Abstract:
A valve assembly comprises a flow control valve including a valve shaft, an electrical actuator comprising an actuator output shaft, and a torsion spring coupling the valve shaft and the actuator output shaft.

Description:
BACKGROUND 
   The present invention relates to a valve assembly. More particularly, the present invention relates to a valve assembly including a valve shaft that is coupled to an actuator output shaft with a torsion spring. 
   A valve assembly, such as a butterfly valve assembly or a ball valve assembly, may be used to control the flow of fluid through a passage, such as tubing or ducting. In this way, the valve assembly may also be referred to as a “flow control valve” or a “pressure control valve.” Typically, a valve member disposed in a valve body controls the flow of fluid through the valve body (which may be connected to other tubing or ducting). In the case of a butterfly valve assembly, the valve member is a valve disc disposed in the valve body and has different angular positions that relate to different fluid flow rates. For example, the valve disc may rotate between a 0° position (open) and a 90° position (closed), where the angles are determined with respect to a center axis of the passage. 
   An electrical/electromechanical rotary actuator may be used to rotate the valve disc to a desired angular position in order to control the flow rate through the valve body. In one configuration, the actuator includes an actuator output shaft that is rigidly connected to a valve shaft, which is coupled to the valve disc. As the actuator output shaft rotates (in response to an electrical and/or pneumatic signal inputted to the actuator), the rotational movement (or torque) is translated (or transmitted) to the valve shaft, which rotates the valve disc. In order to select the angular position of the valve disc, an electrical device/stop/switch is provided to the actuator to stop the actuator output shaft from rotating. Typically, the electrical signal provided to the actuator is proportional to the position of the valve disc. 
   Butterfly valve designs that incorporate an internal face seal between the valve body and disc have a physical stop. The degree of surface contact force between the valve disc and valve body at the stop influences the ability of the face seal to seal. After the valve disc contacts the physical stop, the disc and valve shaft are prevented from further rotating towards the physical stop. 
   It has been found that when the physical stop is contacted prior to the electrical stop of the actuator (e.g., due to hardware tolerance stack-up or misassembly), the actuator output shaft is stopped from rotating, but the electrical current to the actuator is not severed. As a result, the actuator may overheat and prematurely fail. Conversely, during valve closing, if the electrical stop/switch is activated prior to the valve disc contacting the face seal stop, the ability of the valve disc to seal may be adversely affected. 
   BRIEF SUMMARY 
   The present invention is a valve assembly for controlling a flow of fluid through a passage, such as a valve body. The valve assembly includes a valve and an actuator. The valve includes a valve member disposed in the passage and movable between an open and closed position, and a valve shaft coupled to the valve member. The actuator includes an actuator output shaft that is coupled to the valve shaft with a torsion spring, which translates torque/rotational movement from the actuator output shaft to the valve shaft. The valve member angular position is adjusted by rotating the actuator output shaft. The torsion spring provides a compliant connection between the actuator output shaft and valve shaft, and compensates for any angular difference/deviation between the actuator output shaft and valve shaft. For example, the torsion spring allows the actuator output shaft to continue rotating in the event that an electrical signal to the actuator is not severed after the valve member reaches a closed position. Conversely, in a situation where the electrical signal stops prior to the valve member reaching a closed position, the torsion spring, if preloaded, helps bias the valve member towards the closed position. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1A  is a partial perspective cross-sectional view of a valve assembly in accordance with a first embodiment of the present invention, which includes a valve with a valve shaft and an actuator with an actuator output shaft, where the valve shaft and actuator output shaft are coupled together with a flat torsion spring. 
       FIG. 1B  is a cross-sectional plan view of the valve assembly of  FIG. 1A . 
       FIG. 2A  is a partial perspective cross-sectional view of a valve assembly in accordance with a second embodiment of the present invention, where a valve shaft and an actuator output shaft are coupled together with a helical torsion spring. 
       FIG. 2B  is a perspective view of the helical spring of  FIG. 2 . 
   

   DETAILED DESCRIPTION 
     FIG. 1A  is a partial perspective cross-sectional view of valve assembly  10  in accordance with a first embodiment of the present invention, which is suitable for controlling the flow of a fluid through a passage, such as tubing, ducting, etc. Valve assembly  10  includes butterfly valve  12 , electrical/mechanical actuator  14 , and flat torsion spring  15 . Butterfly valve  12  includes a generally cylindrical valve body  16 , valve disc  18 , and valve shaft  20 . Valve body  16  defines a fluid passage  21  (shown in  FIG. 1B ) and may be stainless steel or another suitable material. In alternate embodiments, valve body  16  is another annular shape (e.g., elliptical, oval, circular) or another suitable shape. Disposed within valve body  16  is valve disc  18 , which is rotatable between an open and closed position. Valve shaft  20  is coupled to disc  18 , and shaft  20  may be rotated in order to select a position of disc  18  (e.g., open, closed or a position therebetween). Shaft  20  is positioned between a pair of bearings  24 , which allows shaft  20  to rotate freely within valve body  16 . The flow of a fluid through valve body  16  is manipulated by adjusting the position of disc  18  with respect to center axis  22  of shaft  20 . 
     FIG. 1B  is a cross-sectional view of butterfly valve  12 , which includes valve body  16  defining fluid passage  21 , valve disc  18 , valve shaft  20 , first stop  26 , and second stop  28 . As  FIG. 1  B illustrates, when disc  18  of butterfly valve  12  is in the closed position, disc  18  is substantially perpendicular (i.e., a 90° position) to center axis  22  of fluid passage  21 . When disc  18  is in an open position (position A, in phantom), disc  18  is substantially parallel (i.e., a 0° position) to center axis  22 .  FIG. 1B  also illustrates position B of disc  18  (in phantom), which is between the open and closed positions. 
   The position of disc  18  with respect to stops  26  and  28  also affects the rate of flow of a fluid through passage  21 . Disc  18  rests against first and second stops  26  and  28  in the closed position, thereby preventing fluid from passing past disc  18 . Stops  26  and  28  help define a stopping point for disc  18  in its closed position as well as help prevent fluid from flowing through regions  30 A and  30 B when disc  18  is in its closed position. Stops  26  and  28  may also be referred to as “face seals” or “seals” because stops  26  and  28  help seal regions  30 A and  30 B against fluid flow. The degree of surface contact between valve disc  18  and valve body  16  at stops  26  and  28  influences the ability of disc  18  to seal passage  21 . After disc  18  contacts stops  26  and  28 , disc  18  and valve shaft  20  are prevented from further rotating towards stop  26  and  28  (in  FIG. 1B , in the counterclockwise direction). 
   Returning to  FIG. 1A , electrical actuator assembly  14  includes electrical actuator  32  and output shaft  34 , which is mechanically coupled to and driven by electrical actuator  32 . In order to adjust the position of valve disc  18 , and thereby manipulate the flow of fluid through passage  21  (shown  FIG. 1B ), an electrical signal is provided to actuator  32 , which then rotates output shaft  34  accordingly. In one embodiment, the degree of rotation of output shaft  34  is proportional to the electrical signal provided to actuator  32 . Output shaft  34  is mechanically coupled to valve shaft  20  with torsion spring  15 , which translates the rotational movement (or torque) of output shaft  34  to valve shaft  20 . The rotation of valve shaft  20  rotates disc  18  because valve shaft  20  is mechanically coupled to disc  18 . In a typical actuator  32 , actuator  32  stops rotating shaft  34  in response to “electrical stop,” whether it be a specific electrical signal inputted to actuator  32 , severing power to actuator  32 , or otherwise. 
   Flat torsion spring  15  provides a compliant drive link that transmits rotational movement/torque of output shaft  34  of actuator  14  to valve shaft  20  and disc  18  of valve  12 . First end  1   5 A of torsion spring  15  is connected to valve shaft  20 , while second end  15 B is connected to output shaft  34  of actuator assembly  14 . Any suitable means of connecting torsion spring  15  to valve shaft  20  and output shaft  34  may be used in accordance with the present invention, including a mechanical attachment means as well as an adhesive or welding means. In the first embodiment illustrated in  FIG. 1A , valve shaft  20  and output shaft  34  each include a slot that is configured to receive the respective end  15 A and  15 B of spring  15 . More specifically, slot  20 A in valve shaft  20  is configured to receive and retain first end  15 A of torsion spring  15  and slot  34 A in output shaft  34  is configured to receive and retain second end  15 B of torsion spring  15 . 
   The angular position of valve disc  18 , which is proportional to the angular position of valve shaft  20 , affects the rate of flow of a fluid through passage  21 . Ideally, the angular position of valve disc  18  is proportional to the angular position of output shaft  34  of actuator  14  so that the position of valve disc  18  can be predictably selected by rotating output shaft  34 . In order to close disc  18  to stop the flow of fluid through passage  21 , disc  18  (and valve shaft  20 , which has the same angular value as valve disc  18 ) is placed in a 90° position. In order to achieve the 90° position of disc  18 , actuator  32  rotates output shaft  34  to a 90° angle position. However, due to mismatched tolerances, misassembly, or other reasons, the 90° angle position of actuator output shaft  34  as determined by actuator  32  may not match the 90° position of disc  18  and valve shaft  20 . This is referred to as an “angular difference/deviation.” Due to the angular difference/deviation, an electrical stop may be prematurely provided to actuator  32  or valve disc  18  may prematurely contact surfaces  26  and  28  (i.e., before actuator  32  receives an electrical stop). For example, when an electrical stop is provided to actuator  32  before valve disc  18  contacts stops  26  and  28 , output shaft  34  may be in a 90° position, while valve disc  18  and valve shaft  20  are in a 88° position. In this situation, valve disc  18  does not contact stops  26  and  28 , and further rotation of valve shaft  20  and valve disc  18  is required to close valve disc  18 . However, output shaft  34  has stopped rotating because actuator  32  has stopped in response to the premature electrical stop. This may be problematic because fluid is likely to flow past regions  30 A and  30 B  30  (shown in  FIG. 1B ). 
   Assembly  10  in accordance with the present invention utilizes torsion spring  15  to couple valve shaft  20  and output shaft  34  in a manner that compensates for any angular difference/deviation between shafts  20  and  34 . Torsion spring  15  is stiff enough to transmit the rotational output of output shaft  34  to valve shaft  20 , while at the same time compliant enough to absorb excess torque of output shaft  34  or provide torsional flexure to bias valve disc  18  against stops  26  and  28 . Further, because torsion spring  15  is compliant, valve shaft  20  and output shaft  24  do not need to be coaxial (of course, in some embodiments, valve shaft  20  and output shaft  24  are coaxial). In an alternate embodiment, assembly  10  may include more than one torsion spring between valve shaft  20  and output shaft  34 . 
   When an electrical stop is prematurely provided to actuator  32  and output shaft  34  prematurely stops rotating before valve disc  18  contacts stops  26  and  28 , torsion spring  15  helps bias valve disc  18  towards stops  26  and  28  because torsion spring  15  is preloaded with a torsional load. One means of preloading torsion spring  15  is by adding additional “twist” to torsion spring  15  during initial installation of spring  15 . For example, if valve shaft  20  and output shaft  34  are each in a 90° position when valve disc  18  is in its 90° position (i.e., the closed position), torsion spring  15  may be preloaded by twisting torsion spring  15  to a 93° position with respect to the valve shaft  20  and output shaft  34 , resulting in a pretwist of about 3°. In alternate embodiments, the pretwist may be between about 2° to about 5°, or any other suitable angular range, depending on the type and application of the torsion spring. Pretwisting torsion spring  15  preloads torsion spring  15 , which enables torsion spring  15  to provide a contact load between valve disc  18  and stops  26  and  28 , which improves the ability of disc  18  to seal regions  30 A and  30 B when disc  18  is in a closed position. It was found that in one example, a pretwist of about  30  in a flat torsion spring formed of a spring steel exhibiting a modulus of elasticity of about 1.93×10 8  kilopascals (2.8×10 7  pounds/inch 2 ) exhibited a torsional load of about 5.76 kilogram centimeters (5 pound inches) to 9.22 kilogram centimeters about (8 pound inches), which may be suitable for a pneumatic application of assembly  10 . Of course, in alternate embodiments, torsion spring  15  may not be preloaded. 
   If an electrical signal continues to drive actuator  32  even after disc  18  contacts stops  26  and  28 , torsion spring  15  enables output shaft  34  of actuator assembly  14  to continue rotating, even though disc  18  and valve shaft  20  are stopped from further rotation. This helps prevent actuator  32  from failing due to overheating. Output shaft  24  is able to continue rotating because torsion spring  15  provides a compliant interface between valve shaft  20  and output shaft  34  such that output shaft  34  may rotate without requiring valve shaft  20  to rotate. In contrast, in existing valve assemblies, a valve shaft is rigidly connected to an actuator output shaft, such that the output shaft may only rotate if the valve shaft is able to rotate. 
   Torsion spring  15  may be any suitable torsion spring known in the art. Factors in determining the suitable design (e.g., geometry and material attributes) of torsion spring  15  for a particular assembly include the operational valve shaft  20  loads, torsional output levels of actuator assembly  14 , and the degree of pretwist (or “flex” or “wind-up”) required from torsion spring  15 . In the first embodiment illustrated in  FIGS. 1A and 1B , torsion spring  15  is formed of a spring steel and has a rectangular cross-section. 
   A torsion spring having a round wire cross-section may also be used in accordance with the present invention, as illustrated in  FIG. 2A , which is a partial perspective cross-sectional view of assembly  100  in accordance with a second embodiment of the present invention. Assembly  100  includes butterfly valve  112 , electrical actuator assembly  114 , and helical torsion spring  116 . Assembly  100  is similar to assembly  10  of  FIGS. 1A-1B , except that assembly  100  includes helical torsion spring  116 , rather than flat torsion spring  15  with a first embodiment of the present invention. 
   First end  116 A of helical torsion spring  116  is attached to valve shaft  118  and second end  116 B is attached to output shaft  120  of actuator assembly  114 . More specifically, first end  116 A of helical torsion spring  116  includes opening  122  (shown in  FIG. 2B ) configured to receive a corresponding protrusion in valve shaft  116  and second end  116 B includes opening  124  (shown in  FIG. 2B ) configured to receive a protrusion in valve shaft  116 . In an alternate embodiment, another suitable means of attaching helical torsion spring  116  to valve shaft  118  and output shaft  120  may be used. For example, valve shaft  118  and output shaft  120  may each include slots that are configured to receive first and second end  116 A and  116 B, respectively, of helical torsion spring  116 . 
     FIG. 2B  is a perspective view of helical torsion spring  116  and illustrates opening  122  (in phantom) in first end  116 A and opening  124  (in phantom) in second end  116 B. 
   The present invention is not limited to the specific examples of a butterfly valve, electrical actuator, and flat and helical torsion springs illustrated in  FIGS. 1A-2B . Rather, the present invention is any valve assembly (e.g., ball valve assembly or a butterfly valve assembly) that includes a movable valve member attached to a valve shaft, where the valve shaft is coupled to an actuator output shaft with a torsion spring. The valve assembly may be used to regulate/adjust the flow of a fluid, such as air or a liquid. Furthermore, a valve assembly in accordance with the present invention is also suitable for use in both hot and cold temperature applications. In a hot temperature application, a torsion spring composed of a spring steel including a high nickel content may be used. 
   The terminology used herein is for the purpose of description, not limitation. Specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as bases for teaching one skilled in the art to variously employ the present invention. Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.