Variable pitch turbine blade for an aircraft turbomachine

Abstract

Variable pitch turbine blade (114) for an aircraft turbomachine, this blade (114) comprising: - a blade (16), - a foot (18) defining a pitch axis (A), and - an eccentric (78) attached to and fixed to the foot (18), characterized in that the eccentric (78) is coupled to the foot (18) via a curvic® coupling (100). Figure for the abbreviation: Figure 4

Description

Title of the invention: Variable pitch blade for an aircraft turbomachine Technical field of the invention

[0001] The present invention relates to a variable-pitch blade for an aircraft turbomachine, and in particular for an aircraft turbomachine pusher propeller. Technical background

[0002] The state of the art includes in particular documents FR-A1-3 017 163, FR-A1-3 080 322, FR-A1-3 098 789, WO-A1-2022 / 018353, WO-A1-2022 / 018355 and WO-A1-2024 / 033590.

[0003] An aircraft turbomachine propeller can be shrouded, as is the case of a fan for example, or unshrouded as is the case of an open-rotor type architecture for example.

[0004] A propeller comprises blades which may have variable pitch. The turbomachine then comprises a mechanism for modifying the pitch angle of the blades in order to adapt the thrust generated by the propeller according to the different phases of flight.

[0005] The design of a propeller blade involves several disciplines whose objectives are generally conflicting. It must allow for optimal aerodynamic performance (i.e., provide thrust while maximizing efficiency), guarantee the blade's mechanical strength (i.e., withstand the mechanical stresses resulting from static and dynamic loads), while limiting mass and acoustic signature. In particular, improving the propeller's aerodynamic performance tends toward an increase in the BPR (Bypass Ratio), which translates into an increase in its external diameter and therefore the blade span. However, increasing the BPR goes hand in hand with reducing the FPF (Fan Pressure Ratio). Consequently, a pitch control system (variable-pitch blade) is generally required for the propeller to be operable throughout its entire flight envelope.

[0006] There are several technologies for attaching a variable pitch propeller blade and several technologies for controlling the angular pitch of such a propeller blade.

[0007] A propeller generally comprises a hub which carries blade retention systems and guides for the angular pitch of its blades. The hub has a generally annular or polygonal shape around a first axis which is the longitudinal axis of the turbomachine, and includes orifices distributed around this first axis in which the blade roots and the aforementioned systems are housed.

[0008] Each of these orifices has a substantially radial orientation with respect to the first axis and receives bearings for guiding the foot of a blade around a second radial axis with respect to the first axis, and which is a shimming axis for the corresponding blade.

[0009] Each propeller blade comprises a blade connected to a foot, the foot of each blade being mounted in one of the hub's bores and in the bearings of that bore, and being retained in that bore by a retaining system. Each foot is also associated with an eccentric that connects the blade to the mechanism for actuation of its angular pitch.

[0010] In current technology, the eccentric can be formed in one piece with the foot. However, this solution is not always feasible.

[0011] The hub openings intended to receive the blade feet are radially through-holes so as to allow the propeller and in particular the guide bearings to be mounted according to a particular kinematic.

[0012] According to this kinematic design, the foot of each blade is engaged in the corresponding opening of the hub by translation along the blade's mounting axis, radially from the outside to the inside relative to the first axis. The blade foot is then connected to the actuation mechanism located inside the hub.

[0013] Forming the eccentric in one piece with the foot of each blade can make this assembly impossible and is therefore not always feasible for this reason. Furthermore, forming the eccentric in one piece with the foot of each blade is not always possible, particularly when the distance between the pivot axis and the alignment axis is significant.

[0014] Another solution is to attach and fix the eccentric to the foot. In this case, the eccentric must be coupled to the foot by a linkage that transmits the rotational torque necessary for setting the blade.

[0015] In the current technique, this coupling is achieved by means of grooves, the eccentric comprising a first grooved portion engaged in a grooved portion of complementary shape to the foot. The grooves are engaged with one another and cooperate to transmit the aforementioned torque.

[0016] The eccentric comprises a second part which is connected to the first part and which defines a pivot axis parallel to and at a distance from the alignment axis. The actuation mechanism is articulated to this second part of the eccentric at this pivot axis, generally by a ball joint.

[0017] Forming the eccentric in one piece with the foot of each blade is not always feasible, particularly when the distance between the articulation axis and the alignment axis is significant.

[0018] The eccentric linkage solution has drawbacks. First, the splines are relatively long and are therefore relatively axially bulky. It is not always possible to incorporate them inside the foot, particularly because splines inside the foot do not always have a sufficient diameter to transmit the rotational torque. The solution is therefore to place them at one longitudinal end of the foot, but this solution tends to lengthen the foot, which can be problematic. Reducing the length of the splines must then be considered, but using shorter splines requires combining them with centering bearings on either side of the splines, between the eccentric and the foot, which tends to lengthen the coupling link.

[0019] The invention provides a solution to at least some of these problems, which is simple, effective and economical. Summary of the invention

[0020] The invention relates to a variable-pitch blade for an aircraft turbomachine, this blade comprising;

[0021] - a blade,

[0022] - a foot defining a support axis, and

[0023] - an eccentric attached and fixed to the foot, this eccentric comprising a first an annular part centered on the alignment axis and coupled to the foot, and a second part connected to the first part and defining an articulation axis which is at a distance from the alignment axis, the first and second parts being formed from a single piece,

[0024] characterized in that the first part of the eccentric is coupled to the foot by means of a curvic® coupling type connection, this connection being formed by a first annular row of teeth carried by the eccentric and a second annular row of teeth carried by the foot, the teeth of the first row being distributed around the alignment axis and oriented axially opposite the teeth of the second row so as to be able to be engaged axially between the teeth of the second row, the teeth of one of the rows having first lateral flanks for torque passage which are concavely curved, and the teeth of the other of the rows having second lateral flanks for torque passage which cooperate by bearing in a circumferential direction with the first lateral flanks and which are convexly curved.

[0025] The curvic® coupling type or "curvilinear radial teeth" linkage offers several advantages, including. - Precise centering of the first part of the eccentric with the base, - Maintenance of this centering despite differences in behavior and thermal expansion during operation, - Resistance to the effects of centrifugal forces through the locking of the teeth against each other, due to their complementary concave / convex shapes, - A relatively high torque transmission, - Small footprint, - Interchangeability, etc.

[0026] The blade according to the invention may comprise one or more of the following features the following, taken individually or in combination with each other: - the first row of teeth is located at one end of a cylindrical wall of the first part of the eccentric, - the blade also includes a nut screwed onto the foot and bearing axially on the eccentric to keep the eccentric axially tightened on the foot with respect to the alignment axis, - the first part of the eccentric includes a radially internal annular rim on which said nut bears axially, - said nut bears axially on an internal periphery of said annular rim. - said annular rim extends radially inwards from said cylindrical wall of the first part of the eccentric, - said annular rim includes a lateral annular face located on the side of said foot, which is situated in a plane perpendicular to the alignment axis that passes through a base of the teeth of the first row, - the second row of teeth is located at one end of a first cylindrical wall of the foot, - the foot comprises a second cylindrical wall surrounded by the first cylindrical wall and having a thread for screwing said nut, - the blade also includes a device for locking the nut against rotation relative to the foot around the alignment axis, - the foot includes annular bearing surfaces for mounting roller bearings and in that the second row of teeth is located at a longitudinal end of the foot which is axially offset from these surfaces.

[0027] The present invention also relates to a propeller for an aircraft turbomachine, comprising several blades as described above, a hub having mounting and rotational guidance holes for the feet of these blades, and a blade pitching actuation mechanism which is surrounded by the hub and is articulated to the second part of each of the eccentrics of these blades.

[0028] The present invention also relates to an aircraft turbomachine, comprising blades or a propeller as mentioned above. Brief description of the figures

[0029] Other features and advantages will become apparent from the following description of a non-limiting embodiment of the invention with reference to the accompanying drawings in which:

[0030] [Fig-1] [Fig.1] is a schematic axial cross-sectional view of a blade for a aircraft turbomachine,

[0031] [Fig.2] [Fig.2] is a larger-scale view of part of [Fig.1] and shows the foot of the blade mounted in an opening in a propeller hub,

[0032] [Fig.3] [Fig.3] is a view similar to that of [Fig.2] and shows a variant of realization,

[0033] [Fig.4] [Fig.4] is a schematic axial cross-sectional view of the foot of a blade according to the invention for an aircraft turbomachine,

[0034] [Fig.5] [Fig.5] is a larger scale view of part of [Fig.4],

[0035] [Fig.6] [Fig.6] is a very schematic view of a curvic®- type connection coupling,

[0036] [Fig. 7a-7b] Figures 7a and 7b are schematic perspective views of teeth of a curvic®-coupling bond, and

[0037] [Fig. 8a-8b] Figures 8a and 8b are schematic views of the tooth rows of a curvic®-coupling link and each show a machining path for the production of the flanks of these teeth. Detailed description of the invention

[0038] Fig. 1 shows a propeller 10 for an aircraft turbomachine, this propeller 10 being shrouded or unshrouded.

[0039] The propeller 10 comprises a hub 12 and blades 14 carried by this hub 12.

[0040] The hub 12 has a generally annular or polygonal shape and extends around a first axis not shown.

[0041] In [Fig.1], one of the blades 14 of the propeller 10 is visible and the hub 12 is seen in axial section, the cutting plane passing through the first axis of the hub 12.

[0042] The hub 12 has orifices 12a distributed around the first axis, each of these orifices 12a having a substantially radial orientation with respect to this first axis. Each orifice 12a passes radially through the hub 12, that is to say, each orifice 12a opens radially outwards and radially inwards respectively.

[0043] The blades 14 each comprise a blade 16 and a foot 18. The feet 18 of the blades 14 are respectively engaged in the orifices 12a of the hub 12.

[0044] The blade 16 has an aerodynamic profile and comprises an intrados 16a and an extrados (not visible) which are connected by a leading edge 16c and a trailing edge 16d, the terms upstream and downstream referring to the flow of gases around the blade 16 in operation.

[0045] The blade 16 has an upper end which is free, called the apex, and a lower end which is connected to the foot 18.

[0046] The blade 14 can be made of composite material using an injection molding process called RTM (Resin Transfer Molding). This process involves preparing a fibrous preform by three-dimensional weaving, then placing this preform in a mold and injecting a polymerizable resin, such as an epoxy resin, which will impregnate the preform. After polymerization and hardening of the blade 16, its leading edge 16c is generally reinforced by a metal shield 20 that is attached and fixed, for example, by bonding.

[0047] The shield 20 can be made of titanium or titanium alloy, stainless steel, steel, aluminum, nickel, etc. The intrados 16a or even the extrados of the blade 16 can be covered with a polyurethane film 22 for erosion protection.

[0048] A denotes the axis of extension of the blade 14 and the blade 16, and in particular the axis of adjustment of the blade 14, that is to say the axis around which the angular position of the blade 14 is adjusted. It is generally also a radial axis which therefore extends along a radius with respect to the first axis.

[0049] As can be seen more clearly in [Fig. 2], the foot 18 is hollow and includes an internal recess 18a in the example shown. The foot 18 has an elongated, tubular shape, its internal recess 18a being closed on the side of the blade 16 and open on the side opposite the blade 16.

[0050] The recess 18a of the foot 18 allows to reduce its mass, the shape and dimensions of the foot 18 being optimized to ensure good mechanical support of the blade 14 in operation.

[0051] The foot 18 has in its recess 18a internal grooves 24 which are configured to allow coupling of the foot 18 with a control system for the blade pitching around its pitching axis A (figures 2).

[0052] The grooves 24 extend around the axis A. In the example shown, they are located between two internal cylindrical surfaces 26a, 26b of the recess 18a, located respectively radially outside and inside the grooves 24 with respect to the first axis.

[0053] The foot 18 of the blade 14 further includes at its radially internal free end (opposite the first axis), an annular surface 26c which extends in a plane perpendicular to the axis A.

[0054] The foot 18 of the blade 14 includes one or more stops 28, 30. The stop or each stop 28, 30 has an annular shape and extends around the axis A and radially outwards with respect to this axis A.

[0055] In the example shown, the stop 28 is formed a projection at a radially external end of the foot 18 opposite the first axis, substantially at the level of the closed end of the recess 18a.

[0056] The stop 30 is formed a projection on a median part of the foot 18 opposite the first axis, located between the stop 28 and the free end of the foot 18.

[0057] The foot 18 of the blade 14 further includes an annular groove 32 which opens radially outwards and which is here formed in the vicinity of the free end of the foot 18.

[0058] Between the stop 28 and the groove 32, and more particularly between the stop 30 and the groove 32, the foot 18 comprises an external cylindrical surface 34a provided or not with an external thread.

[0059] The foot 18 of the blade 14 comprises several external cylindrical centering surfaces SI, S2 and S3 in the example shown. The surfaces SI, S2 and S3 have decreasing diameters D1, D2 and D3 and are distributed along the axis A, radially from the outside to the inside with respect to the first axis.

[0060] The SI surface of largest diameter Dl is located between the stops 28, 30.

[0061] The surface S2 of intermediate diameter D2 is located between the stop 30 and the surface 34a.

[0062] The surface S3 of smaller diameter D3 is located between the groove 32 and the free end of the foot 18, and more particularly between the groove 32 and another external thread 34b of the foot 18. The thread 34b has a diameter smaller than that of the surface 34a or of the thread provided on this surface.

[0063] The stop 28 is located at the radially external end of the surface SI with respect to the first axis. The stop 30 is located at the radially external end of the surface S2 with respect to the first axis.

[0064] The hub 12 may include annular fixing flanges 36 at each of its axial ends, as can be seen in [Fig.2].

[0065] In the example shown, each of the orifices 12a of the hub 12 includes stops 38, 40, 42, 44.

[0066] The stop or each stop 38, 40, 42, 44 has an annular shape and extends around the axis A and radially inwards with respect to this axis A.

[0067] The stops 38, 40, 42, 44 are respectively arranged one after the other along the alignment axis A. There is thus a radially external stop 38, a radially internal stop 44 and two intermediate stops 40, 42.

[0068] The stop 38 has a larger diameter than the stop 40, and the stop 44 has a larger diameter than the stop 42.

[0069] The intermediate stops 40, 42 allow to accommodate bearings 46, 48 of guide of the feet 18 of the blades 14.

[0070] The bearings 46, 48 are here two in number and are mounted in the opening 12a of the hub, arranged radially one outside the other. The bearing located radially on the outside is thus designated as the external bearing 46, and the bearing located radially on the inside as the internal bearing 48.

[0071] The bearings 46, 48 are mounted inside the orifice 12a bearing axially (opposite the axis A) on the intermediate stops 40, 42. The bearings 46, 48 are mounted around the foot 18, and in particular around the surfaces SI and S2, bearing axially (opposite the axis A) on the stops 28, 30.

[0072] An intermediate piece is provided between the bearing 48 and the blade root 18, and in particular between the inner ring of the bearing 48 and the surface S2. This is a press-fitted sleeve on the blade root 18, which allows for a harder material than that (for example, titanium) of the root 18 as the bearing surface. Indeed, the inner ring of the bearing 48 cannot have a significant shrink fit on its axis because it is displaced during preloading. Therefore, to avoid an A^fretting phenomenon (material tearing that would result in a fracture initiation on the blade root), this hard intermediate piece can be added.

[0073] The external bearing 46 is configured to be engaged in the orifice 12a from the outside of the hub 12, by moving it radially from the outside to the inside, until it comes to rest on the stop 40. The bearing 46 is here a ball bearing with angular contact and it is its outer ring that bears against the stop 40.

[0074] The internal bearing 48 is configured to be engaged in the orifice 12a from the inside of the hub, by moving it radially from the inside to the outside, until it comes to rest on the stop 42. The bearing 48 is here a ball bearing, and in particular a double row ball bearing, and with angular contact and it is its outer ring which bears on the stop 42.

[0075] As shown in the figure, the foot 18 of the blade 14 is configured to be engaged in the orifice 12a by translation along the axis A, radially from the outside to the inside with respect to the first axis, inside the bearings 46, 48, until the thrust bearing 28 bears axially (with respect to the axis A) on the bearing 46, and in particular its inner ring, and the thrust bearing 30 bears axially (with respect to the axis A) on the bearing 48, and in particular its inner ring. The bearings 46, 48, and in particular their inner rings, are then mounted on the surfaces S1 and S2.

[0076] It is therefore understood that the external bearing 46 has an internal diameter greater than the internal diameter of the internal bearing 48 to allow the mounting of the foot 18 in the orifice 12a, insofar as the bearings 46, 48 are mounted prior to the foot 18 in the example shown.

[0077] The stop 28 of the foot 18 can bear directly (along axis A) on the external bearing 46 and in particular its inner ring. In the example shown, the stop 28 is supported on the external bearing 46 by means of an external annular cover 50 which is mounted around the foot and which covers at least part of the external bearing 46.

[0078] This outer cover 50 has its inner periphery clamped between the stop 28 and the outer bearing 46, and in particular its inner ring. The outer periphery of the cover 50 bears in the direction of axis A on the hub 12 and in particular on the stop 38, either directly or via an annular seal 52 as illustrated in the drawing.

[0079] The stop 30 of the foot 18 can bear directly (along axis A) on the internal bearing 48 and in particular its inner ring. In the example shown, the stop 30 bears on the internal bearing 48 via an annular seal 54.

[0080] An internal annular cover 56 can also be mounted around the foot 18 and cover at least part of the internal bearing 48.

[0081] The inner cover 56 has its outer periphery bearing in the direction of axis A on the hub 12 and in particular on the thrust bearing 44, either directly or via an annular seal 58 as illustrated in the drawing. Alternatively, the outer periphery of the cover 56 could bear in this direction on the inner bearing 48, and in particular on the outer ring of this bearing.

[0082] The hood 56 has its inner periphery which is radially supported with respect to the axis A on the foot 18, in the vicinity of its free end, either directly or via an annular joint 60 as illustrated in the drawing.

[0083] In the example shown, the internal hood 56 includes at least two teeth oriented radially towards the axis A.

[0084] The inner cover 56 may further include an internal cylindrical centering surface 56a which is configured to cooperate with a complementary external cylindrical surface of the inner bearing 48, and for example, of the inner ring of this bearing. This surface 56a may be located on the inner periphery of an internal annular web of the cover 56. This web may include through ports 65 for the passage of fluid, and in particular, lubricating oil for the bearings 46, 48.

[0085] The foot 18 is retained in the orifice 12a of the hub 12 by a retention system which essentially comprises a ring 66 and a screw-nut assembly 68. It is this screw-nut assembly 68 which allows a preload to be applied to the foot of the blade.

[0086] The ring 66 is mounted around the foot 18 of the blade and extends around the axis A. The ring 66 is sectorized and therefore comprises ring sectors arranged circumferentially end to end around the axis A. The number of sectors is not limited and can be reduced to two. The ring 66 then comprises two half-rings.

[0087] Alternatively, the ring could be continuous and not segmented. It could then include a slot to allow elastic deformation of the ring by separating its longitudinal ends.

[0088] The ring 66 is configured to be engaged in the groove 32 of the foot 18. It is understood that it is the sectorization of the ring 66 which allows its mounting in the groove 32. The ring 66 comprises an inner periphery housed in the groove 32 and an outer periphery intended to remain outside the groove 32 to form an axial stop (with respect to the axis A).

[0089] The screw-nut assembly 68 comprises an internal screw 68a and an external nut 68b. The internal screw 68a has an external thread and may include an internal thread or, alternatively, an internal cylindrical surface. When the screw 68a has an internal cylindrical surface, the latter is intended to cooperate by sliding with the surface 34a of the foot during the mounting and positioning of the assembly 68 on the foot. When the screw 68a includes an internal thread, the foot includes a thread on its surface 34a, and the thread is used to screw the nut 68a onto the thread of the foot 18.

[0090] The external nut 68b has an internal thread for screwing onto the external thread of the internal screw 68a.

[0091] Positioning (by simple sliding or screwing / unscrewing) the internal screw 68a on the foot 18 allows it to be moved axially (relative to the axis A) on the foot 18 and positioned along the axis A. The screw 68a is able to bear against the ring 66 on the opposite side of the blade 16 in the direction of the axis A.

[0092] Screwing / unscrewing the external nut 68b allows it to be moved axially (with respect to the axis A) on the nut 68a and to be positioned along the axis A. The external nut 68b is able to bear in the direction of the axis A on the internal bearing 48, and in particular on its inner ring, on the side of the blade 16.

[0093] The double support of the screw-nut assembly 68, respectively on the ring 66 and the bearing 48, and the screwing of the external nut 68b onto the internal screw 68a, allows a certain preload to be applied to the foot 18 of the blade by the retaining system.

[0094] In the example shown in [Fig.2], the internal screw 68a includes an annular rim 70 which is located on the side opposite the blade 16 and which extends around the outer periphery of the ring 66 to prevent the ring 66 from accidentally coming out of the groove 32.

[0095] The screw 68a and the nut 68b each comprise a series of teeth oriented radially outwards with respect to the axis A and configured to cooperate with the teeth of the inner cover 56 in order to immobilize the assembly 68 in rotation around the axis A.

[0096] The series of teeth of the external nut 68b is located on the blade side

[0097] 16 and is configured to cooperate with the hood tooth 56. The series of teeth of the Internal screw 68a is located on the opposite side to blade 16 and is configured to cooperate with hood tooth 56.

[0098] In the example shown, the series of teeth of the internal screw 68a has an external diameter smaller than that of the series of teeth of the external nut 68b.

[0099] The propeller 10 further comprises a blade pitch control system 76, which is associated with the blade's foot 18. The propeller 10 therefore includes as many control systems 76 as there are blades 14 of this propeller.

[0100] Each control system 76 includes an eccentric 78, a first part of which is formed by a bushing 80 and is engaged by translation along the axis A inside the recess 18a of the foot 18, radially from the inside to the outside with respect to the axis A.

[0101] The sleeve 80 has external grooves 82 configured to be engaged in the internal grooves 24 of the foot 18.

[0102] The sleeve 80 further comprises external cylindrical centering surfaces 80a, 80b cooperating with the surfaces 26a, 26b of the recess 18a when the sleeve 80 is inserted into the recess 18a. These surfaces 80a, 80b are located on either side of the grooves 82 along the axis A.

[0103] In the example shown, the sleeve 80 also includes an external annular rim 84.

[0104] A nut 86 is screwed onto the thread 34b of the foot, at its free end, and includes an internal annular rim 86a which bears in the direction of the axis A on the external rim 84 of the sleeve 80, and in the direction of the blade 16 to retain the sleeve 80 in the recess 18a of the foot 18.

[0105] The nut 86 bears in the direction of axis A on the inner periphery of the inner cover 56, either directly or via an annular seal 88.

[0106] The nut 86 may include a series of teeth 90 extending radially outwards with respect to the axis A, to allow the nut 86 to be engaged with a tool for screwing and unscrewing the ring.

[0107] Fig. 2 illustrates a solution for coupling the eccentric 78 to the foot 18 of the blade 14, which consists of providing an internal coupling to the foot via the grooves 24, 82.

[0108] [Fig.3] illustrates another solution of the prior art for coupling the eccentric 78 to the foot 18 of the blade 14, which consists of providing a coupling by means of splines 24, 82 at a longitudinal end of the foot 18. Although the splines 24, 82 have a length L2 less than that L1 of [Fig.2], these splines are associated with cylindrical centering surfaces 80a, 80b which are arranged on either side of the splines 24, 82 and result in an extension of the total length L3 of the coupling between the eccentric 78 and the foot 18 of the blade.

[0109] Reference is now made to figures 4 and 5 which illustrate a blade 114, a propeller 10 and a turbomachine according to an embodiment of the invention.

[0110] The preceding description, made with reference to Figures 1 and 2, may also be considered as illustrating the context of the present invention insofar as it does not contradict or inconsistent with what follows. The references used in the foregoing are repeated in the following description to the extent that they designate identical or similar elements.

[0111] In general, the blade 114 according to the invention has variable pitch and comprises:

[0112] - a blade 16 (not visible in [Fig.4] but similar to that in [Fig.1]),

[0113] - a foot 18 defining a shimming axis A, and

[0114] - an eccentric 78 attached and fixed to the foot 18.

[0115] The eccentric 78 comprises a first annular part 78a centered on the alignment axis A and coupled to the foot 18, and a second part 78b connected to the first part 78a and defining an articulation axis B which is at a distance from the alignment axis A.

[0116] The articulation axis B can be parallel to the shimming axis A, as seen in [Fig.4], or inclined with respect to this axis, as is the case in [Fig.2].

[0117] The first and second parts 78a, 78b of the eccentric 78 are formed from a single piece as can be seen in [Fig.2].

[0118] According to the invention, the first part 78a of the eccentric 78 is coupled to the foot 18 via a curvic® coupling 100.

[0119] A link 100 of this type is formed by a first annular row of teeth 102 carried by the eccentric 78 and a second annular row of teeth 104 carried by the foot 18, these teeth 102, 104 being more clearly visible in figures 5 and following.

[0120] The teeth 102 of the first row are distributed around the alignment axis A and are axially oriented opposite the teeth 104 of the second row so as to be able to be axially engaged between the teeth 104 of the second row. The teeth 104 of the second row are therefore also distributed around the alignment axis A.

[0121] The distribution of the teeth 102, 104 around the axis A is preferably regular. The number of teeth 102, 104 per row may be greater than 30 or 50, for example.

[0122] The particularity of the teeth 102, 104 of a link 100 of this type is that the teeth of one of the rows have first lateral flanks 106a, 106b of torque passage which are concave curved (figures 7a and 8a), and that the teeth of the other of the rows have second lateral flanks 108a, 108b of torque passage which cooperate by support in circumferential direction with the first lateral flanks 106a, 106b and which are convex curved (figures 7b and 8b).

[0123] The flanks 106a, 106b are complementary to the flanks 108a, 108b.

[0124] It is therefore understood that, according to a first embodiment, the concave curved lateral flanks 106a, 106b can be located on the teeth 102 of the eccentric 78, and the convex curved lateral flanks 108a, 108b can be located on the teeth 104 of the foot 18.

[0125] Alternatively, the concave curved lateral flanks 106a, 106b can be located on the teeth 104 of the foot 18, and the convex curved lateral flanks 108a, 108b can be located on the teeth 102 of the eccentric 78.

[0126] Figures 8a and 8b show the machining paths of a milling cutter or grinding wheel for producing these curved flank shapes 106a, 106b, 108a, 108b. In Figure 8a, the path is curved and produces the concave curved flanks 106a, 106b of the teeth. The same path forms one flank of one tooth and also one flank of another tooth. In other words, the same path forms a flank on two teeth that are almost (but not exactly in the example shown) diametrically opposite. In Figure 8b, the path is curved and produces the convex curved flanks 108a, 108b of the teeth. The same path forms one flank of one tooth and also one flank of another tooth.In other words, the same trajectory allows the formation of a flank on two teeth that are almost (but not exactly in the example shown) diametrically opposed.

[0127] The first row of teeth 102 is preferably located at one end of a cylindrical wall 110 of the first part 78a of the eccentric 78 ([Fig.5]).

[0128] The eccentric 78 is preferably held fixedly on the foot 18 by a nut 86. The nut 86 is screwed onto the foot 18 and bears axially on the eccentric 78 to keep the eccentric 78 axially tightened on the foot 18 with respect to the alignment axis A.

[0129] The first part 78a of the eccentric 78 preferably comprises a radially internal annular rim 112 on which this nut 86 bears axially. As in the example shown, the nut 86 can bear axially on an internal periphery of the annular rim 112.

[0130] This annular rim 112 can extend radially inwards from the aforementioned cylindrical wall 110 of the first part 78a of the eccentric 78.

[0131] This annular rim 112 preferably includes a lateral annular face 112a located on the side of the foot 18, which is located in a plane PI perpendicular to the alignment axis A which passes through a base of the teeth 102 of the first row.

[0132] The second row of teeth 104 is preferably located at one end of a first cylindrical wall 116 of the foot 18.

[0133] The foot 18 preferably comprises a second cylindrical wall 118 surrounded by the first cylindrical wall 116 and having a thread 120 for screwing the nut 86.

[0134] A device 122 for locking the nut 86 against rotation vis-à-vis the foot 18 around the shim A is preferably further provided, in particular at the free end of the wall 118.

[0135] It can also be seen in the example shown in [Fig.4] that the foot 18 includes annular bearing surfaces or stops 40, 42 for mounting rolling bearings 48, 50. The second row of teeth 104 is advantageously located at a longitudinal end of the foot 18 which is axially separated from these bearing surfaces or stops 40, 42.

[0136] In general, the curvic® coupling is considered to have both a high power transmission capacity and to ensure good alignment accuracy between components. This coupling is considered self-centering due to the shape of the opposing concave and convex complementary teeth.

Claims

Demands

1. Variable pitch blade (114) for an aircraft turbomachine, this blade (114) comprising; - a blade (16), - a foot (18) defining a shimming axis (A), and - an eccentric (78) attached to and fixed to the foot (18), this eccentric (78) comprising a first annular part (78a) centered on the shimming axis (A) and coupled to the foot (18) and a second part (78b) connected to the first part (78a) and defining a pivot axis (B) which is at a distance from the shimming axis (A), the first and second parts (78a, 78b) being formed of a single piece, characterized in that the first part (78a) of the eccentric (78) is coupled to the foot (18) by means of a curvic® coupling type linkage (100), this linkage (100) being formed by a first annular row of teeth (102) carried by the eccentric (78) and a second annular row of teeth (104) carried by the foot (18),the teeth (102) of the first row being distributed around the alignment axis (A) and oriented axially opposite the teeth (104) of the second row so as to be able to be engaged axially between the teeth (104) of the second row, the teeth (102, 104) of one of the rows having first lateral flanks (106a, 106b) for torque transmission which are concavely curved, and the teeth (104, 102) of the other row having second lateral flanks (108a, 108b) for torque transmission which cooperate by bearing in a circumferential direction with the first lateral flanks (106a, 106b) and which are convexly curved.

2. Blade (114) according to the preceding claim, wherein the first row of teeth (102) is located at one end of a cylindrical wall (110) of the first part (78a) of the eccentric (78).

3. Blade (114) according to any one of the preceding claims, further comprising a nut (86) screwed onto the foot (18) and bearing axially on the eccentric (78) to keep the eccentric (78) axially tightened on the foot (18) with respect to the shim (A).

4. Blade (114) according to claim 3, wherein the first part (78a) of the eccentric (78) comprises a radially internal annular rim (112) on which said nut (86) bears axially.

5. Blade (114) according to claim 4, wherein said nut (86) bears axially on an internal periphery of said annular rim (112).

6. Blade (114) according to claim 4 or 5, depending on claims 2 and 3, wherein said annular rim (112) extends radially inwards from said cylindrical wall (110) of the first part (78a) of the eccentric (78).

7. Blade (114) according to any one of claims 4 to 6, wherein said annular rim (112) comprises a lateral annular face (112a) located on the side of said foot (18), which is situated in a plane (PI) perpendicular to the alignment axis (A) which passes through a base of the teeth (102) of the first row.

8. Blade (114) according to any one of the preceding claims, wherein the second row of teeth (104) is located at one end of a first cylindrical wall (116) of the foot (18).

9. Blade (114) according to claim 8, depending on any one of claims 3 to 7, wherein the foot (18) comprises a second cylindrical wall (118) surrounded by the first cylindrical wall (116) and having a thread (120) for screwing said nut (86).

10. Blade (114) according to any one of claims 3 to 7 and 9, further includes a device (122) for locking the nut (86) against rotation vis-à-vis the foot (18) around the shim (A).

11. Blade (114) according to any one of the preceding claims, wherein the foot (18) comprises annular bearing surfaces for rolling bearings (48, 50) and in that the second row of teeth (104) is located at a longitudinal end of the foot (18) which is axially offset from these surfaces.

12. Propeller (10) for an aircraft turbomachine, comprising several blades (114) according to any one of the preceding claims, a hub (12) comprising mounting and rotational guidance ports (12a) for the feet (18) of these blades (114), and a blade pitch actuating mechanism which is surrounded by the hub (12) and which is articulated to the second part (78b) of each of the eccentrics (78) of these blades (114).

13. Aircraft turbomachine, comprising blades (114) according to any one of claims 1 to 11 or a propeller (10) according to claim 12.

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