Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K15/00—Processes or apparatus specially adapted for manufacturing, assembling, maintaining or repairing of dynamo-electric machines
  • H02K15/02—Processes or apparatus specially adapted for manufacturing, assembling, maintaining or repairing of dynamo-electric machines of stator or rotor bodies
  • H02K15/021—Magnetic cores
  • H02K15/023—Cage rotors
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K17/00—Asynchronous induction motors; Asynchronous induction generators
  • H02K17/02—Asynchronous induction motors
  • H02K17/16—Asynchronous induction motors having rotors with internally short-circuited windings, e.g. cage rotors
  • H02K17/168—Asynchronous induction motors having rotors with internally short-circuited windings, e.g. cage rotors having single-cage rotors
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B64—AIRCRAFT; AVIATION; COSMONAUTICS
  • B64D—EQUIPMENT FOR FITTING IN OR TO AIRCRAFT; FLIGHT SUITS; PARACHUTES; ARRANGEMENT OR MOUNTING OF POWER PLANTS OR PROPULSION TRANSMISSIONS IN AIRCRAFT
  • B64D27/00—Arrangement or mounting of power plants in aircraft; Aircraft characterised by the type or position of power plants
  • B64D27/02—Aircraft characterised by the type or position of power plants
  • B64D27/30—Aircraft characterised by electric power plants
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K1/00—Details of the magnetic circuit
  • H02K1/02—Details of the magnetic circuit characterised by the magnetic material
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K15/00—Processes or apparatus specially adapted for manufacturing, assembling, maintaining or repairing of dynamo-electric machines
  • H02K15/02—Processes or apparatus specially adapted for manufacturing, assembling, maintaining or repairing of dynamo-electric machines of stator or rotor bodies

Definitions

• the present invention relates to the field of electric motors and more particularly relates to the field of electric motor rotors for aeronautical applications.
• one of the preferred ways is to reduce the mass of the electric motors of generation and/or or starting or electric propulsion if we are in the field of "VTOL" (Vertical Take Off and Landing, which means vertical take-off and landing)” or “STOL” (Short Take Off and Landing, which means vertical take-off and landing) short landing).
• VTOL Vertical Take Off and Landing, which means vertical take-off and landing
• STOL Short Take Off and Landing, which means vertical take-off and landing
• the second limitation is the mechanical limitation in the rotation speed of the machines.
• machines (d) are rotor mounted permanent magnet synchronous machines and machines (e) are solid rotor induction asynchronous machines.
• the machine can contain high-energy debris from rotating parts of the machine rotor (i.e. the machine must continue to operate despite the breakage and the presence within it of parts of the rotor). Moreover, in many other cases of failure, it is necessary that the electrical machine continues to operate.
• DC machines are the machines most used in the aeronautical industry. Their main advantage is to operate on direct current networks without the mandatory use of power electronics. Their main disadvantage is to include brushes energizing the rotor which causes premature wear of the latter and imposes limitations in terms of rotation speed (max speed ⁇ 20,000 rpm).
• Wound-rotor synchronous machines are machines which have the main advantage of being very easily controllable in terms of torque and speed. Indeed, it is possible to manage the flux of the machine very easily by injecting a direct current into the inductor of the machine (rotor part) using conductive rings linking the stator and the rotor. These machines have the similar disadvantage of DC machines to have a maximum speed of the rotor relative to the stator of about 25,000 rpm. This speed limitation is due to the presence of conductive rings rubbing on the rotor.
• permanent magnet machines are one of the most efficient categories of machines in terms of torque density, it is moreover for their excellent performance that these machines emerge in aeronautical electrical systems. Their advantage, which is also their main drawback, is that these machines have magnets in the rotor, which has the main advantage that these machines do not have brushes and are self-excited due to the rotation of the magnets. Thus, during an internal fault such as a short-circuit on the stator windings, the short-circuit is self-sustaining due to the rotation of the magnets which generate this short-circuit. It is therefore necessary to be able to stop the rotation of the rotor so that the fault does not propagate.
• variable reluctance synchronous machine is a machine with strong electromagnetic performance
• the rotor is magnetically passive in nature, so in the event of a problem on the stator windings, the machine is de-energized in de-energizing the stator.
• the main drawback of this machine for use in an aeronautical environment is that this machine imposes a very small air gap ( ⁇ 0.5 mm) hence an increased complexity for the integration of this machine in a fairly severe vibratory environment.
• the squirrel cage asynchronous machine is a machine with lower electromagnetic performance compared to synchronous machines due to the fact that the induction of rotor currents generated by the stator currents tend to heat the rotor .
• the concept of sliding is also to be considered in this machine.
• the slip is the difference between the pulsation of the currents created in the rotor and the pulsation of the stator currents. This slip is a fundamental notion because the greater the slip (and tends towards 1), the more torque the machine provides.
• the fundamental problem of this principle is that the Joule effect created in the rotor part of the machine is directly proportional to the slip.
• asynchronous machine with massive rotor To solve this problem of electromagnetic performance limitation, new topologies of asynchronous machines have recently appeared for about ten years called asynchronous machine with massive rotor.
• massive rotor comes from the fact that the rotor, which can be multi-material, is very compact and the rotor is resistant to much greater mechanical stresses than squirrel-cage asynchronous machines.
• the objective of the present invention is to propose a new asynchronous machine rotor topology exhibiting better performance at high speed (ie speeds greater than 30,000 rpm).
• the invention proposes an aircraft electric motor rotor comprising a shaft made of a first material and a skin made of a second material different from the first material, in which the shaft has a shoulder portion on which is fixed the skin, at the shoulder portion, the rotor has an interpenetration layer of the first material and the second material, the interpenetration layer comprising an alloy of the first material and the second material.
• the skin may comprise two rings, a first ring being attached to the rotor at a first end region of the shoulder portion and a second ring being attached to the rotor at a second end region of the shoulder portion.
• the skin and the rings can be in one piece.
• the skin may comprise two half-shells welded together.
• the first material may contain at least iron and carbon.
• the second material may contain at least one of the metals chosen from among copper, aluminum or silver.
• the invention relates to a method for manufacturing a rotor according to the invention, comprising at least one of the steps of:
• the step of inserting the shaft and an element intended to form the skin in a protective tubular envelope may include the phases of:
• the step of inserting the shaft and an element intended to form the skin in a tubular protective casing may comprise a phase of positioning, around the shaft, a powder intended to form the skin.
• the heating and pressurizing step of the assembly can be carried out in a dedicated enclosure and in a neutral atmosphere.
• the heat treatment step may include quenching selected from natural or forced convection gas quenching, water quenching or oil quenching.
• the heat treatment step can be carried out until the first stainless steel material becomes martensitic.
• Figure 1 is a graph representing the maximum power of different electrical machines as a function of rotational speed
• Figure 2 is a sectional view of a rotor according to the invention.
• Figure 3 is a representation of a shaft, two half-shells and an envelope for implementing the method according to the invention
• Figure 4 is a representation of an envelope comprising a shaft and two half-shells
• Figure 5 is a representation of a tree and a skin extracted from the envelope
• Figure 6 is a representation of a rotor obtained by an embodiment of the method according to the invention.
• Figure 7 is a representation of a diagram of the change in microstructure of a steel as a function of the cooling rate
• Figure 8 is a comparative representation of the magnetic hysteresis of two samples of a material having received two different tempers.
• the invention proposes an aircraft electric motor rotor 1 comprising a shaft 2 made of a first material and a skin 4 made of a second material different from the first material.
• the shoulder portion 6 has two end regions 8 (i.e. each being a circular crown). Each end region 8 of the shoulder portion 6 has a groove intended to accommodate a ring 12.
• the shaft 2 may have a longitudinal bore 1.
• Bore 14 may include a splined portion.
• the shaft 2 is made of a magnetic material comprising an alloy of iron and carbon.
• the alloy of the shaft is a steel comprising mainly iron and carbon.
• the alloy is a martensitic steel comprising more than 1% carbon. This structure of the steel allows the shaft 2 to channel the magnetic field lines coming from the windings to the stator (when the rotor is in operation in an electric motor) so that the skin 4 receives as much magnetic field as possible.
• the shaft alloy can be selected from 17-4PH, ⁇ ISI 416 (EN-1 -4005), ⁇ ISI 431 (EN-1 -4057), ⁇ ISI 1020 (XC18), ⁇ ISI 1045 (XC48).
• this alloy can include other components in addition to iron and carbon, so for example to make stainless steel (example: Chrome Cr, Nickel Ni).
• the geometry of the shaft 2 can for example be obtained by turning and the martensitic structure is obtained by heat treatment.
• Skin 4 is a copper cylinder positioned over shoulder region 6. Copper is chosen for its excellent conductivity. According to another embodiment, the skin 4 could for example be made of silver or aluminum.
• the material, such as copper or silver, constituting the skin 4 is not necessarily a pure material and may be an alloy based on copper, based on aluminum or based on silver.
• the copper alloy may include addition elements such as chromium and zirconium or cobalt or even Beryllium.
• the skin 4 consists of two half-shells 18 assembled and permanently bonded by a diffusion welding process.
• the skin can advantageously have a thickness of the order of 1 to 5 millimeters.
• the skin 4 can comprise two rings 12 which are each intended to be positioned in a groove of an end region 8.
• each ring 12 is in one piece with a respective half-shell 18.
• each ring 12 is made in one piece with a respective half-shell 18.
• the rings 12 have a short-circuit function and are used to loop back the induced currents to the rotor.
• the structure in two half-shells 18 makes it possible to assemble the skin 4 on the shaft 2.
• each half-shell 18 has a first end comprising a ring 12 and a second end having a chamfer 22.
• the chamfers 22 of the two half-shells 18 are complementary to each other to facilitate the assembly of the two half-shells 18.
• a half-shell 18 can have a chamfer at +45° and the other half- shell 18 may have a chamfer 22 at -45°.
• complementary assembly it is understood that once assembled the two half-shells 18 form a complete cylinder (i.e. without hole or opening at the junction between the two half-shells 18).
• the skin 4 is welded to the portion of shoulders 6 and the end regions 8 of the shaft 2. This welding is carried out so that the rotor 1 has an interpenetration layer due to the existence of a diffusion of material between the skin 4 and the shaft 2, at the level of the shoulder portion 6 and the regions of ends 8.
• the rotor has an interpenetration layer of the material of the shaft 2 and the material of the skin 4.
• interpenetration is meant a layer of alloy of the material of the shaft 2 (first material) and of the material of the skin 4 (second material).
• this interpenetration is carried out without the addition of a third material.
• the welding of skin 4 and shaft 2 includes only skin 4 and shaft 2 and does not involve any additional material.
• the interpenetration layer is the result of welding by diffusion of the skin 4 and of the shaft 2.
• This arrangement very advantageously makes it possible to have a excellent mechanical strength over the entire surface of the shoulder portion 6, which enables the rotor 1 to withstand rotation speeds greater than 50,000 rpm in the present configuration.
• the invention relates to a method of manufacturing a rotor 1 as described previously.
• the method comprises the steps of:
• diffusion welding is a technique allowing the assembly of elements in solid phase, that is to say without fusion, thanks to the simultaneous application of a temperature and a high pressure on a determined time.
• the step of inserting the shaft 2 and an element intended to form the skin 4 in a protective tubular casing 30 comprises the phases of:
• the step of inserting the shaft 2 and an element intended to form the skin 4 into a protective tubular casing 30 comprises a phase of positioning, around the shaft, a powder intended to form the skin 4.
• the powder during the heating and pressurizing process in the envelope 30, binds and becomes a homogeneous element to form the skin 4.
• the diffusion welding phase can be carried out in an enclosure using a hot isostatic compression (CIC) method.
• CIC hot isostatic compression
• diffusion welding is a technique allowing the assembly of elements in solid phase, that is to say without melting thanks to the simultaneous application of a temperature and a high pressure.
• a hot isostatic pressing (CIC) method may include a step of degreasing and stripping the surfaces of the elements to be assembled, a step of bringing the degreased and stripped surfaces of the elements to be assembled into direct contact, and a step of assembly by diffusion welding of the surfaces of the elements in contact.
• the step of degreasing and pickling the surfaces of the elements to be assembled can consist of conventional treatments for degreasing and pickling metal surfaces.
• the degreasing solvent can be an organic solvent, for example of the acetone, ether, alcohol, alkane type, or of the chlorinated alkene type such as trichlorethylene, or a mixture of these solvents, etc.
• a preferred solvent is a mixture of equal proportions of ethyl alcohol, ether and acetone.
• Another preferred solvent is trichlorethylene.
• Chemical pickling can be carried out with an acid solution, for example a 10% hydrofluoric acid bath or a mixture comprising 1 to 5% hydrofluoric acid with 30 to 40% nitric acid.
• the pickling time can be for example from 10 seconds to 5 minutes, for example from 20 to 30 seconds, at a temperature of 15°C, for example 20°C.
• the pickled surfaces can then be rinsed in one or more successive baths, for example of demineralised water.
• This surface can then be pickled, for example by means of a bath of potassium dichromate, for example at a concentration of 0.23 to 0.30 moles/litre, of sulfuric acid at a concentration for example of 0.1 to 0 .13 moles/litre, and demineralized water, for example 1 to 3 minutes, for example for 1 minute and 30 seconds approximately.
• the surface can then be rinsed in ethanol for example under ultrasound, then in demineralized water and dried for example by means of hot air.
• the next step is a step of bringing the degreased and pickled surfaces of the elements into direct contact.
• This contacting corresponds to a placement or positioning of the elements to be assembled surface against surface, according to a desired stacking.
• this contacting is done within less than one hour following the step of degreasing and stripping the surfaces to be assembled, so as to limit the risks of oxidation, except in the case where special precautions have been taken.
• these precautions possibly consisting, for example, in keeping the elements in a clean and non-oxidizing atmosphere such as nitrogen by means of bagging them in sealed bags.
• the step which follows the bringing into contact of the surfaces of the elements to be assembled is a step of assembly by diffusion welding of the surfaces brought into direct contact.
• the diffusion welding can be carried out for example by isostatic compression or by hot uniaxial pressing, for example, by conventional techniques known to those skilled in the art.
• the materials brought into contact can be introduced into an envelope which makes it possible to isolate the elements to be assembled from the atmosphere and to evacuate the gases in the envelope for the assembly of the elements by diffusion welding therein.
• the contacting step can also be done in the envelope directly.
• the casing 30 can be made of any impermeable material strong enough to withstand an at least partial vacuum therein and to withstand the high temperatures and pressures necessary to assemble the elements.
• the casing can be a metal casing, for example made of stainless steel, mild steel or titanium and its alloys. It can for example be formed from a sheet having a thickness for example of 1 to 20 mm approximately, for example of 1 to 10 mm approximately.
• the envelope can match the external shape of the elements to be assembled.
• the martensitic stainless steel element (the shaft 2) can close the casing 30 by playing the role of cover of the casing 30, the shaft 2 then being able to be welded to the casing 30
• this casing 30 can be made by cutting, optionally by bending and then by welding a metal sheet or by any method known to those skilled in the art.
• the envelope 30 is then degassed so as to create a vacuum therein.
• Degassing can be carried out by means of a vacuum pump and heating of the assembly comprising the elements to be assembled and the envelope.
• An example of degassing may consist in evacuating the envelope 30 at room temperature until a residual vacuum of less than or equal to 10 Pa is obtained, then in heating the assembly to a moderate temperature, for example less than 300 C, for a few hours, for example 5 hours, while continuing to evacuate.
• the casing 30 is made completely sealed by closing the opening which served for its evacuation, the closing being carried out for example using TIG welding.
• the elements brought into contact in the degassed envelope can then be assembled by diffusion welding.
• the assembly can be carried out in a hot isostatic compression chamber.
• the heating step comprises a phase of pressurizing the assembly 32.
• a heating enclosure i.e. an oven
• the pressure inside a heating enclosure can be brought to a value between 1000 and 2000 bars (preferably the pressure can be around 1500 bars).
• the heating is carried out in a so-called neutral atmosphere.
• the heating chamber of the oven used is saturated with an inert gas (i.e. a rare gas according to the periodic table of the elements).
• the neutral gas used may be argon.
• the atmosphere of the heating enclosure can be saturated with nitrogen.
• One of the objectives of the saturation of the heating enclosure with argon or nitrogen is to drive out the oxygen to avoid a potential oxidation reaction.
• the heating step is carried out by bringing the assembly 32 to a temperature allowing welding by diffusion but lower than a temperature of liquefaction of the copper (and consequently of the steel).
• the temperature of the assembly 32 is increased gradually (linearly) up to a maximum temperature, then the maximum temperature is maintained for a fixed period.
• the maximum heating temperature may be between 900° C. and 1040° C. to carry out the dissolution of the metallic components present in the casing 30.
• the heating step is carried out gradually over several hours. In a particularly preferred manner, the heating step lasts about ten hours.
• the heat treatment step may comprise quenching selected from open air quenching, water quenching or oil quenching.
• the quenching can be homogeneous for the whole of the assembly 32 or can be monitored by in-situ measurements.
• the quenching heat treatment step is determined so that the steel of the shaft 2 becomes martensitic. More specifically, the heat treatment step removes any presence of residual austenite in the steel of shaft 2.
• quenching must correspond to a cooling rate greater than the critical rate to create the martensitic phase, i.e. several degrees/second or even several tens of degrees/second (°/s).
• the objective of the quenching is to reach at least the zone bearing the reference V2 in figure 7 and at best the zone bearing the reference V1.
• the quenching step is very advantageous to improve the electromagnetic properties as shown in Figure 8 which shows that the cooling rate has a direct impact on the electromagnetic properties of the material.
• the magnetic hysteresis cycle H1 corresponds to a water quenched material
• the magnetic hysteresis cycle H2 corresponds to air quenching.
• a water-cooled specimen has better electromagnetic properties than an air-cooled specimen.
• the assembly 32 is immersed in a cryogenic bath in order to reduce the presence of residual austenite.
• the cryogenic bath can be at a temperature below ⁇ 20° C.
• the assembly 32 is immersed in the cryogenic bath for a period that can be between 10 minutes and 60 minutes.
• the tempering step makes it possible to obtain the desired characteristics for the copper constituting the skin 4 (mechanical resistance, electrical conductivity, etc.), and makes it possible to soften the martensitic steel to increase its ductility. while preserving its electromagnetic properties, which makes it possible to optimize the overall performance of the rotor 1.
• the tempering step is a step known in the field of metallurgy. In a usual way, income can also be called “ageing”.
• tempering is carried out by bringing assembly 32 to a plateau temperature of between 450° C. and 650° C., over a period of between 1 hour and 4 hours.
• This optimized treatment makes it possible to guarantee for the copper alloy a conductivity equal to or greater than 90% of the conductivity of pure copper (%I ⁇ CS) and ensures that the desired mechanical properties are maintained.
• Separation of casing 30 and rotor 1 is achieved by machining casing 30 to retain only rotor 1 .
• the envelope 30 is extracted by machining, typically by turning.
• the rotor 1 obtained then has rough dimensions, as shown in Figure 5.
• the rotor 1, and more particularly its skin 4 are machined to have the final dimensions and geometries.
• the rotor 1 obtained has the geometric characteristics necessary for its use, and also has structural and electromagnetic characteristics guaranteeing its resistance when used at speeds of rotation greater than 50,000 rpm.
• the bonding zone by interdiffusion on the part obtained according to the process typically has a thickness of a few tens of ⁇ m.
• the rotor 1 having a structure of the monolithic type can easily be statically and dynamically balanced (by localized removal of material), which makes it possible to guarantee the lowest possible vibration level compatible with high-speed operation.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Manufacture Of Motors, Generators (AREA)
• Iron Core Of Rotating Electric Machines (AREA)

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Publications (1)

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• 2021
  • 2021-09-14 FR FR2109612A patent/FR3127085B1/fr active Active
• 2022
  • 2022-09-14 CN CN202280058547.XA patent/CN117882279A/zh active Pending
  • 2022-09-14 US US18/689,650 patent/US20240372448A1/en active Pending
  • 2022-09-14 EP EP22789633.9A patent/EP4402784A1/de active Pending
  • 2022-09-14 WO PCT/FR2022/051731 patent/WO2023041874A1/fr not_active Ceased

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