FR3012698A1 - ELECTRIC MACHINE HAVING A PHASE CHANGE MATERIAL OF A TURBOMACHINE GENERATOR STARTER - Google Patents

Abstract

The invention relates to an electrical machine comprising a first assembly and a second assembly configured to be rotated relative to each other, the second assembly comprising a plurality of permanent magnets, one or the other of first or second assembly further comprising a magnetic circuit and an electrical circuit, a magnetic flux variation in the magnetic circuit inducing an electromotive force in the electrical circuit, the electrical machine further comprising at least one heat sink comprising a material to be changed phase to dissipate heat during the transient phases of said electric machine, said dissipator being disposed closer to the heat sources involved during said transient phases of said electric machine.

Description

GENERAL TECHNICAL FIELD The invention relates to aircraft engines, in particular those of a helicopter. It particularly relates to electric machines integrated in helicopter engines performing the function of generating electrical energy, and / or electrical motorization of certain organs. These electrical machines may be starter generators, starters, alternators or electric pumps which are either DC or AC machines. STATE OF THE ART A motor of an aircraft comprises electrical machines comprising a rotor and a stator rotated relative to one another, the stator comprises a magnetic circuit and an electrical circuit (consisting of a conductive winding) of so that a variation of magnetic flux in the magnetic circuit induces an electromotive force in the electrical circuit to initiate rotation.

In known manner, such electrical machines have transient phases encountered during the starting or accelerating phases of the engine of the aircraft or during the startup and acceleration phases of certain equipment that includes the engine of the aircraft. aircraft. During these transient phases, the electrical machine dissipates a quantity of heat that can be damaging for the electrical machine, heat dissipated in the electrical circuits and / or permanent magnets if the machine includes. To promote the dissipation of heat these elements are of high size. In addition, to optimize the heat dissipation of the electric machine, several solutions are already known.

One solution uses natural convection cooling by finned heatsink at the periphery of the machine to have a large exchange surface between the surrounding environment and the machine. One solution uses forced convection by adding a fan to the machine. Another solution uses forced cooling by injecting a liquid circulating inside the machine or at the periphery (oil, fuel, etc.) or cooling by exchanger. Yet another solution uses thermoelectric module cooling (Peltier effect).

However, in an aeronautical application, that is to say, in the context of an embedded system requiring high constraints in terms of compactness, mass and reliability, the disadvantages of the solutions described above are for each: natural convection with finned heatsink cooling: bulky and massive and requires an airflow at the periphery of the machine; forced convection with the addition of a fan: bulky (by the addition of the fan), damages the integrity of the machine; forced cooling by liquid circulating inside the machine or at the periphery (oil, fuel, etc.) or by exchanger: bulky, massive and machine-intrusive system with fairly short maintenance steps; Thermoelectric module cooling: cooling on very localized areas and also requires a stabilized power supply for thermoelectric power supply. To the above disadvantages, the disadvantage of increasing the size of the components which dissipate heat is added. PRESENTATION OF THE INVENTION The invention makes it possible to reduce the weight and the size of an electric machine of an engine of an aircraft and to improve the electromagnetic performances of the machine.

For this purpose, the invention proposes an electric machine comprising a first set and a second set configured to be rotated relative to each other, the second set comprising a plurality of permanent magnets, one or the other of the first or second assembly further comprising a magnetic circuit and an electrical circuit, a variation of magnetic flux in the magnetic circuit inducing an electromotive force in the electrical circuit, the electric machine further comprising at least one heat sink comprising a phase change material so as to dissipate heat during the transient phases of said electric machine, said dissipator being disposed closer to the heat sources involved during said transient phases of said electric machine.

The invention is advantageously completed by the following features, taken alone or in any of their technically possible combination the heat sink comprises longitudinal tubes housed in a peripheral portion of the first set, said longitudinal tubes comprising said phase change material; the heat sink comprises longitudinal housings each disposed between two permanent magnets, said housings comprising said phase change material; the phase change material is in the form of salts or in the form of organic or eutectic compounds having solid-liquid phase change temperatures greater than about one hundred degrees Celsius, typically between 150 ° C and 300 ° C; the heat sink comprises, in addition to the phase-change material, at least one element which is electrically conductive so as not to disturb the flow of the magnetic field lines in said machine; the phase change material is contained in a sealed metal shell; the first set comprises a magnetic circuit and an electric circuit, the electric circuit consisting of a winding of a conductive wire around the poles of the magnetic circuit; the first set is a stator and the second set is a rotor. The invention also relates to a DC or AC machine such as a generator-starter, an alternator, a pump comprising an electric machine according to the invention.

And the invention further relates to a motor of an aircraft, such as a helicopter, comprising a DC or AC machine such as a generator-starter, an alternator, a pump comprising an electric machine according to the invention. invention. The advantages of the invention are manifold. The invention makes it possible to reduce the overall mass of an engine of an aircraft by decreasing the mass of the electric machine. In particular, the masses of iron (used in the magnetic circuit of the machine) and copper (used for the winding of the electric circuit) are reduced inside the machine. Indeed, by optimally managing the thermal within the machine and more particularly by improving the heat transfer properties closer to the elements subjected to the highest temperature rises can reduce the weight and bulk of electrical machines. In addition, there is no addition of additional systems degrading the mass balance, bulk and the reliability rate of the electrical machine. PRESENTATION OF THE FIGURES Other features, objects and advantages of the invention will emerge from the description. which follows, which is purely illustrative and non-limiting, and should be read with reference to the accompanying drawings in which: - Figure 1 illustrates a schematic sectional view of an electric machine according to a first embodiment of the invention; - Figure 2 illustrates a schematic sectional view of an electric machine according to a second embodiment of the invention; - Figure 3 illustrates a schematic sectional view of an electric machine according to a third embodiment of the invention; FIG. 4 is a curve as a function of time of the heat dissipation of a heat flux with and without use of a phase change material. In the set of figures, similar elements bear identical references.

DETAILED DESCRIPTION OF THE INVENTION In what follows, the term "phase change material" means a material capable of changing its physical state within a given temperature range and which will absorb a large amount of heat energy from its close environment to pass from the solid state to liquid and that restores a portion of the heat energy when the material cools from the liquid state to the solid state. These phase change materials are salts which may be composed of nitrate or hydroxide. The change from solid to liquid phase of the material is at a temperature exceeding one hundred degrees Celsius up to a temperature of the order of 300 ° C. FIG. 1 illustrates an electric machine according to a first embodiment. of the invention. Such an electric machine is used in particular in an aircraft engine. The electrical machine of FIG. 1 is a permanent magnet machine and comprises a stator 1 and a rotor 2. The stator 1 comprises a magnetic circuit 3 and an electric circuit 4. The magnetic circuit 3 comprises a peripheral portion 6 of generally cylindrical shape and the poles 7 extending towards the rotor 2. The electrical circuit 4 is wound around each pole 7 of the magnetic circuit 3. In addition, other forms of winding (winding conductors typically copper) are also conceivable.

The rotor 2 supports permanent magnets 5. In FIG. 1, the electric machine comprises six permanent magnets 5 but a different number can be envisaged. When the rotor 2 is rotated with respect to the stator 1, the magnetic flux in the magnetic circuit 3 varies and therefore induces an electromotive force in the electric circuit 4. During the transient phases which correspond to start-up, change-over phases speed or even stopping the corresponding motor, the electric machine dissipates heat. In particular, the electrical circuit 4 and the permanent magnets dissipate heat.

According to this first embodiment, so as to dissipate the heat during these transient phases, the electrical machine comprises at least one heat sink 8 housed in the peripheral portion 6 of the stator 1. In particular, a heat sink 8 in this first embodiment consists of a longitudinal tube 9 comprising a material 10 with phase change, the longitudinal tube being housed in the peripheral portion 6. The electric machine of Figure 1 comprises twelve longitudinal tubes 9 housed in the peripheral portion at each pole 7 (here twelve poles 7). Of course, it is possible to envisage a different number of heat sink 8. The phase change material 10 is in the form of salts or in the form of organic or eutectic compounds. It can be for example LiNO3, NaNO3, Li2CO3, etc. Preferably, the phase change material is contained in an envelope (not shown) which is sealed to maintain and confine the material in the liquid state. In addition, the envelope and the phase change material to disturb as little as possible the flow of the field lines in the magnetic circuit the envelope is itself metallic and is a good electrical conductor. Moreover, since a phase-change material is by definition an electrical insulator, the heat sink may comprise, in addition to the phase-change material, conductive elements such as carbon nanotubes to also allow the free circulation of the field lines. in the magnetic circuit of the machine. According to this first embodiment, heat dissipators 8 are therefore arranged as close as possible to the various electrical circuits 4 wound around the poles 7. Thus, compared to the prior art, it is possible to have electrical circuits 4 less massive.

In particular, the conductors son constituting the electrical circuits 4 may have a lower section than the conductive son used in such heat sink. Indeed, as the electrical circuits dissipate a lot of heat, it was necessary, in the prior art, to provide conductive son of sufficient section to prevent them from melting. According to this first embodiment a gain in terms of mass on 28Vdc generators / starters implementing such an electric machine is as follows. The addition of heat sinks with a phase change material makes it possible to reduce the cross-section of the conductive wires of the electrical circuits 4 by one size, ie a potential gain of 25% in terms of mass, and the missing section is replaced by materials. phase change which have a density density 4.5 times lower.

Thus, knowing that the mass share of the son making up a machine is about 50% of the total mass, the addition of phase change materials reduces the weight of the machine by about 10%. Figure 2 illustrates an electric machine according to a second embodiment. Elements identical or similar to those of the electric machine according to the first embodiment illustrated in Figure 1 are designated by the same references. According to this second embodiment, the electrical machine comprises at least one heat sink 11 arranged between two permanent magnets 5. According to this embodiment, the heat sink 11 consists of a longitudinal housing 12 comprising a material with a change of heat. phase.

In Figure 2 are shown five longitudinal housing arranged between two permanent magnets 5 (here six permanent magnets). Of course, one can consider a different number of heat sink and have heat sinks differently from the permanent magnets. According to this second embodiment, the heat dissipators 11 are therefore arranged as close as possible to the permanent magnets 5. Compared to the prior art, it is possible to have less solid permanent magnets. Indeed, since the permanent magnets were subjected to a high transient thermal stress, it was necessary in the prior art to provide massive permanent magnets to prevent them from becoming demagnetized. Figure 3 illustrates an electric machine according to a third embodiment.

Elements identical or similar to those of the electric machine according to the first and second embodiments illustrated in Figures 1 and 2 are designated by the same references. According to this third embodiment, the electrical machine comprises at least one heat sink 13 disposed below the permanent magnets 5. According to this embodiment, the heat sink 13 consists of a longitudinal housing 14 comprising a material to phase change. As for the second embodiment, heat sinks 13 are therefore arranged as close to permanent magnets 5. Thus, it is possible to have permanent magnets less massive than in the prior art. In the embodiments described above, as will have been understood, it is the use of a phase change material that absorbs heat. An electric machine with a stator winding has been described here. Of course, the invention also applies to an electric machine with a rotor winding.

The use of phase-change materials allows for cooling closer to critical elements such as electrical circuits or permanent magnets. Indeed, by reaching its melting temperature, thus passing from the solid state to the liquid state, the phase change material absorbs a quantity of heat. As a result, heat transfer will then occur between the heating elements inside the machine and the phase change material. According to a fourth embodiment (not shown), the first embodiment can be combined with the second embodiment and / or the third embodiment. FIG. 4 illustrates the principle and the gain provided by the addition of phase-change material in the vicinity of certain components of the electric machine. In particular, the heat flux (kcomp to be dissipated without a phase change material and the average heat flux 4moy to dissipate with a time-phase-change material) is illustrated, where it is found that without phase-change material. the component is dimensioned in terms of mass and volume to dissipate the heat flow 4comp, with a phase change material the impacted component must dissipate a mean flow 4moy less than the heat flow çbcomp especially during the transient phases (where the flow thermal ikcomp is the most important.) Indeed, the heat flux (kcomp varies during three transient phases ([t041], [t1-t2] and [t2-t3]) while the average flow (kmoy is constant. Indeed, under conditions where a large heat dissipation is required but which is cyclic or transient, the use of phase-change materials allows a better management of the thermal as close as possible. LEMENTS heat sinks. In fact, reaching its melting temperature, thus passing from the solid state to the liquid state, the phase-change material absorbs a quantity of heat, a thermal transfer will then take place between the heating elements inside the the machine and the phase change material. The phase change material will then absorb the peak temperature that will occur at the machine elements if there were no phase change material. In terms of the thermal dimensioning of the machine components such as windings, the magnets can therefore be sized not on a maximum temperature peak but on a lower average temperature. This has the consequence of reducing the dimensioning constraints especially on the section of the windings, the amount of copper in the machine, the thickness of the magnets, etc.

The invention also relates to a DC or AC machine such as a generator-starter, an alternator, a pump comprising an electric machine as described above. And the invention also relates to an engine of an aircraft, such as a helicopter, comprising an electric machine according to the invention.

Claims (10)

REVENDICATIONS1. An electric machine comprising a first set (1) and a second set (2) configured to be rotated relative to each other, the second set (2) comprising a plurality of permanent magnets (5), one or the other of the first or second set further comprising a magnetic circuit (3) and an electric circuit (4), a variation of magnetic flux in the magnetic circuit inducing an electromotive force in the electric circuit (4), the electric machine further comprising at least one heat sink comprising a phase change material (11) so as to dissipate heat during the transient phases of said electric machine, said dissipator (8, 11, 13) being disposed at most near the heat sources involved during said transient phases of said electric machine. 2. The electrical machine according to claim 1, wherein the heat sink comprises longitudinal tubes (9) housed in a peripheral portion (6) of the first set (1), said longitudinal tubes comprising said material (10) with phase change . 3. Electrical machine according to one of the preceding claims, wherein the heat sink comprises longitudinal housings (12) each disposed between two permanent magnets (5), said housing comprising said material (10) phase change. Electric machine according to one of the preceding claims, wherein the phase change material (11) is in the form of salts or in the form of organic or eutectic compounds having solid-liquid phase change temperatures of greater than about 100. of degree Celsius, typically between 150 ° C and 300 ° C. 5. Electrical machine according to one of the preceding claims, wherein the heat sink comprises, in addition to the material (11) phase change at least one element which is electrically conductive so as not to disturb the circulation of the field lines in said machine. 6. Electrical machine according to one of the preceding claims, wherein the material (11) phase change is contained in a sealed metal envelope. 7. Electrical machine according to claim 2, wherein the first set comprises a magnetic circuit (3) and an electric circuit (4), the electric circuit consisting of a winding of a conductive wire around the poles (7) of the circuit. magnetic (3). 8. Electrical machine according to one of the preceding claims, wherein said first set (1) is a stator and the second set (2) is a rotor. 9. AC or AC machine such as a generator-starter, an alternator, a pump comprising an electric machine according to one of the preceding claims. 10. Motor of an aircraft, such as a helicopter, comprising a starter-generator according to the preceding claim.