Abstract:
In some embodiments, a rotorcraft may include a yoke, a blade, a spindle associated with the yoke, and an elastomeric bearing assembly. The center length of the spindle may define a center axis that passes through a center of the elastomeric bearing assembly. The elastomeric bearing assembly may contain a housing coupled to the blade and disposed around the center axis that is configured to rotate in relation to the center axis. The elastomeric bearing assembly may contain an elastomeric shear bearing that has an interior portion coupled to the spindle and an exterior portion coupled to the housing. The elastomeric bearing assembly may contain an elastomeric centrifugal force bearing pressed against the housing. The shear bearing may be configured to counteract a torsional force, and the centrifugal force bearing may be configured to counteract a compression force.

Description:
BACKGROUND 
     Technical Field 
     This present disclosure relates generally to an elastomeric bearing assembly for rotorcraft. 
     Description Of Related Art 
     Typically, the centrifugal force motions and the feathering motions experienced by the blade of a rotorcraft are managed by discrete bearings mounted within separate components. These separate components are generally heavy and complex. Hence, there is a need for an improved device for managing both the centrifugal force and feathering motions in a rotorcraft. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The novel features believed characteristic of the system and method of the present disclosure are set forth in the appended claims. However, the system and method itself, as well as a preferred mode of use, and further objectives and advantages thereof, will best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of a rotorcraft, according to an example embodiment; 
         FIG. 2  is a perspective section view of a rotor system of a rotorcraft, according to an example embodiment; 
         FIG. 3  is a perspective view of an elastomeric bearing assembly, according to an example embodiment; 
         FIG. 4  is a side section view of an elastomeric bearing assembly, according to an example embodiment; 
         FIG. 5  is a perspective view of a spindle, according to an example embodiment; 
         FIG. 6  is a perspective section view of an inboard side of a housing of an elastomeric bearing assembly, according to an example embodiment; 
         FIG. 7  is a perspective section view of an outboard side of a housing of an elastomeric bearing assembly, according to an example embodiment; 
         FIG. 8  is a perspective section view of an elastomeric bearing assembly, according to an example embodiment; 
         FIG. 9  is a partially exploded perspective view of an elastomeric bearing assembly, according to an example embodiment; and 
         FIG. 10  is a partially exploded perspective view of an elastomeric bearing assembly, according to an example embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Illustrative embodiments of the system and method of the present disclosure are described below. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer&#39;s specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
     In the specification, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of the present disclosure, the devices, members, apparatuses, etc. described herein may be positioned in any desired orientation. Thus, the use of terms such as “above,” “below,” “upper,” “lower,” or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the device described herein may be oriented in any desired direction. 
       FIG. 1  shows a rotorcraft  100  according to one example embodiment. Rotorcraft  100  features one or more rotor systems  110 , a fuselage  130 , and a wing  140 . Rotor system  110  can include blades  120 , a control system, and a pitch horn  160  for selectively controlling the pitch of each blade  120  in order to control direction, thrust, and lift of rotorcraft  100 . In the example of  FIG. 1 , rotorcraft  100  represents a tiltrotor aircraft, and rotor system  110  features rotatable nacelles. In this example, the position of the nacelles operate rotorcraft  100  in both helicopter and airplane modes. Fuselage  130  represents the main body of rotorcraft  100  and can be coupled to one or more rotor systems  110  (e.g., via wing  140 ) such that rotor system  110  can provide thrust to move fuselage  130  through the air. Wing  140  can also generate lift during forward flight. 
     Referring now to  FIG. 2 , a propulsion system provides torque to a rotor mast (not shown). Yoke  150  is coupled to the rotor mast such that rotation of the rotor mast causes yoke  150  and rotor blade  120  to rotate about the rotor mast axis  340  of rotation. Each yoke  150  further includes at least one elastomeric bearing assembly  200  for receiving and coupling to each rotor blade  120 . Elastomeric bearing assembly  200  can be configured to treat and react a plurality of dynamic forces, such as centrifugal force  310  and torsional force  320 , that act on blade  120 . 
     Referring now to  FIGS. 3 through 7 , elastomeric bearing assembly  200  may include a spindle  260 , a housing  230 , a shear bearing  270 , a centrifugal force bearing  210 , a cone set  240 , and a cap  250 . Outboard portion  264  of spindle  260  can pass through the center of shear bearing  270 , housing  230 , centrifugal force bearing  210 , and cap  250 . Centrifugal force bearing  210  can be vulcanized to the outboard end of housing  230  and held in place by cone set  240 , which can be two separate pieces that form a cone shape, and cap  250 . 
     Spindle  260  can be fabricated out of any suitable material. For example, spindle  260  can be forged, cast, or machined out of a suitable material such as stainless steel or titanium. The inboard portion  262  of spindle  260  can be attached to yoke  150  by four bolts and the outboard portion  264  of spindle  260  can be rigidly coupled to cap  250 . In another example embodiment, spindle  260  and yoke  150  can be one piece where the spindle is an outer portion of yoke  150 . 
     Housing  230  can be fabricated out of any suitable material. For example, housing  230  can be forged, cast, or machined out of a suitable material such as stainless steel or titanium. On the inboard end of housing  230 , a first cavity with interior wall portion  237  can accommodate shear bearing  270 . The first cavity can have substantially the same diameter as the exterior diameter of shear bearing  270 . As best seen in  FIGS. 6 and 7 , wall  233  may provide support for the first cavity and can also have an exterior wall portion  234  that can be of a similar shape as shear bearing  270 . Wall  233  can be of a suitable thickness, depending on the size of shear bearing  270 . For example, if the diameter of shear bearing  270  is 5.5 inches, a suitable thickness of wall  233  may be 0.5 inches. On the outboard end of housing  230 , a second cavity with interior wall portion  235  can accommodate outboard portion  264  of spindle  260  passing through housing  230 . 
     On the sides of housing  230 , two cavities  232  that are perpendicular to spindle  260 , but parallel to each other, can accommodate bushings  220  and blade bolts configured to couple a flat portion of blade  120  to housing  230 . Cavity  232  can be outboard of spindle bearing  270  but inboard of centrifugal force bearing  210 . 
     In one embodiment, shear bearing  270  is a cylindrical elastomeric bearing which has multiple cylindrical layers that are laminated or vulcanized together. In another embodiment, shear bearing  270  may have conical or spherical layers that are laminated or vulcanized together. Shear bearing  270  can include alternating elastomeric layers  271  and rigid layers  272 . Elastomeric layers  271  may be made of an elastic material such as rubber, and rigid layers  272  may be made of a rigid material such as steel. However, embodiments are not limited to any particular materials, and elastomeric layers  271  and rigid layers  272  may be made of any elastic and rigid materials, respectively. 
     Shear bearing  270  can be vulcanized or adhered to both the outboard portion  264  of spindle  260  and wall portion  237  of housing  230 . Shear bearing  270  can be configured such that housing  230  is allowed to rotate clockwise and counterclockwise about a center axis  330  that runs along the length of each blade  120  and spindle  260 . For example, shear bearing  270  reacts to torsional force  320  by elastically deforming the cylindrical elastomeric layers between each rigid layer. As mentioned, pitch horn  160  can selectively control the pitch of blade  120 . Therefore, as pitch horn  160  rotates blade  120 , torsional force  320  is transferred from blade  120  to housing  230 , from housing  230  to shear bearing  270 . Accordingly, since spindle  260  is not rotatable, torsional force  320  is in relation to spindle  260 . 
     In one embodiment, centrifugal force bearing  210  is a cylindrical elastomeric bearing which has multiple substantially planar layers that are laminated or vulcanized together. In another embodiment, centrifugal force bearing  210  may have conical or spherical layers that are laminated or vulcanized together. The planar layers may run perpendicularly in relation to the length of spindle  260 . Centrifugal force bearing  210  can include alternating elastomeric layers  211  and rigid layers  212 . Elastomeric layers  211  may be made of an elastic material such as rubber, and rigid layers  212  may be made of a rigid material such as steel. However, embodiments are not limited to any particular materials, and elastomeric layers and rigid layers may be made of any elastic and rigid materials, respectively. 
     Centrifugal force bearing  210  can be vulcanized or adhered to surface  236  of housing  230 . Centrifugal force bearing  210  can be configured to counteract centrifugal forces acting on blade  120  as blade  120  spins around yoke  150 . For example, centrifugal forces acting on blade  120  are transferred from blade  120  to housing  230 , housing  230  then exerts a compression force to centrifugal force bearing  210 . Centrifugal force bearing  210  reacts and counteracts the compression force by compressing the elastomeric layers between each rigid layer. 
     In one example embodiment, centrifugal force bearing  210  may not be cylindrical. Those skilled in the art will understand that centrifugal force bearing  210  may be deviated from being cylindrical. For example, centrifugal force bearing  210  may be cube shaped. 
     In one example embodiment, housing  230  includes a plurality of apertures  510  running parallel to spindle  260 , as seen in  FIG. 8 . These apertures can serve several purposes. For example, apertures  510  may make it easier to remove shear bearing  270  from the assembly. Specialized tooling can be made to fit within apertures  510  and pull shear bearing  270  away from housing  230 . Another purpose of apertures  510  is to allow air to flow into apertures  510  in order to cool the elements of elastomeric bearing assembly  200 . During operation, centrifugal force bearing  210  and shear bearing  270  can be repeatedly compressed or twisted due to the compression and torsional forces acting on them. These forces can produce excess heat that can be reduced by apertures  510 . 
     In one example embodiment, shear bearing  270  may include a race  275 , as seen in  FIGS. 9 and 10 . Race  275  can be made out of any suitable metal, such as stainless steel. The outermost layer of shear bearing  270  can be vulcanized or adhered to race  275 . Shear bearing  270  with race  275  can be wet installed, bonded, or thermally fit into housing  230 . One of the advantages of this embodiment is that shear bearing  270  can be easily removed from housing  230  and replaced with a lower risk of damaging the centrifugal force bearing  210 . 
     In yet another example embodiment, shear bearing  270  may include additional anti-rotation features when shear bearing  270  is bonded to race  275  instead of housing  230 . As seen in  FIG. 9 , race  275  may include holes  276 , and housing  230  may include holes  231  that may run transversely in relation to shear bearing  270 . Holes  231  and  276  may accommodate locked set screws  280  that run through housing  230  and race  275 . In another example embodiment, race  275  and housing  230  may include holes  296  that run parallel to race  275 , as seen in  FIG. 10 . Holes  296  can accommodate pinned plates  290  that are secured to housing  230  by screws  295 . 
     One advantage of elastomeric bearing assembly  200  is that both shear bearing  270  and centrifugal force bearing  210  are located in the same assembly. Having both of these bearings in the same assembly makes the assembly more compact and lightweight. Additionally, the design of elastomeric bearing assembly  200  can allow the assembly to be closer to the center of gravity of the rotor system, which can reduce the forces acting on elastomeric bearing assembly  200  and blade  120 . 
     Another advantage of elastomeric bearing assembly  200  is that cavities  232 , which accommodate bushings  220  and the blade bolts, are located close to center axis  330 , and close to each other. A person of skill in the art would recognize that a flat portion  122  of blade  120  is the optimal position for the blade bolts to couple elastomeric bearing assembly  200  to blade  120 . Hence, locating the blade bolts closer to center axis  330  and each other would reduce the width of the flat portion  122  of blade  120 . The reduction of the width of flat portion  122  of blade  120  may reduce manufacturing complexity and cost. 
     For example, if cavities  232  were to exceed a specific width apart, the spar of blade  120  may become equally wide at that location; therefore, the final blade structure may not be dynamically acceptable for certain applications, such as tiltrotor aircraft. A person of skill in the art would recognize that the blades of tiltrotor aircraft are especially sensitive to structural dynamic tuning. 
     The particular embodiments disclosed above are illustrative only, as the system may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Modifications, additions, or omissions may be made to the apparatuses described herein without departing from the scope of the invention. The components of the system may be integrated or separated. Moreover, the operations of the system may be performed by more, fewer, or other components. 
     Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the application. Accordingly, the protection sought herein is as set forth in the claims below. 
     To aid the Patent Office, and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants wish to note that they do not intend any of the appended claims to invoke paragraph 6 of 35 U.S.C. § 112 as it exists on the date of filing hereof unless the words “means for” or “step for” are explicitly used in the particular claim.