Abstract:
A valve is provided for use on a control moment gyroscope (CMG) having a housing separating an internal environment from an external environment. The valve includes a valve housing, a valve element, and bellows. The valve housing is configured to couple to the CMG housing and includes an inner surface defining a cavity, an outer surface, and an opening extending therebetween. The valve element is disposed within the valve housing cavity and is movable between a closed position, in which fluid is prevented from flowing through the valve housing opening, and an open position, in which fluid may flow through the valve housing opening. The bellows is disposed within the valve housing and coupled to the valve element and has an internal chamber. The bellows selectively moves the valve element closed and open in response to a differential pressure between the bellows internal chamber and the valve housing cavity.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention generally relates to control moment gyroscopes or reaction wheels, and more particularly relates to a vent valve for use on a control moment gyroscope or a reaction wheel.  
       BACKGROUND OF THE INVENTION  
       [0002]     The attitude of a spacecraft may be controlled by various rotating inertia members, such as a reaction wheel or a control moment gyroscope (CMG). A CMG typically comprises a rotor with a fixed or variable spin rate, spinning up to 6000 rpm. The CMG may also include a gimbal assembly coupled to the rotor. The spin axis of the CMG can be tilted by moving the CMG using the gimbal assembly. This motion produces a gyroscopic torque orthogonal to the spin axis and gimbal axis.  
         [0003]     Typically, the CMG rotor is disposed within an evacuated housing to reduce windage drag. To eliminate pressure build-up within the housing during rotor spin, at least one housing vent is provided in the CMG housing. The housing vent may be equipped with a valve that is closed when a pressure differential exists between the CMG housing and external environment and is opened when the two pressures are substantially the same.  
         [0004]     Conventionally, a single-acting, passive vent valve has been used on CMG housing vents. The vent valve is generally coupled to the CMG housing and is in fluid communication with one of the housing vents. The vent valve is configured to vent gases between the interior and exterior of the CMG housing when the CMG is placed in a thermal vacuum chamber and the pressure is reduced during testing, or as the CMG travels out of the earth&#39;s atmosphere and reaches orbit.  
         [0005]     Although the conventional vent valve is safe and effective, it suffers certain drawbacks. First, because the vent valve is single-acting, it typically needs to be re-seated to operate. To re-seat the vent valve, the vent valve is manually re-seated. In some configurations, the vent valve includes a valve cover that is removed. However, when the CMG is incorporated into a relatively large spacecraft the vent valve may be inaccessible, which can make manual removal of the valve cover and re-seating of the vent valve problematic. Additionally, the sealing force in the conventional vent valve may be relatively low. As a result, small leaks may develop over time, increasing the need for valve maintenance and causing reduced-efficiency CMG operation during ground testing.  
         [0006]     Accordingly, a valve capable of passive re-seating is desirable. In addition, a valve having a higher sealing force and that requires minimal valve maintenance is also desirable. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     A valve is provided for use on a control moment gyroscope (CMG) housing having an interior. The valve includes a valve housing, a valve element, and bellows. The valve housing is configured to couple to the CMG housing and includes an inner surface that defines a cavity, an outer surface, and an opening extending therebetween. The valve element is disposed at least partially within the valve housing cavity and movable between a closed position, in which fluid is prevented from flowing through the valve housing opening, and an open position, in which fluid may flow through the valve housing opening. The bellows is disposed within the valve housing and coupled to the valve element. The bellows has an internal chamber and is configured to selectively move the valve element between the closed and open position in response to a differential pressure between the bellows internal chamber and the valve housing cavity. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and  
         [0009]      FIG. 1  is a perspective view of an exemplary control moment gyroscope, according to the present invention, may be used;  
         [0010]      FIG. 2  is a schematic of an exemplary valve that may be used with the control moment gyroscope depicted in  FIG. 1 ;  
         [0011]      FIG. 3  is schematic of another exemplary valve that may be used with the control moment gyroscope depicted in  FIG. 1 ;  
         [0012]      FIG. 4  is a schematic of yet another exemplary valve that may be used with the control moment gyroscope depicted in  FIG. 1 ; and  
         [0013]      FIG. 5  is a schematic of still yet another exemplary valve that may be used with the control moment gyroscope depicted in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]     The following detailed description of the invention is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description of the invention. The invention may be used in conjunction with any system having a first environment where the system may be exposed to a second environment, wherein it may be desirable to selectively separate the first and second environments. Such systems include, but are not limited to evacuated components that may be used on a spacecraft, aircraft, watercraft, or any other type of craft.  
         [0015]      FIG. 1  illustrates an exemplary control moment gyroscope (CMG)  100  that is mounted on a spacecraft  102 . The CMG  100  includes an inner gimbal assembly  104 , a torque motor assembly  108 , and slip ring assembly  110 . The torque motor assembly  108  is coupled to one end of the inner gimbal assembly  104  and generally includes a gimbal shaft  106  to which a gimbal motor  114  is coupled. The gimbal motor  114  supplies power to rotate the inner gimbal assembly  104  about a gimbal axis. The rate at which the inner gimbal assembly  104  spins may be monitored by a rate sensor (not shown) that optionally may be coupled to the torque motor assembly  108 . The slip ring assembly  110  is coupled to the other end of the inner gimbal assembly  104  and includes a slip rings  107  for transferring electrical power to a spin motor  118 , which will be described further below.  
         [0016]     The inner gimbal assembly  104  includes a rotor  116  disposed therein which is coupled to the spin motor  118 , which configured to provide power to the rotor  116  causing it to spin about a predetermined rotor axis at a predetermined angular rate, such as, for example, up to 6000 rpm. The inner gimbal assembly  104  is substantially sealed to separate its internal environment from the ambient environment  98  surrounding the CMG  100 . To decrease the effects of, among other causes, windage drag and spin bearing drag, the sum of which may affect the spin rate of the rotor  114 , the internal environment of the inner gimbal assembly  104  is preferably evacuated to substantially 0 psi. The inner gimbal assembly  104  includes at least one assembly opening  142  formed-thereon to selectively vent its internal contents to the ambient environment  98  when ambient pressure and the interior of the inner gimbal assembly  104  are at a predetermined pressure differential, such as when the spacecraft  102  approaches or is in a vacuum environment. To control the venting, at least one valve  120 , which is in fluid communication with the assembly opening  142 , is coupled to the inner gimbal assembly  104 . The valve  120 , which will now be discussed in detail, is configured to passively control the venting.  
         [0017]     Turning to  FIG. 2 , an exemplary embodiment of the valve  120  is provided. Generally, the valve  120  includes a valve housing  122 , a valve seat  124 , a valve element  126 , and sealed bellows  128 . The valve housing  122  has sidewalls  130  and a top wall  132 ; however, it will be appreciated that in other embodiments, the valve housing  122  may have more or fewer walls. At least one vent aperture  138  is formed through the valve housing  122  to vent the cavity  136  to an ambient environment  98  surrounding the valve housing  122 . The vent aperture  138  may be formed into one or more of the sidewalls  130 , the top wall  132 , or both. The valve housing  122  may be constructed of any one of numerous materials capable of withstanding the pressure and temperature changes to which it is exposed. Such materials include, for example, ferrous/non-ferrous metals or plastics.  
         [0018]     The valve seat  124  is coupled to the valve housing  122  to define a cavity  136  therein. In one exemplary embodiment, the valve seat  124  is a wall of the valve housing  122 . The valve seat  124  includes a valve opening  140  and a seal element  134 . The valve opening  140  is formed through the valve seat  124  and is in fluid communication with the assembly opening  142 . The seal element  134  is coupled proximate the valve opening  140 . In this embodiment, the seal element  134  is coupled to the bottom surface of the valve seat  124 ; however, it will be appreciated that the seal element  134  may be located anywhere in the valve  120  so as to provide a contact surface against which the valve element  126  seats, and thereby seal the internal environment of the inner gimbal assembly  104  from the ambient environment  98 . The seal element  134  may have any one of a number of different sealing configurations, such as an O-ring, gasket, gland, or taper seat seal or any other type of sealing mechanism.  
         [0019]     The valve element  126  is partially disposed within the valve housing  122  and is moveable between a closed position and an open position. In the closed position, the valve element  126  contacts the valve seat  124  and/or sealing element  134  and prevents fluid flow through the valve opening  140 . Conversely, in the open position, the valve element  126  does not contact the valve seat  124  and/or sealing element  134  allowing fluid to flow through the valve opening  140 . The valve element  126 , depicted in  FIG. 2 , includes a valve shaft  146 , and a first and a second plate  148   a ,  148   b  that are each coupled to either end of the valve shaft  146 . The valve shaft  146  is slidably disposed within the valve opening  140 , while the first plate  148   a  is disposed within the cavity  136  and the second plate  148   b  is outside of the valve housing  122 . The second plate  148   b  is configured to contact the valve seat  124 . As will be appreciated by those with skill in the art, the valve element  126  may have any one of numerous other configurations that are capable of blocking and unblocking the valve opening  140 , including, but not limited to, a plunger configuration.  
         [0020]     The bellows  128  is coupled to the valve element  126  and has a sealed interior chamber  129  that is pressurized to a predetermined pressure magnitude, for example, between 0 psi and 20 psi. Thus, the bellows  128  will expand and contract in response to a pressure differential between the bellows interior chamber  129  and the valve housing cavity  136 . Because the bellows  128  is coupled to the valve element  126 , the expansion and contraction of the bellows  128  moves the valve element  126  between the open and closed position, respectively. For example, in the embodiment illustrated in  FIG. 2 , if the bellows interior chamber  129  is evacuated and the valve  120  is exposed to a pressure that is greater than 0 psi, the bellows  128  contracts and pulls the valve shaft  146  upward until the second plate  148   b  contacts and seats against the valve seat  124 . Consequently, the valve  120  is in a closed position. If the bellows  128  is exposed to a pressure of substantially 0 psi, such as when it is in space, the bellows  128  freely expands so that the second plate  148   b  is not in contact with the sealing mechanism  142  and the valve  120  is in an open position.  
         [0021]     In addition to being coupled to the valve element  126 , the bellows  128  preferably is coupled to the valve housing  122  or another part of the valve  120  to provide a reference point from which the bellows  128  expands and contracts. In the embodiment depicted in  FIG. 2 , the bellows  128  is disposed within the cavity  136  and can be any one of numerous suitable sizes so that the bellows  128  may be housed within the valve housing  122 . In some embodiments, one or more bellows  128  may be sized slightly smaller than the valve housing  122 . In such case, one or more shims  144  is placed between the bellows  128  and housing  122  in order to obtain a sufficient amount of force against the valve seat  124  and/or pressure to open the valve  120 . In another exemplary embodiment, the bellows  128  is positioned outside of the valve housing  122 .  
         [0022]     It will be appreciated that the embodiment depicted in  FIG. 2  is merely exemplary of any one of numerous configurations that can implement the above-discussed invention. For example,  FIGS. 3-5  depict various other exemplary embodiments, each of which will now be discussed.  
         [0023]     Turning first to  FIG. 3 , another exemplary embodiment of the valve  120  is illustrated. Similar to the previous embodiment, the bellows  128  is disposed within the valve housing  122  and is coupled to the valve element  126 . However, the valve  120  here includes several different features. For instance, the valve  120  includes an intermediate interface  150  that is threadedly engaged with the assembly opening  142 . The intermediate interface  150  further includes a passage  152  formed therethrough that provides fluid communication between the valve opening  140  and the interior of the inner gimbal assembly  104 .  
         [0024]     Similar to the previous embodiment in that it includes a valve shaft  146  that is slidably disposed within the valve opening  140 . However, it differs in that it includes only a single valve plate  148  that is coupled to one end of the valve shaft  146 . Additionally, the valve shaft  146  is beveled so that the other end has a diameter that is larger than the valve seat opening  140 . The valve seat  124  is coupled to the bottom of the valve housing  122  and seal element  134  is disposed within the valve opening  140 . As with the previous embodiment, a shim  144  is positioned between the bellows  128  and top wall  132  of the housing  122 . Though, as before, the valve  120  could be implemented without the shim  140 . To provide further control of the length of expansion of the bellows  128 , the valve plate  148  also includes a bellows stop  152  coupled thereto to provide a separation space between the valve plate  148  and the valve seat  124  such that the fluid can flow freely through the valve seat opening  140  to vent the cavity  136 .  
         [0025]     Similar to the previous embodiment, the bellows interior chamber  129  is either evacuated or pressurized. When the valve  120  is exposed to a pressure that is greater than the pressure of the bellows interior chamber  129 , the bellows  128  contracts and pulls the valve shaft  146  upward until the shaft  146  contacts and seats against the seal element  128  to close the valve  120 . When the valve  120  is exposed to pressure less than the pressure of the bellows interior chamber  129 , the bellows  128  expands so that the shaft  146  is not in contact with the seal element  128  and the valve  120  is open. The bellows stop  152  maintains an open path between the valve plate  148  and the valve seat  124 .  
         [0026]      FIG. 4  illustrates another exemplary embodiment of the valve  120 . Unlike the previous embodiment, the bellows  128  is located outside of the valve housing  122 . The valve housing  122  has an extension  158 . The bellows  128  is at least partially attached to the extension  158  and at least partially coupled to an L-shaped arm  160 . The arm  160  is configured to move the valve element  126  between an open and a closed position in response to the expansion and contraction of the bellows  128 , as will be discussed in detail further below.  
         [0027]     The valve element  126  includes a valve shaft  146 , and a valve plate  148 . The valve shaft  146  is slidably disposed within a shaft opening  164  formed in the top wall  132  of the housing  122  and is coupled on either end to the arm  160  and valve plate  148 . The valve plate  148  is disposed within the housing cavity  136  proximate the seal element  134  and moves vertically in response to the movement of the arm  160  and valve shaft  146 . In this exemplary embodiment, the seal element  134  is coupled to the intermediate interface  150 , which is disposed within the assembly opening  142  and threadedly coupled to the walls of the opening  142 . The intermediate interface  150  includes a passage  152  that provides fluid communication between the valve cavity  136  and the interior of the inner gimbal assembly  104 .  
         [0028]     The bellows  128  is evacuated or pressurized so that when the bellows  128  is exposed to a pressure that is greater than the pressure of the bellows interior chamber  129 , the bellows  128  contracts and pulls the arm  160  inward to cause the lever  162  to push the valve element  126  toward the valve seat  124  and contact the valve seat opening  140 . When the pressure becomes substantially less than the pressure of the bellows interior chamber  129 , the bellows  128  expands and pushes the arm  160  outward. This movement causes the attached lever  162  to lift the valve element  126  away from the valve seat  126  so that the valve  120  is open.  
         [0029]     Still yet another exemplary embodiment is depicted in  FIG. 5 . Similar to the embodiments depicted in  FIGS. 3 and 4 , the valve housing  122  has sidewalls  130  and a top wall  132 . The valve seat  124  is coupled to the valve housing  122  to define a cavity  136 . The valve element  126  has an elongated valve shaft  146  and a first and a second plate  148   a ,  148   b  coupled to each end of the shaft  146 . Positioned between the first and second plates  148   a ,  148   b  are the bellows  128   a ,  128   b . The bellows  128   a ,  128   b  are each at least partially coupled to the top wall  132  and to the first plate  148   a . Although two bellows  128   a ,  128   b . are shown in this embodiment, it will be appreciated that fewer or more bellows may be employed as well. The second plate  148   b  is disposed within the cavity  136 . The valve seat  124  includes a seal element  134  coupled to its top surface proximate the valve seat opening  140 .  
         [0030]     In this embodiment, the bellows  128   a ,  128   b  are evacuated or pressurized and when the valve  120  is exposed to a pressure greater than the internal pressure of the bellows  128   a ,  128   b , the bellows  128   a ,  128   b  both contract and pull the first plate  148   a  downward. As a result, the shaft  146  slides downward through the shaft opening  164  causing the second plate  148   b  to contact the seal element  134 . As the valve  120  is exposed to a pressure less than the internal pressure of the bellows  128   a ,  128   b , the bellows  128   a ,  128   b  expand and push the first plate  148   b  and shaft  146  upward to cause the second plate  148   b  to move away from the seal element  134 .  
         [0031]     While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.