Patent Application
20080148881
This invention relates generally to gas turbine engines, and more specifically to a dual input/output power take-off system configured to start the gas turbine engine and also configured to generate electrical power.
At least some known gas turbine engines used with aircraft include a core engine having, in serial flow arrangement, a compressor which compresses airflow entering the engine, a combustor which burns a mixture of fuel and air, and low and high-pressure turbines which extract energy from airflow discharged from the combustor to generate thrust.
As aircraft accessory power demands have increased, there also has been an increased need to run the gas turbine engines at idle speeds that may be higher than other engines not subjected to increased power demands. More specifically, increasing the gas turbine engine idle speed enables the increased power demands to be met without sacrificing compressor stall margins. However, the increased idle speed may also generate thrust levels for the engine which are higher than desired for both flight idle decent operations and/or during ground idle operations. Over time, continued operation with increased thrust levels during such idle operations may increase maintenance costs and the increased fuel flow requirements may also increase aircraft operating expenses.
In one aspect, a method for assembling a gas turbine engine including a core gas turbine engine, a low-pressure turbine, a starter, and a generator is provided. The method includes coupling a starter to the core gas turbine engine using a first shaft, and coupling a generator to the low-pressure turbine using a second shaft, wherein the first shaft is circumferentially offset from the second shaft by an angle α.
In another aspect, a power take-off system for a gas turbine engine is provided. The system includes a starter coupled to a first spool using a first shaft, and a generator coupled to the second spool using a second shaft, the first shaft is circumferentially offset by the second shaft by an angle α.
In a further aspect, a gas turbine engine assembly is provided. The gas turbine engine assembly includes a first spool, a second spool, and a power take-off system comprising a starter coupled to the first spool using a first shaft, and a generator coupled to the second spool using a second shaft, the first shaft is circumferentially offset by the second shaft by an angle α.
In operation, air flows through fan assembly 12 and a first portion of the airflow is channeled through booster 22. The compressed air that is discharged from booster 22 is channeled through compressor 14 wherein the airflow is further compressed and delivered to combustor 16. Hot products of combustion (not shown) from combustor 16 are utilized to drive turbines 18 and 20, and turbine 20 is utilized to drive fan assembly 12 and booster 22 by way of shaft 31. Gas turbine engine assembly 10 is operable at a range of operating conditions between design operating conditions and off-design operating conditions.
Gas turbine engine assembly 10 also includes a power take-off system 100 that includes a starter 102 and a generator 104. Although starter 102 is described herein as a device that is utilized to start the core gas turbine engine 13, it should be realized, that starter 102 may also be driven by the core gas turbine engine 13 and function as a generator. Moreover, although generator 104 is described herein as an apparatus that is driven by low-pressure turbine 20 to generate electrical energy, it should be realized, that generator 104 may also drive low-pressure turbine 20 to facilitate restarting gas turbine engine assembly 10 during various operational conditions which will be discussed below.
As shown in
In the exemplary embodiment, shaft 112 is disposed at an axial position along axis 11 that is approximately equal to the axial position of shaft 122 along axis 11. As such, shaft 112 and shaft 122 are approximately coplanar with respect to the axial position along longitudinal axis 11.
As shown in
Power take-off system 100 also includes a plurality of bearing assemblies to facilitate maintaining shaft 122 in the proper position within gas turbine engine assembly 10. Specifically, power take-off system 100 includes a first thrust bearing 140 that includes a stationary outer race 142 that is secured to a stationary structure such as a fan frame, a rotating inner race 144 that is secured to pinion 134, and a plurality of rolling elements 146 that are disposed between outer and inner races 142 and 144 respectively. During operation, thrust bearing 140 transmits any residual thrust generated by shaft 31 to ground via the stationary structure.
Power take-off system 100 includes a first roller bearing 150 that includes a stationary outer race 152 that is secured to a stationary structure such as a compressor casing or the fan frame, a rotating inner race 154 that is secured to pinion 134, and a plurality of rolling elements 156 that are disposed between outer and inner races 152 and 154 respectively. During operation, roller bearing 150 facilitates maintaining shaft 122 in a substantially fixed alignment within gas turbine engine assembly 10.
During assembly, the generator/motor 120 is coupled to gearbox 124. Shaft 122 is then coupled between generator/motor 120 and ring gear 136 such that generator/motor 120 is configured to drive or be driven by low-pressure turbine 20. In the exemplary embodiment, low-pressure turbine 20 drives generator/motor 120 such that generator/motor 120 produces additional electrical power that may be used by an aircraft when the core gas turbine engine 13 is required to operate at speeds to minimize engine thrust yet provide for increased electrical power demands.
As shown in
Power take-off system 100 also includes a plurality of bearing assemblies to facilitate maintaining shaft 112 in the proper position within gas turbine engine assembly 10. More specifically, and as shown in
Power take-off system 100 includes a first roller bearing 250 that includes a stationary outer race 252 that is secured to a stationary structure such as a fan frame, a rotating inner race 254 that is secured to pinion 234, and a plurality of rolling elements 256 that are disposed between outer and inner races 252 and 254 respectively. During operation, roller bearing 250 facilitates maintaining shaft 112 in a substantially fixed alignment within gas turbine engine assembly 10.
During assembly, starter 102 is coupled to shaft 112 which is then coupled to ring gear 236 such that motor/generator 110 is configured to drive or be driven by high-pressure turbine 18.
During operation, starter 102 is activated to start the core gas turbine engine 13. Specifically, activating starter/generator 110 causes shaft 112 to rotate causing the high-pressure turbine spool to rotate and thus causes the core gas turbine engine 13 to start as is known in the art. In the exemplary embodiment, starting the core gas turbine engine 13 causes the low-pressure turbine 20 to rotate, thus causing generator/motor 120 to generate electrical energy. Additionally, during flight or other operations, generator/motor 120 may be utilized to assist in the restart the core gas turbine engine. Specifically, since generator 104 may function as a motor, supplying electrical power to generator 104 may cause generator 104 to function as a starter. Specifically, since generator 104 is coupled to low-pressure turbine 20 via shaft 122, operating generator 104 as a motor may cause shaft 122 to rotate the low-pressure turbine 20 and thus restart the core gas turbine engine during certain flight conditions.
Described herein is a method for assembling a gas turbine engine assembly including a core gas turbine engine and a low-pressure turbine disposed downstream from the core gas turbine engine. The method includes coupling a starter to the core gas turbine engine using a first shaft, and coupling a generator to the low-pressure turbine using a second shaft, wherein the first shaft is circumferentially offset from the second shaft by an angle α.
Also, described herein is a gas turbine engine assembly that is configured to extract relatively large amounts of power from the engine while operating the engine at low thrust conditions. Specifically, the gas turbine engine assembly described herein includes a dual input, i.e. starter 102 which may drive or be driven by the first spool 40 and generator 104 which may be driven by or drive the second spool 42. Specifically, the system described herein is configured to extract additional electrical power from the gas turbine engine while the gas turbine engine is operating at low thrust conditions and/or certain flight conditions. For example, the system described herein takes power off of two spools simultaneously in order to share the load requirements so that the overall engine operators in an efficient manner.
For the aircraft/engine mission, the second spool provides the majority of the needed aircraft power and also drives the appropriate engine accessories. Optionally, some accessories may be driven by the first spool via the starter gearbox.
As a result, additional energy is extracted from the low-pressure turbine and fan assembly to support ever increasing electrical demands. Specifically, newer aircraft are designed to require an atypically large amount of electrical power driven by the generator on the engine accessory gearbox. The power requirements during idle conditions thus require the engine to run at idle speeds that are higher than desirable in order to maintain adequate compressor stall margin. This results in thrust levels for the engine that are higher than desired for both flight idle descent points and ground idle conditions, which has both maintenance cost implications for aircraft brakes and excess fuel burn penalties for typical short range missions.
Whereas the system described herein, takes power off both shafts simultaneously in order to share the load requirements. As a result, the system described herein is relatively simple to install, and also provides a low weight solution to this problem. Moreover, the system described herein, allows for reduced thrust during ground idle conditions to reduce aircraft brake maintenance, reduced dirt ingestion, and reduced flight idle thrusts for an improved flight profile and improved short range fuel burn while still maintaining adequate compressor stall margin during high power extraction conditions.
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.
