Aircraft propulsion system comprising a coupling device incorporating two centrifugally disengageable freewheels

Abstract

The invention relates to an aircraft propulsion assembly (1) comprising a main rotor (RP), a first engine (TM) and a second engine (ME), and a transmission system (ST) for driving the main rotor (RP) with the first engine (TM) and / or with the second engine (ME), wherein the transmission system comprises a coupling device (DA) having a first rotating member (2) and a second rotating member (3), characterized in that the first rotating member (2) and the second rotating member (3) are directly coupled to each other by two centrifugally disengaged freewheels (RL+, RL-) having opposite coupling directions. Figure 2

Description

Title of the invention: Aircraft propulsion assembly comprising a coupling device integrating two centrifugally disengaged freewheels. Technical field

[0001] The invention relates to an aircraft propulsion assembly comprising a main rotor connected to two motors by a transmission system incorporating a decoupling element. PREVIOUS STATE OF THE ART

[0002] Such a propulsion system includes, for example, a first engine which is a turbomotor and a second electric motor which is an electric machine that can operate as a motor or as a generator, which then corresponds to a so-called hybrid propulsion system.

[0003] Such an assembly further comprises a main rotor which typically carries a propulsion propeller, and which is driven by at least one motor through the transmission system.

[0004] When a motor is in operation, it rotates at a speed of approximately 15,000 revolutions per minute, while the rotor rotates at a speed of approximately a few hundred revolutions per minute. Therefore, the transmission system includes, in particular, toothed wheels forming a reduction gear to multiply the motor speed.

[0005] The transmission system's decoupling device is arranged, for example, to allow the electric machine to be decoupled without stopping the propulsion system. In the event of a failure of this electric machine, it can thus be isolated so as not to disrupt the rotation of the main rotor. In practice, this may be a permanent magnet electric machine, in which case a short-circuit malfunction requires mechanical decoupling, since such an event cannot be neutralized by de-energizing its rotor.

[0006] There are different architectures for hybrid propulsion systems, such as the so-called parallel architecture or the so-called series architecture. In the parallel architecture, the two engines are connected individually to the transmission system, which is itself connected to the main rotor. In the series architecture, the transmission system connects the turboshaft engine to the main rotor, and it connects the electric motor to the turboshaft engine.

[0007] In the various possible architectures, the decoupling device of the transmission system can be arranged to mechanically decouple the electrical machine from the assembly in order to mechanically isolate it, or for another function.

[0008] The decoupling device can also be provided to decouple either of the two engines, both in the case of a hybrid architecture and in the case of an architecture with two engines of the same type. This then allows the main rotor to be driven selectively with one or the other of the engines, or jointly with both, depending on the flight conditions.

[0009] Generally, engine decoupling in known propulsion systems is performed manually when the system is stationary, thus requiring the entire propulsion system to be shut down and an operator to intervene. In existing systems that allow for in-service decoupling, decoupling under load generally leads to significant deterioration of the transmission system because it uses dog clutch-type couplings, resulting in rapid wear that reduces the device's lifespan.

[0010] The object of the invention is to propose an arrangement enabling decoupling under load without disturbing the rotation of the main rotor. Description of the invention

[0011] To this end, the invention relates to an aircraft propulsion assembly comprising a main rotor, a first engine and a second engine, a transmission system for driving the main rotor with the first engine and / or with the second engine, in which the transmission system comprises a coupling device comprising a first rotating member and a second rotating member, characterized in that the first rotating member and the second rotating member are directly coupled to each other by two centrifugally disengaged freewheels which have opposite coupling directions.

[0012] The invention thus makes it possible to transmit torque from a motor, to transmit torque to a motor, to switch from one operating mode to another, to disconnect under torque without damage, and to reconnect without stopping the propulsion assembly and without manual intervention.

[0013] The invention also relates to an assembly thus defined, comprising an additional uncoupling motor which is rotationally linked to the first rotating member.

[0014] The invention also relates to an assembly thus defined, comprising a set of capacitors ensuring the electrical supply of the uncoupling motor.

[0015] The invention also relates to an assembly thus defined, in which the uncoupling motor is electric.

[0016] The invention also relates to an assembly defined as follows, in which the first rotating member is surrounded by the second rotating member, and in which the two free wheels surround the first rotating member and are surrounded by the second rotating member.

[0017] The invention also relates to an assembly defined as follows, in which the first rotating member is carried by a fixed chassis carrying two bearings having inner rings each surrounding this first rotating member, in which the second rotating member is carried by the first rotating member by means of two other bearings having inner rings enclosing the first rotating member and outer rings surrounded by this second rotating member to carry it.

[0018] The invention also relates to an assembly thus defined, in which the first rotating member is a sleeve having internal grooves intended to receive a shaft linked in rotation to the second motor.

[0019] The invention also relates to an assembly thus defined, in which the second rotating member is a sleeve having external teeth intended to mesh with a toothed wheel linked in rotation to the first motor.

[0020] The invention also relates to an assembly defined as follows, in which the first rotating member forms an inner ring of the free wheels and in which the second rotating member forms an outer ring of the free wheels.

[0021] The invention also relates to an assembly defined as follows, in which the first engine is a thermal engine and the second engine is an electric machine capable of operating as a generator. Brief description of the drawings

[0022] Fig. 1 is a schematic representation of a propulsion assembly according to the invention;

[0023] Fig. 2 is a cross-sectional view of the coupling device when the second motor drives the main rotor;

[0024] Fig. 3 is a half-section view of the coupling device when the first motor drives the second motor;

[0025] Fig. 4 is a half-section view of the coupling device when the second motor is uncoupled;

[0026] The [Fig.5] is a diagram showing the evolution of the speed, the transmitted moment, the state of the free wheels and the coupling state.

[0027] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0028] In [Fig. 1], a propulsion assembly 1 comprises a first motor TM having a first rotor RI coupled in rotation to a transmission system ST, and a second motor ME having a second rotor R2 coupled to the transmission system ST. This assembly 1 further comprises a main rotor RP which is also coupled in rotation to the transmission system ST, and which carries a propulsion propeller denoted HP.

[0029] Thanks to the ST transmission system, the main rotor RP can be driven by the first motor TM, or by the second motor ME, or by both, and the speed of the rotor RP is multiplied relative to that of the motor which drives it.

[0030] In the example of [Fig. 1], the first motor TM is a turbomotor, while the second motor ME is an electric machine that can operate as a motor (when powered by an electric battery not shown), or as a generator (to charge this electric battery).

[0031] The ST transmission system also allows operation in which the rotor RI of the first motor TM drives the rotor R2 of the second motor ME when this second motor is an electric machine, which allows the supply battery to be recharged.

[0032] The ST transmission system incorporates a coupling device DA shown in [Fig.2], which allows the second motor ME to be coupled and uncoupled.

[0033] This coupling device DA comprises two free wheels, namely a positive free wheel RL+ and a negative free wheel RL- which have opposite engagement directions, and which are centrifugally disengaged free wheels.

[0034] When the positive freewheel RL+ is engaged, it allows the transmission of a positive torque, that is to say, by which the rotor R2 of the second motor ME drives the transmission system ST and its main rotor RP into rotation.

[0035] When the negative freewheel RL- is engaged, it allows the transmission of a negative torque, that is to say, by which the rotor R2 of the second motor ME is on the contrary driven in rotation by the transmission system ST.

[0036] As is known in the prior art, a freewheel is a device for coupling a first and a second rotating element, so as to lock them together in rotation 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 or roller wheel, or pawl wheel.

[0037] In practice, a free wheel comprises an inner ring surrounded by an outer ring, between which are interposed rollers (or balls or pawls) by means of which the transmission of a moment from one ring to the other only takes place if it is exerted in the direction of coupling.

[0038] 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.

[0039] In the case of a centrifugally disengaged freewheel, known for example from document US8813931, the rollers located between the rings are arranged to allow disengagement beyond a key speed if the moment exerted by one ring on the other becomes zero.

[0040] Each roller has a counterweight and is supported by the inner ring, being able to pivot relative to it. Each roller is returned by a spring that continuously tends to rotate it to bring its free end back against the outer ring. If the speed exceeds the key speed, the free ends of the rollers tend to move away from the outer ring because the centrifugal forces acting on the counterweights of these rollers then become greater than the returning forces of the springs.

[0041] Below the key speed, a centrifugally disengaged freewheel behaves the same as a simple freewheel. If the torque exerted by the inner ring on the outer ring is oriented in the direction of coupling, the rollers brace themselves with their ends bearing against the outer ring, thus locking the two rings together in rotation thanks to the friction exerted by the roller ends on the outer ring. Conversely, if the torque exerted by the inner ring on the outer ring is oriented in the opposite direction, the roller ends slide on the outer ring so that the two rings rotate independently.

[0042] Beyond the key speed, a centrifugally disengaged freewheel disengages when it is no longer under load, that is, when the torque exerted by the first ring on the second is substantially zero. Indeed, when the freewheel is under load, the frictional forces exerted by the outer ring on the butted roller ends are much greater than the centrifugal forces experienced by the counterweights and prevent these roller ends from moving away from the outer ring. When the load becomes zero, the frictional forces cancel each other out, so that the rollers pivot to move their ends away from the outer ring, the two rings then becoming independent in rotation.

[0043] In the example of [Fig.2], the coupling device DA comprises

[0044] an inner sleeve 2 surrounded by an outer sleeve 3, which are coaxial about an axis AX. The inner sleeve 2 has internal splines 4 enabling it to receive a splined shaft to link it in rotation to the rotor R2 of the second motor ME. The outer sleeve 3 has external teeth 6 by means of which it is linked in rotation to the rotor RI of the first motor TM, by one or more gears (not shown) of the transmission system ST.

[0045] The inner sleeve 2 is supported by a fixed frame 9 carrying two bearings 7 and 8, the inner rings of these bearings each surrounding this sleeve 2. The outer sleeve 3 is supported by the sleeve 2, by means of two other bearings 11, 12 of which the inner rings enclose the inner sleeve 2, and whose outer rings are surrounded by this outer sleeve 3 to support it.

[0046] As can be seen in [Fig.2], bearings 7 and 8 are spaced longitudinally apart from each other, being located at the ends of sleeve 2. The other two bearings 11 and 12 are also spaced longitudinally apart from each other, while being located between bearings 7 and 8.

[0047] The coupling device DA comprises two centrifugally disengaged freewheels RL+ and RL- which are located longitudinally between the bearings 7 and 8. These two freewheels surround the sleeve 2 which constitutes their inner rings, and they are surrounded by the sleeve 3 which constitutes their outer rings.

[0048] The positive freewheel RL+ has a coupling direction which is direct direction located by DIR on the axis AX, and it has rollers called positive rollers G+ located in the space extending radially between the sleeves 2 and 3. The negative freewheel RL- has an indirect coupling direction, that is to say opposite to the direction DIR, and it has rollers called negative rollers G- located in the space extending radially between the sleeves 2 and 3.

[0049] As seen in [Fig.2], the free wheels RL+ and RL- are positioned side by side along the longitudinal axis AX, being located longitudinally between the bearings 11 and 12, so that the positive rollers G+ are contiguous with the negative rollers G- in the longitudinal direction.

[0050] Complementarily, the coupling device DA is equipped with an electric uncoupling motor MD which is directly coupled to the inner sleeve 2, and which is intended to be activated in a substantially punctual manner to cause uncoupling.

[0051] The diagram in [Fig.5] shows the states of the coupling device during the three main phases A, B and C.

[0052] Phase A corresponds to the driving of the rotor RP by the second motor ME: it describes states in which the second motor ME is activated to drive the main rotor RP, the first motor TM being deactivated.

[0053] Phase B corresponds to the driving of the second motor ME, which is an electric machine, by the first motor TM to operate as a generator, for example, to charge a battery (not shown). It describes states in which the first motor TM is activated to drive the main rotor RP and the electric machine constituted by the second motor ME in rotation, thus making it operate as an electric generator.

[0054] Phase C corresponds to the mechanical disengagement of the second ME motor, for example to neutralize a malfunction occurring on it. It describes states in which the second motor ME is mechanically uncoupled from the transmission system ST by means of the activation of the uncoupling motor MD.

[0055] In the initial stage of phase A, both motors TM and ME are deactivated, so that the main rotor RP, the transmission system ST, and the coupling device do not rotate. In this state, the rollers G+ and G- are bearing against the outer ring formed by the outer sleeve 3.

[0056] The beginning of phase A corresponds to the starting of the second motor ME to rotate the inner sleeve 2 in the forward direction DIR. The speed V of the rotor RP is initially 0, and the torque M exerted by the inner sleeve 2 on the outer sleeve 3 has a positive value, denoted M+, so that it is oriented in the direction of coupling. The positive freewheel RL+ is therefore in the coupled state c+ to transmit this torque to the outer sleeve 3. Under these conditions, the coupling state K of the coupling device DA is coupled.

[0057] The negative freewheel RL- is then in the sliding state g-, because its rollers are in contact with the outer ring but slide along it instead of being engaged.

[0058] The main rotor RP then gradually begins to rotate, its speed V increasing from 0 to a value slightly above the key speed Vc of the freewheels RL+ and RL-, which corresponds to the state shown in [Fig. 2]. The rollers G- of the negative freewheel RL- then move away from the outer sleeve 3 to enter the centrifugal state c- because they are not engaged when the key speed Vc is exceeded. The rollers G+ of the wheel RL+ remain in the engaged state e+: they do not move away from the sleeve 3 because they are engaged, i.e., braced so that the centrifugal forces are insufficient to move them apart.

[0059] The speed of the rotor RP then continues to increase up to a maximum value noted Vm, the coupling device remaining coupled by the positive free wheel RL + which remains in the engaged state e+, the negative free wheel RL- remaining in the centrifugal state c-.

[0060] Before the end of phase A, the second motor ME is driven to reduce its speed slightly below the key speed Vc, at which point it is deactivated. Due to reaching a speed lower than Vc, the rollers G- of the negative freewheel RL- are no longer centrifugally spun and therefore come into contact with the outer ring (i.e., the outer sleeve 3), the freewheel RL- then passing into the sliding state g-.

[0061] Due to the deactivation of the second motor ME, the moment M exerted by the inner sleeve 2 on the outer sleeve 3 becomes zero, so that the rollers G+ of the positive free wheel RL+ pass from the engaged state e+ to the sliding state g+.

[0062] At the beginning of phase B, the first motor TM is activated to rotate at the key speed Vc, in order to rotate the outer sleeve 3 in the forward direction DIR. In this situation, it is the outer sleeve 3 that exerts a moment on the inner sleeve 2 oriented in the direct direction DIR. By reaction, the inner sleeve 2 exerts on the outer sleeve 3 a moment oriented in the opposite direction, i.e. a negative moment M-, so that it is then the negative free wheel RL- which engages by passing to the state e-.

[0063] In this situation which corresponds to the state of [Fig.3], the first motor TM drives the second motor ME which is an electric machine then operating as a generator, for example to charge an electric battery not shown.

[0064] The first motor TM is then driven to increase the speed up to the value Vm, so that the rollers G+ of the positive free wheel RL+ pass into the centrifugal state c+ by moving away from the outer sleeve 3, which corresponds to the end of phase B.

[0065] At the beginning of phase C, the uncoupling motor MD is activated to exert on the inner sleeve 2 a moment oriented in the direction DIR, so that this inner sleeve 2 exerts on the inner sleeve a moment that is no longer negative but zero. Under these conditions, since the rotational speed is still greater than the key speed Vc, and the moment M exerted by the inner sleeve 2 on the outer sleeve 3 is zero, the negative freewheel RL- passes into the centrifugal state c-, so that the two freewheels RL+ and RL- are then centrifuged and decoupled, as shown in [Fig.4].

[0066] At this stage, the second motor ME is therefore mechanically decoupled from the first, under load and without stopping rotation, so that it is no longer driven by the first motor TM. Furthermore, in the example of [Fig. 5], the first motor TM is driven to reduce its speed to the value Vc at the end of phase C.

[0067] Phase C corresponds for example to a situation in which a malfunction has occurred on the second ME motor, and is mechanically disengaged to neutralize this malfunction.

[0068] The activation of the MD uncoupling motor is of short duration, so it does not have to be oversized, and can optionally be powered from a set of capacitors.

[0069] Furthermore, instead of being triggered by the MD motor, the uncoupling can be triggered by temporarily increasing the speed of the second ME motor beyond that of the first TM motor. Thus, the uncoupling motor MD essentially ensures uncoupling when the second ME motor malfunctions.

[0070] Generally, the transition from the operating mode corresponding to phase A or B, or from phase B to phase A, necessarily occurs at a speed V lower than the key speed Vc. The transition from phase A or B to phase C necessarily occurs at a speed V higher than the key speed.

[0071] In general, the invention thus makes it possible to transmit a torque to the electric machine, to transmit a torque from the electric machine, to switch from one operating mode to another, to disconnect under torque without damage, and to reconnect without stopping the propulsion assembly and without manual intervention.

Claims

Demands

1. Aircraft propulsion assembly (1) comprising a main rotor (RP), a first engine (TM) and a second engine (ME), a transmission system (ST) for driving the main rotor (RP) with the first engine (TM) and / or with the second engine (ME), in which the transmission system comprises a coupling device (DA) comprising a first rotating member (2) and a second rotating member (3), characterized in that the first rotating member (2) and the second rotating member (3) are directly coupled to each other by two centrifugally disengaged freewheels (RL+, RL-) which have opposite coupling directions.

2. Assembly according to claim 1, comprising an additional uncoupling motor (MD) which is rotationally linked to the first rotating member (2).

3. Assembly according to claim 1, wherein the uncoupling motor (MD) is electric.

4. Assembly according to claim 3, comprising a set of capacitors providing the electrical supply to the uncoupling motor (MD).

5. Assembly according to any one of the preceding claims, wherein the first rotating member (2) is surrounded by the second rotating member (3), and wherein the two free wheels (RL+, RL-) surround the first rotating member (2) and are surrounded by the second rotating member (3).

6. Assembly according to any one of the preceding claims, wherein the first rotating member (2) is carried by a fixed frame (9) carrying two bearings (7, 8) having inner rings each surrounding this first rotating member (2), wherein the second rotating member (3) is carried by the first rotating member (2) by means of two other bearings (11, 12) having inner rings enclosing the first rotating member (2) and outer rings surrounded by this second rotating member (3) to carry it.

7. Assembly according to claim 5, wherein the first rotating member (2) is a sleeve having internal grooves (4) intended to receive a shaft rotationally linked to the second motor (ME).

8. Assembly according to claim 5, wherein the second rotating member (3) is a sleeve having external teeth (6) intended to mesh with a toothed wheel linked in rotation to the first motor (TM).

9. Assembly according to claim 5, wherein the first rotating member (2) forms an inner ring of the free wheels (RL+, RL-) and wherein the second rotating member (3) forms an outer ring of the free wheels (RL+, RL-).

10. Assembly according to any one of the preceding claims, wherein the first engine (TM) is a thermal engine and the second engine (ME) is an electric machine capable of operating as a generator.