Abstract:
A lubrication system includes a control subsystem operable to selectively communicate lubricant from a reserve lubrication subsystem under a pressure to supplement lubricant from a main lubrication subsystem in response to identification of a prolonged reduced-G condition. A gas turbine engine includes a main lubrication subsystem in communication with a geared architecture; a reserve lubrication subsystem in communication with the geared architecture; and a control subsystem operable to selectively communicate lubricant from the reserve lubrication subsystem under a pressure in response to identification of a prolonged reduced-G condition. A method of reducing lubrication starvation from a lubrication system with a main lubrication subsystem and a reserve lubrication subsystem, the main lubrication system in communication with a geared architecture of a gas turbine engine, includes communicating lubricant under a pressure to the geared architecture in response to identifying of a prolonged reduced-G condition.

Description:
[0001]    This application is a continuation of U.S. patent application Ser. No. 13/726,435 filed Dec. 24, 2012. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates to a lubrication system for a gas turbine engine and, more particularly, to a lubrication system that remains operable in reduced gravity (reduced-G) conditions. 
         [0003]    Aircraft gas turbine engines include a lubrication system to supply lubrication to various components. A reserve is also desirable to ensure that at least some components are not starved of lubricant during reduced-G conditions in which acceleration due to gravity is partially or entirely counteracted by aircraft maneuvers and/or orientation. 
       SUMMARY 
       [0004]    A lubrication system according to one disclosed non-limiting embodiment of the present disclosure includes a main lubrication subsystem; a reserve lubrication subsystem; and a control subsystem operable to selectively communicate lubricant from the reserve lubrication subsystem under a pressure to supplement lubricant from the main lubrication subsystem in response to identification of a prolonged reduced-G condition. 
         [0005]    A further embodiment of the present disclosure includes, wherein the pressure is provided via a gas. 
         [0006]    A further embodiment of the present disclosure includes, wherein the gas is an inert gas. 
         [0007]    A further embodiment of the present disclosure includes, wherein the pressure is provided via a liquid. 
         [0008]    A further embodiment of the present disclosure includes, wherein the main lubrication subsystem and the reserve lubrication subsystem are in communication with a geared architecture of a gas turbine engine. 
         [0009]    A further embodiment of the present disclosure includes, wherein the pressure provides lubricant to a journal pin of the geared architecture from the reserve lubrication subsystem to supplements lubricant from the main lubrication subsystem to the journal pin. 
         [0010]    A further embodiment of the present disclosure includes a main lubricant tank solenoid valve in communication with the control subsystem and the main lubrication subsystem, the control subsystem is operable to close the main lubricant tank solenoid valve in response to the prolonged reduced-G condition; and a reserve lubricant tank solenoid valve in communication with the control subsystem, the control subsystem operable to open the reserve lubricant tank solenoid valve in response to the prolonged reduced-G condition. 
         [0011]    A further embodiment of the present disclosure includes, wherein the control subsystem operable to selectively communicate lubricant from the reserve lubrication subsystem under a pressure to supplement lubricant from the main lubrication subsystem in response to a sensor operable to identify the prolonged reduced-G condition. 
         [0012]    A gas turbine engine according to another disclosed non-limiting embodiment of the present disclosure includes a geared architecture; a main lubrication subsystem in communication with the geared architecture; a reserve lubrication subsystem in communication with the geared architecture; and a control subsystem operable to selectively communicate lubricant from the reserve lubrication subsystem under a pressure in response to identification of a prolonged reduced-G condition. 
         [0013]    A further embodiment of the present disclosure includes, wherein the geared architecture drives a fan at a lower speed than a low spool. 
         [0014]    A further embodiment of the present disclosure includes, wherein the reserve lubrication subsystem includes a pressurized reserve lubricant tank that selectively communicates the lubricant. 
         [0015]    A further embodiment of the present disclosure includes, wherein the pressurized reserve lubricant tank is within at least one of a nacelle, an engine pylon and an aircraft wing. 
         [0016]    A further embodiment of the present disclosure includes a multiple of pressurized reserve lubricant tanks. 
         [0017]    A further embodiment of the present disclosure includes, wherein the pressurized reserve lubricant tank is pressurized via a gas. 
         [0018]    A further embodiment of the present disclosure includes, wherein the gas is an inert gas. 
         [0019]    A further embodiment of the present disclosure includes, wherein the pressurized reserve lubricant tank is pressurized via a liquid. 
         [0020]    A method of reducing lubrication starvation from a lubrication system with a main lubrication subsystem and a reserve lubrication subsystem, the main lubrication system in communication with a geared architecture of a gas turbine engine, according to another disclosed non-limiting embodiment of the present disclosure includes communicating lubricant under a pressure to the geared architecture in response to identifying of a prolonged reduced-G condition. 
         [0021]    A further embodiment of the present disclosure includes providing the pressure via a gas. 
         [0022]    A further embodiment of the present disclosure includes providing the pressure via a liquid. 
         [0023]    A further embodiment of the present disclosure includes communicating the lubricant under the pressure to a journal pin of the geared architecture. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiment. The drawings that accompany the detailed description can be briefly described as follows: 
           [0025]      FIG. 1  is a schematic cross-section of a gas turbine engine; 
           [0026]      FIG. 2  is a cross sectional side elevation view of a gear train useful in an aircraft gas turbine engine; 
           [0027]      FIG. 3  is a schematic diagram of a lubrication system; 
           [0028]      FIG. 4  is a schematic diagram of a reserve lubricant tank of the lubrication system; 
           [0029]      FIG. 5  is a block diagram of a control module that executes a reserve lubricant supply logic; 
           [0030]      FIG. 6  is a schematic diagram of a lubrication system according to another disclosed non-limiting embodiment; and 
           [0031]      FIG. 7  is a schematic diagram of a lubrication system according to another disclosed non-limiting embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]      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 . Alternative engines might include an augmentor section (not shown) among other systems or features. The fan section  22  drives air along a bypass flowpath while the compressor section  24  drives air along a core flowpath for compression and communication into the combustor section  26  then expansion through the turbine section  28 . Although depicted as a 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 turbofans as the teachings may be applied to other types of turbine engines such as a three-spool (plus fan) engine wherein an intermediate spool includes an intermediate pressure compressor (IPC) between the LPC and HPC and an intermediate pressure turbine (IPT) between the HPT and LPT. 
         [0033]    The engine  20  generally includes a low spool  30  and a high spool  32  mounted for rotation about an engine central longitudinal axis A relative to an engine static structure  36  via several bearing structures  38 . The low spool  30  generally includes an inner shaft  40  that interconnects a fan  42 , a low pressure compressor  44  (“LPC”) and a low pressure turbine  46  (“LPT”). The inner shaft  40  drives the fan  42  through a geared architecture  48  to drive the fan  42  at a lower speed than the low spool  30 . 
         [0034]    The high spool  32  includes an outer shaft  50  that interconnects a high pressure compressor  52  (“HPC”) and high pressure turbine  54  (“HPT”). A combustor  56  is arranged between the high pressure compressor  52  and the high pressure turbine  54 . The inner shaft  40  and the outer shaft  50  are concentric and rotate about the engine central longitudinal axis A which is collinear with their longitudinal axes. 
         [0035]    Core airflow is compressed by the low pressure compressor  44  then the high pressure compressor  52 , mixed with the fuel and burned in the combustor  56 , then expanded over the high pressure turbine  54  and the low pressure turbine  46 . The turbines  54 ,  46  rotationally drive the respective low spool  30  and high spool  32  in response to the expansion. 
         [0036]    In one non-limiting example, the gas turbine engine  20  is a high-bypass geared architecture engine in which the bypass ratio is greater than about six (6:1). The geared architecture  48  can include an epicyclic gear train, such as a planetary gear system, star gear system or other gear system. The example epicyclic gear train has a gear reduction ratio of greater than about 2.3, and in another example is greater than about 2.5. The geared turbofan enables operation of the low spool  30  at higher speeds which can increase the operational efficiency of the low pressure compressor  44  and low pressure turbine  46  and render increased pressure in a fewer number of stages. 
         [0037]    A pressure ratio associated with the low pressure turbine  46  is pressure measured prior to the inlet of the low pressure turbine  46  as related to the pressure at the outlet of the low pressure turbine  46  prior to an exhaust nozzle of the gas turbine engine  20 . In one non-limiting embodiment, the bypass ratio of the gas turbine engine  20  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). It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present disclosure is applicable to other gas turbine engines including direct drive turbofans. 
         [0038]    In one embodiment, a significant amount of thrust is provided by the bypass flow path due to the high bypass ratio. The fan section  22  of the gas turbine engine  20  is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet. This flight condition, with the gas turbine engine  20  at its best fuel consumption, is also known as bucket cruise Thrust Specific Fuel Consumption (TSFC). TSFC is an industry standard parameter of fuel consumption per unit of thrust. 
         [0039]    Fan Pressure Ratio is the pressure ratio across a blade of the fan section  22  without the use of a Fan Exit Guide Vane system. The low Fan Pressure Ratio according to one non-limiting embodiment of the example gas turbine engine  20  is less than 1.45. Low Corrected Fan Tip Speed is the actual fan tip speed divided by an industry standard temperature correction of (“T”/518.7) 0.5 . in which “T” represents the ambient temperature in degrees Rankine. The Low Corrected Fan Tip Speed according to one non-limiting embodiment of the example gas turbine engine  20  is less than about 1150 fps (351 m/s). 
         [0040]    With reference to  FIG. 2 , the geared architecture  48  includes a sun gear  60  driven by a sun gear input shaft  62  from the low speed spool  30 , a ring gear  64  connected to a ring gear output shaft  66  to drive the fan  42  and a set of intermediate gears  68  in meshing engagement with the sun gear  60  and ring gear  64 . Each intermediate gear  68  is mounted about a journal pin  70  which are each respectively supported by a carrier  74 . A replenishable film of lubricant, not shown, is supplied to an annular space  72  between each intermediate gear  68  and the respective journal pin  70 . 
         [0041]    A lubricant recovery gutter  76  is located around the ring gear  64 . The lubricant recovery gutter  76  may be radially arranged with respect to the engine central longitudinal axis A. Lubricant is supplied thru the carrier  74  and into each journal pin  70  to lubricate and cool the gears  60 ,  64 ,  68  of the geared architecture  48 . Once communicated through the geared architecture the lubricant is radially expelled thru the lubricant recovery gutter  76  in the ring gear  64  by various paths such as lubricant passage  78 . 
         [0042]    The input shaft  62  and the output shaft  66  counter-rotate as the sun gear  60  and the ring gear  64  are rotatable about the engine central longitudinal axis A. The carrier  74  is grounded and non-rotatable even though the individual intermediate gears  68  are each rotatable about their respective axes  80 . Such a system may be referred to as a star system. It should be appreciated that various alternative and additional configurations of gear trains such as planetary systems may also benefit herefrom. 
         [0043]    Many gear train components readily tolerate lubricant starvation for various intervals of time, however, the journal pins  70  may be relatively less tolerant of lubricant starvation. Accordingly, whether the gear system is configured as a star, a planetary or other relationship, it is desirable to ensure that lubricant flows to the journal pins  70 , at least temporarily under all conditions inclusive of reduced-G conditions which may arise from aircraft maneuvers and/or aircraft orientation. As defined herein, reduced-G conditions include negative-G, zero-G, and positive-G conditions materially less than 9.8 meters/sec./sec. (32 feet/sec./sec.). 
         [0044]    With Reference to  FIG. 3 , a lubrication system  80  is schematically illustrated in block diagram form for the geared architecture  48  as well as other components  84  (illustrated schematically) which may require lubrication. It should be appreciated that the lubrication system  80  is but a schematic illustration and is simplified in comparison to an actual lubrication system. The lubrication system  80  generally includes a main lubrication subsystem  86 , a reserve lubrication subsystem  88  and a control subsystem  90 . 
         [0045]    The main lubrication subsystem  86  generally includes a main lubricant tank  92  which is a source of lubricant to the geared architecture  48 . It should be understood that although not shown, the main lubrication subsystem  86  may include numerous other components such as a sump, scavenge pump, main pump and various lubricant reconditioning components such as chip detectors, heat exchangers and deaerators, which need not be described in detail herein. 
         [0046]    The reserve lubrication subsystem  88  generally includes a pressurized reserve lubricant tank  94  and may also include numerous other components which need not be described in detail herein. The pressurized reserve lubricant tank  94  may be located remote from the main lubricant tank  92  such as, for example, within the engine nacelle  96 , an engine pylon  98  or wing  100  ( FIG. 4 ). It should be appreciated that the pressurized reserve lubricant tank  94  may provide less lubricant volume than the main lubricant tank  92 . In one disclosed non-limiting embodiment, the pressurized reserve lubricant tank  94  may provide approximately fifty percent (50%) of the volume of the main lubricant tank  92 . In another disclosed non-limiting embodiment, the pressurized reserve lubricant tank  94  may sized to provide lubricant only to specific components such as the journal pins  70 . 
         [0047]    The pressurized reserve lubricant tank  94  may be pressurized with an inert gas such as nitrogen. A flexible barrier  102  may be located to separate the nitrogen from the lubricant to prevent intermixture thereof. It should be appreciated that other pressurization systems such as a separate pressure source, or other flexible barrier arrangement may alternatively or additionally be provided. 
         [0048]    The control subsystem  90  generally includes a control module  104  that executes a reserve lubricant supply logic  106  ( FIG. 4 ). The functions of the logic  106  are disclosed in terms of functional block diagrams, and it should be understood by those skilled in the art with the benefit of this disclosure that these functions may be enacted in either dedicated hardware circuitry or programmed software routines capable of execution in a microprocessor based electronics control embodiment. In one non-limiting embodiment, the control module  104  may be a portion of a flight control computer, a portion of a Full Authority Digital Engine Control (FADEC), a stand-alone unit or other system. 
         [0049]    The control module  104  typically includes a processor  104 A, a memory  104 B, and an interface  104 C. The processor  104 A may be any type of known microprocessor having desired performance characteristics. The memory  104 B may be any computer readable medium which stores data and control algorithms such as logic  106  as described herein. The interface  104 C facilitates communication with other components such as an accelerometer  108 A, a main lubricant tank valve  110  and a reserve lubricant tank valve  112 . It should be appreciated that various other components such as sensors, actuators and other subsystems may be utilized herewith. 
         [0050]    The lubrication system  80  is operable in both normal G-operation and reduced-G operation. During normal G-operation, the main lubricant tank  92  operates as the source of lubricant to the geared architecture  48 . Although effective during normal-G operation, it may be desirable to extend such operability to reduced-G operation to assure that the geared architecture  48  will always receive an effective lubrication supply irrespective of the lubrication pump (not shown) being unable to generate proper pressure. 
         [0051]    Under reduced-G operation, the accelerometer  108 A will sense this condition and communicate same to the control module  104 . The reserve lubricant supply logic  106  ( FIG. 5 ) will then be identify whether a prolonged reduced-G condition exists. A “prolonged reduced-G condition” is defined herein as a condition that lasts a length of time greater than a transient condition during which G forces are below gravity, e.g., 1G. In one disclosed non-limiting embodiment, the reserve lubricant supply logic  106  identifies a specific continuous time period during which the engine  20  is subject to the reduced-G condition such as, for example only, seven (7) seconds. It should be appreciated that other time periods as well as additional or alternative conditions may be utilized to further refine the logic. 
         [0052]    After the predetermined time period, the reserve lubricant supply logic  106  closes the main lubricant tank valve  110  and opens the reserve lubricant tank valve  112 . The main lubricant tank valve  110  is thereby isolated and the pressurized reserve lubricant tank  94  provides lubricant under gas pressure to the geared architecture  48  irrespective of the reduced-G condition. The geared architecture  48  is thereby assured an effective lubrication supply. 
         [0053]    After the reduced-G condition passes, the main lubricant tank valve  110  is opened to again supply lubricant to the geared architecture  48 . The reserve lubricant tank valve  112  may remain open as even if too much lubricant is then supplied, the excess lubricant can escape via an overflow vent  114 . That is, the additional lubricant is cycled through the system or otherwise removed therefrom. 
         [0054]    With reference to  FIG. 6 , another disclosed non-limiting embodiment of a lubrication system  80 ′ alternatively or additionally includes other sensors such as a lubricant flow sensor  116 . The flow sensor  116  communicates with the control module  104  to identify a prolonged reduced-G condition through identification of a reduced flow of lubricant to the geared architecture  48 . That is, the flow sensor  116  identifies a below desired lubricant flow to the geared architecture irrespective of the G forces. It should be appreciated that flow sensor  116  may be used in addition or in the alternative to the accelerometer  108 . 
         [0055]    With reference to  FIG. 7 , another disclosed non-limiting embodiment of a lubrication system  80 ″ provides a multi-shot system in which a multiple of pressurized reserve lubricant tanks  94 A,  94 B, . . . ,  94   n  communicate with the geared architecture  48  through respective solenoid valves  112 A,  112 B, . . . ,  112   n.  The solenoid valves  112 A,  112 B, . . . ,  112   n  are respectively actuated as described above to provide a multi-shot system which may be sequentially activated should multiple reduced-G conditions occur. 
         [0056]    Once used, the empty pressurized reserve lubricant tank(s) are then replaced or recharged in a maintenance operation once the aircraft has landed. For example, the pressurized reserve lubricant tank  94  may essentially be a line-replaceable unit that need only be plugged into the lubricant system for replacement. Furthermore, as the pressurized reserve lubricant tank  94  may be located in various locations ( FIG. 4 ), maintenance access is readily achieved. 
         [0057]    It should be understood that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” “bottom”, “top”, and the like are with reference to the normal operational attitude of the vehicle and should not be considered otherwise limiting. 
         [0058]    It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom. 
         [0059]    Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present disclosure. 
         [0060]    The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be understood that within the scope of the appended claims, the disclosure may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content.