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 of the valve&#39;s inlet and thruster nozzle and the pressure behind the piston. A pivotable flapper valve regulates this pressure difference. When a change in thrust is required a force is applied to the flapper causing a change in this pressure difference which causes the piston to move until the desired thrust level is obtained.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 09/501,887 filed on Feb. 10, 2000 now abandoned. 
    
    
     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 valves 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 hot gas is dependent upon the exhaust area of these valves, and is thus subject to the ripple creating an uncertainty in pressure level. 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 force driven proportionally controlled thruster valve capable of providing intermediate levels of thrust as a function of a force input into the valve. 
     Another object of the present invention is to provide a method for continuously controlling the output of a thruster valve. 
     The present invention accomplishes these objects by providing a thruster valve having an inlet passage receiving a flow of propulsive gas and a thrust nozzle for generating thrust by expelling the gas. A poppet piston slideably mounted in a sleeve is disposed between the inlet passage and the thrust nozzle so as to control the flow of gas therebetween. Behind the piston is an actuator chamber. A change in the difference between the pressure in the thrust nozzle, the pressure in the inlet annulus, and the pressure in the actuator chamber causes the piston to move. This change is brought about by a change in a force balance on a flapper pivotally mounted in a flapper chamber in the valve. The force balance comprises a force input from a solenoid onto the flapper counterbalanced by the spring force of a resilient member, a nozzle pressure force and an actuation pressure force. Actuation pressure is set by a variable inlet restriction, effected by piston motion, and a variable outlet restriction, effected by flapper motion. Importantly, there is a known relationship between the input force and thrust out the thrust nozzle. When a change in thrust is required, the force input moves the flapper changing the pressure ratio across the piston which causes the piston to move. Because this pressure ratio is tied to the thrust level, once the piston reaches the position that results in the desired thrust, the force balance will be restored on the flapper and the piston will stop moving. 
     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 
     FIG. 1 is a cross sectional schematic of the hot gas proportional thruster valve contemplated by the present invention. 
     FIG. 2 is a cross sectional schematic of an alternative embodiment of the hot gas proportional thruster valve contemplated by the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, 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 a metering section  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 a two graphite ring seals  22 . The head  24  of the piston  20  is conical and extends from the open end of the cavity  14  towards the metering section  18  of the nozzle  16 . Disposed between the metering section  18  and the open end of the cavity  14  is an annulus  26  that surrounds the conical 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 conical head  24  seals against seat  30  to a fully open position where the hot gas flows unrestricted from the annulus  26  to the metering section  18 . 
     A second passage  32  places the annulus  26  in fluid communication with the cavity  14  at a point between the two sealing rings  22 . Disposed in the second passage  32  is a filter  34  which may not be necessary depending on the cleanliness of the hot gas. In the preferred embodiment, the passage  32  and filter  34  are disposed in the housing  12 . Alternatively, they can be disposed in the poppet piston  20  as shown in FIG. 2. A metering orifice or restrictive pneumatic slot  36  places the portion of the cavity  14  between the sealing rings  22  in fluid communication with the actuator chamber  38  which is bounded axially by the back surface of the piston  20  and the back wall of the cavity  14 . The metering orifice  36  can have a fixed area or can be configured as a needle. Importantly, the metering orifice  36  is sized and positioned so that as the piston  20  strokes away from the seat  30 , the orifice opens. The gas flowing through the metering orifice  36  experiences a pressure drop so that the gas pressure in the actuator chamber  38 , represented by Pc, is less than Ps. A third passage  40  places the actuator chamber  38  in fluid communication with a flapper chamber  42  and a fourth passage  44  places the nozzle  16  in fluid communication with the flapper chamber  42 . The exit  41  of passage  40  is a nozzle and is in an opposed relationship across the flapper chamber  42  with exit  45  of passage  44 . The exit  45  is enlarged to receive a pressure sensitive sealing device such as a close tolerance ball  46 . The ball  46  being moveable to allow metering of exit  45 . Alternatives to the ball  46 , which allows tolerable leakage, are pistons or bellows. The inlet of passage  44  is downstream of the inlet  18  so the pressure in the passage is represented by Pn. 
     Both ends of the flapper chamber  42  vent to ambient. The pressure at these ends being represented by Pv. A flapper  60  is rotatably mounted and sealed at its axial center of rotation in the flapper chamber  42  by a conventional ball and socket  56 . One end of the flapper  60  is disposed between the exits  41  and  45 . The opposite end of the flapper  60  is disposed between a spring  62  and a solenoid force motor  64 . 
     Still referring to FIG. 1, in the proportional hot gas thruster valve  10 , there is a force balance on the flapper  60  under steady state conditions. As a result, there is a known proportional relationship between the thrust exiting the nozzle  16  and the force applied by the solenoid to the flapper  60 . This is because thrust is proportional to the nozzle plenum pressure Pn. This pressure is fed back to the flapper  60  through passage  44  where it applies a force that reacts against the force of the solenoid motor  64 . Meanwhile, a small fraction of the hot gas flows through passage  32  and then through metering orifice  36  into the actuator chamber  38  and then through passage  40  where it also applies a force to the flapper  60 . Thus a force balance is set up between the solenoid, the spring, Pn and Pcs. When a change in thrust is required, a control unit, not shown, sends the appropriate signal to the solenoid and the solenoid applies the appropriate force to the flapper  60  and upsets the balance. For example, if more thrust is needed, the solenoid will push down on the flapper forcing it away from nozzle  41  increasing its area which results in the venting of the actuator chamber  38  and a decrease in Pc. As Pc falls, the poppet piston  20  is pushed away from the seat  30  opening the metering section  18 . As more hot gas now flows through the nozzle  16 , thrust increase. As thrust increases, Pn increases and is communicated through passage  44 , which in turn causes an increase in the force applied to the flapper via ball  46 . Thus in turn causes the flapper  60  to rotate towards exit  41  reducing exit  41 &#39;s nozzle area. As a result, with restriction  36  opening in accordance with motion of poppet  20  and the reduced area of exit  41 , Pc returns to its original pressure, the poppet piston  20  stops moving and a pressure balance is restored To reduce thrust the process is reversed. Thus, the piston  20  can be moved continuously between a fully open position to a closed position depending on the amount of thrust desired. Importantly, with continuous movement, the abrupt movements of the prior art on/off valves are eliminated. 
     FIG. 2 shows an alternative embodiment  10   a  of the thrust valve  10 . Many of the components of this alternate embodiment are the same as in the preferred embodiment and are represented by the same reference numerals. The following is a description of the differences. In the thrust valve  10   a,  a pulse width modulated solenoid  64   a  is used instead of a force motor solenoid  64 . The force motor solenoid  64  provides better fidelity and purely proportional control but is larger and heavier and slower in response than solenoid  64   a.  When the pulse width modulated solenoid  64   a  is used, its pulse frequency is set high enough so as not to cause oscillation of the piston  20 . Another difference is that the passage  32  and filter  34  are disposed within the piston  20  instead of in the housing  12 . Also, the exits  41  and  45  both face the same side of the flapper  60   a  but on opposite ends. The flapper  60   a  is “T” shaped, with the base  61   a  disposed between the solenoid  64   a  and the spring  62 . As a result of this different shape, the ball and socket  56   a  is slightly modified, in a manner familiar to those skilled in the art, form of the ball and socket  56 . The operation of the valve  10   a  is the same as for the valve  10  as discussed previously. It should be apparent that the location of the solenoid relative to the flapper determines whether an increase in force results in an increase in thrust or a decrease in thrust. That is, referring to FIG. 2, an increase force cause the flapper to move away from the exit  41  which reduces the actuator chamber pressure which results in increased thrust. However, one could swap the location of the solenoid  64   a  and spring  62  in which case an increase in force will cause the flapper to close exit  41 , which will increase the pressure in the actuator chamber causing the piston to move toward the nozzle and decrease thrust. 
     Various modifications and alterations of the above described sealing apparatus 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.