Patent Publication Number: US-2021190080-A1

Title: Epicyclic drive for gas turbine engine lubricant pump

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/984,792 filed on May 21, 2018. 
    
    
     BACKGROUND 
     This application relates to a drive train for an auxiliary pump for use in a gas turbine engine that includes an epicyclic gear train. 
     Gas turbine engines are known and typically include a fan delivering air into a bypass duct as propulsion air and into a compressor. The air in the compressor is compressed and delivered into a combustor where it is mixed with fuel and ignited. Products of this combustion pass downstream over turbine rotors driving them to rotate. 
     Historically, a turbine rotor drove the fan rotor through a direct connection and at a common speed. More recently, it has been proposed to utilize a gear reduction between the turbine and the fan rotor. This results in several efficiencies. 
     However, it is also important to provide adequate lubrication to the gear reduction. Thus, a primary lubricant system is provided that will supply lubricant to the gear reduction and other engine components during operation of the engine. However, it is also important to recognize that the primary lubricant system could fail. 
     In addition, there are times when the engine may not be powered, but there may still be rotation into the engine. One example is windmilling operation. Windmilling operation can occur when an associated aircraft is on the ground and wind speeds pass across the fan blades driving them to rotate. Another time when windmilling can occur is when the associated aircraft is in the air, but the engine in question is not being driven. The air passing across the engine can cause the fan rotor to rotate. 
     Windmilling can occur in either direction. It is important to provide the lubricant at all times, and thus an auxiliary pump has been provided. 
     In the prior art, a gear train for driving the auxiliary pump has typically been provided with several circumferentially spaced gears, such that a good deal of circumferential space is required. 
     SUMMARY 
     In a featured embodiment, a gas turbine engine includes a fan drive turbine driving a fan rotor through a main gear reduction. A primary lubricant system supplies lubricant to the main gear reduction. An auxiliary oil pump supplies oil to the main gear reduction. An auxiliary pump epicyclic gear train drives the auxiliary pump when the fan rotor is rotating in either direction. The main gear reduction is separate from the auxiliary pump epicyclic gear train. 
     In another embodiment according to the previous embodiment, an input gear rotates when the fan rotor rotates, and in a direction of rotation of the fan rotor and engages a ring gear in the auxiliary pump epicyclic gear train. The ring gear has an outer peripheral envelope and an axis of rotation of the auxiliary pump is within the outer peripheral envelope. 
     In another embodiment according to any of the previous embodiments, the ring gear includes a first ring gear portion selectively driving a second ring gear portion through a first clutch, and the first ring gear portion driving an output shaft which is engaged to drive the auxiliary pump through a second clutch. One of the first and second clutches is operable to transmit rotation when driven in a first direction of rotation, but does not transmit rotation when driven in a second direction of rotation, and the other of said first and second clutches is operable to transmit rotation when driven in the second direction of rotation, but not transmit rotation when driven in said first direction of rotation. 
     In another embodiment according to any of the previous embodiments, when the first ring gear portion drives the second ring gear portion. The second ring gear portion drives a plurality of intermediate gears to, in turn, drive a sun gear, with the sun gear rotating the output shaft. 
     In another embodiment according to any of the previous embodiments, the output shaft drives an output gear, which is, in turn, engaged with an auxiliary pump drive gear to drive the auxiliary pump. 
     In another embodiment according to any of the previous embodiments, the first and second clutches are sprag clutches. 
     In another embodiment according to any of the previous embodiments, the main gear reduction is also an epicyclic gear train. 
     In another embodiment according to any of the previous embodiments, the intermediate gears are supported in a fixed carrier. 
     In another embodiment according to any of the previous embodiments, the output shaft drives an output gear, which is, in turn, engaged with an auxiliary pump drive gear to drive the auxiliary pump. 
     In another embodiment according to any of the previous embodiments, the first and second clutches are sprag clutches. 
     In another embodiment according to any of the previous embodiments, the main gear reduction is also an epicyclic gear train. 
     In another embodiment according to any of the previous embodiments, the first and second clutches are sprag clutches. 
     In another embodiment according to any of the previous embodiments, the main gear reduction is also an epicyclic gear train. 
     In another embodiment according to any of the previous embodiments, the output shaft rotates on an output shaft axis. The auxiliary pump rotates on an auxiliary pump axis, and the input gear rotes about an input gear axis, and the input gear axis is on an opposed side of the output shaft axis relative to the auxiliary pump axis. 
     In another embodiment according to any of the previous embodiments, an output shaft drives an output gear, which is, in turn, engaged with an auxiliary pump drive gear to drive the auxiliary pump. 
     In another embodiment according to any of the previous embodiments, the first and second clutches are sprag clutches. 
     In another embodiment according to any of the previous embodiments, the main gear reduction is also an epicyclic gear train. 
     In another embodiment according to any of the previous embodiments, the main gear reduction is also an epicyclic gear train. 
     In another embodiment according to any of the previous embodiments, the main gear reduction is also an epicyclic gear train. 
     In another embodiment according to any of the previous embodiments, an output shaft drives an output gear, which is, in turn, engaged with an auxiliary pump drive gear to drive said auxiliary pump. 
     These and other features may be best understood from the following drawings and specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically shows a gas turbine engine. 
         FIG. 2  shows a gear train for an auxiliary lubricant pump. 
         FIG. 3  shows the  FIG. 2  gear train in an alternative mode of operation. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates a gas turbine engine  20 . The gas turbine engine  20  is disclosed herein as a two-spool turbofan that generally incorporates a fan section  22 , a compressor section  24 , a combustor section  26  and a turbine section  28 . The fan section  22  drives air along a bypass flow path B in a bypass duct defined within a nacelle  15 , and also drives air along a core flow path C for compression and communication into the combustor section  26  then expansion through the turbine section  28 . Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with two-spool turbofans as the teachings may be applied to other types of turbine engines including three-spool architectures. 
     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 exemplary gas turbine engine  20  is illustrated as a geared architecture  48  to drive a fan  42  at a lower speed than the low speed spool  30 . 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 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. 
     The core airflow 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 over the high pressure turbine  54  and low pressure turbine  46 . The mid-turbine frame  57  includes airfoils  59  which are in the core airflow 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 engine  20  in one example is a high-bypass geared aircraft engine. In a further example, the engine  20  bypass ratio is greater than about six (6), with an example embodiment being greater than about ten (10), the geared architecture  48  is an epicyclic gear train, such as a planetary gear system, star gear system, or other gear system, with a gear reduction ratio of greater than about 2.3 and the low pressure turbine  46  has a pressure ratio that is greater than about five. In one disclosed embodiment, the engine  20  bypass ratio is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor  44 , and the low pressure turbine  46  has a pressure ratio that is greater than about five 5:1. Low pressure turbine  46  pressure ratio is pressure measured prior to 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. The geared architecture  48  may be an epicyclic gear train, such as a planetary gear system, star gear system, or other gear system, with a gear reduction ratio of greater than about 2.3:1 and less than about 5:1. 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. 
     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. “Low fan pressure ratio” is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45. “Low 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 “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second (350.5 meters/second). 
     A primary lubricant system and pump  90  is shown. An auxiliary oil pump  126  is also shown. Both are shown schematically. 
       FIG. 2  shows a gear train for driving an auxiliary lubricant pump  126  to supply lubricant to the gear reduction  48  at least when the primary lubricant system  90  is not operating. 
     In  FIG. 2 , a gear  104  rotates with a shaft  102  rotates when the fan rotor rotates. The gear  104  engages a gear  105  having gear teeth  106  defining an outer peripheral surface. The gear teeth  106  define an outer peripheral envelope dl. The gear  105  is essentially a portion of a ring gear associated with the gear train  100 . Gear  105  rotates a clutch  108  which can selectively drive a second ring gear portion  110 . 
     In the  FIG. 2  mode, the clutch  108  is shown schematically as being open. That is, the first ring gear portion  105  does not drive the second ring gear portion  110 . This may occur when the rotation of the fan is in a forward direction or the normal operational direction for drive of the engine. 
     The ring gear portion  110  is shown engaged with a plurality of intermediate gears  112  and associated with a fixed carrier  114 , which mounts the gears  112 . The gears  112  will drive a sun gear  116  and its shaft  118 . Shaft  118  passes through a clutch  120  to drive a gear  122  which is, in turn, connected to drive a gear  124 , which drives the auxiliary pump  126 . 
     The clutches  108  and  120  may be sprag clutches, or any other type of one-way clutch. Any clutch that can survive the jet engine environment may be considered. One example may be a centrifugal clutch. As known, when driven in a first direction, such clutches will slip and not transmit rotation. However, when driven in the opposed rotational direction, the sprag members will engage in rotation and will be transmitted. The direction of rotation for slipping/transmitting drive between the clutches  108  and  120  is reversed. 
     In the  FIG. 2  mode, drive from gear  104  drives ring gear portion  105 . Clutch  120  is engaged in this direction such that rotation of the gear  105  drives the shaft  118 . On the other hand, the sprag members in clutch  108  slip such that the ring gear portion  105  does not drive the ring gear portion  110 . 
       FIG. 3  shows the opposed direction of rotation, such as when the fan drives the gear  104  in a reverse direction opposed to the normal direction. As shown, the clutch  120  is now open such that drive is not transmitted between the ring gear portion  105  and the shaft  118 . Instead, the clutch  108  is engaged, and ring gear portion  105  drives ring gear portion  110 . This drives the intermediate gears  112  to, in turn, drive the sun gear  116 . In this way, the shaft  118  is rotated such that the gear  122  is again rotated. The gear  124  is, thus, rotated driving the auxiliary pump  126 . 
     In this embodiment, since the gear  124  and a pump drive axis X, are within the outer peripheral envelope di of the ring gear portion  105 , less circumferential space is required for the overall arrangement. Also, input gear  102  is shown rotating on an axis I, that is on an opposed side of an output shaft axis O relative to an auxiliary pump axis X. 
     While a fixed carrier is disclosed, an epicyclic gear system with a fixed ring gear, or no fixed portion may also be used. In such arrangements the location of the clutches may be changed. 
     Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain 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.