Patent Publication Number: US-2016230843-A1

Title: Gearbox for gas turbine engine

Description:
BACKGROUND 
     This disclosure relates to a gearbox for a gas turbine engine and the arrangement of this gearbox relative to the engine. 
     A typical gas turbine engine for an aircraft includes an accessory drive gearbox. The gearbox is rotationally coupled to at least one spool of the engine by a tower shaft. In one configuration, the gearbox is mounted adjacent to an engine core and enclosed by a core nacelle surrounding the engine core. 
     It is desirable to provide a compact gearbox configuration, which more easily packages within the space between the core nacelle and engine core. One example gearbox configuration utilizes an arcuate shaped gearbox assembly with all of the gears within the gearbox parallel to one another. The rotational axes of the gears and the accessory drive components are arranged in the same direction as the axis of the engine. 
     Another gearbox configuration provides a U-shaped housing that is arranged at the bottom of the engine core. The accessory drive component axes are arranged in a generally radial orientation with respect to the engine axis. 
     SUMMARY 
     In one exemplary embodiment, a gearbox for a gas turbine engine includes a housing that includes a cavity provided between opposing first and second mounting surfaces. An input gear shaft is coupled to a drive gear. The drive gear is connected to first and second shaft portions that respectively extend to the first and second mounting surfaces. The first and second shaft portions and the drive gear are coaxial with one another. 
     In a further embodiment of the above, a gear train has multiple drive gears that include the drive gear. Each of the multiple drive gears have first and second shaft portions that are coaxial with one another and their respective drive gear. 
     In a further embodiment of any of the above, the multiple drive gears include first, second and third drive gears. The first drive gear corresponds to the drive gear. 
     In a further embodiment of any of the above, the gear train includes an idler gear that couples at least two of the multiple drive gears. 
     In a further embodiment of any of the above, the gear train includes first and second idler gears. The first idler gear corresponds to the idler gear. The first and second gears are arranged in alternating relationship with the first, second and third drive gears. 
     In a further embodiment of any of the above, all of the shaft portions are parallel with one another. 
     In a further embodiment of any of the above, the multiple drive gears are in the same plane. 
     In a further embodiment of any of the above, accessory drive components include at least two of an air turbine starter, a deoiler, a variable frequency generator, a permanent magnet alternator, a fuel pump, a lubrication pump and a hydraulic pump. At least two of the accessory drive components are configured to be rotationally driven by the multiple drive gears. One of at least two of the accessory drive components are mounted to the first mounting surface. The other of at least two accessory drive components is mounted to the second mounting surface. 
     In a further embodiment of any of the above, at least two accessory drive components are the air turbine starter and the deoiler. 
     In a further embodiment of any of the above, at least two accessory drive components are the variable frequency generator and the permanent magnet alternator. 
     In a further embodiment of any of the above, at least two accessory drive components are the fuel pump and the lubrication pump. 
     In a further embodiment of any of the above, the input gear shaft is coupled to a gear set that is connected to the drive gear. The gear set includes a bevel gear. 
     In a further embodiment of any of the above, the first and second mounting surfaces are parallel to one another. 
     In another exemplary embodiment, a gas turbine engine includes a core that includes a turbine shaft that is configured to rotate about an engine axis. A tower shaft is coupled to the turbine shaft. A gearbox is mounted to the core. The gearbox includes a housing that includes a cavity that is provided between opposing first and second mounting surfaces. An input gear shaft is coupled to the tower shaft. A drive gear is connected to first and second shaft portions that respectively extend to the first and second mounting surfaces. The drive gear is configured to rotate about a gear axis. First and second accessory drive components are respectively mounted to the first and second mounting surfaces and respectively coupled to the first and second shaft portions. 
     In a further embodiment of any of the above, the engine axis and gear axis are perpendicular to one another. 
     In a further embodiment of any of the above, a gear train has multiple drive gears that include the drive gear. Each of the multiple drive gears have first and second shaft portions that are coaxial with one another and their respective drive gear. The multiple drive gears include first, second and third drive gears. The first drive gear corresponds to the drive gear. 
     In a further embodiment of any of the above, the gear train includes an idler gear that couples at least two of the multiple drive gears. 
     In a further embodiment of any of the above, all of the shaft portions are parallel with one another. The first and second mounting surfaces are parallel to one another. The multiple drive gears are in the same plane. 
     In a further embodiment of any of the above, the accessory drive components include at least two of an air turbine starter, a deoiler, a variable frequency generator, a permanent magnet alternator, a fuel pump, a lubrication pump and a hydraulic pump. At least two of the accessory drive components are configured to be rotationally driven by the multiple drive gears. One of at least two of the accessory drive components is mounted to the first mounting surface. The other of the at least two accessory drive components is mounted to the second mounting surface. 
     In a further embodiment of any of the above, at least two accessory drive components are the air turbine starter and the deoiler. 
     In a further embodiment of any of the above, at least two accessory drive components are the variable frequency generator and the permanent magnet alternator. 
     In a further embodiment of any of the above, at least two accessory drive components are the fuel pump and the lubrication pump. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure can be further understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
         FIG. 1A  schematically illustrates a gas turbine engine embodiment. 
         FIG. 1B  is a cross-sectional view of the gas turbine engine shown in  FIG. 1  with a nacelle opened to service to an accessory drive gearbox and its accessory drive components. 
         FIG. 2  is side view of the gearbox mounted to the engine. 
         FIG. 3A  is a bottom perspective view of the gearbox. 
         FIG. 3B  is a right side view of the gearbox. 
         FIG. 3C  is a left side view of the gearbox with covers removed, illustrating multiple gear sets within the gearbox housing. 
         FIG. 4  is a perspective schematic view of a gear train within a gearbox housing. 
         FIG. 5  is a schematic view of an example drive gear supported by bearings within the gearbox. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  schematically illustrates a gas turbine engine  20 . The gas turbine engine  20  is disclosed herein as a two-spool turbofan that generally incorporates 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 in a bypass duct at least partially defined within a fan case  15 , while the compressor section  24  drives air along a core flow path C for compression and communication into the combustor section  26  then expansion through the turbine section  28 . Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with two-spool turbofans as the teachings may be applied to other types of turbine engines including three-spool architectures. 
     The exemplary engine  20  generally includes a low speed spool  30  and a high speed spool  32  mounted for rotation about an engine central longitudinal axis X 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, and the location of bearing systems  38  may be varied as appropriate to the application. 
     The low speed spool  30  generally includes an inner shaft  40  that interconnects a fan  42 , a first (or low) pressure compressor  44  and a first (or low) pressure turbine  46 . The inner shaft  40  is connected to the fan  42  through a speed change mechanism, which in exemplary gas turbine engine  20  is illustrated 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 second (or high) pressure compressor  52  and a second (or high) pressure turbine  54 . A combustor  56  is arranged in exemplary gas turbine  20  between the high pressure compressor  52  and the high pressure turbine  54 . A mid-turbine frame  57  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  57  further supports bearing systems  38  in the turbine section  28 . The inner shaft  40  and the outer shaft  50  are concentric and rotate via bearing systems  38  about the engine central longitudinal axis X which is collinear with their longitudinal axes. 
     The core airflow is compressed by the low pressure compressor  44  then the high pressure compressor  52 , mixed and burned with fuel in the combustor  56 , then expanded over the high pressure turbine  54  and low pressure turbine  46 . The mid-turbine frame  57  includes airfoils  59  which are in the core airflow path C. The turbines  46 ,  54  rotationally drive the respective low speed spool  30  and high speed spool  32  in response to the expansion. It will be appreciated that each of the positions of the fan section  22 , compressor section  24 , combustor section  26 , turbine section  28 , and fan drive gear system  48  may be varied. For example, gear system  48  may be located aft of combustor section  26  or even aft of turbine section  28 , and fan section  22  may be positioned forward or aft of the location of gear system  48 . 
     The engine  20  in one example is a high-bypass geared aircraft engine. In a further example, the engine  20  bypass ratio is greater than about six (6), with an example embodiment being greater than about ten (10), the geared architecture  48  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  46  has a pressure ratio that is greater than about five. In one disclosed embodiment, the engine  20  bypass ratio is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor  44 , and the low pressure turbine  46  has a pressure ratio that is greater than about five 5:1. Low pressure turbine  46  pressure ratio is pressure measured prior to inlet of low pressure turbine  46  as related to the pressure at the outlet of the low pressure turbine  46  prior to an exhaust nozzle. The geared architecture  48  may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3:1. 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 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 (10,668 meters). The flight condition of 0.8 Mach and 35,000 ft (10,668 meters), with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (‘TSFCT’)”—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 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 1.45. “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°R)] 0.5 . The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second (350.5 meters/second). 
     Referring to  FIG. 1B , a schematic view of the engine is shown in which the accessory drive gearbox  64  and its accessory drive component  66  may be serviced. The gearbox  64  is mounted to the core  60 . An outer nacelle  62 , which is mounted in a clam shell configuration about the engine core, may be opened to provide access to the components  66 . 
     As best seen in  FIG. 2 , the gearbox  64  is oriented longitudinally in the direction of the engine axis X. In one example embodiment, the gearbox  64  is arranged at the six o&#39;clock position at the lower bifurcation  71 , which is directly opposite the upper bifurcation  72  arranged at the twelve o&#39;clock position (see also  FIG. 1B ). 
     Returning to  FIG. 2 , a tower shaft  70  couples the gearbox  64  to an outer shaft  50  to transmit the high speed location of the high spool to the gearbox  64 . In the example, embodiment, the gearbox  64  receives rotational drive from only the high spool, although the gearbox may be powered by both low and high spools or only the low spool in other embodiments, if desired. 
     Referring to  FIGS. 3A-3C , the gearbox  64  includes a housing  74  providing first and second mounting surfaces  76 ,  78 . The first and second mounting surfaces  76 ,  78  are parallel to one another in the example embodiment. A fuel pump  80 , a permanent magnet alternator (PMA)  82 , and a deoiler  84  are mounted to the first mounting surface  76 . An air turbine starter (ATS)  86 , a variable frequency generator (VFG)  88 , and a lubrication pump  90  are mounted to the second mounting surface  78 . Different or additional components may also be mounted to the housing  74 , such as a hydraulic pump. The accessory drive components  66  have rotational axes G that are perpendicular to the engine axis X. 
     Referring to  FIGS. 4 and 5 , the housing  74  includes a cavity  92  within which a gear train  94  is arranged. The gear train  94  includes first, second and third drive gears  96 ,  98 ,  100 . In the example, first and second idler gears  102 ,  104  are interconnected between the first, second and third drive gears  96 ,  98 ,  100  to provide spacing between the drive gears to permit sufficient space for mounting the components  66  to the housing  74 . Additionally, the idlers may provide a desired gear reduction between the drive gears. 
     The drive gears  96 ,  98 ,  100  are in the same plane with one another as well as with the idler gears  102 ,  104 , which provides a compact package that is more easily accommodated in the nacelle  62 . 
     A gear set  108  is provided between the input gear shaft  106  and the gear train  94 . In the example, the gear set  108  includes a first bevel gear  110  that drives a second bevel gear  112  coupled to the first drive gear  96 . The gear set  108  may be used to obtain the desired speed for the gearbox  64 . Additionally, the shaft angle of the first and second bevel gears  110 ,  112  can be adjusted and their position changed to locate the gearbox  64  to a desired position and orientation with respect to the core  60 . 
     Each drive gear is connected to first and second shaft portions  114 ,  116  that are coaxial with one another and its respective drive gear (second drive gear  98  shown in  FIG. 5  example). The first and second shaft portions  114 ,  116  are supported by a bearing  118  with respect to the housing  74 . Each component  66  includes a component shaft  120  coupled to a driven element  122 . A splined connection  124  connects the component shaft  120  to one of the shaft portions  114 ,  116 . 
     An accessory drive component  66  is mounted to each side of the housing  74  and is driven by a common drive gear. That is, one component is driven by each of the first and second shaft portions  114 ,  116 , which enables a pair of accessory drive components to be driven by a single drive gear. The components are a matched to one another based on a desired drive speed for the components. For example, the deoiler  84  and ATS  86  are driven by a common gear, the VFG  88  and PMA  82  are driven by a common gear, and the fuel pump  80  and the lubrication pump  90  are driven by a common gear. 
     The disclosed gearbox has one gear train to drive the components. The accessory drive components are mounted to the gearbox in a perpendicular orientation, which improves packaging. With the accessory drive component in the disclosed configuration, the length of external lines to and from these components may be reduced by 20-30%, for example. The position and orientation of the components  66  also improves accessibility with respect to the nacelle  62  during service. 
     It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom. Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present invention. 
     Although the different examples have specific components shown in the illustrations, embodiments of this invention 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. 
     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 the claims. For that reason, the following claims should be studied to determine their true scope and content.