Patent ID: 6892534

Claim:
An electro-hydrostatic actuator unit that includes a sealed pressurized reservoir that is filled with a dielectric fluid, an actuator that includes a hydraulic cylinder that contains a movable piston for separating the interior of said cylinder into a first chamber and a second chamber and a piston rod for connecting the piston to an external load, a bidirectional pump that is immersed in said reservoir said bidirectional pump being operatively connected into a cylinder flow control circuit for exchanging fluid between said chambers to either extend or retract said piston rod, a solenoid actuated directional valve that is mounted in the flow control circuit, said directional valve being in a closed position when de-energizing and an open position when energizing for routing fluid from one side of the piston to the other side of said piston, an accumulator pump that is immersed in said reservoir, said accumulator pump contained in a failsafe flow circuit for delivering pressurized fluid contained in said reservoir to a trip accumulator, a solenoid actuated trip valve mounted in the failsafe circuit, said trip valve being connected to one of said cylinder chambers by a trip line, said trip valve being closed when in an energized condition and opened when in a de-energized condition whereby pressurized fluid in the accumulator is delivered into said one chamber to move said piston rod to a desired position, control means that is immersed in said reservoir and being arranged to sense a failsafe condition and to de-energizing the directional valve and energizing said trip valve when a failsafe condition is sensed whereby the piston rod is moved to a desired failsafe position.