Aircraft propulsion system comprising a gas turbomachine, a fuel cell, two electric machines and a transmission system

Abstract

A propulsion assembly (1) comprising: a gas turbomachine (2); a transmission system (6) mechanically connected to a drive shaft (3) and a low-pressure shaft (4) of the gas turbomachine (2), the transmission system (6) being configured to define a transmission ratio (K) between a first rotational speed (V3) of the drive shaft (3) and a second rotational speed (V4) of the low-pressure shaft (4); a first electric machine (M1) configured to drive the drive shaft (3) in rotation; a second electric machine (M2) connected to the transmission system (6) and configured to modify the transmission ratio (K); and a fuel cell (7) powered by a flow of compressed air (A2) from the gas turbomachine (2), the fuel cell (7) being configured to electrically power the first electric machine (M1) and the second electric machine (M2). Abstract figure: Figure 1

Description

Title of the invention: Propulsion assembly for aircraft comprising a gas turbomachine, a fuel cell, two electric machines and a transmission system Technical field

[0001] The present invention relates to the field of propulsion units used for the propulsion of an aircraft and relates in particular to a propulsion unit comprising a gas turbomachine and a fuel cell.

[0002] Climate change is a major concern for many legislative and regulatory bodies around the world. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by various States. In particular, an ambitious standard applies both to new types of aircraft and those in circulation requiring the implementation of technological solutions in order to make them compliant with current regulations. Civil aviation has been mobilizing for several years now to make a contribution to the fight against climate change.

[0003] Technological research efforts have already made it possible to significantly improve the environmental performance of aircraft. The Applicant takes into consideration the impact factors in all phases of design and development to obtain less energy-intensive, more environmentally friendly aeronautical components and products whose integration and use in civil aviation have moderate environmental consequences with the aim of improving the energy efficiency of aircraft.

[0004] Consequently, the Applicant is constantly working to reduce its negative climate impact by using methods and operating virtuous development and manufacturing processes and minimizing greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity.

[0005] This sustained research and development work covers new generations of aircraft engines, the lightening of aircraft, particularly through the materials used and lighter on-board equipment, the development of the use of electrical technologies to ensure propulsion, and, as essential complements to technological progress, aeronautical biofuels.

[0006] To this end, the invention is the result of technological research aimed at very significantly improving the performance of aircraft and, in this sense, contributes to reducing the environmental impact of aircraft. For this, the invention relates to the field of aircraft comprising a hybrid propulsion unit comprising a fuel cell, for example, to power an electric propulsion machine.

[0007] In a known manner, an aircraft comprises one (or more) propulsion unit(s) to enable its movement from the acceleration of an air flow. The propulsion unit comprises a propulsion member connected to a transmission shaft, designated the drive shaft, itself connected to the engine of the aircraft. The propulsion member converts the rotational movement into an air flow which enables the propulsion of the aircraft. The propulsion unit also comprises an air inlet positioned in the case of a turboprop engine downstream of the propulsion member so as to benefit from the air flow to power a gas turbomachine.

[0008] In the context of the decarbonization of aircraft, a so-called "hybrid" architecture is known in which the propulsion unit comprises a gas turbomachine associated with a fuel cell to enable the generation of electrical energy in order to power in particular an electric propulsion machine. The fuel cell is powered by hydrogen and makes it possible to reduce the consumption of kerosene to ensure the propulsion of the aircraft.

[0009] A fuel cell is a device for carrying out an electrochemical reaction to generate electrical energy from a redox reaction. For this, the fuel cell is powered by an oxidizing fluid and a reducing fluid, for example dihydrogen and dioxygen, which circulate in a plurality of cells and react by means of a catalyst to form the electrochemical reaction and produce electrical energy.

[0010] In a known manner, the fuel cell must be supplied with a flow of pressurized oxygen. In this respect, a propulsion assembly is known in the prior art in which the fuel cell is supplied by a flow of air from a compressor of the gas turbomachine, making it possible to dispense with the addition of a compressor external to the propulsion assembly. However, in such a configuration, it is necessary for the gas turbomachine to operate so that the compressor can supply the fuel cell with the flow of compressed air, which may present a disadvantage, for example, when it is necessary to supply aircraft systems, such as avionics or cabin systems or an electrical machine of a system operating on the ground, for example, or to recharge a battery, without operating the propulsion unit.

[0011] The invention thus aims to eliminate at least some of these drawbacks by proposing a hybrid propulsion unit whose operation is optimal in all circumstances. The propulsion unit according to the invention makes it possible in particular to maintain at least partial operation, with a high level of safety, while limiting the greenhouse gas emissions. PRESENTATION OF THE INVENTION

[0012] The invention relates to a propulsion assembly for an aircraft extending along a longitudinal axis, the propulsion assembly comprising: • a gas turbomachine comprising: • a propulsion member mounted on a propulsion shaft, the propulsion member being configured to generate a thrust force for the aircraft, the propulsion shaft being configured to rotate at a first rotational speed, • a low pressure compressor and a low pressure turbine connected by a low pressure shaft, the low pressure compressor being configured to compress an incoming air flow and to generate a compressed air flow, the low pressure shaft being configured to rotate at a second rotational speed, • a combustion chamber, • a high-pressure compressor and a high-pressure turbine connected by a high-pressure shaft, the high-pressure compressor being configured to receive the flow of compressed air from the low-pressure compressor and generate a flow of supercompressed air so as to supply the combustion chamber, the high-pressure gas turbine being driven by a flow of exhaust air from the combustion chamber, • a transmission system mechanically connected, on the one hand, to the propulsion shaft and, on the other hand, to the low pressure shaft, the transmission system being configured to define a transmission ratio between the first rotation speed of the propulsion shaft and the second rotation speed of the low pressure shaft, • a first electrical machine connected to the propulsion shaft and configured to drive it in rotation, • a second electrical machine connected to the transmission system and configured to modify the transmission ratio, and • at least one fuel cell powered by the flow of compressed air from the low-pressure compressor of the gas turbomachine, the fuel cell being configured to electrically power directly or indirectly the first electric machine and the second electric machine.

[0013] The propulsion unit according to the invention can advantageously operate in different configurations, providing thermal, electric or mixed propulsion of the aircraft as needed. Thus, even in the event of a gas turbine engine failure, for example, the fuel cell can be supplied with a flow of compressed air to enable it to generate electrical energy, which can supply power to the first electric machine and the second electric machine to ensure the propulsion of the aircraft.

[0014] Thanks to the transmission system, the speed of the low pressure compressor can be adapted to provide the fuel cell with an optimal flow of compressed air in each configuration. The speed of the low pressure compressor can be different from the speed of the propulsion member thanks to the transmission ratio which can be adapted between the propulsion shaft and the low pressure shaft.

[0015] The fuel cell powered by an air flow from the gas turbomachine makes it possible to generate electrical energy which can be used by the first electrical machine and / or by the second electrical machine to determine the rotation speed of the propulsion shaft and the low pressure shaft. The electrical energy contributes to the propulsion of the aircraft, which makes it possible to limit the greenhouse gas emissions of the aircraft and thus to reduce its environmental impact.

[0016] In one embodiment, the propulsion assembly comprises an electrical distribution system electrically connecting the fuel cell, the first electrical machine and the second electrical machine, the electrical distribution system being configured to allow the fuel cell to electrically power the first electrical machine and the second electrical machine and / or to allow the first electrical machine and the second electrical machine to exchange electrical power flows. The electrical distribution system allows the second electrical machine to be powered by either the fuel cell or the first electrical machine, even when the gas turbine engine is not operating.The first electric machine can also advantageously directly supply the second electric machine with the electrical energy necessary to change the transmission ratio, for example when the fuel cell and the gas turbomachine are stopped.

[0017] In a preferred embodiment, the transmission system is in the form of an epicyclic gear train comprising a planetary gear, a plurality of satellite gears, a crown gear, and a planet carrier, the propulsion shaft is mechanically connected to the planet carrier, the low pressure shaft is mechanically connected to the planetary gear and the second electrical machine is connected to the crown, so as to adapt the transmission ratio between the planetary gear and the planet carrier by modifying the rotational speed of the crown. The use of an epicyclic gear train makes it possible, while maintaining a constant speed of the propulsion member, to operate the low pressure shaft of the gas turbine, simple and efficient way, at different speeds by deriving electrical energy through electrical machines.

[0018] According to one aspect, the second electrical machine controls the rotation speed of the crown in order to adapt the transmission ratio.

[0019] Preferably, the propulsion assembly comprises a declutching system mounted on the low-pressure shaft and configured to move between an engaged position in which the low-pressure compressor is secured to the low-pressure turbine and a declutched position in which the low-pressure compressor is detached from the low-pressure turbine, so as to decorrelate the rotation of the low-pressure compressor and the rotation of the low-pressure turbine. Such a declutching system advantageously makes it possible, in the declutched position, to prevent the low-pressure turbine from being driven when this is not necessary, for example in the case of operation of the fuel cell alone, which makes it possible to reduce the resistive force on the low-pressure shaft, thus making it possible to reduce energy losses and therefore to limit the supply of electrical energy by the first electrical machine.

[0020] In one embodiment, the propulsion shaft, the low pressure shaft and the high pressure shaft are coaxial.

[0021] The invention also relates to an aircraft comprising at least one propulsion unit as described previously.

[0022] The invention also relates to a method of operating the propulsion assembly as described previously, the combustion chamber of the gas turbomachine being switched off and the fuel cell being switched on, the method comprises: • a step of driving the propulsion shaft by the first electric machine, driving the low pressure shaft via the transmission system, • a step of generating the flow of compressed air by the low pressure compressor to supply at least the fuel cell.

[0023] Thanks to the invention, the propulsion assembly makes it possible to generate, even in the event of the gas turbomachine being stopped, electrical energy in the fuel cell, for example to supply an electrical network of the aircraft in order to ensure the operation of electrical equipment or to recharge an electric battery. When the aircraft is parked, for example, it is possible to generate electrical energy without using the gas turbomachine, which makes it possible to limit the greenhouse gas emissions of the aircraft, as well as the emissions of pollutants. Similarly, in the event of a breakdown of the gas turbomachine, for example, the propulsion assembly according to the invention makes it possible to ensure that the electrical machines are properly supplied to enable them to drive the propulsion member in rotation.

[0024] In one embodiment, in the first step, the second electric machine acts on the transmission system, which makes it possible to determine the ratio transmission between the propulsion shaft and the low pressure shaft.

[0025] Furthermore, the invention relates to a method of operating the propulsion unit as described above, the fuel cell being switched off and the combustion chamber being switched on, the method comprising: • a step of driving the propulsion shaft from the rotation of the low pressure shaft via the transmission system, and • a control step via the second electric machine of the transmission ratio of the transmission system between the low pressure shaft and the propulsion shaft.

[0026] Such an implementation mode corresponds to the conventional operation of a gas turbomachine in which the electrical machines make it possible to act on the transmission system to determine different rotation speeds of the propulsion shaft and the low pressure shaft. The second electrical machine thus makes it possible to apply a rotation speed of the propulsion member different from the speed of the high pressure turbine.

[0027] In one embodiment, the step of controlling the transmission ratio is carried out by an electrical distribution system electrically connected at least to the first electrical machine and to the second electrical machine. The electrical distribution system thus makes it possible to distribute the power between the two electrical machines to make it possible to apply a rotational speed of the propulsion member different from the speed of the high-pressure turbine.

[0028] The invention also relates to a method of operating the propulsion unit as described above, the fuel cell and the combustion chamber being ignited, the method comprises: • a step of driving the propulsion shaft from both the mechanical torque of the low pressure shaft and the mechanical torque supplied by the first electrical machine, the second electrical machine controlling the transmission ratio of the transmission system between the low pressure shaft and the propulsion shaft, • a step of generating the flow of compressed air by the low pressure compressor, so as to supply at least the fuel cell, and • a step of supplying electrical energy, by the fuel cell, to the first electrical machine and the second electrical machine.

[0029] Such an embodiment advantageously allows optimal operation of the gas turbomachine in which the combustion chamber operates at an air regime adapted and optimal for the fuel cell and in which the first electric machine and the second electric machine are electrically powered to provide additional electricity so as to reduce the thermal input of the turbine. bomachine. This operating mode thus makes it possible to limit both the aircraft's fuel consumption and its environmental impact.

[0030] The low pressure shaft is driven to generate the compressed air flow to power both the fuel cell to provide electrical energy to the electrical machines and the high pressure compressor to provide the supercompressed air flow to the combustion chamber.

[0031] Preferably, the rotational speed of the low pressure shaft is determined to provide a flow of compressed air adapted between the needs of the fuel cell and the gas turbomachine, the first electric machine providing an additional mechanical torque to obtain the desired thrust.

[0032] Finally, the invention relates to a method of operating the propulsion unit as described previously, the fuel cell and the combustion chamber being switched off, the method comprises: • a low pressure shaft drive step from the movement of the propulsion shaft, and • a step of generating electrical energy by the first electrical machine to supply an electrical network of the aircraft and / or a battery.

[0033] Such an implementation mode is similar to the operation of a wind turbine, in which the first electrical machine is used as an energy generator. PRESENTATION OF FIGURES

[0034] 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.

[0035] [Fig.l] is a schematic representation of a propulsion assembly according to one embodiment of the invention.

[0036] [Fig.2] is a schematic representation of a propulsion unit in which the transmission system is an epicyclic gear train.

[0037] [Fig.3] is a schematic representation of the operation of the epicyclic gear train of [Fig.2].

[0038] It should be noted that the figures set out the invention in detail for implementing the invention, said figures can of course be used to better define the invention where appropriate. DETAILED DESCRIPTION OF THE INVENTION

[0039] Referring to [Fig.l], there is shown a propulsion unit 1 for an aircraft according to an embodiment of the invention. The propulsion unit 1 extends longitudinally nally along an X axis and is configured to participate in the propulsion of the aircraft by accelerating an air flow A flowing from upstream to downstream. The terms "upstream" and "downstream" refer to the X axis which extends from upstream to downstream of the propulsion unit 1, as shown in [Fig. 1].

[0040] The propulsion unit 1 according to the invention is called “hybrid” and as such comprises a gas turbomachine 2, a fuel cell 7 and two electric machines M1, M2.

[0041] The gas turbomachine 2 comprises a propulsion member 21 mounted on a propulsion shaft 3. The propulsion shaft 3 extends longitudinally along the axis X. According to the invention, the propulsion shaft 3 is configured to rotate about the longitudinal axis X at a first rotational speed V3. The propulsion member 21, driven by the propulsion shaft 3, is configured to generate a thrust force for the aircraft. The gas turbomachine 2 comprises an air inlet 29 for supplying a gas generator of the gas turbomachine 2 with an incoming air flow AL. The figures represent the example of a turboprop, in which the propulsion member 21 is mounted upstream of the air inlet 29, the latter benefits from the air flow generated by the propulsion member 21. It goes without saying that the invention applies to any type of gas turbomachine 2 in which the propulsion member 2 can be a propeller, a ducted or unducted fan, a helicopter rotor, etc.

[0042] The gas turbomachine 2 comprises, downstream of the propulsion member 21, a low-pressure compressor 22 and a low-pressure turbine 23 connected by a low-pressure shaft 4, so as to drive it in rotation about the longitudinal axis X. According to the invention, the low-pressure shaft 4 is configured to rotate at a second rotation speed V4. The low-pressure compressor 22 is configured to receive the incoming air flow A1 and compress it so as to generate a compressed air flow A2.

[0043] Still with reference to [Fig.l], the gas turbomachine 2 also comprises, downstream of the low-pressure compressor 22, a high-pressure compressor 24 and a high-pressure gas turbine 25 connected by a high-pressure shaft 5, so as to drive it in rotation about the longitudinal axis X. The high-pressure compressor 24 is configured to receive a portion of the compressed air flow A2 from the low-pressure compressor 22 and compress it so as to generate a supercompressed air flow A3. The supercompressed air flow A3 is configured to supply a combustion chamber 26 of the gas turbomachine 2, so as to generate an exhaust air flow AE to drive the high-pressure turbine 25 and provide propulsion for the aircraft. The exhaust air flow AE also drives the low-pressure turbine 23.

[0044] In one embodiment, the propulsion shaft 3, the low pressure shaft 4 and the high pressure shaft 5 are coaxial, as shown in Figures 1 and 2. alternatively, the propulsion shaft 3, the low pressure shaft 4 and the high pressure shaft 5 are axially offset and connected, for example, by a gear system.

[0045] According to one aspect of the invention, the propulsion assembly 1 comprises a first electrical machine M1 connected to the propulsion shaft 3. The first electrical machine M1 is configured to be supplied with electrical energy ELEC to operate as a motor. This makes it possible to drive the propulsion shaft 3 if necessary.

[0046] The first electrical machine M1 is also configured to recover mechanical energy on the propulsion shaft 3 to generate electrical energy ELEC (generator mode). Such an embodiment makes it possible, for example, to recharge a battery or to power one or more electrical equipment items of the aircraft, even when the combustion chamber 26 is not operating. The operation of the first electrical machine M1 will be described in more detail later.

[0047] According to one aspect of the invention, as shown in [Fig.l], the propulsion assembly 1 comprises a transmission system 6, mechanically connected, on the one hand, to the propulsion shaft 3 and, on the other hand, to the low pressure shaft 4. The transmission system 6 is configured to define a transmission ratio K between the first rotation speed V3 of the propulsion shaft 3 and the second rotation speed V4 of the low pressure shaft 4. In other words, the second rotation speed V4 of the low pressure shaft 4 is a function of the first rotation speed V3 of the propulsion shaft 3, the ratio being defined by the following formula: K=V4 / V3. In other words, the transmission system 6 is configured to drive the low pressure shaft 4 from the movement of the propulsion shaft 3 and vice versa and to rotate them at distinct speeds.

[0048] The propulsion unit 1 comprises a second electric machine M2 configured to modify the transmission ratio K, as will be presented subsequently.

[0049] In a preferred embodiment, shown in [Fig.2], the transmission system 6 is in the form of an epicyclic gear train.

[0050] As is known, with reference to [Fig. 3], the epicyclic gear train comprises a planetary gear 61, a plurality of satellite gears 62, a planet carrier 64 and a crown gear 63. An epicyclic gear train is known per se to those skilled in the art and its operation will not be presented in more detail.

[0051] In this example, the low-pressure shaft 4 is connected directly to the planetary gear 61 and the propulsion shaft 3 is connected directly to the planet carrier 64, as shown in [Fig. 2]. In other words, in this example, the first electrical machine M1 acts, via the propulsion shaft 3, on the planet carrier 64 of the transmission system 6. The second electrical machine M2 is connected to the crown gear 63. Thus, in one embodiment, the rotational movement of the shaft propulsion 3 drives the planetary gear 61 in rotation according to the first rotation speed V3 and the low pressure shaft 4 is configured to be driven in rotation according to the second rotation speed V4. The second electric machine M2 acts on the crown gear 63 to adjust the transmission ratio K by adapting the rotation speed of the crown gear 63.

[0052] The transmission system 6 makes it possible to adapt the speed of the low-pressure compressor 22 independently of the speed of the propulsion member 21 according to the operating modes of the gas turbomachine 2 as will be described in more detail below.

[0053] As described previously, with reference to [Fig.l], the propulsion unit 1 according to the invention also comprises a fuel cell 7 which is supplied with air by the gas turbomachine 2.

[0054] As is known, the fuel cell 7 is a device for implementing an electrochemical reaction to generate electrical energy ELEC from a redox reaction. To enable the implementation of the redox reaction, the fuel cell 7 is configured to be powered by a fuel flow (not shown), for example dihydrogen H2.

[0055] The fuel cell 7 is also configured to be powered by a pressurized oxygen flow. More specifically, according to one aspect of the invention, the fuel cell 7 is configured to be powered by a portion of the compressed air flow A2 from the low-pressure compressor 22 of the gas turbomachine 2. For this, the low-pressure compressor 22 is preferably configured to generate a compressed air flow A2 which is compatible with the fuel cell 7 and optimal for ensuring its proper operation.

[0056] The first electrical machine M1 is configured to be powered by the electrical energy ELEC generated by the fuel cell 7. In the embodiment in which the first electrical machine M1 is configured to drive the propulsion shaft 3 in rotation, so as to power the low-pressure compressor 22 with the incoming air flow A1 to enable the generation of the compressed air flow A2, the latter is configured to supply air to the fuel cell 7 and / or the high-pressure compressor 24 according to the needs of the gas turbomachine 2, as will be described in more detail later.

[0057] Similarly, the second electrical machine M2 is configured to be powered by the electrical energy ELEC generated by the fuel cell 7. The second electrical machine M2 is also configured to be powered by electrical energy ELEC generated by the first electrical machine M1, as will be described in more detail later.

[0058] Thanks to the invention, the gas turbomachine 2 and the fuel cell 7 can be activated independently, in order to achieve different modes of implementation, as will be described in more detail later. In particular, the propulsion assembly 1 according to the invention is configured to allow solely electric propulsion in which the torque for rotating the propulsion shaft 3 is provided solely by the first electric machine M1, solely thermal propulsion in which the torque is provided solely by the gas turbomachine 2 or mixed propulsion that is both thermal and electric.

[0059] In one embodiment, as shown in [Fig.2], the propulsion unit 1 comprises a declutching system 8 belonging to the low pressure shaft 4 and mounted between the low pressure compressor 22 and the low pressure turbine 23 in order to allow the rotation of one to be decorrelated with respect to the other.

[0060] More precisely, the declutching system 8 is configured to move between an engaged position in which the low-pressure compressor 22 is secured to the low-pressure turbine 23 and a declutched position in which the low-pressure compressor 22 is detached from the low-pressure turbine 23. The declutched position makes it possible to avoid driving the low-pressure turbine 23 while generating the compressed air flow A2, for example to supply only the fuel cell 7.

[0061] In other words, in such an embodiment, the declutching system 8 allows the fuel cell 7 to be supplied with the compressed air flow A2 and therefore to operate, without the low-pressure turbine 23 being driven. This makes it possible to limit the resistive torque to drive the low-pressure compressor 22.

[0062] In this example, the clutch system 8 is in the form of a free wheel.

[0063] In one embodiment, the propulsion assembly 1 comprises an electrical distribution system 9, connected at the input to the fuel cell 7 and at the output to the first electrical machine M1 and to the second electrical machine M2. The electrical distribution system 9 is configured to distribute the electrical energy ELEC to one and / or the other of the electrical machines M1, M2 according to the needs of the propulsion assembly 1, as will be described in more detail later. The electrical distribution system 9 also makes it possible to exchange electrical flows between the first electrical machine M1 and the second electrical machine M2.

[0064] In this example, the propulsion unit 1 comprises an electrical energy storage device B ELEC. In a first embodiment (not shown), the storage device B is connected directly at the input to the fuel cell 7 and at the output to the first electrical machine M1 and / or to the second electrical machine M2. In a second embodiment (shown in [Fig. 2]), the storage device B is connected to the electrical distribution system 9. The storage device B is for example in the form of an electric battery configured to em store and store electrical energy ELEC. Such a storage device B thus makes it possible to supply electrical energy ELEC to the first electrical machine M1 and / or to the second electrical machine M2 even when the fuel cell 7 is not supplied with the compressed air flow A2 or when the latter is stopped.

[0065] The propulsion unit 1 according to the invention is a hybrid propulsion unit in which the fuel cell 7 makes it possible to generate electrical energy ELEC which is transmitted to one and / or the other of the electrical machines M1, M2. The electrical machines M1, M2 thus contribute to the thrust force of the aircraft, which makes it possible to limit greenhouse gas emissions and contributes to reducing the environmental impact of the aircraft. Thanks to the invention, the transmission system 6 allows the propulsion unit 1 to operate in different configurations, for example in the case of a gas turbomachine 2 switched off, as will be described below.

[0066] A method of operating the propulsion unit 1 will now be described according to different implementation modes.

[0067] In a first embodiment, the combustion chamber 26 of the gas turbomachine 2 is extinguished and the fuel cell 7 is ignited.

[0068] In a first step, the first electric machine M1 drives the propulsion shaft 3 in rotation to enable “electric” propulsion. In this step, the second electric machine M2 acts on the transmission system 6 to define the transmission ratio K between the first rotation speed V3 of the propulsion shaft 3 and the second rotation speed V4 of the low-pressure shaft 4. The propulsion shaft 3 connected to the low-pressure shaft 4 via the transmission system 6 then drives the low-pressure shaft 4 in rotation at the speed of its choice. The second rotation speed V4 of the low-pressure shaft 4 is defined from the first rotation speed V3 of the propulsion shaft 3 controlled by the first electric machine M1 and the transmission ratio K controlled by the second electric machine M2.

[0069] The low pressure compressor 22 is then driven in rotation and generates, in a second step, a compressed air flow A2, resulting from the compression of the incoming air flow AL. The second rotation speed V4 of the low pressure shaft 4 is determined so as to provide the fuel cell 7 with an optimal compressed air flow A2.

[0070] In a third step, the compressed air flow A2 supplies the fuel cell 7 which generates electrical energy ELEC to electrically power the first electrical machine M1 and the second electrical machine M2. The generation of electrical energy by the fuel cell 7 is optimal. In this example, the fuel cell 7 electrically supplies the electrical distribution system 9 which distributes then the electrical energy to the first electrical machine Ml and to the second electrical machine M2.

[0071] Thanks to the invention, the fuel cell 7 can be supplied with an optimal air flow even in the event of a breakdown of the gas turbomachine 2. The fuel cell 7 can advantageously continue to electrically supply the first electrical machine M1 and the second electrical machine M2 to enable, for example, the electrical equipment of the aircraft or an electrical energy storage device B to be supplied.

[0072] In one embodiment, the declutching system 8 is placed in the declutched position, so as to prevent the low pressure turbine 23 from being driven and to reduce the resistive force on the low pressure shaft 4. In this example, the declutching system 8 makes it possible to generate only electrical energy ELEC by the fuel cell 7 to supply an electrical network or a storage device B for example.

[0073] In a second embodiment, the fuel cell 7 is switched off and the combustion chamber 26 of the gas turbomachine 2 is switched on. Such an embodiment corresponds to the conventional operation of a gas turbomachine 2 to enable “thermal” propulsion.

[0074] The method then comprises a step of driving the propulsion shaft 3 from the rotation of the low-pressure shaft 4. The high-pressure compressor 24 supplies the combustion chamber 26 with the supercompressed air flow A3, the high-pressure turbine 25 is driven by an exhaust air flow AE from the combustion chamber 26. The low-pressure turbine 23 is also driven by the exhaust flow AE and drives the low-pressure shaft 4 in rotation to drive the propulsion shaft 3 and therefore the propulsion member 21.

[0075] In one embodiment, the second electrical machine M2 acts, in a second step, on the transmission system 6 to determine the transmission ratio K between the low-pressure shaft 4 and the propulsion shaft 3, so as to control the rotational speed of the propulsion member 21. Thus, the rotational speed of the gas turbomachine 2 is adjusted to obtain optimal efficiency. The second electrical machine M2 makes it possible to ensure that the transmission ratio K is optimal for ensuring propulsion. In this example, the second electrical machine M2 is powered by electrical energy previously stored in a storage device B, for example a battery. In an alternative embodiment, the second electrical machine M2 is powered by electrical energy supplied by the first electrical machine M1 via the electrical distribution system 9.

[0076] In a third embodiment, with reference to [Fig.2], the fuel cell 7 and the combustion chamber 26 of the gas turbomachine 2 are ignited.

[0077] In this embodiment, the method comprises a first step E1 of driving the propulsion shaft 3 from the movement of the low-pressure shaft 4 and the energy supplied by the first electrical machine M1. The propulsion shaft 3 makes it possible to drive the propulsion member 21 in rotation around the longitudinal axis X so as to generate the incoming air flow A1. In this step E1, the second electrical machine M2 acts on the transmission system 6 to define the transmission ratio K between the second rotation speed V4 of the low-pressure shaft 4 and the first rotation speed V3 of the propulsion shaft 3.

[0078] The low pressure shaft 4 then drives, in a second step E2, the low pressure compressor 22 which is supplied with the incoming air flow A1 and generates the compressed air flow A2. In a third step E3, the fuel cell 7 is supplied with the compressed air flow A2 and with a fuel flow, for example hydrogen, to generate electrical energy ELEC.

[0079] In parallel, in this third step E3, the high-pressure compressor 24 is supplied by the compressed air flow A2 and generates a supercompressed air flow A3 which supplies the combustion chamber 26. The high-pressure turbine 25 is supplied by the exhaust flow AE and generates the thrust force of the propulsion unit 1 to drive the propulsion of the aircraft.

[0080] In other words, in this embodiment, the fuel cell 7 is powered by an air flow directly from the gas turbomachine 2 and generates electrical energy ELEC which is used by the electrical machines M1 or M2 to participate in driving the propulsion shaft 3. The electrical energy ELEC supplied by the fuel cell 7 in the propulsion assembly 1 participates in the propulsion of the aircraft and makes it possible to limit its fuel consumption, which improves the environmental impact of the aircraft.

[0081] In a fourth embodiment, the gas turbomachine 2 and the fuel cell 7 are switched off.

[0082] In this embodiment, the method comprises a first step of driving the low pressure shaft 4 by the movement of the propulsion shaft 3, itself driven by the propulsion member 21 in the manner of a windmill.

[0083] In a second step, the first electrical machine M1 generates electrical energy ELEC from the movement of the propulsion shaft 3 to supply, for example, an electrical network of the aircraft or a storage device B.

[0084] In other words, this mode of implementation operates in a manner analogous to a wind turbine which makes it possible to generate electrical energy ELEC from the rotation of the propulsion member 21. The first electrical machine M1 then operates in a so-called “generator” mode.

[0085] Thanks to the invention, the transmission system allows the propulsion unit to operate optimally regardless of the configuration of the propulsion system and the state of the fuel cell and the gas turbomachine. In particular, the transmission system allows the speed of the propulsion shaft and the speed of the low-pressure shaft to be controlled relative to each other to provide an optimal flow of compressed air to the fuel cell and / or the gas turbomachine.

Claims

1. Claims Propulsion assembly (1) for aircraft extending along a longitudinal axis (X), the propulsion assembly (1) comprising: • a gas turbomachine (2) comprising: • a propulsion member (21) mounted on a propulsion shaft (3), the propulsion member (21) being configured to generate a thrust force for the aircraft, the propulsion shaft (3) being configured to rotate at a first rotation speed (V3), • a low pressure compressor (22) and a low pressure turbine (23) connected by a low pressure shaft (4), the low pressure compressor (22) being configured to compress an incoming air flow (A1) and to generate a compressed air flow (A2), the low pressure shaft (4) being configured to rotate at a second rotation speed (V4), • a combustion chamber (26), • a high-pressure compressor (24) and a high-pressure turbine (25) connected by a high-pressure shaft (5), the high-pressure compressor (24) being configured to receive the compressed air flow (A2) from the low-pressure compressor (22) and generate a supercompressed air flow (A3) so as to supply the combustion chamber (26), the high-pressure gas turbine (25) being driven by an exhaust air flow (AE) from the combustion chamber (26), • a transmission system (6) mechanically connected, on the one hand, to the propulsion shaft (3) and, on the other hand, to the low pressure shaft (4), the transmission system (6) being configured to define a transmission ratio (K) between the first rotation speed (V3) of the propulsion shaft (3) and the second rotation speed (V4) of the low pressure shaft (4), • a first electrical machine (Ml) connected to the propulsion shaft (3) and configured to drive it in rotation, • a second electrical machine (M2) connected to the system of transmission (6) and configured to modify the transmission ratio (K), and • at least one fuel cell (7) powered by the compressed air flow (A2) from the low pressure compressor (22) of the gas turbomachine (2), the fuel cell (7) being configured to electrically power directly or indirectly the first electric machine (Ml) and the second electric machine (M2).

2. Propulsion assembly (1) according to claim 1, comprising an electrical distribution system (9) electrically connecting the fuel cell (7), the first electrical machine (Ml) and the second electrical machine (M2), the electrical distribution system (9) being configured to allow the fuel cell (7) to electrically power the first electrical machine (Ml) and the second electrical machine (M2) and / or to allow the first electrical machine (Ml) and the second electrical machine (M2) to exchange electrical power flows.

3. Propulsion assembly (1) according to one of claims 1 to 2, in which the transmission system (6) is in the form of an epicyclic gear train comprising a planetary gear (61), a plurality of satellite gears (62), a crown gear (63), and a planet carrier (64), the propulsion shaft (3) is mechanically connected to the planet carrier (64), the low pressure shaft (4) is mechanically connected to the planetary gear (61) and the second electrical machine (M2) is connected to the crown (63).

4. Propulsion assembly (1) according to one of claims 1 to 3, comprising a declutching system (8) mounted on the low pressure shaft (4) and configured to move between an engaged position in which the low pressure compressor (22) is secured to the low pressure turbine (23) and a declutched position in which the low pressure compressor (22) is detached from the low pressure turbine (23), so as to decorrelate the rotation of the low pressure compressor (22) and the rotation of the low pressure turbine (23).

5. Aircraft comprising at least one propulsion unit (1) according to one of claims 1 to 4.

6. Method of operating the propulsion unit (1) according to one of the Claims 1 to 4, the combustion chamber (26) of the gas turbomachine (2) being extinguished and the fuel cell (7) being ignited, the method comprises: a step of driving the propulsion shaft (3) by the first electric machine (Ml), driving the low pressure shaft (4) via the transmission system (6), a step of generating the compressed air flow (A2) by the low pressure compressor (22) to supply at least the fuel cell (7).

7.

8. Method of operating the propulsion unit (1) according to one of the claims 1 to 4, the fuel cell (7) being switched off and the combustion chamber (26) being switched on, the method comprises: a step of driving the propulsion shaft (3) from the rotation of the low pressure shaft (4) via the transmission system (6), and a control step via the second electric machine (M2) of the transmission ratio (K) of the transmission system (6) between the low pressure shaft (4) and the propulsion shaft (3). Method of operating the propulsion unit (1) according to one of claims 1 to 4, the fuel cell (7) and the combustion chamber (26) being ignited, the method comprises: a step of driving the propulsion shaft (3) from both the mechanical torque of the low pressure shaft (4) and the mechanical torque supplied by the first electrical machine (M1), the second electrical machine (M2) controlling the transmission ratio (K) of the transmission system (6) between the low pressure shaft (4) and the propulsion shaft (3), a step of generating the compressed air flow (A2) by the low pressure compressor (22), so as to supply at least the fuel cell (7), and a step of supplying electrical energy (ELEC), by the fuel cell (7), to the first electrical machine (Ml) and the second electrical machine (M2).

9. Method of operating the propulsion unit (1) according to one of claims 1 to 4, the fuel cell (7) and the combustion chamber (26) being switched off, the method comprises: • a step of driving the low pressure shaft (4) from the movement of the propulsion shaft (3), and • a step of generating electrical energy (ELEC) by the first electrical machine (Ml) to supply an electrical network of the aircraft and / or a battery.

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