Abstract:
An annular dashpot damper is utilized to provide flow resistance from viscous shear to an orifice or gap which provides flow metering. This is accomplished by dividing the flow channel into circumferential segments or damping cavities which are sealed and limit rotational flow of the fluid.

Description:
BACKGROUND 
       [0001]    Present embodiments relate generally to structures having rotating shafts. More specifically the present embodiments relate to an annular dashpot damper for structures having rotating shafts, for example gas turbine engines, which dampen radial movement of a shaft during operation. 
         [0002]    In a gas turbine engine for example, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases which flow downstream through turbine stages. These turbine stages extract energy from the combustion gases. A high pressure turbine first receives the hot combustion gases from the combustor and includes a stator nozzle assembly directing the combustion gases downstream through a row of high pressure turbine rotor blades extending radially outwardly from a supporting rotor disk. In a two stage turbine, a second stage stator nozzle assembly is positioned downstream of the first stage blades followed in turn by a row of second stage rotor blades extending radially outwardly from a second supporting rotor disk. This results in conversion of combustion gas energy to mechanical energy. 
         [0003]    The first and second rotor disks are coupled to the compressor by a corresponding high pressure rotor shaft for powering the compressor during operation. A multi-stage low pressure turbine may or may not follow the multi-stage high pressure turbine and may be coupled by a second shaft to a fan disposed upstream from the compressor. 
         [0004]    As the combustion gas flows downstream through the turbine stages, energy is extracted therefrom and the pressure of the combustion gas is reduced. The combustion gas may continue through multiple low stage turbines. 
         [0005]    The annular nozzle assembly is formed of a plurality of nozzle segments which are joined at circumferential ends of the segments. Each high pressure turbine nozzle includes vanes which are hollow and receive a portion of pressurized cooling air from the compressor to cool the vanes during operation. A portion of the vane air is then channeled radially inwardly from a radially outer band or wall through the vane to the inner band or wall. 
         [0006]    In current gas turbine engines, shaft dynamics are controlled by oil filled squeeze film dampers wherein a thin film of oil is positioned between two concentric non-rotating cylinders or rings. The outer ring is stationary and the inner ring is allowed to orbit but does not rotate. Oil flows around the cylinders due to the pumping motion created by movement of the shaft and the inner orbiting ring. The shear of the fluid along with the inertial forces provide damping to resist motion of the inner rings. The desired damping is achieved by adjusting the flow channel gap between an orbiting ring which may be mounted to a shaft bearing and a stationary ring mounted to the engine frame or static structure. The term orbit, or orbiting, as used herein means non-rotating but movable in a radial direction with the shaft. In many cases the gap required to achieve the desired damping may be very small which may overly restrict shaft deflection and create high pressure gradients. In order for this construction to operate properly, the gap between the inner and outer ring that form the flow channel must be very thin. This creates a high potential for the damper to bottom out. Additionally, the gap may generate heat due to the viscous shear in the fluid during the damping reaction. 
         [0007]    It would be desirable to reduce or eliminate these and other deficiencies while providing proper damping for a turbine engine shaft which may move radially due to dynamic loads which occur during operation. 
       SUMMARY 
       [0008]    An annular dashpot damper is utilized to provide flow resistance from viscous shear to an orifice or gap which provides flow metering. This is accomplished by dividing the flow channel into circumferential segments or damping cavities which are sealed and limit rotational flow of the fluid. 
         [0009]    According to some embodiments, an annular damper for a rotating shaft, comprises a first ring which orbits with the engine shaft, the first ring having a plurality of dividers extending radially between the first ring and a second ring and spaced circumferentially, the first ring capable of moving radially with the shaft, the second ring disposed radially outward of the first ring, a plurality of damping cavities defined between the first ring, the second ring and the dividers, the plurality of damping cavities having a damping fluid, wherein the damping fluid damps movement of the first ring and the shaft. 
         [0010]    All of the above outlined features are to be understood as exemplary only and many more features and objectives of the annular dashpot damper may be gleaned from the disclosure herein. Therefore, no limiting interpretation of this summary is to be understood without further reading of the entire specification, claims, and drawings included herewith. 
     
    
     
       BRIEF DESCRIPTION OF THE ILLUSTRATIONS 
         [0011]    The above-mentioned and other features and advantages of these exemplary embodiments, and the manner of attaining them, will become more apparent and the annular dashpot damper feature will be better understood by reference to the following description of embodiments taken in conjunction with the accompanying drawings, wherein: 
           [0012]      FIG. 1  is a side section view of an exemplary gas turbine engine. 
           [0013]      FIG. 2  is a schematic sectional view of an exemplary annular dashpot damper assembly. 
           [0014]      FIG. 3  is a schematic section view of the embodiment of  FIG. 2  with the shaft shifted within the damper assembly. 
           [0015]      FIG. 4  is a schematic section view of an alternate embodiment of an annular dashpot damper assembly including the flow orifices in a stationary ring. 
           [0016]      FIG. 5  is a schematic view of an exemplary dashpot damper assembly. 
           [0017]      FIG. 6  is a section view of a portion of a stationary ring of the damper assembly. 
           [0018]      FIG. 7  is an alternative section view of the embodiment of  FIG. 5 . 
           [0019]      FIG. 8  is an alternate embodiment of the dashpot damper. 
           [0020]      FIG. 9  is a further alternative embodiment utilizing an integral outer bearing race. 
           [0021]      FIG. 10  is an embodiment of a dashpot damper assembly with integral dividers formed on the inner ring of the assembly. 
           [0022]      FIG. 11  is a further embodiment of  FIG. 8  including a biasing spring. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Reference now will be made in detail to embodiments provided, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation, not limitation of the disclosed embodiments. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present embodiments without departing from the scope or spirit of the disclosure. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to still yield further embodiments. Thus it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
         [0024]    Referring to  FIGS. 1-11 , various embodiments of a gas turbine engine are depicted having an annular dashpot damper. The damper assembly includes a plurality of dividers which form multiple damping cavities wherein a damping fluid is disposed. An inner ring is connected either directly or indirectly to an engine shaft and an outer ring is disposed radially outward of the inner ring defining the damping cavities therebetween. The dividers may be formed of one or more pieces allowing movement of the inner ring and shaft in radial directions. Additionally, the assembly may include apertures to allow movement of oil therethrough to further dampen shaft orbital movement. While a gas turbine engine is used as an example in the present disclosure, one skilled in the art should realize that the annular dashpot damper may be utilized in various structures utilizing rotating or vibrating shafts other than gas turbines. For example, the annular dashpot damper may be utilized to stabilize or damp vibration in a helicopter drive shaft. Other uses are well within the scope of this disclosure. 
         [0025]    The terms fore and aft are used with respect to the engine axis and generally mean toward the front of the turbine engine or the rear of the turbine engine in the direction of the engine axis, respectively. The term radially is used generally to indicate a direction perpendicular to an engine axis. 
         [0026]    Referring initially to  FIG. 1 , a schematic side section view of a gas turbine engine  10  is shown having an engine inlet end  12 , a compressor  14 , a combustor  16  and a multi-stage high pressure turbine  20 . The gas turbine  10  may be used for aviation, power generation, industrial, marine or the like. Depending on the usage, the engine inlet end  12  may alternatively contain multi-stage compressors rather than a fan. The gas turbine  10  is axis-symmetrical about engine axis  26  or shaft  24  so that various engine components rotate thereabout. In operation air enters through the air inlet end  12  of the engine  10  and moves through at least one stage of compression where the air pressure is increased and directed to the combustor  16 . The compressed air is mixed with fuel and burned providing the hot combustion gas which exits the combustor  16  toward the high pressure turbine  20 . At the high pressure turbine  20 , energy is extracted from the hot combustion gas causing rotation of turbine blades which in turn cause rotation of the shaft  24 . The shaft  24  passes toward the front of the engine to continue rotation of the one or more compressor stages  14 , a turbofan  18  or inlet fan blades, depending on the turbine design. 
         [0027]    The axis-symmetrical shaft  24  extends through the through the turbine engine  10 , from the forward end to an aft end. The shaft  24  is supported by bearings along its length. The shaft  24  may be hollow to allow rotation of a low pressure turbine shaft  28  therein. Both shafts  24 ,  28  may rotate about the centerline  26  of the engine. During operation the shafts  24 ,  28  rotate along with other structures connected to the shafts such as the rotor assemblies of the turbine  20  and compressor  14  in order to create power or thrust depending on the area of use, for example power, industrial or aviation. 
         [0028]    Referring still to  FIG. 1 , the inlet  12  includes a turbofan  18  which has a plurality of blades. The turbofan  18  is connected by shaft  28  to the low pressure turbine  19  and creates thrust for the turbine engine  10 . The low pressure air may be used to aid in cooling components of the engine as well. 
         [0029]    A damper assembly  40  is shown in the area of the low pressure shaft  28  for point of reference. The damper assembly  40  dampens radial motion of the shaft  28  which occurs due to dynamic loads incurred at the shaft during rotation. However, one skilled in the art should realize that the damper assembly  40  may alternatively be utilized at various other positions along the low pressure shaft or also along various points of the high pressure shaft  24 . 
         [0030]    Referring now to  FIG. 2 , a schematic side section view of an exemplary annular dashpot damper assembly  40  is depicted. The exemplary damper assembly  40  includes an inner ring  42  which is connected to a rotating shaft of a turbine engine  10 . The ring  42  may be defined by an outer bearing race or may be a ring structure as depicted which receives an outer bearing race  43 . In the embodiment depicted, a bearing assembly includes the outer race  43 , an inner race  82  and a plurality of ball bearings or roller bearings  80 . In the embodiment, the inner race  82  is mounted on the shaft  28 . Whether or not the ring  42  is connected to the bearing race  43  or is integrally formed with the race  43 , the ring  42  orbits with the engine shaft  28  so that it moves in radial directions with the shaft  28  during dynamic loading of the shaft. However, the ring  42  does not rotate but is instead fixed so that the shaft  28  and inner race  82  may rotate. 
         [0031]    Disposed radially outwardly of the ring  42  is a stationary ring  44 . The second ring  44  is spaced from the first ring  10  and provides a damping cavity  46  therebetween. Defining the multiple damping cavities  46  between the first ring  42  and the second ring  44 , are a plurality of flow dividers  60 . These dividers  60  allow movement of the first ring  42  relative to the second ring  44  but may inhibit bottoming out of the ring  42  against the second ring  44 . The dividers  60  may be formed of elastomeric or flexible material or may be formed of two or more elements which move relative to one another. Pressure generated within the damping cavities  46  will dampen dynamic loading on the shaft limiting the ring  42  movement relative to the second ring  44 . The dividers  60  according to one embodiment are seated within the inner component and may be formed to allow orbiting movement of the first ring  42 . The dividers  60  may be formed of a multitude of structures including but not limited to blades, elastomeric, Z-seals, C-seals and the like. 
         [0032]    The movement of first ring  42  is in the radial direction but is not rotational. The movement of the dividers  60  through and around oil provide a damping force and may be a plurality of structures which will be described further herein. The damping occurs by generation of pressure on the damping fluid, for example oil, within the cavities  46 . 
         [0033]    The dividers  60  also provide a second function which is to seal the various compartments from one another and therefore limit the rotational fluid of oil flow in the damping cavity  46 . Thus, instead of one large cavity  46  surrounding the ring  10 , a plurality of smaller cavities  46  are created wherein fluid is more readily controlled. By creating smaller cavities  46 , the cavities allow for better control of the damping fluid by way of orifices, clearances, allowances, or other flow metering structures along or around the dividers  60  or spaced away from the dividers  60 . This creates more independently manageable pressure gradients for improved damping of a shaft. Moreover, such structure may be tuned to desirable damping characteristics. 
         [0034]    Although not clearly shown in  FIG. 2 , the second stationary ring  44  is really formed of two rings  44  wherein an inner component  47  is connected to an outer component  45  and joined therebetween by a wall  49 , such that the inner and outer components are concentric. With brief reference to  FIG. 6 , the second stationary ring  44  is generally H-shaped when shown in section perpendicular to the section view of  FIG. 2 . Other shapes may be utilized, for example, a T-shaped stationary ring  44  may be used, or a one piece and/or solid ring for example. 
         [0035]    Referring now to  FIG. 3 , a schematic side section view of the annular dashpot damper assembly  40  is depicted wherein the ring  42  is shifted due to the dynamic loading on the shaft  28  upward towards a twelve o′clock position, for example. The dynamic loading is represented by an arrow D. As shown, the first ring  42  is closer to the second ring at the top dead center position which results in less volume for the damping cavities  46  near the top of the ring  42 . Additionally, the lower cavities  46  near the bottom of the ring  42  have increased volume due to movement of the ring  42 . Additionally, as shown by comparing the upper dividers  60  to the lower dividers  60 , the upper dividers are of decreased length due to movement of the ring  42  upwardly and the lower dividers  60  are of increased length. In the embodiment of  FIGS. 3 and 4 , oil in the cavities  46  moves between sliding surfaces of the dividers  60 . The dividers  60  may be formed in various manners described further herein. 
         [0036]    Referring now to  FIG. 4 , an alternate embodiment of the annular dashpot damper assembly  140  is depicted schematic section. The assembly  140  includes a plurality of flow orifices  148  in the second ring  44 , specifically the inner component  47 . This allows oil to flow from each of the damping cavities  46  to an outer volume formed in part by wall  49  and back in during pumping or suction of the oil. As depicted in  FIG. 4 , the first ring  42  is again depicted in a dynamically loaded position upwardly, for example relative to the second ring  44 . The damping may be adjusted by varying the sizing of the flow orifices  148  in the second ring  14 . Depending on the direction of movement of the first ring  12 , the oil is pumped through the orifices  148  for example at the upper half of the second ring  144 . This causes suction in the flow apertures  148  in the lower half of the second ring  144 . This movement of oil will vary with the movement of the first ring  12  and the gas turbine engine shaft  28 . The orifices  148  may be formed of various structures including controlled end gaps, traditional orifice hole, slots or notches. In additional embodiments, the orifices  148  may be formed through the dividers  60 , such as through axial end surfaces or along inner or outer surfaces. 
         [0037]    Referring now to  FIG. 5 , one embodiment of the dividers  60  is depicted. With reference first to the generally depicted structure, the damper assembly  240  includes an inner ring  42  disposed on an outer race  43  of a bearing assembly including a plurality of balls or rollers  80  and an inner race  82  disposed on the shaft  28 . The stationary ring  144  may include a plurality of orifices  148  for metering oil therethrough. Between the stationary ring  144  and the inner ring  142  are a plurality of damping cavities  46 . Extending between the first inner ring  142  and the second stationary ring  144  are a plurality of dividers  160  defining circumferential segments of the damping cavities  46 . The dividers  160  are formed of a vane or blade  162  which slides within a guide  164 . The vane or blade  162  may be connected to the first ring  42 . Alternatively, the blade or vane  162  may be formed integrally with the first ring  42 . The guide  164 , which receives the blade  162 , is formed with the second ring  144  according to some embodiments. Alternatively, the guides  164  may be connected to the ring  144  by press-fitting for example. 
         [0038]    Also shown at radially outward ends of the guides  164  are heads or stress reliefs  166 . These optionally may be formed with the guides  164  to retain the guides  164  in position within the damper assembly  240 . The stress reliefs  166  also allow damping fluid to flow to both sides of the stationary ring  144 . 
         [0039]    Also shown in  FIG. 5  is a portion of a vane retention ring  70  which extends generally circumferentially about the assembly  240  and between the components  45 ,  47  of the vane retention ring  70 . The vane retention ring  70  is also used, according to the instant embodiment, to retain the vane or blade  162 . Referring briefly to  FIG. 8 , the vane retention rings  70  are placed on both axial sides of an exemplary damper assembly, for example assembly  240  ( FIG. 8 ). The retention ring  70  may also provide a force to push the blades  162  toward the inner ring  142 . The retention ring may be formed through various embodiments including, but not limited to, nested rings, solid rings, C-rings or other structures which may be used to provide the force desired. 
         [0040]    Referring briefly to  FIG. 6 , a section view of one exemplary embodiment of the stationary ring  144  is depicted. The depicted embodiment shows the orifices  148  as well as the vane retention ring  170  on one side of the ring  144 , for purpose of understanding with comparison to  FIG. 5 . The vane retention ring  170  may also, but not necessarily, limit radial travel of the divider  60 ,  160 . 
         [0041]    Referring now to  FIG. 7 , the embodiment of  FIG. 5  is depicted with the section line moved. In the embodiment shown, the damper assembly  240  more clearly shows the vane retention ring  70 . 
         [0042]    Referring now to  FIGS. 8 and 9 , two embodiments of the damper assembly are shown for ease of comparison. Referring first to  FIG. 8 , one embodiment is depicted wherein the bearing outer race  43  is received by the first ring  42 . This may be constructed by press-fitting for example. According to the embodiment of  FIG. 5 , the first ring  42  receives an outer bearing race  43  such as by press fitting, for example. The outer bearing race  43  is a part of a bearing assembly including, according to the exemplary embodiment, a bearing roller  80  and a bearing inner race  82  which engages a rotating shaft  28 . Above the first ring  42  is a damping cavity  46  and the divider  60  which moves with the first ring  43  relative to the second ring  44 . End caps  72  may be positioned at axial ends of the assembly to inhibit leakage of damping fluid from the damping cavities  46 . 
         [0043]    By comparison, and with reference now to  FIG. 9 , the first ring  142  is integrated with the outer bearing race meaning that the first ring is the outer bearing race or is formed integrally therewith. 
         [0044]    Referring to  FIG. 10 , an additional embodiment of a damping assembly  310  is shown wherein the dividers are formed in the manner previously described. Extending from the first ring  242  and integrally formed therewith are a plurality of blades or vanes  262 . Formed integrally in the second ring  244  are a plurality of guides  264 . According to either of these embodiments, additional orifices such as orifices  148  in  FIG. 4  may also be utilized. 
         [0045]    Referring now to  FIG. 11 , an additional embodiment is depicted. According to the instant embodiment, the structure is similar to the embodiments of  FIG. 8 . However, in this embodiment of a dashpot damper assembly, a biasing spring  363  is disposed against outer component  45  and biasing the divider  60  toward the orbiting inner ring  42 . Various types of biasing springs  362  may be utilized including, but not limited to, leaf, band, coil or elastomeric springs. Also, one skilled in the art should realize that various types of biasing springs may be utilized with various of the other embodiments described herein. Further, the biasing springs  362  may be utilized in addition to or in substitution of the vane retaining rings  70 ,  170  in  FIGS. 5-8 . 
         [0046]    While multiple inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the invent of embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure. 
         [0047]    Examples are used to disclose the embodiments, including the best mode, and also to enable any person skilled in the art to practice the apparatus and/or method, including making and using any devices or systems and performing any incorporated methods. These examples are not intended to be exhaustive or to limit the disclosure to the precise steps and/or forms disclosed, and many modifications and variations are possible in light of the above teaching. Features described herein may be combined in any combination. Steps of a method described herein may be performed in any sequence that is physically possible. 
         [0048]    All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms. The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.” The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. 
         [0049]    It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited. 
         [0050]    In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of” shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.