Asynchronous electric machine including a cooling device

Abstract

An asynchronous electric machine for the propulsion and / or electrification of an aircraft, comprising a ferromagnetic body (7) and a winding (9) housed in slots of said ferromagnetic body, said winding having coil heads (15) protruding from said slots. At least one coil head (15) is covered by a heat dissipation casing (22). Figure for the abbreviation: Fig 1

Description

Title of the invention: Asynchronous electric machine including a cooling device. Technical field

[0001] The present invention relates, in general, to electrical machines for the motorization and / or electrification of aircraft.

[0002] More specifically, the invention relates to devices for cooling such machines, to machines equipped with such cooling devices and to aircraft equipped with such machines. Previous techniques

[0003] Climate change is a major concern for many legislative and regulatory bodies worldwide. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies to both new types of aircraft and those already in service, requiring the implementation of technological solutions to bring them into compliance with current regulations. Civil aviation has been actively working for several years now to contribute to the fight against climate change.

[0004] Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. The Applicant takes into account the factors impacting all phases of design and development in order to obtain less energy-intensive and more environmentally friendly aeronautical components and products, whose integration and use in civil aviation have moderate environmental consequences, with the aim of improving the energy efficiency of aircraft.

[0005] Consequently, the Applicant is constantly working to reduce its negative climate impact by using methods and operating virtuous development and manufacturing processes that minimize greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity.

[0006] This sustained research and development work focuses on new generations of aircraft engines, the weight reduction of aircraft, in particular through the materials used and lighter on-board equipment, the development of the use of electrical technologies to provide propulsion, and, as essential complements to technological progress, aviation biofuels.

[0007] With regard to the aforementioned electrical technologies, a concern is that high temperatures limit the overall performance of an electrical machine. These temperatures can result, in particular, from Joule effect losses within the machine and / or from a heat source in its immediate environment, such as a gas turbine, which in an aircraft is frequently associated with an electrical machine.

[0008] Solutions to limit these temperatures have been proposed.

[0009] In particular, a cooling system by air circulation in channels integrated into the permanent magnets of a rotor magnetic circuit has been proposed in document WO 2019 / 097160, the channels having a particular configuration in order to optimize heat dissipation. Description of the invention

[0010] The invention aims to improve the thermal management of an electrical machine and, in particular, to improve performance with regard to limiting temperatures within the machine during its operation.

[0011] The invention proposes for this purpose an asynchronous electric machine for the motorization and / or electrification of an aircraft, comprising a ferromagnetic body and a winding housed in notches of said ferromagnetic body, said winding having coil heads protruding from said notches, characterized in that at least one coil head is covered by a heat dissipation envelope.

[0012] The casing, which is in contact with the coil head, thus captures the heat emitted by the latter and diffuses it to its outer periphery, which is in contact with the surrounding air. Since this outer periphery has a larger surface area than the outer periphery of the coil head, the heat exchange between the coil head and the surrounding air is thus improved.

[0013] Thus, the machine exploits the available space around the coil head to improve heat exchange between it and the surrounding air.

[0014] Furthermore, it has been observed that the reel heads are among the hottest parts of the machine when it is in operation. Thus, the wrappers are efficiently positioned within the machine.

[0015] According to another feature, said casing comprises a barrel having a bottom wall, an opening extending opposite the bottom wall and a tubular wall extending from the bottom wall to the opening, said casing being configured to be fitted onto the reel head by passing it through the opening.

[0016] According to yet another feature, said envelope has a through orifice for the injection of an encapsulation resin.

[0017] In addition, said envelope is fixed to the coil head by an encapsulation resin injected between said envelope and said coil head.

[0018] Moreover, said envelope and / or said encapsulation resin are made of respective materials comprising epoxy, silicone, a polyimide, a polyamide and / or polyurethane.

[0019] According to another feature, said envelope includes heat dissipation fins.

[0020] Advantageously, air circulation is provided to cool said winding, said fins being locally oriented like said airflow.

[0021] In addition, said casing comprises a barrel having a bottom wall, an opening extending opposite the bottom wall and a tubular wall extending from the bottom wall to the opening, said fins being distributed on the tubular wall and / or the bottom wall.

[0022] Moreover, said fins are arranged in several groups distributed alternately with bare regions.

[0023] According to another feature, a single casing covers a plurality of coil heads forming an end portion of said winding. Since the number of casings to be produced is reduced, the electrical machine is more easily industrialized.

[0024] The invention also relates to an aircraft equipped for its motorization and / or electrification with an electric machine such as described above.

[0025] The invention further relates to a method for obtaining such an electrical machine, in which said encapsulation resin is injected between said casing and said coil head in a vacuum environment. Brief description of the drawings

[0026] Other purposes, advantages and features will become apparent from the following description, given for illustrative purposes only and made with reference to the accompanying drawings on which:

[0027] Fig. 1 is a schematic axial cross-sectional view of an electrical machine according to the invention;

[0028] [Fig. 2] illustrates in perspective a finned envelope comprising the machine of [Fig. 1]; and

[0029] Fig. 3 illustrates in perspective a variant of the casing and stator of the electric machine. DETAILED DESCRIPTION

[0030] The electric machine 1 illustrated in [Fig.1] comprises a stator 2, a rotor 3 and bearings 4 and 5 mounted between the rotor 3 and the stator 2.

[0031] Machine 1 is longitudinally oriented along an X axis corresponding to the axis of revolution of rotor 3.

[0032] The stator 2 comprises a housing 6 delimiting an internal space in which the rotor 3 is received, an annular ferromagnetic body 7 integral with the housing 6, and a winding 9 housed in longitudinal notches (not visible) of the body 7.

[0033] The housing 6 is generally cylindrical and comprises two opposing end walls 10 and 11 and a peripheral wall 12 extending from one end wall 10 to the other. The end walls 10 and 11 are annular and thus each define a central orifice 13. Each orifice 13 receives a corresponding bearing, 4 or 5. The peripheral wall 12 is annular and has cooling fins 14 on its exterior.

[0034] The body 7 consists of a stack of laminated sheet metal plates (not shown) configured to limit eddy currents.

[0035] The winding 9 is formed by a wire of insulated conductive material (not shown), here insulated copper. The winding 9, which is generally annular, extends longitudinally (along the X axis) between a first end 26 facing the wall 10 and a second end 27, opposite the first end 26, facing the wall 11. The winding 9 has, on either side of the body 7, portions 15 called coil heads, which protrude longitudinally (along the X axis) out of the notches to the ends 26 and 27 respectively.

[0036] The coil heads 15 are here individually generally cylindrical and axially oriented along the X-axis. The coil heads 15 are further angularly spaced from one another. Alternatively ([Fig. 3]), on one side and / or the other of the body 7, the coil heads 15 are intertwined with one another so as to form a generally annular bun 33, which bun 33 forms the end portion 35 and / or 36 respectively.

[0037] The rotor 3 comprises a hollow shaft 16, rotatably mounted on bearings 4 and 5, a ferromagnetic body 17 and a cage 18 forming an annular assembly coaxial with the shaft 16 and fixed in rotation to the latter.

[0038] The body 17 consists of a stack of laminated sheet metal plates (not shown) configured to limit eddy currents.

[0039] The cage 18 has two short-circuit rings 19 and 20 arranged on either side of the body 17, and conductive bars (not shown) extending from one to the other of the short-circuit rings 19 and 20 through the body 17. The conductive bars are distributed around the periphery of the rotor 3 and longitudinally oriented substantially along the X axis.

[0040] The electrical machine 1 is an asynchronous machine.

[0041] The machine 1 is configured here to operate as an electric motor for an aircraft, which may also include a turboshaft engine forming a hybrid propulsion system with the electric motor. The winding 9 of the stator 2 is thus connected to an alternating current source, and the shaft 16 of the rotor 3 is connected to an output shaft of the aircraft, to which, for example, a movable wing is attached. The supply of electric current to the winding 9 of the stator 2 generates a varying magnetic flux through the body 7 of the stator 2. The field lines of this flux are guided by the ferromagnetic laminations of the body 17 and induce currents in the cage 18 of the rotor 3. The induced currents are responsible for the appearance of a mechanical torque that tends to set the rotor 3 in motion in order to counteract the variation in the magnetic flux. The rotor 3 transmits the mechanical torque to the output shaft of the aircraft.

[0042] Alternatively, the machine is configured to operate as an alternating electric current generator for the aircraft, the rotor of the machine being coupled to an output shaft of an aircraft engine, for example a turboshaft engine, the variation of magnetic flux in the stator coils inducing the electric current.

[0043] Machine 1 can be configured to equip a fixed-wing or rotary-wing aircraft, with conventional, short or vertical takeoff and landing and / or distributed propulsion.

[0044] During operation, certain elements of the machine may, due to the Joule effect, exhibit high temperatures. For example, the applicant was able to measure a temperature exceeding 130°C in a coil head 15, compared to a temperature below 50°C in the hollow shaft 16 at mid-distance between bearings 4 and 5.

[0045] To limit the temperature rise within the machine 1, its elements are arranged so as to allow air circulation 21 between them. The circulation 21 is specifically intended for the cooling of the winding 9.

[0046] Following this circulation 21, and in general, the air enters the housing 6 in the vicinity of the end wall 11 by flowing radially inwards between the end wall 11 and the facing coil heads 15, then flows longitudinally towards the end wall 10 between the rotor 3 and the stator 2, then flows radially outwards between the end wall 10 and the facing coil heads 15, then escapes from the housing 6 in the vicinity of the end wall 10 (the orifices allowing the entry and exit of air through the peripheral wall 12 are not shown).

[0047] It will be noted that in the vicinity of the coil heads 15 the air generally flows longitudinally between the body 7 and the end 26 or 27 of the winding 9, then generally radially between the end 26 or 27 and the end wall 10 or 11 opposite respectively.

[0048] In order to make the heat exchange with the air circulation 21 more efficient, the machine 1 further comprises heat dissipation envelopes 22 each covering a corresponding coil head 15.

[0049] In other words, each envelope 22 is provided with an internal space whose shape is at least partially complementary to that of the coil head 15 which it receives and with which it is at least partially in contact. Furthermore, each envelope 22 interacts via its outer perimeter with the flow 21 in the vicinity of the coil head 15 which it receives, and it should be noted that this outer perimeter has a larger surface area than that offered by the outer perimeter of the coil head 15.

[0050] The envelopes 22 together with the circulation 21 form a cooling device for the machine 1.

[0051] The casings 22 are made of a material with high thermal conductivity. This material is also non-magnetic, electrically insulating, and has good mechanical strength. The material here comprises an epoxy-type polymer resin. Generally, the material is selected from polymer resins containing epoxy, silicone, a polyimide, a polyamide, and / or polyurethane.

[0052] The envelopes 22 are identical here.

[0053] An envelope 22 is shown in more detail in [Fig.2].

[0054] The casing 22 comprises a shaft 28 having a bottom wall 23, an opening 25 (not visible) extending opposite the bottom wall 23 and a tubular wall 24 extending from the bottom wall 23 to the opening 25.

[0055] The barrel 28 is placed on the reel head 15 with the tubular wall 24 extending opposite the part of the outer face of the reel head 15 oriented longitudinally, and with the bottom wall 23 extending opposite the part of the outer face of the reel head 15 oriented transversely, that is to say the part of this outer face forming the end 26. In addition, the tubular wall 24 is here against the body 7, which thus closes the opening 25.

[0056] The barrel 28 is here generally cylindrical. Alternatively, the barrel has another shape to be adapted to another shape of the coil heads, for example parallelepiped.

[0057] The casing 22 further includes a through orifice 29 provided in the bottom wall 23, here in the center of the bottom wall 23. Alternatively, the orifice 29 is provided elsewhere, for example is offset from the center of the bottom wall 23 or is provided in the tubular wall 24.

[0058] The casing 22 further comprises heat dissipation fins 30.

[0059] The fins 30 are distributed along the tubular wall 24, longitudinally oriented along the longitudinal axis X. It should be noted that this orientation corresponds locally to that of the flow 21. The fins 30 also extend substantially perpendicular to the tubular wall 24, that is to say here radially with respect to the cylindrical shaft 28.

[0060] The fins 30 are straight and parallelepiped-shaped. The fins 30 extend along the entire length of the tubular wall 24, and continuously (i.e., without interruption).

[0061] The fins 30 are arranged in several groups 31 distributed around the tubular wall 24, alternating with bare regions 32 of the tubular wall 24, i.e., regions devoid of fins. The fins 30 here form four diametrically opposed groups, arranged in pairs and regularly distributed. The fins 30 are regularly distributed within each group 31. Each group comprises seven fins 30.

[0062] It has been observed that each coil head 15 has areas of its contour with higher heat dissipation and areas of its contour with lower heat dissipation. The areas of higher heat dissipation are, for example, the faces of the coil head 15 that face radially outwards or inwards towards the winding 9. The areas of lower heat dissipation are, for example, the lateral faces of the coil head 15, that is, the faces that face towards one or the other of the neighboring coil heads 15. Advantageously, the casing 22 is arranged on the coil head 15 so that the groups 31 of fins 30 are located over areas of higher heat dissipation of the coil heads 15, while the exposed regions 32 are located over areas of lower heat dissipation of the coil heads 15. The number and arrangement of the fins 30 can thus be optimized.Alternatively, the fins are not grouped together and are regularly distributed around the entire perimeter of the tubular wall 24.

[0063] The casings 22 are here made in one piece, that is to say that the barrel 28 and the fins 30 are made from a single piece of material. The casings 22 are obtained, for example, by thermoforming.

[0064] The envelopes 22 are here pre-formed and then attached to the coil heads 15.

[0065] The installation of a casing 22 on a reel head 15 includes the step of fitting the casing 22 onto the reel head 22 by passing the latter through the opening 25.

[0066] The attachment of the casing 22 includes the step of encapsulating the coil head 15 by injecting an encapsulating polymer resin through the orifice 29 in the bottom wall 23. This polymer resin has high thermal conductivity and is also non-magnetic, electrically insulating, and has good mechanical strength. This polymer resin is, for example, the same as that used to form the casing 22.

[0067] Advantageously, the step of injecting the polymer resin is carried out in a vacuum environment, which improves the impregnation of the resin in the interstices of the coil head.

[0068] Advantageously, the step of injecting the polymer resin is preceded by the step of coating the inside of the casing 22 with glue, in order to improve the adhesion between the casing 22 and the coil head 15.

[0069] It should be noted that during the resin injection step, the envelope 22 acts as a mold which is then left in place on the coil head 15.

[0070] The polymer resin of the encapsulation, which is in contact with the coil head 15 and the casing 22, further improves the heat transfer between these two elements.

[0071] Figure 3 illustrates a variant of the casing 122 and a variant of the stator 102. in a disassembled state. The casing 122 is configured to receive, and therefore cover, all the coil heads 15 forming the end portion 35 of the winding 109. The casing 122 has dimensions greater than the casing 22 in this respect. In addition, the shaft 28 of the casing 122 has a second tubular wall 34 extending from the bottom wall 23 to the opening 25 and opposite the tubular wall 24. The tubular walls 24 and 34 are concentric. The second tubular wall 34 delimits with the bottom wall 23 and the tubular wall 24 an internal annular space configured to receive the end portion 35 of the winding 109. In the assembled state of the casing 122 and the stator 102, the casing 122 is fitted onto the coil heads 15 with the cylindrical barrel 28 radially centered on the longitudinal axis X, the shaft 16 of the rotor 3 (not shown in [Fig.3]) passing through the orifice 29.

[0072] It should be noted that in this configuration of the casing 122, the orifice 29 does not open into the internal annular space delimited by the walls 23, 24, and 34, so it is not possible to use this orifice 29 for resin injection. The casing 122 may therefore have another through orifice 37, formed in one of the tubular walls 24 or 34, or in the bottom wall 23, and opening into the internal annular space. The through orifice 37 is here formed in the tubular wall 24. Alternatively, several orifices such as 37 may be provided.

[0073] It should be noted that the envelope 122 is also suitable for being fitted onto the end portion 35 or the end portion 36 of the machine 1 illustrated in figures 1 and 2. In an unillustrated variant, two envelopes such as the envelope 122 are one fitted onto the heads 15 forming the end portion 35, and the other fitted onto the heads 15 forming the end portion 36.

[0074] It should also be noted that in practice the circulation 21 is not limited to the arrows which represent it very schematically in [Fig. 1] and that parts of this circulation 21 may also be found in other places, for example between the coil heads 15 and the peripheral wall 12 of the casing 6, where in particular the fins 30 of the envelope 122 extend.

[0075] In other variants not illustrated: - fins such as fins 30 are further distributed on the bottom wall 23, being longitudinally oriented in a radial direction relative to the cylindricity of the casing 6, this orientation corresponding locally to that of the circulation 21; - the reel heads 15 located on one side of the body 7, namely the side turned towards the end wall 10, are not the only ones to be equipped with envelopes 22, the reel heads 15 located on the other side of the body 7 also being equipped with envelopes 22; - each envelope receives several reel heads; - the fins have a different shape than parallelepiped and are for example with rounded edges, giving the external surface of the envelope a pleated appearance and / or are not straight but serpentine; - the envelope is entirely devoid of fins; and / or - the machine's rotor is not a cage rotor but a solid rotor carrying magnets.

Claims

Demands

1. Asynchronous electric machine for the motorization and / or electrification of an aircraft, comprising a ferromagnetic body (7) and a winding (9; 109) housed in notches of said ferromagnetic body (7), said winding (9; 109) having coil heads (15) protruding from said notches, characterized in that at least one coil head (15) is covered by a heat dissipation envelope (22; 122).

2. Machine according to claim 1, wherein said casing (22; 122) comprises a barrel (28) having a bottom wall (23), an opening (25) extending opposite the bottom wall (23) and a tubular wall (24) extending from the bottom wall (23) to the opening (25), said casing (22; 122) being configured to be fitted onto the reel head (15) by passing it through the opening (25).

3. Machine according to claim 1 or 2, wherein said envelope (22; 122) has a through orifice (29; 37) for the injection of an encapsulation resin.

4. Machine according to any one of claims 1 to 3, wherein said casing (22; 122) is fixed to the reel head (15) by an encapsulation resin injected between said casing (22) and said reel head (15).

5. Machine according to claim 4, wherein said casing (22; 122) and / or said encapsulation resin are in respective materials comprising epoxy, silicone, a polyimide, a polyamide and / or polyurethane.

6. Machine according to any one of claims 1 to 5, wherein said enclosure (22; 122) comprises heat dissipation fins (30).

7. Machine according to claim 6, wherein said casing (22; 122) comprises a barrel (28) having a bottom wall (23), an opening (25) extending opposite the bottom wall (23) and a tubular wall (24) extending from the bottom wall (23) to the opening (25), said fins (30) being distributed on the tubular wall (24) and / or the bottom wall (23).

8. Machine according to any one of claims 1 to 7, wherein said envelope (122) alone covers a plurality of

9.

10. coil heads (15) forming an end portion (35, 36) of said winding (9; 109). Aircraft equipped for its motorization and / or electrification with an asynchronous electric machine (1) according to any one of claims 1 to 8. Method for obtaining an asynchronous electrical machine (1) according to claim 4, in which said encapsulation resin is injected between said casing (22; 122) and said coil head (15) in a vacuum environment.

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