Abstract:
An oil supply system for a gas turbine engine has a lubricant pump delivering lubricant to an outlet line. The outlet line is split into at least a hot line and into a cool line, with the hot line directed primarily to locations associated with an engine that are not intended to receive cooler lubricant, and the cool line directed through one or more heat exchangers at which lubricant is cooled. The cool line then is routed to a fan drive gear system of an associated gas turbine engine. A method and apparatus are disclosed. The heat exchangers include at least an air/oil cooler wherein air is pulled across the air/oil cooler to cool oil. The air/oil cooler is provided with an ejector tapping compressed air from a compressor section to increase airflow across the air/oil cooler.

Description:
BACKGROUND OF THE INVENTION 
     This application relates to an oil system for providing oil to a gear associated with a geared turbofan in a gas turbine engine. 
     Gas turbine engines are known, and typically include a fan delivering air into a compressor section. Compressed air from the compressor section is delivered into a combustion section, mixed with fuel, and ignited. Products of this combustion pass downstream over turbine rotors which are driven to rotate. 
     A low pressure turbine rotor drives a low pressure compressor, and traditionally has driven a fan at the same rate of speed. 
     More recently, a gear reduction has been included between the low pressure turbine and the fan such that the fan and the low pressure compressor can rotate at different speeds. 
     Oil management systems are known, and typically provide oil to engine bearings and other locations within the engine. As a result of gears being added to turbofan engines, additional components require cooling, thereby necessitating new cooling systems and methodologies. 
     SUMMARY OF THE INVENTION 
     In a featured embodiment, a lubricant supply system for a gas turbine engine has a main lube pump delivering lubricant to an outlet line. The outlet line splits into at least a hot line and into a cool line. The hot line is directed primarily to locations associated with an engine that are not intended to receive cooler lubricant. The cool line is directed through heat exchangers at which lubricant is cooled. The cool line is then routed to a fan drive gear system of an associated gas turbine engine. The heat exchangers include at least an air/oil cooler wherein air is pulled across said air/oil cooler to cool lubricant, and said air/oil cooler being provided with an ejector tapping compressed air from a compressor section to increase airflow across the air/oil cooler. 
     In another embodiment according to the previous embodiment, a valve is positioned on the cool line and splits the cool line into two lines, with a first line directed through a first fuel/oil cooler at which the lubricant will be cooled by fuel leading to a combustion section for the gas turbine engine. The lubricant not directed to the fuel/oil cooler is directed to at least one other cooler through a second line. 
     In another embodiment according to the previous embodiment, the at least one other cooler includes the air-to-oil cooler. 
     In another embodiment according to the previous embodiment, a bypass valve selectively bypasses fuel downstream of the fuel/oil cooler back upstream. 
     In another embodiment according to the previous embodiment, the bypass valve alternatively directs the return fuel upstream of the first fuel/oil cooler, or downstream of the first fuel/oil cooler. 
     In another embodiment according to the previous embodiment, the at least one other cooler also includes an oil-to-oil cooler at which lubricant from a generator exchanges heat with the lubricant in the second line. 
     In another embodiment according to the previous embodiment, the generator is also passed through a second fuel/oil cooler at a location upstream of the first fuel/oil cooler. 
     In another embodiment according to the previous embodiment, the cool line supplies lubricant to a journal bearing in the fan drive gear system. 
     In another embodiment according to the previous embodiment, a valve selectively supplies lubricant from the hot line to the fan drive gear system. 
     In another featured embodiment, a gas turbine engine has a fan, a compressor section, including a low pressure compressor section and a high pressure compressor section, a combustor, and a turbine section including both a low pressure turbine and a high pressure turbine section. The low pressure turbine section drives the low pressure compressor section. A fan drive gear system is provided such that the low pressure turbine further drives the fan. The fan and the low pressure compressor are driven at different rates. A lubricant system includes a main lube pump to deliver lubricant to an outlet line. The outlet line splits into at least a hot line and into a cool line. The hot line is directed primarily to locations in the gas turbine engine that are not intended to receive cooler lubricant. The cool line being is directed through heat exchangers at which the lubricant is cooled, and is then routed to the fan drive gear system. The heat exchangers include at least an air/oil cooler wherein air is pulled across the air/oil cooler to cool lubricant. The air/oil cooler is provided with an ejector tapping compressed air from a compressor section to increase airflow across the air/oil cooler. 
     In another embodiment according to the previous embodiment, the locations in the engine that are not intended to receive cooler lubricant include bearings associated with at least the turbine section. 
     In another embodiment according to the previous embodiment, a valve is positioned on the cool line and splits the cool line into two lines. A first line is directed through a first fuel/oil cooler at which the lubricant will be cooled by fuel leading to a combustion section for the gas turbine engine. The lubricant not being directed to the fuel/oil cooler is directed to at least one other cooler through a second line. 
     In another embodiment according to the previous embodiment, the at least one other cooler includes the air-to-oil cooler. 
     In another embodiment according to the previous embodiment, a bypass valve selectively bypasses fuel downstream of the fuel/oil cooler back upstream. 
     In another embodiment according to the previous embodiment, the bypass valve alternatively directs the return fuel upstream of the first fuel/oil cooler, or downstream of the first fuel/oil cooler. 
     In another embodiment according to the previous embodiment, the at least one other cooler also includes an oil-to-oil cooler at which lubricant from a generator exchanges heat with the oil in the second line. 
     In another embodiment according to the previous embodiment, wherein lubricant from the generator is also passed through a second fuel/oil cooler at a location upstream of the first fuel/oil cooler. 
     In another embodiment according to the previous embodiment, the cool line supplies lubricant to a journal bearing in the fan drive gear system. 
     In another embodiment according to the previous embodiment, the low pressure turbine has a pressure ratio greater than about 5:1. The gear reduction has a ratio of greater than about 2.3. The fan diameter is significantly larger than a diameter of the low pressure compressor. 
     In another featured embodiment, a method of managing lubricant supply for a gas turbine engine includes the steps of moving a lubricant from a main lubricant pump into an outlet line, and splitting the outlet lines into a cool line which is delivered into at least one heat exchanger to cool the lubricant. The cooled lubricant is then delivered to a gear reduction that drives a fan associated with the gas turbine engine. Lubricant is supplied from a hot line that is not passed through the at least one heat exchanger to bearings associated with at least a turbine section in the gas turbine engine. The at least one heat exchanger includes at least an air/oil cooler wherein air is pulled across the air/oil cooler to cool lubricant. The air/oil cooler is provided with an ejector tapping compressed air from a compressor section to increase airflow across the air/oil cooler. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically shows an embodiment of a gas turbine engine. 
         FIG. 2  is a schematic of an embodiment of an oil management system for the gas turbine engine of  FIG. 1 . 
         FIG. 3  shows an embodiment of an air/oil cooler used in the oil management system of  FIG. 2 . 
     
    
    
     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 . Alternative engines might include an augmenter section (not shown) among other systems or features. The fan section  22  drives air along a bypass flowpath B while the compressor section  24  drives air along a core flowpath C 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 including three-spool architectures. 
     The 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. 
     The low speed spool  30  generally includes an inner shaft  40  that interconnects a fan  42 , a low pressure compressor  44  and a low pressure turbine  46 . The inner shaft  40  is connected to the fan  42  through a geared architecture  48  (shown schematically) to drive the 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 high pressure compressor  52  and high pressure turbine  54 . A combustor  56  is arranged between the high pressure compressor  52  and the high pressure turbine  54 . A mid-turbine frame  57  of the engine static structure  36  is 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 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 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. The turbines  46 ,  54  rotationally drive the respective low speed spool  30  and high speed spool  32  in response to the previously mentioned expansion. 
     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 ten (10), the geared architecture  48  is an epicyclic gear train, such as a planetary 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 5. 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 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 epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.5:1. 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. The flight condition of 0.8 Mach and 35,000 ft, with the engine at its best fuel consumption—also known as bucket cruise Thrust Specific Fuel Consumption (“TSFC”). 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 [(Tambient deg R)/518.7)^0.5]. The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second. 
       FIG. 2  illustrates an oil management system for the gas turbine engine system of  FIG. 1 . The oil management system  140  is utilized in association with a fuel system  143 , and an integrated drive generator (“IDG”)  160  and its oil cooling system circuit  162 . 
     Fuel from a fuel tank  142  passes to a fuel/oil cooler  144 . The fuel is heated, and cools a lubricant, as will be explained below. A main fuel pump  146  drives the fuel into further fuel lines  243  and then into a fuel management unit (“FMU”)  148  associated with a combustor, such as combustor  26  as shown in  FIG. 1 . It is known in the art to heat the fuel to improve the efficiency of the overall engine. The fuel/oil cooler  144  provides this function. 
     At the same time, the IDG  160  is driven by turbine rotors to generate electricity for various uses on an aircraft. As shown in oil cooling system circuit  162 , the oil from IDG  160  passes through an oil-to-oil cooler  164 , and may also thereafter pass through a fuel oil cooler  19  before returning to the variable frequency generator  160 . 
     A boost pump  17  may drive the fuel from the tank  142  through the fuel oil cooler  19  to heat the fuel, and cool the oil being returned to the generator  160 . A valve  18  may selectively return fuel to the fuel tank  142 . As also shown, a bypass directional control valve  16  selectively bypasses fuel away from the FMU  148  to either upstream or downstream of the engine FOC ( 144 ). The main fuel pump  146  may be a fixed displacement pump, and thus is less able to provide precise metering of the fuel being delivered to the FMU. The bypass valve  16  assists in ensuring the proper amount of fuel is delivered. As shown, the fuel may be returned through a line  15  to a location upstream of the fuel oil cooler  144  under certain conditions, low power for example. On the other hand, under other conditions, such as high power, the fuel is delivered through a line  14  to a location downstream of the fuel oil cooler. Since the fuel in either line  14  or  15  has already been heated, it may be necessary to provide more cooling to the oil, and thus an improved air/oil cooler  68  is utilized, and will be explained below. 
     An oil supply system  150  includes a main oil pump  70  taking oil from a main oil tank  72 . The terms “oil” and “lubricant” are used interchangeably in this application and cover a fluid used to lubricate surfaces subject to relative rotation. The oil is delivered through a downstream line  73 , and split between two lines  74  and  75 . Line  74  is sent directly to line  86  without cooling. A modulating valve  76  is controlled to achieve a desired fuel temperature for the oil in line  75 . As an example, a sensor  300  may send a signal to a control regarding a sensed temperature of the fuel downstream of the fuel oil cooler  144 . The valve  76  routes the volume of oil between line  78  and  80  to achieve the desired temperature of the fuel. 
     The oil passing to line  78  passes through the fuel/oil cooler  144  and heats the fuel. The oil is cooled before returning to a common downstream line  82 . The downstream line  82  could be called a “cool” oil line, as the oil will be cooler than the oil in “hot” line  74  which has not been cooled in any heat exchanger. For purposes of this application, line  75  is seen as part of the “cool” line even though the lubricant has yet to be cooled. 
     The oil directed by the valve  76  into line  80  passes through an air-to-oil cooler at  68  which is exposed to air which is cooler than the oil in line  80 , and which cools the oil. Downstream of the air-to-oil cooler  68 , the oil passes through the oil-to-oil cooler  164 , and may actually be somewhat heated by cooling the oil for the IDG. Still, the oil reaching line  82  downstream of the oil-to-oil cooler  164  will be significantly cooler than the oil in line  74 . Some of the oil in line  82  is directed through a line  84 , to a journal bearing  152 , which is part of the gear reduction  48  (see  FIG. 1 ). Thus, cooler oil is supplied to the bearing  152  than is supplied from the line  74 . As can be seen, a line  86  branches off of the “cool” line  82  at or near the point at which “cool” line  84  breaks away to go to the journal bearing  152 . The lubricant in line  86  mixes with the lubricant in “hot” line  74 , but downstream of the branch line  84 . As shown, the fan drive gears  154  receive “hot” oil. On the other hand, the fan drive gears  154  may be placed to receive the cooler oil. 
     It is desirable to provide cooler oil to these locations than is necessary to be supplied to bearings  90 , or other locations associated with the engine. The bearings  90  as shown in  FIG. 2  may equate to the several locations of bearings  38  as shown in  FIG. 1 . 
     On the other hand, cooling all of the oil associated with the engine bearings  90  would reduce the overall efficiency of the engine. Thus, splitting the oil, and cooling the oil to be directed to the bearing  152  provides cooler oil to those locations, while still allowing the hotter oil to be directed to locations that do not need cooler oil. 
     In addition, a valve  92  can selectively direct additional oil to the gears  154  if additional oil is necessary, such as at high power times. At other times, the valve  92  may direct lubricant through line  94  back to a return line  95  leading back to the oil tank  72 . 
     The overall configuration thus results in an oil supply system which directs hotter oil to the locations which do not need cooler oil, but which also cools oil to be directed to areas associated with the fan drive gear. 
     Further details of a similar oil management system are disclosed in co-pending U.S. patent application Ser. No. 13/361,997, entitled “Gas Turbine Engine With Geared Turbofan and Oil Thermal Management System, filed on even date herewith, and owned by the assignee of the present application. 
     The differences between the present application and the above referenced application largely relate to the inclusion in the system of the bypass valve  16 . Since fuel which has already been heated is returned by the bypass valve  16 , there is more of a cooling load on the oil in the engine fuel oil cooler. Since the bypass valve  16  is returning fuel which has already been heated to locations upstream of the FMU, and temperature sensor  300 , it is possible that less heating of the fuel, and subsequently less cooling of the oil will occur in the fuel oil cooler. Thus, the cooling load on the air/oil cooler  68  may be higher. For that reason, an ejector  198  is included, and a tap to a compressor source  200  (e.g., the sixth stage of the compressor section, for example, such as shown in  FIG. 1 ) may tap high pressure air through the ejector  198  to draw additional air into a duct  199 , shown schematically, and across the air/oil cooler  68 . This will increase the amount of cooling of the oil in the air/oil cooler  68 , and ensure the oil reaching line  82  is sufficiently cool to be sent to the journal bearing  152 . 
     The use of the fuel oil cooler  19  also heats the fuel, and thus reduces the potential for adequately cooling the oil in the fuel/oil cooler  144  on its own. This again points to the use of the improved air/oil cooler. 
       FIG. 3  schematically shows further details of the air/oil cooler  68 . As shown, a duct  199  bleeds air across the air/oil cooler  68 . An ejector tap  198  from a source of compressed air  200 , increases the flow of air to achieve adequate cooling of the oil. A valve  201  selectively controls this ejector flow. 
     The air/oil cooler is not in series with the fuel/oil cooler, however by further cooling the oil, when it is intermixed, it will be able to compensate for the hotter oil from the fuel/oil cooler  144 . 
     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 invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.