Fastener driving tool

A fastener driving tool comprising:

• a cylinder;
• a drive piston reciprocally movable within said cylinder and having a driver connected thereto, said driver being movable to drive fasteners when said drive piston is moved in a driving direction;
• said drive piston defining a gas chamber in said cylinder for accommodating a gas;
• and
• drive means for moving said drive piston from a first position to a second position in a direction opposite to said driving direction for compressing the gas within said gas chamber, said drive means being operable to permit movement of said drive piston in said driving direction by the pressure of the gas compressed within said gas chamber when said drive piston reaches said second position;
• said drive means including a motor and a drive mechanism provided between the motor and the driving piston for converting rotation of the motor into movement of the drive piston from said first position to said second position;
• said drive mechanism including:
• an intermediate member movable relative to said cylinder in an axial direction of the cylinder between a third position and a fourth position corresponding to said first position and said second position of said drive piston, respectively;
• biasing means for normally biasing said intermediate member toward said third position in the axial direction;
• engaging means for engaging said drive piston with said intermediate member during the movement of the intermediate member from said third position to said fourth position;
• and
• releasing means for disengaging said engaging means when the intermediate member reaches the fourth position.