Propulsion system including a transmission with variable gear ratio

Abstract

An aircraft propulsion system (1) comprising: a propulsion unit (2) mounted on a propulsion shaft (3); a gas turbomachine (4) comprising a compressor (41) and a turbine (43) mounted on a drive shaft (5); a transmission system (6) configured to define a transmission ratio (K) between a propulsion rotational speed (V3) of the propulsion shaft (3) and a motor rotational speed (V5) of the drive shaft (5); a first electric machine (M1) configured to supply or draw control power from the transmission system (6) so as to modify the transmission ratio (K); and a second electric machine (M2) connected to the propulsion shaft (3) or the drive shaft (5) and configured to supply or draw compensating power from the propulsion shaft (3) so as to compensate for residual power induced by the application of the control power. Abstract figure: Figure 2

Description

Title of the invention: Propulsion assembly comprising a gearbox with variable transmission ratio. Technical field

[0001] The present invention relates to the field of propulsion assemblies used for the propulsion of an aircraft and relates in particular to a propulsion assembly comprising a gearbox with variable transmission ratio.

[0002] Climate change is a major concern for many legislative and regulatory bodies worldwide. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies to both new types of aircraft and those already in service, requiring the implementation of technological solutions to bring them into compliance with current regulations. Civil aviation has been actively working for several years now to contribute to the fight against climate change.

[0003] Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. The Applicant takes into account the factors impacting all phases of design and development in order to obtain aeronautical components and products that are less energy-intensive, more environmentally friendly, and 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 that minimize greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity.

[0005] This sustained research and development work focuses on new generations of aircraft engines, the weight reduction of aircraft, in particular through the materials used and lighter on-board equipment, the development of the use of electrical technologies to provide propulsion, and, as essential complements to technological progress, aviation biofuels.

[0006] To this end, the invention is the result of technological research aimed at significantly improving aircraft performance and, in this sense, contributes to reducing the environmental impact of aircraft. For this purpose, the invention relates to an optimized propulsion system.

[0007] In a known manner, with reference to [Fig.1], an aircraft includes one (or more) propulsion assembly(ies) 1 to enable its movement from the acceleration of an airflow A. For this purpose, the propulsion assembly 1 includes a propulsion element 2, mounted on a propulsion shaft 3, which converts the rotational movement into an airflow A which enables the propulsion of the aircraft.

[0008] To drive the rotation of the propulsion unit 2, the propulsion assembly 1 comprises a gas turbomachine 4 which includes, successively along a longitudinal axis X, a compressor 41, a combustion chamber 42, and a turbine 43, the compressor 41 and the turbine 43 being connected by a drive shaft 5. The compressor 41 is configured to receive an incoming airflow A1 and compress it to supply the combustion chamber 42. An exhaust airflow AE, resulting from combustion in the combustion chamber 42, between a fuel flow and the compressed air flow, drives the turbine 43 in rotation, which in turn drives the drive shaft 5 and thus the compressor 41 and the propulsion unit 2, via the rotation of the drive shaft 3. In the example of a turboprop engine, the propulsion unit 2 is mounted upstream of the gas turbomachine 4, which receives a part of the airflow A generated by the propulsion unit 2 to supply the compressor 41.

[0009] In a known manner, as shown in [Fig.1], the propulsion assembly 1 also includes a transmission system 106 which connects the propulsion shaft 3 and the motor shaft 5 and allows a predetermined transmission ratio K to be applied between the rotational speed V3 of the propulsion shaft 3 and the rotational speed V5 of the motor shaft 5, in order to allow the rotational speed of the propulsion shaft 3 to be reduced.

[0010] Depending on the aircraft's flight phases (takeoff, cruise, landing) and its speed, the rotational speed of the propulsion unit 2 must be adjusted to allow for optimal performance while limiting noise. In particular, the rotational speed of the propulsion unit 2 must be at its maximum during takeoff to generate significant thrust. Conversely, during cruise, the rotational speed of the propulsion unit 2 must be lower, both to limit mechanical stress on the propeller blades, improve the aircraft's aerodynamics, and reduce fuel consumption. Due to the transmission system 106, the rotational speed of the propulsion unit 2 and the rotational speed of the turbine 43 are proportional.In practice, it is not possible to adapt the operating regime of the gas turbomachine 4 to optimize the rotational speed of the propulsion unit 2 without degrading the performance of the gas turbomachine 4.

[0011] There is currently no aircraft propulsion system that allows a optimal simultaneous operation of the propulsion unit and the gas turbomachine during all phases of aircraft flight.

[0012] The invention thus aims to eliminate at least some of these drawbacks by providing a simple and efficient aircraft propulsion system for all phases of aircraft flight. In particular, the invention relates to a propulsion system in which the ratio between the rotational speed of the drive shaft and the rotational speed of the propulsion shaft can be continuously adjusted to improve the performance and lifespan of the propulsion system.

[0013] Incidentally, prior art discloses a motor or railway vehicle engine in which an internal combustion engine is coupled to two electric machines to drive an axle. The drive shaft and the axle drive shaft are connected via a transmission system, of the epicyclic type, which defines a transmission ratio between the rotational speed of the drive shaft and the rotational speed of the axle. The transmission system also performs a disengagement function to allow the drive shaft and the drive shaft to rotate at different speeds. PRESENTATION OF THE INVENTION

[0014] The invention relates to an aircraft propulsion system comprising: • a propulsion unit mounted on a drive shaft, the drive shaft being configured to rotate at a propulsion rotational speed, • a gas turbomachine comprising a compressor and a turbine mounted on a drive shaft, the compressor being configured to receive an airflow and to supply a combustion chamber of the gas turbomachine with a compressed airflow, the turbine being driven by an exhaust airflow from the combustion chamber so as to drive the drive shaft in rotation, the drive shaft being configured to rotate at a motor rotational speed, • a transmission system mechanically connected, on the one hand, to the drive shaft and, on the other hand, to the drive shaft, the transmission system being configured to define a transmission ratio between the drive shaft rotation speed and the drive shaft rotation speed, • a first electric machine connected to the transmission system, the first electric machine being configured to supply or draw control power from the transmission system, so as to modify the transmission ratio, the drawing or supply of control power resulting in a supply or withdrawal of residual power on the drive shaft, and • a second electric machine connected to the drive shaft or the motor shaft, the second electric machine being configured to supply or draw compensating power from the drive shaft, so as to compensate for the residual power.

[0015] The propulsion system according to the invention allows the motor speed of the drive shaft and the propulsion speed of the drive shaft to be determined independently. The first electric machine applies torque to the transmission system to adjust the motor speed or the propulsion speed, even when the propulsion speed or motor speed, respectively, is imposed. The second electric machine advantageously compensates for power induced on the drive shaft following the adjustment of the transmission ratio by the first electric machine. The rotation speed of each shaft can thus be continuously and precisely adjusted during all phases of aircraft flight, enabling optimal operation of the propulsion system.

[0016] In other words, for each phase of flight of the aircraft it is possible, thanks to the invention, to independently and precisely adjust both the rotation speed of the propulsion unit and the rotation speed of the turbine of the gas turbomachine to allow optimal performance, which makes it possible to limit any risk of damage and also to extend the life of the propulsion unit.

[0017] Optimal operation of the gas turbomachine also ensures optimal fuel consumption, which helps to limit greenhouse gas emissions and thus reduce the aircraft's environmental impact.

[0018] Preferably, in absolute values, the ratio between the compensation power and the residual power is between 0.9 and 1.1, which ensures that the residual power is effectively compensated. This characteristic thus ensures that the propulsion unit rotates at an optimal speed, even when the transmission ratio between the drive shaft and the drive shaft is modified by the first electric machine.

[0019] Preferably, the propulsion assembly includes a computer configured to: • determine the control power to be supplied or drawn by the first electric machine from the transmission system to control both an optimal propulsion rotation speed and an optimal motor rotation speed, • determine the residual power supplied or drawn by the first electric machine on the drive shaft from the regulating power supplied or drawn from the transmission system, and • determine the compensating power to be taken or supplied, by the second electric machine on the drive shaft, to compensate for the residual power.

[0020] The computer thus makes it possible to determine precisely the residual power which is applied to the propulsion shaft following the modification of the transmission ratio by the first electric machine, which allows a precise and efficient compensation of the rotation speed of the propulsion shaft to allow it to operate at an optimal rotation speed regardless of the phase of flight of the aircraft.

[0021] In one embodiment, the transmission system is an epicyclic train comprising a planetary type gear, a plurality of satellite type gears mounted on a planet carrier and a ring type gear, which allows the use of a transmission system whose operation is known.

[0022] Preferably, the drive shaft, the drive shaft, and the first electric machine are each connected to a different type of gear. The transmission system thus has two input torques and one output torque to independently regulate the rotational speed of each shaft by acting on the third gear via the first electric machine.

[0023] In one embodiment, the drive shaft is connected to the planetary gear, the drive shaft is connected to the planet carrier, and the first electric machine is connected to the ring gear. The drive shaft and the drive shaft are thus coaxial, and the first electric machine acts on the ring gear of the epicyclic gear train to change the transmission ratio between the planetary gear and the planet carrier.

[0024] In a first embodiment, the second electric machine is directly connected to the drive shaft so as to compensate for residual power by supplying or drawing compensating power directly from the drive shaft. In such an embodiment, the torque at the output of the transmission system to drive the rotation of the drive shaft corresponds to the sum of the torque supplied by the transmission system and the torque supplied by the second electric machine. In other words, two output torques are coupled to allow the drive shaft to rotate at the determined drive speed. In other words, such an embodiment allows compensation by two coupled outputs of the transmission system.

[0025] In a second embodiment, the second electric machine is connected to the drive shaft so as to compensate for the residual power by supplying or drawing compensating power from the drive shaft via the transmission system. In such an embodiment, the residual power is This is compensated by adding or subtracting torque from an input of the transmission system, which is then transmitted to the output of the transmission system and thus to the drive shaft. In other words, this embodiment allows compensation through two coupled inputs of the transmission system.

[0026] Preferably, the first and second electric machines are electrically connected directly or indirectly to each other, so as to allow the exchange of electrical power flows between the first and second electric machines. The first electric machine can thus advantageously supply electrical energy to the second electric machine and vice versa in the event of a power supply failure, for example.

[0027] In one embodiment, the first and second electric machines are electrically connected to a storage device configured to supply electrical energy to one or both of the electric machines. The storage device is also configured to receive electrical energy supplied by one or both of the electric machines, which then operates in generator mode by converting the rotational torque of the motor shaft or transmission system into electrical energy. The storage device can thus store electrical energy to compensate, for example, for a subsequent power outage in the electrical grid.

[0028] The invention also relates to an aircraft comprising at least one propulsion assembly as described above.

[0029] Finally, the invention relates to a method of operating a propulsion assembly as described above, the method comprising the steps of: • to determine, using the computer, a transmission ratio to be applied between the propulsion rotation speed and the engine rotation speed, depending on a given flight phase, so that the gas turbomachine operates at an optimal efficiency. • to control, via the first electric machine on the transmission system, an input or output of regulating power according to the determined transmission ratio, the input or output of regulating power resulting in an input or output of residual power on the drive shaft, and • to control, by the second electric machine, respectively an input or withdrawal of compensating power on the propulsion shaft, so as to compensate for the residual power on the propulsion shaft in order to drive the propulsion element according to the predetermined propulsion rotation speed. PRESENTATION OF THE FIGURES

[0030] The invention will be better understood upon reading the following description, 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. 1 is a schematic representation of a propulsion assembly according to the prior art.

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

[0033] The [Fig.3] is a schematic representation of a propulsion assembly according to a second embodiment of the invention.

[0034] Fig. 4 is a schematic representation of a propulsion assembly according to a third embodiment of the invention.

[0035] The [Fig.5] is a schematic representation of a propulsion assembly according to a fourth embodiment of the invention.

[0036] The [Fig.6] is a schematic representation of the operation of the transmission system of the propulsion assembly of the [Fig.3].

[0037] The [Fig.7] is a diagram of the steps of a method of operation of the propulsion assembly of the [Fig.2] according to an implementation method of the invention.

[0038] It should be noted that the figures set out the invention in detail to implement the invention, said figures being of course able to serve to better define the invention where appropriate. DETAILED DESCRIPTION OF THE INVENTION

[0039] With reference to [Fig. 2], a propulsion assembly 1 for an aircraft is shown according to one embodiment of the invention. The propulsion assembly 1 extends longitudinally along an axis X and is configured to participate in the propulsion of the aircraft by accelerating an airflow A.

[0040] For this purpose, the propulsion assembly 1 according to the invention comprises a propulsion unit 2, a gas turbomachine 4 and two electric machines M1, M2.

[0041] With reference to [Fig. 2], the propulsion unit 2 is mounted on a propulsion shaft 3, which in this example extends longitudinally along the X-axis. According to the invention, the propulsion shaft 3 is configured to rotate about the longitudinal axis X at a propulsion rotational speed V3. The propulsion unit 2, driven by the propulsion shaft 3, is configured to generate an airflow A to generate the aircraft's thrust.

[0042] To drive the rotation of the propulsion unit 2, the gas turbomachine 4 comprises successively along the longitudinal axis X, a compressor 41, a chamber of The combustion chamber 42 and a turbine 43 are connected by a drive shaft 5, which rotates the compressor 41 and the turbine 43. Specifically, the compressor 41 is configured to receive an incoming airflow A1 (corresponding in this example of a turboprop engine to a portion of the airflow from the propulsion unit 2) and compress it to supply the combustion chamber 42 with a flow of compressed air AC. An exhaust airflow AE, resulting from combustion in the combustion chamber 42, between the fuel flow and the compressed air flow AC, rotates the turbine 43, which in turn drives the drive shaft 5 and thus the compressor 41 and the propulsion unit 2, via the rotation of the drive shaft 3.As shown in the figures, this document describes the example of a turboprop in which the propulsion element is a fan, however it is understood that the invention applies to any type of turbomachine and to any type of propulsion element, such as a shrouded or unshrouded propeller, a shrouded or unshrouded fan or even a helicopter rotor, etc.

[0043] According to the invention, the motor shaft 5 is configured to rotate around the longitudinal axis X at a motor rotation speed V5.

[0044] Preferably, the drive shaft 3 and the motor shaft 5 are coaxial, as shown in [Fig.2]. The drive shaft 3 and the motor shaft 5 could also be parallel.

[0045] According to one aspect of the invention, with reference to [Fig. 2], 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 drive shaft 5. The transmission system 6 is configured to define a transmission ratio K between the propulsion rotational speed V3 of the propulsion shaft 3 and the drive rotational speed V5 of the drive shaft 5. In other words, the drive rotational speed V5 is a function of the propulsion rotational speed V3, the ratio being defined by the following formula: K = V5 / V3. In other words, the transmission system 6 is configured to drive the propulsion shaft 3 from the movement of the drive shaft 5.

[0046] According to the invention, the propulsion assembly 1 comprises a first electric machine Ml configured to modify the transmission ratio K. For this purpose, the first electric machine Ml is connected to the transmission system 6 and is configured to supply or draw a control power Pr from the transmission system 6. In other words, the first electric machine Ml is configured to operate either in motor mode to generate torque, or in generator mode to draw torque. The drawing or supply of the control power Pr results respectively in the drawing or supply of a residual power Pq on the propulsion shaft 3, as will be shown subsequently.

[0047] According to a preferred aspect of the invention, the transmission system 6 comprises three distinct types of gears linked in a common motion. The transmission system 6 is configured to allow each type of gear to rotate at different speeds.

[0048] In particular, in the transmission system 6 according to the invention, the drive shaft 5 is connected to the first type of gears, the drive shaft 3 is connected to the second type of gears, and the first electric machine M1 is connected to the third type of gears. Thus, the parallel drive of two distinct types of gears at their natural speeds allows the third type of gears to be driven in rotation at a different speed, as will be described in more detail later. In other words, the transmission system 6 has an output whose speed depends on two inputs.

[0049] In a preferred embodiment, with reference to [Fig. 3], the transmission system 6 is in the form of an epicyclic gear train. It is understood that the transmission system 6 could alternatively be in a different form, for example as a gear system like a gearbox in a motor vehicle, provided that the transmission system 6 includes three inputs / outputs.

[0050] As is known from [Fig. 6], the epicyclic gear train comprises a planetary gear 61, a plurality of planetary gears 62, a planet carrier 64, and a ring gear 63. An epicyclic gear train is known in itself to those skilled in the art, and its operation will not be described in further detail in this document. Hereafter, for the sake of brevity, the planetary gear 61 will be referred to as planetary gear 61 and the ring gear 63 will be referred to as ring gear 63.

[0051] In this example, with reference to [Fig. 3], the drive shaft 5 is directly connected to the planetary gear 61 and the drive shaft 3 is directly connected to the planet carrier 64. The first electric machine M1 is connected to the ring gear 63. Thus, in one embodiment, the rotational movement of the drive shaft 5 drives the planetary gear 61 in rotation according to the motor rotational speed V5 and the drive shaft 3 is configured to be driven in rotation, via the planet carrier 64, according to the propulsion rotational speed V3. The first electric machine Ml acts on the crown gear 63 to adjust the transmission ratio K by adapting the rotational speed of the crown gear 63 and therefore of the planet carrier 64 to allow the propulsion shaft 3 to rotate at a predetermined propulsion rotational speed V3 while allowing the gas turbomachine 4 to rotate at a suitable rotational speed.It goes without saying that the drive shaft 5, the drive shaft 3 and the first electric machine Ml could just as easily be . each connected to a different gear in the epicyclic train, as long as each is connected to a distinct gear.

[0052] In other words, the transmission system 6 allows, through the adjustment of the transmission ratio K, the speed of the gas turbomachine 4 to be adapted independently of the speed of the propulsion unit 2 according to the operating modes of the propulsion unit 1, for example for each phase of flight of the aircraft (takeoff, cruise, landing).

[0053] According to one aspect of the invention, the propulsion assembly 1 comprises a second electric machine M2 connected to the propulsion shaft 3 ([Fig. 3]) or to the motor shaft 5 ([Fig. 4]). The second electric machine M2 is configured to compensate for the residual power Pq applied to the propulsion shaft 3 following the application, by the first electric machine M1, of the adjustment power Pr to the transmission system 6. Indeed, the change in the transmission ratio K results in a motor or resistive torque on the propulsion shaft 3 which incidentally modifies the propulsion rotational speed V3.

[0054] To this end, the second electric machine M2 is configured to supply or draw a compensating power Pc directly from the drive shaft 3 or indirectly via the transmission system 6 and the motor shaft 5. More specifically, the second electric machine M2 is configured to supply or draw power from the transmission system 6, which allows the compensating power Pc to be applied to the drive shaft 3. In other words, the second electric machine M2 is configured to operate either in motor mode to generate torque or in generator mode to draw torque. The compensating power Pc is configured to oppose the residual power Pq.

[0055] For this purpose, in a first embodiment shown in [Fig.3], the second electric machine M2 is directly connected to the drive shaft 3 so as to compensate for the residual power Pq by supplying or taking the compensation power Pc directly from the drive shaft 3. It is understood that the second electric machine M2 could be connected to the drive shaft 3 via a gear.

[0056] Such an embodiment makes it possible to obtain a transmission system 6 in which the second electric machine M2 directly compensates for the residual power Pq. Advantageously, the second electric machine M2 is power-controlled to obtain the optimal propulsion rotational speed V3.

[0057] In a second embodiment shown in [Fig. 4], the second electric machine M2 is connected to the motor shaft 5 so as to compensate for the residual power Pq by supplying or drawing the compensating power Pc to the drive shaft 3 via the transmission system 6. In particular, in one embodiment, the drive shaft 5 and the second electric machine M2 are connected in parallel to a common gear connected to the input of the transmission system 6, in this example to the planetary gear 61. This advantageously allows the second electric machine M2 to be positioned downstream of the transmission system 6, which may be convenient depending on the architecture.

[0058] In this embodiment, the compensating power Pc supplied by the second electric machine M2 is thus coupled to the power supplied by the drive shaft 5 at the input of the transmission system 6 to compensate for the residual power Pq. The power of the drive shaft 5 and the compensating power Pc are thus transmitted to the input of the transmission system 6, in this example to the planetary gear 61, to allow the drive shaft 3 to rotate at the drive speed V3 determined by the speed of the drive shaft 5 and by the transmission ratio K imposed by the first electric machine M1, compensating for the losses generated by the transmission system 6. It is understood that the second electric machine M2 could be directly connected to the drive shaft 5. Advantageously, the second electric machine M2 is power-controlled to obtain the optimal drive speed V3.

[0059] In this example, the compensation power Pc is substantially equal, in absolute values, to the residual power Pq. More precisely, in absolute values, the ratio between the compensation power Pc and the residual power Pq is preferably between 0.9 and 1.1, so as to allow effective compensation.

[0060] The second electric machine M2 of the propulsion assembly 1 according to the invention advantageously compensates for the power induced on the propulsion shaft 3 following the adjustment by the first electric machine M1 of the transmission ratio K between the propulsion shaft 3 and the motor shaft 5. The rotational speed of each shaft 3, 5 can thus be adapted and adjusted continuously, independently, and precisely during all phases of flight of the aircraft, which allows for optimal operation of the propulsion assembly 1.

[0061] Figure 3 shows an example in which the first electric machine M1 is directly connected to the crown gear 63 of the epicyclic gear train and the second electric machine M2 is directly connected to the drive shaft 3. It is understood that the first electric machine M1 and / or the second electric machine M2 could alternatively be indirectly connected to separate elements of the transmission system 6, for example via a plurality of gears, as shown in Figure 5.

[0062] Furthermore, a single-toothed epicyclic train comprising a single planetary gear is described; however, it is understood that the invention also applies to double-toothed epicyclic trains and / or those comprising two planetary-type gears, as is known to those skilled in the art.

[0063] In one embodiment, the first electric machine M1 and the second electric machine M2 are electrically connected to each other so as to exchange electrical power flows. For example, when the first electric machine M1 operates in generator mode and recovers torque supplied by the transmission system 6 during a change in the transmission ratio K, it can store electrical energy and transfer it to the second electric machine M2, which should operate in motor mode to supply torque to the drive shaft 3.

[0064] In one embodiment, the propulsion unit 1 includes a computer 9 connected to both the first electric machine M1 and the second electric machine M2, as shown in Figures 2 and 3.

[0065] The computer 9 is configured to determine, for each phase of aircraft flight, the transmission ratio K to be applied to the transmission system 6 to allow both an optimal propulsion rotation speed V3 of the propulsion shaft 3 and an optimal engine rotation speed V5 of the engine shaft 5. The computer 9 is thus configured to determine the adjustment power Pr to be applied by the first electric machine M1 to the transmission system 6 to achieve the determined transmission ratio K and to deduce the residual power Pq then applied to the propulsion shaft 3. In other words, the computer 9 is configured to determine the residual power Pq supplied or withdrawn by the first electric machine M1 on the propulsion shaft 3, from the adjustment power Pr supplied or withdrawn from the transmission system 6.

[0066] The computer 9 is also configured to determine, from the determined residual power Pq, the compensating power Pc to be drawn from or supplied by the second electric machine M2 to the propulsion shaft 3 to compensate for such residual power Pq. More precisely, the computer 9 is configured to determine the power that the second electric machine M2 must supply or draw so that the compensating power Pc is applied to the propulsion shaft 3. Advantageously, the computer 9 allows the first electric machine M1 to be controlled so that the gas turbomachine 4 operates at an optimal speed while maintaining a propulsion rotation speed V3 that is optimal for the flight phase. The computer 9 allows the second electric machine M2 to be controlled so as to obtain the optimal propulsion rotation speed V3 despite the impact induced by the change in the transmission ratio K.

[0067] In one embodiment shown in [Fig. 3], the propulsion assembly 1 includes an electrical energy storage device B. In this example, the storage device B is connected to the first electric machine M1 and the second electric machine M2 and is configured to supply electrical energy to the first electric machine M1 and / or the second electric machine M2 as required. The storage device B is, for example, in the form of an electric battery configured to store electrical energy. It is understood that the architecture could also include a fuel cell to provide electrical power generation.

[0068] The storage device B is also configured to store electrical energy supplied by either of the electric machines M1, M2 from the torque transmitted by the rotation of the drive shaft 3 and the motor shaft 5, with the first electric machine M1 and the second electric machine M2 then operating in generator mode. This allows, for example, the storage device B to be recharged. Thus, even in the event of a power supply failure, for example, the first electric machine M1 and the second electric machine M2 can be electrically supplied.

[0069] A method for operating the propulsion assembly 1 according to an embodiment of the invention will now be described, with reference to [Fig. 3] and [Fig. 7]. In this example, the transmission system 6 is in the form of an epicyclic gear train, in which the drive shaft 5 is connected to the planetary gear 61, the propulsion shaft 3 is connected to the planet carrier 64, and the first electric machine M1 is connected to the ring gear 63. The transmission system 6 provides an initial transmission ratio K between the motor rotational speed V5 of the drive shaft 5 and the propulsion rotational speed V3 of the propulsion shaft 3. Furthermore, in this example, the second electric machine M2 is directly connected to the propulsion shaft 3; however, it is understood that the method could just as easily be described for a second electric machine M2 connected to the drive shaft 5.The procedure will be described for a particular phase of aircraft flight, for example, takeoff.

[0070] In a preliminary step E0, the gas turbomachine 4 operates at an optimal engine speed and the engine shaft 5 rotates at an optimal engine speed V5 and drives, in this example, the planetary gear 61 of the transmission system 6.

[0071] For the specified flight phase, in this example a takeoff phase, it is necessary for the propulsion unit 2 to rotate at a higher rotational speed, which is controlled by the gas turbomachine 4. The computer 9 then determines, in a step 11, the transmission ratio K to be applied between the propulsion rotational speed V3 and the engine rotational speed V5, to allow the shaft to propulsion 3 to rotate at an optimal rotational speed while maintaining high-efficiency engine speed.

[0072] In a second step E2, the calculator 9 determines the setting power Pr to be applied, by the first electric machine Ml, to the transmission system 6, in this example via the crown gear 63, to obtain the determined transmission ratio K.

[0073] In this example, in which the aircraft is during a takeoff phase, the first electric machine M1 takes, in a step E3, a setting power Pr from the transmission system 6 via the ring gear 63 to obtain the transmission ratio K, which has the effect of modifying the rotational speed of the ring gear 63 and therefore the rotational speed of the planetary gear 61 connected to the motor shaft 5. In other words, the computer 9 determines the setting power Pr so that the motor rotational speed V5 remains nominal, to allow the gas turbomachine 4 to have optimal efficiency, while allowing the propulsion unit 2 to rotate at a high propulsion rotational speed V3 to allow the aircraft to take off.

[0074] The extraction of the control power Pr from the transmission system 6 incidentally induces a change in the propulsion rotational speed V3 of the propulsion shaft 3. More precisely, the extraction of the control power Pr from the transmission system 6 results in the extraction of a residual power Pq from the propulsion shaft 3, which incidentally reduces the power transmitted by the gas turbomachine 4 to the propulsion unit 2. The computer 9 then determines, in a step E4, from the control power Pr applied by the first electric machine M1 on the transmission system 6, the residual power Pq that is applied to the propulsion shaft 3.

[0075] The process then includes a step E5 in which the computer 9 determines a compensation power Pc, in this example, to be applied to the propulsion shaft 3 to achieve the optimal power for the takeoff phase. The compensation power Pc is determined from the residual power Pr taken from the propulsion shaft 3.

[0076] In a sixth step E6, the second electric machine M2 controls, in this example, a supply of compensation power Pc to be applied to the propulsion shaft 3 to compensate for the power loss suffered by the propulsion shaft 3 following the withdrawal of the residual power Pq.

[0077] Thanks to the first electric machine M1 and the second electric machine M2, the propulsion shaft 3 and the motor shaft 5 can each rotate at an optimal speed to allow the aircraft to take off without the gas turbomachine 4 being penalized by operating at a suboptimal speed. In other words, The propulsion unit 2 rotates according to the optimal propulsion rotation speed V3 for the determined flight phase, while allowing the gas turbomachine 4 to operate at a suitable speed.

[0078] A method is described in which the adjustment power Pr is taken from the transmission system 6 and the compensation power Pc is supplied to the propulsion shaft 3. It is understood that the propulsion assembly 1 works equally well for reverse operation, in which the adjustment power Pr is supplied to the transmission system 6 to allow the motor shaft 5 to rotate at a nominal motor rotation speed V5 and in which the residual power Pq is then added to the propulsion shaft 3 and the compensation power Pc is taken from the propulsion shaft 3 to compensate for the contribution of the residual power Pq.

Claims

1. Demands Aircraft propulsion unit (1) comprising: • a propulsion element (2) mounted on a propulsion shaft (3), the shaft of pi configured to rotate at a propulsion rotation speed (V3), • a gas turbomachine (4) comprising a compressor (41) and a drive shaft (5), the compressor (41) being configured to receive compressed air (AC) to supply a combustion chamber (42) of the gas turbomachine, the turbine (43) being driven by an exhaust air flow from the combustion chamber (42) so as to drive the drive shaft, the drive shaft (5) being configured to rotate at a rotational speed • a transmission system (6) mechanically connected, on the one hand, to the shaft and, on the other hand, to the drive shaft (5), the transmission system (6) having a transmission ratio (K) between the rotational speed of the propulsion unit (3) and the motor rotational speed (V5) of the drive shaft i • a first electric machine (Ml) connected to the transmission system (electric machine (Ml) being configured to supply or draw power) on the transmission system (6), so as to modify the ratio of the power drawn or the input of the control power (Pr) resulting in a residual power input (Pq) on the drive shaft (3), • a second electric machine (M2) connected to the propulsion shaft (3) ( (5), the second electric machine (M2) being configured to provide compensating power (Pc) on the propulsion shaft (3), so as to have residual power (Pq), and • a calculator (9) configured for: • determine the adjustment power (Pr) to be supplied or taken from the electric motor (Ml) on the transmission system (6) for a given propulsion rotation speed (V3) and a rotary speed, • determine the residual power (Pq) supplied or withdrawn by the electrical system (Ml) on the drive shaft (3) from the power supplied or withdrawn from the transmission system (6), and • determine the compensation power (Pc) to be taken or fed into the electric machine (M2) on the propulsion shaft (3) for residual c< nce (Pq).

2. Propulsion assembly (1) according to claim 1, wherein, in absolute values, the ratio between the compensation power (Pc) and the residual power (Pq) is between 0.9 and 1.

1.

3. Propulsion assembly (1) according to any one of claims 1 to 2, wherein the transmission system (6) is an epicyclic train comprising a planetary type gear (61), a plurality of satellite type gears (62) mounted on a satellite carrier (64) and a crown type gear (63).

4. Propulsion assembly (1) according to claim 3, wherein the drive shaft (5), the propulsion shaft (3) and the first electric machine (M1) are each connected to a gear of a different type.

5. Propulsion assembly (1) according to any one of claims 1 to 4, wherein the second electric machine (M2) is connected directly to the propulsion shaft (3) so as to compensate for the residual power (Pq) by supplying or taking the compensating power (Pc) directly from the propulsion shaft (3).

6. Propulsion assembly (1) according to any one of claims 1 to 4, wherein the second electric machine (M2) is connected to the drive shaft (5) so as to compensate for the residual power (Pq) by supplying or taking the compensating power (Pc) from the drive shaft (3) via the transmission system (6).

7. Propulsion assembly (1) according to any one of claims 1 to 6, wherein the first electric machine (M1) and the second electric machine (M2) are electrically connected directly or indirectly to each other, so as to permit exchanges of electrical power flow between the first electric machine (M1) and the second electric machine (M2).

8. Aircraft comprising at least one propulsion unit (1) according to any one of claims 1 to 7.

9. A method for operating a propulsion system (1) according to any one of claims 1 to 7, the method comprising the steps of: • determining (1E1), by the computer (9), a transmission ratio (K) at a propulsion rotational speed (V3) and the engine rotational speed (V5) for a given flight phase, such that the gas turbomachine (4) operates at optimal efficiency to control (E3), by the first electrical machine (Ml) on the system), an input or output of a set power (Pr) as a function of emission (K) determined, the output or output of the residual power (Pq) on the arbn, and to control (E6), by the second electric machine (M2), respectively drawing a compensating power (Pc) from the drive shaft to compensate for the residual power (Pq) on the drive shaft (3) afir ne propulsive (2) according to the predetermined drive rotation speed (V3)

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