received by the International Bureau on 25 November 2015 (25.11.2015)

In the Claims

What is claimed is:

1. A driveshaft assembly for a downhole motor, the driveshaft assembly comprising:

a driveshaft having a central longitudinal axis, a first end, a second end opposite the first end, a first recess proximate the first end, and a second recess proximate the second end;

a first drive key configured to be at least partially disposed within the first recess;

a second drive key configured to be at least partially disposed within the second recess; a first end housing having a central axis, a first end, a second end opposite the first end, and a first receptacle extending axially from an open end to a closed end, wherein the open end is proximate the first end of the first end housing and wherein the first receptacle includes a first pocket having an inner wall; and

a second end housing having a central axis, a first end, a second end opposite the first end, and a second receptacle extending axially from an open end to a closed end, wherein the open end is proximate the first end of the second end housing and wherein the second receptacle includes a second pocket having an inner wall; a central point disposed along the central longitudinal axis of the driveshaft and substantially equidistant from the closed end of the first receptacle and the closed end of the second receptacle along the central longitudinal axis of the driveshaft; wherein the driveshaft assembly has a first configuration, wherein the first end of the driveshaft is disposed within the first receptacle such that the first drive key engages the inner wall of the first pocket at a first contact point that is spaced from the central point at a distance HI along the central longitudinal axis of the driveshaft, and wherein the second end of the driveshaft is disposed within the second receptacle such that the second drive key engages the inner wall of the second pocket at a second contact point that is spaced from the central point at a distance H2 along the central longitudinal axis of the driveshaft;

wherein HI is greater than H2.

2. The driveshaft of claim 1, wherein the driveshaft assembly has a second configuration, wherein the first end of the driveshaft is disposed within the first receptacle such that the first drive key engages the inner wall of the first pocket at a third contact point that is spaced from the central point at a distance H3 along the central longitudinal axis of the driveshaft, and wherein the second end of the driveshaft is disposed within the second receptacle such that the second drive key engages the inner wall of the second pocket at a fourth contact point that is spaced from the central point at a distance H4 along the central longitudinal axis of the driveshaft; and

wherein H4 is greater than H3.

3. The driveshaft assembly of claim 2, wherein H3 is substantially equal to H2 and wherein H4 is substantially equal to HI .

4. The driveshaft assembly of claim 2, wherein the first drive key is a spherical and has a diameter; and

wherein the difference between HI and H3 is at least 30% of a diameter of the first drive key.

5. The driveshaft assembly of claim 2, wherein no additional components are added or substituted within the driveshaft assembly to transition the driveshaft assembly from the first configuration to the second configuration.

6. The driveshaft assembly of claim 1, wherein the driveshaft assembly has a second configuration, wherein the first end of the driveshaft is disposed within the second receptacle such that the first drive key engages the inner wall of the second pocket at a third contact point that is spaced from the central point at a distance H3, and wherein the second end of the driveshaft is disposed within the first receptacle such that the second drive key engages the inner wall of the first pocket at a fourth contact point that is spaced from the central point at a distance H4; and

wherein H4 is greater than H3.

7. The driveshaft assembly of claim 6, wherein H3 is substantially equal to H2 and wherein H4 is substantially equal to HI .

8. The driveshaft assembly of claim 6, wherein the first drive key is a spherical and has a diameter; and wherein the difference between HI and H4 is at least 30% of a diameter of the first drive key.

9. The driveshaft assembly of claim 6, wherein no additional components are added or substituted within the driveshaft assembly to transition the driveshaft assembly from the first configuration to the second configuration.

10. The driveshaft assembly of claim 2, further comprising:

a first thrust bearing seat having a central axis, a first end, a second end opposite the first end, a first concave, spherical bearing surface disposed on the first end, and a first central length LI measured axially along the central axis of the first thrust bearing seat between the second end and the first concave, spherical bearing surface;

a second thrust bearing seat having a central axis, a first end, a second end opposite the first end, a second concave, spherical bearing surface disposed on the first end, and a second central length L2 measured axially along the central axis of the second thrust bearing seat between the second end and the second concave, spherical bearing surface;

wherein L2 is greater than LI;

wherein when the driveshaft assembly is in the first configuration, the first thrust bearing seat is disposed within the first receptacle such that the central axis of the first thrust bearing seat is coaxially aligned with the central axis of the first end housing and the second thrust bearing seat is disposed within the second receptacle such that the central axis of the second thrust bearing seat is coaxially aligned with the central axis of the second end housing.

11. The driveshaft assembly of claim 10, wherein when the driveshaft assembly is in the second configuration, the first thrust bearing seat is disposed within the second receptacle such that the central axis of the first thrust bearing seat is coaxially aligned with the central axis of the second end housing, and the second thrust bearing seat is disposed within the first receptacle such that the central axis of the second thrust bearing seat is coaxially aligned with the central axis of the first end housing.

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12. The driveshaft assembly of claim 6, wherein the driveshaft further includes: a first pivot point disposed along the central, longitudinal axis of the driveshaft and proximate the first end of the driveshaft;

a second pivot point disposed along the central, longitudinal axis of the driveshaft and proximate the second end of the driveshaft;

wherein the driveshaft is configured to pivot omni-directionally about each of the first pivot point and the second pivot point relative to each of the first end housing and the second end housing;

wherein the first drive key has a center that lies within a first plane that extends perpendicularly to the central longitudinal axis of the driveshaft and passes through the first pivot point when the first drive key is received within the first recess; and

wherein the second drive key has a center that lies within a second plane that extends perpendicularly to the central longitudinal axis of the driveshaft and is axially spaced from the second pivot point when the second drive key is received within the second recess.

13. The driveshaft assembly of claim 12, wherein the driveshaft further includes a first convex spherical bearing surface on the first end having a first center of curvature and a second convex spherical bearing surface on the second end having a second center of curvature;

wherein the first pivot point is positioned at the first center of curvature and the second pivot point is positioned at the second center of curvature.

14. The driveshaft assembly of claim 12, wherein the driveshaft further includes a third recess extending axially from the first end of the driveshaft, and a fourth recess extending axially from the second end of the driveshaft;

wherein the driveshaft assembly further comprises:

a first thrust ball having a center and configured to be disposed within either the third recess or the fourth recess; and

a second thrust ball having a center and configured to be disposed within either the third recess or the fourth recess;

wherein when the first thrust ball is disposed within the third recess, the center of the first thrust ball is positioned at the first pivot point; and

34 wherein when the second thrust ball is disposed within the fourth recess, the center of the second thrust ball is positioned at the second pivot point.

15. A driveshaft assembly, comprising:

a driveshaft having a central longitudinal axis, a first end, a second end opposite the first end, a first recess proximate the first end; and a second recess proximate the second end;

a first drive key configured to be partially received within the first recess;

a second drive key configured to be partially received within the second recess;

a first end housing having a central axis, a first end, a second end opposite the first end, and a first receptacle extending axially from the first end, wherein the first receptacle includes a first pocket having an inner wall;

a second end housing having a central axis, a first end, a second end opposite the first end, and a second receptacle extending axially from the first end, wherein the second receptacle includes a second pocket having an inner wall; a first pivot point disposed along the central longitudinal axis of the driveshaft and proximate the first end of the driveshaft wherein the driveshaft is configured to pivot omni-directionally about the first pivot point relative to the first end housing;

a second pivot point disposed along the central longitudinal axis of the driveshaft and proximate the second end of the driveshaft wherein the driveshaft is configured to pivot omni-directionally about the second pivot point relative to the second end housing;

wherein the first drive key has a center that lies within a first plane that extends radially to the central longitudinal axis of the driveshaft and is axially spaced from the first pivot point when the first drive key is partially received within the first recess;

wherein the second drive key has a center that lies within a second plane that extends radially to the central longitudinal axis of the driveshaft and passes through the second pivot point when the second drive key is partially received within the second recess;

wherein the first end of the driveshaft is received within the first receptacle such that the first drive key is partially received within the first pocket; and

35 wherein the second end of the driveshaft is received within the second receptacle such that the second drive key is partially received within the second pocket.

16. (Cancelled).

17. A driveshaft assembly, comprising:

a driveshaft having a central longitudinal axis, a first end, a second end opposite the first end, a first recess proximate the first end, and a second recess proximate the second end;

a first drive key configured to be at least partially disposed within the first recess;

a second drive key configured to be at least partially disposed within the second recess; a first end housing having a central axis, a first end, a second end opposite the first end, and a first receptacle extending axially from the first end, wherein the first receptacle includes a first pocket having an inner wall; and

a second end housing having a central axis, a first end, a second end opposite the first end, and a second receptacle extending axially from the first end, wherein the second receptacle includes a second pocket having an inner wall; a first thrust bearing seat disposed within the first receptacle and including a central axis that is substantially aligned with the central axis of the first end housing, a first end, a second end opposite the first end, a first concave, spherical bearing surface disposed on the first end, and a first central length LI measured axially along the central axis of the first thrust bearing seat between the second end and the first concave, spherical bearing surface; and

a second thrust bearing seat disposed within the second receptacle and including a central axis that is substantially aligned with the central axis of the second end housing, a first end, a second end opposite the first end, a second concave, spherical bearing surface disposed on the first end, and a second central length L2 measured axially along the central axis of the second thrust bearing seat between the second end and the second concave, spherical bearing surface;

wherein L2 is greater than LI .

18. The driveshaft assembly of claim 17, wherein the first drive key and the second drive key are each spherical such that each has a diameter; and

36 wherein the difference between LI and L2 is at least 30% of the diameter of the first drive key and the second drive key.

A method for drilling a borehole into an earthen formation, the method comprising:

(a) contacting a first end housing at a first axial position with a first drive key, wherein the first end housing has a central axis, a first end, a second end opposite the first end, and a first receptacle extending axially from the first end, and wherein the first drive key is disposed within the first receptacle in the first end housing and radially disposed between the first end housing and a driveshaft;

(b) transferring torque between the first end housing and the driveshaft via the first drive key during (a); and

(c) contacting the first end housing at a second axial position with the first drive key or a second drive key after (b), wherein the second axial position is axially spaced from the first axial position.

The method of claim 19, wherein the first drive key is spherical and has a diameter; and wherein the second axial position is axially spaced from the first axial position by a distance that is at least 30% of the diameter of the first drive key.

The method of claim 19, further comprising:

(d) installing a first thrust bearing seat within the first receptacle before (b), the first thrust bearing seat having a first central length LI; and

(e) installing a second thrust bearing seat within the first receptacle after (b), the second thrust bearing seat having a second central length L2, wherein L2 is different than LI .

The method of claim 19, wherein (a) further comprises:

(al) inserting a first end of the driveshaft into the first receptacle, wherein the first end of the driveshaft includes a first recess and a first pivot point; wherein the first pivot point is disposed along a central longitudinal axis of the driveshaft; and wherein the driveshaft is configured to pivot omni-directionally about the first pivot point relative to the first end housing;

37 (a2) partially inserting the first drive key within the first recess such that a center of the first drive key lies within a first plane that extends radially to the central axis of the driveshaft and is axially spaced from the first pivot point.

The method of 22, wherein (c) further comprises:

(cl) inserting a second end of the driveshaft into the first receptacle, wherein the second end of the driveshaft includes a second recess and a second pivot point; wherein the second pivot point is disposed along the central longitudinal axis of the driveshaft; and wherein the driveshaft is configured to pivot omni-directionally about the second pivot point relative to the first end housing;

(c2) partially inserting the first drive key or a second drive key within the second recess such that the center of the first drive key or a center of the second drive key lies within a second plane that extends radially to the central axis of the driveshaft and passes through the second pivot point.

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