Electrohydrostatic actution system, hydraulic circuit of electrohydrostatic actution system, and steam turbine system including same

An electrohydrostatic actuation system comprising:

• a hydraulic cylinder including:
• a piston to which a valve element biased by a return spring is connected;
• a first chamber;
• and
• a second chamber;
• a hydraulic pump configured to supply hydraulic fluid to the first chamber or the second chamber, or to collect the hydraulic fluid from the first chamber or the second chamber;
• an electric motor configured to drive the hydraulic pump;
• a fuse valve provided in a fluid passage communicating between the hydraulic pump and the first chamber of the hydraulic cylinder;
• and
• a logic valve,
• wherein, when the electric motor loses electric power, and a flow rate of the hydraulic fluid in the fluid passage returning from the hydraulic cylinder to the hydraulic pump exceeds a predetermined value, the fuse valve blocks a flow of the hydraulic fluid in the fluid passage, and
• wherein the logic valve is configured to connect a circuit so as to cause the blocked hydraulic fluid to return to the second chamber of the hydraulic cylinder so that fail-safe shut-off of the valve element is achieved to protect the hydraulic pump.

An electrohydrostatic actuation system comprising:

• a hydraulic cylinder including:
• a piston to which a valve element biased by a return spring is connected;
• a first chamber;
• and
• a second chamber;
• a hydraulic pump configured to supply hydraulic fluid to the first chamber or the second chamber, or to collect the hydraulic fluid from the first chamber or the second chamber;
• an electric motor configured to drive the hydraulic pump;
• a sequence valve;
• and
• a four-port, two-position pilot-operated directional control valve,
• wherein, when a pressure of the hydraulic fluid discharged from the hydraulic pump becomes lower than a predetermined set value, the sequence valve reduces a pilot pressure to be applied to the four-port, two-position pilot-operated directional control valve, and the four-port, two-position pilot-operated directional control valve connects between a discharge port of the hydraulic pump and a pilot line of the hydraulic pump at which a displacement of the hydraulic pump is maximum, and
• wherein, when the pressure of the hydraulic fluid discharged from the hydraulic pump exceeds the predetermined set value, the sequence valve increases the pilot pressure to be applied to the four-port, two-position pilot-operated directional control valve, and the four-port, two-position pilot-operated directional control valve connects between the discharge port of the hydraulic pump and a pilot line of the hydraulic pump at which the displacement of the hydraulic pump is minimum so that a displacement of the hydraulic pump is controlled.

An electrohydrostatic actuation system comprising:

• a hydraulic cylinder including:
• a piston to which a valve element biased by a return spring is connected;
• a first chamber;
• and
• a second chamber;
• a hydraulic pump configured to supply hydraulic fluid to the first chamber or the second chamber, or to collect the hydraulic fluid from the first chamber or the second chamber;
• an electric motor configured to drive the hydraulic pump;
• a pilot-assisted open relief valve;
• and
• a check valve,
• wherein, in an operation of opening the valve element, the hydraulic fluid from the second chamber is blocked by the check valve, and the pilot-assisted open relief valve receives a pilot pressure by a pressure of the hydraulic fluid and is thus opened so that the hydraulic fluid from the second chamber flows through a drain line via the pilot-assisted open relief valve so as to be cooled, and
• wherein, in an operation of closing the valve element, the hydraulic fluid is supplied to the second chamber via the check valve.