Abstract:
An example turbomachine thrust balancing system includes a member coupled in rotation with a turbine for transferring rotational power therefrom. A load carrying device rotatably supports the member. The load carrying device is configured to counteract substantially all of the thrust load generated by the turbine.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/705,708, which was filed on 26 Sep. 2012 and is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    This disclosure relates generally to thrust loads within a turbomachine and, more particularly, to balancing thrust loads to mitigate damage to various turbomachine components. 
         [0003]    Turbomachines, such as gas turbine engines, typically include a fan section, a compression section, a combustor section, and a turbine section. Turbomachines may employ a geared architecture connecting portions of the compression section to the fan section. 
         [0004]    The geared architecture may be an epicyclical gear assembly that causes the fan section and the turbine section to rotate at different speeds, which can increase overall propulsive efficiency. Typically, a shaft driven by one of the turbine sections provides an input to the epicyclical gear assembly that drives the fan section at the reduced speed. Because the turbine drives the fan through the geared architecture, the turbine and the fan are decoupled from one another such that thrust loads associated with the fan do not counteract thrust loads associated with the turbine. 
         [0005]    Direct drive gas turbine engine configurations, by contrast, include turbine sections coupled to the fan section through a common shaft. In direct drive gas turbine engines, the fan and turbine sections provide counteracting thrust forces through the common shaft. 
       SUMMARY 
       [0006]    An exemplary turbomachine thrust balancing system according to an exemplary aspect of the present disclosure includes, among other things, a member coupled in rotation with a turbine for transferring rotational power therefrom. A load carrying device rotatably supports the member. The load carrying device is configured to counteract the thrust load generated by the turbine. 
         [0007]    In a further non-limiting embodiment of the foregoing turbomachine thrust balancing system, the load carrying device may comprise ball bearings. 
         [0008]    In a further non-limiting embodiment of either of the foregoing turbomachine thrust balancing systems, the ball bearings have a diameter that is 0.75 inches or greater. 
         [0009]    In a further non-limiting embodiment of any of the foregoing turbomachine thrust balancing systems, the load carrying device may comprise tapered roller bearings. 
         [0010]    In a further non-limiting embodiment of any of the foregoing turbomachine thrust balancing systems, the thrust load may be rearward relative to a direction of flow through the turbomachine. 
         [0011]    In a further non-limiting embodiment of any of the foregoing turbomachine thrust balancing systems, the member may be rotatably coupled to a geared architecture of a turbomachine. 
         [0012]    In a further non-limiting embodiment of any of the foregoing turbomachine thrust balancing systems, the member may be a fan drive shaft. 
         [0013]    In a further non-limiting embodiment of any of the foregoing turbomachine thrust balancing systems, the load carrying device may be configured to counteract a thrust load of more than 30,000 pounds. 
         [0014]    A turbomachine according to an exemplary aspect of the present disclosure includes, among other things, a fan including a plurality of fan blades rotatable about an axis, and a turbine section includes a fan drive turbine. A geared architecture is configured to be rotatably driven by a member that is rotatably driven by the fan drive turbine to rotate the fan about the axis. A load carrying device supports rotation of the member and counteracts the thrust loads generated by the fan drive turbine. 
         [0015]    In a further non-limiting embodiment of the foregoing turbomachine, the load carrying device may comprise ball bearings. 
         [0016]    In a further non-limiting embodiment of either of the foregoing turbomachines, the ball bearings have a diameter that is at least 0.75 inches. 
         [0017]    In a further non-limiting embodiment of any of the foregoing turbomachines, the load carrying device may comprise tapered roller bearings. 
         [0018]    In a further non-limiting embodiment of any of the foregoing turbomachines, the thrust load may be applied rearward relative to a direction of flow through the turbomachine. 
         [0019]    In a further non-limiting embodiment of any of the foregoing turbomachines, the load carrying device may be configured to counteract a thrust load of more than 30,000 pounds. 
         [0020]    In a further non-limiting embodiment of any of the foregoing turbomachines, a rear disk cavity has a pressure that is less than about 20 psi different than a pressure in a gas path of the turbomachine. 
         [0021]    A method of balancing thrust loads within a turbomachine according to an exemplary aspect of the present disclosure includes, among other things, rotating a member with a turbine; supporting rotation of the member using a load carrying device, driving a geared architecture with the member, and counteracting thrust loads exerted on the member by the turbine using the load carrying device. 
         [0022]    In a further non-limiting embodiment of the foregoing method of balancing thrust loads within a turbomachine, the method includes counteracting the thrust loads with ball bearings having a diameter that is greater than 0.75 inches. 
         [0023]    In a further non-limiting embodiment of either of the foregoing methods of balancing thrust loads within a turbomachine, the method includes counteracting thrust loads greater than 30,000 pounds. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    The various features and advantages of the disclosed examples will become apparent to those skilled in the art from the detailed description. The figures that accompany the detailed description can be briefly described as follows: 
           [0025]      FIG. 1  shows a cross-section view of an example turbomachine. 
           [0026]      FIG. 2  shows a partial section view of a load carrying device of the turbomachine of  FIG. 1 . 
           [0027]      FIG. 3  shows a cross-section of the assembly of  FIG. 2 . 
           [0028]      FIG. 4  shows a partial exploded view of a roller bearing assembly suitable for use with the turbomachine of  FIG. 1 . 
           [0029]      FIG. 5  shows a section view of the assembly of  FIG. 4  in an operating position. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]      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 . 
         [0031]    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. 
         [0032]    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. 
         [0033]    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. 
         [0034]    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. 
         [0035]    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. 
         [0036]    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 . 
         [0037]    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. 
         [0038]    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. 
         [0039]    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. 
         [0040]    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. 
         [0041]    “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 nonlimiting embodiment the low fan pressure ratio is less than about 1.45. 
         [0042]    “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. 
         [0043]    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. 
         [0044]    The engine  20  is an example type of turbomachine. Various areas of the engine  20  experience thrust loads when the engine  20  is operating. For example, the low-pressure turbine  46  and the high-pressure turbine  54  apply a turbine thrust load T T  to both the low-speed spool  30  and the high-speed spool  32 . 
         [0045]    The fan section  42  generates a fan thrust load F T . The fan thrust load F T  and the turbine thrust load T T  are applied in axially opposite directions. These loads are essentially decoupled from each other by the geared architecture  48 . 
         [0046]    At least one of the bearing systems  38  supporting the low-speed spool  30  is a bearing system  38   T  that counteracts a thrust load from the low-pressure turbine  46 . The bearing system  38   T  provides the interface between the rotating rotors of the low-speed spool  30  and the relatively stationary structures of the engine  20 . 
         [0047]    The example bearing system  38   T  interfaces with the shaft  40  of the low-speed spool  30  to counteract the turbine thrust load T T . In another example, the bearing system  38   T  interfaces with a hub, and extension, or another type of member that rotates with the low-pressure turbine  46 . 
         [0048]    The bearing system  38   T  is an example type of load carrying device. Other Examples of load carrying devices include a tapered roller bearing system, or another type of oil-film bearing with rolling elements. In some examples, the load carrying device may include sliding interface bearings using an oil film. In other examples, the load carrying device can be of a type that uses an air pressure cushion or opposing magnetic forces to provide an effective bearing with no or little oil. The sizing of the example load carrying device  38   T  is appropriate for accommodating peak thrust loads of loads greater than 30,000 lbs. 
         [0049]    The example bearing system  38   T  provides a reaction load R L  in a forward direction that counteracts the thrust load T T . The reaction load R L  may be greater than about 5,000 lbs. (2,268 kg) This level of a reaction load R L  may be required when thrust of the engine  20  is at high levels, such as at takeoff. During takeoff of the engine  20  the net load on the bearing system  38   T  is in the aft direction. 
         [0050]    The example low-pressure turbine  46  includes a rear disk cavity  64  having a pressure that is less than about 20 psi different than a pressure in the gas path  70 . These conditions are measured, typically, during a flat-rated, sea level take-off. The example low pressure turbine  46  does not include thrust balancing mechanisms other than the bearing system  38   T . 
         [0051]    Referring now to  FIGS. 2  with continuing reference to  FIG. 1 , one example of the bearing system  38   T  is a ball bearing assembly  78 . The ball bearing assembly  78  includes a radially inner race  82  and a radially outer race  84 , with ball bearings  90  captured therebetween. The ball bearings  90  are held within a carrier  88  such that the ball bearings  90  are circumferentially spaced from each other. The ball bearings  90  are freely rotatable within apertures  90  of the carrier  88 . 
         [0052]    In one example, the shaft  40  is held by the inner race  82 . The ball bearings  90  permit the shaft  40  and inner race  82  to rotate relative to the outer race  84  while maintaining the axial position of the shaft  40  relative to the outer race  84 . The inner race  82  and outer race  84  ride on a thin film of lubricant when moved relative to the ball bearings  90 . The outer race  84  can be directly attached to a fixed structure of the engine  20 . 
         [0053]    The example ball bearing assembly  78  is a thrust ball bearing assembly. The ball bearing assembly  78  counteracts the turbine thrust load T T . In this example, a radially outward extending portion  92  of the inner race  82  extends past a radially inner surface  94  of the ball bearings  90 . A radially inward extending portion  96  of the outer race  84  extends past a radially outermost surface  98  of the ball bearings  90 . The radial overlap between the flanges  92  and  96  and the ball bearings  90  prevents the turbine thrust load T T  from moving the shaft  40  axially relative to the outer race  94  during operation. 
         [0054]    The ball bearings  90  in this example have a diameter d that is greater than 0.75 in (19.05 mm). The example ball bearing assembly  78  is a thrust ball bearing assembly. Within thrust ball bearing assemblies, ball bearings having this diameter are particularly appropriate for accommodating the peak thrust loads of greater than 30,000 lbs. 
         [0055]    Referring to  FIGS. 4 and 5  with continuing reference to  FIG. 1 , another example bearing assembly  38   T  is a roller bearing assembly  100 . The roller bearing assembly  100  includes a radially inner race  102 , a radially outer race  104 . A carrier  108  and roller bearings  110  are captured between the inner race  102  and the outer race  104 . 
         [0056]    Surfaces  112  of the inner race  102  and the outer race  104  interface with the roller bearings  110 . These surfaces  112  are segments of cones. The roller bearings  110  have a tapered outer surface  114 . 
         [0057]    The shaft  40  can be held by the inner race  102 . During operation, the tapered outer surface  114  rotates relative to the surfaces  112 . The rotating surfaces may ride on a relatively thin film of lubricant rather than directly contact each other. The roller bearings  110  are guided by a flange  116  on the inner race  102  during rotation. The flange  116  stops the roller bearings  110  from sliding axially from between the inner race  102  and outer race  104 . 
         [0058]    The conical geometry of the surfaces  112  prevents the turbine thrust load T T  from moving the shaft  40  axially relative to the outer race  102  during operation. The conical geometry may also facilitate carrying higher loads than ball bearing type designs due to the increased interfacing surface area. 
         [0059]    In still other examples, the bearing assembly  38   T  may be a single ball bearing design, tapered ball bearing design, spherical thrust bearing design, tapered roller bearing design, or non-tapered roller bearing design. 
         [0060]    The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. Thus, the scope of legal protection given to this disclosure can only be determined by studying the following claims.