TURBOMACHINE SHAFT

Abstract

The invention concerns a tubular shaft (8) of a turbomachine, comprising, at the inner periphery of same, a bath (11), substantially perpendicular to said splines (9), characterised in that said bath (11) comprises cavities (17) distributed over a circumference centred on the axis of rotation (LL) of the shaft (8). The invention also concerns an assembly comprising said turbomachine shaft, a turbomachine and a method for detecting an oil imbalance.

Claims

1. A tubular turbine engine shaft, having at its inner periphery a trough, wherein said trough has at least one recess made in a surface centred on the axis of rotation of the shaft.

2. The turbine engine shaft according to claim 1, wherein said trough has a part in which said at least one recess is made on a surface generated by the rotation about the axis of rotation of a curve defined in a meridian plane.

3. The turbine engine shaft according to claim 1, comprising at least two recesses distributed on a circumference about the axis of rotation of the shaft.

4. The turbine engine shaft according to claim 3, wherein the recesses are distributed regularly about said axis of rotation.

5. The turbine engine shaft according to claim 4, wherein the recesses are symmetrical in relation to said axis of rotation or in relation to a plane passing through said axis of rotation.

6. The turbine engine shaft according to claim 1, wherein the recess or recesses are obtained by milling or by electrical discharge machining in an internal wall of the shaft.

7. The turbine engine shaft according to claim 1, wherein the recess or recesses are formed by parts forming partitions and extending substantially radially from an internal wall of the shaft.

8. The turbine engine shaft according to claim 7, wherein the parts forming partitions are fixed by brazing or welding.

9. The tubular turbine engine shaft according to claim 1, having connection means disposed at its outer periphery and configured so as to transmit a torque to another shaft.

10. The tubular turbine engine shaft according to claim 9, wherein the trough is situated substantially in line with said connection means.

11. The turbine engine shaft according to claim 9, wherein the connection means are splines.

12. (canceled)

13. (canceled)

14. The turbine engine comprising a shaft according to claim 1.

15. The method for detecting the presence of oil inside a tubular turbine engine shaft according to claim 1, at a trough in its inner periphery, the method comprising a step of measuring a value of an unbalance of the shaft synchronous with a rotation speed of the shaft, and a step of issuing an alert when the difference between said unbalance value and an unbalance value of the shaft alone is above a predetermined threshold, corresponding to the likely presence of oil trapped in one recess at least and producing an unbalance synchronous with the speed of the shaft.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0031] The present invention will be better understood, and other details, features and advantages of the present invention will become more clearly apparent on reading the description that follows of a non-restrictive example, with reference to the accompanying drawings wherein:

[0032] FIG. 1 is a diagrammatic representation of the architecture of a turbine engine according to the prior art;

[0033] FIG. 2 shows a half-section along a meridian plane of an end of a shaft according to the prior art;

[0034] FIG. 3 shows a cross-section along a meridian plane of an end of a shaft according to the prior art with a pocket of oil;

[0035] FIG. 4 shows a half-section along a meridian plane of an end of a shaft according to the invention;

[0036] FIG. 5 shows a shaft according to the invention cut in two along a meridian plane, the inner tubular part having been withdrawn;

[0037] FIGS. 6a and 6b show a section along a plane BB defined in FIG. 5 of different variants of a shaft according to the invention for a first embodiment obtained with a first machining method;

[0038] FIGS. 7a to 7d show a section along a plane BB defined in FIG. 5 of different variants of a shaft according to the invention for a first embodiment obtained with a second machining method; and

[0039] FIGS. 8a and 8b show a section along a plane BB defined in FIG. 5 of different variants of a shaft according to the invention for a third embodiment.

DESCRIPTION OF AN EMBODIMENT

[0040] With reference to FIG. 4, a turbine engine shaft made according to the invention differs from that shown in FIG. 2 in that the shape of the inner surface of the tubular shaft 8 has been modified at the trough 11.

[0041] The surface of the trough 11 has a part closer to the axis of revolution LL, generated by the rotation of a curve 11a in a meridian plane and which gives a first trough shape at the splines 9. However, it has at least one recess 17 obtained in an angular sector given by the junction between this first surface and a line 11b along, in a meridian plane, the maximum radius points on the surface of the recess 17.

[0042] FIG. 5 shows two recesses 17a, 17b formed in this way in the trough 11 on the inner surface of the shaft 8.

[0043] The surface of a recess may or may not follow the line 11b of maximum radii over a certain angular displacement about the axis LL and can be connected in various ways to the surface along the generatrix 11a. The number of recesses can also vary. This depends to a certain extent on the technique used to create these recesses.

[0044] According to a first embodiment, the recesses 17a, 17b can be created by making hollows in the internal wall of the shaft 8.

[0045] With reference to FIGS. 6a and 6b, the hollows can be obtained by milling in the wall of the shaft 8.

[0046] FIG. 6a shows a transverse section of the shaft 8, along a plane BB shown in FIGS. 4 and 5, in which two recesses 17a, 17b have been milled. The splines 9 on the radially outer section of the shaft 8 can be seen. The smaller circle represents the inner section 18 of the shaft 8 between the end 10 and the trough 11. It is through this section that the tools to hollow out the internal wall of the shaft 8 at the trough 11 can be passed.

[0047] A second circle 19 delimits the section of the internal wall in the trough 11 corresponding to the curve 11a, apart from the recesses 17a, 17b. Two recesses 17a and 17b are shown in FIG. 6a. Here, they are symmetrical in relation to a horizontal plane, in the drawing. The radius of their section decreases regularly between the central part, of maximum radius and corresponding to the position of the line 11b in FIG. 4 in the plane of section, and the ends meeting the minimum section 19 in the trough 11. They are symmetrical in relation to a vertical meridian plane. The trough 11 with its recesses 17a, 17b therefore has 2-fold symmetry here.

[0048] Different positions of the section 20 of the milling tool, during its introduction into the trough 11 through the end 10 of the shaft 8, are shown in FIG. 6a. It can be seen that the milling tool is introduced opposite the centre of each recess 17a, 17b before being moved in such a way as to remove the material and create the corresponding hollow. This procedure makes it possible to produce the same shapes for the various recesses by repeating the same sequence of instructions for the tool on each occasion.

[0049] FIG. 6b shows a variant in which three recesses 17a, 17b, 17c are created by milling in the wall of the trough 11 that has an originally circular section 19 corresponding to the curve 11a. Likewise, the milling tool 20 is introduced in front of the centre of each recess 17a, 17b, 17c at the beginning of the milling of each one. Here, the three recesses are identical and regularly spaced; the trough therefore has a 3-fold symmetry.

[0050] According to another machining method, with reference to FIGS. 7a to 7d, the hollows corresponding to the recesses are created by electrical discharge machining in the internal wall 19, corresponding to the curve 11a in FIG. 4, of the shaft 8 at the trough 11.

[0051] FIG. 7a shows a transverse section of the shaft 8 in which two symmetrical recesses 17a, 17b are obtained by this method. Here, the electrode 21 of the tool can be seen in its final position when the upper recess 17a has been created. As before, the electrode 21 has been introduced inside the shaft 8 at the trough 11, through the end 10 of minimum transverse section 18. Here, the electrode 21 has been introduced through the centre and then translated towards the bottom of the recess 17a following the path shown by the hatched area during the electrical discharge machining process. On the opposite recess 17b it can be seen that said recess, in cross-section, has the shape of the mark made by the electrode 21.

[0052] FIGS. 7b, 7c and 7d show variants where the electrode 21 has been used in three, eight or seven directions in order to create the same number of similar, regularly spaced recesses.

[0053] FIG. 7c, with eight recesses, illustrates an instance where, given the width of the electrode 21 and the number of recesses 17a-17h, the edges of the recesses meet. The radius of the minimum section 11a of the trough 11 with the recesses 17a-17h is therefore greater than that of the section 19 of the initial trough 11.

[0054] In fact, in another variant, not described in detail here but available to the person skilled in the art, the two machining methods presented can be used to directly create the trough 11 with its recesses 17a-17h in accordance with a desired shape, inside a shaft 8 the internal wall of which may be cylindrical, without a trough shape made beforehand.

[0055] According to a second embodiment, the recesses can be obtained by filling the space inside a trough 11 initially made in the shaft 8.

[0056] With reference to FIG. 8a, two identical parts 22, having a transverse section corresponding to an annular sector of less than 180°, are installed symmetrically on the right and the left of the internal wall 23 of the initial trough 11, here corresponding to the position of the line 11b at the transverse cross-section BB. Two recesses 17a, 17b, themselves corresponding to angular sectors having the same depth as the parts 22, are thus formed above and below. The assembly has a 2-fold symmetry.

[0057] In a variant, it is rather a series of relatively thin partitions 24, which are installed radially on the internal wall 23 of the initial trough 11. As these partitions 24 are regularly spaced, they form a series of symmetrical recesses 17a-17g, the symmetry being seven-fold in FIG. 8b. The radially inner end of these partitions 24 follows the evolution of the curve 11a of minimum radius shown in FIG. 4. These partitions 24 can be connected to one another by one or more than one internal collar 25 in order to provide their mechanical strength.

[0058] These parts 22 or partitions 24 can be fixed by brazing or welding to the inner surface 23 of the shaft 8, in the trough 11.

[0059] As can be seen from the examples that have just been presented, it is possible to make the shaft 8 without having to modify other parts, in particular the internal tubular part 12 designed in accordance with the prior art. The complete assembly of the shaft can be effected afterwards, in accordance with the prior art, by fitting the internal tubular part 12 in the shaft 8, equipped with recesses 17 in the trough 11.

[0060] The invention has been presented using preferably at least two recesses in order to maintain the symmetry of the shaft when there is no oil but it is also possible to envisage making only a single recess there, which will then necessarily trap the oil in a non-symmetrical manner.

[0061] Furthermore, the production of the recesses has been presented here in a trough made in the area of the connecting means of the shaft because this trough is close to the passage of the oil at the connection end piece of the shaft and therefore corresponds to an identified risk. However, it is evident that the invention can be applied to any shaft having a trough in any place on its inner periphery and where it is feared that oil will accumulate and create unwanted forces as it rotates. In particular, the methods for creating recesses by milling or electrical discharge machining described above can be used, bringing the tools to the trough through one of the open ends of the tubular shaft, as has been described above.

[0062] Lastly, where a shaft such as that just described has been fitted in a turbine engine, it is possible to equip the turbine engine with vibration sensors in accordance with known technologies. If a ring seal 14 of the cavity 13 deteriorates and if oil accumulates in the cavity 13, by virtue of the invention the oil is trapped in at least one of the recesses 17 and the unbalance becomes synchronous with the speed of the shaft. A system for monitoring a turbine engine equipped with a computer that has appropriate software can then measure the value of the shaft unbalance and compare it with a reference unbalance value, measured beforehand for the shaft alone, without oil. If this value differs from the reference value beyond a predetermined threshold, the system can then issue an alert indicating the appearance of vibrations due, probably, to the presence of oil in the recesses 17 of the trough 11 and therefore of an oil unbalance.