Abstract:
An electro-hydrostatic actuator having a sealed housing filled with a dielectric fluid. A motor driven pump and electronics for controlling the pump are all immersed in the fluid. The pump is arranged to deliver fluid from the housing to a hydraulic cylinder to control the positioning of the piston rod. A solenoid operated valve is integrated as a bypass or tip valve for quick fail safe position. The actuator is ideally suited to control various types of plunger valves. In one embodiment of the invention, the hydraulic cylinder is located outside of the housing and in another embodiment the cylinder is located inside of the housing.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The invention relates to an electro-hydrostatic actuator that is ideally suited to control the positioning of a valve or any other similar device.  
           [0002]    More specifically, this invention relates to a compact electrically operated linear actuator integrates all controls and components so rapidly and efficiently heat dissipation and cooling to component parts is provided.  
           [0003]    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, external power supply and controls that are costly to construct and difficult to service and maintain in the field. Typically, the electronic control of the actuator is 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.  
           [0004]    The invention presently here provides a solution to electrical control actuation within a compact package designed to meet uniform cooling and protection for use in hazardous environments.  
           [0005]    In U.S. Pat. No. 2,631,431 to Gerbe, there is disclosed an electrohydraulic 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 can turn with the motor shaft while at the same time moving longitudinally along the axis of the motor 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 through the top wall of the tank. In operation, the motor drives the impeller at a speed so as to increase the pressure of the oil on one side of the piston to a level wherein the piston and piston rod are displaced upwardly to reposition any type of 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.  
           [0006]    Although the Gerbe device provides for improved motor cooling, the electronic controls for the motor are situated at a location remote from the tank housing 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 non-hazardous container, the system is costly to maintain.  
         SUMMARY OF THE INVENTION  
         [0007]    It is therefore a primary object of the present invention to improve electro-hydrostatic actuators.  
           [0008]    It is a further object of the present invention to package both the electrical and mechanical components of an electro-hydrostatic actuator in a single non-hazardous housing.  
           [0009]    A still further object of the present invention to provide fluid cooling to both the mechanical and electrical components of an electro-hydrostatic actuator.  
           [0010]    Another object of the present invention is to provide a more compact, non-hazardous valve actuator.  
           [0011]    Yet another object of the present invention is to reduce transmission loss typical of an electro-hydrostatic valve actuator.  
           [0012]    These and other objects of the present invention are attained by an electro-hydrostatic actuator having a sealed housing filled with a dielectric fluid. A motor driven pump and electrical circuitry for controlling the pump are all immersed in the fluid contained within the housing. The pump is arranged to deliver fluid from the housing to a hydraulic cylinder to move the piston rod of the cylinder to a desired location along its available path of travel. In one form of the invention the piston rod is connected to the stem of a valve and serves to control the flow of a fluid through the valve. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    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:  
         [0014]    [0014]FIG. 1 is a perspective view illustrating an electro-hydrostatic actuator embodying the present invention;  
         [0015]    [0015]FIG. 2 is an exploded view in perspective showing the outer housing removed from the internal components of the actuator;  
         [0016]    [0016]FIG. 3 is an enlarged exploded view in perspective of the internal components of the actuator;  
         [0017]    [0017]FIG. 4 is a schematic diagram illustrating the functional relationship between the actuator components;  
         [0018]    [0018]FIG. 5 is a partial view in section showing a pressure compensating unit employed in the practice of the present invention;  
         [0019]    [0019]FIG. 6 is a perspective view illustrating a further embodiment of the invention;  
         [0020]    [0020]FIG. 7 is an enlarged perspective view showing the internal components of the actuator illustrated in FIG. 6; and  
         [0021]    [0021]FIG. 8 is a front elevation in section of the actuator illustrated in FIG. 6. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    Turning initially to FIGS.  1 - 3  there is illustrated a linear electro-hydrostatic actuator, generally referenced  10 , that embodies the teachings of the present invention. Although, the actuator is ideally suited to control the positioning of a flow control valve, it should be evident from the disclosure below that the actuator is equally adaptable to control the positioning of a wide variety of devices. The actuator includes a cylindrical housing  12  that is seated upon a base plate  13 . The top of the housing is closed by a top cover  15 . Although not shown, the housing is provided with suitable seals preventing fluid from escaping from the housing.  
         [0023]    As illustrated in FIGS. 2 and 3, a support block  17  is mounted upon the base which houses a brushless d.c. motor  18  within a motor compartment  19 . The motor includes a permanent magnet  20  that is mounted upon the rotor section  21  of the motor and windings  22  located upon the motor stator  23 . The motor is designed to yield high energy density due to low rotating inertia and has improved thermal performance due to the windings having a direct thermal path to the exterior surface of the motor. The brushless motor is commutated by an electronic controller  25  rather than by more conventional brushes and commutator bars. Accordingly, there are no brushes to wear out and little or no maintenance is required over the life of the motor.  
         [0024]    An adaptor plate  29  is mounted upon the top of the support block over the motor compartment  19 . A gear pump  30  is, in turn, mounted upon the adaptor plate and the drive shaft  26  of the pump is connected to the rotor shaft of the motor by any suitable means. The outlet port  31  of the pump is connected to a supply channel  33  in the support block by a supply line  35 . The flow channel outlet is connected to a hydraulic cylinder  37  by means of a second supply line  38 . In this embodiment of the invention, the hydraulic cylinder is secured to the bottom surface  39  of the base plate. As will be described in further detail below, the piston rod  40  of the hydraulic cylinder may be connected to the stem of a plunger type valve to regulate the flow through the valve. Although the invention is herein described with the specific reference to a control valve, it should be evident that the actuator may be used to control any linear action type device without departing from the teachings of the present invention.  
         [0025]    The interior of the housing is completely filled with a dielectric oil to totally immerse the motor, the pump and the controller in oil. The inlet to the pump is exposed to the reservoir of oil and as will be explained in greater detail below, the pump is arranged to deliver the oil to a chamber within the hydraulic cylinder on one side of a piston that is connected to the piston rod  40 .  
         [0026]    The controller is mounted upon the base plate immediately adjacent to the support block  17 . The controller is microprocessor based and in addition to the motor communication circuitry, the controller contains circuitry relating to an actuator position loop as well as other status monitoring functions which will be described in further detail below. The motor control circuitry monitors the rotor position via a resolver  27  that is mounted concentric to the rotor and provides a sinusoidal current to the motor windings to control motor torque.  
         [0027]    A solenoid valve  43  is also immersed in the oil reservoir and is placed in fluid flow communication with a bypass channel  44  formed in the support block  17 . The channel connects into the previously noted supply line channel  33  formed in the block. The solenoid valve is normally closed and is opened upon a signal from the controller in the event a fault is detected in one of the monitored function. Opening the solenoid valve causes the supply line to the hydraulic cylinder to be bypassed allowing oil on the pressure side of the piston to be returned rapidly to the reservoir.  
         [0028]    A compensating unit  48  is mounted in the top cover  15  of the housing. The unit is shown in further detail in FIG. 5. The compensating unit  48  provides variable volume for fluid expansion and fluid surge. It also provides positive pressure to the oil reservoir  51 . The unit is housed within a cylindrical vessel  50  that opens through the top cover into the oil reservoir  51  of the adaptor housing. The cylindrical body of the unit passes through a suitable opening in the cover and a clamping flange  52  is secured to the top cover by any suitable means. A seal  53  is placed between the flange and the top cover to prevent fluid from passing between the two members. A piston  55  is mounted inside the vessel and a close sliding fit is provided between the piston and the inner wall of the vessel. A piston shaft  56  is secured at one end to the piston and passes upwardly through the top wall  57  of the vessel. The shaft is slidably contained within a brushing  58  mounted in the top wall of the vessel. A plate  59  containing an orifice  60  is secured to the bottom of the vessel and, in assembly, the plate is placed in contact with the oil contained in the reservoir so that the oil can pass into the chamber  61  below the piston. A compression spring  62  surrounds the piston shaft which acts to bias the piston downwardly with a given force into contact with the oil in the chamber. The piston shaft also provides a visual indication of the oil level within the reservoir.  
         [0029]    A hermetically sealed connector  62  is also contained in the top wall of the housing through which electrical lines are passed into and out of the housing to provide power to the controller as well as carrying data signal to and from the controller.  
         [0030]    The operation of the actuator will now be further explained with reference to the schematic drawing illustrated in FIG. 4 wherein the actuator is shown controlling a plug type valve  63 . As noted above, the brushless motor  18  is connected to pump  30  via drive shaft  26 . The motor is connected to the controller  25  by a suitable electrical line  65 . The microprocessor based controller is arranged to monitor the rotor position of the motor through the resolver  27  which communicates with the controller via data line  66 .  
         [0031]    The pump  30  is arranged to deliver oil from the reservoir  51  to the hydraulic cylinder  37  through supply line  38 . The reservoir is shown for explanatory purposes as a tank with the understanding that the controller, the motor and the pump are all completely immersed within the reservoir. A piston  68  is contained within the hydraulic cylinder that divides the cylinder into an upper chamber  70  and a lower chamber  71 . The piston is attached to piston rod  40  which in turn passes out of the cylinder through bottom wall  72 . The extended end of the piston rod is equipped with a flange  74 . The stem  75  of the valve is similarly equipped with a flange  77  and a spring  78  is interposed between the two flanges. The spring is arranged to normally hold the valve in a closed position when the pump is inoperative.  
         [0032]    To open the valve, the pump is activated and oil under pressure is delivered into chamber  71  beneath the piston causing the piston to rise within the cylinder and thus lift the valve from its valve seat. A linear variable displacement transducer (LVDT)  80  is operatively associated with the piston rod and provides position data to the controller via line  81 . Using data provided by the resolver and the LVDT, the controller can set the valve to any desired position within its operating range. Any fluid that might accumulate in the upper chamber of the hydraulic cylinder is exhausted back to the reservoir via discharge line  83 .  
         [0033]    The solenoid activated trip valve  43  is mounted in the bypass channel  44  and is arranged to open in response to a trip signal from the controller sent over trip line  85 . Opening the solenoid valve provides a path for high pressure oil in the supply line to be discharged rapidly back to the reservoir thereby permitting the control valve to close.  
         [0034]    A pressure transducer  86  is mounted in the reservoir to provide pressure information to the controller by means of line  87 . The oil temperature in the reservoir is also provided to the controller by a thermal sensor  88  via data line  89 . A fluid level sensor  90  is mounted in the reservoir and provides oil level data to the controller via data line  91 .  
         [0035]    Turning now to FIGS.  6 - 8 , there is illustrated a further embodiment of the invention in which the hydraulic cylinder is brought into a housing  100  along with the motor driven pump and the controller. In this embodiment of the invention the housing  100  is split into two sections that include an upper section  101  and a lower section  102 . The lower section is equipped with a contoured base that has a first vertically disposed compartment  105  that passes upwardly into the base through the bottom wall  106  of the lower housing section. A second vertically disposed compartment  107  is similarly passed upwardly into the base through the bottom wall of the lower section of the housing. The second compartment is in parallel alignment-adjacent to the first compartment.  
         [0036]    As best illustrated in FIG. 7, the brushless motor  110  as described above is mounted upon a cover plate  111  and a gear pump  112  is mounted over the motor and is coupled to the motor shaft  112 . The motor stator is arranged to be supported in a stationary condition within the first compartment  105  as illustrated in FIG. 8 and the cover plate is secured to the base by screws to close the recess. With the top section of the housing removed, the pump is connected to the motor shaft and the mounting flanges  114  of the pump are secured by screws to a horizontally disposed shoulder  116  that surrounds the upper opening to the recess.  
         [0037]    The hydraulic cylinder  120  is arranged to be slidably received in the second compartment through the bottom opening thereof. The cylinder is supported in an upright position upon a second cover plate  121  that is arranged, in assembly, to close the bottom opening of the compartment. Again, with the upper section of the housing removed, the cylinder manifold  122  is mounted upon the top of the cylinder and is secured in place using suitable screws. A supply line  125  is connected at one end to the outlet of the pump and at the other end to the inlet channel  127  of the cylinder manifold. A solenoid activated trip valve  126  is secured to one side of the manifold and is connected into the inlet channel of the manifold by means of a bypass channel (not shown).  
         [0038]    Turning once again to FIG. 8, the actuator controller  130  is mounted in the upper section  101  of the housing. The upper section of the housing as well as the two cover plates  111  and  121  are sealed in assembly against the lower section of the housing using suitable seals  132  to render the housing leak proof. The interior cavity  133  of the housing is filled with a dielectric oil which totally immerses all of the component parts of the system contained within the housing. As should now be evident, any heat that is generated by the actuator is rapidly transferred to the walls of the housing and dissipated into the surrounding ambient.  
         [0039]    A piston  140  is contained within the hydraulic cylinder  120  and a piston rod  141  is secured to the piston and passes out of the housing through cover plate  121 . A blind hole  142  passes downwardly through the piston and the piston rod and a linear variable displacement transducer (LVDT)  145  is contained within the hole. The LVDT is arranged to pass upwardly through the cylinder manifold and is connected to the controller to provide piston rod position data to the controller. A resolver  147 , as described above, is mounted upon the rotor of the motor and sends rotor position information to the controller. Although not shown, pressure, temperature and fluid level sensors are mounted within the housing which also sends data to the controller for processing. Inlet and outlet leads are passed into and out of the housing by means of sealed connectors  150  and  151 . A compensator unit  160  as described above is mounted in the top wall of the upper section of the housing.  
         [0040]    As noted above, the piston rod of the actuator may be connected to the stem of a plunger type valve and a spring employed to return the piston to a home position when the pump is de-energized.  
         [0041]    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.