Flexible couplings are provided comprising a male member disposed within a female member in a spaced apart configuration, with the space being filled, at least partially, with an elastically deformable material. The male and female members comprise features that prevent separation from one another after the elastically deformable material is provided in the space between them. For example, the male and female members of one embodiment each comprise a threaded region, with the respective male and female threads being intermeshed but generally spaced apart from each other. At least one of the male and female threads is tapered in two opposing directions with respect to a coupling centerline. The double taper requires the elastically deformable material to be displaced for the male and female members to become separated. However, the elastically deformable materials are constrained by surfaces of the male and female members, and therefore, cannot be displaced.

FIELD OF THE INVENTION 
   The present invention relates to flexible couplings that include a male member fitted within a female member, and a layer of elastically deformable material positioned between adjacent portions of the male and female members. The flexible couplings are suitable for transmitting torque, as well as, for attenuating vibrations and applied stresses. Flexible couplings of the present invention are particularly suited for use in the down hole drilling industry, such as, for interconnecting a plurality of drill pipe sections, and for isolating electronic components within a drill pipe section to reduce the potential damaging transmission of shock pulses from an end-connected drill bit. 
   BACKGROUND OF THE INVENTION 
   Flexible couplings for connecting one component to another component are well known. One identified use for flexible couplings is for connecting a drive source, such as a motor, to a peripheral device, in which the components are susceptible to initial misalignment, or due to the nature of the components, are dynamically misaligned in use. 
   Another identified use for flexible couplings is for reducing the transmission of stress and vibrations between two or more connected components. For example, drilling assemblies used by the oil and gas industry, for retrieving various fluids and gases buried within earth formations, typical comprise a drilling string connected to a drill bit. The drilling string comprises a plurality of interconnected pipe segments with the drill bit positioned at a distal end thereof. As the drill bit cuts through the earth, vibrations, usually at high frequencies, occur and are transmitted along the drilling string. These high frequency vibrations may cause fatigue, deterioration, and finally failure of the components of the drilling assembly. In addition, drill string sections may comprise highly sensitive electronic devices, such as those associated with MWD (Measuring While Drilling) systems. The electronics must be isolated from the same high frequency vibrations, as well as, other applied stresses. Furthermore, the electronic devices must be isolated from torsional loads that occur during acceleration or deceleration of the section carrying the electronics. 
   William Turner and Russell Ide, in U.S. Pat. No. 5,833,541 (“the '541 patent”), describe an elastomeric coupling for suppressing shocks and vibrations associated with down hole drilling assemblies. As can be seen in  FIGS. 1-2 , the coupling includes an interlocked male member  1  and female member  2 , each member having threaded portions, and an elastomer  3  filling the spaces between the threaded portions. Under loading the male and female members are capable of moving relative to one another. The inventors of the '541 patent disclose a method of preserving coupling integrity under a “loosening” torque, comprising a plurality of locking plugs The plugs  5  are inserted into the assemblies after the male portion is threaded into the female portion, but before the elastomer is provided The locking plugs extend through a wall of the female member  2  and between adjacent thread turns extending from an outer surface of the male member  1 . This arrangement substantially prevents the male threaded portion from being unscrewed from the female threaded portion. 
   Although a useful contribution to the arts, the coupling integrity preserving method described in the '541 patent has some disadvantages. The locking plugs are prone to failure due to stress concentrating on the plugs. After the plugs fail, the male and female members can decouple upon the presence a sufficient reverse torque. Moreover, it is extremely difficult to properly position the plugs such that they are functional, yet do not act as a stress/vibration transmission conduit, which will occur if any portion of the plug contacts the male member. 
   Accordingly, a need exists in the art for a flexible coupling that once assembled, will not decouple in any direction due to torsional loads, can effectively attenuate vibrations and other applied stresses, and/or can effectively transmit torque. 
   SUMMARY OF THE INVENTION 
   The present invention provides an improved flexible coupling useful for numerous applications, including, but not limited to, transmitting torque, suspending electronic components from apparatuses carrying the same, and reducing the transmission of vibrations and other applied stresses from interconnected components. 
   In accordance with a preferred embodiment of the present invention, there has now been provided a flexible coupling for use in rotatable devices, the flexible coupling comprising a female member and a male member disposed therein. Each of the female member and the male member comprises a threaded region. A male thread is formed on a male member external surface, and a female thread is formed on a female member internal surface. At least one of the threads is tapered in two opposing directions with respect to a coupling centerline. The female thread and the male thread are intermeshed but generally spaced apart from each other. A layer of elastically deformable material is disposed in the space between the female and male threads. 
   In accordance with additional preferred embodiments of the present invention, there has now been provided flexible couplings similar to that described above for interconnecting sections of drill piper, and for suspending a component within a drill pipe section. 
   In accordance with yet another preferred embodiment of the present invention, there has now been provided a flexible coupling for coupling a drill pipe section to a complementary device. The flexible coupling comprises a female member including a first end an opposing second end, and a male member disposed within the female member. A space exists between an outer diameter of the male member and an inner diameter of the female member. A layer of elastically deformable material is disposed within at least a portion of the space between the female and male members. The male member outer diameter changes size at least twice along the portion of the male member disposed within the female member. 
   In accordance with yet another preferred embodiment of the present invention, there has now been provided a flexible coupling for use in rotatable devices including down hole drilling assemblies. The flexible coupling comprises a female member comprising a closed end, an opposing open end, and an inner diameter. A male member comprising an outer diameter is disposed within the female member such that there is a space between the male member outer diameter and the female member inner diameter. A layer of elastically deformable material disposed within at least a portion of the space between the female and male members. The space at a position proximate the open end is greater than the space at a position proximate the closed end. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is believed to be best understood through the following detailed description of the preferred embodiments and the accompanying drawings herein like reference numerals indicate like features, and wherein: 
       FIG. 1  is a cross-sectional view of a prior art flexible coupling comprising interlocked male and female members having an elastomeric layer therebetween; 
       FIG. 2  is transverse cross-section of the coupling shown in  FIG. 1 , taken along line II—II; 
       FIG. 3  is a perspective view of a flexible coupling embodiment provided by the present invention;  FIG. 4  is a side view of the flexible coupling shown in  FIG. 3 ; 
       FIG. 5  is a cross-sectional view of the flexible coupling shown in  FIG. 4 , taken along line V—V; 
       FIG. 6  is a cross-sectional view of a female member embodiment provided by the present invention; 
       FIG. 7  is a side view of a male member embodiment provided by the present invention; 
       FIG. 8  is a cross-sectional view of the male member shown in  FIG. 7 , taken along line VIII—VIII; 
       FIG. 9   a  is a cross-sectional view of assembled male and female members provided by the present invention, the male and female members comprising double-tapered threads in a back-to-back configuration; 
       FIG. 9   b  is a partial cross-sectional view of the assembled male and female members shown in  FIG. 9   a;    
       FIG. 10  is a partial cross-sectional view of assembled male and female members comprising double-tapered threads in a face-to-face configuration; 
       FIG. 11  is a partial cross-sectional view of assembled male and female members comprising a modified face-to-face configuration; 
       FIG. 12  is a cross-sectional view of assembled male and female members residing in an injection mold, and having elastically deformable material injected into a space between the male and female members; 
       FIG. 13  is a partial cross-sectional view of a drill string section comprising a flexible coupling in the form of a suspension system according to the present invention; 
       FIG. 14  is cross-sectional view of a flexible coupling embodiment provided by the present invention, comprising end portions for connecting a first component to a second component; and 
       FIG. 15  is a partial cross-sectional view of assembled male and female members, wherein the female member comprises a closed end and an open end. 
   


   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the drawings, wherein like reference numerals designate corresponding structure throughout the views, and referring in particular to  FIGS. 3  to  5 , a flexible coupling  10  in the form of a suspension system is provided, comprising a first end region  12 , an opposing second end region  11 , and a female member  20  and a male member  30  aligned along a coupling centerline  60 . A portion of male member  30  is disposed within female member  20  in a spaced apart configuration, thereby defining a space  40 . An elastically deformable material  50  is provided within space  40 . Under loading, the female and male members are capable of moving relative to each other due to the presence of elastically deformable material  50 . 
   As can be seen most clearly in  FIGS. 6-8 , female member  20  and male member  30  each have a helically projecting thread extending from one of its surfaces. A female thread  21  extends from a female member inner surface  25 , and has a thread major diameter  22  and a thread minor diameter  23 . In the embodiments illustrated in the figures, female thread major diameter  22  corresponds with a female member inner diameter  26 . In similar fashion, a male thread  31  extends from a male member external surface  35 , and has a thread major diameter  32  and a thread minor diameter  33 . The major diameter  32  of the male thread corresponds with a male member outer diameter  36 . 
   In preferred embodiments of the present invention, the female and male members  20 ,  30  are constructed from steel, although other materials, such as, for example, aluminum, ceramics, polymers, and composites may be used. For embodiments comprising threaded regions, thread milling, single point milling and turning, and EDM (electric discharge machine) techniques can used to form the male and female threads  31 ,  21 . Preferably, the male and female threads are integrally formed through investment casting of the female and male members. 
   Preferred embodiments of the present invention include the beneficial feature that after the elastically deformable material  50  is provided within space  40 , the female and male members are prevented from separating. One manner of providing this feature is by employing a double taper on at least one of the female thread  21  and the male thread  31 , wherein the two tapers extend in opposing directions. In preferred embodiments, and as shown in the figures, both the female and male threads are tapered in two opposing directions. 
   Female member  20  has a double-tapered female thread  21 . Specifically, the double taper is employed on the female thread minor diameter  23 , while the female thread major diameter  22  is constant. A first taper  27  is defined by a first taper angle α 1  and an opposing second taper  28  is defined by a second taper angle α 2  (measured from female member centerline  61 ). The taper angles are preferably from about 1 degree to about 45 degrees, and more preferably from about 5 to about 10 degrees. 
   Male member  30  employs a corresponding double taper on its thread major diameter  32 . A first taper  37  is defined by a first taper angle β 1  and an opposing second taper  38  is defined by a second taper angle β 2  (measured from male member centerline  62 ). Taper angles  37  and  38  are preferably similar in dimension to that of the corresponding female thread tapers  27 ,  28 . 
     FIGS. 9   a  and  9   b  illustrates the male member embodiment  30  shown in  FIGS. 6 and 7 , disposed within the female member embodiment  20  shown in FIG.  8 . The intermeshed (overlapped) female and male threads  21 ,  31  define a first end region  42  and an opposing second end region  41 . Both the first and second tapers  27 ,  28  on the female member  20  and the first and second tapers  37 ,  38  on the male member  30  are inwardly directed, with respect to coupling centerline  60 , from positions proximate the first and second regions  42 ,  41  and toward a central region  43 . This particular arrangement provides a “back-to-back” double-taper configuration. Several different configuration embodiments are possible by altering the placement of the first and second tapers; that is, on the thread major or minor diameter, by altering the orientation of the tapers (inward or outward); and by altering the position and extension length of the two tapers. In addition to the preferred configuration shown in  FIGS. 9   a  and  9   b , a second preferred configuration is shown in FIG.  10 . Here the first and second tapers on the male and female members are outwardly directed from end regions toward a central region. This configuration is referred to as “face-to-face.”The face-to-face configuration is relatively more flexible as compared to the back-to-back configuration shown in  FIGS. 9   a  and  9   b.    
   Referring now to  FIG. 11 , a third preferred configuration is illustrated, which is a variation of the face-to-face configuration shown in FIG.  10 . The variation includes tapering the female thread major diameter  22  along a portion of the female member  20 . This modified face-to-face configuration permits assembly of the male and female members in one direction only, but a thinner layer of elastically deformable material provided in the taper-to-taper interface portion allows for higher values of torque to be transmitted in the direction of assembly (shown with an arrow and reference character A). 
   The flexible couplings of the present invention are made by first assembling male and female members in a spaced apart arrangement, and then providing elastically deformable material within the defined space.  FIGS. 9  to  11  show assembled male and female members prior to adding the elastically deformable material. Preferably, the elastically deformable material is injection molded into the space between the male and female members. As can be seen in  FIG. 12 , the assembled members are placed into a mold  70 , and elastically deformable material  50  is injected through a sprue  71 , down a runner  72  and into space  40 . 
   In preferred embodiments the elastically deformable material is an elastomer, such as, for example, natural and synthetic rubber, such as Nitrile rubber, styrene rubber, VITON®, butyl rubber, and polysiloxanes; silicone; and polyurethane. Other suitable materials, which may or may not be classified as elastomers, include neoprene; cork; TEFLON®; epoxy, ceramic; metal, such as, for example, sintered and pourable metals; and the like. The type of elastically deformable material used in the present invention will depend on several factors, some of which include the characteristics of the vibrations and other stresses the flexible coupling will likely experience, and the environment the flexible coupling is exposed to. Environmental concerns include temperature, the existence of moisture, and the existence of corroding chemicals, among others. By way of example, inexpensive polyurethanes may be used in low temperature applications. Relatively soft materials such as silicone are suitable where low frequency vibrations are anticipated. VITON®, having a durometer hardness value in the range from about 50 to about 90, is a useful elastically deformable material, as it provides effective vibration and stress damping, has good chemical resistance, and is suitable for high temperature applications. 
   The flexible couplings shown in  FIGS. 3  to  11  are in the form of a suspension system, which is particularly useful in the drilling industry for suspending sensitive electronics within a drill string section. To illustrate this application, and with reference to  FIG. 13 , a drill string section  80  is depicted comprising a pressure tube  81  mounted within a drill pipe  82 . Pressure tube  81  houses an electronic device  83  that is suspended by flexible coupling  10 . 
   It should be appreciated, that the flexible couplings of the present invention are useful for numerous other applications beyond that of a suspension system. Flexible coupling  110 , shown in  FIG. 14 , is generally adapted for connecting a first component to a second component. Thus, flexible coupling  110  can be used to interconnect two sections of drill pipe in a drill string, such that shocks and vibrations are suppressed, while torque is appropriately transmitted to an attached drill bit. 
   Flexible coupling  110  is also useful for connecting components that are misaligned. For example, electric motors for driving rolling units in a steel mill are typically slightly misaligned. The flexible couplings of the present invention can be used between the electric motors and rolling units to prevent damaging strain on the motor, and to utilize the motor's power efficiently. 
   Referring now to  FIG. 15 , another flexible coupling embodiment  210  is shown comprising a female member  220  including a closed end  238  and an opposing open end  239 . A male member  230  is disposed within female member  220  in a spaced apart configuration, thereby defining space  240 . The female and male members each have a thread  221  and  231 , respectively, formed on a surface thereof. Female thread  221  has a major diameter  222  that corresponds to a female member inner diameter  223 . Similarly, male thread  231  has a major diameter  232  that corresponds to a male member outer diameter  233 . Female thread  221  and male thread  231  are tapered in opposing directions, such that the space  240  proximate open end  239  is greater than the space proximate closed end  238 . Upon filling space  240  with an elastically deformable material, the female and male members are prevented from becoming separated from each other. 
   Although all of the accompanying figures depict the male and female members as having threaded regions, the present invention also contemplates non-threaded male and female members. In these non-threaded embodiments, at least one of a male member outer diameter  36 ,  233  and the female member inner diameter  26 ,  223  comprise features, such as, for example, a groove; or have a geometry, such as, for example, a saddle-shape or a diamond-shape, whereby the space between the assembled female and male members and the elastically deformable material provided therein prevents separation of the female and male members. 
   It is to be understood that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only. Accordingly, changes may be made in detail, especially in matters of shape, size and arrangement of features within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.