Patent Publication Number: US-2023151842-A1

Title: Multi-Piece Pinion Shaft Assembly

Description:
FIELD 
     The present disclosure relates to a multi-piece pinion shaft assembly for reciprocating pumps commonly used in hydraulic fracturing applications. 
     BACKGROUND 
     Hydraulic fracturing is a process to obtain hydrocarbons such as natural gas and petroleum by injecting a fracking fluid or slurry at high pressure into a wellbore to create cracks in deep rock formations. The hydraulic fracturing process employs a variety of different types of equipment at the site of the well, including one or more positive displacement pumps, slurry blender, fracturing fluid tanks, high-pressure flow iron (pipe or conduit), wellhead, valves, charge pumps, and trailers upon which some equipment are carried. 
     Positive displacement or reciprocating pumps are commonly used in oil fields for high pressure hydraulic fracturing applications, such as injecting the fracking fluid down the wellbore. A positive displacement pump may include one or more plungers driven by a crankshaft to create flow in a fluid chamber. A positive displacement pump typically has two sections, a power end and a fluid end. The power end includes a crankshaft that changes the rotational motion into linear reciprocating motion to drive the plungers. The crankshaft is mechanically coupled to the input driver via a bull gear and a pinion. The bull gear teeth and the pinion teeth are engaged and enmeshed together to transmit rotational torque. The fluid end of the pump includes cylinders into which the plungers operate to allow fluid into the fluid chamber and then forcibly push the fluid out to a discharge manifold, which is in fluid communication with a well head. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS.  1  and  2    are side and perspective views of an example embodiment of a multi-piece pinion shaft assembly according to the teachings of the present disclosure; 
         FIG.  3    is cross-sectional side view of an example embodiment of a multi-piece pinion shaft before assembly according to the teachings of the present disclosure; 
         FIG.  4    is cross-sectional side view of an example embodiment of a multi-piece pinion shaft after assembly according to the teachings of the present disclosure; 
         FIGS.  5  and  6    are a perspective view and a cross-sectional view of an example embodiment of a multi-piece pinion shaft assembly with roller bearing assembly according to the teachings of the present disclosure; and 
         FIG.  7    is a cross-sectional view of a reciprocating pump that incorporates the multi-piece pinion shaft assembly described herein. 
     
    
    
     DETAILED DESCRIPTION 
     Reference is made to  FIGS.  1 - 6    for various views of an example embodiment of a multi-piece pinion shaft assembly  100  according to the teachings of the present disclosure. The pinion shaft assembly  100  includes a linear tubular member  102  with a circular bore and first and second pinion gear members  104  and  106  that are affixed to the two ends of the tubular member  102 . The first pinion gear member  104  includes a pinion gear  108  and a generally cylindrical-shaped interference fit coupling extension  110  ( FIG.  3   ) that has an outside diameter that corresponds to an inside diameter of the first end  112  of the tubular member  102  to achieve a tight fit therebetween. The coupling may be achieved by shrink fitting, press fitting, friction fitting, or another suitable interference fitting technique. The interference coupling extension  110  of the first end member  104  further includes an alignment key  114  that corresponds to a slot defined on the inner wall of the first end  112  of the tubular member. The alignment key  114 , when disposed in a seat defined in the interference coupling extension  110 , protrudes beyond the outside diameter surface of the interference coupling extension  110 . The use of the alignment key  114  enables the pinion gear member  104  to be inserted and received into the first end  112  of the tubular member  102  in the correct rotational orientation, and helps to prevent rotation of the first pinion gear member  104  relative to the tubular member  102 . The first end  112  of the tubular member  102  further includes a bearing interface  116  proximate to the pinion gear member  104  for receiving roller bearings  502  (shown in  FIGS.  5  and  6   ). 
     The second pinion gear member  106  includes a pinion gear  120  and a generally cylindrical-shaped interference coupling extension  122  ( FIG.  3   ) that has an outside diameter that corresponds to an inside diameter of the second end  124  of the tubular member  102  to achieve a tight friction fit therebetween. The interference coupling extension  122  of the second pinion gear member  106  further includes an alignment key  126  that corresponds to a slot defined on the inner wall of the first end  124  of the tubular member  102 . The alignment key  126 , when disposed in a seat defined in the interference coupling extension  122 , protrudes beyond the outside diameter surface of the interference coupling extension  122 . The use of the alignment key  126  enables the pinion gear member  106  to be inserted and received into the second end  124  of the tubular member  102  in the correct rotational orientation, and helps to prevent rotation of the second pinion gear member  106  relative to the tubular member  102 . The second pinion gear member  106  further includes an extended shaft portion  130  for coupling with a power source, such as a motor or engine. The extended shaft portion  130  may include a keyway  132  such as a longitudinally-oriented groove or slot formed therein, splines or any other mechanism that facilitates coupling to the power source. The second end  124  of the tubular member  102  further includes a bearing interface  136  proximate to the pinion gear member  106  for receiving roller bearings  500  (shown in  FIGS.  5  and  6   ). 
     It should be noted that the alignment key  114 ,  126  may be implemented with alternate suitable mechanisms such as splines, pins, and threaded engagement. As another example, a spring-loaded detent mechanism disposed in the interference coupling extension of the pinion gear member may engage an indentation formed in the inner wall of the tubular member when the pinion gear member is inserted into the tubular member at the correct depth and correct rotational orientation. Further, the shape of the interference coupling extension of the pinion gear members and the tubular member bore may be non-circular, such as square, hexagonal, octagonal, and any suitable shape. It should be noted that assembling the pinion gear members with the tubular member may include cooling the interference coupling extension and/or heating the tubular member so that the parts may be assembled with minimal interference and force. 
     Conventional single-piece pinion shaft implementations suffer from disadvantages of having to correct deformation of the shaft due to heat treatment of the gear teeth. Constructed of separate pieces of materials, the tubular member  102 , and end members  104  and  106  may be fabricated and machined separately and then assembled together. Rather than being fabricated from a single solid piece of material, the tubular member  102  may be made from a hollow tube with the advantage of a significant reduction in weight. Further, the pinion gear teeth of the pinion gear members  104  and  106  may undergo manufacturing steps such as heat treatment without inadvertently damaging or distorting the shaft. The assembly of the pinion gear members  104  and  106  onto the tubular member  102  may be achieved without the use of torque tools as interference coupling is used without the use of fasteners. Being formed of separate pieces, the pinion gear members may be serviced without replacing the entire pinion shaft component. Because the tubular member and the pinion gear members are fabricated separately, they may be constructed from the same or different materials using the same or different manufacturing processes to achieve optimal results. It should be noted that the interference coupling extensions  110  and  122  and the ends  112  and  124  of the tubular member  102  may have other corresponding shapes such as, for example, rectangular extensions for insertion into rectangular cavities. 
       FIG.  7    is a cross-sectional view of a reciprocating pump  700  that incorporates the multi-piece pinion shaft assembly  100  described herein. The reciprocating pump  700  includes a fluid end  702  and a power end  704  operably coupled thereto. The fluid end  702  includes one or more cylinders  706 , each of which includes a fluid chamber  708 . The fluid chambers  708  are in fluid communication with a suction manifold  710  and a discharge manifold  712 . The fluid end  702  further includes plungers  714  that operate within the fluid chambers  708 . Each plunger  714  is adapted to reciprocate within the corresponding fluid chamber  708  during operation of the reciprocating pump  700 . The power end  704  of the reciprocating pump  700  includes a crankshaft  716  that includes one or more crank throws, corresponding to the one or more cylinders  706  of the fluid end  702 , and a main shaft. The crank throws are connected to the main shaft and are each offset from the rotational axis of the crankshaft. The crankshaft  716  is mechanically coupled to a power source (not shown) via a bull gear  718  and a pinion  720  (e.g., multi-piece pinion shaft assembly  100 ). The bull gear  718  is attached to the crankshaft  716  and the pinion  720  is connected to a power source or motor (not shown). The gear teeth of the bull gear  718  mesh with the gear teeth of the pinion  720 , thereby transmitting torque therebetween. The crank throws are each coupled to a respective one of the plungers  714  via a mechanical linkage  722 , each of which includes a connecting rod  724 , a crosshead  726 , and a pony rod  728 . Each of the crossheads  726  is disposed within a corresponding crosshead bore  730 , within which the crosshead  726  is adapted to reciprocate. The connecting rods  724  connect respective ones of the crossheads  726  to respective ones of the crank throws. Further, the pony rods  728  connect respective ones of the crossheads  726  to respective ones of the plungers  714 . 
     In operation, the power source or motor (not shown) rotates the shaft of the multi-piece pinion assembly  100 , which rotates the pinion gear teeth of the pinion gear members  104  and  106  that engage the bull gear  718  and the crankshaft  716 . The crankshaft  716  rotates the crank throws about the central axis of the main shaft. The crank throws, in turn, are operable to drive the mechanical linkages  722 , including respective ones of the connecting rods  724 , the crossheads  726 , and the pony rods  728 , causing the crossheads  726  to reciprocate within the corresponding crosshead bores  730 . The reciprocating motion of the crossheads  726  is transferred to respective ones of the plungers  714  via the pony rods  728 , causing the plungers  714  to reciprocate within the corresponding fluid chambers  708 . As the plungers  714  reciprocate within the respective fluid chambers  708 , fluid is allowed into the pressure chambers  708  from the suction manifold  710  and, thereafter, discharged from the pressure chambers  708  into the discharge manifold  712 . 
     The features of the present disclosure which are believed to be novel are set forth below with particularity in the appended claims. However, modifications, variations, and changes to the exemplary embodiments described above will be apparent to those skilled in the art, and the multi-piece pinion shaft assembly described herein thus encompasses such modifications, variations, and changes and are not limited to the specific embodiments described herein.