Patent Publication Number: US-9845808-B2

Title: Spherical sleeve and bushing bearing for centrifugal pump stage

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Ser. No. 61/914,023, filed Dec. 10, 2013. 
    
    
     FIELD OF THE DISCLOSURE 
     This disclosure relates in general to centrifugal well pumps and in particular to an pump stage bearing having a rotating sleeve that fits within a stationary bushing, with a spherical interface between the sleeve and bushing. 
     BACKGROUND 
     Centrifugal well pumps are commonly used for pumping oil and water from oil wells. The pumps have a large number of stages, each stage having a stationary diffuser and a rotating impeller. The rotating impellers exert a downward thrust as the fluid moves upward. Also, particularly at startup and when the fluid flow is non uniform, the impellers may exert upward thrust. In a common pump design, the impellers float freely on the shaft so that each impeller transfers downward thrust to one of the diffusers. A thrust washer, sleeve, or bearing is located between a portion of each impeller and the upstream diffuser to accommodate the downward thrust. Another thrust washer transfers upward thrust. 
     Some wells produce abrasive materials, such as sand, along with the oil and water. The abrasive material causes wear of the pump components, particularly in the areas where downward thrust and upward thrust are transferred. Tungsten carbide thrust bearings and hearing sleeves along with shaping of components may be employed in these pumps to reduce wear. A number of designs for these components exist, but improvements are desirable. 
     SUMMARY 
     The centrifugal pump of this disclosure has a drive shaft and a plurality of stages, each of the stages having an impeller and a diffuser. The impellers are mounted to the drive shaft for rotation therewith. The diffusers are mounted in a housing of the pump for non rotation. A motor is operatively coupled to the pump for rotating the drive shaft. 
     A bearing in at least one of the stages includes a sleeve having a cylindrical opening coupled to the drive shaft for rotation therewith. The sleeve has upper and lower ends and an outer side wall facing radially outward. The outer side wall curves outward when viewed in a sleeve axis plane, defining upper and lower outer diameters at the upper and lower ends of the sleeve that are smaller than an intermediate outer diameter halfway between the upper and lower ends. 
     A bushing is mounted in the diffuser of at least one of the stages for non rotation. The bushing has a bore with an inner side wall curving inward when viewed in a bore axis sectional plane. The curved inner side wall defines upper and lower inner diameters at upper and lower ends of the hushing that are smaller than an intermediate inner diameter halfway between the upper and lower ends of the bushing. The sleeve locates in the bore with the outer side wall in rotational sliding contact with the inner side wall of the bore about the bore axis. 
     An upper hub member of the impeller of one of the stages located above the sleeve is in engagement with the upper end of the sleeve. The upper huh member applies a downward directed force to the sleeve and from the sleeve to the bushing during down-thrust of the pump. 
     A lower hub member of the impeller of one of the stages located below the sleeve is in engagement with the lower end of the sleeve. The lower hub member applies an upward directed force to the sleeve and from the sleeve to the bushing during up-thrust of the pump. 
     A pair of slots is formed in the bore of the bushing 180 degrees apart from each other and extending into the bore of the hushing from one of the ends of the bushing. Each of the slots has a circumferential width at leak equal to a height of the sleeve from the lower end to the upper end of the sleeve. The slots are radially spaced apart from each other a distance greater than the maximum outer diameter of the sleeve. The slots enable the sleeve to be inserted into the bore of the bushing while the sleeve axis is perpendicular to the bore axis, then tilted so that the sleeve axis coincides with the bore axis. 
     Preferably, the sleeve and the bushing are formed of materials harder than the impeller and diffuser. In the embodiment shown, the slots extend axially from one of the ends of the bushing to a termination point at the intermediate inner diameter of the inner side wall of the bushing. 
     An upper portion of the outer side wall of the sleeve is in rotational sliding engagement with an upper portion of the inner side wall of the bushing. A lower portion of the outer side wall of the sleeve is in rotational sliding engagement with a lower portion of the inner side wall of the bushing. An intermediate portion of the outer side wall of the sleeve is in rotational sliding engagement with an intermediate portion of the inner side wall of the hushing 
     In the embodiment shown, the upper and lower outer diameters of the sleeve equal each other. The upper and lower inner diameters of the inner side wall of the bushing equal each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features, advantages and objects of the disclosure, as well as others which will become apparent, are attained and can be understood in more detail, more particular description of the disclosure briefly summarized above may be had by reference to the embodiment thereof which is illustrated in the appended drawings, which drawings form a part of this specification. It is to be noted, however, that the drawings illustrate only a preferred embodiment of the disclosure and is therefore not to be considered limiting of its scope as the disclosure may admit to other equally effective embodiments. 
         FIG. 1  is a side view of an electrical submersible pump assembly in accordance with this disclosure and installed in a well. 
         FIG. 2  is a sectional view of a portion of the pump of  FIG. 1 , showing one of the sleeve and bushing bearings of one of the pump stages. 
         FIG. 3  is a perspective, partially sectional he sleeve and bushing bearing of  FIG. 2 . 
         FIG. 4  is a perspective view from a different angle of the sleeve and bushing bearing of  FIG. 3 . 
         FIG. 5  is a top view of the bushing of  FIG. 3  with the sleeve removed. 
         FIG. 6  is a sectional view of the bushing of  FIG. 5 , taken along the line  6 - 6  of  FIG. 5 . 
         FIG. 7  is a side view of the sleeve of  FIG. 3  apart from the bushing. 
         FIG. 8  is a perspective view of the sleeve and hushing of  FIG. 3  with the sleeve partially inserted into the bushing. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     The methods and systems of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The methods and systems of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. 
     It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. 
     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 centrifugal pump  15  that 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, such a bellows or bag, 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 he 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 pump axis  26  through housing  23  and is rotated by motor  17 . Shaft  25  is normally made up of a different section for each module 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 . Each stage has an impeller  31  located above the 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 . Downward directed thrust is considered to be in a direction away from the direction the fluid is being pumped. Upward directed thrust can also occur, such as during startup or other conditions. Upward directed thrust is in an opposite direction to downward directed thrust. 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 sleeve  37  to transmit down-thrust from the upper impeller  31  shown to sleeve  37 . Alternately, a tubular spacer (not shown) which can be considered to be a part of hub  35 , may be located between the lower end of hub  35  and the upper end of sleeve  37 . 
     A tubular spacer  38  is shown between the upper side of a next lower impeller  31  and the lower end of sleeve  37  for transmitting up-thrust from the next lower impeller to sleeve  37 . Spacer  38  may also be considered to he a hub member. Sleeve  37  could be employed with only some of the pump stages or in all of the pump stages. That is, if sleeve  37  is only in some of the stages, hubs  35  could transfer thrust from one impeller  31  to another impeller  31  and eventually to sleeve  37 . Sleeve  37  is a single-piece member and may he of a harder material than the material of impellers  31  and diffusers  27 , such as tungsten carbide. 
     Sleeve  37  seats in a thrust bushing  39 , which in turn is nonrotatably supported in a diffuser receptacle  40 . Bushing  39  may be press-fit in diffuser receptacle  40  or secured otherwise, such as by a retaining ring. Bushing  39  is also a single-piece member and may also he of a harder material, such as tungsten carbide, than the material of impellers  31  and diffusers  27 . Sleeve  37  is secured to shaft  25  for rotation but is free to move a limited amount axially relative to shaft  25 . Typically a key (not shown) engages mating axially extending grooves  41  ( FIG. 3 ) in sleeve  37  and shaft  25 . 
     Referring to  FIGS. 3-7 , sleeve  37  has an upper end  43 , a lower end  45  and an external or outer side wall  47  extending from upper end  43  to lower end  45 . A sleeve bore  49  that is cylindrical extends through sleeve  37  from upper end  43  to lower end  45 . Sleeve bore  49  has a sleeve axis  51 . External side wall  47  is convex and spherical from upper end  43  to lower end  45 . The center point of the radius of curvature for side wall  47  could coincide with sleeve axis  51  or it could be smaller. External side wall  47  has a maximum outer diameter halfway between sleeve upper end  43  and sleeve lower end  45 . The outer diameters at upper end  43  and lower end  45  may be the same and are smaller than the outer diameter halfway between sleeve upper end  43  and sleeve lower end  45 . Key groove  41  is formed in sleeve bore  49  and extends parallel to sleeve axis  51  from upper end  43  to lower end  45 . 
     Bushing  39  has an upper end  53 , a lower end  55  and a cylindrical exterior  57 . Bushing has a bore  59  with a bushing bore axis  61 . Bore  59  has an inner or internal side wall  63  that is concave, spherical, and has slightly greater radius of curvature than sleeve external side wall  47 . Bushing internal side wall  63  extends from bushing upper end  53  to bushing lower end  55 . Internal side wall  63  has a maximum inner diameter  69  halfway between bushing upper end  53  and bushing lower end  55 . The inner diameter of internal side wall  63  at upper end  53  and lower end  55  may be the same and are smaller than the maximum inner diameter  69  of internal side wall  63 . The inner diameters of internal side wall  63  at any point from bushing upper end  53  to lower end  55  are slightly greater than the outer diameters of sleeve external side wall  47  at the same places so as to closely receive sleeve  37  in rotating sliding contact. 
     Two slots  65  spaced 180 degrees apart from each other relative to bushing axis  61  are formed in internal side wall  63 . Each slot  65  extends from upper end  53  to approximately one-half the distance between bushing upper end  53  and bushing lower end  55 , which is at the maximum inner diameter. Slots  65  thus do not extend all the way to bushing lower end  55  in this embodiment. Alternately, slots  65  could extend upward from bushing lower end  55  half the distance to bushing upper end  53 . Each slot  65  has a base  67  with two side edges spaced circumferentially apart from each other the width of slot  65 . When viewed in the cross-section of  FIG. 6 , base  67  of each slot  65  appears to be generally flat. However, base  67  has a circumferential curvature when viewed in a plane perpendicular to bushing axis  61  that has a radius equal to the radius of the maximum inner diameter  69  of bushing bore  59 , as shown by the dotted lines in  FIG. 5 . 
     The height or axial dimension of sleeve  37  along sleeve axis  51  from upper end  43  to lower end  45  is shown to be slightly less than the height or axial dimension of bushing  39  along bushing axis  61  from upper end  53  to lower end  55 . The axial dimension along sleeve axis  51  of sleeve  37  is slightly less than the circumferential width of each bushing slot  65 . The maximum outer diameter of sleeve external side wall  47  is slightly less than the radial distance from base  67  of one slot  65  to base  67  of the other slot  65 . The inner diameter of bushing bore  59  at upper end  53  and lower end  55  is smaller than the maximum outer diameter of sleeve external side wall  47 . 
     To assemble sleeve  37  in bushing  39 , an assembler will tilt sleeve  37  so that sleeve axis  51  is perpendicular to bushing axis  61 . The assembler then aligns the tilted sleeve  37  with slots  65  and inserts sleeve  37  into bushing bore  59 , as shown in  FIG. 8 . Sleeve  37  is inserted until its maximum outer diameter portion contacts the lower end of each slot  65 . While still inserted, the assembler tilts sleeve  37  to a position with sleeve axis  51  coinciding with bushing axis  61 . Once axes  51 ,  61  coincide, sleeve  37  will be trapped in bushing  39 . That is, unless one reverses the installation procedure, sleeve  37  cannot be lifted relative to bushing  39  because the maximum outer diameter of sleeve external side wall  47  is greater than the inner diameter of bushing bore  59  at bushing upper end  53 . Similarly, sleeve  37  will not drop downward from bushing  39  because the maximum outer diameter of sleeve external side wall  47  is greater than the inner diameter of bushing bore  59  at bushing lower end  55 . Once assembled, sleeve  37  is free to rotate in bushing  39  about the common axes  51 ,  61 . 
     After assembling sleeve  37  in bushing  39  as shown in  FIG. 4 , the assembler slides the assembly onto pump shaft  25  ( FIG. 2 ) into abutment with the impeller hub  35  directly above. A key (not show) will insert in sleeve groove  41  to lock sleeve  37  to shaft  25  for rotation therewith. The operator slides the adjacent diffuser  27  over shaft  25  and installs hushing  39  in receptacle  40 , such as by an interference fit or a retainer ring (not shown). If by a retainer ring, some mechanism, such a key, will be used to prevent rotation of bushing  39  in receptacle  40 . Bushing  39  will be axially fixed to diffuser  27  in the case of art interference fit, or optionally free to move axially a slight amount in the event a retainer ring is used. 
     During operation, impellers  31  and sleeves  37  rotate with shaft  25 . Down-thrust from the impeller  31  above sleeve  37  transfers through impeller hub  35  to sleeve  37 . The load path for the down-thrust passes through sleeve  37  and bushing  39  to diffuser  27  and housing  23 . The downward force passes from the lower portion of sleeve external side wall  47  to a lower portion of bushing internal side wall  63 . Similarly, during up-thrust, spacer  38  transfers the up-thrust from the next lower impeller  31  to sleeve  37 . The upthrst load path transfers through sleeve  37  and bushing  39  to diffuser  27 . The upward directed force passes through an upper portion of sleeve external side wall  47  into an upper portion of internal side wall  63  of bushing  39 . Sleeve  37  and bushing  39  serve as a radial bearing for shaft  25 , as well as a thrust bearing for upward and downward directed thrust. 
     While, the disclosure has been shown in only one of its forms, it should be apparent to those skilled in the art that is susceptible to changes.