Abstract:
A force balanced butterfly proportional hot gas valve is configured to receive pressurized gas from a pressurized gas source and to selectively divert the pressurized gas to one or both of two outlet nozzles. The valve includes a primary inlet, a flow passage coupled to the primary inlet, a portion of the flow passage formed into a power jet structure, a diffuser, first and second outlet nozzles coupled to the flow passage, and a butterfly element disposed at least partially within the flow passage and moveable therein to selectively divert gas flow to the first, second or both first and second outlet nozzles simultaneously.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/943,196, filed Jun. 11, 2007. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to propulsion control systems used in aerospace, and more particularly, to a force balanced butterfly proportional hot gas valve for solid propellant control systems. 
       BACKGROUND 
       [0003]    Rockets and missiles are often guided by hot gas thruster valves that expel hot gas generated by the combusting of a solid propellant. Because of the difficulty associated with controlling and containing the hot gas, these valves are generally configured as on/off valve or pulse width modulated valves. Current and prior hot gas proportional valve designs can have problems associated with reliability or responsiveness, and can consume large amounts of electrical power. 
         [0004]    A hot gas fluidic diverter valve, a bi-stable device, has a quick response and is a reliable valve. However, the valve is not a proportional valve. Further, the valve size may grow unacceptably large for thrust levels higher than 100 pound force (lbf). For instance, a 250 lbf thrust-level fluidic diverter valve may require a corresponding disk size of 1.3 inches and a disk housing with an outside diameter (OD) of at least 1.5 inches. Such dimensions do not take into account the fluidic size. Further, the operation of such a fluidic diverter valve may produce undesirable jitter. 
         [0005]    Accordingly, there is a continuing need for a design of a hot gas proportional valve for solid propellant in industry which is more reliable, smaller in size, low in electrical power consumption, and fast in response as compared to current valves, which can handle at least thrust levels ranging from about 50 to greater than 1000 lbf. 
       BRIEF SUMMARY 
       [0006]    In one embodiment, and by way of example only, a force balanced butterfly proportional hot gas valve includes a primary inlet, a flow passage coupled to the primary inlet, a portion of the flow passage formed into a power jet structure, a diffuser, first and second outlet nozzles coupled to the flow passage, and a butterfly valve element disposed at least partially within the flow passage and moveable therein to selectively divert gas flow to the first, second or both first and second outlet nozzles simultaneously. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  illustrates a front cross-sectional view of an exemplary force balanced butterfly proportional hot gas valve; 
           [0008]      FIG. 2  illustrates a side, cross sectional view of an exemplary butterfly element and a portion of an actuation shaft to drive the butterfly element; 
           [0009]      FIG. 3  illustrates simplified schematic view of an exemplary control and actuation system for the proportional hot gas valve depicted in  FIGS. 1 and 2 ; 
           [0010]      FIG. 4  illustrates cross sectional view of an additional exemplary proportional hot gas valve in an additional front end, cutaway view representation; 
           [0011]      FIG. 5  illustrates an additional exemplary embodiment of a forced balanced butterfly proportional hot gas valve; and 
           [0012]      FIG. 6  illustrates a partial cross sectional view of an exemplary valve and motor assembly. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    The following detailed description 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 or the following detailed description. 
         [0014]    A hot gas proportional valve design, which in one embodiment can be termed a “force balanced butterfly proportional hot gas valve,” can be implemented which is more reliable, consumes less electrical power, and has a faster response than presently known valves. The force balanced butterfly design is also a simpler and smaller design as opposed to other hot gas proportional valve designs, such as a so-called “pintle” valve design. The force balanced butterfly design, for example, may use only a 0.55 inch diameter butterfly, in comparison to the larger disk size requirements previously described. In addition, the total size, including the motor and the gear train, may be approximately half of the aforementioned fluidic diverter valve design. Such a size-ratio benefit can become more significant at higher thrust levels. 
         [0015]    The proportional hot gas valve design which will be further described is a planar, two-dimensional, three-wave valve design, having an inlet and two outlets. The inlet can be a converging diverging nozzle. Between the inlet and two outlets is a butterfly at the downstream of the inlet diverging flow passage to divert the flow one way or the other. The flow to either or both sides of the outlets is directly proportional to the butterfly angular position. The angular position of the butterfly is, in one embodiment, driven by an angular torque motor with a Hall-effect position sensor for precision position. The inlet diverging section, a diffuser, is preferably designed to ensure uniform flow velocity across the opening at the upstream of the butterfly for linearity. The moment (in ft-lbf) with respect to pivot point of the butterfly is preferably designed close to zero (0) by properly designing the arm ratio to balance out the pressure differences. Therefore, minimum motor power is needed to drive the valve. A smaller motor size and effective gas dynamic design results in a faster response and smaller overall size. Finally, the design achieves good reliability. There is only one moving part in the valve (the butterfly) which is exposed to the high pressure, hot gas. 
         [0016]      FIG. 1  depicts an exemplary proportional hot gas valve  10  incorporating a force balanced butterfly structure, as seen in a front end view. As described previously, the valve  10  may be a planar, two dimensional, three-way valve  10  with an inlet  12  and two outlets  14  and  16 . A butterfly element  18  is disposed between the outlets  14  and  16 , downstream of the inlet  12 , to selectively divert hot gas flow supplied to the inlet  12 . The butterfly element  18  may divert the flow to either side, or both of the outlets  14 ,  16  depending on the butterfly valve element angular position θ. Angular position θ as depicted in  FIG. 1  is about 45 degrees. Length  20  and  22  give the butterfly  18  a total length (l 1 +l 2 ), which in one embodiment is 0.30 inches (l 2 )+0.25 inches (l 1 ), for a total length of 0.55 inches. It will be appreciated, however, that these dimensions may vary. 
         [0017]    Valve  10  includes a power jet structure  26 . In one embodiment, the power jet structure  26  is about 0.2 inches in width by 0.450 inches in height. Diffuser  27 , the divergent section, makes an angle φ with vertical as shown. In one embodiment, the angle φ is less than seven (7) degrees. An adjustable wedge  30  is integrated into the housing  28  to reduce offseat leakage. Finally, the top of butterfly element  18  rests on a shoulder structure  32  to seal the outlet  16  from pressurized gas. 
         [0018]    Valve  10 , as depicted, is a 250 lbf thrust level proportional hot gas valve design. Again, butterfly valve element  18  is positioned at about 45 degrees. In this position, all of the gas flow is diverted to nozzle  1 , via the outlet  14 . In the depicted embodiment, this result in a net thrust of about +250 lbf. To produce a net thrust of zero, the flow should be split evenly between nozzles  1  (via outlet  14 ) and  2  (via outlet  16 ) and the butterfly should be angled at 0 degrees. For a −250 lbf thrust, all the flow should be diverted to nozzle  2  (again via outlet  16 ), and the butterfly should be angled at −45 degrees. These latter two positions are shown in phantom in  FIG. 1 . Hot gas enters inlet  12  at about 2000 pounds per square inch absolute (psia). Off side leakage (in this case, leakage to nozzle  2  via outlet  16 ) can be designed to be less than three (3) percent. The butterfly  18  arm ratio (l 1 /l 2 ) can be designed to balance out pressure differences. 
         [0019]    Turning to  FIG. 2 , a side, cross sectional view  40  of butterfly element  18 , coupled to a portion of an actuation shaft  42 , is seen. Actuation shaft  42  is further coupled, in at least one particular embodiment, to a drive train gear, an angular torque motor, a Hall-effect position sensor device as will be further described. A DC motor, or a step motor, can also be utilized to replace the angular torque motor. A graphfoil seal  44  seals the actuator shaft  42  from the hot, pressurized gas. In one embodiment, the width  46  preferably can vary between about 0.442 inches to about 0.444 inches. Similarly, the width  48  of a respective cavity in which the butterfly element  18  actuates can vary between about 0.449 inches to about 0.451 inches. As a result, the leakage to nozzle  2  (again via outlet  16 ) can be calculated as: (0.451-0.442)/0.443=0.020 (2.0%). 
         [0020]      FIG. 3  illustrates an exemplary simplified schematic view of an actuation system  50  that may be used to move and control the valve  10 . The actuation system  50  includes a controller  62  responsive to a command  64 , an angular torque motor  58 , a Hall-effect position sensor  60  and two gears (i.e., gears  53 - 56 ). A respective gear ratio can be designed for a required torque. For an accurate angular position control, the angular position of the butterfly is detected by the Hall-effect position sensor  60  and fed back to the controller  62  (via signals  70 ) to compare with the command signal. The controller will then send signals  68  to the angular torque motor  58  to correct the angular position. 
         [0021]      FIG. 4  illustrates an additional exemplary cross sectional view of a valve  10 , including the inlet  12 , the outlets  14  and  16 , the butterfly element  18  coupled to the actuation shaft  42 , the power jet structure  26 , the diffuser  27 , and the shoulders  32  integrated into the wall of the housing  28  to provide for sealing. 
         [0022]      FIG. 5  illustrates an additional embodiment of a valve  10  having a single outlet  14  leading to a nozzle. Outlet  16  is replaced with a portion of housing  28  as shown. The valve  10  depicted in  FIG. 5  demonstrates that an implementation similar to those shown with two outlets  14  and  16 , but only having a single outlet  14 , can be constructed for a particular application. 
         [0023]      FIG. 6  illustrates a partial cross sectional view of an exemplary valve and motor assembly  72 . Valve  10  is coupled to motor  58  via a drive mechanism  74 . Motor  58  can include a two-pole angular torque motor with a Hall-effect position sensor. In one embodiment, the motor  58  may be energized from a DC supply of between 24 to 32 volts, with a corresponding motor resistance of about 9 ohms, and peak power of 81 watts at 28 volts. 
         [0024]    Device  10  is a true proportional valve having smooth operation. Precision angular position is maintained through the use of Hall-effect sensor feedback control. In one embodiment, the expected linear range varies from about 5% to about 95%. The device  10  exhibits little or no jitter. 
         [0025]    Device  10  is small in size. A small motor size is realized with a force balanced butterfly design. The size of the butterfly for a 250 Lbf thrust valve  10  as shown is only about 0.701 inches by 0.45 inches. Compared to a 1.3 inch diameter disk in a 250 lbf fluidic disk diverter valve, the overall size of a butterfly valve is approximately one-third of the size of a fluidic diverter valve. 
         [0026]    Device  10  is responsive. A fast response is achieved with small motor size and the fact that the butterfly  18  need rotate only 50 to 90 degrees from fully closed to a fully open position or vise versa. In one embodiment, the response time is expected to be less than six (6) milliseconds (ms) for a 250 lbf thrust level valve, and less than three (3) ms for a 20 lbf thrust valve. The other hot gas proportional valve designs such as a so-called “pintle” valve design need to make several revolutions to fully close or open the valve therefore is much slower than this invention. 
         [0027]    Finally, device  10  is low in cost. A simple design involves only one moving part exposed to hot gas. Device  10  includes few component counts in its respective design. The design involves no challenging manufacturing accuracies and processes. A smaller size design may use much less rhenium than a comparable fluidic diverter valve design. The angular torque motor with Hall-effect sensor costs only a fraction of an implementation using a DC motor with a commutator. The controller/driver for the angular torque motor is also much simpler and cheaper than the DC motor control system. The other hot gas proportional valve designs such as a so-called “pintle” valve design have to employ a DC motor and a more expensive controller/driver for complicated commutation. 
         [0028]    While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention.