US Patent 7395748 Hydraulic drive for displacing an actuator

A hydraulic drive is described for displacing an actuator (7) between two predetermined end positions, comprising a piston unit (4) which can be pressurized in a cylinder unit (3) in opposite directions by way of hydraulic springs and a control device for alternating pressurization in opposite directions of the piston unit (4). In order to provide advantageous constructional conditions it is proposed that the cylinder unit (3) comprises an end section (10) of smaller cross section than the remaining cylinder space (9) and receives in a sealing manner the respective face side (12) of the piston unit (4) in the associated end position, that the end sections (10) connected via a throttle (13) to a return line (14) for the hydraulic medium are delimited by a control edge (11) each relative to the remaining cylinder space (9), and that the control device consists of an actuating drive (28) for an axial relative movement of the control edge (11) relative to the face side (12) of the piston. (FIG. 1)