Aircraft propulsion system comprising a gas turbomachine and an electric machine with a cooling system including a main coupling element and associated operating method

Abstract

An aircraft propulsion assembly (1) comprising at least one propulsion element (10), a gas turbomachine (T) configured to drive the propulsion element (10) in rotation, an electric machine (M), mounted downstream of the gas turbomachine (T), comprising a shaft (M1) fixed in rotation to the gas turbomachine (T), the electric machine (M) being mounted in an enclosure (2) supplied by a cooling airflow (FR) and at least one cooling system for the electric machine (M), mounted in the enclosure (2), comprising at least one ventilation element (3), at least one main coupling element (4) configured, according to a coupling position (P1), to couple the shaft (M1) and the ventilation element (3) in order to drive it in rotation and, according to a decoupling position (P2), to decouple the shaft (M1) and the ventilation element (3) in order not to drive it in rotation. Figure from the summary: Figure 2

Description

Title of the invention: Propulsion assembly for aircraft comprising a gas turbomachine and an electric machine with a cooling system comprising a main coupling member and associated method of use Technical field

[0001] The present invention relates to the field of propulsion units for aircraft, in particular, a propulsion unit comprising a gas turbomachine associated with an electric machine capable of operating as a motor to provide electric propulsion or as a generator to power, for example, an electric battery or an electrical network of the aircraft.

[0002] In a known manner, with reference to [Fig. 1], a propulsion assembly 100 is known comprising a gas turbomachine T driving a propulsion member 10 to provide propulsion for an aircraft. The gas turbomachine T extends axially along an axis X and is a double-flow type. For this purpose, the gas turbomachine T comprises a primary vein VI in which a primary flow F1 from the combustion chamber (not shown) circulates and a secondary vein V2 in which a secondary flow F2 circulates which has been accelerated without circulating through the combustion chamber. The gas turbomachine T comprises a low-pressure body LP, comprising a low-pressure compressor 11 and a low-pressure turbine 14, and a high-pressure body HP, comprising a high-pressure compressor 12 and a high-pressure turbine 13.

[0003] The propulsion assembly 100 also comprises an electrical machine M, mounted downstream of the gas turbomachine T, comprising a shaft, connected to the low pressure body LP or to the high pressure body HP of the gas turbomachine T. An electrical machine M comprises electrical components which must be cooled during its use. Cooling is particularly critical given that the electrical machine M is positioned close to the primary vein V1 whose primary flow Fl, coming from the combustion chamber, has a high temperature.

[0004] For this purpose, it has been proposed to mount the electrical machine M in an enclosure, 101 for example of conical shape called a “plug”, and to supply it with a flow of cooling air FR coming from the secondary vein V2, that is to say, coming from the secondary flow F2 whose temperature is lower than that of the primary flow FL

[0005] In practice, the flow rate of the cooling air flow FR depends on the flow rate of the secondary flow F2 which itself depends on the speed of the gas turbomachine T. In practice, this presents a disadvantage given that the cooling requirements of the electric machine M are decorrelated from the speed of the gas turbomachine T.

[0006] Furthermore, the cooling of an electric machine M must be carried out in a homogeneous manner in order to avoid the appearance of hot spots. In practice, the areas of the electric machine M which are far from the inlet of the cooling air flow FR in the enclosure 101 are insufficiently cooled, which affects the overall efficiency of the electric machine M or its range of use.

[0007] The invention thus aims to eliminate at least some of these drawbacks by proposing a propulsion unit allowing optimal cooling of an electric machine for any operating speed of the turbomachine. PRESENTATION OF THE INVENTION

[0008] The invention relates to a propulsion unit for aircraft comprising: • At least one propulsion member configured to participate in the propulsion of the aircraft by accelerating an air flow circulating along a longitudinal axis from upstream to downstream, • A gas turbomachine configured to rotate the propulsion member, the gas turbomachine comprising a low-pressure body, a high-pressure body and a combustion chamber, the gas turbomachine being a double-flow type and comprising a primary vein in which a primary flow from the combustion chamber circulates, and a secondary vein in which a secondary flow bypassing the combustion chamber circulates, • An electric machine, mounted downstream of the gas turbomachine, comprising a shaft integral in rotation with the gas turbomachine, the electric machine being mounted in an enclosure supplied by a flow of cooling air from the secondary vein, and • At least one cooling system for the electrical machine, mounted in the enclosure, comprising: • at least one ventilation member configured to be driven in rotation in the enclosure by the shaft, • At least one main coupling member configured, according to a coupling position, to couple the shaft and the ventilation member in order to drive it in rotation and, according to a decoupling position, to decouple the shaft and the ventilation member in order not to drive it in rotation.

[0009] This advantageously allows the electric machine and / or its enclosure to be forcibly ventilated with a sufficient air flow rate. Advantageously, even when the gas turbomachine is switched off, the electric machine can be used as a motor to rotate the ventilation member and cool the enclosure. Furthermore, thanks to the main coupling member, the ventilation can be decoupled during of certain phases of operation of the gas turbomachine, in particular, at very high speed and at low speed.

[0010] In the prior art, the cooling air flow depends directly on the speed of the gas turbomachine. As a result, the cooling air flow is not always in line with the cooling requirements. Thanks to the main coupling member, it is possible to decouple the ventilation member to drive it at a rotation speed corresponding to the cooling requirements.

[0011] Preferably, the shaft having a rotation speed, the main coupling member is configured to switch to the decoupling position when the rotation speed is greater than a predetermined high threshold. This makes it possible to protect the ventilation member which is liable to be damaged at very high speed. This makes it possible to avoid using a heavy and bulky ventilation member which can be driven at high speed.

[0012] Preferably, the shaft having a rotational speed, the main coupling member is configured to switch to the decoupling position when the rotational speed is lower than a predetermined low threshold. At a low shaft speed, the forced ventilation is insufficient. The main coupling member makes it possible to achieve decoupling in order to allow independent driving of the shaft of the electrical machine.

[0013] Preferably, the main coupling member is chosen from the assembly comprising: a powder visco-coupler, a mechanical disc clutch, a centrifugal coupler, a freewheel, a magnetic coupler, a splined shaft coupled to a longitudinal actuator. Such a main coupling member makes it possible to switch positions precisely and automatically for a predetermined speed range.

[0014] According to a preferred aspect, the cooling system comprises an auxiliary power source configured to rotate the ventilation member independently of the shaft. Thus, advantageously, the ventilation member can be rotated at a predefined speed and controlled by the auxiliary source when the shaft is rotated at a low speed potentially insufficient to ensure optimal cooling functions.

[0015] Preferably, the cooling system comprises an auxiliary coupling member, mounted between the auxiliary power source and said ventilation member, configured, according to a coupling position, to couple the auxiliary power source and said ventilation member in order to drive it in rotation and, according to a decoupling position, to decouple the auxiliary power source and said ventilation member in order not to drive it in rotation. Thus, the main coupling member and the auxiliary coupling member make it possible to ensure that the ventilation member is only driven by one driving source at a time, which limits the risk of damage.

[0016] Preferably, the cooling system comprises at least one multiplication member, mounted between the shaft and the ventilation member, configured to rotate said ventilation member at a speed different from that of the speed of said shaft. Preferably, the multiplication member has a multiplication coefficient greater than 1 so as to accelerate the ventilation member and obtain improved ventilation performance. This is particularly relevant when the shaft is driven at a speed which is low.

[0017] According to one aspect, the multiplication member is mounted between the main coupling member and the ventilation member. According to another aspect, the multiplication member is mounted between the shaft and the main coupling member.

[0018] Preferably, the assembly comprises at least one overall coupling member, mounted between the shaft and the gas turbomachine, configured, according to a coupling position, to couple the gas turbomachine to the shaft to secure them in rotation and, according to a decoupling position, to decouple the gas turbomachine from the shaft. Such an overall coupling member makes it possible to couple / decouple the electric machine from the gas turbomachine as required. This is particularly advantageous for avoiding taking mechanical power from the gas turbomachine in certain operating modes.

[0019] Preferably, the cooling system comprises at least one ventilation member mounted downstream of the electric machine. This advantageously makes it possible to generate a suction of the cooling air flow while maximizing the use of the space available in the “plug” enclosure. The electric machine can thus be mounted as close as possible to the gas turbomachine, with more advantageous aerodynamic lines.

[0020] Preferably, the cooling system comprises at least one first ventilation member mounted upstream of the electrical machine and at least one second ventilation member mounted downstream of the electrical machine. Such a “tandem” assembly makes it possible to optimize the space available in the enclosure while allowing optimal circulation of the cooling air flow. This also makes it possible to define two compression stages in order to limit the compression ratio per stage in order to avoid operating the stages under degraded operating conditions which could lead to suboptimal cooling.

[0021] According to one aspect of the invention, the enclosure comprises a peripheral separating wall defining at least one inner sub-enclosure, in which the electrical machine is mounted, and an outer sub-enclosure. At least one first ventilation member is mounted in the outer sub-enclosure and at least one second ventilation member is mounted in the inner sub-enclosure so as to cool optimally each sub-enclosure. The outer sub-enclosure advantageously fulfills a thermal barrier function by protecting the inner sub-enclosure in which the electrical machine is mounted against the heat coming from the primary vein.

[0022] The invention also relates to a method of using a propulsion unit for an aircraft as presented previously, the shaft being coupled to the ventilation member in order to drive it in rotation, the method comprising a step of decoupling the ventilation member from the shaft in order not to drive it in rotation. Thus, for certain operating modes of the propulsion unit, the ventilation member can be decoupled to avoid any risk of damage or to improve ventilation.

[0023] The invention further relates to a method of using an aircraft propulsion unit as presented previously, the shaft being coupled to the ventilation member in order to drive it in rotation, the method comprising steps consisting of: decouple the ventilation member from the shaft when the shaft rotation speed is below a predetermined low threshold drive the ventilation member in rotation by an auxiliary power source independently of the shaft.

[0024] Thus, at low speed, the auxiliary power source takes over from the shaft to ensure satisfactory ventilation.

[0025] The invention also relates to a method of using a propulsion unit for an aircraft as presented previously, the method comprising steps, according to an engine mode, consisting of: decouple the shaft from the gas turbine engine, and the ventilation member being coupled to the shaft, driving the ventilation member in rotation by rotation of the shaft so as to cool the electrical machine.

[0026] Thus, when the gas turbomachine is switched off, the electric machine can be used in engine mode to cool the electric machine given that the cooling air flow, coming from the secondary flow, has a low flow rate.

[0027] The invention also relates to a method of using a propulsion unit for an aircraft as presented previously, the method comprising steps, according to a generator mode, consisting of: coupling the shaft to the gas turbine engine so that the electric machine generates electrical energy, the ventilation member being decoupled from the shaft.

[0028] Thus, when the gas turbomachine is in operation, the electric machine can be used in generator mode to generate electrical energy. No mechanical power is advantageously taken from the shaft for ventilation. in order to maximize generation. Advantageously, when the gas turbomachine is in operation the cooling airflow, from the secondary flow, has a high flow rate which is sufficient to ensure cooling.

[0029] The invention relates to a method of using an aircraft propulsion unit as presented previously, in which the shaft of the electric machine rotates in opposite directions in generator mode and in motor mode. PRESENTATION OF FIGURES

[0030] The invention will be better understood on reading the description which follows, given by way of example, and referring to the following figures, given by way of non-limiting examples, in which identical references are given to similar objects.

[0031] [Fig.l] is a schematic representation of a propulsion assembly according to the prior art.

[0032] [Fig.2] is a schematic representation of a propulsion unit according to a first embodiment of the invention.

[0033] [Fig.3] is a close-up schematic representation of the electric machine of [Fig.2],

[0034] [Fig.4] is a schematic representation of the coupling / decoupling positions as a function of the speed of the shaft of the electric machine.

[0035] [Fig. 5] is a schematic representation of a propulsion unit according to a second embodiment of the invention.

[0036] [Fig.6] is a schematic representation of a variant of the second embodiment of the invention of [Fig.5].

[0037] [Fig.7] is a schematic representation of a propulsion unit according to a third embodiment of the invention according to a first variant.

[0038] [Fig.8] is a schematic representation of a propulsion unit according to the third embodiment of the invention according to a second variant.

[0039] [Fig.9] is a schematic representation of a propulsion unit according to a fourth embodiment of the invention.

[0040] [Fig. 10] is a schematic representation of a propulsion unit according to a fifth embodiment of the invention.

[0041] [Fig. 11] is a schematic representation of a propulsion unit according to a first variant of the fifth embodiment of the invention.

[0042] [Fig. 12] is a schematic representation of a propulsion unit according to a second variant of the fifth embodiment of the invention.

[0043] [Fig. 13] and [Fig. 14] are schematic representations of the propulsion unit according to the second embodiment of the invention during a coupling / decoupling of the main coupling member.

[0044] [Fig. 15] and [Fig. 16] are schematic representations of the propulsion unit according to the fourth embodiment of the invention during coupling / decoupling of the overall coupling member.

[0045] It should be noted that the figures set out the invention in detail to implement the invention, said figures can of course be used to better define the invention where appropriate. DETAILED DESCRIPTION OF THE INVENTION

[0046] The invention relates to a propulsion assembly for an aircraft, the aircraft being able to comprise one or more propulsion assemblies to enable its propulsion.

[0047] With reference to [Fig. 2], a longitudinal sectional view of a propulsion unit 1 according to a first embodiment of the invention is shown. The propulsion unit 1 comprises a propulsion member 10 configured to participate in the propulsion of the aircraft by accelerating an air flow F circulating along a longitudinal axis X from upstream to downstream. In this example, the propulsion member 10 is in the form of a fan which is ducted, but it goes without saying that the invention also applies to an unducted propeller.

[0048] With reference to [Fig. 2], the gas turbomachine T is configured to rotate the propulsion member 10. The gas turbomachine T comprises a low-pressure spool LP, a high-pressure spool HP and a combustion chamber (not shown). In particular, the low-pressure spool LP comprises a low-pressure compressor 11 and a low-pressure turbine 13 while the high-pressure spool HP comprises a high-pressure compressor 12 and a high-pressure turbine 14. The gas turbomachine T is a double-flow type and comprises a primary vein VI, in which a primary flow F1 from the combustion chamber circulates, and a secondary vein V2 in which a secondary flow F2 circulates bypassing the combustion chamber, in particular, accelerated by the propulsion member 10.

[0049] Such a gas turbomachine T is known to those skilled in the art and will not be presented in further detail.

[0050] According to the invention, the propulsion assembly 1 comprises an electric machine M, mounted downstream of the gas turbomachine T, comprising a shaft M1 integral in rotation with the gas turbomachine T, in particular, with the low pressure body LP or the high pressure body HP. The electric machine M is configured to operate, on the one hand, in generator mode in order to generate electrical energy from a mechanical torque received on its shaft M1 and, on the other hand, in motor mode to drive the shaft M1 from an electrical source (battery, electrical network, etc.). It nevertheless goes without saying that the invention applies to an electric machine M func- giving only in a generator mode or a motor mode. The general structure of an electric machine M is known to those skilled in the art and will not be presented in more detail. In this example, the electric machine M comprises a mobile rotor part, integral with the shaft M1, and a fixed stator part (not shown). Subsequently, the shaft M1 of the electric machine M has a rotation speed VM.

[0051] With reference to [Fig.2], the electrical machine M is mounted in an enclosure 2 supplied by a cooling air flow FR coming from the secondary vein V2, that is to say, coming from the secondary flow F2 which is, by nature, colder than the primary flow Fl. The enclosure 2 preferably has a conical shape but it goes without saying that it could be different.

[0052] Similarly, [Fig.2] shows an enclosure 2 which is open at its downstream end for the evacuation of the cooling air flow FR, but it goes without saying that the evacuation could be carried out in a different manner.

[0053] In this example, the cooling air flow FR is injected at an upstream part of the enclosure 2 via a cooling pipe (not shown) connected to the secondary vein V2. The cooling pipe could take various forms.

[0054] According to the invention, with reference to figures 2 and 3, the propulsion assembly 1 comprises a system for cooling the electric machine M, mounted in the enclosure 2, which comprises several ventilation members 3 configured to be driven in rotation in the enclosure 2 by the shaft ML. Thus, the cooling air flow FR is accelerated directly in the enclosure 2, which makes it possible, on the one hand, to promote the capture of calories and, on the other hand, to allow homogeneous cooling of the electric machine M independently of the injection position of the cooling air flow FR in the enclosure 2.

[0055] Preferably, the ventilation members 3 are configured to accelerate the cooling air flow FR peripherally in order to cool the outer surface of the electrical machine M homogeneously. The calories generated by the electrical machine M are thus captured in a practical manner.

[0056] The ventilation member 3 may be in the form of a fan, a bladed wheel or a pump.

[0057] According to the invention, with reference to figures 2 and 3, the cooling system comprises a main coupling member 4 configured: • according to a coupling position PI, to couple the shaft Ml and the ventilation member 3 in order to drive it in rotation and, • according to a decoupling position P2, to decouple the shaft M1 and the ventilation member 3 so as not to cause it to rotate.

[0058] Such a main coupling member 4 is advantageous given that it makes it possible to ensure cooling in coupling mode when the rotation speed VM of the electrical machine M is adapted. As soon as this rotation speed VM is no longer adapted, the main coupling member 4 makes it possible to achieve decoupling making it possible either to completely stop the rotation of the ventilation member 3, or to drive the ventilation member 3 at a rotation speed different from that of the shaft M1 and more adapted to the cooling needs of the electrical machine M as will be presented subsequently.

[0059] Thanks to the main coupling member, the ventilation can be stopped during certain operating phases of the gas turbomachine, in particular, during phases where the speed of the shaft M1 is too high or too low.

[0060] The main coupling member 4 is preferably configured to couple / decouple automatically as a function of the speed of the member that drives it, in particular, of the shaft M1. Thus, the coupling / decoupling steps can be practically associated with speed ranges for which the cooling air flow requirements FR are different. Preferably, the main coupling member 4 is chosen from the set comprising: a powder viscous coupling, a mechanical disc clutch, a centrifugal coupling, a freewheel, a magnetic coupler.

[0061] As illustrated in [Fig.4], the main coupling member 4 is configured to switch to the decoupling position P2 when the rotation speed VM is greater than a predetermined high threshold S2, preferably between 500 rpm and 30,000 rpm. Advantageously, high-speed decoupling makes it possible to avoid rotating the ventilation member 3 at excessive speeds likely to damage it.

[0062] Still with reference to [Fig. 4], the main coupling member 4 is configured to switch to the decoupling position P2 when the rotation speed VM is lower than a predetermined low threshold SI, preferably between 0 rpm and 20,000 rpm. Advantageously, low-speed decoupling makes it possible to drive the ventilation member 3 by another source at a higher speed to ensure optimal cooling as will be presented later.

[0063] According to a second embodiment, with reference to [Fig. 5], the cooling system comprises an auxiliary power source 5 configured to drive the ventilation member 3 in rotation independently of the shaft M1. Such an auxiliary power source 5 is of great interest when the main coupling member 4 is in the decoupling position P2, the ventilation member 3 being able to be driven at a speed different from that of the shaft M1, in particular, at a rotation speed determined by the auxiliary power source 5. The use of an auxiliary power source 5 is advantageous when the main coupling member 4 is in the decoupling position P2, the ventilation member 3 being able to be driven at a speed different from that of the shaft M1, in particular, at a rotation speed determined by the auxiliary power source 5. auxiliary power source 5 makes it possible to drive the ventilation member when the power on the shaft M1 is non-existent or insufficient, such as for example at low speed or when the turbomachine is switched off. The auxiliary power source 5 can take various forms, in particular, a low-power electric machine.

[0064] According to a variant, with reference to [Fig. 6], the cooling system comprises an auxiliary coupling member 4', mounted between the auxiliary power source 5 and said ventilation member 3, configured, according to a coupling position, to couple the auxiliary power source 5 and said ventilation member 3 in order to drive it in rotation and, according to a decoupling position, to decouple the auxiliary power source 5 and said ventilation member 3 in order not to drive it in rotation.

[0065] Advantageously, the main coupling member 4 and the auxiliary coupling member 4' make it possible to synergistically drive the ventilation member 3 entirely independently. Preferably, when driven by the shaft M1, the main coupling member 4 is in the coupling position while the auxiliary coupling member 4' is in the decoupling position ([Fig. 13]). Conversely, when driven by the auxiliary source 5, the main coupling member 4 is in the decoupling position while the auxiliary coupling member 4' is in the coupling position ([Fig. 14]).

[0066] Preferably, the auxiliary coupling member 4' is of the same nature as the main coupling member 4 presented previously. Preferably, the auxiliary coupling member 4' and the main coupling member 4 are configured so as not to be in coupling mode simultaneously. For this purpose, the speed ranges associated with the coupling modes of the coupling members 4, 4' are chosen appropriately.

[0067] With reference to Figures 7 and 8, according to a third embodiment, the propulsion assembly 1 comprises a multiplication member 6, mounted between the shaft M1 and the ventilation member 3, configured to rotate said ventilation member 3 at a speed different from that of the speed of said shaft M1, preferably higher. Such a multiplication member 6 advantageously makes it possible to increase the flow rate of the cooling air flow FR while using the rotation of the shaft M1 adapted to the motor / generator operating mode of the electric machine M. This is particularly advantageous when the speed of the shaft M1 is too low compared to the cooling requirements.

[0068] Such a multiplication member 6 makes it possible to obtain a higher flow rate without resorting to an auxiliary power source 5. It nevertheless goes without saying that an auxiliary power source 5 could be used with a multiplication member 6, the embodiments being compatible with each other. In this latter configuration, a so-called differential assembly makes it possible to drive the ventilation unit at speeds independent of the speeds of the main shaft (variable multiplication rate) and to ensure optimal ventilation at all points in the operating range.

[0069] The multiplication member 6 can be in various forms, in particular, an epicyclic train. A multiplication member 6 is associated with a multiplication coefficient which is preferably greater than 1. This multiplication coefficient can be fixed or variable.

[0070] According to a first aspect, with reference to [Fig.7], the multiplication member 6 is mounted between the main coupling member 4 and the ventilation member 3. This configuration makes it possible to use coupling members operating at low speed. It also makes it possible to isolate the multiplier if the reliability of the latter can impact the overall reliability of the system.

[0071] According to a second aspect, with reference to [Fig.8], the multiplication member 6 is mounted between the shaft M1 and the main coupling member 4. This configuration makes it possible to implement coupling members preferably operating at high speed.

[0072] With reference to [Fig.9], according to a fourth embodiment, the propulsion assembly 1 comprises a global coupling member 7, mounted between the shaft M1 and the gas turbine engine T, configured, according to a coupling position, to couple the gas turbine engine T to the shaft M1 to secure them in rotation and, according to a decoupling position, to decouple the gas turbine engine T from the shaft M1. Thus, the global coupling member 7 makes it possible to transmit mechanical power between the shaft M1 and the gas turbine engine T, in particular, with the low pressure spool LP or the high pressure spool HP. Preferably, the global coupling member 7 is of the same nature as the main coupling member 4 presented previously.

[0073] Preferably, when the electric machine M is in generator mode, the overall coupling member 7 is in the coupling position. When the electric machine M is in motor mode, the overall coupling member 7 may be in the coupling position if the electric machine M wishes to contribute to the propulsion or be in the decoupling position if the electric machine M wishes to provide a non-propulsive torque, in particular, for ventilation as will be presented later.

[0074] In the preceding embodiments, the shaft M1 extends only upstream so as to allow the ventilation members 3 to extend upstream of the electrical machine M to cool it optimally.

[0075] Alternatively, with reference to [Fig. 10], according to a fifth embodiment, the shaft M1 also extends downstream and the ventilation members 3 extend downstream of the electric machine M to allow air to be sucked in and bring the electric machine M as close as possible to the gas turbomachine T to gain compactness. In addition, there are space constraints which are lower downstream to allow the installation of a larger and more efficient ventilation unit 3. This finally makes it possible to optimize the use of the turbomachine's "plug" space in order to maintain advantageous aerodynamic lines for the turbomachine

[0076] According to a first variant, with reference to [Fig. 11], ventilation members 3 are positioned upstream and downstream (tandem position) of the electric machine M to improve cooling and optimize the available space while bringing the electric machine M as close as possible to the gas turbomachine T. This also makes it possible to form two compression stages and optimize the circulation of the cooling air flow FR. Such a configuration makes it possible to reduce the compression ratio per ventilation stage and to avoid entering degraded ventilation modes which could cause suboptimal cooling. In [Fig. 11], a main coupling member 4 is shown associated with each ventilation member 3 but it goes without saying that a single ventilation member 3 could be associated with a main coupling member 4.

[0077] According to a second variant, with reference to [Fig. 12], the enclosure 2 comprises a peripheral separating wall 8 defining at least one inner sub-enclosure 21, in which the electrical machine M is mounted, and an outer sub-enclosure 22. At least one ventilation member 3 is rotatably mounted in each sub-enclosure 21, 22 so as to ensure separate cooling. The outer sub-enclosure 22 advantageously makes it possible to form a thermal barrier, between the primary vein VI and the electrical machine M, which can be cooled independently.

[0078] In this example, the peripheral separation wall 8 comprises an upstream part 8a and a downstream part 8b which are separated by a slot 80 in which the ventilation member 3 extends, which is mounted in the external sub-enclosure 22 in order to ventilate it.

[0079] In [Fig. 12], for the sake of clarity, no main coupling member 4 is shown associated with each ventilation member 3, but it goes without saying that such a main coupling member 4 could be associated with one, several or each ventilation member 3.

[0080] Preferably, the ventilation member 3 associated with the external sub-enclosure 22 is mounted on an upstream portion of the shaft M1 of the electrical machine M and the ventilation member 3 associated with the internal sub-enclosure 21 is mounted on a downstream portion of the shaft M1 of the electrical machine M in order to optimize the size and compactness. Nevertheless, it goes without saying that the ventilation members 3 could be positioned all upstream or all downstream.

[0081] An example of implementation of a method of use according to the invention will be given below. now presented with reference to Figures 13 and 14. With reference to [Fig. 13], the shaft M1 is coupled to the ventilation member 3 in order to drive it in rotation. The method comprises a step consisting of: decouple the ventilation member 3 from the shaft Ml so as not to drive it in rotation, in particular, by switching the main coupling member 4 to decoupling mode, when the rotation speed VM of the shaft Ml is lower than the predetermined low threshold SI, drive the ventilation member 3 in rotation by an auxiliary power source 5 independently of the shaft Ml as illustrated in [Fig.14].

[0082] This advantageously makes it possible to provide a greater flow of cooling air FR with the auxiliary power source 5 when the rotation speed VM of the shaft M1 is low. Preferably, the main coupling member 4 is in the coupling position and then switched to the decoupling position. Conversely, the auxiliary coupling member 4' is in the decoupling position and then switched to the coupling position. Thanks to this exemplary implementation, cooling is improved even when the rotation speed VM is low, for example, when the aircraft is in the taxi phase or is moving at low speed.

[0083] According to another aspect of the invention, the electrical machine M is used in generator mode and receives mechanical energy via the gas turbomachine T thanks to the global coupling member 7 which is in the coupling position. According to an exemplary implementation with reference to FIGS. 15 and 16, the method comprises steps, according to a motor mode of the electrical machine M, consisting of: decouple the shaft Ml from the gas turbomachine T by switching the overall coupling member 7 to the decoupling position, and the ventilation member 3 being coupled to the shaft M1 by the main coupling member 4 in coupling mode, driving the ventilation member in rotation 3 by rotation of the shaft Ml so as to cool the electric machine M.

[0084] In this exemplary implementation, the electrical machine M can be dedicated to cooling, which is advantageous for effectively ventilating the enclosure 2, in particular, when the gas turbomachine T is switched off.

[0085] According to another example of implementation, the method comprises steps, according to a generator mode of the electrical machine M, consisting of: coupling the shaft Ml to the gas turbomachine T, by switching the overall coupling member 7 to the coupling position, so that the electric machine M generates electrical energy, the ventilation member 3 being decoupled from the shaft Ml.

[0086] Such an example of implementation makes it possible to use the mechanical energy provided by the Gas turbomachine T primarily for electrical power generation, with no power being taken for cooling. This configuration is advantageous in cases where the ventilation system may fail, or in cases where the supply conditions in the secondary flow are sufficient to ventilate the electric machine without the need to compress the air further through the ventilation system.

[0087] Preferably, the shaft M1 of the electrical machine M rotates in opposite directions in generator mode and in motor mode, making it possible to use “freewheel” type coupling systems for ventilation driven solely by the electrical machine.

[0088] It goes without saying that the multiplication member 6 could also be used in each of the configurations, in particular, when the speed VM is not sufficient to ensure optimal cooling.

Claims

Claims

1. Propulsion assembly (1) for aircraft comprising: • At least one propulsion member (10) configured to participate in the propulsion of the aircraft by accelerating an air flow (F) circulating along a longitudinal axis (X) from upstream to downstream, • A gas turbomachine (T) configured to rotate the propulsion member (10), the gas turbomachine (T) comprising a low pressure (LP) body, a high pressure (HP) body and a combustion chamber, the gas turbomachine (T) being a double flow and comprising a primary vein (VI) in which a primary flow (Fl) from the combustion chamber circulates, and a secondary vein (V2) in which a secondary flow (F2) circulates bypassing the combustion chamber, • An electric machine (M), mounted downstream of the gas turbomachine (T), comprising a shaft (Ml) integral in rotation with the gas turbomachine (T),the electric machine (M) being mounted in an enclosure (2) supplied by a cooling air flow (FR) from the secondary vein (V2), and • At least one cooling system for the electric machine (M), mounted in the enclosure (2), comprising: • at least one ventilation member (3) configured to be driven in rotation in the enclosure (2) by the shaft (Ml), • At least one main coupling member (4) configured, according to a coupling position (PI), to couple the shaft (Ml) and the ventilation member (3) in order to drive it in rotation and, according to a decoupling position (P2), to decouple the shaft (Ml) and the ventilation member (3) in order not to drive it in rotation.,

2. Propulsion assembly (1) according to claim 1, in which, the shaft (Ml) having a rotation speed (VM), the main coupling member (4) is configured to switch to the decoupling position (P2) when the rotation speed (VM) is greater than a predetermined high threshold (S2).

3. Propulsion assembly (1) according to one of claims 1 and 2, in which, the shaft (Ml) having a rotation speed (VM), the main coupling member (4) is configured to switch to the decoupling position (P2) when the rotation speed (VM) is lower than a predetermined low threshold (SI).

4. Propulsion assembly (1) according to one of claims 1 to 3, in which the main coupling member (4) is chosen from the assembly comprising: a powder visco-coupler, a mechanical disc clutch, a centrifugal coupler, a freewheel, a magnetic coupler.

5. Propulsion assembly (1) according to one of claims 1 to 4, in which the cooling system comprises an auxiliary power source (5) configured to drive the ventilation member (3) in rotation independently of the shaft (Ml).

6. Propulsion assembly (1) according to claim 5, wherein the cooling system comprises an auxiliary coupling member (4'), mounted between the auxiliary power source (5) and said ventilation member (3), configured, according to a coupling position, to couple the auxiliary power source (5) and said ventilation member (3) in order to drive it in rotation and, according to a decoupling position, to decouple the auxiliary power source (5) and said ventilation member (3) in order not to drive it in rotation.

7. Propulsion assembly (1) according to one of claims 1 to 6, in which the cooling system comprises at least one multiplication member (6), mounted between the shaft (Ml) and the ventilation member (3), configured to drive said ventilation member (3) in rotation at a speed different from that of the speed of said shaft (Ml).

8. Propulsion assembly (1) according to claim 7, in which the multiplication member (6) is mounted between the main coupling member (4) and the ventilation member (3).

9. Propulsion assembly (1) according to claim 7, in which the multiplication member (6) is mounted between the shaft (Ml) and the main coupling member (4).

10. Propulsion assembly (1) according to one of claims 1 to 9, comprising at least one overall coupling member (7), mounted between the shaft (Ml) and the gas turbomachine (T), configured, according to a coupling position, to couple the gas turbomachine (T) to the shaft (Ml) for the so- lidarize in rotation and, according to a decoupling position, to decouple the gas turbomachine (T) from the shaft (Ml).

11. Propulsion assembly (1) according to one of claims 1 to 10, in which the cooling system comprises at least one ventilation member (3) mounted downstream of the electric machine (M).

12. Propulsion assembly (1) according to one of claims 1 to 11, in which the cooling system comprises at least one first ventilation member (3) mounted upstream of the electric machine (M) and at least one second ventilation member (3) mounted downstream of the electric machine (M).

13. Propulsion assembly (1) according to one of claims 1 to 12, wherein, the enclosure (2) comprising a peripheral separating wall (8) defining at least one inner sub-enclosure (21), in which the electric machine (M) is mounted, and an outer sub-enclosure (22), at least one first ventilation member (3) is mounted in the outer sub-enclosure (22) and at least one second ventilation member (3) is mounted in the inner sub-enclosure (21).

14. Method of using a propulsion unit (1) for an aircraft according to one of claims 1 to 13, the shaft (Ml) being coupled to the ventilation member (3) in order to drive it in rotation, the method comprising a step consisting of: • decoupling the ventilation member (3) from the shaft (Ml) in order not to drive it in rotation.

15. Method of using a propulsion unit (1) for an aircraft according to claims 3 and 5, the shaft (Ml) being coupled to the ventilation member (3) in order to drive it in rotation, the method comprising steps consisting of: • decoupling the ventilation member (3) from the shaft (Ml) when the rotation speed (VM) of the shaft (Ml) is lower than a predetermined low threshold (SI) • driving the ventilation member (3) in rotation by an auxiliary power source (5) independently of the shaft (Ml).

16. Method of using a propulsion unit (1) for an aircraft according to the claim 10, the method comprising steps, according to a motor mode, consisting of: • decoupling the shaft (Ml) from the gas turbomachine (T), and • the ventilation member (3) being coupled to the shaft (Ml), driving the ventilation member (3) in rotation by rotation of the shaft (Ml) so as to cool the electric machine (M).

17. Method of using a propulsion unit (1) for an aircraft according to claim 10, the method comprising steps, according to a generator mode, consisting of: • coupling the shaft (Ml) to the gas turbomachine (T) so that the electric machine generates electrical energy, the ventilation member (3) being decoupled from the shaft (Ml).

18. Method of using a propulsion unit (1) for an aircraft according to claims 16 and 17, in which: • the shaft (Ml) of the electric machine (M) rotates in opposite directions in generator mode and in motor mode.

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