INNER BLADE SUPPORT RING OF A TURBOMACHINE COMPRESSOR STATOR

Abstract

An inner ring for supporting variable-pitch blades of an axial compressor stator of a turbomachine includes two or more ring sectors, assembled to form the inner ring, each ring sector including plural housings for receiving a pivot axis of one of the blades. At each junction plane between the ends of two successive ring sectors, an assembly pin and a cavity for receiving the assembly pin are engaged. The assembly pin is fixed on one end one of the two successive ring sectors and the cavity is formed at the end of the other of the two successive ring sectors. The cavity receives the assembly pin with a mounting clearance allowing a mounting by sliding fit, and the assembly pin is made of a material having a coefficient of thermal expansion greater than a coefficient of thermal expansion of a material constituting the successive ring sectors.

Claims

1. An inner ring for supporting the variable-pitch blades of an axial compressor stator of a turbomachine, wherein the inner ring comprises at least two ring sectors, assembled circumferentially end to end so as to form the inner ring, each ring sector comprising a plurality of housings for receiving a radially inner pivot axis of one of the variable-pitch blades, wherein each ring sector has two ends, wherein there is a junction plane between the ends of two assembled successive ring sectors, wherein at each junction plane between the ends of two successive ring sectors, the assembly of two successive ring sectors is performed by cooperation of an assembly pin and a cavity for receiving the assembly pin, the assembly pin being fixed on one of the two ends of one of the two successive ring sectors and the cavity being formed at one of the two ends of the other of the two successive ring sectors, wherein the cavity is configured and dimensioned to receive the assembly pin with a mounting clearance allowing a mounting by sliding fit, and wherein the assembly pin is made of a material having a coefficient of thermal expansion greater than a coefficient of thermal expansion of a material constituting the successive ring sectors so that during the temperature rise resulting from the use of said axial compressor, the assembly pin expands more inside the cavity than the cavity itself, thus ensuring the inseparable assembly of the two successive ring sectors and so that during the temperature decrease resulting from the cessation of the use of said axial compressor, the assembly pin retracts inside said cavity, by allowing the dismounting of the two successive ring sectors.

2. The inner ring according to claim 1, wherein each ring sector has at one of its two ends, the cavity for receiving an assembly pin and at the other of its two ends, the assembly pin.

3. The inner ring according to claim 1, wherein at least one of the ring sectors has, at each of its two ends, the a receiving cavity and wherein at least one other of the ring sectors has, at each of its two ends, the assembly pin.

4. The inner ring according to claim 1, wherein the inner ring comprises two ring sectors assembled end to end to form said inner ring.

5. The inner ring according to claim 1, wherein the ratio between the coefficient of thermal expansion of the material constituting the assembly pin and the coefficient of thermal expansion of the material constituting the ring sectors is greater than or equal to 1.3 and less than 2.

6. The inner ring according to claim 1, wherein the ratio between the coefficient of thermal expansion of the material constituting the assembly pin and the coefficient of thermal expansion of the material constituting the ring sectors is greater than or equal to 2.

7. The inner ring according to claim 1, wherein the material constituting the assembly pin is chosen from aluminum or a nickel-based steel and wherein the material constituting the ring sectors is chosen from steel or titanium.

8. The inner ring according to claim 1, wherein the assembly pin is cylindrical wherein the cavity for receiving this assembly pin is cylindrical in shape.

9. An axial turbomachine compressor stator comprising a plurality of variable-pitch blades, pivotally mounted between an outer casing for supporting the variable-pitch blades and an inner ring for supporting the variable-pitch blades wherein the inner ring is the inner ring according to claim 1.

10. An axial turbomachine compressor, comprising at least one axial turbomachine compressor stator according to claim 9.

11. A turbomachine comprising at least one axial turbomachine compressor according to claim 10.

Description

DESCRIPTION OF THE FIGURES

[0036] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and not limiting, and which should be read in relation to the appended drawings in which:

[0037] FIG. 1 represents a perspective view of a turbomachine compressor.

[0038] FIG. 2 is a schematic view of an inner ring for supporting the blades of a stator according to the state of the art.

[0039] FIG. 3 is a schematic view of a ring sector according to the state of the art.

[0040] FIG. 4 is a schematic and detail view of the end of a ring sector according to the state of the art.

[0041] FIG. 5 is a front view of an inner ring for supporting the variable-pitch blades of an axial compressor stator of a turbomachine in accordance with the invention.

[0042] FIG. 6 is a detail view of part of the inner ring in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0043] The inner ring for supporting the variable-pitch blades of an axial compressor stator of a turbomachine, in accordance with the invention, will now be described in relation to FIG. 5. This ring bears the general reference 17.

[0044] Just like the previously described inner ring 15, the inner ring 17 comprises at least two ring sectors 170, assembled end to end circumferentially so as to form said complete ring which extends over 360?. Preferably, the inner ring 17 comprises only two ring sectors 170 extending over an angle of 180? each. However, this inner ring 17 could also comprise a greater number of such sectors.

[0045] Each ring sector 170 comprises two ends 171, which constitute contact surfaces with the ends 171 of a neighboring ring sector 170. When two successive ring sectors are assembled, there is therefore a junction plane between their ends 171 in contact. The ends 171 are preferably planar.

[0046] Furthermore, each ring sector 170 comprises a plurality of housings 172 for receiving the radially inner pivot axis of 132 a pivoting blade 13, as described above. These housings 172 open out onto the radially outer face 173 of each ring sector 170.

[0047] At the level of the junction plane (contact plane) between the respective ends 171 of two successive ring sectors, the assembly is carried out by cooperation of an assembly pin 174 with a cavity 175 for receiving this pin.

[0048] More specifically, the assembly pin 174 is fixed to the end 171 of one of the two successive ring sectors and the receiving cavity 175 is arranged at the end 171 of the other of said two successive ring sectors.

[0049] The pin 174 extends along an axis perpendicular to the plane of the end 171 and the same is true for the cavity 175 which opens out onto this end 171.

[0050] Preferably, the assembly pin 174 is cylindrical and the receiving cavity 175 is also a cylindrical bore.

[0051] The pin 174 can be fixed on the ring sector 170 by an interference fit i.e. by shrink-fitting. In this case, a recess (not represented in the figures) is formed at the end 171 and the pin 174 is dimensioned to be forcibly inserted therein and to remain fixed therein even on cessation of the use the compressor.

[0052] The pin 174 can also be fixed on the ring sector 170 by welding or by bonding, or by screwing.

[0053] Furthermore, according to a first variant, and as represented in FIG. 5, each ring sector 170 has at one of its two ends 171, a cavity 175 and is provided at the other of its two ends 171, with the assembly pin 174.

[0054] According to a second variant, not represented in the figures, it is also possible to have at least one ring sector (for example a half-ring) with an assembly pin 174 at each of its two ends 171 and at least one another ring sector (for example another half ring) with a cavity 175 at each of its two ends 171.

[0055] Furthermore, and as best seen in FIG. 6, the cavity 175 is configured and dimensioned with respect to the assembly pin 174 so as to receive the latter with a mounting clearance J3 which allows a mounting by sliding fit. In other words, the pin 174 and the cavity 175 are very finely fitted in order to be able to just slide the pin axially into the cavity 175.

[0056] By way of purely indicative example, this mounting clearance J3 between the side walls of the pin 174 and the inner wall of the cavity 175 is very small, of the order of a few hundredths of millimeters. Still by way of example, for a cylindrical pin with a diameter of a few millimeters, preferably a diameter comprised between 3 mm and 8 mm, a fit of the H6g5 type according to the ISO standard can be used.

[0057] This mounting clearance J3 is very small but nevertheless allows the cold mounting of the parts.

[0058] Finally, the pair of materials making it possible to produce, on the one hand, the pin 174 and, on the other hand, the ring sector 170 having the cavity 175, is chosen so that the coefficient of thermal expansion of the material constituting the pin 174 is greater than the coefficient of thermal expansion of the material constituting the ring sector.

[0059] Thus, during the operation of the turbomachine and therefore of the compressor, the latter rises in temperature and the pin 174 expands more than the cavity 175. The pin 174 then exerts a force, due to its swelling, on the walls of the cavity (See arrows F1 in FIG. 6) and the assembly thus forms a shrink-fitting making the two neighboring (successive) ring sectors inseparable. The problematic opening of the ring sectors at the level of the parting line, described previously, is then no longer possible.

[0060] Conversely, when the compressor stops, the parts cool down and the pin resumes its original diameter by reverse expansion, which has the effect of eliminating the shrink-fitting with the ring sector. The different ring sectors can then be dismounted, if necessary.

[0061] The ring sectors are advantageously made of steel and have an average coefficient of thermal expansion of 12.10.sup.?6/? C. They can also be made of titanium and then have a lower coefficient of thermal expansion, equal to 8.6?10.sup.?6/? C. In the latter case, a higher dilation ratio is thus obtained with the pin 174.

[0062] Steel is preferred in a hot environment, titanium in a cold environment, as explained below.

[0063] Preferably, and in order to obtain the aforementioned technical effect, the ratio between the coefficient of thermal expansion of the material constituting the assembly pin and the coefficient of thermal expansion of the material constituting said ring sectors is greater than or equal to 1.3.

[0064] For hot environments (temperature above 150? C.), it will preferably be chosen a ratio: coefficient of thermal expansion of the material constituting the assembly pin/coefficient of thermal expansion of the material constituting said ring sectors greater than or equal to 1.3 and less than 2.

[0065] Mention may be made, for example, as a material of the pin 174, of a nickel base steel, of the Inconel type which has an average coefficient of expansion of 18.10.sup.?6/? C. or aluminum which has an average coefficient of expansion of 23.10.sup.?6/? C., the aforementioned ratio then being respectively 1.5 and 1.91 with a steel ring sector.

[0066] For cold environments (temperature below 150? C.), it will preferably be chosen a ratio: coefficient of thermal expansion of the material constituting the assembly pin/coefficient of thermal expansion of the material constituting said ring sectors greater than or equal to 2.

[0067] Mention may be made, for example, as a material of the pin 174, of aluminum which has an average coefficient of expansion of 23.10.sup.?6/? C., the aforementioned ratio then being 2.67 with a titanium ring sector.

[0068] In the case of a high-pressure compressor, the first stages of stators will be in a cold environment while the last stages will be in a hot environment, the temperature of the compressor increasing from compression stage to compression stage.

[0069] By combining the sliding assembly clearance with the aforementioned coefficients of expansion ratios, the clamping by expanding the pin in the cavity is thus obtained, and this from low temperatures around 100? C.

[0070] The invention also relates to a stator such as the aforementioned stator 12 comprising the blades 13 and the outer casing 14, as described previously but with the ring 17 in accordance with the invention which replaces the inner ring 15, as it appears better in FIG. 1 (reference 17 in parentheses).

[0071] Similarly, the invention relates to the compressor 1 comprising at least one stage 10, each stage comprising a rotor 11 and a stator 12 comprising the inner ring 17 and finally a turbomachine comprising this compressor 1 with the ring 17.