Patent Publication Number: US-2013247539-A1

Title: Multi-shaft power extraction from gas turbine engine

Description:
BACKGROUND 
     This disclosure relates to a gas turbine engine power generation system, and more particularly, for a multi-shaft power extraction arrangement. 
     Modern aircraft demand significant power from the gas turbine engine to power secondary loads. Increases in electrical power for passenger features, avionics, hydraulics and engine support loads have increased power demands. Engine bleed air usage reductions have also caused an increased demand for electrical power. 
     Providing an efficient design scheme capable of extracting sufficient power can be difficult. 
     SUMMARY 
     In one exemplary embodiment, a gas turbine engine power generation system includes first and second spools respectively connected to first and second turbine sections. First and second shafts respectively are coupled to the first and second spools. First and second generators respectively are configured to provide first and second electrical powers. A generator gearbox operatively connects the first and second shafts respectively to the first and second generators. An electrical summing device is electrically connected to the first and second generators and is configured to receive the first and second electrical powers and combine the first and second electrical powers to produce a common output power. 
     In a further embodiment of any of the above, the first and second shafts are coaxial with one another. 
     In a further embodiment of any of the above, the first and second spools are respectively low and high speed spools. The first and second shafts respectively have first and second input bevel gears coupled to corresponding gears on the low and high speed spools. The first and second input gears and corresponding gears are arranged in a common gearbox. 
     In a further embodiment of any of the above, the generator gearbox includes an epicyclic gear train combining input from the first and second shafts and produces a common output connected to one of the first and second generators. 
     In another exemplary embodiment, a gas turbine engine power generation system includes first and second spools respectively connected to first and second turbine sections. First and second shafts respectively are coupled to the first and second spools. A generator is provided, and a generator gearbox includes at least one epicyclic gear train combining input from the first and second shafts and produces a common output connected to the generator. 
     In a further embodiment of any of the above, the epicyclic gear train is a simple planetary gear train including a sun gear, a ring gear and planetary gears arranged between and intermeshing with the sun gear and the ring gear. 
     In a further embodiment of any of the above, the first shaft is coupled to the sun gear and the second shaft is coupled to the ring gear, and the planetary gears are supported by a carrier that provides the common output. 
     In a further embodiment of any of the above, the first shaft is coupled to the sun gear, the second shaft is coupled to a carrier that supports the planetary gears, and the ring gear provides the common output. 
     In a further embodiment of any of the above, the epicyclic gear train transfers load between the first and second spools. 
     In a further embodiment of any of the above, the first and second shafts are coaxial with one another. 
     In a further embodiment of any of the above, the first and second spools are respectively low and high speed spools. The first and second shafts respectively have first and second input bevel gears coupled to corresponding gears on the low and high speed spools. The first and second input gears and corresponding gears are arranged in a common gearbox. 
     In a further embodiment of any of the above, a second generator is coupled to at least one of the first and second shafts via a secondary gear train. 
     In a further embodiment of any of the above, an electrical summing device is electrically connected to the generator and the second generator, which are configured respectively to provide first and second electrical powers. The electrical summing device is configured to combine the first and second electrical powers to produce a common output power. 
     In a further embodiment of any of the above, only a single generator is provided. 
     In a further embodiment of any of the above, the generator is also a starter. 
    
    
     
       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. 1  is a schematic view of one example gas turbine engine. 
         FIG. 2  is an enlarged schematic view of a gearbox configured to extract power from multiple spools. 
         FIG. 3  is an enlarged view of an example power generation system shown in  FIG. 1 . 
         FIG. 4  is a schematic view of another example power generation system using electrical summing. 
         FIG. 5  is a schematic view of an example power generation system using electrical summing and mechanical summing. 
         FIG. 6  is a schematic view of an example power generation system using mechanical summing. 
         FIG. 7  is a schematic view of another example power generation system using mechanical summing. 
     
    
    
     DETAILED DESCRIPTION 
     A geared turbofan engine  10  is schematically shown in  FIG. 1  and is intended to be exemplary only. The engine  10  includes a core nacelle  12  that houses a low speed spool  14  and a high speed spool  24  rotatable about a common axis. The low speed spool  14  supports low pressure compressor and turbine sections  16 ,  18 . In the example, the low speed spool  14  rotationally drives a fan  20  through a fan drive gear system  22 , which may include an epicyclic gear train, for example. The high speed spool  24  supports high pressure compressor and turbine sections  26 ,  28 . A combustor section  30  is provided between the high pressure compressor and turbine sections  26 ,  28 . 
     The core nacelle  12  is supported within a fan nacelle  34 . A bypass flow path  32  is provided between the core and fan nacelles  12 ,  34 . Airflow enters the fan nacelle  34  and is expelled from the bypass flow path  32  by the fan  20 . 
     The engine  10  includes a power generation system  35  that extracts power from the low and high speed spools  14 ,  24 , which rotate at significantly different speeds, as the low and high speed spools  14 ,  24  are rotationally driven by the low and high pressure turbine sections  18 ,  28 . First and second shafts  36 ,  38  are respectively coupled to the low and high speed spools  14 ,  24  respectively by first and second sets of input bevel gears  40 ,  42 , as shown in  FIG. 2 . The first and second shafts  36 ,  38  are coaxial with one another, providing an arrangement that reduces the footprint of the first and second shafts  36 ,  38  within the flow path of the core and nacelles  12 ,  34 . The first and second sets of input bevel gears  40 ,  42  are arranged in a common gearbox  41 , which provides compact packaging of the gears. 
     First and second generators  48 ,  50  respectively are configured to provide first and second electrical powers  49 ,  51 , which are different than one another, in one example, due to the differing rotational speeds of the low and high speed spools  14 ,  24 . 
     A generator gearbox  52 , shown in  FIG. 3 , operatively connects the first and second shafts  36 ,  38  respectively to the first and second generators  48 ,  50 . The first and second shafts  36 ,  38  are respectively coupled to first and second output shafts  58 ,  60  by first and second sets of output bevel gears  44 ,  46 . 
     In the example shown in  FIG. 3 , the first output shaft  58  is directly coupled to the first generator  48 . It should be understood that the term “directly” does not exclude the use of a clutch, for example, between the directly coupled components. A first gear  62  is provided on the second output shaft  60  and intermeshes with a second gear  64 . A fourth gear  68  is provided on a third gear  66 , which intermeshes with the second gear  64 . An eighth gear  76  is provided on a seventh gear  74 , which is coupled to the fourth gear  68  via fifth  70  and sixth gears  72 . The eighth gear  76  drives a tenth gear  80 , which directly drives the second generator  50 , through a ninth gear  78 . 
     The first and second generators  48 ,  50  rotate at different speeds. An electrical summing device  54  is electrically connected to the first and second generators  48 ,  50  and is configured to receive the first and second electrical powers  49 ,  51  and combine the first and second electrical powers  49 ,  51  to produce a common output power  55 . Examples of commercially available electrical summing devices are manufactured by Hamilton Sundstrand Corporation under part numbers 757183G and 7000045 for the Boeing 777 and 787, respectively. The electrical summing device  54  provides power to loads  56 . 
     A much-simplified gear train is shown in the power generation system  135  illustrated in  FIG. 4 . The generator gearbox  152  houses a first gear  162  mounted on the second output shaft  160 . The first gear  162  drives a third gear  166  via a second gear  164 . The first generator  148  is directly coupled to the first output shaft  158 , and the second generator  150  is directly coupled to the third gear  166 . The electrical summing device  54  receives electrical power from the first and second generators  148 ,  150 . 
     In the example shown in  FIG. 5 , the generator gearbox  252  includes an epicyclic gear train  82  in the power generation system  235 . In the example, the epicyclic gear train  82  is a simple planetary gear train including a sun gear  84 , a ring gear  88  and planetary gears  86  arranged between and intermeshing with the sun gear  84  and the ring gear  88 . The planetary gears  86  are mounted on a carrier  90 . The first output shaft  258  is connected to the sun gear  84 . The carrier  90  is connected to the second output shaft  260 . The ring gear  88  directly drives the first generator  248 . A secondary gear train  92  couples the second generator  250  to the second output shaft  260 , which includes a first gear  262 . A second gear  264  interconnects the first gear  262  to a third gear  266 , which directly drives the second generator  250 . The electrical summing device  54  receives electrical power from the first and second generators  248 ,  250 . 
     In the examples shown in  FIGS. 6 and 7 , the input from the first and second shafts  36 ,  38  ( FIG. 1 ) is combined using a differential simple planetary gear train to produce a common output connected to only one generator  348 ,  448 . By combining the speed of the low and high speed spools  14 ,  24 , a smaller speed range will be produced, which enables a smaller, efficiently sized generator to be used. It should be understood that other gear configurations may be used, such as compound planetary gear trains (e.g., a Ravigneneaux arrangement) to mechanically combine the different rotational speeds of the low and high speed spools  14 ,  24 . The epicyclic gear train also transfers load between the low and high speed spools  14 ,  24 , which can improve engine performance. 
     In the example shown in  FIG. 6 , the power generation system  335  includes a gear box  352  housing a planetary gear train  382 . The planetary gear train  382  includes a sun gear  384 , a ring gear  388  and planetary gears  386  arranged between and intermeshing with the sun gear  384  and the ring gear  388 . The planetary gears  386  are mounted on a carrier  390 , which is connected to the generator  348 . The first output shaft  358  is connected to the sun gear  384 . The ring gear  88  is connected to the second output shaft  360 . 
     In the example shown in  FIG. 7 , the power generation system  435  includes a gear box  452  housing a planetary gear train  482 . The planetary gears  486  are mounted on the carrier  490 . The first output shaft  458  is connected to the sun gear  484 . The carrier  490  is connected to the second output shaft  240 . The ring gear  488  directly drives the generator  448 . 
     Although example embodiments have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For example, it should be understood that the gear configurations disclosed are exemplary, and other gear arrangements may be used and still fall within the claims. In any of the above embodiments, the generators may also be used as a starter. For that reason, the following claims should be studied to determine their true scope and content.