Patent Application
20060269417
The invention relates in general to a turbomachine having a rotor made up of a set of bladed wheels, such as the rotor of a low pressure compressor in a turbojet, for example. The invention relates more particularly to an improvement enabling blade retention to be improved, particularly in the event of a severe incident.
European patent document 1 496 206 filed in the name of the Applicant discloses the importance of the shape of the groove for receiving the blade roots, which groove is defined in the periphery of a rotor wheel. This problem is particularly important for wheels having blades disposed in a stream that is conical, as is the case for the wheels forming the last stages of a low pressure compressor in a two-spool by-pass turbojet. The conical shape is very marked in the last stages, and the blades of these stages extend obliquely relative to a plane perpendicular to the axis of rotation, i.e. obliquely relative to the direction of centrifugal force. This orientation stresses the blades in such a manner that the risk of a blade being loosened is increased in the event of an incident.
That prior document deals more particularly with the problem of holding blades retained in the groove of the wheel by means of fasteners of the “hammerhead” type, the groove being defined by an upstream lip and a downstream lip that are connected to the bottom thereof so as to define respective upstream and downstream annular cavities in which corresponding portions of the blade roots are engaged. In that document, proposals are made to improve the retention capacity of the blades by deepening the connection zone between the bearing surface of the upstream lip and the bottom of the groove so as to be able to install blades having an upstream flank that presents a heel of greater volume, other things remaining equal, and that is thus capable of engaging obliquely more deeply under the upstream lip into the underlying deeper annular cavity. That modification serves to limit the risk of a blade escaping from the groove in the event of a severe impact.
The change to the shape of the cavity can also be provided on an existing wheel, by machining during an overhaul operation.
Mounting blades in the groove also requires an insertion notch to be provided in one of the annular lips, at a point in its periphery. The notch is provided more particularly in the upstream annular lip; it serves to allow each blade root to be inserted into the reception groove prior to causing said blade to be slid along said groove until the blade reaches its final position.
In order to stabilize the blades and prevent them from moving circumferentially after assembly, it is necessary to mount latches in the groove circumferentially on either side of the notch. This ensures that it is not possible for a blade to move back into register with the notch, since that would lead to it being ejected from the wheel.
It has been observed that in the event of an incident occurring on the blades situated in the vicinity of the notch, the impact can lead to local deformation of the upstream annular lip and thus to the reception groove being enlarged in a manner that can lead to a latch escaping. This risk could lead to an accident since under such circumstances, the blades can again move circumferentially in the reception groove and can escape one after another on reaching the location of the insertion slot.
The invention seeks to prevent that major risk by improving latch retention.
The idea on which the invention is based consists in modifying the shape of the latch beside the upstream annular lip so as to reinforce retention thereof in the groove so that in the event of the groove becoming enlarged, the clearance between said latch and the groove remains negative, thus preventing the latch from escaping.
More particularly, the invention provides a bladed wheel for a turbomachine rotor, the wheel including a reception groove for receiving the roots of blades associated with the wheel, said groove being provided with an upstream annular lip and a downstream annular lip respectively defining at the edges of the groove an upstream annular cavity and a downstream annular cavity, the wheel being of the type in which such an annular lip includes an insertion notch for engaging the blade roots in said reception groove, and in which latches are installed in said reception groove on either side of said notch, each latch comprising a base that extends between the upstream and downstream annular cavities, wherein, for said upstream annular cavity including a hollowed-out portion beyond the bottom of the groove, the base of each latch includes an upstream rib.
The rib engages more deeply into the upstream cavity and serves to hold the latch, even in the event of the groove becoming enlarged.
Although the thickness of the latch is designed so as to enable it to slide in the groove during assembly (between the notch and its mounted position) with radial clearance that is just sufficient to allow said sliding to take place, as is also true of the prior art configuration, the presence of the upstream rib does not in any way impede the circumferential sliding of the latch during assembly since the depth of the reception groove is radially increased at said upstream end.
According to another advantageous characteristic, said latch has two weight-reducing notches formed on either side of the base. It also includes a tapped hole. The hole receives the screw. On assembly, the screw bears against the wall of the disk between the two lips and serves to raise and to position the latch finally in a location such that it is situated between two blade roots. The distance between the two latches is such that two blades are held stationary between them.
In one possible embodiment, the tapped hole is formed in a short column extending substantially from the center of the base.
The invention can be better understood and other advantages thereof appear better in the light of the following description, given purely by way of example and made with reference to the accompanying drawings, in which:
In the drawings, there can be seen (
The reception groove 14 is provided with an upstream annular lip 16 and a downstream annular lip 18. These two lips respectively define an upstream annular cavity 20 and a downstream annular cavity 21 in which corresponding portions of the blade roots are engaged, the platform 15 serving to cover a sector of the cavity 14. Once all of the blades have been put in place, the platforms 15, disposed side by side, constitute an annular surface for the compressor stream.
In order to improve retention of the blades in the groove, the upstream annular cavity 20 of the groove includes a deeper annular hollowed-out portion 24. In the example described, this hollowed-out portion extends beyond the bottom 26 of the groove 14 more deeply into the thickness of the wall of the wheel 11. This hollowed-out portion 26 serves to receive the blade roots presenting respective upstream heels of greater volume, thereby reinforcing retention of the blades in the event of an incident.
In addition, assembly of the blades requires at least one insertion notch 30 to be formed in one of the annular lips of the groove, in this case the upstream lip, at a location in the periphery of the wheel 11. This notch serves to engage the blade roots 19 one after another into the groove 14. Once a blade root is engaged in the groove, the corresponding blade is caused to slide circumferentially along the groove to its final position. Once the blades have been mounted, the roots of the two blades closest to the notch 30 are situated circumferentially on either side thereof.
However, in order to ensure that the blades cannot subsequently move circumferentially to such an extent that the root of one of the blades comes into register with the notch, which would lead to the blade escaping, provision is made to mount two keys or latches 32 in the groove 14, the latches being held stationary therein circumferentially on either side of the notch 30 at selected locations that are at equal distances therefrom. In
Each latch comprises a base 40 of thickness substantially equal to a radial sliding height defined by the reception groove. In other words, in order to pass a latch from the location defined by the groove 30 to its final location in register with cutouts 36, 38, the shape and the dimensions of the groove 14 (in radial section, and specifically of the cavities 20, 21), and the shape and the dimensions of the base 40 are determined in such a manner that said base slides freely but with radial clearance that is as small as possible (the minimum clearance needed) from the insertion position (notch 30) to the assembly location (cutouts 36, 38).
The base further comprises guide bulges of shape and size corresponding to the shape and size of the cutouts 36 and 38, respectively. There can be seen an upstream guide bulge 46 and a downstream guide bulge 48. The bulges 46 and 48 co-operate with the cutouts 36, 38 when the latch is in its assembly location. In this position, it can be prevented from moving by means of a screw 50 passing through it, the base rising radially outwards relative to the groove 14 while being guided by the cutouts 36, 38 until the upstream and downstream ends of the base come to bear against the bottom faces of the lips 16, 18. The screw 50 is engaged in a tapped hole 52 in the latch itself and formed in the base 40 and in a short column 54 extending substantially from the center of said base.
In addition, the latch has two weight-reducing notches 56 formed on either side of the base starting from its longitudinal edges.
The latch is shaped to present an upstream facet 57 bearing under the upstream lip 16 and a downstream facet 58 bearing under the downstream lip 18. The bulges 46, 48 project from these facets. The upstream facet 57 is plane and inclined over the entire thickness of the base.
According to a remarkable characteristic of the invention, the base 40 of each latch includes an upstream rib 60 suitable for engaging in the hollowed-out portion 24 during assembly. This upstream rib extends the bottom of the upstream face 57. It extends beyond the bottom face of the base 40. In spite of the presence of this rib, the latch can be engaged without difficulty in the groove 14 during assembly because of the presence of the hollowed-out portion 24 in the upstream cavity 20.
Once the latch is in position (
The edges 17 of the platforms situated on either side of a location for a latch are provided with cutouts 62 enabling the top portion of the short column 54 to be disengaged in order to tighten the screw 50.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0505297 | May 2005 | FR | national |
