Electro-hydrostatic actuator

1. An electro-hydrostatic linear actuator that includes:

a sealed housing mounted upon a base, said housing containing a reservoir for filling the interior of the housing with a dielectric fluid;

a motor having a rotor shaft that is connected to a pump; said motor and said pump being immersed in said fluid reservoir so that said pump can draw fluid from said reservoir;

a hydraulic cylinder located outside of said housing that contains a piston attached to a piston rod that passes out of said cylinder, said piston dividing the cylinder in a first chamber and a second chamber;

means for biasing said piston rod into a home position;

a supply line for connecting the pump outlet to one of said chambers;

and a controller immersed in said fluid that contains circuitry for controlling said motor such that the pump raises the fluid pressure in said one chamber to move the piston rod to a selected operative position.

2. The actuator of claim 1 wherein said hydraulic cylinder is secured to a bottom surface of the base.

3. The actuator of claim 1 wherein said piston rod is connected to a stem of a plunger type valve.

4. The actuator of claim 1 that further includes an adjustable compensating means for maintaining the pressure within the fluid reservoir at a desired level.

5. The actuator of claim 1 that further includes a temperature sensor for detecting the temperature of the fluid in said reservoir and providing temperature data to said control.

6. The actuator of claim 1 that further includes a pressure sensor for detecting the fluid pressure within said reservoir and sending pressure data to said controller.

7. The actuator of claim 1 that further includes a level sensor for detecting the fluid level in said reservoir and providing level data to said controller.

8. The actuator of claim 1 that further includes a resolver associated with the rotor shaft of said motor and providing shaft position data to said controller.

9. The actuator of claim 1 that further includes a linear variable displacement transducer for detecting the position of said piston rod and providing position data to said controller.

10. The actuator of claim 1 that further includes a normally closed solenoid actuated valve that is coupled to said supply line said solenoid actuated valve being arranged to open in response to a signal from said controller to divert fluid from said supply line back to said fluid reservoir.

11. The actuator of claim 1 wherein said pump is a gear pump.

12. An electro-hydrostatic actuator that includes:

a hermetically sealed housing having a base section, said housing containing a fluid reservoir for filling the interior of the housing with a dielectric oil;

a brushless motor mounted in a first compartment in said base section of the housing, said motor having a rotor shaft that extends upwardly into said housing;

a first access cover removably mounted in said base section for closing the first compartment;

a pump connected to the rotor shaft of said motor for drawing fluid from said reservoir and delivering the fluid at an elevated pressure to a supply line;

a hydraulic cylinder mounted in a second compartment in said base section of said housing adjacent said first compartment;

a second access cover removably mounted in said base section for closing the second compartment;

said cylinder having a piston mounted therein for dividing the cylinder into a first chamber and a second chamber and a piston rod connected to said piston, said piston rod passing out of said cylinder through said second access cover;

means for biasing said piston rod into a home position;

said supply line being connected into one of the cylinder chambers to providing fluid under pressure to said chamber; and

a controller being immersed in said fluid reservoir in the upper part of the housing that contains circuitry for controlling said motor such that the pump raises the pressure in said one chamber to move the piston rod to a selected operative position.

13. The actuator of claim 12 wherein said piston rod is connected to the stem of a type valve.

14. The actuator of claim 13 wherein the means for biasing said piston rod includes a spring means acting between the piston rod and the valve stem for normally biasing the piston rod into the home position wherein said valve is closed.

15. The actuator of claim 12 that further includes compensating means for maintaining the pressure within said reservoir at a desired level.

16. The actuator of claim 12 that further includes a temperature sensor for detecting the temperature of fluid in said reservoir and providing temperature data to said controller.

17. The actuator of claim 12 that further includes a level sensor for detecting the fluid level within said reservoir and sending fluid level data to the controller.

18. The actuator of claim 12 that further includes a pressure sensor for detecting the fluid pressure with the reservoir and sending pressure data to said controller.

19. The actuator of claim 12 that further includes a resolver associated in the motor shaft for providing shaft position data to the controller.

20. The actuator of claim 12 that further includes a linear variable displacement transducer for detecting the position of said piston rod and sending position data to said controller.

21. The actuator of claim 12 that further includes a solenoid actuated valve that is coupled to said supply line, said solenoid actuated valve being arranged to open in response to a signal from said controller to divert fluid from the supply line back to said reservoir.

22. The actuator of claim 13 wherein said pump is a gear pump.