Abstract:
Gas turbine engine accessories are mounted on an accessory gearbox therefor which is in turn mounted on a case of the engine such that the accessories extend from the gearbox in directions generally parallel to circumferential tangents to the engine case for compactness, ease in installation and removal of the accessories, reduction of the weight in lines extending from the accessories and minimization of the risk of damage to such accessories and gearbox from the fan blades which may separate from a fan hub upon encountering birds, ice, or other foreign objects.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    This invention relates generally to gas turbine engines and particularly to a mounting arrangement for gas turbine engine accessories such as electrical generators, pumps and the like and gearboxes therefor. 
         [0003]    2. Background Information 
         [0004]    Gas turbine engines, particularly those which power aircraft, are often provided with accessories such as electrical generators, pumps, air turbines and the like, which are required for operation of the engine and an associated aircraft. For example, electrical generators are provided to generate electrical power needed for electrical systems in the engine itself, such as electronic engine controls and variable pitch vanes and the like. Accessory pumps are provided to pressurize lubrication systems within the engine and hydraulically powered engine systems such as thrust reversers and the like and aircraft systems such as adjustable flight control surfaces. Air turbines driven by compressed air from, for example, an external source, provide starting power to the engine. It is common practice to mechanically connect such accessory generator air turbines and pumps to the engine by means of an accessory gearbox which is itself mechanically connected to the rotational shaft of the engine and mounted on the engine stator. It is also a common practice to mount the accessories mentioned hereinabove on the gearbox itself such that the accessories are driven by, or provide driving power to, internal gearing within the gearbox. Therefore, it will be readily appreciated that the ease in which such accessories and gearboxes may be removed for repair and maintenance thereof is largely a function of the manner in which the accessories and gearboxes are mounted on the engine which is determinative of the free space surrounding the accessories and gearbox available for the removal and reinstallation thereof for maintenance and servicing. The elevated operating temperatures at the aft (downstream) end of the gas turbine engine render such a location thermally hostile to accessories and gearboxes mounted thereat. Therefore, one known practice has been to mount the accessories and gearboxes at the cooler forward (upstream) end of the engine at the fan case portion of the stator thereof. 
         [0005]    However, mounting accessories such as pumps and generators at such a forward location requires electrical and fluid lines running from such accessories to traverse significant longitudinal distances from the accessory to a pylon on which the engine is mounted to an associated aircraft, the pylon providing the normal route for the extension of such lines from the engine to systems on the aircraft for which electrical and/or hydraulic power is produced by such accessories. Mounting accessories and gearboxes therefor on the fan case of a gas turbine engine also places such components at risk for damage in the event of breakage or other separation of fan blades from the fan hub in the event of encounters with foreign objects such as ice, birds, or other foreign objects. Furthermore, mounting the accessories and gearbox at such an engine&#39;s forwardmost position at the fan case within the nacelle usually restricts possible rearward-facing mounting positions, reducing the available area for component removal and placement. 
         [0006]    Since it is a common practice to access the accessories and gearbox from outside the engine&#39;s nacelle through openings therein, the relatively large diameter of the engine at the fan case tends to reduce the amount of free space around the accessories and gearbox between those components and the nacelle available for the servicing and maintenance of such components. Accordingly, a mounting arrangement for gas turbine engine accessories and a gearbox therefor in which such accessories and gearbox are conveniently accessible for servicing and maintenance, which does not contribute significantly to the thermal loading of such components by the extreme heat generated by the engine, and which contributes minimally to the length and weight of fluid and electrical lines running from such accessories to associated systems, is sought. 
       SUMMARY OF THE DISCLOSURE 
       [0007]    In accordance with the present invention, an accessory gearbox for a gas turbine engine is mounted on that portion of the engine case which surrounds the engine core and accessory components which mechanically connect to the engine by means of the gearbox, are mounted on the gearbox such that the accessory components extend from the gearbox in a direction generally circumferentially tangent to the engine case. Such a mounting arrangement reduces the radial free space surrounding the accessories required for the removal and reinstallation thereof for maintenance and servicing, thereby reducing the required diameter and weight of any nacelle which surrounds the engine. The location of the accessories and gearbox on the core case rather than the fan case of the engine reduces the risk of damage to such components from the separation of fan blades from a hub therefor in the event of a bird strike or the ingestion of ice or other foreign manner into the engine. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic view of a turbofan gas turbine engine of the type employing the present invention. 
           [0009]      FIG. 2  is a side elevation of a gas turbine engine such as that shown in  FIG. 1 , including the accessory and gearbox mounting arrangement of the present invention. 
           [0010]      FIG. 3  is an isometric view of an accessory gearbox and accessory components mounted thereon in accordance with the present invention. 
           [0011]      FIG. 4  is an aft end view of the gearbox shown in  FIG. 3 . 
           [0012]      FIG. 5  is a side view of the gearbox shown in  FIGS. 3 and 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    Referring to  FIG. 1 , a turbofan gas turbine engine  5  has a longitudinal axis  7  about which the rotors  8  of the engine rotate. A fan  10  disposed at the engine inlet draws air into the engine. A low pressure compressor  15  located immediately downstream of fan  10  compresses air exhausted from fan  10  and a high pressure compressor  20  located immediately downstream of low pressure compressor  15 , further compresses air received therefrom and exhausts such air to combustors  25  disposed immediately downstream of high pressure compressor  20 . Combustors  25  receive fuel through fuel lines  30  and ignite the fuel/air mixture. The burning fuel-air mixture (working medium fluid) flows axially to a high pressure turbine  35  which extracts energy from the working medium fluid and in so doing, rotates hollow shaft  37 , thereby driving the rotor of high pressure compressor  20 . The working medium fluid exiting the high pressure turbine  35  then enters low pressure turbine  40 , which extracts further energy from the working medium fluid. The low pressure turbine rotor provides power to drive the fan  10  and low pressure compressor  15  via low pressure shaft  42 , which is disposed interiorly of the shaft  37 , coaxial thereto. Working medium fluid exiting the low pressure turbine  40  provides axial thrust for powering an associated aircraft (not shown) or a free turbine (also not shown). 
         [0014]    Bearings  43 ,  45 ,  50  and  53  radially support the concentric high pressure and low pressure turbine shafts from separate frame structures  52 ,  54 ,  55  and  56  respectively, attached to engine case  57 , which defines the outer boundary of the engine&#39;s stator which circumscribes rotors  8 . However, it will be appreciated that the present invention is also well suited for mid-turbine frame engine architectures wherein the upstream bearings for the low and high pressure turbines are mounted on a common frame structure disposed longitudinally (axially) between the high and low pressure turbines. 
         [0015]    Referring to  FIG. 2 , an accessory gearbox  60  is mounted on the engine case  57  at that portion of the case which surrounds the core of the engine (high pressure compressor, combustor and turbine). As perhaps best seen in  FIG. 1 , the core case is typically of a smaller diameter than that portion of the engine case which surrounds the fan and low pressure turbine, thereby allowing enhanced access to gearbox  60  and accessories mounted thereon through openings in the engine nacelle (not shown) which surround the engine. To minimize thermal loading of the gearbox from the high engine operating temperatures at the longitudinal locations of the combustors and turbines, in the preferred embodiment, accessory gearbox  60  is mounted on case  57  at a longitudinal location upstream of combustor  25 , for example, at a longitudinal location corresponding to high pressure compressor  20 . 
         [0016]    Still referring to  FIG. 2 , gearbox  60  includes a longitudinal axis  62  which is generally parallel to longitudinal axis  7  of the engine itself. Gearbox  60  is provided with internal gearing, portions of which are shown at  65  ( FIG. 5 ). However, the details of such gearing will depend upon the torque and power characteristics of such accessories as well as the configuration of the mechanical connections thereto and the speed at which accessory gearbox  60  is driven by engine  5 . It will be understood that the present invention may be employed with a variety of gas turbine engines and engine accessories. Therefore, for clarity of description and illustration, details of internal gearing  65  are not shown herein, but will suggest themselves to those skilled in the art based upon the characteristics of the engine and accessories with which the present invention is employed. 
         [0017]    As best seen in  FIGS. 3 and 5 , mechanical input power is provided to gearbox  60  through shaft  70 , driven by the engine rotor, being connected thereto through suitable gearing (not shown) internally of the engine. 
         [0018]    Referring to  FIG. 3 , a number of accessories employed in the auxiliary systems of engine  5  set forth hereinabove are shown mounted on the accessory gearbox  60 . Among those accessories with which the mounting arrangement of the present invention may be employed are hydraulic pump  75  which provides hydraulic fluid pressure to hydraulically operated systems on engine  5  and an associated aircraft (not shown) and oil pump  80  which pressurizes lubrication systems employed in the engine, such as, for the bearings thereof as well as any similar systems on the associated aircraft. Alternator  85  provides electrical power to electrical systems on the engine or associated with the aircraft, and fuel pump  90  pumps fuel from a reservoir thereof (not shown) to combustors  25 . It will be understood that these accessories may be part of modules which include other associated equipment. For example, fuel pump  90  may be part of a module which also includes a fuel filter as well as associated manifolding and fuel metering valving. Also shown in  FIG. 3  is an air turbine starter  100  which receives pressurized air through conduit  105  for providing input power to gearbox  60  upon engine starting. Still referring to  FIG. 3 , the accessories enumerated hereinabove are mounted on a pair of mounting surfaces  110 ,  115 , angularly offset by approximately 110° from one another. Input and output shafts of the accessories illustrated in  FIG. 3  and described hereinabove connect to internal gearing  65  through openings in the mounting surfaces, the accessories being mounted to the mounting surfaces by any suitable means such as bolted connections and the like. The angular offset of mounting surfaces  110  and  115  causes the accessory components mounted thereon to extend from the gearbox in directions generally circumferentially tangent to engine core case  57 . 
         [0019]    Referring to  FIGS. 3-5 , accessory gearbox  60  is mounted on the engine case by means of a forward mounting clevis  125  comprising a pair of spaced lugs  130  which receive thereinbetween a complementary lug (not shown) on the engine case, the clevis lugs and engine case lug being pinned together by pin  135 . Gearbox  60  is connected to the engine case at the aft end of the gearbox by one or more extensible links  140  which connect at the inner ends thereof to the engine case and at the outer ends thereof to a bracket  145  at the aft end of the gearbox housing. It will be appreciated that the pinned connection of the gearbox housing to the engine case at the forward end of the gearbox and the connection at the rear end of the gearbox to extensible links  140  allow limited pivotal movement of the gearbox with respect to the engine case to accommodate torsional reaction of the gearbox housing to loads thereon from the operation of internal gearing  65 . The ability of the gearbox to pivotally move with respect to the engine case also isolates the gearbox from mechanical loads on the engine case due to, for example, engine shaft bending or the like, thereby mitigating damage to the gearbox from such events 
         [0020]    It will thus be seen that the accessory and gearbox mounting arrangement of the present invention allow the accessories to be removed from the gearbox and reinstalled thereon in directions generally tangential to the circumference of the engine case in a compact arrangement minimizing the amount of radical free space outside of the engine case required for such removal and installation. Minimizing the radial free space required for such accessory installation and removal minimizes the required size of an associated nacelle, thereby reducing the weight thereof. Mounting the accessory gearbox on the engine core case reduces the risk of damage to the gearbox and accessories from fan blades which may separate from the fan hub upon strikes from birds, ice or other foreign objects. Moreover, since the engine accessories and gearbox are disposed on the core case, they are located longitudinally on the engine case proximal to the location of the attachment of the case to an associated pylon which supports the engine from an associate aircraft. This minimizes the longitudinal extension of wiring and plumbing from the accessories to the pylon which provides a route for such wiring and plumbing to the aircraft thereby reducing the weight associated with such longitudinal wiring and plumbing extensions. 
         [0021]    While specific accessories have been shown and described as having a specific angular displacement between the mounting surfaces therefor, the present invention may be used with other engine accessories and angular displacements as will be determined by the specific geometry of the engine case. 
         [0022]    Accordingly, it will be understood that these and various other modifications and embodiments may be employed without departing from the true spirit and scope of the present invention as set forth in the claims appended hereto.