Electric machine equipped with a thermal management system including an exchanger integrated into the casing of said machine.

Abstract

An electric machine equipped with a thermal management system comprising a direct cooling device, a liquid-air heat exchanger, and a pump; the direct cooling device having at least one direct cooling channel (3), an inlet distributor (4), and an outlet manifold (5); the liquid-air heat exchanger comprising at least one heat exchanger inlet distributor (6), at least one heat exchanger channel (9), and at least one heat exchanger outlet manifold (7); the liquid-air heat exchanger being formed in a housing (10) comprising the rotor and stator of the electric machine. Figure for the abbreviation: Fig 2

Description

Title of the invention: Electric machine equipped with a thermal management system comprising an exchanger integrated into the casing of said machine. technical field

[0001] The invention has as its technical field the cooling of electrical windings, in particular those of electrical machines or transformers. Previous techniques

[0002] The development of electrically propelled aircraft and the subsequent need for high-power, compact electric machines require that thermal management of these machines be taken into account from the design phase. Indeed, the current densities involved in such machines can reach very high values ​​for power demands on the order of hundreds of kW or even MW.

[0003] A thermal management system includes at least one cooling circuit and one heat removal system.

[0004] The cooling circuit allows the extraction of heat and is used to transport the heat produced by the hot sources via a cold fluid, typically air or a heat transfer fluid.

[0005] The heat dissipation system cools the heated fluid in the cooling circuit by transferring the heat absorbed by the fluid to a cold source, generally the ambient atmosphere. This can be achieved, for example, by adding fins for air cooling or by a remote heat exchanger or liquid-liquid intermediate heat exchanger for liquid cooling. In the case of forced convection, an air compressor or a hydraulic pump is also required.

[0006] In the context of cooling electrical machines, two performance criteria dictate the choice of technology. These two criteria are the ability to cool hot spots and the heat removal capacity (the ability to dissipate heat resulting from electrical losses generated in the machine and converted by the Joule effect). A hot spot is defined as a restricted area of ​​the electrical machine where heat generation is particularly significant. Active cooling of such a hot spot is then necessary to prevent short- or medium-term impairment of the machine's operation.

[0007] For example, such hot spots in an electrical machine are located in the stator windings, which are generally the main sources of losses Electrical components in electrical machines. The maximum temperature of the windings (dictated by the maximum temperature of the conductor insulation) limits the permissible current density, and therefore the torque density of the machine. The resistivity of the conductors and the resulting Joule losses also increase with temperature, which can reduce the machine's efficiency. It is therefore crucial to improve the heat transfer properties as close as possible to the windings.

[0008] Commonly used solutions for cooling electrical machines include natural convection, forced air convection and forced liquid convection.

[0009] Natural convection is the simplest solution, in which heat is largely dissipated through the machine casing. Fins are frequently added to the casing to increase the convection surface area, and thus heat dissipation, by increasing the contact area with the ambient air. Forced air convection cooling systems generally include a fan, which increases the overall heat transfer coefficient but has disadvantages in terms of reliability and overall mass reduction. Liquid-cooled forced convection cooling systems of the "water jacket" type allow for good heat extraction compared to air-cooled methods. However, this liquid must then be cooled by an external heat exchanger.

[0010] In the case of high-power machines, that is, machines ranging from several hundred kW to several MW, the amount of heat to be transferred often necessitates the use of cooling with a heat transfer fluid, comprising a hydraulic circuit, a pump, and a heat exchanger. Typically, the hydraulic circuit is located external to the machine and cools it using a cooling jacket (called a "WaterJacket" or "Liquid Jacket") placed around the machine, through which the cooling fluid circulates. This fluid then extracts the heat from the stator windings by conduction through the stator head. The terminal heat exchanger, which removes the captured heat to the outside of the system, is usually located outside the machine.

[0011] This cooling principle is therefore based on capturing heat generated within the machine from outside the machine, transporting this captured heat to at least one heat exchanger, and then diffusing this heat within said at least one heat exchanger. It should be noted that the last heat exchanger used is always a liquid / air heat exchanger in order to transfer the heat from the machine, captured and transported by the heat transfer fluid, to the cold source, which is the ambient air around the aircraft (airplane, helicopter, car, etc.).

[0012] These heat exchangers all operate on the same principle of heat transfer from one fluid to another through a heat flow via an interface, most often metallic. To achieve this, it is necessary to maximize the exchange surface area of ​​each of the two fluids (liquid, air) with the metallic interface while minimizing the overall size of the latter. To accomplish this, the hydraulic flow of each fluid is subdivided into multiple hydraulic sub-flows, each coming into contact with a multitude of fins. This has the effect of slowing down the fluid circulation within the exchanger and maximizing the exchange time of each fluid with the metallic interface. Such a slowing of the fluid circulation has an effect equivalent to an increase in the heat exchange surface area.

[0013] Such a slowing down of the circulation of the fluids also has the effect of optimizing the heat transfer between the two fluids and thus of effectively cooling the hot fluid of the cooling circuit by dissipating the heat it carries into the cold fluid through the metallic interface represented by the exchanger.

[0014] Thus, unlike the cooling of the electrical machine where the aim is to circulate the cooling fluid rapidly in order to constantly provide a "cold" source to the machine in order to remove the heat produced, the exchanger is a dissipating element which seeks to slow down the circulation of fluids by subdividing their hydraulic flow in order to maximize the heat transfers occurring within it and thus efficiently cool the cooling fluid in order to provide a "cold" source to the machine.

[0015] The external nature of the cooling system relative to the machine, which implies the presence of an external heat sink, however, creates integration and space constraints on the aircraft and reduces its efficiency. This is illustrated in particular by the fact that the heat flux from the windings diffuses through the machine's yoke, effectively maintaining the entire electric machine at a high temperature during operation, hence the proposal for direct cooling of the stator windings detailed below.

[0016] Another limitation of the cooling solutions presented above is that the heat is dissipated via the casing of the electric machine, located at its periphery. The heat produced within the windings must therefore pass through several regions of the machine (enamel, notch paper, magnetic yoke, etc.) before being dissipated.

[0017] Another cooling possibility consists of direct cooling of the stator windings which allows the heat to be extracted directly at the source, either by immersed slots or by hollow conductors.

[0018] It can be connected to a hydraulic jacket or a remote exchanger in a manner similar to the liquid cooling methods described above.

[0019] Such a direct cooling method solves both the problem of directly cooling hot spots and the heat extraction capacity. Nevertheless, the problems of compactness and mass remain.

[0020] It is noted that prior art is known, French patent application FR3123166A1 in the name of the applicant describing the formation of cooling channels integrated within the turns of an electrical machine.

[0021] The technical problem that the invention seeks to solve is thus how to propose a heat management system that allows the hot spots of the machine to be cooled directly and that is more compact and lighter than the systems of the prior art.

[0022] Furthermore, 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 contributing to the fight against climate change for several years now.

[0023] 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.

[0024] 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.

[0025] This sustained research and development work focuses on new generations of aircraft engines, the lightening 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.

[0026] To this end, the invention is the result of technological research aimed at significantly improving aircraft performance and, in this sense, contributes to reducing the environmental impact of aircraft. Description of the invention

[0027] The invention relates to an electric machine equipped with a thermal management system comprising a direct cooling device, a liquid-air heat exchanger and a pump, the direct cooling device being equipped with at least one direct cooling channel, an inlet distributor and an outlet manifold, the liquid-air heat exchanger comprising at least one heat exchanger inlet distributor, at least one channel and at least one heat exchanger outlet manifold, the electric machine being characterized by the fact that the liquid-air heat exchanger is formed in a housing comprising the rotor and the stator of the electric machine.

[0028] By "direct cooling" is meant cooling carried out at the hot spots that one wishes to cool. In other words, the direct cooling carried out by means of the thermal management system is carried out directly in the electrical machine, in particular at the stator windings.

[0029] The stator may be provided with at least one winding made around a fixed stator tooth formed in a stator yoke, the housing being fixed to the stator yoke, at least one direct cooling channel being disposed in a stator tooth or in a winding conductor around a stator tooth, at least one direct cooling channel being connected by a first end to one of said input distributors and by a second end to one of said output collectors.

[0030] The stator may be provided with at least two windings, each made around a stator tooth integral with the housing, one of the direct cooling channels being included in a stator tooth or in a winding conductor around a stator tooth formed in a stator yoke, the housing being integral with the stator yoke, the at least two direct cooling channels being arranged around a stator tooth or in a winding conductor around a stator tooth, neighboring direct cooling channels being connected two by two, so as to be connected to one of said input distributors by the first end of a first direct cooling channel, and to one of said output collectors by the second end of a second direct cooling channel.

[0031] The electric machine may include at least two exchanger inlet distributors and at least two exchanger outlet manifolds, with an immediately adjacent exchanger inlet distributor and exchanger outlet manifold being connected by at least one channel.

[0032] The at least one channel may include at least one plenum.

[0033] In a particular embodiment, at least two plenums can be superimposed and connected in parallel to one of said exchanger inlet distributors and to one of said exchanger outlet manifolds.

[0034] The at least one channel may comprise at least a plurality of micro-channels.

[0035] The micro-channels may have a circular, elliptical, square or rectangular cross-section.

[0036] In a particular embodiment, the plurality of micro-channels is arranged so that at least two sets of channels can be superimposed and connected in parallel to one of said exchanger inlet distributors and to one of said exchanger outlet manifolds.

[0037] The liquid-air exchanger can be equipped on its external surface with means for increasing the exchange surface area, in particular in the form of fins.

[0038] The invention also relates to an aircraft equipped with an electric machine as described above, in particular an electric propulsion machine. Brief description of the drawings

[0039] Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example and made with reference to the accompanying drawings in which:

[0040] - Figure [Fig. 1] illustrates an example of a thermal management system of a electric machine according to the invention,

[0041] - Figure [Fig.2] illustrates a heat exchanger of a thermal management system of an electrical machine according to the invention comprising a set of heat exchanger channels,

[0042] - Figure [Fig.3] illustrates the thermal management system of Figure [Fig.1] without the fins, crankcase, cylinder head and stator teeth,

[0043] - Figure [Fig.4] illustrates a heat exchanger of a thermal management system of an electrical machine according to the invention comprising two sets of heat exchanger channels,

[0044] - Figure [Fig. 5] illustrates a thermal management system similar to that of the figure [Fig.1] without the fins, the casing, the cylinder head and the stator teeth, comprising two sets of superimposed heat exchanger channels,

[0045] - Figure [Fig.6] illustrates the liquid-air heat exchanger of the thermal management system equipped with a plenum, according to one embodiment of the invention,

[0046] - Figure [Fig.7] illustrates the liquid-air heat exchanger of the thermal management system equipped with two plenums, according to another embodiment of the invention,

[0047] - Figure [Fig.8] illustrates the liquid-air heat exchanger of the thermal management system equipped with a set of cooling channels and a plenum, according to another embodiment of the invention,

[0048] - Figure [Fig.9] is a cross-sectional view of an example of a liquid-air heat exchanger of the thermal management system according to the invention equipped with an exchanger inlet distributor and an exchanger outlet manifold, and

[0049] - Figure [Fig. 10] is a cross-sectional view of an example of a liquid-air heat exchanger of the thermal management system according to the invention equipped with two exchanger inlet distributors and two exchanger outlet manifolds. Detailed description

[0050] In order to solve the technical problem, the inventors had the idea of ​​designing a thermal management system for an electric machine comprising a new hydraulic circuit configuration which not only eliminates the need for a cooling jacket but also integrates the heat exchanger system into the electric machine to dissipate the heat produced in the electric machine.

[0051] More specifically, the inventors had the idea of ​​integrating a liquid-air exchanger directly into the body of the electrical machine in place of the cooling jacket.

[0052] Such a system has the advantage of optimizing the entire cooling system and reducing space and integration constraints at the aircraft level. It also eliminates the need for another heat exchanger, typically an intermediate liquid-liquid heat exchanger in the machine and a remote liquid-air heat exchanger.

[0053] In the context of direct cooling, a cooling jacket is no longer necessary because the heat is no longer extracted by conduction from the inside of the machine (stator windings) to the outside (stator yoke) but is directly extracted at the level of the stator windings by placing the cold source in the stator slots.

[0054] The heat is thus directly extracted from the machine and carried outside by the cooling fluid. This cooling fluid must then be sent to the liquid / air heat exchanger to distribute the heat captured in the machine.

[0055] In this configuration, the heat exchanger can then be placed in place of the now absent cooling jacket in order to integrate it into the machine housing and to optimize its size and efficiency.

[0056] Furthermore, in order to dissipate the heat absorbed at the stator level and resulting from all losses (copper losses, ferromagnetic losses, etc.), the direct cooling of the slots is configured so as to direct the outlet of the hot fluid towards the casing of the machine. The casing then acts as a liquid-air heat exchanger to dissipate the machine's losses to the external environment.

[0057] Figure [Fig. 1] illustrates a thermal management system 1 of an electrical machine, contained within a stator yoke 2 of said electrical machine. The electrical machine, a sector of which is partially shown in this figure, is provided with a ferromagnetic part comprising the stator yoke 2 on which several stator teeth 2a are formed, each equipped with a winding. The rotor of the electrical machine is not shown.

[0058] A direct cooling channel 3 is disposed in the conductor surrounding each stator tooth 2a and connected at one end to an input distributor 4 and at the other end to an output collector 5. This is particularly the case when a hollow conductor is used for the stator winding. Alternatively, a direct cooling channel 3 may be provided in the stator tooth 2a. This alternative is not illustrated. In a particular embodiment, adjacent direct cooling channels 3 are connected in pairs, so as to be connected to the input distributor 4 by the first end of the first direct cooling channel, and to the output collector 5 by the second end of the second direct cooling channel.This type of connection is particularly well-suited to a stator in which the windings of one phase are distributed over two adjacent stator teeth, due to the similar and simultaneous heating of the windings around each of the two teeth. In an alternating configuration, the direct cooling channels can be segmented into two so as to provide one direct cooling channel per stator tooth.

[0059] The direct cooling channels 3, the inlet distributor 4 and the outlet manifold 5 form the direct cooling device.

[0060] The outlet manifold 5 itself includes an outlet connected by a conduit to an inlet of an inlet distributor 6 of an exchanger.

[0061] The inlet distributor 4 itself comprises an inlet connected by a pipe to an outlet of an exchanger outlet manifold 7 via a pump 8.

[0062] The operation of the heat exchanger in the thermal management system is similar to that of the heat exchanger described above, transferring heat from one fluid to another via a heat flow through a metallic interface. It therefore remains necessary to maximize the exchange surfaces of each of the two fluids with the metallic interface while minimizing the overall size of the latter.

[0063] The hydraulic flow in the heat exchanger is slowed down so as to maximize the heat exchange time.

[0064] In certain embodiments of the heat exchanger, the slowing down is achieved by subdividing the incoming hydraulic flow into multiple hydraulic subflows in order to slow the circulation within the exchanger and maximize the heat exchange surface area of ​​the fluid with the metallic interface, thereby optimizing heat transfer. Such a division into hydraulic subflows is achieved by using a set of channels 9, in particular microchannels, connected in parallel to the inlet distributor and the outlet manifold. Figure [Fig. 2] schematically illustrates such an embodiment.

[0065] Figure [Fig.3] illustrates more precisely such an embodiment of the thermal management system without the fins 11, the housing 10, the stator cylinder head 2 and the stator teeth 2a.

[0066] The exchanger inlet distributor 6 is connected to a first end of at least one channel 9, the second end of the at least one channel 9 being connected to the exchanger outlet manifold 7.

[0067] The inlet distributor 6 of the heat exchanger, the at least one channel 9 and the outlet manifold 7 of the heat exchanger form the liquid domain of the liquid-air heat exchanger. They are embedded in the metal casing 10 visible in the figure [Fig. 1], in particular made of aluminum in order to give rigidity to the assembly and to have thermal inertia without increasing the mass of the assembly.

[0068] The metal casing 10 is provided with means 11 for increasing the exchange surface area, in particular in the form of fins. Different fin shapes can be provided (corrugated, broken line, etc.) in order to further increase the exchange surface area compared to a flat fin.

[0069] Several sets of channels 9 can be superimposed and connected in parallel to the inlet distributor 6 of the exchanger and at the outlet to the outlet manifold 7 of the exchanger. Figure [Fig.4] illustrates such an embodiment schematically, while Figure [Fig.5] illustrates it in the same frame as Figures [Fig.1] and [Fig.3].

[0070] In certain embodiments, at least one channel is a plenum 9a, connected at its inlet to the inlet distributor 6 of the heat exchanger and at its outlet to the outlet manifold 7 of the heat exchanger. The slowing down is then achieved due to the difference in flow velocity at the plenum 9a compared to the flow velocity at the inlet of the distributor. Figure [Fig. 6] illustrates such an embodiment.

[0071] Several plenums 9a can be superimposed and connected in parallel to the inlet distributor 6 of the heat exchanger and at the outlet to the outlet manifold 7 of the heat exchanger. Figure [Fig.7] illustrates such an embodiment in which two plenums are superimposed and connected in parallel to the inlet distributor 6 of the heat exchanger and at the outlet to the outlet manifold 7 of the heat exchanger.

[0072] In particular embodiments of the invention, it is possible to combine at least one plenum 9a and at least one set of channels 9, for example microchannels, superimposed and connected in parallel to the inlet distributor 6 of the heat exchanger and at the outlet to the outlet manifold 7 of the heat exchanger. Figure [Fig. 8] illustrates such an embodiment.

[0073] Depending on the embodiment, the channels may have a cross-section of different shapes. The circular shape and its variants (elliptical, etc.) are preferred for their ease of implementation. The square or rectangular shape increases the exchange surface area at the liquid-metal interface.

[0074] According to embodiments, at least one plenum 9a and at least one set of channels 9 are entirely contained within the thickness of the wall of the electrical machine housing.

[0075] Finally, depending on the required cooling capacity, a different number of exchanger inlet distributors 6 and exchanger outlet manifolds 7 may be provided.

[0076] For example, an inlet distributor 6 of a heat exchanger and an outlet manifold 7 of a heat exchanger may be provided and arranged so as to be diametrically opposed. At least one plenum 9a and / or a set of channels 9 are then provided on each side of the inlet distributor 6 of the heat exchanger and the outlet manifold 7 of the heat exchanger. Figure [Fig. 9] illustrates such an embodiment.

[0077] In another embodiment, the heat exchanger inlet distributor 6 and the heat exchanger outlet manifold 7 are arranged side by side. At least one plenum 9a and / or a set of channels 9 are then provided on one side of the heat exchanger inlet distributor 6 and the heat exchanger outlet manifold 7 so as to connect them.

[0078] Another embodiment, illustrated by Figure [Fig. 10] provides for two exchanger inlet distributors 6 and two exchanger outlet manifolds 7, each arranged in a quadrant of the housing 10, and such that the two exchanger inlet distributors 6 are diametrically opposed, the two exchanger outlet manifolds 7 also being diametrically opposed.

[0079] At least one plenum 9a and / or a set of channels 9 are provided between an inlet distributor 6 of an exchanger and an outlet manifold 7 of an immediately adjacent exchanger.

[0080] The embodiments described above are considered to be radial embodiments, in which at least one distributor and at least one heat exchanger manifold are arranged in the housing of the electric machine and extend along the axial direction of the machine. The flow in the heat exchanger channels and / or plenums extends in a direction concentric with the axis of rotation of the electric machine.

[0081] Alternatively, at least one distributor and at least one heat exchanger manifold are arranged in the housing of the electric machine and extend in a direction concentric with the axis of rotation of the electric machine. The flow in the heat exchanger channels and / or plenums extends in an axial direction of the electric machine

[0082] Note the difference in cross-sectional shape of the inlet distributor 6 of the heat exchanger and the outlet manifold 7 of the heat exchanger, illustrated on one side in Figures [Fig. 1], [Fig. 3] and [Fig. 5] and on the other side in Figures [Fig. 2], [Fig. 4] and [Fig. 6] to [Fig. 10]. It will be understood that either of the round or square cross-sections can be used interchangeably without departing from the scope of the invention.

[0083] The thermal management system described here differs from state-of-the-art systems by the fact that it involves, firstly, direct cooling of the windings, and, secondly, a liquid-air exchanger integrated into the machine casing.

[0084] The first heat transfer is therefore placed inside the machine and no longer outside, and the exchanger is no longer remote but totally integrated into the electrical machine.

Claims

Demands

1. An electric machine equipped with a thermal management system comprising a direct cooling device, a liquid-air heat exchanger and a pump, the direct cooling device being equipped with at least one direct cooling channel (3), an inlet distributor (4) and an outlet manifold (5), the liquid-air heat exchanger comprising at least one heat exchanger inlet distributor (6), at least one heat exchanger channel (9) and at least one heat exchanger outlet manifold (7), the electric machine being characterized in that the liquid-air heat exchanger is formed in a housing (10) comprising a rotor and a stator of the electric machine.

2. An electric machine according to claim 1, wherein the stator is provided with at least one winding made around a stator tooth formed in a stator yoke (2), the housing (10) being integral with the stator yoke (2), at least one direct cooling channel (3) being disposed in a stator tooth or in a winding conductor around a stator tooth, at least one direct cooling channel (3) being connected by a first end to one of said input distributors (4) and by a second end to one of said output collectors (5).

3. An electric machine according to claim 1, wherein the stator is provided with at least two windings each made around a fixed stator tooth formed in a stator yoke (2), the housing (10) being fixed to the stator yoke (2), the at least two direct cooling channels (3) being arranged in a stator tooth or in a winding conductor around a stator tooth, adjacent direct cooling channels (3) being connected two by two, so as to be connected to one of said input distributors (4) by the first end of a first direct cooling channel, and to one of said output collectors (5) by the second end of a second direct cooling channel.

4. An electrical machine according to any one of claims 1 to 3, comprising at least two exchanger inlet distributors (6) and at least two exchanger outlet manifolds (7), an immediately adjacent exchanger inlet distributor (6) and an exchanger outlet manifold (7) being connected by at least one channel (9).

5. Electrical machine according to any one of claims 1 to 4, wherein at least one channel (9) comprises at least one plenum (9a).

6. Electric machine according to claim 5, wherein at least two plenums (9a) are superimposed and connected in parallel to one of said exchanger inlet distributors (6) and to one of said exchanger outlet manifolds (7).

7. Electrical machine according to any one of claims 1 to 4, wherein at least one channel (9) comprises at least a plurality of micro-channels (9b).

8. An electrical machine according to claim 7, wherein the plurality of microchannels is arranged so that at least two sets of microchannels (9b) are superimposed and connected in parallel to one of said exchanger inlet distributors (6) and to one of said exchanger outlet manifolds (7).

9. An electric machine according to any one of claims 1 to 8, wherein the liquid-air exchanger is provided on its outer surface with means for increasing (11) the exchange surface, in particular in the form of fins.

10. Aircraft equipped with an electric machine according to any one of claims 1 to 9, in particular an electric propulsion machine.

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