Patent Document

FIELD OF THE INVENTION 
     The present invention relates generally to electric motors, and particularly to a stator assembly that facilitates motor construction. 
     BACKGROUND OF THE INVENTION 
     Rotary electric motors are typically comprised of two primary components, a rotor and a stator. The stator is used to produce a rotating magnetic field. The rotating magnetic field induces a rotating force on the rotor that causes the rotor to rotate about an axis. The rotational motion of the rotor can be drivingly coupled to an external device, such as a pump. 
     The stator is typically constructed of conductors wound longitudinally around a core. These longitudinally wound conductors are spaced radially around the stator. The core typically is constructed from metallic laminations that have been stacked and pressed together. The laminations are manufactured with a pattern of openings so that when the laminations are stacked the individual openings form a pattern of continuous longitudinal openings extending through the lamination stack. Typically, the rotor is housed within a cavity formed by a center opening through the laminations. The conductors are wound through longitudinal conductor openings that are disposed around the central opening. The metallic laminations help to couple the magnetic field produced by the conductors to the rotor. 
     To operate the electric motor, the conductive wiring in the stator is coupled to an electrical power source. A magnetic field is produced from the electricity flowing through the conductive wiring. In an exemplary embodiment, the electrical power source provides three-phase alternating current. As the three phases of the alternating current cycle radially around the stator, the conductors produce a rotating magnetic field in the stator. 
     The required size of the stator and rotor depends on the amount of work needed from the motor. The strength of the motor is determined, primarily, from the strength of the magnetic field that can be produced by the stator. The strength of the magnetic field produced by the stator is, in turn, affected by the number of turns of the conductive wiring. All other factors being the same, the greater the number of turns the stronger the magnetic field produced. 
     A submersible electric motor for use in a submersible pumping system may be required to lift wellbore fluids from depths of several thousand feet. A conventional motor that could otherwise be used to provide the equivalent pumping power on the surface cannot be used in a wellbore, because the number of turns of conductive wiring needed to produce the required force would require a motor of such a large diameter that it would be too wide to fit into the wellbore. Therefore, instead of a relatively short, thick motor with a large number of turns, the stators of submersible electric motors are extremely elongated with a smaller number of turns. Elongating the stator allows the motor to produce the required force to drive a pump by developing the magnetic force over a much greater length. 
     Currently, electric motors, particularly elongate motors such as those used in submersible electrical pumping systems for pumping petroleum, are constructed with unitary stators. Depending on the horsepower required of the motor, electric submersible pumping system motors can utilize stator assemblies thirty feet long or more. 
     Traditionally, the stator assemblies have been constructed by stacking individual stator laminations together to form a stator of a desired length. The lamination stack is then inserted into the stator housing. The lamination stack is then compressed and maintained under compression within the stator housing. Maintaining the laminations under compression prevents the laminations from spinning freely inside the stator housing. However, constructing a stator in this manner can be problematic. The sheer size of the stator makes manipulating the stator components difficult. Furthermore, loading the stator laminations into the stator housing by hand is time consuming and difficult. 
     Therefore, it would be advantageous to have a method and system to facilitate assembly of the stator of an elongated, submersible electric motor of the type used with electric submersible pumping systems. 
     SUMMARY OF THE INVENTION 
     Certain aspects commensurate in scope with the originally claimed invention are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below. 
     According to one aspect of the present invention, a method is featured for manufacturing a stator for a submersible electric motor. The method includes placing stator laminations disposed over a mandrel into an automated stator press. The automated stator press has a hydraulic ram and an automatic control system. The method includes placing the stator laminations, while disposed over a mandrel, into a stator housing. The method also includes using the hydraulic ram to compress the stator laminations within the stator housing, and automatically controlling the compression of the stator laminations with the automatic control system. Further, a stop is placed into the stator housing to maintain the stator laminations in a state of compression after the force of the hydraulic ram is removed. The method also includes removing the force of the hydraulic ram and removing the mandrel from the stator housing. 
     According to another aspect of the invention, a method of manufacturing an electric motor is featured. The method includes placing stator laminations, disposed over a mandrel, into an automated stator press. The automated stator press has a hydraulic ram and an automatic control system to compress the stator laminations within a stator housing. The compression of the stator laminations is controlled with the automatic control system. The method further includes placing a stop into the stator housing to maintain the stator laminations in a state of compression after the force of the hydraulic ram is removed. Electrical conductors are routed through aligned openings in the plurality of laminations. 
     According to another aspect of the present invention, a system is featured for assembling stator laminations in a stator housing. The system includes an automated stator press to compress laminations in a stator housing. The stator press utilizes a mandrel upon which a plurality of stator laminations may be located. The system also includes a support frame to support the stator laminations when placed on the mandrel. A control system is designed to automatically operate a hydraulic ram positioned to compress the plurality of stator laminations to a desired length within the stator housing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
     FIG. 1 is a cross-sectional view of an electric motor, according to a preferred embodiment of the present invention; 
     FIG. 2 is a top view of a metallic lamination; 
     FIG. 3 is a cross-sectional view of stator laminations stacked and compressed within a stator housing between two snap rings; 
     FIG. 4 is a front elevational view of an automated stator press, according to a preferred embodiment of the present invention; 
     FIG. 5 is a front elevational view of an automated stator press, illustrating a stator housing disposed over a mandrel and laminations; 
     FIG. 6 is a cross-sectional view of a hydraulic ram, a stator housing, and an air-operated insertion tool, according to a preferred embodiment of the present invention; 
     FIG. 7 is a cross-sectional view of the hydraulic ram, the stator housing, and the air-operated insertion tool, illustrating the hydraulic ram driving the inner portion of the air-operated insertion tool to compress the laminations within the stator housing; 
     FIG. 8 is a cross-sectional view of the hydraulic ram, the stator housing, and the air-operated insertion tool, illustrating the insertion of a snap ring into the stator housing by a snap ring deployment tool on the air-operated insertion tool; 
     FIG. 9 is an end view of a drive system and frame of the automated stator press, according to a preferred embodiment of the present invention; 
     FIG. 10 is an end view of the laminations disposed over a mandrel supported in a saddle by a shoe and a shim respectively, according to a preferred embodiment of the present invention; 
     FIG. 11 is an end view of the stator housing supported in a saddle by a shoe, according to a preferred embodiment of the present invention; 
     FIG. 12 is an end view similar to that of FIGS. 11 and 12, but illustrating the stator housing displacing the shims as the stator housing is moved over the shoe; 
     FIG. 13 is a side elevational view of a mandrel, according to a preferred embodiment of the present invention; and 
     FIG. 14 is a elevational view of a two-piece mandrel, according to an alternative embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring generally to FIG. 1, an electric motor  20  is illustrated according to a preferred embodiment of the present invention. Motor  20  is an exemplary motor, such as an elongate, submersible motor that may be connected in a submersible pumping system of the type deployed in a wellbore to pump production fluids, e.g. petroleum. However, the present invention should not be limited to submersible motors. Electric motor  20  generally includes a stator  22  mounted in a stator housing  24 . The stator  22  is used to produce a magnetic field. A rotor  26  is disposed within the stator  22  and supported by bearings  27 . The rotor is mounted to a shaft  28  for rotation about an axis  30  within the stator housing  24 . The rotor  26  rotates about the axis  30  under the influence of the magnetic field produced by the stator  22 , as is understood by those of ordinary skill in the art. 
     Referring generally to FIGS. 1 and 2, the stator of a typical electric motor is made from a plurality of metallic laminations  32  that are stacked together. The laminations  32  have an interior opening  34  into which the rotor  26  and shaft  28  are received when the motor  20  is fully assembled. Additionally, each lamination  32  includes a plurality, e.g.  18 , of axial openings  35  that are radially outlying from interior opening  34 . As the laminations  32  are stacked together to form a stator  22 , the axial openings  35  are aligned to create longitudinal slots through the stator  22 . Eventually, conductors are disposed through these longitudinal slots. There are typically two different lamination materials used in electric motor construction. The largest number of laminations are made from steel  36 , but bronze laminations  37  are also used as the bearing surfaces for the rotors. A typical electric motor may have 18 inches of steel laminations followed by 2.5 inches of bronze laminations. Finally, the laminations  32  also include at least one keyway  38  for alignment with a key during installation. 
     Referring generally to FIGS. 1 and 3, during assembly the metallic laminations  32  are stacked together on a mandrel and then inserted into the stator housing  24 . The laminations  32  are compressed together inside the stator housing  24  to solidify the stator construction and prevent the laminations  32  from moving or rotating within the stator housing  24 . The laminations  32  are maintained in a state of compression by two snap rings  40 . The snap rings are placed in grooves  41  around the interior of the stator housing  24 . 
     After the laminations  32  are installed within the stator housing  24  conductive wiring  42  is wound through the axial openings  35 . An electrical connector  43  is used to couple an electrical cable  44  from the surface to the conductive wiring  42  in the electric motor  20 . 
     Referring generally to FIGS. 4 and 5, an automatic stator press  46  is used to insert the metallic laminations  32  into the stator housing  24  and to compress the laminations  32  together inside the stator housing  24 . The automatic stator press  46  has a support frame  48  and a plurality of saddles  50  that support the metallic laminations  32  and the stator housing  24 . The laminations  32  are stacked together over mandrel  52  and then placed in saddles  50  at the hydraulic ram end of the automatic stator press  46 . 
     The stator housing  24  is placed in the automatic stator press  46  at the tail end opposite mandrel  52  and metallic laminations  32 . In the illustrated embodiment, a tailstock  56 , is used to drive the stator housing  24  over the mandrel  52  and metallic laminations  32 . Tailstock  56  is a resistance head drive system that travels along rack  60  mounted atop the frame  48 . The stator housing  24  is, in turn, attached to or abutted with the tailstock  56 . As the tailstock  56  travels along the rack  60  it forces the stator housing  24  toward the laminations  32 . Initially, a snap ring  40  is placed inside the stator housing  24  at the end opposite the mandrel  52 . This snap ring  40  abuts the metallic laminations  32  when the stator housing  24  is in proper position over the mandrel  52 . 
     Referring generally to FIG. 5, when the stator housing  24  is in position over the laminations  32  the tailstock  56  can be locked into place. A hydraulic ram  58  is used to compress the laminations  32  inside the stator housing  24 . The hydraulic ram  58  is operated by an automatic control system  61 . An air-operated insertion tool  62  is used with the hydraulic ram  58  to compress the laminations  32  and also to install a second snap ring  40  into a groove  41  inside the stator housing  24 , thus maintaining the laminations  32  under compression. The air-operated insertion tool  62  includes an outer portion  64  that attaches to the stator housing  24  and an inner portion  66  that is driven by the hydraulic ram  58  through the outer portion  64  and into contact with the metallic laminations  32 . A second snap ring  40  can also be inserted into the stator housing  24  by the air-operated insertion tool  62 . 
     The locked tailstock  56  prevents the stator housing  24  and, thus, the laminations  32  from moving away from the force of the hydraulic ram  58 . This results in the laminations  32  being compressed inside the stator housing  24  between the air-operated insertion tool  56  and the tailstock  56 . The tailstock  56  may utilize an adapter sized to fit against the laminations  32  and to thereby assist the first snap ring  40  in compressing the laminations and to prevent the laminations from bowing. A pressure transducer  67  can be included in the tailstock to measure the force of compression provided by the hydraulic ram. An alternative method of operation is to secure the end of the stator housing  24  adjacent the insertion tool  62  to the frame  48 , as opposed to the tailstock  56 . In the former method, the force of the hydraulic ram  58  on the laminations  32  will tend to stretch the stator housing  24 . In the latter method, the force of the hydraulic ram  58  on the laminations  32  will tend to stretch the frame  48 . 
     To determine the amount of stretch of the stator housing, a digital scale  68  is used to measure the length of the stator housing  24  before, during, and after the laminations  32  are compressed. During operation, a stator housing that is initially 10′ long may stretch to 10′⅛″ during compression of the laminations. After compression, when the snap rings are installed, the stator housing may remain stretched to 10′{fraction (1/16)}″. The digital scale travels along a rail (not shown) along the top of the frame  48 . In the illustrated embodiment the digital scale  68  is shown in two positions, at each end of the stator housing  24 . The first position is the zero position  70 . Here the scale  68  is zeroed. The scale  68  is then moved along the rail to a second position  72  at the other end of the stator housing  24 , measuring the length of the housing  24  as it travels. The digital scale  68  is attached to the end of the housing  24  and moves with any change in the length of the housing  24  caused by the compression of the laminations  32 . The digital scale  68  can also be used to provide a signal to the automatic control system  61 . 
     A second digital scale  74  is used to measure the movement of the inner portion  66  of the insertion tool  62 . This scale also can be used to provide a signal to the automatic control system  61 . This scale provides an operator and the automatic control system  61  with an indication of the amount of compression in the laminations  32 . It should be noted that automatic control system  61  may comprise a variety of commercially available controllers, such as a programmable logic controller or a computer numerical control. 
     Referring generally to FIGS. 6,  7  and  8 , the outer portion  64  of the air-operated insertion tool  62  threads into the end of the stator housing  24 . The inner portion  66  of the air-operated insertion tool slides through the outer portion  64 . The inner portion  66  includes an abutment plate  76  that is contacted by the hydraulic ram  58 . The inner portion  66  also includes an outer sleeve  78  and an inner sleeve  80 . 
     In the illustrated embodiment, at the end of the sleeves adjacent to the stator housing  24  is a snap ring deployment assembly  82 . The snap ring deployment assembly  82  retains the second snap ring  42  near the end of the inner sleeve  80 . The snap ring  42  is retained between an outer jacket  84  and a raised portion  86  of the inner sleeve  80  and against a sliding sleeve  88 . There is a narrow passage  90  formed between the inner sleeve  78  and the outer sleeve  80  that leads to the sliding sleeve  88 . A valve assembly  92  couples compressed air to the narrow passage  90  in the air-operated insertion tool. When air is applied, the compressed air forces the sliding sleeve  88  forward, pushing the snap ring  40  away from the outer jacket  84  and the inner sleeve  78 , towards the groove  41  in the stator housing  24 . The snap ring  40  expands into the groove  41 , forming a barrier to the laminations  32 . Thus, the laminations remain compressed even after the force of the hydraulic ram is removed. 
     Referring generally to FIG. 7, the hydraulic ram  58  can be automatically operated by the automatic control system  61  to drive the abutment plate  76  toward the stator housing  24 . This forces the inner portion  66  of the insertion tool  62  against the metallic laminations  32 , compressing the laminations  32 . 
     The automatic control system  61  includes an interface, such as a graphical user interface, and electronic memory to enable an operator to provide the control system with desired process information, such as the amount of desired compression. The control system also receives process information from sensors, such as the pressure transducers and digital scales. The automatic control system  61  also includes a processor to compare the process information stored in the electronic memory to the process information provided by the sensors. This enables the automated stator press  46  to automatically produce the desired amount of compression in the laminations without distorting the shape of the stator housing. 
     Referring generally to FIG. 8, once the desired amount of compression has been achieved by the automated stator press, an operator can perform a series of checks to ensure second snap ring  42  is in proper position for insertion into the groove  41 . The operator can compare the amount of stretch indicated by the first digital scale  68  with the position shown by the second digital scale  74  to ensure that the second snap ring  42  is positioned properly for insertion into the groove  41  inside the stator housing  24 . If satisfied, the operator opens valve assembly  92  and compressed air from the valve assembly  92  passes through the narrow passage  90  toward the sliding sleeve  88 . The second snap ring  42  is then driven forward into the corresponding groove  41 , where it expands for retention in groove  41 . If not satisfied, the operator can manually position the ram to the desired location. 
     Once the second snap ring  42  has been installed, the hydraulic ram  58  is withdrawn and the second snap ring  42  maintains the laminations  32  under compression. The stator housing  24  is then removed from the automatic stator press  46 , and the remainder of the manufacturing process is completed, e.g. winding conductors through the axial openings  35  in the laminations  32 . 
     Elements of the air-operated insertion tool  62  include an isolation valve  94  and a hose connection  96  (see FIG. 6) to provide and control the supply of air. Additionally, a hoist ring also can be used in combination with a hoist or crane to position the insertion tool. Furthermore, various O-rings may be used to create seals between the sleeves, and the insertion tool may include handles to assist in threading the outer sleeve  78  into the stator housing  24 . 
     Referring generally to FIG. 9, the frame  48  and tailstock  56  of an exemplary embodiment of the automated stator press is shown. Rack  60  resides along the top of and on each side of frame  48 . The tailstock  56  travels along rack  60  via two hydraulic motors  100 . The drive shafts  102  of the hydraulic motors  100  are drivingly coupled by chain drives  104  to two gears  106 . Hydraulic fluid lines  104  couple hydraulic fluid to power the hydraulic motors  100 . As the gears  106  rotate, tailstock  56  is driven along rack  60 . The gears  106  are governed together by a coupler  110  to maintain a uniform speed. It should be noted that a variety of different drive systems can used with the automated stator press. For example, electric motors can be used in place of the hydraulic motors and/or a screw drive system can be used rather than a rack-and-pinion system. 
     Referring generally to FIGS. 10,  11 , and  12 , the stator housing  24  and laminations  32  placed over mandrel  52  are supported in frame  48  by saddles  50 . FIG. 10 illustrates laminations  32  and mandrel  52  placed in a saddle  50 . A shoe  112  is placed in each saddle  50 . Shims  114  that sit atop shoes  112  support the laminations and mandrel. Shims  114  help to center the mandrel  52  and laminations  32  inside stator housing  24  during installation. As illustrated in FIG. 11, shoes  112  also support stator housing  24  in each saddle  50 . 
     Referring generally to FIG. 12, stator housing  24  displaces shim  114  as the stator housing is driven over the laminations. The stator housing  24  is supported by the shoe  112  after the shim  114  is displaced. This process continues through each of the three saddles  50  as the stator housing  24  is fully moved over mandrel  52  and laminations  32 . A small quantity of lubricating oil is coated over the laminations to ease the insertion of the laminations into the stator housing. The lubricating oil may also be used to facilitate movement of the stator housing  24  over shoes  112 . Shoes  112  and shims  114  may be formed in a variety of sizes, depending on the size of the stator housing  24  and the laminations  32 . 
     After insertion of laminations  32 , the automatic stator press  46  removes mandrel  52  from stator housing  24 . To facilitate removal, each end of mandrel  52  has a threaded recess  116  to allow a mandrel removal tool (not shown) to be threaded into the mandrel  52 , as illustrated in FIG.  13 . The mandrel removal tool is then connected to the tailstock  56 . The tailstock  56  pulls the mandrel  52  from inside the stator housing  24 . A mandrel shoe, similar to the shoe  112  used to support the stator housing  24 , is placed in each saddle  50  to support the mandrel  52  as it is withdrawn from the stator housing  24 . In the illustrated embodiment, the mandrel  52  has a key  118  for alignment with the keyway  38  formed in metallic laminations  32 . 
     Referring generally to FIG. 14, a mandrel may alternatively be constructed in two-pieces. In the illustrated embodiment, a first mandrel piece  120  with a threaded male end  121  is threadably inserted into a female receptacle  122  in a second mandrel piece  123 . 
     It will be understood that the foregoing description is of a preferred embodiment of this invention, and that the invention is not limited to the specific form shown. For example, the motors used in the drive system may be electric motors rather than hydraulic motors; the size of the components can be adjusted according to the application; and the control system can be adapted to a variety of sensors and configurations. Furthermore, the automated stator press may be used to compress laminations in a stator for a generator, rather than an electric motor. These and other modifications may be made in the design and arrangement of the elements without departing from the scope of the invention as expressed in the appended claims.

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