GB2532197A

GB2532197A - A sealing assembly

Info

Publication number: GB2532197A
Application number: GB1419649.7A
Authority: GB
Inventors: Steele Oliver; John Gibbons
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2014-11-04
Filing date: 2014-11-04
Publication date: 2016-05-18
Anticipated expiration: 2034-11-04
Also published as: GB201419649D0; GB2532197B

Abstract

A bearing chamber sealing assembly 100 is provided. The sealing assembly 100 comprises a centrifugal oil mist separator device110 and a sealing element 140. The centrifugal oil mist separator device 110 comprises: a first axial surface 114; a second axial surface 118; a circumferential surface 122; a peripheral sealing surface 126; and a plurality of first conduits 130. In use, rotation of the centrifugal oil mist separator device 110 draws an oil mist through each of the first conduits 130, with a dynamic pressure in the vicinity of an outlet 124 from the first conduits 130 being greater than a dynamic pressure in the vicinity of an inlet 116, 120 from the first conduits 130. The advantage of the bearing chamber sealing assembly is that oil loss from the bearing housing is reduced most notably during steady state and transient engine operating conditions where the sense of pressurisation may be disrupted. The assembly provides an additional benefit of reducing lip seal wear as a result of operation at high shaft rotational speeds.

Description

A SEALING ASSEMBLY

Field of the Invention

The present invention relates to a bearing chamber sealing assembly and particularly, but not exclusively, to a bearing chamber sealing assembly for a gas turbine engine. s

Background to the Invention

The use of sealing elements to prevent unwanted egress of fluid from rotating equipment, such as gearboxes, transmissions and bearing supports is well known. One example of such a sealing element is a lip seal in which an elastomeric ring is held into contact with the rotating shaft by a circumferential spring element.

Figure 1 shows an example of a conventional lip seal application. The lip seal 10 is located in a housing 20 and seals against a shaft 30. A rubbing portion 12 of the lip seal 10 is pressed against a surface 32 of the shaft 30 by the circumferential spring element 14. In addition, for a conventional lip seal application it is typical for the pressure in region 40 (internal to the rotating equipment) to be greater than in region 50 (external to the rotating equipment) resulting in a pressure differential which acts to apply a proportional radial force to further increase the contact load between the rubbing portion of the lip seal and the shaft. This mechanism is referred to as pressure energisation.

In an application where shaft surface velocities are high, for example in a gas turbine engine, the frictional force between the rubbing portion of a conventional lip seal and shaft results in high surface temperatures due to the radial loads applied by the circumferential spring and pressure energisation. This can degrade the material of the lip seal rubbing portion resulting in mechanical wear and attrition. -2 -

In the arrangement shown in Figure 1, mechanical wear to the sealing element would result in a flow of oil laden air out of the rotating equipment beneath the rubbing portion of the seal, as indicated by arrow A. In order to reduce the level of wear for a given rotational speed (or increase the rotational speed for a given level of wear) the sense of pressurisation of the sealing element can be reversed which acts to reduce the contact load between the rubbing portion of the lip seal and the shaft. Taking the example in Figure 1 the pressure in region 40 would be lower than in region 50. Reversing the direction of pressurisation has the additional benefit of acting in the direction to prevent unwanted egress of fluid from rotating equipment.

However, during certain steady state and transient engine operating conditions the sense of pressurisation may be disrupted resulting in the pressure inside the rotating equipment exceeding the pressure outside the rotating equipment. This would again result in a flow of oil laden air out of the rotating equipment beneath the rubbing portion of the seal, as indicated by arrow A in Figure 1.

In all cases the flow of oil laden air as indicated by arrow A in Figure 1 is undesirable because it results in a loss of oil and a contamination of the region outside the rotating equipment by the oil laden air.

Statements of Invention

According to a first aspect of the present invention there is provided a bearing chamber sealing assembly comprising: a centrifugal oil mist separator device; and a seal element, the centrifugal oil mist separator device comprising: a first axial surface; a second axial surface; a circumferential surface; -3 -a peripheral sealing surface; and a plurality of first conduits, wherein the first axial surface is spaced axially apart from the second axial surface with the circumferential surface extending therebetween, each of the first conduits provides fluid communication between each of a first aperture at the first axial surface, a second aperture at the second axial surface, and a third aperture at the circumferential surface, and the seal element is sealingly engaged with the peripheral sealing surface, the peripheral sealing surface being concentric with the circumferential surface, and in use, rotation of the centrifugal oil mist separator device draws an oil mist axially inwardly into each of the first conduits through corresponding first and second apertures, and exhausts the oil mist radially outwardly through the corresponding third aperture, with a dynamic pressure in the vicinity of the third aperture being greater than a dynamic pressure in the vicinity of the second aperture.

Rotary motion of the centrifugal oil mist separator device causes oil mist to be drawn into each of the first conduits via the corresponding first and second apertures. This oil mist is then exhausted in a radially outward direction from the corresponding third apertures under the action of centrifugal forces generated by the rotary motion.

This radially outward movement causes any oil entrained in the oil mist to be carried to an outer periphery of the bearing chamber where it can be collected and returned to an oil tank.

The bearing chamber sealing assembly of this embodiment therefore provides for the separation of entrained oil from the oil mist within the bearing chamber. This in turn means that any air which escapes from the bearing chamber (via the route A of Figure 1) has little or no entrained oil.

An advantage of this feature is that the sealing assembly reduces oil loss from the bearing housing.

Optionally, the peripheral sealing surface is coincident with the circumferential surface.

In one arrangement the circumferential surface joining the first axial surface and the s second axial surface, forms the peripheral sealing surface on which the sealing element sea lingly engages.

This makes the bearing chamber sealing assembly simpler, lighter, easier to manufacture and more cost-effective for a user.

Optionally, the centrifugal oil mist separator device further comprises a plurality of second conduits, wherein each of the second conduits provides fluid communication between the second axial surface, and the circumferential surface, and, in use, rotation of the centrifugal oil mist separator device draws an oil mist axially inwardly into each of the second conduits through the corresponding second aperture, and exhausts the oil mist radially outwardly through the corresponding third aperture.

The plurality of second conduits provides fluid communication only between the second axial surface and the circumferential surface. Consequently, the second conduits provide flow through the centrifugal oil mist separator device without reducing the pressure inboard of the seal element.

Optionally, the plurality of first conduits or the plurality of second conduits is equia ngularly spaced around a peripheral portion of the centrifugal oil mist separator device.

This provides for a circumferentially regular distribution of oil mist exhausted from the first conduits third apertures. This in turn results in the oil separated from the exhausted air being circumferentially uniformly distributed around the inner periphery of the bearing housing. -5 -

Optionally, each of the second apertures is elliptical or oval with a portion of each of the first and second conduits extending from the corresponding second aperture comprises an angled passage positioned at an acute angle to, and tangential to, the second axial surface.

In one arrangement, the angled passages connected to the second apertures are angled in the direction of rotation of the centrifugal oil mist separator device.

This assists the induction of oil mist into the second apertures and so improves the efficiency of oil mist movement through the centrifugal oil mist separator device.

Optionally, the centrifugal oil mist separator device further comprises a coalescing portion, the coalescing portion being in fluid communication with corresponding ones of at least the first and third apertures.

The coalescing portion is formed from a porous material having a high surface area to volume ratio and collects the oil particles in the oil mist moving through the first and second conduits and is so arranged to minimise restriction to the flow. This in turn results in the oil particles within the oil mist coalescing into larger oil droplets. These larger oil droplets are then carried by the radially outward flow, assisted by centrifugal effects and deposited on the inner periphery of the bearing housing. This increase in droplet size improves the efficiency of the oil separation.

Optionally, the coalescing portion is formed from a material selected from the group comprising glass fibre mesh, ceramic foam, and metal foam.

In one arrangement, the coalescing portion is formed from a metal foam such as RetimetTm. In other arrangements, the coalescing portion may be formed from another cellular material. -6 -

Optionally, the seal element is one of the group comprising lip seal elements, contacting carbon seal elements and air riding carbon seal elements.

The profile of the entry to the contacting surface of the seal may be shaped or featured s to optimise the ability of the fluid flow to lift of partially lift the seal off the shaft The use of a contacting carbon seal element or an air riding carbon seal element provides the advantage of improves sealing efficiency over a lip seal element at high rotational speeds. However, carbon seal elements can be more complex and costly than lip seal elements.

According to a second aspect of the present invention there is provided a gas turbine engine comprising a bearing chamber sealing assembly according to a first aspect of the invention.

Other aspects of the invention provide devices, methods and systems which include and/or implement some or all of the actions described herein. The illustrative aspects of the invention are designed to solve one or more of the problems herein described and/or one or more other problems not discussed.

Brief Description of the Drawings

There now follows a description of an embodiment of the invention, by way of non-limiting example, with reference being made to the accompanying drawings in which: Figure 1 shows a schematic sectional view of a rotating shaft and lip seal element

according to the prior art;

Figure 2A shows a schematic sectional view of a bearing chamber sealing assembly according to a first embodiment of the invention and showing a first conduit; Figure 2B shows an alternative view of the bearing chamber sealing assembly of Figure 2A showing a second conduit; -7 -Figure 3A shows a schematic sectional view of a bearing chamber sealing assembly according to a second embodiment of the invention and showing a first conduit; Figure 3B shows an alternative view of the bearing chamber sealing assembly of Figure 3A showing a second conduit; and Figure 4 shows a schematic sectional view of a bearing chamber sealing assembly according to a third embodiment of the invention.

It is noted that the drawings may not be to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements between the drawings.

Detailed Description

Referring to Figures 2A and 2B, a bearing chamber sealing assembly according to a first embodiment of the invention is designated generally by the reference numeral 100. In the embodiment of Figure 2, the sealing assembly forms part of a bearing housing 104 for a gas turbine engine (not shown).

The bearing chamber sealing assembly 100 comprises a centrifugal oil mist separator device110 and a sealing element 140. The centrifugal oil mist separator device 110 comprises a first axial surface 114, a second axial surface 118, a circumferential surface 122, a peripheral sealing surface 126, a plurality of first conduits 130, and a plurality of second conduits 150.

In this embodiment, each of the first axial surface 114 and the second axial surface 118 is substantially normal to an axis of rotation 112 of the centrifugal oil mist separator device 110. In other arrangements, one or both of the first axial surface 144 and the second axial surface 118 may be angled relative to the axis of rotation 112. -8 -

The first axial surface 114 is spaced axially apart from the second axial surface 118 with the circumferential surface 122 extending between the first axial surface 114 and the second axial surface 118.

The centrifugal oil mist separator device 110 is shown in Figures 2A and 2B as a discrete component. Typically such a component would be formed from a high strength material such as, for example, steel, a titanium alloy or a nickel based alloy.

In other arrangements, the centrifugal oil mist separator device 110 may be integrated with another component such as, for example, a drive shaft, a flange, a connector or similar.

In this arrangement, the sealing element 140 is a conventional lip seal that is mounted in the housing 104. The seal element 140 is sealingly engaged with and rubs against the peripheral sealing surface 126. In this embodiment, the peripheral sealing element 126 is coincident with the circumferential surface 122.

As shown in Figure 2A, each of the first conduits 130 provides fluid communication between a first aperture 116 at the first axial surface 114, a second aperture 120 at the second axial surface 118, and a third aperture 124 at the circumferential surface 122.

Each of the second conduits 150 (see Figure 2B) provides fluid communication between a second aperture 120 at the second axial surface 118, and a third aperture 124 at the circumferential surface 122.

The first conduits 130 and the second conduits 150 are arranged in an alternating equi-spaced array around a peripheral portion 113 of the centrifugal oil mist separator device 110.

In use, rotation of the centrifugal oil mist separator device 110 draws a fluid flow axially inwardly into each of the first conduits 130 through corresponding first and second apertures 116,120, and into each of the second conduits 150, through corresponding -9 -second apertures 120. This fluid flow is then exhausted radially outwardly through each of the corresponding third apertures 124.

A dynamic pressure in the vicinity of the third aperture 124 is greater than a dynamic s pressure in the vicinity of the second aperture 120. This pressure differential prevents fluid flow across the seal element 140.

Referring to Figures 3A and 3B, a bearing chamber sealing assembly according to a second embodiment of the invention is designated generally by the reference numeral 200. Features of the sealing assembly 200 which correspond to those of the sealing assembly 100 have been given corresponding reference numerals for ease of reference.

The bearing chamber sealing assembly 200 comprises a centrifugal oil mist separator device 110 and a sealing element 140. The centrifugal oil mist separator device 110 comprises a first axial surface 114, a second axial surface 118, a circumferential surface 122, a peripheral sealing surface 126, a plurality of first conduits 230, and a plurality of second conduits 250.

Each of the first axial surface 114 and the second axial surface 118 is substantially normal to an axis of rotation 112 of the centrifugal oil mist separator device 110. The first axial surface 114 is spaced axially apart from the second axial surface 118 with the circumferential surface 122 extending between the first axial surface 114 and the second axial surface 118.

As shown in Figure 3A, each of the first conduits 230 provides fluid communication between a first aperture 116 at the first axial surface 114, a second aperture 120 at the second axial surface 118, and a third aperture 124 at the circumferential surface 122. Each of the second conduits 250 (see Figure 3B) provides fluid communication between a second aperture 120 at the second axial surface 118, and a third aperture 124 at the circumferential surface 122.

-10 -The first conduits 230 and the second conduits 250 are arranged in an alternating equispaced array around a peripheral portion 113 of the centrifugal oil mist separator device 110.

In this embodiment, each of the first conduits 230 and the second conduits 250 comprise a coalescing portion 260. This coalescing portion 260 takes the form of a block of reticulated metal foam such as, for example, Retimet'TM. In other arrangements, the coalescing portion 260 may be formed from an alternative cellular or foamed material having a high surface are to volume ratio.

In use, the bearing chamber sealing assembly 200 of this embodiment functions in the same manner as the previous embodiment described above. However, the addition of the coalescing portion 260 serves to coalesce small oil droplets in the oil mist flow passing through the first and second conduits 230,250. This results in oil droplets of a larger size, albeit fewer in number, being exhausted from the corresponding third apertures 124.

Referring to Figure 4, a bearing chamber sealing assembly according to a third embodiment of the invention is designated generally by the reference numeral 300.

Features of the sealing assembly 300 which correspond to those of the sealing assembly have been given corresponding reference numerals for ease of reference.

The bearing chamber sealing assembly 300 comprises a centrifugal oil mist separator device 310 and a sealing element 140. The centrifugal oil mist separator device 310 comprises a first axial surface 314, a second axial surface 318, a circumferential surface 322, a peripheral sealing surface 326, and a plurality of first conduits 330.

Each of the first axial surface 314 and the second axial surface 318 is substantially normal to an axis of rotation 112 of the centrifugal oil mist separator device 310. The first axial surface 314 is spaced axially apart from the second axial surface 318 with the -11 -circumferential surface 322 extending between the first axial surface 314 and the second axial surface 318.

In this embodiment, the peripheral sealing surface 326 is separate from the s circumferential surface 322.

As shown in Figure 4, each of the first conduits 330 provides fluid communication between a first aperture 316 at the first axial surface 314, a second aperture 320 at the second axial surface 318, and a third aperture 324 at the circumferential surface 322.

The first conduits 330 provide a pumping effect and a radial distribution of pressure adjacent to the seal element 140 that can be used to assist the removal of oil from the bearing chamber.

In use, the bearing chamber sealing assembly 300 of this embodiment functions in a broadly similar manner to that of the previous two embodiments. In this regard, rotation of the centrifugal oil mist separator device 310 draws an oil mist axially inwardly into each of the first conduits 130 through corresponding first and second apertures 316,320. This oil mist is then exhausted radially outwardly through each of the corresponding third apertures 324.

In addition to the pressure differential property described above in respect of the first and second embodiments, this embodiment provides the further advantage of reducing wear to the seal element 140 caused by high shaft surface velocity. This is in addition to the reduction in wear achieved through the sense of the applied seal element pressure differential in bearing chamber sealing assemblies 100 and 200.

During operation at high shaft rotational speed the centrifugal oil mist separator device 310 entrains flow from the annular cavity within the seal element 140. This reduces the static pressure relative to the opposite side of the seal element 140 (the 'air side'). The resulting high pressure differential across the seal element 140 will cause the seal element 140 to "lift off" the shaft mitigating wear at high shaft surface velocities.

-12 -During operation at low shaft rotational speed or during negative pressure margin conditions, the seal element 140 will be in contact with the shaft due to the gaiter spring stiffness creating an effective contact seal, thereby minimising bearing chamber oil loss s without causing degradation and wear to the seal element 140.

A dynamic pressure in the vicinity of the third aperture 324 is greater than a dynamic pressure in the vicinity of the second aperture 320. This pressure differential prevents fluid flow across the seal element 140.

The foregoing description of various aspects of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously, many modifications and variations are possible. Such modifications and variations that may be apparent to a person of skill in the art are included within the scope of the invention as defined by the accompanying claims.

Claims

-13 -CLAIMS 1 A bearing chamber sealing assembly comprising: a centrifugal oil mist separator device; and a seal element, the centrifugal oil mist separator device comprising: a first axial surface; a second axial surface; a circumferential surface; a peripheral sealing surface; and a plurality of first conduits, wherein the first axial surface is spaced axially apart from the second axial surface with the circumferential surface extending therebetween, each of the first conduits provides fluid communication between each of a first aperture at the first axial surface, a second aperture at the second axial surface, and a third aperture at the circumferential surface, and the seal element is sealingly engaged with the peripheral sealing surface, the peripheral sealing surface being concentric with the circumferential surface, and in use, rotation of the centrifugal oil mist separator device draws an oil mist axially inwardly into each of the first conduits through corresponding first and second apertures, and exhausts the oil mist radially outwardly through the corresponding third aperture, with a dynamic pressure in the vicinity of the third aperture being greater than a dynamic pressure in the vicinity of the second aperture.
2 The bearing chamber sealing assembly as claimed in Claim 1, wherein the peripheral sealing surface is coincident with the circumferential surface.
3 The bearing chamber sealing assembly as claimed in Claim 1 or Claim 2, the centrifugal oil mist separator device further comprising a plurality of second conduits, wherein each of the second conduits provides fluid communication -14 -between the second axial surface, and the circumferential surface, and, in use, rotation of the centrifugal oil mist separator device draws an oil mist into each of the second conduits through the corresponding second aperture, and exhausts the oil mist through the corresponding third aperture.
4 The bearing chamber sealing assembly as claimed in any one of Claims 1 to 3, wherein the plurality of first conduits or the plurality of second conduits is equiangularly spaced around a peripheral portion of the centrifugal oil mist separator device.
The bearing chamber sealing assembly as claimed in any one of Claims 1 to 4, wherein each of the second apertures is elliptical or oval with a portion of each of the first and second conduits extending from the corresponding second aperture comprises an angled passage positioned at an acute angle to, and tangential to, the second axial surface.
6 The bearing chamber sealing assembly as claimed in any one of Claims 1 to 3, the centrifugal oil mist separator device further comprising a coalescing portion, the coalescing portion being in fluid communication with corresponding ones of at least the first and third apertures.
7 The bearing chamber sealing assembly as claimed in Claim 6, wherein the coalescing portion is formed from a material selected from the group comprising glass fibre mesh, ceramic foam, and metal foam.
8 The bearing chamber sealing assembly as claimed in any one of Claims 1 to 7, wherein the seal element is one of the group comprising lip seal elements, contacting carbon seal elements and air riding carbon seal elements.
9 A gas turbine engine comprising a bearing chamber sealing assembly according to any one of Claims 1 to 8.A bearing chamber sealing assembly substantially as hereinbefore described with reference to the accompanying drawings.s 11 A gas turbine engine substantially as hereinbefore described with reference to the accompanying drawings.CLAIMS1 A bearing chamber sealing assembly comprising: a centrifugal oil mist separator device; and a seal element, the centrifugal oil mist separator device comprising: a first axial surface; a second axial surface; a circumferential surface; a peripheral sealing surface; and a plurality of first conduits, wherein the first axial surface is spaced axially apart from the second axial surface with the circumferential surface extending therebetween, each of the first conduits provides fluid communication between each of a first aperture at the first axial surface, a second aperture at the second axial surface, and a third aperture at the circumferential surface, and the seal element is sealingly engaged with the peripheral sealing surface, the peripheral sealing surface being concentric with the circumferential surface, and in use, rotation of the centrifugal oil mist separator device draws an oil mist axially inwardly into each of the first conduits through corresponding first and second apertures, and exhausts the oil mist radially outwardly through the corresponding third aperture, with a dynamic pressure in the vicinity of the third aperture being greater than a dynamic pressure in the vicinity of the second aperture.2 The bearing chamber sealing assembly as claimed in Claim 1, wherein the peripheral sealing surface is coincident with the circumferential surface.3 The bearing chamber sealing assembly as claimed in Claim 1 or Claim 2, the centrifugal oil mist separator device further comprising a plurality of second conduits, wherein each of the second conduits provides fluid communication between the second axial surface, and the circumferential surface, and, in use, rotation of the centrifugal oil mist separator device draws an oil mist into each of the second conduits through the corresponding second aperture, and exhausts the oil mist through the corresponding third aperture.4 The bearing chamber sealing assembly as claimed in any one of Claims 1 to 3, wherein the plurality of first conduits or the plurality of second conduits is equiangularly spaced around a peripheral portion of the centrifugal oil mist separator device.The bearing chamber sealing assembly as claimed in any one of Claims 1 to 4, wherein each of the second apertures is elliptical or oval with a portion of each of the first and second conduits extending from the corresponding second aperture comprises an angled passage positioned at an acute angle to, and tangential to, the second axial surface.6 The bearing chamber sealing assembly as claimed in any one of Claims 1 to 3, the centrifugal oil mist separator device further comprising a coalescing portion, the coalescing portion being in fluid communication with corresponding ones of at least the first and third apertures.7 The bearing chamber sealing assembly as claimed in Claim 6, wherein the coalescing portion is formed from a material selected from the group comprising glass fibre mesh, ceramic foam, and metal foam.8 The bearing chamber sealing assembly as claimed in any one of Claims 1 to 7, wherein the seal element is one of the group comprising lip seal elements, contacting carbon seal elements and air riding carbon seal elements.9 A gas turbine engine comprising a bearing chamber sealing assembly according to any one of Claims 1 to 8.A bearing chamber sealing assembly substantially as hereinbefore described with reference to the accompanying drawings.s 11 A gas turbine engine substantially as hereinbefore described with reference to the accompanying drawings.