Abstract:
A CV joint for a BHA includes an inner driven rod, an outer drive coupling, and a thrust plate. The inner driven rod includes at least one lobe extending radially therefrom. The outer drive coupling includes a keyway formed therein corresponding to and adapted to receive each lobe. A thrust plate is positioned between at least one side of each lobe and the corresponding keyway. The thrust plate may allow for the reduction of point or line stress loading on the lobe and keyway.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a nonprovisional application which claims priority from U.S. provisional application No. 62/142,684, filed Apr. 3, 2015. 
     
    
     TECHNICAL FIELD/FIELD OF THE DISCLOSURE 
       [0002]    The present disclosure relates generally to power transmission, and specifically to constant velocity joints. 
       BACKGROUND OF THE DISCLOSURE 
       [0003]    In a drill string, the drill bit may be turned by a mud motor, especially when directional drilling using a rotary steerable system (RSS). Mud motors, as understood in the art, often utilize Moineau or progressive cavity pumps. Progressive cavity pumps include a multi-lobed rotor which eccentrically rotates within a correspondingly lobed stator. In order to mechanically couple the eccentrically rotating rotor to a concentrically rotating drive shaft, a transmission assembly may be utilized. In some cases, a flexible shaft, known as a flexshaft, may be utilized. In other cases, a rigid transmission shaft which is mechanically coupled to the rotor and drive shaft by one or more constant velocity joints may be utilized. However, typical constant velocity joints create point or line stress loading forces therein, contributing to wear and excessive stresses on the drives. 
       SUMMARY 
       [0004]    The present disclosure provides for a full contact constant velocity (CV) joint. The full contact CV joint may include an inner driven rod. The inner driven rod may have at least one lobe extending radially therefrom. The full contact CV joint may include an outer drive coupling. 
         [0005]    The outer drive coupling may have a keyway formed therein corresponding to and adapted to receive each lobe. The full contact CV joint may include a thrust plate positioned between at least one side of each lobe and the corresponding keyway. 
         [0006]    The present disclosure also provides for a transmission assembly for coupling between a mud motor and a drive shaft in a bottom hole assembly. The transmission assembly may include a transmission shaft and a first and second full contact constant velocity (CV) joint. The first full contact CV joint may mechanically couple between a rotor of the mud motor and the transmission shaft. The second full contact CV joint may mechanically couple between the transmission shaft and the drive shaft. Each full contact CV joint may include an inner driven rod. The inner driven rod may have at least one lobe extending radially therefrom. The full contact CV joint may include an outer drive coupling. The outer drive coupling may have a keyway formed therein corresponding to and adapted to receive each lobe. The full contact CV joint may include a thrust plate positioned between at least one side of each lobe and the corresponding keyway. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The present disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
           [0008]      FIG. 1  depicts a schematic view of a bottom hole assembly utilizing a constant velocity driveshaft consistent with at least one embodiment of the present disclosure. 
           [0009]      FIG. 2  depicts a cutaway view of a constant velocity joint consistent with at least one embodiment of the present disclosure. 
           [0010]      FIG. 3  depicts a partial cross section view of the constant velocity joint of  FIG. 2 . 
           [0011]      FIG. 4  depicts a cross section view of the constant velocity joint of  FIG. 2 . 
           [0012]      FIG. 5  depicts a cutaway view of a constant velocity joint consistent with at least one embodiment of the present disclosure. 
           [0013]      FIG. 6  depicts a cross section view of the constant velocity joint of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
         [0015]    As depicted in  FIG. 1 , bottom hole assembly (BHA)  10  may include mud motor  20 . Mud motor  20  may utilize a progressive cavity power section. Mud motor  20  may include stator  22  and rotor  24 . Rotor  24  may eccentrically rotate in response to the flow of a fluid such as drilling fluid through stator  22 . BHA  10  may further include bearing shaft  15 . Bearing shaft  15  may be mechanically coupled to bit  17 . Bearing shaft  15  may be mechanically coupled to rotor  24  by transmission assembly  100 . 
         [0016]    Transmission assembly  100  may include transmission shaft  101 . In some embodiments, transmission shaft  101  may be mechanically coupled to one or both of rotor  24  and bearing shaft  15  by full contact constant velocity (CV) joint  103 . Full contact CV joint  103  may transmit rotation from eccentrically rotating rotor  24  to concentrically rotating driveshaft  15 , while allowing 2 degrees of freedom of movement between transmission shaft  101  and full contact CV joint  103 . 
         [0017]    In some embodiments, full contact CV joint  103  may be a sealed driver as understood in the art. As depicted in  FIGS. 2-4 , full contact CV joint  103  may include inner driven rod  105 . Inner driven rod  105  may be mechanically coupled to or formed as an end of transmission shaft  101 . In some embodiments, inner driven rod  105  may include driven rod body  107 . In some embodiments, driven rod body  107  may be a generally cylindrical or tubular member. In some embodiments, driven rod body  107  may be formed as a part of the end of transmission shaft  101 . In some embodiments, driven rod body  107  may be mechanically coupled to an end of transmission shaft  101 . In some embodiments, inner driven rod  105  may include one or more lobes  109 . Lobes  109  may protrude radially from the exterior surface of driven rod body  107 . Lobes  109  may be positioned radially about the exterior of driven rod body  107 . In some embodiments, lobes  109  may be formed integrally with driven rod body  107 . In some embodiments, for example and without limitation, lobes  109  may be formed by milling, turning, or otherwise machining driven rod body  107 . In some embodiments, lobes  109  may be formed separately from driven rod body  107 . In some embodiments, lobes  109  may be mechanically coupled to driven rod body  107  by, for example and without limitation, mechanical welding. 
         [0018]    In some embodiments, lobes  109  may be removable from driven rod body  107 . For example, as depicted in  FIG. 6 , lobes  109 ′ may be formed separately from driven rod body  107 . In some such embodiments, driven rod body  107  may include recesses  110  positioned to receive lobes  109 ′. Recesses  110  may be generally smooth to allow lobes  109 ′ to be inserted thereinto. In some embodiments, recesses  110  may include one or more coupling features including, for example and without limitation, threads, dovetails, or other fasteners. 
         [0019]    In some embodiments, full contact CV joint  103  may further include outer drive coupling  111 . Outer drive coupling  111  may include coupling  113  adapted to mechanically couple to rotor  24  or driveshaft  15  as previously discussed. In some embodiments, coupling  113  may include a threaded coupler such as a pin or box for a box and pin joint. One having ordinary skill in the art with the benefit of this disclosure will understand that coupling  113  may mechanically couple to rotor  24  or driveshaft  15  using any known interface without deviating from the scope of this disclosure. 
         [0020]    Outer drive coupling  111  may further include joint housing  115 . Joint housing  115  may be generally tubular in shape including an inner cavity adapted to receive at least part of inner driven rod  105 . In some embodiments, as depicted in  FIG. 4 , full contact CV joint  103  may further include boot  116  adapted to mechanically couple between driven rod body  107  and joint housing  115  to, for example and without limitation, seal the interior of full contact CV joint  103 . Boot  116  may further contain a lubricant such as grease and inhibit ingress of any contaminates into the interior of full contact CV joint  103 . 
         [0021]    In some embodiments, full contact CV joint  103  may include a thrust transfer feature positioned to transfer longitudinal force between outer drive coupling  111  and inner driven rod  105  while allowing inner driven rod  105  to pivot relative to outer drive coupling  111 . In some embodiments, the thrust transfer feature may be, for example and without limitation, thrust post  118 . Thrust post  118  may include a generally hemispherical end adapted to fit within thrust post receiver  120  formed in driven rod body  107 . 
         [0022]    In some embodiments, as depicted in  FIGS. 2-4 , joint housing  115  may include one or more keyways  117 . Keyways  117  are formed to correspond with the number, geometry, and arrangement of lobes  109  of inner driven rod  105 . In some embodiments, keyways  117  may be generally rectangular in cross section. Keyways  117  may be adapted to transfer torsional loading from outer drive coupling  111  to inner driven rod  105  through lobes  109 . Likewise, keyways  117  may be adapted to receive torsional loading from driven rod  105  through lobes  109 . In some embodiments, full contact CV joint  103  may be adapted to or be optimized to transfer torsional loading in a single direction. Keyways  117  may be formed by any manufacturing process known in the art, including, for example and without limitation, milling, turning, reaming, or wire EDM. 
         [0023]    In some embodiments, as depicted in  FIGS. 2-4 , lobes  109  may be generally box shaped. As depicted in  FIG. 4 , each lobe  109  may include curved top profile  119 . Curved top profile  119  may be adapted to fit within the corresponding keyway  117  and allow substantially continuous contact between at least a portion of lobe  109  and joint housing  115  as driven rod body  107  pivots relative to outer drive coupling  111  in a plane aligned with the lobe  109  and keyway  117 . 
         [0024]    In some embodiments, as depicted in  FIGS. 2, 3 , each lobe  109  may include curved side profiles  121 . In some embodiments, outer drive coupling  111  may further include thrust plate  123 . Thrust plate  123  may be positioned between one or both curved side profiles  121  and keyway  117 . In some embodiments, thrust plate  123  may be positioned between each lobe  109  and keyway  117  on the side of lobe  109  corresponding with the torsional loading resulting from torsional load in a desired direction. In some embodiments, curved side profiles  121  may be adapted to fit within the corresponding keyway  17  and allow continuous contact between at least a portion of lobe  109  and joint housing  115  as driven rod body  107  pivots relative to outer drive coupling  111  in a plane transverse to lobe  109  and keyway  117 . 
         [0025]    In some embodiments, as depicted in  FIGS. 5, 6 , lobes  109 ′ may be generally round in shape. In some embodiments, each lobe  109 ′ may include curved top profile  119 ′. Curved top profile  119 ′ may be adapted to fit within the corresponding keyway  117  and allow continuous contact between at least a portion of lobe  109 ′ and joint housing  115  as driven rod body  107  pivots relative to outer drive coupling  111  in a plane aligned with the lobe  109 ′ and keyway  117 . 
         [0026]    In some embodiments, as depicted in  FIG. 5 , each lobe  109 ′ may include curved side profiles  121 ′. Thrust plate  123  may be positioned between one or both curved side profiles  121 ′ and keyway  117 . In some embodiments, thrust plate  123  may be positioned between each lobe  109 ′ and keyway  117  on the side of lobe  109 ′ corresponding with the torsional loading resulting from torsional load in a desired direction. In some embodiments, curved side profiles  121 ′ may be adapted to fit within the corresponding keyway  117  and allow continuous contact between at least a portion of lobe  109 ′ and joint housing  115  as driven rod body  107  pivots relative to outer drive coupling  111  in a plane transverse to lobe  109 ′ and keyway  117 . 
         [0027]    In some embodiments, as depicted in  FIGS. 3, 5  thrust plate  123  may include curved side profile  125  adapted to correspond to curved side profile  121  of lobe  109 ,  109 ′. In some embodiments, thrust plate  123  may thus allow for full contact between lobe  109 ,  109 ′ and thrust plate  123  as driven rod body  107  pivots relative to outer drive coupling  111  in a plane transverse to lobe  109 ,  109 ′ and keyway  117 . The full contact, indicated as contact patch  127 , may, for example and without limitation, more evenly distribute the torsional loading between lobe  109 ,  109 ′ and keyway  17  across the surface of lobe  109 ,  109 ′ and keyway  17 . 
         [0028]    In some embodiments, thrust plate  123  may be formed from a material generally harder than lobe  109 ,  109 ′ to, for example and without limitation, prevent wear of thrust plate  123  as lobe  109 ,  109 ′ pivots relative thereto. In some embodiments, thrust plate  123  may be formed from a material generally softer than lobe  109 ,  109 ′ to, for example and without limitation, undergo greater wear than lobe  109 ,  109 ′ or keyway  117 . In such an embodiment, thrust plate  123  may be a consumable and replaceable part. 
         [0029]    In some embodiments, thrust plate  123  may be formed as a single unit as depicted in  FIG. 3 . In some embodiments, thrust plate  123  may be formed from multiple units as depicted in  FIG. 5 . 
         [0030]    In some embodiments, as depicted in  FIGS. 4, 6 , full contact CV joint  105  may further include end sub  129 . End sub  129  may be generally annular in shape. End sub  129  may be positioned about inner driven rod  105  and mechanically couple to joint housing  115 . In some embodiments, end sub  129  may be positioned to retain inner driven rod  105  within joint housing  115 . In some embodiments, end sub  129  may also be positioned to retain boot  116  within joint housing  115 . 
         [0031]    The foregoing outlines features of several embodiments so that a person of ordinary skill in the art may better understand the aspects of the present disclosure. Such features may be replaced by any one of numerous equivalent alternatives, only some of which are disclosed herein. One of ordinary skill in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. One of ordinary skill in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.