Stator element of an electric machine for an aircraft

Abstract

Disclosed is a stator element (200) comprising: - an electrical conductor (202) that is elongate and hollow in order to define a flow channel (308) allowing a coolant to flow from one end to the other of the conductor (202), the conductor (202) being designed to pass an electric current; and - a connection element (208; 902) located at one of the ends of the conductor (202), comprising a fluid connection terminal (210) designed to allow coolant to enter the channel (308) or indeed coolant to exit from the channel (308), and an electrical connection terminal (212) designed to electrically connect the conductor (202). The conductor (202) and the connection element (208; 902) are formed of a single unitary part.

Description

Description TITLE: STATOR ELEMENT OF AN AIRCRAFT ELECTRIC MACHINE Technical field of the invention

[0001] The present invention relates to a stator element of an electrical machine of an aircraft, as well as an electrical machine comprising such an element, and an aircraft comprising such an electrical machine. Technological background

[0002] The development of "more electric" aircraft and the subsequent need for high-power, compact electric machines require consideration of thermal issues right from the design phase of electric machines. Indeed, current densities can reach very high values ​​for power demands of the order of hundreds of kW or even MW.

[0003] In this context, stator windings are often the main source of losses in electrical machines. The maximum temperature of the windings (dictated by the maximum temperature of the conductor insulation) limits the current density, and therefore the torque density of the machine. The resistivity of the conductors and the subsequent Joule losses increase with temperature, which can reduce the efficiency of the machine. It is therefore crucial to improve the heat transfer properties as close as possible to the windings.

[0004] Commonly used solutions for cooling electrical machines include natural convection, air-forced convection, and liquid-forced convection.

[0005] Natural convection is the simplest solution, in which the heat is largely dissipated through the machine casing. Fins are often added to the casing to increase the convection surface, and therefore heat dissipation.

[0006] Forced air convection cooling systems typically include a fan, which increases the overall heat transfer coefficient but has disadvantages in terms of reliability and overall mass reduction. Liquid forced convection cooling systems of the "water jacket" type allow good heat extraction, compared to air methods.

[0007] One of the limitations of the cooling solutions presented above is that the heat is evacuated 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 (slot paper, magnetic yoke, etc.) before being evacuated.

[0008] New solutions, known as direct winding cooling, are currently being proposed. These solutions allow the heat generated by the windings to be dissipated at its source. For example, a fluid can circulate inside: a hollow conductor, or a so-called submerged slot or one with oil circulation.

[0009] The invention falls into the first scenario.

[0010] Thus, it is known to use a stator element of an electrical machine, comprising: an elongated and hollow electrical conductor in order to define a channel for the flow of a cooling fluid from one end to the other of the conductor, the conductor being designed to be traversed by an electric current; and a connection element located at one of the ends of the conductor, comprising: • a fluid connection terminal designed to allow an inlet of the cooling fluid into the channel or an outlet of the cooling fluid from the channel, and • an electrical connection terminal designed to electrically connect the conductor.

[0011] In the state of the art, the connection element is attached to the end of the conductor. This requires a soldering or brazing step between the two, while generally respecting a temperature limit of the conductor (around 180 °C for enameled conductors). In addition, it is necessary to ensure the sealing of the assembly, which can be difficult in particular because of the previous constraint of not overheating the conductor and the small size of the conductors and their internal conduit (for example 2 mm x 3 mm with internal conduit of 0.3 mm).

[0012] It may thus be desirable to provide a stator element of an electrical machine which makes it possible to overcome at least some of the aforementioned problems and constraints. Summary of the invention

[0013] There is therefore proposed a stator element of an electrical machine, comprising: an elongated and hollow electrical conductor in order to define a channel for the flow of a cooling fluid from one end to the other of the conductor, the conductor being designed to be traversed by an electric current; and a connection element located at one of the ends of the conductor, comprising: • a fluid connection terminal designed to allow an inlet of the cooling fluid into the channel or an outlet of the cooling fluid from the channel, and • an electrical connection terminal designed to electrically connect the conductor; characterized in that the conductor and the connection element are formed from a single, single piece.

[0014] The invention may further comprise one or more of the following optional features, in any technically possible combination.

[0015] Optionally, the single-piece part is produced by one of: additive manufacturing, wire drawing, machining and molding.

[0016] Optionally, the single-piece part is made of copper, aluminum, or an alloy of one of the two previous materials.

[0017] Optionally also, the flow channel has an inner diameter and the fluid connection element has an inner diameter greater than the inner diameter of the flow channel, as well as a narrowing between the diameter of the connection element and the diameter of the flow channel.

[0018] Optionally, the narrowing is also gradual.

[0019] Optionally, the narrowing has rounded edges.

[0020] Optionally, the electrical connection terminal also has an electrical connection hole, for example a screw hole, for example provided on a tab.

[0021] Optionally, the electrical connection terminal also includes a threaded rod, for example provided on a lug.

[0022] Also optionally, the fluid connection terminal has a male or female end piece, for example, to be connected to a flexible hose.

[0023] Also optionally, the stator element further comprises another connection element located at another end of the conductor, comprising: a fluid connection terminal for an inlet of the cooling fluid into the flow channel or an outlet of the cooling liquid from the flow channel, and an electrical connection terminal for electrically connecting the conductor; the conductor and the two connection elements being formed from the single, single-piece part.

[0024] There is also provided an electrical machine comprising: a rotor; and a stator for driving the rotor, the stator comprising a stator element according to the invention.

[0025] An aircraft comprising an electric machine according to the invention is also proposed. Brief description of the figures

[0026] The invention will be better understood with the aid of the following description, given solely by way of example and with reference to the appended drawings in which: Figure 1 is a three-dimensional view of an example of an electrical machine in which the invention can be implemented, Figure 2 is a three-dimensional view of an example of a stator element according to the invention, which can be used in the electrical machine of Figure 1, Figure 3 is a sectional view of an example of a connection element that can be part of the stator element of Figure 2, Figure 4 is a sectional view of a first alternative of a cooling fluid conduit provided in the connection element of Figure 3, Figure 5 is a sectional view of a second alternative of a cooling fluid conduit provided in the connection element of Figure 3, Figure 6 is a three-dimensional view of another example of a stator element according to the invention, that can be used in the electrical machine of Figure 1, Figure 7 is a three-dimensional view of an example of a hollow electrical conductor that can be used in the stator element of Figure 2, Figure 8 is a sectional view of the hollow electrical conductor of Figure 7, Figure 9 is a three-dimensional view of an alternative connection element,and Figure 10 is a three-dimensional, transparent view of the variant of Figure 9., Detailed description of the invention

[0027] With reference to Figure 1, an example of an electrical machine 100 in which the invention can be implemented will now be described.

[0028] The electrical machine 100 firstly comprises a stator 102 in the form of a cylinder centered on an axis of rotation AA'.

[0029] The stator 102 comprises, for example, longitudinal notches 104 and windings 106 (only one is shown in FIG. 1 for the sake of clarity) having longitudinal portions inserted into the notches 104. The windings 106 may be distributed or concentric.

[0030] The electrical machine 100 further comprises a rotor 108 extending into an interior space of the stator 102 (the rotor 108 is shown extended from the stator 102 in FIG. 1).

[0031] Each winding 106 is designed to be traversed by an electric current, in particular for the generation of a magnetic field for driving the rotor 108 around the axis of rotation AA' when the electric machine 100 operates as a motor.

[0032] With reference to Figure 2, a stator element 200 according to the invention which can be used in the machine of Figure 1 will now be described.

[0033] Generally, a stator element according to the invention can form all or part of a winding 106. In the example illustrated, the stator element 200 forms a winding 106.

[0034] The stator element 200 firstly comprises an elongated and hollow electrical conductor 202 in order to define a flow channel for a cooling fluid (liquid, for example water, glycolated water, silicone oil, bearing lubrication liquid (such as BP oil 380), or gaseous, for example air, nitrogen, helium) from one end of the conductor 202 to the other. For example, the conductor 202 has several longitudinal portions 204, for example designed to be inserted into the notches 104, connected by curved portions 206. The conductor 202 thus forms one or more windings (two in the illustrated example).

[0035] The stator element 200 further comprises, on at least one of the ends of the conductor 202, a connection element 208. For example, as in FIG. 2, a connection element 208 is provided at each end of the conductor 202.

[0036] The connection element 208 firstly comprises a fluid connection terminal 210 designed to allow an inlet of the cooling fluid into the channel or an outlet of the cooling liquid from the channel. The fluid connection terminal 210 is for example in the form of an end piece, for example cylindrical, for example male to be inserted for example into a flexible pipe of the cooling system, for example hydraulic or pneumatic, or female for example so that the flexible pipe is inserted into the end piece.

[0037] Generally, the fluid connection terminal 210 may be threaded, for example, to a liquid or gas standard (for example, BSP gas thread). "British Standard Pipe thread"), NPT (from the English "National Pipe Tapered thread"), etc.) or others (for example, a quick connector). The fluid connection 210 can be male or female.

[0038] The connection element 208 further comprises an electrical connection terminal 212 designed to electrically connect the conductor 202. For example, the electrical connection terminal 212 comprises a hole into which a terminal is intended to be screwed (as in the example of FIG. 2).

[0039] Generally, the electrical connection terminal may be standard (e.g., a lug) or other (e.g., military fitting). Other terminals may be provided on the body 302, for example, fittings required for electrical measurements (e.g., voltage). If the hole of the connection terminal 212 is a through hole, it is possible to connect the lug to bring the current to one end of the hole and to place one or more sensors (e.g., voltage) at the other end of the hole. When the hole of the connection terminal 212 is not a through hole, the lug and the sensor(s) may be connected to the single through end of the hole.

[0040] According to the invention, the conductor 202 and the connection element(s) 208 are formed from a single, single-piece part. This makes it possible to obtain: simplicity of assembly (reduction in costs and the number of assembly steps) and a reduction in the risk of obstruction: when soldering or brazing the conductor with the connection element, tin (or other material) could in fact infiltrate and obstruct the passage of the fluid; a reduction in the electrical resistance between the connection element 208 and the conductor 202; better sealing between the connection element 208 and the conductor 202; and a reduction in the risk of damage to the enamel of the conductor 202: during the soldering / brazing between the conductor and the connection element, the parts are in fact caused to heat up, so that, if the temperature becomes too high (for example, exceeds 180°C), the enamel of the conductor may be damaged.

[0041] For example, this single-piece part can be produced by additive manufacturing. However, for example depending on the geometry of the conductor 202 (and in particular its length), other manufacturing methods can be considered, such as wire drawing, machining or molding. The manufacturing methods allowing the manufacture of a curved (and not straight) conductor 202 make it possible to limit the risks of obstruction, because when bending the straight conductor, the deformations of the fluid passage section can in certain cases (e.g.: small / low radius of curvature) be poorly controlled.

[0042] The single-piece part can be made of copper, aluminum, or an alloy of one of the two previous materials.

[0043] The flow channel may have a round, rectangular, diamond-shaped, or other cross-section. The outer shape of the conductor 202 may differ from that of the cross-section of the flow channel: for example, the cross-section of the flow channel may be round inside a conductor 202 with a rectangular outer cross-section.

[0044] With reference to Figure 3, an example of a connecting element 208 will now be described in more detail.

[0045] The connection element 208 has a body 302 at the end of the electrical conductor 202 and carrying the terminals 210, 212. In the example illustrated, the electrical connection terminal 212 is in the form of a tab 304 having a screwing hole 306, for example to a bus bar.

[0046] Preferably, a chamfer 307 is provided between the body 302 and the electrical conductor 202, in order to mechanically reinforce the connection between the body 302 and the electrical conductor 202.

[0047] The routing channel, designated by the reference 308, has an internal diameter d, while the hydraulic connection terminal 210 has an internal diameter D generally larger than that of the routing channel 304.

[0048] Thus, a narrowing 310 is provided in the body 302 between the diameter D and the diameter d.

[0049] Preferably, the narrowing 310 is gradual, in order to reduce pressure losses. Indeed, according to Barlow's law, the maximum pressure that a tube can withstand depends on its dimensions and its material, so that the maximum pressure losses are given by: [Math. 1] where P is the pressure losses [Pa], a is the yield stress [Pa], S is the thickness of the conductor wall 202 [m], D exf is the outer diameter of the conductor 202.

[0050] In the example illustrated in Figure 3, the narrowing 310 is in steps with straight slopes between the steps. Thus, it is simple to machine, since it is possible to use drills of decreasing diameters.

[0051] Referring to Figure 4, the shrinkage 310 could be abrupt. In this case, the pressure losses are given by: [Math. 2] where P is the pressure drop [Pa], p is the density of the cooling fluid [kg / m 3 ] and 1 / is the average velocity of the fluid after shrinkage [m / s].

[0052] Referring to Figure 5, the shrinkage 310 could be rounded. In this case, the pressure losses are given by: [Math. 3] P = 0.02E>pV 2 where P is the pressure drop [Pa], p is the density of the cooling fluid [kg / m 3 ] and 1 / is the average velocity of the fluid after shrinkage [m / s].

[0053] Referring to Figure 6, the conductor 202 may also be straight.

[0054] With reference to Figures 7 and 8, in particular when the stator element 200 is produced by additive manufacturing, the conductor 202 may further comprise fins or pins 702 extending into the routing channel to improve the heat transfer between the fluid and the conductor 202.

[0055] Figure 9 and Figure 10 illustrate a variant of the connection element 208 of the previous figures, this variant bearing the reference 902.

[0056] The connecting element 902 is identical to the connecting element 208, except that the screw hole 306 is replaced by a threaded rod 904 projecting from of the lug 304. The threaded rod 904 is for example designed to be inserted into a hole in a bus bar and tightened by a bolt or equivalent.

[0057] In conclusion, it will be noted that the invention is not limited to the embodiments described above. It will indeed appear to those skilled in the art that various modifications can be made to the embodiments described above, in light of the teaching which has just been disclosed to them.

[0058] In the detailed presentation of the invention given above, the terms used should not be interpreted as limiting the invention to the embodiments set forth in this description, but should be interpreted to include all equivalents the prediction of which is within the reach of those skilled in the art by applying their general knowledge to the implementation of the teaching just disclosed to them.

Claims

Claims [1] Stator element (200) of an electrical machine (100) of an aircraft, comprising: an elongated and hollow electrical conductor (202) in order to define a channel (308) for the flow of a cooling fluid from one end to the other of the conductor (202), the conductor (202) being designed to be traversed by an electric current; and a connection element (208; 902) located at one of the ends of the conductor (202), comprising: • a fluid connection terminal (210) designed to allow an inlet of the cooling fluid into the channel (308) or an outlet of the cooling fluid from the channel (308), and • an electrical connection terminal (210) designed to electrically connect the conductor (202); characterized in that the conductor (202) and the connection element (208; 902) are formed from a single piece. [2] Stator element (200) according to claim 1, in which the single-piece part is produced by one of: additive manufacturing, wire drawing, machining and molding. [3] Stator element (200) according to claim 1 or 2, in which the single-piece part is made of copper, aluminum, or an alloy of one of the two preceding materials. [4] Stator element (200) according to any one of claims 1 to 3, in which the flow channel (308) has an internal diameter (d) and the fluidic connection element (210) has an internal diameter (D) greater than the internal diameter (d) of the flow channel, as well as a narrowing (310) between the diameter (D) of the connection element and the diameter (d) of the flow channel (308). [5] Stator element (200) according to claim 4, wherein the narrowing (310) is progressive. [6] Stator element (200) according to claim 5, wherein the constriction (310) has rounded edges. [7] Stator element (200) according to any one of claims 1 to 6, wherein the electrical connection terminal (212) comprises an electrical connection hole, for example screw hole (306), for example provided on a tab (304). [8] Stator element (200) according to any one of claims 1 to 6, wherein the electrical connection terminal (212) comprises a threaded rod (904), for example provided on a lug (304). [9] Stator element (200) according to any one of claims 1 to 8, wherein the fluid connection terminal (210) comprises a male or female end piece, for example to be connected to a flexible pipe. [10] Stator element (200) according to any one of claims 1 to 9, further comprising another connection element (208; 902) located at another end of the conductor (202), comprising: a fluid connection terminal (210) for an inlet of the cooling fluid into the flow channel (308) or an outlet of the cooling liquid from the flow channel (308), and an electrical connection terminal (212) for electrically connecting the conductor (202); the conductor (202) and the two connection elements (208; 902) being formed from the single monobloc part. [11] Electrical machine (100) comprising: a rotor (108); and a stator (102) for driving the rotor (108), the stator (102) comprising a stator element (200) according to any one of claims 1 to 10. [12] Aircraft comprising an electric machine (100) according to claim 11.

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