Abstract:
One embodiment of the present invention is a damping system for rotating machinery such as gas turbine engines. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for damping 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 61/290,702, 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. XQ2370220E awarded by the United States government. The United States government may have certain rights in the present application. 
     
    
     FIELD OF THE INVENTION 
       [0003]    The present invention relates to rotating machinery such as gas turbine engines, and more particularly, to a damping system for use in rotating machinery. 
       BACKGROUND 
       [0004]    Damping systems that effectively damp vibrations in rotating structures, such as rotor systems in a gas turbine engines or other rotating machinery, 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 damping system for rotating machinery such as gas turbine engines. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for damping 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 depicts a gas turbine engine in accordance with an embodiment of the present invention. 
           [0008]      FIG. 2  is a cross section of a damping system in accordance with an embodiment of the present invention. 
           [0009]      FIG. 3  is an enlarged cross section of the damping system of  FIG. 2 . 
           [0010]      FIG. 4  is a cross sectional view of an isolator spring employed in the damping system embodiment of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    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. 
         [0012]    Referring now to the drawings, and in particular  FIG. 1 , there is shown a rotating machine in the form of a gas turbine engine  10 . Although embodiments of the present invention are described herein with respect to a gas turbine engine, it will be understood that the present invention is also applicable to other types of rotating machines. 
         [0013]    Gas turbine engine  10  includes a compressor  12 , a combustor  14  and a turbine  16 . Compressor  12  is mechanically coupled to turbine  16  via a shaft  18 , which form a part of a rotor system  20 . Combustor  14  is fluidly disposed between compressor  12  and turbine  16 . Compressor  12 , combustor  14  and turbine  16  are housed within and supported by an engine case system  22 , which generally includes mounting features for mounting gas turbine engine  10  in an air vehicle, such as an aircraft or missile system. 
         [0014]    Coupled to engine case system  22  are static structures, including a front bearing support  24  and an aft bearing support  26 . Housed within front bearing support  24  is a rolling element bearing  28  which supports the front portion of rotor system  20 , e.g., including compressor  12  and the front portion of shaft  18 . Rolling element bearing  28  is a ball thrust bearing. In other embodiments of the present invention, it is alternatively considered that rolling element bearing  28  may be one or more of a roller bearing and/or other type of rolling element bearing. As a thrust bearing, rolling element bearing  28  transmits both thrust loads and radial loads from rotor system  20  into engine case system  22  via front bearing support  24 . 
         [0015]    Housed within aft bearing support  26  is a rolling element bearing  30  which supports the aft portion of rotor system  20 , e.g., including turbine  16  and the aft portion of shaft  18 . Rolling element bearing  30  is a roller bearing. It is alternatively considered that in other embodiments, rolling element bearing  30  may be one or more of a ball bearing and/or other type of rolling element bearing. Rolling element bearing  30  transmits radial loads from rotor system  20  into engine case system  22  via aft bearing support  26 . 
         [0016]    In the depiction of  FIG. 1 , each of rolling element bearing  28  and rolling element bearing  30  are depicted as being mounted directly on shaft  18 . However, it will be understood that the depiction of  FIG. 1  is schematic in nature and not representative of any particular scheme for mounting rolling element bearing  28  and rolling element bearing  30 . Rather, embodiments of the present invention may incorporate one or more of many different possible mounting schemes. 
         [0017]    During steady state operation of gas turbine engine  10 , atmospheric air is drawn into and compressed by compressor  12 . The compressed air is discharged from compressor  12  into combustor  14 , where fuel is added to the compressed air and the mixture is ignited. The resulting hot gases are supplied to turbine  16 , which extracts mechanical energy to drive compressor  12 , and discharges the hot gases, e.g., in the form of jet thrust. 
         [0018]    The operation of gas turbine engine  10  results in steady state and dynamic loads on rotor system  20 , including aerodynamic, gyroscopic, rotor mass and unbalance loads. The rotor system  20  loads are transmitted by rolling element bearings  28  and  30  to engine case system  20 . 
         [0019]    Rotor system  20  aerodynamic loads include axial thrust loads. Aerodynamically imposed thrust loads may be tuned, in conjunction with the radial loads anticipated during engine operation, to optimize the life of the thrust bearing, i.e., rolling element bearing  28 . For example, balance pistons (not shown) may be employed to achieve desired steady state thrust loads. 
         [0020]    Gyroscopic loads occur when rotor system  20  is rotating at the same time engine  10  is rotated in a direction having a component axis of rotation inclined 90° from the axis of rotation of rotor system  20 . Gyroscopic loading results in bending loads in rotor system  20  and radial loads, which are reacted by both rolling element bearing  28  and rolling element bearing  30 . 
         [0021]    Rotor mass loads result from the mass of rotor system  20  in conjunction with gravity and air vehicle acceleration in a direction perpendicular to the axis of rotation of rotor system  20 . Depending on the acceleration experienced by the air vehicle in a direction perpendicular to the axis of rotation of rotor system  20 , the rotor mass loads may be greater or lesser than the weight of rotor system  20 . Rotor mass loads are radial loads, and are reacted by both rolling element bearing  28  and rolling element bearing  30 . 
         [0022]    Dynamic loads include both unbalance loads and critical rotor mode responses, both of which are reacted by both rolling element bearing  28  and rolling element bearing  30 . Unbalance loads result primarily from manufacturing tolerances and wear of rotor system  20  components. Critical rotor mode responses may occur during startup of gas turbine engine  10  as rotor system  20  accelerates through critical speeds, i.e., rotor speeds corresponding to resonant frequencies of rotor system  20 . The critical rotor mode responses may result in substantial dynamic radial loads. In order to damp the critical rotor mode responses as rotor system  20  passes through resonant frequencies, gas turbine engine  10  includes a damping system. 
         [0023]    Referring now to  FIG. 2 , gas turbine engine  10  includes a squeeze film damping system  32  structured to damp vibrations passing from rotor system  20  through rolling element bearing  28  into a static structure. In one form, the static structure is front bearing support  24 . In other embodiments, other static structures may be employed, e.g., including components affixed or coupled to bearing support  24  through which dynamic loads pass before or after reaching bearing support  24 . A similar damping system may be structured to damp vibrations passing from rotor system  20  through rolling element bearing  30  into aft bearing support  26 . 
         [0024]    As depicted in  FIG. 2 , front bearing support  24  includes a bearing cage  34 . Rolling element bearing  28  includes a split inner race  36  and a split outer race  38 . Split outer race  38  of rolling element bearing  28  is subject to radial displacements during the operation of gas turbine engine  10 . The radial displacements may result from critical rotor mode responses during startup of gas turbine engine  10 . Radial displacements may also result from rotor system  20  unbalance loads and gyroscopically induced loads. 
         [0025]    Damping system  32  includes a damper ring  40 , a seal  42  disposed on one side of damper ring  40 , a seal  44  disposed on the other side of damper ring  40 , an isolator spring  46  disposed on one side of damper ring  40  and an isolator spring  48  disposed on the other side of damper ring  40 . In one form, damping system  32  is a squeeze-film damping system. Damping system  32  and split outer race  38  are axially retained between an aft wall  50  of bearing cage  34  and a forward structure  52  affixed to front bearing support  24 . 
         [0026]    Referring now to  FIG. 3  in conjunction with  FIG. 2 , damping system  32  is further described. 
         [0027]    Split outer race  38  includes an outer race pilot surface  54  defined by an outer race pilot diameter. As a piloting feature, outer race pilot surface  54  is a radial positioning surface, which in the present embodiment radially positions split outer race  38 . Split inner race  36  includes an inner race pilot surface  56  defined by an inner race pilot diameter. Bearing cage  34  includes a static inner piloting surface  58  defined by an inside pilot diameter. 
         [0028]    Defined between outer race pilot surface  54  and static inner piloting surface  58  is a cavity  60 . Damper ring  40 , seal  42 , seal  44 , isolator spring  46  and isolator spring  48  are disposed within cavity  60 . Cavity  60  is charged with a fluid, e.g., a viscous damping fluid, such as engine lubricating oil or a grease, which is employed in conjunction with damper ring  40  to provide damping. Cavity  60  may be charged with the damping fluid by a pressurized lubrication system (not shown) of gas turbine engine  10 . 
         [0029]    Damper ring  40  includes a plurality of fluid transfer holes  62  disposed about the circumference of damper ring  40 , which help to distribute the damping fluid about the inner and outer periphery of damper ring  40 . The damping fluid may be supplied by a passage (not shown) through bearing cage  34 . 
         [0030]    Damper ring  40  is an annular squeeze film damper ring, and is structured to provide damping of rotor system  20  based on the radial displacements of split outer race  38  that result from critical rotor mode responses, e.g., during the startup of gas turbine engine  10 . In particular, damper ring  40  is operative to provide viscous damping of radial loads generated in rotor system  20  using the viscous damping fluid, based on clearances between damper ring  40 , inner piloting surface  58  of bearing cage  34  and outer race piloting surface  54  of rolling element bearing  28 . 
         [0031]    Damper ring  40  is a dual-sided damper ring, and includes damper clearance surfaces  64 ,  66 ,  68 ,  70 ,  72  and  74 . Damper clearance surfaces  64 ,  66 ,  68 ,  70 ,  72  and  74  are diametrically sized to provide a predetermined amount of damping in conjunction with the diameters of outer race pilot surface  54  of split outer race  38  and inner piloting surface  58  of bearing cage  34 . Being a dual-sided damper ring, damping is performed based on the diametral clearance between damper clearance surfaces  64 ,  66  and  68  of damper ring  40  and inner piloting surface  58  of bearing cage  34 , and damping is also performed based on the diametral clearance between damper clearance surfaces  70 ,  72  and  74  of damper ring  40  and outer race pilot surface  54  of rolling element bearing  28 . Damping is thus performed on both sides of damper ring  40 . 
         [0032]    For example, because rotor system  20  is spinning during the operation of gas turbine engine  10 , the radial displacement resulting from the critical rotor mode responses of rotor system  20  generates an orbital motion in split outer race  38 . That is, the radial displacement of split outer race  38  rotates approximately about the axis of revolution of rotor system  20 . The orbiting radial displacement of split outer race  38  results in a rotating front of oil being “squeezed” between outer race pilot surface  54  of split outer race  38  and damper ring  40 , and between damper ring  40  and static inner piloting surface  58  of bearing cage  34 , which provides viscous damping due to the viscosity characteristic of the fluid in cavity  60 . In other embodiments, a single-sided damper ring may be employed. 
         [0033]    In one form, a centering force to center split outer race  38  relative to bearing cage  34  is provided by each of isolator spring  46  and isolator spring  48 . In one form, isolator spring  46  and isolator spring  48  are annular springs, each having alternating contact between inner piloting surface  58  of bearing cage  34  and outer race pilot surface  54  of rolling element bearing  28 . In other embodiments, other types of springs may be employed. Isolator spring  46  and isolator spring  48  absorb the radial displacement of rolling element bearing  28  relative to bearing cage  34 . The inclusion of one or more isolator springs allows for dynamic tuning. For example, in some embodiments, isolator spring  46  and/or isolator spring  48  may be used to alter the stiffness of the bearing support system, e.g., in which case the stiffness of isolator spring  46  and/or isolator spring  46  are selected so as to tune the dynamic characteristics of the bearing support system. 
         [0034]    For example, referring now to  FIG. 4 , a cross section through isolator spring  48  is depicted. Isolator spring  46  is structured similar to isolator spring  48 . In one form, isolator springs  46  and  48  are segmented rings. In other embodiments, isolator springs  46  and  48  may be split rings or may be continuous rings. In still other embodiments, isolator springs  46  and  48  may take other forms. Isolator spring  48  includes a plurality of outer contact portions  76 , a plurality of inner contact portions  78 , and a flexural portion  80  disposed between each outer contact portion  76  and inner contact portion  78 . Outer contact portions  76  are piloted by inner piloting surface  58  of bearing cage  34 . Inner contact portions  78  are piloted by outer race pilot surface  54  of split outer race  38 . Radial excursions of split outer race  38  displace inner contact portions  78  relative to outer contact portions  76 , resulting in deflection of flexural portions  80 , which generates restoring forces in a direction opposite the direction of deflection. 
         [0035]    Although the present embodiment employs two (2) isolator springs  46  and  48 , it is alternatively contemplated that other embodiments may employ fewer or greater numbers of isolator springs, or may not include any such isolator springs. 
         [0036]    Referring again to  FIG. 3 , in one form, each of seals  42  and  44  is pressure assisted, i.e., a self-charging seal, wherein the pressure of the fluid sought to be sealed assists in maintaining contact between the relevant sealing surfaces. In other embodiments, other seal types may be employed. Each of seals  42  and  44  are structured to receive charging pressure from the damping fluid contained in cavity  60 . Seals  42  and  44  are polymeric in the present embodiment, e.g., a polyimide, although other materials may be employed in other embodiments of the present invention. By employing seals  42  and  44  to seal against the same surfaces employed for damping via damper ring  40 , e.g., piloting surfaces  54  and  58 , the envelope requirements and costs associated with seal glands for other seal arrangements may be avoided. 
         [0037]    Each of seals  42  and  44  are bifurcated seals disposed adjacent to damper ring  40 , and include a body  82 , an outer leg  84 , an inner leg  86 , and a hollow  88  defined between body  82 , outer leg  84  and inner leg  86 . Each outer leg  84  extends from body  82 , and includes a sealing surface  90  disposed thereon and positioned in proximity to inner piloting surface  58  of bearing cage  34 . Sealing surface  90  is structured to seal against static inner piloting surface  58 , i.e., at the bearing cage  34  inner pilot diameter. Each inner leg  86  extends from body  82 , and includes a sealing surface  92  disposed thereon and positioned in proximity to outer race pilot surface  54  of rolling element bearing  28 . Sealing surface  92  is structured to seal against outer race pilot surface  54 , i.e., at the outer race pilot diameter of split outer race  38 . 
         [0038]    Each hollow  88  is open to cavity  60 , and exposes outer leg  84  and inner leg  86  to the pressure of the damping fluid surrounding damper ring  40  in cavity  60 . The pressure of the damping fluid acts on outer leg  84  and inner leg  86  in the direction of sealing surface  90  and sealing surface  92 , respectively, during the operation of gas turbine engine  10 . This pressure helps to retain sealing surface  90  and sealing surface  92  in sealing contact with inner piloting surface  58  of bearing cage  34  and outer race pilot surface  54  of rolling element bearing  28 , respectively, during the operation of gas turbine engine  10 . The pressure thus assists seals  42  and  44  in retaining the damping fluid in cavity  60 , which is used by damper clearance surfaces  64 ,  66 ,  68 ,  70 ,  72  and  74  of damper ring  40  in conjunction with the diameters of outer race pilot surface  54  of split outer race  38  and inner piloting surface  58  of bearing cage  34  in providing squeeze film damping of rotor system  20 . 
         [0039]    Although the illustrated embodiment of damping system  32  is disposed between split outer race  38  and bearing cage  34  in the present embodiment, it is alternatively contemplated that damping system  32  may be disposed between split inner race  36  and a portion of rotor system  20  in other embodiments. In still other embodiments, it is contemplated that other gas turbine engine  10  components may be intermediately disposed between split outer race  38  and damper ring  40  and/or between damper ring  40  and bearing cage  34 , in which case damping is performed based on the damping fluid surrounding damper ring  40  in conjunction with the clearances between damper ring  40  and any such intermediately disposed components. In yet other embodiments, it is contemplated that damping system  32  may be employed for intershaft damping, wherein damping is performed between two or more rotor systems. 
         [0040]    An embodiment of the present invention may include a rotating machine with a first component having a first component surface subject to radial displacement during operation of the rotating machine. The first component surface may be defined by a first diameter. The second component may have a second component surface spaced apart from the first component surface. The second component surface may be defined by a second diameter different from the first diameter. A squeeze film damper disposed in a cavity may be defined between the first component surface and the second component surface. The squeeze film damper may be structured to provide damping based on the radial displacement. A seal disposed adjacent to the squeeze film damper may have a seal having a first sealing surface and a second sealing surface. The first sealing surface may be structured to seal against the first component surface at the first diameter. The second sealing surface may be structured to seal against the second component surface at the second diameter. 
         [0041]    In one refinement of the embodiment a squeeze film damper is structured as an annular squeeze film damper ring. 
         [0042]    In another refinement of the embodiment the seal is a self-charging seal. 
         [0043]    In another refinement of the embodiment the seal is structured to receive a charging pressure from damping fluid in said cavity. 
         [0044]    In another refinement of the embodiment the seal is a bifurcated seal having a first leg and a second leg. The first sealing surface is disposed on the first leg and the second sealing surface is disposed on the second leg. 
         [0045]    In another refinement of the embodiment the seal includes a hollow defined between the first leg and the second leg. The hollow is open to the cavity. 
         [0046]    In another refinement of the embodiment the first component is a portion of a rolling element bearing. The second component is a static bearing support structure of the rotating machine. 
         [0047]    In another refinement of the embodiment the first component is one of an inner race and an outer race of the rolling element bearing. The first diameter is the one of a corresponding inner race pilot diameter and outer race pilot diameter of the rolling element bearing. 
         [0048]    In another refinement of the embodiment the squeeze film damper is a dual sided damper ring structured to perform damping on both sides of the dual sided damper ring. 
         [0049]    In another refinement of the embodiment the cavity is charged with a fluid that is employed in conjunction with the squeeze film damper to provide the damping. 
         [0050]    Another embodiment of the present invention may include a gas turbine engine. The gas turbine engine may include a rotating engine structure, a static engine structure having a static structure pilot diameter, and a rolling element bearing structured to transmit a load from the rotating engine structure to the static engine structure. The rolling element bearing may have an inner race and an outer race. The inner race may have an inner race pilot diameter and the outer race may have an outer race pilot diameter. The static structure pilot diameter and one of the inner race pilot diameter and the outer race pilot diameter form a cavity and a damping system for damping the load. The damping system may include a squeeze film damper disposed in the cavity. The cavity also may contain a viscous damping fluid. The squeeze film damper may be operative to provide viscous damping of the load using the viscous damping fluid based on clearances between the static engine structure at the static structure pilot diameter and the rolling element bearing at the one of the inner race pilot diameter and the outer race pilot diameter. A seal may be disposed at least partially in the cavity. The seal may have a first sealing surface and a second sealing surface. The first sealing surface may be structured to seal against the static engine structure at the static structure pilot diameter. The second sealing surface may be structured to seal against the rolling element bearing at the one of the inner race pilot diameter and the outer race pilot diameter. 
         [0051]    In a refinement of the embodiment the gas turbine engine may include an isolator spring disposed in the cavity and piloted by the static engine structure at the static structure pilot diameter and the rolling element bearing at the one of the inner race pilot diameter and the outer race pilot diameter. The isolator sprint is structured to absorb radial displacement between the rolling element bearing and the static engine structure. 
         [0052]    In another refinement of the embodiment the isolator spring may be an annular spring having alternating contact between the static structure at the static structure pilot diameter and the rolling element bearing at the one of the inner race pilot diameter and the outer race pilot diameter. 
         [0053]    In another refinement of the embodiment the seal may be a self-charging seal. 
         [0054]    In another refinement of the embodiment the seal may be structured to receive a charging pressure from the viscous damping fluid in the cavity. 
         [0055]    In another refinement of the embodiment the seal may be a bifurcated seal having a first leg and a second leg. The first sealing surface may be on the first leg. The second sealing surface may be disposed on the second leg. 
         [0056]    In another refinement of the embodiment the seal may include a hollow defined between the first leg and the second leg. The hollow may open to the cavity. 
         [0057]    In another refinement of the embodiment the squeeze film damper may be operative to provide viscous damping of the load using the viscous damping fluid based on clearances between the static engine structure at the static structure pilot diameter and the rolling element bearing at the outer race pilot diameter. 
         [0058]    Another embodiment of the present invention may be a rotating machine which may include a rotating structure, a static structure having a static structure pilot diameter, and a rolling element bearing structured to transmit a variable load from the rotating structure to the static structure. The rolling element bearing may have an inner race and an outer race. The inner race may have an inner race pilot diameter and the outer race may have an outer race pilot diameter. The static structure pilot diameter and one of the inner race pilot diameter and the outer race pilot diameter may form a cavity therebetween for damping the variable load and for sealing the means for damping. The sealing may be operative to seal between the static structure pilot diameter and the one of the inner race pilot diameter and the outer race pilot diameter. 
         [0059]    In a refinement of the embodiment the rotating machine may include a means for absorbing radial displacement between the static structure pilot diameter and the one of the inner race pilot diameter and the outer race pilot diameter. 
         [0060]    Another embodiment of the present invention may be a damper system for rotating machinery which may include a squeeze film damper disposed in a cavity defined between a diameter of a static structure of the rotating machinery and one of an inner race diameter and an outer race diameter of a rolling element bearing of the rotating machinery. The cavity also may contain a viscous damping fluid. The squeeze film damper may be operative to provide viscous damping of a load using the viscous damping fluid based on clearances between the static structure diameter and the one of the inner race diameter and the outer race diameter. The embodiment may also include a seal disposed at least partially in the cavity. The seal may have a first sealing surface and a second sealing surface. The first sealing surface may be structured to seal against the static structure at the diameter of the static structure. The second sealing surface may be structured to seal against the rolling element bearing at the one of the inner race diameter and the outer race diameter. 
         [0061]    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.