Method for electrically insulating electrical components in a rotor assembly for a separately excited synchronous machine, and rotor assembly

Abstract

The present invention relates to a method (500; 600) for electrically insulating electrical components in a rotor assembly (100) for a separately excited synchronous machine, comprising: - providing a hollow rotor shaft (1); - inserting a rectifier circuit board for an inductive transmission unit into the rotor shaft (1); and - inserting a slide (20; 20') into the rotor shaft (1) such that a rectifier cavity (7') is formed between the rectifier circuit board (7), an end face of the slide (20; 30) and an inner wall of the hollow rotor shaft (1), in which rectifier cavity the electrical components of the rectifier circuit board (7) are arranged; and - filling the rectifier cavity (7') with a non-conductive plastic. The invention also relates to a rotor assembly (100).

Description

[0001] Method for electrically insulating electrical components in a rotor arrangement for a separately excited synchronous machine and a rotor arrangement

[0002] The present invention relates to a method for electrically insulating electrical components in a rotor arrangement for a separately excited synchronous machine and to a rotor arrangement.

[0003] Separately excited synchronous machines can be used as drive devices in motor vehicles and, unlike permanent-magnet synchronous machines, comprise a rotor-side excitation winding (rotor winding) that can be energized to generate an excitation field. The excitation field interacts with a stator field to generate a rotary motion of the rotor.

[0004] It is known from the prior art that an alternating current provided by the power electronics can be transmitted contactlessly by an inductive (current / rotary) transmission unit. Such an inductive transmission unit can be a (e.g. rotationally symmetrical) transformer comprising a primary unit and a secondary unit, wherein the primary unit comprises a primary ferrite core with an associated primary winding and the secondary unit comprises a secondary ferrite core with an associated secondary winding. The primary ferrite core and the secondary ferrite core are separated from one another by an air gap and are designed to rotate relative to one another. As a rule, the primary unit is fixed in place in the electrical machine, e.g. on the housing, while the secondary unit is rotatable, e.g. through a rotationally fixed connection to the rotor.

[0005] The inductive transmission unit allows an alternating current to be transmitted contactlessly from the primary winding of the primary unit to the secondary winding of the secondary unit. A rectifier unit connected to the secondary winding taps the transmitted alternating current and converts it into a direct current to power the rotor windings. Previous cooling concepts for cooling the inductive transmission unit and / or the rectifier unit use dielectric cooling media such as oil due to the electrically conductive components in the rotor.

[0006] The object of the present invention is to improve the cooling of components of the rectifier unit and / or the inductive transmission unit.

[0007] This object is achieved by a method according to claim 1 and a rotor arrangement according to claim 9.

[0008] According to a first aspect, the present invention relates to a method for electrically insulating electrical components in a rotor arrangement for a separately excited synchronous machine, comprising:

[0009] - Providing a hollow rotor shaft;

[0010] - Inserting a rectifier board for an inductive transmission unit; and

[0011] - Inserting a slider so that a rectifier cavity is formed between the rectifier board, an end face of the slider and an inner wall of the hollow rotor shaft, in which the electrical components of the rectifier board are arranged; and

[0012] - Filling the rectifier cavity with a non-conductive plastic.

[0013] The rotor shaft carries the rotor windings on its outer circumference. The rotor windings can be energized to generate the rotor-side magnetic field (rotor field). The rotor field then interacts with a stator-side magnetic field (stator field), driving the rotor shaft and thus the rotor assembly.

[0014] The inductive transmission unit is designed to transmit the current for rotor field generation to the rotor winding. The transmission unit is arranged at one end of the rotor shaft and is at least partially inserted into the rotor shaft. In some examples, the transmission unit is arranged entirely within the rotor shaft. The end of the rotor shaft with the transmission unit is referred to as the drive-side end. Opposite this end is the output-side end of the rotor shaft.

[0015] The rectifier board is used to rectify and transmit the current from the transmission unit to the rotor windings and is located in the rotor shaft. In addition, other components (of an electronic circuit) can be arranged on the rectifier board in addition to a rectifier unit. These components include, for example, conductor tracks, contact elements (e.g., plug connections for connecting the secondary winding of the transmission unit and the rotor winding to the rectifier unit), circuits (e.g., for smoothing the input current, rectifier circuit), components for limiting induced voltage peaks (e.g., varistors, suppressor diodes (TVS diodes)), and other active and / or passive components for implementing safety functions or transmitting signals.

[0016] A slider (or "insert") is a movable component commonly used in plastic injection molding tools. Typically, after an injection molding process, the slider is moved away from the plastic part. In the present disclosure, the slider is used such that it is at least partially inserted into the rotor shaft, forming a chamber (rectifier cavity) defined by an end face of the slider, an inner wall of the rotor shaft, and a circuit board of the rectifier circuit board. The rectifier circuit board is arranged in the rotor shaft such that the electrical components of the rectifier circuit board are arranged in the rectifier cavity. This means that the electrical components are located on only one side of the circuit board.

[0017] To electrically insulate the electrical components, the rectifier cavity is filled with a non-conductive plastic, e.g., a thermoplastic or thermoset. As a result, the electrical components of the rectifier board are overmolded with the plastic and thus electrically insulated. As a result, electrically conductive fluids with higher thermal capacities (e.g., water-glycol) can now be used to cool the rotor arrangement, e.g., in the area of ​​the rectifier board, thus improving cooling performance. In one embodiment, the rectifier cavity can be filled by transfer molding. Alternatively, other processes such as injection molding or vacuum encapsulation can also be used. In the present disclosure, the terms "filling" and "injection" are used interchangeably to form the plastic encapsulation and do not refer to a specific process.

[0018] In one embodiment, the method may further comprise:

[0019] - inserting the rotor shaft into a laminated core having a plurality of slots and rotor windings accommodated in the plurality of slots; and

[0020] - Filling the plurality of grooves with a non-conductive plastic via an insertion opening provided in the rotor housing.

[0021] The laminated core is formed by a plurality of joined, star-shaped pieces of laminated core. The star shape of the pieces of laminated core creates a plurality of rotor teeth in the laminated core, which are distributed in the circumferential direction of the laminated core and extend from one end of the laminated core to the other. Furthermore, a plurality of slots are arranged between the rotor teeth. Support disks can be provided at the axial ends to seal the laminated core. Slot seals can be provided to seal the plurality of slots in the radial direction.

[0022] The laminated core includes an opening for accommodating the rotor shaft. This means that when the rotor shaft and laminated core are assembled, the rotor shaft protrudes through the laminated core. To electrically insulate the rotor windings, the numerous slots are filled with a non-conductive plastic. This overmolds the rotor windings with the plastic, thus electrically insulating them. The numerous slots are filled via the insertion opening provided in one of the support disks.

[0023] In one embodiment, when filling the plurality of slots, the rotor assembly can be positioned such that the rotor shaft is arranged substantially parallel to the direction of gravity. This results in the filling process working against gravity, thereby reducing air pockets in the molded plastic.

[0024] In one embodiment, the insertion opening can be located on a support disk of the laminated core. In one example, this can be the support disk facing away from the inductive transmission unit, i.e., on the output-side end of the rotor shaft. In this example, the rotor assembly can be aligned parallel to the direction of gravity, so that the insertion opening is located at the bottom. As a result, the plastic is fed from below during a filling process, so that the filling of the plurality of grooves works against gravity, thus reducing air pockets.

[0025] In one embodiment, another support disk of the laminated core can include at least one vent opening. The vent opening can be designed as a through-hole. This can reduce air inclusions during the filling process.

[0026] In one embodiment, the rectifier cavity and the plurality of slots can be filled through a (single) filling process. For example, the rectifier cavity and the plurality of slots for the rotor windings can be fluidly connected to one another, so that the plastic injected through the insertion opening (provided in the rotor housing) first enters the plurality of slots and then, via the fluid connection, enters the rectifier cavity. In some examples, the fluid connection can be formed as a radial through-bore in the wall of the rotor shaft. In this embodiment, the number of filling processes is reduced.

[0027] In one embodiment, the rectifier cavity can be filled via an inlet channel in the slide. The inlet channel can be designed, for example, as a through-hole. This allows the electrical components of the rectifier board located in the rectifier cavity to be overmolded particularly easily. According to a second aspect, the present invention relates to a rotor assembly for a separately excited synchronous machine, the rotor assembly comprising the following:

[0028] - a hollow rotor shaft in a laminated core comprising rotor windings on an outer peripheral side;

[0029] - an inductive transmission unit for the contactless transmission of a current required for rotor field generation to the rotor windings;

[0030] - a rectifier board for rectifying the current transmitted by the transmission unit, wherein the rectifier board is arranged in the rotor shaft, wherein the electrical components of the rectifier board and / or the rotor windings are overmolded with a non-conductive plastic.

[0031] The above statements regarding a rotor arrangement with regard to the first aspect of the present invention also apply to the second aspect.

[0032] Embodiments of the invention will now be described with reference to the following figures.

[0033] Fig. 1a shows a schematic representation of a rotor arrangement of a separately excited synchronous machine;

[0034] Fig. 1b schematically shows an enlarged view of Fig. 1a in the area of ​​an inductive transmission unit;

[0035] Fig. 2a schematically shows a manufacturing state of the rotor arrangement for the separately excited synchronous machine according to a first embodiment;

[0036] Fig. 2b schematically shows an enlarged view of Fig. 2a in the area of ​​the inductive transmission unit;

[0037] Fig. 3a schematically shows a manufacturing state of the rotor arrangement for the separately excited synchronous machine according to a second embodiment;

[0038] Fig. 3b schematically shows an enlarged view of Fig. 3a in the area of ​​the inductive transmission unit; Fig. 4 schematically shows a manufacturing state of the rotor arrangement for the separately excited synchronous machine according to an example;

[0039] Fig. 4a shows a schematic enlarged view of the rotor arrangement of Fig. 4 in the area of ​​the rectifier board; and

[0040] Fig. 5 shows a block diagram of a method for electrically insulating electrical components of the rotor assembly according to the first embodiment; and

[0041] Fig. 6 shows a block diagram of a method for electrically insulating electrical components of the rotor arrangement according to the second embodiment.

[0042] Fig. 1a shows a rotor arrangement 100 of a separately excited synchronous machine (not shown). The rotor arrangement 100 comprises a hollow rotor shaft 1, which is designed as a hollow shaft. The rotor shaft 1 comprises an inductive transmission unit 4 for the contactless transmission of an excitation current to rotor windings 11 of the rotor shaft 1, which are arranged on an outer circumferential side of the rotor shaft 100 and distributed in the circumferential direction. Furthermore, the inductive transmission unit 4 is coupled to a rectifier board 7. The rectifier board 7 serves to rectify the excitation current, initially present as alternating current. The rotor shaft 1 is inserted into a laminated core 2.As already known from the prior art, the laminated core 2 is assembled from a plurality of star-shaped sheet metal pieces, forming a plurality of rotor teeth that are evenly distributed in the circumferential direction of the laminated core 2 and extend axially from one end of the laminated core 2 to the other end. Grooves 11' are formed between the rotor teeth, which accommodate rotor windings 11 wound around the rotor teeth. The laminated core 2 is fluid-tightly sealed in the axial direction by first and second support disks 2a, 2b, which are arranged at an output-side and drive-side end of the rotor shaft 1, respectively. Furthermore, sealing in the radial outward direction is provided by slot closures (not shown) that are inserted into the grooves 11' of the laminated core 2.

[0043] Fig. 1b shows an enlarged and simplified illustration of the rotor shaft 1 in the area of ​​the inductive transmission unit 4, which comprises a primary ferrite core 5 with primary windings 5a and a secondary ferrite core 6 with secondary windings 6a. The secondary windings 6a are electrically connected via a connection 6b to an intermediate board 8, which is electrically coupled to the rectifier board 7, e.g. via a plug connection (not shown). The intermediate board 8 is inserted into an intermediate element 10. The intermediate element 10 comprises an inner collar 10a, which runs along a central opening of the intermediate element 10, and an outer collar 10b, which runs along an outer circumference of the intermediate element 10. The outer collar 10b can be formed integrally with the intermediate element 10 or be present as a separate part.

[0044] The rectifier board 7 is arranged in the rotor shaft 1 such that an outer circumference of the rectifier board 7 is essentially flush with the inner circumference of the rotor shaft 100. In some examples, the rectifier board 7 can be circular. The rectifier board 7 is arranged within the rotor shaft 1 such that the side of the rectifier board 7 with the electrical components faces the inductive transmission unit 4. The axial position of the rectifier board 7 within the rotor shaft 1 is adjusted on the one hand by a stop 1b on the rotor shaft side and on the other hand by a stop sleeve 9. The stop 1b runs in the circumferential direction of the inner circumferential side of the rotor shaft 1 and extends radially inward.An end face of the stop sleeve 9, facing away from the rectifier board 7, and a free end of the outer collar 10b of the intermediate element 10 have correspondingly designed receiving shoulders. The rectifier board 7 conducts the rectified current via winding terminals (not shown) to the rotor windings 11. The winding terminals (e.g., pieces of wire) are led from the rectifier board 7 through penetrations (not shown) in the wall of the rotor shaft 1 outward to the rotor windings 11. Furthermore, the outer collar 10b of the intermediate element 10 and the stop sleeve 9 have recesses (not shown) for passing through the winding terminals.

[0045] In an embodiment not shown, the outer collar 10b of the intermediate element 10 or the stop sleeve 9 can be omitted. In such cases, the axial position of the rectifier board 7 is adjusted on one side by the remaining element. For example, if the stop sleeve 9 is omitted, the outer collar 10b can abut directly on the rectifier board 7. If the outer collar 10b is omitted, the stop sleeve 9 can abut directly on the intermediate board 8.

[0046] To effectively cool the rectifier board 7, only dielectric media such as oil have been used so far due to the conductive components of the rectifier board 7. To increase the cooling performance, electrically conductive cooling media such as water glycol can be used. However, for this purpose, the electrical components (such as the rotor windings 11 and the rectifier board 7) must be electrically insulated. The insulation can be achieved by plastic encapsulation (e.g. by transfer molding, injection molding, or vacuum pressing), as described later for Figs. 2 and 3. Alternatively, a fluid-tight seal of a chamber accommodating the rectifier board 7 (rectifier cavity 7') can be created, as described for Fig. 4. In combination with a plastic-overmolded stator, cooling the stator and the rotor windings with an electrically conductive fluid is also possible.This enables maximum cooling performance and unrestricted use of cooling media.

[0047] Fig. 2a schematically shows a manufacturing state of the rotor shaft 1 according to a first embodiment. In the manufacturing state according to the first embodiment, a plastic encapsulation is present in the area of ​​the rotor windings 11 and the rectifier board 7. For this purpose, an insertion opening 3a is provided in the first support disk 2a, through which the plastic can be injected. Furthermore, radial through-bores 1a are provided in the wall of the rotor shaft 1 in the area of ​​the rectifier board 7. As shown in Fig. 2, two radial through-bores 1a can be provided, which can be arranged diametrically to one another. In an example not shown, only one radial through-bore 1a can be provided. In further examples not shown, a plurality of radial through-bores 1a (more than two) can also be provided, which are arranged regularly or randomly distributed in the circumferential direction of the rotor shaft 1.The radial through-bores 1a can also correspond to the above-mentioned penetrations for the winding terminals for electrically contacting the rotor windings 11. In the manufacturing state shown in Fig. 2a according to the first embodiment, the inductive transmission unit 4 is not yet installed. Instead, a slide (or "insert") 20 is provided, which is at least partially inserted into the rotor shaft 1 and thus seals the rectifier board 7 from the outside in the axial direction.

[0048] Fig. 2b shows an enlarged and simplified illustration of the slide 20. The slide 20 includes a projection 20a on an end face facing the rectifier circuit board 7, which projection projects in the direction of the rectifier circuit board 7. The projection 20a abuts the rectifier circuit board 7. During the injection process, the plastic flows around the projection 20a and thus forms a through-opening through the forming potting compound, which is provided for the passage of the oil lance (not shown). In other words, the projection 20a enables a radial clearance to the oil lance to be provided in the potting compound after the injection process. Furthermore, the slide 20 includes a sealing element 20b at the free end of the projection 20a. A further sealing element 20c, for example in the form of an O-ring, is provided between a circumferential surface of the projection 20a and an inner circumferential surface of the inner collar 10a of the intermediate element 10.

[0049] To inject the plastic, the rotor shaft 1 is positioned such that the longitudinal axis of the rotor shaft 1 is parallel to the direction of gravity and the end of the rotor shaft 1 (drive-side end) with the rectifier board 7 points upwards (as shown in Fig. 2). The following occurs during the injection process: The plastic is injected through the insertion opening 3a and thus fills the grooves 11' present in the laminated core 2. The grooves 11' now fill from bottom to top, whereby at the upper end (ie in the area of ​​the rectifier board 7) the plastic passes through the radial through-holes 1a and thus runs radially inwards in the direction of the rectifier board 7 and there fills a rectifier cavity 7' which is formed by an outer circumferential side of the projection 20a of the slide 20, the intermediate element 10 and the rectifier board 7 as well as the inner wall of the rotor shaft 1.The electrical components of the rectifier board 7 are arranged in the rectifier cavity 7'. The plastic flows through the gap between the winding terminals and the radial through-bores 1a and, in the hardened state, provides or reinforces the electrical insulation at this point.

[0050] The injection process encapsulates the rotor windings 11 and the electrical components of the rectifier board 7 and thus electrically insulates them.

[0051] The second support disc can include vent openings 3b. The air can escape to the outside through the vent openings 3b during the injection process. The vent openings 3b and the injection of the plastic against gravity can reduce the formation of air pockets in the plastic casting.

[0052] 3a and 3b schematically show a manufacturing state of the rotor assembly 100 according to the second embodiment. Fig. 3b shows an enlarged and simplified representation of the slide 20' from Fig. 3a. In the second embodiment, a first potting compound for the rotor windings 11 and a second potting compound for the rectifier board 7 are provided by separate injection processes. In contrast to the first embodiment, the rotor shaft 1 no longer comprises radial through-bores 1a (but still the penetrations for the winding connections). Instead, the slide 20' according to the second embodiment comprises an insertion channel 20d. During the injection process, the plastic is guided towards the rectifier board 7 via the insertion channel 20d, where the rectifier cavity 7' is filled. The injection process encapsulates the electrical components of the rectifier board 7 and thus electrically insulates them.In the embodiment shown in Figs. 2a and 2b, different potting materials can be used for the rectifier board 7 and the rotor windings 11. It should be noted that the penetrations for the winding connections must be sealed with sealing elements (not shown) to prevent the second potting compound from reaching the rotor windings 11'. After the injection process according to Figs. 2a, 2b and 3a, 3b, the slider is

[0053] 20 or slider 20' is removed, and instead the inductive transmission unit 4 is inserted at this point.

[0054] Fig. 4 schematically shows a manufacturing state of the rotor shaft 100 according to an example, and Fig. 4a shows an enlarged view in the area of ​​the rectifier board 7. Unlike in Figs. 2 and 3, electrical insulation is not achieved by plastic encapsulation, but by sealing the rectifier cavity 7' against cooling media. In the present case, an end face of the inductive transmission unit 4 replaces an end face of the slide 20, 20' as a boundary of the rectifier cavity 7'. For this purpose, a first sealing element 13a, for example a silicone compound, is provided on an inner diameter of the rectifier board 7, which runs along the outer circumference of the collar 7b, and a second sealing element 13b, for example an O-ring, is provided on an outer diameter of the rectifier board 7. The second sealing element 13b is provided to seal the feedthroughs for the winding connections.The sealing of the rectifier board 7 against cooling media represents a comparatively simple electrical insulation of the rectifier components against cooling media.

[0055] Fig. 5 shows a method 500 according to the first embodiment for electrically isolating the electrical components of the rectifier board 7 and the rotor windings 11 as shown in Fig. 2.

[0056] In block 501, the rotor shaft 1 is prepared, as shown in Fig. 2. The rotor shaft 1 thus comprises the insertion opening 3a and the vent opening 3b in the first support disk 2a and in the second support disk 2b, respectively. In block 502, the rotor shaft 1 is inserted into the laminated core 2, on which the rotor windings 11 are received in the slots 11' of the laminated core 2. In block 503, a rectifier board 7 is inserted into the rotor shaft 1. In block 504, the slider 20 is inserted into the rotor shaft 1, so that the rectifier cavity 7', in which the electrical components of the rectifier board 7 are arranged, is formed between the rectifier board 7, the circumferential side of the projection 20a of the slider 20, and the inner wall of the hollow rotor shaft 1. In block 505, the rotor shaft 1 is optionally aligned essentially parallel to the direction of gravity.In block 506, the rectifier cavity 7' and the slots 11' for the rotor windings 11 are filled with a non-conductive plastic by a filling or injection process.

[0057] Blocks 503 and 504 and (if present) block 505 can be executed in any order.

[0058] Fig. 6 shows a method 600 according to the second embodiment for electrically isolating the electrical components of the rectifier board 7 as shown in Fig. 3.

[0059] In block 601, the rotor shaft 1 is prepared as shown in Fig. 3. In block 602, the rectifier board 7 is inserted into the rotor shaft 1. In block 603, the slide 20' is inserted into the rotor shaft 1, so that the rectifier cavity 7' is formed between the rectifier board 7, the circumferential side of the projection 20a of the slide 20' and the inner wall of the hollow rotor shaft 1, in which the electrical components of the rectifier board 7 are arranged. In block 604, the slider 20' is inserted into the rotor shaft 1, so that the rectifier cavity 7' is formed between the rectifier board 7, the circumferential side of the projection 20a of the slider 20', and the inner wall of the hollow rotor shaft 1, in which the electrical components of the rectifier board 7 are arranged. In block 605, the rotor shaft 1 is optionally aligned essentially parallel to the direction of gravity.In block 606, the rectifier cavity 7' is filled with a non-conductive plastic via the insertion channel 20d. In block 607, the plurality of grooves 11' is filled with a non-conductive plastic by a filling or injection process.

[0060] Blocks 603 and 604, as well as (if present) block 605, can be executed in any order. Blocks 606 and 605 can also be interchanged. Reference symbols

[0061] 1 rotor shaft

[0062] 1a Radial through holes

[0063] 2 sheet packages

[0064] 2a first support disc

[0065] 2b second support disc

[0066] 3a Insertion opening

[0067] 3b Ventilation openings

[0068] 4 inductive transmission unit

[0069] 7 Rectifier board

[0070] 7' rectifier cavity

[0071] 7b Collar

[0072] 8 Intermediate board

[0073] 9 Stop sleeve

[0074] 10 Intermediate element

[0075] 10a inner collar

[0076] 10b outer collar

[0077] 11 rotor windings 11 ' multitude of slots

[0078] 13a first sealing element

[0079] 13b second sealing element

[0080] 20 sliders

[0081] 20a lead

[0082] 20b Sealing element

[0083] 20c additional sealing element

[0084] 20d insertion channel

[0085] 20' slider

[0086] 100 rotor arrangement

[0087] 500 Method according to a first embodiment

[0088] 600 Method according to a second embodiment

Claims

Patent claims 1 . A method (500; 600) for electrically insulating electrical components in a rotor assembly (100) for a separately excited synchronous machine, comprising: - Providing a hollow rotor shaft (1); - Inserting a rectifier board for an inductive transmission unit (4) into the rotor shaft (1); and - Inserting a slider (20; 20') into the rotor shaft (1 ) so that a rectifier cavity (7') is formed between the rectifier board (7), an end face of the slider (20; 20') and an inner wall of the hollow rotor shaft (1 ), in which the electrical components of the rectifier board (7) are arranged; and - Filling the rectifier cavity (7') with a non-conductive plastic.

2. The method (500; 600) according to claim 1, wherein the filling is carried out by injection molding.

3. The method (500) of claim 1 or 2, further comprising: - inserting the rotor shaft (1) into a laminated core (2) which has a plurality of slots (11') and rotor windings (11) are accommodated in the plurality of slots (11'); and - Filling the plurality of grooves (11') with a non-conductive plastic via an insertion opening (3a) provided in the rotor housing (3).

4. The method (500) according to claim 3, wherein, when filling the plurality of grooves (11'), the rotor assembly (100) is positioned such that the rotor shaft (1) is arranged substantially parallel to the direction of gravity.

5. Method (500) according to claim 3 or 4, wherein the insertion opening (3a) is provided on a support disk (2a) of the laminated core (2).

6. Method (500) according to one of claims 3 to 5, wherein another support disk (2b) of the laminated core (2) comprises at least one vent opening (3b).

7. The method (500) according to any one of claims 3 to 6, wherein the filling of the rectifier cavity (7') and the plurality of grooves (11') is carried out by a filling process.

8. Method (600) according to claim 1 or 2, wherein the filling of the rectifier cavity (7') takes place via an introduction channel (20d) in the slide (20').

9. Rotor arrangement (100) for a separately excited synchronous machine, comprising: - a rotor shaft (1) designed as a hollow shaft in a laminated core which comprises rotor windings (11) on an outer circumferential side; - an inductive transmission unit (4) for the contactless transmission of a current required for rotor field generation to the rotor windings (11); - a rectifier board (7) for rectifying the current transmitted by the transmission unit (4), wherein the rectifier board (7) is arranged in the rotor shaft (1), wherein the electrical components of the rectifier board (7) and / or the rotor windings (11) are overmolded with a non-conductive plastic.

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