Electric machine having an additional cooling system

Abstract

The invention relates to an electric machine (1, 1') comprising: a stator (10, 10'), a rotor (11, 11') which can be rotated relative to the stator (10, 10'), a machine controller (16) which is configured to set a power of the electric machine (1, 1') and in which a threshold value (T) is stored which determines an output which can be set as the maximum in a normal operation of the electric machine (1, 1'), a cooling system (12) for cooling the stator (10, 10') and / or the rotor (11, 11'), wherein the cooling system (12) is designed to continuously discharge at least a maximum normal-operation heat output which can be maximally delivered in normal operation of the electric machine (1, 1'), and an additional cooling system (13) with a reservoir (130) for receiving a consumable fluid (131) which can be delivered to the stator (10, 10') and / or the rotor (11, 11') in order to cool the stator (10, 10') and / or the rotor (11, 11').

Description

[0001] Rolls-Royce Deutschland Ltd & Co KG

[0002] Eschenweg 11 , OT Dahlewitz

[0003] 15827 Blankenfelde-Mahlow

[0004] Electric machine with an additional cooling system

[0005] Description

[0006] The present disclosure relates in particular to an electric machine, to an arrangement comprising a plurality of electric machines, to an aircraft and to a method for producing an electric machine.

[0007] Vehicles, especially aircraft, are powered in a wide variety of ways. Internal combustion engines, such as piston engines or gas turbine engines, enable long ranges and high speeds. Drives with one or more electric motors, on the other hand, enable the use of sustainably generated energy and are sometimes particularly low-maintenance and quiet. Advances in battery and fuel cell technology are opening up ever-expanding areas of application for electric drives.

[0008] In electrical machines, especially those used to power aircraft, cooling systems often contribute significantly to the overall weight. EP 3 893 366 A1 describes a cooling system for electrical machines in which water is sprayed into the cooling air to increase cooling performance. This allows the cooling system to be smaller and, despite the additional components, to have a reduced overall weight.

[0009] The disadvantage of this solution, however, is that a water tank has to be filled regularly, which leads to increased effort in use.

[0010] Cooling systems based on cooling by a circulating coolant can provide strong cooling performance, but typically have an increased risk of failure compared to systems cooled by ambient air.

[0011] The object of the present invention is to improve the cooling of an electrical machine.

[0012] According to one aspect, an electric machine is specified, in particular for an aircraft. The electric machine comprises a stator, a rotor rotatable relative to the stator, and a machine controller configured to adjust the power of the electric machine. The machine controller is further configured to store a threshold value that determines a maximum adjustable power during normal operation of the electric machine. The electric machine further comprises a cooling system for cooling the stator and / or the rotor, wherein the cooling system is configured to dissipate at least a maximum normal operating heat output (in particular continuously), which can be maximally dissipated during normal operation of the electric machine, and an additional cooling system with a reservoir for receiving a consumable fluid that can be discharged to the stator and / or the rotor for cooling the stator and / or the rotor.

[0013] This is based on the idea of ​​dimensioning the cooling system of the electrical machine in such a way that it meets all cooling performance requirements that can occur during normal operation, but not designing it in such a way that it also meets the significantly higher cooling performance requirements that can occur in the event of a fault outside of normal operation. In electrical machines used as electric motors in an electric drive, windings are usually wound around the teeth of a stator. By applying a three-phase alternating voltage to the windings, magnetic fields are built up which cause a permanent magnet rotor, for example, to move relative to the stator. If a short circuit occurs due to aging processes, vibrations or external influences, for exampleWithin one of the windings, between adjacent turns of the winding, very large electrical currents can be induced in the short-circuited winding loop as a result of the rotation of the rotor by the magnetic fields of the rotating rotor. These currents can lead to strong local heating, which can result in a greatly increased cooling requirement. For example, in aircraft with multiple electrical machines, faults are also possible in which one or more of a large number of electrical machines fail. In these cases, it may be necessary to overload the remaining electrical machines for a short period of time to ensure a safe landing, even if the electrical machines then have to be replaced as a result of the overload.For these and similar reasons, electric machines are sometimes designed to withstand, at least for a short time, a thermal load far greater than that encountered during normal operation. However, such measures have so far resulted in significantly increased weight, and thus, in turn, increased energy consumption and reduced range.

[0014] By tailoring the cooling system to the actual requirements during normal operation as proposed, and by providing the additional cooling capacity required only in the event of a fault via the auxiliary cooling system, the weight of the cooling system can be significantly reduced, and the auxiliary cooling system can also be designed to be particularly small and lightweight. Since the consumable fluid is only used in the event of a fault, and not during normal operation, it does not need to be topped up during normal operation. In other words, unless a fault occurs, it never needs to be refilled over the lifetime of the electrical machine (and the aircraft). However, since maintenance or immediate replacement is carried out anyway in the event of a fault, there is no additional need for a maintenance appointment even then. Since the cooling system does not have to keep reserves in case of a fault, it can be designed to be particularly small and lightweight.Typically, this weight reduction is significantly greater than the additional weight of the auxiliary cooling system. This makes it possible to improve the cooling of the electric machine, particularly by enabling particularly effective cooling during normal operation and in the event of a fault, while maintaining a low weight.

[0015] The maximum adjustable power during normal operation of the electrical machine is, for example, the rated power of the electrical machine. The rated power is predefined.

[0016] The auxiliary cooling system can have one or more outlet openings for discharging the consumable fluid. The consumable fluid can be sprayed from the outlet openings, e.g., each with a nozzle. The consumable fluid can dissipate a particularly large amount of heat through evaporation.

[0017] It can be provided that the one or more outlet openings are aligned with one or more coils of the stator. This allows the coils to be cooled particularly effectively. For example, the outlet openings are aligned with particularly hot areas, especially the coils.

[0018] The stator coils can be coated with a hydrophobic coating, particularly by being enclosed by the hydrophobic coating. This prevents the coils from short-circuiting despite the application of the consumable fluid and ensures that they remain operational.

[0019] For example, the hydrophobic coating comprises or consists of polytetrafluoroethylene (PTFE). This material is particularly durable, lightweight, and has advantageous electrically insulating properties. Furthermore, PTFE exhibits low adhesion resistance to surface contaminants and is therefore particularly advantageous in combination with a cooling system designed for ambient air cooling.

[0020] The stator coils can each be arranged in a direct line between two outlet openings located on opposite sides of the respective coil. This allows for particularly fast and direct cooling of the coil. This eliminates the need for heat to be dissipated through a heat conductor, which can prevent the coil from overheating in the event of a fault with particularly rapid heat buildup.

[0021] The cooling system can define an air flow path along which a gas or gas mixture, in particular ambient air, can flow to cool the stator and / or the rotor. At least two outlet openings can be arranged spaced apart from one another along the air flow path. One outlet opening is thus arranged further upstream in the air flow path, the other further downstream. This allows for distributed and particularly uniform cooling.

[0022] It can be provided that at least a portion of the air flow path runs at an angle, in particular perpendicular to a rotational axis of the rotor relative to the stator. This enables particularly effective cooling.

[0023] The auxiliary cooling system can be designed so that, upon activation, it completely releases the consumable fluid stored in the reservoir to the stator and / or the rotor. As soon as it is activated, the auxiliary cooling system releases the entire stored consumable fluid in a particularly uninterrupted release process. This ensures sufficient cooling in the event of a failure. Release occurs, for example, over a period of up to 200 seconds or up to 400 seconds to ensure a safe landing. After activation, the reservoir must be refilled or replaced if it can be reused.

[0024] The auxiliary cooling system may include an ignition device by means of which a (e.g., explosive) propellant charge can be ignited to release the consumable fluid located in the reservoir to the stator and / or rotor. For example, the auxiliary cooling system includes a gas generator. This allows the auxiliary cooling system to be provided as a maintenance-free module for decades.

[0025] Alternatively or additionally, the auxiliary cooling system can include a pump for delivering an adjustable amount of consumable fluid to the stator and / or rotor. This allows the amount to be adjusted as needed and, for example, to provide additional cooling over a longer period.

[0026] The auxiliary cooling system can be configured to be activated based on a signal from a temperature sensor and / or a torque of the electric machine. If the temperature, e.g., of a coil of the electric machine, exceeds a temperature threshold, and if the torque requirement exceeds a torque threshold, the auxiliary cooling system can reliably detect that a fault has occurred and normal operation is no longer possible, and that the auxiliary cooling system must be activated. The auxiliary cooling system is only activated in the event of a fault, e.g., only as a result of a detected defect.

[0027] The electric machine may comprise several electrically separated winding systems, the energization of which (independently of one another) causes the rotor to rotate relative to the stator. The motor controller may be configured to detect a fault in one of the winding systems and, in response, activate the auxiliary cooling system to continue operating the other, non-faulty winding system (despite significant heat generation from the defective winding system and / or a power requirement exceeding the rated power of the non-faulty winding system).

[0028] The fault could be, for example, a short circuit in the faulty winding system. As already mentioned, this can result in significant heat generation, which can be dissipated by the auxiliary cooling system.

[0029] The cooling system is designed, for example, as an air cooling system. This enables particularly simple and fail-safe cooling. The consumable fluid can comprise or consist of water, or another liquid, in particular with a boiling point below the temperature of a surface contacted by the consumable fluid that occurs in the event of a fault. Thus, particularly large amounts of heat can be dissipated by evaporation of the consumable fluid. According to one aspect, an arrangement is provided, in particular for an aircraft.The arrangement comprises a plurality of electrical machines, each having a stator, a rotor rotatable relative to the stator, and a cooling system for cooling the stator and / or the rotor, and an additional cooling system having a reservoir for holding a consumable fluid which can be delivered to the stator and / or the rotor of each of the plurality of electrical machines for cooling the stator and / or the rotor of each of the plurality of electrical machines. With regard to the advantages, reference is first made to the above information on the electrical machine. Furthermore, the aforementioned arrangement allows a particularly significantly reduced weight to be achieved because one reservoir can be provided for several electrical machines.

[0030] According to one aspect, an aircraft is provided, comprising the electric machine according to any embodiment described herein and / or the arrangement according to any embodiment described herein for driving one or more rotor units, each with a plurality of rotor blades. Regarding the advantages, reference is made to the above statements regarding the electric machine and the arrangement. These are particularly relevant in an aircraft.

[0031] Normal operation may include takeoff, flight, and landing of the aircraft. For all of these flight situations (and other typical operating modes in the air or on the ground not mentioned here), the cooling system is sufficient, and the auxiliary cooling system is not activated.

[0032] According to one aspect, a method is provided for producing an electric machine having a stator and a rotor rotatable relative to the stator, in particular the electric machine according to any embodiment described herein. The method comprises determining a maximum normal operating heat output delivered during normal operation of the electric machine; installing a cooling system for cooling the stator and / or the rotor, wherein the cooling system is designed to be able to dissipate at least the maximum normal operating heat output; and installing an additional cooling system with a reservoir for receiving a consumable fluid that can be delivered to the stator and / or the rotor to dissipate additional heat output of the electric machine that exceeds the maximum normal operating heat output. With regard to the advantages, reference is again made to the above information on the electric machine.

[0033] The electric motor can be configured to power an aircraft. Normal operation can include takeoff, flight, and landing of the aircraft.

[0034] Embodiments will now be described by way of example with reference to the figures. The figures show:

[0035] Figure 1 shows an aircraft in the form of an eVTOL aircraft with several electrically driven rotor units;

[0036] Figure 2 shows an aircraft in the form of a fixed-wing aircraft with an electrically driven rotor unit;

[0037] Figure 3 shows an electrical machine of the aircraft according to Figure 1 with a cooling system and an additional cooling system;

[0038] Figure 4 shows an electrical machine of the aircraft according to Figure 2 with a cooling system and an additional cooling system;

[0039] Figure 5 is a sectional view of part of a coil of the electrical

[0040] Machine according to Figure 3;

[0041] Figure 6 shows a method for manufacturing an electrical machine; and

[0042] Figure 7 shows a method for controlling an electrical machine, in particular of an aircraft.

[0043] Figure 1 shows an aircraft 2 having a plurality of rotor units 20. In the present case, the aircraft 2 is embodied, by way of example, as a VTOL aircraft, specifically as an eVTOL aircraft. Aircraft that take off and land vertically, e.g., airplanes, are regularly referred to as VTOL aircraft, with the abbreviation VTOL being derived from “Vertical Take-Off and Landing.” VTOL aircraft are embodied for vertical take-off and landing. Aircraft, in particular VTOL aircraft, particularly benefit from the advantages of the electric machines 1, 1′ described herein. The aircraft 2 comprises a plurality of electric drive units, each having an electric machine 1 and one of the rotor units 20 for generating lift and / or thrust.

[0044] The aircraft 2 comprises a fuselage 21 with wings 22, each of which has several electric drive units mounted on it, specifically two electric drive units at the front and two at the rear. At least some of the electric drive units, here, for example, those mounted at the front, are pivotable, allowing switching between a predominantly lift-generating (upward) orientation and a predominantly thrust-generating (forward) orientation. The aircraft 2 further comprises a cockpit, but could also be autonomously controlled.

[0045] As will be explained in more detail below in connection with Figure 3, each of the electrical machines 1 comprises a cooling system 12. Furthermore, an additional cooling system 13 is provided. This comprises a reservoir 130 for holding a consumable fluid 131, which is arranged in the reservoir 130 according to Figure 1. The consumable fluid 131 can be delivered to each of the electrical machines 1, in particular specifically to the stator and / or the rotor of each of the electrical machines 1, for cooling each of the electrical machines 1, in particular a respective stator and / or rotor. For this purpose, the reservoir 130 is connected to each of the electrical machines 1 via a line 137 for the consumable fluid 131 (is thus in fluid communication).

[0046] A control system 14 is configured to trigger a release of the consumable fluid 131 in order to provide a temporary, additional cooling capacity if at least one of the electrical machines 1 is operated in an emergency mode outside of normal operation, as will be explained in more detail below. Valves are provided on the lines 137 in order to deliver a targeted release of the consumable fluid 131 only to the one or more electrical machines 1 that require a cooling capacity that goes beyond normal operation. If, for example, one or more of the electrical drive units should fail, the remaining ones can be operated at a power that overloads the electrical machines 1, but which is possible for a limited time due to the additional cooling capacity, for example to ensure a safe landing despite the major failure.

[0047] The aircraft 2 thus has an arrangement 3 comprising a plurality of electrical machines 1, each having a stator 10, a rotor 11 rotatable relative to the stator 10 (see Figure 3), and the respective cooling system 12 for cooling the stator 10 and / or the rotor 11. The arrangement 3 further comprises the additional cooling system 13 with the reservoir 130 for receiving the consumable fluid 131, which can be delivered from each of the plurality of electrical machines 1 to the stator 10 and / or the rotor 11 of each of the plurality of electrical machines 1 for cooling the stator 10 and / or the rotor 11.

[0048] Figure 2 shows an aircraft 2' in the form of an electrically powered aircraft with a fuselage 21', wings 22' and a cockpit.

[0049] The aircraft 2' comprises an electrical machine 1' in the form of an electric motor and a rotor unit 20 driven by the electric motor. The rotor unit 20 comprises a plurality of rotor blades 200, here two as an example. In the example shown, the rotor blades 200 are mounted on a hub and thus form a propeller. In alternative embodiments, the aircraft 2' comprises a fan instead of a propeller and / or a plurality of electric drive units, each with at least one propeller or fan. This applies analogously to the electric drive units of the aircraft 2 according to Figure 1.

[0050] The aircraft 2' (like the aircraft 2 according to Figure 1) comprises an energy supply system 23, which supplies electrical energy to the electric machine 1'. The energy supply system 23 here comprises an electric battery system, but could alternatively or additionally also comprise, for example, a fuel cell and / or an internal combustion engine with a generator. In this case, electrical energy can also be generated with the electric machine 1' in generator mode and stored in the energy supply system 23.

[0051] For cooling the electrical machine 1', the aircraft 2' has at least one air inlet 24, here several air inlets 24, through which ambient air L can flow to (here: through) the electrical machine 1' and thus cool it, as will be explained in more detail below with reference to Figure 4.

[0052] Figure 3 shows a cutaway view of an electrical machine 1 of the aircraft 2 according to Figure 1. The electrical machines 1 of the aircraft 2 are structurally identical to one another.

[0053] The electric machine 1 comprises a stator 10. The stator 10 is mounted on one of the wings 22 of the aircraft 2. The stator 10 comprises several electrical coils 100. The coils 100 have several windings and are fixed to the stator 10. Power electronics 17 applies an alternating current to the coils, which then generates a magnetic field.

[0054] The electric machine 1 further comprises a rotor 11 rotatable relative to the stator 10. Mounted on the rotor 11 are several magnets 111, on which forces act due to the magnetic field of the coils 100, causing the rotor 11 to rotate relative to the stator 10 about a rotation axis R. A shaft 110 of the rotor 11 transmits the generated torque to the rotor unit 20, as illustrated in Figure 3 by the thin arrows. The shaft 110 is hollow. The power electronics 17 are arranged inside the shaft 110.

[0055] The electric machine 1 further comprises a machine control 16. The machine control 16 is configured to set a power of the electric machine 1, e.g., an absorbed electrical power and / or an output mechanical power. A threshold value T can be stored and is stored in the machine control 16, which determines a maximum adjustable power during normal operation of the electric machine 1. The maximum adjustable power is the rated power of the electric machine 1. As long as the electric machine 1 is operated during normal operation, the rated power cannot be exceeded. As long as there is no error, e.g., due to a defect, the electric machine 1 is operated during normal operation. Normal operation includes takeoff, flight, and landing of the aircraft 2.

[0056] The electric machine 1 also includes a cooling system 12 for cooling the stator 10 (and / or the rotor 11).

[0057] The cooling system 12 has air flow paths 120 along which ambient air L can flow through the electric machine 1. In this case, the ambient air L is conveyed along the air flow paths 120 by the airstream and the blades driven by the electric machine 1. The shaft 110 forms an air inlet 113 through which the ambient air L can flow. The ambient air L then flows first along the heat sinks of the power electronics 17 and cools them. The ambient air L then flows through air passages of the rotor 11 and along the coils 100 of the stator 10 to directly cool the coils 100. The air flow paths 120 initially extend parallel to the axis of rotation R and then radially outward along the coils 100.

[0058] The cooling system 12 uses ambient air L to first cool the power electronics of the electric machine 1, then the coils 100 of the stator 10.

[0059] The cooling system 12 is designed to continuously dissipate at least a maximum normal operating heat output, which is the maximum that can be dissipated during normal operation of the electric machine 1. The cooling system 12 is therefore sufficiently dimensioned so that the electric machine 1 can be continuously operated, for example, at its rated power. However, the cooling system 12 has no, or at least no substantial, reserve that would enable operation beyond the rated power in the event of a fault. The cooling system 12 alone would not be sufficiently powerful for this.

[0060] For a cooling requirement that goes beyond the dissipation of the maximum normal operating heat output, the electric machine 1 comprises an additional cooling system 13 with a reservoir 130 for holding a consumable fluid 131. The consumable fluid 131 can be delivered to the stator 10 for cooling the stator 10 (and / or the rotor 11). In this way, the additional cooling power required in the event of a fault can be provided. The additional cooling system 13 comprises outlets 137 that are in fluid communication with the reservoir 130 and have a plurality of outlet openings 132, 133 for discharging the consumable fluid 131. According to Figure 3, outlet openings 133 are provided on the air inlet 113. Here, consumable fluid 131 can be sprayed into the inflowing ambient air L. Furthermore, outlet openings 132 are formed in the interior of the stator 10. From there, consumable fluid 131 can be applied directly to the coils 100, in this case sprayed on.Those outlet openings 132 are aligned with the coils 100 of the stator 10, in this case such that the coils 100 of the stator 10 are each arranged in a direct line between two outlet openings 132 arranged on opposite sides of the respective coil 100, as illustrated in Figure 3. Furthermore, a plurality of outlet openings 132 are arranged spaced apart from one another along the air flow path 120.

[0061] The consumable fluid 131 is water in this case, although other cooling fluids, especially liquids, are also conceivable. The consumable fluid 131 is non-flammable. The consumable fluid 131 does not circulate but is consumed through a single application. It is released into the environment after cooling the electric machine 1. The consumable fluid 131 can also be a mixture.

[0062] The auxiliary cooling system 13 further comprises a device by means of which pressure can be built up in the reservoir 130. In the example of Figure 3, an ignition device 134 with a propellant charge 135 is provided. Ignition by the ignition device 134 ignites the propellant charge 135, which then generates a propellant gas. This gas exerts pressure on the reservoir 130, e.g., by a plunger or by being blown into the reservoir 130. As a result of activation of the ignition device 134, the consumable fluid 131 arranged in the reservoir 130 is completely delivered to the stator 10. The auxiliary cooling system 13 can therefore only be activated once. After activation, it provides consumable fluid to the stator 10 for approximately 200 seconds. A control system 14 is provided for activating the auxiliary cooling system 13. The control system 14 can be combined with the machine control system 16 or be separate therefrom.The control system 14 detects signals from temperature sensors 15. The temperature sensors 15 are arranged on the coils 100. If a measured value read from the temperature sensors 15 exceeds a predefined temperature threshold, the control system 14 concludes that an error has occurred and that normal operation is no longer occurring. Based on this, the control system activates the ignition device 134.

[0063] Furthermore, the control system 14 receives values ​​of a torque requested by the electric machine 1 from the machine controller 16. If the torque (or a resulting power) exceeds a torque threshold (or a power threshold), the control system 14 (or the machine controller 16) concludes that a fault has occurred and that normal operation is no longer occurring. Based on this, the control system activates the ignition device 134. The power threshold can be the threshold value T, which determines the maximum adjustable power during normal operation of the electric machine 1, or a value based thereon. Furthermore, the control system 14 can jointly consider the torque value and the temperature value to activate the additional cooling system 13.

[0064] The electrical machine 1 is a transverse flux machine, although other types of electrical machines are also conceivable, e.g. axial or radial flux machines.

[0065] Figure 4 shows a schematic sectional view of the rotating electrical machine 1' of the aircraft 2' from Figure 2, which here is designed in the form of a permanent magnet synchronous machine. From Figure 4 it can be seen that the electrical machine 1' is designed as an internal rotor in the present case, but alternatively the electrical machine 1' could also be designed, for example, as an external rotor. The electrical machine T comprises a stator 10', which has an opening (not designated), in particular a through-opening, in which a rotor 1T is rotatably mounted. The stator 10' comprises a body, here in the form of a laminated core, to which teeth 102 are fixed, which can also be referred to as stator teeth. The teeth 102 are aligned with an air gap L between the body of the stator 10' and the rotor 11'. The teeth 102 protrude radially from the body, in this case radially inward.

[0066] The stator 10' has several winding systems W1, W2. The winding systems W1, W2 are electrically separated from one another. Each of the winding systems W1, W2 has electrical windings for three electrical phases U, V, W. The individual winding systems W1, W2 are only shown schematically here for the sake of simplicity. Electrical conductors of the winding systems W1, W2 are wound around the teeth 102 of the stator 10' in the form of windings 201.

[0067] Each of the winding systems W1, W2 is designed for three-phase operation, i.e., it is connected to a three-phase alternating voltage with phases U, V, W. During normal operation of the electrical machine 1', the winding systems W1, W2 are supplied with the respective alternating voltage.

[0068] In the present case, the rotor 11' is designed, for example, as a salient-pole rotor, which includes permanent magnets to provide the magnetic flux. In the present embodiment, the rotor 11' has exactly one magnetic north pole N and one magnetic south pole S. In alternative embodiments, more magnetic poles can also be provided alternating in the circumferential direction transverse to a rotational axis of the rotor 11' (relative to the stator 10').

[0069] The rotor 11' is rotatably mounted. During normal operation, the three-phase alternating voltage, whose phases U, V, W are each phase-shifted by 120°, generates a rotating magnetic field which interacts with the permanently excited magnetic field provided by the rotor 11', so that during motor operation, a corresponding rotary movement of the rotor 11' relative to the stator 10' can be induced. In the present case, the electric machine 1' is intended to serve as the drive motor for the rotor unit 20 of the aircraft 2'. Figure 4 schematically shows the sections of the winding systems W1, W2 which are assigned to the respective phases U, V, W.

[0070] Each of the (here two) winding systems W1, W2 of the electrical machine T is connected to a three-phase inverter of a power electronics unit 17. The respective inverter provides the electrical alternating voltage with the three phases U, V, W for the corresponding winding system W1, W2. The inverters draw the electrical energy required for proper operation from the energy supply system 23 connected to the power electronics unit 17. Each of the inverters has inverter units assigned to it for providing the phases U, V, W. Each inverter unit has a half-bridge circuit. The respective half-bridge circuit has a series connection of two electronic switching elements (e.g. transistors) which are connected to an intermediate circuit DC voltage of the inverter.The electronic switching elements operate in a pulsed mode, which, for example, provides pulse patterns similar to a PWM signal. The corresponding phases U, V, and W of the three-phase alternating voltage are then available at a respective center tap of the half-bridge circuits. The inductance of the windings provides appropriate filtering, so that a corresponding alternating current is generated for each of the phases U, V, and W, which, with appropriate control of the inverter units, can be nearly sinusoidal.

[0071] The individual inverters are independent of each other. If one of the winding systems W1, W2 or one of the inverters fails, the other inverters and winding systems W1, W2 (here, the second winding system W1, W2 with the respective inverter) can continue to operate.

[0072] In the event of a short circuit, e.g. an inter-turn short circuit, in which adjacent turns within a winding are short-circuited to one another, e.g. as a result of defective insulation, a very large current can be induced in the short-circuited conductor loop by the rotor 1T, which continues to rotate (at least for a certain period of time), even when the current supply to the affected winding system W1, W2 is switched off. This can lead to high thermal stress. The motor controller 16 or the control system 14 communicatively connected thereto is designed to detect a fault, in particular in the form of a short circuit, in one of the winding systems W1, W2 and to activate the additional cooling system 13 in response thereto. The short circuit can be detected, for example, by a rise in temperature and / or a rise in current.

[0073] In the cooling system 12 of the electric machine T, the propeller blows ambient air L through the interior of the stator 10'. The electric machine T is directly air-cooled. Specifically, the electric machine T has directly air-cooled coils 100. The auxiliary cooling system 13 is connected to the interior of the stator 10' via one or more lines 137. The auxiliary cooling system 13 here comprises a pump 136 for delivering an adjustable amount of the consumable fluid 131 to the stator 10'. A predetermined number of sprays of the consumable fluid 131 can be carried out by means of the pump 136.

[0074] Figure 5 shows a cross-section of a section of coil 100 according to Figure 3. Coil 100 has a rectangular cross-section, for example. The electrically conductive material of coil 100, e.g., copper, is surrounded by a hydrophobic coating 101. Hydrophobic coating 101 encloses the section of coil 100. Hydrophobic coating 101 is made of polytetrafluoroethylene (PTFE).

[0075] It should be noted that the rectangular cross-section is only an example and that a coil with, for example, a round conductor cross-section can also be provided with the hydrophobic coating 101.

[0076] Figure 6 shows a method for producing an electrical machine 1, T with a stator 10, 10' and a rotor 11, 1 T rotatable relative to the stator 10, 10'. The method comprises the following steps:

[0077] Step S1: Determining the maximum normal operating heat output of the electric machine 1, T during normal operation. Normal operation includes a takeoff, a flight, and a landing of an aircraft 2, 2' with the electric machine 1, 1'.

[0078] Step S2: Mounting a cooling system 12 for cooling the stator 10, 10' and / or the rotor 11, 11', wherein the cooling system 12 is designed to be able to dissipate at least the maximum normal operating heat output.

[0079] Step S3: Mounting an additional cooling system 13 with a reservoir 130 for receiving a consumption fluid 131, which can be delivered to the stator 10, 10' and / or the rotor 11, 11' to dissipate additional heat output of the electric machine 1, T, which exceeds the maximum normal operating heat output.

[0080] Figure 7 shows a method for controlling the electrical machine 1, 1' optionally according to Figure 3 or 4. The method comprises the following steps:

[0081] Step S10: Determining a current operating mode of the electrical machine 1 , 1 '.

[0082] Step S11: Check whether the current operating mode corresponds to a fault mode (or normal mode). If the current operating mode corresponds to a fault mode (branch Y), the process continues to step S12. Otherwise (branch N), the process repeats step S10.

[0083] Step S12: Activating the auxiliary cooling system 13.

[0084] At this point, it should be noted that the described solution decouples the design of the electric machine 1, 1' from the dimensioning of the auxiliary cooling system 12. Depending on the application, a reservoir 130 of different sizes can simply be used.

[0085] Furthermore, in all examples, multiple reservoirs 130 may be provided instead of just one reservoir 130.

[0086] It should be understood that the invention is not limited to the embodiments described above, and various modifications and improvements may be made without departing from the concepts described herein. Any of the features may be used separately or in combination with any other features, provided they are not mutually exclusive, and the disclosure extends to and encompasses all combinations and subcombinations of one or more of the features described herein.

[0087] Reference symbols

[0088] I , 1' electric machine

[0089] 10, 10' stator

[0090] 100 spool

[0091] 101 hydrophobic coating

[0092] 102 tooth

[0093] II, 11 ' rotor

[0094] 110 Wave

[0095] 111 Magnet

[0096] 112 Air passage

[0097] 113 Air intake

[0098] 12 Cooling system

[0099] 120 Airflow path

[0100] 13 Additional cooling system

[0101] 130 Reservoir

[0102] 131 Consumable fluid

[0103] 132 Exit opening

[0104] 133 Exit opening

[0105] 134 Ignition device

[0106] 135 propellant charge

[0107] 136 Pump

[0108] 137 Line

[0109] 14 Control system

[0110] 15 Temperature sensor

[0111] 16 Machine control

[0112] 17 Power electronics

[0113] 2, 2' aircraft

[0114] 20 Rotor unit

[0115] 200 rotor blades

[0116] 21 , 2T hull

[0117] 22, 22' Wing

[0118] 23 Energy supply system

[0119] 24 Air inlet 3 arrangement

[0120] L Ambient air

[0121] R axis of rotation

[0122] T threshold value W1 , W2 winding system

Claims

Claims 1. An electrical machine (1, T), comprising: a stator (10, 10'), a rotor (11, 11') rotatable relative to the stator (10, 10'), a machine control (16) configured to adjust a power of the electrical machine (1, T) and in which a threshold value (T) is stored that determines a maximum adjustable power during normal operation of the electrical machine (1, T), a cooling system (12) for cooling the stator (10, 10') and / or the rotor (11, 11'), wherein the cooling system (12) is configured to continuously dissipate at least a maximum normal operating heat output that can be maximally dissipated during normal operation of the electrical machine (1, T), and an additional cooling system (13) having a reservoir (130) for receiving a consumable fluid (131) that is used to cool the stator (10, 10') and / or the rotor (11, 11') can be delivered to the stator (10, 10') and / or the rotor (11, 11').

2. Electrical machine (1, T) according to claim 1, wherein the additional cooling system (13) has a plurality of outlet openings (132) for discharging the consumable fluid (131).

3. Electrical machine (1, T) according to claim 2, wherein the outlet openings (132) are aligned with coils (100) of the stator (10, 10').

4. Electrical machine (1, T) according to claim 3, wherein the coils (100) of the stator (10, 10') are provided with a hydrophobic coating (101).

5. Electrical machine (1, T) according to claim 4, wherein the hydrophobic coating (101) comprises or consists of polytetrafluoroethylene.

6. Electrical machine (1, T) according to one of claims 3 to 5, wherein the coils (100) of the stator (10, 10') are each arranged in a direct line between two conductors arranged on opposite sides of the respective coil (100). Outlet openings (132) are arranged.

7. Electrical machine (1, T) according to one of the preceding claims, wherein the cooling system (12) defines an air flow path (120) along which ambient air (L) can flow to cool the stator (10, 10') and / or the rotor (11, 11'), wherein at least two outlet openings (132) are arranged spaced apart from one another along the air flow path (120).

8. Electrical machine (1, T) according to claim 7, wherein the air flow path (120) runs perpendicular to a rotational axis (R) of the rotor (11, 1 T) relative to the stator (10, 10').

9. Electrical machine (1, T) according to one of the preceding claims, wherein the additional cooling system (13) is designed such that, as a result of activation, it completely releases the consumable fluid (131) arranged in the reservoir (130) to the stator (10, 10') and / or the rotor (11, 1 T).

10. Electrical machine (1) according to claim 9, wherein the additional cooling system (13) comprises an ignition device (134) by means of which a propellant charge (135) can be ignited in order to deliver the consumable fluid (131) arranged in the reservoir (130) to the stator (10) and / or the rotor (11).

11. Electrical machine (T) according to one of claims 1 to 9, wherein the additional cooling system (13) comprises a pump (136) for delivering an adjustable amount of the consumable fluid (131) to the stator (10') and / or the rotor (1 T).

12. Electric machine (1, T) according to one of the preceding claims, wherein the additional cooling system (13) is designed to be activated based on a signal from a temperature sensor (15) or a torque of the electric machine (1, T).

13. Electrical machine (1 , T) according to one of the preceding claims, comprising a plurality of electrically separated winding systems (W1 , W2), by the energization of which the rotor (11, 11') can be set into rotation relative to the stator (10, 10') independently of one another, wherein the motor control (16) or a control system (14) communicatively connected thereto is designed to detect a fault in one of the winding systems (W1, W2) and to activate the additional cooling system (13) in response thereto.

14. Electrical machine (1, T) according to claim 13, wherein the fault comprises a short circuit in one of the winding systems (W1, W2).

15. Electrical machine (1, T) according to one of the preceding claims, wherein the cooling system (12) is designed in the form of an air cooling system and the consumption fluid (131) comprises or consists of water.

16. Arrangement (3) comprising: a plurality of electrical machines (1, T), each having a stator (10, 10'), a rotor (11, 11') rotatable relative to the stator (10, 10') and a cooling system (12) for cooling the stator (10, 10') and / or the rotor (11, 1 T) and an additional cooling system (13) with a reservoir (130) for receiving a consumable fluid (131) which can be delivered from each of the plurality of electrical machines (1, T) to the stator (10, 10') and / or the rotor (11, 1 T) of each of the plurality of electrical machines (1, T) for cooling the stator (10, 10') and / or the rotor (11, 11').

17. Aircraft (2, 2') comprising the electric machine (1, T) according to one of claims 1 to 15 and / or the arrangement according to claim 16 for driving at least one rotor unit (20) with a plurality of rotor blades (200).

18. Aircraft (2, 2') according to claim 17, wherein the normal operation comprises a takeoff, a flight and a landing of the aircraft (2, 2').

19. Method for producing an electrical machine (1 , T) with a stator (10, 10') and a rotor (11 , 11') rotatable relative to the stator (10, 10'), the Procedure comprising: Determining a maximum normal operating heat output delivered during normal operation of the electrical machine (1, T); Mounting a cooling system (12) for cooling the stator (10, 10') and / or the rotor (11, 11'), wherein the cooling system (12) is designed to be able to dissipate at least the maximum normal operating heat output; and Mounting an additional cooling system (13) with a reservoir (130) for receiving a consumption fluid (131) which can be delivered to the stator (10, 10') and / or the rotor (11, 1 T) for dissipating additional heat output of the electrical machine (1, T) which exceeds the maximum normal operating heat output.

20. The method according to claim 19, wherein the electric machine (2, 2') is designed to drive an aircraft (2, 2') and the normal operation comprises a takeoff, a flight and a landing of the aircraft (2, 2').

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