TURBOMACHINE WITH FREE TURBINE AND WITH A DEVICE DRIVED BY THE FREE TURBINE

Description

Technical Field

[0001] The present invention relates to the general field of aeronautical free turbine turbomachines, in particular for turbomotors or turbogenerators, and more particularly to an architecture of such a turbomachine allowing the driving of equipment via the free turbine without compromising the operation of the equipment during the start-up of the turbomachine. Previous technique

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

[0003] Traditionally, a gas generator consists of at least one compressor and one turbine coupled in rotation. The operating principle is as follows: fresh air entering the turboshaft engine is compressed by the rotation of the compressor before being sent to a combustion chamber where it is mixed with fuel. The exhaust gases from combustion are then expelled at high speed.

[0004] A first expansion then occurs in the gas generator turbine, during which it extracts the energy needed to drive the compressor and other equipment. The gas generator turbine does not absorb all the kinetic energy of the exhaust gases, and the excess kinetic energy corresponds to the gas flow generated by the gas generator. This gas flow then supplies kinetic energy to the free turbine, causing a second expansion in the free turbine. This second expansion transforms the kinetic energy into mechanical energy to drive a receiving component, such as the helicopter rotor.

[0005] During the startup phase of a turboshaft engine, or turbomachine in general, it is necessary to rotate the gas generator, that is, to rotate the compressor coupled to the turbine as well as the various connected components. As mentioned in the introduction, this is precisely one of the roles of the reversible electric machine, which is most often an electric motor capable of operating reversibly as an electric generator.

[0006] As illustrated on the figure 1This schematic diagram represents a turbomachine with a free turbine, according to the prior art. For startup, an electric machine 1, operating as a motor, drives the mechanical shaft 2 of the gas generator 3 until its rotation is sustained by fuel combustion. The rotation of the gas generator shaft by the reversible electric machine, operating as a motor during the startup phase, also allows for the drive of equipment, not shown in this figure, which can be driven by the shaft 2 via an accessory gearbox. This supplies the turbomachine with fuel and oil and circulates air through the compressor 4, thus supplying compressed air to the combustion chamber 5 to initiate combustion.This combustion then produces the gas flow which drives the turbine 6 of the gas turbine 3 into rotation, as a result of which the compressor 4 and the equipment are driven into rotation by the turbine 6 without the aid of the electric machine, which means that the gas generator 3 operates autonomously, reflecting the end of the start-up phase of the turbomachine.

[0007] Furthermore, for a turbomachine like the one illustrated on the figure 1 , a receiver 7 in contact with the shaft 8 of the free turbine 9, such as a second electric machine or a helicopter rotor possibly associated with a main transmission box, makes it possible to meet the need for mechanical power supply or high power generation.

[0008] On a turbomachine as illustrated on the figure 1Equipment such as the fuel pump and the oil pump are mechanically connected to shaft 2 of the gas generator 3 via the accessory box.

[0009] Equipment that requires mechanical energy to be drawn into rotation, for example pumps, is also called an accessory and is usually mounted on an accessory box which includes at least one gear train to adapt the rotational speeds of the accessories.

[0010] Once the start-up phase is complete, the reversible electric machine can be used in generator mode to produce non-propulsive electrical energy (e.g., a 28V network) to supply power to electrical equipment. The electric machine 1 generates electrical energy by drawing mechanical power from the shaft 2 of the gas generator 3; the rotational kinetic energy extracted from the gas generator is converted into electrical energy by the machine.

[0011] This electrical machine 1 can be non-reversible and consist of a simple starter, such as a starter, if there is no need for electrical generation.

[0012] On the figure 2The diagram illustrates the evolution, as a function of time and the possible configuration of the turbogenerator, of the speed of shaft 2 of the gas generator 3 (solid line) and the speed of shaft 8 of the free turbine 9 (dashed line). It can be seen that the speed evolution of the two shafts is independent. The exit point of 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 withdrawal on the shaft of the gas generator used to generate electrical power by the reversible electric machine 1 in a generator operating mode reduces the performance of the gas generator.

[0014] Indeed, the variation, during flight, of the mechanical power drawn by the electric machine 1 and the equipment from the gas generator results in a shift in the engine's operating line within the compressor field. This shift corresponds to a margin for pumping that must be provisioned, which has the following consequences: penalizing the optimization of the engine's operating line, by prohibiting the use of the compressor at an optimal pressure rate: thereby degrading stabilized performance, with an impact on specific consumption.

[0015] With such a configuration, one solution to avoid drawing mechanical power from the generator shaft to generate electricity is to use one electric machine for the starting function with a disengagement system, and another electric machine attached to the free turbine shaft for the generating function, as illustrated in the... figure 1 which is detrimental in terms of mass and cost, in addition to being rarely used in practice.

[0016] A known architecture for starting a free-turbine turbomachine without the need for a specific starter is disclosed in document FR 2 929 324. This technical solution reduces the overall mass and cost and increases the reliability of the turbogenerator compared to a turbomachine comprising two electric machines, as in the figure 1The technical solution described in this document consists of a switching system using two freewheels to start the gas generator of a free-turbine turboshaft engine, and then to generate non-propulsive electrical power by drawing mechanical energy from the free-turbine shaft. The equipment remains driven via the gas generator and the accessory gearbox.

[0017] This solution makes it possible in particular to improve the transient performance of the gas generator, by avoiding the disadvantages of a kinetic energy extraction on the gas generator, and in particular the problem of the displacement of the engine operating line in the compressor field due to the variation, during the flight, of the mechanical power extracted by the electric machine.

[0018] This architecture with two freewheels is advantageous in a helicopter turbomachine because it avoids driving the main rotor via the electric machine during the startup phase. Since the turbomachine's freewheel turbine is mechanically connected to the main rotor, a coupling between the freewheel turbine shaft and the main rotor that could not be decoupled during startup would necessitate significantly oversizing the energy storage system to ensure the electric machine has sufficient energy to drive the entire drive train (including the main rotor).

[0019] To improve the performance of the free-turbine turbomachine, it would also be advantageous to drive all of the turbomachine's components via the free turbine. However, since the fuel pump's performance is directly related to its rotational speed, the evolution of the free turbine's speed after the startup phase would either not allow for, or would significantly impact, the design of the entire fuel system to ensure a smooth turbomachine startup.

[0020] It is known from documents US2018 / 0252161, US3514945, and FR2921423 of turbomachinery illustrating the state of the art. Description of the invention

[0021] To this end, the present invention proposes a free turbine turbomachine driving one or more electrical machines of sufficient power equipped with a simplified commutation system allowing optimization of mass, cost and reliability.

[0022] In one object of the invention, a turbomachine is proposed comprising a gas generator having a first mechanical shaft, at least one reversible electric machine, a free turbine having a second mechanical shaft and driven in rotation by a gas flow generated by the gas generator, an accessory box, a mechanical power transmission in the context of a helicopter and at least one accessory coupled to the accessory box.

[0023] According to a technical feature of the invention, the turbomachine further comprises a first mechanical coupling means configured to mechanically couple said first mechanical shaft to the accessory box in a first configuration and mechanically decouple said first mechanical shaft from the accessory box in a second configuration, and a second mechanical coupling means configured to mechanically couple said second mechanical shaft to the accessory box in a first configuration and mechanically decouple said second mechanical shaft from the accessory box in a second configuration, the electric machine being sized to drive the gas generator and said at least one accessory when starting the turbomachine.

[0024] The turbomachine according to the invention, comprising an electric machine and two mechanical coupling means, allows both the starting function of the gas generator and the high-power electrical generation to be combined on the electric machine, and prevents the free-running turbine and rotor (in the case of a mechanical transmission) from being driven by the electric machine during the starting phase, thereby reducing inertia and starting torque. Furthermore, this configuration allows the free-running turbine to drive the accessories and the rotor once the turbomachine has started.Indeed, the electric machine allows both the rotation of the accessories and that of the gas generator to be initiated until the gas generator can operate autonomously, then once the free turbine exceeds a certain power from which the second mechanical coupling means mechanically couples the second mechanical shaft to the accessory box, the electric machine can operate in generator mode by being driven by the free turbine via the accessory box to thus provide electrical power to other elements.

[0025] Furthermore, the architecture according to the invention allows, in the event of a break in the free-running turbine shaft during operation, for the direct impact on the accessory drive (including the fuel pump), resulting in the immediate shutdown of the engine and thus limiting the overspeed of the free-running turbine. This architecture effectively protects the free-running turbine from overspeed.

[0026] According to a first aspect of the turbomachine, the turbomachine may further include an electric machine control unit, the control unit being configured to place the electric machine in motor mode when the turbomachine is started, and to place the electric machine in generator mode when the second coupling means is placed in its first configuration.

[0027] By decoupling the gas generator from the accessory box once the gas generator has reached a speed allowing it to operate autonomously, the electrical energy to be delivered by the electric machine (up to the free turbine power speed) is reduced since the amount of energy required only corresponds to that needed to drive the accessories.

[0028] The transition phase between the autonomous operation of the gas generator and the coupling of the free turbine to the accessory box to allow the operation of the electric machine in generator mode, during which the electric machine continues to operate in motor mode but only for the accessories, thus makes it possible to maintain the rotational speed of the equipment, or accessories, high enough to guarantee their proper operation.

[0029] According to a second aspect of the turbomachine, the second mechanical coupling means is placed in its second configuration from the start-up phase of the turbomachine until an operating parameter of the second mechanical shaft or the second mechanical coupling means has exceeded a power threshold from which the free turbine is in a power configuration enabling it to drive said at least one accessory without assistance from the electric machine.

[0030] The value of the operating parameter corresponding to the threshold at which the free turbine is in its power configuration is preferably greater than the value of said operating parameter when the first shaft reaches the start-up phase output speed threshold. In other words, the threshold at which the free turbine can drive the accessories is reached after the gas generator has become self-contained. The electric machine is configured to operate in generator mode once said parameter of the second mechanical shaft or the electric machine has exceeded the power threshold.

[0031] According to a third aspect of the turbomachine, the first mechanical coupling means may include a first free wheel and the second mechanical coupling means may include a second free wheel.

[0032] According to a fourth aspect of the turbomachine, the first mechanical coupling means and the second mechanical coupling means can be included in a housing of the accessory box.

[0033] The gears in the accessory gearbox thus allow the speeds to be adapted for equipment, such as a fuel pump or an oil pump, mechanically coupled to the first mechanical shaft, i.e. to the gas generator.

[0034] According to a fifth aspect of the turbomachine, the turbomachine may further include an additional accessory box connected to the first mechanical shaft to couple additional accessories directly to the gas generator permanently.

[0035] In another aspect of the invention, a rotary-wing aircraft is proposed comprising at least one turbomachine as defined above, a main gearbox and a mechanical coupling between the free turbine and said main gearbox. Brief description of the drawings

[0036] [ Fig. 1 ] There figure 1 The diagram already described is a simplified schematic view of a free-turbine turbomachine according to the prior art. Fig. 2 ] There figure 2 The diagram, already described, is a graphical representation of the evolution, as a function of time and the possible configuration of the turbogenerator, of the speed of the gas generator shaft and the speed of the free turbine shaft of the turbomachine. figure 1 . [ Fig. 3 ] There figure 3 is a diagram of a free turbine turbomachine according to an embodiment of the invention. Fig. 4 ] There figure 4presents a logic diagram of a process for controlling the start-up of the turbomachine of the figure 3 according to an implementation method. Fig. 5 ] There Figure 5 is a graphical representation of the evolution, as a function of time and the possible configuration of the turbogenerator, of the speed of the gas generator shaft and the speed of the free turbine shaft of the turbomachine. figure 3 . Description of the implementation methods

[0037] On the figure 3 is schematically presented a turbomachine 10 with a free turbine according to an embodiment of the invention.

[0038] The turbomachine 10 includes an electric machine 11, a free turbine 12, a gas generator 13, an accessory box 14, a fuel pump 15 and an oil pump 16.

[0039] The gas generator 13 includes a shaft 18 connected and mechanically coupled to the accessory gearbox 14 via a first mechanical coupling means 20. The first mechanical coupling means 20 is configured to mechanically couple the shaft 18 of the gas generator 13 to the accessory gearbox 14 in a first configuration, and to mechanically decouple it from the accessory gearbox 14 in a second configuration, in particular to decouple the shaft 18 of the gas generator 13 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.

[0040] The free turbine 12 includes a shaft 17 connected and mechanically coupled to the accessory gearbox 14 via a second mechanical coupling means 25. The accessory gearbox 14 is mechanically coupled to the electric machine 11. The second mechanical coupling means 25 is configured to mechanically couple the shaft 17 of the free turbine 12 to the accessory gearbox 14 in a first configuration, and to mechanically decouple it from the accessory gearbox 14 in a second configuration, in particular to decouple the shaft 17 of the free turbine 12 from the shaft 18 and the electric machine 11. The shaft 17 of the free turbine 12 is thus selectively coupled to the electric machine 11 via the accessory gearbox 14.

[0041] The turbomachine 10 further comprises a main gearbox 26 and a main rotor 27. The free turbine 12 may also comprise another mechanical shaft 28, which may be an extension of the shaft 17, and which connects the free turbine 12 to the main gearbox 26, the main gearbox 26 being connected elsewhere to the main rotor 27. The free turbine is thus connected to the main rotor 27 via the main gearbox 26.

[0042] The accessory box 14 is also mechanically coupled to the fuel pump 15, on the one hand, and to the oil pump 16, on the other. In other embodiments, other accessories may be mechanically coupled to the accessory box 14.

[0043] The first mechanical coupling means 20 and the second mechanical coupling means 25 each include a freewheel.

[0044] The turbomachine 10 further includes a control unit 30 of the electric machine 11 configured to place the electric machine 11 in a motor mode during a start-up phase of the turbomachine 10 and to place the electric machine 11 in a generator mode when the second mechanical coupling means 25 is placed in its first configuration.

[0045] The first coupling means 20 is mechanically configured to have the electric machine 11 mechanically coupled to the gas generator 13 via the shaft 18 when starting the turbomachine 10.

[0046] In addition, the first coupling means 20 is mechanically configured to decouple the gas generator 13 from the electric machine 11 when the gas generator 13 reaches a starting phase output speed threshold.

[0047] The second coupling means 25 is mechanically configured to have the electric machine 11 mechanically coupled to the free turbine 12 via the shaft 17 when the free turbine 12 is in a power configuration enabling it to drive said at least one accessory without assistance from the electric machine 11.

[0048] On the figure 4 is presented a logic diagram of a method for controlling the start-up of the turbomachine 10 according to an implementation method of the invention.

[0049] On the Figure 5 The evolution, as a function of time and the possible configuration of the turbomachine, of the speed of shaft 18 of the gas generator 13 (solid line) and, (dashed line), of the speed of shaft 17 of the free turbine 12 of the turbomachine 10 is graphically represented. figure 3 during its startup using the process of figure 4 .

[0050] The method for starting the turbomachine 10 includes a first step 405 in which the electric machine 11 is placed in motor mode and started to begin rotating the shaft 18 of the gas generator 13 via the accessory gearbox 14, the first coupling means 20 being placed in its first configuration allowing the shaft 18 of the gas generator 13 to be coupled to the accessory gearbox 14, and the second coupling means 25 being placed in its second configuration allowing the shaft 17 of the free turbine 12 to be mechanically decoupled from the accessory gearbox 14. Indeed, when the accessory gearbox 14 is rotated by the electric machine 11, the first mechanical coupling means 20, which may be a freewheel, automatically transmits the torque necessary for rotating the gas generator 13.

[0051] In a second step 410, when the speed of the shaft 18 of the gas generator 13 exceeds a first threshold, the gas generator 13 can operate autonomously, i.e. without assistance from the electric machine 11. At this moment, the first coupling means 20 is placed in its second configuration to decouple the gas generator 13 from the accessory box 14 and therefore from the electric machine 11.

[0052] The electric machine 11 remains, however, in a motor operating mode to drive the accessories 15 and 16 via the accessory box 14.

[0053] In a third step 415, when the speed of the shaft 17 of the free turbine 12 exceeds a second threshold, the free turbine 12 is in a so-called power operation, enabling it to drive the accessories. At this point, the second coupling means 25 is placed in its first configuration to mechanically couple the free turbine 12 to the accessory gearbox 14 and thus drive the accessories 15 and 16.

[0054] In a fourth step 420, the electric machine 11 is, at the same time as the third step 415, placed in a generator operating mode.

[0055] Thus, the electric machine 11 can operate as an electric generator and produce electrical energy from the rotation of the shaft 17 of the free turbine driven by the rotary motion of the free turbine 12 itself driven by the gas flow delivered by the gas generator 13.

[0056] The transition phase between the autonomous operation of the gas generator 13 and the power operation of the free turbine 12, during which the electric machine 11 continues to operate in motor mode but only to ensure the drive of the accessories, thus makes it possible to maintain a rotational speed of the equipment or accessories high enough to guarantee their proper operation.

[0057] The free turbine turbomachine according to the present invention thus makes it possible to optimize the mass, cost and reliability of the switching system and therefore of the turbomachine.

Claims

1. A turbomachine (10) including a gas generator (13) comprising a first mechanical shaft (18), an accessory gear box (14), at least one reversible electric machine (11) coupled to the accessory gear box (14), a free turbine (12) provided with a second mechanical shaft (17) and rotationally driven by a stream of gas generated by the gas generator (13), and at least one accessory (15, 16) coupled to the accessory gear box (14), characterized in that the turbomachine (10) further comprises a first mechanical coupling means (20) configured to mechanically couple said first mechanical shaft (18) to the accessory gear box (14) in a first configuration of the first mechanical coupling means and to mechanically uncouple said first mechanical shaft (18) from the accessory gear box (14) in a second configuration of the first mechanical coupling means, and a second mechanical coupling means (25) configured to mechanically couple said second mechanical shaft (17) to the accessory gear box (14) in a first configuration of the second mechanical coupling means and to mechanically uncouple said second mechanical shaft (17) from the accessory gear box (14) in a second configuration of the second mechanical coupling means, the electric machine (11) being dimensioned to drive the gas generator and said at least one accessory during the start-up of the turbomachine.

2. The turbomachine (10) as claimed in claim 1, further comprising a control unit (30) of said at least one electric machine (11), the control unit (30) being configured to put the electric machine (11) in motor mode during the start-up of the turbomachine (10), and to put the electric machine (11) in generator mode when the second coupling means (25) is put in its first configuration.

3. The turbomachine (10) as claimed in claim 2, wherein the second mechanical coupling means (25) is put in its second configuration from the start-up phase of the turbomachine (10) until a parameter of the second mechanical shaft (17) or of the second mechanical coupling means (25) has exceeded a power threshold above which the free turbine (12) is in a power configuration allowing it to drive said at least one accessory without the assistance of the electric machine (11).

4. The turbomachine (10) as claimed in one of claims 1 to 3, wherein the first mechanical coupling means (20) comprises a first free wheel and the second mechanical coupling means (25) comprises a second free wheel.

5. The turbomachine (10) as claimed in one of claims 1 to 4, wherein the first mechanical coupling means (20) and the second mechanical coupling means (25) are contained in a casing of the accessory gear box (14).

6. The turbomachine (10) as claimed in one of claims 1 to 5, further comprising an additional accessory gear box connected to the first mechanical shaft (18) to constantly couple additional accessories directly to the gas generator (13).

7. An aircraft with rotary wings comprising at least one turbomachine as claimed in one of claims 1 to 6, a main gear box (26) and a mechanical coupling (28) between the free turbine (12) and said main gear box (26).