Method for controlling rotorcraft, associated rotorcraft and computer program

Abstract

The invention relates to a method for controlling a rotorcraft, an associated rotorcraft and a computer program, said rotorcraft (2) comprising at least two combustion engines (2, 3), at least one regulating system (13) and a transmission system (4), said at least two engines (2, 3) being mechanically connected to said transmission system (4) by at least two couplings (25, 26), respectively. The control method comprises at least identifying N2 to regulate the engine (2), identifying non N2'to regulate the engine (3), and generating a control setpoint limit for at least one first regulating system (12) of the N2 to regulate the engine (2) as a function of a rotational speed N2 of at least one first output shaft (5) of the N2 to regulate the engine (2).

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of FR2311651 filed on October 26, 2023, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The invention relates to a control method for a rotorcraft, a rotorcraft and a computer program associated with the control method. Background Art

[0004] A rotorcraft includes at least one rotor that helps provide lift, and possibly propulsion, to the rotorcraft.

[0005] For example, a rotorcraft may include a main rotor with blades whose pitch is collectively and periodically variable, which helps provide lift and propulsion for the rotorcraft. The rotorcraft may also include a system that helps control yaw motion, such as another main rotor or a rear rotor. The pitch control system may be activated, for example, by a pilot or crew member. Alternatively, the system may be activated by an automatic control system known as an autopilot.

[0006] In order to move one or more rotors, the rotorcraft includes a power plant and a power transmission system leading from the engine to the one or more rotors. The power plant may be a multi-engine power plant.

[0007] For example, two engines are connected to a gearbox that moves one or more rotors. The gearbox thus comprises a mechanical input for each engine that engages a mixing unit that drives a mechanical output of the gearbox for each rotor. The engine input, mixing unit and mechanical output may comprise at least one pinion or one gear, at least one shaft, at least one reduction stage, etc.

[0008] The engines may be heat engines whose output shaft is moved by combustion of fuel. For example, at least one engine may be a turboshaft engine having a gas generator and a free-running turbine connected to the output shaft.

[0009] Each engine may be controlled by a regulation system known as Full Authority Digital Engine Control or FADEC. Such a regulation system comprises an engine computer in communication with sensing devices that measure the value of an operating parameter of the controlled engine or rotorcraft, such as the speed of rotation of the gas generator or free turbine, the internal temperature or the speed of rotation of the rotors of the rotorcraft.

[0010] The engine computer is then configured to control the fuel metering valves feeding the associated engine, for example, to stabilize the rotational speed of the output shaft at a setpoint speed, independently of the power consumed by the output shaft. The variation of this power depends on the action of the pilot on the flight control devices, in particular on the control devices that collectively and / or periodically vary the pitch of the blades of the main rotor on the helicopter. Alternatively, these control devices can be actuated by an automatic flight control system.

[0011] The regulation performed according to the rotational speed (N2) of the output shaft of the turboshaft engine then ensures that the power produced by the output shaft of the engine is permanently matched to the power consumed by one or more rotors, meaning that the one or more rotors rotate at a nominal rotational speed compatible with their function of generating lift for the rotorcraft.

[0012] However, the engine computer is configured to prevent the power generated by the engine from exceeding the acceptable mechanical limits of the engine or the power transmission system. Traditionally, various operating modes are defined that are associated with specific limits and durations of use. For each operating mode, these limits may include, for example, limits on the torque transmitted by the engine, limits on the temperature inside the engine, limits on the rotational speed of the engine shaft, limits on the torque of at least one component of the power transmission system, etc.

[0013] Known operating modes on multi-engine aircraft include an "all engines operating" or AEO operating mode that can be used for specific periods of time when all engines are operating normally, and a "one engine out of operation" or OEI operating mode that can be used for specific periods of time when one of the engines fails. Use of certain operating modes may result in the need for maintenance work on the engines or the power transmission system.

[0014] The engine computer therefore controls the fuel metering valve in order to regulate the power of the associated engine. The first type of regulation consists in bringing the speed of the output shaft close to a set value while avoiding exceeding limits. This type of regulation is called N2 regulation, since it depends on the speed of the output shaft of the associated engine.

[0015] Another type of regulation consists in delivering a predetermined engine power, for example to achieve an optimum operating point in terms of thermodynamic efficiency.

[0016] However, in the case of a rotorcraft, it is advantageous to regulate at least one engine according to the rotational speed N2 of its output shaft. In fact, such regulation (which is called "N2" regulation) can avoid the regular reduction of the rotational speed NR of the lift rotor which is itself directly related to the rotational speed N2.

[0017] When the limit is reached, the engine computer restricts the flow of fuel to the engine, so the power delivered to its output shaft drops below the required power. The pilot then needs to take action on the flight controls to reduce the power required for flight.

[0018] To this end, the rotorcraft may include various indicators that enable the pilot to assess the situation. These indicators may include an indicator indicating the rotational speed of the main rotor and the associated limits, an engine indicator indicating the current values ​​of monitored parameters of the engine (temperature, mode, torque) and the associated limits, an indicator indicating the current values ​​of monitored parameters of the power transmission system and the associated limits, a first limit indicator displaying information related to the parameter of a plurality of monitored parameters that is closest to one of these limits.

[0019] Furthermore, in the event of a malfunction or failure of the engine regulation system, the fuel flow rate feeding the engine in question is fixed at the last flow rate value used. The pilot is informed of this and can then shut down the engine in question for safety reasons or continue the flight as is (i.e., with the engine not regulated by N2).

[0020] If the flight continues as is, the pilot must ensure that the limits of the mechanical power transmission system are not exceeded. For example, on a twin-engine rotorcraft, if the pilot requests power to perform a maneuver, the sum of the power provided by the N2-regulated and non-N2-regulated engines may be higher than the mixing unit of the gearbox allows.

[0021] More generally, the management of a possible intentional or accidental lack of regulation of one of the rotorcraft's engines may create additional workload for the crew in order not to exceed the limits of the mechanical power transmission system.

[0022] In addition, documents US2019 / 382124, US2014 / 283527, US2016 / 221685, EP3251955 and US2013 / 054053 relate to other known control methods for rotorcraft. Summary of the invention

[0023] One object of the invention is therefore to propose a method that helps limit the crew's workload in the event of a malfunction of the engine regulation system on a multi-engine rotorcraft or a lack of regulation of one of the engines. In addition, such a method enables the pilot to carry out piloting maneuvers in complete safety, without the risk of degrading the mechanical power transmission system of the rotorcraft.

[0024] The invention therefore relates to a method for controlling a rotorcraft comprising at least two combustion engines, at least one regulating system and a transmission system, the at least two engines being respectively mechanically connected to the transmission system via at least two couplings.

[0025] According to the present invention, the control method is remarkable in that it comprises at least the following steps:

[0026] identifying at least one engine, referred to as the N2-regulated engine, from the at least two engines, the at least one N2-regulated engine being identified as an engine supplied with fuel at a fuel flow rate regulated as a function of the rotational speed N2 of at least one first output shaft of the at least one N2-regulated engine, provided by at least one fuel metering valve, the at least one fuel metering valve being controlled as a function of a flow rate setpoint transmitted by at least one first regulation system and dependent on the rotational speed N2 of the at least one first output shaft;

[0027] identifying, from the at least two engines, an engine referred to as the non-N2′-regulated engine, the non-N2′-regulated engine being identified as an engine supplied with fuel at a fuel flow rate provided by a second fuel metering valve that is not regulated as a function of the rotational speed N2′ of a second output shaft of the non-N2′-regulated engine, the second fuel metering valve being either not regulated or controlled as a function of a flow rate setpoint transmitted by at least one second regulation system that is independent of the rotational speed N2′ of the second output shaft;

[0028] determining at least one first permissible input torque limit of at least a first coupling of said transmission system connected to said at least one first output shaft;

[0029] determining a second permissible input torque limit of a second coupling of the transmission system connected to the second output shaft;

[0030] determining a first current operating torque transmitted by the second output shaft to the second coupling of the transmission system;

[0031] Determining at least one admissible residual combined torque limit of at least one component of the hybrid unit of the transmission system, the at least one residual combined torque limit being calculated according to the following formula:

[0032] CR1=Cadm-(C1*Z)

[0033] wherein Cadm is the allowable combined torque limit of said at least one component of said mixing unit;

[0034] C1 is a first current operating torque transmitted by the second output shaft to the second coupling of the transmission system; and

[0035] Z is a reduction factor between the rotational speed of the second coupling and the rotational speed of the at least one component of the mixing unit;

[0036] identifying the critical torque limit as a lowest value among the values ​​of the at least one first input torque limit, the second input torque limit, and the at least one residual combined torque limit; and

[0037] Generating a control setpoint limit for the at least one first regulating system, the control setpoint limit being generated as a function of the critical torque limit.

[0038] The step of identifying the non-N2' regulated engines may be accomplished in a variety of ways. For example, on a rotorcraft having identical engines that are required to operate in the same manner, this step may include detecting asymmetric operation of the engines by possibly detecting that a first fuel flow rate provided by a first fuel metering valve supplying fuel to one engine and a second fuel flow rate provided by a second fuel metering valve supplying fuel to the other engine have exceeded a predetermined difference.

[0039] According to another example, a non N2 ′ regulated engine may be identified when the fuel flow rate admitted by its fuel metering valve is constant over a period of time or varies according to a regulation parameter different from the second output shaft speed N2 ′.

[0040] According to another example, a non-N2' regulated engine may be identified when the fuel flow rate allowed by its fuel metering valve, and therefore the position of the metering valve, does not correspond to the flow rate or position setting for the metering valve it has received.

[0041] This step of identifying non-N2' regulated engines can be achieved by a control system that is connected via wired or wireless means to one or more regulation systems, including one or more engine computers, such as FADEC, that manage the fuel flow rate setpoints for each engine. Thus, a controller of the control system can identify N2 regulated engines and non-N2' regulated engines.

[0042] Furthermore, each N2 regulated engine can be identified when the corresponding fuel flow rate is variable within a predetermined time interval according to a regulating parameter that depends on the rotational speed N2 of each first output shaft.

[0043] Furthermore, the steps of determining the first input torque limit and the second input torque limit may be accomplished by calculation, experimentation, or simulation prior to flight of the rotorcraft.The first input torque limit and the second input torque limit are then transmitted and stored by a control system in the rotorcraft.

[0044] The step of determining the first current torque may be implemented by the control system, for example, by torque measurement performed on the input shaft of the transmission system by a sensing device such as a torque meter, or indeed based on information relating to the power and speed transmitted by the engine computer of each of the N2 regulated engine and the non-N2' regulated engine.

[0045] In addition, the values ​​of the allowable torque limit Cadm and the reduction factor Z may be determined through ground tests, flight tests, or simulations.

[0046] Thus, the values ​​of the permissible torque limit Cadm and the reduction factor Z may be stored in at least one memory on board the rotorcraft prior to a mission of the rotorcraft.

[0047] The step of determining at least one residual combined torque limit is carried out during flight after the non-N2' regulating engine has been identified. In practice, the controller of the control system may calculate the one or more residual combined torque limits based on at least one admissible combined torque limit of one or more components of the hybrid unit of the transmission system and a first current operating torque transmitted by the non-N2' regulating engine.

[0048] Said admissible combined torque limits of the respective components of the mixing unit may be determined by calculation, experimentation or simulation before the rotorcraft is flown.Therefore, one or more admissible combined torque limits are predetermined values ​​transmitted and stored in a memory of the control system in the rotorcraft.

[0049] Then, a controller of the control system identifies the critical torque limit by comparing the values ​​of the at least one first input torque limit, the second input torque limit, and the at least one residual combined torque limit.

[0050] Depending on this critical torque limit, the step of generating a control setpoint limit of said at least one first regulating system makes it possible to control and, in practice, limit the total power transmitted to the transmission system by the N2 regulating engine and the non-N2' regulating engine jointly, without pilot intervention, so as to prevent exceeding the input torque limit or the combined torque limit. Such limitation of the power transmitted to the transmission system can be implemented in particular manually by the pilot of the rotorcraft or automatically by an automatic flight control system, in compliance with the control setpoint limits of one or more first regulating systems.

[0051] This control method thus helps to protect the components of the transmission system in the event of a lack of regulation of one of the engines, in particular by limiting the torque transmitted by the engine to the power transmission system.

[0052] Furthermore, each of the first input torque limit and the second input torque limit may be defined for a maximum lifetime of the limit corresponding to a particular operating mode. The plurality of first input torque limits of the first coupling may thus form a first set of input torque limits and the plurality of second input torque limits of the second coupling may thus form a second set of input torque limits.

[0053] Thus, each residual combined torque limit may also be defined for a maximum lifetime of the limit corresponding to a specific operating mode.A plurality of residual combined torque limits of components of the hybrid unit may thus form a set of residual combined torque limits.

[0054] Additionally, a set of residual combined torque limits corresponding to the operating mode is compared to first and second sets of input torque limits corresponding to the same operating mode.

[0055] In other words, the control method may perform multiple identifications of critical torque limits for multiple operating modes simultaneously or sequentially.

[0056] Indeed, before identifying a non-N2' regulated engine, the non-N2' regulated engine may initially be a N2' regulated engine fueled at a regulated fuel flow rate provided by a second fuel metering valve controlled according to a flow rate setpoint transmitted by a second regulation system.

[0057] In other words, the identification of a non-N2' regulated engine can be performed during flight following a deliberate command by the pilot, for example for pilot training purposes. The identification of a non-N2' regulated engine can also be performed during flight following a technical problem.

[0058] Indeed, the identification of a non- N2 ′ regulated engine may be the identification of a fault in the second regulation system.

[0059] For example, such a fault may consist of a failure in one of the electronic boards of the second regulating system and may be detected by identifying inconsistencies in the input data. As described above, such a fault in the second regulating system may be identified when the fuel flow rate allowed by the fuel metering valve does not attempt to move towards the received flow rate setpoint.

[0060] According to another advantageous aspect, the control setpoint limit can be generated such that a second current operating torque transmitted by the at least one first output shaft to the at least one first coupling of the transmission system remains less than or equal to a critical torque limit.

[0061] Furthermore, compliance with the control setpoint limits can be achieved by commanding a reduction in the control setpoints of one or more regulating systems or by commanding a collective pitch lever to reduce the collective pitch of the lift rotor blades. In practice, such a reduction in the collective pitch of the blades can reduce the power required to rotate the rotor at a predetermined rotation speed according to the current operating mode.

[0062] Furthermore, when the critical torque limit is one of the at least one first input torque limit and the second input torque limit, the at least one first regulation system may regulate the fuel flow rate provided by the at least one first fuel metering valve according to a first speed setting Nref1 of at least one lift rotor.

[0063] In practice, the first speed setting value Nref1 may be equal to a predetermined reference value, or may be calculated based on a predetermined reference value, for example, may be equal to 105% of a predetermined reference value. Such a first speed setting value may correspond to one or more first operating modes of the rotorcraft, in which one of the engines is unable to transmit engine torque to the rotor.

[0064] In addition, the first rotation speed setting value Nref1 can be determined through ground tests, flight tests or simulations.

[0065] Thus, the first rotational speed setpoint Nref1 can be stored in at least one memory on board the rotorcraft prior to a mission of the rotorcraft.

[0066] However, when the critical torque limit is the at least one residual combined torque limit, the at least one first regulation system may adjust the fuel flow rate provided by the at least one first fuel metering valve according to the second speed setting value Nref2 of the at least one lift rotor, and the second speed setting value Nref2 is less than the first speed setting value Nref1.

[0067] In this case, the second speed setting value Nref2 may be equal to a predetermined reference value, or may be calculated based on a predetermined reference value, for example, may be equal to 100% of the predetermined reference value. The second speed setting value may correspond to one or more second operating modes of the rotorcraft, in which all engines are able to transmit engine torque to the lift rotor.

[0068] In addition, the second rotation speed setting value Nref2 can also be determined through ground tests, flight tests or simulations.

[0069] Thus, the second rotational speed setpoint Nref2 can be stored in at least one memory on board the rotorcraft prior to a mission of the rotorcraft.

[0070] Furthermore, the control method may include displaying information useful for piloting on a display arranged inside or outside the rotorcraft.

[0071] According to a first alternative, when the critical torque limit is one of said at least one first input torque limit and a second input torque limit, the method may comprise the following steps:

[0072] generating information representative of a first operating mode; and

[0073] Displaying at least one first limit indicator corresponding to the first operating mode on the display.

[0074] Such at least one first limit indicator may thus comprise, for example, an index on a scale. The index represents the current value of the engine torque delivered by the engine. Such an index may thus be shifted relative to the scale, for example depending on the flight and maneuvering conditions performed by the rotorcraft.

[0075] In practice, the value of the critical torque limit may be assigned to a first limit indicator of the at least one first limit indicator.

[0076] Thus, the markings on the first OEI limit indicator scale may represent this current value of said at least one critical torque limit. Such markings then constitute threshold values ​​which must not be exceeded in order to comply with the predetermined load level for the engine or engines which have operated for the longest flight time.

[0077] Furthermore, a plurality of markings on the scale may be displayed simultaneously and may represent different threshold values ​​which are not exceeded to comply with different load levels according to the first operating mode.Each predetermined load level may then correspond to a predetermined maximum lifetime of the respective limit.

[0078] According to a second alternative, when the critical torque limit is the residual combined torque limit, the method may comprise the following steps:

[0079] generating information representative of a second operating mode; and

[0080] Displaying at least one second limit indicator corresponding to the second operating mode on the display.

[0081] As mentioned above, in the first operating mode, such at least one second limit indicator may for example comprise an index and a scale. The index then represents the current value of the torque delivered by the engine.

[0082] Indeed, in this case, one or more values ​​of said at least one critical torque limit are not assigned to said at least one second limit indicator.

[0083] Advantageously, the method may comprise the following steps:

[0084] predetermining threshold values ​​for the at least one first limit indicator and the at least one second limit indicator; and

[0085] • Storing the threshold value in at least one memory.

[0086] In other words, the threshold values ​​of the at least one first limit indicator and the at least one second limit indicator may be determined upstream of the mission of the rotorcraft, for example by bench tests, flight tests or simulations.

[0087] The control system comprises a memory for storing different threshold values ​​of the at least one first limit indicator and the at least one second limit indicator.

[0088] Such a storage device is advantageously located on board the rotorcraft.

[0089] According to another advantageous embodiment, the rotorcraft comprises an automatic flight control system and at least one lifting rotor having blades, the method may comprise calculating a total pitch margin applicable to the blades and controlling the total pitch of the blades in order to automatically control the rotorcraft while respecting the at least one critical torque limit.

[0090] In other words, the control system can be connected to an automatic flight control system of the rotorcraft, which allows the rotorcraft to be controlled along four axes, such as the roll axis, the pitch axis, the yaw axis and the total pitch axis. The controller of the control system can then generate one or more power margins and transmit the one or more power margins to the automatic flight control system, or indeed can directly generate a total pitch margin applicable to the blades and transmit the total pitch margin to the automatic flight control system. The control system can also transmit to the automatic flight control system information representing a first operating mode of the at least two engines, or a signal representing a second current operating mode of the at least two engines.

[0091] The object of the invention is also a rotorcraft comprising at least two combustion engines, at least one regulation system and a transmission system, the at least two engines being mechanically connected to the transmission system respectively by at least two couplings.

[0092] This rotorcraft is notable in that it comprises a control system configured to implement the control method described above.

[0093] Such a control system is integrated into the rotorcraft and constitutes the equipment of the rotorcraft. The control system can then be connected to the flight management device and the automatic flight control system of the rotorcraft.

[0094] Such a control system may comprise, in particular, a computer and a memory.

[0095] The object of the invention is also a computer program comprising instructions which, when this program is executed by a control system of the above-mentioned rotorcraft, enable the above-mentioned control method to be implemented.

[0096] For example, a computer program is executed by a computing device or a computer including at least one processor, at least one integrated circuit, at least one programmable system, at least one logic circuit, and a memory, and these examples do not limit the scope of the expression "computing device" or "computer".

[0097] The memory may be used to store the computer program and various information used by the computer program, namely, control setpoints to be transmitted to the actuator, a current value of a first current operating torque transmitted by the second output shaft to a second coupling of the transmission system, an admissible first input torque limit and a second input torque limit of at least one first coupling and one second coupling of the transmission system, an admissible residual combined torque limit of at least one component of a hybrid unit of the transmission system, and a critical torque limit.

[0098] Such a memory may also be used to store information representative of the first operating mode or information representative of the second operating mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0099] The invention and its advantages appear in more detail in the context of the following description of embodiments given by way of example and with reference to the accompanying drawings, in which:

[0100] Figure 1 is a side view of a rotorcraft according to the present invention;

[0101] Figure 2 is a logic diagram showing a control method according to the present invention;

[0102] Figure 3 is a logic diagram showing a first variation of the control method according to the present invention; and

[0103] Figure 4 is a logic diagram of a second variation of the control method according to the present invention. DETAILED DESCRIPTION

[0104] Elements which appear in more than one figure are given the same reference numerals in each figure.

[0105] As mentioned above, the present invention relates to a control method for a rotorcraft.

[0106] like Figure 1As shown, such a rotorcraft 1 comprises at least two combustion engines 2, 3, including a first engine 2 and a second engine 3. Each of the engines 2, 3 is capable of transmitting engine torque via a transmission system 4 to at least one lift rotor 16, which provides at least a lift force to keep the rotorcraft 1 in the air. The engines 2, 3 are thus connected to the transmission system 4, which is connected to at least one lift rotor 16 having blades 17.

[0107] The transmission system 4 comprises at least one first coupling 25 connected to at least one first output shaft 5 of the first engine 2 , as well as a second coupling 26 connected to the second output shaft 6 of the second engine 3 and at least one output shaft 18 connected to the lift rotor 16 .

[0108] The transmission system 4 comprises a plurality of internal components, such as gears, reduction stages and at least one mixing unit 7 .

[0109] Furthermore, such a rotorcraft 1 comprises at least one first regulating system 12 for regulating the fuel intake of the first engine 2 . The rotorcraft 1 may comprise a second regulating system 13 for varying the fuel intake of the second engine 3 .

[0110] Furthermore, a first fuel metering valve 22 controlled by the first regulating system 12 supplies fuel to the first engine 2. Therefore, the first engine 2 is referred to below as an N2-regulated engine, N2 corresponding to the rotational speed N2 of the first output shaft 5. The first fuel metering valve 22 is able to modify the fuel flow rate transmitted to the N2-regulated engine 2 according to a position or flow rate setpoint transmitted by the first regulating system 12.

[0111] Furthermore, the second engine 3 may be supplied with fuel by a second fuel metering valve 23 controlled by the second regulating system 13, which is either not regulated according to N2' (N2' corresponds to the rotational speed N2' of the second output shaft 6) or is not controlled by the second regulating system 13 when the second engine 3 fails or stops. Alternatively, the second engine 3 may not be regulated according to N2'. Therefore, the second engine 3 may be referred to as a non-N2' regulated engine in the following of the method of the invention.

[0112] The control method according to the invention is thus implemented by a control system 10, which is connected via wired or wireless means to at least the first regulating system 12, and when the second regulating system 13 is present, is also connected to the second regulating system 13. Such a control system 10 may include, for example, a controller 11 (the controller 11 includes one or more sensing devices), 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 of the term "control system". The term "computer" may equally refer to a processor, a central processing unit or CPU, a graphics processing unit or GPU, a digital signal processor or DSP, a microcontroller, etc.

[0113] Furthermore, the memory 14 may be used to store a computer program for implementing the control method according to the present invention.

[0114] Furthermore, the controller 11 of the control system 10 is configured to determine whether the engine is an N2 regulated engine or a non- N2 ′ regulated engine.

[0115] like Figures 2 to 4 As shown, the control method 30 , 40 therefore comprises identification 31 , 41 of the controller 11 as an N2 regulated engine 2 of the at least two engines 2 , 3 , and identification 32 , 42 of the controller 11 as a non- N2 ′ regulated engine 3 of the at least two engines 2 , 3 .

[0116] Furthermore, as mentioned above, a non-N2' regulated engine may be an engine configured not to be regulated in N2' or an engine that was initially regulated in N2'. Thus, except in the case of a failure, the engine is supplied with fuel at a fuel flow rate regulated in N2' provided by the second fuel metering valve 23, which is controlled according to a flow rate setpoint transmitted by the second regulation system 13. Thus, the identification 32 of a non-N2' regulated engine 3 may be achieved by identifying a fault in the second regulation system 13.

[0117] Once the N2 regulated engine 2 and the non-N2′ regulated engine 3 are identified, the control method 30 , 40 comprises determining 33 , 43 at least one first permissible input torque limit E1 of one or more first couplers 25 of the transmission system 4 , and determining 34 , 44 a second permissible input torque limit E2 of a second coupler 26 of the transmission system 4 .

[0118] One or more first and second permissible input torque limits E1, E2 may be determined by flight testing, bench testing, or simulation prior to a current mission of rotorcraft 1. These first and second input torque limits E1, E2 may then be stored in memory 14 of control system 10.

[0119] This control method 30 , 40 then comprises determining 35 , 45 a first current operating torque C1 transmitted by the second output shaft 6 to the second coupling 26 .

[0120] This first current operating torque C1 can in particular be determined by calculation by the controller 11 of the control system 10 based on the current power delivered by the non- N2 ′-regulated engine 3 and the rotational speed of the second output shaft 6 .

[0121] This first current operating torque C1 can also be measured by a torque sensor. The term "sensor" is to be understood as a physical sensor capable of directly measuring the parameter in question (in this case the first current operating torque), but can also be understood as a system that can include one or more physical sensors and means for processing signals that make it possible to provide an estimate of the parameter in question based on the measurements provided by these physical sensors.

[0122] Furthermore, the control method 30, 40 comprises determining 34, 44 at least one admissible residual combined torque limit CR1 of at least one member of the hybrid unit 7 of the transmission system 4. Furthermore, the controller 11 of the control system 10 calculates such at least one residual combined torque limit CR1 as a function of a first current operating torque C1 transmitted by the second shaft 6 of the non-N2' regulated engine 3.

[0123] Therefore, the residual combined torque limit CR1 is equal to the difference between the allowable combined torque limit Cadm of the components of the hybrid unit 7 and the product of the first current operating torque C1 and the reduction factor Z between the rotation speed of the second coupling 26 and the rotation speed of the components of the hybrid unit 7 .

[0124] Furthermore, the permissible torque limit Cadm may be determined by flight tests, bench tests or simulations before the current mission of the rotorcraft 1. The permissible torque limit Cadm may also be stored in the memory 14 of the control system 10.

[0125] The control method 30, 40 then includes identification 37, 47 of at least one critical torque limit CC1 by the controller 11 of the control system 10. Such critical torque limit CC1 is identified as the lowest value of one or more of the values ​​of the first input torque limit E1, the second input torque limit E2 and the residual combined torque limit CR1.

[0126] The control method 30, 40 finally comprises generating 38, 48 control setpoint limits COM of one or more first regulating systems 22 of one or more N2 regulating engines 2. Such control setpoint limits COM are generated by the controller 11 of the control system 10 as a function of said at least one critical torque limit CC1. This step of generating 38 control setpoint limits COM of one or more first regulating systems 22 makes it possible to automatically limit the total power transmitted jointly by the engines 2 and 3 to the transmission system 4 in order to prevent exceeding the admissible input torque limits E1, E2 or the residual combined torque limit CR1.

[0127] Therefore, the control system 10 may limit the control setpoint COM so as to comply with the at least one critical torque limit CC1 .

[0128] Furthermore, when the critical torque limit CC1 is one of the at least one first input torque limit E1 and the second input torque limit E2, the at least one first regulation system 12 may regulate the fuel flow rate provided by the associated first fuel metering valve 22 according to a first speed setting value Nref1 of at least one lift rotor 16 of the rotorcraft 1. Furthermore, such a first speed setting value Nref1 may correspond to a nominal speed of one or more lift rotors 16, or may be calculated based on the nominal speed, for example being equal to 105% of the nominal speed. For example, this first speed setting value Nref1 is also used when one of the engines 2 or 3 does not transmit engine torque to one of the first input shaft 5 and the second input shaft 6.

[0129] However, when the critical torque limit CC1 is the at least one residual combined torque limit CR1, the at least one first regulation system 12 may adjust the fuel flow rate provided by the at least one first fuel metering valve 22 according to the second speed setting value Nref2 of one or more lift rotors 16, and the second speed setting value Nref2 is less than the first speed setting value Nref1.

[0130] Such a second speed setting Nref2 may correspond to a speed equal to 100% of the nominal speed of the one or more lift rotors 16. This second speed setting Nref2 may be used when each of the engines 2 and 3 transmits engine torque to the first input shaft 5 and the second input shaft 6, respectively.

[0131] The control system 10 may then limit the power delivered by the one or more N2 regulating engines 2 according to the critical torque limit CC1 .

[0132] like Figure 3As shown, when the at least one critical torque limit CC1 is one of the at least one first or second input torque limits E1 , E2 , the method 30 may include generating 391 information KOEI representative of an asymmetric or OEI operation of the at least two engines 2 , 3 .

[0133] In this case, the method 30 then includes displaying 392 on the display 8 at least one OEI limit indicator 9 corresponding to the asymmetric OEI operation.

[0134] For example, such display 8 is formed by a screen of an instrument panel of a cockpit equipping rotorcraft 1 , or indeed by a head-up display system worn by the pilot and arranged, for example, on a helmet or visor.

[0135] In this case, the display 8 is connected to the control system 10 via a wired or wireless manner, and may display the value of the critical torque limit CC1 on the OEI limit indicator 9 corresponding to the asymmetric OEI operation of the engines 2 , 3 .

[0136] According to another embodiment, such a display 8 can also be located outside the rotorcraft 1 , for example when the rotorcraft 1 is remotely piloted.

[0137] like Figure 4 As shown, when the at least one critical torque limit CC1 is the at least one residual combined torque limit CR1, the method 40 may include generating 491 information KAEO representing symmetrical or AEO operation of the at least two engines 2, 3, and displaying 48 on the display 8 at least one AEO limit indicator 19 corresponding to the symmetrical AEO operation.

[0138] In addition, if Figure 3 and Figure 4 As shown, the control method 30 , 40 may comprise predetermining 300 , 400 the threshold values ​​SAEO, SOEI of the at least one AEO limit indicator 19 and the at least one OEI limit indicator 9 .

[0139] Furthermore, the control method 30 , 40 may comprise storing 301 , 401 threshold values ​​SAEO, SOEI of the at least one AEO limit indicator 19 and the at least one OEI limit indicator 9 .

[0140] Furthermore, the rotorcraft 1 may also include an automatic flight control system 15 capable of acting on the total pitch of the blades of one or more lift rotors 16. Such an automatic flight control system 15 is connected to the control system 10 via wired or wireless means.

[0141] The method 30, 40 may then comprise calculating 393, 493 a total pitch margin MPC applicable to said blade 17. The calculation 393, 493 may be carried out by the control system 10 which transmits it to the automatic flight control system 15.

[0142] The method 30 , 40 may then comprise controlling 394 , 494 the total pitch PC of the blades 17 in order to autopilot the rotorcraft 1 while respecting the at least one critical torque limit CC1 .

[0143] Naturally, the present invention is subject to many changes in its implementation. Although multiple embodiments are described above, it should be readily understood that it is not possible to exhaustively identify all possible embodiments. Without exceeding the scope of the present invention, it is naturally conceivable to replace any device described with an equivalent device.

Claims

1. A control method (30, 40) for a rotorcraft (1), the rotorcraft (2) comprising at least two combustion engines (2, 3), at least one regulating system (12, 13) and a transmission system (4), the at least two engines (2, 3) being mechanically connected to the transmission system (4) via at least two couplings (25, 26), respectively. The control method (30, 40) comprises at least the following steps: identifying (31, 41) at least one engine, referred to as an N2-regulated engine (2), from the at least two engines (2, 3), the at least one N2-regulated engine being identified as an engine supplied with fuel at a fuel flow rate regulated as a function of the rotational speed N2 of at least one first output shaft (5) of the at least one N2-regulated engine by at least one fuel metering valve (22), the at least one fuel metering valve (22) being controlled as a function of a flow rate setpoint value transmitted by at least one first regulation system (12) and dependent on the rotational speed N2 of the at least one first output shaft (5); identifying (32, 42) from the at least two engines (2, 3) an engine referred to as a non-N2′-regulated engine (3), the non-N2′-regulated engine being identified as an engine supplied with fuel at a fuel flow rate not regulated as a function of the rotational speed N2′ of the second output shaft (6) supplied by a second fuel metering valve (23), the second fuel metering valve (23) being either not regulated or controlled as a function of a flow rate setpoint transmitted by at least one second regulation system (13) and being independent of the rotational speed N2′ of the second output shaft (6); determining (33, 43) at least one first permissible input torque limit (E1) for at least one first coupling (25) of said transmission system (4) connected to said at least one first output shaft (5); determining (33, 44) a second permissible input torque limit (E2) for a second coupling (26) of the transmission system (4) connected to the second output shaft (6); determining (35, 45) a first current operating torque (C1) transmitted by the second output shaft (6) to the second coupling (26) of the transmission system (4); Determining (36, 46) at least one admissible residual combined torque limit (CR1) for at least one component of a hybrid unit (7) of the transmission system (4), the at least one residual combined torque limit (CR1) being calculated according to the following formula: CR1=Cadm-(C1*Z) wherein Cadm is the permissible combined torque limit for said at least one component of said mixing unit (7); C1 is a first current operating torque transmitted by the second output shaft (6) to the second coupling (26) of the transmission system; and Z is a reduction factor between the rotational speed of the second coupling (26) and the rotational speed of the at least one component of the mixing unit (7); identifying (37, 47) a critical torque limit (CC1) as a lowest value among the values ​​of the at least one first input torque limit (E1), the second input torque limit (E2), and the at least one residual combined torque limit (CR1); as well as Generating (38, 48) a control setpoint limit (COM) for the at least one first regulating system (12), the control setpoint limit (COM) being generated as a function of the critical torque limit (CC1).

2. The control method according to claim 1, in, Prior to identifying (32) a non N2' regulated engine (3), the non N2' regulated engine (3) is initially an N2' regulated engine supplied with fuel at an N2' regulated fuel flow rate supplied by the second fuel metering valve (23), the second fuel metering valve being controlled according to a flow rate setpoint transmitted by a second regulation system (13).

3. The control method according to claim 2, in, The identification (32) of a non-N2' regulated engine (3) is the identification of a malfunction of the second regulation system (13).

4. The control method according to claim 1, in, The control setpoint limit (COM) is generated so that a second current operating torque (C2) transmitted by the at least one first output shaft (5) to the at least one first coupling (25) of the transmission system (4) remains less than or equal to the critical torque limit (CC1).

5. The control method according to claim 1, in, When the critical torque limit (CC1) is one of the at least one first input torque limit (E1) and the second input torque limit (E2), the at least one first regulation system (12) regulates the fuel flow rate supplied by the at least one first fuel metering valve (22) according to a first speed setpoint (Nref1) of at least one lift rotor (16) of the rotorcraft (1).

6. The control method according to claim 5, in, When the critical torque limit (CC1) is the at least one residual combined torque limit (CR1), the at least one first regulation system (12) regulates the fuel flow rate supplied by the at least one first fuel metering valve (22) according to a second speed setting value (Nrref2) of the at least one lift rotor (16) of the rotorcraft (1), the second speed setting value (Nrref2) being less than the first speed setting value (Nrref1).

7. The control method according to claim 1, in, When the critical torque limit (CC1) is one of the at least one first input torque limit (E1) and the second input torque limit (E2), the method (30) comprises the following steps: generating (391) information (KOEI) representative of a first operating mode (OEI); and Displaying (392) on a display (8) at least one first limit indicator (91, 92) corresponding to said first operating mode (OEI).

8. The control method according to claim 7, in, The value of the critical torque limit (CC1) is assigned to a first limit indicator (91) of the at least one first limit indicator (91, 92).

9. The control method according to claim 1, in, When the critical torque limit (CC1) is the residual combined torque limit (CR1), the method (40) may include the following steps: generating (491) information (KAEO) representative of a second mode of operation (AEO); and Displaying (492) at least one second limit indicator (191, 192) corresponding to said second operating mode (AEO) on a display (8).

10. The control method according to claim 7, in, When the critical torque limit (CC1) is the residual combined torque limit (CR1), the method (40) comprises the following steps: generating (491) information (KAEO) representative of a second operating mode (AEO); displaying (492) on the display (8) at least one second limit indicator (191192) corresponding to said second operating mode (AEO), and The method (30, 40) comprises the following steps: predetermining (300, 400) threshold values ​​(SAEO, SOEI) of the at least one first limit indicator (9) and the at least one second limit indicator (19); and Storing (301, 401) the threshold values ​​(SAEO, SOEI) in at least one memory (14).

11. The control method according to claim 1, in, The rotorcraft (1) comprises an automatic flight control system (15) and at least one lifting rotor (16) having blades (17), the method (30, 40) comprising calculating (393, 493) a total pitch margin (MPC) applicable to the blades (17) and controlling (394, 494) a total pitch (PC) of the blades (17) in order to autopilot the rotorcraft (1) while complying with the at least one critical torque limit (CC1).

12. An aircraft (1) comprising at least two combustion engines (2, 3), at least one regulating system (13) and a transmission system (4), the at least two engines (2, 3) being mechanically connected to the transmission system (4) via at least two couplings (25, 26), respectively. The rotorcraft (1) comprises a control system (10) configured to implement the control method (30, 40) according to claim 1.

13. A computer program comprising instructions which, when executed by a control system (10) for a rotorcraft according to claim 12, enable the control method according to claim 1 to be implemented.

Images