Importance

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Abstract

A hydraulic drive mechanism for a punching or an embossing tool, with a double-acting drive hydrocylinder with differently large piston areas, the rapid feed operation, the working feed operation, as well as the rapid retraction operation being controllable by the joint or alternative pressurization of these piston areas. For effecting switchover, an area switching valve is provided which switches over, once the driving pressure exceeds, for example, 90% of the maximum initial pressure of the pressure supply unit, from differential operation to unilateral pressurization of the larger drive area. The area switching valve comprises a check valve acted upon, in the opening direction, by the operating pressure in the smaller driving pressure chamber. A locking spring force of the check valve is equivalent to an opening pressure of about 90% of the supply pressure. The area switching valve comprises a pressure-regulated slide valve having a valve body constructed as a stepped piston urged against the check valve body by a return spring. With the check valve being closed, the smaller drive pressure chamber is pressurized. With the check valve being opened, the smaller drive pressure chamber is pressure-relieved, and the larger piston step of the stepped piston is under the pressure ambient in the larger drive pressure chamber. The ratio of the area of the larger piston step to the cross-sectional area defined by the valve seat of the check valve is larger than the ratio of the larger piston area to the smaller piston area of the hydro-cylinder.

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First Claim