Patent Publication Number: US-11378039-B2

Title: Ring gear mounting arrangement with oil scavenge scheme

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/736,013 filed Jan. 7, 2020, which is a continuation of U.S. patent application Ser. No. 16/122,236 filed on Sep. 5, 2018, which is now U.S. Pat. No. 10,527,151 granted Jan. 7, 2020, which is a continuation of U.S. patent application Ser. No. 15/892,210 filed on Feb. 8, 2018, which is now U.S. Pat. No. 10,082,105, granted Sep. 25, 2018, which is a continuation of U.S. patent application Ser. No. 14/753,048 filed on Jun. 29, 2015, which is now U.S. Pat. No. 10,107,231, granted Oct. 23, 2018, which is a continuation-in-part of U.S. patent application Ser. No. 13/346,120, filed on Jan. 9, 2012, which is a continuation-in-part of U.S. patent application Ser. No. 11/504,220, filed on Aug. 15, 2006, which is now U.S. Pat. No. 8,753,243 granted Jun. 17, 2014. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a ring gear used in an epicyclic gear train of a gas turbine engine. 
     Gas turbine engines typically employ an epicyclic gear train connected to the turbine section of the engine, which is used to drive the turbo fan. In a typical epicyclic gear train, a sun gear receives rotational input from a turbine shaft through a compressor shaft. A carrier supports intermediate gears that surround and mesh with the sun gear. A ring gear surrounds and meshes with the intermediate gears. In arrangements in which the carrier is fixed against rotation, the intermediate gears are referred to as “star” gears and the ring gear is coupled to an output shaft that supports the turbo fan. 
     Typically, the ring gear is connected to the turbo fan shaft using a spline ring. The spline ring is secured to a flange of the turbo fan shaft using circumferentially arranged bolts. The spline ring includes splines opposite the flange that supports a splined outer circumferential surface of the ring gear. The ring gear typically includes first and second portions that provide teeth facing in opposite directions, which mesh with complimentary oppositely facing teeth of the star gears. 
     An epicyclic gear train must share the load between the gears within the system. As a result, the splined connection between the ring gear and spline ring is subject to wear under high loads and deflection. Since the spline connection requires radial clearance, it is difficult to get a repeatable balance of the turbo fan assembly. Balance can also deteriorate over time with spline wear. 
     SUMMARY 
     In one exemplary embodiment, a gas turbine engine includes a bypass ratio greater than about ten (10). A fan is supported on a fan shaft and has a plurality of fan blades. There is a gutter with an annular channel. A gear system is connected to the fan shaft. There is a plurality of planetary gears and a ring gear with an aperture that is axially aligned with the annular channel. The ring gear includes a first portion with a first set of opposed angled teeth separated by a trough from a second portion with a second set of opposed angled teeth. A torque frame at least partially supports the gear system. A low pressure turbine has an inlet, an outlet, and a low pressure turbine pressure ratio greater than 5:1 and a low fan pressure ratio of less than 1.45 across the fan blade alone. 
     In a further embodiment of any of the above, a support relative to a fixed housing facilitates segregation of vibrations. 
     In a further embodiment of any of the above, there is an input to the gear system that facilitates segregation of vibrations. 
     In a further embodiment of any of the above, the gear system includes a sun gear that has a sun gear splined connection. 
     In a further embodiment of any of the above, the input includes an input splined connection complementary to the sun gear splined connection. The gear system includes a gear reduction ratio of greater than 2.5. 
     In a further embodiment of any of the above, the fan shaft is supported by at least one tapered roller bearing. 
     In a further embodiment of any of the above, a fan tip speed less than 1150 ft/second. 
     In a further embodiment of any of the above, a fan tip speed is less than 1150 ft/second. A fan is on a fan shaft and has a plurality of fan blades and a low fan pressure ratio of less than 1.45 across the fan blades alone. 
     In a further embodiment of any of the above, the first portion and the second portion of the ring gear each include a radially extending flange that extends radially outward away from a corresponding set of opposed angled teeth. The fan shaft includes a radially extending flange connected to the radially extending flange on the first portion of the ring gear and the radially extending flange on the second portion of the ring gear. 
     In a further embodiment of any of the above, a seal is attached to at least one of the radially extending flanges on the ring gear or the radially extending flange on the fan shaft. 
     In a further embodiment of any of the above, the seal includes an oil return passage. 
     In a further embodiment of any of the above, the oil return passage includes a slot. 
     In a further embodiment of any of the above, the slot is located in the seal. 
     In a further embodiment of any of the above, the slot is located in the radially extending flange on the fan shaft. 
     In a further embodiment of any of the above, the gutter is for collecting oil expelled from the gear system. 
     In a further embodiment of any of the above, a fan tip speed less than 1150 ft/second. 
     In a further embodiment of any of the above, the gutter is formed from a soft material. 
     In a further embodiment of any of the above, the soft material is aluminum. In another exemplary embodiment, a gas turbine engine includes a fan supported on a fan shaft by at least one roller bearing and has a plurality of fan blades. A bypass ratio is greater than about ten (10). There is a gutter with an annular channel. A planetary gear system is connected to the fan shaft. The gear system has a gear reduction ratio of greater than 2.5 and a plurality of intermediate gears. A ring gear with an aperture is axially aligned with the annular channel. The ring gear includes a first portion separated from a second portion. The first portion and the second portion each include a radially extending flange that extends radially outward away from a corresponding set of opposed angled teeth. A torque frame is at least partially supporting the gear system with respect to the housing which facilitates the segregation of vibrations and other transients. 
     In a further embodiment of any of the above, there is an input to the gear system which facilitates segregation of vibrations. 
     In a further embodiment of any of the above, the gear system includes a sun gear that has a sun gear splined connection. The input includes an input splined connection complementary to the sun gear splined connection. 
     In a further embodiment of any of the above, the roller bearing is a tapered roller bearing. 
     In a further embodiment of any of the above, the gutter is for collecting oil expelled from the gear system. 
     In a further embodiment of any of the above, the gutter is formed from a soft material. 
     In a further embodiment of any of the above, the soft material is aluminum. 
     In a further embodiment of any of the above, a low pressure turbine has an inlet, an outlet, and a low pressure turbine pressure ratio greater than 5:1. A low fan pressure ratio of less than 1.45 which is measured across the fan blades alone. 
     In a further embodiment of any of the above, the fan shaft includes a radially extending flange which is connected to the radially extending flange on the first portion of the ring gear and the radially extending flange on the second portion of the ring gear. 
     In a further embodiment of any of the above, a seal is attached to at least one of the radially extending flanges on the ring gear or the radially extending flange on the fan shaft. 
     In a further embodiment of any of the above, the seal includes an oil return passage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial cross-sectional view of a front portion of a gas turbine engine illustrating a turbo fan, epicyclic gear train and a compressor section. 
         FIG. 2  is an enlarged cross-sectional view of the epicyclic gear train shown in  FIG. 1 . 
         FIG. 3  is an enlarged cross-sectional view of an example ring gear similar to the arrangement shown in  FIG. 2 . 
         FIG. 4  is a view of the ring gear shown in  FIG. 3  viewed in a direction that faces the teeth of the ring gear in  FIG. 3 . 
         FIG. 5  shows another embodiment. 
         FIG. 6  shows yet another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A portion of a gas turbine engine  10  is shown schematically in  FIG. 1 . The turbine engine  10  includes a fixed housing  12  that is constructed from numerous pieces secured to one another. A compressor section  14  having compressor hubs  16  with blades are driven by a turbine shaft  25  about an axis A. A turbo fan  18  is supported on a turbo fan shaft  20  that is driven by a compressor shaft  24 , which supports the compressor hubs  16 , through an epicyclic gear train  22 . The engine  10  is a high-bypass geared architecture aircraft engine. In one disclosed, non-limiting embodiment, the engine  10  bypass ratio is greater than about six (6) to ten (10), the gear train  22  is an epicyclic gear train such as a planetary gear system or other gear system with a gear reduction ratio of greater than about 2.3 and the low pressure turbine  18  has a pressure ratio that is greater than about 5. The engine  10  in one non-limiting embodiment is a high-bypass geared architecture aircraft engine. In one disclosed embodiment, the engine  10  bypass ratio is greater than ten (10:1), the turbofan diameter is significantly larger than that of the low pressure compressor  16 , and the low pressure turbine  27   a  (shown schematically) has a pressure ratio that is greater than 5:1. As understood, the low pressure turbine  27   a  is downstream of at least one upstream, or high pressure turbine. The gear train  22  may be an epicycle gear train such as a planetary gear system or other gear system with a gear reduction ratio of greater than 2.5:1. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans. 
     A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan  18  of the engine  10  is designed for a particular flight condition—typically cruise at about 0.8 M and about 35,000 feet. The flight condition of 0.8 M and 35,000 ft, with the engine at its best fuel consumption—also known as “bucket cruise TSFC”—is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. “Low fan pressure ratio” is the pressure ratio across the fan blade alone, without the FEGV system  36 . The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than 1.45. “Low corrected fan tip speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tambient deg R)/518.7){circumflex over ( )}0.5]. The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than 1150 ft/second. 
     The gear train  22  generally includes a fan drive gear system (FDGS)  100  driven by the compressor shaft  24  through an input coupling  102 . The input coupling  102  both transfers torque from the compressor shaft  24  to the gear train  22  and facilitates the segregation of vibrations and other transients therebetween. 
     The input coupling  102  may include an interface spline  102  joined, by a gear spline  106 , to the sun gear  30 . The sun gear  30  is in meshed engagement with multiple star gears  32 . Each star gear  32  is also in meshed engagement with rotating ring gear  38  that is mechanically connected to the fan shaft  20 . Since the star gears  32  mesh with both the rotating ring gear  38  as well as the rotating sun gear  30 , the star gears  32  rotate about their own axes to drive the ring gear  38 . The rotation of the ring gear  38  is conveyed to the fan  20  through the fan shaft  20  to thereby drive the fan  18  at a lower speed than the turbine shaft  25 . 
     In the example arrangement shown, the epicyclic gear train  22  is a star gear train. Referring to  FIG. 2 , the epicyclic gear train  22  includes the sun gear  30  that is connected to the compressor shaft  24 , which provides rotational input, by the splined connection. A carrier  26  is fixed to the housing  12  by a torque frame  28  using fingers (not shown) known in the art. The carrier  26  supports star gears  32  using journal bearings  34  that are coupled to the sun gear  30  by meshed interfaces between the teeth of sun and star gears  30 ,  32 . Multiple star gears  32  are arranged circumferentially about the sun gear  30 . Retainers  36  retain the journal bearings  34  to the carrier  26 . A ring gear  38  surrounds the carrier  26  and is coupled to the star gears  32  by meshed interfaces. The ring gear  38 , which provides rotational output, is secured to the turbo fan shaft  20  by circumferentially arranged fastening elements, which are described in more detail below. 
     The torque frame  28  supports the carrier  26  with respect to the housing  12  such as a front center body which facilitates the segregation of vibrations and other transients therebetween. It should be understood that various gas turbine engine case structures may alternatively or additionally be provided. 
     The fixed housing  12  may further include a number 1 and 1.5 bearing support frame  108  which is commonly referred to as a “K-frame” which supports the number 1 and number 1.5 bearing systems  110 A,  110 B to support the fan shaft  20  ( FIG. 1 ). The number 1 and number 1.5 bearing systems  110 A,  110 B may include tapered roller bearings which provide a line contact. 
     Referring to  FIGS. 3 and 4 , the ring gear  38  is a two-piece construction having first and second portions  40 ,  42 . The first and second portions  40 ,  42  abut one another at a radial interface  45 . A trough  41  separates oppositely angled teeth  43  (best shown in  FIG. 4 ) on each of the first and second portions  40 ,  42 . The arrangement of teeth  43  forces the first and second portions  40 ,  42  toward one another at the radial interface  45 . The back side of the first and second portions  40 ,  42  includes a generally S-shaped outer circumferential surface  47  that, coupled with a change in thickness, provides structural rigidity and resistance to overturning moments. The first and second portions  40 ,  42  have a first thickness T 1  that is less than a second thickness T 2  arranged axially inwardly from the first thickness T 1 . The first and second portions  40 ,  42  include facing recesses  44  that form an internal annular cavity  46 . 
     The first and second portions  40 ,  42  include flanges  51  that extend radially outward away from the teeth  43 . The turbo fan shaft  20  includes a radially outwardly extending flange  70  that is secured to the flanges  51  by circumferentially arranged bolts  52  and nuts  54 , which axially constrain and affix the turbo fan shaft  20  and ring gear  38  relative to one another. Thus, the spline ring is eliminated, which also reduces heat generated from windage and churning that resulted from the sharp edges and surface area of the splines. The turbo fan shaft  20  and ring gear  38  can be rotationally balanced with one another since radial movement resulting from the use of splines is eliminated. An oil baffle  68  is also secured to the flanges  51 ,  70  and balanced with the assembly. 
     Seals  56  having knife edges  58  are secured to the flanges  51 ,  70 . The first and second portions  40 ,  42  have grooves  48  at the radial interface  45  that form a hole  50 , which expels oil through the ring gear  38  to a gutter  60  that is secured to the carrier  26  with fasteners  61  ( FIG. 2 ). The direct radial flow path provided by the grooves  48  reduces windage and churning by avoiding the axial flow path change that existed with splines. That is, the oil had to flow radially and then axially to exit through the spline interface. The gutter  60  is constructed from a soft material such as aluminum so that the knife edges  58 , which are constructed from steel, can cut into the aluminum if they interfere. Referring to  FIG. 3 , the seals  56  also include oil return passages  62  provided by first and second slots  64  in the seals  56 , which permit oil on either side of the ring gear  38  to drain into the gutter  60 . In the example shown in  FIG. 2 , the first and second slots  64 ,  66  are instead provided in the flange  70  and oil baffle  68 , respectively. 
       FIG. 5  shows an embodiment  200 , wherein there is a fan drive turbine  208  driving a shaft  206  to in turn drive a fan rotor  202 . A gear reduction  204  may be positioned between the fan drive turbine  208  and the fan rotor  202 . This gear reduction  204  may be structured and operate like the gear reduction disclosed above. A compressor rotor  210  is driven by an intermediate pressure turbine  212 , and a second stage compressor rotor  214  is driven by a turbine rotor  216 . A combustion section  218  is positioned intermediate the compressor rotor  214  and the turbine section  216 . 
       FIG. 6  shows yet another embodiment  300  wherein a fan rotor  302  and a first stage compressor  304  rotate at a common speed. The gear reduction  306  (which may be structured as disclosed above) is intermediate the compressor rotor  304  and a shaft  308  which is driven by a low pressure turbine section. 
     Although a preferred 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. For that reason, the following claims should be studied to determine the true scope and content of this invention.