Abstract:
A submersible linear motor oil pumping system includes a submersible linear motor ( 100 ), an oil pump ( 200 ), a sealing device ( 300 ), and a balance assembly ( 400 ) installed underground. The submersible linear motor ( 100 ) includes a stator ( 10 ) and a mover ( 20 ) moving reciprocally inside the stator ( 10 ). The oil pump ( 200 ) includes a barrel ( 32 ), a piston ( 34 ), an outer sleeve ( 36 ), and a oil feeding sieve tube ( 38 ). The sealing device ( 300 ) is positioned between the submersible linear motor ( 100 ) and the oil pump ( 200 ). The balance assembly ( 400 ) is positioned at a lower end of the submersible linear motor ( 100 ) and is configured to balance pressure inside and outside the submersible linear motor ( 100 ). The present system omits the sucker rod of existing oil pumping systems, avoiding stroke loss caused by sucker rod elongation and energy loss caused by the weight of the sucker rod and pipe rod offset grinding, thereby improving the efficiency of the system.

Description:
FIELD OF THE INVENTION 
       [0001]    The present disclosure relates to oil pumping systems, and more particularly relates to a highly effective submersible linear motor oil pumping system. 
       BACKGROUND OF THE INVENTION 
       [0002]    The conventional oil pump machine mainly adopts a beam-pumping unit (pumpjack) to pump oil. In the process of pumping oil, the pumpjack, which serves as a mechanical power apparatus, is connected to a piston of an oil pump located thousands of meters underground via an oil pump rod. The oil pump rod reciprocally drives the piston of the oil pump to lift oil to the ground. The oil pump machine mainly has disadvantages as follows: high energy consumption, low pumping efficiency, eccentric wear between the oil pump rod and an oil discharging tube, it requires stopping the machine for adjusting the parameters, and the adjusting range of the parameter is limited. 
         [0003]    Submersible pump driven by linear motor is capable of transferring electric energy into mechanical energy of straight reciprocal motion, not only simplifying the mechanical transmission process, but also effectively improving the efficiency. The pumping parameter can be continuously adjusted, thus providing conditions for realizing an automatic control and meeting a requirement of oil pump technology, it is a promising new type of pumping machine. However, there is room for improving an efficiency of the linear motor of the conventional pumping machine. 
       SUMMARY OF THE INVENTION 
       [0004]    Therefore, it is necessary to provide a submersible linear motor oil pumping system with high efficiency. 
         [0005]    A submersible linear motor oil pumping system includes a submersible linear motor, an oil pump, a sealing device, and a balance assembly, which are disposed underground, wherein the submersible linear motor comprises a stator, and a mover that moves reciprocally inside the stator; the oil pump comprises a barrel, a piston, an outer sleeve, and a oil feeding sieve tube, the barrel is positioned in the outer sleeve, the piston is connected to an upper end of the mover and is reciprocally movable inside the barrel, the piston and the barrel form an oil discharging chamber therebetween, the outer sleeve and the barrel form a first reflux chamber therebetween, the oil feeding sieve tube is positioned at a lower end of the outer sleeve and is in communication with an oil pumping chamber located in the piston; the sealing device is positioned between the submersible linear motor and the oil pump; the balance assembly is positioned at a lower end of the submersible linear motor and is configured to balance pressure inside and outside the submersible linear motor. 
         [0006]    In one embodiment, the stator includes a stator inner tube, a stator outer tube, and a plurality of coils positioned between the stator inner tube and the stator outer tube, the coil is a circular wire pie formed by winding a conductive wire and encapsulating the conductive wire with epoxy resin, two adjacent coils are provided with a silicon steel plate assembly therebetween, the coils are insulated from the silicon steel plate assembly. 
         [0007]    In one embodiment, the stator further comprises a cable connected to the coils, the stator is connected to a control system located on a ground via the cable. 
         [0008]    In one embodiment, the stator further comprises a motor upper coupler and a motor lower coupler positioned on opposite ends of the stator outer tube, the submersible linear motor is connected to the sealing device via the motor upper coupler, and is connected to the balance assembly via the motor lower coupler, glue is filled between the motor upper coupler and the motor lower coupler, and between the stator inner tube and the stator outer tube, such that the stator is solidified as a whole. 
         [0009]    In one embodiment, the mover includes a mover inner tube; a plurality of permanent magnets sleeved on the mover inner tube, a magnetizing direction of each permanent magnet is axial, and the magnetizing directions of two adjacent permanent magnets are opposite; a plurality of magnetic rings sleeved on the mover inner tube, and each magnetic ring being disposed between two adjacent permanent magnets; and a plurality of wearing rings sleeved on the mover inner tube, several permanent magnets being positioned between adjacent two wearing rings, wherein the plurality of wearing rings and the stator inner tube form a friction pair. 
         [0010]    In one embodiment, the stator comprises a stator inner tube, a stator outer tube, and a plurality of coils positioned between the stator inner tube and the stator outer tube, the coil is a circular wire pie formed by winding a conductive wire and encapsulating the conductive wire with epoxy resin, two adjacent coils are provided with a silicon steel plate assembly therebetween, the coils are insulated from the silicon steel plate assembly. 
         [0011]    In one embodiment, the stator further comprises a cable connected to the coils, the stator is connected to a control system located on a ground via the cable. 
         [0012]    In one embodiment, the stator further comprises a motor upper coupler and a motor lower coupler positioned on opposite ends of the stator outer tube, the submersible linear motor is connected to the sealing device via the motor upper coupler, and is connected to the balance assembly via the motor lower coupler, glue is filled between the motor upper coupler and the motor lower coupler, and between the stator inner tube and the stator outer tube, such that the stator is solidified as a whole. 
         [0013]    In one embodiment, the mover includes: a mover inner tube; a plurality of permanent magnets sleeved on the mover inner tube, a magnetizing direction of each permanent magnet is axial, and the magnetizing directions of two adjacent permanent magnets are opposite; a plurality of magnetic rings sleeved on the mover inner tube, and each magnetic ring being disposed between two adjacent permanent magnets; and a plurality of wearing rings sleeved on the mover inner tube, several permanent magnets being positioned between adjacent two wearing rings, wherein the plurality of wearing rings and the stator inner tube form a friction pair. 
         [0014]    In one embodiment, the mover further comprises a plurality of mover outer tubes, each mover outer tube is sleeved on the permanent magnets and the magnetic rings and is positioned between adjacent two wearing rings, an outer diameter of the mover outer tube is less than that of the wearing ring. 
         [0015]    In one embodiment, the mover further comprises two locknuts positioned on opposite ends of the mover outer tube and configured to compress the permanent magnets and the magnetic rings. 
         [0016]    In one embodiment, the mover inner tube is hollow, the mover and the stator are filled with lubricating oil therebetween, the lubricating oil can flow inside the mover inner tube. 
         [0017]    In one embodiment, the barrel comprises an upper barrel and a lower barrel connected to the upper barrel, the piston comprises an upper piston and a lower piston connected to the upper piston, the oil pumping chamber is formed in the upper piston, the oil discharging chamber is formed between the upper piston and the upper, the upper piston is provided with a movable valve at a top end thereof connecting the oil pumping chamber and the oil discharging chamber, the upper barrel is provided with a fixed valve at a top thereof connecting the oil discharging chamber and the first reflux chamber, the lower piston and the upper barrel form a second reflux chamber therebetween that is in communication with the first reflux chamber. 
         [0018]    In one embodiment, the lower piston forms an oil suction chamber therein, the lower piston and the upper piston are provided with a one-way valve therebetween, whereby oil from the oil suction chamber can enter the oil pumping chamber through the one-way valve. 
         [0019]    In one embodiment, an end of the lower piston is provided with a connector configured to be connected to the mover, the connector defines a plurality of oil inlet holes, whereby oil can enter the oil suction chamber through the plurality of oil inlet holes from the oil feeding sieve tube. 
         [0020]    In one embodiment, the oil pump further comprises an oil discharging pipe and a desilting pipe, the oil discharging pipe is connected to the outer sleeve, the desilting pipe is located inside the oil discharging pipe, the oil discharging pipe and the desilting pipe form a circular space therebetween for desilting. 
         [0021]    In one embodiment, the sealing device comprises an outer cylinder, a connecting rod, and a sealing assembly, the outer cylinder is positioned between the submersible linear motor and the oil pump, the connecting rod is movably received in the outer cylinder, a lower end of the connecting rod is fixedly connected to the mover, an upper end of the connecting rod is fixedly connected to the piston, the sealing assembly is positioned between the connecting rod and the outer cylinder. 
         [0022]    In one embodiment, the sealing device further comprises a sand scratcher located between the connecting rod and the outer cylinder, the outer cylinder defines a sewage hole, whereby impurities attached to the connecting rod can be scratched off by the sand scratcher and discharged through the sewage hole. 
         [0023]    In one embodiment, the sealing device further comprises an upper joint to fix an upper end of the outer cylinder to the oil feeding sieve tube, the upper joint is provided with a buffer block therein to buffer impact of the piston. 
         [0024]    In one embodiment, the sealing device further comprises two centralizing blocks positioned at opposite ends of the sealing assembly. 
         [0025]    The system does not use the oil pump rod of the conventional oil pump system, thereby avoiding the stroke loss due to an extension of the oil pump rod. In addition, it avoids the energy loss due to an eccentric wear between the oil pump rod and the hollow rod, thus enhancing an efficiency of the system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    These and other features of the present invention will become readily apparent upon further review of the following specification and drawings. In the drawings, like reference numerals designate corresponding parts throughout the views. Moreover, components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present disclosure. 
           [0027]      FIG. 1  is a cross-sectional view of a submersible linear motor oil pumping system, according to one embodiment; 
           [0028]      FIG. 2  is an enlarged view of the submersible linear motor of  FIG. 1 ; 
           [0029]      FIG. 3 a    is an enlarged, cross-sectional view of an oil pump of  FIG. 1  in one state; 
           [0030]      FIG. 3 b    is an enlarged, cross-sectional view of the oil pump of  FIG. 1  in another state; and 
           [0031]      FIG. 4  is an enlarged view of a portion of a sealing device of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0032]    Embodiments of the invention are described more fully hereinafter with reference to the accompanying drawings. The various embodiments of the invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Elements that are identified using the same or similar reference characters refer to the same or similar elements. 
         [0033]    It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. 
         [0034]    Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
         [0035]    Referring to  FIG. 1 , a submersible linear motor oil pumping system includes a submersible linear motor  100 , an oil pump  200 , a sealing device  300 , and a balance assembly  400 , which are all mounted underground. The oil pump  200  is positioned above the submersible linear motor  100 . The balance assembly  400  is positioned below the submersible linear motor  100 . The sealing device  300  is positioned between the oil pump  200  and the submersible linear motor  100 . 
         [0036]    Referring to  FIG. 2 , the submersible linear motor  100  is a power source of the whole system, and includes a stator  10  and a mover  20  received in the stator  10  for reciprocating movement. 
         [0037]    The stator  10  includes a stator inner tube  14 , a stator outer tube  13 , and a plurality of windings  11  positioned between the stator inner tube  14  and the stator outer tube  13 . The stator outer tube  13  is made of metallic material having a high permeability. The rigidity of the stator outer tube  13  should be taken into consideration, thus avoiding a magnetic saturation of the motor, preventing the deformation of the motor, and protecting an internal structure of the motor. The stator inner tube  14  is made of wear-resisting metal which is not conductible for magnetic. The stator inner tube  14  serves as a component directly contacting the mover  20 , thus the surface thereof should be smooth and wear-resisting. The stator inner tube  14  can be subjected to a special surface hardening treatment, such as a nitrogen treatment, a chromate treatment, or a spraying welding, to adapt to harsh environments of different oil wells. As formed by connecting three-phase coils, the windings  11  are circular copper (or aluminum) wire pies formed by twining a conductive wire and encapsulated with epoxy resin. The windings  11  are arranged along an axial direction of the stator inner tube  14 . A silicon steel plate assembly  12  is provided between two adjacent windings  11 . The silicon steel plate assembly  12  consists of a plurality of silicon steel plates laminated together, thus it has a better magnetic property and less core loss. Insulating layers are provided between the windings  11  and the silicon steel plate assembly  12 . The insulating layers are made of insulating material having a better heat-conducting property so as to ensure a better heat dissipation performance and insulation and improve a reliability of the motor. The stator  10  further includes a cable  15  connected to the windings  11 . The cable  15  can be an armor flat cable special for oil fields. An end of the cable  15  extends to connect with a control system (not shown) on the ground. A wire outlet of the cable  15  on the motor is sealed by squeezing filler, which can be subjected to 30 MPa high pressure environments. The stator  10  further includes a motor upper coupler  16  and a motor lower coupler  17  on opposite ends of the stator outer tube  13 . The submersible linear motor  100  is connected to the sealing device  300  via the motor upper coupler  16 , and connected to the balance assembly  400  via the motor lower coupler  17 . The motor upper coupler  16 , the motor lower coupler  17 , the stator inner tube  14 , and the stator outer tube  13  cooperatively form an airtight cavity to protect the windings  11  and the silicon steel plate assembly  12 . Epoxy resin glue is injected into the airtight cavity to fully fill the clearances inside the stator, and then the whole stator is solidified to form an entire body, which greatly enhances the rigidity and reliability. 
         [0038]    The mover  20  includes a mover inner tube  21 , a mover outer tube  22 , a plurality of permanent magnets  23 , a plurality of magnetic rings  24 , a plurality of wearing rings  25 , and two locknuts  26 . The mover inner tube  21  has a hollow tubular structure. The material of the permanent magnets  23  is preferably made of neodymium iron boron alloy with a high performance and a high coercive force. The permanent magnet  23  is substantially in an annular shape. The plurality of permanent magnets  23  are sleeved on the mover inner tube  21 . The magnetizing direction of each permanent magnet  23  is arranged along an axial direction. The magnetizing directions of two adjacent permanent magnets  23  are opposite. The magnetic ring  24  is also substantially in an annular shape and has a same diameter as that of the permanent magnet  23 . The plurality of magnetic rings  24  is sleeved on the mover inner tube  21 , and each magnetic ring  24  is disposed between two adjacent permanent magnets  23 . The magnetic ring  24  is made of metallic material having a better magnetic conductivity. The wearing ring  25  has an annular shape. The plurality of wearing rings  25  is sleeved on the mover inner tube  21 . The plurality of permanent magnets  23  are provided between every two wearing rings  25 . In the illustrated embodiment, every five permanent magnets  23  are arranged between two wearing rings  25 . The outer diameter of the wearing ring  25  is slightly greater than that of the magnetic ring  24 , thus the surface of the wearing ring  25  protrudes out of the surface of magnetic ring  24 . The wearing ring  25  is made of hard alloy, such as Stellite, which has a high hardness and a better magnetic performance. The wearing ring  25  and the stator inner tube  14  rub against each other during the operation of the motor, which can ensure a smooth travelling of the motor without vibration, such friction pair has a high reliability and a long service life. Further, the mover outer tube  22  is sleeved on the permanent magnets  23  and the magnetic rings  24 , each mover outer tube  22  is positioned between two wearing rings  25 . The mover outer tube  22  has an outer diameter slightly less than the outer diameter of the wearing ring  25 , such that the mover outer tube  22  will not rub against the stator inner tube  14 . The mover outer tube  22  is made of non-magnetic metallic material. As the permanent magnet has a low corrosion resistance and is brittle, the mover outer tube  22  can effectively protect the permanent magnet  23  from corrosion and impact. The locknuts  26  are mounted on opposite ends of the mover outer tube  22  to compress the permanent magnet  23  and the magnetic ring  24  and avoid them from loosing. 
         [0039]    During operation, the parameter can be configured by the numerical control apparatus over-ground according to an actual requirement, and the power is supplied according to specific program, thus allowing the stator  10  to generate a variable magnetic field. The magnetic field of the stator  10  and the magnetic field of the mover  20  cooperatively generate an electromagnetic actuation force, thereby driving the mover  20  to move up and down. Preferably, opposite ends of the motor are sealed, by which an airtight cavity is formed along with the mover  20  and the stator  10 . The chamber is filled with lubricating oil. In the reciprocating movement of the motor, since the mover inner tube  20  has a hollow structure, the lubricating oil can flow inside the mover inner tube  21  rapidly, i.e. moving from an end of the mover  20  to an opposite end of the mover  20 , forming a loop, thereby reducing a resistance. 
         [0040]    Referring to  FIG. 3 a   , the oil pump  200  is a bi-directional piston pump and includes a barrel  32 , a piston  34 , an outer sleeve  36 , an oil feeding sieve tube  38 , and an oil discharging tube  39 . The outer sleeve  36  is sleeved on the barrel  32 , such that a reflux chamber  362  is formed between the outer sleeve  36  and the barrel  32 . The piston  34  is movably positioned in the barrel  32 . The inner sidewall of the barrel  32  and the outer sidewall of the piston  34  are required to be subjected to a surface hardening treatment, such as a chromate treatment. The oil feeding sieve tube  38  is fixed to a lower end of the outer sleeve  36 , configured to filtrate the sediment in the well liquid. 
         [0041]    The barrel  32  includes an upper barrel  322  and a lower barrel  324  fixed to the upper barrel  322 . The upper barrel  322  has a diameter greater than that of the lower barrel  324 . The upper barrel  322  is provided with a fixed valve  321  at a top end thereof. Well liquid can flow into the first reflux chamber  362  via the fixed valve  321 . The upper barrel  322  further defines a reflux hole  323  at a bottom end thereof. 
         [0042]    The piston  34  includes an upper piston  342  and a lower piston  344  fixed to the upper piston  342 , the upper piston  342  can move up and down in the upper barrel  322  accordingly. The upper piston  342  defines an oil pumping chamber  341 . An oil discharging chamber  345  is formed between a top of the upper piston  342  and the upper barrel  322 . The upper piston  342  is further provided with a movable valve  346  at the top end thereof. The well liquid can enter the oil discharging chamber  345  from the oil pumping chamber  341  via the movable valve  346 . The lower piston  344  can move up and down in the lower barrel  324  accordingly. The lower piston  344  defines an oil suction chamber  343  therein. A one-way valve  347  is provided between the lower piston  344  and the upper piston  342 . The well liquid can enter the oil pumping chamber  341  from the oil suction chamber  341  via the one-way valve  347 . The lower piston  344  has a less diameter than that of the upper barrel  322 , such that a second reflux chamber  364  is formed between the lower piston  344  and the upper barrel  322 . The first reflux chamber  362  is in fluid communication with the second reflux chamber  364  via the reflux hole  323 . The lower piston  344  is further provided with a coupler  348  at a terminal end thereof. The piston  34  is connected to the mover  20  of the submersible linear motor  100  via the coupler  348 . The coupler  348  defines a plurality of oil inlet holes  349 . The well liquid can enter the oil suction chamber  343  from the oil feeding sieve tube  38  via the oil inlet holes  349 . 
         [0043]    An upper end of the outer sleeve  36  is connected to the oil discharging tube  39  via a coupler  37 . The oil discharging tube  39  is provided with a desilting pipe  392  therein, which has a diameter than that of the oil discharging tube  39 . An annular space  394  for depositing sand is formed between the oil discharging tube  39  and the desilting pipe  392 , which is conducive to the wear-protection of the pump and the motor. 
         [0044]    The working operation of the oil pump  200  will be fully described hereinafter with reference to  FIG. 3 a    and  FIG. 3   b.    
         [0045]    Referring to  FIG. 3 a   , when the piston  34  moves downward, the fixed valve  321  is closed, the movable valve  346  and the one-way valve  347  are opened. The well liquid is filtrated by the oil feeding sieve tube  38  and enters the oil suction chamber  343 , and then enters the oil discharging chamber  345  via the oil pumping chamber  341 . Meanwhile, the upper piston  342  moves downward and compresses the volume of the second reflux chamber  364 , thus the well liquid in the second reflux chamber  364  can enter the first reflux chamber  362  via the reflux hole  323 , and enters the oil discharging tube  39  via the coupler  37 . 
         [0046]    Referring to  FIG. 3 b   , when the piston  34  moves upward, the fixed valve  321  is opened, the movable valve  346  and the one-way valve  347  are closed. Because the upper piston  342  compresses the volume of the oil discharging chamber  345 , the well liquid in the oil discharging chamber  345  can enter the first reflux chamber  362  via the fixed valve  321 . Some of the well liquid enters the oil discharging tube  39  via the coupler  37 , the rest of the well liquid enters the second reflux chamber  364  via the reflux hole  323 , which will then enter the oil discharging tube  39  during the next down stroke of the piston  34 . 
         [0047]    By analyzing the above movements, it can be inferred that during the up stroke and the down stroke of the piston  34 , the oil pump  200  discharges the oil all the time, therefore the pump efficiency can be enhanced, an oil output capacity is increased. 
         [0048]    It can be understood that, in an alternative embodiment, the lower barrel  324  can have a diameter equal to that of the upper barrel  322 . The reflux hole  323  can also be omitted. When the piston  34  moves downward, the well liquid is filtrated and enters the oil suction chamber  343  from the oil feeding sieve tube  38 , and then the well liquid enters the oil discharging chamber  345  via the oil pumping chamber  341 . When the piston  34  moves upward, the well liquid in the oil discharging chamber  345  enters the first reflux chamber  362  via the fixed valve  321 , and then enters the oil discharging tube  39  via the coupler  37 . The oil pump  200  is a one-way oil pump according to the embodiment. 
         [0049]    The sealing device  300  is positioned between the submersible linear motor  100  and the oil pump  200 , which functions to seal the motor, thus preventing the well liquid and sediment from entering into the motor from an upper of the motor, ensuring a reliability of the motor, prolonging a service life of the motor. 
         [0050]    Referring also to  FIG. 4 , the sealing device  300  includes an external cylinder  40 , a connecting rod  42 , a sealing assembly  44 , and a sand scratcher  46 . 
         [0051]    The external cylinder  40  is substantially a cylindrical tube and is positioned between the submersible linear motor  100  and the oil pump  200 . Specifically, a lower end of the external cylinder  40  is fixedly connected to the motor upper coupler  16  of the submersible linear motor  100  via a sealer lower joint  402 . An upper end of the external cylinder  40  is fixedly connected to the oil feeding sieve tube  38  of the oil pump  200  via a sealer upper joint  404 . The external cylinder  40  further defines a sewage hole  41 . In the illustrated embodiment, the sealer upper joint  404  is further provided with a buffer block  47  therein, configured to buffer an impact coming from the piston  34  of the oil pump  200 . 
         [0052]    The connecting rod  42  is a solid rod movably extending inside the external cylinder  40 . The surface of the connecting rod  42  can be subjected to a hardening treatment, such as chromate treatment. A lower end of the connecting rod  42  is fixed to the mover  20  of the submersible linear motor  100 . An upper end of the connecting rod  42  is fixed to the piston  34  of the oil pump  200 , therefore the upward and downward movements of the mover  20  can be transmitted to the piston  32 . 
         [0053]    The sealing assembly  44  is positioned between the connecting rod  42  and an inner sidewall of the external cylinder  40 . The sealing assembly  44  functions to block impurities such as the well liquid and sediment from entering into the motor. In the illustrated embodiment, the sealing assembly  44  is a combination of sealing members, such as a U shaped sealing ring and M or V shaped sealing rings. The sealing ring is made of material which is wear-resistant and anti-corrosive, thus ensuring a long enough service life and an air-tightness of the sealing device. An upper end and a lower end of the sealing assembly  44  are provided with locknuts  43  used to fix and compress the sealing assembly  44 . The upper end and the lower end of the sealing assembly  44  are provided with a centralizing block  45  to centralize the connecting rod  42 , thus ensuring the connecting rod  42  being in the center of the external cylinder  40 . 
         [0054]    The sand scratcher  46  is positioned between the connecting rod  42  and the inner sidewall of the external cylinder  40  and is located above the sealing assembly  44 . An upper end of the sand scratcher  46  is made of elastic material, and it can always be a close contact with the connecting rod  42 , by which the impurities such as sediment adhered to the connecting rod  42  can be scraped and discharged out of the sealing device  300  via the sewage hole  41  on the external cylinder  40 . 
         [0055]    The balance assembly  400  is positioned on the lower end of the submersible linear motor  100 , which functions to balance an internal pressure and an external pressure of the motor, meanwhile it can decrease a probability that the impurities enter into the motor, thereby improving a sealing effect, a reliability and a service life of the whole system. The interior of the balance assembly  400  and the motor are filled with the same lubricate oil and is in fluid communication with the interior of the motor, which can balance the internal pressure and the external pressure of the motor, obtaining an effective sealing effect. The balance assembly  400  has a long tail pipe connected to a bottom of a capsule protector via threads. It is hard for the impurities, such as the sediment, to reach a bottom of the balance assembly due to gravity, thus further reducing the probability that the impurities enter into the motor, improving the sealing effect, and enhancing the reliability and the service life of the whole system. 
         [0056]    The above described submersible linear motor oil pumping system has advantages as follows: 
         [0057]    (1) The system does not use the oil pump rod of the conventional oil pump system, avoiding the stroke loss due to an extension of the oil pump rod. In addition, it avoids the energy loss due to an eccentric wear between the oil pump rod and the hollow rod, and enhances an efficiency of the system, particularly providing a better solution for the deviated well and the horizontal well. 
         [0058]    (2) The oil pump of the system is positioned above the submersible linear motor, such that the motor is immersed in the well liquid all the time, thus facilitating to the heat dissipation of the motor, and is also conducive to reducing the noise of the motor. And the motor running underground can avoid an unexpected workload and a maintenance fee due to man-made damages. In addition, in the conventional system that the current pump is mounted below the motor, the well liquid has to flow through an inner hole of the mover, thus the liquid output amount is limited by an inner diameter of the mover. However, the well liquid in the present embodiment is not required to flow through an inner hole of the mover, thereby the liquid output amount will not be limited. 
         [0059]    (3) The motor is provided with the sealing device on the upper end, and a balance assembly is provided on the lower end. Thus, the motor can remain in a full-sealing state, preventing the liquid containing sand, gas, H2S, and CO2 which can damage the motor from entering into the motor, obtaining a high reliability and a long service life, enabling the motor to adapt to the harsh environment underground. 
         [0060]    Although the present invention has been described with reference to the embodiments thereof and the best modes for carrying out the present invention, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the present invention, which is intended to be defined by the appended claims.