HYBRID TURBOJET ENGINE WITH VARIABLE SPEED DRIVE

Abstract

Hybrid turbojet engine comprising: an input shaft (a26) configured to be driven by a low-pressure turbine (102); an output shaft (a64) configured to drive an electrical machine (104); a speed variator (106) for adjusting the speed of the output shaft as a function of the speed of the input shaft, comprising: a first planetary gear train (T1) comprising, at the input, a planet carrier (108) connected to the input shaft, a first planet gear (110) and a first ring gear (112); - at the output, a first dog clutch sun gear (130); a second planetary gear train (T2) comprising, at the input, the planet carrier (108), a second ring gear (122) and a second planet gear (120); at the output, a second sun clutch (140); a sleeve (150) with dogs slidably mounted on the output shaft (a64) to be driven by the first sun clutch or the second sun clutch. Figure for the abstract: Fig. 1

Description

Title of the invention: HYBRID TURBOJET ENGINE WITH VARIABLE SPEED DRIVE Technical field of the invention

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

[0002] Climate change is a major concern for many legislative and regulatory bodies around the world. 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 circulation, requiring the implementation of technological solutions in order to make them compliant with current regulations. Civil aviation has been mobilizing for several years now to make a contribution to the fight against climate change.

[0003] Technological research efforts have already made it possible to significantly improve the environmental performance of aircraft. The Applicant takes into consideration the factors impacting all phases of design and development to obtain less energy-intensive, more environmentally friendly aeronautical components and products 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 using methods and operating virtuous development and manufacturing processes and minimizing greenhouse gas emissions to the minimum possible to reduce the environmental footprint of its activity.

[0004] This sustained research and development work covers new generations of aircraft engines, the lightening of aircraft, particularly through the materials used and lighter on-board equipment, the development of the use of electrical technologies to ensure propulsion, and finally aeronautical biofuels.

[0005] In this context, a hybrid turbojet engine has been proposed which has a propulsion configuration which combines both a traditional turbojet engine and at least one electric machine. For example, a so-called high pressure (HP) electric machine is capable of operating “in engine mode”, for example for the start-up phase, or of operating in generator mode, and a so-called low pressure (LP) electric machine additional can operate in engine mode and inject mechanical torque onto the low pressure body of the turbojet or operate in generator mode.

[0006] In a known manner, a hybrid turbojet engine for an aircraft incorporates at least one electrical machine capable of operating “in generator mode”, a function which can be provided by the HP electrical machine or by an additional LP electrical machine on a low pressure (LP) body of the turbojet engine.

[0007] The electric machine is thus 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 electric machine is used in “generator mode”, it is generally referred to as a “generator”. In practice, the electric machine is coupled with a turbine of the LP body called a low pressure turbine (LPT) by means of a rotating drive shaft to generate electrical energy used to electrically power the aircraft and potentially services. The sizing of the electric machine and its control electronics is conditioned by the extent of the rotational speed range of the electric machine so as to deliver a constant electrical power expressed in kW. Indeed, the wider this range, the larger the electric machine and contributes to making the turbojet heavier.

[0009] The turbojet engine comprises a fan, commonly referred to as a "fan" in English, i.e. a rotating member whose rotor is provided with blades which suck air into the turbojet engine. In a known manner, certain types of fans have blades whose orientation (i.e. the pitch) can be adjusted.

[0010] Thanks to a variable pitch of the fan blades, the performance of the hybrid turbojet can be improved but with a limited rotation speed range of the LP body. On the other hand, for a turbojet with fixed pitch (i.e. fixed orientation of the blades), the extent of the rotation speed range of the LP body is almost doubled, which considerably impacts the size of the electrical components of the LP electric machine and consequently contributes to making the turbojet heavier.

[0011] In hybrid turbojets of the prior art, it is known to directly connect the 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, since the LP electric machine and its control electronics remain relatively bulky and contribute to making the turbojet heavier.

[0012] It may thus be desired to provide a hybrid turbojet engine which makes it possible to overcome at least some of the aforementioned problems and constraints. Thus, there is a need to reduce the overall mass and size of a hybrid turbojet engine. the prior art while maintaining the LP electric machine at a constant power. Summary of the invention

[0013] The invention proposes a hybrid turbojet comprising a discontinuous speed variator making it possible to ensure a ratio switching between the low pressure turbine and a LP electric machine as a function of the low pressure speed of the engine (rotation speed of the shaft linked to the low pressure turbine).

[0014] A hybrid turbojet engine is therefore proposed comprising: - a low pressure turbine; - an electric machine, said electric machine being intended to provide constant power in generator mode; - an input shaft configured to be driven by the low pressure turbine; - an output shaft configured to drive the electric machine and aligned with the input shaft; - a means of obtaining a rotational speed of the input shaft; - a speed variator for adjusting the rotational speed of the output shaft as a function of the rotational speed of the input shaft, said variator comprising: a first planetary multiplier train comprising: at the input, a planet carrier connected to the input shaft, a first crown and at least one first planet carried by the planet carrier and engaged with the first crown; at the output, a first sun gear with claws meshed with said at least one first planet and centered on the output shaft, which is aligned with the input shaft, the first train having a first ratio defined between the first sun gear with claws and the first crown and a first multiplication ratio defined between the first sun gear with claws and the planet carrier; a second planetary multiplier train comprising: at the input, the planet carrier connected to the input shaft, the planet carrier being common to both trains, a second crown, and at least one second satellite carried by the planet carrier and engaged with the second crown; at the output, a second sun gear meshed with said at least one second satellite and centered on the output shaft; the second train having a second ratio defined between the second sun gear and the second crown and a second multiplication ratio defined between the second sun gear and the planet carrier; the first ratio being different from the second ratio and the second multiplication ratio being less than the first multiplication ratio, a dog sleeve slidably mounted on the output shaft with two operating modes, a first operating mode in which said dog sleeve is driven by the first dog sun and a second operating mode in which said dog sleeve is driven by the second dog sun; a computer configured to compare the measured speed to a predetermined threshold and to send a control signal to the electric machine in “motor” mode when the measured speed of the input shaft is greater than or equal to the predetermined threshold, so that the sleeve initially engaged with the first dog clutch in “generator” mode and then driven by the electric machine disengages from the first dog clutch and translates along the output shaft so as to engage with the second dog clutch.

[0015] It is thus possible to limit the range of rotation speeds as well as the maximum value of the torque seen by the LP electric machine (i.e. seen by the electric machine and its control electronics) by delivering a constant electrical power. This limitation makes it possible to reduce the mass of the LP electric machine of the hybrid turbojet.

[0016] These characteristics also have the advantage of simplifying the architecture of the turbojet, in particular for the LP electric machine, and of simplifying its control electronics.

[0017] The alignments of the two satellites along the input shaft and of the two suns along the output shaft taken in combination with the dog clutch sleeve advantageously allow the variator to modify the speed ratio between the input shaft and the output shaft, while maintaining a constant electrical power and without requiring additional active equipment. The energy necessary for the disengagement and / or engagement of the dog clutch being delivered by the LP electric machine, the variator preferably does not require any additional device.

[0018] The invention may further comprise one or more of the following optional features, in any technically possible combination.

[0019] - the turbojet engine further comprises an indexing mechanism configured to move to ensure the locking of the dog clutch sleeve either with the first dog clutch sun or with the second dog clutch sun. - the indexing mechanism comprises a spring whose elongation axis is parallel to an extension axis of the dog sleeve. - the first planetary gear is configured so that its ratio is equal to three and its multiplication ratio between the dog sun and the planet carrier is equal to four. - the second planetary gear is configured so that its ratio is equal to unity and its multiplication ratio between the dog sun and the planet carrier is equal to two. - the turbojet engine comprises at the inlet of the turbojet engine and in connection with the input shaft, a fan comprising a plurality of blades having a fixed orientation. - the means of obtaining is a speed sensor configured to measure the speed of instantaneous rotation of the input shaft. - the predetermined threshold, preferably set at 5000 rpm, is determined as a function of the maximum speed, preferably at 20,000 rpm, for a first multiplication ratio of 4 and a second multiplication ratio of 2. - the turbojet engine also includes an electric inverter without a DC-DC converter.

[0020] The invention also relates to a method for controlling the speed variator of the turbojet engine as defined above, the method comprising the following steps: - obtain the rotation speed of the input shaft; - compare the rotation speed obtained with a predetermined threshold; - generating and sending a control signal to the electrical machine so that the sleeve, initially engaged with the first dog clutch in generator mode, is translated along the output shaft so as to engage in motor mode with the second dog clutch when the measured speed of the input shaft is greater than or equal to said predetermined threshold.

[0021] The invention finally relates to a computer program product downloadable from a communication network and / or recorded on a computer-readable medium, characterized in that it comprises instructions for executing the steps of the method as defined previously, 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 with reference to the appended drawings in which: - [Fig. 1] illustrates an embodiment of a hybrid turbojet with variable speed drive according to the invention; - [Fig.2] is a three-dimensional exploded view illustrating an example of a dog clutch sleeve between two planetary gear sets; - [Fig.3] schematically illustrates a method for controlling the speed variator of the turbojet according to one embodiment of the invention; - [Fig.4] illustrates performance results of the turbojet engine of [Fig.l]; and - [Fig.5] illustrates an example of a change in the ratio of the speed variator implemented in the turbojet engine of [Fig.l]. Detailed description of the invention

[0023] With reference to [Fig.l], a hybrid turbojet 100 according to one embodiment of the invention will now be described.

[0024] The turbojet 100 comprises a low pressure turbine 102, a machine electric machine 104 and a speed variator 106 mounted between the turbine 102 and the electric machine 104 so as to transfer mechanical power from the turbine to the electric machine with, advantageously, the narrowest possible speed range seen by the electric machine 104. The electric machine 104 can also be called a low pressure electric machine or LP electric machine.

[0025] The turbojet 100 comprises an input shaft a26 connected to the low pressure turbine 102.

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

[0027] The fan 180 comprises a plurality of blades 182. In the present example, the fan has a fixed pitch, meaning that the orientation of each of the blades 182 is fixed.

[0028] The turbojet engine 100 comprises an output shaft a64 configured to drive the electric machine 104. Thus, the electric machine 104 is driven by the turbine 102 via the speed variator 106, unlike the hybrid turbojet engines of the prior art where the LP electric machine is mounted directly on the low pressure turbine 102 by the same drive shaft.

[0029] The turbine 102 and the electric machine 104 are aligned in the same direction coinciding with the input shaft a26 and the output shaft a64. Thus, the output shaft a64 is aligned with the input shaft a26.

[0030] The speed variator 106 is a discontinuous speed variator for adjusting the rotation speed coME of the electrical machine 104 (i.e. rotation speed of the output shaft a64) as a function of the rotation speed coT of the turbine 102 (i.e. rotation speed of the input shaft a26).

[0031] The speed variator 106 comprises two planetary gear sets T1, T2, preferably epicyclic, and a planet carrier 108 common to both sets. By convention, it is considered that the planet carrier is part of the first planetary gear set T1

[0032] The first planetary gear T1 comprises at the input at least one satellite 110 carried by the satellite carrier 108 and a first ring gear 112 configured to retain the first satellite 110.

[0033] The second planetary gear T2 comprises at the input a planet carrier 108 connected to the input shaft a26 and a second ring gear 122 configured to retain one or more planets 120, retained by the second ring gear.

[0034] The satellites 110, 120 are mounted on the same support shaft of the planet carrier 108, so that the planet carrier 108 is common to the two planetary gear sets T1, T2.

[0035] The first train T1 comprises at the output a first dog clutch sun 130 centered on the output shaft a64. Similarly, the second train T2 comprises at the output a second dog clutch sun 140 centered on the same output shaft a64, which is aligned with the input shaft a26. Thus, the first 130 and second 140 dog clutches are aligned with each other.

[0036] The first dog clutch sun 130 comprises a plurality of dogs 130c arranged on a face of the first sun opposite the speed variator 106. Similarly, the second dog clutch sun 140 comprises a plurality of dogs 140c arranged on a face opposite the speed variator 106.

[0037] According to a feature of the invention, the two planetary gears T1, T2 have a distinct reason.

[0038] By definition, the reason refers to the relationship between the number of teeth of the crown and the number of teeth of the sun (first dog sun 130 relative to the first crown 112, or second dog sun 140 relative to the second crown 122).

[0039] According to a feature of the invention, the two planetary gear sets T1, T2 are both multiplier gear sets and have a distinct multiplication ratio. Preferably, the second gear set T2 has a multiplication ratio lower than that of the first gear set T1.

[0040] In the present example, the first multiplier train T1 has a first ratio RI between the first dog clutch sun 130 and the first stationary ring 112 equal to three. This results in a first multiplication ratio M1 between the dog clutch sun 130 and the planet carrier 108 equal to four. The second multiplier planetary train T2 has a second ratio R2 between the second dog clutch sun 140 and the second stationary ring 122 equal to unity. This results in a second multiplication ratio M2 between the second dog clutch sun 140 and the planet carrier 108 equal to two.

[0041] This combination of reasons for the two planetary gears is particularly advantageous since it allows in the first operating mode (at low speed) to reduce the torque in a ratio 4 and to limit the maximum speed of the machine to 20000 rpm and in the second operating mode (at high speed) to also limit the maximum speed to 20000 rpm while reducing the speed range initially included in a ratio 5 (2000 rpm to 10000 rpm) to a ratio of 2.5 (8000 rpm to 20000 rpm). This reduction in the speed range has a significant impact on the size of the electric machine as well as on the size of the power electronics.

[0042] The variator 106 further comprises a dog clutch sleeve 150 disposed between the first T1 and second T2 gears. In particular, the sleeve 150 is slidably mounted on the output shaft a64 between the first dog clutch sun 130 of the first gear T1 and the second dog clutch sun 140 of the second gear T2.

[0043] With reference to [Fig.2], an example of a dog clutch sleeve 150 intended to be arranged between the first 130 and second 140 suns will now be described.

[0044] As previously described, the first 130 and second 140 suns and the dog sleeve 150 are all aligned with the output shaft a64, which is itself aligned with the input shaft a26.

[0045] The dog clutch sleeve 150 comprises a plurality of dogs 150c arranged on the two faces of the sleeve, i.e. respectively opposite the dogs 130c, 140c of the first and second planetary gear sets T1, T2 so as to couple with the dogs of one or other of the gear sets.

[0046] According to the perspective representation of [Fig.2], only the dogs 150c of the sleeve 150 opposite the first sun 130 appear, the dogs of the sleeve 150 opposite the second sun 140 being masked by the body of the sleeve 150. Similarly, the dogs of the first sun 130 are masked by the body of the first sun 130 but are similar to the dogs 140c of the second sun 140 which are visible.

[0047] The dogs 150c of the sleeve 150 are sized so that each of these dogs can be inserted between two consecutive dogs of one of the two suns 130, 140, when the sleeve 150 is translated towards the sun in question.

[0048] Returning to [Fig.l], the speed variator 106 comprises a means for obtaining a measurement of the rotational speed coT of the input shaft a26. In the present example, this is 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 arranged outside the speed variator 106, in which case the obtaining means may comprise an interface configured to retrieve the speed measurement from the sensor.

[0049] In the present example, the turbojet 100 further comprises a computer 170 connected to the speed sensor 106. The computer 170 is configured to recover data relating to the rotation of the turbine 102, such as the rotation speed coT of the input shaft a26. This computer 170 compares the measured speed coT to a predetermined threshold cos and sends to the electric machine BP a control signal, for example a pulse signal, when the measured speed coT of the input shaft a26 is greater or less than the predetermined threshold cos so that the sleeve 150 uncouples, translates and couples with the first sun 130 or the second sun 140. Under the control of the signal, the electric machine controlled in “motor” mode slows down or accelerates the rotation speed of the sleeve 150 relative to the speed of the coupled sun.The 170 calculator can correspond to a full authority regulation calculator or FADEC (for “Full Authority Digital Engine Control”).

[0050] By this difference in rotation speed, the flanks of the dogs 150c of the sleeve 150 are uncoupled from the flanks of the dogs 130c of the sun 130 or from the flanks of the dogs 140c of the sun 140, and are automatically brought into contact with the flanks inclined dogs of the same sun, so as to generate an axial displacement of the sleeve along a slide on the shaft a64 and in a direction D3 perpendicular to the output shaft a64.

[0051] The speed variator 106 further comprises an indexing mechanism 154 preferably comprising a spring. The spring has an elongation axis parallel to the extension axis of the dog sleeve 150. As will be seen below, the indexing mechanism 154 moves with the spring and cooperates with the dog sleeve 150, here with a tip 152 of the dog sleeve, to ensure the locking of the sleeve 150 sliding along the shaft a64 with the first dog sun 130 or with the second dog sun 140 after the switching phase.

[0052] In this example, the threshold rotation speed cos is set at 5000 revolutions per minute (rpm). However, this threshold value may be adjusted depending on the type of engine considered.

[0053] The turbojet 100 further comprises an inverter or electrical rectifier 190 (or “AC / DC converter” in English) used to convert an alternating voltage V supplied at the output of the electrical machine 104 into a direct voltage U.

[0054] According to a feature of the invention, no direct current to direct current (DC / DC) converter is associated with the electrical inverter 190, unlike a conventional architecture integrating an electrical machine connected to the low-pressure turbine and electronics composed of an AC / DC inverter and a DC / DC converter.

[0055] A method 300 for controlling a speed variator of a turbomachine according to the invention will now be described with reference to [Fig. 3]. The method 300 is for example implemented for controlling a speed variator 106 according to the example described above.

[0056] During a measurement step 302, the instantaneous rotation speed coT of the input shaft a26 is measured by the speed sensor 160.

[0057] During a comparison step 304, the value of the instantaneous rotation speed coT of the input shaft a26 is obtained and compared to the predetermined threshold cos by the computer 170.

[0058] In step 306, if the measured speed coT exceeds the predetermined threshold cos during an increase in the speed of the low-pressure turbine, i.e. coT > cos, the computer 170 sends a signal so as to increase the rotational speed of the sleeve 150 which will move ahead of the turbomachine and therefore of the sun 130 and will be driven away from the sun 130 by the configuration of the dogs to engage with the sun 140. In the example considered, we therefore move from gear 4 to gear 2. The movement observed will follow [Fig.5] (a, located on the left), [Fig.5] (b, located in the middle) and then [Fig.5] (c, located on the right).

[0059] Still in step 306, if the measured speed coT is this time lower than the predetermined threshold cos during a reduction in the speed of the low-pressure turbine, i.e. coT < cos, the computer 170 sends a signal so as to reduce the rotational speed of the sleeve 150 which will fall behind the turbomachine and will therefore be driven away from the sun 140 to engage with the sun 130. In the example considered, we then move from gear 2 to gear 4. The movement observed during this reduction in the speed of the low-pressure turbine will then follow, for example, [Fig.5] (c, located on the right), [Fig.5] (b, located in the middle) and then [Fig.5] (a, located on the left).

[0060] Steps 304, 306, 308 can be implemented by the computer 170 by means of a computer program P stored in the form of instructions in a memory of the computer 170.

[0061] [Fig.4] illustrates experimental results making it possible to estimate the performance of the hybrid turbojet according to the invention compared to the prior art.

[0062] A first curve Cl represents the rotation speed coME of the electrical machine 104, expressed in revolutions per minute (rpm) on the left ordinate, as a function of the rotation speed coT of the turbine 102, expressed in revolutions per minute (rpm) on the abscissa for the turbojet 100 according to the invention.

[0063] A second curve C2 represents the rotation speed of an equivalent electrical machine but in the case of a conventional turbojet (prior art), i.e. where the turbine is connected directly to the electrical machine, i.e. without a speed variator.

[0064] A third curve C3 represents the electrical power P supplied at the output of the electrical machine, expressed in kW on the right-hand ordinate, as a function of the turbine rotation speed coT for a turbojet engine according to the invention and a conventional turbojet engine. This curve C3 indicates that the power P is constant over the entire speed range and identical for both turbojet engines.

[0065] On the first curve C1, two operating modes of the hybrid turbojet 100 according to the invention are distinguished, corresponding to two distinct regimes, depending on the rotation speed coT of the turbine 102, i.e. a low regime BR such that coT < cos and a high regime HR such that coT > cos with cos = 5000 rpm.

[0066] It is assumed that the turbine 102 initially operates at low speed BR, in which case the dog clutch sleeve 150 is coupled with the first sun 130 (i.e. coT< cos=5000 rpm).

[0067] As illustrated in [Fig.5] (a, left), the dogs 150c of the sleeve 150 are, in this first operating mode (at low speed), held between the dogs 130c of the first sun 130. The dog-clutched sleeve 150 is driven by the turbine 102 and the sleeve in turn drives the electric machine 104 with a multiplier ratio equal to 4 by the output shaft a64.

[0068] Returning to [Fig.4], in this first mode of operation (at low speed), the input shaft a26 driven by the turbine 102 rotates at a speed coT of between 1860 and 5000 rpm at the input of the speed variator 106 (which corresponds to a torque of between 720 and 268 Nm), while the output shaft a64 driving the electric machine 104 rotates at a speed coME of between 7440 and 20000 rpm (which corresponds to a torque of between 178 and 67 Nm), as illustrated on the first curve Cl.

[0069] As soon as the rotation speed coT of the input shaft a26 measured by the speed sensor 160 reaches the predetermined threshold cos=5000 rpm, the dog clutch sleeve 150 moves as illustrated in figures 5 (b, in the middle) and 5 (c, on the right) which will now be described.

[0070] [Fig.5] (b, middle) illustrates the speed variator 106 in a phase of switching from a first operating mode (at low speed) to a second operating mode (at high speed), subsequent to the initial phase of [Fig.5] (a, left).

[0071] During this switching phase, an electric current is applied to the electric machine 104 so that it operates like a motor. Indeed, the change of speed during the switching phase by disengagement / engagement of dogs is obtained by controlling the electric machine 104 in motor mode for a period of time corresponding to this switching phase. In normal operation, the electric machine 104 operates in generator mode so as to supply electric current.

[0072] As illustrated, each of the dogs 130c of the first sun 130 has an inclined plane PI adapted to drive the dog 150c of the dog sleeve 150 on a stroke making it possible to modify the indexing in the direction of the second sun 140, so that the dogs 150c of the sleeve 150 couple with the dogs 140c of the second sun 140 in the final position as illustrated in [Fig.5] (c, on the right).

[0073] In this final position of [Fig.5] (c, right), the indexing mechanism 154 is positioned so as to keep the dog-clutch sleeve 150 coupled to the second sun 140.

[0074] The ratio switching carried out during the switching phase according to [Fig.5] (b, in the middle) has the effect of creating a change in regime presenting a discontinuity, precisely when the rotation speed of the input shaft is equal to the predetermined threshold (coT= «s) - This regime discontinuity appears on the first curve Cl of [Fig.4].

[0075] In the present example, the speed ratio between the low-pressure turbine 102 and the electric machine 104 has changed from four to two, as illustrated in [Fig. 4]. Indeed, the first curve Cl at high speed (coT>a>s) has a slope twice as low as at low speed (cot <cüs), signifiant que la vitesse de rotation the electric machine 104 is such that coME = 2.coT, i.e. twice as high as in the case where the speed variator 106 is not used as indicated by the second curve C2.

[0076] When the dog clutch sleeve 150 is coupled to the second sun 140 as illustrated in [Fig.5] (c, right), the input shaft a26 rotates at a speed coT of between 5000 and 10000 rpm (corresponding respectively to a torque of between 260 and 134 Nm), while the output shaft a64 driving the electric machine 104 rotates at a speed of between 10000 and 20000 rpm (corresponding respectively to a torque of between 134 and 67 Nm) as indicated on the first curve Cl of [Fig.4],

[0077] Thus, the speed variator 106 makes it possible to obtain rotation speeds of the electric machine 104 twice as high (20,000 rpm) compared to the prior art thanks to a change in the speed ratio (going from 4 to 2).

[0078] As shown in [Fig. 4], the speed variator 106 makes it possible to significantly reduce the extent of the speed range compared to the prior art. Indeed, for a turbojet of the prior art, i.e. without a speed variator, the speed range extends from 1860 to 10000 rpm, i.e. a factor of 5.4 between the minimum speed and the maximum speed of the electric machine. Thanks to the speed variator 106 according to the invention, the speed range of the electric machine 104 extends from 7440 to 20000 rpm, i.e. a factor of 2.7 between the minimum speed and the maximum speed of the electric machine 104, i.e. a gain of 2 compared to the prior art in terms of speed reduction.

[0079] This gain is found in the extent of the voltage range supplied at the output of the electrical machine 104. Limiting the extent of the voltage range offers the advantage of eliminating the direct-direct (DC / DC) converter implemented in conventional hybrid turbojets, which explains why the turbojet 100 of the invention comprises an inverter 190 without a DC-DC converter. Thus, the electrical architecture of the turbojet is simplified while reducing the size of the electrical machine and its control electronics.

[0080] In the present example described with reference to figures 1 and 4, the low pressure electric machine as well as its control electronics benefit from a factor equal to three in terms of mass reduction compared to a conventional electric machine, which is particularly advantageous in the field of aeronautics.

[0081] Thus, to cover the same rotation speed range of the electric machine, the present invention has the advantage of reducing the mass and size of the electric machine and its control electronics.

[0082] It will also be noted that the invention is not limited to the embodiments described above.

Claims

Claims

1. Hybrid turbojet (100) comprising: - a low pressure turbine (102); - an electric machine (104), said electric machine being intended to provide constant power in generator mode; - an input shaft (a26) configured to be driven by the low pressure turbine (102); - an output shaft (a64) configured to drive the electric machine (104) and aligned with the input shaft (a26); said turbojet (100) being characterized in that it further comprises: - a means for obtaining (160) a rotation speed (œT) of the input shaft (a26); - a speed variator (106) for adjusting the rotational speed of the output shaft (a64) as a function of the rotational speed (œT) of the input shaft (a26), said variator (106) comprising • a first planetary multiplier train (Tl) comprising: - at the input, a planet carrier (108) connected to the input shaft (a26), a first crown (112) and at least one first satellite (110) carried by the planet carrier (108) and engaged with the first crown (112); - at the output, a first dog sun (130) meshed with said at least one first satellite (110) and centered on the output shaft (a64), which is aligned with the input shaft (a26), the first train (Tl) having a first ratio (RI) defined between the first dog clutch sun (130) and the first crown (112) and a first multiplication ratio (Ml) defined between the first dog clutch sun (130) and the planet carrier (108); • a second planetary multiplier train (T2) comprising:

2. - at the input, the planet carrier (108) connected to the input shaft (a26), the planet carrier (108) being common to the two trains (T1, T2), a second crown (122), and at least one second satellite (120) carried by the planet carrier (108) and engaged with the second crown (122); - at the output, a second dog sun (140) meshed with said at least one second satellite (120) and centered on the output shaft (a64); the second train (T2) having a second ratio (R2) defined between the second dog clutch sun (140) and the second crown (120) and a second multiplication ratio (M2) defined between the second dog clutch sun (140) and the planet carrier (108); the first ratio (RI) being different from the second ratio (R2) and the second multiplication ratio (M2) being less than the first multiplication ratio (Ml), • a dog sleeve (150) slidably mounted on the output shaft (a64) with two operating modes, a first operating mode in which said dog sleeve (150) is driven by the first dog sun (130) and a second operating mode in which said dog sleeve (150) is driven by the second dog sun (140); • a calculator (170) configured to compare the measured speed (œT) with a predetermined threshold (cos) and to send to the electric machine (104) a control signal in “motor” mode when the measured speed (œT) of the input shaft (a26) is greater than or equal to the predetermined threshold (cos), so that the sleeve (150) initially engaged with the first dog clutch sun (130) in “generator” mode and then driven by the electric machine (104) disengages from the first dog clutch sun (130) and translates along the output shaft (a64) so ​​as to engage with the second dog clutch sun (140). The turbojet engine (100) of claim 1, further comprising an indexing mechanism (154) configured to move to provide locking the dog clutch sleeve (150) either with the first dog clutch sun (130) or with the second dog clutch sun (140).

3. A turbojet engine (100) according to claim 2, wherein the indexing mechanism (154) comprises a spring having an elongation axis parallel to an extension axis of the dog clutch sleeve (150).

4. Turbojet (100) according to any one of claims 1 to 3, wherein the first planetary gear (Tl) is configured so that its ratio (RI) is equal to three and its multiplication ratio (Ml) between the dog sun (130) and the planet carrier (108) is equal to four.

5. Turbojet (100) according to any one of claims 1 to 4, wherein the second planetary gear (T2) is configured so that its ratio (R2) is equal to unity and its multiplication ratio (M2) between the dog sun (140) and the planet carrier (108) is equal to two.

6. Turbojet (100) according to any one of claims 1 to 5, comprising at the inlet of the turbojet (100) and in connection with the input shaft (a26), a fan (180) comprising a plurality of blades (182) having a fixed orientation.

7. A turbojet engine (100) according to any one of claims 1 to 6, wherein the obtaining means (160) is a speed sensor (160) configured to measure the instantaneous rotational speed (œT) of the input shaft (a26).

8. A turbojet engine (100) according to any one of claims 1 to 7, further comprising an electrical inverter (190) without a DC-DC converter.

9. Method for controlling the speed variator (106) of the turbojet engine (100) according to any one of claims 1 to 7, comprising the following steps: - obtaining (302) the rotational speed (œT) of the input shaft (a26); - comparing (304) the obtained rotational speed (œT) with a predetermined threshold (cos); - generating and sending (308) a control signal (Sc; Sci,Sc2) to the electric machine (104) so ​​that the sleeve (150), initially engaged with the first dog clutch (130) in generator mode, is translated along the output shaft (a64) so ​​as to engage in motor mode with the second dog clutch (140) when the measured speed (œT) of the shaft input (a26) is greater than or equal to said predetermined threshold (cüs).

10. Computer program product (P) downloadable from a communication network and / or recorded on a computer-readable medium, characterized in that it comprises instructions for executing the steps of the method according to claim 9, when said program (P) is executed on a computer (170).

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