GB2176253A

GB2176253A - Bearings or seals

Info

Publication number: GB2176253A
Application number: GB08612818A
Authority: GB
Inventors: Terence Sidwell Wilkinson
Original assignee: Northern Engineering Industries PLC
Current assignee: Rolls Royce Power Engineering PLC
Priority date: 1985-06-08
Filing date: 1986-05-27
Publication date: 1986-12-17
Also published as: GB8612818D0; GB2176253B

Abstract

Bearings or seals (10) have first and second members, e.g. a journal (14) on a shaft (12) and a stationary member (16), respectively, between which a ring (18) is located which is free to rotate at a speed intermediate the speeds of the first and second members. Pairs of mutually opposed surface (20, 22 and 24, 26) of the first member (14) and the ring (18) and of the ring (18) and the second member (16) have respective clearances therebetween to which clearance fluid is supplied during use. The surfaces (20, 22) of at least one of the pairs of surfaces (20, 22 and 24, 26) are substantially part- spherical surfaces in nesting relationship. <IMAGE>

Description

SPECIFICATION Bearings and seals The invention relates to bearings and seals, particularly though not exclusively for use in turbo-generator sets.

It has been proposed to construct bearings which have a ring intermediate a first member and a second member of the bearing, the ring being free to rotate at a speed intermediate the speeds of the first and second members.

As compared to constructions which do not have an intermediate ring, such bearings have reduced turbulent energy dissipation and therefore reduced power losses and/or reduced lubricant flows owing to the lubricant flow being accommodated by two smaller clearances, i.e.

between the first member and the ring and between the ring and the second member, rather than a single clearance.

However, difficulties have been experienced in retaining the ring relative to the first and second members, e.g. a journal and a stationary member, respectively, which can be aggravated by mis-alignment of the journal and the second member. The latter condition can also cause wear to occur between the journal and the ring and/or between the ring and the second member.

In known types of seals, particularly for high speed machines such as turbo-generator sets, the clearances involved are very small to minimise the sealant flow requirement, but are limited by the need to accommodate differential thermal expansion between the seal and the journal.

It is an object of the present invention to provide a bearing or a seal in which one or more of the aforementioned disadvantages is reduced or eliminated.

According to the invention, a bearing or a seal comprises first and second members and a ring located therebetween, the ring being free to rotate at a speed intermediate the speeds of the first and second members, pairs of mutually opposed surfaces of the first member and the ring and of the ring and the second member having respective clearances therebetween to which clearances fluid is supplied during use, the surfaces of at least one of said pairs of surfaces being substantially part-spherical surfaces in nesting relationship.

The pairs of surfaces which are part-spherical and in nesting arrangement have a twofold function. Firstly, the surfaces accommodate mis-alignment between the first member and the second member thereby reducing or obviating wear between the component parts of the bearing or seal. Secondly, the interaction of the surfaces ensures that the ring is retained against axial movement relative to the first member and/or the second member without having to provide other retaining means.

Furthermore, when applied to seal constructions, the relatively large clearance required to accommodate differential thermal expansion is divided into two smaller clearances with a consequent relatively large reduction in sealant flow requirement.

Preferably, the bearing or seal is a journal bearing or seal, the first member comprising a journal.

In that instance, the pair of surfaces between the first member and the ring are substantially part-spherical surfaces in nesting relationship, the pair of surfaces between the ring and the second member being substantially plain cylindrical surfaces; or, alternatively, the pair of surfaces between the ring and the second member are subtantially part-spherical surfaces in nesting relationship, the pair of surfaces between the first member and the ring being substantially plain cylindrical surfaces; or alternatively, the pair of surfaces between the first member and the ring are substantially part-spherical surfaces in nesting relationship and the pair of surfaces between the ring and the second member are substantially part-spherical surfaces in nesting relationship.

Alternatively, the bearing or seal is a face bearing or seal, the first member comprising of shaft section having a generally radially extending surface which is the respective surface of said pair of mutually opposed surfaces of the first member and the ring.

In that instance, the pair of surfaces between the first member and the ring are substantially part-spherical surfaces in nesting relationship, the pair of surfaces between the ring and the second member being substantially plain radial surfaces; or, alternatively, the pair of surfaces between the ring and the second member are substantially part-spherical surfaces in nesting relationship, the pair of surfaces between the first member and the ring being substantially plain radial surfaces; or, alternatively, the pair of surfaces between the first member and the ring are substantially part-spherical surfaces in nesting relationship and the pair of surfaces between ring and the second member are substantially part-spherical surfaces in nesting relationship.

Bearings will now be described to illustrate the invention by way of example only with reference to the accompanying drawings, in which: Figure 1 is a schematic vertical section through one form of journal bearing according to the invention; Figure 2 is a schematic vertical section through a second form of journal bearing according to the invention; Figure 3 is a schematic vertical section through a third form of journal bearing according to the invention; and Figure 4 is a schematic vertical section through a face bearing according to the invention.

Referring to Figure 1, the bearing 10 for a shaft 12 has a first inner member in the form of a journal 14 on the shaft 12; a second stationary member 16; and a ring 18 located between the journal 14 and the member 16, the ring 18 being free to rotate about the journal 14 at a speed lower than speed of the journal 14 (the member 16 being stationary).

Pairs of surfaces 20, 22 and 24, 26 between the journal 14 and the ring 18 and between the ring 18 and the stationary member 16, respectively, define respective clearances to which fluid is supplied during use.

The pair of surfaces 20, 22 are part-spherical surfaces in nesting relationship and the pair of surfaces 24, 26 are plain cylindrical surfaces.

Referring now to Figures 2 and 3, reference numerals used in Figure 1 have been used in these figures for like parts but with the prefixes 1 and 2 , respectively.

In the bearing 110 (Figure 2), the pair of surfaces 124, 126 are part-spherical surfaces in nesting relationship and the pair of surfaces 120, 122 are plain cylindrical surfaces.

In the bearing 210 (Figure 3), the pair of surfaces 220, 222 are part-spherical surfaces in nesting relationship and the pair of surfaces 224, 226 are also part-spherical surfaces in nesting relationship.

In the drawings, the clearances between the respective pairs of surfaces have been exaggerated for clarity.

The difference between the radii of curvature of the part-spherical surfaces in each pair is equal to the respective clearance between the surfaces. Likewise, the difference between the radii of curvature of the pairs of cylindrical surfaces is equal to the respective clearance between the surfaces.

In each of the constructions described above, the pairs of surfaces 20, 22; 124,126; and 220, 222 and 224, 226 have a twofold function as previously discussed, namely the accommodation of misalignment between the shaft 12, 112, 212 and the member 16, 116, 216 and the location of the ring 18, 118, 218 relative to the shaft 12, 112, 212, and the member 16, 116, 216.

Fluid can be supplied to the respective pair of surfaces by any suitable means. For example, fluid can be fed separately to each clearance through respective ducts in the shaft 12, 112, 212 and the member 16, 116, 216; fluid can be fed to one or other of the clearances through ducts in the shaft 12, 112, 212 or the member 16, 116, 216 and through further ducts in the ring 18, 118, 218 or, alternatively, the ring 18, 118, 218 can be porous.

The fluid can be any suitable fluid both liquid or gaseous, e.g. oil, water, air. Fluid pressure in the bearing can be developed either hydrodynamically or hydrostatically, typically hydrodynamically at high speed and hydrostatically at low speed.

The member 16, 116, 216 and/or the ring 18, 118, 218 can be made in one piece or can be made in two or more pieces which are joined together about the journal 14, 114, 214.

The materials used for making the component parts of the bearings can be selected from any suitable combination of materials.

Typically, as shown in the drawings, the shaft 12, 112, 212 and the journal 14, 114, 214 are made of steel, the stationary member 16, 116, 216 is made of high density nylon and the ring 18, 118, 218 is made of aluminium.

However, many other combinations of materials are possible, e.g. steel journal and stationary member and a cast neoprene rubber ring (during casting the neoprene rubber will shrink from the adjacent surfaces to form the clearances between the pairs of surfaces).

Although the constructions described above with reference to Figures 1 to 3 are referred to as bearings, similar constructions in which the clearances between the pairs of surfaces are selected to give a minimum flow of fluid rather than minimising power losses function as seals. Clearly, in some applications, the constructions could function both as a bearing and a seal, the clearances between the pairs of surfaces being selected to give a balance between minimum power losses and minimum flow of fluid.

Modifications are possible within the scope of the invention. For example, the pairs of plain cylindrical surfaces could be curved surfaces having a curvature opposite to the curvature of the part-spherical surfaces; and, in the construction shown in Figure 2, the inner surface 222 of the ring 218 would have a convex curvature, the shaft 212 being waisted to form the journal 214 with a curvature corresponding to the inner surface 222 of the ring 218. In such constructions, the ring is positively retained relative to the respective inner or outer member.

In the constructions shown in Figures 1 and 2, the shaft 12, 112 can move axially relative to the stationary member 16, 116, for example owing to thermal expansion of the shaft in a turbogenerator set.

The construction shown in Figure 3 does not have that capability and, consequently, it would be used in applications in which little or no axial movement of the rotatable member occurs. It will be apparent that small axial thrusts can be accommodated by the construction shown in Figure 3.

If higher axial thrusts have to be accommodated, constructions in which the bearing is a face bearing can be used, for example as shown in Figure 4.

Referring now to Figure 4, reference numerals used in Figure 1 have been used in this figure for like parts but with the prefix '3'.

In the bearing 310, the first member 314 is a shaft portion having a greater diameter than the adjacent shaft portions. In this construction, the surfaces 320, 322, 324, 326 are generally radially-extending surfaces, the pairs of surfaces 320, 322 being substantially plain radial surfaces and the pair of surfaces 324, 326 being substantially part-spherical surfaces in nesting relationship.

The bearing 310 resists thrusts applied to the shaft 312 in the direction of arrow A.

In a modification, the bearing 310 can be adapted to accommodate thrusts in both axial directions by duplicating the ring 318 and second member 316 on the other side of the shaft portion 314. In that instance, the rings 318 could be formed as a single unit enclosing the shaft portion 314, the construction being in effect an extreme version of the construction shown in Figure 3.

A construction similar to that shown in Figure 4 can be used as a face seal or a combined face bearing and face seal.

It will be apparent that variations in construction similar to those described above in relation to journal bearings and seals (see Figures 1 to 3, for example) are applicable to face bearings and seals.

Other modifications are possible within the scope of the invention. For example, the first member could be stationary and the second member rotating; or alternatively, both of the first and second members can rotate, the ring rotating at a speed intermediate the speeds of rotation of the members. When the member 16, 116, 216 is made in two pieces say, one piece can be diametrally off-set by a small amount from the other thereby causing the clearance between that member and the ring to taper in the two halves in the direction of rotation of the ring. Such a construction has the effects of reducing cavitation in the fluid film and also of creating regions of relatively high pressure in the fluid film, which fluid pressure can be used to pump fluid through passages in the ring to the clearance between the ring and the inner member. The pairs of part-spherical surfaces need only be substantially part-spherical in that they can have a small degree of ellipticity in an axial plane. A surface of one or both pairs of surfaces may have a recess formed therein which tapers in the direction of rotation of the ring and into which the fluid is introduced.

Claims

1. A bearing or a seal comprising first and second members and a ring located therebetween, the ring being free to rotate at a speed intermediate the speeds of the first and second members, oairs of mutually opposed surfaces of the first member and the ring and of the ring and the second member having respective clearances therebetween to which clearances fluid is supplied during use, the surfaces of at least one of said pairs of surfaces being substantially part-spherical surfaces in nesting relationship.

2. A bearing or seal according to claim 1, in which the bearing or seal is a journal bearing or seal, the first member comprising a journal.

3. A bearing or a seal according to claim 1 or claim 2, in which the pair of surfaces between the first member and the ring are substantially part-spherical surfaces in nesting relationship, the pair of surfaces between the ring and the stationary member being substantially plain cylindrical surfaces.

4. A bearing or a seal according to claim 1 or claim 2, in which the pair of surfaces between the ring and the second member are substantially part-spherical surfaces in nesting relationship, the pair of surfaces between the first member and the ring being substantially plain cylindrical surfaces.

5. A bearing or a seal according to claim 1, in which the bearing or seal is a face bearing or seal, the first member comprising a shaft section having a generally radially-extending surface which is the respective surface of said pair of mutually opposed surfaces of the first member and the ring.

6. A bearing or a seal according to claim 1 or claim 5, in which the pair of surfaces between the first member and the ring are substantially part-spherical surfaces in nesting relationship, the pair of surfaces between the ring and the second member being substantially plain radial surfaces.

7. A bearing or a seal according to claim 1 or claim 5, in which the pair of surfaces between the ring and the second membere are substantially part-spherical surfaces in nesting relationship, the pair of surfaces between the first member and the ring being substantially plain radial surfaces.

8. A bearing or a seal according to any one of claims 1, 2 or 5, in which the pair of surfaces between the first member and the ring are substantially part-spherical surfaces in nesting relationship and the pair of surfaces between the ring and the second member are substantially part-spherical surfaces in nesting relationship.

9. A bearing or a seal according to claim 1 substantially as hereinbefore described with reference to the accompanying drawings.