Free turbine turbine including equipment driven by a free turbine

Abstract

A turbomachine is disclosed, comprising: a gas generator (13) provided with a first shaft (18); at least one reversible electric machine (11); a free turbine (12) provided with a second shaft (17) and caused to rotate by the gas flow generated by the gas generator (13); an accessory gearbox (14); and at least one accessory (15, 16). During all operating phases of the turbomachine (10), the at least one electric machine (11) is mechanically coupled to the second mechanical shaft (17) via the accessory gearbox (14), the accessory gearbox (14) being coupled to the at least one accessory (15, 16), and the turbomachine (10) further comprising a single mechanical coupling device (20) for mechanically coupling the first mechanical shaft (18) to the accessory gearbox (14) in a first configuration and mechanically decoupling the first mechanical shaft (18) from the accessory gearbox (14) in a second configuration.

Description

Technical Field

[0001] The present invention relates to the general field of aeronautical free turbine turbomachines, in particular turbomachines for turbogenerators, and, more particularly, to a turbogenerator having a structure of such a turbomachine that enables the driving of equipment via the free turbine without impairing the operation of the equipment during the start-up of the turbomachine. 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 and the equipment. 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 and the various parts of the equipment connected thereto. 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] like Figure 1 As shown in Figure 1A free turbine type turbomachine according to the prior art is schematically shown 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 rotation of the shaft of the gas generator by the reversible electric machine operating in motor mode during the starting phase can also drive equipment (not shown in this figure) that can be driven by the shaft 2 via the accessory gearbox. This makes it possible to supply the turbine with fuel and oil and to circulate the air in the compressor 4 and thus bring compressed air into the combustion chamber 5 in order to start the combustion. This combustion then generates an air flow for rotating the turbine 6 of the gas turbine 3, after which the compressor 4 and the equipment are rotated by the turbine 6 without the assistance of the electric machine, which means that the gas generator 3 operates autonomously, reflecting the end of the starting phase of the turboshaft engine.

[0007] In addition, for Figure 1 The turbogenerator shown, coupled to a second electric machine 7 on the shaft 8 of a free turbine 9, makes it possible to meet high power generation needs.

[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] In such Figure 1 On the turbine shown, equipment such as fuel and oil pumps are mechanically connected to the shaft 2 of the gas generator 3 via an accessory gearbox.

[0010] Equipment that requires mechanical energy to be rotated, such as a pump, is also called an accessory and is usually mounted on an accessory gearbox including at least one gear train in order to regulate the rotation speed of the accessory.

[0011] Once the start-up phase is terminated, it is known to use the reversible electric machine in generator operation mode to generate non-propulsion electricity (e.g. 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 into electrical energy by the electric machine.

[0012] 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.

[0013] Figure 2 The evolution of the speed of the shaft 2 of the gas generator 3 is shown as a solid line and the evolution of the speed of the shaft 8 of the free turbine 9 is shown as 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 of exit from the start-up phase is also indicated.

[0014] For a turboshaft engine with a free turbine and a conventional starting system using a reversible electric machine, the mechanical power extracted from the shaft of the gas generator is used to generate electricity by means of the reversible electric machine 1 in generator operation mode, affecting the performance of the gas generator.

[0015] 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:

[0016] - it is not conducive to the optimization of the engine operating line by prohibiting the use of the compressor at the optimal pressure level;

[0017] - This reduces the stable performance and affects the specific consumption.

[0018] With this configuration, a solution that does not take mechanical power from the generator shaft in order to generate electricity consists in using an electric machine for the starting function with a clutch release system, and another electric machine for the generating function integrated with the free turbine shaft, e.g. Figure 1 As shown, this is disadvantageous in terms of weight and cost and is rarely used in practice.

[0019] A known structure is disclosed in document FR 2 929 324, which allows starting a free turbine turbine generator without adding a specific starter. Figure 1 This technical solution makes it possible to reduce the total weight and costs, and to increase the reliability of the turbogenerator, compared to a turbine including two electric machines. The technical solution described in this document consists in a switching system using two freewheels, which enables the start-up of the gas generator of a free turbine turboshaft engine, and then generates non-propulsive electricity by extracting mechanical energy from the free turbine shaft. The device remains driven via the gas generator and the accessory gearbox.

[0020] 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.

[0021] 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 at least an overdimensioning of the energy storage system in order to allow the electric machine to have sufficient energy to be able to rotate the entire kinematic chain (including the main rotor).

[0022] However, this system is not suitable for the case of a free turbine turbine generator of an electrically driven rotorcraft, where the shaft of the free turbine is not coupled to the rotor of the rotor of the aircraft. In other words, this system is relatively too heavy and complex for a free turbine turbine generator, where the inertia of the free turbine shafting is generally low.

[0023] In order to improve the performance of a free turbine turbine, it would also be advantageous to be able to drive all the equipment of the turbine via the free turbine. However, since the performance of the fuel pump is linked to its rotation speed, the evolution of the speed of the free turbine after the starting phase would not allow or strongly influence the design of the fuel system components to ensure a correct starting of the turbine. Summary of the invention

[0024] To this end, the invention proposes a free turbine turbine driving one or more electric machines of sufficient power, equipped with a simplified switching system capable of optimizing weight, costs and reliability.

[0025] For the purpose of the present invention, a turbomachine is disclosed, comprising: a gas generator equipped with a first mechanical shaft; at least one reversible electric machine; a free turbine equipped with a second mechanical shaft and caused to rotate by the gas flow generated by the gas generator; an accessory gearbox; and at least one accessory connected to the accessory gearbox.

[0026] According to the technical features of the present invention, during all operating phases of the turbine, the electric machine is mechanically coupled to the second mechanical shaft via the accessory gearbox, and the turbine further comprises a single mechanical coupling device for mechanically coupling the first mechanical shaft to the accessory gearbox in a first configuration and mechanically decoupling the first mechanical shaft from the accessory gearbox in a second configuration, the size of the electric machine being determined to drive the gas generator, the free turbine and the at least one accessory during startup of the turbine.

[0027] The turbine according to the invention comprises an electric machine and a single free wheel, thus making it possible to use the electric machine reciprocally for the starting function of the gas generator and for high power generation, and to enable the free turbine to drive the accessories once the turbine has started. In fact, it makes it possible to start the rotation of the accessories (free turbine and gas generator) simultaneously, until the gas generator can operate autonomously, and then to continue driving the free turbine and the accessories until the free turbine can also operate autonomously. Once the free turbine is in autonomous rotation, the electric machine can operate in generator mode and, thus, supply power to the other elements.

[0028] The structure of the turbine according to the invention thus 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.

[0029] In a turbo-generator application of a turbomachine, one or more electric machines are sized to produce high levels of electrical power (e.g. for propulsion) and, when used in motor mode, can easily deliver the torque required to drive the gas generator, the free turbine and the equipment during the start-up phase. Indeed, in such an application, the inertia of the free turbine shafting is low, since it is not coupled to the helicopter rotor, such as only the power train and rotor of the electric machine.

[0030] Furthermore, the structure according to the invention makes it possible to directly affect the drive of the accessories (including the fuel pump) in the event of a breakage of the free turbine shaft during operation, with the direct effect of immediately shutting down the motor and thus limiting the overspeed of the free turbine. This structure has the effect of protecting the free turbine from overspeed.

[0031] According to the first aspect of the turbomachine, the turbomachine may further comprise a control unit of the electric machine, the control unit being configured to place the electric machine in motor mode during startup of the turbomachine and in generator mode when the speed of the first mechanical shaft exceeds a speed threshold for exiting the startup phase.

[0032] Once the gas generator has reached a speed enabling its autonomous operation, by decoupling the gas generator from the accessory gearbox, the electrical energy to be delivered by the electric machine (until autonomous operation of the free turbine) is reduced, since the amount of energy required now corresponds only to the amount of energy used to drive the free turbine and the accessories.

[0033] During the transition phase between autonomous operation of the gas generator and autonomous operation of the free turbine, the electric machine continues to operate in motor mode, but only for accessories and the free turbine, thus making it possible to keep the rotation speed of the equipment or accessories high enough to ensure their correct operation.

[0034] According to a second aspect of the turbomachine, the electric machine can be configured to operate in motor mode from a start-up phase of the turbomachine until an operating parameter of the second mechanical shaft or of said electric machine has exceeded a threshold value at which the free turbine is said to be autonomous. The value of the operating parameter corresponding to the threshold value at which the free turbine is autonomous is preferably greater than the value said operating parameter had when the first shaft reached a speed threshold for exiting the start-up phase. In other words, the threshold value at which the free turbine is autonomous is reached after a time when the gas generator has become autonomous. Once the parameter of the second mechanical shaft or of the electric machine has exceeded the threshold value at which the free turbine is autonomous, the electric machine is configured to operate in generator mode.

[0035] The start-up phase and the transition phase can be produced by controlling the torque or the speed.The operating parameter of the second mechanical axis can be its speed or its mechanical torque.

[0036] According to a third aspect of the turbomachine, the control unit is configured to control the electric machine in a motor mode:

[0037] - according to the rotation speed of the first and second mechanical shafts from the start-up of the turbine until the ignition of the gas generator, then

[0038] - according to the torque level required to drive the first mechanical shaft and the second mechanical shaft until the gas generator operates autonomously, and then

[0039] - depending on the rotational speeds of the first and second mechanical shafts, until said parameter of the second mechanical shaft has exceeded a threshold value at which the free turbine is autonomous,

[0040] The control unit controls the electric machine while interacting with the turbine's computer.

[0041] Speed ​​control before detecting ignition makes it possible to remain in the preferred ignition window, in other words the speed interval in which the chances of successful ignition are highest.

[0042] During the transition phase, in other words after the gas generator is decoupled and before entering generator mode of the electric machine, speed control makes it possible to maintain a constant speed during the transition by compensating for torque variations on the accessories coupled to the accessory gearbox.

[0043] As the torque delivered by the free turbine increases, the torque provided by the electric machine will decrease during the transition phase until it is eventually offset.

[0044] According to a fourth aspect of the turbomachine, the mechanical coupling arrangement may comprise a free wheel.

[0045] According to a fifth aspect of the turbomachine, the coupling device may be accommodated in a housing of the accessory gearbox.

[0046] The pinion of the accessory gearbox thus makes it possible to adjust the speed of the device mechanically coupled to the first mechanical shaft, in other words to the gas generator, such as a fuel pump or oil pump, and also ensures that, starting from 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.

[0047] According to a seventh aspect of the turbomachine, the accessory gearbox may be configured to vary a gear ratio between the free turbine and the gas generator when the mechanical coupling is in its first configuration.

[0048] According to a seventh aspect of the turbomachine, an accessory gearbox may be arranged and connectable between the mechanical coupling device and the second mechanical shaft.

[0049] The accessory gearbox makes 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 the auxiliary functions are incorporated.

[0050] This configuration makes it possible to improve the efficiency of ventilation after the engine is shut down, the two shafts being driven simultaneously.

[0051] According to a seventh aspect of the turbomachine, the turbomachine may further comprise an additional accessory gearbox connected to the first shaft for permanently and directly coupling an additional accessory to the gas generator. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 What has been described is a simplified schematic diagram of a free turbine turbine according to the prior art.

[0053] Figure 2 What has been described is Figure 1 Graph of the evolution of the speed of the shaft of the gas generator of a turbomachine and of the speed of the shaft of the free turbine as a function of time and of possible configurations of the turbogenerator.

[0054] Figure 3 is a diagram of a free turbine turbine according to an embodiment of the present invention.

[0055] Figure 4 A method for controlling the Figure 3 Logic diagram of the method of starting up of a turbine.

[0056] Figure 5 yes Figure 3 Graph of the evolution of the speed of the shaft of the gas generator of a turbomachine and of the speed of the shaft of the free turbine as a function of time and of possible configurations of the turbogenerator. DETAILED DESCRIPTION

[0057] Figure 3 A free turbine turbine 10 according to an embodiment of the invention is schematically illustrated.

[0058] 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 .

[0059] The free turbine 12 comprises a shaft 17 which is permanently mechanically connected to the accessory gearbox 14. The accessory gearbox 14 is mechanically coupled to the electric machine 11. The kinematic chain between the electric machine 11 and the free turbine 12 therefore does not comprise any decoupling means, making it possible to couple the turbine 12 to the electric machine 11 during all operating phases of the turbine 10, in particular during the starting phase and the power generation phase.

[0060] The accessory gearbox 14 is also mechanically coupled to both the fuel pump 15 and the oil pump 16. In other embodiments, other accessories may be mechanically coupled to the accessory gearbox 14.

[0061] The gas generator 13 comprises a shaft 18 connected and mechanically coupled to the accessory gearbox 14 via a single mechanical coupling device 20. The single mechanical coupling device 20 is configured for mechanically coupling the shaft 18 of the gas generator 13 to the accessory gearbox 14 in a first configuration and for mechanically decoupling the shaft 18 of the gas generator 13 from the accessory gearbox 14 in a second configuration, in order in particular to decouple the shaft 18 of the gas generator from the shaft 17 and the electric machine 11. The shaft 18 of the gas generator 13 is thus selectively coupled to the electric machine 11 via the accessory gearbox 14.

[0062] The mechanical coupling device 20 comprises a freewheel.

[0063] The turbine 10 further comprises a control unit 30 of the electrical machine 11 configured to place the electrical machine 11 in motor mode during a start-up phase of the turbine 10 and in generator mode when it detects that the free turbine is capable of operating autonomously.

[0064] The coupling device 20 is mechanically configured to mechanically couple the electric machine 11 to the gas generator 13 via the shaft 18 during startup of the turbomachine 10 .

[0065] Furthermore, the coupling device 20 is mechanically configured to decouple the gas generator from the electric machine 11 as soon as the gas generator 13 reaches a speed threshold for exiting the start-up phase.

[0066] Figure 4 A logic diagram of a method for controlling startup of a turbomachine 10 according to an embodiment of the present invention is shown.

[0067] Figure 5 The diagram shows the use of Figure 4 During the startup of the method, the solid line shows Figure 3 The speed of the shaft 18 of the gas generator 13 is shown in dashed lines. Figure 3 Evolution of the speed of the shaft 17 of the free turbine 12 of the turbomachine 10 as a function of time and of possible configurations of the turbogenerator.

[0068] The method for starting the turbomachine 10 comprises a first step 405 in which the electric machine 11 is placed in motor mode and started so as to start the rotation of the shafts 17 and 18 of the free turbine 12 and the gas generator 13 via the accessory gearbox 14. In fact, during the rotation of the accessory gearbox 14 by the electric machine 11, the mechanical coupling device 20, which may be a freewheel, automatically transmits the torque required for rotating the gas generator 13. Starting from the start of the electric machine 11 in the first step 405, the electric machine 11 is controlled, for example by the control unit 30, and then in a second step 410, according to the rotation speed of its mechanical shaft coupled to the accessory gearbox 14, so that the rotation speed of the shaft 17 of the gas generator 13 remains in the ignition window, in other words, in a specified speed range for maximizing the chances of successful ignition of the gas generator combustion chamber. For this control, the control unit 30 may comprise an electronic processing unit, such as a computer, and receives information about the speed of the shaft of the electric machine 11 or of the shaft 17 of the gas generator 13, the two speeds being proportional to each other, with a conversion factor specific to the gear train of the accessory gearbox 14.

[0069] In a third step 415, it is checked whether the combustion chamber of the gas generator 13 is ignited. As long as the ignition of the gas generator 13 is not detected, the speed control of the electric motor 11 is maintained.

[0070] On the other hand, once the ignition of the gas generator 13 is detected in step 415 , in a fourth step 420 , the torque of the electric motor 11 is controlled according to a predetermined curve of torque as a function of the rotation speed of the electric motor 11 .

[0071] In a fifth step 425, the rotational speed of the shaft 18 of the gas generator is compared with a threshold value for autonomous operation of the gas generator. For example, the threshold value for autonomous operation of the gas generator 13 is defined relative to the value of the rotational speed at which the gas generator can operate autonomously. As long as the rotational speed of the shaft 18 of the gas generator 13 has not reached a value corresponding to the threshold value for autonomous operation of the gas generator 13, the torque control of the electric machine 11 is continued in the fourth step 420.

[0072] On the other hand, once the threshold is reached, in a sixth step 430 , the motor 11 is speed controlled according to a threshold enabling correct operation of accessories such as the fuel pump 15 and the oil pump 16 , and the power drawn from the grid is limited.

[0073] In a seventh step 435, a comparison is made, for example, between the torque level delivered by the electric machine and / or its rotational speed at a corresponding threshold at which the free turbine can operate autonomously, in other words at which the flow delivered by the gas generator 13 is sufficient to cause a rotation of the free turbine 12 or to accelerate it. As long as the power available on the free turbine 12 does not allow the torque delivered by the electric machine to be reduced, thus enabling it to maintain its setpoint speed, or as long as there is no positive variation in the rotational speed, the control of the electric machine 11 continues in the sixth step 420 according to the speed setpoint.

[0074] On the other hand, once the threshold is reached, in an eighth step 440, the electric machine 11 changes the operating mode. The electric machine 11 switches from the motor mode to the generator mode.

[0075] 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 is itself driven by the gas flow delivered by the gas generator 13 .

[0076] During the transition phase between the autonomous operation of the gas generator 13 and the autonomous operation of the free turbine 12, the electric machine 11 continues to operate in motor mode but only ensures the drive of the accessories and the free turbine 12, thus making it possible to keep the rotation speed of the equipment or accessories high enough to ensure their correct operation.

[0077] 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), comprising: A gas generator (13) equipped with a first mechanical shaft (18); at least one reversible electric machine (11); a free turbine (12) equipped with a second mechanical shaft (17) and caused to rotate by the gas flow generated by the gas generator (13); an accessory gearbox (14); and at least one accessory (15, 16) coupled to the accessory gearbox (14), Characterized in that during all operating phases of the turbine (10), the at least one reversible electric machine (11) is mechanically coupled to the second mechanical shaft (17) via an accessory gearbox (14), and the turbine (10) further comprises a single mechanical coupling device (20) for mechanically coupling the first mechanical shaft (18) to the accessory gearbox (14) in a first configuration and for mechanically decoupling the first mechanical shaft (18) from the accessory gearbox (14) in a second configuration, wherein the accessory gearbox (14) is arranged between the single mechanical coupling device (20) and the second mechanical shaft (17), and the at least one reversible electric machine (11) is sized to cause the gas generator (13), and the at least one accessory (15, 16) and the free turbine (12) to rotate during startup of the turbine (10).

2. The turbine (10) according to claim 1, further comprising a control unit (30) of the at least one reversible electrical machine (11), the control unit (30) being configured to place the at least one reversible electrical machine (11) in motor mode during startup of the turbine (10) and to place the at least one reversible electrical machine (11) in generator mode when it detects that the free turbine is capable of operating autonomously.

3. The turbine (10) according to claim 2, wherein: At least one reversible electrical machine (11) is configured to operate in motor mode from a start-up phase of the turbine (10) and until one of the mechanical parameters of the second mechanical shaft (17) or of the at least one reversible electrical machine (11) has exceeded a threshold at which the free turbine (12) is autonomous, once said parameter of the second mechanical shaft (17) or of the at least one reversible electrical machine (11) has exceeded a threshold at which the free turbine (12) is autonomous, said at least one reversible electrical machine is configured to operate in generator mode.

4. The turbine according to claim 3, wherein: The control unit (30) is configured to control at least one reversible electric machine (11) in motor mode: - according to the rotation speed of the first mechanical shaft (18) and the second mechanical shaft (17) from the start-up of the turbine (10) until the ignition of the gas generator (13), then - according to the torque level required to drive the first mechanical shaft (18) and the second mechanical shaft (17) until the gas generator (13) operates autonomously, then - depending on the rotational speeds of the first mechanical shaft (18) and the second mechanical shaft (17), until said parameter of the second mechanical shaft (17) has exceeded a threshold at which the free turbine (12) is autonomous.

5. The turbine (10) according to claim 1, wherein: The mechanical coupling device (20) comprises a free wheel.

6. The turbine (10) according to claim 1, wherein: The mechanical coupling device (20) is housed in the housing of the accessory gearbox (14).

7. The turbine (10) according to claim 1, wherein: The accessory gearbox (14) is configured to vary the gear ratio between the free turbine (12) and the gas generator (13) when the mechanical coupling device (20) is in its first configuration.

8. The turbine (10) according to claim 1, wherein: The accessory gearbox (14) is arranged and connectable between the mechanical coupling device (20) and the second mechanical shaft (17).

9. The turbomachine according to claim 1, further comprising an additional accessory gearbox connected to the first mechanical shaft (18) for permanently coupling additional accessories directly to the gas generator (13).

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