Patent ID: 12247574

DETAILED DESCRIPTION OF THE INVENTION

Reference is first made toFIG.1, which shows a first monobloc flexible cage technology10according to the prior art.

The flexible cage10ensures the connection of an outer ring12of a rolling bearing14to an annular support16of this bearing14.

In addition to the outer ring12, the bearing14comprises an inner ring18which is secured to a shaft of the turbine engine, which is not shown. The rings12,18define a roller raceway in the example shown.

The outer ring12is integrated into an inner cylindrical wall10aof the cage10, which comprises a radially outer annular flange10bfor attaching to the support16by screw-nut type means (not shown).

The cage10comprises two series of studs20,22, radially internal and external respectively in relation to the axis X of the bearing14and of the shaft it guides.

The studs20,22are distributed around the axis X and extend parallel to this axis. The studs20extend around the studs22and have a first of their longitudinal ends which is connected to the flange10b, and a second of their longitudinal ends which is connected to the other studs22by an annular segment24with a C-shaped cross-section of the cage10. The studs22extend from the wall10a, in line with it, to this segment24.

The support16forms part of a stator of the turbine engine and here has a substantially frustoconical general shape. At its inner periphery, it comprises an inner cylindrical surface16afor shrink-fitting an annulus26which extends around the wall10aof the cage and which defines with the latter an annular space28supplied with oil in order to form an oil film for damping the vibrations transmitted by the bearing14during operation.

FIG.2shows a second flexible cage technology30with independent studs32, according to the prior technique.

The flexible cage30also ensures the connection of an outer ring12of a rolling bearing14to an annular support16of this bearing14.

In addition to the outer ring12, the bearing14comprises an inner ring18which is secured to a shaft A of the turbine engine. The rings12,18define a roller raceway in the example shown.

The outer ring12comprises a radially outer annular flange12awhich comprises orifices through which the ends32aof the studs32pass. These ends32aare threaded and receive nuts34tightened against the flange12a.

The opposite ends32bof the studs32are attached in holes in the support16.

The cage30comprises a series of studs32which are distributed around the axis X and extend parallel to this axis. The studs32each comprise a body32cwhich is circular in cross-section, and are therefore symmetrical with respect to their axis Y. The studs32are also symmetrical to each other about the axis X.

The flexible cage30is therefore “axisymmetric”, and the stiffness of the cage10and of the bearing14is therefore the same in all transverse directions (perpendicular to the axis X).

However, from a dynamic point of view, it can be interesting to have different stiffnesses in two orthogonal directions: this provides a stabilising effect to the device by delaying the speed of appearance of instabilities due to the inner damping of the shaft. In fact, by creating different flexibilities in at least two directions, at least two modes appear, as opposed to a single mode in the axisymmetric case.

In the case where the initial radial stiffness of the axisymmetric cage K is such that K1<K<K2where K1and K2are the stiffnesses of the asymmetric flexible cage respectively in the different directions1and2transverse to the axis X, then the frequencies of the modes created will be within the frequency of the initial single mode.

In this case, the frequency with which instabilities can occur is increased, thereby allowing to limit the risk of potentially damaging instability for the engine.

The control of the movement of the shaft in azimuth can also be used to improve the performance of the engine. Under mechanical or thermal loading, the motor casing deforms, and these distortions generate different clearance openings and closures depending on the azimuth. This implies a degradation in motor performance which could be limited if the dynamic displacement is optimised to compensate for some of the distortion, for example by stiffening the flexible cage in the direction of clearance closure and softening it in the direction of the clearance opening.

The present invention allows to meet this need by means of axisymmetric studs, some of which are engaged without clearance and others of which are mounted with clearances in the outer ring12and the support16.

FIGS.3to6illustrate an embodiment of a device for centring and guiding an aircraft turbine engine shaft.

The device comprises:an outer ring12of a rolling bearing14, this ring extending about an axis X and comprising orifices42a,42barranged about this axis X and oriented parallel to this axis X,an annular bearing support16extending around the axis X and at least partly around the ring12, this support16comprising orifices44a,44barranged around this axis X and oriented parallel to this axis X, anda series of studs40,41connecting the ring12to the support16.

The studs40,41are distributed around the axis X and extend substantially parallel to this axis X. Each of these studs40,41comprises an elongate body40c,41cextending between a first longitudinal end40a,41aand a second longitudinal end40b,41b. Each of the first ends40a,41ais engaged in one of the orifices42a,42bof the ring12and each of the second ends40b,41bis engaged in one of the orifices44a,44bof the support16.

First studs40and second studs41can be distinguished from the studs40,41. The first studs40have their ends40a,40bengaged without clearance in the orifices42a,44ain the ring12and the support16. The second studs41have their ends41a,41bengaged with clearances in the orifices42b,44bin the ring12and/or the support16. It is understood that the first end41aof a stud41can be engaged with clearance in an orifice42bof the ring12and that the second end41bcan be engaged without clearance in an orifice44bof the support16. It is also understood that the first end41aof a stud41can be engaged without clearance in an orifice42bof the ring12and that the second end41bcan be engaged with clearance in an orifice44bof the support16. It is also understood that the first end41aof a stud41can be engaged with clearance in an orifice42bof the ring12and that the second end41bcan be engaged with clearance in an orifice44bof the support16. The clearances are configured so that the device has different stiffnesses in at least two distinct directions perpendicular to the axis X.

The two directions perpendicular to the axis X are preferably perpendicular to each other.

In what follows, we are interested in the case where the two ends41a,41bof the second studs41are engaged with clearances in the orifices42b,44bof the ring12and the support16.

In the example of embodiment shown inFIG.3, the first studs40alternate with the second studs41around the axis X. It is understood that at least one first stud40can be comprised between two second studs41around the axis X and that at least one second studs41can be comprised between two first studs40around the axis X. In other words, the number of first studs40comprised between two second studs41can be different from one. The number of second studs41between two first studs can also be different from one.

Advantageously, the first ends40a,41aof the studs40,41are generally circular in cross-section. The second ends40b,41balso advantageously have a generally circular cross-section. In another embodiment, not described, the first ends40a,41aand the second ends40b,41bmay have a generally non-circular cross-sectional shape, for example oblong or elliptical.

The ring12is generally L-shaped in axial cross-section and comprises a cylindrical portion12b, one axial end of which is connected to a radially outer annular flange12afor attaching the studs40,41.

The cylindrical portion12bof the ring12comprises at its inner periphery an annular gorge12cfor rolling the balls of the bearing14and at its outer periphery an outer cylindrical surface12ddefining with the support16an annular space for forming a damping oil film.

The support16is partially shown in the drawings.

The support16comprises a first cylindrical wall16bextending around the cylindrical portion12bof the ring12and comprising an inner cylindrical surface16adefining with the surface12dthe aforementioned damping oil film forming space.

The support16comprises a second cylindrical wall16cextending around the first cylindrical wall16b, or even around the flange12aof the ring12. The first and second cylindrical walls16b,16care joined together by a substantially radial annular wall16dcomprising openings46through which the bodies40c,41cof the studs40,41pass with clearance. Advantageously, the openings46are generally circular in cross-section.

In the example shown, it can be seen that the studs40,41pass through an annular space formed between the walls16b,16c. The wall16dis located at one axial end of this space.

The support16also comprises an annular flange16e.

The orifices42a,42bin the ring12and the orifices44a,44bin the support16may comprise first orifices42a,44aand second orifices42b,44b. Advantageously, the first orifices42a,44aare generally circular in cross-section. Alternatively, not shown, the first orifices42a,44amay have a non-circular general cross-sectional shape, for example oblong or elliptical. In this way, the corresponding ends40a,40bof the first studs40can be engaged without clearance in the ring12and in the support16, as shown inFIG.4, which shows a sectional view of the device inFIG.3along the section axis I-I. It is understood that by being engaged without clearance in the ring12and in the support16, the ends40a,40bof the first studs40have a circular cross-section when the first orifices42a,44ahave a generally circular cross-sectional shape, or alternatively the ends40a,40bof the first studs40have a non-circular cross-section when the first orifices42a,44ahave a generally non-circular cross-sectional shape. It is also understood that the size of each of the ends40a,40bis substantially equal to the size of each of the first orifices42a,44a.

Advantageously, the cross-section of the second orifices42b,44bis generally oblong or elliptical. Alternatively, not shown, the second orifices42a,44amay be generally circular in cross-section. In this way, the corresponding ends41a,41bof the second studs41can be engaged with clearance in the ring12and in the support16. As shown in the example inFIG.5, which shows a cross-sectional view of the device inFIG.3along the cross-sectional axis II-II, the second orifices42b,44bmay have an elongated shape, preferably in the same direction. It is understood that the elongated shape of the orifices42b,44bmeans that they have a first longitudinal dimension greater than a second dimension, substantially perpendicular to the first. It is also understood that the first longitudinal dimension is greater than the diameter of the ends41a,41bof the studs41, and that the second dimension is substantially equal to the diameter of the ends41a,41b. In other words, there is a clearance with the studs41only in a longitudinal direction. In another embodiment, not shown, there may be a clearance between the ends41a,41bof the second studs41, which are circular in cross-section, and the second orifices42b,44b, which are generally circular in cross-section. In this embodiment, the diameter of the second orifices42b,44bis greater than the diameter of the ends41a,41band the clearance is uniformly positive in all directions. In yet another embodiment, not shown, there may be a clearance between the ends41a,41bof the second studs41, which are non-circular in cross-section, for example oblong or elliptical, and the second orifices42b,44b, which are generally circular in cross-section. It is understood that, in this embodiment, the cross-section of the ends41a,41bmay have an elongated shape, preferably in the same direction. The elongated shape of the ends41a,41bmeans that they have a first longitudinal dimension greater than a second dimension, substantially perpendicular to the first. It is therefore understood that there is clearance when the diameter of the second orifices42b,44bis substantially equal to the first longitudinal dimension of the cross-section of the ends41a,41b. In other words, there is a clearance with the studs41only in a direction perpendicular to the first longitudinal dimension.

The orifices42a,42bcan be formed in the flange12a. The orifices42aare passed through by the ends40aof the studs40and the orifices42bare passed through by the ends41aof the studs41; these ends40a,41acan be threaded and receive nuts43tightened against the flange12a.

The orifices44a,44bcan be formed in the flange16e. The orifices44aare passed through by the ends40bof the studs40and the orifices44bare passed through by the ends41bof the studs41; these ends40b,41bcan be threaded and receive nuts45tightened against the flange16e.

The body40c,41cof each stud40,41can be connected to each of the ends40a,40b,41a,41bby annular collars40d,41d. The collars40d,41dmay comprise a flattened area which can be supported on the flanges16e,12aof the support16and of the ring12respectively, so that rotation of the studs40,41about their longitudinal axis can be prevented.

In the example shown inFIG.3, the cage10is not axisymmetric with respect to the axis X and its stiffness is not axisymmetric either. The stiffness of the cage10in a transverse direction parallel to the planes P (arrow F2) is greater than the stiffness of the cage10in a direction perpendicular to these planes P (arrow F1). Indeed, when the cage10is loaded in the direction parallel to the planes P (arrow F2), only the first studs40work, generating a certain stiffness. The second studs41, engaged with clearances in the orifices42b,44bin the ring12and the support16, can move in the direction of the load F2in the clearance in the orifices42b,44b. In this way, part of the load F2can be absorbed. When the cage10is loaded in the direction perpendicular to the planes P (arrow F1), all the studs40,41are loaded, and the stiffness of the cage10is greater. This is because the second studs41cannot move in this direction in the orifices42b,44b, as shown inFIG.6, which illustrates the cross-sectional view of the device inFIG.3along the cross-sectional axis III-Ill, parallel to the load F1. In other words, when the cage10is loaded in a given direction and the clearances of the orifices42b,44bare oriented in this same given direction, such as the direction parallel to the planes P (arrow F2), the stiffness is lower in this given direction. It is understood that when the device is loaded in a first direction (arrow F2) perpendicular to the axis X, the second studs41move in the clearances, while the first studs40remain stationary, and that when the device is loaded in a second direction (arrow F1) perpendicular to the axis X, different from the first direction, the first studs40and the second studs41remain stationary in their respective orifices42a,42b,44a,44b. Different stiffnesses are thus obtained depending on the direction of the loads.

The invention also relates to an aircraft turbine engine comprising at least one device as described above.

The device and the flexible cage according to the invention are therefore advantageous in that the stiffness of the cage differs according to the angular position of the force transmitted to the cage in a direction transverse to its main axis.