Abstract:
A submersible pumping system, electrical submersible pump, and method of providing enhanced alignment of motor and driven shafts of submersible pumping systems and electrical submersible pumps, are provided. An example of an electrical submersible pump system includes a pump, a pump motor, and a seal section. The motor drives the pump via motor and driven shafts rotatingly coupled with a coupling assembly. The coupling assembly maintains the shaft ends in coaxial alignment with an alignment device. The alignment device is profiled on opposite ends for mating engagement with the centering profiles extending into the shaft ends.

Description:
RELATED APPLICATIONS 
     This application is a continuation of and claims priority to and the benefit of U.S. patent application Ser. No. 12/332,717, filed Dec. 11, 2008, which is a continuation-in-part of and claims priority to and the benefit of U.S. patent application Ser. No. 12/125,350, filed May 22, 2008, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates in general to electrical submersible well pumps, and in particular to couplings between splined shafts of submersible pumping systems and methods of providing enhanced alignment of motor and driven shafts of submersible pumping systems and electrical submersible pumps. 
     2. Description of the Related Art 
     Electrical submersible pumps (ESP) are commonly used for hydrocarbon well production,  FIG. 1  provides an example of a submersible pumping system  10  disposed within a wellbore  5 . The wellbore  5  is lined with casing  4  and extends into a subterranean formation  6 . Perforations  9  extend from within the wellbore  5  through the casing  4  into the formation  6 . Hydrocarbon fluid flow, illustrated by the arrows A, exits the perforations  9  into the wellbore  5 , where it can either be pumped by the system  10  or migrate to a wellhead  12  disposed on top of the wellbore  5 . The wellhead  12  regulates and distributes the hydrocarbon fluid for processing or refining through an associated production line  7 . 
     The pumping system  10  includes an electrical submersible pump (ESP)  14  with production tubing  24  attached to its upper end. The ESP  14  comprises a motor  16 , an equalizer or seal  18 , a separator  20 , and a pump  22 . A fluid inlet  26  is formed in the housing in the region of the ESP  14  proximate to the separator section  20 . The fluid inlet  26  provides a passage for the produced hydrocarbons within the wellbore  5  to enter the ESP  14  and flow to the pump  22 . Fluid pressurized by the pump  22  is conveyed through the production tubing  24  connecting the ESP  14  discharge to the wellhead  12 . The pump  22  and separator  20  are powered by the motor  16  via a shaft (not shown) that extends from the motor  16 . The shaft is typically coupled to respective shafts in each of the pump  22 , separator  20 , and seal  14 . 
     Delivering the rotational torque generated by an ESP motor  16  typically involves coupling a motor shaft (i.e., a shaft connected to a motor or power source) to one end of a driven shaft, wherein the other end of the driven shaft is connected to and drives rotating machinery. Examples of rotating machinery include a pump, a separator, and tandem pumps. One type of coupling comprises adding splines on the respective ends of the shafts being coupled and inserting an annular collar over the splined ends, where the annular collar includes corresponding splines on its inner surface. The rotational force is well distributed over the splines, thereby reducing some problems of stress concentrations that may occur with keys, pins, or set screws. Examples of a spline cross-section include an involute and a square tooth. Typically, splines having an involute cross-section are smaller than square tooth splines, thereby leaving more of the functional shaft diameter of a shaft to carry a rotational torque load. Additionally, involute spline shapes force the female spline to center its profile on the male spline, thus coaxially aligning the shafts in the coupling with limited vibration. Square tooth splines are made without specialized cutters on an ordinary mill. However square teeth spline couplings do not align like involute teeth unless the clearance is reduced or the male and female fittings are forced together. However, reducing clearance or force fitting square teeth splines prevents ready assembly or disassembly. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, various embodiments of the present invention provide a submersible pumping system for pumping wellbore fluid. An example of a submersible pumping system includes a pump motor, an equalizer or seal section, a motor shaft having a splined end positioned within one end of the shaft coupling, and a driven shaft having a splined end positioned within an opposite end of the shaft coupling opposite to the motor shaft. The driven shaft is driven by the motor shaft via the splined shaft coupling. A centering profile is bored into the terminal end of the motor shaft and into the terminal end of the driven shaft to provide for dynamic aligning of the respective shafts. An alignment element is positioned within the shaft coupling. The alignment element includes a pair of opposite oriented centering guides coaxially engaging the centering profiles extending into the respective terminal ends of the motor shaft and driven shaft positioned within the shaft coupling. The pair of centering guides can comprise a pair of conically shaped protrusions extending from the upper and lower surfaces of the alignment element body. A resilient member may be included within the body of the alignment element. During rotation, the splined ends of the motor shaft and driven shaft are held substantially coaxial within the splined shaft coupling even when manufacturing has placed them at the outer limits of normal tolerances for square tooth splined shaft couplings. Advantageously, the splined ends of the motor and driven shafts can be easily separated from within the splined shaft coupling to allow for ready assembly and disassembly. 
     Various embodiments of the present invention can also include an electrical submersible pump (ESP) including a pump, a pump motor, an equalizer or seal section connected between the pump and the pump motor, a motor shaft mechanically affixed to the pump motor, and a driven shaft driven by the motor shaft. The motor shaft has a splined end portion including a plurality of elongate square tooth spines formed thereon, and has a terminal end portion including a tapered centering profile extending therein, being coaxial with an axis of the motor shaft. The driven shaft has a splined end portion including a plurality of elongate square tooth spines formed thereon, and has a terminal end portion including a tapered centering profile extending therein, being coaxial with an axis of the driven shaft. A splined shaft coupling assembly rotatingly couples the splined ends of the motor shaft and the driven shaft. An alignment element is mounted in portions of the splined shaft coupling assembly. The alignment element includes a tapered centering guide on one side that mates with the tapered centering profile on the motor shaft and a tapered centering profile on an opposite side that mates with the tapered centering profile on the driven shaft. The tapered centering profiles and the tapered centering guides are conical and of substantially same dimensions. 
     Various embodiments of the present invention also include methods of providing enhanced alignment of motor and driven shafts of a submersible pumping system having male square tooth splined ends. This is advantageously performed without reducing clearance between male and female square tooth splines or force fitting the male square tooth splines within the female square tooth splines. Such methods can provide for ready assembly or disassembly of the splined ends of a motor shaft and driven shaft from within a splined shaft coupling. An example of such a method can include the steps of providing a centering profile on each splined shaft end, mounting an alignment element within a splined shaft coupling configured for rotatingly coupling respective splined ends of the motor shaft and the driven shaft, and inserting the splined shaft ends into the splined shaft coupling and engaging oppositely oriented centering guides on the alignment element with the inner surfaces of the centering profiles on the splined shaft end. To facilitate engagement of the centering guides with the centering profiles to thereby maintain coaxial alignment of the shaft ends, each centering guides can comprise a conically shaped protrusion and each centering profile can comprise a conically shaped recess or for having a conically shaped entrance. Optionally, the compressible alignment element may comprise a tolerance ring. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features and advantages of the invention, as well as others which will become apparent, may be understood in more detail, a more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof which are illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the drawings illustrate only various embodiments of the invention and are therefore not to be considered limiting of the invention&#39;s scope as it may include other effective embodiments as well. 
         FIG. 1  is a side view of a prior art submersible electrical pumping system in a wellbore. 
         FIG. 2   a  is an exploded view of a shaft coupling for use with the system of  FIG. 1 . 
         FIG. 2   b  is an assembled view of the shaft coupling of  FIG. 2   a.    
         FIG. 3   a  is an exploded view of an alternative shaft coupling for use with the system of  FIG. 1 . 
         FIG. 3   b  is an assembled view of the shaft coupling of  FIG. 3   a.    
         FIG. 4   a  is an exploded view of an alternative shaft coupling for use with the system of  FIG. 1 . 
         FIG. 4   b  is an assembled view of the shaft coupling of  FIG. 4   a.    
         FIG. 5  is a side partial cut-away view of an alternative shaft coupling for use with the system of  FIG. 1 . 
         FIG. 6  is a side partial cut-away view of an alternative shaft coupling for use with the system of  FIG. 1 . 
         FIG. 7  is a perspective view of an embodiment of an alignment member. 
         FIG. 7A  is an end sectional view of the alignment member of  FIG. 7 . 
         FIG. 8  is a side partial sectional view of the alignment member of  FIG. 7  engaged with opposing shafts. 
         FIG. 9  is a perspective view of an embodiment of a tolerance ring. 
         FIG. 10  is a side partial sectional view of the tolerance ring of  FIG. 9  disposed between a shaft and a shaft coupling. 
     
    
    
     DETAILED DESCRIPTION 
     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. For the convenience in referring to the accompanying figures, directional terms are used for reference and illustration only. For example, the directional terms such as “upper”, “lower”, “above”, “below”, and the like are being used to illustrate a relational location. 
     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. Accordingly, the invention is therefore to be limited only by the scope of the appended claims. 
     The present disclosure includes a description of a submersible pumping system including a square tooth spline coupling with vibration control. The coupling disclosed herein provides sufficient clearance between the respective male and female splines providing ready assembly and disassembly. With reference now to  FIG. 2   a , an exploded side partial cutaway view of one embodiment of a coupling assembly and respective shafts is provided. As noted above, during operation of a pumping assembly, a motor shaft is powered by a pump motor, either directly or through a shaft coupling. The coupling assembly provides a manner of connecting the motor shaft to a driven shaft that drives rotating machinery. The coupling connection also transfers rotational energy between the motor and driven shaft, thus providing power for the rotating machinery. Thus with respect to couplings described herein, the term motor shaft includes any shaft mechanically coupled to the motor that is being coupled to a driven shaft. As such, embodiments exist where one end of a rotating shaft is a driven shaft coupled to a motor shaft and the other end of the rotating shaft is a motor shaft coupled to a driven shaft. Accordingly, ESP systems may include the couplings of the present disclosure at any shaft connection within the system and ESP systems may include multiple couplings of the present disclosure. 
     The coupling assembly  30  of  FIG. 2   a  comprises an annular collar  48  with a bore  50  formed lengthwise therein. Female splines  52  extend axially along the bore  50  inner surface. The bore  50  diameter transitions at a point to form a shoulder  56  that is substantially perpendicular to the collar  48  axis A X . An alignment element  54  is on the shoulder  56 . In the embodiment shown, the alignment element  54  has a disc-like midsection and disposed in the collar  48  with its midsection axis (not shown) largely aligned with or parallel to the collar axis A X . The alignment element  54  outer diameter exceeds the shoulder  56  inner diameter and its lower side abuts on the shoulder  56 . The outer diameter fits closely in the bore  50 . An insert or sleeve  60  is coaxially received within the collar  48  in the portion of the bore  50  having an increased diameter. The insert  60  extends from the upper surface of the alignment member  54  terminating at the upper end of the collar  48 . The insert  60  is optionally threaded on its outer diameter to mate with corresponding threads provided on the collar  48  inner diameter. Female splines  52  are formed along the insert  60  inner diameter. Positioning the insert  60  against the alignment element  54  toward the shoulder  56 , retains the alignment element  54  within the collar  48 . 
     Centering guides ( 62 ,  63 ) are shown extending from the upper and lower surface of the alignment element  54 . In this embodiment, the centering guides ( 62 ,  63 ) comprise conically shaped protusions. Above and below the coupling assembly  30  are an upper shaft  32  and lower shaft  40 . The upper shaft  32  lower end  36  is provided with male splines  34  configured for coupling engagement with the female splines  52  of the coupling assembly  30 . Similarly, the lower shaft  40  upper end  44  includes male splines  42  configured for coupling engagement with the female splines  52 . The shafts ( 32 ,  40 ) are profiled on their terminal ends for centering engagement with the centering guides ( 62 ,  63 ) of the alignment element  54 . In the embodiment shown, the profiling on the shafts comprises recesses or bores ( 38 ,  46 ) extending from the terminal mating tips of the shafts and substantially aligned with the respective axes (A SH , A SL ) of the upper or counterbore lower shafts ( 32 ,  40 ). Each recess ( 38 ,  46 ) has a conical entry way with a taper matching the centering guides ( 62 ,  63 ). The recess and protrusion provide examples of guide profiles formed on the shaft ends and alignment element for engaging the shaft ends to the alignment element. During pumping operations, impellers in the pump create an axial thrust force in the pump shaft forcing the shafts ( 32 ,  40 ) together and engaging the centering guides ( 62 ,  63 ) with the recesses ( 38 ,  46 ). 
     Referring now to  FIG. 2   b , an example of an assembled shaft coupling is shown in side cross-sectional view. The male splines  34  on the lower end  36  of the upper shaft  32  engage the female splines  52  and the upper shaft  32  bore  38  mates with the centering guide  62  that extends from the alignment element  54 . Similarly, the male splines  42  on the upper end  44  of the lower shaft  40  are engaged with the female splines  52  of the collar  48  and the bore  46  on the upper terminal end of the shaft  40  mates with the centering guide  63  that extends from the opposite side of the alignment element  54 . The upper shaft  32  and lower shaft  40  are aligned along a common axis within the collar  48  thus preventing shaft vibration when one of the shafts energizes the other. 
       FIG. 3   a  shows an alternative embodiment of a shaft coupling  30   a  for coupling an upper shaft  36   a  to a lower shaft  44   a . In this embodiment, the alignment element  54   a  has a largely disc-like cross-sectional area and is seated on the shoulder  56 . The insert  60  retains the element  54   a  within the collar  48 . The centering guides ( 62   a ,  63   a ) comprise a conical profile bored into the body of the alignment element  54   a . Similarly, the terminal tips of the upper shaft  36   a  and lower shaft  44   a  include conically profiled protrusions ( 39 ,  47 ) formed to engaged the bores of the centering guides ( 62   a ,  63   a ).  FIG. 3   b  illustrates the assembled shaft coupling  30   a  and engagement of the protrusions ( 39 ,  47 ) with the centering guides ( 62   a ,  63   a ). This configuration also controls shaft vibration during transmission of torque through the coupling  30   a . The profiles on the alignment elements and the terminal tips of the shafts are not limited to the figures described herein, but can include other shapes such as conical, concave, convex, spherical or other curved surfaces. Additionally, cylindrical profiles with may be employed and may include rounded tips on the cylinder end. 
     Yet another embodiment of a shaft coupling  30   b  is provided in side cross-sectional view in  FIG. 4   a . In this embodiment, the centering guides  62   b  and centering guide  63   b  comprise a raised profile on the respective upper and lower sides of the alignment element  54   b . The alignment element  54   b  comprises an upper housing  64 , a lower housing  66 , and a resilient member housed within the upper and lower housings ( 64 ,  66 ). One example of a resilient member is a spring  68 . In this embodiment, the upper and lower housing ( 64 ,  66 ) both comprise a generally cup-like structure having a closed base that is largely perpendicular to the axis of the collar  48   a . The housings have sides extending from the base towards an open end; the sides lie generally concentric with the axis A X  of the collar  48   a . The upper housing  64  inner diameter is greater than the lower housing  66  outer diameter allowing insertion of the lower housing  66  into the upper housing  64  in telescoping relation. The spring  68  provides a resilient force for urging the upper and lower housing ( 64 ,  66 ) apart. 
     As shown in  FIG. 4   b , in some embodiments, a vertical force may move the shaft ( 32 ,  40 ) toward one another and pushes on one of the upper or lower housing ( 64 ,  66 ), thereby compressing the spring  68  there between. One of the advantages of this embodiment is an axial force from one of the shafts ( 32 ,  40 ) is fully absorbed by the spring  68  and not transferred to the other or any other adjacent shaft within a pumping system. Moreover, the resilient nature of the spring  68  can force the housings ( 64 ,  66 ) apart upon absence of the vertical force while continuing axial alignment of the shafts ( 32 ,  40 ) during operation of the pumping system. Because rotational shafts in an ESP seal portion typically are not subjected to axial thrust, the resilient feature may be useful for these couplings. As shown, the housings ( 64 ,  66 ) have protrusions profiled on their respective outer surfaces formed to match recesses ( 38 ,  46 ) on the shafts ( 32 ,  40 ). However, the housings ( 64 ,  66 ) could be fashioned to include recesses and the shafts ( 32 ,  40 ) having corresponding protrusions. 
     Another embodiment illustrating ESP shaft coupling is provided in a side partial cut-away view in  FIG. 5 . Here an upper shaft  36   b  and lower shaft  44   b  are aligned with a retaining pin  70  that extends from a bore  38   b  in the lower terminal end of the upper shaft  36   b  into a corresponding bore  46   b  in the upper terminal end of the lower shaft  44   b . The retaining pin  70  may include an annular shoulder  71  radially disposed around the body of the pin  70  approximately at its mid-section. To accommodate the retaining pin  70 , the bores ( 38   b ,  46   b ) are formed deeper into the shafts ( 36   b ,  44   b ) than the bores ( 38 ,  46 ) illustrated in  FIGS. 2   a  and  2   b.    
     A coupling assembly is presented in side partial cross sectional view in  FIG. 6  that combines concepts described above. An upper shaft  36  with a bore  38  is disposed within a collar  48   b  into coaxial alignment with a corresponding lower shaft  44   b . A protrusion  47   a  extends from the lower shaft  44   b  upper terminal end into the bore  38  and is retained therein for coaxial alignment of the shafts ( 36 ,  44   b ). The protrusion  47   a  of  FIG. 6  is similar to the protrusion  47  of  FIGS. 3   a  and  3   b , but has increased dimensions, including an increased length, to ensure mating cooperation with the bore  38 . The collar  48   b  inner diameter is smaller at its upper end to match the upper shaft  36  outer diameter. The collar  48   b  can be machined or forged as a uni-body configuration, or reduced with an insert (not shown) similar to the collar  48  of  FIGS. 2   a - 3   b.    
     An example of an alternative shaft coupling is provided in  FIGS. 7 and 8 .  FIG. 7  depicts split pin  74  in perspective view. The embodiment of the split pin  74  illustrated is an elongated member having a substantially cylindrical shaped body  75 , however the split pin  74  can also have cross sectional shapes with multiple sides. In the embodiment of  FIG. 7 , a vertical slot  76  initiates from a first end  77  of the body  75  extending through the body  75  to a vertical terminal end  78 . Projecting from the body  75  second end  79  is a horizontal slot  81  that extends past the vertical terminal end  78  to a horizontal terminal end  83 .  FIG. 7  illustrates the first end  77  in forward looking view depicting an optional filler material  80  inserted within the slot  76 . The filler material  80  should compress to allow pin  74  insertion and may include a fiber type material, such as cotton, felt, or fiberglass. Other materials include foam, cork, polymers, elastomeric polymers, and the like. 
     With reference now to  FIG. 8 , an example of a shaft coupling is provided in a side partial sectional view. Here an embodiment of the split pin  74  is coaxially disposed between an upper end  44   b  and a lower end  36   b . Similar to the embodiment of  FIG. 5 , the split pin  74  has an end extending into the bore  38   b  of the lower end  36   b  and an opposite end extending into the bore  46   b  of the upper end  44   b . The pin  74  ends can have an outer dimension approximately the same or greater than the bores  38   b ,  46   b . The slots  76 ,  81  enable the ends  77 ,  79  to be compressed and inserted within the bores  38   b ,  46   b . Forming the split pin  74  from an elastic material, such as steel, results in the pin  74  ends outwardly pushing against the inner circumference of the bores  38   b ,  46   b;  this couples the pin  74  to the ends of the shafts. The bores  38   b ,  46   b  being substantially aligned with the respective shaft axes shaft, provides alignment of the shaft ends  38   b ,  44   b  during use when the split pin  74  is coupled with the bores  38   b ,  46   b.    
     Another optional compressive alignment element is illustrated in  FIGS. 9 and 10 . With reference to  FIG. 9 , an annular sleeve  82  is shown in perspective view. The annular sleeve  82  is a tubular member having a corrugated outer peripheral surface formed by protrusions  84  extending therefrom. Optionally, the protrusions  84  may extend from the sleeve  82  inner surface, or from both the inner and outer surfaces. The protrusions  84  are preferably formed from an elastic material, such as steel, that is able to be deformed and then return to its previous shape and also exert a resistive force while in the deformed state. An example of an annular sleeve  82  suitable for use as herein disclosed is a tolerance ring, that may be purchased from Rencol, 85 Route 31 North, Pennington, N.J. 08534, Tel: 609-745-5000, Fax: 609-74.5-5012, www.usatoterancerings.com. 
       FIG. 10  illustrates a side partial sectional view of a shaft  86  having splines  87  formed on the end of the shaft  86 . An optional collar  88  is depicted on the end of the shaft  86 , having on its inner circumference a corresponding profile of splines  89  for mating with the splines  87  on the shaft  86 . A pin  85  is pictured inserted into bores  91 ,  92  formed on the ends of the shafts  86 ,  90  to align and stabilize the shafts  86 ,  90  during rotation. An embodiment of the annular sleeve  82 , with protrusions  84 , circumscribes the pin  85  ends to enhance coupling stability between the pin  85  and bores  91 ,  92 . The protrusions  84  on the annular sleeve  82  are in temporary deformable compression when the pin  85  is in the bores  91 ,  92 . The elasticity of the protrusions  84  couples the pin  85  within each bore  91 ,  92  thereby aligning the ends of the shafts  86 ,  92 . As shown, two annular sleeves  82  are provided on each pin  85  end, but other arrangements are possible. For example, a pin  85  may have a single sleeve  82  on one end with a pair of sleeves  82  on its opposite end. Embodiments exist with more than two sleeves  82  on an end of a pin  85 . 
     The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims. 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 to various changes without departing from the scope of the invention.