Abstract:
A dampening system for a miniature high-speed turbojet engine provides single or multiple resilient mounting which includes a seal with an at least partially encapsulated spring for forward and aft bearings which mount a rotor shaft. The self-induced first engine order of the rotating rotor shaft is transmitted through the forward and aft bearing and is then absorbed in the resilient mountings. Dependable seal and vibration reduction is thereby provided irrespective of long term storage.

Description:
The present application is a Continuation-in-Part of, and claims priority to, U.S. patent application Ser. No. 10/453,747, filed Jun. 3, 2003, and entitled DAMPING SYSTEM FOR AN EXPENDABLE GAS TURBINE ENGINE. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to a miniature gas turbine engine and, more particularly, to a rotor shaft vibration dampening system which provides dependable sealing and vibration reduction irrespective of long term storage. 
   Miniature gas turbine or turbojet engines (100 lbf thrust and smaller) are often utilized in single usage applications such as reconnaissance drones, cruise missiles, decoy and other weapon applications, including air-launched and ground-launched weapon systems. The use of such an engine greatly extends the range of the weapon in comparison to the more conventional solid fuel rocket engine. Miniature gas turbine engines are difficult to fabricate economically for general expendable usage in large numbers. 
   To achieve economically feasible extended range expendable propulsion sources for such applications, it is necessary that the gas turbine engines be manufactured relatively inexpensively yet provide a high degree of reliability and efficiency. One component that greatly affects performance yet is rather complicated to manufacture is the rotating component, such as the rotor system which typically includes a shaft mounted turbine and compressor wheel. 
   Rotor systems of miniature gas turbine engines typically operate at greater than 100,000 rpm. Such high rotations in the relatively small miniature gas turbine engines may generate high first engine order (1 st  EO) vibration characteristics that can be damaging to the engine, its vehicle, and/or the payload thereof. 
   Vibration dampening devices are commonly utilized in relatively large turbomachinery and conventional gas turbine engines. These applications typically operate at relatively lower speeds of below 100,000 rpm.  
   As the relatively large applications provide minimal packaging restrictions and are not designed to be expendable, relatively complicated and expensive dampening systems are feasible. As such, conventional dampening devices are impractical and cost prohibitive for miniature gas turbine engines. Heretofore, miniature gas turbine engines avoided most vibration damping systems altogether. 
   Moreover, known dampening devices typically require periodic maintenance to assure reliability. Such maintenance may be difficult and time consuming particularly for vehicles which are required to be stored for unknown periods prior to usage. 
   Accordingly, it is desirable to provide a reliable, inexpensive, and uncomplicated dampening system for an expendable gas turbine engine in which long term storage is of minimal concern. 
   SUMMARY OF THE INVENTION 
   The dampening system according to the present invention for a miniature gas turbine engine provides single or multiple a rotary seal resilient mounting for the forward and aft shaft bearings. Self-induced first engine order vibrations of the rotating rotor shaft are transmitted through the forward and aft bearing&#39;s inner race, common balls and outer race and then absorbed in the resilient mountings. Dependable seal and vibration reduction is thereby provided irrespective of long term storage. 
   The present invention therefore provides a reliable, inexpensive, and uncomplicated dampening system for an expendable gas turbine engine. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows: 
       FIG. 1  is a general perspective view an exemplary vehicle embodiment for use with the present invention;  
       FIG. 2  is a schematic view of a gas turbine engine having a dampening system according to the present invention; 
       FIG. 3  is an expanded view of the dampening system of  FIG. 2 ; 
       FIG. 4  is a graphical representation of the reduction in high first engine order (1 st  EO) vibration characteristics achieved by a dampening system according to the present invention; 
       FIG. 5  is an expanded view of another dampening system; and 
       FIG. 6  is an expanded perspective view of a resilient member of  FIG. 5 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  illustrates a general schematic view of a vehicle  100  including a miniature gas turbine engine  10  according to the present invention. The vehicle  100  includes a body  102  and one or more aerodynamic surfaces  104 . The engine  10  is coupled to, or within, the body  102 . An intake  106  provides air to the engine  10 , and an exhaust pipe  108  exhausts the thrust therefrom. The engine  10  of the invention may also be used in other single usage and reusable applications such as reconnaissance drones, cruise missiles, decoys and other weapon and non-weapon applications. 
   Referring to  FIG. 2 , the miniature gas turbine engine  10  generally includes a housing  14 , a rotor shaft  16  rotationally mounted to a forward bearing  18  and an aft bearing  20 , a combustion system  21  and an exhaust pipe (nozzle)  22 . The rotor shaft  16  rotates about a longitudinal axis X although other forms of rotors, such as a monorotor configuration, would also benefit from the present invention. In the illustrated rotor configuration, a rotor system  24  includes compressor blades  26  facing forward toward an inlet  28  and turbine blades  30  facing rearward toward the exhaust  22  to define a turbine wheel. The forwardly extending shaft  16  is received in the bearings  18 ,  20  and is preferably coupled to a fuel pump (illustrated schematically at  32 ) to provide fuel to an annular combustor liner  34  through a fuel manifold  36 . 
   Referring to  FIG. 3 , an expanded view of the rotor system  24  is illustrated. The forward bearing  18  and the aft bearing  20  are installed on the shaft  16 . The forward bearing  18 , and aft bearing  20 , are separated by a bearing spacer  38  and are held in place by a rotor  nut  40 . The forward bearing  18  is pre-loaded with a preload spring  42  and bearing preload spacer  44 . It should be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit from the instant invention. 
   The forward and aft bearings  18 ,  20  are preferably in contact with a dampening system  46  located between each bearing  18 , 20  and the housing  14  or other static structure. That is, the bearings  18 ,  20  are closely mounted within a bore  49  in the housing  14  but are supported upon the dampening system  46 . It should be understood that other bearing mounting static structure will also benefit from the present invention. 
   Preferably, each dampening system  46  includes one or more grooves  48  within the housing  14  which receives a resilient member  50  such as O-rings and/or elastomeric strips. It should be understood that other elastomeric, non-metallic, plastic, teflon, composite or other spring type resilient members will benefit from the present invention. The resilient members  50  provide for vibration absorption or dampening of the shaft  16  1 st  EO characteristics ( FIG. 4 ). 
   Alternatively or in addition, an annular sleeve  52  includes the grooves  48  and the resilient member  50 . The annular sleeve  52  is particularly preferred to provide a single mounting surface for a forward bearing  18  which is often located at an interface I between multiple engine housing portions such as the housing  14  and a forward inlet cap  54 . The annular sleeve  52  thereby bridges the interface I to provide a stable and consistent mounting location for the bearing  18 . 
   Referring to  FIG. 5 , the forward and aft bearings  18 ,  20  are preferably in contact with another dampening system  46 ′ located between each bearing  18 , 20  and the housing  14  or other static structure. That is, the bearings  18 ,  20  are closely mounted within a bore  49  in the housing  14  but are supported upon the dampening system  46 ′. It should be understood that other bearing mounting static structure will also benefit from the present invention. 
   Preferably, each dampening system  46 ′ includes one or more grooves  48 ′ within the housing  14  which receives a resilient member  50 ′ such as a rotary seal  56  such as the rotary seal manufactured by BAL SEAL ENGINEERING COMPANY INC., of Foothill Ranch, Calif. The rotary seal  56  generally includes a non-organic plastic C-seal  58  with an at least  partially encapsulated stainless steel spring  60  (also illustrated in  FIG. 6 ). The resilient members  50 ′ likewise provide for vibration absorption or dampening of the shaft  16  1 st  EO characteristics ( FIG. 4 ) but with a long term storage capability. 
   Referring to  FIG. 6 , the coils of the stainless steel spring  60  are canted within the plastic C-seal  58 . The canted coils provide a near-constant load even after normal seal wear and despite changes in temperature or variation in compression. Dependable seal operation and reliability is thereby provided irrespective of long term storage. Such a long term reliability is particularly appropriate for the life of the for a vehicle  100  ( FIG. 1 ) which may be subjected to long term storage of an unknown period prior to usage. 
   The foregoing description is exemplary rather than defined by the limitations within. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.