Abstract:
A bearing system includes a lubricant circulation apparatus to provide a continuous supply of a cooled lubricant fluid to a bearing device. The bearing device may be a hydrodynamic sleeve bearing having a bearing housing defining a sump for maintaining lubricant fluid therein. The bearing sump is in fluid communication with a reservoir which maintains a supply of lubricant. A pump communicates with the reservoir to draw a desired quantity of lubricant fluid therefrom and deliver it to a heat exchanger. The heat exchanger uses an existing source of air from an operative pump motor to increase the air circulation through the cooling fins of the heat exchanger. The cooled lubricant is thereafter delivered to the bearing inlet and provides a cooler operating environment for the bearing system.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to the art of lubricant circulation systems used to provide a continuous supply of lubricant fluid to hydrodynamic sleeve bearings. 
     Hydrodynamic sleeve bearings are configured so that the shaft rides upon a thin film of lubricant fluid such as a petroleum-based or synthetic oil. In such bearings, the shaft extends through a sleeve material. Further, the bearing typically includes an oil ring to supply the lubricant fluid from a sump defined in the bearing housing to the top of the shaft. 
     As set forth in U.S. Pat. No. 5,733,048, which is commonly assigned to the applicant and which is incorporated herein by reference, an apparatus and process is provided to supplement the lubrication provided by the oil ring. To accomplish this, a reservoir is provided which is in fluid communication with a bearing outlet such that the lubricant fluid will flow from the sump to the reservoir. The reservoir is configured to maintain therein a predetermined quantity of lubricant fluid. A pump having a pump inlet and a pump outlet provides fluid communication with the reservoir. A pump communicates with the reservoir to draw the lubricant fluid therefrom and deliver it to the bearing inlet. The pump mechanism is regulated such that any excess lubricant flow from the pump is directed back to the reservoir. A filter is used to remove impurities from the lubricant fluid prior to delivery to the bearing housing. 
     The lubricant circulation apparatus referenced above improves the quality of the lubricant fluid and provides a reliable mechanism for maintaining an appropriate level of oil within the hydrodynamic sleeve bearing sump. However, there remains room for improvement and variation within the art. 
     SUMMARY OF THE INVENTION 
     The present invention recognizes and addresses that the foregoing prior art constructions and methods may be varied. Accordingly, it is an object of the present invention to provide an improved lubrication apparatus and process for facilitating the rotation of a mechanical shaft as may be associated with oil film sleeve bearings, hydrodynamic bearings, rolling element bearings, and gear reducers. 
     It is a further object of the present invention to provide an improved bearing system which continually supplies a cooled lubricant fluid to a bearing device. 
     It is a more particular object of the present invention to provide a lubricant fluid cooling apparatus and process which uses an existing flow of air to provide cooling of the lubricant. 
     Some of these objects are achieved by a bearing system for facilitating rotation of a mechanical shaft. The bearing housing defines a sump for maintaining a lubricant fluid therein. A bearing inlet and a bearing outlet are also defined in the housing permitting flow of lubricant fluid through the bearing housing at a predetermined flow rate. A reservoir is in fluid communication with the bearing outlet such that the lubricant fluid will flow from the sump to the reservoir. The reservoir is in further fluid communication with a heat exchanger via a pump. The heat exchanger is operatively disposed within the pathway of a cooling fan associated with a reservoir pump. 
     Other objects of the invention are achieved by a method of providing a cooled lubricant fluid to a hydrodynamic sleeve bearing. The method involves the steps of draining a defined amount of a lubricant fluid from the sump into a reservoir. Lubricant fluid is then removed by the pump from the reservoir and is passed through a filter for removing contaminants. The filtered lubricant fluid is then introduced into a heat exchanger, such as a fan-assisted radiator cooling apparatus. As the heated lubricant enters the heat exchanger at a first temperature, a flow of cooler air is passed over the heat exchange fins, thereby cooling the lubricant to a lower discharge temperature. The now cooled lubricant is then supplied via the pump pressure to a location radially above a shaft supported by the bearing such that the cooled lubricant fluid is deposited on top of the shaft. The movement of air used with the heat exchanger is supplied by the airflow created by cooling fan of the lubricant circulation pump. The introduction of a cooled lubricant extends the operating life of the lubricated components as well as extends the service interval of the lubricant fluid. 
     These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A full and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying drawings. 
     FIG. 1 is a perspective representation of a bearing lubrication system constructed in accordance with the present invention; 
     FIG. 2 is a perspective view of the air receiving element associated with the lubricant cooling system as seen in FIG. 1; 
     FIG. 3 is a perspective view of the air discharge surface of the lubricant fluid cooling apparatus seen in FIG. 1; 
     FIG. 4 is a diagrammatic representation illustrating the connection of a lubrication circulation conduit to the bearing housing of a lubrication system as seen in FIG. 1; and 
     FIG. 5 is a diagrammatic representation illustrating the connection of the lubrication circulation conduits to the heat exchanger and as utilized in the lubrication system of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference now will be made in detail to preferred embodiments of the invention, one or more examples of which are set forth below. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. Other objects, features, and aspects of the present invention are disclosed in, or are obvious from, the following detailed description. It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary constructions. 
     As used herein, the terms “cool” or “cooling” are used in a relative sense and in reference to the operative temperature of a fluid lubricant sump supply or reservoir supply as may be employed by oil film sleeve bearings, hydrodynamic bearings, rolling element bearings, or a gear reducer. As such, a fluid stream, even when having a temperature greater than that of the ambient environment, may be referred to as “cool” or “cooling” when the fluid stream is used to remove heat from a fluid lubricant. 
     FIG. 1 illustrates a hydrodynamic sleeve bearing lubrication system indicated generally at  10  which operatively supports a mechanical shaft  12 . Bearing  10  includes a bearing housing  14  defining a sump for maintaining a lubricant fluid such as a petroleum-based or synthetic oil therein. As is well known and as best seen in reference to U.S. Pat. No. 5,733,048 referenced above, shaft  12  extends through a supporting sleeve structure maintained within housing  14 . 
     As seen in FIG. 4, an oil ring  22  extends about shaft  12  into lubricant  16  maintained in the sump. Oil ring  22  will tend to lift oil  16  from the sump and deposit it on the top of shaft  12  as shaft  12  rotates. As a result, a supply of oil is directed from the sump to the bearing sleeve to maintain a desired oil film thereon. A lubricant circulation apparatus  24  includes fluid conduits  26  and  28  in respective fluid communication with a bearing inlet and a bearing outlet defined in housing  14  of bearing  10 . The bearing inlet is preferably situated at a location readily above shaft  12  such that the lubricant field is deposited on top of shaft  12 . The bearing outlet, in contrast, is preferably situated at a location below shaft  12  at approximately the desired level at which accumulated oil is to be maintained in the sump. 
     As best seen in reference to FIGS. 1-3 and  5 , the various functional components of a lubrication circulation apparatus  24  will be described. Apparatus  24  includes a reservoir  30  for maintaining a quantity of oil  16  therein. Reservoir  30  is preferably situated at a location below bearing  10  so that oil may return by gravity from the bearing sump. As is conventional within the art, reservoir  30  may include a sight gauge  39  or other fluid level indications, such as a dip stick, to allow an indication of the fluid level therein. 
     A pump  40  is located within a pump housing  42 . Pump  40  comprises a gear pump or other suitable pump mechanism. In one embodiment of the invention, pump mechanism  40  is driven by drive motor  44  such as a suitable electric fan-cooled motor via conventional couplings. Pump  42  defines a pump inlet connected to conduit  28  and a pump outlet connected to conduit  126 . A terminal box  48  is provided to contain the electrical contacts and the like through which the electrical energy is provided to motor  44 . 
     Apparatus  24  may further include a pressure gauge  50  of conventional design and operation which indicates the pressure in conduit  126 . A filter  52  is provided to remove impurities in the oil passing through conduit  126 . As seen, filter  52  may be of a cylindrical hydraulic filter having a suitable thread mount  54 . However, other conventional and well known types of filters may be used based upon the requirements of any particular application. 
     Pump mechanism  40  draws oil from reservoir  30  at a known rate of flow. For instance, a flow rate within the range of approximately 0.5 to 1.0 gpm has been found useful, and pumps having such outputs are commercially known and available. 
     As pump  40  withdraws oil from reservoir  30 , a selected quantity of the oil is passed through filter  52 , and excess oil may be returned to the reservoir through a conduit (not pictured), or as described in U.S. Pat. No. 5,773,048 referenced above. Upon  15  exiting the filter, the oil is directed through conduit  126  to an intake  70  of heat exchanger  72 . The heat exchanger  72  defines a housing  74 . A receiving end of the housing  74  defines a substantially circular collar  76  which engages the fan cooled motor housing. As best seen in FIG. 3, conduit  126  is operatively disposed within the heat exchanger  72  and repeatedly traverses the width of exchanger  72  via a series of 180 degree bends  128  defined by portions of conduit  126 . Conduit  126 , preferably provided from copper tubing, is in intimate thermal contact with a plurality of cooling fins  80 . Each cooling fin  80  comprises a thin sheet of metal having a thickness of about 0.025 inches. The fins  80  are preferably selected from metals, such as aluminum, having high thermal conducting properties. A gap of about 0.07 inches is defined between adjacent fins and allows for the passage of air between the fins. 
     The transfer of heat from the conduit  126  via fins  80  is increased by the passage of an airstream across the heat exchanger  72 . Preferably, the airstream is provided by the cooling fan associated with the electric motor of pump  40 . The fan generated air stream pulls air from the receiving face  77  of heat exchanger  72 . The air flow, indicated by the solid arrows in FIG. 5, passes through the defined gaps between fins  80  before exiting the discharge face  75  of heat exchanger  72 . The now cooled lubricant fluid exits an upper side of heat exchanger  72  along conduit  26 . Conduit  26  is connected to the associated sleeve bearing as seen in FIG. 1, thereby permitting the introduction of cooled lubricant as best seen in FIG.  4 . 
     The cooling air stream typically exhibits a 10° F. temperature increase over the temperature of the ambient air entering the heat exchanger  70 . It has ben found that the airflow, though slightly heated, will cool the motor  44  without adverse effects. It is also envisioned that the direction of the airflow through the heat exchanger may be reversed as indicated by the dashed arrows in FIG.  5 . For instance, where the cooling fan associated with motor  44  is used to pull air past the motor, the “exhaust” air may be further directed to pass through the heat exchanger, albeit in a reverse flow path. While the fan exhaust air stream is warmed slightly by the motor, the resulting air stream is nonetheless cooler than the temperature of the lubricant fluid circulated within the heat exchanger, and thereby serves to lower the temperature of the lubricant fluid. 
     For instance, a typical hydraulic sleeve bearing system as illustrated in FIG. 1 may achieve a 20-30° F. drop in lubricant fluid temperature compared to the identical system operated without the heat exchange element. It has been found that the temperature of the oil introduced into the bearing sleeve operated at about 2000 RPM may be reduced from an original temperature range of 150-180° F. to a lower temperature range of between 130-150° F. The reduction is carried out using the existing electric fan air flow to increase the efficiency of the heat exchanger. In this manner, an existing air stream is used to provide a cooling airflow across the heat exchanger. However, it is envisioned within the scope of the present invention that a different or separate airflow supply may be used. 
     It is appreciated by one having ordinary skill in the art that the rate of heat exchange is influenced by many factors, some of which may be varied to advantage. For instance, all else being equal, higher shaft speeds will result in a higher initial temperature of the lubricant fluid. As a result, a larger value temperature drop would result from the operation of the heat exchange system described above. Likewise, the size and thermal transfer properties of the heat exchanger may be modified so as to achieve a desired level of cooling as evaluated by the endpoint temperature of the cooled lubricant reintroduced into the bearing shaft. 
     It is also recognized that the reservoir walls could be constructed of selected material and shapes so as to increase the heat exchange capabilities of the lubricant fluid which resides within the reservoir. Likewise, the materials and lengths of the lubricant fluid conduits may also be varied so as to affect the heat transfer rate as may the lubricant fluid flow rate and volume which is passed through the heat exchanger. It is also appreciated that the lubricant fluid, especially a synthetic or petroleum based oil, is designed to operate at a desired temperature range and viscosity. A lubricant temperature which is too high (inefficient cooling) or too low (excessive cooling) may adversely alter the desired viscosity of the lubricant. 
     The illustrated embodiment makes economical use of an existing pump pressure and air flow to achieve a favorable decrease in fluid lubricant temperature. The temperature drop is obtained using an air supply which provides cooling capabilities for both the heat exchanger and the associated pump motor. Further, the temperature differential between the oil within the heat exchanger and the temperature of available air streams are such that a reverse flow direction which makes use of slightly heated fan exhaust is operative with the present apparatus and method. 
     The resulting temperature drop increases the operating life of the sleeve bearing. Further, the service life and quality of the oil lubricant is also increased. The present method may be adapted for the use of other types of heat exchangers. Such heat exchangers may include water cooled jackets, radiators, and/or the inclusion of oil turbulators within the heat exchange system. 
     Although a preferred embodiment of the invention have been described using specific terms, devices, and methods, such description is for illustrative purposes only. The words used are words of description rather than of limitation. It is to be understood that changes and variations may be made by those of ordinary skill in the art without departing from the spirit or the scope of the present invention, which is set forth in the following claims. In addition, it should be understood that aspects of the various embodiments may be interchanged, both in whole or in part. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained therein.