Abstract:
A combination bearing supporting a shaft interconnecting the turbine and compressor wheels of a turbocharger incorporates a dual film floating journal bearing, a squeeze film damper and ball bearing carrier, and a ball bearing assembly. An angular contact ball bearing with an outer race mounted in the carrier rolls on an inner race mounted against a should on the shaft. The squeeze film damper and ball bearing carrier is pinned to preclude axial or rotational movement. A thrust collar is sandwiched between the ball bearing inner race and the compressor wheel to carry thrust loads.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of copending application Ser. No. 60/103,062 filed on Oct. 5, 1998 having the same title as the present application. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to the field of turbochargers and, more particularly, to a bearing rotor assembly used to support a rotating shaft within a turbocharger. 
     BACKGROUND OF THE INVENTION 
     Turbochargers for gasoline and diesel internal combustion engines are known devices used in the art 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, rotation 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 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 rotation; (2) controlling axially directed shaft thrust effects and radially directed shaft vibrations; and (3) providing necessary lubrication to the rotating shaft to minimize friction effects and related wear. The common shaft as used in turbocharger applications is known to have shaft-rotating speeds on the order of 60,000 to 80,000 rpm. Under such operating conditions it is imperative that the bearing assembly provide sufficient lubrication to the shaft to minimize the extreme friction effects that take place at such high rotating speeds, thereby extending shaft service life. 
     Bearing assemblies known in the art for turbocharger shaft applications include roller bearings and ball bearings to accommodate the high-speed shaft rotation. However, it has been found that bearing assemblies that make exclusive use of such ball or roller bearings do not provide a desired service life for turbochargers in vehicle applications. Other bearing assemblies known in the art for turbocharger applications make use of sleeve bearings. However, sleeve bearings have been found to be objectionable in such applications because their design do not tolerate a practical degree of shaft imbalance and do not operate to dampen resonant vibrations caused by such imbalance, such imbalance being a characteristic of rotating turbocharger shafts. Further, the inability of such sleeve bearings to accommodate shaft imbalance at such high speeds is known to cause oil film breakdown and metal-to-metal contact, also reducing the shaft operating life. 
     In an effort to address the disadvantages of these prior art bearing systems, bearing assemblies have been constructed in the form of a free-floating bushing, positioned between the rotating shaft and a stationary housing cavity, that include a roller or ball bearing system. The use of a roller or ball bearing system in conjunction with the free-floating bushing is designed to both provide a desired degree of lubrication to the shaft and to absorb vibration caused by the shaft during rotating movement at such high speeds. Such bearing systems also employ thrust-bearing surfaces to control axial shaft movement during rotary operation. 
     For example, U.S. Pat. No. 4,641,977 discloses a bearing system comprising an anti-friction rolling bearing that cooperates with a full-floating sleeve to carry the rotating turbocharger shaft. More specifically, the bearing system comprises an outer race having an integral one-piece elongated cylindrical outer bearing surface that is adapted to be carried rotatably on a film of lubricant at its interface with the turbocharger housing. The outer race cooperates with a full-floating sleeve at one of its ends and with the roller bearing at an opposite end. The roller bearing is interposed between the outer race and an inner race that is positioned concentrically around the shaft diameter. An end of the outer race adjacent the rolling bearing includes outwardly projecting surfaces that form thrust bearings stationary machine element. The shaft rotates within the assembly between the roller bearing and the full-floating sleeve. 
     While the above-discussed bearing system is known to meet the extreme lubrication and damping demands required in turbocharger shaft applications, its design and construction does not lend itself to cost effective production and assembly. Specifically, in an effort to reduce the costs associated with manufacturing turbochargers it is desired that low-cost components, rather than specially made components, be adapted for use within the turbocharger. 
     It is, therefore, desirable that a bearing assembly for use in a turbocharger be constructed in a manner that: (1) meets the lubrication requirements of a rotating turbine shaft under operating conditions; (2) provides necessary damping to a vibrating turbine shaft during operation; (3) provides thrust surfaces to control turbine shaft axial movement during rotary operation; and (4) is constructed using one or more low-cost component to reduce turbocharger component costs. 
     SUMMARY OF THE INVENTION 
     Turbocharger rotor and low-cost ball bearing assemblies, constructed according to principles of this invention includes: (1) an annular rotating journal bearing disposed concentrically within a stationary turbocharger shaft housing bearing assembly cavity and disposed concentrically around a turbine shaft outside diameter; (2) a cylindrical squeeze film damper disposed within the cavity adjacent an end of the rotating journal bearing and disposed concentrically around the turbine shaft; (3) a thrust (anti rotation) pin disposed within the cavity and connecting with the damper to prevent damper axial and rotational movement within the cavity; and (4) low-cost ball bearings interposed between a ball bearing inner race attached around the turbine shaft, and a ball bearing outer race disposed within a damper end. Bearing assemblies of this invention function to lubricate the turbine shaft under operating conditions, dampen vibrations caused by the rotating turbine shaft, and control axial thrust movement of the turbine shaft during operation without having to use specially designed bearings, through the use of low-cost angular contact ball bearings. 
     Although bearing assemblies of this invention can be used with any type of high-speed machinery having a shaft that is rotated at high speeds, e.g., 60,000 to 80,000 rpm, they are especially well suited for application within turbochargers for use with internal combustion engines. When placed in turbocharger use, the bearing assembly is disposed within a turbocharger shaft housing around a common rotating shaft having one end attached to a turbine that is disposed within a turbocharger turbine housing, and an opposite end attached to a compressor that is disposed within a turbocharger compressor housing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The details and features of the present invention will be more clearly understood with respect to the detailed description and the following drawings, wherein: 
     FIG. 1 illustrates a cross-sectional side elevation of a first embodiment turbocharger bearing assembly constructed according to principles of this invention; and 
     FIG. 2 illustrates a cross-sectional side elevation of a second embodiment turbocharger bearing assembly constructed according to principles of this invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIG. 1, a first embodiment turbocharger rotor with low-cost bearing assembly  10  of this invention is disposed within a bearing assembly cavity  12  extending through a stationary turbocharger shaft or center housing  14 . A common turbine/compressor shaft  16  is disposed within and extends axially through the cavity  12 . A turbine  17  is attached to one end of the shaft  16  illustrated on the right-hand side of FIG. 1, and a compressor  18  is attached to an opposite end of the shaft  16  illustrated on the left-hand side of FIG.  1 . 
     Moving leftwardly from the right-hand side of FIG. 1, the bearing assembly  10  comprises a turbine-side dual film rotating journal bearing  20  disposed concentrically within the cavity  12  and concentrically around an outside shaft diameter  22 . The rotating journal bearing  20  can be made from those materials conventionally used in such applications, and is in the form of an annular ring that is disposed within the cavity  12  adjacent the turbine side of the shaft  16 . The journal bearing  20  includes axially directed surfaces  24  that taper inwardly moving radially towards the shaft  16  that are designed to minimize the contact surface area between adjacent axial shaft surfaces, thereby minimizing unwanted friction and wear effects between these adjacent surfaces. 
     The journal bearing  20  also includes one or more lubrication passages  26  that extend radially therethrough from the cavity  12  to the outside shaft diameter  22 . The journal bearing lubrication passages  26  are positioned for fluid communication with an oil passageway  28  through the shaft housing  14  to facilitate the transport of lubricating oil to the rotating journal bearing and shaft and, more specifically, between both the adjacent cavity and rotating journal bearing surfaces, and between the adjacent rotating journal bearing and outside shaft diameter surfaces. Lubrication between the rotating journal bearing and cavity is desired, in addition to providing lubrication to the shaft, because the journal bearing is designed to rotate within the cavity. The journal bearing has an outside diameter that is sized to facilitate its rotation within the cavity, and has an inside diameter that is sized to facilitate rotation of the outside shaft diameter therein. 
     An annular squeeze film damper  32  is disposed concentrically within the cavity  12  and is generally cylindrical in shape. The damper  32  extends axially through the cavity from an end  34  positioned adjacent the journal bearing  20  towards a compressor end of the cavity. The damper  32  includes an axially extending wall  36  having an outside diameter sized to fit within the cavity  12 , and has an inside diameter sized larger than the journal bearing inside diameter to facilitate the passage of lubricant between the damper and outside shaft diameter  22  to form a vibration absorbing lubricant film therebetween during shaft rotation. The damper can be formed from materials conventionally used for such applications. 
     The damper includes a hole  38  that extends radially through a section of the damper wall  36  adjacent the compressor end of the cavity. The hole  38  is provided to accommodate placement of a thrust pin  40  therein. The thrust pin  40  is disposed radially within the shaft housing  14  and includes a terminal end  42  that is positioned within the damper hole  38  to prevent the damper  32  from either moving axially or rotating within the cavity during turbocharger operation and shaft rotation. The thrust pin  40  includes a center passageway  44  that is designed to facilitate the passage of lubricating oil therethrough from the shaft housing and to the damper and outside shaft diameter. The cavity  12  includes an enlarged diameter section  46  that extends circumferentially around the damper wall  36 , and that is designed to accommodate a volume of lubricating oil therein for purposes of cooling the damper during shaft rotation. 
     The damper  32  includes an enlarged diameter section  48  at an end of the damper wall  36  opposite end  24  and adjacent the cavity compressor end. The damper enlarged diameter section  48  extends axially a desired distance towards the compressor and has an inside diameter that is greater than the damper wall  36 . The damper enlarged diameter section  48  is designed to accommodate placement of a bearing element outer race therein. The damper enlarged diameter section  48  includes an axially-facing surface that is positioned against a complementary cavity axially-facing surface  50  adjacent to the compressor  18  that is formed by a radially outwardly extending cavity wall section. The damper  32  includes a lubricant passage  52  through a shoulder section of the damper wall  36  formed between the damper wall and the damper enlarged diameter section  48 . The lubricant passage  52  is designed to facilitate the passage of lubricating oil from the thrust pin center passageway  44  to the outside shaft diameter  22  and, more specifically, to bearing elements disposed within the cavity as described below. Lubricant flows from the thrust pin center passageway  44 , through the lubricant passage  52 , and to the rotating shaft  16  and bearing elements during turbocharger operation. 
     A thrust element  54  fits within a groove  56  in the shaft housing  14 , and is positioned concentrically around the damper enlarged diameter section  48 . The thrust element  54  is in the form of an annular ring and is designed having an axial end  58  that projects beyond an axial surface of the damper enlarged diameter section  48  to make contact with an adjacent seal gland as better described below. 
     The shaft  16  includes a reduced diameter section  60  positioned concentrically within the damper enlarged diameter section  48 . A ball bearing inner race  62  is disposed concentrically around the shaft reduced diameter section  60 , and includes a shoulder  64  along an outside diameter surface that is shaped to accommodate placement of a bearing element, e.g., a ball bearing, inside diameter section thereagainst. The inner race shoulder  64  is designed to transmit shaft thrust directed to the compressor vis-a-vis bearing elements by angular contact therewith. The bearing inner race  62  includes an axial surface that faces in the direction of the turbine and that is positioned against a shoulder formed in the shaft at its transition to the reduced diameter section. 
     A ball bearing outer race  66  is positioned concentrically within the damper enlarged diameter section  48  and has a groove  68  extending circumferentially along its inside diameter surface to accommodate placement of and limit axial displacement of bearing elements therein. The bearing outer race is shaped generally in the form of an annular ring and is pressed fit into the damper enlarged diameter section  48  so that it remains fixed axially therewith during turbocharger operation. The bearing outer race  66  has a first axial end that is placed against an adjacent axial surface of the damper shoulder, and has a second axial end that is coterminous with a terminal end of the damper enlarged diameter section  48 . 
     A plurality of bearing elements  70 , in the form of low-cost ball bearings, are interposed between the bearing inner race  62  and the bearing outer race  68 . The bearing elements  70  can be made of conventional materials known in the art for use in such applications, and are arranged together by a single-piece bearing element retainer  72  to form an integral bearing element and retainer assembly. The bearing elements  70  are supported along an inside diameter surface by the shoulder  64  formed along the bearing inner race outside diameter, and along an outside diameter by the groove  68  formed in the bearing outer race inside diameter. Constructed in this manner, rotor thrust transferred by the shaft during turbocharger operation is allowed to be transferred by the ball elements through angular contact of the ball elements by both the bearing inner race and bearing outer race. For example, shaft thrust transmitted from the turbine towards the compressor is transmitted to the bearing elements by angular contact with the inner race, which in turn transmit the thrust to the outer race and damper. The shaft thrust that is transmitted to the damper is absorbed and controlled by the thrust pin, which restricts axial damper and shaft movement. 
     An annular seal gland  74  is positioned concentrically around a section of the shaft  16  adjacent the bearing inner race  62 . The seal gland is interposed axially between a compressor backplate  76  and the shaft housing  14  and is fixed axially therebetween by attachment between the compressor backplate and shaft housing. The seal gland includes an axially-facing surface  78  that is positioned against an axially-facing surface of the thrust element  54  to provide a thrust surface pair. Axial end surfaces of both the damper enlarged diameter section  48  and bearing outer race  66  do not extend axially a sufficient distance to contact the seal gland axially-facing surface  78 , thereby not forming thrust surfaces therewith. With this in mind, shaft thrust loads from the compressor are transmitted by the shaft to the seal gland, which is transmitted to the thrust element by its contact with the seal gland the axially-facing surface  78 . The thrust element  54  acts to absorb the thrust load by its fixed axial placement within the shaft housing  14 . The seal gland  74  includes an annular sealing ring  80 , disposed circumferentially around a gland outside diameter, that is interposed between adjacent gland compressor backplate surfaces to form a leak-tight seal therebetween. 
     A feature of the first embodiment bearing assembly of this invention is the use of low-cost ball bearings to transmit compressor directed thrust loads from the shaft to the damper where they are absorbed without the need for specialty/complex bearings or thrust load assemblies. Specifically, the bearing assembly design enables shaft thrust loads from the turbine to be transmitted from the shaft, via angular contact between the bearing elements and bearing inner and outer races, to the damper where they are absorbed and controlled by the thrust pin. The first embodiment bearing assembly of this invention is also designed to enable shaft thrust loads from the compressor to be transmitted via thrust surfaces between the seal gland and thrust element, interposed between the seal gland and shaft cavity, where they are absorbed and controlled by the thrust element. 
     FIG. 2, illustrates a second embodiment turbocharger rotor with low-cost bearing assembly  82  of this invention. The second embodiment bearing assembly  82  comprises the following primary components that are identical to those of the first bearing assembly; shaft  84 , rotating journal bearing  86 , squeeze film damper  88 , thrust pin  90 , bearing inner race  92 , bearing elements  94 , and bearing outer race  96 . The only difference between the first and second embodiment bearing assemblies lies in construction of the seal gland  98  and the thrust surfaces that are formed between the seal gland and other bearing assembly components to accommodate turbine directed shaft thrust load transmission. 
     Unlike the first embodiment, the second embodiment bearing assembly  82  comprises a damper enlarged diameter section  100  having an axially-facing end  102  that projects axially a sufficient distance to contact the adjacent seal gland axially-facing surface  104 , forming a first thrust load surface pair. The outer bearing race  96  also includes an axially-facing surface  106  that makes contact with the adjacent seal gland axially-facing surface  104 , forming a second thrust load surface pair. The design and presence of first and second thrust load surface pairs enables the second embodiment bearing assembly to be constructed without the need for a separate thrust element. Rather, turbine directed shaft thrust loads are transmitted from the seal gland  98 , via the first and second thrust load surface pairs, to the damper where they are absorbed and controlled by the thrust pin. Thus, unlike the first embodiment bearing assembly of FIG. 1, that provides the thrust element  54  to absorb turbine directed shaft thrust loads and provides the thrust pin  40  to absorb compressor directed shaft thrust loads, the second embodiment bearing assembly of FIG. 2 provides the thrust pin to absorb and control shaft thrust loads in both axial directions. Other components and features of the second embodiment bearing assembly of this invention are understood to be identical to that described above and illustrated in FIG.  1 . 
     During turbocharger operation, and rotary movement of the shaft, both bearing assembly embodiments of this invention function in the following manner. The rotating journal bearing both directs lubricating oil to the shaft and carries the rotational movement of the shaft adjacent the turbine while rotating to a lessor extent within the cavity. The damper functions to both provide a thin film of lubricating oil between the shaft and damper inside diameter to lubricate the shaft and hydraulically dampen shaft radial vibrations. The damper also functions to route lubricating oil from the shaft housing to the bearing elements. The thrust pin functions to both route lubricating oil to the damper and bearing elements, and prevents the dampener from rotating or being moved axially within the cavity. The bearing outer race, low-cost bearing elements, and bearing inner race enables the use of low-cost ball bearings to transmit compressor directed shaft thrust loads to the damper and thrust pin, where they are absorbed and controlled. In a first bearing assembly embodiment, turbine directed shaft thrust loads are transmitted to and absorbed by a thrust element separated from the damper and interposed between the compressor backplate and shaft housing. In a second bearing assembly embodiment, turbine directed shaft thrust loads are transmitted to the damper and are absorbed by the same thrust pin that is used to absorb and control compressor directed shaft thrust loads. 
     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.