# Patent

## Title
Dual series pitch link bearing

## Abstract

According to one embodiment, a bearing is situated between a pitch link and a swashplate or a hub. The bearing comprises an outer housing having a first opening therethrough, an intermediate housing adjacent the housing inside the first opening and having a second opening therethrough, and an inner housing adjacent the intermediate housing inside the second opening and having a third opening therethrough. The inner housing comprising a first inner surface and a second inner surface defining the third opening. A first member is adjacent the first inner surface inside the third opening having a fourth opening therethrough. A second member is adjacent the second inner surface inside the third opening having a fifth opening therethrough coaxial with the fourth opening.

## Background
RELATED APPLICATIONS
Pursuant to 35 U.S.C. §119 (e), this application claims priority to U.S. Provisional Patent Application Ser. No. 61/971,771, entitled Dual Series Pitch Link Bearing, filed Mar. 28, 2014. U.S. Provisional Patent Application Ser. No. 61/971,771 is hereby incorporated by reference.
Pursuant to 35 U.S.C. §120, this application is a continuation-in-part of and claims priority to U.S. patent application Ser. No. 13/532,910, entitled 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 dual series pitch link 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'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, and cocking forces. A technical advantage of one embodiment may include the capability to provide a bearing with a lower replacement cost. A technical advantage of one embodiment may also include the capability to allow continued operation through a bearing failure by providing dual bearing surfaces that operate in series.
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 112a and a drive shaft 112b. Power source 112a, drive shaft 112b, 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 112b receives torque or rotational energy from power source 112a and rotates hub 114. Rotation of rotor hub 114 causes blades 120 to rotate about drive shaft 112b. 
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 116a and a rotating swashplate ring 116b. Non-rotating swashplate ring 116a does not rotate with drive shaft 112b, whereas rotating swashplate ring 116b does rotate with drive shaft 112b. In the example of FIG. 2, pitch links 118 connect rotating swashplate ring 116b to blades 120.
In operation, according to one example embodiment, translating the non-rotating swashplate ring 116a along the axis of drive shaft 112b 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 116a causes the rotating swashplate 116b 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 116b to blades 120. Pitch links 118 may be subject to various forces at its connection points with swashplate ring 116b 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, a removable housing 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, removable housing 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 removable housing 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.
Removable housing 220 resides inside outer housing 210 and forms a second opening therethrough. Removable housing 220 features an inner surface 220a that defines the second opening. Other bearing components, such as inner housing 230, conical members 240, bearing surfaces 250, and seals 260, may reside inside the second opening. In one example embodiment, removable housing 220 is a metallic hollow cylinder having variable radii. For example, removable housing 220 may have a curved inner surface 220a that defines a partially-spherical second opening. In some embodiments, removable housing 220 may feature a locking portion 222. This locking portion 222 may allow removable housing 220 to be removed (along with the components within the second opening) and replaced by another assembly. Teachings of certain embodiments recognize that locking portion 222 may reduce operation costs by reducing the cost of replacement bearings and reducing the time necessary to install replacement bearings.
In the example of FIGS. 3A-3C, inner housing 230 is a metallic hollow cylinder having variable radii that resides inside removable housing 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 230a and an inner surface 230b. Inner surface 230a is oriented at a reflex angle α relative to inner surface 230b such that the interior diameter of the third opening (d1) is smaller than the exterior diameter of the third opening (d2).
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 240a and conical member 240b. Conical member 240a resides inside the third opening adjacent inner surface 230a, and conical member 240b resides inside the third opening adjacent inner surface 230b. In the example of FIGS. 3A-3C, conical members 240a and 240b have outer conical surfaces oriented at angles corresponding to the positions of inner surfaces 230a and 230b, respectively. As such, the outer surface of conical member 240a matches the inner surface 230a of inner housing 230, and the outer surface of conical member 240b matches the inner surface 230b 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 240a and 240b 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 230b. Conical members 240a and 240b may also contact or be equidistant from the imaginary plane. In some embodiments, inner surfaces 230a and 230b intersect to form a closed curve, and the closed curve lies on the imaginary plane.
Conical member 240a forms a fourth opening therethrough, and conical member 240b 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 may be described as coaxial because a single axis may cross through each of these openings (e.g., through opening 270). Teachings of certain embodiments recognize that providing coaxial openings may allow members such as removable housing 220 and inner housing 230 to move, slide, and/or rotate about potentially coincident points and/or axes. In the example of FIG. 3B, the intersection between the single axis and the boundary between conical members 240a and 240b may be coincident with a point about which all axial, radial, cocking, and/or torsional movement occurs.
Bearing surfaces 250 separate removable housing 220 from inner housing 230 and inner housing 230 from conical members 240. In one example embodiment, bearing 200 features three bearing surfaces 250: bearing surface 250a, bearing surface 250b, and bearing surface 250c. Bearing surface 250a is in contact with removable bearing surface 220a and inner bearing housing 230, bearing surface 250b is in contact with inner bearing surface 230a and conical member 240a, and bearing surface 250c is in contact with inner bearing surface 230b and conical member 240b. Bearing surfaces 250 may be coupled to removable housing 220, 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 removable housing 220, inner housing 230, and/or 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 260a and 260b. Seal 260a is located adjacent inner housing member 230 and conical member 240a, and seal 260b is located adjacent inner housing member 230 and conical member 240b. 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, removable housing 220 is inserted into outer housing 210, and inner housing 230 is inserted into removable housing 220. In some embodiments, removable housing 220 and inner housing 230 may be inserted in a single step, such as by curing removable housing 220 between outer housing 210 and inner housing 230. Conical members 240a and 240b 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 240a and 240b. 
Teachings of certain embodiments recognize that bearing 200 may accommodate a variety of forces, such as some or all of the torsional, radial, axial, and cocking forces illustrated in FIGS. 4A and 4B.
For example, in some embodiments, bearing 200 may operate as a dual series bearing. For example, bearing surfaces 250b and 250c may facilitate movement between inner bearing surfaces 230a/230b and conical members 240a/240b in response to rotational movement. If one or both of bearing surfaces 250b and 250c fail, however, bearing surface 250a may allow bearing 200 to continue to operate by facilitating movement between removable bearing surface 220a and inner bearing housing 230 in response to rotational movement. In this manner, bearing surface 250a may operate in series with bearing surfaces 250b and 250c. Although the primary purpose of bearing surface 250a may be to facilitate movement in response to cocking loads, the ability of bearing surface 250a to accommodate rotational movement may provide redundancy to bearing 200.
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 260a, and the pitch horn 114′ of FIG. 5A. As seen in FIG. 5B, pitch horn 114′ holds seal 260a in place against conical member 240a. In this example, conical member 240a does not directly contact pitch horn 114′. Rather, conical member 240a and pitch horn 114′ are separated by opening 270, and conical member 240a is free to rotate relative to pitch horn 114′. In some embodiments, seal 230a may move relative to pitch horn 114′, inner housing 230, and/or conical member 240a. 
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.

## Claims

1. A rotorcraft, comprising:
a body;
a power train coupled to the body and comprising a power source and a drive shaft coupled to the power source;
a hub coupled to the drive shaft;
a rotor blade coupled to the hub;
a swashplate positioned about the drive shaft;
a pitch link coupled between the swashplate and the hub corresponding to the rotor blade;
a bearing coupled between either the pitch link and the swashplate or the pitch link and the hub, the bearing comprising:
an outer housing having a first opening therethrough;
an intermediate housing adjacent the outer housing inside the first opening and having a second opening therethrough;
an inner housing adjacent the intermediate housing inside the second opening and having a third opening therethrough, the inner housing comprising a first inner surface and a second inner surface defining the third opening, the second inner surface oriented at a reflex angle relative to the first inner surface such that an interior diameter of the third opening is smaller than an exterior diameter of the third opening;
a first bearing surface in contact with the intermediate housing and the inner housing and separating the intermediate housing from the inner housing;
a first member adjacent the first inner surface inside the third opening having a fourth opening therethrough;
a second bearing surface in contact with the first inner surface and the first member and separating the first inner surface from the first member;
a second member adjacent the second inner surface inside the third opening having a fifth opening therethrough coaxial with the fourth opening; and
a third bearing surface in contact with the second inner surface and the second member and separating the second inner surface from the second member.

2. The rotorcraft of claim 1, further comprising a second bearing coupled to the pitch link opposite the first bearing, the second bearing comprising:
an outer housing having a first opening therethrough;
an intermediate housing adjacent the housing inside the first opening and having a second opening therethrough;
an inner housing adjacent the intermediate housing inside the second opening and having a third opening therethrough, the inner housing comprising a first inner surface and a second inner surface defining the third opening, the second inner surface oriented at a reflex angle relative to the first inner surface such that an interior diameter of the third opening is smaller than an exterior diameter of the third opening;
a first bearing surface in contact with the intermediate housing and the inner housing and separating the intermediate housing from the inner housing;
a first member adjacent the first inner surface inside the third opening having a fourth opening therethrough;
a second bearing surface in contact with the first inner surface and the first member and separating the first inner surface from the first member;
a second member adjacent the second inner surface inside the third opening having a fifth opening therethrough coaxial with the fourth opening; and
a third bearing surface in contact with the second inner surface and the second member and separating the second inner surface from the second member.

3. The rotorcraft of claim 1, wherein the bearing threads into the pitch link.

4. The rotorcraft of claim 1, wherein the first bearing surface is comprised of polytetrafluoroethylene.

5. The rotorcraft of claim 1, wherein the first bearing surface facilitates movement between the intermediate housing and the inner housing in response to rotational and cocking loads.

6. The rotorcraft of claim 5, wherein the second bearing surface facilitates movement between the first inner surface and the first member in response to rotational loads.

7. The rotorcraft of claim 1, wherein the intermediate housing comprising a locking portion configured to facilitate removal and replacement of the intermediate housing.

8. The rotorcraft of claim 1, wherein the first member comprises an outer conical surface oriented at an angle corresponding to the orientation of the first inner surface.

9. The rotorcraft of claim 1, wherein the first opening, the second opening, the third opening, the fourth opening, and the fifth opening are coaxial.

10. A method for manufacturing a bearing, comprising:
providing an outer housing having a first opening therethrough;
inserting an intermediate housing adjacent the outer housing inside the first opening, the intermediate housing having a second opening therethrough;
inserting an inner housing adjacent the intermediate housing inside the second opening, the inner housing having a third opening therethrough, the inner housing comprising a first inner surface and a second inner surface defining the third opening, the second inner surface oriented at a reflex angle relative to the first inner surface such that an interior diameter of the third opening is smaller than an exterior diameter of the third opening, wherein a first bearing surface is in contact with the intermediate housing and the inner housing and separates the intermediate housing from the inner housing;
inserting a first member adjacent the first inner surface inside the third opening, the first member having a fourth opening therethrough, wherein a second bearing surface is in contact with the first inner surface and the first member and separates the first inner surface from the first member; and
inserting a second member adjacent the second inner surface inside the third opening, the second member having a fifth opening therethrough coaxial with the fourth opening, wherein a third bearing surface is in contact with the second inner surface and the second member and separates the second inner surface from the second member.

11. The method of claim 10, wherein the first bearing surface is a fluorocarbon bearing.

12. The method of claim 10, wherein the first bearing surface facilitates movement between the intermediate housing and the inner housing in response to rotational and cocking loads.

13. The method of claim 12, wherein the second bearing surface facilitates movement between the first inner surface and the first member in response to rotational loads.

14. The method of claim 10, wherein the intermediate housing comprising a locking portion configured to facilitate removal and replacement of the intermediate housing.

15. The method of claim 10, wherein the second member is inserted such that the first member and the second member are in contact.

16. A bearing, comprising:
an outer housing having a first opening therethrough;
an intermediate housing adjacent the outer housing inside the first opening and having a second opening therethrough;
an inner housing adjacent the intermediate housing inside the second opening and having a third opening therethrough, the inner housing comprising a first inner surface and a second inner surface defining the third opening, the second inner surface oriented at a reflex angle relative to the first inner surface such that an interior diameter of the third opening is smaller than an exterior diameter of the third opening;
a first bearing surface in contact with the intermediate housing and the inner housing and separating the intermediate housing from the inner housing;
a first member adjacent the first inner surface inside the third opening having a fourth opening therethrough;
a second bearing surface in contact with the first inner surface and the first member and separating the first inner surface from the first member;
a second member adjacent the second inner surface inside the third opening having a fifth opening therethrough coaxial with the fourth opening; and
a third bearing surface in contact with the second inner surface and the second member and separating the second inner surface from the second member.

17. The bearing of claim 16, wherein the first bearing surface is comprised of polytetrafluoroethylene.

18. The rotorcraft of claim 16, wherein the first bearing surface facilitates movement between the intermediate housing and the inner housing in response to rotational and cocking loads.

19. The rotorcraft of claim 18, wherein the second bearing surface facilitates movement between the first inner surface and the first member in response to rotational loads.

20. The rotorcraft of claim 16, wherein the intermediate housing comprising a locking portion configured to facilitate removal and replacement of the intermediate housing.