Patent ID: 7373777

Claim:
A die drive unit having a cylinder mechanism for driving a moving die of a molding machine, the cylinder mechanism comprising: a cylinder body; a piston member housed in the cylinder body and movable along an axis of the cylinder body in a first direction and a second direction opposite thereto; a first pressure generating portion including a first oil chamber defined by a first pressure receiving surface of the piston member and the inner surface of the cylinder body and configured so that the capacity of the first oil chamber increases as the piston member moves in the first direction; a second pressure generating portion including a second oil chamber and a third oil chamber defined by a second pressure receiving surface of the piston member and the inner surface of the cylinder body and configured so that the capacity of the second and third oil chambers is reduced as the piston member moves in the first direction, wherein the third oil chamber is pressurized in order to open the moving die in the second direction; and a differential circuit including an oil passage connecting the first oil chamber and the second oil, the differential circuit configured to: cause oil to flow from the second oil chamber into the first oil chamber when the piston member is moved in the first direction, and cause the oil to flow from the first oil chamber into the second oil chamber when the piston member is moved in the second direction.