FREE TURBINE TURBOMACHINE COMPRISING EQUIPMENT DRIVEN BY THE FREE TURBINE

Abstract

Disclosed is a turbomachine, comprising a gas generator (13) equipped with a first shaft (18), at least one reversible electrical machine (11), a free turbine (12) provided with a second shaft (17) and caused to rotate by a gas flow generated by the gas generator (13), an accessory gear box (14) and at least one accessory (15, 16).

Said at least one electrical machine (11) is mechanically coupled to said second mechanical shaft (17) via the accessory gear box (14) during all phases of operation of the turbomachine (10), the accessory gear box (14) is coupled to the at least one accessory (15, 16) and the turbomachine (10) further comprises a single mechanical coupling means (20) for mechanically coupling said first mechanical shaft (18) to the accessory gear box (14) in a first configuration and mechanically uncoupling said first mechanical shaft (18) from the accessory gear box (14) in a second configuration.

Claims

1. A turbomachine (10) comprising a gas generator (13) equipped with a first mechanical shaft (18), at least one reversible electrical machine (11), a free turbine (12) provided with a second mechanical shaft (17) and caused to rotate by a gas flow generated by the gas generator (13), an accessory gear box (14), and at least one accessory (15, 16) coupled to the accessory gear box (14), characterised in that said at least one electrical machine (11) is mechanically coupled to the second mechanical shaft (17) via the accessory gear box (14) during all the phases of operation of the turbomachine (10), and the turbomachine (10) further comprises a single mechanical coupling means (20) for mechanically coupling said first mechanical shaft (18) to the accessory gear box (14) in a first configuration and mechanically uncoupling said first mechanical shaft (18) from the accessory gear box (14) in a second configuration, the electrical machine (11) being sized to cause the gas generator (13), as well as said at least one accessory (15, 16) and the free turbine (12) to rotate during start-up of the turbomachine (10).

2. The turbomachine (10) according to claim 1, further comprising a control unit (30) of said at least one electrical machine (11), the control unit (30) being configured to place the electrical machine (11) in motor mode during start-up of the turbomachine (10), and to place the electrical machine (11) in generator mode when it is detected that the free turbine can operate autonomously.

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

4. The turbomachine according to claim 3, wherein the control unit (30) is configured to control the electrical machine (11) in motor mode: as a function of the speed of rotation of the first and second mechanical shafts (17 and 18) from the starting of the turbomachine (10) until ignition of the gas generator (13), then as a function of the level of torque required to drive the first and second mechanical shafts (17 and 18) until the gas generator (13) operates autonomously, then as a function of the speed of rotation of the first and second mechanical shafts (17 and 18) until said parameter of the second mechanical shaft (17) has exceeded a threshold at which the free turbine (12) is autonomous.

5. The turbomachine (10) according to one of claims 1 to 4, wherein the mechanical coupling means (20) comprises a free wheel.

6. The turbomachine (10) according to one of claims 1 to 5, wherein the mechanical coupling means (20) is contained in a casing of the accessory gear box (14).

7. The turbomachine (10) according to one of claims 1 to 6, wherein the accessory gear box (14) is configured to change the gear ratio between the free turbine (12) and the gas generator (13) when the mechanical coupling means (20) is in its first configuration.

8. The turbomachine (10) according to one of claims 1 to 5, wherein the accessory gear box (14) is arranged and can be connected between the mechanical coupling means (20) and the second mechanical shaft (17).

9. The turbomachine according to one of claims 1 to 8, further comprising an accessory gear box additionally connected to the first shaft (18) for permanently coupling additional accessories directly to the gas generator (13).

Description

BRIEF DESCRIPTION OF THE FIGURES

[0052] FIG. 1, already described, is a simplified schematic view of a free turbine turbomachine according to the prior art.

[0053] 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.

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

[0055] FIG. 4 shows a logic diagram of a method for controlling the start-up of the turbomachine of FIG. 3 according to an embodiment.

[0056] 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

[0057] FIG. 3 schematically shows a free turbine turbomachine 10 according to an embodiment of the invention.

[0058] The turbomachine 10 comprises an electrical machine 11, a free turbine 12, a gas generator 13, an accessory gear box 14, a fuel pump 15 and an oil pump 16.

[0059] The free turbine 12 comprises a shaft 17 permanently mechanically connected to the accessory gear box 14. The accessory gear box 14 is mechanically coupled to the electrical machine 11. Hence, the kinematic chain between the electrical machine 11 and the free turbine 12 does not comprise any uncoupling device, which thus makes it possible to have the turbine 12 coupled to the electrical machine 11 during all the phases of operation of the turbomachine 10, in particular during the start-up phase and the electrical generation phase.

[0060] The accessory gear box 14 is likewise mechanically coupled to both the fuel pump 15 and to the oil pump 16. In other embodiments, other accessories can be mechanically coupled to the accessory gear box 14.

[0061] The gas generator 13 comprises a shaft 18 connected and mechanically coupled to the accessory gear box 14 via a single mechanical coupling means 20. The single mechanical coupling means 20 is configured for mechanically coupling the shaft 18 of the gas generator 13 to the accessory gear box 14 in a first configuration, and for mechanically uncoupling from the accessory gear box 14 in a second configuration in order, in particular, to uncouple the shaft 18 of the gas generator from the shaft 17 and the electrical machine 11. The shaft 18 of the gas generator 13 is thus selectively coupled to the electrical machine 11 via the accessory gear box 14.

[0062] The mechanical coupling means 20 comprises a free wheel.

[0063] The turbomachine 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 turbomachine 10, and to place the electrical machine 11 in generator mode when it is detected that the free turbine can operate autonomously.

[0064] The coupling means 20 are mechanically configured to have the electrical machine 11 mechanically coupled to the gas generator 13 via the shaft 18 during the start-up of the turbomachine 10.

[0065] In addition, the coupling means 20 is mechanically configured for uncoupling the gas generator from the electrical machine 11 once the gas generator 13 reaches a speed threshold for exit from the start-up phase.

[0066] FIG. 4 shows a logic diagram of a method for controlling the start-up of the turbomachine 10 according to an embodiment of the invention.

[0067] 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 18 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 of FIG. 3 during its start-up using the method of FIG. 4.

[0068] The start-up method of the turbomachine 10 comprises a first step 405 in which the electrical machine 11 is placed in motor mode and started in order to begin rotation of the shafts 17 and 18 of the free turbine 12 and of the gas generator 13 via the accessory gear box 14. Indeed, during the rotating of the accessory gear box 14 by the electrical machine 11, the mechanical coupling means 20, which may be a free wheel, automatically transmits the torque required for rotating the gas generator 13. Starting from the start-up of the electrical machine 11 in the first step 405, the electrical machine 11 is controlled, for example, by the control unit 30, then in a second step 410 as a function of the speed of rotation of its mechanical shaft coupled to the accessory gear box 14, in order that the speed of rotation of the shaft 17 of the gas generator 13 remains in the ignition window, in other words in a specified speed range for maximising the chances of successful ignition of the gas generator combustion chamber. For this control, the control unit 30 can comprise an electronic processing unit such as a computer and receive information on the speed of the shaft of the electrical machine 11 or the shaft 17 of the gas generator 13, these two speeds being proportional to one another with a reduction factor specific to the gear train of the accessory gear box 14.

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

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

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

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

[0073] In a seventh step 435, a comparison is made, for example, between the level of torque delivered by the electrical machine and/or its speed of rotation 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 the rotation of the free turbine 12 or to accelerate it. So long as the power available on the free turbine 12 does not allow the torque delivered by the electrical machine to be reduced, enabling its setpoint speed to be maintained, or so long as there is no positive change to the speed of rotation, the control of the electrical machine 11 continues to be performed as a function of the speed setpoint in the sixth step 420.

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

[0075] 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 driven by the rotary movement of the free turbine 12, itself driven by the gas flow delivered by the gas generator 13.

[0076] The transition phase between the autonomous operation of the gas generator 13 and the autonomous operation of the free turbine 12, during which the electrical machine 11 continues to operate in motor mode, but only to ensure the driving of the accessories and the free turbine 12, thus makes it possible to maintain a speed of rotation of the equipment or accessories that is sufficiently high to guarantee their correct operation.

[0077] 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.