Bearings – Rotary bearing – Plain bearing
Patent
1997-02-12
1998-04-28
Footland, Lenard A.
Bearings
Rotary bearing
Plain bearing
F16C 1703
Patent
active
057436576
DESCRIPTION:
BRIEF SUMMARY
This invention relates to journal bearings of the tilting pad type in which a ring of circumferentially spaced bearing pads are disposed in a housing to surround coaxially a rotating shaft, and are capable of tilting in the housing on at least an axis substantially parallel with the shaft.
A number of different arrangements exist by which each of the bearing pads is able to tilt about at least one axis with respect to the housing. All have the ability to tilt relative to the housing about an axis extending parallel to the shaft rotation axis and some have the ability to tilt relative to the housing about other axes to accommodate misalignment between the longitudinal axis of the housing and the shaft.
Patent specification GB-A-1397551 discloses a tilting pad journal bearing in which pads are loosely contained in a circumferential direction between stops extending radially inwardly from the housing. In operation, with a shaft present, the stops prevents the pads from being dragged in a circumferential direction by the shaft. However, it is also arranged that the circumferential separation of the ends of the stops is less than the maximum circumferential length of each pad such that the loosely assembled pads are incapable of falling out radially in the absence of a shaft. One or more of the stops may be apertured to provide a lubricant supply duct and each pad surface adjacent the housing to bear thereon in operation is of a smaller radius of curvature than the housing to permit the rocking or tilting action of the pad relative to the housing.
Although such a pad structure is apparently simple it has drawbacks both in terms of manufacture and operation. Each pad requires to be supported between radially extending pins which act as locating means to prevent the pads from being displaced circumferentially by the rotating shaft and act as pad stops to prevent the inverted pads from falling from the housing wall when the shaft is removed. The positioning of the pins between each pad puts constraints on pad disposition within a split housing. Each bearing pad tilts by rolling of cylindrical surfaces, so that tilting is restricted to rotation about an effective axis parallel to the longitudinal axis of the housing and is unable to tolerate shaft misalignment. Furthermore, such rolling action is achieved by way of a line contact by which all radial loading on the pad is transferred to the housing. It is therefore possible for the load concentration to result in plastic deformation of the bearing pad and for any radial play in the bearing to increase, that is, for the bearing to lose radial stiffness.
GB-A-2180888 discloses a vertically aligned bearing arrangement in which the bearing pads do not have to support the vertical loading of a shaft and are able to pivot with respect to the housing about many axes by virtue of a part-spherical protuberance on each pad. However, such a protuberance not only increases the complexity of the pad but results in a point contact between the bearing pad and the housing, which is even more likely to deform and reduce radial stiffness if used to support a heavy load.
CH-B-558,481 discloses a tilting pad bearing on which each bearing pad has on its radially outer surface an integral part-spherical protuberance which rests in a correspondingly curved recess in a pan whose radial position with respect to the housing is adjustable by rams. The pad is complex to manufacture by virtue of the protuberance but because the contact between protuberance and pan is on a larger area than a point or line, there should be improved radial stiffness. However, the part-spherical interface also acts as locating means to transfer circumferential loading due to shaft rotation into the housing and the slight curvature of the pan reacts this in a generally radial direction which affects the radial loading and thus the effective stiffness. Furthermore, if and when a shaft is removed, there is no means of retaining each bearing pad with respect to it supporting pan so that assembly and maintenance is diff
REFERENCES:
patent: 3053587 (1962-09-01), Wallgren
patent: 4714357 (1987-12-01), Groth et al.
O'Reilly Peter D
Stopp Peter G
Footland Lenard A.
The Glacier Metal Company Limited
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