Downhole hammer assembly

1. A drill bit assembly, comprising:

a bit body intermediate a shank and a working face, the shank being adapted for connection to a drill string, the drill string comprising a fluid passage at least partially disposed within the bit body;

a moveable carrier disposed within the bit body, the carrier being coupled with a hammer; and

a valve adapted to obstruct at least a portion of a fluid flow within the fluid passage, the valve including a first plurality of ports formed in the moveable carrier, the moveable carrier being adapted to alternately move the first plurality of ports into and out of fluidic communication with a second plurality of ports formed in an annular structure surrounding the moveable carrier.

2. The drill bit of claim 1 , wherein the hammer comprises a distal end which extends beyond the working face of the drill bit.

3. The drill bit of claim 1 , wherein the hammer is supported by a lower bearing and an upper bearing.

4. The drill bit of claim 3 , wherein at least one of the upper bearing and the lower bearing is supported by a centralizer.

5. The drill bit of claim 1 , wherein the moveable carrier is coupled to the bit body with a biasing element, the biasing element being adapted to move the moveable carrier along a longitudinal axis of the bit body.

6. The drill bit of claim 5 , wherein the biasing element is a spring.

7. A drill bit comprising:

a bit body with a fluid passage therethrough configured to allow a fluid to flow through the bit body and to exit from an opening on a working face of the drill bit;

a shank adapted for connection to a drill string; and,

a hammer assembly disposed within the fluid passage, the hammer assembly including:

a carrier coupled to a hammer;

a biasing element coupled to the bit body and the carrier;

the carrier configured to be acted upon by the fluid to create a pressure that urges the carrier to move in an axial direction to extend the hammer when the pressure exceeds an opposing force from the biasing element acting on the carrier; and,

an increased flow area configured to reduce the pressure on the carrier.

8. The drill bit of claim 7 , further comprising a centralizer disposed in the fluid passage, the centralizer disposed around a proximal end of the hammer assembly.

9. The drill bit of claim 8 , wherein the centralizer further comprises a passage for fluid to flow therethrough.

10. The drill bit of claim 7 , wherein the fluid passageway includes an inward taper that reduces the flow area of the fluid passage.

11. The drill bit of claim 10 , wherein the inward taper includes an undercut that creates the increased flow area.

12. The drill bit of claim 7 , wherein the increased flow area further comprises fluidic communication between a first plurality of ports and a second plurality of ports.

13. The drill bit of claim 12 , further comprising a valve adapted to obstruct at least a portion of a fluid flow within the fluid passage, the valve including the first plurality of ports formed in a moveable carrier, the moveable carrier adapted to move the first plurality of ports into fluidic communication with the second plurality of ports.

14. The drill bit of claim 13 , wherein the second plurality of ports are formed in an annular structure surrounding the carrier.