Rotor assembly, electric machine and electric drive train

Abstract

The invention relates to a rotor arrangement (1) for an electric machine (2) of a drive train (3) of a motor vehicle (4) comprising a rotor (5) with a rotor body (6) which is arranged non-rotatably on a rotor shaft (7), a cooling circuit (8) which runs sectionally through the rotor (5), wherein the cooling circuit (8) in the rotor body (6) has a plurality of circumferentially distributed rotor cooling channels (9) extending axially through the rotor body (6), wherein the rotor (5) has a fluid outlet opening (35) with a first flow cross-section (60) through which the cooling circuit (8) passes, so that a cooling fluid (11) can leave the rotor (5) through the fluid outlet opening (35) after flowing through the rotor cooling channels (9), and the rotor (5) further comprises a fluid drain opening (61) with a second flow cross-section (62).wherein the fluid drain opening (61) is arranged radially above the fluid outlet opening (35) and the first flow cross-section (60) is larger than the second flow cross-section (62).

Description

[0001] The present invention relates to a rotor assembly for an electric machine of a motor vehicle drive train, comprising a rotor with a rotor body that is arranged in a rotationally fixed manner on a rotor shaft, a cooling circuit that extends partially through the rotor, wherein the cooling circuit has a plurality of rotor cooling channels in the rotor body that are arranged circumferentially and extend axially through the rotor body. The invention further relates to an electric machine and an electric drive train.

[0002] Electric motors are increasingly being used to power motor vehicles, creating alternatives to combustion engines that require fossil fuels. Considerable efforts have already been made to improve the everyday suitability of electric drives and also to provide users with the same level of driving comfort they are accustomed to.

[0003] A detailed description of an electric drive can be found in an article in the magazine ATZ, Volume 113, May 2011, pages 360-365, by Erik Schneider, Frank Fickl, Bernd Cebulski, and Jens Liebold, titled "Highly Integrated and Flexible Electric Drive Unit for Electric Vehicles." Such drive units are also referred to as e-axles or electrically operated drivetrains.

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

[0005] In the development of electric motors intended for electric axles and hybrid modules, there is a continuing need to increase their power densities, making the necessary cooling of the electric motors increasingly important. Due to the necessary cooling performance, hydraulic fluids, such as cooling oils, have become the preferred solution in most concepts for dissipating heat from the thermally stressed areas of an electric motor.

[0006] For the stators of electrical machines, for example, jacket cooling and winding head cooling are known from the state of the art for cooling electrical machines using hydraulic fluids. While jacket cooling transfers the heat generated at the outer surface of the rotor core into a cooling circuit, with winding head cooling, the heat is transferred directly to the fluid at the conductors outside the rotor core in the area of ​​the winding heads.

[0007] In addition to cooling the stators, it is also generally known that the rotors of electrical machines need to be cooled. In this case, undesirable leaks between the rotor laminations can lead to drag torque in the air gap between the rotor and stator and uncontrolled coolant loss, which is often undesirable.

[0008] In addition to such fluid-cooled rotors with a hollow shaft, air-cooled rotors are also known from the prior art, for example, with a blade wheel mounted axially on the rotor. A summary of the relevant prior art can be found, for example, in DE 10 2018 220 810 A1.

[0009] It is also known that centrifugal force can be used to guide a coolant in the rotor at speed. For example, US11146133B2 uses cooling channels with increasing pitch diameters, while DE102017112348A1 depicts a conically expanding shaft. In these cases, the work of pumping the coolant is performed by the electric motor itself and not by an external oil pump.

[0010] JP 2009-273285 A discloses a cooling system for a motor comprising a stator core with a hollow portion and a rotor core rotatably disposed within the hollow portion. The invention describes end plates mounted at the axial ends of the rotor core and having cooling fluid inlet channels for introducing cooling fluid into the end plates. These end plates are equipped with a plurality of circumferentially arranged spaces serving as reservoirs for the cooling fluid, as well as cooling fluid nozzles that expel the stored cooling fluid toward the coil ends.

[0011] CN 2 16 134 331 U discloses a motor with a special cooling system characterized by the arrangement of flow channels in the axial and radial directions of the rotor shaft and the rotor core. The shaft cavity and the various flow channels form a cooling liquid channel and an air channel, which contribute to improving the cooling performance and efficiency of the motor. The design includes several silicon steel sheets arranged in a laminated configuration to form the flow channels. This arrangement enables effective heat dissipation and contributes to increasing the motor's performance.

[0012] JP 2011-114987 A discloses a cooling structure for an electric motor that offers high cooling performance and minimizes losses due to oil acceleration. The structure comprises a rotating shaft with a rotor having magnetic poles, and a cylindrical section with a stator that influences the magnetic poles by changing the current. A coolant path is arranged axially between the wall of an end plate and the end face of the rotor, with the end plate having a groove and a supply hole for the coolant. The coolant channel is designed in a zigzag shape to ensure efficient cooling.

[0013] JP 2011-142788 A discloses a cooling structure for an electric motor that aims to provide adequate cooling performance and suppress oil loss. The structure includes an end plate with a groove through which a coolant path passes, which is located between the wall of the end plate and the end surface of the rotating core. The coolant is supplied from a supply port to this path to cool the rotating core and then discharged through a first outlet port. Furthermore, the end plate is provided with a circular drain groove and a second drain port for discharging the coolant from the outer peripheral side of the coolant path.

[0014] JP 2011-234505 A discloses a rotating electric machine having a structure for cooling the rotor by introducing lubricating oil into the interior of the rotor. The rotor is equipped with a lubricating oil passage leading from a clearance in the rotor through an oil drain hole to the outside of the rotor. Furthermore, the rotor includes a contaminant storage part formed on the lubricating oil path, a contaminant drain hole opening to the outside of the rotor, and a control valve for adjusting the opening degree of the contaminant drain hole.

[0015] JP 2007 - 228 669 A discloses a cooling device for electric motors comprising an electric motor with a rotor and a stator. The rotor consists of a rotor shaft and a rotor core equipped with permanent magnets. The device includes channels for the cooling oil that run both through the rotor core and along the rotor shaft, as well as a check valve that controls the oil flow. The oil pump rotates synchronously with the rotor and supplies the cooling oil channels, with the check valve opening at higher speeds to drain the oil.

[0016] EP 1 953 896 A1 discloses a rotor for an electric rotating machine that improves the cooling performance of the machine through a special structure. This structure includes D-axis through-holes arranged outside the outer periphery of a rotor core, and hollow shafts formed in the parts of a rotating shaft not inserted into the rotor core. Pressure plates are arranged on axially opposite sides of the rotor core to support the rotor core, and hollow shaft walls are formed in the hollow shafts. A refrigerant is passed through the hollow shafts and the D-axis through-holes to ensure cooling of the rotor.

[0017] In separately excited synchronous machines (SMMs) with fluid-cooled rotors, it is known that imbalances can occur during passive operation of the separately excited synchronous machine due to unevenly distributed cooling fluid within the rotor body. For example, if the cooling channel outlet opening is not located as radially outward as possible, a residual amount of cooling fluid may remain in the rotor cooling system if the rotor shaft comes to a sudden stop. However, a maximally radially outer outlet opening should generally be avoided, as the resulting pumping effect during rotor operation would be excessive, and the rotor's cooling channels filled with cooling fluid would empty themselves at high speeds, thus negatively impacting cooling performance.

[0018] In certain operating conditions and drivetrain configurations, it may also happen that the vehicle is moving but the rotor is not actively powered, for example, because there is a second electric motor on a second axle or the vehicle is rolling down a hill. When the passive rotor shaft, which is firmly connected to the vehicle's axle, begins rotating again after coming to a standstill and the coolant pump is switched off, this residual oil, which is distributed unevenly in the individual cooling channels, can create an imbalance in the rotor. This imbalance can then exert considerable stress on bearings and components at high speeds.

[0019] The object of the invention is therefore to avoid or at least mitigate the problems known from the prior art and to provide a correspondingly improved rotor arrangement. Furthermore, the object of the invention is to realize an optimized electric machine and an improved electric drive train.

[0020] This object is achieved by a rotor arrangement for an electric machine of a drive train of a motor vehicle, comprising a rotor with a rotor body which is arranged in a rotationally fixed manner on a rotor shaft, a cooling circuit which runs sectionally through the rotor, wherein the cooling circuit has a plurality of rotor cooling channels arranged in the rotor body and extending in the axial direction through the rotor body, wherein the rotor has a fluid outlet opening with a first flow cross-section through which the cooling circuit runs, so that a cooling fluid can leave the rotor through the fluid outlet opening after flowing through the rotor cooling channels, and the rotor further has a fluid discharge opening with a second flow cross-section, wherein the fluid discharge opening is arranged radially above the fluid outlet opening and the first flow cross-section is larger than the second flow cross-section.

[0021] In addition to the "normal" cooling circuit outlet opening with a small inner diameter, a smaller fluid discharge opening, which acts similarly to a hydraulic orifice, is arranged at the outermost diameter of the rotor. The fluid discharge opening allows the rotor cooling channels to slowly empty when the rotor is at a standstill. The pumping effect that occurs during normal rotor operation is limited by the ratio of the flow cross-sections of the fluid outlet and fluid discharge openings.

[0022] By allowing the cooling fluid to drain away when the rotor is stationary, the risk of hydraulic imbalances occurring during start-up and rotation of the rotor can be significantly reduced. The creation of openings in the rotor also represents a reliable and cost-effective way to effectively reduce these imbalances.

[0023] Preferably, the rotor can be controlled such that a fluid drain opening is positioned at the geodetically lowest point when the rotor is at a standstill, which promotes safe and complete emptying of the rotor of cooling fluid.

[0024] First, the individual elements of the claimed subject matter of the invention are explained in the order of their relevance or their mention in the set of claims, and particularly preferred embodiments of the subject matter of the invention are described below.

[0025] A rotor is the rotating part of an electrical machine. The rotor includes, in particular, a rotor shaft. The rotor shaft can be hollow, which reduces weight and allows for the supply of lubricant or coolant to the rotor body.

[0026] For the purposes of the invention, a rotor body is understood to mean the rotor without the rotor shaft. The rotor body is therefore composed, in particular, of a rotor core and the permanent magnets incorporated into the pockets of the rotor core or fixed circumferentially to the rotor core, as well as any axial cover parts for closing the pockets.

[0027] The rotor preferably has a plurality of rotor bodies. Particularly preferably, the rotor bodies are formed from substantially the same part, in particular substantially identical. It is most preferred for the rotor bodies to be formed from substantially the same part, in particular substantially identical rotor laminations. The rotor bodies are therefore particularly preferably formed from a rotor lamination stack, which is composed of a plurality of laminated individual laminations or rotor laminations, generally made of electrical steel sheet, which are layered and stacked one on top of the other to form a stack, the so-called rotor lamination stack. The individual laminations can be held together in the rotor lamination stack by gluing, welding, or screwing. A rotor lamination stack can, in particular, also have permanent magnets introduced into the pockets of the rotor lamination stack or fixed circumferentially to the rotor lamination stack.It is possible for the rotor cores to be interlaced, meaning they are arranged at an angle to each other. This interlacing can be linear or V-shaped to avoid or at least reduce axial forces.

[0028] The rotor can be designed as a permanently excited rotor or a separately excited rotor.

[0029] The separately excited rotor is a component of an electric radial flux machine used to convert electrical energy into mechanical energy or vice versa. A separately excited rotor is a rotor powered by a separate power source, usually a direct current source. Unlike a self-regulated rotor, which derives its excitation from the stator's alternating current, a separately excited rotor typically requires an external direct current source.

[0030] The separately excited rotor may preferably have a cylindrical rotor body, advantageously made of laminated iron to reduce eddy current losses. Several grooves or slots may be provided on the surface of the rotor body, into which the rotor winding is inserted. This rotor winding is preferably formed from insulated copper or aluminum wires and is guided through the grooves or slots to ensure mechanical stability.

[0031] The rotor winding of the separately excited rotor is preferably divided into coils that are electrically connected to each other. These coils are wound parallel to the rotor axis and are usually designed as multiphase windings to enable efficient conversion of electrical energy into mechanical energy. The number of coils and their arrangement depend on the specific requirements of the machine.

[0032] The external DC power source can be connected to the rotor winding via slip rings and carbon brushes, for example. The carbon brushes ensure a low-friction electrical connection between the stationary power source and the rotating rotor winding. The application of the external DC power source creates a magnetic field in the rotor, which interacts with the magnetic field of the stator-side winding system, thus influencing the torque and power of the machine.

[0033] The separately excited rotor offers the advantage of external control over the rotor excitation. By varying the direct current fed into the rotor, the power and torque of the electric machine can be precisely controlled.

[0034] A rotor body can, in particular, be formed from one or more rotor lamination stacks. A rotor lamination stack is understood to be a plurality of laminated individual laminations or rotor laminations, usually made of electrical steel sheet, which are stacked and stacked one on top of the other to form a so-called rotor lamination stack. The individual laminations can then be held together in the lamination stack by gluing, welding, or screwing. A rotor lamination stack for a permanently excited rotor can, in particular, also have magnetic elements incorporated into the pockets of the rotor lamination stack or fixed circumferentially to the rotor lamination stack, as well as any axial cover parts for closing the pockets and the like.

[0035] The electric machine can be designed, in particular, as a rotary machine. The rotary machine can be configured, in particular, as a radial flux machine. A radial flux machine is characterized by the fact that the magnetic field lines in the air gap formed between the rotor and stator extend in a radial direction. The air gap is the gap between the rotor and stator. In a radial flux machine, this is a circular-ring-shaped gap in cross-section with a radial width corresponding to the distance between the rotor body and the rotor body.

[0036] The electric machine is intended in particular for use within a drive train of a hybrid or fully electric motor vehicle. In particular, the electric machine is dimensioned such that vehicle speeds greater than 50 km / h, preferably greater than 80 km / h, and in particular greater than 100 km / h can be achieved. The electric motor particularly preferably has an output greater than 50 kW, preferably greater than 80 kW, and in particular greater than 150 kW. It is further preferred that the electric machine provides rotational speeds greater than 8,000 rpm, particularly preferably greater than 12,000 rpm, and most particularly preferably greater than 15,000 rpm.

[0037] For the purposes of this application, motor vehicles are defined as land vehicles that are propelled by mechanical power without being tied to railway tracks. A motor vehicle can, for example, be selected from the group of passenger cars (PCs), trucks (HGVs), mopeds, light motor vehicles, motorcycles, buses (KOMs), or tractors.

[0038] The rotor assembly may further comprise a control unit. A control unit, as can be used in the present invention, serves in particular for the electronic control and / or regulation of one or more technical systems of the rotor assembly and / or the electric machine, such as the control / regulation of the coolant pump and / or the current supply to a rotor winding.

[0039] A control unit preferably has a wired or wireless signal input for receiving electrical signals, such as sensor signals. Furthermore, a control unit preferably also has a wired or wireless signal output for transmitting electrical signals, in particular.

[0040] Control and / or regulation operations can be performed within the control unit. It is particularly preferred that the control unit comprises hardware configured to execute software. The control unit preferably comprises at least two electronic processors for executing program sequences defined in a respective software. The two processors can also be structurally integrated into a processor as computer cores, with the corresponding computer cores then each representing a processor within the meaning of the invention.

[0041] The control unit may further comprise one or more electronic memories in which the data contained in the signals transmitted to the control unit can be stored and read again. Furthermore, the control unit may comprise one or more electronic memories in which data can be stored in a modifiable and / or non-modifiable manner.

[0042] A control unit can comprise a plurality of control units, which are arranged, in particular, spatially separated from one another in the motor vehicle. Control units are also referred to as electronic control units (ECUs) or electronic control modules (ECMs) and preferably have electronic microcontrollers for performing computing operations for processing data, particularly preferably using software. The control units can preferably be networked with one another, enabling wired and / or wireless data exchange between control units. In particular, it is also possible to network the control units with one another via bus systems present in the motor vehicle, such as the CAN bus or LIN bus.

[0043] Most preferably, the control unit has at least one processor and at least one memory, which in particular contains a computer program code, wherein the memory and the computer program code are configured, with the processor, to cause the control unit to execute the computer program code.

[0044] The control unit can particularly preferably comprise power electronics for supplying current to the stator or rotor. Power electronics is preferably a combination of various components that control or regulate a current to the electrical machine, preferably including the peripheral components required for this purpose, such as cooling elements or power supplies. In particular, the power electronics contains one or more power electronic components that are designed to control or regulate a current. These are particularly preferably one or more power switches, e.g., power transistors. The power electronics particularly preferably has more than two, particularly preferably three, separate phases or current paths, each with at least one dedicated power electronic component.The power electronics are preferably designed to control or regulate a power with a peak power, preferably continuous power, of at least 10 W, preferably at least 100 W, particularly preferably at least 1000 W per phase.

[0045] According to another particularly preferred embodiment of the invention, the rotor can be separately excited by means of a rotor winding capable of being energized, and the rotor arrangement can include a control unit for energizing the rotor winding. The ability to separately excite the rotor by means of a rotor winding capable of being energized allows for greater flexibility in controlling the machine. The control unit makes it possible to vary the rotor current and thus control the torque, speed, or other operating parameters of the machine. This enables more precise adaptation to different operating conditions, load requirements, or control objectives.

[0046] Particularly preferably, a coolant pump is arranged in the cooling circuit, which pumps the cooling fluid through the cooling circuit. Furthermore, a control unit for controlling the coolant pump can be provided in order to achieve the most precise control of the cooling performance in the rotor. Advantageous embodiments of the invention (additional panel)

[0047] According to an advantageous embodiment of the invention, the first flow cross-section can be between 5 and 50 times larger than the second flow cross-section. This allows the pumping effect that occurs at higher rotor speeds to be particularly effectively reduced, while simultaneously ensuring sufficient fluid flow through the fluid outlet opening and thus a corresponding cooling performance in the rotor. The flow cross-section of the outlet opening is then also still sufficiently large to allow the cooling fluid to flow out when the rotor is stationary.

[0048] Preferably, the flow cross-section of a discharge opening is between 0.01-0.3 mm 2 , which allows sufficiently rapid emptying through the drain opening, but on the other hand the bypass flow through the orifice and the pumping effect does not become too great.

[0049] According to a further preferred development of the invention, it can also be provided that the fluid outlet opening extends axially through the rotor and / or the fluid discharge opening extends axially through the rotor. Due to the axial extension, the pressure loss in the section of the cooling circuit running through the rotor can be kept low, which allows, for example, the coolant pump to be dimensioned accordingly compactly and energy-efficiently. Furthermore, the axial extension of the fluid discharge channel can also ensure sufficiently good drainage of the cooling fluid, while simultaneously further reducing the pumping effect occurring during rotor operation.If both the fluid outlet opening and the drain opening are axial, this can also simplify the production of the rotor, since both openings can be formed, for example, by similarly oriented holes or contours in an injection molding tool.

[0050] Furthermore, according to a similarly advantageous embodiment of the invention, the rotor may have a plurality of fluid outlet openings and / or a plurality of fluid discharge openings. This can further improve both the balance and the cooling performance of the rotor.

[0051] The presence of multiple outlet ports allows the fluid to be distributed more evenly and efficiently across the entire rotor, which can contribute to improved performance and efficiency of the corresponding electric machine. Furthermore, the cooling fluid flowing through multiple outlet ports distributes the pressure and mechanical stress on the rotor more evenly, which can also contribute to reducing unwanted stresses and vibrations in or on the rotor. For high-performance rotors or when the rotor is operating at its performance limits, heat dissipation can be critical; in these cases, multiple outlet ports can help the cooling fluid flow more effectively through the rotor, thus enabling better cooling.Using multiple fluid outlets can reduce the flow velocity of the cooling fluid in each outlet, which can contribute to optimized flow behavior and a reduced likelihood of cavitation. The presence of multiple fluid outlets can also help reduce local overheating areas (so-called "hot spots"), as a uniform cooling fluid flow minimizes temperature differences across the rotor.

[0052] The presence of several fluid drain openings in the rotor enables reliable drainage of the cooling fluid regardless of the rotor position, as this increases the probability that at least one fluid drain opening is located at the geodetically lowest point of the rotor when the rotor is stationary. This simplifies rotor control and increases operational reliability with regard to effective drainage of cooling fluid from the rotor. If one of the drain openings becomes blocked or restricted (e.g., by dirt or deposits), the other openings continue to provide an outlet for the cooling fluid, which increases the operational reliability of the system. For rotors with cooling circuits where air bubbles can be a problem, multiple drain openings also facilitate venting the system.

[0053] According to a further particularly preferred embodiment of the invention, it can be provided that the number of fluid outlet openings corresponds to the number of rotor cooling channels and / or the number of fluid drain openings corresponds to the number of rotor cooling channels. If the number of fluid outlet openings and / or fluid drain openings corresponds exactly to the number of rotor cooling channels, this can result in particular in a 1:1 assignment between the cooling channels and the openings, which can bring about several technical advantages. Each rotor cooling channel can thus have a dedicated outlet or drain opening, so that the cooling fluid flowing through a specific channel can be guided out of the rotor, in particular directly and without detours. This ensures efficient and rapid heat dissipation from each cooling channel.Because each cooling channel has its own outlet, the likelihood of a uniform temperature distribution across the entire rotor is higher, supporting thermal efficiency and the structural integrity of the rotor. By having each rotor cooling channel with its own outlet, the flow velocity of the cooling fluid in each channel can be optimized. Flows that are too fast or too slow, which could cause efficiency problems or cavitation, can be avoided.

[0054] Furthermore, the invention can also be further developed such that a plurality of the fluid outlet openings, preferably all fluid outlet openings, are arranged on a common first diameter, and a plurality of the fluid drain openings, preferably all fluid drain openings, are arranged on a common second diameter, wherein the first diameter is smaller than the second diameter. This configuration allows, in particular, improved support of the balancing properties of the rotor. In this context, it is particularly preferred that the second diameter is somewhat smaller than the diameter of the rotor body, so that a fluid drain opening is positioned at the geodetically lowest point in the stalled state of the rotor, which accordingly promotes complete emptying of the rotor of the cooling fluid.Preferably, the first diameter and the second diameter are arranged coaxially to each other, which also contributes to good balancing of the rotor.

[0055] In a likewise preferred embodiment of the invention, it can also be provided that the rotor body has a first rotor cover on a first end face, in which at least one fluid outlet opening, preferably a plurality of fluid outlet openings, particularly preferably all fluid outlet openings is / are formed and / or in which at least one fluid drain opening, preferably a plurality of fluid drain openings, particularly preferably all fluid drain openings is / are formed. By arranging all fluid outlet and / or drain openings in the rotor cover, the fluid flow can be centralized, which enables simpler and more efficient fluid guidance and control. By integrating the openings directly into the rotor cover, the need for additional attachments or piping systems that direct the fluid flow is reduced or eliminated.This simplifies the design and can lead to cost savings in production and assembly. The central location of fluid ports in the rotor cover can also reduce the number of required seals and connections, minimizing the risk of leaks. The central integration of the ports into the rotor cover also makes the overall rotor design more compact and space-saving. The rotor cover also allows for a certain degree of modular adaptability, as with the rotor cover as the central element for fluid ports, specific cover designs for different applications or operating conditions can be more easily implemented or exchanged.

[0056] It may also be advantageous to further develop the invention such that the rotor cover is made of a plastic. Plastics are generally lighter than metals, so a lighter rotor cover can reduce the overall mass of the rotor, which can contribute to improved efficiency and performance, as well as a reduction in the mechanical stress on the entire system. Plastics can also be easily formed into complex shapes, allowing for a high degree of flexibility in the design of the rotor cover. This can be particularly useful for achieving specific hydrodynamic properties with respect to the cooling fluid. Furthermore, plastics can dampen vibrations and noise better than many metals, which can contribute to quieter operation.Furthermore, plastics are generally non-conductive, so they also provide electrical insulation, which can be particularly advantageous in the context of separately excited rotors. In many cases, manufacturing a rotor cover from plastic can be more cost-effective than using metals, both in terms of material costs and manufacturing processes. Finally, some plastics also exhibit comparatively low thermal conductivities, which can be advantageous in a given rotor assembly application to provide thermal insulation or reduce heat transfer. Ring channel design:

[0057] According to a further embodiment variant, it is also possible for the rotor arrangement for an electric machine of a drive train of a motor vehicle to comprise a rotor with a rotor body which is arranged in a rotationally fixed manner on a rotor shaft, a cooling circuit which runs partially through the rotor, wherein the cooling circuit in the rotor body has a plurality of rotor cooling channels which are arranged in a circumferentially distributed manner and extend in the axial direction through the rotor body, wherein the rotor body has a circumferentially extending hydraulic path which connects the rotor cooling channels to one another in the circumferential direction.

[0058] This provides the advantage that the cooling fluid can be distributed in the rotor cooling channels via the circumferential hydraulic path during rotor operation so that all rotor cooling channels are either equally filled or completely empty, thus preventing imbalance when the rotor starts rotating from a standstill. A hydraulic connection of the rotor cooling channels via the circumferential hydraulic path at the largest diameter is particularly advantageous, as this allows the cooling fluid to be distributed optimally across the circumference.

[0059] Due to the circumferential hydraulic path, which hydraulically connects the rotor cooling channels, cooling fluid collected in the rotor cooling channels located at the bottom in the direction of gravity can be evenly distributed to the other rotor cooling channels connected to the hydraulic path at speed.

[0060] The hydraulic path can be divided into several separate paths or consist of a single path. Particularly preferably, the hydraulic path is designed as a single channel, which allows for a particularly defined and precise routing of the cooling fluid within the rotor.

[0061] According to an advantageous embodiment of the invention, the hydraulic path can be designed as an annular channel. The advantage of this design is that the annular channel is particularly simple in design and thus also inexpensive to manufacture. To ensure the balance of the rotor, it is preferable for the annular channel to be circular. It would also be possible to provide several annular channels arranged coaxially to one another to further improve the distribution of the cooling fluid during rotor start-up.

[0062] According to a further preferred development of the invention, it can also be provided that the annular channel connects the radially outermost rotor cooling channels. It would also be conceivable for the annular channel to connect the rotor cooling channels at their radially outermost regions, particularly if these channels themselves have a radial extension. This can result in a particularly rapid and complete elimination of an imbalance during rotor rotation.

[0063] Furthermore, according to a likewise advantageous embodiment of the invention, the rotor body can have a first rotor cover on a first end face, in which the annular channel is formed. The advantageous effect of this embodiment is that the annular channel on the rotor cover can be manufactured particularly easily. In particular, the rotor cover can also be provided as an injection-molded plastic part, which makes the manufacture of the annular channel particularly simple.

[0064] According to a further particularly preferred embodiment of the invention, it can be provided that the first rotor cover has a plurality of fluid channels extending in the radial direction, which open into the annular channel and which are further hydraulically connected to the rotor cooling channels, which can contribute to a particularly effective distribution of the cooling fluid when the rotor is loosened.

[0065] Furthermore, the invention can also be further developed in such a way that the first rotor cover has a fluid outlet opening on its front side through which the cooling fluid can flow, which allows the provision of a structurally simple cooling circuit through the rotor.

[0066] In a likewise preferred embodiment of the invention, the rotor body can also have a second rotor cover on a second end face, which has a fluid channel extending in the radial direction and hydraulically connects the rotor shaft, which is designed as a hollow shaft and through which the cooling fluid flows, to the rotor cooling channels. This also makes it possible to provide a cooling circuit through the rotor that is structurally simple to implement. The second rotor cover can also preferably be formed from a plastic injection molding.

[0067] It may also be advantageous to further develop the invention in such a way that a plurality of the rotor cooling channels are arranged on a common diameter, which again contributes to a good balance of the rotor.

[0068] During extended downtimes, as already described above, it is possible that a certain residual amount of cooling fluid remains in the lowest rotor cooling channels in the direction of gravity. These extended downtimes, especially at low temperatures, can cause the coolant to change viscosity, resulting in lower flow rates and thus slower emptying or refilling. To counteract this, the cooling fluid in the rotor cooling channels can be specifically heated, for example, by targeted rotor coil excitation. Heating can also occur before the vehicle starts rotating or driving off, for example, as soon as the vehicle is unlocked or when a brake or clutch pedal is pressed.Thus, as an alternative or in addition to the delivery states of the coolant pump, the control unit can cause the rotor body to heat up when a second start-up signal is present before and / or when the rotor starts rotating from a standstill.

[0069] In a likewise preferred embodiment of the invention, it can also be provided that the rotor shaft is rotatably mounted on at least one rolling bearing, with the cooling circuit being routed through the rolling bearing. This allows for improved lubrication and cooling of the rolling bearing, which subsequently also has a positive effect on the efficiency of the rotor assembly. Design of check valve

[0070] In a further preferred embodiment, the rotor arrangement for an electric machine of a drive train of a motor vehicle has a rotor with a rotor body which is arranged in a rotationally fixed manner on a rotor shaft, a cooling circuit which runs sectionally through the rotor, wherein the cooling circuit has a plurality of rotor cooling channels arranged in the rotor body and extending in the axial direction through the rotor body, wherein the rotor has at least one fluid outlet opening through which the cooling circuit runs, so that a cooling fluid can leave the rotor through the fluid outlet opening after flowing through the rotor cooling channels, wherein a valve is arranged in the fluid outlet opening which closes the fluid outlet opening when the speed of the rotor falls below a predefined speed and opens it above the predefined speed of the rotor.

[0071] The valve at the rotor outlet thus prevents the cooling fluid from draining when the rotor is stationary. Consequently, the rotor cooling channels remain evenly filled with cooling fluid, preventing imbalances caused by unevenly distributed cooling fluid when the rotor starts up from a standstill. This contributes significantly to reducing bearing loads during rotor startup and thus also to an extended service life and reliability of the rotor assembly.

[0072] According to an advantageous embodiment of the invention, the valve can be configured such that it closes the fluid outlet opening when the rotor speed falls below a selected range of 100-200 rpm. The advantage of this configuration is that it ensures a good compromise between avoiding imbalance and providing good cooling performance even in the lower rotor speed range.

[0073] According to a further preferred development of the invention, the valve can also be designed as a spring-loaded check valve. The spring force of the check valves is preferably designed such that the check valves are closed below a rotor speed of 100-200 rpm. At speeds above 100-200 rpm, the check valve can be opened by a combination of the pressure created by the centrifugal force on the cooling fluid and / or additional pump pressure from a coolant pump.

[0074] Furthermore, according to a likewise advantageous embodiment of the invention, it can be provided that the cooling circuit has a coolant pump by means of which the cooling fluid can be pumped through the cooling circuit, wherein the valve and the coolant pump are configured such that the valve can be opened by the hydraulic pressure that can be built up in the cooling circuit by means of the coolant pump. Thus, for example, in order to cool electronic components or bring the cooling fluid to operating temperature (preconditioning), a check valve can be opened by a coolant pump even when the rotor is at a standstill. The valve at the outlet of the rotor thus prevents the cooling fluid from draining out when the rotor is at a standstill and when the coolant pump is switched off. This ensures that the rotor cooling channels of the rotor body remain evenly filled.

[0075] According to another particularly preferred embodiment of the invention, the rotor may have a plurality of fluid outlet openings, each of which contains a valve. This allows, in particular, an improved cooling effect, a reduced pressure loss in the coolant circuit, and a uniform outflow of cooling fluid from the rotor to be achieved.

[0076] Furthermore, the invention can also be further developed such that the rotor body has a first rotor cover on a first end face, in which at least one of the fluid outlet openings, preferably a plurality of the fluid outlet openings, particularly preferably all of the fluid outlet openings is / are formed. The advantageous effect of this embodiment is based on the fact that the fluid outlet openings on the rotor cover can be manufactured particularly easily. In particular, the rotor cover can also be provided as an injection-molded part made of plastic, which makes the manufacture of the fluid outlet openings particularly simple. In this case, the fluid outlet openings preferably extend in the axial direction through the rotor cover.

[0077] In a likewise preferred embodiment variant of the invention, it can also be provided that the number of fluid outlet openings corresponds to the number of rotor cooling channels, which has proven to be particularly advantageous with regard to reducing the pressure loss in the coolant circuit and achieving good cooling performance.

[0078] It may also be advantageous to further develop the invention in such a way that a plurality of the fluid outlet openings, preferably all fluid outlet openings, are arranged on a common diameter, which also promotes a uniform flow of the cooling fluid out of the rotor.

[0079] It is also particularly preferred if the fluid outlet opening(s) are arranged in a radially inner region of the rotor, which reduces the risk of an unintentional pumping effect of the fluid outlet openings during operation of the rotor. Design of drain valve

[0080] According to a further preferred embodiment of the rotor arrangement for an electric machine of a drive train of a motor vehicle, said rotor arrangement can comprise a rotor with a rotor body which is arranged in a rotationally fixed manner on a rotor shaft, a cooling circuit which runs in sections through the rotor, wherein the cooling circuit has in the rotor body a plurality of rotor cooling channels which are arranged circumferentially and extend in the axial direction through the rotor body, wherein the rotor has in the region of its outer circumferential surface a fluid drain opening from which a cooling fluid can flow out of the rotor under the effect of gravity, wherein a drain valve is arranged in the fluid drain opening and is configured such that it opens the fluid drain opening when the rotor is at a standstill and closes it when the rotor is rotating.

[0081] The valve is located on the outer diameter of the rotor in addition to the "normal" fluid outlet opening and closes the fluid drain opening as the speed increases. When the rotor is stationary, the valve is pushed open by the spring, allowing the rotor to be drained of the cooling fluid.

[0082] The ball of the check valve actuates a slotted disc spring under centrifugal force and closes the outlet at a speed of min. 150 rpm

[0083] According to an advantageous embodiment of the invention, the drain valve can be configured to open the fluid drain port when the rotor speed falls below a selected range of 100-200 rpm. The advantage of this configuration is that it ensures a good compromise between avoiding imbalance and providing good cooling performance even in the lower rotor speed range.

[0084] According to a further preferred development of the invention, the drain valve can also be designed as a check valve spring-loaded by a spring element. Furthermore, according to a likewise advantageous embodiment of the invention, the spring element can be a disc spring, which has proven particularly advantageous with regard to the required spring force and characteristic curve. Thus, it is particularly preferred that a ball of the check valve actuates a slotted disc spring under centrifugal force, thus closing the fluid discharge opening at a speed of at least 100-200 rpm.

[0085] According to a further particularly preferred embodiment of the invention, it can be provided that the rotor has a plurality of fluid discharge openings, in each of which a discharge valve is arranged.

[0086] The presence of several fluid drain openings in the rotor enables reliable drainage of the cooling fluid regardless of the rotor position, as this increases the probability that at least one fluid drain opening is located at the geodetically lowest point of the rotor when the rotor is stationary. This simplifies rotor control and increases operational reliability with regard to effective drainage of cooling fluid from the rotor. If one of the drain openings becomes blocked or restricted (e.g., by dirt or deposits), the other openings continue to provide an outlet for the cooling fluid, which increases the operational reliability of the system. For rotors with cooling circuits where air bubbles can be a problem, multiple drain openings also facilitate venting the system.

[0087] The presence of multiple outlet ports allows the fluid to be distributed more evenly and efficiently across the entire rotor, which can contribute to improved performance and efficiency of the corresponding electric machine. Furthermore, the cooling fluid flowing through multiple outlet ports distributes the pressure and mechanical stress on the rotor more evenly, which can also contribute to reducing unwanted stresses and vibrations in or on the rotor. For high-performance rotors or when the rotor is operating at its performance limits, heat dissipation can be critical; in these cases, multiple outlet ports can help the cooling fluid flow more effectively through the rotor, thus enabling better cooling.Using multiple fluid outlets can reduce the flow velocity of the cooling fluid in each outlet, which can contribute to optimized flow behavior and a reduced likelihood of cavitation. The presence of multiple fluid outlets can also help reduce local overheating areas (so-called "hot spots"), as a uniform cooling fluid flow minimizes temperature differences across the rotor.

[0088] Furthermore, the invention can also be further developed such that the rotor body has a first rotor cover on a first end face, in which at least one of the fluid drain openings, preferably a plurality of the fluid drain openings, particularly preferably all of the fluid drain openings is / are formed. By arranging all fluid drain openings in the rotor cover, the fluid flow can be centralized, which enables simpler and more efficient fluid guidance and control. By integrating the openings directly into the rotor cover, the need for additional attachments or piping systems that direct the fluid flow is reduced or eliminated. This simplifies the design and can lead to cost savings in production and assembly. The central arrangement of fluid openings in the rotor cover can further reduce the number of required seals and connections, thereby minimizing the risk of leaks.The central integration of the openings into the rotor cover also allows for a more compact and space-saving overall rotor design. The rotor cover also allows for a certain degree of modular adaptability, as the rotor cover serves as the central element for fluid openings, making it easier to implement or replace specific cover designs for different applications or operating conditions.

[0089] It may also be advantageous to further develop the invention such that the rotor cover is made of a plastic. Plastics are generally lighter than metals, so a lighter rotor cover can reduce the overall mass of the rotor, which can contribute to improved efficiency and performance, as well as a reduction in the mechanical stress on the entire system. Plastics can also be easily formed into complex shapes, allowing for a high degree of flexibility in the design of the rotor cover. This can be particularly useful for achieving specific hydrodynamic properties with respect to the cooling fluid. Furthermore, plastics can dampen vibrations and noise better than many metals, which can contribute to quieter operation.Furthermore, plastics are generally non-conductive, so they also provide electrical insulation, which can be particularly advantageous in the context of separately excited rotors. In many cases, manufacturing a rotor cover from plastic can be more cost-effective than using metals, both in terms of material costs and manufacturing processes. Finally, some plastics also exhibit comparatively low thermal conductivities, which can be advantageous in a given rotor assembly application to provide thermal insulation or reduce heat transfer.

[0090] In a likewise preferred embodiment of the invention, it can also be provided that the number of fluid outlet openings corresponds to the number of rotor cooling channels. If the number of fluid outlet openings corresponds exactly to the number of rotor cooling channels, this can result in a 1:1 assignment between the cooling channels and the openings, which can bring several technical advantages. Each rotor cooling channel can thus have a dedicated outlet opening, so that the cooling fluid flowing through a specific channel can be guided out of the rotor, in particular directly and without detours. This ensures efficient and rapid heat dissipation from each cooling channel.

[0091] It may also be advantageous to further develop the invention in such a way that the fluid discharge openings extend in the radial direction through the rotor, which promotes the most complete outflow of cooling fluid from the rotor.

[0092] The object of the invention is further achieved by an electrical machine comprising a rotor arrangement according to one of claims 1-8.

[0093] Finally, the object of the invention can also be achieved by an electric drive train of a motor vehicle, comprising an electric machine according to claim 9.

[0094] The invention will be explained in more detail below with reference to figures without limiting the general inventive concept.

[0095] It shows: Fig. 1 a motor vehicle with an electric drive train in a schematic representation, Fig. 2 an electrical machine in a schematic representation, Fig. 3 a rotor arrangement in a schematic axial section, Fig. 4 a rotor cover in a perspective view Fig. 5 a rotor arrangement in a schematic axial section, Fig. 6 a rotor arrangement in a schematic axial section, Fig. 7 a rotor arrangement in a schematic axial sectional view.

[0096] The Fig. 2 shows a rotor arrangement 1 for an electric machine 2 of a drive train 3 of a motor vehicle 4, as is also shown in the Fig. 1. In the illustrated embodiment of the Fig. 1, the electric machine 2 is coupled to a transmission arrangement 26 and forms a structural unit with it, which can also be referred to as an axle drive train.

[0097] As can be seen from the Fig. 2-3, the rotor arrangement 1 comprises a rotor 5 with a rotor body 6, which is arranged in a rotationally fixed manner on a rotor shaft 7, a cooling circuit 8, which runs partially through the rotor 5, wherein the cooling circuit 8 has a plurality of rotor cooling channels 9 in the rotor body 6, which are arranged circumferentially and extend in the axial direction through the rotor body 6. Furthermore, the rotor arrangement 1 in the embodiment shown has a coolant pump 10 arranged in the cooling circuit 8, which pumps a cooling fluid 11 through the cooling circuit 8, as well as a control unit 12 for controlling the coolant pump 10. In the exemplary embodiment shown, the electrical machine 2 is designed as a radial flow machine, with a hollow cylindrical stator 23, in which the rotor 5 is rotatably received.

[0098] As can be seen from the Fig. 3, the hollow cylindrical rotor shaft 7 has a plurality of openings in its outer surface through which the cooling fluid 11 can flow radially outward into an annular fluid channel 38 of the rotor 5. This fluid channel 38 is connected to the rotor cooling channels 9. On the opposite axial side, the cooling fluid 11 is then led out of the rotor 5 again at a radially inner outlet opening 35 and can from there be fed, for example, to a rolling bearing 20, as shown in the Fig. 3 is shown.

[0099] With this solution, a residual amount of cooling fluid 11 always remains in the lowest rotor cooling channels 9 in the direction of gravity when the rotor 5 is stationary. Extended downtimes at low temperatures can cause the cooling fluid 11 to change viscosity, resulting in lower flow rates and thus slower emptying. To counteract this, the cooling fluid 11 located in the rotor cooling channels 9 can be heated by targeted rotor coil excitation. This can also occur before the vehicle starts rotating or driving off, for example, as soon as the vehicle is unlocked or when the accelerator, brake, or clutch pedal is depressed.

[0100] The rotor 1 can be separately excited by means of an energizable rotor winding 19, and the rotor assembly 1 has a control unit with a rotor power supply 24 for energizing the rotor winding 19. This can be electrically connected to the rotor shaft 7 or the rotor winding 19 via a sliding contact 25. The rotor power supply 24 is connected to the control unit 12. When a second start-up signal 13 is present before and / or when the rotor 5 spins up from a standstill, the energized rotor winding 19 can heat the rotor body 6. The rotor shaft 7 is rotatably mounted on at least one rolling bearing 20, with the cooling circuit 8 being guided through the rolling bearing 20.

[0101] The control unit 12 for controlling the rotor assembly 1 comprises a processor 21 and a memory 22 containing computer program code. The memory and the computer program code are configured, together with the processor 21, to cause the control unit 12 to perform a method that will be described in more detail below. The control unit 12 can have inputs for various signals 13, 15, 17, by means of which the operation of the rotor assembly 1 is controlled or regulated. Figure 3-4 RING CHANNEL

[0102] The rotor body 6 further comprises a circumferentially extending hydraulic path 30, which connects the rotor cooling channels 9 in the circumferential direction, which can also be clearly seen from the overview of the Fig. 3-4 can be understood.

[0103] The hydraulic path 30 is designed as an annular channel 31, which connects the radially outermost of the rotor cooling channels 9. The rotor body 6 has a first rotor cover 33 on a first end face 32, in which the annular channel 31 is formed. As can be clearly seen from the Fig. 4, the first rotor cover 33 has a plurality of fluid channels 40 extending in the radial direction, which open into the annular channel 31 and which, in the assembled state of the first rotor cover 33, are also hydraulically connected to the rotor cooling channels 9.

[0104] The first rotor cover 33 has a fluid outlet opening 35 on its end face 32, through which the cooling fluid 11 can flow. The rotor body 6 further has a second rotor cover 37 on a second end face 36, which has a radially extending fluid channel 38 that hydraulically connects the rotor shaft 7, designed as a hollow shaft 39 and through which the cooling fluid 11 can flow, to the rotor cooling channels 9. Figure 5 "Check valve"

[0105] In the Fig. 5 shows a further embodiment of a rotor arrangement 1, in which the rotor 5 has at least one fluid outlet opening 35 through which the cooling circuit 8 passes, so that a cooling fluid 11 can leave the rotor 5 through the fluid outlet opening 35 after flowing through the rotor cooling channels 9. A valve 41 is arranged in the fluid outlet opening 35, which closes the fluid outlet opening 35 when the speed of the rotor 5 falls below a predefined speed and opens it above the predefined speed of the rotor 5.

[0106] The valve 41 is now configured to close the fluid outlet opening 35 when the speed of the rotor 5 falls below a selected speed between 100-200 rpm. Fig. 5 it can be clearly seen that the valve 41 is designed as a spring-loaded check valve.

[0107] As in the Fig. As shown in Figure 5, the cooling circuit 8 has a coolant pump 10, by means of which the cooling fluid 11 can be conveyed through the cooling circuit 8. The valve 41 and the coolant pump 10 are configured such that the valve 41 can be opened by the hydraulic pressure that can be built up in the cooling circuit 8 by the coolant pump 10. The rotor 5 has a plurality of fluid outlet openings 35, in each of which a valve 41 is arranged.

[0108] In the Fig. 5 further shows that the rotor body 6 has a first rotor cover 33 on a first end face 32, in which all fluid outlet openings 35 are formed. In the example shown, the number of fluid outlet openings 35 corresponds to the number of rotor cooling channels 9. The fluid outlet openings 35 are also arranged on a common diameter. Figure description 6 "Drain valve"

[0109] In the in the Fig. In the embodiment shown in Figure 6, the rotor 5 has a fluid discharge opening 51 in the region of its outer surface 50, from which a cooling fluid 11 can flow out of the rotor 5 under the effect of gravity. For this purpose, the fluid discharge openings 51 extend radially through the rotor 5.

[0110] A drain valve 52 is arranged in the fluid drain opening 51 and is configured to open the fluid drain opening 51 when the rotor 5 is stationary and to close it when the rotor 5 rotates. The drain valve 52 is configured to open the fluid drain opening 51 when the rotor 5 speed falls below a selected speed between 100 and 200 rpm. In the embodiment shown, the drain valve 52 is designed as a check valve spring-loaded by a spring element 53, wherein the spring element 53 in this specific case is a disc spring.

[0111] The rotor 5 has a plurality of fluid discharge openings 51, in each of which a discharge valve 52 is arranged.

[0112] In the Fig. 6 further shows that the rotor body 6 has a first rotor cover 33 on a first end face 32, in which the fluid discharge openings 51 are formed. The number of fluid discharge openings 51 corresponds to the number of rotor cooling channels 9. Figure 7 "Aperture"

[0113] The Fig. 7 shows a further embodiment of a rotor arrangement 1, in which the rotor 5 has a fluid outlet opening 35 with a first flow cross-section 60, through which the cooling circuit 8 passes, so that a cooling fluid 11 can leave the rotor 5 through the fluid outlet opening 35 after flowing through the rotor cooling channels 9. The rotor 5 further has a fluid drain opening 61 with a second flow cross-section 62, wherein the fluid drain opening 61 is arranged radially above the fluid outlet opening 35 and the first flow cross-section 60 is larger than the second flow cross-section 62.

[0114] The fluid outlet opening 35 and the fluid drain opening 61 extend in the axial direction through the rotor 5, wherein the rotor 5 has a plurality of fluid outlet openings 35 and a plurality of fluid drain openings 61.

[0115] In the example shown, the number of fluid outlet openings 35 corresponds to the number of rotor cooling channels 9 and the number of fluid drain openings 61 corresponds to the number of rotor cooling channels 9.

[0116] All fluid outlet openings 35 are arranged on a common first diameter. All fluid drain openings 61 are also arranged on a common second diameter, wherein the first diameter is smaller than the second diameter.

[0117] The rotor body 6 has on a first end face 32 a first rotor cover 33 formed from plastic, in which all fluid outlet openings 35 and fluid drain openings 61 are formed.

[0118] It is understood that the features of the embodiments of the Fig. 2-7 can be combined with each other in any way, even if this is not explicitly shown in the embodiments.

[0119] The invention is not limited to the embodiments illustrated in the figures. The above description is therefore not to be considered restrictive, but rather explanatory. The following claims are to be understood in such a way that a stated feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. Where the claims and the above description define 'first' and 'second' features, this designation serves to distinguish between two similar features without establishing a priority. List of reference symbols 1 Rotor arrangement 2 machines 3 Drivetrain 4 Motor vehicle 5 Rotor 6 rotor bodies 7 Rotor shaft 8 Cooling circuit 9 rotor cooling channels 10 Coolant pump 11 Cooling fluid 12 Control unit 13 Approach signal 15 Exit signal 17 Exit signal 19 Rotor winding 20 rolling bearings 21 processor 22 storage 23 Stator 24 Rotor power supply 25 sliding contact 26 Gear arrangement 30 Hydraulic path 31 Ring Canal 32 front side 33 Rotor cover 35 Fluid outlet opening 36 front side 37 Rotor cover 38 Fluid channel 39 Hollow shaft 40 fluid channels 41 Valve 50 lateral surface 51 Fluid drain opening 52 drain valve 53 spring element 60 flow cross-section 61 Fluid drain opening 62 Flow cross-section

Claims

[1] Rotor arrangement (1) for an electric machine (2) of a drive train (3) of a motor vehicle (4) comprising • a rotor (5) with a rotor body (6) which is arranged in a rotationally fixed manner on a rotor shaft (7), • a cooling circuit (8) which runs in sections through the rotor (5), wherein the cooling circuit (8) has in the rotor body (6) a plurality of rotor cooling channels (9) which are arranged in a circumferentially distributed manner and extend in the axial direction through the rotor body (6), wherein the rotor (5) has a fluid outlet opening (35) with a first flow cross-section (60) through which the cooling circuit (8) runs, so that a cooling fluid (11) can leave the rotor (5) through the fluid outlet opening (35) after flowing through the rotor cooling channels (9), and the rotor (5) further comprises a fluid discharge opening (61) with a second flow cross-section (62), wherein the fluid discharge opening (61) is arranged radially above the fluid outlet opening (35) and the first flow cross-section (60) is larger than the second flow cross-section (62). [2] Rotor arrangement (1) according to claim 1, wherein the first flow cross-section (60) is between 5-50 times as large as the second flow cross-section (62). [3] Rotor arrangement (1) according to claim 1 or 2, wherein the fluid outlet opening (35) extends in the axial direction through the rotor (5) and / or the fluid drain opening (61) extends in the axial direction through the rotor (5). [4] Rotor arrangement (1) according to one of the preceding claims, wherein the rotor (5) has a plurality of fluid outlet openings (35) and / or a plurality of fluid drain openings (61). [5] Rotor arrangement (1) according to one of the preceding claims, wherein the number of fluid outlet openings (35) corresponds to the number of rotor cooling channels (9) and / or the number of fluid discharge openings (61) corresponds to the number of rotor cooling channels (9). [6] Rotor arrangement (1) according to one of the preceding claims, wherein a plurality of the fluid outlet openings (35), preferably all fluid outlet openings (35) are arranged on a common first diameter and a plurality of the fluid discharge openings (61), preferably all fluid discharge openings (61) are arranged on a common second diameter, wherein the first diameter is smaller than the second diameter. [7] Rotor arrangement (1) according to one of the preceding claims, wherein the rotor body (6) has a first rotor cover (33) on a first end face (32), in which at least one fluid outlet opening (35), preferably a plurality of the fluid outlet openings (35), particularly preferably all the fluid outlet openings (35) is / are formed and / or in which at least one fluid drain opening (61), preferably a plurality of the fluid drain openings (61), particularly preferably all the fluid drain openings (61) is / are formed. [8] Rotor arrangement (1)) according to claim 7, wherein the rotor cover (33) is made of a plastic. [9] Electrical machine (2) comprising a rotor arrangement (1) according to one of the preceding claims. [10] Electric drive train (3) of a motor vehicle (4), comprising an electric machine (2) according to claim 9.

Images