Rotor shaft and motor

Abstract

The invention relates to a rotor shaft for a rotor of an electric machine. The rotor shaft includes a hollow shaft extending in an axial direction from a first axial end section to a second axial end section. In addition, the rotor shaft comprises an extension element, which is preferably sleeve-like and forcibly separate from the hollow shaft. Therefore, the rotor shaft comprising the hollow shaft and the extension element is formed in at least two parts. The extension element is connected to a first end section of the hollow shaft by means of a first bearing device in a rotatable manner with the hollow shaft and extends axially beyond the first end section of the hollow shaft in order to axially extend the hollow shaft. Furthermore, the rotor shaft has a second bearing device, which is arranged externally on a second end section of the hollow shaft and is rotatably or rotationally fixed to the hollow shaft.

Description

Technical Field

[0001] The invention relates to a rotor shaft for a rotor of an electric machine and to an electric machine having such a rotor shaft. Background Art

[0002] Conventional rotor shafts for electric machines are usually designed in the form of a plurality of cylinders with different diameters and the interconnection of respectively different functional elements for forming bearing points, forming seats for rotor cores and balancing disks, accommodating cable guides and the like when the electric machine is an externally excited synchronous machine.

[0003] This geometrical interconnection of the individual functional elements results in a relatively high installation space requirement with regard to the axial longitudinal extension of the rotor shaft.

[0004] A conventional rotor shaft is usually designed as a hollow shaft and has two bearing arrangements which are arranged axially spaced apart from one another for rotatably mounting the rotor shaft.

[0005] For the sake of simplicity, the two bearing arrangements are usually designed to be identical or at least to have identical dimensions, even though due to the different strengths of the loads on the two bearing arrangements a separate design of the two bearing arrangements may be provided. Summary of the invention

[0006] Against this background, the object of the present invention is to point out new paths in the development of a rotor shaft for an electric machine or a rotor of said electric machine. In particular, an improved embodiment for a rotor shaft is to be proposed which is distinguished by a reduced installation space requirement compared to conventional rotor shafts while having a simple technical design and thus reduced manufacturing costs.

[0007] The basic idea of ​​the invention is therefore that the two bearing arrangements for rotatably mounting the rotor shaft are not designed in the same way, but that one of the two bearing arrangements is connected to the hollow shaft via an extension element that is designed separately from the actual hollow shaft. The extension element is thus designed rotatably relative to the actual hollow shaft by means of the bearing arrangements, so that the extension element can be fastened in a fixed position, for example to the stator or housing of the electric machine.

[0008] By means of the extension element, the hollow shaft can be mechanically rigidly and stably fastened and rotatably supported on a fixed component of the motor, such as the stator or housing of the motor. This is accompanied by an advantageous reduction in undesired bending of the hollow shaft during operation of the rotor shaft. As a result, advantageously, not only the mechanical loads occurring on the side with low loads are reduced, but also the mechanical loads occurring on the side that is loaded, i.e., that transmits the load, and thus the mechanical loads occurring in the two bearing arrangements of the rotor shaft are reduced. In principle, this is accompanied by the following advantageous possibility: the dimensions of the bearing arrangement connected to the extension element are determined to be smaller than the dimensions of the other of the two bearing arrangements. Finally, the extension element can be manufactured independently of the rotor shaft and can therefore be manufactured more cost-effectively than a conventional rotor shaft with a conventional bearing journal.

[0009] According to the basic concept of the present invention, the rotor shaft of the rotor of the electric machine according to the present invention comprises a hollow shaft, which extends from a first axial end section to a second axial end section in the axial direction. In addition, the rotor shaft comprises an extension element which is preferably sleeve-shaped and forcibly separated from the hollow shaft. That is, the rotor shaft comprising the hollow shaft and the extension element is constructed in at least two parts. The extension element is connected to the first end section of the hollow shaft by means of a first bearing device in a manner that can rotate with the hollow shaft, and extends axially beyond the first end section of the hollow shaft in order to extend the hollow shaft in the axial direction. In addition, the rotor shaft has a second bearing device, which is arranged externally on the second end section of the hollow shaft and is rotatably or non-rotatably connected to the hollow shaft.

[0010] According to an advantageous extension, a bearing cover is molded or arranged, in particular integrally molded or arranged, on the hollow shaft in the region of the first end section axially, which extends radially inwardly into the interior space and on which the first bearing device is supported and / or fastened.

[0011] According to another advantageous embodiment, an electrical line or cable bushing is provided on the hollow shaft and on the extension element in the axial direction in the region of the first end section, in particular for providing an electrical connection of the stationary extension element to the rotating hollow shaft and thus for transmitting electrical energy from the extension element to the rotor shaft. The design of the rotor shaft according to the invention with the stationary extension element simplifies the design of such a line or cable bushing and the guidance of electrical lines or cables to the rotatable hollow shaft, including the fluid-tightness of this guidance, since this sealing can be achieved on the stationary extension element.

[0012] If the rotor shaft according to the invention is used as part of a rotor in an electric machine, the electrical line or cable bushing can be used in particular to supply electrical energy to rotor coils for generating a rotor magnetic field, which are arranged on the rotor and can be energized. Thus, electrical energy is transferred from a stationary stator system to a rotor system that rotates during operation of the electric machine by means of the electrical line or cable bushing. The structural space that is ready for use in the first end section or in the region of the extension element can be effectively used to supply electrical energy or current to components arranged on the rotor shaft, in particular the rotor coils of the rotor.

[0013] Particularly preferably, the electrical line or cable bushing can be designed as an electric rotary transformer for wireless electrical energy transmission. In the case of such a rotary transformer, the energy transmission from the stationary extension element to the rotatable or rotating hollow shaft is carried out inductively and thus wirelessly. In the case of the electric rotary transformer, due to the electrical connection between the stationary extension element and the rotating hollow shaft, undesirable wear effects are avoided, which would occur, for example, in the case of a wired electrical connection, for example, in the case of a wired sliding contact, due to the sliding friction that occurs.

[0014] In another preferred embodiment, the rotary transformer comprises a rotary transformer rotor and a rotary transformer stator, wherein the rotary transformer rotor is connected to the hollow shaft in a rotationally fixed manner, the rotary transformer stator is arranged axially spaced apart from the rotary transformer rotor and is inductively coupled to the rotary transformer rotor, and the rotary transformer stator is firmly or rotationally connected to the extension element. Such a rotary transformer stator and such a rotary transformer rotor can each have at least one rotary transformer stator coil or rotary transformer rotor coil that can be energized, and the rotary transformer stator coil or rotary transformer rotor coil generates a magnetic field when energized. Here, the rotary transformer stator coil and the rotary transformer rotor coil need to be magnetically coupled to each other, so that when the rotary transformer stator coil is energized, an alternating voltage and thus an alternating current are induced according to the induction law due to the magnetic coupling with the rotary transformer rotor coil. After rectifying the alternating current, the alternating current can be used to energize the rotor of the motor. Therefore, the rotor can be driven by magnetic interaction with the stator of the motor. This functional principle is particularly applied in externally excited synchronous motors, so that the use of the rotary transformer described above in externally excited synchronous motors has proven to be particularly advantageous.

[0015] In a particularly preferred embodiment, the rotary transformer can be arranged axially on the side of the first bearing device or / and the bearing cover facing away from the interior space, i.e., can be arranged outside the interior space. This variant enables workers to have particularly good access to the rotary transformer, so that the rotary transformer can be particularly easily assembled, but the rotary transformer can also be removed again.

[0016] In an alternative embodiment to the one described above, which is still also particularly preferred, the rotary transformer can be arranged axially on the side of the first bearing device or / and the bearing cover facing the interior space, i.e., can be arranged in the interior space surrounded by the hollow shaft. Particularly preferably, the rotary transformer can most preferably be arranged completely in the interior space. This variant requires particularly little construction space, because the interior space present in the hollow shaft can be used to accommodate the rotary transformer. In this way, no additional construction space is required outside the hollow shaft to accommodate the rotary transformer. Therefore, the entire rotor shaft with the rotary transformer also requires particularly little construction space.

[0017] In another preferred embodiment of the rotor shaft according to the invention, the electrical line or cable bushing is designed for wired electrical energy transmission and can for this purpose have at least one slip ring as part of the sliding contact, which is preferably connected to the extension element or to the hollow shaft in a rotationally fixed manner.

[0018] In another preferred embodiment of the rotor shaft according to the invention, the first bearing arrangement is supported radially on the outside on the hollow shaft and radially on the inside on the extension element, in particular on the peripheral wall of the extension element. In this way, the hollow shaft can be supported mechanically rigidly and also particularly stably in rotation by the first bearing arrangement.

[0019] According to another advantageous development of the rotor shaft according to the invention, a coupling device can be formed in the second end section of the hollow shaft for drivingly coupling the rotor shaft to an external component. In this case, the coupling device forms a driven element for transmitting the rotational movement of the rotor shaft to the external component by means of the drive connection. The coupling device or the drive element can be formed in particular by a surface structure, which is arranged on the outer circumference or the inner circumference of the rotor shaft.

[0020] The diameter of the hollow shaft in the second end section can be reduced. That is, the hollow shaft has a smaller diameter in its second end section than in at least one axial section different from the second end section. The axial section can in particular include the first end section. The axial section can be complementary to the second end section.

[0021] In another preferred embodiment, the extension of the second end section of the hollow shaft measured in the axial direction is greater than the extension of the extension element beyond the first end section of the hollow shaft measured in the axial direction. This means that the rotor shaft is designed to be particularly compact in the axial direction in the first axial end section. This embodiment has proven to be advantageous in particular in conjunction with the coupling device already explained above, which is provided in the second end section for drivingly coupling the rotor shaft to an external component, if the coupling device is arranged outside the second end section, preferably on the outer circumference of the second end section.

[0022] In another preferred embodiment, the first bearing device is arranged radially between the hollow shaft and the extension element. In this way, the required installation space of the rotor shaft in the radial direction can be kept small. In the two variants explained above, the entire rotor shaft requires particularly little installation space in the axial direction compared to a conventional rotor shaft with a double bearing structure.

[0023] In another preferred embodiment, the first bearing device is arranged axially in the region of the first end section in an interior space delimited at least radially by the hollow shaft. This variant also reduces the installation space required by the rotor shaft in the radial direction.

[0024] Particularly expediently, the first and / or the second bearing arrangement can be designed as a radial bearing.

[0025] In a preferred embodiment, the first bearing device is also connected to the extension element in a rotationally fixed manner and is rotatably connected to the hollow shaft relative to the hollow shaft. In an alternative variant, the first bearing device can be connected to the hollow shaft in a rotationally fixed manner and is also rotatably connected to the extension element. Thus, a person skilled in the art can select and implement the most advantageous variant in a specific application.

[0026] In another preferred embodiment, the second bearing device has a larger spatial extension than the first bearing device. Alternatively or additionally, in this variant, the second bearing device is designed to receive larger bearing forces than the first bearing device.

[0027] In addition, the present invention relates to an electric machine. The electric machine according to the present invention comprises a housing, which surrounds, in particular at least radially, an interior space of the housing. In addition, the machine comprises a stator and a rotor, which is arranged in a fixed manner relative to the housing in the interior space of the housing, the rotor is at least partially arranged in the interior space of the housing and can rotate relative to the stator and is magnetically coupled to the stator, and the rotor can be driven by the stator by means of magnetic interaction. According to the present invention, the rotor comprises the rotor shaft according to the present invention introduced above, on which a magnetic field generating element for generating a rotor magnetic field is arranged in a rotationally fixed manner. Therefore, the advantages of the rotor shaft according to the present invention explained above are transferred to the electric machine according to the present invention. The magnetic field generating element can be formed in particular by a rotor coil that can be energized or by a permanent magnet. In the electric machine according to the present invention, the extension element of the rotor shaft is firmly, in particular rigidly connected to the housing or / and to the stator. In addition, the hollow shaft is rotatably supported on the housing or / and on the stator by means of a second bearing device.

[0028] Further important features and advantages of the invention emerge from the drawings and the associated description of the figures based on the drawings.

[0029] It is self-evident that the features mentioned above and those yet to be explained below can be used not only in the respectively specified combination but also in other combinations or alone without departing from the scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Preferred exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description, wherein identical reference numerals refer to identical or similar components or components having the same function.

[0031] The accompanying drawings schematically show:

[0032] Figure 1 A first example of a rotor shaft according to the invention is shown;

[0033] Figure 2 Show Figure 1 A first embodiment of a rotor shaft in the region of an extension element has an electrical line or cable bushing for wired energy transmission from the stationary extension element to the rotor shaft.

[0034] Figure 3 and Figure 4 Show Figure 1 A second or third embodiment of the rotor shaft in the region of an extension element comprises an electrical line or cable bushing for wireless energy transmission from the stationary extension element to the rotor shaft. DETAILED DESCRIPTION

[0035] Figure 1 In the roughly schematic sectional view, an example of an electric machine 15 according to the invention is shown, which has a rotor shaft 1 according to the invention, which is disposed at Figure 1 The figures are shown in a greatly enlarged manner to illustrate the facts.

[0036] according to Figure 1 The electric machine 15 according to the invention comprises a housing 18, which is shown in a greatly simplified manner and which encloses a housing interior space 19. The stator 16 is arranged in the housing interior space 19 in a fixed position relative to the housing 18, and can be fastened to the housing 18 and Figure 1 It is only roughly shown schematically.

[0037] The electric motor 15 further comprises a rotor 17 which is arranged in a housing interior 19 and is rotatable relative to a stator 16 about a predetermined rotation axis D, and comprises a rotor shaft 1 according to the invention. The stator 16 and the rotor 17 can each have stator coils or rotor coils (not shown) which can be energized and generate a magnetic field when energized.

[0038] The rotor shaft 1 includes a hollow shaft 2, a rotor coil 24 (in Figure 1 The rotor coils 24 (indicated only roughly schematically in the figure) can be arranged as part of the rotor 17 on the outer circumference 23 of the hollow shaft in a rotationally fixed manner relative to the hollow shaft 2 or relative to the rotor shaft 1, with the help of which the rotor magnetic field can be generated. The use of rotor coils 24 is particularly advantageous if the electric machine 15 is an externally excited synchronous machine 15a. Due to the magnetic interaction of the stator magnetic field with the magnetic rotor, the rotor 17 including the rotor shaft 1 can be driven and thus set into a rotational movement about the rotation axis D relative to the stator 16 or the housing. Instead of the rotor coils 24, permanent magnets (not shown) can also be used.

[0039] like Figure 1 As shown, the rotor shaft 1 is constructed in multiple parts and comprises at least one hollow shaft 2 and an extension element 4 constructed separately from the hollow shaft 2 , which can extend in an axial direction A and can be arranged coaxially with respect to one another as shown. The hollow shaft 2 delimits an interior space 8 of the rotor shaft 1 .

[0040] In the exemplary scenario, the common central longitudinal axis M of the hollow shaft 2 and of the extension element 4 forms the rotation axis D of the rotor shaft 1. The radial direction R extends perpendicularly to the axial direction A away from the central longitudinal axis M or the rotation axis D. The circumferential direction U extends perpendicularly to the axial direction A and also perpendicularly to the radial direction R around the central longitudinal axis M or around the rotation axis D.

[0041] like Figure 1It is also shown that the extension element 4 of the rotor shaft 1 is rigidly and therefore firmly connected to the housing 18 and in this way—indirectly via the housing 18—is also firmly connected to the stator 16 of the electric machine 15. In a variant that is not shown, a direct, firm or rigid connection of the extension element 4 to the stator 16 is also conceivable. Both connection variants can be realized, for example, by means of a clamping connection (not shown).

[0042] The hollow shaft 2 extends along the axial direction A from a first axial end section 3a to a second axial end section 3b. Figure 1 , the extension element 4 can be constructed in a sleeve-like manner and, similar to the hollow shaft 2, also surround an element interior space 27, which can be fluidically connected to the interior space 8. The extension element 4 is rotatably connected to the first end section 3a of the hollow shaft 2 by means of a first bearing device 5a, and extends axially beyond the first end section 3a of the hollow shaft in order to extend the hollow shaft 2 in the axial direction, so that the extension element 4 extends the hollow shaft 2 in the axial direction. Here, as shown in the figure, the first bearing device 5a can be arranged axially in the region of the first end section 3a in the interior space 8 delimited by the hollow shaft 2. In addition, as shown in the figure, the first bearing device 5a can be arranged radially between the hollow shaft 2 and the extension element 4. Here, the first bearing device 5a is supported radially on the inner peripheral side 25 of the hollow shaft 2 and radially on the outer peripheral side 30 of the peripheral wall 6 of the extension element 4.

[0043] In addition, the rotor shaft 1 comprises a second bearing device 5b, which is arranged on the outer circumference 23 of the second end section 3b of the hollow shaft 2 and is rotatably connected to the hollow shaft. The hollow shaft 2 is rotatably supported on the housing 18 by means of the second bearing device 5b, for which purpose the second bearing device 5b can be firmly connected to the housing 18.

[0044] The two bearing devices 5a, 5b can be configured as radial bearings respectively. Compared with the first bearing device 5a (not shown), the second bearing device 5b can have a larger spatial extension or spatial extension, and compared with the first bearing device 5a, the second bearing device can also be configured to receive a larger bearing force.

[0045] Furthermore, a coupling device 7 can be formed in the second end section 3 b of the hollow shaft 2 for drivingly coupling the rotor shaft 1 to an external component. Figure 1 In the example of , the coupling device 7 is formed by a toothing 26 or by another suitable surface structure, which extends on the outer circumference 23 of the hollow shaft 2 along the circumferential direction U. The coupling device 7 forms a driven element for transmitting the rotational movement of the rotor shaft 1 to the external component by means of the drive connection.

[0046] Suitably, such as Figure 1 As shown, the diameter D of the hollow shaft 2 in the second end section 3b of the hollow shaft, measured along the radial direction R, can be reduced. That is, the value D2 of the diameter D of the hollow shaft 2 in the second end section 3b of the hollow shaft is smaller than the value D1 of the diameter D in the region of the first end section D1, and is also smaller than the value D0 of the diameter D of the hollow shaft 2 in the axial region 3c between the two end sections 3a, 3b.

[0047] Furthermore, as shown in the example, an extension E2 of the second end section 3 b of the hollow shaft 2 measured in the axial direction A can be greater than a projection E1 of the extension element 4 beyond the first end section 3 a of the hollow shaft 2 measured in the axial direction A.

[0048] In the axial direction, in the region of the first end section 3 a , an annular bearing cover 9 can be integrally formed on the hollow shaft 2 , which extends inwardly in the radial direction R into the interior 8 and to which the first bearing device 5 a is supported and can also be fastened.

[0049] exist Figure 1 In the example scenario, the first bearing device 5a is connected to the extension element 4 in a rotationally fixed manner and is rotatably connected to the hollow shaft 2. However, in a variant alternative thereto, the first bearing device 5a can also be connected to the hollow shaft 2 in a rotationally fixed manner and is correspondingly rotatably connected to the extension element 4.

[0050] Figure 2 Show Figure 1 In this embodiment, an electrical line or cable leadthrough 10 is formed not only on the hollow shaft 2 but also on the extension element 4 in the axial direction in the region of the first end section 3a, for transmitting electrical energy from the extension element 4 to the rotor shaft 2 which can rotate relative to the extension element 4. In the exemplary scenario, the electrical line or cable leadthrough 10 is used to supply electrical energy to the rotor coil 24 which can be energized in order to generate a rotor magnetic field, and the rotor coil is arranged on the rotor 17 (at Figure 2 Not shown, see Figure 1 That is, by means of the electrical line or cable lead-through device 10, the electrical energy from the fixed stator system is transmitted to the motor 15 (see Figure 1 ) on the rotor system that rotates during operation.

[0051] exist Figure 2In the example of , the line or cable lead-through device 10 is configured for wired power transmission. To this end, the line or cable lead-through device 10 has two sliding contacts 14a, 14b arranged spaced apart from each other in the axial direction. Each of the two sliding contacts 14a, 14b includes a conductive slip ring 20a or 20b, which is arranged on the outer peripheral side 30 of the extension element 4 and extends along the circumferential direction U. In addition, each of the two sliding contacts 14a, 14b includes a conductive brush 21a or 21b, which cooperates with the corresponding slip ring 20a or 20b and rotates with the hollow shaft 2, that is, the brush slides against the corresponding slip ring 20a, 20b during the rotational movement of the hollow shaft 2 to construct a conductive connection. By means of the two sliding contacts 14 a , 14 b , an electrical line 22 a , 22 b arranged in a fixed position relative to the electrical connecting element 4 can be electrically connected to an electrical line 23 a or 23 b rotating with the hollow shaft 2 .

[0052] Figure 3 Show Figure 1 The second embodiment of the invention is an alternative embodiment of the rotor shaft of the electric motor 15. According to the second embodiment, the electric line or cable lead-through device 10 can be constructed as an inductive rotary transformer 11 of an electric motor 15 for wireless power transmission, the inductive rotary transformer comprising a rotary transformer rotor 12 connected to the rotatable hollow shaft 2 in a rotationally fixed manner and a rotary transformer stator 13 connected to the extension element 4 in a rotationally fixed manner and inductively coupled to the rotary transformer rotor 12, so that the rotary transformer rotor 12 can rotate relative to the rotary transformer stator 13. In such a rotary transformer 11, energy is transferred from the rotary transformer stator 13 to the rotary transformer rotor 12 in an inductive manner. The alternating magnetic field generated by the rotary transformer stator 13 by correspondingly energizing the rotary transformer stator coils (not shown) of the rotary transformer stator induces an alternating current in the rotary transformer rotor coils (not shown) of the rotary transformer rotor 12 through axial magnetic coupling, and the rotor coils 24 (see FIG. 2 ) of the electric motor 15 can be energized by the alternating current. Figure 1 ) is powered. Suitably, Figure 3 As shown, the rotary transformer 11 can be arranged axially on a side 28 of the bearing cover 9 facing away from the interior 8 and thus also on the first bearing device 5 a , ie outside the interior 8 .

[0053] Figure 4 Draw Figure 1 The third extension scheme of the example is Figure 3 An alternative variant of the second embodiment of Figure 3 and 4As shown, the third embodiment differs from the second embodiment in that the rotary transformer 11 is arranged axially on the side 29 of the first bearing device 5a facing the interior space 8 and can therefore also be arranged on the bearing cover 9. That is, the rotary transformer 11 is arranged in the interior space 8.

[0054] exist Figure 3 and 4 In the example of FIG. 5 , the transfer of electrical energy from two electrical lines 22a, 22b to two electrical lines 23a or 23b is achieved, that is, wirelessly.

Claims

1. A rotor shaft (1) for a rotor (17) of an electric machine (15), - having a hollow shaft (2) which extends along the axial direction (A) from a first axial end section (3a) to a second axial end section (3b), - having an extension element (4), which is designed separately from the hollow shaft (2) and preferably has a sleeve-shaped design, which is connected to the first end section (3a) of the hollow shaft by means of a first bearing device (5a) so as to be rotatable relative to the hollow shaft (2) and extends axially beyond the first end section (3a) of the hollow shaft in order to extend the hollow shaft (2) in the axial direction, A second bearing device (5b) is arranged externally on a second end section (3b) of the hollow shaft (2) and is connected to the hollow shaft in a rotatable or rotationally fixed manner.

2. The rotor shaft according to claim 1, It is characterized in that Axially in the region of the first end section (3a), a bearing cover (9) is formed, in particular integrally formed, on the hollow shaft (2), which extends radially inwardly into the interior space (8) and on which the first bearing device (5a) is supported.

3. The rotor shaft according to claim 1 or 2, It is characterized in that An electrical line and / or cable bushing (10) is located axially in the region of the first end section (3a), on the hollow shaft (2) and on the extension element (4), in particular for transmitting electrical energy from the extension element (4) to the rotor shaft (2).

4. The rotor shaft according to claim 3, It is characterized in that For wireless, in particular inductive, electrical energy transmission, the electrical line and / or cable bushing (10) is designed as part of a rotary transformer (11), is such a rotary transformer (11), or comprises such a rotary transformer (11).

5. The rotor shaft according to claim 4, It is characterized in that The rotary transformer (11) comprises a rotary transformer rotor (12) which is connected to the hollow shaft (2) in a rotationally fixed manner, and a rotary transformer stator (13), which is arranged axially spaced apart from the rotary transformer rotor (12) and is inductively coupled to the rotary transformer rotor, and which is firmly, in particular rotationally fixedly, connected to the extension element (4).

6. The rotor shaft according to claim 5, in particular claim 5 as a reliance on claim 2, It is characterized in that The rotary transformer (11) is arranged axially on a side (28) of the first bearing device (5a) and / or the bearing cover (9) facing away from the interior space (8).

7. The rotor shaft according to claim 5, in particular claim 5 as a reliance on claim 2, It is characterized in that The rotary transformer (11) is arranged axially on a side (29) of the first bearing device (5a) and / or the bearing cover (9) that faces the interior space (8).

8. The rotor shaft according to claim 5 or 7, It is characterized in that The rotary transformer (11) is arranged in an inner space (8) bounded by the hollow shaft (2).

9. The rotor shaft according to any one of claims 1 to 3, It is characterized in that The electrical line and / or cable bushing (10) is designed for wired electrical energy transmission and preferably has at least one slip ring (21a, 21b) as part of a sliding contact (14a, 14b), which is particularly preferably connected to the extension element (4) or to the hollow shaft (2) in a rotationally fixed manner.

10. A rotor shaft according to any one of the preceding claims, It is characterized in that The first bearing device (5a) is supported radially on the outside on the hollow shaft (2) and radially on the inside on the extension element (4), in particular on the peripheral wall (6) of the extension element (4).

11. A rotor shaft according to any one of the preceding claims, It is characterized in that A coupling device (7) is formed in the second end section (3b) of the hollow shaft (2) for drivingly coupling the rotor shaft (1) to an external component.

12. A rotor shaft according to any one of the preceding claims, It is characterized in that The diameter (D) of the hollow shaft (2) is reduced in the second end section (3b).

13. A rotor shaft according to any one of the preceding claims, It is characterized in that The extension (E2) of the second end section (3b) of the hollow shaft (2) measured along the axial direction (A) is greater than the extension (E1) of the extension element (4) beyond the first end section (3a) of the hollow shaft (2) measured along the axial direction (A).

14. A rotor shaft according to any one of the preceding claims, It is characterized in that The first bearing device (5a) is arranged radially between the hollow shaft (2) and the extension element (4).

15. A rotor shaft according to any one of the preceding claims, It is characterized in that The first bearing device (5a) is arranged axially in the region of the first end section (3) in an interior space (8) delimited by the hollow shaft (2).

16. A rotor shaft according to any one of the preceding claims, It is characterized in that The first bearing device (5a) is connected to the extension element (4) in a rotationally fixed manner and is connected to the hollow shaft (2) in a rotatable manner; or The first bearing device (5a) is connected to the hollow shaft (2) in a rotationally fixed manner and is connected to the extension element (4) in a rotatable manner.

17. A rotor shaft according to any one of the preceding claims, It is characterized in that - the second bearing device (5b) has a larger spatial extension than the first bearing device (5a); or / and The second bearing device (5b) is designed to receive greater bearing forces than the first bearing device (5a).

18. An electric motor (15), - having a housing (18) which encloses a housing interior space (19), - having a stator (16) and a rotor (17), the stator being arranged in a fixed manner relative to the housing (18) in the housing interior (19), the rotor being arranged at least partially in the housing interior (19) and being rotatable relative to the stator (16) and being magnetically coupled to the stator, the rotor being drivable by the stator in particular by means of magnetic interaction, -in, The rotor (17) comprises a rotor shaft (1) according to any one of the preceding claims, on which a magnetic field generating element (24) for generating a rotor magnetic field is arranged in a rotationally fixed manner, - wherein the extension element (4) of the rotor shaft (1) is firmly, in particular rigidly, connected to the housing (18) and / or the stator (16), and the hollow shaft (2) is rotatably supported on the housing (18) and / or on the stator (16) by means of the second bearing device (5b).

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