Improved transmission device for hybrid aircraft and disengagement method using such a device

Abstract

Improved transmission device for hybrid aircraft and disengagement method using such a device Transmission device (1) comprising a first reversible electric machine (30) coupled to a free turbine (14) via a first deactivatable coupling means (32), and to a main rotor (52) of the aircraft, and a second reversible electric machine (40) coupled to the main rotor (52) via a second deactivatable coupling means (42) configured to be activated when the second electric machine (40) rotates in a first direction of rotation (SIH), and to be deactivated when the second electric machine (40) rotates in a second direction of rotation (SH), the second electric machine (40) being further adapted to be coupled to the gas generator (12) via a breakable section (69) configured to break when a torque greater than a predetermined value is exerted on the breakable section (69),the second electric machine (40) rotating in the first direction of rotation (SIH) only in a failure condition of the gas generator (12). Figure for abstract: Fig. 2.,

Description

Title of the invention: Improved transmission device for hybrid aircraft and disengagement method using such a device 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, a hybrid aircraft comprising such a transmission device, and a disengagement method using such a transmission device. Prior art

[0002] In a known manner, 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 a fuel. The gases burned due to the combustion are then evacuated at high speed. A first expansion then occurs in the turbine of the gas generator, during which the latter extracts the energy necessary to drive the compressor. The turbine of the gas generator does not absorb all the kinetic energy of the burned 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 in motor mode or in generator mode. electric.

[0005] The rotational drive of the compressor by the reversible electric machine operating in motor mode 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.

[0006] It is known that aircraft, in which such turbomachines are intended to be integrated, include electrical equipment that needs to be powered by electrical energy. For example, for a helicopter it is necessary to power the electrical equipment that equips it, such as the electrical controls, heating, air conditioning, and winch.

[0007] 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 operating line of the engine 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.

[0008] Document FR2929324 addressed this problem 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 not to 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.

[0009] The improvement in power density and reliability of the equipment in the electrical chain (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 power of the turbine, allows in particular a power supply for transient phases (resources, take-off, 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 electric machine to generate electricity (for current consumption and / or to recharge batteries).

[0010] To ensure 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).

[0011] It is known to use such electrical machines, and in particular several hybrid architectures, making it possible to perform different functions such as starting the gas generator, generating electricity on the ground, or supplying electrical power to the main rotor. Document FR2104791 discloses a device comprising two electrical machines making it possible to perform such functions.

[0012] However, although existing architectures allow a number of functions to be performed by electrical machines, they have various drawbacks. In particular, these architectures involve the use of biocable freewheels, which may be used frequently and are associated with high criticality. In other words, given the frequent use of the functions with which these engageable elements are associated, the risks of malfunction are significant, limiting the reliability of the device.

[0013] Nevertheless, the use of these engageable elements remains particularly advantageous for the applications envisaged and for the performance of the aforementioned functions by the electrical machines, such that it may prove difficult to replace them with other devices.

[0014] There is therefore a need for a transmission device having an architecture that meets at least part of the aforementioned drawbacks. Statement of the invention

[0015] The present disclosure relates to a transmission device for a hybrid aircraft, in particular a helicopter, the aircraft comprising a turbomachine comprising at least one gas generator, a free turbine driven in rotation by a gas flow generated by the gas generator, and a main rotor, the 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 the main rotor via a second deactivatable coupling means. configured to be activated when the second electrical machine rotates in a first direction of rotation, and to be deactivated when the second electrical machine rotates in a second direction of rotation opposite to the first direction of rotation first direction of rotation, the second reversible electrical machine being further adapted to be coupled to a shaft of the gas generator via a breakable section configured to break when a torque greater than a predetermined value is exerted on the breakable section, the transmission device being configured such that the second electrical machine rotates in the first direction of rotation only in a gas generator failure condition.

[0016] The transmission device according to the present disclosure is particularly advantageous in that the two electrical machines can be specialized in order to provide complementary functions, while together ensuring the level of redundancy necessary on the critical functions to increase flight safety.

[0017] More specifically, the first electrical machine can ensure the collection from the free turbine or the main rotor, so as not to affect the performance of the gas generator, or the injection of power into the main rotor so as to assist the latter in certain operating phases.

[0018] Furthermore, 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 second direction of rotation allows coupling with the gas generator in order to start the latter on the ground, but also to supplement the thermodynamic power in certain flight phases, for assistance in transient phases or modification of the engine operating point for example.

[0019] 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 and the free turbine.

[0020] By "gas generator failure condition" is meant that this is an exceptional operating regime of the gas generator distinct from a nominal operation, such a nominal operation corresponding to normal flight conditions during which the engine is running at full speed. Conversely, a gas generator failure condition designates a situation in which the gas generator stops, or slows down below a certain percentage of its nominal rotation speed, such a slowdown being able to be voluntary (for example if the operator is forced to shut down the engine for safety reasons or an emergency such as a fire) or not.

[0021] It is thus understood that under nominal operating conditions, the second electrical machine rotates in the second direction of rotation and is thus coupled only to the shaft of the gas generator via the section to be broken, the second deactivatable coupling means being moreover deactivated. In this context, only the first electrical machine can be used to assist the rotation of the main rotor.

[0022] Thus, under nominal operating conditions, constituting the majority of the operating time of the gas turbine, only the first deactivatable coupling means, allowing the coupling between the first reversible electrical machine and the shaft of the free turbine, is likely to be used.

[0023] Consequently, rotating the second electrical machine in the first direction of rotation only in a gas generator failure condition (and consequently rotating it in the second direction of rotation during nominal operation) and using a breakable section between the second electrical machine and the gas generator, is particularly advantageous in that it makes it possible to limit the risks of malfunction intrinsic to the deactivatable coupling means, and thus to improve the reliability of the device, while improving its simplicity.

[0024] This solution is particularly advantageous, although it may involve difficulties that may make it counter-intuitive. Indeed, unlike deactivatable coupling means, for example a freewheel, which requires a specific direction of rotation (here the first direction of rotation) of the second electrical machine, and a sufficient rotation speed of the latter to allow its synchronization with the main rotor, the section to be broken involves a coupling of the second electrical machine to the gas generator regardless of its direction or speed of rotation. Thus, when it is desired to rotate the second electrical machine in the first direction of rotation to assist the rotation of the main rotor, an over-torque is created by the gas generator to which the second electrical machine is coupled, the latter driving the gas generator "in reverse".

[0025] However, it is possible to overcome this difficulty by judiciously dimensioning the section to be broken, in particular the predetermined value of the torque allowing it to break, or by controlling the second electrical machine so that the section to be broken breaks as quickly as possible, in order to decouple the second electrical machine from the gas generator, and thus to be able to use the second electrical machine to assist the rotation of the main rotor. It is thus possible to use a reversible electrical machine which can be selectively coupled to the gas generator or, exceptionally, to the main rotor according to its direction of rotation, while limiting the number of deactivatable coupling means, and therefore in improving the reliability and simplicity of the device.

[0026] In some embodiments, the predetermined torque is at least three times equal to a value of a torque exerted on the section to be broken during nominal operation of the gas generator.

[0027] In some embodiments, the section to be broken is a first section to be broken, the first reversible electric machine being able to be coupled to the main rotor via a second section to be broken.

[0028] In some embodiments, the first and second deactivatable coupling means comprise a freewheel.

[0029] In some embodiments, the first and second electrical machines are configured to operate in generator mode, in which they are rotated to generate electrical energy, or in motor mode in which they are capable of providing power.

[0030] 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.

[0031] 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.

[0032] In some embodiments, the device comprises a control unit configured to control at least the first electrical machine and the second electrical machine.

[0033] The present disclosure also relates to a disengagement method using a hybrid aircraft transmission device according to any one of the preceding claims, the method comprising: - detection of a gas generator failure, - the pulse control of the second electrical machine, comprising at least one pulse in which the second electrical machine is controlled successively in a motor mode then in a generator mode so as to exert a torque greater than a predetermined breaking value on the section to be broken, - reversing the direction of rotation of the second electrical machine to the first direction of rotation and controlling it in motor mode.

[0034] By "pulse control" and "pulse", it is understood that after switching to motor mode, the second electrical machine is immediately controlled in generator mode. Thus, a pulse comprises a switch to motor mode followed instantly from a switch to generator mode. Similarly, two successive pulses include a first switch to motor mode followed instantly by a first switch to generator mode, then a second switch to motor mode followed instantly by a second switch to generator mode.

[0035] This pulse command, involving a rapid reversal of the direction of transfer of the power in the generator shaft, and therefore in the section to be broken, generates a torque peak (or several torque peaks in the case of several pulses), which accelerates the reaching of the torque threshold value allowing the breaking of the section to be broken. It is thus possible to reverse the direction of rotation of the second electrical machine more quickly in order to be able to use it in the motor mode to assist the rotation of the main rotor.

[0036] This solution thus makes it possible to limit the risks of malfunction intrinsic to the coupling means which can be deactivated by using a section to be broken, and thus to improve the reliability and simplicity of the device, while ensuring safety in the event of a breakdown, by limiting the duration during which it is not possible to use the second electrical machine to assist the rotation of the main rotor.

[0037] In some embodiments, after detecting the fault, and before pulse-controlling the second electrical machine, the method comprises controlling the second electrical machine in the generator mode at a maximum generator power.

[0038] In some embodiments, the failure of the gas generator is detected when a rotational speed of the gas generator is less than or equal to a first rotational speed threshold value, the second electrical machine being controlled in the generator mode at the maximum generator power up to a second rotational speed threshold value.

[0039] In certain embodiments, when the rotation speed of the gas generator is less than or equal to the second rotation threshold value, an attempt to relight the gas generator is made, the pulse control of the second electrical machine then being carried out only in the event of failure of the attempt to relight the gas generator.

[0040] In some embodiments, during the pulse control of the second electrical machine, during the at least one pulse, the second electrical machine is controlled in the motor mode at a maximum motor power for a duration of less than one second, then in the generator mode at the maximum generator power.

[0041] In certain embodiments, the pulse control of the second electrical machine comprises a plurality of pulses during which oscillatory stresses are exerted on the shaft of the gas generator.

[0042] In some embodiments, the oscillatory stresses are exerted on the shaft of the gas generator at a frequency equal to the frequency of the first torsional mode of the shaft of the gas generator.

[0043] In some embodiments, after reversing the direction of rotation of the second electric machine to the first direction of rotation, the second electric machine is driven in the motor mode at maximum motor power.

[0044] In some embodiments, upon detection of a gas generator failure, the first reversible electrical machine is controlled in the motor mode so as to drive the main rotor.

[0045] In some embodiments, the section to be broken is a first section to be broken and the first reversible electrical machine is capable of being coupled to the main rotor via a second section to be broken, the method comprising pulse control of the first electrical machine, comprising at least one pulse in which the first electrical machine is controlled successively in a motor mode then in a generator mode so as to exert a torque greater than a predetermined breaking value on the second section to be broken. This decoupling method applied to the first electrical machine may be useful for example when the latter is short-circuited.

[0046] 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.

[0047] In some embodiments, the hybridized aircraft is a helicopter. Brief description of the drawings

[0048] 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:

[0049] [Fig-1] [Fig.l] represents a sectional view of a turbomachine according to the invention,

[0050] [Fig.2] [Fig.2] schematically represents an embodiment of a device of transmission of the invention,

[0051] [Fig.3] [Fig.3] represents the transmission device of [Fig.2], according to an operating mode during a first step of a disengagement process,

[0052] [Fig.4A-4B] Figures 4A,4B represent the transmission device of the [Fig.2], according to an operating mode during a second step of the disengagement process, before disengagement (image 4A) and after disengagement (image 4B),

[0053] [Fig.5] [Fig.5] represents the transmission device of [Fig.2], according to an operating mode during a third step of the disengagement process,

[0054] [Fig.6] [Fig.6] schematically represents the evolution of the rotation speed of a gas generator as a function of time during the disengagement process,

[0055] [Fig.7] [Fig.7] is a Bode diagram representing the amplitude response as a function of the frequency of the pulses exerted on the section to be broken. Description of the embodiments

[0056] An embodiment of the invention will be described in the remainder of the description, with reference to FIGS. 1 to 7.

[0057] [Fig.l] 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.

[0058] It will also be noted in general that, for the sake of clarity, Figures 2 to 5 schematically and in a functional and simplified manner represent a transmission device 1 and a mode of operation thereof, without representing all the details of the elements constituting the turbomachine and the various power transmission members. In particular, the pinions and possible speed ratios are not shown.

[0059] 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 gas flow 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 [Fig.l] 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.

[0060] 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 air Fresh gas is compressed by the compressor 20 which delivers it to 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 driving the shaft 18 of the gas generator 12 and, consequently, the compressor 20 into rotation. The speed of rotation of the shaft 18 of the gas generator 12 is determined by the flow rate of fuel entering the combustion chamber 24.

[0061] Despite the extraction of kinetic energy by the turbine 22, the gas flow exiting the gas generator has significant kinetic energy. As understood from [Fig. 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.

[0062] 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.

[0063] Preferably, the first deactivatable coupling means 32 comprises a freewheel mounted such that rotation of the shaft 16 can rotate the main rotor 52 and the first electrical machine 30 when the latter is operating in generator mode in order to provide electricity, but that, on the contrary, rotation 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 towards the first main rotor 52 and the first electrical machine 30, but not vice versa. On a helicopter, this freewheel is commonly called a "motor freewheel".

[0064] One advantage of the freewheel is that it does not need to be controlled electronically or mechanically by an external operator. 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. 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 "engagement direction". 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 crown, and, conversely, the deactivatable coupling means are deactivated when the hub of the freewheel does not rotate the peripheral crown.

[0065] 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.

[0066] 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.

[0067] The transmission device according to the present disclosure further comprises a second reversible electrical machine 40, similar to the first reversible electrical machine 30. In particular, the second reversible electrical machine 40 is capable of operating reversibly as an electrical generator.

[0068] It will be noted that the power of the second electrical machine 40 is 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 10 kW, 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.

[0069] As described below, it is possible to reverse the direction of rotation of the second reversible electrical machine 40, so that the latter is able to operate in the four operating quadrants, that is to say in generator mode or in motor mode in one direction of rotation, and in generator mode or in motor mode in the other direction of rotation.

[0070] The second reversible electrical machine 40 is mechanically coupled to the shaft 18 of the gas generator 12 via a breakable section 69. The breakable section 69 may be a portion of the shaft joining the gas generator 12 to the second reversible electrical machine 40, mechanically weaker (for example thinner) than on the rest of the shaft, such that a lower torque than for the rest of the shaft is necessary to break this portion of the shaft. In other words, by increasing the torque exerted on the shaft, the first portion of the shaft to mechanically yield will be the breakable section 69.

[0071] Unlike the first coupling means 32, the section to be broken 69 is not deactivatable. Thus, the 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 40 operates in electric motor mode, and the rotation of the shaft 18 of the gas generator 12 can rotate the shaft 48 of the second reversible electric machine 40 operating in generator mode. In other words, a rotational torque can be transferred in the direction of the second electric machine 40 to the gas generator 12, and vice versa.

[0072] The second electrical machine 40 is also capable of being coupled to the main rotor 52, by means of a second reversible coupling means 42 similar to the first coupling means 32 and preferably comprising a freewheel, such that the second electrical machine 40, operating in electric motor mode (second coupling means 42 activated), is capable of driving the main rotor 52 in rotation.

[0073] According to the transmission device 1 of the present disclosure, the second electrical machine 40 is capable of rotating in a first direction of rotation in which it is mechanically coupled to the main rotor 52, and in a second direction of rotation, opposite to the first direction of rotation, in which it is mechanically coupled to the shaft 18 of the gas generator 12.

[0074] By convention, in the remainder of the description a positive direction, or clockwise direction SH, will be understood as a direction of rotation of the second electrical machine 40 in which the second coupling means 42 is deactivated, and a negative direction, or counterclockwise direction SIH, as a direction of rotation of the second electrical machine 40 in which the second coupling means 42 is activated. In particular, the element represented by "-1" in [Fig.2] and the following figures represents 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 42 is deactivated, and when the second electrical machine 40 rotates in the negative direction, the second coupling means 42 can be activated.

[0075] Furthermore, the first electrical machine 30 can also be coupled to the main rotor 52 and to the turbine shaft 16 via a breakable section 68, similar to the breakable section 69. This breakable section 69 can be useful for decoupling the main rotor 52 from the first electrical machine 30, in the event of the rotor of the first electrical machine 30 being blocked, to limit the power draw from the main rotor 52.

[0076] Typically, the sections to be broken 68, 69 are configured to break from a predetermined threshold value of torque exerted on the shaft carrying the section to be broken 68, 69. The predetermined torque may for example be at least three times equal to a value of a torque exerted on the section to be broken during nominal operation. of the gas generator, in particular when the gas generator 12 is operating at full capacity. Such a value makes it possible to limit the risks of unwanted breakage of the sections to be broken 68, 69, while reaching the threshold value sufficiently quickly in the event of overtorque, when this breakage is desired.

[0077] Furthermore, the first electrical machine 30 is electrically connected to the second electrical machine 40 via electrical connections 70, each of the electrical machines being further connected to a battery 72. The electrical connections 70 may comprise electrical shaping devices (rectification, inverters, voltage conversion). These connections 70 allow the electrical machines 30, 40 to draw power from the battery 72 when they operate in motor mode, or conversely to recharge the battery 72 when they operate in generator mode. These connections 70 also allow the electrical machines 30, 40 to exchange electrical power between them.

[0078] For example, this 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. 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.

[0079] Furthermore, the electrical power taken from the gas generator 12 by the second electrical machine 40 operating in generator mode can be transferred to the first electrical machine 30. In other words, the second electrical machine 40 can be used to take power from the gas generator 12 and thus provide electrical power to the on-board network in “APU” (for “Auxilary Power Unit” in English) 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 30 in the event of its failure for example.

[0080] The operation of the second electrical machine 40 in generator mode also makes it possible to slow down the rotation speed of the gas generator 12 more quickly when this proves necessary, for example in the event of the gas turbine 10 being stopped as described below. Furthermore, the electrical power thus generated on the second electrical machine 40 can be used by the first electrical machine 30 or to recharge the battery 72, via the electrical connections 70.

[0081] It will also be noted that the use of two reversible electrical machines 30, 40 according to this architecture is particularly advantageous in that it makes it possible to supply power to the main rotor 52, by the first electrical machine 30, while at the same time allowing the gas turbine 10 to be restarted by the second electric machine 40 in certain operating phases.

[0082] A disengagement method according to one embodiment, using a transmission device 1 described above, will be detailed in the remainder of the description, with reference to FIGS. 3 to 6. Such a method makes it possible to disengage the second electrical machine 40 from the gas generator 12 when necessary, in particular in the event of a breakdown of the gas turbine 10.

[0083] It will be noted that [Fig.6] schematically represents the evolution of the rotation speed of the gas generator 12 as a function of time, when the second electric machine 40 rotates in the clockwise direction SH, and of the main rotor 52 when the second electric machine 40 rotates in the counterclockwise direction SIH.

[0084] During nominal operation of the gas generator 12, the latter rotates at full speed at a rotation speed NI. In this context, the second electrical machine 40 rotates in the clockwise direction SH, and can operate in generator mode by being rotated by the gas generator 12 via the shaft 18 and the section to be broken 69, and thus recharge the battery 72. In [Fig. 6], this configuration corresponds to a situation before a time t0, during which the gas generator 12 rotates at 100% of its nominal speed NI (step S0).

[0085] At time t0, an event occurs causing a breakdown of the gas generator 12, involving a slowdown, or even a shutdown thereof. A first step of the method (step S1) consists of detecting such a breakdown of the gas generator 12. To do this, the device 1 may comprise a control unit (not shown) of the “FADEC” (for “Full Authority Digital Engine Control” in English) type, also controlling the electrical machines 30, 40, and making it possible to detect an abnormal drop in the rotation speed of the gas generator 12.

[0086] For example, a rotation speed less than or equal to 98% of the nominal speed NI, detected at a time tl, can be determined by the control unit as representative of a failure of the gas generator 12. The speed 98%N1 thus constitutes a first threshold value of rotation speed of the gas generator 12. The duration tl - t0 corresponds to the time of detection of the failure by the control unit.

[0087] Preferably, when the control unit detects a failure of the gas generator 12 at time t1, it can control the second electrical machine 40 to operate in generator mode at a maximum generator power (step S2), corresponding to the maximum electrical power that the second electrical machine 40 is able to generate. This makes it possible to accelerate the slowing down of the gas generator 12, and to limit the duration during which the second electrical machine 40 cannot be used to assist the main rotor 52 in the manner described below.

[0088] This step S2 is shown in [Fig.3]. In this figure, as well as in Figures 4A, 4B and 5, the broken arrows represent a direction of transmission of mechanical power between two elements. In [Fig.3] for example, mechanical power is transmitted from the gas generator 12 to the second electrical machine 40, the latter, operating at maximum generating power, then serving as a brake for the gas generator 12. Furthermore, the first electrical machine 30 is controlled by the control unit in motor mode to assist the rotation of the main rotor 52 which no longer benefits from the driving power of the gas generator 12.

[0089] It will further be noted that during this step S2, the electrical power generated on the second electrical machine 40 at maximum generating power can be used by the first electrical machine 30, or to recharge the battery 72, via the electrical connections 70.

[0090] In this example, this step S2, during which the second electrical machine 40 operates in generator mode at maximum generator power, is carried out up to a time t2 from which the rotation speed of the gas generator 12 is less than or equal to 10% of its nominal speed NI. The speed 10%Nl thus constitutes a second threshold value for the rotation speed of the gas generator 12. Thanks to this step of generating electrical energy at maximum power by the second electrical machine 40, the time t2 - tl of reduction of the rotation speed of the gas generator 12 is shortened, which makes it possible to reach the ignition window described below more quickly.

[0091] Typically, a rotation speed of the gas generator 12 between 0%Nl (zero speed) and 10%Nl is representative of a rotation speed within the ignition window of the gas generator 12, in which it is possible to take advantage of its low rotation speed to attempt ignition or re-ignition thereof. Thus, when the rotation speed of the gas generator 12 becomes less than or equal to the second speed threshold value 10%Nl from time t2, the method may comprise a step of attempting to re-ignite the gas generator 12 (step S3), between time t2 and a time t3, during which at least one attempt to re-ignite the gas generator 12 is made.

[0092] The operating time in the failure condition of the gas generator 12 having been minimized by the preceding steps, this step of attempting to relight allows rapid relighting of the gas turbine 12 and the turbomachine 100, and thus to return to a nominal operating regime.

[0093] However, in the event of failure of the attempt to relight the gas generator 12, the method then comprises, at time t3, a step of pulse control of the second electrical machine 40 (step S4). This step makes it possible to decouple the second electrical machine 40 from the gas generator 12 as quickly as possible, in order to be able to use the second electrical machine 40 to assist the rotation of the main rotor 52.

[0094] To do this, the pulse control of the second electrical machine 40 by the control unit comprises at least one pulse, during which the second electrical machine 40 is controlled to operate in the motor mode from time t3 to time t4, then immediately in the generator mode.

[0095] By “immediately”, it is understood that the second electrical machine 40 operates in motor mode for a very short duration such that, for example, t4 - t3 < 1 sec. The rotation speed of the gas generator 12 is therefore briefly accelerated, as symbolized by the speed peak at time t4 in [Fig.6], before decreasing again when the second electrical machine 40 returns to generator mode.

[0096] This pulse command makes it possible to create a torque peak on the shaft 18, and therefore on the section to be broken 69, promoting the breakage of the latter. Preferably, during operation in the motor mode between t3 and t4, the second electrical machine 40 is controlled to operate at its maximum driving power, then, from t4, to operate at its maximum generating power. This makes it possible to maximize the overtorque exerted on the section to be broken 69 by maximizing the torque difference between a “positive” maximum torque (in motor mode) and a “negative” maximum torque (in generator mode), and thus to reach even more quickly the predetermined threshold torque value allowing the breakage of the section to be broken 69.

[0097] Images 4A and 4B represent the pulse control of the second electric machine 40. Initially (image 4A), the second electric machine 40 operates at its maximum driving power by driving the gas generator 12. The second electric machine 40 is then immediately switched to the generator mode at its maximum generating power, which causes the section to be broken 69 to break (image 4B). The second electric machine 40 is then decoupled from the gas generator 12, as illustrated in image 4B.

[0098] Although the example illustrated in [Fig.6] represents a single pulse, it is possible in step S4 to perform two or more pulses, during which the second electrical machine 40 operates successively in motor mode at maximum motor power, then in generator mode at maximum generator power. This makes it possible to accelerate the breaking of the section to be broken 69 when several pulses are necessary to reach the predetermined threshold value.

[0099] The successive pulses can thus take the form of oscillatory torque stresses, for example sinusoidal, of the shaft 18 and of the section to be broken 69. Typically, the oscillatory stresses are exerted on the shaft 18 of the gas generator 12 at a frequency typically of several tens of Hertz, equal to the frequency of the first torsion mode of the shaft 18 of the gas generator 12. This makes it possible to reach the resonance frequency of the shaft 18 more quickly, and to further accelerate the breaking of the section to be broken 69.

[0100] [Fig.7] is a Bode diagram representing the amplitude A of the stresses as a function of the frequency F. This graph makes it possible to represent the response of the torsional chain comprising the shaft 48, the section to be broken 69 and the shaft 18, to an impulse caused by the second electrical machine 40. The solid lines represent the response for a theoretical nominal case, and the broken lines represent the dispersion due to the inherent manufacturing dispersions of the components of the aforementioned torsional chain. By controlling the second electrical machine 40 to operate successively at its maximum and minimum driving power in a frequency interval AF between F1 and F2, which are the lower and upper limits of the targeted excitation frequency range encompassing all of the “peaks” in broken lines, it is possible to obtain an amplitude response sufficient to break the section to be broken 69.

[0101] At this stage, the rotation of the gas generator 12 can slow down to zero speed (0%Nl), the second electrical machine 40 and the gas generator 12 being mechanically decoupled from each other. Thus, once such decoupling is obtained, allowing the release of the second electrical machine 40, it is possible to reverse the direction of rotation of the latter in the counterclockwise direction SIH (step S5), without the gas generator 12 constituting a brake hindering the free rotation of the second electrical machine 40.

[0102] During step S5 of reversing the direction of rotation, the second electrical machine 40 is also controlled to operate in the motor mode, so as to be able to drive the main rotor 52 in rotation ([Fig.5]). In particular, the docking (in other words the coupling or synchronization) of the second electrical machine 40 to the main rotor 52 by means of the second deactivatable coupling means 42 takes place during the docking step S6 at time t5.

[0103] Preferably, the second electrical machine 40 is controlled to operate in the motor mode at its maximum driving power in order to approach (synchronize) the freewheel of the second deactivatable coupling means 42 as quickly as possible. This makes it possible to assist the rotation of the main rotor 52 more quickly, minimizing the duration t5 - t4.

[0104] Thus, from time t5, the two electrical machines 30, 40 assist the rotation of the main rotor 52 to help the autorotation thereof, or even allow a level departure flight before landing. In particular, the main rotor 52 can thus reach a nominal rotation speed NR thanks to the assistance of the electrical machines 30, 40.

[0105] In the device and method of the invention, the freewheel of the second coupling means 42 is used only during failure conditions of the gas turbine 10, these failures being infrequent compared to the operating time under nominal conditions. In order to improve the safety and reliability of the device 1, it may therefore be necessary to limit the risks of dormant failures of the freewheel of the second coupling means 42, which would go unnoticed due to its low frequency of use.

[0106] To do this, the freewheel 42 can be tested so as to be driving in the first direction of rotation SIH. The procedure consists, for example, with the helicopter on the ground and the gas turbine 10 switched off and at zero speed, in electrically powering the second electrical machine 40 so that it produces a torque in the SIH direction. Thus, if the first electrical machine 30 must provide a torque equivalent to that of the second electrical machine 40 to maintain the main rotor 52 at zero speed, this means that the freewheel of the second coupling means 42 is functional.

[0107] 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.

[0108] It is also obvious that all the characteristics described with reference to a method are transposable, alone or in combination, to a device, and conversely, all the characteristics described with reference to a device are transposable, alone or in combination, to a method.

Claims

Claims

1. Transmission device (1) for a hybrid aircraft, in particular a helicopter, the aircraft comprising a turbomachine comprising at least one gas generator (12), a free turbine (14) driven in rotation by a gas flow generated by the gas generator, and a main rotor (52), the transmission device (1) comprising a first reversible electric machine (30) capable of being coupled to a shaft (16) of the free turbine (14) via a first deactivatable coupling means (32), and to the main rotor (52), and a second reversible electric machine (40) capable of being coupled to the main rotor (52) via a second deactivatable coupling means (42) configured to be activated when the second electric machine (40) rotates in a first direction of rotation (SIH),and to be deactivated when the second electrical machine (40) rotates in a second direction of rotation (SH) opposite to the first direction of rotation, the second reversible electrical machine (40) being further adapted to be coupled to a shaft (18) of the gas generator (12) via a breakable section (69) configured to break when a torque greater than a predetermined value is exerted on the breakable section (69), the transmission device (1) being configured such that the second electrical machine (40) rotates in the first direction of rotation (SIH) only in a fault condition of the gas generator (12).,

2. A transmission device according to claim 1, wherein the predetermined torque is at least three times equal to a value of a torque exerted on the section to be broken (69) during nominal operation of the gas generator (12).

3. A transmission device according to claim 1 or 2, wherein the breakable section (69) is a first breakable section, the first reversible electric machine (30) being adapted to be coupled to the main rotor (52) via a second breakable section (68).

4. Disengagement method using a transmission device (1) for a hybrid aircraft according to any one of the preceding claims, the method comprising: - the detection (SI) of a failure of the gas generator (12), - the pulse control (S4) of the second electrical machine (40), comprising at least one pulse in which the second electric machine (40) is controlled successively in a motor mode then in a generator mode so as to exert a torque greater than a predetermined breaking value on the section to be broken (69), - reversing the direction of rotation (S5) of the second electric machine (40) towards the first direction of rotation (SIH) and controlling it in the motor mode.

5. Disengagement method according to claim 4, wherein, after the detection (SI) of the failure, and before the pulse control (S4) of the second electric machine (40), the method comprises controlling the second electric machine (40) in the generator mode at a maximum generator power (S2).

6. A disengagement method according to claim 4 or 5, wherein the failure of the gas generator (12) is detected when a rotational speed of the gas generator (12) is less than or equal to a first rotational speed threshold value, the second electrical machine (40) being controlled in the generator mode at the maximum generator power up to a second rotational speed threshold value.

7. Disengagement method according to claim 6, wherein, when the rotation speed of the gas generator (12) is less than or equal to the second rotation threshold value, an attempt to re-ignite (S3) the gas generator (12) is made, the pulse control (S4) of the second electrical machine (40) then being carried out only in the event of failure of the attempt to re-ignite the gas generator (12).

8. Disengagement method according to any one of claims 4 to 7, wherein, during the pulse control (S4) of the second electric machine (40), during the at least one pulse, the second electric machine (40) is controlled in the motor mode at a maximum motor power for a duration of less than one second, then in the generator mode at the maximum generator power.

9. Disengagement method according to any one of claims 4 to 8, in which the pulse command (S4) of the second electrical machine (40) comprises a plurality of pulses during which oscillatory stresses are exerted on the shaft (18) of the gas generator (12).

10. A disengagement method according to claim 9, wherein the sol- oscillatory stresses are exerted on the shaft (18) of the gas generator (12) at a frequency equal to the frequency of the first torsion mode of the shaft (18) of the gas generator (12).

11. A disengagement method according to any one of claims 4 to 10, wherein, after reversing the direction of rotation (S5) of the second electric machine (40) to the first direction of rotation (SIH), the second electric machine (40) is controlled in the motor mode at maximum motor power.

12. A disengagement method according to any one of claims 4 to 11, wherein, upon detection of a failure of the gas generator (12), the first reversible electrical machine (30) is controlled in the motor mode so as to drive the main rotor (52).

13. A disengagement method according to any one of claims 4 to 12, the section to be broken (69) being a first section to be broken, the first reversible electric machine (30) being able to be coupled to the main rotor (52) via a second section to be broken (68), the method comprising pulse control of the first electric machine (30), comprising at least one pulse in which the first electric machine (30) is controlled successively in a motor mode then in a generator mode so as to exert a torque greater than a predetermined breaking value on the second section to be broken (68).

14. A hybrid aircraft comprising a turbomachine (100) having at least one gas generator (12), a free turbine (14) driven in rotation by a gas flow generated by the gas generator (12), a main rotor (52), and comprising a transmission device (1) according to any one of claims 1 to 3.

15. A hybrid aircraft according to claim 14, the hybrid aircraft being a helicopter.

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