Patent Publication Number: US-2019170184-A1

Title: Connection type between a power source and a progressing cavity pump for submersible application

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to submersible apparatuses, and in particular a shaft and shaft assembly connecting a progressing cavity pump and a driving part. 
     2. Background Art 
     A progressing cavity pump is a volumetric rotor pump that absorbs and discharges liquid through the volumetric change of a series of sealed chambers. The simplest design of the progressing cavity pump consists of a single external helix that revolves eccentrically within an internal double helix. The internal helix has the same minor diameter and twice the pitch length of the external helix. The eccentricity is the locus of the rotor axis as its geometry rotates against the geometry of the stator. For oil field applications, the rotor is metal and the stator an elastomer that is injection molded within tubing. The rotor and stator are assembled with a compression fit. When the stator and rotor are assembled a series of cavities are formed. The cavities are sealed by the fit comprised of two lines on the rotor 180° apart. As the rotor turns the cavities spiral (progress) along the pump axis so that as one cavity diminishes, the following cavity increases. The fluid cross section is unchanged throughout the length of the stator, regardless of rotor position, resulting in a pulsation-free, positive axial flow. 
     A progressing cavity pump can also consist of a multiple helix rotor and corresponding stator—a multi-lobe pump. These are the preferred elements for drilling mud motors. Multiple helix designs can have any number of helices as long as there is one more helix in the stator than on its mating rotor. For pumps, the most affordable and practical multi-lobe pump design is a double helix rotor with a triple helix stator. 
     There is no inherent directionality in the progressing cavity pump elements. There is no top or bottom until other equipment is attached. Though the helices of a pump are conventionally right hand, there is nothing between pump elements that dictate the direction of rotation. If a stator is constrained horizontally on a bench, the pump maybe assembled by inserting the rotor in one end then rotating it clockwise into the stator. The rotor is backed out with counterclockwise rotation. In operation, both rotor and stator are held against axial movement. If the rotor is rotated clockwise, the fluid moves toward the viewer and the thrust away. If counterclockwise, the fluid moves away from the viewer and the thrust opposite. Some of the power driving a progressing cavity pump is converted to thrust since the liquid moves along the same axis as the rotating parts. 
     A shaft connection between a motor, which shaft revolves concentrically, and an above described progressing cavity pump must, necessarily, accommodate eccentric revolution on one end to match the motion of the pump rotor. Such connection is most reliably accomplished with a torque shaft. 
     The shaft connections for progressing cavity pumps that are currently available in the market have the following disadvantages: 
     Splines of conventional design, which are commonly employed at both ends of the shaft of the pump in the prior art, are easily susceptible to stress fatigue in spline connection when the pump operates continuously, resulting in problems such as a damage or fracturing of the spline. 
     Conventional splines require expensive machining processes for both shaft and mating parts. 
     Damaged conventional splines are difficult to repair, especially in the field. 
     Often, in conventional spline shafts, the spline is cut directly on a bar of one continuous diameter so that the outside diameter of the spline is the same as the diameter of the body of the shaft. Thus, the transverse cross section of the shaft is reduced at the spline, decreasing the maximum possible torque transmission. 
     In practical use, the pump rotation needs to be reversed for some reason. For example, the pump may be reversed for cleanup when the sand is produced in the oil wells. The pump rotor will move upwards when operated in reverse rotation. Thus, in the prior art, a thrust plate is additionally placed on the top of the pump for preventing the pump rotor from being detached from the connector. The thrust plate is usually fixed by welding, and it requires a precise shop measurement to correctly position the thrust plate. This practice to some extent increases the workload. 
     There remains a need for a shaft design that can address the technical problems in the prior art, such as a short service life due to stress fatigue readily caused by the torque shaft. 
     SUMMARY OF THE INVENTION 
     The present invention provides for a torque shaft, including a shaft body, wherein the torque shaft includes shaft heads and a shaft body, the shaft heads are provided on both ends of the shaft body, respectively, and the shaft heads are configured to fix the shaft body to a driving and driven member, and each of the shaft heads has a transverse cross section of a hexagonal shape. 
     The present invention also provides for a connector for connecting a progressing cavity pump and a driving part, wherein the connector includes the torque shaft above, and further includes a driver coupling and a pump coupling, wherein the couplings are provided with a hexagonal cavity compatible with the shaft heads, the driver coupling is installed on and fixed to one shaft head, and the pump coupling is installed on and fixed to the other shaft head, one end of the driving coupling has a mating feature appropriate for attachment to the driving part shaft, one end of the pump coupling has a mating feature appropriate for attachment to the pump rotor, and each of the couplings is fixed to the shaft head by two fasteners passing through its outside diameter into either side of the shaft head aperture, fixing the coupling to the shaft head from axial motion. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Other advantages of the present invention are readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
         FIG. 1  is a schematic diagram of the torque shaft provided according to the First Embodiment; 
         FIG. 2  is a side view of the torque shaft provided according to the First Embodiment; 
         FIG. 3  is a schematic diagram of a connector for connecting a pump and a driving part, as provided according to the Second Embodiment; and 
         FIG. 4  is a partial enlarged view of the connector for connecting the pump and the driving part, and of the driving part connection end, as provided according to the Second Embodiment. 
     
    
    
     The present invention generally provides for a torque shaft, as well as couplings for connecting a progressing cavity pump and a driving part. 
     The torque shaft includes shaft heads  20  and a shaft body  10 , where the shaft heads  20  are provided on both ends of the shaft body  10  and the shaft heads  20  are configured to fix the shaft body  10  to a driving and driven member. 
     The shaft heads  20  have a transverse cross section of hexagonal shape. 
     Further, a transition part is provided between the shaft head  20  and the shaft body  10 . 
     A second object of the present invention is to provide a connector for connecting a progressing cavity pump and a driving part, so as to address the technical problems in the prior art. 
     The connector is composed of internal, rotating components, such as a torque shaft  100 , and external, stationary components, such as a casing  170 . 
     Provided is a connector for connecting a pump and a driving part, where the connector includes the above-mentioned torque shaft  100  and further includes a driver coupling  110  and a pump coupling  120 . The torque shaft heads are inserted into corresponding hexagonal cavities in the driver coupling  110  and the pump coupling  120 . 
     Further, a fastener is also included for each coupling. The fastener passes through the outside diameter of each coupling into an aperture in each shaft head, so as to fix the shaft heads to the couplings. 
     The driver coupling  110  possesses a suitable mating feature for the driving part on one end. The pump coupling  120  possesses a suitable mating feature for the pump rotor on one end. A thrust nut  140  is attached to the driver coupling  110 . 
     Further, a connector base  150 , a thrust nipple  190 , a connector casing  170 , and a pump stator adaption  160  are included. 
     The base  150  is fixedly connected to the driver part housing, the thrust nipple  190  is fixedly connected to the connector base  150 , the connector casing  170  is fixedly connected to the thrust nipple  190 , the pump stator adaption  160  is fixedly connected to the connector casing  170 , and the pump stator is fixedly connected to the pump stator adaption  160 . 
     The connector base  150  has an internal diameter nominally the same size as a corresponding diameter of the driver coupling  110 . The diameter serves as a bearing surface for the coupling  110  so that the driver coupling  110  rotates concentrically with the driver part shaft. 
     The thrust nipple  190  has an internal surface perpendicular to the axis of the driver coupling  110 . This surface serves as an up thrust bearing when the coupling  110  is moved upward by reverse rotation of the pump rotor, engaging the thrust nut  140  attached to the driver coupling  110 . The thrust nut  140  does not contact the thrust surface of the thrust nipple  190  when the pump is operating normally, the pump rotor is thrust is directed away from the thrust surface. 
     The connector casing  170  is provided outside the shaft body  10 . The casing  170  is perforated to allow entry of well fluid to the suction end of the progressing cavity pump. 
     The present invention has the following beneficial effects: 
     The present invention provides a torque shaft including a shaft body  10 ; the shaft body  10  includes a shaft head  20  and a shaft body  10 ; and a shaft head  20  is provided on both ends of the shaft body  10 . The shaft head  20  has a transverse cross section of hexagonal shape, namely, the shaft head  20  is provided as a hexagonal shaft head. The outer sidewall of the shaft segment of the shaft head  20  has six corners, and a planar structure with a certain width is provided between adjacent corners. This increases the contact area when the shaft head  20  is connected, and addresses the defects in splined connection, as employed in the traditional technology, which is susceptible to stress fatigue when the torque is transmitted due to multiple-corner structure of the spline. Corners, both at diametral changes in cross section in the transverse plane, increase the concentration of torque stress leading to increased probability of damage or fracture at the spline. Further, the hexagonal cross section provides increased cross section area when compared to a conventional spline of similar size, leading to increased torque capacity. 
     The present invention also provides a connector for connecting a pump and a driving part, which includes the above-mentioned torque shaft  100 , a driver coupling  110 , with thrust nut  140 , and a pump coupling  120  and further includes a connector base  150 , thrust nipple  190 , connector casing  170 , and pump stator adaption  160 . Prior art includes a thrust plate welded on top of the progressing cavity pump stator, which location is carefully established by shop measurements. The thrust plate is made necessary since a progressing cavity pump rotor will move upward when the rotation is reversed, thus disengaging elements of the shafting string between the driving part and the pump. In the present invention, welding and measurement to establish location are eliminated. Further, the thrust surface provided in this disclosure is larger than is possible at the top of a pump stator, and thus is more reliable. 
     The technical solutions of the present invention will be described clearly and comprehensively by referring to the figures below. It is apparent that the embodiments to be described are part, but not all, of the embodiments of the present disclosure. All of the other embodiments obtained by those skilled in the art from the embodiments of the present invention without making an inventive effort will fall within the scope of the present invention as claimed. 
     It should be noted that, in the description of the present invention, unless otherwise expressly specified or defined, terms of “mount”, “couple”, and “connect” should be understood in broad sense. For example, a connection could be a fixed connection, a detachable connection, or an integrated connection; it could be a mechanical connection or an electric connection; or it could be a direct connection, or an indirect connection via an intermediate medium, or it could be an internal communication between two elements. The specific meanings of the above-mentioned terms in the present invention could be understood by those skilled in the art according to specific situations. 
     Transverse is to be understood as perpendicular to the nominal axis of the shaft. 
     FIRST EMBODIMENT 
     As shown in  FIGS. 1-2 , the torque shaft provided in this embodiment includes a shaft body  10 ; a shaft head  20  is provided on both ends of the shaft body  10 . The shaft head  20  is configured to fix the shaft body to a driving member. The transverse cross section of the shaft head  20  has a hexagonal shape. 
     Specifically, the torque shaft is comprised of a shaft body  10  transitioning on both ends to a shaft head  20 . The shaft head  20  is a shaft segment configured for fitting with a rotational component. Therefore, through the shaft head  20 , the shaft body can be fixedly connected to the driving and driven member, for transmitting rotational motion and torque. The shaft body  10  is a non-fitting shaft segment connected to the shaft head  20 . 
     Here, the shaft head  20  has a transverse cross section of hexagonal structure. Namely, the shaft head  20  is provided as a hexagonal shaft head  20 . The outer sidewall of its shaft segment has six corners, and there is a planar structure with a certain width between the adjacent corners. This increases the contact area when the shaft head  20  is connected, and also distributes evenly the stress generated from connection. By fixing the shaft body  10  having a hexagonal shaft head  20  to the rest of the driving members, it addresses the problems associated with splined connection in the traditional technology, that is, due to multiple small radii inherent in splines of any type, which are stress concentrators, the spline is susceptible to stress fatigue when the torque is transmitted, which leads to a damage or fracture of the spline. 
     In the optional aspects of this embodiment, as shown in  FIGS. 1-2 , the shaft head  20  is provided thereon with a fixing aperture  30 . The fixing aperture  30  passes through the shaft head  20  perpendicular to the axis of the shaft head  20 . 
     Specifically, the fixing aperture  30  is provided on the shaft head  20  close to the end face, and the fixing aperture  30  is configured to pass through the shaft head  20  perpendicular to the axis of the shaft head  20 . The torque shaft can be fixedly connected to other components by a connecting member such as a screw passing through or into the fixing aperture  30 . 
     Here, a fixed connection is achieved by a locking screw passing through the fixing aperture  30 . 
     Specifically, one end of the torque shaft is coupled to the progressing cavity pump rotor and the other end is coupled to the driving part, so the torque shaft is mainly configured to transmit motion and torque. The torque shaft includes a shaft body  10  and shaft heads  20  at both ends. The shaft head  20  is configured to connect to the pump rotor and to the driving part, and the shaft body  10  acts as a joining part; when the shaft head  20  is coupled to the pump rotor and to the driving part, in order to prevent the connection from separating, the shaft head  20  needs to be fixed to the coupling thereto. Thus, a screw or other fastener is inserted through the coupling into the aperture  30 . 
     In the optional aspect of this embodiment, as shown in  FIGS. 1-2 , a transition area is provided between the shaft heads  20  and the shaft body  10 . 
     In an optional aspect of this embodiment, as shown in  FIGS. 1-2 , the transition part includes a circular arc transition area  40  and a cylindrical transition area  50 . 
     Specifically, the transition part is provided between the shaft body  10  and the shaft head  20 . The transition part includes a cylindrical transition area  50  and a circular arc transition area  40 . The circular arc transition area  40  is provided at a position where the shaft body  10  is between part and the cylindrical transition area  50  is provided between the circular arc transition area  40  and shaft head  20 . 
     Here, the circular arc transition area  40  is configured to reduce the stress concentration at the shaft body  10  of the torque shaft due to an abrupt change in the cross section between the shaft body  10  and the head  20  which will otherwise reduce the service life of the torque shaft. The cylindrical transition area  50  is configured to provide a standoff surface to protect the shaft head  10  during handling and storage. 
     Here, the torque shaft, consisting of the main body  50 , the circular arc transition area  40 , the cylindrical transition area  40 , and the shaft head  10 , is made from a single blank sucker rod forging. 
     Specifically, since sucker rods are used to drive progressing cavity pumps in some applications, transmit similar torque, transmit similar motion, are exposed to well fluid, and have similar geometry, the sucker rod forging is an especially suitable selection for torque shaft material. Such a forging is made so that the main body  10  is already formed and it transitions through an already formed circular arc  40  to upset ends with a diameter larger than the main body  10  and larger than the cylindrical transition area and shaft head. The upset ends are machined to form the cylindrical transition area and shaft head. 
     Here, the forged transition to a larger diameter is an improvement over current practice of turning bar down to the diameter of the main body in that the forging forms the grain of the material to follow the contour of the ultimate torque shaft surface in contrast to cutting across the material grain when making shaft in current practice. The continuous grains provide a more fatigue resistant torque shaft. 
     SECOND EMBODIMENT 
     The present invention also provides a connector for connecting a progressing cavity pump and a driving part. As shown in  FIGS. 3-4 , the connector for connecting the progressing cavity pump and the driving part as provided according to this embodiment has rotating components which include the above-mentioned torque shaft  100 , and also include a driver coupling  110 , a thrust nut  140 , and a pump coupling  120 . Further, this embodiment has static components which include a connector base  150 , a thrust nipple  190 , a connector casing, and a pump stator adaption  160 . 
     Here, the one end of the driving coupling  110  is configured to connect a driving part, for example, to connect a protector in the driving part, and one end of the driven coupling  120  is configured to connect a progressing cavity pump. 
     Specifically, the driver and driving couplings each have a hexagonal cavity on one end corresponding to the transverse hexagonal cross section of the shaft head  20 . The driver coupling  110  is internally splined on one end corresponding to the conventionally provided external spline of the driving part. The driven coupling  120  is internally threaded on one end corresponding to the conventionally provided sucker rod thread on the pump rotor. The driven coupling is installed onto the pump rotor, applying the torque appropriate for the pump rotor thread size, thus fixing the driven coupling to the pump rotor. One torque shaft head  20  is inserted into the driving coupling  110  cavity and fixed by inserting locking screws  130  through the coupling into the aperture  30 , similarly, the other torque shaft head  20  is inserted into the driven coupling  120  cavity and fixed using locking screws  130 . Thus, the driving coupling  110 , torque shaft  100 , the driven coupling, and the pump rotor are fixed torsionally and axially so will move as one assembly. 
     A thrust nut  140  is installed onto the driving coupling  110 , and it rotates and travels axially as one with the driving coupling  110 . 
     Specifically, the nut  140  is threaded onto the outside diameter of the driven coupling  110  and located firmly at one end against a shoulder. The nut  140  able to bear an axial force imposed in an upward direction. During normal operation of the progressing cavity pump, the thrust nut  140  is spaced so that there is no contact with any portion of the static components of the connector. 
     By fixedly connecting the pump rotor, the driving coupling  110 , with thrust nut  140 , the torque shaft  100 , and the driven coupling  120 , the thrust nut  140  will engage the thrust nipple  190  when the pump rotor is revolving in reverse. Thus, the rotor will remain in place. Moreover, in the prior art, in order to prevent the progressing cavity pump from moving upwards when run in reverse, a thrust plate is welded on the top of the progressing cavity pump. Since the thrust plate is welded onto the progressing cavity pump, it is not easy to replace the thrust plate after being damaged. Furthermore, careful shop measurements are necessary to correctly position the thrust plate. To some extent, the assembly time is increased. In the present embodiment, however, the extensive measurement and welding are avoided. 
     In an additional aspect of this embodiment, as shown in  FIGS. 3-4 , a spacer  180  is further included. The spacer  180  is provided on the driving coupling  110  between the connector base  150  and the driver coupling  110 . The spacer  180  is configured to limit downward movement of the driving coupling  110  during handling. Once the connector is installed with the driving part, the spacer  180  serves no further purpose. 
     In an optional aspect of this embodiment, as shown in  FIGS. 3-4 , this embodiment has static components which include a connector base  150 , a thrust nipple  190 , a connector casing, and a pump stator adaption  160 . 
     Specifically, the connector base  150  attaches to the housing of the driving part and threads into the thrust nipple  190 . Additionally, internally, the connector base  150  has a cylindrical bearing surface which is sized for the outside diameter of the lower part of the driving coupling  110 . The driving coupling  110  revolves within and against the connector base  150 , thus the revolution of the driving coupling  110  is concentric with the axis of the driving part assuring that one end of the torque shaft  100  is revolving concentrically and isolating the driving part from the orbiting eccentricity of the pump rotor. The thrust nipple  190  threads onto the base  150  and threads into the connector casing  170 . Additionally, internally, the thrust nipple  190  has a transverse bearing surface which serves to engage the thrust nut  140  should the pump rotor travel upward on reverse rotation of the pump. The connector casing  170  threads onto the thrust nipple  150  and threads onto the pump stator adaption  160 . Additionally, the connector casing is perforated with multiple small holes to allow the passage of well fluid, thus the connector casing  170  serves as the progressing cavity pump intake. The pump stator adaption  160  threads into the connector casing  170  and threads into the pump stator. The pump stator adaption  160  adapts the connector casing to the various progressing cavity pump stator thread sizes and types. 
     Finally, it should be noted that the above embodiments are merely intended to explain the technical solutions of the application and are not intended to limit the application. Although the present invention has been illustrated in detail with reference to the foregoing embodiments, it would be understood by persons of ordinary skill in the art that the technical solutions described in the foregoing embodiments can still be modified, or that part or all of the technical features thereof can be replaced by equivalent substitution. These modifications or substitutions do not cause the principle of the corresponding technical solutions to depart from the scope of the technical solutions of the embodiments of the application. 
     Throughout this application, various publications, including United States patents, are referenced by author and year and patents by number. Full citations for the publications are listed below. The disclosures of these publications and patents in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which this invention pertains. 
     The invention has been described in an illustrative manner, and it is to be understood that the terminology, which has been used is intended to be in the nature of words of description rather than of limitation. 
     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention can be practiced otherwise than as specifically described.