Abstract:
A turbocharger bearing system comprising a shaft ( 211 ) including at least one shoulder (A 2 ) with a rotor ( 212 ) disposed on the shaft ( 211 ). First and second bearing sleeves ( 254 ) are disposed on the shaft ( 211 ) at opposite ends of the rotor ( 212 ). Each bearing sleeve ( 254 ) includes a collar ( 213 ) and a journal portion ( 225 ). A journal bearing ( 249 ) is disposed on each journal portion ( 225 ) and the journal portion ( 225 ) of the first bearing sleeve ( 254 ) abuts the shoulder (A 2 ) of the shaft ( 211 ). In certain aspects of the technology described herein, the bearing sleeves ( 254 ) may be oriented in opposite directions. The shaft ( 211 ) is the same diameter where the bearing sleeves ( 254 ) are positioned. Accordingly, the bearing sleeves ( 254 ) may be interchangeable, as well as the journal bearings ( 249 ).

Description:
BACKGROUND 
       [0001]    Turbochargers are a type of forced induction system. Turbochargers deliver air, at greater density than would be possible in a normally aspirated configuration. The greater air density allows more fuel to be combusted, thus boosting the engine&#39;s horsepower without significantly increasing engine weight. A smaller turbocharged engine, replacing a normally aspirated engine of a larger physical size, will reduce the mass of the engine and can reduce the aerodynamic frontal area of the vehicle. 
         [0002]    With reference to  FIG. 1 , turbochargers use the exhaust flow from the engine exhaust manifold to drive a turbine wheel  10 . The energy extracted by the turbine wheel is translated to a rotating motion which then drives a compressor wheel  20 . The compressor wheel draws air into the turbocharger, compresses the air, and delivers it to the intake side of the engine. The rotating assembly is supported by a bearing system. Some bearing systems consist of sleeve type hydrodynamic bearings and some consist of rolling element type bearings. 
         [0003]    As the mass flow of exhaust to the turbocharger changes, the rotational speed changes (from 80,000 RPM for large turbochargers, to 250,000 RPM for smaller turbochargers). Some of the parameters affecting the time for the rotating assembly to change from one equilibrium condition to another equilibrium condition are, for example: the inertia of the rotating assembly, the friction losses in the bearing system, and the aerodynamic efficiency of the wheels. 
         [0004]    Electrically assisted turbochargers can use power supplied by an external source or power generated directly by the engine. The challenges of fitting an electric motor into a turbocharger are not minor. Most electrically assisted systems have either a connection to the (relatively) cold compressor-end of the rotating assembly or are fitted between the wheels. For example, U.S. Pat. No. 6,845,617 teaches an electric motor fitted to the compressor-end of the turbocharger outboard of the bearing system. 
         [0005]    In the example depicted in  FIGS. 1 and 2 , an electric motor is disposed between the journal bearings in a split turbocharger bearing housing. The bearing housing is split into an upper portion  89  with a flange  91  and a lower portion  90  with a flange  92 . When the two flanges ( 91 ,  92 ) are mechanically clamped together, the assembly functions as that of a unified turbocharger bearing housing. A laminated rotor  12  is mechanically mounted to the shaft  11  of the turbocharger such that it rotates about the axis  1  of the turbocharger with the shaft and wheels, becoming part of the rotating assembly of the turbocharger. A laminated stator  40 , with power windings  42  providing the magnetic force to drive the aforementioned rotor  12 , is mounted concentric with the rotor. 
         [0006]    The surface finish and accuracy of the shaft surfaces, upon which the internal oil film for the journal bearings is generated, may have for example a surface finish of Rz4 coupled with a cylindricity requirement of 0.005 mm. The surface finish of the surfaces ( 24 ,  25 ), which support the journal bearings ( 49 C,  49 T) respectively, are sufficiently fine that they could not tolerate scratches or grooves generated by pressing the rotor  12  over these surfaces. To prevent damage to the journal bearing surfaces when the collars and rotor stack are assembled to the shaft  11 , the diameters of the various portions of the shaft are stepped down towards the compressor-end of the shaft, which is the end of the shaft over which parts are assembled onto the shaft. 
         [0007]    As depicted in  FIG. 2 , a ring boss  15  locates the piston ring  5  that provides a seal between the exhaust gases in the turbine stage and the oil and air within the bearing housing. The turbine-end journal bearing  49 T is disposed about journal  25 . The turbine-end electric motor collar  13 T is secured to (i.e. pressed onto) diameter  26 . Journal  25  is bound on one side by shoulder A, which is located between the ring boss  15  and journal  25 . At the other end, journal  25  is defined by step B, which is located between journal  25  and diameter  26 . Each transition to a different diameter along the shaft is referred to as a step. Each step is associated with a shoulder against which components may be located. 
         [0008]    Rotor  12  is secured to the shaft along diameter  27 . Step C marks the transition between diameter  26  and diameter  27 . Compressor-end collar  13 C is also secured to diameter  27 . Compressor-end journal bearing  49 C is disposed about journal  24 . The transition between diameter  27  and journal  24  is marked by step D. Step S marks the transition between journal  24  and the stub shaft  16 . The axial constraint, in the direction of the electric motor rotor, is provided by the clamping load of the compressor nut  17  on the compressor wheel  20 , flinger  53 , and thrust washer  52 , against shoulder S. 
         [0009]    While the above described multiple diameters provide assembly protection for the very accurate and fine surface finishes of the various portions of the shaft, the inside diameters of the compressor-end journal bearing  49 C and motor collar  13 C are smaller (and hence different) from those parts ( 49 T,  13 T) on the turbine side of the electric motor rotor  12 . This difference means that the part number count per turbocharger increases and the potential for incorrect assembly of the journal bearings and motor collars exists. It also means that the journal bearings can run at different speeds since the speed defining features (inside diameter, ratio of inside diameter to outside diameter etc.) are different turbine-end to compressor-end. In this case, the compressor-end journal bearing will run at a lower speed than does the turbine-end journal bearing. 
         [0010]    Accordingly, there is a need for a bearing system for use in an electrically assisted turbocharger that provides the desired bearing surface finishes while minimizing the complexity and part count associated with existing designs. 
       SUMMARY 
       [0011]    Provided herein is a turbocharger bearing system comprising a shaft including at least one shoulder and a bearing sleeve disposed on the shaft. The bearing sleeve includes a collar with a journal portion extending therefrom. A journal bearing is disposed on the journal portion and the journal portion abuts the shoulder of the shaft. In an embodiment the bearing system comprises two bearing sleeves and a corresponding journal bearing disposed on each bearing sleeve. 
         [0012]    In certain aspects of the technology described herein, the bearing sleeves may be oriented in opposite directions. In an embodiment, the shaft is the same diameter where the bearing sleeves are positioned. Accordingly, the bearing sleeves may be interchangeable, as well as the journal bearings. In another aspect of the technology, an electric motor rotor is disposed between the two bearing sleeves, and may be clamped between the two bearing sleeves. 
         [0013]    In an embodiment, a turbocharger bearing system comprises a shaft including at least one shoulder with a rotor disposed on the shaft. First and second bearing sleeves are disposed on the shaft at opposite ends of the rotor. Each bearing sleeve includes a collar and a journal portion. A journal bearing is disposed on each journal portion and the journal portion of the first bearing sleeve abuts the shoulder. 
         [0014]    Also contemplated herein is a turbocharger incorporating the disclosed bearing system. The turbocharger comprising a compressor wheel and a turbine wheel disposed on opposite ends of a shaft with a housing supporting the shaft. A stator is disposed in the housing and a corresponding rotor is disposed on the shaft. First and second bearing sleeves are disposed on the shaft at opposite ends of the rotor, wherein each bearing sleeve includes a collar and a journal portion extending therefrom. A journal bearing is disposed on each journal portion. 
         [0015]    These and other aspects of the bearing system and turbocharger incorporating the same will be apparent after consideration of the Detailed Description and Figures herein. It is to be understood, however, that the scope of the invention shall be determined by the claims as issued and not by whether given subject matter addresses any or all issues noted in the background or includes any features or aspects recited in this summary. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Non-limiting and non-exhaustive embodiments of the bearing system, including the preferred embodiment, are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified. 
           [0017]      FIG. 1  is a side view in cross-section illustrating a turbocharger with an electric motor disposed between the bearings; 
           [0018]      FIG. 2  is an enlarged partial side view in cross-section of the turbocharger shown in  FIG. 1 ; 
           [0019]      FIG. 3  is an enlarged partial side view in cross-section of a turbocharger bearing system according to a first exemplary embodiment; 
           [0020]      FIG. 4  is an enlarged partial side view in cross-section of the bearing shown in  FIG. 3 ; 
           [0021]      FIG. 5  is an enlarged partial side view in cross-section of a turbocharger bearing system according to a second exemplary embodiment; 
           [0022]      FIG. 6  is an enlarged partial side view in cross-section of a turbocharger bearing system according to a third exemplary embodiment; 
           [0023]      FIG. 7  is an enlarged partial side view in cross-section of a turbocharger bearing system according to a fourth exemplary embodiment; 
           [0024]      FIG. 8  is an enlarged partial side view in cross-section of a turbocharger bearing system according to a fifth exemplary embodiment; and 
           [0025]      FIG. 9  is an enlarged partial side view in cross-section of a turbocharger bearing system according to a sixth exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    Embodiments are described more fully below with reference to the accompanying figures, which form a part hereof and show, by way of illustration, specific exemplary embodiments. These embodiments are disclosed in sufficient detail to enable those skilled in the art to practice the technology of the application. However, embodiments may be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein. The following detailed description is, therefore, not to be taken in a limiting sense. 
         [0027]    While the design for locating and mounting the rotor of an electric motor onto the shaft of a turbocharger, as described above, is technically functional, it causes several problems from a performance, cost, and from a quality perspective. In order to protect the surface finish of sensitive regions of the shaft, multiple diametrical steps are formed along the shaft. These differences in diameter mean that there must be a unique turbine-end journal bearing  13 T, a unique compressor-end journal bearing  13 C, a unique turbine-end motor collar  13 T, and a unique compressor-end motor collar  13 C. While not only increasing the part number count by two items for each turbocharger, the potential for assembly error by assembling the turbine-end journal bearing (and/or collar) on the compressor-end, or vice versa, can present a quality problem. 
         [0028]    Provided herein is a bearing system for use in an electrically assisted turbocharger that provides protection for the bearing surface finishes while minimizing the complexity and part count associated with existing designs. As shown in  FIGS. 3 and 4 , a bearing system according to a first exemplary embodiment includes sleeves  154 . Each sleeve  154  is disposed on shaft  111  on diameter  125 , thus the sleeves are coaxial with the centerline axis  101  of the shaft. Each sleeve has two cylindrical surfaces ( 156 ,  157 ) separated by a flange  155 . 
         [0029]    The sleeves have a surface  156  upon which the journal bearings ( 149 C,  149 T) rotate. On the other side of the flange  155 , is a surface  157  for radially locating the motor collars ( 113 C,  113 T). The flange feature  155  on the outside of the sleeve  154  axially constrains the motor collars ( 113 C,  113 T) against rotor  112 . On the turbine-end, sleeve  154  is axially constrained by a shoulder Al located between the ring boss  115  and diameter  125 . Thus, the turbine-end of the rotor  112  of the electric motor is axially located relative to the ring boss shoulder A 1 . 
         [0030]    In this embodiment, the sleeve  154  used for the compressor-side of the electric motor rotor  112  is the same as that used for the turbine-side of the electric motor, albeit oriented in the opposite direction. On the compressor-side of the electric motor, the compressor side collar  113 C is located closest to the electric motor rotor  112 , and the compressor-side journal bearing  149 C is axially located on the other side of the flange  155 . The axial constraint, in the direction of the electric motor rotor, is provided by the clamping load of the compressor nut (not shown) on the compressor wheel  120 , flinger  153 , and thrust washer  152 , against shoulder S 1 . This load is transferred through the compressor-end sleeve  154  to the compressor-end collar  113 C to clamp the laminations of the rotor  112  of the electric motor against the turbine-end collar  113 T, and, as explained above, the turbine-end sleeve is constrained against the shoulder A 1  of the ring boss  115 . Accordingly, shaft  111  is the same diameter along the length of the shaft that supports the bearing sleeves  154  and rotor  112 , thereby simplifying the manufacture of the shaft  111 . It should be appreciated that journal bearings  149 C and  149 T ride on sleeves  154 . As such, the shaft surface finishes may be relaxed. 
         [0031]    Furthermore, in this embodiment, the journal bearings are interchangeable compressor-end to turbine-end, and the motor collars  113 C,  113 T may also be similarly interchangeable. Diameter  125  of the shaft may be the same as the diameter of a standard turbocharger of the same size. The clamping load of the force exerted by the compressor nut on the laminations of the rotor not only assists in the radial alignment of the lamination pack, but also forces the rotor to rotate at the same speed as the shaft (i.e. there is no relative rotational motion between the rotor and the shaft). The sleeves may be comprised of hardened steel and the bearings are comprised of bronze type bearing material, as is known in the art. 
         [0032]    In a second exemplary embodiment, as depicted in  FIG. 5 , bearing sleeve  254  incorporates a motor collar  213 , thereby further reducing the number of parts in the assembly. The axial position of the collar (and hence the laminations of the rotor  212 ) is determined by journal portion  225  that extends from the motor collar  213 . The rotor  212  is positioned within stator  240 . Journal portion  225  locates the motor collar  213  by butting against the shoulder A 2  of the ring boss  215 . The compressive load on the laminations of the rotor  212  is provided in the same manner as that of the first embodiment by the load exerted by the compressor nut (not shown). In this case, the journal bearings  249 T ( 249 C not shown) are identical, and the bearing sleeves are identical, albeit oriented in opposite directions. Accordingly, the shaft  211  is the same diameter where the bearing sleeves  254  are positioned. 
         [0033]    In a third exemplary embodiment, as depicted in  FIG. 6 , the laminations of the rotor  312  have an inside diameter larger than the diameter of shaft  311 . A cylindrical sleeve  370  is positioned between the rotor  312  and shaft  311 . The cylindrical sleeve  370  may be integrated with one of the collars, such as collar  313 T as shown or with collar  313 C. Alternatively the sleeve could stand alone as a separate piece to the two collars  313 T,  313 T. In this case, cylindrical sleeve  370  includes a collar portion  313 T and a rotor sleeve portion  372  extending axially therefrom. A journal portion  326  extends axially from the collar portion  313 T opposite the rotor sleeve portion  372 . With this variation, the laminations of the rotor  312  of the electric motor can be delivered to the turbocharger assembly site, and the assembly of the rotor assembly to the shaft  311  is simplified. The closer the fit of the inside diameter of the lamination to the outside surface of the shaft, the better the initial balance, due the rotor lamination pack, of the rotating assembly. But contrary to this potential gain, the tighter the clearance between the rotor laminations and the surface of the shaft, the greater the propensity for the laminations to cock and resist assembly force. By incorporating sleeve  370  to deal with the tighter lamination inside diameter the final assembly is made more straightforward. By incorporating a collar and a sleeve into one piece, the laminations can be compressed against the collar  313 T and therefore will be more stable at the turbocharger assembly step. The unitary collar and sleeve  370  could be either on the compressor-end or the turbine-end of the motor. In this variation, the clamping load of the compressor nut on the collars and the sleeve prevents rotation of the sleeve and laminations, relative to the shaft. This embodiment also incorporates a bearing sleeve  354  similar to that described above with respect to the second exemplary embodiment. Sleeve  354  includes a journal portion  325 . Accordingly, journal bearings  349 C and  349 T ride on journal portions  325  and  326  respectively. It should be noted that cylindrical sleeve  370  and bearing sleeve  354  have the same inside diameter. Therefore, shaft  311  has the same diameter  373  between steps A 3  and S 3 . 
         [0034]    In a fourth exemplary embodiment, as depicted in  FIG.7 , dimensions and features of both journal bearings ( 449 C,  449 T) are the same as those of the standard turbocharger. The step A 4  transitioning from the piston ring boss  415  to journal  425  is similar to a standard turbocharger. Journal  425 , about which the turbine-end journal bearing  449 T is supported, is stepped down at B 4  to a smaller diameter  473 . Cylindrical sleeve  470  includes a motor collar portion  413 T with a rotor sleeve portion  472  extending therefrom. Cylindrical sleeve  470  does not include a bearing sleeve as in the previous embodiment. Therefore, journal bearing  449 T is disposed on diameter  425  rather than a journal sleeve. Shaft  411  transitions to diameter  474  at step S 4 . Bearing sleeve  454  is disposed on diameter  474 . Bearing sleeve  454  includes a motor collar portion  413 C with a bearing sleeve portion  426  extending therefrom. The diameter of bearing sleeve portion  426  is the same as that of journal  425 , thereby allowing the same journal bearing to be used in both locations. 
         [0035]    In a fifth exemplary embodiment, as depicted in  FIG. 8 , shaft  511  is sized to extend through the rotor  512  and includes a protruding threaded stub  564 . A threaded extension shaft  516  is screwed onto the stub  564 . Extension shaft  516  includes a motor collar portion  513 C and a journal portion  525  for supporting journal bearing  549 C. Extension shaft  516  also includes female threads  562  that mate with male threads  563  disposed on stub  564 . Shaft  511  transitions to journal  524  at step A 5 . Journal  524  transitions to diameter  526  at step B 5 . Journal bearing  549 T is disposed on journal  524  and motor collar  513 T is secured to diameter  526 . Rotor  512  is also disposed on diameter  526  and is clamped between collar  513 T and collar portion  513 C. In this embodiment, the clamp load of the compressor wheel  520 , flinger  553 , and thrust washer  552  is applied by a typical compressor nut (not shown) against the abutment of the typical stub shaft step S 5 . The clamp load, compressing the laminations pack of the rotor  512 , is generated by the threading of the extension shaft  516  down the stub  564  of shaft  511 . 
         [0036]    In a sixth exemplary embodiment, as depicted in  FIG. 9 , shaft  611  extends just past the rotor  612  and the motor collar  613 C is pressed onto shaft  611  to provide the compressive force, keeping the laminations of the rotor, clamped against the turbine-end collar (not shown). Shaft  611  includes female threads  663  that mate with male threads  662  disposed on extension shaft  616 . Extension shaft  616  includes a journal  625  that supports journal bearing  649 C. Compressor nut  617  exerts a clamping load on the compressor wheel  620 , flinger  653 , and thrust washer  652 , against the shoulder of the step S 6  located adjacent journal  625 . 
         [0037]    Accordingly, the bearing system has been described with some degree of particularity directed to the exemplary embodiments. It should be appreciated; however, that the present invention is defined by the following claims construed in light of the prior art so that modifications or changes may be made to the exemplary embodiments without departing from the inventive concepts contained herein.