Abstract:
A drive means for downhole use comprises an input shaft and an output shaft, the input shaft being coupled to a means of rotation, the input shaft and the output shaft being torsionally coupled, the output shaft being coupled to the rotor of the progressive cavity pump, the input shaft lies in a first axis and the output shaft lies in a second axis, the second axis being parallel to the first axis but spaced from it so that the output shaft rotates about its axis while describing a circular path.

Description:
This application claims priority to and the benefit of Great Britain patent application numbers GB0809966.5, filed Jun. 2, 2008, the entirety of which application is hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     This invention relates to drive means, particularly drive means for progressive cavity pumps. 
     BACKGROUND OF THE INVENTION 
     A progressive cavity pump usually comprises a helical rotor disposed in a double helical bore. Sealed cavities exist between the surfaces of the rotor and stator, and as the rotor turns, these sealed cavities progress along the length of the pump. Thus fluid entering a forming cavity at one end of the pump is transported the length of the pump until the cavity reaches the other end of the pump. The rotor rotates about a central axis, however no part of the rotor lies on this axis, rather each part of the rotor is spaced from the central axis it orbits. Since a drive means usually generates a rotating output that is coincident with the axis of rotation, a jointed or flexible shaft is used to connect the drive output to the rotor. 
     OBJECTS OF THE INVENTION 
     Jointed or flexible shafts may suffer from wear. An object of the present invention is to provide an alternative means of driving the rotor. 
     SUMMARY OF THE INVENTION 
     According to the invention there is provided a drive means for downhole use, comprising an input shaft and an output shaft, the input shaft being coupled to a means of rotation, the input shaft and the output shaft being torsionally coupled, the output shaft being coupled to the rotor of the progressive cavity pump, wherein the input shaft lies in a first axis and the output shaft lies in a second axis, the second axis being parallel to the first axis but spaced from it so that the output shaft rotates about its axis while describing a circular path. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described, by way of example and not intended to be limiting, by the following embodiments, of which 
         FIG. 1  is an exploded perspective view of the drive means with an output shaft of the drive means coupled to a rotor of a progressive cavity pump 
         FIG. 2  is an exploded perspective view of the drive means viewed from another angle 
         FIG. 3  is an exploded perspective view of the drive means viewed from another angle 
         FIG. 4  is an exploded perspective view of the drive means viewed from another angle 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIGS. 1 and 2 , the drive means comprises an input shaft  10  coupled to an output shaft  12 , disposed in a housing  30 . The input shaft  10  protrudes through the bore  15  of an input end cap  14  which is secured to the housing  30 . Similarly, the output shaft  12  protrudes through the bore  17  of an output end cap  16  which is secured to the housing  30 . A connector member  18  fits over the output end cap  16  and attaches to the housing  30  with a thread. The input shaft  10  and output shaft  12  are supporting inside the housing  30  by eccentric bearings  21 ,  23  respectively. 
     The input drive shaft  10  is coupled to some conventional drive means, that rotates the input drive shaft  10  about its central axis. The input drive shaft includes a head  20  having a female outer rotor  201  of a gerotor, ideally this is a three-lobed  200  shape. The input drive head  20  is supported on an eccentric element  21 . The output drive has a corresponding output drive shaft head  22 , which features a male inner rotor  101  of a gerotor, ideally having a two-lobed  100  shape, which engages with the female outer rotor of the input drive head  20 . The output drive shaft head  22  is similarly supported on an eccentric bearing  23 . 
     Referring to  FIG. 4 , the housing  30  has a bore  45  which accommodates the input drive shaft head  20  and output drive shaft head  22 . The bore has a two lobed section, in which the crescent-shaped eccentric bearings  21 ,  23  sit, the bearings facing each other when the bore is considered axially. Each bearing  21 ,  23  has a ridge  31 ,  32  which engages in slots  41 ,  42  on the inner surface of the bore  45  in order to locate them. The two-lobed shape of the bore  45  is offset from the central axis, so that the eccentric bearing  21  is radially displaced further than the eccentric bearing  23 . When the input drive shaft head  20  is resting in the bore  45  against the eccentric bearing  21 , the input drive shaft  10  is coincident with the center axis of the housing  30 . The output drive shaft head  22  is disposed eccentrically, so that when it rests in the bore  45  against the eccentric bearing  23 , the output drive shaft  12  is spaced from the center axis of the housing  30 . 
     After the input and output drive shaft heads  20 ,  22  have been positioned in the housing  30  with their respective eccentric bearings  21 ,  23 , so that the male inner rotor of the output drive shaft head  22  engages with the female outer rotor of the input drive shaft head  20 , the input and output drive shafts  10  and  12  are secured together by input end cap  14  and output end cap  16  to the housing  30 , with the input shaft  10  protruding through the central bore  15  of the input end cap  14 , and the output shaft  12  protruding from the eccentric bore  17  of the output end cap  16 . The input end cap can be secured for example by pins placed in corresponding holes  34 ,  35  in the input end cap and the housing. The output end cap is rotationally constrained to the housing pins  25  which pass through output end cap holes  24  and engage in corresponding holes in the housing. Connector member  18  is then fitted over the output end cap. 
     In use, the input shaft  10  is rotated about its central axis. As the input shaft head  20  rotates, the engagement of the female outer rotor causes the male inner rotor of the output shaft head  22 , and therefore also the output shaft  12  itself, to also rotate. However, the male inner rotor is offset from the axis of rotation of the input shaft, always engaging the female outer rotor at a radially spaced position, the radial spacing being constrained by the eccentric bearing  23 . 
     Although the radial spacing of the output shaft  12  is constrained by the eccentric bearing, the output shaft and housing are free to rotate relative to the outer housing upon which it is conveyed into the well and relative to the stator of a progressive cavity pump suspended beneath the drive means. The output shaft  12  is connected to the rotor  300 R of a progressive cavity pump  300  having a stator  300 S. As seen in  FIG. 1 , the rotor  300 R of the progressive cavity pump  300  is offset from the central axis of the stator  300 S. As the input shaft  10  rotates and causes output shaft  12  to rotate, the output shaft  12  and progressive cavity pump rotor  300 R not only rotate about their central axis  12 A ( FIG. 1 ), but also move around a circular path relative to the stator  300 S of the progressive cavity pump  300  (whose axis coincides with the axis of the input shaft  10 ). As the input shaft  10  is rotated, and so causes the output shaft  12  and the connected progressive cavity pump rotor  300 R to rotate, the output shaft  12  and the connected progressive cavity pump rotor  300 R also describe a circular path relative to the axis of the stator  300 S of the progressive cavity pump  300 , the housing rotating to accommodate this movement. 
     Thus it will be seen that the progressive cavity pump rotor  300 R may be driven in the required manner without the use of a flexible or jointer member. 
     It will be noted that since the outer rotor of the input shaft  10  is a three-lobed gerotor shape and the inner rotor of the output shaft  12  is a two-lobed gerotor shape, a single revolution of the input shaft causes the output shaft to turn by approximately 1.5 revolutions (it will not be exactly 1.5 because of the circular movement of the output shaft itself). It will be realized that other gear ratios may be chosen, and also that the input shaft could feature a male shape and the output shaft could feature a female shape. Also, the bore of the housing could be shaped so that separate bearing elements are not required. 
     Alternative embodiments using the principles disclosed will suggest themselves to those skilled in the art upon studying the foregoing description and the drawings. It is intended that such alternatives are included within the scope of the invention, which is limited only by the claims.