Bearings – Rotary bearing – Antifriction bearing
Reexamination Certificate
1999-11-30
2001-12-04
Footland, Lenard A. (Department: 3682)
Bearings
Rotary bearing
Antifriction bearing
C384S624000
Reexamination Certificate
active
06325546
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to turbofan gas turbine engines and ore particularly to support systems for the fan assemblies of such engines.
A turbofan gas turbine engine used for powering an aircraft in flight typically includes, in serial flow communication, a fan assembly, a low pressure compressor or booster, a high pressure compressor, a combustor, a high pressure turbine, and a low pressure turbine. The combustor generates combustion gases that are channeled in succession to the high pressure turbine where they are expanded to drive the high pressure turbine, and then to the low pressure turbine where they are further expanded to drive the low pressure turbine. The high pressure turbine is drivingly connected to the high pressure compressor via a first rotor shaft, and the low pressure turbine is drivingly connected to both the fan assembly and the booster via a second rotor shaft.
The fan assembly includes a plurality of circumferentially spaced apart fan blades extending radially outwardly from a rotor disk that is drivingly connected to the low pressure shaft. Each fan blade generally has an airfoil section and an integral dovetail root section that attaches the blade to the rotor disk. The fan assembly is rotatively supported on a nonrotatable frame, commonly referred to as the fan frame, by a support system that typical includes a number of bearings and bearing support structure.
During engine operation, there is a remote possibility that a foreign body, such as a bird, could impact the fan assembly and cause part or all of a fan blade to become detached from the rotor disk. Such a blade loss would create a large imbalance, which could result in the transmission of potentially damaging imbalance forces to the fan frame. To alleviate the transmission of such imbalance forces, it is known to provide the support system with a decoupler, which is a frangible structure designed to fail in response to a predetermined load. Thus, in the event of a blade loss, the unbalanced rotation of the fan assembly will cause the decoupler to fail such what substantial imbalance forces are not transmitted to the fan frame. Accordingly, use of a decoupler effectively reduces the overall weight of the engine because the fan frame and related structure need not be made sufficiently strong to withstand substantial imbalance forces. This structural decoupling will also decrease the natural frequency of the fan assembly.
Although standard procedure is to quickly shut down the engine in the rare event of a blade loss, the fan assembly will continue to rotate due to windmilling caused by the forward motion of the engine. As the fan assembly slows down to the lower windmilling speed, “recoupling” of the fan assembly and the fan frame will occur through the contact load paths between the booster rotor blades and the booster stator and/or between the fan blades and the fan casing. Such recoupling will provide a new transmission path to the fan frame for the imbalance forces, resulting in undesirable engine and/or airframe vibration. This vibration can be particularly troublesome if the depressed natural frequency of the fan assembly is equal to or close to the windmilling speed because of the resulting resonant or slightly off-resonant operation.
Accordingly, there is a need for a fan assembly support system which reduces in-flight engine and airframe vibration at windmilling speeds after a fan blade loss induced structural decoupling of the fan rotor from its support system.
BRIEF SUMMARY OF THE INVENTION
The above-mentioned needs are met by the present invention which provides a support system for rotatively supporting a fan assembly on a fan frame. The support system includes primary and secondary bearing supports separately secured to the fan frame and a bearing disposed between the primary bearing support and the fan assembly. A damper assembly is disposed between the primary bearing support and the secondary bearing support to dissipate vibration energy and retune the natural frequency of the fan assembly to be above windmilling speeds. The damper assembly includes a journal formed on the primary bearing support and a bumper ring attached to the secondary bearing support in surrounding relationship with the journal.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.
REFERENCES:
patent: 4947639 (1990-08-01), Hibner et al.
patent: 5791789 (1998-08-01), Van Dutn et al.
J. M. Vance et al., “Experimental Evaluation of a Met-L-Flex Bearing Damper in a High Speed Test Rig ” Apr. 1997, Turbomachinery Laboratory, Texas A&M University, TRC-RD-5-97.
E.J. Gunter, “Rotor Bearing Stability,” Proceedings of the First Turbomachinery Symposium, Texas A&M University, Sep. 13, 1995, pp. 333-335.
Footland Lenard A.
General Electric Company
Herkamp Nathan D.
Hess Andrew C.
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