Rotary shafts – gudgeons – housings – and flexible couplings for ro – Shafting – Hollow or layered shaft
Reexamination Certificate
1999-09-07
2001-05-22
Browne, Lynne H. (Department: 3629)
Rotary shafts, gudgeons, housings, and flexible couplings for ro
Shafting
Hollow or layered shaft
C464S179000
Reexamination Certificate
active
06234912
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to torque-carrying members. More particularly, this invention relates to a high-stiffness shaft for transmitting torque between large bearing spans at high rotational speeds and temperatures, such as a power turbine output shaft for a gas turbine engine.
BACKGROUND OF THE INVENTION
Shafts intended as torque-carrying members have been formed of metal matrix composite (MMC) materials. One example is a titanium composite shaft containing reinforcing fibers, such as silicon carbide or boron fibers. The shaft is fabricated by forming composite sheets of titanium foil and fibers using known consolidation processes, wrapping the resulting composite sheets around a mandrel, and then consolidating the sheets at high temperatures and pressures. While acceptable in many respects, this fabrication process does not easily lend itself to high volume production or allow uniform fiber distribution necessary to obtain the full benefit of the composite structure. Nor does the process enable the achievement of precise and repeatable material distribution and runouts required to balance the shaft. Accurate and repeatable balancing is an absolute requirement of particular concern for turbine output shafts of gas turbine engines. Finally, titanium matrix materials are generally not suitable for mechanical coupling features such as shaft splines, which necessitates separate fabrication steps during which an attachment with an appropriate coupling feature is brazed to one or both ends of the shaft. The separate fabrication steps are undesirable from the standpoint of production yields and processing costs.
Given the state of the art, it should be noted that composite materials offer a potential avenue to increase power output shaft stiffness, which is critical in terms of the dynamic performance of gas turbine engines. For example, higher shaft stiffness permits higher operational (turbine) speeds before critical speeds are reached, which allows for fewer turbomachinery stages and better turbine performance over larger bearing support spans. As a result, the stiffness of a turbine output shaft of a small gas turbine engine affects in one way or another the design of the compressor (e.g., axial or centrifugal), the number of turbine stages, type of rotor support bearings, bumper bearings on critical shafting, and bearing cooling and clearance control. A very high-stiffness output shaft can make possible significantly improved and lower-cost engine designs. However, shafts that exhibit greater stiffness and acceptable dynamic balance have been difficult to achieve.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a composite shaft whose construction and fabrication enable precise placement and orientation of reinforcement fibers, enable close control of runout, and eliminate a separate joining operation for attaching mechanical drive couplings.
According to this invention, the composite shaft includes fiber bundles disposed in each of a number of longitudinally-extending cavities in a spacing member. The shaft also has an outer portion that encases the fiber bundles in the spacing member. The outer portion may be an integral portion of the spacing member, such that the cavities are internal channels within the spacing member. Alternatively, the outer portion can be a tubular-shaped outer shell circumscribing the spacing member, in which case the cavities are external slots in a radially-outward surface of the spacing member. Finally, the shaft preferably includes an inner shell circumscribed by the spacing member, and extensions attached to both ends of the shaft and adapted as mechanical coupling features. At least the spacing member and fiber bundles are joined in a manner that defines a metal matrix surrounding and encasing the reinforcement fiber bundles, yielding a shaft whose mechanical properties can be modeled accurately by analysis because of the precise placement of the fiber bundles in the metal matrix.
In view of the above, it can be seen that a significant advantage of this invention is that the shaft can be fabricated to have a very stiff composite structure, particularly if titanium is employed as the main structural subcomponents, e.g., the inner shell, spacing member and outer portion of the shaft, to provide a titanium matrix in which reinforcement fiber bundles can be oriented in any desired manner within the cavities defined in the titanium matrix. In addition, using a reusable mold the shaft can be accurately produced from the subcomponents, which are prefabricated and then diffusion bonded together to achieve high dimensional precision and accurate placement of the fiber bundles. As a result, the present invention enables the manufacture of shafts that are more likely to have low levels of imbalance and can be readily balanced through material removal from balance lands. Another advantage of the invention is that expensive titanium powders and foils are no longer required.
Other objects and advantages of this invention will be better appreciated from the following detailed description.
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Fleck James N.
Koschier Angelo V.
Mauch Hagen R.
Browne Lynne H.
General Electric Company
Hess Andrew C.
Thompson Kenn
Young Rodney M.
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