IMPROVED TRANSMISSION FOR HYBRID AIRCRAFT

Description

Technical Field

[0001] The present invention relates to the field of hybrid aircraft, comprising at least one turbomachine such as a turboshaft or a turboprop, for flying machines such as helicopters or airplanes. In particular, the invention relates to a transmission device for a hybrid aircraft, and a hybrid aircraft comprising such a transmission device. Prior art

[0002] As is known, a turbomachine, for example a turboshaft engine, in particular 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. In addition, a hybrid aircraft generally comprises, in addition to this turbomachine, a reversible electrical machine coupled to the gas generator, so as to set the gas generator in rotation during a start-up phase of the turbomachine, or in flight so as to provide the non-propulsive electrical needs of the aircraft.

[0003] Traditionally, the gas generator comprises at least one compressor and one turbine coupled in rotation. The operating principle is as follows: the fresh air entering the gas turbine is compressed due to the rotation of the compressor before being sent to a combustion chamber where it is mixed with fuel. The burnt gases resulting from the combustion are then evacuated at high speed. An initial expansion then occurs in the gas generator turbine, during which the latter extracts the energy necessary to drive the compressor. The gas generator turbine does not absorb all the kinetic energy of the burnt gases and 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] During the start-up phase of the turbomachine, it is necessary to rotate the gas generator, i.e. to rotate the compressor coupled to the turbine. As mentioned above, this is precisely one of the roles of the reversible electric machine, known elsewhere, which is most often an electric motor capable of operating reversibly as an electric generator.

[0005] The rotational drive of the compressor by the reversible electric machine operating as a motor in fact makes it possible to circulate air in the compressor and therefore to bring compressed air into the combustion chamber in order to initiate combustion. This combustion then produces the gas flow making it possible to drive the turbine in rotation, following which the compressor is directly driven in rotation by the turbine, which means that the gas generator operates autonomously, reflecting the end of the start-up phase of the turbomachine. It is known that aircraft, in which such turbomachines are in particular intended to be integrated, include electrical equipment which must be powered by electrical energy.For example, for a helicopter it is necessary to supply electrical energy to the electrical equipment that equips it, such as the electrical controls, heating, air conditioning, and winch.

[0006] Until now, in flight, the reversible electric machine was used to supply electricity to electrical equipment. To do this, the electric machine, this time operating as an electric generator, was driven in rotation by the gas generator, the rotational kinetic energy taken from the gas generator being transformed into electrical energy by said machine. For a helicopter, however, taking energy from the gas generator has disadvantages. The variation, during flight, of the mechanical power taken by the electric machine from the gas generator results in a displacement of the engine's operating line in the compressor field.This displacement corresponds to a pumping margin that must be provided, which has the consequence of penalizing the optimization of the engine operating line, by prohibiting the use of the compressor at an optimal pressure rate, and thereby degrading the stabilized performances, with an impact on the specific consumption.

[0007] Document FR2929324 addressed this issue by allowing the same electrical machine to start the engine by driving the gas generator, then to operate in electrical generation by drawing power from the free turbine. This solution makes it possible in particular to not draw power from the gas generator and thus improve the specific consumption of the gas turbine. However, this architecture does not allow the injection of mechanical power into the main rotor of the helicopter for autorotation assistance, for example.

[0008] The improvement in power density and reliability of the electrical chain equipment (storage, conversion, electrical machines) now makes it possible to consider hybridizing the main rotor, i.e. having at least one electrical machine connected to the main rotor and capable of providing it with power. This power, complementary to the turbine power, allows in particular a power supply for transient phases (resources, takeoff, etc.), a power supply to relieve the gas turbine and optimize its lifespan, and also 100% electric operation in the event of loss of the gas turbine, for a limited period. In addition, it is possible to use this electrical machine to generate electricity (for current consumption and / or to recharge batteries).

[0009] To perform these functions, the electrical machine(s) must be sized to a power much higher than that of the generators / starters usually used, typically one or several hundred kilowatts, instead of around ten kilowatts. It is therefore desirable to pool the two types of electrical machines (the turbine generator / starter and the electrical machine connected to the rotor).

[0010] It is known to use such electric machines, and in particular several hybrid architectures, allowing different functions to be performed such as starting the gas generator, generating electricity on the ground, or supplying electrical power to the main rotor.

[0011] However, the proposed architectures do not allow certain functions to be performed by electric machines. In particular, these architectures only allow the electric machine to provide power to the gas generator during start-up. It is also not possible to continuously draw power from the helicopter rotor with an electric machine and continuously reinject this power into the gas generator with another electric machine. More specifically, assistance to the gas generator in flight is only possible by activating at least one lockable freewheel or clutch at each use. However, such a lockable freewheel or clutch system is likely to be used frequently, and is associated with high criticality.In other words, given the frequent use of the functions with which these interlocking elements are associated, the risks of malfunction are significant, limiting the reliability of the device. In addition, such architectures do not ensure an optimal level of redundancy, and also involve a high number of components and connections.

[0012] Documents FR3066444 and WO 2019 / 155173 A1 disclose other examples of hybrid architectures enabling power transfers between rotors of a turbomachine.

[0013] However, the architectures proposed in this document do not allow addressing certain functionalities specific to helicopter applications in which the main rotor and the free turbine may be desynchronized. By way of example, and in a non-limiting manner, assistance with autorotation by electric machines by injecting power into the transmission, or electrical generation to power the on-board systems, downstream of the engine freewheel, is not permitted, in particular following a failure of the turbomachine.

[0014] Finally, the architectures presented in this document require two reversible electrical machines in the engine perimeter, and capable of rotating in both directions of rotation thanks to four disengageable coupling systems. This strong integration in the engine perimeter, as well as the number of couplings required, is a barrier to use on helicopters due to the presence of numerous common failure modes.

[0015] There is therefore a need for a transmission device having an architecture that at least partially meets the aforementioned drawbacks. Statement of the invention

[0016] The present disclosure relates to a turbomachine for a hybrid aircraft, in particular a helicopter, the turbomachine comprising at least one gas generator, a free turbine driven in rotation by a gas flow generated by the gas generator, a main rotor, and a transmission device comprising a first reversible electrical machine capable of being coupled to a shaft of the free turbine via a first deactivatable coupling means, and to the main rotor, and a second reversible electrical machine capable of being coupled to a shaft of the gas generator via a second deactivatable coupling means, and of being coupled to the main rotor via a third deactivatable coupling means, the second deactivatable coupling means being configured to be activated when the second electrical machine rotates in a first direction of rotation,and the third deactivatable coupling means being configured to be activated when the second electrical machine rotates in a second direction of rotation opposite to the first direction of rotation.,

[0017] By "deactivatable coupling means" is meant that the coupling means can be in an activated position in which the members connected to said coupling means are coupled, or in a deactivated position in which said members are decoupled, it being understood that by "member" is meant the electrical machines, the main rotor, the gas generator and the free turbine.

[0018] The drive device according to the present disclosure is particularly advantageous in that the two electrical machines are specialized in order to provide complementary functions, while together ensuring the necessary level of redundancy on the critical functions to increase flight safety. More specifically, the first electrical machine can provide the tapping on the free turbine or the main rotor, so as not to affect the performance of the gas generator, or the injection of power on the main rotor so as to assist the latter in certain operating phases. In addition, the second electrical machine can be used in one direction of rotation to be mechanically coupled to the gas generator, and in the other direction of rotation to be mechanically coupled to the main rotor.In particular, the second electrical machine rotating in the first direction of rotation allows coupling with the gas generator in order to start the latter on the ground, but also coupling with the gas generator in order to supplement the thermodynamic power in certain phases of flight, for assistance in transient phases or modification of the engine operating point for example.

[0019] Furthermore, the second electrical machine rotating in the first direction of rotation makes it possible to restart the gas generator in flight, for example following a failure thereof, without requiring the activation of another mechanical component such as a clutch. Furthermore, even when the second electrical machine is used in the first direction of rotation to restart the electrical generator in flight, the first electrical machine can be used in parallel to drive the main rotor.

[0020] Furthermore, the second electric machine rotating in the second direction of rotation makes it possible to drive the main rotor as a replacement for the first electric machine in the event of the latter's failure, or as a supplement to it in certain flight phases requiring an additional supply of power.

[0021] Consequently, the architecture according to the present disclosure has the advantage of being simple by limiting the number of components and connections, while ensuring a good level of redundancy and making it possible to carry out a high number of functions, and thus to improve the reliability of the device. In addition, according to the invention, the second reversible electrical machine makes it possible to both start or assist the gas generator or the main rotor. In a particular embodiment, a single active system also makes it possible to supply electricity by drawing from the gas generator for recharging the batteries on the ground, or in the event of failure of the first electrical machine for example.

[0022] In some embodiments, the first, second, and third deactivatable coupling means comprise a freewheel.

[0023] An advantage of the freewheel is that it does not need to be controlled electronically or mechanically by an external operator. The freewheel also has significant reliability. Such a freewheel generally consists of a hub and a peripheral crown rotatably mounted on the hub. The hub can generally drive the peripheral crown in rotation but not vice versa. It should be noted that in certain cases, the freewheel is arranged in such a way that the peripheral crown can drive the hub in rotation, but not vice versa, without calling into question the principle of the present invention. Also, the hub can only drive the crown when the hub rotates in a predetermined direction relative to the crown, which will be called the "direction of engagement". Otherwise, the hub and the peripheral crown rotate freely relative to each other.In this case, the deactivatable coupling means are activated when the hub of the freewheel rotates the peripheral ring gear, and, conversely, the deactivatable coupling means are deactivated when the hub of the freewheel does not rotate the peripheral ring gear. Using freewheels as coupling elements between the various components, in the absence of other coupling means such as clutches or dogs, makes it possible to improve the reliability of the transmission device.

[0024] In certain embodiments, the first electrical machine is configured to operate in generator mode, in which it is rotated by transmission members and the main rotor, which can themselves be driven by the free turbine via the first coupling means, so as to generate electrical energy, or in motor mode in which it provides power to the main rotor.

[0025] The first electric machine can thus generate electrical energy without drawing power from the gas generator, thereby improving the specific consumption of the gas turbine. In addition, the transmission device of the present disclosure allows simultaneous supply of electrical power to the main rotor by the first electric machine, and to the gas generator by the second electric machine.

[0026] In certain embodiments, the device comprises a rotor brake capable of being arranged between the free turbine and the main rotor while being movable between a braking position preventing the main rotor from being driven by the free turbine, and a free position allowing the main rotor to be driven by the free turbine.

[0027] More precisely, the first electrical machine and the free turbine are coupled to the main rotor, while a mobile rotor brake arranged on the drive train allows it to be blocked. During start-up, the hot gases drive the free turbine. The latter, connected to the main rotor via the first coupling means, can be either free when the rotor brake is in the free position, or blocked by the rotor brake when the latter is in the braking position. This braking position therefore allows the free turbine, and therefore the main rotor, to be blocked, particularly in the event of start-up in strong winds.

[0028] In some embodiments, the first electrical machine is configured to rotate in a direction opposite to the direction of rotation of the main rotor, so as to brake the drive of the main rotor by the free turbine. In other words, the first electrical machine is configured to generate a resistive torque, making it possible to counter the torque of the free turbine driving the main rotor. The first electrical machine can thus perform the functions of the rotor brake described in the previous paragraph, without requiring the use of the latter. This alternative is advantageous insofar as a rotor brake, which is an expensive element, must be regularly checked and changed. It also presents a risk of unwanted activation in flight. This alternative therefore makes it possible to limit costs and improve the reliability of the device.

[0029] In some embodiments, the device comprises a dog clutch, or a clutch disposed between the rotor brake and the free turbine, the dog clutch being movable between a coupling position in which the shaft of the free turbine is coupled with the main rotor, and a decoupling position in which the shaft of the free turbine and the main rotor are decoupled, the first electrical machine being coupled to the free turbine upstream of the dog clutch, such that the free turbine can supply electrical power to the first electrical machine even when the dog clutch is in the decoupling position.

[0030] The term "upstream" refers to the direction of flow of mechanical energy to the main rotor, in other words, the "free turbine - main rotor" direction. In certain operational phases, it is necessary to be able to generate electrical power while keeping the rotor locked. Moving the dog clutch to the decoupling position thus allows the rotor brake to be used, while keeping the free turbine switched on to generate electrical power on the first electrical machine, without damaging the free turbine.

[0031] In some embodiments, the first electrical machine is electrically connected to the second electrical machine, such that the device is capable of transferring electrical power from the main rotor to the gas generator via the first electrical machine and the second electrical machine rotating in the first direction of rotation.

[0032] In certain phases of flight, it may be desirable to transfer power from the main rotor to the gas generator. In this case, the first electrical machine connected to the main rotor and the free turbine takes power, transmitted in the form of electric current to the second electrical machine which restores it to the gas generator via the second coupling means, rotating in the first direction of rotation. Exchanging electrical power between the gas generator and the main rotor makes it possible to modify the operating point of the turbine to increase the net power seen by the main rotor at iso lifetime of the gas turbine or increase the lifetime of the gas turbine at iso net power seen by the main rotor of the helicopter.

[0033] In some embodiments, the second coupling means comprises a locking means movable between a free position in which the gas generator cannot rotate the second electrical machine, and a locked position in which the gas generator is able to rotate the second electrical machine, so that the second electrical machine draws electrical power from the gas generator.

[0034] In some embodiments, the device is configured such that electrical power drawn from the gas generator by the second electrical machine is transferred to the first electrical machine.

[0035] The locking means is a means for forcing the coupling between the second electrical machine and the gas generator. For example, when the coupling means comprises a freewheel and a locking means, the freewheel is called a "lockable freewheel", such that in the locked position, the hub of the freewheel can rotate the peripheral ring gear of the lockable freewheel. In other words, the gas generator is capable of rotating the second electrical machine. In other words, the second electrical machine can be used to draw power from the GG and thus provide electrical power to the onboard network in APU (Auxilary Power Unit) mode on the ground for recharging the batteries for example, or in flight in addition to or as a replacement for the first electrical machine in the event of its failure for example.This also makes it possible to slow down the rotational speed of the gas generator more quickly when necessary, for example in the event of a gas turbine shutdown. Furthermore, the electrical power thus generated on the second electrical machine can be used by the first electrical machine, via an electrical connection between the first electrical machine and the second electrical machine.

[0036] In some embodiments, the device comprises a control unit configured to control the first electric machine, the second electric machine, the locking means, the rotor brake and the dog clutch.

[0037] The present disclosure also relates to a hybrid aircraft, in particular a helicopter, comprising a turbomachine having at least one gas generator, a free turbine driven in rotation by a gas flow generated by the gas generator, a main rotor, and comprising a transmission device according to any one of the preceding embodiments. The term "hybrid aircraft" means an aircraft comprising a heat engine making it possible to drive a main rotor in rotation, and at least one electrical machine making it possible to supply power to the heat engine.

[0038] In some embodiments, the hybrid aircraft is a helicopter. Brief description of the drawings

[0039] The invention and its advantages will be better understood upon reading the detailed description given below of different embodiments of the invention given as non-limiting examples. This description refers to the appended pages of figures, in which: [ Fig. 1 ] There figure 1 represents a sectional view of a turbomachine according to the invention, [ Fig. 2 ] There figure 2 schematically represents a first embodiment of a transmission device of the invention, [ Fig. 3A-3B ] THE figures 3A et 3B represent the transmission device of the figure 2 , according to two examples of a first mode of operation, [ Fig. 4 ] There figure 4 represents the transmission device of the figure 2 , according to a second mode of operation, [ Fig. 5 ] There figure 5 represents the transmission device of the figure 2 , according to a third mode of operation, [ Fig. 6 ] There figure 6 represents the transmission device of the figure 2 , according to a fourth mode of operation, [ Fig. 7 ] There figure 7 represents the transmission device of the figure 2 , according to a fifth mode of operation, [ Fig. 8A-8C ] THE figures 8A à 8C represent the transmission device of the figure 2 , at different stages of a sixth mode of operation, [ Fig. 9 ] There figure 9 represents the transmission device of the figure 2 , according to a seventh mode of operation, [ Fig. 10 ] There figure 10 schematically represents a second embodiment of a transmission device of the invention, [ Fig. 11 ] There figure 11 represents the transmission device of the figure 10 , according to a first mode of operation, [ Fig. 12 ] There figure 12 represents the transmission device of the figure 10 , according to a second mode of operation, [ Fig. 13 ] There figure 13 represents the transmission device of the figure 10 , according to a third mode of operation, [ Fig. 14 ] There figure 14 represents the transmission device of the figure 10 , according to a fourth mode of operation, [ Fig. 15 ] There figure 15 schematically represents an example of a third embodiment of a transmission device of the invention, [ Fig. 16 ] There figure 16 schematically represents a fourth embodiment of a transmission device of the invention, [ Fig. 17 ] There figure 17 schematically represents an alternative embodiment of a transmission device of the invention. Description of the embodiments

[0040] A first embodiment of the invention, corresponding to a first architecture of the transmission device 1, will be described in the remainder of the description, with reference to figures 1 à 9 .

[0041] There figure 1 schematically represents a turbomachine 100 in accordance with the present description, intended in particular to drive in rotation transmission members 50 of a helicopter carrying a propeller or a main rotor 52. The turbomachine 100 comprises a gas turbine 10 having a gas generator 12 and a free turbine 14 capable of being driven in rotation by a flow of gas generated by the gas generator 12. The free turbine 14 is mounted on a shaft 16 which transmits the rotational movement to a receiving member such as a main rotor 52 of the helicopter via the transmission members 50. According to this example, the gas turbine 10 shown in the figure 1 is of the front power take-off type with coaxial shaft return. One could very well consider, without departing from the scope of the present invention, a free turbine gas turbine of the front power take-off type with internal or external shaft return, or a free turbine turbomachine of the rear power take-off type.

[0042] The gas generator 12 comprises a rotating shaft 18 on which a compressor 20 and a turbine 22 are mounted, as well as a combustion chamber 24 arranged axially between the compressor 20 and the turbine when the gas generator 12 is considered in the axial direction of the rotating shaft 18. The gas turbine 10 has a casing 26 provided with an air inlet 28 through which the fresh air enters the gas generator 12. After its admission into the enclosure of the gas generator 12, the fresh air is compressed by the compressor 20 which delivers it towards the inlet of the combustion chamber 24 in which it is mixed with fuel. The combustion which takes place in the combustion chamber 24 causes the burnt gases to be evacuated at high speed towards the turbine 22, which has the effect of rotating the shaft 18 of the gas generator 12 and, consequently, the compressor 20.The rotational speed of the shaft 18 of the gas generator 12 is determined by the flow rate of fuel entering the combustion chamber 24.

[0043] Despite the extraction of kinetic energy by the turbine 22, the gas flow exiting the gas generator has significant kinetic energy. As understood with the help of the figure 1 , the gas flow F is directed towards the free turbine 14 which has the effect of causing an expansion in the free turbine 14 leading to the rotation of the turbine wheel and the shaft 16.

[0044] A transmission device 1 comprises a first reversible electric machine 30 consisting in this case of an electric motor capable of operating reversibly as an electric generator. It will be noted that although the first reversible electric machine 30 can be arranged in the turbomachine perimeter, this arrangement is not limiting. The reversible electric machine 30 can in fact be arranged in perimeters of the helicopter distinct from the turbomachine 100, without departing from the scope of the invention. This remark applies generally to the entire transmission device also comprising the second electric machine and the various coupling means described in the remainder of the description. The first reversible electric machine 30 is mechanically coupled to the shaft 16 of the free turbine 14 by means of a first deactivatable coupling means 32.

[0045] Preferably, the first deactivatable coupling means 32 comprises a freewheel mounted such that the rotation of the shaft 16 can rotate the main rotor 52 and a shaft 38 of the first electrical machine 30 when the latter is operating in generator mode in order to provide electricity, but that, on the contrary, the rotation of the shaft 38 of the first electrical machine 30 cannot rotate the shaft 16 of the free turbine 14. In other words, the freewheel of the first coupling means 32 can only transfer a rotational torque in the direction of the free turbine 14 to the main rotor 52 and the first electrical machine 30, but not vice versa. On a helicopter, this freewheel is commonly called a "motor freewheel". It will be noted that the use of a freewheel for the deactivatable coupling means is not limiting, the freewheel being able to be replaced by any dog ​​clutch or clutch system.

[0046] The first electric machine 30 is also capable of being coupled to the main rotor 52 in such a way that the first electric machine 30, operating in electric motor mode, is capable of driving the main rotor 52 in rotation. As indicated above, the first electric machine 30 in electric motor mode can drive the main rotor 52 in rotation, but not the free turbine 14, taking into account the presence of the freewheel of the first coupling means 32.

[0047] The device preferably comprises a rotor brake 60 disposed between the first electrical machine 30 and the main rotor 52. The rotor brake 60 is movable between a braking position (represented by a cross on the figure 3B for example), preventing rotation of the main rotor 52 and the free turbine 14, and a free position allowing rotation of the main rotor 52 and the free turbine 14. It will be noted, however, that although the figures 1 à 16 represent a device comprising such a rotor brake 60, 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 electrical machine 30 which, by being controlled in such a way as to create a torque opposing the rotation of the main rotor 52, makes it possible to brake, or even block the latter. Such an alternative embodiment is shown in the figure 17 , and is applicable to all the embodiments described in the remainder of the presentation.

[0048] The transmission device according to the present disclosure further comprises a second reversible electric machine 40, similar to the first reversible electric machine 30. The second reversible electric machine 40 is mechanically coupled to the shaft 18 of the gas generator 12 by means of a second deactivatable coupling means 44.

[0049] Preferably, the second deactivatable coupling means 44 comprises a freewheel mounted such that rotation of a shaft 48 of the second reversible electric machine 40 can rotate the shaft 18 of the gas generator 12 when the second electric machine is operating in electric motor mode (second coupling means 44 activated), but that, on the contrary, rotation of the shaft 18 of the gas generator 12 cannot rotate the shaft 48 of the second reversible electric machine 40. In other words, the freewheel of the second coupling means 44 can only transfer a rotational torque in the direction of the second electric machine 40 to the gas generator 12, but not vice versa.

[0050] The second electric machine 40 is also capable of being coupled to the main rotor 52, by means of a third reversible coupling means 42 similar to the first and second coupling means and preferably comprising a freewheel, such that the second electric machine 40, operating in electric motor mode (third coupling means 42 activated), is capable of driving the main rotor 52 in rotation.

[0051] According to the transmission device 1 of the present disclosure, the second electrical machine 40 is able to rotate in a first direction of rotation in which it is mechanically coupled to the shaft 18 of the gas generator 12, and in a second direction of rotation, opposite to the first direction of rotation, in which it is mechanically coupled to the main rotor 52. By convention, a positive direction will be understood in the remainder of the description, as a direction of rotation of the second electrical machine 40 in which the second coupling means 44 is activated, and a negative direction, as a direction of rotation of the second electrical machine 40 in which the third coupling means 42 is activated. In particular, the element represented by "-1" on the figure 2 and the following figures represent gears, for example pinions, allowing the reversal of the direction of rotation. It will thus be understood that when the second electrical machine 40 rotates in the positive direction, the second coupling means 44 can be activated, and the third coupling means 42 is deactivated, and when the second electrical machine 40 rotates in the negative direction, the second coupling means 44 is deactivated, and the third coupling means 42 can be activated.

[0052] Given this first architecture, different functions can be carried out by the transmission device. These different functions are described below with reference to the figures 3A à 9 . In these figures, the broken arrows represent a direction of transmission of mechanical or electrical power between two elements. On the figure 3A for example, mechanical power is transmitted from the second electrical machine 40 to the gas generator 12, and from the free turbine 14 to the main rotor 52. It will further be noted in general that, for the sake of clarity, the figures 3A à 16 represent schematically and in a functional and simplified manner the different operating modes of the device, without representing all the details of the elements constituting the turbomachine and the different power transmission components. In particular, the pinions and possible speed ratios are not represented.

[0053] THE figures 3A et 3B represent an operating mode allowing the gas turbine 10 to be started. The second electrical machine 40 is controlled, 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 second coupling means 44, allowing the gas generator 12 to be started. During start-up, the hot gases drive the free turbine 14. The latter, connected to the main rotor 52 via the freewheel of the first coupling means 32, can be either free, when the rotor brake 60 is in the free position ( figure 3A ), or blocked by the rotor brake when it is in the braking position ( figure 3B ). This last configuration, illustrated on the figure 3B , can be useful in the event of starting in strong winds. In addition, the power of the second electric machine 40 being of the order of one or several hundred kilowatts, it is possible to start the turbine much more quickly than with a starter with a power of the order of 10kW, usually used. This provides in particular an operational advantage in the case of medical rescue type missions, or during attempts at rapid restart in flight.

[0054] There figure 4 represents nominal operation, i.e. in flight and in the absence of a breakdown, allowing the first electric machine 30 to operate in electrical generator mode. In this configuration, the gas generator 12 operates autonomously and is no longer driven by the second electric machine 40. Furthermore, the free turbine 14 drives the main rotor 52 and the first electric machine 30 via the freewheel of the first coupling means 32. The electrical power generated by the first electric machine 30 can be used to power the on-board electrical accessories or charge the battery.

[0055] There figure 5 represents a nominal operation allowing power to be supplied to the main rotor 52 by the first electric machine 30 and the second electric machine 40, each operating in electric motor mode. The second electric machine 40 then rotates in the negative direction. This configuration can be useful in certain phases of flight requiring an additional power supply, for example during takeoff. The first electric machine 30 and the second electric machine 40 thus make it possible to supplement the power supplied to the main rotor 52 by the free turbine 14.

[0056] There figure 6 represents a nominal operation allowing the first electrical machine 30 to operate in electrical generator mode as in the configuration illustrated in the figure 4 , and at the same time allowing a power supply to the gas generator 12 by the second electric machine 40. The second electric machine 40 then rotates in the positive direction. This configuration can be useful in certain phases of flight, for example for assistance to the gas generator during rapid accelerations, or for modifying the engine operating point in “high altitude - hot weather” flight operating conditions.

[0057] There figure 7 represents a nominal operation allowing a supply of power to both the main rotor 52 by the first electric machine 30, and to the gas generator 12 by the second electric machine 40, each operating in electric motor mode. The second electric machine 40 then rotates in the positive direction. This allows in particular a different strategy from the figure 6 for assistance with rapid transients, in which the electric machine 30 assists the rotor 52 to limit the drop in revolution, while the electric machine 40 assists the gas generator 12 to improve the power availability time on the free turbine 14.

[0058] THE figures 8A à 8C have an operating mode allowing the gas turbine 10 to be restarted in flight, in the event of it stopping. The stopping of the gas turbine 10 causes the free turbine 14 of the main rotor 52 to become desynchronized via the freewheel of the first coupling means 32. Immediately after detecting the stopping of the turbomachine, the first electric machine 30 operates in electric motor mode to provide emergency power to the main rotor 52 ( figure 8A ). The speed of the gas generator 12 then decreases to an ignition window, allowing the turbomachine to restart. During this time, the second electric machine 40 can advantageously be rotated in the positive direction at a speed slightly lower than the re-ignition speed. This saves time and facilitates the resynchronization of the freewheel of the second coupling means 44.

[0059] When the ignition window is reached, the second electrical machine 40 rotating in the positive direction then drives the gas generator 12 via the freewheel of the second coupling means 44, allowing the gas turbine 10 to be restarted ( figure 8B ).

[0060] Once the gas turbine 10 has started, the electrical machine 40 can contribute to the rapid ramp-up of the gas turbine to reduce the engine power availability time. In another logic, when the gas turbine 10 is autonomous and while waiting for the resynchronization of the freewheel of the first coupling means 32, the second electrical machine 40 can otherwise be used to drive the main rotor 52, by rotating in the negative direction, via the third coupling means 42, and thus supplement the power supply of the first electrical machine 30 ( figure 8C ) to limit the loss of speed of the rotor 52. The free turbine 14 accelerates and thus resynchronizes with the main rotor 52, allowing a return to the nominal situation. Once the nominal situation is returned, the first and second electrical machines 30, 40 can stop the supply of power to the main rotor 52.

[0061] This architecture is particularly advantageous in that it allows, with only two electrical machines, to provide power to the main rotor 52, by the first electrical machine 30 and the second electrical machine 40, while allowing the gas turbine 10 to be restarted by the second electrical machine 40 in certain operating phases. It will also be noted that the various steps described above can be carried out by the control unit (not shown), making it possible to detect the stopping of the engine, the rotation speed of the shafts of the gas generator and the free turbine, and to control the electrical machines.

[0062] Furthermore, in the event that in-flight restart is impossible, does not work, or is not desired, for example, in the event of a fire in the gas turbine 10 or loss of a bearing, the two electrical machines 30 and 40 (rotating in the negative direction) can provide a power input to the main rotor 52 to assist the autorotation thereof, or even allow a level departure flight before landing. This phase of flight is functionally equivalent to the configuration illustrated in the figure 8C In this configuration, the main rotor 52 benefits from all of the available electrical power, provided by the first and second electrical machines 30, 40. In addition, in the event of failure of one of the electrical machines, the remaining electrical machine is capable of providing half of the installed electrical power.

[0063] There figure 9 represents a nominal operation allowing the first electrical machine 30 to operate in electrical generator mode and allowing at the same time a supply of power to the gas generator 12 by the second electrical machine 40, as in the configuration illustrated in the figure 6 . Furthermore, the first electrical machine 30 is electrically connected to the second electrical machine 40 via an electrical connection 70. The electrical connection 70 may comprise electrical shaping devices (rectification, inverters, voltage conversion). This connection allows the first electrical machine 30, connected to the main rotor 52 and to the free turbine 14, to take electrical power, and to transmit it in the form of electric current via the electrical connection 70 to the second electrical machine 40, which then restores it to the gas generator 12, via the second coupling means 44 rotating in the positive direction. It is thus possible to transfer electrical power from the main rotor 52 to the gas generator 12, in certain flight phases requiring such a transfer.

[0064] A second embodiment of the invention, corresponding to a second architecture of the transmission device, will be described in the remainder of the description, with reference to figures 10 à 14 .

[0065] According to this second architecture, the second deactivatable coupling means 44 also comprises a blocking means 46. The blocking means 46 is movable between a free position in which the gas generator 12 cannot drive the second electrical machine 40 in rotation, and a blocked position making it possible to block the freewheel of the second deactivatable coupling means 44 and thus to force the coupling between the gas generator 12 and the second electrical machine 40. In other words, when the blocking means 46 is in the blocked position, the second coupling means 44 acts as a shaft such that the gas generator 12 is able to drive the second electrical machine 40 in rotation, despite the presence of the freewheel of the second deactivatable coupling means 44.It will be noted that the change of position of the locking means 46 can be carried out by an electrical, pneumatic or hydraulic component and controlled by a user or a control unit.

[0066] Apart from the presence of this locking means 46, the transmission device according to the second embodiment is identical to the transmission device according to the first embodiment described above. Consequently, when the locking means 46 is in the free position shown schematically in the figure 10 , the functions performed by this second architecture are the same as the functions described above, with reference to the first architecture. The figures 11 à 14 have functions achievable by this second architecture, when the locking means 46 is in the locking position.

[0067] There figure 11 has an operation enabling the gas turbine 10 to be restarted more quickly in flight, in the event of it stopping. The operation of the device, in this case, is identical to that described above with reference to figures 8A à 8C However, thanks to the blocking means 46 making it possible to block the freewheel of the second coupling means 44, the second electrical machine 40 can be used to draw power from the gas generator 12, and thus slow down the rotation speed of the gas generator 12 more quickly, to consequently reach the ignition window more quickly.

[0068] Furthermore, the electrical power thus generated on the second electrical machine 40 can be advantageously used by the first electrical machine 30, via the electrical connection 70 between the first electrical machine 30 and the second electrical machine 40.

[0069] There figure 12 has an operation allowing redundant electrical generation on both the first electrical machine 30 and the second electrical machine 40. Indeed, it is sometimes desirable for the helicopter to have two redundant electrical power sources. This is possible by using the second electrical machine 40 as an auxiliary generation source, via the lockable freewheel, more precisely the locking means 46 in the locking position. The use of this function may for example be limited to the case of a failure of the electrical machine 30. figure 13 has an operation allowing a transfer of electrical power from the gas generator 12 to the main rotor 52. In this case, the second electrical machine 40 is connected to the gas generator 12 via the freewheel of the second coupling means 44, the freewheel being blocked by the blocking means 46. The second electrical machine 40 thus draws power, transmitted in the form of electric current via the electrical connection 70 to the first electrical machine 30 which restores it to the main rotor 52. It will be noted that before blocking the freewheel of the second coupling means 44, it is preferable to synchronize the speeds on either side of said freewheel, by controlling the speed of the second electrical machine 40 via the control unit for example, knowing moreover the speed of the gas generator 12 via the engine regulation system.

[0070] There figure 14 has an operation allowing electricity to be generated on the ground. More precisely, this operating mode, called “APU” mode or function (for “Auxiliary Power Unit” in English) is an operating mode where the gas turbine drives an electric generator without driving the main rotor of the helicopter, to provide power to electrical devices on the ground, such as batteries, flight equipment, heating or air conditioning. In particular, this mode allows the batteries to be recharged which can be used in flight to power the electrical machines to provide electrical assistance to the main rotor 52 from the takeoff phase for example.

[0071] To perform this function, the blocking means 46 is in the blocking position so that the gas generator 12 can drive the second electrical machine 40. The second electrical machine 40 thus draws power to restore it to the electrical equipment, while the free turbine 14 is blocked by the rotor brake 60, then in the braking position.

[0072] A third embodiment of the invention, corresponding to a third architecture of the transmission device, will be described in the remainder of the description, with reference to the figure 15 .

[0073] The third architecture differs from the second architecture in that the transmission device further comprises a coupling system 80, for example a dog clutch or a clutch. The coupling system 80 is movable between a coupling position in which the shaft 16 of the free turbine 14 is coupled with the main rotor 52, and a decoupling position in which the shaft 16 of the free turbine 14 and the main rotor are decoupled.

[0074] When the coupling system 80 is in the coupling position (not shown in the figure 15 ), the functions performed by the device according to this third architecture are the same as those described above with reference to the second architecture.

[0075] Furthermore, the terms “upstream” and “downstream” refer to the direction of energy flow from the free turbine 14 to the main rotor 52, in other words, to the “free turbine - main rotor” direction.

[0076] There figure 15 illustrates a first example of the third architecture, presenting an operation allowing electricity to be generated on the ground (“APU” mode). To perform this function, the blocking means 46 is in the blocking position, and the dog clutch 80 in the decoupling position. The gas generator 12 thus drives the second electric machine 40 via the blocked freewheel of the second coupling means 44. The second electric machine 40 consequently takes power to restore it to the electrical equipment, while the free turbine 14 can drive the first electric machine 30. Indeed, in this first example, the dog clutch 80 is arranged downstream of the coupling between the first electric machine 30 and the free turbine 14.

[0077] The presence of the dog clutch 80 in this position allows the use of the rotor brake 60, while allowing the first electrical machine 30 to be driven by the free turbine 14 to generate electrical power. Indeed, in certain operational phases on the ground, it is necessary to be able to generate electrical power while keeping the main rotor 52 blocked. However, on certain gas turbines, operation with the free turbine 14 blocked can damage it. Decoupling the free turbine 14 from the main rotor 52 by the dog clutch 80 makes it possible to limit this disadvantage.

[0078] A fourth embodiment of the invention, corresponding to a fourth architecture of the transmission device, will be described in the remainder of the description, with reference to the figure 16 .

[0079] The fourth architecture is similar to the first architecture, but differs from it in that the transmission device further comprises a dog clutch 80, arranged downstream of the coupling between the first electric machine 30 and the free turbine 14. The dog clutch 80 of the fourth architecture may also be identical to the dog clutch 80 of the third architecture.

[0080] When the dog clutch 80 is in the coupling position, the functions performed by the device according to the fourth architecture are identical to those performed by the device according to the first architecture. Furthermore, according to this fourth architecture, when the dog clutch 80 is in the decoupling position, in “APU” mode, electrical generation is only possible by the first electrical machine 30.

[0081] Although the present invention has been described with reference to specific exemplary embodiments, it is obvious that modifications and changes may 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 illustrated / mentioned embodiments may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

Claims

1. Turbomachine for a hybrid aircraft, particularly a helicopter, the turbomachine including at least one gas generator (12), a free turbine (14) rotationally driven by a stream of gas generated by the gas generator, a main rotor (52), and a transmission device (1) comprising a first reversible electric machine (30) coupled to a shaft (16) of the free turbine (14) by way of a first deactivatable coupling means (32), and to the main rotor (52), and a second reversible electric machine (40) coupled to a shaft (18) of the gas generator (12) by way of a second deactivatable coupling means (44), and coupled to the main rotor (52) by way of a third deactivatable coupling means (42), the turbomachine being characterized in that the second deactivatable coupling means (44) is configured to be activated when the second electric machine (40) rotates in a first direction of rotation, and the third deactivatable coupling means (42) is configured to be activated when the second electric machine (40) rotates in a second direction of rotation opposite to the first direction of rotation.

2. The turbomachine as claimed in claim 1, wherein the first, second and third deactivatable coupling means (32, 44, 42) comprise a free wheel.

3. The turbomachine as claimed in claim 1 or 2, wherein the first electrical machine (30) is configured to operate in generator mode, in which it is rotationally driven by transmission members (50) and the main rotor (52), themselves driven by the free turbine (14) by way of the first coupling means (32), in such a way as to generate electrical energy, or in motor mode in which it inputs power to the main rotor (52).

4. The turbomachine as claimed in any of claims 1 to 3, comprising a rotor brake (60) disposed between the free turbine (14) and the main rotor (52) by being movable between a braking position preventing the driving of the main rotor (52) by the free turbine (14), and a free position allowing the driving of the main rotor (52) by the free turbine (14).

5. The turbomachine as claimed in claim 4, comprising a dog clutch (80) disposed between the rotor brake (60) and the free turbine (14), the dog clutch (80) being movable between a coupling position in which the shaft (16) of the free turbine is coupled with the main rotor (52), and an uncoupling position in which the shaft (16) of the free turbine and the main rotor (52) are uncoupled, the first electric machine (30) being coupled to the free turbine (14) upstream of the dog clutch (80), in such a way that the free turbine (14) can input electrical power to the first electric machine (30) even when the dog clutch (80) is in the uncoupling position.

6. The turbomachine as claimed in any of claims 1 to 5, wherein the first electric machine (30) is electrically connected to the second electric machine (40), in such a way that the device is able to transfer electrical power from the main rotor (52) to the gas generator (12) by way of the first electric machine (30) and of the second electric machine (40) rotating in the first direction of rotation.

7. The turbomachine as claimed in any of claims 1 to 6, wherein the second coupling means (44) comprises a locking means (46) movable between a free position in which the gas generator (12) cannot rotationally drive the second electric machine (40), and a locked position in which the gas generator (12) rotationally drives the second electric machine (40), in such a way that the second electric machine (40) is able to draw electrical power off the gas generator (12).

8. The turbomachine as claimed in claim 7, configured such that the electrical power drawn off the gas generator (12) by the second electric machine (40) is transferred to the first electric machine (30).

9. A hybrid aircraft comprising a turbomachine as claimed in any of the preceding claims.

10. The hybrid aircraft as claimed in claim 9, the hybrid aircraft being a helicopter.