Electric drive system having a cooling system therefor

Abstract

Proposed is an electric drive system (1), in particular for aircraft. The drive system (1) comprises an electric motor (2) that is accommodated in a housing (5). The surface (7) of the housing (5) defines a cooling structure (8). A cooling housing (10) is provided, in which the electric motor (2) is seated. The cooling structure (8) of the electric motor (2) is in thermal contact with an inner surface (11) of the cooling housing (10). The cooling housing (10) is filled with a cooling medium (25), which at least also surrounds the cooling structure (8) of the electric motor (2).

Description

[0001] Electric drive system with cooling system for this

[0002] The invention relates to an electric drive system, particularly for aircraft. The drive system has an electric motor consisting of a stator and a rotor. The components of the electric motor are housed in a housing whose surface defines a cooling structure.

[0003] French patent application FR 3063403 A1 relates to a motor with a rotor, a stator, and a cooling system. The cooling system defines a housing in which the stator is mounted. The housing accommodates the rotor and stator and is configured to define a substantially annular channel with the stator. The annular channel allows the passage of a fluid flow. A series of fins is attached to the stator and protrudes into the channel.

[0004] IIS patent application US 2023 / 010555 A1 relates to a rotating mechanical system having an electric motor and a housing that at least partially houses one or more components of the electric machine. The housing defines an electrical cavity and a coolant cavity. The electrical cavity houses one or more electrical components, such as a stator, of the electric machine. The coolant cavity is configured to receive a liquid coolant, such as ethylene glycol and water, from a liquid coolant system. The housing is configured to seal a two-phase refrigerant within the electrical cavity to transfer heat from the one or more electrical components to a wall of the electrical cavity and from the wall of the electrical cavity to the liquid coolant.

[0005] European patent application EP 1 593 192 A1 relates to a cooling system for rotating machines. A housing comprises an inlet and an outlet. A rotor is mounted within the housing for rotation about an axis, the rotor having an outer surface. Within the housing, a stator is arranged around the rotor, the inner surface of the stator being adjacent to the outer surface of the rotor. A gap sufficient to reduce friction and enable convection cooling is formed between the inner and outer surfaces. The gap is in fluid communication with the inlet and outlet, and a pumping device pumps a cooling gas from the inlet into the gap and through the outlet. The pumping device comprises an impeller attached to an end portion of the rotor to generate an axial airflow into the gap. Preferably, the air cooling system of the present invention is used in conjunction with a liquid cooling system arranged external to the stator.The liquid cooling system reduces the amount of air that needs to flow between the gaps to remove the desired amount of heat from the machine.

[0006] Electric drive systems for aircraft today are typically cooled with air or liquid, usually oil or water, or water-antifreeze mixtures. In addition, such drives often have an (oil-lubricated) gearbox to adapt the motor speed to the required propeller speed or to achieve the highest possible power density of the system in order to reach the ideal operating point for both the motor and the propeller. For the sake of technical simplicity and because fewer components are required, each of which could fail individually and thus increase the overall risk of failure, air cooling is often used. Electric drive systems for aircraft are typically designed redundantly. This means that several drive systems are operated simultaneously to keep the aircraft in the air and / or move it.If one engine fails, the remaining engines increase their power to keep the aircraft in the air. This operating mode is usually only required for a short time, for example, until the aircraft can safely approach a landing site. Therefore, a high thermal mass of the engine is a great advantage, because the engine's power loss can then be temporarily stored in the engine's thermal mass, eliminating the need to design the engine and / or cooling system for this high power.

[0007] Thermal mass is a property of materials that indicates how much heat energy they can store. It is often used in architecture and construction to improve the energy efficiency of buildings. The heat capacity of a body is the ratio of the heat supplied to it to the resulting temperature increase. The unit of heat capacity is J / K. The heat capacity of a body can be calculated as the product of its specific heat capacity and its mass. The specific heat capacity is a material constant and is tabulated in relevant reference works.

[0008] A high thermal mass generally has the disadvantage that it also increases the mass of the motor, which limits its use in weight-sensitive areas. Therefore, the use of materials with a high heat capacity / weight ratio, such as oil or water, would be advantageous. Liquid cooling of the motor would therefore be advantageous, due to the significantly higher power density that the motor or drive system can then achieve. In particular, the thermal mass can then be slightly increased if necessary - e.g., in the event of a design change to the aircraft or if safety requirements change. This can be achieved, for example, by increasing the amount of coolant. In this case, the losses that arise due to the always finite efficiency of the drive would then be offset for a limited time - usuallyan emergency situation - in which higher performance is required, temporarily stored in the coolant.

[0009] The actual cooling system, usually a liquid-to-air heat exchanger, can therefore be designed for a lower output and thus be smaller and lighter. However, liquid cooling brings with it the problem that it requires a large number of components, such as pumps, reservoirs, and liquid-to-air heat exchangers, which, as described above, therefore carry an increased risk of failure. However, to ensure the highest possible reliability and thus safety of the propulsion system, which is essential for an aircraft, the goal is to minimize the number of components.

[0010] The object of the invention is to provide an electric drive system with cooling that, on the one hand, maintains the technical simplicity and the number of components of an air cooling system, but, on the other hand, has a higher power density and, in particular, a higher thermal mass. Furthermore, the drive unit should be easily adaptable to changing requirements. This object is achieved by an electric drive system comprising the features of claim 1.

[0011] The electric drive system has a cooling housing in which the electric motor is located. The electric motor, with its cooling structure, is in thermal contact with an inner surface of the cooling housing, and the cooling housing is filled with a cooling medium that surrounds at least the cooling structure of the electric motor.

[0012] The advantage of the invention is that the electric motor of the drive system has cooling geometries on its outer surface to increase the surface area, which are optimized for exchange with liquid coolant. The electric motor is placed in a cooling housing with a cooling medium, and the cooling housing also has cooling geometries on its outer surface that are optimized for exchange with air. Due to the invention, the electric motor, the cooling medium, the cooling housing, and the ambient air are in the best possible thermal exchange.

[0013] The electric motor according to the invention can have a cooling structure on its outermost diameter, which can be smooth or preferably provided with cooling fins. It has proven particularly advantageous if the surface of the electric motor is designed as a so-called fin-pin cooler. This design has a particularly large surface area and thus provides good heat exchange.

[0014] According to another possible embodiment, the electric motor comprises a can. The stator of the electric motor is positioned between the cooling structure of the electric motor and the can. The stator of the electric motor is in thermal contact with the housing of the electric motor and the can. Furthermore, the stator is accessible to the cooling medium. Thus, not only the housing of the electric motor but also the stator is surrounded by the cooling medium. The stator is delimited at its inner diameter by a can, which prevents the cooling medium from entering the rotor space.

[0015] The advantage is that the contact of the coolant with the stator of the electric motor increases cooling performance. According to another possible embodiment, the cooling structure of the electric motor can have a smooth surface, or the surface of the electric motor can be provided with cooling fins. The housing of the electric motor is in thermal contact with the cooling housing.

[0016] The electric motor housing is located in the cooling housing, which contains a cooling medium, e.g., water, but preferably oil. The electric motor housing is in thermal exchange with the cooling housing through the cooling structure. The cooling medium in the cooling housing, the electric motor housing, and the ambient air are in optimal thermal exchange.

[0017] According to a further embodiment of the electric drive system, a central shaft of the drive system is designed as a hollow shaft. The hollow shaft communicates with the space for the cooling medium at its lower and upper ends. The lower diameter of the bore of the central shaft is smaller than the upper diameter of the central shaft.

[0018] The advantage of the hollow shaft is that the cooling medium is transported through the central shaft, which is a hollow shaft, solely by centrifugal forces. The cooling medium exits at the upper end of the central shaft and is distributed by centrifugal forces. The advantage is that the central shaft of the electric motor, and thus the rotor of the electric motor, is cooled. In addition, the cooling medium is continuously circulated, thus increasing the cooling effect of the electric motor. At the same time, by distributing the cooling medium throughout the housing, its recooling by air is improved. According to a further embodiment, a gearbox is provided in the cooling housing. The gearbox is operatively connected to the central shaft. The advantage is that the cooling medium exiting at the upper end of the central shaft comes into contact with all internal housing surfaces of the cooling housing and also of the gearbox, and is therefore effectively cooled. Likewise, the gearbox and / or the bearings are well lubricated.When the electric drive system is aligned accordingly, the cooling medium flows back into the cooling housing by gravity. In the cooling housing, the cooling medium surrounds the electric motor and cools it. A particular advantage of this embodiment of the invention is that this greatly simplified circulation cooling and lubrication system does not require a single additional component. The additional functionality can be achieved by cleverly designing the existing components to ensure circulation cooling and lubrication.

[0019] According to a further embodiment, a pump can additionally be provided, which ensures the exchange of cooling medium from a space between the housing of the electric motor and the cooling housing to the space in the cooling housing for the transmission. Even if said pump were to fail, this would only result in limited performance of the electric motor. A pump failure in a conventional liquid cooling system would result in a complete failure of the electric motor.

[0020] The embodiment of the invention with the additional pump, which is driven either directly by the central shaft of the electric motor, by the gearbox, or via a separate electric motor, is responsible for exchanging oil between the gearbox and the electric motor. It is particularly advantageous if a pump driven by a separate electric motor is used. This pump can only be used in emergencies to transport the cooling medium. This means that during normal operation, the drive system is operated passively. If high power is required in certain situations, the pump is switched on for a short time and ensures an increased exchange of cooling medium. To enhance this effect, the pump's oil circuit can also have an additional heat exchanger that cools the cooling medium with air.

[0021] According to a further advantageous embodiment, the described electric drive system and the cooling system used for it can also be used particularly advantageously if the power electronics required to operate the electric motor are mounted directly on the electric motor. The power electronics are housed in a housing, and this housing for the power electronics is attached directly to the housing for the electric motor. Here, the same cooling principle is used as for the electric motor. This design is particularly advantageous when so-called silicon carbide transistors are used as power semiconductors, because they can be operated at very high temperatures and therefore harmonize very well with the temperature level of an electric motor.

[0022] Oil is preferably used as a cooling medium to cool the central shaft and thus also the rotor of the electric motor of the electric drive system.

[0023] Furthermore, a magnet is placed in the cooling medium chamber, close to the lower end of the central shaft (hollow shaft) of the electric motor. The magnet serves to trap metal chips. A sieve is placed at the upper end of the cooling housing to catch any foreign matter.

[0024] The advantage of the recirculating cooling system used in the electric drive system designs is that this greatly simplified recirculating cooling and lubrication system requires no additional components. The additional functionality can be achieved through clever design of existing components.

[0025] If a substance is used as the cooling medium that undergoes a phase change at the elevated operating temperature of the electric motor, this effect can be additionally utilized to cool the motor in such (emergency) operating situations. The cooling medium can absorb additional heat due to the phase change. Examples of suitable materials include paraffins, which change from solid to liquid at a specific temperature, or another medium that evaporates at a certain temperature.

[0026] The invention and its advantages are described in more detail below with reference to the attached schematic drawings.

[0027] Figure 1 shows a possible embodiment of the drive unit in which the electric motor is housed in a cooling housing.

[0028] Figure 2 shows another possible embodiment of the drive unit, in which the cooling structure of the electric motor housing is in thermal contact with the cooling casing. Figure 3 shows a possible embodiment of the surface of the motor housing.

[0029] Figure 4 shows another possible embodiment of the drive unit, in which the cooling medium oil is guided through the central shaft of the electric motor.

[0030] Figure 5 shows another possible embodiment of the drive unit

[0031] Figure 6 shows the embodiment of the drive unit from Fig 5, in which a gear interacts with the central shaft.

[0032] Figure 7 shows the embodiment of the drive unit from Fig. 6, in which a pump is provided which serves to exchange the oil between the gearbox and the engine.

[0033] Figure 8 shows the embodiment of the drive unit from Fig. 6, in which the necessary power electronics for operating the electric motor are mounted directly on the motor.

[0034] In the following, exemplary embodiments will explain the invention and its advantages in more detail with reference to the accompanying figures. The proportions in the figures do not always correspond to the actual proportions, as some shapes are simplified and others are shown enlarged relative to other elements for better illustration.

[0035] Figure 1 shows a possible embodiment of the drive unit 1, in which the electric motor 2 is housed in a cooling housing 10. Normally, the housing 5 of an electric motor 2 has on its surface 7 (outermost diameter 6) either cooling fins 9 for air cooling or a cooling jacket with integrated fins (liquid cooling) (not shown).

[0036] The drive unit 1 according to the invention can be smooth on its surface 7 (outermost diameter 6) or, according to a preferred embodiment, can have cooling fins 9. It has proven particularly advantageous if the cooling fins 9 on the surface 7 of the electric motor 2 are designed such that they form a pin-fin structure 18 (see Fig. 3). The pin-fin structure 18 has a defined number of pins 19, which extend in a radial or radial-axial or radial-tangential direction away from the housing 5 of the electric motor 2. The pin-fin structure 18 has a particularly large surface area and thus good heat exchange. The design of the surface 7 of the electric motor 2 can be smooth, in the form of cooling fins 9, or in the form of a pin-fin structure 18 (see Fig. 3). In the following, each design of the surface 7 of the electric motor 2 is generally referred to as a cooling structure 8.

[0037] As can be seen from Fig. 1, the electric motor 2 with the cooling structure 8 is located in a container, which is referred to below as the cooling housing 10. A cooling medium, e.g., water, but preferably oil, is located in the cooling housing 10, with which the electric motor 2 is in thermal exchange with the cooling housing 10 via its cooling structure 8.

[0038] Ideally, the cooling structure 8 of the electric motor 2 has a fit dimension on its outer diameter 6 like the cooling housing W, so that the electric motor 2 with cooling structure 8 can be positioned precisely in the cooling housing W. This simultaneously and directly ensures good heat exchange between the electric motor 2 and the cooling housing 10. The electric motor 2 rests with the cooling structure 8 against the inner surface 11 of the cooling housing 10. The cooling housing 10, in turn, has cooling fins 14 or similar on its outer surface 13 to ensure the best possible heat exchange with the ambient air. The ambient air can be static or actively moved through the cooling structure by a fan (not shown), which is driven separately or directly by the electric motor 2.

[0039] A further possible embodiment of the drive unit 1 is shown in Figure 2, wherein the stator 3 of the electric motor 2 is located between the housing 5 of the electric motor 2 and the cooling structure 8. The rotor 4 is designed to be rotatable about the central shaft 20 in the housing 2. The thermal contact between the housing 5 of the electric motor 2 and the cooling structure 8 is established via the stator 3. The cooling structure 8 is in thermal contact with the inner surface 11 of the cooling housing 10. According to a particularly advantageous embodiment of the drive unit 1, the cooling structure 8 for the housing 5 of the electric motor 2 and the surrounding cooling housing 10 with its cooling structure 12 are manufactured in one piece. The one-piece production can be carried out, for example, using a casting process or also additively.

[0040] In this embodiment, it is particularly advantageous that the cooling medium 25 (see Figure 4) not only surrounds the electric motor 2 on the surface 7 (see Figure 1), but also directly surrounds the interior of the electric motor 2, the so-called stator 3, with the cooling medium 25. The electric motor 2 has a so-called can 55 to limit the cooling medium 25 to the stator 3 of the electric motor 2.

[0041] Figure 3 shows a possible design of the cooling structure 8 of the housing 5 of the electric motor 2. The surface 7 of the housing 5 of the electric motor 2 is designed in the form of a pin-fin structure 18. The design as a pin-fin structure 18 is particularly advantageous because this design has a particularly large surface area and good heat exchange. The fin-pin structure 18 (fin-pin cooler) has a defined number of pins 19, which extend away from the housing 5 of the electric motor 2 in a radial, radial-axial, or radial-tangential direction.

[0042] Figure 4 shows a further possible embodiment of the drive unit 1, which uses oil as the cooling medium 25. In this embodiment, the cooling medium 25 is guided through a central shaft 20 (hollow shaft) of the electric motor 2. The central shaft 20 has a stepped bore 22 in the rotor 4. The central shaft 20 of the electric motor 2 is a hollow shaft, which is in communication with the space of the cooling medium 25 at a lower end 31 and at an upper end 32. The diameter of the stepped bore 22 is smaller than the diameter of the rest of the bore of the central shaft 20. The central shaft 20 of the electric motor 2 and thus also the rotor 4 of the electric motor 2 are thereby cooled.

[0043] Figure 5 shows another possible embodiment of the drive unit 1. Here, a sieve 27 is positioned before the cooling medium 25 enters the cooling housing 10. The sieve 27 serves to collect foreign matter. Likewise, a magnet 30 is positioned in the space for the cooling medium 25 and in the immediate vicinity of the lower end 31 of the central shaft 20 (hollow shaft) of the electric motor 2. The magnet 30 serves to collect metallic or magnetic chips, as also shown in Figs. 6 and 7.

[0044] Figure 6 shows the embodiment of the drive unit 1 from Figure 5, in which a gear 21 interacts with the central shaft 20. The gear 21 is also located within the cooling housing 10. The oil used as the cooling medium 25 ideally exchanges with a gear 21 located next to, above, or below it, where it is also used for lubrication. In the embodiment shown here, the gear 21 is provided above the housing 5 of the electric motor 2. It is self-evident that the arrangement shown in Figure 6 should not be construed as a limitation of the invention.

[0045] The cooling medium 25, such as oil, is guided in the central shaft 20 (hollow shaft). The cooling medium 25 is transported through the central shaft 20 solely by centrifugal forces and exits at the upper end 32 of the central shaft 20. There, the cooling medium 25 is distributed by centrifugal forces, whereby it cools the central shaft 20 of the electric motor 2 and thus the rotor 4 of the electric motor 2. After exiting the central shaft 20, the cooling medium 25 is also spun around by centrifugal forces, whereby it comes into contact with the inner surface 11 of the cooling housing 10 and also the gear 21, thereby achieving improved cooling. Likewise, the gear 21 and / or bearing points (not shown) are well lubricated. In this embodiment, the cooling medium 25 flows back into the cooling housing 10 by gravity, where it surrounds the electric motor 2 and cools it.

[0046] Figure 7 shows the embodiment of the drive unit 1 from Fig. 6, in which a pump 26 is provided for exchanging the cooling medium 25 from the underside of the gearbox 21 and electric motor 2. The pump 26 can be driven either directly by the shaft 20 of the electric motor 2, by the gearbox 21, or via a separate electric motor (not shown). In particular, if the pump 26 is driven by a separate electric motor, the pump 26 can also be used exclusively for emergencies. Fig. 6 shows the "normal" operation (passive operation) of the drive unit 1. If high power is required in certain situations, the pump 26 is switched on for a short time and ensures an increased exchange of the cooling medium 25.

[0047] Figure 8 shows the embodiment of the drive unit 1 from Figure 6, in which the power electronics 40 required to operate the electric motor 2 is mounted directly on the electric motor 2 in a housing 50 for the power electronics 40. The housing 5 for the electric motor 2 and the housing 50 for the power electronics 40 have the same diameter and are therefore in thermal contact with the inner surface 11 of the cooling housing. The central shaft 20 (hollow shaft) leads from the lower end 31 to an upper end 32 of the central shaft 20 and thus transports the cooling medium 25 through the power electronics 40 and the electric motor 2 and ensures its cooling. This design is particularly advantageous when so-called silicon carbide transistors are used as power semiconductors 42 because these can be operated at very high temperatures and therefore harmonize very well with the temperature level of the electric motor 2 in terms of temperature.

[0048] In all these designs that use a liquid cooling medium 25, the use of an oil based on polyalphaolefin has proven particularly advantageous.

[0049] It is believed that the present disclosure and many of the advantages recited therein will be understood from the foregoing description. It will be apparent that various changes in form, construction, and arrangement of components may be made without departing from the disclosed subject matter. The form described is merely illustrative, and it is the intention of the appended claims to encompass and embrace such changes. Accordingly, the scope of the invention should be limited only by the appended claims.

[0050] 1 Electric drive system

[0051] 2 electric motor

[0052] 3 Stator

[0053] 4 Rotor

[0054] 5 Electric motor housing

[0055] 6 Outer diameter

[0056] 7 Surface

[0057] 8 Cooling structure

[0058] 9 cooling fins

[0059] 10 cooling housings

[0060] 11 Inner surface

[0061] 12 Cooling structure of the cooling housing

[0062] 13 Exterior surface

[0063] 14 cooling fins

[0064] 18 pin fin structure

[0065] 19 pen

[0066] 20 Central Wave

[0067] 21 gearboxes

[0068] 22 Stepped bore

[0069] 25 Cooling medium

[0070] 26 Pump

[0071] 27 Sieve

[0072] 30 Magnet

[0073] 31 Lower end

[0074] 32 Upper end

[0075] 40 Power electronics

[0076] 42 power semiconductors

[0077] 50 housings for power electronics

[0078] 55 split tube

Claims

Patent claims 1 . An electric drive system (1 ), in particular for aircraft, comprising an electric motor (2) comprising a stator (3) and a rotor (4), which is accommodated in a housing (5), the surface (7) of which defines a cooling structure (8), characterized by a cooling housing (10) in which the electric motor (2) is located and with its cooling structure (8) is in thermal contact with an inner surface (11) of the cooling housing (10), wherein a cooling medium (25) is filled in the cooling housing (10), which surrounds at least the cooling structure (8) of the electric motor (2).

2. Electric drive system (1) according to claim 1, wherein the electric motor (2) comprises a can (55) and the stator (3) of the electric motor (2) is seated between the cooling structure (8) of the electric motor (2) in the can (55), wherein the stator (3) of the electric motor (2) is in thermal contact with the housing (5) of the electric motor (2) and the can (55) and is accessible to the cooling medium (25).

3. Electric drive system (1) according to one of the preceding claims, wherein the cooling structure (8) of the electric motor (2) has a smooth surface (7) or the surface (7) is provided with cooling fins (9).

4. Electric drive system (1) according to claim 3, wherein the cooling fins (9) of the housing (5) of the electric motor (2) are designed in the form of a pin-fin structure (18).

5. Electric drive system (1) according to one of the preceding claims, wherein a central shaft (20) of the drive system (1) is designed as a hollow shaft which is in exchange at its lower end (31) and at its upper end (32) with space for the cooling medium (25).

6. Electric drive system (1) according to claim 5, wherein a magnet (30) is placed opposite the lower end (31) of the central shaft (20) of the electric motor (2) and / or a sieve (27) is placed at the upper end (32) of the central shaft (20) before the cooling medium (25) enters the cooling housing (10).

7. Electric drive system (1) according to one of the preceding claims, wherein a gear (21) which is operatively connected to the central shaft (20) is accommodated in the cooling housing (10) and the cooling medium (25) can also be used for lubricating and cooling the gear (21).

8. Electric drive system (1) according to claim 7, wherein a pump (26) is provided which ensures an exchange of the cooling medium (25) from a space between the housing (5) of the electric motor (2) and the cooling housing (10) and the space of the cooling housing (10) for the transmission (21).

9. Electric drive system (1) according to one of claims 7 or 8, wherein a power electronics unit (40) is accommodated in a housing (50) and the housing (50) for the power electronics unit (40) is mounted directly on the housing (5) for the electric motor (2).

10. Electric drive system (1) according to one of the preceding claims, wherein the cooling medium (25) is a polyalphaolefin-based oil.

Images