Method for checking the freewheeling units of the rotor of a twin-engine helicopter

Abstract

The invention relates to a method for checking the freewheeling units (RL1, RL2) of an aircraft, the aircraft comprising a main rotor (RP) coupled to a first engine (M1) and to a second engine (M2) by a first and a second freewheeling unit (RL1, RL2), respectively, and wherein the first and second engines (M1, M2) and the main rotor (RP) are provided with speed sensors (C1, C2, CP), the speed sensors (C1, C2, CP) being connected to a monitoring and control unit (UCC), this method comprising the steps of: - activating the first engine (M1) to rotate it at a nominal speed and deactivating the second engine (M2), then recording the speeds of the first and second engines (M1, M2) and of the main rotor (RP); - issuing an alert signal if the difference between the speed of the first engine (M1) and that of the main rotor (RP) is greater than a threshold value, or if the speed of the second engine (M2) is greater than the threshold value.

Description

[0001] DESCRIPTION

[0002] TITLE: Procedure for verifying the rotor drive freewheels of a twin-engine helicopter

[0003] TECHNICAL FIELD

[0004] The invention relates to a propulsion system comprising two engines coupled together to a main rotor by two freewheels, such a propulsion system being found, in particular, in a twin-engine helicopter. The invention aims to verify the integrity of the freewheels.

[0005] PREVIOUS STATE OF THE ART

[0006] In the case of a single-engine assembly, the propulsion unit typically comprises a turboshaft engine and a main rotor carrying a propeller driven in rotation by the engine via a transmission system.

[0007] The engine rotates at a speed that can be around 20,000 revolutions per minute, while the rotor rotates at a speed of a few hundred revolutions per minute, so the transmission system includes, among other things, toothed wheels forming a reducer to multiply the speed of the engine.

[0008] In the case of a helicopter, the transmission system incorporates a freewheel, because there are situations in which the main rotor rotates at a higher speed than the engine's drive speed. This corresponds, for example, to situations during descent or autorotation of the helicopter, in which the engine runs at an idle speed.

[0009] To enable such a mode of operation, the transmission system incorporates a freewheel which allows the main rotor to rotate at a higher speed than the engine's drive speed if necessary.

[0010] In a two-motor propulsion system, a first freewheel is interposed between the first motor and the main rotor, and a second freewheel is interposed between the second motor and the main rotor. When only the first motor is activated to drive the main rotor, the second motor is not rotated by the second freewheel. Conversely, when only the second motor is activated, the first motor is not rotated.

[0011] In a hybrid powertrain, the first engine is a turbocharger and the second is an electric motor. The two-wheel drive system ensures that when only the first, internal combustion engine is activated, it does not drive the second, electric motor and therefore cannot be slowed down by it.

[0012] When both engines are turboshaft engines, a malfunction of one of the engines causing it to seize or brake cannot seize or brake the other engine, thus improving operational safety.

[0013] In other words, in such a propulsion system, a motor that is not driving the rotor is automatically disengaged in order to isolate it, to avoid a propulsion malfunction.

[0014] Under these conditions, a malfunction of either of the freewheels is detrimental to safety, so the integrity of these freewheels must be regularly checked. In the current state of the art, such a check is carried out visually by an operator or by a dedicated operational procedure, on a periodic basis.

[0015] The aim of the invention is to provide a simple solution for checking the integrity of freewheels in an automated way.

[0016] DESCRIPTION OF THE INVENTION

[0017] The invention relates to a method for checking the freewheels of an aircraft propulsion assembly, this propulsion assembly comprising a main rotor coupled jointly to a first motor and a second motor, respectively by a first freewheel and a second freewheel, and in which the first motor, the second motor and the main rotor are each equipped with a rotation speed sensor, the motors and the sensors being connected to a control and command unit, this method comprising the steps of: - from the control and command unit, activating the first motor to rotate it at a nominal speed and deactivating the second motor, then collecting via the sensors the speeds of the first and second motors and the main rotor;

[0018] - from the control and command unit, issue an alert signal if the difference between the speed of the first motor and the speed of the main rotor is greater than a threshold value, or if the speed of the second motor is greater than a threshold value.

[0019] The invention thus enables automated verification of the integrity of freewheels in a simple and rapid manner, so that this verification can, for example, be performed before each flight. Where applicable, the propulsion system can already be equipped with speed measurement devices and / or access to rotor and motor speed measurements, allowing for the integration of the verification process implementation with very few modifications to the propulsion system.

[0020] The invention also relates to a method defined as follows, further comprising the steps of:

[0021] - from the control and command unit, operate the first motor to rotate it at a reduced speed which is lower than the nominal speed and activate the second motor to rotate it at the nominal speed, of the first and second motors and of the main rotor;

[0022] - from the control and command unit, issue an alert signal if the difference between the speed of the second motor and the speed of the main rotor is greater than a threshold value, or if the speed of the first motor is greater than a threshold value increased by the reduced speed.

[0023] The invention also relates to a method defined as follows, in which the threshold value is zero.

[0024] The invention also relates to a method defined as follows, in which the freewheel verification steps are automatically triggered by the control and command unit during an aircraft start-up phase.

[0025] The invention also relates to a system for implementing a process thus defined, comprising a control and command unit connected to three sensors and to a motor control system or to the motors, as well as programmed means for implementing verification.

[0026] The invention also relates to an aircraft propulsion assembly comprising a main rotor coupled to a first engine and a second engine, respectively by a first freewheel and a second freewheel, this propulsion assembly comprising a system thus defined whose speed sensors equip the engines as well as the main rotor, and whose control and command unit is connected to the engines and the sensors.

[0027] The invention also relates to a propulsion assembly defined as follows, in which the second motor is an electric motor comprising an inductor circuit and an induced circuit, and in which the speed sensor equipping this second electric motor includes an induced current sensor.

[0028] BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The single figure is a schematic view of a propulsion assembly equipped with means for implementing the process according to the invention.

[0030] DETAILED DESCRIPTION OF SPECIFIC METHODS OF IMPLEMENTATION

[0031] In Figure 1, a propulsion assembly includes two motors M1 and M2 arranged to drive a main rotor carrying an HP propulsion propeller in rotation.

[0032] The first motor M1 has a fixed body driving a rotor RI, and similarly, the second motor M2 has a fixed body driving its rotor R2. The first rotor RI is coupled to a gearbox TR via a first freewheel RL1, and the second rotor R2 is coupled to this same gearbox TR via a second freewheel RL2. The main rotor RP is directly coupled to this gearbox. In the figure, the freewheels RL1 and RL2 are shown attached to the gearbox, although in practice they can be integrated into it. As will be understood, the gearbox TR, which contains gears not shown, allows the motors M1 and M2 to drive the main rotor.Thanks to the RL1 and RL2 freewheels, either of the two motors can be the only one to rotate to drive the main rotor, and both motors can also rotate jointly to drive this main rotor together.

[0033] In service, if a malfunction of a motor tends to slow down or block its rotor, the freewheel by which it is coupled to the TR transmission allows it to be automatically disengaged so that it cannot slow down or block the other motor.

[0034] The RL1 and RL2 freewheels are safety-critical components, so it is essential to ensure they function correctly. In practice, a freewheel is considered malfunctioning when it fails to engage or disengage properly.

[0035] As is known from the prior art, a freewheel is a device for coupling a first and a second rotating element, so that they rotate together only if the torque exerted by the first element on the second is oriented in a predetermined direction, called the "coupling direction." Freewheels are also commonly referred to by other names such as ratchet wheel, roller wheel, or pawl wheel.

[0036] In practice, a freewheel consists of an inner ring surrounded by an outer ring, between which are interposed rollers (or balls or pawls) through which the transmission of a moment from one ring to the other only takes place if it is exerted in the direction of coupling.

[0037] Thus, when the inner ring rotates in the coupling direction, it drives the outer ring, but if the inner ring rotates in the opposite direction, the outer ring is not driven. Conversely, when the outer ring rotates in the opposite direction, it drives the inner ring, but if the outer ring rotates in the coupling direction, it does not drive the inner ring.

[0038] According to the invention, the integrity of the freewheels is checked automatically by activating the two motors in turn and measuring the speeds of these motors and that of the main rotor, which makes it possible to identify a fault in engagement or disengagement of one or the other of the two freewheels.

[0039] As can be seen in the figure, the motor M1 or its rotor RI is equipped with a speed sensor Cl, the motor M2 or its rotor R2 is equipped with another speed sensor C2, and the main rotor RP is also equipped with a speed sensor CP.

[0040] These sensors, which monitor the rotational speed of rotor RI, rotor R2, and the main rotor RP, are connected to a control and command unit (UCC) for the propulsion system. This UCC is also connected to the two engines M1 and M2 to selectively activate them so that they rotate at a speed corresponding to a setpoint value that it sends to them.

[0041] According to the invention, the freewheel verification is ensured from the control and command unit UCC. When this unit performs the verification, in a first phase, it drives the first motor M1 to activate it so that it rotates at a nominal speed, and it drives the second motor M2 to deactivate it so that it does not rotate.

[0042] When the first motor has reached its rated speed, the control and command unit collects the speeds read by sensors Cl, C2 and CP.

[0043] If the difference between the speed of the main rotor RP and that of the first motor M1 exceeds a threshold value, it means that the first freewheel RL1 is not properly engaged. This can correspond to a case where the main rotor RP is not rotating, meaning that the first freewheel RL1 is not engaged at all, or to a case where it is rotating but at a lower speed than the motor M1, so that the first freewheel RL1 is not actually properly engaged.

[0044] In this case, the control unit emits a warning signal indicating that one of the freewheels is malfunctioning.

[0045] If the speed of the second motor M2 exceeds a certain threshold, it means that it is being driven by the transmission, and therefore that the second freewheel RL2 is not disengaged. This can occur when the second motor M2 rotates at the same speed as the first motor M1, meaning that the second freewheel RL2 is not disengaged at all, or when it rotates at a lower speed than the first motor M1, meaning that the second freewheel is not properly disengaged.

[0046] In this case, the control unit emits a warning signal indicating that one of the freewheels is malfunctioning.

[0047] In a second phase of this verification, the control and command unit drives the first motor M1 to activate it so that it rotates at a reduced speed compared to the nominal speed, and it drives the second motor M2 so that it rotates at the nominal speed.

[0048] When the first motor has reached its reduced speed and the second motor has reached its nominal speed, the control and command unit collects the speeds read by sensors Cl, C2 and CP.

[0049] If the difference between the speed of the main rotor RP and that of the second motor M2 exceeds a threshold value, it means that the second freewheel RL2 is not properly engaged. This can occur when the main rotor RP rotates at the reduced speed of the motor M1, meaning that the second freewheel RL2 is not engaged at all, or when it rotates at a speed lower than that of the motor M2 but higher than that of the motor M1, so that the second freewheel RL2 is not properly engaged.

[0050] If the speed of the first motor M1 exceeds a threshold value increased by the value of the reduced speed, this means that it is being driven by the transmission, and therefore that the first freewheel RL1 is not disengaged. This case can correspond to the first motor M1 rotating at the speed of the second motor M2, meaning that the first freewheel RL1 is not disengaged at all, or to it rotating at a speed that is lower than that of the second motor M2 but higher than the reduced speed (which is its setpoint speed), meaning that the first freewheel RL1 is not properly disengaged.

[0051] The speed threshold value used during the verification corresponds to a residual speed value, which is determined based on the aircraft design and its freewheels. In practice, when a functional freewheel is disengaged, it can transmit residual torque capable of rotating the engine to which it is connected at a so-called residual speed.

[0052] This residual speed, which is normally very low, then constitutes the basic data used to determine the speed threshold value. Alternatively, the threshold value can be chosen to be equal to zero.

[0053] In practice, the sensors can be fitted to the rotors RI, R2 and RP as shown schematically in the figure, or can also be integrated into the motors and / or the transmission TR.

[0054] In a conventional propulsion system, both engines are turboshaft engines, but in a hybrid propulsion system, the first engine is a turboshaft engine, while the second is an electric motor with a field winding and an armature winding. In this latter case, the electric motor's sensor C2 can advantageously determine the speed of the motor M2 based on a measurement of the current and / or voltage of its armature.

[0055] The control and command unit (CCU) includes programmed means to implement the process by controlling the engines and processing or interpreting the data provided by the sensors. It can be integrated into an engine control system equipping the aircraft. This control and command unit can also be a separate component connected to the engine control system and the speed sensors, thus allowing an existing aircraft to be equipped to perform the verification according to the invention without major modifications to its layout.

[0056] Regarding the implementation of the method according to the invention, it can advantageously be triggered before each flight, during engine start-up, thus ensuring the integrity of the freewheels before takeoff. In practice, during engine start-up, the control and command unit is activated, for example, by the engine control system, to perform the check. If a freewheel malfunction is detected, the alert issued by the control and command unit (CCU) is transmitted to the cockpit to inform the pilot of the failure of one of the freewheels and the procedure to follow in this situation.At the end of the second verification phase, if no fault is detected, the control and command unit pilots the first engine M1 to run at its nominal speed (and no longer at its reduced speed), and it deactivates, if necessary (depending on the flight conditions specified by the pilot), the second engine M2, the propulsion system then being ready for takeoff.

[0057] This procedure could also be performed in flight over a certain power range, allowing this freewheel integrity check to be coupled with other checks, for example, a check of the power level control of the propulsion systems (electric and / or thermal). In the described implementation of the invention, the two verification phases are performed successively to conclude the test, but it is also possible in some cases to perform only one of the two phases, in order to save time during startup, for example, if only the engagement of the first engine and the disengagement of the second need to be verified before flight.In general, the invention is advantageously applicable to a twin-engine type helicopter, and more advantageously to a hybrid type twin-engine helicopter, that is to say, comprising a thermal engine and an electric machine that can operate as a generator or as a motor.

Claims

DEMANDS 1. A method for verifying the freewheels (RL1, RL2) of an aircraft propulsion system, this propulsion system comprising a main rotor (RP) coupled jointly to a first engine (M1) and a second engine (M2), respectively by a first freewheel (RL1) and a second freewheel (RL2), and in which the first engine (M1), the second engine (M2) and the main rotor (RP) are each equipped with a rotational speed sensor (C1, C2, CP), the engines (M1, M2) and the sensors (C1, C2, CP) being connected to a control and command unit (CCU), this method comprising the steps of: - from the control and command unit (CCU), activate the first motor (M1) to rotate it at a nominal speed and deactivate the second motor (M2), then collect via the sensors the speeds of the first and second motor (M1, M2) and the main rotor (RP); - from the control and command unit (CCU), issue an alert signal if the difference between the speed of the first motor (M1) and the speed of the main rotor (RP) is greater than a threshold value, or if the speed of the second motor (M2) is greater than a threshold value.

2. A method according to claim 1, further comprising the steps of: - from the control and command unit (CCU), control the first motor (M1) to rotate it at a reduced speed which is lower than the nominal speed and activate the second motor (M2) to rotate it at the nominal speed, of the first and second motor (M1, M2) and of the main rotor (RP); - from the control and command unit (CCU), issue an alert signal if the difference between the speed of the second motor (M2) and the speed of the main rotor (RP) is greater than a threshold value, or if the speed of the first motor (M1) is greater than a threshold value increased by the reduced speed.

3. A method according to claim 1 or 2, wherein the threshold value is zero.

4. Method according to claim 1, wherein the freewheel verification steps (RL1, RL2) are automatically triggered by the control and command unit (CCU) during an aircraft start-up phase.

5. System for implementing the method according to claim 1, comprising a control and command unit (CCU) connected to three speed sensors (Cl, C2, CP) and to a motor control system or to the motors, as well as programmed means for implementing verification.

6. Aircraft propulsion assembly comprising a main rotor (RP) coupled to a first engine (M1) and a second engine (M2), respectively by a first freewheel (RL1) and a second freewheel (RL2), this propulsion assembly comprising a system according to claim 3 whose speed sensors (Cl, C2, CP) equip the engines as well as the main rotor, and whose control and command unit (UCC) is connected to the engines (M1, M2) and the sensors.

7. Propulsion assembly according to claim 4, wherein the second motor (M2) is an electric motor comprising an inductor circuit and an induced circuit, and wherein the speed sensor (C2) equipping this second electric motor (M2) comprises an induced current sensor.

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