Abstract:
Disclosed is an improved hydrodynamic bearing assembly for use in a motor assembly. The motor assembly typically includes a shaft with an axially oriented fluid channel and at least one radial shaft port extending through the wall of the shaft. The bearing assembly includes a bearing sleeve and a bearing collar. Preferably, the radial thickness of the bearing sleeve is at least the radial thickness of the bearing collar. It is also preferred that the bearing sleeve includes at least one bearing port that can be aligned with the shaft port to provide a path of fluid travel from inside the axially oriented fluid channel through the bearing sleeve.

Description:
FIELD OF THE INVENTION 
   This invention relates generally to the field of rotor bearings for motors, and more particularly, but not by way of limitation, to a motor bearing assembly for an electric motor. 
   BACKGROUND 
   Submersible pumping systems are often deployed into wells to recover petroleum fluids from subterranean reservoirs. Typically, the submersible pumping system includes a number of components, including one or more electric motors coupled to one or more high performance centrifugal pumps. Each of the components in a submersible pumping system must be engineered to withstand the inhospitable downhole environment. 
   Like conventional motors, submersible motors typically operate by using a “stator” to create a series of moving electromagnetic fields that cause a ferromagnetic “rotor” to spin about a fixed axis. In submersible motors, the stators usually surround the rotors, which are secured to a center shaft that is used to transfer the output of the motor. In this way, the rotor and shaft spin about a common axis inside the motionless stator. 
   Submersible motors can vary in length from a few feet to nearly one hundred feet and may be rated up to hundreds of horsepower. In longer submersible motors, it may be desirable to employ a number of separate rotor sections within a single stator. Each rotor section is usually constructed from a number of thin pieces of material, or laminations, that are held in place by electrically conductive rods inserted through openings in the laminations. The shaft can be secured within the inner diameter of the rotor sections with a keyed connection or by one of several other well-known methods. 
   Bearing assemblies are typically placed between adjacent rotor sections to center the rotor and shaft within the stator. Most rotor bearing assemblies include a bearing sleeve that rotates in close proximity with a surrounding bearing collar. The bearing sleeve is typically fixed to the motor&#39;s shaft and the bearing collar is fixed in a stationary condition to the stator. In most submersible motors, the rotor bearing assemblies are “hydrodynamic,” and rely on the presence of a thin film of lubricant in the annulus between the bearing sleeve and bearing collar. 
   In some prior art designs, lubricant is pumped into the annulus between the bearing sleeve and bearing collar by the centrifugal force generated by the spinning shaft and bearing sleeve and shaft. Lubricant is supplied to the bearing sleeve through a hollow channel in the motor shaft that is connected to a lubricant reservoir. Linearly aligned ports in the shaft and bearing sleeve deliver the lubricant from the hollow channel in the shaft to the annulus between the bearing sleeve and collar. The lubricant then flows into the spaces between the rotor sections and the stator, thereby protecting these components. 
   By way of illustration,  FIG. 1  shows a prior art rotor bearing assembly  200  includes a rotor bearing sleeve  202  that is secured to a hollow shaft  204  and a rotor bearing collar  206  that is attached to the stator  208 . The rotor bearing sleeve  202  may be secured to the shaft  204  and the bearing collar  206  to the stator  208  by any of a number of well known methods, such as keyed connections  210  and  212 . An oil-filled annulus  214  occupies the space between the bearing sleeve  202  and bearing collar  206 . As the bearing sleeve  202  and shaft  204  rotate, lubricant is drawn out of the shaft  204  and pushed into the annulus  214  through a port  216 . In this way, the bearing sleeve  202  propels lubricant from the shaft  204  into the annulus  214  through the port  216 . 
   As motors continue to increase in speed and power, the need for effective lubrication also increases. Although effective to a limited degree, prior art rotor bearings fail to circulate sufficient quantities of lubricant to satisfy the demands of next generation motors. Without sufficient lubrication, the moving components of the submersible motor can become worn and result in mechanical or electrical failure. Failure of the components in the motor can result in expensive repairs and work stoppages. Cost savings can be realized with motors that last longer and incur minimal downtime. 
   There is therefore a continued need for improving the lubrication of submersible motors. It is to these and other deficiencies in the prior art that the present invention is directed. 
   SUMMARY OF THE INVENTION 
   Preferred embodiments of the present invention provide an improved hydrodynamic bearing assembly for use in a motor assembly. The motor assembly typically includes a shaft with an axially oriented fluid channel and at least one radial shaft port extending through the wall of the shaft. The bearing assembly includes a bearing sleeve and a bearing collar. Preferably, the radial thickness of the bearing sleeve is at least the radial thickness of the bearing collar. It is also preferred that the bearing sleeve includes at least one bearing port that can be aligned with the shaft port to provide a path of fluid travel from inside the axially oriented fluid channel through the bearing sleeve. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a top cross-sectional view of a Prior Art bearing assembly and motor shaft. 
       FIG. 2  is an elevational view of an electric submersible pumping system disposed in a wellbore constructed in accordance with a preferred embodiment of the present invention. 
       FIG. 3  is an elevational partial cross-sectional view of a portion of the motor assembly of the submersible pump of FIG.  2 . 
       FIG. 4  is a top plan view of a first preferred embodiment of the rotor bearing sleeve of the bearing assembly of the motor assembly of FIG.  2 . 
       FIG. 5  is a top plan view of a second preferred embodiment of the rotor bearing sleeve of the bearing assembly of the motor assembly of FIG.  2 . 
       FIG. 6  is a perspective view of the rotor bearing sleeve of FIG.  3 . 
       FIG. 7  is an elevational partial cross-sectional view of a portion of the motor assembly of FIG.  2 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In accordance with a preferred embodiment of the present invention,  FIG. 2  shows an elevational view of a pumping system  100  attached to production tubing  102 . The pumping system  100  and production tubing are disposed in a wellbore  104 , which is drilled for the production of a fluid such as water or petroleum. As used herein, the term “petroleum” refers broadly to all mineral hydrocarbons, such as crude oil, gas and combinations of oil and gas. The production tubing  102  connects the pumping system  100  to a wellhead  106  located on the surface. 
   The pumping system  100  preferably includes some combination of a pump assembly  108 , a motor assembly  110  and a seal section  112 . The seal section  112  shields the motor assembly  110  from axial thrust loading produced by the pump assembly  108  and ingress of fluids produced by the well. The motor assembly  110  is provided with power from the surface by a power cable  114 . 
   Although only one pump assembly  108  and only one motor assembly are shown, it will be understood that more than one of each can be connected when appropriate. The pump assembly  108  is preferably fitted with an intake section  116  to allow well fluids from the wellbore  104  to enter the pump assembly  108 . The intake section  116  has holes to allow the well fluid to enter the pump assembly  108 , where the well fluid is forced to the surface through the production tubing  102 . 
   Referring now to  FIG. 3 , shown therein is an elevational partial cross-sectional view of a portion of the motor assembly  110 . The motor assembly  110  generally includes a motor housing  118 , a stator assembly  120 , one or more rotor assemblies  122 , a shaft  124  and one or more bearing assemblies  126 . The structure and interrelated function of each of these components is discussed below. 
   The motor housing  118  is preferably cylindrical and fabricated from a durable, anti-corrosive material. The motor housing  118  encompasses and protects the internal portions of the motor assembly  110  and preferably eliminates the entry of well fluids into the motor assembly  110 . In certain applications, it is preferred that the motor housing  118  be fitted with flanges or other adapters for connection to adjacent downhole components. 
   Adjacent the motor housing  118  is a stationary stator assembly  120  that remains fixed in position adjacent the motor housing  118 . The stator assembly  120  is preferably constructed from a plurality of circular laminations (not separately designated) that are aligned and stacked under compression. Windings (not shown) between the laminations are used to conduct electricity through the stator assembly  120 . As is known in the art, electricity flowing through the stator assembly  120  according to predefined commutation states creates a rotating magnetic field. 
   Although three rotor assemblies  122  (individually designated as  122   a ,  122   b  and  122   c ) are shown in  FIG. 3 , it will be understood that the number and configuration of rotor assemblies  122  can vary depending on the particular requirements of the motor assembly  110 . For example, several differently sized rotor assemblies  122  can be used within a single motor assembly  110 . Like the stator assembly  120 , the rotor assemblies  122  preferably include a plurality of laminations (not separately designated) that are aligned and stacked. 
   Each rotor assembly  122  also includes conductive rotor bars (not shown) that extend axially from opposing end rings  128  (individually designated as  128   a ,  128   b ,  128   c  and  128   d ). The conductive rotor bars are preferably constructed and configured to cause the rotor assembly  122  to rotate in response to the moving magnetic fields produced by the stator assembly  120 . The end rings  128  are used to retain the rotor bars, compress the laminations and support the weight of the rotor assembly  120  on a thrust washer or support ring (not shown), and to conduct current flowing in the rotor assembly  122 . 
   The shaft  124  extends substantially the length of the motor assembly  110  and transfers the motion generated by the motor assembly  110  to the pump assembly  108 . The shaft  124  includes an axially oriented lubricant channel  130  that is connected to a motor lubricant reservoir (not shown) at the bottom of the motor assembly  110 . The lubricant channel  130  is configured to permit the flow of motor lubricant from the lubricant reservoir through the shaft  124 . The shaft  124  also includes one or more shaft ports  132  that extend radially from the lubricant channel  130  to the outer diameter of the shaft  124 . 
   Also shown in  FIG. 3  are two bearing assemblies  126  (individually designated as  126   a  and  126   b ). The bearing assemblies  126  each include a bearing collar  134  and a bearing sleeve  136 . The bearing collars  134  are secured to the stator assembly  120  by a keyed connection (not shown) or any of several other methods known in the art. Likewise, the bearing sleeves  136  are secured to shaft  124  using any of several methods known in the art such as a keyed connection or shrink fitting. 
   Now also referring to  FIG. 4 , shown therein is a top plan view of a first preferred embodiment of the bearing sleeve  136 . The bearing sleeves  136  are constructed with one or more bearing ports  138 . The bearing ports  138  are linearly aligned with the shaft ports  132  to provide a conduit for the flow of lubricant from the lubricant channel  130  to the outer diameter of the bearing sleeve  136 . Although each bearing sleeve  136  is shown with two bearing ports  138  that mate with two shaft ports  132 , the present invention is not so limited. Greater or fewer numbers of bearing ports  138  may be desirable and are encompassed within the scope of the present invention. To minimize vibration during rotation, it is typically desirable to evenly space the bearing ports  138  and shaft ports  132  about the bearing sleeve  136  and shaft  124 , respectively. 
   Unlike prior art bearing sleeves, the inventive bearing sleeve  136  is significantly larger relative to the bearing collar  134 . A primary cause of the deficient pumping ability in prior art bearings is the short length of the ports (such as  216  in  FIG. 1 ) in the bearing sleeve  136 . In the past, it has been desirable to use thin bearing sleeves to minimize the rotational speed at the outer diameter of the bearing sleeve and to limit the intertial mass supported by the shaft. Because the total diameter of the rotor bearing is limited by the diameter of the motor, prior art bearings typically include a large bearing collar (such as  206 ) and a small bearing sleeve (such as  202 ). In many prior art bearings, bearing collars are four times thicker than the associated bearing sleeves. 
   The enlarged bearing sleeve  136  and longer bearing ports  138  provide improved pumping action because the outer diameter of the bearing sleeve  136  rotates at a higher velocity. Additionally, the longer bearing ports  138  impart energy to the lubricant over a greater distance, thereby improving the acceleration of lubricant through the bearing sleeve  136 . It is believed that noticeably improved pumping action occurs when the bearing sleeve  136  is at least as thick as the bearing collar  134 . 
   Turning now to  FIG. 5 , shown therein is a top plan view of a second preferred embodiment of the bearing sleeve  136 . In the second preferred embodiment, bearing ports  140  are connected to the shaft ports  132  at angles, which further increases the length of the bearing ports  140 . Increasing the length of the bearing ports  140  can improve the lubricant pumping action of the bearing sleeve  136 . With the bearing ports  140  at the angle shown in  FIG. 5 , the bearing assembly  136  is preferably rotated in a counterclockwise direction to optimize the centrifugal pumping action. The relative vertical position of the bearing ports  140  is demonstrated by the perspective view of the bearing sleeve  136  in FIG.  6 . 
   Although the bearing ports  140  shown are straight, it will be understood that curved and multi-angled bearing ports  140  are also encompassed within the scope of the present invention. It may, however, be easier to fabricate bearing sleeves  136  that include straight bearing ports  140 . It will also be understood that the bearing ports  140  can be configured at a non-horizontal angle with respect to the shaft  124 . 
     FIG. 7  shows an elevational partial cross-sectional view of a portion of a motor assembly  110  constructed in accordance with a preferred embodiment of the present invention. Lubricant flow paths are indicated with arrows to show the migration of the lubricant throughout the motor assembly  110 . As the bearing sleeve  136  rotates, lubricant is drawn into the bearing ports  138  out of the lubricant channel  130 . The spinning bearing ports  138  impart energy to the lubricant, which is thrown out of the bearing sleeve  136  into the annulus adjacent the bearing collar  134 . The lubricant then flows back to the bottom of the motor assembly  110  through the spaces between the stator assembly  120  and the rotor assembly  122 . The lubricant is preferably filtered before returning to the hollow lubricant channel  130  for continued circulation. 
   As the lubricant is pumped out of the bearing sleeve  136 , additional lubricant is drawn up the shaft  124  in response to the pressure gradient in the lubricant channel  130 . It will be understood that lubricant which does not exit the lubricant channel  130  at bearing ports  138  continues migrating upward and exits the shaft  124  at an upper bearing sleeve or alternative outlet (not shown). 
   The lubricant flow paths and motor assembly  110  have been set forth above for the purposes of disclosing preferred embodiments of the rotor bearing assembly  126 . It will be understood, however, that the rotor bearing assembly  126  can be configured to provide alternate lubricant flow paths within the motor assembly  110 . Furthermore, it will also be understood that the bearing assembly  126  can be used in motors that are configured differently than motor assembly  110 . For example, although preferred embodiments are disclosed herein with reference to a submersible pumping system  100 , it will be understood that the these embodiments also find utility in non-submersible applications, such as surface-based horizontal pumping systems. 
   In accordance with one aspect of a preferred embodiment, the present invention provides an apparatus for increasing the flow of lubricant in a motor, thereby increasing the motor&#39;s operating life. It is to be understood that even though numerous characteristics and advantages of various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and functions of various embodiments of the invention, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. It will be appreciated by those skilled in the art that the teachings of the present invention can be applied to other systems without departing from the scope and spirit of the present invention.