Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to fluid film bearings. In more particular aspects, the invention relates to improved motor bearings for electrical submersible pumps and the like whose motor shafts are maintained in a substantially vertical position during operation. 
     2. Description of the Related Art 
     Electrical submersible pumps (ESP&#39;s) include an electric motor and a pump that is used to pump oil or other fluids within a wellbore. The electric motors have a rotatable rotor that is contained within a stationary stator. The rotors for the submersible pumps are usually disposed in a substantially vertical position by virtue of their placement in wellbores, which typically are vertical shafts. Therefore, during operation, the rotor shaft of the motor is oriented in the vertical position. 
     The bearings which surround the rotor shaft are often of the fluid film variety. However, fluid film bearings require a side load to provide optimal dynamic stability. Since the rotor shaft is rotating in a vertical position, there is little or no side load being applied to the bearing during operation. This causes instability in the bearings, which results in excessive motor vibration. Excessive vibration in the bearings can cause the bearing sleeves to break through the oil film resulting in metal to metal contact that can lead to premature wear and motor failure. 
     Alternative bearing systems have not proven effective in the long term. High wellbore temperatures make elastomers undesirable in such a bearing, particularly as a wear surface. Friction fit rotor bearing assemblies tend to become loose as temperatures change in the wellbore. 
     Fluid film bearings or bearings that support the shaft of a rotor on fluid are not new. For example, U.S. Pat. No. 3,118,384 issued to Sence et al. describes fluid pressure bearings wherein high pressure fluid is injected to prevent the rotor from contacting the stator. U.S. Pat. No. 3,196,301 issued to Turk discusses fluid film bearings and describes a technique for using an impeller to axially draw fluid in to the bearing to provide clearance between the rotor and stator. However, these arrangements are, in practice, vulnerable to damage from vibration of the rotor shaft within the stator. Mere flowing of fluid around the rotor does not provide effective resistance or dampening of strong vibrations, such as tend to occur in downhole motors. 
     It would be desirable to have devices and methods that address the problems of the prior art. 
     SUMMARY OF THE INVENTION 
     A novel bearing assembly and bearing system for a motor is described wherein a fluid shock absorber is provided to cushion and dampen vibration of the rotor shaft. Lubricating fluid is supplied under pressure to lubricate and replenish the fluid film located between the rotating, inner bearing sleeve and the outer, stationary sleeve insert of the bearing assemblies of a motor. The sleeve insert is provided with fluid metering passages that permit lubricating fluid to pass through the body of the sleeve insert. The sleeve insert is disposed radially within a sleeve insert holder, and a fluid gap is defined between the two components. 
     During operation, vibration of the rotor shaft within the stator bore is damped by the fluid spring created by the metering of fluid through the sleeve insert. As a result, friction is reduced and the lifespan of the motor increased. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side cross-sectional view of an exemplary motor bearing assembly constructed in accordance with the present invention. 
     FIG. 2 is a side view, partially in cross-section, of an exemplary bearing sleeve and sleeve insert used in the assembly shown in FIG.  1 . 
     FIG. 3 is a side cross-sectional view of a portion of an exemplary bearing assembly shown apart from the stator. 
     FIG. 4 is a close-up cross-sectional view illustrating some of the fluid-related features of the bearing in greater detail. 
     FIGS. 5A and 5B are a side cross-sectional view of an exemplary motor incorporating bearing assemblies constructed in accordance with the present invention as well as a vibration and temperature sensing arrangement. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIGS. 1 through 4 illustrate a bearing assembly constructed in accordance with the invention. FIG. 1 shows a portion of an electrical submersible pump motor  10  that has an outer housing  12  that encloses a stator  14 . The stator  14  is made up of a number of laminations  16  and encloses a bore  17 . A rotor shaft  18  is rotatably disposed within the bore  17  of the stator  14  and supported by bearing assembly  20 . It is pointed out that, while only a single bearing assembly  20  is depicted here, there are, in fact, a number of similar bearing assemblies, all of which surround the rotor shaft  18  within the same motor  10 . The bearing assembly  20  is representative of each of these, and it should be recognized that a number of such assemblies, in combination, will form a bearing system for support of the rotor shaft  18  in the motor  10 . 
     The rotor shaft  18  carries cylindrical laminated plates  19 , and thrust washers  21  surround the rotor shaft  18  and abut the bearing assembly  20 . The rotor shaft  18  also defines a central longitudinal bore  23  having lateral fluid flow passages  25  that extend radially outwardly from the central bore  23 . 
     The bearing assembly  20  includes several concentric members that will be described from the radial outside moving inward. The bearing assembly  20  includes an annular bearing sleeve insert holder  22  that presents a central portion  24  of enlarged diameter and two axial portions  26  of reduced diameter. A pair of grooves  28  are disposed in the enlarged diameter portion  24 . Annular anti-rotation extension springs  30  are disposed each of the grooves  28 . When so disposed, the springs  30  extend outwardly slightly from the grooves  28  (see FIG.  4 ). When the bearing sleeve insert holder  22  is inserted into the bore  17 , the springs  30  are urged against the bore  17  and are compressed to form a resilient seal. 
     A sleeve insert  32  is located radially within the bearing sleeve insert holder  22 . The sleeve insert  32  (shown apart from the bearing assembly in FIG. 2) is an annular ring that has two grooves  34  in its external surface  36 . As will be apparent, the sleeve insert  32  contacts the fluid within a fluid chamber along its external radial surface while its internal radial surface contacts a fluid film barrier that helps to support the rotor shaft  18  and reduce damage to the rotor shaft  18  due to friction and abrasion. Fluid metering holes  38  are disposed through the insert  32 . There are preferably only two such holes  38  that have a minimal diameter so that fluid is transmitted, or metered, through the holes  38  slowly and some of the mechanical energy that has been imparted to the fluid will be converted to heat energy via such metering. Currently, a diameter of about {fraction (1/16)}th of an inch is believed to be optimal for the holes  38 . 
     Anti-rotation extension springs  40  reside within the grooves  34  so that the sleeve insert  32  is prevented from rotating with respect to the sleeve insert holder  22 . At either axial end of the sleeve insert  32 , an annular oil seal  42  and oil seal compression cap  44  are located. Each oil seal  42  supplements the resilient seal provided by the spring  40  in closing off the fluid chamber (described shortly) which is defined in part by the springs  40 . A snap ring  46  is positioned outside of either compression cap  44 . The snap rings  46  engage the inner surface of the bearing sleeve insert holder  22  and thereby help to lock the insert holder  22  and the sleeve insert  32  together. 
     A bearing sleeve  50  is disposed radially within the sleeve insert  32 . The bearing sleeve  50  is an annular member that is keyed to the rotor shaft  18  so as to rotate with the shaft  18  and functions as a wear sleeve that protects the rotor shaft  18  from abrasion and friction damages. The bearing sleeve  50  contains four (only three visible in FIG. 2) fluid communication openings  52  that are disposed at 90 degree angles from one another about the periphery of the sleeve  50 . There are key notches  54  cut into the sleeve  50  at the upper and lower axial ends of the sleeve  50  into which complimentary shaped key members  56  on the shaft  18  will reside to spline the bearing sleeve  50  to the shaft  18 . 
     Referring now to FIG. 4, the construction of one side of the bearing assembly  20  is shown in close up with some of the gaps and spaces between various components being exaggerated in order to facilitate explanation of portions of the invention. As illustrated there, there is a narrow chamber  60  defined between the sleeve insert  32  and the sleeve insert holder  22  within which a fluid film  62  of fluid resides. The most common and preferred type of fluid to be used for this application is oil, which is substantially incompressible. The chamber  60  is closed off at each end by the contact between anti-rotation springs  40  and the sleeve insert holder  22 . It is noted, however, that the width of the chamber  60  can vary by virtue of the fact that contact with the inner surface of the sleeve insert holder  22  is accomplished by springs that are initially compressed when inserted into the holder  22 . 
     A gap  64  is present between the sleeve insert  32  and the bearing sleeve  50 . A second fluid film  66  resides within the gap  64 . During normal operation and absent system vibrations, the chamber  60  has a width of approximately 0.005 inches while the gap  64  is approximately 0.003 inches in width. The fluid within chamber  60  and gap  64  is disposed therein by pumping through bore  23  and lateral fluid passages  25  and then transmitted through the fluid communication openings  52  of the bearing sleeve  50 . It is pointed out that the oil is also present within the fluid metering passages  38  of the insert  32 . 
     In operation, the rotor  18  rotates and the bearing sleeve  50  rotates with it. The sleeve insert  32  and sleeve insert holder  22  do not rotate. During operation, fluid, such as an oil lubricant, is transmitted through the central bore  23  under pressure, the lateral fluid passages  25  and fluid communication openings  52  to continually replenish the fluid film layer  66  in gap  64 . 
     The use of the pumped in fluid and the fluid metering openings  38  provide a shock absorption function against vibration of the rotor  18  within the stator  14  and thereby curb instability in the system due to vibration. As the rotor shaft  18  moves laterally within the bore  17 , such as would result from system vibration, one side of the bearing sleeve  50  is compressed against the sleeve insert  32  causing the fluid entrapped therebetween to be metered through the metering passages  38  and into the chamber  60 . The metering passages  38  act like hydraulic metering valves. The fluid absorbs the vibration and converts the mechanical energy associated with it into heat. 
     Conversely, when the rotor shaft  18  moves in the opposite direction as a result of vibration (i.e., so that the bearing sleeve  50  is moved away from the sleeve insert  32 , oil is drawn from the gap  60  through the metering passages  38  into the second gap  64 . One the opposite side of the rotor shaft  18 , the opposite actions occur. In either case (whether the shaft  18  and bearing sleeve  50  are moved toward or away from the sleeve insert  32 ), fluid is drawn through the metering passages  38  and the mechanical energy associated with the vibration is converted into heat energy. 
     The sizes of gaps  60  and  64  may vary as required by the type of lubricating fluid used. However, the gaps  64  should be of sufficient size to permit a fluid film to reside therein that will resist friction between the bearing sleeve  50  and the sleeve insert  32 . Any incidental friction or vibration induced contact is borne by the bearing sleeve  50  rather than the rotor shaft  18  itself. The resilient sealing of the fluid chamber  60 , which is provided by the annular springs  40 , is desirable in that it permits the volume of the fluid chamber  60  to expand and contract slightly to accommodate increases and decreases in the amount of fluid that is retained within the chamber  60 . 
     It can be seen, then, that the bearing assembly  20  provides a fluid spring that dampens vibrations of the rotor shaft  18  within the stator bore  17 . In addition, the pressurized fluid within bore  23  constantly lubricates and replenishes the bearing assembly  20 . Since the bearing assembly  20  does not rely upon elastomeric components to provide wear surfaces, the assembly can be operated at very high temperatures. 
     Referring now to FIGS. 5A and 5B, there is shown an enlarged view of the lower portion of the exemplary motor  10  which incorporates bearing assemblies to support the rotor  18  within stator  14 . Only the two lower bearing assemblies  60 ,  62  are shown. It should be understood that there are additional bearing assemblies (not shown) located at regular intervals within the motor  10 . The bearing assemblies  60 ,  62  are constructed and operate in the manner of the bearing assembly  20  described earlier. In this view, it is possible to see the wire bundles  61  that form the terminus of the laminations and windings  16 ,  19  of the stator  14 . A tubular base  62  is secured within the housing  12  below the bundles. 
     A processor sub  64  is shown affixed to the lower end of the motor  10 . The processor sub  64  houses a multi-measurement sensor that is capable of processing sensed parameters and transmitting that information to the surface of the wellbore. One example of a suitable processor sub  64  is “The Tracker,” a device manufactured and marketed by the assignee of the present invention. 
     A variety of exemplary sensor devices are shown schematically within the motor  10  for sensing abnormalities in the operation of the bearing assemblies  60 ,  62 , such as excessive vibration. A first thermocouple sensor  66  is disposed between adjacent laminations  16  in the stator  14 . The first thermocouple sensor  66  is located within the stator  14  to be proximate the upper bearing assembly  60  and extends downwardly through the stator  14  to the processing sub  64 . The thermocouple sensor  66  is an elongated, wire-like sensor that is made of two dissimilar metals. Each of these metals will expand and contract at different rates to changes in temperature proximate the upper bearing assembly  60 , and the amount of differential expansion can be detected by the processor sub  64 . Although the thermocouple sensor  66  is depicted within the motor housing  12  as being disposed vertically through the laminations  16 , it should be understood that this depiction is schematic only, and that in actuality, the sensor  66  is layered in a coiled fashion with the laminated winds  16  of the stator  14 . A second thermocouple sensor  70  is disposed between adjacent laminations  16  in the stator  14 , but is located within the stator  14  so as to be proximate the lower bearing assembly  62 . The second thermocouple  70  senses changes in temperature proximate the lower bearing assembly  62 . 
     As can be seen in FIG. 5B, there is an accelerometer  72  secured to the lower end of the base  63 . The accelerometer  72  detects vibrations in the base  63  that are transmitted to it by vibration of the rotor  18 . Cable  74  interconnects the accelerometer  72  to the processor sub  64 . 
     Excessive vibration of the rotor  18  within the stator  14  during operation of the motor  10  is sensed by some or all of the sensors ( 66 ,  70 ,  72 ) described above. The sensed information is transmitted to the processor sub  64  where it is recorded and/or transmitted to the surface of the well. Excessive vibration of the rotor  18  proximate a particular bearing assembly ( 60  or  62 ) would be expected to raise the temperature proximate that bearing assembly. This rise in temperature would be detectable by the processor sub  64  via the thermocouple sensor ( 66  or  74 ) located near that particular bearing assembly. Additionally, general excessive vibration of the rotor  18  at or around its lower end would be detected by the accelerometer  72  with this detected condition being transmitted to the processor sub  64 . 
     While the invention has been shown in only some 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.

Technology Category: 2