Improved propulsion assembly for a multi-engine hybrid aircraft

Abstract

The invention relates to a propulsion assembly (100) comprising a first and second engine (1, 2) each having a gas generator (12, 22) and a free turbine (11, 21), a main rotor (62) coupled to the free turbine (11, 21), the engines (1, 2) each comprising a first electric machine (30, 40) coupled to the gas generator (12, 22) only, a second electric machine (32, 42) coupled to the gas generator (12, 22) via a first coupling means (34, 44) when said machine rotates in a first direction, and coupled to the free turbine (11, 21) via a second coupling means (36, 46) when said machine rotates in a second direction, the first electric machine (30, 40) operating selectively in a motor or generator mode, the second electric machine (32, 42) operating in the motor mode when it rotates in the first direction, and selectively in the motor mode or the generator mode when it rotates in the second direction.

Description

Description Title of the invention: Improved propulsion system for multi-engine hybrid aircraft Technical Field

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

[0002] As is well known, a turbomachine, for example a turboshaft engine, particularly for a helicopter, comprises a gas turbine with a gas generator and a free turbine driven by the gas flow generated by the gas generator. The free turbine is completely independent of the gas generator, which includes one or two compressors (high and low pressure) and one or two turbines (high and low pressure). In particular, the shaft of the free turbine and the shaft of the gas generator (carrying the compressor(s) and turbine(s)) are not connected. The free turbine is therefore distinct from the turbine(s) (high and low pressure) mounted on the gas generator shaft, which are connected to the compressor. Thus, the defining characteristic of a free turbine turboprop lies in the separation of the "engine" (gas generator) and "power turbine" (or free turbine) components.

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

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

[0005] One of the key aspects of SEO mode lies in the ability to reactivate the standby turbine in case of a power loss in the operating turbine. To ensure the fastest possible reactivation, it is possible to keep the turbine in standby mode (or "super idle"), meaning that the gas generator continues to run solely using an electric motor, without any fuel input. The generator is then maintained within its "ignition window" (typically 10-30% of the speed of nominal rotation of the gas generator) in order to allow immediate ignition of the combustion chamber, or in "super-idle" mode by means of combustion at a low speed threshold and assisted by means of a mechanical power input via an electric machine, in order to benefit from a combustion chamber already lit but with a controlled internal temperature.

[0006] Twin-engine applications involve numerous functions, such as in-flight starting or restarting of the gas generator, onboard electrical power generation, and supplying mechanical power to the main rotor. Existing solutions for performing some of these functions are not fully optimized. In particular, they do not maximize the number of functions that can be performed while minimizing the impact of electrical load on the engine, nor the number of components in these architectures, and therefore their mass. There is thus a need for a propulsion system for twin-engine or multi-engine aircraft with an architecture that at least partially addresses the aforementioned drawbacks. Description of the invention

[0007] This presentation concerns a propulsion system for a hybrid aircraft, in particular a multi-engine helicopter, comprising: - at least one first engine and a second engine, each having a gas generator and a free-spinning turbine driven in rotation by a gas flow generated by the gas generator, - a main rotor coupled to the free turbine of the first and second engines, - the first and second engines, each comprising a first electric machine capable of being coupled only to the gas generator, and a second electric machine capable of being coupled to the gas generator via a first coupling means when rotating in a first direction of rotation, and of being coupled to a shaft of the free turbine via a second coupling means when rotating in a second direction of rotation opposite to the first direction of rotation, the first electric machine being capable of operating selectively in engine mode or in a generator mode, and the second electrical machine being capable of operating in motor mode when rotating in the first direction of rotation, and of operating selectively in motor mode or generator mode when rotating in the second direction of rotation.

[0008] It is understood that, according to the present exposition, each of the first and second motors is equipped with a first electric machine and a second electric machine, preferably in a symmetrical manner.

[0009] It is further understood that the first and second electric machines are reversible, so that they can operate selectively in motor mode or generator mode. Thus, the first electric machine can operate in motor mode to drive the gas generator by providing it with torque, or in generator mode by being driven by the gas generator, the current thus generated being able to be transferred to the second electric machine or to a battery to recharge it.

[0010] Similarly, the second electric machine can operate in motor mode to drive the gas generator when rotating in the first direction, or the main rotor when rotating in the second direction. The second electric machine can also operate in generator mode when rotating in the second direction, driven by the free turbine; the current thus generated can be transferred to the first electric machine of the first and / or second motor, or to a battery to recharge it.

[0011] Therefore, for each of the first and second motors, the first electric machine is capable of operating in two quadrants of operation, namely in motor mode or in generator mode by rotating in a single direction of rotation, and the second electric machine is capable of operating in three quadrants of operation, namely in motor mode by rotating in a first direction of rotation, and in the mode engine or in generator mode by rotating in the second direction of rotation.

[0012] This use of electric machines, within the framework of a multi-motor application, offers a wide range of operation and has the advantage of being simple by limiting the number of components and connections, while ensuring a good level of redundancy, by performing bidirectional internal hybridization, each electric machine being able to generate and transfer electrical power to the other electric machine, and by allowing a high number of functions to be performed, in particular during operation in SEO mode or during rapid reactivation, the first and second electric machines both being able to operate as generators, and thus improving the reliability of the device.

[0013] In some embodiments, the first coupling means and the second coupling means are switchable coupling means.

[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" means the electrical machines, the main rotor and the gas generator.

[0015] In some embodiments, the first and second disabling coupling means include a freewheel.

[0016] The freewheel has the advantage of not requiring electronic or mechanical control by an external operator. Such a freewheel generally consists of a hub and a peripheral ring mounted to rotate on the hub. The hub can drive the peripheral ring, but not the other way around. Therefore, the hub can only drive the ring when it rotates in a predetermined direction, called the "direction of engagement." Otherwise, the hub and the peripheral ring rotate freely relative to each other. In this case, the disengageable coupling means are activated when the freewheel hub drives the peripheral ring into rotation, and, conversely, the disabling coupling means are deactivated when the freewheel hub does not drive the peripheral ring into rotation.

[0017] In some embodiments, the main rotor is coupled to the free turbine of the first and second motors via a first and second main coupling means, respectively. Furthermore, the free turbine of each of the first and second motors may be directly connected to the main rotor, or via a mechanical gearbox.

[0018] In some embodiments, the first and second coupling means of the first motor are the only coupling means upstream of the first main coupling means, and the first and second coupling means of the second motor are the only coupling means upstream of the second main coupling means.

[0019] The term "upstream" refers to the direction of power transfer from the first electric machine to the main rotor. In other words, apart from the first and second main coupling means that connect the first and second motors to the main rotor, each of the first and second motors comprises only two coupling means, for example, two freewheels. Minimizing the number of coupling means in each motor simplifies the overall architecture, reduces its mass and cost, and minimizes potential failures of these coupling means, such as unwanted jamming.

[0020] In some embodiments, the second coupling means of the first and second motors includes a movable locking means between a free position in which the free turbine cannot drive the second electric machine in rotation, and a locking position in which the free turbine is able to drive the second electric machine in rotation.

[0021] The locking mechanism is a means of forcing the coupling between the second electrical machine and the shaft of the free turbine. For example, when the coupling means includes a freewheel and a locking mechanism, the freewheel is called a "biocable freewheel," such that in the locked position, the hub of the freewheel can drive the peripheral ring of the biocable freewheel. In other words, the free turbine is able to drive the rotation of the second electrical machine, which can then operate in generator mode.

[0022] In some embodiments, when one of the first or second motor drives the main rotor alone, the gas generator of the other of the first or second motor is kept in standby mode, via the first or second electric machine.

[0023] When the aircraft is operating in SEO mode, the second engine, for example, provides all the power, while the first engine is intentionally shut down, or preferably placed in standby mode, to optimize specific fuel consumption. Standby mode keeps the first engine's gas generator within a range of 5 to 40%, preferably 5 to 30%, of its rated speed, to allow for a rapid restart if necessary, particularly when the second engine loses power.

[0024] In some embodiments, when the gas generator of one of the first or second motors is kept in standby mode by means of the first electric machine, the second electric machine of the other of the first or second motor is configured to operate in generator mode by rotating in the second direction of rotation, and to transmit the generated electric current to the first electric machine keeping said first or second motor in standby mode.

[0025] According to this configuration, the shaft of the free turbine advantageously drives the rotation of the second electrical machine, operating as an electric generator, such that the kinetic energy intended to be The energy converted into electrical energy is advantageously drawn from the shaft of the free turbine (which itself drives the main rotor), and not from the gas generator. This allows electricity to be supplied to the first electric machine to assist it, thus providing redundancy, while limiting the impact on the engine's efficiency. As a result, the turboshaft engine according to the invention advantageously provides electricity without significantly compromising its efficiency.

[0026] In some embodiments, the second electric machine operating in generator mode is configured to also transmit the generated electric current to the first electric machine from that of the first or second motor driving the main rotor alone.

[0027] Thus, the electric current generated by the second electric machine can also, as a replacement or in addition, be transmitted to the first electric machine of the motor driving the main rotor alone, to assist the latter.

[0028] In some embodiments, the first electric machine is coupled to the gas generator only, via a breakable section.

[0029] In some embodiments, the assembly includes a control unit configured to drive the first and second electric machines by selecting the motor mode to drive the gas generator and / or the main rotor, or the generator mode to transfer the electric current generated by one of the first or second electric machines to the other of the first or second electric machines.

[0030] In some embodiments, the control unit is configured so that, after detecting a power loss in one of the first or second motors driving the main rotor alone, it drives the first and second electric machines of the other first or second motor operating in standby mode, so that they operate in motor mode, the second electric machine rotating in the first direction of rotation, so as to cause the gas generator of said first or second engine operating in standby mode to rotate.

[0031] The control unit thus ensures redundancy by adapting the operation of the different electrical machines according to flight conditions. For example, when a rapid reactivation is required following a power loss in one of the two engines, the control unit operates the first and second electrical machines of the other engine so that they both run in engine mode, thereby accelerating the reactivation of the gas generator, which was in standby mode.

[0032] This presentation also relates to a hybrid aircraft comprising a propulsion system according to any of the preceding embodiments, the hybrid aircraft being a multi-engine helicopter, in particular a twin-engine one.

[0033] The term "hybrid aircraft" refers to an aircraft comprising a thermal engine capable of driving a main rotor in rotation, and at least one electric machine capable of providing power to the thermal engine. Brief description of the drawings

[0034] The invention and its advantages will be better understood upon reading the detailed description below of various embodiments of the invention, given by way of non-limiting examples. This description refers to the accompanying figure pages, on which:

[0035] [Fig. 1] Figure 1 shows a cross-sectional view of a propulsion assembly for a twin-engine aircraft according to the invention,

[0036] [Fig. 2] Figure 2 represents a functional diagram of the propulsion system shown in Figure 1,

[0037] [Fig. 3] Figure 3 represents the functional diagram of the propulsion system of Figure 2 according to a first mode of operation,

[0038] [Fig. 4] Figure 4 represents the functional diagram of the propulsion assembly of Figure 2 according to a second mode of operation. Description of the implementation methods

[0039] An architecture of a propulsion assembly 100 according to an embodiment of the invention will be described in the following description, with reference to figures 1 to 4.

[0040] It should be noted that, for the sake of clarity, the figures schematically represent a simplified, functional architecture of the device, without showing all the details of the components of the turbomachinery and the various power transmission elements. In particular, the gears that drive shafts 13 and 14 with the electric machines, and vice versa where applicable, and any speed ratios, are not shown.

[0041] Figure 1 schematically represents a propulsion system 100 of a twin-engine aircraft, comprising a first engine, in this example a first turbomachine 1, and a second engine, in this example a second turbomachine 2, driving in rotation transmission components 60 of a helicopter carrying a propeller or a main rotor 62. The turbomachines may be turboshaft engines or turboprop engines. Although the propulsion system described below comprises two turbomachines, this example is not limiting, the invention also applying to propulsion systems of multi-engine aircraft comprising more than two engines.

[0042] The first turbomachine 1 and the second turbomachine 2 are preferably identical and have the same characteristics. Therefore, the description below refers to both the first and second turbomachines 1 and 2.

[0043] The first turbomachine 1 and the second turbomachine 2 respectively comprise a gas turbine 10, 20 having a gas generator 12, 22 and a free turbine 11, 21 capable of being driven in rotation by a gas flow generated by the gas generator 12, 22. The free turbine 11, 21 is mounted on a shaft 13, 23 which transmits the rotational motion to a receiving element such as a The main rotor 62 of the helicopter is driven by means of the transmission components 60. According to this example, the gas turbine 10, 20 shown in Figure 1 is of the front-drive type with coaxial shaft drive. Without departing from the scope of the present invention, one could also consider a free-turbine gas turbine of the front-drive type with internal or external shaft drive, or a free-turbine turbomachine of the rear-drive type. Similarly, the free turbine can be directly driven by the main rotor 62 or incorporate a speed reducer without altering the principle of the invention.

[0044] The gas generator 12, 22 comprises a rotating shaft 14, 24 on which are mounted a compressor 15, 25 and a turbine 16, 26, as well as a combustion chamber 17, U arranged axially between the compressor 15, 25 and the turbine 16, 26 when the gas generator 12, 22 is considered along the axial direction of the rotating shaft 14, 24. The gas turbine 10, 20 has a casing 18, 28 equipped with an air inlet 19, 29 through which fresh air enters the gas generator 12, 22. After its admission into the chamber of the gas generator 12, 22, the fresh air is compressed by the compressor 15, 25 which forces it towards the inlet of the combustion chamber 17, I in which it is mixed with fuel. The combustion which takes place in the combustion chamber 17, ZI causes the burnt gases to be evacuated at high speed to the turbine 16, 26, which in turn causes the shaft 14, 24 of the gas generator 12, 22 to rotate and, consequently, the compressor 16, 26.The rotational speed of the shaft 14, 24 of the gas generator 12, 22 is determined by the fuel flow entering the combustion chamber 17, 27.

[0045] Since the propulsion assembly 100 is of the free turbine type, it will be understood that the generator shaft 14, 24 is independent of the turbine shaft 13, 23. In other words, the free turbine 11, 21 and the turbine shaft 13, 23 are totally independent of the generator shaft 14, 24 and the compressor 15, 25, unlike the turbine 16, 26 which is linked to the compressor 15, 25.

[0046] Despite the extraction of kinetic energy by turbine 16, 26, the gas flow exiting the gas generator possesses significant kinetic energy. As can be seen from Figure 1, the gas flow F is directed towards the free turbine 11, 21, which causes an expansion in the free turbine 11, 21, leading to the rotation of the turbine wheel and shaft 13, 23.

[0047] The main rotor 62 is coupled, via the transmission elements 60, to the shaft 13 of the free turbine 11 of the first gas turbine 10 by means of a first main coupling means 51. The main rotor 62 is also coupled, via the transmission elements 60, to the shaft 23 of the free turbine 21 of the second gas turbine 20 by means of a second main coupling means 52.

[0048] Preferably, the first and second main coupling means 51, 52 include a freewheel mounted such that the rotation of the shaft 13, 23 can drive the main rotor 62, but conversely, the rotation of the main rotor 62 cannot drive the shaft 13, 23 of the free turbine 11, 21. In other words, the freewheel of the first and second main coupling means 51, 52 can only transfer rotational torque from the free turbine 11, 21 to the main rotor 62, but not the other way around. On a helicopter, this freewheel is commonly called a "motor freewheel" or "power freewheel." It should be noted that the use of a freewheel for the main coupling means 51, 52 is not limiting; the freewheel can be replaced by any dog ​​clutch or clutch system.

[0049] The turbomachines 1, 2 each further comprise a first electric machine 30, 40 including an electric motor capable of reversibly operating in motor mode or in electric generator mode. The first electric machine 30, 40 is mechanically coupled to the shaft 14, 24 of the gas generator 12, 22 only, preferably by means of a breakable section, or frangible shaft 91, 92, allowing the electric machine 30, 40 to be irreversibly released in the event of its blockage. In other words, the breakable section 91, 92 is configured to allow disconnection of the first electric machine 30, 40 with the generator shaft 14, 24 in case of blockage of the gas generator 12, 22 for example during an accidental stop or failure of the latter.

[0050] The turbomachines 1, 2 each also include a second electric machine 32, 42, which also comprises an electric motor capable of reversibly operating in motor mode or in electric generator mode. The second electric machine 32, 42 is mechanically coupled to the shaft 14, 24 of the gas generator 12, 22 via a first switchable coupling means 34, 44, comprising a freewheel (hereinafter referred to as the freewheel 34, 44).

[0051] The freewheel 34, 44 is mounted such that the rotation of the second electric machine 32, 42, operating in motor mode, can drive the gas generator 12, 22 in rotation, but conversely, the rotation of the gas generator 12, 22 cannot drive the second electric machine 32, 42. In other words, the freewheel 34, 44 can only transfer a rotational torque in the direction from the second electric machine 32, 42 to the gas generator 12, 22.

[0052] The second electric machine 32, 42 is further mechanically coupled to the shaft 13, 23 of the free turbine 11, 21 by means of a second switchable coupling means 36, 46, comprising a free wheel (hereafter referred to as free wheel 36, 46).

[0053] The freewheel 36, 46 is mounted such that the rotation of the second electric machine 32, 42, operating in motor mode, can drive the free turbine 11, 21, but conversely, the rotation of the free turbine 11, 21 cannot drive the rotation of the second electric machine 32, 42, except when the freewheel 36, 46 is locked according to the configuration described below. In other words, the unlocked freewheel 36, 46 can only transfer rotational torque from the second electric machine 32, 42 to the free turbine 11, 21.

[0054] According to the arrangement of this presentation, the second electric machine 32, 42 is capable of rotating in a first direction of rotation in which it is mechanically coupled to the shaft 14, 24 of the gas generator 12, and in a second direction of rotation, opposite to the first direction of rotation, in which it is mechanically coupled to the shaft 13, 23 of the free turbine 11, 21, and can thus drive the main rotor 62 via the shaft 13, 23 of the free turbine 11, 21.

[0055] By convention, the following description will use a positive direction, such as the direction of rotation of the second electric machine 32, 42 in which the freewheel 34, 44 is activated, and a negative direction, such as the direction of rotation of the second electric machine 32, 42 in which the freewheel 36, 46 is activated. In particular, the element represented by "-1" in Figure 2 and the following figures represents gears, for example pinions, enabling the reversal of the direction of rotation.

[0056] It will thus be understood that when the second electric machine 32, 42 rotates in the positive direction, the free wheel 34, 44 can be activated, and the free wheel 36, 46 is deactivated, and when the second electric machine 32, 42 rotates in the negative direction, the free wheel 34, 44 is deactivated, and the free wheel 36, 46 can be activated.

[0057] According to this embodiment, the freewheel 36, 46 is of the biocable type. In particular, the second coupling means also includes a locking means 38, 48. The locking means 38, 48 is movable between a free position in which the free turbine 11, 21 cannot drive the second electric machine 32, 42 in rotation, given the orientation of the freewheel 36, 46 (configuration shown in Figure 2), and a locked position that allows the freewheel 36, 46 to be locked and thus forces coupling between the free turbine 11, 21 and the second electric machine 32, 42 (configuration shown in Figure 3 for the locking means 48). In other words, when the locking means 38, 48 is in the locked position, the second coupling means acts as a shaft such that the free turbine 11, 21 is capable of driving the second electric machine 32, 42 in rotation, despite the presence of the free wheel 36, 46. The second electric machine 32, 42 can thus operate in electric generator mode by drawing power from the shaft 13, 23 of the free turbine 11, 21. It should be noted that the change of position of the locking means 46 can be achieved by an electrical, pneumatic or hydraulic component and controlled by a user or a control unit.

[0058] In this regard, the assembly according to the invention also includes a current storage means, for example a battery 70 or "battery pack", and a control unit 80.

[0059] Battery 70 is capable of storing the current generated by the various electrical machines when they operate in generator mode, and of supplying the necessary current to these electrical machines when they operate in motor mode. It should be noted that, although the electrical connection between battery 70 and the electrical machines is not shown in all the figures, for the sake of clarity, this connection is always present.

[0060] The control unit 80 is typically a computer or electronic control unit, commonly referred to by the acronym ECU. It is capable of controlling the first electric machine 30, 40 and the second electric machine 32, 42 of each of the motors 1, 2 to operate them selectively in motor or generator mode; the battery 70 to transmit electrical current from the battery to the electric machines as needed and possibly measure its state of charge; and also the locking means 38, 48, to move them from the free position to the locked position, and vice versa. The control unit 80 and its connections to these various components, shown only in Figure 1, are also present in the other figures but are omitted for clarity.

[0061] Thus, the first electric machine 30, 40 is capable of operating in two quadrants of operation (motor mode or generator mode, controlled by the control unit 80), and the second electric machine 32, 42 is capable of operating in three quadrants of operation (motor mode on the gas generator 12, 22 rotating in the positive direction or motor mode on the main rotor 62 rotating in the negative direction, and generator mode rotating in the negative direction, the locking means 38, 48 being in the locked position).

[0062] This simple architecture of the propulsion assembly 100, using for each motor 1, 2 only two free wheels 34, 44 and 36, 46 upstream of the main coupling means 51, 52, makes it possible to efficiently achieve different modes of operation described in the rest of the description, and thus makes it possible to optimize the operation of the propulsion assembly 100.

[0063] Figure 3 illustrates Single Engine Operative (SEO) mode, made possible by the presence of two turbomachines 1 and 2. In this mode, only the second turbomachine 2 (in this example) is operating, providing all the power to the main rotor 62, while the first turbomachine 1 is intentionally put into standby mode. When SEO mode is engaged, the gas generator 12 is put into standby (or assisted super-idle), meaning it no longer supplies motive power to the main rotor 62. To reactivate it as quickly as possible, the gas generator 12 is driven into the ignition window (within a range of 5 to 30%, for example, 10% of its rated speed) by the first electric machine 30 in this example.It should be noted in this regard that in Figure 3 (as well as in Figure 4 described below), the thickened lines and arrows represent the direction of transmission of the mechanical power supplied or taken from the electrical machines.

[0064] Conversely, the first electric machine 40 of the second turbomachine 2, driving the main rotor 62 alone, supplies electrical power to the gas generator 22 so that it operates at its nominal rotational speed, in order to drive the free turbine 21 and its shaft 23, and consequently the main rotor 62 via the transmission elements 60.

[0065] At the same time, the second electric machine 42 of the second turbomachine 2 is used to extract mechanical power from the shaft 23 of the free turbine 21. To do this, the second electric machine 42 is driven to operate in generator mode (represented by a small lightning bolt in Figure 3) by rotating in the negative direction, the locking means 48 being driven into the locking position to block the free wheel 46.

[0066] The electricity generated by the second electric machine 42 is transmitted, via electrical connections represented by dashed lines in Figure 3, to the first electric machine 40 of the second turbomachine 2, operating in motor mode, the first electric machine 40 thus injecting mechanical power into the high-pressure body of the gas generator 22. This internal hybridization without a battery improves the lifespan of the second turbomachine 2.

[0067] The electricity generated by the second electric machine 42 is also transmitted electrically to the first electric machine 30 of the first turbomachine 1 operating in standby mode. The first electric machine 30 operates in engine mode and also injects mechanical power into the high-pressure body of the gas generator 12, but at a lower power (on the order of 10% of the rated speed of the first turbomachine 1) than the first electric machine 40 does in the second turbomachine 2.

[0068] Figure 4 represents operation in the case of a rapid reactivation. Indeed, from operation in SEO mode, it may be necessary to rapidly reactivate the first turbomachine 1 in the case of an emergency situation when the second turbomachine 2, which was operating at full power to supply the main rotor 62 alone, loses power, or when the power requirement at the main rotor 62 becomes very rapidly greater than what a single turbomachine can supply.

[0069] In this scenario, the first electric machine 30 and the second electric machine 32 of the first turbomachine 1 are driven to to operate in motor mode, and supply mechanical power to the gas generator 12. The second electric machine 32 rotates in the positive direction. As internal hybridization is not possible in this case, the first electric machine 30 and the second electric machine 32 are electrically powered by the battery 70.

[0070] More specifically, such a process for optimizing the reactivation of the propulsion assembly 100 can initially include the detection, by the control unit 80, of the loss of power of the second turbomachine 2 or of a significant drop in the rotational speed of the main rotor 62. The high-pressure body of the gas generator 12 of the first turbomachine 1 is then maintained in the ignition speed window by the first electric machine 30, which is powered by the battery 70, until the ignition of the combustion chamber 17 is detected.

[0071] When ignition of combustion chamber 17 is detected, the first electric machine 30 and the second electric machine 32 of the first turbomachine 1 are then driven to operate in engine mode, being electrically powered by the battery 70, to assist the gas generator 12 in order to quickly reactivate the first turbomachine 1. It should be noted that the above steps also apply to a normal reactivation of either of the turbomachines 1 and 2, outside of an emergency situation.

[0072] It should also be noted that the first electric machine 30, 40 and the second electric machine 32, 42 are preferably high-power electric machines, specifically several tens of kilowatts, allowing the turbine to start much more quickly than with a starter motor of around 10 kW. Thus, each of the first and second electric machines can ensure the rapid reactivation of the turbomachine 1, 2, which is in standby mode. The rapid reactivation function is therefore redundant and remains possible even if one of the first 30, 40 or second 32, 42 electric machines fails, thereby ensuring a high availability rate.

[0073] It should be noted, however, that this configuration is not limiting; the first electric machine may have a higher power output than the second, and vice versa, without departing from the scope of the invention. Furthermore, the first and second electric machines may operate sequentially or synchronously.

[0074] 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 restrictive sense.

[0075] 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

Claims

1. Propulsion assembly (100) for hybrid aircraft, in particular a multi-engine helicopter, comprising: - at least a first engine (1) and a second engine (2) each having a gas generator (12, 22) and a free turbine (11, 21) driven in rotation by a gas flow generated by the gas generator, - a main rotor (62) coupled to the free turbine (11, 21) of the first and second engines (1, 2), - the first and second motors (1, 2) each comprising a first electrical machine (30, 40) capable of being coupled to the gas generator (12, 22) only, and a second electrical machine (32, 42) capable of being coupled to the gas generator (12, 22) via a first coupling means (34, 44) when it rotates in a first direction of rotation, and of being coupled to a shaft (23) of the free turbine (11, 21) via a second coupling means (36, 46) when it rotates in a second direction of rotation opposite to the first direction of rotation, the first electrical machine (30, 40) being capable of operating selectively in a motor mode or in a generator mode, and the second electrical machine (32, 42) being capable of operating in the motor mode when it rotates in the first direction of rotation, and of operating selectively in the motor mode or the generator mode when it rotates in the second direction of rotation.

2. A propulsion assembly (100) according to claim 1, wherein the first coupling means (34, 44) and the second coupling means (36, 46) are deactivatable coupling means.

3. Propulsion assembly (100) according to claim 2, in which the first and second deactivatable coupling means (34, 44, 36, 46) comprise a freewheel.

4. A propulsion assembly (100) according to any one of claims 1 to 3, wherein the main rotor (62) is coupled to the free turbine (11, 21) of the first engine (1) and the second engine (2) via a first and a second main coupling means (51, 52) respectively.

5. A propulsion assembly (100) according to claim 4, wherein the first and second coupling means (34, 44) of the first engine (1) are the only coupling means upstream of the first main coupling means (51), and the first and second coupling means (36, 46) of the second engine (2) are the only coupling means upstream of the second main coupling means (52).

6. Propulsion assembly (100) according to any one of claims 1 to 5, in which the second coupling means (36, 46) of the first and second motors (1, 2) comprises a locking means (38, 48) movable between a free position in which the free turbine (11, 21) cannot drive the second electric machine (32, 42) in rotation, and a locking position in which the free turbine (11, 21) is able to drive the second electric machine (32, 42) in rotation.

7. A propulsion assembly (100) according to any one of claims 1 to 6, wherein, when one of the first or second motors (1, 2) drives the main rotor (62) alone, the gas generator (12, 22) of the other of the first or second motors (1, 2) is maintained in a standby mode, by means of the first electrical machine (30, 40) or the second electrical machine (32, 42).

8. A propulsion assembly (100) according to claim 7, wherein, when the gas generator (12, 22) of one of the first or second engine (1, 2) is maintained in the standby mode via the first electric machine (30, 40), the second electric machine (32, 42) of the other of the first or second engine (1, 2) is configured to operate in the generator mode by rotating in the second direction of rotation, and to transmit the generated electric current to the first electric machine (30, 40) maintaining said first or second engine (1, 2) in the standby mode.

9. Propulsion assembly (100) according to claim 8, wherein the second electric machine (32, 42) operating in the generator mode is configured to also transmit the generated electric current to the first electric machine (30, 40) from that of the first or second motor (1, 2) driving the main rotor (62) alone.

10. A propulsion assembly (100) according to any one of claims 1 to 9, wherein the first electrical machine (32, 42) is coupled to the gas generator (12, 22) only, via a breakaway section (91, 92).

11. A propulsion assembly (100) according to any one of claims 1 to 10, comprising a control unit (80) configured to control the first and second electrical machines (30, 40, 32, 42) by selecting the engine mode to drive the gas generator (12, 22) and / or the main rotor (62), or the generator mode to transfer the electrical current generated by one of the first or second electrical machines (30, 40, 32, 42) to the other of the first or second electrical machines (30, 40, 32, 42).

12. Propulsion assembly (100) according to claim 11, wherein the control unit (80) is configured to, after detecting a loss of power of one of the first or second motor (1, 2) driving the main rotor (62) alone, control the first and second electrical machines (30, 40, 32, 42) of the other of the first or second motor (1, 2) operating in a standby mode, so that they operate in the motor mode, the second electrical machine (32, 42) rotating in the first direction of rotation, so as to rotate the gas generator (12, 22) of said first or second motor (1, 2) operating in the standby mode.

13. Hybrid aircraft comprising a propulsion unit (100) according to any one of the preceding claims, the hybrid aircraft being a multi-engine helicopter, in particular a twin-engine helicopter.

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