Patent Publication Number: US-9845826-B2

Title: Hybrid spherical and thrust bearing

Description:
RELATED APPLICATIONS 
     Pursuant to 35 U.S.C. §120, this application is a continuation of and claims priority to U.S. patent application Ser. No. 13/532,910, HYBRID SPHERICAL AND THRUST BEARING, filed Jun. 26, 2012. U.S. patent application Ser. No. 13/532,910 is hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to bearings, and more particularly, to a hybrid spherical and thrust bearing. 
     BACKGROUND 
     A rotorcraft may include one or more rotor systems. One example of a rotorcraft rotor system is a main rotor system. A main rotor system may generate aerodynamic lift to support the weight of the rotorcraft in flight and thrust to counteract aerodynamic drag and move the rotorcraft in forward flight. Another example of a rotorcraft rotor system is a tail rotor system. A tail rotor system may generate thrust in the same direction as the main rotor system&#39;s rotation to counter the torque effect created by the main rotor system. A rotor system may include one or more pitch links to rotate, deflect, and/or adjust rotor blades. 
     SUMMARY 
     Particular embodiments of the present disclosure may provide one or more technical advantages. A technical advantage of one embodiment may include the capability to provide a bearing that protects against a variety of forces, such as torsional, radial, axial, and cocking forces. A technical advantage of one embodiment may include the capability to provide a bearing with a longer life expectancy. A technical advantage of one embodiment may also include the capability to reduce torsional buildup in an elastomeric bearing. 
     Certain embodiments of the present disclosure may include some, all, or none of the above advantages. One or more other technical advantages may be readily apparent to those skilled in the art from the figures, descriptions, and claims included herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To provide a more complete understanding of the present invention and the features and advantages thereof, reference is made to the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  shows a rotorcraft according to one example embodiment; 
         FIG. 2  shows the rotor system and blades of the rotorcraft of  FIG. 1  according to one example embodiment; 
         FIG. 3A  shows a plan view of a bearing of the rotor system of  FIG. 2  according to one example embodiment; 
         FIG. 3B  shows a cross-section view of the bearing of  FIG. 3A ; 
         FIG. 3C  shows a perspective view of the bearing of  FIG. 3A ; 
         FIGS. 4A and 4B  show forces that may be exerted on the bearing of  FIG. 3A ; and 
         FIGS. 5A and 5B  show the bearing of  FIG. 3A  installed in the rotor system of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a rotorcraft  100  according to one example embodiment. Rotorcraft  100  features a rotor system  110 , blades  120 , a fuselage  130 , a landing gear  140 , and an empennage  150 . Rotor system  110  may rotate blades  120 . Rotor system  110  may include a control system for selectively controlling the pitch of each blade  120  in order to selectively control direction, thrust, and lift of rotorcraft  100 . Fuselage  130  represents the body of rotorcraft  100  and may be coupled to rotor system  110  such that rotor system  110  and blades  120  may move fuselage  130  through the air. Landing gear  140  supports rotorcraft  100  when rotorcraft  100  is landing and/or when rotorcraft  100  is at rest on the ground. Empennage  150  represents the tail section of the aircraft and features components of a rotor system  110  and blades  120 ′. Blades  120 ′ may provide thrust in the same direction as the rotation of blades  120  so as to counter the torque effect created by rotor system  110  and blades  120 . Teachings of certain embodiments relating to rotor systems described herein may apply to rotor system  110  and/or other rotor systems, such as other tilt rotor and helicopter rotor systems. It should also be appreciated that teachings from rotorcraft  100  may apply to aircraft other than rotorcraft, such as airplanes and unmanned aircraft, to name a few examples. 
       FIG. 2  shows rotor system  110  and blades  120  of  FIG. 1  according to one example embodiment. In the example of  FIG. 2 , rotor system  110  features a power train  112 , a hub  114 , a swashplate  116 , and pitch links  118 . In some examples, rotor system  110  may include more or fewer components. For example,  FIG. 2  does not show components such as a gearbox, a swash plate, drive links, drive levers, and other components that may be incorporated. 
     Power train  112  features a power source  112   a  and a drive shaft  112   b . Power source  112   a , drive shaft  112   b , and hub  114  are mechanical components for transmitting torque and/or rotation. Power train  112  may include a variety of components, including an engine, a transmission, and differentials. In operation, drive shaft  112   b  receives torque or rotational energy from power source  112   a  and rotates hub  114 . Rotation of rotor hub  114  causes blades  120  to rotate about drive shaft  112   b.    
     Swashplate  116  translates rotorcraft flight control input into motion of blades  120 . Because blades  120  are typically spinning when the rotorcraft is in flight, swashplate  116  may transmit flight control input from the non-rotating fuselage to the hub  114 , blades  120 , and/or components coupling hub  114  to blades  120  (e.g., grips and pitch horns). References in this description to coupling between a pitch link and a hub may also include, but are not limited to, coupling between a pitch link and a blade or components coupling a hub to a blade. 
     In some examples, swashplate  116  may include a non-rotating swashplate ring  116   a  and a rotating swashplate ring  116   b . Non-rotating swashplate ring  116   a  does not rotate with drive shaft  112   b , whereas rotating swashplate ring  116   b  does rotate with drive shaft  112   b . In the example of  FIG. 2 , pitch links  118  connect rotating swashplate ring  116   b  to blades  120 . 
     In operation, according to one example embodiment, translating the non-rotating swashplate ring  116   a  along the axis of drive shaft  112   b  causes the pitch links  118  to move up or down. This changes the pitch angle of all blades  120  equally, increasing or decreasing the thrust of the rotor and causing the aircraft to ascend or descend. Tilting the non-rotating swashplate ring  116   a  causes the rotating swashplate  116   b  to tilt, moving the pitch links  118  up and down cyclically as they rotate with the drive shaft. This tilts the thrust vector of the rotor, causing rotorcraft  100  to translate horizontally following the direction the swashplate is tilted. 
     In the example of  FIG. 2 , pitch links  118  couple rotating swashplate ring  116   b  to blades  120 . Pitch links  118  may be subject to various forces at its connection points with swashplate ring  116   b  and blades  120 , such as torsional, radial, axial, and cocking forces. Teachings of certain embodiments recognize the capability to provide a bearing that protects against some or all of these forces. A particular embodiment is described below with regard to  FIGS. 3A, 3B, 3C, 4A, 4B, 5A, and 5B . 
       FIGS. 3A-3C  show a bearing  200  according to one example embodiment.  FIG. 3A  shows a plan view of bearing  200 ,  FIG. 3B  shows a cross-section view of bearing  200 , and  FIG. 3C  shows a perspective view of bearing  200 . Bearing  200  features an outer housing  210  having a threaded portion  215 , an elastomeric bearing  220 , an inner housing  230 , conical members  240 , bearing surfaces  250 , and seals  260 . Components of bearing  200  form an opening  270  through bearing  200 . In  FIG. 3C , portions of housing  210 , elastomeric bearing  220 , an inner housing  230 , conical members  240 , bearing surfaces  250 , and seals  260  have been removed to provide additional clarity. 
     In the example of  FIGS. 3A-3C , outer housing  210  is a metallic hollow cylinder having variable radii that forms a first opening therethrough. Other bearing components, such as elastomeric bearing  220 , inner housing  230 , conical members  240 , bearing surfaces  250 , and seals  260 , may reside inside the first opening. Outer housing  210  also includes a threaded portion  215  for attaching bearing  200  to another device. For example, in one embodiment, threaded portion  215  may thread into an end of a pitch link, such as pitch link  118 . In one example embodiment, a first bearing  200  threads into one end of pitch link  118 , and a second bearing  200  threads into the opposite end of pitch link  118 . 
     Elastomeric bearing  220  resides inside outer housing  210  and forms a second opening therethrough. Other bearing components, such as inner housing  230 , conical members  240 , bearing surfaces  250 , and seals  260 , may reside inside the second opening. Elastomeric bearing  220  is formed from an elastomeric material. In one example embodiment, elastomeric bearing  220  features a series of elastomeric and metal shims, which allow global dithering through local small elastomeric deflections. An elastomeric material is a material, such as a polymer, having the property of viscoelasticity (colloquially, “elasticity”). An example of an elastomeric material is rubber. Elastomeric materials generally have a low Young&#39;s modulus and a high yield strain when compared to other materials. Elastomeric materials are typically thermosets having long polymer chains that cross-link during curing (i.e., vulcanizing). Elastomeric materials may absorb energy during compression but may also be prone failure during tension and torsion. 
     In the example of  FIGS. 3A-3C , inner housing  230  is a metallic hollow cylinder having variable radii that resides inside elastomeric bearing  220  and forms a third opening therethrough. Other bearing components, such as conical members  240 , bearing surfaces  250 , and seals  260 , may reside inside the third opening. Inner housing  230  features two inner surfaces that define the third opening: an inner surface  230   a  and an inner surface  230   b . Inner surface  230   a  is oriented at a reflex angle α relative to inner surface  230   b  such that the interior diameter of the third opening (d 1 ) is smaller than the exterior diameter of the third opening (d 2 ). 
     In the example of  FIGS. 3A-3C , conical members  240  are metallic hollow cylinders having variable radii that reside inside inner housing  230  and forms opening  270 . In one example embodiment, bearing  200  features two conical members  240 : conical member  240   a  and conical member  240   b . Conical member  240   a  resides inside the third opening adjacent inner surface  230   a , and conical member  240   b  resides inside the third opening adjacent inner surface  230   b . In the example of  FIGS. 3A-3C , conical members  240   a  and  240   b  have outer conical surfaces oriented at angles corresponding to the positions of inner surfaces  230   a  and  230   b , respectively. As such, the outer surface of conical member  240   a  matches the inner surface  230   a  of inner housing  230 , and the outer surface of conical member  240   b  matches the inner surface  230   b  of inner housing  230 . 
     In the example of  FIGS. 3A-3C , inner housing  230  and conical members  240  are also symmetric. For example, the outer surfaces of conical members  240   a  and  240   b  incline at approximately the same angle. In addition, an imaginary plane that bisects inner housing  230  also bisects the reflex angle α relative to inner surface  230   b . Conical members  240   a  and  240   b  may also contact or be equidistant from the imaginary plane. In some embodiments, inner surfaces  230   a  and  230   b  intersect to form a closed curve, and the closed curve lies on the imaginary plane. 
     Conical member  240   a  forms a fourth opening therethrough, and conical member  240   b  forms a fifth opening therethrough. The fourth and fifth openings, in combination, represent opening  270 . In the example of  FIGS. 3A-3C , first, second, and third openings have a variable diameter, whereas the fourth and fifth openings have a relatively constant diameter. The first, second, third, fourth, and fifth openings described are coaxial because a single axis may cross through each of these openings (e.g., through opening  270 ). 
     Bearing surfaces  250  separate inner housing  230  from conical members  240 . In one example embodiment, bearing  200  features two bearing surfaces  250 : bearing surface  250   a  and bearing surface  250   b . Bearing surface  250   a  is in contact with inner bearing surface  230   a  and conical member  240   a , and bearing surface  250   b  is in contact with inner bearing surface  230   b  and conical member  240   b . Bearing surfaces  250  may be coupled to inner housing  230  and/or conical members  240 . 
     Bearing surfaces  250  may be comprised of any suitable material. In one example embodiment, bearing surfaces  250  are comprised of a polytetrafluoroethylene (PTFE), a synthetic fluoropolymer of tetrafluoroethylene. The most well known brand name of PTFE is Teflon by DuPont Co. PTFE is a fluorocarbon solid, as it is a high-molecular-weight compound consisting wholly of carbon and fluorine. In another example embodiment, bearing surfaces  250  may be represented by a lubricant (e.g., grease) applied to conical members  240 . 
     In the example of  FIGS. 3A-3C , seals  260  are rings located adjacent inner housing member  230  and conical members  240 . In one example embodiment, bearing  200  features two seals  260 : seal  260   a  and  260   b . Seal  260   a  is located adjacent inner housing member  230  and conical member  240   a , and seal  260   b  is located adjacent inner housing member  230  and conical member  240   b . Seals  260  may cover the joints between inner housing member  230  and conical members  240  where bearing surfaces  250  are located. Teachings of certain embodiments recognize that seals  260  may help prevent foreign objects from damaging bearing surfaces  250 . In addition, teachings of certain embodiments recognize that seals  260  may help retain conical members  240  in place when bearing  200  is installed in a device and is subjected to various forces. Seals  260  are described in greater detail with regard to  FIGS. 5A and 5B . 
     Bearing  200  may be assembled in any suitable manner. In one example embodiment, elastomeric material  220  is inserted into outer housing  210 , and inner housing  230  is inserted into elastomeric material  220 . In some embodiments, elastomeric material  220  and inner housing  230  may be inserted in a single step, such as by curing elastomeric material  220  between outer housing  210  and inner housing  230 . Conical members  240   a  and  240   b  may be inserted into the third opening of inner housing member  230 , and seals  260  may be inserted around conical members  240  to retain seals  260  in place. In one example embodiment, seals  260  are inserted in a lip of inner housing  230  and allowed to slip against conical members  240   a  and  240   b.    
     Bearing  200  may operate as a hybrid elastomeric bearing and thrust bearing. For example, elastomeric material  220  may represent the “elastomeric bearing” portion of the hybrid bearing, and conical elements  240  and bearing surfaces  250  may represent the “thrust bearing” portion of the hybrid bearing. Teachings of certain embodiments recognize that a hybrid elastomeric bearing and thrust bearing such as bearing  200  may protect against a variety of forces, such as torsional, radial, axial, and cocking forces. The torsional, radial, axial, and cocking forces are illustrated in  FIGS. 4A and 4B . 
     In some embodiments, the elastomeric bearing portion of bearing  200  may carry the forces due to cocking motions. In addition, conical members  240   a  and  240   b  may allow the elastomeric bearing portion of bearing  200  to center itself while taking cocking loads. The thrust bearing portion of bearing  200 , on the other hand, may carry axial loads in two directions. In addition, conical members  240  are free to rotate relative to inner housing member  230 . Teachings of certain embodiments recognize that allowing conical members  240  to rotate relative to housing member  230  may relieve elastomeric material  220  of torsional loading and prevent the need of anti-rotation features on the mating assemblies. 
     As explained above, bearing  200  may be installed at either end of pitch link  118 . Thus, bearing  200  may be coupled either between pitch link  118  and swashplate  116  or between pitch link  118  and hub  114 . 
       FIG. 5A  shows bearing  200  coupled between pitch link  118  and a pitch horn  114 ′ associated with hub  114 . As seen in  FIG. 5A , bearing  200  fits within a recess in pitch horn  114 ′. Seals  260  abut walls of the recess, which may keep seals  260  in place. Seals  260  may retain conical members  240  in place. In some embodiments, bushings may be provided in the recess in pitch horn  114 ′ to apply pre-tensional force against conical members  240  and prevent conical members  240  from rotating. Conical members  240  may also receive force from inner housing  230  and transmit and transmit some of this force against the walls of the recess in pitch horn  114 ′. 
       FIG. 5B  shows a closer view of a cross-section of the interaction between conical members  240 , seal  260   a , and the pitch horn  114 ′ of  FIG. 5A . As seen in  FIG. 5B , pitch horn  114 ′ holds seal  260   a  in place against conical member  240   a . In this example, conical member  240   a  does not directly contact pitch horn  114 ′. Rather, conical member  240   a  and pitch horn  114 ′ are separated by opening  270 , and conical member  240   a  is free to rotate relative to pitch horn  114 ′. In some embodiments, seal  230   a  may move relative to pitch horn  114 ′, inner housing  230 , and/or conical member  240   a.    
     In one alternative embodiment, inner member  230  features a lip that holds seal  260  in place, which in turn retains conical members  240  in place. In this example embodiment, conical members  240  do not rotate with respect to pitch horn  114 ′. Inner member  230  is free to rotate torsionally (about the axis of opening  270 ) about bearing surfaces  250 . This example embodiment may also feature bushings in the recess in pitch horn  114 ′ to apply pre-tensional force against conical members  240 . 
     Modifications, additions, or omissions may be made to the systems and apparatuses described herein without departing from the scope of the invention. The components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses may be performed by more, fewer, or other components. The methods may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. 
     Although several embodiments have been illustrated and described in detail, it will be recognized that substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the appended claims. 
     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.