Patent ID: 7401661

Claim:
A powered hammer comprising: a housing; a tool holder coupled to the housing which is capable of holding a tool; a motor within the housing; a cylinder within the housing; a piston slideably received within the cylinder; a drive mechanism which converts rotary output of the motor into a reciprocating motion of the piston within the cylinder; a ram slideably mounted within the cylinder, forward of the piston, and which is reciprocatingly driven by the piston; a beat piece support structure that supports a beat piece, the beat piece being repetitively struck by the reciprocating ram and which in turn repetitively strikes an end of the tool when held in the tool holder to transfer the momentum of the ram to the tool; a first chamber formed within the housing; a second chamber formed within an end of the cylinder facing the beat piece support structure, forward of the ram; a passageway in communication with the first and second chambers; and a counter mass slideably mounted within the first chamber, wherein, when the hammer is operated, the counter mass is caused to oscillate to counteract vibration in the housing and to cause lubrication fluid to move between the first and second chambers.