Patent ID: 7240744

Claim:
A drill bit assembly ( 10 ) comprising: a rotary drill bit ( 12 ) having a proximal end adapted for connection to a drillpipe ( 34 ) that supplies drilling mud or foam and a distal end designed and arranged to bore a hole in the earth due to rotation about a longitudinal axis ( 24 ) thereof, said drill bit characterized by having a longitudinal passage ( 22 ) formed therein; a single impact bit ( 26 ) having at least a portion thereof slideably housed in said passage and having a distal end designed and arranged to impact the earth; and a hydraulically actuated impact engine ( 32 ) disposed within and coupled to said drillpipe and having a reciprocating member ( 44 , 46 ) coupled to said impact bit, said impact engine fluidly coupled to said drillpipe for receiving said drilling mud or foam which acts on said reciprocating member; wherein said impact engine includes, a hydraulic cylinder ( 42 ) formed longitudinally therein and disposed tandem to and in communication with said passage, a piston assembly ( 44 , 46 ) slideably received within and generally dynamically sealed against said cylinder and defining a first chamber ( 48 ) and a second chamber ( 50 ) therein, said piston assembly defining said reciprocating member, an energy accumulator ( 38 ) operatively coupled to said piston assembly, a conduit ( 40 ) fluidly coupling a point at said proximal end of said impact engine to said cylinder, and an isolatable fluid path ( 58 , 62 ) disposed between said first chamber and said second chamber; whereby said impact engine is designed and arranged to cause said impact bit to strike the earth and said drilling mud or foam provides energy to said energy accumulator, which is subsequently converted to longitudinal motion of said piston assembly for causing said impact bit to strike the earth.