HYBRID TURBOJET ENGINE INCLUDING A VARIABLE SPEED DRIVE FOR TWO ELECTRIC MACHINES

Abstract

Hybrid turbomachine comprising: an input shaft (a26) configured to be driven by a low-pressure turbine (102); an output shaft (a64) to drive an electric machine (104) and another output shaft (a64') to drive another electric machine (104'); a speed variator (106) to adjust the speed of each output shaft (a64, a64') according to a speed of the input shaft, comprising: a first planetary gear train (T1) having, at the input, a planet carrier (108) connected to the input shaft, a ring gear (112) and a planet (110); at the output, a first sun gear (130) connected to said output shaft, a second planetary gear train (T2) having, at the input, the ring gear (112) and another planet (120); At the output, a second sun (140) is connected to the other output shaft, and a means (MB) is provided for locking or freeing the crown. Figure for the abbreviation: Fig. 1

Description

Title of the invention: HYBRID TURBOJET ENGINE COMPRISING A VARIABLE SPEED DRIVE FOR TWO ELECTRIC MACHINES Technical field of the invention

[0001] The present invention is in the field of aeronautics and relates more particularly to a hybrid turbojet engine. Technological background

[0002] Climate change is a major concern for many legislative and regulatory bodies worldwide. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies both to new types of aircraft and to those currently in service, requiring the implementation of technological solutions to bring them into compliance with current regulations. Civil aviation has been actively working for several years now to contribute to the fight against climate change.

[0003] Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. The Applicant takes into account the factors impacting all phases of design and development in order to obtain aeronautical components and products that are less energy-intensive, more environmentally friendly, and whose integration and use in civil aviation have moderate environmental impacts, with the aim of improving the energy efficiency of aircraft. Consequently, the Applicant is constantly working to reduce its climate impact by employing methods and operating virtuous development and manufacturing processes that minimize greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity.

[0004] This sustained research and development work focuses on new generations of aircraft engines, the weight reduction of aircraft, in particular through the materials used and lighter on-board equipment, the development of the use of electrical technologies to provide propulsion, and finally aviation biofuels.

[0005] In this context, a hybrid turbojet engine has been proposed featuring a propulsion configuration that combines both a traditional turbojet engine and at least one electric machine capable of operating in engine mode and generator mode.

[0006] In a known manner, a hybrid jet engine for aircraft integrates at least one electric machine on a high-pressure (HP) body and / or on a low-pressure (LP) body of the jet engine.

[0007] The electric machine is coupled with the shaft of the HP or BP body. It can be used either in "generator mode" to generate an electric current from mechanical energy, or conversely in "motor mode" to provide mechanical energy from an electric current.

[0008] When the electrical machine is used in "generator mode", it is generally referred to as a "generator".

[0009] In practice, the electric machine is driven by a low-pressure (LP) turbine in the engine body, known as a low-pressure (LP) turbine, by means of a rotating drive shaft to generate electric current used to power the aircraft. This is referred to as the LP electric machine. The sizing of the LP electric machine and its control electronics is determined by the wide range of the electric machine's rotational speed in order to deliver a constant electrical power output, expressed in kW. Indeed, the wider this range, the larger the electric machine and the greater its weight, which contributes to the overall weight of the turbojet engine.

[0010] The turbojet engine includes a fan, i.e., a rotating component whose rotor is equipped with blades that draw air into the turbojet. As is known, some types of fans have blades whose orientation (i.e., pitch) can be adjusted.

[0011] Thanks to variable fan blade pitch, the performance of the hybrid turbojet can be ensured, but with a limited low-pressure (LP) core speed range. In contrast, for a turbojet with fixed pitch (i.e., fixed blade orientation), the LP core speed range is almost doubled, which significantly impacts the size of the LP electric machine's electrical components and consequently contributes to increasing the turbojet's weight.

[0012] In prior art hybrid turbojets, it is known to directly connect the low-pressure (LP) electric machine to the low-pressure turbine by means of a common drive shaft. However, these turbojets are not optimized in terms of volume and mass: the LP electric machine and its control electronics remain relatively bulky and contribute to the turbojet's weight.

[0013] It may therefore be desirable to design a hybrid turbojet engine that overcomes at least some of the aforementioned problems and constraints. Thus, there is a need to reduce the overall mass of a prior art hybrid turbojet engine while maintaining the low-pressure electric machine at a constant power output. Summary of the invention

[0014] The invention includes in the hybrid turbojet a speed variator enabling a ratio switching between the low pressure turbine and a set of two LP electric machines stressed differently according to the low pressure regime of the engine (rotation speed of the shaft linked to the low pressure turbine).

[0015] More specifically, he therefore proposed a hybrid turbojet engine comprising: a low-pressure turbine; a first electric machine and a second electric machine, said electric machines being intended to together provide a constant power; an input shaft configured to be driven by the low-pressure turbine; a first output shaft configured to drive the first electric machine and a second output shaft configured to drive the second electric machine; a means of obtaining a rotational speed of the input shaft; a speed variator for adjusting the rotational speed of each output shaft according to the rotational speed of the input shaft, said variator comprising: a first planetary gear train including: - at the input, a planet carrier connected to the input shaft, a ring gear and at least one first planet carried by the planet carrier and engaged with the ring gear; - at the output, a first sun gear meshed with said at least one first planet gear and centered on the first output shaft, which is aligned with the input shaft, the first train having a first defined multiplication ratio between the rotational speed of the first output shaft and the rotational speed of the given input shaft and a first defined ratio between the crown and the first sun also given; a second planetary multiplying train comprising: - at the input, the crown, at least one satellite engaged with the crown and carried by a fixed axis, - at the output, a second sun meshed with the second satellite and centered on the second output shaft, which is aligned with the input shaft, the second train having a second multiplication ratio, defined between the rotational speed of the second output shaft and the rotational speed of the input shaft, lower than the first multiplication ratio defined for the first train and, a second ratio, defined between the crown and the second sun, identical to the first ratio defined for the first train, a means of locking the crown with two modes of operation, a first mode of operation in which the crown is locked and prevents any rotation of the second satellite carrier and therefore of the second electrical machine, and a second mode of operation in which the crown is left free; a calculator to compare the rotational speed obtained to a predetermined threshold and, when the rotational speed obtained is greater than said predetermined threshold, sends a control signal to the locking means to release the ring gear, and to the first electrical machine so that it could drive the first sun at a constant speed.

[0016] It is thus possible to limit the rotational speed range of one of the LP electric machines as well as the maximum torque value experienced by each of the electric machines, while delivering a constant overall electrical power (sum of the contribution of the two electric machines). This limitation of the speed range of at least one electric machine is significant and makes it possible to reduce the overall mass of the LP generator of the hybrid turbojet.

[0017] These characteristics also have the advantage of simplifying the architecture of the turbojet, in particular for the size and mass of the LP generator composed of two electrical machines, and of simplifying their control electronics.

[0018] The invention may further include one or more of the following optional features, in any technically feasible combination:

[0019] - the first planetary gear train is configured so that the first ratio of multiplication is equal to four and the first reason is equal to three, and in which the second planetary train is configured so that the second multiplication ratio is equal to at most two and the second reason is equal to three. - the turbojet engine includes at the inlet and in connection with the inlet shaft, a fan comprising a plurality of blades having a fixed orientation. - the means of obtaining the rotational speed of the input shaft is a speed sensor configured to measure the instantaneous rotational speed of the input shaft. - the predetermined threshold, preferably set at 5000 rpm, is defined as a function of a maximum speed, preferably of 20000 rpm for a multiplication ratio of four. - the means of locking the crown, which can be unlocked to allow the crown to move freely, is a braking device located on the second output shaft. - the means of locking the crown which can be unlocked to leave the crown free is the short-circuit torque of the second electrical machine on its own resistance. - the turbojet also includes an electrical inverter specific to each electrical machine, without a DC-DC converter.

[0020] The invention also relates to a method for controlling a turbojet engine as defined above, comprising the following steps: obtaining the rotational speed of the input shaft; compare the rotational speed thus obtained to the predetermined threshold; If the resulting rotational speed exceeds the predetermined threshold, send a control signal to the crown locking mechanism to release the crown. and towards the first electrical machine so that it could drive the first sun at a constant speed.

[0021] The invention also relates to a computer program product downloadable from a communication network and / or stored on a computer-readable medium, characterized in that it includes instructions for executing the steps of the process defined above, when said program is executed on a computer. Brief description of the figures

[0022] The invention will be better understood with the aid of the following description, given solely by way of example and made with reference to the accompanying drawings in which: - [Fig.1] illustrates a hybrid turbojet with variable speed drive according to an example of the invention, in a first mode of operation; - [Fig.2] illustrates the hybrid turbojet of [Fig.1] in a second operating mode; - [Fig.3] schematically illustrates a method of controlling the turbojet according to one embodiment of the invention; - Figure 4 illustrates results showing the speed behavior of the low-pressure turbine and the electrical machines of the hybrid turbojet engine according to a possible example; and - Fig. 5 illustrates other results showing the torque behavior of the low-pressure turbine and the electrical machines of the turbojet according to a possible example. Detailed description of the invention

[0023] With reference to [Fig.1] and [Fig.2], a hybrid turbojet 100 according to an embodiment of the invention will now be described.

[0024] The turbojet 100 comprises a low-pressure turbine 102, a first electric machine 104, a second electric machine 104' and a variable speed drive 106 mounted between the low-pressure turbine 102 and each electric machine 104, 104' so as to transfer mechanical power from the low-pressure turbine 102 to the two electric machines 104, 104'.

[0025] The turbojet 100 includes an input shaft a26 connected to the low-pressure turbine 102, so as to be driven by the latter.

[0026] Upstream of the low-pressure turbine 102, the turbojet 100 includes a fan 180 for injecting an air flow F. The fan 180 is connected to the inlet shaft a26.

[0027] The blower 180 comprises a plurality of blades 182. In the present example, the blower has a fixed pitch, meaning that the orientation of each of the blades 182 is fixed. However, within the framework of the invention, a blower with variable pitch could be provided.

[0028] The turbojet 100 includes a first output shaft a64 configured to drive the first electric machine 104 and a second output shaft a64' to drive the second electric machine 104'. Thus, each electric machine 104, 104' is driven by the low-pressure turbine 102 via the variable speed drive 106, unlike prior art hybrid turbojets where the electric machine is mounted directly on the low-pressure turbine 102.

[0029] The turbine 102 and the electrical machines 104, 104' are aligned along the same direction coinciding with the input shaft a26 and the output shafts a64, a64'.

[0030] The speed variator 106 is designed to adjust, on the one hand, the rotational speed coM E of the first electric machine 104 (i.e., the rotational speed of the output shaft a64) and, on the other hand, the rotational speed co'M E of the second electric machine 104' (i.e., the rotational speed of the output shaft a64') as a function of the rotational speed of the turbine 102 (i.e., the rotational speed coT of the input shaft a26).

[0031] The speed variator 106 comprises two planetary trains T1, T2, which are multiplying planetary trains, preferably epicyclic.

[0032] The first planetary train Tl includes at the input, a planet carrier 108 connected to the input shaft a26, a ring 112 and at least one first satellite 110 carried by the planet carrier 108 and retained by the ring 112.

[0033] The first planetary train Tl includes at the output, a first sun 130 meshed with the first satellite 110 and centered on the first output shaft a64, which is aligned with the input shaft a26.

[0034] The first planetary train Tl has a first defined multiplication ratio between the rotation speed of the first output shaft a64 and the rotation speed of the input shaft a26 given and a first defined ratio between the crown 112 and the first sun 130 also given.

[0035] The second planetary train T2 includes at the input, the ring 112, at least a second satellite 120 retained by the ring 112 and carried by a fixed axis AF.

[0036] The second planetary train T2 includes at the output, a second sun 140 meshed with the second satellite 120 and centered on the second output shaft a64', which is aligned with the input shaft a26.

[0037] The second planetary gear train T2 has a second multiplication ratio, defined between the rotational speed of the second output shaft a64' and the rotational speed of the input shaft a26, which is lower than the first multiplication ratio defined for the first gear train TL. This second gear train also has a second ratio, defined between the ring gear 112 and the second sun gear 140, which is identical to the first ratio defined for the first gear train TL.

[0038] As can be understood, the first satellite 110 is likely to be driven by a support shaft of the satellite carrier 108, while the second satellite 120 is likely to be driven by the ring 112. This ring 112 is common to the satellites 110, 120.

[0039] According to a particular feature of the invention, it will be noted that the two planetary gear trains T1, T2 have an identical ratio k. As a result, the torque at the first output shaft a64 of the first electric machine 104 is identical to the torque at the second output shaft a64' of the second electric machine 104'.

[0040] By definition, the reason k here refers to the relationship between the number of teeth of the crown 112 and the number of teeth of the sun 130, 140.

[0041] With the crown 112 blocked, the speed of the first output shaft a64 corresponds to the speed of the input shaft a26 multiplied by the ratio 1-k.

[0042] The speed variator 106 includes a means 160 for obtaining the rotational speed coT of the input shaft a26. For example, it may be a speed sensor 160 configured to measure the rotational speed coT of the input shaft a26. In alternative embodiments (not shown), the speed sensor may be disposed outside the speed variator 106, in which case the means for obtaining the speed includes an interface configured to retrieve the speed measurement from the sensor.

[0043] The turbojet 100 also includes a locking means MB for the ring gear 112, which can be unlocked to allow the ring gear to rotate freely. The locking means MB can be a mechanical means, such as a braking device located on the second output shaft a64', which thus applies a torque to the second electric machine 104'. Alternatively, however, it is possible to dispense with such a mechanical means for the ring gear 112, and for the locking means MB to be an electrical means, such as the application of a short-circuit torque from the second electric machine 104' to its own resistance. Other ways of implementing the locking means MB, which is schematically represented in Figures 1 and 2, can be considered.

[0044] The turbojet 100 further includes a computer 170 for comparing the rotational speed coT obtained for the input shaft a26 to a predetermined threshold cos and, when the rotational speed coT obtained is greater than said predetermined threshold cos, sends a control signal Sc to the locking means MB so that it leaves the ring gear 112 free and to the first electric machine 104 so that it drives the first sun 130, preferably at a constant speed. The computer 170 is therefore configured to retrieve data relating to the rotation of the turbine 102, such as the rotational speed coT of the input shaft a26. For example, the computer 170 may be a microcontroller comprising a processor, optionally a read-only memory (e.g., ROM), It includes random access memory (e.g., RAM), peripheral units, and input / output interfaces. The 170 control unit can be a full authority control unit or FADEC (Full Authority Digital Engine Control).

[0045] For example, the threshold rotation speed cos can be set at 5000 revolutions per minute (rpm) for a ratio k = 3, resulting in a multiplication ratio of 4 between the speed of the sun gear 130 and the speed of the input shaft a26 at low speed, with the ring gear 112 locked. This threshold of 5000 rpm corresponds to a speed of 20000 rpm of the sun gear 130 connected to the electric machine 104. This threshold allows for the definition of two operating modes of the speed controller 106 according to the invention: a first operating mode in which the ring gear 112 is locked ([Fig. 1]) by the locking means MB, and a second operating mode in which the ring gear 112 is unlocked ([Fig. 2]) and the speed of the sun gear 130 is controlled at a constant speed by the first electric machine 104.

[0046] The turbojet 100 further includes, for each electric machine 104, 104', an electric inverter or rectifier 190, 190' (or "AC / DC converter" in English) used to convert an alternating voltage V supplied at the output of the electric machine 104 into a direct voltage U.

[0047] According to a particular feature of the invention, no direct-direct current converter (DC / DC: "Direct Current to Direct Current") is preferentially associated with the electrical inverter 190, 190' unlike a conventional architecture integrating an electrical machine BP and electronics composed of an AC / DC inverter and a DC / DC converter.

[0048] A method for controlling the speed variator 106 of the turbojet 100 according to the invention will now be described with reference to [Fig.3].

[0049] During a measurement step 302, the instantaneous rotational speed coT of the input shaft a26 is measured by the speed sensor 160.

[0050] During a comparison step 304, the value of the instantaneous rotational speed coT of the input shaft a26 is retrieved and compared to the predetermined threshold cos by the computer 170.

[0051] During a test step 306, if the measured speed coT is greater than the predetermined threshold cos, the computer 170 determines that the ring 112 must be released. By default, i.e., below this threshold, the locking means MB (the braking element, or alternatively the short-circuit torque of the electric machine 104' on its own resistance) locks the ring 112. The computer 170 generates and sends, during a control step 308, a first control signal Sc to said means MB. blocking, to leave the 112 ring free. In the event that the threshold is not reached, the speed coT is still measured.

[0052] The steps of the process described above are repeated, as soon as a new value of rotational speed coT is measured by the speed sensor 160.

[0053] In the present example, steps 304, 306, 308 are implemented by the computer 170 by means of a computer program product P stored as instructions in a memory of the computer 170.

[0054] Fig. 4 illustrates results allowing representation of the behavior of the hybrid turbojet according to the invention, in particular in relation to the prior art.

[0055] A first curve Cl (solid lines) represents the rotational speed coME of the first electric machine 104, expressed in revolutions per minute (rpm) on the left ordinate, as a function of the rotational speed coT of the low-pressure turbine 102, expressed in revolutions per minute (rpm) on the abscissa for the turbojet 100 according to the invention.

[0056] A second curve C2 (solid lines) represents the rotational speed coME of the second electric machine 104', expressed in revolutions per minute (rpm) on the left ordinate, as a function of the rotational speed coT of the low-pressure turbine 102, expressed in revolutions per minute (rpm) on the abscissa for the turbojet 100 according to the invention.

[0057] A third curve C3 (solid lines) represents the rotational speed of an equivalent (single) electrical machine but in the case of a conventional turbojet, i.e. where the turbine is directly connected to the electrical machine, i.e. without a speed variator.

[0058] A fourth curve C4 (dotted line) represents the electrical power P supplied at the output of the first electrical machine 104, expressed in kW on the right ordinate, as a function of the rotational speed of the turbine coT for a turbojet according to the invention.

[0059] A fifth curve C5 (dotted line) represents the electrical power P supplied at the output of the second electrical machine 104', expressed in kW on the right ordinate, as a function of the rotational speed of the turbine coT for a turbojet according to the invention.

[0060] A seventh curve C6 (dotted line) represents the electrical power P supplied at the output of the low-pressure turbine 102, expressed in kW on the right-hand axis, as a function of the turbine rotational speed coT for a turbojet engine according to the invention. This power is constant over the range of turbine shaft rotational speeds a26, here from 2000 to 10000 rpm.

[0061] The sum of the power supplied by the first electric machine 104 and the power supplied by the second electric machine 104' is constant and corresponds to the power supplied by the low pressure turbine.

[0062] Below the threshold speed of 5000 rpm (low engine speed, coT <cos), la couronne 112 est bloquée, la deuxième machine électrique 104’ ne fournit aucune puissance et seule la première machine électrique 104 est en fonctionnement. La puissance fournie par la première machine électrique 104 se confond donc avec celle de la turbine basse pression 102. Sur la courbe Cl, on observe d’ailleurs que le régime de la première machine électrique augmente, selon un rapport de quatre avec le régime de la turbine basse pression, et on observe sur la courbe C2 que ce régime reste à zéro.

[0063] From the threshold speed and beyond (high speed, cot>cüs), the ring gear 112 is unlocked, and the second electric machine 104' receives some of the power from the turbine. There is therefore a power distribution between the two electric machines 104 and 104'. On curve C1, we observe that the speed of the first electric machine 104 no longer increases. On the other hand, on curve C2, we observe the increase in the speed of the second electric machine by a ratio not exceeding two. The maximum speed thus reached by the second electric machine 104' finally reaches that of the first electric machine 104 at 20,000 rpm.

[0064] As shown in [Fig. 4], the variable speed drive 106 significantly reduces the speed range compared to the prior art. Indeed, for a prior art turbojet engine, i.e., without a variable speed drive, the speed range for the electric motor extends from 1860 to 10000 rpm, representing a factor of 5.4 between the minimum and maximum speeds of the electric motor. Thanks to the variable speed drive 106, the speed range of the electric motor 104 extends from 7440 to 20000 rpm, representing a factor of 2.7 between the minimum and maximum speeds of the electric motor 104, or a gain of 2 compared to the prior art in terms of speed reduction.

[0065] This gain is reflected in the wider voltage range supplied at the output of the electrical machines 104, 104'. Limiting the voltage range offers the advantage of eliminating the DC-DC converter used in conventional hybrid turbojets, which explains why the turbojet 100 according to one example of the invention comprises, for each electrical machine, an inverter 190, 190' without a DC-DC converter. Thus, the electrical architecture of the turbojet is simplified while reducing the size of each of the electrical machines 104, 104' by a factor of 4.

[0066] Fig. 5 illustrates other results allowing representation of the behavior of the hybrid turbojet according to the invention, in particular in relation to the prior art.

[0067] In this [Fig. 4], we find the curves Cl, C2 and C3 from [Fig. 3]. However, on the ordinates on the right, it is no longer the power that is expressed, but the torque in Nm

[0068] Thus, curve C40 expresses the torque supplied by the first electric machine 104 as a function of the speed, in rpm, of the low-pressure turbine 102. Curve C50, on the other hand, expresses the torque supplied by the second electric machine 104' as a function of the speed of the low-pressure turbine. Curves C40 and C50 coincide: the torque produced at each electric machine 104, 104' is therefore identical. This is due to the fact that, for each train T1, T2, the factors are identical.

[0069] Curve C60 expresses the torque supplied by the low-pressure turbine 102 at the shaft a26 as a function of the speed, in rpm, of the low-pressure turbine 102.

[0070] During the switching from the first operating mode (low speed) to the second operating mode (high speed), the torque seen by the second electric machine 104' is therefore equal to that of the low pressure turbine 102 at the threshold value (in the example 5000 rpm) at constant power, i.e. lower than that associated with the 1860 rpm speed and further reduced by a factor of 4. It is therefore understood that the recovery torque of the second electric machine in the second operating mode is a reduced torque of the torque at 1860 rpm (minimum speed of the low pressure turbine observable on [Fig.4]) by a factor of 5000 / 1860 (i.e. practically 3) and by a factor of 4, i.e. approximately 10.7. The second electric machine 104' and its inverter 190' will therefore be components with a mass reduced by a factor of approximately 9, compared to the electric machine BP and its associated electronic components of a conventional hybrid turbojet (i.e.without speed variator).

[0071] At low speed, it could also be shown, in our example, that the first electric machine 104 and its inverter 190 will be components with a mass reduced by a factor of about 3, in reference to the electric machine and its associated electronic components of a conventional hybrid turbojet (i.e. without a speed variator).

[0072] Thus, to cover the same range of rotational speed of the electric machine, the present invention has the advantage of reducing the mass and size of the electric machine and its control electronics.

[0073] It should also be noted that the invention is not limited to the embodiments described above.

Claims

1. Demands Hybrid turbojet (100) comprising: - a low pressure turbine (102); - a first electrical machine (104) and a second electrical machine (104'), said electrical machines (104, 104') being intended to provide together a constant power; - an input shaft (a26) configured to be driven by the low-pressure turbine (102); - a first output shaft (a64) configured to drive the first electric machine (104) and a second output shaft (a64') configured to drive the second electric machine (104'); - a means of obtaining (160) a rotation speed (œT) of the input shaft (a26); - a speed variator (106) for adjusting the rotational speed of each output shaft (a64, a64') according to the rotational speed (œT) of the input shaft (a26), said variator (106) comprising: • a first planetary multiplying train (Tl) comprising: - at the input, a satellite carrier (108) connected to the input shaft (a26), a ring (112) and at least one first satellite (110) carried by the satellite carrier (108) and engaged with the ring (112); - at the output, a first sun (130) meshed with said at least one first satellite (110) and centered on the first output tree (a64), which is aligned with the input tree (a26), the first train (Tl) having a first defined multiplication ratio between the rotation speed of the first output shaft (a64) and the rotation speed of the input shaft (a26) given and a first defined ratio between the crown (112) and the first sun (130) also given; • a second planetary gear train (T2) comprising: - at the input, the crown (112), at least one second satellite (120) engaged with the crown (112) and carried by a fixed axis (AF), - at the output, a second sun gear (140) meshed with the second satellite (120) and centered on the second output shaft (a64'), which is aligned with the input shaft (a26), the second gear train (T2) having a second multiplication ratio, defined between the rotational speed of the second output shaft (a64) and the rotational speed of the input shaft (a26), lower than the first multiplication ratio defined for the first gear train (T1), and a second ratio, defined between the crown (112) and the second sun gear (130), identical to the first ratio defined for the first gear train (T1), • a means (MB) for locking the crown (112) with two operating modes, a first operating mode in which the crown (112) is locked and prevents any rotation of the second satellite (120) and therefore of the second electric machine (104'),and a second operating mode in which the ring (112) is left free; • a computer (170) to compare the rotational speed (œT) obtained to a predetermined threshold (œs) and, when the rotational speed (œT) obtained is greater than said predetermined threshold (cos), send a control signal (Sc) to the blocking means (MB) to leave the ring (112) free, and to the first electric machine (104) so ​​that it drives the first sun (130) at a constant speed.

2. Turbojet (100) according to claim 1, wherein the first planetary gear train (T1) is configured such that the first multiplication ratio is equal to four and the first ratio is equal to three, and wherein the second planetary gear train (T2) is configured such that the second multiplication ratio is equal to at most two and the second ratio is equal to three.

3. Turbojet (100) according to any one of claims 1 or 2, comprising at the inlet of the turbojet (100) and in connection with the inlet shaft (a26), a fan (180) comprising a plurality of blades (182) having a fixed orientation.

4. Turbojet (100) according to any one of claims 1 to 3, wherein the means for obtaining the rotational speed (coT) of the input shaft (a26) is a speed sensor configured to measure the instantaneous rotational speed of the input shaft (a26).

5. Turbojet (100) according to any one of claims 1 to 4, wherein the predetermined threshold (cos), preferably fixed at 5000 rpm, is defined as a function of a maximum speed, preferably of 20000 rpm for a multiplication ratio of four.

6. Turbojet (100) according to any one of claims 1 to 5, wherein the ring locking means (MB) (112) capable of being unlocked to leave the ring free is a braking element disposed on the second output shaft (a64').

7. Turbojet (100) according to any one of claims 1 to 5, wherein the ring (112) locking means (MB) capable of being unlocked to leave the ring free is the short-circuit torque of the second electrical machine (104') on its own resistance.

8. Turbojet (100) according to any one of claims 1 to 7, further comprising an electrical inverter (190, 190') specific to each electrical machine, without a DC-DC converter.

9. A method for controlling a turbojet (100) according to any one of claims 1 to 8, comprising the following steps: - obtaining (302) the rotational speed (œT) of the input shaft (a26); - comparing (304) the rotational speed (œT) thus obtained to the predetermined threshold (cos); - if the rotational speed (œT) obtained is greater than the predetermined threshold, sending (308) a control signal (S c) to the ring locking means (MB) (112) to leave the ring free and to the first electric machine (104) so ​​that the latter drives the first sun (130) at a constant speed.

10. Product computer program (P) downloadable from a communication network and / or stored on a computer-readable medium, characterized in that it includes instructions for carrying out the steps of the process according to claim 9, when said program (P) is executed on a computer (170).

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