TURBORE ACTUATOR WITH A POWER SUPPLY DEVICE

Description

TECHNICAL FIELD

[0001] This presentation concerns the field of aircraft, and more particularly a turbojet engine which can be used for aeronautical propulsion. TECHNOLOGICAL BACKGROUND

[0002] In recent years, aircraft engines have undergone numerous improvements, which have increased their performance and significantly reduced their fuel consumption and greenhouse gas emissions. Currently, the efforts required to achieve similar gains in the coming years are proportionally much higher. This implies significantly increased costs, but also increasing complexity of the systems implemented, so much so that the operability of the engines and their performance / cost ratio could deteriorate.

[0003] There is therefore a need for a new type of aircraft engine, particularly a turbojet, which forms a more acceptable compromise between different parameters such as specific consumption, drag, geometry, mass, simplicity and costs.

[0004] Document US 2004 / 0255590 A1 describes a prior art turbojet engine. GENERAL PRESENTATION

[0005] For this purpose, the present disclosure relates to a dual-flow turbojet engine according to claim 1, comprising a fan, a casing arranged downstream of the fan and separating a primary stream from a secondary stream, a compressor, a combustion chamber and a turbine being arranged in the primary stream, the turbojet engine comprising a differential transmission coupled to the turbine, and a power supply device configured to provide additional power to that provided by the turbine to drive the compressor.

[0006] In this presentation, the axis of the turbojet engine is its axis of symmetry or quasi-symmetry, which forms the axis of rotation of the compressor and the turbine. The axial direction corresponds to the direction of the axis of the turbojet engine and a radial direction is a direction perpendicular to this axis and intersecting this axis. Similarly, an axial plane is a plane containing the axis of the turbojet engine and a radial plane is a plane perpendicular to this axis. A circumference is understood to be a circle belonging to a radial plane and whose center belongs to the axis of the turbojet engine. A tangential or circumferential direction is a direction tangent to a circumference; it is perpendicular to the axis of the turbojet engine but does not pass through the axis.

[0007] Unless otherwise specified, the adjectives forward and aft are used in reference to the axial direction, with the understanding that the turbojet engine inlet is located on the front side of the turbojet engine, while its outlet is located on the rear side. The adjectives upstream and downstream are used in reference to the normal flow direction of gases in the turbojet engine.

[0008] Finally, unless otherwise specified, the adjectives interior (internal) and exterior (external) are used in reference to a radial direction so that the interior part of an element is, in a radial direction, closer to the axis of the turbojet than the exterior part of the same element.

[0009] The turbojet engine is said to be double-flow in that it comprises a primary vein receiving a primary flow and a secondary vein receiving a secondary flow. The casing separating the primary vein and the secondary vein is sometimes called the internal casing.

[0010] As indicated, the differential transmission is coupled to the turbine, i.e. there is a functional, possibly permanent, connection between the turbine and the differential transmission. The differential transmission can be configured to drive the fan and / or the compressor, using the mechanical energy supplied by the turbine. The differential transmission is a power transmission allowing the speed ratio and / or torque to be changed between at least one input, in this case the turbine, and at least one output, in this case the fan and / or the compressor. For the purposes of this disclosure, the differential transmission can have a transmission ratio less than one, in which case it is sometimes referred to as a reduction system, but also greater than one, depending on what is considered to be the input or output, in which case it is sometimes referred to as a multiplier system. The differential transmission can be electromechanical or purely mechanical.

[0011] The turbojet engine can be a single-spool turbojet engine. A single-spool turbojet engine comprises a single rotating assembly, connecting one or more compressors to one or more turbines via a common kinematics, which does not mean that all the components rotate at the same speed but that their rotations are linked. In contrast, a twin-spool turbojet engine comprises two kinematically independent rotating assemblies, each of these assemblies connecting its own compressors and turbines via its own kinematics independent of that of the other assembly. In the following, for the sake of brevity but without loss of generality, we will assume that the single spool comprises a compressor and a turbine.

[0012] Unlike current developments which are based in the vast majority, if not entirely, on twin-spool turbojets, this presentation proposes to implement a single-spool turbojet. Such an architecture makes it possible to greatly simplify the turbojet, for example by eliminating complex components such as shafts, bearings and supports, and to reduce its mass and cost.

[0013] Furthermore, due to the fact that the turbojet engine comprises a power supply device configured to provide additional power to that provided by the turbine to drive the compressor, it is possible, depending on the speed, to operate the compressor in a desired operating range whereas the turbine alone, in the speed considered, in particular at low speed, would not allow operation in this range. As a result, the performance of the turbojet engine is of a level comparable to that of existing turbojet engines elsewhere, regardless of the speed of the turbojet engine, or else has a much better performance / cost ratio than an existing turbojet engine.

[0014] In some embodiments, the turbojet engine further comprises a control unit configured to control the power supply device as a function of a rotational speed of the turbine. Thus, the power supply device can be controlled as a function of the speed of the turbojet engine. This makes it possible to finely adapt the parameters of the turbojet engine and to optimize the operation of the turbojet engine.

[0015] In some embodiments, the power supply device comprises an electric motor configured to rotate the compressor. In these embodiments, the power supply device can be controlled very flexibly, depending on the power requirements, in particular continuously over a range covering zero power up to the maximum design power of the power supply device.

[0016] In some embodiments, the power supply device comprises an electric generator configured to be driven by the turbine. The electric generator may be configured to power the aforementioned electric motor, directly or via electricity storage means.

[0017] Indeed, in some embodiments, the turbojet engine comprises electricity storage means electrically connected to the electric motor or to the electric generator. Thus, during certain flight phases, for example at high speed, the turbine can drive the electric generator so that the excess mechanical power is stored, in electrical form, in the electricity storage means. During other flight phases, for example at low speed, the compressor can be driven by the turbine and by the electric motor, the electric motor drawing its energy from the electricity storage means. However, other variants are possible. For example, instead of being recharged by an electric generator driven by the turbine, the electricity storage means could be recharged using a power supply external to the turbojet engine.

[0018] Thus, in some embodiments, the power supply device includes a connector configured to be connected to an external power supply.

[0019] In some embodiments, the power supply device comprises a variable mechanical transmission coupled on the one hand to the compressor shaft, and on the other hand to the turbine shaft. Thus, the variable mechanical transmission makes it possible to draw power from the turbine to drive the compressor, said power being able to be regulated, for example according to the speed of the turbojet engine. The variable mechanical transmission can be connected to or disconnected from the compressor and / or the turbine. The variable mechanical transmission can transmit a fixed or variable proportion of the turbine power to the compressor. The variable mechanical transmission can comprise any of the following elements: a clutch, a gearbox, a variator, etc.

[0020] In some embodiments, the power supply device comprises an electromagnetic transmission coupled on the one hand to the compressor shaft, on the other hand to the turbine shaft. The electromagnetic transmission may be, for example, a magnetic gear transmission. An electromagnetic transmission has many advantages, including the absence of mechanical fatigue, lubrication, losses due to mechanical contacts, noise, as well as very high efficiency.

[0021] In some embodiments, the maximum additional power provided by the power supply device is greater than 1.5 megawatts (MW). Such maximum additional power is useful for compensating for power not provided by the turbine during certain turbojet engine speeds.

[0022] In some embodiments, the power supply device is configured to be deactivated when the rotational speed of the turbine is greater than 95% of the maximum nominal rotational speed of the turbine. Thus, it is possible to size the power supply device only for operation at moderate mechanical speeds where its role is useful, thereby minimizing its mass and complexity. For example, the power supply device may be configured to be deactivated when the rotational speed of the turbine is sufficient to drive the compressor alone at a reduced speed, of at least 50% of the nominal speed, preferably at least 70%. Conversely, the power supply device may be configured to be activated when the rotational speed of the turbine is insufficient to drive the compressor alone at a reduced speed of at least 50% of the nominal speed, preferably at least 70%.

[0023] The present disclosure also relates to a single-spool dual-flow turbojet engine, comprising a fan, a casing arranged downstream of the fan and separating a primary stream from a secondary stream, a compressor, a combustion chamber and a turbine being arranged in the primary stream, the turbojet engine comprising a differential transmission coupled to the turbine, in which the dilution ratio between the secondary stream and the primary stream is greater than or equal to 12.

[0024] The dilution ratio between the secondary vein and the primary vein, more simply called the dilution ratio or in English by-pass ratio (BPR), is the ratio of the air flow entering the secondary vein to the air flow entering the primary vein. Increasing the BPR increases the performance of the turbojet, since the thrust is mainly provided by the air circulated by the fan and which passes through the secondary vein.

[0025] Increasing the BPR, however, requires increasing the diameter of the blower, which also leads to increasing the section of the secondary vein.

[0026] By virtue of the fact that the bypass ratio between the secondary stream and the main stream is greater than or equal to 12, the performance of the turbojet engine is further improved. For example, such a bypass ratio can be obtained within the framework of a subsonic ejection speed at the outlet of the turbojet engine, preferably between Mach 0.8 and Mach 1 at the throat of the ejection nozzle, for a corresponding aircraft speed between Mach 0.7 and Mach 0.9.

[0027] The differential transmission includes a first reducer configured to change the rotational speed transmission ratio between the turbine and the fan and a second reducer configured to change the rotational speed transmission ratio between the turbine and the compressor.

[0028] Thus, the rotation of the fan can be decoupled from the rotation of the compressor, which allows for different rotation speeds for these two components. This makes it possible to maintain the compressor rotation speed at a certain level while reducing the rotation speed of the fan. However, the rotation speed of the fan determines the tangential speed of the radially external part of the fan blades, also called the blade tip. The speed of the blade tip must respect certain constraints, in particular remaining subsonic, for example less than or equal to 310 meters per second (m / s). Consequently, being able to reduce the rotation speed of the fan allows, at the same blade tip speed, to increase the diameter of the fan. This results in even better performance for the turbojet.

[0029] In some embodiments, the second reducer is coupled to an output of the first reducer.

[0030] In some embodiments, the first reducer is a differential reducer having an input wheel rotationally connected to the turbine, a first output wheel rotationally connected to the fan, a second output wheel rotationally connected to an input wheel of the second reducer, and the second reducer is an epicyclic reducer having an output wheel rotationally connected to the compressor.

[0031] A reducer is a device for changing the speed ratio and / or torque between at least one input wheel and at least one output wheel. For the purposes of this disclosure, a reducer may have a transmission ratio less than one, but also greater than one, depending on what is considered to be the input or the output (a reducer is a generally reversible transmission), in which case it is sometimes referred to as a multiplier. A differential reducer may combine the rotation of three wheels, for example one input wheel and two output wheels, or two input wheels and one output wheel. An epicyclic reducer may combine the rotation of two wheels, for example one input wheel and one output wheel.

[0032] The differential reducer and / or the epicyclic reducer may be provided in the form of an epicyclic gear train. An epicyclic gear train generally has an outer sun gear, also called a crown gear, as well as an inner sun gear, also called a sun gear or sun. The sun gear and the crown gear are coupled via one or more planet gears, the planet gears being coupled to each other by a planet carrier. For the purposes of this disclosure, the term "wheel" is generically used to refer to any of the crown gear, the planet carrier, or the sun gear. Each wheel may be used as an input or output of a mechanical transmission.

[0033] In this case, the rotation of the turbine is transmitted, via the first reduction gear, to the fan. This results in a first transmission ratio, for example a first torque ratio, between the turbine and the fan. The second output wheel of the first reduction gear drives an input wheel of the second reduction gear, the output of which drives the compressor. This results in a second transmission ratio between the turbine and the compressor. Thus, the use of a differential reduction gear makes it possible to decouple the rotation of the fan and the compressor. To limit the complexity of the turbojet, the epicyclic reduction gear can be coupled to the differential reduction gear and not directly to the turbine.

[0034] In some embodiments, the ratio of the number of teeth of the first output wheel of the first reducer to the number of teeth of the input wheel of the first reducer is greater than 1. This ratio may be greater than 1.2, more preferably greater than 1.4. Furthermore, this ratio may be less than 1.8, more preferably less than 1.6. This ratio may be approximately equal to 1.5. In the case of nominal operation, the first reducer is therefore configured to provide the blower with a lower rotational speed than that provided to the compressor.

[0035] In some embodiments, the ratio of the number of teeth of the crown of the second reducer to the number of teeth of the output wheel of the second reducer is greater than 2. In the case of an epicyclic gear train, the crown of the second reducer may be fixed relative to the internal casing of the turbojet engine. This ratio makes it possible to increase the rotational speed of the compressor relative to the speed supplied at the input of the second reducer by the first reducer. This ratio may be greater than 5, preferably even greater than 6. Furthermore, this ratio may be less than 9, preferably even less than 8. This ratio may be approximately equal to 7.

[0036] In certain embodiments, the ratio of the number of teeth of the first output wheel of the first reducer to the number of teeth of the input wheel of the first reducer is less than the ratio of the number of teeth of the crown of the second reducer to the number of teeth of the output wheel of the second reducer. This is the ratio of the two aforementioned ratios; it is also verified, in the examples given, that 1.5 is less than 7. In this configuration, the diameter of the different wheels of the differential transmission can be reduced and the overall production cost of the differential transmission can be limited.

[0037] In some embodiments, the second reducer has a transmission ratio greater than 3. The transmission ratio is the ratio of the rotational speed of the output wheel to the rotational speed of the input wheel. In the case of satellites, the rotational speed of the planet carrier is considered, which corresponds to the speed of revolution of the satellites around the sun gear and not the rotational speed of the satellites on themselves.

[0038] This transmission ratio may be greater than 6, more preferably greater than 7. Furthermore, this ratio may be less than 10, more preferably less than 9. This ratio may be approximately equal to 8.

[0039] In some embodiments, the fan compression ratio at cruising speed is between 1.3 and 1.45. According to the usual definition, the fan compression ratio is the ratio of the volume-averaged total pressure of a given air mass at the fan inlet to the volume-averaged total pressure of the same air mass at the fan outlet. A relatively low compression ratio makes it possible to increase the performance of the turbojet engine.

[0040] In some embodiments, the compression ratio of the compressor is greater than or equal to 25 at a compressor rotational speed of 15,500 revolutions per minute. Such a compression ratio is adapted to the aerodynamics of the compressor and the turbine. For example, the compressor may comprise at least eight stages of moving blades, preferably at least nine or ten stages.

[0041] In some embodiments, the overall pressure ratio is greater than or equal to 30 at the top of climb. The overall pressure ratio, referred to in English as overall pressure ratio or OPR, is the ratio of the total air pressure at the compressor outlet to the total air pressure at the fan inlet. The so-called "top of climb" point is the point at which the climb to cruising altitude is completed, this point being conventionally calculated so that the climb is as economical and short as possible. A high OPR improves the thermal efficiency and therefore the performance of the turbojet's gas generator. An OPR between 30 and 40 may seem less advantageous than on twin-spool turbojets, but this is offset by a significant gain in simplicity, operability and cost.

[0042] Furthermore, unless otherwise stated, the values ​​of the quantities mentioned in this presentation are measured when the turbojet engine is stationary in a standard atmosphere, as defined by the International Civil Aviation Organization (ICAO) manual, Doc 7488 / 3, 3rd edition, and at sea level.

[0043] The present disclosure also relates to a turbojet engine comprising a fan, a compressor, a combustion chamber, and a turbine configured to rotate the fan via a first reduction gear and the compressor via a second reduction gear, wherein an output of the first reduction gear is rotationally coupled to an input of the second reduction gear by a reduction shaft, the reduction shaft being supported by a bearing arranged between the first reduction gear and the second reduction gear.

[0044] Thus, it is understood that the aforementioned bearing can be arranged axially between the first reducer and the second reducer. The bearing can be supported relative to a fixed casing of the turbojet engine, in particular fixed relative to the combustion chamber.

[0045] Thanks to the fact that the reduction shaft is supported by a bearing arranged between the first reducer and the second reducer, the turbojet engine has a good dynamic situation, i.e. good mechanical and aerodynamic behavior in operating mode, and main vibration modes, i.e. harmful to the turbojet engine, located outside the operating mode. In addition, said bearing makes it possible to properly maintain the first reducer and the second reducer, avoiding or limiting dynamic couplings between these two reducers.

[0046] In some embodiments, the bearing is a roller bearing. Said bearing therefore allows axial movement of the reduction shaft.

[0047] In some embodiments, the bearing is supported by said casing. By supporting the bearing by the inner casing, the bearing support structure can be simplified, thereby limiting the increase in mass of the turbojet engine, simplifying its overall structure and improving its performance.

[0048] In some embodiments, said bearing is arranged radially outside the compressor shaft, the turbine shaft and the reduction shaft. This allows the dynamic situation of the turbojet engine to be further optimized.

[0049] In some embodiments, the reduction shaft is a planet carrier common to the first reducer and the second reducer.

[0050] In addition to the characteristics just mentioned, the proposed turbojet engine may include one or more other bearings according to the following characteristics, considered in isolation or according to technically possible combinations: a fan bearing arranged between the fan shaft and the casing. The fan bearing supports the fan shaft relative to the casing; a compressor bearing arranged between the compressor shaft and the casing. The compressor bearing, also called the first compressor bearing, supports the compressor shaft relative to the casing; a second bearing, such as a roller bearing, arranged to support the reduction shaft. Using two roller bearings to support the reduction shaft prevents hyperstaticity; an intershaft bearing, for example a roller bearing, arranged between the compressor shaft and the turbine shaft.The intershaft bearing may be arranged radially between the compressor shaft and the turbine shaft and support these two shafts relative to each other; a compressor bearing arranged between the compressor shaft and a structural member downstream of the compressor, said structural member being able to be, for example, the combustion chamber casing or the diffuser located between the compressor and the combustion chamber. The compressor bearing, also called second compressor bearing, supports the compressor shaft relative to the structural member. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The invention and its advantages will be better understood upon reading the following detailed description of embodiments given as non-limiting examples. This description refers to the appended drawings, in which: there figure 1 is a schematic representation of a turbojet engine according to one embodiment; the figure 2 schematically illustrates an axial half-section of a turbojet according to a second embodiment; the figure 3 schematically illustrates a half axial section of a turbojet according to a third embodiment; the figure 4 schematically illustrates an axial half-section of a turbojet according to a fourth embodiment; the figure 5 schematically illustrates an axial half-section of a turbojet according to a fifth embodiment. DETAILED DESCRIPTION OF EMBODIMENTS

[0052] A turbojet engine 10 according to one embodiment is shown schematically in the figure 1 . In this case, the turbojet engine 10 is a single-spool dual-flow turbojet engine. Indeed, the turbojet engine 10 comprises a fan 20, an internal casing 30 arranged downstream of the fan 20 and separating a primary stream 12 from a secondary stream 14. A compressor 60, a combustion chamber 70 and a turbine 80 are arranged in the primary stream 12, from upstream to downstream. Because the turbojet engine 10 is a single-spool engine, it comprises a single rotating assembly comprising the compressor 60 and the turbine 80. In this case, the turbojet engine comprises a single compressor 60 driven directly or indirectly by a single turbine 80, the turbine 80 being set in motion by the combustion gases from the combustion chamber 70.

[0053] The fan 20 may comprise a wheel of moving blades. The fan 20 may be sized so that its compression ratio in cruising mode is between 1.3 and 1.45, at a rotational speed of approximately 2600 revolutions per minute. The diameter of the fan 20 may be between 2 and 2.7 meters, more precisely between 2.2 meters and 2.4 meters. By diameter of the fan 20, we will understand here the radial distance between the axis of the turbojet 10 and the head of the fan blades.

[0054] The compressor 60 may comprise between five and fifteen stages, in particular between eight and twelve stages, preferably approximately ten stages, each stage being formed of a fixed blade wheel and a moving blade wheel. It is recalled that the moving blades of the stages of the same compressor are integral in rotation around the axis of the compressor. The compressor may be dimensioned so that its compression ratio is greater than or equal to twenty-five at a rotation speed of approximately 15,500 revolutions per minute, which may correspond to the cruising speed.

[0055] Thus, in this embodiment, the OPR of the turbojet 10 may be greater than or equal to thirty.

[0056] The turbine 80 may comprise between two and six stages, in particular between three and five stages, preferably approximately four stages. It is recalled that the moving blades of the stages of the same turbine are integral in rotation around the axis of the turbine. The turbine may be designed to rotate at approximately 8600 revolutions per minute in cruising mode.

[0057] In this embodiment, the turbine 80 rotates the compressor 60. The turbine 80 also rotates the fan 20. More specifically, the turbojet 10 comprises a differential transmission coupled to the turbine 80. In this case, as illustrated in the figure 1 , the differential transmission is coupled to the blower 20 and the compressor 60 and comprises, here, a first reducer 40 configured to modify the rotational speed transmission ratio between the turbine 80 and the blower 20, and a second reducer 50 configured to modify the rotational speed transmission ratio between the turbine 80 and the compressor 60.

[0058] In this embodiment, the dilution ratio between the secondary vein 14 and the primary vein 12, also called BPR, is greater than or equal to twelve, preferably greater than or equal to fourteen, or even 14.5. In this embodiment, such a BPR can be achieved thanks to the diameter of the fan, the compression ratio of the fan, and the number of stages of the turbine 80. However, other parameters could be brought into play: for example, a high BPR can also be achieved by the joint increase of the OPR and the turbine inlet temperature, this conjunction contributing to reducing the mass flow rate of the primary vein, therefore increasing the BPR.

[0059] As indicated previously, in the turbojet 10, the rotational speed of the fan 20 can be decoupled from that of the compressor 60. For example, the ratio of the rotational speed of the compressor 60 to the rotational speed of the fan 20 can be between 5.5 and 6.5 at full power points. Furthermore, unlike a single differential reducer, the use of two reducers makes it possible to alleviate the mechanical and aerodynamic constraints on the turbine 80.

[0060] THE figures 2 à 5 show the turbojet 10 in other embodiments. In these figures, the elements corresponding or identical to those of the first embodiment will receive the same reference sign and will not be described again.

[0061] There figure 2 illustrates in more detail the structure of the turbojet 10.

[0062] It is first noted that due to the presence of the differential transmission, the fan shaft 22, the compressor shaft 62 and the turbine shaft 82 are distinct from each other.

[0063] As shown in the figure 2 , the first reducer 40 is a differential reducer having an input wheel 44, in this case a planetary (also called planetary 44), integral in rotation with the turbine 80, here via a turbine shaft 82, and a first output wheel 48, in this case a crown (also called crown 48), integral in rotation with the fan 20, here via a fan shaft 22. Preferably, the ratio R1 of the number of teeth of the first output wheel 48 to the number of teeth of the input wheel 44 is greater than 1 and is, in this embodiment, approximately 1.5.

[0064] The sun gear 44 and the crown wheel 48 are engaged via satellites 46. One or more satellites 46 may be provided. For the purposes of this disclosure, the expression "engaged" reflects a reciprocal engagement of two elements, whether this engagement is mechanical, electromagnetic or of another nature. The planet carrier 42 connected to the satellite(s) 46 forms the second output wheel of the first reduction gear 40.

[0065] Furthermore, the second reducer 50 is an epicyclic reducer. As indicated previously, the second reducer 50 has an input wheel integral in rotation with the second output wheel 42 of the first reducer 40. In this case, as illustrated in the figure 2 , the planet carrier 42 forms both the second output wheel of the first reducer 40 and the input wheel of the second reducer 50. Consequently, the planet carrier 42 also forms a reduction shaft between the first reducer 40 and the second reducer 50. Subsequently, in this embodiment, the following terms will be used interchangeably: planet carrier 42, reduction shaft, second output wheel of the first reducer 40, input wheel of the second reducer 50. However, in general, these members may be distinct from one another, in which case an output of the first reducer 40 is coupled in rotation to an input of the second reducer 50 by a reduction shaft 42.

[0066] The transmission shaft 42 is a planet carrier for the first reducer 40 and, independently, is also a planet carrier for the second reducer 50. Thus, the second reducer 50 comprises one or more planets 56 whose revolution is caused by the rotation of the planet carrier 42.

[0067] The second reducer 50 comprises, in addition to its input wheel 42, an output wheel 54, in this case a sun gear (also called sun gear 54), integral in rotation with the compressor 60, here via a compressor shaft 62. In this embodiment, the sun gear 54 is engaged with the satellites 56. The satellites 56 can also be engaged with a crown 58, here fixed relative to the casing 30.

[0068] Preferably, the ratio R2 of the number of teeth of the crown 58 of the second reducer 50 to the number of teeth of a satellite 56 is greater than 2 and is, in this embodiment, approximately 7.

[0069] Furthermore, in this embodiment, the aforementioned ratio R1 is lower than the ratio R2.

[0070] The second reducer can be sized to have a transmission ratio greater than 3, for example approximately 8.

[0071] As it emerges from the figure 2 , the first and second reducers 40, 50, are coaxial.

[0072] Bearings may be provided to support the aforementioned shafts. In particular, the reduction shaft 42 may be supported by a bearing 41 arranged between the first reducer 40 and the second reducer 50, so as to improve the dynamic situation of the differential transmission. More precisely, as illustrated in the figure 2 , the bearing 41, in this case a roller bearing, is arranged axially between the first reducer 40 and the second reducer 50, and radially between the reduction shaft 42 and the housing 30, to support the reduction shaft 42 relative to the housing 30.

[0073] If necessary, the reduction shaft 42 may be supported by a second bearing 43. The second bearing 43 may be provided in front of the first reduction gear 40 or, as shown in the figure 2 , at the back of the deuxième reducer 50. The second bearing 43 may be a roller bearing. The second bearing 43 may be arranged radially between the reduction shaft 42 and the housing 30. The second bearing 43 may support the reduction shaft 42 relative to the housing 30.

[0074] Furthermore, the fan shaft 22, the compressor shaft 62 and the turbine shaft 82 may each, independently of one another, be supported by at least one bearing, or, in this embodiment, at least two bearings.

[0075] According to one example, the fan shaft 22 is supported relative to the casing 30 by a front fan bearing 21 and a rear fan bearing 23. Furthermore, according to one example, the compressor shaft 62 is supported by a front compressor bearing 61 relative to the casing 30, and by a rear compressor bearing 63 relative to a structural member 72 downstream of the compressor, here a combustion chamber casing. Furthermore, according to one example, the turbine shaft 82 is supported by a rear turbine bearing 83 relative to an exhaust casing 84, also known as a “turbine rear frame” (TRF).

[0076] Furthermore, the compressor shaft 62 may be coaxial with the turbine shaft 82 and externally fitted onto the turbine shaft 62. In this perspective, an inter-shaft bearing 81 may be provided arranged between the compressor shaft 62 and the turbine shaft 82, in particular radially between these two shafts. The inter-shaft bearing 81 supports the compressor shaft 62 relative to the turbine shaft 82 and allows their relative rotation.

[0077] For each of these shafts 22, 62, 82, it may be provided that one of the bearings ensures axial locking of the shaft, for example in the form of a ball bearing, while the other of the bearings allows axial movement of the shaft, for example in the form of a roller bearing, to avoid hyperstaticism while controlling the axial position of the shaft.

[0078] In this example, the front fan bearing 21 and the intershaft bearing 81 are roller bearings, while the rear fan and turbine bearings 23, 83 are ball bearings. In this example, the front compressor bearing 61 is a ball bearing, while the rear compressor bearing is a roller bearing.

[0079] It is noted that to further improve the dynamics, in this case by reducing the length of the relevant shafts 22, 62, 82 so that their natural modes occur at higher speeds potentially outside the operating speed of the turbojet, it is possible to position the ball bearings 23, 61 as close as possible to the inlet casing of the fan 20 and the compressor 60, respectively. For example, it is possible to place said bearings as close to the inlet casing of the fan 20 and the compressor 60, respectively, as the geometry of these casings allows.

[0080] As illustrated in the figure 2 , the first bearing 41 supporting the reduction shaft 42 may be a so-called “high radius” bearing, that is to say one whose radius is relatively close to that of the casing 30 on which it is fixed. In this case, said bearing 41 is arranged radially outside the compressor shaft 62, the turbine shaft 82 and the reduction shaft 42.

[0081] It is noted that due to the simplified structure of the turbojet 10, a fortiori for a single-spool turbojet 10, the distance between the bearings supporting the same shaft can be reduced compared to the more complex architectures currently developed. This results in better rotational dynamics of the components of the turbojet 10. Generally speaking, reducing the length to diameter ratio of a shaft makes it possible to improve the dynamics of the shaft.

[0082] From the point of view of mass, the inventors estimate the mass gain between 5% and 15% for the turbojet 10 of the second embodiment, compared to a conventional double-spool dual-flow engine with single reducer.

[0083] In the third to fifth embodiments, shown in the figures 3 à 5 respectively, in order to reduce the risk that the compressor 60 is at too low a speed when the turbine 80 is running at idle speed or more generally at a non-zero but low speed, a power supply device 90 may be provided configured to provide additional power to that provided by the turbine 80 to drive the compressor 60. Of course, such a power supply device may be compatible with the embodiments previously described.

[0084] The power supply device may be of various types. For example, the power supply device 90 may be configured to provide power from a source separate from the turbine 80, said power therefore not being provided, directly or indirectly, instantaneously or in a delayed manner, by the turbine 80. Typically, in the third embodiment, the power supply device 90 comprises an electric motor 91 configured to rotate the compressor 60. As illustrated in the figure 3 , the electric motor 91 may be engaged with the compressor shaft 62. The electrical energy of the electric motor 91 may come from an electric generator 92 configured to be driven by the turbine 80, or more precisely by the turbine shaft 82, in this embodiment.

[0085] Alternatively or in addition, the power supply device 90 may comprise a connector 94 configured to be connected to an electrical power supply external to the turbojet engine and to provide the electric motor 91 with the necessary electrical energy, it being understood that the additional power to drive the compressor 60 despite the idle speed of the turbine 80 is essentially useful when the turbojet engine 10 is operating in idle speed, on the ground as well as in flight, for example during the descent phase.

[0086] Alternatively or in addition, as illustrated in the figure 4 with reference to the fourth embodiment, the electrical energy intended to power the electric motor 91 may come from electricity storage means 96 electrically connected to the electric motor. If necessary, the electricity storage means 96 may be connected to the electric generator 92 or to the connector 94 illustrated in the third embodiment. Depending on the configuration, the electricity storage means 96 may act as a buffer to accumulate the energy produced by the electric generator 92 independently of its consumption by the electric motor 91.

[0087] The electricity storage means 96 may comprise one or more batteries, or any other suitable storage means.

[0088] However, it is not necessary for the power supplied by the power supply device 90 to be transmitted in electrical form. In the fifth embodiment, shown in the figure 5, the power supply device 90 comprises a variable mechanical or electromagnetic transmission coupled on the one hand to the shaft 62 of the compressor 60, on the other hand to the shaft 82 of the turbine 80. More precisely, the power supply device 90 comprises a first engagement element 98a integral in rotation with the compressor shaft 62, a second engagement element 98b integral in rotation with the turbine shaft 82. The first and second engagement elements 98a, 98b can be engaged with each other, in a variable manner (which includes the possibility of decoupling them), by means of a mechanical or electromagnetic connection 98c. For example, the connection 98c can be a clutch, a differential system, an electromagnetic coupler or any other variable transmission of mechanical energy.

[0089] The third, fourth and fifth embodiments have in common that the power supplied to the compressor 60 by the power supply device 90 is variable and can be controlled. For this purpose, a control unit 99 may be provided configured to control the power supply device 90. For example, the control unit 99 may control the power supply device as a function of a rotational speed of the turbine 80 or of another parameter representative of the speed of the turbojet engine 10. For example, it may be useful to activate the power supply device 90 when the turbine rotates at a speed less than or equal to 95% of its maximum nominal rotational speed, and to deactivate the power supply device 90 for a rotational speed of the turbine greater than 95% of its maximum nominal rotational speed.Thus, even when the turbine 80 is idling, the compressor 60 can be maintained in a stable rotational regime and offering good operability, that is to say a capacity to maintain the stabilized and transient operating points of the turbomachine at a distance sufficiently far from the zones of aerodynamic instability.

[0090] The power supply device 90 may be sized such that the maximum additional power provided by the power supply device may be greater than 1.5 Megawatts (MW), preferably greater than or equal to 1.8 MW, more preferably greater than or equal to 2.1 MW.

[0091] Although presented to increase the rotational speed of the compressor 60 when the turbine 80 is idling, the power supply device 90 can, incidentally, be used as an assistance in accelerating the turbojet 10, for example during start-up or during rapid transient maneuvers.

[0092] Furthermore, the power supply device may be used in the context of a twin-spool, twin-flow turbojet engine, which comprises, in addition to the aforementioned compressor and turbine which form a high-pressure spool, a low-pressure compressor or booster and a low-pressure turbine, positioned on either side of the high-pressure spool and forming a low-pressure spool. The low-pressure compressor is driven by the low-pressure turbine. For example, the power supply device may be used to supply power to the high-pressure shaft in order to improve the operability of the high-pressure compressor by lowering its operating line, which is conventionally defined as the locus of the points described in the compressor in a coordinate system [compression ratio; reduced mass flow], during all possible engine operating conditions, in particular between full throttle and idle.When the power supply device is used, the supplied power can be taken from the low pressure shaft, which improves the operability of the low pressure compressor by lowering its operating line.

[0093] Although the present description refers to specific exemplary embodiments, modifications may be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various illustrated / mentioned embodiments may be combined in additional embodiments. Therefore, the description and the drawings should be considered in an illustrative rather than restrictive sense.

Claims

1. A turbofan (10), comprising a fan (20), a casing (30) positioned downstream of the fan (20) and separating a primary flowpath (12) from a secondary flowpath (14), a compressor (60), a combustion chamber (70) and a turbine (80) being arranged in the primary flowpath (12), the turbofan comprising a differential transmission coupled to the turbine (80), to the compressor (60) and to the fan (20), and a power supply device (90) configured to provide additional power to that provided by the turbine (80) to drive the compressor (60), wherein the differential transmission comprises a first reduction gear (40) configured to modify the rotation speed transmission ratio between the turbine (80) and the fan (20), characterized in that the differential transmission comprises a second reduction gear (50) configured to modify the rotation speed transmission ratio between the turbine (80) and the compressor (60).

2. The turbofan according to claim 1, further comprising a control unit (99) configured to control the power supply device (90) depending on a rotation speed of the turbine (80).

3. The turbofan according to claim 1 or 2, wherein the power supply device (90) comprises an electric motor (91) configured to drive the compressor (60) in rotation and / or an electrical generator (92) configured to be driven by the turbine (80), and preferably, the turbofan comprises electricity storing means (96) electrically connected to the electric motor (91) or to the electrical generator (92).

4. The turbofan according to any one of claims 1 to 3, wherein the power supply device (90) comprises a connector (94) configured to be connected to an external electrical power supply.

5. The turbofan according to any one of claims 1 to 4, wherein the power supply device (90) comprises a variable mechanical transmission (98a, 98b, 98c) coupled on the one hand to the shaft (62) of the compressor and on the other hand to the shaft (82) of the turbine.

6. The turbofan according to any one of claims 1 to 5, wherein the power supply device (90) comprises an electromagnetic transmission (98a, 98b, 98c) coupled on the one hand to the shaft (62) of the compressor and on the other hand to the shaft (82) of the turbine.

7. The turbofan according to any one of claims 1 to 6, wherein the maximum additional power provided by the power supply device (90) is greater than 1.5 MW.

8. The turbofan according to any one of claims 1 to 7, wherein the power supply device (90) is configured to be deactivated when the rotation speed of the turbine (80) is greater than 95% of the nominal maximum rotation speed of the turbine (80).

9. The turbofan according to any one of claims 1 to 8, wherein the turbofan (10) is a single-spool turbofan and the by-pass ratio between the secondary flowpath (14) and the primary flowpath (12) is greater than or equal to 12.

10. The turbofan according to any one of claims 1 to 9, wherein the first reduction gear (40) is a differential reduction gear having an input wheel (44) rotatably secured to the turbine (80), a first output wheel (48) rotatably secured to the fan (20), a second output wheel (42) rotatably secured to an input wheel of the second reduction gear (42), and the second reduction gear (50) is an epicyclic reduction gear having an output wheel (54) rotatably secured to the compressor (60); and, preferably, wherein the ratio of the number of teeth of the first output wheel (48) of the first reduction gear (40) to the number of teeth of the input wheel (44) of the first reduction gear (40) is greater than 1.

11. The turbofan according to claim 10, wherein the ratio of the number of teeth of the ring gear (58) of the second reduction gear (50) to the number of teeth of the output wheel (54) of the second reduction gear (50) is greater than 2.

12. The turbofan according to claim 10 or 11, wherein the ratio of the number of teeth of the first output wheel (48) of the first reduction gear (40) to the number of teeth of the input wheel (44) of the first reduction gear (40) is less than the ratio of the number of teeth of the ring gear (58) of the second reduction gear (50) to the number of teeth of the output wheel (54) of the second reduction gear (50).

13. The turbofan according to any one of claims 1 to 12, wherein the second reduction gear (50) has a transmission ratio greater than 3 and / or wherein the compression ratio of the fan (20) at cruising speed is comprised between 1.3 and 1.45.

14. The turbofan according to any one of claims 1 to 13, wherein the compression ratio of the compressor (60) is greater than or equal to 25 at a rotation speed of the compressor of 15,500 revolutions per minute.

15. The turbofan according to any one of claims 1 to 14, wherein the overall pressure ratio is greater than or equal to 30 at top of climb.