Abstract:
A laser cutting device ( 100 ) is configured to etch an inner surface of a journal bearing ( 18 ). The laser cutting device ( 100 ) includes a laser ( 102 ); a beam directing tool ( 130 ) that receives a beam ( 108 ) emitted from the laser ( 102 ) and selectively changes the direction of travel of the beam ( 108 ); a fixture ( 170 ) that supports the journal bearing ( 18 ) in a desired position relative to the beam directing tool ( 130 ); an actuator ( 148 ) connected to one of the beam directing tool ( 130 ) and the fixture ( 170 ), the actuator ( 148 ) providing relative movement between the beam directing tool ( 130 ) and the fixture ( 170 ); and a controller ( 180 ) that controls the intensity and duration of the beam ( 108 ) emitted from the laser ( 102 ); and the actuator ( 148 ), whereby material can be re moved from a surface of the journal bearing ( 18 ) to a precise width and depth, and in any pattern.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and all the benefits of U.S. Provisional Application No. 61/975,043, filed on Apr. 4, 2014, and entitled “Method and Laser Device For Forming Grooves In Bearing Surfaces, And Bearings Include Such Grooves,” which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a turbocharger with an improved bearing assembly and to a laser device and method for forming grooves on an inner surface of a journal bearing. 
       BACKGROUND 
       [0003]    An exhaust gas turbocharger is a type of forced induction system in which engine exhaust gases drive a turbine wheel. The turbine wheel is connected via a shaft to a compressor impeller. Ambient air is compressed by the compressor impeller and is fed into the intake manifold of the engine, allowing the engine to combust more fuel, and thus to produce more power for a given displacement. Considering the volumetric gas intake requirements of an engine operating at peak performance and the comparatively small size of a turbocharger, it can be appreciated that a turbocharger may be expected to rotate at speeds of up to 300,000 rpm and higher. In addition, the engine exhaust gas that drives the turbine wheel may have a temperature as high as 1,300 F. Thus, turbochargers generally operate at extremely high rotational speeds, and under conditions of high temperature and varying load. 
         [0004]    The shaft is supported by a bearing system that includes a single or two spaced-apart journal bearings, which function to stabilize the shaft and dampen oscillations. The bearing system is cooled using a lubrication system in which oil is channeled through the bearing system for removal of heat. The oil flow behavior between the shaft and the inner diameter of the journal bearing can influence the rotordynamics of shaft motion and transmitted vibrations. 
       SUMMARY 
       [0005]    In some aspects, a laser cutting device is configured to etch a surface of a work product. The laser cutting device includes a laser; a beam directing tool that is configured to be inserted inside the work product and to receive a beam of electromagnetic radiation emitted from the laser and selectively change the direction of travel of the beam; a fixture configured to support the work product in a desired position relative to the beam directing tool; an actuator connected to one of the beam directing tool and the fixture, the actuator configured to provide relative movement between the beam directing tool and the fixture; and a controller. The controller is configured to control the actuator and the intensity and duration of the beam output from the laser. 
         [0006]    The laser cutting device may include one or more of the following features: The beam directing tool includes a tube having a first end, a second end opposed to the first end, and a tube longitudinal axis. The beam direct tool includes a mirror supported on the tube such that the mirror is at an angle to the tube longitudinal axis. The beam directing tool includes an opening disposed between the first end and the second end, and the mirror is fixed within the tube at an axial location corresponding to the opening. The beam directing tool includes a drive shaft disposed within the tube and extending in parallel with the tube longitudinal axis; and a gear set that connects the mirror to the drive shaft and is configured to transmit rotation of the drive shaft into a rotation of the mirror. The mirror is rotatably supported on the second end of the tube via a pin. The device includes a vacuum source and a vacuum line extending between the vacuum source and the work product, the vacuum source and the vacuum line configured to remove cutting byproducts from the work product. The device includes a cooling fluid source and a fluid line extending between the cooling fluid source and the work product, the cooling fluid source and the fluid line configured to provide a cooling fluid to the work product. The position of the fixture is fixed, and the beam directing tool is connected to the actuator, which is configured to vary the position of the beam directing tool relative to the fixture. The position of the beam directing tool is fixed, and the fixture is connected to the actuator, which is configured to vary the position of the fixture relative to the beam directing tool. 
         [0007]    In some aspects, a journal bearing includes a first end, a second end opposed to the first end, a longitudinal axis that extends between the first end and the second end, and a semi-continuous groove pattern formed on an inner surface of the bearing that is configured to disturb formation of oil whirl. 
         [0008]    The journal bearing may include one or more of the following features: The semi-continuous groove pattern comprises chevron-shaped recesses. The recesses are arranged along a line. The line is angled relative to the longitudinal axis. The chevron-shaped recesses are oriented such that an apex of each recess points circumferentially in the direction of bearing rotation. The recesses are arranged along multiple lines that are angled relative to the longitudinal axis, where the lines intersect at a location corresponding a radially-extending lubrication bore. 
         [0009]    Subsynchronous vibrations are vibrations having a frequency that is lower than the rotational frequency of the shaft. Subsynchronous vibrations can be generated in the bearing system of a turbocharger during various operating conditions, including but not limited to cold starts and light to moderate accelerations. When they occur, subsynchronous vibrations can transmit unwanted noise into a vehicle. To address such vibrations, some turbocharger journal bearings include a groove that is formed along an inner surface thereof to alter oil whirl, and thus reduce subsynchronous vibration. Due to the relatively small size of some journal bearings, and the location of the groove (e.g., on the bearing inner surface), conventional methods of groove formation such as machining permit limited groove configurations. By using a laser cutting device and method to form one or more grooves on an inner surface of the journal bearings, the groove can be formed having any width, depth and/or pattern, permitting optimization of bearing design and improved vibration reduction. 
         [0010]    By providing a pattern of grooves on the journal bearing inner surface, the oil whirl frequency can be changed by the depth and size of the groove pattern. Advantageously, the onset of subsynchronous vibration can be avoided by designing some eccentricity into the rotor system during operation. In addition, the amount of oil cooling and the flow rate of oil can be varied by the sizing of the grooves depending on the thermal requirements of the bearing system. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]      FIG. 1  is a cross-sectional view of an exhaust gas turbocharger including journal bearings. 
           [0012]      FIG. 2  is a perspective view of a journal bearing including grooves formed on an inner surface. 
           [0013]      FIG. 3  is a side sectional view of a journal bearing including a helical groove formed on an inner surface. 
           [0014]      FIG. 4  is a side sectional view of a portion of a journal bearing wall illustrating a shape of the groove of  FIG. 3 . 
           [0015]      FIG. 5  is a schematic view of a laser cutting device. 
           [0016]      FIG. 6  is a schematic view of an alternative laser cutting device. 
           [0017]      FIG. 7  is a cross-sectional view of an alternative beam directing tool. 
           [0018]      FIG. 8  is a side cross-sectional view of a journal bearing including a uniform herringbone pattern of grooves formed on an inner surface. 
           [0019]      FIG. 9  is a side cross-sectional view of a journal bearing including a non-uniform herringbone pattern of grooves formed on an inner surface. 
           [0020]      FIG. 10  is a side cross-sectional view of a journal bearing including axially-extending grooves formed on an inner surface. 
           [0021]      FIG. 11  is a side cross-sectional view of a journal bearing including angled grooves formed on an inner surface. 
           [0022]      FIG. 12  is a side cross-sectional view of a journal bearing including a single circumferential groove formed on an inner surface. 
           [0023]      FIG. 13  is a side cross-sectional view of another journal bearing including axially extending grooves formed on an inner surface. 
           [0024]      FIG. 14  is a side cross-sectional view of a journal bearing including a spiral groove of non-uniform width formed on an inner surface. 
           [0025]      FIG. 15  is a side cross-sectional view of a journal bearing including a fish scale pattern formed on an inner surface. 
           [0026]      FIG. 16  is a side cross-sectional view of a journal bearing including another fish scale pattern formed on an inner surface. 
           [0027]      FIG. 17  is a side cross-sectional view of a journal bearing including another fish scale pattern formed on an inner surface. 
           [0028]      FIG. 18  is a perspective view of a journal bearing including grooves formed on an outer surface. 
           [0029]      FIG. 19  is a side cross-sectional view of a portion of a journal bearing including a sleeve disposed within the journal bearing. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    Referring to  FIG. 1 , an exhaust gas turbocharger  1  includes a turbine section  2 , a compressor section  6 , and a center bearing housing  10  disposed between, and connecting, the compressor section  6  to the turbine section  2 . The turbine section  2  includes a turbine housing (not shown) and a turbine wheel  4  disposed in the turbine housing. The compressor section  6  includes a compressor housing (not shown) and a compressor impeller  8  disposed in the compressor housing. The turbine wheel  4  is connected to the compressor impeller  8  via a shaft  14 . 
         [0031]    The shaft  14  is supported for rotation about a rotational axis  16  within in the bearing housing  10  via a pair of axially spaced journal bearings  18 ,  20 . For example, a compressor-side journal bearing  18  supports the shaft  14  adjacent the compressor section  6 , and a turbine-side journal bearing  20  supports the shaft  14  adjacent to the turbine section  2 . The journal bearings  18 ,  20  are semi-floating ring bearings which employ an inner oil film and an outer oil film to reduce noise (i.e., unbalance moan/whine and constant tone induced by rotor unbalance and inner oil whirl or whip in the bearing) and rotor amplitude at resonant frequencies. The inner oil film functions to carry the rotor against the external forces acting on the rotor, whereas the outer oil film, which is thick relative to the inner oil film, provides the rotor with a large damping coefficient to reduce rotor deflection at resonances and suppress noise. 
         [0032]    The axial spacing between the compressor-side journal bearing  18  and the turbine-side journal bearing  20  is maintained by cylindrical a journal bearing spacer  26 . In addition, a thrust bearing assembly  28  is disposed in the bearing housing  10  so as to provide axial support for the shaft  14 . The shaft  14  is reduced in diameter on the compressor side of the compressor-side journal bearing  18 , and a shoulder  15  is formed at the transition between diameters. The compressor impeller  8  and the thrust bearing assembly  28 , including a thrust bearing  22 , a thrust washer assembly  23 , and an oil flinger  24 , are all supported on the shaft  14  in the reduced diameter portion. The terminal end  14   a  of the shaft  14  extends axially beyond the compressor impeller  8  and includes an external thread. A nut  30  engages the thread, and is tightened sufficiently to clamp the compressor impeller  8  and the thrust bearing assembly  28  against the shoulder  15 . 
         [0033]    In use, the turbine wheel  4  in the turbine housing is rotatably driven by an inflow of exhaust gas supplied from the exhaust manifold of an engine. Since the shaft  14  connects the turbine wheel  4  to the compressor impeller  8  in the compressor housing, the rotation of the turbine wheel  4  causes rotation of the compressor impeller  8 . As the compressor impeller  8  rotates, it increases the air mass flow rate, airflow density and air pressure delivered to the engine&#39;s cylinders via an outflow from the compressor section  6 , which is connected to the engine&#39;s air intake manifold (not shown). 
         [0034]    The turbocharger bearing system is lubricated by oil from the engine. The oil is fed under pressure into the bearing housing  10  via an oil supply port  32  to lubricate the bearing surfaces within and about the journal bearings  18 ,  20 . More specifically, oil passes through individual bearing supply channels  34  and  36  for lubricating the journal bearings  18 ,  20 . The supply channels  34  and  36  open at generally axially centered positions with respect to the two journal bearings  18 ,  20  such that oil flow may occur in both directions axially to lubricate the bearing surfaces. The journal bearings  18 ,  20  have axially centered lubricating oil flow bores  60  that receive oil from the respective supply channels  34 ,  36 . Oil flowing over and through the journal bearings  18 ,  20  is eventually collected within a bearing housing sump chamber  38  for return circulation through an outlet port  40 . 
         [0035]    A bearing spacer  26  is disposed between the journal bearings  18 ,  20  for precise axial location and retention of the journal bearings  18 ,  20  within the bore  12 . The outer diameter of the spacer  26  is formed having an outer diameter that is less than the outer diameters of the journal bearings  18 ,  20 . Similarly, the inner diameter of the bearing spacer  26  is formed having a diameter that is larger than the inner diameter of the journal bearings  18 ,  20 . Furthermore, the spacer  26  has large central opening  27  that permits lubricating oil flow therethrough. 
         [0036]    Referring to  FIGS. 2-4 , the journal bearings  18 ,  20  are substantially structurally similar, whereby only the compressor-side journal bearing  18  will be described in detail. The journal bearing  18  is generally in the form of a hollow cylinder having a first end  52 , and a second end  54  opposed to the first end  52 . A longitudinal axis  62  extends between the first end  52  and the second end  54 . The axially-centered oil flow bore  60  is a radially-extending through opening that permits lubricating oil to flow from an outer surface  58  to an inner surface  56 . Adjacent each respective axial end  52 ,  54 , the inner surface  56  defines an inner bearing portion  57  that is shaped and dimensioned to fit with relatively close clearance about the shaft  14  with sufficient gap for the inner oil film. Likewise, adjacent each respective axial end  52 ,  54 , the outer surface  58  defines an outer bearing portion  59  that is shaped and dimensioned to fit with relatively close clearance within a bore  12  formed in the center bearing housing  10 , with sufficient gap for the outer oil film. The journal bearing  18  can be formed by various manufacturing techniques utilizing a variety of known bearing materials, such as leaded or unleaded bronze, aluminum, etc. 
         [0037]    The inner bearing portion  57  of the journal bearing  18  includes at least one groove  64  that extends between the first end  52  and the second end  54  along a helical path that is arranged at a helix angle θ 1  relative to the bearing longitudinal axis  62 . The helix angle θ 1  may be selected from any angle, and will be determined based on the requirements of the specific application. The groove width and depth will also be determined based on the requirements of the specific application. In addition, the groove edges  64   a ,  64   a , may be rounded or smoothed ( FIG. 4 ) to reduce turbulence in the vicinity of the groove  64 . The helical groove serves to alter oil whirl, whereby subsynchronous shaft motion and resulting vibration of the bearing is reduces, and thus noise is reduced. 
         [0038]    Referring to  FIG. 5 , the groove  64  is cut in the inner bearing portion  57  of the inner surface  56  using a laser cutting device  100  that includes a laser  102  and a beam directing tool  130 . Laser cutting using the laser cutting device  100  is advantageous since precise and accurate groove patterns can be formed on the interior surface  56  of the relatively small diameter bearing  18 . 
         [0039]    The type of laser used for cutting will depend on the specific application. For example, the laser  102  may be a carbon dioxide laser (CO 2 ) or neodymium-doped yttrium-aluminum-garnet (Nd:YAG) laser. The Nd:YAG laser uses a solid crystal substance to focus light onto its target. It can fire a continuous or rhythmic infrared beam that can be enhanced by secondary equipment, like optical pumping lamps or diodes. The CO 2  laser is a more powerful alternative to the Nd:YAG type, and uses a gas medium instead of a crystal for focusing light. As its name suggests, the laser&#39;s gas discharge consists of a large portion of carbon dioxide mixed with smaller amounts of nitrogen, helium, and hydrogen. Due to its cutting strength, the CO 2  laser is capable of shaping bulky steel plates up to 25 millimeters thick, as well as cutting or engraving thinner materials at lower power. 
         [0040]    The beam directing tool  130  is dimensioned to fit within the interior space of the bearing  18 . The beam directing tool  130  includes an elongate tube  132 , and a mirror  150  mounted within the tube  132 . The tube  132  includes a first end  134 , a second end  136  that is opposed to the first end  134 , and a longitudinal axis  140  that extends between the first end  134  and the second end  136 . The tube  132  includes an opening  138  disposed between the first and second ends  134 ,  136 . The mirror  150  is fixed within the tube at an axial position corresponding to the location of the opening  138 , and is oriented at a 45 degree angle relative to the tube longitudinal axis  140  with the reflective surface facing the opening  138 . The tube first end  134  is connected to an actuator  148  via, for example, a chuck  144 . The actuator  148  is configured to rotate the tube  132  about the tube longitudinal axis  140 , and translate the tube  132  along the tube longitudinal axis  140  in both directions. A precision bearing  149  supports the tube second end  136 . 
         [0041]    In use, the bearing  18  is mounted in a fixture  170  that holds the bearing  18  such that the position of the bearing  18  is fixed relative to the laser  102 , and such that the bearing longitudinal axis  62  is aligned with the beam  108  output from the laser  102 . In addition, the beam directing tool  130  is inserted into the bearing  18  such that the tube  132  is positioned within the bearing  18  so that the tube longitudinal axis  140  is coaxial with the bearing longitudinal axis  62 . In addition, the opening  138  is positioned facing the inner bearing portion  57  of the bearing inner surface  56 . By this configuration, the mirror  150  lies in the path of the laser beam  108 . The mirror  150  redirects the laser beam toward the inner bearing portion  57 , whereby grooves (i.e., grooves  64 ) can be formed in the inner bearing portion  57 . The position of the tube  132 , and thus the mirror  150 , is controlled by the actuator  148 . A controller  180  is used to coordinate the output of the laser  102  (e.g., power and duration) and the actuator  148 , whereby material can be removed from the bearing inner surface  56  (particularly, the inner bearing portion  57 ) to a precise width and depth, and in any pattern, including, but not limited to, the helical groove  64  described above with respect to  FIGS. 2-4 . 
         [0042]    The laser cutting device  100  further includes a vacuum source  182  and a vacuum line  184  that extends from the vacuum source  182  to the vicinity of the cutting operation. For example, the line  184  may open within the bearing  18  to remove the vaporized material during cutting, and prevent the vaporized material from coating the bearing surfaces  56 ,  57 ,  58 ,  59 . In the illustrated embodiment, the vacuum line  184  extends within the tube  132  to the vicinity of the opening  138 , and the tube sidewall adjacent the opening  138  includes one or more perforations  142  that permit the vapors to pass into the interior space of the tube  132  and be withdrawn from the bearing  18  via the vacuum line  184 . 
         [0043]    In some embodiments, the laser cutting device  100  may also include a cooling gas source  186  (i.e., air or inert gas), and a gas supply line  188  that extends within the tube  132  to the vicinity of the opening  138 . In addition, the perforations  142  in the tube distal end  136  permit a flow of gas through the tube sidewall toward the bearing inner surface  56 , whereby the surface  56  can be cooled. 
         [0044]    Referring to  FIG. 6 , an alternative laser cutting device  200  includes all the components of the laser cutting device  100  described above, in a slightly different configuration. For example, in the laser cutting device  200 , the position of the tube  132 , and thus the mirror  150 , is fixed relative to the laser  102 , and the fixture  170 , which supports the bearing  18 , is connected to the actuator  148 . The actuator  148  is configured to rotate the fixture  170  about the tube longitudinal axis  140 , and translate the fixture  170  along the tube longitudinal axis  140  in both directions. The controller  180  coordinates the output of the laser  102  (e.g., power and duration) and the actuator  148 , whereby material can be removed from the inner bearing portion  57  of the bearing surface in a desired pattern. 
         [0045]    The laser cutting device  200  includes a slightly modified beam directing tool  230 . The beam directing tool  230  is dimensioned to fit within the interior space of the bearing  18 . The beam directing tool  230  includes an elongate tube  232 , and the mirror  150  mounted within the tube  132 . The tube  232  includes a first end  234  that is fixed relative to the laser  102 , a second end  236  that is opposed to the first end  234 , and a longitudinal axis  240  that extends between the first end  234  and the second end  236 . The mirror  150  is fixed to the tube second end  236 , and is oriented at a 45 degree angle relative to the tube longitudinal axis  240 . 
         [0046]    In this embodiment, the vacuum line  184  and the gas supply line  188  are external to the beam directing tool  230 . 
         [0047]    Referring to  FIG. 7 , another modified beam directing tool  330  is dimensioned to fit within the interior space of the bearing  18 , and can be used in the earlier-described laser cutting device  100 . The beam directing tool  330  includes an elongate tube  332 . The tube  332  includes a first end  334  that is supported by the actuator  148  (not shown in  FIG. 7 ), a second end  336  that is opposed to the first end  334 , and a longitudinal axis  340  that extends between the first end  334  and the second end  336 . The mirror  150  is rotatably supported on the tube second end  336  via a pivot pin  358  such that the angle of the mirror  150  relative to the tube longitudinal axis  340  can be varied. In addition, the beam directing tool  330  includes a drive shaft  356  rotatably supported inside the tube  332  and extending in parallel with the tube longitudinal axis  340 , and a gear set  352  that connects the drive shaft  356  to the mirror  150 . The gear set  352  may include a pair of bevel gears  354   a ,  354   b  that transmit the rotational motion of the drive shaft  356  to a rotational motion of the mirror  150  about the pin  358 , which is oriented transverse to the tube longitudinal axis  340 . The actuator  148  is configured to rotate the drive shaft  356  about the tube longitudinal axis  340 , and translate the tube  332  along the tube longitudinal axis  340  in both directions. The controller  180  coordinates the output of the laser  102  (e.g., power and duration) and the actuator  148 , whereby material can be removed from the inner bearing portion  57  of the bearing inner surface  56  in a desired pattern. 
         [0048]    As previously discussed, the laser cutting device  100 ,  200  can be used to remove material from the bearing inner surface  56  to a precise width and depth, and in any pattern, including, but not limited to, the helical groove  64  described above with respect to  FIGS. 2-4 . Several additional exemplary groove patterns will now be described. 
         [0049]    Referring to  FIG. 8 , a journal bearing  160  includes a first end  166 , and a second end  168  opposed to the first end  166 . A longitudinal axis  162  extends between the first end  166  and the second end  168 . The journal bearing  180  includes a radially-extending oil flow bore  169  that is axially centered within each inner bearing portion  163  of the inner surface  167 . The oil flow bores  169  permit lubricating oil to flow from an outer surface  165  to the inner bearing portion  163 . The inner bearing portion  163  of the journal bearing  180  includes a series of grooves  164  in a herringbone pattern. In particular, each groove  164  is V shaped, is of uniform width and depth, and has the same width and depth as the adjacent groove  164 . The grooves  164  are equally spaced about the circumference of the inner bearing portion  163 , whereby lands  161  are provided between the grooves  164 . One of the grooves  164  intersects the oil flow bore  169 . 
         [0050]    Referring to  FIG. 9 , another journal bearing  260  includes a first end  266 , and a second end  268  opposed to the first end  266 . A longitudinal axis  262  extends between the first end  266  and the second end  268 . The journal bearing  260  includes a radially-extending oil flow bore  269  that is axially centered within each inner bearing portion  263  of the inner surface  267 . The oil flow bores  269  permit lubricating oil to flow from an outer surface  265  to the inner bearing portion  263 . The inner bearing portion  263  of the journal bearing  260  includes a series of grooves  264  in a herringbone pattern. Each groove  264  is V shaped, and is of uniform depth. However, in this embodiment, the width of the grooves is varied. For example, a first groove  264   a  has a first width, and the adjacent groove  264   b  has a second width that is greater than the first width. The grooves  264  may have alternating widths (as shown), or have progressively increasing (or decreasing) widths. The grooves  264  are equally spaced about the circumference of the inner bearing portion  263 , whereby lands  261  are provided between the grooves  264 . One of the grooves  264  intersects the oil flow bore  269 . It is contemplated that the depth dimension and/or groove spacing can be varied rather than, or in addition to, varying the width dimension. In addition the lands  261  may be omitted. 
         [0051]    Referring to  FIG. 10 , another journal bearing  360  includes a first end  366 , and a second end  368  opposed to the first end  366 . A longitudinal axis  362  extends between the first end  366  and the second end  368 . The journal bearing  360  includes an axially-centered oil flow bore  369  that permits lubricating oil to flow from an outer surface  365  to an inner surface  367 . The inner bearing portion  363  of the inner surface  367  of the journal bearing  360  includes a series of grooves  364  that extend axially. In the illustrated embodiment, adjacent grooves  364  have the same width and depth, and are equally spaced apart from each other about the circumference of the inner surface  367  whereby lands  361  are provided between the grooves  164 . In other embodiments, adjacent grooves  364  are not equally spaced apart from each other about the circumference, or the lands  361  may be omitted. The axially-extending grooves  364  force the rotor to operate at a higher eccentricity, thus lowering whirl frequency. In addition, the axially-extending grooves  364  aid oil flow within the bearing  360 . 
         [0052]    Referring to  FIG. 11 , another journal bearing  460  includes a first end  466 , and a second end  468  opposed to the first end  466 . A longitudinal axis  462  extends between the first end  466  and the second end  468 . The journal bearing  460  includes an axially-centered oil flow bore  469  that permits lubricating oil to flow from an outer surface  465  to an inner surface  467 . The inner bearing portion  463  of the inner surface  467  of the journal bearing  460  includes a series of grooves  464  that extend between the first end  466  and the second end  468  at an angle θ 2  relative to the bearing longitudinal axis  462 . In the illustrated embodiment, the angle θ 2  is a positive, acute angle for a bearing rotation that is counterclockwise when viewed from the bearing second end  468 . The adjacent grooves  464  are equally spaced apart from each other about the circumference of the inner surface  467 , whereby lands  461  are defined between the grooves  464 . In other embodiments, adjacent grooves  464  are not equally spaced apart from each other about the circumference or the lands  416  may be omitted. The angled grooves  464  reduce oil whirl speed and aid oil flow within the bearing  460 . 
         [0053]    Referring to  FIG. 12 , another journal bearing  560  includes a first end  566 , and a second end  568  opposed to the first end  566 . A longitudinal axis  562  extends between the first end  566  and the second end  568 . An inner surface  567  of the journal bearing  560  defines a bearing portion  563  adjacent each of the first and second ends  566 ,  568 . Each inner bearing portion  563  of the inner surface  567  includes multiple radially-extending oil flow bores  569  that are axially centered within the inner bearing portion  563 . The oil flow bores  569  permit lubricating oil to flow from an outer surface  565  to the inner bearing portion  563 . For each bearing portion  563 , the inner surface  567  of the journal bearing  560  includes a single groove  546  that extends circumferentially and intersects each bore  569 . The groove  546  serves as a relief groove, whose shorter effective length results in higher eccentricity. The groove  546  may have a uniform width, or a non-uniform width, depending on the requirements of the specific application. 
         [0054]    Referring to  FIG. 13 , another journal bearing  660  includes a first end  666 , and a second end  668  opposed to the first end  666 . A longitudinal axis  662  extends between the first end  666  and the second end  668 . The journal bearing  660  includes multiple radially-extending oil flow bores  669  that are axially centered within each inner bearing portion  663  of the inner surface  667 . The oil flow bores  669  permit lubricating oil to flow from an outer surface  665  to the inner bearing portion  663 . The inner bearing portion  663  of the inner surface  667  includes a series of grooves  664  that extend axially, and each groove  664  intersects a single bore  669 . Like the journal bearing  360  described above with respect to  FIG. 10 , the axially-extending grooves  664  force the rotor to operate at a higher eccentricity, thus lowering whirl frequency. In addition, the axially-extending grooves  664  aid oil flow within the bearing  660 . 
         [0055]    Referring to  FIG. 14 , another journal bearing  760  includes a first end  766 , and a second end  768  opposed to the first end  766 . A longitudinal axis  762  extends between the first end  766  and the second end  768 . The journal bearing  760  includes a radially-extending oil flow bore  769  that is axially centered within each inner bearing portion  763  of the inner surface  767 . The oil flow bores  769  permit lubricating oil to flow from an outer surface  765  to the inner bearing portion  763 . The inner bearing portion  763  of the inner surface  767  includes a tapered spiral groove  764 . The groove  764  intersects the oil flow bore  769 . The width of the groove  764  is relatively narrow in the vicinity  764   a  of the oil flow bore  769  compared to a width of the groove at locations  764   b  spaced apart from the oil flow bore  769 , for example at the intersection with the first and second ends  766 ,  768 . The relatively wide groove width adjacent the first and second ends  766 ,  768  provides increased oil flow, which may be required in some applications to provide increased bearing cooling. 
         [0056]    Referring to  FIGS. 15-17 , another journal bearing  860  includes a first end  866 , and a second end  868  opposed to the first end  866 . A longitudinal axis  862  extends between the first end  866  and the second end  868 . The journal bearing  860  includes a radially-extending oil flow bore  869  that is axially centered within each inner bearing portion  863  of the inner surface  867 . The oil flow bores  869  permit lubricating oil to flow from an outer surface  865  to the inner bearing portion  863 . The inner bearing portion  863  of the inner surface  867  includes a “fish scale” pattern. The fish scale pattern includes an ordered arrangement of chevron-shaped recesses  864 . For example, the recesses  864  are arranged along a line L 1  that is at an angle θ 3  relative to the bearing longitudinal axis  862 . In addition, the chevron-shaped recesses  864  are oriented such that the apex of the chevron points circumferentially in the direction of bearing rotation ( FIG. 15 ). The line L 1  intersects the bore  869 . The fish scale pattern is a “semi-continuous” groove pattern since the individual recesses  864  are non-intersecting but positioned in sufficiently close proximity to approximate a continuous groove. The fish scale pattern is configured to disturb formation of oil whirl, thus reducing subsynchronous vibrations. In addition, the recess shape also helps the lubricating oil to flow out more quickly towards each axial end  866 ,  868 . To provide increased reduction of whirl, the chevron-shaped recesses  864  can be arranged along multiple lines L 1 , L 2  that are angled relative to the bearing longitudinal axis  862 , where the lines L 1 , L 2  are intersecting, for example, at a location corresponding to the bore  869  ( FIG. 16 ). Again, the chevron-shaped recesses  864  can be oriented such that the apex of the chevron points in the direction of rotation. To provide still further increased reduction of whirl, the chevron-shaped recesses  864  can be oriented such that the apex of the chevron points circumferentially in a direction opposite the direction of bearing rotation ( FIG. 17 ). 
         [0057]    Referring to  FIG. 18 , the bearings  18 ,  20  described above have included grooves  64  formed on an inner surface  56  thereof. It is contemplated that grooves  64 ′ may be provided on the bearing outer surface  58  in addition to, or as an alternative to, the grooves  64  formed on the inner surface. For example, in some embodiments, the grooves  64 ′ are formed on the outer bearing portion  59  of the bearing outer surface  58 . The laser cutting device  100 ,  200  can be used to remove material from the bearing outer surface  58  to a precise width and depth, and in any pattern, including, but not limited to, the angled groove  64 ′ illustrated in  FIG. 18 . 
         [0058]    The laser cutting device  100 ,  200  described above provides groove patterns having a depth of 0.0254 mm, consistent with some laser etching processes. However, the laser cutting device is not limited to this depth, and may provide groove patterns having a depth of 0.50 mm, which is consistent with some laser engraving processes, or more, depending on the requirements of the specific application. 
         [0059]    The laser cutting device  100 ,  200  described above provides groove patterns in which the groove is a shallow curve having edges  64   a ,  64   a  that are rounded or smoothed to reduce turbulence in the vicinity of the groove. However, the groove shape is not limited to this, and may be formed having a rectilinear or other shape, depending on the requirements of the specific application. 
         [0060]    Referring to  FIG. 19 , the laser cutting device  100 ,  200  described above includes a vacuum source  182  and a vacuum line  184  that are configured to remove the vaporized material during cutting, and prevent the vaporized material from coating the bearing surfaces  56 ,  57 ,  58 ,  59 . In addition to, or as an alternative to, including the vacuum source  182  and vacuum line  184 , the laser cutting device  100 ,  200  may further include a sleeve  90  that is received coaxially within the journal bearing  18 ,  760 . The sleeve  90  includes a cutout  92  having the profile of the groove  64 ,  764  to be formed on an inner surface of the bearing  18 ,  760 , and is placed inside the bearing  18 ,  760  prior to laser cutting. The sleeve  90  serves to prevent the vaporized material from depositing on the bearing surfaces. In the exemplary embodiment of  FIG. 19 , the cutout  92  has the profile of the tapered spiral groove  764  described above with respect to  FIG. 14 , but is not limited to this profile. In particular, the cutout  92  can be any shape and dimension, and has a profile that is selected to correspond to the shape and dimension of the groove to be cut on the bearing surface. Moreover, the sleeve  90  is not limited to being used internally, and can be employed externally to protect external bearing surfaces for cases where a groove is formed on an external surface. 
         [0061]    The exhaust gas turbocharger  1  includes floating ring bearings which employ an inner oil film and an outer oil film to reduce noise (i.e., unbalance whistle and constant tone induced by rotor unbalance and inner oil whirl in the bearing) and rotor amplitude at resonant frequencies. The illustrated embodiments include semi-floating ring bearings  18 ,  20  which include a bearing ring that does not rotate. The turbocharger  1  is not limited to this type of floating ring bearing, and can, for example, employ rotating floating ring bearings which include a rotating bearing ring. The grooves can be formed on the inner surface of the rotating floating ring bearings. The turbocharger  1  may also include other types of journal bearings, including, but not limited to, three lobe and lemon bore bearings. 
         [0062]    Although the etched bearings have been described herein with respect to supporting a rotating shaft in a turbocharger, the etched bearings described herein are not limited to this application. For example, the etched bearings could be employed to support rotating shafts in other applications found within passenger and commercial vehicles, and in applications outside the automotive field, such as, but not limited to, marine, military, agriculture, aerospace, power generation, heating and cooling, recreational equipment, etcetera. 
         [0063]    Similarly, although the laser cutting device has been described herein with respect to machining a surface of bearing, the laser cutting device is not limited to this application, and can be used to remove material from the surfaces of other metal and non-metal objects. 
         [0064]    Selected illustrative embodiments of the invention are described above in some detail. It should be understood that only structures considered necessary for clarifying the present invention have been described herein. Other conventional structures, and those of ancillary and auxiliary components of the system, are assumed to be known and understood by those skilled in the art. Moreover, while working examples of the laser cutting device and bearings produced using the same have been described above, the laser cutting device and bearings produced using the same are not limited to the working examples described above, but various design alterations may be carried out without departing from the present invention as set forth in the claims.