Abstract:
In one possible implementation, a misalignment-tolerant hydraulic actuator, e.g., for a submersible hydraulic diaphragm insert pump (HDI), has a floating piston that can reciprocate while decoupled from collinearity with a cylinder barrel and a central feed rod that slides through a central axis of the piston. The floating seal can be integrated or provided by a separate insert and provides a pivotable interface between the piston and center rod, allowing these components freedom of motion to avoid elastic deformation, friction, power loss, and early wear when misalignment or transverse forces on an external end of the piston rod are present. Bearing placement can also be selected to eliminate over-constraint.

Description:
BACKGROUND 
       [0001]    Conventional hydraulic cylinders (hydraulic actuators, linear hydraulic motors) are mechanical devices that can provide reciprocating linear displacement power to submersible pumps, such as hydraulic diaphragm insert pumps (HDIs). 
         [0002]      FIG. 1  shows a conventional hydraulic actuator  100  suitable for submersible pump applications. The conventional hydraulic cylinder  100  includes an outer cylinder piece known as the barrel  102 , a sliding piston  104  inside the barrel  102 , a piston rod  106  to transfer power from the piston  104  to an external submersible pump  108 , and a central “feed” rod (“center rod”)  110  that slides in a cylindrical hole through a central longitudinal axis of the piston  104 . The center rod  110 , since it passes through the piston  104 , provides hydraulic fluid through a hollow bore to the far side of the piston for retraction. 
         [0003]    In conventional designs, the piston  104 , piston rod  106 , center rod  110 , and other moving parts are over-constrained to strict and unforgiving linear displacement with no tolerance for misalignment, resulting in extra load and efficiency loss as the components struggle against each other along conflicting axes, forcing some elastic deformation, friction, power loss, and early wear of the parts. 
       SUMMARY 
       [0004]    An adaptive hydraulic cylinder with floating seal interface is provided. In an implementation, a deformation-tolerant hydraulic actuator, e.g., for a submersible hydraulic diaphragm insert pump (HDI), has a floating piston that can reciprocate while decoupled from strict collinearity with the cylinder barrel and the central feed rod that slides through the central axis of the piston. The floating seal can be integrated or provided by a separate insert and provides a pivotable interface between the piston and center rod, allowing these components some freedom of motion to avoid elastic deformation, friction, power loss, and early wear when misalignment or transverse forces on the external end of the piston rod are present. Bearing placement is also selected to eliminate over-constraint. Bearings on the piston, the floating seal interface, center rod and the piston rod support, for example, are placed singly or close together on each component to approximate a single contact ring that allows the components to self-adjust to different axes, while maintaining a hydraulic seal between all components. 
         [0005]    This summary section is not intended to give a full description of an adaptive hydraulic cylinder with floating seal interface, or to provide a list of features and elements. A detailed description of example embodiments follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a diagram of a conventional, prior art, over-constrained hydraulic cylinder. 
           [0007]      FIG. 2  is a diagram of an example adaptable hydraulic actuator with floating seal interface. 
           [0008]      FIG. 3  is a diagram of an example piston and floating seal interface implemented as an insert. 
           [0009]      FIG. 4  is an elevation view of an example piston and floating seal interface implemented as an insert. 
           [0010]      FIG. 5  is an elevation view of an example piston and integrated seal interface. 
           [0011]      FIG. 6  is a diagram of an example floating piston self-adjustment along a new longitudinal axis. 
           [0012]      FIG. 7  is a cross-sectional view of an example adaptable hydraulic actuator with a floating seal interface. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Overview 
         [0014]    This disclosure describes an adaptive hydraulic cylinder with floating seal interface.  FIG. 2  shows an example adaptive hydraulic actuator  200  (cylinder, motor) that is misalignment-tolerant and deformation-tolerant, and suitable for applications such as powering a submersible hydraulic diaphragm insert pump (HDI). The example hydraulic actuator  200  may be used for other devices besides an HDI and in other settings.  FIG. 2  is a stylized diagram, for purposes of illustrating the components and the functions of the example hydraulic actuator  200 . Other configurations and variations can also be used. 
         [0015]    The example hydraulic actuator  200  has moving parts that are fully constrained by bearings and contacts between components for proper operation. But the components are not over-constrained to the point of having no tolerance for slight misalignment and slight elastic deformation under stress. The moving components can self-adjust their positions and/or their travel trajectories to a degree to adapt to misalignment forces, while maintaining proper operation and intact hydraulic seals throughout the hydraulic actuator  200 . 
         [0016]    Example Apparatus 
         [0017]    The example hydraulic actuator  200  has a floating, but fully constrained piston  202 , yet when stressed or affected by a misalignment in the component stack, the piston  202  can self-adjust to longitudinal axes other than the main central axis of the overall hydraulic actuator  200 . That is, the piston  202  is not loose, but is free to move in directions and orientations besides the main direction of its displacement stroke while maintaining hydraulic seals in order to relieve binding forces and loading caused by misaligned or stressed parts. The longitudinal axis (or axes) of the piston  202  as it adapts may be different from the longitudinal central axis of the barrel  204  and different from the longitudinal central axis of the center rod  206  (these axes, the central longitudinal axis of the barrel  204  and of the center rod  206  may be the same axis, but not necessarily). 
         [0018]      FIGS. 3-4  viewed in conjunction with  FIG. 2 , show an example implementation of the piston  202  and the floating seal interface  208 , shown in this case as a separate insert. The floating seal interface  208  is integrated or fits soundly inside the piston  202  but with some tolerances that allow the piston  202  to decouple from the rigid constraint that is conventionally imposed by the center rod  206  around which the piston  202  slides. In  FIG. 4 , an inner bore  402  of the floating seal interface  208  makes a snug, closely-fitting bearing interface with the center rod  206  (e.g., metal-to-metal, polymer-to-metal, polymer-to-polymer, composite polymer, etc.) and makes a seal  408  with the piston cap. In one implementation, the outside surface  404  of the floating seal interface  208 , however, does not make such a closely fitting bearing interface. Instead, a seal  302  provides an interface between the floating seal interface  208  and the piston  202  and in some implementations provides a pivot point or gimbal plane from which the piston  202  may adapt to misalignment forces. In one implementation, the seal  302  may be effected by a gland securing an O-ring, but many other types of seals may be utilized. The floating seal interface  208  and piston  202  interaction is relatively loose compared to the conventional interface machined to have no “give” between the cylindrical metal surfaces of the center rod  206  and the piston  202 , and in one implementation the floating seal interface  208  may be loose enough to rattle when not pressurized by hydraulic fluid. This allows the piston  202  to “float,” that is, allows the piston  202  several different degrees of freedom of motion with respect to the fixed center rod  206 . The piston  202  floats in rotational and translational degrees of freedom with respect to the floating seal interface  208  (and thus with respect to the center rod  206 ). The forward edge of the floating seal interface  208  makes a seal  408  with the cap of the piston  202  when under pressure during a retraction stroke. 
         [0019]    By a similar token, if the center rod  206  is out of alignment or stressed, the center rod  206  and the piston  202  can both “self-align” to relieve stress via the play allowed by the floating seal interface  208 , whether the floating seal interface  208  is integrated into the piston  202 , integrated into the center rod  206 , or provided by a separate insert. 
         [0020]      FIG. 5  shows a piston that has a floating seal interface  208  integrated into the fabric of the piston  202 . That is, the floating seal interface  208  is not removable as a separate insert or other part. The integrated form of the seal interface  208  performs the same or equivalent functions in allowing degrees of movement as a removable insert implementation of the floating seal interface  208 . 
         [0021]      FIG. 6  shows an example piston  202  (above) in normal “straight” alignment and in adaptive alignment (below), aligned with at least one component having a new, self-adjusted trajectory along an axis  116  that is different from the central longitudinal axis  602  of the example hydraulic actuator  200  (the illustrated deviation in axes is greatly exaggerated for purposes of description). In this example, the actual self-adjustment and deviation between the piston&#39;s axis  602  and the longitudinal axis  116  of the center rod  206  may be relatively small, even microscopic, but such exemplary self-adjustment is not possible in a conventional hydraulic cylinder because the parts are so over-constrained as to be rigidly fixed, except in the exact direction of intended travel. The self-adjustment capability of the example hydraulic actuator  200  allows the components to avoid binding forces, wear, and even seizing. 
         [0022]    Returning to  FIG. 2 , in order for the piston  202  to self-adjust its comportment or stroke with respect to the other components using the advantages provided by the floating seal interface  208 , the piston bearing  210  should also allow some play, since the conventional piston bearings  120  ( FIG. 1 ) do not allow significant play. In an implementation, the center rod stop  212  has no contact  216  with the inner bore of the piston rod  214 . In another implementation, the center rod stop  212  uses a seal and/or bearing that contacts the inner bore of the piston rod  214  as a single ring of contact instead of the conventional stable pair of seals, allowing the piston rod some degrees of freedom of movement from the linearity of the center rod  206  itself. A cylinder end cap  218  (terminal piston rod support  218 , or end seal) may likewise use a support scheme with a bearing  220  that provides a single ring of contact with the piston rod  214  in order to allow the piston rod  214  to pivot slightly or deflect as needed, instead of the conventional separated pair of seals. 
         [0023]      FIG. 7  shows an example implementation of the hydraulic actuator  200 . In this implementation, the example floating piston  202  slides within the barrel  204  of the hydraulic actuator  200 , also pivotably sliding on the center rod  206 , which has an inner lumen that feeds hydraulic fluid to the backside of the piston for a retraction stroke. The example floating seal interface  208  intervenes between the piston  202  and the center rod  206 . The floating seal interface  208 , when it is a separate insert, may be held in place longitudinally by a stop washer  706 . The tolerance for slight movement and the ability to float may be achieved by many techniques. In one version, a seal provides a pivotable contact ring between the floating seal interface  208  and the piston  202 . 
         [0024]    Support for the floating piston  202  within the barrel  204  can be gathered into one single contact ring  210 , such as a single bearing, so that the piston  202  can re-orient itself with respect to this single ring of contact  210 . A piston seal  702  may also be present, and may be situated near the single contact ring  210  to make a group of rings, bearings, or seals that still act like a single ring of contact. To summarize, the ring of bearing support  210  is kept single when possible, and associated seals are drawn close to still maintain a single ring, or a short cylinder, of bearing support around the piston  202  so that the piston  202  may pivot and float as needed. Wipers or absorbers, such as ingestion rings  704  may also be present, but do not impede the self-adjustment of the piston  202 . With the fully constrained but not over-constraining presence of the floating seal interface  208 , the seal  302 , and the single ring of bearing support  210  for the piston  202 , the piston  202  is free to self-adjust in response to misalignment forces that would otherwise work to bind and seize the parts against each other. 
         [0025]    Since the piston rod  214  is connected to the piston  202 , it is also desirable to free the piston rod assembly from an over-constraining design. The center rod  206  has a center rod stop  212  that provides a physical stop for the piston  202  in its extension. The center rod stop  212  also has a hole to pass the hydraulic fluid from the lumen of the center rod  206  to the inner bore of the piston rod  214 . The outside diameter of the center rod stop  212  may slide within the inner bore of the piston rod  214 . In an implementation, the center rod stop  212  has no radial contact  216  with the inner bore of the piston rod  214 , thus freeing the piston rod  214  from constraint by the center rod stop  212 . In another implementation, the center rod stop  212  does slide with contact inside the inner bore of the piston rod  214 , but the piston rod  214  is freed from over-constraint of the center rod stop  212  by shortening the length of the center rod stop  212  and/or by placing a single ring bearing around the center rod stop  212  (instead of multiple, separated support bearings or contact areas) so that the piston rod  214  can pivot, rotate, or otherwise adjust in relation to the center rod stop  212  present in its inner bore. 
         [0026]    In each case where a single bearing or single ring of support is used to afford a component some additional degrees of freedom, the single or closely gathered bearings and seals can be modeled as one point of pivotable support (in a 2-dimensional cross-sectional model). In the example hydraulic actuator  200 , the multiple constraints placed on the piston  202  have been replaced by a single constraint. The piston rod  214  and center rod stop  212  interaction is not over-constrained. And the piston  202  to barrel  204  interface is also fully constrained but not over-constrained. The center rod  206  sealing portion of the piston assembly is separated from the rest of the piston  202  and/or allowed to float in rotational and translational degrees of freedom. The seal between the piston  202  and the center rod  206  is distributed into a pivotable seal  302  along the longitudinal axis of the piston  202  and a seal  408  induced between the end of the floating seal interface  208  (when an insert is used) and the piston cap, when energized by differential pressure during the retraction stroke of the piston  202 . 
         [0027]    Thus, the design of the example hydraulic actuator  200  removes two couples (two independent and fixed cylindrical displacement trajectories) and replaces them with a single, properly constrained couple on the piston and piston rod assembly. The design inserts a rotational (primary) and translational (secondary) degree of freedom between the cylindrical displacement trajectory of the piston and piston rod assembly, and the floating seal interface  208  (integrated, or implemented as an insert). So no component in the stack is over-constrained, just fully constrained. All components thus interface with each other without excess loading. 
         [0028]    Conclusion 
         [0029]    Although exemplary systems have been described in language specific to structural features and/or methodological acts, it is to be understood that 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 exemplary forms of implementing the claimed systems, methods, and structures.