TURBOMACHINE FUEL SUPPLY SYSTEM

Abstract

The invention relates to a fuel supply system for a turbomachine (100), the system comprising a fuel circuit (102) comprising at least: a counter-rotating centrifugal pump (200) comprising at least one external impeller (2021) and a central impeller (2022) having opposite directions of rotation; a hydromechanical group (204) configured to control at least one fuel outlet to a combustion chamber (108); the system being configured to regulate a fuel flow rate to said combustion chamber (108) from a flow rate setpoint (Pc) in a hydraulic circuit downstream of the hydromechanical group, by varying the rotation speed of the central impeller either from an evaluated pressure drop (∆P2) or from an evaluated pressure difference (∆P1), so as to adapt the pressure supplied by the pump to a need linked to the flow rate setpoint. Figure for the abstract: Fig. 4

Description

Title of the invention: TURBOMACHINE FUEL SUPPLY SYSTEM Technical field of the invention

[0001] The present invention relates to the field of turbomachines. It relates more particularly to a fuel supply system, a turbomachine comprising the supply system and a method for regulating the fuel flow in the system. Technological background

[0002] The turbomachines installed on an aircraft are equipped with a fuel supply circuit 102, delivering the fuel to the combustion chamber, which must be regulated as needed according to the flight conditions. With reference to [Fig.l], the fuel supply circuit 102 generally comprises a high-pressure main pump 200 of the volumetric type which sends the fuel to a hydromechanical group 204 before injection into the combustion chamber 108. The assembly is arranged to ensure, at the outlet to the combustion chamber, a fuel flow adapted to the need. A control unit 222 generally controls the hydromechanical group 204 so that it adapts the flow sent by the pump 200 to the need of the combustion chamber 108.

[0003] In general, the pump 200 is driven by an output shaft 106 of the accessory relay box 104 of the turbomachine, itself driven by a motor shaft of the primary body of the turbomachine, not shown in [Fig.l]. A transmission device 220 is generally installed between the shaft of the accessory relay box 104 and the pump 200 to adapt the rotation speeds between these two pieces of equipment. This device determines a ratio K between the speed of the pump 200 and the rotation speed co of the motor shaft of the turbomachine. This device generally also drives a supply means 216 of the circuit 102 from the fuel tanks R. The linear characteristic Cyl of the pump 200 between the fuel flow rate and its drive speed depends in particular on its displacement.The pump 200 must be sized in such a way that this displacement makes it possible to deliver the required flow rates for all operating speeds of the turbomachine, therefore the speed of the output shaft of the accessory relay box 104, both at low speed and at high speed.

[0004] As can be seen in [Fig.2], representing the variations in flow rate F as a function of the rotation speed co of the shaft of the engine axis of the turbomachine, the fuel requirement Fl varies in a non-linear manner as a function of the speed of the tur- bomachine. The rotation speed co of the turbomachine's engine shaft varies between a minimum value comin, for ignition of the turbomachine, and a maximum value comax for takeoff. The speed corresponding to a cruising flight is between these two extremes.

[0005] Depending on the application, the crucial point is located either at low speed ignition or at takeoff, at high speed. In [Fig.2], this crucial point is located at the ignition level, the displacement of the pump must be chosen in such a way that its linear characteristic is equal to the value Cyll, to ensure sufficient flow during all flight conditions. This value Cyll can be significantly higher than the minimum value Cylmin necessary in certain flight conditions, or even that Cyl2 necessary during takeoff.

[0006] According to this dimensioning, the flow rate supplied by the pump therefore follows the line L1 on the flow rate / rotation speed diagram in [Fig.2]. During a large training speed phase, particularly in cruising flight, the pump therefore delivers a flow rate greater than the fuel flow requirement, therefore a surplus F2 of fuel.

[0007] The hydromechanical group 204 must therefore return to the pump, via a Brec recirculation loop, the surplus fuel F2 compared to the requirement.

[0008] This problem of regulating the fuel flow rate is further accentuated when the fuel supply circuit 102 is used, as shown in [Fig.l], to actuate variable geometries 212 of the turbomachine. The actuation of the variable geometries 212 creates variations in fuel requirements in the circuit which must be taken into account in the sizing of the pump 200, in the operation of the hydromechanical group 204 and in the characteristics of the Brec recirculation loop.

[0009] This architecture of the fuel supply system has several drawbacks. The excess flow injected by the pump 200 induces an excess power draw on the accessory relay box 104 compared to the requirement, which is detrimental to the efficiency of the turbomachine. The excess mechanical power is transformed into thermal power dissipated in the Brec recirculation loop which must be evacuated. This has a negative influence on the size and mass of the fuel circuit, in particular for heat exchangers, not shown, placed to evacuate the heat in this circuit.

[0010] It may thus be desirable to provide a fuel supply system which makes it possible to overcome at least some of the aforementioned problems and constraints. Summary of the invention

[0011] A fuel supply system for a turbomachine is therefore proposed, the turbomachine comprising at least one accessory box comprising at least one output shaft, the system comprising a fuel circuit comprising: - the output shaft of the accessory relay box; - a counter-rotating centrifugal pump comprising at least two concentric impellers including: • at least one external impeller configured to be rotated in a first direction by the output shaft of the accessory relay box of the turbomachine so as to send a flow of fuel into said circuit; • at least one central impeller configured to rotate in a second direction opposite to that of the external impeller; • a hydromechanical group configured to control at least one fuel outlet to a combustion chamber; the system being configured to regulate a fuel flow to said combustion chamber from a flow setpoint in a hydraulic circuit downstream of the hydromechanical unit, characterized in that: - the hydromechanical group comprises at least one measuring device configured to evaluate a pressure deviation from the flow rate setpoint or a pressure loss relative to the flow rate setpoint; and - the system further comprises a speed regulation device configured to control a rotation speed of the central impeller and at least one control unit for controlling said speed regulation device either from said evaluated pressure loss or from the evaluated pressure difference, to vary the rotation speed of the central impeller of the pump, so as to adapt the pressure supplied by the pump, via the drive of the external impeller, to a need linked to the flow rate setpoint.

[0012] The inventors have noted the appearance of certain technical problems in certain turbomachines, when using a hybrid solution in which the output shaft of the turbomachine accessory relay box and an electric motor were associated for the control of a volumetric pump via an epicyclic gear train. At operating points with very low rotational speeds of the volumetric pump but also at high power operating points, these problems affect the service life of the bearings of the volumetric pump (operating point at very low speeds) or cause significant variability in the injection flow rate (operating point at high power). It has also been noted that the solutions to circumvent these constraints could involve an increase in the mass and size of the pump and an increase in the power of the electric motor.

[0013] The solution as described also allows the speed of the device to be controlled either by the pressure drop at the terminals of the regulating valve or by a pressure difference at the terminals of the metering device in order to achieve high-speed driving of the pump while having an efficiency compatible with the need to reduce thermal rejection. In particular, it is no longer necessary to have a recirculation loop. The invention also allows a saving in energy and material resources by adapting to the pressure requirement while avoiding oversizing the pump components to achieve maximum power.

[0014] The invention may further comprise one or more of the following optional features, in any technically possible combination: - The pump includes two impellers (external and internal) which are mechanical or electrical; - the pump includes at least one mechanical impeller and one electric impeller - the electric spinning wheel is the central spinning wheel and the speed regulating device is an electric motor; - the central impeller is sized to provide a power of the order of 25% of the total power required for the flow rate setpoint and the external impeller is sized to provide a power of the order of 75% of said total power; - the central and external impellers are sized so that the rotation speed of the central impeller, driven by the speed regulation device, is + / -30% that of the external impeller, driven by the output shaft of the turbomachine accessory relay box; - the hydromechanical group also includes at least: • a metering device configured to send a flow rate equal to the flow rate setpoint to the fuel outlet; • a servovalve configured to receive the flow rate instruction and control the position of the doser; • a regulating valve arranged downstream of the metering device and configured to maintain a constant pressure difference across the terminals of the metering device; - the measuring devices include at least: • a first pressure sensor placed at the terminals of the metering device to assess a pressure difference compared to the flow rate setpoint; • a second pressure sensor configured to evaluate a pressure drop across the regulating valve, the pressure drop corresponding to a pressure variation; - the circuit also includes: • a means of supplying the circuit driven either by the output shaft of the turbomachine accessory relay box or by the re speed regulation; • a variable geometry supply loop for the turbomachine; • a filter connected at least to the supply means, to the variable geometry supply loop and to the pump to at least trap fuel contaminants.

[0015] The invention also relates to a turbomachine comprising a system described above.

[0016] The invention also relates to a method for regulating a centrifugal pump in a turbomachine as described above, the method implementing laws for controlling the rotation speed of an impeller of the centrifugal pump, which increase or, respectively, decrease this speed when the pressure difference or the pressure drop decreases or increases, so that the flow rate and the pressure at the outlet of the circuit are adapted to the flight conditions of the aircraft.

[0017] The method may further comprise one or more of the following optional features, in any technically possible combination: - the control laws are configured to also adapt the pressure supplied by the pump and the pressure in the circuit to the conditions of use of variable geometries or secondary supply circuits; - the piloting laws include at least: • receipt of a debit instruction; • the evaluation of a pressure deviation from the flow rate setpoint or a pressure loss relative to the flow rate setpoint; • variation in the rotation speed of the central impeller of the pump either from the assessed pressure difference or from the assessed pressure loss, so as to adapt the pressure supplied by the pump according to the need linked to the flow rate setpoint. Brief description of the figures

[0018] The invention will be better understood with the aid of the following description, given solely by way of example and with reference to the appended drawings in which: - [Fig. 1] shows very schematically a fuel circuit according to the state of the art, - [Fig.2] presents a rotation speed and flow diagram showing the difference between the flow supplied by the fuel pump and the requirement for a circuit according to [Fig.l]; - [Fig.3] shows very schematically a half-section of a turbomachine capable of using the invention; - [Fig.4] shows very schematically a first embodiment of a fuel supply system according to the invention, - [Fig.5] shows an exploded view of a counter-rotating centrifugal pump that can be used by the invention; - [Fig.6] shows very schematically the structure of the hydromechanical group according to the invention; - [Fig.7] shows very schematically a variant of the first embodiment of a fuel supply system according to the invention; and - [Fig.8] shows very schematically the stages of the control laws of a pump according to the invention. Detailed description of the invention

[0019] Figures 1 and 2 have been described in the above.

[0020] With reference to [Fig.3], a turbomachine 100 according to the invention will be described.

[0021] In this example, the turbomachine is a dual-flow turbomachine. The turbomachine 100 comprises at least one fan 110, low-pressure 114 and high-pressure 118 compressors, a combustion chamber 108, high-pressure 120 and low-pressure 122 turbines.

[0022] The turbomachine further comprises a motor shaft 116. Generally, the assembly of high-pressure compressors 118 and high-pressure turbines 120 rotates as a unit on a motor shaft 116 and forms the motor part of the turbomachine 100 with the combustion chamber 108.

[0023] The turbomachine may further comprise an accessory relay box 104 and a fuel supply circuit 102. The accessory relay box 104 may comprise several gear trains connected to output shafts to drive various equipment. Here one of the output shafts 106 is connected to the supply circuit 102 which supplies the combustion chamber.

[0024] Generally, the accessory relay box 104 provides the link between the motor shaft 116 and a starter / generator, not shown in [Fig. 3], which can be used to drive the turbomachine 100 during the start-up phases or generate an electric current when the turbomachine is switched on.

[0025] The turbomachine may further comprise variable geometries 212 (not shown in [Fig. 3]), previously mentioned, which can be activated under certain conditions of use. These variable geometries 212 are, for example and in a non-limiting manner, variable-pitch blades at the inlet of a high-pressure compressor.

[0026] Still with reference to [Fig. 3], the air flow leaving the blower 110 is divided into a primary flow Q entering the engine and a secondary flow S surrounding the latter. The primary flow then passes through low pressure compressors 114 and high pressure compressors 115. pressure 118, the combustion chamber 108 supplied by the fuel supply circuit 102 previously mentioned, then the high pressure 120 and low pressure 122 turbines.

[0027] With reference to [Fig.4], the fuel supply system according to the invention will be described.

[0028] The system comprises a circuit 102. The circuit 102 comprises at least the output shaft 106 of the accessory relay box 104 of the turbomachine 100 described above.

[0029] Unlike the circuit described in [Fig.l], the circuit 102 of the present invention further comprises a counter-rotating pump 200 connected at least to the output shaft 106 of the accessory relay box 104 of the turbomachine 100 and a hydroelectric group 204 connected to the pump 200 and configured to control at least one fuel outlet to the combustion chamber 108.

[0030] The counter-rotating centrifugal pump 200 comprises at least a first impeller called external 202i and a second impeller called central 2022. The external 202i and internal 2022 impellers are concentric, as illustrated for example in [Fig.5].

[0031] The external impellers 202i and internal impellers 2022 may be mechanical or electrical. Preferably, the pump 200 comprises at least one mechanical impeller and at least one electric impeller. Preferably, the electric impeller is the central impeller 2022

[0032] The pump 200 may further comprise at least one shaft 210 carrying at least one impeller as illustrated in [Fig.5]. The shaft 210 is preferably coaxial with the drive shaft of the external impeller 202i.

[0033] The external impeller 202i is configured to be rotated in a first direction Si by the output shaft of the accessory relay housing 104 of the turbomachine so as to send a flow of fuel into the supply circuit 102.

[0034] The pump further comprises a volute 203 for sending fuel through the circuit 102. The volute 203 is the body of the pump 200 which acts as a pressure containment vessel and which channels a flow of fuel into and out of the pump 200. The volute 203 receives the flow of fuel accelerated by the rotation of the external 202i and / or central 2022 impellers and converts the kinetic energy of the flow of fuel into pressure. The section of the volute 203 can be scalable or constant depending on the sizing requirement.

[0035] The power supply system further comprises a speed regulating device 208, connected to the central impeller 2022 to drive the latter in rotation in a second direction S2 opposite to that of the external impeller 202i. The device or electric motor comprises at least one motor shaft 207 for driving the central impeller 2022.

[0036] The speed control device 208 may be an electrical or mechanical or hydraulic system. Preferably, the device 208 is an electric motor.

[0037] The speed control device is configured to control the speed of the central impeller independently of the speed of the output shaft of the relay housing.

[0038] In some embodiments, the connection of the outer 202i and central 2022 impellers may also be reversed, i.e., the central impeller is driven by the output shaft 106 of the accessory housing 104 and the outer impeller is rotated by the electric device or motor 208. In this case, the outer impeller 202i is the electric impeller and the central impeller is the mechanical impeller.

[0039] In some embodiments, the drive of the central impeller 2022 by the electric device or motor 208 may not be direct. The drive may be done for example, and in a non-limiting manner, via an epicyclic gear train driven by an output shaft of the accessory relay box 104 with an element regulated by a regulating device 208.

[0040] The circuit 102 further comprises a control unit 206 configured to control the device or electric motor 208.

[0041] The circuit 102 further comprises a power supply means 216 of the circuit 102 driven by the output shaft 106 of the accessory relay box 104 of the turbomachine 100. According to a variant, not shown, the power supply means 216 of the circuit 102 can be driven by the device or electric motor 208.

[0042] The supply means 216 is connected to a reservoir R, not shown in [Fig.4], as described previously.

[0043] The circuit 102 further comprises a variable geometry supply loop 212 of the turbomachine 100 connecting the pump 200 and the variable geometries 212.

[0044] The circuit may further comprise a filter 214. The filter 214 may be connected to the supply means 212, to the variable geometry supply loop 212 and to the pump 200 to trap, for example, contaminants from the fuel in the circuit and in particular fuel coming from the tank R or from the variable geometries 212 and being conveyed to the pump 200.

[0045] Fuel passing through the filter can also be routed to other hydraulic circuits.

[0046] The circuit further comprises a hydromechanical group 204 configured to control at least one fuel outlet to a combustion chamber 108.

[0047] The hydromechanical group 204 can be configured to receive a flow rate instruction Pc issued by a computer of the turbomachine 100, not shown, in order to meet a need. For example, and in a non-limiting manner, a takeoff.

[0048] The hydromechanical group 204 can further be connected to the control unit 206 of the device or electric motor 208 in order to transmit at least one correction instruction relating to the flow rate instruction Pc. The correction instruction can be a pressure variation APreg to be provided and / or an action or a series of actions to be applied to the level of the centrifugal pump 200 to achieve the pressure variation APreg in order to regulate the supply of fuel in the circuit 102 and meet the needs of the turbomachine 100. These actions may be, for example, and in a non-limiting manner, an increase or a decrease in the rotation speed of at least one impeller 202b 2022 of the centrifugal pump 200.

[0049] In another variant, the hydroelectric group can be directly connected to the device or electric motor 208. In this configuration, the control unit 206 of the speed regulation device can be integrated into the hydromechanical group 204.

[0050] With reference to [Fig.6], the hydromechanical group will now be described.

[0051] The hydromechanical group 204 comprises at least one metering device 302 configured to send a flow equal to or corresponding to the flow setpoint Pc to the fuel outlet.

[0052] The hydromechanical group 204 further comprises a servovalve 300 connected to the metering device 302. The servovalve is configured to receive the flow rate instruction Pc and control the position of the metering device 302.

[0053] When the turbomachine is switched on, the pump 200 is driven at a minimum rotation speed and provides a pressure P (for example P=Po) at the output. When the servovalve 300 is activated after receiving the setpoint Pc, it controls the position of the metering device 302 so that the pressure downstream of the metering device is equal to the pressure Pc. This will induce a pressure variation APi at the terminals of the metering device 302.

[0054] The hydromechanical group 204 further comprises a regulating valve 304 arranged downstream of the metering device 302 and configured to keep the pressure difference or variation APi constant across the terminals of the metering device 302. The regulating valve sets the pressure variation APi constant across the terminals of the metering device by implementing a variable restriction to adapt to the characteristic of the centrifugal pump 200. For example, in the case of high pressure upstream of the regulating valve, and for a given pressure of a circuit downstream of the valve which is dependent on the flow rate and the flight conditions, there will be too much pressure loss. The passage section (restriction) of the regulating valve will open. This will reduce the upstream pressure until the desired pressure difference or variation is obtained. The regulating valve 304 is therefore hydraulically controlled by the constant APi of the dosing device 302, on the other hand the pressure loss at the terminals of the regulating valve 304 is variable.This pressure loss corresponds to a pressure variation AP2.

[0055] The hydromechanical group may further comprise a cut-off valve 310 located downstream of the regulating valve for injecting fuel into the combustion chamber 108 in order to cut off the fuel injection and ensure the sealing of the circuit.

[0056] Still with reference to [Fig.6], the hydromechanical group 204 further comprises a measuring device 3062 arranged at the terminals of the regulating valve 304 to detect or evaluate the pressure drop AP2 relative to the flow rate setpoint Pc.

[0057] The measuring device 3062 may be a pressure sensor or a slide / furring whose movement is controlled by the pressure drop APi and whose position can vary an element to modify the speed of the impeller (for example by continuously variable transmission). Preferably, the measuring device 3062 is a pressure sensor.

[0058] The hydromechanical group 204 may further comprise a measuring device 306i, for example a pressure sensor or a slide / sleeve, arranged at the terminals of the metering device to detect or evaluate a pressure deviation from the flow rate setpoint Pc.

[0059] The hydromechanical group 204 is further configured to, in the event of detection or evaluation of either the pressure loss AP2 relative to the flow rate setpoint or the pressure difference APi relative to the flow rate setpoint Pc, transmit a correction setpoint to the control unit 206 of the speed regulation device 208 so that the control unit 206 controls the speed regulation device 208 either from said evaluated pressure loss AP2 or from the evaluated pressure difference APi, to vary the rotation speed of the central impeller 2022 of the pump, so as to adapt the pressure supplied by the centrifugal pump 200 according to the need of a hydraulic circuit downstream of the hydromechanical group or of the regulating valve.

[0060] The hydromechanical group may further comprise a selector, not shown, making it possible to select either the pressure drop or the pressure difference according to a predetermined criterion.

[0061] The central impeller 2022 is sized to provide a power of the order of 25% of a total power required for the flow rate setpoint and the external impeller 202i is sized to provide a power of the order of 75% of said total power.

[0062] Furthermore, the central 2022 and external 202i impellers are dimensioned so that the rotational speed of the central impeller 2022, driven by the speed regulation device 208, is preferably + / -30% that of the external impeller 202b driven by the output shaft 106 of the accessory relay box 104 of the turbomachine 100.

[0063] The counter-rotating centrifugal pump 200, as described, makes it possible to obtain a pressure with a radial footprint smaller than a conventional single-stage centrifugal pump, and of the same order of magnitude as a double centrifugal pump.

[0064] In operation, a variation in the pressure AP supplied at the output by the counter-rotating pump 200 can be described by the relation:

[0065] [Math.l] AP = p.gj'^U^Cu^ +- 2.Uj.CUj - U^Cue) where s, e and i are the indices indicating a parameter considered at the pump outlet, at the pump inlet and at the interface of the central and external impellers; U, the tangential speed of the impeller; Cu the tangential speed of the fuel; g is the intensity of the gravity field; p the density of the fuel and q an efficiency.

[0066] The terms at the interface of the two impellers add up and thus increase the outlet pressure.

[0067] An illustrative, and non-limiting, example of the mode of operation of the power supply system will now be described.

[0068] For a given requirement relating to a flight point, for example and in a non-limiting manner a takeoff, a flow rate setpoint Pc is sent in the form of a setpoint current to the servovalve 300 by the computer of the turbomachine 100, mentioned above. The servovalve 300 is then activated and controls the position of the metering valve 302 to provide the requested flow rate. Depending on the pressure P delivered by the centrifugal pump 200 and the flow rate requirement, a pressure drop AP2 will be obtained at the terminals of the regulating valve 304.

[0069] For example, for a high rotation speed and a low flow rate requirement of the circuit downstream of the hydromechanical group 204 or of the regulating valve 304, the pressure of the pump will be high. The regulating valve 304 will then close to obtain the correct pressure drop AP2 measured by the measuring device 3062 at its terminals or a pressure variation AP at the terminals of the metering device 302. If the pressure drop AP2 or the pressure difference at the terminals of the metering device APi is greater than the second given threshold, this means that the pressure P supplied by the pump upstream of the metering device 302 is too high and that the rotation speed of the pump 200 must be reduced to reduce the pressure P at the outlet of the pump 200.

[0070] A correction instruction is then transmitted by the hydromechanical group 204 to the control unit 206 of the speed regulation device 208. When the correction instruction is received, the control unit adjusts the rotation speed of the central impeller 2022, so that the pressure loss AP2 or the pressure difference APi is equal to the pressure APreg of the correction instruction received.

[0071] Similarly, in the event of a flow rate call from the variable geometries 212, the pressure P at the outlet of the pump would decrease. To adapt to the characteristic of the pump, the regulating valve 304 opens, thus reducing its pressure loss APb. This will result in an increase in the rotation speed of the device 208 in order to increase the pressure P at the outlet of the pump 200.

[0072] The invention as described also makes it possible to cover the entire flight envelope in the event of loss of sensor 306i, 3062. If the sensor 306i, 3062 is no longer functional, the regulation can lead to the maximum speed of the impellers of the pump 200 which, in this case, will deliver high power. The power may no longer be suitable for a given operating point but the power supply system as described above makes it possible to meet the needs of the turbomachine at all operating points in the domain.

[0073] Advantageously, those skilled in the art will understand that the hybrid fuel circuit architecture, as described, using an output shaft 106 of the turbomachine 100 and a speed regulation device 208 to drive the impellers 202b 2022 of a counter-rotating centrifugal pump makes it possible to modulate the pressure level to adapt to the needs of the turbomachine 100 and thus gain in drive power.

[0074] The invention also makes it possible to eliminate the Brec recirculation loop as described in [Fig.l].

[0075] Furthermore, regulation via a pressure drop measurement at the terminals of the regulating valve 304 makes it possible to have a fuel supply system that is always operational in the event of failure of the measuring device at the terminals of the valve. Regulation is therefore improved.

[0076] With reference to [Fig.7], a variant of the fuel supply system is described.

[0077] The fuel system comprises a circuit 102' similar to the circuit 102 described above, except that the circuit 102' further comprises a secondary fuel circuit 218. The circuit 102' thus comprises a main circuit comprising the combustion chamber supply branch 108 and the secondary circuit 218.

[0078] The secondary fuel circuit 218 may comprise a hydromechanical group 204' configured to control at least one fuel outlet for use in a circuit 124 supplying another zone of the turbomachine.

[0079] Regulation of the fuel supply at the secondary circuit 218 does not result in regulation in the main circuit. The system is configured so that the regulation is carried out by the branch of the circuit comprising the supply of the combustion chamber 108, i.e. the main circuit. Thus, if there is a call for fuel in the secondary circuit 218, this will result in a fuel deficit in the main circuit. Regulation as described above can then be carried out.

[0080] Advantageously, those skilled in the art will understand that due to the architecture of the supply circuit as described, it is possible to supply several secondary circuits, via the centrifugal pump 200 which is a pressure source, while ensuring the regulation of the supply of fuel in the main circuit.

[0081] The invention also relates to a method for regulating a fuel pump for a turbomachine comprising a supply system according to the invention in an aircraft.

[0082] The method for regulating the pump 200 implements control laws 400 for the rotation speed of an impeller of the pump 200, which increase or, respectively, decrease this speed when the pressure difference or the pressure loss decreases or increases, so that the flow rate and the pressure at the outlet of the circuit 102 are adapted to the flight conditions of the aircraft.

[0083] Said control laws 400 are configured to also adapt the flow rate supplied by the pump 200 and the pressure in the circuit 102 to the conditions of use of the variable geometries 212 or secondary supply circuits 218.

[0084] With reference to [Fig.8], the piloting laws 400 comprise at least: - receipt 500 of a flow instruction; - the evaluation 502 of a pressure deviation APi compared to the flow rate setpoint Pc or a pressure loss AP2 relative to the flow rate setpoint Pc; - the variation 504 of the rotation speed of the central impeller 2022 of the pump 200 either from the evaluated pressure difference APi or from the evaluated pressure loss AP2, so as to adapt the pressure supplied by the pump 200, according to the need linked to the flow rate setpoint Pc.

[0085] It is clear from the above description that the invention, and in particular the control of the speed of the speed regulating device either by the pressure drop at the terminals of the regulating valve or by a pressure difference at the terminals of the metering device, makes it possible to achieve low and high speed driving of the pump while having an efficiency compatible with the need to reduce thermal rejection. In particular, it is no longer necessary to have a recirculation loop.

[0086] The invention also allows a saving in energy and material resources by adapting to the pressure requirement while avoiding oversizing the pump components to achieve maximum power or adding an epicyclic gear train to control the speed of the pump impellers.

Claims

Claims

1. Fuel supply system for a turbomachine (100), the turbomachine (100) comprising at least one accessory housing (104) comprising at least one output shaft, the system comprising a fuel circuit (102) comprising: - the output shaft (106) of the accessory relay box (104); - a counter-rotating centrifugal pump (200) comprising at least two concentric impellers (202i, 2022) including: • at least one external impeller (2020 configured to be driven in rotation in a first direction by the output shaft of the accessory relay housing (104) of the turbomachine so as to send a flow of fuel into said circuit (102); • at least one central impeller (2022) configured to rotate in a second direction opposite to that of the external impeller; - a hydromechanical group (204) configured to control at least one fuel outlet to a combustion chamber (108); the system being configured to regulate a fuel flow to said combustion chamber (108) from a flow setpoint (Pc) in a hydraulic circuit downstream of the hydromechanical group (204), characterized in that: - the hydromechanical group (204) comprises at least one measuring device (306i, 3062) configured to evaluate a pressure difference (APi) relative to the flow rate setpoint (Pc) or a pressure drop (AP2) relative to the flow rate setpoint (Pc); and - the system further comprises a speed control device (208) configured to control a rotation speed of the central impeller (2022) and at least one control unit (206) for controlling said speed control device (208) to vary the rotation speed of the central impeller (2022) of the pump either from said evaluated pressure drop (AP2) or from the pressure difference (APi) evaluated, so as to adapt the pressure supplied by the pump (200), via the drive of the external impeller (2020, to a need linked to the flow rate instruction (Pc).

2. The system of claim 1, wherein the pump (200) comprises at least one mechanical impeller and one electric impeller.

3. The system of claim 1 or 2, wherein the electric wheel is the central wheel (2022) and the speed control device (208) is an electric system or motor.

4. System according to any one of claims 1 to 3, in which the central impeller (2022) is sized to provide a power of the order of 25% of a total power required for the flow rate setpoint (Pc) and the external impeller (2020) is sized to provide a power of the order of 75% of said total power.

5. System according to any one of claims 1 to 4, in which the central impeller (2022) and external impeller (2020) are dimensioned so that the rotation speed of the central impeller (2022), driven by the speed regulation device (208), is + / -30% that of the external impeller (2020), driven by the output shaft (106) of the accessory relay box (104) of the turbomachine (100).

6. System according to any one of claims 1 to 5, in which the hydromechanical group (204) further comprises at least: - a metering device (302) configured to send a flow rate equal to the flow rate setpoint (PO) to the fuel outlet; - a servovalve (300) configured to receive the flow rate setpoint (PO) and control the position of the metering device (302); - a regulating valve (304) arranged downstream of the metering device (302) and configured to maintain the pressure difference (AP0) constant across the terminals of the metering device (302).

7. System according to claim 6, in which the measuring devices (306i, 3062) comprise at least: - a first pressure sensor (3060 arranged at the terminals of the dosing device (302) to evaluate a pressure deviation (APO) relative to the flow rate setpoint (PO; - a second pressure sensor (3062) configured to evaluate a pressure drop (AP2) across the regulating valve (304), the pressure drop corresponding to a pressure variation.

8. System according to any one of claims 1 to 7, in which the circuit (102) further comprises: - a supply means (216) of the circuit (102) driven either by the output shaft (106) of the accessory relay box (104) of the turbomachine (100) or by the speed regulation device (208); - a variable geometry supply loop (212) of the turbomachine (100); - a filter (214) connected at least to the supply means (216), to the variable geometry supply loop (212) and to the pump (200) to at least trap contaminants from the fuel.

9. Turbomachine (100) comprising a system according to one of the preceding claims.

10. Method for regulating a centrifugal fuel pump (200) for a turbomachine (100) according to claim 9 in an aircraft, characterized in that it implements control laws (400) of the rotation speed of an impeller of the pump (200), which increase or, respectively, decrease this speed when the pressure difference or the pressure loss decreases or increases, so that the flow rate and the pressure at the outlet of the circuit (102) are adapted to the flight conditions of the aircraft.

11. Method for regulating a pump according to the preceding claim, in which said control laws (400) are configured to also adapt the pressure supplied by the pump and the pressure in the circuit (102) to the conditions of use of the variable geometries (212) or secondary supply circuits (218).

12. Method for regulating a pump according to one of claims 10 or 11, in which the control laws (400) comprise at least: - the reception (500) of a flow rate setpoint (Pc); - the evaluation (502) of a pressure difference (APi) with respect to the flow rate setpoint (Pc) or a pressure drop (AP2) relative to the flow rate setpoint (Pc); the variation of the rotation speed of the central impeller (2022) of the pump (200) either from the evaluated pressure difference (APi) or from the evaluated pressure loss (AP2), so as to adapt the pressure supplied by the pump (200) according to the need linked to the flow rate setpoint (Pc).

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