method for controlling a rotary-wing aircraft, computer program and associated rotary-wing aircraft

Abstract

The present invention relates to a method for controlling a rotorcraft (1), said rotorcraft (1) comprising at least two combustion engines (2, 3), at least one control system (13), and a transmission system (4), said at least two engines (2, 3) being mechanically connected to said transmission system (4) respectively by at least two couplings (25, 26). Such a control method comprises at least one identification of an engine regulated in N2 (2), one identification of an engine not regulated in N2' (3), and the generation of a control setpoint limit for at least a first control system (12) of the engine regulated in N2 (2), dependent on the rotational speed N2 of at least a first output shaft (5) of the engine regulated in N2 (2). Abstract figure: Figure 1

Description

Title of the invention: method for controlling a rotorcraft, associated computer program and rotorcraft

[0001] The present invention relates to a method of controlling a rotorcraft, a computer program and a rotorcraft associated with the control method.

[0002] A rotorcraft has at least one rotor participating in its lift, or even its propulsion.

[0003] For example, a rotorcraft may comprise a main rotor participating in its lift and propulsion, this main rotor having blades with collectively and cyclically variable pitch. In addition, the rotorcraft may comprise a system participating in the control of the yaw movement, such as another main rotor or a tail rotor for example. The pitch control system can be activated for example by the pilot or the crew. Alternatively, the system can be activated by an automatic control system, called an autopilot.

[0004] To set the rotor(s) in motion, the rotorcraft comprises a power plant, possibly multi-engine, and a power transmission chain going from the engines to one or more rotors.

[0005] For example, two motors are connected to a power transmission box, this power transmission box setting in motion the rotor(s). The power transmission box then comprises a mechanical input per motor, the mechanical inputs being engaged with a combiner, the combiner driving a mechanical output of the power transmission box per rotor. The motor inputs, the combiner, and the mechanical outputs may comprise at least one pinion or toothed wheel, at least one shaft, at least one speed reduction stage, etc.

[0006] The engines may be heat engines having an output shaft driven by the combustion of fuel. For example, at least one engine may be a turboshaft engine having a gas generator and a free working turbine connected to the output shaft.

[0007] Each engine can be controlled by a regulation system known by the acronym FADEC and the English expression “Full Authority Digital Engine Control”. Such a regulation system comprises an engine computer in communication with sensors measuring values ​​of operating parameters of the controlled engine, or even of the rotorcraft, such as a rotation speed of a gas generator or a free turbine, an internal temperature, a rotation speed of a rotor of the rotorcraft.

[0008] This engine computer is then configured to control a fuel meter powering the associated engine in order, for example, to stabilize a rotational speed of the output shaft at a set speed, regardless of the power consumed by this output shaft. This power varies according to the actions of a pilot on flight controls, in particular on controls varying collectively and / or cyclically the pitch of the main rotor blades on a helicopter. Alternatively, these controls can be actuated by an autopilot system.

[0009] Regulation as a function of the rotation speed (N2) of the output shaft of the turbo-engine then ensures a permanent match between the power produced by the output shafts of the engines and the power consumed by the rotor(s), so that this or these rotor(s) rotate at a nominal rotation speed compatible with their function of generating lift for the rotorcraft.

[0010] Nevertheless, the engine computer is configured to prevent the power developed by an engine from causing the engine or the transmission chain to exceed an acceptable mechanical limit. Usually, various operating regimes associated with specific limits and usage durations are then defined. For each operating regime, these limits may include, for example, a torque limit of an engine torque delivered by an engine, a limit of an internal temperature of an engine, a limit of rotation speed of a shaft of an engine, a torque limit of at least one member of the transmission chain, etc.

[0011] On a multi-engine aircraft, there are known operating regimes called "AEO", for the English expression "All Engines Operative" usable for certain durations when all the engines are operating normally, and operating regimes called "OEI", for the English expression "One Engine Inoperative" usable for certain durations when one of the engines is out of order. The use of certain operating regimes can induce a maintenance action on the engines, or even on the power transmission chain.

[0012] From then on, an engine computer controls the fuel metering device so as to modulate the power of the associated engine. A first type of regulation consists of making the rotation speed of the output shaft tend towards a set value, while avoiding exceeding a limit. This type of regulation is called N2 regulation because it is dependent on the rotation speed of the output shaft of the associated engine.

[0013] Another type of regulation consists of delivering a predefined power for the engine, for example to reach an optimal operating point in terms of thermodynamic efficiency.

[0014] However, in the case of a rotorcraft, it is advantageous for at least one of the engines to be regulated as a function of the rotation speed N2 of its output shaft. Indeed, such a so-called “N2” regulation makes it possible to avoid a regular reduction in the rotation speed NR of the lift rotor which is itself directly linked to the speed of rotation N2.

[0015] When a limit is reached, the engine computer limits the fuel flow transmitted to the engine, and consequently the power delivered by its output shaft becomes less than the power required. The pilot must then act on the flight controls to reduce the power required for flight,

[0016] For this purpose, the rotorcraft may include various indicators allowing a pilot to assess the situation. These indicators may include an indicator indicating the rotational speed of the main rotor and the associated limits, engine indicators indicating the current values ​​of the engine monitoring parameters (temperature, speed, torque) and the associated limits, indicators indicating the current values ​​of the power transmission chain monitoring parameters and the associated limits, a first limitation indicator displaying information relating to the parameter closest to one of these limits, among several monitored parameters.

[0017] Furthermore, in the event of a failure or breakdown of the engine regulation system, the fuel flow supplying the engine concerned is frozen at the last flow value used. A pilot is informed of this and can then either shut down the engine concerned for safety reasons or continue the flight as is, i.e. with an engine not regulated in N2.

[0018] If the flight continues as is, the pilot must ensure that no limit of the mechanical transmission chain is exceeded. On a twin-engine rotorcraft, if a power call is made by a pilot to perform a maneuver, the sum of the powers delivered by the N2-regulated engine and the non-N2-regulated engine could become greater than the value admissible by the combiner of a power transmission box, for example.

[0019] More generally, managing a lack of regulation, which may be voluntary or accidental, of one of the engines of a rotorcraft may require an additional workload from the crew in order not to exceed a limit of the mechanical transmission chain.

[0020] The present invention therefore aims to propose a method for limiting the workload of a crew in the presence of a failure of an engine regulation system on a multi-engine rotorcraft or in the absence of regulation of one of the engines. Furthermore, this method can allow a pilot to carry out piloting maneuvers in complete safety, without risking degrading the mechanical transmission chain of the rotorcraft.

[0021] The invention therefore relates to a method for controlling a rotorcraft, the rotorcraft comprising at least two combustion engines, at least one regulation system and a transmission system, said at least two engines being mechanically connected to the transmission system respectively by at least two couplings.

[0022] According to the invention, such a control method is remarkable in that it comprises at least the following steps: - identification of at least one so-called N2-regulated engine among said at least two engines, said at least one N2-regulated engine being identified as an engine supplied with fuel with a fuel flow regulated as a function of the N2 rotation speed of at least one first output shaft of said at least one N2-regulated engine and supplied by at least one first fuel metering device controlled as a function of a flow setpoint transmitted by at least one first regulation system dependent on the N2 rotation speed of said at least one first output shaft, - identification of a so-called non-N2' regulated engine among said at least two engines, the non-N2' regulated engine being identified as an engine supplied with fuel with a fuel flow rate not regulated as a function of the rotation speed N2' of a second output shaft of the non-N2' regulated engine and supplied by a second fuel metering device being either unregulated or controlled as a function of a flow rate setpoint transmitted by at least one second regulation system independent of the rotation speed N2' of the second output shaft, - determination of at least one first permissible input torque limit for at least one first coupling of the transmission system connected to said at least one first output shaft, - determination of a second permissible input torque limit for a second coupling of the transmission system connected to the second output shaft, - determination of a first current operating torque transmitted by said second output shaft to the second coupling of the transmission system, - determination of at least one permissible residual combined torque limit for at least one component of a combiner of the transmission system, said at least one residual combined torque limit being calculated according to the formula:

[0023] CRI — Cadm - ( C1*Z ) WHERE Cadm is an admissible combined torque limit for said at least one member of the combiner, Cl is the first current operating torque transmitted by the second output shaft to the second coupling of the transmission system, and Z a reduction coefficient between a rotation speed of the second coupling and a rotation speed of said at least one member of the combiner,

[0024] - identification of a critical torque limit as the smallest of the values among said at least one first input torque limit, second input torque limit and at least one residual combined torque limit, - generation of a control setpoint limit of said at least one first regulation system, the control setpoint limit being generated as a function of said critical torque limit.

[0025] The step of identifying an engine not regulated in N2' can be implemented in different ways. For example, on an aircraft having identical engines that must operate in the same way, this step can include detecting an asymmetrical operation of the engines by possibly detecting an exceeding of a predetermined difference between a first fuel flow rate supplied by a first fuel metering device supplying fuel to one engine and a second fuel flow rate supplied by a second fuel metering device supplying fuel to another engine.

[0026] According to another example, an engine not regulated in N2' can be identified when the fuel flow admitted by its fuel metering device is constant in a time interval or varies according to a regulation parameter different from the rotation speed N2' of the second output shaft.

[0027] According to another example, an engine not regulated in N2' can be identified when the fuel flow admitted by its fuel metering device, and therefore the position of the metering device, does not correspond to a setpoint of discharge or position of the metering device that it receives.

[0028] Such a step of identifying an engine not regulated in N2' can be implemented by means of a control system connected by wire or wireless means to one or more control systems comprising one or more engine computers, such as FADECs, managing the fuel flow instructions of each engine. A controller of the control system can thus identify the engines regulated in N2 and the engines not regulated in N2'.

[0029] Furthermore, each N2 regulated engine can be identified when the corresponding fuel flow rate is variable within a predetermined time interval by following a regulation parameter dependent on the N2 rotation speed of each first output shaft.

[0030] Furthermore, the steps of determining the first and second input torque limits may be implemented by calculations, tests or simulations prior to a flight of the rotorcraft. The first and second input torque limits are then transmitted and stored by the control system in the rotorcraft.

[0031] The step of determining a first current torque can be implemented by the control system, for example, by a torque measurement carried out on the input shafts of the transmission system by means of sensors such as torque meters or even from power and rotation speed information transmitted by engine computers of each of the N2-regulated and non-N2'-regulated engines.

[0032] Furthermore, the values ​​of the permissible torque limit Cadm and the reduction coefficient Z can be determined by ground tests, flight tests or even by simulations.

[0033] The values ​​of the permissible torque limit Cadm and the reduction coefficient Z can thus be stored prior to a rotorcraft mission in at least one memory on board the rotorcraft.

[0034] The step of determining at least one residual combined torque limit is implemented in flight after having identified an engine not regulated in N2'. Indeed, the controller of the control system can calculate the residual combined torque limit(s) from, on the one hand, at least one admissible combined torque limit of the member(s) of a combiner of the transmission system and, on the other hand, the first current operating torque transmitted by the engine not regulated in N2'.

[0035] Said admissible combined torque limit for a respective member of the combiner may be determined by calculations, tests or simulations prior to a flight of the rotorcraft. The admissible combined torque limit(s) are therefore predetermined values ​​transmitted and stored in a memory of the control system in the rotorcraft.

[0036] The controller of the control system then identifies the critical torque limit by comparing the values ​​of said at least one first input torque limit, second input torque limit and at least one residual combined torque limit.

[0037] Depending on this critical torque limit, the step of generating a control setpoint limit of said at least one first regulation system makes it possible to control without pilot intervention, or even to limit, the total power transmitted jointly by the engines, regulated in N2 and not regulated in N2', to the transmission system to avoid exceeding an input torque limit or a combined torque limit. This limitation of the power transmitted to the transmission system can in particular be carried out manually by a rotorcraft pilot or automatically by an automatic pilot system to comply with the control setpoint limit of the first regulation system(s).

[0038] Such a control method thus makes it possible to protect the components of a transmission system, and in particular by limiting the torque transmitted by motors to a power transmission chain, in the event of a lack of regulation of one of the motors.

[0039] Furthermore, each of the first and second input torque limits may be defined for a maximum duration of use of the limit corresponding to a particular operating regime. A plurality of first input torque limits of a first coupling may then form a first set of input torque limits and a plurality of second input torque limits of a second coupling may then form a second set of input torque limits.

[0040] As a result, each of the residual combined torque limits can also be defined for a maximum duration of use of the limit corresponding to a particular operating regime. Several residual combined torque limits of a combiner component can then form a set of residual combined torque limits.

[0041] Furthermore, the residual combined torque limit of an assembly corresponding to an operating regime is compared with the input torque limits of the first assembly and the second assembly corresponding to this same operating regime.

[0042] In other words, the control method can implement simultaneously or sequentially several identifications of a critical torque limit for several operating regimes.

[0043] In practice, prior to the identification of an engine not regulated in N2', the engine not regulated in N2' may initially be an engine regulated in N2' which is supplied with fuel with a regulated fuel flow provided by the second fuel metering device controlled according to a flow setpoint transmitted by a second regulation system.

[0044] In other words, the identification of an engine not regulated in N2' can be carried out in flight and follow a command carried out voluntarily by the pilot, for example for pilot training purposes. The identification of an engine not regulated in N2' can also be carried out in flight and follow a technical problem.

[0045] In practice, the identification of an engine not regulated in N2' can be an identification of a failure of the second regulation system.

[0046] Such a failure may for example consist of a breakdown occurring at the level of one of the electronic cards of the second regulation system and may be detected by identifying an inconsistency between input data. As previously indicated, this failure of the second regulation system may in fact be identified when the fuel flow admitted by a fuel meter does not seek to approach the flow setpoint received.

[0047] According to another advantageous aspect, the control setpoint limit can be generated so that a second current operating torque transmitted by the at least one first output shaft to said at least one first coupling of the transmission system is maintained equal to or lower than the critical torque limit.

[0048] Furthermore, compliance with the control setpoint limit can be implemented by commanding a reduction in the control setpoint of one or more regulation systems or by commanding a reduction in a collective pitch of the blades of a lift rotor using a collective pitch lever. Indeed, such a reduction in the collective pitch of the blades makes it possible to reduce the power required to drive the rotor in rotation at a predetermined rotational speed depending on the current operating regime.

[0049] Furthermore, when the critical torque limit is one of said at least one first input torque limit and second input torque limit, said at least one first regulation system can regulate the fuel flow rate supplied by said at least one first fuel metering device as a function of a first rotation speed setpoint Nrrefl of at least one lift rotor.

[0050] In practice, this first rotation speed setpoint Nrrefl may be equal to a predetermined reference value or calculated from a predetermined reference value and for example be equal to 105% of a predetermined reference value. Such a first rotation speed setpoint may correspond to one or more first operating regimes of the rotorcraft in which one engine among all the engines is not capable of transmitting an engine torque to the rotor.

[0051] Furthermore, the first rotation speed setpoint Nrrefl can be determined by ground tests, flight tests or even by simulations.

[0052] This first rotation speed instruction Nrrefl can thus be stored prior to a rotorcraft mission in at least one memory on board the rotorcraft.

[0053] On the other hand, when the critical torque limit is said at least one residual combined torque limit, said at least one first regulation system can regulate the fuel flow rate supplied by said at least one first fuel metering device as a function of a second rotation speed setpoint Nrref2 of said at least one lift rotor, the second rotation speed setpoint Nrref2 being lower than the first rotation speed setpoint Nrrefl.

[0054] In this case, this second rotation speed setpoint Nrref2 may be equal to a predetermined reference value or calculated from a predetermined reference value and for example be equal to 100% of a predetermined reference value. This second rotation speed setpoint may correspond to one or more second operating regimes of the rotorcraft in which all the engines are capable of transmitting engine torque to the lift rotor.

[0055] Furthermore, this second rotation speed setpoint Nrref2 can also be determined by ground tests, flight tests or even by simulations.

[0056] This second rotation speed instruction Nrref2 can thus be stored prior to a rotorcraft mission in at least one memory on board the rotorcraft.

[0057] Furthermore, the control method may comprise a display of information useful for piloting on a display arranged in the rotorcraft or outside the rotorcraft.

[0058] According to a first alternative, when the critical torque limit is one of said at least one first input torque limit and second input torque limit, the method may comprise the following steps: - generation of information representative of a first operating regime, and - display on a display of at least a first limit indicator corresponding to the first operating mode.

[0059] Such at least one first limit indicator may then, for example, comprise an index opposite a graduated scale. The index is then representative of a current value of engine torque transmitted by the engines. Such an index may thus move relatively to the scale, for example, depending on the flight conditions and the maneuvers performed by the rotorcraft.

[0060] In practice, a value of the critical torque limit may be assigned to a first limit indicator among said at least one first limit indicator.

[0061] Thus, a mark on the graduated scale of the first OEI limit indicator may be representative of this current value of said at least one critical torque limit. Such a mark then constitutes a threshold value not to be crossed in order to comply with a predetermined level of stress on the engine(s) in operation for a maximum flight duration.

[0062] Furthermore, several marks on the graduated scale can be displayed simultaneously and can represent different threshold values ​​not to be crossed in order to comply with different stress levels according to this first operating regime. Each predetermined stress level can then correspond to a predetermined maximum usage duration of the corresponding limit.

[0063] According to a second alternative, when the critical torque limit is the residual combined torque limit, the method may comprise the following steps: - generation of information representative of a second operating regime, and - display on a display of at least a second limit indicator corresponding to the second operating mode.

[0064] As previously in the first operating mode, such at least one second limit indicator may then, for example, comprise an index and a graduated scale. The index is then representative of a current value of torque transmitted by the motors.

[0065] In practice, the value(s) of said at least one critical torque limit are in this case not assigned to said at least one second limit indicator.

[0066] Advantageously, the method can comprise the following steps: - preliminary determination of threshold values ​​of said at least one first limit indicator at least one second limit indicator, and - storage of threshold values ​​in at least one memory.

[0067] In other words, the threshold values ​​of said at least one first limit indicator and at least one second limit indicator can be determined upstream of a rotorcraft mission, for example by bench tests, by flight tests or by simulation.

[0068] The control system then comprises a memory making it possible to store the different threshold values ​​of said at least one first limit indicator and at least one second limit indicator.

[0069] Such a memory is then advantageously embedded in the rotorcraft.

[0070] According to another advantageous embodiment, the rotorcraft comprising a system automatic piloting and at least one lift rotor provided with blades, the method may comprise a calculation of a collective pitch margin applicable to the blades and a control of a collective pitch of the blades to automatically pilot the rotorcraft while respecting said at least one critical torque limit.

[0071] In other words, the control system can be connected to an automatic pilot system of the rotorcraft allowing it to be piloted along four axes such as a roll axis, a pitch axis, a yaw axis and a collective pitch axis. The controller of the control system can then generate and transmit to the automatic pilot system one or more power margins or even directly collective pitch margins applicable to the blades. The control system can also transmit to the automatic pilot system either information representative of the first operating regime of said at least two engines, or information representative of the second current operating regime of said at least two engines.

[0072] The present invention also relates to a computer program comprising instructions which, when the program is executed, lead to the implementation of the aforementioned control method.

[0073] The computer program is for example executed by a computer or a calculator, comprising at least one processor, at least one integrated circuit, at least one programmable system, at least one logic circuit, and a memory, these examples not limiting the scope given to the expression “computer” or “calculator”.

[0074] The memory makes it possible to store the computer program as well as various information used by the computer program, namely the control instructions to be transmitted to said actuators, the current value of a first current operating torque transmitted by the second output shaft to the second coupling of the transmission system, first and second permissible input torque limits for at least a first coupling and a second coupling of the transmission system, the permissible residual combined torque limit(s) for at least one member of a combiner of the transmission system and the critical torque limit.

[0075] Such a memory also makes it possible to store information representative of the first operating mode or information representing the second operating mode.

[0076] The present invention also relates to a rotorcraft comprising at least two combustion engines, at least one regulation system and a transmission system, said at least two engines being mechanically connected to the transmission system respectively by at least two couplings.

[0077] Such a rotorcraft is remarkable in that it comprises a control system configured to implement the aforementioned control method.

[0078] Such a control system is then integrated into the rotorcraft and as such constitutes equipment of the rotorcraft. The control system can then be connected to a flight management device of the rotorcraft and to an automatic pilot system.

[0079] Such a control system may in particular comprise a computer and a memory.

[0080] The invention and its advantages will appear in more detail in the context of the description which follows with examples given for illustrative purposes with reference to the appended figures which represent:

[0081] [Fig.l], a side view diagram of a rotorcraft according to the invention,

[0082] [Fig.2], a flowchart illustrating a control method in accordance with the invention,

[0083] [Fig.3], a flowchart illustrating a first variant of the control method in accordance with the invention, and

[0084] [Fig.4], a flowchart illustrating a second variant of the control method according to the invention.

[0085] Elements present in several distinct figures are assigned a single reference.

[0086] As already mentioned, the invention relates to a method for controlling a rotorcraft.

[0087] As shown in [Fig.l], such a rotorcraft 1 comprises at least two combustion engines 2, 3, including a first engine 2 and a second engine 3. The engines 2, 3 are each capable of transmitting an engine torque, via a transmission system 4, to at least one lift rotor 16 ensuring at least one lift in the air of the rotorcraft 1. The engines 2, 3 are thus connected to the transmission system 4 which is connected to at least one lift rotor 16 provided with blades 17.

[0088] The transmission system 4 comprises at least one first coupling 25 connected with at least one first output shaft 5 of the first motor 2 and a second coupling 26 connected with a second output shaft 6 of the second motor 3 and at least one output shaft 18 connected to the lift rotor 16.

[0089] The transmission system 4 comprises several internal components such as gears, speed reduction stages and at least one combiner 7 for example.

[0090] Furthermore, such a rotorcraft 1 also comprises at least a first regulation system 12 making it possible to regulate the fuel intake of the first engine 2. Optionally, the rotorcraft 1 may comprise a second regulation system 13 making it possible to modify the fuel intake of the second engine 3.

[0091] Furthermore, the first engine 2 is supplied with fuel by a first fuel metering device 22 controlled by the first regulation system 12. The first engine 2 is thus designated hereinafter as being an N2-regulated engine corresponding to the rotation speed N2 of the first output shaft 5. The first fuel metering device 22 is then capable of modifying a fuel flow rate transmitted to the N2-regulated engine 2 as a function of a position or flow rate setpoint transmitted by the first regulation system 12.

[0092] Furthermore, the second engine 3 may be supplied with fuel by a second fuel metering device 23 controlled by a second regulation system 13 whose regulation is not in N2' corresponding to the rotation speed N2' of the second output shaft 6, or else without being controlled by the second regulation system 13 when it is faulty or blocked. The second engine 3 may alternatively not be regulated in N2'. The second engine 3 may thus be designated subsequently as being an engine not regulated in N2' within the framework of the method of the invention.

[0093] The control method according to the invention is then implemented by a control system 10 connected by wire or wireless means at least to the first regulation system 12, or even also to the second regulation system 13 when the latter is present. Such a control system 10 may comprise, for example, a controller 11 comprising one or more sensors, one or more computers and at least one memory 14, at least one integrated circuit, at least one programmable system, at least one logic circuit, these examples not limiting the scope given to the expression “control system”. The term computer may also designate a processor, a central processing unit known by the acronym CPU, a graphics processing unit GPU, a digital unit known by the acronym DSP, a microcontroller, etc.

[0094] Furthermore, the memory 14 can be used to store a computer program implementing the control method according to the invention.

[0095] Furthermore, the controller 11 of the control system 10 is configured to determine whether an engine is an N2 regulated or non-N2' regulated engine.

[0096] As shown in Figures 2 to 4, the control method 30, 40 then comprises an identification 31, 41, by the controller 11, of an engine regulated in N2 2 among the at least two engines 2, 3 and an identification 32, 42, by the controller 11, of an engine not regulated in N2' 3 among the at least two engines 2, 3.

[0097] Furthermore, as previously indicated, the non-N2' regulated engine may be an engine configured not to be regulated in N2' or an engine initially regulated in N2'. Except in the event of a breakdown, this engine is therefore supplied with fuel with a fuel flow regulated in N2' provided by the second fuel metering device 23 controlled according to a flow rate instruction transmitted by the second regulation system 13. The identification 32 of an engine not regulated in N2' 3 can thus be implemented by identifying a failure of the second regulation system 13.

[0098] Once the N2-regulated motor(s) 2 and the non-N2'-regulated motor 3 have been identified, the control method 30, 40 comprises a determination 33, 43 of at least one first permissible input torque limit E1 for the first coupling(s) 25 of the transmission system 4 and a determination 34, 44 of a second permissible input torque limit E2 for the second coupling 26 of the transmission system 4.

[0099] The first permissible input torque limit(s) El and the second permissible input torque limit E2 may be determined prior to a current mission of the rotorcraft 1 by flight tests, bench tests or simulations. These first and second input torque limits El, E2 may then be stored in the memory 14 of the control system 10.

[0100] Such a control method 30, 40 then comprises a determination 35, 45 of a first current operating torque C1 transmitted by the second output shaft 6 to the second coupling 26.

[0101] Such a first current operating torque C1 can in particular be determined by a calculation carried out by the controller 11 of the control system 10 from a current power delivered by the non-regulated motor in N2' 3 and a rotation speed of the second output shaft 6.

[0102] Such a first current operating torque C1 can also be measured by torque sensors. By sensor is meant here a physical sensor capable of directly measuring the parameter in question, in this case the first current operating torque, but also a system which can comprise one or more physical sensor(s) as well as signal processing means making it possible to provide an estimate of the parameter in question from the measurements provided by these physical sensors.

[0103] Furthermore, the control method 30, 40 comprises a determination 34, 44 of at least one residual combined torque limit CRI admissible for at least one member of the combiner 7 of the transmission system 4. Such at least one residual combined torque limit CRI is furthermore calculated by the controller 11 of the control system 10 as a function of the first current operating torque C1 transmitted by the second shaft 6 of the non-N2' regulated engine 3.

[0104] A residual combined torque limit CRI is thus equal to the difference between an admissible combined torque limit Cadm for a member of the combiner 7 and the product between the first current operating torque Cl and a reduction coefficient Z between a rotation speed of the second coupling 26 and a rotation speed of the combiner member 7.

[0105] Furthermore, this permissible torque limit Cadm can be determined prior to a current mission of the rotorcraft 1 by flight tests, bench tests or simulations. This permissible torque limit Cadm can also be stored in the memory 14 of the control system 10.

[0106] The control method 30, 40 then comprises an identification 37, 47 by the controller 11 of the control system 10 of at least one critical torque limit CCI. Such a critical torque limit CCI is then identified as being the smallest of the values ​​among the first input torque limit(s) El, the second input torque limit E2 and the residual combined torque limit(s) CRI.

[0107] The control method 30, 40 finally comprises a generation 38, 48 of a control setpoint limit COM of the first regulation system(s) 22 for the N2-regulated engine(s) 2. Such a control setpoint limit COM is then generated by the controller 11 of the control system 10 as a function of said at least one critical torque limit CCI. This step of generation 38 of the control setpoint limit COM of the first regulation system(s) 22 in fact makes it possible to automatically limit the total power transmitted jointly by the engines 2 and 3, to the transmission system 4 to avoid exceeding an input torque limit E1, E2 or a residual combined torque limit CRI.

[0108] The control system 10 can thus limit the control setpoint COM in order to respect this at least one critical torque limit CCI.

[0109] Furthermore, when the critical torque limit CCI is one of said at least one first input torque limit E1 and second input torque limit E2, said at least one first regulation system 12 can regulate the fuel flow rate supplied by the associated first fuel metering unit 22 as a function of a first rotation speed setpoint Nrrefl of at least one lift rotor 16 of the rotorcraft 1. Such a first rotation speed setpoint Nrrefl can moreover correspond to a nominal rotation speed of the lift rotor(s) 16 or be calculated from the nominal rotation speed by being equal for example to 105% of the nominal rotation speed. This first rotation speed setpoint Nrrefl is furthermore for example used when one of the engines 2 or 3 does not transmit engine torque to one of the first and second input shafts 5, 6.

[0110] On the other hand, when the critical torque limit CCI is said at least one residual combined torque limit CRI, said at least one first regulation system 12 can regulate the fuel flow rate supplied by said at least one first fuel metering device 22 as a function of a second rotation speed setpoint Nrref2 of the or lift rotors 16, the second rotation speed setpoint Nrref2 being lower than the first rotation speed setpoint Nrrefl.

[0111] Such a second rotation speed setpoint Nrref2 may correspond to a rotation speed equal to 100% of the nominal rotation speed of the lift rotor(s) 16. This second rotation speed setpoint Nrref2 may be used when each of the motors 2 and 3 transmits a motor torque respectively to the first and second input shafts 5, 6.

[0112] The control system 10 can then limit the power delivered by the N2-regulated engine(s) 2 according to the critical torque limit CCI.

[0113] As shown in [Fig. 3], when said at least one critical torque limit CCI is one of said at least one first or second input torque limits E1, E2, the method 30 may comprise a generation 391 of information KO E1 representative of an asymmetric operation, called OEI, of said at least two motors 2, 3.

[0114] In this case, the method 30 then comprises a display 392 on a display 8 of at least one OEI limit indicator 9 corresponding to the asymmetric OEI operation.

[0115] Such a display 8 is for example formed by a screen equipping a dashboard of a cockpit of the rotorcraft 1 or by a head-up display system worn by a pilot and arranged for example on a helmet or glasses.

[0116] In this case, the display 8 is then connected by wire or wireless means to the control system 10 and can display a value of the critical torque limit CCI on the limit indicator OEI 9 in accordance with an asymmetrical operation OEI of the motors 2, 3.

[0117] According to another exemplary embodiment, such a display 8 can also be remoted outside the rotorcraft 1, for example when the latter is piloted remotely.

[0118] As shown in [Fig.4], when said at least one critical torque limit CCI is said at least one residual combined torque limit CRI, such a method 40 can then comprise a generation 491 of KAEO information representative of a symmetrical operation, called AEO, of said at least two motors 2, 3, and a display 48 on the display 8 of at least one AEO limit indicator 19 corresponding to the symmetrical AEO operation.

[0119] Furthermore, as shown in Figures 3 and 4, the control method 30, 40 may comprise a preliminary determination 300, 400 of threshold values ​​SAEO, SOEI of said at least one AEO limit indicator 19 and at least one OEI limit indicator 9.

[0120] Furthermore, the control method 30, 40 may include storage 301, 401 of the SAEO, SOEI threshold values ​​of said at least one AEO limit indicator 19 and at minus one OEI 9 limit indicator.

[0121] Furthermore, the rotorcraft 1 may also include an automatic piloting system 15, which has the capacity to act on the collective pitch of the blades of the lift rotor(s) 16. Such an automatic piloting system 15 is then connected by wire or wireless means to the control system 10.

[0122] The method 30, 40 can then comprise a calculation 393, 493 of the collective pitch margins MPC applicable to said blades 17. The calculation 393, 493 can be implemented by the control system 10 which transmits it to the automatic pilot system 15.

[0123] The method 30, 40 can then comprise a control 394, 494 of a collective pitch PC of the blades 17 to automatically pilot the rotorcraft 1 while respecting said at least one critical torque limit CCI.

[0124] Naturally, the present invention is subject to numerous variations as to its implementation. Although several embodiments have been described, it is understood that it is not conceivable to exhaustively identify all possible modes. It is of course conceivable to replace a means described by an equivalent means without departing from the scope of the present invention.

Claims

Claims

1. Method for controlling (30, 40) a rotorcraft (1), said rotorcraft (1) comprising at least two combustion engines (2, 3), at least one regulation system (12, 13) and a transmission system (4), said at least two engines (2, 3) being mechanically connected to said transmission system (4) respectively by at least two couplings (25, 26), characterized in that the control method (30, 40) comprises at least the following steps: - identification (31, 41) of at least one so-called N2-regulated engine (2) among said at least two engines (2, 3), said at least one N2-regulated engine (2) being identified as an engine supplied with fuel with a fuel flow regulated as a function of the N2 rotation speed of at least one first output shaft (5) of said at least one N2-regulated engine and supplied by at least one first fuel metering device (22) controlled as a function of a flow setpoint transmitted by at least one first regulation system (12) dependent on the N2 rotation speed of said at least one first output shaft (5), - identification (32, 42) of a so-called non-N2' regulated engine (3) among said at least two engines (2, 3), said non-N2' regulated engine (3) being identified as an engine supplied with fuel with a fuel flow rate not regulated as a function of the rotation speed N2' of a second output shaft (6) and supplied by a second fuel metering device (23) being either non-regulated or controlled as a function of a flow rate setpoint transmitted by at least one second regulation system (13) independent of the rotation speed N2' of said second output shaft (6), - determination (33, 43) of at least one first admissible input torque limit (El) for at least one first coupling (25) of said transmission system (4) connected to said at least one first output shaft (5), - determination (34, 44) of a second permissible input torque limit (E2) for a second coupling (26) of said transmission system (4) connected to said second output shaft (6), - determination (35, 45) of a first current operating torque (Cl) transmitted by said second output shaft (6) to said second coupling (26) of said transmission system (4), - determination (36, 46) of at least one residual combined torque limit (CRI) admissible for at least one member of a combiner (7) of said transmission system (4), said at least one residual combined torque limit (CRI) being calculated according to the formula: C7d = Cadm-(C1*Z) where Cadm is an admissible combined torque limit for said at least one member of said combiner (7), Cl is said first current operating torque transmitted by said second output shaft (6) to said second coupling (26) of said transmission system, and Z a reduction coefficient between a rotation speed of said second coupling (26) and a rotation speed of said at least one member of said combiner (7), - identification (37, 47) of a critical torque limit (CCI) as being the smallest of the values ​​among said at least one first input torque limit (El), second input torque limit (E2) and at least one residual combined torque limit (CRI), - generation (38, 48) of a control setpoint limit (COM) of said at least one first regulation system (12), said control setpoint limit (COM) being generated as a function of said critical torque limit (CCI).

2. Control method according to claim 1, characterized in that, prior to said identification (32) of a non-N2' regulated engine (3), said non-N2' regulated engine (3) is initially an N2' regulated engine which is supplied with fuel with a N2' regulated fuel flow rate supplied by said second fuel metering device (23) controlled as a function of a flow rate setpoint transmitted by a second regulation system (13).

3. Control method according to claim 2, characterized in that said identification (32) of an engine not regulated in N2' (3) is an identification of a failure of said second regulation system (13).

4. Control method according to any one of claims 1 to 3, characterized in that said control setpoint limit (COM) is generated so that a second current operating torque (C2) transmitted by said at least one first output shaft (5) to said at least one first coupling (25) of said transmission system (4) is maintained equal to or lower than said critical torque limit (CCI).

5. Control method according to any one of claims 1 to 4, characterized in that, when said critical torque limit (CCI) is one of said at least one first input torque limit (El) and second input torque limit (E2), said at least one first regulation system (12) regulates the fuel flow supplied by said at least one first fuel metering device (22) as a function of a first rotation speed setpoint (Nrrefl) of at least one lift rotor (16) of said rotorcraft (1).

6. Control method according to claim 5, characterized in that, when said critical torque limit (CCI) is said at least one residual combined torque limit (CRI), said at least one first regulation system (12) regulates the fuel flow supplied by said at least one first fuel metering device (22) as a function of a second rotation speed setpoint (Nrref2) of said at least one lift rotor (16) of said rotorcraft (1), said second rotation speed setpoint (Nrref2) being lower than said first rotation speed setpoint (Nrrefl).

7. Control method according to any one of claims 1 to 6, characterized in that, when said critical torque limit (CCI) is one of said at least one first input torque limit (El) and second input torque limit (E2), said method (30) comprises the following steps: - generation (391) of information (KOEI) representative of a first operating speed (OEI), and - display (392) on a display (8) of at least one first limit indicator (91, 92) corresponding to said first speed operating environment (OEI).

8. Control method according to claim 7, characterized in that a value of said critical torque limit (CCI) is assigned to a first limit indicator (91) among said at least one first limit indicator (91, 92).

9. Control method according to any one of claims 1 to 6, characterized in that, when said critical torque limit (CCI) is said residual combined torque limit (CRI), said method (40) may comprise the following steps: - generation (491) of information (KAEO) representative of a second operating mode (AEO), and - display (492) on a display (8) of at least one second limit indicator (191, 192) corresponding to said second operating mode (AEO).

10. Control method according to claims 7 and 9, characterized in that said method (30, 40) comprises the following steps: - preliminary determination (300, 400) of threshold values ​​(SAEO, SOEI) of said at least one first limit indicator (9) and at least one second limit indicator (19), and - storage (301, 401) of said threshold values ​​(SAEO, SOEI) in at least one memory (14).

11. Control method according to any one of claims 1 to 10, characterized in that, said rotorcraft (1) comprising an automatic piloting system (15) and at least one lift rotor (16) provided with blades (17), said method (30, 40) comprises a calculation (393, 493) of a collective pitch margin (MPC) applicable to said blades (17) and a control (394, 494) of a collective pitch (PC) of said blades (17) to automatically pilot said rotorcraft (1) while respecting said at least one critical torque limit (CCI).

12. Computer program comprising instructions which, when said program is executed, lead to implementing the control method according to any one of claims 1 to 11.

13. Rotorcraft (1) comprising at least two combustion engines (2, 3), at least one regulation system (13) and a transmission system (4), said at least two engines (2, 3) being mechanically connected to said transmission system (4) respectively by at least two couplings (25, 26), characterized in that said rotorcraft (1) comprises a control system (10) configured to implement said control method (30, 40) according to any one of claims 1 to 11.

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