The present invention concerns the area of turbo machines and looks at an axial turbine ring distributor formed by distributor segments which are arranged in ring sectors. More particularly, the invention concerns a device for preventing said sectors from rotating inside the casing.
A gas turbine engine such as used in aeronautics includes an upstream inlet through which air is sucked in and then compressed by being guided through the compressor stages. The compressed air is introduced into a combustion chamber, the fuel also being admitted into said combustion chamber and mixed with the air and combustion taking place in said chamber. The hot combustion gases are expanded in the different turbine stages, one of which is generally a high pressure stage directly downstream of the chamber and which receives the gases at the highest temperature compatible with the behavior of the materials. After said first expansion, the gases are expanded again by being guided through the so-called low pressure turbine stages. One turbine stage includes a wheel of distributors upstream of a turbine runner.
A distributor wheel with axial flow includes a plurality of blades arranged radially with regard to the axis of the machine connecting a ring-shaped element radially inside and a ring-shaped element radially outside; the assembly forms a ring-shaped vein facing the runner blades of a turbine wheel. The runner is itself made up of blades which extend radially from the rim of a disk or a moving drum about a rotational axis. The blades are traversed in an axial manner by the engine gases. In this way, the low pressure section of an engine generally includes several turbine stages.
The distributor wheels are segmented into a plurality of sectors which are distributed around the axis of the machine, each segment being formed by a plurality of blades between two ring sectors. Each segment is mounted inside the casing of the turbine by the ring sector radially outside. Said latter includes a retaining means upstream and a retaining means downstream. Said means, for example, are ring-shaped rails which are provided in the inside wall of the casing on which support surfaces, which are arranged on the ring sectors of the distributor segments, come to bear. The assembly is arranged so as to allow the relative expansion of the distributor with regard to the casing which is a function of the variations of the working of the machine. On account of the axial symmetry of the distributor wheels and of the tangential stresses resulting from the gaseous flow which traverses them, it is necessary to provide means for blocking the sectors from rotating.
Patent FR 2 743 603 in the name of SNECMA describes a method of assembling such distributor segments inside a casing. The distributor segments include a peripheral outside rib, at right angles to the axis of the distributor, resting by way of faces, one radially outside, the other downstream, on corresponding faces of the inside wall of the casing. Clamps, formed by the turbine ring downstream of said level, hold the segments and keep them in position against the radial movements. A protrusion on the upstream face of the rib of each segment includes a notch in which a rotation-proofing peg is housed. Said peg is made up by a head which is housed in said notch and a rod which is slid into a radial bore of the wall of the casing. In this way, said peg prevents any rotational movement of the distributor segment about the axis of said latter.
So as to protect the wall of the casing against radiant heat produced by the distributor segments, a sheet is provided interposed between the segment and the inside wall of the casing. Said heat shield sheet bears upstream against a radial surface portion which is arranged in the inside wall of the casing. The upstream edge of the shield sheet is curved radially toward the inside in order to form a pin which also bears on an upstream edge of the segment and participates in the holding of said segment against the upstream rail of the casing. Downstream the shield sheet includes an indentation with a tab in the bottom of the indentation which bears against the rotation-proofing peg of the segment. The tab is in effect wedged in a fine groove of the peg.
Said assembly provides complete satisfaction as regards holding the distributor inside the casing and protecting it thermally.
However, it has been observed that the sheet was likely to release itself from its contact with the rotation-proofing peg, the tab coming out of the bearing groove provided on the peg. By not being retained against the peg, the downstream part of the sheet, where the tab is located, is able to go and rub against the inside face of the wall of the casing, and scratch the same. It would be desirable to eliminate said risk of wear on the casing.
The object of the present invention is to alleviate said problem.
According to the invention, said problem is resolved with a turbo machine which is provided with a device for preventing the rotation of a distributor segment in the form of a ring sector which is housed inside a ring-shaped casing of the turbo machine, with the interposing of a heat shield sheet between the inside wall of the casing and the outside wall of the segment, including a rotation-proofing peg which is mounted both in a notch arranged on the segment and a housing arranged on the casing, the heat shield sheet including a tab bearing against the rotation-proofing peg. The turbo machine is characterized by the fact that the device includes the arranging of a surface portion radially between the tab and said inside wall of the casing, forming an abutment in the event of possible radial displacement of the heat shield sheet during the operation of the turbo machine.
By interposing an abutment between the casing and the part of the sheet likely to move during the operation of the machine, the risk of contacting the inside wall of the casing is thus eliminated.
According to one embodiment, the peg includes a head which is housed in the notch of the segment and a rod entering the housing which is arranged on the casing, said surface portion being integral with the head of the rotation-proofing peg.
The advantage of said embodiment is that it only concerns the rotation-proofing peg, the remaining parts: the distributor segment, the heat shield sheet and the casing remaining unchanged. An important economic advantage follows, it being possible to replace the existing peg by the modified peg without modifying the surrounding parts.
Said replacement can be carried out from new for preventive purposes or on the occasion of a repair.
In an advantageous manner, the said surface portion is made up by a shoulder machined in the head of the rotation-proofing peg; more particularly said surface portion is formed by a lug which extends parallel to the axis of the distributor and bears against the inside wall of the casing.
The device of the invention has an interesting application in the configuration described in patent FR 2 743 603, the distributor segment including a rib, at right angles to the axis of the distributor, bearing against the inside wall of the casing, and said notch of which is formed in a protrusion which is provided on one side of the rib. In this case, the heat shield sheet is preferably in the form of a ring sector with an indentation corresponding to said protrusion, the tab being arranged in the bottom of the indentation. More particularly, the shield sheet is provided upstream with regard to the rib of the distributor segment and the rotation-proofing peg.
Insofar as the characteristic of the invention concerns just the rotation-proofing peg, the invention also concerns a rotation-proofing peg capable of being used in the device above, the peg including a straight rod and a head with a first face parallel to the axis of the rod and a surface portion at right angles with respect to said first face, on the side opposite the rod.
In a preferable manner, the peg includes a lug at right angles with respect to the axis of the straight rod, said surface portion being arranged on the lug.
The invention also concerns a gas turbine engine including a turbine stage with a device such as described above.
The invention will now be described by way of the following accompanying figures which are for illustrative purposes and are not restrictive, in which
With reference to
The distributor 8 is formed by fixed blades which are arranged in a wheel divided into a plurality of segments 80 which are distributed circumferentially around the axis of the machine. Each segment 80 includes several adjacent fixed blades which are integral with an element in the ring sector 81. The distributor segment 80 is held upstream by a rib in the form of a rail 101 which extends axially from the inside wall of the casing 10; an upstream hook 82, which is integral with the element in the ring sector 81, bears against the radially outer face of the rail 101. Downstream the element 81 includes a peripheral radial rib 83, at right angles to the axis of the distributor, which rests by way of a radially outside face 83a and a downstream face 83b on the corresponding faces of a ring-shaped rail 102 which extends axially from the inside wall of the casing 10 with a downstream edge turned toward the axis.
As can also be seen in
A heat shield sheet 30 is arranged between the ring sector 81 of the segment 80 and the inside wall of the casing. The sheet has the general form of a ring sector which upstream bears against an abutment surface arranged in the casing which can be at the level of the upstream rail 101. Downstream the shield sheet 30 is cut away into an indentation which follows the contour of the protrusion 83′ of the rib. A tab 30a in the bottom of the indentation bears against the rotation-proofing peg 20. As the sheet is lightly deformable, a spring effect can be provided in order to ensure the sheet is held in position during the operation of the turbo machine.
It has been shown that this has not been sufficient and that the downstream edge of the shield sheet was likely to go and rub against the inside face of the casing, possibly resulting in the forming of unwanted grooves.
The rotation-proofing peg has been modified according to the invention. The rotation-proofing peg according to the invention has the same references as the peg of the prior art, to which 100 has been added.
Said peg 120 can be seen in
For preventive purposes, it is possible when the machine is visited to replace the existing rotation-proofing pegs 20 by the pegs 120 of the invention. The anti-rotation function is assured in the same way with, in addition, protection of the inside wall of the casing.
Number | Date | Country | Kind |
---|---|---|---|
1054263 | Jun 2010 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/FR11/51251 | 5/31/2011 | WO | 00 | 11/28/2012 |