Abstract:
A gas turbine engine and an accessory gear box (AGB) are provided for. The gas turbine engine comprises a drive shaft, a compressor, a combustor and an exhaust turbine, where the exhaust turbine and the compressor are coaxially connected by the drive shaft. The gas turbine engine further comprises an engine casing of varying diameters circumferentially enveloping the compressor, the combustor and the exhaust turbine with a waist located between the compressor and the combustor. The gas turbine engine also includes an accessory gear box (AGB) attached to the engine casing at the waist, the AGB comprising a gear rotating on an axis extending in a transverse direction relative to that of the drive shaft.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with Government support under contract number W911W60820001 awarded by the Unites States Army under the Advanced Affordable Turbine Engine program. The Government has certain rights in this invention. 
    
    
     TECHNICAL FIELD 
     The present invention generally relates to gas turbine engines, and more particularly relates to an arrangement and connection of an accessory gear box to the power shaft. 
     BACKGROUND 
     An accessory gear box (AGB) is mounted on a gas turbine engine and drives various support components required to sustain engine operation. The support components include but are not limited to a fuel pump, an oil pump, an air driven starter, and air/oil separator, and an electrical generator. These components, the gearbox and the engine itself must fit within a confined space called an engine nacelle. 
     Referring to  FIG. 1 , a typical gas turbine engine  100  comprises of a compressor section  5 , a combustion section  10  and a turbine section  15  arranged sequentially in that order. All of these sections are roughly cylindrical and oriented coaxially. A set of compressor blades in the compressor section  5  and a set of turbine blades in the turbine section  15  are driven in tandem by the engine drive shaft  30  extending coaxially completely through the gas turbine engine  100  from the compressor section  5  to the turbine section  15 . 
     A tower shaft that is driven by bevel gears off of the drive shaft is typically used to transfer power from the drive shaft  30  to the auxiliary gearbox that is located outside of the exterior casing of the gas turbine engine and inside the nacelle or engine bay. A conventional gear box has at least one gear axis  41  running parallel with the engine drive shaft  30 . The AGB  40  drives the support components  42  via a series of interlocking drive gears (See,  FIG. 1B ) that are oriented orthogonally to the gear axis  41 . Each of the support components  42  are arranged arcuately around the engine casing  50  and located radially away from the drive shaft  30  and are situated outboard of the widest cylindrical section of the gas turbine engine (e.g., the air collector  45 ) in order to fit within the nacelle or the engine bay and also not interfere with the engine casing  50 . This positioning is necessary because the irregular radius of the gas turbine engine casing  50  physically precludes the combined auxiliary gear box  40  and its support components  42  from being installed any closer to the drive shaft of the gas turbine engine. 
     The relatively long tower shaft  35  driving the AGB  40  and the disbursed, arcuate arrangement of the support components  42  (see,  FIG. 1B ) produces a significant churning of lubrication oil within the AGB  40  and results in less than efficient lubrication and lubrication oil scavenging. The arrangement also requires an unnecessarily large amount of space within the nacelle or engine bay (See,  FIG. 3 ). 
     Accordingly, it is desirable to provide an alternative gearbox architecture that allows the gearbox to be compactly contoured and positioned closer to the exterior engine casing to reduce weight and improve oil scavenging. 
     In addition, it is desirable to provide a gearbox architecture providing superior oil scavenging from the gearbox housing. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention. 
     BRIEF SUMMARY 
     A gas turbine engine is provided. The gas turbine engine comprises a drive shaft, a compressor, a combustor, and an exhaust turbine, where the exhaust turbine and the compressor are coaxially and serially connected by the drive shaft. The gas turbine further comprises an engine casing of varying diameters that circumferentially envelopes the compressor, the combustor and the exhaust turbine. The gas turbine engine and engine casing has a waist located between the compressor and the combustor. The gas turbine engine also comprises an accessory gear box (“AGB”) attached to the engine casing at or near the waist. The AGB comprises a gear rotating on an axis extending in a transverse direction relative to that of the drive shaft. 
     An AGB is provided. The AGB comprises a housing defining an opening and two or more gears mounted within the housing. Each of the two or more gears rotates about its own axis where each axis is transverse to the drive shaft of the gas turbine engine. 
     A gas turbine engine is provided. The gas turbine engine comprises a drive shaft; and an accessory gear box (AGB). The AGB further comprises a housing having an opening and two or more gears mounted within the housing, each of the two or more gears rotating about its own axis, each axis being transverse to an axis of the drive shaft of the gas turbine engine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
         FIG. 1  is a left side cutaway view of an exemplary gas turbine engine with a conventional longitudinal accessory Gear Box (AGB); 
         FIG. 1A  is a perspective view of the gas turbine engine with a conventional AGB wrapped around the top of the engine casing; 
         FIG. 1B  is a disembodied view of a gearing arrangement of a conventional longitudinal AGB; 
         FIG. 2  is a left side cutaway view of a gas turbine engine with an exemplary transverse AGB installed at the engine casing waist according to embodiments; 
         FIG. 2A  is a perspective view of the gas turbine engine with an exemplary transverse AGB installed at the engine casing waist according to embodiments; 
         FIG. 2B  is a disembodied view of an exemplary view of a gearing arrangement of an exemplary transverse AGB according to embodiments; and 
         FIG. 3  is a comparison plan view of the dimensions of the gas turbine engine with the conventional AGB and an exemplary transverse AGB installed. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Thus, any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. All of the embodiments described herein are exemplary embodiments provided to enable persons skilled in the art to make or use the invention and not to limit the scope of the invention which is defined by the claims. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary, or the following detailed description. 
       FIG. 1  is a simplified cross sectional side view of a gas turbine engine  100  and a conventional AGB  40  mounted thereon at the periphery of the air collector  45 . A typical gas turbine engine includes an air intake bellmouth  25 , a compressor  5 , a combustion section  10 , an exhaust turbine  15 , an exhaust plenum  20  and a conventional AGB  40 . The compressor  5 , the exhaust turbine  15  and the AGB  40  are all coaxially driven by the drive shaft  30 , which is shown only in part in the interest of brevity and clarity. 
     With the exception of the AGB  40 , the entire engine is enclosed in an engine casing  50 . The engine casing  50  and the AGB  40  must all fit with the confines of an aerodynamic nacelle or within an engine bay. A nacelle is a cover housing that is separate from the aircraft fuselage that holds engines, fuel, or equipment. 
     Conventionally, accessories  42  that are driven by the accessory gearbox are arranged in a direction that is coaxial with the drive shaft  30  and are dispersed arcuately along an angular segment of the air collector  45  section of the engine casing  50  (See,  FIG. 1A ). This arrangement permits the accessories  42  to fit between a wall of an engine bay and the engine casing  50 . Thus, in conventional architectures the AGB  40  must also be arcuate. 
       FIG. 1B  is a simplified typical gearing architecture of a conventional AGB  40 . The AGB  40  may include, inter alia, gearing for a starter  110 , an inlet particle accelerator fan  115 , a compound idler gear  120 , lubrication oil pump  125 , an air oil separator  130 , a generator shaft  135  and a fuel pump  140 . The AGB  40  is driven by the drive shaft  30  via a relatively long tower shaft  35  (See  FIG. 1 ) and its associated bevel gears. 
     Referring again to  FIG. 1 , the accessories  42  driven by the AGB  40  must be positioned around the circumference of the engine casing  50  to locations on the air collector  45  that are radially the closest to the drive shaft of the gas turbine engine  100  in order to maximize the space available between the nacelle and the engine casing  50 . As can be seen in  FIG. 1 , it is shown that the AGB  40  must be simultaneously positioned distantly from the drive shaft  30  to allow the accessories  42  that are mounted on the forward or aft side of the AGB  40  to clear the air collector  45  portion of the engine casing  50 . Thus, the tower shaft  35  must be long enough to extend from the drive shaft  30  to the gearing (See,  FIG. 1A ) of the AGB  40 . Because the accessories  42  are arrayed around the circumference of the engine casing  50 , the AGB  40  is necessarily laid out in the narrow arcuate configuration that wraps around the engine casing at a distance required to clear the radial profile of the engine casing  50 . The resulting arcuate arrangement of the AGB  40  makes oil management more difficult because the oil is susceptible to gear churn as it travels along inside the AGB  40  to the various scavenger ports (not shown) towards either distal end of the AGB  40 . Thus, the arcuate arrangement requires more oil scavenging points to collect the lubricating oil and return it to the lubricating oil pump. 
       FIG. 2  is a simplified cross sectional side view of the gas turbine engine  100  and an exemplary transverse AGB  40 ′ mounted thereon according to embodiments. The gas turbine engine  100  includes the air intake bellmouth  25 , the compressor  5 , the combustion section  10 , the exhaust turbine  15 , the exhaust plenum  20  and a transverse AGB  40 ′. The compressor  5 , the combustion section  10 , the exhaust turbine  15  and the transverse AGB  40 ′ are all driven by the drive shaft  30 , which is shown in part in the interest of brevity and clarity. 
     A salient feature of the embodiments of  FIG. 2  is the rotational axes  41 ′ of the transverse AGB  40 ′ are perpendicular to the drive shaft  30 . Thus, the rotational axes  41 ′ of all of the accessories (not shown) driven by the transverse AGB  40 ′ are also perpendicular to the drive shaft  30 . Although the rotational axes  41 ′ of the transverse AGB  40 ′ are disclosed as being perpendicular, it will be appreciated that the rotational axes  41 ′ need not be precisely perpendicular. The rotational axes  41 ′ of the transverse AGB  40 ′ may deviate from true perpendicularity as may be required by the overarching design of the gas turbine engine  100 . 
     Another salient feature of the embodiments of  FIG. 2  is that the mounting for the transverse AGB  40 ′ may be moved aft from the air collector  45  towards the combustion section  10  to take advantage of the narrower radius of the engine casing in the vicinity of a narrowing (commonly referred to as the waist)  51  of the engine casing  50  that is located in the vicinity of the high pressure stages  7  of the compressor  5 . Thus, the accessories (not shown) may be aggregated together more compactly in the transverse AGB  40 ′ to fit into the space available at the waist  51 . In the case of the conventional AGB  40  (See,  FIG. 1 ), the length of the various accessories attached thereto prevented any space savings because the physical size of the accessories clashed either with the air collector  45  or the engine casing  50  in the vicinity of the combustion section  10 . An additional advantage that may be realized from the use of a transverse AGB  40 ′ is that the tower shaft  35 ′ may be reduced in length thereby eliminating weight and reducing torsion strain that would otherwise occur in a longer tower shaft (such as tower shaft  35  of  FIG. 1 ). The tower shaft  35 ′ has a first end  202  and a second end  203 . The first end  202  is connected to the gearing  42 ′ of the transverse AGB  40 ′ via a translational gear  43  and the second end  203  is connected to the drive shaft  30  via a bevel gear via the opening  36 ′ in the housing  20 ′. 
     Further, oil scavenging is improved. By reducing the width and increasing the depth of the transverse AGB  40 ′, most of the AGB lubrication oil returns to the engine casing via the tower shaft opening  36 ′ in the transverse AGB  40 ′. Thus, fewer scavenging ports  44  are required in the AGB housing  20 ′ to collect and return the AGB lubrication oil. Whatever number of scavenging ports  44  that may be required can be located at the lowest points in the transverse AGB  40 ′. This may be desirable to scavenge oil when the gas turbine engine  100  is in a non-level flight attitude such that the tower shaft opening  36 ′ is not the lowest point in the transverse AGB  40 ′.  FIG. 2  illustrates one scavenging port  44  at a potential low point in the transverse AGB  40 ′. Such illustration is merely exemplary and should not be construed as limiting the number of scavenging ports disclosed herein to the single scavenging port  44 . 
       FIG. 2A  is an rendition of an exemplary installation on an HPW3000 gas turbine engine produced by from Advanced Turbine Engine Company (ATEC) with a exemplary transverse mounted AGB  40 ′ according to embodiments. The gas turbine engine  100  includes the housing  50 , the air intake bellmouth  25 , the compressor  5 , the combustion section  10 , the exhaust turbine  15 , the exhaust plenum  20  (See,  FIG. 2 ) and the transverse AGB  40 ′. The accessories  42 ′ driven by the transverse AGB may include a starter  110 , an inlet particle accelerator fan  115 , one or more pumps ( 120 , 125 ), an air oil separator  130 , an air turbine starter  135  and a fuel control unit  140 . 
       FIG. 2B  is a disembodied view of an exemplary gearing arrangement for a transverse AGB  40 ′. The transversal AGB  40 ′ is driven by the tower shaft  35 ′ (via a bevel gear) and drives a number of gears ( 110 ′- 140 ′) for the accessories  42 ′. Exemplary accessories may include the air oil separator  130 ′, fuel pump  120 ′, idler gear  25 ′, starter  110 ′, generator shaft  135 ′ and a lubrication oil pump  140 ′ (See, also  FIG. 2A ). 
       FIG. 3  is a side by side comparison of plan views of an exemplary gas turbine engine with a conventional AGB  40  and with a transverse AGB  40 ′. As may be seen, the width requirement of the transverse AGB  40 ′ is 4.2 in. as compared to the conventional AGB  40  that has a width requirement of 19.2 in., which is a 79% reduction. The length requirement in this particular embodiment increases slightly from 10.4 inches to 14.1 inches. Because the AGB  40  represents the widest component of the engine; it is the controlling factor in regard to space constraints within the engine bay or nacelle. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.