Abstract:
An annular balance adjusting device ( 50 ) is included in the clamping region of a turbocharger ( 1 ) rotating assembly. The annular balance adjusting device ( 50 ) includes an annular member ( 51, 61 ) having a non-uniform weight distribution. By setting the rotational orientation of the annular member ( 51, 61 ) relative to the rotating assembly ((not labeled)), imbalance of the rotating assembly can be addressed. The annular balance adjusting device ( 50 ) can be used to correct the imbalance of the rotating assembly, thereby reducing turbocharger ( 1 ) vibration and increasing turbocharger ( 1 ) durability.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and all the benefits of U.S. Provisional Application No. 62/059,235, filed on Oct. 3, 2014, and entitled “Devices and Method for Adjusting Turbocharger Rotating Assembly Balance”, which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention eliminates a potential source of imbalance in high speed rotating assemblies, and in particular in rotating assemblies used in turbochargers. 
       BACKGROUND 
       [0003]    A turbocharger is a type of forced induction system used with internal combustion engines. Turbochargers deliver compressed air to an engine intake, allowing more fuel to be combusted, thus boosting the horsepower of the engine without significantly increasing engine weight. As such, turbochargers permit the use of smaller engines that develop the same amount of horsepower as larger, normally aspirated engines. Using a smaller engine in a vehicle has the desired effect of decreasing the mass of the vehicle, increasing performance, and enhancing fuel economy. Moreover, the use of turbochargers permits engine downsizing which results in reduced CO 2  emissions, a highly desirable goal for the environment. 
         [0004]    Turbochargers typically include a turbine housing connected to the exhaust manifold of the engine, a compressor housing connected to the intake manifold of the engine, and a center bearing housing disposed between and coupling the turbine and compressor housings together. A turbine wheel in the turbine housing is rotatably driven by an inflow of exhaust gas supplied from the exhaust manifold or cylinder head. A shaft is radially supported for rotation in the center bearing housing, and connects the turbine wheel to a compressor impeller in the compressor housing so that rotation of the turbine wheel causes rotation of the compressor impeller. The shaft connecting the turbine wheel and the compressor impeller defines a line which is the axis of rotation. As the compressor impeller rotates, it increases the air mass flow rate, airflow density and air pressure delivered to the cylinders of the engine via the engine intake manifold. 
         [0005]    During operation of the turbocharger, the rotating assembly of the turbocharger, comprising turbine wheel, compressor wheel, and connecting shaft, may rotate at 10,000 RPM to 300,000 RPM or more. As part of the turbocharger manufacturing process, the rotating assembly is balanced to reduce vibration, thus improving turbocharger durability. In this regard, the turbine wheel is materially fused to the shaft to make a unitary shaft-and-wheel assembly. The shaft-and-wheel assembly can be accurately machined with shaft diameters ground to tolerances in the 2.5 micron regime; thus, an inherent balance of the shaft-and-wheel assembly is generally within acceptable limits for some applications. In other applications, some component balancing may be required. The compressor wheel, on the other hand, is an extremely difficult part to machine and balance. In addition, the compressor wheel is secured to the free end of the shaft of the shaft-and-wheel assembly via a nut, whereby further imbalance can sometimes be introduced into the rotating assembly. 
       SUMMARY 
       [0006]    In some aspects, an annular balance adjusting device includes two or more washers of known imbalance that are disposed on the compressor wheel-end of the shaft at a location outboard relative to the compressor wheel, where the term “outboard” refers to being further from the turbine housing of the turbocharger, and the term “inboard” refers to being closer to the turbine housing of the turbocharger. The rotational orientation of the washers relative to each other, and the relative rotational orientation of the group of washers relative to the rotating assembly is set to correspond to a desired balance change, which in some examples offsets a measured imbalance of the rotating assembly. By this approach, adjustment of the balance of the rotating assembly is performed without a machining process that includes removal of material from the compressor nut. Moreover, the adjustment process can be performed manually and in the field. By removing the machining operations from the balancing process, the time, complexity, required expertise required for turbocharger balancing are reduced. In addition, the potential for turbocharger contamination is also reduced since there is no longer a need to remove material from the compressor nut by machining and infiltration of machining chips and debris into the turbocharger is avoided. 
         [0007]    Moreover, the annular balance adjusting device permits adjustment of the balance of the turbocharger without removal of the turbocharger from the vehicle. This is advantageous, since it permits adjustment, and readjustment, of the balance of the turbocharger over its operational life. For example, by providing the annular balance adjusting device on the rotating assembly, imbalance increases due to operation and wear of the turbocharger (e.g., migration) can be corrected in the field without removal of the turbocharger from the vehicle, thus reducing time required for servicing the engine system. 
         [0008]    Rather than reducing rotating assembly imbalance, the annular balance adjusting device can alternatively be used to quickly and reversibly generate imbalance and/or control the level of imbalance in the rotating assembly for testing purposes. For example, the ability to quickly, reversibly and adjustably control rotating assembly imbalance can be beneficial when it is necessary to correlate the sensitivity of the acoustics of the entire vehicle to the imbalance of the turbocharger. The annular balance adjusting device permits adjustment of the imbalance of a single turbocharger which remains installed in the vehicle and can present with multiple imbalance levels. This can be compared to some conventional methods of correlating the sensitivity of the acoustics of the entire vehicle to the imbalance of the turbocharger in which multiple turbochargers of varying imbalance level are sequentially tested within the vehicle. 
         [0009]    The rotating assembly includes a shaft having a first end, a second end and a rotational axis that extends through the first end and the second end. The rotating assembly includes a turbine wheel rigidly connected to the second end of the shaft, a compressor wheel disposed on the shaft such that a nose of the compressor wheel is adjacent to the first end of the shaft, a nut that engages the first end of the shaft so as to secure the compressor wheel to the first end of the shaft, and the annular balance adjusting device disposed on the shaft between the nose and the first end of the shaft. The annular balance adjusting device has a predetermined non-uniform mass distribution along its circumference, and is configured to be selectively rotated about the rotational axis relative to the nose so as to adjust the balance of the rotating assembly. 
         [0010]    In some aspects, the annular balance adjusting device is selectively rotatable about the rotational axis between predetermined discrete rotational orientations relative to the nose. The annular balance adjusting device includes a first washer and a second washer that is selectively rotatable relative to the first washer. Each of the first washer and the second washer has a predetermined non-uniform mass distribution along its respective circumference. The first washer has a first set of surface features on a first side thereof that cooperate with surface features provided on the nose to retain the first washer in a desired rotational orientation relative to the nose, and a second set of surface features on a second side thereof that cooperate with surface features provided on the second washer to retain the first washer in a desired rotational orientation relative to the second washer. The first set of surface features comprise one of detents and protrusions, and the surface features provided on the nose comprise the other of the detents and protrusions, and the second set of surface features comprises one of detents and protrusions, and the surface features provided on the second washer comprise the other of the detents and protrusions. The annular balance adjusting device is disposed on the shaft between the nut and the nose, and the nut is used to retain the annular balance adjusting device in a desired rotational orientation relative to the nose. The annular balance adjusting device includes a first washer and a second washer that is selectively rotatable relative to the first washer. Each of the first washer and the second washer has a predetermined non-uniform mass distribution along its respective circumference. A fastener secures the first washer and the second washer to the shaft and maintains the first washer in a desired rotational orientation with respect to the second washer. 
         [0011]    In some aspects, the nut includes a compressor wheel-facing surface, an axially outward-facing surface that is opposed to the compressor wheel-facing surface, and an outer edge that extends between the compressor wheel-facing surface and the axially outward-facing surface. The annular balance adjusting device comprises a hollow cylindrical collar that encloses the axially outward-facing surface of the nut and at least a portion of the outer edge of the nut. The collar comprises a predetermined non-uniform mass distribution along its circumference, and includes a fastener that secures the collar to the nut. The outer edge of the nut includes nut surface features that are configured to engage corresponding collar surface features formed on an inner surface of the collar so as to rotationally locate the collar relative to the nut. The nut surface features comprise axially-extending grooves formed on at least a portion of the outer edge of the nut, and the collar surface features comprise axially-extending grooves formed on the inner surface of the collar. 
         [0012]    In some aspects, the nut comprises a compressor wheel-facing surface, an axially outward-facing surface that is opposed to the compressor wheel-facing surface, and an outer edge that extends between the compressor wheel-facing surface and the axially outward-facing surface. The annular balance adjusting device comprises a hollow cylindrical collar that encloses the axially outward-facing surface and at least a portion of the outer edge. The collar includes a predetermined non-uniform mass distribution along its circumference, and includes an elastic member disposed between the collar and the axially outward-facing surface. The elastic member provides a spring force that urges the collar to move axially along the shaft in a direction away from the compressor wheel. The nose comprises a radially outward-protruding flange and the collar includes a radially inward-protruding lip wherein the collar encircles the radially outward-protruding flange such that the radially outward-protruding flange is disposed between the radially inward-protruding lip and a closed end face of the collar. The radially inward-protruding lip is urged against the radially outward-protruding flange via the spring force of the elastic member and the collar is retained on the nose by engagement of the radially inward-protruding lip with the radially outward-protruding flange. The outer edge of the nut includes nut surface features that are configured to engage corresponding collar surface features formed on an inner surface of the collar so as to rotationally locate the collar relative to the nut. The collar is configured to move relative to the nose between a first position in which the radially inward-protruding lip is urged against the radially outward-protruding flange via the spring force of the elastic member and the collar is axially retained on the nose by engagement of the radially inward-protruding lip with the radially outward-protruding flange, and a second position in which the radially inward-protruding lip is axially spaced apart from the radially outward-protruding flange and the nut surface features no longer engage the corresponding collar surface features, so as to permit rotation of the collar about the rotational axis relative to the nose, and wherein the elastic member biases the collar to the first position. The rotational orientation of the collar relative to the nose is fixed via engagement of the nut surface features with the corresponding collar surface features. 
         [0013]    In some aspects, a turbocharger includes a bearing housing that rotatably supports a shaft including a first end, a second end and a rotational axis that extends through the first end and the second end. The turbocharger includes a turbine wheel that is rigidly connected to the second end of the shaft, a compressor wheel disposed on the shaft such that a nose of the compressor wheel is adjacent to the first end of the shaft. The compressor wheel, the turbine wheel and the shaft, together provide a rotating assembly of the turbocharger. A nut engages the first end of the shaft so as to secure the compressor wheel to the first end of the shaft. The turbocharger further includes an annular balance adjusting device disposed on the shaft between the nose and the first end of the shaft. The annular balance adjusting device has a predetermined non-uniform mass distribution along its circumference, and is configured to be selectively rotated about the rotational axis relative to the nose so as to adjust the balance of the rotating assembly. 
         [0014]    In some aspects, a method for adjusting the balance of a rotating assembly is provided. The rotating assembly includes a shaft, a turbine wheel fixed to one end of the shaft, and a compressor wheel secured to an opposed end of the shaft via a nut. The method includes providing an annular balance adjusting device on the opposed end of the shaft, the annular balance adjusting device having a predetermined non-uniform mass distribution along its circumference, where the annular balance adjusting device is configured to be selectively rotated about a rotational axis of the shaft relative to the compressor wheel. The method further includes rotating the annular balance adjusting device about the rotational axis relative to the compressor wheel so as to adjust the balance of the rotating assembly. 
         [0015]    The method may involve the annular adjusting device including at least the following features: a first washer and a second washer that is selectively rotatable relative to the first washer; each of the first washer and the second washer having a predetermined non-uniform mass distribution along its respective circumference; the first washer has a first set of surface features on a first side thereof that cooperate with surface features provided on the nose to retain the first washer in a desired rotational orientation relative to the nose; and a second set of surface features on a second side thereof that cooperate with surface features provided on the second washer to retain the first washer in a desired rotational orientation relative to the second washer. Moreover, the method may include the steps of determining a balance change vector that corresponds to a magnitude and direction of a desired balance change to be applied to the rotational assembly; selecting a rotational orientation of the first washer relative to the compressor wheel corresponding to a first imbalance vector and a rotational orientation of the second washer relative to the compressor wheel corresponding to a second imbalance vector such that the sum of the first imbalance vector and the second imbalance vector is made equal to the balance change vector; and securing the first washer and the second washer to the rotating assembly such that the rotational orientation of the first washer relative to the compressor wheel and the rotational orientation of the second washer relative to the compressor wheel are maintained. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The present invention is illustrated by way of example and not limitation in the accompanying drawings in which like reference numbers indicate similar parts, and in which: 
           [0017]      FIG. 1  is a cross-sectional view of an exhaust gas turbocharger including an annular balance adjusting device in the clamping region of the rotating assembly; 
           [0018]      FIG. 2  is an enlarged cross-sectional view of the clamping region of the rotating assembly showing the annular balance adjusting device; 
           [0019]      FIG. 3  is a schematic illustration of selection of adjustment angles of washers of the annular balance adjusting device to provide a known overall imbalance vector; 
           [0020]      FIG. 4  is an end view of the washers of the annular balance adjusting device including axial openings used to provide washer imbalance; 
           [0021]      FIG. 5  is an end view of an alternative embodiment of the washers of the annular balance adjusting device including radial openings used to provide washer imbalance; 
           [0022]      FIG. 6  is an end view of another alternative embodiment of the washers of the annular balance adjusting device including scallops formed in the washer peripheral edge to provide washer imbalance; 
           [0023]      FIG. 7  is a perspective view of another alternative embodiment of the washers of the annular balance adjusting device including a localized mass in the form of a set screw to provide washer imbalance; 
           [0024]      FIG. 8  is a perspective view of the washers of the annular balance adjusting device including protrusions and detents formed on axial surfaces and used to retain relative rotational orientations of the washers; 
           [0025]      FIG. 9  is an enlarged cross-sectional view of the clamping region of the rotating assembly showing an alternative configuration of the annular balance adjusting device of  FIG. 1 ; 
           [0026]      FIG. 10  is an enlarged cross-sectional view of the clamping region of the rotating assembly showing another alternative configuration of the annular balance adjusting device of  FIG. 1 ; 
           [0027]      FIG. 11  is a side cross-sectional view of the compressor wheel end of the rotating assembly showing an alternative embodiment annular balance adjusting device; 
           [0028]      FIG. 12  is a cross-sectional view of the alternative embodiment annular balance adjusting device as seen along line  12 - 12  of  FIG. 11 ; 
           [0029]      FIG. 13  is a side cross-sectional view of the compressor wheel end of the rotating assembly showing another alternative embodiment annular balance adjusting device; and 
           [0030]      FIG. 14  is a side cross-sectional view of the compressor wheel end of the rotating assembly showing another alternative embodiment annular balance adjusting device; and 
           [0031]      FIG. 15  is a side cross-sectional view of the compressor wheel end of the rotating assembly showing another alternative embodiment annular balance adjusting device. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    Referring to  FIGS. 1 and 2 , an exhaust gas turbocharger  1  includes a compressor section  10 , a turbine section  20 , and a center bearing housing  8  disposed between and connecting the compressor section  10  to the turbine section  20 . The turbine section  20  includes a turbine housing  22  that defines an exhaust gas inlet  24 , an exhaust gas outlet  28 , and a turbine volute  26  disposed in the fluid path between the exhaust gas inlet  24  and exhaust gas outlet  28 . A turbine wheel  30  is disposed in the turbine housing  22  between the turbine volute  26  and the exhaust gas outlet  28 . The turbine wheel  30  is fixed to an end  4  of a shaft  2  for example by welding. The shaft  2  is rotatably supported within in the bearing housing  8 , and extends into the compressor section  10 . The compressor section  10  includes a compressor housing  12  that defines an air inlet  16 , an air outlet (not shown), and a compressor volute  18 . A compressor wheel  14  is disposed in the compressor housing  12  between the air inlet  16  and the compressor volute  18 . The compressor wheel  14  is disposed on an opposed, stub end  6  of the shaft  2 , and secured to the stub end  6  by a nut  34 . The turbine wheel  30 , the compressor wheel  14 , and the shaft  2  together form the rotating assembly (not labeled) of the turbocharger  1 . 
         [0033]    In use, the turbine wheel  30  in the turbine housing  22  is rotatably driven by an inflow of exhaust gas supplied from the exhaust manifold of an engine. Since the turbocharger shaft  2  is rotatably supported in the bearing housing  8  and connects the turbine wheel  30  to the compressor wheel  14 , the rotation of the turbine wheel  30  causes rotation of the compressor wheel  14  within the compressor housing  12 . As the compressor wheel  14  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 air outlet, which is connected to the engine&#39;s intake manifold. 
         [0034]    The turbocharger  1  further includes an annular balance adjusting device  50  disposed on the shaft  2  between the compressor wheel  14  and the stub end  6  of the shaft  2 . The annular balance adjusting device  50  is retained on the shaft stub end  6  via the nut  34 . The annular balance adjusting device  50  is selectively rotatable about the rotational axis R between predetermined discrete rotational orientations relative to the compressor wheel  14  and shaft  2  to permit adjustment of the imbalance level of the rotating assembly (not labeled) of the turbocharger  1 , as discussed further below. 
         [0035]    Referring to  FIG. 3 , the annular balance adjusting device  50  includes a first washer  51 , and a second washer  61  that is selectively rotatable relative to the first washer  51 . The first washer  51  is a thin, disc-shaped plate having a central opening  55 . The first washer  51  includes a first side  52  (not shown) that faces the compressor wheel nose  13 , and a second side  53  that is opposed to the first side  52  (not shown) and faces the second washer  61 . Similarly, the second washer  61  is a thin, disc-shaped plate having a central opening  65 . The second washer  61  includes a first side  62  that faces the first washer  51 , and a second side  63  (not shown) that is opposed to the first side  62  and faces the nut  34 . Each of the first and second washers  51 ,  61  have an outer diameter defined by an outer peripheral edge  54 ,  64  that corresponds generally to an outer diameter of a nose  13  of the compressor wheel  14 , and an inner diameter that corresponds generally to an outer diameter of the shaft stub end  6  with minimal clearance. 
         [0036]    Each of the first washer  51  and the second washer  61  also has a predetermined, non-uniform mass distribution along a circumference thereof. The mass distribution (e.g., magnitude and direction) of the first washer  51  can be represented by a first vector V 1 . Likewise, the mass distribution of the second washer can be represented by a second vector V 2 . When the first washer  51  is arranged with the second washer  61  in a stacked configuration and in a given relative rotational orientation, the sum of first and second vectors V 1 , V 2  corresponds to an overall imbalance vector Vo that represents the magnitude and direction of imbalance that is provided by the annular balance adjusting device  50  when the washers  51 ,  61  are in the given orientation. The overall imbalance of the annular balance adjusting device  50  can be selected by strategically selecting the relative orientations of the first and second washers  51 ,  61 . 
         [0037]    Referring to  FIG. 4 , there are many ways to achieve the predetermined non-uniform mass distribution of the washers  51 ,  61 . In some embodiments, each of the first and second washers  51 ,  61  have one or more weight distributing openings  58 ,  68  disposed between the central opening  55 ,  65  and the outer peripheral edge  54 ,  64  thereof that function to provide a known, imbalanced weight distribution about a circumference of the washer  51 ,  61 . In particular, the arrangement of the openings (e.g., size, shape, location, and orientation) is selected to provide a predetermined non-uniform mass distribution along a circumference of the washer  51 ,  61 . 
         [0038]    In one example, the weight distributing openings  58 ,  68  extend axially. In this example, the mass distribution of the first washer  51  is different than that of the second washer  61 , but the washers  51 ,  61  are not limited to this. The first washer  51  includes four axial weight distributing openings  58  that are disposed mid-way between the central opening  55  and the outer peripheral edge  54 , and are spaced apart along a circumference of the first washer  51 , resulting in a first washer imbalance vector V 1 . The second washer  61  includes three axial weight distributing openings  68  that are disposed mid-way between the central opening  65  and the outer peripheral edge  64 , resulting in a first washer imbalance vector V 2 . Although the weight distributing openings  68  are spaced apart along a circumference of the second washer  61 , they are grouped within a common semi-circular region of the second washer  61 . 
         [0039]    Referring to  FIG. 5 , in another example, the weight distributing openings  158 ,  168  extend radially. In this example, the mass distribution of the first washer  151  is the same as that of the second washer  161 , but the washers  151 ,  161  are not limited to this. The first washer  151  includes at least one radially-extending weight distributing opening  158  that extends between the central opening  55  and the outer peripheral edge  54  resulting in a first washer imbalance vector V 1 . The second washer  161  includes at least one radially-extending weight distributing opening  168  that extends between the central opening  65  and the outer peripheral edge  64 , resulting in a second washer imbalance vector V 2 . 
         [0040]    Referring to  FIG. 6 , in still another example, the weight distributing openings  258 ,  268  extend radially to a limited extent. In this example, the mass distribution of the first washer  251  is the same as that of the second washer  261 , but the washers  251 ,  261  are not limited to this. The first washer  251  includes at least one scallop-shaped, weight distributing opening  258  formed in the outer peripheral edge  54 , resulting in a first washer imbalance vector V 1 . The second washer  261  includes at least one scallop-shaped, weight distributing opening  268  formed in the outer peripheral edge  64 , resulting in a second washer imbalance vector V 2 . 
         [0041]    Referring to  FIG. 7 , in still another example, an annular balance adjusting device  350  includes three washers  351 ,  361 ,  371 , and each washer  351 ,  361 ,  371  includes a single radially-extending weight distributing opening  358 ,  368 ,  378 . The weight distributing openings  358 ,  368 ,  378  are threaded. The first washer  351  includes a first weight distributing screw  359  disposed in the weight distributing opening  358 , resulting in a first washer imbalance vector V 1 . The second washer  361  includes a second weight distributing screw  369  disposed in the weight distributing opening  368 , resulting in a second washer imbalance vector V 2 . The third washer  371  includes a third weight distributing screw  379  disposed in the weight distributing opening  378 , resulting in a third washer imbalance vector V 3 . The weight distribution vector V 1 , V 2 , V 3  of each washer  351 ,  361 ,  371  can be set by adjusting one or more of a) the length, b) the mass, and c) the relative position within the opening  358 ,  368 ,  378  of the respective weight distributing screw  359 ,  369 ,  379 . 
         [0042]    In the embodiment illustrated in  FIGS. 1 and 2 , the annular balance adjusting device  50  is disposed between the nut  34  and the compressor wheel nose  13  such that the first washer  51  abuts the compressor wheel  14 , and the second washer  61  is disposed between the first washer  51  and the nut  34 . When the annular balance adjusting device  50  is assembled on the shaft  2  in this location and placed in the desired rotational orientation relative to the compressor wheel  14  and/or the shaft  2 , the nut  34  is tightened on the shaft stub end  6  to an extent that the axial position and rotational orientation of the compressor wheel  14  and the annular balance adjusting device  50  are fixed relative to the shaft  2 . 
         [0043]    Referring to  FIG. 8 , the first side  52  (not shown) and second side  53  of the first washer  51 , and the first side  62  and second side  63  (not shown) of the second washer  61  are generally planar and free of surface features. In this case, a surface friction force between the respective abutting surfaces of the second washer  61  with the first washer  51 , and also of the first washer  51  with the compressor wheel nose  13  due the compressive axial force applied by the nut  34  serves to retain the annular balance adjusting device  50  in the desired rotational orientation relative to the compressor wheel  14 , and also serves to retain the first washer  51  in the desired rotational orientation relative to the second washer  61 . 
         [0044]    However, depending on the requirements of the specific application, it may be beneficial to provide an additional mechanical connection (e.g., a mechanical connection that is in addition to that provided by surface friction) between the annular balance adjusting device  50  and the compressor wheel  14 , and between the washers  51 ,  61  of the annular balance adjusting device  50  to prevent relative rotation once the annular balance adjusting device  50  is arranged in the desired configuration. For example, in some embodiments, the first washer  51  includes a first set of surface features  56  (not shown) on the first side  52  (not shown) thereof that are configured to cooperatively engage with surface features  17  (not shown) provided on the compressor wheel nose  13 . The first washer  51  is retained a desired rotational orientation relative to the compressor wheel nose  13  via the engagement of the respective sets of surface features  17  (not shown),  56  (not shown). In addition, the first washer  51  includes a second set of surface features  57  on the second side  53  thereof that are configured to cooperatively engage with surface features  66  provided on a first side  62  of the second washer  61 . The second washer  61  is retained in desired rotational orientation relative to the first washer  51  via the engagement of the respective sets of surface features  57 ,  66 . 
         [0045]    The sets of surface features  17  (not shown),  56  (not shown),  57 ,  66  provide increased mechanical connection between respective engaging surfaces  13 ,  52  and  53 ,  62 . In addition, the sets of surface features may be configured to provide indexed adjustment by including fixed angles to which the washers  51 ,  61  can be set. 
         [0046]    In some embodiments, the surface features may be in the form of stippling or radially extending grooves. In other embodiments, the mating sets of surface features are complementary rather than identical. This feature is illustrated in  FIG. 8 , in which the surface features  66  of the second washer  61  includes a series of equidistantly spaced surface features  66  in the form of detents formed on the first side  62  thereof, and the second set of surface features  57  of the first washer  51  include at least one protrusion formed on a second side  53  thereof. 
         [0047]    Referring to  FIG. 9 , the annular balance adjusting device  50  can be secured to the shaft  2  via an alternative arrangement in which two nuts  34 ,  35  are serially disposed on the shaft stub end  6  outboard of the compressor wheel nose  13 . As in the arrangement shown in  FIG. 2 , the annular balance adjusting device  50  is disposed between the compressor nose and the nut  34 . In this alternative arrangement, however, the two adjacent nuts  34 ,  35  provide a self-locking member which secures the annular balance adjusting device  50  together with the compressor wheel  14  in a desired axial position and rotational orientation relative to the shaft  2 . 
         [0048]    Referring to  FIG. 10 , the annular balance adjusting device  50  can be secured to the shaft  2  via another alternative arrangement in which one nut  35  abuts the compressor wheel nose  13 , and the compressor wheel  14  is secured to the shaft  2  via the nut  35  and independently of the annular balance adjusting device  50 . In addition, the annular balance adjusting device  50  is disposed on the shaft  2  between the stub end  6  and a second nut  34 , and the second nut  34  is disposed on the shaft  2  outboard of the annular balance adjusting device  50 . The second nut  34  is threaded on the shaft stub end  6  and secures the annular balance adjusting device  50  to the shaft  2  in the desired rotational orientation. 
         [0049]    Referring to  FIGS. 11 and 12 , an alternative annular balance adjusting device  450  includes a nut  434  that secures the compressor wheel  14  to the shaft  2 , a collar  440  disposed on the nut  434 , and a fastener  460  such as a set screw that secures the collar  440  to the nut  434 . The collar  440  is generally a hollow cylindrical collar that is cup-shaped and includes a closed base  442  and a cylindrical sidewall  443  that extends normally from the closed base  442 . The collar  440  has a predetermined, non-uniform weight distribution about a circumference thereof. The collar  440  encloses a portion of the nut  434  such that the closed base  442  abuts an axially outward-facing surface  438  of the nut  434 , and the sidewall  443  surrounds at least a portion of the radially-outward facing surface  436  of the nut  434 . In addition, an inner surface  444  of the sidewall  443  includes collar surface features  445  in the form of axially-elongated protrusions (e.g., ridges) that engage corresponding nut surface features  439  in the form of axially-extending grooves formed in the nut radially-outward facing surface  436 . The cooperative engagement between the collar surface features  445  of the collar  440  and the nut surface features  439  of the nut  434  serve to retain the collar  440  in a selected rotational orientation relative to the nut  434 , and thus relative to the shaft  2 . 
         [0050]    The fastener  460  is received within a radially-extending, threaded through hole  446  formed in the collar sidewall  443 . The fastener  460  retains the collar  440  axially wherein the collar surface features  445  are engaged with the nut surface features  439 . In some embodiments, the fastener  460  further functions to provide a desired imbalance to the collar  440 . In other embodiments, the fastener  460  functions solely to retain the collar on the nut  434 , and desired non-uniform weight distribution of the collar  440  is achieved by other methods, including, but not limited to, the methods described above with respect to the either of the washers  51 ,  61 . 
         [0051]    In use, the annular balance adjusting device  450  provides a predetermined imbalance to the rotating assembly (not labeled). In some cases, the predetermined imbalance provided by the annular balance adjusting device  450  is used to compensate for a measured imbalance of the rotating assembly (not labeled). In other cases, the predetermined imbalance is used to generate a desired imbalance in the rotating assembly (not labeled). The amount of imbalance is determined by the configuration of the collar  440  or the combination of the collar  440  and the fastener  460 . The direction of imbalance is determined by the rotational orientation of the collar  440  relative to the nut  434 . The rotational orientation of the collar  440  relative to the nut  434  can be adjusted by removing the fastener  460 , sliding the collar  440  axially in an outboard direction so as to disengage the collar surface features  445  from the nut surface features  439  and remove the collar  440  from the nut  434 , rotating the collar  440  to a desired rotational orientation corresponding to a desired imbalance, sliding the collar  440  axially in an inboard direction so as to re-engage the collar surface features  445  with the nut surface features  439 , and securing the collar  440  relative to the nut  434  via the fastener  460 . 
         [0052]    Referring to  FIG. 13 , another alternative annular balance adjusting device  550  includes a nut  434  that secures the compressor wheel  14  to the shaft  2 , a collar  540  disposed on the nut  434 , and the fastener  460  such as a set screw or pin that secures the collar  540  to the nut  434 . The annular balance adjusting device  550  shown in  FIG. 12  is substantially similar to the annular balance adjusting device  450  shown in  FIG. 11 . For this reason common reference numbers will refer to common elements, and the description of the common elements will not be repeated. The annular balance adjusting device  550  shown in  FIG. 12  differs from the annular balance adjusting device  450  only in that the fastener  460  extends axially rather than radially. To accommodate the axially-extending fastener  460 , the collar  540  includes an axially-extending, threaded through hole  546  formed in the closed base  442  that receives the fastener  460 . The through hole  546  is aligned with the rotational axis R of the shaft  2 , whereby the fastener  460  does not affect the weight distribution of the collar  540 . 
         [0053]    Referring to  FIG. 14 , yet another alternative annular balance adjusting device  650  includes a nut  634  that secures the compressor wheel  14  to the shaft  2 , a collar  640  disposed on the nut  634 , and an elastic member  680  disposed between the nut  634  and the collar  640 . The collar  640  is generally a hollow cylindrical collar that is cup-shaped and includes a closed base  642  and a cylindrical sidewall  643  that extends normally from the closed base  642 . The collar  640  has a predetermined, non-uniform weight distribution about a circumference thereof. In the illustrated embodiment, the non-uniform weight distribution is achieved by securing a localized mass  690  to the sidewall  643 , but is not limited to this configuration. The collar  640  encloses the nut  634  such that the closed base  642  faces an axially outward-facing surface  638  of the nut  634 , and the sidewall  643  surrounds the entire radially outward-facing surface  636  of the nut  634 . In addition, an inner surface  644  of the sidewall  643  includes collar surface features  645  in the form of axially-elongated protrusions (e.g., ridges) that engage corresponding nut surface features  639  in the form of axially-extending grooves formed in the nut radially outward-facing surface  636 . The cooperative engagement between collar surface features  645  of the collar  640  and the nut surface features  639  of the nut  634  serve to retain the collar  440  in a selected rotational orientation relative to the nut  634 , and thus relative to the shaft  2 . 
         [0054]    The collar sidewall  643  has a sufficient axial dimension to surround a portion of the nose  13  of the compressor wheel  14  when the closed base  642  is slightly axially spaced apart from the axially outward-facing surface  638  of the nut  634 . In addition, an inwardly-protruding lip  647  is formed on an inner surface  644  of the collar  640 . The nose  13  of the compressor wheel  14  is provided with a radially-outwardly protruding flange  19 , and the inwardly-protruding lip  647  is disposed on the inner surface  644  of the collar  640  at a location that is inboard (e.g., closer to the bearing housing  8 ) relative to the radially-outwardly protruding flange  19 . The inwardly-protruding lip  647  and the radially-outwardly protruding flange  19  overlap when viewed along an axial direction of the turbocharger  1 . 
         [0055]    The elastic member  680  is disposed under compression between the axially outward-facing surface  638  of the nut  634  and the base  642  of the collar  640 , whereby the elastic spring force generated by the elastic member  680  urges the collar  640  away from the compressor wheel  14  to an extent that the inwardly-protruding lip  647  of the collar  640  engages the radially-outwardly protruding flange  19 . In the illustrated embodiment, the elastic member  680  is a spring washer such as a Belleville washer, a wave washer, a curved disc spring, etc. However, the elastic member  680  is not limited to this type of spring. For example, in some embodiments, the elastic member  680  is a coil spring. 
         [0056]    The collar  640  is configured to move axially relative to the compressor wheel nose  13  between a first axial position and a second axial position, and is urged to the first axial position by the presence of the elastic member  680 . In the first position, the inwardly-protruding lip  647  is urged against the radially-outwardly protruding flange  19  via the spring force of the elastic member  680 , and the collar  640  is axially retained on the compressor wheel nose  13  by engagement of the inwardly-protruding lip  647  with the radially-outwardly protruding flange  19 . In addition, the rotational orientation of the collar  640  relative to the compressor wheel nose  13  is fixed via engagement of the nut surface features  639  of the nut  634  with the corresponding collar surface features  645  of the collar  640 . In the second position, the inwardly-protruding lip  647  is axially spaced apart from the radially-outwardly protruding flange  19 , and the nut surface features  639  no longer engage the corresponding collar surface features  645 , so as to permit rotation of the collar  640  about the rotational axis R relative to the compressor wheel  14  and shaft  2 . 
         [0057]    In use, the annular balance adjusting device  650  provides a predetermined imbalance to the rotating assembly (not labeled). In some cases, the predetermined imbalance provided by the annular balance adjusting device  650  is used to compensate for a measured imbalance of the rotating assembly (not labeled). In other cases, the predetermined imbalance is used to generate a desired imbalance in the rotating assembly (not labeled). The amount of imbalance is determined by the configuration of the collar  640 . The direction of imbalance is determined by the rotational orientation of the collar  640  relative to the nut  634 . The rotational orientation of the collar  640  relative to the nut  634  can be adjusted by manually sliding the collar  640  axially in an inboard direction against the spring force generated by the elastic member  680  to the second axial position so as to disengage the collar surface features  645  from the nut surface features  639 , rotating the collar  640  to a desired rotational orientation corresponding to a desired imbalance, releasing the collar  640  so as to permit the spring force to move the collar  640  axially to the first axial position whereby the collar surface features  645  are reengaged with the nut surface features  639 . 
         [0058]    Referring to  FIG. 15 , yet another alternative annular balance adjusting device  750  includes a nut assembly  734  that secures the compressor wheel  14  to the shaft  2 . The nut assembly  734  includes a nose member  735  and an adjusting nut  736 . The nose member  735  includes a cone-shaped head  737  and an integral collar  740 . The integral collar  740  is cylindrical and includes interior surface features  740   a  and exterior surface features  740   b . The interior surface features  740   a  and the exterior surface features  740   b  can be threads. The interior threads  740   a  mate with the shaft  2  (described in detail below) and the exterior threads  740   b  mate with surface features  736   a  formed on the interior of the adjustable nut  736 . Surface features  736   a  can also be threads. The cone-shaped head  737  includes a cut-out  738 . The cut-out  738  can also include surface features (not shown) that may be threads. The surface features (not shown) formed in the cut-out  738  can be formed at least partially or fully about a depth  738   a  of the cut-out  738 . The cut-out  738  is aligned with the rotational axis R of the shaft  2 , whereby the cone-shaped head  737  does not affect the weight distribution of the integral collar  740  about the shaft  2 . 
         [0059]    The cone-shaped head  737  further includes an imbalance divot  739  and a test weight slot  741 . The imbalance divot  739  can be any shape; however, a spherical or conical shape is preferable. The imbalance divot  739  can be machined, laser cut, or formed by electrical discharge machining (EDM) into the cone-shaped head  737 ; and the test weight slot  741  can be drilled, milled or reamed into the cone-shaped head  737 . The test weight slot  741  can be tapered and/or include surface features (not shown) such as threads, and can have a depth  742   a . The depth  742   a  of the test weight slot  741  can extend into the cut-out  738  or can have a dimension that prevents the test weight slot  741  from extending into the cut-out  738 . A test weight  742  is included for receipt into the test weight slot  741 . Test weight  742  can be inserted into the test weight slot  741  to a depth equal to, more than, or less than the depth  742   a  of the test weight slot  741 . The test weight  742  can also have a taper which compliments the taper of the test weight slot  741 ; or the test weight  742  can include surface features (not shown) such as threads to allow the test weight  742  to be threaded into the test slot  741 ; or the test weight  742  can be press-fit into the test weight slot  741 . Otherwise, the test weight slot  741  can be filled with weld material or a powdered metal that is sintered with a laser to ensure receipt of the test weight  742  within the test weigh slot  741 . 
         [0060]    Shaft  2  includes a first portion  2   a  and a second portion  2   b . The first portion  2   a  of the shaft  2  is a cylindrical shaft; however, the second portion  2   b  of the shaft  2  includes surface features  2   c  such as threads. The second threaded shaft portion  2   b  of the shaft  2  begins at an end  13   a  of the nose  13  of the compressor wheel  14  and the first cylindrical shaft portion  2   a  ends at the end  13   a  of the nose  13  of the compressor wheel  14 . The second threaded shaft portion  2   b  of the shaft  2  has a depth  2   d  that can be equal to, less than, or slightly greater than a depth  740   c  of the integral collar  740 . Threads  2   c  of the second threaded shaft portion  2   b  mate with the interior threads  740   a  of the integral collar  740 . 
         [0061]    In use, the annular balance adjusting device  750  provides a predetermined imbalance to the rotating assembly (not labeled). In some cases, the predetermined imbalance provided by the annular balance adjusting device  750  is used to compensate for a measured imbalance of the rotating assembly (not labeled). In other cases, the predetermined imbalance is used to generate a desired imbalance in the rotating assembly (not labeled). The amount of imbalance is determined by the configuration of the collar  640 . The direction of imbalance is determined by the rotational orientation of the nose member  735  and the adjusting nut  736 . The rotational orientation of the nose member  735  and the adjusting nut  736  can be adjusted by manually rotating the nose member  735  axially in an inboard direction with respect to the shaft  2  and adjusting nut  736 . 
         [0062]    The nose member  735  is threaded onto the second threaded shaft portion  2   b  of the shaft  2  on the compressor side of the rotor. The nose member  735  is threaded onto the second threaded shaft portion  2   b  of the shaft  2  with or without the test weight  742  disposed within the test slot and/or with or without the imbalance divot  739  formed into the cone-shaped head  737 . The test weight  742  and the imbalance divot  739  can be used together or interchangeably depending upon the imbalance and amount of adjusting required. The nose member  735  is rotated close to the nose  13  of the compressor wheel  14 . When the test weight  742  has been located at the desired angular position, the adjusting nut  736  is tightened onto the compressor wheel nose  13 . The adjusting nut  736  is then torqued to a level that achieves the required clamping load with minimal migration and stresses that warrant optimal life of the rotor group. In practice, the diameter of the compressor wheel nose may need to be increased slightly in order to have sufficient clamping surface area, between adjusting nut  736  and compressor wheel  14 . 
         [0063]    Although the annular balance adjusting device  50  described with respect to  FIGS. 1 ,  2 ,  9  and  10  includes first and second washer  51 ,  61  having an outer diameter that corresponds generally to an outer diameter of the compressor wheel nose  13 , the first and second washers  51 ,  61  are not limited to this diameter. For example, in some embodiments, one or both of the first washer  51  and the second washer  61  have an outer diameter that is greater or less than that of the compressor wheel nose  13 . 
         [0064]    Although several methods for providing the washers  51 ,  61  and/or collars  440 ,  540 ,  640 ,  740  with the predetermined, non-uniform mass distribution have be described herein, the methods are not limited to those described, and the mass distribution of the washers  51 ,  61  and/or collars  440 ,  540 ,  640 ,  740  can be configured in other ways and by other methods than those described herein. 
         [0065]    The annular balance adjusting device s and methods described herein are not limited to use in a turbocharger for adjustment of the imbalance level of the turbocharger rotating assembly (not labeled). For example, the annular balance adjusting devices and methods can be used to adjust the balance of an electric boost device having a turbine wheel connected to a compressor wheel via a common shaft, and further having an electric motor disposed between the turbine and compressor wheels and connected to the common shaft. In another example, the annular balance adjusting devices and methods can be used to adjust the balance of an electric boost device having a compressor wheel and electric motor having a common shaft. 
         [0066]    Aspects of the disclosure have been described herein in an illustrative manner, and it is to be understood that the terminology used is intended to be in the nature of words of description rather than limitation. Many modifications and variations of the present disclosure are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the disclosure may be practiced other than as specifically enumerated within the description.