Patent Publication Number: US-8979483-B2

Title: Mid-turbine bearing support

Description:
TECHNICAL FIELD 
     The invention relates to spool support structures used within gas turbine engines in general, and to spool support structures for multi-spool gas turbine engines in particular. 
     BACKGROUND OF THE INVENTION 
     A gas turbine engine generally includes a fan, a low pressure compressor, a high pressure compressor, a combustor section, a low pressure turbine, and a high pressure turbine disposed along a common longitudinal axis. The fan and compressor sections input work into the ambient air drawn into the engine, thereby increasing the pressure and temperature of the air. Fuel is added to the worked air and the mixture is burned within the combustor section. The combustion products and any unburned air subsequently power the turbine sections and exit the engine and may produce thrust. A low pressure spool (sometimes referred to as an “axial shaft”) connects the fan, which may also produce thrust, and a low pressure compressor and the low pressure turbine. A high pressure spool (sometimes referred to as an “axial shaft”) connects the high pressure compressor and the high pressure turbine. The low pressure spool and high pressure spool are rotatable about the longitudinal axis. 
     It is known to use support frames (e.g., with circumferentially distributed struts) to support the low and high pressure spools within the gas turbine engine. The support frames extend radially toward each respective spool and have a bearing disposed at a distal end, which bearing is in contact with the spool. The bearings facilitate rotation of the spools and provide a load path between the spool and the support frame. 
     The angular momentum (“L”) of the axial shaft, which is a function of its angular velocity (“.omega.”), imparts a torque to the frame to which the bearing is mounted. The torque, in turn, creates shear stress within the frame. To accommodate the torque and concomitant stress, the frame may include a torque box. 
     SUMMARY OF THE INVENTION 
     According to an embodiment disclosed herein, a bearing assembly for a gas turbine engine includes a bearing, an outer assembly disposed about an axis and having an angled perimeter, and an inner assembly supporting the bearing and having a surface angled to slide against and attach to the angled perimeter as the bearing is aligned with the axis. 
     According to a further embodiment disclosed herein, an assembly for supporting a bearing includes an outer casing, an inner casing having an outer surface, and a plurality of struts connecting the inner casing and the outer casing, each strut having a surface disposed at a complimentary angle to the outer surface. The surface and the outer surface move relative to each other in plane as the bearing is aligned along an axis. A fastener attaches the surface to the outer surface after the bearing is aligned with the axis. 
     According to a further embodiment disclosed herein, a method of assembling a rotating engine includes the steps of: providing a bearing, providing an outer assembly disposed about an axis and having an angled perimeter greater than zero degrees; providing an inner assembly for supporting the bearing and having a surface angled at a same angle as the perimeter; and sliding the angled perimeter along the surface in plane while aligning the bearing along the axis. 
     These and other features of the invention would be better understood from the following specifications and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional perspective view of gas turbine engine. 
         FIG. 2  is a perspective view of an assembly that forms a portion of the gas turbine engine of  FIG. 1 . 
         FIG. 3  is an exploded view of the assembly of  FIG. 2 . 
         FIG. 4  shows the assembly of  FIG. 2  within the environment of a gas turbine engine. 
         FIG. 5  shows a portion of the assembly of  FIG. 4  in a disassembled state. 
         FIG. 6  shows a portion of the assembly of  FIG. 5  in a reassembled state. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1-2 , a gas turbine engine  10  includes a fan  12 , a low pressure compressor  14 , a high pressure compressor  16 , a combustor  18 , a high pressure turbine  20 , a low pressure turbine  22 , a low pressure spool  24 , a high pressure spool  26 , and a nozzle  28 . Each compressor and turbine section  14 ,  16 ,  20 ,  22  include a plurality of stator vane stages and rotor stages (shown generally herein). Each stator vane stage includes a plurality of stator vanes that guide air into or out of a rotor stage in a manner designed in part to optimize performance of that rotor stage. Each rotor stage includes a plurality of rotor blades attached to a rotor disk. The low pressure spool  24  extends between, and connects the low pressure compressor  14  to the high pressure turbine  20  and the fan  12 . The high pressure spool  26  extends between, and is connected with, the high pressure compressor  16  and the low pressure turbine  22 . The low pressure spool  24  and the high pressure spool  26  are concentric and rotatable about the longitudinally extending axis  30  of the engine. One of ordinary skill in the art will recognize that other arrangements of the components of the gas turbine engine  10  are within the teachings made herein. 
     Referring now to  FIGS. 2-4 , an embodiment of an assembly  38  (shown schematically in  FIG. 2 ) is disposed between the high pressure turbine  20  and the low pressure turbine  22 . The assembly  38  supports bearings rotatably supporting the low pressure spool  24  and the high pressure spool  26  as will be discussed herein below. The assembly  38  has a casing  39 , a ring structure  40  disposed within the casing  39 , and a cover  45  for attaching the assembly  39  to a bearing structure  50 . The casing  39  is attached to the ring structure  40  (e.g., an inner assembly) by struts  32  (e.g., an outer assembly). The ring structure and the cover  45  form a torque box that resists bending and thrust moments. 
     Referring to  FIG. 4 , each strut  32  fits within a hot air passage  55  through which highly energized air passes from the high pressure turbine  20  to the low pressure turbine  22 . Each strut  32  is enclosed by a fairing  60 , which directs air to the low pressure turbine  22  at a particular angle as is known in the art. The bearing structure  50  has a high pressure spool bearing  65 , and a low pressure spool bearing  70  that are supported thereby and as will be discussed herein. 
     Referring back to  FIGS. 2-4 , struts  32  are welded at their outer diameters  75  to the casing  39 . The inner diameter portions  80  of each strut  32  form the shape of a cone about a virtual perimeter  83  thereof. A pair of bolt holes  85  is disposed in an inner diameter  80  of the struts  32 . Each strut  32  essentially forms an I-beam shape  90  and has a pair of beams  95  each having a bolt hole  85  therein. The beams  95  are connected by a web  100 . The struts  32  are disposed at a particular angle relative to the air flow passing through the gas turbine engine  10  to provide stiffness in the radial and axial directions to counteract the massive torque created by combustion gases passing over turbine airfoils within the gas turbine engine  10 . An inner diameter  80  has an angle α relative to axis  30  passing through the gas turbine engine  10  to conform with the shape of the hot air passage  55  (see  FIGS. 4 and 6 ). The beams  95  are circular but other shapes are within the teachings described herein. The struts have good stiffness and torsional rigidity fore and aft. The angles of the struts could be between 30° and 60° relative to a direction of flow through the engine  10 . 
     The ring structure  40  has an outwardly angled surface  105  that cooperates with the inner diameter  80  of the struts  32  also at angle α relative to axis  30  passing through the gas turbine engine  10 . The surface  105  creates a conical surface about the ring structure perimeter  107 . Oversized holes  110  passing through the angled surface  105  receive bolts  115  (e.g., fasteners) there through that attach within the bolt holes  85  in the beams  95  of the struts  32 . See also  FIG. 6 . 
     Referring now to  FIGS. 4-6 , the ring structure  40  has a first radially inwardly extending flange  120  extending from a first end  125  thereof, and a second radially inwardly extending flange  130  extending from a second end  135  thereof. A first axially extending flange  140  extends axially aft from the first radially inwardly extending flange  120  to mate with the inner cover  45  as will be discussed herein. Similarly, the second radially inwardly extending flange  130  also mates with the cover assembly  45  as will be discussed herein. 
     The cover  45  is the second axially extending flange  145  cooperating with the first axially extending flange  140  for attachment thereto by bolts or other means. The third radially extending flange  150  cooperates with the second radially extending flange  120  on the ring structure  40 . A fourth radially extending flange  155  that extends radially outwardly from the second axially extending flange  145  attaches to the bearing structure  15  as will be discussed herein. The third radially extending flange  150  and fourth radially extending flange  155  are connected by an axially extending connector  160 . 
     The bearing structure  50  has an upright bracket  170  that attaches to the fourth radially inwardly extending flange  155  by bolts or otherwise. An angled support  175  extends axially forward and has an attaching attachment  180  that supports a U-shaped land  185  having a land surface  190 . The land surface  190  supports bearings  65  attaching to the high pressure spool bearing  65 . Similarly, complimentary bracket  195  (see  FIG. 3-4 ) extends radially aft and supports a land  200  which supports bearings bearing  70  about which the low pressure spool rotates. 
     While machining is remarkably accurate, there are always some intolerances within an engine  10 . In order to minimize the effect of the intolerances, and the stresses that may accompany them, the assembly  38  takes the intolerances into account. For instance, oversized holes  110  allow sliding along the inner diameter end  80  of the struts and the angled surface  105  of the ring structure as the low pressure spool  24  and the high pressure spool  26  are aligned along axis  30 . The perimeter of the struts  32  aligns with the perimeter  107  of the angled surface  105 . Because the lands  190  and  200  are oversized, any sliding between the strut inner diameter  80  and the ring structure outer angled surface  105  causes the lands  190 ,  200  to move axially along the bearings  65 ,  70  to account for tolerance deviations thereof. 
     Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. One of ordinary skill in the art will recognize that the teachings herein are applicable to other bearing assemblies, including other bearing assemblies in gas turbine engines. 
     For that reason, the following claims should be studied to determine the true scope and content of this invention.