US20090155073A1

US20090155073A1 - Sealing the fastening of a bearing support in a turbomachine

Info

Publication number: US20090155073A1
Application number: US12/329,925
Authority: US
Inventors: Regis Eugene Henri Servant
Original assignee: SNECMA SAS
Current assignee: Safran Aircraft Engines SAS
Priority date: 2007-12-14
Filing date: 2008-12-08
Publication date: 2009-06-18
Also published as: EP2071141A1; RU2008149140A; EP2071141B1; JP2009144715A; FR2925123A1; CA2646976A1

Abstract

A turbomachine including a shaft guided in an upstream bearing and a downstream bearing, the upstream bearing being carried by a first annular support that is fastened by bolts to a casing via a second annular support that carries the downstream bearing, wherein the ends of the fastener bolts are covered by an annular cover sealingly fastened to the second support or to the casing.

Description

TECHNOLOGICAL BACKGROUND OF THE INVENTION

A bypass turbomachine includes a fan arranged at its upstream end and driven in rotation by a shaft that is guided by upstream and downstream bearings carried by respective first and second annular supports. The upstream bearing is carried by the upstream end of the first support whose own downstream end includes a plurality of orifices distributed around its circumference, thereby enabling it to be fastened by bolting to a radially outer portion of the second support, which is in turn fastened by bolting to an intermediate casing situated downstream from a low-pressure compressor.
The downstream end of the first support includes an annular rim formed with a plurality of notches that receive the upstream portions of bolts for fastening the first support to the second support. These notches open out into cavities machined in the rim of the support for receiving the heads of the bolts. Washers are engaged on the bolts to form continuous bearing surfaces for the heads of the bolts against the rim of the support.
Sealing against the lubricating oil for the upstream and downstream bearing is provided by means of a first sealing ring situated radially outside the fastener bolt in an annular groove in the upstream radial face of the second support that comes into contact with the downstream end of the first support, and by means of a second sealing ring placed in an annular groove between facing cylindrical surfaces of the second support and of the intermediate casing.
Nevertheless, that type of fastening presents several drawbacks. Firstly, making cavities in the downstream rim of the first support is lengthy and difficult. Furthermore, the bolts mounted in the notches of the first support are not retained until the second support is in place, thereby complicating the assembly process.
The fastener bolts used are fuse bolts. Thus, in the event of a blade being lost, the resulting unbalance gives rise at the first support to a traction force on the fastener bolts, which are designed to break when the applied load exceeds a predetermined value. Nevertheless, locating these bolts inside the first support leads to bolt debris being ejected into the inter-bearing enclosure, and that can damage the upstream and downstream bearings and other parts located therein such as enclosure de-oilers, oil nozzles, etc. In addition, the bolts come into contact with the lubricating oil for the upstream and downstream bearings and therefore need to comply with strict cleanliness criteria.

SUMMARY OF THE INVENTION

A particular object of the present invention is to avoid those drawbacks of the prior art in a manner that is simple, effective, and inexpensive.
To this end, the invention provides a turbomachine including a shaft guided in an upstream bearing and a downstream bearing, the upstream bearing carried by a first annular support that is fastened by bolts to a casing via a second annular support that carries the downstream bearing, wherein the ends of the bolts for fastening the first support to the second support are covered by an annular cover sealingly fastened to the second support or to the casing.
The use of an annular cover makes it possible to use a single part to cover all of the ends of the bolts and, in the event of a blade being lost, serves to avoid debris from the bolts escaping into the inter-bearing enclosure.
Advantageously, the bolts for fastening the first support are on the outside of the support, thus making it possible to avoid solid particles present on the fuse bolts penetrating into the inter-bearing enclosure and polluting the lubricating oil for the upstream and downstream bearings. Placing the bolts outside relative to the first support also makes it possible, in the event of a blade being lost, to keep the debris of the upstream portions of the fuse bolts outside the inter-bearing enclosure.
The downstream end of the first bearing support is fastened to the second support more simply, and it is no longer necessary to make use of washers since the heads of the bolts can bear around their entire circumference. It is also simple to fabricate the first support since this part no longer presents a complex shape at its downstream end, as it does in the prior art.
Advantageously, the annular cover is of U-shaped section comprising two parallel walls sealingly engaged against a cylindrical wall of the second support and inside a cylindrical wall of the casing.
According to another feature of the invention, a sealing ring is mounted in an annular groove in an upstream radial face of the second support or in a corresponding downstream radial face of the first support, and sealing rings are mounted in annular grooves in the walls of the cover or in cylindrical walls of the second support and of the cover, thereby enabling a small number of sealing rings to seal the connection between the first support and the second support and preventing oil from escaping from the inter-bearing enclosure via the bolts.
In order to guarantee good sealing in operation, the cover is preferably made of a material having a coefficient of expansion similar to the coefficients of expansion of the second support and of the casing.
The cover is held in position covering the ends of the bolts by means of a downstream cylindrical rim of the cover that is fastened by bolts to a downstream cylindrical rim of the second support. The cover may also be fastened directly to the casing by means of bolts.
The invention also provides an annular sealing cover for use in a turbomachine as described above, wherein the cover presents a U-shaped section with two parallel cylindrical walls that are respectively a radially inner wall and a radially outer wall, with at least the radially outer wall including an outer annular groove for receiving a sealing ring.
According to another feature of the invention, the cover includes a cylindrical rim extending its radially inner cylindrical wall in the opposite direction and including regularly distributed orifices for passing fastener means.
The cover may be made of a composite material or of a metal, e.g. titanium.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood and other details, advantages, and characteristics of the invention appear on reading the following description made by way of non-limiting example, with reference to the accompanying drawings, in which:

FIG. 1 is a partial schematic half-view in axial section of a turbomachine with a prior art bearing support;

FIG. 2 is a partial perspective view seen from downstream showing the upstream bearing support of FIG. 1;

FIG. 3 is a partial schematic half-view in axial section of a turbomachine with a bearing support according to the invention; and

FIG. 4 is a view on a larger scale showing a detail of FIG. 3 marked by a box of chain-dotted outline.

DETAILED DESCRIPTION

Reference is made initially to FIG. 1 showing an upstream portion of a prior art turbomachine that includes a fan wheel 10 driven in rotation about the axis 12 of the turbomachine by a shaft 14 having its upstream end fastened by bolts 16 to a frustoconical wall 18 that is secured to the fan wheel 10. The shaft 14 is fastened to the end of a shaft 20 of a low-pressure turbine (not shown). The fan wheel 10 is secured to the rotor 22 of a low-pressure compressor that is associated with an intermediate casing 24.
The shaft 14 is supported and guided by upstream and downstream bearings 26 and 28. The upstream bearing 26 is carried by the upstream end of a first annular support 30 having its downstream end fastened by fuse bolts 32 to a radially outer portion of a second annular support 34 that carries the downstream bearing 28 at its radially inner end. The second support 34 is fastened by bolts 36 to a flange 38 of the intermediate casing 24.
The downstream end of the first support 30 has notches 40 facing radially towards the inside of the turbomachine, which notches are distributed around the entire circumference of an annular rim of the first support 30 in order to receive the upstream ends of the fuse bolts 32 (FIG. 2). Each notch 40 opens out into a cavity 42 in which there is received the head 44 of a fuse bolt 32. The heads 44 of the fuse bolts 32 come into abutment against the ends of the notches 40 when the nuts 48 are tightened onto the fuse bolts 32. Washers 46 are interposed between the heads 44 of the bolts 32 and the notches 40 so as to enable the heads 44 of the bolts 32 to bear continuously all around their circumference.
Each fuse bolt 32 presents a narrowing in its portion situated in the notch 40, thereby enabling the corresponding bolt 32 to break at that location when the load that is applied thereto is too great. In the event of a blade being lost, the appearance of unbalance on the fan shaft 14 can lead to high levels of traction force on the fuse bolts 32. Decoupling the first and second supports 30 and 34 makes it possible to accommodate the unbalance and to limit the transmission of forces to the intermediate casing 24 and to the turbomachine as a whole.
As mentioned above, this technique for fastening the first and second supports 30 and 34 presents several drawbacks.
According to the invention, and as shown in FIG. 3, these drawbacks are avoided by the fact that the downstream of the first support 50 is fastened to the radially outer portion of the second support 52 by fuse bolts 32 that are radially at the outside of the first support 50, with a leak-tight connection being provided in a manner that is simple and inexpensive.
The first support 50 comprises a frustoconical wall 56 of section that tapers going upstream, carrying at its upstream end the upstream bearing 26, and connected at its downstream end to a cylindrical wall 58 with its downstream end including an annular rim 60 that extends radially outwards. Bolt-passing orifices are formed in the annular rim 60 in alignment with corresponding orifices in the radially outer portion of the second support 52 for receiving the fuse bolts 32. The upstream end of each fuse bolt 32 has a head 44 bearing axially over its entire circumference against the upstream face of the annular rim 60, its downstream end receiving a nut 62 that is tightened against the radially outer portion of the second support 52.
The downstream ends of the bolts 32 and of the nuts 62 are covered by an annular cover 54 that presents a U-shaped cross-section and that comprises two parallel walls, respectively a radially inner wall 64 and a radially outer wall 66, the inner wall 64 being connected to a cylindrical rim 68 that extends downstream and that includes orifices for passing bolts that are regularly distributed around the axis 12 of the turbomachine.
The cover 54 covers the downstream end of the fuse bolts 32 and its radially inner 64 and outer 66 walls are sealingly engaged against a cylindrical wall 70 of the second support 52 and in a cylindrical wall 72 of the flange 38 of the intermediate casing 24. The cover 54 is held in position by bolts 73 inserted in the orifices through the downstream cylindrical rim 68 of the cover 54 and through corresponding orifices in a cylindrical rim 74 of the second support 52.
The radially outer wall 66 of the cover 54 and the cylindrical wall 70 of the second support 52 include respective annular grooves facing radially outwards and receiving sealing rings 76 and 78. These two sealing rings 76 and 78 prevent lubricating oil from the upstream 26 and downstream 28 bearings escaping via the orifices through which the fuse bolts 32 pass and via the contact zones between the second support 52 and the intermediate casing 24.
A third sealing ring 80 is mounted in an annular groove in an upstream radial face of the second support 52, this upstream face being in contact with a radial downstream face of the first support 50. This sealing ring 80 lies radially inside the fuse bolts 32 so as to prevent oil from escaping via the bolt-passing orifices in the rim 60.
In the event of the first and second supports 50 and 52 being decoupled, the annular cover 54 serves to contain the debris of the downstream ends of the fuse bolts 32, while fastening the bolts 32 radially outside the first support 50 serves to avoid the debris of the heads 44 of the bolts 32 penetrating into the inter-bearing enclosure and damaging the parts situated therein.
The cover 54 also serves to seal the downstream end of the fuse bolts 32 and to simplify fabrication of the first support 50 since it is no longer necessary to make notches and cavities in a rim of said support.
It is no longer essential to use washers since the head 44 of each fuse bolt 32 bears around its entire circumference against the upstream face of the annular rim 60.
The radially outer end of the second support 52 is fastened to the intermediate casing 24 by means of bolts 36 screwed into a flange 38 of the intermediate casing 24.
Advantageously, the cover 54 is made of a material that presents a coefficient of thermal expansion close to those of the materials of the second support 52 and of the intermediate casing 24 so as to guarantee good sealing by the sealing rings 76, 78, and 80 at the temperatures to which these various parts are subjected.
The cover 54 may be made of composite material or of metal, such as titanium, for example.
In a variant of the invention, the cover 54 may include a downstream radial annular rim fastened by bolts to a downstream annular rim of the second support 52 or of the flange 38 of the intermediate casing 24.

Claims

1. A turbomachine including a shaft guided in an upstream bearing and a downstream bearing, the upstream bearing being carried by a first annular support that is fastened by bolts to a casing via a second annular support that carries the downstream bearing, wherein the ends of the bolts for fastening the first support to the second support are covered by an annular cover sealingly fastened to the second support or to the casing.

2. A turbomachine according to claim 1, wherein the bolts for fastening the first support are on the outside of the support.

3. A turbomachine according to claim 1, wherein the cover is of U-shaped section comprising two parallel walls sealingly engaged against a cylindrical wall of the second support and inside a cylindrical wall of the casing.

4. A turbomachine according to claim 3, wherein annular sealing rings are mounted in annular grooves in the walls of the cover or in the cylindrical walls of the second support and of the cover.

5. A turbomachine according to claim 1, wherein the ends of the bolts situated inside the cover carry nuts.

6. A turbomachine according to claim 1, wherein a sealing ring is mounted in an annular groove in an upstream radial face of the second support or in a corresponding downstream radial face of the first support.

7. A turbomachine according to claim 1, wherein the cover is made of a material having a coefficient of expansion similar to the coefficients of expansion of the second support and of the casing.

8. A turbomachine according to claim 1, wherein the cover has a downstream cylindrical rim fastened by bolts to a downstream cylindrical rim of the second support.

9. A turbomachine according to claim 1, wherein the cover is fastened by bolts to the casing.

10. An annular sealing cover for use in a turbomachine according to claim 1, wherein the cover presents a U-shaped section with two parallel cylindrical walls that are respectively a radially inner wall and a radially outer wall, with at least the radially outer wall including an outer annular groove for receiving a sealing ring.

11. A cover according to claim 10, made of composite material or of metal, such as titanium, for example.

12. A cover according to claim 10, including a cylindrical rim extending its radially inner cylindrical wall in the opposite direction and including regularly distributed orifices for passing fastener means.