Patent Publication Number: US-2015071799-A1

Title: Self-Aligning and Vibration Damping Bearings in a Submersible Well Pump

Description:
FIELD OF THE DISCLOSURE 
     This disclosure relates in general to electrical submersible pumps for wells and in particular to bearings in the pump assemblies that have self-aligning features as well as vibration damping. 
     BACKGROUND 
     Electrical submersible pumps (ESP) are widely used to pump oil production wells. A typical ESP has a rotary pump driven by an electrical motor. A seal section is located between the pump and the motor to reduce the differential between the well fluid pressure on the exterior of the motor and the lubricant pressure within the motor. A drive shaft, normally in several sections, extends from the motor through the seal section and into the pump for rotating the pump. The pump may be a centrifugal pump having a large number of stages, each stage having an impeller and diffuser. 
     During operation, the impellers create thrust, which can be both in downward and upward directions. The impellers transmit the thrust in various manners to the diffusers. Some pumps are particularly used in abrasive fluid environments. In those pumps, an abrasion resistant thrust runner may be coupled to the shaft to receive thrust from one or more impellers. A bushing may be secured into a receptacle in the diffuser to transfer the thrust. The thrust runner and the bushing may be formed of an abrasion resistant material, such as tungsten carbide, that is harder than the material of the diffuser. The bushing is commonly installed in the receptacle with a press fit. 
     Damage and misalignment may occur when the hard metal bushing is press fit into the diffuser. The wear resistant bushing may misalign slightly when pressed into the bearing carrier. Load concentrations may occur, causing the brittle carbide material to crack. Some pumps tend to vibrate, particularly at higher fluid flow pressures, and the vibration can lead to carbide chattering and cracking. 
     SUMMARY 
     An electrical submersible pump assembly has a plurality of modules, including a rotary pump module, a motor module, and a seal section module located between the motor module and the pump module. A bearing in at least one of the modules has a sleeve coupled to a drive shaft in said one of the modules for rotation therewith. A bushing has a bore that receives the sleeve in sliding, rotational engagement. A stationarily mounted supporting member has a receptacle that receives the bushing. The supporting member is of a material having less hardness than the material of the bushing. The bushing has an exterior portion of smaller diameter than a portion of the receptacle, defining an annular gap. An elastomeric radial compliant member in the gap allows limited radial movement of the bushing relative to the supporting member. For axial compliance, the bushing is free to move axially a limited amount relative to the receptacle. 
     A key and keyway arrangement may be between the bushing and the supporting member for preventing rotation of the bushing relative to the supporting member. The key and keyway arrangement may include a key integrally formed on the bushing and a slot in the receptacle. 
     The radial compliant member may comprise at least two elastomeric rings. Alternately, the compliant member may comprise a layer of elastomeric material bonded to the bushing and to the receptacle. 
     A resilient axial compliant member may be positioned to urge the bushing upward relative to the receptacle. In one embodiment, the axial compliant member comprises an elastomeric ring. In another embodiment, the layer of elastomeric material extends between a thrust receiving shoulder of the receptacle and the bushing to serve as an axial compliant member. 
     The pump may be a centrifugal pump having a plurality of stages, each of the stages having an impeller and a diffuser, with the bearing being located in at least one of the stages. The sleeve in that instance comprises a thrust runner that receives thrust from the impeller of one of the stages and has a thrust transferring face in engagement with a thrust receiving end of the bushing. The bushing has a thrust transferring surface that engages a thrust receiving shoulder in the receptacle of said one of the stages. The supporting member comprises a diffuser, or it could be a bearing spacer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of an electrical submersible pump assembly in accordance with this disclosure. 
         FIG. 2  is a sectional view of a portion of the pump of the pump assembly of  FIG. 1 . 
         FIG. 3  is an enlarged sectional view of one of the thrust runners and bushings of the pump of  FIG. 2  and shown installed in a diffuser. 
         FIG. 4  is an isometric view of the thrust runner shown in  FIG. 3 . 
         FIG. 5  is a sectional view of a first alternate embodiment of the thrust runner and bushing of  FIG. 2 . 
         FIG. 6  is a sectional view of a second alternate embodiment of the thrust runner and bushing of  FIG. 2 . 
         FIG. 7  is a sectional view of a third alternate embodiment of thrust runner and bushing of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     Referring to  FIG. 1 , electrical submersible pump assembly (ESP)  11  is illustrated as being supported on production tubing  13  extending into a well. Alternately, ESP  11  could be supported by other structure, such as coiled tubing. ESP  11  includes several modules, one of which is a rotary pump  15  that is illustrated as being a centrifugal pump. Pump  15  has an intake  16  for drawing in well fluid. Another module is an electrical motor  17 , which drives pump  15  and is normally a three-phase AC motor. A third module comprises a protective member or seal section  19  coupled between pump  15  and motor  17 . Seal section  19  has components to reduce a pressure differential between dielectric lubricant contained in motor  17  and the pressure of the well fluid on the exterior of ESP  11 , Intake  16  may be located in an upper portion of seal section  19  or on a lower end of pump  15 . A thrust bearing  21  for motor  17  may be in a separate module or located in seal section  19  or motor  17 . 
     ESP  11  may also include other modules, such as a gas separator for separating gas from the well fluid prior to the well fluid flowing into pump  15 . The various modules may be shipped to a well site apart from each other, then assembled with bolts or other types of fasteners. 
     Referring to  FIG. 2 , pump  15  includes a housing  23  that is cylindrical and much longer than its diameter. A drive shaft  25  extends along longitudinal axis  26  through housing  23  and is rotated by motor  17 . Shaft  25  is normally made up of several sections connected together with splined ends. A large number of stages are normally within housing  23 , each stage including a stationary diffuser  27 . Diffusers  27  are stacked on one another and secured against rotation in housing  23 . Diffusers  27  have flow passages  29  leading upward and inward toward axis  26 . An impeller  31  is rotatably located within a central receptacle  30 , which is a part of each diffuser  27 . Impellers  31  have flow passages  33  that lead from a central area upward and outward from axis  26 . The terms “downward” and “upward” are used only for convenience, since pump  15  is not always oriented vertically as shown. The example of  FIG. 2  is a mixed flow type, wherein the flow passages  29 ,  33  extend both axially as well as radially. Alternately, pump  15  could be a radial flow type wherein the flow passages extend primarily radially and not axially. 
       FIG. 2  illustrates how thrust imposed on each impeller  31  is transferred to one of the diffusers  27 , which serves as a supporting member. When pump  15  is pumping fluid, the thrust may be in a downward direction away from the overall direction the fluid is being pumped. Upward directed thrust can also occur, during normal operation. Each impeller  31  has a hub  35 , which is a cylindrical member having a bore through which shaft  25  passes. In this example, a thrust runner or sleeve  37  is located below hub  35 . The lower end of hub  35  abuts an upper end of thrust runner  37 . Alternately, a spacer sleeve (not shown) could be located between thrust runner  37  and hub  35 . Also, rather than being separate as shown, hub  35  and thrust runner  37  could be integrally formed together. Further, thrust runners  37  could be employed with only part of the impellers  31 , rather than all, as shown. That is, hubs  35  could transfer thrust from one impeller  31  to another impeller  31  and eventually to thrust runner  37 . Thrust runner  37  may be of a harder material than the material of impeller hub  35 , such as tungsten carbide. 
     Thrust runner  37  seats in a thrust bushing  39 , which in turn is nonrotatably supported in diffuser receptacle  30 .  FIG. 2  shows an optional upthrust thrust runner  41 , which is an inverted image of downthrust runner  37 . Upthrust runner  41  has a lower end that abuts an upper end  45  of impeller  31 . Upthrust runner  41  seats in an upthrust bushing  43 , which in turn is non rotatably supported in diffuser receptacle  30 . Runners  37 ,  41  are secured to shaft  25  for rotation but are free to move a limited amount axially relative to shaft  25 . Typically a key (not shown) engages mating axially extending grooves in runners  37 ,  41  and shaft  25 . 
     Referring to  FIG. 3 , in a first embodiment, thrust runner  37  has a radially extending flange  47  on its upper end. The upper side of flange  47  may be conical, with the maximum diameter at the lower edge of flange  47 . Flange  47  has on its lower side a thrust transferring face  49  that is illustrated as being in a plane perpendicular to axis  26  ( FIG. 2 ) and facing in a downward direction. Thrust transferring face  49  may alternately be conical. A cylindrical body  51  extends downward from thrust transferring face  49  and has a smaller outer diameter than flange  47 . Bushing  39  has a flat, thrust receiving surface  53  on its upper end that is engaged by thrust transferring face  49  in rotating, sliding contact. 
     Bushing  39  has a cylindrical body  55  with a radially extending flange  57  at its upper end. In this example, the maximum outer diameter of bushing flange  57  is slightly greater than the maximum outer diameter of runner flange  47 . Bushing body  55  has a smaller outer diameter than the outer diameter of bushing flange  57 . Bushing flange  57  is shown in  FIG. 3  as having an upward facing retaining shoulder  59  extending radially outward. Retaining shoulder  59  is at an elevation lower and has a greater outer diameter than bushing thrust receiving surface  53 . 
     Diffuser receptacle  30  has an upper bore section  61  into which bushing flange  57  extends. A retaining ring  62 , such as a split ring, fits into a groove in upper bore section  61  and extends over bushing retaining shoulder  59  at a distance selected to allow limited axial movement of bushing  39  relative to receptacle  30 . Diffuser receptacle  30  has a lower bore section  63  extending downward from upper bore section  61  and being of a smaller inner diameter. The difference in diameters between lower bore section  63  and upper bore section  61  results in an upward facing thrust receiving shoulder  65 . Bushing flange  57  has a flat lower side or thrust transferring surface  66  that is in engagement with thrust receiving shoulder  65  to transmit downward directed thrust. In the  FIG. 3  embodiment, retaining ring  62  and receptacle shoulder  66  allow limited axial movement of bushing  39  relative to diffuser  27 . When in a lower position, bushing shoulder  66  will contact thrust receiving shoulder  65  to transfer downward directed thrust. 
     The cylindrical exterior of runner body  51  is only slightly less in diameter than the bore of bushing  39 , The cylindrical exterior of bushing body  55  is significantly less in diameter than the inner diameter of receptacle lower bore section  63 . The difference in diameter results in an annular gap  67  that is exaggerated in the drawings. Annular gap  67  can be either greater than or less than the clearance between the outer diameter of thrust runner body  51  and the inner diameter of bushing  39 . 
     A resilient, radial compliant member locates in annular gap  67 , and in  FIGS. 3-6 , it comprises a pair of elastomeric rings  69  axially spaced apart from each other. Compliant rings  69  may be located in mating grooves  70 , which may be either in bushing  39 , as shown, or in receptacle lower bore section  63 . Compliant rings  69  allow some radial movement of bushing  39  relative to diffuser  27 . Compliant rings  69  also form a seal between bushing  39  and diffuser  27  and may be O-rings. Compliant rings  69  may be formed of an absorptive material and coated with oil prior to installation. After installation, complaint rings  69  absorb the oil and expand to create a tighter engagement with diffuser  27 . 
     Bushing  39  and diffuser  27  also have an anti-rotation means to prevent rotation of bushing  39  in diffuser  27 . For example, the anti-rotation means may comprise a keyway and key arrangement. Key  71  is illustrated in  FIG. 4  as being a lug integrally formed on the outer diameter of bushing body  55 . A mating axially extending slot  73  is formed in receptacle lower bore section  63 . 
     Upthrust runner  41 , upthrust bushing  43  and the lower portion of diffuser receptacle  30  may be the same as shown in  FIG. 3 , except inverted. In the operation of the embodiment of  FIGS. 1-4 , motor  17  rotates shaft  25 , causing impellers  31  to rotate. The pump stages pump well fluid through impeller flow passages  33  and diffuser flow passages  29 . Downward thrust imposed on impellers  31  passes through impeller hubs  35  to thrust runners  37 , which are in rotating engagement with stationary thrust bushings  39 . The downward thrust passes from bushings  39  to diffuser receptacle shoulders  65 . Compliant rings  69  allow slight radial movement of bushings  39  relative to diffuser receptacles  30 . The radial movement helps bushings  39  align with runners  37  and dampens vibration. 
       FIG. 5  illustrates a second embodiment. The components that are the same as  FIG. 3  have the same numerals. In this second embodiment, a resilient axial compliant ring  75  is employed in addition to urge bushing  39  upward relative to diffuser  27 . Axial compliant ring  75  is of a resilient energy absorbing material located between bushing thrust transferring surface  66  and receptacle thrust receiving shoulder  65 . In the example shown, axial compliant ring  75  is an elastomeric ring. Axial compliant ring  75  is within a groove that may be either in thrust receiving shoulder  65 , as shown, or in thrust transferring surface  66 . As in  FIG. 3 , retaining ring  62  is positioned to allow slight axial movement of bushing  39  relative to receptacle  30 . The axial movement enhances the ability of bushing  39  to align with runner  37 . Axial compliant ring  75  urges thrust transferring surface  66  away from receptacle thrust receiving shoulder  65 . 
       FIG. 6  illustrates a third embodiment, wherein an axial compliant ring  75  is optionally used, as well. In this embodiment, runner flange  77  extends radially outward to a greater extent than runner flange  47  in  FIGS. 3 and 5 . Runner flange  77  has an outer diameter that is only slightly less than the inner diameter of receptacle upper bore section  61 . In  FIGS. 3 and 5 , runner flange  47  has an outer diameter that is considerably less than the inner diameter of upper bore section  61 . The gap between the outer diameter of runner flange  77  and the inner diameter of receptacle upper bore section  61  is at least equal to the annular gap between the outer diameter of bushing body  55  and diffuser lower bore portion  63 . In  FIG. 6 , the outer diameter of runner flange  77  is approximately the same as the outer diameter of bushing retaining shoulder  59 , thus runner flange  77  extends over retaining shoulder  59 . Also, the upper side of runner flange  77  may have a flat margin at its outer diameter, rather than being entirely conical as in  FIGS. 3 and 5 . The purpose of the extended flange  77  is to create a hydraulic seal between flange  77  and receptacle upper bore section  61 . The hydraulic seal further reduces the ability of debris to become lodged between bushing  39  and diffuser receptacle  30 . 
     In the embodiment of  FIG. 7 , annular gap  67  is filled with a layer  79  of compliant material, rather than elastomeric rings  69 ,  75 . Compliant layer  79  extends the full length of bushing  39  from the lower end to the upper end. A portion of compliant layer is located between flange lower side  66  and receptacle thrust receiving shoulder  65 , providing axial compliance. Preferably, complaint layer  79  is cured in place between bushing  39  and receptacle  30 , thereby bonding bushing  39  to receptacle  30 . Compliant layer  79  thus creates a seal between diffuser receptacle  30  and bushing  39 . The bonding of compliant layer  79  limits axial movement of bushing  39  in receptacle  30 , thus retaining ring  62  ( FIGS. 3 and 5 ,  6 ) is not required. Optionally, anti-rotation key  71  and slot  73  could he eliminated, with the bonded compliant layer  79  serving as an anti-rotation means. 
     While the disclosure has been shown in only a few of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the disclosure. For example, although shown only in connection with a pump stages, the complaint bushing could also be employed with shaft bearings in the pump, seal section, motor, and gas separator, if used. In addition the downthrust flange of the bushing could be a separate member from the body portion of the bushing.