Patent ID: 7370615

Claim:
An actuator, comprising: a housing having first and second ports; each of the first and second ports being switched between at least two different fluid pressures: a stroke controller slideably disposed in the housing; first and second partial cylinders in the housing and the stroke controller, respectively, defining a longitudinal axis and having cylinder first and second ends in first and second directions, respectively; an actuation piston disposed between the first and second partial cylinders with first and second surfaces moveable along the longitudinal axis; a spring subsystem exerting force both in the first and second directions and having a tendency to bring the actuation piston to a neutral state; a first fluid space defined by the cylinder first end and the first surface of the actuation piston; a second fluid space defined by the cylinder second end and the second surface of the actuation piston; a first piston rod connected to the first surface of the actuation piston; a first bore in the housing, adjacent to the first fluid space in the first direction, receiving the first piston rod; a second piston rod connected to the second surface of the actuation piston; a second bore through the stroke controller, adjacent to the second fluid space in the second direction, receiving the second piston rod; a bypass passage that short-circuits the first and second fluid spaces when the actuation piston does not overlap either of the first and second partial cylinders; a first flow control subsystem including one or more flow mechanisms controlling fluid communication between the first fluid space and the first port; a second flow control subsystem including one or more flow mechanisms controlling fluid communication between the second fluid space and the second port; at least one of the first and second flow control subsystems is at least partially closed when the actuation piston does not overlap either of the first and second partial cylinders; and wherein each of the first and second flow control subsystems is at least partially open when the actuation piston overlaps at least one of the first and second partial cylinders.