阅读说明：本技术 用于涡轮机启动器/发电机的具有相变材料的电机 (Electric machine with phase change material for a turbine starter/generator ) 是由 托马斯·克洛诺夫斯基 凯莫·塞尔吉耶 于 2018-05-03 设计创作，主要内容包括：一种电机,包括定子(1)和转子(2),所述定子和所述转子配置成被驱动以相对于彼此旋转,转子(2)包括多个永磁体(5),转子进一步包括磁路(3),所述磁路包括向转子(2)延伸的磁极(7),该电机包括：环绕每个磁极(7)的、导电元件的绕组；和布置在导电元件内部和/或导电元件之间的至少一个散热器(8),该散热器包括相变材料。(An electric machine comprising a stator (1) and a rotor (2), which are configured to be driven for rotation relative to each other, the rotor (2) comprising a plurality of permanent magnets (5), the rotor further comprising a magnetic circuit (3) comprising magnetic poles (7) extending towards the rotor (2), the electric machine comprising: a winding of conductive elements surrounding each pole (7); and at least one heat sink (8) arranged inside and/or between the conductive elements, the heat sink comprising a phase change material.)

1. An electric machine comprising a stator (1) and a rotor (2) configured to be driven for rotation relative to each other, the rotor (2) comprising a plurality of permanent magnets (5), the stator further comprising a magnetic circuit (3) comprising magnetic poles (7) extending towards the rotor (2), the electric machine comprising: a winding (4, 50') of conductive elements surrounding each pole (7); and at least one heat sink (8, 8', 8 ") arranged inside and/or between the electrically conductive elements, the heat sink comprising a phase change material (82).

2. The electric machine of claim 1, comprising a heat sink (8, 8', 8 ") arranged between the conducting elements, the heat sink being substantially cylindrical, the heat sink extending along the conducting elements.

3. an electric machine as claimed in any one of claims 1 or 2, in which the winding is a set of hollow cylindrical wires.

4. An electric machine as claimed in any one of claims 1 or 2, in which the windings are hollow bar windings.

5. An electric machine as claimed in claim 4, wherein the winding is formed as one piece and is preferably obtained according to an additive manufacturing method.

6. A machine as claimed in any of claims 1 to 5, said phase change material being capable of changing physical state between solid and liquid states within a given temperature range.

7. The electric machine according to any of claims 1-6, wherein the phase change material (82) is in the form of a salt or an organic or eutectic compound having a solid-liquid phase transition temperature above about one hundred degrees Celsius, which is adjusted according to constraints of use of the electric machine, typically between 100 and 300 ℃.

8. the electric machine according to any of claims 1-7, wherein the heat sink comprises at least one element, other than the phase change material (82), which is electrically conductive so as not to disturb the circulation of the magnetic field lines in the electric machine.

9. The machine according to any of claims 1-8, wherein the phase change material (11) is contained in a sealed metal housing (81), which is electrically or electrically non-conductive and thermally conductive.

10. The electric machine according to claim 9, wherein at least one heat sink (8, 8', 8 ") is arranged inside the electrically conductive element, the phase change material of the thermal conductor being accommodated in a sealed metal housing (81).

11. A direct current or alternating current electric machine, such as a starter-generator, an alternator, a pump comprising an electric machine according to any one of claims 1 to 10.

12. An engine for an aircraft, such as a helicopter, comprising a starter-generator according to claim 11.

Technical Field

The present invention relates to aircraft engines, and more particularly to helicopter engines. The invention relates in particular to an electric machine mounted on a helicopter engine, which can perform the function of generating electric energy and/or of motorizing some mechanical components. These motors may be starter-generators, starters, alternators or electric pumps, these motors being direct current motors or alternating current motors.

Background

The engine of an aircraft comprises an electric machine comprising a rotor (rotating part) and a stator (fixed part), the stator comprising a magnetic circuit and an electric circuit, the electric circuit consisting of a set of windings consisting of conducting wires.

In a known manner, such electric machines have a transient operating phase, mainly encountered during the starting or acceleration sequence of the aircraft engine or of some device comprised by the aircraft engine.

During these transient phases, the electrical machine subjected to such high stresses emits a large amount of heat harmful to itself, mainly in the electrical circuit and/or on the permanent magnets (if they are contained in the electrical machine).

In a known manner, in order to promote heat dissipation and thus ensure the integrity of the machine, the elements making up the machine are oversized, which can have a negative effect on the mass and bulk of the machine.

In practice, the structure and dimensions of the machine are determined by its thermal resistance, which is mainly a function of the amplitude of the current it supports in the conductive windings (for example, a machine operating at a mains voltage of 28Vdc and a power of several kW or kVA will generate high intensity currents of up to hundreds of amperes).

In order to optimize the heat dissipation of the electrical machine, various solutions are known and used.

The first solution uses natural convection, cooling by means of finned radiators around the motor to have a large exchange surface with the surrounding environment. However, this solution has a large volume and weight and generally requires an air flow around the motor.

a second solution is to carry out forced convection by adding a fan connected to the motor shaft, the air flow of which thus generated will be exchanged with the motor external and/or internal components. However, this solution is bulky and can create an additional source of damage.

The third option is forced cooling by injecting a liquid (water, oil, fuel, etc.) circulating inside the machine or in dedicated pipes around it, and mostly requires additional exchangers to ensure cooling of this liquid. However, this solution also has a large volume and weight and is invasive and requires relatively shorter maintenance steps (i.e. management of the seal).

A fourth solution is cooling by means of thermoelectric modules (Peltier) effect). However, with this solution, cooling can only be achieved in localized areas, and there is also a need for a stable power supply that enables the supply of thermoelectric power.

Therefore, the existing solutions are not satisfactory in aeronautical applications, that is to say in the environment of on-board systems with high constraints on compactness, weight and reliability.

Disclosure of Invention

The invention makes it possible to reduce the weight and size of the electrical machine of an aircraft engine and to improve the electromagnetic performance.

To this end, the invention proposes an electric machine comprising a stator and a rotor configured to be driven in rotation with respect to each other, the rotor comprising a plurality of permanent magnets, the stator further comprising a magnetic circuit comprising magnetic poles extending towards the rotor, the electric machine comprising: a winding of conductive elements surrounding each pole; and at least one heat sink disposed inside and/or between the conductive elements, the heat sink comprising a phase change material.

The invention is advantageously achieved by the following features, alone or in any of their technically possible combinations.

A heat sink is disposed between the conductive elements, the heat sink being substantially cylindrical, and the heat sink extending along the conductive elements.

The winding is a set of hollow cylindrical wires.

The winding is a hollow bar winding (barre creux).

The winding is formed as one piece and is preferably obtained according to an additive manufacturing method.

The phase change material is in the form of a salt or an organic or eutectic compound having a solid-liquid phase transition temperature above about one hundred degrees celsius, which is adjusted according to the constraints of the use of the electric machine, typically between 100 and 300 ℃.

In addition to the phase change material, the heat sink comprises at least one element that is electrically conductive so as not to disturb the circulation of the magnetic field lines in the electric machine.

Phase change materials are capable of changing physical state between solid and liquid states within a given temperature range.

The phase change material is contained in a sealed metal enclosure that is either electrically conductive or electrically non-conductive, and is thermally conductive.

The heat sink is arranged inside the electrically conductive element, the phase change material of the thermal conductor being accommodated in a thermally and electrically conductive, sealed metal housing.

The invention also relates to a direct current motor or an alternating current motor, such as a starter-generator, an alternator and a pump comprising a motor according to the invention.

And the invention also relates to an engine for an aircraft, such as a helicopter, comprising a starter-generator according to the invention.

The use of phase change materials enables the cooling material to be as close as possible to the heat generating element. In fact, by reaching its melting temperature, the phase change material therefore absorbs a large amount of heat by transforming from the solid state to the liquid state. Heat transfer will occur between the heat generating element and the phase change material.

The invention makes it possible to reduce the overall weight of the aircraft engine by reducing the weight of the electric machine. In particular, the weight of the ferromagnetic components inside the machine (used in the magnetic circuit of the machine) and the weight of the copper (used in the windings of the circuit) can be reduced.

In fact, by optimizing the heat transfer so that it is as close as possible to the element subjected to the highest temperature rise, it is possible to reduce the weight and the bulk of the machine.

Furthermore, without adding additional systems (i.e., exchangers, finned radiators), the weight balance, bulk and reliability of the motor are compromised by the additional systems.

drawings

other characteristics, objects and advantages of the invention will become apparent from the following description, purely by way of illustration and not by way of limitation, with reference to the accompanying drawings, in which:

Fig. 1 shows a schematic cross-sectional view of an electrical machine according to an embodiment of the invention;

Fig. 2a and 2b show diagrams of a conductive element of an electrical machine according to the invention;

Fig. 3a, 3b, 3c show cross-sectional views of wires constituting a winding of an electrical machine according to the invention;

Fig. 4 and 5 show diagrams of hollow bar windings according to two variants of an electric machine according to the invention;

Fig. 6 shows a graph of the temperature rise in the groove of a stator containing windings and phase change material as a function of the thermal stress duration, i.e. the transient phase of the electrical machine in connection with the start-up of the aircraft engine.

Throughout the drawings, similar elements have the same reference numerals.

Detailed Description

In the following, the term "phase change material" means a material capable of changing physical state in a given temperature range, which will absorb a large amount of thermal energy from its surroundings to change from a solid to a liquid state and recover part of the thermal energy when the material cools down as it changes from a liquid to a solid state. These phase change materials are salts, which may include nitrates or hydroxides. The change of the material from the solid state to the liquid state occurs at a temperature in excess of one hundred degrees celsius to about 300 degrees celsius.

Fig. 1 shows an electrical machine according to an embodiment of the invention. Such electric machines are used in particular in aircraft engines.

The 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. The magnetic circuit 3 comprises a generally cylindrical peripheral portion 6 and poles 7 extending towards the rotor 2, the stator 1 comprising an electric circuit 4, the electric circuit 4 comprising a winding of N conductive elements 41 surrounding each pole 7 of the magnetic circuit 3. In this figure, the conductive element 41 has a cylindrical cross-section but other cross-sections are also conceivable.

The rotor 2 carries permanent magnets 5. In fig. 1, the motor comprises 6 permanent magnets 5, but different numbers are also conceivable.

The topology of this kind of machine makes it possible to operate in generator mode (i.e. the rotor 2 is rotated by an external mechanical moment and the variation of the magnetic flux in the circuit 4 induces a current) or in engine mode (i.e. the power supply of the circuit 4 generates a magnetic flux through the magnetic circuit 3, the interaction of which with the magnetic flux from the magnets 5 generates a rotation of the rotor 2, thus generating a mechanical moment externally).

In order to facilitate, in particular, the heat dissipation of the electrical machine during the transient phase described above, hollow conductive elements for the windings and at least one heat sink 8 housed inside the at least one conductive element and/or arranged between the conductive elements are provided (see fig. 2a and 2b, which depict a heat sink between the conductive elements 41, with or without a heat sink 8 inside the conductive elements).

In particular, in the example of fig. 2a, a cylindrical heat sink 8 extends in the space arranged between the conductive elements 41, which themselves have the shape of cylindrical wires. The heat sink 8 extends along the conductive elements 41 in an extension direction substantially parallel to those conductive elements.

As depicted in fig. 3a, 3b, 3c, the heat sink 8, 8', 8 "comprises a housing 81, 81', 81" containing a phase change material 82. The housing 81, 81', 81 "is sealed to hold and confine the material in the liquid state.

In a non-limiting manner, in fig. 3a, the heat sink is cylindrical to accommodate the conductive wires of the winding, which are also cylindrical. Of course, other shapes are possible and depend on the shape of the conductive element: such as

A diamond shape in fig. 3b, such as a star shape in fig. 3 c.

Depending on the application, more particularly in the context of high-power electrical machines for more electrical applications of aircraft, the stator windings (i.e. the windings of the stator: the electrical circuit) may advantageously be of a topology known as "bar windings"; that is to say the coils of the cylindrical wire are replaced by massive, uniform and rigid windings in order to have a better slot filling ratio (i.e. equal to the ratio of effective copper surface/total slot surface) and thus in order to enable an increase in the electrical power for the same weight of the machine or to minimize the copper weight required for a constant power.

The heat dissipation problem in this case is much more severe than in the case of windings consisting of N cylindrical wires, because when the bar windings are supplied with a relatively high frequency alternating current in excess of kHz, the joule losses increase by the "skin effect" (i.e. the apparent resistance of the conductor decreases as the current is concentrated more and more around the conductor during an increase in the power frequency).

fig. 4 depicts a bar winding 50, which is composed of two rigid conductors 50a and 50b plated together. The shape of the two conductors 50a, 50b is such that the two conductors 50a, 50b define a housing 51 which enables a heat sink (not shown) to be housed inside it. In this figure, the housing 51 is "star" shaped, but may have another shape.

Advantageously, the bar winding is formed as one piece and comprises one or more bars, as depicted in fig. 5. Further, in this figure, the bar winding includes a housing in the shape of a "diamond".

Advantageously, the bar winding is formed as a whole or comprises a set of unit bars, and is obtained by an additive manufacturing method (i.e. "selective laser melting" of the SLM type or similar) which enables complex shapes to be made inside the winding, promoting optimization of the heat transfer (i.e. an increase in the exchange surface between the phase change material and the conductor), and therefore the housing 51 contains a heat sink and therefore enables a limited rise in temperature and ensures a high level of reliability (i.e. in particular the strength of the winding insulation).

in the case of a heat sink arranged inside the electrically conductive element, the housing, which itself is metallic and a good conductor, and the phase change material must as far as possible not disturb the circulation of the magnetic lines of force in the magnetic circuit.

Also in this case, the phase change material is by definition an electrical insulator, and in addition to the phase change material, the heat sink may comprise electrically conductive elements (e.g. carbon nanotubes) to also enable free circulation of the magnetic field lines in the magnetic circuit of the motor.

However, where a heat sink is provided between the conductive elements, the housing is insulated so as not to facilitate the transfer of current.

The phase change material is in the form of a salt or an organic compound or eutectic compound having a solid-liquid phase transition temperature above about one hundred degrees celsius, the solid-liquid phase transition temperature typically being preferably between 100 ℃ and 300 ℃. The phase change material may be, for example, a nitrate or hydroxide (LiNO)₃、NaNO₃、Li₂CO₃...), preferably with graphite.

Fig. 6 depicts the rise in temperature with time duration:

Curve a corresponds to the rise in winding temperature without the heat sink;

The dotted curve corresponds to the rise in radiator temperature;

the solid curve corresponds to the rise in temperature of the winding with the heat sink.

In fig. 6, the network of curves corresponds to a plurality of thermal resistances called "Rth". This thermal resistance represents the efficiency of heat transfer from one medium to another. The lower the value of Rth, the more efficient the heat transfer occurs. In fig. 6, the thermal resistance Rth increases from a to C.

Temperatures above 200 ℃ are observed to be reached without a heat sink, which may for example cause degradation of the insulation of the winding. By adding a heat sink and taking into account the optimized thermal resistance between the heat sink and the support, the maximum temperature reached on the sensitive components is kept below its limit temperature.

In a complementary manner, in addition to housing the heat sink represented by the phase change material, the heat sink may be arranged at other positions of the motor inside the bar winding, as described in document FR3012698 in the name of the applicant.

An electrical machine having stator windings has been described herein. Of course, the invention also applies to electrical machines having rotor windings, such as those known as wound rotor synchronous machines (i.e. in this case the permanent magnets are advantageously replaced by electromagnets to generate magnetic flux).

The invention also relates to a direct current motor or an alternating current motor, such as a starter-generator, an alternator and a pump comprising a motor as described above.

The invention also relates to an engine for an aircraft, such as a helicopter, comprising an electric machine according to the invention.