Contactless energy transmission device, rotor and electric machine

Abstract

The invention relates to a contactless energy transmission device (1) having an energizable primary winding (5) and having a secondary winding (6) which is spaced from and arranged coaxially with respect to said primary winding and which is electrically conductively couplable to a winding of the rotor (2), and the primary winding (5) is arranged in a first winding window (21) of an annular primary core (7) having a first U-shaped cross-section, and the secondary winding (6) is arranged in a second winding window (22) of an annular secondary core (8) having a second U-shaped cross-section, wherein: the primary core (7) has a first free leg (9) and a second free leg (10) extending parallel to the first free leg, and the secondary core (8) has a third free leg (11) and a fourth free leg (12) extending parallel to the third free leg; the legs (9, 10) of the primary core (7) and the legs (11, 12) of the secondary core (8) are directed toward one another; the first leg (9) and the third leg (11) have a first region of overlap (13) and the second leg (10) and the fourth leg (12) have a second region of overlap (14); and the axial extent (15) of the first leg (9) in the first region of overlap (13) differs from the axial extent (16) of the third leg (11), and the axial extent (17) of the second leg (10) in the second region of overlap (14) differs from the axial extent (18) of the fourth leg (12).

Description

[0001] P240795

[0002] - 1 -

[0003] Contactless energy transfer device, rotor and electric machine

[0004] 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 which has a currentable primary winding and a secondary winding spaced apart and arranged coaxially thereto, which can be electrically coupled to a winding of the rotor, and the primary winding is arranged in a first winding window of an annular primary core with a first U-shaped cross-section and the secondary winding is arranged in a second winding window of an annular secondary core with a second U-shaped cross-section, wherein the primary core has a first free leg and a second free leg parallel thereto, and the secondary core has a third free leg and a fourth free leg parallel thereto.wherein the legs of the primary core and the legs of the secondary core are directed towards each other, wherein the first leg and the third leg have a first overlap region and the second leg and the fourth leg have a second overlap region. The invention further relates to a rotor and an electric machine.

[0005] In connection with contactless energy transfer devices for rotors of electrical machines, in particular separately excited synchronous machines within a motor vehicle's drivetrain, it is known from the prior art that energy transfer from the stator to the rotor is effected by means of inductive transmitters. These transmitters typically function as transformers arranged axially in front of the rotor. The transformer is designed such that the radial air gap between the primary and secondary parts allows the stationary primary part to be separated from the rotating secondary part. This arrangement creates the prerequisite for contactless energy transfer, which is necessary for exciting the rotor windings. P240795

[0006] - 2 -

[0007] Although such systems are capable of ensuring the necessary energy transfer without mechanical wear, they are associated with significant challenges and disadvantages. A key problem is the severely limited axial installation space available in modern vehicles. This limitation makes it difficult to integrate transformers with sufficient power output into the system without significantly increasing the size of the powertrain. This is particularly problematic in vehicles with a compact design, where every millimeter of installation space can be crucial.

[0008] Another significant disadvantage of existing technology is the sensitivity of transformers to axial tolerances. Because the transformer is designed with separate yet tightly coupled primary and secondary sections, even minor axial displacements or manufacturing tolerances can significantly impair power transmission efficiency. This can result in the transformer being unable to deliver its full power, thus affecting the synchronous machine's operational capability. The need to ensure high performance while maintaining a high tolerance for axial deviations presents a major challenge for designers.

[0009] These problems and disadvantages illustrate that current solutions for contactless energy transfer devices for rotors of separately excited synchronous machines do not yet fully meet the requirements of modern vehicle propulsion systems. In particular, further development is needed regarding the optimization of installation space and robustness against manufacturing tolerances in order to further improve the efficiency and reliability of such systems.

[0010] It is therefore an object of the invention to provide a contactless energy transfer device for a rotor of an electric machine that avoids or at least reduces the disadvantages known from the prior art. It is also an object of the invention to realize an improved rotor and an optimized electric machine. P240795

[0011] - 3 -

[0012] 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 can be electrically coupled to a winding of the rotor, and the primary winding is arranged in a first winding window of an annular primary core with a first U-shaped cross-section and the secondary winding is arranged in a second winding window of an annular secondary core with a second U-shaped cross-section, wherein the primary core has a first free leg and a second free leg parallel thereto, and the secondary core has a third free leg and a fourth free leg parallel thereto.wherein the limbs of the primary nucleus and the limbs of the secondary nucleus are directed towards each other, wherein the first limb and the third limb have a first overlap region and the second limb and the fourth limb have a second overlap region, wherein the axial extent of the first limb in the first overlap region is different from the axial extent of the third limb and the axial extent of the second limb in the second overlap region is different from the axial extent of the fourth limb.

[0013] This energy transfer device offers increased robustness against axial tolerances. The differing axial extensions of the legs in the overlapping areas ensure that minor deviations in the axial position of the cores do not significantly impair transfer efficiency. This improves energy transfer reliability, particularly in applications where precise axial alignment is difficult to guarantee, such as in rotating systems. Furthermore, the compact design is maintained, as no additional installation space is required compared to conventional energy transfer devices. P240795

[0014] - 4 -

[0015] First, the individual elements of the claimed invention are explained in the order in which they are mentioned in the claim set, and subsequently, particularly preferred embodiments of the invention are described.

[0016] Energy transfer device

[0017] For the purposes of this patent application, an energy transfer device is a technical device that serves to transfer electrical energy contactlessly from a stationary part to a rotating part. This device is designed in particular for use in rotating machines, such as separately excited synchronous machines in the drive trains of motor vehicles. The energy transfer device ensures a reliable supply of electrical energy to the rotor without the need for mechanical contacts that could be subject to wear.

[0018] The energy transfer device functions based on the principle of inductive coupling. Electrical energy is inductively transferred from a primary winding, located, for example, on a stationary primary core, to a secondary winding, located, for example, on a rotating secondary core. The primary and secondary cores are arranged coaxially, allowing for efficient magnetic flux transfer between them. The primary winding is housed in a first winding window of the primary core, while the secondary winding is located in a second winding window of the secondary core. The core sections surrounding these winding windows are designed to facilitate magnetic coupling in the areas where the two cores overlap.

[0019] The primary core has two free legs that run parallel to each other and are aligned with the secondary core. Correspondingly, the secondary core also has two parallel legs that are aligned with the legs of the primary core. Inductive coupling occurs in the areas where these legs overlap, and the axial extent of the legs can vary to adapt the device to specific requirements. An asymmetric P240795

[0020] - 5 -

[0021] Designing the legs can advantageously help to increase the robustness of the device against axial tolerances without affecting the available installation space.

[0022] Preferably, the energy transfer device can be designed such that the axial extent of the legs of the primary and secondary cores differs to allow optimal adaptation to various operating conditions. This adaptation can, for example, consist of the axial extent of one leg being larger or smaller than that of the opposite leg to achieve targeted control of the magnetic flux. Another preferred embodiment can provide that the axial extent of the winding windows of the primary and secondary cores is essentially the same to ensure a uniform distribution of the winding material and thus improved thermal performance.

[0023] It is also conceivable that the primary core is mounted in a rotationally fixed position, while the secondary core is rotatably mounted around the primary core. This configuration enables constant energy transfer, even at high rotor speeds, and contributes to the mechanical stability of the entire machine. Alternatively, the primary core can be rotatably mounted, while the secondary core is designed to be rotationally fixed.

[0024] rotor

[0025] For the purposes of this patent application, a rotor is a rotating component of an electric machine that serves to generate rotational motion through interaction with a magnetic field or to convert such motion into electrical energy. A separately excited rotor is a special embodiment of a rotor in which the excitation field necessary for generating the magnetic field is not produced by permanent magnets or by the self-induction of the rotor itself, but by an external electrical excitation. This excitation is generally achieved by supplying current via an excitation winding arranged around the rotor. P240795

[0026] - 6 -

[0027] The separately excited rotor is designed to include an excitation winding that is energized via a contactless energy transfer device, as described in this patent application. This device ensures that the energy required for the excitation winding is transferred efficiently and without mechanical wear. The rotor itself typically consists of a ferromagnetic core that guides and focuses the magnetic fluxes. The excitation winding is arranged on this core and generates a magnetic field through the external energy supply. This magnetic field then interacts with the machine's stator to produce the desired rotational motion.

[0028] The function of the separately excited rotor in an electric machine is therefore primarily to convert the magnetic fields generated by the excitation winding into mechanical rotational motion or, in the case of regeneratively powered machines, to convert mechanical energy into electrical energy. The contactless energy transfer ensures that the rotor can rotate freely and does not require any mechanical sliding contacts that could be subject to wear. This increases the machine's service life and enables operation at higher speeds and under demanding operating conditions.

[0029] Inductive transformer

[0030] For the purposes of this patent application, an inductive transformer is a device for transmitting electrical energy between two spatially separated but magnetically coupled windings connected by electromagnetic induction. The inductive transformer essentially comprises a primary winding and a secondary winding arranged on magnetically conductive cores that focus and conduct the magnetic fields. These windings are arranged such that the magnetic flux generated by the primary winding is guided through the secondary winding to induce an electrical voltage there. This configuration enables contactless energy transfer, which is particularly suitable for applications where mechanical connections are undesirable or technically difficult to implement. P240795

[0031] - 7 -

[0032] The inductive transformer consists of a primary core, which houses the primary winding, and a secondary core, which supports the secondary winding. The cores are preferably made of a soft magnetic material to ensure efficient magnetic flux conduction. The legs of the U-shaped cores are oriented towards each other and overlap in specific areas known as overlap zones. These overlap zones are crucial for magnetic flux transfer, as they define the region where the magnetic flux passes from the primary to the secondary winding.

[0033] Functionally, the inductive transformer serves primarily to transfer electrical energy from a stationary component, such as the primary winding, to a rotating component, such as the secondary winding of the rotor. This is achieved through the magnetic flux generated in the primary winding, which induces an electrical voltage in the secondary winding. This voltage is then used to excite the rotor. The contactless transmission eliminates the need for slip rings or other mechanical contact points, significantly increasing the reliability and service life of the system, especially at high speeds or in environments with high mechanical loads.

[0034] For the purposes of this patent application, a primary winding is an electrically conductive winding arranged in an electromagnetic transformer and used to generate a magnetic field for contactless operation.

[0035] Energy transfer is utilized. The primary winding is designed so that it can be energized with an electric current, thereby generating a magnetic flux field. This magnetic field is then transferred to a secondary winding located in close proximity to the primary winding, thus enabling energy transfer from the primary to the secondary side without mechanical contact.

[0036] The function of the primary winding is therefore to generate a magnetic field that transfers energy to the secondary winding. This is where the P240795

[0037] - 8 -

[0038] The primary winding is preferably arranged in a first winding window of an annular primary core with a U-shaped cross-section. This arrangement ensures optimal coupling of the magnetic flux between the primary and secondary windings and minimizes losses that could arise from leakage fluxes.

[0039] The primary winding can consist of several turns of an electrically conductive material, such as copper wire. These turns are arranged to concentrate and amplify the magnetic field in the desired direction. The primary winding wire can be insulated to prevent short circuits between the turns and ensure electrical safety. The primary windings are preferably designed to generate a high current density and thus a high magnetic field strength to ensure efficient energy transfer.

[0040] Various primary winding configurations are conceivable, depending on the specific application requirements. For example, the primary winding can be a single coil or multiple coils connected in parallel to increase current-carrying capacity or optimize magnetic field distribution. Another configuration could involve manufacturing the primary winding from flat, ribbon-shaped conductors to achieve better heat dissipation and reduce the winding's overall height. The number of turns and the winding geometry can also vary depending on the required field strength and spatial constraints, in order to create the most compact and efficient power transmission device possible.

[0041] Secondary winding

[0042] For the purposes of this patent application, a secondary winding is an electrically conductive winding arranged in an electromagnetic transformer and serving to absorb the magnetic field generated by the primary winding and convert it into electrical energy. The secondary winding is designed to absorb electrical currents induced by the magnetic field of the primary winding. P240795

[0043] - 9 - which can then be used to supply a connected load or to forward to other electrical components.

[0044] The function of the secondary winding is therefore, in particular, to convert the magnetic field generated by the primary winding into electrical energy. This conversion occurs through electromagnetic induction, in which the alternating magnetic field in the secondary winding generates a current flow. The secondary winding is preferably arranged in a second winding window of an annular secondary core with a U-shaped cross-section. This arrangement ensures optimal magnetic coupling to the primary winding and minimizes leakage losses, resulting in higher energy transfer efficiency.

[0045] The secondary winding preferably consists of several turns of an electrically conductive material, such as copper wire, arranged to absorb the magnetic field. The wire of the secondary winding is preferably insulated to prevent short circuits between the turns and to ensure operational reliability. The windings are designed to deliver a high voltage or a high current, depending on the application requirements. This is determined by the number of turns and their specific arrangement, which are tailored to the desired electrical parameters of the generated energy.

[0046] Possible embodiments of the secondary winding vary depending on the specific requirements of the application. For example, the secondary winding could be designed as a single coil or as multiple coils to achieve higher power density or improved matching to the magnetic field of the primary winding. Another embodiment could involve the use of flat, ribbon-shaped conductors, which allow for better heat dissipation and reduce the overall height of the winding. The geometry and number of turns can also be adapted to maximize energy conversion efficiency and minimize the size of the power transmission device. P240795

[0047] - 10 -

[0048] Primary core

[0049] For the purposes of this patent application, a primary core is a component of the contactless energy transfer device whose function is to guide and concentrate the magnetic field in order to ensure efficient energy transfer between the primary and secondary windings. The primary core is ring-shaped and has a U-shaped cross-section comprising two parallel legs and a connecting yoke. The primary winding is arranged in one of the winding windows of the primary core and is energized to generate a magnetic field. This magnetic field is guided through the primary core and directed towards the secondary core to induce the secondary winding there and thus transfer energy.

[0050] The primary core is made of a ferromagnetic material with high magnetic permeability, effectively focusing the magnetic field and minimizing losses. The axial extent of the primary core's legs plays a crucial role in the efficiency of the magnetic field guidance and its robustness against axial tolerances. The preferred asymmetric design of the legs in the overlapping areas allows the primary core to be both compact and tolerant of manufacturing inaccuracies, thus improving the overall performance of the energy transfer device.

[0051] Secondary nucleus

[0052] For the purposes of this patent application, a secondary core is a component of the contactless energy transfer device that serves to absorb and concentrate the magnetic field generated by the primary core in order to transfer the induced energy to the secondary winding. The secondary core is ring-shaped and, like the primary core, also has a U-shaped cross-section with two parallel legs and a connecting yoke. The secondary winding is arranged in one of the winding windows of the secondary core and is electromagnetically coupled to the magnetic field of the primary core, thus absorbing the transferred energy. P240795

[0053] - 11 -

[0054] The secondary core consists of a ferromagnetic material with high magnetic permeability, enabling it to focus and guide the magnetic field of the primary core. The axial extent of the secondary core's legs is crucial for the quality of the magnetic field guidance and its adaptation to axial tolerances. A preferably asymmetrical design of the legs in the overlapping areas allows for precise control of the magnetic flux, which improves energy transfer and compensates for potential axial displacements.

[0055] According to an advantageous embodiment of the invention, the axial extent of the first leg in the first intersection region can be greater than the axial extent of the third leg, and the axial extent of the second leg in the second intersection region can be smaller than the axial extent of the fourth leg. Advantageously, the greater axial extent of the first leg in the first intersection region and the smaller axial extent of the second leg in the second intersection region allow for targeted adaptation of the magnetic flux paths. This leads to improved magnetic coupling and thus more efficient energy transfer, while simultaneously ensuring the mechanical stability of the system. Furthermore, this arrangement reduces the risk of space constraints, as the asymmetrical design of the legs facilitates adaptation to confined spaces.

[0056] According to a further preferred embodiment of the invention, the axial extent of the first leg in the first intersection region can also be smaller than the axial extent of the third leg, and the axial extent of the second leg in the second intersection region can be larger than the axial extent of the fourth leg. This configuration also offers the advantage that the different axial extents of the legs in the intersection regions enable a targeted distribution of the magnetic fluxes. This allows the energy transfer in one direction to be optimized, which is particularly important for applications with specific flux requirements. Furthermore, this arrangement also contributes to the tolerance of axial dislocations.

[0057] - 12 - without reducing the available winding window, which also helps, for example, to increase the flexibility in the design of the rotor.

[0058] Furthermore, according to another advantageous embodiment of the invention, the axial extent of the first leg can be substantially the same as the axial extent of the fourth leg. Advantageously, the approximately equal axial extent of the first and fourth legs enables a symmetrical and balanced load distribution on the transmission system. This symmetry improves mechanical stability and reduces the risk of deformation or mechanical stress during operation. Moreover, this arrangement contributes to the efficiency of energy transmission because it ensures a uniform distribution of the magnetic forces.

[0059] According to a further particularly preferred embodiment of the invention, the axial extent of the third leg can be substantially the same as the axial extent of the second leg. This combination of features offers the advantage that the identical axial extent of the second and third legs enables homogeneous magnetic coupling, resulting in uniform energy transfer across the entire rotor area. This is particularly advantageous in applications where a uniform energy supply is necessary to ensure constant rotor performance. Furthermore, this symmetry contributes to reducing unwanted vibrations and increasing the service life of the components.

[0060] Furthermore, the invention can also be further developed such that the axial extent of the first winding window essentially corresponds to the axial extent of the second winding window. This adjustment ensures that the winding material is used efficiently without creating unnecessary installation space. This reduces the size of the energy transfer device, which is particularly advantageous in applications with limited installation space, and contributes to improved thermal properties because the winding material is distributed evenly. P240795

[0061] - 13 -

[0062] The object of the invention can also be achieved by a rotor of an electric machine, in particular a separately excited one.

[0063] A synchronous machine within the powertrain of a motor vehicle, comprising a contactless energy transfer device according to any one of claims 1-6. The rotor benefits from the integration of the contactless energy transfer device, as this enables a reliable and wear-free energy supply to the rotating components. This results in a longer service life for the electric machine, since no mechanical contacts are required that could be subject to wear. Furthermore, the contactless transfer allows for a higher rotor speed, as there is no limitation imposed by mechanical contact points, leading to an increase in the machine's efficiency.

[0064] It can also be advantageous to further develop the invention such that the primary core is arranged in a rotationally fixed manner, while the secondary core is rotatably mounted around the primary core. This leads to increased mechanical stability of the overall system and enables reliable and constant energy transfer even at high rotational speeds.

[0065] Finally, the object of the invention can also be achieved by an electric machine, in particular a separately excited synchronous machine within a motor vehicle powertrain, comprising a rotor according to claim 7 or 8. The electric machine benefits from the implementation of a rotor with a contactless energy transfer device, as this significantly increases the efficiency and service life of the machine. In particular, in separately excited synchronous machines used in motor vehicle powertrains, contactless transfer leads to a reduction in maintenance requirements and an improvement in overall performance. The machine can operate efficiently in a wide range of operating conditions, resulting in greater flexibility and reliability in operation. P240795

[0066] - 14 -

[0067] The invention will now be explained in more detail with reference to figures, without limiting the general concept of the invention.

[0068] It shows:

[0069] Figure 1 shows an electric machine with a contactless energy transfer device in a schematic axial section view.

[0070] Figure 2 shows a contactless energy transfer device in a schematic axial section view.

[0071] Figure 1 shows a contactless energy transfer device 1, specifically designed for a rotor 2 of an electric machine 3. This machine is preferably a separately excited synchronous machine used within the powertrain of a motor vehicle. The energy transfer device 1 comprises an inductive transformer 4, designed to enable efficient and wear-free energy transfer from the stationary part of the machine to the rotating rotor 2.

[0072] In the embodiment shown in Figure 1, the primary core 7 is rotatably mounted, while the secondary core 8 is arranged non-rotatably around the primary core 7. It is understood that it is also possible for the primary core to be arranged non-rotatably, while the secondary core 8 is rotatably mounted around it.

[0073] As can be clearly seen in Figure 2, the inductive transformer 4 consists of a currentable primary winding 5 and a coaxially arranged secondary winding 6 spaced apart from it. The primary winding 5 is housed in a first winding window 21 of an annular primary core 7, while the secondary winding 6 is arranged in a second winding window 22 of a similarly annular secondary core 8. Both windings are designed to enable electrical coupling with a winding of the rotor 2, thereby transferring the energy necessary for the operation of the separately excited synchronous machine. P240795

[0074] - 15 -

[0075] The primary core 7, made of a ferromagnetic material, has a U-shaped cross-section and comprises two parallel legs, the first leg 9 and the second leg 10. These legs are designed to efficiently guide and focus the magnetic field generated by the primary winding 5. The secondary core 8, also with a U-shaped cross-section, has a third leg 11 and a fourth leg 12. The legs of the primary core 7 and the secondary core 8 are oriented towards each other, with the first leg 9 and the third leg 11 forming a first intersection region 13 and the second leg 10 and the fourth leg 12 forming a second intersection region 14.

[0076] The axial extent 15 of the first leg 9 in the first intersection region 13 differs from the axial extent 16 of the third leg 11, just as the axial extent 17 of the second leg 10 in the second intersection region 14 differs from the axial extent 18 of the fourth leg 12. This asymmetry in the axial extent of the legs serves to increase the robustness of the device with respect to axial tolerances without impairing the energy transfer performance. By selectively varying the axial lengths of the legs, the magnetic flux can be optimized and the installation space can be used efficiently.

[0077] In the embodiment shown here, the axial extent 15 of the first leg 9 in the first intersection region 13 is smaller than the axial extent 16 of the third leg 11, while the axial extent 17 of the second leg 10 in the second intersection region 14 is larger than the axial extent 18 of the fourth leg 12. This configuration allows for adjustment of the magnetic flux, thereby meeting specific requirements for magnetic coupling and tolerance compensation.

[0078] Furthermore, Figure 2 also shows that the axial extent 15 of the first leg 9 essentially corresponds to the axial extent 18 of the fourth leg 12. Likewise, the axial extent 16 of the third leg 11 essentially corresponds to the axial extent 17 of the second leg 10. This P240795

[0079] - 16 -

[0080] Symmetry in the axial extensions of the legs supports a uniform magnetic field distribution and contributes to the mechanical stability of the energy transmission device.

[0081] It is also clearly evident that the axial extent 19 of the first winding window 21 essentially corresponds to the axial extent 20 of the second winding window 22. This equality of the winding window dimensions ensures that the winding material is optimally utilized in both the primary and secondary windings, thus maximizing energy transfer efficiency while minimizing the thermal stress on the windings.

[0082] A key feature, clearly illustrated in Figure 2, is the design of the legs 9, 10, 11, and 12 of the cores 7 and 8, which are responsible for guiding the magnetic flux. The legs 9 and 10 of the primary core 7 and the legs 11 and 12 of the secondary core 8 are designed—as outlined earlier—to have an asymmetrical thickening. This asymmetry means that the legs 9, 10, 11, and 12 have different axial extensions 15, 16, 17, and 18 in the overlapping regions 13 and 14, which is specifically used to maximize the robustness of the energy transfer device 1 with respect to axial tolerances. This asymmetric thickening enables the energy transfer device 1 to ensure efficient energy transfer even in the event of deviations in the axial alignment of the cores 7,8.

[0083] Essential for understanding the energy transfer device 1 shown in Figure 2 is that thickening the legs 9, 10, 11, 12 beyond the necessary thickness generally leads to increased robustness against tolerances, but also increases the space requirement of the energy transfer device 1. The innovative solution shown in the figure demonstrates how robustness can be maximized by asymmetrically thickening the legs 9, 10, 11, 12 without exceeding the available installation space. This is particularly important in applications such as in the powertrain of a motor vehicle, where installation space is limited and a P240795

[0084] - 17 -

[0085] Exceeding this limit could lead to design and functional limitations.

[0086] Figure 2 further illustrates that this asymmetric thickening makes it possible to increase the robustness of the energy transfer device 1 in a specific direction without reducing the winding window 21, 22. This means that the primary winding 5 and the secondary winding 6 continue to have the same space available to transfer the necessary energy, thus contributing to maintaining the efficiency of the energy transfer device 1. Figure 2 therefore demonstrates that the targeted, asymmetric design of the legs 9, 10, 11, 12 not only improves tolerance but also optimizes space utilization within the existing installation space without impairing the functionality of the windings 5, 6.

[0087] The presented technical solution illustrates how an adjustment of the geometry of the core elements – specifically the legs 9, 10, 11, 12 – leads to a high tolerance for axial displacements, while simultaneously keeping the overall size of the energy transfer device 1 compact. This makes the energy transfer device 1 particularly suitable for use in modern electrical machines 3, where both efficiency and space saving are of paramount importance.

[0088] 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 any hierarchy. P240795

[0089] - 18 -

[0090] List of reference signs

[0091] 1 Energy transmission device

[0092] 2 Rotor

[0093] 3 electric machine

[0094] 4 transformers

[0095] 5 Primary winding

[0096] 6 Secondary winding

[0097] 7 Primary nucleus

[0098] 8 Secondary nucleus

[0099] 9 thighs

[0100] 10 thighs

[0101] 11 thighs

[0102] 12 thighs

[0103] 13 Overlap area

[0104] 14 Overlap area

[0105] 15 Extension

[0106] 16 Extension

[0107] 17 Extension

[0108] 18 Extension

[0109] 19 Extension

[0110] 20 Extension

[0111] 21 changing windows

[0112] 22 changing windows

Claims

P240795 - 19 - 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 (6) spaced apart and arranged coaxially thereto, which can be electrically coupled to a winding of the rotor (2), and the primary winding (5) is arranged in a first winding window (21) of an annular primary core (7) with a first U-shaped cross-section and the secondary winding (6) is arranged in a second winding window (22) of an annular secondary core (8) with a second U-shaped cross-section,wherein the primary core (7) has a first free leg (9) and a second free leg (10) running parallel thereto, and the secondary core (8) has a third free leg (11) and a fourth free leg (12) running parallel thereto, wherein the legs (9, 10) of the primary core (7) and the legs (11, 12) of the secondary core (8) are directed towards each other, wherein the first leg (9) and the third leg (11) have a first overlap region (13) and the second leg (10) and the fourth leg (12) have a second overlap region (14), characterized in that the axial extent (15) of the first leg (9) in the first overlap region (13) differs from the axial extent (16) of the third leg (11) and the axial extent (17) of the second leg (10) differs in the second area of ​​overlap (14) from the axial extent (18) of the fourth leg (12).

2. Energy transmission device (1) according to claim 1, characterized in that the axial extent (15) of the first leg (9) in the first overlap region (13) is greater than the axial extent (16) of the P240795 - 20 - third leg (11 ) and the axial extent (17) of the second leg (10) in the second overlap area (14) is smaller than the axial extent (18) of the fourth leg (12).

3. Energy transmission device (1 ) according to claim 1 , characterized in that the axial extent (15) of the first leg (9) in the first overlap region (13) is smaller than the axial extent (16) of the third leg (11 ) and the axial extent (17) of the second leg (10) in the second overlap region (14) is larger than the axial extent (18) of the fourth leg (12).

4. Energy transmission device (1 ) according to one of the preceding claims, characterized in that the axial extent (15) of the first leg (9) corresponds substantially to the axial extent (18) of the fourth leg (12).

5. Energy transmission device (1 ) according to one of the preceding claims, characterized in that the axial extent (16) of the third leg (11 ) corresponds substantially to the axial extent (17) of the second leg (10).

6. Energy transmission device (1 ) according to one of the preceding claims, characterized in that the axial extent (19) of the first winding window (21 ) corresponds substantially to the axial extent (20) of the second winding window (22).

7. 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 1-6.

8. Rotor (2) according to claim 7, characterized in that P240795 - 21 - the primary core (7) is arranged in a rotationally fixed manner, while the secondary core (8) is rotatably mounted around the primary core (7).

9. Electric machine (3), in particular a separately excited synchronous machine within a drive train of a motor vehicle, comprising a rotor (2) according to claim 7 or 8.

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