IMPROVED DRIVE ASSEMBLY FOR MULTI-ENGINE HYBRID AIRCRAFT

Description

Technical Field

[0001] The present invention relates to the field of hybrid aircraft, comprising at least two engines such as turboshaft or turboprop engines, for flying machines such as helicopters or twin-engine airplanes. In particular, the invention relates to a propulsion system for a multi-engine hybrid aircraft, especially a twin-engine one, and to a hybrid aircraft comprising such a propulsion system. Previous technique

[0002] As is known, a turbomachine, for example a turbomotor, especially for a helicopter, comprises a gas turbine having a gas generator and a free turbine driven in rotation by the gas flow generated by the gas generator.

[0003] Traditionally, a gas generator consists of at least one compressor and one turbine coupled in rotation. The operating principle is as follows: fresh air entering the gas turbine is compressed by the compressor's rotation before being sent to a combustion chamber where it is mixed with fuel. The exhaust gases from combustion are then expelled at high speed. A first expansion occurs in the gas generator's turbine, during which it extracts the energy necessary to drive the compressor. The gas generator's turbine does not absorb all the kinetic energy of the exhaust gases; the excess kinetic energy corresponds to the gas flow generated by the gas generator.The latter therefore provides kinetic energy to the free turbine so that a second expansion occurs in the free turbine which transforms this kinetic energy into mechanical energy in order to drive a receiving organ, such as the rotor of the helicopter.

[0004] Some aircraft have two or more turbomachines, each comprising a gas turbine as described above. This is particularly true of twin-engine or multi-engine helicopters. Such aircraft allow for operation in SEO (Single Engine Operative) mode. SEO mode is an operating mode for a twin-engine configuration in which one of the gas turbines is intentionally shut down, while the other provides all the power. This mode optimizes specific fuel consumption, which decreases with the power delivered by a turbomachine. Indeed, since the specific fuel consumption of a turbine decreases with the power delivered, it is preferable to provide 100% of the power with one turbine, rather than 50% with each of them.

[0005] One of the critical aspects of SEO mode lies in the ability to restart a stopped turbine in the event of a power loss in the operating turbine. To ensure the fastest possible restart, it is possible to keep the stopped turbine in standby mode (or "super idle"), meaning that the gas generator continues to run solely using an electric motor, without any fuel input. The generator is then maintained within its "ignition window" (typically 10-30%) to allow for immediate fuel ignition, or in "super-idle" mode using super-idle combustion assisted by an electric motor, thus benefiting from a hot combustion chamber.

[0006] To perform these functions, existing solutions propose, for example, using the power supplied by the operating turbine, drawn from the main rotor, to power the electric machine that provides power to the turbine in standby mode, by means of a dedicated electric machine on each gas generator. This configuration therefore requires four electric machines in total. More generally, twin-engine applications involve numerous functions, such as starting the gas generator, generating electricity on the ground, or supplying electrical power to the main rotor. FR 3 039 614 A1 discloses an example of a twin-engine aircraft, and US 8 727 820 B2 and US 2011 / 049891 A1 disclose examples of hybrid propulsion systems including an electric machine.

[0007] Existing solutions for performing these functions require a large number of electrical machines, some with power outputs far exceeding those of the generators / starters typically used—typically several tens to hundreds of kilowatts, instead of around ten kilowatts—and are not entirely satisfactory. Therefore, there is a need for a propulsion system for twin-engine or multi-engine aircraft with an architecture that at least partially addresses the aforementioned drawbacks. Description of the invention

[0008] This presentation concerns a propulsion system for a hybrid aircraft, particularly a multi-engine helicopter, comprising: at least one first gas turbine and a second gas turbine, each having a gas generator and a free turbine driven in rotation by a gas flow generated by the gas generator, a main rotor coupled to the free turbine of the first gas turbine and the second gas turbine via a first and a second main coupling means respectively, a first reversible electric machine and a second reversible electric machine, each capable of being coupled to the gas generator of the first gas turbine and the second gas turbine respectively, via a first switchable coupling means, and of being each coupled to the main rotor via a second switchable coupling means, the first switchable coupling means each being configured to be activated when the first and second electric machines rotate in a first direction of rotation,and the second switchable coupling means being configured to be activated when the first and second electrical machines rotate in a second direction of rotation opposite to the first direction of rotation.

[0009] By "switchable coupling means" it is understood that the coupling means can be in an activated position in which the components connected to said coupling means are coupled, or in a deactivated position in which said components are decoupled, it being understood that "component" means the electrical machines, the main rotor and the gas generator.

[0010] It is also understood that each electric machine is associated with a first switchable coupling means and a second switchable coupling means. In other words, the first reversible electric machine is coupled to the gas generator of the first gas turbine via a first switchable coupling means, and is coupled to the main rotor via a second switchable coupling means. Similarly, the second reversible electric machine is coupled to the gas generator of the second gas turbine via a first switchable coupling means, and is coupled to the main rotor via a second switchable coupling means.

[0011] The propulsion system described herein is particularly advantageous in that each gas turbine is associated with a single electric machine, the electric machines being able to alternately perform specific functions and perform complementary functions, while together ensuring the level of redundancy necessary on critical functions to increase flight safety.

[0012] More specifically, the first and second electric machines can be used in one direction of rotation to be mechanically coupled to the gas generator of the first and second gas turbines, and in the other direction of rotation to be mechanically coupled to the main rotor. In particular, the first (and / or second) electric machine rotating in the first direction of rotation allows coupling with the gas generator of the first (and / or second) gas turbine to start the latter on the ground, but also allows coupling with said gas generator to supplement the thermodynamic power during certain phases of flight, for assisting transient phases or modifying the engine operating point, for example.

[0013] Furthermore, the first (and / or second) electric machine, rotating in the first direction of rotation, allows the gas generator of the first (and / or second) gas turbine to be restarted in flight, for example, following a failure, without requiring the activation of another mechanical component such as a clutch. Moreover, even when the first (or second) electric machine is used in the first direction of rotation to restart the gas generator in flight, the second (or first) electric machine can be used in parallel to assist the second gas turbine by providing additional power to the main rotor.

[0014] Furthermore, the first and / or second electric machine rotating in the second direction of rotation allows the main rotor to be driven in place of the first and / or second gas turbine in case of failure of the latter, or in addition to it in certain phases of flight requiring an additional supply of power.

[0015] Furthermore, during SEO operation, when the first (or second) gas turbine alone drives the main rotor, the second (or first) electric machine can be used to keep the gas generator of the second (or first) gas turbine in standby mode, or to supply electrical power to the first (or second) electric machine when standby mode is ensured by a coupling means such as a clutch or dog clutch as described below.

[0016] Simultaneously, the first (or second) electric machine can be used to supplement the power output of the first (or second) gas turbine's gas generator. In other words, this architecture allows, in SEO mode, one of the gas generators to be kept in standby mode, enabling a rapid restart, while also allowing internal hybridization—that is, power exchange between the electric machines and the gas generators—to limit the aging of the gas turbine that remains running.

[0017] Therefore, the multi-motor architecture described herein offers the advantage of simplicity by limiting the number of components and connections. This makes it possible to streamline and reduce the number of electrical machines, while still enabling a high number of functions by sharing them, and reducing the overall mass of the device.

[0018] In some embodiments, the first electric machine and the second electric machine are configured to operate in motor mode in which they are capable of supplying power to the main rotor or the gas generator of the first and second gas turbine respectively, according to their direction of rotation, or in generator mode in which they are capable of being driven into rotation by the main rotor or by said gas generator by blocking one or the other of the first or second switchable coupling means, so as to generate electrical energy.

[0019] The switchable coupling means associated with each electric machine can be lockable. They can, for example, include movable locking means between a free position in which the gas generator (for example) cannot drive the electric machine in rotation, and a locked position in which the gas generator is able to drive the electric machine in rotation, so that the electric machine draws electrical power from the gas generator.

[0020] Locking the switchable coupling means allows for forced coupling between the electric machines and the gas generator (or main rotor). For example, when the coupling means includes a freewheel and a locking mechanism, the freewheel is called a "lockable freewheel," such that in the locked position, the freewheel hub can drive the peripheral ring gear of the lockable freewheel. In other words, the gas generator (or main rotor) is able to drive either the first or second electric machine.

[0021] In other words, the electric machines can be used to draw power from the gas generator or the main rotor and thus provide electrical power to the onboard network in APU (“Auxiliary Power Unit”) mode on the ground for recharging batteries for example, or in flight as a supplement or replacement for one of the electric machines in case of failure of the latter for example, via an electrical connection between the first electric machine and the second electric machine.

[0022] In some embodiments, the propulsion assembly comprises a first coupling means coupled to the main rotor and the gas generator of the first gas turbine, and a second coupling means coupled to the main rotor and the gas generator of the second gas turbine, the first and second coupling means being movable between a decoupling position, and a coupling position in which the main rotor is coupled with the gas generator of the first and second gas turbines respectively.

[0023] The first and second coupling means can be mechanical systems such as clutches, dog clutches, or chamfered dog clutches allowing automatic disengagement in the event of a rapid restart. In the uncoupled position, the main rotor cannot drive the gas generator. In the coupled position, the main rotor and the gas generator of the first (or second) gas turbine are mechanically linked, such that the gas generator can be driven, even at low speeds, by the main rotor.

[0024] The first coupling system, for example, thus constitutes a bypass branch allowing the first electric machine and its associated switchable coupling means to be circumvented, so that the standby mode of the first gas turbine can be maintained while freeing up the first electric machine. The latter can then be used for other functions such as internal hybridization (supplying electrical energy to the second electric machine, for example), in generator mode by blocking the second switchable coupling means.

[0025] The presence of coupling means eliminates the need for a third electric machine, which would be required for internal hybridization by supplying electrical power to the first and second electric machines without coupling. Thus, only two electric machines are needed in SEO mode to perform the desired functions, simplifying the architecture and reducing the overall mass of the propulsion system.

[0026] In some embodiments, when one of the first or second gas turbines drives the main rotor alone, the gas generator of the other of the first or second gas turbine is kept in a standby mode, at a power of less than 5kW, by means of the first or second coupling means in the coupling position.

[0027] When the aircraft operates in SEO mode, the first gas turbine, for example, provides all the power, while the second gas turbine is intentionally shut down, or preferably placed in standby mode, to optimize specific fuel consumption. Standby mode keeps the second gas turbine's generator at low power, below 5 kW, or within a range of 5 to 30% of its rated speed, to allow for rapid restart if necessary, particularly if the first gas turbine shuts down unintentionally. Maintaining standby mode via the second coupling, in the coupled position, also frees up the second electric machine for other functions such as internal hybridization.This configuration is particularly advantageous insofar as the electric machines, sized to quickly start the gas turbines by supplying several tens of kilowatts or to assist the rotor by supplying a few hundred kilowatts, are not tied up for maintenance in standby mode, requiring less than 5kW.

[0028] In some embodiments, when the first gas turbine drives the main rotor alone, the first electric machine operates in motor mode so as to supply power to the gas generator of the first gas turbine, and the second electric machine operates in generator mode so as to supply electrical energy to the first electric machine.

[0029] It is understood that the first electric machine operates in motor mode, rotating in the first direction of rotation, so as to supply power to the gas generator of the first gas turbine via the first switchable coupling. Similarly, the second electric machine operates in generator mode, driven by the main rotor, with the second switchable coupling locked in this position, in order to supply electrical energy to the first electric machine and thus limit its wear. It should be noted that the first electric machine can be electrically connected to the second electric machine via an electrical connection.

[0030] In certain embodiments, when the second gas turbine drives the main rotor alone, the second electric machine operates as a motor to supply power to the gas generator of the second gas turbine, and the first electric machine operates as a generator to supply electrical energy to the second electric machine. This architecture makes it possible, using only two electric machines, to limit the aging of the single operating gas turbine while ensuring internal hybridization, with one of the electric machines supplying electricity to the other.

[0031] In some embodiments, the propulsion assembly is configured such that, when the first gas turbine driving the main rotor alone stops, the second electric machine operates in motor mode so as to supply a power greater than or equal to 50 kW to the gas generator of the second gas turbine.

[0032] In some embodiments, the propulsion assembly is configured such that, when the second gas turbine driving the main rotor alone stops, the first electric machine operates in motor mode so as to supply a power greater than or equal to 50 kW to the gas generator of the first gas turbine.

[0033] When the aircraft is operating in SEO mode, and one or the other of the gas turbines driving the main rotor alone stops unintentionally, the other of the gas turbines kept in standby mode can thus be quickly restarted by injecting a large power, greater than or equal to 50 kW, into the latter's gas generator.

[0034] In some embodiments, the propulsion assembly includes a third reversible electric machine suitable for being coupled to the main rotor and the free turbine of the first gas turbine and the second gas turbine via the first main coupling means and the second main coupling means respectively.

[0035] In some embodiments, the third electric machine is configured to operate in generator mode, in which it is capable of being driven in rotation by the main rotor, itself driven by the free turbine of the first and / or second gas turbine via the first and / or second main coupling means, so as to generate electrical energy, or in motor mode in which it is capable of supplying power to the main rotor.

[0036] Although redundant with the first and second electric machines in most operating modes, the use of a third electric machine enables symmetrical internal hybridization when both gas turbines are running, which is not possible when only the first and second electric machines are present. It also eliminates the need for a second switchable coupling mechanism, thus simplifying the overall structure (only the first switchable coupling mechanism would then be switchable), by allowing electricity generation from the main rotor.

[0037] In some embodiments, when the first gas turbine alone drives the main rotor, the gas generator of the second gas turbine is kept in standby mode, at a power output of less than 5 kW, by means of the second electric machine operating in motor mode. Preferably, the first electric machine operates in motor mode to supply power to the gas generator of the first gas turbine, and the third electric machine operates in generator mode to supply electrical energy to both the first and second electric machines.

[0038] The use of a third electric machine eliminates the need for the first and second coupling devices, thus reducing the number of transmission components. In SEO mode, the third electric machine can be used as a generator to power the second electric machine, which keeps the second gas turbine in standby mode, and to power the first electric machine to achieve internal hybridization and reduce the aging of the first gas turbine. The third electric machine can also be used as a motor to supplement the power supplied by the first gas turbine during certain operating phases. It should be noted that the propulsion system can also include the third electric machine in combination with the aforementioned coupling devices to increase the level of redundancy.

[0039] In some embodiments, when the second gas turbine alone drives the main rotor, the gas generator of the first gas turbine is kept in a standby mode, at a power output of less than 5 kW, by means of the first electric machine operating in motor mode. Preferably, the second electric machine operates in motor mode so as to supply power to the gas generator of the second gas turbine, and the third electric machine operates in generator mode so as to supply electrical energy to the first and second electric machines.

[0040] In some embodiments, the propulsion assembly includes a rotor brake suitable for being disposed between the free turbine of the first and second gas turbine, and the main rotor, being movable between a braking position preventing the main rotor from being driven by the free turbine of the first and / or second gas turbine or by external forces, and a free position allowing the main rotor to be driven by said free turbine.

[0041] More specifically, the free turbine of the first and second gas turbines is coupled to the main rotor, while a movable rotor brake located on the drive train allows it to be locked. During startup, the hot gases drive the free turbine. This turbine, connected to the main rotor via the first or second main coupling, can be either free when the rotor brake is in the free position, or locked by the rotor brake when the latter is in the braking position. This braking position thus allows the main rotor to be locked and, as a side effect, the free turbine, particularly in the event of a start-up in strong winds.

[0042] In some embodiments, the first and second main coupling means, and the first and second switchable coupling means associated with each of the first and second electric machines, include a freewheel.

[0043] One advantage of a freewheel is that it does not require electronic or mechanical control by an external operator. Furthermore, the freewheel offers significant reliability. Such a freewheel generally consists of a hub and a peripheral ring mounted to rotate on the hub. The hub can typically drive the peripheral ring when torque is applied in the intended direction. The peripheral ring can also drive the hub when torque is applied in the opposite direction without compromising the principle of the present invention. Therefore, the hub can only drive the ring when it rotates in a predetermined direction relative to the ring, which will be called the "direction of engagement." Otherwise, the hub and the peripheral ring rotate freely relative to each other.

[0044] In this case, the switchable coupling means are activated when the freewheel hub drives the peripheral ring gear, and conversely, the switchable coupling means are deactivated when the freewheel hub does not drive the peripheral ring gear. Using freewheels as coupling elements between the various components, in the absence of other coupling means such as clutches or dog clutches, improves the reliability of the entire drive system.

[0045] In some embodiments, the propulsion assembly includes a control unit configured to control the first electric machine, the second electric machine, the third electric machine, the switchable coupling means, and the rotor brake.

[0046] This presentation also relates to a hybrid aircraft comprising a propulsion system according to any of the preceding embodiments, the hybrid aircraft being a multi-engine helicopter, in particular a twin-engine one.

[0047] The term "hybrid aircraft" refers to an aircraft comprising a thermal engine capable of driving a main rotor in rotation, and at least one electric machine capable of providing power to the thermal engine. Brief description of the drawings

[0048] The invention and its advantages will be better understood upon reading the detailed description below of various embodiments of the invention, given by way of non-limiting examples. This description refers to the accompanying figure pages, on which: [ Fig. 1 ] There figure 1 represents a cross-sectional view of a propulsion assembly for a twin-engine aircraft according to the invention, [ Fig. 2 ] There figure 2 schematically represents the propulsion system of the figure 1 , [ Fig. 3 ] There figure 3 represents the propulsive assembly of the figure 2 , according to a first mode of operation, [ Fig. 4 ] There figure 4 represents the propulsive assembly of the figure 2 , according to a second mode of operation, [ Fig. 5 ] There figure 5 represents the propulsive assembly of the figure 2 , according to a third mode of operation, [ Fig. 6 ] There figure 6 represents the propulsive assembly of the figure 2 , according to a fourth mode of operation, [ Fig. 7 ] There figure 7 represents the propulsive assembly of the figure 2 , according to a fifth mode of operation, [ Fig. 8 ] There figure 8 represents the propulsive assembly of the figure 2 , according to a sixth mode of operation, [ Fig. 9 ] There figure 9 represents the propulsive assembly of the figure 2 , according to a seventh mode of operation, [ Fig. 10 ] There figure 10 represents the propulsive assembly of the figure 2 , according to an eighth mode of operation, [ Fig. 11 ] There figure 11 represents the propulsive assembly of the figure 2 , according to a ninth mode of operation, [ Fig. 12 ] There figure 12 represents the propulsive assembly of the figure 2 , according to a tenth mode of operation, [ Fig. 13 ] There figure 13 represents the propulsive assembly of the figure 2 , according to an eleventh mode of operation, [ Fig. 14 ] There figure 14 represents the propulsive assembly of the figure 2 , according to a twelfth mode of operation, [ Fig. 15 ] There figure 15 represents the propulsive assembly of the figure 2 , according to a thirteenth mode of operation, [ Fig. 16 ] There figure 16 represents the propulsive assembly of the figure 2 , according to a fourteenth mode of operation, [ Fig. 17 ] There figure 17 represents the propulsive assembly of the figure 2 , according to a fifteenth mode of operation, [ Fig. 18 ] There figure 18 represents the propulsive assembly of the figure 2 , according to a sixteenth mode of operation. Description of the implementation methods

[0049] An architecture of a propulsion system 100 according to an embodiment of the invention will be described in the following description, with reference to figures 1 à 18 .

[0050] There figure 1 This schematically represents a propulsion system 100 of a twin-engine aircraft, comprising a first turbomachine 1 and a second turbomachine 2, driving in rotation the transmission components 60 of a helicopter carrying a propeller or a main rotor 62. The turbomachines may be turboshaft engines or turboprop engines. Although the propulsion system described below comprises two turbomachines, this example is not limiting, as the invention also applies to propulsion systems of multi-engine aircraft comprising more than two engines.

[0051] The first turbomachine 1 and the second turbomachine 2 are preferably identical and have the same characteristics. Therefore, the description below refers to both the first and second turbomachines 1 and 2.

[0052] The first turbomachine 1 and the second turbomachine 2 respectively comprise a gas turbine 10, 20 having a gas generator 12, 22 and a free turbine 11, 21 capable of being driven into rotation by a gas flow generated by the gas generator 12, 22. The free turbine 11, 21 is mounted on a shaft 13, 23 which transmits the rotational motion to a receiving element such as a main rotor 62 of the helicopter via the transmission elements 60. According to this example, the gas turbine 10, 20 shown in the figure 1 is of the front-drive type with coaxial shaft drive. Without departing from the scope of the present invention, one could also consider a free-turbine gas turbine of the front-drive type with internal or external shaft drive, or a free-turbine turbomachine of the rear-drive type. Similarly, the turbine could be directly driven or incorporate a speed reducer without altering the principle of the invention.

[0053] The gas generator 12, 22 comprises a rotating shaft 14, 24 on which are mounted a compressor 15, 25 and a turbine 16, 26, as well as a combustion chamber 17, 27 arranged axially between the compressor 15, 25 and the turbine 16, 26 when the gas generator 12, 22 is considered along the axial direction of the rotating shaft 14, 24. The gas turbine 10, 20 has a casing 18, 28 equipped with an air inlet 19, 29 through which fresh air enters the gas generator 12, 22. After its admission into the chamber of the gas generator 12, 22, the fresh air is compressed by the compressor 15, 25 which forces it towards the inlet of the combustion chamber 17, 27 where it is mixed with fuel. The combustion which takes place in the combustion chamber 17, 27 causes the burnt gases to be evacuated at high speed towards the turbine 16, 26, which in turn causes the shaft 14, 24 of the gas generator 12, 22 to rotate and, consequently, the compressor 16, 26.The rotational speed of the shaft 14, 24 of the gas generator 12, 22 is determined by the fuel flow entering the combustion chamber 17, 27.

[0054] Despite the extraction of kinetic energy by turbine 16, 26, the gas flow exiting the gas generator possesses significant kinetic energy. As can be understood from the figure 1 , the gas flow F is directed towards the free turbine 11, 21 which has the effect of causing an expansion in the free turbine 11, 21 leading to the rotation of the turbine wheel and the shaft 13, 23.

[0055] The main rotor 62 is coupled, via the transmission elements 60, to the shaft 13 of the free turbine 11 of the first gas turbine 10 by means of a first main coupling means 51. The main rotor 62 is also coupled, via the transmission elements 60, to the shaft 23 of the free turbine 21 of the second gas turbine 20 by means of a second main coupling means 52.

[0056] Preferably, the first and second main coupling means 51, 52 include a freewheel mounted such that the rotation of the shaft 13, 23 can drive the main rotor 62, but conversely, the rotation of the main rotor 62 cannot drive the shaft 13, 23 of the free turbine 11, 21. In other words, the freewheel of the first and second main coupling means 51, 52 can only transfer rotational torque from the free turbine 11, 21 to the main rotor 62, but not the other way around. On a helicopter, this freewheel is commonly called a "motor freewheel." It should be noted that the use of a freewheel for the main coupling means 51, 52 and the disengageable coupling means described below is not limiting; the freewheel can be replaced by any dog ​​clutch or clutch system.

[0057] The propulsion unit 100 further comprises a first reversible electric machine 30, mechanically coupled to the shaft 14 of the gas generator 12 by means of a first switchable coupling means 31.

[0058] Preferably, the first switchable coupling means 31 includes a freewheel mounted such that the rotation of the first reversible electric machine 30 can drive the shaft 14 of the gas generator 12 when the first electric machine is operating in electric motor mode (first coupling means 31 activated), but conversely, the rotation of the shaft 14 of the gas generator 12 cannot drive the first reversible electric machine 30 if the first switchable coupling means 31 is not blocked. In other words, the freewheel of the first switchable coupling means 31 can only transfer rotational torque in the direction from the first electric machine 30 to the gas generator 12, but not the other way around, in order to combine the high reliability of the freewheel with critical functions such as restarting the turbine in flight.

[0059] The first electric machine 30 is also suitable for being coupled to the main rotor 62, via a second switchable coupling means 32 similar to the first switchable coupling means 31 and preferably comprising a freewheel, so that the first electric machine 30, operating in electric motor mode (second coupling means 32 activated), is suitable for driving the main rotor 62 in rotation.

[0060] The propulsion unit 100 also includes a second reversible electric machine 40, mechanically coupled to the shaft 24 of the gas generator 22 by means of a first switchable coupling means 41.

[0061] Preferably, the first switchable coupling means 41 includes a freewheel mounted such that the rotation of the second reversible electric machine 40 can drive the shaft 24 of the gas generator 22 when the second electric machine is operating in electric motor mode (first coupling means 41 activated), but conversely, the rotation of the shaft 24 of the gas generator 22 cannot drive the second reversible electric machine 40 if the first switchable coupling means 41 is not blocked. In other words, the freewheel of the first switchable coupling means 41 can only transfer rotational torque from the second electric machine 40 to the gas generator 22, but not the other way around.

[0062] The second electric machine 40 is also suitable for being coupled to the main rotor 62, via a second switchable coupling means 42 similar to the first switchable coupling means 41 and preferably comprising a freewheel, in such a way that the second electric machine 40, operating in electric motor mode (second coupling means 42 activated), is suitable for driving the main rotor 62 in rotation.

[0063] In accordance with the propulsion assembly 100 of this presentation, the first and second electric machines 30, 40 are capable of rotating in a first direction of rotation in which they are respectively mechanically coupled to the shaft 14, 24 of the gas generator 12, 22, and in a second direction of rotation, opposite to the first direction of rotation, in which they are respectively mechanically coupled to the main rotor 62. By convention, in the following description, a positive direction will be understood as a direction of rotation of the first and second electric machines 30, 40 in which the first switchable coupling means 31, 41 is activated, and a negative direction as a direction of rotation of the first and second electric machines 30, 40 in which the second coupling means 32, 42 is activated.

[0064] In particular, the element represented by "-1" on the figure 2 and the following figures represent gears, for example pinions, allowing the direction of rotation to be reversed. It will thus be understood that when the first and second electrical machines 30, 40 rotate in the positive direction, the first switchable coupling means 31, 41 is activated, and the second coupling means 32, 42 is deactivated, and when the first and second electrical machines 30, 40 rotate in the negative direction, the first switchable coupling means 31, 41 is deactivated, and the second coupling means 32, 42 is activated.

[0065] The first and second reversible electric machines 30, 40 each consist of an electric motor capable of operating reversibly as an electric generator. To achieve this, either the first switchable coupling means 31, 41 or the second switchable coupling means 32, 42 can be blocked, by means of a locking mechanism, so that it can be driven in rotation by the main rotor 62 or by the gas generator 12, 22, and thus generate electrical energy. This electrical energy generated by the electric machines 30, 40 can then be transferred to other elements of the propulsion system, for example to a battery pack (not shown), or can be exchanged between the electric machines 30, 40 to achieve internal hybridization.

[0066] It should be noted that although the first and second reversible electric machines 30, 40 can be arranged within the turbomachine perimeter, this arrangement is not limiting. The reversible electric machines 30, 40 can in fact be arranged in separate areas of the helicopter from the turbomachines 1, 2, without departing from the scope of the invention. This observation applies generally to the entire propulsion system, which also includes the third electric machine and the various coupling means described later in this description.

[0067] A third reversible electric machine 50 can be mechanically coupled to the shaft 13, 23 of the free turbine 11, 21 via the first and second main coupling means 51, 52.

[0068] The first and second main coupling means 51, 52 comprising a free wheel can also be mounted such that the rotation of the shaft 13, 23 can drive the third electric machine 50 in rotation when it is operating in generator mode to supply electricity, but conversely, the rotation of the third electric machine 50 cannot drive the shaft 13, 23 of the free turbine 11, 21 in rotation. The third electric machine 50 can also operate in electric motor mode so as to drive the main rotor 62 in rotation for takeoff assistance or transients for example.

[0069] It should be noted, however, that although most of the figures represent a propulsion system including a third electric machine 50, it is also possible to dispense with its use without departing from the scope of the invention. Indeed, although the third electric machine 50 increases the level of redundancy, the mere presence of the first and second electric machines 30, 40 in this architecture ensures a large number of functions. In particular, in the case of SEO mode operation described below with reference to the figure 16 , the absence of the third electric machine 50 can be compensated by the presence of a first coupling means 81 in the first turbomachine 1, and a second coupling means 82 in the second turbomachine 2.

[0070] The first and second coupling means 81, 82 are referred to hereafter as clutches, but other types of coupling means may be used, such as dog clutches. The clutches 81, 82 are movable between a coupling position in which the main rotor 62 is coupled with the gas generator 12, 22 of the first and second gas turbines 10, 20 respectively, and a decoupling position in which these elements are not coupled.

[0071] In the decoupled position, the main rotor 62 cannot drive the gas generator 12, 22. In the coupled position, the main rotor 62 and the gas generator 12, 22 are mechanically linked, such that the gas generator 12, 22 can be driven, even at low speed, by the main rotor 62. This will notably allow the gas generator 12, 22 to be driven into its ignition window without monopolizing or stressing the electric machine 30, 40. It should be noted, in the following description, that the coupled position of the clutches 81, 82, and the locked position of the first reversible coupling means 31, 41 and the second reversible coupling means 32, 42, are symbolized in the figures by a cross crossing these elements.

[0072] Furthermore, the device may also include a rotor brake 70 disposed between the third electric machine 50 and the main rotor 62. The rotor brake 70 is movable between a braking position (represented by a cross on the figure 4 for example), preventing the rotation of the main rotor 62 and the free turbine 11 and / or 21, and a free position allowing the rotation of the main rotor 62 and the free turbine 11 and / or 21. It should be noted, however, that although the figures 1 à 18 While the devices represented include such a rotor brake 70, it is also possible to dispense with the use of the latter without departing from the scope of the invention. Indeed, the rotor brake function can also be fulfilled by the first and second electric machines 30, 40 operating in generator mode so as to create a torque opposing the rotation of the main rotor 62, thus braking or even locking it. In this case, the rotor brake 70 can be undersized or absent, or even replaced by a locking system such as a clutch or dog clutch.

[0073] Given this architecture, the propulsion system can perform various functions. These functions are described below with reference to figures 3 à 18 In these figures, the dashed arrows represent the direction of mechanical or electrical power transmission between two elements. On the figure 3 For example, mechanical power is transmitted from the first electric machine 30 to the shaft 14 of the gas generator 12 of the first gas turbine 10. It should also be noted generally that, for the sake of clarity, the figures 2 à 18 These diagrams schematically, functionally, and in a simplified manner represent the different operating modes of the device, without depicting all the details of the components of the turbomachine and the various power transmission elements. In particular, gears and any speed ratios are not shown.

[0074] There figure 3 This represents an operating mode enabling the starting of the first turbomachine 1, in particular the first gas turbine 10. The first electric machine 30 is driven, for example by a control unit (not shown), so as to rotate in the positive direction. Thus, it drives the gas generator 12 via the freewheel of the first coupling means 31, enabling the starting of the gas generator 12.

[0075] During start-up, the hot gases drive the free turbine 11. The latter, connected to the main rotor 62 via the freewheel of the first main coupling means 51, can be either free, when the rotor brake 60 is in the free position ( figure 3 ), or blocked by the rotor brake when it is in the braking position ( figure 4 This latter configuration can be useful in the event of a start-up in strong winds. Furthermore, since the power of the first electric machine 30 is on the order of several tens to a few hundred kilowatts, it is possible to start the turbine much more quickly than with a starter motor of around 10 kW, which is usually used. This provides a particular operational advantage in the case of medical rescue missions, or during attempts at rapid in-flight restarts (described below and illustrated in particular on the figure 13 ).

[0076] In the scenario where the rotor brake 60 is in the braking position, the first electric machine 30 can then operate in generator mode, the "generator" mode being represented by a small lightning bolt on the figure 4 and the following figures. The figure 4 This system demonstrates how electricity is generated on the ground. More specifically, this operating mode, known as the "APU" (Auxiliary Power Unit) mode or function, is a mode in which the first gas turbine 10 drives an electric generator without driving the helicopter's main rotor. This ensures the power supply to electrical devices on the ground, such as batteries, flight equipment, heating, and air conditioning. In particular, this mode recharges the batteries, which can then be used in flight to power the electrical machines that provide electrical assistance to the main rotor 62, for example, during the takeoff phase.

[0077] To perform this function, a locking means (not shown) is actuated to block the first reversible coupling means 31, so that the gas generator 12 of the first gas turbine 10 can drive the first electric machine 30. The first electric machine 30 thus takes power to deliver to the electrical equipment, while the free turbine 11 is blocked by the rotor brake 70, then in the braking position.

[0078] It should be noted that the start-up of the second turbomachine 2 is carried out following the same pattern as the first turbomachine 1, and the second electric machine 40 can also operate in generator mode in "APU" mode, in the same way as the first electric machine, by blocking the first reversible coupling means 41.

[0079] There figure 5 represents nominal operation with electrical generation on the ground (APU mode, rotating rotor) or in flight. Following the start-up of the first gas turbine 10, the first free turbine 11 drives the main rotor 62 via the main coupling means 51. The first free turbine 11 also drives the third electric machine 50, which then operates in generator mode, as well as the first electric machine 30, which also operates in generator mode, with the second reversible coupling means 32 blocked.

[0080] There figure 6 This represents an alternative example in which the two gas turbines 10, 20 are ignited and drive the main rotor 62, and the first and second electric machines 30, 40 operate in generator mode, with the second coupling means 32, 42 respectively blocked. This operating mode can be used on the ground or in flight, and notably allows for limiting the fuel draw from the gas generators and thus reducing the impact on performance. This very high simultaneous generation also allows for the recharging of a high-power battery pack, for example.

[0081] There figure 7 represents nominal operation allowing power to be supplied to the main rotor 62 by the third electric machine 50 and the figure 8 This represents nominal operation, allowing power to be supplied to the main rotor 62 by the first and second electric machines 30 and 40, each operating as an electric motor and rotating in the opposite direction. This configuration can be useful during certain flight phases requiring additional power, such as during takeoff. The first electric machine 30 and the second electric machine 40 thus supplement the power supplied to the main rotor 62 by the free-wheeling turbines 11 and 21. It should be noted that this power supply to the main rotor 62 is intermittent and potentially recurring, and does not require an active system such as a dog clutch or a clutch. Therefore, the free-wheeling turbines offer an advantage in terms of reliability.

[0082] There figure 9 This represents nominal operation with power supplied to the shafts 14, 24 of the gas generators to improve responsiveness during transient phases. In certain flight phases, for example during significant torque demands, the rotational speed of the free turbines can drop abruptly, requiring a high level of responsiveness from the gas generator 12, 22. In this case, the first and / or second electric machine 30, 40 can, by rotating in the positive direction, contribute to accelerating the speed of the gas generator 12, 22 to deliver the required power as quickly as possible. The power can come from a battery pack (not shown), but also from the third electric machine 50, as illustrated in the figure. figure 9 The third electric machine 50 then operates in generator mode, and is electrically connected to the first and second electric machines 30, 40 via an electrical connection 90.

[0083] There figure 10 represents nominal twin-engine operation with internal hybridization and power transfer from the gas generator to the main rotor. In certain twin-engine flight phases, it can be useful to implement internal hybridization, i.e., power transfers between the main rotor and the gas generators, or vice versa. On the figure 10 The first coupling means 31, 41 are blocked. The first and second electric machines 30, 40 then operate in generator mode, and transfer electrical energy to the third electric machine 50 via an electrical connection 90, the third electric machine itself operating in motor mode to drive the main rotor 62.

[0084] THE figures 11 And 12represent other examples of operation with internal hybridization. On a twin-engine assembly, it may appear that the first turbomachine 1 (for example) reaches its cyclic fatigue more quickly than the second turbomachine 2. It is then possible, in the absence of a third electric machine in particular, to carry out an asymmetric internal hybridization, using the second electric machine 40 to generate electrical power through the first or second reversible coupling means 41, 42, in order to assist the first gas turbine 10.

[0085] Thus, on the figure 11 The second electric machine 40 operates in generator mode by drawing power from the shaft 24 of the gas generator 22, the first reversible coupling means 41 being blocked. On the figure 12 The second electric machine 40 operates in generator mode, drawing power from the main rotor 62, with the second reversible coupling 42 locked. In both configurations, power is transferred from the second electric machine 40 to the first electric machine 30 (which operates in motor mode, rotating in the positive direction) via an electrical connection 90.

[0086] There figure 13 represents operation in the event of the unintentional shutdown of one of the turbomachines in flight. In the event of the shutdown of the second turbomachine 2, following the example of the figure 13 The first turbomachine 1 supplies all the power to the main rotor 62. The second electric machine 40 then rotates in the positive direction to drive, via the first reversible coupling 41, the gas generator 22 of the second gas turbine 20, in an attempt to restart it. Since the power of the second electric machine 40 is on the order of several tens to a few hundred kilowatts, it is possible to start the gas generator 22 much more quickly than with a starter motor of around 10 kW, which is usually used. Furthermore, the first and / or third electric machines 30, 50 (the first electric machine 30 then rotating in the negative direction in motor mode) can be used to provide additional power to the main rotor 62, thus avoiding or delaying the use of the emergency operating modes of the second turbomachine 2.

[0087] If the restart attempt fails, or is not possible, the flight can continue on a single turbine (in this example, the first gas turbine 10), with the first and / or second and / or third electric machines 30, 40, 50 used in motor mode to provide power to the main rotor 62 during operating phases that require it (e.g., clearing a danger zone or landing), within the limits of battery capacity. This configuration is shown on the figure 14 .

[0088] THE figures 15 And 16These represent operation in SEO (Single Engine Operative) mode, in which only the first turbomachine 1 is running, providing all the power to the main rotor 62, while the second turbomachine 2 is intentionally shut down. When SEO mode is engaged, the second gas turbine 20 is put into standby (or assisted super-idle), meaning it no longer supplies power. However, to start it as quickly as possible, its gas generator 22 is driven into the ignition window (within a range of 5 to 30% of its rated rotational speed) by the second electric machine 40 via the first reversible coupling means 41.

[0089] In the example shown on the figure 15 , a third electric machine 50 is used in generator mode to supply, via the electrical connection 90, the second electric machine 40 which keeps the second gas turbine 20 in standby, and also the first electric machine 30 to achieve internal hybridization and limit the aging of the first gas turbine 10. It should be noted that the third electric machine 50 can also be used in motor mode to supplement the power supplied by the first gas turbine 10 to the main rotor 62, in certain operating phases requiring it.

[0090] In the example shown on the figure 16 Clutches 81, 82 are used in place of the third electric machine 50. More specifically, the second clutch 82 is placed in the coupling position so as to couple the main rotor 62 with the gas generator 22 of the second gas turbine 20, in order to keep the second gas turbine 20 in standby, without using the second electric machine 40. In this configuration, the second electric machine 40 is then used in generator mode, by blocking the second reversible coupling means 42, so as to achieve internal hybridization (via the electrical connection 90) between the second electric machine 40 and the first gas turbine 10, while keeping the second gas turbine 20 in standby.

[0091] When exiting SEO mode is desired, the second gas turbine 20 is restarted with the same sequence as for a conventional start-up, described above with reference to the figure 3 However, in the event of a power loss in the first gas turbine 10, a rapid restart of the second gas turbine 20 may be necessary. To achieve this, the second electric machine 40 supplies a significant amount of power (on the order of 50 kW) to the gas generator 22 of the second gas turbine 20. At the end of the sequence, the second gas turbine 20 supplies all of its power, possibly at an emergency operating level.

[0092] Advantageously, between the power loss of the first gas turbine 10 and the power being made available to the second gas turbine 20 by restarting the latter, the third (when in use) and / or the first (rotating in the negative direction) electric machines 50, 30 can be used to supply power to the main rotor 62 and limit its speed drop. This mode of operation for the rapid restart of the second gas turbine 20 with the assistance of the first and third electric machines 30, 50 is shown in the figure 17 .

[0093] After restarting the second gas turbine 20, the first and / or second and / or third electric machines 30, 40, 50 can be used in motor mode to power the main rotor 62 and thus relieve the second gas turbine 20 operating alone. This configuration is shown in the figure 18Alternatively, they can be used in generator mode, if the second gas turbine 20 is able to provide the power needed to recharge the battery pack and prevent potential further use.

[0094] It should be noted that it is also possible to use uncoupling devices such as breakaway sections to limit risks in the event of component failures. In particular, a breakaway section can be installed on the drives of the first, second, and third electric machines 30, 40, 50 to protect the components from failure of the electric machines. It is also possible to add a breakaway section to the shafts of the first and second electric machines 30, 40 to guard against potential overtorque of the electric machine and to protect the gears and freewheels. Such breakaway sections could similarly prevent a potential blockage of the gas generator 10, 20 of the turbine in standby mode and driven by the clutches 81, 82.

[0095] Although the present invention has been described with reference to specific embodiments, ilIt is evident that modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various embodiments illustrated / mentioned can be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than a restrictive sense.

Claims

1. A propulsive assembly (100) for a hybrid aircraft, particularly a multi-engine helicopter, comprising: - at least a first gas turbine (10) and a second gas turbine (20) each having a gas generator (12, 22) and a free power turbine (11, 21) rotationally driven by a stream of gas generated by the gas generator, - a main rotor (62) coupled to the free power turbine (11, 21) of the first gas turbine (10) and of the second gas turbine (20) by way of a first and a second main coupling means (51, 52) respectively, - a first reversible electric machine (30) and a second reversible electric machine (40) each coupled to the gas generator (12, 22) of the first gas turbine (10) and of the second gas turbine (20) respectively, by way of a first deactivatable coupling means (31, 41), and each coupled to the main rotor (62) by way of a second deactivatable coupling means (32, 42), the first deactivatable coupling means (31, 41) being each configured to be activated when the first and the second electric machine (30, 40) are rotating in a first direction of rotation, and the second deactivatable coupling means (32, 42) being configured to be activated when the first and the second electric machine (30, 40) are rotating in a second direction of rotation opposite to the first direction of rotation.

2. The propulsive assembly (100) as claimed in claim 1, wherein the first electric machine (30) and the second electric machine (40) are configured to operate in motor mode in which they are able to input power to the main rotor (62) or to the gas generator (12, 22) of the first and of the second gas turbine (10, 20) respectively, according to their direction of rotation, or in generator mode in which they are able to be rotationally driven by the main rotor (62) or by said gas generator (12, 22) by locking one or the other of the first or the second deactivatable coupling means, in such a way as to generate electrical energy.

3. The propulsive assembly (100) as claimed in claim 1 or 2, comprising a first coupling means (81) coupled to the main rotor (62) and to the gas generator (12) of the first gas turbine (10), and a second coupling means (82) coupled to the main rotor (62) and to the gas generator (22) of the second gas turbine (20), the first and the second coupling means (81, 82) being movable between a decoupling position, and a coupling position in which the main rotor (62) is coupled with the gas generator (12, 22) of the first and of the second gas turbine respectively.

4. The propulsive assembly (100) as claimed in claim 3, wherein, when one of the first or the second gas turbine (10, 20) is the only one driving the main rotor (62), the gas generator (12, 22) of the other of the first or the second gas turbine (10, 20) is kept in a standby mode, at a power of less than 5kW, by way of the first or the second coupling means (81, 82) in the coupling position.

5. The propulsive assembly (100) as claimed in claim 2 and any of claims 3 or 4, wherein, when the first gas turbine (10) is the only one driving the main rotor (62), the first electric machine (30) operates in motor mode in such a way as to input power to the gas generator (12) of the first gas turbine (10), and the second electric machine (40) operates in generator mode in such a way as to input electrical energy to the first electric machine (30).

6. The propulsive assembly (100) as claimed in claim 2 and any of claims 3 or 4, configured so that, when the first gas turbine (10) that is the only one driving the main rotor (62) stops, the second electric machine (40) operates in motor mode in such a way as to input a power greater than or equal to 50 kW to the gas generator (22) of the second gas turbine (20).

7. The propulsive assembly (100) as claimed in claim 1 or 2, comprising a third reversible electric machine (50) able to be coupled to the main rotor (62) and to the free power turbine (11, 21) of the first gas turbine (10) and of the second gas turbine (20) by way of the first main coupling means (51) and the second main coupling means (52) respectively.

8. The propulsive assembly (100) as claimed in claim 7, wherein the third electric machine (50) is configured to operate in generator mode, in which it is able to be rotationally driven by the main rotor (62), itself driven by the free power turbine (11, 21) of the first and / or of the second gas turbine (10, 20) by way of the first and / or the second main coupling means (51, 52), in such a way as to generate electrical energy, or in motor mode in which it is able to input power to the main rotor (62).

9. The propulsive assembly (100) as claimed in claim 8 wherein, when the first gas turbine (10) is the only one driving the main rotor (62), the gas generator (22) of the second gas turbine (22) is kept in standby mode, at a power of less than 5kW, by way of the second electric machine (40) which operates in motor mode, the first electric machine (30) operating in motor mode in such a way as to input power to the gas generator (12) of the first gas turbine (10), and the third electric machine (50) operates in generator mode in such a way as to input electrical energy to the first and to the second electric machine (30, 40).

10. The propulsive assembly (100) as claimed in any of claims 1 to 9, wherein the first and the second main coupling means (51, 52), and the first and the second deactivatable coupling means (31, 41, 32, 42) associated with each of the first and the second electric machine (30 ,40), comprise a free wheel.

11. A hybrid aircraft comprising a propulsive assembly (100) as claimed in any of the preceding claims, the hybrid aircraft being a multi-engine helicopter, particularly a twin-engine helicopter.