Power plants – Combustion products used as motive fluid – Process
Reexamination Certificate
2000-11-20
2003-02-11
Gartenberg, Chud (Department: 3746)
Power plants
Combustion products used as motive fluid
Process
C060S039080
Reexamination Certificate
active
06516618
ABSTRACT:
This invention relates to a gas-turbine engine which is provided in the turbine interior with a bearing chamber for a turbine shaft, the bearing chamber being sealed by sealing elements, and with a scavenge line for the lubricating oil which is supplied to the bearing chamber, in particular is sprayed onto the bearing(s) arranged therein. For background art, reference is made to Specification EP 0 127 563 B1, by way of example.
Various designs of bearing chambers for one or several shafts, in particular of an aircraft gas-turbine engine, are known in the prior art. Special measures are to be provided, in particular for the bearing chamber which is located on the hot turbine side of the engine, to preclude the bearing chamber lubricating oil from exiting into the turbine interior, this interior being filled with the relatively hot sealing air. Otherwise, the exiting lubricating oil could ignite in the turbine interior, in particular on the rotor disks of the turbine section of the gas-turbine engine carrying the turbine blades, thereby causing damage to these components. Therefore, a sealing-air system is usually provided on that side of each sealing element which faces away from the bearing chamber, this system consisting of a sealing-air chamber and a scavenge chamber. An airflow is supplied into the sealing-air chamber to create a pressure therein which is higher than the pressure in the adjacent scavenge chamber. The sealing airflow supplied to the sealing-air chamber as well as the sealing air supplied to the turbine interior are usually taken from a compressor stage of the compressor arranged upstream of the turbine section and the combustion chamber of the gas-turbine engine.
As is known (and as already mentioned), the bearing chambers of gas-turbine engines are continuously flown with lubricating oil, i.e. fresh or cooled lubricating oil is continuously sprayed onto the bearing(s) in the bearing chamber, this oil being thereafter scavenged from the bearing chamber and supplied to a lubricating-oil collecting compartment. Usually, several scavenge lines are provided for this purpose in the state of the art, these scavenge lines being connected to the mostly large-diameter annular bearing chamber in equal distribution about its circumference. The scavenge lines are routed from the bearing chamber through the turbine interior to an outside location, since the regeneration and the pumping of the oil for re-use can be accomplished at an outside location only. Due to this arrangement, the scavenge lines cross the flow pass of the engine, this pass carrying the hot working gas of the gas turbine burnt upstream in the engine combustion chamber.
If such a scavenge line broke in the area of this working-gas flow pass, hot working gas could theoretically enter the bearing chamber via this fracture, i.e. via the broken scavenge line. In the known state of the art, this situation is avoided by the pressure prevailing in the bearing chamber being set at least as high as the pressure prevailing in the flow pass in the area of crossing of the flow pass and the scavenge line, thereby ensuring that no positive pressure difference will be present between this section of the flow pass and the inner of the bearing chamber. This is achieved in that a small flow of air, upon being throttled at the said sealing elements, is continuously fed from the sealing-air chambers into the bearing chamber and in that orifices are provided in the scavenge line outside of the core of the gas-turbine engine.
The disadvantage of this design, however, lies in the fact that a relatively large sealing airflow is continuously required, i.e. sealing air must be taken from the compressor arranged upstream of the turbine section of the engine, this take-off impairing the overall efficiency of the gas-turbine engine. Moreover, the sealing-air systems with supply lines and vent ducts for the scavenge chambers entail a considerable construction effort.
In a broad aspect, the present invention provides a gas-turbine engine which is improved in the above respect in accordance with the generic part of claim
1
.
It is a particular object of this invention to provide this improvement by appropriately sizing the cross-section of the single scavenge line connected to a suitable lubricating oil-collecting compartment and by providing sealing elements with such a high sealing effect that the pressure in the bearing chamber is essentially equal to the pressure in the lubricating-oil collecting compartment and maximally half the pressure in the turbine interior. Further arrangements and enhancements of this invention are cited in the subclaims.
An essential characteristic of this invention is that the pressure or the absolute pressure, respectively, prevailing in the bearing chamber under normal operating conditions of the engine is considerably lower than the pressure in the turbine interior in which the bearing chamber is arranged. By selection of suitable sealing elements with high sealing effect in the area of passage of the turbine shaft through the bearing chamber wall, a pressure level in the magnitude of 1.5 bar can be set in the bearing chamber, this pressure level amounting to only a third of the pressure value in the surrounding turbine interior. This pressure difference will preclude the lubricating oil from exiting the bearing chamber upon failure of a sealing element. Accordingly, no additional measures must be provided to preclude the lubricating oil exiting the bearing chambers from getting onto the turbine disks in the interior of the turbine.
These advantages are also obtained, or the disadvantages mentioned further above avoided to a considerable extent, if the absolute pressure in the bearing chamber amounts to maximally half the pressure in the turbine interior.
Said pressure difference between the bearing chamber and the turbine interior is achieved by arranging sealing elements with appropriately large sealing effect between these areas, by appropriately sizing the scavenge line returning the lubricating oil from the bearing chamber to a lubricating-oil-collecting compartment and by furnishing this scavenge line with an appropriately sized orifice, providing with these features that the pressure in the bearing chamber has essentially the same amount as the pressure in the lubricating-oil collecting compartment. Moreover, in terms of an advantageous combination of functions, this lubricating-oil collecting compartment can be a conventional accessory gearbox which is arranged outside of the engine casing forming the outer wall of the working-gas duct of the engine and which provides the accessory drives.
However, the previous measures could incur the hazard of a bearing chamber fire already described if one of the several scavenge lines usually provided in the prior art should break in the turbine interior in the area of the working-gas flow pass, in which case the hot working gas would enter the broken scavenge line at the fracture and be forced into the bearing chamber by the pressure difference and finally be discharged through another, sound scavenge line. Such a flow of hot turbine working gas through the bearing chamber would inevitably give rise to a bearing chamber fire. To avert this hazard, the provision of only a single scavenge line is now proposed in accordance with the present invention.
If this single scavenge line should break (generally an unlikely event), the hot working gas would also enter the bearing chamber, but only until the pressure in the bearing chamber and the pressure in said turbine interior are equal. Subsequently, the working gas will flow from the flow pass via the fracture through the scavenge line in the direction of the lubricating-oil collecting compartment, cooling down on the way to such a degree that the lubricating oil in the lubricating-oil collecting compartment will not be ignited. While a fire of the lubricating oil discharged from the bearing chamber via the (broken) scavenge line cannot be avoided, this fire is considered relatively uncritical since it takes p
Gartenberg Chud
Rolls-Royce Deutschland Ltd & Co. KG
The Law Offices of Timothy J. Klima
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