Bearings – Rotary bearing – Fluid bearing
Patent
1996-05-09
1997-06-03
Footland, Lenard A.
Bearings
Rotary bearing
Fluid bearing
384122, 384306, 384309, F16C 1710
Patent
active
056347251
DESCRIPTION:
BRIEF SUMMARY
The present invention is concerned with bearing assemblies of both the journal and thrust bearing types and is an improved bearing assembly.
Bearing assemblies are used in a very wide range of applications to afford radial and/or axial support for rotating shafts or spindles. While unitary journals or thrust rings are widely used, there are considerable advantages in constructing a bearing assembly from several discrete pads, which individually abut the shaft or thrust collar and are able to rock about a pivot to provide a wedge-shaped clearance between each pad and the rotating member. The introduction of oil into the bearing assembly by suitable means allows the development of a hydrodynamic film of oil between the bearing element and the rotating shaft or collar. This working film of oil prevents direct contact between the shaft or collar and the surface of the bearing element, which may be coated with an anti-friction material such as white metal.
The majority of prior bearing pad assemblies have depended upon line contact between the pad and the adjacent housing and the pads have typically been designed to rock by some 5 to 10 degrees of arc about the line of contact. This considerable freedom to rock allows adequate freedom for adjustment of the pad position and makes only moderate demands on the accuracy required of the relevant components.
FIG. 1 of the accompanying drawings illustrates, in sectional view transverse to the axis of the rotating shaft, three conventional forms of bearing pad mounting. In FIG. 1a, a journal pad 10 is shown supported on an integral bar or ridge pivot 10a. The pad 11 shown in FIG. 1b is supported upon a bar pivot 12 formed as an insert of hardened metal incorporated in the pad. Pads of this latter type are a feature of the journal bearing described in U.S. Pat. No. 3,022,123.
FIG. 1c illustrates a journal pad 13 with a curved back. The difference in curvature between the back of the pad and the adjacent housing allows some 5 to 10 degrees of rocking about the line of contact between these components, which line moves to a relatively small extent around the curved surface of the housing as the bearing pad rocks. Pads of this type are described in U.S. Pat. No. 3,711,169.
During rotation of a shaft supported by a bearing assembly of the foregoing types, the formation of the oil film in the wedge between bearing pad and shaft is accompanied by the rocking of the pad. A stable condition is reached where the position of the shaft and the loads upon it are in balance with the forces produced by the various oil film pressures on the bearing elements.
The only constraint on the position of the shaft arises from the oil pressure generated within the clearance between the shaft and the operating surfaces of the bearing elements. The shaft may be subject to variations in its load, which in turn results in changes in the thickness of the oil films and in the pressure profiles and the position of the shaft. Although these changes are usually small, they can result in changes in the pad position by rocking about its line of pivoted contact with the surface of the housing. In the case of some prior bearing assemblies, this movement of the pad can adversely affect bearing performance, where instability can result. Factors such as the risk of such instability may unduly influence the machine designer's choice of bearing type, for example between plain sleeve bearings and journal pad bearings.
Bearings operating at high rotational speeds, which are most likely to suffer instability problems, also tend to be fairly lightly loaded, which light loading contributes to the tendency of the shaft to orbit within the available bearing space. Bearings likely to suffer such problems are usually specifically designed to overcome the potential problems because there is no alternative solution generally available. Attempts to counter the problem by controlling the external damping or modifying the machine performance rarely succeed.
Against the foregoing background, it is an object of the present inv
REFERENCES:
patent: 4059318 (1977-11-01), Hollingsworth
patent: 4643592 (1987-02-01), Lewis et al.
patent: 4738550 (1988-04-01), Gardner
patent: 4743125 (1988-05-01), Dammel et al.
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