Abstract:
A thruster valve has a continuously positionable piston between a closed position and a maximum open position. The piston moves in response to the difference in pressure between the pressure in the intermediate annulus and the pressure behind the piston. A pivotable flapper valve regulates this pressure difference. When a change in thrust is required, the position of the flapper is changed causing a change in this pressure difference which causes the piston to move until the desired thrust level is obtained.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to gas valves and in particular to proportionally controlled gas thruster valves. 
     BACKGROUND OF THE INVENTION 
     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. A disadvantage to these types of valves is that their abrupt movement, on and off, can cause undesirable vibration and jitter in the vehicle and/or in the vehicle&#39;s guidance system. Another disadvantage is that these valves either provide maximum thrust or zero thrust and do not have the capability of providing a thrust level in between. In addition, the pressure of the solid propellant gas generator is dependent upon the exhaust area of these valves, and is thus subject to the ripple and uncertainty of pressure level which results. A system of proportional valves can provide trimming of the exhaust area, which in turn allows pressure control of the solid propellant motor. This feature can be exploited to also provide mission extension by selectively effecting high and low pressure, or high and low flow, segments of the overall mission. This leads to longer range and higher efficiency of the rocket or missile. On/off valves lack this capacity. 
     Accordingly, a need exists for a hot gas thruster valve that can operate smoothly and also provide intermediate thrust levels and solid propellant gas generator pressure control. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a position driven proportionally controlled thruster valve capable of providing intermediate levels of thrust as a function of a position input to the valve. 
     The present invention accomplishes this object by providing a thruster valve having a thrust nozzle and a piston slideably mounted in the valve. The piston be positionable to close and open the thrust nozzle. A front annulus surrounding the piston receives a hot gas at a pressure Ps. Passages flow a portion of this gas to an intermediate annulus at a pressure Pf and to a back chamber at a pressure Pa. Both the intermediate annulus and the back chamber have a nozzle and corresponding metering slot configured so that in the steady state condition the sum of their flow areas is a constant. A flapper is disposed between those nozzles. Movement of the flapper changes the flow area of the nozzles which changes the pressure differential between Pf and Pa causing the piston to move. As the piston moves the flow areas of the metering slots respectively change. When the system returns to the steady state condition, the piston stops moving. 
     Thus by changing the position of the flapper, the piston can be moved continuously from a closed position to an open position thus eliminating the abrupt movements of the prior art on/off valves and providing proportional control of the thrust produced by the thrust nozzle. 
     These and other objects, features and advantages of the present invention, are specifically set forth in, or will become apparent from, the following detailed description of a preferred embodiment of the invention when read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The sole FIGURE is a cross sectional schematic of the hot gas proportional thruster valve contemplated by the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawing, a proportional hot gas thruster valve is generally denoted by the reference numeral  10 . The valve  10  includes a housing or casing  12  having a cylindrical sleeve or cavity  14  open at one end. The casing  12  also has a nozzle  16  having an inlet  18  in opposed and spaced apart relation to the open end of the cavity  14 . Slideably mounted in the cavity  14  is a poppet piston  20 . The piston  20  is sealed within the sleeve  14  by three graphite ring seals  22   a,    22   b,  and  22   c . The head  24  of the piston  20  is conical and extends from the open end of the cavity  14  towards the inlet  18  of the nozzle  16 . Disposed between the nozzle inlet  18  and the open end of the cavity  14  is an annulus  26  that surrounds the conical or curved head  24  of the piston. A first passage  28  brings the hot gas generated by the combusting of a solid propellant to the annulus  26  at pressure designated as Ps. The piston  20  is moveable between a closed position where head  24  seals against seat  30  to a fully open position where the hot gas flows unrestricted from the annulus  26  to the inlet  18 . 
     A second passage  32  places the annulus  26  in fluid communication with actuator chamber  38  which is bound axially by piston  20  and cavity  14 . Disposed in the second passage  32  is a filter  34 , which may not be necessary depending on the cleanliness of the hot gas, and an orifice  33 . In the preferred embodiment, the passage  32  and filter  34  are disposed in the piston  20 . Alternatively, they can be disposed in the housing  12 . A third passage  40  communicates between passage  32 , downstream of the filter  34  and a second annulus  42  circumscribing the piston  20  and located between seals  22   a  and  22   b . An orifice  43  is disposed in the passage  40 . The pressure in annulus  42  is designated Pf. The pressure in chamber  38  is designated Pa. 
     A first metering orifice or restrictive pneumatic slot  44  places the annulus  42  in fluid communication with a passage  50  that communicates with low pressure region in the nozzle  16 . The metering orifice  44  can have a fixed area or can be configured as a needle. In the preferred embodiment, the orifice  44  is comprised of two slots 180 degrees apart. The gas flowing through the orifice  44  experiences a pressure drop so that the downstream pressure is very low when compared to Pf. This pressure is designated Pn. 
     A second metering orifice or restrictive pneumatic slot  54  places the actuator chamber  38  in fluid communication with passage  50 . The metering orifice  54  is configured like the orifice  44  in that it can be fixed area or a needle. In the preferred embodiment, the orifice  54  is comprised of two slots 180 degrees apart and the gas flowing through the orifice  54  experiences a pressure drop so that the downstream pressure is the same as the pressure downstream pressure of slots  44 , that is Pn. 
     To the side of the piston  20  out of plane with the slots  44  and  54  is a flapper  60 . The flapper  60  is coupled to a solenoid or torque motor  62  and is disposed in a flapper chamber  64  which is part of the housing  12 . On opposite sides of the flapper  60  are a first nozzle  66  in fluid communication with annulus  42  and a second nozzle  68  in fluid communication with the actuator chamber  38 . The flapper  60  is continuously positionable from a first position where nozzle  68  is closed to a second position where the nozzle  66  is closed and to all positions therebetween. The flapper chamber  64  vents to a low pressure area of the nozzle  16  through passage  70 . Passages  71  and  72  port gas from chambers  42  and  38  to flapper nozzles  66  and  68 , respectively. 
     Importantly, in the steady state condition when the piston  20  is not moving the sum of the flow areas of the nozzle  66  and the slot  44  equals a constant and the sum of the flow areas of the nozzle  68  and the slot  54  equals a constant. 
     In operation starting with the nozzle closed, that is head  24  abutting seat  30  and flapper  60  is positioned to close nozzle  68 , a command for thrust is sent to the solenoid or torque motor  62  which moves the flapper  60  away from nozzle  68  and towards nozzle  66 . The flow area of the nozzle  68  increases and the flow area of nozzle  66  decreases, thus upsetting the steady state condition. As a result, Pa decreases and Pf increases and the difference between these pressures causes the piston  20  to move away from the seat  30 . As the piston  20  opens, the slot  44  opens and slot  54  closes. That is the flow area of slot  44  increases and the flow area of slot  54  decreases. When the flow areas of these slots, in combination with nozzle flow areas  66  and  68 , return to the steady state condition, the piston  20  stops moving. Thus there is known relationship between thrust, position of the piston  20 , the position of the flapper  60  and the current into the solenoid or torque motor  62 . Thus, by adjusting the current applied to the torque motor, the piston can be moved continuously from a closed position to an open position thus eliminating the abrupt movements of the prior art on/off valves and providing proportional control of the thrust from the nozzle  16 . 
     Various modifications and alterations of the above described thruster valve will be apparent to those skilled in the art. Accordingly, the foregoing detailed description of the preferred embodiment of the invention should be considered exemplary in nature and not as limiting to the scope and spirit of the invention as set forth in the following claims.