Patent Application
20130266247
This section provides background information to facilitate a better understanding of the various aspects of the invention. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.
Submersible pumping systems have been employed in the pumping of oil and water from wells for many years. Commonly, a submersible pumping system comprises an electric motor, a motor protector and a pump suspended colinearly in a well by tubing or cable. The pump is generally a centrifugal pump which is coupled to the motor. The motor rotates a power transmission shaft that concurrently operates the pump. The motor and motor protector are filled with oil to aid in heat dissipation, to maintain proper internal lubrication of the motor, and to separate the internal components of the motor from surrounding wellbore fluids.
Because these pumping systems are generally disposed within a narrow well, the motor, motor protector, and pump are generally long and cylindrically shaped. The motors vary in horsepower depending on the application. Accordingly, the motors of submersible pumping systems can be quite long leading to particular difficulties not encountered in other electric motor applications.
The motors of submersible pumping systems typically comprise a stator secured within a tubular housing and a rotor secured to a power transmission shaft that rotates within the stator. The rotor typically is made up of a number of rotor sections, the number of rotor sections depending upon the length and power rating of the motor. Generally, each rotor section comprises laminated steel plates or disks secured by copper rods. The rotor sections are spaced apart from each other, and a rotor bearing assembly is located between each rotor section. Each rotor section is connected to the shaft so that all of the rotor sections rotate as the shaft rotates.
Each rotor bearing assembly within a rotor section acts to support the shaft and to maintain it in proper axial alignment. A rotor bearing assembly comprises a sleeve connected to the shaft so that the sleeve and shaft rotated together and a journal (e.g., bearing, bushing) disposed coaxially around the sleeve. The sleeve and journal are rotatively coupled to one another. The journal may be configured to frictionally engage the inner wall of the stator (e.g., housing) to prevent the journal from rotating and to maintain proper alignment of the shaft. Thus, a portion of the rotor bearing assembly is rigidly coupled to the shaft but not to the stator.
Due to the high operating temperatures within the well, thermal expansion tends to cause the shaft, rotor, and stator to grow axially. Generally, the rotor and shaft tend to grow axially downward during high temperature operation. The stator also tends to grow axially downward, however, to a lesser extent than the rotor and the shaft. Due to these thermal expansion effects, the motor is constructed so that each rotor bearing assembly attached to the motor shaft within a rotor section offers a limited amount of axial mobility. Thus, because each rotor bearing assembly is coupled to the motor shaft, the shaft retains the same limited amount of axial mobility. In some pumps, axial mobility is limited by thrust washers adjacent to each rotor bearing assembly.
Angular misalignment of the shaft within the motor can occur because the rotor, shaft, and stator are subject to these dimensional changes due to thermal expansion and because of imbalances in the rotating assembly. Misalignment of the shaft during operation opposes the centering, or aligning force of the bearing assembly and causes vibrations within the motor. Excess vibration can lead to premature motor or component failure.
Ideally, the journal remains stationary while the sleeve, rotor, and shaft are rotating. Rotor bearing assemblies have been used in which the peripheral surface of the journal frictionally engages the inner surface of the stator through metal-to-metal contact, such as via a metallic washer. Such metal-to-metal frictional fit rotor bearing assemblies have a tendency to become loose and then to rotate with the shaft. Rotation of the journal tends to gouge and deface the inner surface of the stator. Once the journal begins to rotate with the shaft, the centering force of the rotor bearing assembly is diminished leading to increasing angular misalignment, vibration, and motor failure. This type of construction is also unsatisfactory because due to thermal expansion of the bearing assembly during motor operation, the journal may tightly engage the stator wall which can cause angular misalignment of the shaft and thus excessive thrust loads onto the thrust bearing surfaces adjacent to the rotor bearing assembly.
Some electric submersible pumps utilize ceramic carbide (e.g., tungsten carbide, silicon carbide, aluminum nitrite, boron carbide, cobalt) bearings (e.g., sleeve and/or bushing) to resist the abrasive action of sand or other hard particles in the well fluid and to function with very low viscosity lubrication. A major challenge with ceramic carbide devices is securing the mating bearing components in a manner that does not create serious stress raisers that make the ceramic carbide susceptible to cracking. Cracking may be caused by shock loads encountered during shipping, handling or installation. Cracking may also be caused by thermal expansion stresses due to running in a poor lubricant that insufficiently lubricates or cools the bearing, such as low viscosity fluid or in a well fluid with a high gas content. Cracking may also be caused by axial or transverse shocks during operation, particularly as the pump shaft constantly moves upward and downward during gas slugging. A catastrophic pump failure may occur, if even one of the cracked bearings (e.g., sleeves) in the rotor (e.g., impeller) stack actually breaks apart.
A bearing assembly for a rotating shaft uses a carbide sleeve to prevent wear and carry load. The carbide sleeves provide increased life for rotating components used in the severe environments in the oil and gas industries. Various mechanisms can couple the carbide sleeve to the rotating shaft, including keys, keyways, drive rings, reaction rings, and other members to provide particular benefits. These mechanisms allow the carbide sleeve to bear the compressive load of other components, for example, or to slide axially on the shaft, when needed. This summary section is not intended to give a full description of a rotor bearing assembly. A detailed description with example implementations follows.
The invention is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of various features may be arbitrarily increased or reduced for clarity of discussion.
It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify the disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. Moreover, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact.
Aspects of the invention relate to rotor bearing assemblies which may be utilized for example in various types of pumps, compressors separators and the like. For purposes of clarity and brevity, aspects of the invention are described generally with reference to electric submersible pumps and wellbore operations. How to utilize aspects of the invention in devices (e.g., intakes, pumps, compressors, etc.) other than electric submersible pumps will be understood by those skilled in the art in view of this disclosure.
As used herein, the terms “up” and “down”; “upper” and “lower”; “top” and “bottom”; and other like terms indicating relative positions to a given point or element are utilized to more clearly describe some elements. Commonly, these terms relate to a reference point as the surface from which drilling operations are initiated as being the top point and the total depth of the well being the lowest point, wherein the well (e.g., wellbore, borehole) is vertical, horizontal or slanted relative to the surface.
The non-rotating group includes a stator 34 and journal(s) 36. Depicted stator 34 is constructed of metal laminations. Stator 34 may be configured with slots running axially through the stator body through which windings 38 run. Each journal 36 is disposed circumferentially about a sleeve 48 and is positioned between stator 34 and the respective sleeve 48. According to one or more aspects of the invention, each rotor bearing assembly 30 comprises a sleeve 48 and journal 36. Rotor sections 28 lie immediately adjacent above and below each journal 36 in the embodiment depicted in
Rotor sections 28, while rotatively coupled to shaft 26, are not individually axially coupled to shaft 26. The lower most rotor section at the end of shaft 26 is, however, axially locked to the shaft in order to support the other rotor sections. Sleeves 48, while rotatively coupled to shaft 26 are likewise not axially locked to shaft 26. Thus, the rotor sections 28 and the sleeves 48 have a certain amount of freedom to move in an axial direction, i.e., either upward or downward due to relative thermal expansion and contraction. In the embodiment depicted in
The non-rotating group includes stator 34 and journals 36. Each journal 36 is disposed circumferentially about a sleeve 48. Thus, where sleeve 48 and journal 36 abut one another is a rotating interface 50. Multiple axially disposed cylindrical passageways 52 through journal 36 provide for oil flow through journal 36 in order that the oil filling the motor can communicate with adjacent rotor sections for cooling and lubrication.
Journal 36 extends radially outward from sleeve 48 to a peripheral surface 54. Peripheral surface 54 is slightly spaced apart from the inner surface 46 of stator 34 in the depicted embodiment. Clearance between these components is commonly about 0.005″ to about 0.009″. Thus, there is no material-to-material contact between journal 36 and stator 34 in the embodiment of
In the embodiment of
Members and/or features of the invention may be utilized in rotor bearing assemblies such as the rotor bearing depicted in
Refer now to
In this embodiment, sleeve assembly 49 assembly includes sleeve 48 member, a key 72 have opposing tabs 74 (e.g., ears), and a drive ring 66. Sleeve assembly 49 may further comprise a reaction ring 76. Drive ring 66 comprises a face 78 having a protrusion 80. Protrusion 80 may be formed in various manners, such as and without limitation as a tab, peg, arm or other portion. In the depicted embodiment, face 78 is a contoured surface (e.g., sinusoidal) which forms protrusion 80. Protrusion 80 is adapted to mate with notch 82 formed along the shoulder 84 of sleeve 48.
The contact between protrusion 80 of drive ring 66 and shoulder 84, for example at notch 82, of sleeve 48 generates a small axial force that tends to separate the members. Key 72 couples drive ring 66 and sleeve 48 and tends to maintain face 78 and shoulder 84 in contact countering the separation that may occur for example because of the slack that is provided to address thermal expansion in the rotor and bearing stack. Reaction ring 76 may be disposed along the opposing shoulder (e.g., end) of sleeve 48 from drive ring 66. Reaction ring 76 and drive ring 66 are coupled to sleeve 48 via key 72 and opposing key tabs 74. Sleeve assembly 49 provides a mechanism for rotationally locking (e.g., attaching, coupling) sleeve 48 with shaft 26, so that they rotate together, and allow for axial movement relative to shaft 26 for example to address thermal expansion. Key 72 and drive ring 66 provide a locking mechanism that eliminates a need to cut a keyway in sleeve 48 that creates an undesired stress raiser. Further, the utilization of key 72, drive ring 66 and optional retainer ring 76 may reduce the axial load that is applied to sleeve 48, for example by the rotor sections and/or impellers. The locking features, for example key 72, drive ring 66 and retainer ring 76 may be constructed of various materials such as metal and steel.
Sleeve 48 is constructed of a carbide material, such as silicon carbide. Sleeve 48 comprises an internal bore 48a defined by a tapered internal surface 86. A cylindrical member 88 (e.g., collet, bushing) having an outer surface 90 and an inner surface 92 forming a bore 88a is disposed between sleeve 48 and shaft 26. Member 88 is a metal member in this embodiment. Outer surface 90 is tapered surface, tapering down in thickness from one end 102a of member 88 to the other end 102b. Tapered outer surface 90 corresponds with internal tapered surface 86 of sleeve 48. Member 88 forms an axial (e.g., longitudinal) slit 94 which extends radially through member 88 from the inner surface 92 to outer surface 90 and may extend partially or entirely along the axial length of member 88. One or more slits 94 may be formed. For example, instead of forming a slit 94 extending the axial length of member 88 it may be desired to utilize one or more slits 94 that extend less than the full axial length of member 88. Slit(s) 94 permit member 88 to forcefully expand and/or contract in diameter and to provide a friction lock around shaft 26. According to one or more aspects of the invention sleeve assembly 49, comprising carbide sleeve 48 and member 88, may reduce the forces (e.g., loads) applied to the carbide sleeve 48. Ceramic carbide sleeve 48 is not required to deflect and does not have any stress raising notches, keyways and the like.
In the depicted sleeve assembly 49, member 88 receives shaft 26 in bore 88a and carbide bearing sleeve 48 is receives member 88 in bore 48a (e.g., coaxially aligned with member 88). The opposing ends 102a, 102b of inner member 88 extend beyond the axial opposing ends of carbide bearing sleeve 48. In this embodiment, a member 96 (e.g., collar) is attached to member 88 (e.g., at end 102b), for example via threading, adjacent to an end of sleeve 48 (e.g., the bottom end). A hole 98a is depicted for connecting a spanner wrench to threadedly couple collar 96 to member 88. A biasing member 98 is depicted disposed between collar 96 and sleeve 48. Biasing member 98 (e.g., leaf spring, Belleville spring, wave spring, etc.) maintains the fit of sleeve 48 with member 88 across a range of thermal contraction and expansion of the members relative to one another. According to one or more aspects of the invention, sleeve assembly 49, comprising member 88 (e.g., metal), carbide sleeve 48 and one or more of collar 96 and biasing member 98 may reduce the axial force applied to carbide sleeve 48.
Cutting a keyway into the inside diameter of sleeve 48 to engage a loose key, which may engage a shaft keyway, creates as stress raiser. In the depicted embodiment, one or more attachment (e.g., linking, fastening) features 106, which are depicted as keys in
The depicted embodiment further depicts grooves 108. Scoring ceramic carbide sleeve 48 for example to form grooves 108 may promote controlled cracking of sleeve 48. In another embodiment, described with reference to
The inner metal member may comprise strain relief features to alleviate problems, due to differential thermal expansion for example, by allowing the metal member 102 to yield in one direction while retaining its strength in another direction. For example, a metal sleeve or liner may include axial slits 94 (e.g., slots) as depicted in
Metal alloys that are commonly used in electric submersible pumps have a coefficient of thermal expansion (“CTE”) significantly higher than that of ceramic carbide materials used in bearing components. The CTE (microinches/in/F) of tungsten carbide is 3.9, while alloy steels range from about 6.3 to 8.3 (e.g., Monel is 7.8 and Inconel is 6.4). This differential CTE can lead to cracking or spalling of the carbide. To alleviate such problems, the metal components can be made, for example, of iron-nickel or iron-nickel-cobalt alloys having CTE's more closely matching the CTE of the ceramic carbide members.
The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the invention. The features and/or aspects of the depicted embodiments are provided for purposes of illustration and description, therefore it will be recognized by those skilled in the art that various features and aspects of the depicted embodiments may be combined with one another in manners not illustrated. Those skilled in the art will appreciate that they may readily use the disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art will also realize that such equivalent constructions do not depart from the spirit and scope of the invention, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the invention. The scope of the invention should be determined only by the language of the claims that follow. The term “comprising” within the claims is intended to mean “including at least” such that the recited listing of elements in a claim are an open group. The terms “a,” “an” and other singular terms are intended to include the plural forms thereof unless specifically excluded.
Conclusion
Although exemplary systems and methods have been described in language specific to structural features or techniques, the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as example forms of implementing the claimed systems, methods, and structures.
This divisional patent application claims the benefit of priority to copending U.S. patent application Ser. No. 12/643,223, filed Dec. 21, 2009, and entitled, “Rotor Bearing Assembly,” which is incorporated herein by reference in its entirety, and in turn claims priority to U.S. Provisional Patent Application No. 61/140,939 filed Dec. 27, 2008, which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61140939 | Dec 2008 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12643223 | Dec 2009 | US |
| Child | 13769772 | US |
