Patent ID: 8011455

Claim:
A down-hole drilling tool adapted for operation under the influence of motive fluid, the down-hole drilling tool comprising: a bit adapted to drill rock, the bit having an exterior surface; a hammer assembly operable to deliver impact loading to the bit to facilitate rock drilling; an actuator flow path adapted to conduct an actuator flow portion of the motive fluid to the hammer assembly, the actuator flow driving operation of the hammer assembly and becoming actuator exhaust after driving operation of the hammer assembly; and an actuator exhaust path adapted to vent at least a portion of the actuator exhaust from the tool above the bit such that substantially none of the actuator exhaust flows over the exterior surface of the bit; wherein the bit is in a bottom end of the drilling tool; wherein the actuator exhaust path vents the actuator exhaust through a top end of the drilling tool, opposite the bottom end; wherein the hammer assembly includes a piston that is movable to apply impact loading to the drill bit, the drilling tool further comprising a drive chamber above the piston and a return chamber between the piston and the drill bit; wherein the piston is supported for reciprocating movement toward and away from the drill bit in response to the actuator flow alternatingly communicating with the drive and return chambers, respectively; and wherein reciprocating movement of the piston at least temporarily cuts off communication between the drive chamber and the actuator exhaust path while placing the drive chamber in communication with the actuator flow path and the return chamber in communication with the actuator exhaust path, and at least temporarily cuts off communication between the return chamber and the actuator exhaust path while placing the return chamber in communication with the actuator flow path and the drive chamber in communication with the actuator exhaust path; the drilling tool further comprising a drive exhaust port communicating with the actuator exhaust path; and a return exhaust port communicating with the actuator exhaust path; wherein reciprocating movement of the piston at least temporarily cuts off communication between the drive chamber and the actuator exhaust path by covering the drive exhaust port with a portion of the piston; and wherein reciprocating movement of the piston at least temporarily cuts off communication between the return chamber and the actuator exhaust path by covering the return exhaust port with a portion of the piston.