Abstract:
A self-aligning bearing assembly is disclosed which is capable of reacting both radial and axial loads. An inner bearing race is connected to a rotatable shaft that is subjected to such loads. An outer bearing race is installed within a housing and is capable of movement in multiple directions with respect to the housing. The outer bearing race can rotate in planes corresponding to longitudinal sections of the outer race, i.e., rotational displacement. In addition, the outer bearing race can translate with respect to an inner wall of the housing in an axial direction of the housing, i.e., axial displacement. Such movement is enabled by the use of radially displaceable thrust rings which contact the outer bearing race, and control of the geometry of the outer bearing race and inner wall of the housing.

Description:
FIELD OF THE INVENTION 
     The present invention relates to bearing assemblies, and more particularly relates to bearing assemblies that are capable of reacting radial and axial loads in various applications such as in the rotating flight shafts that support the rotodomes of surveillance aircrafts. 
     BACKGROUND INFORMATION 
     Bearing assemblies are often used in applications where a rotating shaft is subjected to radial and axial loads. For example, the gearbox and rotating flight shaft of radar-equipped aircraft such as the rotodome of early warning command and control aircraft are subjected to substantial radial loads on the rotodome flight shaft due to air loads acting on the rotodome during flight. In addition, the flight shaft is subjected to substantial axial loads due to the weight of the rotodome and the aerodynamic forces applied during flight on the disk-shaped rotodome. In conventional rotodome gearbox and flight shaft designs, a highly complex bearing system is used, including upper and lower bearing assemblies offset along the length of the shaft from a lower “X” bearing assembly in the rotodome gearbox that is required in order to react the substantial axial loads on the shaft. This arrangement has several drawbacks including substantial wear of the upper and lower pylon bearing assemblies when the flight shaft bends, which causes unwanted walking, rotation at the inner and outer diameters of the bearings that, in turn, causes scoring of the structural support assembly. Other disadvantages of the conventional design include uneven loading of the “X” bearing that results in brinelling of the bearing races and reduced life. The current arrangement also requires time consuming maintenance procedures due to the fact that the flight shaft and gearbox are secured with common fasteners requiring removal of the flight shaft load from the gearbox as a prerequisite for removal and replacement of the gearbox. 
     The present invention has been developed in view of the foregoing, and to address other deficiencies of prior bearing assembly designs. 
     SUMMARY OF THE INVENTION 
     The present invention provides a self-aligning bearing assembly which is capable of reacting both radial and axial loads, as well as moment loads. An inner bearing race is connected to a rotatable shaft that is subjected to such loads. An outer bearing race is installed within a housing and is capable of movement in multiple directions with respect to the housing. The outer bearing race can rotate in planes corresponding to longitudinal sections of the outer race, i.e., “rotational displacement”. In addition, the outer bearing race can translate within limits with respect to an inner wall of the housing in an axial direction of the housing, i.e., “axial displacement”. Such movement is achieved by controlling the geometry of the outer bearing race and inner wall of the housing, and by the use of radially displaceable thrust rings which contact the outer bearing race. 
     An aspect of the present invention is to provide a bearing assembly comprising a bearing housing, an outer bearing race and inner bearing race. The inner bearing race can be singular or made up of multiple segments. A portion of a radial outer surface of the outer bearing race contacts an inner wall of the bearing housing. When a radial or bending load is applied to a rotatable shaft connected to the inner race, the axial centerlines of the inner and outer races are displaced with respect to the axial centerline of the bearing housing, causing both rotational displacement and axial displacement of the outer bearing race with respect to the inner wall of the bearing housing. 
     Another aspect of the present invention is to provide a rotatable shaft and bearing assembly comprising a bearing housing, an outer bearing race disposed in the bearing housing, an inner bearing race disposed radially inside the outer bearing race, and a rotatable shaft connected to the inner bearing race, wherein a radial load applied to the rotatable shaft causes axial displacement of the outer bearing race with respect to the bearing housing. 
     These and other aspects of the present invention will be more apparent from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal sectional view of a rotodome flight shaft and a self-aligning bearing assembly in accordance with an embodiment of the present invention. 
         FIG. 2  is a longitudinal sectional view of the lower portion of the rotodome flight shaft and the self-aligning bearing assembly shown in  FIG. 1 . 
         FIG. 3  is an isometric view of a self-aligning bearing assembly in accordance with an embodiment of the present invention. 
         FIG. 4  is a longitudinal sectional view of the self-aligning bearing assembly of  FIG. 3 . 
         FIGS. 5   a - 5   c  are isometric longitudinal sectional views showing a portion of a self-aligning bearing assembly in accordance with an embodiment of the present invention.  FIG. 5   a  illustrates the positions of inner and outer bearing races, and upper and lower thrust rings, within the bearing assembly when a rotating shaft connected to the inner race is aligned with the axial centerline of the bearing assembly housing.  FIGS. 5   b  and  5   c  illustrate rotational displacement and axial displacement of the bearing races, as well as radial displacements of the thrust rings, when the axis of the rotating shaft is misaligned with respect to the axial centerline of the bearing assembly. 
         FIG. 6  is a longitudinal sectional view of a portion of a self-aligning bearing assembly showing an anti-rotation pin and a lubricant port extending through the housing of the bearing assembly in accordance with an embodiment of the present invention. 
         FIG. 7  is a longitudinal sectional view of a self-aligning bearing assembly having an extended inner race with a scalloped lower surface in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a longitudinal sectional view of a rotatable shaft  5  connected to a self-aligning bearing assembly  10  in accordance with an embodiment of the present invention. In the embodiment shown in  FIG. 1 , the rotatable shaft  5  is the rotodome flight shaft of an early warning command and control aircraft. Although a rotodome flight shaft is primarily described herein, it is to be understood that other types of rotatable shafts may be used in association with the self-aligning bearing assembly of the present invention. For example, the rotatable shaft could be part of a jet engine drive shaft, electrical generator drive shaft or the like. 
     As illustrated in  FIG. 1 , the rotatable shaft  5  rotates about its longitudinal axis as shown by the arrow R. The rotatable shaft  5  is subjected to a radial load L R  and an axial load L A . Such loads may be generated in various ways. For example, when the rotatable shaft  5  is part of an aircraft rotodome support structure, the radial load L R  may be generated during takeoff, flight and landing of the aircraft due to acceleration, air resistance and deceleration of the aircraft. In this case, the direction of the radial load L R  on the rotatable shaft  5  generally corresponds to either the fore or aft direction of the aircraft. When the rotatable shaft  5  is part of a rotodome support structure, the axial load L A  may be generated from downward forces developed during flight of the aircraft as a result of the slight forward slope of the disk-shaped rotodome. In addition, at least part of the axial load L A  may be generated by the weight of the rotodome. The rotodome weight imposes a significant load factor, particularly during landing and take off as might be the case on catapult and arrestment during carrier operations. 
     In certain embodiments, it may be desirable to include additional bearing assemblies for the rotatable shaft  5 . For example, when the shaft  5  is a rotodome flight shaft, an upper bearing assembly  110  may be connected to the shaft  5 , as shown in  FIG. 1 . 
     As shown in  FIG. 2 , the lower portion of the rotatable shaft  5  is connected directly or indirectly to an inner race  12  of the self-aligning bearing assembly  10 . The bearing assembly  10  also includes an outer race  20 . The bottom end of the rotatable shaft  5  may have holes  7  for connection to a drive assembly (not shown). Although holes  7  are shown in  FIG. 2 , any other suitable means for connection of the rotatable shaft  5  to a drive assembly may be used. The connection between the rotatable shaft  5  and inner race  12  may be of any suitable design, such as vertically oriented fasteners that pass through vertically oriented clearance holes integral to the inner race and engage threaded holes integral to the flight shaft, mechanical fasteners radially disposed to attach a separate collar that traps the bearing inner race between the collar and the lower shoulder of the flight shaft, and the like. 
     As shown in  FIG. 3 , the self-aligning bearing assembly  10  includes a bearing housing  30  within which the inner race  12  is located. As more fully described below, an upper retaining ring  50  and locking tabs  54  secure the various components of the bearing assembly within the housing  30 . As also more fully described below, a pin  60  extends through the bearing housing  30  for securing the outer race  20  against rotation. Holes  34  may be provided through the bottom portion of the bearing housing  30  in order to facilitate attachment of the bearing housing to any suitable type of support structure. The connection between the housing  30  of the bearing assembly and the support structure may be of any suitable design, such as holes  34  integral to a flange located on the upper portion of the housing  30 , or holes integral to flanges on both upper and lower positions of the bearing housing, which may facilitate access to the mechanical connections. 
       FIG. 4  is a longitudinal sectional view of the self-aligning bearing assembly  10  including the inner race  12 , outer race  20 , upper thrust ring  40 , lower thrust ring  42  and upper retaining ring  50 . The inner race  12  includes a roller bearing channel  14 , and upper and lower ball bearing channels  15  and  16 , respectively. The outer race  20  has an outer spherical curved surface  21 , an upper spherical curved surface  22  and a lower spherical curved surface  23 . As shown in  FIG. 4 , these curved surfaces can be defined by longitudinal sections taken through the outer bearing race  20 . The outer race  20  includes a roller bearing channel  24 , and upper and lower ball bearing channels  25  and  26 , respectively. Although not shown in  FIG. 4 , any suitable number and size of roller bearings may be provided in opposing channels  14  and  24 , and any suitable number and size of ball bearings may be provided in opposing channels  15  and  25 , and opposing channels  16  and  26 . Although three bearing channels are shown in  FIG. 4 , any other desirable number and type of ball bearing and/or roller bearing channels may be used. The rollers and ball bearings used are well known and any configuration may be used, such as angular contact ball bearings, x-type ball bearings and crowned or tapered rollers. 
     As shown in  FIG. 4 , the bearing housing  30  includes an inner wall  32  having a cylindrical shape against which a portion of the outer curved surface  21  of the outer race  20  is contacted. A lower retaining rim  36  extends radially inward near the bottom of the housing  30 . An upper retaining ring  50  helps retain the outer race  20  and other components of the bearing assembly within the housing  30 . The upper retaining ring  50  is secured to the housing  30  by locking tabs  54 . 
     As illustrated in  FIG. 4 , an upper thrust ring  40  is positioned against the upper curved surface  22  of the outer race  20  and against a thrust surface  52  of the upper retaining ring  50 . A lower thrust ring  42  is positioned against the lower curved surface  23  of the outer race  20  and against a thrust surface of the lower retaining rim  36 . As more fully described below, the upper and lower thrust rings  40  and  42  move radially in opposite directions within the bearing housing  30  when the rotating shaft  5  connected to the inner race  12  is dislocated due to radial or bending loads L R  applied thereto. As illustrated in  FIG. 4 , in a preferred embodiment of the present invention, the bearing assembly is provided with sliding clearances between components, as more fully described below. 
     As shown in  FIG. 4 , the outer spherical curved surface  21  of the outer race  20 , defined by a longitudinal section taken through the outer race, has a radius of curvature R O  that has its center on the axial centerline of the bearing. This central axis coincides with the center axis of the rotating shaft  5 . The radius of curvature R O  is in close proximity to the inner cylindrical surface  32  of the housing  30  while allowing rotational clearance between the center sphere and the cylindrical surface  32 . The upper curved surface  22  of the outer race  20  has a spherical radius of curvature R U , while the lower curved surface  23  of the outer race  20  has a spherical radius of curvature of R L . In accordance with an embodiment of the present invention, the radius of curvature R O  of the outer surface  21  is less than the radius of curvature R U  of the upper curved surface  22  and the radius of curvature R L  of the lower curved surface  23 . The upper and lower radii of curvature R U ,R L  are typically 1.05 to 3.5 times greater than the outer radius of curvature R O , i.e., R U ,R L :R O  is from about 1.05:1 to about 3.5:1. The upper surface  22  of the outer race  20  defines a spherical surface with its center on the axis of rotation of the bearing. However, the center of the sphere defined by the spherical radius R U  of the upper surface  22  is vertically disposed below the spherical radius R O  of the outer surface  21 . Similarly, the lower surface  23  of the outer race  20  defines a spherical surface with its center on the axis of rotation of the bearing. However, the center of the sphere defined by the spherical radius R L  of the lower surface  23  is vertically disposed above the spherical radius R O  of the outer surface  21 . 
     In one embodiment, the radius of curvature R U  of the upper curved surface  22  is the same as the radius of curvature R L  of the lower curved surface  23  of the outer race  20 . While this feature is not a necessity, provisions would have to be made in the configuration of the bearing assembly if the the radius of curvature R U  of the upper curved surface  22  is not the same as the radius of curvature R L  of the lower curved surface  23 . 
     The magnitude of the vertical displacements of the upper and lower spherical surfaces  22  and  23  may be influenced by the magnitude of the axial load to be reacted by the bearing. The smaller the vertical disposition between each of the upper and lower spheres (having radii R U  and R L , respectively) to the center sphere (having radius R O ), the smaller the projected area available to react axial loads. Conversely, the greater the vertical disposition between the upper and lower sphere to the center sphere, the greater the projected area available to react axial loads. 
     As shown in  FIG. 4 , the upper thrust ring  40  has an outer race contact surface  40   a  which contacts the upper curved surface  22  of the outer race  20 . The outer race contact surface  40   a  of the upper thrust ring  40  may have a shape which substantially matches the curvature of the upper curved surface  22  of the outer race  20 . However, it may be preferred to provide a substantially straight conical shape for the outer race contact surface  40   a  in order to reduce and simplify fabrication of the upper thrust ring  40 . In this case, only a limited portion of the outer race contact surface  40   a  may touch the upper curved surface  22  of the outer race  20 . The upper thrust ring  40  also has an upper retaining ring contact surface  40   b  which contacts the thrust surface  52  of the upper retaining ring  50 . The upper retaining ring contact surface  40   b  may be substantially flat in order to conform with the substantially flat thrust surface  52 . 
     The lower thrust ring  42  preferably has a shape and size that mirrors the upper thrust ring  40 . Thus, the lower thrust ring  42  has an outer race contact surface  42   a  which contacts the lower curved surface  23  of the outer race  20 . The lower thrust ring  42  also has a lower retaining rim contact surface  42   b  which contacts and slides radially against the thrust surface of the lower retaining rim  36 . 
     The various components of the bearing assembly  10  may be made of any suitable materials. For example, the housing  30  may be made of steel, bronze, titanium or aluminum, while the inner and outer bearing races  12  and  20  may be made of steel, bronze, titanium or aluminum. The upper and lower thrust rings  40  and  42  may be made of any suitable material such as steel or the like. In one embodiment, the outer race contact surfaces  40   a  and  42   a  and/or the retaining ring or rim contact surfaces  40   b  and  42   b  of the thrust rings  40  and  42  may be coated with a lubricant and/or friction reducing material, such as polytetrafluoroethylene or the like. 
       FIG. 5   a  illustrates the positions of the inner and outer bearing races  12  and  20 , and the positions of the upper and lower thrust rings  40  and  42 , within the bearing housing  30  when the rotating shaft (not shown) connected to the inner race  12  is aligned with the axial centerline of the bearing housing  30 . In  FIG. 5   a , the inner and outer races  12  and  20  are positioned within the bearing housing  30  such that all of their axial centerlines are aligned. 
       FIGS. 5   b  and  5   c  illustrate rotational displacements and axial displacements of the bearing races  12  and  20 , as well as radial displacements of the thrust rings  40  and  42 , when the axis of the rotating shaft connected to the inner race  12  is misaligned with respect to the axial centerline of the bearing housing  30  and a downward axial load L A  is applied on the shaft. In  FIGS. 5   b  and  5   c , the axial centerlines of the inner and outer races  12  and  20  are misaligned with respect to the axial centerline of the bearing housing  30  due to radial or bending movement in the direction L R  of the rotating shaft to which the inner race  12  is attached. In  FIG. 5   b , the upper portion of the rotating shaft (not shown) is radially displaced in a leftward or counterclockwise direction shown by the arrow L R , while in  FIG. 5   c  the upper portion of the rotating shaft (not shown) is radially displaced in a rightward or clockwise direction shown by the arrow L R . 
     In  FIG. 5   b , under load conditions where the axial load L A  on the shaft is in a downward direction and the shaft is displaced in a counterclockwise direction L R , the outer race  20  undergoes counterclockwise rotational displacement D R  in relation to the straight cylindrical inner wall surface  32  of the bearing housing  30 . In addition, due to the downward axial force L A  on the shaft, the outer race  20  undergoes an upward axial displacement D A  with respect to the straight cylindrical inner wall surface  32  of the bearing housing  30 . The upward axial displacement D A  is caused by a downward vertical displacement of the center of the sphere defined by the lower spherical surface  23  of the outer race  20 , which has the radius R L  shown in  FIG. 4 . Axial loads push the lower surface  23  of the outer race  20  against the outer race contact surface  42   a  of the lower thrust ring  42 . When the center of the sphere defined by radius R L  tries to move in a downward direction, the center of the sphere defined by the radius R O  of the outer race surface  21  (shown in  FIG. 4 ) will be lifted up since the thrust ring  42  is in immediate contact with respect to the lower surface  23 . It follows that when the shaft bends, e.g., due to aerodynamic loading, and the axis of rotation of the shaft misaligned with respect to the housing  30 , the center of the sphere defined by the radius R L  of the lower surface  23  of the outer race  20  will move radially from its undeflected position. Since the thrust ring  42  is always in immediate contact with respect to the lower surface  23  it will be displaced radially in the same direction as the the center of the sphere defined by the radius R L  by virtue of the fact that surface  23  is nested in the conical shape of surface  42 . Similarly, the center of the sphere defined by the radius R U  of the upper surface  22  of the outer race  20  will displace in equal but opposite direction to that of surface  23 . As a consequence, since the thrust ring  40  is always in immediate contact with respect to the upper surface  22 , it will be displaced radially in the same direction as the the center of the sphere defined by the radius R U  by virtue of the fact that surface  22  is nested in the conical shape of surface  40 . 
       FIG. 5   c  illustrates what happens when the rotating shaft is radially displaced in a rightward or clockwise direction shown by the arrow L R , i.e., in the opposite direction compared with  FIG. 5   b . In  FIG. 5   c , the outer race  20  undergoes clockwise rotational displacement D R  in relation to the straight cylindrical inner wall surface  32  of the bearing housing  30 . In addition, due to the downward axial force L A  on the shaft, the outer race  20  undergoes an upward axial displacement D A  with respect to the straight cylindrical inner wall surface  32  of the bearing housing  30 . The upward axial displacement D A  is caused by a downward vertical displacement of the center of the sphere defined by radius R L . Axial loads push the lower surface  23  of the outer race  20  against the outer race contact surface  42   a  of the lower thrust ring  42 . When the center of the sphere defined by radius R L  tries to move in a downward direction, the center of the sphere defined by radius R O  will be lifted up since the thrust ring  42  is in immediate contact with respect to the lower surface  23 . It follows that when the flight shaft bends due to aerodynamic loading, and the axis of rotation of the lower portion of the flight shaft misaligned with respect to the housing  30 , the center of the sphere defined by the radius R L  of the lower surface  23  of the outer race  20  will move radially from its undeflected position. Since the thrust ring  42  is always in immediate contact with respect to the lower surface  23  it will be displaced radially in the same direction as the the center of the sphere by virtue of the fact that surface  23  is nested in the conical shape of surface  42 . Similarly, the center of the sphere defined by the radius R U  of the upper surface  22  of the outer bearing  20  will displace in equal but opposite direction to that of surface  23 . As a consequence, since the thrust ring  40  is always in immediate contact with respect to the upper surface  22 , it will be displaced radially in the same direction as the the center of the sphere by virtue of the fact that surface  22  is nested in the conical shape of surface  40 . 
       FIGS. 5   b  and  5   c  illustrate the rotational and axial displacements D R  and D A  which occur when a downward axial load L A  is applied through the shaft to which the inner race  12  is connected. As shown in both  FIGS. 5   b  and  5   c , the axial displacement D A  is in an upward direction when the axial load L A  is downward. Alternatively, if the axial load L A  is in an upward direction, the axial displacement D A  would be in a downward direction. In this case, when the axial load L A  is upward, the direction of the arrows D A  would be switched to a downward direction in  FIGS. 5   b  and  5   c , while the directions of the rotational displacement arrows D R  would remain the same. 
       FIG. 6  illustrates details of the pin  60  which extends through the bearing housing  30 . The pin  60  has a generally cylindrical shape with a slightly larger diameter portion extending radially inward from the housing  30 . This portion of the pin  60  is received in a groove  61  on the outside of the outer race  20 , which prevents rotation of the outer race  20  around its central axis with respect to the housing, while allowing the displacements D R  and D A  illustrated in  FIGS. 5   b  and  5   c . Further, the pin  60  may rotate about its axis due to the rotational and axial displacements D R  and D A  of the outer race  20 . Thus, the pin  60  can slide in the groove  61  but prevents the outer race  20  from rotating around its central axis within the housing  30 . The pin  60  includes a lubricant port having a grease fitting  62 . The grease fitting  62  may be of any known design and may be used in conjunction with the application of conventional high pressure grease guns for the injection of a lubricating grease to the rotating elements of the bearing assembly. The port extending through the pin  60  allows lubricating grease to be injected into the housing  30 . A lubricant hole  64  is provided through the outer bearing race  20  in order to allow access of the lubricant to the bearing channels of the inner and outer races  12  and  20 . In a preferred embodiment, two pins  60  are located at diametrically opposed locations around the circumference of the bearing housing  30 . The particular circumferential locations of the pins  60  may be selected based on the likely radial loading direction of the rotatable shaft  5 . For example, when the shaft  5  is a rotodome flight shaft which is typically radially loaded in either the fore or aft direction of the aircarft, the pins  60  may be positioned circumferentially on the sides of the shaft, i.e., rotated 90 degrees from the fore/aft direction of the aircraft. In this manner, misalignment of the pins  60  with the lubricant hole  64  through the outer race  20  may be minimized. Further, contact surfaces  21  and  32  are maximized in the direction of highest load. 
       FIG. 7  illustrates an alternative inner bearing race configuration for a self-aligning bearing assembly in accordance with an embodiment of the present invention. In this embodiment, the inner race  112  has an extended lower portion having a scalloped edge  114 . Holes  116  are provided through the lower extended portions of the scalloped edge. The holes  116  and scalloped edge  114  configuration may be connected to a drive assembly (not shown). The embodiment shown in  FIG. 7  also includes a sleeve  31  inside the bearing housing  30  which contacts the outer race  20 . 
     Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.