Bearing preload

Details Bearing preload Bearing preload

1998-05-11

2001-04-24

Look, Edward K. (Department: 3745)

Fluid reaction surfaces (i.e., impellers)

Specific working member mount

Adjustable

C416S207000, C416S209000, C416S22000A, C416S001000, C384S556000

Reexamination Certificate

active

06220820

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a bearing with a preload arrangement, and a method of preloading a bearing, especially a variable pitch propeller bearing.
2. Description of the Related Art
The increase in the power handling characteristics and diameters of propeller systems makes it increasingly necessary to preload the bearings within the propeller hub which allow the propeller blades to change pitch. The preload serves many purposes, the primary one of which is to ensure that all of the bearing elements are kept stable during all flight conditions. Preloading also serves to align the blade root within the propeller hub and, in applications having removable blades, also provides a means for locking the blades into the hub.
A known propeller blade root assembly typically comprises a split upper inner race which faces radially outward of the propeller blade and is inclined with respect to the axis of the blade so as to face slightly towards the propeller root. An outer bearing race is disposed generally radially outwards of the inner bearing race and has an inwardly facing bearing surface which is slightly inclined so as to be generally parallel to the bearing surface of the inner bearing race. Motion of the outer bearing race along the axis of the propeller varies the distance between the bearing surfaces of the inner and outer bearing races and this feature is exploited to preload the bearings. The outer bearing race has an outwardly facing screw thread located thereon which cooperates with a preload nut which is wound down to bear against the hub, either directly or indirectly (to prevent fretting). The winding down of the nut causes the outer bearing race to be moved axially of the propeller blade and to preload the propeller blade bearings. The preload is applied via a spanner acting on the nut and considerable effort may be required. The friction between the nut, the thread, and the hub makes it difficult to determine the torque required to obtain a desired preload. This often necessitates the performing of tests in order to determine what preload had been achieved.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided a bearing having a preload arrangement for preloading the bearing, comprising a first member having a first bearing surface movable with respect to a second member having a second bearing surface so as to bear against at least one bearing located between the first and second bearing surfaces, a fluid operated actuator for urging the first member to move with respect to the second member so as to apply a load to the bearing, and mechanical locking means for locking the first member against return movement.
It is thus possible to apply a preload to a bearing without relying solely on the force applied by rotation of a preload nut. The preload force may be more easily applied and accurately controlled than is the case with the known arrangement described hereinbefore.
Once the preload has been applied using the fluid actuator, the mechanical locking means is operated so as to lock the first member in position such that the bearings remain preloaded when fluid pressure is removed from the actuator.
The fluid operated actuator may advantageously be used to apply a force to preload the bearing during assembly or maintenance of a device incorporating the bearing.
Advantageously, the first member is moved in a first direction to apply a load to a bearing and further comprises, or cooperates with, the locking means for preventing motion of the first member in a return direction opposing the first direction. The locking means may comprise a threaded portion located on the first member which, in use, cooperates with a retaining nut which bears directly or indirectly against a fixed surface.
Advantageously, the first member cooperates with a third member to define a chamber and the first member has a third surface which forms a movable wall of the chamber, such that fluid pressure within the chamber exerts a force against the third wall and thereby urges the first member to move along the first direction. Advantageously, the fixed surface is a surface of the third member. Thus, the fluid operated actuator is formed between the first member and the third member which are moved apart by fluid pressure applied therebetween, and between which the locking means cooperates to hold them apart.
Preferably, the bearing is part of a bearing arrangement having third and fourth bearing surfaces arranged to engage bearings therebetween, and one of the third and fourth surfaces is movable in response to relative movement of the first member such that the bearings between these surfaces also become preloaded when the actuator is operated.
The third member is associated with one of the third and fourth surfaces and serves to store a preload reaction force between the bearings of the first and second surfaces and the third and fourth surfaces.
Preferably, the bearing arrangement is provided at the fixing region of a propeller blade.
Preferably, the first bearing surface is coaxial with and outwardly radially disposed of the second bearing surface, the first and second bearing surfaces being substantially parallel with one another and inclined with respect to their common axis (i.e. the surfaces are portions on a conic surface having the same or substantially the same cone angles) such that longitudinal motion of the first member with respect to the second member changes the clearance between the first and second bearing surfaces. The fixing region of the propeller blade also has a third bearing surface which faces radially outwardly and away from the base of the propeller blade root and cooperates with an opposing fourth bearing surface to retain bearings therebetween. Operation of the actuator preloads the bearings between the first and second bearing surfaces, and in so doing, causes the blade root to move so as to preload the bearings between the third and fourth bearing surfaces, and also places the blade root portion intermediate the bearings under tension.
Thus, when the fluid pressure is released from the actuator, the tension stored in the blade root maintains the preload on all the bearings.
Preferably, the first member is substantially cylindrical and is arranged to fit within a corresponding recess within a housing.
Preferably, the first member is arranged to engage within a corresponding recess within a propeller hub so as to hold the propeller against wobble about its own axis.
According to a second aspect of the present invention, there is provided a preload arrangement for a propeller blade, comprising a member movable in response to fluid pressure acting on a surface thereof so as to preload the bearings of the propeller blade.
According to a third aspect of the present invention, there is provided a method of preloading a bearing having a preload arrangement, the preload arrangement comprising a first member having a first bearing surface movable with respect to a second member having a second bearing surface so as to bear against at least one bearing between the first and second bearing surfaces, a fluid operated actuator for urging the first member to move with respect to the second member so as to apply a load to the bearing, and mechanical locking means for locking the first member against return movement, the method comprising the steps of: applying fluid pressure to the fluid operated actuator; and operating the locking means to lock the first member against return movement.
Advantageously, the fluid pressure is removed after the locking means has been operated.


REFERENCES:
patent: 3558199 (1971-01-01), Raiser et al.
patent: 4551032 (1985-11-01), Mottershead
patent: 4611351 (1986-09-01), Nakamura
patent: 4611934 (1986-09-01), Piotrowski et al.
patent: 5415527 (1995-05-01), Godwin
patent: 1579285 (1969-08-01), None
patent: 2585422 (1987-01-01), None
patent: 2244525 (1991-12-01), None
patent: 2271392 (1994-04-01), None

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