Improved coupling system for coupling two aircraft turbine engine parts, preferably two turbine engine shafts

Abstract

The invention relates to a coupling system (20) for coupling two aircraft turbine engine parts, the system comprising a clamping nut (32), the first part comprising an end provided with a first number N1 of first axial slots (44a), and the coupling system comprising a locking member (50) fitted with retaining tabs and a coupling tab (62) which are accommodated in first slots (44a). The system comprises a second number N2 of first, male radial splines (54a), and an anti-rotation ring (38) comprising: an inner surface provided with second, female radial splines (52b) engaged with the first splines (54a), and a third number N3 of second axial slots (44b) provided on the anti-rotation ring (38), and non-uniformly distributed around the axis of the system.

Description

[0001] DESCRIPTION

[0002] TITLE: IMPROVED COUPLING SYSTEM FOR TWO AIRCRAFT TURBOMACHINE COMPONENTS, PREFERABLY TWO TURBOMACHINE SHAFTS

[0003] TECHNICAL FIELD

[0004] The invention relates to the field of coupling systems for two parts of an aircraft turbomachine, such as for example a turbojet or a turboprop.

[0005] Preferably, the invention relates to a coupling system for two shafts of an aircraft turbomachine, for example, a compressor shaft and a turbine shaft, but it is not limited to this preferred application. The coupling system can nevertheless be applied to any assembly of two aircraft turbomachine components, including one shaft, two shafts, or even two components other than shafts, such as flanges, discs, or any rotor component.

[0006] Another application of the invention lies, for example, in the coupling of a bearing onto a turbomachine shaft.

[0007] PREVIOUS STATE OF THE ART

[0008] Aircraft turbomachinery component coupling systems have been extensively developed in the prior art.

[0009] In some turbomachine designs, such a coupling system may include a nut for tightening the two parts. The nut is then provided with a thread that meshes with another thread on one of the parts to be coupled. The coupling system also includes an anti-rotation ring that works with the nut; this ring is designed to limit or prevent the nut's rotation relative to the aforementioned part.

[0010] The assembly process for such a system generally requires tightening the nut to a minimum torque to achieve the coupling between the two parts. Then, the nut is tightened further, a process known as over-tightening, solely to align the various mechanisms that enable the nut's anti-rotation function.

[0011] Typically, the means enabling the anti-rotation function include axial notches on the shaft, implying significant over-torques to be applied during assembly.

[0012] Previous designs of this type can prove problematic because the excessive torque applied to the nut introduces undesirable mechanical stresses within the assembly. Oversizing may then be required to withstand such stresses, impacting both mass and cost. Furthermore, to mitigate these stresses, it is possible to reduce the pitch of anti-rotation features, such as the aforementioned axial notches, but this strategy inevitably leads to increased manufacturing costs.

[0013] It should also be noted that the designs proposed above require tightening the nut in several stages, which introduces a potential source of error and risks of costly assembly non-conformities. Furthermore, applying over-torque can lead to excessive tightening, potentially complicating the loosening operation and increasing the risk of damage to the components. Additionally, alignment verification can be complicated by limited accessibility, sometimes requiring the removal and reinstallation of the clamping device, which is a significant feature of this type of nut.

[0014] Therefore, there remains a need to improve the design of prior art coupling systems.

[0015] DESCRIPTION OF THE INVENTION

[0016] To meet the need mentioned above, the invention first relates to a coupling system for two parts of an aircraft turbomachine, comprising a nut for clamping the two parts against each other, the nut being provided with an internal nut thread intended to cooperate with a thread of the first part made on one of the two parts, the first part comprising a coupling end provided with a first number NI of first axial notches distributed uniformly around a longitudinal central axis of the coupling system, the latter also comprising a locking member intended to limit / prevent the rotation of the nut relative to the first part, the locking member being equipped with one or more retaining tabs each housed in one of the first axial notches of the first part, as well as a coupling tab housed in another of said first axial notches.

[0017] According to the invention, the coupling system further comprises a second number N2 of first radial male splines distributed uniformly around the longitudinal central axis, on an external surface of the nut, as well as an anti-rotation ring comprising:

[0018] - an internal surface provided with second radial female grooves distributed uniformly around the central longitudinal axis, the second radial female grooves being engaged with the first radial male grooves and provided in the same second number N2;

[0019] - a third number N3 of second axial notches provided at one end of the anti-rotation ring, the second axial notches being non-uniformly distributed around the longitudinal central axis, such that the second axial notches and some of the second female radial grooves form pairs in each of which an angular offset, between the second axial notch and the second female radial groove of the pair, is different, the coupling leg of the locking member also being housed in one of the second axial notches of the anti-rotation ring.

[0020] Thus, the invention offers the advantage of eliminating the need to apply excessive torque to the nut to lock it against rotation, or of significantly reducing this excess torque. Consequently, the parts remain subjected to lower stresses, reduced by approximately 5 to 12%, and this advantage translates into gains in weight and cost. Generally speaking, since the nut can be tightened in a single step, without overtightening or with significantly reduced overtightening, all the drawbacks mentioned above, related to implementing a multi-step nut tightening process, are advantageously eliminated or greatly mitigated.

[0021] Furthermore, the invention is based on a simple and reliable design, allowing for easy coupling. Indeed, after tightening the nut to the required torque, the anti-rotation ring can easily be engaged around the nut in a position that aligns a first axial notch on the first component with a second axial notch on the anti-rotation ring. Thanks to the variation in angular offset within the different aforementioned pairs, between the second axial notch and the second radial female spline of each pair, no over-tightening of the nut is normally required, or it remains extremely minimal.In this regard, according to a preferred embodiment of the invention, the numbers NI, N2 and N3, as well as the angular offsets within the various aforementioned pairs, ensure a correspondence between a first axial notch of the first part and a second axial notch of this anti-rotation ring, without requiring over-tightening of the nut, whether during the initial tightening phase of the nut, or after the assembly of the anti-rotation ring.

[0022] Next, the locking mechanism can be inserted onto the clamped assembly, so that its locking tab fits into the two aforementioned notches, in correspondence.

[0023] Finally, thanks to the presence of the first grooves on the nut's outer surface, tightening is easier because they provide a good grip with the tightening tool. The time and costs required for rotational coupling are significantly reduced.

[0024] It is noted that all the elements mentioned below are preferably centered on the longitudinal central axis of the coupling system of the two aircraft turbomachine parts, namely the clamping nut, the nut's internal thread, the thread of the first part, the coupling end of the first part, the locking member, the anti-rotation ring, and the end of the anti-rotation ring. The same is preferably true for the additional features defined below. The invention preferably includes at least one of the following optional features, taken individually or in combination.

[0025] Preferably, the first, second and third numbers N2 and N3 satisfy formula (a) below:

[0026] (

[0027] 1 a) - — < 0.1 ' PPCM (N1,N2)*N3

[0028] Even more preferably, the value of 0.1 in formula (a) above can be lowered to 0.07.

[0029] Preferably, the angular offset between the second axial notch and the second female radial spline of each of said pairs is less than or equal to a maximum value DAmax of angular offset, corresponding to formula (b) below: / il — . 360

[0030] (

[0031] 1 b) DAmax = - - - - ' PPCM (N1,N2)

[0032] Preferably, these pairs have angular offsets satisfying formula (c) below:

[0033] , . „ . . DAmax * i

[0034] 1 c DAci = - ' N3 with i corresponding to an integer from 1 to N3.

[0035] Preferably, the coupling leg extends radially, over a radial length greater than that of the retaining legs of the locking member.

[0036] Preferably, the first number NI of the first axial notches is eight, the second number N2 of the first male radial splines is thirty-seven, and the third number N3 of the second axial notches is eighteen. Other numbers could, however, be used, without departing from the scope of the invention, and preferably satisfying all or part of the formulas indicated above.

[0037] Preferably, the circumferential width of the second axial notches of the anti-rotation ring should be greater than the circumferential width of the first axial notches on the first part. An inverse solution can nevertheless be adopted, but it is more practical to use a slightly wider notch on the larger diameter part, particularly to facilitate manufacturing.

[0038] The invention also relates to an assembly for an aircraft turbomachine comprising two parts, as well as such a system coupling the two parts, which are preferably two turbomachine shafts, for example a low-pressure turbine shaft and a low-pressure compressor shaft.

[0039] The invention also relates to an aircraft turbomachine comprising at least one such assembly.

[0040] Finally, the invention relates to a method for mounting a coupling system on two aircraft turbomachine parts to be coupled, comprising the following steps:

[0041] - tightening the nut on the first part, via the threads of the nut and the first part, so as to axially press the first part against the second part;

[0042] - mounting the anti-rotation ring around the nut;

[0043] - assembly of the locking device so as to house each retaining lug in one of the first axial notches of the first part, and so as to house the coupling lug in another of the said first axial notches, as well as in one of the second axial notches of the anti-rotation ring which is corresponding.

[0044] Other advantages and features of the invention will appear in the detailed, non-limiting description below.

[0045] BRIEF DESCRIPTION OF THE DRAWINGS

[0046] [Fig. 1] is a longitudinal cross-sectional view of a turbojet engine;

[0047] [Fig. 2] is a longitudinal half-sectional view of a coupling system for two parts of the turbojet engine shown in the previous figure, the system being in the form of a preferred embodiment of the invention;

[0048] [Fig. 3] is a perspective view of the coupling system shown in Figure 2;

[0049] [Fig. 4] is a partial perspective view of part of the coupling system shown in Figures 2 and 3, which shows in particular the alignment of the notches of the anti-rotation ring and the part to be coupled, with the anti-rotation coupling lug which passes through these two aligned notches;

[0050] [Fig. 5] is a front view of the coupling system shown in figures 2 to 4;

[0051] [Fig. 6] is a perspective view of a clamping nut belonging to the coupling system shown in Figures 2 to 4; [Fig. 7] is a perspective view of an anti-rotation ring belonging to the coupling system shown in Figures 2 to 4;

[0052] [Fig. 8] is a front view of the anti-rotation ring shown in the previous figure;

[0053] [Fig. 9] is a partial, enlarged view of part of the anti-rotation ring shown in Figures 7 and 8; and

[0054] [Fig. 10] is a flowchart showing the different steps of a method for assembling the coupling system shown in the previous figures, according to a preferred embodiment of the invention.

[0055] DETAILED DESCRIPTION OF THE INVENTION

[0056] With reference first to Figure 1, an aircraft turbomachine 1 is shown, according to a preferred embodiment of the invention. This is a twin-spool, turbofan engine. However, it could be a turbomachine of another type, for example a turboprop, without departing from the scope of the invention.

[0057] The turbojet 1 has an X-axis around which its various components extend; this X-axis is called the longitudinal axis of the turbojet. It comprises, from upstream to downstream along a principal direction 5 of gas flow through this turbojet, a fan 3, a low-pressure compressor 4, a high-pressure compressor 6, a combustion chamber 11, a high-pressure turbine 7, and a low-pressure turbine 8.

[0058] Conventionally, after passing through the blower, the air splits into a central primary flow 12a and a secondary flow 12b that surrounds the primary flow. The primary flow 12a flows into a main gas circulation channel 14a, passing through the compressors 4, 6, the combustion chamber 11, and the turbines 7, 8. The secondary flow 12b flows into a secondary channel 14b, radially delimited outwards by an engine casing, surrounded by a nacelle 9.

[0059] Figures 2 to 9 depict a coupling system 20 for two rotating parts of the turbojet engine 1, sharing the same axis of rotation X. This system consists of a first shaft 22 corresponding to a low-pressure turbine shaft, and a second shaft 24 corresponding to a low-pressure compressor shaft. Both shafts 22 and 24 are hollow, and the upstream end of the first shaft 22 fits into the downstream end of the second shaft 24, thus being coupled in translation along the axial direction via the system 20. The two shafts 22 and 24, concentric and centered on the X axis, together with their coupling system 20, form an assembly 30. Several assemblies of this type can be provided within the turbojet engine, with the coupled parts potentially belonging to various turbojet engine modules, including the fan, compressors, combustion chamber, or turbines.

[0060] It is noted that the coupling of the two parts is achieved by tightening the nut, which will be described below, and which allows the two parts to be axially clamped against each other. Preferably, this is a translational coupling of the two parts, but rotational coupling is also possible. For rotational coupling of the two parts, system 20 can be supplemented by a conventional splined system fitted to these two parts, in the form of two annular rows of splines cooperating with each other. As this splined system is conventional, it will not be described further.

[0061] The coupling of parts with large diameters is preferred here. This is particularly the case for the architecture partially shown in Figure 2, which depicts the coupling system 20 in its assembled state, in which the two shafts 22, 24 are coupled, arranged axially one in line with the other, while also being able to overlap radially at their junction ends, as indicated above. This is preferentially the case regardless of the nature of the two parts 22, 24 considered.

[0062] The coupling system 20 comprises, firstly, a clamping nut 32 for the two shafts, this nut being centered on the X-axis and having internally a first thread 34a, or nut thread, cooperating with a second thread 34b, or first part thread, formed on an external surface of the first shaft 22, at its upstream end. As can be seen in particular in Figure 2, in the assembled state of the coupling system 20, the downstream end of the nut 32 exerts an axial force on the second shaft 24, and more precisely on an internal shoulder 25 of the latter. This axial force pushes the second shaft 24 downstream against an external shoulder 23 of the first shaft 22, with an axial shim 36 possibly interposed between the two shoulders, as shown schematically by way of example in Figure 2. The axial tightening force of the nut 32 is sufficient to generate the desired coupling between the two shafts 22, 24.Moreover, preferably, once the tightening has been carried out with the desired torque, no further over-tightening is carried out on nut 32.

[0063] The first shaft 22 has, upstream of its thread 34b, a coupling end corresponding to the upstream end of this shaft 22. This coupling end is provided with a number NI of first axial notches 44a, distributed uniformly around the X-axis, which also corresponds to a longitudinal central axis of the coupling system 20. These first axial notches 44a are circumferentially spaced from each other by first axial protrusions extending upstream, referenced 46a. It is these protrusions 46a that circumferentially define the first axial notches 44a, the number NI of which is, for example, eight in the preferred embodiment described.

[0064] As shown in Figure 2, the downstream axial bottom of the first notches 44a receives a hollow ventilation tube 37, which then runs downstream inside the first shaft 22. The upstream connecting part of this tube 37 is effectively axially clamped between the bottom of the first notches 44a, and a locking member 50 forming part of the locking system 20, which will be described later.

[0065] The system 20 also includes a second number N2 of first radial male splines 54a, distributed uniformly around the X-axis on an external surface of the nut 32. The first radial male splines 54a alternate with first radial female splines 52a, defined circumferentially between the first radial male splines 54a. The number N2 of the first radial male splines 54a is, for example, thirty-seven, and therefore also corresponds to the number of first radial female splines 52a. The first radial male splines 54a extend radially in height with respect to the X-axis, and in length along this same X-axis direction. They prove beneficial for tightening the nut 32, since they facilitate gripping the nut with a tightening tool.However, the main function of the first male radial splines 54a is to engage in second female radial splines 52b, belonging to an anti-rotation ring 38 of the coupling system.

[0066] Indeed, the anti-rotation ring 38 is centered on the X-axis and arranged radially around the nut 32 between the two shafts 22 and 24. Thus, the radially internal surface of the anti-rotation ring 38 is provided with N2 female radial second splines 52b, distributed uniformly around the X-axis. These female radial second splines 52b alternate with male radial second splines 54b, circumferentially defining the female radial second splines 52b. The number N2 of male radial second splines 54b is therefore, for example, thirty-seven, and it also corresponds to the number of female radial second splines 52b. In the assembled state of the coupling system 20, the first radial splines 52a, 54a are engaged with the second radial splines 52b, 54b, as can be seen for example in figure 4.This engagement provides a direct rotational coupling between the nut 32 and the anti-rotation ring 38.

[0067] The anti-rotation ring 38 is also equipped, upstream of its second radial splines 52b, 54b and at one upstream coupling end, with a third set N3 of second axial notches 44b. As will be detailed below, the second axial notches 44b are distributed non-uniformly around the X-axis, i.e., irregularly. They are circumferentially spaced from each other by second axial protrusions extending upstream, referenced 46b. These protrusions 46b circumferentially define the second axial notches 44b. Their number N3 is, for example, eighteen here.

[0068] Thus, for example, the number N3 is strictly less than the second number N2, and strictly greater than the first number NI. However, other conceptions remain possible, such as making the number N3 higher, for example greater than or equal to the number N2.

[0069] More generally, the aforementioned integers NI, N2 and N3 are preferentially chosen to satisfy the following formula:

[0070] (

[0071] 1 a) - — < 0.1 ' LCM (N1,N2)*N3 ' Even more preferably, these three numbers N1, N2, N3 satisfy the following formula: 0.07

[0072] In these formulas, the notation "LCM(NI, N2)" corresponds to the least common multiple of the numbers NI and N2. Thus, the expression "(360 / LCM(NI, N2)) / N3" expresses the maximum value of the smallest angular offset, in degrees (°), between a first axial notch 44a and a second axial notch 44b, after mounting the anti-rotation ring 38 around the nut 32, in a manner that will be detailed later. This angular offset is therefore less than or equal to 0.1°, and even more preferably less than or equal to 0.07°, which indicates a perfect or nearly perfect angular correspondence between these two notches 44a and 44b.

[0073] Furthermore, the irregular distribution of the second axial notches 44b is such that, within the anti-rotation ring 38, these second axial notches 44b and some of the second female radial splines 52b form pairs. Within each of these pairs, there is a different angular offset between the second axial notch 44b and the second female radial spline 52b of the pair.

[0074] Therefore, a number N3 of these pairs, called "ci", are defined and are circumferentially spaced apart. Within each of these pairs ci, an angular offset DAci is provided between the second axial notch 44b and the second radial female spline 52b of the pair. These offsets are preferably very small, and each is preferably less than or equal to a maximum value DAmax of angular offset, preferably corresponding to the formula below:

[0075] ,. . _ 360

[0076] (

[0077] 1 b) DAmax = - - - ? ' PPCM (N1,N2)

[0078] Even more preferably, the pairs shown here exhibit angular shifts satisfying the formula below:

[0079] DAmax * i

[0080] (c) DAci = — — — , with i corresponding to an integer from 1 to N3.

[0081] Thus, in the preferred embodiment which is described, taking into account the aforementioned NI, N2 and N3 values, the values ​​of the angular offsets DAci for each of the eighteen pairs ci are given in the table below (in degrees).

[0082] As can be seen in the figures, each angular offset DAci is small, even extremely small, compared to the circumferential width of the second axial notches 44b and the second radial female splines 52b. The angular offset between these two elements 44b, 52b corresponds to the angle between their radially extending centerlines, as shown schematically in Figure 9.

[0083] Thanks to this additional degree of freedom in the adjustment of the elements to be coupled, and as mentioned previously, it is easily possible to match, in the circumferential / angular direction, one of the first axial notches 44a with one of the second axial notches 44b.

[0084] This allows the mounting of the locking member 50, which is designed to limit / prevent the rotation of the nut 32 relative to the first shaft 22, via the anti-rotation ring 38. The locking member 50 is equipped with one or more retaining tabs 60, spaced circumferentially from each other and projecting radially outwards from a ring 61 of this member 50, preferably centered on the X-axis. In the mounted position of the system 20, each of the retaining tabs 60 is axially housed in one of the first axial notches 44a of the first shaft 22. Here, therefore, three retaining tabs 60 are respectively housed in three different first notches 44a, as is most clearly visible in Figures 3 and 5.

[0085] Furthermore, the locking member 50 includes a coupling lug 62 which also extends radially outwards from the ring 61, but over a greater radial length than the retaining lugs 60. This coupling lug 62 is initially housed axially in one of the first axial notches 44a, which it passes radially through. It then continues to extend radially outwards to be housed axially in one of the second axial notches 44b, which is located in the circumferential / angular direction relative to the X-axis.

[0086] This alignment of the two axial notches 44a, 44b can be achieved by precisely matching the angles of these two notches. However, a very slight offset of these two second axial notches 44a, 44b is acceptable, provided it allows the axial insertion of the coupling lug 62 into each of them. In this regard, it should be noted that to facilitate this insertion, the circumferential width of the second axial notches 44b of the anti-rotation ring 38 can be slightly greater than the circumferential width of the first axial notches 44a of the first shaft 22. In such a case, the difference in circumferential widths, corresponding to a difference in the angular extents of these second axial notches 44a, 44b, remains extremely small, for example, less than or equal to 0.1°, or even less than or equal to 0.07°.

[0087] The coupling system 20 is completed by a retaining member 64 that moves in the direction of the locking member 50, in order to prevent its axial extraction upstream. This retaining member 64, shown in Figure 2, can be a circlip or a retaining ring, arranged internally in a groove 66 in the coupling end of the first shaft 22. The coupling between the two parts

[0088] Figure 10 schematically illustrates different stages of a preferred method for mounting the coupling system 20. First, in a first stage 11, the nut 32 is tightened onto the first shaft 22 via the threads 34a, 34b. This tightening preferably corresponds to a single, final tightening of the nut, and it serves to axially clamp the first shaft 22 against the second shaft 24 by applying a predefined tightening torque. Applying an over-torque is advantageously not required.

[0089] Next, the second step E2 involves mounting the anti-rotation ring 38 around the nut 32. Thanks to the splines 52a, 54a, 52b, and 54b, the angular positioning of the anti-rotation ring 38 on the nut 32 is possible in multiple ways. However, the positioning adopted is that which results in the aforementioned correspondence between the axial notches 44a and 44b. To achieve this, the first radial male spline 54a of the nut 32 is identified as having the smallest angular offset with one of the first axial notches 44a of the shaft 22, after tightening this nut 32. This first radial male spline 54a is called the reference spline, while the smallest angular offset is also called the reference angular offset. This reference angular offset will therefore be less than the maximum angular offset given by the same formula as formula (b) mentioned above: ... 360

[0090] (

[0091] 1b) DAmax = - - - - ' PPCM (N1,N2)

[0092] Thus, in the preferred embodiment, regardless of the tightening performed on the nut 32, the reference angular offset between the first male radial spline 54a of reference, and its corresponding first axial notch 44a on the shaft 22, is necessarily less than or equal to the DAmax value of 1.216°.

[0093] Next, it is simply a matter of identifying, among the eighteen aforementioned pairs of the anti-rotation ring 38, the one that has an angular offset DAci of the same value as, or as close as possible to, that of the reference angular offset. Once the pair is identified, the anti-rotation ring 38 is inserted axially around the nut 32, engaging the first male radial spline 54a of the nut with the second female spline 52b of the pair identified on the ring 38.

[0094] This allows for compensation between the two angular offsets, in order to obtain the desired correspondence between the first axial notch 44a associated with the first reference male radial spline 54a, and the second axial notch 44b of the identified pair. To obtain such compensation, which is preferably total or almost total, it is necessary, for example, to consider that the reference angular offset is observed in the direction from the first axial notch 44a towards the first reference male radial spline 54a, while the angular offset DAci within each pair ci is observed in the opposite direction, from the second female radial spline 52b, towards the second axial notch 44b of that pair.

[0095] The design of the invention thus advantageously provides for a number N3 of values ​​for compensating the reference angular offset after tightening the nut 32. Consequently, for the two corresponding axial notches 44a and 44b, the maximum angle of angular offset observed between these two notches is 0.068°, corresponding to the DAmax value of 1.216° divided by the N3 value of eighteen. This angle remains extremely small and is not such as to compromise the axial insertion of the coupling lug 62, especially since, as previously indicated, the circumferential width of the second axial notches 44b is slightly greater than that of the first notches 44a.

[0096] The third step E3 of the method consists of mounting the locking member 50 so as to insert each of the three retaining tabs 60 into the first three axial notches 44a of the first shaft 22. This insertion, achieved by an axial displacement of the locking member 50, is carried out in such a way as to simultaneously house the coupling tab 62 in another of the first axial notches 44a, as well as in the second axial notch 44b, which is circumferentially / angularly aligned. Finally, the last step E4 of the method consists of placing the stop member 64 on the coupling end of the first shaft 22, in order to axially lock the locking member 50.

[0097] Of course, various modifications can be made by a person skilled in the art to the invention just described, only by way of non-limiting examples, and the scope of which is defined by the attached claims.

Claims

DEMANDS 1. A coupling system (20) for two aircraft turbomachine parts (22, 24), comprising a nut (32) for clamping the two parts (22, 24) against each other, the nut (32) having an internal nut thread (34a) for cooperating with a thread in the first part (34b) formed on a first (22) of the two parts (22, 24), the first part comprising a coupling end having a first number NI of first axial notches (44a) distributed uniformly around a longitudinal central axis (X) of the coupling system, the latter also comprising a locking member (50) for limiting / preventing rotation of the nut (32) relative to the first part (22), the locking member (50) being equipped with one or more retaining lugs (60), each housed in one of the first axial notches (44a) of the first part (22), as well as a coupling lug (62) housed in another of the said first axial notches (44a),characterized in that it further comprises a second number N2 of first radial male splines (54a) distributed uniformly around the central longitudinal axis (X), on an external surface of the nut (32), as well as an anti-rotation ring (38) comprising:, - an internal surface provided with second female radial grooves (52b) distributed uniformly around the central longitudinal axis (X), the second female radial grooves (52b) being engaged with the first male radial grooves (54a) and provided in the same second number N2; - a third number N3 of second axial notches (44b) provided at one end of the anti-rotation ring (38), the second axial notches (44b) being non-uniformly distributed around the longitudinal central axis (X), such that the second axial notches (44b) and some of the second female radial splines (52b) form pairs (ci) in each of which an angular offset (DAci), between the second axial notch (44b) and the second female radial spline of the pair (52b), is different, and in that the coupling lug (62) of the locking member (50) is also housed in one of the second axial notches (44b) of the anti-rotation ring (38).

2. Coupling system according to claim 1, characterized in that the first, second and third numbers NI, N2 and N3 satisfy formula (a) below: 0.1 3. Coupling system according to claim 1 or 2, characterized in that the angular offset (DAci) between the second axial notch (44b) and the second female radial spline (52b) of each of said pairs (ci) is less than or equal to a maximum value DAmax of angular offset, corresponding to formula (b) below: . . _ A 360 ( 1 b) DAmax = - - - ? ' PPCM (N1,N2) 4. Coupling system according to claim 3, characterized in that said couples (ci) respectively have angular offsets (DAci) satisfying formula (c) below: , > ~ . DAmax * i 1 c DAci = - ' N3 with i corresponding to an integer from 1 to N3.

5. Coupling system according to any one of the preceding claims, characterized in that the coupling lug (62) extends radially, over a radial length greater than that of the retaining lugs (60) of the locking member (50).

6. Coupling system according to any one of the preceding claims, characterized in that a circumferential width of the second axial notches (44b) of the anti-rotation ring (38) is greater than a circumferential width of the first axial notches (44a) on the first part (22).

7. Assembly (30) for aircraft turbomachine comprising two parts (22, 24), as well as a system (20) according to any one of the preceding claims, coupling the two parts (22, 24) which are preferably two turbomachine shafts.

8. Aircraft turbomachine (1) comprising at least one assembly (30) according to claim 7.

9. Method of mounting a coupling system (20) according to any one of claims 1 to 6, on two aircraft turbomachine parts (22, 24) to be coupled, comprising the following steps: - realization (El) of tightening the nut (32) on the first part (22), via the threads of the nut and of the first part (34a, 34b), so as to axially press the first part (22) against the second part (24); - mounting (E2) of the anti-rotation ring (38) around the nut (32); - assembly (E3) of the locking member (50) so as to house each retaining lug (60) in one of the first axial notches (44a) of the first part (22), and so as to house the coupling lug (62) in another of the said first axial notches (44a), as well as in one of the second axial notches (44b) of the anti-rotation ring being in correspondence.

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