FUEL MEASURING UNIT FOR AN AIRCRAFT ENGINE

Description

FIELD OF THE INVENTION

[0001] The present invention relates to the general field of aeronautics.

[0002] It relates more specifically to the field of fuel supply regulation systems for an aircraft engine. This engine is, for example, a turbomachine such as a turbojet. STATE OF THE ART

[0003] As is known, the control system of an aircraft engine comprises a main electronic computer which is in the form of a box containing one or a plurality of electronic cards responsible for ensuring various functions.

[0004] In current engines, the engine control system is generally responsible for controlling a fuel metering unit, corresponding to a hydromechanical block more commonly called FMU (“Fuel Metering Unit”).

[0005] The hydromechanical block communalizes several functions. It ensures, by a metering device, the metering of the fuel, that is to say the translation of the information of required flow rate within the total flow rate provided by the pumping system, which results from a need dictated by a control unit of the regulation system according to the flight phase, with the relative precision required. It also allows, by a cut-off device, the cut-off of the fuel flow following a pilot command, and the cut-off and / or regulation of the fuel flow in the emergency case of an overspeed (engine speed which exceeds a threshold beyond which the centrifugal forces are critical and risk causing a breakage of parts, which requires for safety reasons an engine cut-off) detected by a speed sensor of the high and / or low pressure part of the engine.

[0006] For better operability precision of the systems, and especially for the flexibility of control / parameterization of the operability, but also for reasons of weight and volume savings, engine regulation computers today integrate certain electronic functions formerly fulfilled by hydromechanical blocks, such as in particular the "overspeed protection" function allowing the engine to be protected in a case where the engine speed exceeds the predefined maximum speed threshold (overspeed), by monitoring the speed and cutting off the engine if an overspeed is detected.

[0007] However, the behavior of an engine computer (regulation computer, also called FADEC for "Full Authority Digital Engine Control" in English, and more generally called EEC,for "Electronic Engine Controller" in English) in the event of overheating or fire is difficult to predict, which leads engine manufacturers to consider the worst cases for the certification of computers (by the aeronautical equipment certification authorities). Thus, certification constraints require not to suffer a simple electrical or electronic failure that could cause a risky event. For example, an engine overspeed event caused by an erroneous command to actuation of the metering device (called in English "Fuel Metering Valve": FMV) of the hydromechanical block (for example, reaching the maximum mechanical metering limit, normally protected by a regulation limit).

[0008] InConsequently, in the context of a degraded engine operating mode such as during a fire scenario, in which the overspeed event is a feared event, it must be possible to demonstrate that the overspeed protection function provided by the overspeed detection and engine cut-off functions is still operational at the time when the regulation function provided by the computer dies. This scenario is called "clean death" of the regulation system control unit.

[0009] Otherwise, if we consider a "non-clean death", the overspeed protection function "dies" first, leaving the regulation function in sole control on board. The worst-case scenario would then be an erroneous command from the regulation system to a component regulating the engine, for example an erroneous position command to an actuator of a fuel metering unit which would put the actuator in a maximum flow position, leading to an engine overspeed condition in which the overspeed protection function could not accommodate the failure and consequently shut down the engine before it is damaged.

[0010] To deal with such an eventuality, various solutions are envisaged in the state of the art.

[0011] One solution is to use electronic components for the overspeed protection function that are resistant to very high temperatures. This is to ensure that in the scenario considered above, a failure of an electronic card responsible for the overspeed protection function would occur after a failure of a card (of the engine computer) responsible for the regulation function.

[0012] However, historically, such components have been developed in small quantities for very specific military aeronautical applications. They are therefore very expensive and difficult to obtain, and subject to early obsolescence.

[0013] An alternative solution consists of installing the overspeed protection function in a computer located in a so-called “non-fire” zone, in other words in an environment different from that of the regulation computer.

[0014] In the case of certain engines developed by the applicant, the overspeed management functions are integrated into the engine computer. This solution requires resolving computer certification issues, particularly with regard to fire management events, in particular by segregating the two subsystems containing the components performing the regulation and protection functions, within the same housing.

[0015] In another solution, as is the case on other engines developed by the applicant, an independent computer is developed for the implementation of the overspeed protection functions in the “non-fire zone” and placed away from the regulation computer (engine computer), which is placed in the fire zone. However, the impacts in terms of mass (additional housing, harness, supports, etc.) are considered significant and result in particular in an increase in specific fuel consumption. Furthermore, the development costs of an aircraft electronic computer are very high; an architecture comprising two independently developed computers is therefore particularly expensive.

[0016] In another alternative solution, Snecma's publication FR2957667A1 discloses a device for detecting overheating affecting an engine computer such as a FADEC, having at least one temperature sensor located inside the computer, and at least one overheating detector located outside the computer in the vicinity thereof.

[0017] This publication does not disclose a detection strategy to discriminate overheating not linked to the start of a fire.

[0018] On the other hand, the solution in this publication does not allow for sufficient thermal margin, considering thermal inertia, to ensure a "clean death" of the regulation computer.

[0019] Consequently, considering the current state of the art, there is no very satisfactory solution for a fuel supply regulation system with an overspeed protection function for an aircraft engine, which does not penalize in terms of mass, installation cost, and which makes it possible to comply with the certification constraints for accommodating a degraded operating mode of the engine such as in response to a fire. STATEMENT OF THE INVENTION

[0020] The proposed invention aims in particular to enable the implementation in an aircraft engine of an overspeed protection system capable of cutting the engine in the event of detection of a fire or overtemperature event, before endangering the electronics dedicated to the regulation or protection of the engine.

[0021] For examples of prior art dosing units, reference may advantageously be made to the following various publications: FR2956380A1, FR2965698A1, US4998949A1, FR2960906A1.

[0022] For this purpose, the invention provides an aircraft as defined by claim 1. Advantageously, the aircraft also comprises the following characteristics: the engine control computer is also configured to transmit a position control signal to the metering member of the metering unit to regulate the fuel flow rate from the metering member, as a function of the flow rate setpoint received; the fuel metering unit also comprises an engine power control computer configured to receive the flow rate setpoint and generate said control signal for the metering member to regulate the fuel flow rate from the metering member, as a function of the flow rate setpoint received; the engine control computer is configured to be electrically powered by an electric generator of the engine, and said engine control computer is configured to electrically power the engine power control computer;the protection computer is electrically powered by an electrical power supply network serving on-board systems of the aircraft.;

[0023] Advantageously, the invention makes it possible to rationalize the integration of an electronic card within a conventional dosing unit by adding motor protection functionalities, thereby facilitating the system certification strategy while limiting costs and physical impacts (mass, volume) and improving the performance of the motor (via improving dosing precision). DESCRIPTION OF FIGURES

[0024] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings, in which: [ Fig. 1A ] there Figure 1Aillustrates a system for regulating a turbojet engine of an aircraft according to a first embodiment of the invention; [ Fig. 1B ] there Figure 1B illustrates in more detail a system for regulating a turbojet engine of an aircraft according to the first embodiment of the invention [ Fig. 2A ] there Figure 2A illustrates a system for regulating a turbojet engine of an aircraft according to a second embodiment of the invention; and [ Fig. 2B ] there Figure 2B illustrates in more detail a system for regulating a turbojet engine of an aircraft according to the second embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] The term calculator refers in particular to a controller / control unit for physical devices, usually comprising a processor, memories, and input-output interfaces. The calculator is physically represented by one or more electronic cards implementing its functionalities. First embodiment

[0026] There Figure 1A illustrates a regulation and protection system 100 of an aircraft engine, implemented by a distributed architecture, according to a first embodiment.

[0027] Thus, the system 100 comprises an engine control computer 110 which generates a fuel mass flow instruction C101, to ensure the thrust requested by the aircraft in real time.

[0028] This instruction C101 is then transmitted to an electro-hydromechanical metering unit 120 which carries out the fuel metering.

[0029] The instruction C101 is more precisely transmitted to a power regulation calculator 123 of the electro-hydromechanical dosing unit 120.

[0030] The regulation computer 123 determines, as a function of the flow rate setpoint C101, a theoretical position setpoint Cth of a fuel metering member 125 (for example of the FMV type) of the electro-hydromechanical metering unit 120.

[0031] Depending on the displacement instruction Cth, the regulation computer 123 transmits an electrical control instruction C102 to a servovalve 121 (for example of the EHSV type for “Electro Hydraulic Servo Valve” in English) of the fuel metering member 125. The servovalve 121 generates, in correspondence with the control instruction C102, a hydraulic power command C103 intended for a hydraulic actuator 122 making it possible to move a shutter element (such as a slide) of the fuel metering member 125. Depending on said command, the hydraulic actuator 122 carries out the fuel metering, for example by moving a movable metering slide.

[0032] The metering member 125 is associated with a position sensor of the shutter element (for example the position of the metering slide, giving a fluid passage section) which transmits the information measured by said sensor to the regulation computer 123 (arrow C104). The position sensor can be of the LVDT type (for “Linear Variation Displacement Transducer” in English).

[0033] The fuel flow is then regulated by the regulation computer 123 using a correction network (traditionally of the PID type: Proportional - Integral - Derivative) making it possible to cancel the difference between the theoretical Cth position setpoint and the measured position of the shutter element.

[0034] The fuel flow rate can be obtained using the following formula: Q = K × S × ρ × Δ P ,with Q corresponding to the volume flow rate, K a constant, S a fluid passage section - function of the position of the shutter element, ρ the density of the fuel and ΔP corresponding to the differential pressure.

[0035] The regulation functions are therefore directly provided by the electro-hydromechanical dosing unit 120.

[0036] The regulation and protection system 100 may also comprise a flow meter 127 as described in Snecma's application FR3053396A1. By flow meter, reference is made to any measuring device making it possible to know a mass flow rate of fluid, in this case a flow rate of liquid fuel here.

[0037] The flow meter makes it possible to measure the mass flow rate of fuel leaving the electro-hydromechanical metering unit 120. This measurement is then communicated to the regulation computer 123 to calculate the density of the fuel and determine, by means other than the position of the metering system, a reconstructed flow rate.

[0038] In In fact, it is possible to observe significant differences between the actual flow rate and the setpoint flow rate. This reconstructed flow rate has improved accuracy compared to reconstructed flow rates corresponding to a theoretical flow rate passing through the metering valve. Advantageously, it is possible to improve the metering accuracy by generating a flow rate setpoint, using the determined reconstructed flow rate.

[0039] There Figure 1B illustrates in more detail the regulation and protection system 100 according to the first embodiment.

[0040] The architecture as presented separates the functions related to dosing from those related to protection and engine shutdown.

[0041] As seen previously, the electro-hydromechanical metering unit 120 comprises the regulation computer 123 which interacts (arrow C102) with a metering member 125, taking charge of controlling actuators of said member, linked to the metering of the fuel coming from the upstream part 130 of a fuel supply system (arrow F101). For this, the regulation computer 123 is configured for the acquisition of measurements and characteristics (of the relevant sensors and actuators) as illustrated by the arrow C104.

[0042] The system 100 also comprises a protection and cut-off computer 124. The latter interacts with a cut-off member 126, taking charge of controlling the actuators of said member (arrow C105), linked to the fuel cut-off, for example a servovalve for controlling a fuel system pressurization and cut-off valve HPSOV (“High Pressure Shut Off Valve” in English).

[0043] The metered fuel from the metering member 125 can subsequently pass through the cut-off member 126 (arrow F102) before reaching the downstream part 135 of the fuel supply system (arrow F103).

[0044] The 124 protection and cut-off calculator also integrates all the functions linked to overspeed management, in particular: the acquisition of the speeds of the high pressure and low pressure bodies of the engine (double-spool turbojet) by one or more sensors 145 (arrow C106); the comparison of the acquired engine speeds with predefined threshold engine speeds; the detection of an “overspeed” state of the high pressure or low pressure body if the engine speeds are higher than the threshold values; and the transmission of a control signal to a cut-off control member contained in the fuel cut-off member 126 to exit the overspeed state as illustrated by the arrow C105; said control causing the actuation linked to the accommodation (generally the cutting of the fuel flow).

[0045] Other protection functions can be integrated into the 120 electronic dosing unit: fire protection, over-thrust protection, thrust loss control protection, etc.

[0046] The electronic dosing unit 120 communicates mainly with the engine control computer 110, said unit 120 can also be in interface with the aircraft (which can issue an engine shutdown order) and / or a maintenance management unit (which can be at the aircraft or engine level).

[0047] Advantageously, the engine control computer 110 is powered by a generator 150 (arrow A101), for example of the permanent magnet generator type (PMA, PMG, etc.) of the engine. The computer 110 itself powers the regulation computer 123 (arrow A102).

[0048] The protection and cut-off computer 124 is supplied (arrow A103) by the same power supply network 140 as that serving the various on-board systems (electric generator, auxiliary power unit).

[0049] Thus, a power supply problem by the motor does not cause a power failure at the level of the protection and cut-off functions simultaneously.

[0050] The regulation computer 123 and the protection and cut-off computer 124 can be positioned on two different electronic boards. They can also be positioned on the same electronic board. However, in the latter case, there is a mechanical boundary between these two computers.

[0051] Thus, the latter are mutually segregated (functionally and physically) to comply with the requirements of the CS-E certification basis. This ensures that the two computers cannot corrupt each other and risk creating a dangerous event such as uncontrolled overspeed.

[0052] In this first embodiment, the protection and cut-off calculator 124 is contained in the electronic fuel metering unit 120, and is therefore located in a “fire zone”, because by definition it is surrounded by fuel.

[0053] Only compartments that contain ignition sources and the risk of flammable liquid leakage are classified as fire zones, i.e. containing potential ignition sources in the event of a failure that could result in a temperature higher than the auto-ignition temperature of any fluids present in the compartment. In contrast, a non-fire zone is an area that is not in the configuration defining the fire zone.

[0054] InConsequently, the regulation and protection system 100 comprises functions / means allowing the detection of the fire event, for example temperature sensors arranged outside or inside a housing of the electronic dosing unit 120. Second embodiment

[0055] There Figure 1B illustrates a subsystem 200 for controlling the regulation and protection system 100 according to a second embodiment.

[0056] The electronic fuel metering unit 120 houses the hydraulic servovalve 121 and the actuator 122 (FMV), as well as its position sensor.

[0057] However, unlike the first embodiment, some of the functions linked to the fuel metering are implemented in the engine control computer 110: the generation of the flow rate setpoint, the correction network, the generation of the position command, as well as the acquisition of at least one position sensor which provides information on the position of the mobile slide of the FMV.

[0058] As in the first embodiment, the regulation and protection system 100 may also include a flow meter as described in the first embodiment. The flow meter makes it possible to measure the mass flow rate of fuel exiting the electro-hydromechanical metering unit 120. Unlike the first embodiment, this measurement is then communicated to the engine control computer 110 to calculate the density of the fuel and determine a reconstructed flow rate.

[0059] There Figure 2Billustrates in more detail the regulation and protection system 100 according to the second embodiment.

[0060] As in the first embodiment, the electronic dosing unit 120 integrates the functions linked to overspeed management, they are preferably entirely located in the protection and cut-off computer 124, in particular: the acquisition of the speeds by the protection and cut-off computer 124; the comparison of the acquired engine speeds with threshold engine speeds predefined by the protection and cut-off computer 124; the detection of an “overspeed” state of the high pressure or low pressure body if the engine speeds are higher than the threshold values ​​by the protection and cut-off computer 124; and the transmission of a control signal to a cut-off control member contained in the cut-off member 126 by the protection and cut-off computer 124, said control causing the actuation linked to the accommodation (generally the cutting of the fuel flow) by the protection and cut-off computer 124.

[0061] Other protection functions can be integrated into the 120 electronic dosing unit: fire protection, over-thrust protection, thrust loss control protection, etc.

[0062] Thus, the architecture of the electronic dosing unit 120 in this second embodiment is identical in the division of functions in the computers 123 and 124, except that the regulation computer 123 integrates fewer functionalities than the regulation computer 123 implemented in the first embodiment.

[0063] In this second embodiment, several contexts for installing the control computers 110 and electronic dosing unit 120 are possible: In an example that is not part of the invention, the engine control computer 110 is installed in a zone declared "non-fire". In this context, the management of the fire event (or other "local events" defined in the certification standard) is easy thanks to the physical segregation of the protection and control functions. In the event of a fire in the area of ​​the fuel metering unit 120, the protection and cut-off computer 124 risks "dying" but it will never be able to trigger an overspeed event (it only acts on the cut-off member). At worst, the engine will not be able to be protected against an overspeed event within the time period considered. After the regulatory 5 minutes, the engine can be cut off by the aircraft pilots via the aircraft's fuel cut-off valve, or via the engine HPSOV if a direct link with the aircraft exists.According to the invention, the electronic metering unit 120 is installed in a fire zone different from that of the engine control computer 110. The management of the fire event (or of the other “local events” defined in the CS-E) is easy thanks to the physical segregation of the protection and control functions: ∘ In the event of a fire in the zone of the electronic metering unit 120, the protection and cut-off computer 124 risks “dying”, but it will never be able to trigger an overspeed event (it only acts on the cut-off member). After the 5 minutes prescribed by regulation, the engine can be cut off by the pilots via the aircraft’s fuel cut-off valve, or via the engine HPSOV if a direct link with the aircraft exists. ∘ In the event of a fire in the area of ​​the engine control computer 110, said computer may suffer an “unclean death” (erratic) which could generate an engine overspeed, for example by commanding the FMV to fully open.However, the segregation of the zones by definition makes it possible to guarantee that the fire will not be able to also the electronic metering unit 120. The protection functions will therefore not be affected and the protection and cut-off computer 124 of the metering unit 120 will cut the engine in the event of overspeed. In an example which is not part of the invention, the electronic metering unit 120 is installed in the same zone (fire) as the engine control computer 110. As for the first embodiment, the control (fuel metering) and protection functions being located in the same fire zone, the regulation and protection system 100 comprises functions / means allowing the detection of the fire event, for example temperature sensors arranged outside or inside the housing of the metering unit 120.

[0064] The electronic dosing unit 120 described therefore makes it possible to rationalize the integration of an electronic card on a conventional dosing unit by adding engine protection functionalities. This choice makes it possible to limit the additional costs linked to the integration of an electronic card on a dosing unit, because these protection functions will have to be integrated whatever happens (either in the main engine control computer or in a specific independent computer) and cause significant non-recurring costs.

[0065] In addition, the integration of protection into an electronic dosing unit makes it possible to limit the physical impacts (mass, volume) on the overall architecture of the engine (compared to a remote protection calculator with its own specific housing). In effect the reduction / limitation of interfaces induced by the grouping constitutes a significant gain.

[0066] InIn addition, the proposed architectures facilitate the system certification strategy (in particular with regard to local events, such as fire), compared to protection integrated into the main engine control computer.

[0067] In Consequently, the invention described makes it possible to facilitate the system certification strategy while limiting costs and physical impacts (mass, volume) and improving engine performance (via improving dosing precision).

Claims

1. Aircraft, comprising : a first fire zone and a second fire zone distinct from the first fire zone, corresponding to zones of the aircraft that contain sources of ignition and the risk of a flammable liquid leak, and a fuel supply regulation and protection system (100) for an aircraft engine, comprising an engine control computer (110) generating a fuel mass flowrate setpoint; a fuel metering unit (120) for the aircraft engine, comprising a metering member (125) configured to receive a command signal and to meter the fuel supply to the engine as a function of said command ; a shut-off member (126) configured to shut off the fuel supply to the engine wherein the fuel metering unit (120) further comprises an engine protection and shut-off computer (124) configured to : receive data for evaluating the instantaneous value of the engine speed ; compare the instantaneous engine speed value with a predefined engine speed threshold value and determine a potential overspeed condition on the basis of this comparison; transmitting a control signal to a shut-off control member contained in the shut-off member (126) to shut off fuel supply to the engine if an engine overspeed condition is determined, and characterised in that the fuel metering unit (120) is installed in the first fire zone of the aircraft, and the engine control computer (110) is installed in the second fire zone.

2. Aircraft according to the preceding claim, wherein the engine control computer (110) is also configured to transmit a position command signal to the metering member (125) of the fuel metering unit (120) in order to regulate the flow of fuel from the metering member, as a function of the flowrate setpoint received.

3. Aircraft according to claim 2, wherein the fuel metering unit (120) also comprises an engine power regulation computer (123) configured to receive the flowrate setpoint and to generate the control signal for the metering member (125) in order to regulate the flow rate of fuel from the metering member, as a function of the flowrate setpoint received.

4. Aircraft according to the preceding claim, wherein the engine control computer (110) is configured to be supplied electrically by an electrical generator of the engine, and the engine control computer (110) is configured to supply electrically the power regulation computer (123) of the engine.

5. Aircraft according to any one of claims 1 to 4 in which the protection and shut-off computer (124) is supplied electrically by an electrical supply network serving on-board systems of the aircraft.