Bearings – Rotary bearing – Fluid bearing
Reexamination Certificate
1999-11-10
2001-11-20
Bucci, David A. (Department: 3682)
Bearings
Rotary bearing
Fluid bearing
C384S118000, C384S120000
Reexamination Certificate
active
06318896
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to fluid film bearings and, more particularly, to an annular fluid film bearing formed by a stationary element and a rotating element that are concentrically mounted such that an annular clearance is defined between the elements for the flow of fluid therethrough.
BACKGROUND OF THE INVENTION
Rotating machines generally include bearings enabling the rotating portion of the machine to rotate relative to stationary portions of the machine without excessive frictional forces being exerted on the rotating portion. One class of bearings is characterized by rolling elements, such as balls or rollers, confined in a raceway defined between inner and outer ring-shaped races. The rotating portion of the machine is fixed to one of the races, and as it rotates about the axis defined by the bearing, the rolling elements roll along the surfaces of the races. In many rotating machines, bearings of this type are capable of providing relatively long bearing life and meeting the desired performance characteristics.
Fluid film bearings define another class of bearings. In a fluid film bearing, a film of fluid is disposed in a space defined between the rotating and stationary bearing elements. Thus, instead of rolling elements, fluid is used for supporting the rotating bearing element and preventing contact between the rotating bearing element and the stationary bearing element. Because there is no metal-to-metal contact within the bearing, galling and other types of physical degradation of the bearing caused by metal-metal contact are reduced or eliminated. Fluid film bearings in many cases can also offer improved damping compared to ball or roller bearings, and the damping characteristics can be tuned by suitable selection of the clearance between the rotating and stationary bearing components, surface finish of the bearing components, and other factors, in order to provide the desired performance characteristics. Thus, fluid film bearings can offer improved performance relative to conventional ball or roller bearings, especially for very high-speed machinery such as turbopumps or the like.
Annular fluid film bearings are used in some types of rotating machines. An annular bearing has a relatively small radial clearance between the rotating element and the stationary element, and hydrostatic pressure of the fluid within the clearance supports the rotating element in the radial direction and enables the rotating element to rotate. The fluid in the annular clearance provides stiffness and damping for the bearing. In some types of high-performance machines, the rotating component frequently must operate at a speed that is above the first and second shaft critical speeds. In order to avoid high vibrations when passing through the critical speeds, the rotating component, and therefore the bearings, should have a high degree of direct damping and stiffness and a low cross-coupled stiffness.
SUMMARY OF THE INVENTION
The present invention facilitates increased damping and stiffness and reduced cross-coupled stiffness in an annular fluid film bearing, by providing a diffuser and inlet flow guide for the bearing. The diffuser and flow guide increases the static pressure of the fluid entering the annular bearing, which has been found to improve the direct damping and stiffness of the bearing. The diffuser and flow guide also reduces the tangential velocity of the fluid entering the annular clearance of the bearing. It has been found that a high tangential velocity of the fluid within the annular bearing clearance causes a destabilizing drag force on the rotating element. By reducing the tangential velocity of the fluid, the diffuser and flow guide reduces the destabilizing force on the rotating element, thereby improving the dynamic stability of the bearing.
In accordance with a preferred embodiment of the invention, an annular bearing includes a rotatable element mounted for rotation about an axis of the bearing, and a stationary element mounted concentrically with the rotatable element and radially spaced therefrom such that an annular clearance is defined therebetween for the flow of fluid therethrough from an inlet end of the annular clearance to an outlet end thereof. The bearing also includes a diffuser and inlet flow guide proximate the inlet end of the annular clearance and mounted such that the rotatable element rotates relative to the diffuser and inlet flow guide. The diffuser and flow guide includes a plurality of vanes defining a plurality of flow passages spaced about a circumference of the diffuser and flow guide. The flow passages are operable to reduce the tangential velocity of the fluid flowing through the annular clearance and to diffuse the fluid so as to increase the static pressure of the fluid entering the annular clearance.
In accordance with a further preferred embodiment of the invention, the stationary element comprises a stator ring that surrounds the rotatable element and has an inner surface opposing the rotatable element, and the diffuser and inlet flow guide comprises a diffuser ring having an inner surface that opposes the rotatable element and is spaced therefrom by a radial clearance, the flow passages comprising slots formed in the inner surface of the diffuser ring. Preferably, the flow passages are configured to turn the fluid such that fluid exiting the diffuser ring is axial or has a tangential velocity component opposite to the rotation of the rotatable element.
Each flow passage advantageously has an entrance portion extending from an upstream end of the diffuser ring in a generally circumferential direction corresponding to the direction of rotation of the rotatable element, and a turning portion for turning the fluid such that the fluid leaving the diffuser ring and entering the bearing clearance is axial or has a tangential velocity component opposite to the direction of rotation of the rotatable element. Preferably, the turning portions of the flow passages are configured to turn the fluid such that the fluid exiting the diffuser ring is directed in a generally circumferential direction opposite to the rotation of the rotatable element. The entrance portion of each passage preferably is aligned with the direction of fluid flow at the upstream end of the diffuser ring. Generally, the fluid approaching the diffuser ring can vary from axial to highly tangential, and thus may have a flow angle of about 0° to 90° relative to the axial direction of the bearing. Accordingly, the entrance portion of each passage preferably defines a helix angle of about 0° to 90° (measured from the axial direction) such that fluid approaching the diffuser ring will be captured by and enter the entrance portion with minimal loss of total pressure. The exit portion preferably defines a helix angle of about 0° to −90° (where −90° denotes the direction opposite to rotation of the rotatable bearing element) such that fluid exiting the diffuser ring and entering the bearing clearance will enter the clearance in an axial direction or in a direction having a tangential component opposite to rotation, thereby reducing the tangential velocity of fluid within the clearance.
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Gulden Richard L.
Lunde Kevin Joseph
McVey Scott Elder
Meng Sen Yih
Alston & Bird LLP
Bucci David A.
Joyce William C
The Boeing Company
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