High speed positive displacement motor

Abstract

According to the present invention, a downhole motor converts hydraulic energy from drilling fluid passing through the motor into mechanical power that is useful to rotate a drillbit. The downhole motor includes a tubular housing and a stator mounted within the tubular housing. A rotor is positioned within the stator for rotation relative thereto. The stator has a central first axis and the rotor has a central second axis. The rotor is rotated about the second axis and nutated about the first axis within the stator by drilling fluid passing through the stator. The rotor further has a concentric lower end portion thereon. A cylindrical coupling is disposed within the tubular housing beneath the rotor and has an axis substantially aligned with the first axis and an inner cylindrical opening the axis of which is substantially aligned with the second axis, the opening being adapted for receiving the lower end portion of the rotor. A first bearing assembly is disposed in the opening of the coupling for rotatably receiving and supporting the lower end portion of the rotor, whereby nutation of the lower end portion of the rotor about the first axis induces rotation of the coupling about the first axis. A second bearing assembly is disposed between the coupling and the tubular housing for supporting rotation of the coupling relative to the tubular housing. A transmission shaft and bit box are connected to the coupling for rotation. In this manner, nutation of the rotor about the first axis results in rotation of the transmission shaft and the bit box. A related method is also provided.

What is claimed is:  
     
         1 . A downhole motor for converting hydraulic energy from drilling fluid passing through the motor into mechanical power that is useful to rotate a drillbit, comprising: 
 a tubular housing;    a stator mounted within said tubular housing, said stator having a first axis;    a rotor positioned within said stator for rotation relative thereto, said rotor having a second axis and being rotated about the second axis and nutated about the first axis within said stator by drilling fluid passing through said stator, said rotor further having a concentric lower end portion;    a cylindrical coupling disposed within said tubular housing beneath the rotor and having an axis substantially aligned with the first axis and an inner cylindrical opening the axis of which is substantially aligned with the second axis, the opening adapted for receiving the lower end portion of said rotor;    a first bearing assembly disposed in the opening of said coupling for rotatably receiving and supporting the lower end portion of said rotor, whereby nutation of the lower end portion of said rotor about the first axis induces rotation of said coupling about the first axis;    a second bearing assembly disposed between said coupling and said tubular housing for supporting rotation of said coupling relative to said tubular housing; and    a transmission shaft and bit box connected to said coupling for rotation, whereby nutation of the rotor about the first axis results in rotation of said transmission shaft and said bit box.    
     
     
         2 . The downhole motor of  claim 1 , wherein said cylindrical coupling has a peripheral opening therein for passage of drilling fluid through said cylindrical coupling.  
     
     
         3 . The downhole motor of  claim 2 , wherein the peripheral opening is shaped to optimize the structural integrity of said cylindrical coupling while minimizing the resistance to flow of the drilling fluid therethrough.  
     
     
         4 . In a downhole motor including a tubular stator housing, a helical stator having a first axis and connected to the stator housing, and a helical rotor having a second axis, the rotor being rotated about the second axis and nutated about the first axis within the stator by drilling fluid passing through the stator, an apparatus for transmitting torque developed at the rotor to a bit box, comprising: 
 a pin connected to the lower end of the rotor, said pin having an axis aligned with the second axis whereby nutation of the rotor about the first axis induces nutation of said pin about the first axis;    a cylindrical coupling disposed within the stator housing beneath the rotor and having an axis substantially aligned with the first axis and an inner cylindrical opening the axis of which is substantially aligned with the second axis, the opening adapted for receiving said pin;    a first bearing assembly disposed in the opening of said coupling for rotatably receiving and supporting said pin, whereby nutation of said pin about the first axis induces rotation of said coupling about the first axis;    a second bearing assembly disposed between said coupling and the stator housing for supporting rotation of said coupling relative to the stator housing; and    a transmission shaft and bit box connected to said coupling for rotation, whereby nutation of the rotor about the first axis results in rotation of said transmission shaft and said bit box.    
     
     
         5 . The downhole motor of  claim 1 , wherein said cylindrical coupling has a peripheral opening therein for passage of drilling fluid through said cylindrical coupling.  
     
     
         6 . The downhole motor of  claim 2 , wherein the peripheral opening is shaped to optimize the structural integrity of said cylindrical coupling while minimizing the resistance to flow of the drilling fluid therethrough.  
     
     
         7 . A method for converting hydraulic energy from drilling fluid passing through a drill string into mechanical power that is useful to rotate a drillbit, comprising: 
 placing a tubular housing in the drill string;    mounting a stator within the tubular housing, the stator    having a first axis;    positioning a rotor within the stator for rotation relative thereto, the rotor having a second axis and being rotated about the second axis and nutated about the first axis within the stator by drilling fluid passing through the stator; and    converting the nutation of the rotor about the first axis into rotation of a transmission assembly and bit box.    
     
     
         8 . The method of  claim 7 , wherein the converting step includes: 
 equipping the rotor with a concentric lower end portion, whereby nutation of the rotor about the first axis induces nutation of the lower end portion about the first axis;    placing a coupling within the tubular housing beneath the rotor, the coupling having an axis substantially aligned with the first axis and an inner opening the axis of which is substantially aligned with the second axis, the opening adapted for receiving the lower end portion of the rotor, whereby nutation of the lower end portion of the rotor induces rotation of the coupling about the first axis; and    applying the rotation of the coupling to a transmission assembly and bit box to rotate the transmission assembly and bit box.    
     
     
         9 . The method of  claim 8 , further comprising the steps of: 
 placing a first bearing assembly in the opening of the coupling for rotatably receiving and supporting the lower end portion of the rotor;    placing a second bearing assembly between the coupling and the tubular housing for supporting rotation of said coupling relative to said tubular housing.