Abstract:
A centrifugal pump has a stationary diffuser with a bore. A thrust bearing is pressed into the diffuser bore and has a curved interior. A thrust runner having a curved exterior is correspondingly and closely received by the thrust bearing interior. The thrust runner is keyed to a shaft and transmits thrust from a rotating impeller to the diffuser via the thrust bearing. The curved surface of the thrust bearing allows for handling of both axial and radial thrust without the need for multiple thrust bearings. The increased surface area of the curved surface in the thrust bearing can also handle higher loads.

Description:
FIELD OF INVENTION 
     This invention relates in general to electrical submersible well pumps and in particular to thrust bearings for a centrifugal pump. 
     BACKGROUND OF THE INVENTION 
     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 nonuniform, 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 bearing 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 OF THE INVENTION 
     The centrifugal pump stage of this invention has a stationary diffuser having a bore. A thrust bearing has a tubular portion that inserts into the bore of the diffuser. A generally cylindrical base or shoulder extends radially outward and bears against a support surface formed in the bore of the diffuser for transmitting downward thrust from an upstream impeller to the diffuser. In addition, a tapered shoulder extends from the external shoulder and bears against a correspondingly tapered support surface formed on the diffuser for transmitting thrust radially from the impeller to the diffuser. 
     A thrust runner rotatably engages a curved interior surface on a downstream end of the thrust bearing for transmitting the downward axial thrust from the downstream impeller to the diffuser via a sleeve in contact with both the impeller and the thrust runner. The thrust runner and thrust bearing may also be considered collectively as a bearing. The thrust runner has an upstream curved end that corresponds with the interior surface of the thrust bearing, resulting in a greater surface area on the upstream end than on a downstream end. The curved upstream end of the thrust runner transmits thrust radially to the bearing. Further, the greater surface area between the curved interior surface of the thrust bearing and the corresponding curved upstream end of the thrust runner allow for handling of higher loads. The thrust bearing, sleeve, and thrust bearing are preferably constructed of hard wear resistant materials, such as tungsten carbide. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic elevational view of a pump in accordance with this invention and shown within a well. 
         FIG. 2  is a sectional view of a stage of a pump constructed in accordance with this invention. 
         FIG. 3  is a perspective view of a thrust bearing and runner of the pump stage of  FIG. 2 , shown removed from the pump. 
         FIG. 4  is a side view of a thrust runner of the pump stage of  FIG. 2 , shown removed from the pump. 
         FIG. 5  is a perspective sectional view of a thrust bearing and runner of the pump stage of  FIG. 2 , shown removed from the pump. 
         FIG. 6  is a top view of the thrust runner of  FIG. 2 . 
         FIG. 7  is a sectional view of another embodiment of a stage of a pump constructed in accordance with this invention. 
         FIG. 8  is a sectional view of another embodiment of a stage of a pump constructed in accordance with this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , a pump assembly is shown in a well having a casing  11 . Perforations  13  within casing  11  allow well fluid to flow into the casing  11 . An electrical submersible pump (“ESP”)  15  is shown suspended in the well on a string of production tubing  17 . Pump  15  has an intake  19  for drawing in well fluid and pumping it through tubing  17  to the surface. Alternately, in some instances pump  15  will discharge into casing  11  above a packer (not shown). 
     Pump  15  has a seal section  21  connected to its lower end. An electrical motor  23  connects to the lower end of seal section  21 . Seal section  21  reduces a pressure differential between lubricant within motor  23  and the hydrostatic pressure in the well. An electrical power cable  24  extends downward from the surface to motor  23  for supplying power. 
     Referring to  FIG. 2 , a stage of pump  15  ( FIG. 1 ) is illustrated in this embodiment. However, pump  15  is a centrifugal pump and will include a plurality of stages. Each stage has a diffuser  27 , and an upstream impeller  28 . Diffuser  27  discharges into a downstream impeller  29 . Each impeller  28 ,  29  rotates and has passages  30  that lead upward and outward from a lower inlet. Diffusers  27  stack on top of each other within a cylindrical housing  25 . Diffusers  27  are non-rotatable relative to housing  25 . Each diffuser  27  has a plurality of passages  31  that extend from a lower or upstream inlet to an upper or downstream outlet. The inlet is farther radially from a longitudinal axis of pump  15  than the outlet. In this embodiment, the stages are a mixed flow type, wherein passages  30 ,  31  extend both radially and axially. This invention is applicable also to radial flow types, wherein the passages of the stages are primarily radial. 
     Diffuser  27  has an axial bore with a lower portion  33   a , an upward facing shoulder or support surface  33   b , a tapered shoulder or support surface  33   c , and an upper portion  33   d . The terms “upper” and “lower” are used herein for convenience only and not in a limiting manner. Lower portion  33   a  has the smallest diameter, while the tapered shoulder  33   c  is recessed radially outward by an amount defined by the upward facing shoulder  33   b . The tapered shoulder  33   c  slopes radially upward to meet the upper portion  33   d , which is cylindrical and has the largest diameter of the bore. In this embodiment, lower portion  33   a  has a greater length than either of the shoulders  33   b ,  33   c , or  33   d . The various portions  33   b ,  33   c  and  33   d  form a generally concave shape. 
     Continuing to refer to  FIG. 2 , in this embodiment, a shaft  35  extends rotatably through diffuser bore portions  33   a ,  33   b ,  33   c  and  33   d  for rotating impellers  28 ,  29 . A thrust bearing base  37  is non-rotatably mounted in portions  33   b ,  33   c , and  33   d  of the diffuser bore, such as by an interference fit or other means. Thrust bearing base  37  may be a generally bowl-shaped member having a generally cylindrical bottom or shoulder  42  at an upstream side that extends radially outward. Bottom shoulder  42  at least partially bears against the upward facing shoulder  33   b  formed in the bore of the diffuser  27  to transmit downward thrust from the upstream impeller  29  to the diffuser  27 . Further, a tapered exterior shoulder  45  on thrust bearing base  37  extends upward bottom shoulder  42  and bears against the corresponding tapered support shoulder  33   c  formed on the diffuser  27  to thereby transmit thrust from the downstream impeller  29  to the diffuser  27 . The outer diameter of bottom shoulder  42  is less than the outer diameter of the upper portion  33   d  of the bore, defining the lower end of tapered shoulder  45  of the thrust bearing base  37 . The upper end of tapered shoulder  45  joins a cylindrical surface on thrust bearing base  37 . The cylindrical surface mates with surfaces  33   d  in diffuser  27 . The lower side of thrust bearing base  37  is thus generally convex and thus conforms to the upper side portions,  33   b ,  33   c  and  33   d , of diffuser  27 . Although the lower side of thrust bearing base  37  is generally convex and the mating upper side of diffuser  28  generally concave, other shapes are feasible. The bearing base  37  is suitably bonded to diffuser  28 . 
     The upper or downstream side  43  of thrust bearing base  37  terminates substantially flush with the outlet of passages  31 . A generally concave thrust face  41  is formed on the downstream or upper side of thrust bearing base  37 , with a curvature extending from an inner diameter of the thrust bearing base  37  to a rim  43  at the downstream end of the thrust bearing base  37 . Concave thrust face  41  is shaped similar to the lower side portions  42 ,  45  of thrust bearing base  37  providing a substantially uniform thickness for thrust bearing base  37 . In this embodiment, concave thrust face  41  is a portion of a sphere. 
     In this embodiment a thrust runner  57  has an upstream or lower convex end  48  that mates with and rotatably engages the corresponding, concave thrust face  41  of the thrust bearing base  37 , as shown in  FIG. 3 . The thrust runner  57  transmits downward axial thrust from the downstream impeller  29  to the diffuser  27  via a sleeve  51  in contact with both impeller  29  and thrust runner  57 . Sleeve  51  may have a cylindrical flat lower end  59  that is in contact with a downstream side  59  of the thrust runner  57 . 
     A downward extending impeller hub  65  of the adjacent downstream impeller  29  or a spacer (not shown) if used, contacts the upper end of sleeve  51 . The adjacent upstream impeller  28  has an upward extending hub  67  that fits in an annular space defined by the lower bore portion  33   a  and a portion of thrust bearing base  37 . The upper end of hub  67  does not contact thrust bearing base shoulder  42 . Sleeve  51  and thrust runner  57  are keyed to the shaft  35  to cause sleeve  51  and thrust runner  57  to rotate with shaft  35 . Sleeve  51  and thrust runner  57  are free to move axially on shaft  35  a limited distance that is defined by axial movement of the downstream impeller  29 . In this embodiment, the axial length of sleeve  51  is more than the axial length of the thrust bearing base  37 . Sleeve  51  and thrust runner  57  could be integrally joined to each other. 
     The convex and concave surfaces  48 ,  41  of the thrust runner  57  and the thrust bearing base  37 , respectively, provide a greater surface area for handling larger axial loads than a flat surface. As shown in  FIG. 5 , downward thrust transmitted to thrust bearing base  37  has an outward or radial component because of the concave/convex curvature of the mating surface of thrust runner  57  and thrust bearing base  37 . The surface area of the convex upstream side  48  of the thrust runner  57  is substantially the same as the surface area of the concave thrust face  41  of thrust bearing base  37 . As shown in  FIGS. 3 and 4 , spiral or helical grooves  55  may be formed on convex side  48  of thrust runner  57 . Grooves  55  facilitate the introduction of lubricant between the thrust runner  57  and the thrust bearing base  37 . Grooves  55  may be parallel to each other and curve from the lower to upper side of thrust runner  57 . Alternately, grooves  55  could be formed in concave face  41  of thrust bearing base  37 . In this embodiment, an internal key slot  63  ( FIGS. 5 and 6 ) in thrust runner  57  receives a key (not shown) on the shaft  35  to cause rotation of thrust runner  57 . 
     Thrust bearing base  37 , sleeve  51  and thrust runner  57  may be constructed of a harder and more wear resistant material than the material of diffusers  27  and impellers  28 ,  29 . In a preferred embodiment, the material comprises a carbide, such as tungsten carbide. Tungsten carbide provides better abrasion resistance against abrasive materials such as sand than the material of diffuser  27  and impeller  28 ,  29 . 
     In operation, motor  23  ( FIG. 1 ) rotates shaft  35  ( FIG. 2 ), which in turn causes impellers  28 ,  29 , thrust runner  57  and sleeve  51  to rotate. The rotation of impellers  28 ,  29  causes fluid to flow through impeller passages  30  and diffuser passages  31 . The fluid pressure of the flowing fluid increases with each pump stage. Impellers  28 ,  29  are keyed to shaft  35  for rotation, but not fixed to shaft  35  axially. Downward axial thrust exerted by the pumping action is applied by each impeller  28 ,  29 . The lower end of hub  65  of the downstream impeller  29  transmits the axial thrust through rotating thrust runner  57  into the stationary thrust bearing base  37 . The axial thrust and a radial component transfers through diffuser  27  to the diffuser (not shown) located below it, and eventually to the lower end of pump housing  25 . 
     Under some circumstances, up thrust occurs, causing hub  67  of upstream impeller  28  to move upward into contact with an upstream facing shoulder on the lower portion  33   a  of the diffuser  27 . The upward force transfers from the diffuser  27  and into housing  25 . 
     If desired, each stage could have one of the thrust bearing bases  37 , thrust runners  57 , and sleeve  51 . Alternately, as shown in  FIG. 7  some of the stages could be of conventional type, not having a thrust runner, thrust bearing, or sleeve as described. Spacer sleeves  69  are located between the impeller hubs  57  of these conventional stages and thrust sleeves  51  to the next stage having a thrust runner  57  and thrust bearing base  37  as described. A thrust runner  57  and thrust bearing base  37  arrangement identical to that described previously is installed within one of the stages. An additional thrust bearing base  80  and a thrust runner  82  is located within a diffuser  84  located downstream of the upstream thrust  57  runner and bearing base  37 . Two conventional stages  71 ,  73  are located between thrust bearing base  80  and thrust bearing base  37 . Downward thrust from the stage  71  passes through its thrust sleeve  51  and spacer  69  to stage  73 . The thrust is passed from stages  73  through hub  67  to thrust sleeve  51 , thrust runner  57  and thrust bearing base  37  to the associated diffuser  27 . This arrangement provides additional thrust handling capacity in the ESP  15 . 
     In yet another embodiment illustrated in  FIG. 8 , opposite-facing thrust bearing and runner arrangements are shown. The upstream thrust bearing base and runner  37 ,  57  handling down thrust is identical to a previously discussed embodiment and transfers the down thrust to the diffuser  27 . A downstream thrust bearing base  90  is installed within a downward-facing side of diffuser  94 , and an up thrust runner  92  rotatably engages thrust bearing base  90 . The downstream arrangement is identical to the upstream arrangement, however the downstream thrust bearing base  90  and thrust runner  92  are installed in a direction that faces the upstream arrangement and handles up thrust. An upper end of the hub  67  of the adjacent impeller  28  abuts the lower side of thrust runner  92  to transfer upward thrust. The arrangement described in this embodiment, may thus handle either up thrust or down thrust. In addition, if either thrust runner becomes disengaged from a thrust bearing, the other engaged thrust runner will still be capable of handling thrust. In the embodiment of  FIG. 8 , spacer  69  transmit both down thrust and up thrust between hubs  67  and thrust runner  51 . 
     The invention has significant advantages. The thrust bearing provides transfers both thrust axial and radial component to the diffuser. The thrust bearing base and runner also provide radial support for the shaft. The thrust faces are considerably larger in cross-sectional area than flat face due to the curved surfaces employed. More thrust can be handled in less height because individual bearings for handling radial loads are not required. The decrease in parts also lowers cost and increases reliability. 
     While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible o various changes without departing from the scope of the invention.