Abstract:
A bearing sleeve assembly includes a rigid inner element having a cylindrical inner diameter bore and an outer surface that is non-cylindrical. Also included is a rigid outer element spaced radially outwardly from the rigid inner element, the rigid outer element comprising a cylindrical member with a uniform cross-section that forms a ring with an inner-diameter surface and an outer-diameter surface, the outer element&#39;s inner-diameter surface and the non-cylindrical outer surface of the inner element defining a non-uniform annulus therebetween. Further included is an elastomeric core disposed between the rigid inner element and the rigid outer element within the non-uniform annulus, the elastomeric core having a first thickness at a first location and a second thickness at a second location, the first thickness being greater than the second thickness.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to U.S. Provisional Application No. 62/274,490, filed on Jan. 4, 2016, the contents of which are incorporated by reference herein in their entirely. 
     
    
     FEDERAL RESEARCH STATEMENT 
       [0002]    The content of this disclosure was made with Government support under Contract No. W911W6-13-2-0003 with the United States Army. The Government has certain rights in the application. 
     
    
     BACKGROUND 
       [0003]    The embodiments herein relate to bearing assemblies and, more particularly, to a bearing sleeve assembly that may be used within a rotor system; namely within a rotary-wing aircraft. 
         [0004]    Rotary wing aircraft include rotor systems and rotor blade assemblies to generate lift and allow for controlled operation of the air vehicle. During vehicle operation, the rotor blades are influenced by aerodynamic and inertial forces. Accordingly, each blade will experience elastic deformation as well as rigid body motion as a consequence of the forces acting upon it, referred to herein as blade dynamics. As a result of blade dynamics, rotor systems may be susceptible to forms of aero-elastic and aero-mechanical instabilities. In the pursuit of increased vehicle performance, new compound rotorcraft designs incorporate a coaxial rotor configuration with rigid rotor blades. A byproduct of such a configuration is that no appreciable relative motion occurs between the blade and the hub assembly, which precludes the ability to integrate a damping mechanism. Thus, aero-elastic stability is predominantly dictated by the combined elastic stiffness of the main rotor blade and hub assembly. 
         [0005]    To address dynamic stability issues, it is desirable for significant separation to exist in the blade&#39;s natural frequencies (namely the first flatwise and edgewise modes). The primary means of ensuring frequency separation in under-damped systems is through the tailoring of stiffness in the degrees of freedom of concern. In the context of a rotor system, one area that has a significant effect on the edgewise and flatwise stiffness values is the hub assembly. Helicopters utilize bearings, which are contained within the hub assembly, to accommodate pitch changes of rotor blades. However, in a rigid rotor design the blade&#39;s flapping and lagging hinges are removed and made rigid. Thus, the blade bending moments imposed on the hub are increased in comparison to an articulated rotor configuration. The increased loading present in rigid rotor systems shifts the design towards the need to incorporate metallic pitch-bearing designs so as not to accommodate large radial load capacity as well as to ensure low impedance in accommodating changes in blade pitch. Rotary bearings of metallic construction incorporate cylindrical raceways that have an isotropic radial stiffness gradient through the element due to the symmetry of the design. Therefore, the isotropic radial stiffness properties of the bearing race results in equal stiffness values in the flatwise and edgewise directions. A challenge exists in the design of such a rotor system to accommodate the desirable traits of a rigid rotor system, while accommodating tailored stiffness values in the edgewise and flatwise orientations to avoid aero-elastic instability. 
       BRIEF DESCRIPTION 
       [0006]    According to one embodiment, a bearing sleeve assembly includes a rigid inner element having a cylindrical inner diameter bore and an outer surface that is non-cylindrical. Also included is a rigid outer element spaced radially outwardly from the rigid inner element, the rigid outer element comprising a cylindrical member with a uniform cross-section that forms a ring with an inner-diameter surface and an outer-diameter surface, the outer element&#39;s inner-diameter surface and the non-cylindrical outer surface of the inner element defining a non-uniform annulus therebetween. Further included is an elastomeric core disposed between the rigid inner element and the rigid outer element within the non-uniform annulus, the elastomeric core having a first thickness at a first location and a second thickness at a second location, the first thickness being greater than the second thickness. 
         [0007]    In addition to one or more of the features described above, or as an alternative, further embodiments may include that the rigid inner element is formed of a metallic material. 
         [0008]    In addition to one or more of the features described above, or as an alternative, further embodiments may include that the rigid outer element is formed of a metallic material. 
         [0009]    In addition to one or more of the features described above, or as an alternative, further embodiments may include that the bearing sleeve assembly has a first stiffness proximate the first location of the elastomeric core and a second stiffness proximate the second location of the elastomeric core, the second stiffness being greater than the first stiffness. 
         [0010]    In addition to one or more of the features described above, or as an alternative, further embodiments may include that the bearing sleeve assembly is operatively coupled to a connecting a rotor hub and a rotor blade. 
         [0011]    In addition to one or more of the features described above, or as an alternative, further embodiments may include that the outer surface of the rigid inner element is elliptical. 
         [0012]    According to another embodiment, a rotor system includes a rotor hub, a rotor blade and a spindle assembly operatively connecting the rotor hub within a non-pitching frame and the rotor blade within the pitching frame, the spindle assembly having a first bearing assembly. The first bearing assembly includes a first pitch bearing and a first bearing sleeve assembly, the bearing sleeve assembly including a first rigid inner element connected to the first pitch bearing. The first bearing sleeve assembly also includes a first rigid outer element spaced radially outwardly from the first rigid inner element, the first rigid inner element and the first rigid outer element defining a first non-uniform annulus therebetween. The first bearing sleeve assembly further includes a first elastomeric core disposed between the first rigid inner element and the first rigid outer element within the first non-uniform annulus, the first elastomeric core having a non-uniform thickness. 
         [0013]    In addition to one or more of the features described above, or as an alternative, further embodiments may include a second bearing sleeve assembly disposed closer to the rotor hub relative to the first bearing sleeve assembly. 
         [0014]    In addition to one or more of the features described above, or as an alternative, further embodiments may include a second bearing sleeve assembly disposed further from the rotor hub relative to the first bearing sleeve assembly. 
         [0015]    In addition to one or more of the features described above, or as an alternative, further embodiments may include the first rigid inner element having a cylindrical inner diameter bore and an outer surface that is elliptical, the first rigid outer element having a cylindrical inner diameter. 
         [0016]    In addition to one or more of the features described above, or as an alternative, further embodiments may include the first elastomeric core having a first thickness at a first location and a second thickness at a second location, the first thickness being greater than the second thickness, wherein the bearing sleeve assembly has a first stiffness proximate the first location of the first elastomeric core and a second stiffness proximate the second location of the first elastomeric core, the second stiffness being greater than the first stiffness. 
         [0017]    In addition to one or more of the features described above, or as an alternative, further embodiments may include that the first stiffness is in an edgewise direction of the rotor blade and the second stiffness is in a flatwise direction of the rotor blade. 
         [0018]    In addition to one or more of the features described above, or as an alternative, further embodiments may include that the rigid inner element is formed of a metallic material. 
         [0019]    In addition to one or more of the features described above, or as an alternative, further embodiments may include that the rigid outer element is formed of a metallic material. 
         [0020]    In addition to one or more of the features described above, or as an alternative, further embodiments may include that the second bearing sleeve assembly includes a second rigid inner element. Also included is a second rigid outer element spaced radially outwardly from the second rigid inner element, the second rigid inner element and the second rigid outer element defining a second non-uniform annulus therebetween. Further included is a second elastomeric core disposed between the second rigid inner element and the second rigid outer element within the second non-uniform annulus, the second elastomeric core having a non-uniform thickness. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The subject matter which is regarded as the present disclosure is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the present disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0022]      FIG. 1  is a perspective view of a rotary-wing aircraft; 
           [0023]      FIG. 2  is a plan view of a connector assembly connecting a hub, a spindle assembly and a rotor blade according to an embodiment; 
           [0024]      FIG. 3  is a cross-sectional view of hub, spindle assembly and rotor blade taken along line A-A of  FIG. 2 ; 
           [0025]      FIG. 4  is an elevational view of a bearing assembly; 
           [0026]      FIG. 5  is a cross-sectional view of the bearing assembly taken along line B-B of  FIG. 4 ; 
           [0027]      FIG. 6  is a cross-sectional view of the bearing assembly taken along line C-C of  FIG. 4 ; 
           [0028]      FIG. 7  is a perspective view of a hub, spindle assembly and rotor blade according to another embodiment; 
           [0029]      FIG. 8  is a top view of the spindle assembly of  FIG. 7 ; 
           [0030]      FIG. 9  is a cross-sectional view of the spindle assembly taken along line D-D of  FIG. 8 ; 
           [0031]      FIG. 10  is an elevational front view of the spindle assembly of  FIG. 7 ; and 
           [0032]      FIG. 11  is a cross-sectional view of the spindle assembly taken along line E-E of  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION 
       [0033]    Referring to  FIG. 1 , a rotor system, such as a helicopter  10 , is provided. The helicopter  10  includes a fuselage  11  that is formed to define an interior cabin in which a pilot and passengers may be situated. The fuselage  11  includes a pylon section  12  at a top portion thereof and a tail section  13  at a trailing end thereof. The pylon section  12  is supportive of a main rotor shaft  14  that is rotatable about its longitudinal or vertical axis relative to the fuselage  11 . The main rotor shaft  14  is respectively coupled to substantially rigid coaxial main rotor blades  15  and  16  proximate a rotor hub  20 , which rotate with the main rotor shaft  14  to provide a lift force for the helicopter  10 . The tail section  13  is supportive of a propeller shaft (not shown) that is rotatable about a longitudinal axis thereof relative to the fuselage  11  and in a plane defined transversely with respect to a rotational plane of the main rotor shaft  14 . The propeller shaft is coupled to a pusher propeller  17 , which rotates with the propeller shaft, to provide thrust to the helicopter  10 . As illustrated, the helicopter  10  is a compound or coaxial helicopter although it is to be understood that the embodiment is merely illustrative and that the description provided herein may be applicable to various rotor system designs. For example, a rotary wing aircraft with a single main rotor system and an anti-torque tail rotor system will also benefit from the disclosure. 
         [0034]    Although the disclosed embodiments are described herein in the context of a helicopter, it is to be appreciated that any machine or system that includes oscillatory motion may benefit from the disclosure. For example, the disclosed embodiments may be employed with components associated with wind turbines or fixed wing systems with thrust providing propeller style propulsion systems. 
         [0035]    Referring now to  FIGS. 2 and 3 , with continued reference to  FIG. 1 , a single rotor blade  22  that is one of the rotor blades  15  and/or  16  is illustrated and described. In particular, a connector assembly  24  is illustrated. The connector assembly  24  is employed to operatively couple the rotor blade  22  to the rotor hub  20 . The connector assembly  24  includes a cuff  26  coupled to the rotor blade  22  proximate a first end  28  of the cuff  26  and coupled to a T-bar  30  proximate a second end  32  of the cuff  26 . The T-bar  30  is coupled to the rotor hub  20 . The aforementioned assembly operatively couples the rotor blade  22  to the rotor hub  20 . At least one bearing assembly  34  is included as part of the connector assembly  24 , the bearing assembly  34  accommodating pitch changes of the rotor blade  22  during operation. As will be described below, a bearing sleeve assembly  36  is provided in the bearing assembly  34  to overcome challenges associated with rigid rotor blades. 
         [0036]    In the illustrated embodiment, a first bearing assembly  38  and a second bearing assembly  40 , each with respective bearing sleeve assemblies  36 , are included, with the first bearing assembly  38  being disposed further from the rotor hub  20  relative to the second bearing assembly  40 . These may be designated as an outboard bearing assembly and an inboard bearing assembly, respectively. The first bearing assembly  38  is connected to the hub  20  and T-bar  30 , and the second bearing assembly  40  is connected to the hub  20  and the cuff  26  of the rotor blade  22  The bearing sleeve assembly  36  described below may be implemented in the first bearing assembly  38  and/or the second bearing assembly  40 . In other words, either or both of the bearing assemblies may utilize the bearing sleeve assembly  36  described herein. 
         [0037]    It is to be appreciated that numerous alternative rotor systems may benefit from the embodiments described herein. For example, alternatives to the cuff and sleeve embodiment described above and shown in  FIGS. 2 and 3  may include the bearing assembly  34  described herein. A spindle assembly  80  is shown in  FIGS. 7-11  to illustrate such an example. The spindle assembly  80  may be used in a wide variety of applications spanning numerous industries, including but not limited to wind turbine applications, for example. The spindle assembly  80  includes a rotor blade  82 , a rotor hub  84  and a spindle connector assembly  86 . As shown in the sectional views of  FIGS. 9 and 11 , one or more bearing assemblies represented generally with numeral  34  may be included and connect the rotor hub  84  and the spindle connector assembly  86 . The bearing assemblies  34  correspond to the first bearing assembly  38  and the second bearing assembly  40  described in detail in relation to  FIGS. 2 and 3 . 
         [0038]    Referring now to  FIGS. 4-6 , the bearing assembly  34  is illustrated in greater detail. The bearing assembly  34  includes bearing components, referred to generally with numeral  42 , the bearing components  42  including a roller element  44  and a bearing race  46 , for example. Irrespective of the particular bearing components included, the bearing components  42  are generally cylindrical and are concentrically surrounded by an inner element  48  that is substantially rigid. The inner element  48  may be formed of any suitable rigid material. In some embodiments, the inner element  48  is formed of a metallic material. The inner element  48  includes a radially inner surface  50  that is substantially cylindrical and a radially outer surface  52  that is substantially non-circular. Together, the radially inner surface  50  and the radially outer surface  52  cause the inner element  48  to have a non-uniform thickness radially. In the illustrated embodiment, the radially outer surface  52  is elliptical to achieve the non-uniform thickness of the inner element  48 . In the case of an elliptical radially outer surface, the thickness of the inner element  48  varies in an axisymmetric manner, as shown. 
         [0039]    The bearing sleeve assembly  36  also includes an outer element  54  that is substantially rigid. The outer element  54  may be formed of any suitable rigid material and may be connectable to an element such as the cuff  26  or the hub  20 . In some embodiments, the outer element  54  is formed of a metallic material. The outer element  54  includes a radially inner surface  56  that is cylindrical and is spaced radially outwardly from the inner element  48 . The radially inner surface  56  of the outer element  54  and the radially outer surface  52  of the inner element  48  define a non-uniform annulus  58  therebetween due to the non-circular geometry of the radially outer surface  52 . 
         [0040]    A core  60  is fittingly disposed between the inner element  48  and the outer element  54  within the non-uniform annulus  58 . The core  60  is formed of an elastomeric material to be compliant in response to loads applied on the bearing assembly  34 . The core  60  is in contact with the radially outer surface  52  of the inner element  48  and the radially inner surface  56  of the outer element  54 . Due to the non-uniform annulus  58 , the core  60  is formed to have a non-uniform thickness. In the case of the illustrated elliptical outer surface  52  of the inner element  48 , the inner surface of the core  60  is correspondingly elliptical and the outer surface is cylindrical to correspond to the inner surface  56  of the outer element  54 . In such an embodiment, the thickness of the core  60  is axisymmetric to result in a first thickness  62  at a first location and a second thickness  64  at a second location. Notably, in an axisymmetric embodiment identical thicknesses are present on opposing sides of each of the first thickness  62  and the second thickness  64 . As shown, the first thickness  62  is greater than the second thickness  64 . The thicker elastomeric section (i.e., first thickness  62 ) results in more overall deformation under an applied radial load, thereby yielding a lower effective thickness in response to loads applied in an edgewise direction  70  of the rotor blade  22 . Conversely, the thinner elastomeric section (i.e., second thickness  64 ) results in less overall deformation under an applied radial load, thereby yielding a higher effective stiffness in response to loads applied in a flatwise direction  72  of the rotor blade  22 . 
         [0041]    The above-described core  60 , in combination with the rigid inner and outer elements  48 ,  52 , provides a directional stiffness gradient through the bearing assembly  34  that may be tailored to suit the load demands of the particular application. This is particularly advantageous for rigid rotor configurations where it is desirable to significantly separate the natural frequencies that exist in the blade flatwise and edgewise orientations. The embodiments described herein allow tailoring of the stiffness gradient by relying on largely metallic load path resistance in one direction, while utilizing largely elastomeric load path resistance in the other direction. 
         [0042]    While the present disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to such disclosed embodiments. Rather, the present disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the present disclosure. Additionally, while various embodiments of the present disclosure have been described, it is to be understood that aspects of the present disclosure may include only some of the described embodiments. Accordingly, the present disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.