Fuel metering system for an aircraft turbomachine fuel supply circuit

Abstract

The invention relates to a fuel metering system (10) for an aircraft turbomachine, comprising: - a main metering device, configured to deliver fuel at the outlet of the metering system (10) at a flow rate conforming to a flow rate setpoint given by a control unit (16); - an auxiliary metering device, disposed upstream of the main metering device with respect to the direction of fuel flow, the auxiliary metering device being connected in series and in parallel with the main metering device, the auxiliary metering device being controlled by the control unit (16) to maintain the operation of the metering system in the event of a failure of the main metering device. Figure 2.

Description

Title of the invention: Fuel metering system for an aircraft turbomachine supply circuit technical field

[0001] The present invention relates to the field of aeronautics. It relates more particularly to fuel supply systems for aircraft turbomachinery, including in particular turboprops and turbojets for aircraft. State of the art

[0002] Aircraft turbomachinery are traditionally equipped with a fuel metering system, generally designated by the acronym FMU (corresponding to the English term "Fuel Metering Unit") or the acronym HMU (corresponding to the English term "Hydro Mechanical Unit").

[0003] The fuel metering system ensures fuel metering, that is, the regulation of the fuel flow supplied to the turbomachine's combustion chamber injectors, according to a setpoint dictated by an aircraft control unit based on the flight phase, with the required precision. It also allows fuel to be shut off following a pilot command, as well as the shut-off and / or regulation of the fuel flow in certain emergency situations, for example, in the event of turbomachine overspeed, detected by a speed sensor on the high and / or low pressure section of the turbomachine.

[0004] A dosing system generally comprises several subsystems, including: - a metering unit, generally designated by the acronym FMV (corresponding to the English term "Fuel Metering Valve"), whose main function is to control the injection flow by the gradual closing of a calibrated fuel passage slot using a moving part, generally called a shutter; - a servovalve, connected to the metering unit to control its position, - a regulating valve (generally referred to by the English term "By-pass Valve"), ensuring recirculation of uninjected fuel (depending on the flow demand). The regulating valve also serves to maintain a constant fuel pressure differential (AP) between the upstream and downstream sides of the metering unit. It typically consists of a purely passive device, comprising a movable shutter acting against the action of a spring calibrated to a predetermined value of the AP differential to be maintained. The shutter is generally perforated to allow fuel to flow through a pipe leading to the recirculation loop, depending on its equilibrium position against the spring's action.

[0005] The metering unit constitutes a pilot-operated valve for metering the flow of fuel sent to the injectors of the combustion chamber of the turbomachine.

[0006] The dosing system is thus configured to supply a turbomachine with fuel, this fuel coming from one or more on-board tanks.

[0007] However, certain failures of the metering system can lead to inappropriate power output, either too high or too low, due to an unsuitable fuel flow rate. These failures are often compensated for by shutting down the engine, which has a significant impact on flight. Indeed, shutting down the engine affected by the failure results in a complete loss of power to that engine. Currently, no fuel metering system is known that can perform failure compensation adapted to the flight phase. The objective of the invention is to overcome this deficiency. Description of the invention

[0008] To this end, the invention relates to a fuel metering system for an aircraft turbomachine, the system comprising: - a main dosing device, configured to deliver fuel at the outlet of the dosing system with a flow rate conforming to a flow rate setpoint given by a control unit; - an auxiliary dosing device, positioned upstream of the main dosing device relative to the direction of fuel flow, the auxiliary dosing device being connected in series and in parallel with the main dosing device, the auxiliary dosing device being controlled by the control unit to: • that in the event of normal operation of the main dosing device, the auxiliary dosing device does not modify the flow of fuel entering the dosing system and reaching the main dosing device; • that in the event of a failure of the main dosing device resulting in a fuel flow rate at the outlet of the dosing system exceeding the set flow rate, the auxiliary dosing device limits the fuel flow rate reaching the main dosing device; and • that in the event of a failure of the main dosing device resulting in a fuel flow at the outlet of the dosing system lower than the flow setpoint, the auxiliary dosing device delivers fuel directly at the outlet of the dosing system by partially or totally bypassing the main dosing device.

[0009] Thus, by providing for the integration of an auxiliary dosing system in series with and in parallel with the main dosing device, the invention makes it possible to regulate the fuel flow supplied to the injection system according to the different cases of failure. of the dosing system that may occur. The auxiliary dosing device is advantageously controlled by the engine control unit in the event of a failure of the main dosing device. The invention thus makes it possible to provide fault accommodation modes that allow the engine to continue running and prevent it from shutting down.

[0010] The dosing system according to the invention may include one or more of the following optional features, considered alone or according to all possible combinations.

[0011] According to one feature, the auxiliary dosing device is connected in series to the main dosing device via a main line, and connected in parallel to the main dosing device via a bypass line connecting the auxiliary dosing device to a main output of the dosing system.

[0012] According to one feature, the auxiliary dosing device can be selectively placed in at least three configurations, among which: - a neutral configuration, in which the auxiliary dosing device does not modify the incoming fuel flow and directs the fuel exclusively to the main line; - at least one flow limitation configuration, in which the auxiliary metering device directs fuel exclusively to the main line and limits the flow supplied to the main metering device to a maximum value; - at least one flow increase configuration, in which the auxiliary metering device directs the fuel to both the main line and the bypass line, so as to increase the flow delivered at the outlet of the metering system to a minimum value.

[0013] According to one feature, the change in configuration of the auxiliary dosing device is controlled by the control unit.

[0014] According to one feature, the auxiliary dosing device can be selectively set: - in at least two flow limitation configurations, each flow limitation configuration being characterized by a respective maximum flow value; and / or - in at least two flow rate increase configurations, each flow rate increase configuration being characterized by a respective minimum flow rate value.

[0015] The invention also relates to a fuel supply circuit for an aircraft turbomachine comprising a metering system as defined above.

[0016] According to one feature, the supply circuit includes a control unit configured to determine a fuel flow setpoint to be supplied by the supply circuit, the control unit being further configured to detect a failure of the main metering device on the basis of one or more operating parameters of the turbomachine, and, in the event of detection of a failure of the main metering device, to determine an appropriate flow setpoint and command a change in the configuration of the auxiliary metering device according to the appropriate flow setpoint.

[0017] The invention also relates to an aircraft turbomachine, comprising a metering system conforming to that defined above, and / or a supply circuit as defined above.

[0018] The invention also relates to an aircraft comprising at least one turbomachine and at least one power supply circuit as defined above.

[0019] According to one feature, the aircraft is an airplane comprising at least two turbomachines, each turbomachine being supplied by a tank located in a wing of the airplane, the airplane comprising, for each turbomachine, a supply circuit conforming to that defined above. Brief description of the drawings

[0020] [Fig-1] Fig. 1 is a schematic perspective view of an aircraft equipped with two turbojets and two power supply circuits according to the invention.

[0021] [Fig.2] The [Fig.2] is a diagram illustrating a power supply circuit according to the invention.

[0022] [Fig.3] Fig.3 is a diagram illustrating a dosing system according to the invention

[0023] [Fig.4] The [Fig.4] is a diagram illustrating the dosing unit according to the invention, in a first configuration of the auxiliary dosing device.

[0024] [Fig.5] The [Fig.5] is a diagram illustrating the dosing unit according to the invention, in a second configuration of the auxiliary dosing device.

[0025] [Fig.6] The [Fig.6] is a diagram illustrating the dosing unit according to the invention, in a third configuration of the auxiliary dosing device. Detailed description

[0026] Figure 1 represents an aircraft equipped with several engines, and comprising a fuel supply system according to the invention for each engine. In the example, aircraft 1 is an airplane equipped with two engines 2, which are turbomachines, and more specifically turbofan engines. Each fuel supply system 3 draws fuel from a respective fuel tank 4, located in one of the wings 1 of the airplane, via a fuel line 5.

[0027] The fuel supply circuit 3 according to the invention is shown schematically in [Fig.2]. Each fuel supply circuit 3 comprises in series, in the direction of fuel flow: a low pressure pump 6, a main heat exchanger 7 (generally referred to as FCOC, an acronym corresponding to the English term "Fuel Oil Exchanger"), using the fuel as a cold source, a fuel filter 8, a high pressure pump 9, and the fuel metering system 10 according to the invention.

[0028] The high-pressure pump 9 is, for example, a gear pump whose fixed displacement is optimized with respect to the engine speed of the turbomachine at takeoff.

[0029] In addition to supplying fuel to the combustion chamber, the high-pressure pump 9 also supplies fuel to equipment referred to as "variable geometries" 11 of the engine, which are turbomachine equipment or components that include moving parts, requiring variable hydraulic power to be drawn in order to operate.

[0030] These equipment 11 include, for example, a cylinder, a servovalve, an adjustable compressor relief valve, a transient compressor relief valve, and / or an air flow control valve for a rotor blade tip clearance adjustment system for a low pressure turbine or a high pressure turbine.

[0031] For this purpose, fuel can be derived from the fuel supply circuit, on a branch B supplying the equipment 11, which extends between a node E, located between the high pressure pump 9 and the metering system 10, and a node C, located between the low pressure pump 6 and the high pressure pump 9, and more specifically, in the example, between the low pressure pump 6 and the main heat exchanger 7.

[0032] At node E, the supply circuit 3 includes a self-cleaning filter 12 for filtering the fraction of the diverted fuel flow. This self-cleaning filter 12 is washed by the fuel flow circulating in the supply circuit 3 towards the fuel metering system 10. Branch B may further include, upstream of the equipment 11, an auxiliary heat exchanger 13 for temperature control of the diverted fuel.

[0033] The combustion chamber fuel supply circuit also includes a recovery circuit 14, also called a fuel recirculation branch, connecting the fuel metering system 10 to a point in the supply circuit located upstream of the main heat exchanger 7, and located in the example between the low pressure pump 6 and the main heat exchanger 7, i.e. at node C. The excess fuel flow supplied to the fuel metering system 10 can thus be returned, through this recovery circuit 14, upstream of the main heat exchanger 7, to the main fuel filter 8 and the high pressure pump 9.

[0034] When an engine 2 needs to be supplied with fuel, the fuel from the tank 4 is drawn by the low-pressure pump 6 and sent to the main heat exchanger 7, where the fuel is cooled. The fuel is then filtered in the fuel filter 8. Downstream of the fuel filter 8, the fuel is drawn by the high-pressure pump 9 and sent, under high pressure, to the node E, at which point, as explained above, a portion of the fuel flow is diverted to the equipment 11 and passes through the self-cleaning filter 12.

[0035] The non-derived portion of the fuel flow passes through the self-washable filter 12, and is directed to the fuel dosing system 10, cleaning the self-washable filter 12.

[0036] The fuel metering system 10 ensures, in particular, the metering of the fuel flow supplied to the engine's combustion chamber via injectors 15, according to a setpoint imposed by a control unit 16, which may be constituted or housed by an engine control unit (generally designated by the acronym EEC for "Electronic Engine Controller" or by the acronym FADEC for "Full Authority Digital Engine Control"). A flow meter 17 is connected to the control unit 16. In addition, injection filters 18 are arranged upstream of the injectors 15.

[0037] The fuel dosing system 10 according to the invention is schematically illustrated in [Fig.3]. As mentioned above, it is located in the supply circuit 3, downstream of the high-pressure pump 9 and upstream of the injectors 15 which it supplies.

[0038] The metering system 10 includes a regulating valve 20, connected in particular to the recirculation branch 14 which ensures the fuel return. The regulating valve 20 maintains a constant pressure differential between the inlet and outlet of the metering system. The regulating valve 20, generally referred to by its English name "by-pass valve", is a purely passive component which, through the action of a spring, maintains a certain pressure differential between the inlet and outlet of the metering system.

[0039] To ensure flow metering, the metering system 10 includes a main metering device 22, comprising in this example a metering valve 220, generally called FMV (Fuel Metering Valve). The metering valve 220 is controlled by the control unit 16, via a servovalve 222, the control unit 16 determining the mass flow rate to be supplied to the engine.

[0040] The dosing system 10 further includes an auxiliary dosing device 24, intended to compensate for malfunctions of the main dosing device 22, and in particular malfunctions leading to the blockage of the dosing valve 220, which is then no longer able to perform its dosing function. For this purpose, the auxiliary dosing device 24 is positioned upstream of the main dosing device 22, so as to be able to limit, if necessary, the flow of fuel reaching the main dosing device, and therefore the flow at the outlet of the dosing system 10. The auxiliary dosing device 24 is further configured to be able to bypass the main dosing device 22, so as to be able to compensate for a zero or insufficient flow coming from the main dosing device 22, and thus ensure a sufficient flow at the outlet of the dosing system 10.

[0041] As shown in Figure 1a [Fig. 3], the metering system 10 comprises an inlet 10a, a main outlet 10b, and an auxiliary outlet 10c. The auxiliary metering device 24 is located downstream of the inlet 10a and upstream of the main metering device 22. A main line 10d connects the auxiliary metering device 24 to the main metering device 22, the latter being located upstream of the main outlet 10b. A bypass line 10e connects the auxiliary metering device 24 to the main outlet 10b. Upstream of the main outlet 10b and downstream of the main metering device 22, a discharge line 10of redirects a portion of the fuel to an inlet 20a of the regulating valve 20, while an outlet 20b of the regulating valve 20 is connected to the auxiliary outlet 10c. In the example, the bypass pipe 10e opens into the discharge pipe lOf.

[0042] As can be seen in [Fig. 3], the auxiliary metering device 24 is connected to the main metering device 22 in both series and parallel. This architecture allows the auxiliary metering device 24, as detailed below, to compensate for both a blockage of the metering valve 220 leading to a zero or insufficient flow rate and a blockage leading to a flow rate that is too high relative to the fuel requirements.

[0043] Figures 4 to 6 partially represent the dosing system 10, and show the auxiliary dosing device 24 in different configurations, depending on whether the main dosing device 22 is operating normally or is affected by a failure.

[0044] As shown in [Fig. 4], when the main metering device 22 is operating normally, no action is required from the auxiliary metering device 24. The auxiliary metering device 24 is then in a first configuration, called the neutral configuration, in which it is configured not to alter the fuel flow rate reaching the main metering device 22, and in particular not to limit this flow rate. Thus, in this case, fuel metering relies solely on the action of the main metering device 22, the auxiliary metering device 24 being then "transparent". In the configuration of [Fig. 4], the entire flow rate Fl arriving at the inlet of the auxiliary metering device 24 is directed to the device of main metering 22, via the main line 10d. The flow circulating in the bypass line 10e towards the main outlet 10b is then zero.

[0045] Figure 5 represents a case in which the main metering device 22 is not functioning normally, being blocked in a position that does not allow it to provide a sufficient flow rate relative to the current flow rate setpoint. In this case, the auxiliary metering device 24 is put into a second configuration, or flow increase configuration, in which fuel is sent to the main outlet 10b via the bypass line 10e, thus bypassing (partially or totally) the main metering device 22, which is unable to supply fuel at a sufficient flow rate. In the configuration of Figure 5, the main metering device 22 is connected to the main line 10b.[5] A first part F2 of the flow Fl arriving at the inlet of the auxiliary dosing device 24 is directed to the main dosing device 22, via the main line 1Od, and a second part F2 of the incoming flow Fl is directed to the bypass line 10e and therefore to the main outlet 10b. The outgoing flow at the main outlet 10b is therefore equal to the flow Fl arriving at the inlet of the auxiliary dosing device 24.

[0046] In the event that the main dosing device 22 is blocked in a position which does not allow any flow to be supplied, then the entire flow Fl arriving at the inlet of the auxiliary dosing device 24 is directed to the main outlet 10b, via the bypass line lOd.

[0047] Figure 6 represents a case in which the main metering device 22 is not functioning normally, being stuck in a position in which it delivers a flow rate that is too high relative to the current flow rate setpoint. In this case, the auxiliary metering device 24 is in a third configuration, or flow rate reduction configuration, in which fuel is sent to the main outlet 10b exclusively via the main line 10d, limiting the flow rate F4 passing through the main metering device 22, in order to deliver fuel at the outlet of the metering system 10 with a flow rate conforming to that requested by the control unit.

[0048] The modification of the configuration of the auxiliary metering device 24 is preferably controlled directly by the control unit 16. As mentioned above, the control unit 16 can be constituted or housed by the engine control computer (referred to as FADEC or EEC). The control unit 16 is configured to detect a failure of the main metering device 22, for example, based on one or more operating parameters of the turbomachine 2 concerned, and, in the event of detection of a failure of the main metering device 22, to determine an appropriate flow rate setpoint corresponding to a failure accommodation mode, and to control the auxiliary metering device 24 according to the setpoint of The flow rate is adjusted accordingly. Therefore, a failure of the main dosing device 22 can advantageously be managed without pilot intervention. Applying a failure accommodation mode allows the motor to continue operating and prevents it from shutting down in the event of a failure of the main dosing device 22. Each failure accommodation mode corresponds to at least one configuration of the auxiliary dosing device 24.

Claims

Demands

1. Fuel metering system (10) for an aircraft turbomachine (2) (1), the system comprising: - a main metering device (22), configured to deliver fuel at the outlet of the metering system (10) at a flow rate conforming to a flow rate setpoint given by a control unit (16); - an auxiliary metering device (24), disposed upstream of the main metering device (22) with respect to the direction of fuel flow, the auxiliary metering device (24) being connected in series and in parallel with the main metering device (22), the auxiliary metering device (24) being controlled by the control unit (16) so that: • in the event of normal operation of the main metering device (22), the auxiliary metering device (24) does not modify the flow rate of fuel entering the metering system (10) and reaching the main metering device (22);• that in the event of a failure of the main dosing device (24) resulting in a fuel flow rate at the outlet of the dosing system exceeding the set flow rate, the auxiliary dosing device (24) limits the fuel flow rate reaching the main dosing device (22); and • that in the event of a failure of the main dosing device (24) resulting in a fuel flow rate at the outlet of the dosing system below the set flow rate, the auxiliary dosing device (24) delivers fuel directly at the outlet of the dosing system (10) by partially or totally bypassing the main dosing device (22).

2. Dosing system (10) according to claim 1, wherein the auxiliary dosing device (24) is connected in series to the main dosing device (22) via a main line (10d), and connected in parallel to the main dosing device (22) via a bypass line (10e) connecting the auxiliary dosing device (24) to a main outlet (10b) of the dosing system (10).

3. A metering system (10) according to claim 2, wherein the auxiliary metering device (24) can be selectively placed in at least three configurations, including: - a neutral configuration, in which the auxiliary metering device (24) does not modify the incoming fuel flow rate and directs the fuel exclusively to the main line (lOd); - at least one flow-limiting configuration, in which the auxiliary metering device (24) directs the fuel exclusively to the main line (lOd) and limits the flow rate supplied to the main metering device (22) to a maximum value; - at least one flow-increasing configuration, in which the auxiliary metering device (24) directs the fuel to both the main line (lOd) and the bypass line (10e), so as to increase the flow rate delivered at the outlet of the metering system (10) to a minimum value.

4. Dosing system (10) according to claim 3, wherein the change in configuration of the auxiliary dosing device (24) is controlled by the control unit (16).

5. Dosing system (10) according to any one of claims 3 and 4, wherein the auxiliary dosing device (24) can be selectively placed: - in at least two flow limitation configurations, each flow limitation configuration being characterized by a respective maximum flow value; and / or - in at least two flow increase configurations, each flow increase configuration being characterized by a respective minimum flow value.

6. Fuel supply circuit (3) of an aircraft turbomachine (2) comprising a metering system (10) according to one of the preceding claims.

7. Fuel supply circuit (3) according to the preceding claim, comprising a control unit (16) configured to determine a setpoint for the fuel flow rate to be supplied by the fuel supply circuit, the control unit (16) being further configured to detect a failure of the main dosing device (22) on the basis of one or more operating parameters of the turbomachine (2), and, in the event of detection of a failure of the main dosing device (22), to determine an appropriate flow setpoint and command a change in configuration of the auxiliary dosing device (24) according to the appropriate flow setpoint.

8. Turbomachine (2) for aircraft, comprising a metering system according to one of claims 1 to 5 or a supply circuit (3) according to one of claims 6 and 7.

9. Aircraft (1) comprising at least two turbomachines (2), each turbomachine (2) being supplied by a tank (4) disposed in a wing (la) of the aircraft (1), the aircraft (1) comprising, for each turbomachine (2) a supply circuit (3) conforming to one of claims 6 and 7.

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