Patent ID: 7010912

Claim:
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.