EP2867499A1

EP2867499A1 - Sleeve for turbine bearing stack

Info

Publication number: EP2867499A1
Application number: EP20130809881
Authority: EP
Inventors: Marc J. Muldoon
Original assignee: United Technologies Corp
Current assignee: RTX Corp
Priority date: 2012-06-29
Filing date: 2013-06-25
Publication date: 2015-05-06
Also published as: WO2014004491A1; US20140010648A1; EP2867499A4

Abstract

A support bearing arrangement comprises a gas turbine rotor shaft, a bearing stack, a bearing sleeve, and a support bearing. The bearing stack comprises a fore seal plate, and aft seal plate, and a bearing mount situated axially between the fore and aft seal plates. The bearing sleeve surrounds at least a portion of the rotor shaft, and is configured to form an insulating air gap between the rotor shaft and the bearing stack. The support bearing is mounted on the bearing mount to couple the gas turbine rotor shaft to a stationary structure, thereby centering and retaining the gas turbine rotor shaft.

Description

SLEEVE FOR TURBINE BEARING STACK

BACKGROUND

The present invention relates generally to turbomachinery, and specifically to bearing protection structures. In particular, the invention concerns a thermal protection sleeve for gas turbine radial support bearings.

Gas turbine engines are rotary-type combustion engines comprising a compressor, a combustor, and a turbine. Gas drawn in at an upstream inlet is compressed by the compressor via a plurality of alternating airfoil stages of non-rotating compressor vanes and rotating compressor blades. This compressed gas is fed into the combustor and mixed with fuel. The resulting fuel-air mixture is then ignited to generate hot combustion gas. The turbine extracts energy from the expanding combustion gas via a series of alternating airfoil stages of non-rotating turbine vanes and rotating turbine blades in the form of rotation of at least one axial shaft. Gas is expelled from the turbine at an outlet which may provide reactive thrust from exhaust. Energy extracted by the turbine drives the compressor, and may also power gearboxes, generators, and other external devices.

Gas turbine engines provide efficient, reliable power for a wide range of applications, including aviation and industrial power generation. Many larger gas turbine engines include multiple stages of compressors and turbines arranged in series. A conventional two-stage gas turbine engine comprises, in flow-path order from inlet to outlet: a fan, a low pressure compressor (LPC), a high pressure compressor (HPC), a combustor, a high pressure turbine (HPT), and a low pressure turbine (LPT). The fan, LPT, and LPC are connected by a common low pressure shaft that turns at a first speed, while the HPC and HPT share a common high pressure shaft that turns at a second, higher speed. These high pressure and low pressure shafts are arranged in coaxially nested spools. Some two stage gas turbine engines include a mid-turbine frame (MTF), an intermediate non-rotating vane structure situated between the high pressure turbine and the low pressure turbine.

High pressure and low pressure shafts of gas turbine engines are centered and radially supported against stationary casing structures by means of radial support bearings. These bearings allow stationary structures such as vane stages, combustors, and MTFs to radially and axially position and retain the shafts. In some gas turbine engines, radial support bearings may be situated on or near a hot shaft. Excessive heat can damage bearings, and cause coking or congestion of lubricant oil. SUMMARY

The present invention is directed toward a support bearing arrangement having a gas turbine rotor shaft, a bearing stack, a bearing sleeve, and a support bearing. The bearing stack comprises a fore seal plate, and aft seal plate, and a bearing mount situated axially between the fore and aft seal plates. The bearing sleeve surrounds at least a portion of the rotor shaft, and is configured to form an insulating air gap between the rotor shaft and the bearing stack. The support bearing is mounted on the bearing mount to couple the gas turbine rotor shaft to a stationary structure, thereby centering and retaining the gas turbine rotor shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a gas turbine engine.

FIG. 2 is a cross-sectional view of a bearing region of the gas turbine engine of

FIG. 1.

DETAILED DESCRIPTION FIG. 1 depicts gas turbine engine 10, comprising fan 12, compressor 14, combustor 16, and turbine 18, and casing 20. Compressor 14 comprises low pressure compressor (LPC) 22 and high pressure compressor (HPC) 24, and turbine 18 comprises high pressure turbine (HPT) 26, mid-turbine frame (MTF) 28, and low pressure turbine (LPT) 30. LPC 22, HPC 24, HPT 26, and LPT 30 each comprise a plurality of alternating airfoils stages of non-rotating vanes and rotating blades. HPT 26, in particular, comprises at least one HPT rotor disk 32 adjacent MTF 28, and at least one HPT stator 34 adjacent HPT rotor disk 32. Although FIG. 1 depicts a two spool engine having a high pressure spool and a low pressure spool, the present invention may additionally or alternatively be applied to engines having only one spool, or three or more spools. In particular, the bearing sleeve that is the subject of the present invention can be applied embodiments of gas turbine engine 10 having a third, intermediate pressure (IP) spool in addition to low and high pressure (LP, HP) spools.

Fan 12, LPC 22, and LPT 30 share a common low pressure shaft 36, while HPC 24 and HPT 26 share a common high pressure shaft 38. Low pressure shaft 34 and high pressure shaft 36 are rotor shafts centered and supported by support bearings 40, which carry axial and radial load from both shafts to casing 20 via non-rotating structures including MTF 28. MTF 28 is a non-rotating structure including a plurality of stationary vanes disposed between HPT 26 and LPT 30. Gas turbine engine 10 is a two-stage gas turbine engine wherein fan 12 receives and propels airflow F axially aft. A portion of airflow F enters and is pressurized by LPC 22 and HPC 24, each of which comprises a plurality of alternating stages of rotor and stator airfoils. Pressurized gas from HPC 24 is fed into combustor 16, where it is mixed with combustible fuel. The resulting fuel-air mixture is ignited to produce a hot working fluid that drives HPT 26 and LPT 30 before exiting gas turbine engine 10. HPT 26 and LPT 30 comprise a plurality of alternating stages of rotor and stator airfoils. The working fluid rotates turbine rotors such as HPT rotor disk 32, thereby driving high pressure shaft 38 and low pressure shaft 36. High pressure shaft 38 in turn drives HPC 24, while low pressure shaft 36 drives LPC 22 and fan 12. In some embodiments, high pressure shaft 38 and/or low pressure shaft 36 may additionally drive a generator (not shown) or other powered system, either directly or via a gearbox.

Low pressure shaft 36 and high pressure shaft 38 are substantially rigid coaxial cylinders. Fan 12, LPC 22, and LPT 30 are mounted on low pressure shaft 36, while HPC 24 and HPT 26 are mounted on high pressure shaft 38. High pressure shaft 38 and low pressure shaft 26 are both centered and supported by casing 20. Casing 20 is a rigid external structure of gas turbine 10 that retains and positions components of gas turbine engine 10 including LPC 22, HPC 24, HPT 26, MTF 28, and LPT 30. Low pressure shaft 36 and high pressure shaft 38 ride bearings 40, which form interfaces between the shafts and non-rotating structures of compressor 14 and turbine 18, including MTF 28. These non-rotating structures carry axial and radial loads from high pressure shaft 38 and low pressure shaft 36 to casing 20, which provides a substantially rigid foundation to align and retain both shafts. Support bearings 40 may, for instance, be roller bearings arranged in rings about low pressure shaft 36 and high pressure shaft 38. In some instances, bearings 40 may be lubricated with oil. Support bearings 40 may be located between low pressure shaft 36 and stationary portions of LPC 22 and LPT 30, and between high pressure shaft 38 and MTF 28.

During operation of gas turbine engine 10, HPT rotor disk 32 and high pressure shaft 38 can reach high temperatures capable of damaging or degrading support bearings 40, and causing coking and congestion of lubricant oil. Accordingly, at least some support bearings 40 located near high pressure shaft 38 are provided with a protective sleeve that forms a thermal barrier between support bearings and high pressure shaft 38 and HPT rotor disk 32 (see sleeve 116 of FIG. 2, described in further detail below). FIG. 2. is a cross-sectional view of a region 2 of gas turbine engine 10 (see FIG. 1). FIG. 2 depicts MTF 28, HPT rotor disk 32, high pressure shaft 38, support bearings 40, tubular HPT portion 42, bearing mount 102, oil scoop 104, oil source 106, fore seal plate 108, aft seal plate 110, fore seal 112, aft seal 114, bearing sleeve 116, minidisk 118, NPT nut 120, bearing nut 122, and radial air gap 124.

Support bearing 40 is one of an annular ring of bearings that provide an interface between MTF 28 and high pressure shaft 38 to retain, center, and support high pressure shaft 38. Support bearing 40 may, for instance, be a lubricated roller bearing. MTF 28 is an intermediate vane structure located between HPT 26 and LPT 30, and rigidly attached to casing 20 (see FIG. 1). MTF 28 carries radial load between support bearing 40 and casing 20 to anchor high pressure shaft 38. Bearing mount 102 is a rotating structure configured to receive support bearings 40 and distribute lubricating oil from oil scoop 104 to support bearings 40. Oil scoop is a rotating structure configured to draw oil radially inward from oil source 106 to adjacent a radially outer surface of bearing sleeve 116. Oil scoop 104 has lubricant channels configured to allow oil to centripetally flow axially aft and radially outward to bearing mount 102 to lubricate support bearings 40. Oil scoop 104 receives lubricant oil from oil source 106, a non-rotating tube or nozzle that drips or sprays oil onto oil scoop 104 at metered rate. Scallops or angled channels in oil scoop 104 draw oil radially inward from oil source 106 as oil scoop 104 rotates. Oil source 106 may, for instance, receive oil from tubing extending through MTF 28 to casing 20.

Fore and aft seal plates 108 and 110 are rotating structures that form a face seal with fore and aft seals 112 and 114. Fore and aft seals 112 and 114 are non-rotating components such as static carbon seals. Fore and aft seals 112 and 114 mate with fore and aft seal plates 108 and 110 to create an oil seal that prevents leakage of oil from oil source 106 into surrounding regions of gas turbine engine 10. Fore and aft seals 112 and 114 may be mounted to MTF 28 or to other local non-rotating structures. In some embodiments, seal plates 108 and 110 may receive lubricating oil from bearing mount 102 and/or oil scoop 104.

Bearing sleeve 116 is a rigid cylindrical heat shield formed of a material such as

Waspaloy. Materials for bearing sleeve 116 may further be selected to closely match the thermal expansion coefficients of surrounding materials (e.g. MTF 28 and HPT rotor disk 32). Bearing sleeve 116 surrounds tubular HPT portion 42, an axially aft-extending cylindrical section of HPT rotor disk 32. Bearing sleeve 116 and tubular HPT portion 42 are constructed to form radial air gap 124, an open space between bearing sleeve 116 and tubular HPT portion 42 that at least partially thermally isolates the bearing stack comprising fore seal plate 108, bearing mount 102, oil scoop 104, and aft seal plate 110 from high pressure shaft 38. Bearing sleeve 116 is constructed to contact tubular HPT portion 42 at locations situated remotely from bearing mount 102, so as to limit thermal impact on bearing fits and bore temperature. As described above with respect to FIG. 1, high pressure shaft 38 may reach sufficiently high temperatures during operation of gas turbine engine 10 to cause damage to support bearing 40 and/or fore and aft seal plates 108 and 110. High temperatures can also cause coking and congestion of lubricant oil within channels of bearing mount 102 and oil scoop 104, impeding lubrication of support bearing 40. Bearing sleeve 116 carries axial load from bearing nut 122 to minidisk 118 while protecting the bearing stack from excessive heating by separating bearing stack components from HPT rotor disk 32 and high pressure shaft 38 by radial air gap 124, which acts as an insulator.

Minidisk 118 is a substantially disk-shaped cover plate that abuts HPT rotor disk

32. Minidisk 118 provides axial retention for blades of HPT rotor disk 32, and in some embodiments may direct conditioning air along the aft face of HPT rotor disk 32. Minidisk 118 is axially retained against HPT rotor disk 32 by bearing sleeve 116, which fits radially over and axially abuts minidisk 118. HPT nut 120 and bearing nut 122 are threaded load-bearing nuts that screw onto a threaded tie shaft region of high pressure shaft 38. HPT nut 120 retains HPT rotor disk 32, while bearing nut 122 retains the bearing stack (comprising bearing mount 102, oil scoop 104, and fore and aft seal plates 108 and 110) against bearing sleeve 116, thereby securing minidisk 118 against HPT rotor disk 32. In some embodiments, minidisk 118 may meet HPT rotor disk 32 in a bayonet or anti-rotation crenellation at the inner diameter of minidisk 118. In these embodiments, bearing sleeve 116 may secure minidisk 118 against the bayonet or anti- rotation crenellation, thereby preventing minidisk 118 from moving relative to HPT rotor disk 32.

Although the preceding description has focused on embodiments wherein support bearing 40 and bearing sleeve 116 are situated at an aft end of high pressure shaft 38 near MTF 28, the present invention may also be applied to shield support bearings and carry axial loads at other locations on high pressure shaft 38 or low pressure shaft 36. Support bearings 40 located close to high pressure shaft 36 are particularly likely to be exposed to high temperatures that can result in oil coking, and are therefore in particular need of the thermal protection provided by bearing sleeve 116. Some configurations of gas turbine engine 10 may also expose support bearings 40 to oil coking temperatures at locations radially or axially further from high pressure shaft 38, however, necessitating similar protection.

While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

In one embodiment of the present invention, a support bearing arrangement includes a gas turbine rotor shaft, a bearing stack, a bearing sleeve, and a support bearing. The bearing stack comprises a fore seal plate, and aft seal plate, and a bearing mount situated axially between the fore and aft seal plates. The bearing sleeve surrounds at least a portion of the rotor shaft, and is configured to form an insulating air gap between the rotor shaft and the bearing stack. The support bearing is mounted on the bearing mount to couple the gas turbine rotor shaft to a stationary structure, thereby centering and retaining the gas turbine rotor shaft.

Additional and/or alternative embodiments include a rotor disk affixed to the rotor shaft, such that the bearing sleeve and an axially-extending cylindrical portion of the rotor disk surrounding the rotor shaft define the insulating air gap. Some such embodiments include a blade retention minidisk disposed between the rotor disk and the bearing sleeve, and an axial nut configured to attach to the gas turbine rotor shaft and bear axial load from the minidisk through the bearing sleeve. Further embodiments include fore and aft seal plates that mate to form air seals with adjacent respective fore and aft seals; an oil scoop situated between the fore and aft seal plates that provides oil to lubricate the bearing mount; and forming the bearing sleeve of a material such as Waspalloy selected to closely match the thermal expansion coefficients of surrounding components.

In another embodiment of the invention, a gas turbine engine comprises a gas turbine rotor disk mounted on a rotatable shaft, a bearing sleeve, and a bearing stack. The gas turbine rotor disk has an axially aft-extending cylindrical portion. The bearing sleeve sheaths the aft extending cylindrical portion of the rotor disk so as to define an insulating radial air gap between the bearing sleeve and the aft-extending cylindrical portion of the rotor disk. The bearing stack comprises a bearing mount axially between fore and aft face seals situated radially atop the bearing sleeve, and thermally shielded from the gas turbine rotor disk and the rotatable shaft by the insulating radial air gap.

Additional and/or alternative embodiments include a minidisk mounted on the aft-extending cylindrical portion of the rotor disk to retain blades of the gas turbine rotor disk; a first nut configured to axially retain the gas turbine rotor disk on the rotatable shaft; and/or a second nut configured to axially retain the minidisk against the gas turbine rotor disk by means of axial load transferred through the bearing stack and the bearing sleeve. In some embodiments, the gas turbine rotor shaft may be a high pressure shaft of a two-stage gas turbine engine; the bearing mount may accept a support bearing configured to transfer radial load from the gas turbine rotor shaft to a stationary structure, thereby retaining and centering the gas turbine rotor shaft; the support bearing may be a roller bearing; the stationary structure may be a mid-turbine frame comprising a plurality of stationary vanes disposed between a high pressure turbine and a low pressure turbine of a two-stage gas turbine engine; and/or the bearing mount may be lubricated with oil collected by an oil scoop also mounted axially between the fore and aft seal plates

Claims

CLAIMS:

1. A support bearing arrangement comprising:

a gas turbine rotor shaft;

a bearing stack comprised of a fore seal plate, an aft seal plate, and a bearing mount situated axially between the fore and aft seal plates; a bearing sleeve surrounding at least a portion of the rotor shaft, and configured to form an insulating air gap between the rotor shaft and the bearing stack; and

a support bearing mounted on the bearing mount to couple the gas turbine rotor shaft to a stationary structure, thereby centering and retaining the gas turbine rotor shaft.

2. The support bearing arrangement of claim 1, further comprising a rotor disk affixed to the rotor shaft, wherein the bearing sleeve and an axially-extending cylindrical portion of the rotor disk surrounding the rotor shaft define the insulating air gap.

3. The support bearing arrangement of claim 2, further comprising a blade retention minidisk disposed axially between the rotor disk and the bearing sleeve, and an axial load nut configured to attach to the gas turbine rotor shaft and bear axial load from the minidisk through the bearing sleeve.

4. The support bearing arrangement of claim 1, wherein the fore seal plate and the aft seal plate mate with adjacent fore and aft seals, respectively, to form oil seals.

5. The support bearing arrangement of claim 4, wherein the bearing mount is lubricated with oil collected by an oil scoop situated axially between the fore and aft seal plates.

6. The support bearing arrangement of claim 1, wherein the bearing sleeve is formed of a material selected to closely match the thermal expansion coefficients of surrounding components.

7. The support bearing arrangement of claim 6, wherein the bearing sleeve is formed of Waspalloy.

8. The support bearing arrangement of claim 1, wherein the stationary structure is a mid-turbine frame situated between a high pressure turbine and a low pressure turbine of a two-stage gas turbine engine.

9. A gas turbine shaft assembly comprising:

a gas turbine rotor disk mounted on a rotatable shaft, the gas turbine rotor disk having an axially aft-extending cylindrical portion; a bearing sleeve sheathing the aft-extending cylindrical portion of the rotor disk so as to define an insulating radial air gap between the bearing sleeve and the aft-extending cylindrical portion of the rotor disk; and a bearing stack comprising a bearing mount axially between fore and aft face seals situated radially atop the bearing sleeve, and thermally shielded from the gas turbine rotor disk and the rotatable shaft by the insulating radial air gap.

10. The gas turbine shaft assembly of claim 9, further comprising a minidisk mounted on the aft-extending cylindrical portion of the rotor disk to retain blades of the gas turbine rotor disk.

11. The gas turbine shaft assembly of claim 10, further comprising a first nut configured to axially retain the gas turbine rotor disk on the rotatable shaft, and a second nut configured to axially retain the minidisk against the gas turbine rotor disk by means of axial load transferred through the bearing stack and the bearing sleeve.

12. The gas turbine shaft assembly of claim 9, wherein the gas turbine rotor shaft is a high pressure shaft of a two-stage gas turbine engine.

13. The gas turbine shaft assembly of claim 9, wherein the bearing mount accepts a support bearing configured to transfer radial load from the gas turbine rotor shaft to a stationary structure, thereby retaining and centering the gas turbine rotor shaft.

14. The gas turbine shaft assembly of claim 15, wherein the support bearing is a roller bearing.

15. The gas turbine shaft assembly of claim 15, wherein the stationary structure is a mid-turbine frame comprising a plurality of stationary vanes disposed between a high pressure turbine and a low pressure turbine of a two-stage gas turbine engine.

16. The gas turbine shaft assembly of claim 9, wherein the bearing mount is lubricated with oil collected by an oil scoop also mounted axially between the fore and aft seal plates.