HYBRID PROPULSION SYSTEM FOR AN AIRCRAFT

Abstract

Hybrid propulsion system (2) comprising: - a turboshaft engine (3) comprising a high-pressure casing (4) and a low-pressure casing (5), the low-pressure casing (5) comprising a reduction gear (11), the reduction gear (11) being part of a transmission housing (12) which is axially disposed at a forward end (13) of the propulsion system (2); - first and second electric machines (14, 15) mechanically connected respectively to the high-pressure and low-pressure casings (4, 5), the electric machines (14, 15) being configured to operate in so-called engine and generator modes, the first and second electric machines (14, 15) being fixed to the transmission housing (12); - a control system (16) which is configured to allow power transfer between the high-pressure and low-pressure casings (4, 5) via the first and second electric machines (14, 15). Figure for the abstract: 1

Description

Title of the invention: HYBRID PROPULSION SYSTEM FOR AN AIRCRAFT Technical field of the invention

[0001] The present invention relates to a hybrid propulsion system for an aircraft. Technical background

[0002] Hybrid electric propulsion of an aircraft is one of the solutions to significantly reduce the carbon footprint of air transport.

[0003] Such propulsion combines, for example, a thermal turbomachine and one or more electric machines capable of replacing or supplementing the turbomachine.

[0004] The combination of thermal and electrical energy makes it possible to significantly reduce the fuel consumption of the turbomachine, and consequently its carbon dioxide emissions.

[0005] Application FR-B1-3062882 in the name of the applicant describes a hybrid propulsion system for a helicopter comprising a main turbine engine and an electric machine which is used in an emergency situation (for example during a breakdown of the main turbine engine), in order to temporarily provide power to the helicopter for certain maneuvers.

[0006] Such a propulsion system can be improved, with engine manufacturers studying the different possibilities for best integrating one or more electric machines, in particular so as to optimize the overall size of the propulsion system, minimize modifications, and facilitate maintenance of the electric machine(s).

[0007] The objective of the present invention is therefore to propose a simple, effective and economical solution making it possible to respond to the aforementioned problems. Summary of the invention

[0008] The invention thus proposes a hybrid propulsion system for an aircraft comprising: - a turbine engine comprising a high pressure body and a low pressure body which are mobile in rotation, the high pressure body comprising a compressor and an expansion turbine mechanically connected to each other by a high pressure shaft, the low pressure body comprising a power turbine which rotates a power take-off via a reduction gear, the reduction gear forming part of a transmission housing which is arranged axially at a front end of the propulsion system; - first and second electrical machines mechanically connected respectively to the high pressure and low pressure bodies, the electrical machines being configured to operate in so-called motor and generator modes, the first and second electrical machines being fixed to the transmission housing; - a control system which is configured to enable power transfer between the high pressure and low pressure bodies via the first and second electrical machines.

[0009] Such positioning of the electrical machines not only makes it possible to optimize the overall size of the propulsion system, but also to minimize the modifications caused by the integration of the electrical machines, and finally to facilitate maintenance operations, the electrical machines being accessible and arranged in a clear environment.

[0010] The transmission box ensures, for each electrical machine, the transmission of the rotational movement between the body and the electrical machine while offering the possibility of modifying the parameters associated with the movement (speed, torque, etc.), so as to operate the body and the electrical machine in the desired operating ranges.

[0011] The transfer of power between the high pressure and low pressure bodies via the electrical machines makes it possible to optimize the performance of the propulsion system over all of its operating regimes.

[0012] The propulsion system according to the invention may comprise one or more of the following characteristics and / or steps, taken in isolation from one another or in combination with one another: - the first and second electrical machines are fixed on a front face of the transmission box; - the first electrical machine is connected to the high pressure body via a first transmission mechanism arranged in the transmission housing, the first transmission mechanism preferably being a gear mechanism; - the second electrical machine is connected to the low pressure body via a second transmission mechanism arranged in the transmission housing, the second transmission mechanism preferably being a gear mechanism; - the power turbine and the reducer are mechanically connected to each other by a low pressure shaft, the low pressure and high pressure shafts being coaxial, the low pressure shaft passing internally through the high pressure shaft; - the power take-off is capable of driving a main transmission box of the aircraft; - the first and second electrical machines are high-voltage electrical machines which are connected to a high-voltage electrical network of the control system; - the first electric machine is configured to start the turboshaft engine; - the propulsion system is configured to operate in one of the following operating modes: - a first hybrid operating mode in which the first electrical machine operates in generator mode and the second electrical machine operates in motor mode, the electrical energy produced by the first electrical machine being used to electrically power the second electrical machine, so as to transfer power from the high pressure body to the low pressure body; - a second hybrid operating mode in which the first electric machine operates in motor mode and the second electric machine operates in generator mode, the electrical energy produced by the second electric machine being used to electrically power the first electric machine, so as to transfer power from the low pressure body to the high pressure body.

[0013] The present invention also relates to an aircraft comprising a hybrid propulsion system as described above. Brief description of the figures

[0014] The invention will be better understood and other details, characteristics and advantages of the invention will appear more clearly on reading the following description given by way of non-limiting example and with reference to the appended drawings in which:

[0015] [Fig-1] [Fig.l] is a schematic view of an aircraft comprising a system hybrid propulsion according to the invention;

[0016] [Fig.2] [Fig.2] is a detailed front and perspective view of the propulsion system illustrated in [Fig.l]; Detailed description of the invention

[0017] In [Fig.l] a helicopter 1 is schematically represented comprising a hybrid propulsion system 2.

[0018] The illustrated example is in no way limiting, the hybrid propulsion system 2 could be used to power, for example, an airplane, a drone or any other rotorcraft such as a gyrodyne.

[0019] According to the invention, the hybrid propulsion system 2 comprises: - a turboshaft engine 3 comprising a high-pressure body 4 and a low-pressure body 5 which are movable in rotation, the high-pressure body 4 comprising a compressor 6 and an expansion turbine 7 mechanically connected to each other by a high-pressure shaft 8, the low-pressure body 5 comprising a power turbine 9 which rotates a power take-off 10 via a reduction gear 11, the reduction gear 11 being part of a transmission housing 12 which is arranged axially at a front end 13 of the propulsion system 2; - first and second electrical machines 14, 15 mechanically connected respectively to the high pressure and low pressure bodies 4, 5, the electrical machines 14, 15 being configured to operate in so-called motor and generator modes, the first and second electrical machines 14, 15 being fixed on the transmission box 12; - a control system 16 which is configured to allow a transfer of power between the high pressure and low pressure bodies 4, 5 via the first and second electrical machines 14, 15.

[0020] Such positioning of the electrical machines not only makes it possible to optimize the overall size of the propulsion system, but also to minimize the modifications caused by the integration of the electrical machines, and finally to facilitate maintenance operations, the electrical machines being accessible and arranged in an unobstructed environment.

[0021] The transmission box ensures, for each electrical machine, the transmission of the rotational movement between the body and the electrical machine while offering the possibility of modifying the parameters associated with the movement (speed, torque, etc.), so as to operate the body and the electrical machine in the desired operating ranges.

[0022] The transfer of power between the high pressure and low pressure bodies via the electrical machines makes it possible to optimize the performance of the propulsion system over all of its operating regimes.

[0023] As illustrated in [Fig.l], the propulsion system 2 drives a main rotor 17 provided with a rotating wing via a main gearbox 18 (known by the acronym BTP), and a rear tail rotor 19 (also known by the acronym RAC for “anti-torque rotor”) via a rear gearbox 20 (known by the acronym B TA).

[0024] More precisely, the main transmission box 18 is mechanically connected to the power take-off 10 of the turbine engine 3 via an upper transmission shaft 21. The rear transmission box 20 is mechanically connected to the main transmission box 18 via a lower transmission shaft 22. The lower transmission shaft 22 is located vertically below the upper transmission shaft 21.

[0025] As illustrated in the figures, the high-pressure body 4 is part of a gas generator of the turboshaft engine 3 which comprises the compressor 6, a combustion chamber 23 and the expansion turbine 7. The compressor 6 is supplied with air via an air inlet 24 and comprises one or more compression stages, each stage being axial or centrifugal. The air inlet 24 is here arranged axially between the transmission housing 12 and the compressor 6. The combustion chamber 23 is supplied with compressed air via the compressor 6 and with fuel via one or more injectors. The air / fuel mixture is burned under the action of one or more ignition devices. The exhaust gases from the combustion chamber 23 are expanded in the expansion turbine 7. The expansion turbine 7 comprises one or more expansion stages, each stage being axial or centripetal. The expansion turbine 7 drives the compressor 6 via the high-pressure shaft 8 which is movable about an axis X. The exhaust gases from the turboshaft engine 3 are discharged via an exhaust nozzle 25 which is arranged axially at a rear end 26 of the propulsion system 2.

[0026] As illustrated in the figures, the power turbine 9 is driven by the exhaust gases generated by the gas generator. The power turbine 9 is thus located axially at the rear of the gas generator. The power turbine 9 rotates the power take-off 10 via the reduction gear 11. The reduction gear 11 makes it possible to reduce the rotational speed of the power take-off 10 relative to that of the power turbine 9. The power turbine 9 and the reduction gear 11 are mechanically connected to each other by a low-pressure shaft 27. The low-pressure and high-pressure shafts 27, 8 are coaxial and movable about the axis X. The low-pressure shaft 27 passes internally through the high-pressure shaft 8. The reduction gear 11 is part of the transmission housing 12 which is arranged axially at the front end 13 of the propulsion system 2. Advantageously, the reduction gear 11 is a gear reduction gear.The transmission box 12 carries the first and second electrical machines 14, 15 but also various other accessories such as oil / fuel services, an air / oil separator, etc. The transmission box 12 thus achieves the desired power transfers between the accessories and the moving bodies 4, 5 of the turboshaft engine 3.

[0027] By convention, in the present application, the terms “front” and “rear” define the axial positions of the elements of the propulsion system 2, while knowing that the transmission housing 12 is arranged axially at a front end 13 of the propulsion system 2, and the exhaust nozzle 25 is arranged axially at a rear end 26 of the propulsion system 2.

[0028] Furthermore, by convention, in the present application, the terms "axial" or "axially" refer to any direction parallel to the X axis.

[0029] As indicated above and illustrated in the figures, the first electrical machine 14 is mechanically connected to the high pressure body 4 of the turboshaft engine 3, and is fixed to the transmission housing 12.

[0030] More precisely, the first electrical machine 14 is fixed on a front face 28 of the transmission housing 12. The first electrical machine 14 is arranged next to the second electrical machine 15. The first electrical machine 14 is located vertically above the second electrical machine 15. The first electrical machine 14 is here fixed on the transmission housing 12 via a flange 29 provided with screws, but it could be fixed for example via a collar.

[0031] The first electrical machine 14 is connected to the high pressure body 4 via a first transmission mechanism 30 arranged in the transmission housing 12. The first transmission mechanism 30 may have a fixed or variable transmission ratio, this transmission ratio being able to be equal to 1, less than 1 (reducer) or greater than 1 (multiplier).

[0032] Advantageously, the first transmission mechanism 30 is a gear mechanism. The transmission housing 12 then contains one or more gears of the first transmission mechanism 30.

[0033] The first transmission mechanism 30 is common to or distinct from the gear transmission device(s) associated with the other accessories. Furthermore, the first transmission mechanism 30 is common to or distinct from the gear transmission device of the reducer 11.

[0034] The first electrical machine 14 is configured to operate in so-called motor and generator modes, and in other words the first electrical machine 14 is reversible. In motor mode, the first electrical machine 14 introduces mechanical power to the high-pressure body 4 of the turbine engine 3. In generator mode, the first electrical machine 14 draws mechanical power from the high-pressure body 4 of the turbine engine 3.

[0035] Advantageously, the first electrical machine 14 is a high-voltage electrical machine, in particular so as to be able to transfer significant powers.

[0036] The first electrical machine 14 may be a direct current electrical machine or an alternating current electrical machine.

[0037] Advantageously, the first electrical machine 14 is also configured to start the turbine engine 3.

[0038] As indicated above and illustrated in the figures, the second electrical machine 15 is mechanically connected to the low pressure body 5 of the turboshaft engine 3, and is fixed to the transmission housing 12.

[0039] More precisely, the second electrical machine 15 is fixed on a front face 28 of the transmission housing 12. The second electrical machine 15 is arranged next to the first electrical machine 14. The second electrical machine 15 is located vertically below the first electrical machine 14. The second electrical machine 15 is here fixed on the transmission housing 12 via a flange 29 provided with screws, but it could be fixed for example via a collar.

[0040] The second electrical machine 15 is connected to the low pressure body 5 via a second transmission mechanism 31 arranged in the transmission housing 12. The second transmission mechanism 31 may have a fixed or variable transmission ratio, this transmission ratio being able to be equal to 1, less than 1 (reducer) or greater than 1 (multiplier).

[0041] Advantageously, the second transmission mechanism 31 is a mechanism with gears. The transmission housing 12 then contains one or more gears of the second transmission mechanism 31.

[0042] The second transmission mechanism 31 is common to or distinct from the gear transmission device(s) associated with the other accessories. Furthermore, the second transmission mechanism 31 is common to or distinct from the gear transmission device of the reducer 11. Finally, the second transmission mechanism 31 is common to or distinct from the first transmission mechanism 30.

[0043] In the same way as the first electric machine 14, the second electric machine 15 is configured to operate in so-called motor and generator modes, and in other words the second electric machine 15 is reversible. In motor mode, the second electric machine 15 introduces mechanical power to the low pressure body 5 of the turbine engine 3. In generator mode, the second electric machine 15 takes mechanical power from the low pressure body 5 of the turbine engine 3.

[0044] Advantageously, the second electrical machine 15 is a high voltage electrical machine, in particular so as to be able to transfer significant powers.

[0045] The second electrical machine 15 may be a direct current electrical machine or an alternating current electrical machine.

[0046] As illustrated in the figures, the transmission housing 12 is arranged axially at a front end 13 of the propulsion system 2. The transmission housing 12 is formed of two parts 32 bearing against each other along a transverse joint plane (plane perpendicular to the axis X) and held in position via fixing means such as screws. The transmission housing 12 contains the first and second transmission mechanisms 30, 31 associated with the first and second electrical machines 14, 15, the transmission devices associated with the other accessories and the gear transmission device of the reducer 11.

[0047] The control system 16 of the propulsion system 2 comprises a turboshaft engine computer called FADEC, a low voltage electrical network 33 and a high voltage electrical network 34, these networks 33, 34 being able to be connected to each other or independent of each other.

[0048] The high-voltage electrical network 33 is notably used to transfer significant electrical power between the first and second electrical machines 14, 15, this network 33 being in this respect commonly called an “internal hybrid electrical network”. Thus, advantageously and as indicated above, the first and second electrical machines 14, 15 are high-voltage electrical machines which are connected to the high-voltage electrical network 33.

[0049] The low voltage electrical network 34 is notably used to supply the various accessories of the propulsion system 2 and of the helicopter 1.

[0050] The control system 16 imposes an operating mode on the propulsion system 2, depending in particular on the different flight phases of the helicopter 1 (takeoff, cruise, landing, search, obstacle, standby, emergency (turboengine failure for example)).

[0051] The control system 16 can in particular impose a thermal operating mode in which the propulsive mechanical energy necessary for driving the rotors 17, 19 is solely provided by the turbine engine 3.

[0052] The control system 16 can also impose hybrid operating modes in which the propulsive mechanical energy necessary for driving the rotors 17, 19 is provided both by the turbine engine 3 but also by the first electrical machine 14 and / or by the second electrical machine 15 operating in engine mode.

[0053] As indicated above, the control system 16 is configured to allow a transfer of power between the high pressure and low pressure bodies 4, 5 via the first and second electrical machines 14, 15.

[0054] The propulsion system 2 can thus operate according to a first hybrid operating mode in which the first electric machine 14 operates in generator mode and the second electric machine 15 operates in motor mode, the electrical energy produced by the first electric machine 14 being used to electrically power the second electric machine 15, so as to transfer power from the high pressure body 4 to the low pressure body 5.

[0055] The propulsion system 2 can also operate according to a second hybrid operating mode in which the first electric machine 14 operates in motor mode and the second electric machine 15 operates in generator mode, the electrical energy produced by the second electric machine 15 being used to electrically power the first electric machine 14, so as to transfer power from the low pressure body 5 to the high pressure body 4.

[0056] Advantageously, the control system 16 comprises one or more electrical energy storage devices 35 which are each configured to store the electrical energy produced by the first electrical machine 14 and / or the second electrical machine 15. Each electrical energy storage device 35 comprises, for example, one or more batteries or supercapacitors. The stored electrical energy is, for example, used to power the first electrical machine 14 and / or the second electrical machine 15 operating in engine mode during certain flight phases, or to power the electrical accessories of the propulsion system 2 and / or the helicopter 1.

[0057] The control system 16 may comprise one or more power converters configured to convert an alternating current into a direct current (or vice versa). Such a converter is for example used to enable a transfer of power between the electrical machines 14, 15 via a high voltage direct current bus called HVDC bus.

[0058] Advantageously, the control system 2 comprises protection devices making it possible in particular to protect the electrical networks 33, 34 against short circuits, overvoltages and overcurrents.

[0059] The various mobile elements of the propulsion system 2 can be linked in rotation to each other via coupling means such as splines (floating or fixed), screwed flanges or by shrink-fitting the shafts. The coupling means can comprise a clutch or elastically deformable means called flexible couplings.

[0060] Advantageously, the first and second electrical machines 14, 15 are cooled and lubricated via the cooling and lubrication circuit of the propulsion system 2. Such a circuit is already used to cool and lubricate the transmission housing 12.

[0061] Such a choice makes it possible to pool the cooling and lubrication devices which are associated with the different elements of the propulsion system 2, so as to optimize the overall mass of the propulsion system 2.

[0062] Concerning the first and second electrical machines 14, 15, the cooling and lubrication circuit is notably used to cool the rotors and the stators of the electrical machines 14, 15 but also to lubricate the bearings guiding the rotors and the dynamic seals. Concerning the transmission housing 12, the cooling and lubrication circuit is notably used to cool and lubricate the gears and the bearings present inside this housing 12.

[0063] The cooling and lubrication circuit is for example supplied with oil.

Claims

Claims

1. Hybrid propulsion system (2) for an aircraft (1) comprising: - a turbine engine (3) comprising a high pressure body (4) and a low pressure body (5) which are rotatable, the high pressure body (4) comprising a compressor (6) and an expansion turbine (7) mechanically connected to each other by a high pressure shaft (8), the low pressure body (5) comprising a power turbine (9) which rotates a power take-off (10) via a reduction gear (11), the reduction gear (11) being part of a transmission housing (12) which is arranged axially at a front end (13) of the propulsion system (2);- first and second electrical machines (14, 15) mechanically connected respectively to the high pressure and low pressure bodies (4, 5), the electrical machines (14, 15) being configured to operate in so-called motor and generator modes, the first and second electrical machines (14, 15) being fixed to the transmission housing (12); - a control system (16) which is configured to allow a transfer of power between the high pressure and low pressure bodies (4, 5) via the first and second electrical machines (14, 15).;

2. Propulsion system (2) according to claim 1, characterized in that the first and second electrical machines (14, 15) are fixed on a front face (28) of the transmission housing (12).

3. Propulsion system (2) according to one of the preceding claims, characterized in that the first electrical machine (14) is connected to the high-pressure body (4) via a first transmission mechanism (30) arranged in the transmission housing (12), the first transmission mechanism (30) preferably being a gear mechanism.

4. Propulsion system (2) according to one of the preceding claims, characterized in that the second electrical machine (15) is connected to the low pressure body (5) via a second transmission mechanism (31) arranged in the transmission housing (12), the second transmission mechanism (31) preferably being a gear mechanism.

5. Propulsion system (2) according to one of the preceding claims, characterized in that the power turbine (9) and the reducer (11) are mechanically connected to each other by a low pressure shaft (27), the low pressure and high pressure shafts (27, 8) being coaxial, the low pressure shaft (27) passing internally through the high pressure shaft (8).

6. Propulsion system (2) according to one of the preceding claims, characterized in that the power take-off (10) is capable of driving a main transmission box (18) of the aircraft (1).

7. Propulsion system (2) according to one of the preceding claims, characterized in that the first and second electrical machines (14, 15) are high-voltage electrical machines which are connected to a high-voltage electrical network (33) of the control system (16).

8. Propulsion system (2) according to one of the preceding claims, characterized in that the first electrical machine (14) is configured to start the turbine engine (3).

9. Propulsion system (2) according to one of the preceding claims, characterized in that it is configured to operate according to one of the following operating modes: - a first hybrid operating mode in which the first electric machine (14) operates in generator mode and the second electric machine (15) operates in motor mode, the electrical energy produced by the first electric machine (14) being used to electrically power the second electric machine (15), so as to transfer power from the high pressure body (4) to the low pressure body (5);- a second hybrid operating mode in which the first electric machine (14) operates in motor mode and the second electric machine (15) operates in generator mode, the electrical energy produced by the second electric machine (15) being used to electrically power the first electric machine (14), so as to transfer power from the low pressure body (5) to the high pressure body (4).;

10. Aircraft (1) comprising a hybrid propulsion system (2) according to one of the preceding claims.

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