Cylindrical elastomeric bearing with tapered shims

A cylindrical elastomeric bearing including a plurality of elastomeric layers arranged about a central bore. The elastomeric layers are characterized by a middle portion having a first thickness and two outer portions having a second thickness, the second thickness being greater than the first thickness, the one or more elastomeric layers being tapered between the middle portion and the outer portions. One or more shim layers, each of the plurality of shim layers being arranged between two of the plurality of elastomeric layers. The shim layers are shaped to fit with the elastomer layers.

BACKGROUND

The present disclosure relates generally to an elastomeric bearing and, more particularly, to cylindrical bearings for rotor devices and systems.

Cylindrical elastomeric bearings are used in many applications. Cylindrical elastomeric bearings typically include alternating layers of elastomeric material and metallic or composite shims. These bearings often replace non-lubricated or self-lubricated bearings such as Teflon fabric lined bearings. Typical aerospace elastomeric bearing applications include spherical rod end bearings for pitch control rods and dampers, spherical blade retention bearings for fully articulated rotors, and cylindrical bearings for semi-articulated rotors and fluid-elastic damper seals. Some cylindrical elastomeric bearings are exposed to both axial and radial loads. Elastomer layers tend to bulge at the edges due to radial and bending moment loads going through the bearing. These shear stresses are a limitation on the size of the bearing and can require significant growth of a bearing size in order to achieve an adequate design. Accordingly, the industry is receptive to innovations that extend the life of cylindrical elastomeric bearings, particularly those that are exposed to both radial and axial loads.

SUMMARY

Disclosed herein is a cylindrical elastomeric bearing having a plurality of elastomeric layers arranged about a central bore. The elastomeric layers are characterized by a middle portion having a first thickness and two outer portions having a second thickness, the second thickness being greater than the first thickness. The one or more elastomeric layers are tapered between the middle portion and the outer portions. One or more shim layers are arranged between two of the plurality of elastomeric layers.

In addition to one or more of the features described above, or as an alternative, in further embodiments, wherein each of the one or more shims is tapered to fit with the one or more elastomeric layers being tapered.

In addition to one or more of the features described above, or as an alternative, in further embodiments, wherein the one or more elastomeric layers are tapered on one side and are flat on one side.

In addition to one or more of the features described above, or as an alternative, in further embodiments, wherein the one or more elastomeric layers are tapered on a radially inward facing side.

In addition to one or more of the features described above, or as an alternative, in further embodiments, wherein at least one of the elastomeric layers is tapered frustoconically.

In addition to one or more of the features described above, or as an alternative, in further embodiments, wherein at least one of the elastomeric layers is tapered frustospherically.

In addition to one or more of the features described above, or as an alternative, in further embodiments, wherein the second thickness is at least 10% greater than the first thickness.

In addition to one or more of the features described above, or as an alternative, in further embodiments, wherein the second thickness is at least 20% greater than the first thickness.

Another aspect of the disclosure provides a cylindrical elastomeric bearing having a plurality of elastomeric layers arranged about a central bore and a plurality of shim layers, each of the shim layers being arranged between two of the elastomeric layers. The shim layers have a radially inward facing side that is substantially uniform in diameter. A radially outward facing side of the shim layers is tapered between a middle section and two outer sections, the middle section having a first thickness and the outer sections having a second thickness, the first thickness being greater than the second thickness.

In addition to one or more of the features described above, or as an alternative, in further embodiments, wherein at least one of the plurality of shim layers is tapered frustoconically.

In addition to one or more of the features described above, or as an alternative, in further embodiments, wherein at least one of the plurality of shim layers is tapered frustospherically.

In addition to one or more of the features described above, or as an alternative, in further embodiments, wherein the second thickness is at least 10% greater than the first thickness.

In addition to one or more of the features described above, or as an alternative, in further embodiments, wherein the second thickness is at least 20% greater than the first thickness.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures. It is to be understood that other embodiments may be utilized and changes may be made without departing from the scope of the present disclosure. In particular, the disclosure provides various examples related to rotor systems for rotary wing aircraft, whereas the advantages of the present disclosure as applied in a related field would be apparent to one having ordinary skill in the art and are considered to be within the scope of the present invention.

FIG. 1illustrates a rotary wing aircraft1according to an aspect of the present disclosure. The aircraft1includes a rotor system2for rotating a plurality of rotor blades3about an axis of rotation A. The rotor hub4connects the plurality of blades to the rotor system2. The cylindrical elastomeric bearing of the present disclosure may be used in connection with any rotary wing aircraft1or any device in which rotational motion is included. By way of example, while shown in the context of a coaxial rotorcraft having two sets of counter rotating blades, aspects could be used in conventional single axis rotorcraft, fixed wing aircraft, wind turbines, maritime applications, automotive applications and/or applications in which cylindrical bearings are used. As will be apparent to those in the art, the present disclosure will be particularly useful where the cylindrical elastomeric bearing is subject to shearing stresses due to axial and radial loads.

FIGS. 2A and 2Billustrate a rotary device5, (i.e., a pitch control device for a rotary wing aircraft), that employs a cylindrical elastomeric bearing6of an aspect of the present disclosure. The rotary device5includes a mounting bracket7that attaches to the rotor blades3(seeFIG. 1). The mounting bracket7is attached to the hub4via the cylindrical elastomeric bearing6, an inner sleeve8, and a control rod9arranged in a central bore10of the cylindrical elastomeric bearing6. In operation, the pitch of the rotor blades3is controlled by turning the control rod9, thereby defining a pitch control axis.

Axial and radial forces are exerted on the bearing6, in part, by the centrifugal force of the rotor blades3in motion and the weight of the rotor blades3.FIGS. 3A-3Cillustrate various configurations of the cylindrical elastomeric bearing6, and the elastomer layers11and shim layers12contained therein, that improve the resiliency of the bearing6under the shear stresses that result from the axial and radial forces. As shown inFIGS. 3A-3C, the elastomeric layers11are arranged about the central bore10(not shown, seeFIG. 2A), and have a middle portion13with a first thickness and outer portions14with a second thickness, the second thickness being greater than the first thickness. The inner sleeve8separates the innermost elastomer layer11from the central bore10(seeFIG. 2A). An outermost elastomer layer11is against an outer sleeve, which may, for example, form a portion of the mounting bracket7or another structure.

As shown inFIGS. 3A-3C, the “middle” portion is defined as the portion that is either roughly half of the length of the elastomer layer11in a longitudinal direction or the thinnest portion of the elastomer layer11. Similarly, the “middle” section of the shim layers12is defined as the portion that is either roughly half of the length of the shim layer12in the longitudinal direction or the thickest portion of the shim layer12. While shown with the longitudinal axis substantially parallel with the pitch axis, it is understood that the longitudinal axis could be in other directions in other implementation of aspects of the invention.

As shown inFIGS. 3A and 3B, the shape of the elastomer layers11may be flat (cylindrical) on a radially outward facing side, i.e., having a substantially constant diameter. Between the middle portion13and the outer portions14, the elastomer layers11are tapered, i.e., there is a gradual change in the thickness of the elastomer layers11between the middle portion13and the outer portions14. The tapering of the elastomer layers11may be frustoconical, as shown inFIG. 3A, frustospherical, as shown inFIG. 3B, or some other shape, e.g., parabolic, etc. In some cases, the thickness of the outer portions14of the elastomer layers11is at least 10% greater than the thickness of the middle portion13. In other examples, the outer portions14have a thickness that is greater than the middle portion13by at least 20%.

The shim layers12are shaped to complement the shape of the elastomer layers11. For example, each of the shim layers12has a middle section15that is thicker than outer sections16. As shown inFIGS. 3A and 3B, the shim layers12may be configured to have a radially inward facing side that is substantially flat, i.e., cylindrical. The radially outward facing side of the shim layers12is tapered, similar to the elastomer layers11described above. The tapering of the shim layers12may be, for example, frustoconical, as shown inFIG. 3A, frustospherical, as shown inFIG. 3B, or some other shape (e.g., parabolic, elliptical, curvilinear, etc.). In some cases, the thickness of the middle section15of the shim layers12is greater than a thickness of the outer sections16by at least 10%. In further embodiments, the thicknesses differ by at least 20%. The shim layers12may be constructed of a metallic or other rigid material. For example, the shim layers12may be steel, fiber composite, titanium, or another material known in the art.

FIG. 3Cillustrates an alternative embodiment in which the shim layers12are tapered on both a radially inward facing surface and a radially outward facing surface. This results in the elastomer layers11having an hourglass shape except at the surfaces adjacent to the bracket7and the inner sleeve8. As will be apparent to those in the art, many other configurations are possible.

The arrangement of elastomer layers11and shim layers12as discussed herein minimizes the shear stresses at the outer portions14of the elastomer layers due to the thickening of the elastomer layers11. This is beneficial for bending loads in the bearing. Under such loads, the outer portions of the elastomeric layers11tend to bulge if the layers11lack tapering, greatly increasing the shear stresses as a result. However, the bulging of elastomeric layers11is decreased where the layers increase in thickness towards the outer portions, which necessarily leads to a reduction in shear stresses. In some examples, this configuration may theoretically reduce the shear stresses in the elastomer by 25-35%. Shear stresses in the shim layers12may also be reduced by about 15%. These reductions in shear stresses correlate to increased lifespan of the cylindrical elastomeric bearing6.

Further, the features of the present disclosure may be used to improve other configurations of cylindrical elastomeric bearings. For example, cylindrical elastomeric bearings where the elastomer layers are constructed with uniform thickness, wherein the durometer of the elastomer layers is varied to compensate for the thickening described above may also benefit from the present disclosure. In particular, the tapering of elastomer layers described above will further reduce the shears stresses in the elastomer compared to changing durometer alone.

While the invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are unless otherwise stated used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited. Moreover, the use of the terms first, second, etc., do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.