Free turbine type turbine generator comprising a reversible electric machine coupled to a free turbine

Abstract

A turbogenerator (10) is disclosed, in particular for an electrically driven rotorcraft, comprising a gas generator (13) provided with a first shaft (18), at least one reversible electric machine (11) and a free turbine (12), the free turbine being provided with a second shaft (17) and being caused to rotate by the airflow generated by the gas generator (13). The second shaft (17) is coupled to the at least one electric machine (11) during all operating phases of the turbogenerator (10), and the turbogenerator (10) further comprises a single mechanical coupling device (20) for coupling the first mechanical shaft (18) to the second mechanical shaft (17) when the electric machine (11) is operating in motor mode, and for mechanically decoupling the first mechanical shaft (18) from the second mechanical shaft (17) when the electric machine (11) is operating in generator mode.

Description

Technical Field

[0001] The present invention relates to the general field of aviation turbomachines, and more particularly to switching between a gas generator and a free turbine of a free turbine type turbogenerator. Background Art

[0002] A free turbine turboshaft engine for a helicopter generally comprises a gas generator and a free turbine caused to rotate by the gas flow generated by the gas generator and a reversible electric machine which can be coupled to the gas generator, in particular in order to rotate the gas generator during the start-up phase of the turboshaft engine.

[0003] Conventionally, a gas generator comprises at least one compressor and a rotationally coupled turbine. The operating principle is as follows: the fresh air entering the turboshaft engine is compressed due to the rotation of the compressor before being sent to the combustion chamber, where it is mixed with fuel. The combusted gases are then discharged at high speed during combustion.

[0004] Then, there is a first expansion in the turbine of the gas generator, during which the gas generator obtains the energy necessary to drive the compressor. The turbine of the gas generator does not absorb all the kinetic energy of the combustion gases, and the excess kinetic energy corresponds to the air flow produced by the gas generator. This therefore provides kinetic energy to the free turbine, so that it produces a second expansion in the free turbine, which converts this kinetic energy into mechanical energy in order to drive a receiving member, such as the rotor of a helicopter.

[0005] During the start-up phase of a turboshaft engine, it is necessary to rotate the gas generator, in other words the compressor coupled to the turbine. As mentioned in the preamble, this is precisely one of the roles of a reversible electric machine, which is most often an electric motor capable of reversibly operating as a generator.

[0006] As shown in FIG. 1 , FIG. 1 schematically shows a free turbine type turbomachine according to the prior art, for starting in motor operation, the electric machine 1 driving the mechanical shaft 2 of the gas generator 3 until its rotation is maintained by the combustion of fuel. The shaft 8 of the free turbine 9 is mechanically decoupled from the shaft 2 of the gas generator, the electric machine 1 not driving the shaft 8. The free turbine 9 is then driven exclusively by the gas flow leaving the gas generator. Rotating the compressor by the electric machine 1 operating as a motor does indeed allow the air to circulate in the compressor 4 and thus bring compressed air into the combustion chamber 5 in order to start the combustion. This combustion then generates a gas flow for rotating the turbine 6 of the gas turbine 3, after which the compressor 4 is rotated directly by the turbine 6, which means that the gas generator 3 operates autonomously, reflecting the end of the startup phase of the turboshaft engine.

[0007] Furthermore, for the free turbine type turbine generator as shown in FIG. 1 , a second electric machine 7 may be provided, which is coupled to the shaft 8 of the free turbine 9 so that it can meet the needs of high power generation.

[0008] It is known that the aircraft in which such a turboshaft engine is particularly to be incorporated comprises many electrical components that need to be powered. For example, for an aircraft with vertical take-off and landing with electric propulsion, it is necessary to supply electricity to all the electric rotors with which the aircraft is equipped.

[0009] On a turbomachine as shown in FIG. 1 , equipment or accessories such as fuel pumps and oil pumps are mechanically connected to the shaft 2 of the gas generator 3 via an accessory gearbox.

[0010] Once the start-up phase is terminated, it is known to use the electric machine 1 in generator operation mode, if it is a reversible electric machine, to generate non-propulsion electricity (for example, 28V grid) in order to supply electrical equipment. The electric machine 1 generates electricity by taking mechanical power from the shaft 2 of the gas generator 3, the kinetic energy of the rotation taken from the gas generator being converted by said electric machine into electrical energy.

[0011] If no electrical power generation is required, the electrical machine 1 may be non-reversible and comprise a simple starter, such as a starter motor.

[0012] Figure 2 shows the evolution of the speed of the shaft 2 of the gas generator 3 in a solid line and of the speed of the shaft 8 of the free turbine 9 in a dashed line as a function of time and of a possible configuration of the turbogenerator. It can be seen that the evolution of the speeds of the two shafts is independent. The point corresponding to the time of exit from the start-up phase is also indicated.

[0013] For a turboshaft engine with a free turbine and a conventional starting system using a reversible electric machine, the mechanical power taken from the shaft of the gas generator is used to generate electricity by the reversible electric machine in generator operation mode, affecting the performance of the gas generator.

[0014] In fact, during flight, the changes in the mechanical power taken by the electric motor 1 and the equipment from the gas generator lead to a shift in the working line of the engine in the compressor sector. This shift corresponds to the pumping margin that must be provided, which results in:

[0015] - it is not conducive to the optimization of the engine operating line by prohibiting the use of the compressor at the optimal pressure level;

[0016] - This reduces the stable performance and affects the specific consumption.

[0017] With this configuration, a solution that does not take mechanical power from the generator shaft for electricity generation consists in using an electric motor for the starting function with a clutch release system and another electric motor for the electricity generation function integrated with the free turbine shaft, as shown in FIG1 , which is disadvantageous in terms of weight and cost and is rarely used in practice.

[0018] A known structure is disclosed in document FR 2 929 324, which allows starting a free turbine turbogenerator without adding a specific starter. This technical solution makes it possible to reduce the total weight and costs, and increase the reliability of the turbogenerator, compared to a turbomachine including two electric machines as in FIG. 1 . The technical solution described in this document consists in using a switching system of two free wheels, which enables starting of the gas generator of a free turbine turboshaft engine, and then generating non-propulsive electricity by extracting mechanical energy from the free turbine shaft. The device remains driven via the gas generator and the accessory box.

[0019] This solution makes it possible, in particular, to improve the transient performance of the gas generator by avoiding the disadvantages of extracting kinetic energy from the gas generator and, in particular, avoiding the problems of displacement of the working line of the engine in the compressor sector due to variations in the mechanical power extracted by the electric motor during flight.

[0020] In the context of a helicopter turbine, such a structure with two free wheels is advantageous in order not to drive the main rotor via the electric machine during the starting phase. Indeed, since the free turbine of the turbine is mechanically connected to the main rotor, a coupling between the shaft of the free turbine and the main rotor that cannot be decoupled during the starting phase would require oversizing the electric machine and the energy storage system in order to drive each component in rotation.

[0021] However, such a system remains relatively heavy, expensive and complex. However, it is not applicable to the case of a free turbine turbogenerator of an electrically driven rotorcraft, wherein the shaft of the free turbine is exclusively or substantially dedicated to supplying electrical energy through an electric machine of mechanical power taken from the shaft. In particular, this prior art system is not applicable to the case where the shaft of the free turbine is not coupled to a relatively high inertia mechanism such as, for example, the rotor of the rotor of the aircraft. In other words, such a system is too heavy and complex for a free turbine turbogenerator, wherein the inertia of the free turbine shafting is generally low. Summary of the invention

[0022] To this end, the invention proposes a free turbine type turbine driving one or more electric machines of sufficient power, equipped with a simplified switching system capable of optimizing weight, cost and reliability. The useful energy produced by the turbine becomes exclusively electrical and the free turbine is therefore only mechanically connected to the one or more electric machines.

[0023] For the purpose of the invention, a turbomachine is disclosed, comprising a gas generator equipped with a first mechanical shaft, at least one reversible electric machine, and a free turbine equipped with a second mechanical shaft and caused to rotate by the gas flow generated by the gas generator.

[0024] According to a technical feature of the invention, the second mechanical shaft is directly mechanically connected to the at least one electrical machine during all operating phases of the turbine, and the turbine further comprises a single mechanical coupling device configured to mechanically couple the first mechanical shaft to the second mechanical shaft in a first configuration and to mechanically decouple the first mechanical shaft from the second mechanical shaft in a second configuration. The electrical machine is sized to drive both the gas generator and the free turbine during startup of the turbine.

[0025] The structure of the turbine according to the invention therefore makes it possible to have only a single mechanical coupling device, such as a free wheel, which makes it possible to simplify the switching system and, in particular, to reduce weight and costs compared to known solutions while increasing its reliability.

[0026] In applications of turbine-generator type turbines, such as for electrically driven rotorcraft, the electric motor or motors are dimensioned to produce high levels of electricity (for propulsion energy) and to be able to easily deliver the high torque required for driving the gas generator and the free turbine during the start-up phase. In fact, in such applications, the inertia of the free turbine shafting is relatively low, since it is not coupled to a relatively high inertia mechanism, such as a helicopter main rotor. Thus, the low inertia of the shafting can substantially correspond to a power train with a rotor of an electric motor. Alternatively, the free turbine shaft can be coupled to a relatively low inertia mechanism, such as a rotor from a multi-rotor group of a rotor of an aircraft, while the wing assembly further comprises at least one rotor electrically driven by at least one generator of a turbine generator.

[0027] Generally, the use of a turbine of the turbogenerator type according to the invention does not prevent the free turbine from supplying mechanical energy in parallel with the electrical energy, when this mechanical energy remains relatively modest compared to the electrical energy produced.

[0028] According to the first aspect of the turbomachine, the turbomachine may preferably further comprise a control unit of the electric machine, the control unit being configured to place the electric machine in motor mode during start-up of the turbomachine and in generator mode when the gas generator becomes autonomous.

[0029] Preferably, the control unit may be configured to detect that the gas generator is autonomous when the speed of the first mechanical shaft exceeds a starting phase output speed threshold.

[0030] According to a second aspect of the turbomachine, the mechanical coupling arrangement may comprise a freewheel configured such that the first mechanical shaft rotates at a speed greater than a rotational speed of the second mechanical shaft when the first mechanical shaft is mechanically decoupled from the second mechanical shaft.

[0031] The free wheel may transfer power between the two shafts in one direction only. The gas generator may never drive the free turbine.

[0032] According to a third aspect of the turbine, the turbine may further include at least one intermediate pinion having a gear ratio different from number 1, the at least one intermediate pinion being installed between the freewheel and the second mechanical shaft and / or between the freewheel and the first mechanical shaft.

[0033] This makes it possible to adjust the rotational speed at the end of the freewheel and to connect two shafts that do not necessarily rotate at the same rotational speed.

[0034] The gear ratio is determined, for example, by technical considerations or by the need to extract power in order to drive accessories. But also to ensure that, outside the start-up phase, the input speed of the freewheel, in other words the input speed at the mechanical end of the freewheel coupled to the second mechanical shaft, is always less than the output speed of the freewheel, in other words the output speed at the mechanical end of the freewheel coupled to the first mechanical shaft. This is the case throughout the nominal operating range of the gas generator and the free turbine, and therefore outside the start-up phase. The goal is to ensure that the power of the free turbine cannot be transferred to the gas generator of the turbine engine that will produce the linkage.

[0035] One or more intermediate pinions make it possible to vary the gear ratio by taking into account its sign, in other words by offering the possibility of ensuring the ability of the two shafts to rotate in opposite directions, while ensuring that an auxiliary function is incorporated.

[0036] In one embodiment, the control unit may be configured to detect that the gas generator is autonomous when a torque exerted by the shaft of the free turbine on the output of the free wheel exceeds a torque threshold.

[0037] In another embodiment, the control unit may be configured to detect that the gas generator is autonomous when the input and output of the freewheel begin to rotate at different speeds.

[0038] According to a third aspect of the turbomachine, the turbomachine may further include an accessory box to which the piece of equipment is mechanically coupled.

[0039] The pinion of the accessory box thus makes it possible to vary the speed of an accessory, such as a fuel pump or an oil pump, which is mechanically coupled to the first mechanical shaft, in other words to the gas generator.

[0040] According to a fourth aspect of the turbine, where a free turbine type turbine uses only a single electric machine, the electric machine may be driven directly by the mechanical shaft of the free turbine, and preferably without the need for an intermediate power pinion.

[0041] Preferably, the electric machine may have a nominal rotational speed which is equal to or close to the nominal rotational speed of the free turbine.

[0042] This configuration makes it possible to improve the efficiency of ventilation after the engine is shut down, the two shafts being driven simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] FIG. 1 has already been described as a simplified schematic diagram of a free turbine turbine according to the prior art.

[0044] FIG. 2 has already been described as a diagram of the evolution of the speed of the shaft of the gas generator of the turbomachine of FIG. 1 and of the speed of the shaft of the free turbine as a function of time and of a possible configuration of the turbogenerator.

[0045] FIG. 3 is a diagram of a free turbine turbine according to an embodiment of the present invention.

[0046] 4 is a schematic diagram of a mechanical coupling arrangement between the electric machine, the gas generator and the free turbine of the turbine of FIG. 3 .

[0047] FIG. 5 is a diagram of the evolution of the speed of the shaft of the gas generator of the turbomachine of FIG. 3 and of the speed of the shaft of the free turbine as a function of time and of a possible configuration of the turbogenerator. DETAILED DESCRIPTION

[0048] FIG3 schematically shows a free turbine turbine 10 according to an embodiment of the present invention.

[0049] The turbomachine 10 includes an electric machine 11 , a free turbine 12 , a gas generator 13 , an accessory gearbox 14 , a fuel pump 15 , and an oil pump 16 .

[0050] The free turbine 12 comprises a shaft 17 that is mechanically permanently connected to the electric machine 11, in other words during all operating phases of the turbine 10, in particular the starting phase and the power generation phase. This mechanical connection between the electric machine 11 and the shaft 17 can be made directly, so that the shaft 17 and the rotor of the electric machine 11 rotate at the same speed. It can also be made indirectly, through a reduction gear, in such a way that a different rotation speed is obtained between these two components, in particular in the case where the nominal rotation speeds of these two components are provided to be different.

[0051] The accessory box 14 includes a plurality of mechanical output couplings, a first mechanical output coupling mechanically connected and coupled to the fuel pump 15 and a second mechanical output coupling mechanically connected and coupled to the oil pump 16. In other embodiments, other accessories may be mechanically coupled to other mechanical output couplings of the accessory box 14.

[0052] The gas generator 13 includes a shaft 18 that is permanently connected and mechanically coupled to the accessory box 14 .

[0053] The turbomachine 10 further comprises a single mechanical coupling device 20 configured to mechanically couple the shaft 18 of the gas generator 13 to the shaft 17 of the free turbine 12 in a first configuration and to mechanically decouple the two shafts 17 and 18 in a second configuration.

[0054] As shown in Fig. 4, a possible embodiment of the mechanical coupling device 20 includes a freewheel 21 and an intermediate pinion 22 mounted between the freewheel 21 and the shaft 18 of the gas generator 13. The freewheel 21 corresponds to a mechanical element of the mechanical coupling device 20, making it possible to couple the shaft 17 of the free turbine 12 to the shaft 18 of the gas generator 13, or not to couple to the shaft 18 of the gas generator 13. The intermediate pinion 22 includes two wheels 22A and 22B with different diameters mounted integrally on the same pinion shaft 22C, so as to have a gear ratio different from 1, and therefore a rotation speed of the shaft 17 of the free turbine 12 different from the rotation speed of the shaft 18 of the gas generator 13.

[0055] In the alternative in which the turbine is configured for counter-rotation of the shaft 17 of the free turbine 12 relative to the shaft 18 of the gas generator 13 , the mechanical coupling 20 would further comprise a transmission stage (such as an additional pinion) between the freewheel 21 and the intermediate pinion 22 .

[0056] As shown in FIG3 , the turbine 10 further comprises a control unit 30 of the electric machine 11, which is configured to place the electric machine 11 in motor mode during the start-up phase of the turbine 10 and to place the electric machine 11 in generator mode when the gas generator 13 becomes autonomous and therefore no longer needs to be driven by the electric machine 11. The detection of the autonomy of the gas generator by the control unit 30 can be performed by detecting the time when the speed of the shaft 18 of the gas generator 13 exceeds a so-called threshold of the output speed during the start-up phase. Alternatively, if the mechanical coupling device 20 comprises a freewheel, this detection by the control unit 30 can be performed by measuring the torque exerted by the shaft 17 of the free turbine on the output of the freewheel, the output of which is mechanically connected to the shaft 18 of the gas generator 13. If this torque is offset or becomes less than a threshold close to zero, this means that the electric machine 11 no longer drives the gas generator 13: it has become autonomous. As another alternative, this detection by the control unit 30 can be performed by detecting the time when the input and output of the freewheel begin to rotate at different speeds. In fact, when the gas generator 13 becomes autonomous, the output of the freewheel no longer rotates at the same speed as the input; it starts to rotate faster.

[0057] The coupling device 20 is mechanically configured to mechanically couple the electric machine 11 to the free turbine 12 and the gas generator 13 via the shafts 17 and 18 during the start-up of the turbomachine 10. In practice, the rotational speed at the output of the freewheel 21 (image of the rotational speed of the shaft 18) is zero or equal to the input speed of the freewheel 21 (image of the rotational speed of the shaft 17), the freewheel is connected, in other words mechanically engaged, and allows the torque to be transmitted between the shafts 17 and 18.

[0058] Furthermore, when the gas generator 13 becomes autonomous and reaches the start-up phase output speed threshold (the electric machine no longer starts as a motor), the coupling device 20 is mechanically configured to disconnect the two shafts 17 and 18. In fact, the electric machine 11 is no longer in "motor" mode and it will be driven by the free turbine 12, which will cause a speed difference at the end of the free wheel 21, causing it to be disconnected, in other words, causing it to be mechanically disengaged. The electric machine 11 can thus operate as a generator and generate electricity from the rotation of the shaft 17 of the free turbine 12, which is driven by the rotational movement of the free turbine 12, which itself is driven by the air flow delivered by the gas generator 13.

[0059] Alternatively, in a design corresponding to the diagram of FIG3 , it is possible to have an arrangement in which the mechanical output of the freewheel is coupled to the first mechanical shaft (the shaft 18 of the gas generator) via the accessory box 14. Thus, it is possible to couple this mechanical output directly to a pinion of the gear train of the accessory box, the shaft of the gas generator being coupled directly to another pinion of the same gear train, so that the gear ratio between the output of the freewheel and the shaft of the gas generator can be different from the number 1.

[0060] 5 shows in solid line the evolution of the speed of the shaft 2 of the gas generator 13 of FIG. 3 and in dashed line the speed of the shaft 17 of the free turbine 12 of the turbine 10 of FIG. 3 as a function of time and of a possible configuration of the turbogenerator.

[0061] By comparing the graph of Figure 2 with the graph of Figure 5, it can be seen that the structure of the turbine 10 according to the invention makes it possible to increase the speed of the gas generator 13 and the free turbine 12 simultaneously until the start-up phase output threshold is reached. After the start-up phase, the speed of the electric machine 11 can be temporarily reduced for the time when the power available at the free turbine is sufficient to drive the components (free turbine and electric machine) at a constant speed.

[0062] The free turbine turbine according to the invention thus makes it possible to optimize the weight, costs and reliability of the switching system and therefore of the turbine.

Claims

1. A turbine (10) of the free turbine turbogenerator type for use in an electrically driven rotorcraft or for the electrical power needs of an aircraft, comprising a gas generator (13) equipped with a first mechanical shaft (18), at least one reversible electric machine (11) and a free turbine (12) provided with a second mechanical shaft (17) and caused to rotate by the airflow generated by the gas generator (13), It is characterized in that The second mechanical shaft (17) is mechanically connected to the at least one reversible electrical machine (11) and the free turbine (12) during all operating phases of the turbomachine (10), and, The turbine (10) further comprises a single mechanical coupling device (20) configured for mechanically coupling the first mechanical shaft (18) to the second mechanical shaft (17) when at least one reversible electrical machine (11) is operated in motor mode, and for mechanically decoupling the first mechanical shaft (18) from the second mechanical shaft (17) when at least one reversible electrical machine (11) is operated in generator mode, the at least one reversible electrical machine (11) being sized to drive the gas generator (13) and the free turbine (12) during start-up of the turbine (10).

2. The turbine (10) according to claim 1, further comprising a control unit (30) of the at least one reversible electric machine (11), the control unit (30) being configured to place the at least one reversible electric machine (11) in motor mode during startup of the turbine (10) and to place the at least one reversible electric machine (11) in generator mode when the gas generator (13) becomes autonomous.

3. The turbine according to claim 2, wherein: The control unit (30) is configured to detect that the gas generator (13) is autonomous when the speed of the first mechanical shaft (18) exceeds a start-up phase output speed threshold.

4. The turbine (10) according to claim 1, wherein: The mechanical coupling device (20) comprises a freewheel (21) configured such that the first mechanical shaft (18) rotates at a speed greater than the rotational speed of the second mechanical shaft (17) when the first mechanical shaft (18) is mechanically decoupled from the second mechanical shaft (17).

5. The turbine (10) according to claim 4, further comprising at least one intermediate pinion (22) having a gear ratio different from the number 1, the at least one intermediate pinion (22) being mounted between the freewheel (21) and the second mechanical shaft (17) and / or between the freewheel (21) and the first mechanical shaft (18).

6. The turbine according to any one of claims 2 and 4, wherein: The control unit (30) is configured to detect that the gas generator (13) is autonomous when a torque applied by a second mechanical shaft (17) of the free turbine (12) on the output of the free wheel exceeds a torque threshold.

7. A turbine according to any one of claims 2 and 4, wherein: The control unit (30) is configured to detect that the gas generator (13) is autonomous when the input and output of the freewheel (21) begin to rotate at different speeds.

8. The turbomachine (10) of claim 1, further comprising an accessory box (14) mechanically coupled to the first machine shaft (18), and to which parts of the equipment (15, 16) are mechanically coupled.

9. The turbine (10) according to claim 8, wherein: The turbine (10) comprises a single reversible electric machine (11) which is driven directly by a second mechanical shaft (17) of a free turbine (12).

10. The turbine (10) according to claim 9, wherein: The reversible electric machine (11) has a nominal rotational speed which is equal to or close to the nominal rotational speed of the free turbine (12).

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