Abstract:
A submersible pump assembly having first and second components that are coupled together has a removable externally splined sleeve. A key is located in the keyway between the shaft sleeve and the shaft for transmitting torque. A threaded fastener secures to a threaded hole extending inward from an end face of the shaft end coaxial with an axis of the shaft end. The fastener has a head that engages an outward facing shoulder of the shaft sleeve to releasably secure the shaft sleeve to the shaft. A coupling sleeve has internal splines that engage the external splined section of the shaft sleeve. The coupling sleeve is in engagement with a shaft end assembly of the second component for transmitting torque between the shafts of the first and second components. The head that of the fastener transmits axial loads between the shafts of the first and second components.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    Applicants claim the benefit of provisional application Ser. No. 60/299,065 filed Jun. 18, 2001. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates generally to electric submersible pump connections. More specifically, the present invention relates to a splined connection for connecting submersible pumps that is removable.  
           [0004]    2. Description of the Related Art  
           [0005]    It is sometimes advantageous to couple multiple pumps to one motor in an electric submersible pump system. To do so shafts must pass from the motor through one pump to the next and continue to any successive pumps. Therefore, in a two pump system the lower pump drive shaft is connected to the motor at one end, extends through the lower pump and is connected to the second pump at the other end. These pump assemblies can be quite long, with a length to diameter ration greater than 250 being not uncommon.  
           [0006]    In order to transmit the high torque between the motor and the pumps, a relatively large diameter coupling is preferred. Such couplings are typically a splined connection wherein each of the ends have matching splines. Normally in a one or two pump assembly, the shaft has a constant diameter, and the grooves for the splines are cut into the shaft at each end. A coupling sleeve having internal splines slides over the upper end of a lower shaft and the lower end of an upper shaft.  
           [0007]    Where the second pump connects to the first, less torque is being transmitted (approximately half as much) so conventionally-sized splined ends may be used. Having the shaft ends at the same diameter as the shaft allows the pump components to be assembled and disassembled over the splined ends. The pumps are typically assembled by sliding impellers and diffusers over one end of the pump shaft, each impeller and diffuser having a central bore that closely receives the shaft.  
           [0008]    A disadvantage of having the splined ends at the same diameter as the shaft is that the splines form a weak point in the shaft because the shaft has less cross-sectional area at the splined ends due to the splines. The amount of torque that a conventional splined end can handle is significantly less than if the splined end had the same cross-sectional area as the remaining portions of the shaft. The ability to transmit torque is related to the cube of the diameter, so that small decreases in the diameter of splined ends due to the spline grooves mean that the shaft can transmit much less torque. This is typically not a problem in two pump systems because the torque being transmitted from the first pump to the second is about half the torque being transmitted from the motor to the first pump.  
           [0009]    For three or more pump systems, one approach is to utilize larger diameter shafts in the motor and each of the pumps. A larger shaft is not a particular disadvantage for the motor. However, larger shafts for the pumps results in less radial distance between the inner and outer portions of the flow channels of the impellers and diffusers, unless the housings are also made larger. It may not be possible to increase the diameters of the housings. Consequently, the pumps with larger shafts may not be as efficient as pumps with smaller diameter shafts.  
           [0010]    Another approach is to provide an enlarged end on the lower end of the shaft of the lower pump so that it has the same strength as the remaining portion of the shaft. One prior art technique involves welding or brazing a shaft sleeve, also called a knob spline, onto the end of the shaft. One of the problems with this approach is that the process is very sensitive and the welding requires skilled welders and machinists. Also, this technique results in a permanently enlarged end. However, having a permanently enlarged end does not create a problem if it is only on one end of the shaft because the impellers and diffusers could be assembled over the other end of the shaft.  
           [0011]    When more than two pumps are used the torque passed from the first pump to the second pump increases. For example, when five pumps are used the torque being transmitted from the first pump to the second pump is approximately 80% of the torque being transmitted from the motor to the first pump. Because of this, a conventional splined end connection may not be an option between the first and second pump. Both ends of the shaft of the first pump can&#39;t be permanently enlarged because the impellers and diffusers will not slide over a permanently enlarged end. This either limits design flexibility or requires a work around.  
         SUMMARY OF THE INVENTION  
         [0012]    A shaft sleeve is attached to a downhole pump drive shaft with a high strength key to transmit high torque loads from one pump to another. Because the shaft sleeve is attached with a key, it is easily removable. The shaft sleeve has exterior splines and effectively increases the diameter of the connection so that larger loads may be transmitted. The shaft sleeve and key can each be manufactured from a variety of high strength materials to deliver the most cost effective coupling for the application.  
           [0013]    The shaft sleeve is secured to the shaft end by a threaded section. Preferably, the threaded section is a threaded hole formed in the end face of the shaft end. A fastener with a head secures to the threaded hole. The head of the fastener engages a shoulder on the shaft sleeve to secure it to the shaft end against axial movement. Preferably, a shaft sleeve is mounted to both ends of the shaft of the first pump and to the lower end of the shaft of the second pump. A splined coupling sleeve slides over the shaft sleeves of the mating shaft ends, engaging the external splines to transmit torque from the shaft of the first pump to the shaft of the second pump. The shaft end assembly of the second pump transfers axial down thrust through the head of the fastener to the shaft of the first pump.  
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a sectional view of a shaft sleeve and shaft end constructed in accordance with this invention.  
         [0015]    [0015]FIG. 2 is a cross sectional view of the shaft sleeve of FIG. 1 taken along line  2 - 2  of FIG. 1.  
         [0016]    [0016]FIG. 3 is an enlarged plan view of a portion of the key of the shaft end of FIG. 1.  
         [0017]    [0017]FIG. 4 is a schematic elevational view illustrating a submersible pump assembly having at least one shaft connection in accordance with this invention.  
         [0018]    [0018]FIG. 5 is a sectional view of two shaft ends in accordance with claim 1 shown connected together.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]    As shown in FIG. 1, a shaft sleeve  10  is connected to a shaft  12  with a key  14  to transmit high torque loads from one shaft  12  to another. A key  14  between shaft sleeve  10  and shaft  12  secures shaft sleeve  10  with shaft end  12  for rotation therewith.  
         [0020]    Shaft  12  is preferably formed of hard, corrosion resistant materials such as K500 Monel, or Inconel X-750. Other materials may also be suitable depending on the application. Shaft  12  is generally cylindrical with two ends. Shaft sleeve  10  generally attaches to one end of shaft  12 , although it could be attached to both ends, if desired. Shaft  12  has an end face  16  and a shaft keyway slot  18  machined into its outer diameter  20  from end face  16  a selected distance. In the preferred embodiment, a threaded hole  22  is machined into end face  16  coaxial with the axis of shaft  12 .  
         [0021]    Shaft sleeve  10  is an annular member with a bore  24  and an exterior  26 . Shaft sleeve has three general sections along its length. At end  37 , shaft sleeve  10  has external splines  28  on its exterior  26 , while at the opposite end  39 , exterior  26  of shaft sleeve  10  has a cylindrical full outer diameter section  30 . Between splines  28  and full diameter section  30  is a spline transition  32 , wherein splines  28  terminate. Splines  28  are machined into exterior  26  to create spline recesses  34  and spline teeth  36  as is more clearly seen in FIG. 2. In the preferred embodiment splines  28  extend from end  37  of shaft sleeve  10  to the spline transition  32 . Spline recesses  30  become shallower in spline transition  32  such that full diameter section  30  is relatively smooth. The total length of shaft sleeve  10  is substantially larger than the length of splines  28 . In the preferred embodiment, the length of splines  28  is about 50 to 70% of the length of shaft sleeve  10 . In the preferred embodiment full diameter section  30  transmits a majority of the torque from shaft  12  to shaft sleeve  10 , while splines  28  transmit torque from shaft sleeve  10  to an adjacent shaft (not shown in FIG. 1). By spreading these torque loads between the two sections, stress concentrations are reduced.  
         [0022]    A keyway slot  38  is machined into inner diameter  24  and runs the length of the shaft sleeve  10  in the preferred embodiment. Keyway slot  38  is approximately the same size as shaft keyway slot  18  so that when aligned, they form a keyway receptacle for key  14 . Key  14  runs the majority of the length of shaft sleeve  10 , extending from shaft end face  16  to the end of shaft sleeve  10 . A protuberance is located in shaft sleeve keyway slot  38  at end  39  of shaft sleeve to retain key  14 . Key  14  has a tapered section  39  at its end farthest from shaft end face  16  that is slightly tapered in width to prevent stress concentrations. The length of the tapered section  39  is much shorter than the length of key  14 . Keyway slots  18 ,  38  remain constant in width through their lengths, resulting in a tapered clearance adjacent shaft end face  16 . For interchangeability, both the leading and trailing edges of key  14  are tapered in tapered section  39 . However, only the taper on the trailing edge reduces stress concentrations. Also, both ends of key  14  could have a tapered section  39 , if desired for interchangeability. Alternately, the tapered clearance could be achieved by tapering keyway slots  18 ,  38  and making key  14  of constant width.  
         [0023]    In the preferred embodiment, an annular retaining groove  40  is also machined into inner diameter  24  and runs the full circumference of inner diameter  24  near end  37  of shaft sleeve  10 . A retaining ring  44  snaps into retaining groove  40  and abuts end face  16  of shaft  12 . A threaded fastener  46  engages a threaded receptacle  22  to secure shaft sleeve  10  against axial loads. Fastener  46  has a head  48  that engages retaining ring  44 , which serves as a shoulder of shaft sleeve  10  to hold shaft sleeve  10  on shaft  12 . Head  48  preferably has an outer diameter that is cylindrical and only slightly smaller than bore  24  of shaft sleeve  10 . Head  48  is spaced slightly from shaft end face  16  by the width of retaining ring  44 . The outer end of head  48  is substantially flush with end  37  of shaft sleeve  10 , and preferably protrudes past slightly.  
         [0024]    The combination of retaining ring  44  and retaining bolt  46  is the preferred approach because of the inherent redundancy of such a system. Because axial loads do not compare in magnitude to the rotational loads on the shaft sleeve  10 , the axial retention system may be easily changed without degrading the performance of the invention. For example, a set screw could be inserted laterally through a hole in shaft sleeve  10  into engagement with shaft  12 . Alternately, internal threads could be formed in shaft sleeve  10  for engaging external threads on shaft  12  for preventing axial movement of shaft sleeve  10 . The threads in such instance need not be tightened because torque would be transmitted through key  14 .  
         [0025]    Bore  24  of shaft sleeve  10  is very close to outer diameter  20  of shaft  12 . The preferred embodiment has outer diameter  20  of {fraction (11/16)} in, or 0.6875″. Inner diameter  24  of the preferred embodiment is no more that 0.003″ larger, or 0.6878″. The difference between the inner diameter of bore  24  and outer diameter  20  is known as the diametrical clearance. When the diametrical clearance in the preferred embodiment is over approximately 0.005″, key  14  (approximately {fraction (1/16)} in. square or 0.0625″) will tend to roll and the coupling may fail. Therefore, machining tolerances are critical to the success of the present invention.  
         [0026]    [0026]FIG. 4 illustrates an application for the coupling described. Submersible pump assembly  50  has a number of modules or components. These include an electrical motor  52  that is secured to a seal section  54 . Seal section  54  equalizes pressure of lubricant in motor  52  with that of the downhole environment. A first pump  54  is mounted to the upper end of seal section  54 . A second pump  58  is mounted to the upper end of first pump  54 . A third pump  59  is mounted to the upper end of second pump  58 . There may be more pumps, or third pump  59  may be connected to a string of production tubing through which the produced well fluid flows. Each pump  56 ,  58 , and  59  is a centrifugal pump with a driven shaft that rotates impellers (not shown) within diffusers. Pump  56  has the sole intake to the well fluid and discharges into second pump  58 . Second pump  58  discharges into third pump  59 . First pump  56  has to be able to handle the necessary torque to rotate both of the upper pumps  58 ,  59 . Consequently, both ends of the shaft of first pump  56  are preferably enlarged in diameter over the shaft diameter.  
         [0027]    [0027]FIG. 5 shows the upper end of shaft  12  of first pump  56  and the lower end of shaft  60  of second pump  58 . Shaft sleeve  10  is shown installed on the upper end of shaft  12  of first pump  56 , and a similar shaft sleeve  10  will be installed on the lower end of shaft  12  of first pump  56 . The shaft of motor  52  will have a diameter that matches the outer diameter of shaft sleeve  10 . Prior to installing shaft sleeve  10  with key  14  and fastener  46  on either the upper or lower end of shaft  12 , the impellers and diffusers (not shown) of first pump  56  are slid over shaft  12 . Shaft  60  of second pump  58  also has an enlarged diameter lower end created by installing a similar shaft sleeve  10 . The upper end of shaft  60  does not need to be enlarged by a shaft sleeve  10  if it is driving only one pump  59  above it. If there are more pumps above pump  59 , it might be feasible to provide a removable shaft sleeve  10  on the upper end of shaft  60 .  
         [0028]    A coupling sleeve  62  has internal splines that engage external splines  28  of shaft sleeve  10  on shaft  12  and external splines  28  of shaft sleeve  10  on shaft  60 . Coupling sleeve  62  transmits torque from shaft sleeve  10  to shaft  60 . Coupling sleeve  62  also has one or more buttons or pins  64  that extend inward from its sidewall that engage the two fastener heads  48 . Pin  64  positions coupling sleeve  62  between the end assemblies of the two shafts  10  and  60 . Tension is not transferred from shaft  12  to shaft  60  in this embodiment, however, down thrust on shaft  60  transmits to shaft  12 . The load path is from shaft  60  through fastener head  48  secured thereto to pin  64  and from pin  64  through the fastener head  48  of shaft  12 .  
         [0029]    The invention has significant advantages. The shaft sleeve is readily removable to allow diffusers and impellers to be mounted on and removed from the shaft. The key provides for a full torque transmission up to the yield strength of the shaft. The shaft sleeve assembly also transmits axial thrust.  
         [0030]    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.