Abstract:
A lubricant supply system for a gas turbine engine has a lubricant lube 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 for an associated gas turbine engine. A method and apparatus are disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of co-pending application Ser. No. 13/361,997, filed on 31 Jan. 2012. 
    
    
     BACKGROUND 
     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 
     In a featured embodiment, a lubricant supply system for a gas turbine engine has a lubricant pump delivering lubricant to an outlet line, which is split into at least a hot line and 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 one or more heat exchangers at which lubricant is cooled, and is then routed to a fan drive gear. At least one of the one or more heat exchangers is a fuel/oil cooler. The fuel/oil cooler is downstream of a point where the outlet line splits into the hot line and the cool line, such that the hot line is not directed through the 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. 
     In another embodiment according to any of the previous embodiments, a valve selectively supplies lubricant from the hot line to the fan drive gear when additional lubricant is necessary. 
     In another embodiment according to any of the previous embodiments, the hot line intermixes with a portion of the lubricant in the cool line prior to being directed to the locations associated with an engine that are not intended to receive cooler lubricant. 
     In another embodiment according to any of the previous embodiments, the hot line does not intermix back into the cool line until a point after the cool line has been routed to a bearing for the fan drive gear. 
     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, 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 is provided such that the low pressure turbine further drives the fan, with the fan and low pressure compressor being driven at different rates. A lubricant system includes a lubricant pump that delivers lubricant to an outlet line. The outlet line splits into at least a hot line and 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 is directed through one or more heat exchangers at which the lubricant is cooled. The cool line is then routed to the fan drive gear. At least one of the one or more heat exchangers is a fuel/oil cooler at which the lubricant will be cooled by fuel leading to a combustion section for the gas turbine engine. The fuel/oil cooler is downstream of a point where the outlet line splits into the hot line and the cool line, such that the hot line is not directed through the fuel/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 any of the previous embodiments, the cool line supplies lubricant to a journal bearing in the fan drive gear. 
     In another embodiment according to any of the previous embodiments, a valve selectively supplies lubricant from the hot line to the fan drive gear when additional lubricant is necessary. 
     In another embodiment according to any of the previous embodiments, lubricant in the hot line does not intermix back into the cool line until a point after the cool line has been routed to a bearing for the fan drive gear. 
     In another embodiment according to any of the previous embodiments, the lubricant in the hot line is intermixed with a portion of the lubricant from the cool line prior to being delivered to the locations in the gas turbine engine that are not intended to receive cooler lubricant. 
     In another featured embodiment, a lubricant supply system for a gas turbine engine has a lubricant pump delivering lubricant to an outlet line. The outlet line splits into at least a hot line and 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 one or more heat exchangers at which lubricant is cooled. The cool line is then routed to a fan drive gear. A valve is positioned on the cool line, at a location downstream of a point where the hot line splits off from the cool line. The valve splits the cool line into two lines, with a first line directed through one or more heat exchanger, and a second line directed through at least one other cooler. 
     In another embodiment according to the previous embodiment, the at least one other cooler is an air-to-oil cooler. 
     In another embodiment according to any of the previous embodiments, the at least one other cooler also includes an air-to-oil cooler at which oil from a generator exchanges heat with the oil in the second line. 
     In another embodiment according to any of the previous embodiments, one or more heat exchanger includes a fuel/oil cooler at which the lubricant in the first line will be cooled by fuel leading to a combustion section for a gas turbine engine. The fuel/oil cooler is downstream of a point where the outlet line splits into the hot line and the cool line, and such that the hot line is not directed through the fuel/oil cooler. 
     In another embodiment according to any of the previous embodiments, the hot line does not intermix back into the cool line until a point after the cool line has been routed to a bearing for the fan drive gear. 
     In another embodiment according to any of the previous embodiments, one or more heat exchangers, and at least one other cooler, include at least one of a fuel/oil cooler, an air/oil cooler and an oil/oil cooler. 
     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 is provided such that the low pressure turbine further drives the fan, with the fan and the low pressure compressor being driven at different rates. A lubricant system includes a lubricant pump delivering lubricant to an outlet line. The outlet line splits into at least a hot line and 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 is directed through one or more heat exchangers at which the lubricant is cooled. The cool line is then routed to the fan drive gear. A valve is positioned on the cool line, at a location downstream of a point where the hot line splits off from the cool line. The valve splits the cool line into two lines, with a first line being directed through one or more heat exchanger, and a second line being directed through at least one other cooler. 
     In another embodiment according to the previous embodiment, the at least one other cooler is an air-to-oil cooler. 
     In another embodiment according to any of the previous embodiments, at least one other cooler also includes an air-to-oil cooler at which oil from a generator exchanges heat with the oil in the second line. 
     In another embodiment according to any of the previous embodiments, one or more heat exchanger includes a fuel/oil cooler at which the lubricant in the first line will be cooled by fuel leading to a combustion section for a gas turbine engine. The fuel/oil cooler is downstream of a point where the outlet line splits into the hot line and the cool line, and such that the hot line is not directed through the fuel/oil cooler. 
     In another embodiment according to any of the previous embodiments, lubricant in the hot line does not intermix back into the cool line until a point after the cool line has been routed to a bearing for the fan drive gear. 
     In another embodiment according to any of the previous embodiments, one or more heat exchangers, and at least one other cooler, include at least one of a fuel/oil cooler, an air/oil cooler and an oil/oil cooler. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically shows a gas turbine engine. 
         FIG. 2  is a schematic of an oil management system for the gas turbine engine of  FIG. 1 . 
     
    
    
     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 (‘TSFCT’)”—is the industry standard parameter of 1 bm of fuel being burned divided by 1 bf 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. 
       FIG. 2  is 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 a variable frequency generator  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 nozzles  148  in 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 variable frequency generator  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 passes through an oil-to-oil cooler  164 , and may also pass through an air-to-oil cooler  66  before returning to the variable frequency generator  160 . 
     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 . The point where the two lines split is a connection that is open, and is not closed by a valve. Line  74  is sent directly to line  86  without cooling. A modulating valve  76  is controlled to achieve a desired fuel temperature. 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 variable frequency generator. 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 into a line  84 , to a journal bearing  152 , and to the fan drive gears  154 . Thus, cooler oil is supplied to the bearing  152  and gears  154  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  and the gears  154 . A return line  88  is downstream of the journal bearing  152  and gears  154 . The lubricant in line  86  mixes with the lubricant in “hot” line  74 , but downstream of the branch line  84 . 
     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 . The journal bearing  152  and the fan drive gears  154  would be part of the geared architecture  48  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 bearings  152  and/or gears  154  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. 13/362,094, entitled “Gas Turbine Engine With Geared Turbofan and Oil Thermal Management System With Unique Heat Exchanger Structure, owned by the assignee of the present application. 
     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.