Patent ID: 8978604
Filing Date: 2015-03-17
Classification: F01L,F15B

Abstract:
1. An actuator, comprising: A housing, comprising upper and lower ports; an actuation cylinder in the housing, having actuation-cylinder first and second ends in first and second longitudinal directions, respectively; an actuation piston moveable longitudinally in the cylinder, with actuation-piston first and second surfaces; a first fluid space defined by the actuation-cylinder first end and the actuation-piston first surface; a second fluid space defined by the actuation-cylinder second end and the actuation-piston second surface; a first piston rod connected to the actuation-piston first surface; a second piston rod connected to the actuation-piston second surface; a fluid bypass short-circuiting the first and second fluid spaces when the actuation piston is not substantially proximate to either the actuation-cylinder first or second end; a first spring system connected to the first piston rod, biasing the actuation piston in the second direction, with at least two initial states to provide at least two different preloads on the actuation piston; a second spring system biasing the actuation piston in the first direction; a first flow mechanism, in conjunction with the first piston rod, controlling fluid communication between the first fluid space and the upper port; and a second flow mechanism, in conjunction with the second piston rod, controlling fluid communication between the second fluid space and the lower port; wherein: at least one of the first and second flow mechanisms is closed when the fluid bypass is substantially open; each of the first and second flow mechanisms is at least partially open when the fluid bypass is substantially closed; the first spring system comprises a first actuation spring, a spring retainer, a spring-control cylinder body, a fluid chamber, a flow passage and a plunger; the first actuation spring is situated between the spring retainer and the spring-control cylinder body; the spring retainer is connected to the first piston rod; the fluid chamber is situated inside the spring-control cylinder body; the flow passage passes through the plunger; the housing contains a cavity and a start port; the first spring system is situated in the cavity; the flow passage in the plunger provides connection between the fluid chamber and the start port; and the spring-control cylinder body is longitudinally moveable relative to the housing, whereby changing the extent of compression of the first actuation spring along the longitudinal axis.