Internal casing for stator

CA 02363201 2001-11-22 1 INTERNAL STATOR FERRULE DESCRIPTION The subject of this invention is an internal stator ferrule.

Controlling thermal expansion has become essential in the field of turbojets in order to ensure good efficiency by adjusting the clearance between the stator and the tips of the rotor blades.

A frequently encountered stator structure is twofold and includes a housing surrounding an internal ferrule in contact with the machine propellants.

It is then usual for the outer casing to be formed in one piece so that it has good mechanical strength and that it can be cooled by ventilation with good regularity favored by its continuity, but that the shell is on the contrary composite. , formed of successive circumferences of elements in a sector of a circle.

Thanks to this arrangement, the internal stresses which could have developed in the ferrule due to the more rigid housing mounting and the exposure to the hot gases of the stream remain at a moderate level, and the different circumferences can be ventilated to different intensities to independently adjust their diameters. The prior art includes a certain number of illustrations of this double stator, of which we can cite French patents 2,683,851 and 2,695,164 issued to the applicant.

Figure 1 shows one of these designs, where the outer casing bears the reference 1, SP 18607 JCI CA 02363201 2001-11-22 2 the ferrule elements reference 2 and the rotor reference 3; the ferrule elements 2 are assembled to the adjacent elements 2, located on the neighboring circumferences, by assemblies 4 composed of a tenon 5 on one of the elements 2 and a groove 6, into which the tenon 5 penetrates, on the other of items 2.

Fastening points 7, better represented in FIG. 2, unite the ferrule elements 2 to the casing 1.

They essentially comprise a bolt 8 engaged through a boss 9 of the housing 1 and a contact surface 10 to the housing 1, located at the end of a rib 11 of the ferrule element 2.

The bolts 8 are generally arranged obliquely in order to ensure the axial and radial retention of the rectifier sectors (the ferrule elements 2).

Circular elastic seals 12 are arranged behind the circumferences of ferrule elements 2 and comprise a heel 13 clamped between the contact surface 10 and a shoulder 14 of the housing 1 and, rising below the heel 13, a lip sealing 15, the end of which rests on a flat sealing face 16 at the rear of the ferrule elements 2.

Thus, individual chambers 17 are isolated between the casing 1 and each of the circumferences of ferrule elements 2.

The objective of obtaining a good adjustment of the diameters of the ferrule circumferences is not, however, fully achieved, since variations in diameter and undulations of the circumferences easily appear.

This drawback is attributed here to the presence of the fixing points 7, which appear as structural irregularities in the shell elements 2.

More precisely, the inventors considered that the presence of a plurality of fixing points 7 was harmful and proposed to use only one per ferrule element 2.

As a single point of attachment would not make it possible on its own to retain a ferrule element 2 satisfactorily, it is also recommended to use a single fulcrum per ferrule element 2 instead of the fixing points deleted.

This fulcrum comprises a tenon fixed to the ferrule element and penetrating into a groove of an associated flange, which is fixed to the housing.

The ferrule elements have the ability to move slightly in the axial and circumferential directions of the machine at the fulcrum by sliding the tenons in the grooves, without excessive movements being tolerated because stop states would be reached.

We then succeed in reconciling a suitable assembly of the ferrule elements to the casing and an assembly flexibility which avoids deforming them irregularly.

Other characteristics and advantages of the invention will now be described with reference to the following figures.

^ Figure 1, already described, illustrates a composite stator, ^ Figure 2, already described, illustrates a ferrule element attachment point to a casing, ^ and the other Figures 3 to 6 illustrate certain embodiments of the invention: Figure 3 , a first achievement; FIG. 4, a member of the ferrule thereof; and Figures 5 and 6, essential details of two other embodiments.

Many elements of the prior art already discussed with regard to Figures 1 and 2 are found in the invention.

This concerns in particular the structure of the fixing points 7 and the presence of the connecting elements 4 between the circumferences of the shell and the elastic seals 12 for damping the vibrations.

A characteristic aspect of the invention is that each ferrule element 2 is only associated with a single fixing point 7 which is located near a lateral end 20 (and not far from an axial edge of the element. ferrule 2).

A fulcrum 21 is also disposed on each ferrule element 2 symmetrically to the attachment point 7, near the same axial edge and not far from the opposite side end 22.

A notable teaching of Figure 3 is also that it is advantageous that the shell elements 2 are staggered, that is to say that their ends 20 or 22 are in the extension of center lines of the shell elements 2 adjacent circumferences.

By adopting this arrangement, a shell with a coherent structure, despite the few fixing points 7 and support 21 of its elements, is obtained.

This can be explained by noting that each ferrule element (such as the element denoted 20) is surrounded by two elements belonging to adjacent circumferences and whose fixing points (denoted 70) extend approximately to mid-length of the l 'item 20.

These fixing points 7o also restrict the radial deformations of the element 2.o SP 18607 JCI CA 02363201 2001-11-22 thanks to the tenon 5 and mortise 6 connections between the circumferences of ferrule 2 elements.

This advantage is even more appreciable if the fixing points 5 7 and support 21 are frankly at the ends of the ferrule elements 2, which is advantageous because they can then cooperate with each other, since the fixing points 7o of the adjacent elements are indeed mid-length of the element 20, at the place where it would have been the least supported without them.

If the structure is rigid enough against radial deformations, it is on the contrary quite flexible according to the axial deformations and in conference thanks to the sliding nature of the support points 21, which allows said deformations within certain limits.

We therefore reconcile the need to allow the shell to deform according to the thermal stresses while maintaining a round shape of little variable diameter.

Figure 4 shows that the support points 21 include a tenon 23 located at the end of a handle 24 rising from the ferrule element 2.

This tenon 23 rests on the bottom surface of a groove 25 integral with the housing 1.

In this embodiment where the fixing and support points 7 and 21 are close to the lateral ends 20 and 22 of the ferrule elements 2, they are adjacent to those of the neighboring ferrule elements 2, so that the groove 25 can here be operated in the rib 11 of the attachment point 7 of the neighboring ferrule element 2.

The tenon 23 extends in the tangential direction of the machine to protrude from the element SP 18607 JCI CA 02363201 2001-11-22 6 of ferrule 2 to which it belongs on the next element.

It will be seen that other configurations are possible, but in all cases the support points 21 allow moderate mutual axial and circumferential displacements of the neighboring shell elements 2.

Here as in other embodiments, the attachment points 7 are designed with two parallel bolts 8, which does not change the uniqueness of the attachment point 7 since these bolts 8 are close together.

The pair of bolts 8 makes it possible to obtain a more secure fixing and sometimes to eliminate the bending moments exerted by the aerodynamic forces on the shell elements 2: if the resultant F of these forces, or its projection in the radial direction, passes between the bolts 8, the reaction is exerted by comparable forces produced therein, without the ferrule element 2 itself being subjected to significant bending.

In an alternative embodiment illustrated in FIG. 5, the tenon of the fixing points is of more complicated shape and bears the reference 26; it engages in a groove 27 made between the locations of the bolts 8 and then comprises successively, after the handle 24, a shelf 28 slipped under the heel 10 of the fixing point 7 and an end 29 which is more massive and in particular wider, for project axially and extend between the two portions of the heel 10 as far as the groove 27, which is made in the rib 11.

Here, the essential portion of the tenon 26 has an axial extension rather than tangential, which does not modify the support conditions.

SP 18607 JCI CA 02363201 2001-11-22 7 In other embodiments, the flanges on which the notches are established do not belong to the attachment points 7 but to independent parts. This is illustrated in Figure 6, where the fixing points 7, which here only include a single bolt 8 but remain located near the side end 20, no longer have a groove 25 nor 27: there is then a flange 30, composed of a bar 31 joined to the housing 1 by a bolt 32 similar and parallel to the bolt 8 and hollowed out with a groove 33, near the fixing point 7 so that the heel 10 overhangs the end of bar 31 and closes groove 33.

The fulcrum 21 of the ferrule element 2 further comprises a tenon 34 at the end 35 projecting axially in the groove 33 to establish the desired connection. The end 35 is linked to the main body of the ferrule element 2 adjacent to that which carries the fixing point 7 by a handle 36 adjacent to the lateral end 22 and in a radial direction.

In these various embodiments, it will have been noticed that the support 21 and attachment points 7 belonging to consecutive ferrule elements 2 on a circumference cooperate with each other, that is to say that the attachment point 7 offers at least a stop surface or bearing surface against the tenon of the fulcrum 21: in the embodiment of FIG. 4, the tenon 23 bears radially in the groove 25 and abuts tangentially against the contact surface 10 or the rib 11 of the fixing point 7; in the embodiment of FIG. 5, the tenon 26 abuts tangentially against the contact surfaces SP 18607 JCI CA 02363201 2001-11-22 8 10 which surround it and rests radially on the groove 27; and in the embodiment of FIG. 6, the tenon 35 abuts tangentially on the contact surface 10 and the bar 31, and rests radially on the bottom of the groove 33.

This cooperation of the attachment points 7 and of support 21 simplifies the structure by making it possible not to resort to flanges of complex shape to ensure the sliding of tenons from the fulcrum while limiting it.

It is also desirable to allow moderate displacements of the shell elements in the axial direction at the support points 21.

The stops can be provided either by the side faces of a sliding groove such as 25, or by the very structure of the fixing point 7, for example the rib 11 in the solution of FIG. 5, or by a flange portion or a stand-alone bar as in the solution of FIG. 6; the elastic seals 12 can also serve as a stop, as can be seen clearly in this same FIG. 6.

The proximity of the fulcrum 21 and fixing points 7 of adjacent shell elements 2 optionally makes it possible to maintain the fulcrum 21 in a good position in the radial direction without an additional part being used, as is the case. the case in FIG. 4 where the tenon 23 of the fulcrum 21 bears radially in the groove 25 adjacent to the fixing point 7 and hollowed out in the neighboring ferrule element 2.

JCI SP 18607