Abstract:
A thrust bearing assembly comprising a rotating bearing runner and a stationary bearing carrier, the carrier defining a plurality of thrust pad sites annularly around the carrier, with a thrust pad disposed at a site and with the carrier constraining movement of the thrust pad in a direction generally radial to the longitudinal axis of the runner while allowing the thrust pad to move in a direction generally parallel to the longitudinal axis. An embodiment comprises a rotating bearing runner having a wear resistant face and a stationary bearing carrier defining cavities disposed annularly around the carrier. A deflection element (e.g., Belleville washer) is disposed in a cavity and a pad is disposed over the deflection element. The pad is at least partially disposed within the cavity. The wear resistant face contacts the pad. Another embodiment rigidly connects pads disposed on opposite sides of a stationary bearing carrier.

Description:
[0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 11/148,178, filed Jun. 9, 2005, which is herein incorporated by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to thrust bearing assemblies, and more particularly to a hydrodynamic thrust bearing assembly having thrust pads individually mounted on resilient deflection elements, such as Belleville washers. 
         [0004]    2. Background of the Invention 
         [0005]    Most conventional downhole drilling motors use rolling element-type bearings, such as ball rollers or angular contact rollers. U.S. Pat. No. 5,074,681 to Turner et al. discloses an example of ball rollers. U.S. Pat. No. 5,248,204 to Livingston et al. discloses an example of angular contact rollers. Typically, these rolling element-type bearings are lubricated by the drilling fluid (mud) or by clean oil when encased in a sealed oil chamber. Due to the high loads, pressure, and abrasive conditions, bearing life is typically only several hundred hours. 
         [0006]    Motors typically have a multiple number of bearings. The bearings can be resiliently supported on Belleville washers to equalize loading among bearings and to absorb shock. Rolling element type bearings are not tolerant of abrasives and thus wear quickly when exposed to mud lubrication. Once wear occurs, loads between the  individual balls become uneven and wear rates accelerate. Indeed, rolling element balls taken from failed units are sometimes half their original diameter. For the oil-lubricated bearings, once the seals fail, wear occurs in a similar way. 
         [0007]    Another type of bearing used in downhole drilling motors is a hydrodynamic or sliding surface type. U.S. Pat. No. 4,560,014 to Geezy discloses an example of this hydrodynamic bearing type, which uses rigidly mounted pads manufactured of industrial diamond. The diamond pads are mud-lubricated and slide against each other. These bearings, however, are extremely expensive and only marginally increase service life. 
         [0008]    Other examples of hydrodynamic bearings are disclosed in the inventor&#39;s previous U.S. Pat. Nos. 5,441,347 to Ide and 5,620,260 also to Ide, both of which are incorporated herein by reference. These pad type hydrodynamic thrust bearings include a carrier and a plurality of bearing pads circumferentially spaced about the carrier. The pads may be provided with individual support structures and supported in the carrier, or may be integrally formed with the carrier. 
       SUMMARY OF THE INVENTION 
       [0009]    An embodiment of the present invention provides a hydrodynamic thrust bearing assembly in which each thrust pad is individually mounted on a deflection element. Rather than mounting an entire bearing having fixed pads on a resilient member (e.g., spring), the present invention resiliently mounts the individual thrust pads, thereby avoiding costly finish-grinding/lapping of the complete bearing assembly. 
         [0010]    An exemplary thrust bearing assembly according to an embodiment of the present invention comprises a rotating bearing runner having a wear resistant face and a stationary bearing carrier defining a plurality of cavities disposed annularly around the carrier. A deflection element is disposed in a cavity of the plurality of cavities and a pad is disposed over the deflection element. The pad is at least partially disposed within the cavity. The wear resistant face of the rotating bearing runner contacts the pad. 
         [0011]    Another embodiment of the present invention provides a thrust bearing assembly for a downhole motor comprising a first stationary bearing carrier defining a first plurality of cavities disposed annularly around the first stationary bearing carrier, a second stationary bearing carrier defining a second plurality of cavities disposed annularly around the second stationary bearing carrier, and a rotating bearing runner disposed between the first stationary bearing carrier and the second stationary bearing carrier. The rotating bearing runner has a first wear resistant face and a second wear resistant face. Each cavity of the first plurality of cavities and the second plurality of cavities holds a deflection element and a pad disposed over the deflection element. The first wear resistant face is in contact with the pads of the first stationary bearing carrier. The second wear resistant face is in contact with the pads of the second stationary bearing carrier. 
         [0012]    Another embodiment of the present invention provides a downhole drilling apparatus that includes a progressive cavity drive train. The apparatus comprises a housing structure, a stator, a rotor, and a thrust bearing assembly. The stator has a longitudinal axis. The rotor has a true center and is located within the stator. The stator and the rotor each have coacting helical lobes that are in contact with one another at any transverse section. The stator has one more helical lobe than the rotor such that a plurality of progressive cavities is defined between the rotor and the stator. 
         [0013]    The rotor is adapted to rotate within the stator such that the true center of the rotor orbits the axis of the stator. The orbit has a predetermined radius and the orbiting motion of the rotor causes a progression of the progressive cavities in the direction of the axis of the stator. The thrust bearing assembly is coupled to the rotor and comprises a rotating bearing runner having a wear resistant face and a stationary bearing carrier defining a plurality of cavities disposed annularly around the carrier. 
         [0014]    A deflection element is disposed in a cavity of the plurality of cavities and a pad is disposed over the deflection element. The pad is at least partially disposed within the cavity. The wear resistant face of the rotating bearing runner contacts the pad. 
         [0015]    Another embodiment of the present invention provides a thrust bearing assembly in which pads disposed opposite to each other on opposite sides of a bearing carrier are rigidly connected to each other, such that the two pads move in unison. 
         [0016]    For example, on a first side of a bearing carrier, a first pad mounted over a first deflection element can be rigidly connected to a second pad mounted over a second deflection element disposed on a second side of the bearing carrier opposite to the first side. In one implementation, the pads are rigidly connected by a pin that passes through the bearing carrier. The pin can be attached to the pads or can include integral or non-integral pad holders in which the pads are disposed. In one implementation, the pin has an integral first pad holder and is mechanically coupled to a second pad holder on the opposite side of the bearing carrier. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0017]      FIG. 1  is an elevation view partly in section of the overall structure of a downhole drilling apparatus according to an embodiment of the present invention. 
           [0018]      FIG. 2A  is a sectional view of an exemplary thrust bearing assembly installed in a downhole motor, according to an embodiment of the present invention. 
           [0019]      FIG. 2B  is an enlarged view of a portion of the thrust bearing assembly of  FIG. 2A . 
           [0020]      FIG. 2C  is a sectional view of the thrust bearing assembly of  FIG. 2A  prior to welding. 
           [0021]      FIG. 2D  is an enlarged sectional view of an exemplary thrust bearing assembly having rigidly connected opposing pads, in this case connected by a pin, according to an embodiment of the present invention. 
           [0022]      FIG. 3A  is a plan view of an exemplary bearing carrier, according to an embodiment of the present invention. 
           [0023]      FIG. 3B  is a sectional view of the bearing carrier of  FIG. 3A  along line A-A. 
           [0024]      FIG. 3C  is an isometric view of a section of the bearing carrier of  FIG. 3A  along line A-A. 
           [0025]      FIG. 4A  is a plan view of an exemplary runner, according to an embodiment of the present invention. 
           [0026]      FIG. 4B  is a sectional view of the runner of  FIG. 4A  along line A-A. 
           [0027]      FIG. 4C  an isometric view of a section of the runner of  FIG. 4A  along line A-A. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]    Embodiments of thrust bearing assemblies are described in this detailed description of the invention. In this detailed description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of embodiments of the present invention. One skilled in the art will appreciate, however, that embodiments of the present invention may be practiced without these specific details. In other instances, structures and devices are shown in block diagram form. Furthermore, one skilled in the art can readily appreciate that the specific sequences in which methods are presented and performed are illustrative and it is contemplated that the sequences can be varied and still remain within the spirit and scope of embodiments of the present invention. 
         [0029]    An embodiment of the present invention provides a novel, longer life, higher capacity, lower cost hydrodynamic bearing that operates in, for example, a mud-lubricated or sealed oil bath-lubricated drilling motor bearing system. The pad wear surface can be made of a material that is harder than the particles typically found in the mud and that does not wear when maximum loads are kept in approximately the 1000 to 2000 psi range. Examples of suitable pad wear material include silicon carbide and tungsten carbide. Load equalization among individual pads within each bearing can be accomplished by resiliently mounting each thrust pad on deflection elements, such as Belleville washers. This resilient mounting differs from mounting the entire bearing, encompassing fixed pads, on a resilient element (spring), as has been done in the prior art. Indeed, resiliently mounting individual pads eliminates costly finish-grinding/lapping of the complete bearing assembly. 
         [0030]    When designed to fit into existing motor bearing envelopes, thrust loading of approximately 1000 psi or less can be achieved. Tests conducted in mud lubrication at these loads have shown virtually no wear. In a preferred embodiment, the present invention includes a number of rotating disc members of abrasion-resistant hard wear surfaces and a number of stationary pad-type bearing members opposite one or both sides of the rotating member. The bearing members comprise pad carriers with a plurality of cavities for fitting hard ceramic wear pads on resilient elements, such as Belleville washers. 
         [0031]    In an embodiment of a method for manufacturing a thrust bearing according to the present invention, the components are first loosely assembled. The stationary bearing carriers are then bolted or welded together after assembly with a preload (e.g., a slight compression) on the springs. This construction ensures that all components are held in position for proper alignment. Because of the difficulty in predicting precise loads downhole, the present invention can be designed with an overload protection blank runner that engages prior to bottoming of the Belleville washers. For example, a blank runner can be coupled to a bearing carrier of the thrust bearing assembly and configured to engage a blank overload stop. As used herein, the term “coupled” encompasses a direct connection, an indirect connection, or a combination thereof. 
         [0032]    Illustrating one particular application of the present invention,  FIG. 1  shows the overall structure of a progressive cavity drilling apparatus in which a hydrodynamic pad type thrust bearing of the present invention can be used. As shown, the apparatus includes a drill string  15 , a progressive cavity drive train, a drill bit drive shaft  16 , and a drill bit  26 . The drive train includes a progressive cavity device and a coupling for converting the motion of the rotor of the progressive cavity device, e.g., orbiting of the rotor and the rotational motion of the rotor, into rotation about a single axis at the same speed. This coupling, which is contained in the lower part of housing  10  and is not visible in  FIG. 1 , is ajoint assembly including one or more thrust bearing members of the present invention. The joint assembly can be, for example, either a mud-lubricated or sealed oil bath-lubricated drilling motor bearing system. 
         [0033]    As illustrated in  FIG. 1 , the progressive cavity device A has a stator, a rotor, a passageway  11  for fluid to enter between the stator and the rotor, and a passageway  20  for the fluid to exit therefrom. In the drawings, the housing  10  and its flexible lining  14  are held against movement so that they function as the stator in the device A and the shaft  12  functions as the rotor. The housing  10  is tubular and its interior communicates with inlet  11  in the top portion of the lining  14  to provide a passageway for fluid to enter the progressive cavity device A. Outlet  20  in the bottom portion of the lining  19  serves as the passageway for fluid to discharge from the progressive cavity device A. The shaft  12  is precisely controlled so as to roll within the lining  14 . The progressive cavity device A is attached to the lower end of a drill string  15 . 
         [0034]    The lower end of the rotor shaft  12  includes a shaft connection  18   a . The shaft connection allows the rotor  12  to be directed to a stub shaft of the coupling. One end of the coupling is directly connected, by threading, splining, or the like, to the rotor shaft  12 . The other end of the coupling is similarly connected to a drill bit drive shaft  16 . Typically, the coupling includes separate stub shafts that are connected to the rotor shaft  12  and drive shaft  16  by connecting means such as threads, splines, and the like. Of course, a stub shaft could be integrally formed (connected) to either of these shafts, if desired. The drill bit drive shaft  16  is rotatably connected to a conventional drill bit  26 . 
         [0035]    The progressive cavity train functions as a fluid motor or driving apparatus for driving the drilling apparatus shown in  FIG. 1 . Thus, a pressurized fluid, typically water carrying suspended particles commonly referred to as “mud,” is forced into the progressive cavity device. The rotor  12  responds to the flowing fluid to produce a rotor driving motion that is simultaneously a rotation, an oscillation, and an orbit. 
         [0036]    The coupling attached to the rotor  12  at connection point  18   a  and aligned with the true center  28  of the rotor described above converts this rotor driving motion into rotational driving motion substantially about a single axis. 
         [0037]      FIGS. 2A and 2B  show sectional views of an exemplary thrust bearing assembly  150  installed in a downhole motor, according to an embodiment of the present invention. As shown, a drill motor shaft  104  is coupled to a drill bit (not shown) located below the thrust bearing assembly  150 . Drill motor shaft  104  is housed in drill casings  102  and  103 . Stationary bearing members  10  and  101  are fixed between the drill casings  102  and  103 . Stationary bearing members  10  are bearing carriers. Stationary bearing member  101  is a blank overload stop. Bearing carriers  110  and blank overload stop  101  are fixed in the drill string assembly via compressive forces on the top and bottom applied by drill casings  102  and  103 . 
         [0038]    Rotating bearing runners  106  are locked to the rotating shaft  104  with compressive forces on the top and bottom by the threaded drill casing member  105 . 
         [0039]    Wear resistant inserts  111  (e.g., made of silicon carbide and tungsten carbide) are fitted to rotating bearing runners  106  with adhesive. Optionally, wear resistant inserts  111  can be omitted if rotating bearing runners  106  have integral wear resistant faces. 
         [0040]    For example, bearing runners  106  can be entirely made from a wear resistant material, such as silicon carbide and tungsten carbide. 
         [0041]    Each stationary bearing carrier  110  includes one or more thrust pads. Each thrust pad can be resiliently mounted within an individual cavity. In one embodiment shown in  FIG. 3A  and discussed below, the individual thrust pads are disposed annularly around a carrier. As shown in the cross-sectional view of  FIG. 2B , a pad  109  can be resiliently mounted on a deflection element  107  within a counterbore  115  of bearing carrier  110 . In this case, pad  109  is a hard ceramic disc and deflection element  107  is a resilient washer, such as a Belleville washer. A steel disc  108  can optionally be provided between the pad  109  and deflection element  107  to uniformly distribute the deflection element loads to the bottom of the pad  109  to eliminate any stress risers. 
         [0042]    As shown in  FIG. 2A , to provide overload protection, an exemplary thrust bearing assembly of the present invention can include a blank steel runner  100  that engages the blank overload stop  101  just prior to bottoming of the deflection elements  107 . 
         [0043]    As shown in  FIG. 2B , welds  152  at the base of each bearing carrier  110  lock the entire assembly together and hold the individual components in position.  FIG. 2C  illustrates a sectional view of bearing assembly  150  prior to this welding, showing blank overload stop  101 , blank steel runner  100 , stationary bearing carrier  110 , rotating bearing runners  106 , and a pad  109  (e.g., a ceramic wear disc) assembled together. 
         [0044]      FIGS. 3A-3C  illustrate an exemplary bearing carrier  110  for use in a thrust bearing assembly of an embodiment of the present invention. As shown in  FIGS. 3A and 3C , bearing carrier  110  includes a bearing carrier housing having two groups of cavities annularly disposed around the carrier. The first group faces in one direction generally along the axis of the carrier  110 , and the second group faces in generally the opposite direction along the axis. A deflection element  107  is disposed in each cavity. A pad  109  (e.g., a wear resistant insert) is disposed over each deflection element  107 . Optionally, a load distribution washer  108  is disposed between the deflection element  107  and the pad  109 . Deflection element  107  is a resilient washer, such as a Belleville washer. Load distribution washer  108  is a steel disc, for example. Pad  109  is, for example, an abrasion resistant circular pad as shown. In one embodiment, deflection element  107 , load distribution washer  108 , and pad  109  are loosely assembled within cavity  115 , are held in place by the confines of cavity  115  and by bearing runner  106  (specifically, insert  111 , if provided), and are not attached to each other. 
         [0045]    In an aspect of the present invention, as shown in  FIGS. 2B ,  3 B, and  3 C, pad  109  is at least partially disposed within cavity  115 . In this manner, pad  109  is constrained radially within cavity  115 , but is still free to move axially as deflection element  107  compresses and expands. Thus, each pad  109  can float axially within its cavity  115  as bearing runner  106  rotates and contacts pads  109 . Such independent axial movement provides load equalization among the individual pads within the bearing carrier  110 . 
         [0046]      FIG. 2D  illustrates an enlarged sectional view of an exemplary thrust bearing assembly having rigidly connected opposing pads, according to a further embodiment of the present invention. As shown in this example, the assembly includes a bearing carrier  10 , a first pad  109   a  disposed on a first side of bearing carrier  110 , a second pad  109   b  disposed on a second side of the bearing carrier  110  opposite to the first side and rigidly connected to the first pad  109   a  through an opening  199  defined in the bearing carrier  110 , and one or more deflection elements  107  disposed between pad  109   a  and bearing carrier  110  and/or between pad  109   b  and bearing carrier  110 . The rigid connection between pads  109   a ,  109   b  enables the pads  109   a ,  109   b  to move in unison and to maintain a constant spacing between the pads  109   a ,  109   b  and between adjacent runners. Pad  109   a  could, for example, be on the top or downthrust side of bearing carrier  110 , with pad  109   b  on the bottom or upthrust side. The pads  109   a ,  109   b  move relative to the bearing carrier  110 . 
         [0047]    The rigid connection between pads  109   a ,  109   b  can be accomplished in a number of ways. For example, pads  109   a ,  109   b  can be integrally formed with an interconnecting member between them, thereby forming a unitary part. As another example, a separate member could be attached to both pads  109   a  and  109   b , for example, by welding or an adhesive. 
         [0048]    In another embodiment, the pads  109   a ,  109   b  are disposed in pad holders, wherein the pad holders are connected to each other. For example, as illustrated in  FIG. 2D , pad  109   a  can be disposed in a pad holder  112  having an integral pin portion  191  extending therefrom. As shown, the pin portion  191  extends through the opening  199  in the bearing carrier  110 . Pin portion  191  is not fixed to the bearing carrier  110  and can move within opening  199  at least in a direction generally from pad  109   a  to pad  109   b  (e.g., a vertical direction in  FIG. 2D ). The distal end of pin portion  191  is mechanically coupled to another pad holder  113  in which pad  109   b  is disposed. In this manner, pad  109   a  and pad holder  112  (with integral pin portion  191 ) are rigidly connected to pad holder  113  and pad  109   b.    
         [0049]    By providing a rigid pad-to-pad connection, the pads  109   a ,  109   b  move together and maintain a constant spacing among the runners and pads. This spacing minimizes shock loading when loads change across the bearing carrier, e.g., when loads change from downthrust to upthrust and vice versa. Indeed, surprisingly, the gap provided by the rigid connection dramatically reduces the negative effect of a transitional shock. 
         [0050]      FIGS. 4A-4C  illustrate an exemplary bearing runner  106  for use in a thrust bearing assembly of an embodiment of the present invention. Bearing runner  106  rotates with the drill motor shaft. As shown best in  FIG. 4B , bearing runner  106  includes a bearing runner housing with wear resistant, or abrasion resistant, rings  111  that are fitted to the runner, for example, by adhesive. Optionally, rings  111  can be omitted if bearing runner  106  has integral wear resistant faces. 
         [0051]    Although embodiments of the present invention have been described in the context of downhole drilling motors, one of ordinary skill in the art would appreciate that the thrust bearing assemblies of the present invention are equally applicable to other applications for thrust bearings, such as in rock crushing equipment. Therefore, notwithstanding the particular benefits associated with applying the present invention to drilling motors, the present invention should be considered broadly applicable to any application in need of thrust bearings. 
         [0052]    The foregoing disclosure of the preferred embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. 
         [0053]    Many variations and modifications of the embodiments described herein will be apparent to one of ordinary skill in the art in light of the above disclosure. The scope of the invention is to be defined only by the claims appended hereto, and by their equivalents. 
         [0054]    Further, in describing representative embodiments of the present invention, the specification may have presented the method and/or process of the present invention as a particular sequence of steps. However, to the extent that the method or process does not rely on the particular order of steps set forth herein, the method or process should not be limited to the particular sequence of steps described. As one of ordinary skill in the art would appreciate, other sequences of steps may be possible. 
         [0055]    Therefore, the particular order of the steps set forth in the specification should not be construed as limitations on the claims. In addition, the claims directed to the method and/or process of the present invention should not be limited to the performance of their steps in the order written, and one skilled in the art can readily appreciate that the sequences may be varied and still remain within the spirit and scope of the present invention.