Patent Application
20050011188
The invention relates to an electro-hydrostatic actuator that is ideally suited to control the positioning of a valve or any other similar device.
More specifically, this invention relates to a compact electrically operated linear actuator that integrates all controls and components to provide rapid and efficient heat dissipation and cooling to all heat producing parts.
Current demands on power generation systems and valve controls require that the actuators be electrically controlled and include fail safe features. In many countries, linear actuator of the type herein disclosed also require certification when employed in an environment where an explosion might take place as for example in controlling valves utilized in gas or oil pipelines or in certain processing plants where volatile chemicals are used in the process. In order to gain certification, many of the actuators are housed in rather bulky complex structures and employ external power supplies and controls which are costly to construct and difficult to service and maintain in the field. Typically, the electronic controls of the actuator are designed to be located in separate remote housing having a non-hazardous controlled environment. The cabling between the actuator and the controller can be relatively long which can lead to signal transmission loses and other related difficulties.
The invention presented here provides a solution to electrical control actuation within a compact package and is designed to meet uniform cooling and protection for use in hazardous environments along with an integrated hydraulic failsafe system for rapidly bringing the actuator to a shut down position when a potentially hazardous situation is sensed.
In U.S. Pat. No. 2,631,431 to Gerbe, there is disclosed an electro-hydraulic actuator in which an electric motor is located in a tank filled with oil. The motor is equipped with a hollow shaft and the shaft of a pump impeller is slidably contained within the hollow motor shaft. The impeller of the motor is arranged so that it can turn with the motor shaft while at the same time moving longitudinally along the axis of the shaft. The pump impeller is situated inside a hollow piston that is secured to a piston rod. The piston rod extends upwardly and passes out of the tank. In operation, the motor drives the impeller at a speed to increase the pressure of the oil on one side of the piston to a desired level wherein the piston and piston rod are displaced upwardly to position a linear device that is secured to the piston rod. A weight or spring is used to return the piston to its home position when the motor is de-energized.
Although the Gerbe device provides for improved motor cooling, the electronic controls for the motor are situated at a location remote from the tank that houses the motor and is therefore subject to all the problems associated with transmission lines of any appreciable length. Furthermore, because the electrical unit associated with the actuator must be housed in its own hazardous area container, the system is rather costly to build and maintain. The Gerbe device does not include a failsafe feature.
It is therefore a primary object of the present invention to improve electro-hydrostatic actuators.
It is a further object of the present invention to package both the electrical and mechanical components of an electro-hydrostatic actuator including a failsafe system in a single non-hazardous environment.
A still further object of the present invention to provide fluid cooling to both the mechanical and electrical components of an electro-hydrostatic actuator.
Another object of the present invention is to provide a more compact, hazardous area valve actuator that includes a failsafe system.
Yet another object of the present invention is to reduce transmission loss of the type generally found in electro-hydrostatic valve actuator units.
Still another object of the present invention is to immerse the electrical and mechanical components of an electro-hydraulic actuator in a reservoir of dielectric oil along with a hydraulic failsafe system.
These and other objects of the present invention are attained by an electro-hydrostatic actuator having a pressurized sealed housing containing a reservoir of dielectric fluid. A motor driven pump and electrical circuitry for controlling the pump are all immersed in the fluid contained within the reservoir. An electrical controller is also immersed in the reservoir for regulating the pump motor so that the pump delivers fluid from the reservoir to a hydraulic cylinder to move the piston rod of the cylinder to a desired location along the stroke path of the piston. Also immersed in the reservoir is a fluidic failsafe system that is arranged to rapidly bring the actuator to a shut off position when a potentially hazardous condition is sensed. Fluid for the failsafe system is also drawn from the reservoir.
For a further understanding of these and objects of the present invention, reference will be made to the following detailed description of the invention which is to be read in association with the accompanying drawings, wherein:
Turning initially to
A pressure compensating unit 20 is also mounted in the top wall of the unit and is illustrated in greater detail in
As illustrated in
The piston rod can be coupled to any suitable device that requires linear actuation. As noted above, the actuator unit is ideally well suited for positioning the valve stem 44 of a plunger type valve 45.
A second vertically disposed opening is formed in the bottom end wall of the housing which contains a bi-directional d.c. brushless motor 47 that is arranged to drive a bi-directional gear pump 48. The motor includes a permanent magnet mounted upon the rotor section of the motor and winding situated upon the motor stator. The motor is designed to yield high energy density due to its low rotating inertia and has an improved thermal performance due to the windings having a direct thermal path to the exterior of the motor casing. The brushless motor is commutated by an electronic controller 50 rather than the more conventional brush and commutator arrangement. As a result there are no brushes to wear out and little if any required maintenance over the life of the motor.
The controller 50 is mounted in the upper part of the housing and is also completely immersed in the fluid reservoir. The housing, in turn, is fabricated of a material having a high co-efficient of heat transfer. Accordingly, any heat that is generated by the electronics, the motor and the hydraulic cylinder is absorbed by the fluid and rapidly passed through the housing walls to the surrounding ambient.
A linear position transducer 51 is operatively connected to the piston rod of the cylinder which provides positioning data to the controller and as will be explained below in further detail the controller is able to extend or retract the piston rod to any desired position within the available stroke of the cylinder.
A second d.c. motor 52 and its associated pump 53 are similarly mounted in the base of the housing adjacent to the hydraulic cylinder. The motor and the pump are shown schematically in
Turning now to
A solenoid actuated cylinder flow control valve 60 is contained in the circuitry of the control section which functions to allow fluid to be exchanged between the two chambers of the actuator cylinder. The flow control valve is connected to both sides of the gear pump 48 by flow lines 61 and 62. Filters 63 and 64 are placed in the flow lines to remove any contaminants that might find their way into the fluid. The flow control valve is normally closed when in a de-energized condition. When the piston rod extension mode is selected by the controller, the control valve is energized and thus opened upon receiving a signal from the controller 50 via electrical line 66.
When in the cylinder extend mode of operation, the motor 47 is instructed by the controller via electrical lead 66 to turn in a direction so that fluid is drawn from chamber 41 via flow line 68, through the now open control valve and back to the low pressure side of the pump via flow line 62. The pressure in the fluid is then raised by the pump and is returned to cylinder chamber 40 through lines 61 and 69 causing the piston to move downwardly and thus extending the piston rod outwardly from the cylinder.
The position of the piston rod is sensed by the linear position transducer 51 and this data is delivered to the controller via electrical line 70. When the piston rod has moved to the desired extended position, the motor 47 will slow down the driving pump 48 so that the pump provides sufficient flow to overcome internal leakage and to maintain the desired piston rod position.
As illustrated in
The flow control circuit is connected to the pressurized fluid in the reservoir 23 by means of two pressure actuated valves 71 and 72. One side of each pressure actuated valve is connected directly to the pressurized fluid in reservoir 23 by flow lines 74, 75 and 76. The opposite side of pressure actuated valve 71, in turn, is connected into flow line 61 in the flow control circuit while pressure actuated valve 72 is connected into flow line 62. The pressure actuated valves are normally closed when pump 48 is inactive. The pressure activated valves are arranged so that when the pump is activated, the valve on the low pressure side of the pump will open and the valve on the high pressure side of the pump will remain closed. The pressure difference between the reservoir and the low pressure side of the pump is such that fluid in the low pressure reservoir 23 will be permitted to enter or exit the flow control circuit to accommodate the difference in volumes 40 and 41 as well as making up any fluid that is lost from the circuit due to leaks and the like. Upon closing of the control valve, shutting down of the flow control circuit, and motor 47, both pressure actuated valves move to a closed position.
Although, not shown, data is provided to the controller relating to one or more hazardous conditions which, if detected, require the cylinder to be moved rapidly to a position wherein the plunger valve 45 will be moved to an inoperative failsafe position. In this case, the piston rod will be moved to a fully extended position to close the valve. In other applications, the failsafe position might however, be one wherein the piston rod is moved to a fully retracted position.
The failsafe circuit 56 for carrying out the failsafe mode of operation is illustrated in
In practice, the pressurized reservoir can be replaced by an accumulator. The two accumulators can be mounted either inside or outside the unit housing 12. However, because of space considerations, it is preferred that the accumulators be located outside the housing as illustrated in
A solenoid actuated failsafe control valve 88 is mounted in flow line 82 and a solenoid actuated poppet valve 89 is placed in the line between the high pressure accumulator and the failsafe control valve. The two valves 88 and 89 are energized and thus closed during normal operation of the actuator. When the valves are closed the poppet valves shield the control valve from the high pressure in the high pressure accumulator thus minimizing the danger of the failsafe control valve from developing leaks.
In the event a failsafe condition is sensed, the controller de-energizes both the poppet valve 89 and the failsafe control valve 88 via electrical lines 90 and 91 thus opening both valves. At the same time, pumps 47 and 52 are shut down and flow control valve 60 is closed. Closing valve 88 places the high pressure accumulator in communication with chamber 40 of the actuator cylinder by means of the accumulator line 82 and supply line 93. Cylinder chamber 41 at this time is placed in communication with the pressurized reservoir accumulator through means of return line 94, valve 88 and line 74.
While the present invention has been particularly shown and described with reference to the preferred mode as illustrated in the drawing, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims.
