FR3149644A1 - Fuel control system - Google Patents

Abstract

The present disclosure relates to a fuel control system (2) for a turbomachine (1), the system (2) comprising:a main pumping device (22); anda transmission device (3) comprising:a mechanical differential (31); an electric motor (32); and an electric power source (33). Figure for abstract: Fig. 3

Description

Fuel control system

This presentation concerns the aeronautical field. More specifically, this presentation concerns the regulation of fuel within an aircraft engine.

STATE OF THE ART

An aircraft engine typically includes a control system configured to respond, sometimes strictly, to the fuel supply requirements of the engine combustion chamber and, possibly, of an afterburner circuit and/or variable engine geometries, regardless of the engine operating speed.

The efficiency, safety and service life of the fuel control system depend, in particular, on the properties of the pumps which compose it and their drive method.

Fuel control systems using a positive displacement pump, or a centrifugal pump, driven directly, or via transmission devices, by the engine accessory box, have been proposed, but are not entirely satisfactory.

GENERAL PRESENTATION

An aim of this presentation is to increase the service life and improve the efficiency, particularly thermal, of a fuel regulation system of a turbomachine, in a simple and inexpensive manner, without increasing its mass.

For this purpose, according to one aspect of the present disclosure, there is provided a fuel regulation system for a turbomachine, the system comprising:
a main pumping device comprising a discharge capable of being connected to a combustion chamber and to a variable geometry of the turbomachine in order to provide a fuel supply thereto, the main pumping device comprising a first main centrifugal pump comprising a rotor part and a stator part;
a transmission device configured to modulate a drive speed of the rotor portion of the first main centrifugal pump relative to the stator portion of the first main centrifugal pump, the transmission device comprising:
an epicyclic gear train comprising a sun pinion, a crown, a series of satellites meshed by the sun pinion and by the crown, and a planet carrier on which the series of satellites is mounted, in which:
the crown is connected to the rotor portion of the first main centrifugal pump and configured to rotate the rotor portion of the first main centrifugal pump relative to the stator portion of the first main centrifugal pump; and
the planet carrier is capable of being connected to an accessory housing of the turbomachine to be driven in rotation by the accessory housing, so that the drive speed of the first main centrifugal pump is modulated according to an operating speed of the turbomachine; and
an electric machine connected to the sun pinion of the epicyclic gear train and configured to rotate the sun pinion, such that the drive speed of the first main centrifugal pump is further modulated according to a speed of the electric machine;
an auxiliary pumping device comprising a discharge; and
a switching device configured to connect the discharge of the auxiliary pumping device to the combustion chamber and to the variable geometry depending on a fuel pressure at the discharge of the main pumping device.

Advantageously, but optionally, the system may comprise at least one of the following features, taken alone or in any combination:
- the switching device is configured to connect the discharge of the auxiliary pumping device to the combustion chamber and to the variable geometry when the fuel pressure at the discharge of the main pumping device is below a threshold;
- in the system:
the auxiliary pumping device comprises a piston pump comprising a discharge capable of being connected to a nozzle of the turbomachine in order to provide a fuel supply thereto; and
the switching device includes:
an auxiliary conduit connecting the piston pump discharge to the combustion chamber and to the variable geometry; and
a valve arranged on the auxiliary conduit and configured to allow the circulation of fluid from the discharge of the piston pump to the combustion chamber and with variable geometry depending on the fuel pressure at the discharge of the main pumping device;
- the piston pump further comprises a rotor part and a stator part, the rotor part of the piston pump being able to be connected to the accessory housing to be driven in rotation, by the accessory housing, relative to the stator part of the piston pump;
- the main pumping device further comprises a second main centrifugal pump mounted in series with the first main centrifugal pump and comprising a rotor part and a stator part, the crown of the mechanical differential being further connected to the rotor part of the second main centrifugal pump and configured to rotate the rotor part of the second main centrifugal pump relative to the stator part of the second main centrifugal pump, such that a drive speed of the rotor part of the second main centrifugal pump relative to the stator part of the second main centrifugal pump is modulated as a function of the operating speed of the turbomachine and the speed of the electric machine;
- the system further includes:
a direct current electrical power source; and
a converter connecting the direct current electrical power source to the electrical machine; and
- the system further comprises a centrifugal post-combustion pump comprising a rotor part, a stator part and a discharge, the rotor part of the centrifugal post-combustion pump being able to be connected to the accessory housing to be driven in rotation, by the accessory housing, relative to the stator part of the centrifugal post-combustion pump, the discharge of the centrifugal post-combustion pump being able to be connected to a post-combustion chamber of the turbomachine in order to provide a fuel supply thereto.

According to another aspect, there is provided a turbomachine comprising:
a combustion chamber;
a variable geometry; and
a system as previously described, in which the discharge of the first main centrifugal pump is connected to the combustion chamber and to the variable geometry in order to ensure the fuel supply thereto.

According to another aspect, there is provided a method of controlling a system as previously described, the method comprising controlling the electric machine and the switching device as a function of the fuel pressure at the discharge of the main pumping device.

DESCRIPTION OF FIGURES

Other features, aims and advantages will emerge from the following description, which is purely illustrative and not limiting, and which must be read in conjunction with the attached drawings in which:

There illustrates an aircraft schematically.

There is a schematic sectional view of an aircraft engine.

There schematically illustrates a fuel control system.

In all figures, similar elements bear identical references.

DETAILED DESCRIPTION Aircraft

An aircraft 100 is a device configured to rise and move in the air, and may, for example, be an airplane, civil or military, or even a helicopter. An aircraft 100 comprises an airframe which, in the case of an airplane, is composed of a fuselage, a wing comprising two wings, empennages, flight control surfaces and landing gear.

Propulsion system

A propulsion system 1 (or turbomachine) has a main direction extending along a longitudinal axis XX. The propulsion system 1 is configured to be fixed on the cell of an aircraft 100 , for example under its wings, in the case of an airplane, and this by means of a pylon (or mast). The propulsion system 1 can also be mounted on the wing of the airplane or even at the rear of its fuselage, or even be integrated into its fuselage.

The propulsion system 1 may be a twin-spool, dual-flow, direct-drive, afterburning turbojet engine, as described below, but may also have a different number of spools and/or flows, and/or be another type of turbojet engine, such as a geared turbojet engine or a turboprop, with or without afterburning.

Unless otherwise specified, the terms “upstream” and “downstream” are used in reference to the overall direction of airflow through the propulsion system 1 in operation. Similarly, an axial direction corresponds to the direction of the longitudinal axis XX and a radial direction is a direction perpendicular to the longitudinal axis XX and intersecting the longitudinal axis XX. Furthermore, an axial plane is a plane containing the longitudinal axis XX and a radial plane is a plane perpendicular to the longitudinal axis XX. A circumference is understood to be a circle belonging to a radial plane and whose center belongs to the longitudinal axis XX. A tangential or circumferential direction is a direction tangent to a circumference: it is perpendicular to the longitudinal axis XX but does not pass through the longitudinal axis XX. Finally, the adjectives "inner" (or "internal") and "outer" (or "external") are used in reference to a radial direction so that the inner part of an element is, in a radial direction, closer to the longitudinal axis XX than the outer part of the same element.

The propulsion system 1 comprises, from upstream to downstream, a fan 10 , a compression section 12 , comprising a low-pressure compressor 120 and a high-pressure compressor 122 , a combustion chamber 14 and a turbine section 16 , comprising a high-pressure turbine 162 and a low-pressure turbine 160. The propulsion system further comprises an afterburner chamber 18 and a nozzle 19 .

The compressor section 12 comprises a succession of stages each comprising a wheel of moving blades (rotor) rotating in front of a wheel of fixed blades (stator). The turbine section 16 also comprises a succession of stages each comprising a wheel of fixed blades (stator) behind which a wheel of moving blades (rotor) rotates.

The combustion chamber 14 comprises a fuel injection rail and a plurality of ignition injectors. The injection rail and/or the ignition injectors constitute members of the propulsion system 1 which are fuel consumers. A dedicated circuit supplies the injection rail and/or the ignition injectors of the combustion chamber 14 , to ensure combustion, the different combustion stages determining different levels of fuel injection pressure within this circuit.

The afterburner chamber 18 comprises a channel attached and fixed to the nozzle 19 , so as to extend it axially upstream, afterburner injectors being arranged within the channel. The afterburner injectors constitute other members of the propulsion system 1 which are consumers of fuel. A dedicated circuit supplies the afterburner injectors, to ensure afterburner, the different afterburner stages determining different levels of fuel injection pressure within this circuit.

The nozzle 19 may be of variable section and thus comprise a plurality of flaps 191 , 192 , distributed circumferentially around the longitudinal axis XX. A control device 190 , such as a ring of hydraulic cylinders, is then connected to the flaps 191 , 192 to actuate them so that they adjust the opening of the air flow that they delimit. The actuating fluid of the hydraulic cylinders may be fuel. A dedicated circuit supplies, if necessary, the control device 190 to ensure its actuation, the different actuation levels of the control device 190 determining different levels of activation pressure of the fluid within this circuit.

The fan 10 , the rotor part of the low-pressure compressor 120 , and the rotor part of the low-pressure turbine 160 are connected to each other by a low-pressure shaft 170 extending along the longitudinal axis XX, the fan 10 , the low-pressure compressor 120 , the low-pressure shaft 170 , and the low-pressure turbine 160 then forming a low-pressure body 10 , 120 , 160 , 170. The rotor part of the high-pressure compressor 122 and the rotor part of the high-pressure turbine 162 are connected to each other by a high-pressure shaft 172 extending along the longitudinal axis XX, the high-pressure compressor 122 , the high-pressure shaft 172 , and the high-pressure turbine 162 then forming a high-pressure body 122 , 162 , 172 . The low pressure shaft 170 is generally housed, over a section of its length, in the high pressure shaft 172 and is coaxial with the high pressure shaft 172 .

The high-pressure compressor 122 , the combustion chamber 14 and the turbine section 16 are surrounded by a first casing 151 , while the fan 10 , the low-pressure compressor 120 and the afterburner 18 are surrounded by a second casing 152. The second casing 152 also surrounds the first casing 151 , i.e. it extends radially outside the first casing 151 , all around the longitudinal axis XX. The second casing 152 may be attached and fixed to the airframe of the aircraft 100 , for example by being integrated into the fuselage, the first casing 151 being connected to the second casing 152 in a fixed manner, the stator parts of the compression section 12 and the turbine section 16 , the combustion chamber 14 and the afterburner chamber 18 also being connected to the first casing 151 in a fixed manner.

The longitudinal axis XX forms the axis of rotation for the fan 10 , the rotor portion of the compression section 12 and the rotor portion of the turbine section 16 , which are capable of being driven in rotation about the longitudinal axis XX relative to each of the first casing 151 and the second casing 152 .

The propulsion system 1 also comprises at least one accessory box 30 , called AGB (for “Accessory gear box” in English terminology), which can be fixedly mounted relative to the second casing 152. The accessory box 30 comprises a set of rotating elements, such as gears, making it possible to drive a plurality of shafts in rotation around their own axis, accessories being mounted on these shafts to derive useful mechanical power from their rotation. The gear assembly is itself driven using a power take-off shaft connecting, possibly via a transfer case, the accessory case 30 to at least one of the high-pressure body 122 , 162 , 172 , and the low-pressure body 10 , 120 , 160 , 170 , typically by being meshed with at least one of the high-pressure shaft 172 and the low-pressure shaft 170. In this way, mechanical power is capable of being taken from at least one of the high-pressure body 122 , 162 , 172 , and the low-pressure body 10 , 120 , 160 , 170 , to be delivered to the at least one of the accessories via the accessory case 30 .

The propulsion system 1 comprises a certain number of members (or equipment) configured to be actuated by means of fuel. More precisely, these members are hydraulically actuated and it is intended to use pressurized fuel to ensure their operation. These members are usually designated under the name "variable geometry equipment (or accessories) 14' " or, more simply, "variable geometries 14' ". Examples of variable geometries 14' are: variable-pitch blades (eg, stator blades of the high-pressure compressor 122 ), discharge valves of the primary vein A or of the secondary vein B (described below). These variable geometries 14' therefore need the hydraulic energy linked to the fuel pressure to operate. However, unlike an injector of the combustion chamber 14 or of the post-combustion chamber 18 , the variable geometries 14' do not consume fuel, because they do not degrade it by combustion. A dedicated circuit supplies the 14' variable geometries to ensure their actuation, the different actuation levels of the 14' variable geometries determining different activation pressure levels of each of the 14' variable geometries.

The circuits dedicated to the fuel supply of the variable geometries 14' , of the combustion chamber 14 , of the post-combustion chamber 18 and of the nozzle 19 (eg, of its control device 190 and/or of its flaps 191 , 192 ) may be independent of each other, or be common in whole or in part.

A controller may also be provided to provide the interface between the propulsion system 1 and the aircraft 100 , but also to ensure control of the propulsion system 1 . Typically, the controller may provide the functions of: regulating the circulation of the various fluids necessary for the operation of the propulsion system 1 , starting the propulsion system 1 , transmitting various measured parameters of the propulsion system 1 to the cockpit of the aircraft 100 , managing thrust or reverse thrust, etc. Such a controller may implement digital-type regulation and include a computer, a memory and various data exchange channels that interact with each other. Typically, the controller may be of the FADEC type (for “Full Authority Digital Engine Control” in English terminology).

In operation, the blower 10 and the low-pressure compressor 120 draw in an air flow, a portion of which, circulating within a primary vein A passing through the propulsion system 1 from one side to the other, is successively compressed within the high-pressure compressor 122 , ignited within the combustion chamber 14 by combustion of fuel, and expanded within the turbine section 16 before being transferred to the afterburner chamber 18. Another portion of the air flow circulates within a secondary vein B which takes an elongated annular shape surrounding the first casing 151 and the afterburner chamber 18. An upstream portion of the second casing 152 defines an air inlet through which the blower 10 and the low-pressure compressor 120 draw in the air flow circulating through the propulsion system 1 . A downstream portion of the second casing 152 defines, with the first casing 151 and the afterburner chamber 18 , then the flaps 191 , 192 of the nozzle 19 , the secondary stream B. Between the turbine section 16 and the afterburner chamber 18 , the flow of the primary stream A can mix with the flow of the secondary stream B , typically to become enriched with oxygen. Within the afterburner chamber 18 , air can flow before being ejected from the propulsion system 1 to generate thrust, or fuel can be vaporized in the air flow. Indeed, the air circulating within the afterburner chamber 18 has a high speed and still contains sufficient oxygen to cause combustion. The flames created by the afterburner stabilize a little further downstream in one or more toric gutters of the afterburner chamber 18 , called flame holders, which hold gas recirculation cores in their wake. A boost in thrust due to this new combustion can thus be obtained. The nozzle 19 makes it possible to guide the air flow downstream of the propulsion system 1 to promote thrust. The variable nature of the nozzle 19 makes it possible to obtain a gain in thrust regardless of the operating regime of the propulsion system 1 , i.e. with or without the use of the afterburner. The thrust obtained can, for example, be used for the benefit of the aircraft 100 on which the propulsion system 1 is attached and fixed.

Fuel control system

In order to manage a fuel supply to the fuel-consuming organs, such as the injectors of the combustion chamber 14 and the afterburner chamber 18 , the variable geometries 14' and the nozzle 19 , which is as close as possible to their needs, the propulsion system 1 comprises a fuel regulation system 2. Insofar as the fuel regulation system 2 is configured to meet the strict fuel supply requirement, its thermal rejections are reduced, or even cancelled, which improves its efficiency, in particular when it is connected to a heat exchanger system of the propulsion system 1 .

The fuel regulation system 2 comprises a plurality of pumps 22 , 24 , 26 , 28 connected together by a hydraulic circuit 200 .

The fuel control system 2 further comprises a fuel source 20 provided to supply fuel for the actuation of the variable geometries 14' and the nozzle 19 , and for combustion within the combustion chamber 14 and the afterburner chamber 18. The fuel source 20 may be a tank for storing fuel or a fuel supply circuit.

Among the plurality of pumps 22 , 24 , 26 , 28 , the fuel regulation system 2 comprises a booster pump 28 , preferably of the centrifugal type, for pressurizing the circuit 200. In this regard, the booster pump 28 is connected to the fuel source 20 and configured to deliver fuel admitted from the fuel source 20 to the circuit 200 .

The fuel control system 2 further comprises a main pumping device 22 whose inlet is connected, where appropriate, to the feed pump 28. The discharge of the main pumping device 22 is connected to at least one fuel-consuming member, preferably at least one of the injectors of the combustion chamber 14 and/or to at least one variable geometry 14' , in order to ensure, at least in part, their fuel supply. The main pumping device 22 comprises at least one centrifugal pump and, preferably, two centrifugal pumps mounted in series with each other, which improves the efficiency of the main pumping device 22 . The use of centrifugal pumps, and not positive displacement pumps, in particular in a fuel control system 2 meeting the strict fuel supply requirement, makes it possible to make the fuel control system 2 more compact and lighter, in particular because, unlike positive displacement pumps, it is not necessary to oversize the bearings for operation at low flow rates. Indeed, a centrifugal pump does not have to be driven at low speeds to deliver a low flow rate, but rather operates as a pressure source. As a result, the fuel control system 2 can be used for the benefit of propulsion systems requiring that a fuel supply be provided with a large variability of flow rates, regardless of the speed of the propulsion system. In addition, a centrifugal pump is more robust than a positive displacement pump. Where appropriate, it is the inlet port of the centrifugal pump, or of the first of the centrifugal pumps, which is connected to the discharge port of the feed pump 28 , and the discharge port of the centrifugal pump, or of the second of the centrifugal pumps, which is connected to the fuel consuming member and/or to at least one variable geometry 14 ' , the discharge port of the first centrifugal pump being connected to the inlet port of the second centrifugal pump. In this regard, the supply circuit of the variable geometry 14 ' may be arranged in parallel with the main pumping device 22 or only with the second of the centrifugal pumps of the main pumping device 22 .

The fuel control system 2 comprises a valve 36 positioned between the discharge port of the main pumping device 22 and the fuel consuming member and/or the at least one variable geometry 14 '. The valve 36 has a pressure drop controlled by a flow meter 37. The valve 36 is controllable, and is designed to be controlled in particular so as to induce a low pressure drop at the discharge of the main pumping device 22 at operating speeds of the propulsion system 1 where the flow rate discharged by the main pumping device 22 is low and the pressure requirement of the variable geometries 14' is greater than the pressure requirement of the combustion chamber 14 . If the fuel regulation system 2 were not configured to ensure the strict need for the fuel supply, the valve 36 would also be controlled to generate a pressure drop, sometimes significant, and a source of thermal rejections, at the operating speeds of the propulsion system 1 where the flow rate delivered by the main pumping device 22 is greater than the needs of the fuel consuming member and/or the variable geometries 14' .

Furthermore, the fuel regulation system 2 comprises an auxiliary pumping device for supporting the main pumping device 22 in order to meet the pressure requirements of the fuel consuming member and/or of at least one of the variable geometries 14' , at speeds of the propulsion system 1 which are low.

The auxiliary pumping device may comprise a piston pump 24 , preferably a piston pump whose displacement is variable and which, more preferably, is self-regulating in flow rate and pressure. The discharge port of the piston pump 24 is connected to the nozzle 19 to supply it with fuel and thus ensure the actuation of the flaps 191 , 192 of the nozzle 19. The piston pump 24 is mounted in parallel with the main pumping device 22 , that is to say by being arranged so that its intake port is connected to the feed pump 28 .

Furthermore, the fuel control system 2 comprises a switching device configured to connect the delivery of the auxiliary pumping device to the fuel consuming member and/or to the at least one variable geometry 14' depending on a fuel pressure at the delivery of the main pumping device 22. More specifically, the switching device is configured to connect the delivery of the auxiliary pumping device to the fuel consuming member and/or to the at least one variable geometry 14' when the fuel pressure at the delivery of the main pumping device 22 is below a threshold. Thus, at low speeds of the propulsion system 1 , the auxiliary pumping device is able to support the main pumping device 22 in order to meet the pressure requirements of the fuel consuming member and/or of at least one of the variable geometries 14' . The switching device may comprise an auxiliary conduit connecting the discharge port of the piston pump 24 to the fuel consuming member and/or to the at least one variable geometry 14', and a valve 38 arranged on the auxiliary conduit and configured to allow the circulation of fluid from the discharge port of the piston pump 24 to the fuel consuming member and/or to the at least one variable geometry 14' depending on the fuel pressure at the discharge of the main pumping device 22 , and more precisely when the fuel pressure at the discharge of the main pumping device 22 is below the threshold. The valve 38 may, if necessary, be controlled, preferably by the controller, to regulate the circulation of fuel from the discharge port of the piston pump 24 to the fuel consuming member and/or to the at least one variable geometry 14' . More specifically, the valve 38 is then controlled to allow the circulation of fuel from the discharge port of the piston pump 24 to the fuel-consuming member and/or to the at least one variable geometry 14' , when the main pumping device 22 is unable to provide the injection pressure necessary for the operation of the combustion chamber 14 and/or the activation pressure necessary for the actuation of variable geometries 14' . A non-return valve may be provided at the discharge of the main pumping device 22 , to protect the centrifugal pumps therefrom when, at low speeds of the propulsion system 1 , the auxiliary pumping device delivers to the fuel-consuming member and/or the at least one variable geometry 14' .

Furthermore, the fuel control system may comprise an afterburner pump 26 , preferably of the centrifugal type. The discharge port of the afterburner pump 26 is connected to the injectors of the afterburner chamber 18 in order to ensure, at least in part, its supply of fuel at a predetermined pressure. The afterburner pump 26 may be mounted in parallel with the main pumping device 22 , if necessary only in parallel with the second centrifugal pump of the main pumping device 22 , i.e. by being arranged so that its inlet port is connected to the feed pump 28 , if necessary to the discharge port of the discharge port of the first centrifugal pump of the main pumping device 22 , or, alternatively, be mounted in series with the main pumping device 22 , i.e. by being arranged so that its inlet port is connected to the discharge of the main pumping device 22. In the parallel arrangement, the afterburner centrifugal pump 26 ensures the fuel supply to the injectors of the afterburner chamber 18 independently, while in the series arrangement, the afterburner centrifugal pump 26 participates in the fuel supply to the injectors of the afterburner chamber 18 . injectors of the afterburner chamber 18 , in support of the main pumping device 22 .

It should be noted that, in certain cases, the fuel control system 2 may be devoid of a centrifugal afterburner pump 26. Where appropriate, it is the main pumping device 22 which alone ensures the fuel supply to the injectors of the afterburner chamber 18 , the delivery of the main pumping device 22 being, where appropriate, connected to the injectors of the afterburner chamber 18. Optionally, the piston pump 24 may also participate in the fuel supply to the injectors of the afterburner chamber 18 , the fuel delivered by the piston pump 24 to injectors of the combustion chamber 14 and/or to the at least one variable geometry 14' then also being able to circulate to the injectors of the afterburner chamber 18 .

Each of the pumps 22 , 24 , 26 , 28 comprises a rotor part and a stator part, the rotor part being movable in rotation relative to the stator part, the rotation speed of the rotor part relative to the stator part determining a drive speed of the pump 22 , 24 , 26 , 28 .

The rotational drive of the rotor part, relative to the stator part, of each of the pumps 22 , 24 , 26 , 28 , is implemented by mechanical sampling.

To do this, a gear of the accessory housing 30 is connected to the rotor part of the piston pump 24 and another, or the same, gear of the accessory housing 30 is connected to the rotor part of the afterburner pump 26 to drive it in rotation relative to the stator part.

A transmission device 3 is arranged between the accessory housing 30 and the main pumping device 22 , in order to modulate the speed of the centrifugal pumps of the main pumping device 22 as a function, in particular, of the operating speed of the propulsion system 1. This transmission device 3 thus makes it possible, even at low operating speeds of the propulsion system 1 , to ensure the supply of fuel to the fuel-consuming members, typically for the activation of the variable geometries 14' .

The transmission device 3 comprises a mechanical differential 31 , an electrical machine 32 , an electrical power source 33 and, where appropriate, a converter 34 .

The mechanical differential 31 comprises two inputs 311 , 312 and one output 310 .

The first input 311 is connected to the accessory housing 30 , more precisely to a gear of the accessory housing 30 to be driven in rotation. Thus, a rotation speed of the first input 311 corresponds to a speed of the body of the propulsion system 1 from which the accessory housing 30 draws mechanical power, possibly corrected by a reduction or multiplication factor introduced by the accessory housing 30 and/or by any type of reduction or multiplication device that can be arranged between the accessory housing 30 and the first input 311 .

The second input 312 is connected to the electric machine 32 to be driven in rotation. Thus, a rotation speed of the second input 312 corresponds to a speed of the electric machine 32 , which is configured to inject or draw mechanical power from within the mechanical differential 31 by transmitting a given torque, at a given speed, to the second input 312 .

The output 310 is connected to the rotor part of each of the centrifugal pumps of the main pumping device 22 and, where appropriate, of the booster pump 28 , to drive it in rotation relative to its stator part. Thus, a rotation speed of the output of the mechanical differential 31 corresponds to a speed of the centrifugal pump 22 , 28 to which the output 310 of the mechanical differential 31 is connected.

The mechanical differential 31 is preferably an epicyclic gear train comprising a sun pinion 312 , centered on an axis of rotation of the mechanical differential 31 , a crown 310 coaxial with the sun pinion 312 and a series of satellites distributed circumferentially around the axis of rotation between the sun pinion 312 and the crown 310 , each satellite being meshed internally with the sun pinion 312 and externally with the crown 310 . The series of satellites is mounted on a planet carrier 311 .

Each of the sun pinion 312 , the crown 310 and the planet carrier can act as input 311 , 312 or output 310 of the mechanical differential 31 . However, it is preferably the crown 310 which acts as the output 310 so that a rotation of the crown 310 about the axis of rotation of the mechanical differential 31 causes a rotation of the rotor part of the centrifugal pump 22 , 28 relative to its stator part, the planet carrier 311 which acts as the first input 311 so that a rotation of the gear of the accessory housing 30 to which the planet carrier 311 is connected causes a rotation of the planet carrier 311 about the axis of rotation of the mechanical differential 31 , and the sun pinion 312 which acts as the second input 312 so that a rotation of an output shaft of the electric machine 32 to which the sun pinion 312 is connected causes a rotation of the sun pinion 312 about the axis of rotation of the mechanical differential 31 . This configuration is in fact the one which best preserves the electric machine 32 and the various rotating parts 310 , 311 , 312 of the mechanical differential, whatever the operating regime of the propulsion system 1 , that is to say whatever the drive speed of the accessory box 30 and the speed of the centrifugal pumps 22 , 28. Indeed, the maximum speed likely to be reached by the accessory box 30 is always lower than the speed of the centrifugal pump 22 , 28 to which the output 310 is connected.

The electrical power source 33 is configured to exchange electrical power with the electrical machine 32 . The electrical machine 32 is configured to transform electrical power received from the electrical power source 33 into mechanical power to be injected into the mechanical differential 31 , via an imparted torque, at a given speed, by its output shaft to the second input 312 of the mechanical differential 31 . The electrical machine 32 is also configured to extract mechanical power from the mechanical differential 31 , via a braking torque imparted to the second input 312 of the mechanical differential 31 by its output shaft, and to transform this extracted mechanical power into electrical power supplied to the electrical power source 33 , which is capable of storing it. In this way, the main pumping device 22 is able to deliver the strict fuel supply requirement to the fuel consuming organs and/or to the at least one variable geometry 14 ', in particular by controlling the drive speed of the electric machine 32 as a function of the flow rate recorded by the flow meter 38 .

The electrical power source 33 may be alternating current or direct current, such as a battery. In the latter case, the transmission device 3 may further comprise a converter 34 connecting the direct current electrical power source 33 to the electrical machine 32 and configured to convert an electrical signal emitted in continuous form by the direct current electrical power source 33 into an electrical signal in alternating form to be transferred to the electrical machine 32 .

In operation, when the fuel pressure at the discharge of the main pumping device 22 is greater than the requirement of the fuel consuming member and/or of the at least one variable geometry 14' , the electric machine 32 is controlled in a braking mode to reduce the drive speed of the centrifugal pumps of the main pumping device 22 , which reduces the pressure delivered by the main pumping device 22 , the pressure delivered by a centrifugal pump being proportional to the square of its drive speed. Furthermore, when the electric machine 32 is controlled at zero speed, the drive speed of the pumps of the main pumping device 22 is directly correlated to the speed of the propulsion system 1 , via the reduction box 30 and the transmission device 3 . The fuel control system 2 is sized so that, when the electric machine 32 is driven at zero speed, the drive speed reached by the pumps of the main pumping device 22 is sufficient to ensure the delivery of a pressure corresponding to the needs of the fuel-consuming member and/or of the at least one variable geometry 14' , and this for all operating speeds of the propulsion system 1 , except for low speeds where the auxiliary pumping device is provided to provide support. This sizing is carried out taking into account two constraints: the pumps of the main pumping device 22 are chosen so that their maximum drive speed is not reached in order to meet the flow rate variability required at each of the different drive speeds of the propulsion system 1 , and the electric machine 32 and the transmission device 3 are chosen so that the maximum braking speed of the electric machine 32 does not exceed its maximum drive speed. In this mode of operation of the fuel control system 2 , the electric machine 32 operates only in a braking mode, i.e. as an electric generator, the electrical power source 33 serving as a storage battery. This is particularly advantageous in the event of a blockage of the transmission device 3 or a breakdown of the electric machine 32 . Indeed, the excess pressure is, in this case, released by the valve 36 .

In an operating mode where the auxiliary pumping device is absent, the electric machine 32 is designed to operate in an engine mode at the speeds of the propulsion system 1 at which the pressure delivered by the main pumping device 22 is too low compared to the needs of the fuel-consuming member and/or the at least one variable geometry 14' . This operating mode has the advantage of reducing the braking power of the electric machine 32 , and therefore its mass and size.

In any case, it is possible to avoid dimensioning the fuel regulation system 2 so that, when the electric machine 32 is driven at zero speed, the pressure delivered by the main pumping device 22 is sufficient to meet the needs of the fuel-consuming member and/or of the at least one variable geometry 14' , regardless of the operating speed. Indeed, such dimensioning would inevitably involve exceeding the maximum drive speeds of the centrifugal pumps of the main pumping device 22 at high operating speeds of the propulsion system 1 and therefore would require oversizing the electric machine 32 to brake them sufficiently.

By means of the fuel regulation system 2 , it is thus possible to implement a fuel regulation method within the propulsion system 1 in which, regardless of the speed of the body of the propulsion system 1 from which the accessory housing 30 draws mechanical power, the speed of the centrifugal pumps of the main pumping device 22 is adjusted to the exact pressure requirement of the combustion chamber 14 and/or the variable geometries 14' , while respecting the braking power limitation of the electric machine 32 , but also its maximum drive speed limitation, and the maximum drive speed limitation of the centrifugal pumps of the main pumping device 22 , and without penalizing the mass and size of the centrifugal pumps of the main pumping device 22 .

Claims (9)

Fuel control system (2) for a turbomachine (1), the system (2) comprising:
a main pumping device (22) comprising a discharge capable of being connected to a combustion chamber (14) and to a variable geometry (14') of the turbomachine (1) in order to provide a fuel supply thereto, the main pumping device (22) comprising a first main centrifugal pump comprising a rotor part and a stator part;
a transmission device (3) configured to modulate a drive speed of the rotor part of the first main centrifugal pump relative to the stator part of the first main centrifugal pump, the transmission device (3) comprising:
an epicyclic gear train (31) comprising a sun pinion (312), a crown (310), a series of satellites meshed by the sun pinion (312) and by the crown (310), and a planet carrier (311) on which the series of satellites is mounted, in which:
the crown (310) is connected to the rotor portion of the first main centrifugal pump and configured to rotate the rotor portion of the first main centrifugal pump relative to the stator portion of the first main centrifugal pump; and
the planet carrier (311) is capable of being connected to an accessory housing (30) of the turbomachine (1) to be driven in rotation by the accessory housing (30), so that the drive speed of the first main centrifugal pump is modulated according to an operating speed of the turbomachine (1); and
an electric machine (32) connected to the sun pinion (312) of the epicyclic gear train (31) and configured to rotate the sun pinion (312), such that the drive speed of the first main centrifugal pump is further modulated according to a speed of the electric machine (32);
an auxiliary pumping device comprising a discharge; and
a switching device configured to connect the discharge of the auxiliary pumping device to the combustion chamber (14) and to the variable geometry (14') depending on a fuel pressure at the discharge of the main pumping device (22). System (2) according to claim 1, wherein the switching device is configured to connect the discharge of the auxiliary pumping device to the combustion chamber (14) and to the variable geometry (14') when the fuel pressure at the discharge of the main pumping device (22) is below a threshold. System (2) according to any one of claims 1 and 2, in which:
the auxiliary pumping device comprises a piston pump (24) comprising a discharge capable of being connected to a nozzle (19) of the turbomachine (1) in order to provide a fuel supply thereto; and
the switching device includes:
an auxiliary conduit connecting the discharge of the piston pump (24) to the combustion chamber (14) and to the variable geometry (14'); and
a valve arranged on the auxiliary conduit and configured to allow the circulation of fluid from the discharge of the piston pump (24) to the combustion chamber (14) and to the variable geometry (14') depending on the fuel pressure at the discharge of the main pumping device (22). System (2) according to claim 3, wherein the piston pump (24) further comprises a rotor part and a stator part, the rotor part of the piston pump (24) being adapted to be connected to the accessory housing (30) to be driven in rotation, by the accessory housing (30), relative to the stator part of the piston pump (24). System (2) according to any one of claims 1 to 4, wherein the main pumping device (22) further comprises a second main centrifugal pump mounted in series with the first main centrifugal pump and comprising a rotor part and a stator part, the crown (310) of the mechanical differential (31) being further connected to the rotor part of the second main centrifugal pump and configured to rotate the rotor part of the second main centrifugal pump relative to the stator part of the second main centrifugal pump, so that a drive speed of the rotor part of the second main centrifugal pump relative to the stator part of the second main centrifugal pump is modulated as a function of the operating speed of the turbomachine (1) and the speed of the electric machine (32). System (2) according to any one of claims 1 to 5, further comprising:
a direct current power supply (33); and
a converter (34) connecting the direct current power source (33) to the electric machine (32). System (2) according to any one of claims 1 to 6, further comprising a centrifugal post-combustion pump (26) comprising a rotor part, a stator part and a discharge, the rotor part of the centrifugal post-combustion pump (26) being able to be connected to the accessory housing (30) to be driven in rotation, by the accessory housing (30), relative to the stator part of the centrifugal post-combustion pump (26), the discharge of the centrifugal post-combustion pump (26) being able to be connected to a post-combustion chamber (18) of the turbomachine (1) in order to provide a fuel supply thereto. Turbomachine (1) comprising:
a combustion chamber (14);
a variable geometry (14'); and
a system (2) according to any one of claims 1 to 7, in which the discharge of the first main centrifugal pump is connected to the combustion chamber (14) and to the variable geometry (14') in order to ensure the fuel supply thereto. Method for controlling a system (2) according to any one of claims 1 to 7, the method comprising controlling the electric machine (32) and the switching device as a function of the fuel pressure at the discharge of the main pumping device (22).