Patent Application
20170030404
The present disclosure relates generally to a foil bearing with a split key, and more specifically, to a thin foil, hydrodynamic gas bearing comprising a split key to eliminate a foil fatigue failure mode.
In general, thin foil, hydrostatic journal bearings are used to support a rotating element in rotating machinery such as air cycle machines. Historically, the predominant journal loading was assumed to be static, (due to gravity or acceleration) or synchronous (1 time per shaft rotation); however, recent experience has shown that there are environments that impose a non-synchronous, high-cycle load on the thin foil, hydrostatic journal bearings. The journal bearing is comprised of several elements: top and intermediate foils are formed from a single-piece, double wrap cylindrical foil supported by a corrugated bump foil. When subjected to high levels of nonsynchronous loading, the formed key (anti-rotation) integral to the top/intermediate foil cracks (and in some cases separates). The crack initiates at a tight radius at a bottom of the formed key. The cracking is in part due to the geometry of the tight radius, which is an inherently high stress riser. Further, a forming operation necessary to fold the foil into a 180° bend exceeds an ultimate elongation of the foil itself, which leads to an orange peel condition and a degradation in the material fatigue strength.
Embodiments include a gas bearing within a cylinder. The gas bearing comprises an anti-rotation tab comprising a first side and a second side, the anti-rotation tab sitting within a key way of the cylinder. Further, the gas bearing also comprises a first foil extending in a first direction from a first end to the first side of the anti-rotation tab and a second foil extending in a second direction from a second end to the second side of the anti-rotation tab.
Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein. For a better understanding of the disclosure with the advantages and the features, refer to the description and to the drawings.
The subject matter that is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
Embodiments described herein relate to a foil bearing with a split key, and more specifically, to a thin foil, hydrodynamic gas bearing comprising a split key to reduce or eliminate a non-synchronous or reverse on the thin foil, hydrodynamic gas bearing. An example application of the foil bearing is employing the foil bearing in an air cycle machine in an aerospace environment.
Turning now to
In general, the thin foil, hydrodynamic gas 120 can be a component of rotating machinery such as an air cycle machine that sits within the cylinder 110 supporting a rotating shaft. The thin foil, hydrodynamic gas bearing comprises a foil and an air film. The foil is a static portion of the thin foil, hydrodynamic gas bearing 120 that does not rotate and sits within a key way. The air film supports the rotating shaft (i.e., the rotating shaft rides on the air film).
Further, the foil is positioned via a key within the cylinder with respect to the key way (e.g., a thin sleeve, slot, or grove down the length of the cylinder). The intersection of the key and the key way prevents the foils from rotating, moving, sliding, etc. Embodiments of this intersection will be shown with respect to
In view of the load issues with the double wrap foil 220,
The trailing edge key 320D is an anti-rotation tab that sits within the key way 225 and can float to either side of the keyway 225. The trailing edge key 320D has a large radius 320E (i.e., in contrast to the 180° bend of the key 220C) that significantly reduces or eliminates stress riser associated with the key 220C. The trailing edge key 320D can be formed without exceeding ultimate elongation of the foil 320. Thus, the trailing edge key 320D eliminates the 180° bend of the double wrap foil 220 (e.g., replaces it with key on the trailing edge of the second loop or intermediate foil).
Turning now to
The first foil 420 extends from a first end 420A in a counter clockwise fashion to form a first loop within the inner surface 110A. The first loop concludes at an intermediate portion 420B before turning into the key way 225 and forming a first side 400A of the split key 400.
The second foil 430 extends from a second end 430A in a clockwise fashion to form a second loop between the inner surface 110A and the first foil 420. The second loop concludes by turning into the key way 225 and forming a second side 400B of the split key 400.
The second side 400B of the split key 400 abuts a side of the key way 225 opposite of the corrugated foil 230A, while the first side 400A of the split key 400 resides between the second side 400B and the corrugated foil 230A.
The first foil 420 and a second foil 430 eliminate the double wrap foil 220; thereby replacing the key 220C formed via the 180° bend with the first and second sides 400A, 400B of the split key 400. That is, the single anti-rotation tab (and its 180° bend) is replaced with two separate tabs for the now separate top foil and intermediate foil. Both of the first and second sides 400A, 400B are formed with large radii 420C, 430C, which have a lower stress riser than the tight 180° bend of the double wrap foil 220. Additionally, the larger radius of each tab can be formed with exceeding the foil ultimate strength and suffering the associated degradation in material fatigue strength.
The technical effects and benefits of embodiments of the present invention include creating a foil bearing that is tolerant of non-synchronous or reverse loading and further that comprises a measurably high load capacity. This foil bearing can be utilized in applications with either a high external vibration environment (such as helicopters or engine mounted equipment) or with equipment that experience intermittent reverse rotation (such as permanent magnet electric motors).
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one more other features, integers, steps, operations, element components, and/or groups thereof.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention.
Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
