Abstract:
A bearing assembly for a gas turbine engine rotor includes a damper bearing configured to support the rotor, a bearing centering sub-assembly configured to position the damper bearing relative to the rotor, and a retainer. The damper bearing includes a frame that defines a bearing bore, an inner race, and an outer race, said inner and outer races within said bearing bore. The bearing centering apparatus sub-assembly includes a plurality of first springs and a plurality of second springs. The retainer is coupled to the bearing housing and is configured to maintain an axial position of the bearing outer race with respect to the support structure.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This application relates generally to gas turbine engine rotor assemblies and, more particularly, to bearing assemblies for gas turbine engine rotor assemblies.  
           [0002]    Gas turbine engines typically includes a fan rotor assembly, a compressor, and a turbine. The fan rotor assembly includes a fan including an array of fan blades extending radially outward from a rotor shaft. The rotor shaft transfers power and rotary motion from the turbine to the compressor and the fan, and is supported longitudinally with a plurality of bearing assemblies. Bearing assemblies support the rotor shaft and typically include rolling elements located within an inner race and an outer race.  
           [0003]    Additionally, at least some known bearing assemblies include a plurality of identical springs attached to the bearing outer race. The springs are spaced equally in a single row that extends circumferentially around the rotor shaft to provide radial stiffness to the bearing and to center the outer race with respect to the support frame. A first end of the springs is attached to the bearing assembly outer race, and a second end of the springs is attached to a flange coupled to a support frame.  
           [0004]    During operation, an unbalance within the engine may cause the engine rotor shaft to displace radially. The radial displacements of the shaft are transmitted to the bearing assembly and may cause the bearing outer race to orbit within the support frame. The rotation of the outer race may cause the springs to fail in bending. After spring failure, the outer race is not axially retained, and axial movement of the outer race may permit the rotor to inadvertently contact the support frame, and may cause unpredictable static radial loads to be transmitted to the fan rotor assembly, and dynamic radial loads to be transmitted to the support structure.  
         BRIEF DESCRIPTION OF THE INVENTION  
         [0005]    In one aspect of the invention, a bearing assembly for a gas turbine engine rotor is provided. The bearing assembly includes a damper bearing configured to support the rotor, a bearing centering sub-assembly configured to position the damper bearing relative to the rotor, and a retainer. The damper bearing includes a frame that defines a bearing bore, an inner race, and an outer race, said inner and outer races within said bearing bore. The bearing centering apparatus subassembly includes a plurality of first springs and a plurality of second springs. The retainer is coupled to the bearing housing and is configured to maintain an axial position of at least one of the bearing inner race and the bearing outer race.  
           [0006]    In another aspect, a method for reducing dynamic loading of a gas turbine engine rotor assembly is provided. The engine includes a rotor shaft, a support frame, and a bearing assembly including a bearing centering sub-assembly and a damper bearing. The bearing centering sub-assembly includes a plurality of first springs and a plurality of second springs. The method includes supporting the rotor shaft on the support frame with the bearing assembly, coupling the bearing centering sub-assembly first spring to the bearing assembly second spring such that the each of the first springs is radially aligned with respect to each of the second springs, and operating the gas turbine engine such that radial forces within the rotor shaft are transmitted through the bearing centering sub-assembly to the support frame.  
           [0007]    In a further aspect, a rotor assembly including a rotor shaft, a support frame, a bearing assembly, and a retainer is provided. The support frame defines a bearing bore. The bearing assembly is configured to support the rotor shaft on the support frame such that dynamic loads to the support frame are reduced. The bearing assembly includes a bearing centering sub-assembly, a damper bearing, and a retainer. The bearing centering sub-assembly is configured to position the bearing relative to the rotor shaft. The bearing centering sub-assembly includes a plurality of first springs and a plurality of second springs. Each of said first springs radially aligned with respect to each of the second springs. The damper bearing includes an inner race and an outer race. The inner and outer races are within the support frame bore. The retainer is coupled to the support frame and is configured to maintain an axial position of at least one of the bearing inner race and the bearing outer race relative to the support frame. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is schematic illustration of a gas turbine engine;  
         [0009]    [0009]FIG. 2 is a cross-sectional view of an exemplary embodiment of a rotor assembly used in the gas turbine engine shown in FIG. 1;  
         [0010]    [0010]FIG. 3 is a partial end view of a bearing centering subassembly used with the rotor assembly shown in FIG. 2; and  
         [0011]    [0011]FIG. 4 is a radial view of the bearing centering subassembly shown in FIG. 3. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]    [0012]FIG. 1 is a schematic illustration of a gas turbine engine  10  including a fan assembly  12 , a high pressure compressor  14 , and a combustor  16 . Engine  10  also includes a high pressure turbine  18 , a low pressure turbine  20 , and a booster  22 . Fan assembly  12  includes an array of fan blades  24  extending radially outward from a rotor disc  26 . Engine  10  has an intake side  28  and an exhaust side  30 .  
         [0013]    In operation, air flows through fan assembly  12  and compressed air is supplied to high pressure compressor  14 . The highly compressed air is delivered to combustor  16 . Airflow (not shown in FIG. 1) from combustor  16  drives turbines  18  and  20 , and turbine  20  drives fan assembly  12 .  
         [0014]    [0014]FIG. 2 is a cross-sectional view of an exemplary embodiment of a rotor and bearing assembly  40  that may be used with a gas turbine engine, such as engine  10  shown in FIG. 1. In one embodiment, the gas turbine engine is a GE90 available from General Electric Company, Cincinnati, Ohio. Rotor and bearing assembly  40  includes rotor disc  26  (shown in FIG. 1) and a rotor shaft  42  which supports an array of fan blades  24  (shown in FIG. 1) that extend radially outward from rotor disc  26 . Rotor shaft  42  is rotatably secured to a structural support frame  44  with a plurality of bearing assemblies  46  that support rotor shaft  42 . In one embodiment, bearing assembly  46  is a fan roller bearing, and is known as an engine number one bearing. In an alternative embodiment, bearing assembly  46  is a fan thrust bearing (not shown).  
         [0015]    In an exemplary embodiment, each bearing assembly  46  includes a paired race  50  and a rolling element  52 , positioned within a bearing bore  53  defined by frame  44 . In one embodiment, bearing assembly  46  is a damper bearing. Paired race  50  includes an outer race  54  and an inner race  56  radially inward from outer race  54 . Rolling element  52  is located between inner race  56  and outer race  54 . Bearing assembly  46  is enclosed within a bore within a sealed annular compartment  58  radially bounded by rotor shaft  42  and bearing support  44 .  
         [0016]    Support frame  44  includes an annular support sleeve  70  and a plurality of rings  72  sized to be received within a plurality of grooves  74  defined within outer race  54 . More specifically, outer race  54  includes a pair of grooves  74  that receive rings  72 , and a separate groove  76  that is upstream from grooves  74 . Grooves  74  and  76  extend radially inward from an outer surface  78  of outer race  54 . Outer race  54  is positioned such that a gap  80  is defined between race  54  and annular support sleeve  70 . A face  84  of outer race  54  receives rolling element  52  in rollable contact.  
         [0017]    Bearing outer race  54  is coupled to support frame  44  by a fastener  86  and a retainer  88 . Retainer  88  includes an annular body  90  and a shoulder  92 . Retainer annular body  90  has a width  94  that is wider than a thickness  96  of support frame  44  adjacent outer race  54 . Accordingly, because retainer annular body width  94  is larger than frame thickness  96 , retainer  88  extends a distance  100  radially inward from frame  44  towards outer race  54 . More specifically, because retainer annular body  90  has a thickness  98  that is thinner than a width of outer race groove  76 , retainer  88  extends from frame  44  into groove  76 , such that an axial clearance  101  is defined between retainer  88  and frame  44 . Retainer shoulder  92  extends radially downstream from annular body  90  and contacts frame  44 . In one embodiment, shoulder  92  is known as an anti-rotation shoulder.  
         [0018]    Fastener  86  extends through retainer  88  to couple retainer  88  to support frame  44 . In one embodiment, fastener  86  is a threaded bolt. Because retainer  88  extends radially into outer race groove  76 , fastener  86  also functions to maintain, as described in more detail below, outer race  54  coupled to support frame  44 .  
         [0019]    Inner race  56  includes an inner surface  110  and a face  112  that receives rolling element  52  in rollable contact. Inner race  56  is secured within a recess  116  in shaft  42  such that inner race inner surface  110  is adjacent recess  116 .  
         [0020]    A bearing centering sub-assembly  200  positions bearing assembly  46  within rotor assembly  40 . More specifically, bearing centering subassembly  200  centers outer race  54  within bearing assembly  46 . Bearing centering sub-assembly  200  includes a plurality of springs  202  that extend circumferentially around engine  10 . More specifically, bearing centering sub-assembly  200  includes a plurality of first springs  204  and a plurality of second springs  206 . First springs  204  and  206  extend circumferentially around engine  10  in rows (not shown in FIG. 2).  
         [0021]    Each bearing centering sub-assembly first spring  204  includes a forward end  210 , an aft end  212 , and a body  214  extending therebetween. Each first spring forward end  210  is coupled to a downstream side  212  of outer race  54 , such that first spring body  214  extends downstream from outer race  54 . More specifically, each first spring  204  is attached a radial distance  218  outward from rolling element  52 . Each first spring aft end  212  is coupled to an annular elbow  220  downstream from bearing assembly  46  within sealed annular compartment  58 .  
         [0022]    Each bearing centering sub-assembly second spring  206  includes a forward end  221 , an aft end  222 , and a body  224  extending therebetween. Each second spring forward end  221  includes a flange  226  that is coupled to support frame  44  with a fastener  228 , such that second spring body  224  extends downstream from support frame  44 . Additionally, as fastener  228  secures flange  226  to support frame  44 , outer race  54  is then secured in position to support frame  44 .  
         [0023]    Each bearing centering sub-assembly second spring  206  is attached a radial distance  230  outward from rolling element  52 . Radial distance  230  is greater than radial distance  218 . Each second spring aft end  222  is coupled to annular elbow  220  downstream from bearing assembly  46  within sealed annular compartment  58 , such that annular elbow  220  extends between bearing centering subassembly springs  204  and  206 .  
         [0024]    Bearing centering sub-assembly first and second spring bodies  214  and  224  each include an inner surface  236  and  238 , respectively. Because each surface  236  and  238  is substantially planar, and because spring bodies  214  and  224  are substantially parallel, a distance  239  between bearing centering sub-assembly springs  204  and  206  remains substantially constant.  
         [0025]    During engine operation, in the exemplary embodiment, an unbalance of engine  10  may cause high radial forces to be applied to fan assembly  12  (shown in FIG. 1) and bearing assembly  46 . More specifically, during engine operation high rotor deflection may induce radial movement of outer race  54 . During engine operation, retainer  88  only contacts frame  44  and fastener  86 , and as such, axial clearance  101  is maintained between retainer  88  and frame  44 . The radial force is transmitted to support frame  44  through bearing centering sub-assembly  200 . More specifically, as outer race  54  is forced radially outward as a result of rotor deflection, because bearing centering sub-assembly first spring  204  is attached to outer race  54 , the radial movement is transmitted to bearing centering sub-assembly first spring  204 .  
         [0026]    During operation of engine  10 , due to damper radial clearance, a high unbalance may cause outer race  54  to orbit within support frame  44 . The orbiting produces a torque through springs  204  and  206  called harmonic drive. The torque is proportional to the radial load and coefficient of the mating surfaces. At radial loads less than one fan blade out, the torque may cause springs  204  and  206  to fail in bending. More specifically, springs  204  and  206  may fail in bending as a result of continued orbiting of outer race  54  within bore  53 .  
         [0027]    After spring failure, retainer  88  will contact outer race  54  to maintain an axial position of outer race  54  with respect to frame  44 . Retainer  88  will still permit outer race  54  to orbit within bore  53  and will not resist torque loading. More specifically, retainer  88  will maintain an axial position of outer race  54  such that radial loading from rotor  40  is still transmitted into frame  44 . Furthermore, retainer shoulder  92  prevents fastener  86  from rotating and inadvertently unthreading or uncoupling from frame  44 . Accordingly, because axial movement of outer race  54  is facilitated to be reduced, inadvertent contact between rotor shaft  42  and frame  44  is facilitated to be prevented post spring failure. As a result, retainer  88  facilitates extending a useful life of bearing assembly  40  in a cost-effective and reliable manner.  
         [0028]    [0028]FIG. 3 is a partial end view of bearing centering subassembly  200 . FIG. 4 is a top view of bearing centering sub-assembly  200 . Bearing centering sub-assembly first springs  204  and second springs  206  extend circumferentially around engine  10  (shown in FIGS. 1 and 2) in rows  240  and  242 , respectively. Additionally, because each row  240  and  242  of springs  204  and  206 , respectively, is coupled with annular elbow  220 , springs  204  and  206  are sometimes referred to as serially connected or doubled back, and in a hair-pin arrangement.  
         [0029]    More specifically, bearing centering sub-assembly springs  204  and  206  are oriented circumferentially such that each first spring  204  is radially aligned with respect to each second spring  206 , as shown in FIG. 4. As a result, when bearing centering sub-assembly  200  is not anti-rotated, both springs  204  and  206  yield in bending and reduce in length by an equal amount when circumferential force is transmitted to bearing centering sub-assembly  200 . Circumferential force is created when rotor unbalance loads are significant such that the radial gap between race  54  and support sleeve  70  is diminished or bottomed. This results in a net axial translation or displacement of rolling elements  52  on bearing inner race surface  112  equal approximately zero. As a result, because the net axial translation or displacement is approximately zero, retainer  88  may be fabricated such that retainer annular body thickness  98  does not need to withstand high axial loading.  
         [0030]    The above-described rotor assembly is cost-effective and highly reliable. The rotor assembly includes a retainer that includes an anti-rotational shoulder. Following bearing centering sub-assembly spring failure, the retainer maintains an axial position of the outer race relative to the support frame. Accordingly, radial loading is still transmitted into the frame, and inadvertent contact between the rotor shaft and the frame is prevented. As a result, the retainer facilitates extending a useful life of the bearing assembly when the engine is operating in a damaged condition.  
         [0031]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.