Abstract:
A method of assembling a gas turbine assembly includes providing a core gas turbine engine including a high-pressure compressor, a combustor, and a turbine, coupling a low-pressure turbine to the core gas turbine engine, coupling a booster compressor to a gearbox, and coupling the gearbox to the low-pressure turbine such that the booster compressor is driven by the low-pressure turbine.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to gas turbine engines, and more specifically to gas turbine engine assemblies and methods of assembling the same. 
     At least some known gas turbine engines include a fan assembly, a core engine, and a low-pressure or power turbine. The core engine includes at least one compressor, a combustor, and a high-pressure turbine that are coupled together in a serial flow relationship. Air entering the core engine is mixed with fuel and ignited to form a high energy gas stream. The high energy gas stream flows through the high-pressure turbine to rotatably drive the high-pressure turbine and thus the compressor via a first drive shaft. The gas stream further expands through the low-pressure turbine, which rotatably drives the fan assembly through a second drive shaft. 
     To improve engine efficiency, it is desirable to operate the fan assembly at a relatively lower speed than the operating speed of the high-pressure turbine. However, operating the fan at a relatively slow speed may be detrimental to the operation of a booster compressor. As such, additional booster stages may be required in order to produce the desired overall pressure ratio, thus increasing the overall cost, design complexity, and weight of the gas turbine engine. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect, a method of assembling a gas turbine engine is provided. The method includes coupling a low-pressure turbine to the core gas turbine engine, coupling a booster compressor to a gearbox, and coupling the gearbox to the low-pressure turbine such that the booster compressor is driven by the low-pressure turbine. 
     In another aspect, a turbine engine assembly is provided. The turbine engine assembly includes a core gas turbine engine including a high-pressure compressor, a combustor, and a turbine. The turbine engine assembly also includes a low-pressure turbine coupled to the core gas turbine engine, a booster compressor, and a gearbox coupled between the low-pressure turbine and the booster compressor such that the booster compressor is driven by the low-pressure turbine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a portion of an exemplary gas turbine engine assembly that includes a gear-driven booster; 
         FIG. 2  is an enlarged cross-sectional view of a portion of the turbine engine assembly shown in  FIG. 1 ; and 
         FIG. 3  is a cross-sectional view of a portion of another exemplary gas turbine engine assembly that includes a gear-driven booster. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a schematic illustration of an exemplary gas turbine engine assembly  10  having a longitudinal axis  11 . Gas turbine engine assembly  10  includes a fan assembly  12 , and a core gas turbine engine  13  that includes a high-pressure compressor  14 , a combustor  16 , and a high-pressure turbine  18 . In the exemplary embodiment, gas turbine engine assembly  10  also includes a low-pressure turbine  20  and a multi-stage booster compressor  22 . 
     Fan assembly  12  includes an array of fan blades  24  extending radially outward from a rotor disk  26 . Gas turbine engine assembly  10  has an intake side  28  and an exhaust side  30 . Fan assembly  12  and low-pressure turbine  20  are coupled together via a gearbox  100  driven by a first rotor shaft  31 , and compressor  14  and high-pressure turbine  18  are coupled together by a second rotor shaft  32 . 
       FIG. 2  is an enlarged cross-sectional view of a portion of the turbine engine assembly shown in  FIG. 1 . As shown in  FIG. 2 , booster  22  includes a plurality of circumferentially-spaced structural vanes  34  that function as inlet guide vanes (IGV) to facilitate channeling airflow entering gas turbine engine assembly  10  downstream through booster  22 . In the exemplary embodiment, booster  22  also includes a plurality of outlet guide vane (OGV) assemblies  36 . Moreover, in the exemplary embodiment booster  22  includes two stages  40 , wherein each stage includes a rotor section and a disk section. Specifically, each rotor section includes a plurality of rotor blades  42  that are each coupled to a respective rotor disk  44 . Booster compressor  22  is positioned downstream from inlet guide vane assembly  34  and upstream from core gas turbine engine  13 . Although booster compressor  22  is shown as having only two rows of rotor blades  42 , it should be realized that booster compressor  22  may have a single row of rotor blades  42 , or three or more rows of rotor blades  42  that are interdigitated with a plurality of rows of guide vanes  46 . In one embodiment, inlet guide vanes  34  are fixedly coupled to a booster case  50 . In another embodiment, inlet guide vanes  34  are movable during engine operation to facilitate varying a quantity of air channeled through booster compressor  22 . 
     In the exemplary embodiment, booster compressor  22  is rotatably coupled to a gearbox  100  such that booster compressor  22  rotates at a rotational speed that is different than a rotational speed of fan assembly  12  and low-pressure turbine  20 . Specifically, gearbox  100  is coupled between shaft  31  and booster compressor  22  to facilitate rotating booster compressor in either the same or an opposite direction than fan assembly  12 . 
     In the exemplary embodiment, gearbox assembly  100  has a gear ratio of approximately 2 to 1 such that fan assembly  12  rotates at a rotational speed that is approximately one-half the rotational speed of booster  22 . Accordingly, in the exemplary embodiment, booster compressor  22  rotates at a rotational speed that is faster than the rotational speed of fan assembly  12 . In the exemplary embodiment, gearbox  100  is an epicyclic gearbox that substantially circumscribes shaft  31  and includes a support structure  102 , at least one gear  103  coupled within support structure  102 , an input  104  gear, and an output gear  106 . 
     More specifically, gearbox  100  is supported by, and maintained in a substantially fixed orientation within gas turbine engine assembly  10 , utilizing support structure  102  which is coupled to structural vanes  34 . Gas turbine engine assembly  10  also includes a fan thrust bearing assembly  110  that is configured to support fan assembly  12 . Fan thrust bearing assembly  110  is coupled between structural vanes  34  and shaft  31  such that the residual thrust generated by fan assembly  12  and low-pressure turbine  20  is transmitted to structure  34 . More specifically, and in the exemplary embodiment, fan bearing assembly  110  includes a rotating inner race  112  and a stationary outer race  114  that is coupled to bearing housing  116 . As such, fan bearing assembly  110  includes a plurality of rolling elements  118  that are disposed between races  112  and  114 , respectively. 
     Gas turbine engine assembly  10  also includes a second bearing assembly  120  and a third fan bearing assembly  130 . Specifically, second and third bearing assemblies  120  and  130  are coupled radially outwardly from a drive shaft extension  140  that is coupled to gearbox  100  via a flex connection  142 . In the exemplary embodiment, second bearing assembly  120  is a roller bearing that is utilized to provide radial support for drive shaft extension  140 , and thus gearbox  100 . Bearing assembly  130  is a thrust bearing that is utilized to provide axial support for drive shaft extension  140 , and also to absorb thrust generated by booster  22 . 
     Moreover, and in the exemplary embodiment, gas turbine engine assembly  10  may also include a generator  180 , a generator drive shaft  182  that includes a first end  184  that is coupled to generator  180 , a second end  186 , and a bevel gear  188  that is coupled to drive shaft second end  186 . To operate generator  180 , shaft  140  includes a bevel gear  190  that is splined to a downstream end of shaft  140  that is configured to mesh with bevel gear  188 . As such, generator  180  may provide additional electrical energy to peak demand periods during normal engine operation and during idle speeds, for example. More specifically, during operation, power generated by booster compressor  22  is utilized to drive shaft  140 . Since shaft  140  is coupled to generator drive shaft  182  utilizing bevel gears  188  and  190 , work is extracted from booster compressor  22  to drive generator  180 . As a result, additional energy is extracted from the booster compressor to drive the generator  180  to support ever increasing electrical demands. Specifically, newer aircraft are designed to require an atypically large amount of electrical power. As a result, generator  180  may be utilized to meet the ever increasing electrical demands of newer aircraft. 
     During assembly, input gear  104  is splined to shaft  31  utilizing a cone or disk  150  such that the rotational force generated by low-pressure turbine  20  through shaft  31  is transmitted to gearbox  100  and also to fan assembly  12 . Output gear  106  is splined to drive shaft extension  140  via flex connection  142  such that the rotational force is transmitted from gearbox  100  to drive shaft extension  140 . As shown in  FIG. 2 , booster rotor disk  44  is coupled to an aft end of drive shaft extension  140  utilizing a shaft  160 . 
     During operation, core gas turbine engine  13  causes low-pressure turbine  20  to rotate and thus causes shaft  31  to rotate. Since shaft  31  is coupled to gearbox  100  via drive shaft extension  140 , torque developed by low-pressure turbine  20  is provided to both fan assembly  12  and gearbox  100 . The torque transferred by gearbox  100  is then utilized to drive booster  22 . In the exemplary embodiment, gearbox  100  is located within a sump  170 . During operation, gearbox  100  is continuously lubricated. 
       FIG. 3  is a cross-sectional view of a portion of another exemplary gas turbine engine assembly  200  that includes a gear driven booster  22 . As discussed above, gearbox  100  includes an input gear  104  and an output gear  106 , and a plurality of gears  108 . In this embodiment, booster  22  is coupled to output gear  106  utilizing a disk  202 , and shaft  31  is coupled to input gear  104  utilizing an extension apparatus  204 . 
     More specifically, gas turbine engine assembly  200  includes a bearing  210  that is coupled between disk  202  and shaft  31 . In the exemplary embodiment, bearing assembly  210  is a thrust bearing that acts as a differential bearing assembly in combination with a bearing assembly  220  to support booster  22  and fan assembly  12  and/or transfer thrust loads and/or forces from booster compressor  22  to a frame  208 . In one embodiment, bearing assembly  210  includes a radially outer race  212  that is mounted to cone  202 , and a radially inner race  214  that is mounted with respect to shaft  31 . Bearing assembly  210  also includes a plurality of rolling elements  216  that are mounted between outer and inner races  212  and  214 . As shown in  FIG. 3 , gas turbine engine assembly  200  also includes a bearing assembly  230 . In the exemplary embodiment, bearing assembly  230  is a thrust bearing assembly that is utilized to transfer the residual thrust generated by fan assembly  12 , low-pressure turbine  20 , and booster  22  to a frame  208 . In one embodiment, bearing assembly  230  includes a radially outer race  232  that is mounted to frame  208  and to gearbox  100  such that both gearbox  100  and outer race  232  are maintained in a substantially fixed position within gas turbine engine assembly  200 . Bearing assembly  230  also includes a radially inner race  234  that is coupled to shaft  31  utilizing a shaft extension  236 . Bearing assembly  230  also includes a plurality of rolling elements  238  that are mounted between outer and inner races  232  and  234 . In this embodiment, gas turbine engine assembly includes a three stage booster compressor  22 . 
     The gas turbine engine assemblies described herein each include a low-pressure turbine that is configured to drive both the fan assembly and the booster compressor. Specifically, the turbine engine assemblies described herein each include a smaller, high speed, higher pressure ratio, booster that is driven by the low-pressure turbine utilizing a gearbox. In the exemplary embodiment, the gearbox has a ratio of between approximately 1.5 to 1 and approximately 2.4 to 1. Moreover, the booster compressor is coupled to the low-pressure turbine via a flex connection to facilitate smoothly transferring torque generated by the low-pressure turbine to the gearbox. As such, the geared booster enables a smaller core gas turbine engine to be utilized with reduced stage count. 
     Exemplary embodiments of a gas turbine engine assembly that includes a gearbox coupled to a fan assembly are described above in detail. The components are not limited to the specific embodiments described herein, but rather, components of each system may be utilized independently and separately from other components described herein. The gearbox driven booster compressor described herein can also be used in combination with other known gas turbine engines. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.