VARIABLE-SETTING STATOR BLADE GUIDANCE DEVICE IN AN AXIAL TURBOMACHINE

Abstract

The present invention relates to a variable-setting stator blade guidance device of an axial turbomachine, the blade comprising an airfoil (22), a platform (23) and a pivot (24) mounted in the casing of the turbomachine. The device is characterized in that it comprises a bearing integrated into the platform. In particular, the device comprises a bush (26b) between the platform and the casing, and the integrated bearing is formed between the bush and the platform. In particular, the bush comprises a cylindrical surface portion (26b1) on the side of the platform interacting with a matching cylindrical surface portion (23b1) on the platform to form said integrated bearing.

Description

Other features and advantages will appear on reading two nonlimiting embodiments of the invention with reference to the appended drawings in which:

FIG. 1 represents a variable-setting stator blade of the prior art, mounted in a compressor casing;

FIG. 2 represents a variable-setting stator blade with a guidance device according to a first embodiment;

FIG. 3 shows a variable-setting stator blade with a guidance device according to a second embodiment.

FIG. 2 shows a variable-setting, cantilever-mounted stator blade 20 with an airfoil 22, a platform 23 and a pivot 24. The pivot 24 is housed in a radial bore of the casing 3 which is for example that of the compressor of a gas turbine engine. The blade is held by a nut 28 in its top portion and connected to a setting control lever 27 as is known. The terms “top” and “bottom” indicate the position relative to the axis of the engine, a top element being further from the axis than a bottom element. The blade guidance device here consists of a cylindrical bush 25 between the pivot 24 and the housing in the casing 3. This bush also provides the seal. A bush 26 in the bottom portion of the pivot comprises a cylindrical portion 26a between the bottom portion of the pivot and the housing in the casing. The bush is extended by a generally disk-shaped portion 26b between the platform 23 and the bottom of the facing of the casing forming the housing of the latter. According to the invention, a bearing is formed at the platform. According to this embodiment, the bearing is formed by the interaction of a rib 26b1 and a groove 23b1. The circular rib is made on the face of the bush turned toward the platform 23. The term “circular” also comprises the embodiment in which the rib extends over one or more arcs of circles. According to this example, this rib has a square section and is adjusted in the matching-shaped groove 23b1, hollowed out in the face of the platform turned toward the bush 26. The two portions, rib and groove, form an integrated bearing 23b1-26b1 which sustains the aerodynamic forces applied to the airfoil and transmits them to the casing 3.

Note that, in this embodiment, there is no sliding contact between the bottom portion of the pivot 24 and the bush 26a. The top portion of the pivot forms a top bearing 29.

Note also that the radius of the integrated bearing is chosen so that the frictions between the rib 26b1 of the bush 26 and the groove 23b1 of the platform induce a resistance to the axial pivoting of the blade that is acceptable and does not disrupt the operation of the setting control means. During the rotation of the blade about its axis, the bush 26 remains immobile relative to the casing.

As an example, the advantage of this disposition has been calculated: the forces present are the aerodynamic force F, the reaction force F1 of the casing on the bottom portion of the guidance device and the reaction force F2 of the casing on the top portion of the guidance device.

L, 50 mm, is the distance between the point of application of F and the bottom bearing; L1, 40 mm, is the distance between the bottom bearing and the top bearing. For a value F of 100 daN, the values of F1 and F2 are then respectively 225 daN and 125 daN.

The table below shows that bringing the bottom bearing 8 mm closer to the airfoil, the gain in reduced force is 17% and 30% respectively.

	Prior art	Invention	Gain
	F (daN)	100	100
	F1 (daN)	225	187.5	17%
	F2 (daN)	125	87.5	30%
	L (mm)	50	42
	L1 (mm)	40	48
	Moment	5000	4200

FIG. 3 shows a variant of the invention according to which the bearing is kept at the bottom of the pivot relative to the preceding solution. With this bottom bearing duplicating the bearing integrated into the platform, the load is distributed between F1 and F1′. The reference numbers are the same as for the preceding solution. Note the additional bottom bearing formed by the interaction of the shrink-fitted band 31 mounted on the pivot 24 with the cylindrical portion 26a of the bush 26.

Claims

1. A variable-setting stator blade guidance device in an axial turbomachine, the blade comprising an airfoil (22), a platform (23) and a pivot (24) by which the blade is mounted in the casing (3) of the turbomachine, wherein the device comprises a bush (26) with a disk-shaped portion (26b) between the casing and the platform (23), a circular rib (26b1) being made on said disk-shaped portion interacting with a matching groove (23b1) made on the platform, so as to form a smooth bearing between them.

2. The guidance device as claimed in claim 1, comprising a top bearing between the top portion of the pivot (24) and its housing in the casing (3).

3. The guidance device as claimed in claim 1 or 2, comprising a supplementary bottom bearing (31) between the bottom portion of the pivot (24) and its housing in the casing.

4. The guidance device as claimed in claim 1, whereof the bush (26) comprises a cylindrical portion (26a) between the pivot (24) and the casing.

5. A turbomachine with variable-setting stator blades, the blades comprising a pivot (24) by which they are cantilever-mounted in the casing (3) of the turbomachine and a platform (23) wherein a bush (26) with a disk-shaped portion is interposed between the casing (3) and the platform (23), the bush comprising a rib (26b1) made on said disk-shaped portion and the platform comprising a circular rib (23b1), the rib and the groove forming a smooth bearing.