Rotorcraft and method for adjusting the variable rotation speed of a rotor

Abstract

The invention relates to a method of adjusting the rotational speed of a rotor (5) of a rotorcraft (1) having at least two engines (10), the rotorcraft (1) comprising an adjustment system (55) adjusting each engine (10) as a function of at least one setpoint speed implemented by the rotor (5). During an asymmetric operating mode, the method comprises: i) in the presence of a forward speed greater than a first threshold, determining the setpoint speed using the adjustment system (55) by applying an alternative law increasing the setpoint speed relative to a default law applied during a coordinated mode.

Description

[0001] Cross-reference of related applications

[0002] This application claims the benefit of French application FR2504456, filed on April 28, 2025, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] This invention relates to rotorcraft and a method for adjusting the variable rotational speed of the rotor.

[0004] Rotorcraft may include a power unit that moves a rotor that forms a rotating wing. For example, a helicopter includes at least one main rotor that contributes to its lift and may also contribute to its propulsion.

[0005] The power unit may include multiple internal combustion engines, or more simply, an "engine," which moves the mechanical system that drives the rotor to rotate. For example, the engine is mechanically connected to the power transmission gearbox that moves the rotor.

[0006] Such an engine can be a turboshaft engine, which includes a gas generator and at least one working turbine that moves the output shaft of the turboshaft engine. The output shaft is then mechanically connected to a mechanical system.

[0007] On the other hand, the rotorcraft includes a control system whose primary function is to control the driving force delivered by each engine via fuel flow. The purpose of this control system can be to maintain the rotor speed of the rotorcraft at a predetermined setpoint value. Such a control system typically includes an engine computer and individual fuel metering devices for each engine, as well as various sensors.

[0008] For example, helicopters are piloted primarily by the pitch of the rotor blades acting on the main rotor. Increasing the pitch tends to slow the rotational motion of the main rotor, while also increasing its lift and aerodynamic drag. To prevent excessive reduction in the main rotor's rotational speed, the power generated by the engine must be increased to maintain a substantially constant rotational speed. Similarly, when the blade pitch decreases, the power delivered by the engine must be reduced.

[0009] In addition, the regulation of fuel flow must be controlled to avoid, for example, engine surge or stalling.

[0010] For example, a sensor measures the first rotational speed NTL of the working turbine of a turboshaft engine. In this case, a first value is determined that corresponds to the value that the first rotational speed NTL must have in order for the rotor's rotational speed to equal its setpoint. Therefore, if the first rotational speed NTL differs from this first value, the computer generates a command to accelerate or decelerate the engine to reach the setpoint rotational speed of the main rotor. Under these conditions, the engine computer determines a second value, for example, by using a predictive law based on the total pitch of the main rotor blades. This second value corresponds to the value that the second rotational speed NG of the moving component of the gas generator of the turboshaft engine must reach in order for the first rotational speed NTL to equal the first value.

[0011] Rotorcraft control systems can be used to achieve variable rotor speeds. In practice, significant variations in the rotor's rotational speed (NR) are utilized, for example, to reduce noise pollution near the ground and / or improve performance. As an indication, the main rotor's rotational speed can be controlled to be variable within a range that may be between 90% and 110% of the reference speed.

[0012] Specifically, the known law of variation of the rotor's rotational speed NR can specify that the setpoint speed NR* equals the maximum speed, for example, on the order of 105% of the reference speed when the aircraft has an airspeed below a first threshold. This first threshold is, for example, approximately 50 knots (kt, one knot equals 1.852 kilometers per hour). This feature is designed to optimize performance at low speeds, and particularly when the rotorcraft is in a hovering position.

[0013] Furthermore, when the aircraft has an airspeed greater than the second threshold, this known law defines the reference speed NR* as equal to the minimum speed, for example, on the order of 90% of the reference speed. This second threshold is, for example, approximately 75 knots. This feature allows for the specific limitation of forces applied to dynamic components at high speeds, and / or the limitation of noise pollution.

[0014] Finally, when the aircraft has an airspeed that increases from the first threshold to the second threshold, the known law defines a linear decrease in the setpoint speed NR* from the maximum speed to the minimum speed.

[0015] Optionally, the minimum speed varies with altitude to optimize aircraft performance and / or avoid low rotor speeds at high altitudes, where engine performance is poor. For example, the regulation law may include multiple equations, each relating to a range of altitudes.

[0016] In conventional rotorcraft, except in the event of a malfunction, multi-engine power units operate in a cooperative mode, where each engine generates a shared driving force that contributes to the movement of the mechanical system. This law for regulating rotational speed NR is particularly effective.

[0017] In contrast, the power plant can also optionally operate in an asymmetric mode by placing at least one of the combustion engines in a standby mode. In a twin-engine rotorcraft, during asymmetric operation, the active engine is regulated to ensure rotor rotation by transmitting non-zero drive power to the rotor via its power shaft. The passive engine, on the other hand, remains in standby so as not to transmit drive power to the rotor.

[0018] An engine in standby mode can be shut down by closing the combustion chamber. The passive engine's combustion chamber is then no longer supplied with fuel, and on the turboshaft engine, the rotating components of the gas generator may or may not be moved by an electric motor. Alternatively, the engine in standby mode can operate in idle or over-idle mode, with the combustion chamber ignited and supplying fuel. The engine in standby mode operates at very low speeds and does not transmit power to the rotor, while one or more active engines provide the entire power supply. For example, the passive engine may be in idle mode at approximately 40% of its rated speed.

[0019] In a twin-engine rotorcraft, if the active engine fails, the rotorcraft enters a non-maneuvering autorotation phase for the time required to reactivate the backup engine. During this period, the pilot reduces the pitch of the rotor blades to limit the decrease in the rotor's rotational speed NR and reach the setpoint speed. Background Technology

[0020] Documents FR3061142 and FR3027124 are known, but both are far removed from the problem at hand. Document FR3061142 describes a device for adjusting the rotational speed of the gas generator shaft of a rotorcraft turbine engine. Document FR3027124 describes a method for adjusting the speed of the rotor of a rotorcraft driven under icing conditions.

[0021] Document EP3803082B1 describes a power plant equipped with a first turboshaft engine and a second turboshaft engine. The first turboshaft engine is equipped with a heat exchanger. A computer limits the acceleration and deceleration capabilities of the first turboshaft engine to limit the mechanical and thermal stresses applied to the heat exchanger. The first turboshaft engine can operate at a near-constant power level to provide a portion of the propulsive energy required by the aircraft. In the event of a failure of the first turboshaft engine, the second turboshaft engine takes over and delivers all necessary power. In the event of a failure of the second engine, the acceleration and deceleration capabilities of the first turboshaft engine are no longer limited.

[0022] Documents US2022 / 306308A1, US2020 / 362754A1, and US2022 / 106913A1 are also known. Summary of the Invention

[0023] Therefore, one object of the present invention is to provide an innovative method and rotorcraft for optimizing the spin phase after an active engine failure during the application of an asymmetric operating mode.

[0024] Therefore, the present invention relates to a method for adjusting the rotational speed of a rotor of a rotary-wing aircraft. The rotary-wing aircraft includes a power plant having at least two engines and a power transmission system for driving the rotor rotation. Each engine has a power component connected to the power transmission system. The rotary-wing aircraft includes an adjustment system that adjusts each engine according to at least one setpoint speed to be achieved by the rotor. During an asymmetric operation mode, the adjustment system actively adjusts at least one of the at least two active engines at a given speed and keeps at least one of the at least two passive engines in standby mode. During a cooperative operation mode, the adjustment system actively adjusts the engines at a given speed. During the cooperative operation mode, the adjustment system determines the at least one setpoint speed by applying a default law, which gives the setpoint speed at least based on the forward speed of the rotary-wing aircraft. When the forward speed is greater than a first threshold, the setpoint speed is equal to a minimum value.

[0025] During asymmetric operation mode, the method includes: i) determining a setpoint speed by applying a substitution law using an adjustment system when there is a forward speed greater than a first threshold and at the same altitude, the substitution law generating a setpoint speed greater than the setpoint speed generated by a default law; and ii) adjusting the active engine to achieve the setpoint speed.

[0026] Specifically, each engine can be a turboshaft engine, and each power unit includes at least one expansion turbine and at least one power shaft.

[0027] According to one example, the regulating system can determine the setpoint speed to be achieved by the rotor and derive from it the target rotational speed to be achieved by the components of each power unit. The regulating system then regulates the engine in the usual manner.

[0028] Furthermore, the control system applies a default law during cooperative operation mode, which is based at least on the aircraft's forward velocity and possibly also on altitude. Each engine is controlled to operate at an active speed to generate driving force that contributes to rotor rotation, thereby achieving the setpoint speed.

[0029] When engaged in cooperative operating mode, all engines generate driving power. A failure in one engine is compensated for by the other. Therefore, even at high speeds where the setpoint speed is minimized, the rotor speed is almost unaffected by engine failure (if any).

[0030] On the other hand, during the asymmetric operation mode, the control system actively regulates at least one of the two internal combustion engines at an active speed and puts at least one of the two internal combustion engines in standby mode. The active engine uses its power shaft to generate non-zero drive power to participate in the rotor rotation, while the passive engine does not transmit power to the rotor.

[0031] When asymmetric operating mode is activated, the rotor is thus propelled by one or more active rotors, and particularly by a single active engine on a twin-engine aircraft. If an active engine fails, the rotor is no longer driven by the engine for a short period required to reactivate the passive engine. The pilot then performs a spin process to limit the reduction in rotor speed as the passive engine is reactivated. However, at high speeds, the default law typically requires adjusting the rotor speed to a minimum. Therefore, during the period required to reactivate the passive engine, the rotor speed may be close to an acceptable lower limit.

[0032] This invention solves this problem. In fact, when the asymmetric operating mode is active and at a high forward speed, the setpoint speed to be achieved within at least one altitude range is greater than the setpoint speed to be achieved when the cooperative operating mode is active and under the same conditions (i.e., at the same speed and altitude). Therefore, the substitution law allows for a greater margin relative to the rotor's permissible maximum rotational speed when the asymmetric operating mode is activated.

[0033] Therefore, this method enables the retention of the advantages associated with using the usual default laws during cooperative operation mode, while ensuring sufficient safety margins when asymmetric operation mode is active.

[0034] The method may also include one or more of the following features, used individually or in combination.

[0035] According to one possibility, for a forward speed less than the second threshold, which is less than the first threshold, the setpoint speed can be equal to the same maximum value according to the default law and the substitution law.

[0036] Under both the default and alternative laws, the maximum value is greater than the setpoint value reached when there is a forward speed exceeding the first threshold. In other words, at low speeds, the default and alternative laws provide the same maximum value for the setpoint speed. This feature is designed to achieve the same maximum value, particularly for obtaining the desired performance during hovering.

[0037] According to a possibility compatible with the aforementioned possibilities, for a forward speed greater than the first threshold, the setpoint speed can be equal to the minimum value according to the default law and the minimum value according to the substitution law, the minimum value being the first value according to the default law and the minimum value being the second value according to the substitution law, the second value being greater than the first value at the same altitude.

[0038] Both the first and second values ​​are less than the maximum values ​​mentioned above. Therefore, at high speeds, when applying the asymmetric operation mode, the setpoint speed uses a higher minimum value under the same conditions (i.e., for the same altitude) than during the cooperative operation mode.

[0039] Optionally, the first and second values ​​can vary depending on the altitude.

[0040] This feature allows for optimization of power unit operation by taking altitude into account. This altitude can be density altitude or pressure altitude. Density altitude corresponds to pressure altitude corrected for temperature effects. Pressure altitude is calculated in a conventional manner based on atmospheric pressure, for example, measured using a barometer. On the other hand, density altitude is calculated in a conventional manner from atmospheric pressure, for example, measured using a barometer, and temperature, measured using a thermocouple or other temperature sensing element.

[0041] According to a possibility compatible with the aforementioned possibilities:

[0042] When the asymmetric operating mode is activated, the method may include adjusting the active engine by linearly varying the setpoint velocity from the first value to the second value; and

[0043] When the asymmetric operating mode is disabled, the method may include adjusting the engine by linearly changing the setpoint speed from the second value to the first value.

[0044] These features enable optimized transitions during the shift from cooperative to asymmetric operation modes, and vice versa.

[0045] According to a possibility compatible with the aforementioned possibilities, for a forward velocity greater than or equal to the second threshold and less than or equal to the first threshold, the setpoint velocity can be linearly reduced from the maximum value to the minimum value according to the default law and the substitution law.

[0046] In addition to one method, the present invention also relates to a rotorcraft comprising a power unit having at least two engines and a power transmission system for driving rotor rotation, each engine having a power component connected to the power transmission system, the rotorcraft including an adjustment system that adjusts each engine according to at least one setpoint speed to be achieved by the rotor, the adjustment system adjusting at least one active engine of the at least two engines at an active speed during an asymmetric operation mode and keeping at least one passive engine of the at least two engines in standby mode, the adjustment system adjusting the engines at an active speed during a cooperative operation mode, the adjustment system determining the at least one setpoint speed by applying a default law during the cooperative operation mode, the default law giving the setpoint speed at least according to the forward speed of the rotorcraft, the setpoint speed being equal to a minimum value when the forward speed is greater than a first threshold value.

[0047] The regulating system is configured to implement the method of the present invention.

[0048] One possibility is that the control system may include a speed sensor that measures the forward speed of the rotorcraft.

[0049] For example, a speed sensor can measure actual airspeed or ground speed.

[0050] One possibility is that the conditioning system may include an altitude sensor that measures altitude.

[0051] The term sensor, as used below, may refer to a component that includes one or more sensing elements, and may also refer to a computer.

[0052] Therefore, an altitude sensor may include a barometer for assessing pressure altitude or a barometer for assessing density altitude, as well as thermocouples or other types of temperature sensing elements. Attached Figure Description

[0053] The invention and its advantages will become more apparent from the following description of examples given by way of illustration with reference to the accompanying drawings, wherein:

[0054] Figure 1 This is a diagram illustrating a rotorcraft according to the present invention;

[0055] Figure 2 A diagram illustrating the method of the present invention; and

[0056] Figure 3 This is a diagram illustrating the method of the present invention. Detailed Implementation

[0057] Elements present in more than one figure are given the same reference numerals in each of them.

[0058] Figure 1 An example of a rotorcraft 1 according to the present invention is shown. The rotorcraft 1 includes a rotor 5. The rotor 5 is provided with a plurality of blades 6, which are rotatable relative to the fuselage about an axis ROT and can be supported by a hub 7 or equivalent. For example, the rotor 5 forms a rotary wing.

[0059] The rotorcraft 1 has a power unit 2 for rotating the rotor 5. The power unit 2 is equipped with at least two engines 10. Reference numeral 10 indicates any engine, and reference numerals 11 and 12 indicate specific engines if necessary.

[0060] According to one example, at least one engine 10 may be a turboshaft engine. Such a turboshaft engine 10 includes a gas generator 15 equipped with at least one compression turbine 16, at least one combustion chamber 17 into which fuel is injected, and at least one expansion turbine 18 constrained to rotate together with one or more compression turbines 16. Furthermore, the turboshaft engine 10 may include a power assembly 14 having at least one operating turbine 19 that directly or indirectly moves the power shaft 20 of the engine 10. Reference numeral 20 indicates any power shaft, and reference numerals 21 and 22 indicate specific power shafts of the two engines 11 and 12, respectively.

[0061] Regardless of the type of engine, each engine 10 therefore includes a power unit 14 connected to the power transmission system 25. The power transmission system 25 is then connected to the rotor 5 in the usual manner.

[0062] For example, the power transmission system 25 may be provided with a power transmission gearbox 26 mechanically inserted between the engine 10 and the rotor 5. The power transmission gearbox 26 may be provided with an input shaft 30 for each engine 10 and various gears arranged between the input shaft 30 and the rotor rod 35 fixed to the hub 7.

[0063] The powertrain 25 may include, for example, at least one flywheel 51, 52 between each engine 10 and the power transmission gearbox 26, and / or at least one connecting shaft 53, 54, and / or at least one connector that allows for misalignment. Various types of power transmission gearboxes and various mechanical transmission systems are described in the literature; the examples described are given by way of illustration only.

[0064] Furthermore, engine 10 is an internal combustion engine that runs on fuel and can be started by starters 36 and 37. The rotorcraft 1 therefore includes a control system 55 for controlling starters 36 and 37 and the power output by each engine 10 via its power shaft 20.

[0065] Therefore, the regulating system 55 includes a fuel metering device 69 for each engine 10. Each engine 10 is then connected to at least one fuel tank 70 via its own fuel metering device 69. Reference numeral 69 indicates any fuel metering device, and reference numerals 71 and 72 indicate specific fuel metering devices for the two engines 11 and 12, respectively.

[0066] The control system 55 may include a control unit for each engine 10, such as FADEC (Full Authority Digital Engine Control). Each control unit includes an engine computer 60 for each engine 10. Each engine computer 60 may include a processing unit. Such a processing unit may have, for example, at least one processor 64 and at least one memory 65, at least one integrated circuit, at least one programmable system, or at least one logic circuit; these examples do not limit the scope of the term "processing unit". The engine computers 60 may communicate with each other via wired or wireless links.

[0067] According to the described example, the regulating system 55 includes two engine computers 61 and 62 that control two engines 11 and 12 respectively. Each engine computer 60 is configured to control the associated engine 10 and operate it at a desired speed. In particular, each engine computer 61 and 62 can control the fuel metering devices 71 and 72 of the engine 11 and 12. Each engine computer 61 and 62 can be connected to multiple sensors to control the associated engine 11 and 12, such as, for example, a temperature sensor 930 that measures, for example, the gas temperature at the inlet of a free turbine; a speed sensor that measures, for example, the rotational speed of the gas generator 15 of the turbine shaft engine 10; torque meters 910 and 920 that measure the engine torque on the rotating member of the power assembly; speed sensors 940 and 950 that measure, for example, the rotational speed of the rotating member; a torque meter 960 that measures the torque applied to the rotor rod 35; a speed sensor 970 that measures, for example, the rotational speed of the rotor rod 35; a sensor that measures external pressure; a sensor that measures external temperature; and so on.

[0068] The term "sensor" should be understood to mean a physical sensing element capable of directly measuring the parameter in question, and also to mean a system that may include one or more physical sensing elements, and means for processing signals such that estimates of the parameter can be provided based on the measurements provided by these physical sensing elements. Similarly, the concept of a measurement parameter refers to both the raw measurement from the physical sensing element and the measurement obtained through relatively complex processing of the raw measurement signal.

[0069] The engine computer 60 can form a controller 75 that applies the method of the present invention, or the management computer 78 of the regulation system 55 can be used as the controller 75.

[0070] If necessary, the management computer 78 may be a computer abbreviated as AMC and referred to as "Aircraft Management Computer". For example, the management computer 78 may include at least one processing unit. The management computer 78 may communicate with each engine computer 60 via a wired or wireless link. The management computer 78 may communicate directly or via the engine computer 60 with each of the aforementioned measurement systems.

[0071] Furthermore, the controller 75 can communicate with at least one human-machine interface 85, or with a separate human-machine interface 85 for each engine 10, i.e., two interfaces 86 and 87 according to the given example. Each human-machine interface 85 can, for example, transmit signals carrying stop commands, idle commands, or flight speed commands for the relevant engine 10. Figure 1 The interfaces in the three-position stop POS1 / idle POS2 / flight POS3 for this purpose are shown.

[0072] Additionally, the controller 75 can communicate with a human-machine interface 88, which can be manipulated to manually activate or deactivate the asymmetric operation mode.

[0073] Each human-machine interface 85, 88 may include equipment that can be operated by the pilot, such as buttons or joysticks, touchscreens, voice commands, etc. According to the example shown, human-machine interfaces 85, 88 communicate with management computer 78. Alternatively or additionally, human-machine interfaces 85, 88 communicate with one or each engine computer unit 60.

[0074] In addition, the controller 75 can communicate directly or indirectly with one or more of the following sensors:

[0075] • A speed sensor 82, which measures the current forward speed Vcur of the rotorcraft 1, and for example measures real airspeed or ground speed, such a speed sensor 82 can include, for example, a satellite positioning system and / or a pitot tube system; and

[0076] • An altitude sensor 83 for measuring altitude, such as a sensor that includes a sensing element for measuring the pressure of the air around the rotorcraft 1 and may also include a temperature sensing element.

[0077] For example, the AMC computer acquires measurement results from one or more of the aforementioned sensors and transmits them to the engine computer 60.

[0078] Under these conditions, the regulating system 55 is configured to regulate the drive power generated by each engine 10 by applying the regulating method of the present invention. In particular, the controller is configured to apply the method of the present invention so that the regulating system 55 controls the fuel metering device 69 of each engine 10, causing the rotor 5 to move at a setpoint rotational speed.

[0079] For this purpose, the regulating system 55, in particular the controller 75, controls the fuel metering device 69 of each engine 10 to achieve the setpoint speed Vcons of the rotor 5.

[0080] Independent of this aspect, during cooperative operation mode, each engine 10 is a so-called active engine, which is regulated by the control system 55 to output non-zero active drive power via its power shaft 20 to contribute to the rotation of the rotor 5. For example, a first human-machine interface 86 is set at position POS3 and transmits control signals to the engine computer 61. Similarly, a second human-machine interface 87 is set at position POS3 and transmits control signals to the engine computer 62.

[0081] During cooperative operation mode, the adjustment method includes using speed sensor 82 to measure the current forward speed Vcur, and possibly also using altitude sensor 83 to measure the altitude of the aircraft.

[0082] The controller 75 then determines the setpoint speed Vcons by applying a stored default law Lawdef based on the current forward speed Vcur and possibly also on the altitude. The regulating system then adjusts all engines so that the rotor speed tends towards the setpoint speed Vcons.

[0083] According to the example shown, the management computer 78 applies a regulation law at each moment, based solely on the usage... Figure 2 Example speed sensor 82 measures the current forward speed and may also be based on the speed measured by the sensor. Figure 3 The altitude sensor 83 measures the altitude to determine the setpoint speed Vcons. The management computer 78 or engine computer 60 derives the speed setpoint NTL* of the rotational speed NTL of each power component of the engine 10 in a conventional manner, for example, through stored control laws. The engine computer 60 then servo-controls the fuel metering device of the engine 10 to cause the rotational speed NTL measured using speed sensors 940, 950 to tend towards the setpoint rotational speed NTL*.

[0084] To activate the asymmetric operation mode, the pilot can operate the human-machine interface 88 during the preparatory steps.

[0085] During asymmetric operation, the regulating system 55 keeps at least one engine (referred to as the "active engine EACT") active and at least one engine (referred to as the "passive engine EPAS") in standby mode. The one or more passive engines EPAS are then shut down by one or more associated engine computers by shutting down the combustion chamber (optionally in the case of at least one compressor and one turbine of the gas generator in motion), or by idling so that drive power is not transmitted via the associated flywheels 51, 52.

[0086] The adjustment method then includes using speed sensor 82 to measure the current forward speed Vcur, and possibly also using altitude sensor 83 to measure the aircraft's altitude.

[0087] Furthermore, the method includes: during step STP1, using an adjustment system 55 or a controller 75, and possibly a management computer 78, and if applicable, determining a setpoint speed Vcons by applying an alternative law lawy, which increases the setpoint speed relative to the default law Lawdef for the same altitude when the forward speed Vcur is greater than a first threshold S1.

[0088] The method then includes adjusting to achieve a setpoint speed Vcons during step STP2 and using an adjustment system 55 or controller 75 and possibly a corresponding engine computer 60 of the active engine EACT.

[0089] According to the aforementioned example, at each moment, the management computer 78 applies the regulation law used to determine the setpoint speed Vcons to the management computer 78 or the engine computer 60 of the active engine by inferring the speed setpoint NTL* of the rotational speed NTL of the active engine's power components. Then, the engine computer 60 servo-controls the fuel metering device of the active engine so that the rotational speed NTL measured using the associated speed sensor tends to the setpoint rotational speed NTL*.

[0090] Figure 2 A graph is shown showing the setpoint speed Vcons of rotor 5 based on the forward speed Vcur measured using speed sensor 82. The setpoint speed Vcons is expressed as a percentage of the reference rotational speed, and the forward speed Vcur is expressed as knot (kt).

[0091] Curve C1 shows the default law, and curve C2 shows the alternative law.

[0092] according to Figure 2 The default law (lawdef) specifies that the velocity at the setpoint is equal to:

[0093] • For forward speed Vcur less than the second threshold S2, the setpoint speed is equal to the maximum value Vmax, and the second threshold S2 is less than the first threshold S1;

[0094] • For forward speeds Vcur greater than the first threshold S1, the setpoint speed is equal to the first value V1; and

[0095] • For a forward velocity Vcur that increases from the second threshold S2 to the first threshold S1, the setpoint velocity is equal to the value that decreases linearly from the maximum value Vmax to the first value V1.

[0096] Therefore, the substitution law stipulates that when there is a forward velocity Vcur greater than the first threshold S1, the setpoint velocity Vcons is equal to the minimum value Vmin, the minimum value Vmin is equal to the second value V2, and the second value V2 is greater than the first value V1. This feature allows the rotational speed of rotor 5 to move away from the lower limit.

[0097] Alternatively, the substitution law specifies that the setpoint velocity Vcons equals

[0098] • For forward speeds Vcur below the second threshold S2, the setpoint speed Vcons is equal to the maximum value Vmax; and

[0099] • For a forward velocity Vcur that increases from the second threshold S2 to the first threshold S1, the setpoint velocity Vcons is equal to the value that decreases linearly from the maximum value Vmax to the second value V2.

[0100] When the asymmetric operating mode is activated, the method may include adjusting the STPA active engine EACT by linearly varying the setpoint speed from a first value V1 to a second value V2 corresponding to arrow F1.

[0101] On the other hand, when the asymmetric operating mode is disabled, the method may include adjusting the STPR engine 10 by linearly changing the setpoint speed from a second value V2 to a first value V1 corresponding to arrow F2.

[0102] According to the other hand, each law can take the form of one or more equations implemented by the controller 75.

[0103] In addition, according to Figure 2 The first value V1 and the second value V2 are fixed.

[0104] Therefore, according to Figure 2The method shown includes using a controller 75 to measure the current forward speed Vcur using a speed sensor 82, then using the controller to determine a setpoint speed based on the current forward speed Vcur, using a default law during cooperative operation mode and an alternative law during asymmetric operation mode, and then adjusting each active engine based on the setpoint speed Vcons.

[0105] In comparison, Figure 3 Another variation is shown where the minimum value Vmin varies depending on altitude or altitude range.

[0106] Therefore, the first value V1 and the second value V2 depend on the altitude.

[0107] The method then includes: using a controller 75, using an altitude sensor 83 to measure the current altitude, using a speed sensor 82 to measure the current forward speed Vcur, and using a default law during cooperative operation mode and an alternative law during asymmetric operation mode to determine a setpoint speed Vcons based on the current altitude and the current forward speed, and then adjusting each active engine based on the setpoint speed Vcons.

[0108] Figure 3 The default law is shown in the form of three curves C11, C12, and C13 for three altitude ranges, as well as the alternative law which includes three corresponding curves C21, C22, and C23.

[0109] This invention can naturally be modified in many ways in its specific implementation. Although several embodiments have been described above, it should be understood that not all possible embodiments can be identified exhaustively. Of course, any of the described devices can be replaced with equivalent devices without departing from the scope of this invention and the claims.

Claims

1. A method for adjusting the rotational speed of a rotor (5) of a rotorcraft (1), the rotorcraft (1) comprising: The rotorcraft (1) comprises a power unit (2) having at least two engines (10) and a power transmission system (25) for driving the rotation of the rotor (5), each engine (10) having a power assembly (14) connected to the power transmission system (25), the rotorcraft (1) including an adjustment system (55) that adjusts each engine (10) according to at least one setpoint speed (Vcons) to be reached by the rotor (5), the adjustment system (55) actively adjusting at least one of the at least two engines (10) at an active speed during asymmetric operation mode, and causing the at least two engines (10) to rotate. At least one passive engine (EPA) of the engines (10) is in standby mode, and the regulation system (55) regulates the engines (10) at active speed during the cooperative operation mode. The regulation system (55) determines the at least one setpoint speed (Vcons) by applying a default law during the cooperative operation mode. The default law gives the setpoint speed (Vcons) based at least on the forward speed (Vcur) of the rotorcraft (1). When the forward speed (Vcur) is greater than a first threshold (S1), the setpoint speed (Vcons) is equal to a minimum value (Vmin). During the asymmetric operation mode, the method includes: i) using the adjustment system (55) to determine (STP1) the setpoint speed by applying a lawasy, which generates a setpoint speed greater than the setpoint speed generated by the default law in the presence of a forward speed (Vcur) greater than the first threshold (S1) and at the same altitude; and ii) adjusting (STP2) the active engine (EACT) to achieve the setpoint speed (Vcons).

2. The method according to claim 1, in, For a forward velocity (Vcur) less than the second threshold (S2), which is less than the first threshold (S1), the setpoint velocity is equal to the same maximum value (Vmax) according to the default law and the substitution law.

3. The method according to claim 2, in, For a forward speed (Vcur) that is greater than or equal to the second threshold (S2) and less than or equal to the first threshold (S1), the setpoint speed (Vcons) decreases linearly from the maximum value (Vmax) to the minimum value (Vmin) according to the default law (Lawdef) and the substitution law (lawasy).

4. The method according to claim 1, in, For a forward speed (Vcur) greater than the first threshold (S1), the setpoint speed is equal to the minimum value (Vmin) according to the default law (Lawdef) and the alternative law (lawasy). The minimum value (Vmin) takes a first value (V1) according to the default law (Lawdef), and the minimum value (Vmin) takes a second value (V2) according to the alternative law (lawasy). The second value (V2) is greater than the first value (V1) at the same altitude.

5. The method according to claim 4, The first value (V1) and the second value (V2) vary according to altitude.

6. The method according to claim 4, in: When the asymmetric operating mode is activated, the method includes: adjusting (STPA) the active engine by linearly varying the setpoint velocity from the first value (V1) to the second value (V2); and • When the asymmetric operating mode is deactivated, the method includes: adjusting (STPR) the engine by linearly changing the setpoint speed from the second value (V2) to the first value (V1).

7. A rotorcraft (1), said rotorcraft (1) comprising: The rotorcraft (1) comprises a power unit (2) having at least two engines (10) and a power transmission system (25) for driving the rotor (5) to rotate, each engine (10) having a power assembly (14) connected to the power transmission system (25), the rotorcraft (1) including an adjustment system (55) that adjusts each engine (10) according to at least one setpoint speed to be achieved by the rotor (5), the adjustment system (55) actively adjusting at least one of the at least two engines (10) at an active speed during asymmetric operation mode, and The system keeps at least one passive engine (EPA) of at least two engines (10) in standby mode, and the regulating system actively regulates the engine (10) during the cooperative operation mode by applying a default law to determine at least one setpoint speed, which is given at least based on the forward speed (Vcur) of the rotorcraft (1), and the setpoint speed is equal to a minimum value (Vmin) when the forward speed (Vcur) is greater than a first threshold (S1). The regulating system (55) is configured to implement the method according to claim 1.

8. The rotorcraft (1) according to claim 7. in, The control system (55) includes a speed sensor (82) that measures the forward speed (Vcur) of the rotorcraft (1).

9. The rotorcraft (1) according to claim 7. in, The adjustment system (55) includes an altitude sensor (83) for measuring altitude.

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