Abstract:
A gas bearing system for use in a turbocompressor or similar device that embodies a uniquely configured thrust washer or disk that exhibits superior strength characteristics when the disk is rotated at high speed. The thrust washer is a generally circular-shaped disk, has a predetermined diameter and comprises a body portion having spaced apart faces and a generally “V” shaped groove formed intermediate the spaced-apart faces to define a pair of radially outwardly extending segments.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to gas bearing turbocompressors. More particularly, the invention concerns turbocompressors embodying a novel, uniquely configured thrust washer in which centrifugal stresses are significantly reduced. 
     2. Discussion of the Prior Art 
     Turbocompressors have been in use as turbochargers for internal combustion engines for many years. These types of turbocompressors have generally embodied oil-lubricated bearings. The trend in recent years in turbocompressor design has been towards higher compression ratios requiring higher revolutions per minute (RPM) of the spindle of the turbocompressor and resulting in higher exhaust temperatures. Under such conditions, oil lubrication of the bearings becomes inadequate and can possibly result in cavitation in the bearings as a result of the higher rubbing speed, and in thermal decomposition as a consequence of the higher temperatures. A solution to the aforementioned problems is provided by the use of gas bearings such as the bearings disclosed in U.S. Pat. No. 4,808,070 issued to the present inventor. The novel gas bearings disclosed in U.S. Pat. No. 4,808,070 can easily handle the required RPM and rubbing speeds of most types of modem turbo compressors. 
     Another application of oil free bearings is in the air feed of fuel cells which are poisoned by oil vapor. 
     In a typical turbocharger the compressor is fed through a filter that causes a significant pressure drop at the inlet to the compressor resulting in an inlet pressure lower than the atmosphere. On the other hand, the conventional turbine discharges to atmosphere through a muffler or catalytic converter also causing a pressure drop which results in a pressure higher than atmosphere at the exhaust of the turbine. The resulting pressure difference between the compressor housing and the turbine housing causes a net thrust to develop in the shaft connecting the compressor wheel and the turbine wheel. In an oil-lubricated turbocharger this thrust is absorbed by a traditional oil-lubricated thrust washer. However, in the case of gas bearings the thrust is typically compensated by the arrangement described in U.S. Pat. No. 5,567,129 issued to the present inventor. Because of the relevance of the U.S. Pat. Nos. 4,808,070 and 5,567,129 to a complete understanding of the present invention, both of these patents are hereby incorporated by reference as though fully set forth herein. 
     U.S. Pat. No. 6,231,302 entitled Thermal Control System for Gas Bearing turbocompressor, also issued to the present inventor is directed toward solving the problems caused by large temperature differences between the ends of the turbocompressor. This latter patent, U.S. Pat. No. 6,231,302, is also incorporated by reference as though fully set forth herein. 
     An important component of the turbocompressor disclosed in U.S. Pat. No. 6,231,302 is the thrust washer (therein described as “third wheel”) which is there provided in the form of a thin disk that is mounted on a rotating shaft. The thrust washer of necessity is provided with a hole in the center that is needed for the physical assembly of the turbocompressor. It is, of course, fundamental that the central hole weakens the disk against stresses generated by centrifugal forces when the disk is spinning at high speed. Such stresses increase with the diameter of the disk as well as the square of the angular speed and may exceed the strength of the material resulting in the destruction of the disk if either diameter or angular speed exceed a limiting value. Since the angular speed is predetermined by gas dynamic requirements of the turbine and compressor wheels, the diameter is limited by the strength of the material. However, the diameter is desired to be as large as possible because the aerodynamic stiffness of the thrust bearing is proportional to the square of the diameter. 
     One objective of the present invention is the reduction of the centrifugal stresses in the apertured disk so as to allow an increase in the diameter of the disk and consequently an increase in the aerodynamic stiffness of the bearing. Another object of the invention is to accomplish the reduction of the centrifugal stresses while retaining the flatness and parallelism of the faces of the disk so as to maintain the gas dynamic performance of the thrust bearings. Still another object is to reduce the stresses at the center hole of the disk by removing existing stress concentrations resulting from auxiliary openings in the disk such as those found in the prior art. 
     It is well known that the stressing a spinning wheel or disk is largest at the edges of a central hole, and that this stress can be substantially decreased by tapering the axial thickness of the wheel from a maximum near the center to a minimum at the edge. 
     It is also well known that holes in a plate under stress double the tangential stress at the edge of the hole and thereby act as stress concentrators. Since the design of the high temperature thrust bearing requires communication of gas from one face to the other, the apertures  179  provided in the disk  162  as shown in FIG. 3 of U.S. Pat. No. 6,231,302 are such stress concentrators. In the manner to be described hereinafter, this stress can be reduced by transferring the openings from the disk to the rotating shaft. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an improved gas bearing system for use in a turbocompressor or similar device, such as that disclosed in incorporated by reference U.S. Pat. No. 6,231,302 which embodies a uniquely configured thrust washer or disk that exhibits superior strength characteristics when the disk is rotated at high speed. More particularly, it is an object of the invention to provide such a thrust washer in which the stresses found at the edges of the central hole in the disk are substantially decreased by tapering the axial thickness of the disk from a maximum near the center of the disk to a minimum proximate the edge of the disk. 
     Another object of the invention is to accomplish a reduction in the centrifugal stresses in the thrust washer so as to allow an increase in the diameter of the disk and consequently an increase in the aerodynamic stiffness of the bearing. 
     Another object of the invention is to accomplish a reduction in the centrifugal stresses while retaining the flatness and parallelism of the faces of the disk so as to retain the gas dynamic performance of the thrust bearings. 
     Another object of the invention is to provide a thrust washer as described in the preceding paragraphs which is generally circular shaped disk, has a predetermined diameter and comprises a body portion having spaced apart faces and a groove formed intermediate the spaced apart faces to define a pair of radially outwardly extending segments. 
     Another object of the invention is to provide a thrust washer as described in the preceding paragraph in which the groove formed intermediate the spaced apart faces has sloping sidewalls and has a depth generally greater than one-half the radius of the thrust washer. 
     These and other objects are realized by the turbocompressor described in the paragraphs that follow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic, side elevation, cross-sectional view of a prior art, gas bearing turbocompressor apparatus of the character disclosed in U.S. Pat. No. 6,231,302. 
     FIG. 2 is a diagrammatic, side elevation, cross-sectional view of one form of the gas bearing turbocompressor apparatus of the present invention showing the novel thrust washer of the invention installed there within. 
     FIG. 3 is a fragmentary, side-elevational, cross-sectional view showing in greater detail the novel thrust washer of the invention and the modified shaft upon which the disk is mounted. 
     FIG. 4 is a cross-sectional view taken along lines  4 — 4  of FIG.  3 . 
     FIG. 4A is a cross-sectional view similar to FIG. 4 illustrating the flow path of the gases through an alternate construction of the apparatus. 
     FIG. 5 is a cross-sectional view taken along lines  5 — 5  of FIG.  3 . 
     FIG. 6 is a generally perspective, exploded view of the thrust washer and shaft shown in FIG.  3 . 
     FIG. 7 is a fragmentary, generally perspective rear view of the connector hub shown in FIG.  6 . 
    
    
     DESCRIPTION OF THE INVENTION 
     Referring to the drawings and particularly to FIG. 1, a prior art turbocompressor of the character disclosed in incorporated by reference U.S. Pat. No. 6,231,302 is there shown. This turbocompressor is similar in many respects to the turbocompressor of the present invention and like numbers are used in the drawings of the turbocompressor of the present invention to identify like components. 
     As shown in FIG. 1 of the drawings, the apparatus of the present invention comprises a support  50  and an elongated, generally cylindrical shaft  56 , which is rotatable within the bore of support  50 , has first and second ends and an intermediate portion that is disposed between the first and second ends. Shaft  56 , which is of a predetermined diameter less than the diameter of the bore also has a longitudinally extending bore there through, and includes an outer surface provided with a plurality of circumferentially spaced, longitudinally extending grooves  63  and a plurality of recessed areas C of predetermined depth; 
     A first closure member  65  is connected to support  50  to define a first chamber  65   a . A first wheel  24  is disposed within first chamber  65   a  and is connected to the first end of shaft  56  for rotation therewith. 
     A second closure member  67  is also connected to support  50  to define a second chamber. A second wheel  22  is disposed within the second chamber and is connected to second end of shaft  56  for rotation therewith. A third wheel or disk (“Thrust washer”)  162  having a central opening  162   a  is received over shaft  56  and is disposed within an intermediate chamber  163 . As is discussed in the &#39;302 patent, equalizing means are provided for substantially equalizing axial forces upon rotation of the shaft so that the shaft will remain substantially axially centered within the bore. 
     In operating the turbocompressor shown in FIG. 1 seal gas is admitted through a single gas inlet  100 . The gas then flows through a circumferential groove  102  in the housing  50  and is delivered via longitudinal grooves  63  to a circumferential groove  56   b  formed in the shaft. Next the gas flows to gaps  174  and  175  of the third thrust bearing and finally out to a volume  173 . The second thrust bearing receives seal gas through openings  179  formed in disk  162  in the proximity of shaft  56 , forming a direct channel of communication between circumferential grooves  56   a  and  56   b . From groove  56   a  the gas then proceeds through gaps  181   a  and  182  to collecting volume  173 . 
     With the novel constructions described in the preceding paragraph, the apparatus can function in the same manner as described in the &#39;302 patent without having to provide openings in the wheel such as openings  179 . 
     As is also shown in FIG. 1, a third gas supply means or third gas inlet  187  is provided in or near the axis of support member  67 . This third gas inlet is interconnected with a circumferential groove  189  located in the middle of labyrinth  191 , and is provided with teeth  193  on either side. 
     Reference should be made to U.S. Pat. No. 6,231,302 for a more detailed explanation of the construction and operation of the turbo compressor illustrated in FIG.  1 . 
     Turning next to FIGS. 2 through 8 one form of the improved turbo compressor of the present invention is there illustrated. This turbo compressor is similar in many respects to that shown in FIG.  1  and like numerals are used in Figures  2  through  8  to identify like components. As previously mentioned, the primary differences between the turbo compressor of this invention and that shown in FIG. 1 include a differently constructed shaft and the provision of an intermediately located thrust washer of unique construction. 
     Referring particularly to FIG. 2 the improved turbo compressor of the present invention can be seen to comprise a support  250  that is disposed within a fluid atmosphere and includes longitudinally spaced first, second, faces F- 1  and F- 2 . Support  250  also has a longitudinally extending bore  252   a  that is generally circular in cross section at any point and defines an inner surface  251 . Each of the third and fourth faces of support  250  have a recess provided therein which is concentric with bore  252   a  and is in fluid communication therewith. 
     An elongated, generally cylindrical shaft  256 , which is rotatable within bore  242   a  of support  250  has a first portion  256   a  and a second, reduced diameter portion  256   b . Reduced diameter portion  256   b  is provided with a plurality of flow passages  259  that communicate with grooves  257  provided in shaft  256  that feed gas to recessed areas C of shaft  256  (see also FIGS. 4,  5 , and  6 ). Shaft  256 , which is of a predetermined diameter less than the diameter of bore  252   a , also has a longitudinally extending central bore  225  there through. 
     A first closure member  65 , which is identical to closure member  65  of the &#39;302 patent, defines a first chamber  65   a . A first wheel  24 , which is also identical to wheel  24  of the &#39;302 patent, is disposed within first chamber  65   a  and is connected to shaft  256  for rotation therewith. 
     A second closure member  267  is also connected to support  250  to define a second chamber  290 . A second wheel  262  is disposed within second chamber  290  and, in a manner presently to be described, is connected to reduced diameter portion  256   b  of said shaft  256  for rotation therewith. A third wheel or disk  263 , functioning a thrust washer, has a central opening “CO” that is received over reduced diameter portion  256   b  of said shaft. 
     It should be noted that the opening in third wheel  162  (FIG. 1) and the opening  263   a  in disk  263  (FIG. 2) are needed for the physical assembly of the respective turbocompressors even though the openings play no part in the principles of operation of the thrust bearing. 
     As previously mentioned, the central opening as well as the openings  179  in wheel  162  weaken the disk against stresses generated by centrifugal forces when the disk is spinning at high speed. Such stresses increase with the diameter of the disk as well as the square of the angular speed, and may exceed the strength of the material resulting in the destruction of the disk if either diameter or angular speed exceed a limiting value. Since the angular speed is predetermined by gas dynamic requirements of the turbine and compressor wheels, the diameter is limited by the strength of the material. However, the diameter is desired to be as large as possible, because the aerodynamic stiffness of the thrust bearing is proportional to the square of the diameter. In light of the foregoing, a primary objective of the present invention is the reduction of the centrifugal stresses in the disk so as to allow an increase in the diameter of the disk and consequently an increase in the aerodynamic stiffness of the bearing. A further objective of the invention is to accomplish the reduction of centrifugal stresses while at the same time retaining the flatness and parallelism of the faces of the disk so as to maintain the gas dynamic performance of the thrust bearings. Still another important objective of the present invention is to reduce the stresses in the disk by removing the stress concentrations resulting from openings, such as the openings  179  that are found in wheel  162  of the &#39;302 patent. 
     It is well known that the stress in a spinning wheel or disk is largest at the edges of a central hole, and that this stress can be substantially decreased by tapering the axial thickness of the disk from a maximum near the center to a minimum at the edge. This can be uniquely reconciled with the requirement that the faces of the disk be flat and parallel by machining a deep, profiled groove  263   a  (FIG. 3) from the edge of the disk  263  toward the center, whereby the facing surfaces of the groove generate the required change of axial thickness of the remaining material between the groove and either flat face. The thickness of the remaining material can be computed to provide essentially constant stress in accordance with mathematical methods well known in the art. 
     It is also well known that holes in a plate under stress double the tangential stress at the edge of the hole and thereby act as stress concentrators. Since the design of the high temperature thrust bearing requires communication of gas from one face to the other, apertures, such as apertures  179  in the third wheel  162  of the prior art turbocompressor shown in FIG. 1, comprise such stress concentrators. This undesirable stress can be reduced by transferring the flow openings from the disk to the shaft. This is precisely what has been done in the embodiment of the present invention as shown in FIGS. 2 through 8. More specifically, in this improved turbocompressor, openings, such as the openings  179 , in the third wheel of &#39;302 patent have been eliminated in favor of the previously identified grooves or flow passages  259  (FIG. 2) that take the form of a continuation of grooves  257  which are provided exist in shaft  256  for the purpose of feeding gas to recesses C. 
     With the forgoing in mind, thrust washer  263  is constructed in the unique configuration best seen in FIGS. 2 and 3 and has spaced-apart faces F- 3  and F- 4 . As there illustrated, disk  263  is generally circular shaped, has a diameter “D” (FIG. 3) and comprises a body portion  263   b . Body portion  263   b  has spaced-apart, generally parallel faces  263   c  and  263   d . Inward facing faces  267   a  and  267   b  define the generally “V” shaped groove  264  that is formed intermediate the generally parallel spaced-apart faces. These spaced-apart faces, in turn, define the radially outwardly extending segments  267  and  269 , each of which has a stepped portion  272  (FIG.  3 ). Groove  263   a  has a depth typically greater than one-half of the radius of the disk having a diameter “D” and has sloping sidewalls  267   a  and  267   b  profiled to provide essentially constant stress in body  263   b . More specifically, the sloping sidewalls of groove  263   a  define first and second faces each being disposed in a plane extending at an acute angle relative to the planes of spaced apart faces  263   c  and  263   d  of third wheel  263 . 
     As best seen in FIG. 2, when the improved turbo compressor is fully assembled wheel  263  is received over shaft portion  256   b  and is securely clamped between a shoulder  273  formed at the junction of shaft portions  256   a  and  256   b  and a shoulder  262   a  formed on member  262 . Member  262  is maintained in the position shown in FIG. 2 by a threaded retaining nut “N”. In this configuration, on one side of disk  263 , flow passageways  257  formed in shaft portion  256   a  communicate with radial flow passageways  269  (see also FIGS.  5  and  6 ), which, in turn, communicate with chamber  265 . On the other side of disk  263 , flow passageways  257  communicate with chamber  265  via radial flow passageways  271 . Turning to FIG. 4A, it is to be noted that flow passageways  259  do not have to be aligned with passageways  271 . 
     In operating the improved turbocompressor shown in FIGS. 2 through 7, seal gas is admitted through a single gas inlet  300 . The gas then flows through a circumferential groove  302  in the housing  250  and is delivered via longitudinal grooves  257  to flow passageways  269 . The gas then flows into chamber  265  on one side of wall  263   c  and finally out to a volume  173  in the direction of the arrow  177 . In the manner indicated by the arrows  279  of FIG. 3, the second thrust bearing that is located on the other side of wheel  263  receives seal gas through flow passageways  259  and  271  which form a direct channel of communication with the portions of chamber  265  that are located on either side of disk  263  (see also FIG.  4 ). 
     With the novel constructions described in the preceding paragraph, the apparatus can function in the same manner as described in the &#39;302 patent without having to provide openings in the thrust washer such as openings  179 . 
     For more discussion of the construction and theory of operation of the thrust bearings of this latest form of the invention, reference should be made to incorporate by reference U.S. Pat. No. 6,231,302. 
     As is also shown in FIG. 2, a third gas supply means or third gas inlet  287 , which functions in the same manner as the third gas supply means of the &#39;302 patent, is provided in or near the axis of support member  267 . This third gas inlet is interconnected with a circumferential groove  289  located in the middle of labyrinth  291 , and is provided with teeth  293  on either side. 
     Having now described the invention in detail in accordance with the requirements of the patent statutes, those skilled in this art will have no difficulty in making changes and modifications in the individual parts or their relative assembly in order to meet specific requirements or conditions. Such changes and modifications may be made with out departing from the scope and spirit of the invention, as set forth in the following claims.