Drive device for a movable part, especially a mold closure device for an injection molding machine, and method for operating such a drive device

A drive device for driving a first movable part (11) in an advance stroke, a power stroke and a return stroke, the drive device being suitable for operating a mold closure device for an injection molding machine, the drive device comprising the following:

• a first, receiving hydraulic cylinder-and-piston unit (10) having a first pressure chamber (19), which can be subjected to the action of pressure in a power stroke alone, and having a third pressure chamber (25) to be subjected to the action of pressure on the return stroke;
• a second, delivering cylinder-and-piston unit (13) having a fourth pressure chamber (32) which is connected to the third pressure chamber (25) at least on the advance stroke and on the return stroke, and having a fifth pressure chamber (34) which is connected to the first pressure chamber (19) on the advance stroke and on the power stroke;
• a drive motor (12) by which the piston (30, 30, 58) and cylinder (29) of the second cylinder-and-piston unit (13) are movable relative to one another;
• a second pressure chamber (20) in one of the two cylinder-and-piston units (10, 13);
• a valve arrangement (45) via which, during the advance stroke, pressure medium can be forced from the second pressure chamber (20) into the first pressure chamber (19) and, during the power stroke, the second pressure chamber (20) can be relieved of pressure separately from the first pressure chamber (19);
• a cross section of the third pressure chamber (25) and of the fourth pressure chamber (32) are dimensioned relative to each other such that pressure medium forced out of the third pressure chamber (25) during the advance stroke can be received by the fourth pressure chamber (32).