United States Patent (19) 11) 4,151,710 Griffin et al. 45) May 1, 1979

(54) LUBRICATION COOLING SYSTEM FOR 3,797,561 3/1974 Clark et al...... 60/39.08 ACCESSORY OTHER PUBLICATIONS (75) Inventors: James G. Griffin, West Hartford; Irwin D. Singer, Glastonbury, both of Garrett Corp., TFE731 Pamphlet (1974). Conn.; Roger L. Summers, Lafayette, Pratt & Whitney, "The Aircraft Engine Ind. and Its Operation' (1974) p. 126. (73) Assignee: United Technologies Corporation, Primary Examiner-Louis J. Casaregola Hartford, Conn. Attorney, Agent, or Firm-Norman Friedland (21) Appl. No.: 777,233 57 ABSTRACT 22 Filed: Mar. 11, 1977 This invention serves to cool the lubricant used by a (51 Int. Cl’...... " ...... so so so so FO2C 7/06 mechanical constant speed drive (CSD) driving an air 52 U.S. C...... 60/39.08; 60/226 R; craft alternator which aircraft is powered by a turbofan 184/6.11 engine. The system cooling capacity is supplemented by 58) Field of Search ...... 60/39.07, 39.08, 39.33, an existing engine fuel/oil heat exchanger thereby effec 60/226R; 184/6.11 tuating a reduction in size of the CSD fan air/oil heat exchanger and minimizing an aircraft engine perfor (56) References Cited mance penalty. U.S. PATENT DOCUMENTS 2,865,580 12/1958 Marshall ...... 60/39.08 4 Claims, 3 Drawing Figures

FUEL-OL COOLER

CONSTANT SPEED DRIVE UNIT U.S. Patent May 1, 1979 4,151,710

ENGINE FUEL-OL

CONSTANT SPEED DRIVE

4,151,710 2 during a descent mode of the aircraft, improving the life LUBRICATION COOING SYSTEM FOR of the . AIRCRAFT ENGINE ACCESSORY Other features and advantages will be apparent from the specification and claims and from the accompanying BACKGROUND OF THE INVENTION drawings which illustrate an embodiment of the inven This invention relates to turbofan engines utilizing a tion. mechanical constant speed drive and particularly to the cooling system for the lubricant used in the constant BRIEF DESCRIPTION OF THE DRAWING speed drive. FIG. is a partly schematic and partly block diagram As is well known the constant speed drive, which is a 10 showing the CSD lubricant cooling system. gear and clutch arrangement, serves to generate elec FIG. 2 is a partial view in perspective showing the tricity for the aircraft. In a turbofan driven aircraft, the fan air/oil heat exchanger mounted in the fan duct. fan air/lubricant cooler is located in the fan duct (as FIG. 3 is a perspective view of the aircraft utilizing stown in G. 2) and extends into the fan airstream. this invention. Associated with this type of plate/in heat exchanger is 5 a pressure loss which is refected it: terms of aircraft DESCRIPTION OF THE PREFERRED performance penalty. in a given installation utilizing the EMBODIMENT T-9D engine (ianufactured by the P&WA division of As is illustrated in FIGS. 1-3 the invention is contem : TC, the assignee) this pressure css amounted to ap plated as being utilized on aircraft as the one illustrated proximately a loss of 0.8% of TSFC ( specific fuel 20 by reference numeral 10 powered by a suitable engine constigiption). generally illustrated by reference numeral 9. In this it has also been well known that a typical coastait preferred embodiment the aircraft may be for example speed drive lubricant cooling system would use a single the Boeing designated model 747 manufactured by the heat exchanger which is of the plate/fin type in the fan Boeing Airplane Company and the engine may be the airstream as described above. 25 JT9D manufactured by the Pratt & Whitney Aircraft We have found that we can is prove TSFC by reduc Group division of UTC, the assignee of this application. ing the size of the fan air/oil heat exchanger because fan It is to be understood that this invention is not limited stream pressure losses have been reduced by utilizing to the above named engine and aircraft, as one skilled in the engine/cil heat exchanger that is already in exis this art will appreciate that this invention has utility in tence. When the JT-9D was upgraded to increase its 30 other engine/aircraft installations. However, the inven thrust, a doubling in size of the existing fan air/oil tion is particularly efficacious in an application where cooler would have been necessary. By virtue of this the lubricant for the constant speed drive is cooled by a invention, the size of the cooler on the upgraded engine heat exchanger that is mounted in the fan airstream of was actually reduced in size by a factor of 6, or approxi the engine. As noted in FIG. 2, the oil cooler 14 for the mately of the predecessor engine cooler. In terms of 35 constant speed drive is mounted on the fan duct 16. In TSFC, an improvement of 1% was realized. this instance the oil cooler 14 is a plate/fin cross flow Moreover, there are advantages gained from utilizing design where the air passages 18 alternate with oil pas the engine fuel/oil cooler that wasn't available hereto sages 21 for indirect heat transfer for chilling the lubri fore. Namely, because of fuel pump inefficiency and Cant. engine oil heat transfer, a large temperature rise of the As is apparent from FIG. 2, heat exchanger 14 ex fuel is occasioned during aircraft. descent. This is pri tends in the fan airstream and represents a pressure loss marily due to the pilot cutting back on the power lever which is directly related to the frontage area exposed in reducing thrust and engine power, which causes the the stream. Obviously, by reducing its size, which has fuel to recirculate resulting in a higher fuel temperature. been done by virtue of this invention and which is illus Connecting the CSD lubricant to the engine fuel/oil 45 trated by the dashed outline of the unit illustrating the heat exchanger now serves to reduce the temperature of heretofore size, the pressure loss can be correspond the fuel prior to it being admitted to the engine's com ingly reduced. In this particular installation the reduc bustor. This lower fuel temperature, in effect, reduces tion of size of the heat exchanger 14 was sufficient to the adverse effect of the higher temperature fuel during realize a 1% increase in TSFC. descent on the combustor, resulting in a longer life of 50 Referring now to FIG. 1, constant speed drive 24 the combustor. which is typically mounted to engine 9 generates ap By locating the CSD fuel/oil portion of the engine proximately 1000 BTU/minute which heat is dissipated fuel/oil cooler in a downstream position, relative to fuel by the lubricant continuously flowing therethrough. flow, the heat transfer from the CSD lubricant does not Heretofore the lubricant was cooled by a suitable heat interfere with the engine lubrication system. 55 exchanger similar to heat exchanger 14 sized to cool the CSD for its most severe operating conditions. The heat SUMMARY OF THE INVENTION exchanger 14 is represented in FIG. 1 with a like desig An object of this invention is to provide for a me nation. chanical constant speed drive for a turbofan engine It is customary, as is shown in FIG. 1, to cool the powered aircraft an improved lubricant cooling system. 60 engine lubrication system with a plate/tube heat ex A still further object of this invention is to provide for changer as is illustrated by reference numeral 20. On the a CSD as described a lubrication system that utilizes the installation noted above, heat exchanger 20 existed and engine fuel as a supplementary heat sink. A feature of it consisted of a plurality of tubes 28 receiving engine this invention is to utilize the existing tube/plate engine fuel fed into header 30 via line 32, pump 34 and fuel tank fuel/oil heat exchanger thereby reduding the size of the 65 36. The fuel flows straight through and is collected in plate/fin CSD heat exchanger improving engine perfor outlet header 36 where it then is fed to the engine's mance and TSFC. The heat transfer on the fuel serves combustor (not shown). The heated engine lubricant is to chill the fuel prior to admittance to the combustor conducted from engine 9 via line 46, flows over the 4,151,710 3 4. pipes 28 and is directed through a circuitous path reduced temperature fuel has the effect of prolonging formed by baffle plates 42 to discharge through outlet the life of the combustor. 44 and returned to the engine via line 40. It should be understood that the invention is not lim In accordance with this invention the heretofore ited to the particular embodiments shown and described 5 herein, but that various changes and modifications may existing engine fuel-oil cooler 20 was modified to accept be made without departing from the spirit or scope of the lubricant from the CSD. Hence, portion 50 was this novel concept as defined by the following claims. added by extending tubes 28 through the wall 52 and We claim: the oil from the CSD 24 is directed into portion 50 via 1. Lubrication system for a constant speed drive me line 54 and is circuitously routed via baffles 56 over 10 chanically driven by a turbofan engine having a fuel to tubes 28 to outlet pipe 58. lubricant heat exchanger for cooling the engine lubri It is apparent from the foregoing that the heated cant with the engine's fuel prior to combustion by indi lubricant when the CSD is operating under its most rect heat exchange relation, a cooling system for the severe condition is directed through the fan air/oil lubricant of the constant speed drive including a plate/- cooler 14 via line 60 and through the CSD fuel/oil 15 fin heat exchanger for indirect heat exchange of the cooler 50 via line 54 and returned chilled to CSD 24 via lubricant and fan air mounted on the fan duct and ex line 58. tending in the fan air stream, a cooling loop for the To assure that the temperature of lubricant for CSD lubricant of the constant speed drive including an exten doesn't fall below a predetermined value, say 140 F. a sion of said fuel to lubricant heat exchanger for indirect bypass 62 and temperature responsive valve 64 are in 20 heat exchange of said constant speed drive lubricant and cluded. Hence if the temperature in line 58 downstream engine fuel, thereby minimizing the size of the fan of valve 64 falls below 140 F. setting, the fuel/oil mounted plate/fin heat exchanger and improving en cooler 50 will be bypassed. During engine startup with gine performance, said cooling loop includes conduit cold oil the bypass line 66 will flow lubricant around means for directing said lubricant to said fuel to lubri heat exchanger 14 via a pressure relief valve 68. Simi 25 cant heat exchanger, and means to separate said lubri larly, valve 64 has a cold oil pressure relief function in cant for the constant speed drive from the engine lubri addition to the above-mentioned temperature control cant such that the lubricant for the constant speed drive function. is downstream of the engine lubricant relative to the It is apparent from the drawing that because portion flow of fuel. 50 of heat exchanger 26 is downstream relative to the 30 2. A lubrication system as in claim 1 including a by flow of fuel of the engine lubricant, the addition to heat pass means for bypassing said plate/fin heat exchanger exchanger 26 has no adverse effect on the engine lubri when said lubricant goes below a predetermined tem cating system. perature value. Furthermore, during descent of the aircraft in a land 3. A lubrication system as in claim 2 including an ing mode, the excessfuel being pumped by pump 34 and 35 other bypass means for bypassing said fuel to lubricant not being combusted, due to a reduced power setting, is heat exchanger whenever said temperature reaches a recirculated and by virtue thereof is reheated. The fan predetermined condition. air/oil cooler 14 is able to reduce the lubricant from the 4. A lubrication system as in claim 1 wherein said fuel CSD to a temperature that is lower than this now to lubricant heat exchanger includes a plurality of axi heated fuel. This results in a heat transfer from the fuel 40 ally extending tubes for conducting the flow of fuel to the CSD lubricant, reducing the temperature of the prior to being delivered to the combustor of said engine. fuel being admitted to the engine's combustor. The

45

50

55

60

65