Abstract:
An electrical submersible pump (ESP) having a sleeve coupled to the shaft that rotates as the shaft rotates. The sleeve can be a base portion of a pump impeller, a journal bearing, or a bushing. A drive collar mounts around the shaft and has an end with a portion that projects past an end of the sleeve profiled to correspond with the shape of the projecting portion. As the shaft rotates the drive collar the projecting portion of the drive collar pushes against the profiled end of the sleeve to rotate the sleeve. The projecting portion can be a wedge shaped tab on the drive collar, or an angular segment of the drive collar extending axially past the remaining segments. The profiled end of the sleeve can include a recess formed to receive the tab and can have an angular segment corresponding to that on the drive collar.

Description:
BACKGROUND 
       [0001]    1. Field of Invention 
         [0002]    The present disclosure relates to downhole electric submersible pump (ESP) systems that are submersible in wellbore fluids. More specifically, the present disclosure involves a device and method for coupling a sleeve to a shaft so that the shaft transmits a rotational force to the sleeve without imparting angular deflections in the shaft to the sleeve. 
         [0003]    2. Description of Prior Art 
         [0004]    Submersible pumping systems are often used in hydrocarbon producing wells for pumping fluids from within the wellbore to the surface. These fluids are generally liquids and include produced liquid hydrocarbon as well as water. One type of system used employs an electrical submersible pump (ESP). ESPs are typically disposed at the end of a length of production tubing and have an electrically powered motor. Often, electrical power may be supplied to the pump motor via a cable. The pumping unit is usually disposed within the well bore just above where perforations are made into a hydrocarbon producing zone. This placement thereby allows the produced fluids to flow past the outer surface of the pumping motor and provide a cooling effect. 
         [0005]    With reference now to  FIG. 1 , shown in a partial sectional view is a cased wellbore  8  having an ESP system  10  disposed therein. The ESP system  10  is made up of a motor  12 , a seal section  14 , and a pump  16  and is disposed within the wellbore  8  on production tubing  18 . Seal section reduces a pressure differential between wellbore fluid and lubricant in motor  12 . Energizing the motor  12  drives a shaft coupled between the motor  12  and the pump section  16 . The source of the fluid drawn into the pump comprises perforations  20  formed through the casing of the wellbore  10 ; the fluid is represented by arrows extending from the perforations  20  to the pump inlet. The perforations  20  extend into a surrounding hydrocarbon producing formation  22 . Thus the fluid flows from the formation  22 , past the motor  12  on its way to the inlets. 
         [0006]    Traditionally, ESP systems  10  include bearing assemblies along the shafts in the motor section, seal section, and pump. Often, the bearings are plain sleeve bearings that provide radial support. One example of a bearing assembly provided in a motor section is provided in a cross sectional view in  FIG. 2 . Shown is a shaft  24  with an outer sleeve  26  that is circumscribed by a stator stack  28 . The sleeve  26  couples to the shaft  24 , such as by a key  27 , and rotates along with the shaft  24 . A housing  30  encases the outer circumference of the stator stack  28 . A bearing assembly  32  is set between the outer sleeve  26  and stator stack  28  that radially encompasses a portion of the sleeve  26 . The motor bearing assembly  32  may have an insert  34  mounted on the outer circumference of the sleeve  26 ; a bearing carrier  36  encircles the insert  34  and in the absence of an insert directly mounts on the shaft sleeve. A T-ring  38  may be included that mounts to the inner surface of the stator stack  28  for preventing bearing rotation. The sleeve  26 , and therefore the shaft  24 , is radially supported by the insert  34  or the bearing carrier  36 . A lubricant film (not shown) allows for sleeve  26  rotation within the insert  34  or the bearing carrier  36 . 
         [0007]    Referring to  FIG. 3 , shown in a side sectional view is a prior art example of bearings in a pump section of an ESP system. Diffusers  40  are typically coaxially stacked in close contact within a housing  30 . An impeller  42  is stacked between each successive diffuser  40 , where each impeller  42  is coupled to and rotates with the shaft  24 . Passages  44  curve radially and lengthwise throughout the diffusers  40  that register with passages  46  that similarly curve radially and lengthwise through the impellers  42 . Rotating the shaft  24 , and thus the impellers  42 , forces fluid through the passages  44 ,  46  to pressurize the fluid as it passes along the stack of diffusers  40  and impellers  42 . A sleeve bearing  48  couples around and rotates with the shaft  24  to provide a bearing surface between the shaft  24  and inner circumference of the diffusers  40 . As the shaft  24  rotates, a film of lubricating fluid is maintained between the bearing  48  and diffuser  40 . A key  27  is used for securing the impellers  42  to the shaft  24 . The sleeve  26 , impeller  42 , and/or bushings (not shown) that mount to the shaft  24  are typically formed from a hard brittle material such as tungsten carbide or cermets. The shaft  24  is generally made from a more elastic material (i.e. steel) and during high torque conditions, such as pump start up, the shaft  24  can angularly deform along its axis (twist). If the shaft  24  deformation is adjacent where it couples to a sleeve  26  or impeller  42 , the twist is transferred via the key  27  to the sleeve  26  or impeller  42  to concentrate stresses therein and create fractures. 
       SUMMARY OF INVENTION 
       [0008]    The present disclosure describes example embodiments of an electrical submersible pump (ESP). In one embodiment the ESP includes a drive collar mounted to a shaft, where the drive collar engages a sleeve so that when the shaft rotates it rotates the drive collar that in turn rotates the sleeve. The drive collar rotates the sleeve without transmitting stress to the sleeve from torsion in the shaft. The sleeve has an end that engages an end of the drive collar. The engaging ends of the sleeve and drive collar are made such that either the sleeve or drive collar can slide with respect to one another, but an area of contact is maintained between the drive collar and the sleeve. Example embodiments exist where the sleeve can be a journal bearing, a base portion of an impeller, or a bushing. A wedge shaped protrusion is provided on the end of the drive collar for engaging the annular sleeve by axially inserting into a recess provided on the end of the sleeve; in this example contact between the protrusion and the recess define the interface. In an example embodiment, lateral edges of the protrusion and the recess are beveled to increase the area of contact between the drive collar and the sleeve. In an example embodiment, the interface is in a plane oblique to an axis of the shaft. In an example embodiment, at least a portion of the respective ends of the sleeve and the drive collar in engagement are beveled at an angle oblique to the axis. In an example embodiment, the material of the drive collar is more elastic than the material of the sleeve so that when the shaft experiences circumferential deflection, the sleeve is isolated from the deflection by the drive collar. 
         [0009]    Also disclosed herein is an example of a submersible pump that includes a drive shaft driven by a motor, and an annular drive collar mounted on the shaft that rotates with the shaft and can slide along the shaft. The drive collar has an engaging end where at least a portion has a generally linear profile oriented oblique to an axis of the shaft. Also included on the shaft is an annular sleeve that also has an engaging end, a portion of which is configured with a generally linear profile that corresponds to the profile on the engaging end of the drive collar. When the engaging ends of the drive collar and sleeve are mated, the engaging ends are in contact along an interface that maintains a defined area with axial relative movement between the sleeve and the drive collar. In an example embodiment, the engaging end of the drive collar is a wedge shaped member axially protruding from a portion of a circumference of the engaging end of the drive collar. In an example embodiment, the engaging end of the sleeve is a wedge shaped recess configured to receive the member of the drive collar. In an example embodiment, the member has lateral edges that are beveled thereby increasing the area of the interface. In an example embodiment, the engaging end of the drive collar approximates a circle, and wherein the portion of the engaging end of the drive collar on a side of a line bisecting circle project past the portion of the engaging end of the drive collar on an opposing side of the line. In an example embodiment, the engaging end of the sleeve is profiled to correspond to the engaging end of the drive collar, so that the interface lies in a plane that is oblique to the axis. In an example embodiment, a terminal surface on the engaging end of the drive collar is profiled so that an angle between the collar terminal surface and axis varies along a circumference of the engaging end of the drive collar. In an example embodiment, a terminal surface on the engaging end of the sleeve is profiled so that an angle between the sleeve terminal surface and axis varies along a circumference of the engaging end of the sleeve. In an example embodiment, the drive collar is formed from a material that is more elastic than a material of the sleeve. In an example embodiment, a key slot extends from within the shaft and into the drive collar and a key in the key slot mounts the drive collar to the shaft. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]    Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: 
           [0011]      FIG. 1  is a side partial sectional view of a prior art submersible pumping system disposed in a wellbore. 
           [0012]      FIGS. 2 and 3  are a side sectional views of prior art bearing systems for use in a submersible pumping system. 
           [0013]      FIGS. 4A and 5A  are side sectional views of respective embodiments of a driver bushing and a driven bushing in accordance with the present disclosure. 
           [0014]      FIGS. 4B and 5B  are end views respectively of the bushings of  FIGS. 4A and 5A . 
           [0015]      FIG. 6  is an enlarged side view of a portion of the bushings of  FIGS. 4A and 5A . 
           [0016]      FIGS. 7A and 7B  are side sectional views of an alternate embodiment of the bushings of  FIGS. 4A and 5A . 
           [0017]      FIG. 8  is a side sectional view of an alternate embodiment of a drive bushing and a driven bushing. 
           [0018]      FIG. 9  is a side sectional view of an alternate embodiment of a drive bushing and a driven bushing. 
           [0019]      FIG. 10  is an example embodiment of a pumping system having the drive and driven bushings in accordance with the present disclosure. 
       
    
    
       [0020]    While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION OF INVENTION 
       [0021]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments of the invention are shown. This invention may, however, be embodied 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 the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. 
         [0022]    A side sectional view of an example embodiment of a driver collar  52  is provided in  FIG. 4A . In this example, the collar  52  is shown as a generally annular member and having an optional keyway  54  formed axially along a portion of its inner surface. Registering the keyway  54  with a keyway on a shaft (not shown), the driver collar  52  can be rotated by rotation of the shaft while allowing the driver collar  52  to axially move along the shaft. The driver collar  52  is further shown having a wedge-shaped tooth  56  protruding from its upper end. The thickness of the tooth  56  is approximately the same as the thickness of the side wall of the driver collar  52 . The width of the tooth  56  can vary depending on its application and embodiments exist wherein the width of the tooth  56  ranges from about 5% to about 20% of the circumference of the driver collar  52 .  FIG. 4B  is an overhead view of the driver collar  52  showing a tooth  56  on opposing sides of the driver collar  52  and approximately 180 degrees from one another. Example embodiments exist wherein the driver collar  52  has a single tooth  56  or more than two. 
         [0023]      FIG. 5A  illustrates a side sectional view of a sleeve  58 , that as will be described in more detail below, is driven by the driver collar  52 . More specifically, the sleeve  58  is a generally annular member and as shown has a recess  60  formed along the terminal end of the sleeve  58  that faces the driver collar  52 . A plan view of the lower end of the sleeve  58  is shown in  FIG. 5B  wherein another recess  60  is shown on the lower end of the sleeve  58  at about 180 degrees apart from the first recess  60 . As will be described in further detail below, the driver collar  52 , which attaches to a shaft, is rotated with a shaft rotation that in turn rotates the sleeve  58  by contact between the tooth  56  and recess  60 . 
         [0024]    Example embodiments exist wherein the driver collar  52  is formed from a material that is more elastic than the material used for forming the sleeve  58 . Example materials for the sleeve include tungsten carbide and/or cermet. Example materials for the driver collar  52  include carbide or iron alloys having nickel content ranging from 14 to 25% by weight. 
         [0025]    An example embodiment of the tooth  56  and recess  60  of  FIGS. 4A and 5A  is shown in a side perspective view in  FIG. 6 . The tooth  56  is shown having lateral edges  62  that extend from an upper end  64  of the driver collar  52  up to a crest  66  that defines the upper terminal end of the tooth  56 . The lateral edges  62 , as illustrated by the dashed line, are beveled at angles that depend towards a mid-portion of the tooth  56 . Similarly, the recess  60  has lateral edges  68  shown extending from a lower end of the sleeve  58  and joining at a base  72  defined at the upper end of the recess  60 . The lateral edges  68  of the recess  60  are also beveled and depend in a direction towards the mid-portion of the recess  60  and so that the lateral edges  68  of the recess  60  correspond with the beveled lateral edges  62  of the tooth  56 . An advantage of the beveling of the lateral edges  62 ,  68  on the driver collar  52  and sleeve  58  is to increase the area along which the tooth  56  and recess  60  contact (also referred to herein as an interface), thereby reducing localized concentrated stresses. Further, the profiles of the lateral edges  62 ,  68  are shown as being a generally linear path so that during use, one of the driver collar  52  or sleeve  58  may move in an axial direction with respect to the other while still maintaining an area of contact interface between the driver collar  52  and sleeve  58 . That is, as shown in  FIG. 6 , beveling is apparent along lateral edge  68 , whereas lateral edge  62  appears flat. It should be pointed out that the respective contours of the lateral edges  62 ,  68  are such that when and if the driver collar  52  and sleeve  58  axially reciprocate back and forth, the lateral edges  62 ,  68  continue to remain in contact along a defined area rather than a contact point. Some prior art designs, such as those having a wave-type profile, contact along a point when being axially reciprocated, which can produce highly concentrated stress loads that may lead to fracture of one or more of the components. In an example, compressive forces exist along a major portion of the driving or contact surface. Stress concentrations can develop in the corners and can be troublesome if left sharp; which can be alleviated with radiuses at these corners, whose surfaces may be described by rays perpendicular to the axis. 
         [0026]      FIGS. 7A and 7B  are side sectional views of alternate embodiments of a driver collar  52 A and sleeve  58 A. In the example embodiment of  FIGS. 7A and 7B , the driver collar  52 A includes a tooth  56 A projecting from an upper end  64 A and having a bevel on a lateral edge  62 A. Unlike the embodiment of  FIG. 6 , the bevel on lateral edge  62 A angles inward towards the middle portion of the tooth  56 A with travel from the outer surface of the driver collar  52 A. In the example embodiments of  FIGS. 7A and 7B , the inwardly projecting lateral edges  62 A angle inward in the direction from outer surface of the driver collar  52 A towards an inner surface of the driver collar  52 A. Similarly, the sleeve  58 A of  FIGS. 7A and 7B  includes a recess  60 A on its lower end  70 A with beveled lateral edges  68 A that, as shown by the dashed line, angle outward away from one another in a direction from the inner surface of the sleeve  58 A towards the outer surface of the sleeve  58 A. Referring to  FIG. 7B , the angle of the beveling of the lateral edges  62 A,  68 A can be seen wherein the line of the interface projects away from an upper end  73 A of the sleeve  58 A with distance from the outer surfaces of the sleeve  58 A and driver collar  52 A. Alternate embodiments exist, wherein different teeth and/or recesses provided respectively on the driver collar  52 ,  52 A and sleeve  58 ,  58 A may alternate in the direction of projection from the outer to inner surfaces of these annular members. In one example, malleable materials are used to form the drive collar  52  and more brittle materials make up the sleeve  58 , the difference in the plasticity between the materials can allow the more malleable member to act like a wedge and built tensile stresses in locations such as the corner  72 . To alleviate the concentration of tensile stress the driving surface can be cut at a constant angle to the shaft axis rather than a perpendicular ray, as shown in  FIGS. 7A and 7B . The angle can be such that the malleable surface will be angled radially outward and at the interface so that, along with the compressive force at the face from the torque and thrust, it will develop a radially inward compression force as the malleable drive collar  52  inward on the sleeve  58 . 
         [0027]    In  FIG. 8 , alternate embodiments of a driver collar  52 B and sleeve  58 B are illustrated in a side sectional view. In this example, the terminal ends of the driver collar  52 B and sleeve  58 B that engage one another are angled so that when in contact they form an interface that runs generally oblique to an axis A X  of the driving collar  52 B and sleeve  58 B. The angled profile shown in  FIG. 8  produces opposing ends wherein approximately one half of the circumference of each end protrudes past the other half. For example, when viewed from the sleeve  58  and along the axis A X , if end of the driver collar  52 B is bisected with a line (not shown) that projects perpendicular to the figure, the length of projection increases with distance away from the bisecting line. In contrast, the shorter side is truncated with distance away from the bisecting line. This in turn defines a heel side  74 , i.e., a shorter side of the engaging end of the driver collar  52 B, and a toe side  76  defined along the axially longer side of the engaging end of the driver collar  52 B. Similarly, a heel side  78  and a toe side  80  is provided on the sleeve  58 B, wherein the heel side  74  is substantially aligned with the toe side  80  and the toe side  76  is aligned with the heel side  78 . As such, when the driver collar  52 B and the sleeve  58 B are brought into axial contact, an interface is formed between the driver collar  52 B and sleeve  58 B that runs oblique to the axis A X . 
         [0028]    In the embodiment of  FIG. 8 , the drive collar  52 B is cut in the shape of a helical spiral and can allow axial and radial displacement between the drive collar  52 B and sleeve  58 B and still maintain a surface to surface contact. This helical shape can maintain surface to surface contact for torque and thrust transmission to the sleeve  58 B even with radial/axial displacement. In an example, the helix of  FIG. 8  can have a pitch in excess of about 30°. In an embodiment, the respective contacting surfaces of the sleeve  58 B and drive collar  52 B follow a spiral helix path progressing “up” (along the shaft in the axial direction for 180° of rotation), then proceed back “down” the shaft to complete a full rotation at the point where it began. In one example, the contacting surface is coplanar with a radial rays perpendicular to the axis of the sleeve  58 B and drive collar  52 B. In an embodiment, an axial length is comparable to half the diameter of the sleeve  58 B. Alternatively, the aforementioned contact surface can be set on one or more “teeth” projecting from the end of the sleeve/driver and aligning with matching slots in its mating part ( FIG. 4A ). 
         [0029]    Optionally, the upper end  64 B of the driver collar  52 B may be profiled so that it is oriented at an angle with the axis A X , wherein the angle can vary with respect to the angular location on the driver collar  52 B around the axis A X . A similar beveling is shown on the lower end  70 B of the sleeve  58 B that corresponds with the beveling on the upper end  64 B of the driving collar  52 B. Beveling the ends  64 B,  70 B increases the area of contact between the driver collar  52 B and sleeve  58 B over that of ends that are not beveled. A keyway  54 B is shown on an inner surface of the driver collar  52 B. 
         [0030]      FIG. 9  depicts in side sectional view an alternate embodiment of a sleeve coupling where a driver collar  52 C and sleeve  58 C are shown with opposing upper and lower ends  64 C,  70 C that are angled similar to the upper and lower ends  64 B,  70 B of  FIG. 8 . The upper and lower ends  64 C,  70 C run generally perpendicular between the respective inner and outer surfaces of the driver collar  52 B and sleeve  58 B thereby lacking the beveling of  FIG. 8 . Thus, the upper and lower ends  64 C,  70 C remain substantially within a plane intersecting the axis A X  at an oblique angle. 
         [0031]      FIG. 10 , a side sectional view of an electrical submersible pump assembly  82  is illustrated. In this example embodiment, the pump assembly  82  includes a body  84  on its outer circumference for housing a stack of diffusers  86  set within the housing with impellers  88  alternatingly set between the diffusers  86 . The impellers  88  are coupled to and driven by a shaft  90 , so that when rotated, the impellers  88  pressurize and move fluid through the pump assembly  82 . A key  92  is shown mounting an example embodiment of a driver collar  52  onto the shaft  90 . The driver collar  52  axially couples with a hub portion of the impeller  88  in one of the embodiments of  FIGS. 4A through 9 , so that as the driver collar  52  is rotated by rotation of the shaft  90 , the impeller  88  also is rotated. An example interface  94  is illustrated along a line of contact between the driver collar  52  and impeller  88 . Optionally, the coupling configurations described above may be employed in the assembly of  FIG. 2  so that a sleeve  26  may be indirectly driven by the shaft  90 , thus when torque on the shaft causes the shaft to angularly displace along its axial length, the angular displacement is absorbed by the more elastic driver collar  52  and not by the more brittle sleeve, impeller base, or bushing. As the shaft  90  twists, the drive collar  52  may rotate slightly relative to the sleeve  26 . This causes the sleeve  26  to move axially slightly relative to the drive collar  52 . 
         [0032]    It is to be understood that the invention 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 of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation.