Power take-off system and gas turbine engine assembly including same

A power take-off system for a gas turbine engine includes a starter coupled to a second spool, and a clutch assembly coupled between the starter and a first spool, the clutch assembly configured to couple the first spool to the starter when starting the gas turbine engine assembly. A method of assembling a gas turbine engine assembly that includes the power take-off system, and a gas turbine engine assembly including the power take-off system are also described.

BACKGROUND OF THE INVENTION

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 descent 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.

BRIEF SUMMARY OF THE INVENTION

In one aspect, a method for assembling a gas turbine engine assembly is provided. The gas turbine engine assembly includes a first spool including a high-pressure compressor, a high-pressure turbine, and shaft coupled between the high-pressure compressor and the high-pressure turbine, and a second spool that is disposed coaxially with the first spool. The method includes coupling a starter to the second spool using a drive shaft, and coupling a clutch assembly between the starter and the first spool such that the clutch assembly is configured to couple the starter to the first spool when starting the gas turbine engine assembly.

In another aspect, a power take-off system for a gas turbine engine is provided. The system includes a starter coupled to the second spool, and a clutch assembly coupled between the starter and the first spool, the clutch assembly configured to couple the first spool to the starter when starting the gas turbine engine assembly.

In a further aspect, a gas turbine engine assembly is provided. The gas turbine engine assembly includes a first spool comprising a high-pressure compressor, a high-pressure turbine, and shaft coupled between the high-pressure compressor and the high-pressure turbine, a second spool that is disposed coaxially with the first spool, and a power take-off system including a starter rotatably coupled to the second spool and selectively coupled to the first spool when starting the gas turbine engine assembly.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a cross-sectional view of a gas turbine engine assembly10having a longitudinal axis11. Gas turbine engine assembly10includes a fan assembly12and a core gas turbine engine13. Core gas turbine engine13includes a high-pressure compressor14, a combustor16that is disposed downstream from high-pressure compressor14, and a high-pressure turbine18that is coupled to high-pressure compressor14via a first shaft32. In the exemplary embodiment, gas turbine engine assembly10also includes a low-pressure turbine20that is disposed downstream from core gas turbine engine13, a multi-stage fan assembly12, and a shaft31that is used to couple fan assembly12to low-pressure turbine20. In the exemplary embodiment, gas turbine engine assembly10is a two spool engine wherein the high-pressure compressor14, high-pressure turbine18and shaft32form a first spool40, and fan assembly12, low-pressure turbine20and shaft31form a second spool42.

In operation, air flows through fan assembly12. A portion of the compressed air that is discharged from fan assembly12is channeled through compressor14wherein the airflow is further compressed and delivered to combustor16. Hot products of combustion (not shown) from combustor16are utilized to drive turbines18and20, and turbine20is utilized to drive fan assembly12by way of shaft31. Gas turbine engine assembly10is operable at a range of operating conditions between design operating conditions and off-design operating conditions.

FIG. 2is a cross-sectional view of a portion of the gas turbine engine assembly10shown inFIG. 1including an exemplary power take-off system100. Power take-off system100includes a starter102that includes a motor/generator110. Starter, as used herein, is defined as a device that in one mode is operable as a motor to start the first spool40, and is also operable in a second mode as a generator that may be driven by either the first spool40and/or the second spool42to generate electrical power during predetermined engine operations that are discussed below.

Starter102includes a motor/generator110and a shaft112that is utilized to couple starter102to first spool40and/or second spool42. More specifically, shaft112includes a first end130that is coupled to and thus driven by motor/generator110. Shaft112also includes a second end132and a pinion134that is coupled or splined to second end132. Moreover, power take-off system100also includes a first ring gear136that is coupled or splined to rotor shaft31, and a second ring gear138that is coupled to an extension shaft140that will be discussed further below. In the exemplary embodiment, pinion134, ring gear136, and ring gear138are each bevel gears that are machined such that pinion134is intermeshed with ring gears136and138.

FIG. 3is a cross-sectional view of a portion of the exemplary power take-off system100shown inFIG. 2.FIG. 4is a cross-sectional view of a portion of the exemplary power take-off system100shown inFIG. 2in a second configuration. In one embodiment, second ring gear138is formed unitarily with extension shaft140. Optionally, second ring gear138is coupled to extension shaft140using a plurality of splines, for example. In the exemplary embodiment, first ring gear136has a first diameter150and second ring gear138has a second diameter152that is approximately equal to first diameter150. As such, and as shown inFIG. 3, drive shaft112is approximately perpendicular to centerline axis11. Optionally, as shown inFIG. 4, first ring gear136has a first diameter150and second ring gear138has a second diameter152that is less that first diameter150such that drive shaft112is disposed at an angle α with respect to centerline axis11. In the exemplary embodiment, angle α is between approximately 45 degrees and approximately ninety degrees depending on the diameters of rings gears136and138.

To support both drive shaft112and extension shaft140, power take-off system100also includes a shaft support structure160that is coupled to a rigid structure, such as a fan frame162. Power take-off system100also includes a plurality of bearing assemblies to facilitate maintaining shaft112in the proper position within gas turbine engine assembly10. Specifically, power take-off system100includes a first thrust bearing170that includes a stationary outer race172that is secured to a stationary structure such as support structure160, a rotating inner race174that is secured to pinion134, and a plurality of rolling elements176that are disposed between outer and inner races172and174respectively.

Power take-off system100includes a first roller bearing180that includes a stationary outer race182that is secured to support structure160, a rotating inner race184that is secured to pinion134, and a plurality of rolling elements186that are disposed between outer and inner races182and184respectively. During operation, roller bearing180facilitates maintaining shaft112in a substantially fixed radial alignment within gas turbine engine assembly10.

Power take-off system100includes a second roller bearing190that includes a stationary outer race192that is secured to support structure160, a rotating inner race194that is secured to pinion134, and a plurality of rolling elements196that are disposed between outer and inner races192and194respectively. During operation, roller bearing190facilitates maintaining shaft112in a substantially fixed radial alignment within gas turbine engine assembly10. In the exemplary embodiment, second roller bearing assembly190is disposed radially inwardly from first roller bearing assembly180.

During operation, and as shown inFIGS. 2,3, and4, starter102is coupled to and thus drives or is driven by second spool42during all engine operations. That is, pinion134is always coupled to ring gear136such that the second spool42drives or is driven by starter102. For example, in one embodiment, after core engine13is running, thus causing the second spool42to rotate from expansion energy extracted from turbine20, starter102is thus caused to rotate such that starter102is functioning as a generator to produce electrical power that may be utilized by the aircraft or as desired. Optionally, since starter102is always coupled to second spool42, starter102may be utilized as a motor to restart the core gas turbine engine during selected flight conditions.

Since, under typical operations the first spool40is rotating at a rotational speed that is different than the rotational speed of second spool42. Power take-off system100is configured to compensate for the different rotational speeds. More specifically, the diameters of ring gears136and138are each selected based on the rotational speed of the components that are driven by or are driving starter102. For example, in this embodiment, since ring gear136is coupled to second spool42which in this embodiment rotates at a speed that is less than the rotational speed of the first spool40, ring gear36has a diameter150that is greater than a diameter152of ring gear138to compensate for the speed differential between the first and second spools40and42. As such, it should be realized that the diameters150and152of the ring gears36and38are selected based on the rotational speeds of the first and seconds spools40and42and thus may be resized to operate with different type engine and fan assemblies operating at different speeds as shown inFIGS. 6 and 7.

As discussed and illustrated above, starter102is also selectively engageable to the first spool40when starting the gas turbine engine assembly. For example, to start the core gas turbine engine13, including the first spool40, starter102is selectively coupled to the first spool40. Starter102is then operated as a motor to rotate the first spool40and thus restart core gas turbine engine13. To selectively couple starter102to the first spool40, power take-off system100also includes a clutch200and a clutch actuator202that is utilized to activate or engage clutch200. In the exemplary embodiment, clutch actuator202includes at least a solenoid204and a spring206.

Clutch200includes a first clutch portion210that is securely coupled to extension shaft140, and a second clutch portion212that is movably coupled to first spool40. In the exemplary embodiment, second clutch portion212is coupled to shaft32utilizing a plurality of splines such that second clutch portion212is enabled to be moved in either an upstream direction220or a downstream direction222.

For example, during a first mode of operation in which an operator desires to start core gas turbine engine13, solenoid204is activated, depressing spring206, and causing second clutch portion212to move in the upstream direction220and thus contact or engage first clutch portion210. Starter102is then activated causing both the first spool40and second spool42to rotate. While the first spool40is rotating, fuel may be supplied to the core gas turbine engine13to be started as known in the art.

In a second mode of operation, after core gas turbine engine13is running, solenoid204may be deactivated, causing spring206to push second clutch portion212in the downstream direction222and thus disengage from first clutch portion210. In this mode, only second spool42is driving starter102, and starter102is functioning as a generator to produce electrical power.

Although actuator202is described herein as including solenoid204that is activated to engage clutch200, it should be realized that solenoid204and spring206may be repositioned such that solenoid204is deactivated to engage clutch200and activated to disengage clutch200. Moreover, although clutch200is described as a friction clutch, it should be realized the clutch200may be of any type of clutch that is capable of engaging starter102to first spool40. For example, clutch200may be an overrunning clutch or include a clutch pack assembly.

FIG. 5is a cross-sectional view of another exemplary gas turbine engine assembly300having a longitudinal axis11. Gas turbine engine assembly300is substantially similar to gas turbine engine assembly10shown inFIG. 1. Accordingly, items illustrated inFIG. 1that are also included inFIG. 5will identified with the same number. In this embodiment, gas turbine engine assembly300is a multispool engine that includes a fan assembly12and a core gas turbine engine13.

Core gas turbine engine13includes a high-pressure compressor14, a combustor16that is disposed downstream from high-pressure compressor14, and a high-pressure turbine18that is coupled to high-pressure compressor14via a first shaft32. In the exemplary embodiment, gas turbine engine assembly300also includes a low-pressure turbine20that is disposed downstream from core gas turbine engine13, and a shaft31that is used to couple fan assembly12to low-pressure turbine20. Gas turbine engine assembly300has an intake side28and an exhaust side30. In the exemplary embodiment, gas turbine engine assembly300is a three spool engine wherein the high-pressure compressor14, high-pressure turbine18and shaft32form a first spool40, and fan assembly12, low-pressure turbine20and shaft31form a second spool42.

Gas turbine engine assembly300also includes a third spool46that includes a booster compressor48that is disposed axially between the fan assembly12and high-pressure compressor14and a booster turbine50that is disposed between high-pressure turbine18and low-pressure turbine20. Third spool46also includes a shaft52that couples booster compressor48to booster turbine50.

In operation, air flows through fan assembly12and a first portion of the airflow is channeled through booster compressor48. The compressed air that is discharged from booster compressor48is channeled through compressor14wherein the airflow is further compressed and delivered to combustor16. Hot products of combustion (not shown) from combustor16are utilized to drive turbines18,50and20. Gas turbine engine assembly300is operable at a range of operating conditions between design operating conditions and off-design operating conditions.

FIG. 6is a simplified illustration of another exemplary power take-off system400that may be used with any multispool gas turbine engine including the two spool engine10shown inFIG. 1and the three spool engine shown inFIG. 5. As discussed above, each exemplary power take-off system described herein is configured to be continuously coupled to either the second or third spool of a gas turbine engine and selectively coupled to the first spool, i.e. the core gas turbine engine, during selected engine operations.

In this arrangement, since under typical starting operations the first spool40is rotating at a rotational speed that is different than the rotational speed of the other spool, either second or thirds spools42or46, power take-off system400is configured to compensate for the different rotational speeds. More specifically, in this embodiment, shaft112includes a first pinion410that is disposed proximate to shaft second end132and a second pinion412that is disposed radially outwardly from first pinion410on shaft112. Power take-off system400also includes a first ring gear420that is coupled to the extension shaft140and thus to the first spool40via clutch200. Moreover, power take-off system400also includes a second ring gear422, that in one embodiment is coupled to shaft31if a two spool engine is utilized or to shaft52if a three spool engine is utilized. First pinion410has a first diameter430and second pinion412has a second diameter432that in the exemplary embodiment is greater than the first pinion diameter430. Ring gear420has a first diameter434and ring gear422has a second diameter436that in the exemplary embodiment is greater than the diameter of first ring gear diameter434. The diameters for each of the first and second ring gears and the first and second pinions are each selected based on the rotational speed of the components that are driven by or are driving starter102.

For example, in this embodiment, since ring gear422is coupled to either second spool42or third spool46which in this embodiment each rotate at a speed that is less than the rotational speed of the first spool40, ring gear422has a diameter436that is greater than a diameter434of ring gear420to compensate for the speed differential between the first spool40and the second and third spools42and/or46. Moreover, each respective pinion coupled to a respective ring gear is also sized to reflect this increased diameter based on the rotational speeds of the various spools. As such, it should be realized that diameters430,432,434, and436are selected based on the rotational speeds of the first and second and/or third spools40,42, and/or46, and the desired starter capacity or desired generator output110.

FIG. 7is a simplified illustration of another exemplary power take-off system500that may be used with any multispool gas turbine engine including the two spool engine10shown inFIG. 1and the three spool engine300shown inFIG. 5. In this arrangement, power take-off system500is configured to be coupled to a counter-rotating gas turbine engine. Specifically, power take-off system500is configured to coupled to a gas turbine engine that includes a least a first spool that rotates in a first direction and a second spool that rotates in an opposite second direction. In the exemplary embodiment, the first spool40is the core engine spool, and the second spool may be either second spool42if a two-spool engine10is utilized or spool46if a three-spool engine300is utilized.

More specifically, to coupled each spool to a single shaft112and thus drive starter102, first ring gear420is disposed on the downstream side of first pinion410. In this arrangement, each ring gear420and422will drive shaft112in a single rotational direction while at least two of the spools are counter-rotating.

Described herein is a method for assembling a gas turbine engine assembly is provided. The gas turbine engine assembly includes a first spool including a high-pressure compressor, a high-pressure turbine, and shaft coupled between the high-pressure compressor and the high-pressure turbine, and a second a second spool that is disposed coaxially with the first spool. The method includes coupling a starter to the second spool using a drive shaft, and coupling a clutch assembly between the starter and the first spool such that the clutch assembly is configured to couple the starter to the first spool when starting the gas turbine engine assembly.

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. input from both the first spool40and at least one of the second spool42and the third spool46, that may be used to drive starter102during ground start to rotate both spools of gas turbine engine assembly10. 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.

More specifically, the power take-off system described herein includes a clutch assembly that may be utilized to engage or disengage the first spool from the starter such that during a first mode the starter may be engaged to start the core gas turbine engine, and during a second mode the starter may be disengaged such that the starter is driven solely by the second spool and functions as a generator to produce electrical power.

For the aircraft/engine mission, the second spool provides the majority of the needed aircraft power and also drives the appropriate engine accessories. As a result, additional energy is extracted from the second spool including either the booster turbine or the low-pressure turbine to support ever increasing electrical demands. Specifically, newer aircraft are designed to require an atypically large amount of electrical power to be supplied 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 the second spool to provide the majority of the power 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.