Contactless energy transmission device and rotor of an electric machine

Abstract

The invention relates to a contactless energy transmission device (1) for a rotor (2) of an electric machine (3), in particular a separately excited synchronous machine within the drive train of a motor vehicle, comprising an inductive transformer (4), which has a primary winding (5) that can be supplied with a current and a secondary winding (6) situated coaxially and at a distance thereto, said secondary winding being connected, with the interposition of rectifier electronics (23), to a rotor (2) winding (7) that can be supplied with a current such that, during the operation of the rotor (2), the rectifier electronics (23) are subjected to centrifugal forces, said rectifier electronics (23) having a plurality of electronically active components (40) that are provided on at least one printed circuit board (41) and are enclosed by a potting compound (42) at least in some areas.

Description

[0001] Contactless energy transfer device and rotor of an electric machine

[0002] The present invention relates to a contactless energy transmission device for a rotor of an electric machine, in particular a separately excited synchronous machine within a drive train of a motor vehicle, comprising an inductive transformer having a currentable primary winding and a coaxially arranged secondary winding spaced apart from it, which in turn is connected to a currentable winding of the rotor via an interposed rectifier electronics unit, so that the rectifier electronics are subjected to centrifugal forces during operation of the rotor, wherein the rectifier electronics comprise a plurality of electronically active components arranged on at least one circuit board and at least partially enclosed by a potting compound. The invention further relates to a rotor of an electric machine.

[0003] Electric motors are increasingly being used for propulsion in motor vehicles to create alternatives to combustion engines that require fossil fuels. Considerable efforts have already been made to improve the everyday usability of electric drives and to offer users the familiar driving comfort.

[0004] In addition to purely electric powertrains, hybrid powertrains are also known. Such powertrains in hybrid vehicles typically comprise a combination of an internal combustion engine and an electric motor, enabling – for example, in urban areas – purely electric operation while simultaneously providing sufficient range and availability, especially on long-distance journeys. Furthermore, it is possible to use both the internal combustion engine and the electric motor simultaneously in certain operating situations.

[0005] In the development of electric machines intended for e-axles or hybrid modules, there is a continuing need to increase their power density and efficiency while simultaneously reducing manufacturing costs, as the vehicle's cost and weight are largely determined by the battery size. In this context, it is also known to design the electric machines as separately excited synchronous machines (FSMs). Here, electrical power must be transferred to the rotor of a separately excited synchronous machine to excite the rotor windings. For traction machines, a contact-based transformer is typically used for this purpose. When these windings are energized, a magnetic field is generated, which, in combination with the stator's magnetic field, produces a torque. The strength of the rotor field can be adjusted by varying the current applied.This allows the machine's behavior to be continuously adapted to the respective driving situation in an efficiency-optimized manner.

[0006] The disadvantages of such a contact-based transmitter include mechanical and electrical losses in the contact between stationary and rotating components. Further disadvantages are the wear of the rubbing components and the associated contamination from abrasion, as well as the comparatively large installation space requirement.

[0007] As an alternative to such contact-based transformers, contactless inductive transformers are also known. An inductive transformer is typically a rotationally symmetrical transformer with an air gap, consisting of a primary and a secondary winding. An inductive transformer usually also has a core, for example made of ferrite. Such a core can be made of one or more parts.

[0008] For example, all parts of the core can be attached to the stationary side of an electric machine, with the secondary winding rotating inside the core. Alternatively, core parts can be attached to the rotating part of the machine. In this case, the primary and secondary core parts are separated by an air gap. This gap must be large enough to ensure that the core parts do not touch, taking all tolerances and operating conditions into account. The rotating transformer parts are often fitted with a bandage or integrated into another component to support them at high speeds. An example of such a design can be found in DE102017214776A1 or DE201210201826 A1.

[0009] DE102021212010A1 describes a contactless

[0010] A power transmission device comprising a primary and secondary winding, as well as rectifier electronics to supply energy to the rotor. One of the main difficulties with such devices lies in the thermal and mechanical stability of the rectifier electronics. Due to the high centrifugal forces acting during operation, mechanical stresses and component degradation can occur. These forces often result in insufficient mechanical stability of the electronic components. Another problem is the effective dissipation of the generated heat.

[0011] If the rectifier is mounted on a circuit board with soldered electronic components, centrifugal forces and thermal distortion can cause significant problems. The high centrifugal forces, which occur particularly in rotating systems such as a motor vehicle's powertrain, place considerable mechanical stress on the solder joints. This stress can cause microcracks or complete breaks in the solder joints, impairing or disrupting the electrical connection between the components.

[0012] Thermal distortion is another problem. Differences in the coefficient of thermal expansion between the circuit board and the components soldered to it lead to mechanical stresses during temperature changes. These stresses can also lead to microcracks or other damage in the solder joints. Especially with repeated temperature cycling, as occurs in many applications, this damage can accumulate and eventually lead to the failure of the entire assembly.

[0013] While DE102021212010A1 offers approaches to solving the described problems, there is still room for improvement in several aspects, particularly regarding thermal and mechanical stability, heat dissipation, electrical insulation and / or EMC, as well as material selection and the composition of the potting compound. These shortcomings lead to limited reliability and service life of the energy transfer device, which impairs the efficiency and practicality of its application in a motor vehicle drive system.

[0014] It is therefore an object of the invention to provide a contactless energy transmission device for a rotor of an electric machine, in particular a separately excited synchronous machine within a drive train of a motor vehicle, which eliminates or at least reduces the problems known from the prior art. It is also an object of the invention to realize an optimized rotor.

[0015] This problem is solved by a contactless energy transmission device for a rotor of an electric machine, in particular a separately excited synchronous machine within a drive train of a motor vehicle, comprising an inductive transformer which has a currentable primary winding and a spaced-apart and coaxially arranged secondary winding which in turn is connected to a currentable winding of the rotor via an interposed rectifier electronics, so that in operation of the rotor the rectifier electronics are subjected to centrifugal forces, wherein the rectifier electronics comprise a plurality of electronically active components which are arranged on at least one circuit board and are at least partially enclosed by a potting compound, wherein a reinforcing ring surrounds the electronically active components at least partially and the potting compound is radially supported on the reinforcing ring.The reinforcing ring has a Young's modulus between 100 GPa and 300 GPa and a temperature coefficient that is ± 30% of the circuit board's temperature coefficient, while the potting compound has a Young's modulus between 8 GPa and 18 GPa and a temperature coefficient that is less than four times the circuit board's temperature coefficient. This results in the thermal expansion of the reinforcing ring being very similar to the circuit board's temperature coefficient. Consequently, the reinforcing ring and the circuit board expand and contract uniformly under thermal loads, improving the structural integrity and reliability of the rectifier electronics. The high Young's modulus of the reinforcing ring also ensures that its expansion under centrifugal force is of the same order of magnitude as that of the circuit board, increasing the mechanical stability of the power transmission device. The use of the potting compound,The radial support provided by the reinforcing ring contributes to additional mechanical stabilization and protects the electronically active components from external influences and mechanical stresses. Furthermore, the potting compound enables simple and efficient integration of the components, simplifying manufacturing processes and reducing production costs.

[0016] Energy transmission device

[0017] For the purposes of this patent application, an energy transfer device is an assembly that serves to transfer electrical energy contactlessly from a stationary part to a rotating part of an electric machine and / or vice versa. This device is particularly suitable for use in a separately excited synchronous machine within the drive train of a motor vehicle.

[0018] The function of the energy transfer device is to ensure the efficient and reliable transfer of electrical energy without a direct electrical connection between the static and rotating components. This is achieved through induction between the primary and secondary windings. For example, the primary winding can be supplied with alternating current, generating an alternating magnetic field that induces a voltage in the coaxially arranged secondary winding. This voltage is then used to supply the rotor winding of the electric machine. Inductive transformer

[0019] For the purposes of this patent application, an inductive transformer is a device used for the contactless transmission of electrical energy by induction between two spatially separated windings. This transformer is particularly useful in electrical machines, such as separately excited ones.

[0020] Synchronous machines within a motor vehicle drivetrain to enable the transfer of energy from the static part to the rotating part.

[0021] The function of the inductive transformer is to generate a magnetic field through induction, which induces a voltage in a spatially separated winding. This enables contactless energy transfer, minimizing wear and maintenance and increasing the reliability of the entire device.

[0022] rectifier electronics

[0023] For the purposes of this patent application, rectifier electronics are electronic circuit units that convert alternating current (AC) into direct current (DC). The primary function of rectifier electronics is therefore to convert the inductively transmitted alternating current into direct current required for the operation of the rotor windings of an electric machine. Rectifier electronics consist of several electronically active components arranged on a circuit board. These components include, for example...

[0024] Rectifier diodes: These components are advantageously arranged to convert alternating current into pulsating direct current. They conduct the current in only one direction and block it in the other, thus enabling the conversion from AC to DC.

[0025] Smoothing capacitors: These capacitors are integrated into the circuit to smooth out the voltage ripples produced by rectification. They store electrical energy and release it as needed, resulting in a smoother and more stable DC voltage. Varistors and transistors: Varistors protect the circuit from overvoltages by absorbing high voltage spikes. Transistors can be used to regulate and amplify current flows, improving the efficiency and controllability of the rectifier electronics.

[0026] Inductive components: These can be used to further stabilize the output voltage and minimize electromagnetic interference. Inductive components help reduce switching losses and optimize the overall performance of the rectifier electronics.

[0027] Heat sinks and thermal management: Since the conversion of alternating current to direct current generates heat, heat sinks or other thermal management solutions are integrated to control the operating temperature of electronic components and extend their service life.

[0028] The rectifier electronics can, for example, be designed as an integrated rectifier module. This module combines several rectifier diodes and additional circuit components in a compact unit, which simplifies assembly and reduces space requirements.

[0029] circuit board

[0030] For the purposes of this patent application, a circuit board is a flat, disk-like support structure that mechanically supports electronic components and enables electrical connections between them. The circuit board primarily serves as a carrier for the electronic components and as a conductive connection between these components. It consists of an insulating base material provided with conductive copper traces that form the electrical circuits. These copper traces are embedded on or in the circuit board and electrically connect the various electronic components. Electronic components such as resistors, capacitors, diodes, transistors, and integrated circuits are soldered onto the circuit board or attached using other connection techniques. This arrangement mechanically stabilizes the circuit. The circuit board can comprise multiple layers, with each layer containing additional copper layers and insulating materials.These multi-layer circuit boards, also known as multi-layer boards, allow for a higher density of connections and more complex circuits in a limited space.

[0031] Advantageously, the circuit board is made of plastic materials, preferably such as FR4 (glass-fiber reinforced epoxy resin), which offers good electrical insulation properties and mechanical stability. Other possible materials include polyimide for high temperature resistance or ceramics for special high-frequency applications. The conductive layers are preferably made of copper, which is widely used due to its excellent electrical conductivity and processability. For special applications, aluminum or gold can also be used to improve specific electrical properties.

[0032] The simplest form of a printed circuit board (PCB) has conductive traces on only one side of the insulating base material. It is primarily used in simple, cost-effective applications. However, double-sided PCBs are also possible, which have conductive traces on both sides of the base material, enabling more complex circuits. Connections between the two sides are made, for example, by vias. A PCB can also be designed as a multi-layer board. These complex boards consist of several conductive and insulating layers stacked on top of each other and interconnected. They offer the highest density of connections and enable compact, high-performance electronic circuits.

[0033] For the purposes of this patent application, a potting compound is a material used for embedding and protecting electronic components and circuits by enclosing them, at least partially, and preferably completely. The potting compound thereby provides mechanical support, electrical insulation, and protection against environmental influences such as moisture, dust, and chemical substances.

[0034] Preferably, a potting compound is formulated to dissipate and distribute heat from the electronic components, thereby preventing overheating and ensuring the thermal stability of the circuit.

[0035] The potting compound preferably consists of a base polymer combined with various additives and fillers to achieve the desired mechanical, electrical, and thermal properties. Epoxy resins, polyurethanes, or silicones are preferred. Epoxy resins offer high strength and good electrical insulation, polyurethanes are flexible and resistant to mechanical stress, and silicones offer excellent temperature resistance and flexibility. To improve thermal properties and increase mechanical strength, fillers such as aluminum oxide, silicon dioxide, or glass fibers can be added. These fillers improve the thermal conductivity and mechanical stability of the potting compound. To meet the specific requirements of the application, additives such as flame retardants, UV stabilizers, or antioxidants can be incorporated into the potting compound.

[0036] According to a further preferred embodiment of the invention, the temperature coefficient of the potting compound can also be between 10 and 50 ppm / K. This ensures that the thermal properties of the potting compound are matched to those of the circuit board and the reinforcing ring. This reduces the differences in the thermal expansion of the materials, minimizing mechanical stresses and potential damage to the electronically active components. Because the potting compound undergoes only minor volume changes during thermal modifications, this ensures a stable mechanical connection between the electronic components and the reinforcing ring and reduces the risk of cracking or delamination. Thus, the protective effect of the potting compound is improved even under fluctuating operating temperatures.

[0037] For the purposes of this patent application, a reinforcing ring is a component that enhances the mechanical stability and structural integrity of an electronic assembly by surrounding and supporting it. The reinforcing ring is used, in particular, to enclose electronic components and mechanically support the surrounding potting compound, thereby distributing loads and protecting the components from mechanical and thermal influences. The primary function of the reinforcing ring is thus to ensure the mechanical stability of the electronic assembly. The reinforcing ring surrounds the electronically active components and acts as a barrier that prevents the potting compound from yielding or cracking under load. This improves the structural integrity of the entire assembly and minimizes the risk of damage from mechanical shocks or vibrations.

[0038] The reinforcement ring is preferably constructed from a high-strength material that offers both mechanical strength and thermal stability. Depending on the specific application requirements, the reinforcement ring can be made from various materials. Materials with a high modulus of elasticity and a suitable temperature coefficient are preferred to control thermal expansion and minimize mechanical stress. Steel is a preferred material due to its high mechanical strength and high modulus of elasticity. Aluminum can also be used, particularly when a lighter weight is desired. If electrical insulation is required, the reinforcement ring can be coated with an insulating layer, such as a ceramic coating or an insulating plastic.

[0039] Reinforcement rings can be designed in various shapes and configurations. A simple and effective form is a closed ring that completely surrounds the electronic components, providing maximum protection. Alternatively, the reinforcement ring can be designed as a segmented ring that only encloses specific areas of the components to save material and weight. In some cases, the reinforcement ring can also be designed as a combined structure with integrated cooling fins or other heat-dissipating features to improve thermal performance.

[0040] Additionally, the reinforcing ring can be used in conjunction with other structural components, such as brackets or fasteners, to facilitate assembly and integration into the overall system. These combinations can further increase mechanical stability and simplify installation.

[0041] Advantageous embodiments of the invention

[0042] According to an advantageous embodiment of the invention, the temperature coefficient of the amplification ring can be between 9.5 and 12 ppm / K. This results in even more precise thermal matching with the circuit board and thus improves the reliability and service life of the rectifier electronics. This precise matching minimizes thermally induced mechanical stresses, which further increases the overall stability of the power transmission device.

[0043] Adjusting the temperature coefficient of the potting compound to a range between 10 and 50 ppm / K can also minimize thermal stresses between the potting compound and the circuit board. This thermal compatibility helps prevent cracks and other damage that could result from uneven thermal expansion. This increases the reliability and durability of the encapsulated electronic components, which is particularly important in demanding environments such as the powertrain of a motor vehicle.

[0044] To determine the temperature coefficient of a material in ppm / K, various standardized measurement methods according to DIN, ISO, and ASTM can be applied. DIN EN ISO 11359-2 describes the method for measuring the linear thermal expansion of solid materials using a dilatometer. This involves measuring the change in length of a test specimen under a defined temperature change and calculating the temperature coefficient from this measurement. ISO 11359-2 is equivalent to DIN EN ISO 11359-2 and also describes the measurement of linear thermal expansion using a dilatometer. The ASTM E831 standard method determines the linear temperature coefficient of solid materials by dilatometry. It measures the change in length of a test specimen under a temperature change and calculates the temperature coefficient from this measurement.

[0045] Furthermore, according to another advantageous embodiment of the invention, the electronically active components can be arranged point-symmetrically around the rotor's axis of rotation. This point-symmetrical arrangement of the electronically active components around the rotor's axis of rotation offers the advantage of a uniform mass distribution. This minimizes imbalances and vibrations during operation, resulting in smoother running and reduced mechanical stress on the overall system. Consequently, the efficiency and service life of the electric machine are improved.

[0046] According to a further particularly preferred embodiment of the invention, the electronically active components may comprise components selected from a group consisting of diodes, varistors, capacitors, and / or transistors. The selection of electronically active components allows the power transfer device to be flexibly adapted to different requirements. This diversity enables the optimization of electrical properties and functions, thereby increasing the performance and adaptability of the device.

[0047] The point-symmetrical arrangement of the electronically active components around the rotor's axis of rotation ensures a uniform distribution of centrifugal forces. When identical components of a group, such as transistors, capacitors, diodes, and varistors, are arranged in mirror-image configurations, the mechanical load is distributed symmetrically across the components. This reduces mechanical stress and minimizes the risk of damage from uneven loads. Furthermore, this symmetrical arrangement can contribute to a more uniform heat distribution, preventing localized overheating of individual components.

[0048] Furthermore, the invention can be further developed such that the reinforcement ring is made of an electrically conductive material. The use of a reinforcement ring made of an electrically conductive material offers the advantage that it can also function as an electrical conductor, potentially enabling additional functionalities and reducing the complexity of the electrical circuits. The reinforcement ring, made of an electrically conductive material, can also act as a Faraday cage. This means that the reinforcement ring shields against electromagnetic interference (EMI) and thus improves the electromagnetic compatibility of the power transmission device. The electronic components are thereby better protected against external electromagnetic influences, which increases the interference immunity and reliability of the entire device.A reinforcement ring made of a metallic material can also shield internal electromagnetic interference emanating from the active components. This prevents interference signals from affecting the surrounding environment or disrupting other sensitive components of the device. This is particularly important in complex electrical systems such as those in vehicle powertrains, where many electronic components operate in close proximity.

[0049] Preferably, the reinforcing ring is made of a metallic material. Metallic materials generally have high thermal conductivity. The reinforcing ring can therefore also act as a heat sink and efficiently dissipate the heat generated by the electronic components. This also contributes to the thermal stability and longevity of the components.

[0050] In a preferred embodiment of the invention, the reinforcing ring can also be provided with electrical insulation. Integrating electrical insulation into the reinforcing ring offers the advantage of preventing electrical short circuits and unintended electrical connections. This is particularly important in high-voltage environments, as the insulation ensures the safety and reliability of the power transmission device. This measure protects the sensitive electronic components from electrical damage and increases the service life of the device.

[0051] It can also be advantageous to further develop the invention such that the insulation comprises a first insulating ring arranged on a first end face of the reinforcing ring and / or a second insulating ring arranged on a second end face of the reinforcing ring. The arrangement of insulating rings on the end faces of the reinforcing ring further improves the electrical insulation. This additional insulating layer prevents potential short circuits and ensures reliable electrical separation, thus increasing the operational reliability of the device. This is particularly relevant for applications in high-voltage environments, where reliable insulation is crucial.

[0052] According to a further preferred embodiment of the invention, the circuit board may have an annular disk shape. The annular disk shape of the circuit board offers the advantage of optimal use of the available space within the energy transmission device. This shape enables a compact and space-saving arrangement of the electronic components, which contributes to a reduction in the overall size of the device. This is particularly important for use in confined installation spaces, such as those frequently found in vehicle powertrains.

[0053] Finally, the problem of the invention can also be solved by a rotor of an electric machine, in particular a separately excited synchronous machine within a drive train of a motor vehicle, comprising a contactless energy transmission device according to one of claims 1-9.

[0054] The application of the described contactless energy transfer device in the rotor of an electric machine, particularly a separately excited synchronous machine within a motor vehicle's powertrain, offers the advantages of high energy transfer efficiency and reliability. This device enables contactless energy transfer, reducing wear and maintenance requirements. Furthermore, the robust mechanical and thermal design of the device ensures a long service life and high operational reliability, even under the demanding conditions of a vehicle's powertrain.

[0055] The invention will now be explained in more detail with reference to figures, without limiting the general concept of the invention.

[0056] It shows:

[0057] Figure 1 shows an electric machine with a separately excited rotor in a schematic axial sectional view.

[0058] Figure 2 shows a separately excited rotor with a contactless energy transfer device in an exploded axial section view.

[0059] Figure 3 shows a rectifier electronics unit in a perspective exploded view.

[0060] Figure 4 shows a rectifier electronics in an axial section view.

[0061] Figure 1 shows a contactless energy transfer device 1 for a rotor 2 of an electric machine 3, in particular a separately excited synchronous machine within a drive train of a motor vehicle. The rotor 2 is configured as an internal rotor and rotates within the hollow cylindrical stator 25.

[0062] For power supply, the rotor 2 has an inductive transformer 4, which has a primary winding 5 capable of conducting current and a secondary winding 6 spaced apart from it and arranged coaxially, which in turn can be electrically coupled to a winding 7 of the rotor 2. In the illustrated embodiment, the primary winding 5 is stationary, while the secondary winding 6 rotates with the rotor 2. The secondary winding 6 is coupled to the rotor 2 via the housing 26.

[0063] On the secondary side, the secondary winding 6 is connected to the winding 7 of the rotor 2 via an interposed rectifier electronics 23, which is designed in an annular disk shape and arranged coaxially to the rotor axis of rotation, as can be clearly seen in Figure 2. The secondary winding 6 is in turn connected to the currentable winding 7 of the rotor 2 via an interposed rectifier electronics 23, so that during operation of the rotor 2 the rectifier electronics 23 is subjected to centrifugal forces.

[0064] As can be clearly seen from Figures 3-4, the rectifier electronics 23 has a plurality of electronically active components 40, which are arranged on at least one circular disk-shaped circuit board 41 and are enclosed at least partially by a potting compound 42, wherein a reinforcing ring 43 surrounds the electronically active components 40 at least partially and the potting compound 42 is supported radially on the reinforcing ring 43.

[0065] In the illustrated embodiment, the reinforcing ring 43 has a Young's modulus between 100 GPa and 300 GPa and a temperature coefficient that is ± 30% of the temperature coefficient of the circuit board 41. The potting compound 42 has a Young's modulus between 8 GPa and 18 GPa and a temperature coefficient that is less than four times the temperature coefficient of the circuit board 41. This enables reliable control of centrifugal forces and temperature changes during the operation of the rotor 2 with regard to the rectifier electronics 23.

[0066] As shown in Figure 3, the electronically active components 40 are arranged point-symmetrically around the axis of rotation of the rotor 2. The electronically active components 40 can comprise components selected from a group including diodes, varistors, capacitors, and / or transistors. As a result, identical diodes, varistors, capacitors, or transistors are arranged point-symmetrically opposite each other, which is also clearly visible in Figure 3. For improved cooling of the rectifier electronics 23, these are connected to a fluid guide ring 47, which supplies a cooling fluid to the rectifier electronics 23 and partially dissipates it radially outwards by centrifugal force.

[0067] In the illustrated embodiment, the reinforcing ring 43 is made of an electrically conductive material, preferably a metal such as steel. Therefore, the reinforcing ring 43 has electrical insulation 44. In this embodiment, the insulation 44 has a first insulating ring 45 arranged on a first end face of the reinforcing ring 43. Furthermore, the insulation 44 has a second insulating ring 46 arranged radially outside the first insulating ring 45, which at least partially surrounds the reinforcing ring 43. In other words, the second insulating ring 46 rests on the first insulating ring 45.

[0068] The area shown in dashed lines in Figure 4 is filled with the potting compound 42 and thus fixes the components 40, the circuit board 41, the insulation 44 and the reinforcing ring 43.

[0069] The invention is not limited to the embodiments illustrated in the figures. The foregoing description is therefore not to be considered limiting, but rather explanatory. The following claims are to be understood as meaning that a named feature is present in at least one embodiment of the invention. This does not preclude the presence of further features. Insofar as the claims and the foregoing description define 'first' and 'second' features, this designation serves to distinguish between two similar features without establishing a hierarchy. List of reference symbols

[0070] 1 Energy transmission device

[0071] 2 Rotor

[0072] 3 electric machine

[0073] 4 transformers

[0074] 5 Primary winding

[0075] 6 Secondary winding

[0076] 7 windings

[0077] 23 Rectifier electronics

[0078] 25 Stator

[0079] 26 cases

[0080] 40 components

[0081] 41 circuit board

[0082] 42 Potting compound

[0083] 43 Reinforcing ring

[0084] 44 Insulation

[0085] 45 Insulation ring

[0086] 46 Insulation ring

[0087] 47 Fluid guide ring

Claims

Claims 1. Contactless energy transmission device (1) for a rotor (2) of an electric machine (3), in particular a separately excited synchronous machine within a drive train of a motor vehicle, comprising an inductive transformer (4) which has a currentable primary winding (5) and a secondary winding spaced apart and arranged coaxially therefrom (6) which in turn is connected to a currentable winding (7) of the rotor (2) via an intermediate rectifier electronics (23), so that during operation of the rotor (2) the Rectifier electronics (23) are subjected to centrifugal forces, wherein the rectifier electronics (23) comprise a plurality of electronically active components (40) arranged on at least one circuit board (41) and enclosed at least partially by a potting compound (42), characterized in that a reinforcing ring (43) surrounds the electronically active components (40) at least partially and the potting compound (42) is radially supported on the reinforcing ring (43), wherein the reinforcing ring (43) has a modulus of elasticity between 100 GPa and 300 GPa and a temperature coefficient corresponding to ± 30% of the temperature coefficient of the circuit board (41), and the potting compound (42) has a modulus of elasticity between 8 GPa and 18 GPa and a temperature coefficient that is less than four times the temperature coefficient of the circuit board (41).

2. Energy transfer device (1) according to claim 1, characterized in that the temperature coefficient of the amplification ring (43) is between 9.5 and 12 ppm / K.

3. Energy transfer device (1) according to claim 1 or 2, characterized in that the temperature coefficient of the potting compound (42) is between 10 and 50 ppm / K.

4. Energy transmission device (1) according to one of the preceding claims, characterized in that the electronically active components (40) are arranged point-symmetrically around the axis of rotation of the rotor (2).

5. Energy transfer device (1) according to one of the preceding claims, characterized in that the electronically active components (40) comprise components selected from a group comprising diodes, varistors, capacitors and / or transistors.

6. Energy transmission device (1) according to one of the preceding claims, characterized in that the reinforcing ring (43) is made of an electrically conductive material.

7. Energy transmission device (1) according to one of the preceding claims, characterized in that the reinforcing ring (43) has an electrical insulation (44).

8. Energy transmission device (1) according to claim 7, characterized in that the insulation (44) comprises a first insulation ring (45) arranged on a first end face of the reinforcing ring (43) and / or a second insulation ring (45) arranged on a second end face of the reinforcing ring (43). has a second insulating ring (46) arranged on the front face of the reinforcing ring (43).

9. Energy transmission device (1) according to one of the preceding claims, characterized in that the circuit board (41) has a circular disk-like shape.

10. Rotor (2) of an electric machine (3), in particular a separately excited synchronous machine within a drive train of a motor vehicle, comprising a contactless energy transmission device (1) according to one of claims 1-9.

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