Abstract:
An accessory drive system for an aircraft gas turbine engine is disclosed. The system may comprise an engine case including a core engine cowl and at least a first accessory drive gearbox disposed within the core engine cowl. The at least first accessory drive gearbox may be operatively connected to one or more accessories remotely located therefrom.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application is a US National Stage under 35 U.S.C. §371, claiming priority to International Application No. PCT/US13/76088 filed on Dec. 18, 2013, which claims priority under 35 U.S.C. §119(e) to U.S. Patent Application Ser. Nos. 61/828,396 filed on May 29, 2013 and 61/790,459 filed on Mar. 15, 2013. 
     
    
     TECHNICAL FIELD 
       [0002]    The subject matter of the present disclosure relates generally to gas turbine engines and, more particularly, relates to accessory drive gearboxes for gas turbine engines. 
       BACKGROUND 
       [0003]    Many gas turbine engines include accessory drive gearboxes to drive the various accessory systems needed to operate the engine. As engine and aircraft designs have changed over time, the number of accessories driven by the gearbox has increased. Some of the accessories, to name a few, include electrical power generators, primary gas generator combustor fuel pumps, augmenter fuel pumps, oil pumps, hydraulic pumps and lubrication system scavenge pumps. Typically, during normal engine operation, the gearbox is driven by a tower shaft, which is connected to and driven by a main engine shaft such as the compressor shaft. During the engine start sequence, this loading is reversed and external power is supplied to the gearbox that drives a tower shaft to impart rotation to the compressor. The location of the gearbox can vary depending on engine cycle and application. For moderate to high bypass ratio turbofans used for commercial and transport applications, the gearbox is usually mounted under the core engine cowl onto the engine case. The accessories, in turn, are commonly mounted onto the gearbox housing. For instance, the fuel pump is often bolted to the gearbox on a mounting flange provided at the face of the gearbox. 
         [0004]    While effective, the available space between the core engine cowl and the core engine is very limited. In addition to containing the gearbox and the accessories mounted thereon, the space under the core engine cowl also contains engine structural mounts, actuators, plumbing, brackets, controls, fuel lines, air or fluid heat exchangers/coolers and other components. While the number of accessories and components contained under the core engine cowl limit the amount of available space, space is further limited because the gearbox, accessories and components cannot be placed in certain sections of this space due to elevated operating temperatures in those sections. In addition, the operating temperature under the core engine cowl is not evenly distributed. For example, often times the downstream section under the core engine cowl is much hotter than the upstream section. As a result, the gearbox and the accessories are commonly mounted to the upstream section of the engine case in order to prevent exposure to the extreme heat in the downstream section. 
         [0005]    Arrangement of the gearbox and accessories under the core engine cowl is also determined by the ease with which the gearbox and accessories can be removed for repair and maintenance. Furthermore, trends for future engine designs suggest that the available space under the core engine cowl will become even more limited. Thus, there is a need to configure the arrangement of the gearbox and accessories in order to maximize use of the limited available space under the core engine cowl. 
       SUMMARY 
       [0006]    In accordance with an aspect of the disclosure, an accessory drive system for a gas turbine engine is provided. The accessory drive system may comprise a core engine surrounded by a core engine cowl. A core engine envelope is defined between the core engine and the core engine cowl. At least a first accessory drive gearbox is disposed within the core engine envelope. The at least first accessory drive gearbox may be operatively connected to one or more accessories remotely located therefrom, thereby maximizing use of spatial storage limitations within the core engine envelope. 
         [0007]    In accordance with another aspect of the disclosure, the first accessory drive gearbox is operatively connected to a second accessory and a second accessory drive gearbox is operatively connected to a third and fourth accessory. 
         [0008]    In accordance with yet another aspect of the disclosure, an electrical power supply may be disposed within the core engine envelope. The electrical power supply may be operatively connected to at least one electrical accessory remotely located therefrom. 
         [0009]    In accordance with still yet another aspect of the disclosure, the first accessory drive gearbox receives power from at least one spool and the second accessory drive gearbox receives power from at least one spool. 
         [0010]    In further accordance with another aspect of the disclosure, the first accessory drive gearbox is operatively connected to the first accessory via a first flexible shaft, the first accessory drive gearbox is operatively connected to the second accessory via a second flexible shaft, the second accessory drive gearbox is operatively connected to the third accessory via a third flexible shaft and the second accessory drive gearbox is operatively connected to a fourth accessory via a fourth flexible shaft. 
         [0011]    In further accordance with yet another aspect of the disclosure, the first and second accessories are disposed within the core engine envelope, and the third and fourth accessories are disposed exterior to the core engine cowl. 
         [0012]    In accordance with another aspect of the disclosure, an accessory drive system for a gas turbine engine is provided. The accessory drive system comprises a core engine case. At least a first accessory drive gearbox is disposed on the engine case. The at least first accessory drive gearbox may be operatively connected to at least a first accessory remotely located therefrom. 
         [0013]    In accordance with yet another aspect of the disclosure, the first accessory drive gearbox is operatively connected to a second accessory and a second accessory drive gearbox is operatively connected to a third and fourth accessory. 
         [0014]    In accordance with still another aspect of the disclosure, an electrical power supply may be disposed on the at least first accessory drive gearbox. The electrical power supply may be operatively connected to at least one electrical accessory remotely located therefrom. 
         [0015]    In accordance with still yet another aspect of the disclosure, the first accessory drive gearbox receives power from at least one spool and the second accessory drive gearbox receives power from at least one spool. 
         [0016]    In further accordance with another aspect of the disclosure, the first accessory drive gearbox is operatively connected to the first accessory via a first flexible shaft, the first accessory drive gearbox is operatively connected to the second accessory via a second flexible shaft, the second accessory drive gearbox is operatively connected to the third accessory via a third flexible shaft and the second accessory drive gearbox is operatively connected to a fourth accessory via a fourth flexible shaft. 
         [0017]    In further accordance with yet another aspect of the disclosure, the first and second accessories are disposed on the engine case, and the third and fourth accessories are disposed in a nacelle envelope. 
         [0018]    In accordance with another aspect of the disclosure, a method of arranging gearboxes and accessories in a gas turbine engine is provided. The method entails providing at least a first accessory drive gearbox within a core engine envelope. Another step is to operatively connect the at least first accessory drive gearbox to one or more accessories that are remotely located from the at least first accessory drive gearbox. 
         [0019]    In accordance with yet another aspect of the disclosure, the first accessory drive gearbox is operatively connected to a second accessory, and a second accessory drive gearbox is operatively connected to a third and fourth accessory. 
         [0020]    In accordance with still another aspect of the disclosure, the first through fourth accessories are disposed within the core engine envelope. 
         [0021]    In accordance with still yet another aspect of the disclosure, the first accessory drive gearbox is operatively connected to the first accessory via a first power extension shaft, the first accessory drive gearbox is operatively connected to the second accessory via a second power extension shaft, the second accessory drive gearbox is operatively connected to the third accessory via a third power extension shaft and the second accessory drive gearbox is operatively connected to a fourth accessory via a fourth power extension shaft. 
         [0022]    In further accordance with another aspect of the disclosure, the first accessory drive gearbox is operatively connected to the first accessory via a first flexible shaft, the first accessory drive gearbox is operatively connected to the second accessory via a second flexible shaft, the second accessory drive gearbox is operatively connected to the third accessory via a third flexible shaft and the second accessory drive gearbox is operatively connected to a fourth accessory via a fourth flexible shaft. 
         [0023]    In further accordance with still another aspect of the disclosure, the first and second accessories are disposed within the core engine envelope, and the third and fourth accessories are disposed in a nacelle envelope. 
         [0024]    In further accordance with yet another aspect of the disclosure, the method entails providing an electrical power supply onto the at least first accessory drive gearbox. The electrical power supply may be operatively connected to at least one electrical accessory remotely located therefrom. 
         [0025]    In further accordance with still yet another aspect of the disclosure, the first accessory drive gearbox receives power from at least one spool and the second accessory drive gearbox receives power from at least one spool. 
         [0026]    Other aspects and features of the disclosed systems and methods will be appreciated from reading the attached detailed description in conjunction with the included drawing figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    For further understanding of the disclosed concepts and embodiments, reference may be made to the following detailed description, read in connection with the drawings, wherein like elements are numbered alike, and in which: 
           [0028]      FIG. 1  is a schematic side view of a gas turbine engine with portions of the nacelle thereof sectioned and broken away to show details of the present disclosure; 
           [0029]      FIG. 2  is an end view of a gas turbine engine, taken along line A-A in  FIG. 1 , constructed in accordance with the teachings of this disclosure; 
           [0030]      FIG. 3  is an end view similar to  FIG. 2 , but depicting an alternative embodiment of a gas turbine engine constructed in accordance with this disclosure; 
           [0031]      FIG. 4  is an end view similar to  FIG. 3 , but having the gearboxes and accessories removed for clarity; and 
           [0032]      FIG. 5  is a flowchart illustrating the steps of the present disclosure. 
       
    
    
       [0033]    It is to be noted that the appended drawings illustrate only typical embodiments and are therefore not to be considered limiting with respect to the scope of the disclosure or claims. Rather, the concepts of the present disclosure may apply within other equally effective embodiments. Moreover, the drawings are not necessarily to scale, emphasis generally being placed upon illustrating the principles of certain embodiments. 
       DETAILED DESCRIPTION 
       [0034]    Referring now to  FIG. 1 , a gas turbine engine constructed in accordance with the present disclosure is generally referred to by reference numeral  10 . The gas turbine engine  10  includes a compressor  12 , a combustor  14  and a turbine  16 . The serial combination of the compressor  12 , the combustor  14  and the turbine  16  is commonly referred to as a core engine  18 . The core engine  18  lies along a longitudinal central axis  20 . A core engine cowl  22  surrounds the core engine  18 . 
         [0035]    As is well known in the art, air enters compressor  12  at an inlet  24  and is pressurized. The pressurized air then enters the combustor  14 . In the combustor  14 , the air mixes with jet fuel and is burned, generating hot combustion gases that flow downstream to the turbine  16 . The turbine  16  extracts energy from the hot combustion gases to drive the compressor  12  and a fan  26 , which has fan blades  28 . As the turbine  16  drives the fan  26 , the fan blades  28  rotate so as to take in more ambient air. This process accelerates the ambient air to provide the majority of the useful thrust produced by the engine  10 . Generally, in modem gas turbine engines, the fan  26  has a much greater diameter than the core engine  18 . Because of this, the volumetric flow through the fan  26  can be 5-10 times higher, or more, than the volumetric flow through the core engine  18 . The ratio of flow through the fan  26  relative to flow through the core engine  18  is known as the bypass ratio. 
         [0036]    The fan  26  and core engine cowl  22  are surrounded by a fan cowl  30  forming part of a nacelle  32 . A fan duct  34  is functionally defined by the area between the core engine cowl  22  and the fan cowl  30 . The fan duct  34  is substantially annular in shape so that it can accommodate the air flow produced by the fan  26 . This air flow travels the length of the fan duct  34  and exits downstream at a fan nozzle  36 . A tail cone  38  may be provided at the core engine exhaust nozzle  40  to smooth the discharge of excess hot combustion gases that were not used by the turbine  16  to drive the compressor  12  and fan  26 . Moreover, core engine cowl  22  is radially spaced apart from the core engine  18  so that a core engine envelope  42  is defined therebetween. 
         [0037]    While the foregoing provides for an effective engine  10 , it can be seen that space within the core engine envelope  42  is increasingly more limited. The present disclosure greatly improves on this issue. It does so by, among other things, mounting multiple accessory drive gearboxes under the core engine cowl  22  and connecting the same to remote accessories using shafts, including flexible shafts, as will be described in further detail below. Referring now to  FIG. 2 , in addition to  FIG. 1 , a primary accessory drive gearbox  44  and a secondary accessory drive gearbox  46  are shown mounted onto an engine case  48 . The engine case  48  surrounds the core engine  18  in such a way that it generally follows the contours of the core engine  18 . The primary accessory drive gearbox  44  may be mounted onto the engine case  48  in an area that is below the central axis  20  and the secondary accessory drive gearbox  46  may be mounted onto the engine case  48  in an area that is above the central axis  20 . Although the gearboxes  44 , 46  may be mounted onto the engine case  48  in this manner, it is appreciated that gearboxes  44 , 46  may be mounted onto any location on the 360° circumferential contour of the engine case  48  that is suitable and thus maximize space usage. Reference throughout the disclosure to the gearboxes and accessories being mounted “above” and “below” the central axis  20  is merely used to describe the locations of the gearboxes and accessories as illustrated in the figures and is not meant to limit the locations of the gearboxes and accessories. 
         [0038]    Moreover, the primary accessory drive gearbox  44  may be in operative association with both a first accessory  50  via a first power extension shaft  52  and a second accessory  54  via a second power extension shaft  56 . Both the first and second accessories  50 , 54  are mounted to the engine case  48  in an area that is remote from the primary accessory drive gearbox  44 . Similarly, the secondary accessory drive gearbox  46  may be in operative association with both a third accessory  58  via a third power extension shaft  60  and a fourth accessory  62  via a fourth power extension shaft  64 . Both the third and fourth accessories  58 , 62  are mounted to the engine case  48  in an area that is remote from the secondary accessory drive gearbox  46 . The first through fourth power extension shafts  52 , 56 , 60 , 64  transmit power through a prescribed combination of torque and rotational speed suitable to drive the remote accessories  50 , 54 , 58 , 62 . 
         [0039]    First through fourth accessories  50 , 54 , 58 , 62  may be any of the various types of accessories used to operate the engine. For instance, the first through fourth accessories  50 , 54 , 58 , 62  may be, but are not limited to, a power generator, a fuel pump, an oil pump, a hydraulic pump or a scavenge pump. In conventional gas turbine engines, a single gearbox drives the accessories. However, as shown in  FIGS. 1 and 2 , two gearboxes  44 , 46  are used to drive the various remote accessories  50 , 54 , 58 , 62  in accordance with the present disclosure. Although two gearboxes are described, it is appreciated that multiple gearboxes may be used, including three or more. Using two smaller gearboxes, as opposed to one larger gearbox, allows for more arrangement options within the core engine envelope  42 . More arrangement options are also available because the first through fourth accessories  50 , 54 , 58 , 62  are remote from their associated gearbox. Because the size of the gearboxes is reduced and the accessories are remote, the gearboxes and the accessories may be placed in smaller areas within the core engine envelope  42 . 
         [0040]    As shown in  FIG. 1 , a high spool  66  powers primary accessory drive gearbox  44  via a primary tower shaft  68 . In similar manner, a low spool  70  powers secondary accessory drive gearbox  46  via a secondary tower shaft  72 . Although primary accessory drive gearbox  44  is shown to be powered by the high spool  66 , the gearbox  44  may be alternatively powered by the combination of the high spool  66  and the low spool  70 . The secondary accessory drive gearbox  46  also may be powered by the combination of the high spool  66  and the low spool  70 . Generally, an accessory drive gearbox may be powered by a single spool or by a combination of multiple spools. This is also true for engines that employ three or more spools, in which an accessory drive gearbox may be powered by a combination of one or more spools. 
         [0041]    In an alternative embodiment shown in  FIG. 3 , the first through fourth accessories  150 , 154 , 158 , 162  are driven by their associated gearboxes  144 , 146  via first through fourth flexible shafts  152 , 156 , 160 , 164 . The flexible shafts allow for more freedom in the arrangement of the gearboxes and accessories. In particular, the flexible drive shafts consist of a flexible outer sheath surrounding a rotatable flexible inner shaft that transmits rotational power. The flexible outer sheath is flexible, but fixed with respect to the inner shaft such that the inner shaft rotates within the outer sheath. Lubrication of the inner shaft can be performed via closed/passive lubrication or via open/active lubrication, which may also control frictional heating of the flexible shaft assembly. In addition to arranging the accessories in various positions in the core engine envelope  142 , the flexible shafts allow the accessories to be mounted in the nacelle envelope  165  as well. The nacelle envelope  165  is defined by the area between the nacelle  132  and the fan cowl  130 . 
         [0042]    In particular,  FIG. 3  shows a primary accessory drive gearbox  144  mounted onto the engine case  148  below the central axis  120 . Because the first and second flexible shafts  152 , 156  operatively connect the first and second accessories  150 , 154 , respectively, to the gearbox  144 , the first and second accessories  150 , 154  may be placed in a wider variety of locations remote from the gearbox  144 . The first and second accessories  150 , 154  may be mounted to the engine case  148  below the central axis  120  as before, may be mounted to the engine case  148  above the central axis  120  as shown in  FIG. 3  or may be mounted onto any location on the 360° circumferential contour of the engine case  148  that is suitable. 
         [0043]    Moreover, instead of only mounting the accessories in the core engine envelope  142 , the third and fourth flexible shafts  160 , 164  allow their respective third and fourth accessories  158 , 162  to be placed in the nacelle envelope  165 . For example, the secondary accessory drive gearbox  146  is operatively connected to the third and fourth accessories  158 , 162  via third and fourth flexible shafts  160 , 164 , respectively. The secondary accessory drive gearbox  146  is mounted to the engine case  148  above the central axis  120 . The third and fourth flexible shafts  160 , 164  may be routed from the secondary accessory drive gearbox  146  to the third and fourth accessories  158 , 162 , respectively, through the fan exit guide vane (not shown) and to the nacelle envelope  165 . 
         [0044]    The accessories described thus far are mechanically powered accessories. However, the engine may also include accessories that are electrically powered, which also need to be arranged within the core engine envelope or elsewhere. Referring to  FIG. 4 , with the secondary accessory drive gearbox and other accessories removed for clarity, a primary accessory drive gearbox  444  is shown to be mounted onto the engine case  448 . An electrical power supply or generator  474  may be located within the core engine envelope  442  and may be mounted onto the primary accessory drive gearbox  444 . The generator  474  may be operatively connected to a remotely located fifth or electrical accessory  476  via a fifth flexible shaft  478 . The fifth flexible shaft  478  may be an electrical conduit. The generator  474  may be powered by either the high or low spool via the primary accessory drive gearbox  444 . Alternatively, the generator  474  may be directly mounted to the high or low spool. The fifth accessory  476  is shown to be mounted on the engine case  448 , but may be alternatively located in the nacelle envelope  465 . Although  FIG. 4  only shows one electrical accessory  476 , it is appreciated that multiple electrical accessories may be utilized and may be operatively connected to the generator  474  or another electrical power supply in a similar manner. 
         [0045]      FIG. 5  illustrates a flowchart  500  of a method of arranging gearboxes and accessories in a gas turbine engine  10 . Box  510  shows the step of providing at least a primary accessory drive gearbox  44  within a core engine envelope  42 . Another step, shown in box  512 , is to operatively connect the at least primary accessory drive gearbox  44  to one or more accessories that are remotely located from the at least primary accessory drive gearbox  44 . 
         [0046]    Although the disclosure describes the primary and secondary accessory drive gearboxes as each driving two accessories, it is appreciated that the disclosure is not limited to two accessory drive gearboxes, but may include multiple accessory drive gearboxes each of which may drive any number of accessories. Furthermore, the gearboxes and accessories may be arranged in various combinations of the particular arrangements described above. 
         [0047]    While the present disclosure has shown and described details of exemplary embodiments, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the disclosure as defined by claims supported by the written description and drawings. Further, where these exemplary embodiments (and other related derivations) are described with reference to a certain number of elements it will be understood that other exemplary embodiments may be practiced utilizing either less than or more than the certain number of elements.