Abstract:
An electrically operated valve actuator with an eddy current clutch is disclosed. The use of the eddy current clutch provides an actuator that can control the rate of closing of the valve in a predetermined linear manner to avoid slamming the valve shut in an emergency shutdown.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a valve actuator that is electrically operated and used to selectively move a valve closure member in a gate valve between open and closed positions and thereby control flow through the valve. The actuator is used in emergency situations to quickly close the valve by tripping a release means that allows a coiled spring acting in combination with the residual pressure in the valve acting on the stem to rapidly move the valve closure member from a first, typically open, position to a second, typically closed, position. 
     Valve actuators that are hydraulically, pneumatically or electrically operated are well known and frequently used in the oil and gas industry. These valve actuators are required to be able to open the valve and hold the valve open against the full working pressure of the valve. This internal valve pressure may exert a substantial force against the actuator, trying to overcome the opening force generated by the actuator. Simultaneously, the actuator must be able to react in an emergency situation and close the valve in a matter of seconds. 
     This closing operation is typically accomplished by using a large diameter coil spring acting in combination with the residual pressure in the valve acting on the stem to provide the motive force to urge the valve to its closed or failsafe position in a few seconds. This spring must be sized to have sufficient force to close the valve at the valve&#39;s rated working pressure. In the case where it is necessary to close the valve while the pressure in the valve is a relatively small percentage of the valve&#39;s rated pressure, the spring is now somewhat oversized causing the valve to “slam” shut under a great accelerative force thereby causing increased wear on the valve actuator&#39;s components. It is thus desirable to be able to control the rate at which the valve is closed and thereby minimize actuator component wear. 
     Previous attempts to control this closing force have focused on controlling the rate at which the actuator is closed. Various devices such as viscous rotary dampers, centrifugal clutches and centrifugal pumps with metering valves have been used. These devices suffer from various deficiencies including high breakout torque, large torque variance with temperature changes and leakage of the fluid used as the damping media. It is therefore desirable to have a clutching mechanism or similar apparatus that has a low breakout torque, is minimally affected by temperature changes and requires no fluids for operation. 
     2. Description of Related Art 
     U.S. Pat. No. 5,261,446 to Gerald S. Baker shows a self-contained emergency shutdown valve and actuator assembly with a hydraulic pilot pressure control system for determining when an emergency shutdown of the valve is required. Movement of the valve stem is done by use of a recirculating ball and nut shaft arrangement. 
     U.S. Pat. No. 6,152,167 to Gerald S. Baker discloses a valve actuator with an emergency shutdown feature that includes a wrap spring clutch to control movement of the actuator in one direction but not in the other unless acted upon by the tripping system. 
     U.S. patent application Ser. No. 09/915,796 by Johnny Newport and Todd Mosley, filed Jul. 26, 2001 and assigned to the same. assignee as the present application, shows a roller screw actuator for use with subsea chokes that uses a planetary roller screw to operate a choke. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a valve actuator having a cylindrical housing with a bonnet secured to one end of the actuator housing. The bonnet has a stem bore therethrough and a stem positioned therein that is configured for attachment to a gate in a gate valve such that movement of the stem moves the gate of the gate valve between open and closed positions corresponding to operating and failsafe positions of the gate valve. A biasing module, positioned in the actuator housing, is connected to the stem and having a coil spring to urge the stem and valve gate to a closed, i.e., failsafe position. A transmission module including a low friction planetary roller screw is adjacent the biasing module and moves the stem and valve between the open and closed positions. Movement of the transmission module is opposed by the spring and the valve bore pressure. A power module drives the transmission module. An eddy current clutch is connected to the transmission module to control the movement of the stem at a preselected, linear rate as the stem is moved by the spring to the failsafe position. A pair of wrap spring clutches are used to restrain and control movement of the planetary roller screw. A control module is provided to allow selective release of the wrap spring clutch and thereby allow the spring to move the stem and valve gate to their failsafe position. 
     A principal object of the present invention is to provide an electrically operated valve and actuator assembly with a clutch apparatus having a substantially linear torque versus speed relationship. 
     Another object of the present invention is to provide an electrically operated valve and actuator assembly with a clutch apparatus with a low breakout torque. 
     A further object of the present invention is to provide an electrically operated valve and actuator assembly with a clutch apparatus that is minimally affected by temperature changes. 
     A final object of the present invention is to provide an electrically operated valve and actuator assembly with a clutch apparatus that requires no fluids for operation. 
     These with other objects and advantages of the present invention are pointed out with specificness in the claims annexed hereto and form a part of this disclosure. A full and complete understanding of the invention may be had by reference to the accompanying drawings and description of the preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and advantages of the present invention are set forth below and further made clear by reference to the drawings, wherein: 
     FIGS. 1A-1D are a sectional view of embodiment of the valve and valve actuator assembly of the present invention. 
     FIG. 2 is a partial sectional view, taken along lines  2 — 2  of FIG. 1, showing part of the control module. 
     FIG. 3 is an elevation view, taken along lines  3 — 3  of FIG. 2, showing the details of the releasing means. 
     FIG. 4 is an elevation view, partly in section, showing details of the power module. 
     FIGS. 5A and 5B are a section view of the transmission module. 
     FIG. 6 is an elevation view, showing details of the biasing module. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the drawings, and particularly to FIGS. 1A-1D, valve actuator assembly  10  embodying the principles of the present invention is shown. Valve actuator assembly  10  includes actuator housing  12  attached to valve bonnet  14  by threaded engagement  16 . Valve bonnet  14  is sealingly secured to gate valve  18  (shown in partial section) by suitable securing means as studs  20  and nuts  22 . Gate valve  18  is of a conventional configuration well known to those of ordinary skill in the art with valve closure member in the form of valve gate  24  movable therein between open and closed positions by valve actuator assembly  10  to control fluid flow through bore  26  (not shown). Valve gate  24  is typically a reverse acting gate, i.e., when the actuator moves the gate, typically upward, away from the valve bore to the closed position, the bore in the gate moves out of alignment with the inlet and outlet passages and flow is stopped. This position is referred to as the failsafe position while when the bore in valve gate  24  is aligned with the bore  26  of the valve this position is the open or operating position. Such a valve is referred to as a reverse acting gate valve or fail closed gate valve. A valve designed to fail open is accomplished with a gate having the bore moved inwardly or more closely to the end of the gate, referred to as a direct acting gate valve. Either configuration may be used with the actuator of the present invention without departing from the scope of the invention. 
     Valve actuator assembly  10  also includes biasing module  28 , transmission module  30 , power module  32  and control module  34 . Valve bonnet  14  has stem bore  36  extending therethrough with stem  38  centrally located therein. The inner end of stem  38 , i.e., the end located closest to gate valve  18 , has enlarged diameter section  40  formed thereon which engages shoulder  42  of bonnet  14  when stem  38  is stroked to the position shown. The contact between enlarged diameter section  40  and shoulder  42  determines the up stroke of stem  38 . Lip seal  44  is disposed in stem bore  36  and seals on the exterior of stem  38 . 
     The opposite end of actuator housing  12  has power module  32  attached thereto with cap screws  46 . Referring to FIG. 4, power module  32  is shown in greater detail and includes electric motor  48  secured to motor mount housing  50  by cap screws  52 . The use of an electric motor as the motive force for driving the actuator in power module  32  is considered illustrative only and not limiting. It is envisioned that power module  32  could utilize other motive forces such as hydraulic or pneumatic without departing from the scope of the present invention and such modifications are considered within the scope of the present invention. Junction box  54  is mounted on the side of electric motor  48  and electrical cable (not shown) is attached for supplying electrical power. Motor mount housing  50  is a cylindrical cup shaped member with annular flange  56  formed on its end. Electric motor  48  has ratchet clutch  58  and clutch coupling  60  positioned on its output shaft to connect motor  48  to speed reducer gearbox  62 . Speed reducer gearbox  62  is used to control the speed of electric motor  48  as it powers transmission module  30 , in manner to be described hereinafter. Torque coupling  64  is mounted on the output side of speed reducer gearbox  62  and has coupling  66  formed on its inside to mate with transmission module  30 . 
     Cap screws  46  attach power module  32  to actuator housing  12  as best seen in FIG. 1C where power module  32  is coupled to transmission module  30 . FIGS. 5A and 5B provide an enlarged view of the details of transmission module  30 . Transmission module  30  includes upper end cap  68  to which wrap spring cap  70  is secured by cap screws  72 . Threaded holes  74  are formed in the end of upper end cap  68  to receive cap screws  46  and secure power module  32  to transmission module  30 . Upper end cap  68  is a generally cup shaped member with threads  76  formed on the opposite end for engagement with threads  78  on actuator housing  12  to secure transmission module within actuator housing  12 . Mounted to upper end cap  68  by cap screws  80  are upper stator  82 , lower stator  84  and damper mount  86  and therefore cannot rotate with respect to actuator housing  12 . 
     Extending through wrap spring cap  70  is spindle  88  with flat end  90  formed on its end for engagement with coupling  66  of power module  32 . Thus the rotation of electric motor  48  is transmitted through speed reducer gearbox  62  to rotate spindle  88  of transmission module  30 . Positioned on spindle  88  adjacent flat end  90  is clutch rotor  92  held on spindle  88  by snap ring  94 . Clutch rotor  92  has drive keys  96  on its interior that engage spindle  88  so that rotation of spindle  88  causes rotation of clutch rotor  92 . Positioned on clutch rotor  92  and upper stator  82  is wrap spring clutch  98 . Wrap spring clutch  98  is of the type disclosed in U.S. Pat. No. 5,261,446 and is sized to fit tightly on clutch rotor  92  and upper stator  82 . Wrap spring clutch  98  is wound to allow power module  32  to rotate spindle  88  and move valve gate  24  toward valve  18  and into its operating position. For reasons to be explained hereinafter, wrap spring clutch  98  resists movement of spindle  88  in a direction opposite to that just described to prevent “overhauling”, i.e., spindle  88  from turning the opposite direction after motor  48  is turned off. Wrap spring clutch  98  resists this movement by being wrap onto upper stator  82  which is prevented from rotating by being connected to actuator housing  12  through upper end cap  68 . 
     Spindle  88  is supported by axially and radially by thrust bearings  100  and roller bearings  102  within upper stator  82  and lower stator  84 . Counter bore  104  is formed on the inner end of spindle  88  and has low friction transmission means in the form of planetary roller screw  106  positioned therein. Planetary roller screw  106  is of the type commercially available from various vendors such as INA Bearing and also used in U.S. patent application Ser. No. 09/915,796 by Johnny Newport and Todd Mosley, filed Jul. 26, 2001 and assigned to the same assignee as the present application and incorporated herein by reference. Planetary roller screw  106  includes roller cage  108 , drive rollers  110  and roller shaft  112 . Drive key  114  fits in counter bore  104  and transmits rotation of spindle  88  to roller cage  108 , drive rollers  110  and roller shaft  112 . Roller shaft  112  does not rotate however as it is prevented from rotating by keys  116  positioned in slot  118  of lower rotor  120 . Lower rotor  120  is a generally cylindrical member with a stepped shoulder on its exterior. Lower rotor is supported by axially and laterally by thrust bearings  122  and roller bearings  124  and  126  within lower stator  84  and damper mount  86 . 
     Positioned on lower rotor  120  and lower stator  84  is wrap spring clutch  128 . Wrap spring clutch  128  is the same as that of spring clutch  98  except it is wound so that as spindle  88  drives planetary roller screw  106  to move valve gate  24  toward valve  18 , wrap spring clutch  128  prevents lower rotor  120  from rotating with respect to lower stator  84  and thereby causes roller shaft  112  to translate, i.e., move linearly toward valve  18 , as keys  116  prevent rotation of roller shaft  112  with respect to lower rotor  120 . This linear motion causes roller shaft  112  to push on biasing module  28  and urge valve gate  24  to its operating position. When it is desired to quickly close valve  18 , a releasing means is provided that moves tang  130  on wrap spring clutch  128  to release the clutch in a manner that will be described hereinafter. 
     Damper mount  86  has clutch assembly in the form of eddy current clutch  132  mounted on its end. Eddy current clutch  132  is of the type commercially available from Magnetic Technologies Ltd., Oxford, Mass. Such clutches have a linear relationship between torque and speed. The interior of eddy current clutch  132  has key  134  disposed therein which connects to lower rotor  120  to control its speed of rotation as will be described hereinafter. Dust shield  136  connects between upper end cap  68  and damper mount  86 . 
     Control module  34  is shown in FIG.  5  and in greater detail in FIGS. 2 and 3. Control module  34  includes a releasing means  138  comprising solenoid  140 , plunger  142  and link arm  144 . When solenoid  140  is operated, plunger  142  bears on the end of link arm  144  which causes link arm  144  to pivot on screw  146  that attaches link arm  144  to lower stator  84 . Surface  148  is milled on the side of lower stator  84  to allow clearance for the movement of link arm  144 . 
     Biasing module  28  is shown in greater detail in FIG.  6  and includes spring retainer cap  150  with bearing plate  152  secured thereto. Spring retainer cap  150  includes annular flange  154  formed on one end that contacts biasing member in the form of spring  156  as best seen in FIG.  1 . Bearing plate  152  includes thrust and roller bearings  158  and  160  that support roller plate  162 . Bearing plate  152  is attached to end plate  164  by cap screws  166 . Hex head cap screw  168  secures biasing module  28  to stem  38  while retainer screws  170  secure biasing module  28  to housing end plate  172 . Housing end plate  172  is secured to actuator housing  12  by threaded engagement  174 . Referring to FIG. 1, a second part of control module  34  is shown in the form of limit switches  176  that detect the position of annular flange  154  of spring retainer cap  150  as the actuator move valve gate  24  between its operating and failsafe positions. 
     A typical sequence of operations would be as follows. Valve gate  24  would be in the position shown in FIG. 1, i.e., its failsafe position with the bore of valve  18  closed. Wrap spring clutch  128  is in its locked position, i.e., lower rotor  120  cannot rotate with respect to lower stator  84 . Electrical power is supplied to motor  48  which then drives spindle  88  through speed reducer gearbox  62  and torque coupling  64 . Spindle  88  rotates and turns roller cage  108  through drive key  114 . Wrap spring clutch  98  is oriented to allow rotation in this direction. Rotation of roller cage  108  is transmitted to roller shaft  112  through drive rollers  110 . Roller shaft  112  cannot rotate as keys  116  in slot  118  of lower rotor  120  prevent rotation because wrap spring clutch  128  prevents rotation of lower rotor  120  with respect to lower stator  84  and damper mount  86 . This cause roller shaft  112  to move linearly toward valve  18  and bear on roller plate  162  of biasing module  28 . Continued movement of roller shaft  112  urges stem  38  and valve gate  24  into valve  18  thereby opening valve  18  to its operating position. Simultaneously, spring  156  is being compressed and opposing the aforementioned linear movement of stem  38 . At this point, limit switches  176  can detect the position of biasing module  28  and ascertain if valve  18  is open. Power to electric motor  48  can then be turned off. Pressure within valve  18  that acts across the diameter defined by seal  46  on stem  38  will attempt to attempt to backdrive or “overhaul” electric motor  48 . This is prevented by wrap spring clutch  98  that prevents opposite rotation of roller shaft  112  as previously described. 
     When it is desired to shut the valve, i.e., move it from its operating to failsafe position, releasing means  138  is activated by removing electrical power from solenoid  140  and extending plunger  142  and moving link arm  144  which in turn moves tang  130  to release wrap spring clutch  128 . This allows spring  156  and the pressure end load acting on stem  38  to urge stem  38  outwardly, i.e., away from valve  18 . This causes a rapid movement of stem  38  and roller plate  162  that is bearing on roller shaft  112 . As roller shaft  112  moves upwardly and rotates on drive rollers  110 , roller cage  108  attempts to rotate also. However, key  114  between roller cage  108  and spindle  88  prevents rotation of roller cage  108  as spindle  88  is locked against rotation by wrap clutch  98  which prevents backdriving of spindle  88  as previously described. Thus roller shaft  112  rotates upwardly into spindle  88  to return to the position of FIG.  1 . This rotation of roller shaft  112  is transmitted to lower rotor  120  and through key  134  to eddy current clutch  132 . As the outer portion of eddy current clutch  132  is restrained from movement by being pinned to damper mount  86 , the rate of rotation of roller shaft  112  is controlled by eddy current clutch  132 . The drag thus produced controls the rate at which spring  156  can urge stem  38  and valve gate  24  outwardly to the failsafe position. This drag of the eddy current clutch allows the valve to thereby be closed at a reduced rate without “slamming” the valve shut. 
     The construction of my electric valve actuator with eddy current clutch will be readily understood from the foregoing description and it will be seen that I have provided an electrically operated valve and actuator assembly with a clutch apparatus having a substantially linear torque versus speed relationship. Furthermore, while the invention has been shown and described with respect to certain preferred embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of the specification. The present invention includes all such equivalent alterations and modifications, and is limited only by the scope of the appended claims.