Abstract:
A small gas turbine engine with a bearing cooling and lubricating passage arrangement for a high speed rotor shaft. The engine includes a bypass fan and a compressor. The rotor shaft includes a central passage extending through the entire shaft, and where the rotor shaft is supported by a forward bearing and a rearward bearing. Cooling air for the bearings is diverted from the bypass air and is channeled through the bearings. Fuel is added to the cooling air at a location upstream of the bearing to provide lubrication. The cooling air and lubricating fuel passes through the bearings and into the rotating central shaft, and is then forced to flow toward a radial passage located adjacent to the combustor. The fuel is collected on the central shaft surface and forced out the radial passage and into the combustor. The cooling air continuous out from the central shaft to be mixed with the engine exhaust.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit to an earlier filed Provisional application 60/753,321 filed on Dec. 21, 2005 and entitled SMALL GAS TURBINE ENGINE WITH LUBRICATED BEARINGS. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a small or micro gas turbine engine, and more specifically to a fuel and air delivery structure that also is used to cool and lubricate the bearings. 
     2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98 
     Small or micro gas turbine engines are used for powering small unmanned air vehicles such as drones and missiles. In the early stages of development, larger gas turbine engines where simply scaled down to the required small size that would fit within the very limited space in these UAVs, or unmanned air vehicles. However, gas turbine engines are not readily scaled down in an effective cost proportional basis and a thrust proportional basis. As the gas turbine engine is reduced in size, the smaller sized rotors must operate at higher rotational speeds in order to achieve adequate performance levels. To take a regular gas turbine engine used in a typical modern jet would require the turbine parts to be reduced in size while operating the rotor shaft at much higher rotational speeds. At these high rotational speeds, the original designed parts such as the rotor shaft and the bearings would not be able to withstand the higher speeds. Rotor dynamics would cause the original design rotor shaft to vibrate so much that the shaft would explode. Also, the bearings would operate at speeds above the design speed. The bearings would burn up or vibrate so much that they would explode as well. Thus, it is an entirely new design challenge to take a regular gas turbine engine and scale it down to the size that would operate effectively in a small gas turbine engine powered vehicle. 
     The prior art gas turbine engine of Brooks et al, U.S. Pat. No. 5,526,640 issued on Jun. 18, 1996 discloses a small gas turbine engine with a rotor supported by bearings, and in which air and fuel is mixed and then passed through the bearings in order to cool the bearings prior to being burned in the combustor. A fuel slinger propels the air/fuel mixture into the combustor. A separate pump is used to enhance the slinger delivery of the fuel. 
     U.S. Pat. No. 6,925,812 B2 issued to Condevaux et al on Aug. 9, 2005 entitled ROTARY INJECTOR discloses a turbine engine with a rotary injector supported by ball bearings, and which in the FIG. 14b embodiment (of this patent) discloses that the forward and rearward roller bearings are respectively cooled by spraying pressurized liquid fuel in the first and second cylindrical grooves from respective orifices in a sleeve surrounding the central shaft between the pair of roller bearings (see column 7, lines 9-25). 
     U.S. Pat. No. 3,932,988 issued to Beaufrere on Jan. 20, 1976 entitled FUEL SLINGER COMBUSTOR discloses a fuel slinger combustor used in a gas turbine engine in which helical grooves are oriented on a rotary shaft to move fuel from grooves inwardly to grooves as the shaft rotates during operation of the engine and the fuel so moved is supplied via grooves to the radial bores of the slinger injector. 
     There is a need in the prior art for a small gas turbine engine with improved fuel efficiency in order to increase the hover time of the UAV. There is also a need in the prior art to decrease the overall size of the engine in order that the engine can be fitted in a small space. There is also a need in the prior art to reduce the cost of the small gas turbine engine without reducing the performance. 
     It is an object of the present invention to provide for a small gas turbine engine with bearings capable of being cooled such that a small engine is capable of operating at the required high speeds. 
     It is another object of the present invention to provide for a small gas turbine engine with lubricated bearings that is more efficient than the prior art engines. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a small gas turbine engine that includes a rotor supported by bearings, and a fuel delivery system that delivers fuel in a passage that passes through the bearings in order to cool and to lubricate the bearings. During times of low fuel consumption by the combustor, a fuel regulating valve is used to increase fuel flow through the bearings in order to provide adequate lubrication. The fuel to lubricate the bearings is channeled through a hollow rotor shaft, and in some embodiments is then discharged through a slinger in the shaft into the combustor. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  shows a cross section view of a gas turbine engine having bearings lubricated by fuel that is directed into the hollow shaft before discharging into the combustor through a slinger. 
         FIG. 2  shows a cross section view of a gas turbine engine of  FIG. 1  in which a dual burn zone is supplied with fuel from dual slingers located in the rotor shaft. 
         FIG. 3  shows a cross section view of a gas turbine engine in which the fuel slinger is located in the compressor rotor. 
         FIG. 4  shows a cross section view of a gas turbine engine with a separate fuel supply for the combustor and the bearing lubrication flow paths. 
         FIG. 5  shows a cross section view of a gas turbine engine with a spiral shaped groove formed on an inner surface of the hollow shaft used to direct liquid fuel along the shaft and into the combustor. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A small gas turbine engine  10  is shown in  FIG. 1  and includes a rotor shaft  20  with a hollow passage  22  through the shaft, the rotor shaft being supported for rotation by a front bearing  52  and a rear bearing  51 , the rotor  20  having a centrifugal compressor  30  for discharging compressed air into a diffuser  32 . The rotor shaft  20  also having a turbine  40  with a turbine blade  42  to produce rotation from impact of a hot gas stream from a combustor  50 . A guide vane  43  directs the hot gas stream from the combustor  50  into the turbine blade  42  for improved efficiency. The guide vane  43  includes a cooling air passage  44  to provide cooling for the guide vane  43 . A fuel supply means  61  and  62  is used to deliver fuel to the compressed air that leads into the combustor  50 . A fan  70  is connected to a front end of the rotor shaft  22  and produces a bypass fan flow  72  that flows around the engine for propulsion of an aircraft, and in which some of the bypass air  72  is used as bearing cooling air. 
     The gas turbine engine  10  of the present invention operates as follows. The compressor  30  delivers compressed air into the diffuser  32 . From the diffuser  32 , the compressed air branches off into one of three paths. A first path passes over a front portion of the combustor  50  and enters the combustor from the inside at a point about midway through the combustor  50 . A second path passes compressed air from the diffuser  32  over a rear portion of the combustor  50 , passing through the cooling passage  44  in the guide vane  43  and into the combustor at the midpoint in which the compressed air from the first path enters the combustor  50 . A third path for compressed air is from the fan  70  that produces bypass flow  72  around the engine core (compressor, combustor and turbine) that produces propulsion for an aircraft. Some of the bypass flow  72  is diverted to flow through the forward bearing  52  for the third path of compressed air. A fourth path for compressed air is diverting some of the bypass flow  72  in the aft end to flow through the aft bearing  51 . Fuel supply means  61  and  62  injects fuel into the third and fourth compressed air flows before the compressed air flows through the two bearings  51  and  52 . 
     Compressed air from the diffuser and fuel from the fuel supply means  51  and  52  passes through the front and rear bearings  52  and  51 , and is then directed through passage in the rotor shaft  20  into the central passage  22  toward a slinger passage  24  located in the rotor shaft  20 . An inner surface  25  of the hollow passage  22  is slanted toward the slinger passage  24  in order to promote the formation of liquid fuel on the inner surface  25  of the central passage  22  such that the fuel will pass into the slinger passage  24 . The high speed rotation of the rotor shaft  20  will sling the fuel through the slinger passage  24  at a high pressure and sling the fuel into the combustor  50  at the opening therein. The air and fuel through the bearings and central passage is due to the compressed air exiting the diffuser  32 . A high pressure differential is established between the diffuser  32  output and the central passage  22  in the rotor shaft  20 . This pressure differential forces the compressed air and the fuel through the bearings and the passages through the shaft  20 . The rotation of the shaft  20 —along with the slanted surfaces  25  along the shaft  20 —promotes the flow of liquid fuel toward the slinger passage  24 . The compressed air that passes into the central passage  22  with the fuel is directed out the rear of the central passage  22  to be discharged with the exhaust gas from the turbine  40 . The fuel delivery means  61  and  62  can be a restrictor, a variable flow valve device, or a pulse width modulated valve connected to a source of fuel such as the fuel tank of the vehicle. 
     Another embodiment of the present invention is shown in  FIG. 2 . The  FIG. 2  embodiment takes the  FIG. 1  embodiment and includes an additional fuel slinger passage in the rotor shaft  20 . The combustor  50  of this embodiment includes a primary combustion chamber located upstream in the combustor, and a secondary combustion chamber located downstream in the combustor  50 . A forward slinger passage  24  slings fuel into the upstream or primary combustion chamber, and a rearward slinger passage  27  slings fuel into the downstream or secondary combustor chamber. The compressed air from the diffuser  32  and compressed air a fuel supply means passes through the bearings  51  and  52  and into the central passage  22  as in the first embodiment of  FIG. 1 . slanted surfaces  25  on the inside of the central passage  22  promotes buildup of fuel on the inner surface  25 , and directs the fuel toward the passages  24  and  27  to be slung into the combustor  50  from the high rotational speed of the rotor shaft  20 . 
     An additional embodiment of the gas turbine engine  10  is shown in  FIG. 3 , in which the slinger passages  24  and  27  of the previous embodiments are replaced with a passage  28  through the compressor  30 . The outlet of compressor passage  28  is at a higher radius than the passages  24  and  27  in the rotor shaft  20 , and therefore the fuel is raised to a higher pressure before entering the compressed air leading into the combustor  50 . The inner surface  25  of the central passage  22  is still slanted to promote the flow of fuel along the inner wall  25  and into the slinger passage  28 . A seal member  53  is used to prevent mixing of the compressed air and fuel mixture entering the combustor  50  with compressed air passing through the guide vane  43 . the compressed air passing through the guide vane  43  passes into the combustor  50  through a plurality of holes spaced around the combustor  50 , and mixes with the compressed air and fuel than enters upstream of the seal. 
     The operation of the engine of  FIG. 3  is the same as the operation of the engine in  FIGS. 1 and 2 . Compressed air from the diffuser  32  promotes the flow of air through the bearings  51  and  52  and into the passages through the rotor shaft  20  and through the central passage  22 . Fuel is injected into the compressed air upstream of the bearings in order to lubricate and cool the bearings. High speed rotation of the shaft  20  promotes a slinging effect of the fuel through the slinger passage  28  and into the compressed air leading into the combustor  50 . 
       FIG. 4  shows a different embodiment of the present invention that any of the first three embodiments. Compressed air is delivered to the combustor  50  through upstream and downstream passages around the front portion of the combustor  50  and rear portion of the combustor  50 , entering the combustor as in the first embodiment of  FIG. 1 . However, fuel delivered to the engine in this embodiment ( FIG. 4 ) is delivered into the combustor  50  without premixing with the compressed air. A variable displacement pump  65  is used to regulate a flow of fuel into the engine  10  and through the bearings  51  and  52 . A fuel tank  66  contains a reservoir of fuel for delivery to the pump  65 . A control valve  64  is used to regulate a supply of fuel into the bearings. 
     Operation of the engine of  FIG. 4  is as follows. Compressed air is delivered into the combustor  50  from the diffuser  32  at an opening on the inner surface of the combustor  50  after the air passes around the upstream portion and downstream portion of the combustor  50 . Fuel is delivered into the combustor  50  by the variable displacement pump  65 . The regulation of the fuel into the combustor  50  is controlled by regulating the flow from the pump  65 . 
     A control valve  64  is used to deliver fuel from the pump  65  into the central passage  22  through the rotor shaft  20 , and through the bearings. Compressed air from the diffuser  32  is diverted into a passage through the upstream bearings  52 , where fuel is injected through the control valve  64 . Fuel and compressed air is then directed into the central passage  22  and flows toward the downstream bearing  51 , where the fuel is delivered into the bearings through a passage in the rotor shaft  20 . The compressed air is separated from the fuel due to rotation of the rotor shaft  20 . The separated air passing out the rear of the central passage  22  to be mixed with the exhaust gas stream from the turbine  40 . Fuel passing through the rear bearing  51  is collected and delivered back into the fuel tank  66 . In this  FIG. 4  embodiment, the engine power is regulated by varying the flow of fuel from the pump  65  into the combustor, while the flow of fuel through the bearings  51  and  52  is regulated by the control valve  64 . The inner wall  27  of the central passage  22  is slanted toward the rear bearings  51  to promote the flow of liquid fuel in that direction. 
     Regulation of the fuel flow is required to ensure proper lubrication of the bearings. When the engine  10  is operating at high load, enough fuel is used to pass through the bearings and into the combustor to lubricate and cool the bearings. However, during cruising speed, when the fuel flow into the combustor  50  is low, not enough fuel would flow through the bearings. Thus, when the engine  10  operates at cruising speed and fuel flow into the combustor is minimum, fuel flow into the bearings through the control valve  64  can remain high by maintaining the flow through the control valve  64 . because the pump outlet pressure is high (about 200 psia), there is enough pressure head in the fuel to allow for the control valve  64  to regulate fuel flow from low flow to high flow rates. 
       FIG. 5  shows an embodiment of the present invention similar to the engine in  FIG. 1 . Instead of the inner surface  25  and  26  of the hollow passage  22  being slanted toward the slinger passage  24  for fuel delivery to the combustor  50  of the  FIG. 1  embodiment, the  FIG. 5  embodiment makes use of spiral channels  28  and  29  formed on the inner surfaces  25  and  26 . The hollow passage  22  has a constant diameter. The spiral channels are angled such that rotation of the rotor  20  with force the fuel along the spiral passages toward the slinger passage  24 . Spiral passage  28  will move the fuel from forward bearing  52  toward the slinger passage  24  during rotation of the rotor  20 , while spiral channel  29  will move fuel from rearward bearing  51  toward the slinger passage  24 . The spiral channels  28  and  29  are shown in  FIG. 5  with exaggerated angles for description purposes. In the actual engine, because the rotation speed of the rotor is above 100,000 rpms, the spiral channels will be angled more like the grooves found in a gun barrel. The angle of the spiral channels with respect to the longitudinal axis of the rotor will be on the order of a few degrees. As the fuel and air pass through the bearings and into the central passage  22  within the rotor  20 , the fuel will form along the inner surfaces  25  and  26  of the central passage  22  and the spiral channels  28  and  29  will move the fuel toward the slinger passage  24  due to rotation of the rotor. The angle of the spiral passages  28  and  29  will depend upon the rotation speed of the rotor and the viscosity of the liquid fuel. Air passing through the central passage  22  will continue to flow out the rear of the rotor  20  as in other embodiments. 
     A slight variation of the  FIG. 5  embodiment is shown in  FIG. 6 . An additional fuel injection means is used in the  FIG. 6  embodiment. A third fuel delivery means  63  is used to inject fuel directly into the combustor  50 . The first and second fuel delivery means  61  and  62  as used in the  FIG. 5  embodiment are still used to delivery fuel in droplet form to the compressed air from the bypass fan  70  that is directed through the bearings  51  and  52  for lubrication. The fuel that passes through the bearings is also delivered to the combustor through the slinger passage  24 . Thus, fuel is delivered into the combustor from the slinger passage  24  and from direct injection into the combustor from the third fuel delivery means  63 .