Abstract:
A bearing can include a ball member, a race, and a liner located on an interior surface of the race, the liner having a first surface bonded to an interior surface of the race, the liner having a second surface that is adjacent to the ball member. The bearing also includes a wafer having a wear surface that is aligned with the second surface of the liner, the wafer being an electrically conductive member. Operational wear of the liner can be calculated by comparing a measured resistance of the wafer to an original known resistance of the wafer.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to a system and method for monitoring wear in a bearing. 
         [0003]    2. Description of Related Art 
         [0004]    Bearings can be used in a wide variety of implementations. One conventional implementation is the use of a rod end bearing in a rotor system of a helicopter. The rod end can have a liner between the ball and the race in order to reduce friction therebetween. Over time, the liner can wear away and necessitate replacement of the bearing. Conventionally, the amount of wear is detected by applying a load and measuring the amount of relative motion between the ball and the race of the bearing. This process is labor intensive, inaccurate, and can require special procedures and equipment to perform. 
         [0005]    There is a need for an improved system and method of monitoring wear in a bearing. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0006]    The novel features believed characteristic of the embodiments of the present disclosure are set forth in the appended claims. However, the embodiments themselves, 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: 
           [0007]      FIG. 1  is a side view of a rotorcraft, according to an example embodiment; 
           [0008]      FIG. 2  is perspective view of the rotor hub of the rotorcraft, according to an example embodiment; 
           [0009]      FIG. 3  is a perspective view of a pitch link, according to an example embodiment; 
           [0010]      FIG. 4  is a perspective view of a rod end having a spherical bearing, according to an example embodiment; 
           [0011]      FIG. 5  is a side view of a bearing, according to an example embodiment; 
           [0012]      FIG. 6  is a cross-sectional view of the bearing, taken from section lines  6 - 6  in  FIG. 5 , according to an example embodiment; 
           [0013]      FIG. 7  is a detail view of the bearing, according to an example embodiment; 
           [0014]      FIG. 8  is a perspective view of a wafer, according to an example embodiment; 
           [0015]      FIG. 9  is a side view of a bearing, according to another example embodiment; 
           [0016]      FIG. 10  is a cross-sectional view of the bearing, taken from section lines  10 - 10  in  FIG. 9 , according to an example embodiment; 
           [0017]      FIG. 11  is a detail view of the bearing, according to an example embodiment; and 
           [0018]      FIG. 12  is a perspective view of a wafer, according to an example embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0019]    Illustrative embodiments of the system and method are described below. In the interest of clarity, all features of an actual implementation may not be described in this specification. 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. 
         [0020]    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 application, 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. 
         [0021]    Referring now to  FIG. 1  in the drawings, a rotorcraft  101  is illustrated. Rotorcraft  101  has a rotor system  103  with a plurality of rotor blades  105 . The pitch of each rotor blade  105  can be selectively controlled in order to selectively control direction, thrust, and lift of rotorcraft  101 . Rotorcraft  101  further includes a fuselage  107 , anti-torque system  109 , and an empennage  111 . Rotorcraft  101  further includes a landing gear system  113  to provide ground support for the aircraft. It should be appreciated that rotorcraft  101  is merely illustrative of a variety of aircraft that can implement the embodiments disclosed herein. Other aircraft implementations can include hybrid aircraft, tilt rotor aircraft, unmanned aircraft, gyrocopters, and a variety of helicopter configurations, to name a few examples. It should be appreciated that even though aircraft are particularly well suited to implement the embodiments of the present disclosure, non-aircraft vehicles and devices can also implement the embodiments. 
         [0022]    Referring also to  FIG. 2  in the drawings, rotor hub  103  is illustrated in further detail. Rotor hub  103  includes a yoke  109  coupled to a mast  113 . Each rotor blade  105  is coupled to the yoke  115  with a grip  119 . An inboard portion of each grip  119  is secured within an opening of the yoke  115  with a centrifugal force bearing  135 . Rotor blade  105  is attached to the outboard portion of grip  119 . A pitch horn  123  is interposed between rotor blade  105  and grip  119 . A damper  121  is attached between yoke  115  and pitch horn  123 . A pitch link  125  transfers pitch changes from a swashplate  127  to pitch horn  123 . During operation, pitch link  125  can endure a high frequency of cycles. 
         [0023]    Referring now also to  FIGS. 3 and 4 , pitch link  125  is illustrated in further detail. Pitch link  125  can include a link body  201  coupled between a first rod end  203  and a second rod end  205  that are substantially similar to each other. Rod end  203  can include a housing  207  and a shaft  209 . Housing  207  is adapted for securing a bearing  211  therein. In the illustrated embodiment, bearing  211  is swaged into housing  207 ; however, it should be appreciated that bearing  211  can be coupled into housing  207  in other ways, such as adhesive bonding. In another embodiment, bearing  211  is integral with housing. Bearing  211  is illustrated as a spherical type bearing for exemplary purposes. 
         [0024]    Referring now also to  FIGS. 5-8 , one example embodiment of bearing  211  is illustrated in further detail. Bearing  211  can include ball  213  having an attachment hole  215  located therethrough. Ball  213  fits within a race  217  that has an interior spherical surface with a liner  219  thereon. An outer surface of race  217  has an outer diameter that is configured for securedly locating within a component or structure, such as housing  207  of rod end  203 , for example. Ball  213  is configured to rotate in relation to liner  219 , such that the outer surface of ball  213  rubs against the friction surface of liner  219 . Liner  219  is preferably made with a material having a low coefficient of friction, such as polytetrafluoroethylene (PTFE). 
         [0025]    Bearing  211  includes a wafer  221  embedded in liner  219 . Wafer  221  is an electrically conductive material that has a defined volume with a known electrical resistance. Leads  223  are electrically coupled to both wafer  221  and a terminal  225 . Terminal  225  is located at an easily accessible external surface, such as on an outer surface of race  217 . Leads  223  can be embedded in liner  219  or located between liner  219  and race  217 . A wear surface B 1  of wafer  221  is configured to wear as liner  219  wears, while a surface A 1  is fixed to the inner surface of race  217 . As wear surface B 1  is eroded, the thickness T 1  between surfaces A 1  and B 1  is reduced, resulting in a reduction in wafer volume and resistance. In the illustrated embodiment, wafer  221  is approximately ring shaped with an outer radial surface A 1  and inner radial surface B 1  that are concentric. An axis  227  corresponding with axial loads of pitch link  125  intersects wafer  221  twice. A center of wafer  221  intersects both axis  227  and hole axis  229 . A predicted wear pattern will be most severe at the locations at either intersect of axis  227  and wafer  221 . The ring geometry of wafer  221  allows bearing  211  to be located in any orientation within housing  207  while maintaining two intersections with axis  227 , thus insuring that wafer  221  will be subjected to the most severe wear within the wear pattern, regardless of the orientation of bearing  211  within housing  207 . 
         [0026]    Wafer  221  and liner  219  can be attached to the interior of race  217  in a number of different methods. One method is to locate and bond wafer  221  around the centerline interior of race  217  prior to injection molding liner  219  adjacently to both sides of wafer  221  onto the interior of race  217 . 
         [0027]    During operation, wafer  221  is worn at the same rate as liner  219 . In order to easily quantify the amount of wear of liner  219 , an Ohm meter can be coupled to leads  223  at terminal  225  to measure the resistance of wafer  221 . The measured resistance can be compared to an initial or pre-worn resistance in order to calculate a wear percentage of wafer  221 , which corresponds to a wear percentage of liner  219 . In another embodiment, leads  223  are electrically coupled to a monitoring system in the aircraft such that the wear percentage of wafer  221  and liner  219  can be accessed and read on a display within the aircraft. In another embodiment, the resistance measurement of wafer  221  is wirelessly transmitted to a receiver to avoid the time and effort associated with manually coupling an Ohm meter to terminal  225 . However it should be appreciated that even manually coupling an Ohm meter to terminal  225  to calculate a percentage of wear of liner  219  is much more accurate and efficient compared with the conventional methods of testing for wear of liner  219 . 
         [0028]    Referring now also to  FIGS. 9-12 , another embodiment of bearing  211  is illustrated. Bearing  911  illustrated in  FIGS. 9-12  is substantially similar in form and function as the bearing  211  illustrated in  FIGS. 5-8 , except for the geometry and location of wafer  921 . As illustrated in  FIGS. 9-12 , the geometry of wafer  921  can be such that the lengthwise axis of wafer  921  extends from a first face  229  to a second face  231  of race  217 . The wafer  921  intersects axis  227 , axis  227  corresponding with an axial load path of pitch link  125 . Thus wafer  921  has an arc shaped volume extends from first face  229  to second face  231  rather than being a ring shaped member similar to wafer  221 . 
         [0029]    The embodiments herein are illustrated with regard to a pitch link on a main rotor assembly on a rotorcraft; however, it should be appreciated that the embodiments may be adaptable to any bearing and structure incorporating such a bearing. For example, bearings  211  and  921  can be incorporated into a swashplate drive link, anti-drive link, control link, tail rotor pitch link, and lined journal bearings, to name a few examples. 
         [0030]    The particular embodiments disclosed above are illustrative only, as the apparatus 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 apparatus may be integrated or separated. Moreover, the operations of the apparatus may be performed by more, fewer, or other components. 
         [0031]    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. 
         [0032]    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.