BEARING COMPARTMENT PROTECTION SYSTEM

Abstract: A buffer zone for an encapsulated bearing compartment (38) mounted in the hot section of a gas turbine engine is defined adjacent the carbon seals (40) of the compartment (38) to prevent the hotter air surrounding the combustor from migrating to the oil within the compartment (38) in the event of a seal leakage. The buffer zone is supplied with high pres­ sure compressor air that has first been cooled prior to being admitted into the buffer zone.

Description: Description Bearing Compartment Protection System Technical Field This invention relates to gas turbine power plants for powering aircraft and particularly to means for buffering the bearings mounted in proximity to the hot section of the power plant. Background Art In recent years, the industry has been undertaking an intensive effort in designing, developing and manufacturing power plants that exhibited a high thrust specific fuel consumption (TSFC). To this end it is desirous to operate the engine during at least a portion of its operating envelope at a higher temperature than has heretofore been achieved. One of the consequences of these "hotter" engines is that the bearings supporting the rotating machinery is disposed in a hotter environment than similar sections in other engines have heretofore encountered. This is particularly true in engines that locate the bearings in the hottest section of the engine, namely the combustion section. while buffer zones and insulation means have been employed heretofore, the typical method of such systems has been to continuously flow cooler air at a relatively low pressure into a:cavity surrounding the bearing or in close proximity thereto and then discharge the air after it has dissipated the heat in the surrounding environment. Obviously, such a system has a twofold disadvantage, one being that it requires a substantial amount of air for rejecting the heat associated with the bearing and secondly, it discharges the now heated air overboard and/or to the lower energy turbine stages. The consequence of such systems is that they result in a penalty to the performance of the engine inasmuch as this routed air bypasses the high pressure turbine. This invention serves to solve the particular problem enumerated above by providing a high pressure, cooler air buffer zone for a bearing that is encapsulated adjacent the combustion section. I have found that I can obtain a satisfactory environment, that minimizes the likelihood of inadvertent fires in the area of the bearings by applying adjacent the seals of the bearing compartment high pressure compressor discharge air that has been cooled to some temperature below the flash point of the oil/air mixture associated with the bearing's cooling and lubrication system. The pressure of the buffer air is higher than the hotter ambient air so that the hotter air will not migrate to the bearing compartment during normal operations as well as in the event of the seal malfunctioning. Disclosure of Invention An object of this invention is to provide for a gas turbine engine means for buffering the bearing compartment so as to insulate this compartment from the hotter environment in close proximity thereto. A feature of this invention is to supply high pressure air from the compressor after first passing through a heat exchanger to cool the air to surround and buffer the bearing compartment seals. Other features and advantages will be apparent from the specification and claims and from the accompanying drawings which illustrate an embodiment of the invention. Brief Description of Drawing(s) Fig. 1 is a schematic and perspective of a gas turbine engine with the heat exchanger utilized to cool the compressor air prior to being returned as the buffer air, and Fig. 2 is a fragmentary view partly in section and partly in schematic showing a first embodiment of this invention. Best Mode for Carrying Out the Invention The invention can best be understood by referring to Figs. 1 & 2, showing a typical fan-jet engine generally indicated by reference numeral 10, having a fan section, compressor section, combustor section, turbine section and exhaust section. For the sake of simplicity and convenience, the details of a suitable gas turbine engine is omitted herefrom but reference should be made to the JT 9D engine manufactured by Pratt & Whitney of United Technologies Corporation, the assignee of this patent application. Suffice it to say that the power plant comprises a twin spool having axial flow compressor and turbine stages, where each set of stages of the compressor and turbine are interconnected by a shaft. The burner section is disposed between the compressor and turbine sections for developing sufficient energy to power the compressor and develop thrust for application. As noted in more detail in Fig. 2, the high pressure spool or gas generator (not shown) consists of shaft 12 suitably supported by roller bearings generally indicated by reference numeral 14. These bearings are well known and consists of an inner ring 16 mounted adjacent shaft 12 an outer ring 18, a plurality of rollers 20 sandwiched therebetween, cage 22 and, being surrounded by fluid damper 26. The damper and bearing are, in turn, supported and grounded to the annular support member 30 which is supported between flanges 32 & 34 of the bearing case 36. Bearing case 36 encapsulates the bearing 14. For more details of a bearing and fluid damper construction reference should be made to U.S. Patent No. 4,337,983 granted to D. H. Hibner on July 6, 1982 and U.S. Patent No. 4,385,788 granted to P. F. Brown, Jr. et al on May 31, 1983, both of which are assigned to the same assignee as this patent application and which are both incorporated herein by reference As is apparent from the foregoing the bearing is encapsulated in the bearing compartment 38 defined by housing 36 surrounding the shaft 12. The ends of the compartment 38 is sealed by suitable carbon seals 40 and 40' which are spring loaded (not shown) against the face of the seal plates 42 and 42' respectively. The construction of the carbon seals are well known and an example of a suitable construction is shown in U.S. Patent No. 2,992,842 granted to Shevchenko et al on July 18, 1961 also assigned to the same assignee as the patent application and incorporated herein by reference. As is well known, the cavity 38 is continuously subjected to the flow of oil which serves to lubricate and cool the bearings which oil is returned through the pump return line 44 mounted on the bottom of housing 36. In this installation the bearing housing is supported to the diffuser case partially shown as reference numeral 46 which surrounds the burner liner (not shown) and defines therewith a cavity 49 that surround and shrouds the burner liner. Since the bearing compartment is radially disposed relative to the combustor and typically is exposed to the already heated compressor discharge air surrounding the bearing compartment, under certain operating conditions this location of the engine has the propensity of becoming extremely hot. This is particularly true when some of that air is utilized to pressure the bearing compartment. One method of insulating the bearing cavity 38 from this excessive heat is by wrapping an insulating blanket 50 of suitable material (partially shown) around the housing 36. In addition thereto or as an alternate to the insulation system a buffer zone is disposed at the inside diameter of the carbon seals. This buffer zone is supplied with cool, high pressure air bled from the compressor. The temperature of this air is cooler and at a higher pressure than the ambient air surrounding the bearing compartment. Consequently, the hotter ambient air is prevented from entering into the bearing compartment during normal conditions as well as during a failure of the seal, save for some quantity that might mix with the buffer air. In the embodiment shown in Fig. 2, the cooler pressurized air is introduced at the inner diameter of the carbon seal in the annulus 48 and 48' by pipes 60 and 60' to fill the spaces between the shaft 12, seal support structure 52 up to the seal plate 42 on the left hand side of the bearing 14 and between the sleeve 56, seal support 52' up to the seal plate 42', on the right hand side of bearing 14. While only a single feed line is shown on either side of the bearing, each side may carry more than one pipe, (two pipes spaced 1800 apart are contemplated in the system). Pipes 60 and 62 are concentrically mounted in an outer tube 64 & 66 respectively which serves to insulate the inner pipe and maintain the air flowing to the buffer zone at a proper temperature level. The cooler pressurized air, as can be seen from Fig. 1, is bled from a suitable station in the compressor section, routed outside of the engine via line 68, through the fan heat exchanger 70 and returned internally via line 69 to the pipes 60 and 62 through manifold 72, (Fig. 2). By utilizing the high pressure air, for example, the air at the discharge end of the compressor, and then cooling that air prior to being admitted into the buffer zone, the system is satisfied with a minimal amount of air. The amount of compressor bleed air that is necessary for a suitable buffer zone is only that amount that is necessary to satisfy the carbon seal leakage requirements, although on this configuration certain amount may leak out of gaps 80 and 80' in the event this gap isn't sealed. In addition to the advantage of using a small amount of bleed air, which contrasts from heretofore buffer systems that continuously feed cooler air (not pressurized) and relies on the quantity flowing over the bearing for maintaining the cooling and buffering effort, this system affords these other advantages although not limited thereto. It reduces the potential for bearing compartment fires by reducing the carbon seal leakage air temperature by 4000 to 5000 F. It provides cold air at high pressures to buffer the compartment; the buffer air temperature is colder for a given pressure level than air directly drawn off the compressor system. It increases the compartment environmental pressure and temperature level at which one can safely operate the bearing compartment. In the event of a carbon seal failure, there is sufficient cold buffer air supplied to prevent a compartment oil fire. By using a high pressure source and metering the flow, normal small variations in buffer cavity pressures produce insignificant variations in buffer flow. It should be understood that the invention is not limited to the particular embodiments shown and described herein, but that various changes and modifications may be made without departing from the spirit and scope of this novel concept as defined by the following claims.

Claims: I claim: 1. For a bearing supporting a shaft carrying the compressor of a turbine gas power plant and being encapsulated in a housing having oil contained therein, the housing surrounding said shaft and having rotating carbon seals mounted on the ends of said housing adjacent said shaft to prevent oil from escaping out and air from ingesting onto said bearing compartment, the housing being subjected to a hotter environment than the temperature of the oil within said housing, a buffer zone surrounding said shaft adjacent the inside diameter of said rotating carbon seals, and means for supplying high pressure air to said buffer zone, said pressure being higher than the ambient air adjacent said encapsulated bearing compartment, and means for cooling said higher pressure air prior to being admitted into said buffer zone. 2. For a bearing as in claim 1 wherein said air is bled from the discharge end of the compressor and is cooled externally of said power plant.

Inventors: PUTMAN, ROBERT LOUIS
Applicants: UNITED TECHNOLOGIES CORPORATION
Application year: 1984
Main classification: F02C7
IPC codes: F02C7, F01D25, F01D11