Abstract:
A bi-directional auxiliary lubrication system which allows lubricant to be supplied to moving engine components after a loss of lubricant pressure from a main lubricant tank is disclosed. In a gas turbine engine, the lubrication system may siphon compressed air from a compressor to draw lubricant from a reserve lubricant tank and deliver that lubricant to the engine components. The same conduits used by the lubrication during normal operations are utilized in an opposite direction to provide the flow of lubricant from the reserve lubricant tank during such auxiliary or low-lubricant-pressure operations.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The United States Government has certain rights in this invention pursuant to contract number 5148262-0302-0343 between the United States Army and United Technologies Corporation. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure generally relates to gas turbine engines and, more specifically, to lubrication systems for gas turbine engines. 
     BACKGROUND OF THE DISCLOSURE 
     Gas turbine engines of modern aircraft require a constant supply of oil to mechanical components such as, but not limited to, bearings to ensure proper operation of the engine. The oil can be used as a lubricant or a coolant for such components. Typical lubrication systems have a separate and redundant back-up or auxiliary system to guaranty a supply of oil to the critical engine components at all times. Such auxiliary lubrication systems are typically operating constantly while the engine is active, which may reduce the performance of the engine during normal operations. Additionally, such auxiliary lubrication systems may require separate pumps and conduits to supply the engine components with the necessary oil. Other auxiliary lubrication systems may not run constantly, but require a processor which can determine that the auxiliary lubrication system is needed and provide for actuation of same. While effective, all such systems add cost to the overall engine, require maintenance, and contribute to the weight of the associated aircraft. 
     Therefore, it can be seen that a need exists for an auxiliary lubrication system which operates only when needed yet does not require a processor. Additionally, minimizing extra components to create such an auxiliary lubrication system for an aircraft is also needed, as space, weight, and maintenance are important on any aircraft. 
     SUMMARY OF THE DISCLOSURE 
     In accordance with one aspect of the disclosure, a lubrication system is disclosed. The lubrication system may include a three-way valve having a first opening, a second opening, and a third opening. A main conduit may be connected to the three-way valve at the first opening and may communicate a lubricant from a main lubricant tank to at least one working component. A reserve lubricant tank may be connected to the three-way valve at the second opening. A working fluid check valve may be connected to the three-way valve at the third opening and may control a flow of a working fluid into the lubrication system. 
     In a refinement, the working fluid check valve may be a pressure valve biased to a closed position. 
     In another refinement, the working fluid may be compressed air. 
     In yet another refinement, the lubrication system may further include a lubricant check valve positioned in the main conduit between the main lubricant tank and the three-way valve. 
     In a further refinement, the lubricant-check valve may be a pressure valve biased to a closed position. 
     In yet another refinement, the working component may be a bearing of a gas turbine engine. 
     In accordance with another aspect of the disclosure, a gas turbine engine including a compressor, a combustor downstream from the compressor, and a turbine downstream from the combustor and connected to the compressor by an engine shaft is disclosed. The gas turbine engine may further include a lubrication system. The lubrication system may have a three-way valve connected to a main lubricant tank at a first opening of the three-way valve by a main conduit. A reserve lubricant tank may be connected to a second opening of the three-way valve and an air-check valve may be connected to a third opening of the three-way valve. The air-check valve may prevent compressed air from entering the three-way valve. The lubrication system may provides a lubricant to engine components via the main conduit. 
     In a refinement, the air-check valve may be a pressure valve biased to a closed position. 
     In another refinement, an air conduit may provide a passage for compressed air to flow from the compressor to the air-check valve. 
     In yet another refinement, the engine may further include a lubricant-check valve positioned in the main conduit between the main lubricant tank and the three-way valve. 
     In a further refinement, the lubricant-check valve may be a pressure valve biased to a closed position. 
     In accordance with yet another aspect of the present disclosure, a method of lubricating a component of a gas turbine engine is disclosed. The method may include pumping lubricant in a first direction from a main lubricant tank to the engine component with a lubricant pump and lubricating the engine component with the lubricant from the main lubricant tank during the normal mode of operation. The method may further include reversing lubricant flow direction to a second direction with compressed air from a compressor passing through a three-way valve, drawing lubricant from a reserve lubricant tank with the compressed air by suction, and lubricating the engine component with the lubricant from the reserve lubricant tank during a low-lubricant-pressure mode of operation. 
     In a refinement, the method may further include opening a lubricant-check valve with the lubricant from the main lubricant tank during the normal mode of operation. 
     In a further refinement, the method may further include closing the lubricant-check valve with the compressed air during the low-lubricant-pressure mode of operation. 
     In another refinement, the method may further include closing an air-check valve with the lubricant from the main lubricant tank during the normal mode of operation. 
     In a further refinement, the method may further include opening the air-check valve with the compressed air before entering the three-way valve during the low-lubricant-pressure mode of operation. 
     In another refinement, the method may further include creating an air-lubricant mixture by combining the compressed air and the lubricant from the reserve lubricant tank during the low-lubricant-pressure mode of operation. 
     In yet another refinement, the method may further include circulating the lubricant in the reserve lubricant tank by driving the old lubricant from the reserve lubricant tank with new lubricant from the main lubricant tank during the normal mode of operation. 
     In yet another refinement, the method may further include switching automatically from the normal mode of operation to the low-lubricant-pressure mode of operation. 
     In still another refinement, the method may further include switching automatically from the low-lubricant-pressure mode of operation to the normal mode of operation. 
     These and other aspects and features of the present disclosure will be better understood in light of the following detailed description when read in light of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial sectional view of a gas turbine engine constructed in accordance with an embodiment of the present disclosure. 
         FIG. 2  is a cross-sectional view of a lubrication system constructed in accordance with an embodiment of the present disclosure and in a normal operation. 
         FIG. 3  is a cross-sectional view of the lubrication system of  FIG. 2 , but depicted in a low-lubrication-pressure operation. 
     
    
    
     It should be understood that the drawings are not necessarily to scale and that the disclosed embodiments are sometimes illustrated diagrammatically and in partial views. In certain instances, details which are not necessary for an understanding of this disclosure or which render other details difficult to perceive may have been omitted. It should be understood, of course, that this disclosure is not limited to the particular embodiments illustrated herein. 
     DETAILED DESCRIPTION 
     Referring now to the drawings, and with specific reference to  FIG. 1 , a gas turbine engine, depicted as a turbofan engine, is disclosed and generally referred to by numeral  10 . The gas turbine engine  10  has a number of components axially aligned along a central axis  12  including, but not limited to, a fan  14 , a compressor section  16  downstream of the fan  14 , a combustor  18  downstream of the combustor  18 , a turbine section  20  downstream of the combustor  18 . As used herein, “downstream” is defined as further along the air flow path through the engine  10 . 
     The engine  10  depicted is a dual-spool engine and thus includes a first engine shaft  22  and a second engine shaft  23 . It should be understood, however, this engine is only exemplary and this disclosure may be applied to a three spool engine. The second engine shaft  23  is concentrically mounted around the first engine shaft  22 , and both engine shafts  22 ,  23  extend through the center of the engine  10  along the central axis  12  from a forward end  24  of the engine  10  to an aft end  26  of the engine  10  connecting the fan  14 , compressor  16 , and turbine  20 . 
     The fan  14  is positioned on the forward end  22  of engine  10  such that when the fan  14  is rotated by the engine shaft  22  ambient air is drawn into the engine  10 . The compressor section  16  is pictured as a dual spool compressor having a low-pressure compressor  27  mechanically coupled to the first shaft  22 , and a high-pressure compressor  28  mechanically coupled to the second shaft  23 . The compressor section  16  includes a plurality of blades  29  extending radially outward. As the compressor section  16  rotates on the engine shafts  22 ,  23 , ambient air drawn in by the fan  14 , compressed, and forced downstream toward the aft end  26  of the engine  20 . The combustor  18  is positioned downstream from the compressor  16  and accepts the compressed air  19  to be used for combustion and cooling. The air used for combustion is combined with a fuel and ignited to produce an exhaust, while the air used for cooling is used to cool the combustor  18  and then also burnt with the fuel and combustion air. The exhaust expands out of the combustor  18  and through the turbine section  20  positioned axially downstream from the combustor  18 . The turbine section  20  is also depicted as a dual-spool turbine having a high-pressure turbine  30  mechanically coupled to the second shaft  23 , a low-pressure turbine  31  mechanically coupled to the first shaft  22 , and a plurality of blades  32  extending radially outward. The expanding exhaust from the combustor  18  causes the turbine blades  32  to rotate on the engine shafts  22 ,  23 . The rotation of the shafts  22 ,  23  also cause rotation of the fan  14  and the compressor section  16 . It can therefore be seen that this process is self-sustaining once it has begun. 
     The gas turbine engine  10  includes a plurality of engine components  33  which require a flow of lubricant  34  (see  FIG. 2 ), such as, but not limited to, the engine shafts  22 ,  23  or bearings  36  for the engine shafts  22 ,  23 . The bearings  36  require the lubricant  34  to facilitate smooth movement of the engine shafts  22 ,  23 . The lubricant  34  may also remove heat from the bearings  36  gained from frictional contact with the engine shafts  22 ,  23 . To facilitate the movement of the lubricant  34  to each of the engine components  33 , the engine  10  has a lubrication system  38 . 
     As seen in  FIG. 2 , the lubrication system  38  may have a main lubricant tank  40  in which the lubricant  34  can be stored when not being used. The lubrication system  38  may have a pump  42  to pump the lubricant  34  from the main lubricant tank  40  through a main conduit  44  to each of the bearings  36  (or other engine component needed lubrication). The main conduit  44  may connect to a three-way valve, such as a venturi valve  46 , at a first opening  48 . The venturi valve  46  may further have a second opening  50  and a third opening  52 . The lubricant  34  flows from the main conduit  44  through the first opening  48  into the venturi valve  46  and out the second opening  50  into a reserve lubricant tank  54 . From the reserve lubricant tank  54 , the lubricant  34  flows through a lubricant jet hole  55  to the bearings  36 . Thereafter, the lubricant rejoins the rest of the lubricant  34  which has been delivered to the bearings  36  by the main conduit  44 . This retrieved flow of lubricant  34  from the venturi valve  46  is greater than the flow out of the reserve lubricant tank  54 , and thus allows the reserve lubricant tank  54  to build and hold a fresh supply of lubricant  34  at all times. A scavenger system may also be provided to remove the used lubricant  34  from the bearings  36  and return the lubricant  34  to the main lubricant tank  40 . 
     The third opening  52  of the venturi valve  46  may be connected to an air-check valve  56 . The air-check valve  56  is pictured as a spring loaded pressure valve, however, other valves are possible. The air-check valve  56  may be biased to keep the compressed air  19 , siphoned from the compressor section  16  through an air conduit  58 , from entering the venturi valve  46 . In alternate embodiments, the compressed air  19  may be any desired working fluid and the air-check valve  56  may be a working fluid check valve designed to operate with such a working fluid. 
     During a normal mode of operation of the presented lubrication system  38  in a gas turbine engine  10 , the lubricant  34  flows in a first direction  64  from the main lubricant tank  40  through the main conduit  44  to the engine components  33  and to the venturi valve  46 . At the venturi valve  46 , the pressure of the lubricant  34  on the air-check valve  56  may be greater than the pressure of the compressed air  19  on the air-check valve  56 , which keeps the air-check valve  56  closed. Thus, the lubricant  34  flows through the venturi valve  46  and into the reserve lubricant tank  54 . The lubricant  34  in the reserve lubricant tank  54  may be driven out of the reserve lubricant tank  54  through the lubricant jet hole  55  to the engine components  33  by new incoming lubricant  34  from the main lubricant tank  40 . The lubricant  34  in the reserve lubricant tank  54  may thereby be recycled during the normal mode of operation to keep fresh lubricant  34  in the reserve lubricant tank  54 . 
     The lubrication system  38  also has an auxiliary or low-lubricant-pressure mode, such as is depicted in  FIG. 3 . This low-lubricant-pressure mode of operation is automatically activated by the compressed air pressure on the air-check valve  56  becoming greater than the lubricant  34  pressure, which allows the air-check valve  56  to open. The compressed air  19  then flows through the venturi valve  46  from the third opening  52  to the first opening  48  and into the main conduit  44 . As the compressed air  19  flows through the venturi valve  46 , the compressed air  19  creates a pressure drop which draws lubricant  34  from the reserve lubricant tank  54  through the second opening  50  through the first opening  48  and into the main conduit  44 . The lubricant  34  and compressed air  19  mix in the main conduit  44  and flow in a second direction  66  (opposite to the first direction  64 ) to the engine components  33  as an air-lubricant mixture  60 . The air-lubricant mixture  60  may be expelled from the main conduit  44  as an air-lubricant mist onto the engine components  33 . 
     Since lubricant  34  from the reserve lubricant tank  54  may not be resupplied during the low lubricant mode of operation of the lubrication system  38 , an inexhaustible supply of lubricant  34  to the engine components  33  may not be available. In such an occurrence, air  61  may be drawn into the reserve lubricant tank  54  from the engine components  33  through the lubricant jet hole  55 . In the case of an aircraft, this temporary supply of lubricant  34  may allow the pilot of the aircraft time to land or repair the lubrication system to return the lubrication system back to normal lubrication pressure without damage to the engine  10 . 
     A lubricant-check valve  62  may also be positioned in the main conduit  44  between the engine components  33  and the main lubricant tank  40 . The lubricant-check valve  62 , pictured as a spring loaded pressure valve in  FIGS. 2 and 3 , may be biased to a closed position during low lubricant pressure operations, this may prevent the air-lubricant mixture  60  from entering into the main lubricant tank  40 . During normal operation however, the lubricant-check valve  62  may be held open by the lubricant pressure on the lubricant-check valve  62  from the lubricant  34  flowing from the main lubricant tank  40 . 
     In operation, the presented lubrication system  38  operates in a normal mode while normal lubricant pressure exists and automatically switches to operate in a low-lubricant-pressure mode, or auxiliary mode, when the lubricant pressure drops below a desired level as determined by the relative pressures of the lubricant  34  and compressed air  19 , as well as the strength of the air-check valve  58 . The auxiliary mode may utilize the same conduits as the normal mode and thereby reduce the space and weight of equipment necessary to implement the presented lubrication system  38  of the present disclosure, as composed to other lubrication systems. The lubrication system  38  may also switch automatically from the low-lubricant-pressure mode of operation to the normal mode of operation when the lubricant pressure from the lubricant  34  traveling in the first direction  64  becomes greater than the pressure of the air-lubricant mixture  60  traveling in the second direction  66 . This may allow the lubricant-check valve  62  to be opened and the air-check valve  56  to be closed, which may return a flow of lubricant  34  from the main lubricant tank  40  to the engine components  33 . 
     INDUSTRIAL APPLICABILITY 
     From the foregoing, it can be seen that the technology disclosed herein has industrial applicability in a variety of settings such as, but not limited to, providing a flow of lubricant to engine components for a gas turbine engine during low lubricant pressure operations. The low lubricant pressure system utilizes the same conduits which the normal lubrication system utilizes, thereby creating a lubrication system which still operates effectively without main lubricant pressure for a limited time while requiring very little additional equipment. This may be of particular benefit to aircraft where space and weight are limited. 
     While the present disclosure has been in reference to a gas turbine engine and an aircraft, one skilled in the art will understand that the teachings herein can be used in other applications as well. It is therefore intended that the scope of the invention not be limited by the embodiments presented herein as the best mode for carrying out the invention, but that the invention will include all equivalents falling within the spirit and scope of the appended claims as well.