Abstract:
The inventive stator includes a helical cavity component made from a material chosen to reinforce an elastomer liner deployed thereon. The contouring of the elastomer liner is asymmetrical, such that the elastomer liner is relatively thick on the loaded side of a lobe as compared to its thickness on the unloaded side of the lobe.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application Ser. No. 60/514,848 entitled Asymmetric Contouring of Elastomer Liner on Lobes in Moineau Style Power Section Stator, filed Oct. 27, 2003. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates generally to Moineau style power sections useful in subterranean drilling motors, and more specifically to the contouring of elastomer on lobes in the helical portion of stators in such power sections.  
       BACKGROUND OF THE INVENTION  
       [0003]     Moineau style power sections are well known. They are useful in drilling motors for, e.g., subterranean drilling applications, in which they are used to covert a flow of drilling fluid into torque and rotary power. The general principle on which Moineau style power sections operate involves locating a helical rotor within a stator having a helical cavity. Helical cavity stators, when viewed in circular cross-section, show a series of peaks and valleys. The valleys are where the helical cavity is formed into the inside of the stator. The peaks are typically referred to as “lobes.” 
         [0004]     The furthest outside diameter of the rotor is generally selected so as to allow the rotor to rotate within the stator while maintaining close proximity to the lobes on the stator. In most conventional Moineau style power sections, the rotor and the lobes on the stator are preferably an interference fit, with the rotor including one fewer lobes than the stator. Then, when fluid (such as drilling fluid) is passed through the helical spaces between rotor and stator, the flow of fluid causes the rotor to rotate.  
         [0005]     Stators in Moineau style power sections typically show at least two components in circular cross-section. The outer portion includes a hollow cylindrical metal tube. The inner portion includes a helical cavity component. The helical cavities are formed in the inner surface of the helical cavity component. The helical cavity component also has a cylindrical outer surface that abuts the inner surface of the hollow metal tube.  
         [0006]     Conventional stators in Moineau style power sections also advantageously include elastomer (e.g. rubber) surfaces on the inside of the helical cavities, and preferably on the lobes, to facilitate the interference fit with the rotor. The elastomer provides a resilient surface with which to contact the rotor as the rotor rotates. Many stators are known where the helical cavity component is made substantially entirely of elastomer.  
         [0007]     It has been observed in operations using Moineau style power sections that the elastomer portions of the lobes are subject to considerable cyclic deflection. This deflection is caused not only by the interference fit with the rotor, but also by reactive torque from the rotor. The cyclic deflection and rebound of the elastomer causes a build up of heat in the elastomer. In conventional stators, especially those in which the helical cavity component is made substantially entirely from elastomer, the heat build up has been observed to concentrate near the center of the lobe. The heat build up weakens the elastomer, leading to a premature “chunking” breakdown of the elastomer. A cavity in the lobe also eventually develops as the deteriorated elastomer separates and falls away. This causes loss of lobe integrity, which causes loss of interference fit with the rotor, resulting in fluid leakage between rotor and stator as fluid is passed through the power sections. This fluid leakage in turn causes loss of drive torque, and if left unchecked will eventually lead to stalling of the rotor.  
         [0008]     In other stators, such as described in exemplary embodiments disclosed in commonly-assigned, co-pending U.S. patent application Ser. No. 10/694,557, “COMPOSITE MATERIAL PROGRESSING CAVITY STATORS,” the elastomer may be a liner deployed on the helical cavity component, the helical cavity component comprising a fiber reinforced composite reinforcement material for the elastomer liner.  
         [0009]     The deployment of a reinforcement material in the lobes addresses the problems of deterioration of an all-elastomer lobe due to heat build up. For example, lower resilience in the reinforcement material is likely to localize resilient displacement in the liner, where, in some embodiments, heat build up may dissipate more quickly. Care is required, however, in selection of reinforcement material and elastomer liner thickness. Contact stresses are caused on the reinforced lobes as the rotor rotates within the interference fit with the stator. Without sufficient resilience in the interference fit, the reinforcement may be too hard and/or the liner may be too thin, such that the contact stresses cause the elastomer liner to crack or split as the rotor contacts the stator lobe. Additionally, without care in choice of materials or elastomer liner thickness, the cyclic contact stresses can cause the lobes to crack or fail prematurely, particularly on the loaded side of the rotor/stator interface.  
       SUMMARY OF THE INVENTION  
       [0010]     These and other needs and problems in the prior art are addressed by a stator comprising asymmetrical contouring of elastomer. The inventive stator includes a helical cavity component made from a material chosen to reinforce an elastomer liner deployed thereon. The contouring of the elastomer liner is asymmetrical, such that the elastomer liner is relatively thick on the loaded side of a lobe as compared to its thickness on the unloaded side of the lobe.  
         [0011]     It is therefore a technical advantage of the invention to still provide reinforcement to an elastomer surface on the lobes on the helical cavity component. The problems caused by heat build up in the lobes may thus be addressed. At the same time, an elastomer liner is provided with a thickness profile having increased thickness, and therefore increased resilience, on the loaded side of a lobe. This increased resilience deters liner breakdown (or reinforcement breakdown) due to contact stresses between rotor and stator.  
         [0012]     According to one aspect of the present invention a stator for use in a Moineau style power section is provided. The stator includes a plurality of internal stator lobes, each of which includes a resilient liner deployed on an interior surface of the stator. The liner is disposed to engage rotor lobes on a helical outer surface of a rotor when the rotor is positioned within the stator so that the rotor lobes are in a rotational interference fit with the stator lobes. Rotation of the rotor in a predetermined direction causes the rotor lobes to contact the stator lobes on a loaded side thereof as the interference fit is encountered and to pass by the stator lobes on a non-loaded side thereof as the interference fit is completed. Each of the stator lobes further includes a reinforcement material for the resilient liner. The stator further includes a shape, when viewed in circular cross section, in which a thickness of the liner is greater on the loaded sides of the stator lobes than on the non-loaded sides thereof.  
         [0013]     According to another aspect, this invention includes a subterranean drilling motor. The drilling motor includes a rotor having a plurality of rotor lobes on a helical outer surface thereof and a stator including a helical cavity component. The helical cavity component provides an internal helical cavity and includes a plurality of internal stator lobes. The rotor is deployable in the helical cavity of the stator such that the rotor lobes are in a rotational interference fit with the stator lobes. Rotation of the rotor in a predetermined direction causes the rotor lobes to contact the stator lobes on a loaded side thereof as the interference fit is encountered and to pass by the stator lobes on a non-loaded side thereof as the interference fit is completed. The stator lobes include a reinforcement material and a resilient liner, the liner disposed to engage an outer surface of the rotor. The liner has a non-uniform thickness such that it is thicker on the loaded sides of the lobes than on the non-loaded sides of the lobes.  
         [0014]     Certain exemplary embodiments of this invention may also include at least one transition layer separating the liner and the reinforcement material, the transition layers made from material that is less resilient than the liner, but more resilient than the reinforcement material.  
         [0015]     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:  
         [0017]      FIG. 1  depicts a prior art rotor and stator assembly in circular cross section;  
         [0018]      FIG. 2  depicts a rotor and stator assembly, also in circular cross section, in which elastomer liner  212  is reinforced by reinforcement material  215  provided by helical cavity component  210  on stator  205 ;  
         [0019]      FIG. 3  depicts an embodiment of the present invention, comprising again a rotor and stator assembly in circular cross section, in which elastomer liner  312  is contoured asymmetrically, thicker on the loaded side of lobes  360  than on the unloaded side;  
         [0020]      FIG. 4  depicts another embodiment of the present invention having an alternative asymmetric contouring of elastomer liner  412 ; and  
         [0021]      FIG. 5  depicts yet another embodiment of the present invention including a transition layer  590  deployed between the liner  512  and the reinforcement material  515 .  
     
    
     DETAILED DESCRIPTION  
       [0022]      FIGS. 1 through 5  each depict circular cross-sections through Moineau style power sections in an exemplary ¾ design. In such a design, the differing helical configurations on rotor and stator provide, in circular cross section, 3 lobes on the rotor and 4 lobes on the stator. It will be appreciated that this ¾ design is depicted purely for illustrative purposes only, and that the present invention is in no way limited to any particular choice of helical configurations for the power section design.  
         [0023]      FIG. 1  depicts a conventional Moineau style power section  100  in circular cross-section, in which stator  105  provides a helical cavity portion  110 . In the embodiment of  FIG. 1 , helical cavity portion  110  is of an all-elastomer construction. Rotor  150  is located within stator  105 . Stator  105  further comprises outer tube  140 . Helical cavity portion  110  is deployed on the inside of outer tube  140 , as is well known in the art.  
         [0024]      FIG. 1  illustrates zones  170  in lobes  160  in which heat build up is known to occur during operation of power section  100 . As described above, the cyclic deflection and rebound of elastomer in the interference fit between rotor  150  and stator  105  contributes to the heat build up in zones  170 . Reactive torque from rotor  150  may also contribute to heat build up. As the heat build up deteriorates the elastomer in zones  170 , weakness develops, and eventually cavities, cracks, and/or other types of failure have been observed to occur in these zones.  
         [0025]      FIG. 2  depicts a Moineau style power section  200  in circular cross-section as described in exemplary embodiments disclosed in commonly-assigned, co-pending U.S. patent application Ser. No. 10/694,557, “COMPOSITE MATERIAL PROGRESSING CAVITY STATORS.” In  FIG. 2 , rotor  250  is located within stator  205 . Stator  205  provides outer tube  240  retaining helical cavity portion  210 . Helical cavity portion  210  includes an elastomer liner  212 . In the embodiment of  FIG. 2 , elastomer liner  212  has an even (uniform) thickness. Helical cavity portion  210  reinforces elastomer liner  212  and is made from a fiber reinforced composite reinforcement material  215 .  
         [0026]     As noted above, in view of contact stresses in the interference fit between rotor  250  and lobes  260 , care is required in the selection of the thickness of elastomer liner  212  in stators  205  such as shown in  FIG. 2  to avoid breakdown of elastomer liner  212 . For analogous reasons, care is also required in the selection of reinforcement material  215  to avoid breakdown of reinforcement in lobes  260 .  
         [0027]      FIG. 3  depicts an exemplary embodiment of the present invention.  FIG. 3  shows a Moineau style power section  300  in circular cross-section similar to that depicted in  FIG. 2 . In  FIG. 3 , rotor  350  is located within stator  305 . Stator  305  provides outer tube  340  retaining helical cavity portion  310 . Helical cavity portion  310  includes an elastomer liner  312  having a non-uniform thickness as described in more detail below. Helical cavity portion  310  reinforces elastomer liner  312  and is advantageously made from a reinforcement material  315  that deteriorates less than elastomer in the presence of heat build up in lobes  360 . Reinforcement material  315  may be selected from any suitable material, such as (for example): hardened elastomer, steel wire in reinforced elastomer, extruded plastics, liquid crystal resin, fiberglass or other fiber reinforced composites, and metal (including copper, aluminum or steel castings, steel helical cavity portion formed integral with outer tube, or powdered metal fused in place by, e.g., brazing or HIP process).  
         [0028]     In the exemplary embodiments shown on  FIG. 3 , elastomer liner  312  is contoured asymmetrically to provide thicker portions  380  on one side of lobes  360 . Advantageously, thicker portions  380  are deployed on the loaded sides of lobes  360  as shown by the arrow of rotation R of rotor  350  (depicting clockwise rotation of the rotor as looking down the drill string in the exemplary embodiment shown). It will be appreciated that this invention is not limited by the direction of rotation of the rotor  350 . In exemplary embodiments according to  FIG. 3 , thicker portions  380  of elastomer liner  312  may be, at their thickest point on the loaded sides of lobes  360 , about 1.5 times as thick, and in some embodiments about twice as thick, than the thickness of elastomer liner  312  on the unloaded sides. It will be appreciated, however, that the invention is not limited in this regard.  
         [0029]     It will also be appreciated that the invention is also not limited to any particular cross-sectional shape of thicker portions  380 . For example only,  FIG. 4  depicts an alternative cross-sectional shape. Referring to  FIG. 4 , there is shown a further exemplary embodiment of the present invention with Moineau style power section  400  in circular cross-section generally as depicted in  FIG. 3 . Part numbers identified on  FIG. 4  in the  400  series correspond to part numbers identified on  FIG. 3  in the  300  series. Comparing  FIG. 4  now to  FIG. 3 , however, it will be seen that elastomer liner  412  is asymmetrically contoured to provide thicker portions  480 . In the embodiment of  FIG. 4 , the Moineau style profile of the inner surface of the liner  412  is rotationally offset from Moineau style profile (i.e., having helical lobes and grooves) of the outer surface of the liner  412  (or the inner surface of the reinforcement material  415 ). Again, analogous to the exemplary embodiment depicted in  FIG. 3 , the embodiment of  FIG. 4  shows thicker portions  480  advantageously deployed on the loaded sides of lobes  460  as shown by the arrow of rotation R of rotor  450 .  
         [0030]     In other embodiments, such as the exemplary embodiment shown on  FIG. 5 , there may be transition layers  590  in the stator lobe reinforcement of the elastomer liner  512 . For example,  FIG. 5  depicts the exemplary embodiment shown on  FIG. 3  having one transition layer  590  with the elastomer liner  512  deployed thereon. Part numbers identified on  FIG. 5  in the  500  series correspond to part numbers identified on  FIG. 3  in the  300  series. The transition layer  590  separates the elastomer liner  512  and harder stator lobe reinforcement material  515 , such as metal or other examples that have been herein described. The shape of the transition layer  590  in circular cross section may follow the asymmetrical contouring of the elastomer liner  512  as disclosed in exemplary fashion above. The transition layer  590  is advantageously made of a less resilient material than the elastomer liner  512 , but of a more resilient material than the stator lobe reinforcement material  515 . In this way, deeper resilience in the stator lobes  560  may be achievable to facilitate the interference fit between rotor  550  and stator  505  as the rotor  550  rotates. Harder stator lobe reinforcement material behind the transition layer  590  is also available to absorb heat build up better than elastomer or the transition layer.  
         [0031]     With regard to transition layer embodiments, it will be appreciated that the invention is not limited to the foregoing description of the exemplary embodiment shown on  FIG. 5  in which only one transition layer was described, and wherein the transition layer shape in circular cross section followed that of the elastomer liner. It will be understood that embodiments of the invention may have multiple transition layers. Similarly other embodiments may have transition layers whose shape in circular cross-section varies from that of the elastomer liner.  
         [0032]     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alternations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.