Patent Publication Number: US-2019195129-A1

Title: Fuel lubricated foil bearing

Description:
BACKGROUND 
     Engines, such as those which power aircraft and industrial equipment, may employ a compressor to compress air that is drawn into the engine and a turbine to capture energy associated with the combustion of a fuel-air mixture. Bearings are used in an engine to interface a first (e.g., static) structure and a second (e.g., movable) structure. 
     Hydrodynamic bearings are well known and have been used effectively as supports for rotating machinery, including high speed applications. The term hydrodynamic bearing, as used herein, defines a class of fluid-film bearings which has its surfaces separated by a thin layer of either liquid or gas, the film being established and the pressure generated therein by the relative motion between the bearing surfaces. This is distinguished from bearings of the hydrostatic type which require a feed of pressurized fluid from an external source. Various embodiments of hydrodynamic bearings are disclosed in the U.S. Pat. No. 4,247,155. The contents of U.S. Pat. No. 4,247,155 are incorporated herein by reference. 
     In many applications, oil is used as a lubricating fluid for a bearing. An oil system typically includes tanks, pumps, heat exchangers/coolers, deaerators, and other components to support the lubrication of bearings with oil. U.S. patent application publication number 2014/0076661 describes and illustrates various lubrication systems and components that may be used. The contents of U.S. patent application publication number 2014/0076661 are incorporated herein by reference. 
     The components of an oil lubrication system represent a penalty in terms of, e.g., the complexity/cost that they add to the engine. Additionally, the components serve as a potential source of unreliability of the engine, e.g., one or more of the components may become inoperable. Additionally, the components contribute weight to the engine; this additional weight may lead to inefficiencies in some applications (e.g., aerospace applications). 
     In some applications, a gas (e.g., air) is used as a lubricating fluid for a bearing. The use of a gas as the lubricating fluid is a cleaner, more environmentally-friendly implementation relative to oil. However, gases have a lower viscosity than oil such that for the same working fluid pressure, gas-lubricated bearings will have a lower/reduced load capacity relative to oil-lubricated bearings. This lower load capacity may make the use of gas-lubricated bearings impractical in some applications. 
     BRIEF SUMMARY 
     The following presents a simplified summary in order to provide a basic understanding of some aspects of the disclosure. The summary is not an extensive overview of the disclosure. It is neither intended to identify key or critical elements of the disclosure nor to delineate the scope of the disclosure. The following summary merely presents some concepts of the disclosure in a simplified form as a prelude to the description below. 
     Aspects of the disclosure are directed to a bearing assembly for an engine, comprising: a first structure, a second structure that is movable relative to the first structure, and a foil membrane disposed between the first structure and the second structure, where the foil membrane includes at least one perforation that supplies liquid fuel in a region between the foil membrane and the second structure, where the liquid fuel is combusted by the engine. In some embodiments, the second structure is rotatable relative to the first structure. In some embodiments, the first structure includes a case of the engine, and the second structure includes a shaft of the engine. In some embodiments, the bearing assembly further comprises a plurality of spring pads coupled to the first structure, where the spring pads are disposed between the first structure and the foil membrane. 
     Aspects of the disclosure are directed to a system for an engine, comprising: a fuel tank, at least one pump that provides liquid fuel from the fuel tank to a nozzle of a combustion section of the engine, and a bearing assembly that includes a first structure, a second structure that is movable relative to the first structure, and a membrane disposed between the first structure and the second structure, where the membrane includes a plurality of perforations that receive liquid fuel from the at least one pump and supply the received liquid fuel in a region between the membrane and the second structure. In some embodiments, the at least one pump includes a first pump and a second pump. In some embodiments, the first pump provides liquid fuel from the fuel tank to the nozzle, and where the second pump provides liquid fuel from the fuel tank to the bearing assembly. In some embodiments, the bearing assembly receives liquid fuel from the at least one fuel pump via a first channel, and where the bearing assembly returns liquid fuel to at least one of the fuel tank or the at least one pump via a second channel and a filter coupled to the at least one of the fuel tank or the at least one pump. In some embodiments, the at least one pump includes a first pump that supplies liquid fuel to the nozzle and liquid fuel to the bearing assembly. In some embodiments, the system further comprises a first channel that couples the first pump and the nozzle, and a second channel that couples the first pump and the bearing assembly. In some embodiments, the second channel is tapped off of the first channel, and the first channel is connected to the first pump. In some embodiments, the second structure is rotatable relative to the first structure. In some embodiments, the first structure includes a case of the engine, and the second structure includes a shaft of the engine. In some embodiments, the system further comprises a plurality of spring pads coupled to the first structure, where the spring pads are disposed between the first structure and the membrane. 
     Aspects of the disclosure are directed to an engine comprising: a case, a shaft, an inlet, a compressor section that compresses air received at the inlet, a combustor section that combusts a mixture of compressed air provided by the compressor section and fuel, a turbine section that extracts energy from combusted mixture to drive the compressor section via a rotation of the shaft, where the shaft couples the compressor section and the turbine section, and a bearing assembly that supports the shaft, the bearing assembly including a membrane disposed between the shaft and the case, where the membrane includes at least one perforation that supplies liquid fuel to a region between the membrane and the shaft. In some embodiments, the engine is free of oil. In some embodiments, the combustor section includes at least one fuel nozzle that supplies the liquid fuel included in the mixture. In some embodiments, the engine further comprises a fuel tank, and a fuel pump that receives liquid fuel from the fuel tank and supplies the received liquid fuel to the at least one fuel nozzle and the bearing assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is illustrated by way of example and not limited in the accompanying figures in which like reference numerals indicate similar elements. The figures are not necessarily drawn to scale unless explicitly indicated otherwise. 
         FIG. 1  is a side cutaway illustration of an axial flow turbojet engine. 
         FIG. 1A  is a side cutaway illustration of a centrifugal/radial flow turbojet engine. 
         FIG. 2  illustrates an axial bearing assembly in accordance with this disclosure. 
         FIG. 2A  illustrates a radial bearing assembly in accordance with this disclosure. 
         FIGS. 3 and 3A  illustrate fuel systems in accordance with this disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     It is noted that various connections are set forth between elements in the following description and in the drawings (the contents of which are included in this disclosure by way of reference). It is noted that these connections are general and, unless specified otherwise, may be direct or indirect and that this specification is not intended to be limiting in this respect. A coupling between two or more entities may refer to a direct connection or an indirect connection. An indirect connection may incorporate one or more intervening entities. 
     In accordance with various aspects of the disclosure, apparatuses, systems, and methods are described for applying a lubricant to one or more bearings of an engine. In some embodiments, the lubricant may include a fuel that is combusted by the engine. 
     Aspects of the disclosure may be applied in connection with an engine.  FIG. 1  is a side cutaway illustration of an axial flow turbojet engine  100 . The engine  100  may extend along a longitudinal axial centerline  104  between an upstream/forward airflow inlet  108  and a downstream/aft airflow exhaust nozzle  112 . The engine  100  may include a compressor section  116 , a combustor section  120 , and a turbine section  124 . 
     During operation, air may enter the engine  100  through the inlet  108  where it may be compressed by the compressor section  116 . The compressed air may be provided to the combustor section  120 . In the combustor section  120 , the compressed air may be mixed with fuel provided by one or more fuel nozzles  120   a  and ignited to power the engine  100 . The output of the combustor section  120  may be provided to the turbine section  124 . The turbine section  124  may extract energy from the output of the combustor section  120  to drive the compressor section  116  via a rotation of a shaft  128  that couples (e.g., mechanically couples) the compressor section  116  and the turbine section  124 . The combusted fuel-air mixture may be exhausted via the nozzle  112 . 
       FIG. 1A  is a side cutaway illustration of centrifugal/radial flow turbojet engine  100 ′. The engine  100 ′ may include an inlet  108 ′, a compressor section  116 ′, a combustor section  120 ′, a turbine section  124 ′, and an exhaust nozzle  112 ′. The engine  100 ′ (and its associated sections/devices/components) may be similar to the engine  100 . The engine  100 ′ may differ from the engine  100  in that the compressor section  116 ′ may direct the incoming airflow through the inlet  108 ′ in a circumferential direction and/or in a radial (outboard) direction (relative to the engine centerline/axis  104 ′). This airflow may be redirected by, e.g., an engine case  134 ′ downstream of the compressor section  116 ′ so as to be more parallel to the axis  104 ′. 
       FIGS. 1 and 1A  represent possible configurations for an engine. Aspects of the disclosure may be applied in connection with other environments, including additional configurations for engines. For example, aspects of the disclosure may be applied in connection with turbofan engines, turboprops, turboshafts, etc. 
     Hardware of an engine may be supported by one or more bearings/bearing assemblies. For example,  FIG. 2  illustrates an embodiment of a bearing assembly  200  in accordance with aspects of this disclosure. The bearing assembly  200  may include a first structure  12  and a second structure  14 . The second structure  14  may be movable (e.g., rotatable) relative to the first structure  12 . The first structure  12  may be a stationary structure. In some embodiments, the first structure  12  may include a housing/case (e.g., the case  134 ′ of  FIG. 1A ). In some embodiments, the second structure  14  may include a shaft (e.g., the shaft  128 / 128 ′ of  FIG. 1 / 1 A). 
     The bearing assembly  200  may include a compliant foil membrane  16  supported by one or more resilient spring pads  18 . The spring pads  18  may be coupled to the first structure  12 , such that the spring pads  18  are disposed between the first structure  12  and the foil membrane  16 . The foil membrane  16  may include one or more thin, foil-like sheets of metal (or other suitable material) that are compliant, i.e., a sheet of metal whose thickness relative to its lateral dimensions is sufficiently small to allow local bending/deflection. 
     As shown, the foil membrane  16  may include perforations  20 . The perforations  20  may be arrayed in one or more lines as shown in  FIG. 2 . The perforations  20  may extend across some, or even an entirety of, a dimension of the foil membrane  16 . The perforations  20  may accommodate a load during engine operation. For example, the perforations  20  may represent relative weakness in the foil membrane  16  to accommodate a deflection of the second structure  14  relative to the first structure  12  during engine operation. 
     The perforations  20  may provide a passageway through which fluid may flow uniformly to an area/region between the foil  16  and movable member  14  in order to increase (e.g., maximize) pressure maintenance by efficiently replacing any fluid that may be displaced/circulated. The perforations  20  may be positioned above the space between successive spring pads  18  to enable a deflection of the foil membrane  16  and an unobstructed flow of fluid through the perforations  20 . The spring pads  18  may provide the foil membrane  16  with resilient support. 
       FIG. 2A  illustrates a bearing assembly  250  in accordance with aspects of this disclosure. The bearing assembly  250  may include a first structure  262  and a second structure  264 . The second structure  264  may be movable (e.g., rotatable) relative to the first structure  262 . The first structure  262  may be a stationary structure. In some embodiments, the first structure  262  may include a housing/case (e.g., a bearing housing). In some embodiments, the second structure  264  may include a shaft/journal. 
     Disposed between the first structure  262  and the second structure  264  may be a foil structure/membrane. In particular, the foil membrane may include a first (e.g., top) foil  276  and a second foil  278 . The second foil  278 , which may be referred to as a bump foil, may provide a compliant support structure for the bearing assembly  250 . For example, the second foil  278  may accommodate a deflection of the second structure  264  relative to the first structure  262 . The foil membrane may provide fluid (e.g., liquid fuel) in an area/region between the foil membrane and the second structure  264  via, e.g., one or more perforations (e.g., perforations  20  of  FIG. 2 ). 
     Referring to  FIG. 3 , a fuel system  300  is shown. The system  300  may include a fuel tank  304 . The fuel tank  304  may serve as a reservoir/storage of fuel (e.g., liquid fuel). The fuel tank may include one or more fuel pumps, such as for example a first fuel pump  310   a  and a second fuel pump  310   b . While the fuel pumps  310   a  and  310   b  are shown as being included in the fuel tank  304 , one or both of the pumps  310   a  and  310   b  may be separate components (relative to the fuel tank  304 ) in some embodiments. 
     The first fuel pump  310   a  may provide fuel to one or more fuel nozzles, such as for example a fuel nozzle  320   a , via one or more fuel pipes/channels  330   a . The fuel nozzle  320   a  may correspond to the fuel nozzle  120   a  of  FIG. 1 . The fuel nozzle  320   a , which may be included in a combustor section of an engine (e.g., combustor section  120 / 120 ′ of  FIG. 1 / 1 A), may provide fuel that it receives from the first fuel pump  310   a  for purposes of combustion. 
     The second fuel pump  310   b  may provide fuel to a bearing assembly  320   b  via one or more fuel channels  330   b - 1 . The bearing assembly  320   b  may correspond to the bearing assembly  200  of  FIG. 2  or the bearing assembly  250  of  FIG. 2A . The fuel provided by the fuel pump  310   b  to the bearing assembly  320   b  via the channel  330   b - 1  may be used to form a film of fuel between two or more components of the bearing assembly  320   b  (e.g., between the foil membrane  16  and the second structure  14  of  FIG. 2 ; in  FIG. 2A  between one or both of the first foil  276  and the second foil  278  on the one hand and the second structure  264  on the other hand). A closed loop/circuit may be formed between the fuel tank  304  and the bearing assembly  320   b , such that the fuel that is supplied via the channel  330   b - 1  may be returned to the fuel tank  304  and/or the second fuel pump  310   b  via a return channel  330   b - 2 . One or more filters  340  may be included to filter the fuel that is conveyed via the return channel  330   b - 2  prior to (re)introducing the fuel to, e.g., the fuel tank  304 . 
     As shown in  FIG. 3 , the system  300  may provide separate channels/lanes in terms of fuel used by the fuel nozzle  320   a  relative to fuel used by the bearing assembly  320   b . Such separation may be useful for purposes of reliability, maintenance (e.g., trouble-shooting), etc., due to the segregation/isolation that is obtained. 
       FIG. 3A  illustrates an embodiment of a system  300 ′ that at least partially combines the lanes. For example, the channels  330   a  and  330   b - 1  may be combined in the system  300 ′. For example, in the system  300 ′ fuel provided to the bearing assembly  320   b  via the channel  330   b - 1  may be obtained from the channel  330   a  (e.g., the channel  330   b - 1  may be tapped from the channel  330   a , and the channel  330   a  may be connected to a fuel pump  310 ). Whereas  FIG. 3  illustrates the use of two fuel pumps  310   a  and  310   b , in  FIG. 3A  a single fuel pump  310  may be used. Relative to the system  300 , the system  300 ′ may be lighter (e.g., may weigh less) due to the inclusion of less fuel pumps and/or a sharing of lane/channel resources. 
     The system  300  and/or the system  300 ′ may be included as part of an engine (e.g., the engine  100 / 100 ′ of  FIG. 1 / 1 A). 
     Aspects of the disclosure may utilize fuel (e.g., liquid fuel) as a lubricating fluid for a bearing (e.g., a foil bearing). The use of fuel as the lubricating fluid may reduce (or even completely eliminate) components that are used in a conventional lubrication system (e.g., a conventional oil lubrication system). For example, in some embodiments an engine might not include oil; e.g., the engine may be free of oil. Furthermore, the use of fuel as a lubricating fluid may leverage existing hardware (e.g., fuel pumps, fuel tanks, fuel channels, etc.), thereby promoting efficiency (e.g., reducing weight). The use of fuel as a lubricating fluid may increase a load capacity relative to the use of, e.g., air as a lubricating fluid, thereby enabling a larger load (e.g., larger engine hardware) to be accommodated/supported. 
     Aspects of the disclosure have been described in terms of illustrative embodiments thereof. Numerous other embodiments, modifications, and variations within the scope and spirit of the appended claims will occur to persons of ordinary skill in the art from a review of this disclosure. For example, one of ordinary skill in the art will appreciate that the steps described in conjunction with the illustrative figures may be performed in other than the recited order, and that one or more steps illustrated may be optional in accordance with aspects of the disclosure. One or more features described in connection with a first embodiment may be combined with one or more features of one or more additional embodiments.