Abstract:
A disclosed intershaft seal assembly for a gas turbine engine includes a support fixed to a static structure. A first seal housing is supported radially outboard of the support for holding a first seal. A second seal housing is supported radially inboard of the support and supports a second seal. A first biasing member is provided between the support and the first seal housing that biases the first seal housing in a first direction away from the support. A second biasing member between the support and the second seal housing biases the second seal housing in a second direction away from the support.

Description:
BACKGROUND 
       [0001]    A gas turbine engine typically includes a compressor section, a combustor section and a turbine section. Air entering the compressor section is compressed and delivered into the combustion section where it is mixed with fuel and ignited to generate a high-speed exhaust gas flow. The high-speed exhaust gas flow expands through the turbine section to drive the compressor and the fan section. 
         [0002]    In gas turbine engines, mechanical seal assemblies are used to prevent hot, high pressure air from entering a bearing compartment that operates at a low pressure and temperature. For example, a front bearing compartment in a multiple spool gas turbine engine is filled with an oil mist to lubricate the bearings that support the high speed rotor shaft and the low speed rotor shaft. The high speed rotor shaft and the low speed rotor shaft are separated by a gap filled with working medium gas. The working medium gas cools the rotor shaft. An intershaft seal assembly is required to keep leakage between the two regions within acceptable amounts during operation. 
         [0003]    Speed variations between shafts experienced by each face seal can result in uneven loading. Moreover, limited space is available within bearing compartments at the interface between shafts sealing between the high and low speed rotor shafts. 
         [0004]    Accordingly, it is desirable to provide a dual configuration intershaft seal assembly for a rotational assembly having rotor shafts including different sealing requirements that reduce seal assembly design space, reduces cost and reduces the overall weight of the assembly. 
       SUMMARY 
       [0005]    A intershaft seal assembly according to an exemplary embodiment of this disclosure, among other possible things includes a support fixed to a static structure, a first seal housing supported radially outboard of the support for holding a first seal, a first biasing member disposed between the support and the first seal housing biasing the first seal housing in a first direction away from the support, a second seal housing supported radially inward of the support for holding a second seal, and a second biasing member disposed between the support and the second seal housing biasing the second seal housing in a second direction away from the support. 
         [0006]    In a further embodiment of the foregoing intershaft seal assembly, the first seal comprises an annular seal biased into contact with a first rotating seal plate. 
         [0007]    In a further embodiment of any of the foregoing intershaft seal assemblies, the second seal comprises an annular seal biased into contact with a second rotating seal plate. 
         [0008]    In a further embodiment of any of the foregoing intershaft seal assemblies, first biasing member comprises a first coil spring and the second biasing member comprises a second biasing member. The first biasing member extends in the first direction and the second biasing member extends in the second direction. 
         [0009]    In a further embodiment of any of the foregoing intershaft seal assemblies, the first coil spring comprises a first plurality of first coil springs spaced circumferentially apart about the support, and the second coil spring comprises a second plurality of coils springs spaced circumferentially apart about the support. 
         [0010]    In a further embodiment of any of the foregoing intershaft seal assemblies, includes a first anti-rotation pin fixed to the support and extending in the first direction through a first opening in the first housing for preventing rotation of the first seal housing relative to the support, and a second anti-rotation pin fixed to the support and extending in the second direction through a second opening in the second housing for preventing rotation of the second seal housing relative to the support. 
         [0011]    In a further embodiment of any of the foregoing intershaft seal assemblies, includes a first radial seal between the first seal housing and the support having a first diameter and a second radial seal between the second seal housing and the support having a second diameter different than the first diameter. 
         [0012]    In a further embodiment of any of the foregoing intershaft seal assemblies, the first diameter is larger than the second diameter. 
         [0013]    In a further embodiment of any of the foregoing intershaft seal assemblies, the support comprises a plurality of flanges extending radially outward from an outer circumference. 
         [0014]    A gas turbine engine according to an exemplary embodiment of this disclosure, among other possible things includes a compressor section including a first compressor supported for rotation on a first shaft and a second compressor supported for rotation on a second shaft, a combustor in fluid communication with the compressor section, a turbine section in fluid communication with the combustor including a first turbine driving the first compressor through the first shaft and a second turbine driving the second compressor through the second shaft, an intershaft seal disposed between the first shaft and the second shaft, the intershaft seal including a support fixed to a static structure, a first seal housing supported radially outboard of the support for holding a first seal, a first biasing member disposed between the support and the first seal housing biasing the first seal housing in a first direction away from the support, a second seal housing supported radially inward of the support for holding a second seal, and a second biasing member disposed between the support and the second seal housing biasing the second seal housing in a second direction away from the support. 
         [0015]    In a further embodiment of the foregoing gas turbine engine, includes a first seal plate on the first shaft and a second seal plate on the second shaft. The first seal comprises an annular seal biased into contact with the first seal plate and the second seal comprises an annular seal biased into contact with the second seal plate. 
         [0016]    In a further embodiment of any of the foregoing gas turbine engines, the first biasing member comprises a first plurality of first coil springs spaced circumferentially apart about the support, and the second biasing member comprises a second plurality of coil springs spaced circumferentially apart about the support. 
         [0017]    In a further embodiment of any of the foregoing gas turbine engines, includes a first anti-rotation pin fixed to the support and extending in the first direction through a first opening in the first housing for preventing rotation of the first seal housing relative to the support, and a second anti-rotation pin fixed to the support and extending in the second direction through a second opening in the second housing for preventing rotation of the second seal housing relative to the support. 
         [0018]    In a further embodiment of any of the foregoing gas turbine engines, includes a first radial seal between the first seal housing and the support having a first diameter and a second radial seal between the second seal housing and the support having a second diameter different than the first diameter. 
         [0019]    A method for sealing a gap between first and second coaxial shafts of a gas turbine engine according to an exemplary embodiment of this disclosure, among other possible things includes positioning a first seal housing supporting a first seal having a first configuration adjacent a first shaft, positioning a second seal housing supporting a second seal having a second, different configuration adjacent the second shaft, and supporting the first seal housing and the second seal housing on a common support. 
         [0020]    In a further embodiment of the foregoing method, includes biasing the first seal in a first direction away from the support with a first coil spring and biasing the second seal in a second direction away from the support with a second coil spring. 
         [0021]    In a further embodiment of any of the foregoing methods, includes assembling a first radial seal between the first seal housing and the support having a first diameter and a second radial seal between the second seal housing and the support having a second diameter different than the first diameter. 
         [0022]    Although the different examples have the specific components shown in the illustrations, embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples. 
         [0023]    These and other features disclosed herein can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a schematic view of an example gas turbine engine. 
           [0025]      FIG. 2  is a schematic view of an example industrial gas turbine engine. 
           [0026]      FIG. 3  is a perspective view of an example intershaft seal. 
           [0027]      FIG. 4  is a cross-sectional view of the example intershaft seal assembly. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]      FIG. 1  schematically illustrates an example gas turbine engine  20  that includes a fan section  22 , a compressor section  24 , a combustor section  26  and a turbine section  28 . Alternative engines might include an augmenter section (not shown) among other systems or features. The fan section  22  drives air along a bypass flow path B while the compressor section  24  draws air in along a core flow path C where air is compressed and communicated to a combustor section  26 . In the combustor section  26 , air is mixed with fuel and ignited to generate a high pressure exhaust gas stream that expands through the turbine section  28  where energy is extracted and utilized to drive the fan section  22  and the compressor section  24 . 
         [0029]    Although the disclosed non-limiting embodiment depicts a turbofan gas turbine engine, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings may be applied to other types of turbine engines; for example a turbine engine including a three-spool architecture in which three spools concentrically rotate about a common axis and where a low spool enables a low pressure turbine to drive a fan via a gearbox, an intermediate spool that enables an intermediate pressure turbine to drive a first compressor of the compressor section, and a high spool that enables a high pressure turbine to drive a high pressure compressor of the compressor section. 
         [0030]    The example engine  20  generally includes a low speed spool  30  and a high speed spool  32  mounted for rotation about an engine central longitudinal axis A relative to an engine static structure  36  via several bearing systems  38 . It should be understood that various bearing systems  38  at various locations may alternatively or additionally be provided. 
         [0031]    The low speed spool  30  generally includes an inner shaft  40  that connects a fan  42  and a low pressure (or first) compressor section  44  to a low pressure (or first) turbine section  46 . The inner shaft  40  drives the fan  42  through a speed change device, such as a geared architecture  48 , to drive the fan  42  at a lower speed than the low speed spool  30 . The high-speed spool  32  includes an outer shaft  50  that interconnects a high pressure (or second) compressor section  52  and a high pressure (or second) turbine section  54 . The inner shaft  40  and the outer shaft  50  are concentric and rotate via the bearing systems  38  about the engine central longitudinal axis A. 
         [0032]    A combustor  56  is arranged between the high pressure compressor  52  and the high pressure turbine  54 . In one example, the high pressure turbine  54  includes at least two stages to provide a double stage high pressure turbine  54 . In another example, the high pressure turbine  54  includes only a single stage. As used herein, a “high pressure” compressor or turbine experiences a higher pressure than a corresponding “low pressure” compressor or turbine. 
         [0033]    The example low pressure turbine  46  has a pressure ratio that is greater than about 5. The pressure ratio of the example low pressure turbine  46  is measured prior to an inlet of the low pressure turbine  46  as related to the pressure measured at the outlet of the low pressure turbine  46  prior to an exhaust nozzle. 
         [0034]    A mid-turbine frame  58  of the engine static structure  36  is arranged generally between the high pressure turbine  54  and the low pressure turbine  46 . The mid-turbine frame  58  further supports bearing systems  38  in the turbine section  28  as well as setting airflow entering the low pressure turbine  46 . 
         [0035]    The core airflow C is compressed by the low pressure compressor  44  then by the high pressure compressor  52  mixed with fuel and ignited in the combustor  56  to produce high speed exhaust gases that are then expanded through the high pressure turbine  54  and low pressure turbine  46 . The mid-turbine frame  58  includes vanes  60 , which are in the core airflow path and function as an inlet guide vane for the low pressure turbine  46 . Utilizing the vane  60  of the mid-turbine frame  58  as the inlet guide vane for low pressure turbine  46  decreases the length of the low pressure turbine  46  without increasing the axial length of the mid-turbine frame  58 . Reducing or eliminating the number of vanes in the low pressure turbine  46  shortens the axial length of the turbine section  28 . Thus, the compactness of the gas turbine engine  20  is increased and a higher power density may be achieved. 
         [0036]    The disclosed gas turbine engine  20  in one example is a high-bypass geared aircraft engine. In a further example, the gas turbine engine  20  includes a bypass ratio greater than about six (6), with an example embodiment being greater than about ten (10). The example geared architecture  48  is an epicyclical gear train, such as a planetary gear system, star gear system or other known gear system, with a gear reduction ratio of greater than about 2.3. 
         [0037]    In one disclosed embodiment, the gas turbine engine  20  includes a bypass ratio greater than about ten (10:1) and the fan diameter is significantly larger than an outer diameter of the low pressure compressor  44 . It should be understood, however, that the above parameters are only exemplary of one embodiment of a gas turbine engine including a geared architecture and that the present disclosure is applicable to other gas turbine engines. 
         [0038]    A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section  22  of the engine  20  is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft., with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (‘TSFC’)”—is the industry standard parameter of pound-mass (lbm) of fuel per hour being burned divided by pound-force (lbf) of thrust the engine produces at that minimum point. 
         [0039]    “Low fan pressure ratio” is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.50. In another non-limiting embodiment the low fan pressure ratio is less than about 1.45. 
         [0040]    “Low corrected fan tip speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram ° R)/518.7) 0.5 ]. The “Low corrected fan tip speed”, as disclosed herein according to one non-limiting embodiment, is less than about 1150 ft/second. 
         [0041]    The example gas turbine engine includes the fan  42  that comprises in one non-limiting embodiment less than about 26 fan blades. In another non-limiting embodiment, the fan section  22  includes less than about 20 fan blades. Moreover, in one disclosed embodiment the low pressure turbine  46  includes no more than about 6 turbine rotors schematically indicated at  34 . In another non-limiting example embodiment the low pressure turbine  46  includes about 3 turbine rotors. A ratio between the number of fan blades  42  and the number of low pressure turbine rotors is between about 3.3 and about 8.6. The example low pressure turbine  46  provides the driving power to rotate the fan section  22  and therefore the relationship between the number of turbine rotors  34  in the low pressure turbine  46  and the number of blades  42  in the fan section  22  disclose an example gas turbine engine  20  with increased power transfer efficiency. 
         [0042]    Referring to  FIG. 2 , an example industrial gas turbine engine assembly  65  includes a gas turbine engine  67  that is mounted to a structural land based frame to drive a generator  69 . The example gas turbine engine  67  includes many of the same features described in the gas turbine engine  20  illustrated in  FIG. 1  and operates in much the same way. The land based industrial gas turbine engine  67 , however, may include additional features such as a shaft to drive the generator  69  and is not constrained by the same weight restrictions that apply to an aircraft mounted gas turbine engine. As appreciated, many of the parts that are utilized in an aircraft and land based gas turbine engine are common and therefore both aircraft based and land based gas turbine engines will benefit from this disclosure and are within the contemplation of this disclosure. 
         [0043]    Referring back to  FIG. 1 , an intershaft seal  62  is provided between the outer shaft  50  and the inner shaft  40 . The intershaft seal  62  maintains separation between buffer air that is circulated within the shafts  40 ,  50  and oil within the bearing compartments  38 . 
         [0044]    In this example, the outer shaft  50  supports rotation of the high pressure compressor section  52  and the inner shaft  40  supports rotation of the low pressure compressor section  44 . Each of the shafts  40 ,  50  rotate at different speeds and therefore the intershaft seal  62  include features that accommodate differing speeds while maintaining the desired seal of buffer air within the shafts  40 ,  50 . 
         [0045]    Referring to  FIGS. 3 and 4 , the example intershaft seal  62  includes a support  64  that is fixed to a static structure such as the engine static structure or case  36  through flanges  66  that extend radially outward from an outer perimeter  68 . The flanges include openings through which fasteners may extend such that the intershaft seal  62  can be rigidly attached to the engine static structure  36 . 
         [0046]    The support  64  defines a radially inner surface  72  and a radially outer surface  70 . On the radially outer surface  70  is provided a groove  74  for a first radial seal  76 . A first seal housing  78  is disposed radially outward of the support  64  and engages the first radial seal  76 . 
         [0047]    The first seal housing  78  is biased axially rearward by a first biasing member  82  such that a seal  80  is biased against a seal plate  90 . The seal plate  90  is attached to the outer shaft  50  that rotates at a speed common with the high pressure compressor  52 . The seal plate  90  rotates with the shaft  50  and the seal  80  maintains a fixed position relative to the rotating seal plate  90 . 
         [0048]    The first seal housing  78  includes a guide  84  that helps align the biasing member  82 . In this example, the biasing member  82  is a coil spring that is supported on a first side within a recess  86  defined on the support  64  and on a second side by the guide  84  attached to the first seal housing  78 . The first seal housing  78  includes a configuration that is in contact with the seal  80 . In this example, the seal  80  is a carbon seal that extends annularly about the axis A and is placed in contact with the seal plate  90 . The seal  80  includes a seal face  88  having a desired area corresponding with the forces required to provide the desired seal between the seal face  88  and the seal plate  90 . 
         [0049]    A second seal housing  98  is supported radially inward of the support  64  and includes a second radial seal  112  disposed within a groove  110  defined on the second seal housing  98 . The second radial seal  112  is biased into contact with the radially inward surface  72  of the support  64 . In this example, the first radial seal  76  includes a diameter  96  that is greater than a second diameter  98  on which the second radial seal  112  is disposed. As appreciated, the difference in the first diameter  96  and the second diameter  98  define different pilot diameters that generate different biasing forces and loads on the corresponding seals. 
         [0050]    The second seal housing  98  supports a second seal  100  against a second seal plate  104  that rotates with the inner shaft  40 . As appreciated, the inner shaft  40  drives the low pressure compressor  44  about the axis A. The seal  100  includes a seal face  102  that is abutted and seals against the rotating second seal plate  104 . 
         [0051]    A second biasing member  106  is disposed between the support  64  and the second seal housing  98 . The second seal housing  98  supports a guide  108  that in turn guides the biasing member  106  during operation. In this example, the first biasing member  82  and the second biasing member  106  are coil springs that extend in opposite directions from the support  64 . The first biasing member  82  and the second biasing member  106  are spaced circumferentially apart about the support  64  and are not coaxial. 
         [0052]    Moreover, each of the first biasing member  82  and the second biasing member  106  define different biasing forces that exert different loads on the corresponding first seal  80  and the second seal  100 . The differing speeds of the outer shaft  50  and inner shaft  40  require different sealing configurations that are provided by the example intershaft seal  62 . The different sealing loads and forces are provided by the differing first and second diameters  96  and  98  along with the different biasing forces exerted by the corresponding first biasing member  82  and the second biasing member  106 . 
         [0053]    Each of the first seal  80  and the second seal  100  are grounded to the engine static structure  36  through the common support  64 . Although each of the first seal  80  and second seal  100  are grounded through the common support  64 , each of the first seal  80  and the second seal  100  operate and move independently to provide the desired sealing loads corresponding with the corresponding shaft speeds. Moreover, the example disclosed intershaft seal assembly  62  includes secondary radial seals  112  and  76  that are disposed at different diameters about the axis A to provide different pilot diameters that correspond with forces required for generating the desired seal of buffer air within the cavities defined by the inner and outer shafts  40 ,  50 . 
         [0054]    Accordingly, the example intershaft seal assembly  62  provides for different sealing between different rotating shaft assemblies within a radially and axially compact area. 
         [0055]    Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the scope and content of this disclosure.