Abstract:
A cam-type apparatus is included in a support link between outer and inner cases of gas turbine engines for centering the cases one to another. The cam-type apparatus is lockable to allow locking an adjusted position of the cam-type apparatus.

Description:
CROSS REFERENCED TO RELATED APPLICATION 
       [0001]    The present application is a divisional application of U.S. patent application Ser. No. 12/466,454 filed on May 15, 2009, the entire content of which is herein incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The application relates generally to a gas turbine engine and, more particularly, to a gas turbine engine having lockable adjustment features for support-links between annular outer and inner cases. 
       BACKGROUND OF THE ART 
       [0003]    A turbofan gas turbine engine basically includes a core portion which must be mounted inside a bypass duct. A traditional engine mount system for a fuselage mount turbofan gas turbine engine reacts to thrust, lateral and vertical loads at the front mounting plane (on the intermediate case of the engine), and reacts to lateral and vertical loads at the rear mount. The rear mount is usually located either on the bypass duct, forming a cantilever core as schematically shown in  FIG. 9 , or on the engine core, typically near the turbine exhaust case, forming a rear core mount as schematically shown in  FIG. 10 . However, the cantilever core suffers from distortion due to inertia loads and tends to droop from the burden of these loads, resulting in tip clearance loss which is critical to the functioning of an axial compressor. The rear core mount suffers from significant bending of the core portion caused by thrust loads. The rear mount carries a load due to a moment created by the engine thrust line of action being offset from the thrust reaction plane. Thus, the core portion is loaded analogous to a simply supported beam with a point moment located at the front mount plane. This effect is critical, particularly on an axial compressor, since the maximum deflection occurs at the rear compressor stages, where small tip clearances are needed to maintain engine operability. 
         [0004]    Accordingly, there is a need to provide an improved mounting system for gas turbine engines. 
       SUMMARY 
       [0005]    In one aspect, there is provided a support-link having lockable adjustment features for interconnecting an annular outer case and an annular inner case of a gas turbine engine, the annular inner case being co-axially positioned within the annular outer case, the support link comprising: a plurality of rods having opposed inner and outer ends, each rod being connected at the outer end to the annular outer case and connected at the inner end to the annular inner case; and a plurality of lockable adjusting devices for adjustably connecting the respective rods to one of the annular outer and inner cases, each of the lockable adjusting devices including a pin and a connecting base attached to said one of the outer and inner cases, the pin having a connecting section and a base section, the connecting section having a central axis eccentric to a central axis of the base section, the connecting section being received in a hole defined in one of the outer and inner ends of one rod and the base section being received in a hole defined in the connecting base, the pin being rotatable relative to the respective rod and connecting base in order to select an angular position of an eccentric distance between the central axes of the respective connecting section and base section of the pin before the pin is locked in position to secure the rod to the connecting base. 
         [0006]    In a second aspect, there is provided a turbofan gas turbine engine comprising: a core portion of the engine; an annular bypass duct wall coaxially surrounding and supporting the core portion, thereby to define an annular bypass air passage radially between the core portion and the bypass duct for directing a bypass air flow passing therethrough; and a support link interconnecting the core portion and the annular bypass duct wall, the support link including a cam-type apparatus adjustable for centering the core portion with respect to the annular bypass duct wall, the cam-type apparatus being lockable to allow locking an adjusted position of the cam-type apparatus, the cam-type apparatus being located outside the annular bypass air passage while the support link extends across the annular bypass air passage. 
         [0007]    Further details of these and other aspects of the present invention will be apparent from the detailed description and drawings included below. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0008]    Reference is now made to the accompanying drawings, in which: 
           [0009]      FIG. 1  is a schematic cross-sectional view of a turbofan gas turbine engine as an exemplary application of the describe subject matter; 
           [0010]      FIG. 2  is a perspective view of a rear mounting assembly according to one embodiment, as used in the engine of  FIG. 1 ; 
           [0011]      FIG. 3  is a partial perspective view of the rear mounting assembly of  FIG. 2  in an enlarged portion, showing one of the connecting brackets with a mounting portion; 
           [0012]      FIG. 4  is a partial perspective view of the circled area  4  of the rear mounting assembly of  FIG. 2 , looking into the inside surface of a bypass duct wall in an enlarged scale, showing the attachment of link rods to the connecting brackets; 
           [0013]      FIG. 5  is a cross-sectional view of the link rod taken along line  5 - 5  in  FIG. 4 , showing the aerodynamic profile of the link rod; 
           [0014]      FIG. 6  is a partial perspective view (partially exploded) of the rear mounting assembly of  FIG. 2  in an enlarged scale, showing a lockable adjustment device for connection of the link rods to a mid turbine frame (MTF) of a core portion of the engine; 
           [0015]      FIG. 7   a  is a top plan view of a pin used in the lockable adjustment device of  FIG. 6 , showing an annular position of an eccentric distance between the central axes of the respective connecting section and base section of the pin; 
           [0016]      FIG. 7   b  is a side elevational view of the pin in  FIG. 7   a  with a connected inner end of a link rod shown in broken lines; 
           [0017]      FIG. 8  is a perspective view of a lockable adjustment device according to another embodiment; 
           [0018]      FIG. 9  is a schematic illustration of a prior art turbofan gas turbine engine mounting system, showing a cantilever core portion; and 
           [0019]      FIG. 10  is a schematic illustration of a prior art turbofan gas turbine engine mounting system, showing a rear core portion mount. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    Referring to  FIG. 1  a long duct mixed flow (LDMF) turbofan gas turbine engine (not numbered) includes an annular bypass duct wall  10 , a low pressure spool assembly (not numbered) which includes a fan assembly  14 , a low pressure compressor assembly  16  and a low pressure turbine assembly  18  connected by a shaft  12 , and a high pressure spool assembly (not numbered) which includes a high pressure compressor assembly  22  and a high pressure turbine assembly  24  connected by a shaft  20 . A core portion  13  accommodates the high pressure compressor  22  and the low and high pressure turbine assemblies  18 ,  24 , to define a main fluid path (not numbered) therethrough. In the main fluid path there is provided a combustor  26  to generate combustion gases to power the high and low pressure turbine assemblies  24 ,  18 . A mid turbine frame (MTF)  28  as part of the core portion  13  is disposed between the high and low pressure turbine assemblies  24  and  18 . The core portion  13  is coaxially positioned within the annular bypass duct wall  10  and an annular bypass air passage  30  is defined radially between the annular bypass duct wall  10  and the core portion  13  of the engine for directing a bypass air flow  32  driven by the fan assembly  14 , to pass therethrough. 
         [0021]    Referring to  FIGS. 1-5 , a front mounting assembly  34  is attached to the annular bypass duct wall  10  at a front axial position indicated by line  36  (representing a front mounting plane) located close to an inlet (not numbered) of the annular bypass air passage  30 , to mount the engine to an aircraft (not shown). Radial struts  38  are provided near the axial location of the front mounting plane  36  and extend between the bypass duct wall  10  and the core portion  13  to support the core portion within the bypass duct  10 , transferring thrust, lateral and vertical loads to the front mounting assembly  34 . 
         [0022]    A rear mounting assembly  40  is also attached to the annular bypass duct wall  10  at a rear axial position indicated by line  42  (representing a rear mounting plane), close to an outlet (not numbered) of the bypass air passage  30 . The rear mounting assembly  40  includes a plurality of circumferentially spaced apart connecting brackets  44  which are attached to the bypass duct wall  10 , and a plurality of link rods  46  having opposed inner and outer ends (not numbered), extending across the annular bypass air passage  30 , and substantially tangential to the core portion  13  of the engine. Each link rod  46  is connected at the outer end thereof to the bypass duct wall  10  by means of connecting brackets  44  and is attached at the inner end thereof to the MTF  28  of the core portion  13 . 
         [0023]    The link rods  46  include a first group in which each rod  46   a  extends from the outer end to the inner end thereof in a substantially tangential direction to the core portion  13  corresponding to a first circumferential direction  48   a,  and a second group in which each link rod  46   b  extends from the outer end to the inner end thereof in a substantially tangential direction to the core portion  13  corresponding to a second circumferential direction  48   b  opposite to the first circumferential direction  48   a.    
         [0024]    Each of the connecting brackets  44  according to this embodiment, is connected with two adjacent link rods  46 , i.e. one link rod  46   a  in the first group and the other link rod  46   b  in the second group. In particular, the connecting bracket  44  has a generally U-shaped cross-section formed by two spaced apart side walls (not numbered) interconnected by a bottom wall  50  which is curved to match the configuration of a portion of a peripheral surface of the annular bypass duct wall  10 . The connecting bracket  44  is mounted to the outer side of the bypass duct wall  10 , and is axially positioned between and affixed to two axially spaced apart flanges  52  which extend radially and outwardly from the annular bypass duct wall  10 . At least one of the connecting brackets  44  includes a mounting portion  54  with one or more mounting openings (not numbered) defined therein, extending radially and outwardly from the annular bypass duct wall  10  for connection with a mounting device of the aircraft (not shown), two of the four connecting brackets  44  have the mounting portions as shown in  FIG. 2 . A cavity  56  with a closed top and open bottom is provided at the middle of each of the connecting brackets  44 , defined between the axially spaced apart side walls of the connecting brackets  44  and between two circumferentially spaced apart end walls  58 . The two circumferentially spaced apart end walls  58  extend divergently from each other, substantially in the tangential directions corresponding to those of the two adjacent link rods  46  (one rod  46   a  and the other rod  46   b ) which are connected to the said connecting bracket  44 . 
         [0025]    The tangential link rods  46  form a short circuit across the annular bypass air passage  30  to transfer the core portion related inertia-induced loads from the MTF  28  to the connecting brackets  44  and the bypass duct wall  10 . 
         [0026]    The link rods  46  function as an effective load path to the rear mounting assembly  40  for inertia-induced loads originating from the core portion  13 , thus reducing core deflections from that source (inertia-induced meaning loads from gravity or acceleration). The core portion  13  is therefore supported at both mount planes represented by lines  36 ,  42 , rather than the “cantilever” mount of  FIG. 9  which does not support the core portion  13  at the rear and hence causes core droop effect. 
         [0027]    It should be noted that if only engine thrust is applied to the structure of an engine which is of a rear core mount as shown in  FIG. 10 , the center of the bypass would shift laterally from the center of the engine core. This is because the core is bending like a simply supported beam and has a certain amount of bending rotation at the front mount. This rotation is then carried through to the bypass flange at the outside of the intermediate case and gives a slope to the bypass relative to the core, which in turn leads to a lateral shifting of bypass center relative to the core center at the rear mount. In contrast, the rear mounting assembly  40  of this embodiment adds in the link rods  46 , and moves the rear mount reaction point to the bypass duct wall  10 . This relative centerline shift associated with the rear core mount of  FIG. 10 , is largely prevented by the tie-up with the link rods  46 . The bypass duct wall  10  is a stiffer load path than the core portion  13 , and thus the bypass duct wall  10  rather than the core portion  13 , carries the bulk of the moment produced by the rear mount reaction, thereby reducing carcass bending of the core portion  13 . 
         [0028]    A plurality of openings  60  in the annular bypass duct wall  10  are provided aligning with the cavities  56  of the respective connecting brackets  44 , in order to allow the outer end of each link rod  46  to access the cavity  56  in the connecting bracket  44  mounted to the outside of the bypass duct wall  10 , from the inside of the bypass air passage  30 . The inner ends of the two adjacent link rods  46  are secured to the circumferentially spaced end walls  58  of each connecting bracket  44  by means of screw fasteners (not numbered), respectively. 
         [0029]    Each of the link rods  46  may have an aerodynamic profile in cross-section (see  FIG. 5 ), defined with side surfaces  62  extending between a leading edge  64  and a trailing edge  66  with respect to the bypass air passage  30  of the engine. The cross-sectional profile of the link rod  46  may have a dimension “C” between the side surfaces  62  smaller than a dimension “X” between the leading and trailing edges  64 ,  66  in order to reduce air pressure loss in the bypass air flow  32  caused by the link rods  46 . A hollow configuration of the link rod  46  may also be an option. 
         [0030]    The tangential link rods  46  may be connected at their inner ends directly to the MTF  28  or by means of any type of connector assemblies. For example, the link rods  46  are usually fabricated in a same length for manufacturing economy and installation mistake-proofing. Therefore, an additional adjustability feature may be required to accommodate the eccentric condition of the bypass duct wall  10  and the MTF  28  of the core portion  13  caused by manufacturing and assembly tolerances thereof. Therefore, the tangential link rods  46  may be connected to the MTF  28  by means of a lockable adjustment device  68  which is able to maintain the link rod  46  in the correct orientation to the flow. 
         [0031]    Referring to  FIGS. 1-2  and  5 - 7   b,  the lockable adjusting device  68  includes at least one pin  70  and a connecting base  72  to connect at least one link rod  46  to the MTF  28 . In the embodiment shown in  FIGS. 2 and 6 , two pins  70  are provided to each connecting base  72  such that each connecting base  72  can connect two adjacent link rods  46  to the MTF  28  (one rod  46   a  and the other rod  46   b ). For convenience and precision of description, only one pin  70  and its connection to the connecting base  72  is described. It should be noted that the other pin  70  and its connection to the same connecting base  72  is substantially the same. 
         [0032]    The connecting bases  72  are circumferentially spaced apart and attached to the core portion  13 , for example to a flange  74  radially and outwardly extending from the MTF  28  of the core portion  13 . Each of the connecting bases  72  defines two holes  76  extending substantially radially therethrough. The pin  70  includes a connecting section  78  with a central axis  80  and a base section  82  with a central axis  84 . The central axis  80  of the connecting section  78  is eccentric to the central axis  84  of the base section  82 , at an eccentric distance “d”. The connecting section  78  is received in a hole  86  of a link rod  46  ( FIG. 7   b ), and the base section  82  is received in one of the holes  76  defined in the connecting base  72  ( FIG. 6 ). Therefore, an angular position “A” of the eccentric distance d with respect to a direction represented by line  88  which is parallel to the connected link rod  46 , may be selected by rotating the pin  70  before the pin  70  is locked in position to secure the rod  46  to the connecting base  72 . When the angular position A of the eccentric distance d changes within 180 degrees, a link length “L” which is measured in the direction of line  88  (or in the direction of the connected link rod  46 ) will change in a range of d×2. 
         [0033]    The base section  82  of the pin  70  and the hole  76  defined in the connecting base  72 , may be tapered complimentarily to each other. The pin  70  may further have a threaded section  90  extending from the small end of the tapered base section  82 , for engagement with a locking nut  92  such that the tapered base section  82  of the pin  70  is secured within the tapered hole  76  of the connecting base  72  to lock the selected angular position of the pin  70  when the locking nut  92  is tightly engaged with the threaded section  90 . The base section  82  of the pin  70  and the hole  76  of the connecting base  72  may be tapered in an angle smaller than a self locking tapering angle such that the eccentric pin  70  is self-locked with the connecting base  72  against the rotation resulting from offset loads (torque) introduced by the link rods  46  even if the locking nut  92  accidentally loosens from engagement with the threaded section  90 . 
         [0034]    The connecting section  78  may further have a threaded end portion (not numbered) for engagement with a second locking nut  94  with a washer (not numbered) to prevent the connected link rod  46  from disconnecting from the connecting section  78  of the pin  70 . 
         [0035]    The pin  70  may further define a hexagonal recess (not numbered) defined in the end of the connecting section  78  as a means to rotate and hold the pin to maintain the selected angular position of the pin  70  while tightening the nut  92 . The lockable adjustment device  68  provides a compact configuration to ensure the concentricity of the bypass duct wall  10  and the MTF  28 . This compact configuration can be conveniently attached to the MTF  28  and located outside of the annular bypass air duct  30 . The adjustment of the eccentric pin  70  does not affect the orientation of the aerodynamic profile of the link rods  46  in the bypass air flow  24 . The self-locking tapering feature of the eccentric pin  70  provides a level of mistake-proofing in the field. Furthermore, there is no need to re-adjust the pins  70  once the engine is assembled, and the link rods  46  may be freely removed and re-installed in the field for maintenance purposes because the connecting base  72  which receives the respective link rods  46  is independently affixed to the MTF flange  74 , thereby maintaining the adjustment. 
         [0036]      FIG. 8  shows a lockable adjustment device  68   a  according to another embodiment in which similar components and features are indicated by numerals similar to those used for the lockable adjustment device  68  of  FIG. 6  for ease of description. The difference between devices  68  of  FIGS. 6 and 68   a  of  FIG. 8 , lies in that the pin  70  of adjustment device  68   a  further includes an extension  96  extending from the connecting section and is concentric with the base section  82 . The extension  96  is received in a hole  97  defined in a supporting member such as a plate  98 . After the pin  70  is locked in its adjusted position in the connecting base  72  and an inner end of a link rod  46  is attached to the connecting section  78  of the pin  70  (similar to that shown in  FIG. 7   b ), the plate  98  is attached to the extension  96  of the pin  70  by receiving the extension  96  to extend through the hole  97  therein. The plate  98  is then affixed by fasteners (not shown) to the connecting base  72  or to the MTF  28 . The extension  96  may optionally have a threaded end portion  100  such that the locking nut  94  with a bushing (not numbered), may be used to further secure the plate  98  to the pin  70 . The lockable adjustment device  68   a  provides the connecting base  72  and plate  98  as two spaced apart support elements flanking the connecting section  78  which connects the link rod  46 , thereby forming a double-shear version of an adjustable pin connecting arrangement, in contrast to the device  68  of  FIG. 6  which is a single-shear version of an adjustable pin connecting arrangement. 
         [0037]    It should be understood that a support-link lockable adjustment arrangement as illustrated by devices  68  or  68   a  is described as a part of a support link of a mounting system for a long duct mixed flow (LDMF) turbofan gas turbine engine in the above-described embodiments. However this support-link lockable adjustment arrangement may be applicable to support links of other types for interconnecting an annular outer case and an annular inner case of a gas turbine engine. This compact cam-type of support-link lockable adjustment arrangement can be used at either end of the link in its attachment to an outer case or an inner case, conveniently located outside of the annular bypass air duct. This support-link lockable adjustment arrangement may be used with tangential links as described in this application, or with radial support links. The eccentric pin may extend either in a substantially radial direction as described in the embodiments or may extend in a substantially axial direction. 
         [0038]    The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the concept disclosed. For example, the short circuit for transferring inertia-induced loads directly from the MTF to the bypass duct casing may be configured differently from the particular embodiments described above and may be applicable to any bypass duct gas turbine engine different from the engine as described. The mounting assembly incorporated with the connector for connecting the link rods to the bypass duct wall may be configured differently form the described embodiments of the connecting brackets. Still other modifications which fall within the scope of described concept will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.