Improved backup system for hybrid aircraft and method using such a system

Abstract

Backup device (1) for a hybrid aircraft, comprising a turbomachine having at least one gas generator (12), a free turbine (14), and a main rotor (52), the device (1) comprising a first reversible electric machine (30) coupled to the main rotor (52) by means of a first and a second switchable coupling means (32, 42) mounted in parallel, operating in a motor mode so as to drive the main rotor (52) by means of the first switchable coupling means (32), and operating in a generator mode to generate electrical power by being driven by the main rotor (52) by means of the second switchable coupling means (42), the latter being deactivated when a rotational speed of the main rotor (52) is greater than or equal to a first predetermined stall threshold value (N1),such that the first electric machine (30) cannot be driven in generator mode by the main rotor (52). Fig. 2.

Description

Title of the invention: Improved backup device for hybrid aircraft and 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 engine or turboprop, for flying machines such as helicopters or airplanes. In particular, the invention relates to an emergency device for a hybrid aircraft, a hybrid aircraft comprising such an emergency device, and a method using such an emergency device. Prior art

[0002] As is known, a turbomachine, for example a turboshaft engine, particularly 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, besides this turbomachine, at least one reversible electric machine coupled to the gas generator, so as to rotate the gas generator during a turbomachine start-up phase, or in flight so as to supply the aircraft's non-propulsive electrical requirements.

[0003] Traditionally, the gas generator comprises at least one compressor and one turbine coupled in rotation. The operating principle is as follows: fresh air entering the gas turbine is compressed by the rotation of the compressor before being sent to a combustion chamber where it is mixed with a fuel. The exhaust gases from combustion are then expelled at high speed. A first expansion then occurs in the gas generator turbine, during which the turbine extracts the energy necessary to drive the compressor. The gas generator turbine does not absorb all the kinetic energy of the exhaust 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 main rotor of the helicopter.

[0004] During the turbomachine start-up phase, it is necessary to rotate the gas generator, that is, 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 electric power generator mode.

[0005] The rotational drive of the compressor by the reversible electric machine operating in motor mode effectively circulates air within the compressor, thus supplying compressed air to the combustion chamber to initiate combustion. This combustion then produces the gas flow that drives the turbine to rotate, after which the compressor is directly driven in rotation by the turbine, meaning that the gas generator operates autonomously, marking the end of the turbomachine's start-up phase.

[0006] A reversible electric machine can also be integrated into a propulsion system known as a backup system, by being coupled to the main rotor of the turbomachine. Indeed, with the development of electric hybridization for aeronautical propulsion systems, these backup systems make it possible to extend the operational range of aircraft.

[0007] The electric machine can then, by operating in motor mode, provide temporary power boosts to the main rotor to perform emergency maneuvers. For example, in the case of single-engine helicopters, for which an uncommanded in-flight stoppage (known as an "AEVNC" event) requires an autorotation maneuver, the backup system can provide assistance with this autorotation, or an emergency maneuver to bring the aircraft back to the takeoff point.

[0008] For an application of this type, a freewheel typically allows the electric machine of said backup device to be coupled to the main rotor. This freewheel allows the electric machine to drive the main rotor when necessary, particularly in the event of a failure of the internal combustion engine, but conversely prevents the main rotor from driving the electric machine. Indeed, the backup device must be ready to supply power, without, however, being driven continuously during flight, which could lead to premature wear of the electric machine as well as excessive fuel consumption.

[0009] Thus, the use of a freewheel, which is a one-way clutch, prevents the electric machine from being driven unintentionally. However, given that the main rotor cannot drive the electric machine, it is then not possible to use the electric machine in generator mode and therefore to recharge the backup device's battery without an external system.

[0010] However, the battery may be subject to discharge for various reasons (due to system availability tests, or self-discharge during storage, for example). This can be problematic in certain situations, for example when the aircraft has to land on infrastructure (for example, an urban hospital). not equipped with a device-specific charger. In this case, the aircraft might not be able to take off again if the backup system was not available.

[0011] There is therefore a real need for a backup device that is free, at least in part, from the drawbacks inherent in the aforementioned known configuration. Description of the invention

[0012] The present description relates to an emergency device for a hybrid aircraft, in particular a helicopter, the aircraft comprising a turbomachine having 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 emergency device comprising a first reversible electric machine capable of being coupled to the main rotor by means of a first switchable coupling means and a second switchable coupling means mounted in parallel, and of operating in a motor mode so as to drive the main rotor by means of the first switchable coupling means, and of operating in a generator mode so as to generate electrical power by being driven by the main rotor by means of the second switchable coupling means,The second switchable coupling means is configured to be deactivated when the main rotor speed is greater than or equal to a first predetermined stall threshold value, such that the first electric machine cannot be driven into generator mode by the main rotor.

[0013] By "reversible", it is understood that the first electrical machine is configured to operate in generator mode, in which it is driven in rotation so as to generate electrical energy, or in motor mode in which it is capable of supplying power.

[0014] By "switchable coupling means", it is understood that the coupling means can be in an activated position in which the components connected to said coupling means are coupled, or in a deactivated position in which said components are decoupled, it being understood that "component" in this presentation means the electrical machines, the main rotor, the free turbine and the gas generator as appropriate.

[0015] With this device, power can thus be transmitted in two directions, namely from the first electric machine to the main rotor via the first switchable coupling means, or from the main rotor to the first electric machine via the second switchable coupling means.

[0016] It is therefore understood that when the first electric machine operates in motor mode, it can transmit mechanical power to the main rotor via the first switchable coupling means, which is activated, the second The switchable coupling means is then deactivated. Conversely, when the first electric machine operates in generator mode to generate electrical power, it can be driven by the main rotor via the second switchable coupling means, which is activated, the first switchable coupling means being deactivated.

[0017] However, according to the invention, the second switchable coupling means is configured to be deactivated when the rotational speed of the main rotor is greater than or equal to a first predetermined stall threshold value. In other words, even when the first electric machine is in generator mode (i.e., in the "receiver" position), the main rotor cannot drive it via the second switchable coupling means, which is then deactivated when the rotational speed of the main rotor exceeds the first predetermined stall threshold value.

[0018] Thus, it is possible to determine a stall threshold value so as, for example, to generate electrical power by the first electric machine operating in generator mode, only for low rotational speeds of the main rotor, for example when the aircraft is on the ground and the main rotor is idling.

[0019] According to the invention, it is thus possible to use the backup device to generate electrical power only within limited operating ranges, for example, when the aircraft is on the ground to recharge the device's battery, without the main rotor having to drive the first electric machine throughout the entire flight phase. This makes it possible to maintain a sufficient battery charge level without causing excessive fuel consumption in flight, and thus improves the device's lifespan.

[0020] In some embodiments, the first switchable coupling means includes a first freewheel, and the second switchable coupling means includes a second freewheel, the first and second freewheel being mounted in opposition, the second freewheel being a centrifugally released freewheel, configured such that it is switched off when the rotational speed of the main rotor is greater than the first predetermined stall threshold value.

[0021] In some embodiments, the first switchable coupling means includes a first reducer having a first reduction coefficient, and the second switchable coupling means includes a second reducer having a second reduction coefficient.

[0022] In some embodiments, a minimum flight speed is a minimum rotational speed of the main rotor in a phase of flight of the aircraft, and a ground speed is a rotational speed of the main rotor in a configuration in which the aircraft is on the ground, the first stall threshold value being less than the minimum flight speed, and greater than the ground decelerated speed.

[0023] In certain embodiments, the device is configured to, in a phase of deceleration of the main rotor before landing of the aircraft, command the first electric machine in motor mode so as to increase its rotational speed up to a second predetermined threshold value of re-engagement lower than the first predetermined threshold value of disengagement and higher than the ground idle speed.

[0024] In certain embodiments, the device includes a second reversible electric machine capable of being coupled to the main rotor by means of a third switchable coupling means configured to be activated when the second electric machine rotates in a first direction of rotation, and to be deactivated when the second electric machine rotates in a second direction of rotation opposite to the first direction of rotation, the second electric machine being further capable of being coupled to a shaft of the gas generator by means of a breakable section.

[0025] The present description also relates to a hybrid aircraft 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 backup device according to any of the preceding embodiments.

[0026] The present description also relates to a method for controlling electrical power generation using a backup device for a hybrid aircraft according to any one of the preceding embodiments, the method comprising: - the control of the first reversible electric machine so as to generate electrical power by being driven by the main rotor via the second switchable coupling means, when the gas generator is on and the aircraft is on the ground, - increasing the rotational speed of the main rotor up to a rotational speed greater than or equal to the first predetermined stall threshold value so as to deactivate the second switchable coupling means, so that the first electric machine cannot be driven into generator mode by the main rotor during an aircraft takeoff phase.

[0027] In some embodiments, the method includes controlling the first electric machine in motor mode when the rotational speed of the main rotor is greater than or equal to the first predetermined stall threshold value, during the takeoff phase.

[0028] In certain embodiments, the method includes, during a flight phase in which the rotational speed of the main rotor is between a minimum flight speed, which is greater than the first predetermined stall threshold value and is a minimum rotational speed of the main rotor in the flight phase of the aircraft, and a maximum flight speed which is a maximum rotational speed of the main rotor in the flight phase of the aircraft, the control of the first electrical machine in generator mode.

[0029] In certain embodiments, the method includes, during a landing phase of the aircraft, controlling the first electric machine in motor mode and so as to increase its rotational speed up to a second predetermined threshold value of re-engagement lower than the first predetermined threshold value of disengagement and higher than a ground idle speed, which is a rotational speed of the main rotor in a configuration in which the aircraft is on the ground.

[0030] In certain embodiments, the method includes controlling the first electric machine in generator mode when the first electric machine has reached the second predetermined threshold value for re-engagement and the aircraft is on the ground, with the main rotor rotating at ground idle speed. Brief description of the drawings

[0031] The accompanying drawings are schematic and are intended primarily to illustrate the principles of the exposition. On these drawings, from one figure to another, identical elements (or parts of elements) are identified by the same reference symbols.

[0032] [Fig-1] Fig. 1 represents a cross-sectional view of a turbomachine according to the invention,

[0033] [Fig.2] Fig.2 schematically represents one embodiment of a device rescue of the invention,

[0034] [Fig.3] Fig.3 represents the backup device of Fig.2, according to an operating mode during a first step of an electrical power generation control process,

[0035] [Fig.4] Fig.4 represents the backup device of Fig.2, according to an operating mode during a second stage of an electrical power generation control process,

[0036] [Fig.5] Fig.5 represents the backup device of Fig.2, according to an operating mode during a third stage of an electrical power generation control process,

[0037] [Fig.6] Fig.6 schematically represents the evolution of the rotational speed of the main rotor and the first electric machine as a function of time during the electrical power generation control process. Description of the implementation methods

[0038] To make the explanation more concrete, an example of a rescue device and a method using this device are described in detail below, with reference to the accompanying drawings. It should be noted that the invention is not limited to this example.

[0039] Figure 1 schematically represents a turbomachine 100 according to the invention, intended in particular to drive the rotation of transmission components 50 of a helicopter carrying a main rotor 52 such as a propeller. Figure 2 schematically represents an emergency device 1 according to the invention, integrated into the turbomachine 100.

[0040] It should also be noted in general that, for the sake of clarity, Figures 2 to 5 schematically and functionally represent a backup device 1 and its operating mode, without showing all the details of the components of the turbomachine and the various power transmission elements. In particular, the gears and any speed ratios are not shown.

[0041] 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 motion to a receiving element such as a main rotor 52 of the helicopter via transmission elements 50. According to this example, the gas turbine 10 shown in [Fig. 1] is of the front-drive type with coaxial shaft drive. Without departing from the scope of the present invention, one could also consider a gas turbine with a free turbine of the front-drive type with internal or external shaft drive, or a turbomachine with a free turbine of the rear-drive 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 along the axial direction of the rotating shaft 18. The gas turbine 10 has a casing 26 equipped with an air inlet 28 through which 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 forces it towards the inlet of the combustion chamber 24 where it is mixed with fuel. The combustion taking place in the combustion chamber 24 causes the exhaust gases to be expelled at high speed towards the turbine 22, which in turn drives the shaft 18 of the gas generator 12 to rotate and, consequently, the compressor 20. The rotational speed of the shaft 18 of the gas generator 12 is determined by the fuel flow entering the combustion chamber 24.

[0043] Despite the extraction of kinetic energy by the turbine 22, the gas flow exiting the gas generator possesses significant kinetic energy. As can be seen from [Fig. 1], the gas flow F is directed towards the free turbine 14, which causes an expansion in the free turbine 14, leading to the rotation of the turbine wheel and shaft 16.

[0044] A backup system 1 comprises a first reversible electric machine 30, in this case consisting of an electric motor capable of operating reversibly as an electric generator. It should be noted that although the first reversible electric machine 30 can be located within the turbomachine perimeter, this is not a limiting factor. The reversible electric machine 30 can indeed be located in areas of the helicopter separate from the turbomachine 100, without departing from the scope of the invention. This observation applies generally to the entire backup system, which also includes the second electric machine and the various coupling means described later in this description.

[0045] In this example, the first reversible electric machine 30 is mechanically coupled to the shaft 16 of the free turbine 14 by means of a motor coupling means 45.

[0046] Preferably, the motor coupling means 45 includes a freewheel mounted such that the rotation of the shaft 16 can drive the main rotor 52 and the first electric machine 30 when the latter is operating in generator mode to supply electricity, but conversely, the rotation of the first electric machine 30 cannot drive the shaft 16 of the freewheel 14. In other words, the freewheel of the motor coupling means 45 can only transfer rotational torque in the direction from the freewheel 14 to the first main rotor 52 and the first electric machine 30, but not the other way around. On a helicopter, this freewheel is commonly called a "motor freewheel".

[0047] One advantage of the freewheel is that it does not require electronic or mechanical control by an external operator. Such a freewheel generally consists of a hub and a peripheral ring rotatably mounted on the hub. The hub can generally rotate the peripheral ring, but not the other way around. Therefore, the hub can only drive the ring when it rotates in a predetermined direction relative to the ring, which will be called the "direction of engagement." Otherwise, the hub and the peripheral ring rotate freely relative to each other. In this case, the switchable coupling means are activated when the freewheel hub rotates the peripheral ring, and conversely, the switchable coupling means are deactivated. are deactivated when the freewheel hub does not rotate the peripheral ring.

[0048] It should be noted that the use of a freewheel for the disabling coupling means is not limiting, the freewheel being able to be replaced by any dog ​​clutch or clutch system.

[0049] The first electric machine 30 is also suitable for being coupled to the main rotor 52 in such a way that the first electric machine 30, operating in electric motor mode, is suitable for 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, given the presence of the free wheel of the motor coupling means 45.

[0050] According to the invention, the first electric machine 30 is coupled to the main rotor 52 by means of a first switchable coupling means 32, and a second switchable coupling means 42. The first switchable coupling means 32 and the second switchable coupling means 42 are mounted in parallel with each other, between the first electric machine 30 and the main rotor 52, such that the first electric machine 30 operating in motor mode can drive the main rotor 52 by means of the first switchable coupling means 32, and that the first electric machine 30 operating in generator mode (or receiver mode) can be driven by the main rotor 52 (or by the free turbine 30) by means of the second switchable coupling means 42.

[0051] More specifically, as can be seen in [Fig.2], the first switchable coupling means 32 comprises a first free wheel 34 and, preferably, a first reducer 36, having a first reduction coefficient Kl, disposed between the first electric machine 30 and the first free wheel 34.

[0052] The first freewheel 34 is mounted such that the reversible electric machine 30 can drive the main rotor 52 in rotation when the reversible electric machine 30 is operating in electric motor mode (first coupling means 32 activated), but conversely, the rotation of the main rotor 52 cannot drive the reversible electric machine 30 in rotation (first coupling means 32 deactivated). In other words, the first freewheel 34 can only transfer rotational torque from the reversible electric machine 30 to the main rotor 52, and not the other way around.

[0053] Thus, the rotation of the reversible electric machine 30 is capable of driving the main rotor 52 in rotation in order to provide temporary power supplements to the main rotor for emergency maneuvers. Advantageously, the first reduction coefficient Kl is chosen so that the speed of the reversible electric machine 30 is adapted to the speed range required for the rotation of the main rotor 52.

[0054] Furthermore, the second switchable coupling means 42 comprises a second freewheel 44 and, preferably, a second gearbox 46 disposed between the second freewheel 44 and the first reversible electric machine 30. This second gearbox 46 has a second reduction ratio K2 chosen such that the speed of the first reversible electric machine 30 is adapted to the speed range required to enable the supply of electricity. The second freewheel 44 is mounted such that it can transmit rotational torque only from the main rotor 52 (or from the shaft 16 of the freewheel turbine 14) to the first electric machine 30.

[0055] It should be noted that, by design, to reduce the mass of electrical machines, it is preferable to run them at high speeds. Consequently, K1 and K2 can be between 1 and 8. More generally, the values ​​of these reduction coefficients can be bounded by values ​​specific to each application, according to the nominal, permitted, or desired speeds of the helicopter rotor and the electrical machines, as well as the gas turbine.

[0056] In other words, thanks to the second freewheel 44, the first reversible electric machine 30 can be driven by the main rotor 52 (second coupling means 42 activated), or by the free turbine 14, but cannot drive the main rotor 52 (second coupling means 42 deactivated). When the main rotor 52 (or the free turbine 14) drives the first reversible electric machine 30, the latter operates as an electric generator and produces electricity.

[0057] As can be seen in [Fig. 2], the first and second freewheels 34, 44 are mounted in opposition. In this case, they have opposite directions of engagement. Thus, when the first reversible electric machine 30, operating in motor mode, drives the main rotor 52 (first freewheel 34 engaged, i.e., first coupling means 32 activated), the second freewheel 44 does not transmit the rotational torque from the first reversible electric machine 30 to the main rotor 52 (second freewheel 44 disengaged, i.e., second coupling means 42 deactivated). It should also be noted that during a starting phase, the second freewheel 44, even if driven at both its terminals, cannot transmit torque from the main rotor 52 to the first electric machine 30, the latter operating in motor mode.

[0058] Conversely, when the main rotor 52 drives the first reversible electric machine 30 operating as an electric generator (second freewheel 44 engaged, i.e., second coupling means 42 activated), the first freewheel 34 does not transmit the rotational torque of the main rotor 52 to the first electric machine 30 (first free wheel 34 disengaged, i.e. first coupling means 32 deactivated).

[0059] It should be noted that the first freewheel 34 is preferably a so-called "conventional" freewheel, similar to the freewheel of the motor coupling means 45 described above. In contrast, the second freewheel 44 is configured so that it can deactivate when a rotational speed of the input shaft, i.e., of the main rotor 52, is greater than or equal to a certain value, called the first predetermined stall threshold value Ni, such that for rotational speeds of the main rotor 52 greater than or equal to Ni, the first electric machine 30 cannot be driven by the main rotor 52, even when it is controlled in generator mode (in other words, in the "receiver" position).

[0060] Typically, the second freewheel 44 can be a centrifugally released freewheel, configured to be deactivated when the rotational speed of the main rotor 52 is greater than or equal to the first predetermined stall threshold value Nb

[0061] For example, the second freewheel 44 may include movable rollers that move outwards due to centrifugal force when the rotational speed reaches and exceeds Ni. This centrifugal movement of the rollers disengages the second freewheel 44, thereby decoupling the main rotor 52 from the first electric machine 30.

[0062] In other words, beyond the first predetermined stall threshold value Ni, the second coupling means 42 is deactivated, so that the main rotor 52 can no longer drive the first electric machine 30 in generator mode.

[0063] Therefore, it is possible to choose the first predetermined stall threshold value Ni so as to ensure that the first electric machine 30 is driven in generator mode only for low speeds, the main rotor 52 being decoupled from the first electric machine 30 for speeds above Ni.

[0064] For example, speeds lower than Ni may correspond to the rotational speeds of the main rotor 52 when the aircraft is on the ground and the gas generator 12, and therefore the main rotor 52, are idling. These speeds lower than Ni may also correspond to rotational speeds during takeoff phases, when the rotational speed of the main rotor 52 increases to allow takeoff, in the case where Ni is slightly higher than the rotational speed allowing takeoff, or conversely during landing phases, when the rotational speed of the main rotor 52 slows down to allow landing.

[0065] Thus, the first predetermined stall threshold value Ni can be greater than a speed Nsoi, which is the nominal idle speed of the main rotor 52 when the aircraft is on the ground. In other words, Nsoi is the speed at which the main rotor 52, i.e., the helicopter's propeller, can rotate when the helicopter is on the ground, before increasing the rotational speed of the main rotor 52 during takeoff.

[0066] Furthermore, the first predetermined stall threshold value Ni may be less than a speed Nmin, which is a minimum rotational speed (or minimum idle speed) of the main rotor 52 during a flight phase of the helicopter. It should be noted in this regard that during a nominal flight phase of the helicopter, i.e., excluding takeoff and landing, the rotational speed of the main rotor 52 is between the minimum flight speed Nmin and a maximum flight speed N1 “max*

[0067] Thus, during takeoff, the stall speed Ni is reached and exceeded during a transitional phase between the start of the acceleration of the main rotor 52 from speed Nsoi and the attainment of the nominal flight phase from speed Nmin. In other words, the stall, and therefore the disengagement of the second freewheel 44, is rapidly reached during a takeoff phase, which avoids braking and hindering the rotation of the main rotor 52 by the electric machine 30.

[0068] Furthermore, during a landing phase, the rotational speed of the main rotor 52 falls below Nmin again until it reaches the speed Nsoi when the aircraft lands. In order to reattach the first electric machine 30 to the main rotor 52, in other words to reactivate the second coupling means 42 by re-engaging the second freewheel 44, a second predetermined reattachment threshold value N2 is defined, which is lower than the first predetermined stall threshold value Ni and higher than the ground idle speed Nsoi.

[0069] During a landing phase, it is thus possible to control the first electric machine 30 in motor mode so as to reach the second predetermined threshold value of re-engagement N2, so that when the rotational speed of the main rotor 52 itself reaches N2 during its deceleration, the first electric machine 30 and the main rotor 52 are again synchronized (in other words, docked).

[0070] It is then again possible to generate electricity by the first electric machine 30 operating in generator mode by being driven by the main rotor 52 through the second coupling means 42.

[0071] In other words, the second freewheel 44 can be disengaged from the stall speed N just before the nominal flight phase, and re-engaged just before the helicopter lands, from the re-engagement speed N2. It is thus It is possible to use the first electric machine 30 in generator mode only in short transient phases during takeoff and landing, and when the aircraft is on the ground, without hindering the rotation of the main rotor 52 when the aircraft is in flight.

[0072] The backup device according to the present description may also include a second reversible electric machine 40, analogous to the first reversible electric machine 30. In particular, the second reversible electric machine 40 is capable of operating reversibly as an electric generator.

[0073] It should be noted that the power of the second electric machine 40 can be on the order of one or several hundred kilowatts. It is therefore possible to start the turbine much more quickly than with a starter motor with a power output on the order of 10 kW, which is usually used. This provides a particular operational advantage in the case of medical rescue missions, or during attempts at rapid in-flight restarts.

[0074] In this example, it is possible to reverse the direction of rotation of the second reversible electric machine 40, so that the latter is able to operate in all four quadrants of operation, i.e. 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.

[0075] The second reversible electric machine 40 is mechanically coupled to the shaft 18 of the gas generator 12, which is a shaft of the high-pressure casing of the gas turbine 10, via a breakable section 69. The breakable section 69 can be a portion of the shaft connecting the gas generator 12 to the second reversible electric machine 40, which is mechanically weaker (for example, thinner) than the rest of the shaft, such that a lower torque than for the rest of the shaft is required to break this portion of the shaft. In other words, by increasing the torque applied to the shaft, the first portion of the shaft to mechanically fail will be the breakable section 69.

[0076] It should be noted that the use of a breakable section 69 to couple the second reversible electric machine 40 and the gas generator 12 is not limiting. It is also possible to couple the second reversible electric machine 40 and the gas generator 12 by means of a switchable coupling means similar to the motor coupling means 45, including in particular a freewheel.

[0077] The second electric machine 40 is also suitable for being coupled to the main rotor 52, via a third switchable coupling means 43 analogous to the first coupling means 32 and the motor coupling means 45, and preferably comprising a freewheel, such that the second machine electric 40, operating in electric motor mode (third coupling means 43 activated), is capable of driving the main rotor 52 in rotation.

[0078] According to the architecture of the present exposition, the second electric 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.

[0079] By convention, a positive direction, or clockwise direction SH, is designated as a direction of rotation of the second electrical machine 40 in which the third coupling means 43 is deactivated, and a negative direction, or counterclockwise direction SIH, as a direction of rotation of the second electrical machine 40 in which the third coupling means 43 is activated. In particular, the element represented by "-1" in [Fig. 2] and the following figures represents gears, for example pinions, enabling 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 third coupling means 43 is deactivated, and when the second electrical machine 40 rotates in the negative direction, the third coupling means 43 can be activated.

[0080] The second electric machine 40 can rotate in the negative direction SIH in emergency situations, when it is necessary to assist the rotating main rotor 52. For this purpose, in these situations, the second electric machine 40 can first be driven in the positive direction SH to generate sufficient torque to break the section to be broken 69 and thus decouple the second electric machine 40 from the shaft 18 of the gas generator 12, and then immediately driven in the negative direction SIH to assist the main rotor 52.

[0081] Furthermore, the first electric machine 30 can be electrically connected to the second electric machine 40 via electrical connections 70, each of the electric machines being further connected to a battery 72 of the backup device 1. The electrical connections 70 may include electrical conditioning devices (rectifiers, inverters, voltage converters). These connections 70 allow the electric machines 30, 40 to draw power from the battery 72 when operating in motor mode, or conversely, to recharge the battery 72 when operating in generator mode. These connections 70 also allow the electric machines 30, 40 to exchange electrical power with each other.

[0082] The backup device 1 also includes a control unit 60 of the “FADEC” type (for “Full Authority Digital Engine Control” in English), controlling in particular the electrical machines 30, 40. It should be noted that the various connections between the control unit 60 and the elements it controls are not shown.

[0083] A method for controlling the generation of electrical power according to one embodiment, using the backup device 1 described above, is then described with reference to Figures 3 to 6. In Figures 3 to 5, the dashed arrows represent the direction of mechanical or electrical power transmission between two elements. In [Fig. 3], for example, mechanical power is transmitted from the main rotor 52 to the first electrical machine 30, the latter operating in generator mode, symbolized by the lightning bolt next to the first electrical machine 30.

[0084] Furthermore, [Fig.6] schematically represents, on the one hand, the variations of the rotational speed N of the main rotor 52 as a function of time t, represented by the curve in thick solid line, and on the other hand the variations of the rotational speed of the rotor of the first electric machine 30, represented by the curve in thin line including the white circles.

[0085] Initially, the aircraft, in this case the helicopter, is on the ground, with the gas turbine 10 switched off. At an initial time t0, the gas generator 12 is switched on. This then drives the free turbine 14, which in turn drives the main rotor 52. The rotational speed of the main rotor 52 then increases from 0 until it reaches, at a time tb, the nominal idle speed Nsoi. As long as the aircraft remains on the ground, the rotational speed of the main rotor 52 can be maintained constant at the nominal speed Nsoi for the desired duration, for example, until a time t2.

[0086] From time t2, the speed of the gas generator 12, and therefore of the main rotor 52, is increased in order to cause the helicopter to take off. The actual takeoff of the aircraft, that is to say, the moment when the aircraft leaves the ground, can take place, for example, at time t3, when the rotational speed of the main rotor 52 is still below the first stall speed threshold value Ni, which is reached at time t4. Alternatively, the actual takeoff of the aircraft could take place just after exceeding the stall speed Ni, and before reaching the speed N min*

[0087] During the phase from t0 to t4, the second coupling means 42 is activated and the first electric machine 30 is controlled to operate in generator mode, driven by the main rotor 52 via the second freewheel 44 ([Fig. 3]). Conversely, the first coupling means 32 is deactivated. In [Fig. 3], in particular, the cross on the first freewheel 34 symbolizes the fact that it is disengaged, the rotational speed of the main rotor 52 thus being unable to be transmitted between the two ends of the first freewheel 34, as symbolized by the shortened vertical arrow.

[0088] During the increase in rotational speed of the main rotor 52, when the stall speed threshold value Ni is reached at time t4, the second means The coupling 42 is deactivated. Thus, the first electric machine 30 can no longer be driven in generator mode by the main rotor 52.

[0089] On the other hand, at time t4, the first electric machine 30 can be controlled to operate in motor mode, so as to be able to drive the main rotor 52 in rotation by means of the first coupling means 32 which is activated, the second coupling means 42 being deactivated ([Fig.4]).

[0090] Preferably, the first electric machine 30 is controlled so that the increase in its rotational speed follows the increase in the rotational speed N of the main rotor 52 throughout the rest of the takeoff phase, from the instant t4 of stall of the second free wheel 44 to an instant t5 marking the end of the takeoff phase.

[0091] This ensures that the first freewheel 34 remains attached to the main rotor 52 throughout the takeoff phase, and that the backup device 1 is ready to provide power until the end of the takeoff phase to assist the main rotor 52 via the first electric machine 30 if necessary.

[0092] It should be noted that in this example, the takeoff phase extends from time t2 to time t5. During this phase, the rotational speed of the main rotor 52 increases up to the maximum flight speed Nmax, and remains constant for a few moments, for example 60 seconds, at the speed Nmax until the end of the takeoff phase.

[0093] At time t5, the first electric machine 30 is switched back into generator mode. However, since the rotational speed of the main rotor 52 is greater than the first stall threshold value Ni, the second coupling means 42 remains deactivated and the main rotor 52 cannot drive the first electric machine 30. Furthermore, in generator mode, the first coupling means 32 is itself deactivated due to the orientation of the first freewheel 34 ([Fig. 5]). Consequently, the rotational speed of the first electric machine 30 drops from t5 onwards ([Fig. 6]).

[0094] The helicopter then enters a nominal flight phase from t5, during which the rotation speed of the main rotor 52 remains between Nmin and Nmax, and can oscillate between these two values.

[0095] When a landing is desired, the rotation speed of the main rotor 52 is slowed down until it falls below the speed Nmin and the aircraft lands on the ground at a time t8.

[0096] Preferably, during this landing phase, the backup device 1 can again control the first electric machine 30 in motor mode at a time t6 prior to the actual landing of the helicopter at time t8, in order to increase the rotation speed of the first electric machine 30 up to the second predetermined threshold value of reattachment N2.

[0097] Thus, during the slowing down of the main rotor 52, the first electric machine 30 can again synchronize with the main rotor 52 at time t7. The first electric machine 30 is then switched back into generator mode at time t7, just before the actual landing of the helicopter at time t8.

[0098] From time t8, the helicopter is therefore on the ground, the main rotor 52 being again driven in rotation by the gas generator 12 and the free turbine 14 rotating at idle, at constant speed Nsoi. During this phase from t7 to t9, the second coupling means 42 is therefore activated again, and the first electric machine 30 can produce electricity by being driven by the main rotor 52 via the second free wheel 44, the first free wheel 34 being disengaged ([Fig.3]).

[0099] At time t9, the gas generator 12 is stopped, the rotation speed of the main rotor 52, and consequently that of the first electric machine 30 still operating in generator mode, then falls to 0.

[0100] Although the present invention has been described with reference to specific embodiments, it is evident that modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various embodiments illustrated / mentioned can be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than a restrictive sense.

[0101] It is also evident that all the characteristics described with reference to a process 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 process.

Claims

Demands

1. Backup device (1) for a hybrid aircraft, in particular a helicopter, the aircraft comprising a turbomachine having 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 backup device (1) comprising a first reversible electric machine (30) capable of being coupled to the main rotor (52) by means of a first switchable coupling means (32) and a second switchable coupling means (42) mounted in parallel, and of operating in a motor mode so as to drive the main rotor (52) by means of the first switchable coupling means (32), and of operating in a generator mode so as to generate electrical power by being driven by the main rotor (52) by means of the second switchable coupling means (42),the second switchable coupling means (42) being configured to be switched off when a rotational speed of the main rotor (52) is greater than or equal to a first predetermined stall threshold value (Ni), such that the first electric machine (30) cannot be driven into generator mode by the main rotor (52).

2. Device (1) according to claim 1, wherein the first switchable coupling means (32) comprises a first freewheel (34), and the second switchable coupling means (42) comprises a second freewheel (44), the first and second freewheels (34, 44) being mounted in opposition, the second freewheel (44) being a centrifugally released freewheel, configured such that it is switched off when the rotational speed of the main rotor (52) is greater than the first predetermined stall threshold value (Ni).

3. Device (1) according to claim 1 or 2, wherein the first switchable coupling means (32) comprises a first reducer (36) having a first reduction coefficient (K1), and the second switchable coupling means (42) comprises a second reducer (46) having a second reduction coefficient (K2).

4. Device (1) according to any one of claims 1 to 3, wherein a minimum flight speed (Nmin) is a minimum speed of rotation of the main rotor (52) in a phase of flight of the aircraft, and a ground slow speed (Nsoi) is a rotation speed of the main rotor (52) in a configuration in which the aircraft is on the ground, the first predetermined stall threshold value (Ni) being less than the minimum flight speed (Nmin), and greater than the ground slow speed (Nsoi).

5. Device (1) according to claim 4, the device (1) being configured to, in a main rotor (52) deceleration phase prior to aircraft landing, command the first electric machine (30) in motor mode so as to increase its rotational speed up to a second predetermined re-engagement threshold value (N2) lower than the first predetermined stall threshold value (Ni) and higher than the ground idle speed (Nsoi).

6. Device (1) according to any one of claims 1 to 5, comprising a second reversible electric machine (40) capable of being coupled to the main rotor (52) by means of a third switchable coupling means (43) 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) opposite to the first direction of rotation (SIH), the second electric machine (40) further being capable of being coupled to a shaft (18) of the gas generator (12) by means of a breakable section (69).

7. 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 backup device (1) according to any one of claims 1 to 6.

8. A method for controlling electrical power generation using a backup device (1) for a hybrid aircraft according to any one of claims 1 to 6, the method comprising: - controlling the first reversible electric machine (30) so as to generate electrical power by being driven by the main rotor (52) via the second means of switchable coupling (42), when the gas generator (12) is on and the aircraft on the ground, - the increase of the rotational speed of the main rotor (52) up to a rotational speed greater than or equal to the first predetermined stall threshold value (Ni) so as to switch off the second switchable coupling means (42), so that the first electric machine (30) cannot be driven into generator mode by the main rotor (52), during a takeoff phase of the aircraft.

9. Method according to claim 8, comprising controlling the first electric machine (30) in motor mode when the rotational speed of the main rotor (52) is greater than or equal to the first predetermined stall threshold value (Ni), during the takeoff phase.

10. A method according to claim 8 or 9, comprising, during a flight phase in which the rotational speed of the main rotor (52) is between a minimum flight speed (Nmin), which is greater than the first predetermined stall threshold value (Ni) and is a minimum rotational speed of the main rotor (52) in the flight phase of the aircraft, and a maximum flight speed (Nm ax), which is a maximum rotational speed of the main rotor (52) in the flight phase of the aircraft, the control of the first electric machine (30) in generator mode.

11. A method according to any one of claims 8 to 10, comprising, during a landing phase of the aircraft, controlling the first electric machine (30) in motor mode and so as to increase its rotational speed up to a second predetermined threshold value of re-engagement (N2) lower than the first predetermined threshold value of disengagement (Ni) and higher than a ground idle speed (Nsoi), which is a rotational speed of the main rotor (52) in a configuration in which the aircraft is on the ground.

12. Method according to claim 11, comprising controlling the first electric machine (30) in generator mode when the first electric machine (30) has reached the second predetermined threshold value of reattachment (N2) and the aircraft is on the ground, the main rotor (52) rotating at ground idle speed (Nsoi).

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