Aircraft propulsion system including a hydrodynamically disengageable freewheel

Abstract

Aircraft propulsion assembly, comprising an engine driving a main rotor via a coupling device comprising a first rotating member and a second rotating member coupled by a hydrodynamically disengaging freewheel (RL) having rollers (G) extending between an inner ring (2) and an outer ring (3), in which: – the inner ring (2) has through channels (12) to supply oil to the space extending between the rings (2, 3); – the inner ring (2) carries a reinjection wheel (9) the outer periphery of which extends opposite the outer ring (3); – the reinjection wheel (9) has reinjection channels each having an inlet opening located on its outer periphery and extending in a plane containing an axis having an orthoradial orientation;– each channel has a discharge opening located near the inner ring (2) and oriented to inject oil towards the radially inner ends of the rollers (G). Figure for the abbreviation: Figure 2;

Description

Title of the invention: Aircraft propulsion assembly comprising a hydrodynamically disengaged freewheel. Technical field

[0001] The invention relates to a freewheel of a propulsion assembly of an aircraft such as a helicopter. PREVIOUS STATE OF THE ART

[0002] Such a propulsion assembly typically comprises a turboshaft engine and a main rotor carrying a propeller, which is driven into rotation by the engine via a transmission system.

[0003] The motor rotates at a speed of approximately 20,000 revolutions per minute while the rotor rotates at a speed of approximately a few hundred revolutions per minute, so that the transmission system includes, among other things, toothed wheels forming a reducer to multiply the speed of the motor.

[0004] In the case of a helicopter, the transmission system incorporates a freewheel, because there are situations in which the main rotor rotates at a speed higher 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.

[0005] 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 drive speed if necessary.

[0006] A simple freewheel 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 occurs only if this moment is applied in the so-called coupling direction. When the freewheel is engaged, the rollers are braced between the two rings to transmit the moment from one ring to the other, and when it is disengaged, they slide along one of the rings instead of being braced.

[0007] In practice, the freewheel of a propulsion unit is integrated into a stage of the transmission system, ensuring that it rotates at reduced speeds compared to the turbine speed. The turbine can also be of the geared type, that is, incorporate a reduction gear by which its output shaft rotates at a reduced speed of around 6,000 to 8,000 revolutions per minute, which then allows the freewheel to be integrated at the input of the transmission device. However, when the freewheel is disengaged, the Roller slippage generates significant friction which damages the bushings.

[0008] US patent 3175661 discloses a hydrodynamically disengaged freewheel, in which the disengagement of the rollers is caused by oil circulation that increases when passing through the key gear, causing the rollers to tilt and disengage. This known freewheel, however, can only operate at a rotational speed below 3000 revolutions per minute.

[0009] The object of the invention is to provide a hydrodynamically disengaged freewheel arrangement capable of rotating at speeds of around 20,000 revolutions per minute and above. Description of the invention

[0010] To this end, the invention relates to an aircraft propulsion assembly, comprising an engine and a main rotor driven via a coupling device comprising a hydrodynamically disengaged freewheel, this freewheel comprising an inner ring surrounded by an outer ring which are coaxial about an axis of rotation, and rollers extending between these rings, characterized in that:

[0011] - the inner ring has radial oil supply channels;

[0012] - the inner ring carries a reinjection wheel, the outer periphery of this wheel reinjection extending opposite the outer ring;

[0013] - the reinjection wheel comprises reinjection channels, each comprising a intake opening located at the outer periphery of the reinjection wheel;

[0014] characterized in that:

[0015] - each inlet opening extends in a plane containing an axis having a orthoradial orientation relative to the axis of rotation;

[0016] - each reinjection channel has a discharge opening located in the vicinity of the inner ring, being oriented to inject oil towards the radially internal ends of the rollers to tilt them in order to disengage them.

[0017] With this arrangement, the intake openings of the reinjection wheel do not form reliefs likely to disturb the oil bath in which the reinjection wheel is immersed.

[0018] The invention also relates to an assembly defined as follows, in which the outer ring has an internal circumferential groove in which the outer periphery of the reinjection wheel extends.

[0019] The invention also relates to an assembly thus defined, in which the outer ring is formed of two parts jointly delimiting the internal circumferential groove.

[0020] The invention also relates to an assembly defined as follows, in which the free wheel comprises two reinjection wheels located on either side of the rollers.

[0021] The invention also relates to an assembly defined as follows, in which each intake opening of the reinjection wheel extends in a plane parallel to the axis of rotation.

[0022] The invention also relates to an assembly defined as follows, in which each inlet opening of the reinjection wheel is formed at an external cylindrical peripheral face of the reinjection wheel.

[0023] The invention also relates to an assembly defined as follows, comprising a reinjection wheel having a number of reinjection channels greater than or equal to the number of rollers.

[0024] The invention also relates to an assembly defined as follows, comprising a reinjection wheel having a number of reinjection channels greater than or equal to twice the number of rollers.

[0025] The invention also relates to an assembly thus defined, in which the reinjection wheel is fixed to the inner ring by shrink fitting.

[0026] The invention also relates to an assembly defined as follows, in which the channels of the reinjection wheel are formed by drilling. Brief description of the drawings

[0027] Fig. 1 is a schematic representation of an aircraft propulsion system;

[0028] Fig. 2 is a general longitudinal cross-sectional view of the freewheel according to the invention;

[0029] Fig. 3 is a front view of a freewheel roller in the engaged or sliding state;

[0030] Fig. 4 is a front view of a freewheel roller in the disengaged state;

[0031] Fig. 5 is a general perspective view of a reinjection wheel shown alone ;

[0032] Fig. 6 is a perspective and cross-sectional view of a reinjection wheel shown alone;

[0033] Fig. 7 is a longitudinal cross-sectional view of the freewheel according to the invention in the engaged or sliding state;

[0034] Fig. 8 is a longitudinal cross-sectional view of the freewheel according to the invention in the disengaged state.

[0035] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0036] In [Fig. 1], a propulsion assembly 1 comprises a motor TM having a rotor RT coupled in rotation to a transmission system ST, and a main rotor RP carrying a propulsion propeller denoted HP which is coupled to the transmission system ST.

[0037] The ST transmission system allows the main rotor RP to be driven at a speed that is multiplied relative to that of the engine TM, which is typically a turboshaft engine. This ST transmission system includes a coupling device DA incorporating a hydrodynamically disengaged freewheel RL visible in [Fig. 2].

[0038] When the freewheel RL is engaged, it transmits a positive torque, i.e., the rotor RT of the engine TM drives the main rotor RP in rotation. Disengaging this freewheel RL allows the rotor to rotate at a higher speed than the drive speed of the engine TM, for example, during a descent phase of the aircraft when the airflow through the propeller HP drives its rotation.

[0039] As is known from the prior art, a simple freewheel is a device for coupling a first and a second rotating element, so as to lock them in rotation only if the moment 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.

[0040] 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 takes place only if this moment is exerted in the direction of coupling.

[0041] 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.

[0042] In the case of a centrifugally or hydrodynamically disengaged freewheel, the rollers located between the rings are arranged to disengage beyond a key speed if the moment exerted by one ring on the other becomes zero, i.e. if the freewheel is not under load.

[0043] Below the key speed, a freewheel with centrifugal or hydrodynamic disengagement behaves the same as a simple freewheel. Above the key speed, a freewheel with centrifugal or hydrodynamic disengagement... disengages when it is no longer under load, that is, when the moment exerted by the first ring on the second is substantially zero.

[0044] US patent 3175661 discloses a hydrodynamically disengaged freewheel. This freewheel incorporates an oil circulation that causes its rollers to disengage by tilting beyond the key speed when the torque exerted by one ring on the other is zero. However, this known freewheel is not suitable for operation at the high rotational speeds corresponding to an aircraft propulsion system, as it cannot operate beyond 3000 revolutions per minute.

[0045] In the example of [Fig. 2], the coupling device DA, incorporating the hydrodynamically disengaged freewheel RL according to the invention, comprises an inner sleeve 2 surrounded by an outer sleeve 3, which are coaxial about an axis AX. The inner sleeve 2 receives, for example, a splined shaft to connect it in rotation to the rotor RT of the motor TM. The outer sleeve 3 is connected in rotation to the main rotor RP by one or more gears (not shown) of the transmission system ST.

[0046] The inner sleeve 2 is supported by a fixed frame carrying two bearings not shown, the inner rings of these bearings each surrounding this sleeve 2. The outer sleeve 3 is supported by the inner sleeve 2, by means of two other bearings 4, 6 whose inner rings enclose the inner sleeve 2, and whose outer rings are surrounded by this outer sleeve 3.

[0047] Bearings 4 and 6 are spaced longitudinally apart from each other by being located longitudinally on either side of the free wheel RL, the bearings not shown carrying the inner sleeve being located on either side of bearings 4 and 6.

[0048] The freewheel RL surrounds the sleeve 2 which constitutes its inner ring, and it is surrounded by the sleeve 3 which constitutes its outer ring.

[0049] This free wheel RL has a coupling direction which is the direct direction identified by DIR on the axis AX, and it includes rollers G located in the space extending radially between the sleeves 2 and 3.

[0050] If the moment exerted by the inner ring 2 on the outer ring 3 is oriented in the coupling direction, the rollers G brace themselves with their ends bearing against the rings, thus locking them in rotation due to the friction exerted by these ends, as shown in [Fig. 3]. If, on the other hand, the moment exerted by the inner ring on the outer ring is oriented in the opposite direction, the radially external ends of the rollers slide along the outer ring so that the two rings are independent in rotation.

[0051] As can be seen in [Fig. 3], the freewheel RL includes a return spring 7 which continuously tends to return the rollers G to an orientation such that their radially internal ends Ei and radially external ends Er are supported respectively on the inner ring 2 and on the outer ring 3. This return spring 7 is a circumferential helical spring which extends between the two rings through each roller G, each roller having for this purpose a through hole 8.

[0052] The disengagement of the freewheel RL is achieved by pivoting the rollers G against the return spring 7, around axes parallel to the axis AX, to substantially move their radially external ends Er away from the outer ring 3, which corresponds to the situation in [Fig. 4]. In practice, contact between the rollers G and the outer ring 3 is not completely lost, but the forces exerted by the rollers on the ring are very significantly reduced or even eliminated.

[0053] This disengagement is achieved by applying a circumferentially directed force F to the radially internal ends Ei of the rollers G in order to tilt them. This force F is generated by an oil jet directed towards the radially internal end of the roller G, which is established by a reinjection wheel 9 when the freewheel RL rotates beyond the key speed, this reinjection wheel being integrated into the freewheel RL.

[0054] As shown in [Fig. 2], the reinjection wheel 9 has a general washer shape extending between the inner and outer rings, opposite the flanks of the rollers G. It is rigidly rotationally fixed to the inner ring 2 that carries it, being attached to it by shrink fitting, clamping, or by means of splines. The outer periphery of this wheel 9 is opposite the outer ring 3, being engaged in a circumferential groove 11 of the outer ring 3. In addition, the inner ring has radial channels 12 opening into the space containing the rollers G, and which allow oil to be supplied to this space by centrifugal force of the oil through these channels 12.

[0055] In general, the reinjection wheel 9 cooperates with the groove 11 to establish a recirculation of the oil towards the radially internal ends of the rollers G, when the outer ring rotates at a speed greater than the key speed.

[0056] As can be seen more clearly in [Fig.5], this reinjection wheel 9 has a general washer shape with a significant thickness, the central opening 13 of which has a diameter corresponding to the external diameter of the inner ring 2, and the external diameter of which corresponds to the diameter of the groove 11. It has an external peripheral face 14 which is cylindrical.

[0057] This wheel 9 has oil reinjection channels 16. Each channel 16 has an inlet opening 17 opening into the cylindrical outer face and having a circular contour, and a discharge opening 18 opening into a lateral face of the wheel, in the vicinity of its central opening 13.

[0058] As can be seen more clearly in [Fig. 6], each channel comprises an inlet portion 19 extending from the inlet opening 17 and extending radially by relative to the axis AX, which is extended by a discharge portion 21, having a role of nozzle, and ending in the lateral face by the discharge opening 18. In the example of the figures, the two portions of each channel are straight and obtained by drilling.

[0059] In the example shown in the figures, each inlet opening 17 extends into the cylindrical face 14, but it could also extend into a lateral face of the wheel. The determining factor with regard to each inlet opening 17 is that it extends in a plane containing an axis orthoradial to the axis AX, in order to significantly reduce the turbulence generated in the oil flow when the wheel 9 is driven in rotation. In other words, the inlet openings 17 are arranged so as not to constitute raised elements capable of creating turbulence in the oil flow, so that the freewheel behaves the same at low and high speeds.

[0060] Each discharge portion 21 extends along a direction D which is oblique to a plane which contains the axis AX and which passes through the discharge opening 18 ending this portion 21.

[0061] The orientation of the direction D of a discharge portion 21 is such that a jet of oil expelled through the opening 18 of a discharge portion 21 is thus expelled at the radially internal ends Ei of the rollers G, oriented to tend to tilt them so that they disengage. The discharge portions 21 thus constitute oil injectors oriented towards the rollers to tilt them by generating jets whose orientation has a tangential component.

[0062] During operation, when the outer ring 3 rotates, the groove 11, in which the outer periphery of the wheel 9 extends, is immersed in oil that is centrifugally expelled by the rotation of the ring 3, of which this groove 11 is a part. This centrifugation generates an increase in the static pressure of the oil present in the groove 11, which is higher the greater the rotational speed.

[0063] In the situation of [Fig.7], the speed of the outer ring 3 is lower than the key speed. In this case, the oil conveyed to the freewheel by the conduits 12 flows longitudinally, in particular through the groove 11, before being discharged, for example through the bearing 4, and the oil present in the channels 16 stagnates in these channels.

[0064] In the situation of [Fig.8], the speed of the outer ring 3 is greater than the key speed, so that centrifugation causes a strong increase in the static oil pressure in the groove 11, which becomes significantly greater than the oil pressure in the vicinity of the inner ring 2. Under these conditions, the significant pressure difference between the inlet openings 17 and the outlet openings 18 generates a centripetal oil circulation in the channels 16.

[0065] The oil jets, designated by J, which are expelled through the discharge openings 18, are then directed towards the radially inner ends Ei of the rollers G to pivot them in order to disengage them. When the key speed is reached, the impact pressure of the jets J is sufficient to pivot the rollers G, if they are not braced, so that their radially outer ends Ee move away from the ring 3 and no longer slide along it.

[0066] The number of channels 16 is chosen to be greater than or equal to the number of rollers G to ensure that the number of jets J is sufficient to impact all the rollers G so as to disengage them all. In practice, the wheel 9 has a number of channels 16 greater than twice the number of rollers G.

[0067] As can be seen in figures 2, 7 and 8, the outer ring 3 is formed of two parts identified by 22 and 23 forming two half-sleeves which extend in line with each other and are rigidly joined together, to delimit at their junction the groove 11.

[0068] In the example of the figures, the end of the first part 22 has at the level of the internal edge of its end of attachment to the other part 23, an internal shoulder 24 or fillet having in section the shape of the letter L, and which is completed by the flank of the end of attachment of the second part 23.

[0069] The U-shaped groove is thus delimited by the L-shaped shoulder 24 of part 22 and by the side of part 23, to form a removable internal groove in which the periphery of the wheel 9 is housed. This allows the wheel 9 to be positioned so that its periphery extends into the groove 11. In practice, the wheel 9 can be placed in the chamfer 24 before bringing the second part 23 against the first part 22 to fix them together.

[0070] In the example shown in the figures, the freewheel RL includes a re-injection wheel 9, located to the left of the rollers G in the figures, but it is also possible to provide another re-injection wheel located to the right of the rollers. In this case, the outer ring is advantageously formed of three parts to define two removable internal grooves.

[0071] In general, the invention enables the implementation of centripetal pumping of oil in the reinjection wheel, which can operate at high speeds, because the external surface of the wheel 9 is a surface of revolution. In other words, thanks to the orientation of the discharge openings in planes containing orthoradial axes, the freewheel does not have external protrusions in order to avoid generating significant turbulence in the oil bath when this wheel rotates.

Claims

Demands

1. Aircraft propulsion assembly (1), comprising an engine (TM) and a main rotor (RP) driven via a coupling device (DA) comprising a hydrodynamically disengaging freewheel (RL), this freewheel (RL) comprising an inner ring (2) surrounded by an outer ring (3) which are coaxial about an axis (AX) of rotation, and rollers (G) extending between these rings (2, 3), in which: - the inner ring (2) has radial oil supply channels (12); - the inner ring (2) carries a reinjection wheel (9), the outer periphery of this reinjection wheel (9) extending opposite the outer ring (3); - the reinjection wheel (9) has reinjection channels (16) each having an inlet opening (17) located at the outer periphery of the reinjection wheel (9);characterized in that: - each inlet opening (17) extends in a plane containing an axis having an orthoradial orientation with respect to the axis of rotation (AX); - each reinjection channel (16) has a discharge opening (18) located in the vicinity of the inner ring (2) and is oriented to inject oil towards the radially internal ends of the rollers (G) to tilt them in order to disengage them.

2. Assembly according to claim 1, wherein the outer ring (3) has an internal circumferential groove (11) in which the outer periphery of the reinjection wheel (9) extends.

3. Assembly according to claim 2, wherein the outer ring (3) is formed of two parts jointly delimiting the inner circumferential groove (11).

4. Assembly according to any one of the preceding claims, wherein the free wheel (RL) comprises two reinjection wheels (9) located on either side of the rollers (G).

5. Assembly according to any one of the preceding claims, wherein each inlet opening (17) of the reinjection wheel (9) extends in a plane parallel to the axis of rotation (AX).

6. Assembly according to claim 5, wherein each inlet opening (17) of the reinjection wheel (9) is formed at an external cylindrical peripheral face of the reinjection wheel (9).

7. Assembly according to any one of the preceding claims, comprising a reinjection wheel (9) having a number of reinjection channels (16) greater than or equal to the number of rollers (G).

8. Assembly according to any one of the preceding claims, comprising a reinjection wheel (9) having a number of reinjection channels (16) greater than or equal to twice the number of rollers (G).

9. Assembly according to any one of the preceding claims, wherein the reinjection wheel (9) is fixed to the inner ring by shrink fitting.

10. Assembly according to any one of the preceding claims, wherein the channels (16) of the reinjection wheel (9) are formed by drilling.

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