Bearings – Rotary bearing – Fluid bearing
Reexamination Certificate
2001-03-26
2002-10-29
Butler, Douglas C. (Department: 3683)
Bearings
Rotary bearing
Fluid bearing
C384S012000
Reexamination Certificate
active
06471404
ABSTRACT:
The invention relates to bearing assemblies.
In designing a rotor system comprising a rotary shaft held in bearings mounted on a frame, one consideration is for the frame to be able to support the bearings in correct alignment with the shaft upon its rotation at operational speeds. Errors in the construction or assembly of the rotor system, or thermal or other distortions of the frame, in operation, might cause the bearings to become dangerously misaligned with the shaft if the bearings were held rigidly with respect to the frame. It is known in the art to mount journal and thrust bearings in spherical shells so that they have some degree of freedom to align themselves with their shafts in the event of distortion of the frame, such bearings being referred to as “self-aligning bearings”. In some circumstances, however, such spherical shells are not an attractive means of providing self-alignment.
The invention provides a bearing assembly for supporting or locating a rotary shaft in a frame, the assembly comprising an outer shell for fixing relative to the frame, the outer shell providing a pair of coaxial annular surfaces spaced apart and facing inwardly towards each other, and an inner shell within the outer shell, the inner shell providing a pair of coaxial annular surfaces, each of which faces outwardly towards one of the inwardly-facing annular surfaces of the outer shell and is arranged substantially coaxially with, and adjacent to, its associated inwardly-facing annular surface, the inner shell being able to move axially relative to and to tilt relative to the outer shell and to move axially relative to and to tilt relative to the shaft, and each of said inwardly-facing annular surfaces and/or its associated outwardly-facing annular surface having one or more channels arranged to extend around the surface, the bearing assembly also comprising means for supplying a fluid from a high pressure source to each of the said channels through flow resistance means.
With such a bearing assembly, the inner shell may be arranged as a journal bearing or as a thrust bearing for a rotary shaft.
In operation, the outer shell of the bearing assembly is fixed relative to a frame provided to support the rotary shaft. The inner shell holds the rotary shaft in its journal or thrust bearing. Fluid from the high pressure source is introduced through the flow resistance means, which is preferably one or more entry passages of restricted cross-sectional area for each channel, into the channels of the annular surfaces. The fluid flows around the channels and leaves the channels to flow radially inwards and outwards through gaps between the associated inwardly- and outwardly-facing annular surfaces of the shells, from where it escapes to the surroundings outside the outer shell at ambient pressure. The channels are generally of such radial width and depth, and the gaps between each inwardly-facing annular surface and its associated outwardly-facing annular surface are sufficiently narrow, that the resistance to the flow of fluid around the channels is small compared to the resistance to flow through the gaps between the annular surfaces of the inner and outer shells. Consequently, the pressure exerted by the fluid around each channel is effectively constant and is determined by the width of the associated gap, increasing as the width of the gap decreases, and decreasing as the width of the associated gap increases.
Accordingly, movement of the inner shell in one direction along the axis relative to the outer shell will cause the pressure exerted by the fluid in the channel or channels to increase on the side of the inner shell on which its. spacing with the outer shell has decreased and to decrease in the channel or channels on the other side of the inner shell where the spacing with the outer shell has increased. The pressure difference across the inner shell creates a restoring force on it urging it back to an equilibrium position, for example, a central position within the outer shell. In such an arrangement, the restoring force exerted on the inner shell can provide substantial resistance to displacement of the inner shell in an axial direction relative to the outer shell.
The channel or channels in each of the said inwardly-facing annular surfaces and/or its associated outwardly-facing annular surface advantageously extend substantially entirely around the surface, and preferably extend substantially concentrically around the surface. Advantageously, each of the said inwardly-facing annular surfaces and/or its associated outwardly-facing annular surface has a continuous channel. With such an arrangement, the pressure distribution around each of the said annular surfaces at a given radius is substantially uniform, in operation. The mean radius of such a channel is preferably substantially equal to the square root of the product of the inner and outer radii of the annular surface in which it is located. The channel in each surface need not, however, be a continuous channel, and there may be two or more arcuate channels of equal mean radius, or even two or more channels of different mean radii in each of the said annular surfaces, and the configuration of the channel or channels in one annular surface need not be the same as that of another, but the pressure distribution around each annular surface at a given radius is preferably substantially uniform, in operation.
When the bearing assembly is arranged to provide a journal bearing, the inner shell advantageously comprises a journal bearing through which the shaft, or journal, can extend, and an annular flange on the journal bearing, which provides the said outwardly-facing annular surfaces. Such an arrangement can, by exerting a substantial restoring force on the flange of the inner shell should it move in an axial direction from its predetermined position relative to the outer shell, provide positive location of the journal bearing relative to the apparatus frame while allowing inclination of the flange of the inner shell relative to the outer shell and, hence, self-alignment of the journal bearing with the rotary shaft. The extent to which the flange of the inner shell can become inclined to the outer shell, and hence the limits of the self-aligning capability of the journal bearing, is determined by the dimensions of the inner and outer shells and the sizes of the gaps between the annular surfaces.
In an arrangement in which continuous channels are provided in the annular surfaces, although it is possible to arrange for the bearing assembly to provide a substantial restoring force against relative displacement of the inner shell in an axial direction as discussed above, if associated annular surfaces become slightly inclined to each other the pressure will still be substantially uniform at a given radius around each surface and no significant restoring moment against that inclination will be created. Thus, in the event of inclination of the inner shell with respect to the outer shell, as, for example, on self-alignment of a journal bearing as referred to above, the inner shell will remain inclined to the outer shell. Such an arrangement is suitable for journal bearings having self-generating capabilities, that is to say, the capability, on rotation of the shaft at a rate of rotation above a threshold rate, of generating a continuous film of lubricant fluid between the bearing and the shaft to prevent solid to solid contact. Examples of suitable self-generating journal bearings are a simple self-generating journal bearing of circular bore, a tilting-pad journal bearing, a journal bearing with fixed lands, or a journal bearing as described and claimed in our co-pending patent application No. (case II) filed on the same date as this patent application.
When the bearing assembly is arranged to provide a thrust bearing, the inner shell advantageously provides inwardly-facing thrust and surge bearing surfaces for acting on each side of a thrust collar of a rotary shaft. With such an arrangement, thrust exerted by the thrust collar on the thrust be
Corac Group PLC
Pezzlo Ben
LandOfFree
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