Patent ID: 6889885

Claim:
A combustion-powered tool for driving a fastener into a workpiece, comprising: a housing having an upper portion and a lower end; a push lever supported at the lower end of the housing; a head cover disposed at the upper portion of the housing; a cylinder fixedly disposed in the housing and formed with an exhaust hole; a piston slidably movably disposed in the cylinder and dividing the cylinder into an upper chamber and a lower chamber, the piston being movable toward its lower dead center and its upper dead center; a combustion chamber frame disposed within the housing and movable in interlocking relation to the movement of the push lever to bring into contact with and out of contact from the head cover for selectively defining a combustion chamber in combination with the head cover and the piston, the combustion chamber frame being formed with a through hole at a position defining a part of the combustion chamber; a driver blade extending from the piston in the lower chamber; a spark plug exposed to the combustion chamber for igniting a fuel/air mixture provided in the combustion chamber; a check valve disposed at the exhaust hole for normally closing the exhaust hole; a magazine disposed at the lower end of the housing for accumulating therein a plurality of fasteners; a tail cover disposed at the lower end of the housing and positioned below the driver blade, each fastener being fed into the tail cover from the magazine; and a shut-off mechanism provided at an outer side of the combustion chamber frame for closing an outlet end of the through hole during an initial fastener driving operation but opening the through hole only when an inner pressure of the upper chamber exceeds a predetermined pressure during the movement of the piston toward the upper dead center.