Powered nailer with positive piston return

1. A powered nailer comprising:

a power source including a driving element reciprocatable within a cylinder between a pre-firing position and a fastener driving position, the driving element being in the fastener driving position when the driving element engages a bumper disposed at a bottom of the cylinder;

an outer wall partially defining a combustion chamber in fluid communication with said cylinder, the combustion chamber configured to receive a dose of fuel and air prior to a user-generated ignition;

a valve element at least partially surrounding the outer wall and reciprocatable relative to the outer wall; and

a return chamber in fluid communication with said cylinder via a plurality of openings between the return chamber and the cylinder, wherein the plurality of openings are circumferentially-spaced about the cylinder, and wherein the return chamber:

receives a supply of pressurized air through the plurality of openings, wherein the pressurized air is generated by said driving element as said driving element moves from the pre-firing position to the fastener driving position; and

releases the pressurized air through the plurality of openings to act on an underside of said driving element to return said driving element to the pre-firing position.

2. The nailer of claim 1 wherein said combustion chamber is configured such that, after an ignition in said combustion chamber, said driving element returns to the pre-firing position through action of the pressurized air stored in said return chamber simultaneously with exhausting of the combustion chamber.

3. The nailer of claim 1 , wherein said return chamber is defined in part by an annular, radially-inwardly projecting flange with a sealing relationship to an exterior wall of said cylinder.

4. The nailer of claim 1 wherein said combustion chamber is configured to open to atmosphere upon said driving element reaching said bumper.

5. The nailer of claim 4 , wherein said return chamber is sized to store sufficient pressurized air to push said driving element to the pre-firing position, and wherein the nailer is configured such that post fastener-driving tool recoil automatically opens said combustion chamber post firing.

6. The nailer of claim 1 further including a mechanism configured to delay opening of said combustion chamber post-ignition and configured to open said combustion chamber before return of said driving element to the pre-firing position.

7. The nailer of claim 1 wherein the return chamber has a pressure of 8 psi when the driving element is in the fastener driving position.

8. The nailer of claim 1 wherein said cylinder is continuous from an upper end adjacent the pre-firing position to a bumper area at an opposite end from said upper end.

9. A powered nailer comprising:

a cylinder;

a driving element reciprocatable within the cylinder;

an outer wall partially defining a combustion chamber in fluid communication with the cylinder, the outer wall defining a plurality of ports in fluid communication with the combustion chamber; and

a reciprocating valve element surrounding the outer wall, movable between an open position before and after combustion occurs, and a closed position during combustion,

wherein each of the ports enables both intake of air before combustion occurs in the combustion chamber and exhaust of gases after combustion occurs in the combustion chamber, while the reciprocating valve element is in the open position.