Dual rod directional drilling system

1. A coupling system for a dual rod drilling system comprising:

a coupler comprising:

an inner bore having a non-circular profile and a longitudinal axis;

a cross aperture having an axis that is perpendicular to the longitudinal axis, the cross aperture having a first width;

an inner member comprising:

a torque-carrying section having a non-circular profile adapted to mate with the non-circular profile of the inner bore of the coupler;

a non-torque carrying section having a cross-sectional width smaller than a cross-sectional width of the inner bore of the coupler; and

a groove positioned between the torque-carrying section and the non-torque carrying section, the groove having a width at least equal to the first width of the cross aperture of the coupler and the groove extending circumferentially about an entire circumference of the inner member; and

a pin positioned within the cross aperture of the coupler and within the groove of the inner member so as to secure the inner member at least partially within the coupler;

wherein the coupler further comprises a collar positioned around an exterior surface, wherein the collar includes at least one axial drilling fluid flow passage.

2. The coupling system of claim 1 , wherein the groove has a width larger than the first width of the cross aperture of the coupler, and wherein the coupler and the inner member are axially movable with respect to one another.

3. The coupling system of claim 2 , further comprising a spring positioned between the coupler and the inner member, wherein the spring biases the coupler and the inner member to a first position.

4. The coupling system of claim 3 , wherein, when in the first position, the pin is positioned at a first end of the groove.

5. The coupling system of claim 1 , wherein the collar includes a plurality of drilling fluid flow passages positioned circumferentially around the exterior surface of the coupler.

6. The coupling system of claim 1 , wherein the inner member is an end of a drill rod.

7. The coupling system of claim 1 , wherein the inner member includes an inner bore aligned with the inner bore of the coupler, and wherein the pin is not positioned within the inner bore of the inner member.

8. The coupling system of claim 1 , wherein the inner member and the coupler are sized and shaped to be surrounded by an outer member.

9. The coupling system of claim 8 , wherein the outer member is an outer drill rod and the inner member is an inner drill rod.

10. The coupling system of claim 9 , further comprising an annular fluid flow passage between the inner drill rod and the outer drill rod.

11. The coupling system of claim 10 , wherein the coupler is secured to a first end of the inner drill rod, the coupling system further comprising a fluid flow collar positioned around a second end of the inner drill rod, and wherein the fluid flow collar includes at least one peripheral fluid passage that allows fluid flow therethrough, wherein the at least one peripheral fluid passage of the fluid flow collar is positioned within the annular fluid flow passage between the inner drill rod and the outer drill rod.

12. The coupling system of claim 1 , wherein the axis of the cross aperture is nonintersecting with the longitudinal axis.

13. The coupling system of claim 1 , wherein the cross aperture is a first cross aperture, the coupler comprising a second cross aperture that is perpendicular to the longitudinal axis and spaced on an opposite side of the longitudinal axis from the first cross aperture; and

wherein the pin is a first pin positioned within the first cross aperture, the system further comprising a second pin positioned within the second cross aperture of the coupler and within the groove of the inner member.

14. A coupler for a drill rod, the coupler comprising:

a main body having an inner bore, the inner bore having a non-circular profile and a longitudinal axis;

a cross aperture disposed in the main body, the cross aperture having an axis that is nonintersecting with the longitudinal axis of the main body; and

a sleeve positioned around an exterior surface of the main body;

wherein the sleeve includes a main body and a ring portion, wherein the ring portion has a larger outer diameter than the main body; and

wherein the sleeve includes a plurality of drilling fluid flow passages radially disposed around the periphery of the sleeve in both the ring portion and the main body.

15. The coupler of claim 14 , wherein the sleeve is press-fit onto the exterior surface of the main body.

16. A coupling system for an inner rod of a dual rod drilling system, the dual rod drilling system having a plurality of dual rod assemblies, each dual rod assembly made-up of an inner rod retained within an outer rod having a shoulder defined by a minimum inner diameter, the coupling system comprising:

a coupler comprising:

an inner bore having a non-circular profile and a longitudinal axis;

a portion having an outer diameter that is greater than the minimum inner diameter of the shoulder of the outer rod;

a cross aperture having an axis that is perpendicular to the longitudinal axis, the cross aperture having a first width;

an inner rod comprising:

a torque-carrying section having a non-circular profile adapted to mate with the non-circular profile of the inner bore of the coupler;

a non-torque carrying section having a cross-sectional dimension smaller than a cross-sectional dimension of the inner bore of the coupler; and

a groove positioned between the torque-carrying section and the non-torque carrying section, the groove having a width at least equal to the first width of the cross aperture of the coupler; and

a pin positioned within the cross aperture of the coupler and within the groove of the inner rod so as to secure the inner rod at least partially within the coupler, thereby retaining the inner rod within the outer rod.

17. A coupling system for a dual rod drilling system comprising:

a coupler comprising:

an inner bore having a non-circular profile and a longitudinal axis;

a cross aperture having an axis that is perpendicular to the longitudinal axis, the cross aperture having a first width;

an inner member comprising:

a torque-carrying section having a non-circular profile adapted to mate with the non-circular profile of the inner bore of the coupler; and

a groove spaced from an end of the inner member and adjacent the torque-carrying section, the groove having a width at least equal to the first width of the cross aperture of the coupler and the groove extending circumferentially about an entire circumference of the inner member; and

a pin positioned within the cross aperture of the coupler and within the groove of the inner member so as to secure the inner member at least partially within the coupler;

wherein the coupler further comprises a collar positioned around an exterior surface, wherein the collar includes at least one axial drilling fluid flow passage.

18. The coupling system of claim 17 , wherein the groove has a width larger than the first width of the cross aperture of the coupler, and wherein the coupler and the inner member are axially movable with respect to one another.

19. The coupling system of claim 17 , wherein the inner member is a drill rod.

20. The coupling system of claim 17 , wherein the inner member and the coupler are sized and shaped to be surrounded by an outer member.

21. The coupling system of claim 20 , wherein the outer member is an outer drill rod and the inner member is an inner drill rod.

22. The coupling system of claim 21 , further comprising an annular fluid flow passage between the inner drill rod and the outer drill rod.

23. The coupling system of claim 17 , wherein the cross aperture is a first cross aperture, the coupler comprising a second cross aperture that is perpendicular to the longitudinal axis and spaced on an opposite side of the longitudinal axis from the first cross aperture; and

wherein the pin is a first pin positioned within the first cross aperture, the system further comprising a second pin positioned within the second cross aperture of the coupler and within the groove of the inner member.

24. The coupling system of claim 17 , wherein the collar includes a plurality of drilling fluid flow passages positioned circumferentially around the exterior surface of the coupler.