Bearing lubrication system for a turbomachine

Abstract

A bearing lubrication system for a turbomachine having a lubrication chamber which defines a lubrication space surrounding the bearings has lubricant feeding devices for supplying lubricant to the lubrication space, a lubricant removing device for removing lubricant from the lubrication space, and a buffer case surrounding the lubrication chamber, that is located in the fluid space of the turbomachine, and defines a buffer space communicating with the atmosphere. Shaft contact seals are provided between the buffer case and the fluid space, and shaft seals are provided between the buffer space and the lubrication space.

Description

[0002] The invention relates to the lubrication of turbomachines, and more specifically to a bearing lubrication system for a gas turbine engine.

BACKGROUND OF THE INVENTION

[0003] It is a common practice in gas turbine engines to provide a lubrication chamber surrounding the shaft bearings using seals that separate the interior space, or lubrication space, of the lubrication chamber from the fluid space of the gas turbine engine. Lubricant is supplied to the lubrication space through, e.g., a mist forming nozzle, and the lubricant is removed from the lubrication space through a drain by gravity or by means of a scavenging pumps. The lubrication system of this type usually requires a separator to separate oil from the air, because the lubricant contains air and gas owing to the pressure fluctuations in the fluid space. The lubricant is recovered from the bottom of the separator, and the air escapes through an exhaust duct. If the speed of the gas turbine engine falls below a certain level, the gage pressure which normally prevails outside the lubrication chamber suddenly drops for a certain time period below the pressure in the lubrication chamber. This will cause lubricant to escape from the lubrication space, resulting in the lubricant entering the fluid space of the gas turbine engine. The negative impact of such lubricant leak into the fluid space of a gas turbine engine is well known to those skilled in the art. In addition, if a large quantity of lubricant escapes from the lubrication system, the lubricant tank level will drop substantially, and the system may lack lubricant.

[0004] A prior art depressurization device disclosed in U.S. Pat. No. 5,429,208 to Christian Largiller et al. was aimed at eliminating this disadvantage. The depressurization device is made in the form of a jet nozzle which communicates with the lubrication space. The jet nozzle ejects air (with lubricant) from the lubrication space using air from the engine compressor as a carrier fluid. When the speed of the gas turbine engine drops below a certain level, and there is a danger of the pressure in the fluid space of the engine falling below the pressure in the lubrication space, a sensor in a control circuit sends a signal to a valve to open the jet nozzle to the compressor. As a result, the excessive air (with lubricant) is removed from the lubrication space to establish a reduced pressure in the lubrication space.

[0005] Prior art bearing lubrication systems such as that described above require lubricant/air separators because the lubrication chamber is pressurized. The lubricant/oil separators are devices that have to be manufactured and installed on the gas turbine engine. In addition, the lubricant/air separators consume a certain amount of the engine output power, thus lowering engine efficiency. The depressurization of the lubrication space during engine deceleration requires the provision of a jet nozzle or an evacuation pump and a control system with a sensor and controls to activate the depressurization system. Apart from the added cost of these devices, their use in gas turbine engine impairs its reliability. These devices require periodic checks and maintenance. A malfunction of one of these devices may result in lubricant entering the fluid space of the gas turbine engine.

[0006] It should be added that even a small quantity of lubricant which inevitably escapes from the lubrication system with air leaving the lubricant/air separator (because even the best separators cannot ensure the 100% separation), as well as the lubricant that escapes from the jet nozzle is irrecoverably lost. Moreover, the discharge of the lubricant into the open air has an adverse effect on the environment.

[0007] It is thus an object of the invention to provide a bearing lubrication system for a turbomachine which would prevent pressure from increasing in the lubrication space.

[0008] Another object of the invention is to provide a bearing lubrication system for a turbomachine which would be reliable in operation.

[0009] Further object of the invention is to provide a bearing lubrication system for a turbomachine which requires minimum maintenance.

[0010] Still another object of the invention to provide a bearing lubrication system for a turbomachine which would be simple in design and easy to manufacture.

[0011] One more, it is an object of the invention to prevent lubricant from being irrecoverably lost.

[0012] Finally, it is an object of the invention to prevent the adverse environmental effect of lubricant.

SUMMARY OF THE INVENTION

[0013] The above and other objects of the invention are accomplished by providing a bearing lubrication system for a turbomachine having a lubrication chamber that defines a lubrication space surrounding the bearings, lubricant feeding devices for supplying lubricant to the lubrication space, a lubricant removing device for removing lubricant from the lubrication space, and a buffer case surrounding the lubrication chamber, located in the fluid space of the turbomachine, and defining a buffer space communicating with the atmosphere. Shaft contact seals are provided between the buffer case and the fluid space and shaft seals are provided between the buffer space and the lubrication space.

[0014] These and other objects and advantages of the invention will become apparent from the following detailed description of preferred embodiments of a bearing lubrication system for a turbomachine, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is a schematic sectional view that shows a bearing lubrication system for a turbomachine according to the invention;

[0016] FIG. 2 is another embodiment of a bearing lubrication system for a turbomachine according to the invention, which shows details of sealing.

DETAILED DESCRIPTION OF THE DRAWINGS

[0017] In FIG. 1, a turbomachine 10, which can be, among other machines, a gas turbine engine, has a fluid space 12 communicating with the gas turbine engine flow duct in which a gas turbine 14 and a compressor 15 are installed. Turbine 14 and compressor 15 are installed on a shaft 16. Shaft 16 is supported by bearings 18 and 20 which are installed in a lubrication chamber 22. Lubrication chamber 22 is made as a closed chamber in a turbomachine casing 23. The lubrication chamber 22 has a lubrication space shown at LS which is used to lubricate bearings 18 and 22. Devices 24 feed lubricant into the lubrication space LS. These devices may be spray nozzles for generating a lubricant mist in the lubrication space LS in proximity to bearings 18 and 20. Lubrication chamber 22 has a drain 26 to remove from lubrication space LS lubricant splashing from bearings 18 and 20. Drain 26 may be connected to a lubricant tank (not shown) to remove lubricant by gravity, or it may be connected to a scavenging pump (not shown) which removes lubricant and pumps it back to the lubricant tank. The systems for lubricant supply and removal are well known to those skilled in the art and are not discussed in detail here. These systems would normally use lubricant/air separators to separate lubricant from the air and gas that would be present in the lubricant leaving the lubrication chamber in the conventional lubrication systems. Such lubricant/air separators are not used in the bearing lubrication system of a turbomachine according to the invention.

[0018] A buffer case 28 is provided in fluid space 12, and this buffer case is surrounded by fluid space 12. Buffer case 28 surrounds the lubrication chamber 22 and communicates with the atmosphere through an opening 30 as shown by arrow A. It will be understood that lubrication chamber 22 will be under the pressure that establishes in the interior of buffer space BS of buffer case 28 (which is about equal to the atmospheric pressure). The pressure in lubrication chamber 22 will never be higher than atmospheric pressure.

[0019] Buffer case 28 is separated from fluid space 12 of gas turbine engine 10 by contact seals 32 and 34. Contact seals 32 and 34 allow only a minimal leak from fluid space 12 into buffer space BS if the fluid pressure in the fluid space is greater than atmospheric pressure, or they allow only a minimal leak of air or gas from buffer space BS into fluid space 12. In any case, the pressure in buffer space BS will always be about equal to atmospheric pressure. The lubrication space LS of lubrication chamber 22 is separated from buffer space BS of buffer case 28 by seals 36 and 38. Seals 36 and 38 are provided to prevent oil from escaping from lubrication space LS into buffer space BS from which oil might escape into the atmosphere. As shown in FIG. 1, all contact seals 32 and 36 are made as brush seals. Brush seals are known in the art. As an example, the construction of a brush seal is disclosed in U.S. Pat. No. 5,201,530. Brush seals 32 and 34 ensure a minor gas leakage from fluid space 12 into buffer space BS of buffer case 28. Any leakage will escape to the atmosphere, so with any leakage flow through brush seals 32 and 34, the pressure in buffer space BS will be about atmospheric pressure.

[0020] In FIG. 2, which illustrates another embodiment of the invention in which the same parts are shown at the same reference numerals as in FIG. 1 with the addition of 100, the construction of the lubrication system is the same as that shown in FIG. 1.

[0021] The shaft contact seals 132 and 134 are made as brush seals as shown in the left-hand part and in the right hand part of the drawing. Shaft seals 136 separating the lubrication space LS of lubrication chamber 122 from buffer space BS of buffer case 128 may be made as the contact seals (as shown in left hand part of the drawing in FIG. 2). On the other hand, shaft seals 138 separating the lubrication space LS of the lubrication chamber 122 from the buffer space BS of the buffer case 128 may be made as labyrinth seals (as shown in the right hand part of the drawing in FIG. 2) or any other type of seal. Their main function is to minimize lubricant flow from lubrication space LS into buffer space BS.

[0022] It will be apparent from the above description that the invention prevents lubricant from escaping into the fluid space of a turbomachine or into the atmosphere without using complicated mechanical devices and control systems.

Claims

1. A bearing lubrication system for a turbomachine, said turbomachine having a fluid space and a shaft supported by bearings, said bearing lubrication system comprising: a lubrication chamber, said lubrication chamber having a lubrication space surrounding said bearings; a lubricant feeding means for supplying lubricant to said lubrication space; a lubricant removing means for removing lubricant from said lubrication space; a buffer case adapted to be located in said fluid space, said buffer case having a buffer space vented so as to have a substantially atmospheric pressure, said buffer case surrounding said lubrication chamber; a plurality of first shaft sealing means provided between said buffer case and said fluid space; and a plurality of second shaft sealing means provided between said buffer space and said lubrication space.

2. The bearing lubrication system of claim 1, wherein at least one of said plurality of first shaft sealing means comprises a contact seal.

3. The bearing lubrication system of claim 1, wherein at least one of said plurality of second shaft sealing means comprises a contact seal.

4. The bearing lubrication system of claim 2, wherein at least one of said plurality of second shaft sealing means comprises a contact seal.

5. The bearing lubrication system of claim 4, wherein at least one of said contact seals comprises a brush seal.

6. The bearing lubrication system of claim 1, wherein at least one of said plurality of second shaft sealing means comprises a labyrinth seal.