Drive Shaft Assembly for Downhole Drilling and Method for Using Same

Abstract

A drive shaft assembly for use with downhole mud motors is capable of handling greater torque and thrust forces. The drive shaft assembly has an elongated central drive shaft, and at least one end housing optionally disposed at one or both ends of the central drive shaft. At least one end of the central drive shaft defines a rounded or partially-spherical outer end surface and a plurality of elongate protrusions or “keys” that extend radially outward from the exterior surface of the shaft. Each end housing has a concave interior surface defining a seat for receiving a rounded end surface of the central drive shaft, as well as a plurality of circumferentially spaced axial keyways adapted to receive and engage with the keys in mating relationship. The shaft and end assemblies cooperate to facilitate omnidirectional pivotal movement and the transfer of torque forces between the shaft and each of said end housings.

What is claimed: 
     
         1 . A drive shaft assembly for coupling downhole components comprising:
 a) an end housing having a central bore defining an inner space, a concave seat surface and a plurality of circumferentially spaced keyways disposed within said inner space; and   b) a drive shaft, further comprising a first end having a partially spherical end surface and a plurality of elongated keys extending radially outward from said shaft, wherein said first end is received within said inner space of said end housing, and wherein said partially spherical end surface has a center-point of rotation and is movably received on said seat surface, and each of said plurality of keys comprises a lateral outer surface, a first load contact surface having a cylindrical convex shape and an axis of rotation, and an opposing second load contact surface having a cylindrical convex shape and an axis of rotation, and wherein said plurality of keys is received within said plurality of keyways and are configured to transfer torque forces between said drive shaft and said end housing.   
     
     
         2 . The drive shaft assembly of  claim 1 , wherein said first load contact surface axis of rotation is perpendicular to said second load contact surface axis of rotation. 
     
     
         3 . The drive shaft assembly of  claim 1 , wherein said first load contact surface axis of rotation and said second load contact surface axis of rotation intersect with said partially spherical end surface center-point of rotation. 
     
     
         4 . The drive shaft assembly of  claim 1 , wherein said first end of said drive shaft is configured for omnidirectional pivotal movement relative to said end housing about said center-point of rotation. 
     
     
         5 . The drive shaft assembly of  claim 1 , wherein said partially spherical end surface engages against said seat surface during pivotal movement of said drive shaft relative to said end housing. 
     
     
         6 . The drive shaft assembly of  claim 1 , wherein each key of said plurality of keys slides and rotates within a corresponding keyway of said plurality of said keyways during pivotal movement of said drive shaft relative to said end housing. 
     
     
         7 . The drive shaft assembly of  claim 1 , wherein each of said keyways of said plurality of keyways have perpendicular opposing flat surfaces configured to engage with said opposed convex load contact surfaces of said plurality of keys.