Improved propulsion assembly for multi-engine hybrid aircraft

Abstract

A propulsion assembly (100) for a hybrid aircraft is disclosed, comprising a first engine (1) and a second engine (2), each having a gas generator (12, 22) and a free turbine (11, 21), a main rotor (62) being coupled to the free turbines (12, 21) of the first and second engines (1, 2), the first engine (1) comprising a first electric machine (30) and a second electric machine (32) of lower power than the first electric machine, one of the first and second electric machines (30, 32) is coupleable to the gas generator (12) and rotates the gas generator during a start-up phase of the engine and is coupleable to the free turbine (11) to generate electrical energy after the start-up phase, the other of the first and second electric machines being coupled only to the gas generator (12).

Description

Technical Field

[0001] The present invention relates to the field of hybrid aircraft comprising at least two engines, such as turbine engines or turboprop engines, and for use in flying machines such as helicopters or twin-engine aircraft. In particular, the present invention relates to a propulsion assembly for a multi-engine hybrid aircraft, in particular a twin-engine aircraft, a hybrid aircraft comprising such a propulsion assembly and a method of using such a propulsion assembly. Background Art

[0002] In a known manner, a turbomachine, such as a turbomachine, in particular a turbomachine for a helicopter, comprises a gas turbine having a gas generator and a free turbine driven in rotation by the gas flow generated by the gas generator.

[0003] Traditionally, a gas generator comprises at least one compressor and one turbine coupled in rotation. The operating principle is as follows: the fresh air entering the gas turbine, after being compressed due to the rotation of the compressor, is conveyed to the combustion chamber, where it is mixed with fuel. The burnt gases due to the combustion are then discharged at high speed. A first expansion then takes place in the gas generator turbine, during which the gas generator turbine extracts the energy required to drive the compressor. The gas generator turbine does not absorb all the kinetic energy of the burnt gases, the excess kinetic energy corresponding to the airflow generated by the gas generator. The latter therefore provides kinetic energy to the free turbine, so that a second expansion takes place in the free turbine, which converts this kinetic energy into mechanical energy, thereby driving the receiving member, such as the rotor of a helicopter.

[0004] Some aircraft include two or more turbines, each including a gas turbine as described above. This is particularly true of twin-engine or multi-engine helicopters. Such aircraft allow operation in SEO (Single Engine Operation) mode. SEO mode is an operating mode of a twin-engine architecture in which one of the gas turbines is automatically stopped and the other ensures the entire power supply. This mode makes it possible to optimize the specific consumption, which decreases with the power supplied by the turbine. In fact, the specific consumption of the turbine decreases with the power supplied, so it is better to have one turbine supplying 100% of the power than to have each turbine supplying 50% of the power.

[0005] One of the key points of SEO mode is the ability to re-ignite the stopped turbine in the event of a loss of power to the running turbine. To ensure the fastest restart, the stopped turbine can be kept in standby (or super-idle) mode, i.e. continuing to run its gas generator using only the electric motor, without delivering fuel. The generator is then kept in its "ignition window" (usually 10-30% of the nominal speed of the gas generator) to allow immediate ignition of the fuel; or in "super-idle" mode, using combustion at a low speed threshold, assisted by mechanical power delivery via the electric motor, to benefit from a combustion chamber that is already ignited but with a controlled internal temperature.

[0006] Twin engine applications involve many functions, such as starting the gas generator, generating electricity on board, or providing mechanical power to the main rotor. Existing solutions for performing some of these functions are not entirely satisfactory. In particular, they do not provide the necessary redundancy for the function of starting an engine in standby mode, nor do they limit the impact of the power drawn from the engine when the helicopter is not operating in SEO mode. Therefore, there is a need for a twin or multi-engine aircraft propulsion assembly having an architecture that at least partially meets the above-mentioned disadvantages. Summary of the invention

[0007] The present disclosure relates to a propulsion assembly for a hybrid aircraft, in particular a multi-engine helicopter, comprising: - at least a first engine and a second engine, each having a gas generator and a free turbine driven in rotation by the gas flow generated by the gas generator; - a main rotor coupled to the free turbines of the first and second engines; -The first engine comprises a first electric machine and a second electric machine of lower power than the first electric machine, one of the first electric machine or the second electric machine being capable of being coupled to the gas generator and causing the gas generator to rotate during the starting phase of the engine and also being capable of being coupled to the free turbine in order to generate electrical energy after the starting phase, the other of the first electric machine or the second electric machine being coupled only to the gas generator.

[0008] The main rotor can be connected to the free turbines of the first engine and the second engine via the first main coupling device and the second main coupling device, respectively. In addition, the shaft of the free turbine of each of the first engine and the second engine can be directly engaged with the main rotor, or engaged via a mechanical reduction gear.

[0009] It should be understood that according to the present disclosure, the first engine is equipped with at least a first motor and a second motor. In some embodiments, the second engine includes a third motor, which is preferably less powerful than the first motor and can drive the gas generator of the second engine during the starting phase and can be driven by the gas generator after the starting phase to generate electrical energy.

[0010] Alternatively, the second engine may be equipped with the first motor and the second motor, and then the first engine may be equipped with the third motor, or each of the first engine and the second engine may be symmetrically equipped with two motors.

[0011] While one of the first or second electric machine can be coupled to the gas generator and / or the free turbine, depending on the operating phase and architecture of the engine, the other electric machine is coupled only to the gas generator. The first electric machine is further dimensioned to be able to provide a higher power than the second electric machine, in particular during the rapid start phase. Thus, the power of the first electric machine is very high, of the order of one kilowatt or several hundred kilowatts, while the power of the second electric machine (and the third electric machine of the second engine, if appropriate) is very low, of the order of 10 kilowatts, such as is commonly used in generators / starters for aircraft engines.

[0012] According to this configuration, at least after the start-up phase of the turbine engine, one of the first or second electric machines can be connected to the free turbine to generate electrical energy. In other words, in flight, the free turbine advantageously drives the first or second electric machine in rotation, operating as a generator, thereby advantageously extracting the kinetic energy to be converted into electrical energy from the free turbine rather than from the gas generator. This makes it possible to provide electrical power while limiting the impact on the efficiency of the engine. In this way, the turbine engine according to the invention advantageously makes it possible to provide electrical power without having too much impact on its efficiency.

[0013] It should be noted that in flight, when the first or second electric machine driven by the free turbine of the first engine is generating electricity, a third electric machine driven by the gas generator of the second engine may be redundant or provide additional power where appropriate.

[0014] Furthermore, when operating in SEO mode, the first motor or the second motor of the first engine operating in standby mode can be used to keep the gas generator of this engine rotating at a low speed, while the second engine alone drives the main rotor. The first high-power motor can also be used to quickly restart the engine in standby mode, especially in emergency situations. It is also possible to use both motors simultaneously to increase the power injected into the gas generator during the fast restart phase, thereby reducing the restart time. Furthermore, the first motor or the second motor can be used independently to allow for a normal restart, thereby allowing redundancy.

[0015] Thus, the multi-engine architecture according to the present disclosure has the advantage of simplicity by limiting the number of components and connections. Specifically, it improves the reliability of the engine start-up in standby mode as part of the SEO mode and optimizes the engine performance by extracting via one of the motors on the free turbine after the start-up phase of conventional twin-engine operation. Thus, it is possible to rationalize and optimize the number of motors and the architecture of the propulsion assembly, while allowing the execution of a large number of functions and reducing the mass of the equipment.

[0016] In some embodiments, the first electric machine is coupled to the shaft of the gas generator via a first deactivatable coupling device, the first deactivatable coupling device being configured to be activated during a startup phase and to be deactivated after the startup phase.

[0017] "Deactivatable connecting device" means that the connecting device can be in a starting position or a deactivation position. In the starting position, the components connected to the connecting device are connected, and in the deactivation position, the components are disconnected. It can be understood that "components" refer to the motor, the main rotor and the gas generator.

[0018] According to the invention, the first electric machine is preferably reversible and operates as a motor when the first coupling device is activated in order to drive the gas generator in rotation during the start-up phase of the engine. Correspondingly, after the start-up phase of the engine, that is to say substantially in flight, the first reversible electric machine operates as a generator to generate electricity by extracting kinetic energy from the free turbine. During the post-startup phase of the engine, the first coupling device is deactivated so that the gas generator cannot drive the first electric machine.

[0019] It should be understood that according to this embodiment, the second motor is only coupled to the gas generator. However, it should be noted that a configuration in which the second motor and the first motor are interchanged is also possible.

[0020] In some embodiments, the first electric machine is coupled to the shaft of the free turbine by direct engagement with the shaft of the free turbine.

[0021] By “directly coupled” it is understood that the first electric machine is coupled to the shaft of the free turbine via a simple shaft or possibly by means of a pinion, but no deactivatable coupling device (eg a freewheel) is provided between the first electric machine and the free turbine shaft.

[0022] In other words, when the first electric machine is coupled to the shaft of the gas generator by means of a deactivatable coupling device that can be deactivated in particular after the starting phase, the first electric machine is coupled to the shaft of the free turbine by direct engagement with the shaft of the free turbine, so that the electric machine also drives the free turbine during the starting phase of the engine and is always associated with it. This architecture makes it possible to reduce the overall mass of the propulsion assembly.

[0023] In some embodiments, the first electric machine is coupled to the shaft of the free turbine via a second deactivatable coupling device, the first deactivatable coupling device and the second deactivatable coupling device being configured not to be activated simultaneously.

[0024] When the second coupling device is activated, the first coupling device is deactivated, i.e. the first electric machine is coupled to the free turbine while being disconnected from the gas generator, and conversely, when the first coupling device is activated, the second coupling device is deactivated, i.e. the first reversible electric machine is coupled to the gas generator while being disconnected from the free turbine. Without departing from the framework of the invention, an intermediate position can also be provided in which the first coupling device and the second coupling device are simultaneously deactivated.

[0025] When the first coupling device is activated, the first electric machine operates as a motor in order to drive the gas generator in rotation during the engine starting phase. Correspondingly, after the engine starting phase, that is to say substantially in flight, the first reversible electric machine operates as a generator when the second coupling device is activated in order to generate electricity by extracting kinetic energy from the free turbine. In other words, the first electric machine is coupled to the free turbine only after the starting phase.

[0026] Since the first coupling device and the second coupling device cannot be started at the same time, an undesirable situation in which the free turbine drives the gas generator to rotate is avoided.

[0027] In some embodiments, the first deactivatable coupling device comprises a first freewheel, the second deactivatable coupling device comprises a second freewheel, and the first freewheel and the second freewheel are mounted opposite each other.

[0028] One advantage of a freewheel is that it does not require electronic or mechanical control by an external operator. Such a freewheel usually consists of a hub and a peripheral ring gear rotatably mounted on the hub. The hub can drive the peripheral ring gear in rotation, but not vice versa. Furthermore, the hub can only drive the ring gear when the hub rotates in a predetermined direction, which will be referred to as the "engagement direction". Otherwise, the hub and the peripheral ring gear rotate freely relative to each other. In this case, the deactivatable coupling device is activated when the hub of the freewheel drives the peripheral ring gear in rotation, and conversely, the deactivatable coupling device is deactivated when the hub of the freewheel does not drive the peripheral ring gear in rotation.

[0029] “Oppositely mounted” means that the first freewheel can transmit rotational torque from the first electric machine, and the second freewheel can transmit rotational torque to the first electric machine.

[0030] In some embodiments, the first deactivatable coupling device includes a first reduction gear having a first reduction coefficient, and the second deactivatable coupling device includes a second reduction gear having a second reduction coefficient, and the ratio of the first reduction coefficient to the second reduction coefficient is less than a limit value.

[0031] "Reduction gear" refers to one or more reduction stages, including, for example, a gear train. Such reduction gears are known elsewhere. Since the gas generator and the free turbine usually rotate much faster than the first electric machine, the reduction gear enables the rotational speed of the electric machine to be adapted to the speed of the gas generator and the free turbine.

[0032] Preferably, the limit value is selected such that the first freewheel and the second freewheel do not engage simultaneously. Preferably, the limit value is proportional to the ratio of the nominal speed of the gas generator to the nominal speed of the free turbine.

[0033] In some embodiments, when the second engine drives the main rotor alone, the gas generator of the first engine is maintained in a standby mode by the first motor or the second motor.

[0034] When the aircraft is operating in SEO mode, the second engine can, for example, ensure the entire power supply, while the first engine stops autonomously or preferably enters standby mode in order to optimize specific consumption. Standby mode makes it possible to keep the gas generator of the first engine within a range of 5% to 30% of its nominal speed in order to quickly re-ignite it if necessary, especially in the event of a non-autonomous stop of the second engine.

[0035] It should be noted that when the first electric machine is directly coupled to the shaft of the free turbine and is used to keep the gas generator of the first engine in standby mode, it inevitably also drives the free turbine. This configuration is possible because the free turbine of the first engine rotates at a lower speed than the main rotor, and the first main coupling device is then deactivated.

[0036] In some embodiments, the second electric machine is coupled only to the gas generator via a freewheel.

[0037] Thus, the second motor can drive the gas generator during the start-up phase, but conversely, the gas generator cannot drive the second motor. The latter therefore remains stationary when not in use. According to this configuration, only the first motor is therefore able to generate electrical energy.

[0038] The present disclosure also relates to a hybrid aircraft, comprising a propulsion assembly according to any one of the aforementioned embodiments, the hybrid aircraft being a multi-engine, in particular a twin-engine helicopter.

[0039] A "hybrid aircraft" is an aircraft comprising a heat engine for driving a main rotor in rotation and at least one electric machine for powering the heat engine.

[0040] The present disclosure also relates to a method for optimizing the operation of a multi-engine aircraft using a propulsion assembly according to any of the preceding embodiments, wherein, during a starting phase of the first engine, the first electric motor and / or the second electric motor drives a gas generator of the first engine, and after the starting phase, the free turbine of the first engine drives one of the first electric motor or the second electric motor to generate electrical energy.

[0041] In some embodiments, the second engine can be operated alone, and then the first engine is operated in the standby mode by being idling driven by the first motor or the second motor, and the first engine operated in the standby mode is restarted by the first motor at least in the fast restart stage.

[0042] The power of the first motor is about tens to hundreds of kilowatts, and the use of the first motor can start the gas generator more quickly at least in the fast restart phase.

[0043] In some embodiments, during a starting phase of the first engine, when the first electric machine is connected to the shaft of the free turbine via a second deactivatable coupling device including a second free wheel, the first electric machine and / or the second electric machine drives the gas generator of the first engine without driving the free turbine.

[0044] In a normal ground starting configuration or when exiting SEO mode, due to the presence of the second deactivatable coupling means, neither the first nor the second electric machine can drive the shaft of the free turbine. Therefore, it is possible to use either or both electric machines in SEO mode to keep the gas generator of the first engine in standby mode without driving the free turbine. Likewise, during a normal ground start or a normal restart in flight, i.e. in non-emergency situations, either electric machine (or both) can be used without driving the free turbine.

[0045] In some embodiments, the second engine is capable of operating alone, and when the first electric motor is connected to the shaft by direct engagement with the shaft of the free turbine of the first engine, the first engine operating in standby mode is then driven at idle by the second electric motor connected only to the gas generator, or the first electric motor, and the main rotor is connected to the free turbine of the first engine via the main coupling device, and the main rotor is driven by the second engine to rotate at a speed higher than the shaft of the free turbine of the first engine, so that the main coupling device is deactivated.

[0046] In this operating configuration in SEO mode, since there is no deactivatable coupling device between the first electric machine and the free turbine, the first electric machine is permanently linked to the free turbine, so that when it is used to keep the first engine in standby mode at idle speed, it also drives the shaft of the free turbine. This configuration is possible because the free turbine of the first engine rotates at a lower speed than the main rotor, and the main coupling device is then deactivated. In addition, the driving of the gas generator at idle speed by the first electric machine, thus driving the free turbine and the gas generator simultaneously, makes it possible to reconnect the shaft of the free turbine to the main rotor more quickly in the event of a rapid start-up.

[0047] Alternatively, the second electric machine coupled to the gas generator may be used only to idle-drive the gas generator of the first engine without driving the free turbine.

[0048] Furthermore, in this case, during the rapid restart phase, at least the first engine operating in the standby mode can be restarted by the first electric machine.

[0049] In some embodiments, when the first electric motor is connected to the shaft by direct engagement with the shaft of the free turbine of the first engine, the first engine is started only by one of the first electric motor or the second electric motor connected to the gas generator when the second engine is stopped, or by the first electric motor and / or the second electric motor when the second engine has been started in advance.

[0050] In the case of a first ground start, the main rotor is stopped and the first electric motor, directly coupled to the free turbine shaft, cannot be used to drive the gas generator and start the first engine, the inertia and drag torque of the main rotor are indeed too great. Therefore, the second electric motor, which is only coupled to the gas generator, is used to start the first engine. On the other hand, when the second engine has been previously started and then drives the main rotor, the first electric motor can be used to start the gas generator of the first engine and drive the free turbine at the same time. The first engine is then started in a turbine called the coupled turbine. Given this architecture and the presence of two electric motors, it is possible to optimize the operation of a multi-engine aircraft and its start-up according to the scenario. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The invention and its advantages will be better understood by reading the following detailed description of different embodiments of the invention given as non-limiting examples. This description refers to the accompanying drawings, in which:

[0052] [ Figure 1 ] Figure 1 A cross-sectional view showing a propulsion assembly for a twin-engine aircraft according to a first embodiment of the present invention;

[0053] [ Figure 2 ] Figure 2 Shows Figure 1 Functional schematic diagram of the propulsion assembly;

[0054] [ Figure 3 ] Figure 3 A cross-sectional view showing a propulsion assembly for a twin-engine aircraft according to a second embodiment of the present invention;

[0055] [ Figure 4 ] Figure 4 Shows Figure 3 Functional schematic of the propulsion components. DETAILED DESCRIPTION

[0056] In the remainder of this specification, reference will be made to Figure 1 and Figure 2 A configuration of a propulsion assembly 100 according to a first embodiment of the present invention is described.

[0057] In general, for the sake of clarity, the drawings schematically illustrate the architecture of the device in a functional and simplified manner, without representing all the details of the elements constituting the turbine and the various power transmission members. In particular, the pinion P allowing the shafts 13, 14 to be driven by the motor, and vice versa where appropriate, is schematically shown, and without showing any speed ratios.

[0058] Figure 1 A propulsion assembly 100 of a twin-engine aircraft is schematically shown, comprising a first engine, in this example a first turbine 1, and a second engine, in this example a second turbine 2, which drives a transmission member 60 of a helicopter carrying a propeller or main rotor 62 for rotation. The turbine may be a turbine engine or a turboprop engine. Although the propulsion assembly described in the remainder of this specification comprises two turbines, this example is not restrictive, and the invention also applies to propulsion assemblies of multi-engine aircraft comprising more than two engines.

[0059] The first turbine 1 and the second turbine 2 are largely identical and have common features. In addition, the following description relates to common features of the first turbine 1 and the second turbine 2 .

[0060] The first turbine 1 and the second turbine 2 each comprise a gas turbine 10, 20 having a gas generator 12, 22 and a free turbine 11, 21 which can be driven in rotation by the 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 movement via a transmission member 60 to a receiving member, such as a main rotor 62 of a helicopter. According to this example, Figure 1The gas turbines 10, 20 shown in the figure are of the front power take-off type, with a transmission through a coaxial shaft. Without departing from the framework of the invention, it is quite possible to consider a gas turbine with a free turbine of the front power take-off type, which is transmitted through an inner shaft or an outer shaft, or a gas turbine with a free turbine of the rear power take-off type. Likewise, the turbines can be directly coupled or integrated with the reduction gears 51, 52, without questioning the principle of the invention.

[0061] The gas generator 12, 22 comprises a rotating shaft 14, 24, on which a compressor 15, 25 and a turbine 16, 26 are mounted, and a combustion chamber 17, 27, with the combustion chamber 17, 27 being axially arranged between the compressor 15, 25 and the turbine 16, 26, as long as the gas generator 12, 22 is considered to be in the axial direction of the rotating shaft 14, 24. The gas turbine 10, 20 has a housing 18, 28 provided with an air inlet 19, 29, through which fresh air enters the gas generator 12, 22. After being introduced into the enclosure of the gas generator 12, 22, the fresh air is compressed by the compressor 15, 25, and then pushed back to the air inlet of the combustion chamber 17, 27, where it is mixed with the fuel. The combustion that takes place in the combustion chamber 17, 27 causes the burnt gases to be discharged at high speed towards the turbine 16, 26, which has the effect of driving the shaft 14, 24 of the gas generator 12, 22 in rotation and thus the compressor 16, 26. The rotation speed of the shaft 14, 24 of the gas generator 12, 22 is determined by the fuel flow entering the combustion chamber 17, 27.

[0062] Although the turbines 16, 26 extract kinetic energy, the gas stream leaving the gas generator still has significant kinetic energy. Figure 1 As can be appreciated, the air flow F is directed towards the free turbine 11 , 21 , which has the effect of causing the free turbine 11 , 21 to expand, thereby causing the turbine and shaft 13 , 23 to rotate.

[0063] The main rotor 62 is coupled to the shaft 13 of the free turbine 11 of the first gas turbine 10 via the transmission member 60 by means of a first main coupling device 510 disposed between the reduction gear 51 and the transmission member 60. The main rotor 62 is also coupled to the shaft 23 of the free turbine 21 of the second gas turbine 20 via the transmission member 60 by means of a second main coupling device 520 disposed between the reduction gear 52 and the transmission member 60.

[0064] Preferably, the first main coupling device 510 and the second main coupling device 520 include freewheels, which are installed so that the rotation of the shaft 13, 23 can drive the main rotor 62 to rotate, but conversely, the rotation of the main rotor 62 cannot drive the shaft 13, 22 of the free turbine 11, 21 to rotate. In other words, the freewheels of the first main coupling device 510 and the second main coupling device 520 can only transmit the rotational torque to the main rotor 62 in the direction of the free turbine 11, 21, but not vice versa. On helicopters, such freewheels are usually called "engine freewheels". It should be noted that the use of freewheels in the main coupling devices 510, 520 is not restrictive, and the freewheels can be replaced by any dog ​​gear or clutch system.

[0065] The turbomachine 1 also comprises a first electrical machine 30 , preferably reversible and comprising an electric motor capable of reversibly operating as a generator. The first electrical machine 30 is mechanically coupled to the shaft 14 of the gas generator 12 by means of first deactivatable coupling means 310 .

[0066] The first deactivatable coupling device 310 comprises a first freewheel 312 and, preferably, also comprises a first speed adaptation reduction gear 314 arranged between the gas generator 12 and the first freewheel 312 .

[0067] The first freewheel 312 is mounted so that the rotation of the first electric machine 30 operating in motor mode can drive the gas generator 12 in rotation, but conversely, the rotation of the gas generator 12 cannot drive the first electric machine 30. In other words, the freewheel 312 of the first deactivatable coupling device 310 can only transmit a rotational torque in the direction of the first electric machine 30 towards the gas generator 12.

[0068] The first electrical machine 30 is further mechanically coupled to the shaft 13 of the free turbine 11 by means of a second deactivatable coupling device 320 .

[0069] The second deactivatable coupling device 320 comprises a second free wheel 322 , and preferably, further comprises a second speed adaptation reduction gear 324 arranged between the free turbine 11 and the second free wheel 322 .

[0070] The second freewheel 322 is installed so that the rotation of the free turbine 11 can drive the first electric machine 30 to rotate and then operate in generator mode, but conversely, the rotation of the first electric machine 30 cannot drive the free turbine 11. In other words, the freewheel 322 of the second deactivatable coupling device 320 can only transmit rotational torque in the direction of the free turbine 11 toward the first electric machine 30.

[0071] The first freewheel 312 and the second freewheel 322 are installed opposite to each other. In this case, their engagement directions are opposite. Therefore, when the first reversible electric machine 30 operates in motor mode to drive the shaft 14 of the gas generator 12 to rotate (the first freewheel 312 is engaged, that is, the first coupling device 310 is started), the second freewheel 322 does not transmit the rotational torque of the first electric machine 30 to the shaft 13 of the free turbine 11 (the second coupling device 320 is deactivated). On the contrary, when the shaft 13 of the free turbine 11 drives the first electric machine 30 operating in generator mode to rotate (the second freewheel 322 is engaged, that is, the second coupling device 320 is started), the first freewheel 312 does not transmit the rotational torque of the first electric machine 30 to the shaft 14 of the gas generator 12 (the first coupling device 310 is deactivated).

[0072] The first speed adaptation reduction gear 314 has a first reduction coefficient K1, which is preferably selected so that the speed of the first motor 30 is adapted to the speed range required to start the gas generator 12. The second speed adaptation reduction gear 324 has a second reduction coefficient K2, which is preferably selected so that the speed of the first motor 30 is adapted to the speed range required to allow power supply.

[0073] In order to prevent the free turbine 11 from driving the shaft 14 of the gas generator 12 to rotate, the first free wheel 312 must not be engaged. To this end, the reduction coefficients K1, K2 of the first reduction gear 314 and the second reduction gear 324 are appropriately selected. For example, but not necessarily, the reduction coefficients K1, K2 follow the ratios described in document FR2929324.

[0074] The turbomachine 1 also comprises a second electric machine 32 mechanically coupled only to the shaft 14 of the gas generator 12 , preferably via a third freewheel 33 , allowing the second electric machine not to be driven by the gas generator when not in use.

[0075] In this example, although the first motor 30 is a high-power motor, particularly a motor of several hundred kilowatts, the second motor 32 may be a commonly used starter with a power of about 10 kilowatts. However, it should be noted that this configuration is not restrictive, and the first motor and the second motor can be interchanged without departing from the framework of the present invention.

[0076] Furthermore, the turbine 2 may be equipped with a third electric machine 40, which preferably also has a lower power than the first electric machine 30, for example a starter equivalent to the second electric machine 32. The third electric machine 40 is coupled only to the gas generator 22 and is able to drive the gas generator 22 during the startup phase and to be driven by the gas generator 22 after the startup phase to generate electrical energy.

[0077] This architecture of the propulsion assembly 100 allows for different operating modes described in the remainder of this specification and makes it possible to optimize the operation of the propulsion assembly 100 .

[0078] The presence of two turbines 1, 2 allows operation in SEO (Single Engine Operation) mode, in which only the second turbine 2 is in operation, ensuring full power supply to the main rotor 62, the first turbine 1 being autonomously stopped. When SEO mode is engaged, the gas generator 12 is in standby state (or auxiliary over-idle), i.e. it no longer provides power. On the other hand, in order to start as quickly as possible, the gas generator 12 is driven by the first electric machine 30 or the second electric machine 32 within the ignition window (in the range of 5% to 30% of its nominal speed).

[0079] By optimizing the operation of the aircraft, it is possible to restart the first turbine 1 within the framework of a normal restart, that is, in a non-emergency situation requiring a quick restart. This optimization method firstly consists in driving the gas generator 12 by means of the first electric machine 30 and / or the second electric machine 32 during the start-up phase of the first turbine 1, without driving the free turbine 11. In fact, the first electric machine 30 cannot drive the free turbine 11 in rotation, given the presence of the second free wheel 322 mounted opposite the first free wheel 312. Moreover, the second electric machine 32 is only coupled to the gas generator 12 and therefore cannot drive the free turbine 11.

[0080] The first motor 30 and the second motor 32 may be piloted by a monitoring unit (not shown). Thus, the first motor 30 and / or the second motor 32 drive the gas generator 12 via the freewheels 312, 33, respectively, thereby allowing the gas generator 12 to start. When the gas generator 12 starts, the hot gas drives the free turbine 11, which is connected to the main rotor 62 via the first freewheel 312, the reduction gear 51, and the freewheel of the first main coupling device 510.

[0081] In a second step, after the start-up phase, the free turbine 11 drives the first motor 30 via the second free wheel 322 to generate electrical energy. The first motor 30 can be electrically connected to the power grid of the propulsion assembly 100 in order to power different electrical devices (not shown). It should be noted that the above steps also apply to a normal start-up of the turbine 1 in non-emergency situations (not restarting from SEO mode).

[0082] Furthermore, after the start-up phase, when both gas generators 12 , 22 are operating (eg after the turbine 1 is re-ignited to exit the SEO mode), the third electric machine 40 may generate redundant electrical energy together with the first electric machine 30 .

[0083] It should be noted that Figure 2In the example shown, the second electric machine 32 cannot be driven to operate in generator mode due to the presence of the third freewheel 33, so that only the first electric machine 30 can generate electrical energy. However, in the absence of the third freewheel 33, the first electric machine 30 and the second electric machine 32 can each generate electrical energy for each other without departing from the framework of the present invention.

[0084] Furthermore, it is possible to quickly restart the first turbine 1 in standby mode. This rapid restart is identical to the start-up or restart procedure described above, but in this case the first high-power electric machine 30 must be used alone, or possibly supplemented by the second electric machine 32, in order to optimize the restart time. In fact, the power of the first electric machine 30 is of the order of tens to hundreds of kilowatts, which allows starting the gas generator 12 more quickly than the starters of the order of 10 kW that are usually used. This provides an operational advantage in particular in the case of medical rescue missions or during attempts at a rapid restart in flight.

[0085] In the remainder of this specification, reference will be made to Figure 3 and Figure 4 A configuration of a propulsion assembly 100 ′ according to a second embodiment of the present invention is described.

[0086] The features of the propulsion assembly 100' according to the second embodiment are substantially the same as those of the propulsion assembly 100 according to the first embodiment, and therefore will not be repeated. The operating mode described above with reference to the first embodiment also applies to the second embodiment.

[0087] However, the propulsion assembly 100 ′ according to the second embodiment differs from the propulsion assembly 100 according to the first embodiment in that it does not comprise a second deactivatable coupling device. In other words, the first electric machine 30 is directly engaged with the shaft 13 of the free turbine 11 and is therefore permanently coupled to the shaft 13 of the free turbine 11, including during the start-up phase.

[0088] In view of this architecture, during operation in SEO mode, the gas generator 12 of the turbine 1 can be kept at idle speed by the second electric machine 32, thereby not driving the free turbine 11, or kept at idle speed by the first electric machine 30. In the second case, the shaft 13 of the free turbine 11 is also driven. However, the main rotor 62 is driven by the turbine 2 and rotates at a higher speed than the shaft 13 of the free turbine 11, so that the main coupling device, in particular the free wheel 510, is deactivated.

[0089] Similarly, during the first ground start, if the turbine 2 has been previously ignited and is already driving the main rotor 62, the gas generator 12 can be started by using the first motor 30. On the other hand, if the turbine 2 has not yet been started, the gas generator 12 of the turbine 1 is started by using the second motor 32 coupled only to the gas generator 12.

[0090] Although the present invention has been described with reference to specific exemplary embodiments, it is apparent that these examples can be modified and altered without departing from the overall scope of the present invention as defined in the claims. Specifically, the various features of the various embodiments illustrated / mentioned can be combined into other embodiments. Therefore, this specification and the drawings should be considered in an illustrative rather than a restrictive sense.

[0091] It is also self-evident that all features described with reference to a method can be converted, individually or in combination, into a device and conversely, all features described with reference to a device can be converted, individually or in combination, into a method.

Claims

1. A propulsion assembly (100) for a 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 the gas flow generated by the gas generator; - a main rotor (62) coupled to the free turbines (11, 21) of the first and second engines (1, 2); - the first engine (1) comprises a first electric machine (30) and a second electric machine (32) of lower power than the first electric machine (20), one of the first or second electric machines (30, 32) being capable of being coupled to the gas generator (12) and setting the gas generator in rotation during a start-up phase of the engine and also being capable of being coupled to the free turbine (11) in order to generate electrical energy after the start-up phase, the other of the first or second electric machines being coupled only to the gas generator (12).

2. The propulsion assembly (100) according to claim 1, characterized in that The first electric machine (30) is coupled to the shaft (14) of the gas generator (12) via a first deactivatable coupling device (310), the first deactivatable coupling device (310) being configured to be activated during a start-up phase and to be deactivated after the start-up phase.

3. The propulsion assembly (100) according to claim 2, characterized in that The first electric machine (30) is coupled to the shaft (13) of the free turbine (11) by direct engagement with the shaft.

4. The propulsion assembly (100) according to claim 2, characterized in that The first electric machine (30) is coupled to the shaft (13) of the free turbine (11) via a second deactivatable coupling device (320), the first and second deactivatable coupling devices being configured not to be activated simultaneously.

5. The propulsion assembly (100) according to claim 4, characterized in that The first deactivatable coupling device (310) includes a first free wheel (312), the second deactivatable coupling device (320) includes a second free wheel (322), and the first free wheel and the second free wheel are installed opposite to each other.

6. The propulsion assembly (100) according to claim 4 or 5, characterized in that: The first deactivatable connecting device (310) includes a first reduction gear (314) having a first reduction coefficient (K1), and the second deactivatable connecting device (320) includes a second reduction gear (324) having a second reduction coefficient (K2), and the ratio of the first reduction coefficient to the second reduction coefficient (K1, K2) is less than a limit value.

7. The propulsion assembly (100) according to any one of claims 1 to 6, characterized in that: When the second engine (2) drives the main rotor (62) alone, the gas generator (12) of the first engine (1) is maintained in a standby mode via the first motor or the second motor (30, 32).

8. The propulsion assembly (100) according to any one of claims 1 to 7, characterized in that: The second electric machine (32) is coupled exclusively to the gas generator (12) via a freewheel (33).

9. The propulsion assembly (100) according to any one of claims 1 to 8, characterized in that: The second engine (2) comprises a third electric machine (40) which is capable of driving the gas generator (22) of the second engine (2) during a starting phase and is capable of being driven by the gas generator (22) after the starting phase to generate electrical energy.

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

11. A method for optimizing the operation of a multi-engine aircraft using a propulsion assembly (100) according to any one of claims 1 to 9, wherein: During a starting phase of the first engine (1), the first motor (30) and / or the second motor (32) drives the gas generator (12) of the first engine (1), and after the starting phase, the free turbine (11) of the first engine (1) drives one of the first motor (30) or the second motor (32) to generate electrical energy.

12. The method according to claim 11, characterized in that The second engine (2) is capable of operating independently, and then the first engine (1) is operated in a standby mode by being driven at idle speed by the first motor or the second motor (30, 32), and the first engine (1) operating in the standby mode is restarted by the first motor (30) at least in a fast restart phase.

13. The method according to claim 11, characterized in that During the starting phase of the first engine (1), when the first motor (30) is connected to the shaft (13) of the free turbine (11) via a second deactivatable connecting device (320) including the second free wheel (322), the first motor (30) and / or the second motor (32) drives the gas generator (12) of the first engine (1) without driving the free turbine (11).

14. The method according to claim 11, characterized in that The second engine (2) is capable of operating alone, wherein, when the first motor (30) is coupled to the shaft (13) of the free turbine (11) of the first engine (1) by direct engagement with the shaft (13), the first engine (1) operating in standby mode is then driven at idle speed by the second motor (30, 32) coupled only to the gas generator (12), or the first motor (30), the main rotor (62) is coupled to the free turbine (11) of the first engine (1) via a main coupling device (510), the main rotor (13) is driven by the second engine (2) to rotate at a speed higher than the shaft (13) of the free turbine (11) of the first engine (1), so that the main coupling device (510) is deactivated.

15. The method according to claim 11, characterized in that When the first motor (30) is coupled to the shaft (13) of the free turbine (11) of the first engine (1) by direct engagement therewith, the first engine (1) is started only by one of the first motor or the second motor (30, 32) coupled to the gas generator (12) when the second engine (2) is stopped, or by the first motor and / or the second motor (30, 32) when the second engine (2) has been started in advance.

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