A drive device, in particular for driving a movable part of a closing unit or of an injection unit of a plastic injection molding machine during an adjusting movement and for subsequent build-up and exertion of a high force, comprising
- a drive element (14) movable axially by means of a drive motor (12), in particular by means of an electric motor,
- a hydraulic unit (17) movable as a result of movement of the drive element (14) in same direction as the latter, wherein
- the hydraulic unit (17) is a force intensifier with a first and a second of two hydraulic pistons (16, 20) movable in relation to one another and differing from one another in the size of their active surfaces (30, 25) and with an intermediate part (22), wherein the first hydraulic piston (16) having the smaller active surface (30) is connected mechanically to the drive element (14), wherein
- for the adjusting movement, the hydraulic unit (17) is movable as a whole, wherein
- for exerting a high force by means of the second hydraulic piston (20) having the larger active surface (25), the intermediate part (22) can be blocked against displacement in relation to a fixed stand (10), and wherein
- the first hydraulic piston (16) being adjacent with its active surface (30) to a first pressure space (31) in or on a housing formed by the second hydraulic piston (20) or by the intermediate part (22), said pressure space being fluidically connectable to a second pressure space (24), which is adjacent to the second hydraulic piston (20), in one position of a valve (50), via the latter, and to a pressure source (45) in another position of the valve (50), wherein
- a third hydraulic piston (35) designed as a stepped piston is present with a first active surface (40) at a first piston portion (36) and with a second active surface at a second piston portion (37), wherein
- the third hydraulic piston (35), by action of pressure upon a third pressure space (38) adjacent to its first active surface (40), is pressable in direction of adjusting movement of the first hydraulic piston (16) against a stop (41) fixed in relation to the housing (20), with a force which is higher than the force exerted on the housing (20) in same direction by the pressure in the first pressure space (31), wherein
- when the third pressure space (38) is relieved of pressure, the third hydraulic piston (35) is movable away from the stop (41) in direction opposite to the adjusting movement of the first hydraulic piston (16), and wherein
- the second piston portion (37) of the third hydraulic piston (35) forms, with a fourth hydraulic piston (55, 65) having an active surface larger than the second active surface of the third hydraulic piston (35), a hydraulic force intensifier for acting upon the second hydraulic piston (20) opposite to the adjusting movement.