Multi-part rotor shaft for an electric machine

Abstract

A multi-part rotor shaft (1) for an electric machine (21), comprising the multi-part rotor shaft (1): - a first shaft journal (2) with a first end flange (3) and with a first axial through bore (12), - a second wave journal (4) with a second end flange (5), - a tubular support (6) for a rotor lamination stack (7) and - a conduit element (9) for conveying a cooling medium, wherein - the support (6) for the rotor lamination stack (7) is arranged between the first shaft journal (2) and the second shaft journal (4), - the support (6), the first end flange (3) and the second end flange (5) define a cavity (8) between them, - the conduit element (9) forms a cooling channel (10) within the cavity (8), wherein the cooling channel (9) is connected to the first axial through-bore (12) and extends between the first shaft journal (2) and the second shaft journal (4), characterized in that - the conductor element (9) consists of a metal foam.

Description

[0001] The invention relates to a multi-part rotor shaft for an electric machine. The invention further relates to a rotor and an electric machine.

[0002] Multi-section rotor shafts for electric machines are known. Such a rotor shaft typically comprises a cylindrical shell closed at both ends by end flanges, with a shaft journal located at each end flange. Usually, at least one of the end flanges, particularly the shaft journal, has a coaxial access bore, providing access for a medium to a shaft cavity surrounded by the cylindrical shell. Such hollow rotor shafts can be used particularly where a lightweight design is essential.

[0003] In particular, a cooling medium can be passed through the hollow rotor shafts for the purpose of cooling the rotor. In this regard, reference is made, for example, to DE 10 2014 107 845 A1, which describes supplying a cooling medium to a cavity via a pipe and discharging it again via an outlet. However, this type of cooling may be insufficient under certain circumstances and may not be proportionate to the design effort and the deterioration of the motor's running characteristics.

[0004] Furthermore, electrical machines are known in which a medium, e.g., a lubricant or coolant, must be transported from one end face to the other. In this case, the rotor has a purely conveying function, for which previously known hollow shafts are hardly suitable. In such machines with a conveying function, running irregularities can occur due to the considerable expansion of the conductor cross-section, caused by the expansion of the medium in the hollow shaft and by turbulence within the hollow shaft. Moreover, a hollow shaft completely filled with liquid medium can negate the advantage of weight savings. In particular, filling a hollow cylinder with liquid can negatively affect its rotational moment of inertia with regard to its use in the electrical machine.

[0005] Various solutions are also known for directing and distributing a cooling medium to the heat transfer surface, which usually involve a complete, forced guidance of the coolant in channels or bores over the entire axial and radial path.

[0006] Ultimately, the known cooling systems exhibit at least one of the following disadvantages: On the one hand, in order to reduce the required volume, the cross-sections of the coolant lines are chosen to be too small. Such a small through-hole hardly reduces the weight of the rotor shaft being cooled. Furthermore, due to the already small surface area, the coolant can only reach the components to be cooled, especially the highly heated laminated core, to a limited extent. The coolant often only wets small areas on the heated surface, and widespread distribution across the entire circumference is impossible.

[0007] On the other hand, large pipe cross-sections and cavities in the rotor shaft allow not only for a large surface area for heat transfer but also for a particularly lightweight design. However, in this case, it is a disadvantage that the hollow cylinder must be almost completely filled with coolant during operation, as this increases the coolant requirement, which in turn leads to an increase in the moving mass, which is precisely what the lightweight design is intended to avoid.

[0008] DE102015223631A1 describes a multi-part rotor shaft according to the preamble of claim 1.

[0009] From DE102014202056A1, an electric machine is known which has a stator and a rotor, wherein the rotor comprises a rotor shaft designed as a hollow shaft, and a closed cavity is formed in the hollow shaft in which a negative pressure prevails and in which a heat-transferring medium is contained. The hollow shaft has an evaporation zone and a condensation zone, wherein a vapor channel is provided in the cavity, and the surface of the cavity has structures which, through rotation, cause the transport of the condensate of the heat-transferring medium.

[0010] From DE102011006280A1, an electric machine with a rotor shaft supporting a rotor is known. In the contact area between the rotor and the rotor shaft, at least approximately groove-like areas are provided in a lateral surface of the rotor shaft facing the rotor shaft and / or in an inner lateral surface of the rotor facing the rotor shaft, through which fluid can be guided to regulate at least one operating temperature of the rotor shaft and one operating temperature of the rotor.

[0011] The object of the present invention can therefore be to provide a structurally simple and cost-effectively manufactured multi-part rotor shaft for an electric machine, wherein the rotor shaft is designed as a hollow shaft and, with low weight and good running properties, fulfills an efficient cooling and conduction function as well as enabling increased sound and / or vibration damping.

[0012] The problem is solved by the subject matter of the independent patent claims. Advantageous embodiments are the subject matter of the dependent claims, the following description, and the figures.

[0013] According to a first aspect of the invention, a multi-part rotor shaft for an electric machine is provided. The multi-part rotor shaft comprises a first shaft journal with a first end flange and a first axial through-bore, a second shaft journal with a second end flange, a tubular support for a rotor lamination stack, and a conduit element for conveying a cooling medium, wherein the support for the rotor lamination stack is arranged between the first shaft journal and the second shaft journal, wherein the support, the first end flange, and the second end flange define a cavity between them, wherein the preferably hollow cylindrical conduit element forms a cooling channel within the cavity, wherein the cooling channel is connected to the first axial through-bore and extends between the first shaft journal and the second shaft journal, and wherein the conduit element is made of a metal foam.

[0014] The shaft journals can be fixed to the support so that the support rotates when the shaft journals rotate. Similarly, the conductor element can be fixed to the support and / or the end flanges so that the conductor element rotates when the shaft journals rotate.

[0015] The rotor shaft according to the invention ensures media transport, in particular the transport of liquids, e.g. lubricants or coolants, especially an insulating coolant such as oil, but also oil mist or gases through the preferably hollow cylindrical rotor shaft.

[0016] In particular, it can be provided that no complete flushing takes place, but only a wetting of the surfaces to be cooled with coolant. Thus, with a small quantity of coolant and a correspondingly small flow rate, only enough of the total shaft cavity is traversed to wet only the internal surfaces essential for heat exchange, and in particular an inner surface of the support. Due to the small quantity of coolant, there is therefore only a minimal increase in the moving masses and thus in the moment of inertia.

[0017] In particular, heat can be dissipated in the area of ​​the rotor lamination stack. For this purpose, the medium can be introduced into the cooling channel of the ducting element via the first axial through-bore, which serves as the medium inlet, and then conveyed via the cooling channel to the other axial shaft end, which is formed by the second shaft journal. Alternatively, the medium can be conveyed to radial outlets at the other shaft end. In this way, cooling of the rotor shaft from the inside is possible.

[0018] By appropriately reducing temperatures, a higher rotor performance can be achieved, particularly at a defined component limit temperature, resulting in an improved power-to-weight ratio and power-to-volume ratio for an electric machine. The invention thus enables a lightweight rotor design with minimal coolant usage and highly efficient cooling. It is particularly advantageous that the rotating mass can remain low despite the coolant content. A low rotor weight is especially valuable for drive efficiency, as it is a rotating component. This also offers efficiency advantages during acceleration. Furthermore, efficient rotor cooling can lower the temperature class required when using permanent magnets, resulting in potential cost savings.

[0019] The metallic foam, arranged in the preferably large-volume, cylindrical cavity, enables an enormous weight reduction of approximately 90% compared to the solid material. Plastics are also suitable for this lightweight construction concept.

[0020] A particular advantage of the conduit element is that only minor structural modifications are required to the assembled rotor to implement the cooling concept and the flow-through function – even as a modular solution. The additional conduit element can be integrated into the rotor shaft via a simple connection geometry and connected to the supply lines, resulting in a simple cooling system and flow-through design with a minimal number of additional components.

[0021] A known approach to reducing rotor weight involves punching out sections of inactive lamination. According to the present invention, however, an architecture is created that is limited to an actively magnetic flux-guiding lamination stack cross-section. This significantly reduces the rotor's weight and thus its moment of inertia. A maximum bore diameter for the lamination stack can be selected. Inactive filler material between the rotor shaft and the active electrical steel material can be omitted. Instead, a conductor element is inserted into the support for the rotationally fixed mounting of the rotor lamination stack. This conductor element combines very low weight with a large surface area, thus combining a lightweight design with optimal rotor cooling.

[0022] Furthermore, the metal foam makes it possible to reduce the structure-borne noise emission of the component and shift it into other frequency ranges, thus also allowing a combination of lightweight construction and sound / vibration damping.

[0023] According to one embodiment, the metal foam is open-pored. This facilitates the flow of cooling medium through the cooling channel. Furthermore, the cooling medium can penetrate the open-pored metal foam radially and wet the inner surface of the rotor lamination stack's support, thus enabling efficient cooling of the rotor lamination stack. The duct element allows for efficient and uniform application of a relatively small, yet sufficient, quantity of cooling fluid to the inner surfaces of both the duct element itself and the cylindrical support surrounding the cavity.

[0024] A medium flowing through open-cell metal foam can absorb heat from the metal matrix of the foam. This medium, flowing radially through the foam, can be driven, in particular, by centrifugal forces from the rotating rotor shaft. Cooling elements made of open-cell metal foam offer maximum efficiency with extremely small dimensions. When viewed up close, an open-cell metal foam, due to its delicate structure, offers an enormous surface area, which is ideal for cooling purposes. For example, metal foams with an initial size of 450 x 250 x 40 mm can have a surface area equivalent to a football field. Due to its bone-like structure, open-cell metal foam also exhibits very good mechanical properties and is therefore ideally suited for lightweight components.

[0025] According to a further embodiment, the metal foam is closed-cell. In this embodiment, the conduit element can be arranged, in particular, in a media-tight manner within the cavity. A plastic conduit element is also suitable for this embodiment. According to this embodiment, the conduit element can be supported, in particular, on an inner surface of the support. For example, the conduit element can have a star-shaped cross-section, with radially outer ends of such a star-shaped conduit element being able to be supported on the inner surface of the support. A star-shaped cross-section represents a particularly good compromise between high heat dissipation and good support on the one hand, and significant weight savings on the other.

[0026] Furthermore, it can be advantageous for the metal foam to be based on an aluminum or copper alloy. These materials offer particularly high thermal conductivity, and therefore particularly effective and efficient cooling of the rotor, especially in the area of ​​the rotor lamination stack.

[0027] Another embodiment is characterized in that the conduit element has a thread on its outer circumference for guiding cooling medium over an inner surface of the support. This enables the cooling fluid to be guided particularly effectively over the inner surface of the cylindrical support, especially in the direction of the shaft journals.

[0028] Furthermore, it can be advantageous for the thread to be multi-start in both directions. The multi-start thread allows for a particularly large pitch of the individual threads, which has a particularly positive effect on the wetting of the inner surface of the cylindrical support. In this context, the feature "multi-start in both directions" can be understood to mean, in particular, that the thread has a first thread section that is left-handed and that the thread has a second thread section that is right-handed. When the pipe element rotates, the left-hand thread section can convey coolant from a central area of ​​the pipe element to one of the shaft journals. Similarly, when the pipe element rotates, the right-hand thread section can convey coolant from the central area to the other shaft journal.

[0029] Furthermore, a conveying spiral can be arranged within the cooling channel. The conveying spiral can be connected to the piping element in a rotationally fixed manner. In this way, the conveying spiral can be configured, in particular, to convey a cooling medium, such as a screw pump, through the cooling channel when the piping element rotates.

[0030] Alternatively, the conical conduit element can be designed to allow the conveyance of coolant, which has been conveyed radially outwards through the open-pored metal foam, in the longitudinal direction of the conduit element towards the shaft journals.

[0031] Furthermore, a further development provides that the second shaft journal has a second axial bore connected to the cooling channel. This second axial bore can be either a blind or a through bore. Thus, a cooling medium can be supplied to the first shaft journal, guided through the cooling channel within the rotor lamination stack support, and discharged via the second shaft journal. In this manner, the coolant can absorb heat and thus cool a particularly large portion, especially of the rotor, of the electric machine.

[0032] According to a further embodiment, the second shaft journal has at least one radial bore connected to the second axial bore. This radial bore can form a nozzle shaped and oriented such that coolant from the cooling channel is directed into the second axial bore and the radial bore, and then ejected from the radial bore by centrifugal force, allowing the coolant to reach, for example, the stator winding heads of the electric machine and cool them. This embodiment is particularly effective when used with a conduit element made of closed-cell metal foam or plastic. Furthermore, the first shaft journal can also have at least one corresponding radial bore connected to the first axial through-bore.

[0033] According to a second aspect of the invention, a rotor for an electric machine is provided. The rotor comprises a multi-part rotor shaft according to the first aspect of the invention and a rotor lamination stack which is mounted non-rotatably on the support of the multi-part rotor shaft.

[0034] According to a third aspect of the invention, an electric machine is provided for a vehicle. The electric machine comprises a rotor according to the second aspect of the invention. The vehicle is, for example, a motor vehicle such as a car, bus, or truck, or also a rail vehicle, a ship, an aircraft such as a helicopter or airplane, or, for example, a bicycle.

[0035] The electric machine, which, with ideal heat dissipation and without significant influence of cooling on acceleration behavior, can be built relatively small and yet provide high continuous electrical power or a correspondingly high continuous torque, is ideally suited for use in motor vehicles, especially in electric or hybridized powertrains, since high performance in a minimal installation space is one of the core requirements here. The electric machine according to the invention is therefore preferably used in such an application field, in which it is employed for motor vehicle powertrains, in particular as a motor, generator and / or motor-generator in series or parallel hybridized powertrains as well as in purely electric powertrains.

[0036] Exemplary embodiments of the invention are explained in more detail below with reference to the partially schematic drawing. This shows Fig. 1 a longitudinal sectional view of an embodiment of a rotor shaft according to the invention with a guide element made of a closed-pore metal foam or plastic, Fig. 2 a cross-sectional view of the rotor shaft according to Fig. 1, Fig. 3 a longitudinal sectional view of an embodiment of a rotor shaft according to the invention with a guide element made of an open-pore metal foam, Fig. 4 a longitudinal sectional view of an embodiment of a rotor shaft according to the invention with a conveying spiral in a guide element, Fig. 5 a perspective view of a further embodiment of a rotor shaft according to the invention, Fig. 6 a perspective view of a conduit element with a conveying spiral for the rotor shaft according to Fig. 5, Fig. 7 a longitudinal sectional view of an embodiment of a rotor shaft according to the invention with a guide element made of an open-pore metal foam and with a double multi-start spiral groove, Fig. 8 a side view of a conduit element for the rotor shaft according to Fig. 7, Fig. 9 a perspective view of the conductor element according to Fig. 8, Fig. 10 a longitudinal sectional view of an embodiment of a rotor shaft according to the invention with a guide element made of an open-pore metal foam, with a conveying spiral inside the guide element and with a spiral groove, Fig. 11 a longitudinal sectional view of an embodiment of a rotor shaft according to the invention with a conically shaped guide element made of an open-pore metal foam, and Fig. 12 a longitudinal section view of an embodiment of an electrical machine according to the invention.

[0037] Fig. 1, Fig. 2 and Fig. Figure 4 shows a rotor shaft 1, which is designed as a hollow shaft. The rotor shaft 1 comprises a first shaft journal 2 with a first end flange 3 and a second shaft journal 4 with a second end flange 5. Furthermore, the rotor shaft 1 has a support 6 in the form of a tube, wherein the support 6 non-rotatably holds a rotor lamination stack 7, which surrounds the support 6 in the radial direction r.

[0038] The first end flange 3 closes off the tubular support 6 on a first end face, which is in Fig. 1 is shown on the left. The second end flange 5 closes the tubular support 6 on a second end face, which is in Fig. 1 is shown on the right. In particular, the support 6 can be connected to the end flanges 3, 5 in a rotationally fixed manner.

[0039] A cylindrical cavity 8 with a circular cross-section is defined between the tubular support 6, the first end flange 3, and the second end flange 5. A conduit element 9 is arranged within the cavity 8, forming a cooling channel 10, which is located in the Fig. In the embodiment shown in Figure 1, the guide element 9 runs coaxially around a longitudinal axis L of the rotor shaft 1. The guide element 9 has a star-shaped cross-section, with the radially outer tips of the star-shaped guide element 9 bearing against an inner surface 11 of the tubular support 6 (see in particular Figure 1). Fig. 2) The conductor element 9 can be connected in a rotationally fixed manner to the support 6 and / or to the end flanges 3, 5.

[0040] The cooling channel 10 can connect a first central through-bore 12 of the first shaft journal 2 with a second axial through-bore 13 of the second shaft journal 4. The first / second central through-bore 12 / 13 can run coaxially around the longitudinal axis L of the rotor shaft 1. Furthermore, in the Fig. In the embodiments shown in Figure 1, the first axial through-bore 12, the cooling channel 10, and the second axial through-bore 13 each have the same diameter and extend at the same height in the radial direction r. In particular, a medium, for example a cooling fluid, can be supplied to the first axial through-bore 12, which is then guided through the cooling channel 10 and discharged again via the second axial through-bore 13.

[0041] The first shaft journal 2 can have several first radial bores 14 (see Fig. 4), which connect the first axial through-bore 12 with an outer circumferential surface 15 of the first shaft journal 2. Similarly, several second radial bores 16 can be provided in the second shaft journal 4, which connect the second axial through-bore 13 with an outer circumferential surface 17 of the second shaft journal 4.

[0042] When the rotor shaft 1 rotates, centrifugal forces are generated, which cause, for example, coolant located within the first / second axial through-bore 12 / 13 to be flung outwards through the first / second radial bores 14 / 16. The first / second radial bores 14 / 16 can be arranged and oriented on the first / second shaft journal 2 / 4 such that coolant exiting the radial bores 14 / 16 is directed to a stator winding head 18, 19 of a stator 20 of an electric machine 21 (see Figure 1). Fig. 12) can be ejected to cool the stator winding heads 18, 19. Possible flow paths of coolant through the rotor shaft 1 are shown in Fig. 1 illustrated by arrows 22.

[0043] The through Fig. 1 and Fig. The conduit element 9 shown in Figure 2 can, for example, be made of a closed-cell metal foam or of a plastic. In this way, a media-tight connection between the cooling channel 10 and the axial through-bores 12 and 13 can be created, for which purpose the conduit element 9 can additionally be sealed against the end flanges 4 / 6 by means of an O-ring 23 (see Figure 2). Fig. 4) Together, the rotor shaft 1 and the rotor lamination stack 7 form a rotor 24. Fig. Figure 4 further shows that a conveying spiral 25 can be arranged within the cooling channel 10, which is connected to the conduit element 9 in a rotationally fixed manner. When the conduit element 9 rotates, the conveying spiral 25 rotates accordingly and, in the sense of an Archimedean screw, can convey a cooling medium in the axial direction L through the cooling channel 10.

[0044] Fig. Figure 3 shows another rotor 24 with a hollow rotor shaft 1, which has a similar basic structure to the rotor shaft 1 according to Fig. 1. However, the rotor shaft 1 shows Fig. 3 A differently designed conduit element 9, consisting of an open-pore metal foam, is provided. A medium, in particular a coolant, can be supplied to the cooling channel 10 via the first axial through-bore 12 of the first shaft journal 2. When the conduit element 9 rotates, the conduit element 9 made of open-pore metal foam rotates with it. Due to the centrifugal forces generated, the coolant can penetrate the pores of the conduit element 9 in the radial direction r and reach the inner surface 11 of the support 6, thus wetting the inner surface 11 for cooling purposes.

[0045] Fig. Figure 5 shows another hollow rotor shaft 1 with a first shaft journal 2 including a first end flange 3, with a second shaft journal 3 including a second end flange 4 and with a support 6 for a rotor lamination stack not shown (cf. e.g. Fig. 1 to 4). The shaft journals 2 and 3 can have radial bores 14, 16, as described in connection with Fig. 1 to 4 has been described (an outlet of such a radial bore 14 within the first shaft journal 2 is in Fig. 5 shown). Fig. Figure 6 shows a conductor element 9 which is located inside the tubular support 6. Fig. 5 may be arranged, similarly to what is done in connection with Fig. 1 to 4 are described. The conductor element 9 has a cross-section which differs from the cross-section according to Fig. 1 to 4 differs. Also in the conductor element 9 after Fig. 6 is a conveying spiral 25 arranged.

[0046] Fig. Figure 7 shows another rotor 24 with a hollow rotor shaft 1, which has a similar basic structure to the rotor shaft 1 according to Fig. 3. The rotor shaft 1 after Fig. 7 comprises a conduit element 9 made of open-pore metal foam. A medium, in particular a coolant, can be supplied to the cooling channel 10 via the first axial through-bore 12 of the first shaft journal 2. When the conduit element 9 rotates, the open-pore metal foam conduit element 9 rotates with it. The resulting centrifugal forces allow the coolant to penetrate the pores of the conduit element 9 in the radial direction r and reach the inner surface 11 of the support 6, thus cooling the support. The conduit element 9 can also have a thread 26, in particular a multi-start thread, on its outer circumferential surface. In the illustrated embodiment, this thread is configured as both left-hand and right-hand threads. The thread 26 enables the flow of coolant in the axial direction L towards the first shaft journal 2 and towards the second shaft journal 4.

[0047] Fig. 8 and Fig. Figure 9 shows how a thread 26 for the conductor element 9 is attached. Fig. 7 can be implemented. Thus, the thread 26 can have a first multi-start spiral groove 27, which is designed to be left-handed. Furthermore, the thread 26 can have a second multi-start spiral groove 28, which is designed to be right-handed. When the conduit element 9 rotates, the left-hand spiral groove 27 can convey coolant from a central area 29 of the conduit element (relative to the longitudinal axis L of the conduit element 9) to the first shaft journal 2 (cf. Fig. 7) Similarly, the right-hand spiral groove 28 can convey coolant from the central area 29 to the second shaft journal 4 when the conductor element 9 is rotating (see ). Fig. 7).

[0048] Fig. Figure 10 shows another rotor 24 with a hollow rotor shaft 1, which has essentially the same construction as the rotor shaft 1 according to Fig. 7. Additionally, similar to, for example, through Fig. 4 shown - a conveying spiral 25 is arranged within the cooling channel 10 formed by the conduit element 9.

[0049] Fig. Figure 11 shows another rotor 24 with a hollow rotor shaft 1, which extends from the rotor shaft 1 to Fig. 10 differs in particular in that the conduit element 9 is conical and has no thread 26. In particular, the conduit element 9 can have a first conical element 30 and a second conical element 31. Both elements 30 and 31 taper towards the center 29 of the conduit element 9 (relative to the longitudinal axis L of the conduit element 9). The outer conical surface 32 of the conical elements 30 and 31 facilitates the conveyance of coolant towards the end flanges 3 and 5, from which it can exit through openings. Possible flow directions of coolant are shown in Fig. 11 with arrows 22 shown.

[0050] Fig. Figure 12 shows an electric machine 21, which has a hollow rotor shaft 1 with a first shaft journal 2, with a second shaft journal 4, with a support 6 (in Fig. 12 (not shown) and has a conductor element 9 made of an open-pore metal foam. The rotor shaft 1 can, for example, be designed similarly to that shown by Fig. 3, Fig. 7, Fig. 10 or Fig. 11 is shown.

[0051] The shaft journals 2, 4 are each rotatably mounted in a shaft bearing 32, the shaft bearings 32 being fixedly mounted in a housing 33 of the electric machine 21. A stator 20 surrounds a rotor lamination stack 7 in the radial direction r, which is fixedly attached to the support 6. Two stator winding heads 18, 19 of the stator 20 extend longitudinally L beyond the rotor lamination stack 7 and can be wetted by coolant, in particular oil or an oil mist. As the rotor shaft 1 rotates, the coolant is flung out of radial bores 14, 16 in the shaft journals 2, 4. The coolant can then drip into a coolant sump 34 at the bottom of the electric machine 21 and collect there.

[0052] From the coolant sump 34, the coolant can be fed to a heat exchanger 35 of a recirculating cooling circuit 36 ​​for recooling. The coolant can then be fed back to the rotor shaft 1, in particular via the first axial through-bore 12 of the first shaft journal 2. Cooling water from a main cooling circuit 37 can also be passed through the heat exchanger 35, and this cooling water can be recooled via a main water cooler 38.

[0053] Possible flow directions of coolant are in Fig. 12 with arrows 22 shown. Fig. Figure 12 further shows that the electric machine 21 can have an integrated gearbox 39 which has several gears 40, wherein the gearbox 39 can be coupled to the second shaft journal 4.

Claims

[1] A multi-part rotor shaft (1) for an electrical machine (21), the multi-part rotor shaft (1) comprising: - a first shaft journal (2) with a first end flange (3) and with a first axial through-bore (12), - a second shaft journal (4) with a second end flange (5), - a tubular support (6) for a rotor core (7) and - a line element (9) for conducting a cooling medium, wherein - the support (6) for the rotor core (7) is arranged between the first shaft journal (2) and the second shaft journal (4), - the support (6), the first end flange (3) and the second end flange (5) define a cavity (8) between them, - the conducting element (9) forms a cooling channel (10) within the cavity (8), wherein the cooling channel (9) is connected to the first axial through-bore (12) and extends between the first shaft journal (2) and the second shaft journal (4), characterized by , that - the conducting element (9) consists of a metal foam. [2] The multi-part rotor shaft (1) according to claim 1, wherein the metal foam is open-pored. [3] The multi-part rotor shaft (1) according to claim 1 or 2, wherein the metal foam is closed-pore. [4] The multi-part rotor shaft (1) according to one of the preceding claims, wherein the metal foam is based on an aluminum material or on a copper material. [5] The multi-part rotor shaft (1) according to one of the preceding claims, wherein the conducting element (9) has a thread (26) on its outer circumference for conducting cooling medium over an inner circumferential surface (11) of the carrier (6). [6] The multi-part rotor shaft (1) according to claim 5, wherein the thread (26) is multi-start in both directions. [7] The multi-part rotor shaft (1) according to one of the preceding claims, wherein the guide element (9) is conical. [8] The multi-part rotor shaft (1) according to one of the preceding claims, wherein a conveyor spiral (25) is arranged within the cooling channel (10). [9] The multi-part rotor shaft (1) according to one of the preceding claims, wherein the second shaft journal (4) has a second axial bore (13) which is connected to the cooling channel (10). [10] The multi-part rotor shaft (1) according to one of the preceding claims, wherein the second shaft journal (4) has at least one radial bore (16) which is connected to the second axial bore (13). [11] A rotor (24) for an electrical machine (21), the rotor (24) comprising a multi-part rotor shaft (1) according to one of the preceding claims and a rotor laminated core (7) which is mounted in a rotationally fixed manner on the carrier (6) of the multi-part rotor shaft. [12] An electric machine (21) for a vehicle, the electric machine (21) comprising a rotor (24) according to claim 11.

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