Abstract:
Gas journal bearing systems are provided. An exemplary gas journal bearing system comprises a vortex generator, a housing and a journal. The vortex generator is operative to receive a flow of gas and to impart an angular acceleration to the gas. The housing is in fluid communication with the vortex generator, with housing having a first exhaust through which the gas is exhausted. The journal is supported within the housing by a vortex of the gas as the gas swirls along at least a portion of a length of the journal. Methods and other systems also are provided.

Description:
GOVERNMENT INTEREST 
     The invention described herein may be manufactured, used, and licensed by or for the United States Government. 
    
    
     BACKGROUND 
     1. Technical Field 
     The invention generally relates to bearings. 
     2. Description of the Related Art 
     Generally, there are two types of bearings: 1) thrust bearings that support loads axially along their journals, and 2) journal bearings that support loads orthogonal to the journal axes. Of journal bearings, there are generally two types, namely, hydrodynamic journal bearings and gas journal bearings. 
     A prior art hydrodynamic journal bearing is depicted schematically in  FIG. 1 . As shown in  FIG. 1  (which is an end view), a journal bearing  10  includes a tube  12  filled with a lubricant  14 . The lubricant (e.g., oil) surrounds a rotating journal  16 . As the journal rotates (as indicated by arrow A), adhesion of the lubricant to the journal and the viscosity of the lubricant creates a wedge  18  of lubricant between the journal and the inner wall  20  of the tube. Wedge  18  supports the load on the journal and maintains separation between the journal and the inner wall. 
     The load-carrying capacity of the journal bearing  10  depends on the viscosity of the lubricant and the clearance between the journal and the inner wall. Higher viscosity lubricants provide higher load-carrying capacity (bearing stiffness), but the higher viscosity also causes resistance to journal rotation. 
     If a journal bearing, such as depicted in  FIG. 1 , operates in a high-speed and/or a high-temperature environment, the viscosity of the lubricant has a major impact on the performance of the bearing. Specifically, high-temperatures decrease the viscosity and the load-carrying capacity of the bearing. Also, high-speed journal rotation increases the turbulence and the oil temperature and decreases the oil viscosity. 
     Gas journal bearings (sometimes referred to as “air journal bearings”) are widely used, especially in high-speed and high-temperature applications. Air or inert gases are commonly used as the lubricant because of the extremely low viscosity and resistance to high temperatures. 
     Generally, there are two types of gas journal bearings: (1) aerodynamic (self actuating) gas journal bearings, and (2) externally pressurized gas journal bearings. An aerodynamic gas journal bearing creates a lubricating cushion of gas when the relative motion of two surfaces rams gas into the small space between them. In effect, these bearings create a “wedge” of gas with sufficient static pressure to support a load in the same manner that the hydrodynamic journal bearings create a wedge of oil. These bearings do not require an external source of gas but, due to the typically low viscosity of gas, require extremely close tolerances with small distances between the two surfaces. These bearings are typically used in small instruments, such as computer disk drives. 
     Externally pressurized gas journal bearings use gas from a compressor and/or a compressed gas tank source that forces gas into the space between the two surfaces to create a bearing. Thus, the wedge of gas is forcefully created independent of the relative motion between the two surfaces. Some externally pressurized gas journal bearings use the static pressure between two plates to form the bearing, while others create a dynamic pressure by directing a stream of gas at a high velocity orthogonal to a surface to form a bearing. Both techniques require a constant replenishment of the gas in the bearing to maintain the required pressure and bearing stiffness. Thus, complex channeling of the gas through porous material or directional inlets is typically required to create such bearings. 
     SUMMARY 
     Gas journal bearing systems and related methods are provided. An embodiment of a gas journal bearing system comprises a vortex generator, a housing, and a journal. The vortex generator is operative to receive a flow of gas and to impart an angular acceleration to the gas. The housing is in fluid communication with the vortex generator, with the housing having a first exhaust through which the gas is exhausted. The journal is supported within the housing by a vortex of the gas as the gas swirls along at least a portion of a length of the journal. 
     Another embodiment of a gas journal bearing system comprises a journal and means for generating a vortex of gas, such that the vortex of gas supports the journal. 
     An embodiment of a method for supporting a journal comprises: providing a journal and generating a vortex of gas such that the vortex of gas supports the journal. 
     Other systems, methods, features and/or advantages will be or may become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features and/or advantages be included within this description and be protected by the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The components in the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a schematic end view of a prior art hydrodynamic journal bearing. 
         FIG. 2  is a perspective view of an embodiment of a vortex tube gas journal bearing. 
         FIG. 3  is a schematic diagram of the vortex tube gas journal bearing of  FIG. 2 . 
         FIG. 4A  is a schematic diagram of the vortex tube gas journal bearing of  FIGS. 2 and 3 , viewed in the direction of section line  4 - 4  of  FIG. 3 , with the journal removed for clarity. 
         FIG.4B  is a schematic diagram depicting the pressure forces on the journal of the vortex tube gas journal bearing of  FIGS. 2-4A , viewed in the direction of section line  4 - 4  of  FIG. 3 , under a no-load condition. 
         FIG. 5  is a schematic diagram of another embodiment of a vortex tube gas journal bearing. 
         FIG.6  is a schematic diagram depicting the pressure forces on the journal of the vortex tube gas journal bearing of  FIG. 5 , viewed in the direction of section line  6 - 6  of  FIG. 5 , under a load condition (without drag). 
         FIG.7  is a schematic diagram depicting the pressure forces on the journal of the vortex tube gas journal bearing of  FIG. 5 , viewed in the direction of section line  6 - 6  of  FIG. 5 , under a load condition (with drag). 
         FIG. 8  is a schematic diagram of an embodiment of a vortex tube gas journal bearing with a pressurized gas source and nozzle. 
         FIG. 9  is a schematic diagram of an embodiment of a vortex tube gas journal bearing with dual vortex generators. 
         FIG. 10  is a schematic diagram of an embodiment of a vortex tube gas journal bearing in a spindle configuration. 
         FIG. 11  is a schematic diagram of an embodiment of a vortex tube gas journal bearing used in a hybrid thrust/journal bearing configuration. 
         FIG. 12  is a schematic diagram of an embodiment of a vortex tube gas journal bearing with dual, outside-mounted vortex generators. 
     
    
    
     DETAILED DESCRIPTION 
     Gas journal bearing systems are provided that involve the use of vortex tubes. As will be described in detail, such systems can provide load-compensating, high-stiffness, oil-free and/or omni-directional bearings that can be applied to a wide range of mechanical and industrial problems. 
       FIG. 2  is a perspective view of an embodiment of a vortex tube gas journal bearing. As shown in  FIG. 2 , vortex tube gas journal bearing  30  includes an inlet  32 , a vortex generator  34 , a housing  36 , a journal  38  and exhausts  40  and  42 . The inlet  32  allows gas (e.g. air) to enter the vortex generator  34 . From the vortex generator, the gas enters the housing  36 , which, in this embodiment, is a tube that is oriented perpendicular to the vortex generator  34 . At least a portion of journal  38  is located within the housing  36 . Journal  38  is supported by the gas provided to the housing by the vortex generator. The gas used to support the journal within the housing is discharged by the exhausts  40  and  42 . 
     In operation, a compressed gas source (not shown in  FIG. 2 ) injects gas through inlet  32  into vortex generator  34  in a direction generally perpendicular to the longitudinal axis  43  of the housing  36 . As shown in  FIG. 3 , the gas (generally depicted by arrows) enters the vortex generator  34  and is directed along a radius of curvature within the vortex generator that is longer than that of the housing  36 . Thus, as the gas is forced into the smaller radius of the housing, conservation of angular momentum increases the velocity of the gas and forms a vortex within the housing. The strength of the vortex can be changed by adjusting the velocity of the gas entering the generator. 
     The vortex of gas located in the housing surrounds the journal  38  and spirals along the length of the housing toward the exhausts  40 ,  42 . The pressure profile of the vortex provides support and stiffness to the journal  38 . Specifically, the well-known Bernoulli equation describes the pressure profile across the vortex within the housing. The journal, which preferably rotates counter to the rotation of the vortex, can be analogized to a cylinder embedded in a uniform flow. Therefore, the “Kutta-Joukowski Lift Theorem” and the “Magnus Effect” equations are applicable for subsonic vortices. 
     The vortex  44  located in the housing is shown in greater detail in the schematic, end view of  FIG. 4A  (the journal  38  being removed for clarity). As shown in  FIG. 4A , vortex  44  includes a vortex eye  45  that has a velocity of zero. Therefore, the static pressure at the vortex eye is relatively low. The velocity rapidly increases from zero at the eye edge  46  to a maximum, and then drops off to zero again at the boundary, i.e., at the inner wall  48  of the housing. The dynamic pressure of the vortex is proportional to the square of the velocity. Therefore, the velocity profile includes a ring  50  of relatively high dynamic pressure encircling the low static pressure within the vortex eye  45 . 
       FIG. 4B  depicts the pressure forces on a journal under no-load conditions. The housing  36  contains the vortex  44 , as depicted in  FIG. 4A , that surrounds the unloaded journal  38 . The pressure profile of the vortex creates a pressure field  52  (depicted by the inward-facing arrows) that is directed towards the eye of the vortex. The magnitude of the pressure field is highest where the velocity is the highest and, therefore, the pressure field exhibits its highest magnitude at ring  50 , as depicted in  FIG. 4A . 
     Under the no-load condition of  FIG. 4B  with the journal at the center of the housing, the pressure field created by the vortex is symmetrical. However, under a load (as will be described later), the journal is displaced at some distance away from the center in the direction of the load. The pressure field compensates for the displacement and becomes asymmetrical. 
       FIG. 5  is a schematic diagram of the embodiment of the vortex tube gas journal bearing of  FIGS. 2-4B , with journal  38  supporting a load  60  (indicated by downward arrows) and without drag. As shown in  FIG. 6 , load  60  displaces journal  38  from the center of the housing. As the journal crosses from the relatively low pressure area near the eye wall of the vortex toward the high-pressure ring surrounding the eye wall, pressure exerted on the underside of the journal increases. This increase in exerted pressure tends to re-center the journal. Specifically, the upward arrows indicate the resultant asymmetrical pressure field  62  that counters the load  60  and tends to re-center the journal  38  within housing  36 . Note that the asymmetry of the pressure field  62  not only creates a resisting force in direct opposition to the load, but the stiffness of the bearing increases. Thus, the bearing is not only load compensating, but resistant to load shocks as well. 
       FIG. 7  is a schematic diagram of the embodiment of the vortex tube gas journal bearing of  FIGS. 2-6 , with journal  38  supporting load  60  and with drag. Note that the vortex generator is removed for clarity. 
     Specifically, when journal  38  is displaced from the center of the housing  36 , the journal is subjected to a drag force  64  in the same direction as the vortex flow. This drag force tends to displace the journal at an angle θ from the load vector. As the journal is displaced, the vertical component  66  of the drag force resists the load  60  as well as the pressure field (not shown) created by the vortex. Thus, equilibrium should be reached with the journal being at a location other than the exact center of the housing. Note that the location of equilibrium tends to drift for a given vortex strength depending upon journal rotational speed, load, and drag. 
     As will be described next, embodiments of a vortex,tube journal air bearing can be provided in various configurations. For instance, the number and location of vortex generators, exhaust vents, and/or locations for accommodating loads can vary. 
     In this regard,  FIG. 8  is a schematic view of another embodiment of a vortex tube journal air bearing that includes a pressurized gas source. Specifically, bearing  70  uses a pressurized gas source  72  to provide a pressurized flow of gas to a nozzle  74 . The nozzle  74 , e.g., a Venturi-type nozzle, increases the velocity of the gas and provides the gas at a higher velocity to the vortex generator  78 . 
       FIG. 9  is a schematic view of another embodiment of a vortex tube journal air bearing that includes dual vortex generators. Specifically, bearing  80  includes vortex generators  82 ,  84  that support a journal  86 . The journal  86  extends through the housings  88 ,  90  of the bearing and, thus, provides multiple locations at which a load can be supported. In particular, locations  92 ,  94  and  96  can support loads, which are generally depicted as downwardly directed arrows (the upwardly directed arrows represent the resulting pressure field). 
       FIG. 10  is a schematic view of another embodiment of a vortex tube journal air bearing. Specifically, bearing  100  exhibits a spindle configuration and includes a vortex generator  102  and a journal  104 . In contrast to the housings of previous embodiments, housing  106  of bearing  100  includes only one open end  108  through which journal  104  extends. Note that a load located toward the end  110  of the journal creates a moment that tends to rotate the journal with respect to a longitudinal axis of the journal. The pressure field created within the housing tends to compensate for this rotation as described before. 
       FIG. 11  is a schematic view of another embodiment of a vortex tube journal air bearing. In particular, bearing  120  is configured as a hybrid thrust/journal bearing that includes a vortex generator  122 , a housing  124 , and a journal  126 . Unlike a journal bearing, a thrust bearing can support a load along the longitudinal axis of the journal. In this embodiment, the closed end  128  of the housing includes a packed bearing  130 , e.g., ball bearings, that surround an end  132  of the journal. The packed bearing  130  supports the end  132  of the journal and assists in maintaining the position of the end  132  of the journal in response to side loads and resulting moments. 
       FIG. 12  is a schematic view of another embodiment of a vortex tube journal air bearing. Specifically, bearing  140  includes vortex generators  142 ,  144  that support a journal  146 . The journal  146  extends between opposing open ends  148 ,  150  of the respective housings  152 ,  154  of the bearing. In this configuration, the bearing can accommodate a load at location  156 . 
     It should be emphasized that many variations and modifications may be made to the above-described embodiments. For instance, modifying the exterior surface of a journal, e.g., by incorporating grooves, dimples, ridges, and/or bumps, can alter the aerodynamic performance of a bearing. The journal shape can even be modified to look more like a camshaft or elliptical rather than circular in cross section. 
     All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.