Patent Application
20160238068
The present disclosure is directed to a bearing having a first portion configured to respond to frequent but small relative movements between inner and outer portions of the bearing and a second portion configured to respond to large, infrequent, relative movements between the inner and outer portions, and, more specifically, to a bearing having an laminated bearing portion configured to respond to frequent but small relative movements between inner and outer portions of the bearing and a spherical bearing portion configured to respond to larger, infrequent, relative movements between the inner and outer portions.
Laminated bearings may be used to accommodate relative movement between inner and outer components, which movement may occur along and/or about any one of three mutually perpendicular axes. Such bearings generally comprise a plurality of alternating, generally tubular elastomeric laminae and metallic laminae nested coaxially about a central axis. One common application of such bearings is at the ends of the pitch arms of rotary wing aircraft, which pitch arms connected between a rotary swash plate and a pitch horn of a blade grip that secures one of the blades. However, such bearings are used in other environments as well.
The degree of movement allowed by a laminated bearing is determined in part by the number of elastomeric lamellae used as well as their properties. For example, each of the elastomeric lamellae is formed from an elastomeric material having an elastic limit. Each lamina can therefor be subjected to forces of up to a predetermined amount and still return elastically to its original shape and size. Forces greater than the elastic limit of the lamina will permanently deform the lamina. The plurality of the lamella in the laminated bearing thus allow the bearing to withstand a given level of strain without being permanently deformed. The entire bearing may therefore be described as having its own elastic limit, that is, a maximum force or strain to which the bearing can be subjected without permanently damaging the bearing.
While a laminated bearing can be subjected to forces or strains that approach its elastic limit without causing permanent damage, the amount of strain applied to the bearing will affect its usable life. It is therefore generally desirable to limit the forces to which a laminated bearing is subjected to some fraction of the elastic limit of that bearing. In general, the lower the maximum strain levels to which a bearing is subjected, the longer the operating life of the bearing will be. On the other hand using a bearing such that it is never subjected to more than, for example, 1 percent of its elastic limit generally results in bearing that is much larger and more expensive than necessary. A balance must therefore be struck between the size of the bearing and the length of its operating life.
The maximum strain level to which a bearing can be subjected without unnecessarily shortening its operating life will depend on many factors, including the materials used for the elastomeric and metallic lamellae, the number of lamellae provided, the configuration of the bearing, and the types of forces to which the bearing is subjected, e.g., rotational, radial, axial, tilting, etc. However, it may generally be assumed that subjecting a bearing to strains less than 50% of the elastic limit of the bearing is desirable.
It would therefore be desirable to provide an improved laminated bearing that provides the benefits of conventional laminated bearings and that limits the maximum strains to which the laminated bearing is subjected in order to increase the service life of the bearing while at the same time accommodating a large range of forces in a non-destructive manner.
These problems and others are addressed by embodiments of the present disclosure, a first aspect of which comprises a bearing that includes a laminated bearing portion and a spherical bearing portion, and in which the spherical bearing portion is disposed within the laminated bearing portion or the laminated bearing portion is disposed within the spherical bearing portion.
Another aspect of the disclosure comprises a method of operating a bearing which bearing includes a laminated bearing portion and a spherical bearing portion, the spherical bearing portion being disposed within the laminated bearing portion or the laminated bearing portion being disposed within the spherical bearing portion. The spherical bearing portion comprises a generally annular outer race having a concave inner circumferential surface, the inner surface being partially spherical and defining a central opening, and a ball disposed within the outer race central opening and having a convex, partially spherical, outer surface in contact with the inner surface of the outer race portion. The ball and the outer race are configured such that the ball is locked in the outer race and such that a given break-out force is required to move the ball relative to the outer race. The method includes repeatedly applying first forces to the bearing to deform the laminated bearing portion without exceeding the given break-out force of the spherical bearing.
A further aspect of the disclosure comprises a bearing having an inner bore, an outer housing, and means between the inner bore and outer housing for repeatedly elastically accommodating relative movement between the inner bore and the outer housing of up to a first magnitude and for repeatedly slidably accommodating relative movement between the inner bore and the outer housing of a second magnitude greater than the first magnitude.
These and other aspects and features of the disclosure will be better understood upon a reading of the following detailed description together with the attached drawings, wherein
Referring now to the drawings, wherein the showings are for purposes of illustrating presently preferred embodiments of the disclosure only and not for the purpose of limiting same,
The bearing 10 includes an outer member 14 having a radially outer surface 16 and a radially inner surface 18 and having a first thickness in the axial direction. The outer surface 16 is convex and the inner surface 18 is concave, and, preferably, the inner surface 18 (or at least part of the inner surface 18) is a spherical surface, that is, a surface all points of which are a constant distance from a center point. The bearing also includes an inner member 20 having a radially outer surface 22 and a radially inner surface 24 and having a second thickness in the axial direction. The radially outer surface 22 is convex and preferably spherical, and the second axial thickness of the inner member 20 is less than the first axial thickness of the outer member 14. The outer member 14 and the inner member 20 are coaxial, and the inner member 20 is axially centered with respect to the outer member 14.
A first sheet or lamina of elastomeric material 26a is bonded to the inner surface 18 of the outer member 14, and a thirteenth sheet or lamina of elastomeric material 26m is bonded to the outer surface 22 of the inner member 20. Eleven central lamellae 26b-26l are disposed between the first lamina 26a and the thirteenth lamina 26m in this embodiment, and one metallic shim or metallic lamina 28 is disposed between each adjacent pair of elastomeric laminae 26a-26m. A total of twelve metallic shims 28a-28l are present in this embodiment, with a first metallic shim 28a disposed between the first elastomeric lamina 26a and the second elastomeric lamina 26b. Different numbers of elastomeric laminae and metallic shims can be used without exceeding the scope of this disclosure, and this number will be based on the forces that must be accommodated by the laminated bearing.
The axial lengths of the elastomeric lamellae 26a-26m decrease in the direction from the first elastomeric lamella 26a to the thirteenth elastomeric lamella 26m, and the axial lengths of the metallic lamellae 28a-28l decrease from the first metallic lamella 28a to the twelfth metallic lamella 28l as well so that the axial length of the bearing, defined by edges of the nested elastomeric lamellae 26 and the metallic lamellae 28 decreases from the outer member 14 to the inner member 20.
The bearing 10 further comprises a shell 30 mounted inside the inner member 20, the shell 30 having an outer side 32 connected to the radially inner surface 24 of the inner member 20 and an inner surface 34 that is concave and preferably spherical. The inner surface 34 of the shell 30 forms a race for a spherical bearing ball 36, and the bearing ball 36 has a spherical outer surface 38 in contact with the inner surface 34 of the shell 30 and a central bore 40 coaxial with the shell 30.
The outer member 14, the inner member 20 and the plurality of nested elastomeric lamellae 26a-26m and metallic lamellae 28a-28l together form a laminated bearing 42. The laminated bearing is configured to allow small amounts of relative axial, radial, rotational and tilting movement between the outer member 14 and the inner member 20, and, in particular, is configured to accommodate small changes that are frequent and/or rapid. The shell 30 and the spherical ball 36 together form a spherical bearing 44. The bearing 10 may therefore be described as a spherical bearing 44 mounted inside a laminated bearing 42.
Each of the elastomeric lamellae 26 that form the laminated bearing 42 has various properties. In this embodiment, each of the elastomeric lamellae 26 is formed from the same material, and the elastomeric lamellae 26 thus have similar or substantially identical properties. However, various ones of the elastomeric lamellae 26 could be formed of different materials and have different properties if desired. One of the properties of the elastomeric lamellae is the elastic limit of the material from which they are formed. That is, each of the elastic lamellae can withstand a given stress or force per unit area without being permanently deformed. Greater amounts of stress or force, on the other hand, will change the structure of the lamellae in such a manner that the lamella will not return to its original shape or form when the stress or force is removed.
Conventional laminated bearings are designed so that the elastic limit of the elastomeric layers of the bearing will not be exceeded during use. That is, a conventional bearing must be designed to withstand the greatest forces to which it is likely to be subjected in a particular environment. These extreme forces may rarely occur, but if the bearing is not designed to accommodate them, the bearing will be permanently damaged any time they are encountered. Conventional bearings therefore generally operate over a range of forces that are only a faction of the elastic limit of the elastomeric materials contained therein in order to provide a margin of error and to accommodate occasional extreme forces.
In addition, it has been found that it is generally desirable to limit the forces to which a laminated bearing is exposed so that the lamellae of the bearing are prevented from exceeding a certain fraction of the elastic limit of each lamella—below 75 percent or 50 percent or 25 percent of the elastic limit of the material used in the lamellae, for example. This is because repeated exposure to forces close to the elastic limit of the lamellae may shorten the life of the bearing. Thus, in conventional laminated bearings, not only must the bearing be designed so that the elastic limit of the elastomeric material is not exceeded under any anticipated use conditions, but it may be desirable to design the elastomeric bearing so that the forces to which the bearing is exposed do not exceed, for example, 50% of the elastic limit of the material from which the lamellae are formed. This can lead to the use of oversized or overdesigned laminated bearings in order to ensure a sufficiently long life of the bearing.
Laminated bearings are well-suited for use in environments where small changes occur in the relative positions of the inner and outer portions of the bearing, especially when these changes are rapid and/or frequent. However, conventional laminated bearings are not able to accommodate relatively large changes in the relative positions of the inner and outer portions. Spherical bearings, made from metal or other materials, on the other hand, can withstand significant forces and accommodate larger angular and rotational changes between an inner member or ball and an outer member or race. However, the frictional contact between the ball and the race may lead to rapid wear, especially when such bearings are used to accommodate frequent small, and in particular, rapid changes in the relative positions of the elements supported by the bearing.
The present inventor has addressed these issues by mounting a spherical bearing 44 inside a laminated bearing 42 to provide the laminated bearing 42 with some of the beneficial qualities of spherical bearings. To this end, the ball 36 of the spherical bearing 44 is fitted or swaged in the shell 30 so that a certain minimum level of force is required to cause the ball 36 to move in the race formed by the inner surface 34. This force may sometimes be referred to as a “break-out” force and may be applied to the ball 36 by a shaft (not illustrated) running through the axial bore 40 of the ball 36. Conventional spherical bearings are generally designed to have a low break-out force to allow a smooth transition to dynamic motion. In the present embodiment, the break-out force is significantly greater than normal.
An amount of force smaller than the break-out force is required to keep the ball 36 from re-locking in the shell 30 after the break-out force has been exceeded The phrase “dynamic friction force” will be used herein to refer to the level of force at which the ball 36 relocks in the shell 30. The spherical bearing 44 thus does not begin to operate until an applied force exceeds the break-out force, and will continue to operate until the applied force falls below the dynamic friction force. At that point, the spherical bearing 44 relocks in the shell 30, and the laminated bearing 42 again begins to operate. The dynamic friction force may be, for example, 80% or more of the break-out force.
The break-out force and dynamic friction forces are selected such that the bearing 10 will function with the spherical bearing 42 locked under most operating conditions. Under such conditions, the spherical bearing 44 behaves essentially as part of the inner member 20 of the laminated bearing and merely transmits forces from the shaft in the central bore 40 to the elastomeric lamellae 26a-26m. Under these operating conditions, the laminated bearing 42 will absorb substantially all forces applied to the bearing. However, when forces are applied to the bearing 10 greater than the spherical bearing break-out force, the ball 36 will shift in the shell 30. The spherical bearing 42 will thereafter move and accommodate changes in the orientation of the shaft and the outer member 14 until the force applied to the bearing falls below the dynamic friction force and the ball 36 once again locks in the shell 36. At this time, the laminated bearing 42 will once again accommodate all forces applied to the bearing 10. In typical use, it is expected that the relative movement allowed by the ball 36 breaking free of the shell 36 will quickly relieve stress on the bearing 10 so that the forces experienced by the bearing 10 rapidly fall below the dynamic friction force and allow the laminated bearing 42 to once again become the primary mechanism for accommodating changes in the relative positions of the inner and outer parts of the bearing 10.
The break-out force may be exceeded when the rotational or angular movement between the shaft and the outer member 14 is greater than can be accommodated by the laminated bearing 42, that is, at the point that the laminated bearing 42 has been stressed to a predetermined maximum amount. The break-out force will then be exceeded, and the ball 36 will move in the shell 30 to prevent any further increase of force on the laminated bearing 42. Alternately, sudden, large forces may exceed the break-out force and release the ball 36 from the shell 30, thereby also protecting the laminated bearing 42 from potentially damaging levels of stress. However, because the laminated bearing 42 accommodates most forces, the spherical bearing 44 operates infrequently and thus wears at an acceptably slow rate.
The break-out force is generally set, by appropriate swaging of the ball 36 and the shell 30, to be a fraction of the elastic limit of the materials from which the lamellae 26a-26m are formed. The dynamic friction force is determined largely by the materials from which the ball 36 and shell 30 are formed and the materials with which they are coated. The application of suitable low-friction materials, such as polytetrafluoroethylene (PTFE), to the friction surfaces of the ball 36 and the shell 30 will keep the dynamic friction force and break-out force relatively close together. The break-out force must not exceed the elastic limit of the elastomeric lamellae 26a-26m in the laminated bearing 42, and thus may be set to be from about e.g., 5% to about 75% of the elastic limit of the lamellae, for example, to 10%, 20%, 30%, 40% or 50% of the elastic limit. In general, the operating life of a laminated bearing can be determined based on the number and magnitude of oscillations to which it is subjected. Laminated bearings will last longer when they are not subjected to forces that approach the elastic limit of their lamellae. Therefore, laminated bearings are generally configured to withstand forces of up to a given amount. If greater forces need to be accommodated, a larger laminated bearing, that is, one having larger lamellae and/or a greater number of lamellae should be used.
Those of ordinary skill in the art of laminated bearing design may identify an optimal operating range for a laminated bearing. That is, the bearing may have an intended operating life of a certain number of cycles or oscillations as long as the oscillations are below a certain size. The size may be expressed as an amount of force applied against the bearing or, alternately, as an amount of movement, for example, rotational or other angular movement in degrees, or radial or axial displacements in millimeters. Bearing manufacturers thus may identify, for a given laminated bearing, a level of force or an angular or other amount of movement which should not be exceeded if a user wishes to maximize the life of the laminated bearing. The present inventor contemplates setting the break-out force of the spherical bearing to be approximately equal to the high end of this design range of the laminated portion of the bearing so that the laminated bearing substantially always operates within its design range and such that the spherical bearing does not operate until larger forces and/or larger movements need to be accommodated.
In operation, the bearing 50 performs in substantially the same manner and the bearing 10 discussed above. That is, the relative motion between a shaft mounted in the central bore 80 of the inner member and the shell 56 is accommodated by the laminated bearing as long as the level of force and/or amount of movement that must be accommodated is below a given level. When that level is exceeded, the break-out force that holds the ball 62 in the shell 56 is also exceeded, and further relative motion between the central bore 80 of the inner member and the shell 56 is accommodated by the movement of the ball 62 in the shell 56.
Bearings such as the bearings 10 and 50 described above may be used in various environments. One common use of such bearings is at the ends of the pitch arms of rotary wing aircraft, which pitch arms are connected between a rotary swash plate and a pitch horn of a blade grip that secures one of the blades. In this environment, small and/or frequent and/or rapid changes occur between the ends of the pitch arm and the structures to which they are mounted, and most of these motions are accommodated by the laminated bearing 42 of the bearing 10 or the laminated bearing 52 of the bearing 50. However, when the pitch arm moves to a greater extend relative to the structure to which it is mounted, the spherical bearing 44 of the bearing 10 or the spherical bearing 54 of the bearing 50 breaks free and accommodates the motion. In this manner, the laminated bearing need only be sized to accommodate the most common degree of relative movement likely to be encountered in a given environment, and the spherical bearing can accommodate the less common motions without requiring the use of an oversized laminated bearing.
The present invention has been described herein in terms of several presently preferred embodiments. Modifications and additions to these embodiments may become apparent to persons of ordinary skill in the art upon reading the foregoing description. It is intended that all such modifications and additions comprise a part of the present invention to the extent they fall within the scope of the several claims appended hereto.
The present application claims the benefit of U.S. Provisional Patent Application No. 62/115,437 filed Feb. 12, 2015, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62115437 | Feb 2015 | US |
