Abstract:
A constant velocity universal joint is assembled as a crown ball meshed within a housing socket for rotation about respective rotational axes. The outside diameter of the crown ball is greater than the inside diameter of the socket. A plurality of channels, equally spaced around the crown ball perimeter are cut into the crown ball surface generally along or parallel with the crown ball drive axis. An arcuate cup is cut into each crown ball channel to confine a respective torque transfer element. A number, corresponding to the number of crown ball channels, of partial cylinder channels are cut into the inside surface of the housing socket. One of opposite side walls for each housing channel is given an arcuate radius corresponding to that of the force transfer elements. Ridges between adjacent crown ball channels mesh with ridges between adjacent housing socket channels. Torque transfer elements confined within said crown ball cups engage the partial cylinder wall of the housing channels to transfer drive forces between the crown ball and socket housing through a departure angle between the respective rotational axes.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    Not applicable 
       BACKGROUND OF THE INVENTION 
       [0002]    Field of the Invention 
         [0003]    This invention relates to earthboring, in general, and specifically to constant velocity universal joints. Universal joints have general utility in the realm of power transmission as a mechanism for redirecting an axial line of rotary torque. The present invention has particular value to the industrial art of directional well drilling. 
         [0004]    Discussion of Prior Art 
         [0005]    One procedure for directional drilling of boreholes in the earth includes a downhole drilling motor (also called a mud motor) for rotatively driving the drill bit. Drilling motors are modern adaptions of the ancient Archimedes screw used for lifting or pumping water but is operated in reverse. To drill directionally, drilling fluid essential for rotary drilling is pumped down the central bore of a pipe string. Just prior to reaching the drill bit, the drilling fluid is directed through the drilling motor. At the uphole end of the drilling motor the Archimedes screw is used to convert fluid energy into rotating mechanical energy. The drilling fluid acts against a helically lobed shaft, known as a rotor, which rotates about its axis within a correspondingly lobed housing known as a stator. The stator along with the drill string above and drilling motor outer housings below remain stationary. Only the rotor, output drive shaft and drill bit rotate when drilling in this mode. 
         [0006]    To directionally drill or generate arced curvature of the wellbore, the rotary drive axis of the drill bit must be deviated from the uphole axis of the drilling motor. The traditional means for changing the angular direction of the motor output drive shaft is with a mechanism characterized as a universal joint. All universal joints must transmit both compressive and torque load from the rotor/stator power section to the bearing assembly. One of the most popular universal joint mechanisms favored by the earthboring industry is that described as a “constant velocity” or CV joint. 
         [0007]    Generally, CV joints comprise mirrored upper and lower ball and socket housing arrangements. To accommodate axial compression loads, most employ some method of spherical ball bearing or semi-spherical ball shape secured to the end of a drive shaft which fits within a socket housing having a mating, semi-spherical pocket. 
         [0008]    To transmit torque loads, the CV joint ball and socket housing are mechanically linked by a plurality of torque transfer balls. The drive shaft ball, hereafter characterized as the “ball”, typically confines the torque transfer balls within mating cups. The cups are angularly spaced equally about the ball perimeter in the diametric plane transverse to the in-drive axis. The cup diameters are substantially the same as the torque transfer balls but less than half the hemisphere depth. 
         [0009]    The socket housing pocket, hereafter characterized as the housing “socket”, typically contains a plurality of race channels parallel with the socket out-drive axis distributed about the internal surface of the pocket. The number of race channels must exactly match the circumferential location of the mating driveshaft ball cups and are angularly spaced equally about the pocket perimeter. The channel depth is less than a hemisphere of each ball. 
         [0010]    As the in-drive and out-drive shafts rotate, torque transfer balls shift along the socket channels from one side of a transverse diameter plane to the other. The torque force is transferred through the torque transfer balls from the socket surface area to an axially moving arced line across a respective channel. Consequently, most of the mechanical wear on the joint occurs to the socket channels in the area of the shifting ball contact line. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The advantages and further features of the invention will be readily appreciated by those of ordinary skill in the art as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference characters designate like or similar elements throughout. 
           [0012]      FIG. 1  is an elevation view of a directional drilling motor assembly. 
           [0013]      FIG. 2  is an expanded, sectioned view of a drilling motor assembly 
           [0014]      FIG. 3  is an enlarged and segmented view of the  FIG. 2  section. 
           [0015]      FIG. 4  is an axial cross section of a first embodiment of the invention CV joint. 
           [0016]      FIG. 5  is a transverse cross section of the first invention embodiment as viewed along cutting plane V-V of FIG. 4 . 
           [0017]      FIG. 6  is an enlarged detail of the  FIG. 5  portion circumscribed as VI. 
           [0018]      FIG. 7  is a pictorial view of the first embodiment ball element. 
           [0019]      FIG. 8  is an elevation view of the first embodiment ball element. 
           [0020]      FIG. 9  is a cross section of the first embodiment ball element as viewed along cutting plane IX-IX of  FIG. 8 . 
           [0021]      FIG. 10  is a cross section of the first embodiment ball element viewed along cutting plane X-X of  FIG. 9 . 
           [0022]      FIG. 11  is a cross section of the invention housing. 
           [0023]      FIG. 12  is a pictorial view of the invention housing. 
           [0024]      FIG. 13  is an assembly cross section of a second embodiment of the invention. 
           [0025]      FIG. 14  is a pictorial view of the second embodiment ball element. 
           [0026]      FIG. 15  is an elevation view of the second embodiment ball element 
           [0027]      FIG. 16  is a section view of the second embodiment viewed along cutting plane XVI-XVI of  FIG. 15   
           [0028]      FIG. 17  is a section view of the second embodiment viewed along cutting plane XVII-XVII of  FIG. 16 . 
           [0029]      FIG. 18  is an axial cross-section of a third embodiment of the invention 
           [0030]      FIG. 19  is a transverse cross-section of the  FIG. 18  invention embodiment shown along cutting plane XIX of  FIG. 18 . 
           [0031]      FIG. 20  is a pictorial view of a crown ball for the third invention embodiment. 
           [0032]      FIG. 21  is a pictorial view of a cylindrical force transfer element for the third invention embodiment. 
           [0033]      FIG. 22  is a pictorial view of a partial sphere force transfer element for the third invention embodiment. 
           [0034]      FIG. 23  is a pictorial view of a partial ellipse force transfer element for the third invention embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0035]    As used herein, the terms “up” and “down”, “upper” and “lower”, “upwardly” and “downwardly”, “upstream” and “downstream”; “above” and “below”; and other like terms indicating relative positions above or below a given point or element are used in this description to more clearly describe some embodiments of the invention. However, when applied to equipment and methods for use in wells that are deviated or horizontal, such terms may refer to a left to right, right to left, or other relationship as appropriate. Moreover, in the specification and appended claims, the terms “pipe”, “tube”, “tubular”, “casing”, “liner” and/or “other tubular goods” are to be interpreted and defined generically to mean any and all of such elements without limitation of industry usage. 
         [0036]    The term “sub”, as used herein, is a drilling industry term of art for describing a segment of drill string usually having a length less than a full pipe joint and formed or constructed to perform a specific task in the drilling or well completion process. 
         [0037]      FIG. 1  provides an overall representation of the invention operating environment. The lower distal end of a deviated direction drill string traditionally comprises one or more drill collars  10  which are, approximately, 30 ft. lengths of pipe having an exceptionally thick annulus section. The drill collars  10  provide the end-biased weight upon the cutting bit at the distal end of the drill string. Theoretically, that portion of the drill string above the collars is under tensile stress. 
         [0038]    Below the collars is a directional drilling motor  12  driven by a flow of circulating drilling fluid. Referring to  FIG. 2 , a directional drilling motor broadly comprises a power section  14 , a transmission assembly  16 , a bearing assembly  18  and a bit box  20 . Within the transmission assembly  16 , between the power section  14  and the bearing assembly  18  is a bent housing assembly  17 . Below the bent housing assembly  17  is a wear collar or stabilizer  19 . 
         [0039]    With respect to  FIG. 3 , the power section  14  comprises a housing  22  and internal rotor  24 . The housing  22  has an axially developed internal bore profile that corresponds with the external helical profile of the internal rotor shaft  24 . Drilling fluid pumped through the housing bore between the housing and rotor shaft profiles drives rotation of the rotor shaft  24  about its axis of revolution. As the rotor shaft  24  rotates about its axis, the rotor axis also orbits about the central axis of the housing  22 . 
         [0040]    The downhole end of the rotor shaft  24  is secured to the housing sub  25  of an uphole CV joint  26 . The uphole CV joint  26  transfers rotation of rotor shaft  24  to the transmission shaft  29  as it accommodates the orbit of the rotor shaft  24 . The downhole end of the transmission shaft  29  rotatively drives a second CV joint  28 , substantially identical to CV joint  26 , which transfers shaft  29  rotation to the bearing shaft  30 . The rotational axis of the bearing shaft  30  is determined by the bent housing  17  which may redirect the drive axis from the motor rotor shaft  24  axis by small angles up to about 3°, for example. Accordingly, both CV joints  26  and  28  accommodate an angular departure of an output rotational axis relative to the input rotational axis. 
         [0041]    The bearing assembly  18  includes a bearing housing  31  and bearing shaft  30  for transfer of drilling torque and weight to the bit box  20 . The bearing shaft  30  delivers rotating torque to a drill bit (not shown) secured in the bit box  20  and accommodates the consequential drilling shock. The housing  31  secures radial alignment for the bearing shaft  30  and transfers the collar drilling weight to the bit. 
         [0042]    With respect to  FIG. 4 , the CV joint  26  of the present invention broadly comprises a crown ball  40  and socket housing  50 . The crown ball  40  has a substantially spherical surface secured to the distal end of a transmission shaft  29 . The crown ball  40  may be an integrally forged portion of the transmission shaft  29 . A plurality, usually four to eight, of arced force transfer elements such as balls  60  mechanically link the crown ball  40  to the socket housing  50 . A thrust seat  51  transfers the axial thrust of the drilling fluid static and dynamic loads from the drilling motor rotor shaft  24  to the crown ball  40 . 
         [0043]    The crown ball  40 , shown by  FIGS. 7 through 10 , is a partial sphere about a center point  36  that is intersected by the crown ball axis  34 . Normally, the crown ball axis  34  is coincident with the drive axis of transmission shaft  29 . A number of chord traversing channels  41  are cut into the spherical surface of crown ball  40 . In this example, the selected number of chord traversing channels  41  is six; each aligned in substantial parallelism with the axis  34  and distributed about the axis  34  in equal increments of 60°. With respect to  FIG. 7  and for the purpose of descriptive nomenclature, each channel  41  comprises a channel bottom  43 , a loaded side wall  44  and a back wall  47 . Between each loaded side wall  44  and adjacent channel back wall  47  is a ridge  46 . It is also appropriate to explain that the term “chord”, as used and intended herein, is not necessarily a linear or straight line segment between two points on the surface of a sphere. A preferred embodiment of the invention aligns the channels bottoms  43  substantially parallel with the crown ball axis  34  and consequently, parallel with the torque axis of transmission shaft  29 . However, the channels  41  may also be skewed with respect to the crown ball axis  34  or even arced following a substantially constant radius from the axis  34 . The term “chord” is used to encompass all appropriate channel configurations. 
         [0044]    Centered in the transverse center plane ( FIG. 8  cutting plane IX-IX) of each crown ball  40  is an arced cup  42  cut into the bottom  43  and loaded side wall  44  of each channel  41 . The cups  42  are cut to an arced inside radius corresponding to the outside radius  61  of force transfer elements  60  ( FIGS. 4 and 6 ). The outside diameter  45  ( FIG. 9 ) of the crown ball  40  as measured between diametrically opposite channel ridge crests  46 , is greater than the inside diameter  52  of the socket housing  50  as shown by  FIG. 11 . The crown ball ridge crest radius about axis  34  coincides with the outside diameter  45 . This important relationship will be further developed with respect to  FIG. 6 . 
         [0045]    Referring to  FIGS. 11 and 12 , the joint socket housing  50  comprises a major inside cylindrical boring ID  52  about the housing axis  53 . Into the inside surface of the cylindrical boring, six partial-cylinder channels  54  are cut to an axial depth, parallel with the housing axis  53 , sufficient to accommodate the crown ball  40  OD. These partial cylinder channels  54  are formed to substantially the same inside arc radius as the outside arc radius  61  of the force transfer elements  60 . Those of ordinary skill will understand that there is a dimensional tolerance difference between the outside arc radius  61  of the force transfer elements  60  and the inside arc radius of the cups  42  (and cylinder channels  54 ). The reference to the outside arc radius  61  of the force transfer elements  60  as being the inside arc radius of the cups  42  and cylinder channels  54  is a literary convenience. Usually, the two radii are not identical but differ dimensionally by a slight degree. 
         [0046]    As a partial cylinder, each channel  54  has two opposing walls. One wall  55  of the radius  61  is the loading wall opposite from the cup  42 . The back wall  56 , diametrically opposite from the loading wall  55 , is a tangential expansion of the channel  54  for crown ball ridge  46  relief space  58 . Housing structure between the loading wall  55  and the back wall  56  forms a socket ridge  57 . 
         [0047]    From the foregoing general assembly description, it will be understood that dimensions are coordinated to maximize the loading area of the arced cup  42  against the force transfer elements  60 . Similarly, the compressive line contact of the crown ball  40  against the cylindrical channel  54  is also increased. The detail of  FIG. 6  illustrates a single force transfer element  60  and the approximate directions of load distribution as torque from the crown ball  40  to the socket housing  50 . By countless wear tests and measurements, it has been found that prior art CV joints transfer torque load by line contact between the force transfer elements and the socket housing channels by about 60° as represented by arc “B” of  FIG. 6 . Although there is contact between the force transfer elements  60  and the cylinder loading wall  54  as represented by arc D, the load transferred over this arc is insignificant. 
         [0048]    Comparatively, applicants&#39; invention has an effective load transfer from the force transfer elements  60  to the housing channel loading walls  54  over an arc “A” of about 75° for an effective load arc increase of about 15°, or approximately 20%, as represented by arc “C”. Such an increase in the load transfer arc has resulted in a synergistic increase in operational life of the CV joint. 
         [0049]    The meshed assembly of the crown ball ridge crests  46  into the socket housing relief space  58  allows a transfer vector between the crown ball  40  and the socket housing  50  that is more normal to the axes  34  and  53  of respective components. As a corollary to the foregoing result, the magnitude of an ineffective radial force vector (arc D) is reduced. Additionally, a greater load arc (arc A) between the crown ball  60  and loading wall  54  is made available for greater operating life. 
         [0050]    An alternative embodiment of the invention is represented by  FIGS. 13 through 17 . This alternative embodiment differs from the previous  FIG. 7  embodiment mainly in the provision of a trough  72  cut into the juncture between the loaded wall  44  and the channel bottom  43 . As shown by  FIG. 16 , the trough profile is substantially cylindrical with a radius corresponding to that of the force transfer elements  60 . The trough  72  length should be sufficient to accommodate rolling displacement of the torque transfer ball as the crown ball  70  completes rotation about its axis  34 . 
         [0051]    Another embodiment of the invention is represented by  FIGS. 18 through 23 . In a first configuration of this third embodiment, the force transfer elements are rollers  84  as shown by  FIG. 21  having circular surface formed about the axis  82  between relatively flat end-faces  85 . Distinctively, the force transfer element channels  94  in the crown ball that link the socket housing  90  to the crown ball  80  have relatively flat bottoms  94  to interface with relatively flat roller end-faces  85 . The rollers  84  are aligned in the crown ball channels  92  with the roller axis  82  normal to the crown ball torque axis  34 . 
         [0052]    The third invention embodiment may also include a force transfer element in the form of a partial sphere  86  as illustrated by  FIG. 22  having spherical surfaces about axis  82  between relatively flat end-faces.  FIG. 23  illustrates a partially elliptical force transfer element. 
         [0053]    The primary utility of the above described invention is envisioned to be as a drilling motor transmission joint. In that application reverse drive occasions are rare to non-existent. Consequently, the invention is normally expected to be designed for applications restricted to a single rotation direction. However, to a limited degree, the present CV joint is capable of reverse torque transmission. In such an event, a reverse rotation about the axes  34  and  53  will engage the back wall  47  of crown ball ridge  46  with the back wall  56  of housing channel  54  for transfer of torsional forces. 
         [0054]    Although the invention disclosed herein has been described in terms of specified and presently preferred embodiments which are set forth in detail, it should be understood that this is by illustration only and that the invention is not necessarily limited thereto. Alternative embodiments and operating techniques will become apparent to those of ordinary skill in the art in view of the present disclosure. Accordingly, modification of the invention are contemplated which may be made without departing from the spirit of the claimed invention.