Patent Application
20230332546
This application relates to an accessory gearbox arrangement for gas turbine engine accessories which provides a speed that is approximately constant.
Gas turbine engines are known, and typically include a plurality of accessories to support the operation of the engine. Examples would include fuel pumps, hydraulic pumps, oil pumps and generators.
The gas turbine engine typically includes a high pressure turbine driving a high pressure compressor and a low pressure turbine driving a low pressure compressor. The low pressure turbine will typically drive a fan rotor, sometimes through a gear reduction.
The fan rotor, low pressure compressor and low pressure turbine are known as a low speed spool. The high pressure compressor and high pressure turbine are known as a high speed spool.
The fan provides air into a bypass duct as propulsion air, and into the low pressure compressor. The air is compressed in the low and high pressure compressors, and then delivered into a combustor where it is mixed with fuel and ignited. Products of this combustion pass over the high pressure turbine and then the low pressure turbine, driving them to rotate. The turbines in turn drive their respective spools.
Rotational power for the accessories is typically provided by tower shafts which are driven to rotate with the spools. However, it is known that over the course of operation of a gas turbine engine the speed of the low speed spool and high speed spool varies by a significant amount.
In a featured embodiment, a gas turbine engine includes a high speed turbine and a high speed compressor connected by a high speed shaft to define a high speed spool. A low speed turbine and a low speed compressor are connected by a low speed shaft to define a low speed spool. A high speed tower shaft is driven by the high speed spool and a low speed tower shaft is driven by the low speed spool. The low speed tower shaft drives a low speed input gear in an accessory drive differential. The high speed tower shaft drives a high speed input gear in the accessory drive differential. One of the high speed input gear and the low speed input gear increases an output speed of an output gear, and the other decreases an output speed of the output gear. The output gear drives at least one accessory for the gas turbine engine.
In another embodiment according to the previous embodiment, the accessory drive differential is an epicyclic gear reduction. The low speed input gear drives a ring gear in the epicyclic gear reduction in a first direction. The high speed input gear drives a carrier in the epicyclic gear reduction in the first direction. The output gear is a sun gear driven to rotate in the first direction.
In another embodiment according to any of the previous embodiments, the sun gear drives at least one of a hydraulic pump, an alternator and a generator.
In another embodiment according to any of the previous embodiments, the low speed tower shaft also drives at least one additional accessory through low drive gears.
In another embodiment according to any of the previous embodiments, the high speed spool also drives at least one additional accessory through high drive gears.
In another embodiment according to any of the previous embodiments, the additional accessories and the accessories driven by the accessory drive gear reduction are housed in a common housing.
In another embodiment according to any of the previous embodiments, the common location is on an outer surface of a core engine housing the high speed spool and low speed spool.
In another embodiment according to any of the previous embodiments, the common location is in a strut positioned between the high pressure turbine and the low pressure turbine.
In another embodiment according to any of the previous embodiments, the common location is within a fan case surrounding a fan also driven by the low speed turbine.
In another embodiment according to any of the previous embodiments, a speed range of a speed of the sun gear at an idle condition for the gas turbine engine compared to a speed of the sun gear at a takeoff condition is within 10% such that a takeoff speed of the sun gear is less than or equal to 110% of a speed of the sun gear at an idle condition.
In another embodiment according to any of the previous embodiments, a star speed ratio defined as a ratio of the pitch diameter of the ring gear compared to the pitch diameter of the sun gear is between 1.3 and 3.2.
In another embodiment according to any of the previous embodiments, the star speed ratio is between 1.8 and 2.5.
In another embodiment according to any of the previous embodiments, the low pressure turbine drives a fan rotor through a drive gear reduction.
In another embodiment according to any of the previous embodiments, a speed range of a speed of the sun gear at an idle condition for the gas turbine engine compared to a speed of the sun gear at a takeoff condition is within 10% such that a takeoff speed of the sun gear is less than or equal to 110% of a speed of the sun gear at an idle condition.
In another embodiment according to any of the previous embodiments, a speed range of a speed of the output gear at an idle condition for the gas turbine engine compared to a speed of the output gear at a takeoff condition is within 10% such that a takeoff speed of the output gear is less than or equal to 110% of a speed of the output gear at an idle condition.
In another embodiment according to any of the previous embodiments, a star speed ratio defined as a ratio of the pitch diameter of the low speed input gear compared to the pitch diameter of the output gear is between 1.3 and 3.2.
In another embodiment according to any of the previous embodiments, the accessory drive differential is an epicyclic gear reduction. The low speed input gear drives a carrier in the epicyclic gear reduction in a first direction. The high speed input gear drives a ring gear in the epicyclic gear reduction in a second direction opposed to the first direction. The output gear is a sun gear driven to rotate in the second direction.
In another embodiment according to any of the previous embodiments, the accessory drive differential is an epicyclic gear reduction. The low speed input gear drives a sun gear in the epicyclic gear reduction in a first direction. The high speed input gear drives a carrier in the epicyclic gear reduction in the first direction. The output gear is a ring gear driven to rotate in the first direction.
In another embodiment according to any of the previous embodiments, the sun gear drives at least one of a hydraulic pump, an alternator, and a generator.
In another embodiment according to any of the previous embodiments, the accessory drive differential includes the high speed input gear driving a ring gear that in turn drives a differential gear, the low speed input gear engaging the differential gear, and the differential gear driving the output gear.
The present disclosure may include any one or more of the individual features disclosed above and/or below alone or in any combination thereof.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
The exemplary engine 20 generally includes a low speed spool 30 and a high speed spool 32 mounted for rotation about an engine central longitudinal axis A relative to an engine static structure 36 via several bearing systems 38. It should be understood that various bearing systems 38 at various locations may alternatively or additionally be provided, and the location of bearing systems 38 may be varied as appropriate to the application.
The low speed spool 30 generally includes an inner shaft 40 that interconnects, a first (or low) pressure compressor 44 and a first (or low) pressure turbine 46. The inner shaft 40 is connected to the fan 42 through a speed change mechanism, which in the exemplary gas turbine engine 20 is illustrated as a geared architecture 48 to drive the fan 42 at a lower speed than the low speed spool 30. The inner shaft 40 may interconnect the low pressure compressor 44 and low pressure turbine 46 such that the low pressure compressor 44 and low pressure turbine 46 are rotatable at a common speed and in a common direction. In other embodiments, the low pressure turbine 46 drives both the fan 42 and low pressure compressor 44 through the geared architecture 48 such that the fan 42 and low pressure compressor 44 are rotatable at a common speed. Although this application discloses geared architecture 48, its teaching may benefit direct drive engines having no geared architecture. The high speed spool 32 includes an outer shaft 50 that interconnects a second (or high) pressure compressor 52 and a second (or high) pressure turbine 54. A combustor 56 is arranged in the exemplary gas turbine 20 between the high pressure compressor 52 and the high pressure turbine 54. A mid-turbine frame 57 of the engine static structure 36 may be arranged generally between the high pressure turbine 54 and the low pressure turbine 46. The mid-turbine frame 57 further supports bearing systems 38 in the turbine section 28. The inner shaft 40 and the outer shaft 50 are concentric and rotate via bearing systems 38 about the engine central longitudinal axis A which is collinear with their longitudinal axes.
Airflow in the core flow path C is compressed by the low pressure compressor 44 then the high pressure compressor 52, mixed and burned with fuel in the combustor 56, then expanded through the high pressure turbine 54 and low pressure turbine 46. The mid-turbine frame 57 includes airfoils 59 which are in the core flow path C. The turbines 46, 54 rotationally drive the respective low speed spool 30 and high speed spool 32 in response to the expansion. It will be appreciated that each of the positions of the fan section 22, compressor section 24, combustor section 26, turbine section 28, and fan drive gear system 48 may be varied. For example, gear system 48 may be located aft of the low pressure compressor, or aft of the combustor section 26 or even aft of turbine section 28, and fan 42 may be positioned forward or aft of the location of gear system 48.
The low pressure compressor 44, high pressure compressor 52, high pressure turbine 54 and low pressure turbine 46 each include one or more stages having a row of rotatable airfoils. Each stage may include a row of vanes adjacent the rotatable airfoils. The rotatable airfoils are schematically indicated at 47, and the vanes are schematically indicated at 49.
The engine 20 may be a high-bypass geared aircraft engine. The bypass ratio can be greater than or equal to 10.0 and less than or equal to about 18.0, or more narrowly can be less than or equal to 16.0. The geared architecture 48 may be an epicyclic gear train, such as a planetary gear system or a star gear system. The epicyclic gear train may include a sun gear, a ring gear, a plurality of intermediate gears meshing with the sun gear and ring gear, and a carrier that supports the intermediate gears. The sun gear may provide an input to the gear train. The ring gear (e.g., star gear system) or carrier (e.g., planetary gear system) may provide an output of the gear train to drive the fan 42. A gear reduction ratio may be greater than or equal to 2.3, or more narrowly greater than or equal to 3.0, and in some embodiments the gear reduction ratio is greater than or equal to 3.4. The gear reduction ratio may be less than or equal to 4.0. The fan diameter is significantly larger than that of the low pressure compressor 44. The low pressure turbine 46 can have a pressure ratio that is greater than or equal to 8.0 and in some embodiments is greater than or equal to 10.0. The low pressure turbine pressure ratio can be less than or equal to 13.0, or more narrowly less than or equal to 12.0. Low pressure turbine 46 pressure ratio is pressure measured prior to an inlet of low pressure turbine 46 as related to the pressure at the outlet of the low pressure turbine 46 prior to an exhaust nozzle. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans. All of these parameters are measured at the cruise condition described below.
A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section 22 of the engine 20 is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet (10,668 meters). The flight condition of 0.8 Mach and 35,000 ft (10,668 meters), with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (‘TSFC’)”—is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. The engine parameters described above, and those in the next paragraph are measured at this condition unless otherwise specified.
“Fan pressure ratio” is the pressure ratio across the fan blade 43 alone, without a Fan Exit Guide Vane (“FEGV”) system. A distance is established in a radial direction between the inner and outer diameters of the bypass duct 13 at an axial position corresponding to a leading edge of the splitter 29 relative to the engine central longitudinal axis A. The fan pressure ratio is a spanwise average of the pressure ratios measured across the fan blade 43 alone over radial positions corresponding to the distance. The fan pressure ratio can be less than or equal to 1.45, or more narrowly greater than or equal to 1.25, such as between 1.30 and 1.40. “Corrected fan tip speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram ° R)/(518.7 ° R)]0.5. The corrected fan tip speed can be less than or equal to 1150.0 ft/second (350.5 meters/second), and can be greater than or equal to 1000.0 ft/second (304.8 meters/second).
The tower shaft 110 is shown driving accessories 130A and 130B. Among the potential accessories would be an augmented fuel pump. As will be explained below, the low speed tower shaft will have its speed vary considerably across the operation of the gas turbine engine. At low power operation of the engine, its speed may be as an example 60% of what it might be at takeoff operation. However, an augmented fuel pump has a reduced power draw at low power operations such as idle and cruise, and thus the very low speed will not prove problematic.
The epicycle gear reduction 132 is shown having a ring gear 140 driven by the low speed tower shaft 110 through gears 202 and 204. The epicyclic gear 132 also has a carrier 142 driven with the high speed tower shaft 106, through gears 210, 208 and 206. A sun gear 144 is driven by the combination of the ring gear 140 and carrier 142 to in turn drive accessories 146 and 147. Accessories 146 and 147 may include a hydraulic pump or permanent magnet alternator or a permanent magnet generator. These accessories benefit from having near constant speed.
While the tower shafts are shown driving the carrier 142 and ring gear 140 through intermediate gears, the tower shafts could drive their respective gears directly with the intermediate gears being driven in some other manner to drive their respective accessories.
As shown in
As carrier 142 is driven to rotate, it moves intermediate gears 150 which engage and drive a sun gear 144. The sun gear 144 will in turn be rotated in the same direction at a speed Nsun. By having this arrangement, the ring gear effectively limits the speed provided to the sun gear by the carrier 142.
The speed Nsun is defined by the following formula:
N
sun
=N2*(SR+1)−N*SR
The SR component is defined as the pitch diameter of the ring gear divided by the pitch diameter of the sun gear. In one embodiment it is 2.0, and that embodiment provides the speed numbers that are disclosed below with regard to
Thus, as can be seen, the low speed drive provided to the ring gear effectively reduces the speed of the sun gear.
As shown in
While three separate housings are disclosed in a particular geometric relationship, any of the three housings could be in any geometric relationship relative to the other. Moreover, there could also be an embodiment where there are only two housings with one of the two housings enclosing two of the three components specifically mentioned in the
Providing near constant speed to the hydraulic pump 146 is beneficial. Hydraulic power to drive aircraft and engine control features such as wing flaps and exhaust area is needed regardless of engine power level, so it is typically designed for full pump power at idle speed. When the engine then operates at higher power settings, it drives the pump much faster than is necessary which overproduces unneeded power. Providing near constant speed to the alternators and/or generators is also beneficial. As they drop speed, they produce less voltage and thus require more amperage to meet the power demand. Having a smaller speed range would allow these components to be sized smaller with reduced amperage.
In embodiments, the speed ratio SR can be between 1.3 and 3.2. In further embodiments, a speed ratio can be between 1.8 and 2.5. Returning to
While the above embodiment utilizes an epicyclic gear reduction, other differentials can provide the functionality of this disclosure. As an example,
Again, the approximate equal output speed benefits will be achieved by both the
The example gear trains shown in
A gas turbine engine under this disclosure could be said to include a high speed turbine and a high speed compressor connected by a high speed shaft to define a high speed spool. A low speed turbine and a low speed compressor are connected by a low speed shaft to define a low speed spool. There is a high speed tower shaft driven by the high speed spool and a low speed tower shaft driven by the low speed spool. The low speed tower shaft drives a low speed input gear in an accessory drive differential. The high speed tower shaft drives a high speed input gear in the accessory drive differential. One of the high speed input gear and low speed input gear increases an output speed of an output gear, and the other decreases an output speed of the output gear. The output gear drives at least one accessory for the gas turbine engine.
Although embodiments have been disclosed, a worker of ordinary skill in this art would recognize that modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the true scope and content of this disclosure.
