FREE TURBINE TURBOGENERATOR COMPRISING A REVERSIBLE ELECTRICAL MACHINE COUPLED TO THE FREE TURBINE

Abstract

Disclosed is a turbogenerator, in particular for an electrically-driven rotary wing aircraft, comprising a gas generator equipped with a first shaft, at least one reversible electrical machine, and a free turbine provided with a second shaft and caused to rotate by a gas flow generated by the gas generator. The second shaft is coupled to the at least one electrical machine during all phases of operation of the turbomachine, and the turbomachine further comprises a single mechanical coupling means for coupling the first mechanical shaft to the second mechanical shaft when the electrical machine is operating in motor mode and mechanically uncoupling the first mechanical shaft from the second mechanical shaft when the electrical machine is operating in generator mode.

Claims

1. A turbomachine of the free turbine turbogenerator type, in particular for an electrically-driven rotary wing aircraft or for the electrical power needs of an aircraft, comprising a gas generator equipped with a first shaft, at least one reversible electrical machine and a free turbine provided with a second mechanical shaft and caused to rotate by a gas flow generated by the gas generator, wherein said second mechanical shaft is mechanically connected to said at least one electrical machine during all phases of operation of the turbomachine, and the turbomachine further comprises a single mechanical coupling means configured to mechanically couple said first mechanical shaft to said second mechanical shaft when the electrical machine is operating in motor mode and mechanically uncoupling said first mechanical shaft from said second mechanical shaft when the electrical machine is operating in generator mode, the electrical machine being sized so as to drive the gas generator and the free turbine during start-up of the turbomachine.

2. The turbomachine according to claim 1, further comprising a control unit of the electrical machine, the control unit being configured to place the electrical machine in motor mode during start-up of the turbomachine, and to place the electrical machine in generator mode when the gas generator becomes autonomous.

3. The turbomachine according to claim 2, in which the control unit is configured to detect that the gas generator is autonomous when the speed of the first mechanical shaft exceeds a start-up phase output-speed threshold.

4. The turbomachine according to claim 1, in which the mechanical coupling means comprises a free wheel configured so that the first mechanical shaft, when it is mechanically uncoupled from the second mechanical shaft turns at a speed greater than the speed of rotation of the second mechanical shaft.

5. The turbomachine according to claim 4, further comprising at least one intermediate pinion having a gear ratio different from the number one, said at least one intermediate pinion being mounted between the free wheel and second mechanical shaft and/or between the free wheel and the first mechanical shaft.

6. The turbomachine according to claim 2, wherein the mechanical coupling means comprises a free wheel configured so that the first mechanical shaft, when it is mechanically uncoupled from the second mechanical shaft, turns at a speed greater than the speed of rotation of the second mechanical shaft, and in which the control unit is configured to detect that the gas generator is autonomous when the torque exerted by the shaft of the free turbine on the output of the free wheel exceeds a torque threshold.

7. The turbomachine according to claim 2, wherein the mechanical coupling means comprises a free wheel configured so that the first mechanical shaft, when it is mechanically uncoupled from the second mechanical shaft, turns at a speed greater than the speed of rotation of the second mechanical shaft, and in which the control unit is configured to detect that the gas generator is autonomous when the input and output of the free wheel start to rotate at different speeds.

8. The turbomachine according to claim 1, further comprising an accessories box mechanically coupled to the first mechanical shaft and to which items of equipment are mechanically coupled.

9. The turbomachine according to claim 8, in which the turbomachine comprises a single electrical machine, the electrical machine being driven directly by the mechanical shaft of the free turbine.

10. The turbomachine according to claim 9, in which the electrical machine has a nominal speed of rotation equal to or close to that of the free turbine.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0043] FIG. 1, already described, is a simplified schematic view of a free turbine turbomachine according to the prior art.

[0044] FIG. 2, already described, is a graphical representation of the evolution, as a function of time and of the possible configuration of the turbogenerator, of the speed of the shaft of the gas generator and of the speed of the shaft of the free turbine of the turbomachine of FIG. 1.

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

[0046] FIG. 4 is a schematic representation of the mechanical couplings between the electrical machine, the gas generator and the free turbine of the turbomachine of FIG. 3.

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

DESCRIPTION OF THE EMBODIMENTS

[0048] FIG. 3 schematically shows a free turbine turbomachine 10 according to an embodiment of the invention.

[0049] The turbomachine 10 comprises an electrical machine 11, a free turbine 12, a gas generator 13, an accessories box 14 and a fuel pump 15 and an oil pump 16.

[0050] The free turbine 12 comprises a shaft 17 permanently mechanically connected to the electrical machine 11, in other words during all the operating phases of the turbomachine 10, in particular the start-up phase and the electrical generation phase. This mechanical connection between the electrical machine 11 and the shaft 17 can be made directly, so that the shaft 17 and the rotor of the electrical machine 11 rotate at the same speed. It can also be made indirectly by means of a reduction gear in such a way as to obtain different speeds of rotation between the two members, in particular in the case where the nominal speeds of rotation of the two members are provided to be different.

[0051] The accessories box 14 comprises a plurality of mechanical output couplers, a first mechanical output coupler being mechanically connected and coupled to the fuel pump 15 and a second mechanical output coupler being mechanically coupled and connected to the oil pump 16. In other embodiments, other accessories can be mechanically coupled to other mechanical output couplers of the accessories box 14.

[0052] The gas generator 13 comprises a shaft 18 permanently connected and mechanically coupled to the accessories box 14.

[0053] The turbomachine 10 further comprises a single mechanical coupling means 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 uncouple the two shafts 17 and 18 in a second configuration.

[0054] As illustrated in FIG. 4, a possible embodiment of the mechanical coupling means 20 comprises a free wheel 21 and an intermediate pinion 22 mounted between the free wheel 21 and the shaft 18 of the gas generator 13. The free wheel 21 corresponds to the mechanical element of the mechanical coupling means 20 making it possible to couple, or not, the shaft 17 of the free turbine 12 to the shaft 18 of the gas generator 13. The intermediate pinion 22 comprises two wheels 22A and 22B of different diameters, integrally mounted on a same pinion axis 22C, in order to have a gear ratio different from 1 and thus to have a speed of rotation of the shaft 17 of the free turbine 12 that is different from the speed of rotation of the shaft 18 of the gas generator 13.

[0055] In an alternative where the turbomachine is configured by having the shaft 17 of the free turbine 12 counter-rotating with respect to the shaft 18 of the gas generator 13, the mechanical coupling means 20 would further comprise a transmission stage (such as an additional pinion) between the free wheel 21 and the intermediate pinion 22.

[0056] As this is illustrated in FIG. 3, the turbomachine 10 further comprises a control unit 30 of the electrical machine 11 configured to place the electrical machine 11 in a motor mode during a start-up phase of the turbomachine 10, and to place the electrical machine 11 in a generator mode when the gas generator 13 becomes autonomous and therefore no longer needs to be driven by the electrical machine 11. The detection of the autonomy of the gas generator by the control unit 30 can be made by detecting the time when the speed of the shaft 18 of the gas generator 13 exceeds a so-called start-up phase output-speed threshold. Alternatively, if the mechanical coupling means 20 comprise a free wheel, this detection by the control unit 30 can be made by measuring the torque exerted by the shaft 17 of the free turbine on the output of the free wheel mechanically connected to the shaft 18 of the gas generator 13. If this torque is cancelled or becomes less than a threshold close to zero, this means that the electrical machine 11 is no longer driving the gas generator 13: it has become autonomous. As another alternative, this detection by the control unit 30 can be carried out by detecting the time when the input and the output of the free wheel start to rotate at different speeds. Indeed, when the gas generator 13 becomes autonomous, the output of the free wheel no longer turns at the same speed as the input; it starts to rotate quicker.

[0057] The coupling means 20 are mechanically configured to mechanically couple the electrical machine 11 to the free turbine 12 and to the gas generator 13 via the shafts 17 and 18 during the start-up of the turbomachine 10. Indeed, the speed of rotation at output of the free wheel 21 (image of the speed of rotation of the shaft 18) being zero or equal to the input speed of the free wheel 21 (image of the speed of rotation of the shaft 17), the latter is connected, in other words mechanically engaged, and allows the transfer of torque between the shaft 17 and the shaft 18.

[0058] In addition, the coupling means 20 are mechanically configured to disconnect the two shafts 17 and 18 when the gas generator 13 becomes autonomous and reaches the start-up phase output-speed threshold (the electrical machine is no longer activated as a motor). Indeed, the electrical machine 11 being no longer in “motor” mode, it will be driven by the free turbine 12 which will cause a speed differential at the terminals of the free wheel 21 leading to its disconnection, in other words to its mechanical disengagement. Hence, the electrical machine 11 can operate as an electric generator and produce electrical power from the rotation of the shaft 17 of the free turbine 12 driven by the rotary movement of the free turbine 12, itself driven by the gas flow delivered by the gas generator 13.

[0059] Alternatively, in a design corresponding to the diagram of FIG. 3, it is possible to have an arrangement in which the mechanical output terminal of the free wheel is coupled to the first mechanical shaft (the shaft 18 of the gas generator) by means of the accessories box 14. Hence, it is possible to directly couple this mechanical output terminal to a pinion of a gear train of the accessories box, the shaft of the gas generator being directly coupled to another pinion of the same gear train, such that the gear ratio between the output of the free wheel and the shaft of the gas generator can be different to the number one.

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

[0061] By comparing the graph of FIG. 2 and that of FIG. 5, it can be seen that the architecture of the turbomachine 10 according to the invention enables a simultaneous increase in the speed of the gas generator 13 and of the free turbine 12 until the start-up phase output threshold is reached. The speed of rotation of the electrical machine 11 after the start-up phase can temporarily reduce the time that the power available at the free turbine can be sufficient for driving the assembly (free turbine and electrical machine) at constant speed.

[0062] The free turbine turbomachine according to the present invention thus makes it possible to optimise the weight, cost and reliability of the switching system and therefore of the turbomachine.