Patent ID: 7370559
Filing Date: 2008-05-13
Classification: B25B

Abstract:
1. A pneumatically operated screw driver comprising: an outer frame; a pneumatic motor disposed in the outer frame and rotatable about its axis; a cylinder fixedly disposed in the outer frame and formed with at least one compressed air introduction hole and at least one compressed air flowage hole, a return chamber being defined between the outer frame and the cylinder so that a compressed air is flowed from the cylinder to the return chamber through the air flowage hole and is flowed from the return chamber into the cylinder through the air introduction hole; a main piston slidably disposed in the cylinder and movable in an axial direction of the cylinder between its top dead center and a bottom dead center, the main piston being in a form of a sleeve like configuration defining an inner space and an outer space and being formed with a first communication hole permitting fluid communication between the inner space and the outer space, the main piston having an abutment end; a seal member disposed at the main piston and in sealing contact with the cylinder; a bumper disposed at the cylinder, the abutment end of the main piston being abuttable on the bumper; and an auxiliary piston movable in the axial direction between its top dead center and a bottom dead center and rotatable about its axis by the rotation of the pneumatic motor, the auxiliary piston having a hollow section, an intermediate section, and another end portion provided with a piston section and a driver bit attaching portion, at least the intermediate section and the another end portion being disposed in the inner space of the main piston, and the piston section being slidably movable with respect to the main piston, a second communication hole being formed at the intermediate section in communication with the hollow section and the inner space of the main piston, the air flowage hole being positioned to allow compressed air in the inner space to direct into the return air chamber through the first communication hole after the seal member of the main piston moves past the air flowage hole during movement of the main piston toward its bottom dead center and after the piston section opens the first communication hole and before the auxiliary piston reaches its bottom dead center.