Abstract:
An enhanced bearing system for turbochargers incorporates a thrust collar centrally mounted on the rotating shaft interconnecting the turbine and compressor and a thrust bearing centrally located within the center housing to constrain the thrust collar. Central placement of the thrust collar allows journal bearings and journal seals to be placed immediately adjacent the turbine and compressor wheel attachment points on the shaft enhancing the shaft motion characteristics and sealing capability.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to the field of turbochargers and, more particularly, to a turbocharger bearing system comprising a turbocharger shaft thrust collar positioned within a turbocharger center housing to provide a smaller overall turbocharger package, and an overall better stabilized turbocharger shaft operation. 
     BACKGROUND OF THE INVENTION 
     Turbochargers for gasoline and diesel internal combustion engines are devices known in the art that are used for pressurizing or boosting the intake air stream, routed to a combustion chamber of the engine, by using the heat and volumetric flow of exhaust gas exiting the engine. Specifically, the exhaust gas exiting the engine is routed into a turbine housing of a turbocharger in a manner that causes an exhaust gas-driven turbine to spin within the housing. The exhaust gas-driven turbine is mounted onto one end of a shaft that is common to a radial air compressor mounted onto an opposite end of the shaft. Thus, rotary action of the turbine also causes the air compressor to spin within a compressor housing of the turbocharger that is separate from the exhaust housing. The spinning action of the air compressor causes intake air to enter the compressor housing and be pressurized or boosted a desired amount before it is mixed with fuel and combusted within the engine combustion chamber. 
     The common shaft extending between the turbine and compressor is disposed through a turbocharger center housing that includes a bearing assembly for: (1) facilitating shaft rotating action; (2) controlling axially directed shaft thrust effects and radially directed shaft vibrations; (3) providing necessary lubrication to the rotating shaft to minimize friction effects and related wear; and (4) providing a seal between the lubricated assembly and the turbine and compressor housings. The common shaft as used in turbocharger applications is known to have shaft-rotating speeds on the order of 120,000 to 250,000 rpm or higher. Under such operating conditions it is imperative that the bearing assembly provide shaft axial and radial stabilization to maximize shaft balance, thereby maximizing turbocharger housing sealability and compressor/turbine wheel stability. 
     Various prior art turbocharger housing bearing assemblies include a first annular seal at a housing turbine-side axial end, a second journal bearing adjacent the first annular seal, a second journal bearing, a generally dead space between the first and second journal bearings, a thrust collar at a housing compressor-side axial end, and a second annular seal disposed adjacent the thrust collar. Configured in this manner, a conventional turbocharger housing is axially lengthy, the journal bearing are spaced relatively close together, and a relatively long moment arm or cantilever exists between the second journal bearing and the compressor wheel. 
     It is, therefore, desired that a turbocharger bearing system be constructed that provides a more compact turbocharger package and better shaft stabilization and balance when compared to conventional bearing assemblies. It is further desired that the bearing system be constructed to improve these properties without adversely impacting the lubricating and thrust load handling capabilities of the bearing system. 
     SUMMARY OF THE INVENTION 
     Turbocharger bearing systems, constructed according to principles of this invention incorporate (1) a pair of journal bearings disposed adjacent respective compressor and turbine ends of the center housing; (2) a pair of journal seals positioned at adjacent respective compressor and turbine ends of the center housing next to respective journal bearings; and (3) a thrust collar disposed within the center housing and interposed between the journal bearings, wherein the thrust collar is positioned at an approximate axial center of the housing and cooperates with a central housing flange to control axial shaft movement. Configured in this manner, bearing systems of this invention improve shaft stability and balance, reduce turbocharger package size, and improve center housing sealability. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood with reference to the following drawings and detailed description in which: 
     FIG. 1 is an elevation section view of a turbochager center housing and rotating assembly incorporating the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A bearing system  10  of this invention is illustrated FIG.  1 . Generally, the bearing system is disposed within a turbocharger having an extended compressor housing backplate  12  and a center housing  13  having a central opening  14  extending axially therethrough from a turbine end  16  to a compressor end  18 . The extended backplate attaches to the center housing at an approximate midpoint of the turbocharger and the rotating group which includes a turbine  20  is attached to one end of a shaft  22  that projects from end  16  of the housing. A compressor wheel  24  is attached to the opposite end of the shaft  22  that projects from end  18  of the housing. 
     Moving from left to right across the figure, the bearing system of this invention incorporates a first annular seal  26  that is disposed within the housing opening  14  at end  18 . The first annular seal has a central shaft opening  28  that is sized to accommodate placement of the shaft  22  therein, and includes a groove  30  disposed circumferentially around an outside diameter surface that is sized and shaped to accommodate placement of a seal ring  32  therein. The seal ring  32  provides a leak-tight seal between the first annular seal  26  and the central opening  14 . The first annular seal extends axially a distance within the housing and makes abutting contact with a thrust collar  34 . 
     The thrust collar  34  comprises a central shaft opening  36  to accommodate placement of the shaft  22  therein, and includes a first diameter section  38  that extends a distance axially away from the first annular seal. As better described below, the first diameter section  38  is sized having an outside diameter that fits within a first journal bearing  40 . The thrust collar  34  includes first and second extended diameter sections  42  and  44  that are spaced apart from one another, and that each extend radially outwardly a distance away from the first diameter section  38 . The extended diameter sections  42  and  44  are separated by a reduced diameter section  46  that, in a preferred embodiment, has a diameter that is approximately that of the first diameter section  38 . Each extended diameter section includes frontside and backside axially-facing surfaces  48  and  50 . 
     The thrust collar  34  is restrained axially within the housing  12  by placement of the extended diameter sections  42  and  44  on either side of a thrust bearing  52  that is supported in the housing and extends radially inwardly towards the thrust collar. Specifically, the thrust bearing  52  is horse-shoe shaped in the embodiment shown and has an inside diameter  54  that is less than that of each extended diameter section outside diameter, but that is slightly greater than that of the thrust collar reduced diameter section  46  to trap the thrust collar axially within the housing. To provide fluid for the hydrodynamic bearing, the thrust bearing  52  can include an oil passage disposed radially therethrough to facilitate lubricating the bearing and collar. 
     In alternative embodiments, the thrust collar extended diameter sections and reduced diameter section are divided into two or three separate elements to accommodate a 360 degree thrust bearing. 
     A first journal bearing  40  is disposed axially within the housing central opening  14  between the first annular seal  26  and the thrust collar  34 . The bearing  40  is annular, having an inside diameter  56  that is sized to accommodate placement of the thrust collar first diameter section  38  therein. The thrust collar first diameter section  56 , thus extends axially completely through the first journal bearing  40  such that a thrust collar axial end  58  make abutting contact against an adjacent first annular seal axial surface  60 . The first journal bearing  40  includes at least one oil passage disposed radially therethrough for facilitating oil passage to and from the journal bearing. 
     Moving axially past the thrust collar  34 , the shaft  22  includes an enlarged diameter section  63  that extends axially from the thrust collar extended diameter section  44  backside axial surface  50  to a second annular seal  62 . The enlarged diameter section  63  make abutting contact against the thrust collar and has an outside diameter  64  that is sized to fit within a second annular journal bearing  66  that is disposed within the housing central opening  14 . Specifically, the shaft enlarged diameter section is sized to fit within an inside diameter  68  of the second annular journal bearing  66 . The second annular journal bearing  66  includes one or more oil passage disposed radially therethrough to facilitate the passage of oil to and from the floating journal bearing. 
     A second annular journal seal  62  is disposed within the housing central opening  14 , and comprises a groove  70  disposed circumferentially therearound, and a seal ring  72  disposed therein to provide a leak-tight seal with the housing. 
     A key feature of turbocharger bearing systems of this invention is the design of the thrust collar that permits its placement within the middle of the turbocharger center housing, rather than at the housing compressor side. Placement of the thrust collar within the center of the housing is desirable because is reduces the overall axial length of the housing, when compared to a conventional housing built to accommodate a compressor-side located thrust collar. Additionally, placement of the thrust collar in the center of the housing permits the journal bearings to be spaced apart along the shaft a greater distance that was previously possible. The wider journal bearing spacing within the housing is desired because it acts to provide better shaft stabilization and balance, thereby improving journal bearing and journal seal life. Further, relocating placement of the thrust collar from the housing compressor end, and the end of the bearing system, reduces the amount of cantilever or overhang of the compressor wheel. Reducing this overhang further improves shaft balance, shaft sealing, and rotor stability. The configuration preserves the ability to assemble the turbocharger rotating group including the compressor wheel, shaft, annular seals, journal bearings, thrust collar and turbine wheel as a single unit with lockup provided through a threaded end nut  74  on the compressor wheel nose or a threaded hub on a compressor wheel without a through bore. 
     Having now described the invention in detail as required by the patent statutes, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present invention as described in the following claims: