Abstract:
One embodiment of the present invention is a unique gas turbine engine. Another embodiment is a unique gas turbine engine foil bearing system. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for gas turbine engines and gas turbine engine bearing systems. Further embodiments, forms, features, aspects, benefits, and advantages of the present application shall become apparent from the description and figures provided herewith.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of U.S. Provisional Patent Application 61/290,852, filed Dec. 29, 2009, and is incorporated herein by reference. 
     
    
     GOVERNMENT RIGHTS 
       [0002]    The present application was made with United States government support under contract no. N00014-04-D-0068-002, awarded by the United States Navy. The United States government may have certain rights in the present application. 
     
    
     FIELD OF THE INVENTION 
       [0003]    The present invention relates to gas turbine engines, and more particularly, to a gas turbine engine foil bearing system. 
       BACKGROUND 
       [0004]    Foil bearing systems in gas turbine engines remain an area of interest. Some existing systems have various shortcomings, drawbacks, and disadvantages relative to certain applications. Accordingly, there remains a need for further contributions in this area of technology. 
       SUMMARY 
       [0005]    One embodiment of the present invention is a unique gas turbine engine. Another embodiment is a unique gas turbine engine foil bearing system. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for gas turbine engines and gas turbine engine bearing systems. Further embodiments, forms, features, aspects, benefits, and advantages of the present application shall become apparent from the description and figures provided herewith. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
           [0007]      FIG. 1  schematically illustrates a gas turbine engine in accordance with an embodiment of the present invention. 
           [0008]      FIG. 2  schematically illustrates a foil bearing system in accordance with an embodiment of the present invention. 
           [0009]      FIG. 3  depicts a skewed relationship between an axis of rotation of a gas turbine engine rotor and a centerline of a foil bearing. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    For purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nonetheless be understood that no limitation of the scope of the invention is intended by the illustration and description of certain embodiments of the invention. In addition, any alterations and/or modifications of the illustrated and/or described embodiment(s) are contemplated as being within the scope of the present invention. Further, any other applications of the principles of the invention, as illustrated and/or described herein, as would normally occur to one skilled in the art to which the invention pertains, are contemplated as being within the scope of the present invention. 
         [0011]    Referring now to the drawings, and in particular,  FIG. 1 , a non-limiting example of a gas turbine engine  10  in accordance with an embodiment of the present invention is schematically depicted. In one form, gas turbine engine  10  is an axial flow machine, e.g., an air-vehicle power plant. In other embodiments, gas turbine engine  10  may be a radial flow machine or a combination axial-radial flow machine. It will be understood that the present invention is equally applicable to various gas turbine engine configurations, for example, including turbojet engines, turbofan engines, turboprop engines, and turboshaft engines having axial, centrifugal and/or axi-centrifugal compressors and/or turbines. 
         [0012]    In the illustrated embodiment, gas turbine engine  10  includes a compressor  12  having a plurality of blades and vanes  14 , a diffuser  16 , a combustor  18 , a turbine  20  having a plurality of blades and vanes  22 , and a shaft  24  coupling compressor  12  with turbine  20 . Combustor  18  is in fluid communication with compressor  12  and turbine  20 . Turbine  20  is drivingly coupled to compressor  12  via shaft  24 . Turbine  20  is supported radially by a foil bearing system  26 . Although only a single spool is depicted, it will be understood that the present invention is equally applicable to multi-spool engines. The number of stages of blades and vanes  14  of compressor  12 , and the number of blades and vanes  22  of turbine  20  may vary with the application, e.g., the power output requirements of a particular installation of gas turbine engine  10 . In various embodiments, gas turbine engine  10  may include one or more fans, additional compressors and/or additional turbines. 
         [0013]    During the operation of gas turbine engine  10 , air is received at the inlet of compressor  12 . Blades and vanes  14  compress the air received at the inlet of compressor  12 . Diffuser  16  is positioned downstream of compressor  12 . Diffuser  16  reduces the velocity of the pressurized air discharged from compressor  12 . After having been compressed and diffused, the air is discharged from diffuser  16  into combustor  18 . The pressurized air is then mixed with fuel and combusted in combustor  18 . The hot gases exiting combustor  18  are directed into turbine  20 . Turbine  20  extracts energy from the hot gases to, among other things, generate mechanical shaft power to drive compressor  12  via shaft  24 . In one form, shaft  24  is coupled to compressor  12  and turbine  20 . In other embodiments, shaft  24  may be coupled to only one of compressor  12  and turbine  20 , and may be integral with the other. In still other embodiments, shaft  24  may be integral with both compressor  12  and turbine  20 . In one form, the hot gases exiting turbine  20  are directed into a nozzle (not shown), and provide a thrust output for gas turbine engine  10 . In other embodiments, additional compressor and/or turbine stages in one or more additional rotors upstream and/or downstream of compressor  12  and/or turbine  20  may be employed, e.g., in single or multi-spool gas turbine engines. 
         [0014]    Foil bearing system  26  is operative to react and transmit rotor loads from a rotor to another structure. In one form, foil bearing system  26  is operative to react and transmit loads from a rotor to a static engine structure. In other embodiments, foil bearing system  26  is operative to react and transmit loads from one rotor to another rotor. Rotor loads may include radial and thrust loads resulting from rotor weight and inertial loading, as well as pressure/thrust loading and dynamic loading. In the illustrated example, foil bearing system  26  reacts radial loads from turbine  20 , whereas another bearing system B supports compressor  12  and reacts radial and thrust loads. In other embodiments, foil bearing system  26  may support compressor  12  in addition to or in place of turbine  20 . In one or more of various embodiments, foil bearing system  26  may react radial and/or thrust loads for all or part of any rotor system of a gas turbine engine such as engine  10 . 
         [0015]    Referring now to  FIG. 2 , a non-limiting example of foil bearing system  26  in accordance with an embodiment of the present invention is schematically depicted. Foil bearing system  26  includes a foil bearing  28 , a bearing housing  30 , a self-aligning foil bearing mount  32  and two offset snubbers  34 . In one form, foil bearing system  26  is operative to transmit loads from a rotor  36  to a static engine structure  38 , such as an engine case structure or other rotor support structure. In one form, rotor  36  is a turbine rotor. In other embodiments, rotor  36  may be a compressor rotor. In one form, shaft  24  is considered to be part of rotor  36 , and in such embodiments, foil bearing system  26  may be positioned about shaft  24  to react rotor  36  loads via shaft  24 . In other embodiments, foil bearing system may be positioned to react loads directly from compressor  12  and/or turbine  20  directly. In one form, foil bearing system  26  is positioned adjacent to turbine  20  in order to react turbine  20  loads and transmit the loads to static engine structure  38 . In other embodiments, foil bearing system  26  may be positioned adjacent to compressor  12  or in other locations to react and transmit loads from compressor  12  and/or other rotating components of engine  10 . In still other embodiments, foil bearing system  26  may react and transmit rotor loads from one rotor to another rotor of a gas turbine engine. 
         [0016]    Foil bearing  28  is a gas bearing. In one form, foil bearing  28  is a compliant foil air bearing. In one form, foil bearing  28  includes a bump foil  40  and a plurality of hydrodynamic foils, referred to herein as a top foils  42 . In some embodiments, a plurality of bump foils  40  may be employed in foil bearing  28 . In some embodiments, only a single top foil  42  may be employed. In one form, top foils  42  are preloaded against rotor  36 , e.g., using a spring (not shown). In other embodiments, top foils  42  may not be preloaded, or may be preloaded by virtue of the shape of each top foil  42 . Other types of foil bearings may be used in other embodiments. Bump foil  40  and top foils  42  are disposed within housing  30 . 
         [0017]    Rotor  36  forms a journal employed by foil bearing  28 . Rotation of engine rotor  36  generates a hydrodynamic air film between rotor  36  and top foil  42 . The hydrodynamic air film thickness and load bearing capacity increase with the rotational speed of rotor  36 . During startup of engine  10 , top foil  42  rubs against rotor  36  until the hydrodynamic air film pressure is sufficient to overcome the supported rotor  36  loads and any preload. At normal operating speeds, the hydrodynamic air film separates rotor  36  and top foil  42 , thereby preventing contact between rotor  36  and top foil  42  during normal engine operation. The hydrodynamic air film supports engine rotor  36 . Rotor  36  loads are transmitted through the hydrodynamic air film to top foil  42 . Top foil  42  is supported by bump foil  40 , which transmits the loads to housing  30 , and also provides additional compliance to foil bearing  28 . The loads are transmitted from housing  30  to static structure  38  via self-aligning foil bearing mount  32 . 
         [0018]    In one form, self-aligning bearing mount  32  is a rigid structure. In other embodiments, self-aligning bearing mount  32  may be configured to achieve a desired compliance and/or accommodate varying degrees of thermal expansion. For example, in some embodiments, self-aligning bearing mount  32  may have a cross-sectional shape configured to function as a spring, and/or may incorporate one or more springs in order to achieve the desired compliance and/or accommodate anticipated thermal expansion. Self-aligning bearing mount  32  includes a crown  44  that extends radially outward from bearing housing  30 . Crown  44  includes a crown surface  46 . In one form, crown surface  46  is a load bearing surface. In one form, crown surface  46  is spherical. Crown surface  46  may be an interrupted surface, e.g., such as embodiments wherein the tip of crown  44  is cylindrical or another non-spherical shape. In other embodiments, crown surface  46  may not be spherical, but may be any shape having spherical and/or non-spherical portions that are suited to the particular application. In one form, crown  44  is integral with housing  30 . In other embodiments, crown  44  may be formed separately and affixed to housing  30 . 
         [0019]    Self-aligning foil bearing mount  32  also includes a receiver  48  coupled to foil bearing  28  via crown  44  and housing  30 . Self-aligning foil bearing mount  32  is formed of both crown  44  and receiver  48 . Receiver  48  is disposed in static structure  38 . In one form, receiver  48  is split to as to allow assembly with crown  44 . In one form, receiver  48  is installed into static structure  38 . In a particular form, receiver  48  is secured in static structure  38  by a threaded nut  38 A. Other embodiments may employ other means of securing receiver  48 . In still other embodiments, receiver  48  may be partially or fully integral with static structure  38 . In some embodiments, receiver  48  may be anti-rotated by means not shown. 
         [0020]    Receiver  48  includes a receiver surface  50  in sliding contact with one or more portions of crown surface  46 . In one form, receiver surface  50  is a load bearing surface. In one form, receiver surface  50  is spherical. In other embodiments, receiver surface  50  may not be spherical, but may be any shape having spherical and/or non-spherical portions that are suited to the particular application. Receiver surface  50  may be an interrupted surface. Crown surface  46  and receiver surface  50  are operable to slide relative to each other. In the form of spherical surfaces, crown surface  46  and receiver surface  50  permit displacement in the form of rotation of crown  44  and housing  30  about an axis that is perpendicular to the rotation of rotor  36 . The rotation results from crown surface  46  sliding against receiver surface  50 . In some embodiments, crown  44  and/or bearing housing  30  may include anti-rotation features (not shown), e.g., such as one or more pins or slots that engage respective mating slots or pins (not shown) in receiver  48  or static structure  38  to prevent the rotation of housing  30  about the axis of rotation of rotor  36 . 
         [0021]    Crown  44  is a movable component of mount  32 , whereas receiver  48  is a static component of mount  32 . In one form, mount  32  is a spherical bearing. Self-aligning foil bearing mount  32  is operative to align foil bearing  28  with the axis of rotor  36 . In particular, self-aligning foil bearing mount  32  is operable to self-align by displacing crown  44  relative to receiver  48 . More particularly, crown  44  is operable to rotate in a direction perpendicular to the axis of rotation of rotor  36  to self-align bearing  28 . In one form, the rotation of the movable component (which, in the present non-limiting example is crown  44 ) is rotation of the entirety of the movable component, i.e., as opposed to a flexible mount component that flexes to allow a rotation of part of the flexible mount structure. Hence, the self-alignment of self-aligning foil bearing mount  32  is not achieved by flexure of mount  32  or any of its components. 
         [0022]    The operation of foil bearing  28  is dependent upon maintaining the hydrodynamic air film between rotor  36  and top foil  42  to prevent contact between rotor  36  and top foil  42  during normal engine  10  operation. In order to generate the hydrodynamic air film, it is preferable that the axis of rotation of rotor  36  be aligned with the geometric centerline of bearing  28 , e.g., so that the hydrodynamic loading on top foil  42  and the air film thickness are generally uniform along the operating length of bearing  28 , e.g., the left to right direction in the depiction of  FIG. 2 . 
         [0023]    Referring now to  FIG. 3  in conjunction with  FIGS. 1 and 2 , an axis of rotation  52  of rotor  36  and a geometric centerline  54  of bearing  28  are depicted as being skewed with respect to each other at an angle φ. The skewed axes result in a non-uniform loading on top foil  42  and a non-uniform hydrodynamic air film thickness along the operating length of bearing  28 , which reduces foil bearing  28  performance. It is preferable that the skew angle φ be small or zero so as to promote a uniform hydrodynamic air film pressure along the operating length of bearing  28  to maximize the load bearing capacity of foil bearing  28 . Various factors may adversely effect the angular relationship between receiver surface  50  and centerline  52 . For example engine  10  component tolerances may generate misalignment between the radial positions of bearing B and foil bearing  28 , resulting in a non-zero skew angle φ. 
         [0024]    Because crown surface  46  is permitted to slide against receiver surface  50 , self-aligning foil bearing mount  32  has only a limited ability to react moment loading. The ability of mount  32  to react a moment is based on the amount of friction between surfaces  44  and  50 . The amount of friction may be controlled by various means, including controlling the tightness or looseness of the fit between surfaces  44  and  50 , as well as by selection of the materials and/or coatings used on crown  44  and receiver  48 . In one form, the amount of friction is controlled, by design, to allow the non-uniform loading on top foils  42  that results from skew angle φ to be sufficient to overcome the frictional load and impart rotation of crown  44  relative to receiver  48  to reduce skew angle φ. In one form, the amount of reduction of skew angle φ is based primarily on the compliance of foil bearing  28  and the friction between surfaces  44  and  50 , and may vary with the application. In some embodiments, loads transmitted from rotor  36  to snubbers  34  due to skew angle φ may be employed to impart rotation of crown  44  relative to receiver  48  to reduce skew angle φ. In various embodiments, self-aligning foil bearing mount  32 , e.g., crown  44  and receiver  48 , may be dimensioned so as to provide a desired operating clearance. In some embodiments, compliant springs may be employed to provide a positive fit. In some embodiments, coatings may be employed, e.g., on crown surface  46  and/or receiver surface  50 , e.g., to reduce friction and wear, depending on the needs of the particular application. One example of a suitable material for use as crown surface  46  and/or receiver surface  50  in some embodiments is Graphalloy®, available from the Graphite Metallizing Corporation of Yonkers, N.Y., USA. 
         [0025]    Snubbers  34  are operative to transmit rotor  36  loads to static structure  38 . In one form, snubbers  34  are configured to limit the deflection of bump foil  40 , e.g., to prevent or reduce damage to bump foil  40  during dynamic loading events. In one form, snubbers  34  include openings or slots (not shown) to permit cooling air to pass through snubbers  34  and bump foil  40 . In other embodiments, cooling air may be provided to snubbers  34  and/or bump foil  40  via one or more other schemes in addition to or in place of openings or slots in snubbers  34 . In still other embodiments, cooling air may not be provided. In one form, snubbers  34  are operative to transmit rotor  36  loads to static structure  38  in parallel with foil bearing  28 , thereby sharing the rotor loads with foil bearing  28 . In one form, the rotor loads are radial loads. In other embodiments, snubbers  34  may be structured transmit thrust loads in addition to or in place of radial loads. In some embodiments, snubbers  34  may not be employed. In embodiments that employ snubbers  34 , snubbers  34  share the rotor  36  loads with foil bearing  28  under transient operating conditions. For example, when foil bearing  28  design loads are exceeded, snubbers  34  rub against rotor  36  to react rotor  36  loads. Snubbers  34  may be formed of metallic and/or composite materials. Although two snubbers  34  are depicted in  FIG. 2 , it will be understood that in other embodiments, any number of snubbers  34  may be employed. In some embodiments, only a single snubber  34  may be employed, e.g., at one end of bump foil  40  and/or top foil  42 ; or in between a split bump foil  40  and/or a split top foil  42 . In various embodiments, one or more snubbers  34  may be positioned opposite rotor  36  behind top foil  42 , e.g., whereby transient rotor  36  loads are first transmitted through top foil  42 , and then from top foil  42  to snubber(s)  34 . In one form, snubbers  34  are made from a carbon based material, such as steel. In other embodiments, a carbon-fiber composite may be employed. The material for snubbers  34  may vary with the needs of the application, and in various embodiments may be, for example, any suitable metallic, intermetallic and/or composite material. In some embodiments, one or more coatings, e.g., such as alcrona (AICrN) and/or other coatings may be employed on snubbers  34 , e.g., to reduce friction and wear, depending on the needs of the particular application. In some embodiments, snubbers  34  may include a portion made from, layered with and/or otherwise treated with a low friction material, an example of which is Graphalloy®. In other embodiments, other materials that meet the requirements of the particular application may be employed. Design considerations include operating temperatures, friction characteristics, oxidation resistance, heat transfer and dissipation capabilities, and mechanical and thermal loading parameters. Other suitable materials include, for example, stainless steel or iron. Suitable materials for rotor  36 , i.e., the portions of rotor  36  that are rubbed by snubbers  34 , may include, for example, any suitable metallic (e.g., nickel based alloys and/or iron-based alloys), intermetallic and/or composite material. In some embodiments, one or more coatings, e.g., such as alcrona (AICrN) and/or other coatings may be employed on rotor  36 , e.g., to reduce friction and wear, depending on the needs of the particular application. In some embodiments, rotor  36  may include a portion made from, and/or may be layered with and/or otherwise treated with a low friction material, an example of which is Graphalloy®. In some embodiments, the materials for snubbers  34  and rotor  36  may be selected to have a similar coefficient of thermal expansion. In one form, the use of snubbers  34  to share rotor  36  loads with foil bearing  28  allows foil bearing  28  to be sized for a lower design load, while retaining the capability to handle short duration transient peak loads. By being sized for a lower design load than that which would be required absent the use of snubbers  34 , foil bearing  28  may be smaller and lighter than otherwise. 
         [0026]    Embodiments of the present invention include a gas turbine engine, comprising: a compressor; a turbine; a static structure; a foil bearing system operative to transmit rotor loads from at least one of the compressor and the turbine to the static structure, wherein the foil bearing system includes a foil bearing and a self-aligning foil bearing mount coupled to the foil bearing, wherein the self-aligning foil bearing mount is operative to align the foil bearing with an axis of rotation of the at least one of the compressor and the turbine; and a snubber operative to transmit rotor loads from at least one of the compressor and the turbine to the static structure in parallel with the foil bearing. 
         [0027]    In a refinement, the self-aligning foil bearing mount includes a static component and a movable component, and wherein the self-aligning foil bearing mount is operable to self-align by displacing the movable component relative to the static component. 
         [0028]    In another refinement, the movable component is operable to rotate relative to the static component. 
         [0029]    In yet another refinement, rotation of the movable component is rotation of the entire movable component. 
         [0030]    In still another refinement, the static component includes a first surface; wherein the movable component includes a second surface in sliding contact with the first surface; and wherein displacement of the movable component relative to the static component includes the second surface sliding against the first surface. 
         [0031]    In yet still another refinement, self-alignment is not achieved by flexure of the self-aligning foil bearing mount. 
         [0032]    In a further refinement, the self-aligning foil bearing mount is a spherical bearing. 
         [0033]    In a yet further refinement, the engine includes a shaft coupled to at least one of the compressor and the turbine, wherein rotor loads are transmitted from the shaft through the foil bearing, and from the foil bearing to the static structure via the self-aligning foil bearing mount. 
         [0034]    In a still further refinement, the shaft couples the compressor to the turbine. 
         [0035]    In a yet still further refinement, the engine includes a rotating journal and a housing disposed opposite to the rotating journal, wherein the snubber is operative to limit the proximity of the housing relative to the journal. 
         [0036]    Embodiments of the present invention include a gas turbine engine, comprising: a rotor; a static structure; a foil bearing system operative to transmit rotor loads from the rotor to the static structure, wherein the foil bearing system includes: a foil bearing; and a self-aligning foil bearing mount operative to align the foil bearing with an axis of rotation of the rotor, wherein the self-aligning foil bearing mount has a static component and a movable component; and wherein the self-aligning foil bearing mount is operable to self-align with the axis of rotation of the rotor by sliding displacement of the movable component relative to the static component. 
         [0037]    In a refinement, the self-aligning foil bearing mount is a spherical bearing. 
         [0038]    In another refinement, the engine further includes a snubber operative to transmit rotor loads from the rotor to the static structure in parallel with the foil bearing. 
         [0039]    In yet another refinement, the engine also includes a bearing housing for housing the foil bearing, wherein the snubber is positioned within the bearing housing. 
         [0040]    In still another refinement, the snubber is positioned adjacent to the bearing housing. 
         [0041]    In yet still another refinement, the snubber is formed of a composite material. 
         [0042]    In a further refinement, the foil bearing is a compliant foil radial air bearing. 
         [0043]    Embodiments of the present invention include a foil bearing system for a gas turbine engine, comprising: a foil bearing operative to transmit rotor loads from a rotor of the gas turbine engine to a static structure of the gas turbine engine; and means for aligning the foil bearing with an axis of rotation of the rotor. 
         [0044]    In a refinement, the foil bearing system further includes means for sharing the rotor loads with the foil bearing. 
         [0045]    In another refinement, the means for aligning includes a spherical bearing. 
         [0046]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment(s), but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as permitted under the law. Furthermore it should be understood that while the use of the word preferable, preferably, or preferred in the description above indicates that feature so described may be more desirable, it nonetheless may not be necessary and any embodiment lacking the same may be contemplated as within the scope of the invention, that scope being defined by the claims that follow. In reading the claims it is intended that when words such as “a,” “an,” “at least one” and “at least a portion” are used, there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. Further, when the language “at least a portion” and/or “a portion” is used the item may include a portion and/or the entire item unless specifically stated to the contrary.