Abstract:
A compact pulse-rocket engine assembly comprising an elongated substantially cylindrical housing containing an axially extending substantially cylindrical combustion chamber which terminates at one end in a nozzle means. Within the housing at the opposite end of the combustion chamber are a pair of charging chambers. Intermediate the charging chambers and the combustion chambers are a pair of valve means which are parallel and linked together for ensuring that the valves operate in unison.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention broadly relates to compact pulse-firing pocket engine assemblies. More particularly, the invention relates to such an engine which utilizes a pair of cross-linked parallel piston valves. The present invention is particularly adapted for spin stabilization and guidance of small vehicles. 
     2. Description of the Prior Art 
     Both liquid and solid fuel rocket engines have been known for many years. The liquid or fluid fueled rocket engines have provided the primary propulsion systems for virtually all of the world&#39;s exploration of space. Indeed, in most programs which requires high performance and low weight, the liquid or fluid fueled rockets have been preferred over the solid rockets. A particular advantage of liquid rockets is that they may be started and stopped substantially as desired whereas solid rockets are traditionally &#34;one-shot&#34; devices. A disadvantage of the liquid rockets, however, is that they are inherently more complex than solid rockets. The complexity of the liquid rockets is a result of the requirements for some means of providing propellants at pressure such as by pressurization of the storage tanks, a positive expulsion mechanism, pumps or the like. In addition, the liquid fueled rockets require sophisticated valves and elaborate plumbing for delivery of the fuel and regulation of its flow. Obviously, these factors add to the weight and bulk of the liquid rocket propulsion systems. 
     In addition to the main propulsion engines which are used to launch vehicles, there is a need for smaller reaction or rocket engines which are capable of intermittent firing for vehicle attitude adjustment, course changes, stabilization and the like. An example of a valve for such applications, is described in U.S. Pat. No. 3,479,818. The patent discloses an apparatus and method for feeding pulsating fluid propellant rocket engines. The method utilizes an energy-operated pump and an elastic storing member such as a spring. The method comprises storing pump operating energy by using the operating pressure of the rocket engine during each high pressure phase of operation and utilizing the stored energy during the low pressure phase of operation to drive the energy-operated pump and to direct the propellant into the combustion chamber so that the cycle is repeated. A disadvantage of this apparatus and method is that it utilizes a spring-operated pump device which is not only heavy, but lacks a rapid pulse response time. Further, the apparatus chamber pressure is limited by the spring utlized. 
     More recently, there has been suggested in U.S. Pat. No. 4,258,546 a rocket propulsion system which utilizes vehicles&#39; spin forces to charge a specific amount of propellant through a differential area piston to create high chamber pressure. A disadvantage of this system, however, is that it utilizes a plurality of valves adding to its weight and complexity and more importantly, is not amenable to scaling down to small sizes. Accordingly, there exists a need for a small, compact engine suitable for use with, for example, a so-called kinetic energy weapon. Typically such weapons will require no more than 10 to 20 pounds of thrust for pulse durations of a few milliseconds to provide the desired spin stabilization, course correction, or both. 
     SUMMARY OF THE INVENTION 
     The disadvantages of the prior art are overcome with the present invention and a pulse rocket engine assembly is provided which is compact, reliable, light in weight and amenable to scaling down to small sizes, for example, to provide thrust in the 10 to 20 pounds force range. In addition, the assembly of the present invention is useful with propellants which are either hypergolic or which require an igniter. Accordingly, it will be seen that the rocket engine assembly of the present invention is particularly suitable and uniquely adaptable for spin stabilization and course correction of small vehicles such as kinetic energy devices. 
     The present invention provides a compact pulse-rocket engine assembly which is contained within an elongated substantially cylindrical housing. The housing contains and defines an axially extending substantially cylindrical combustion chamber and includes a nozzle means also located within the housing and in fluid communication with and adjacent to an end of the combustion chamber. The housing also contains a pair of charging chambers located adjacent an opposite end of the combustion chambers. One of the charging chambers being for receiving fuel and the other chambers being for receiving an oxidizer. 
     Also contained within said housing are a pair of valve means, one valve means being located intermediate one of said charging chambers and said combustion chamber. One of the valve means provides for the injection of a fuel into the combustion zone and the other of the valve means provides for the injection of an oxidizer into the combustion zone. Each of the valve means includes a hollow valve body slideably mounted within the housing, the valve body having fluid passageways therein to provide fluid communication between one of the charging chambers and the combustion chamber. Each valve body has an end adjacent the combustion chamber defining a differential area piston. A valve stop is located within the hollow body for controlling the flow of fluid from the charging chamber through the passageways in said hollow body to the combustion chamber. A biasing means is provided for resiliently urging the valve stop to a closed position to prohibit fluid flow from the charging chamber through the valve body to the combustion chamber. 
     The engine assembly further includes an actuation means for overcoming the biasing means and moving the valve stop to a position which permits fluid flow from the charging chamber through the passageways in the valve body to the combustion chamber. In addition, there is provided a linkage means interconnecting each of the valve means for ensuring that the valve bodies move in unison. The engine assembly also includes means for introducing an oxidizer to one of the charging chambers and means for introducing the fuel to the other of the charging chambers. 
     It is an object of the invention to provide a rocket engine assembly suitable for guidance or stabilization of a kinetic energy missile. 
     It is another object of the invention to provide a rocket engine assembly which is readily scalable to a small size. 
     It is still another object of the invention to provide a compact pulse rocket engine assembly which will reliably inject propellants in a desired ratio. 
     It is still another object of the invention to provide a compact rocket engine assembly which can utilize a propellant feed pressure substantially less than the combustion chamber operating pressure. 
     These and other objects of the invention will be more readily apparent from the following description of the drawings and preferred embodiment of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a rocket engine assembly constructed in accordance with the present invention; and 
     FIGS. 2a and 2b are cross-sectional views of the rocket engine assembly taken along the lines 2--2 showing the valve means at the beginning and end respectively of a firing pulse. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, therein is shown a particularly preferred embodiment of the rocket engine assembly 10 of the present invention. It is a particular advantage of rocket engine assembly 10 that it may be fabricated in a small compact size. For example, in accordance with the following teaching of the invention, it is possible to build such an engine which will fit within an overall envelope of approximately 21/4 inches long by 0.67 inches in diameter, and which would produce a thrust of approximately 13 lbs. 
     Engine assembly 10 includes an outer housing 12 having an outlet end 14 for discharge of hot combustion gases and an injection end 16. Injection end 16 contains the propellant valves which will be described in more detail later and further includes inlet means 18 and 20 for the introduction of propellants such as an oxidizer and a fuel. There also is provided an inlet 22 for the introduction of a pressurized fluid, typically a gas, for actuating the propellant valves and initiating a combustion pulse. 
     The details of the invention are best seen in FIGS. 2a and 2b which are cross-sectional views showing the engine assembly just prior to initiation of a combustion pulse and at the end of a combusion pulse, respectively. As seen in FIGS. 2a and 2b the exhaust end 14 of housing 12 contains a combustion chamber 24 which is defined by a liner 26. Liner 26 will typically be formed from a material which is capable of withstanding the high temperature of the hot combustion gases such as a quartz phenolic. At the exhaust end of combustion chamber 24 there is provided an insert 28 which defines a converging/diverging nozzle to accelerate the hot gases produced and impart reactive forces to rocket engine assembly 10. Typically insert 28 is formed from a carbide, such as SiC to withstand the temperature and erosive effects of the high velocity hot gases. 
     Adjacent the opposite end of combustion chamber 24 and located within injector end 16 of housing 12 there are provided two substantially identical propellant valve assemblies 30 and 32. Each of valve asseblies 30 and 32 includes a hollow valve body assembly 34 terminating at one end adjacent combustion chamber 24 in a differential area piston 36. The piston will have a larger surface area facing the combustion chamber than that facing a charging chamber to be described later. Generally the area facing the combustion chamber will be from about 1.5 to 2 times that facing the charging chamber. Each of valve bodies 34 has an opposite end 38 interconnected or mechanically linked by a pin member 40. Located within hollow valve body assembly 34 is an elongated valve stop member 42 which is provided at one end with a valve stop portion 44 and at the opposite with a piston portion 46. Located adjacent piston portion 46 and confined within hollow valve body 34 is a coil spring 48. The two parts 36 and 38 which form valve body assembly 34 and elongated valve stop member 42 are interconnected by pin members 50. 
     Each of inlet means 18 and 20 includes an attachment member 52 which is affixed to a portion of housing 12 and confines a ball member 54 and spring 56 whose function will be described later. Valve stop member 42 is provided with an opening 51 which is larger than pin member 50 to permit some axial movement of stop member 42 within valve body assembly 34. 
     Referring now to FIG. 2a in particular, therein is depicted the condition of the rocket engine assembly prior to initiating a firing pulse. Propellants are supplied to inlet means 18 and 20, for example, a fuel to 18 and an oxidizer to 20. The propellants preferably are hypergolic and will ignite spontaneously upon injection into combustion chamber 24. The propellants are introduced under sufficient pressure, to overcome spring 56 such that they flow past ball 54 into a charging chamber 58. From charging chamber 58, the propellants flow through an opening 60 in valve body assembly 34 and into a cavity 62 surrounding the valve stop portion 44 of valve stop member 42. Propellant flow from cavity 62 is prevented by valve stop portion 44 and a seal member 64. As illustrated, charging chamber 58 also is provided with a pair of axially, spaced-apart seal members 66 and 68. Typically, each of the seal members will comprise an O ring seal. 
     To initiate a combustion pulse, a pressurized fluid, typically a gas, is introduced through inlet 22 where it flows through a passage 70 to exert pressure on piston portion 46 of valve stop member 42. The fluid is introduced under sufficient pressure to overcome the biasing effect of coil spring 48 and force valve stop member 42 away from combustion chamber 24 whereby the propellants in charging chamber 58 and cavity 62 flow through an injection port 72 located in differential area piston 36. 
     Injection ports 72 are angled such that the propellants impinge upon one another in combustion chamber 24, typcially, at an angle α of about 60°. Ignition of the propellants creates pressure within combustion chamber 24 forcing valve assemblies 30 and 32 rearwardly increasing the pressure of the propellants contained in charging cavity 58. Since the surface area of differential area piston 36 facing the combustion chamber is substantially greater than that facing the charging chamber, the pressure within the charging chamber will be substantially greater than the pressure in the combustion chamber. The burning of the propellants will accelerate the rearward movement of differential area piston 36 and thus continue the flow of oxidizer and fuel until the rearward limit of movement is reached. As will be seen in FIGS. 2a and 2b the axial movement or stroke of valve assemblies 30 and 32 is limited by enagement of flange portions 76 and 78 on valve body assembly 34 with inwardly projecting abutment portions 80 and 82 of injector end 16 of housing 12. 
     When that limit is reached, propellants will no longer be forced to flow into combustion chamber 24, as a result, the combustion will cease. Further, as valve assemblies 30 and 32 move rearwardly, the pneumatic or fluid pressure acting on piston portion 46 will be vented, for example, through an opening 74 in housing 12. Venting of the fluid pressure permits spring 48 to move valve stop member 42 forwardly sealing off injection passages 72 once combustion ceases. Upon cessation of combustion, propellants may once again be delivered to charging chamber 58 to drive valve body assembly forward in preparation for another firing pulse. 
     Numerous variations and modifications to the invention may be made without departing from the scope of the invention. Accordingly, it should be clearly understood that the form of the present invention described above and shown in the accompanying drawing, are illustrative only and are not intended to limit its scope.