Claim 10 , wherein a thermal coupling material (240) is attached between the primary winding (215) and the secondary winding (220). Transformer arrangement, comprising a transformer (200) according to one of Claims 1 until 9 and a cooling element (210), the cooling element (210) having a recess (510) for receiving a portion of the transformer (200) remote from the circuit board (205). DC-DC converter (130), in particular for use on board an electrically driven motor vehicle (105), the DC-DC converter (130) having a transformer (200) according to one of Claims 1 until 9 or a transformer arrangement Claim 11 or 12 includes. Motor vehicle (105), comprising an electrical energy storage device, an electric drive machine and a DC-DC converter (130) according to Claim 13 , wherein the energy store is designed to provide a driving voltage for the electric drive machine and the DC-DC converter (130) is designed to feed a low-voltage on-board network.

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